A method for grading submarine pipeline scour disaster hazards and obtaining operation and maintenance time

Abstract

The present invention provides a method for grading the danger of submarine pipeline scour disasters and obtaining operation and maintenance time, which belongs to the field of submarine pipeline operation and maintenance technology; collects index data and stratifies them according to the formulated index system; performs index correlation and sensitivity analysis to determine important indicators; quantifies and assigns values ​​to indicators, and calculates index weights based on the analytic hierarchy process; performs disaster grading based on the submarine pipeline hazard assessment model; determines the operation and maintenance time of scour disasters based on the scour development model; collects on-site data of the project to be evaluated, the minimum bending radius, and the critical span length under scour action, and outputs the safe operation and maintenance time of the submarine pipeline based on three types of standards. The invention clarifies the main influencing factors and their weights of submarine scour disasters, and realizes the quantitative grading of submarine pipeline scour disasters; at the same time, it realizes the grading of the degree of operation and maintenance of submarine pipeline scour disasters in different sea areas, and provides guidance on whether operation and maintenance is needed and how many levels of operation and maintenance are needed.

Description

Technical Field

[0001] The present invention belongs to the technical field of submarine pipeline operation and maintenance, and in particular relates to a method for grading submarine pipeline scour disaster hazards and obtaining operation and maintenance time thereof. Background Art

[0002] Under the action of waves and currents, submarine pipelines often suffer from scouring disasters. However, there is no quantitative evaluation standard for what degree of scouring is a threat to the safety of submarine pipelines. The existing evaluation standards and evaluation systems usually involve a lot of subjective judgments due to the existence of many factors (disaster-causing factors), and cannot correctly guide the reasonable operation and maintenance of the relative projects.

[0003] Each disaster-causing factor (evaluation indicator) has a certain degree of influence on the occurrence of disasters and the degree of vulnerability, and the degree of influence varies. The influence of a certain indicator relative to other indicators can be expressed by weight. The degree of influence of each disaster-causing factor on the occurrence of disasters and vulnerability is sometimes difficult to determine and assign a quantitative value.

[0004] Most existing technologies are qualitative judgments, and are classified according to different scenarios, but the classification is not accurate enough. Some existing papers use mathematical models for calculation, but they are not combined with actual projects (that is, the indicators used to judge the level of scour disasters are difficult to obtain from actual projects), nor are there any analysis of the application field of scour disasters, nor are there any analysis of the indicators of submarine pipeline scour disasters. In addition, the hierarchical analysis method and fuzzy analysis method used still have human subjective judgment consciousness. Summary of the invention

[0005] In order to address the deficiencies of the prior art, the present invention combines a large number of experimental results and adopts a sensitivity analysis method to express the weights between parameters in a more quantitative manner, thereby reducing the subjectivity of risk assessment.

[0006] A first aspect of the present invention provides a method for grading the risk of submarine pipeline scour disasters, comprising the following process:

[0007] S1, the various factors affecting the safety of submarine pipeline scouring are defined as three layers, the submarine pipeline scouring hazard is defined as the target layer F; pipeline deformation factors, pipeline stability factors, seabed scouring factors and human factors are defined as the criterion layer ; The corresponding indicator factors under the criterion layer are defined as sub-criterion layers ;

[0008] S2, correlation and sensitivity analysis of indicator factors; by determining the correlation and sensitivity, determine the sub-criteria level and Criteria Layer The sensitivity ranking is based on the correlation R below 0.1. Eliminate;

[0009] S3, quantitative assignment of indicator factors; each sub-criteria layer indicator determined by S2 The value range is divided into several different intervals, and then a specific value is assigned to each interval. Each evaluation factor is quantitatively assigned 1, 3, and 6 according to low risk, medium risk, and high risk to obtain the quantitative assignment ;

[0010] S4, calculate the weight index according to the hierarchical analysis method; determine the mutual importance of the index factors by comparing them two by two, and compare the various relationships between the index factors, and calculate the weight R of the evaluation index;

[0011] S5, sub-criteria layer based on participation evaluation Quantitative assignment of The comprehensive index method is used to evaluate the hazard, and qualitative judgment is used to perform risk assessment zoning. The scour disaster hazard index is used to reflect the degree of disaster danger.

[0012] Preferably, in S2, a large amount of experimental and historical field data is collected, and the RBF neural network method is used to obtain the mapping relationship between the neural network criterion layer parameters and the sub-criterion layer indicators, and the correlation calculation is performed in turn after the target indicator is eliminated, and the sensitivity is determined from large to small according to the correlation coefficient R from small to large. Among them, if R is greater than 0.9 after eliminating the parameter, that is, the correlation of this indicator is lower than 0.1, then the sensitivity of this parameter is low and needs to be eliminated.

[0013] Preferably, the quantitative assignment of the indicator factors in S3 includes the following methods:

[0014] The transverse buckling deformation and longitudinal buckling deformation of the pipeline are assigned values ​​according to the minimum allowable bending radius. When the deformation is lower than the minimum allowable bending radius, it is defined as low risk and assigned a value of 1; when the deformation is greater than the minimum allowable bending radius, it is defined as high risk and assigned a value of 6; the rest of the states are medium risk and assigned a value of 3;

[0015] Among them, when the scour suspension length is less than the critical length under the hinged support boundary, it is defined as low risk and assigned a value of 1; when the scour suspension length is greater than the critical length under the fixed support boundary, it is defined as high risk and assigned a value of 6; the rest of the states are defined as medium risk and assigned a value of 3;

[0016] Among them, the extreme scour depth is calculated according to the scour prediction formula, and the quantitative values ​​are assigned as 1, 3, and 6, respectively, according to the ratio of scour depth to extreme scour depth of 30%, 60%, and 90% for low risk, medium risk, and high risk of scour disaster;

[0017] Among them, relative density is defined as low risk, medium risk and high risk according to the standards of dense, medium and loose, and the values ​​are assigned as 1, 3 and 6;

[0018] Among them, undrained shear strength is defined as low risk, medium risk and high risk according to dense, medium and weak, and the values ​​are assigned as 1, 3 and 6;

