Method for rapidly solving intensity directivity of low-frequency sound target

Abstract

The invention provides a method for rapidly solving intensity directivity of a low-frequency sound target. The method comprises the following steps: (1) constructing a geometric model of an underwater structure and carrying out grid division on the geometric model; (2) establishing a linear equation set of the structure surface by using a finite element method, and solving the equation set by using an LU decomposition method to obtain a sound pressure level of the structure surface; (3) defining and initializing a matrix used for storing field point information according to structure surface nodes, discretizing a Helmholtz integral equation by using numerical integration, and constructing and storing as a field point matrix; (4) calculating the field point sound pressure based on the results of the structure surface sound pressure level and the field point matrix, and obtaining the full-space sound target intensity of the underwater structure; and (5) ensuring that the geometric model can realize sound target intensity directivity real-time calculation of the structure at different incident angles and excitation source positions under different incident angles and excitation source positions.

Description

Technical Field

[0001] The invention belongs to the technical field of underwater detection simulation, and in particular relates to a method for quickly solving the intensity directivity of a low-frequency acoustic target. Background Art

[0002] In the fields of underwater target detection, ship stealth design, underwater acoustic communications, and marine engineering, target strength (TS) is an important physical quantity used to measure the detectability of underwater targets, especially in the low-frequency band. Low-frequency sound waves (10Hz–100Hz) exhibit greater penetration and lower propagation attenuation in complex marine environments due to their longer wavelengths, enabling them to maintain a high signal-to-noise ratio during long-range detection. However, the interaction between low-frequency sound waves and underwater structures involves complex scattering mechanisms, including reflection, diffraction, and elastic vibration coupling effects. This makes the acoustic scattering characteristics of target structures play a decisive role in far-field identification. Therefore, accurately predicting the target strength and directivity of underwater structures in the low-frequency band is of great significance for optimizing ship design, improving acoustic stealth performance, and enhancing underwater detection capabilities.

[0003] At present, the numerical simulation of low-frequency acoustic target intensity mainly relies on the finite element method (FEM) and the boundary element method (BEM). Traditional methods require the assembly, solution and field point integration of the system matrix in a single calculation, which is significantly time-consuming. Especially when the incident angle or the position of the excitation source changes, existing commercial software (such as COMSOL and ANSYS) needs to repeatedly reconstruct the global stiffness matrix and mass matrix, and recalculate the Green's function integral of the field point matrix. For large-scale structures or high-precision mesh models, this process will consume a lot of computing resources, resulting in low computational efficiency and difficulty in meeting the real-time analysis requirements of multiple working parameters (such as multiple incident angles and multiple excitation sources).

[0004] In recent years, the engineering field has introduced several optimization strategies, such as matrix pre-decomposition techniques and parallel computing acceleration, but their application remains limited. While matrix pre-decomposition can reduce repetitive calculations, it cannot solve the problem of real-time updates of the field matrix. Parallel computing is highly dependent on hardware resources, making it difficult to efficiently deploy on common computing platforms. Furthermore, the unique nature of low-frequency acoustic problems further exacerbates the computational challenges: due to the long wavelength, a more refined mesh is required to ensure accuracy, which significantly increases the computational burden. Summary of the Invention

[0005] Purpose of the invention, in response to the above problems, the present invention proposes a method for quickly solving the intensity directivity of low-frequency acoustic targets. This method realizes the rapid calculation and real-time response of the acoustic target intensity under different incident angles and excitation source positions under the condition of fixed excitation frequency through an innovative calculation optimization scheme. Specifically, the method first constructs a geometric model of the underwater structure and performs meshing, uses the finite element method to establish a linear equation group for the surface of the structure, and solves the surface sound pressure distribution through LU decomposition; then, by discretizing the Helmholtz integral formula, the frequency-related field point matrix is ​​pre-calculated and stored; finally, combined with the predefined field points, the far-field sound pressure in each direction is quickly obtained through post-processing integration, and then the intensity directivity of the acoustic target is calculated. This method avoids the overhead of repeatedly assembling the system matrix in the traditional method through matrix reuse and preprocessing technology, significantly improves the computational efficiency, is particularly suitable for large-scale structures and multi-operating parameter scenarios, and provides efficient support for underwater acoustic analysis.

