Simulation and evaluation method of Doppler frequency shift characteristics of underwater vehicle's transmitting and receiving echoes

Abstract

The present invention provides a method for simulating and evaluating the Doppler frequency shift characteristics of echoes from a separate transmitting and receiving configuration for an underwater vehicle. The method primarily includes analyzing the overall design results of the underwater vehicle and sorting out structural modeling parameters; establishing a geometric structure simulation model for the underwater vehicle; establishing single-hull and double-hull underwater vehicle acoustic scattering prediction models based on the Kirchhoff approximation; and simulating and evaluating the Doppler frequency shift characteristics of echoes in different acoustic signal transmission frequency bands. The method quantitatively simulates and calculates the Doppler frequency shift characteristics of echoes from separate transmitting and receiving configurations for single-hull and double-hull underwater vehicles, significantly improving the rationality and accuracy of the evaluation results for the Doppler frequency shift characteristics of echoes from separate transmitting and receiving configurations for the underwater vehicle.

Description

Technical Field

[0001] The present invention relates to the technical field of simulation, prediction and analysis of Doppler frequency shift characteristics of echoes of underwater vehicles, and in particular to a method suitable for simulation and evaluation of Doppler frequency shift characteristics of echoes of underwater vehicles. Background Art

[0002] With the continuous development of underwater target positioning technology, acoustic signal-based underwater target positioning technology provides reliable technical services for target positioning and ensures the safety of underwater acoustic engineering projects. Therefore, underwater acoustic target positioning technology is gaining increasing attention and is widely used in military and civilian applications. In particular, when the underwater target and sensor are in relative motion, the Doppler effect produces Doppler frequency shift information between the sensor and the target. The sensor can use this Doppler frequency shift measurement information to locate the underwater target. However, there is a lack of effective calculation methods for the Doppler frequency shift characteristics of echoes detected by high-frequency sonar, and no evaluation methods based on quantitative calculation or simulation have been established.

[0003] During the overall design phase of the underwater vehicle, the overall design results include documents and drawings such as the overall design specification, basic structure design specification, line drawings, basic structure drawings, general layout drawings, and appendage structure drawings. The parameters such as the form, size, shell thickness of the underwater vehicle's inner shell structure, base structure, and side structure related to the overall design of the underwater vehicle, as well as the sound scattering characteristic indicators, active sonar sound source characteristic data and other information have been preliminarily clarified.

[0004] If a simulation and evaluation method for the Doppler frequency shift characteristics of the echoes of underwater vehicles with separate transmitters and receivers is established with these parameters as input, a quantitative risk assessment of the Doppler frequency shift characteristic indicators of the overall echo scheme of the underwater vehicle can be achieved, which can be used to evaluate and analyze the Doppler frequency shift characteristics of the echoes of underwater vehicles under multi-base detection, and has important practical application value. Summary of the Invention

[0005] Purpose of the invention: To provide a method suitable for simulating and evaluating the Doppler frequency shift characteristics of the echoes of the underwater vehicle with separate transmission and reception. The method can evaluate the Doppler frequency shift characteristics of different transmitting and receiving azimuths and acoustic signal transmission frequency bands based on the overall design plan of the underwater vehicle and with the sound source characteristic data of the separate transmission and reception active sonar as input, and compare the method with the requirements of the Doppler frequency shift characteristic indicators and the actual application needs to realize the risk assessment of the Doppler frequency shift characteristic indicators of the separate transmission and reception echoes.

