Damage combination method suitable for fatigue analysis of marine high-temperature and high-pressure container

Abstract

The invention relates to the technical field of fatigue analysis of high-temperature and high-pressure containers, and discloses a damage combination method suitable for fatigue analysis of a marine high-temperature and high-pressure container, which comprises the following steps: (1) establishing a finite element model of the high-temperature and high-pressure container; (2) performing harmonic response analysis on the high-temperature and high-pressure container based on a finite element model to obtain a transfer function from an acceleration spectrum to a stress response spectrum; (3) performing hydrodynamic analysis on the high-temperature and high-pressure container based on a finite element model to calculate a transfer function from a sea wave spectrum to a displacement spectrum; (4) transfer function conversion is carried out, and a transfer function from a sea wave spectrum to an acceleration spectrum is converted; and (5) respectively calculating fatigue damage under different load effects to obtain two different fatigue damage data. Through accurate establishment of a finite element model, multi-aspect analysis, reasonable transfer function conversion and the like, an analysis result conforms to related standards, the fatigue condition of the container can be accurately evaluated, and the accuracy is higher than that of a traditional method.

Description

Technical Field

[0001] The invention relates to the technical field of fatigue analysis of high-temperature and high-pressure vessels, and in particular to a damage combination method suitable for fatigue analysis of high-temperature and high-pressure vessels for ships. Background Art

[0002] Under the action of marine environmental loads (such as wind, waves, currents, etc.), ships will move in multiple directions. The high-temperature and high-pressure vessels in them must not only withstand low-frequency fatigue caused by temperature and pressure, but also withstand the swaying inertia force generated by waves for a long time. The appearance of alternating loads will accelerate the fatigue damage of the structure and easily cause fatigue failure of the high-temperature and high-pressure vessels before the design life. Therefore, it is crucial to the safety of the structure to accurately analyze the fatigue damage of high-temperature and high-pressure vessels during the design stage.

[0003] At present, in the frequency domain of fatigue damage analysis of marine structures, fatigue analysis of high-temperature and high-pressure vessels mostly adopts time domain methods. There is no complete and convenient method for fatigue analysis of marine high-temperature and high-pressure vessels. Traditional fatigue analysis methods have certain limitations. If the requirements of relevant specifications for high-pressure vessels are followed, fatigue analysis requires superposition calculation of transient loads. However, the transient loads caused by waves with different wave heights and periods are complex and diverse. If each transient load is considered for time domain nonlinear coupling calculation, it will take a lot of time. For the design stage, this approach cannot meet the needs and may change at any time. If fatigue is calculated using the frequency domain method, the requirements of high-pressure vessel specifications cannot be met. This method cannot guarantee the accuracy of fatigue analysis of marine high-temperature and high-pressure vessels.

[0004] The time domain method commonly used in ship specifications and high-pressure vessel specifications can be applied to relatively simple structures, so that the calculation time will be greatly reduced. However, for marine high-temperature and high-pressure vessels, due to the special service environment and the special position in the ship, its calculation model will not be a simple structure. In addition, the thermal pressure process is very slow, and the frequency of wave action is relatively high. Therefore, the time step selected for the simulation calculation is very long, and the calculation is very time-consuming. However, if the fatigue damage under two different loads is calculated separately and then added, the fatigue damage will be underestimated. This method of fatigue damage analysis is very dangerous for marine high-temperature and high-pressure vessels. Therefore, the present invention provides a damage combination method suitable for fatigue analysis of marine high-temperature and high-pressure vessels to address the shortcomings of the prior art. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention provides a damage combination method suitable for fatigue analysis of marine high-temperature and high-pressure vessels, which solves the problem that fatigue calculation in the prior art is time-consuming and has poor accuracy under different environments.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: A damage combination method suitable for fatigue analysis of marine high-temperature and high-pressure vessels, comprising the following steps: (1) Establish a finite element model of high temperature and high pressure vessels; (2) Perform harmonic response analysis on high temperature and high pressure vessels based on finite element models to obtain the transfer function from acceleration spectrum to stress response spectrum; (3) Perform hydrodynamic analysis on high-temperature and high-pressure vessels based on finite element models to calculate the transfer function from wave spectrum to displacement spectrum; (4) Perform transfer function conversion to convert the wave spectrum into the acceleration spectrum; (5) Calculate the fatigue damage under different loads to obtain two different fatigue damage data; (6) Use the combined method to calculate the fatigue damage under the combined action of different loads to calculate the final required data.

[0007] Preferably, in (2), acceleration excitation is applied to the high temperature and high pressure vessel in finite element software to perform harmonic response calculation, and response data at the target verification point is extracted; the response data obtained in the harmonic response calculation are combined so that the rows in the transfer function matrix represent different response points, and the table indicates the responses at different frequencies, thereby obtaining the transfer function matrix of the marine high temperature and high pressure vessel.

