Urban gas pipeline Internet of Things safety assessment three-dimensional GIS system

Abstract

The invention discloses a three-dimensional GIS (geographic information system) system for safety assessment of an urban gas pipeline internet of things. A gas pipe network monitoring and assessment system combining the internet of things, a mobile internet and BIM / GIS information is established. Firstly, an overall framework based on sensing, transmission, knowing and use of the internet of things is established; secondly, a front-end sensing system deployment scheme is established, a database system is built, and index data are collected and stored; thirdly, a gas leakage hazard model is constructed, and possible hazard consequences are evaluated; 4, a pipe network monitoring system application layer module is constructed, and underground space information management, safety analysis, prediction and early warning and an auxiliary decision making module are achieved; and establishing a gas pipe network risk identification module, a basic information checking module, a monitoring and explosion early warning module, a three-dimensional visualization module and an auxiliary decision-making module. The system monitors the operation condition of the gas pipe network in real time, analyzes the operation rule of the gas pipe network, evaluates the risk of the gas pipe network, predicts, early warns and decides in time, changes passive first-aid repair into active protection, and is high in monitoring stability, precision and efficiency.

Description

Technical Field

[0001] The present application relates to a safety assessment system for a gas pipeline network, and particularly to a three-dimensional GIS system for safety assessment of an urban gas pipeline Internet of Things, belonging to the technical field of GIS assessment of a gas pipeline network. Background Art

[0002] Accidents in gas pipeline networks occur frequently, and it is urgent to promote relevant monitoring and emergency management work. It is necessary to promote the integration of the digital urban management system with the comprehensive information management system and the smart city. Utilize modern information technology to do a good job in construction planning, urban construction, operation management, emergency protection, etc., and prevent problems before they occur. Currently, it is a critical period for the transformation towards green and low-carbon development, and it is particularly important to improve the safety inspection mechanism of the urban gas industry. It is necessary to innovate the safety management mechanism and enhance the risk control ability. It is particularly urgent and important to monitor and effectively control each key link of the gas pipeline network in real time, effectively reduce the accident risk, and achieve proactive safety guarantee. At present, the development of the Internet of Things and safety technology is becoming increasingly mature, providing a basis for the safety monitoring and emergency management of gas pipeline networks.

[0003] The urban gas pipeline network safety assessment system is a gas pipeline network monitoring project. The implementation of this project conforms to the important decision of improving the public safety system, improves the safety emergency decision-making and dispatching capabilities of various departments, and is of great significance for promoting the construction of a smart city.

[0004] The gas pipeline network in the city is buried underground and often adjacent to or crosses underground spaces such as rainwater pipe networks, sewage pipe networks, and underground parking lots. Through summarizing previous accident cases, it is found that these areas are high-risk areas where gas leakage and explosion lead to serious consequences. The spaces where gas leakage and explosion occur are divided into two categories: one is other pipelines adjacent to it, including sewage pipes, rainwater pipes, cable trenches, etc. Gas leakage spreads along the pipeline and mostly encounters a fire source at the wellhead connected to the ground, resulting in explosion and fire accidents. The other is enclosed spaces, including civil air defense projects, underground parking lots, and above-ground buildings. Such spaces are relatively close to the gas pipeline network. Once gas leakage accumulates, there is a risk of explosion.

[0005] The problems that need to be solved by the existing gas pipeline network safety assessment system and the key technical difficulties of the present application include:

[0006] (1) Due to the flammable, explosive, and toxic nature of gas itself and its disaster-causing properties after leakage, related accidents occur frequently. Limited by historical reasons for the development of gas safety management, there are the following problems in the safety management of gas pipelines at present: First, there is a timeliness problem in manual detection: Manual inspections cannot achieve real-time and effective coverage, and the gas leakage situation in relevant areas cannot be grasped in a timely manner, and early warnings cannot be issued for gas leakage in a timely manner; Second, the adjacent underground spaces of gas pipelines are complex, and there is a lack of an information sharing platform. The urban underground pipeline network system has a complex structure, and data collection is not systematic, resulting in insufficient information, making it impossible to understand the diffusion situation after gas leakage and unable to detect risks in a timely manner; Third, there is no management mechanism based on urban public safety: Gas leakage monitoring involves gas monitoring in multiple types of underground spaces. Based on urban public safety, overall consideration, unified planning, and a relatively complete monitoring system need to be established. Currently, there is an urgent need for a gas pipeline GIS evaluation system that meets system stability, fault tolerance and self-adaptive performance, ease of maintenance, security, scalability, adaptability, and ease of operation. In addition, it also needs to meet functional and performance requirements.

[0007] (2) With the expansion of the city and the continuous increase in the length of gas pipelines, gas leakage or explosion accidents caused by pipeline aging or damage occur frequently. At present, there are still major problems in gas safety management. There is a lack of a scientific and efficient urban gas pipeline network safety evaluation system, and a gas pipeline network monitoring and evaluation system that combines the Internet of Things, mobile Internet, and BIM / GIS information based on public safety is lacking. It is impossible to monitor the operation status of gas pipelines, analyze the operation rules of gas pipelines, conduct risk assessment of gas pipelines, make timely predictions, early warnings, and decision-making and handling, and it is impossible to change from passive repair to active protection. The underground gas pipelines have not been BIM modeled, and it is impossible to match the positions of monitoring units in the BIM model. The risk levels of the pipeline network have not been evaluated, and pipelines with higher risk levels have not been warned. The safety management level of gas pipelines is relatively low.

[0008] (3) The existing gas pipeline network management system has limitations in safety management and lacks the overall architecture of the urban gas pipeline network safety assessment system with the Internet of Things sensing, transmission, knowledge, and application as the architecture system. The existing technology lacks the analysis of data collection and storage requirements, lacks the deployment plan for the front-end sensing system, has not built a database system, and cannot collect and store index data. It has not constructed a gas leakage hazard model, has not evaluated the possible hazard consequences, lacks the basis for the inspection and maintenance of the gas pipeline network, and cannot provide support for scientific decision-making and emergency response by relevant departments. It has not constructed the application layer module of the pipeline network monitoring system and cannot realize underground space information management, safety analysis, prediction and early warning, and auxiliary decision-making. It has not established a risk identification module for the gas pipeline network, a module for viewing basic information, monitoring and explosion early warning, three-dimensional visualization, and auxiliary decision-making. It cannot solve the problem of no timeliness in manual monitoring, cannot realize the information sharing of pipeline network data, has not achieved the goal of digital management of the gas pipeline network and its adjacent underground space, cannot provide accurate monitoring and evaluation information and scientific basis for management decision-makers, and cannot improve the early warning ability of pipeline network accidents. Summary of the Invention

[0009] This application establishes a gas pipeline network monitoring and evaluation system based on public safety, integrating the Internet of Things, mobile Internet, and BIM / GIS information: First, establish the overall architecture of the urban gas pipeline network safety assessment system with the Internet of Things sensing, transmission, knowledge, and application as the architecture system; Second, based on the analysis of data collection and storage requirements, establish a deployment plan for the front-end sensing system, build a database system, and collect and store index data; Third, construct a gas leakage hazard model, evaluate the possible hazard consequences, and provide a basis for the inspection and maintenance of the gas pipeline network; Fourth, construct the application layer module of the pipeline network monitoring system to realize underground space information management, safety analysis, prediction and early warning, and auxiliary decision-making modules; The urban gas pipeline network safety assessment establishes a risk identification module for the gas pipeline network, a module for viewing basic information, monitoring and explosion early warning, three-dimensional visualization, and auxiliary decision-making. It can monitor the operation status of the gas pipeline network in real time, analyze the operation rules of the gas pipeline network, conduct risk assessment of the gas pipeline network, predict, warn, and make decisions in a timely manner, change from passive repair to active protection, and has high monitoring stability, accuracy, and efficiency.

[0010] To achieve the above technical effects, the technical solutions adopted in this application are as follows:

[0011] Urban Gas Pipeline Internet of Things Safety Assessment 3D GIS System. Based on public safety, a gas pipeline network monitoring and assessment system combining the Internet of Things, mobile Internet, and BIM / GIS information is established to monitor the operation status of the gas pipeline network, analyze the operation rules of the gas pipeline network, conduct risk assessment of the gas pipeline network, predict, warn, and make decisions in a timely manner, and change from passive emergency repair to active protection. First, establish the overall architecture of the urban gas pipeline network safety assessment system with the Internet of Things sensing, transmitting, knowing, and using as the architecture system. Second, based on the analysis of data collection and storage requirements, establish a deployment plan for the front-end sensing system, build a database system, and collect and store index data. Third, construct a gas leakage hazard model to evaluate the possible hazard consequences and provide a basis for the inspection and maintenance of the gas pipeline network. Fourth, construct the application layer module of the pipeline network monitoring system to realize the management of underground space information, safety analysis, prediction, warning, and auxiliary decision-making modules. The urban gas pipeline network safety assessment establishes risk identification of the gas pipeline network, viewing of basic information, monitoring and explosion warning, 3D visualization, and auxiliary decision-making modules.

[0012] Overall process of the gas pipeline network safety assessment system: First, conduct a flammable gas explosion risk assessment of the underground pipeline network and adjacent spaces to determine the risk level distribution of each space. On this basis, optimize the layout of sensors, and conduct hierarchical monitoring of underground spaces with different risk levels. The monitoring methods include using fixed flammable gas monitors to monitor the concentration of flammable gas, mobile monitoring equipment to monitor possible gas leaks, and network public opinion monitoring. According to the monitoring results, divide the risk of explosion in the underground space, calculate and locate the leakage position, and analyze the development trend of the risk, and release a risk map and warning information for the accident information. The system will also generate an emergency auxiliary decision-making plan, including a resource allocation map and an intelligent plan.

[0013] The key innovative technologies of the system include 3D modeling, dangerous space identification, optimized layout of measuring points, explosion damage analysis, and gas leakage diffusion analysis.

[0014] Preferably, the overall architecture: adopts a five-layer and two-wing structure. The five layers are the front-end sensing system, network communication system, database system, application software system, and platform front-end display system in sequence. The two wings are the laws, regulations, standards, norms, and security guarantee systems followed by the system construction.

[0015] The system is built with the technical architecture of "sensing, transmitting, knowing, and applying" in the Internet of Things. Among them, sensing is the front-end sensing system, including various sensor facilities installed on the gas pipeline network; transmitting is to transmit the front-end monitoring data to the monitoring center in a wired and wireless manner through the sensing network and the wide area network, realizing the collection and transmission of sensor data and the data interaction during system application to ensure the normal operation of the system; knowing is the database system for data collection and storage; applying is the application software system, which is the core of the whole system and conducts analysis and processing based on the information sensing, transmission, and collection of urban gas pipeline network monitoring and early warning.

[0016] Preferably, the front-end sensing system includes the establishment of underground pipeline network and spatial information, sensor layout, and monitoring system construction. The concentration of combustible gas in the adjacent underground space of the gas pipeline network is monitored by the front-end gas collection and monitoring instrument.

[0017] The monitoring objects are combustible gas and toxic gas, including methane, ethane, hydrogen sulfide, carbon monoxide, and carbon dioxide. The collection method is the multi-channel air sampling and extraction method. The system will use an aspirating multi-channel gas collection and monitoring instrument to monitor the combustible and toxic gas in the underground space. The gas is collected by the extraction method, and a set of analysis equipment monitors and analyzes multiple points.

[0018] The gas collection work process is as follows: After the gas is extracted and collected from the underground space, it first passes through a multi-channel solenoid valve, and the combustible gas at the monitoring point is selectively collected by controlling the on-off of the solenoid valve. It is necessary to carry out water-vapor separation treatment on the extracted gas, and a waterproof switch is specially set to prevent the gas sampler from inhaling groundwater and damaging the entire monitoring equipment. After the gas passes through the filter to adsorb other impurities, it enters the gas detector for concentration analysis.

[0019] The gas collection instrument of this application consists of: gas filter, water-vapor separator, suction pump, flow controller, gas dryer, combustible gas detector.

[0020] Preferably, the gas pipeline network database system stores information related to gas safety monitoring, including pipeline network basic data, model data, monitoring data, pre-plan information, event information, backup data, common basic information, monitoring information, and early warning information.

[0021] (1) Basic information database: Stores data related to underground pipe networks; (2) Monitoring information database: Stores monitoring data obtained from sensors, sensor addresses, time, and status information; (3) Early warning database: Stores detailed early warning information generated by the system, including early warning types, levels, dates, and statuses; (4) Event information database: Stores safety event information, prediction and early warning information, and safety event handling process information of urban lifeline pipe networks; (5) Geographic information database: Geographic information with urban lifelines as a reference, including digital maps, remote sensing images, pipe network road networks, inspection well distributions, and important target distribution data; The forms of geographic information carriers include: Digital line graphic DLG stored in vector form, digital elevation model data specifically used to express terrain undulations, raster format data of aerospace images, place name data, geographic metadata, and geographic information data in professional fields; (6) Model database: Stores data related to models, including basic information of models, model chains, model utilization situations, and model parameter data; (7) Plan database: The plan database stores accident emergency plans related to pipe networks, including overall emergency plans, special plans, and departmental plans; (8) Case database: Stores historical emergency event information and their response plans, providing an effective reference during disasters; (9) Knowledge database: A structured, easy-to-operate, easy-to-utilize, comprehensive, organized, and interconnected knowledge collection, including: general knowledge, summary knowledge, strategic knowledge, laws and regulations, standards, and technical specifications; (10) Document database: Stores document information, including existing safety management documents, official documents, and newly generated documents;

[0022] Data engineering construction includes: construction of database systems, processing of three-dimensional geographic data, and collection, processing, and archiving of engineering archive data.

