A method and device for calculating fatigue load spectrum of offshore platform

Abstract

The present invention provides a method and device for calculating fatigue load spectrum of an ocean platform. The method comprises: constructing an overall structural finite element model of an ocean deepwater structure; calculating the fatigue damage value corresponding to each wave direction working condition and the number of cycles of stress generated by waves on the ocean deepwater structure under different wave directions within the design life in a preset stress range according to the wave distribution diagram of the real sea area where the ocean deepwater structure is located and the overall structural finite element model; calculating the number of test cycles of wave loads under different wave directions according to the number of cycles and the fatigue damage value; calculating the equivalent hot spot constant stress amplitude according to the number of cycles and the preset hot spot S-N curve; performing simulation tests on the model corresponding to the ocean deepwater structure according to the equivalent hot spot constant stress amplitude and the number of test cycles to obtain a wave fatigue load spectrum. The present invention can accurately measure the fatigue life of an ocean structure under actual working conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of fatigue life data processing of marine structures, and in particular to a method and device for calculating fatigue load spectrum of an offshore platform. Background Art

[0002] my country's marine products are currently gradually developing towards deepwater and ultra-deepwater areas. Deepwater marine structures are facing more changeable and severe wave environments, and are subjected to alternating fatigue loads caused by waves. Their key nodes determine the length of their service life, so fatigue design at key nodes is extremely important.

[0003] At present, the SN curve method is mainly used in the design of general fatigue strength. The SN curve method is mainly based on the SN curve and Miner cumulative damage criterion. BV, DNV and CCS have provided relatively similar simplified fatigue assessment algorithms. The simplified fatigue assessment algorithm includes stress calculation, selection of SN curve, fatigue strength analysis and calculation of fatigue life. When performing fatigue strength assessment on structural details, the reasonable selection of SN curve is a very important issue. Generally, it is necessary to select the corresponding SN curve for calculation based on the structure type, load action mode, etc.

[0004] However, the details of deep-water ocean structures are complex and the loads they bear are also relatively complex. It is difficult to determine the corresponding SN curve based on existing methods, resulting in low accuracy when performing fatigue assessments at key nodes. Summary of the invention

[0005] The embodiment of the present invention provides a method and device for calculating fatigue load spectrum of an offshore platform, so as to solve the problem of low accuracy in fatigue assessment at key nodes in the prior art.

[0006] In a first aspect, an embodiment of the present invention provides a method for calculating a fatigue load spectrum of an offshore platform, comprising:

[0007] Construct the overall structural finite element model of deep-water marine structures;

[0008] According to the wave distribution diagram of the real sea area where the deep-water structure is located and the finite element model of the overall structure, the fatigue damage value corresponding to each wave direction working condition and the number of cycles of stress generated by waves on the deep-water structure at different wave directions within the design life within a preset stress range are calculated;

[0009] According to the number of cycles and the fatigue damage value, the number of test cycles of wave loads under different wave conditions is calculated;

[0010] According to the number of cycles and the preset hot spot SN curve, an equivalent hot spot constant stress amplitude is calculated;

[0011] A simulation test is performed on a model corresponding to the deep-water structure in the ocean according to the equivalent hot spot constant stress amplitude and the test cycle number to obtain a wave fatigue load spectrum.

[0012] In a possible implementation, based on the wave distribution diagram of the real sea area where the deep-water structure is located and the overall structural finite element model, the fatigue damage value corresponding to each wave direction condition and the number of cycles of stress generated by waves on the deep-water structure under different wave directions within the design life within a preset stress range are calculated, including:

[0013] According to the wave distribution diagram of the real sea area where the deep-water structure is located, wave parameters in multiple directions are counted, and the wave parameters are input into the finite element model of the overall structure to obtain the fatigue damage value corresponding to each short-term sea condition of the overall structure;

[0014] According to the fatigue damage value corresponding to each short-term sea condition of the overall structure, the fatigue damage value corresponding to each short-term sea condition at the key node position is determined;

[0015] According to the fatigue damage value corresponding to each short-term sea condition at the key node position, the fatigue damage value of the key node position under each wave is obtained;

[0016] According to the wave parameters, calculating the average zero-crossing period of the probability density function in the stress range under each sea state;

[0017] The number of cycles within a preset stress range of stress generated by waves at different wave directions on the deep-water structure in the ocean within the design life is calculated based on the average zero-crossing period.

[0018] In a possible implementation, the number of cycles of stress generated by waves at different wave directions on the deep-water structure in the ocean within the design life within a preset stress range is calculated based on the average zero-crossing period, including:

[0019] According to the average zero-crossing period and the wave parameters, the number of times the stress generated on the deep-water marine structure under each sea condition within the design life is within a preset stress range is obtained;

[0020] The number of times the stress generated on the deep-water structure in each sea condition is within a preset stress range is accumulated, and the number of cycles of the stress generated on the deep-water structure in the preset stress range by waves under different wave conditions is calculated.

[0021] In a possible implementation, the wave parameter includes the probability of wave occurrence;

[0022] According to the average zero-crossing period and the wave parameters, the number of times the stress generated on the deep-water structure in each sea condition within the design life is within a preset stress range is obtained, including:

[0023] according to Obtaining the number of times the stress generated on the deep-water marine structure under each sea condition within the design life is within a preset stress range;

[0024] Where N i represents the number of times the stress generated on the deep-water structure in the i-th direction is within the preset stress range, T 设 Indicates the design life, P i represents the probability of the wave appearing in the i-th direction, T 过 Represents the average zero-crossing period.

