Shallow sea full-waveguide low-frequency sound field modeling and component analysis method

Abstract

The invention discloses a shallow sea full-waveguide low-frequency sound field modeling and component analysis method, which comprises the following steps: establishing a shallow sea full-waveguide sound field model in a three-dimensional cylindrical coordinate system based on the setting that the seabed is a uniform isotropic elastic medium and considering the influence of non-horizontal terrain on sound wave propagation; discretizing a sound field by adopting a time domain finite element method, and introducing a perfect matching layer to process a boundary so as to absorb boundary sound waves and avoid reflection interference; inputting Ricker wavelet pulse signals into the shallow sea full-waveguide sound field model, and calculating propagation paths, energy distribution and fluctuation component characteristics of sound waves under different non-horizontal terrain conditions; sound field fluctuation components are analyzed on the basis of non-horizontal submarine topography, and grazing angle change, energy leakage and interaction between sound waves and the seabed are studied. The method can provide accurate description of complex submarine topography on sound wave propagation, also has an analysis function, and provides technical support for underwater acoustic target detection, resource exploration and marine environment monitoring.

Description

Technical Field

[0001] The invention belongs to the fields of ocean acoustics, hydroacoustic engineering and seabed resource detection, and in particular relates to a shallow sea full-waveguide low-frequency sound field modeling and component analysis method. Background Art

[0002] With the rapid development of underwater detection technology and the increasing demand for seabed resource exploration, the study of the propagation characteristics of very low frequency sound waves has gradually become a core issue in the field of hydroacoustics. Very low frequency sound waves are widely used in seabed resource exploration, marine environment monitoring and underwater communications due to their strong penetration ability and low attenuation characteristics. However, the current mainstream sound field calculation models are mostly based on the idealized horizontal seabed assumption, which makes it difficult to accurately reflect the significant impact of complex seabed topography (such as wedge-shaped slopes and submarine mountains) on sound wave propagation. This assumption limits the applicability and prediction accuracy of the model in actual shallow sea environments.

[0003] Existing studies have shown that complex non-horizontal seabed topography has an important influence on the propagation path, energy distribution and wave characteristics of the sound field. For example, reference [1] ("Analysis of acoustic field characteristics in shallow sea non-horizontal terrain", published in "Acta Physica Sinica" No. 64 in 2015, starting page 217) points out that the wedge-shaped upslope seabed will increase the grazing angle of the sound wave and enhance energy leakage, while the wedge-shaped downslope environment will extend the propagation distance of the sound wave. Reference [2] ("Study on interface wave characteristics under non-ideal seabed topography", published in "Acta Acoustica Sinica" No. 46 in 2018, starting page 128) shows that the propagation characteristics of interface waves (Scholte waves) also change significantly under non-horizontal seabed conditions, changing the distribution law of the sound field. However, although the existing simple normal wave model and frequency domain analysis method can calculate the energy distribution of the sound field, it is difficult to describe the dynamic characteristics and coupling laws of the multi-component sound waves under complex terrain environments. In addition, the propagation characteristics of very low frequency sound waves under non-horizontal terrain conditions also involve the excitation and conversion laws of seabed shear waves, longitudinal waves and interface waves. Reference [3] (“Numerical simulation of sound wave propagation under non-horizontal terrain”, published in Science China (Series G: Physics, Mechanics and Astronomy) No. 49 in 2020, starting at page 401) points out that the interaction of multiple wave components caused by complex terrain is difficult to fully characterize through simplified models, which is crucial for accurately predicting the sound field distribution and energy dissipation laws.

[0004] Therefore, developing a shallow-water full-waveguide low-frequency acoustic field modeling and component analysis method is of great theoretical and practical significance. This method needs to comprehensively consider the impact of complex terrain on the propagation of multi-component very low-frequency sound waves to improve the accuracy of the description of the acoustic field characteristics and provide technical support for ocean exploration, resource exploration and hydroacoustic engineering applications. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and propose a shallow sea full-waveguide low-frequency sound field modeling and component analysis method.

