Liquefied natural gas (LNG) liquid cargo system health evaluation method

Abstract

The invention provides an LNG (Liquefied Natural Gas) liquid cargo system health evaluation method. The LNG liquid cargo system health evaluation method comprises the following steps: respectively and correspondingly defining measuring points, parts and equipment as a bottom layer, a middle layer and a top layer; the evaluation result generation mode of the top layer and / or the middle layer is as follows: obtaining the evaluation result of the top layer and / or the middle layer through a dynamic network analytic hierarchy process according to a dynamic weight adjustment factor and a bottom layer evaluation result. Test points, parts, equipment and a system to be tested are divided through layers, then evaluation results are fitted together through dynamic weight adjustment factors, and the technical problem that in the prior art, a health evaluation method under the mutual relation of complex parts is lacked is solved.

Description

Technical field:

[0001] The invention relates to the field of LNG liquid cargo system design, and in particular to a health evaluation method for an LNG liquid cargo system. Background technology:

[0002] Accurate assessment of the health status of LNG cargo systems is of vital importance to ensuring the safe operation of LNG ships and improving operational efficiency. Existing methods often focus on current or recent data, lacking comprehensive consideration of long-term system performance degradation or historical failure modes. Especially in the face of complex interactions between equipment and dynamic changes in key parameters over time, traditional static assessment methods often fail to meet the requirements of real-time and accuracy, and lack the dynamic impact of the passage of time and the increase in equipment service life on health assessment.

[0003] There is an urgent need for a health assessment method for an LNG liquid cargo system, which can help solve the technical problem of the lack of a health assessment method under the relationship between complex components in the prior art. Summary of the invention:

[0004] In one embodiment, the present invention provides a method for evaluating the health of an LNG liquid cargo system, in which the measured points, components, equipment and systems to be tested are divided into layers, and then the evaluation results are fitted together through dynamic weight adjustment factors, which helps to solve the technical problem of the lack of a health evaluation method under the relationship between complex components in the prior art.

[0005] The LNG liquid cargo system health assessment method includes:

[0006] Define the measuring points, components, and equipment as the bottom layer, middle layer, and top layer respectively;

[0007] The evaluation results of the top layer and / or the middle layer are generated as follows:

[0008] The evaluation results of the top layer and / or the middle layer are obtained by dynamic network analytic hierarchy process according to the dynamic weight adjustment factor and the bottom layer evaluation results.

[0009] In one embodiment, the dynamic network hierarchy analysis method includes:

[0010] Dynamic weight adjustment factor w i =f k (T i ,M i ,F i ,), define T i is the cumulative running time of device i, M i is the number of maintenance times of equipment i, F i is the historical failure frequency of device i;

[0011] w i =β1*T i +β2*M i +β3*F i

[0012] Among them, β i is the weight coefficient;

[0013]

[0014] T is the current running time of the device, T max The maximum safe operating time designed for the equipment;

[0015]

[0016] N j represents the number of failures within a specified time window, T win is the length of the time window.

[0017] In one embodiment, the bottom layer is evaluated as follows:

[0018] The bottom-level evaluation result is obtained through the hierarchical analysis method according to the system parameter index weights and basic scores, as well as the time decay factor.

[0019] In one embodiment, the system includes a cargo tank, a gas replacement unit, a BOG compression unit, a fuel gas gasification unit, and a reliquefaction unit;

[0020] The equipment includes a cargo unloading pump and a tank cleaning spray fuel pump;

[0021] The indicators of the measuring points include vibration, temperature and pressure.

[0022] In one embodiment, the health value calculation formula of the measuring point is:

[0023] H i =base i *η i *score i

[0024] Among them, base i is the measurement point weight, score i The deviation degree of the key data of the equipment from the normal range is expressed as:

[0025] score i =|score-μ i | / σ i

[0026] μ i is the mean value, σj is the standard deviation of the parameter, which is used to measure the degree to which the data deviates from the normal range, η i is the time decay factor, expressed as:

[0027] η i =e t / 30 .