[0019] Among them, the median particle size is defined as low risk with a particle size less than 1mm and a dense seabed shear strength greater than 5Kpa, and is assigned a value of 1; the particle size is less than 1mm and the liquefied seabed shear strength is less than 1Kpa, which is prone to scouring and foundation instability, and is defined as high risk, and is assigned a value of 6; the rest of the particle sizes less than 1mm are defined as medium risk, and are assigned a value of 3; the fine sand dense seabed with a particle size of 1mm-4mm is defined as low risk, and is assigned a value of 1; the fine sand loose seabed with a particle size of 1mm-4mm is prone to scouring, and is defined as high risk, and is assigned a value of 6; the fine sand with a particle size of 1mm-4mm in other cases is defined as medium risk, and is assigned a value of 7; the sediment with a particle size greater than 4mm is large and not easy to scour, and is defined as low risk, and is assigned a value of 1;

[0020] Among them, the sediment uniformity coefficient is defined as low risk, medium risk and high risk according to the sediment uniformity coefficient σ>4, 4<σ<1, and σ<1, respectively, and the values ​​are 1, 3, and 6;

[0021] Among them, life-destructive activities are defined as low risk, medium risk, and high risk according to no damage, slight damage, and detectable damage, respectively, and are assigned values ​​of 1, 3, and 6;

[0022] Among them, pipeline installation connection defects are defined as low risk, medium risk and high risk according to composite connection, flexible connection and rigid connection, and are assigned values ​​of 1, 3 and 6 respectively.

[0023] Preferably, in S4, the method of pairwise comparison between factors is used to score the relevant factors under each criterion layer, and finally obtain a number of pairwise comparison matrices; through calculation and analysis and comparison, the judgment matrix is ​​appropriately adjusted to achieve good consistency of the judgment matrix, and the judgment matrix is ​​obtained. ; Use this matrix to calculate the sub-criteria layer in turn First-level weight and criteria layer The indicator weight of the secondary weight is finally multiplied by the weight to obtain the total weight of each indicator target layer ,matrix As shown below:

[0024] ;

[0025] In the formula, each data in the matrix is It is expressed as the importance ratio of index factor p to index factor q; n represents the sub-criteria layer used for calculation Total number of;

[0026] Under the same criterion level, when comparing any two factors, the importance of index factor p and index factor q is , and the ratio of the index factor q to the index factor p is 1 / , are reciprocals of each other;

[0027] in The value selection method is as follows: the index ranking obtained by the sensitivity analysis method is defined as 1 for the importance of two factors with adjacent ranks, 3 for the one with one rank difference, and 5 for the one with two rank differences. The ranking is based on sensitivity, and is ranked in order of 7 and 9.

[0028] Among them, 1 means that the two factors are equally important; 3 means that one factor is slightly more important than the other; 5 means that one factor is obviously more important than the other; 7 means that one factor is strongly more important than the other; 9 means that one factor is extremely more important than the other; 2, 4, 6, and 8 are the medians of the above adjacent judgments.

[0029] Preferably, the indicator weight calculation process is:

[0030] Calculate the elements of each row of the judgment matrix The product of:

[0031] ;

[0032] Calculate the nth root of Mp:

[0033] ;

[0034] Vector After normalization, we get the feature vector ,in:

[0035] ;

[0036] This characteristic vector is the weight of each indicator, each criterion layer , The weights are , , the total weight is ;

[0037] Then, a total hierarchical ranking is performed, that is, the ranking weight of the relative importance of each indicator factor in the indicator layer is calculated respectively, and the total ranking is checked for consistency to ensure accuracy.

[0038] Preferably, in S5, a comprehensive index method is used to evaluate the risk, and qualitative judgment is used to perform risk assessment and zoning. The mathematical model for evaluating the risk index is:

[0039] ;

[0040] In the formula, F is the disaster risk index; n is the total number of risk assessment indicators; R(j) is the weight value of each assessment indicator; Assign quantitative data to each risk index;

[0041] Substitute the values ​​of 1, 3, 6, etc. of the indicators into the model to calculate the upper and lower limits of F. and , calculate the hazard index F. The higher the hazard index, the lower the safety of the submarine pipeline in place and the higher the risk of danger. and ,according to , , , , divided into four risk levels: low risk, medium risk, relatively high risk and high risk.

[0042] The second aspect of the present invention provides a method for obtaining the operation and maintenance time of a submarine pipeline scour disaster, using the hazard level obtained by the submarine pipeline scour disaster hazard classification method as described in the first aspect, and comprising the following process:

[0043] S1, determine the time corresponding to the on-site scouring depth ;

[0044] S2, based on the on-site hydrological and seabed parameters, the scour development model is calculated to be greater than The pipeline scouring depth at different times is input into the mathematical model for hazard index evaluation;

[0045] S3, until a certain moment when the mathematical model of the hazard index evaluation outputs a high risk, the moment corresponding to the high-risk scour depth is determined ;

[0046] S4, output Time obtained , which is the number of days allowed for operation and maintenance under this condition.

[0047] Preferably, the functional expression of the scour development model is:

[0048]

[0049] Where S(t) is the absolute value of the scouring depth under the pipeline at any time, t is any scouring time; S eq is the dimensionless time scale of the equilibrium flushing below the pipeline T * The expression is:

[0050]

[0051] Where T is the time scale, which refers to the time when substantial scour occurs, s is the relative density ratio, and d is the relative density ratio. 50 is the median particle size of the sediment on the seabed, g is the acceleration of gravity, and D is the diameter of the pipe;

[0052] In the formula, pipeline flushing time scale T and Shields number θ sc Based on a large number of experimental results, the Hill number θ under steady flow conditions is proposed. sc The dimensionless time scale prediction formula is:

[0053]

[0054] Where, the dimensionless shear stress θ when the water flow acts on the seabed under complex seabed conditions is sc The expression is corrected to:

[0055]

[0056] In the formula, is the critical starting shear stress, g is the acceleration of gravity, calculated according to the specification; is the bulk density of sediment, is the water specific gravity, is the median particle size of sediment.