[0025] In a possible implementation, calculating the number of test cycles of wave loads under different wave conditions according to the number of cycles and the fatigue damage value includes:

[0026] Normalizing the number of cycles within a preset stress range of stresses generated by waves at different wave directions on the deep-water structure within the design life;

[0027] According to the product of the normalized number of cycles and the fatigue damage value, the ratio of the number of cycles generated by waves under different wave directions within the design life is obtained;

[0028] The number of test cycles of wave loads under different wave directions is obtained by multiplying the ratio of the number of cycles generated by waves within the design life under different wave directions and the product of the preset number of cycles base.

[0029] In a possible implementation, the equivalent hotspot constant stress amplitude is calculated according to the number of cycles and a preset hotspot SN curve, including:

[0030] according to The equivalent hot spot constant stress amplitude is calculated;

[0031] Where S0 represents the constant stress amplitude of the equivalent hot spot, K and m represent the coefficients in the preset hot spot SN curve, and N i ' represents the number of cycles after normalization.

[0032] In a possible implementation, the wave parameters are input into the overall structure finite element model to obtain the fatigue damage value corresponding to each wave direction condition of the overall structure, including:

[0033] A stress response spectral density function can be obtained by calculating the wave parameters;

[0034] According to the stress response spectrum density function, a stress response spectrum order moment is obtained;

[0035] According to the spectrum parameters in the stress response spectrum order, the fatigue damage value corresponding to each wave direction condition of the overall structure is obtained.

[0036] In a possible implementation, the fatigue damage value corresponding to each wave direction condition of the overall structure is obtained according to the spectrum parameters in the stress response spectrum order, including:

[0037] (1) Calculation of fatigue stress transfer function H σ (w / θ)

[0038] (2) Determine the fatigue stress energy spectrum

[0039] S σ (w / H S ,T Z ,θ)=|H σ (W / θ)| 2 S η (W / HS,T Z )

[0040] Where: S σ (w / H S ,T Z ,θ) is the energy spectrum, H S is the significant wave height, T Z is the average zero-crossing period.

[0041] (3) Calculation of spectral distance under different wave loads

[0042]

[0043] (4) The distribution of each short-term wave load is assumed to obey the Rayleigh distribution, and the short-term probability density function of the stress range is:

[0044]

[0045] Where: S is the stress range,

[0046] (5) Based on the principle of linear fatigue damage accumulation and the Palmgren-Minler law, the fatigue damage during the entire service life can be obtained by linearly superposing the fatigue damage caused by various short-term sea conditions:

[0047]

[0048] The long-term probability density function of the stress range is

[0049]

[0050] (6) The total fatigue cumulative damage D can be calculated as

[0051]

[0052] Where: f0 is the average frequency of the stress range; T D is the design life, A, M are the relevant parameters in the fatigue SN curve, f 0i is the average zero-crossing frequency of the stress response, m0 is the zero-order moment of the stress response spectrum, m2 is the second-order moment of the stress response spectrum, and p i is the probability of occurrence of each short-term sea state, g i is the probability density function of each short-term sea state, M is the total number of short-term sea states in the wave distribution diagram, is the total number of cycles of the design life,

[0053] In a possible implementation, according to the wave parameters, the average zero-crossing period of the probability density function in the stress range under each sea state is calculated, including:

[0054] according to Calculate the average zero-crossing period of the probability density function in the stress range under each sea state;

[0055] Where m0 represents the zero-order moment of the stress response spectrum under each sea condition, and m2 represents the second-order moment of the stress response spectrum under each sea condition.

[0056] In a second aspect, an embodiment of the present invention provides a device for calculating fatigue load spectrum of an offshore platform, comprising:

[0057] Construction module, used to construct the overall structural finite element model of deep-water marine structures;

[0058] A calculation module, for calculating the fatigue damage value corresponding to each wave direction condition and the number of cycles within a preset stress range of the stress generated by the waves on the deep-water structure at different wave directions within the design life according to the wave distribution diagram of the real sea area where the deep-water structure is located and the finite element model of the overall structure;

[0059] The calculation module is further used to calculate the test cycle number of wave loads under different wave conditions according to the cycle number and the fatigue damage value;

[0060] The calculation module is further used to calculate the equivalent hot spot constant stress amplitude according to the number of cycles and the preset hot spot SN curve;

[0061] The processing module is used to perform a simulation test on the model corresponding to the deep-water structure in the ocean according to the equivalent hot spot constant stress amplitude and the test cycle number to obtain a wave fatigue load spectrum.

[0062] The embodiment of the present invention provides a method and device for calculating the fatigue load spectrum of an offshore platform. By combining a wave distribution diagram of a real sea area where a deep-water marine structure is located with a finite element model for calculation, the number of test cycles of wave loads under different wave conditions is obtained. According to a preset hotspot SN curve, an equivalent hotspot constant stress amplitude is obtained, so that the randomly fluctuating wave loads in the sea area where the deep-water marine structure is located can be converted into a constant testable fatigue load spectrum. Compared with the simple uniaxial tensile or bending load measurement of the deep-water marine structure in the prior art, this embodiment can not only test the fatigue life of the marine structure under actual working conditions, but also more accurately measure its service life under actual working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0064] Figure 1 is a flow chart of the method for calculating the fatigue load spectrum of an offshore platform provided by an embodiment of the present invention;

[0065] Figure 2 It is a flowchart for calculating the fatigue damage value corresponding to each wave direction condition and the number of cycles of stress generated by waves on deep-water structures in the ocean under different wave directions within the design life within a preset stress range, provided by an embodiment of the present invention;

[0066] Figure 3 is a schematic diagram of overall structural fatigue analysis results provided by an embodiment of the present invention;

[0067] Figure 4 is a schematic diagram of a local structure fatigue analysis result provided by an embodiment of the present invention;

[0068] Figure 5 It is a schematic diagram of the structure of a calculation device for fatigue load spectrum of an offshore platform provided by an embodiment of the present invention;

[0069] Figure 6 is a schematic diagram of a terminal provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0070] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0071] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0072] Figure 1 A flow chart of a method for calculating fatigue load spectrum of an offshore platform provided by an embodiment of the present invention is described in detail as follows:

[0073] Step 101, constructing an overall structural finite element model of an ocean deepwater structure.

