A low-frequency underwater acoustic emission transducer structure optimization method based on finite element simulation

Abstract

The application discloses a low-frequency underwater acoustic emission transducer structure optimization method based on finite element simulation, relates to the technical field of low-frequency underwater acoustic transducer optimization design in ocean engineering, and establishes a low-frequency underwater acoustic emission transducer finite element model containing a vibrating diaphragm and a shell, and generates a corresponding fluid field and a low-frequency underwater acoustic emission transducer grid when the low-frequency underwater acoustic emission transducer finite element model is placed in the fluid field; and the velocity at the fluid field grid interface is subjected to interpolation correction, which is used for decoupling the numerical correlation between the pressure field and the velocity field. The application discloses a quantitative relationship between the vibrating diaphragm radius, the axis diameter ratio of the elliptical head, the shell shape and the seawater pressure through a K-Epsilon model system, provides a theoretical basis for optimization design, and concentrates the vibrating diaphragm kinetic energy along the axial direction by optimizing the vibrating diaphragm radius, the axis diameter ratio and the shell, enhances the axial water pushing efficiency, reduces the fluid flow loss, and optimizes the near-field pressure distribution.

Description

Technical Field

[0001] This invention relates to the field of low-frequency underwater acoustic transducer optimization design technology in marine engineering, specifically a method for optimizing the structure of a low-frequency underwater acoustic transducer based on finite element simulation. Background Technology

[0002] Controlled ocean seismic sources (a type of low-frequency underwater acoustic transducer) are an innovative method of marine exploration, but their key technologies are currently monopolized by a few developed Western countries, leaving my country with a technological gap. Importing marine exploration equipment from overseas is not only expensive but may also pose security risks to oil and gas data, thus slowing down the exploration process and impacting national economic progress. For example, in 2023, a domestically developed low-frequency underwater acoustic transducer was demonstrated in the waters near Zhanjiang.

[0003] However, existing low-frequency underwater acoustic transducers have the following technical defects: (1) Traditional design methods rely on repeated physical experiments and have not established a quantitative relationship between structural parameters and sound pressure output. The optimization process is highly blind, has a long cycle, and is costly.

[0004] (2) The diaphragm radius is a key parameter affecting the sound radiation capability, but the existing technology lacks a deep understanding of the transmission mechanism of "diaphragm size → seawater pressure → sound pressure level", and cannot determine the optimal size range.

[0005] (3) Most existing transducers use flat circular diaphragms, and the sound pressure radiation is axially symmetric, resulting in energy dispersion. There is a lack of systematic numerical analysis methods to achieve sound pressure enhancement in a specified direction through shape optimization.

[0006] (4) The transducer housing serves as a support structure for the diaphragm, and its shape also affects the hydrodynamic characteristics and sound pressure distribution. Existing technologies do not include the housing in the scope of optimization design.

[0007] Therefore, there is an urgent need for a method to optimize the structure of low-frequency underwater acoustic transmitter transducers through numerical simulation. Summary of the Invention

[0008] The purpose of this invention is to provide a method for optimizing the structure of a low-frequency underwater acoustic transmitter based on finite element simulation, so as to solve the problems mentioned in the background art.

[0009] To address the aforementioned technical problems, this invention provides the following technical solution: a method for optimizing the structure of a low-frequency underwater acoustic transmitter based on finite element simulation, comprising: S1. Establish a finite element model of a low-frequency underwater acoustic transmitter transducer including a diaphragm and a shell, and generate the corresponding fluid field and low-frequency underwater acoustic transmitter transducer mesh when the finite element model of the low-frequency underwater acoustic transmitter transducer is placed in a fluid field; and perform interpolation correction on the velocity at the interface of the fluid field mesh to decouple the numerical correlation between the pressure field and the velocity field. S2. Set the acceleration function of the diaphragm so that the diaphragm vibrates according to the control signal generated by the set acceleration function and couples with seawater, and radiates the acoustic signal generated by the diaphragm vibration into the fluid field; S3. Change the diaphragm radius within the preset range, couple the obtained diaphragm model with the generated fluid field mesh, and obtain the pressure / sound pressure level change curves of diaphragms with different radii at fixed monitoring points through the obtained fluid field solution. Take the diaphragm radius with the largest peak amplitude of the corresponding change curve as the optimal diaphragm radius. S4. Under the constraint of the obtained optimal diaphragm radius, change the shaft diameter ratio parameter of the diaphragm, couple the newly obtained diaphragm model with the generated fluid field mesh, and obtain the pressure / sound pressure level change curves of diaphragms with different shaft diameter ratios at fixed monitoring points through the solution of the obtained fluid field. Analyze the influence of shaft diameter ratio change on pressure distribution, and obtain the optimal diaphragm shaft diameter ratio according to the engineering objectives. S5. Under the constraints of the obtained optimal diaphragm radius and the best diaphragm shaft diameter ratio, construct a low-frequency underwater acoustic transmitter model with different shell shape profiles and couple it with the generated fluid field mesh to obtain the obtained fluid field solution. Obtain the pressure / sound pressure level change curves with time obtained by simulation at fixed monitoring points for different shell shape profiles, simulate the influence of different shell shape profiles on fluid field characteristics, and screen the optimal shell shape profile. S6. Based on the obtained optimal diaphragm radius, optimal diaphragm shaft-to-diameter ratio, and optimal shell shape profile, construct the overall optimization scheme for the corresponding low-frequency underwater acoustic transmitter transducer.

