Water surface ship radiation sound field prediction method in underwater acoustic channel environment

Abstract

The invention discloses a water surface ship radiation sound field prediction method in an underwater acoustic channel environment, and relates to the technical field of ship radiation sound field prediction, and the method comprises the steps: dispersing a ship body wet surface, and symmetrically mapping the dispersed ship body wet surface to a position above a water surface; acquiring an acceleration vector at a field point on the wet surface element, determining a fluid-solid coupling boundary condition, and determining a radiation sound pressure theoretical formula by using a ball source distribution method; constructing a virtual spherical surface, arranging a plurality of field points, and solving a radiation sound pressure theoretical value at each field point by using a radiation sound pressure theoretical formula; and according to the equivalent relationship between the radiation sound pressure of the directional point sound source at each field point and the radiation sound pressure theoretical value, determining the sound pressure parameter of each directional point sound source, and determining the far-zone radiation sound field of the ship in the underwater acoustic channel environment by using an underwater acoustic propagation calculation method. According to the method, the ship is equivalent to the spherical sound source and the directive point sound source, so that the calculation amount is greatly reduced, and rapid prediction of the near-region and far-region radiation sound fields of the ship is realized.

Description

Technical Field

[0001] The present application relates to the technical field of ship radiation sound field prediction, and in particular to a method for predicting the radiation sound field of a surface ship in an underwater acoustic channel environment. Background Art

[0002] Acoustic radiation generated by underwater vibrations of ship structures has long been a key research topic in engineering and environmental protection. Therefore, rapid prediction of the radiated sound field from surface ships is crucial for applications such as acoustic field monitoring and vibration and noise reduction. However, since the actual ocean is not an ideal acoustic medium flow field, with complex underwater acoustic channel environmental factors such as seabed boundaries and seawater sound velocity stratification, far-field sound wave propagation no longer follows a simple linear law. Consequently, significant differences exist between the near- and far-field radiated sound fields of a ship.

[0003] With the development of numerical calculation technology, the finite element method (FEM), boundary element method (BEM) and wave superposition method have been widely used in the sound radiation analysis of complex structures. In theory, the finite element method can be used to calculate the sound radiation of any structure, but when calculating the far-field radiation sound field, as the calculation sea area widens, the gradually increasing number of grids causes the amount of calculation to grow exponentially, which makes it difficult to meet the engineering efficiency requirements. Similarly, the boundary element method and the wave superposition method also have the problem of huge amount of calculation when calculating the radiation sound field of large ships, and there are also problems of integral singularity, irregular frequency and matrix ill-conditioning, which will lead to distortion of the calculation results. At present, there is no method in the existing technology that can quickly and accurately predict the near-field and far-field radiation sound fields of large surface ships in the underwater acoustic channel environment. Summary of the Invention

[0004] In response to the above-mentioned problems and technical needs, this application proposes a method for predicting the sound field radiated by a surface ship in an underwater acoustic channel environment. The technical solution of this application is as follows:

[0005] A method for predicting the sound field radiated by a surface ship in an underwater acoustic channel environment comprises the following steps:

[0006] The wet surface of the hull below the water surface is discretized into multiple wet surface elements, and the acceleration vector of the hull shell vibration at the field point on each wet surface element is obtained;

[0007] Taking the water surface as the symmetry plane, all wet surface elements are symmetrically mapped to the surface above the water surface. The acceleration vectors at the field points on each wet surface element and its mapped wet surface element have the same magnitude and antisymmetric direction.

[0008] Based on the acceleration vectors at the field points on each wetted surface element and its mapping, the fluid-structure coupling boundary conditions at each wetted surface element and its mapping are determined. Based on the fluid-structure coupling boundary conditions, the theoretical formula for the radiated sound pressure of the ship at any field point is determined using the spherical source distribution method.

[0009] A virtual sphere is constructed with the origin of the ship coordinate system as the center, and multiple field points are arranged on the virtual sphere according to the field point arrangement requirements. The theoretical value of the radiation sound pressure at each field point on the virtual sphere is obtained by solving the radiation sound pressure theory formula. The radius of the virtual sphere is much larger than the length of the ship, and several directional point sound sources are arranged on the x-axis of the ship coordinate system.

[0010] According to the equivalent relationship between the radiation sound pressure of a directional point sound source at each field point on the virtual sphere and the theoretical value of the radiation sound pressure, the sound pressure parameters of each directional point sound source are determined; based on the sound pressure parameters of each directional point sound source, the underwater sound propagation calculation method is used to determine the far-field radiation sound field of the ship in the underwater acoustic channel environment.

[0011] A further technical solution is that for any directional point sound source m, the sound pressure parameters include the directivity coefficient Directivity coefficient Angle θ with space m and projection angle Related to, the space angle θ m It is the angle between the line connecting the field point on the virtual sphere and the directional point sound source m and the z-axis of the hull coordinate system, the projection angle It is the angle between the projection of the line connecting the field point on the virtual sphere and the directional point sound source m on the xy plane of the hull coordinate system and the x-axis of the hull coordinate system; the origin of the hull coordinate system is the projection position of the center of gravity of the ship on the water surface, the positive direction of the x-axis is from the stern to the bow, the positive direction of the y-axis is from the starboard to the port, and the positive direction of the z-axis is vertically upward; arranging multiple field points on the virtual sphere includes:

[0012] Determine the directivity coefficient of the directional point sound source m according to the calculation requirements of the underwater sound propagation calculation method The corresponding spatial angles θ m and projection angle combination;

[0013] According to the spatial angle and projection angle combination corresponding to the directivity coefficient of all directional point sound sources, the orientation of each field point corresponding to each spatial angle and projection angle combination is determined, and multiple field points are arranged at the intersection position of each field point orientation and the virtual sphere.

