Interface wave target scattering calculation method and system based on finite element

Abstract

The invention provides a finite element-based interface wave target scattering calculation method and system, and the method comprises the steps: S1, selecting a calculation model dimension, and defining model parameters; s2, establishing a geometric model according to the model parameters, dividing the geometric model into a calculation area and an absorption area, setting a fluid area and a solid area in the calculation area according to a calculation scene, and setting the absorption area outside the calculation area to simulate an infinite boundary; s3, setting a sound field model according to a pressure acoustic module and a solid mechanics module in the finite element calculation software; s4, carrying out grid division on the calculation area and the absorption area respectively; s5, carrying out model calculation, and determining a time calculation range according to the longitudinal wave propagation velocity, the transverse wave propagation velocity and the interface wave propagation velocity; and S6, analyzing the incident and scattered sound fields of the interface waves according to the calculation result. The method can accurately calculate the interface wave scattering sound field, and is suitable for calculation of simple and complex geometrical targets.

Description

Technical Field

[0001] The present invention relates to the technical field of interface wave target scattering calculation, and specifically, to a method for calculating interface wave target scattering based on finite element. Background Art

[0002] The acoustic scattering characteristics and laws of targets are of great significance for target detection and recognition. Currently, most of the existing methods for calculating target acoustic scattering are for the case of longitudinal wave incidence, lacking a calculation and analysis method for the scattered sound field under the condition of interface wave incidence. Different from longitudinal wave incidence, due to the presence of solid media, the calculation of the scattered sound field of liquid-solid interface waves needs to consider the problems of liquid-solid two-phase media and acoustic-solid coupling, and the model is complex. At the same time, the excitation of interface waves inevitably generates other modes of sound waves, such as longitudinal waves, transverse waves, interface waves, etc. It is difficult to absorb all incident sound waves through a simple perfectly matched layer or low-reflection boundary. Therefore, it is necessary to develop a calculation method for the target scattered sound field suitable for interface waves to study the scattering laws and mechanisms of interface waves. Summary of the Invention

[0003] Aiming at the defects in the prior art, the present invention provides a method and system for calculating interface wave target scattering based on finite element.

[0004] According to a method and system for calculating interface wave target scattering based on finite element provided by the present invention, the solution is as follows:

[0005] In a first aspect, a method for calculating interface wave target scattering based on finite element is provided, and the method includes:

[0006] Step S1: Select the dimension of the calculation model and define the model parameters;

[0007] Step S2: Establish a geometric model according to the model parameters, divide the geometric model into a calculation region and an absorption region, simulate the sound field in the calculation region, and set an absorption region outside the calculation region to absorb sound waves including incident longitudinal waves, transverse waves, and interface waves propagating in the sound field, simulating an infinite region;

[0008] Step S3: Set the sound field model according to the pressure acoustics module and solid mechanics module in the finite element calculation software;

[0009] Step S4: Conduct mesh division on the calculation region and the transition region respectively;

[0010] Step S5: Conduct model calculation, and determine the time calculation range according to the longitudinal wave propagation speed, transverse wave propagation speed, and interface wave propagation speed;

[0011] Step S6: Analyze the incident interface wave and the scattered sound field according to the calculation results.

[0012] Preferably, step S1 includes:

[0013] Select the dimension of the calculation model, determine the dimension of the problem to be analyzed, add the pressure acoustics module and the solid mechanics module in the finite element calculation software, and select the time domain solution;

[0014] Define the calculation frequency, the fastest and slowest sound speeds in the fluid and the solid, the calculation time step, the excitation parameters, the grid expansion multiple, and the viscoelasticity enhancement multiple;

[0015] Among them, the calculation time step is set according to the grid size to satisfy the CFL condition, so that the CFL number satisfies 0.2.