[0074] Deepwater structures in the ocean may include deepwater platforms, offshore wind turbines, and drilling platforms, etc. These items are located deep in the ocean and cannot be directly tested for fatigue. In this embodiment, the random wave loads borne by the key nodes of the deepwater structure are converted into fatigue applied loads for fatigue testing, so that fatigue testing can be performed on the key nodes of the deepwater structure, thereby obtaining the fatigue load spectrum of the key nodes of the deepwater structure.

[0075] In one embodiment, four units, SHELL63, BEAM188, MPC184, and MASS21, in ANASYS software are used to construct an overall structural finite element model according to the structure of an actual deep-water ocean structure. Among them, SHELL63 is a 3D thin-walled unit used to simulate the shell building in the actual deep-water ocean structure, and the influence of shear deformation is considered; BEAM188 is a 3D beam unit used to simulate the beam structure in the structure of an actual deep-water ocean structure, based on the Timoshenko beam theory, that is, a first-order shear beam, considering the influence of shear deformation; MPC184 is a multi-point constraint unit that simulates the rod and rigid beam structure of the actual structure; MASS21 is a mass unit that applies multi-directional degrees of freedom to the structure of the actual deep-water ocean structure to ensure the accuracy of the simulation results.

[0076] Step 102, based on the wave distribution diagram of the real sea area where the deep-water ocean structure is located and the overall structural finite element model, calculate the fatigue damage value corresponding to each wave direction condition and the number of cycles of stress generated by waves on the deep-water ocean structure under different wave directions within the design life within a preset stress range.

[0077] The wave distribution diagram is a diagram formed by the wave statistical data of the real sea area where the deep-water ocean structure is located after a long period of statistics. It is the real parameters of actual waves over many years. We use these real parameters combined with the constructed overall structural finite element model to perform damage calculation on the deep-water ocean structure.

[0078] In one embodiment, see Figure 2 As shown, according to the wave distribution diagram of the real sea area where the deep-water ocean structure is located and the overall structural finite element model, the fatigue damage value corresponding to each wave direction condition and the number of cycles of the stress generated by waves on the deep-water ocean structure under different wave directions within the design life within a preset stress range can be calculated, which can include the following steps.

[0079] Step 201, based on the wave distribution diagram of the real sea area where the deep-water structure is located, the wave parameters in multiple directions are counted, and the wave parameters are input into the finite element model of the overall structure to obtain the fatigue damage value corresponding to each short-term sea condition of the overall structure.

[0080] The obtained wave distribution diagram is divided into i main directions according to the southeast, northwest and northeast directions, and the probability, wave height and frequency of wave occurrence in the i main directions are statistically obtained. The value of i here can be set according to requirements, and the value of i is not limited in this embodiment. For example, the value of i can be 16, 18, etc. In this embodiment, the value of i is 16 for exemplary description.

[0081] When calculating fatigue damage of deep-water structures in the ocean, spectrum analysis can be used for calculation. In one embodiment, wave parameters are input into the finite element model of the overall structure to obtain the fatigue damage value corresponding to each short-term sea condition of the overall structure. This may include: obtaining the stress response spectrum density function according to the wave parameter calculation; obtaining the stress response spectrum moment according to the stress response spectrum density function; obtaining the fatigue damage value corresponding to each short-term sea condition of the overall structure according to the spectrum parameters in the stress response spectrum moment. Figure 3 As shown, this is a schematic diagram of the overall structure fatigue analysis results.

[0082] Optionally, the stress response spectral density function is obtained according to the probability, wave height and frequency of the waves in the wave parameters.

[0083] The stress response spectrum moments may include stress spectrum zero-order moment, stress spectrum second-order moment, stress spectrum fourth-order moment and spectrum width.

[0084] In one embodiment, obtaining the fatigue damage value corresponding to each short-term sea condition of the overall structure according to the spectrum parameters in the stress response spectrum order may include:

[0085] (1) Calculation of fatigue stress transfer function H σ (w / θ)

[0086] (2) Determine the fatigue stress energy spectrum

[0087] S σ (w / H S ,T Z ,θ)=|H σ (W / θ)| 2 S η (W / HS,T Z )

[0088] Where: S σ (w / H S ,T Z ,θ) is the energy spectrum, H S is the significant wave height, T Z is the average zero-crossing period.