[0006] In view of this, the present invention proposes a shallow sea full-waveguide low-frequency sound field modeling and component analysis method, including:

[0007] Step 1: Based on the assumption that the seabed is a uniform isotropic elastic medium and considering the influence of non-horizontal terrain on sound wave propagation, a shallow sea full waveguide acoustic field model is established in a three-dimensional cylindrical coordinate system;

[0008] Step 2: The acoustic field is discretized using the time-domain finite element method, and a perfectly matched layer is introduced to process the boundary to absorb boundary sound waves and avoid reflection interference;

[0009] Step 3: Input the Ricker wavelet pulse signal into the shallow sea full waveguide acoustic field model to calculate the propagation path, energy distribution and wave component characteristics of the sound wave under different non-horizontal terrain conditions;

[0010] Step 4: Analyze the acoustic field fluctuation components based on the non-horizontal seabed topography to study the changes in grazing angles, energy leakage, and the interaction between sound waves and the seabed.

[0011] Preferably, the non-horizontal terrain in step 1 includes: a wedge-shaped uphill slope and an underwater mountain.

[0012] Preferably, the shallow sea full waveguide acoustic field model established in step 1 is: an ideal fluid seawater layer S w and uniform isotropic elastic seabed S b The liquid / solid two-layer environment model consists of the seawater layer S w The density and speed of sound of the sea floor S b The longitudinal wave speed, transverse wave speed and density are clearly defined;

[0013] Seawater layer S w Depth H 1 As the horizontal distance r changes, based on the axial symmetry of cylindrical coordinates, the mutual coupling of acoustic energy between each (r, z) vertical plane in each θ direction is ignored in the calculation, and the N×2D assumption is used to transform the three-dimensional sound field calculation into a calculation problem on the two-dimensional (r, z) plane, where θ is the angular coordinate on the horizontal plane, describing the propagation direction of the sound wave in the horizontal direction, and z is the height or depth coordinate in the vertical direction, describing the propagation of the sound wave in the vertical direction and the depth change of the seawater layer.

[0014] Preferably, the step 2 comprises:

[0015] A perfectly matched layer is set at the boundary of the solution area of ​​the shallow sea full waveguide acoustic field model.

[0016] Add an absorption coefficient to the finite element equation to transform the finite element equation into a PML equation:

[0017]

[0018] where σ is the absorption coefficient, v i , p i are the velocity and sound pressure amplitude in the perfectly matched layer domain respectively, k represents the wave number, ω is the angular frequency, σ i is the absorption coefficient, representing the absorption characteristics of the medium, p is the physical quantity sound pressure, is the partial derivative with respect to the spatial coordinate x i , the imaginary unit j is used to represent the propagation characteristics of the wave, i represents the index of different spatial directions, where i = 1, 2 corresponds to the two-dimensional space, and i = 1, 2,... represents the case applicable to higher dimensions.

[0019] Preferably, step 3 includes:

[0020] Input a Ricker wavelet pulse signal as the sound source in the shallow water full waveguide sound field model, set the frequency range to 10 - 100 Hz, and adjust the sound source position according to the requirements of the target research area; under different non-horizontal terrain conditions, obtain the dynamic evolution process of the sound field through numerical calculation, including the sound wave propagation path, energy distribution, and wave characteristics.

[0021] Preferably, step 4 includes:

[0022] Use a wedge-shaped upslope and seamount to analyze the sound wave propagation characteristics through the time-domain waveform diagram and sound pressure loss curve, and study how the change in the grazing angle affects energy leakage, propagation distance extension, and the interaction between the sound wave and the seabed.

[0023] Compared with the prior art, the advantages of the present invention are:

[0024] The present invention provides a high-precision shallow water full waveguide sound field modeling method applicable to complex non-horizontal seabed terrain, and this method has an analysis function. By introducing the finite element method in the time domain, the perfectly matched layer (PML), and the multi-path time delay difference calculation, the present invention can more accurately model the sound field of different seabed terrains, simulate the influence of sound wave propagation, and overcome the limitations of traditional methods in non-horizontal seabed environments. At the same time, by adopting the multi-waveguide sound field analysis method, not only can the accuracy of sound source localization be effectively improved, but also the wave components can be accurately identified, significantly enhancing the sound field simulation ability under complex terrain conditions in deep sea and shallow sea, while maintaining a high calculation efficiency. Description of the Drawings

[0025] Figure 1(a) is a schematic diagram of the model in a three-dimensional cylindrical coordinate system;