[0028] In one embodiment, the analytic hierarchy process includes:

[0029] Constructing a hierarchical model, wherein the hierarchical model includes a target layer and a solution layer, the target layer is the health of different components, and the solution layer is the known device-level health of each subsystem;

[0030] Construct the discriminant matrix;

[0031] After scaling the matrix amplitude according to a predetermined scaling method, a hierarchical single arrangement of the target layer is performed;

[0032] A consistency check is performed, and if satisfied, the hierarchy is always ordered.

[0033] In one embodiment, performing consistency checking includes:

[0034] If it is not satisfied, adjust the judgment matrix and rebuild the judgment matrix.

[0035] In one embodiment, the consistency index CI is calculated by the discriminant matrix:

[0036]

[0037] Find the corresponding average random consistency index RI and calculate the consistency ratio CR:

[0038]

[0039] When CR is less than 0.1, it indicates that the consistency of the judgment matrix is ​​considered to be within the allowable range, and the eigenvector of the judgment matrix is ​​used to calculate the weight vector; if CR is greater than or equal to 0.1, the judgment matrix A should be modified.

[0040] In one embodiment, the consistency check is performed, and if it is satisfied, then after the step of total hierarchical sorting, the weights of the cargo hold, the gas replacement unit, the BOG compression unit, the fuel gasification unit and the reliquefaction unit, the method further comprises:

[0041] The health assessment results of the LNG cargo system are as follows:

[0042] H 液货系统 =∑(w1*H 货舱 , w2*H 气体置换单元, w3*H BOG压缩单元 , w4*H 燃气气化单元 ,w5*H 再液化单元 )

[0043] w j is the dynamic weight adjustment factor of the j-th subsystem, and H is the health score of the subsystem.

[0044] In one embodiment, the predetermined scaling method is a 1-9 scaling method. Description of the drawings:

[0045] Figure 1 It is a schematic flow chart of a method for health assessment of an LNG liquid cargo system in one embodiment of the present invention;

[0046] Figure 2 A schematic diagram of a health status assessment process in another embodiment of the present invention;

[0047] Figure 3 The figure is a schematic diagram of the analytic hierarchy process in another embodiment of the present invention. Specific embodiment:

[0048] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0049] Various aspects and features of the present application are described herein with reference to the accompanying drawings.

[0050] These and other characteristics of the present application will become apparent from the following description of a preferred form of embodiment given as a non-limiting example with reference to the accompanying drawings.

[0051] It should also be understood that, although the present application has been described with reference to some specific examples, those skilled in the art will be able to realize many other equivalent forms of the present application that have the features described in the claims and are therefore within the scope of protection defined thereby.

[0052] The above and other aspects, features and advantages of the present application will become more apparent in view of the following detailed description when taken in conjunction with the accompanying drawings.

[0053] Specific embodiments of the present application are described hereinafter with reference to the accompanying drawings; however, it should be understood that the embodiments applied for are merely examples of the present application, which may be implemented in a variety of ways. Well-known and / or repeated functions and structures are not described in detail to determine the true intent based on the user's historical operations and to avoid unnecessary or redundant details that make the present application unclear. Therefore, the specific structural and functional details applied for herein are not intended to be limiting, but are merely used as the basis and representative basis for the claims to teach those skilled in the art to use the present application in a variety of ways with substantially any suitable detailed structure.

[0054] This specification may use the phrases "in one embodiment," "in another embodiment," "in yet another embodiment," or "in other embodiments," all of which may refer to one or more of the same or different embodiments according to the present application.