[0008] Preferably, in said (4), based on the influence of the change in the attitude of the high-temperature and high-pressure container due to the coordinate transformation, the transfer function from the wave spectrum to the acceleration spectrum is calculated; in the two-dimensional rotation, it is stipulated that the counterclockwise rotation of the coordinate system along the Y axis is positive, and the rotation angle is , and then calculate the rotated coordinates.

[0009] Preferably, after calculating the rotated coordinates in (4), the coordinates are expanded into three-dimensional rotation to obtain the displacement data of the pitch, roll and bow of the hull motion.

[0010] Preferably, in (5), the spectral analysis method is used to calculate the fatigue damage under wave load, and the wave spectrum is used as the power spectrum density function of the input process during the calculation, and the stress power spectrum density function of the response process is obtained by combining the transfer function calculation.

[0011] Preferably, in (5), a transient method is used to calculate fatigue damage under hot-pressing loads, transient working conditions at different times are calculated, stress response data of the entire lifting process are obtained by linear interpolation of stress response processes under different transient conditions, and then the rain flow counting method is used in combination with the SN curve to calculate fatigue damage under hot-pressing process.

[0012] Preferably, the derivation of the nonlinear fatigue damage calculation formula for load interaction in (6) is combined with the interaction between different loads and the damage equivalent theory to derive a new nonlinear fatigue damage calculation formula for load interaction, which is expressed as follows: ; In the expression is the fatigue damage under thermal compression load, is the fatigue damage under wave load, is the zero-order spectral moment of the power spectral density function of the response, is the stress amplitude during the thermal compression process.

[0013] The present invention provides a damage combination method suitable for fatigue analysis of high-temperature and high-pressure marine vessels. It has the following beneficial effects: 1. The present invention can be applied to fatigue analysis of marine high-temperature and high-pressure vessels. It integrates the advantages of fatigue analysis in different fields and fully considers the various loads on marine high-temperature and high-pressure vessels in complex marine environments. In the calculation process, by accurately establishing finite element models, conducting multi-faceted analysis, and reasonable transfer function conversion, the analysis results meet relevant standards and can accurately evaluate the fatigue condition of the container, which is more accurate than traditional methods.

[0014] 2. The damage combination method in the present invention deeply studies the interaction between loads under different working environments. When deriving the fatigue damage calculation formula, based on the damage equivalence theory, the mutual influence of wave load and thermal pressure load is taken into consideration. In this way, when calculating fatigue damage, the actual stress condition of the container can be more realistically reflected, avoiding errors caused by ignoring load interactions, thereby significantly improving the accuracy of fatigue analysis.

[0015] 3. Compared with conventional methods, the present invention does not require a large amount of time-consuming simulation calculations. By combining the advantages of frequency domain and time domain analysis methods, it reduces unnecessary calculation steps, adopts appropriate algorithms and formulas, avoids the calculation of complex transient loads one by one, greatly shortens the time required for analysis and calculation, and effectively saves computing resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a work flow chart of the present invention; Figure 2 It is a schematic diagram of loads under the combined action of different loads of the present invention; Figure 3 It is a damage equivalent schematic diagram of the present invention; Figure 4 It is a schematic diagram of the effective element model of the hull of the present invention; Figure 5 It is a schematic diagram of a high temperature and high pressure container of the present invention; Figure 6 This is a fatigue damage comparison diagram based on Tp=4s, Hs=2m of the present invention; Figure 7 This is a schematic diagram of fatigue damage based on Tp=6s, Hs=3m of the present invention; Figure 8 This is a schematic diagram of fatigue damage based on Tp=7s, Hs=3.5m of the present invention; Fig. 9 This is a schematic diagram of fatigue damage based on Tp=8s, Hs=4m of the present invention. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Please refer to the attached Figure 1 -Attached Fig. 9 The embodiment of the present invention provides a damage combination method suitable for fatigue analysis of high-temperature and high-pressure vessels for ships, comprising the following steps: (1) establishing a finite element model of the high-temperature and high-pressure vessel, determining the operating position of the ship, and obtaining the wave spectrum of the sea area in which it is located.

[0019] (2) Based on the finite element model, a harmonic response analysis of the high temperature and high pressure container is performed to obtain the transfer function from the acceleration spectrum to the stress response spectrum. In (2), acceleration excitation is applied to the high temperature and high pressure container in the finite element software to perform harmonic response calculation and extract the response data at the target verification point.

