Closed-loop analysis optimization method for acoustic subsurface buoy system

Abstract

The invention provides a closed-loop analysis optimization method for an acoustic subsurface buoy system, and belongs to the technical field of marine monitoring system optimization. According to the method, a mode of combining overall static force calculation, VIV characteristic calculation, local CFI calculation and FW-H acoustic ratio simulation calculation is provided, and analysis on the influence of the VIV characteristics of the subsurface buoy system, the self noise of the hydrophone and the noise of other hydrophones is achieved; according to the method, the problem that CFI numerical simulation cannot be directly carried out on the whole is solved, and static characteristic and whole VIV characteristic calculation is carried out on the system so as to carry out local CFI numerical simulation and FW-H acoustic ratio simulation calculation; the whole calculation process can be circularly optimized for multiple times. According to the method, the analysis work of each part is considered as a whole, an organic overall closed-loop system is formed, multiple times of cyclic optimization can be carried out according to the index requirements of the subsurface buoy system, and the optimal design of the acoustic subsurface buoy system is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of ocean monitoring system optimization, and in particular relates to a closed-loop analysis and optimization method for an acoustic buoy system. Background Art

[0002] With the advent of the ocean age, the importance of ocean exploration has become increasingly prominent for all countries. Many countries have realized the importance of submerged buoy systems for ocean exploration and have followed up to carry out systematic research. The submerged buoy system can collect data continuously and for a long time without supervision, allowing researchers to understand the uninterrupted physical conditions of the ocean during this period. The acoustic submerged buoy system is a submerged buoy system that is difficult to develop. The existence of hydrophone self-noise seriously interferes with its detection of target data. This problem has seriously restricted my country's ability to detect ocean sounds. Research on this issue has been slow. One of the major reasons is that the investment in submerged buoy experiments is large, but the useful information obtained is relatively small, and there is also the possibility of experimental failure. Therefore, it is very important to optimize the design of the submerged buoy system reasonably before the actual deployment of the submerged buoy system.

[0003] However, most of the current research objects are non-acoustic buoy systems, and there are few studies on acoustic buoys, especially noise control. Most of the research is isolated research on a certain problem, lacking the study of the flow field and noise of local noise-sensitive units under the influence of the overall movement of the system, as well as the study of the propagation of noise of adjacent sensitive units. Therefore, most of the research content is difficult to be directly applied to the design of acoustic buoy systems. In view of this problem, it is of great practical significance to design a set of design analysis and optimization systems and processes for acoustic buoys. Summary of the invention

[0004] In order to solve the deficiencies of the prior art, the present invention provides a closed-loop analysis and optimization method for an acoustic buoy system, comprising the following steps:

[0005] Step 1: Preliminary design of acoustic buoy layout plan, obtaining the position, mass, volume, towing area and drag coefficient of all equipment of the buoy system, as well as the diameter, unit length mass, axial stiffness and drag coefficient of the mooring cable;

[0006] Step 2: Based on the acquired position, mass, volume, towing area and towing force coefficient of all equipment of the buoy system, as well as the diameter, unit length mass, axial stiffness and towing force coefficient of the mooring cable, the lumped mass method is used to perform steady-state calculation and analysis on the attitude of the buoy system to obtain the static position, tension distribution and deflection change of the buoy system model;

[0007] Step 3, based on the steady-state calculation result of the buoy system attitude in step 2, the overall VIV characteristic of the buoy system is calculated to obtain the oscillation motion trajectory of each hydrophone and other key positions;

[0008] Step 4: Based on the vibration trajectory calculated in Step 3, perform local CFD flow field simulation to obtain the flow field change information near the hydrophone, including velocity and vorticity;

[0009] Step 5: Calculate the self-noise of each hydrophone and its influence on the noise of other hydrophones based on the FW-H acoustic analogy theory;

[0010] Step 6: Evaluate the results of the self-noise of the hydrophone and its influence on the noise of other hydrophones, adjust the positions of the hydrophones according to the requirements, and form an optimized acoustic mooring buoy layout plan;

[0011] Continue to repeat the above steps until the final optimization is completed.