[0016] Preferably, step S3 includes: performing calculations through the pressure acoustics module and the solid mechanics module; among them, the water area and the sediment layer are connected by the acoustic-solid coupling boundary condition, and the acoustic parameters of the sediment layer are represented by the longitudinal wave, the transverse wave, and the density;

[0017] Select rock as the hard bottom medium and sediment as the soft bottom medium; the radiated sound source in water is simulated by the point source in pressure acoustics, and the normal force source is implemented by adding a force source in the direction perpendicular to the interface at the water-sediment interface.

[0018] Preferably, step S4 includes: setting the grid of the calculation area to be less than 1 / 8 of the propagation wavelength of the minimum sound speed, that is, the grid of the water area is less than 1 / 8 of the longitudinal wave sound speed in water, and the grid of the sediment layer area is less than 1 / 8 of the transverse wave sound speed in the solid; the grid of the transition area is gradually increased to reduce the overall calculation amount of the model, that is, multiple absorption layers are set outside the calculation area, and the minimum size of each absorption layer grid is multiplied by the grid expansion multiple for expansion.

[0019] Preferably, step S6 includes: analyzing the sound field without a target and analyzing the components of each part; analyzing the sound field with a target, and exploring the interface wave scattering law by comparing the time domain waveforms of the sound field without a target; analyzing the interface wave scattering law according to the time domain waveforms with and without a target.

[0020] In the second aspect, a calculation system for interface wave target scattering based on finite element is provided, and the system includes:

[0021] Module M1: Select the dimension of the calculation model and define the model parameters;

[0022] Module M2: Establish a geometric model according to the model parameters, divide the geometric model into a calculation area and an absorption area, simulate the sound field in the calculation area, and set an absorption area outside the calculation area to absorb the sound waves including the incident longitudinal wave, transverse wave, and interface wave propagating in the sound field, simulating an infinite large area;

[0023] Module M3: Set up the sound field model according to the pressure acoustics module and the solid mechanics module in the finite element calculation software;

[0024] Module M4: Conduct mesh generation for the calculation region and the transition region respectively;

[0025] Module M5: Conduct model calculation, and determine the time calculation range according to the longitudinal wave propagation speed, the transverse wave propagation speed, and the interface wave propagation speed;

[0026] Module M6: Analyze the incident and scattered sound fields of the interface wave according to the calculation results.

[0027] Preferably, the module M1 includes:

[0028] Select the dimension of the calculation model, determine the dimension of the problem to be analyzed, add the pressure acoustics module and the solid mechanics module in the finite element calculation software, and select the time domain solution;

[0029] Define the calculation frequency, the fastest and slowest sound speeds in the fluid and the solid, the calculation time step, the excitation parameters, the grid expansion multiple, and the viscoelasticity improvement multiple;

[0030] Among them, the calculation time step is set according to the grid size to satisfy the CFL condition, so that the CFL number satisfies 0.2.

[0031] Preferably, the module M3 includes: Conduct calculations through the pressure acoustics module and the solid mechanics module; among them, the water area and the sediment layer are connected by the acoustic-solid coupling boundary condition, and the acoustic parameters of the sediment layer are represented by the longitudinal and transverse waves and the density;

[0032] Select rock as the hard bottom medium and sediment as the soft bottom medium; the radiation sound source in water is simulated by the point source in pressure acoustics, and the normal force source is implemented by adding a force source in the direction perpendicular to the water-sediment interface.

[0033] Preferably, the module M4 includes: The grid setting of the calculation region is less than 1 / 8 of the propagation wavelength of the minimum sound speed, that is, the grid of the water area is less than 1 / 8 of the longitudinal wave sound speed in water, and the grid of the sediment layer region is less than 1 / 8 of the transverse wave sound speed in the solid; the grid of the transition region is gradually increased to reduce the overall calculation amount of the model, that is, multiple absorption layers are set outside the calculation region, and the minimum size of each absorption layer grid is multiplied by the grid expansion multiple for expansion.