[0020] Specifically, in the transfer function, the row data represents different frequencies, and the column data represents the response data at different frequencies, that is, the data in the i-th row and j-th column of the frequency response function matrix at a single frequency is the response data of the i-th point at the j-th frequency. By combining all the response data in the harmonic response analysis according to the above rules, the frequency response function matrix of the marine high-temperature and high-pressure container is obtained. This is the transfer function from the acceleration spectrum to the response spectrum, recorded as In the Hydrodynamic diffraction module in Workbench, the transfer function from the wave spectrum to the displacement spectrum can be obtained. At the same time, based on the influence of the inertial force of the coordinate transformation, this transfer function is converted into the transfer function from the wave spectrum to the acceleration spectrum, which is recorded as .

[0021] (3) Perform hydrodynamic analysis on high-temperature and high-pressure vessels based on finite element models to calculate the transfer function from wave spectrum to displacement spectrum; (4) Perform transfer function conversion, convert the transfer function of the wave spectrum to the acceleration spectrum, calculate the impact of the change in the posture of the high-temperature and high-pressure container based on the coordinate transformation in (4), and convert the change in inertial force caused by the movement of the hull into accelerations in three directions, so as to calculate the impact of the inertial load caused by the change in the posture of the ship's high-temperature and high-pressure container.

[0022] Specifically, in two-dimensional rotation, the coordinate system is defined as rotating counterclockwise along the Y axis as positive, and the rotation angle is , the coordinate calculation after rotation can be expressed as: ; Represented as a matrix: ; For a three-dimensional rotation, only three two-dimensional rotations are required, which can be obtained by extrapolation, with the coordinate axis along the bottom , , The axes rotate in sequence, and the corresponding coordinate transformation is: ; After calculating the rotated coordinates in (4), the three-dimensional rotation is expanded to obtain the displacement data of the pitch, roll and bow of the hull motion, and the gravitational acceleration can be converted into linear acceleration in three directions.

[0023] (5) The fatigue damage under different loads is calculated respectively to obtain two different fatigue damage data. In (5), the spectral analysis method is used to calculate the fatigue damage under wave load. The wave spectrum is used as the power spectrum density function of the input process, and the stress power spectrum density function of the response process is obtained by combining the transfer function. The corresponding expression is: ; In the expression, is the frequency point within the frequency interval of the linear time-invariant system; Represents the frequency response function matrix of the marine high temperature and high pressure container; represents the transfer function from the wave spectrum to the acceleration spectrum; represents the spectrum of ocean waves; Represents the power spectral density function of the response.

[0024] Specifically, the transient method is used in (5) to calculate the fatigue damage under the action of thermal pressure load, and the transient working conditions at different times are calculated. The stress response process under different transient conditions is obtained by linear interpolation to obtain the stress response data of the entire lifting process, and then the rain flow counting method is used in combination with Curve calculation of fatigue damage during hot pressing process.

[0025] (6) Use the combined method to calculate the fatigue damage under the combined action of different loads, which is used to calculate the final required data. The nonlinear fatigue damage calculation formula for load interaction is derived in (6). The commonly used fatigue analysis method in the shipbuilding industry is the narrow band method ( The specific expression is: ; In the expression is the zero-order spectral moment, calculated by the following formula: ; The fatigue damage under wave load is calculated according to the above formula and recorded as ; Calculated Individual records are considered , the fatigue damage calculation under the action of hot-pressing load is completed in the finite element software.

[0026] Specifically, consider each transient situation under a certain working condition, solve and obtain the response data under each transient state, combine all transient data to obtain a set of transient response data distributed according to time, use the rain flow counting method to count different cycle amplitudes and cycle times for this set of data, and then combine - The fatigue damage under this condition is calculated by the curve and recorded as ; Record the stress amplitude under this condition, denoted as , calculated by the above method , , and , calculated according to the following formula, the fatigue damage considering the load is obtained: ; In the expression is the fatigue damage under thermal compression load, is the fatigue damage under wave load, is the zero-order spectral moment of the power spectral density function of the response, is the stress amplitude during the thermal compression process.

[0027] Based on the coordinate transformation, the influence of the change of inertial acceleration caused by the change of the posture of the high-temperature and high-pressure container for ships is calculated. The power spectrum density function of the response process is used to reversely calculate the amplitude data of the wave action process. The wave action process is generally in the form of irregular wave action, and multiple groups of different amplitudes will appear in a period of time. The power spectrum density function (PSD) of the wave action contains information such as the period, intensity and distribution range of the wave process. From the power spectrum density function, the relevant amplitude information of the wave process can be reversed. For a signal under a unit bandwidth, the power spectrum is the square of the root mean square amplitude spectrum. The power spectrum can be regarded as the integral of the power spectrum density over a certain frequency interval. Therefore, the data of the root mean square amplitude spectrum can be obtained from the power spectrum density function. The relevant expression is: ; In the expression is the amplitude spectrum, is the power spectral density function, and are the starting and ending frequencies of the power spectral density function. The wave action process is often regarded as a zero-mean Gaussian random process. Numerically and the zeroth order spectral moment of the power spectral density function are equal, so calculate The formula can be expressed as: ; In the expression is the zero-order spectral moment of the power spectral density function, and its calculation formula is as follows: ; The RMS amplitude is considered as Used to calculate fatigue damage using the combined method.