[0006] Technical solution: To achieve the above-mentioned purpose, the present invention proposes a method for quickly solving the intensity directionality of low-frequency sound targets, which includes the following steps:

[0007] (1) Construct a geometric model of the underwater structure and perform meshing;

[0008] (2) Using the finite element method to establish a linear equation system for the structural surface, the equation system is solved by the LU decomposition method to obtain the sound pressure level on the structural surface;

[0009] (3) Define and initialize a matrix for storing field point information based on the surface nodes of the structure, discretize the Helmholtz integral equation using numerical integration, construct and store it as a field point matrix;

[0010] (4) Based on the surface sound pressure level of the structure and the results of the field point matrix, the field point sound pressure is calculated to obtain the full-space acoustic target intensity of the underwater structure;

[0011] (5) The geometric model is set to a frequency range of 10 Hz to 100 Hz. Under the condition of fixed excitation frequency, when switching different incident angles and excitation source positions, the real-time calculation of the acoustic target intensity directivity of the structure is realized.

[0012] Furthermore, in step (1), constructing a geometric model of the underwater structure includes:

[0013] An ellipsoid model is adaptively established according to the model size, and a PML (Perfect Matched Layer) layer is added. The PML thickness is 1 / 2 to 1 / 4 of the wavelength to simulate ocean acoustic conditions. When meshing the structure, the maximum mesh size is no larger than 1 / 6 of the wavelength as a prerequisite for ensuring calculation accuracy.

[0014] Furthermore, in step (2), determining the sound pressure level of the structure surface includes: based on the divided grid file, reading the surface node coordinates and unit node number data, using the finite element method to establish a linear equation group of the structure surface, assembling the sparse matrix of the linear equation group to obtain a global sparse matrix, decomposing the global sparse matrix by the LU decomposition method, calculating the linear equation group by LU solution, and obtaining the sound pressure level of the structure surface includes:

[0015]

[0016] in, is a global sparse matrix, [p] is the sound pressure value vector of the structure surface node, [F] is the external excitation vector; for the global sparse matrix After LU decomposition, the linear equations are solved to obtain the sound pressure values ​​of the nodes on the surface of the structure;

[0017]

[0018] Where [K] is the global stiffness matrix, [M] is the global mass matrix, [C] is the damping matrix, and w is the angular frequency.

[0019] Furthermore, in step (3), determining the field point matrix includes:

[0020] Based on the read surface node data, the matrix storing the field point information is initialized, the Helmholtz integral is discretized through numerical integration, and the Helmholtz integral is converted into the contribution of each unit to the field point sound pressure. The solution includes:

[0021]

[0022] Among them, A coeff,m It is the contribution of the normal derivative of the Green's function to the sound pressure at the field point. Traverse all units and add the contribution of the normal derivative of the local Green's function of each unit to the field point matrix A, N according to the global degree of freedom number of its node. m (r′) is the shape function, is the normal derivative of the Green's function;

[0023] B coeff,m =∫ element N m (r′)G(r,r′)dS′

[0024] Among them, B coeff,m It is the contribution of Green's function to the field point sound pressure. Traverse all units and add the contribution of each unit's local Green's function to the field point matrix B according to the global degree of freedom number of its node. m(r′) is the shape function, and G(r,r′) is the Green's function.

[0025] Furthermore, in step (4), the acoustic target intensity is calculated:

[0026]

[0027] Among them, TS is the acoustic target intensity, I r is the scattered sound intensity, I i is the incident sound intensity.

[0028] Furthermore, in step (5), the numerical real-time response to the whole-space acoustic target intensity of the structure includes:

[0029] S101, when the user inputs an external excitation frequency in the range of 10 Hz to 100 Hz and keeps it fixed, the global sparse matrix in the linear equations constructed by the finite element method remains unchanged. The global stiffness matrix [K] is independent of the frequency f, and the global mass matrix [M] is independent of the frequency. At the same time, when the frequency f remains unchanged, ω also remains unchanged, and the global sparse matrix does not need to be recalculated.