[0010] Furthermore, in the process of interpolating and correcting the velocity at the fluid field mesh interface in S1, the Rhie-Chow interpolation method is used to correct the velocity at the fluid field mesh interface, specifically including: Let the centers of two adjacent grid cells on the transducer diaphragm be respectively H and J In the fluid field mesh interface H and J Location points in the public area between O The corresponding uncorrected velocity interpolation is denoted as The calculation formulas involved are as follows: in, Represents the location point in the fluid field mesh interfaceO Based on location points H and location points J Distance bias coefficient; Represents the location point in the fluid field mesh interface H To the location point O The distance; Represents the location point in the fluid field mesh interface J To the location point O The distance; Represents the location point in the fluid field mesh interface H The corresponding uncorrected velocity interpolation; Represents the location point in the fluid field mesh interface J The corresponding uncorrected velocity interpolation; Based on the conversion relationship between velocity and pressure, the fluid field mesh interface is obtained. H and J Location points in the public area between O The corresponding corrected velocity interpolation is denoted as ; in, Indicates location point H The corresponding diagonal factor related to the mesh volume; Indicates location point J The corresponding diagonal factor related to the mesh volume; Indicates location point O The corresponding diagonal factor related to the mesh volume; This indicates the pressure collected from the simulated water area. p along H arrive J The derivative of the direction of the line at the location point J The value at; This indicates the pressure collected from the simulated water area. p along H arrive J The derivative of the direction of the line at the location point H The value at; This indicates the pressure collected from the simulated water area. p along H arrive J The derivative of the direction of the line at the location point O The value at that location.

[0011] Furthermore, the conversion relationship between velocity and pressure is as follows: in, Represents the location point in the fluid field mesh interface H The corresponding corrected velocity interpolation amount; Represents the location point in the fluid field mesh interface H The corresponding corrected velocity interpolation amount; And based on the pressure collected in the simulated water area p Obtain the sound pressure level at the corresponding sampling point, denoted as . ; in, This indicates the preset reference pressure.

[0012] Furthermore, the acceleration function of the diaphragm in S2 is as follows: in, Indicates the maximum acceleration; This indicates the frequency of the control signal within the low-frequency underwater acoustic operating band. Indicates the window function; The acoustic signal generated by the diaphragm of this invention includes the frequency range of the signal (usually focusing on the low-frequency band), amplitude, waveform type and duration, to simulate the actual low-frequency underwater acoustic emission scenario, while taking into account the stability and repeatability of the signal.

[0013] Furthermore, in the process of obtaining the pressure-time variation curves of diaphragms with different radii at fixed monitoring points by solving the fluid field obtained in S3, the pressure of the diaphragm at different time points at fixed monitoring points is obtained by solving the fluid field obtained in the K-Epsilon turbulent finite element model. The turbulent kinetic energy in the K-Epsilon turbulent finite element model... and dissipation rate The transport equations are as follows: in, For time-averaged velocity components, and For spatial coordinates, and Customize source items for users; This represents the turbulent kinetic energy generated by the average velocity gradient; This represents the turbulent kinetic energy generated by buoyancy; This indicates the contribution of compressible turbulent pulsating expansion to dissipation; This represents the turbulent eddy viscosity coefficient, and ; Indicates fluid density; Indicates the dynamic viscosity of the fluid; , , , , and All are model constants.