[0057] Preferably, the safe operation and maintenance time of submarine pipelines under the influence of various factors is determined according to the following standards:

[0058] Category I standard: When the transverse buckling and longitudinal buckling detected at the site of the project to be evaluated are greater than the minimum allowable bending radius, immediate repairs are carried out, and the repair time is less than 3 days; when the scour suspension length detected at the site of the project to be evaluated is greater than the critical suspension length, immediate repairs are carried out, and the repair time is less than 3 days;

[0059] Category II standard: When the pipeline is extremely damaged, it is repaired immediately and the repair time is less than 3 days;

[0060] Category 3 standards: When the lateral buckling, longitudinal buckling, scour suspension length and extreme damage do not meet the Category 1 and Category 2 criteria, the maintenance time shall be based on the scour disaster operation and maintenance time of the submarine pipeline; when the scour disaster operation and maintenance time is greater than the regular pipeline inspection time, the operation and maintenance inspection shall be carried out according to the inspection time, and the pipeline safety assessment shall be re-performed; when the operation and maintenance time is less than the regular pipeline inspection time, the scour disaster operation and maintenance time shall be used as the basis for corresponding treatment and testing.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] The present invention clarifies the main influencing factors and their weights of submarine scouring disasters, and realizes the quantitative classification of submarine pipeline scouring disasters; at the same time, it realizes the classification of the operation and maintenance degree of submarine pipeline scouring disasters in different sea areas, and provides a calculation method for whether operation and maintenance is required and the operation and maintenance time for scouring disasters that account for the main destructive impact on the submarine pipeline site, solving the engineering problem that the operation and maintenance of submarine pipeline scouring disasters can only be carried out by periodic side sweeps, which is costly; and provides guidance on the overall submarine pipeline safety operation and maintenance level and operation and maintenance time, taking into account safety factors such as scouring, overhanging and deformation;

[0063] Among them, the present invention considers more comprehensive indicators when grading scour disasters, integrating four factors: pipeline deformation factors, pipeline stability factors, seabed scour factors, and human factors, and considering the joint influence of more than ten sub-criteria layers to form a multi-factor, systematic, and comprehensive grading system. The indicators of this scheme are all indicators that can be directly obtained at the construction site, which is more convenient for use at the construction site;

[0064] Among them, a new index grade assignment method for submarine pipeline scour disasters and deformation disasters was designed. In particular, in the index grade assignment of submarine pipeline scour, the combined effect of two indicators, the median particle size of the seabed and the shear strength of the seabed, was considered comprehensively, which is more in line with the complex working conditions of actual submarine engineering and is a more objective and comprehensive evaluation process.

[0065] Among them, a new method of using sensitivity to determine the weight assignment of indicators was designed. Compared with the artificially specified method in the original hierarchical analysis method, it achieved a more objective evaluation and improved the objectivity of the disaster assessment process based on the hierarchical analysis method.

[0066] Among them, a new method for calculating the operation and maintenance time for the scouring disaster that accounts for the main destructive effect on the submarine pipeline site was designed, which solved the engineering problem that the on-site engineering can only be scanned periodically and the operation and maintenance time cannot be calculated scientifically, and provided a reference for on-site control of scouring disasters. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In order to more clearly illustrate the technical solutions of the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, what is described below is only one embodiment of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0068] Figure 1 It is an overall flow chart of the method for grading the risk of submarine pipeline scour disasters and obtaining operation and maintenance time thereof according to the present invention.

[0069] Figure 2 It is a schematic diagram of the submarine pipeline scour disaster evaluation index system of the present invention.

[0070] Figure 3 It is a specific flow chart of the method for obtaining submarine pipeline operation and maintenance time of the present invention. DETAILED DESCRIPTION

[0071] The present invention provides a method for grading the risk of submarine pipeline scour disasters and obtaining operation and maintenance time. The overall process is as follows: Figure 1 As shown:

[0072] S1, the various factors affecting the safety of submarine pipeline scouring are defined as three layers, the submarine pipeline safety assessment is defined as the target layer F; pipeline deformation factors, pipeline stability factors, seabed scouring factors and human factors are defined as the criterion layer ; The corresponding indicator factors under the criterion layer are defined as sub-criterion layers ;

[0073] S2, correlation and sensitivity analysis of indicator factors; by determining the correlation and sensitivity, determine the sub-criteria level and Criteria Layer The correlation and sensitivity of the sub-criteria layer indicators with correlation less than 0.01 Eliminate;

[0074] S3, quantitative assignment of indicator factors; each sub-criteria layer indicator determined by S2 The value range is divided into several different intervals, and then a specific value is assigned to each interval. Each evaluation factor is quantitatively assigned 1, 3, and 6 according to low risk, medium risk, and high risk to obtain the quantitative assignment ;

[0075] S4, calculate the weight index according to the hierarchical analysis method; determine the mutual importance of the index factors by comparing them two by two, and compare the various relationships between the index factors, and calculate the weight R of the evaluation index;

[0076] S5, sub-criteria layer based on participation evaluation Quantitative assignment of and weight R(j), as well as the corresponding real-time data obtained, the comprehensive index method is used to evaluate the hazard, and qualitative judgment is used to perform risk assessment zoning, and the scour disaster hazard index is used to reflect the hazard level of the disaster;

[0077] S6, collects the on-site data, minimum curvature radius, and critical overhang length of the project to be evaluated, calculates the scouring operation and maintenance time of the project to be evaluated, and outputs the corresponding operation and maintenance time according to the three types of standards.

[0078] The present invention first provides a submarine pipeline scour disaster evaluation index system, which are all parameters that can be detected on site, such as Figure 2 As shown, it includes the target layer F and the criterion layer and sub-criteria layer There are three layers of content, among which the sub-criteria layer is the indicator layer.

[0079] The target layer is the safety hazard of submarine pipelines; the criterion layer includes pipeline deformation factors, pipeline stability factors, seabed scour development factors and human factors, which correspond to four specific classification criteria: axial stress, natural frequency, scour depth and damage degree. The sub-criteria layer corresponds to three criteria in turn. The axial stress includes three indicators: pipeline lateral buckling, pipeline longitudinal buckling and pipeline elastic modulus. The natural frequency includes three indicators: flow velocity, scour depth and suspended length. The seabed scour depth includes four indicators: relative density, undrained shear strength, median particle size and sediment unevenness coefficient. Human factors include two indicators: damage from life activities and pipeline installation and connection defects.