[0006] Technical solution: A simulation and evaluation method for the Doppler frequency shift characteristics of the underwater vehicle's transmitting and receiving echoes includes the following steps:

[0007] Step 1. Based on the overall design results and structural modeling parameters of the underwater vehicle, a geometric structure simulation model of the underwater vehicle is established, which mainly includes:

[0008] Analyze the overall design results of the underwater vehicle, including the overall design specification, basic structure design specification, line drawings, basic structure drawings, general arrangement drawings and other documents and drawings, as well as the form, size, shell thickness and other parameters of the underwater vehicle's hull structure related to the overall design of the underwater vehicle; for structures without clear thickness parameters, refer to the relevant parameters of standard underwater vehicles for reference;

[0009] Step 2. Based on the geometric parameters determined in step 1, a full-scale geometric model of the underwater vehicle is established. The inner and outer shells of the geometric model are divided into triangular surface meshes, which mainly include:

[0010] Step 2.1: Based on the relevant data parameters obtained in Step 1, use a 3D modeling method to create a full-scale geometric model of the underwater vehicle structure. The model includes the form, structure, and dimensions of the inner and outer shells. The model does not need to be a solid model with thickness; only a shell model is required. The coordinate origin is preferably adjusted to the geometric acoustic center of the model.

[0011] Step 2.2: Use finite element software to divide the inner and outer shells of the real-scale geometric model of the underwater vehicle structure into triangular surface meshes, and export the topological information and node information of the meshes and save them as txt files respectively.

[0012] Step 3: Determine the coordinates of the incident and receiving points and describe them using the horizontal azimuth angle and the distance between the incident / receiving point and the equivalent geometric acoustic center of the underwater vehicle;

[0013] Step 4: Based on the single-hull structure or double-hull structure of the underwater vehicle, the reflection coefficient and transmission coefficient of the underwater vehicle shell at different frequencies are evaluated;

[0014] Step 5: Read the node information and triangular surface mesh file, draw the mesh models of the inner and outer shells respectively, and after setting the initial transmitting and receiving points, ensure that the normal direction of the mesh faces the outside of the underwater vehicle;

[0015] Step 6: Establishing an acoustic scattering evaluation model for the underwater vehicle hull through step 5;

[0016] Step 6.1 Kirchhoff approximation principle, assuming that at high frequencies, the contribution of the geometric shadow area to the sound field is ignored and the scatterer surface satisfies the rigidity condition. Ignore the time factor e -jw , the scattering wave potential function under the condition of separate transmitter and receiver is expressed as Where S is the scatterer surface; r1 and r2 are the radius vectors of the incident and scattering points, respectively, and are r when they are the same; α1 and α2 are the angles between the surface normal and the radius vectors of the incident and scattering points, respectively, and are α when they are the same; V(α) is the surface reflection coefficient;

[0017] Step 6.2: Based on the topological information and node information of the real-scale geometric model grid saved in step 2, use a program to read the txt files of its nodes and grids, and draw the grid models of the inner and outer shells respectively. After setting the initial transmitting and receiving points, check the normal of the grid to ensure that the normal of the grid is facing the outside of the underwater vehicle.

[0018] Step 6.3: Use the bin summation to obtain the total scattered sound pressure;

[0019] Step 7: Based on the basic principle of Doppler frequency shift, a simulation evaluation method for the Doppler frequency shift characteristics of the underwater vehicle's transmitted and received echoes is established.

[0020] Step 7.1 The basic principle of Doppler shift is to assume that the relative speed of the sound source and the target is vm / s and the carrier frequency of the signal is f c Hz, the propagation speed of the signal in the medium is cm / s, the angle between the transmission direction of the signal and the relative motion direction is θrad, and the Doppler shift frequency is f d Hz, the expression is:

[0021] Step 7.2 Simulation evaluation method for the Doppler frequency shift characteristics of the underwater vehicle's transmitted and received split echoes. Select a typical evaluation frequency and calculate how the underwater vehicle's Doppler frequency shift characteristics of the underwater vehicle's transmitted and received split echoes in different sound wave signal transmission frequency bands change with horizontal distance, as well as how the Doppler frequency shift frequency changes with relative speed at typical frequency points.

[0022] Principle of the invention: During the overall design phase, based on the overall design plan of the underwater vehicle, the Kirchhoff approximation is used to evaluate the echo Doppler frequency shift characteristics of different transmitting and receiving azimuths and acoustic signal transmission frequency bands using the characteristic data of the active sonar source with separate transmitting and receiving locations as input, and compared with the index requirements and actual application needs to realize the risk assessment of the echo Doppler frequency shift characteristic indicators of the underwater vehicle with separate transmitting and receiving locations.