[0026] Figure 1(b) is a diagram of the solution area of ​​the finite element method in the two-dimensional (r, z) plane;

[0027] Figure 2 It is a schematic diagram of the rOz cross section of the ocean environment model under horizontal seabed topography;

[0028] Figure 3 is the Ricker wavelet pulse emitted by the sound source;

[0029] Figure 4 It is a schematic diagram of the rOz cross section of the ocean environment model under upslope seafloor topography;

[0030] FIG5( a ) is a snapshot of the sound field with a propagation time of 0.5 s in an uphill terrain with a slope of 0.72° in an embodiment of the present invention;

[0031] FIG5( b ) is a snapshot of the sound field with a propagation time of 0.6 s in an uphill terrain with a slope of 0.72° in an embodiment of the present invention;

[0032] FIG5( c ) is a snapshot of the sound field with a propagation time of 1.0 s in an uphill terrain with a slope of 0.72° in an embodiment of the present invention;

[0033] FIG5( d ) is a snapshot of the sound field with a propagation time of 2.0 s in an uphill terrain with a slope of 0.72° in an embodiment of the present invention;

[0034] FIG6( a ) is a snapshot of the sound field with a propagation time of 0.5 s in an uphill terrain with a slope of 1.43° in an embodiment of the present invention;

[0035] FIG6( b ) is a snapshot of the sound field with a propagation time of 0.6 s in an uphill terrain with a slope of 1.43° in an embodiment of the present invention;

[0036] FIG6( c ) is a snapshot of the sound field with a propagation time of 1.0 s in an uphill terrain with a slope of 1.43° in an embodiment of the present invention;

[0037] FIG6( d ) is a snapshot of the sound field with a propagation time of 2.0 s in an uphill terrain with a slope of 1.43° in an embodiment of the present invention;

[0038] Figure 7 is a shallow sea sound propagation path diagram of an uphill seabed in an embodiment of the present invention;

[0039] Figure 8 is a time domain waveform diagram of the time domain sound pressure under horizontal seabed and two types of uphill seabed conditions in an embodiment of the present invention;

[0040] Fig. 9 is a sound pressure propagation loss curve under three seabed environments at the same position in an embodiment of the present invention;

[0041] FIG10( a ) is a time domain signal waveform diagram of an uphill seabed acoustic field with a slope of 0.72° in an embodiment of the present invention;

[0042] FIG10( b ) is a time domain signal waveform diagram of the seabed acoustic field with a slope of 1.43° in an embodiment of the present invention;

[0043] FIG. 11( a ) is a curve diagram of acoustic energy loss in an uphill seabed acoustic field with a slope of 0.72° in an embodiment of the present invention;

[0044] FIG. 11( b ) is a curve diagram of acoustic energy loss in an uphill seabed acoustic field with a slope of 1.43° in an embodiment of the present invention;

[0045] Fig.12 It is a schematic diagram of the ocean environment model under the submarine mountain terrain;

[0046] FIG. 13( a ) is a snapshot of the sound field with a propagation time of 0.8 s under a submarine mountain terrain where the distance from the top of the submarine mountain to the water surface is 60 m in an embodiment of the present invention;

[0047] FIG. 13( b ) is a snapshot of the sound field with a propagation time of 1.1 s under a submarine mountain terrain where the distance from the top of the submarine mountain to the water surface is 60 m in an embodiment of the present invention;

[0048] FIG. 13( c ) is a snapshot of the sound field with a propagation time of 1.4 s under a submarine mountain terrain where the distance from the top of the submarine mountain to the water surface is 60 m in an embodiment of the present invention;

[0049] FIG. 13( d ) is a snapshot of the sound field with a propagation time of 1.7 s under a submarine mountain terrain where the distance from the top of the submarine mountain to the water surface is 60 m in an embodiment of the present invention;

[0050] FIG. 14( a ) is a snapshot of the sound field with a propagation time of 0.8 s under a submarine mountain terrain where the distance from the top of the submarine mountain to the water surface is 30 m in an embodiment of the present invention;

[0051] FIG14( b ) is a snapshot of the sound field with a propagation time of 1.1 s under a submarine mountain terrain where the distance from the top of the submarine mountain to the water surface is 30 m in an embodiment of the present invention;

