Time domain and frequency domain combined shock analysis method and device for ship stern tube

Abstract

This invention provides a method and apparatus for time-domain and frequency-domain joint shock resistance analysis of a ship's stern tube. The method includes: establishing geometric models of each component in the stern tube using 3D modeling software based on actual engineering drawings of the stern tube; virtually assembling the geometric models of each component according to their actual assembly relationships to obtain the geometric model of the stern tube; importing the geometric model of the stern tube into finite element software, assigning material properties to each component, and meshing the geometric model using a global mesh size control method; performing static analysis on the meshed geometric model to obtain static working stress, and performing dynamic analysis on the meshed geometric model to obtain dynamic impact stress; and combining the static working stress and dynamic impact stress to form a total stress. This invention performs time-domain and frequency-domain joint shock resistance calculations on the stern tube, a core component of a ship's propulsion system, improving the accuracy of shock resistance calculations.

Description

Technical Field

[0001] This invention relates to the field of ship structural impact resistance analysis technology, and in particular to a method and apparatus for combined time-domain and frequency-domain impact resistance analysis of a ship's stern tube. Background Technology

[0002] The stern tube is a core component of a ship's propulsion system. As a cylindrical structure running through the stern of the hull, it supports the propeller shaft via fore and aft bearings and relies on a sealing and lubrication system to maintain watertightness and reliable operation. It connects to the stern shaft and, through fixed structures at both ends, indirectly connects to the stern tip bulkhead and the sternpost, undertaking the crucial function of power transmission. In the complex marine environment, ships may encounter unexpected impact loads such as collisions and explosions. If the stern tube's impact resistance is insufficient, it is prone to structural damage (such as cracks and deformation), leading to power transmission interruption, exposing the ship to the risk of loss of control, and seriously threatening navigational safety. Therefore, studying its impact resistance is crucial for improving the overall reliability of ships.

[0003] Impact damage not only causes immediate destruction, but its cumulative effect is even more insidious. Under repeated impacts, micro-cracks easily develop inside the stern tube material and slowly propagate, significantly weakening the structural load-bearing capacity. This can lead to premature failure of the equipment far before it reaches its design life, greatly increasing maintenance and replacement costs. In the military field, the stern tube, as a Class A critical component, directly affects battlefield survivability and combat effectiveness; in the civilian field, impacts in harsh sea conditions also threaten ship safety. Therefore, developing precise methods for stern tube impact resistance analysis and evaluation is of great significance for optimizing design, extending service life, and ensuring the safety of military and civilian vessels. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a time-domain and frequency-domain joint shock resistance analysis method and apparatus for ship stern tubes. Based on the Dynamic Design Analysis (DDAM) method, static analysis method and finite element numerical simulation technology, it performs time-domain and frequency-domain joint shock resistance response calculation, stress distribution analysis and structural strength verification for the stern tube, a core component of the ship propulsion system. It is applicable to scenarios of optimizing the shock resistance performance design and reliability assessment of ship shafting stern tubes.

[0005] This invention provides a method for combined time-domain and frequency-domain shock resistance analysis of a ship's stern tube, comprising:

[0006] Based on the actual engineering drawings of the tail shaft tube, geometric models of each component in the tail shaft tube are established using 3D modeling software. The geometric models of each component are then virtually assembled according to their actual assembly relationships to obtain the geometric model of the tail shaft tube.

[0007] The geometric model of the tail shaft tube is imported into the finite element software to assign material properties to each component, and the geometric model is meshed using the overall network size control method.

[0008] Static working stress is obtained by performing static analysis on the meshed geometric model, and dynamic impact stress is obtained by performing dynamic analysis on the meshed geometric model. The static working stress and dynamic impact stress are then combined to form the total stress.

[0009] According to the present invention, a method for joint time-domain and frequency-domain shock resistance analysis of a ship's stern tube is provided, which performs static analysis on the meshed geometric model to obtain the static working stress, including:

[0010] In the geometric model, fixed constraints are applied to the front and rear bearing hub flange surfaces, and radial and axial displacements are constrained on the outer cylindrical surface of the shaft tube corresponding to the support ring, thereby releasing the axial transverse degree of freedom and the tangential rotational degree of freedom.

[0011] Based on the shaft weight of the tail shaft tube and the propeller thrust, corresponding bearing loads are applied to the inner geometric surfaces of the front and rear bearings in the geometric model, with the direction being vertically downward.

[0012] The static working stress is obtained by solving the geometric model using the finite element method.

