A mechanical estimation method for long-period fatigue life of marine floating structures

Abstract

The present invention discloses a mechanical estimation method for the long-cycle fatigue life of an ocean floating structure. First, a three-dimensional model of the ocean floating structure is built, and the model is substituted into a fluid dynamics numerical model to obtain four failure evaluation indicators under ocean working conditions. Then, corresponding splines are prepared from the ocean floating structure to be evaluated, and the splines are subjected to a material performance cycle test on a fatigue testing machine, and the attenuation values ​​of the corresponding materials under different loading working conditions are obtained through testing. Linear regression calculation is performed based on the obtained data to obtain attenuation curves of the four indicators, and four thresholds are substituted into the attenuation curves to obtain the maximum life of the destructive failure of the corresponding four indicators, respectively. The minimum value of the four lifespans is the estimated life of a specific structure built of a specific material under specific working conditions. The expected lifespan evaluated by the estimation method of the present invention is consistent with the actual lifespan, and the service life of the ocean floating structure is effectively and accurately evaluated.

Description

Technical Field

[0001] The invention relates to an ocean floating structure, and in particular to a mechanical estimation method for the long-period fatigue life of an ocean floating structure. Background Art

[0002] At present, for fishery and tourism platforms on the ocean, the allowable value of static load plus a certain safety factor is generally used to check the load of the structure. Simply using static load + safety factor to judge the life span lacks theoretical basis and is inaccurate because it does not consider the long-term performance attenuation changes of the material and the coupling effect of the environment and the structure.

[0003] If the linear regression algorithm of pressure-temperature-life in the field of pressure plastic pipes is used, since this method is only applicable to the situation of pure internal pressure, it cannot be applied to the complex load conditions at sea where tension, compression, bending and torsion exist simultaneously and change with time, so it cannot be fully matched.

[0004] To this end, the present invention proposes a convenient, fast and effective mechanical estimation method for the long-period fatigue life of marine floating structures. Summary of the invention

[0005] In view of the existing problems, the purpose of the present invention is to provide a mechanical estimation method for the long-period fatigue life of a marine floating structure, so as to effectively and accurately evaluate the service life of the marine floating structure.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A mechanical estimation method for long-period fatigue life of an ocean floating structure comprises the following steps:

[0008] Step 1: First determine the ocean working conditions, which include wave height, current velocity and wave period. Input the ocean working conditions and then build a three-dimensional model of the offshore floating structure.

[0009] Step 2: Substitute the three-dimensional model of the offshore floating structure built in step 1 into the established fluid dynamics numerical model, and obtain four failure evaluation indicators of the structure under the working conditions of the ocean after analysis;

[0010] Step 3: Determine the material of the marine floating structure to be evaluated, and then prepare the corresponding specimens from the marine floating structure to be evaluated. Each test group of specimens requires at least 3 samples;

[0011] Step 4: Determine the loading conditions of each test group on the fatigue testing machine;

[0012] Step 5: subjecting the sample prepared in step 3 to a material performance cycle test on a fatigue testing machine, and testing to obtain the attenuation value of the corresponding material under different loading conditions;

[0013] Step 6: Perform linear regression calculation based on the data obtained in step 5 to obtain the attenuation curves of the four indicators;

[0014] Step 7: Substitute the four failure evaluation indicators obtained in step 2 into the curve obtained in step 6, and obtain the maximum life of the corresponding four indicators (t1, t2, t3, t4). The minimum value of the four lifespans is the estimated life t=min (t1, t2, t3, t4) of a specific structure built with specific materials under specific working conditions.

[0015] Furthermore, in step one, a three-dimensional model of the offshore floating structure is constructed on a finite element simulation platform.

[0016] Furthermore, the four failure evaluation indicators in step 2 mainly include four thresholds of tensile strength σ1, bending strength σ2, tensile strain ε1, and bending strain ε2.

[0017] Furthermore, the process of preparing the spline in step 3 is as follows:

[0018] First, the marine floating platform to be evaluated is divided into a floating structure, a frame structure 1, a frame structure 2, a superstructure and a connecting structure, and then a sample with a length of 200±2mm and a width of 50±1mm is taken from each structure.

[0019] Furthermore, the connection structure is connection structure one, connection structure two or connection structure three.

[0020] Furthermore, the material of the marine floating structure is HDPE or its modified material.