[0080] The present invention provides a method for determining the operation and maintenance time based on on-site observable data and taking into account submarine pipeline scour disasters. The overall process is as follows: Figure 3 As shown, including:

[0081] S1, determine the time corresponding to the on-site scouring depth ;

[0082] S2, based on the on-site hydrological and seabed parameters, the scour development model is calculated to be greater than The pipeline scouring depth at different times is input into the mathematical model for hazard index evaluation;

[0083] S3, until a certain moment when the mathematical model of the hazard index evaluation outputs a high risk, the moment corresponding to the high-risk scour depth is determined ;

[0084] S4, output Time obtained , which is the number of days allowed for operation and maintenance under this condition.

[0085] The present invention provides a method for determining the safe operation and maintenance time of a submarine pipeline under various factors, which includes three types of standards:

[0086] Category I standard: When the transverse buckling and longitudinal buckling detected at the site of the project to be evaluated are greater than the minimum allowable bending radius, immediate repairs are carried out, and the repair time is less than 3 days; when the scour suspension length detected at the site of the project to be evaluated is greater than the critical suspension length, immediate repairs are carried out, and the repair time is less than 3 days;

[0087] Category II standard: When the pipeline has extreme damage, such as detectable leakage, rupture and other disasters, it should be repaired immediately, and the repair time should be less than 3 days;

[0088] Category III standards: When the lateral buckling, longitudinal buckling, scour suspension length and extreme damage do not meet the criteria for Category I and Category II, the maintenance time shall be based on the operation and maintenance time of submarine pipeline scour disasters. When the operation and maintenance time of scour disasters is longer than the regular inspection time of pipelines, operation and maintenance inspections shall be carried out according to the inspection time, and the pipeline safety assessment shall be re-performed. When the operation and maintenance time is less than the regular inspection time of pipelines, the operation and maintenance time of scour disasters shall be used as the basis for corresponding treatment and testing.

[0089] 1. Get the sub-criteria layer indicator parameters

[0090] Among the factors of pipeline deformation, the transverse buckling of the pipeline, the longitudinal buckling of the pipeline, the scouring depth and the hanging length are identified by imaging methods such as on-site sonar, hydroacoustic and remote sensing;

[0091] The relative density and undrained shear strength of the scour development and bearing factors are determined by field penetration tests; the median particle size and sediment heterogeneity coefficient are determined in the laboratory after field tubular sampling;

[0092] Among the human factors, damage caused by life activities and defects in pipeline installation connections are identified by on-site visual or acoustic imaging on the seabed.

[0093] 2. Correlation and sensitivity analysis between sub-criteria level indicators and criterion level parameters

[0094] A correlation analysis model between sub-criteria layer indicators and criterion layer parameters is established, and a large amount of experimental and historical field data is collected. The mapping relationship between the neural network criterion layer parameters and the sub-criteria layer indicators is obtained through the RBF neural network method. All sub-criteria layer indicators are used as input and criterion layer parameters are used as output. The neural network multivariate calculation is performed in sequence to obtain the correlation coefficient between the input and output. After that, one of the indicators is eliminated in turn, and the eliminated sub-criteria layer parameters are used as input and the criterion layer is used as output. The correlation between the remaining parameters and the criterion layer parameters after the parameters are eliminated is calculated. Based on this, the elimination calculation of all indicators is completed in turn, and the sensitivity is determined from large to small according to the correlation coefficient R of each eliminated indicator model from small to large. Among them, if R is greater than 0.9 after eliminating the parameter, the sensitivity of this parameter is low and needs to be eliminated. That is, the sub-criteria layer indicators with a correlation R lower than 0.1 Eliminate.

[0095] The correlation analysis model of pipeline deformation factors is:

[0096]

[0097] Culling The subsequent calculation model is:

[0098]

[0099] Culling The subsequent calculation model is:

[0100]

[0101] Culling The subsequent calculation model is:

[0102]

[0103] The correlation analysis model of pipeline stability factors is:

[0104]

[0105] Culling The subsequent calculation model is:

[0106]

[0107] Culling The subsequent calculation model is:

[0108]

[0109] Culling The subsequent calculation model is:

[0110]

[0111] The correlation analysis model of seabed scour factors is as follows (the sandy seabed is not considered , clay seabed is not considered ):

[0112]

[0113] Culling The subsequent calculation model is:

[0114]

[0115] Culling The subsequent calculation model is:

[0116]

[0117] Culling The subsequent calculation model is:

[0118]

[0119] Culling The subsequent calculation model is:

[0120]

[0121] Human factors are accident types that can be directly predicted and are all indicators with strong correlation, so no correlation analysis is required.

[0122] 3. Quantitative assignment of indicators at the sub-criteria level

[0123] The transverse buckling deformation and longitudinal buckling deformation of the pipeline are assigned values ​​according to the minimum allowable bending radius. When the deformation is lower than the minimum allowable bending radius, it is defined as low risk and assigned a value of 1; when the deformation is greater than the minimum allowable bending radius, it is defined as high risk and assigned a value of 6; the rest of the states are medium risk and assigned a value of 3;

[0124] When the pipe deformation modulus is lower than 50% of the maximum pipe deformation modulus, it is defined as low risk and assigned a value of 1; when the pipe deformation modulus is greater than the maximum pipe deformation modulus, it is defined as high risk and assigned a value of 6; the rest of the states are defined as medium risk and assigned a value of 3;

[0125] When the scouring suspended length is less than the critical length under the hinged support boundary, it is defined as low risk and assigned a value of 1; when the scouring suspended length is greater than the critical length under the fixed support boundary, it is defined as high risk and assigned a value of 6; the rest of the states are defined as medium risk and assigned a value of 3;

[0126] When the water flow velocity is less than the critical starting velocity of sediment, it is defined as low risk and assigned a value of 1; when the water flow velocity is greater than the critical starting velocity of sediment, it is defined as high risk and assigned a value of 6;

[0127] The ultimate scour depth is calculated according to the scour prediction formula, and the quantitative values ​​are assigned as 1, 3, and 6, respectively, according to the ratio of scour depth to ultimate scour depth of 30%, 60%, and 90% for low risk, medium risk, and high risk of scour disasters;

[0128] Relative density is defined as low risk, medium risk, and high risk according to the dense, medium, and loose standards, and is assigned values ​​of 1, 3, and 6;