[0034] Preferably, the module M6 includes: analyzing the scattering sound field of interface waves based on the finite element calculation results. When there is no target, the propagation law of interface waves can be analyzed, and the influence laws of sound source parameters, sediment layer parameters, etc. on the phase displacement, tangential displacement, and particle motion trajectory distribution of the interface wave method can be discussed. After adding the target, the scattering law of interface waves can be further explored, including the target strength distribution law under the conditions of co-located transceiver and separated transceiver for different types of targets, etc.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The present invention can analyze the incident and scattering sound fields of complex interface waves, and consider the rigid and elastic scattering of interface waves. It simulates an infinite region and can accurately analyze the incident and scattering sound fields;

[0037] 2. The present invention absorbs the longitudinal wave, transverse wave, and interface wave signals generated by the incident sound field through a self-made absorption layer. The gradient-changing grid and viscoelastic layer effectively reduce the sound reflection caused by the sudden change of the grid or viscoelasticity and reduce the overall calculation amount of the model;

[0038] 3. The present invention can consider the target scattering changes caused by different water depths, different target sizes, materials, and bottom sediment changes.

[0039] Other beneficial effects of the present invention will be elaborated in the specific implementation manners through the introduction of specific technical features and technical solutions. Those skilled in the art should be able to understand the beneficial technical effects brought by the technical features and technical solutions through these introductions. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] By reading the detailed description of the non-restrictive embodiments with reference to the following drawings, other features, objectives, and advantages of the present invention will become more obvious:

[0041] Figure 1 It is a schematic diagram of the interface wave scattering calculation method;

[0042] Figure 2 It is a schematic diagram of the two-dimensional simulation model;

[0043] Figures 3a to 3d It is a two-dimensional simulation result diagram of the interface wave scattering sound field; among them, Figure 3a 3a is the sound field at 25 μs, 3b is the sound field at 35 μs, 3c is the sound field at 40 μs, and 3d is the sound field at 50 μs;

[0044] Figures 4a to 4d It is a time-domain waveform diagram of the forward scattering of the interface wave target; among them, Figure 4a 4a is the time-domain waveform of the normal displacement, Figure 4b 4b is the time-domain spectrum of the normal displacement, Figure 4cis the tangential displacement time-domain waveform, Figure 4d is the tangential displacement time-domain spectrum;

[0045] Figure 5 is the 3D modeling diagram of the interface wave target scattering method;

[0046] Figures 6a to 6d is the 3D simulation result diagram of the interface wave scattering sound field; where, Figure 6a is the sound field at 10 μs, 6b is the sound field at 14 μs, 6c is the sound field at 19 μs, and 6d is the sound field at 23 μs. Specific implementation manners

[0047] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several changes and improvements can still be made. These all belong to the protection scope of the present invention.

[0048] The embodiment of the present invention provides a method for calculating the target scattering of interface waves based on finite elements, and uses finite element simulation software to carry out simulation calculation and analysis. Since the sound field of the liquid-solid interface wave is relatively complex, the calculation is carried out through the time-domain analysis module, and the laws of the incident sound field and the scattered sound field of the interface wave are analyzed by analyzing the changes of the sound field at different times. Referring to Figure 1 as shown, the method specifically includes:

[0049] Step S1: Define model parameters;

[0050] First, determine the dimension of the problem to be analyzed, select the dimension of the calculation model, such as a two-dimensional or three-dimensional model; further add the pressure acoustics module and the solid mechanics module, and select the time-domain solution. Define the calculation frequency, the fastest and slowest sound speeds in the fluid and the solid, the calculation time step, the excitation parameters, the grid expansion multiple, and the viscoelasticity enhancement multiple; the calculation time step is set according to the grid size to satisfy the Courant-Friedrichs-Lewy (CFL) condition, so that the CFL number satisfies 0.2.

[0051] Step S2: Establish a geometric model;

[0052] The simulation model is divided into a calculation area and an absorption layer area. Referring to Figure 2 , the calculation area simulates the sound field, and an absorption layer area is set outside the calculation area to absorb acoustic waves such as incident longitudinal waves, transverse waves, and interface waves propagating in the sound field, simulating an infinite area.