[0055] The present invention provides a health assessment method for a liquid cargo system of an LNG ship based on a dynamic network analytic hierarchy process, which can not only comprehensively consider the interdependence between various devices in the system, but also reflect the dynamic changes of the health status of the system, equipment and components in real time, and provide a scientific basis for maintenance decisions. If 100 represents normal and 0 represents fault, then a continuous variable from 100 to 0 can be used to characterize the health of the equipment, and the health status of the equipment and the system can be characterized by defining the health degree. The health assessment of the liquid cargo system is carried out by comprehensively utilizing multi-dimensional input information. Through the redundancy and complementarity of the multi-dimensional input information, the uncertainty of the information is reduced, the fault tolerance and self-adaptation of the health index are improved, and more accurate and reliable estimates and judgments can be generated than a single information source. The key to the health assessment of the liquid cargo system under multi-dimensional input conditions is the effective fusion of the multi-dimensional input information, and the characterization of the useful information of the health assessment is realized to the greatest extent. Finally, the input information is quantified into a score of 0-100 through a dynamic network analytic hierarchy model and displayed intuitively, which is convenient for users to intuitively understand and judge the system.

[0056] Figure 1 It is a schematic flow chart of a method for health assessment of an LNG liquid cargo system in one embodiment of the present invention; Figure 2 A schematic diagram of a health status assessment process in another embodiment of the present invention; Figure 3 FIG. 1 is a schematic diagram of the analytic hierarchy process in another embodiment of the present invention. Figures 1 to 3 As shown, in one embodiment, the present invention provides a LNG liquid cargo system health evaluation method, the LNG liquid cargo system health evaluation method comprising:

[0057] S101, defining the measuring points, components, and equipment as a bottom layer, a middle layer, and a top layer, respectively.

[0058] This step provides a specific layering step for defining the measuring points, components, and equipment as a bottom layer, a middle layer, and a top layer, respectively.

[0059] S102, the evaluation result of the top layer and / or the middle layer is generated as follows:

[0060] The evaluation results of the top layer and / or the middle layer are obtained by dynamic network analytic hierarchy process according to the dynamic weight adjustment factor and the bottom layer evaluation results.

[0061] In this step, a specific step is provided for obtaining the evaluation results of the top layer and / or the middle layer through the dynamic network analytic hierarchy process according to the dynamic weight adjustment factor and the system evaluation result.

[0062] The present invention provides a specific implementation of a method for health assessment of an LNG liquid cargo system.

[0063] In one embodiment, the dynamic network hierarchy analysis method includes:

[0064] Dynamic weight adjustment factor w i =f k (T i ,M i ,F i ,), define T i is the cumulative running time of device i, M i is the number of maintenance times of equipment i, F i is the historical failure frequency of device i;

[0065] w i =β1*T i +β2*M i +β3*F i

[0066] Among them, β i is the weight coefficient;

[0067]

[0068] T is the current running time of the device, T max The maximum safe operating time designed for the equipment;

[0069]

[0070] N j represents the number of failures within a specified time window, T win is the length of the time window.

[0071] In one embodiment, the bottom layer is evaluated as follows:

[0072] The bottom-level evaluation result is obtained through the hierarchical analysis method according to the system parameter index weights and basic scores, as well as the time decay factor.

[0073] In one embodiment, the system includes a cargo tank, a gas replacement unit, a BOG compression unit, a fuel gas gasification unit, and a reliquefaction unit;

[0074] The equipment includes a cargo unloading pump and a tank cleaning spray fuel pump;

[0075] The indicators of the measuring points include vibration, temperature and pressure.

[0076] The target layer of health status assessment is defined as “LNG liquid cargo system health”, which aims to comprehensively evaluate the operating status of the entire LNG liquid cargo system and ensure that it can perceive the overall situation of the system in real time.