[0129] Undrained shear strength is defined as low risk, medium risk, and high risk according to dense, medium, and weak, and is assigned values ​​of 1, 3, and 6;

[0130] The median particle size is defined as low risk with a particle size less than 1mm and a dense seabed shear strength greater than 5Kpa, and is assigned a value of 1; the particle size is less than 1mm and the liquefied seabed shear strength is less than 1Kpa, which is prone to scouring and foundation instability, and is defined as high risk, and is assigned a value of 6; the rest of the particle sizes less than 1mm are defined as medium risk, and are assigned a value of 3; the fine sand dense seabed with a particle size of 1mm-4mm is defined as low risk, and is assigned a value of 1; the fine sand loose seabed with a particle size of 1mm-4mm is prone to scouring, and is defined as high risk, and is assigned a value of 6; the fine sand with a particle size of 1mm-4mm is defined as medium risk in other cases, and is assigned a value of 7; the sediment with a particle size greater than 4mm is large and not easy to scour, and is defined as low risk, and is assigned a value of 1;

[0131] The sediment uniformity coefficient is defined as low risk, medium risk and high risk according to the sediment uniformity coefficient σ>4, 4<σ<1, and σ<1, respectively, and the values ​​are assigned as 1, 3, and 6;

[0132] Life-destructive activities are defined as low risk, medium risk, and high risk according to no damage, slight damage, and detectable damage, respectively, and are assigned values ​​of 1, 3, and 6;

[0133] Pipeline installation connection defects are defined as low risk, medium risk and high risk according to composite connection, flexible connection and rigid connection, and are assigned values ​​of 1, 3 and 6 respectively.

[0134] 4. Calculation of indicator weights

[0135] The method of pairwise comparison between factors is used to score the relevant factors under each criterion layer, and finally several pairwise comparison matrices are obtained; through calculation and analysis and comparison, the judgment matrix is ​​appropriately adjusted to achieve good consistency of the judgment matrix, and the judgment matrix is ​​obtained. ; Use this matrix to calculate the sub-criteria layer in turn First-level weight and criteria layer The indicator weights of the secondary weights are finally multiplied by weights to obtain the total weight R of each indicator target layer, matrix As shown below:

[0136] ;

[0137] In the formula, each data in the matrix is It is expressed as the importance ratio of index factor p to index factor q; n represents the sub-criteria layer used for calculation Total number of;

[0138] Under the same criterion level, when comparing any two factors, the importance of index factor p and index factor q is , and the ratio of the index factor q to the index factor p is , are reciprocals of each other;

[0139] Calculate the elements of each row of the judgment matrix The product of:

[0140] ;

[0141] Calculate the nth root of Mp:

[0142] ;

[0143] Vector After normalization, we get the feature vector ,in:

[0144] ;

[0145] This characteristic vector is the weight of each indicator, each criterion layer , The weights are , , as shown in Table 1. Calculated as .

[0146] Table 1 - Judgment matrix and weights

[0147]

[0148] The total ranking of the levels is to find out the ranking weights of the relative importance of each factor in the indicator layer of the disaster risk evaluation index system. The total ranking should also be tested for consistency to ensure accuracy. Generally, the larger the CI value, the more consistent the judgment matrix is; CR is used to judge whether the judgment matrix has satisfactory consistency. It is generally believed that when CR≥0.1, the judgment matrix has satisfactory consistency; when CR≥0.1, the consistency of the judgment matrix is ​​poor, and the judgment matrix needs to be adjusted until it meets the consistency requirements. Therefore, this scheme requires that when both CI and CR values ​​are less than 0.1, it meets the requirements.

[0149]

[0150] Where: CI is the consistency index, —The maximum eigenvalue of the judgment matrix; n – The order of the elements of the judgment matrix.

[0151]

[0152] Where RI(n) is obtained by randomly generating positive reciprocal matrices of the same order multiple times and calculating the average value of their consistency index. The value of RI is only related to the order n of the judgment matrix. The specific values ​​are shown in Table 2.

[0153] Table 2 RI(n) value table

[0154]

[0155] 5. Hazard assessment model calculation and classification

[0156] The comprehensive index method is used for risk assessment, and qualitative judgment is used for risk assessment zoning. The mathematical model for risk index evaluation is:

[0157] ;

[0158] In the formula, F is the disaster risk index; n is the total number of risk assessment indicators; is the weight value of each evaluation index; Assign quantitative data to each risk index;

[0159] Substitute the values ​​of 1, 3, 6, etc. of the indicators into the model to calculate the upper and lower limits of F. and , calculate the hazard index F. The higher the hazard index, the lower the safety of the submarine pipeline in place and the higher the risk of danger. and According to the 1 / 5 classification, it is divided into four risk levels: low risk, medium risk, relatively high risk and high risk, as shown in Table 3.

[0160] Table 3 Classification standards for submarine pipeline disaster risk levels

[0161]

[0162] In particular, according to the pipeline damage standard, when the lateral bending degree and longitudinal bending degree are greater than the minimum allowable bending radius and the scour suspension length is greater than the critical suspension length, a high risk should be output directly.

[0163] In particular, when the pipeline has extreme damage, such as detectable leakage, rupture and other disasters, high danger should be output directly.

[0164] 6. Calculation of operation and maintenance time for scour disasters

[0165] Based on the field data, calculate the dimensionless shear stress θ when the water flows on the seabed sc :

[0166]

[0167] In the formula, is the critical starting shear stress, g is the acceleration of gravity, calculated according to the specification; is the bulk density of sediment, is the water specific gravity, is the median particle size of sediment.

[0168] Calculation of the development of infinite rigidity scour in submarine pipelines :

[0169] ;

[0170] ;

[0171] Where D is the pipe diameter, s is the relative density ratio, and T is the time scale, which is the actual time when scour occurs.

[0172] Calculate the ultimate scour depth S eq :

[0173] ;

[0174] ;

[0175] Where: is the Froude number, is the seabed surface velocity.

[0176] Computational scour development model:

[0177]

[0178] Where S(t) is the absolute value of the scouring depth below the pipeline at any time, and t is any scouring time.