[0023] Preferably, the gas pipeline application software system includes: an underground space information management system, a safety analysis system, a prediction and early warning system, and an emergency auxiliary decision-making system;

[0024] 1 - Underground space information management system: Integrates and displays various pipelines or underground spaces in the city where gas leakage may occur, including static information and dynamic information:

[0025] (1) Static information includes the name, geographical location, construction year, safety level, historical maintenance records, and historical calculation information of relevant data of the monitored object; (2) Dynamic information includes real-time monitoring data, safety status, and alarm signal display of sewage pipes, rainwater pipes, elevator shafts, civil air defense projects, and cable trenches;

[0026] 2 - Safety analysis system: Includes: assessment of combustible gas concentration in confined spaces, detection and assessment of combustible gas leakage in confined spaces, analysis and assessment of gas diffusion, prediction and assessment of gas leakage consequences, and other special assessments;

[0027] 3 - Prediction and Early Warning System: including: Information Integration, Comprehensive Prediction Analysis, Early Warning Information Management;

[0028] 1) Comprehensive Information Integration: Integrate the professional monitoring and analysis result data required by the prediction and early warning system, and deliver the comprehensive result to the comprehensive prediction analysis to generate early warning information; (1) Regional Pipeline Network Information: The monitoring system reports the comprehensive pipeline information of the area where potential risks are located, including the distribution information of gas pipelines, rainwater pipelines and inspection wells; (2) Urban Geographic Information: Evaluate the physical environment of the risk area, including road traffic conditions, surrounding space, high-rise buildings, crowded places, and real-time weather conditions; (3) Social Information: Evaluate the potential impact of social factors on the risk area, including major social events, population distribution, and social economy;

[0029] 2) Comprehensive Prediction Analysis: Use the various data obtained after information integration to make early warning decisions, provide multiple comprehensive prediction analysis methods, analyze the targets, hazard sources, population and economic information within the scope of the event impact, comprehensively evaluate the consequences of the event impact, and adopt three early warning analysis methods: (1) Index Early Warning: Evaluate the state of the monitored object by formulating a comprehensive index to predict the turning point of the safety cycle of the pipeline network system; (2) Calculation Early Warning: Use calculation methods to discover the fluctuation law of the monitored object (such as the concentration of combustible gas in a confined space); (3) Model Early Warning: Construct a mathematical model to evaluate the state of the monitored object.

[0030] Preferably, 3D modeling: Use the CityMaker platform for modeling. Adopt the method of fine manual modeling of key components and external import, and automatic modeling of large-scale pipelines for pipeline network modeling. The specific modeling process is as follows:

[0031] The first step, data preparation: The pipeline and pipe point data in the shapefile format in data engineering construction, and the 2D CAD data of the pipe point auxiliary facilities;

[0032] The second step, fine modeling of auxiliary facilities and key parts: Use the 3ds Max manual modeling software to finely model the key components such as tees, crosses, straight points, reduced diameters, elbows, pipe offset points, reserved openings and the auxiliary facilities such as tees, crosses, straight points, reduced diameters, elbows, pipe offset points, reserved openings of the gas pipeline network, and export them in the OSG format;

[0033] Step 3, Pipeline Network Modeling: The reference elements of pipelines include pipe length, pipe diameter, starting point coordinates, and starting point elevation. The reference elements of pipe points include pipe point type and pipe point burial depth. Configure the color attributes of different pipelines and model the pipeline network. The automatic modeling process using CityMaker Builder is as follows: 1) Configure the data source: Create a basic library, a planning library, and a municipal library. The basic library stores the data structure of the system and the styles of the 3D models of pipe points and pipelines. The municipal library stores pipeline data, and the planning library stores vector data for specific scenarios. 2) Color Library Management: Manage the colors required during data driving, which are applied in the editing of pipeline styles and represent pipeline types when driving pipelines. 3) Attribute Structure Export: Extract the attribute structure of the original data. 4) Configure Reference Elements: The modeling reference elements for pipelines include pipe length, pipe diameter, starting point coordinates, and starting point elevation. The modeling reference elements for pipe points include pipe point type and pipe point burial depth. 5) Synchronize the Municipal Library: The synchronized municipal library contains various facility types set in the facility library. 6) Facility Assignment: Assign the data in the temporary layer to the corresponding facility layer classes and set the matching relationship between the styles of pipelines and pipe points and the pipelines. 7) Add Terrain Data: Add terrain files in ted format and above-ground building models to form an integrated 3D scene of above and below ground. 8) Drive the generation of the 3D scene;

[0034] Step 4, Model Decoration and Quality Inspection: Check whether there are any intersections or misalignments in the pipelines, and whether the pipelines and pipe point attachments are fully matched. For pipelines with errors, check and correct the data. If the data quality is okay, make local adjustments or translations to the attachments or pipelines to meet the visualization requirements;

[0035] Step 5, Export the Project: Export the generated 3D model data of pipelines and attachments in fdb format, store them separately by category, and the naming should reflect uniqueness;

[0036] Step 6, Scene Publishing: Publish it as a local scene file in scd format or publish it to the database to form a data service.

[0037] Preferably, Hazardous Space Identification: Determine the hazard sources by conducting risk assessments on each underground space. The risk assessment is divided into two levels. First, conduct a risk assessment on each road within the monitoring range to determine the explosion risk in the area and overallocate the number of measurement points in the area. Then, conduct precise explosion risk calculations on each underground space adjacent to the gas pipeline network to determine the risk level of each underground space;

[0038] 1 - Regional Risk Assessment

[0039] First, according to the risk assessment model, by conducting vulnerability and consequence assessments on high-consequence areas, the risk characteristic values of these areas are obtained. Then, considering the pipeline failure probability in these areas, the risk values are calculated. Subsequently, based on the pipeline length, the risk quantity of these areas is calculated, and the number of measuring points is deduced accordingly.

[0040] The risk assessment model is established based on the product of probability, vulnerability, and consequence. The length or volume of each high-risk area is different, and the pipeline length and leakage probability corresponding to each high-risk area are also different. In the evaluation, by assessing the vulnerability and consequence of high-risk areas as the risk characteristic values of these high-risk areas, and then calculating the risk according to the length and leakage probability of the gas pipelines in these areas.

[0041] (1) Calculate the risk characteristic value F

[0042] The risk characteristic value F is expressed as the product of vulnerability and consequence. Vulnerability is based on road levels and high-consequence areas, considering the spatial volume where an explosion may occur. The road level is related to the drainage capacity of the drainage pipelines under the road, and the drainage capacity is related to the pipeline diameter. The size of the high-consequence area is directly related to the actual underground space volume of this area. The consequence considers the traffic flow of people and vehicles in this area. The established method for calculating the risk characteristic value is as follows:

[0043] F = (a×D + b×G)×(C×M + d×R) Equation 1

[0044] In the formula, a, b, c, and d are the weight coefficients of each evaluation index; D is the road level; G is the type of high-consequence area; M is the traffic flow; R is the pedestrian flow.

[0045] (2) Analysis of evaluation elements

[0046] ① Road level D: According to the types of urban roads, urban roads are divided into five levels: one-way lane, two-way double lanes, two-way four lanes, two-way six lanes, two-way eight lanes and above. The more lanes there are, the higher the assigned value of the road level. The weight coefficient of the road level is 0.2. ② Type of high-consequence area G: It is divided according to the types and uses of buildings around gas pipelines. The weight coefficient of the type of high-consequence area is 0.3. ③ Traffic flow M: The traffic flow of each section is monitored in real time, and the average value of the traffic flow of each section is calculated, which is divided into three levels: sparse, medium, and dense. The greater the traffic flow, the higher the score, with an overall score of 1 - 9. The weight coefficient of the traffic flow is 0.2. ④ Pedestrian flow R: The pedestrian flow of each section is monitored in real time, and the average value of the pedestrian flow of each section is calculated, which is divided into three levels: sparse, medium, and dense. The greater the pedestrian flow, the higher the score, with an overall score of 1 - 9. The weight coefficient of the pedestrian flow is 0.3.

[0047] (3) Risk level classification

[0048] Risk value = f(Failure probability, Risk characteristic value). The risk level is the product of the pipeline failure probability and the risk characteristic value, and it is divided into four levels according to the results of risk quantification;

[0049] 2 - Risk assessment of underground space explosion

[0050] The risk assessment results are presented in a three - dimensional matrix. The probability assessment method is used to evaluate the risk level of each adjacent underground space of the gas pipeline network. The risk level is given according to the evaluation value, and the monitoring points are determined according to the risk level. The risk score of the risk assessment model:

[0051] D = V×P×C Equation 2

[0052] Where P is the probability of a leakage accident occurring; C is the consequence that will be caused once an accident occurs; V represents the probability of reaching the explosion condition after leakage, that is, the vulnerability of the space under leakage conditions. The magnitude of the D value is positively correlated with the system's danger. If the probability of danger is high, countermeasures need to be taken to reduce the probability of explosion and reduce the risk score to the safe range. A semi - quantitative method is used for value calculation, and each component level is divided according to the empirical model;

[0053] (1) Vulnerability V of accident occurrence

[0054] The vulnerability of accident occurrence consists of two parts: one is the probability V1 of the concentration of combustible gas accumulating to the explosion limit, with a weight of W1; the other is the probability V2 of having an ignition source with sufficient energy, with a weight of W2;

[0055] V = V1×W1 + V2×W2 Equation 3

[0056] ① V1: The sources of underground combustible gas are hydrogen sulfide, carbon monoxide, and carbon dioxide produced by the decay of organic substances in wells, and combustible gases methane and ethane volatilized from gas pipeline network leaks. The areas where various combustible and dangerous gases flow are connected pipe networks (sewage pipe networks and rainwater pipe networks). Secondly, after the gas pipeline leaks, it diffuses through the soil to various independent inspection wells or connected inspection wells and pipelines, and then diffuses upstream and downstream through the pipelines. According to the sources and diffusion scale of combustible gases, various pipelines and inspection wells are classified. The combustible substances reaching the explosion limit are the prerequisite for the entire accident, and the weight W1 is 0.7;

[0057] ② V2: The ignition source is a necessary condition for the explosion of combustible gas. Whether it is easy to generate an ignition source is closely related to the explosion accident of the manhole. Wells with power supply equipment are prone to explosion, so the danger level is 2. For wells without power supply equipment, the probability of having an ignition source in the well is low, so the danger level is 1, and the weight W2 is 0.3;

[0058] (2) Pipeline leakage probability P

[0059] The gas source of urban combustible gas explosion is the gas pipeline. There is an obvious positive correlation between the leakage probability of urban gas pipelines and the pipeline materials. The corresponding score values of gas pipeline materials are: 10 points for cast iron pipelines, 3 points for steel pipelines, and 1 point for PE pipes;

[0060] (3) Consequences C resulting from an accident

[0061] The accident consequences are divided into the original explosion damage range S1, the secondary damage range S2, the density of people and vehicles E within the damage range, and the hidden loss C3, with weights W3, W4, and W5 respectively;

[0062] C = S1×E1×W3 + S2×E2×W4 + C3×W5 Formula 4

[0063] ① S1: The larger the space, the greater the accumulation capacity of combustible gas. After an explosion, the impact on surrounding pipelines and objects in the above-ground space is greater. Therefore, the C1 classification is quantitatively classified by the volume of the underground space, and the weight W3 is 0.6;

[0064] ② S2: In addition to considering serial explosions, if there are flammable substances around the wellhead during an explosion, the explosion will ignite the flammable substances and cause a fire, and the weight W4 is 0.3;

[0065] ③ Classification of the density of people and vehicles E: The greater the pedestrian and vehicle flow on the road surface, the higher the population density, and the more serious the consequences of the explosion will be;

[0066] ④ C3: Considering the number of pipelines around the explosion hazard source, the hidden loss consequence is light, and the weight W is 0.1;

[0067] (4) Risk analysis and measuring point layout

[0068] The comprehensive wind risk calculation of combustible gas explosion in gas pipelines and their adjacent spaces is as follows:

[0069] R = (V1×W1 + V2×W2)×P×(S1×E1×W3 + S2×E2×W4 + C3×W5) Formula 5

[0070] By determining each score value, and analyzing, evaluating, and utilizing the multiplication extreme value, the degree of operation danger is obtained, and the size of the evaluation danger is judged.