[0030] S102, when the external excitation frequency is not changed, the global sparse matrix Only one LU decomposition is performed, and when the excitation source term F is changed, the surface acoustic pressure value p of the structure under different excitations is solved;

[0031] S103, when the external excitation frequency is not changed, the Helmholtz decomposition is discretized and the calculation of the field point sound pressure is written as a matrix form P(x) = S x p, S x is the combined field point matrix, where S x =A+B, which is only related to the structure shape and frequency f. Therefore, when the external excitation frequency remains unchanged, the field point matrix does not need to be calculated multiple times. By reusing the field point matrix, the calculation efficiency of the field point sound pressure is improved.

[0032] S104, based on the calculation result of the field point sound pressure P(x) in S103, calculate the scattered sound intensity using the sound intensity formula Incident sound intensity Where ρ is density, c is sound velocity, and P0 is the incident sound pressure amplitude; substitute the scattered sound intensity and the incident sound intensity into the definition of the sound target intensity: Under the condition of a fixed excitation frequency, it is only necessary to update the excitation source term F and reuse the pre-decomposed LU factors and field point matrix to achieve real-time response calculation of the acoustic target intensity under different incident angles or excitation source positions.

[0033] In addition, the present invention provides a computer program product that can be run on any computer device including a memory and a processor. The computer program product includes executable instructions. When the instructions are executed, any one of the above-mentioned calculation methods is implemented.

[0034] Beneficial effects: Compared with the prior art, the present invention has the following beneficial technical effects:

[0035] The present invention avoids the overhead of reassembling the system matrix and the calculation field point matrix each time the excitation conditions change by calculating and reusing the frequency-dependent matrix in the preprocessing stage, thereby achieving rapid simulation and real-time response to different excitation working conditions under the condition of fixed excitation frequency, significantly improving the efficiency of low-frequency acoustic target intensity calculation, and is suitable for large-scale acoustic analysis tasks in multi-angle and multi-source position scenarios. At present, for the real-time solution of acoustic target intensity at different incident angles and different excitation source positions at a specific frequency, existing simulation software needs to reassemble the system matrix and the calculation field point matrix each time the incident conditions change, and cannot achieve real-time response to the solution of acoustic target intensity. This method significantly improves the calculation efficiency and is suitable for large-scale, multi-working condition parameter scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] To more clearly understand the exemplary embodiments of the present invention and its potential advantages and core features, please read the following detailed description in conjunction with the accompanying drawings. It should be noted that the accompanying drawings only provide several embodiments by way of example and do not constitute any limitation of the present invention:

[0037] Figure 1 Flowchart of a method for quickly solving the directivity of low-frequency sound targets according to the present invention;

[0038] Figure 2 Schematic diagram of actual application scenario according to the present invention;

[0039] Figure 3 Schematic diagram of geometric modeling, PML layer construction, and meshing according to the present invention;

[0040] Figure 4 Schematic diagram of real-time response to acoustic target intensity solution according to the present invention. DETAILED DESCRIPTION

[0041] like Figure 1 As shown, the present invention proposes a method for quickly solving the intensity directionality of low-frequency acoustic targets, which includes the following steps:

[0042] (1) Construct a geometric model of the underwater structure and perform meshing;

[0043] (2) Using the finite element method to establish a linear equation system for the structural surface, the equation system is solved by the LU decomposition method to obtain the sound pressure level on the structural surface;

[0044] (3) Define and initialize a matrix for storing field point information based on the surface nodes of the structure, discretize the Helmholtz integral equation using numerical integration, construct and store it as a field point matrix;

[0045] (4) Based on the surface sound pressure level of the structure and the results of the field point matrix, the field point sound pressure is calculated to obtain the full-space acoustic target intensity of the underwater structure;

[0046] (5) The geometric model is set to a frequency range of 10 Hz to 100 Hz. Under the condition of fixed excitation frequency, when switching different incident angles and excitation source positions, the real-time calculation of the acoustic target intensity directivity of the structure is realized.