[0014] A further technical solution is that arranging multiple field points on the virtual sphere further includes:

[0015] On the virtual sphere, a predetermined number of field points are arranged at positions other than the intersection positions of the field point orientations corresponding to the directivity coefficients of all directional point sound sources and the virtual sphere, so as to achieve the field point arrangement requirement that the total number of combinations of spatial angles and projection angles corresponding to the directivity coefficients of all directional point sound sources is no more than the total number of field points arranged on the virtual sphere.

[0016] A further technical solution is that when the total number of combinations of spatial angles and projected angles corresponding to the directivity coefficients of all directional point sound sources is equal to the total number of field points arranged on the virtual sphere, determining the sound pressure parameters of each directional point sound source includes:

[0017] Determine the directional point sound source m at any field point r on the virtual sphere f The equivalent radiated sound pressure at And each directional point sound source is placed at the field point r f The radiation sound pressure at the superposition is the superimposed radiation sound pressure Equivalent radiated sound pressure It is related to the sound pressure parameter of the directional point sound source m, which characterizes the sound radiation characteristics of the directional point sound source;

[0018] According to the field point r f The superimposed radiation sound pressure at The theoretical value of the radiation sound pressure p(r f ) to determine the field point r f The equivalent equation of the radiated sound pressure at

[0019] The radiation sound pressure equivalent equations at all field points are combined to obtain the radiation sound pressure matrix equation, and the radiation sound pressure matrix equation is solved to obtain the sound pressure parameters of each directional point sound source.

[0020] A further technical solution is to place each directional point sound source at the field point r f The equivalent radiation sound pressure at the superposition is the superimposed radiation sound pressure M is the total number of directional point sound sources, and the integer parameter M≥1.

[0021] A further technical solution is that the sound pressure parameter also includes the sound pressure intensity of the directional point sound source;

[0022] According to the directivity coefficient of the directional point sound source m and sound pressure intensity I m , determine the directional point sound source m at any field point r on the virtual sphere f The equivalent radiated sound pressure at

[0023] Among them, R m is the directional point sound source m and the field point r f distance, i is the imaginary unit, and k is the wave number of the radiated sound wave in the water.

[0024] A further technical solution is to determine each wet surface element and any field point r on the wet surface element obtained by mapping n The fluid-structure interaction boundary conditions at include:

[0025] According to the boundary condition that the vibration velocity of the hull shell and the radiated sound wave velocity are equal in the normal direction of the hull wet surface, the arbitrary field point r on each wet surface element and its mapped wet surface element is determined. n The fluid-structure coupling boundary condition at is:

[0026]

[0027] Where a is the field point r n The acceleration vector at , n is the unit normal vector, Φ(r n ) is the velocity potential of the radiated sound waves generated by the vibration of the hull shell, i is the imaginary unit, ω is the angular frequency, represents the derivative with respect to the normal direction.

[0028] A further technical solution is to use underwater sound propagation calculation methods to determine the far-field radiation sound field of a ship in an underwater sound channel environment, including:

[0029] Based on the underwater acoustic channel environmental parameters, the underwater acoustic transfer function H of any directional point sound source m at any far field point r of the ship is determined using the underwater acoustic propagation calculation method. m (r);

[0030] According to the sound pressure parameters of the directional point sound source m and combined with the underwater acoustic transfer function H m (r), determine the actual radiated sound pressure of the directional point sound source m at the far field point r of the ship

[0031] The actual radiation sound pressure of each directional point sound source at the far field point r of the ship is superimposed to obtain the radiation sound pressure at the far field point r of the ship M is the total number of directional point sound sources, and the integer parameter M≥1; the far-field radiation sound field of the ship in the underwater acoustic channel environment is determined based on the radiation sound pressure at each far-field point of the ship.

[0032] A further technical solution is that the sound pressure parameters include directivity coefficient and sound pressure intensity; determine the actual radiation sound pressure of the directional point sound source m at the far field point r of the ship include:

[0033] According to the sound pressure intensity I of the directional point sound source m m , directivity coefficient Combined with the underwater acoustic transfer function H m (r), determine the actual radiated sound pressure of the directional point sound source m at the far field point r of the ship for:

[0034]

[0035] Among them, {H m (r)} represents the column vector of underwater acoustic transfer function, represents the directivity coefficient column vector, {·} T Represents matrix transpose.

[0036] Its further technical solution is that the spherical source point of the spherical source distribution method is arranged on the x-axis of the ship coordinate system, and the spherical source distribution method is used to determine the ship's position at any field point r n The theoretical formula for the radiation sound pressure at is:

[0037] p(r n )=-iωρ0Φ(r n )

[0038] Where i is the imaginary unit, ω is the angular frequency, ρ0 is the water density; Φ(r n ) is the velocity potential of the radiated sound waves generated by the ship vibration and r j is the jth spherical source point on the x-axis of the ship coordinate system, N s is the total number of spherical source points arranged on the x-axis of the hull coordinate system, N L is the order of the truncated spherical source, is the first type of spherical sound source of the jth spherical source point The source of strength, is the second type of spherical sound source of the jth spherical source point The source of strength; is the first type of spherical sound source of the jth spherical source point The spherical source function, is the second type of spherical sound source of the jth spherical source point spherical source function;

[0039] The first type of spherical sound source at the jth spherical source point Spherical source function The expression is:

[0040]

[0041] The second type of spherical sound source at the j-th spherical source point Spherical source function The expression is:

[0042]

[0043] Among them, R j is the j-th sphere source point r j With field point r n distance, k is the number of radiated sound waves in water, θ j is the j-th sphere source point r j With field point r n The spatial angle between the line connecting the two and the z-axis of the hull coordinate system is, is the j-th sphere source point rj With field point r n The angle between the projection of the line connecting the two on the xy plane of the hull coordinate system and the projection of the x-axis of the hull coordinate system; l is the spherical source order of the j-th spherical source point, is a spherical Hankel function of the second kind, P l () is the Legendre polynomial, P l 1 () is the associated Legendre function of the first-order derivative, and is a parameter used to improve the matrix properties and R c is a positive constant.