[0071] Preferably, the measuring point is optimized and arranged: Considering the combustible gas diffusion effect among gas, sewage, rainwater pipelines and connecting wells, the leakage of combustible gas is comprehensively affected by diffusion time, diffusion quantity, diffusion pressure, soil composition, moisture content, soil surface cover, and temperature factors;

[0072] (1) Optimization of measuring points between connecting wells

[0073] It is determined that the gas concentration distribution is nearly the same within a certain area (R < 10 m), and all sewage and rainwater wells on the road section are included in the monitoring scope to accumulate data for the optimization of the measuring points of the connected wells;

[0074] (2) Optimization of measuring points between non-connected wells

[0075] Considering the scenario where gas leaks and spreads into the surrounding pipelines and manholes, the connected sewage and rainwater wells have been set as measuring points during monitoring. The optimization calculation of non-connected wells is based on the premise that sewage and rainwater wells must be monitored. According to the rules of the widest safety monitoring area of adjacent underground spaces in the gas pipeline network, the smallest overlapping monitoring area, and the highest monitoring efficiency, two optimization schemes are established:

[0076] ① Optimization method driven by the maximum diffusion range: Points A, B, and C respectively represent three adjacent inspection wells. Taking these 3 points as the centers and R as the maximum leakage diffusion radius, circles are drawn with a radius of R. The chords intersecting with the gas pipeline network are the pipeline ranges that each inspection well can monitor as a measuring point;

[0077] When there is a section in the monitoring range of point B that cannot be monitored by two adjacent points, following the rule that as many oil and gas pipelines as possible should be monitored, point B needs to be monitored as a measuring point; when the distance between point A and point C shrinks, and the monitoring range of point B is exactly covered by the monitoring ranges of point A and point C, point B is in a critical state of being monitored or not; when the distance between point A and point C further shrinks, and the monitoring range of point B is completely covered by the monitoring ranges of point A and point C, the monitoring range of point B has been fully monitored by point A and point C, and point B does not need to be monitored;

[0078] Assume that the coordinates of the three wells A, B, and C are (x1, y1), (x2, y2), (x3, y3) respectively, and the pipeline is located at y = 0:

[0079]

[0080] When the formula 6 is satisfied, point B does not need to be monitored;

[0081] ② Optimization method driven by the minimum diffusion distance: Points A, B, and C are three adjacent inspection wells around the pipeline. The coordinates of the three inspection wells are A(x1, y1), B(x2, y2), C(x3, y3) respectively, and the pipeline is located at y = 0. The distances from any point D(x4, 0) on the pipeline to points A, B, and C are d1, d2, and d3 respectively. If d2 < min(d1, d3), it means that there is a point on the pipeline with the shortest diffusion distance to B, and point B needs to be measured; otherwise, the diffusion distance from any point on the pipeline to A or C is shorter than that to B, and point B does not need to be monitored;

[0082] First, discretize the pipeline, evenly divide the pipeline into n segments, and take a point on each segment to represent the distance between this segment and each inspection well. The larger the value of n, the higher the accuracy, but the greater the computational effort. Considering the effective utilization rate of the measurement points, to achieve an appropriate distance and high utilization rate, optimize the second solution again:

[0083] In the optimization method driven by the minimum diffusion distance in B, based on its optimization results, continue the optimization calculation according to the shortest diffusion distance optimization method, and then generate a set of measurement points calculated based on the distribution of existing wells; compared with the previous optimization results, the number of monitoring points decreases, but at the same time the monitoring efficiency also decreases. If the reduced monitoring efficiency is acceptable, the optimization result after deleting some points has a reduced number of measurement points and a reduced investment cost, then this measurement point solution is more suitable. Considering the shortest diffusion distance with the least investment cost, find a set of measurement points with the least investment cost;

[0084] There are unpredictable variables among the influencing factors of the diffusion distance. Take the possible diffusion distances within one year as a probability function. When the measurement point is within the diffusion range, a leak is detected, that is, there is a probability function P between the distance R of the measurement point from the leak point and whether a leak can be detected. There is always a minimum value R min and a maximum value R max , when R ≤ R min , it is certain that a leak is detected, so the probability P = 1; when R > R max , it is certain that the measurement point cannot detect a leak, so the probability P = 0; when R min <R ≤ R max , assume P = f(R), and R is a continuous random variable;

[0085] When the position of the measurement point is determined, the distance R between each point on the pipeline and the measurement point is obtained through calculation, and a relationship curve representing the relationship between the distance R and the corresponding pipeline length l is obtained. Assume l = F(R). For different pipelines and different combinations of measurement points, the functional relationship of the function l = F(R) is different. The effective monitoring length is the expected value of the pipeline being monitored, that is:

[0086] L′ = Pl Equation 7

[0087] Substitute P = f(R) and l = F(R) into Equation 6 to get:

[0088]

[0089] The monitoring efficiency is the ratio of the expected value of the pipeline being monitored to the total length (L) of the pipeline, that is:

[0090] E = L′ / L Equation 9

[0091] In the leakage monitoring of gas pipelines, the cost performance V represents the ratio of the effective monitoring length to the investment funds. The cost performance is represented by the ratio of the effective monitoring length to the number of measurement points n, that is:

[0092] V = L′ / n Equation 10

[0093] The specific optimization method is as follows:

[0094] ① Calculate the preliminary distribution of measurement points by using the optimization method driven by the minimum diffusion distance; ② Calculate the pipeline length l’ monitored by each measurement point; ③ Calculate the effective monitoring length L’ according to Equation 8; ④ Calculate the monitoring efficiency E according to Equation 9; ⑤ Calculate the cost performance V according to Equation 10; ⑥ Sort l’ in descending order, and delete the measurement point with the smallest l’; Recalculate according to ① to ⑥ to obtain L’, E, and V corresponding to different numbers of measurement points, and select the scheme according to the requirements of L’, E, and V.

[0095] Preferably, for the explosion damage analysis: quantitatively analyze the thermal radiation and shock wave damages respectively, and divide the hazard consequences into four hazard areas: the death area, the serious injury area, the minor injury area, and the safe area according to the degree of damage;

[0096] 1 - Quantitative evaluation method for thermal radiation damage

[0097] The quantitative evaluation is carried out in the following steps:

[0098] (1) Calculate the thermal radiation intensity at any point:

[0099]

[0100] In the formula, t is the time s when the human body is exposed to thermal radiation, q is the thermal radiation intensity absorbed by the human body W / m; A and B are thermal radiation experimental parameters. For the death area, A = 41.38 and B = 2.56; for the serious injury area, A = 48.14 and B = 3.02; for the minor injury area, A = 44.83 and B = 3.02; for the safe area, A = 44.83 and B = 3.02;

[0101] (2) Calculate the damage radius R of thermal radiation:

[0102]

[0103] In the formula, D is the horizontal distance m from the target to the center of the fireball, q is the radiation intensity on the surface of the fireball, and the value of q0 is related to the shape of the leakage source. Take q0 = 240 KW / m 2 , and the solution of the damage radius is completed with the help of a computer;

[0104] (3) Calculate the action length: The action length is the pipeline length that generates specific hazards. The size of the action length depends on the distance from the target to the dangerous object and the external shape of the dangerous object. The calculation formula is as follows:

[0105]

[0106] In the formula, D is the horizontal distance from the target to the center of the fireball in m, and R is the damage radius in m;

[0107] (4) Calculate the risk value:

[0108] R g = L fb Pf r Formula 14

[0109] In the formula, P is the probability of the event occurring, and f r is the pipeline rupture frequency;

[0110] 2 - Quantitative evaluation method for shock wave damage

[0111] The TNT equivalent is used to represent the explosion power of a certain percentage of the vapor cloud participating in the explosion and making an actual contribution to the formation of the shock wave, and calculate the explosion pressure:

[0112]

[0113] ω is the TNT equivalent, with the unit of kg, and r is the distance, with the unit of m;

[0114] Preferably, for gas leakage and diffusion analysis:

[0115] Step 1, calculate the leakage amount: The leakage of the natural gas pipeline is the orifice outflow of compressible gas. Considering the local frictional resistance loss in the actual gas leakage process, the leakage velocity is less than the theoretical calculated value. Therefore, the orifice velocity coefficient is used for correction to calculate the leakage velocity and volume flow rate. The velocity of the gas leaking from the orifice is related to its flow state. When calculating the leakage amount, it is necessary to first determine whether the gas belongs to sonic or subsonic flow;

[0116] Step 2, calculate the Gaussian plume diffusion concentration;

[0117] Step 3, calculate the Gaussian puff diffusion concentration;

[0118] Use the above models to calculate the leakage velocity, flow rate, and diffusion concentration of the natural gas pressure pipeline, and estimate and determine the leakage coverage area of the natural gas to determine its diffusion influence range.

[0119] Compared with the prior art, the innovation points and advantages of this application are:

[0120] (1) This application meets the requirements of gas pipeline network safety management and solves several problems in the current stage of gas pipeline network safety management: First, manual detection has timeliness issues. Manual inspections cannot achieve real-time and effective coverage, and the gas leakage situation in relevant areas cannot be promptly grasped, making it impossible to issue early warnings about gas leakage in a timely manner. Second, the adjacent underground spaces of gas pipeline networks are complex, and there is a lack of an information sharing platform. The urban underground pipeline network system has a complex structure, and data collection is not systematic, resulting in insufficient information. It is impossible to understand the diffusion situation after gas leakage and discover risks in a timely manner. Third, there is no management mechanism based on urban public safety. Gas leakage monitoring involves gas monitoring in multiple types of adjacent underground spaces. Based on urban public safety, overall consideration, unified planning, and the establishment of a relatively complete monitoring system are required. The overall design framework of an urban gas pipeline network safety assessment system with the architecture system of "sensing, transmitting, knowing, and applying" has been established; the front-end sensing system deployment plan is designed using measurement point optimization technology to collect and store index data; the possible harmful consequences are evaluated to provide a scientific basis for the inspection and maintenance of gas pipeline networks and support for scientific decision-making and emergency response by relevant departments; the function modules of underground space information management, safety analysis, prediction and early warning, and auxiliary decision-making have been realized, and function demonstrations have been carried out. The key links of gas pipeline networks are monitored and effectively controlled in real time, effectively reducing accident risks and achieving proactive safety protection, providing a foundation for gas pipeline network safety monitoring and emergency management.

[0121] (2) This application establishes a gas pipeline network monitoring and assessment system based on public safety, integrating the Internet of Things, mobile Internet, and BIM / GIS information: First, the overall architecture of an urban gas pipeline network safety assessment system with the architecture system of Internet of Things sensing, transmitting, knowing, and applying is established; second, based on the analysis of data collection and storage requirements, a front-end sensing system deployment plan is established, a database system is built, and index data is collected and stored; third, a gas leakage hazard model is constructed to evaluate the possible harmful consequences and provide a basis for the inspection and maintenance of gas pipeline networks; fourth, the application layer module of the pipeline network monitoring system is constructed to realize the modules of underground space information management, safety analysis, prediction and early warning, and auxiliary decision-making; the urban gas pipeline network safety assessment establishes modules for risk identification of gas pipeline networks, viewing of basic information, monitoring and explosion early warning, three-dimensional visualization, and auxiliary decision-making. The operating conditions of gas pipeline networks are monitored in real time, the operating rules of gas pipeline networks are analyzed, risk assessments of gas pipeline networks are carried out, early warnings and decision-making processes are predicted and carried out in a timely manner, changing passive repair to proactive protection, and the monitoring stability, accuracy, and efficiency are high.

[0122] (3) This application utilizes information technologies such as the Internet of Things and GIS technology to establish a gas management safety assessment system, eliminating the backward manual management mode, realizing the automation and intelligence of gas safety monitoring, enhancing the safety management ability of urban lifelines, and being conducive to improving the safety management ability and emergency response ability of gas pipeline network management departments. The social benefits are very obvious: First, it improves the safety management level of gas pipeline networks. BIM modeling will be carried out on underground gas pipeline networks, and the monitoring units will be position-matched in the BIM model, facilitating the intuitive management of the safety monitoring system by the management department and obtaining corresponding information from it, which can significantly improve the safety management level of relevant departments. Second, it reduces the incidence of gas accidents. The risk levels of pipeline networks are evaluated, and early warnings are issued for pipelines with higher risk levels. Relevant personnel conduct inspections and repairs on pipelines with higher risk levels based on the early warning information, thereby reducing the occurrence of sudden accidents and changing the passive situation of post-disaster repair in the past by using an active defense method. Third, it can enhance the safety dispatching and emergency decision-making ability of decision-making departments. It can provide decision-makers with normal inspection functions and wartime dispatching functions. When an accident occurs, the system can accurately and timely display the accident location on the map and generate corresponding rescue plans, facilitating the dispatching of manpower, greatly improving the efficiency of disaster relief and rescue, accelerating the emergency response speed of relevant departments, and significantly reducing casualties and property losses.