[0047] Furthermore, in step (1), constructing a geometric model of the underwater structure includes:

[0048] An ellipsoid model is adaptively established according to the model size, and a PML (Perfect Matched Layer) layer is added. The PML thickness is 1 / 2 to 1 / 4 of the wavelength to simulate ocean acoustic conditions. When meshing the structure, the maximum mesh size is no larger than 1 / 6 of the wavelength as a prerequisite for ensuring calculation accuracy.

[0049] Furthermore, in step (2), determining the sound pressure level of the structure surface includes: based on the divided grid file, reading the surface node coordinates and unit node number data, using the finite element method to establish a linear equation group of the structure surface, assembling the sparse matrix of the linear equation group to obtain a global sparse matrix, decomposing the global sparse matrix by the LU decomposition method, calculating the linear equation group by LU solution, and obtaining the sound pressure level of the structure surface includes:

[0050]

[0051] in, is a global sparse matrix, [p] is the sound pressure value vector of the structure surface node, [F] is the external excitation vector; for the global sparse matrix After LU decomposition, the linear equations are solved to obtain the sound pressure values ​​of the nodes on the surface of the structure;

[0052]

[0053] Where [K] is the global stiffness matrix, [M] is the global mass matrix, [C] is the damping matrix, and w is the angular frequency.

[0054] Furthermore, in step (3), determining the field point matrix includes:

[0055] Based on the read surface node data, initialize the matrix storing the field point information, and through numerical integration, discretize the Helmholtz integral to convert the Helmholtz integral into solving the contribution of the sound pressure of each unit to the field point, including:

[0056]

[0057] Wherein, A coeff,m is the contribution value of the normal derivative of the Green function to the sound pressure of the field point, and by traversing all units, the contribution of the normal derivative of the local Green function of each unit is accumulated to the field point matrix A according to the global degree of freedom number of its nodes, N m (r') is the shape function, is the normal derivative of the Green function;

[0058] B coeff,m = ∫ element N m (r')G(r,r')dS'

[0059] Wherein, B coeff,m is the contribution value of the Green function to the sound pressure of the field point, and by traversing all units, the contribution of the local Green function of each unit is accumulated to the field point matrix B according to the global degree of freedom number of its nodes, N m (r') is the shape function, and G(r,r') is the Green function.

[0060] Further, in step (4), the sound target intensity is calculated:

[0061]

[0062] Wherein, TS is the sound target intensity, I r is the scattered sound intensity, and I i is the incident sound intensity.

[0063] Further, in step (5), the numerical real-time response of the structure to the full-space sound target intensity includes,

[0064] S101, when the user inputs an arbitrary frequency in the range of 10Hz to 100Hz and fixes it, the global sparse matrix in the linear equation system constructed by the finite element is unchanged, the global stiffness matrix [K] is independent of the frequency f, the global mass matrix [M] is independent of the frequency, and when the frequency f is unchanged, ω is also unchanged, and the global sparse matrix does not need to be recalculated;

[0065] S102, without changing the external excitation frequency, the global sparse matrix is only decomposed once, and when the excitation source term F is changed, the sound pressure value p of the structure under different excitations is solved;

[0066] S103, when the external excitation frequency is not changed, the Helmholtz decomposition is discretized and the calculation of the field point sound pressure is written as a matrix form P(x) = S x p, S x is the combined field point matrix, where S x =A+B, which is only related to the structure shape and frequency f. Therefore, when the external excitation frequency remains unchanged, the field point matrix does not need to be calculated multiple times. By reusing the field point matrix, the calculation efficiency of the field point sound pressure is improved.

[0067] S104, based on the calculation result of the field point sound pressure P(x) in S103, calculate the scattered sound intensity using the sound intensity formula Incident sound intensity Where ρ is density, c is sound velocity, and P0 is the incident sound pressure amplitude; substitute the scattered sound intensity and the incident sound intensity into the definition of the sound target intensity: Under the condition of a fixed excitation frequency, it is only necessary to update the excitation source term F and reuse the pre-decomposed LU factors and field point matrix to achieve real-time response calculation of the acoustic target intensity under different incident angles or excitation source positions.