[0179] 7. Safe operation and maintenance time of submarine pipelines

[0180] The critical suspended length of the submarine pipeline is calculated based on the project to be evaluated, and the final operation and maintenance time is determined based on the following three standards:

[0181] Category I standard: When the transverse buckling and longitudinal buckling detected at the site of the project to be evaluated are greater than the minimum allowable bending radius, immediate repairs are carried out, and the repair time is less than 3 days; when the scour suspension length detected at the site of the project to be evaluated is greater than the critical suspension length, immediate repairs are carried out, and the repair time is less than 3 days;

[0182] Category II standard: When the pipeline has extreme damage, such as detectable leakage, rupture and other disasters, it should be repaired immediately, and the repair time should be less than 3 days;

[0183] Category III standard: When the lateral buckling, longitudinal buckling, scour suspension length and extreme damage do not meet the Category I and Category II criteria, the maintenance time is based on the hazard level of the submarine pipeline.

[0184] When the danger level of the submarine pipeline is IV, emergency treatment is required within three days;

[0185] When the submarine pipeline hazard level is III, it needs to be promptly treated within 30 days;

[0186] When the submarine pipeline is at risk level II, it needs to be treated as needed within 90 days;

[0187] When the submarine pipeline hazard level is I, no treatment is required temporarily.

[0188] The evaluation method of the present invention is further described below in conjunction with specific embodiments.

[0189] Part I: Collect indicator data and stratify indicators.

[0190] Taking the scouring model test of submarine pipelines on a large sandy seabed as an example, relevant data are collected and the indicators are divided into Figure 2 Three layers shown.

[0191] Part II: Calculate the correlation and sensitivity ranking of each indicator.

[0192] According to the experimental data, the correlation between the sub-criterion layer index and the criterion layer index is calculated, and the RBF neural network analysis module in the SPSS software is used to calculate and Correlation between The model correlation after is shown in the formula, and the RBF input module parameters are shown in Table 4 (taking the pipeline scour factor as an example, the calculations are The model parameters are is the output of the neural network).

[0193] The correlation analysis model of pipeline scouring factors is:

[0194]

[0195] The scouring factor of sandy soil pipeline is not considered , then its correlation analysis model is:

[0196]

[0197] Culling The subsequent calculation model is:

[0198]

[0199] Culling The subsequent calculation model is:

[0200]

[0201] Culling The subsequent calculation model is:

[0202]

[0203] Table 4 Summary of input parameters of pipeline deformation factor RBF model

[0204]

[0205] In order to determine each indicator and Criteria Layer The sensitivity of each index is calculated by using RBF neural network. and The correlation coefficient R is used to rank the sensitivity. The R calculation results are shown in Table 5:

[0206]

[0207] Table 5 Results of sensitivity analysis of pipeline deformation factors

[0208]

[0209] According to the R calculation results, and The correlation coefficient is greater than 0.9, which indicates strong correlation and no need to eliminate parameters. After that, the correlation coefficient is the lowest, which means right The calculation of has the greatest impact and is the most sensitive parameter. Therefore, the sensitivity of each parameter is .

[0210] Based on this, we can calculate: The relevant indicators are , the sensitivity ranking is: , The relevant indicators are , the sensitivity ranking is: .

[0211] They are human factors, all of which are correlation indicators, and the sensitivity ranking is: .

[0212] Part III: Quantitative Assignment of Indicators

[0213] The intervals are divided according to the indicators, and the importance of the levels is assigned. In this example, the indicators are assigned the following values:

[0214] The transverse buckling deformation of the pipeline is lower than the minimum allowable bending radius, which is defined as low risk and assigned a value of 1. =1;

[0215] The longitudinal buckling deformation of the pipeline is lower than the minimum allowable bending radius, which is defined as low risk and assigned a value of 1. =1;

[0216] The elastic modulus of the pipeline is lower than the maximum elastic modulus, which is defined as low risk and assigned a value of 1. =1;

[0217] The water flow velocity is greater than the critical starting velocity of sediment, which is defined as high risk and assigned a value of 6. =1;

[0218] The ratio of scour depth to extreme scour depth is 50%, which is in the range of 30%-60%, indicating medium risk and is assigned a value of 3. =3;

[0219] The scour overhang length is less than the critical length under the hinged boundary, which is defined as low risk. =1;

[0220] The relative density of the seabed is loose, which is defined as low risk and assigned a value of 1. =1;

[0221] The medium-density seabed with a median particle size of less than 1 mm is of medium risk and is assigned a value of 3. =3;

[0222] The sediment uniformity coefficient is 4<σ<1, which is defined as low risk and assigned a value of 3. =3;

[0223] No detectable damage is defined as low risk and is assigned a value of 1. =1;

[0224] The pipeline installation connection defect is a rigid connection, which is defined as high risk and assigned a value of 6. =6.

[0225] Part 4: Calculation of indicator weights

[0226] Judge and calculate weights based on the importance of the criteria:

[0227] For the same type of projects that evaluate the impact of scouring disasters on submarine pipelines, it is considered that , , , The importance of follows Table 6, and its weight matrix is:

[0228] ;

[0229] The calculation results are shown in Table 6.

[0230] Table 6 Judgment matrix and weights

[0231]

[0232] According to the sensitivity of each indicator, ,but and Equally important, =1; , and they are adjacent to each other, then =2, =1 / 2, ,but =1 / 2, b 31 =2, determine the order in turn, then the weight matrix is:

[0233]

[0234] The calculation results are shown in Tables 7 to 11.

[0235] Table 7 - Judgment matrix and weights

[0236]

[0237] Table 8 - Judgment matrix and weights

[0238]

[0239] Table 9 - Judgment matrix and weights

[0240]

[0241] Table 10 - Judgment matrix and weights

[0242]

[0243] The total weight is:

[0244] Table 11 Weights of local scour disaster vulnerability assessment indicators

[0245]

[0246] Part V: Hazard Assessment Model

[0247] Weight By introducing the risk assessment model, we can obtain:

[0248]

[0249] Substituting the upper limit 6 and lower limit 1 of the index into the model, we can obtain: =0.998; =5.989.

[0250] The classification model is shown in Table 12:

[0251] Table 12 Classification standards for submarine pipeline disaster risk levels

[0252]

[0253] Index hazard level assignment weight Substituting into the risk assessment model, we can get:

[0254] W =2.025, which is a relatively high risk.