[0044] The beneficial technical effects of this application are:

[0045] The present application proposes a method for predicting the sound field radiated by a surface ship in an underwater acoustic channel environment. It creatively proposes to symmetrically map the wetted surface elements above the water surface, thereby realizing the symmetrical mirroring of the field points on the wetted surface elements above and below the water surface and the antisymmetric mirroring of the acceleration vector, which naturally satisfies the boundary condition that the sound pressure at the water surface is zero. The model constructed in this way is more in line with the actual water surface conditions and can more accurately predict the sound field radiated by the ship under the water surface boundary. Combined with the spherical source distribution method, the spherical source points are arranged on a line inside the hull, which fundamentally solves the problems of singular integrals and irregular frequencies. Overall, the three-dimensional acoustic problem is transformed into a quasi-one-dimensional discrete unit problem. Compared with the traditional boundary element method and wave superposition method, the amount of calculation is greatly reduced and the calculation efficiency is improved, thereby ensuring the rapid prediction of the sound field radiated in the near area of ​​the ship.

[0046] By constructing a virtual sphere centered at the origin of the ship's coordinate system and with a diameter much greater than the ship's length, and taking into account the fluctuations of far-field sound waves, the ship is simplified into a directional point sound source to simulate the ship's far-field radiated sound field. Based on the concept of equivalence of radiated sound pressure at a point on the virtual sphere in an unbounded ideal acoustic medium flow field, the sound pressure parameters of a directional point sound source equivalent to the entire surface ship are calculated. This allows the calculation of the realistic far-field radiated sound field of the ship in the underwater acoustic channel environment using underwater acoustic propagation calculation methods. This allows for rapid prediction of the far-field radiated sound field under the influence of the surface and seabed boundaries and the stratification of seawater sound velocity.

[0047] Considering that the sound radiation intensity of a directional point sound source varies at each field point, the underwater acoustic propagation calculation method only requires the sound pressure parameters at the specified field point location as input. The field points are arranged on the virtual sphere according to the calculation requirements of the underwater acoustic propagation calculation method to ensure that the number of equations in the constructed radiation sound pressure matrix equation is at least the same as the number of unknown quantities. The sound pressure parameters can then be obtained by solving the radiation sound pressure matrix equation. This method of field point arrangement ensures that valid sound pressure parameters are obtained while reducing unnecessary calculations, helping to further improve computational efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of the method for predicting the sound field radiated by surface ships.

[0049] Figure 2 It is a schematic diagram of the underwater acoustic channel environment model taking into account the influence of the undulating boundaries of the seabed.

[0050] Figure 3 It is a schematic diagram of the water surface symmetric mapping of the ship.

[0051] Figure 4 It is a schematic diagram of the wet surface element and the field points on the wet surface element obtained by mapping.

[0052] Figure 5 This is a schematic diagram of the distribution of spherical source points inside the ship.

[0053] Figure 6 The figure is a schematic diagram of a model corresponding to the upper and lower rigid body translation of a semi-cylindrical floating body in an embodiment.

[0054] Figure 7 This is a comparison chart of radiated sound pressure prediction results from an embodiment.

[0055] Figure 8 This is a schematic diagram showing that a ship is equivalent to three directional point sound sources. DETAILED DESCRIPTION

[0056] The specific implementation of this application will be further described below with reference to the accompanying drawings.

[0057] This application proposes a method for predicting the sound field radiated by a surface ship in an underwater acoustic channel environment. Please refer to Figure 1 The specific steps of the method are as follows:

[0058] Step 1: Discretize the wetted surface of the hull below the water surface into multiple wet bins and obtain the acceleration vector of the hull shell vibration at the field point on each wet bin. Using the water surface as the symmetry plane, all wet bins are symmetrically mapped above the water surface. The acceleration vectors at the field points on each wet bin and the corresponding wet bins have the same magnitude and antisymmetric direction.

[0059] The actual sea area is not an ideal medium flow field, such as Figure 2 As shown, the underwater acoustic channel environment in which a ship is located has factors such as the water surface boundary, the seabed boundary, and the seawater sound velocity stratification. The ship's radiated sound field can be divided into a near zone and a far zone. When predicting the near-zone radiated sound field of a ship, the influence of the underwater acoustic channel environment factors such as the seabed boundary and the seawater sound velocity stratification can be approximately ignored. However, the underwater acoustic channel environment has a significant impact on the ship's far-zone radiated sound field. Sound waves no longer propagate in a straight line. Therefore, the influence of the underwater acoustic channel environment factors such as the seabed boundary and the seawater sound velocity stratification cannot be ignored in the prediction of the ship's far-zone radiated sound field. The specific division of the near and far zones can be determined based on actual experience and experimental data.