[0023] Beneficial effects: The method of the present invention is reasonable and easy to implement. It overcomes the current lack of effective calculation difficulties for the echo Doppler frequency shift characteristics under high-frequency sonar detection at home and abroad, and the lack of an evaluation method based on quantitative calculation or simulation. It obtains the evaluation conclusion of the risk size of the echo Doppler frequency shift characteristic indicator of the overall plan through the comparison of indicator requirements, effectively solves the current calculation difficulties of the echo Doppler frequency shift characteristics under high-frequency sonar detection, and can greatly improve the rationality and accuracy of the simulation evaluation results of the echo Doppler frequency shift characteristics of the overall plan of the underwater vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the geometric model of a Benchmark underwater vehicle in a preferred embodiment of the underwater vehicle echo Doppler frequency shift characteristic simulation evaluation method of the present invention;

[0025] Figure 2 yes Figure 1 A schematic grid diagram of the underwater vehicle shell in the illustrated embodiment;

[0026] Figure 3 yes Figure 1 Schematic diagram of the hull grid of the Benchmark underwater vehicle in the embodiment shown;

[0027] Figure 4 yes Figure 1 A schematic diagram of the mesh normals of the Benchmark underwater vehicle hull in the illustrated embodiment;

[0028] Figure 5 yes Figure 1 Schematic diagram of the hull mesh normals of the Benchmark underwater vehicle in the embodiment shown;

[0029] Figure 6 yes Figure 1 In the embodiment shown, the calculation results of the Doppler frequency shift characteristics of the Benchmark underwater vehicle transmitting and receiving split echoes at a frequency of 20 to 40 kHz as a function of horizontal distance (-400 to 400 m) are shown;

[0030] Table 1 is Figure 1 The embodiment shown shows the variation of Doppler shift frequency with relative speed of the Benchmark underwater vehicle at a typical frequency of 20 to 40 kHz. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] The simulation and evaluation method of the Doppler frequency shift characteristics of the underwater vehicle's transmitting and receiving split echoes in this embodiment specifically includes:

[0034] Step 1. Based on the overall design results of the underwater vehicle and referring to the structural parameters of similar underwater vehicles, sort out the structural modeling parameters of the underwater vehicle: Analyze the overall design results of the underwater vehicle, including the overall design specification, basic structure design specification, line drawings, basic structure drawings, general arrangement drawings, and appendage structure drawings, and clarify the modeling parameters such as the form, size, shell thickness, and material properties of the hull structure of the underwater vehicle. For unclear thickness parameters and material properties, refer to the structural parameters of similar underwater vehicles, i.e., the mothership;

[0035] Step 2. Based on the geometric parameters determined in step 1, a full-scale geometric model of the underwater vehicle is established. The inner and outer shells of the geometric model are divided into triangular surface meshes, which mainly include:

[0036] Step 2.1 Based on the underwater vehicle structure modeling parameters obtained in step 1, a three-dimensional modeling method is used to establish a full-scale geometric simulation model of the underwater vehicle. The model includes the inner and outer shell structures, such as Figure 1 As shown, the established real-scale geometric model of the underwater vehicle structure ignores the internal structure of the inner shell and the between-ship structure in the real-scale geometric model of the underwater vehicle structure.

[0037] Step 2.2 Use COMSOL finite element software to divide the inner and outer shells of the underwater vehicle structure into triangular surface meshes as follows: Figure 2 and Figure 3 As shown, the topology information and node information of the grid are exported and saved as txt files respectively.

