A geometric characteristic analysis method for the line spectrum of hydrodynamic noise of a quasi-cylindrical shell

Abstract

The present invention discloses a geometric characteristic analysis method of a line spectrum of hydrodynamic noise of a quasi-cylindrical shell, the method comprising the following steps: using Gambit software to divide CFD grids and grids of the shell finite element surface; obtaining a .cgns format file of wall pressure pulsation data; importing the grid of the shell finite element surface divided by Gambit into ICEM to convert the grid data format; importing the grid format .bdf file into Nastran to perform shell material properties, calculate the free mode to obtain a .op2 format file; setting a numerical model of hydrodynamic radiation noise; setting a boundary layer type; establishing a data recovery surface, setting a sensor on the data recovery surface, and solving a sound pressure frequency response diagram at the sensor position. The characteristic analysis method of the method is solved by a numerical method, and the correlation between the length dimension of the quasi-cylindrical shell and the line spectrum frequency can be obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of signal processing, and in particular relates to a method for analyzing geometric characteristics of a line spectrum of hydrodynamic noise of a quasi-cylindrical shell. Background Art

[0002] When a quasi-cylindrical shell passes through a water medium, a turbulent boundary layer is formed on its surface. The unstable flow is blocked by the shell surface, and the momentum fluctuations near the wall are balanced by the pressure fluctuations on the interface. The pressure fluctuations in the boundary layer serve as a random excitation source to generate hydrodynamic noise. The hydrodynamic noise is caused by the disturbance in the surrounding turbulent boundary layer generated when the quasi-cylindrical shell passes through a water medium, the pulsating pressure on the wall, and the structural vibration caused by the coupling of the fluid and the solid. Generally speaking, the value of hydrodynamic noise is much lower than that of mechanical noise and propeller noise, but as the speed of movement increases, the proportion of hydrodynamic noise in the total noise will increase.

[0003] At present, there are three main numerical calculation methods for hydrodynamic noise: theoretical analysis, numerical prediction and experimental methods. Theoretical analysis has rigorous mathematical and physical derivation formulas, but it is limited to shell models with simple geometric shapes and requires the actual model to be simplified. Theoretical methods are limited in dealing with actual engineering problems. Summary of the invention

[0004] Purpose of the invention: In view of the problems and shortcomings of the above-mentioned existing methods, the present invention provides a method for analyzing the geometric characteristics of the hydrodynamic noise line spectrum of a quasi-cylindrical shell. The numerical prediction has certain adaptability to hydrodynamic noise problems with complex structures and boundaries and has strong engineering practicality.

[0005] Technical solution: In order to achieve the above invention purpose, the present invention adopts the following technical solution: A method for analyzing the geometric characteristics of the hydrodynamic noise line spectrum of a quasi-cylindrical shell, comprising the following steps:

[0006] Step 1, using Gambit software to divide the CFD grid and the shell finite element surface grid;

[0007] Step 2: Perform steady-state flow field calculation in Fluent, and then perform unsteady-state calculation to obtain the wall pressure pulsation data in .cgns format.

[0008] Step 3, import the mesh of the shell finite element surface divided by Gambit into ICEM to convert the mesh data format into .bdf format;

[0009] Step 4, import the mesh format .bdf into Nastran to set the shell material properties, and calculate to obtain the free mode .op2 format file; the material property is set to steel, indicating that the material property is set to steel.

[0010] Step 5, import the free steady-state .op2 format file of Nastran and the shell wall pressure pulsation pressure data exported by Fluent into VA ONE software to set up the numerical model of hydrodynamic radiation noise;

[0011] Step 6, add the turbulent boundary layer load to the finite element model surface of the cylindrical shell and set the boundary layer type;

[0012] Step 7, establishing a data recovery surface, setting it as a boundary element model, wherein the data recovery surface is a spherical data recovery surface with the center of the propeller; setting a sensor on the data recovery surface, and using VA ONE software to solve the hydrodynamic noise sound pressure frequency response diagram at the sensor position;

[0013] Step 8, analyzing the characteristics of the hydrodynamic noise sound pressure frequency response line spectrum of the cylindrical shells of different lengths, so as to obtain the relationship between the length size of the cylindrical shell and the hydrodynamic noise sound pressure frequency response line spectrum.

[0014] Beneficial effects: Compared with the existing methods, the present invention has the following beneficial effects:

[0015] (1) The estimation method of the present invention solves the hydrodynamic noise in VA ONE software, quickly solves the relationship between the length dimension of the quasi-cylindrical shell and the hydrodynamic noise line spectrum, and has strong engineering practicability;

[0016] (2) The estimation method of the present invention can solve the problem of analyzing the line spectrum characteristics of hydrodynamic noise with complex structures and boundaries; BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the process of the present invention;

[0018] Figure 2 This is the numerical calculation model diagram of the cylindrical shell;

[0019] Figure 3 is the spatial distribution map of the test points;

[0020] Figure 4 This is the frequency response diagram of the hydrodynamic noise sound pressure of a cylindrical shell;

[0021] Figure 5 The sound pressure frequency response diagram of hydrodynamic noise of cylindrical shells of different lengths;

[0022] Figure 5 (a) is the sound pressure frequency response diagram of hydrodynamic noise when the length of the cylindrical shell is 5m;

[0023] Figure 5 (b) is the sound pressure frequency response diagram of the hydrodynamic noise when the length of the cylindrical shell is 5.5m;

[0024] Figure 5 (c) is the sound pressure frequency response diagram of the hydrodynamic noise when the length of the cylindrical shell is 5.98533m;