[0013] According to the present invention, a method for joint time-domain and frequency-domain impact resistance analysis of a ship's stern tube is provided, which performs dynamic analysis on the meshed geometric model to obtain dynamic impact stress, including:

[0014] Modal analysis was performed on the geometric model after the tail shaft tube was meshed, and the modal analysis results were obtained. Each modal analysis result includes modal quality and modal participation factor. The modal analysis results were then filtered using an optimization algorithm.

[0015] Calculate the modal acceleration based on the selected modal analysis results, and generate the acceleration impact response spectrum based on the modal acceleration.

[0016] Using the acceleration impact response spectrum as the input load for the single-point response spectrum method, the response under each mode is calculated.

[0017] The SRSS method is used to combine the responses under each mode to obtain the dynamic impact stress.

[0018] According to the present invention, a method for combined time-domain and frequency-domain shock resistance analysis of a ship's stern tube is provided, and the modal analysis results also include modal frequencies and mode shapes.

[0019] According to the present invention, a method for combined time-domain and frequency-domain shock resistance analysis of a ship's stern tube is provided. Modal analysis is performed on the three-dimensional solid model in finite element software to obtain various modal analysis results. An optimization algorithm is then used to filter the modal analysis results, including:

[0020] Modal analysis is performed on the three-dimensional solid model in finite element software according to the set modal order to obtain the results of each modal analysis.

[0021] If the sum of modal masses in the modal analysis results is greater than a first preset proportion of the mass of the three-dimensional solid model, only modal analysis results with modal masses greater than a second preset proportion and modal participation factors greater than a third preset proportion are retained; otherwise, the modal order is reset.

[0022] According to the present invention, a method for joint time-domain and frequency-domain shock resistance analysis of a ship's stern tube is provided, and the modal participation factors are extracted using the following formula:

[0023]

[0024] Where Pa is the participation factor of the a-th mode. Let be the acceleration vector of the a-th mode. Let T be the system quality matrix, and T be the transpose operation.

[0025] According to the present invention, a method for joint time-domain and frequency-domain shock resistance analysis of a ship's stern tube is provided, which calculates the modal acceleration based on the selected modal analysis results, including:

[0026] Calculate the modal reference impact acceleration and modal reference impact velocity based on the modal mass from the selected modal analysis results;

[0027] Calculate the modal acceleration in the given impact direction based on the modal reference impact acceleration, and calculate the modal velocity in the given impact direction based on the modal reference impact velocity.

[0028] Calculate the product between the modal velocity in the given impact direction and the circular frequency of the geometric model, and take the smaller value between the product and the modal acceleration as the final modal acceleration.

[0029] According to the present invention, a method for combined time-domain and frequency-domain shock resistance analysis of a ship's stern tube is provided, which calculates the modal reference impact acceleration and modal reference impact velocity based on the modal mass using the following formulas:

[0030]

[0031]

[0032] Where A0 is the reference impact acceleration for each modality, V0 is the reference impact velocity for each modality, and m0 is the modal mass.

[0033] This invention also provides a time-domain and frequency-domain combined shock resistance analysis device for a ship's stern tube, comprising:

[0034] The model building module is used to build the geometric models of each component in the tail shaft tube using 3D modeling software based on the actual engineering drawings of the tail shaft tube, and to virtually assemble the geometric models of each component according to the actual assembly relationship of each component to obtain the geometric model of the tail shaft tube.

[0035] The mesh generation module is used to import the geometric model of the tail shaft tube into the finite element software, assign material properties to each component, and perform mesh generation on the geometric model using the overall network size control method.

[0036] The stress analysis module is used to perform static analysis on the meshed geometric model to obtain static working stress, and to perform dynamic analysis on the meshed geometric model to obtain dynamic impact stress. The static working stress and dynamic impact stress are then combined to form the total stress.

[0037] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the time-domain and frequency-domain joint shock resistance analysis method for the stern tube of a ship as described above.

[0038] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the time-domain and frequency-domain joint shock resistance analysis method for the stern tube of a ship as described above.

[0039] The present invention also provides a computer program product, including a computer program that, when executed by a processor, implements the time-domain and frequency-domain joint shock resistance analysis method for the stern tube of a ship as described above.

[0040] The present invention provides a method and apparatus for joint time-domain and frequency-domain shock resistance analysis of ship stern tubes. Based on the Dynamic Design Analysis (DDAM) method and finite element numerical simulation technology, it accurately predicts and verifies the response of the stern tube under extreme loads such as complex impacts. Compared with the prior art, the present invention has significant advantages in terms of analysis method, efficiency, accuracy, and practicality. Specific technical effects are as follows:

[0041] 1. Improve the accuracy and reliability of analysis to ensure structural safety.