[0012] Preferably, the specific process of Step 2 is as follows:

[0013] After performing the modeling of the mooring buoy system in the corresponding software and inputting the sea current velocity required for the calculation, calculate the steady state of the mooring buoy system attitude based on the lumped mass method; set the interval of the lumped mass nodes of the mooring cable; the mooring buoy equipment is suspended at specific positions on the mooring cable in the form of attachments, and the bending stiffness and torsional stiffness are simplified to 0; according to the sea current profile adaptation model in the deep-sea environment, obtain the flow velocity profile model at the corresponding water depth through interpolation method; calculate and obtain the settlement of the main floating body, the displacement of the mooring buoy system in the flow direction, the change of the mooring cable tension, and the change of the deviation angle between the mooring cable and the horizontal direction under various flow velocities as required.

[0014] Preferably, the specific calculation process of using the lumped mass method to perform steady state calculation and analysis of the mooring buoy system attitude in Step 2 is as follows:

[0015] Assume that the mooring cable is divided into n segments, and the mass of each segment is m, then there is:

[0016]

[0017] The bending stiffness of the mooring cable is taken as 0, mainly considering the tensile stiffness. The tension of each segment is represented by a linear spring k and a damper C, where:

[0018]

[0019] A is the cross-sectional area of the mooring cable, E is the Young's modulus of the mooring cable, l is the unstretched length of the mooring cable, and ζ is the structural damping ratio of the mooring cable;

[0020] Since the main body of the mooring buoy is below the water surface, during the static analysis process, in addition to its own gravity and buoyancy, only the influence of the sea current needs to be considered. Take the i-th unit of the mooring system for force analysis. The loads acting on the i-th unit include gravity G i , buoyancy F i , drag forces Q in three directions ix , Qiy , Q iz and the tensile forces T of the mooring lines at both ends i , T i+1 ; the angle between the upper half of the unit and the z - direction is the angle between its projection on the x - y plane and the x - axis is θ i , the angle between the lower half of the unit and the z - direction is the angle between its projection on the x - y plane and the x - axis is θ i+1 ;

[0021] Thus, the force balance equations in three directions can be obtained:

[0022]

[0023] Under the action of the ocean current drag force, through multiple iterative calculations, the mooring buoy system gradually tends to the equilibrium state from the initial state, and the position and deflection angle information of the unit are deduced accordingly. By taking the difference from the initial position and initial deflection angle of the unit, the settlement of the main float, the displacement of the mooring buoy system in the flow direction, and the change of the deflection angle of the mooring line with respect to the horizontal direction can be obtained. The drag force acting on the mooring line can be calculated by the following formula:

[0024]

[0025] where ρ is the density of seawater, j = j(x, y, z), C Dj is the drag coefficient in the j - direction, A j is the drag area in the j - direction, v j is the velocity of the fluid relative to the device in the j - direction. The change value of the mooring line tension can also be obtained by taking the difference from the initial value.

[0026] Preferably, the specific process of step 3 is as follows:

[0027] Based on step 2, the VIV time - domain calculation of the whole mooring line is carried out. Each n - meter mooring line is used as a node unit, the calculation time is m seconds, the analysis data starts from t seconds after the formal calculation, the calculation time step is 0.01 s, the time - domain vibration results of the main float and the hydrophone are calculated, and the fast Fourier transform is performed on the time - domain vibration results to obtain the lateral vibration frequency results of the main float and the hydrophone, and finally the amplitude and main frequency of the calculation condition are obtained.

[0028] Preferably, the VIV time - domain calculation of the whole mooring line is carried out based on the wake oscillator model, and this model is based on the Van der Pol equation, and its expression is:

[0029]

[0030] ε is the Van der Pol parameter, f is the force, ω f is the vortex shedding frequency, and q is a variable.

[0031] Preferably, the specific process of step 4 is as follows:

[0032] Use corresponding software to establish a three-dimensional model, divide the computational domain therein, and use the vibration results calculated in step 3 as displacement boundary conditions to perform local hydrodynamic simulation on the part where the hydrophone is located;

[0033] The establishment of the three-dimensional model simplifies the battery compartment into a cylinder with a length of L and a diameter of D. The division of the computational domain includes an overlapping region and a background region; it is set that the flow velocity flows in from the left direction, and the coordinate system is the same as that for the overall VIV calculation; the grid attributes and overlapping grid attributes are set. For the background grid, a surface grid generator and a volume grid generator are selected to perform surface reconstruction and tetrahedral grid generation respectively. For the overlapping grid, a prism layer grid generator is used for the region near the wall boundary layer, and the wake field grid is encrypted using the body control method to create an encrypted body; the k-ω SST-DDES model is used to solve the flow field state around the hydrophone. For the part of the hydrophone that is locally focused on, local hydrodynamic simulation is performed with the vortex-induced vibration result at this position in the overall analysis as the boundary condition to obtain vorticity and flow velocity.