[0038] Step 3. Determine the coordinates of the incident / receiving point and describe them using the horizontal azimuth angle and the distance between the incident / receiving point and the equivalent geometric acoustic center of the underwater vehicle;

[0039] Set the coordinates of the incident point to x = -10000cos(θ×π / 180°), y = -10000sin(θ×π / 180°), z = 0, where θ is the angle between the signal transmission direction and the relative motion direction. Since the transmitter and receiver are separated, the coordinates of the signal incident / receiving points should not be in the same position. The receiving coordinates are x = -10000cos(145°×π / 180°), y = -10000sin(145°×π / 180°), z = 0.

[0040] Step 4. Based on the single-hull structure or double-hull structure of the underwater vehicle, the reflection coefficient and transmission coefficient of the underwater vehicle shell at different frequencies are evaluated;

[0041] Theoretical model calculation of the acoustic scattering problem of arbitrary multilayers For any layer l, the following acoustic wave potential function is defined:

[0042] φ l =[A l exp(iα l z)+B l exp(-ia l z)]exp[i(σx-ωt)] (1)

[0043] ψ t =[C t exp(iβ t z)+D t exp(-iβ t z)]exp[i(σx-ωt] (2) Among them, φ l is the longitudinal wave potential function, ψ t is the bending wave potential function.

[0044] B l and D t is the incident wave amplitude; A l and C t is the reflected wave amplitude, and:

[0045]

[0046]

[0047] σ l =k t sinθ l (5)

[0048] Among them, k l and K t are the wave numbers of longitudinal and flexural waves.

[0049] Through a series of derivation processes, the expression of the acoustic reflection coefficient can be finally obtained as follows:

[0050]

[0051] in,

[0052] C ij =F IJ -F 4J *F i1 / F 41 (7)

[0053] Z0=ρ0c0 / cosθ0 (8)

[0054] Z n+1 =ρ n+1 c n+1 / cosθ n+1 (9)

[0055] According to the condition that the sum of the squares of the reflection coefficient and the transmission coefficient is 1 when the loss is ignored, the projection coefficient can be calculated from the reflection coefficient;

[0056] Step 5. Based on the Kirchhoff principle, read the node information and triangular surface mesh file, draw the mesh models of the inner and outer shells respectively, and after setting the initial transmitting and receiving points, ensure that the normal direction of the mesh faces the outside of the underwater vehicle, such as Figure 4 and Figure 5 shown.

[0057] The basic principle of Kirchhoff principle is to assume that in high frequency conditions, the contribution of geometric shadow area to the sound field is ignored and the surface of the scatterer satisfies the rigidity condition. Ignore the time factor e -jwt , the scattering wave potential function under the condition of separate transmitter and receiver is expressed as Where S is the surface of the scatterer; r1 and r2 are the radius vectors of the incident point and the scattering point, respectively, and are r when they are the same; α1 and α2 are the angles between the outer normal direction of the surface and the radius vectors of the incident point and the scattering point, respectively, and are α when they are the same; V(α) is the surface reflection coefficient.

[0058] Step 6. Through step 5, establish an acoustic scattering evaluation model for the underwater vehicle shell, use the surface element summation to obtain the total scattered sound pressure, and then establish a simulation evaluation method for the Doppler frequency shift characteristics of the underwater vehicle's transmit and receive echo based on the basic principle of Doppler frequency shift.

[0059] Step 6.1 The basic principle of Doppler shift is to assume that the relative speed of the sound source and the target is vm / s and the carrier frequency of the signal is f c Hz, the propagation speed of the signal in the medium is cm / s, the angle between the transmission direction of the signal and the relative motion direction is θrad, and the Doppler shift frequency is f d Hz, the expression is:

[0060] Step 6.2 Simulation evaluation method for the Doppler frequency shift characteristics of the underwater vehicle's transmission and reception split echoes. Select a typical evaluation frequency of 20 to 40 kHz and calculate the variation of the Doppler frequency shift of the underwater vehicle's transmission and reception split echoes with the horizontal distance of -400 to 400 m in different acoustic signal transmission frequency bands, i.e., 20 to 40 kHz, with a 1 kHz analysis frequency step. Figure 6 shown.