[0077] Solution layer:

[0078] In the LNG liquid cargo system, it can be divided into cargo hold, gas replacement unit, BOG compression unit, gas gasification unit and reliquefaction unit according to the system function. The key equipment in the cargo hold includes unloading pump and tank cleaning spray fuel pump. The gas replacement unit includes high-load compressor, high-load heater and forced gasifier. The core equipment in the BOG compression unit is BOG compressor. The gas gasification unit includes gas gasifier and gas heater. Each key equipment can be further subdivided into more specific components or parameters, such as vibration, temperature, pressure and other key indicators of the compressor, that is to say, not limited to the above three measurement point indicators. These data are obtained through real-time monitoring of sensors to form a multi-level evaluation system.

[0079] Establishment of subsystem-level and device-level health assessments:

[0080] First, the health of each measuring point in the bottom layer is calculated. The corresponding fault weight is assigned according to the importance of the measuring point and the alarm level. At the same time, the influence of time factors on the severity of the fault is included in the health assessment through the time decay factor.

[0081] In one embodiment, the health of each secondary component depends on the status of the monitoring points included in the component. The health value calculation formula of the monitoring points is:

[0082] H i =base i *η i *score i

[0083] Among them, base i is the measurement point weight, score i The deviation degree of the key data of the equipment from the normal range is expressed as:

[0084] score i =|score-μ i | / σ i

[0085] μ i is the mean value, σ j is the standard deviation of the parameter, which is used to measure the degree to which the data deviates from the normal range, η i is the time decay factor, expressed as:

[0086] η i =e t / 30 .

[0087] The time decay factor takes into account the correlation between the fault occurrence time and the health assessment, making the health of a single measuring point more reasonable.

[0088] The health assessment results of the measuring points are weighted to form the health of the equipment / subsystem to evaluate its failure degree in the historical time period; finally, the health of the top-level system is calculated based on the dynamic network hierarchical analysis method.

[0089] In one embodiment, the analytic hierarchy process includes:

[0090] Constructing a hierarchical model, wherein the hierarchical model includes a target layer and a solution layer, the target layer is the health of different components, and the solution layer is the known device-level health of each subsystem;

[0091] Construct the discriminant matrix;

[0092] After scaling the matrix amplitude according to a predetermined scaling method, a hierarchical single arrangement of the target layer is performed;

[0093] Target layer settings:

[0094] A consistency check is performed, and if satisfied, the hierarchy is always ordered.

[0095] Establishment of system-level health assessment:

[0096] Considering the complex interaction between the equipment of the LNG cargo system and the time series transformation of key parameters, the dynamic network analytic hierarchy process is used to evaluate the health status of the LNG cargo system. First, the initial hierarchical model is constructed. The target layer is the health of the power system, and the solution layer is the known health value of each subsystem equipment level. Then the discriminant matrix is ​​constructed. For each criterion in the middle layer, the relative importance is compared between each other to form a judgment matrix. It is assumed that the weight of each criterion layer to the target layer is determined by the subjective judgment of experts or decision makers.

[0097] The analytic hierarchy process is used to evaluate the health status of the power system. The principle of the analytic hierarchy process is that before analyzing a phenomenon or problem, the phenomenon or problem is first decomposed into relevant factors according to their nature, and classified according to the relationship between them to form a multi-level structural model. Then, through experience or experts, the relative importance of low-level factors to high-level factors is judged and measured, and the weight ranking is obtained according to the degree of importance, which can then be quantitatively analyzed and compared.

[0098] In the application of AHP, there are four main steps. The first step is to build a hierarchical model. The second step is to construct a judgment matrix. The third step is to sort the hierarchy and its consistency test, which is to weight the indicators. The fourth step is to sort the hierarchy and its consistency test.

[0099] First, a hierarchical model is constructed. The target layer is the health of the LNG liquid cargo system, the criterion layer is the health of the cargo tank, the health of the gas replacement unit, the health of the BOG compression unit, the health of the gas gasification unit and the health of the reliquefaction unit, and the solution layer is the known health values ​​of each subsystem equipment level.

[0100] Then, a discriminant matrix is ​​constructed. For each criterion in the middle layer, the relative importance is compared between each other to form a judgment matrix. Assuming that the subjective judgment of experts or decision makers is used, the 1-9 scale method is used to determine the weight of each criterion layer to the target layer.