[0014] Furthermore, the diaphragm-to-diameter ratio parameter in S4 represents the diaphragm's sagittal height or axial thickness along the vibration axis. a 0 and the radius of the diaphragm at the section perpendicular to the vibration axis c The ratio of 0 to 1. In this invention, the shaft-to-diameter ratio corresponds to a portion of the major and minor semi-axis and is used to define the geometric curvature characteristics of the front-end diaphragm.

[0015] Furthermore, during the process of coupling the low-frequency underwater acoustic emission transducer model with different shell outlines in S5 with the generated fluid field mesh, the low-frequency underwater acoustic emission transducer model with different shell outlines includes at least: a transducer structure with a flat diaphragm at the front end, a transducer structure with an elliptical head diaphragm at the front end, and a double elliptical head transducer structure with both the front end and the rear end being elliptical heads.

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) This invention provides a method for optimizing the structure of a low-frequency underwater acoustic transducer by using Reynolds time-averaged simulation. The simulation technology generates an aquatic environment that is more in line with the actual sea conditions. The simulation simulates the movement of a controllable ocean source in the water. By changing the diaphragm radius, shaft diameter ratio and shell shape of the low-frequency underwater acoustic transducer, fluid-structure interaction analysis of low-frequency underwater acoustic transducers with different shapes is carried out. The motion law and output pressure data of low-frequency underwater acoustic transducers with different shapes are studied. Then, the main factors affecting the output pressure of the low-frequency underwater acoustic transducer are determined, and a low-frequency underwater acoustic transducer with stronger output sound pressure in a specified direction is designed based on the factors. (2) This invention reveals the quantitative relationship between diaphragm radius, elliptical head axis-to-diameter ratio, shell shape and seawater pressure through the K-Epsilon model system, providing a theoretical basis for optimization design; and by optimizing the diaphragm radius, axis-to-diameter ratio and shell, the diaphragm kinetic energy is concentrated along the axial direction, enhancing the axial water-pushing efficiency, reducing fluid flow loss, and optimizing the near-field pressure distribution. In the double elliptical head structure, the front elliptical head of the diaphragm actively pushes water, and the rear elliptical head of the shell guides the wake, thus synergistically enhancing the axial sound pressure. Attached Figure Description

[0017] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart illustrating a method for optimizing the structure of a low-frequency underwater acoustic transmitter transducer based on finite element simulation, according to the present invention. Figure 2This is a schematic diagram of the mesh generation and correction principle based on Rhie-Chow interpolation in an embodiment of a low-frequency underwater acoustic transmitter structure optimization method based on finite element simulation of the present invention. Figure 3 (a) is a schematic diagram of the coupling results between diaphragms of different radii and seawater in an embodiment of the present invention, including the design of the inner diaphragm radius and pressure analysis; Figure 3 (b) is a schematic diagram of the pressure change at the monitoring point in the water under the coupling results of diaphragms with different radii and seawater in an embodiment of the present invention; Figure 4 (a) is a schematic diagram of the diaphragm design of different shapes with different shaft diameter ratios and the coupling results with seawater in the embodiments of the present invention; Figure 4 (b) is a schematic diagram of the pressure change at the monitoring point in the water under different diaphragm ratios and the coupling results with seawater in an embodiment of the present invention; Figure 5 (a) is a schematic diagram of the internal transducer structure design and pressure analysis of the coupling results between transducers with different shell structures and seawater in embodiments of the present invention; Figure 5 (b) is a schematic diagram of the pressure change at the monitoring point in the water under the coupling results of transducers with different shell structures and seawater in the embodiments of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In one specific embodiment, a low-frequency underwater acoustic transducer structure is disclosed. This structure is optimized to increase output sound pressure and provides a reference for improving actual equipment using a modified model. The structure mainly consists of three parts: diaphragms of different radii, diaphragm shapes with different shaft-to-diameter ratios, and underwater acoustic transducers with different housing structures. The core function of the diaphragm is to output vibration signals under driving force; the housing ensures structural stability and prevents seawater infiltration that could corrode internal equipment.

