A method and system for analyzing fatigue strength of a ship structure

Abstract

The application provides a ship structure fatigue strength analysis method and system, which calculates the main engine vibration load and the wave load received by the ship structure based on the ship data, the characteristic data of the ship structure and the global sea state data, then calculates the stress response process under the combined action of the wave load and the main engine vibration load, the spectral density function of the stress response process, each order spectral moment of the stress response process and the zero-crossing rate of the stress response process, then calculates the stress response and the stress response peak of the ship structure under the action of the sinusoidal vibration load, calculates the stress cycle number of the ship structure based on the stress response and in combination with the fatigue life S-N curve, further calculates the fatigue damage under the action of the main engine vibration load, and finally calculates the total coupling fatigue damage under the long-term sea state, and further calculates the fatigue damage of the ship structure under the combined action of the high and low frequency loads, which effectively improves the accuracy and reliability of the ship structure fatigue strength calculation.

Description

Technical Field

[0001] This invention relates to the field of fatigue analysis technology for ship structures, specifically to a method and system for fatigue strength analysis of ship structures under combined high and low frequency loads. Background Technology

[0002] Ships play a vital role in shipping as the primary means of water transport on oceans and inland waterways. Consequently, ships operating at sea for extended periods and facing the ever-changing and unpredictable marine environment endure immense stress. The hull is constantly eroded by seawater during navigation, and over time, this erosion leads to structural fatigue, resulting in structural quality problems. Fatigue damage is considered one of the main forms of damage to ship and marine engineering structures.

[0003] During normal navigation, ship structures are subjected to continuous wave loads. In addition, it should be noted that local structures of the ship are subjected to other types of loads, particularly the main engine base structure. Under long-term, high-intensity operation, the main engine also operates continuously, generating vibration loads. Therefore, these loads need to be considered in the fatigue damage calculation of the main engine base structure. Wave loads are low-frequency loads, while vibration loads are high-frequency loads. The combined action of these two loads creates a coupling effect. For fatigue damage calculation under this load coupling, a method needs to be derived that can effectively and quickly calculate the fatigue damage of the main engine base structure under the combined action of wave and vibration loads, obtain relatively accurate calculation results, and demonstrate the rationality of the calculation.

[0004] Current methods for calculating the fatigue strength of ship structures under high- and low-frequency loads, or combined loads, primarily focus on marine structures, with less attention paid to ship structures, especially main engine foundation structures. The calculated loads mainly consider wave loads and wind loads, or wave loads and current loads, rarely considering wave loads combined with main engine vibration loads. Furthermore, the methods for handling these two types of loads mainly include simple addition and load superposition methods. While the simple superposition method is straightforward, its results are often risky; the constant amplitude load method within the load superposition method typically yields conservative results and is complex to apply. Therefore, there is no efficient and absolutely reliable method for calculating fatigue damage under the combined action of two long-term distributed loads.

[0005] Therefore, there is an urgent need for a method for analyzing the fatigue strength of ship structures that takes into account wave loads and main engine vibration loads, and that has fast calculation speed and high accuracy. Summary of the Invention

[0006] To address the issues of low accuracy, safety, economy, and reliability in current fatigue strength analysis of ship structures, particularly when high- and low-frequency loads, especially the coupled effects of vibration and wave loads, the present invention provides a method for fatigue strength analysis of ship structures. Based on ship data, characteristic data of the ship structure, and global sea state data, the main engine vibration load and wave load are calculated. Using specific calculation methods based on the wave load and main engine vibration load, the fatigue damage of the ship structure under the combined action of wave load and main engine vibration load is calculated, effectively improving the accuracy and reliability of fatigue strength calculation for ship structures under combined high- and low-frequency loads. The present invention also relates to a fatigue strength analysis system for ship structures.

[0007] The technical solution of the present invention is as follows:

[0008] A method for analyzing the fatigue strength of ship structures, characterized by comprising the following steps:

[0009] Data acquisition and calculation steps: acquire ship data, ship structure characteristic data and global sea state data, calculate the main engine vibration load based on the main engine vibration frequency and amplitude in the characteristic data, and use wave load calculation software to calculate the wave load on the ship structure. The ship data includes the ship's sailing life and sailing time.

[0010] Zero-crossing rate calculation steps: Based on the Gaussian narrowband process of wave load and the Gaussian narrowband process of host vibration load, calculate the stress response process under the combined action of wave load and host vibration load. Then, based on the spectral density function of the Gaussian narrowband process of wave load and the spectral density function of the Gaussian narrowband process of host vibration load, calculate the spectral density function of the stress response process. Based on the spectral density function of the stress response process, calculate the spectral moments of each order of the stress response process. Based on the spectral moments of each order of the stress response process, calculate the zero-crossing rate of the stress response process.

[0011] The calculation steps for main engine vibration fatigue damage are as follows: The vibration mode of the main engine vibration load is set to sinusoidal vibration to obtain sinusoidal vibration load. Based on the sinusoidal vibration load, the stress response and peak value of the ship structure under the sinusoidal vibration load are calculated. Based on the stress response and combined with the fatigue life SN curve, the number of stress cycles of the ship structure during the ship's sailing life and the number of stress cycles of the ship structure when the ship structure is damaged are calculated respectively. Then, the fatigue damage under the main engine vibration load is calculated.