[0021] Furthermore, the loading conditions in step 4 include loading speed, loading frequency, and deformation.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1) The method of the present invention can effectively evaluate the estimated life of an offshore floating structure built with specific materials under specific working conditions through the finite element model and the long-term attenuation model of material properties, and through the linear regression algorithm of the long-term service life of polymer materials;

[0024] 2) The method of the present invention considers the interaction between the structure and the environmental load through the finite element model, and considers a series of complex environmental boundary conditions such as wave height, flow velocity, and period;

[0025] 3) The present invention combines the finite element model and the long-term attenuation model of material properties to obtain a life estimation method for a specific structure built with a specific material under a specific cycle load, which takes more comprehensive factors into consideration. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a long-cycle fatigue life estimation flow chart of the present invention;

[0027] Figure 2 This is a three-dimensional diagram of the marine floating structure of the present invention;

[0028] Figure 3 for Figure 2 A magnified detail in the middle;

[0029] Figure 4 A top view of the marine floating structure of the present invention;

[0030] Figure 5 It is a side view of the marine floating structure of the present invention;

[0031] Figure 6 It is the linear regression curve of Example 1.

[0032] In the figure: 2. Connection structure 1; 3. Frame structure 1; 4. Upper structure; 5. Frame structure 2; 6. Connection structure 2; 7. Connection structure 3. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the described scope.

[0034] like Figure 1 As shown, a mechanical estimation method for long-cycle fatigue life of a marine floating structure comprises the following steps:

[0035] Step 1: First determine the ocean working conditions, which include wave height, current velocity and wave period. Input the ocean working conditions and then build a three-dimensional model of the offshore floating structure.

[0036] Step 2: Substitute the three-dimensional model of the offshore floating structure built in step 1 into the established fluid dynamics numerical model, and obtain four failure evaluation indicators of the structure under the working conditions of the ocean after analysis;

[0037] Step 3: Determine the material of the marine floating structure to be evaluated, and then prepare the corresponding specimens from the marine floating structure to be evaluated. Each test group of specimens requires at least 3 samples;

[0038] Step 4: Determine the loading conditions of each test group on the fatigue testing machine;

[0039] Step 5: subjecting the sample prepared in step 3 to a material performance cycle test on a fatigue testing machine, and testing to obtain the attenuation value of the corresponding material under different loading conditions;

[0040] Step 6: Perform linear regression calculation based on the data obtained in step 5 to obtain the attenuation curves of the four indicators;

[0041] Step 7: Substitute the four failure evaluation indicators obtained in step 2 into the curve obtained in step 6, and obtain the maximum life of the corresponding four indicators (t1, t2, t3, t4). The minimum value of the four lifespans is the estimated life t=min (t1, t2, t3, t4) of a specific structure built with specific materials under specific working conditions.

[0042] In step one, a three-dimensional model of the offshore floating structure is constructed on a finite element simulation platform.

[0043] The four failure evaluation indicators in step 2 mainly include four thresholds: tensile strength σ1, bending strength σ2, tensile strain ε1, and bending strain ε2.

[0044] The process of preparing the spline in step 3 is as follows: Figure 2-Figure 5 Shown

[0045] Firstly, the marine floating platform to be evaluated is divided into a floating structure, a frame structure 1 3, a frame structure 2 5, a superstructure 4 and a connecting structure, and then a sample with a length of 200±2mm and a width of 50±1mm is taken from each structure.

[0046] The connection structure is connection structure one 2, connection structure two 6 or connection structure three 7.

[0047] The material of the marine floating structure is HDPE or its modified material.

[0048] The loading conditions in step 4 include loading speed, loading frequency, and deformation.

[0049] Example 1

[0050] There is a glass fiber high-rigidity marine fishing pedal product, and it is necessary to evaluate its estimated life under the action of waves with a wave height of 5m, a flow rate of 1m / s, and a period of 2s.