[0034] Preferably, the specific process of step 5 is as follows:

[0035] On the basis of the local hydrodynamic flow field setting in step 5, the FW-H acoustic analogy method is added. The FW-H sound source emission surface is set as the cylinder wall. Probes are set as FW-H point receivers above the cylinder starting from the sound source according to the influence positions required for the moored buoy system calculation, with a maximum extension of 10 m, and a total of 26 point receiver probes; after 0.1 s of calculation, each point receiver starts to receive sound pressure information and continues to receive it until the calculation ends, so as to obtain the self-noise of each hydrophone and the noise to other hydrophones;

[0036] The equation expression of FW-H is:

[0037]

[0038] Among them, c0 is the magnitude of the sound speed, p is the magnitude of the sound pressure at the observation position, ρ0 is the fluid density, f = 0 is the integration plane of the equivalent sound source position, u i , n j are respectively the fluid velocity vector and the unit outer normal vector in the y i direction, u n , v n are respectively the fluid velocity perpendicular to the integration surface and the moving velocity, p ij is the stress tensor, and δ(f) and H(f) are the Dirac function and the Heaviside function.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The traditional analysis of moored buoy design is limited to attitude analysis based on static characteristics calculation. This method conducts VIV characteristics calculation and local CFD numerical simulation calculation on the basis of the static characteristics calculation of the moored buoy system, realizing the provision of more valuable reference information such as the static characteristics, VIV characteristics, self-noise of the hydrophone, and the influence on the noise of other hydrophones for the design and deployment of the moored buoy system;

[0041] 2. The aspect ratio of the moored buoy system is extremely large, and it is impossible to directly conduct physical model experiments and numerical simulation analysis on the entire moored buoy system. This solution combines overall static calculation, VIV characteristics calculation with local CFD calculation and FW-H acoustic analogy calculation, realizing the analysis of the self-noise and noise influence of the hydrophone mounted on the acoustic moored buoy system under the consideration of global influence, greatly reducing the required computing resources and ensuring the calculation accuracy;

[0042] 3. Considering the analysis work of each part as a whole to form an organic overall closed-loop system, multiple cyclic optimizations can be carried out according to the index requirements of the moored buoy system to achieve the optimal design of the acoustic moored buoy system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following description is only one embodiment of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0044] Figure 1 It is a schematic diagram of the overall technical route for moored buoy analysis of the present invention.

[0045] Figure 2 It is a layout diagram of a moored buoy in the prior art.

[0046] Figure 3 It is a comparison diagram of the attitude change in the x direction between the prior art and the present invention.

[0047] Figure 4 It is a comparison diagram of the change in mooring line tension between the prior art and the present invention.

[0048] Figure 5 It is a comparison diagram of the deviation angle between the mooring line and the horizontal direction between the prior art and the present invention.

[0049] Figure 6 It is a schematic diagram of the Delft riser model experiment.

[0050] Figure 7 It is a comparison diagram of the lift coefficient and drag coefficient of three types of grid calculations.

[0051] Figure 8 It is a comparison diagram of the verification results of the frequency-domain sound pressure of the point receiver at 1 m.

[0052] Figure 9 It is a schematic diagram of the subsurface buoy system in the embodiment of the present invention.

[0053] Figure 10 It is a schematic diagram of the displacement of the flow direction subsurface buoy system under 6 working conditions in the embodiment of the present invention.

[0054] Figure 11 It is a schematic diagram of the change of the mooring cable tension of the subsurface buoy system under 6 working conditions in the embodiment of the present invention.

[0055] Figure 12 It is a schematic diagram of the change of the deflection angle between the mooring cable and the horizontal direction under 6 working conditions in the embodiment of the present invention.

[0056] Figure 13 It is a schematic diagram of the comparison results of the main frequency along the mooring cable under 6 flow velocity working conditions in the embodiment of the present invention.

[0057] Figure 14 It is a schematic diagram of the change of the grid cut-off frequency under 6 working conditions in the embodiment of the present invention.