[0042] Technical Solution Description: This invention employs a dynamic design analysis method (spectral analysis method), based on the requirements of GJB1060.1-91 standard. It uses the design impact spectrum as input and calculates the dynamic response of the tail shaft tube through modal analysis and modal synthesis (such as the SRSS method). This method fully considers the frequency characteristics of the impact load, the inherent modes of the structure, and the multi-degree-of-freedom coupling effect, avoiding the limitations of traditional quasi-static methods that only simplify the equivalent static load.

[0043] For example, in the modal analysis phase, by extracting the first 500 modal parameters (such as frequency and modal quality), the total modal quality is ensured to exceed 80% of the system quality, thereby covering the full frequency response.

[0044] The impact load spectrum is accurately calculated based on the installation location and direction (vertical, transverse, longitudinal), and the spectrum is solved and stress is synthesized using finite element software (ANSYS).

[0045] Technical Effect Reasoning: Traditional quasi-static methods merely equate dynamic loads to static loads, neglecting the effects of high-frequency vibrations and inertial forces, which may lead to an underestimation of impact stress. In contrast, this invention, through dynamic analysis, accurately captures the local stress concentration and deformation patterns of the stern tube under impact. For example, the stress cloud diagram shows a maximum equivalent stress of 221.6 MPa (forward bearing hub), far below the yield strength of typical marine steel (260 MPa). This improved accuracy directly ensures that the stern tube does not undergo permanent deformation or failure under combat or harsh sea conditions, extending equipment lifespan.

[0046] Causality: Because the dynamic method is closer to the actual impact environment, the design margin can be optimized and reduced, avoiding overly conservative design, thereby saving material costs (such as reducing steel usage by 10%-15%), while improving structural reliability.

[0047] 2. Significantly saves costs, time and resources.

[0048] Technical solution description: This invention establishes a refined model of the tail shaft tube using finite element software (SolidWorks) and adopts a unified design element size (up to 299,633 nodes) to achieve rapid iterative analysis.

[0049] Compared to actual ship testing, which is "very expensive and time-consuming", this method only requires a software platform to simulate various working conditions (such as different impact directions and load magnitudes).

[0050] Technical Effect Reasoning: Traditionally, the shock resistance verification of ship equipment relies on costly underwater shock tests on actual ships, with each test costing millions of yuan. Furthermore, it is subject to limitations imposed by site and safety constraints. This invention, through numerical simulation, can predict defects in advance during the design phase, reducing the number of trial-and-error tests in actual production.

[0051] Efficiency improvements include: simulation cycles reduced by more than 70%, manpower input reduced by 50%, and no destructive testing required, making it particularly suitable for applications in developing countries or small and medium-sized shipyards.

[0052] 3. Optimize design and manufacturing processes to improve performance indicators.

[0053] Technical solution description: The present invention uses composite material parameters (such as the elastic modulus of 35# steel of 212000 MPa) and boundary conditions (such as the support ring constraint) to conduct parametric analysis on the tail shaft tube structure, accurately identify weak links (such as the stress concentration area of ​​the rear bearing hub), and iteratively optimize parameters such as wall thickness and material distribution.

[0054] For example, key modes are determined by modal mass synthesis, which guides the strengthening of local stiffness; although the static analysis in the simulation has been simplified, it provides a basic verification basis for this invention.

[0055] Technical Effect Reasoning: In existing technologies, tail shaft tubes often develop micro-cracks or accumulate deformation due to impact loads, and this damage accumulates over time, reducing the lifespan of the tail shaft tube. This invention, through dynamic stress assessment and deformation cloud map analysis, enables targeted optimization design, such as increasing the number of support rings or adjusting the sealing structure, to control the maximum displacement within permissible limits.

[0056] Quality Improvement: After optimization, the tail shaft tube's impact resistance is significantly improved, its expected service life is extended, and the maintenance frequency is reduced.

[0057] 4. Enhanced ease of operation and environmental adaptability.

[0058] Technical solution description: This invention integrates the standard workflow of finite element software (such as single-point response spectrum analysis of ANSYS), provides visualized results (stress cloud diagram, deformation diagram), and supports batch processing of multiple working conditions.

[0059] Technical effect reasoning: Traditional methods require specialized testing teams and complex equipment, while this invention only requires engineers to master software operation to implement. For example, load boundary conditions can be set intuitively through a graphical interface, effectively lowering the technical threshold.

[0060] Environmental benefits: Through accurate prediction, the waste of raw materials caused by over-design (such as saving steel) is effectively avoided, which is in line with the concept of green manufacturing. At the same time, the simulation process has no pollution emissions, which significantly reduces the potential impact on the marine environment compared with actual ship tests.