[0089] (3) Calculation of spectral distance under different wave loads

[0090]

[0091] (4) The distribution of each short-term wave load is assumed to obey the Rayleigh distribution, and the short-term probability density function of the stress range is:

[0092]

[0093] Where: S is the stress range,

[0094] (5) Based on the principle of linear fatigue damage accumulation and the Palmgren-Minler law, the fatigue damage during the entire service life can be obtained by linearly superposing the fatigue damage caused by various short-term sea conditions:

[0095]

[0096] The long-term probability density function of the stress range is

[0097]

[0098] (6) The total fatigue cumulative damage D can be calculated as

[0099]

[0100] Where: f0 is the average frequency of the stress range; T D is the design life, A, M are the relevant parameters in the fatigue SN curve, f 0i is the average zero-crossing frequency of the stress response, m0 is the zero-order moment of the stress response spectrum, m2 is the second-order moment of the stress response spectrum, and p iis the probability of occurrence of each short-term sea state, g i is the probability density function of each short-term sea state, M is the total number of short-term sea states in the wave distribution diagram, is the total number of cycles of the design life,

[0101] After obtaining the corresponding fatigue damage value of the overall structure under each short-term sea condition through the finite element model, the key nodes can be determined. For example, the connection position between the main beam and the deck is the key node, and its life is the shortest in the structure of the entire deep-water ocean structure. Therefore, it can characterize the life of the deep-water ocean structure.

[0102] Step 202, according to the fatigue damage value corresponding to each short-term sea condition of the overall structure, the fatigue damage value corresponding to each short-term sea condition at the key node position is determined.

[0103] This step is local structural analysis. Local structural analysis is based on the overall structural analysis, i.e. step 201. The local model is cut out, and then the boundary conditions of the cut local model are extracted, such as displacement, bending moment, load and other related information. This ensures that the local model is subjected to normal force. The purpose of this is to make the grid division more refined and relatively easier, and the calculation more accurate.

[0104] The construction of local models mainly involves refining the grid. The finer the grid, the more convergent and accurate the calculation results are. However, as the number of grids increases, the amount of calculation will also increase. Therefore, the overall structure is first divided into coarse grids, and then the local model is constructed and fine grid division is performed. This can reduce the amount of calculation and improve the calculation efficiency while ensuring the accuracy of the calculation results.

[0105] When determining the corresponding fatigue damage value of each short-term sea condition at the key node position, the boundary conditions of the key node and the node position NODE node refinement model are constructed, and the spectral analysis method is used to calculate the corresponding fatigue damage value of each short-term sea condition at the key node position through the stress response spectral density function and stress response spectral moment. Figure 4 As shown, this is a schematic diagram of the local structure fatigue analysis results.

[0106] The calculation method is consistent with the calculation of the fatigue damage value corresponding to each short-term sea condition of the overall structure in step 201, and will not be repeated here.

[0107] Step 203, according to the fatigue damage value corresponding to each short-term sea condition at the key node position, the fatigue damage value of the key node position under each wave is obtained.

[0108] Since there are too many short-term sea conditions, it is impossible to simulate all short-term sea conditions in actual fatigue testing. Therefore, the short-term sea conditions are normalized, that is, they are processed according to different wave directions. The fatigue damage values ​​under all short-term sea conditions are counted separately according to different wave directions to obtain the fatigue damage values ​​of the key node positions under each wave.

[0109] Step 204, calculating the average zero-crossing period of the probability density function in the stress range under each sea condition according to the wave parameters.

[0110] In one embodiment, calculating the average zero-crossing period of the probability density function in the stress range under each sea state according to the wave parameters may include:

[0111] according to Calculate the average zero-crossing period of the probability density function in the stress range under each sea state;

[0112] Where m0 represents the zero-order moment of the stress response spectrum under each sea condition, and m2 represents the second-order moment of the stress response spectrum under each sea condition.

[0113] Step 205, calculating the number of cycles within a preset stress range of stresses generated by waves on the deep-water structure at different wave directions within the design life according to the average zero-crossing cycle.

[0114] In one embodiment, according to the average zero-crossing period and the wave parameters, obtaining the number of times the stress generated on the deep-water structure in each sea condition within the design life is within a preset stress range may include:

[0115] according to Obtain the number of times the stress generated on the deep-water structure in each sea condition within the design life is within the preset stress range;

[0116] Where N i represents the number of times the stress generated on the deep-water structure in the ocean in the i-th direction is within the preset stress range. In this embodiment, N1-N 16 . T 设 Indicates the design life, P i represents the probability of the wave appearing in the i-th direction, T 过 Represents the average zero-crossing period.

[0117] Here, the design life is the design years. The design years multiplied by the probability of the corresponding short-term sea conditions can be used to get the sea condition action time. Then, in the zero-crossing cycle, the number of cycles of the sea conditions occurring within the design life can be obtained.

[0118] Step 103, calculating the test cycle numbers of wave loads under different wave conditions according to the cycle numbers and fatigue damage values.

[0119] In one embodiment, calculating the number of test cycles of wave loads under different wave conditions according to the number of cycles and the fatigue damage value may include:

[0120] Normalize the number of cycles of stress generated by waves on deep-water structures at different wave speeds within the design life within the preset stress range to ensure the convenience of subsequent design;

[0121] According to the product of the normalized number of cycles and the fatigue damage value, the ratio of the number of cycles generated by waves under different wave directions within the design life is obtained;

[0122] The number of test cycles of wave loads under different wave directions is obtained by multiplying the ratio of the number of cycles generated by waves within the design life under different wave directions and the product of the preset number of cycles base.

[0123] The preset cycle number base is the test load cycle number designed according to the test period, for example, the value may be 5000.

[0124] The purpose of calculating the number of test cycles here is to shorten the test time. Since the normal design life may be several decades, the experiment cannot be carried out for such a long time. Therefore, in order to reduce the test time, the number of test cycles is calculated, and the test is carried out according to the number of test cycles, and different fatigue loads are applied in each test.

[0125] Step 104, calculating the equivalent hot spot constant stress amplitude according to the number of cycles and the preset hot spot SN curve.