[0053] Step S3: Set the sound field model;

[0054] The calculation is carried out through the pressure acoustics module and the solid mechanics module, where the water area and the sediment layer are connected by the acoustic-solid coupling boundary condition. The acoustic parameters of the sediment layer are represented by the longitudinal wave, the transverse wave and the density. Rock is selected as the hard bottom medium and sediment as the soft bottom medium. The radiated sound source in water is simulated by the point source in pressure acoustics, and the normal force source is implemented by adding a force source perpendicular to the interface direction at the water-sediment interface.

[0055] Step S4: Conduct mesh generation;

[0056] The mesh of the calculation area is set to be less than 1 / 8 of the propagation wavelength of the minimum sound speed, that is, the mesh of the water area is less than 1 / 8 of the longitudinal wave sound speed in water, and the mesh of the sediment layer area is less than 1 / 8 of the transverse wave sound speed of the solid. The mesh of the transition area is gradually increased to reduce the overall calculation amount of the model, that is, multiple absorption layers are set outside the calculation area, and the minimum size of each absorption layer mesh is multiplied by the mesh expansion multiple for expansion.

[0057] Step S5: Conduct simulation model calculation;

[0058] Determine the time calculation range according to the longitudinal wave propagation speed, the transverse wave propagation speed and the interface wave propagation speed. The time interval is greater than 10 times of 1 / fs, where fs is the sampling rate required for the calculation.

[0059] Step S6: Sound field analysis;

[0060] Analyze the interface wave scattering sound field according to the finite element calculation results. When there is no target, the propagation law of the interface wave can be analyzed, and the influence laws of the sound source parameters, the sediment layer parameters, etc. on the normal phase displacement, the tangential displacement and the particle motion trajectory distribution of the interface wave can be discussed. After adding the target, the interface wave scattering law can be further explored, including the target strength distribution law of different types of targets in the case of co-located transmitting and receiving and separated transmitting and receiving, etc.

[0061] This method can be further extended to the three-dimensional case to calculate the scattering sound fields at different angles.

[0062] The present invention also provides a finite element-based interface wave target scattering calculation system. The finite element-based interface wave target scattering calculation system can be realized by executing the process steps of the finite element-based interface wave target scattering calculation method, that is, those skilled in the art can understand the finite element-based interface wave target scattering calculation method as the preferred implementation manner of the finite element-based interface wave target scattering calculation system. This system specifically includes:

[0063] Module M1: Model parameter definition;

[0064] First, select the dimension of the calculation model, such as a two-dimensional or three-dimensional model, and determine the dimension of the problem to be analyzed; further add the pressure acoustics module and the solid mechanics model, and select the time domain solution. Define the calculation frequency, the fastest and slowest sound speeds in the fluid and solid, the calculation time step, the excitation parameters, the grid expansion factor, and the viscoelasticity enhancement factor; the calculation time step is set according to the grid size to satisfy the Courant-Friedrichs-Lewy (CFL) condition, such that the CFL number satisfies 0.2.

[0065] Module M2: Establish the geometric model;

[0066] The model is divided into a calculation region and a transition region. Set the fluid region and the solid region according to the calculation scenario, and set an absorption layer outside the calculation region to absorb incident longitudinal waves, transverse waves, interface waves, etc. propagating in the sound field, simulating an infinite region.

[0067] Module M3: Set the sound field model;

[0068] The calculation is carried out through the pressure acoustics module and the solid mechanics module. Among them, the water area and the sediment layer are connected by the fluid-structure interaction boundary condition. The acoustic parameters of the sediment layer are represented by the longitudinal wave, transverse wave, and density. Rock is selected as the hard bottom medium and sediment as the soft bottom medium. The radiation sound source in water is simulated by a point source in pressure acoustics, and the normal force source is implemented by adding a force source in the direction perpendicular to the water-sediment interface.