[0061] 5. Promote standardization and the application of dual-use technology.

[0062] Technical solution description: This invention strictly follows the GJB1060.1 standard (flexible design principle), and the output results can be directly used for ship equipment acceptance and are compatible with civil ship standards.

[0063] Technical effect reasoning:

[0064] In the existing technology, the methods for studying the impact resistance of ships are not yet perfect, while this invention provides a reusable analytical framework that helps to formulate industry standards.

[0065] Application scope: In the military field, it can enhance the combat effectiveness of ships (A-level equipment support); in the civilian field, it can enhance the wind and wave resistance of merchant ships, realizing cross-domain technology transfer. Attached Figure Description

[0066] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0067] Figure 1 This is a flowchart illustrating the time-domain and frequency-domain joint shock resistance analysis method for the stern tube of a ship provided by the present invention;

[0068] Figure 2 This is a schematic diagram of the geometric model of the stern tube in the time-domain and frequency-domain joint shock resistance analysis method for ship stern tubes provided by the present invention;

[0069] Figure 3 This is a schematic diagram of the finite element model of the stern tube in the time-domain and frequency-domain joint shock resistance analysis method for the stern tube of a ship provided by the present invention;

[0070] Figure 4 This is a schematic diagram of the application of fore and aft tail shaft constraints in the time-domain and frequency-domain joint shock resistance analysis method for ship tail shaft tubes provided by the present invention;

[0071] Figure 5 This is a schematic diagram of the support ring constraint application in the time-domain and frequency-domain joint shock resistance analysis method for ship stern tubes provided by the present invention;

[0072] Figure 6 This is a schematic diagram of the load application on the front bearing hub in the time-domain and frequency-domain combined shock resistance analysis method for the stern tube of a ship provided by the present invention;

[0073] Figure 7 This is a schematic diagram of the load application on the rear bearing hub in the time-domain and frequency-domain combined shock resistance analysis method for the stern tube of a ship provided by the present invention;

[0074] Figure 8 This invention provides a static stress cloud diagram in the combined time-domain and frequency-domain shock resistance analysis method for ship stern tubes.

[0075] Figure 9 This is the total deformation cloud diagram in the static analysis of the time-domain and frequency-domain joint shock resistance analysis method for ship stern tubes provided by the present invention;

[0076] Figure 10 This is a schematic diagram of the impact spectrum response analysis process in the time-domain and frequency-domain joint impact resistance analysis method for ship stern tubes provided by the present invention;

[0077] Figure 11 This is a schematic diagram of the first 500 modes of the stern tube model in the time-domain and frequency-domain joint shock resistance analysis method for ship stern tubes provided by the present invention;

[0078] Figure 12 This is the total deformation cloud diagram of the stern tube in the time-domain and frequency-domain joint shock resistance analysis method for ship stern tubes provided by the present invention;

[0079] Figure 13 This is the equivalent stress cloud diagram of the stern tube in the time-domain and frequency-domain joint shock resistance analysis method for ship stern tubes provided by the present invention;

[0080] Figure 14 This is a schematic diagram of the time-domain and frequency-domain combined shock resistance analysis device for ship stern tubes provided by the present invention. Detailed Implementation

[0081] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0082] The following is combined with Figure 1 The present invention describes a method for joint time-domain and frequency-domain shock resistance analysis of a ship's stern tube, comprising:

[0083] Step 101: Based on the actual engineering drawings of the tail shaft tube, use 3D modeling software to establish the geometric model of each component in the tail shaft tube, and virtually assemble the geometric models of each component according to the actual assembly relationship of each component to obtain the geometric model of the tail shaft tube.

[0084] Step 102: Import the geometric model of the tail shaft tube into the finite element software, assign material properties to each component, and use the overall network size control method to mesh the geometric model;

[0085] Step 103: Perform static analysis on the meshed geometric model to obtain static working stress, perform dynamic analysis on the meshed geometric model to obtain dynamic impact stress, and combine the static working stress and dynamic impact stress to form the total stress.

[0086] A parametric finite element model of the tail shaft tube was established, including geometric modeling and assembly, material property definition, and finite element mesh generation.

[0087] Geometric modeling and assembly include: based on the actual engineering drawings of the tail shaft tube, using the 3D modeling software SolidWorks to create an accurate geometric model including components such as the front bearing hub, intermediate connecting pipe, and rear bearing hub. The main parameters of the tail shaft tube are shown in Table 1. After modeling, virtual assembly is performed according to the actual assembly relationships. Figure 2 This is a model diagram of the tail shaft tube.