[0058] Figure 15 It is a schematic diagram of the change of the total surface term at 4 different distances under the working condition of 0.75 m / s in the embodiment of the present invention.

[0059] Figure 16 It is the spectrogram at 0.75 m / s in the embodiment of the present invention.

[0060] Figure 17 It is a schematic diagram of the change law of the distance between the sound pressure level and the sound source under 6 working conditions in the embodiment of the present invention.

[0061] Figure 18 It is the static analysis diagram of the node of the present invention. Specific embodiments

[0062] The present invention will be further described below in combination with specific experiments and specific embodiments.

[0063] The present invention proposes a closed-loop design analysis method for an acoustic subsurface buoy system that combines the calculation of the overall attitude and vortex-induced vibration and the simulation of the sound propagation of local hydrophones, as Figure 1Shown as follows: Step 1, preliminarily design the acoustic mooring buoy layout plan; Step 2, conduct a steady-state calculation and analysis of the mooring buoy system attitude based on the lumped mass method to obtain the static position, tension distribution, and deflection angle change of the mooring buoy system model; Step 3, conduct an overall VIV characteristic calculation of the mooring buoy system based on the steady-state calculation results of the mooring buoy system attitude in Step 2 to obtain the oscillating motion trajectories of each hydrophone and other key positions; Step 4, conduct a local CFD flow field simulation based on the vibration trajectories calculated in Step 3 to obtain the flow field change information near the hydrophone, including velocity and vorticity; Step 5, select and calculate the self-noise of each hydrophone and its influence on the noise of other hydrophones based on the FW-H acoustic analogy theory; Step 6, conduct a design evaluation of the self-noise of each hydrophone and its influence on the noise of other hydrophones, adjust the positions of the hydrophones according to the requirements, form an optimized acoustic mooring buoy layout plan, and continue to repeat the above steps.

[0064] The feasibility of the calculation method is verified separately below. For the verification of the steady-state calculation and analysis of the mooring buoy system attitude based on the lumped mass method in Step 2, the present invention verifies by adopting the results of the existing layout plan. The mooring buoy layout diagram is as Figure 2 shown.

[0065] According to the layout of the mooring buoy system, the present invention inputs the wave and flow conditions of the mooring buoy system in the OrcaFlex software. The interval of the lumped mass nodes is set to 1 m, and the equipment is suspended at specific positions on the mooring line in the form of attachments. The bending stiffness and torsional stiffness are simplified to 0. The calculation results are as Figure 3 、 Figure 4 、 Figure 5 shown. The maximum height deviation at the same position in the x-z plane between the present invention and the prior art is 3.4 m (0.48%), the maximum upper end tension difference is 171.5 N, the maximum lower end tension difference is 130.3 N, the maximum upper end deflection angle difference is 0.4°, and the maximum lower end deflection angle difference is 0.4°, meeting the accuracy requirements and verifying that the calculation method is feasible.

[0066] The verification of Step 3 is to calculate based on 5 kinds of riser VIV characteristic calculation methods provided by the official of the OrcaFlex software, and compare with the corresponding experimental results and official calculation results, so as to verify and select the most suitable calculation method. In view of the fact that both the riser and the mooring buoy system belong to slender flexible structures and their dynamic characteristics have similar features, and the VIV research of the riser is more mature with more relevant research results. Therefore, this method verifies the experimental results of the riser VIV model mentioned in the prior art, and thus uses this method to calculate the VIV characteristics of the mooring buoy system. The existing experimental results are from the riser model experiment conducted in the hydraulic laboratory. This patent independently models and calculates this model experiment based on the OrcaFlex software, and makes comparative verifications with the results of this model experiment and the OrcaFlex official verification results respectively. The schematic diagram of the riser model experiment is as Figure 6As shown in the figure, a 7.54m high vacuum tank is fixed at the upper end. Negative pressure is formed by pumping air from the upper end. When the opening of the vacuum tank is underwater, the atmosphere presses water into the vacuum tank. When the moving part moves according to the set working conditions, a uniform flow is caused at the lower end due to relative movement, and the flow velocity is in the opposite direction of the same magnitude under the same working conditions. The riser under the uniform flow accounts for 45% of its total length. Since the water in the riser and the vacuum tank remains relatively stationary at the upper end, the upper riser is in a static water state during the movement process. Thus, the entire riser is in a state of step flow. The flow velocity at the lower end changes due to different working conditions, and the upper end is always in a static water state. At the bottom, a riser with a length of 13.12m is installed at the connection between the rigid installation point at the bottom and the top of the vacuum tank, and the bottom is 0.36m away from the bottom of the water.