[0069] Module M4: Conduct mesh generation;

[0070] The grid size of the calculation region is set to be less than 1 / 8 of the propagation wavelength of the minimum sound speed, that is, the grid of the water area is less than 1 / 8 of the longitudinal wave sound speed in water, and the grid of the sediment layer domain is less than 1 / 8 of the transverse wave sound speed in the solid. The grid of the transition region is gradually increased to reduce the overall calculation amount of the model, that is, multiple absorption layers are set outside the calculation region, and the minimum size of each absorption layer grid is multiplied by the grid expansion factor for expansion.

[0071] Module M5: Conduct model calculation;

[0072] Determine the time calculation range according to the longitudinal wave propagation speed, transverse wave propagation speed, and interface wave propagation speed. The time interval is greater than 10 times 1 / fs, where fs is the sampling rate required to be satisfied for the calculation.

[0073] Module M6: Sound field analysis;

[0074] Analyze the scattering sound field of the interface wave according to the finite element calculation results. When there is no target, the propagation law of the interface wave can be analyzed, and the influence laws of sound source parameters, sediment layer parameters, etc. on the phase displacement, tangential displacement, and particle motion trajectory distribution of the interface wave method can be discussed. After adding the target, the scattering law of the interface wave can be further explored, including the target strength distribution law in the case of co-located transmitting and receiving and separated transmitting and receiving for different types of targets, etc.

[0075] Next, the present invention will be described in more detail through specific embodiments.

[0076] Embodiment 1:

[0077] Combined with a target diameter of 0.425 mm, steel material, and liquid-solid interface wave incident on the water-sand interface, calculate and analyze the two-dimensional scattering sound field in the semi-buried case.

[0078] The first step is to define the model parameters;

[0079] First, select the two-dimensional model for calculation, add the pressure acoustics module and the solid mechanics model, select the time-domain solution, define the calculation frequency, the fastest and slowest sound speeds in the fluid and solid, the calculation time step, the excitation parameters, the grid expansion multiple, and the viscoelasticity improvement multiple. The calculation frequency selected this time is 0.4 MHz, the time calculation step is set to 1e-8 s, the excitation selects a 5-cycle sine signal under cosine modulation, the grid expansion multiple is 1.2, and the viscoelasticity parameter is increased from 0.4 Pas to 12 Pas.

[0080] The second step is to establish the geometric model;

[0081] The model is divided into a calculation area and a transition area. The calculation area is 25 mm in length and 6 mm in height, with the fluid area and the solid area each accounting for half. An absorption layer is set outside the calculation area to absorb incident longitudinal waves, transverse waves, interface waves, and other sound waves propagating in the sound field, simulating an infinite large area.

[0082] The third step is to set the sound field model;

[0083] The calculation is carried out through the pressure acoustics module and the solid mechanics module. The water area and the sediment layer are connected through the fluid-solid coupling boundary condition. The acoustic parameters of the sediment layer are represented by longitudinal and transverse waves and density. The specific material calculation parameters are shown in Table 1. The normal force source is implemented by adding a force source perpendicular to the interface direction at the water-sand interface.

[0084] Table 1 Medium simulation parameters

[0085]

[0086] The fourth step is to carry out grid division;

[0087] The computational domain grid is set to be less than 1 / 8 of the propagation wavelength of the minimum sound speed, that is, the water domain grid is less than 1 / 8 of the longitudinal wave sound speed in water, and the sediment layer domain grid is less than 1 / 8 of the shear wave sound speed in solids. The grid in the transition region is gradually increased to reduce the overall computational workload of the model, that is, multiple absorption layers are set outside the computational domain, and the minimum size of each absorption layer grid is multiplied by the grid expansion factor for expansion.

[0088] Step 5: Conduct model calculations;

[0089] Determine the time calculation range. Considering the propagation time and sampling rate, the time length is calculated up to 60 μs, and the time recording interval is 0.1 μs.