[0255] Part 6: Calculation of Operation and Maintenance Time for Scour Disasters

[0256] Substituting the parameters of this experiment into the formula, it can be calculated that under this calculation model, the time for scour disaster to occur is 30 days. According to the prediction model, when the scour development depth is 80% of the ultimate scour depth, it is a high-risk state. The corresponding time for 80% of the ultimate scour depth is 45 days. It is necessary to conduct scour disaster operation and maintenance observation within 45-30=15 days, and carry out governance when necessary.

[0257] Part 7: Determine the final operation and maintenance time

[0258] This model belongs to the third category of judgment criteria, and the operation and maintenance time is usually 20 days. In this case, operation and maintenance must be carried out according to the operation and maintenance time for scour disasters, that is, operation and maintenance work must be carried out within 15 days.

[0259] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0260] Although the above describes the specific implementation methods of the present invention, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A method for grading the risk of submarine pipeline scour disasters, characterized in that: The process includes: S1, the various factors affecting the safety of submarine pipeline scouring are defined as three layers, the submarine pipeline scouring hazard is defined as the target layer F; pipeline deformation factors, pipeline stability factors, seabed scouring factors and human factors are defined as the criterion layer X i ; The corresponding indicator factor under the criterion layer is defined as the sub-criterion layer indicator X ij ; Get the sub-criteria layer index X under the corresponding scenario ij Various indicator factors; The target layer is the safety hazard of submarine pipelines; the criterion layer includes pipeline deformation factors, pipeline stability factors, seabed scouring development factors and human factors, which correspond to four specific classification criteria: axial stress, natural frequency, scouring depth and damage degree. The sub-criteria layer corresponds to three criteria in turn. The axial stress includes three indicators: pipeline lateral buckling, pipeline longitudinal buckling and pipeline elastic modulus. The natural frequency includes three indicators: flow velocity, scouring depth and suspended length. The seabed scouring depth includes four indicators: relative density, undrained shear strength, median particle size and sediment unevenness coefficient. Human factors include two indicators: damage from life activities and pipeline installation and connection defects. S2, correlation and sensitivity analysis of indicator factors; by determining the correlation and sensitivity, determine the sub-criteria layer indicator X ij With the criteria layer X i The sensitivity ranking is to sort the sub-criteria layer indicators X with correlation R lower than 0.

1. ij Eliminate; By collecting a large amount of experimental and historical field data, the RBF neural network method is used to obtain the mapping relationship between the neural network criterion layer parameters and the sub-criterion layer indicators, and the correlation calculation is carried out in turn after the target indicator is eliminated. According to the correlation coefficient R from small to large, the sensitivity is determined from large to small. Among them, if R is greater than 0.9 after eliminating the parameter, that is, the correlation of this indicator is lower than 0.1, then the sensitivity of this parameter is low and needs to be eliminated; S3, quantitative assignment of indicator factors; each sub-criteria layer indicator X determined by S2 ij The value range of is divided into several different intervals, and then a specific value is assigned to each interval. Each evaluation factor is quantitatively assigned 1, 3, and 6 according to low risk, medium risk, and high risk to obtain the quantitative assignment W(i,j); S4, calculate the weight index according to the hierarchical analysis method; determine the mutual importance of the index factors by comparing them two by two, and compare the various relationships between the index factors, and calculate the weight R(j) of the evaluation index; S5, sub-criteria level indicator X based on participation evaluation ij The quantitative assignment W(i,j) and weight R(j), as well as the corresponding real-time data obtained, are used to evaluate the hazard index using the comprehensive index method, and qualitative judgment is used to perform risk assessment zoning, and the scour disaster hazard index is used to reflect the degree of danger of the disaster.

2. A method for grading the risk of submarine pipeline scour disasters according to claim 1, characterized in that: The quantitative assignment of the indicator factors in S3 includes the following methods: The transverse buckling deformation and longitudinal buckling deformation of the pipeline are assigned values ​​according to the minimum allowable bending radius. When the deformation is lower than the minimum allowable bending radius, it is defined as low risk and assigned a value of 1; when the deformation is greater than the minimum allowable bending radius, it is defined as high risk and assigned a value of 6; the rest of the states are medium risk and assigned a value of 3; Among them, when the scour suspension length is less than the critical length under the hinged support boundary, it is defined as low risk and assigned a value of 1; when the scour suspension length is greater than the critical length under the fixed support boundary, it is defined as high risk and assigned a value of 6; the rest of the states are defined as medium risk and assigned a value of 3; Among them, the extreme scour depth is calculated according to the scour prediction formula, and the quantitative values ​​are assigned as 1, 3, and 6 respectively according to the ratio of scour depth to extreme scour depth of 30%, 60%, and 90% for low risk, medium risk, and high risk of scour disaster; Among them, relative density is defined as low risk, medium risk and high risk according to the standards of dense, medium and loose, and the values ​​are assigned as 1, 3 and 6; Among them, undrained shear strength is defined as low risk, medium risk and high risk according to dense, medium and weak, and the values ​​are assigned as 1, 3 and 6; Among them, the median particle size is defined as low risk with a particle size less than 1mm and a dense seabed shear strength greater than 5Kpa, and is assigned a value of 1; the particle size is less than 1mm and the liquefied seabed shear strength is less than 1Kpa, which is prone to scouring and foundation instability, and is defined as high risk, and is assigned a value of 6; the rest of the particle sizes less than 1mm are defined as medium risk, and are assigned a value of 3; the fine sand dense seabed with a particle size of 1mm-4mm is defined as low risk, and is assigned a value of 1; the fine sand loose seabed with a particle size of 1mm-4mm is prone to scouring, and is defined as high risk, and is assigned a value of 6; the fine sand with a particle size of 1mm-4mm in other cases is defined as medium risk, and is assigned a value of 7; the sediment with a particle size greater than 4mm is large and not easy to scour, and is defined as low risk, and is assigned a value of 1; Among them, the sediment uniformity coefficient is defined as low risk, medium risk and high risk according to the sediment uniformity coefficient σ>4, 4<σ<1, and σ<1, respectively, and the values ​​are 1, 3, and 6; Among them, life-destructive activities are defined as low risk, medium risk, and high risk according to no damage, slight damage, and detectable damage, respectively, and are assigned values ​​of 1, 3, and 6; Among them, pipeline installation connection defects are defined as low risk, medium risk and high risk according to composite connection, flexible connection and rigid connection, and are assigned values ​​of 1, 3 and 6 respectively.

