CN117454688A - Wind power dynamic cable fatigue life prediction method considering nonlinear stress - Google Patents
Wind power dynamic cable fatigue life prediction method considering nonlinear stress Download PDFInfo
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Abstract
The invention discloses a wind power dynamic cable fatigue life prediction method considering nonlinear stress, and relates to the technical field of fatigue life prediction. The method comprises the steps of obtaining external environment load information of wind power dynamic cables running in place, establishing an overall analysis numerical model according to the external environment load information, simulating the motion line type of the dynamic cables in a dynamic marine environment, and analyzing and obtaining the fatigue load and fatigue failure dangerous point positions of the dynamic cables under different working conditions according to a nonlinear time domain analysis method; and (3) performing bending behavior analysis on the spiral winding unit, establishing a nonlinear stress model of the section of the dynamic cable according to a curved beam theory, inputting fatigue loads of the dynamic cable under different working conditions into the nonlinear stress model of the section of the dynamic cable, obtaining stress amplitude values and times of the steel wire unit in the cable body, calculating accumulated damage, performing fatigue damage analysis and life prediction by combining a stress life method, and predicting the fatigue life of the dynamic cable. The method is beneficial to accurately solving the stress of the internal steel wire unit in the dynamic cable fatigue process and improves the life prediction precision.
Description
Technical Field
The invention relates to the technical field of fatigue life prediction, in particular to a wind power dynamic cable fatigue life prediction method considering nonlinear bending stress.
Background
The offshore wind power generation has the advantages of sufficient wind resources, large installed capacity, small occupied area and the like, the global popularization degree is continuously improved, the offshore wind power is inevitably developed to a farther and deeper sea area along with the development of a large amount of intertidal zone and offshore resources, and the future floating wind power technology has a wider application prospect. A typical offshore floating wind power system generally consists of a wind turbine, a floating platform, a mooring device, and a cable. Wherein, the cable suspended between the floating platform and the seabed and between the platform and the platform is influenced by dynamic loads such as waves, flows, platform movements and the like for a long time, and special designs are needed, which are called as 'dynamic cables'. The failure risk of the wind power dynamic cable is far higher than that of a static cable fixed on a pile foundation or laid on a seabed, and particularly the fatigue failure of the static cable under the periodic marine environment load is important. The top end of the dynamic cable is repeatedly bent under the influence of the motion of the platform, waves and ocean currents while bearing the dead weight of the cable suspension, and is the most dangerous part for fatigue failure. Meanwhile, the wind power dynamic cable is quite complex in section form, internal units are distributed in a non-bonding spiral winding structure, sliding can occur among the units, the bending behavior of the cable body is caused to be nonlinear, and further the accuracy of the fatigue life prediction of the dynamic cable is affected.
At present, offshore wind power development is an emerging industry, and a fatigue design specification of a wind power dynamic cable is not formed, and a simple fatigue life prediction method is not provided. The nonlinear bending behavior of the dynamic cable can be obtained through finite element method calculation, but partial parameters are difficult to obtain in the finite element method, the number of layers of the wind power dynamic cable spiral winding unit is large, the contact form is complex, the grid division of the finite element model is difficult, the calculation efficiency is low, and convergence is difficult. Therefore, most of engineering adopts a linear fatigue life prediction model (namely, the section stress of the cable body is assumed to be linear), and an excessively conserved safety coefficient is used for covering the influence of nonlinear stress factors on the fatigue life of the dynamic cable, and meanwhile, the fatigue resistance design of the structure of the dynamic cable is extremely difficult.
Therefore, the wind power dynamic cable fatigue life prediction method considering the nonlinear bending stress of the section is provided to solve the problems of the prior art that the number of layers is large, the contact form is complex, the grid division of the finite element model is difficult, the calculation efficiency is low, and the convergence is difficult, and the method is a problem to be solved by a person skilled in the art.