[0126] In one embodiment, the preset hotspot SN curve is the SN curve in the "Guidelines for Fatigue Strength Assessment of Marine Engineering Structures", and the equivalent hotspot constant stress amplitude corresponding to the corresponding number of cycles can be obtained according to the preset hotspot SN curve.

[0127] According to the number of cycles and the preset hot spot SN curve, the equivalent hot spot constant stress amplitude is calculated, which may include:

[0128] according to The equivalent hot spot constant stress amplitude is calculated;

[0129] Where S0 represents the constant stress amplitude of the equivalent hot spot, K and m represent the coefficients in the preset hot spot SN curve, and N i ' represents the number of cycles after normalization.

[0130] Step 105 , performing a simulation test on a model corresponding to the deep-water structure in the ocean according to the equivalent hot spot constant stress amplitude and the number of test cycles to obtain a wave fatigue load spectrum.

[0131] The model corresponding to the deep-water ocean structure may be a structural-level scaled model, which is a model obtained by scaling down the deep-water ocean structure in equal proportion.

[0132] The embodiment of the present invention constructs an overall structural finite element model of an ocean deepwater structure; calculates the fatigue damage value corresponding to each wave direction condition and the number of cycles of stress generated by waves on the ocean deepwater structure under different wave directions within the design life in a preset stress range according to a wave distribution diagram of the real sea area where the ocean deepwater structure is located and the overall structural finite element model; calculates the number of test cycles of wave loads under different wave directions according to the number of cycles and the fatigue damage value; calculates the equivalent hot spot constant stress amplitude according to the number of cycles and a preset hot spot SN curve; performs a simulation test on the model corresponding to the ocean deepwater structure according to the equivalent hot spot constant stress amplitude and the number of test cycles to obtain a wave fatigue load spectrum. The embodiment of the present invention combines the wave distribution diagram of the real sea area where the deep-water marine structure is located with the finite element model to calculate, and obtains the test cycle number of wave loads under different wave conditions. According to the preset hot spot SN curve, the equivalent hot spot constant stress amplitude is obtained, so that the randomly fluctuating wave load in the sea area where the deep-water marine structure is located can be converted into a constant testable fatigue load spectrum. Compared with the simple uniaxial tensile or bending load measurement of the deep-water marine structure in the prior art, this embodiment can not only test the fatigue life of the marine structure under actual working conditions, but also more accurately measure its service life under actual working conditions.

[0133] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0134] The following is an embodiment of the device of the present invention. For details not described in detail therein, reference may be made to the corresponding method embodiment described above.

[0135] Figure 5 The schematic diagram of the structure of the calculation device of the fatigue load spectrum of the marine platform provided by the embodiment of the present invention is shown. For the convenience of explanation, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0136] like Figure 5 As shown, the calculation device 5 for fatigue load spectrum of an offshore platform includes: a construction module 51 , a calculation module 52 and a processing module 53 .

[0137] A construction module 51 is used to construct an overall structural finite element model of the deep-water marine structure;

[0138] The calculation module 52 is used to calculate the fatigue damage value corresponding to each wave direction condition and the number of cycles of stress generated by waves on the deep-water structure under different wave directions within the design life within a preset stress range according to the wave distribution diagram of the real sea area where the deep-water structure is located and the finite element model of the whole structure;

[0139] The calculation module 52 is further used to calculate the test cycle number of wave loads under different wave conditions according to the cycle number and the fatigue damage value;

[0140] The calculation module 52 is also used to calculate the equivalent hot spot constant stress amplitude according to the number of cycles and the preset hot spot SN curve;

[0141] The processing module 53 is used to perform a simulation test on a model corresponding to the deep-water structure in the ocean according to the equivalent hot spot constant stress amplitude and the number of test cycles to obtain a wave fatigue load spectrum.

[0142] In a possible implementation, the calculation module 52 calculates the fatigue damage value corresponding to each wave direction condition and the number of cycles of stress generated by waves on the deep-water structure under different wave directions within the design life within a preset stress range according to the wave distribution diagram of the real sea area where the deep-water structure is located and the overall structural finite element model, and is used to:

[0143] According to the wave distribution diagram of the real sea area where the deep-water structure is located, the wave parameters in multiple directions are counted, and the wave parameters are input into the finite element model of the overall structure to obtain the corresponding fatigue damage value of the overall structure under each short-term sea condition;

[0144] According to the fatigue damage value corresponding to each short-term sea condition of the overall structure, the fatigue damage value corresponding to each short-term sea condition at the key node position is determined;

[0145] According to the fatigue damage value corresponding to each short-term sea condition at the key node position, the fatigue damage value of the key node position under each wave is obtained;

[0146] According to the wave parameters, the average zero-crossing period of the probability density function in the stress range under each sea state is calculated;

[0147] Based on the average zero-crossing cycle, the number of cycles within the preset stress range of stress generated by waves on deep-water structures at different wave directions within the design life is calculated.

[0148] In a possible implementation, the calculation module 52 calculates the number of cycles of stress generated by waves on the deep-water structure at different wave speeds within the design life within a preset stress range based on the average zero-crossing cycle, and is used to:

[0149] According to the average zero-crossing cycle and wave parameters, the number of times the stress generated on the deep-water structure in the ocean is within the preset stress range under each sea condition within the design life is obtained;

[0150] The number of times the stress generated on the deep-water structure in each sea condition is within the preset stress range is accumulated, and the number of cycles of the stress generated on the deep-water structure by waves under different wave conditions within the preset stress range is calculated.