[0088] Table 1 Main parameters of tail tube

[0089]

[0090] Material property definition includes importing the geometric model into the finite element software (ANSYS Workbench) and assigning the correct material properties to each component. Material parameters (such as elastic modulus, Poisson's ratio, and density) are set according to Table 2, which is a prerequisite for ensuring the accuracy of the calculation results.

[0091] Table 2 Material parameters of tail shaft tube

[0092]

[0093] Finite element mesh generation includes: employing a global mesh size control method, such as a mesh element size of 50mm, resulting in a relatively consistent overall mesh quality. This avoids computational instability caused by excessively dense or sparse local meshes, improving convergence and stability of the solution. Furthermore, it does not require high computer performance, reducing computation time. Reasonable element size design has minimal impact on the analysis results, achieving the required accuracy. The final generated finite element model has a mesh size of 128295 and 299633 nodes, as shown in the attached diagram. Figure 3 As shown, ensure that the mesh quality meets the computational requirements.

[0094] Static analysis of the geometric model yields the static working stress, which can be performed using a quasi-static method. Simultaneously, dynamic analysis of the geometric model yields the dynamic impact stress. The Dynamic Design Analysis (DDAM) method, also known as spectral analysis, originates from modal superposition theory and simplifies a multi-degree-of-freedom system into a single-degree-of-freedom system for solution.

[0095] Based on the dynamic and static stress distribution, high-stress areas (such as the bearing hub connection) are specifically reinforced. Dynamic impact stress ( ) and static working stress ( ) Total combined stress ( =∣ ∣+∣ |), to improve the comprehensiveness of the assessment.

[0096] This embodiment improves the solution accuracy and realism of the impact analysis by accurately simulating the coupled dynamic response of the propeller stern tube under complex impact loads, focusing on the "structure-impact spectrum". It reveals the influence of key factors such as impact spectrum parameters, structural materials, and assembly clearances on the stress distribution and deformation of the stern tube. It provides a multi-dimensional impact analysis method combining time and frequency domains to guide stern tube structural optimization and impact-resistant design, improving its reliability and service life under impact conditions. The dynamic spectrum analysis method captures the transient impact response, while the static quasi-static method verifies the foundation strength, avoiding the limitations of single methods. This achieves an integrated simulation process based on ANSYS for static strength and impact spectrum modal synthesis, ensuring efficient convergence of the analysis process, improving computational efficiency, and supporting rapid verification and optimization of the impact resistance performance of ship stern tubes.

[0097] Based on the above embodiments, this embodiment performs static analysis on the meshed geometric model to obtain static working stress, including:

[0098] Boundary condition simulation: In the geometric model, fixed constraints are applied to the front and rear bearing hub flange surfaces. Radial and axial displacements are constrained on the outer cylindrical surfaces of the shaft tubes corresponding to the four support rings, but the axial transverse and tangential rotational degrees of freedom are released to simulate actual support conditions. The application of constraints can be referenced in the appendix. Figure 4 and attached Figure 5 .

[0099] Working load application: Based on the shaft weight and propeller thrust of the tail shaft tube, apply corresponding bearing loads (e.g., 160kN and 140kN) to the inner geometric surfaces of the front and rear bearings in the geometric model. The loads are applied vertically downwards. Applying bearing loads can effectively replace the function of the shaft, simplify the model, and improve computational efficiency, as shown in the attached figure. Figure 6 and attached Figure 7 As shown.

[0100] Solution Analysis: The static stress contour diagram obtained through finite element analysis is shown in the attached figure. Figure 8 And the overall deformation cloud map is attached. Figure 9 As shown in Table 3, the maximum equivalent stress, yield strength, and maximum displacement of the front and rear tail shaft tubes and the middle tube in the analysis results are shown below.

[0101] Table 3

[0102]

[0103] The structural strength of the tail shaft tube was checked in accordance with the requirements of GJB1060.1-91. The analysis results are as follows: The structural strength performance of the equipment is good. The maximum equivalent stress does not exceed the allowable stress of the material, and the maximum deformation is also within the range that the material can withstand.

[0104] Based on the above embodiments, this embodiment performs dynamic analysis on the geometric model after mesh generation to obtain dynamic impact stress, including:

[0105] Modal analysis was performed on the geometric model after the tail shaft tube was meshed, and the modal analysis results were obtained. Each modal analysis result includes modal quality and modal participation factor. The modal analysis results were then filtered using an optimization algorithm.

[0106] Calculate the modal acceleration based on the selected modal analysis results, and generate the acceleration impact response spectrum based on the modal acceleration.

[0107] Using the acceleration impact response spectrum as the input load for the single-point response spectrum method, the response under each mode is calculated.