[0012] The steps for calculating coupled fatigue damage are as follows: First, calculate the peak stress response of the ship structure under the combined action of wave load and main engine vibration load based on the wave load and main engine vibration load. Then, calculate the peak stress probability density function under a short-term sea state based on the zero-order spectral moment of the stress response process, the peak stress response under sinusoidal vibration load, and the peak stress response under the combined action of wave load and main engine vibration load. Next, calculate the coupled fatigue damage under a short-term sea state based on the peak stress probability density function, the peak stress response under the combined action of wave load and main engine vibration load, the sailing time, the zero-crossing rate of the stress response process, and the wave direction from global sea state data. Finally, calculate the total coupled fatigue damage under a long-term sea state based on the coupled fatigue damage under the short-term sea state. Finally, calculate the fatigue damage of the ship structure under the combined action of wave load and main engine vibration load based on the total coupled fatigue damage and the fatigue damage under the main engine vibration load.

[0013] Preferably, in the data acquisition and calculation steps, the ship data further includes the ship mobile service identification code, ship name, ship latitude and longitude location information, navigation status, timestamp, ground speed, draft, port of departure, port of destination, and estimated arrival time; the global sea state data includes wave direction, global typhoon data, and global marine meteorological data.

[0014] Preferably, in the zero-crossing rate calculation step, the spectral moments of each order of the Gaussian narrowband process of the wave load are calculated based on the spectral density function of the Gaussian narrowband process of the wave load, and the spectral moments of each order of the Gaussian narrowband process of the host vibration load are calculated based on the spectral density function of the Gaussian narrowband process of the host vibration load. The zero-crossing rate of the stress response process is then calculated based on the spectral moments of each order of the Gaussian narrowband process of the wave load and the spectral moments of each order of the Gaussian narrowband process of the host vibration load.

[0015] Preferably, in the data acquisition and calculation steps, the ship structure is the ship's main engine base structure.

[0016] Preferably, the characteristic data of the ship structure include the main engine vibration frequency, amplitude, rotational speed, and power.

[0017] A ship structure fatigue strength analysis system, characterized in that it comprises a data acquisition and calculation module, a zero-crossing rate calculation module, a main engine vibration fatigue damage calculation module, and a coupled fatigue damage calculation module connected in sequence.

[0018] The data acquisition and calculation module acquires ship data, ship structure characteristic data, and global sea state data. It calculates the main engine vibration load based on the main engine vibration frequency and amplitude in the characteristic data, and uses wave load calculation software to calculate the wave load on the ship structure. The ship data includes the ship's sailing life and sailing time.

[0019] The zero-crossing rate calculation module calculates the stress response process under the combined action of wave load and host vibration load based on the Gaussian narrowband process of wave load and host vibration load. Then, it calculates the spectral density function of stress response process based on the spectral density function of wave load and host vibration load, calculates the spectral moments of stress response process based on the spectral density function of stress response process, and calculates the zero-crossing rate of stress response process based on the spectral moments of stress response process.

[0020] The main engine vibration fatigue damage calculation module sets the vibration mode of the main engine vibration load to sinusoidal vibration to obtain sinusoidal vibration load. Based on the sinusoidal vibration load, it calculates the stress response of the ship structure under the sinusoidal vibration load and the peak value of the stress response under the sinusoidal vibration load. Based on the stress response and combined with the fatigue life SN curve, it calculates the number of stress cycles of the ship structure during the ship's sailing life and the number of stress cycles of the ship structure when the ship structure is damaged, and then calculates the fatigue damage under the main engine vibration load.

[0021] The coupled fatigue damage calculation module calculates the peak stress response of the ship structure under the combined action of wave load and main engine vibration load based on wave load and main engine vibration load. It then calculates the peak stress probability density function under a short-term sea state based on the zero-order spectral moment of the stress response process, the peak stress response under sinusoidal vibration load, and the peak stress response under the combined action of wave load and main engine vibration load. Based on the peak stress probability density function, the peak stress response under the combined action of wave load and main engine vibration load, the sailing time, the zero-crossing rate of the stress response process, and the wave direction in global sea state data, it calculates the coupled fatigue damage under a short-term sea state. Based on the coupled fatigue damage under the short-term sea state, it calculates the total coupled fatigue damage under the long-term sea state. Finally, based on the total coupled fatigue damage and the fatigue damage under the main engine vibration load, it calculates the fatigue damage of the ship structure under the combined action of wave load and main engine vibration load.

[0022] Preferably, the ship data further includes the ship's mobile service identification code, ship name, ship's latitude and longitude location information, navigation status, timestamp, ground speed, draft, port of departure, port of destination, and estimated arrival time; the global sea state data includes wave direction, global typhoon data, and global marine meteorological data.