[0051] Step 1: Determine the necessary parameters, input the ocean working conditions, including wave height, current velocity, and wave period, and then build a three-dimensional model of the offshore structure. Figure 2 As shown;

[0052] Step 2: Substitute the above data into the analysis to obtain the four failure evaluation indicators of the structure under this working condition, and get σ1=310MPa, σ2=85MPa, ε1=2.46*10-3 , ε2=3.5*10 -3 ;

[0053] Step 3: Determine the glass fiber prepreg tape as the base material and prepare the corresponding specimens. Each test group of specimens requires at least 3 samples;

[0054] Step 4: Determine the loading conditions of each test group on the fatigue testing machine, and determine the loading speed: 30 times per minute (corresponding to a wave period of 2s), loading frequency: 1000, 5000, 10000, 20000 times, and deformation 10cm (corresponding to a wave height of 5m under the actual pedal length);

[0055] Step 5: Conduct a material performance cycle test and test the attenuation value of the corresponding material under no loading conditions. The results are shown in Table 1 below:

[0056] Table 1 shows the attenuation values ​​of the four indicators.

[0057]

[0058] Step 6: Perform linear regression calculation based on the data values ​​obtained in step 5 to obtain the attenuation curves of the four indicators. Take the bending strain as an example, its value is the ratio of bending strength to bending modulus, and then take the logarithm as shown in Table 2 below, and perform linear regression calculation together with the logarithm of time to obtain the attenuation curve y = -0.1534x + 1.3318, R² = 0.8271, as shown in Figure 6 shown.

[0059] Table 2 shows the logarithmic values ​​of bending strain and time.

[0060]

[0061] Step 7: Under this condition, the bending strain threshold ε2=3.5*10 -3 Substituting the curve, the estimated life under bending strain failure conditions is t4 = 15.6 years. Similarly, the estimated life of the other three indicators is t1 = 27.2 years, t2 = 8.6 years and t3 = 18.1 years, which means that the estimated life of the modified product under the corresponding sea conditions is 8.6 years, and the final possible form of failure is bending stress fatigue failure.

Claims

1. A mechanical estimation method for long-period fatigue life of marine floating structures, characterized in that The steps include: Step 1: First determine the ocean working conditions, which include wave height, current velocity and wave period. Input the ocean working conditions and then build a three-dimensional model of the offshore floating structure. Step 2: Substitute the three-dimensional model of the offshore floating structure built in step 1 into the established fluid dynamics numerical model to obtain a finite element model, and after analysis, obtain four failure evaluation indicators of the structure under the working conditions of the ocean; Step 3: Determine the material of the marine floating structure to be evaluated, and then prepare the corresponding specimens from the marine floating structure to be evaluated. Each test group of specimens requires at least 3 samples; Step 4: Determine the loading conditions of each test group on the fatigue testing machine; Step 5: subject the sample prepared in step 3 to a material performance cycle test on a fatigue testing machine, and obtain the attenuation value of the corresponding material under different loading conditions, which is the material performance long-term attenuation model; Step 6: Perform linear regression calculation using the life linear regression algorithm based on the data obtained in step 5 to obtain the attenuation curves of the four failure evaluation indicators; Step 7: Substitute the four failure evaluation indicators obtained in step 2 into the curve obtained in step 6, and obtain the maximum life of the corresponding four failure evaluation indicators (t1, t2, t3, t4). The minimum value of the four lifespans is the estimated life t=min (t1, t2, t3, t4) of a specific structure built with specific materials under specific working conditions.

2. The mechanical estimation method for long-cycle fatigue life of a marine floating structure according to claim 1 is characterized in that In step one, a three-dimensional model of the offshore floating structure is constructed on a finite element simulation platform.

3. The mechanical estimation method for long-cycle fatigue life of a marine floating structure according to claim 1 is characterized in that The four failure evaluation indicators in step 2 include four thresholds: tensile strength σ1, bending strength σ2, tensile strain ε1, and bending strain ε2.

4. The mechanical estimation method for long-cycle fatigue life of a marine floating structure according to claim 1 is characterized in that The process of preparing the spline in step 3 is as follows: First, the marine floating platform to be evaluated is divided into a floating structure, a frame structure 1 (3), a frame structure 2 (5), a superstructure (4) and a connecting structure. Then, a sample with a length of 200±2mm and a width of 50±1mm is taken from each structure.

5. The mechanical estimation method for long-cycle fatigue life of a marine floating structure according to claim 4 is characterized in that The connection structure is connection structure one (2), connection structure two (6) or connection structure three (7).

6. The mechanical estimation method for long-period fatigue life of a marine floating structure according to claim 4 is characterized in that The material of the marine floating structure is HDPE or its modified material.

7. The mechanical estimation method for long-cycle fatigue life of a marine floating structure according to claim 1 is characterized in that The loading conditions in step 4 include loading speed, loading frequency, and deformation.

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