Disclosure of Invention
In view of the above, the invention provides a wind power dynamic cable fatigue life prediction method considering nonlinear stress, which can achieve the effect of improving the speed and accuracy of wind power dynamic cable fatigue life prediction.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a wind power dynamic cable fatigue life prediction method considering nonlinear stress comprises the following steps:
s1, acquiring external environment load information of the wind power dynamic cable in-situ operation, and establishing an overall analysis numerical model according to the external environment load information;
s2, simulating the motion line type of the dynamic cable in the dynamic marine environment by utilizing the integral analysis numerical model, and analyzing and obtaining the fatigue load and fatigue failure dangerous point positions of the dynamic cable under different working conditions according to a nonlinear time domain analysis method;
s3, bending behavior analysis is carried out on the spiral winding unit, a nonlinear stress model of the section of the dynamic cable is established according to a curved beam theory, fatigue loads of the dynamic cable under different working conditions obtained in the S2 are input into the nonlinear stress model of the section of the dynamic cable, and stress amplitude values and times of the steel wire unit in the cable body are obtained to calculate accumulated damage;
and S4, carrying out fatigue damage analysis and life prediction on the stress amplitude and the number of times of calculation accumulated damage of the steel wire units in the cable body by a stress life method, and predicting the fatigue life of the dynamic cable.
According to the method, optionally, the whole analysis numerical model in S1 is constructed by adopting a Line unit in OrcaFlex, the dynamic cable is divided into Line segments and nodes by using a centralized quality method, grids with different densities are used for dividing, and fatigue failure dangerous areas of the whole analysis numerical model are finely divided.
In the above method, optionally, the fatigue failure dangerous point in S2 is that an external environmental load parameter is input into the oscaflex, a curvature time curve is output, and a position corresponding to the maximum value of the curvature amplitude along the cable length distribution is found.
In the above method, optionally, the local stress combination of the spiral winding unit in S3 is expressed as an axial stress, a bending stress and a friction stress, where the axial stress is determined by the tensile stiffness of the dynamic cable structure and the steel wire unit, and the overall linear change, and the nonlinear local stress is mainly expressed as the sum of the bending stress and the friction stress.
The method is characterized in that the stress life method in S4 is based on the S-N curve of the material or the part, and the fatigue life calculation is carried out by combining with the Miner linear damage theory.
According to the method, the S-N curve is optionally a curve of the relation between the fatigue strength and the fatigue life of the standard test piece under a certain cycle characteristic, and the Goodman correction formula is adopted to simplify the S-N curve and correct the average stress.
According to the method, optionally, based on the Miner linear damage theory, dynamic cable fatigue damage caused by loads with different stress amplitudes is not affected, and the corrected stress amplitudes and the cycle times are linearly accumulated to obtain the total fatigue damage.
Compared with the prior art, the wind power dynamic cable fatigue life prediction method considering nonlinear stress provided by the invention has the following beneficial effects:
1) According to the method, a nonlinear stress theoretical model of the dynamic cable section is established, the contact sliding characteristic of the non-adhesive spiral winding structure is considered, so that the non-adhesive spiral winding structure is closer to the real fatigue stress state of the cable body, the fatigue life prediction of the dynamic cable is more accurate, and guidance can be provided for evaluating and improving the service life of the wind power dynamic cable.
2) According to the method, the nonlinear stress model and the nonlinear time domain analysis method are combined, so that the calculation efficiency of fatigue life prediction is greatly improved, and the defects that the finite element modeling grid division is difficult and the convergence is difficult in the existing fatigue life prediction method are overcome.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a wind power dynamic cable fatigue life prediction method considering nonlinear stress;
FIG. 2 is an annual wave rose diagram of the wind power dynamic cable disclosed in the embodiment under in-place working conditions;
FIG. 3 is a schematic diagram of an overall analysis model of a wind power dynamic cable disclosed in the present embodiment;
fig. 4 is a schematic bending view of a single steel wire unit disclosed in this embodiment;
fig. 5 is a schematic diagram of a nonlinear local stress model of a wind power dynamic cable disclosed in the present embodiment.