[0023] Preferably, in the zero-crossing rate calculation module, the spectral moments of each order of the Gaussian narrowband process of the wave load are calculated based on the spectral density function of the Gaussian narrowband process of the wave load, and the spectral moments of each order of the Gaussian narrowband process of the host vibration load are calculated based on the spectral density function of the Gaussian narrowband process of the host vibration load. The zero-crossing rate of the stress response process is calculated based on the spectral moments of each order of the Gaussian narrowband process of the wave load and the spectral moments of each order of the Gaussian narrowband process of the host vibration load.

[0024] Preferably, the ship structure is a ship main engine base structure.

[0025] Preferably, the characteristic data of the ship structure include the main engine vibration frequency, amplitude, rotational speed, and power.

[0026] The beneficial effects of this invention are as follows:

[0027] This invention provides a method for analyzing the fatigue strength of ship structures. First, it acquires ship data, characteristic data of the ship structure, and global sea state data. Based on the main engine vibration frequency and amplitude from the characteristic data, it calculates the main engine vibration load and uses wave load calculation software to calculate the wave load on the ship structure. Then, based on the Gaussian narrowband process of the wave load and the Gaussian narrowband process of the main engine vibration load, it calculates the stress response process under the combined action of the wave load and the main engine vibration load. Next, based on the spectral density functions of the wave load and the main engine vibration load, it calculates the spectral density function of the stress response process, further calculating the spectral moments of each order of the stress response process, and then calculating the zero-crossing rate of the stress response process. Then, it sets the vibration mode of the main engine vibration load to sinusoidal vibration to obtain a sinusoidal vibration load. Based on the sinusoidal vibration load, it calculates the stress response and peak stress response of the ship structure under the sinusoidal vibration load. Based on the stress response and combined with the fatigue life SN curve, it calculates the number of stress cycles of the ship structure during its sailing life and the number of stress cycles at the time of structural damage, thus calculating the fatigue damage under the main engine vibration load. By incorporating the vibration load generated during long-term operation of the main engine into the calculation, it significantly increases the subsequent impact on the main engine base structure. The accuracy of fatigue damage calculation is improved. Finally, the peak stress response of the ship structure under the combined action of wave load and main engine vibration load is calculated. Based on the calculated parameters and using specific calculation formulas, the peak stress probability density function under the combined action of wave load and main engine vibration load under a certain short-term sea state is calculated, as well as the coupled fatigue damage under a certain short-term sea state. Based on the coupled fatigue damage under the short-term sea state, the total coupled fatigue damage under the long-term sea state is calculated. Based on the total coupled fatigue damage and the fatigue damage under the action of main engine vibration load, the fatigue damage of the ship structure under the combined action of wave load and main engine vibration load is calculated. Considering the different navigation conditions of the ship in different navigation areas, the corresponding sea state data is selected to calculate the low-frequency wave load. At the same time, considering the different high-frequency vibration loads on different structures, the high-frequency vibration load is calculated. In this invention, by fully considering the vibration load generated by the long-term operation of the main engine and the coupling effect generated by the combined action of wave load and main engine vibration load, the coupling effect under the combined action of high and low frequency loads is taken into account in the calculation. The corresponding calculation method is innovatively designed, which can quickly calculate the fatigue damage of the main engine base structure under the combined action of wave load and vibration load, effectively improving the accuracy and reliability of the fatigue strength calculation of the ship structure. Furthermore, the method of this invention has strong scalability and has certain application value in the calculation and research of fatigue strength of local structures under high and low frequency loads.

[0028] This invention also relates to a ship structure fatigue strength analysis system, which corresponds to the aforementioned ship structure fatigue strength analysis method. This system can be understood as a system that implements the aforementioned ship structure fatigue strength analysis method. It includes a data acquisition and calculation module, a zero-crossing rate calculation module, a main engine vibration fatigue damage calculation module, and a coupled fatigue damage calculation module connected sequentially. These modules work collaboratively to calculate the main engine vibration load and the wave load on the ship structure based on ship data, ship structure characteristic data, and global sea state data. Based on the wave load and main engine vibration load, and using a specific calculation method, it calculates the fatigue damage of the ship structure under the combined action of wave load and main engine vibration load. It fully considers the fatigue damage of the ship structure under the combined action of long-term distributed loads, and takes into account the coupling effect under the combined action of high and low frequency loads in the calculation. This allows for a more reasonable and accurate calculation of the fatigue damage of the ship structure under the combined action of high and low frequency loads, effectively improving the accuracy and reliability of fatigue strength calculation for ship structures under combined loads. Attached Figure Description

[0029] Figure 1 This is a flowchart of the ship structure fatigue strength analysis method of the present invention.

[0030] Figure 2 This is a schematic diagram of the host base structure.

[0031] Figure 3 This is a schematic diagram of the stress process under low-frequency wave load.

[0032] Figure 4 This is a schematic diagram of the stress process of high-frequency host vibration load.

[0033] Figure 5 This is a schematic diagram of the stress process caused by a combination of high and low frequency loads. Detailed Implementation

[0034] The present invention will now be described with reference to the accompanying drawings.