3. A method for grading the risk of submarine pipeline scour disasters according to claim 1, characterized in that: In S4, the method of pairwise comparison between factors is used to score the relevant factors under each criterion layer, and finally obtain several pairwise comparison matrices; through calculation and analysis comparison, the judgment matrix is ​​appropriately adjusted to achieve good consistency of the judgment matrix, and the judgment matrix Q is obtained; this matrix is ​​used to calculate the sub-criterion layer X in turn. ij First-level weight and criteria layer X i The indicator weights of the secondary weights are finally multiplied by weights to obtain the total weight R of each indicator target layer. The matrix Q is shown as follows: In the formula, each data in the matrix is ​​represented by b pq It is expressed as the importance ratio of index factor p to index factor q; n represents the sub-criteria layer index X used for calculation ij Total number of; Under the same criterion level, when comparing any two factors, the importance of index factor p and index factor q is compared to obtain b pq , and the ratio of the index factor q to the index factor p is 1 / b pq , are reciprocals of each other; where b pq The value selection method is as follows: the index ranking obtained by the sensitivity analysis method is defined as 1 for the importance of two factors with adjacent ranks, 3 for the one with one rank difference, and 5 for the one with two rank differences. The ranking is based on sensitivity, and is ranked in order of 7 and 9. Among them, 1 means that the two factors are equally important; 3 means that one factor is slightly more important than the other; 5 means that one factor is obviously more important than the other; 7 means that one factor is strongly more important than the other; 9 means that one factor is extremely more important than the other; 2, 4, 6, and 8 are the medians of the above adjacent judgments.

4. A method for grading the risk of submarine pipeline scour disasters as claimed in claim 3, characterized in that: The indicator weight calculation process is: Calculate the element b of each row of the judgment matrix pq The product of: Calculate the nth root of Mp: Vector After normalization, we get the eigenvector W = (w1, w2, …w n ) T ,in: This feature vector is the weight of each indicator, each criterion layer X i , Sub-criteria level index X ij The weights are R(i) and R(ij) respectively, and the total weight is R(j) = R(i)·R(ij); Then, a total hierarchical ranking is performed, that is, the ranking weight of the relative importance of each indicator factor in the indicator layer is calculated respectively, and the total ranking is checked for consistency to ensure accuracy.

5. A method for grading the risk of submarine pipeline scour disasters according to claim 1, characterized in that: In S5, a comprehensive index method is used to evaluate the risk index, and qualitative judgment is used to perform risk assessment zoning. The mathematical model used for the risk index evaluation is: In the formula, F is the disaster risk index; n is the total number of risk assessment indicators; R(j) is the weight value of each assessment indicator; W(i,j) is the quantitative assignment data of each risk indicator; Substitute the index values ​​1, 3, 6, etc. into the model to calculate the upper and lower limits of F. min and F max , calculate the hazard index F. The higher the hazard index, the lower the safety of the submarine pipeline in place and the higher the risk of danger. min and F max ,according to There are four risk levels: low risk, medium risk, relatively high risk and high risk.

6. A method for obtaining the operation and maintenance time of a submarine pipeline scour disaster, characterized in that: The hazard level obtained by the submarine pipeline scour disaster hazard classification method according to claim 5 includes the following process: S1, determine the time t1 corresponding to the on-site scouring depth; S2, based on the on-site hydrological and seabed parameters, obtain the scour development model, calculate the pipeline scour depth at different times greater than time t1, and input it into the mathematical model for hazard index evaluation; S3, until at a certain moment the mathematical model output of the hazard index evaluation is high risk, and the moment t2 corresponding to the high risk scour depth is determined; S4, output t2-t1 to get the time t w , which is the number of days allowed for operation and maintenance under this condition.

7. A method for obtaining operation and maintenance time of a submarine pipeline scour disaster according to claim 6, characterized in that: The functional expression of the scour development model is: Where S(t) is the absolute value of the scouring depth under the pipeline at any time, t is any scouring time; S eq is the dimensionless time scale of the equilibrium flushing below the pipeline T * The expression is: Where T is the time scale, which refers to the time when substantial scour occurs, s is the relative density ratio, and d is the relative density ratio. 50 is the median particle size of the sediment on the seabed, g is the acceleration of gravity, and D is the diameter of the pipe; Where, the dimensionless pipeline flushing time scale T * and Shields number θ sc Based on a large number of experimental results, the Hill number θ under steady flow conditions is proposed. sc The dimensionless time scale prediction formula is: Where, the dimensionless shear stress θ when the water flow acts on the seabed under complex seabed conditions is sc The expression is corrected to: In the formula, τ c is the critical starting shear stress, g is the gravitational acceleration, calculated according to the specification; γ s is the bulk density of sediment, γ is the bulk density of water, d 50 is the median particle size of sediment.

8. A method for acquiring operation and maintenance time of a submarine pipeline scour disaster as claimed in claim 6, characterized in that: The safe operation and maintenance time of submarine pipelines under the influence of various factors is determined according to the following standards: Category I standard: When the transverse buckling and longitudinal buckling detected at the site of the project to be evaluated are greater than the minimum allowable bending radius, immediate repairs are carried out, and the repair time is less than 3 days; when the scour suspension length detected at the site of the project to be evaluated is greater than the critical suspension length, immediate repairs are carried out, and the repair time is less than 3 days; Category II standard: When the pipeline is extremely damaged, it is repaired immediately and the repair time is less than 3 days; Category 3 standards: When the lateral buckling, longitudinal buckling, scour suspension length and extreme damage do not meet the Category 1 and Category 2 criteria, the maintenance time shall be based on the scour disaster operation and maintenance time of the submarine pipeline; when the scour disaster operation and maintenance time is greater than the regular pipeline inspection time, the operation and maintenance inspection shall be carried out according to the inspection time, and the pipeline safety assessment shall be re-performed; when the operation and maintenance time is less than the regular pipeline inspection time, the scour disaster operation and maintenance time shall be used as the basis for corresponding treatment and testing.

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