[0028] In Miner's linear criterion, the formula for calculating fatigue damage under different loads is: ; In a marine high temperature and high pressure vessel, under the simultaneous action of thermal pressure load and wave load, the above formula is rewritten as: ; In the expression is the fatigue damage under thermal compression load, Fatigue damage under wave load.

[0029] like Figure 3 As shown, based on the concept of damage curve, fatigue life analysis is performed under the conditions of piecewise constant and continuous change of cycle amplitude: ; In the expression is the number of cycles corresponding to the fatigue limit.

[0030] Analyzing the exponential part of the above formula, we can get: ; Therefore, the fatigue life analysis under two-level loading can be rewritten as: ; According to the damage equivalence theory, the damage under different loads can be equivalently transformed: ; From this we can get: ; Combination Curve expression: ; ; In the expression and are all constants, so we can assume and stress amplitude Therefore, the above formula can be further expressed as: ; In the expression, is the wave load amplitude, is the amplitude of the thermal pressure load, then the fatigue damage calculation of the marine high temperature and high pressure vessel combined with the Miner criterion is expressed as: ; use To express the mutual influence between loads, the above formula can be further expressed as: ; In marine high temperature and high pressure vessels, this formula can be expressed as: ; This formula is the nonlinear fatigue damage calculation formula that takes into account load interaction. is the peak load value.

[0031] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A damage combination method suitable for fatigue analysis of high-temperature and high-pressure marine vessels, characterized in that: The following steps are involved: (1) Establish a finite element model of high temperature and high pressure vessels; (2) Perform harmonic response analysis on high temperature and high pressure vessels based on finite element models to obtain the transfer function from acceleration spectrum to stress response spectrum; (3) Perform hydrodynamic analysis on high-temperature and high-pressure vessels based on finite element models to calculate the transfer function from wave spectrum to displacement spectrum; (4) Perform transfer function conversion to convert the wave spectrum into the acceleration spectrum; (5) Calculate the fatigue damage under different loads to obtain two different fatigue damage data; (6) Use the combined method to calculate the fatigue damage under the combined action of different loads to calculate the final required data.

2. A damage combination method suitable for fatigue analysis of marine high-temperature and high-pressure vessels according to claim 1, characterized in that: In the above (2), acceleration excitation is applied to the high temperature and high pressure container in the finite element software to perform harmonic response calculation, and the response data at the target verification point is extracted; the response data obtained in the harmonic response calculation are combined so that the rows in the transfer function matrix represent different response points, and the table indicates the responses at different frequencies, thereby obtaining the transfer function matrix of the marine high temperature and high pressure container.

3. The damage combination method suitable for fatigue analysis of marine high-temperature and high-pressure vessels according to claim 1, characterized in that: In (4), based on the influence of the change in the attitude of the high-temperature and high-pressure container on the coordinate transformation, the transfer function from the wave spectrum to the acceleration spectrum is calculated; in the two-dimensional rotation, the coordinate system is defined to rotate counterclockwise along the Y axis as positive, and the rotation angle is , and then calculate the rotated coordinates.

4. The damage combination method suitable for fatigue analysis of marine high-temperature and high-pressure vessels according to claim 3, characterized in that: After the rotated coordinates are calculated in (4), they are expanded into three-dimensional rotation to obtain the displacement data of the pitch, roll and bow of the hull motion.

5. The damage combination method suitable for fatigue analysis of marine high-temperature and high-pressure vessels according to claim 1, characterized in that: In (5), the spectral analysis method is used to calculate the fatigue damage under wave load. During the calculation, the wave spectrum is used as the power spectrum density function of the input process, and the stress power spectrum density function of the response process is obtained by combining the transfer function calculation.

6. The damage combination method for fatigue analysis of high-temperature and high-pressure marine vessels according to claim 1, characterized in that: In (5), the transient method is used to calculate the fatigue damage under the action of hot-pressing load, the transient working conditions at different times are calculated, the stress response process under different transient conditions is obtained by linear interpolation to obtain the stress response data of the entire lifting process, and then the rain flow counting method is used in combination with the SN curve to calculate the fatigue damage under the hot-pressing process.

7. The damage combination method for fatigue analysis of high-temperature and high-pressure marine vessels according to claim 1, characterized in that: The derivation of the nonlinear fatigue damage calculation formula for load interaction in (6) is combined with the interaction between different loads and the damage equivalent theory to derive a new nonlinear fatigue damage calculation formula for load interaction, which is expressed as follows: ； In the expression is the fatigue damage under thermal compression load, is the fatigue damage under wave load, is the zero-order spectral moment of the power spectral density function of the response, is the stress amplitude during the thermal compression process.

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