[0035] This invention relates to a method for analyzing the fatigue strength of ship structures. When calculating the fatigue damage of structures under the combined action of high and low frequency loads, the vibration load is set to a simple sinusoidal form. Based on the fatigue strength calculation of ship structures based on spectral analysis, the stress response of the vibration load is coupled with the stress response under the wave load under each short sea state to obtain the peak stress probability density function under the combined action of high and low frequency loads. The final fatigue damage is divided into high-frequency damage components and high- and low-frequency envelope damage components. The results are calculated separately and then summed to obtain the final fatigue damage under the combined action of high and low frequency loads.

[0036] The principle of this invention is as follows: The fatigue strength calculation of ship structures based on spectral analysis is a method for studying load and structural response in ship and marine engineering, grounded in the linear system transformation theory of stochastic processes. Ship and marine engineering structures are typical dynamic systems. For ship-sea structures, the input of the linear dynamic system is the wave process, and the output or response is the alternating stress response process generated by waves acting on the structure. The stress response of ship structures under low-frequency linear wave loads and the calculated stress response spectrum in the frequency domain can be considered as a narrow-band Gaussian process. The stress peak of the alternating stress process follows a Rayleigh distribution, meaning the stress response spectrum in the frequency domain can be considered a single-peak spectrum with only one peak. However, the stress response spectrum of structures under high- and low-frequency loads is no longer a simple single-peak narrow-band Gaussian distribution, but a stochastic distribution process with two peaks within the frequency range. Based on selected sea state data, fatigue damage is calculated for each short-term sea state, and the total damage is calculated using cumulative damage theory.

[0037] For large ships navigating in rough seas, the long-term fatigue life of the main engine base structure is calculated under the combined effects of wave loads and main engine vibration loads. The wave load is a low-frequency load, and the sea state data used for calculation can be the North Atlantic sea state. The vibration load is a high-frequency load, and the vibration mode is taken as simple sinusoidal vibration. Figure 2 The diagram shows the host base. The four elbow plate toe ends of the host base can be selected as computational hotspots for fatigue life analysis. The flowchart of this method is shown below. Figure 1 As shown, the steps are as follows:

[0038] I. Data Acquisition and Calculation Steps: Acquire ship data, characteristic data of ship structure, and global sea state data. Calculate the main engine vibration load based on the main engine vibration frequency and amplitude in the characteristic data. Use wave load calculation software to calculate the wave load on the ship structure. Ship data includes the ship's design life and sailing time.

[0039] Specifically, first, ship data and global sea state data are acquired, and characteristic data of the ship's main engine operation are retrieved. Based on the main engine vibration frequency and amplitude in the characteristic data, the main engine vibration load generated by the ship's main engine is calculated. For different types of main engine vibration loads, the corresponding load frequency and amplitude are selected during calculation, and the same method can be used for calculation. Then, the loading conditions, mass distribution, and hull lines data from the retrieved ship data are input into the three-dimensional wave load calculation software to calculate the ship structure (preferably the main engine base mechanism, such as...). Figure 2 The wave load (shown) is a low-frequency load, while the host machine vibration load is a high-frequency load. The stress process of the low-frequency wave load is as follows: Figure 3 As shown, the stress process of the high-frequency host vibration load is as follows: Figure 4 As shown, the stress process of combined high and low frequency loads is as follows: Figure 5 As shown, in addition to the above, the ship data also includes the ship's mobile service identification code, ship name, ship's latitude and longitude location information, navigation status, timestamp, ground speed, draft, port of departure, port of destination, and estimated arrival time. Preferably, the ship's structural characteristic data includes the main engine vibration frequency, amplitude, speed, and power. Preferably, the global sea state data includes wave direction, global typhoon data, and global marine meteorological data.

[0040] II. Zero-crossing rate calculation steps: Based on the Gaussian narrowband process of wave load and the Gaussian narrowband process of host vibration load, calculate the stress response process under the combined action of wave load and host vibration load. Then, based on the spectral density function of wave load and host vibration load, calculate the spectral density function of stress response process. Based on the spectral density function of stress response process, calculate the spectral moments of each order of stress response process. Based on the spectral moments of each order of stress response process, calculate the zero-crossing rate of stress response process.

[0041] Specifically, we first assume that the stress response process Y(t) under the combined action of wave load (wave load is a low-frequency load) and host vibration load (host vibration load is a high-frequency load) (i.e., under the combined action of high and low frequency loads) is the sum of two independent Gaussian narrowband processes X1(t) (i.e., the Gaussian narrowband process of low-frequency wave load) and X2(t) (i.e., the Gaussian narrowband process of high-frequency host vibration load), as shown in the following equation:

[0042] Y(t)=X1(t)+X2(t) (1)

[0043] In the above formula, X1(t) is the Gaussian narrowband process of wave load, and X2(t) is the Gaussian narrowband process of host vibration load.