[0123] (4) This application constructs a front-end perception system, including the establishment of underground pipe networks and spatial information, the layout of sensors, and the construction of a monitoring system. The concentration of combustible gases such as methane, ethane, carbon monoxide, and hydrogen sulfide in the underground space of the gas pipeline network is monitored through a front-end gas collection and monitoring instrument, so as to design the selection of monitoring methods and optimize the layout of monitoring points, achieving the widest monitoring coverage area, the highest monitoring efficiency, the lowest cost, and obtaining the data of each monitoring point in a timely and effective manner. Research and develop public safety technologies such as underground space risk identification technology, explosion protection, and gas leakage diffusion. Evaluate the risk level of the underground space, conduct consequence assessment and injury range prediction for possible explosions, and estimate the harmful area of gas diffusion, so as to facilitate hazard protection and take emergency measures in a timely manner. Design an application software system to integrate data collection, monitoring, and evaluation and analysis functions, and establish the following subsystems: ① Underground space information management system. Integrate and display the gas pipeline and underground space information collected in the early stage in the system, support the viewing, display, and editing of the location distribution of pipelines, manholes, underground parking lots, monitoring information, and historical data, facilitating the overall view of the underground pipe network and underground space information and providing great convenience for system visitors; ② Safety analysis system. Combine public safety theory to realize functions such as monitoring and evaluation of combustible gas leakage, analysis and display of combustible gas diffusion, and prediction of combustible gas hazards; ③ Prediction and early warning system. According to the danger information, analyze and calculate the situation, predict possible secondary disasters and derivative disasters, as well as estimate the impact method, hazard range, and hazard degree of the event, and give warnings in the system in a timely manner according to the early warning level and give relevant suggestions; ④ Auxiliary decision-making system. Give the best repair route, summarize and analyze the historical early warning situations, provide intelligent auxiliary decision-making functions, and facilitate decision-makers to issue relevant instructions. Description of the Drawings

[0124] Figure 1 is a schematic diagram of the gas collection work process. Figure 2 is a system logic architecture diagram of the pipeline Internet of Things transmission system. Figure 3 is a schematic diagram of the operation of the prediction and early warning system. Figure 4 is the overall flowchart of the gas pipeline network safety assessment system. Figure 5 is the road-level scoring standard diagram of this application. Figure 6 is a schematic diagram of the corresponding scores of high consequence area types of this application. Figure 7 is a schematic diagram of the accuracy analysis of image relationship construction. Figure 8 is a schematic diagram of the classification of the density of pedestrians and vehicles. Figure 9 is a classification diagram of the number of pipelines around the explosion hazard source and the degree of hidden loss consequences. Figure 10 is a classification diagram for determining the degree of judgment and evaluation of the operation risk level based on the obtained scores. Figure 11 is a schematic diagram of the optimization method driven by the maximum diffusion range. Figure 12Schematic diagram of the optimization method driven by the minimum diffusion distance. Figure 13 Schematic diagram of the login interface of the system browser of the present application. Figure 14 Schematic diagram of the three-dimensional map operation and three-dimensional scene display of the system of the present application. Figure 15 Design diagram of the map plotting interface of the present application. Specific implementation manners

[0125] The following further describes the technical solution of the three-dimensional GIS system for urban gas pipeline Internet of Things security assessment provided by the present application with reference to the accompanying drawings, so that those skilled in the art can better understand the present application and be able to implement it.

[0126] The present application establishes a gas pipeline network monitoring and evaluation system combining the Internet of Things, mobile Internet, and BIM / GIS information based on public safety, monitors the operation status of the gas pipeline network, analyzes the operation rules of the gas pipeline network, conducts risk assessment of the gas pipeline network, predicts, warns, and makes decisions in a timely manner, and changes from passive repair to active protection: (1) Analyze the limitations of the existing gas pipeline network management system in safety management, and establish the overall architecture of the urban gas pipeline network safety assessment system with the Internet of Things sensing, transmitting, knowing, and using as the architecture system; (2) Based on the analysis of data collection and storage requirements, establish a deployment plan for the front-end sensing system, build a database system, and collect and store index data; (3) Construct a gas leakage hazard model, evaluate the possible hazard consequences, provide a basis for the inspection and maintenance of the gas pipeline network, and provide support for relevant departments to make scientific decisions and emergency responses; (4) Construct an application layer module of the pipeline network monitoring system to implement underground space information management, safety analysis, prediction and warning, and auxiliary decision-making modules.

[0127] The urban gas pipeline network safety assessment establishes risk identification of the gas pipeline network, viewing of basic information, monitoring and explosion warning, three-dimensional visualization, and auxiliary decision-making modules.

[0128] The construction of the urban gas pipeline network safety assessment system aims to solve the problem of lack of timeliness in manual monitoring, realize the information sharing of pipeline network data, achieve the goal of digital management of the gas pipeline network and its adjacent underground space, provide accurate monitoring and evaluation information and scientific basis for management decision-makers, increase benefits and reduce losses, improve the early warning ability of pipeline network accidents, and contribute to public safety.

[0129] I. Design and construction of the system

[0130] Perform centralized, reliable, and mass storage of the collected data, multi-source information fusion analysis, big data mining, and normalized management, achieve professional analysis such as unified monitoring, multi-level early warning, safety assessment, and decision-making support, and provide real-time, regular, and irregular multi-level, multi-scale, and multi-dimensional urban gas pipeline network safety operation monitoring information services to relevant departments such as municipal, transportation, and gas, so as to facilitate the healthy operation of the gas pipeline network.

[0131] (I) Overall Architecture

[0132] Adopt a five-layer and two-wing structure. The five layers are the front-end perception system, network communication system, database system, application software system, and platform front-end display system in sequence; the two wings are the laws, regulations, standards, norms, and security guarantee systems followed by the system construction.

[0133] The system is constructed with the technical architecture of perception, transmission, knowledge, and application of the Internet of Things. Among them, perception is the front-end perception system, including various sensor facilities installed on the gas pipeline network. Transmission is to transmit the front-end monitoring data to the monitoring center in a wired and wireless manner through the perception network and the wide area network, realize the collection and transmission of sensor data, and data interaction during system application to ensure the normal operation of the system. Knowledge is the database system for data collection and storage. Application is the application software system, which is the core of the whole set of systems. It analyzes and processes based on the information perception, transmission, and collection of urban gas pipeline network monitoring and early warning, and escorts the safety of the entire urban lifeline.

[0134] (II) Front-end Perception System

[0135] Include the establishment of underground pipeline network and spatial information, sensor layout, and monitoring system construction, and monitor the concentration of combustible gas in the adjacent underground space of the gas pipeline network through the front-end gas collection monitor.

[0136] The monitoring objects are combustible gas and toxic gas, including methane, ethane, hydrogen sulfide, carbon monoxide, and carbon dioxide. The collection method is the multi-channel air sampling and extraction method. The system will use an aspirating multi-channel gas collection monitor to monitor the combustible and toxic gas in the underground space. The gas is collected by the extraction method, and a set of analysis equipment monitors and analyzes multiple points.

[0137] The gas collection work process is as follows: After the gas is extracted and collected from the underground space, it first passes through multiple solenoid valves, and the combustible gas at the monitoring points is selectively collected by controlling the on-off of the solenoid valves. It is necessary to perform water-vapor separation treatment on the extracted gas, and a special waterproof switch is set to prevent the gas sampler from inhaling groundwater and damaging the entire monitoring equipment. After the gas passes through the filter to adsorb other impurities, it enters the gas detector for concentration analysis. The gas collection work process is as Figure 1 shown.

[0138] The gas collector of this application consists of: a gas filter, a water vapor separator, an air suction pump, a flow controller, a gas dryer, and a combustible gas detector.

[0139] (3) Pipeline Internet of Things Transmission System

[0140] Two parts of transmission networks are involved in the data transmission process:

[0141] (1) Front-end sensing network transmission: Various sensors collect various gas concentration signals in real time, and use the CAN bus protocol to converge to the gateway module. The converged signals are subjected to A / D conversion and encoding, and then converted into the TCP / IP protocol for network transmission. After the data collected by the front-end sensors are converted by the gateway, they are transmitted to the monitoring center through the communication module via the mobile network of the telecommunications operator. The security of the transmission process is guaranteed through the application layer node authentication during the transmission process;

[0142] (2) Monitoring center network convergence: Configure an Ethernet router with VPN function to access the Internet, and store the information in the monitoring center database through a switch; The specific network topology is as Figure 2 shown.

[0143] The network transmission equipment includes the front-end Internet of Things access gateway module, the front-end preprocessing module, the communication module, and the router and switch in the monitoring center part.

[0144] (4) Gas Pipeline Network Database System

[0145] The database system stores information related to gas safety monitoring, including pipeline network basic data, model data, monitoring data, pre-plan information, event information, backup data, common basic information, monitoring information, and early warning information.

[0146] (1) Basic information database: storing data related to underground pipe networks; (2) Monitoring information database: storing monitoring data obtained by sensors, sensor addresses, time, and status information; (3) Early warning database: storing detailed early warning information generated by the system, including early warning types, levels, dates, and statuses; (4) Event information database: storing safety event information, prediction and early warning information, and safety event handling process information of urban lifeline pipe networks; (5) Geographic information database: geographic information with urban lifelines as a reference, including digital maps, remote sensing images, pipe network road networks, inspection well distributions, and important target distribution data; the forms of geographic information carriers include: digital line graphic DLG stored in vector form, digital elevation model data specifically used to express terrain undulations, raster format data of aerospace images, place name data, geographic metadata, and geographic information data in professional fields; (6) Model database: storing data related to models, including basic information of models, model chains, model utilization situations, and model parameter data; (7) Emergency plan database: the emergency plan database stores accident emergency plans related to pipe networks, including overall emergency plans, special emergency plans, and departmental emergency plans; (8) Case database: storing historical emergency event information and their response plans to provide effective references during disasters; (9) Knowledge database: a structured, easy-to-operate, easy-to-utilize, comprehensive, organized, and interconnected knowledge collection, including: general knowledge, summary knowledge, strategic knowledge, laws and regulations, standards, and technical specifications; (10) Document database: storing document information, including existing safety management documents, official documents, and newly generated documents.

[0147] Data engineering construction includes: construction of database systems, processing of three-dimensional geographic data, and collection, processing, and filing of engineering archive data.

[0148] 1. Processing of geographic information data

[0149] Including vector data, remote sensing images, aerial survey images, and digital elevation model data, which are processed and filed into the database by professional software ERDAS and ESRI ArcGIS. The data processing process includes coordinate system conversion, image mosaicing, image rectification, and two- and three-dimensional data fusion;

[0150] (1) DLG data: DLG provides spatial positioning services for the system and stores the spatial relationship of each element and related attribute information. The DLG data is processed as follows: 1) Check whether the geodetic datum, elevation datum, map projection method, and zoning of the original DLG data meet the requirements of the digital line drawing product standard; 2) Check the correctness and integrity of the data, the correctness and completeness of the definition of attribute items, the correctness of the data items, and whether the element attribute items are complete and in the correct order; 3) Check whether the layer names are correct, the definition of attribute items, the relationship between attribute items, and the topological relationship are correct, and whether the topology is rebuilt after editing; 4) Check the data edge connection; 5) Establish a vector data symbol library;

[0151] (2) DEM (digital elevation model) data: It is a multi-scale, multi-resolution database. DEM data of different scales use different grid spacings to make the represented ground model have different levels of detail. At the same time, it is used in conjunction with other data of the corresponding scale. DEM is stored in the corresponding sub-database according to the proportion. DEM data database construction includes: data preparation and inspection; data format conversion, projection conversion; data splicing, cutting according to standard map sheets; data storage according to the designed logical structure; data storage according to scale; pyramid establishment; database trial operation; data inspection after storage;

[0152] (3) Place name data: including information on administrative divisions, settlements, transportation place names, and various natural geographical place names. Place name data are stored separately according to proportion, and data of different sheets at the same proportion are stored in the same table in the database.

[0153] 2. Data preparation for pipeline network modeling

[0154] Modeling the underground space pipe network is to model the pipelines and pipe points. The modeling reference elements for pipelines include pipe length, pipe diameter, and starting point elevation. The modeling reference elements for pipe points include pipe point type and pipe point burial depth.

[0155] After the data attribute table format is adjusted, follow the steps below to complete the data preparation before modeling:

[0156] (1) Obtain the gas pipeline point data in shp format from the pipeline office; (2) Define the coordinate system for the shp data and convert it into a spherical coordinate system using coordinate conversion rules; (3) Perform spatial correction on the gas pipeline point data to correct the positions of the gas pipeline point data; (4) Delete duplicate gas pipeline point data; (5) Convert the corrected gas pipeline point data into a plane coordinate system; (6) Use professional software to generate the length of the pipeline data; (7) Re-fill the fields with null values in the gas pipeline point data with reference to the other pipeline attributes at their locations; (8) Use 3D GIS software to generate a gas pipeline point model from the shp format gas pipeline point data; (9) Check the generated gas pipeline point model. If large-scale unreasonable areas are found, check the shp format gas pipeline point data against the generated gas pipeline point model data until successful.