[0060] First, the wetted surface of the hull below the water surface, where it contacts the water, is discretized into multiple wetted bins. Since the vibration of the hull shell is non-uniform and related to the hull structure, it is necessary to measure the acceleration vector of the hull shell vibration at a field point on each wetted bin. Specifically, an accelerometer is placed at a field point on each wetted bin to measure the normal acceleration at that point. When the number of accelerometers is insufficient to cover all wetted bins, the normal acceleration at the wetted bins without accelerometers can be interpolated from the normal accelerations measured by the already placed accelerometers to calculate the normal acceleration at the field points of the wetted bins without accelerometers, thereby obtaining the normal acceleration at all wetted bins. The present application does not restrict the specific method for discretizing the hull wetted surface; regular or irregular trapezoids, triangles, and other shapes can be used. Furthermore, there is no restriction on the size of each wetted bin. Since accelerometers cannot be placed at arbitrary locations in practical engineering applications, the present method facilitates the placement of accelerometers, compared to the traditional finite element and boundary element methods, which rely heavily on meshes, and is more conducive to practical engineering applications.

[0061] For the prediction of the near-zone radiated sound field of a ship, it is necessary to meet the boundary condition that the sound pressure at the water surface is zero. Since the ship floats on the water surface, only a part of the hull surface is in contact with the water. Directly using the boundary integral method to calculate the radiated sound field at the field point on the wet surface element where the hull contacts the water does not meet the water surface boundary condition, so there is a large deviation in the calculation result. In order to solve this problem, the present application creatively proposes to use the water surface as the symmetry plane to symmetrically map the wet surface elements on the wet surface of the hull to above the water surface, so as to construct a wet surface element model that meets the water surface boundary condition. Figure 3 As shown in the figure, the solid line part below the water surface is the actual wet surface of the hull, and the dotted line part above the water surface is the mapped wet surface of the hull. Each red point on the wet surface of the hull corresponds to a wet surface element, and the red point represents the field point on the wet surface element, where n represents the normal unit vector at the field point. Figure 3It can be seen that the field points on each wet surface element and the field points on the wet surface element obtained by its mapping are mirror-symmetric about the water surface, and the acceleration vectors at the field points on each wet surface element and the wet surface element obtained by its mapping are mirror-antisymmetric about the water surface.

[0062] For the total number of discrete wet facets, this application sets the number of wet facets to be greater than the number of spherical source points in the spherical source distribution method based on the calculation requirements. The specific location of the field points on the wet facets is set according to the actual application customization. This application arranges the field points at the center of the wet facets. Taking the irregular quadrilateral wet facet as an example, the wet facet and the field points on the wet facets obtained by mapping are shown in the figure below. Figure 4 shown.

[0063] Step 2: Determine the fluid-solid coupling boundary conditions at each wet surface element and the field points on the wet surface element obtained by mapping it according to the acceleration vectors at the field points on each wet surface element and the wet surface element obtained by mapping it; based on the fluid-solid coupling boundary conditions, use the spherical source distribution method to determine the theoretical formula for the radiation sound pressure of the ship at any field point.

[0064] Since the wet surface of the hull is the boundary where the ship contacts the water, it satisfies the fluid-solid coupling boundary condition. Specifically, at each field point on the wet surface, in one embodiment, the field points r on each wet surface element and its mapped wet surface element are determined. n The fluid-structure interaction boundary conditions at include:

[0065] According to the boundary condition that the vibration velocity of the hull shell and the radiated sound wave velocity are equal in the normal direction of the ship's wet surface, in the frequency domain calculation, the arbitrary field point r on each wet surface element and its mapped wet surface element is determined. n The fluid-structure coupling boundary condition at is:

[0066]

[0067] Where i is the imaginary unit, ω is the angular frequency, and a is the field point r n The acceleration vector at , n is the unit normal vector, Φ(r n ) is the velocity potential of the radiated sound waves generated by the vibration of the hull shell, represents the derivative with respect to the normal direction.

[0068] Based on the above fluid-structure coupling boundary conditions, the spherical source distribution method is used to calculate the sound field radiated by the ship in an unbounded ideal fluid medium. First, spherical source points are arranged inside the hull, such as Figure 5 As shown in the figure, the spherical source points of the spherical source distribution method are arranged on the x-axis of the hull coordinate system, with the intersection of the fore and stern of the hull longitudinal section and the water surface as the boundary, and the spherical source points are evenly distributed on the x-axis of the hull coordinate system. Each spherical source point is combined with two types of spherical sound sources. The first type is a spherical sound source with a sound field distribution symmetrical about the xz plane. The second type is a spherical sound source whose sound field distribution is antisymmetric about the xz plane. The origin of the hull coordinate system is the projection of the ship's center of gravity on the water surface. The positive x-axis points from the stern to the bow, the positive y-axis points from the starboard to the port, and the positive z-axis points vertically upward. For the specific calculation process of the spherical source distribution method, please refer to the applicant's published article "Zou, MS, Yang, YN, Liu, SXA spherical source distribution method for calculating acoustic radiation of elastic underwater structures. Engineering Analysis with Boundary Elements, 169 (2024) 105945."

[0069] The velocity potential of the radiated sound waves generated by the ship vibration Φ(r n ) is:

[0070]

[0071] Among them, r j is the jth spherical source point on the x-axis of the ship coordinate system, N s is the total number of spherical source points arranged on the x-axis of the hull coordinate system, N L is the order of the truncated spherical source, is the first type of spherical sound source of the jth spherical source point The source of strength, is the second type of spherical sound source of the jth spherical source point The source of strength; is the first type of spherical sound source of the jth spherical source point The spherical source function, is the second type of spherical sound source of the jth spherical source point spherical source function.