[0044] Therefore, the stress response process Y(t) under the combined action of wave load and host vibration load is also a Gaussian process. Furthermore, the spectral density function G of the stress response process Y(t) can be calculated based on the spectral density function G1(f) of the Gaussian narrowband process X1(t) of the wave load and the spectral density function G2(f) of the Gaussian narrowband process X2(t) of the host vibration load. Y (f), and the spectral density function G of Y(t) Y (f) can also be written as a sum of two components, as shown in the following equation:

[0045] G Y (f)=G1(f)+G2(f) (2)

[0046] In the above formula, G1(f) is the spectral density function of X1(t), and G2(f) is the spectral density function of X2(t).

[0047] Then, the spectral moments of each order of the stress response process are calculated based on the spectral density function of the stress response process. The spectral moments of each order of Y(t) can be calculated according to the following formula:

[0048]

[0049] In the above formula, n is the order and m is the spectral moment.

[0050] In addition, the spectral moments of the Gaussian narrowband process of the wave load can be calculated from the spectral density function G1(f) of the Gaussian narrowband process of the wave load, and the spectral moments of the Gaussian narrowband process of the host vibration load can be calculated from the spectral density function G2(f) of the Gaussian narrowband process of the host vibration load. The 0th order spectral moments of the Gaussian narrowband processes X1(t) of the wave load and X2(t) of the host vibration load are calculated according to the following formula:

[0051]

[0052] In the above formula, n is the order, m is the spectral moment, and v is the zero-crossing rate.

[0053] Meanwhile, the formula for calculating the spectral distance can be approximately expressed as:

[0054]

[0055] Finally, the zero-crossing rate of the stress response process under the combined action of wave load and host vibration load is calculated based on the spectral moments of each order of the stress response process, or the zero-crossing rate of the stress response process is calculated based on the spectral moments of each order of the Gaussian narrowband process of the wave load and the Gaussian narrowband process of the host vibration load, according to the following formula:

[0056]

[0057] III. Calculation Steps for Main Engine Vibration Fatigue Damage: First, set the vibration mode of the main engine vibration load to sinusoidal vibration to obtain the sinusoidal vibration load. Then, calculate the stress response and peak value of the ship structure under the sinusoidal vibration load based on the sinusoidal vibration load. Based on the stress response and combined with the fatigue life SN curve, calculate the number of stress cycles of the ship structure (i.e., the main engine base structure) during the ship's sailing life and the number of stress cycles of the main engine base structure when damage occurs (e.g., cracks appear). Finally, calculate the fatigue damage D under high-frequency main engine vibration load based on the ratio of the number of stress cycles of the main engine base structure during the ship's sailing life to the number of cycles when damage occurs. HF (Also known as high-frequency vibration damage D) HF ).

[0058] IV. Calculation Steps for Coupled Fatigue Damage: Calculate the peak stress response of the ship structure under the combined action of wave load and main engine vibration load based on the wave load and main engine vibration load. Calculate the peak stress probability density function under a short-term sea state based on the zero-order spectral moment of the stress response process, the peak stress response under sinusoidal vibration load, and the peak stress response under the combined action of wave load and main engine vibration load. Calculate the coupled fatigue damage under a short-term sea state based on the peak stress probability density function, the peak stress response under the combined action of wave load and main engine vibration load, the sailing time, the zero-crossing rate of the stress response process, and the wave direction in global sea state data. Calculate the total coupled fatigue damage under a long-term sea state based on the coupled fatigue damage under the short-term sea state. Calculate the fatigue damage of the ship structure under the combined action of wave load and main engine vibration load based on the total coupled fatigue damage and the fatigue damage under the main engine vibration load.

[0059] Specifically, the damage under the combined action of wave load and host vibration load (i.e., under the combined action of high and low frequency loads) is first calculated as two fatigue damage components. The fatigue damage caused by Y(t) comes from two separate contributions: one from the envelope of Y(t), which includes all the large stress cycles; and the other from the envelope of the high-frequency component X2(t), which includes all the smaller stress reversals. The envelope p(t) of Y(t) can be approximated as the sum of the CL envelopes R2(t) of the slow process X1(t) and the fast process X2(t).

[0060] In fatigue damage calculation based on spectral analysis, it is known that the peak stress response distribution under low-frequency wave loads follows a Rayleigh distribution, while the stress response process under high-frequency sinusoidal vibration loads is constant in amplitude, with a fixed peak stress response. Furthermore, the frequency of the high-frequency stress response is much higher than that of wave loads. Therefore, the envelope curve of the peak stress response after the coupling of these two loads can be considered as the original envelope curve plus the peak stress response under sinusoidal vibration loads. In other words, the peak stress of the stress alternation process under a short-term sea state follows a Rayleigh distribution, and the probability density function of the peak stress under the combined action of wave loads and main engine vibration loads can be calculated using the following formula:

[0061]

[0062] In the above formula, a is the peak value of the stress response under sinusoidal vibration load, S is the peak value of the stress response under the combined action of host vibration load and wave load, and m0 is the zero-order spectral moment of the stress response process under the combined action of host vibration load and wave load.