[0061] The results of the Doppler shift frequencies at different typical frequency points, i.e., 20kHz, 25kHz, 30kHz, 35kHz, and 40kHz, changing with the relative speeds, i.e., 4 knots, 6 knots, and 12 knots, are shown in Table 1.

[0062] Table 1

[0063]

[0064] Example 2

[0065] This embodiment proposes to conduct a simulation evaluation of the Doppler frequency shift characteristics of the echo of the underwater vehicle with separate transmission and reception during the scheme design stage. According to the overall design scheme of the underwater vehicle, the Kirchhoff approximation and the basic principle of Doppler frequency shift can be used to evaluate the echo Doppler frequency shift characteristics of different sound wave signal transmission frequency bands with the characteristic data of the active sonar sound source with separate transmission and reception as input, and compare them with the index requirements to realize the risk assessment of the echo Doppler frequency shift characteristic index of the overall scheme.

[0066] The method comprises the following steps: 1. determining the geometric model parameters, material parameters and the coordinate origin of the geometric model of the underwater vehicle;

[0067] Step 2. Based on the geometric parameters determined in step 1, a full-scale geometric model of the underwater vehicle is established, and the inner and outer shells of the geometric model are divided into triangular surface meshes respectively;

[0068] Step 3. Determine the coordinate description method of the equivalent geometric acoustic center of the underwater vehicle and the far-field calculation point;

[0069] Step 4. Evaluate the reflection coefficient and transmission coefficient of the underwater vehicle shell at different frequencies and angles;

[0070] Step 5. Establish an acoustic scattering model for underwater vehicles;

[0071] Step 6. Establish a simulation and evaluation method for the Doppler frequency shift characteristics of the underwater vehicle's transmit and receive echoes.

[0072] Among them, the analysis of the overall design results of the underwater vehicle and the sorting of structural modeling parameters are mainly based on the sorting of the overall design data of the underwater vehicle, the extraction of structural drawings, line data, main hulls and command consoles and other design data required for evaluation modeling and acoustic scattering analysis; the establishment of the underwater vehicle geometric structure simulation model is mainly based on the relevant data parameters obtained in step 1, and a three-dimensional modeling method is used to establish a full-scale geometric simulation model of the underwater vehicle structure; the establishment of a single / double-hull underwater vehicle acoustic scattering prediction model based on the Kirchhoff approximation method is mainly based on the full-scale geometric simulation model of the underwater vehicle structure established in step 2, and the Kirchhoff approximation method (plate element method) is used to establish an underwater vehicle structure plate element acoustic scattering evaluation model; the simulation evaluation of the echo Doppler shift characteristics in different acoustic wave signal transmission frequency bands is based on the single / double-hull underwater vehicle acoustic scattering prediction model established in steps 3-5, combined with the basic principle of Doppler shift, selecting typical evaluation frequencies, and calculating the changes in the Doppler shift characteristics of the underwater vehicle's transmitted and received echoes in different acoustic wave signal transmission frequency bands with horizontal distance, as well as the Doppler shift frequency changes at typical frequency points. This method can realize the calculation of the Doppler frequency shift characteristics of the underwater vehicle's transmitted and received echoes. It has the advantages of fast calculation speed and reliable evaluation results. It can be widely used in the evaluation and design of underwater vehicle and underwater equipment acoustic targets, and evaluate the acoustic scattering characteristics of underwater equipment under multi-base detection.