[0157] 3. Archive data collation and warehousing

[0158] The data processed for the gas pipeline network and its adjacent underground space includes the gas pipeline network geographical location data collection or electronic original business data, and engineering CAD drawing data. The specific contents include: (1) Gas pipeline network geographical location data collection; (2) Use GPS positioning to manually confirm or collect the gas pipeline network geographical location positioning data; (3) Scan and warehouse the paper-based plan of the gas pipeline network; (4) Scan the paper-based as-built drawings of the gas pipeline network to form high-definition pictures and upload them to the system for warehousing. The as-built drawings of the gas pipeline network required for BIM modeling are in CAD format. For paper-based data, manual electronic conversion is required before BIM modeling; (5) Collect, collate, and enter the gas pipeline network archives and related data; (6) Include gas pipeline network archives, equipment and facilities archives, engineering archives data, as well as gas pipeline network-related plans, cases, knowledge, and contact list data. For paper-based materials, after collation and analysis, they are directly entered into the system manually; for electronic data, after format analysis and collation, batch import is performed.

[0159] (V) Gas pipeline network application software system

[0160] It includes an underground space information management system, a safety analysis system, a prediction and early warning system, and an emergency auxiliary decision-making system.

[0161] 1. Underground space information management system

[0162] Integrated management and display of various gas leakage-prone pipelines or underground spaces in the city, including static information and dynamic information: (1) Static information includes the name, geographical location, construction year, safety level, historical maintenance records, and historical calculation information of relevant data of the monitored objects; (2) Dynamic information includes real-time monitoring data, safety status, and alarm signal display of sewage pipelines, rainwater pipelines, elevator shafts, civil air defense projects, and cable trenches.

[0163] 2. Safety analysis system: including: evaluation of combustible gas concentration in confined spaces, detection and evaluation of combustible gas leakage in confined spaces, analysis and evaluation of gas diffusion, prediction and evaluation of consequences of gas leakage, and other special evaluations.

[0164] 3. Prediction and early warning system: including: information integration, comprehensive prediction and analysis, and early warning information management. Figure 3 It is a schematic diagram of the operation of the prediction and early warning system.

[0165] 1) Comprehensive information integration: Integrate the professional monitoring and analysis result data required by the prediction and early warning system, and deliver the comprehensive results to the comprehensive prediction and analysis to generate early warning information; (1) Regional pipeline network information: The monitoring system reports the comprehensive pipeline information in the area where potential risks are located, including the distribution information of gas pipeline networks, rainwater pipeline networks, and inspection wells; (2) Urban geographic information: Evaluate the physical environment of the risk area, including road traffic conditions, surrounding spaces, high-rise buildings, crowded places, and current weather conditions; (3) Social information: Evaluate the potential impact of social factors on the risk area, including major social events, population distribution, and social economy;

[0166] 2) Comprehensive prediction and analysis: For the various aspects of data obtained after information integration, achieve early warning decision-making, provide multiple comprehensive prediction and analysis methods, analyze the targets, hazard sources, population and economic information within the scope of the event's impact, comprehensively evaluate the consequences of the event's impact, and adopt three early warning analysis methods: (1) Index early warning: Evaluate the state of the monitored object by formulating a comprehensive index, and predict the turning point of the safety cycle of the pipeline network system; (2) Calculation early warning: Use calculation methods to discover the fluctuation law of the monitored object (such as the concentration of combustible gas in a confined space); (3) Model early warning: Construct a mathematical model to evaluate the state of the monitored object.

[0167] (VI) Overall process

[0168] The overall process of the gas pipeline network safety assessment system is as Figure 4 shown. First, conduct a combustible gas explosion risk assessment on the underground pipeline network and adjacent spaces to determine the risk level distribution of each space. On this basis, optimize the layout of sensors, and conduct hierarchical monitoring on underground spaces with different risk levels. The monitoring methods include using fixed combustible gas monitors to monitor the concentration of combustible gas, mobile monitoring equipment to monitor possible gas leaks, and network public opinion monitoring. According to the monitoring results, divide the risk of explosion in the underground space, and through calculation, locate the leakage position and analyze the development trend of the risk. The system will release a risk map and early warning information about the accident information to relevant departments, and the system will also generate an emergency auxiliary decision-making plan, including a resource allocation map and the generation of an intelligent plan.

[0169] II. Key Technologies of the System

[0170] It includes 3D modeling, identification of dangerous spaces, optimized layout of measuring points, analysis of explosion damage, and analysis of gas leakage and diffusion.

[0171] (1) 3D Modeling: The CityMaker platform is used for modeling. For pipeline network modeling, a method of fine manual modeling of key components imported externally and automatic modeling of large-scale pipelines is adopted. The specific modeling process is as follows:

[0172] The first step is data preparation: the pipeline and pipe point data in the shapefile format in data engineering construction, and the 2D CAD data of pipe point auxiliary facilities;

[0173] The second step is fine modeling of auxiliary facilities and key parts: Using the 3ds Max manual modeling software, fine modeling is carried out for the key components of the gas pipeline network (tees, crosses, straight points, diameter changes, elbows, pipe deviation points, reserved openings) and auxiliary facilities (valve wells, condensate cylinders, right pipe caps, valves, underground and above-ground connections, pressure regulating boxes, left pipe caps, pressure regulating stations), and exported in the OSG format;

[0174] The third step is pipeline network modeling: The pipeline reference elements include pipe length, pipe diameter, starting point coordinates, and starting point elevation, and the pipe point reference elements include pipe point type and pipe point burial depth. Configure the color attributes of different pipelines, and model the pipeline network. The automatic modeling process using CityMaker Builder is as follows: 1) Configure the data source: Create a basic library, a planning library, and a municipal library. The basic library stores the data structure of the system and the style of the 3D models of pipe points and pipelines. The municipal library stores pipeline data, and the planning library stores vector data and specific scenarios; 2) Color library management: Manage the colors required during data driving, apply them in the editing of pipeline styles, and use colors to represent pipeline types when driving pipelines; 3) Export the attribute structure: Extract the attribute structure of the original data; 4) Configure reference elements: The modeling reference elements for pipelines include pipe length, pipe diameter, starting point coordinates, and starting point elevation, and the modeling reference elements for pipe points include pipe point type and pipe point burial depth; 5) Synchronize the municipal library: The synchronized municipal library has various facility types set in the facility library; 6) Facility designation: Designate the data in the temporary layer to the corresponding facility layer class, and set the matching relationship between the styles of pipelines and pipe points and the pipelines; 7) Add terrain data: Add terrain files in the ted format and above-ground building models to form an integrated 3D scene above and below the ground; 8) Drive the generation of the 3D scene.

[0175] The fourth step is model finishing and quality inspection: Check whether there are intersections or misalignments in the pipelines, and whether the pipelines and pipe point attachments are completely matched. For pipelines with errors, check and correct the data. If the data quality is okay, make local adjustments or translations to the attachments or pipelines to meet the visualization requirements;

[0176] Step 5: Export the project: export the generated pipeline and accessory 3D model data into fdb format, store them according to categories, and make the naming unique;

[0177] Step 6: Publish the scene: publish it in the local scene file scd format or publish it to the database to form a data service.

[0178] (II) Hazardous Space Identification

[0179] The hazard source is determined by conducting a risk assessment on each underground space. The risk assessment is divided into two levels. First, a risk assessment is conducted on each road within the monitoring range to determine the explosion risk in the area and coordinate the number of measuring points in the area. Then, an accurate explosion risk calculation is performed on each underground space adjacent to the gas pipeline network to determine the risk level of each underground space.

[0180] 1-Regional risk assessment: First, according to the risk assessment model, the vulnerability and consequence assessment of the high consequence area is carried out to obtain the risk characteristic value of the area. Then, the probability of pipeline failure in the area is considered to obtain the risk value. Then, the risk amount of the area is calculated according to the length of the pipeline, and the number of measuring points is calculated based on this.

[0181] The risk assessment model is based on the product of probability, vulnerability and consequence. The length or volume of each high-risk area is different, and the corresponding pipeline length and leakage probability of each high-risk area are also different. In the evaluation, the vulnerability and consequences of the high-risk area are evaluated as the risk characteristic value of the high-risk area, and then the risk is calculated based on the gas pipeline length and leakage probability of the area.

[0182] (1) Calculate the risk characteristic value F

[0183] The risk characteristic value F is expressed as the product of vulnerability and consequence. Vulnerability is based on road level and high consequence area, taking into account the volume of space where explosion may occur. Road level is related to the drainage capacity of the drainage pipeline under the road, and the drainage capacity is related to the diameter of the pipeline. The size of the high consequence area is directly related to the actual underground space volume in the area. The consequence takes into account the flow of people and vehicles in the area. The calculation method of the established risk characteristic value is as follows:

[0184] F = (a × D + b × G) × (C × M + d × R) Formula 1

[0185] In the formula, a, b, c, d are the weights of each evaluation index; D is the road level; G is the type of high consequence area; M is the traffic volume; R is the human flow;

[0186] (2) Analysis of evaluation factors

[0187] ① Road level D: According to the types of urban roads, urban roads are divided into five levels: one-way lane, two-way two-lane, two-way four-lane, two-way six-lane, two-way eight-lane and above. The more lanes there are, the higher the road level assignment. The road level scoring criteria are as Figure 5 ; The weight coefficient of the road level is 0.2; ② High-consequence area type G: According to the types and uses of buildings around gas pipelines, high-consequence areas include the following parts as Figure 6 , The weight coefficient of the high-consequence area type is 0.3; ③ Traffic flow M: The traffic flow of each section is monitored in real time, and the average value of the traffic flow of each section is calculated, which is divided into three levels: sparse, medium, and dense. The greater the traffic flow, the higher the score, and the overall score is 1-9. The weight coefficient of the traffic flow is 0.2; ④ Pedestrian flow R: The pedestrian flow of each section is monitored in real time, and the average value of the pedestrian flow of each section is calculated, which is divided into three levels: sparse, medium, and dense. The greater the pedestrian flow, the higher the score, and the overall score is 1-9. The weight coefficient of the pedestrian flow is 0.3;

[0188] (3) Risk level division

[0189] Risk value = f(failure probability, risk characteristic value). The risk level is the product of the pipeline failure probability and the risk characteristic value, and it is divided into four grades according to the results of risk quantification;

[0190] 2 - Underground space explosion risk assessment

[0191] The risk assessment results are represented in a three-dimensional matrix. The probability evaluation method is used to evaluate the risk level of each adjacent underground space of the gas pipeline network. According to the evaluation value, the risk level is given, and the monitoring measurement points are determined according to the risk level. The risk score of the risk assessment model:

[0192] D = V × P × C Formula 2

[0193] In the formula, P is the probability of a leakage accident; C is the consequence that will be caused once an accident occurs; V represents the probability of reaching the explosion condition after leakage, that is, the vulnerability of the space under leakage conditions. The size of the D value is positively correlated with the danger of the system. If the possibility of danger is high, countermeasures need to be taken to reduce the possibility of explosion and reduce the risk score to the safe range. Considering that the quantitative calculation process of V, P, and C is too cumbersome, and at the same time, the scientific reliability of the model needs to be considered, a semi-quantitative method is adopted for value calculation, and the levels of each component are divided according to the empirical model;

[0194] (1) Vulnerability V of accident occurrence: The vulnerability of accident occurrence consists of two parts: one is the possibility V1 of the concentration of combustible gas accumulating to the explosion limit, with a weight of W1; the other is the possibility V2 of having an ignition source with sufficient energy, with a weight of W2;

[0195] V = V1 × W1 + V2 × W2 Formula 3

[0196] ①V1: The sources of underground combustible gases are hydrogen sulfide, carbon monoxide, and carbon dioxide generated by the decomposition of organic substances in the well, as well as combustible gases such as methane and ethane volatilized from the leakage of the gas pipeline network. The areas where various combustible and dangerous gases flow are the connected pipe networks (sewage pipe network and rainwater pipe network). Secondly, after the gas pipeline leaks, it diffuses through the soil to various independent inspection wells or connected inspection wells and pipelines, and then diffuses upstream and downstream through the pipelines. According to the sources and diffusion scale of combustible gases, the following classification is made for various pipelines and inspection wells as Figure 7 , the combustible substances reaching the explosion limit is the prerequisite for the entire accident, and the weight W1 is 0.7;

[0197] ②V2: The ignition source is a necessary condition for the explosion of combustible gases. Whether it is easy to generate an ignition source is closely related to the explosion accident of manholes. Wells with power supply equipment are prone to explosion, so the danger level is 2. For wells without power supply equipment, the probability of having an ignition source in the well is low, so the danger level is 1, and the weight W2 is 0.3.