[0052] FIG. 14( c ) is a snapshot of the sound field with a propagation time of 1.4 s under a submarine mountain terrain where the distance from the top of the submarine mountain to the water surface is 30 m in an embodiment of the present invention;

[0053] FIG. 14( d ) is a snapshot of the sound field with a propagation time of 1.7 s under a submarine mountain terrain where the distance from the top of the submarine mountain to the water surface is 30 m in an embodiment of the present invention;

[0054] FIG. 15( a ) is a time domain signal waveform comparison diagram of a submarine mountain with a distance of 30 m from the top of the submarine mountain to the water surface and a horizontal seabed in an embodiment of the present invention;

[0055] FIG15( b ) is a time domain signal waveform comparison diagram of the distance from the top of the submarine mountain to the water surface of 30 m and 60 m in an embodiment of the present invention;

[0056] Fig.16 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0057] The present invention provides a shallow sea full-waveguide low-frequency sound field modeling and component analysis method, which aims to solve the deficiencies in the existing technology in the study of complex seabed terrain sound fields. By establishing an accurate three-dimensional cylindrical coordinate model and combining the Perfect Matched Layer (PML) technology, this method can accurately simulate the influence of different non-horizontal seabed terrains (such as wedge-shaped slopes and seabed mountains) on the propagation of very low-frequency sound waves, and has an analysis function, which can comprehensively analyze the wave components such as sound waves, underwater waves, interface waves (Scholte waves), longitudinal waves and transverse waves, and reveal the influence mechanism of seabed terrain on the sound wave propagation path, energy leakage and interference effect.

[0058] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0059] Example

[0060] The embodiment of the present invention proposes a shallow sea full waveguide low-frequency sound field modeling and component analysis method. This method aims at the influence of non-horizontal seabed topography on the wave components of the sound field, and proposes a calculation and analysis method based on the time domain finite element method. By establishing a full waveguide model of shallow sea water and seabed, the propagation law and wave component characteristics of very low frequency sound waves under different non-horizontal terrain conditions can be effectively analyzed.

[0061] First, a shallow sea full-waveguide acoustic field model is constructed in a three-dimensional cylindrical coordinate system, assuming that the seawater is an ideal fluid and the seabed is a uniform isotropic elastic medium. Typical non-horizontal terrains such as wedge-shaped upslope, wedge-shaped downslope and submarine hills are allowed to be included. The perfect matching layer (PML) technology is used to process the infinite field boundary to absorb the sound wave energy and avoid reflection interference. Secondly, the model is numerically solved by the time-domain finite element method, and the Ricker wavelet pulse is input as the sound source signal to obtain the dynamic evolution information of the sound field over time, including the propagation path and energy distribution of wave components such as underwater sound waves, submarine interface waves (Scholte waves), submarine longitudinal waves and transverse waves. The wedge-shaped upslope and downslope terrains are simulated to analyze the influence of the change of the sound wave grazing angle on the energy leakage and propagation distance; the reflection and transmission laws of sound waves are studied for the submarine hill terrain, as well as its modulation effect on the sound field interference and energy distribution. Finally, the significant influence of non-horizontal terrain on the sound field is verified. The results show that uphill terrain accelerates the attenuation of acoustic energy and enhances the leakage effect; downhill terrain reduces leakage and extends the propagation distance; and submarine mountains significantly modulate the acoustic path and increase local energy loss. This method overcomes the limitations of the traditional horizontal seabed assumption and can effectively analyze the full waveguide acoustic field under non-horizontal terrain, providing theoretical support and technical tools for shallow water acoustic target detection, resource exploration and environmental monitoring.

[0062] The present invention simplifies the complexity of the model and has strong applicability. It can realize efficient calculation and precise analysis of the acoustic field fluctuation components under various non-horizontal terrain conditions in shallow sea environments, and provides a new solution for the field of underwater acoustic engineering.

[0063] The implementation process of the present invention is divided into the following steps: Fig.16 As shown:

[0064] Step 1: Establish a shallow sea full-waveguide acoustic field model in a three-dimensional cylindrical coordinate system, assuming that the seabed is a uniform isotropic elastic medium, and consider the influence of non-horizontal terrain (such as wedge-shaped upslope, downslope and submarine mountain) on sound wave propagation.