[0072] The first type of spherical sound source at the jth spherical source point Spherical source function The expression is:

[0073]

[0074] The second type of spherical sound source at the j-th spherical source point Spherical source function The expression is:

[0075]

[0076] Among them, R j is the j-th sphere source point rj With field point r n The distance from the source point r j =(x j ,0,0), field point r n =(x n ,y n ,z n ), k is the wave number of the radiated sound wave in water and k = ω / c0, c0 is the speed of sound in water; θ j is the j-th sphere source point r j With field point r n The spatial angle between the line connecting the two and the z-axis of the hull coordinate system is, is the j-th sphere source point r j With field point r n The angle between the projection of the line connecting the two on the xy plane of the hull coordinate system and the projection of the x-axis of the hull coordinate system, cosθ j =z n / R j , l is the spherical source order of the j-th spherical source point, is a spherical Hankel function of the second kind, P l () is the Legendre polynomial, P l 1 () is the associated Legendre function of the first-order derivative, and is a parameter used to improve the matrix properties and R c It is a positive constant, which can be taken as the minimum distance between the spherical source point and the wet surface element.

[0077] Substituting formula (2) into formula (1) we can get the field point r n The specific fluid-solid coupling boundary condition equation is:

[0078]

[0079] By using the least squares method to solve the overdetermined matrix equations composed of the fluid-structure coupling boundary condition equations at each field point, the source intensity at each spherical source point in formula (2) can be obtained. Substituting the source intensity back into formula (2) can calculate the ship's radiated sound wave velocity potential. Using a multiscale approach to matrix processing when solving overdetermined equations can effectively improve matrix ill-conditioning. For multiscale methods, please refer to the existing technology for implementation methods.

[0080] The radiation sound pressure in the flow field corresponds to the radiation sound wave velocity potential. Combining formula (2), we can get the ship in the frequency domain at any point r n The theoretical formula for the radiation sound pressure at is:

[0081] p(r n)=-iωρ0Φ(r n ) (6)

[0082] where i is the imaginary unit, ω is the angular frequency, and ρ0 is the water density.

[0083] Since the near-field radiation sound field can approximately ignore the influence of the underwater acoustic channel environmental factors such as the seabed boundary and the seawater sound velocity stratification, the fluid medium in which the surface ship is located is approximately an unbounded ideal acoustic medium flow field. Therefore, the radiation sound pressure theoretical formula of formula (6) can be used to calculate the near-field radiation sound field of the ship.

[0084] A simulation experiment was conducted to verify the accuracy of the proposed method in calculating the near-field radiated sound field of a ship. A finite element model of the upper and lower rigid body translation of a semi-cylindrical floating body with a diameter of 1 meter and a length of 3 meters on the water surface was constructed. The mapping diagram of the finite element model is shown in the figure below. Figure 6 The exact solution of the near-field radiation sound field of the semi-cylindrical floating body when it moves at unit speed is compared with the prediction result calculated by the method of this application. Figure 7 shown. Figure 7 (a) is the sound pressure level at a point 3 m below the center of the cylinder, Figure 7 (b) is the sound pressure level at a point 30 meters below the center of the cylinder. The calculation results of the sound pressure levels at the two points by the calculation method of the present application are in good agreement with the precise solution and have high accuracy.

[0085] Step 3: Construct a virtual sphere with the origin of the hull coordinate system as the center and arrange multiple field points on the virtual sphere according to the field point arrangement requirements; use the theoretical formula of radiation sound pressure to solve and obtain the theoretical value of radiation sound pressure at each field point on the virtual sphere; the radius of the virtual sphere is much longer than the hull length, and several directional point sound sources are arranged on the x-axis of the hull coordinate system. The radius of the virtual sphere is much longer than the hull length, which means that the difference between the size of the virtual sphere and the size of the hull reaches a predetermined threshold to achieve the effect of simulating the far zone, while ensuring that the virtual sphere completely surrounds the ship. In this application, the radius of the virtual sphere is set to several hundred meters.

[0086] Since the fluctuation mode of the spherical sound source does not meet the sound wave fluctuation mode of the ship's far zone, the spherical source point in the spherical source distribution method cannot be used as the ship's equivalent sound source point for calculating the ship's far zone radiation sound field. Considering that the underwater sound propagation calculation method needs to use a point sound source as input, and the fluctuation mode of the point sound source conforms to the sound wave fluctuation mode of the ship's far zone. In addition, considering the regularity of different sound radiation intensities at field points in different orientations of the hull vibration, this application uses a directional point sound source equivalent to a ship. Compared with conventional non-directional point sound sources, the sound radiation intensity of directional point sound sources changes with changes in orientation. Similarly, in order to simplify the calculation, the directional point sound source is arranged on the x-axis of the hull coordinate system. The specific number of directional point sound sources is set according to the hull structure and the calculation accuracy requirements. This application comprehensively considers the calculation amount and calculation accuracy, and arranges three directional point sound sources at the bow, middle, and stern of the hull based on the hull structure, such as Figure 8 As shown, the red * in the figure represents a directional point sound source.

[0087] Considering that the underwater sound propagation calculation method only requires the sound pressure parameters of the specified field point orientation as input, in order to reduce unnecessary calculations, there is no need to arrange too many field points. For any directional point sound source m, the sound pressure parameters include the directivity coefficient Directivity coefficient Angle θ with space m and projection angle Related to, the space angle θ m It is the angle between the line connecting the field point on the virtual sphere and the directional point sound source m and the z-axis of the hull coordinate system, the projection angle is the angle between the projection of the line connecting the field point on the virtual sphere and the directional point sound source m on the xy plane of the hull coordinate system and the x-axis of the hull coordinate system. In one embodiment, the specific method of arranging multiple field points on the virtual sphere is:

[0088] Determine the directivity coefficient of the directional point sound source m according to the calculation requirements of the underwater sound propagation calculation method The corresponding spatial angles θ m and projection angle combination;

[0089] According to the spatial angle and projection angle combination corresponding to the directivity coefficient of all directional point sound sources, the orientation of each field point corresponding to each spatial angle and projection angle combination is determined, and multiple field points are arranged at the intersection position of each field point orientation and the virtual sphere.