[0151] In one possible implementation, the wave parameters include the probability of the wave occurring;

[0152] The calculation module 52 obtains the number of times the stress generated on the deep-water structure in the ocean under each sea condition within the design life is within the preset stress range based on the average zero-crossing period and the wave parameters, and is used to:

[0153] according to Obtain the number of times the stress generated on the deep-water structure in each sea condition within the design life is within the preset stress range;

[0154] Where N i It indicates the number of times the stress generated on the deep-water structure in the i-th direction is within the preset stress range, T 设 Indicates the design life, P i represents the probability of the wave appearing in the i-th direction, T 过 Represents the average zero-crossing period.

[0155] In a possible implementation, the calculation module 52 calculates the number of test cycles of wave loads under different wave conditions according to the number of cycles and the fatigue damage value, and is used to:

[0156] Normalize the number of cycles within a preset stress range of stress generated by waves on deep-water structures at different wave directions within the design life;

[0157] According to the product of the normalized number of cycles and the fatigue damage value, the ratio of the number of cycles generated by waves under different wave directions within the design life is obtained;

[0158] The number of test cycles of wave loads under different wave directions is obtained by multiplying the ratio of the number of cycles generated by waves within the design life under different wave directions and the product of the preset number of cycles base.

[0159] In a possible implementation, when the calculation module 52 calculates the equivalent hotspot constant stress amplitude according to the number of cycles and the preset hotspot SN curve, it is used to:

[0160] according to The equivalent hot spot constant stress amplitude is calculated;

[0161] Where S0 represents the constant stress amplitude of the equivalent hot spot, K and m represent the coefficients in the preset hot spot SN curve, and N i ' represents the number of cycles after normalization.

[0162] In a possible implementation, the calculation module 52 inputs the wave parameters into the finite element model of the overall structure to obtain the fatigue damage value corresponding to each wave direction condition of the overall structure, which is used to:

[0163] The stress response spectrum density function can be obtained by calculating the wave parameters;

[0164] According to the stress response spectrum density function, the stress response spectrum order moment is obtained;

[0165] According to the spectrum parameters in the stress response spectrum order, the corresponding fatigue damage value of the overall structure under each wave direction condition is obtained.

[0166] In a possible implementation, when the calculation module 52 obtains the fatigue damage value corresponding to each wave direction condition of the overall structure according to the spectrum parameters in the stress response spectrum order, it is used to:

[0167] (1) Calculation of fatigue stress transfer function H σ (w / θ)

[0168] (2) Determine the fatigue stress energy spectrum

[0169] S σ (w / H S ,T Z ,θ)=|H σ (W / θ)| 2 S η (W / HS,T Z )

[0170] Where: S σ (w / H S ,T Z ,θ) is the energy spectrum, H S is the significant wave height, T Z is the average zero-crossing period.

[0171] (3) Calculation of spectral distance under different wave loads

[0172]

[0173] (4) The distribution of each short-term wave load is assumed to obey the Rayleigh distribution, and the short-term probability density function of the stress range is:

[0174]

[0175] Where: S is the stress range,

[0176] (5) Based on the principle of linear fatigue damage accumulation and the Palmgren-Minler law, the fatigue damage during the entire service life can be obtained by linearly superposing the fatigue damage caused by various short-term sea conditions:

[0177]

[0178] The long-term probability density function of the stress range is

[0179]

[0180] (6) The total fatigue cumulative damage D can be calculated as

[0181]

[0182] Where: f0 is the average frequency of the stress range; T D is the design life, A, M are the relevant parameters in the fatigue SN curve, f 0i is the average zero-crossing frequency of the stress response, m0 is the zero-order moment of the stress response spectrum, m2 is the second-order moment of the stress response spectrum, and p i is the probability of occurrence of each short-term sea state, g i is the probability density function of each short-term sea state, M is the total number of short-term sea states in the wave distribution diagram, is the total number of cycles of the design life,

[0183] In a possible implementation, the calculation module 52 calculates the average zero-crossing period of the probability density function in the stress range under each sea state according to the wave parameters, and is used to:

[0184] according to Calculate the average zero-crossing period of the probability density function in the stress range under each sea state;

[0185] Where m0 represents the zero-order moment of the stress response spectrum under each sea condition, and m2 represents the second-order moment of the stress response spectrum under each sea condition.

[0186] The above-mentioned calculation device for fatigue load spectrum of marine platform constructs the overall structural finite element model of marine deepwater structure through the construction module; according to the wave distribution diagram of the real sea area where the marine deepwater structure is located and the overall structural finite element model, the calculation module calculates the fatigue damage value corresponding to each wave direction condition and the number of cycles of stress generated by waves on the marine deepwater structure under different wave directions within the design life within a preset stress range; according to the number of cycles and fatigue damage value, the calculation module calculates the number of test cycles of wave loads under different wave directions; according to the number of cycles and the preset hot spot SN curve, the calculation module calculates the equivalent hot spot constant stress amplitude; the processing module performs simulation test on the model corresponding to the marine deepwater structure according to the equivalent hot spot constant stress amplitude and the number of test cycles to obtain the wave fatigue load spectrum.

[0187] The embodiment of the present invention combines the wave distribution diagram of the real sea area where the deep-water marine structure is located with the finite element model to calculate, and obtains the test cycle number of wave loads under different wave conditions. According to the preset hot spot SN curve, the equivalent hot spot constant stress amplitude is obtained, so that the randomly fluctuating wave load in the sea area where the deep-water marine structure is located can be converted into a constant testable fatigue load spectrum. Compared with the simple uniaxial tensile or bending load measurement of the deep-water marine structure in the prior art, this embodiment can not only test the fatigue life of the marine structure under actual working conditions, but also more accurately measure its service life under actual working conditions.