[0065] Firstly, a sound field calculation model of shallow sea full waveguide environment is established in a three-dimensional cylindrical coordinate system. The model consists of an ideal fluid seawater layer and an elastic seabed layer, and their density and sound velocity parameters are defined respectively. The model assumes that the seabed is a uniform isotropic elastic medium and allows the terrain to have non-horizontal characteristics, including a variety of typical terrains such as wedge-shaped upslope, wedge-shaped downslope and submarine mountains. The model also takes into account the multi-wave component characteristics of very low frequency sound waves.

[0066] A waveguide model that conforms to the characteristics of shallow sea environment is established in a three-dimensional cylindrical coordinate system, that is, an ideal fluid seawater layer S w and uniform isotropic elastic seafloor S b The liquid / solid two-layer environment model consists of the seawater layer S w Depth 1It changes with the horizontal distance r. Due to the axial symmetry of the cylindrical coordinates, the mutual coupling of the acoustic energy between the vertical planes (r, z) in each θ direction is ignored in the calculation, that is, the N×2D assumption is adopted to transform the three-dimensional sound field calculation into a calculation problem on the two-dimensional (r, z) plane. The schematic diagram of the waveguide model is shown in Figure 1(a).

[0067] In Figure 1(a): c w , w is the model fluid seawater layer S w The speed and density of sound in c p 、c s , b is the model elastic seabed S b The longitudinal wave speed, transverse wave speed and density in the cylindrical coordinate system; the point sound source coordinates are located on the axis z s Depth: H 1 (r) is the depth of the seawater layer. For the shallow seawater body / seafloor full waveguide model shown in Figure 1(a), the definition domain of the finite element method during the solution process is given in Figure 1(b).

[0068] Step 2: The acoustic field is discretized using the time-domain finite element method, and a perfectly matched layer (PML) is introduced to process the boundary to absorb boundary sound waves and avoid reflection interference.

[0069] The time-domain finite element method is used to discretize the acoustic field calculation area and transform the three-dimensional problem into a two-dimensional cylindrical coordinate plane problem. In order to simulate the sound wave propagation in the infinite far field, the model introduces a perfect matching layer (PML) at the boundary of the calculation area to absorb the boundary sound waves and avoid reflection interference to ensure the calculation accuracy.

[0070] Assuming that the seawater layer S w Discretized into a finite number of units and N nodes, the sound pressure p(r,t) at any point t in the space can be expressed as:

[0071] p(r, t) = N T (r)p′(t)

[0072] Where N(r) is the basis function N of each node element n (r) is arranged into a column vector, p′(t) is the sound pressure p at each node n (t) is a column vector composed of n=1,2,…,N.

[0073] For an ideal fluid seawater layer S w The sound pressure p(r,t) at the coordinate r, considering the point sound source, the wave equation satisfied by the sound pressure at this point is:

[0074]

[0075] Considering the elastic seabed S bIn the case of sound energy propagating in the system, it will be affected by not only longitudinal waves but also transverse waves. Therefore, the displacement motion equation is usually selected as the research object, and its form is:

[0076]

[0077] Where: s(r) is the displacement vector at the spatial coordinate point; λ and μ are the Lame constants; f is the body force. Applying the finite element method, it can also be discretized into a discrete form such as the wave equation:

[0078] s(r, t) = N T (r)s′(t)

[0079] Where N(r) is the basis function N of each node element n (r) is arranged into a column vector, s′(t) is the displacement s at each node n (t) is a column vector composed of n=1,2,…,N.

[0080] In the seawater layer S w and elastic sea floor S b At the liquid / solid interface, the boundary conditions follow:

[0081]

[0082] Where: n is the unit normal vector of the interface; is the gradient operator; ρ w is the fluid density; U is the displacement at the interface. Substituting the discretized acoustic pressure field and displacement field, its boundary conditions can be further expressed as:

[0083]

[0084] The stiffness matrix K ij and the damping matrix C ij , mass matrix M ij They are all n×n matrices, and the subscripts w, s, and τ represent the acoustic matrix, mechanical structure matrix, and coupling matrix, respectively. The coupling matrix is ​​defined as K τ 、M s , F st 、F wt are the coupled loads of the seabed and seawater media respectively.