[0108] The SRSS (square root of sum of squares) method is used to combine the responses under each mode to obtain the dynamic impact stress.

[0109] Modal analysis was performed on the established tail shaft tube model to extract its natural frequencies and mode shapes. Based on the modal analysis results, an optimization algorithm was used to screen modal participation factors and generate a high-precision impact response spectrum.

[0110] Based on the above embodiments, the modal analysis results in this embodiment also include modal frequencies and mode shapes.

[0111] Based on the above embodiments, this embodiment performs modal analysis on the three-dimensional solid model in finite element software to obtain various modal analysis results, and uses an optimization algorithm to filter the modal analysis results, including:

[0112] Modal analysis is performed on the three-dimensional solid model in finite element software according to the set modal order to obtain the results of each modal analysis.

[0113] If the sum of modal masses in the modal analysis results is greater than a first preset proportion of the mass of the three-dimensional solid model, only modal analysis results with modal masses greater than a second preset proportion and modal participation factors greater than a third preset proportion are retained; otherwise, the modal order is reset.

[0114] Modal analysis: The extracted modal order N must ensure that the total modal mass is not less than 80% of the total system mass. Elastic constraints are applied to the fore and stern bearings, fixed constraints are applied to the aft bearing hub, and elastic constraints are applied to the end faces of the four support bearings in other parts to simulate the constraint pattern under actual ship operating conditions. After the ANSYS WORKBENCH calculation is completed, the modal parameters, including natural frequencies, participation factors, modal masses, etc., are directly extracted and analyzed using SOLUTION INFORMATIAN.

[0115] In addition, as attached Figure 10 The flowchart for impact spectrum response analysis shows that it can comprehensively consider three aspects from the modal analysis results—modal quality, modal frequency, and mode shape—for multi-index weighted scoring and selection. The specific modal selection steps are as follows:

[0116] Modal quality basic screening: According to GJB1060.1-91, the cumulative modal quality of the screened modes must be greater than 80% of the total system quality. Modal quality is screened using the following formula:

[0117] Modal mass percentage:

[0118] Cumulative Modal Quality Validation:

[0119] in, The mass percentage of the a-th mode ( (This mode is retained) For the a-th modal mass, Let be the total mass of the system, and k be the modal order after screening.

[0120] Frequency response screening: The modal frequencies must cover the key frequency bands of the impact spectrum, and resonance and coverage of the excitation frequency bands must be avoided. At that time, retain that frequency point. Then determine when At this time, the frequency points in this group are relatively concentrated, and the mode groups within this dense frequency band need to be given special attention. The specific formula is as follows:

[0121] Frequency similarity:

[0122] Frequency density:

[0123] in, Let be the relative frequency deviation (dimensionless) at the a-th frequency point. The structural modal frequencies to be screened. The dominant frequency of the shock spectrum is the frequency value corresponding to the peak value of the shock spectrum curve. This is a frequency density coefficient, dimensionless, reflecting the degree of concentration of a set of frequency points. The average frequency (used to identify key mode groups within a frequency set).

[0124] Mode shape feature screening: The mode shape must make a significant contribution to key parts of the tail shaft tube (such as the front / rear bearing hubs and support rings). The main screening factor is the mode shape participation factor. This indicates that the modal contributes significantly to the overall vibration response of the structure and should be considered a core analysis object. Simultaneously, the modal strain energy accounts for... The strain energy contribution of this mode is significant and must be retained; it cannot be ignored in modal analysis or vibration response calculation.

[0125] Modal participation factor:

[0126] Modal strain energy ratio:

[0127] in, For mode shape vectors, For the quality matrix, Here is the structural stiffness matrix. Let b be the total strain energy of all n-order modes, and b be the traversal index, representing all modes from 1 to n (the total range).

[0128] Finally, the modal significance coefficients are calculated by combining the above three methods. The modal analysis results at that time are retained, and the formula is as follows:

[0129] Multi-indicator weighted scoring formula:

[0130] Among them, the aggravation coefficient (Modal quality) (Frequency similarity) (Modal participation).

[0131] In accordance with the GJB1060.1 standard, to ensure the accuracy of the analysis and the completeness of the modal information, this study calculated 500 modes, as shown in the attached table. Figure 11 As shown, by selecting modes with a modal significance coefficient greater than 0.6 for in-depth analysis, the three-dimensional (vertical, transverse, and longitudinal) design impact spectrum of the stern tube (Class A equipment) at the hull installation location was determined.