[0090] Since the spatial angle and projection angle corresponding to the field point on the virtual sphere can be any combination of angles from 0° to 360°, the calculation requirements of the underwater acoustic propagation calculation method only need to specify the directivity coefficient of the field point orientation as input. For example, the underwater acoustic propagation calculation method needs to calculate the directivity coefficient ξ of the field point m at the field point orientation with a spatial angle of 30° and a projection angle of 60°. m (30°, 60°). In this case, only the field points need to be placed at the intersection of the field point orientation and the virtual sphere, where the spatial angle is 30° and the projected angle is 60°. This approach is equivalent to limiting the granularity of the grid division, preventing redundant calculations and improving computational efficiency.

[0091] Each field point corresponds to a radiated sound pressure calculation equation for a directional point sound source. The unknowns in this equation include the directivity coefficient. To ensure that every directivity coefficient required for underwater sound propagation calculations can be solved, the number of radiated sound pressure calculation equations must be at least the same as the number of unknowns.

[0092] In one embodiment, arranging multiple field points on the virtual sphere further includes: arranging a predetermined number of field points at positions on the virtual sphere other than the intersection positions of the field point orientations corresponding to the directivity coefficients of all directional point sound sources and the virtual sphere, so as to achieve a field point arrangement requirement in which the total number of combinations of spatial angles and projected angles corresponding to the directivity coefficients of all directional point sound sources does not exceed the total number of field points arranged on the virtual sphere. The number of additional field points is set based on computational accuracy requirements, but it should be noted that, to ensure computational efficiency, an excessive number of additional field points should not be arranged.

[0093] Since the constructed virtual sphere is symmetrical with the water surface, after considering the water surface mirror image, the virtual sphere can be equivalent to an unbounded ideal acoustic medium fluid. Therefore, the theoretical value of the radiation sound pressure at each field point on the virtual sphere can be calculated using the radiation sound pressure theoretical formula of formula (6).

[0094] Step 4: Determine the sound pressure parameters of each directional point sound source based on the equivalent relationship between the radiation sound pressure of each directional point sound source at each field point on the virtual sphere and the theoretical value of the radiation sound pressure; based on the sound pressure parameters of each directional point sound source, use the underwater sound propagation calculation method to determine the far-zone radiation sound field of the ship in the underwater sound channel environment.

[0095] Specifically, when the total number of combinations of spatial angles and projected angles corresponding to the directivity coefficients of all directional point sound sources is equal to the total number of field points arranged on the virtual sphere, the specific steps for determining the sound pressure parameters of each directional point sound source are as follows:

[0096] (1) Determine the directional point sound source m at any field point r on the virtual sphere f The equivalent radiated sound pressure at And each directional point sound source is placed at the field point r f The radiation sound pressure at the superposition is the superimposed radiation sound pressure Equivalent radiated sound pressure It is related to the sound pressure parameter of the directional point sound source m, which characterizes the sound radiation characteristics of the directional point sound source.

[0097] In one embodiment, each directional point sound source is placed at a field point r f The equivalent radiation sound pressure at the superposition of the superimposed radiation sound pressure is:

[0098]

[0099] Where M is the total number of directional point sound sources, and the integer parameter M≥1.

[0100] The directivity coefficient is introduced into the calculation formula of the radiation sound pressure of the non-directional point sound source to obtain the calculation formula of the radiation sound pressure of the directional point sound source. In one embodiment, the sound pressure parameter also includes the sound pressure intensity of the directional point sound source; according to the directivity coefficient of the directional point sound source m and sound pressure intensity I m , determine the directional point sound source m at any field point r on the virtual sphere f The equivalent radiated sound pressure at is:

[0101]

[0102] Among them, R m is the directional point sound source m and the field point r f distance, i is the imaginary unit, and k is the wave number of the radiated sound wave in the water.

[0103] (2) According to the field point r f The superimposed radiation sound pressure at The theoretical value of the radiation sound pressure p(r f ) to determine the field point r f The equivalent equation of the radiated sound pressure at

[0104] (3) The radiation sound pressure equivalent equations at all field points are combined to obtain the radiation sound pressure matrix equation, and the radiation sound pressure matrix equation is solved to obtain the sound pressure parameters of each directional point sound source.

[0105] When the total number of combinations of spatial angles and projection angles corresponding to the directivity coefficients of all directional point sound sources is less than the total number of field points arranged on the virtual sphere, the sound pressure parameters of each directional point sound source can be solved by the least squares method. The specific content of the least squares method belongs to the existing technology and will not be repeated in this application.

[0106] After calculating the sound pressure parameters of each directional point sound source, they are input into the underwater sound propagation calculation method to calculate the far-field radiated sound pressure of the ship. In one embodiment, the specific method for determining the far-field radiated sound field of the ship in the underwater acoustic channel environment using the underwater sound propagation calculation method is as follows:

[0107] Based on the underwater acoustic channel environmental parameters, the underwater acoustic transfer function H of any directional point sound source m at any far field point r of the ship is determined using the underwater acoustic propagation calculation method. m (r) The underwater sound propagation calculation method can adopt the existing technical methods, such as the ray method, which takes into account the sound reflection and absorption effects of the seabed boundary and the sound refraction effect of the seawater sound velocity stratification.