[0085] Combined with the continuity condition on the fluid / elastic interface, the finite element discrete equation (4) in the coupled fluid layer and the discrete equation in the elastic seabed layer realizes the simultaneous solution of the acoustic field equations under the finite element method, and further realizes the solution of the physical objects studied in each layer of the medium.

[0086] In order to simulate the propagation of acoustic signals in an infinite ocean environment, a perfectly matched layer (PML) is set outside the solution area as shown in Figure 1(b). The finite element equation is converted into a PML equation by adding the absorption coefficient.

[0087]

[0088] Where σ is the absorption coefficient; v i , p i are the velocity and sound pressure amplitude in the matching layer domain, respectively, and i represents the index of different directions in space. The front i=1,2 corresponds to two-dimensional space, and the back i=1,2,… indicates that the formula is applicable to higher-dimensional situations. After PML is used to process the boundary, the Smerfield far-field extinction condition is met on the boundary layer, realizing the simulation of the infinite space around the waveguide.

[0089] Step 3: Input the Ricker wavelet pulse signal into the model and calculate the propagation path, energy distribution and wave characteristics of the sound wave under different non-horizontal terrain conditions.

[0090] Ricker wavelet pulse signals are input as sound sources in the model, and the frequency range is set to 10-100 Hz. The location of the sound source can be flexibly adjusted according to the needs of the target research area. Under different non-horizontal terrain conditions, the dynamic evolution of the sound field is obtained through numerical calculation, including the sound wave propagation path, energy distribution and wave characteristics.

[0091] First, the shallow ocean wave field under the horizontal seabed is discussed as a reference for the study of ocean wave field under non-horizontal seabed terrain. The acoustic parameters of the acoustic field model are set as follows: Figure 2 The seawater layer and the bottom layer are set as uniform isotropic fluid medium and elastic medium respectively. The sound source depth z is set during simulation s 20m underwater, horizontal seabed depth H 1 (r) is 100m; the sound source transmits a signal S(t) of Ricker wavelet pulse with a main frequency of f=50Hz, and its expression is given by the following formula, the waveform is as follows Figure 3 As shown in the figure, the time step is set to 0.2ms and the propagation time is set to 2.5s in the calculation.

[0092]

[0093] Step 4: Analyze the sound wave propagation characteristics under wedge-shaped upslope, downslope and submarine hills, and study the changes in grazing angles, energy leakage, and the interaction between sound waves and the seabed.

[0094] The following sound field characteristics under typical terrain conditions are simulated and analyzed:

[0095] (1) Wedge-shaped terrain: Study the changes in the sound wave propagation path under the wedge-shaped uphill terrain, and analyze the impact of increasing or decreasing the grazing angle on the sound wave energy leakage, the extension of the propagation distance, and the interaction between the underwater sound waves and the seabed.

[0096] Figure 4 The figure is a schematic diagram of the shallow sea environment model under the upslope seabed, and the horizontal propagation distance is set to 4000m. For the upslope seabed model, two wedge-shaped upslope terrains with slope angles α = 0.72° and 1.43° are set respectively, that is, the seabed rises by 50m and 100m from the initial position r = 0 to r = 4000m under the two terrains. During the simulation discussion, the sound source depth, the seabed depth at the initial position r = 0, the underwater acoustic parameters and the seabed acoustic parameters are set to be the same as Figure 2 Be consistent.