[0067] The present invention has carried out calculations for 9 working conditions according to the 5 VIV calculation models officially provided by OrcaFlex software. Based on R-Square as the measurement standard, the results are compared as shown in Table 1. The calculation results of the present invention have a high degree of coincidence with the official verification results of OrcaFlex and have a high degree of credibility. The calculation results of the present invention have the highest correlation with the experimental measurement results of the Delft model when applying the Milan original model for calculation, and the value is 0.913. Therefore, the Milan original model is selected as the empirical model for subsequent VIV time-domain analysis.

[0068] Table 1 Comparison of relevant analysis results of the present invention, model experiment and software official

[0069]

[0070] Step 5 Use STAR-CCM+ to perform local CFD simulation on the mooring buoy system and conduct grid independence verification. Table 2 shows the data tables of three grid densities used for grid independence analysis. The present invention selects a flow velocity of 1m / s as the initial condition for independence calculation. Use the k-ω SST-IDDES model to solve the flow field state around the hydrophone. Extract the VIV lateral movement trajectory of one of the hydrophones from the time-domain model simulation and apply it to the overlapping grid. At the same time, the background grid remains stationary. Select the trajectory time period as 100 - 110s and select the comparison benchmarks for the lift coefficient and drag coefficient. The results are as Figure 7 shown. It can be clearly seen from the results that there is a large gap between the coarse grid and the medium grid and the fine grid in both the lift coefficient and the drag coefficient. The medium grid and the fine grid have a high degree of coincidence in the lift coefficient and the drag coefficient. Select the fine grid for local CFD simulation of the hydrophone according to factors such as Y+ value.

[0071] Table 2 Data tables of three grid densities used for grid independence analysis

[0072]

[0073] Step 6 Before conducting the research on the acoustic propagation of the hydrophone, the aeroacoustic propagation model in STAR-CCM+ was computationally verified. The geometry of this model is a cylinder with a diameter of 20 mm, and the computational domain is a coaxial cylinder with a height of 0.6 m and a diameter of 0.6 m. The air flow velocity is 50 m / s, and the Mach number is 0.144. The k-ω SST-DDES model is used to capture the aeroacoustic noise source. Then, the FW-H method is adopted to solve the Farassat_1A equation to simulate the aeroacoustic propagation of the cylinder. The cylinder wall surface is regarded as the sound source surface, and the receiving point is set 1 m away from the wall surface. The time step is 2.5×10 -5 s, and the total calculation duration is 0.0533 s. The frequency-domain results of the sound pressure are obtained through FFT calculation. Figure 8 For the comparison of the verification results of the frequency-domain sound pressure of the point receiver at 1 m, it can be seen from the figure that the frequency-domain sound pressure level curve is in good agreement with the verification results. Both peak frequencies are around 530 Hz, which proves that the FW-H method embedded in the software has good accuracy and stability for the present invention.

[0074] Through the above verification, it is proved that this set of calculation methods is feasible. Next, a set of 900 m moored buoy system deployed at a water depth of 1000 m is taken as an example to demonstrate the calculation method.

[0075] First, according to the research needs, the overall steps of the acoustic moored buoy system are preliminarily designed, and a set of acoustic moored buoy systems for analysis is obtained as Figure 9 shown. The uppermost part is a streamlined main float, which provides the main buoyancy. Nine hydrophones are divided into three groups, and each group is placed in the upper, middle, and lower regions of the moored buoy system respectively. Two groups of float balls are placed in the middle of the three groups of hydrophones as the buoyancy adjustment part. The parallel release device is placed 50 m away from the seabed, and the cable is a 10 mm Kevlar rope.

[0076] In the second step, according to the layout of the moored buoy system in the first step, after inputting the moored buoy system modeling and flow conditions in OrcaFlex software based on the lumped mass method, the static calculation of the moored buoy is carried out. The specific operation settings are that the lumped mass node interval is set to 2 m, the equipment is suspended at specific positions on the mooring line in the form of attachments, and the bending stiffness and torsional stiffness are simplified to 0. And according to the deep-sea environmental current profile adaptation model proposed by Malone et al., the velocity profile model at a water depth of 1000 m is obtained through interpolation method. Running the calculation to obtain the settlement of the main float (Table 3), the displacement of the moored buoy system in the flow direction ( Figure 10 ), the change of the mooring line tension ( Figure 11 ), and the change of the angle between the mooring line and the horizontal direction ( Figure 12 ) at 6 flow velocities of 0.25 m / s, 0.5 m / s, 0.75 m / s, 1.0 m / s, 1.25 m / s, and 1.5 m / s. The node static analysis during the calculation process is as Figure 18 shown.