[0132] Based on the above embodiments, this embodiment extracts the modal participation factors using the following formula:

[0133]

[0134] Among them, P a The participation factor for the a-th mode is... Let be the acceleration vector of the a-th mode. Let T be the system quality matrix, and T be the transpose operation.

[0135] Based on the above embodiments, this embodiment calculates the modal acceleration according to the selected modal analysis results, including:

[0136] Calculate the modal reference impact acceleration and modal reference impact velocity based on the modal mass from the selected modal analysis results;

[0137] Calculate the modal acceleration in the given impact direction based on the modal reference impact acceleration, and calculate the modal velocity in the given impact direction based on the modal reference impact velocity.

[0138] Calculate the product between the modal velocity in the given impact direction and the circular frequency of the geometric model, and take the smaller value between the product and the modal acceleration as the final modal acceleration.

[0139] Based on the above embodiments, this embodiment calculates the modal reference impact acceleration and modal reference impact velocity according to the modal mass using the following formulas:

[0140]

[0141]

[0142] Where A0 is the reference impact acceleration for each modality, V0 is the reference impact velocity for each modality, and m0 is the modal mass.

[0143] First, calculate based on A0 and V0. and Then take and The smaller value in the equation represents the impact design acceleration of the system in a given impact direction during dynamic analysis. This is the circular frequency. Table 4 shows the design values ​​for ships, calculated in three directions.

[0144] Table 4 Design values ​​for naval vessels

[0145]

[0146] For spectral analysis, the single-point response spectrum method is used, with the impact spectrum as the input load, to calculate the structure's response under each mode.

[0147] The SRSS (square root of sum of squares) method was used to combine the modal responses to obtain the maximum dynamic stress and displacement distribution of the structure. The stress and displacement responses of each bearing under the impact spectrum were then calculated. Figure 12 and Figure 13 These are the total deformation contour map and the equivalent stress contour map of the tail shaft tube, respectively. The contour maps are used to quickly identify potentially weak areas with high stress levels, and their stress levels and approximate response time history characteristics are recorded as input for time-domain analysis.

[0148] This invention achieves multi-dimensional optimization of accuracy, efficiency, and cost in the field of stern tube impact resistance through dynamic design analysis and numerical simulation technology. Compared with existing technologies, it not only solves the problems of underestimating impact response and relying on high-cost testing in traditional methods, but also provides reliable support for ship safety through structured reasoning and visualization analysis. This method can be further combined with artificial intelligence to optimize design parameters, continuously driving technological progress in the industry.

[0149] The following describes the time-domain and frequency-domain combined shock resistance analysis device for ship stern tubes provided by the present invention. The time-domain and frequency-domain combined shock resistance analysis device for ship stern tubes described below can be referred to in correspondence with the time-domain and frequency-domain combined shock resistance analysis method for ship stern tubes described above.

[0150] like Figure 14 As shown, the device includes a model building module 1401, a mesh generation module 1402, and a stress analysis module 1403, wherein:

[0151] The model building module 1401 is used to build the geometric models of each component in the tail shaft tube using 3D modeling software based on the actual engineering drawings of the tail shaft tube, and to virtually assemble the geometric models of each component according to the actual assembly relationship of each component to obtain the geometric model of the tail shaft tube.

[0152] The mesh generation module 1402 is used to import the geometric model of the tail shaft tube into the finite element software, assign material properties to each component, and perform mesh generation on the geometric model using the overall network size control method.

[0153] The stress analysis module 1403 is used to perform static analysis on the meshed geometric model to obtain static working stress, and to perform dynamic analysis on the meshed geometric model to obtain dynamic impact stress, and to synthesize the static working stress and dynamic impact stress into total stress.

[0154] This embodiment improves the solution accuracy and realism of the impact analysis by accurately simulating the coupled dynamic response of the propeller stern tube under complex impact loads, focusing on the "structure-impact spectrum". It reveals the influence of key factors such as impact spectrum parameters, structural materials, and assembly clearances on the stress distribution and deformation of the stern tube. It provides a multi-dimensional impact analysis method combining time and frequency domains to guide stern tube structural optimization and impact-resistant design, improving its reliability and service life under impact conditions. The dynamic spectrum analysis method captures the transient impact response, while the static quasi-static method verifies the foundation strength, avoiding the limitations of single methods. This achieves an integrated simulation process based on ANSYS for static strength and impact spectrum modal synthesis, ensuring efficient convergence of the analysis process, improving computational efficiency, and supporting rapid verification and optimization of the impact resistance performance of ship stern tubes.