[0097] The simulation analyzes the impact of uphill seabeds with different slopes on the shallow sea acoustic field, and explores the propagation path, energy loss and fluctuation characteristics of sound waves under non-horizontal seabed terrain. Through the time domain waveform and sound pressure loss curve, the acceleration effect of the uphill seabed on the attenuation and leakage of sound wave energy is analyzed, and the propagation characteristics of Scholte waves on the seabed surface are studied, revealing the difference in the energy attenuation of sound waves in the water and the seabed surface due to slope changes, providing theoretical support for sound source positioning, environmental monitoring and underwater acoustic engineering applications. Figures 5 and 6 show snapshots of the sound field of two wedge-shaped uphill seabeds with slopes of 0.72° and 1.43° respectively. Figure 5(a) is a snapshot of the sound field with a propagation time of 0.5s under an uphill terrain with a slope of 0.72° in an embodiment of the present invention, Figure 5(b) has a propagation time of 0.6s, Figure 5(c) has a propagation time of 1.0s, and Figure 5(d) has a propagation time of 2.0s; Figure 6(a) is a snapshot of the sound field with a propagation time of 0.5s under an uphill terrain with a slope of 1.43°, Figure 6(b) has a propagation time of 0.6s, Figure 6(c) has a propagation time of 1.0s, and Figure 6(d) has a propagation time of 2.0s. A larger slope angle α causes the seabed to rise faster, the sound wave reflection period to be shorter, the sound waves with a smaller grazing angle to be converted into sound waves with a larger grazing angle, the total energy of the sound waves in the water decays faster, and the interference of the sound waves with a smaller grazing angle remaining in the far field is simpler. The sound propagation path of the uphill seabed is as follows: Figure 7 As shown, the sound wave grazing angle increases gradually, and the energy continues to leak to the seabed. Figure 8 and Fig. 9 The energy loss characteristics of the uphill seabed to the sound wave propagation are demonstrated. Figure 8 It shows that as the slope increases, the attenuation of sound waves in the upslope seabed becomes more significant and the sound energy decreases significantly. Fig. 9This trend is further verified. The increase in slope significantly increases the acoustic energy loss. Figures 10(a) and 10(b) show the time domain waveforms of the acoustic field of uphill seabeds with different slopes, respectively, indicating that the uphill seabed causes more acoustic wave energy to leak to the seabed, resulting in increased acoustic wave attenuation in the water and lower far-field energy. Figures 11(a) and 11(b) show the acoustic energy loss curves of the uphill seabed. The greater the slope, the more significant the acoustic energy loss in the water.

[0098] (2) Seamount topography: Study the reflection and transmission patterns of sound waves when passing through seamounts, and evaluate the modulation effect of seamounts on the sound wave propagation path and energy distribution.

[0099] Submarine mountains are another common non-ideal form, which has a more significant impact on shallow water sound propagation characteristics. Based on the above research, this section will discuss the impact of submarine mountains on the very low frequency sound field fluctuations in shallow water full waveguides. Fig.12 The diagram of the seabed mountain terrain model used in the study is shown in Figure 1. The seabed mountain is set to be an isosceles triangle with the center located at a horizontal distance of r = 2000m and a horizontal span of 1000m. ΔH is the distance from the top of the seabed mountain to the water surface. During the simulation discussion, the sound source depth, the seabed depth at the initial position of r = 0, the underwater acoustic parameters, and the seabed acoustic parameters are all set to be the same as Figure 3 Consistent.

[0100] The simulation analyzes the influence of submarine hills at different heights on the propagation of sound waves, and explores the modulation effect of submarine hill terrain on the propagation path, energy distribution and wave characteristics of sound waves. The sound wave reflection and transmission laws of submarine hills are analyzed, the propagation characteristics of sound waves in the front and rear areas are observed, and the influence of energy loss, interference phenomenon and sound wave leakage are explored. At the same time, the energy changes of sound waves at different submarine hill heights are analyzed using time domain signal waveform diagrams, revealing the complex modulation effect of submarine hills on sound wave propagation, and providing theoretical support for acoustic exploration and hydroacoustic engineering. Figures 13 and 14 show snapshots of the sound field when the submarine hill is ΔH=60m and ΔH=30m from the sea surface, respectively. The propagation time of Figure 13(a) is 0.8s, the propagation time of Figure 13(b) is 1.1s, the propagation time of Figure 13(c) is 1.4s, and the propagation time of Figure 13(d) is 1.7s; Figure 14(a) is a snapshot of the sound field with a propagation time of 0.8s under the submarine mountain terrain with a distance of 30m from the top of the submarine mountain to the water surface; Figure 14(b) is a snapshot of the sound field with a propagation time of 1.1s; Figure 14(c) is 1.4s, and Figure 14(d) is 1.7s.