[0077] Table 3 Settlement data of the main floating body under 36 working conditions

[0078]

[0079] The third step mainly conducts the system time-domain VIV calculation and analysis. Based on the OrcaFlex software, the Milan original empirical model that is verified to be most suitable for the present invention is used to perform the VIV time-domain calculation on the entire mooring line. Each 2m mooring line is used as a node unit, the calculation time is 300 seconds, the analysis data starts from 100s after the formal calculation, the calculation time step is 0.01s, and the fast Fourier transform is performed on the results, so that the lateral time-domain and frequency vibration results of the main floating body and the hydrophone can be obtained. Based on the time-domain displacement data, the frequency calculation and processing are carried out for each working condition, and the main frequency is taken. The distribution results of the frequencies of 6 working conditions along the mooring line are as Figure 13 shown.

[0080] The fourth step mainly conducts the local hydrodynamic simulation. The software used is STAR-CCM+. The three-dimensional model is established, the computational domain is divided and the calculation is carried out therein. The three-dimensional model establishment mainly simplifies the battery compartment into a cylinder with a length L = 0.044m and a diameter D = 0.067m. The computational domain division is mainly into an overlapping area and a background area. The size of the background area is 15D×12D×9D, and the size of the overlapping area is 4.5D×4.5D×7.5D. The distance from the front end of the computational domain to the cylinder axis is 5D. The flow velocity is set to flow in from the left direction, and the coordinate system is the same as that of the overall VIV calculation, which is convenient for the subsequent import and utilization of data. The main mesh attributes used are a base size of 0.01m, a target surface size of 0.01m, a minimum surface size of 0.001m, a surface mesh growth rate of 1.3, a volume mesh growth rate of 1.2, and a wake field mesh is encrypted using the volume control method to create an encrypted volume of 12D×6D×8D. The overlapping mesh attributes are a base size of 0.0022m, a target surface size of 0.0022m, a minimum surface size of 2.2×10 -4 m, 6 prism layers, a prism layer extension of 1.5, and a total prism layer thickness of 7.3×10 -4 m. The k-ω SST-DDES model is used to solve the flow field state around the hydrophone. For the locally focused part (which is the hydrophone for the acoustic mooring buoy system), the VIV results at this position in the overall analysis are used as the boundary conditions for the local hydrodynamic simulation, considering the influence of the overall on the local. Three point probes are set near the cylinder to monitor the pressure during the operation of the solver. Since the cylinder itself moves according to the trajectory, the point probes are set to move synchronously with the cylinder. And it is concluded from the calculation results that for the local motion and the overall motion of the mooring buoy system, the two cannot be separated and analyzed separately.

[0081] In the fifth step, based on the flow field calculation, the sound field is further analyzed. The method adopted is the FW-H acoustic analogy method. Before that, the grid cut-off frequencies under different working conditions are analyzed in the steady-state calculation to provide a reference for the FW-H calculation. The results are as Figure 14 shown.

[0082] In the fifth step, based on the unsteady setting, the FW-H acoustic analogy method is added. The FW-H sound source emission surface is set as the cylinder wall surface. Starting from the sound source, a probe is set every 0.4 m above the cylinder as the FW-H point receiver, with a maximum extension of 10 m, for a total of 26 point receiver probes. In order to obtain more stable data, after 0.1 s of calculation, each point receiver starts to receive the sound pressure information and continues to receive it until the calculation ends. To visualize the sound emitted from the cylinder surface and received by the far-field receiver, the total surface top is selected as the research object, and the variation of the total surface top at different distances under the same flow velocity is explored for the 0.75 m / s working condition. Four positions with distances of 0.4 m, 1.2 m, 2.0 m, and 2.8 m are selected as the research objects (the results are as Figure 15 shown), and the received sound pressure signal can also be subjected to a fast Fourier transform. The results are as Figure 16 shown.