[0020] like Figure 1 As shown, this embodiment provides a method for optimizing the structure of a low-frequency underwater acoustic transmitter based on finite element simulation, including: S1. Establish a finite element model of a low-frequency underwater acoustic transmitter transducer including a diaphragm and a shell, and generate the corresponding fluid field and low-frequency underwater acoustic transmitter transducer mesh when the finite element model of the low-frequency underwater acoustic transmitter transducer is placed in a fluid field; and perform interpolation correction on the velocity at the interface of the fluid field mesh to decouple the numerical correlation between the pressure field and the velocity field. In this embodiment, S1 specifically includes: S1.1 Import the model into the fluid dynamics simulation software and place it in a preset fluid field environment to simulate actual underwater working conditions, including fluid medium, density, gravitational acceleration, and excitation diaphragm signal frequency settings. For example, in this embodiment, seawater with a density of 1024.5 kg / m³ is used as the fluid medium. 3 The gravitational acceleration in seawater is set to 9.8 m / s². 2 The excitation signal frequency is 10Hz.

[0021] S1.2 Use mesh generation tools to generate high-quality fluid field meshes and transducer structure meshes, ensuring that the mesh density is fine enough to accurately capture sound wave propagation, fluid interaction and boundary effects, laying the foundation for subsequent simulations.

[0022] Specifically, in the process of S1 interpolating and correcting the velocity at the fluid field grid interface, the Rhie-Chow interpolation method is used to correct the velocity at the fluid field grid interface, which specifically includes: Let the centers of two adjacent grid cells on the transducer diaphragm be respectively H and J In the fluid field mesh interface H and J Location points in the public area between O The corresponding uncorrected velocity interpolation is denoted as The calculation formulas involved are as follows: in, Represents the location point in the fluid field mesh interface O Based on location points H and location points J Distance bias coefficient; Represents the location point in the fluid field mesh interface H To the location point O The distance; Represents the location point in the fluid field mesh interface J To the location point O The distance; Represents the location point in the fluid field mesh interface H The corresponding uncorrected velocity interpolation; Represents the location point in the fluid field mesh interface JThe corresponding uncorrected velocity interpolation; Based on the conversion relationship between velocity and pressure, the fluid field mesh interface is obtained. H and J Location points in the public area between O The corresponding corrected velocity interpolation is denoted as ;like Figure 2 As shown, the conversion relationship between velocity and pressure is as follows: in, Represents the location point in the fluid field mesh interface H The corresponding corrected velocity interpolation amount; Represents the location point in the fluid field mesh interface H The corresponding corrected velocity interpolation amount; in, Indicates location point H The corresponding diagonal factor related to the mesh volume; Indicates location point J The corresponding diagonal factor related to the mesh volume; This represents the diagonal coefficient related to the mesh volume corresponding to location point O; This indicates the pressure collected from the simulated water area. p along H arrive J The derivative of the direction of the line at the location point J The value at; This indicates the pressure collected from the simulated water area. p along H arrive J The derivative of the direction of the line at the location point H The value at; This indicates the pressure collected from the simulated water area. p along H arrive J The derivative of the direction of the line at the location point O The value at that location.

[0023] This embodiment introduces a correction value. We can obtain: Therefore, it can be based on The corrected equation is obtained as follows: For the pressure phase, we have: In this way, the newly generated pressure value will be appropriately corrected, achieving accurate simulation of the coupling process between seawater and the transducer.

[0024] This embodiment is also based on pressure collected in simulated water. p Obtain the sound pressure level at the corresponding sampling point, denoted as . ; in, This indicates the preset reference pressure.

[0025] S2. Set the acceleration function of the diaphragm so that the diaphragm vibrates according to the control signal generated by the set acceleration function and couples with seawater, and radiates the acoustic signal generated by the diaphragm vibration into the fluid field; the acoustic signal generated by the diaphragm includes the frequency range of the signal (usually focusing on the low frequency band), amplitude, waveform type and duration, in order to simulate the actual low frequency underwater acoustic emission scenario, while considering the stability and repeatability of the signal.

[0026] The acceleration function of the diaphragm in S2 is as follows: in, Indicates the maximum acceleration; This indicates the frequency of the control signal within the low-frequency underwater acoustic operating band. Represents the window function.