[0198] (2) Pipeline leakage probability P: The gas source of urban combustible gas explosion is the gas pipeline. There is an obvious positive correlation between the leakage probability of urban gas pipelines and the pipeline material. The corresponding score values for gas pipeline materials are: 10 points for cast iron pipelines, 3 points for steel pipelines, and 1 point for PE pipes;

[0199] (3) Consequences C of the accident: The accident consequences are divided into the original explosion damage range S1, the secondary damage range S2, the density E of people and vehicles in the damage range, and the hidden loss C3, with weights W3, W4, and W5 respectively;

[0200] C = S1 × E1 × W3 + S2 × E2 × W4 + C3 × W5 Equation 4

[0201] ①S1: The larger the space, the greater the accumulation capacity of combustible gases. After an explosion, the impact on surrounding pipelines and objects in the above-ground space is greater. Therefore, the C1 classification is quantitatively classified by the volume of the underground space, and the weight W3 is 0.6; ②S2: In addition to considering chain explosions, if there are flammable substances around the wellhead during an explosion, the explosion will ignite the flammable substances and cause a fire, and the weight W4 is 0.3; ③The degree classification E of the density of people and vehicles: The larger the number of pedestrians and vehicles on the road surface and the higher the population density, the more serious the consequences of the explosion will be. The degree classification is shown in Figure 8 ; ④C3: Considering the number of pipelines around the explosion hazard source, the degree classification of the hidden loss consequences is shown in Figure 9 , and the weight W is 0.1;

[0202] (4) Risk analysis and measuring point layout

[0203] The comprehensive wind risk calculation of the explosion of combustible gases in the gas pipeline network and its adjacent space is:

[0204] R = (V1 × W1 + V2 × W2) × P × (S1 × E1 × W3 + S2 × E2 × W4 + C3 × W5) Equation 5

[0205] By determining each score value, and through the analysis, evaluation, and utilization of the multiplication extreme values, the degree of operation risk is obtained, and the size of the evaluated risk is judged. For the degree classification, see Figure 10 .

[0206] (III) Optimal layout of measuring points

[0207] Considering the diffusion effect of combustible gas among gas pipelines, sewage pipelines, rainwater pipelines, and connecting wells, the leakage of combustible gas is comprehensively affected by factors such as diffusion time, diffusion volume, diffusion pressure, soil composition, moisture content, soil surface cover, and temperature.

[0208] (1) Optimization of measuring points between connecting wells

[0209] It is determined that the concentration distribution of gas is nearly the same within a certain area (R < 10 m), and all sewage and rainwater wells on the road section are included in the monitoring scope to accumulate data for the optimization of measuring points of connecting wells;

[0210] (2) Optimization of measuring points between non-connecting wells

[0211] Considering the scenario where combustible gas leaks and diffuses into surrounding pipelines and manholes, the connected sewage and rainwater wells have been set as measuring points during monitoring. The optimization calculation of non-connecting wells is based on the premise that sewage and rainwater wells must be monitored. According to the rules of the widest safety monitoring area of adjacent underground spaces of gas pipe networks, the smallest overlapping monitoring area, and the highest monitoring efficiency, two optimization schemes are established:

[0212] ① Optimization method driven by the maximum diffusion range: For example, Figure 11 , points A, B, and C respectively represent three adjacent inspection wells. Taking these 3 points as the centers, and R as the maximum leakage diffusion radius, circles are drawn with R as the radius. The chords intersecting with the gas pipe network are the pipeline ranges that each inspection well can monitor as a measuring point;

[0213] For example, Figure 11 (a), when there is a section between the monitoring ranges of point B that cannot be monitored by adjacent two points, following the rule that as many oil and gas pipelines as possible should be monitored, point B needs to be monitored as a measuring point; For example, Figure 11 (b), when the distance between point A and point C shrinks, and the monitoring range of point B is exactly covered by the monitoring ranges of point A and point C, point B is in a critical state of being monitored or not; For example, Figure 11 (c), when the distance between point A and point C further shrinks, and the monitoring range of point B is completely covered by the monitoring ranges of point A and point C, the monitoring range of point B has been fully monitored by point A and point C, and point B does not need to be monitored;

[0214] Assume that the coordinates of three wells A, B, and C are (x1, y1), (x2, y2), and (x3, y3) respectively, and the pipeline is located at y = 0:

[0215]

[0216] When the condition of Equation 6 is satisfied, point B does not need to be monitored.

[0217] ② Optimization method driven by the minimum diffusion distance: As Figure 12 shown, there are three adjacent inspection wells around the pipelines at points A, B, and C. The coordinates of the three inspection wells are A(x1, y1), B(x2, y2), and C(x3, y3) respectively. The pipeline is located at y = 0. The distances from any point D(x4, 0) on the pipeline to points A, B, and C are d1, d2, and d3 respectively. As Figure 12 (a) shows, if d2 < min(d1, d3), it means that there is a point on the pipeline with the shortest diffusion distance to B, and point B needs to be measured. Otherwise, the diffusion distance from any point on the pipeline to A or C is shorter than that to B. As Figure 12 (b) shows, point B does not need to be monitored;

[0218] First, discretize the pipeline. Divide the pipeline evenly into n segments, and take a point on each segment to represent the distance between this segment and each inspection well. The larger the value of n, the higher the accuracy, but the greater the computational amount. Considering the effective utilization rate of the measuring points, to achieve an appropriate distance and high utilization rate, optimize the second scheme again:

[0219] In the optimization method driven by the minimum diffusion distance in B, based on its optimization result, continue to perform optimization calculations according to the shortest diffusion distance optimization method, and then generate a set of measuring points calculated according to the distribution of the existing wells. Compared with the previous optimization result, the number of monitoring points decreases, but at the same time, the monitoring efficiency also decreases. If the reduced monitoring efficiency is acceptable, and the number of measuring points in the optimization result after deleting some points decreases and the input cost decreases, then this solution of measuring points is more suitable. Considering the shortest diffusion distance with the input funds, find a set of measuring points with the least input cost;

[0220] There are unpredictable variables among the influencing factors of the diffusion distance. Take the possible diffusion distances within one year as a probability function. When the measuring point is within the diffusion range, a leakage is detected, that is, there is a probability function P between the distance R from the measuring point to the leakage point and whether a leakage can be detected. There is always a minimum value R min and a maximum value R max of the diffusion distance. When R ≤ R min , a leakage is definitely detected, so the probability P = 1; when R > R max , the measuring point definitely cannot detect a leakage, so the probability P = 0; when R min < R ≤ R maxWhen P = f(R), where R is a continuous random variable;

[0221] After the measuring point position is determined, the distance R from each point on the pipeline to the monitoring point is calculated, and a relationship curve representing the relationship between the distance R and the corresponding pipeline length l is obtained. Assuming l = F(R), for different pipelines and different combinations of measuring points, the functional relationship of l = F(R) is different. The effective monitoring length is the expected value of the pipeline being monitored, that is:

[0222] L′ = Pl Equation 7

[0223] Substitute P = f(R) and l = F(R) into Equation 6, and we get:

[0224]

[0225] The monitoring efficiency is the ratio of the expected value of the pipeline being monitored to the total pipeline length (L), that is:

[0226] E = L′ / L Equation 9

[0227] In the leakage monitoring of the gas pipeline network, the cost performance V represents the ratio of the effective monitoring length to the investment funds. The ratio of the effective monitoring length to the number of measuring points n is used to represent the cost performance, that is:

[0228] V = L′ / n Equation 10

[0229] The specific optimization method is as follows: ① Use the optimization method driven by the minimum diffusion distance to calculate the preliminary distribution of measuring points; ② Calculate the pipeline length l′ monitored by each measuring point; ③ Calculate the effective monitoring length L′ according to Equation 8; ④ Calculate the monitoring efficiency E according to Equation 9; ⑤ Calculate the cost performance V according to Equation 10; ⑥ Sort l′ from largest to smallest, and delete the measuring point with the smallest l′; Recalculate according to ① to ⑥ to obtain the corresponding L′, E, V for different numbers of measuring points, and select the scheme according to the requirements of L′, E, V;

[0230] This method provides a scheme with the lowest cost while meeting the requirements of the effective monitoring length, the scheme with the highest cost performance, and also selects the most suitable monitoring scheme according to the change law of the cost performance with reference to the existing economic situation. It also provides the best scheme to meet the monitoring efficiency according to the requirements of the monitoring efficiency.

[0231] (IV) Explosion damage analysis

[0232] Quantitative analysis is carried out on the thermal radiation and shock wave damages respectively. According to the degree of damage, the harmful consequences are divided into four harmful areas: the death area, the serious injury area, the minor injury area, and the safe area.

[0233] 1 - Quantitative evaluation method for thermal radiation damage: The quantitative evaluation is carried out in the following steps:

[0234] (1) Calculate the thermal radiation intensity at any point:

[0235] In the formula, t is the time (s) that the human body is exposed to thermal radiation, q is the thermal radiation intensity absorbed by the human body (W / m²); A and B are thermal radiation experiment parameters. In the fatal area, A = 41.38 and B = 2.56; in the serious injury area, A = 48.14 and B = 3.02; in the minor injury area, A = 44.83 and B = 3.02; in the safe area, A = 44.83 and B = 3.02.

[0236] (2) Calculate the damage radius R of thermal radiation:

[0237] In the formula, D is the horizontal distance (m) from the target to the center of the fireball, q is the radiation intensity on the surface of the fireball, and the value of q0 is related to the shape of the leakage source. Take q0 = 240 KW / m² 2 , and the solution of the damage radius is completed with the help of a computer;

[0238] (3) Calculate the action length: The action length is the length of the pipeline that generates specific hazards. The size of the action length depends on the distance from the target to the dangerous substance and the external shape of the dangerous substance. The calculation formula is as follows:

[0239]

[0240] In the formula, D is the horizontal distance (m) from the target to the center of the fireball, and R is the damage radius (m);

[0241] (4) Calculate the risk value: R g = L fb Pf r Equation 14

[0242] In the formula, P is the probability of the event occurring, and f r is the pipeline rupture frequency.

[0243] 2 - Quantitative evaluation method for shock wave damage: Use the TNT equivalent to represent the explosion power of a certain percentage of the vapor cloud that participates in the explosion and makes an actual contribution to the formation of the shock wave, and calculate the explosion pressure:

[0244]

[0245] ω is the TNT equivalent, with the unit of kg, and r is the distance, with the unit of m.

[0246] (V) Gas leakage and diffusion analysis

[0247] Step 1, leakage volume calculation: The leakage of natural gas pipelines is the orifice outflow of compressible gas. Considering the local frictional resistance loss in the actual gas leakage process, the leakage velocity is less than the theoretical calculated value. Therefore, use the orifice velocity coefficient Correction, calculate the leakage rate and volume flow. The velocity of gas leakage from an orifice is related to its flow state. When calculating the leakage amount, it is necessary to first determine whether the gas is in sonic or subsonic flow. Step 2, calculate the Gaussian plume diffusion concentration; Step 3, calculate the Gaussian puff diffusion concentration; Use the above models to calculate the leakage rate, flow rate, and diffusion concentration of natural gas pipelines, estimate and determine the leakage coverage area of natural gas, and determine its diffusion influence range.

[0248] III. System Module Architecture

[0249] The system module includes gas risk identification, gas basic information, gas monitoring and alarm, gas explosion warning, auxiliary decision-making management, gas comprehensive calculation, and 3D visualization system. (1) System main interface: Users can enter the system login interface through a browser. As Figure 13 shown, by entering the corresponding login account and password, they can enter the main interface. (2) 3D visualization system: Realize functions such as basic operations of 3D maps, 3D scene display (3D model display), access to real-time monitoring data of monitoring devices, situation plotting, and display of monitoring data. The system meets the usage requirements of multiple roles such as system operation and maintenance units, experts, and government users.

[0250] System operators can enter the GIS screen by clicking the menu item "Real-time Monitoring" on the main interface. Reducing the map scale can enter the 3D map mode. As Figure 14 shown.

[0251] (1) Map operation: It is the basic function operation of the 3D map, realizing functions such as map street view browsing mode, full-screen display, roaming mode, sliding mode, full-map mode, map screenshot, and map clearing screen operation; (2) Hotspot management: Realize functions such as quick positioning of key positions and key areas, and user-defined hotspots (adding, deleting, modifying); (3) Layer management: Realize the display and hiding control management of vector layers; (4) Map measurement: Spatial measurement realizes the measurement and display of horizontal distance, vertical distance, spatial distance, and area in the 3D map; (5) Path tour: By setting a certain path, view the gas pipeline from multiple angles, specifically divided into above-ground building and underground pipeline tour modes; (6) Map plotting: Realize the addition and deletion functions of symbol plotting, text plotting, line plotting, surface plotting, circle plotting, and arrow plotting on the map. The map plotting interface design is as Figure 15 shown; (7) Comprehensive query: Divided into surrounding search and global search, by setting query conditions, query and filter out data that meet the query conditions. Locate resources, view information, and view detailed information of data cards. The comprehensive query not only searches for information on gas pipe networks, hazard sources, and protection targets, but also searches for buildings and institutions that meet the search conditions within a Figure 1 certain range.