[0188] Figure 6 is a schematic diagram of a terminal provided by an embodiment of the present invention. Figure 6 As shown, the terminal 6 of this embodiment includes: a processor 60, a memory 61, and a computer program 62 stored in the memory 61 and executable on the processor 60. When the processor 60 executes the computer program 62, the steps in the above-mentioned embodiments of the method for calculating the fatigue load spectrum of the marine platform are implemented, for example Figure 1 Alternatively, when the processor 60 executes the computer program 62, the functions of each module / unit in the above-mentioned device embodiments are realized, for example Figure 5 The functions of each module / unit are shown.

[0189] Exemplarily, the computer program 62 may be divided into one or more modules / units, which are stored in the memory 61 and executed by the processor 60 to implement the present invention. The one or more modules / units may be a series of computer program instruction segments capable of implementing specific functions, which are used to describe the execution process of the computer program 62 in the terminal 6. For example, the computer program 62 may be divided into Figure 5 The modules / units shown.

[0190] The terminal 6 may include, but is not limited to, a processor 60 and a memory 61. Those skilled in the art will appreciate that Figure 6 It is only an example of terminal 6 and does not constitute a limitation on terminal 6. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the terminal may also include input and output devices, network access devices, buses, etc.

[0191] The processor 60 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0192] The memory 61 may be an internal storage unit of the terminal 6, such as a hard disk or memory of the terminal 6. The memory 61 may also be an external storage device of the terminal 6, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the terminal 6. Further, the memory 61 may also include both an internal storage unit of the terminal 6 and an external storage device. The memory 61 is used to store the computer program and other programs and data required by the terminal. The memory 61 may also be used to temporarily store data that has been output or is to be output.

[0193] The technicians in the relevant field can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated in a processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0194] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0195] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0196] In the embodiments provided by the present invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are only schematic. For example, the division of the modules or units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0197] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0198] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0199] If the integrated module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, the steps of the above-mentioned calculation device method for fatigue load spectrum of each marine platform can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium.

[0200] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for calculating fatigue load spectrum of an offshore platform, characterized in that: include: Construct the overall structural finite element model of deep-water marine structures; According to the wave scatter diagram of the real sea area where the deep-water structure is located and the finite element model of the overall structure, the fatigue damage value corresponding to each wave direction condition and the number of cycles within a preset stress range of the stress generated by the waves on the deep-water structure at different wave directions within the design life are calculated; According to the number of cycles and the fatigue damage value, the number of test cycles of wave loads under different wave conditions is calculated; According to the number of cycles and the preset hot spot SN curve, an equivalent hot spot constant stress amplitude is calculated; Performing a simulation test on a model corresponding to the deep-water structure according to the equivalent hot spot constant stress amplitude and the test cycle number to obtain a wave fatigue load spectrum; According to the wave scatter diagram of the real sea area where the deep-water structure is located and the finite element model of the overall structure, the fatigue damage value corresponding to each wave direction condition and the number of cycles of stress generated by waves on the deep-water structure at different wave directions within the design life within a preset stress range are calculated, including: According to the wave scatter diagram of the real sea area where the deep-water structure is located, wave parameters in multiple directions are counted, and the wave parameters are input into the finite element model of the overall structure to obtain the fatigue damage value corresponding to each short-term sea condition of the overall structure; According to the fatigue damage value corresponding to each short-term sea condition of the overall structure, the fatigue damage value corresponding to each short-term sea condition at the key node position is determined; According to the fatigue damage value corresponding to each short-term sea condition at the key node position, the fatigue damage value of the key node position under each wave is obtained; According to the wave parameters, calculating the average zero-crossing period of the probability density function in the stress range under each sea state; According to the average zero-crossing period, the number of cycles within a preset stress range of stress generated by waves at different wave directions on the deep-water structure within the design life is calculated; According to the average zero-crossing cycle, the number of cycles of stress generated by waves at different wave directions on the deep-water structure in the ocean within the preset stress range within the design life is calculated, including: According to the average zero-crossing period and the wave parameters, the number of times the stress generated on the deep-water marine structure under each sea condition within the design life is within a preset stress range is obtained; The number of times the stress generated on the deep-water structure in each sea condition is within a preset stress range is accumulated, and the number of cycles of the stress generated on the deep-water structure in the preset stress range by waves under different wave conditions is calculated.

2. The method for calculating fatigue load spectrum of an offshore platform according to claim 1, characterized in that: The wave parameters include the probability of wave occurrence; According to the average zero-crossing period and the wave parameters, the number of times the stress generated on the deep-water structure in each sea condition within the design life is within a preset stress range is obtained, including: according to Obtaining the number of times the stress generated on the deep-water marine structure under each sea condition within the design life is within a preset stress range; Where N i represents the number of times the stress generated on the deep-water structure in the i-th direction is within the preset stress range, T 设 Indicates the design life, P i represents the probability of the wave appearing in the i-th direction, T 过 Represents the average zero-crossing period.

3. The method for calculating fatigue load spectrum of an offshore platform according to claim 1, characterized in that: According to the number of cycles and the fatigue damage value, the number of test cycles of wave loads under different wave conditions is calculated, including: Normalizing the number of cycles within a preset stress range of stresses generated by waves at different wave directions on the deep-water structure within the design life; According to the product of the normalized number of cycles and the fatigue damage value, the ratio of the number of cycles generated by waves under different wave directions within the design life is obtained; The number of test cycles of wave loads under different wave directions is obtained by multiplying the ratio of the number of cycles generated by waves within the design life under different wave directions and the product of the preset number of cycles base.