FIG. 6 is a graph of curvature versus fatigue life data as disclosed in this example.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In this application, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions, and the terms "comprise," "include," or any other variation thereof, are intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
Referring to FIG. 1, the invention discloses a wind power dynamic cable fatigue life prediction method considering nonlinear stress, which comprises the following steps:
a wind power dynamic cable fatigue life prediction method considering nonlinear stress comprises the following steps:
s1, acquiring external environment load information of the wind power dynamic cable in-situ operation, and establishing an overall analysis numerical model according to the external environment load information;
s2, simulating the motion line type of the dynamic cable in the dynamic marine environment by using the integral analysis numerical model, and analyzing and obtaining the fatigue load and fatigue failure dangerous point positions of the dynamic cable under different working conditions according to a nonlinear time domain analysis method;
s3, bending behavior analysis is carried out on the spiral winding unit, a nonlinear stress model of the section of the dynamic cable is established according to a curved beam theory, fatigue loads of the dynamic cable under different working conditions obtained in the S2 are input into the nonlinear stress model of the section of the dynamic cable, and stress amplitude values and times of the steel wire unit in the cable body are obtained to calculate accumulated damage;
and S4, carrying out fatigue damage analysis and life prediction on the stress amplitude and the number of times of calculation accumulated damage of the steel wire units in the cable body by a stress life method, and predicting the fatigue life of the dynamic cable.
Furthermore, the whole analysis numerical model in S1 is constructed by adopting a Line unit in OrcaFlex, a dynamic cable is divided into Line segments and nodes by using a centralized quality method, grids with different densities are used for dividing, and fatigue failure dangerous areas of the whole analysis numerical model are finely divided.
Further, in the step S2, fatigue failure dangerous points are positions corresponding to the distribution of the maximum value of the curvature amplitude along the cable length are found out by inputting external environment load parameters into OrcaFlex and outputting a curvature time course curve.
Further, the local stress combination of the spiral winding unit in S3 is expressed as an axial stress, a bending stress and a friction stress, wherein the axial stress is determined by the tensile rigidity of the dynamic cable structure and the steel wire unit, the whole is linearly changed, and the nonlinear local stress is mainly expressed as the sum of the bending stress and the friction stress.
Furthermore, the stress life method in S4 is based on the S-N curve of the material or the part, and the fatigue life calculation is carried out by combining with the Miner linear damage theory.
Further, the S-N curve is a curve of the relation between the fatigue strength and the fatigue life of the standard test piece under a certain cycle characteristic, and the S-N curve is simplified and the average stress is corrected by adopting a Goodman correction formula.
Further, based on the Miner linear damage theory, dynamic cable fatigue damage caused by loads with different stress amplitudes is not affected, and the corrected stress amplitudes and the cycle times are linearly accumulated to obtain the total fatigue damage.
In a specific embodiment, a method for predicting fatigue life of a wind power dynamic cable by considering nonlinear stress specifically includes:
s1: and acquiring an annual wave rose diagram of a platform where the wind power dynamic cable is located under in-place working conditions according to sea state statistical data, wherein the annual wave rose diagram is shown in fig. 2, and the main wave direction is E. Table 1 lists the wave extremum at various rendition periods. According to the Longuet-Higgins equation, the wave dispersion diagram of the sea condition where the wind power dynamic cable is located can be decomposed into single regular wave dispersion, 6 wave heights and 8 wave periods are selected, and the coverage rate of the regular wave dispersion diagram obtained by converting the probability distribution of the wave heights and the spectrum peak periods is 98.1%. The float motion RAO uses default parameters in OrcaFlex. And establishing a wind power dynamic cable overall analysis model according to the mechanical performance index and the linear design parameters of the cable body, as shown in fig. 3. The whole dynamic cable model is divided into 4 parts, the grid of the connection part of the upper end and the floating body and the ground point area is thinned, the grid is scattered into a plurality of calculation units with the length of 1 meter, and the static part and the middle part on the seabed are scattered into a plurality of calculation units with the length of 5 meters.
Specifically, S1 includes:
s1.1: when external load information is collected, the influence of wave load and motion response of the floating body needs to be considered seriously. The wave load adopts a random analysis method, and the response characteristic of the wave load is described by regarding an irregular wave on the actual sea surface as the superposition of a plurality of simple waves, namely a wave spectrum. Based on the Longuet-Higgins equation, the given irregular wave joint probability distribution is discretized into a wave scatter diagram of regular waves, and the working conditions in the wave scatter diagram are calculated by adopting the regular waves. The calculation formula of the actual occurrence times of a certain working condition in one year is as follows:
wherein P is the probability percentage of occurrence times within one year under the ith working condition; t (T) Z Is the period of the ith working condition; is the actual occurrence number within one year of the ith working condition. For the handling of the floating body, RAO (Response Amplitude Operator) which directly acquires the motion of the floating body can be selected to be applied to the top end of the dynamic cable as dynamic boundary constraint.