[0083] According to the requirements, in order to measure the variation law of the sound pressure propagation generated by the vibration of the hydrophone, that is, the self-noise generated by the hydrophone in the mooring buoy system and its influence on the noise of other hydrophones, the present invention calculates and summarizes the effective sound pressure levels of the 26 point receivers during the calculation time. The variation law of the effective sound pressure levels within 10 m from the sound source under 6 working conditions is obtained. The results are as Figure 17 shown. Guiding conclusions for the hydrophone arrangement can be obtained based on this figure, and then the hydrophone arrangement can be optimized again and recycled for optimization.

[0084] The above is only the preferred embodiment of the present application and is not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

[0085] Although the specific implementation manners of the present invention are described above, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications or deformations that can be made without creative labor on the basis of the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A closed-loop analysis and optimization method for an acoustic mooring buoy system, characterized in that It includes the following steps: Step 1: Initially design the acoustic mooring buoy layout plan, and obtain the positions, masses, volumes, drag areas and drag force coefficients of all equipment of the mooring buoy system, as well as the diameters, unit length masses, axial stiffnesses and drag force coefficients of the mooring cables; Step 2: Based on the positions, masses, volumes, drag areas and drag force coefficients of all equipment of the mooring buoy system obtained, and the diameters, unit length masses, axial stiffnesses and drag force coefficients of the mooring cables, use the lumped mass method to conduct a steady-state calculation and analysis of the attitude of the mooring buoy system, and obtain the static position, tension distribution and deflection angle change of the mooring buoy system model; Step 3: Based on the steady-state calculation results of the attitude of the mooring buoy system in Step 2, conduct an overall VIV characteristic calculation of the mooring buoy system to obtain the oscillating motion trajectories of each hydrophone and other key positions; Step 4: Conduct a local CFD flow field simulation based on the vibration trajectories calculated in Step 3 to obtain the flow field change information near the hydrophone, including velocity and vorticity; Step 5: Calculate the self-noise of each hydrophone and its influence on the noise of other hydrophones based on the FW-H acoustic analogy theory; Step 6: Evaluate the results of the self-noise of the hydrophone and its influence on the noise of other hydrophones, adjust the positions of the hydrophones according to the requirements, and form an optimized acoustic mooring buoy layout plan; Continue to repeat the above steps until the final optimization is completed.

2. The closed-loop analysis and optimization method for an acoustic moored buoy system according to claim 1, wherein: The specific process of Step 2 is as follows: After modeling the mooring buoy system in the corresponding software and inputting the sea current velocity required for the calculation, conduct a steady-state calculation of the attitude of the mooring buoy system based on the lumped mass method; set the interval of the lumped mass nodes of the mooring cable; the mooring buoy equipment is suspended at specific positions on the mooring cable in the form of attachments, and the bending stiffness and torsional stiffness are simplified to 0; according to the sea current profile adaptation model in the deep-sea environment, obtain the velocity profile model at the corresponding water depth through interpolation; calculate and obtain the settlement of the main floating body, the displacement of the sea current direction towards the mooring buoy system, the change of the mooring cable tension, and the change of the deflection angle between the mooring cable and the horizontal direction under various flow velocities as required.

3. The closed-loop analysis and optimization method for an acoustic moored buoy system according to claim 2, wherein: The specific calculation process of using the lumped mass method to conduct a steady-state calculation and analysis of the attitude of the mooring buoy system in Step 2 is as follows: Assume that the mooring cable is divided into n segments, and the mass of each segment is m, then there is: The bending stiffness of the mooring cable is taken as 0, mainly considering the tensile stiffness. The tension of each segment is represented by a linear spring k and a damper C, where: A is the cross-sectional area of the mooring cable, E is the Young's modulus of the mooring cable, l is the unstretched length of the mooring cable, and ζ is the structural damping ratio of the mooring cable; Since the main body of the subsurface buoy is located below the water surface, during the static analysis, in addition to its own gravity and buoyancy, only the influence of ocean currents needs to be considered. Take the i-th unit of the mooring system for force analysis. The loads acting on the i-th unit include the gravity G i , buoyancy F i , drag forces Q in three directions ix , Q iy , Q iz and the tensions T of the mooring lines at both ends i , T i+1 ; the angle between the upper half of the unit and the z-direction is The angle between its projection on the x-y plane and the x-axis is θ i , the angle between the lower half of the unit and the z-direction is The angle between its projection on the x-y plane and the x-axis is θ i+1 ; From this, the force balance equations in three directions can be obtained: Under the action of the sea current drag force, through multiple iterative calculations, the mooring buoy system gradually tends to the equilibrium state from the initial state, and the position and deflection angle information of the unit can be deduced accordingly. By taking the difference from the initial position and initial deflection angle of the unit, the settlement of the main floating body, the displacement of the sea current direction towards the mooring buoy system, and the change of the deflection angle between the mooring cable and the horizontal direction can be obtained. The drag force acting on the mooring cable can be calculated by the following formula: where ρ is the seawater density, j = j(x, y, z), C Dj is the drag coefficient in the direction of j, A j is the drag area in the direction of j, v j is the velocity of the fluid relative to the device in the direction of j, and the change value of the mooring line tension can also be obtained by subtracting the initial value.