[0027] S3. Within a preset value range, change the diaphragm radius, couple the resulting diaphragm model with the generated fluid field mesh, and obtain the pressure / sound pressure level versus time curves simulated at fixed monitoring points for diaphragms of different radii using the obtained fluid field solution. Figure 3 (a) Keeping the diaphragm thickness constant, design the diaphragm radius. ,radius ,radius and radius The pressure generated by the corresponding diaphragm at a fixed monitoring point is obtained; Figure 3 In (b), when the diaphragm radius is 0.15m, the maximum pressure reaches 0.01Pa, corresponding to a pressure level of 80dB; when the radius is 0.20m, the maximum pressure is 0.04Pa, and the pressure level rises to 92dB; when the radius is 0.35m, the maximum pressure is 0.12Pa, and the pressure level is 101.6dB; when the radius is 0.45m, the maximum pressure is 0.24Pa, and the pressure level further increases to 107.6dB. Therefore, if engineering needs require, the diaphragm radius can be set to 0.45m; the diaphragm radius with the largest peak amplitude corresponding to the change curve is taken as the optimal diaphragm radius. In the process of obtaining the pressure-time variation curves of diaphragms with different radii at fixed monitoring points by solving the fluid field obtained in S3, the pressure of the diaphragm at different time points at fixed monitoring points is obtained by simulating the fluid field obtained by solving the fluid field obtained in S3 using the K-Epsilon turbulent finite element model. The turbulent kinetic energy in the K-Epsilon turbulent finite element model... and dissipation rate The transport equations are as follows: in, For time-averaged velocity components, and For spatial coordinates, and Customize source items for users; This represents the turbulent kinetic energy generated by the average velocity gradient; This represents the turbulent kinetic energy generated by buoyancy; This indicates the contribution of compressible turbulent pulsating expansion to dissipation; This represents the turbulent eddy viscosity coefficient, and ; Indicates fluid density; Indicates the dynamic viscosity of the fluid; , , , , and All are model constants. Simultaneously, step S1 corrects and converts the relationship between velocity and pressure. The new pressure can be obtained through a fixed monitoring point, and the pressure level can be calculated using the following formula: In the formula, Expressed as sound pressure level, The pressure was collected in a simulated water area. For reference pressure, 0.000001 Pa is used in this embodiment.

[0028] S4. Under the constraint of the obtained optimal diaphragm radius, change the diaphragm's axis-to-diameter ratio parameter. In S4, the diaphragm's axis-to-diameter ratio parameter represents the ratio of the diaphragm's sag or axial thickness a0 along the vibration axis to the radius c0 of the section perpendicular to the vibration axis. Figure 4 As shown in (a), the diaphragm's axis-to-diameter ratio parameter can be described as the diaphragm's cross-sectional thickness along the vibration axis. a 0 and the projected radius of the diaphragm on a plane perpendicular to the vibration axis. c The ratio of 0; a series of shaft diameter ratios were designed in this embodiment. (That is, the diaphragm is mainly a flat plate structure). , , , (That is, there is a hemispherical structure on the diaphragm plate.) Structures such as these are coupled with fluid field meshes, and the simulation process is repeated. Pressure data is acquired at fixed monitoring points, and the shaft-to-diameter ratio parameter is adjusted to simulate diaphragm variants from thin to thick, ensuring coverage of the actual design range.

[0029] The newly acquired diaphragm model is coupled with the generated fluid field mesh. The pressure / sound pressure level versus time curves for diaphragms with different shaft-to-diameter ratios are obtained by solving the fluid field at fixed monitoring points. The influence of shaft-to-diameter ratio variation on pressure distribution is analyzed, and the optimal diaphragm shaft-to-diameter ratio is obtained based on engineering objectives. Figure 4 (b) The relationship between the axial diameter ratio and pressure exhibits a "spoon" shape. The initial pressure at the point is 0.20 Pa. Location (corresponding to point in the diagram) a min The pressure value is at its minimum. Location (corresponding to point in the diagram) a equal The pressure rose to 0.242 Pa. Pressure increases gradually; if If the engineering requirements are met, a diaphragm of this shape can be designed.

[0030] S5. Under the constraints of the obtained optimal diaphragm radius and optimal diaphragm shaft-to-diaphragm ratio, a low-frequency underwater acoustic transducer model with different shell outlines is constructed and coupled with the generated fluid field mesh to further obtain the pressure generated by the corresponding diaphragm at a fixed monitoring point; such as cylindrical and composite structures, to simulate the influence of shell shape on fluid field characteristics. See the example. Figure 5 (a) Based on the principle of elliptical head, three matching schemes of shell and diaphragm are designed. The first scheme uses a flat diaphragm (the diaphragm surface is surface 1), the second scheme uses an elliptical head diaphragm (the diaphragm surface is surface 2), and the third scheme is a double elliptical head transducer structure (the diaphragm surface is surface 2 and there is a surface 3 at the tail).