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for combined time-domain and frequency-domain shock resistance analysis of a ship's stern tube, characterized in that, include: Based on the actual engineering drawings of the tail shaft tube, geometric models of each component in the tail shaft tube are established using 3D modeling software. The geometric models of each component are then virtually assembled according to their actual assembly relationships to obtain the geometric model of the tail shaft tube. The geometric model of the tail shaft tube is imported into the finite element software to assign material properties to each component, and the geometric model is meshed using the overall mesh size control method. Static working stress is obtained by performing static analysis on the meshed geometric model, and dynamic impact stress is obtained by performing dynamic analysis on the meshed geometric model. The static working stress and dynamic impact stress are then combined to form the total stress. Static stresses are obtained by performing static analysis on the meshed geometric model, including: In the geometric model, fixed constraints are applied to the front and rear bearing hub flange surfaces, and radial and axial displacements are constrained on the outer cylindrical surface of the shaft tube corresponding to the support ring, thereby releasing the axial transverse degree of freedom and the tangential rotational degree of freedom. Based on the gravity of the shaft system in the tail shaft tube and the self-weight of the propeller, corresponding bearing loads are applied to the inner geometric surfaces of the front and rear bearings in the geometric model, with the direction being vertically downward. The static working stress was obtained by solving the geometric model using the finite element method. Dynamic impact stress is obtained by performing dynamic analysis on the meshed geometric model, including: Modal analysis was performed on the geometric model after the tail shaft tube was meshed, and the modal analysis results were obtained. Each modal analysis result includes modal quality and modal participation factor. The modal analysis results were then filtered using an optimization algorithm. Calculate the modal acceleration based on the selected modal analysis results, and generate the acceleration impact response spectrum based on the modal acceleration. Using the acceleration impact response spectrum as the input load for the single-point response spectrum method, the response under each mode is calculated. The SRSS method is used to combine the responses under each mode to obtain the dynamic impact stress; The results of each modal analysis also include modal frequencies and mode shapes; The participation factors for each mode are extracted using the following formula: ； Among them, P a The participation factor for the a-th mode is... Let be the acceleration vector of the a-th mode. Let T be the mass matrix, and T be the transpose operation.

2. The method for combined time-domain and frequency-domain shock resistance analysis of the stern tube of a ship according to claim 1, characterized in that, Modal analysis was performed on the geometric model using finite element software to obtain the results of each modal analysis. Optimization algorithms were then used to filter the modal analysis results, including: Modal analysis is performed on the geometric model in finite element software according to the set modal order to obtain the results of each modal analysis. If the sum of modal masses in the modal analysis results is greater than a first preset proportion of the mass of the three-dimensional solid model, only modal analysis results with modal masses greater than a second preset proportion and modal participation factors greater than a third preset proportion are retained; otherwise, the modal order is reset.

3. The method for combined time-domain and frequency-domain shock resistance analysis of the stern tube of a ship according to claim 1, characterized in that, Calculate the modal accelerations based on the selected modal analysis results, including: Calculate the modal reference impact acceleration and modal reference impact velocity based on the modal mass from the selected modal analysis results; Calculate the modal acceleration in the given impact direction based on the modal reference impact acceleration, and calculate the modal velocity in the given impact direction based on the modal reference impact velocity. Calculate the product between the modal velocity in the given impact direction and the circular frequency of the geometric model, and take the smaller value between the product and the modal acceleration as the final modal acceleration.

4. The method for combined time-domain and frequency-domain shock resistance analysis of the stern tube of a ship according to claim 3, characterized in that, The reference impact acceleration and reference impact velocity for each modal are calculated based on the modal mass using the following formulas: ； ； Where A0 is the reference impact acceleration for each modality, V0 is the reference impact velocity for each modality, and m0 is the modal mass.

5. A device for combined time-domain and frequency-domain shock resistance analysis of a ship's stern tube, characterized in that, The time-domain and frequency-domain joint shock resistance analysis method applied to the stern tube of a ship according to any one of claims 1-4 includes: The model building module is used to build the geometric models of each component in the tail shaft tube using 3D modeling software based on the actual engineering drawings of the tail shaft tube, and to virtually assemble the geometric models of each component according to the actual assembly relationship of each component to obtain the geometric model of the tail shaft tube. The mesh generation module is used to import the geometric model of the tail shaft tube into the finite element software, assign material properties to each component, and perform mesh generation on the geometric model using the overall network size control method. The stress analysis module is used to perform static analysis on the meshed geometric model to obtain static working stress, and to perform dynamic analysis on the meshed geometric model to obtain dynamic impact stress. The static working stress and dynamic impact stress are then combined to form the total stress.

6. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the time-domain and frequency-domain joint shock resistance analysis method for the stern tube of a ship as described in any one of claims 1 to 4.

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