[0090] Step 6: Sound field analysis;

[0091] Based on the calculation results, analyze the incident and scattered sound fields of the interface wave. It can be seen that in the sound field excited by the normal force source, in addition to the liquid-solid interface wave, there are also longitudinal waves, shear waves, and head waves in solids and longitudinal waves in water, etc. When the interface wave acts on the target, wave packets such as transmitted interface waves, reflected interface waves, reflected longitudinal waves, transmitted shear waves, and reflected shear waves are generated. Refer to Figures 3a to 3d as shown. Further, the scattering process can be analyzed from the time-domain waveform. Part of the interface wave signal passes through the steel ball and simultaneously generates new longitudinal wave components and shear wave components. From the time-domain of the tangential displacement, it can be clearly seen the longitudinal wave packet near 0.1 s and the interface wave packet near 0.12 s. From the frequency domain, it can also be seen that the interface wave signal is weakened due to the presence of the target. Refer to Figures 4a to 4d as shown.

[0092] Example 2:

[0093] Combined with a target diameter of 0.425 mm, the incident of the liquid-solid interface wave at the water-sand interface with steel material, and the three-dimensional scattering sound field calculation and analysis in the semi-buried case.

[0094] Step 1: Define model parameters;

[0095] First, select the three-dimensional model for calculation, add the pressure acoustics module and the solid mechanics model, select the time-domain solution, and define the calculation frequency, the fastest and slowest sound speeds in the fluid and solid, the calculation time step, the excitation parameters, the grid expansion factor, and the viscoelasticity enhancement factor. In this calculation, the calculation frequency is selected as 0.4 MHz, the time calculation step is set to 1e-8 s, the excitation is a 5-cycle sine signal under cosine modulation, the grid expansion factor is 1.2, and the viscoelasticity parameter is increased from 0.4 Pas to 12 Pas.

[0096] Step 2: Establish the geometric model;

[0097] The model is divided into a computational region and a transition region. Since the three-dimensional model is large, the size of the computational region is reduced. The computational region is 5 mm in length and 2 mm in height, with the fluid region and the solid region each accounting for half. An absorption layer is set outside the computational region to absorb incident longitudinal waves, transverse waves, interface waves, etc. propagating in the sound field, simulating an infinite region, referring to Figure 5 ;

[0098] Step 3: Set up the sound field model;

[0099] The calculation is carried out through the pressure acoustics module and the solid mechanics module. The water area and the sediment layer are connected by the fluid-structure interaction boundary condition. The acoustic parameters of the sediment layer are represented by longitudinal and transverse waves and density. The specific material calculation parameters are shown in Table 2. The normal force source is implemented by adding a force source perpendicular to the interface direction at the water-sediment interface.

[0100] Table 2 Medium simulation parameters

[0101]

[0102] Step 4: Conduct mesh generation;

[0103] The mesh in the computational region is set to be less than 1 / 8 of the propagation wavelength of the minimum sound speed, that is, the mesh in the water area is less than 1 / 8 of the longitudinal wave sound speed in water, and the mesh in the sediment layer region is less than 1 / 8 of the transverse wave sound speed in solids. The mesh in the transition region is gradually increased to reduce the overall computational amount of the model, that is, multiple absorption layers are set outside the computational region, and the minimum size of each absorption layer mesh is multiplied by the mesh expansion factor for expansion.

[0104] Step 5: Conduct model calculation;

[0105] Determine the time calculation range. Considering the propagation time and sampling rate, the time length is calculated up to 60 μs, and the time recording interval is 0.1 μs.

[0106] Step 6: Sound field analysis;

[0107] An xy-plane slice is established in the dataset, located in the solid medium, 0.01 m away from the interface. The calculation results analyze the incident and scattered sound fields of the interface wave point source. Figures 6a to 6d It is a graph of the normal displacement varying with time. It can be seen that when the interface wave acts on the target, transmission and reflection phenomena occur.

[0108] Through this method, the time-domain sound field of the interface wave can be calculated, and the scattering interaction between the interface wave and the target can be analyzed.