[0108] According to the sound pressure parameters of the directional point sound source m and combined with the underwater acoustic transfer function H m (r), determine the actual radiated sound pressure of the directional point sound source m at the far field point r of the ship

[0109] The sound pressure parameters include directivity coefficient and sound pressure intensity, and the real radiated sound pressure of the directional point sound source at the far field point of the ship can be calculated based on the directivity coefficient and sound pressure intensity. In one embodiment, the real radiated sound pressure of the directional point sound source m at the far field point r of the ship is determined. include:

[0110] According to the sound pressure intensity I of the directional point sound source m m , directivity coefficient Combined with the underwater acoustic transfer function H m (r), determine the actual radiated sound pressure of the directional point sound source m at the far field point r of the ship for:

[0111]

[0112] Among them, {H m (r)} represents the column vector of the underwater acoustic transfer function. Since the directivity coefficient of a directional point sound source includes the directivity coefficients corresponding to the combination of multiple spatial angles and projection angles, the directivity coefficient of the directional point sound source m is Written in the form of a column vector, represents the directivity coefficient column vector, {·} T Represents matrix transpose.

[0113] The actual radiation sound pressure of each directional point sound source at the far field point r of the ship is superimposed to obtain the radiation sound pressure at the far field point r of the ship M is the total number of directional point sound sources, and the integer parameter M≥1. According to the radiation sound pressure at each far-field point of the ship, the radiation sound pressure distribution at each far-field point is determined, and then the far-field radiation sound field of the ship in the underwater acoustic channel environment is determined.

[0114] Since this application only calculates the sound propagation problem of three directional point sound sources, the amount of calculation is greatly reduced compared with traditional finite element, boundary element and other methods, and overall it achieves the rapid prediction of the far-zone radiation sound field of surface ships in the underwater acoustic channel environment.

[0115] The above description is only a preferred embodiment of the present application, and the present application is not limited to the above embodiments. It is understood that other improvements and variations directly derived or imagined by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the scope of protection of the present application.

Claims

1. A method for predicting the sound field radiated by a surface ship in an underwater acoustic channel environment, characterized in that: The method for predicting the sound field radiated by a surface ship comprises: The wet surface of the hull below the water surface is discretized into multiple wet surface elements, and the acceleration vector of the hull shell vibration at the field point on each wet surface element is obtained; Taking the water surface as the symmetry plane, all wet surface elements are symmetrically mapped to the surface above the water surface. The acceleration vectors at the field points on each wet surface element and its mapped wet surface element have the same magnitude and antisymmetric direction. Determine the fluid-structure coupling boundary conditions at each wetted surface element and the field points on the wetted surface element obtained by mapping thereof based on the acceleration vectors at the field points on each wetted surface element and the field points on the wetted surface element obtained by mapping thereof; and determine the theoretical formula for the radiation sound pressure of the ship at any field point using the spherical source distribution method based on the fluid-structure coupling boundary conditions; A virtual sphere is constructed with the origin of the hull coordinate system as the center, and multiple field points are arranged on the virtual sphere according to the field point arrangement requirements; the theoretical value of the radiation sound pressure at each field point on the virtual sphere is obtained by solving the radiation sound pressure theory formula; the radius of the virtual sphere is much larger than the hull length, and a plurality of directional point sound sources are arranged on the x-axis of the hull coordinate system; According to the equivalent relationship between the radiation sound pressure of the directional point sound source at each field point on the virtual sphere and the theoretical value of the radiation sound pressure, the sound pressure parameters of each directional point sound source are determined; based on the sound pressure parameters of each directional point sound source, the underwater sound propagation calculation method is used to determine the far-zone radiation sound field of the ship in the underwater sound channel environment.

2. The method for predicting the sound field radiated by a surface ship according to claim 1, characterized in that: For any directional point sound source m, the sound pressure parameters include the directivity coefficient The directivity coefficient Angle θ with space m and projection angle Related to, the space angle θ m It is the angle between the line connecting the field point on the virtual sphere and the directional point sound source m and the z-axis of the hull coordinate system, the projection angle is the angle between the projection of the line connecting the field point on the virtual sphere and the directional point sound source m on the xy plane of the hull coordinate system and the x-axis of the hull coordinate system; the origin of the hull coordinate system is the projection position of the center of gravity of the ship on the water surface, the positive direction of the x-axis is from the stern to the bow, the positive direction of the y-axis is from the starboard to the port, and the positive direction of the z-axis is vertically upward; Arranging a plurality of field points on the virtual spherical surface comprises: Determine the directivity coefficient of the directional point sound source m according to the calculation requirements of the underwater sound propagation calculation method The corresponding spatial angles θ m and projection angle combination; According to the spatial angle and projection angle combination corresponding to the directivity coefficients of all directional point sound sources, the orientation of each field point corresponding to each spatial angle and projection angle combination is determined, and multiple field points are arranged at the intersection position of each field point orientation and the virtual sphere.

3. The method for predicting the sound field radiated by a surface ship according to claim 2, characterized in that: Arranging a plurality of field points on the virtual spherical surface further comprises: On the virtual sphere, a predetermined number of field points are arranged at positions other than the intersection positions of the field point orientations corresponding to the directivity coefficients of all directional point sound sources and the virtual sphere, so as to achieve the field point arrangement requirement that the total number of combinations of spatial angles and projection angles corresponding to the directivity coefficients of all directional point sound sources is no more than the total number of field points arranged on the virtual sphere.