Claims

1. A simulation and evaluation method for the Doppler frequency shift characteristics of the underwater vehicle's transmitting and receiving echoes, characterized in that The following steps are involved: Step 1. According to the overall design plan of the underwater vehicle, determine the structural geometric parameters, material parameters and the coordinate origin of the underwater vehicle geometric model; Step 2. Establish the overall outer contour geometric model of the underwater vehicle; divide the underwater vehicle geometric model into triangular surface meshes, and derive the topological information and node information of the meshes; Step 3. Determine the location of the sound wave incident / receiving point and describe it in the form of coordinates in the form of horizontal azimuth and the distance between the incident / receiving point and the equivalent geometric acoustic center of the underwater vehicle; Step 4. Based on the shell wall thickness and material parameters of the underwater vehicle, evaluate the reflection coefficient and transmission coefficient of the underwater vehicle shell at different frequencies and angles; Step 5. Read the node information and triangular surface mesh file, draw the mesh models of the inner and outer shells respectively, and after setting the initial transmitting and receiving points, ensure that the normal direction of the mesh faces the outside of the underwater vehicle; Step 6. Based on the Kirchhoff approximation principle, establish an acoustic scattering evaluation model for underwater vehicles and obtain the total scattered sound pressure by using the bin summation method. Step 7. Based on the basic principle of Doppler frequency shift, establish a simulation evaluation method for the Doppler frequency shift characteristics of the underwater vehicle's transmit and receive echoes.

2. The method for simulating and evaluating the Doppler frequency shift characteristics of the underwater vehicle's transmitting and receiving echoes according to claim 1 is characterized in that: The overall design results and structural modeling parameters of the underwater vehicle in step 1 include the overall design specification, basic structure design specification, line drawing, basic structure drawing and general arrangement drawing, and the underwater vehicle body shell structure form, size and shell thickness parameters related to the overall design of the underwater vehicle.

3. The method for simulating and evaluating the Doppler frequency shift characteristics of the underwater vehicle's transmitting and receiving echoes according to claim 2 is characterized in that: In step 1, for structures with unclear thickness parameters, refer to the relevant parameters of standard underwater vehicles for reference.

4. The method for simulating and evaluating the Doppler frequency shift characteristics of the underwater vehicle's transmitting and receiving echoes according to claim 1, characterized in that: In step 2, the inner and outer shells of the underwater vehicle structure are divided into triangular meshes respectively, and the size of each triangular mesh meets R min >D 2 / λ condition, ensuring that the calculation point is in the far field; where R min is the minimum distance at which the scattering point radius vector can be calculated, D is the maximum size of each plate, and λ is the wavelength of the incident wave.

5. The method for simulating and evaluating the Doppler frequency shift characteristics of the underwater vehicle's transmitting and receiving echoes according to claim 1, characterized in that: The Kirchhoff approximation principle in step 6 assumes that at high frequencies, the contribution of the geometric shadow area to the sound field is ignored and the scatterer surface satisfies the rigidity condition; the time factor e is ignored. -jwt , the scattering wave potential function under the situation of separate transmitter and receiver is expressed as: Where S is the surface of the scatterer; r1 and r2 are the radius vectors of the incident point and the scattering point, respectively, and are r when they are the same; α1 and α2 are the angles between the outer normal direction of the surface and the radius vectors of the incident point and the scattering point, respectively, and are α when they are the same; V(α) is the reflection coefficient of the shell surface.

6. The method for simulating and evaluating the Doppler frequency shift characteristics of the underwater vehicle's transmitting and receiving echoes according to claim 1, characterized in that: The Doppler shift principle in step 7 is to assume that the sound source and target are in relative motion, and obtain the Doppler shift expression: Among them, f d Doppler shift frequency, unit Hz; v relative speed of movement, unit m / s; f c The carrier frequency of the signal, in Hz; c is the propagation speed of the signal in the medium, in m / s; θ is the angle between the transmission direction of the signal and the relative motion direction, in rad.

7. The method for simulating and evaluating the Doppler frequency shift characteristics of the underwater vehicle's transmitting and receiving echoes according to claim 1, characterized in that: The simulation evaluation method for the Doppler frequency shift characteristics of the underwater vehicle's receiving and transmitting split echoes in step 7 includes selecting a typical evaluation frequency, calculating how the underwater vehicle's Doppler frequency shift characteristics of the receiving and transmitting split echoes in different acoustic wave signal transmission frequency bands change with horizontal distance, and how the Doppler frequency shift frequency changes with relative speed at typical frequency points.

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