[0025] Figure 5 (d) is the sound pressure frequency response diagram of the hydrodynamic noise when the length of the cylindrical shell is 6.5m;

[0026] Figure 5 (e) is the sound pressure frequency response diagram of the hydrodynamic noise when the length of the cylindrical shell is 7m;

[0027] Figure 5 (f) is the sound pressure frequency response diagram of the hydrodynamic noise when the length of the cylindrical shell is 7.5m;

[0028] Figure 5 (g) is the sound pressure frequency response diagram of the hydrodynamic noise when the length of the cylindrical shell is 7.8m;

[0029] Figure 5 (h) is the sound pressure frequency response diagram of hydrodynamic noise when the length of the cylindrical shell is 8.2m. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0031] like Figure 1 As shown, a method for analyzing geometric characteristics of a line spectrum of hydrodynamic noise of a quasi-cylindrical shell of the present invention comprises the following steps:

[0032] (1) The dimensional parameters of the quasi-cylindrical shell are set as follows: the thickness of the quasi-cylindrical shell h = 0.027m, the radius r = 0.533m, the length of the front frustum L = 0.2132m, the length of the quasi-cylindrical shell L = 4.867883m, and the experimental propeller T1 is used as the propeller, with a diameter of 0.2482m and a four-blade large side-skew propeller. The CFD calculation grid and the finite element surface grid of the shell are divided using Gambit software;

[0033] (2) In Fluent, steady-state flow field calculation is first performed, and then unsteady-state flow field calculation is performed. The iteration step of unsteady-state calculation is 0.000462963s, the ambient pressure is 113kPa, the rotation speed is 30r / s, and the wall pressure pulsation data is exported in .cgns format file;

[0034] (3) Import the mesh of the shell finite element surface divided by Gambit into ICEM for mesh data format conversion into .bdf format;

[0035] (4) Import the mesh format .bdf into Nastran to set the shell material properties. Set the shell material properties to steel and the cylindrical shell density ρ p =7800kg / m3, Poisson's ratio σ=0.3, Young's modulus E=2.1×1011, and the free mode .op2 format file is calculated;

[0036] (5) Import the free steady-state .op2 format file of Nastran and the shell wall pressure pulsation pressure data .cgns format file exported by Fluent into the VA ONE software to set up the numerical model of hydrodynamic radiation noise;

[0037] (6) Add the turbulent boundary layer load to the surface of the finite element model of the cylindrical shell, the speed of sound in water C0 = 1500 m / s, the seawater density ρ0 = 1000 kg / m3, and set the turbulent boundary layer type;

[0038] (7) Establish a data recovery surface, set it as a boundary element model, set sensors on the data recovery surface, establish a spherical data recovery surface with a length of 2.5 m with the center of the propeller as the origin, and set 8 sensors on the data recovery surface as receivers for hydrophone testing of cylindrical shell hydrodynamic noise. The numerical calculation model and the spatial distribution diagram of the test points are shown in Figure 2. Figure 2 and Figure 3 With the above settings, VA ONE software solves the sound pressure frequency response diagram at the sensor location, as shown in Figure 4 shown.

[0039] (8) Analyze the line spectrum characteristics of the sound pressure frequency response of hydrodynamic noise of cylindrical shells of different length sizes.

[0040] The length parameters of the quasi-cylindrical shell are set to 5m, 5.5m, 5.98533m, 6.5m, 7.0m, 7.5m, 7.8m and 8.2m respectively. According to steps 1-7, the sound pressure frequency responses of the 8 sensor positions corresponding to the different quasi-cylindrical shell length parameters are obtained respectively, as shown in order. Figure 5 As shown in (a)-5(h), the strongest line spectrum frequency in the sound pressure frequency response diagram of different length parameters is found. As shown in Table 1, as the length of the line spectrum increases, the frequency of the corresponding line spectrum decreases.

[0041] Table 1 Line spectrum distribution of hydrodynamic noise corresponding to different cylindrical shell lengths

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Claims

1. A geometric characteristic analysis method for the line spectrum of hydrodynamic noise of a quasi-cylindrical shell, characterized in that: The steps include: Step 1, using Gambit software to divide the CFD grid and the shell finite element surface grid; Step 2: Perform unsteady-state calculation in Fluent to obtain the wall pressure pulsation data in .cgns format; Step 3, import the mesh of the shell finite element surface divided by Gambit into ICEM to convert the mesh data format into .bdf format; Step 4, import the mesh data format .bdf into Nastran to set the shell material properties and calculate the free mode .op2 format file; Step 5, import the free mode .op2 format file of Nastran and the shell wall pressure pulsation pressure data exported by Fluent into VA ONE software to set up the numerical model of hydrodynamic radiation noise; Step 6, add the turbulent boundary layer load to the mesh on the surface of the finite element model of the cylindrical shell and set the boundary layer type; Step 7, establish a spherical data recovery surface with the propeller center as the origin, set it as a boundary element model, set a sensor on the data recovery surface, and use VA ONE software to solve the hydrodynamic noise sound pressure frequency response line spectrum at the sensor position; Step 8, analyzing the characteristics of the hydrodynamic noise sound pressure frequency response line spectrum of the cylindrical shells of different lengths, so as to obtain the relationship between the length of the cylindrical shell and the hydrodynamic noise sound pressure frequency response line spectrum; In step 2, the steady-state flow field calculation is first performed in Fluent, and then the unsteady-state flow field calculation is performed to obtain the wall pressure pulsation data in .cgns format file; In step 4, the material property is set to steel.

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