[0068] In addition, the present invention provides a computer program product that can be run on any computer device including a memory and a processor. The computer program product includes executable instructions, and when the instructions are executed, any one of the above-mentioned computing methods is implemented.

[0069] like Figure 2 As shown in the figure, active sound waves emitted by a surface ship propagate to the submarine's location. The sound waves vibrate the submarine's surface, and the sound waves, upon impacting the hull, produce scattering effects such as reflection and diffraction. To accurately simulate this reality, this method employs a refined modeling of the underwater submarine. Specifically, this method involves the following aspects: First, a precise geometric model is constructed based on the submarine's actual geometry and dimensions to ensure that the simulation accurately reflects the submarine's acoustic characteristics. Second, tiling is performed at different locations on the submarine's surface. By rationally setting the tile distribution and, in combination with the acoustic properties of the submarine material, realistic parameters such as reflection and transmission coefficients are set to simulate the effect of differences in the submarine's surface acoustic properties on sound wave scattering. Through these optimization measures, the simulated acoustic target intensity is closer to the actual measurement results, providing a reliable basis for accurate calculation and analysis of submarine stealth.

[0070] like Figure 3As shown in the figure, when modeling the structure, this method needs to adaptively construct an ellipsoid model according to the actual size of the model to ensure that the geometric shape can accurately represent the external features of the structure. When meshing the structure, in order to ensure the accuracy of the calculation results, the maximum size of the mesh is strictly controlled to be no more than 1 / 6 of the wavelength, thereby improving the accuracy of the simulation. In order to simulate the boundless underwater acoustic environment and avoid the non-physical reflection waves of sound waves at the simulation boundary, a PML (perfectly matched layer) needs to be added to the outer surface of the structure. The thickness of the PML is designed to be 1 / 4 to 1 / 2 of the wavelength to fully absorb the outgoing sound waves, simulate the natural attenuation characteristics of sound waves in the ocean, and ensure that the simulation results are closer to the actual underwater acoustic conditions.

[0071] like Figure 4 As shown in the figure, when calculating the target intensity of structure-borne sound, the linear equations constructed by the finite element method are used to pre-process the global sparse matrix by LU decomposition, and the decomposition factors are saved to reduce the overhead of repeated matrix decomposition in subsequent calculations. Before calculating the field point sound pressure, the field point matrix is ​​further pre-processed, and the contribution coefficient A of the field point matrix is ​​calculated and stored by numerical integration. coeff,m and B coeff,m This ensures efficient reuse of the field point matrix, thus avoiding redundant matrix calculations when switching the incident angle or excitation source position. This method can quickly respond to changes in incident angle and excitation source position at a fixed excitation frequency, enabling real-time calculation of the acoustic target intensity directivity.

[0072] The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiment. Any equivalent modifications or changes made by ordinary technicians in this field based on the contents disclosed in the present invention should be included in the protection scope recorded in the claims.

Claims

1. A method for quickly calculating the intensity directivity of a low-frequency acoustic target, characterized in that: The method comprises the following steps: (1) Construct a geometric model of the underwater structure and perform meshing; (2) Using the finite element method to establish a linear equation system for the structural surface, the equation system is solved by the LU decomposition method to obtain the sound pressure level on the structural surface; (3) Define and initialize a matrix for storing field point information based on the surface nodes of the structure, discretize the Helmholtz integral equation using numerical integration, construct and store it as a field point matrix; (4) Based on the surface sound pressure level of the structure and the results of the field point matrix, the field point sound pressure is calculated to obtain the full-space acoustic target intensity of the underwater structure; (5) The geometric model is set to a frequency range of 10 Hz to 100 Hz. Under the condition of fixed excitation frequency, when switching different incident angles and excitation source positions, the real-time calculation of the acoustic target intensity directivity of the structure is realized.

2. A method for quickly determining the intensity directivity of a low-frequency acoustic target according to claim 1, characterized in that: In step (1), constructing a geometric model of the underwater structure includes: An ellipsoid model is adaptively established according to the model size, and a PML (Perfect Matched Layer) layer is added. The PML thickness is 1 / 2 to 1 / 4 of the wavelength to simulate ocean acoustic conditions. When meshing the structure, the maximum mesh size is no larger than 1 / 6 of the wavelength as a prerequisite for ensuring calculation accuracy.