4. The closed-loop analysis and optimization method for an acoustic moored buoy system according to claim 1, wherein The specific process of Step 3 is as follows: Based on Step 2, the VIV time-domain calculation of the entire mooring cable is carried out. Each n-meter mooring cable is used as a node unit, and the calculation time is m seconds. The analysis data starts from t seconds after the formal calculation. The calculation time step is 0.01 s. The time-domain vibration results of the main floating body and the hydrophone are obtained by calculation, and the fast Fourier transform is performed on the time-domain vibration results to obtain the lateral vibration frequency results of the main floating body and the hydrophone. Finally, the amplitude and main frequency of the calculation condition are obtained.

5. The closed-loop analysis and optimization method for an acoustic moored buoy system according to claim 4, wherein: The VIV time-domain calculation of the entire mooring cable is based on the wake oscillator model for calculation. This model is based on the Van der Pol equation, and its expression is: ε is the Van der Pol parameter, f is the force, ω f is the vortex shedding frequency, and q is a variable.

6. The closed-loop analysis and optimization method for an acoustic moored buoy system according to claim 1, characterized in that The specific process of Step 4 is as follows: Use the corresponding software to establish a three-dimensional model, divide the calculation domain, and use the vibration results calculated in Step 3 as the displacement boundary condition to perform local hydrodynamic simulation on the part where the hydrophone is located; In the three-dimensional model establishment, the battery compartment is simplified into a cylinder with a length of L and a diameter of D. The calculation domain division includes an overlapping area and a background area; it is set that the flow velocity flows in from the left direction, and the coordinate system is the same as that of the overall VIV calculation; the grid attributes and overlapping grid attributes are set. For the background grid, a surface grid generator and a volume grid generator are selected to perform surface reconstruction and tetrahedral grid generation respectively. For the overlapping grid, a prism layer grid generator is used for the area near the wall boundary layer, and the body control method is used to encrypt the wake field grid to create an encrypted body; the k-ω SST-DDES model is used to solve the flow field state around the hydrophone. For the part of the hydrophone that is locally focused on, the vortex-induced vibration results at this position in the overall analysis are used as the boundary condition to perform local hydrodynamic simulation to obtain the vorticity and flow velocity.

7. The closed-loop analysis and optimization method for an acoustic moored buoy system according to claim 1, characterized in that, The specific process of Step 5 is as follows: On the basis of the local hydrodynamic flow field setting in Step 5, the FW-H acoustic analogy method is added. The FW-H sound source emission surface is set as the cylinder wall. Probes are set as FW-H point receivers starting from the sound source above the cylinder according to the influence positions required for the calculation of the subsurface buoy system, with a maximum extension of 10 m, and a total of 26 point receiver probes; After 0.1 s of calculation, each point receiver starts to receive sound pressure information and continues to receive it until the calculation ends, so as to obtain the self-noise of each hydrophone and the noise to other hydrophones; The equation expression of FW-H is: where \(c_0\) is the speed of sound, \(p'\) is the sound pressure at the observation position, \(\rho_0\) is the fluid density, \(f = 0\) is the integration plane at the equivalent sound source position, \(u\) i and \(n\) j are the fluid velocity vector and the unit outer normal vector in the \(y\) i direction respectively, \(u\) n and \(v\) n are the fluid velocity perpendicular to the integration plane and the moving velocity respectively, \(p\) ij is the stress tensor, \(\delta(f)\) and \(H(f)\) are the Dirac function and the Heaviside function.

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