[0031] The fluid field was obtained by solving for the pressure / sound pressure level versus time curves simulated at fixed monitoring points for different shell shapes. This simulated the influence of different shell shapes on the fluid field characteristics, and the optimal shell shape was selected; as in the example. Figure 5(b) Three structural models were considered. The transducer structure with surface 1 generated a maximum pressure of 30.32 Pa at a fixed monitoring point, with a pressure level of 149.63 dB, which served as the reference. The transducer structure with surface 2 generated a maximum pressure of 38.12 Pa at a fixed monitoring point, with a pressure level of 151.62 dB, an improvement of 2.0 dB compared to the reference. The transducer structure with surfaces 2 and 3 (dual elliptical head - streamlined type) generated a maximum pressure of 43.36 Pa, with a pressure level of 152.74 dB, an improvement of 3.1 dB. Considering only pressure and pressure level, the transducer structure combining surfaces 2 and 3 was the optimal solution.

[0032] In the process of coupling the low-frequency underwater acoustic emission transducer model with different shell outlines constructed in S5 with the generated fluid field mesh, the low-frequency underwater acoustic emission transducer model with different shell outlines includes at least: a transducer structure with a front diaphragm as a flat plate diaphragm, a transducer structure with a front diaphragm as an elliptical head diaphragm, and a double elliptical head transducer structure with both the front diaphragm and the tail end being elliptical heads.

[0033] S6. Based on the obtained optimal diaphragm radius, optimal diaphragm shaft-to-diameter ratio, and optimal shell shape profile, construct the overall optimization scheme for the corresponding low-frequency underwater acoustic transmitter transducer.

[0034] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0035] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for optimizing the structure of a low-frequency underwater acoustic transmitter based on finite element simulation, characterized in that, include: S1. Establish a finite element model of a low-frequency underwater acoustic transmitter transducer that includes a diaphragm and a shell, and generate the fluid field and the low-frequency underwater acoustic transmitter transducer mesh when the finite element model of the low-frequency underwater acoustic transmitter transducer is placed in a fluid field. Furthermore, the velocity at the interface of the fluid field grid is interpolated and corrected to decouple the numerical correlation between the pressure field and the velocity field; S2. Set the acceleration function of the diaphragm so that the diaphragm vibrates according to the control signal generated by the set acceleration function and couples with seawater, and radiates the acoustic signal generated by the diaphragm vibration into the fluid field; S3. Change the diaphragm radius within the preset range, couple the obtained diaphragm model with the generated fluid field mesh, and obtain the pressure / sound pressure level change curves of diaphragms with different radii at fixed monitoring points through the obtained fluid field solution. Take the diaphragm radius with the largest peak amplitude of the corresponding change curve as the optimal diaphragm radius. S4. Under the constraint of the obtained optimal diaphragm radius, change the shaft diameter ratio parameter of the diaphragm, couple the newly obtained diaphragm model with the generated fluid field mesh, and obtain the pressure / sound pressure level change curves of diaphragms with different shaft diameter ratios at fixed monitoring points through the solution of the obtained fluid field. Analyze the influence of shaft diameter ratio change on pressure distribution, and obtain the optimal diaphragm shaft diameter ratio according to the engineering objectives. S5. Under the constraints of the obtained optimal diaphragm radius and the best diaphragm shaft diameter ratio, construct a low-frequency underwater acoustic transmitter model with different shell shape profiles and couple it with the generated fluid field mesh to obtain the obtained fluid field solution. Obtain the pressure / sound pressure level change curves with time obtained by simulation at fixed monitoring points for different shell shape profiles, simulate the influence of different shell shape profiles on fluid field characteristics, and screen the optimal shell shape profile. S6. Based on the obtained optimal diaphragm radius, optimal diaphragm shaft-to-diameter ratio, and optimal shell shape profile, construct the overall optimization scheme for the corresponding low-frequency underwater acoustic transmitter transducer.