3. A method for quickly determining the intensity directivity of a low-frequency acoustic target according to claim 1, characterized in that: In step (2), determining the sound pressure level of the structure surface includes: based on the divided grid file, reading the surface node coordinates and unit node number data, using the finite element method to establish a linear equation group of the structure surface, assembling the sparse matrix of the linear equation group to obtain a global sparse matrix, decomposing the global sparse matrix by the LU decomposition method, calculating the linear equation group by LU solution, and obtaining the sound pressure level of the structure surface includes: in, is a global sparse matrix, [p] is the sound pressure value vector of the structure surface node, [F] is the external excitation vector; for the global sparse matrix After LU decomposition, the linear equations are solved to obtain the sound pressure values ​​of the nodes on the surface of the structure; Where [K] is the global stiffness matrix, [M] is the global mass matrix, [C] is the damping matrix, and w is the angular frequency.

4. A method for quickly determining the intensity directivity of a low-frequency acoustic target according to claim 1, characterized in that: In step (3), determining the field point matrix includes: Based on the read surface node data, the matrix storing the field point information is initialized, the Helmholtz integral is discretized through numerical integration, and the Helmholtz integral is converted into the contribution of each unit to the field point sound pressure. The solution includes: Among them, A coeff,m It is the contribution of the normal derivative of the Green's function to the sound pressure at the field point. Traverse all units and add the contribution of the normal derivative of the local Green's function of each unit to the field point matrix A, N according to the global degree of freedom number of its node. m (r ′ ) is the shape function, is the normal derivative of the Green's function; B coeff,m =∫ e1ement N m (r′)G(r,r′)dS′ Among them, B coeff,m is the contribution of the Green's function to the field point sound pressure. Traverse all units and add the contribution of the local Green's function of each unit to the field point matrix B according to the global degree of freedom number of its node. N m (r ′ ) is the shape function, G(r,r ′ ) is the Green's function.

5. The method for quickly determining the intensity directivity of a low-frequency acoustic target according to claim 1, wherein: In step (4), the acoustic target intensity is calculated: Among them, TS is the acoustic target intensity, I r is the scattered sound intensity, I i is the incident sound intensity.

6. A method for quickly determining the intensity directivity of a low-frequency acoustic target according to claim 5, characterized in that: In step (5), the real-time numerical response to the full-space acoustic target intensity of the structure includes: S101, when the user inputs an external excitation frequency in the range of 10 Hz to 100 Hz and keeps it fixed, the global sparse matrix in the linear equations constructed by the finite element method remains unchanged. The global stiffness matrix [K] is independent of the frequency f, and the global mass matrix [M] is independent of the frequency. At the same time, when the frequency f remains unchanged, ω also remains unchanged, and the global sparse matrix does not need to be recalculated. S102, when the external excitation frequency is not changed, the global sparse matrix Only one LU decomposition is performed, and when the excitation source term F is changed, the surface acoustic pressure value p of the structure under different excitations is solved; S103, when the external excitation frequency is not changed, the Helmholtz decomposition is discretized and the calculation of the field point sound pressure is written as a matrix form P(x) = S x p, S x is the combined field point matrix, where S x =A+B; S104, based on the calculation result of the field point sound pressure P(x) in S103, calculate the scattered sound intensity using the sound intensity formula Incident sound intensity Where ρ is density, c is sound velocity, and P0 is the incident sound pressure amplitude; substitute the scattered sound intensity and the incident sound intensity into the definition of the sound target intensity: Under the condition of a fixed excitation frequency, it is only necessary to update the excitation source term F and reuse the pre-decomposed LU factors and field point matrix to achieve real-time response calculation of the acoustic target intensity under different incident angles or excitation source positions.

7. A computer program product, operable on any computer device comprising a memory and a processor, characterized in that: The computer program product comprises executable instructions, which, when executed, implement the computing method according to any one of claims 1 to 6.

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