[0101] The discriminant matrix A of the LNG liquid cargo system is obtained:

[0102]

[0103] Among them, the elements in A satisfy:

[0104] a ij >0

[0105]

[0106] a ii =1

[0107] Therefore, for the criterion layer: cargo hold health, gas replacement unit health, BOG compression unit health, gas gasification unit health and reliquefaction unit health, the 5*5 discriminant matrix that can be constructed is:

[0108] cargo hold Gas exchange unit BOG Compression Unit Gas gasification unit Reliquefaction unit cargo hold 1 Gas exchange unit 1 BOG Compression Unit 1 Gas gasification unit 1 Reliquefaction unit 1

[0109] After the experts assign values ​​to the matrix elements according to the 1-9 scale method, hierarchical single sorting is performed. Hierarchical single sorting means that all elements in this layer are evaluated in pairs for an element in the previous layer, and hierarchical sorting is performed to arrange the order of importance. The specific calculation can be performed based on the judgment matrix A. Here, the maximum characteristic root of A is λ max , corresponding to λ max The normalized eigenvector of is W, and is the component of W, which refers to the weight, corresponding to the single order of its corresponding elements. The judgment matrix is ​​used to calculate the weight (weight coefficient) of each factor on the target layer.

[0110] The square root method calculates weights as follows:

[0111]

[0112] In one embodiment, performing consistency checking includes:

[0113] If it is not satisfied, adjust the judgment matrix and rebuild the judgment matrix.

[0114] In one embodiment, in order to avoid contradictions in the discriminant matrix, the consistency ratio CR is calculated. When CR is less than 0.1, it means that the consistency of the discriminant matrix is ​​acceptable. Otherwise, the discriminant matrix needs to be corrected.

[0115] The consistency index Cl is calculated by the discriminant matrix:

[0116]

[0117] Find the corresponding average random consistency index RI and calculate the consistency ratio CR:

[0118]

[0119] When CR is less than 0.1, it indicates that the consistency of the judgment matrix is ​​considered to be within the allowable range, and the eigenvector of the judgment matrix is ​​used to calculate the weight vector; if CR is greater than or equal to 0.1, the judgment matrix A should be modified.

[0120] In one embodiment, the consistency check is performed, and if it is satisfied, then after the step of total hierarchical sorting, the weights of the cargo hold, the gas replacement unit, the BOG compression unit, the fuel gasification unit and the reliquefaction unit, the method further comprises:

[0121] The health assessment results of the LNG cargo system are as follows:

[0122] H 液货系统 =∑(w1*H 货舱 , w2*H 气体置换单元 , w3*H BOG压缩单元 , w4*H 燃气气化单元 ,w5*H 再液化单元 )

[0123] w j is the dynamic weight adjustment factor of the j-th subsystem, and H is the health score of the subsystem.

[0124] After determining the judgment matrix, the initial evaluation weights of the health of each equipment level are obtained and integrated into the initial health evaluation results of the LNG liquid cargo system level. As time goes by and the service life of the equipment increases, the LNG liquid cargo system health status evaluation method based on dynamic network hierarchical analysis takes into account the evolution of equipment and parameters in the system over time, integrates multi-dimensional dynamic feedback such as equipment operating time, the latest collected data, and historical fault frequency, and continuously optimizes and adjusts the evaluation criteria and preference weights in the hierarchical model to form a more sophisticated and complex dynamic network model, which more accurately reflects the dynamic evolution of the LNG liquid cargo system health evaluation process and ensures that the evaluation conclusion is closer to the actual situation of the system.

[0125] In one embodiment, the predetermined scaling method is a 1-9 scaling method.

[0126] The above embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention. The protection scope of the present invention is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present invention.