S1.2: the dynamic cable model is built using Line units in OrcaFlex. The centralized mass method divides the dynamic cable into a series of segments without mass and corresponding nodes, each segment simulates the axial, torsional and bending rigidity and other mechanical properties of the dynamic cable structure, and the mass, gravity and other properties of buoyancy are all centralized on corresponding particles. The top end of the dynamic cable model is fixedly connected with the floating body, and the tail end of the dynamic cable model is anchored on the seabed. In order to truly reflect the motion of the dynamic cable as much as possible, different grid division is adopted, and the fatigue failure dangerous area in the dynamic cable is divided in a refinement mode according to the stress deformation condition of the top end of the dynamic cable connected with the floating body.
TABLE 1 dynamic Cable wave Main polar parameter Table
Table 2 dynamic Cable fatigue calculation rule wave Condition
S2: and 6390 regular wave working conditions are selected by using a regular wave method, and analysis is carried out on the integral analysis model established in the step S1 under different sea conditions by using a nonlinear time domain analysis method, so that the average axial tension of the wind power dynamic cable is 14.5kN. And outputting the distribution condition of the curvature along the length of the dynamic cable under different sea conditions, and comparing the curvature amplitude values to obtain the fatigue failure dangerous position of the whole wind power dynamic cable at the position 3.3m away from the floating body connection point, wherein the fatigue failure dangerous position is due to the fact that the top end connection point can receive the combined action of larger tension and bending moment.
Specifically, the vicinity of the fatigue failure dangerous point of the wind power dynamic cable in the S2 bears the repeated bending load caused by the tensile load and the environmental load caused by the dead weight of the cable body. Because the wind power dynamic cable has a generally shallow water depth, which means that the dynamic cable has a small dead weight, the alternating tension has a small contribution to the fatigue damage of the cable body structure, and the top tension can be simplified into a dead load as the average stress correction parameter in the step S42. Meanwhile, alternating curvature generated by environmental load on the cable body is taken as a main cause of fatigue failure, and a position corresponding to the maximum value of curvature amplitude along the cable length distribution is found out according to the curvature time curve output by OrcaFlex, and the position is a fatigue failure dangerous point of the wind power dynamic cable structure.
S3: and outputting the tensile load and curvature distribution conditions born by the dynamic cable under each working condition through OrcaFlex software, and calculating the real stress condition on the internal unit of the dynamic cable by using a nonlinear stress model. Critical slip curvature k when single steel wire slides cr The method comprises the following steps:
wherein f i The resultant force of friction force born by the ith layer of steel wire unit is E, wherein E is the steel wire elastic modulus, alpha is the steel wire winding angle, R is the spiral winding radius of the steel wire unit, and A is the cross section area of the steel wire unit. According to the formula (3), the critical slip curvature of the armored steel wire of the wind power dynamic cable is calculated to be 0.007m -1 。
Specifically, S3 includes:
s3.1: in the process of establishing a nonlinear stress model of a dynamic cable section, the accuracy of an analysis result can be greatly influenced by friction force and bending hysteresis effect between components in a cable body, and important consideration is needed in establishing the nonlinear stress model. As a main stress unit of the dynamic cable, the armored steel wire layer is easy to generate local hot spot stress and is tired first. The local stress combinations of the wire units can be expressed as axial stress, bending stress and friction stress, i.e.:
σ＝σT+σB+σf(2)
wherein sigma T For armouring the axial stress of the wire, sigma B For armouring the wire bending stress, sigma f Is the friction stress of the armoured steel wire. The axial stress is determined by the dynamic cable structure and the tensile rigidity of the steel wire unit, and the whole is in linear change. Under the condition of being in place, the dynamic cable usually bears the combined load action of stretching and bending, the stretching force can cause larger interlayer circumferential extrusion force, a certain friction force exists between steel wire layers, and the bending behavior of the dynamic cable is nonlinear, so that nonlinear local stress mainly appears as bending stress and friction stressAnd (3) summing.
S3.2: the tensile stress in the dynamic cable spiral winding unit is as follows:
wherein T is tension, p i And p is as follows e Is the internal and external pressure of the steel wire unit layer, R i And R is R e Is the inner and outer radius of the steel wire unit layer, n t Is the number of steel wire units in the layer.