4. The method for calculating fatigue load spectrum of an offshore platform according to claim 3, characterized in that: According to the number of cycles and the preset hot spot SN curve, the equivalent hot spot constant stress amplitude is calculated, including: according to The equivalent hot spot constant stress amplitude is calculated; Where S0 represents the constant stress amplitude of the equivalent hot spot, K and m represent the coefficients in the preset hot spot SN curve, and N i ' represents the number of cycles after normalization.

5. The method for calculating fatigue load spectrum of an offshore platform according to claim 1, characterized in that: The wave parameters are input into the overall structure finite element model to obtain the fatigue damage value corresponding to each wave direction condition of the overall structure, including: A stress response spectral density function can be obtained by calculating the wave parameters; According to the stress response spectrum density function, a stress response spectrum order moment is obtained; According to the spectrum parameters in the stress response spectrum order, the fatigue damage value corresponding to each wave direction condition of the overall structure is obtained.

6. The method for calculating fatigue load spectrum of an offshore platform according to claim 5, characterized in that: According to the spectrum parameters in the stress response spectrum order, the fatigue damage value corresponding to each wave direction condition of the overall structure is obtained, including: (1) Calculation of fatigue stress transfer function H σ (w / θ) (2) Determine the fatigue stress energy spectrum S σ (w / H S ,T Z ,θ)=|H σ (w / θ)| 2 S η (w / H S ,T Z ) Where: S σ (w / H S ,T Z ,θ) is the energy spectrum, H S is the significant wave height, T Z is the average zero-crossing period; (3) Calculation of spectral distance under different wave loads (4) The distribution of each short-term wave load is assumed to obey the Rayleigh distribution, and the short-term probability density function of the stress range is: Where: S is the stress range, m0 represents the zero-order moment of the stress response spectrum (5) Based on the principle of linear fatigue damage accumulation and the Palmgren-Minler law, the fatigue damage during the entire service life can be obtained by linearly superposing the fatigue damage caused by various short-term sea conditions: The long-term probability density function of the stress range is (6) The total fatigue cumulative damage D can be calculated as Where: f0 is the average frequency of the stress range; T D is the design life, A, m are the relevant parameters in the fatigue SN curve, f 0i is the average zero-crossing frequency of stress response under the i-th short-term sea condition, m 0i is the zero-order moment of the stress response spectrum under the i-th short-term sea condition, m 2i is the second-order moment of the stress response spectrum under the i-th short-term sea condition, p i is the probability of occurrence of each short-term sea state, g i is the probability density function of each short-term sea state, M is the total number of short-term sea states in the wave scatter diagram, is the total number of cycles of the design life, 7. The method for calculating fatigue load spectrum of an offshore platform according to claim 1, characterized in that: According to the wave parameters, the average zero-crossing period of the probability density function in the stress range under each sea state is calculated, including: according to Calculate the average zero-crossing period of the probability density function in the stress range under each sea state; Where m0 represents the zero-order moment of the stress response spectrum under each sea condition, and m2 represents the second-order moment of the stress response spectrum under each sea condition.

8. A calculation device for fatigue load spectrum of an offshore platform, characterized in that: include: Construction module, used to construct the overall structural finite element model of deep-water marine structures; A calculation module, for calculating the fatigue damage value corresponding to each wave direction condition and the number of cycles within a preset stress range of the stress generated by waves on the deep-water structure at different wave directions within the design life according to the wave scatter diagram of the real sea area where the deep-water structure is located and the finite element model of the overall structure; The calculation module is further used to calculate the test cycle number of wave loads under different wave conditions according to the cycle number and the fatigue damage value; The calculation module is further used to calculate the equivalent hot spot constant stress amplitude according to the number of cycles and the preset hot spot SN curve; A processing module, used for performing a simulation test on a model corresponding to the deep-water structure of the ocean according to the equivalent hot spot constant stress amplitude and the number of test cycles to obtain a wave fatigue load spectrum; The calculation module calculates the fatigue damage value corresponding to each wave direction condition and the number of cycles of stress generated by waves on the deep-water structure at different wave directions within the design life within a preset stress range according to the wave scatter diagram of the real sea area where the deep-water structure is located and the finite element model of the overall structure, and is used to: According to the wave scatter diagram of the real sea area where the deep-water structure is located, wave parameters in multiple directions are counted, and the wave parameters are input into the finite element model of the overall structure to obtain the fatigue damage value corresponding to each short-term sea condition of the overall structure; According to the fatigue damage value corresponding to each short-term sea condition of the overall structure, the fatigue damage value corresponding to each short-term sea condition at the key node position is determined; According to the fatigue damage value corresponding to each short-term sea condition at the key node position, the fatigue damage value of the key node position under each wave is obtained; According to the wave parameters, calculating the average zero-crossing period of the probability density function in the stress range under each sea state; According to the average zero-crossing period, the number of cycles within a preset stress range of stress generated by waves at different wave directions on the deep-water structure within the design life is calculated; The calculation module calculates the number of cycles within a preset stress range of stress generated by waves at different wave directions on the deep-water structure of the ocean within the design life according to the average zero-crossing period, and is used to: According to the average zero-crossing period and the wave parameters, the number of times the stress generated on the deep-water marine structure under each sea condition within the design life is within a preset stress range is obtained; The number of times the stress generated on the deep-water structure in each sea condition is within a preset stress range is accumulated, and the number of cycles of the stress generated on the deep-water structure in the preset stress range by waves under different wave conditions is calculated.

Images