Claims

1. A method for evaluating the health of an LNG cargo system, characterized in that: The LNG liquid cargo system health assessment method includes: Define the measuring points, components, and equipment as the bottom layer, middle layer, and top layer respectively; The evaluation results of the top layer and / or the middle layer are generated as follows: The evaluation results of the top layer and / or the middle layer are obtained by dynamic network analytic hierarchy process according to the dynamic weight adjustment factor and the bottom layer evaluation results.

2. The LNG liquid cargo system health assessment method according to claim 1, characterized in that: The dynamic network hierarchical analysis method comprises: Dynamic weight adjustment factor w i =f k (T i ,M i ,F i ,), define T i is the cumulative running time of device i, M i is the number of maintenance times of equipment i, F i is the historical failure frequency of device i; w i =β1*T i +β2*M i +β3*F i Among them, β i is the weight coefficient; T is the current running time of the device, T max The maximum safe operating time designed for the equipment; N j represents the number of failures within a specified time window, T win is the length of the time window.

3. The LNG liquid cargo system health assessment method according to claim 2 is characterized in that: The bottom layer is evaluated as follows: The bottom-level evaluation result is obtained through the hierarchical analysis method according to the system parameter index weights and basic scores, as well as the time decay factor.

4. The LNG liquid cargo system health assessment method according to claim 3 is characterized in that: The system includes a cargo hold, a gas replacement unit, a BOG compression unit, a fuel gas gasification unit and a reliquefaction unit; The equipment includes a cargo unloading pump and a tank cleaning spray fuel pump; The indicators of the measuring points include vibration, temperature and pressure.

5. The LNG liquid cargo system health assessment method according to claim 4 is characterized in that: The calculation formula of the health value of the measuring point is: H i =base i *η i *score i Among them, base i is the measurement point weight, score i The deviation degree of the key data of the equipment from the normal range is expressed as: score i =|score-μ i | / s i μi is the average value, σ j is the standard deviation of the parameter, which is used to measure the degree to which the data deviates from the normal range, η i is the time decay factor, expressed as: or i =e t / 30 。 6. The LNG liquid cargo system health assessment method according to claim 5, characterized in that: The analytic hierarchy process includes: Constructing a hierarchical model, wherein the hierarchical model includes a target layer and a solution layer, the target layer is the health of different components, and the solution layer is the known device-level health of each subsystem; Construct the discriminant matrix; After scaling the matrix amplitude according to a predetermined scaling method, a hierarchical single arrangement of the target layer is performed; A consistency check is performed, and if satisfied, the hierarchy is always ordered.

7. The LNG liquid cargo system health assessment method according to claim 6, characterized in that: The consistency check comprises: If it is not satisfied, adjust the judgment matrix and rebuild the judgment matrix.

8. The LNG liquid cargo system health assessment method according to claim 7, characterized in that: The consistency index CI is calculated by the discriminant matrix: Find the corresponding average random consistency index RI and calculate the consistency ratio CR: When CR<0.1, it indicates that the consistency of the judgment matrix is ​​considered to be within the allowable range, and the eigenvector of the judgment matrix is ​​used to calculate the weight vector; if CR≥0.1, the judgment matrix A should be modified.

9. The LNG liquid cargo system health assessment method according to claim 8, characterized in that: The consistency check is performed, and if it is satisfied, the weights of the cargo hold, the gas replacement unit, the BOG compression unit, the fuel gasification unit and the reliquefaction unit after the hierarchical total sorting step are further calculated. The method further comprises: The health assessment results of the LNG cargo system are as follows: H 液货系统 =Σ(w1*H 货舱 ,w2*H 气体置换单元 ,w3*H BOG压缩单元 ,w4*H 燃气气化单元 ,w5*H 再液化单元 w j is the dynamic weight adjustment factor of the j-th subsystem, and H is the health score of the subsystem.

10. The LNG liquid cargo system health assessment method according to claim 9, characterized in that: The predetermined scaling method is a 1-9 scaling method.

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