[0063] Therefore, based on the calculated peak stress probability density function under the combined action of wave load and main engine vibration load in a certain short-term sea state, the peak stress response under the combined action of wave load and main engine vibration load, the ship's sailing time in that short-term sea state, the zero-crossing rate of the stress response process in that short-term sea state, and the wave direction in global sea state data, and according to Miner's cumulative damage theory, the coupled fatigue damage D in a certain short-term sea state is calculated. ij Calculate according to the following formula:

[0064]

[0065] In the above formula, i represents a short-term sea state, j represents the wave direction under that short-term sea state, S represents the peak stress response under the combined action of main engine vibration load and wave load, and T ij This indicates the sailing time under that short sea state, f 0ij T represents the zero-crossing rate of the stress response process under the combined action of wave loads and main engine vibration loads in this short-term sea state. ij f 0ij The stress cycle number is represented by A and m, where A and m are the parameters of the SN curve.

[0066] After calculating the coupled fatigue damage under a certain short-term sea state, the total fatigue damage under the long-term sea state is the algebraic sum of the fatigue damage under all short-term sea states calculated according to their probability of occurrence under those short-term sea states. The calculation method is similar to the direct calculation of fatigue strength using spectral analysis. Therefore, the total coupled fatigue damage D of the entire main engine base structure under long-term time T is calculated. p (Also known as high- and low-frequency envelope damage D) p Calculate according to the following formula:

[0067]

[0068] In the above formula, i represents a short-term sea state, j represents the wave direction under that short-term sea state, and n S n represents the total number of sea states in the sea state distribution data. H This indicates the total number of headings.

[0069] Among them, high and low frequency envelope damage D p and high-frequency vibration damage D HF The calculation results are shown in Table 1.

[0070] Table 1

[0071] Hot Topics <![CDATA[High and low frequency envelope fatigue damage D P > <![CDATA[High-frequency main engine vibration damage D HF <!-- 7 -->]]> Hot Topic 1 0.005347 0.004347 Hot Topic 2 0.002764 0.004041 Hot Topic 3 0.002203 0.003841 Hot Topic 4 0.002189 0.003691

[0072] Then, based on the total coupled fatigue damage D p Fatigue damage D under host vibration load HFThe fatigue damage of the ship structure under the combined action of wave loads and main engine vibration loads (i.e., high and low frequency loads) is calculated. The fatigue damage D under the combined action of high and low frequency loads is calculated according to the following formula:

[0073] D = D P +D HF (10)

[0074] Finally, the fatigue damage under combined high and low frequency loads can be compared with the fatigue damage results calculated by the direct superposition method and the time-domain rainflow counting method, respectively, to verify that the fatigue damage effect under combined high and low frequency loads is better. The fatigue damage calculation results of different methods are shown in Table 2.

[0075] Table 2

[0076] Hot Topics The method of this invention calculates damage D Damage D calculated by direct superposition method Damage D calculated using time-domain rainflow counting method Hot Topic 1 0.011147 0.009694 0.012364 Hot Topic 2 0.007727 0.006805 0.008156 Hot Topic 3 0.006838 0.006044 0.007115 Hot Topic 4 0.006675 0.005880 0.006898

[0077] Since the calculation results using the time-domain rainflow counting method are closest to the actual results, this method is very cumbersome, time-consuming, and labor-intensive, making it unsuitable for engineering applications. However, its results can be used as a reference. Therefore, as can be seen from Table 2, compared with the direct superposition method, the calculation results of the method of the present invention are closer to the calculation results of the time-domain rainflow counting method, demonstrating the necessity and reliability of the calculation method of the present invention.

[0078] This invention also relates to a ship structure fatigue strength analysis system, which corresponds to the aforementioned ship structure fatigue strength analysis method and can be understood as a system for implementing the aforementioned method. The system includes a data acquisition and calculation module, a zero-crossing rate calculation module, a main engine vibration fatigue damage calculation module, and a coupled fatigue damage calculation module connected in sequence. Specifically,

[0079] The data acquisition and calculation module acquires ship data, ship structure characteristic data, and global sea state data. It calculates the main engine vibration load based on the main engine vibration frequency and amplitude in the characteristic data, and uses wave load calculation software to calculate the wave load on the ship structure. The ship data includes the ship's sailing life and sailing time.

[0080] The zero-crossing rate calculation module calculates the stress response process under the combined action of wave load and host vibration load based on the Gaussian narrowband process of wave load and host vibration load. Then, it calculates the spectral density function of stress response process based on the spectral density function of wave load and host vibration load, calculates the spectral moments of stress response process based on the spectral density function of stress response process, and calculates the zero-crossing rate of stress response process based on the spectral moments of stress response process.

[0081] The main engine vibration fatigue damage calculation module sets the vibration mode of the main engine vibration load to sinusoidal vibration to obtain sinusoidal vibration load. Based on the sinusoidal vibration load, it calculates the stress response of the ship structure under the sinusoidal vibration load and the peak value of the stress response under the sinusoidal vibration load. Based on the stress response and combined with the fatigue life SN curve, it calculates the number of stress cycles of the ship structure during the ship's sailing life and the number of stress cycles of the ship structure when the ship structure is damaged, and then calculates the fatigue damage under the main engine vibration load.