S3.3: when the armoured steel wire layer is subjected to bending load, the steel wire unit starts to slide from the neutral layer firstly along with the gradual increase of curvature, then slides gradually to two sides of the bending direction along the circumferential direction of the winding cylinder, and meanwhile, the local stress of the armoured steel wire layer can show obvious nonlinearity. Based on the curved beam principle, the bent single steel wire slides along the initial spiral angle, and the curvature of the steel wire in each direction is the projection of the corresponding cylindrical curvature. Therefore, the critical slip curvature kappa can be determined when a single steel wire slips cr The method comprises the following steps:
wherein f i The resultant force of friction force born by the ith layer of steel wire unit is E, wherein E is the steel wire elastic modulus, alpha is the steel wire winding angle, R is the steel wire spiral winding radius, and A is the cross section area of the steel wire unit.
The coordinate diagram of the spiral winding unit in the bending dynamic cable is shown in fig. 4, and the bending stress sigma of the steel wire unit is shown in the figure B The bending direction can be divided into bending normal stress and bending shear stress, and the bending normal stress sigma n And bending shear stress sigma t Can be expressed as a function of the curvature κ:
σ n ＝E cos 4 α·cosθ·κX 2 (4)
σ t ＝E cosα(1+sin 2 α)sinθ·κX 3 (5)
where θ is the phase angle of the wire unit and κ is the curvature of the wire unit.
S3.4: friction stress sigma of steel wire unit f Can be expressed as:
wherein f is the friction force of the unit length of the steel wire unit.
S3.5: the alternating stress of the section under the fatigue load of the dynamic cable is the resultant force of the bending stress and the friction stress, and a nonlinear local stress model is established as shown in fig. 5. In the same unit layer, because the sliding of the steel wire units is expanded from the two sides of the neutral axis, when the phase angle of the unit is 0 DEG, the unit is furthest from the neutral layer, the unit stress is also maximum, and the maximum alternating stress in each layer of steel wire units can be obtained as follows:
and r is the radius of the steel wire unit, and the maximum alternating stress in each unit layer is selected as the key control stress in fatigue calculation to calculate the fatigue life.
S4: the fatigue failure life prediction of the wind power dynamic cable is based on a metal fatigue failure theory, theoretical calculation is carried out according to the stress state of the armored steel wire layer, and the corrected stress amplitude and cycle number can be converted into structural fatigue damage based on a Miner linear damage theory.
Specifically, S4 includes:
s4.1: and (3) taking the maximum nonlinear stress in each unit of the armored steel wire obtained in the step (S3.4) as a key local stress in fatigue calculation, and carrying out fatigue damage analysis and life prediction by combining the stress amplitude and the corresponding cycle times with a stress life method. The stress life method is based on the S-N curve of the material or the part, and combines with the Miner linear damage theory to calculate the fatigue life. The S-N curve is a curve representing the relationship between the fatigue strength and the fatigue life of a standard test piece under a certain cycle characteristic, and the mathematical expression is generally written in the logarithmic form of a power function and can be expressed as:
logNi＝loga-mlog(Δσi)(8)
wherein Δσ i For alternating stress amplitude, N i For alternating stress delta sigma i The number of cycles to failure, a and m, is a material parameter, which is usually obtained by fatigue test and its value is shown in Table 3.
TABLE 3 armored steel wire S-N curve parameter table
S4.2: the S-N curve of the material is obtained under the symmetrical circulation condition, under the real fatigue working condition, an asymmetric circulation load is born by a steel wire unit in the dynamic cable, the stress is formed by superposing an alternating stress component and an average stress component, and the S-N curve is simplified and the average stress is corrected by adopting a Goodman correction formula:
wherein sigma ref Is the material strength limit.
S4.3: based on Miner linear damage theory, dynamic cable fatigue damage caused by loads with different stress amplitudes is not affected, and the corrected stress amplitude and cycle times can be linearly accumulated to obtain total fatigue damage. Dynamic cable structure fatigue damage can be expressed as:
wherein N is the number of fatigue working conditions, D is the accumulated amount of fatigue damage, N i Is the actual cycle number, and the fatigue life of the dynamic cable structure is the reciprocal of the accumulated amount of fatigue damage, namely
Based on Miner linear damage theory, fatigue damage under each working condition is calculated as shown in FIG. 6, so that the dynamic cable fatigue life considering nonlinear local stress influence is 46.9 years.