2. The method for optimizing the structure of a low-frequency underwater acoustic transmitter based on finite element simulation according to claim 1, characterized in that: In the process of S1 interpolating and correcting the velocity at the fluid field mesh interface, the Rhie-Chow interpolation method is used to correct the velocity at the fluid field mesh interface, specifically including: Let the centers of two adjacent grid cells on the transducer diaphragm be respectively H and J In the fluid field mesh interface H and J Location points in the public area between O The corresponding uncorrected velocity interpolation is denoted as The calculation formulas involved are as follows: in, Represents the location point in the fluid field mesh interface O Based on location points H and location points J Distance bias coefficient; Represents the location point in the fluid field mesh interface H To the location point O The distance; Represents the location point in the fluid field mesh interface J To the location point O The distance; Represents the location point in the fluid field mesh interface H The corresponding uncorrected velocity interpolation; Represents the location point in the fluid field mesh interface J The corresponding uncorrected velocity interpolation; Based on the conversion relationship between velocity and pressure, the fluid field mesh interface is obtained. H and J Location points in the public area between O The corresponding corrected velocity interpolation is denoted as ; in, Indicates location point H The corresponding diagonal factor related to the mesh volume; This represents the diagonal coefficient related to the mesh volume corresponding to location point J; Indicates location point O The corresponding diagonal factor related to the mesh volume; This indicates the pressure collected from the simulated water area. p along H arrive J The derivative of the direction of the line at the location point J The value at; This indicates the pressure collected from the simulated water area. p along H arrive J The derivative of the direction of the line at the location point H The value at; This indicates the pressure collected from the simulated water area. p along H arrive J The derivative of the direction of the line at the location point O The value at that location.

3. The method for optimizing the structure of a low-frequency underwater acoustic transmitter based on finite element simulation according to claim 2, characterized in that, The conversion relationship between velocity and pressure is as follows: in, Represents the location point in the fluid field mesh interface H The corresponding corrected velocity interpolation amount; This represents the corrected velocity interpolation value corresponding to position point H in the fluid field mesh interface. And based on the pressure collected in the simulated water area p Obtain the sound pressure level at the corresponding sampling point, denoted as . ; in, This indicates the preset reference pressure.

4. The method for optimizing the structure of a low-frequency underwater acoustic transmitter based on finite element simulation according to claim 1, characterized in that, The acceleration function of the diaphragm in S2 is as follows: in, Indicates the maximum acceleration; This indicates the frequency of the control signal within the low-frequency underwater acoustic operating band. Represents the window function.

5. The method for optimizing the structure of a low-frequency underwater acoustic transmitter based on finite element simulation according to claim 1, characterized in that, In the process of obtaining the pressure-time variation curves of diaphragms with different radii at fixed monitoring points by solving the fluid field obtained in S3, the pressure of the diaphragm at different time points at fixed monitoring points is obtained by simulating the fluid field obtained by solving the fluid field obtained in S3 using the K-Epsilon turbulent finite element model. The turbulent kinetic energy in the K-Epsilon turbulent finite element model... and dissipation rate The transport equations are as follows: in, For time-averaged velocity components, and For spatial coordinates, and Customize source items for users; This represents the turbulent kinetic energy generated by the average velocity gradient; This represents the turbulent kinetic energy generated by buoyancy; This indicates the contribution of compressible turbulent pulsating expansion to dissipation; This represents the turbulent eddy viscosity coefficient, and ; Indicates fluid density; Indicates the dynamic viscosity of the fluid; , , , , and All are model constants.

6. The method for optimizing the structure of a low-frequency underwater acoustic transmitter based on finite element simulation according to claim 1, characterized in that, The diaphragm diameter ratio parameter in S4 represents the diaphragm's sagittal height or axial thickness along the vibration axis. a 0 and the radius of the section perpendicular to the vibration axis c The ratio of 0 to 1.

7. The method for optimizing the structure of a low-frequency underwater acoustic transmitter based on finite element simulation according to claim 1, characterized in that: In the process of coupling the low-frequency underwater acoustic emission transducer model with different shell outlines constructed in S5 with the generated fluid field mesh, the low-frequency underwater acoustic emission transducer model with different shell outlines includes at least: a transducer structure with a front diaphragm as a flat plate diaphragm, a transducer structure with a front diaphragm as an elliptical head diaphragm, and a double elliptical head transducer structure with both the front diaphragm and the tail end being elliptical heads.

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