Claims

1. Three-dimensional GIS system for safety assessment of urban gas pipeline Internet of Things, characterized in that Based on public safety, a gas pipeline network monitoring and evaluation system integrating the Internet of Things, mobile Internet, and BIM / GIS information is established to monitor the operation status of the gas pipeline network, analyze the operation rules of the gas pipeline network, conduct risk assessment of the gas pipeline network, predict and warn in a timely manner, and make decisions for handling, changing from passive repair to active protection: First, establish the overall architecture of the urban gas pipeline network safety assessment system with the Internet of Things' sense, transmission, knowledge, and application as the architecture system; Second, based on the analysis of data collection and storage requirements, establish a deployment plan for the front-end perception system, build a database system, and collect and store index data; Third, construct a gas leakage hazard model to evaluate the possible hazard consequences and provide a basis for the inspection and maintenance of the gas pipeline network; Fourth, construct the application layer module of the pipeline network monitoring system to realize the management of underground space information, safety analysis, prediction and warning, and auxiliary decision-making modules; The urban gas pipeline network safety assessment establishes risk identification of the gas pipeline network, viewing of basic information, monitoring and explosion warning, 3D visualization, and auxiliary decision-making modules; The overall process of the gas pipeline network safety assessment system: First, conduct a flammable gas explosion risk assessment of the underground pipeline network and adjacent spaces to determine the risk level distribution of each space. On this basis, optimize the layout of sensors, and conduct hierarchical monitoring of underground spaces with different risk levels. The monitoring methods include using fixed flammable gas monitors to monitor the concentration of flammable gas, mobile monitoring equipment to monitor possible gas leakage, and network public opinion monitoring. According to the monitoring results, divide the risk of explosion in the underground space, calculate and locate the leakage location, and analyze the development trend of the risk, and release a risk map and warning information for the accident information. The system will also generate an emergency auxiliary decision-making plan, including a resource allocation map and an intelligent plan; The key innovative technologies of the system include 3D modeling, dangerous space identification, optimized layout of measurement points, explosion damage analysis, and gas leakage diffusion analysis.

2. The three-dimensional GIS system for the safety assessment of the urban gas pipeline Internet of Things according to claim 1, wherein Overall architecture: Adopt a five-layer and two-wing structure. The five layers are the front-end perception system, network communication system, database system, application software system, and platform front-end display system in sequence; The two wings are the laws, regulations, standards, norms, and security guarantee systems followed by the system construction; The system is constructed with the Internet of Things' sense, transmission, knowledge, and application as the technical architecture. Among them, sense is the front-end perception system, including various sensor facilities installed on the gas pipeline network. Transmission is to transmit the front-end monitoring data to the monitoring center in a wired and wireless manner through the perception network and wide area network, realize the collection and transmission of sensor data, and data interaction during system application to ensure the normal operation of the system. Knowledge is the database system for data collection and storage. Application is the application software system, which is the core of the whole system and conducts analysis and processing based on the information perception, transmission, and collection of the urban gas pipeline network in monitoring and early warning.

3. The three-dimensional GIS system for urban gas pipeline Internet of Things security assessment according to claim 1, characterized in that, Front-end perception system: Include the establishment of underground pipeline network and space information, sensor layout, and monitoring system construction. Monitor the concentration of flammable gas in the adjacent underground space of the gas pipeline network through the front-end gas collection monitor; The monitoring objects are combustible gases and toxic gases, including methane, ethane, hydrogen sulfide, carbon monoxide and carbon dioxide. The sampling method is multi-channel air sampling and extraction. The system will use an aspirating multi-channel gas sampling and monitoring instrument to monitor combustible and toxic gases in underground spaces. The gas is collected by the extraction method, and a set of analysis equipment is used to monitor and analyze multiple points. The gas collection work process is as follows: After the gas is extracted and collected from the underground space, it first passes through a multi-channel solenoid valve. By controlling the on-off of the solenoid valve, the combustible gas at the monitoring point is selectively collected. It is necessary to carry out water-vapor separation treatment on the extracted gas. A waterproof switch is specially set to prevent the gas sampler from inhaling groundwater and damaging the entire monitoring equipment. After the gas passes through the filter to adsorb other impurities, it enters the gas detector for concentration analysis. The gas collection instrument of this application consists of: a gas filter, a water-vapor separator, an aspirating pump, a flow controller, a gas dryer, and a combustible gas detector.

4. The three-dimensional GIS system for urban gas pipeline Internet of Things security assessment according to claim 1, wherein Gas pipeline network database system: Stores information related to gas safety monitoring, including pipeline network basic data, model data, monitoring data, pre-plan information, event information and backup data, common basic information, monitoring information, and early warning information. (1) Basic information database: Stores data related to underground pipe networks. (2) Monitoring information database: Stores monitoring data obtained by sensors, sensor addresses, time, and status information. (3) Early warning database: Stores detailed early warning information generated by the system, including early warning types, levels, dates, and statuses. (4) Event information database: Stores safety event information, prediction and early warning information, and safety event handling process information of urban lifeline pipe networks. (5) Geographic information database: Geographic information with urban lifelines as a reference, including digital maps, remote sensing images, pipe network road networks, inspection well distributions, and important target distribution data; The forms of geographic information carriers include: digital line graphic DLG stored in vector form, digital elevation model data specially used to express terrain undulations, raster format data of aerospace images, place name data, geographic metadata, and geographic information data in professional fields. (6) Model database: Stores data related to models, including basic information of models, model chains, model utilization situations, and model parameter data. (7) Pre-plan database: The pre-plan database stores accident emergency plans related to pipe networks, including overall emergency plans, special plans, and departmental plans. (8) Case database: Stores historical emergency event information and their response plans, providing an effective reference during disasters. (9) Knowledge database: A structured, easy-to-operate, easy-to-utilize, comprehensive, organized, and interconnected knowledge collection, including: general knowledge, summary knowledge, strategic knowledge, laws and regulations, standards, and technical specifications. (10) Document database: Stores document information, including existing safety management documents, official documents, and newly generated documents. Data engineering construction includes: database system construction, three-dimensional geographic data processing, and collection, processing, and storage of engineering archive data.

5. The three-dimensional GIS system for the safety assessment of the urban gas pipeline Internet of Things according to claim 1, wherein Gas pipeline network application software system: It includes an underground space information management system, a safety analysis system, a prediction and early warning system, and an emergency auxiliary decision-making system; 1 - Underground space information management system Integrated management and display of various pipelines or underground spaces in the city where gas leakage may occur, including static information and dynamic information: (1) Static information includes the name, geographical location, construction year, safety level, historical maintenance records, and historical calculation information of relevant data of the monitored object; (2) Dynamic information includes real-time monitoring data, safety status, and alarm signal display of sewage pipelines, rainwater pipelines, elevator shafts, civil air defense projects, and cable trenches; 2 - Safety analysis system It includes: evaluation of combustible gas concentration in confined spaces, detection and evaluation of combustible gas leakage in confined spaces, analysis and evaluation of gas diffusion, prediction and evaluation of gas leakage consequences, and other special evaluations; 3 - Prediction and early warning system It includes: information integration, comprehensive prediction analysis, and early warning information management; 1) Comprehensive information integration: Integrate the professional monitoring and analysis result data required by the prediction and early warning system, and deliver the comprehensive result to the comprehensive prediction analysis to generate early warning information; (1) Regional pipeline network information: The monitoring system reports the comprehensive pipeline information of the area where potential risks are located, including the distribution information of gas pipeline networks, rainwater pipeline networks, and inspection wells; (2) Urban geographic information: Evaluate the physical environment of the risk area, including road traffic conditions, surrounding space, high-rise buildings, crowded places, and current weather conditions; (3) Social information: Evaluate the potential impact of social factors on the risk area, including major social events, population distribution, and social economy; 2) Comprehensive prediction analysis: Use the data from all aspects obtained after information integration to achieve early warning decision-making, provide various comprehensive prediction analysis methods, analyze the targets, hazard sources, population, and economic information within the scope of the event's impact, comprehensively evaluate the consequences of the event's impact, and adopt three early warning analysis methods: (1) Index early warning: Evaluate the state of the monitored object by formulating a comprehensive index to predict the turning point of the safety cycle of the pipeline network system; (2) Calculation early warning: Use calculation methods to discover the fluctuation law of the monitored object (such as the concentration of combustible gas in a confined space); (3) Model early warning: Construct a mathematical model to evaluate the state of the monitored object.

6. The three-dimensional GIS system for the safety assessment of the urban gas pipeline Internet of Things according to claim 1, wherein, 3D modeling: Use the CityMaker platform for modeling. Adopt the method of fine manual modeling of key components and external import, and automatic modeling of large-scale pipelines for pipeline network modeling. The specific modeling process is as follows: The first step, data preparation: The pipeline and pipe point data in the shapefile format in data engineering construction, and the 2D CAD data of pipe point auxiliary facilities; The second step, fine modeling of auxiliary facilities and key parts: Use the 3ds Max manual modeling software to finely model the key components such as tees, crosses, straight points, diameter changes, elbows, pipe offset points, and reserved openings of the gas pipeline network, as well as the auxiliary facilities of tees, crosses, straight points, diameter changes, elbows, pipe offset points, and reserved openings, and export them in the OSG format; The third step is to model the pipe network: the reference elements of the pipeline include the pipe length, pipe diameter, starting point coordinates, and starting point elevation. The reference elements of the pipe point include the pipe point type and pipe point burial depth. Configure the color attributes of different pipelines and model the pipe network. The automatic modeling process using CityMakerBuilder is as follows: 1) Configure data source: create a new basic database, planning database, and municipal database. The basic database stores the system data structure and the style of the 3D model of the pipe points and pipelines. The municipal database stores the pipeline data. The planning database stores the vector data and specific scenarios. 2) Color library management: manage the colors needed for data driving, which is used in pipeline style editing. When driving pipelines, colors are used to indicate pipeline types. 3) Attribute structure export: extract the attribute structure of the original data; 4) Configuration reference elements: The modeling reference elements for pipelines include pipe length, pipe diameter, starting point coordinates, and starting point elevation; the modeling reference elements for pipe points include pipe point type and pipe point burial depth; 5) Synchronize the municipal database: The synchronized municipal database contains all types of facilities set in the facility database; 6) Facility formulation: Facility designation assigns the data of the temporary layer to the corresponding facility layer class, and sets the style of pipelines and pipe points to match the pipelines; 7) Add terrain data: add terrain file ted format and ground building model to form a three-dimensional scene integrating the ground and underground; 8) Drive 3D scene generation; Step 4: Model finishing and quality inspection: Check whether there are any intersections or misalignments in the pipelines, and whether the pipelines and pipe point attachments are completely matched. For pipelines with errors, check and correct the data. If there is no problem with the data quality, it is necessary to make local adjustments or translations to the attachments or pipelines to make the visualization effect meet the requirements. Step 5: Export the project: export the generated pipeline and accessory 3D model data into fdb format, store them according to categories, and make the naming unique; Step 6: Publish the scene: publish it in the local scene file scd format or publish it to the database to form a data service.