In addition, the dynamic cable fatigue life prediction process provided by the invention needs to consider a safety factor of 10 times according to the recommendation of the umbilical cable design specification API-17B similar to the dynamic cable structural form.
In this specification, each embodiment is described in a progressive manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment mainly describes differences from other embodiments. In particular, for a system or system embodiment, since it is substantially similar to a method embodiment, the description is relatively simple, with reference to the description of the method embodiment being made in part. The systems and system embodiments described above are merely illustrative, wherein the elements illustrated as separate elements may or may not be physically separate, and the elements shown as elements may or may not be physical elements, may be located in one place, or may be distributed over a plurality of network elements. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art will understand and implement the present invention without undue burden.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (7)
1. A wind power dynamic cable fatigue life prediction method considering nonlinear stress is characterized by comprising the following steps:
s1, acquiring external environment load information of the wind power dynamic cable in-situ operation, and establishing an overall analysis numerical model according to the external environment load information;
s2, simulating the motion line type of the dynamic cable in the dynamic marine environment by using the integral analysis numerical model, and analyzing and obtaining the fatigue load and fatigue failure dangerous point positions of the dynamic cable under different working conditions according to a nonlinear time domain analysis method;
s3, bending behavior analysis is carried out on the spiral winding unit, a nonlinear stress model of the section of the dynamic cable is established according to a curved beam theory, fatigue loads of the dynamic cable under different working conditions obtained in the S2 are input into the nonlinear stress model of the section of the dynamic cable, and stress amplitude values and times of the steel wire unit in the cable body are obtained to calculate accumulated damage;
and S4, carrying out fatigue damage analysis and life prediction on the stress amplitude and the number of times of calculation accumulated damage of the steel wire units in the cable body by a stress life method, and predicting the fatigue life of the dynamic cable.
2. The method for predicting fatigue life of a wind power dynamic cable taking nonlinear stress into consideration as recited in claim 1, wherein,
and S1, constructing an integral analysis numerical model by adopting a Line unit in OrcaFlex, dividing a dynamic cable into Line segments and nodes by using a centralized quality method, and dividing grids with different densities, wherein fatigue failure dangerous areas of the integral analysis numerical model are finely divided.
3. The method for predicting fatigue life of a wind power dynamic cable taking nonlinear stress into consideration as recited in claim 1, wherein,
and S2, inputting external environment load parameters into the OrcaFlex, outputting a curvature time-course curve, and finding out the position corresponding to the maximum value of the curvature amplitude along the cable length distribution.
4. The method for predicting fatigue life of a wind power dynamic cable taking nonlinear stress into consideration as recited in claim 1, wherein,
the local stress combination of the spiral winding unit in the S3 is expressed as axial stress, bending stress and friction stress, wherein the axial stress is determined by the tensile rigidity of the dynamic cable structure and the steel wire unit, the whole is in linear change, and the nonlinear local stress is mainly expressed as the sum of the bending stress and the friction stress.
5. The method for predicting fatigue life of a wind power dynamic cable taking nonlinear stress into consideration as recited in claim 1, wherein,
the stress life method in S4 is based on the S-N curve of the material or the part, and the fatigue life calculation is carried out by combining with the Miner linear damage theory.
6. The method for predicting fatigue life of a wind power dynamic cable taking nonlinear stress into consideration as recited in claim 5, wherein,
the S-N curve is a curve of the relation between the fatigue strength and the fatigue life of the standard test piece under a certain cycle characteristic, and the Goodman correction formula is adopted to simplify the S-N curve and correct the average stress.
7. The method for predicting fatigue life of a wind power dynamic cable taking nonlinear stress into consideration as recited in claim 5, wherein,
based on Miner linear damage theory, dynamic cable fatigue damage caused by loads with different stress amplitudes is not affected, and the corrected stress amplitude and cycle times are linearly accumulated to obtain total fatigue damage.
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| 张振国 等: "浮式风电动态缆疲劳分析方法研究", 《应用科技》, 25 October 2022 (2022-10-25), pages 1 - 9 * |
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