[0109] The embodiment of the present invention provides a method and system for calculating the scattering of interface waves based on finite elements. The pressure acoustics module and the solid mechanics model in the finite element calculation software are used to model the fluid and the solid respectively, and at the same time, the fluid and the solid are connected by the acoustic-structure boundary to simulate the liquid-solid boundary and realize the transfer of stress and displacement, so as to establish a simulation model of the liquid-solid interface wave sound field. In addition, in order to eliminate various sound waves such as longitudinal waves, transverse waves, and interface waves and simulate an infinite boundary, an absorption layer is designed outside the calculation area. By continuously increasing the viscoelastic parameters and continuously reducing the grid volume, the absorption of various sound waves is realized, the calculation amount is reduced, and at the same time, the artificial reflection caused by grid or viscoelastic mutation is avoided, and the calculation of the liquid-solid interface wave sound field is realized. This method can accurately calculate the scattering sound field of interface waves, can consider rigid and elastic scattering, and is applicable to the calculation of targets with simple and complex geometric shapes.

[0110] As known to those skilled in the art, in addition to implementing the system and its various devices, modules, and units provided by the present invention in the form of pure computer-readable program code, the method steps can be logically programmed to enable the system and its various devices, modules, and units provided by the present invention to be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers, etc. to achieve the same functions. Therefore, the system and its various devices, modules, and units provided by the present invention can be regarded as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be regarded as the structure within the hardware component; the devices, modules, and units for implementing various functions can also be regarded as either software modules for implementing the method or the structure within the hardware component.

[0111] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. Without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A finite element-based method for calculating the scattering of an interface wave by a target, characterized in that, Including: Step S1: Select the dimension of the calculation model and define the model parameters; Step S2: Establish a geometric model according to the model parameters, divide the geometric model into a calculation region and a transition region, set the fluid region and the solid region according to the calculation scenario, and set an absorption layer outside the calculation region to absorb acoustic waves including incident longitudinal waves, transverse waves, and interface waves propagating in the acoustic field, simulating an infinite region; Step S3: Set the acoustic field model according to the pressure acoustics module and the solid mechanics module in the finite element calculation software; Step S4: Perform mesh generation on the calculation region and the transition region respectively; Step S5: Conduct simulation model calculation, and determine the time calculation range according to the longitudinal wave propagation speed, transverse wave propagation speed, and interface wave propagation speed; Step S6: Analyze the incident and scattered acoustic fields of the interface wave according to the calculation results.

2. The method for calculating the scattering of an interface wave target based on finite elements according to claim 1, wherein The said Step S1 includes: Select the dimension of the calculation model, determine the dimension of the problem to be analyzed, add the pressure acoustics module and the solid mechanics module in the finite element calculation software, and select the time domain solution; Define the calculation frequency, the fastest and slowest sound speeds in the fluid and the solid, the calculation time step, the excitation parameters, the mesh expansion multiple, and the viscoelasticity enhancement multiple; Among them, the calculation time step is set according to the mesh size to satisfy the CFL condition, so that the CFL number satisfies 0.

2.

3. The method for calculating the scattering of an interface wave target based on finite elements according to claim 1, wherein The said Step S3 includes: Conduct calculations through the pressure acoustics module and the solid mechanics module; among them, the water area and the sediment layer are connected by the acoustic-solid coupling boundary condition, and the acoustic parameters of the sediment layer are represented by the longitudinal wave, transverse wave, and density; Select rock as the hard bottom medium and sediment as the soft bottom medium; the radiation sound source in water is simulated by a point source in pressure acoustics, and the normal force source is implemented by adding a force source in the direction perpendicular to the water-sediment interface at the water-sediment interface.

4. The method for calculating the target scattering of interface waves based on finite elements according to claim 1, characterized in that The said Step S4 includes: The mesh setting of the calculation region is less than 1 / 8 of the propagation wavelength of the minimum sound speed, that is, the mesh of the water area is less than 1 / 8 of the longitudinal wave sound speed in water, and the mesh of the sediment layer domain is less than 1 / 8 of the transverse wave sound speed in the solid; the mesh of the transition region is gradually increased to reduce the overall calculation amount of the model, that is, multiple absorption layers are set outside the calculation region, and the minimum size of each absorption layer mesh is multiplied by the mesh expansion multiple for expansion.