[0082] The coupled fatigue damage calculation module calculates the peak stress response of the ship structure under the combined action of wave load and main engine vibration load based on wave load and main engine vibration load. It then calculates the peak stress probability density function under a short-term sea state based on the zero-order spectral moment of the stress response process, the peak stress response under sinusoidal vibration load, and the peak stress response under the combined action of wave load and main engine vibration load. Based on the peak stress probability density function, the peak stress response under the combined action of wave load and main engine vibration load, the sailing time, the zero-crossing rate of the stress response process, and the wave direction in global sea state data, it calculates the coupled fatigue damage under a short-term sea state. Based on the coupled fatigue damage under the short-term sea state, it calculates the total coupled fatigue damage under the long-term sea state. Finally, based on the total coupled fatigue damage and the fatigue damage under the main engine vibration load, it calculates the fatigue damage of the ship structure under the combined action of wave load and main engine vibration load.

[0083] Preferably, the ship data also includes the ship's mobile service identification code, ship name, ship's latitude and longitude location information, navigation status, timestamp, ground speed, draft, port of departure, port of destination, and estimated arrival time; the global sea state data includes wave direction, global typhoon data, and global marine meteorological data.

[0084] Preferably, in the zero-crossing rate calculation module, the spectral moments of each order of the Gaussian narrowband process of the wave load are calculated based on the spectral density function of the Gaussian narrowband process of the wave load, and the spectral moments of each order of the Gaussian narrowband process of the host vibration load are calculated based on the spectral density function of the Gaussian narrowband process of the host vibration load. The zero-crossing rate of the stress response process is calculated based on the spectral moments of each order of the Gaussian narrowband process of the wave load and the spectral moments of each order of the Gaussian narrowband process of the host vibration load.

[0085] Preferably, the ship structure is a ship main engine base structure.

[0086] Preferably, the characteristic data of the ship structure include the main engine vibration frequency, amplitude, rotational speed, and power.

[0087] This invention provides an objective and scientific method and system for assessing ship fouling using multi-feature parameter algorithms. Based on ship data, characteristic data of the ship structure, and global sea state data, it calculates the main engine vibration load and the wave load on the ship structure. Based on the wave load and the main engine vibration load, and using a specific calculation method, it calculates the fatigue damage of the ship structure under the combined action of wave load and main engine vibration load. It fully considers the fatigue damage of the ship structure under the combined action of long-term distributed loads, and effectively improves the accuracy and reliability of fatigue strength calculation of the ship structure under the combined action of loads.

[0088] It should be noted that the specific embodiments described above enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. Therefore, although the present invention has been described in detail with reference to the accompanying drawings and embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. In short, all technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention patent.

Claims

1. A method for analyzing the fatigue strength of ship structures, characterized in that, Includes the following steps: Data acquisition and calculation steps: acquire ship data, ship structure characteristic data and global sea state data, calculate the main engine vibration load based on the main engine vibration frequency and amplitude in the characteristic data, and use wave load calculation software to calculate the wave load on the ship structure. The ship data includes the ship's sailing life and sailing time. Zero-crossing rate calculation steps: Based on the Gaussian narrowband process of wave load and the Gaussian narrowband process of host vibration load, calculate the stress response process under the combined action of wave load and host vibration load. Then, based on the spectral density function of the Gaussian narrowband process of wave load and the spectral density function of the Gaussian narrowband process of host vibration load, calculate the spectral density function of the stress response process. Based on the spectral density function of the stress response process, calculate the spectral moments of each order of the stress response process. Based on the spectral moments of each order of the stress response process, calculate the zero-crossing rate of the stress response process. The calculation steps for main engine vibration fatigue damage are as follows: The vibration mode of the main engine vibration load is set to sinusoidal vibration to obtain sinusoidal vibration load. Based on the sinusoidal vibration load, the stress response and peak value of the ship structure under the sinusoidal vibration load are calculated. Based on the stress response and combined with the fatigue life SN curve, the number of stress cycles of the ship structure during the ship's sailing life and the number of stress cycles of the ship structure when the ship structure is damaged are calculated respectively. Then, the fatigue damage under the main engine vibration load is calculated. The steps for calculating coupled fatigue damage are as follows: First, calculate the peak stress response of the ship structure under the combined action of wave load and main engine vibration load based on the wave load and main engine vibration load. Then, calculate the peak stress probability density function under a short-term sea state based on the zero-order spectral moment of the stress response process, the peak stress response under sinusoidal vibration load, and the peak stress response under the combined action of wave load and main engine vibration load. Next, calculate the coupled fatigue damage under a short-term sea state based on the peak stress probability density function, the peak stress response under the combined action of wave load and main engine vibration load, the sailing time, the zero-crossing rate of the stress response process, and the wave direction from global sea state data. Finally, calculate the total coupled fatigue damage under a long-term sea state based on the coupled fatigue damage under the short-term sea state. Finally, calculate the fatigue damage of the ship structure under the combined action of wave load and main engine vibration load based on the total coupled fatigue damage and the fatigue damage under the main engine vibration load.