[0101] Comparative analysis shows that the presence of submarine hills rapidly increases the sound wave propagation angle, and some sound waves penetrate into the seabed and are converted into longitudinal and transverse waves, while sound waves with a depth less than ΔH = 60m are almost unaffected. Larger submarine hills have a more significant hindering effect on sound wave propagation, resulting in enhanced interference and increased reflected sound wave energy, further proving the significant influence of submarine hill geometric characteristics on low-frequency sound wave propagation. Figures 15(a) and 15(b) show the stress time domain waveforms of underwater sound waves at different submarine hill heights (70m and 40m). The results show that the sound wave energy is equal at 1500m, the sound field with submarine hills at 2000m receives more energy, and the opposite is true at 2500m and 3000m. Higher submarine hills (70m) lead to more sound energy loss, especially between 2000m and 2500m, where the sound energy gradually weakens.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A shallow sea full waveguide low-frequency sound field modeling and component analysis method, comprising: Step 1: Based on the assumption that the seabed is a uniform isotropic elastic medium and considering the influence of non-horizontal terrain on sound wave propagation, a shallow sea full waveguide acoustic field model is established in a three-dimensional cylindrical coordinate system; Step 2: The acoustic field is discretized using the time-domain finite element method, and a perfectly matched layer is introduced to process the boundary to absorb boundary sound waves and avoid reflection interference; Step 3: Input the Ricker wavelet pulse signal into the shallow sea full waveguide acoustic field model to calculate the propagation path, energy distribution and wave component characteristics of the sound wave under different non-horizontal terrain conditions; Step 4: Analyze the acoustic field fluctuation components based on the non-horizontal seabed topography to study the changes in grazing angles, energy leakage, and the interaction between sound waves and the seabed.

2. The shallow sea full-waveguide low-frequency sound field modeling and component analysis method according to claim 1 is characterized in that: The non-horizontal terrain in step 1 includes: wedge-shaped uphill slopes and submarine mountains.

3. The shallow sea full-waveguide low-frequency sound field modeling and component analysis method according to claim 1 is characterized in that: The shallow sea full waveguide acoustic field model established in step 1 is: ideal fluid seawater layer S w and uniform isotropic elastic seabed S b The liquid / solid two-layer environment model consists of the seawater layer S w The density and speed of sound of the sea floor S b The longitudinal wave speed, transverse wave speed and density are clearly defined; Seawater layer S w The depth H1 varies with the horizontal distance r. Based on the axial symmetry of cylindrical coordinates, the mutual coupling of acoustic energy between the (r, z) vertical planes in the θ direction is ignored in the calculation. The N×2D assumption is used to transform the three-dimensional sound field calculation into a calculation problem on the two-dimensional (r, z) plane, where θ is the angular coordinate on the horizontal plane, describing the propagation direction of the sound wave in the horizontal direction, and z is the height or depth coordinate in the vertical direction, describing the propagation of the sound wave in the vertical direction and the depth change of the seawater layer.

4. The shallow sea full-waveguide low-frequency sound field modeling and component analysis method according to claim 1 is characterized in that: The step 2 comprises: A perfectly matched layer is set at the boundary of the solution area of ​​the shallow sea full waveguide acoustic field model. Add the absorption coefficient to the finite element equation and transform the finite element equation into the PML equation: Where σ is the absorption coefficient, v i , p i are the velocity and sound pressure amplitude in the matching layer domain, k represents the wave number, ω is the angular frequency, σ i is the absorption coefficient, which indicates the absorption characteristics of the medium, p is the physical quantity sound pressure, is the spatial coordinate x i The imaginary unit j is used to represent the propagation characteristics of the wave, and i represents the index of different directions in space, where i=1,2 corresponds to two-dimensional space, and i=1,2,… indicates that it is applicable to higher-dimensional situations.

5. The shallow sea full-waveguide low-frequency sound field modeling and component analysis method according to claim 1 is characterized in that: The step 3 comprises: The Ricker wavelet pulse signal is input as the sound source in the shallow sea full-waveguide acoustic field model. The frequency range is set to 10-100 Hz, and the sound source position is adjusted according to the needs of the target research area. Under different non-horizontal terrain conditions, the dynamic evolution process of the sound field is obtained through numerical calculation, including the sound wave propagation path, energy distribution and wave characteristics.

6. The shallow sea full waveguide low-frequency sound field modeling and component analysis method according to claim 2 is characterized in that: The step 4 comprises: By using wedge-shaped upslopes and submarine hills, the propagation characteristics of sound waves are analyzed through time domain waveforms and sound pressure loss curves, and how changes in grazing angles affect energy leakage, propagation distance extension, and the interaction between sound waves and the seabed are studied.

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