5. The method for calculating the target scattering of interface waves based on finite elements according to claim 1, wherein The said Step S6 includes: Analyze the scattered acoustic field of the interface wave according to the finite element calculation results; When there is no target, analyze the propagation law of the interface wave, and discuss the influence laws of the sound source parameters and sediment layer parameters on the normal phase displacement, tangential displacement, and particle motion trajectory distribution of the interface wave; after adding the target, further explore the scattering law of the interface wave, including the target strength distribution laws of different types of targets in the co-located and separated transmitter-receiver cases.

6. A finite element-based interface wave target scattering calculation system, characterized in that Including: Module M1: Select the dimension of the calculation model and define the model parameters; Module M2: Establish a geometric model according to the model parameters, divide the geometric model into a calculation region and an absorption region, and set an absorption region outside the calculation region to absorb acoustic waves including incident longitudinal waves, transverse waves, and interface waves propagating in the acoustic field, simulating an infinite region; Module M3: Set the acoustic field model according to the pressure acoustics module and the solid mechanics module in the finite element calculation software; Module M4: Perform mesh generation on the calculation region and the transition region respectively; Module M5: Conduct model calculations to determine the time calculation range based on the longitudinal wave propagation velocity, transverse wave propagation velocity, and interface wave propagation velocity. Module M6: Analyze the incident and scattered sound fields of the interface wave based on the calculation results.

7. The finite element-based interface wave target scattering calculation system according to claim 6, characterized in that, The module M1 includes: Select the calculation model dimension, determine the dimension of the problem to be analyzed, add the pressure acoustics module and the solid mechanics module in the finite element calculation software, and select the time domain solution. Define the calculation frequency, the fastest and slowest sound speeds in the fluid and solid, the calculation time step, the excitation parameters, the grid expansion multiple, and the viscoelastic enhancement multiple. Among them, the calculation time step is set according to the grid size to satisfy the CFL condition, so that the CFL number satisfies 0.

2.

8. The finite element-based interface wave target scattering calculation system according to claim 6, characterized in that The module M3 includes: Conduct calculations through the pressure acoustics module and the solid mechanics module; among them, the water area and the sediment layer are connected by the acoustic-solid coupling boundary condition, and the acoustic parameters of the sediment layer are represented by the longitudinal and transverse waves and the density. Select rock as the hard bottom medium and sediment as the soft bottom medium; the radiation sound source in water is simulated by a point source in pressure acoustics, and the normal force source is implemented by adding a force source in the direction perpendicular to the interface at the water-sediment interface.

9. The finite element-based interface wave target scattering calculation system according to claim 6, wherein The module M4 includes: Set the grid of the calculation area to be less than 1 / 8 of the propagation wavelength of the minimum sound speed, that is, the grid of the water area is less than 1 / 8 of the longitudinal wave sound speed in water, and the grid of the sediment layer area is less than 1 / 8 of the solid transverse wave sound speed; the grid of the transition area is gradually increased to reduce the overall calculation amount of the model, that is, multiple absorption layers are set outside the calculation area, and the minimum size of each absorption layer grid is multiplied by the grid expansion multiple for expansion.

10. The finite element-based interface wave target scattering calculation system according to claim 6, wherein The module M6 includes: Analyze the scattered sound field of the interface wave according to the finite element calculation results. When there is no target, analyze the propagation law of the interface wave, and discuss the influence laws of the sound source parameters and sediment layer parameters on the normal phase displacement, tangential displacement, and particle motion trajectory distribution of the interface wave; after adding the target, further explore the scattering law of the interface wave, including the target strength distribution laws of different types of targets in the co-located and separated transmitter-receiver cases.

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