2. The method for analyzing the fatigue strength of ship structures according to claim 1, characterized in that, In the data acquisition and calculation steps, the ship data also includes the ship mobile service identification code, ship name, ship latitude and longitude location information, navigation status, timestamp, speed over land, draft, port of departure, port of destination, and estimated arrival time; the global sea state data includes wave direction, global typhoon data, and global marine meteorological data.

3. The method for analyzing the fatigue strength of ship structures according to claim 1, characterized in that, In the zero-crossing rate calculation step, the spectral moments of each order of the Gaussian narrowband process of the wave load are calculated based on the spectral density function of the Gaussian narrowband process of the wave load, and the spectral moments of each order of the Gaussian narrowband process of the host vibration load are calculated based on the spectral density function of the Gaussian narrowband process of the host vibration load. The zero-crossing rate of the stress response process is then calculated based on the spectral moments of each order of the Gaussian narrowband process of the wave load and the spectral moments of each order of the Gaussian narrowband process of the host vibration load.

4. The method for analyzing the fatigue strength of ship structures according to claim 1, characterized in that, In the data acquisition and calculation steps, the ship structure is the ship's main engine base structure.

5. The method for analyzing the fatigue strength of ship structures according to claim 4, characterized in that, The characteristic data of the ship structure include the main engine vibration frequency, amplitude, rotational speed, and power.

6. A fatigue strength analysis system for ship structures, characterized in that, It includes a data acquisition and calculation module, a zero-crossing rate calculation module, a host vibration fatigue damage calculation module, and a coupled fatigue damage calculation module, which are connected in sequence. The data acquisition and calculation module acquires ship data, ship structure characteristic data, and global sea state data. It calculates the main engine vibration load based on the main engine vibration frequency and amplitude in the characteristic data, and uses wave load calculation software to calculate the wave load on the ship structure. The ship data includes the ship's sailing life and sailing time. The zero-crossing rate calculation module calculates the stress response process under the combined action of wave load and host vibration load based on the Gaussian narrowband process of wave load and host vibration load. Then, it calculates the spectral density function of stress response process based on the spectral density function of wave load and host vibration load, calculates the spectral moments of stress response process based on the spectral density function of stress response process, and calculates the zero-crossing rate of stress response process based on the spectral moments of stress response process. The main engine vibration fatigue damage calculation module sets the vibration mode of the main engine vibration load to sinusoidal vibration to obtain sinusoidal vibration load. Based on the sinusoidal vibration load, it calculates the stress response of the ship structure under the sinusoidal vibration load and the peak value of the stress response under the sinusoidal vibration load. Based on the stress response and combined with the fatigue life SN curve, it calculates the number of stress cycles of the ship structure during the ship's sailing life and the number of stress cycles of the ship structure when the ship structure is damaged, and then calculates the fatigue damage under the main engine vibration load. The coupled fatigue damage calculation module calculates the peak stress response of the ship structure under the combined action of wave load and main engine vibration load based on wave load and main engine vibration load. It then calculates the peak stress probability density function under a short-term sea state based on the zero-order spectral moment of the stress response process, the peak stress response under sinusoidal vibration load, and the peak stress response under the combined action of wave load and main engine vibration load. Based on the peak stress probability density function, the peak stress response under the combined action of wave load and main engine vibration load, the sailing time, the zero-crossing rate of the stress response process, and the wave direction in global sea state data, it calculates the coupled fatigue damage under a short-term sea state. Based on the coupled fatigue damage under the short-term sea state, it calculates the total coupled fatigue damage under the long-term sea state. Finally, based on the total coupled fatigue damage and the fatigue damage under the main engine vibration load, it calculates the fatigue damage of the ship structure under the combined action of wave load and main engine vibration load.

7. The ship structure fatigue strength analysis system according to claim 6, characterized in that, The ship data also includes the ship's mobile service identification code, ship name, ship's latitude and longitude location information, navigation status, timestamp, speed over land, draft, port of departure, port of destination, and estimated arrival time; the global sea state data includes wave direction, global typhoon data, and global marine meteorological data.

8. The ship structure fatigue strength analysis system according to claim 6, characterized in that, In the zero-crossing rate calculation module, the spectral moments of each order of the Gaussian narrowband process of the wave load are calculated based on the spectral density function of the Gaussian narrowband process of the wave load, and the spectral moments of each order of the Gaussian narrowband process of the host vibration load are calculated based on the spectral density function of the Gaussian narrowband process of the host vibration load. The zero-crossing rate of the stress response process is calculated based on the spectral moments of each order of the Gaussian narrowband process of the wave load and the spectral moments of each order of the Gaussian narrowband process of the host vibration load.

9. The ship structure fatigue strength analysis system according to claim 6, characterized in that, The ship structure is the ship's main engine base structure.

10. The ship structure fatigue strength analysis system according to claim 9, characterized in that, The characteristic data of the ship structure include the main engine vibration frequency, amplitude, rotational speed, and power.

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