4. The method for predicting the sound field radiated by a surface ship according to claim 3, characterized in that: When the total number of combinations of spatial angles and projected angles corresponding to the directivity coefficients of all directional point sound sources is equal to the total number of field points arranged on the virtual sphere, the sound pressure parameters of each directional point sound source are determined as follows: Determine the directional point sound source m at any field point r on the virtual sphere f Equivalent radiated sound pressure at And each directional point sound source is placed at the field point r f The radiation sound pressure at the superposition is the superimposed radiation sound pressure The equivalent radiated sound pressure It is related to the sound pressure parameter of the directional point sound source m, which characterizes the sound radiation characteristics of the directional point sound source; According to the field point r f The superimposed radiation sound pressure at The theoretical value of the radiation sound pressure p(r f ) to determine the field point r f The equivalent equation of the radiated sound pressure at The radiation sound pressure equivalent equations at all field points are combined to obtain a radiation sound pressure matrix equation, and the radiation sound pressure matrix equation is solved to obtain the sound pressure parameters of each directional point sound source.

5. The method for predicting the sound field radiated by a surface ship according to claim 4, characterized in that: Place each directional point sound source at the field point r f The equivalent radiation sound pressure at the superposition is the superimposed radiation sound pressure M is the total number of directional point sound sources, and the integer parameter M≥1.

6. The method for predicting the sound field radiated by a surface ship according to claim 5, characterized in that: The sound pressure parameters also include the sound pressure intensity of the directional point sound source; According to the directivity coefficient of the directional point sound source m and sound pressure intensity I m , determine the directional point sound source m at any field point r on the virtual sphere f The equivalent radiated sound pressure at Among them, R m is the directional point sound source m and the field point r f distance, i is the imaginary unit, and k is the wave number of the radiated sound wave in the water.

7. The method for predicting the sound field radiated by a surface ship according to claim 1, characterized in that: The determination of each wet bin and any field point r on the wet bin obtained by mapping n The fluid-structure interaction boundary conditions at include: According to the boundary condition that the vibration velocity of the hull shell and the radiated sound wave velocity are equal in the normal direction of the hull wet surface, the arbitrary field point r on each wet surface element and its mapped wet surface element is determined. n The fluid-structure coupling boundary condition at is: Where a is the field point r n The acceleration vector at , n is the unit normal vector, Φ(r n ) is the velocity potential of the radiated sound waves generated by the vibration of the hull shell, i is the imaginary unit, ω is the angular frequency, represents the derivative with respect to the normal direction.

8. The method for predicting the sound field radiated by a surface ship according to claim 1, characterized in that: The method of determining the far-field radiation sound field of a ship in an underwater acoustic channel environment by using an underwater acoustic propagation calculation method includes: Based on the underwater acoustic channel environmental parameters, the underwater acoustic transfer function H of any directional point sound source m at any far field point r of the ship is determined using the underwater acoustic propagation calculation method. m (r); According to the sound pressure parameters of the directional point sound source m and combined with the underwater acoustic transfer function H m (r), determine the actual radiated sound pressure of the directional point sound source m at the far field point r of the ship The actual radiation sound pressure of each directional point sound source at the far field point r of the ship is superimposed to obtain the radiation sound pressure at the far field point r of the ship M is the total number of directional point sound sources, and the integer parameter M≥1; the far-field radiation sound field of the ship in the underwater acoustic channel environment is determined based on the radiation sound pressure at each far-field point of the ship.

9. The method for predicting the sound field radiated by a surface ship according to claim 8, characterized in that: The sound pressure parameters include directivity coefficient and sound pressure intensity; determine the real radiation sound pressure of the directional point sound source m at the far field point r of the ship include: According to the sound pressure intensity I of the directional point sound source m m , directivity coefficient Combined with the underwater acoustic transfer function H m (r), determine the actual radiated sound pressure of the directional point sound source m at the far field point r of the ship for: Among them, {H m (r)} represents the column vector of underwater acoustic transfer function, represents the directivity coefficient column vector, {·} T Represents matrix transpose.

10. The method for predicting the sound field radiated by a surface ship according to claim 7, characterized in that: The spherical source points of the spherical source distribution method are arranged on the x-axis of the ship coordinate system, and the spherical source distribution method is used to determine the position of the ship at any field point r n The theoretical formula for the radiation sound pressure at is: p(r n )=-iωρ0Φ(r n ) Where i is the imaginary unit, ω is the angular frequency, ρ0 is the water density; Φ(r n ) is the velocity potential of the radiated sound waves generated by the ship vibration and r j is the jth spherical source point located on the x-axis of the ship coordinate system, N s is the total number of spherical source points arranged on the x-axis of the hull coordinate system, N L is the order of the truncated spherical source, is the first type of spherical sound source of the jth spherical source point The source of strength, is the second type of spherical sound source of the jth spherical source point The source of strength; is the first type of spherical sound source of the jth spherical source point The spherical source function, is the second type of spherical sound source of the jth spherical source point spherical source function; The first type of spherical sound source at the jth spherical source point Spherical source function The expression is: The second type of spherical sound source at the j-th spherical source point Spherical source function The expression is: Among them, R j is the j-th sphere source point r j With field point r n distance, k is the number of radiated sound waves in water, θ j is the j-th sphere source point r j With field point r n The spatial angle between the line connecting the two and the z-axis of the hull coordinate system is, is the j-th sphere source point r j With field point r n The angle between the projection of the line connecting the two on the xy plane of the hull coordinate system and the projection of the x-axis of the hull coordinate system; l is the spherical source order of the j-th spherical source point, is a spherical Hankel function of the second kind, P l () is the Legendre polynomial, P l 1 () is the associated Legendre function of the first-order derivative, and is a parameter used to improve the matrix properties and R c is a positive constant.

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