7. The three-dimensional GIS system for urban gas pipeline Internet of Things security assessment according to claim 1, wherein Dangerous space identification: The hazard source is determined by conducting risk assessment on each underground space. The risk assessment is divided into two levels. First, a risk assessment is conducted on each road within the monitoring range to determine the explosion risk in the area and coordinate the number of measurement points in the area. Then, accurate explosion risk calculations are performed on each underground space adjacent to the gas pipeline network to determine the risk level of each underground space; 1- Regional risk assessment First, according to the risk assessment model, the vulnerability and consequence assessment of the high consequence area is carried out to obtain the risk characteristic value of the area. Then, the probability of pipeline failure in the area is considered to obtain the risk value. Then, the risk amount of the area is calculated according to the pipeline length, and the number of measuring points is calculated based on this. The risk assessment model is based on the product of probability, vulnerability and consequence. The length or volume of each high-risk area is different, and the corresponding pipeline length and leakage probability of each high-risk area are also different. In the evaluation, the vulnerability and consequences of the high-risk area are evaluated as the risk characteristic value of the high-risk area, and then the risk is calculated based on the gas pipeline length and leakage probability of the area. (1) Calculate the risk characteristic value F The risk characteristic value F is expressed as the product of vulnerability and consequence. The vulnerability is based on the road level and high-consequence areas, considering the spatial volume where an explosion may occur. The road level is related to the drainage capacity of the drainage pipeline under the road, and the drainage capacity is related to the pipeline diameter; the size of the high-consequence area is directly related to the actual underground space volume of the area. The consequence considers the traffic flow of people and vehicles in the area. The established calculation method for the risk characteristic value is as follows: F = (a×D + b×G)×(C×M + d×R) Equation 1 Where a, b, c, and d are the weights of each evaluation index; D is the road level; G is the type of high-consequence area; M is the traffic flow; R is the pedestrian flow; (2) Analysis of evaluation elements ① Road level D: According to the types of urban roads, urban roads are divided into five levels: one-way lane, two-way double lanes, two-way four lanes, two-way six lanes, two-way eight lanes and above. The more lanes there are, the higher the assigned value of the road level. The weight coefficient of the road level is 0.2; ② Type of high-consequence area G: Divided according to the types and uses of buildings around gas pipelines. The weight coefficient of the type of high-consequence area is 0.3; ③ Traffic flow M: The traffic flow of each section is monitored in real time, and the average value of the traffic flow of each section is calculated, which is divided into three levels: sparse, medium, and dense. The larger the traffic flow, the higher the score. The overall score is 1 - 9. The weight coefficient of the traffic flow is 0.2; ④ Pedestrian flow R: The pedestrian flow of each section is monitored in real time, and the average value of the pedestrian flow of each section is calculated, which is divided into three levels: sparse, medium, and dense. The larger the pedestrian flow, the higher the score. The overall score is 1 - 9. The weight coefficient of the pedestrian flow is 0.3; (3) Risk level classification The risk value = f(failure probability, risk characteristic value). The risk level is the product of the pipeline failure probability and the risk characteristic value, and is divided into four levels according to the results of risk quantification; 2 - Risk assessment of underground space explosion The risk assessment results are presented in a three-dimensional matrix. The probability evaluation method is used to evaluate the risk level of each adjacent underground space of the gas pipeline network. The risk level is given according to the evaluation value, and the monitoring points are determined according to the risk level. The risk score of the risk assessment model: D = V×P×C Equation 2 Where P is the likelihood of a leakage accident occurring; C is the consequence that will occur once an accident occurs; V represents the likelihood of reaching the explosion condition after a leakage, that is, the vulnerability of the space under leakage conditions. The magnitude of the D value is positively correlated with the danger of the system. If the likelihood of danger is high, countermeasures need to be taken to reduce the likelihood of explosion and reduce the risk score to the safe range. A semi-quantitative method is used for value calculation, and the levels of each component are divided according to the empirical model; (1) Vulnerability V of accident occurrence The vulnerability of accident occurrence consists of two parts: one is the likelihood V1 of the concentration of combustible gas accumulating to the explosion limit, with a weight of W1; the other is the likelihood V2 of having an ignition source with sufficient energy, with a weight of W2; V = V1×W1 + V2×W2 Equation 3 ①V1: The sources of underground combustible gases are hydrogen sulfide, carbon monoxide, and carbon dioxide generated by the decomposition of organic substances in the well, and combustible gases such as methane and ethane volatilized from the leakage of the gas pipeline network. The areas where various combustible and dangerous gases flow are the connected pipe networks (sewage pipe network and rainwater pipe network). Secondly, after the gas pipeline leaks, it diffuses through the soil to various independent inspection wells or connected inspection wells and pipelines, and then diffuses upstream and downstream through the pipelines. According to the sources and diffusion scales of combustible gases, various pipelines and inspection wells are classified. The combustible substances reaching the explosion limit are the prerequisite for the entire accident, and the weight W1 is 0.7; ②V2: The ignition source is a necessary condition for the explosion of combustible gases. Whether it is easy to generate an ignition source is closely related to the explosion accident of the manhole. Wells with power supply equipment are prone to explosion, so the danger level is 2. For wells without power supply equipment, the probability of having an ignition source in the well is low, so the danger level is 1, and the weight W2 is 0.3; (2) Pipeline leakage probability P The gas source of urban combustible gas explosion is the gas pipeline. There is an obvious positive correlation between the leakage probability of urban gas pipelines and the pipeline materials. The corresponding score values of gas pipeline materials are: 10 points for cast iron pipelines, 3 points for steel pipelines, and 1 point for PE pipes; (3) Consequences C of the accident The accident consequences are divided into the original explosion damage range S1, the secondary damage range S2, the density of people and vehicles E within the damage range, and the hidden loss C3, with weights W3, W4, and W5 respectively; C = S1×E1×W3 + S2×E2×W4 + C3×W5 Equation 4 ①S1: The larger the space, the greater the accumulation capacity of combustible gases. After an explosion, the impact on surrounding pipelines and objects in the above-ground space is greater. Therefore, the classification of C1 is quantitatively classified by the volume of the underground space, and the weight W3 is 0.6; ②S2: In addition to considering chain explosions, if there are flammable substances around the wellhead during the explosion, the explosion will ignite the flammable substances and cause a fire, and the weight W4 is 0.3; ③Classification of the density of people and vehicles E: The greater the pedestrian and vehicle flow on the road surface and the higher the population density, the more serious the consequences of the explosion will be; ④C3: Considering the number of pipelines around the explosion hazard source, the hidden loss consequence is light, and the weight W is 0.1; (4) Risk analysis and measuring point layout The comprehensive wind risk calculation of the explosion of combustible gases in the gas pipeline network and its adjacent space is: R = (V1×W1 + V2×W2)×P×(S1×E1×W3 + S2×E2×W4 + C3×W5) Equation 5 By determining each score value, as well as the analysis, evaluation, and utilization of the multiplication extreme value, the degree of operation danger is obtained, and the size of the evaluation danger is judged.

8. The three-dimensional GIS system for the safety assessment of the urban gas pipeline Internet of Things according to claim 1, characterized in that, Optimized layout of measuring points: Considering the diffusion effect of combustible gases among gas, sewage, rainwater pipe networks and connected wells, the leakage of combustible gases is comprehensively affected by diffusion time, diffusion volume, diffusion pressure, soil composition, moisture content, soil surface cover, and temperature factors; (1) Optimization of measuring points between connected wells It is determined that the gas concentration distribution is almost the same within a certain area (R < 10 meters), and all sewage and rainwater wells on the road section are included in the monitoring scope to accumulate data for the optimization of measuring points of connected wells; (2) Optimization of measuring points between non-connected wells Considering the scenario where gas leaks and spreads into surrounding pipelines and manholes, the connected sewage and rainwater wells have been set as measurement points during monitoring. The optimization calculation for non-connected wells is based on the premise that sewage and rainwater wells must be monitored. According to the rules of the widest safety monitoring area, the smallest overlapping monitoring area, and the highest monitoring efficiency for adjacent underground spaces in the gas pipeline network, two optimization schemes are established: ① Optimization method driven by the maximum diffusion range: Points A, B, and C respectively represent three adjacent inspection wells. Taking these 3 points as the centers and R as the maximum leakage diffusion radius, draw circles with radius R. The chords intersecting with the gas pipeline network are the pipeline ranges that each inspection well can monitor as a measurement point; When there is a section in the monitoring range of point B that cannot be monitored by two adjacent points, following the rule that as many oil and gas pipelines as possible should be monitored, point B needs to be monitored as a measurement point; When the distance between point A and point C decreases and the monitoring range of point B is exactly covered by the monitoring ranges of point A and point C, point B is in a critical state of being monitored or not. When the distance between point A and point C further decreases and the monitoring range of point B is completely covered by the monitoring ranges of point A and point C, the monitoring range of point B has been fully monitored by point A and point C, and point B does not need to be monitored; Assume the coordinates of the three wells A, B, and C are (x1, y1), (x2, y2), and (x3, y3) respectively, and the pipeline is located at y = 0; When Equation 6 is satisfied, point B does not need to be monitored; ② Optimization method driven by the minimum diffusion distance: Points A, B, and C are three adjacent inspection wells around the pipeline. The coordinates of the three inspection wells are A(x1, y1), B(x2, y2), and C(x3, y3) respectively, and the pipeline is located at y = 0. The distances from any point D(x4, 0) on the pipeline to points A, B, and C are d1, d2, and d3 respectively. If d2 < min(d1, d3), it means that there is a point on the pipeline with the shortest diffusion distance to B, and point B needs to be measured. Otherwise, the diffusion distance from any point on the pipeline to A or C is shorter than that to B, and point B does not need to be monitored; First, discretize the pipeline, evenly divide the pipeline into n segments, and take a point on each segment to represent the distance between this segment and each inspection well. The larger the value of n, the higher the accuracy, but the greater the computational effort. Considering the effective utilization rate of the measurement points, to achieve a suitable distance and high utilization rate, optimize Scheme 2 again: In the optimization method driven by the minimum diffusion distance in B, continue the optimization calculation according to the optimization result in the shortest diffusion distance optimization method, and a set of measurement points calculated based on the distribution of existing wells will be generated; compared with the previous optimization result, the number of monitoring points decreases, but at the same time the monitoring efficiency also decreases. If the reduced monitoring efficiency is acceptable, and the number of measurement points in the optimization result after deleting some points decreases and the investment cost decreases, then this measurement point solution is more suitable. Considering the shortest diffusion distance with the investment cost, find a set of measurement points with the least investment cost; There are unpredictable variables among the influencing factors of the diffusion distance. The possible diffusion distances within one year are regarded as a probability function. When a leak is detected at a measuring point within the diffusion range, that is, there is a probability function P between the distance R from the measuring point to the leak point and whether the leak can be detected. There is always a minimum value R of the diffusion distance min and a maximum value R max , when R ≤ R min , the leak is definitely detected, so the probability P = 1; when R > R max , the measuring point definitely cannot detect the leak, so the probability P = 0; when R min <R ≤ R max , assume P = f(R), where R is a continuous random variable; After the measuring point location is determined, the distance R from each point on the pipeline to the monitoring point is calculated, and a relationship curve representing the relationship between the distance R and the corresponding pipeline length l is obtained. Assuming l = F(R), for different pipelines and different combinations of measuring points, the functional relationship of l = F(R) is different. The effective monitoring length is the expected value of the pipeline being monitored, that is: L′ = Pl Equation 7 Substitute P = f(R) and l = F(R) into Equation 6 to get: The monitoring efficiency is the ratio of the expected value of the pipeline being monitored to the total pipeline length (L), that is: E = L′ / L Equation 9 In the leakage monitoring of the gas pipeline network, the cost performance V represents the ratio of the effective monitoring length to the investment funds. The ratio of the effective monitoring length to the number of measuring points n is used to represent the cost performance, that is: V = L′ / n Equation 10 The specific optimization method is as follows: ① Use the optimization method driven by the minimum diffusion distance to calculate the preliminary distribution of measuring points; ② Calculate the pipeline length l’ monitored by each measuring point; ③ Calculate the effective monitoring length L’ according to Equation 8; ④ Calculate the monitoring efficiency E according to Equation 9; ⑤ Calculate the cost performance V according to Equation 10; ⑥ Sort l’ from largest to smallest, and delete the measuring point with the smallest l’; Recalculate according to ① to ⑥ to obtain the corresponding L’, E, V for different numbers of measuring points, and select the plan according to the requirements of L’, E, V.

9. The three-dimensional GIS system for the safety assessment of the urban gas pipeline Internet of Things according to claim 1, characterized in that, Analysis of explosion damage: Quantitatively analyze the heat radiation and shock wave damage respectively, and divide the harmful consequences into four harmful areas: death area, serious injury area, minor injury area and safety area according to the degree of damage; 1 - Quantitative evaluation method for heat radiation damage The quantitative evaluation is carried out in the following steps: (1) Calculate the heat radiation intensity at any point: where t is the time s for the human body to be exposed to heat radiation, q is the heat radiation intensity absorbed by the human body W / m; A, B are heat radiation experimental parameters, A = 41.38, B = 2.56 in the death area, A = 48.14, B = 3.02 in the serious injury area, A = 44.83, B = 3.02 in the minor injury area, A = 44.83, B = 3.02 in the safety area; (2) Calculate the damage radius R of heat radiation: where D is the horizontal distance from the target to the center of the fireball in m, q is the radiation intensity on the surface of the fireball, and the value of q0 is related to the shape of the leakage source. Take q0 = 240 KW / m 2 , and the solution of the damage radius is completed with the aid of a computer; (3) Calculate the action length: The action length is the pipeline length that produces specific hazards. The size of the action length depends on the distance from the target to the dangerous object and the external shape of the dangerous object. The calculation formula is as follows: where D is the horizontal distance m from the target to the center of the fireball, R is the damage radius m; (4) Calculate the risk value: R g = L fb Pf r Equation 14 where P is the probability of the event occurring, and f r is the pipeline rupture frequency; 2 - Quantitative evaluation method for shock wave damage Use the TNT equivalent to represent the explosion power of a certain percentage of the vapor cloud that participates in the explosion and makes an actual contribution to the formation of the shock wave, and calculate the explosion pressure: ω is the TNT equivalent, in kg, r is the distance, in m.

10. The three-dimensional GIS system for urban gas pipeline Internet of Things security assessment according to claim 1, characterized in that, Analysis of gas leakage and diffusion: Step 1, leakage calculation: The leakage of a natural gas pipeline is the orifice outflow of a compressible gas. Considering the local frictional resistance loss in the actual gas leakage process, the leakage velocity is less than the theoretically calculated value. Therefore, the orifice velocity coefficient is used for correction to calculate the leakage velocity and volume flow rate. The velocity of the gas when leaking from the orifice is related to its flow state. When calculating the leakage amount, it is necessary to first determine whether the gas is in sonic or subsonic flow; When the gas is in sonic flow, the leakage velocity Step 2, calculate the Gaussian plume diffusion concentration; Step 3, calculate the Gaussian puff diffusion concentration; Use the above models to calculate the leakage velocity, flow rate, diffusion concentration of the natural gas pressure pipeline, estimate and determine the leakage coverage area of the natural gas, and determine its diffusion influence range.

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