Ship water pressure field forecasting method based on RANS method

Abstract

The invention provides a ship water pressure field forecasting method based on an RANS method, and the method comprises the steps: obtaining a main scale parameter value corresponding to a ship, and obtaining the ship speed at a preset water depth according to the main scale parameter value; according to the preset water depth and the ship navigational speed, calculating the ship navigational water depth Fedede number; constructing a virtual numerical value pool according to the ship navigation water depth and Rroude number; according to the main scale parameter value, the preset water depth and the ship navigational speed, presetting boundary conditions, scales and damping wave absorbing lengths corresponding to the top, the bottom, the side edges, the outlet, the inlet, the symmetry plane and the ship body of the virtual numerical value pool; performing grid division on the virtual numerical pool to generate a computational domain grid virtual numerical pool and a free surface grid virtual numerical pool; and performing ship water pressure field forecasting according to the computational domain grid virtual numerical value pool and the free surface grid virtual numerical value pool, and obtaining a forecasting result when the speed is a ship navigation water depth Fedede number at a preset pressure measuring point position and a preset water depth.

Description

Technical Field

[0001] The invention relates to the technical field of ships, and in particular to a ship water pressure field prediction method based on a RANS method. Background Art

[0002] When a ship is sailing in the water, the surrounding velocity field and pressure field will change. This change in flow field pressure caused by the movement of the ship is called the ship's water pressure field. The ship's water pressure field is difficult to eliminate and difficult to simulate artificially. Therefore, since the Second World War, water pressure mines that are triggered and detonated by the signal characteristics of the ship's water pressure field have been widely used by navies of various countries. Research on the ship's water pressure field, especially the pressure distribution characteristics and change laws caused by ships at the bottom of the water, can provide a basis for the design of water pressure fuses for bottom mines, the development of water pressure minesweeping equipment, and the protection of ships themselves, and is therefore of great significance.

[0003] At present, the research methods for ship water pressure field are mainly divided into experimental methods, theoretical methods and numerical simulation methods.

[0004] The underwater dynamic pressure caused by ships in normal cruising speed and water depth generally varies within a few hundred Pa. Due to the interference of wind, waves, currents, tides and other environmental factors on the water pressure field, it is difficult to accurately measure the water pressure field of the actual ship. Model tests have the advantages of less environmental interference factors, accurate positioning of the relative pressure sensor of the ship model, easy calibration of the measurement system, guaranteed measurement accuracy, and convenience for conducting series of tests. Through ship model water pressure field tests and similar conversion, the purpose of systematically obtaining the characteristic magnitude and distribution law of the water pressure field of the actual ship can be achieved.

[0005] After decades of research, scientists have gradually proposed theoretical calculation methods for water pressure differences in uniform water depth, open sea, and low-speed ships, theoretical calculation methods for water pressure fields of ships in open seas considering the influence of dispersion effects, theoretical calculation methods for water pressure fields of ships with limited water depths based on thin ship theory, and theoretical calculation methods for water pressure fields of ships with limited water depths based on the panel method. Although the theoretical calculation method has high numerical calculation efficiency and can provide a reference for the stealth design of ship water pressure fields in the early stages of ship design, there are still major deficiencies in numerical prediction accuracy.

[0006] References:

[0007] [1] Ship water pressure field Zhang Zhihong et al. Summary of the invention

[0008] The purpose of the technical solution of the present invention is to propose a ship water pressure field prediction method based on the RANS method, taking into account the viscosity of the fluid and the strong nonlinear effect of the free liquid surface, so as to improve the prediction accuracy of the ship water pressure field.

[0009] In order to achieve the above-mentioned invention object, the technical solution of the present invention provides a ship water pressure field prediction method based on the RANS method, comprising the following steps:

[0010] Obtain the main scale parameter value corresponding to the ship, and obtain the ship speed at the preset water depth according to the main scale parameter value;

[0011] Calculate the ship's navigation depth Fu Rude number according to the preset water depth and ship speed;

[0012] According to the Froude number of the ship's navigation depth, a virtual numerical water pool with top, bottom, side, outlet, inlet, symmetry plane and hull is constructed;

[0013] According to the main scale parameter values, preset water depth and ship speed, preset the boundary conditions, scales and damping wave-absorbing lengths corresponding to the top, bottom, sides, outlet, inlet, symmetry plane and hull of the virtual numerical water pool;

[0014] Meshing the virtual numerical pool to generate a computational domain mesh virtual numerical pool and a free surface mesh virtual numerical pool;

[0015] The ship water pressure field is predicted based on the computational domain grid virtual numerical pool and the free surface grid virtual numerical pool, and the prediction results are obtained when the speed is the Rude number of the ship's navigation depth at the preset pressure measuring point position and the preset water depth.

[0016] Preferably, the main scale parameter values ​​include ship length, draft and ship width.

[0017] Preferably, the calculation formula of the Rudd number for the ship's navigation depth is as follows:

[0018]

[0019] Where: V represents the ship speed (m / s), g represents the acceleration of gravity (m / s2), and h represents the water depth (m).

[0020] Preferably, the boundary condition of the inlet is a velocity inlet, the boundary condition of the outlet is a pressure outlet, the boundary condition of the side is a velocity inlet, the boundary condition of the bottom is a no-slip wall, the boundary condition of the top is a symmetry plane, the boundary condition of the symmetry plane is a symmetry plane, and the boundary condition of the hull is a no-slip wall.

[0021] Preferably, the corresponding dimensions of the outlet and the side are larger than their corresponding damping wave-breaking lengths.

[0022] Preferably, when the dimension of the outlet is 2.5L_pp, the damping wave-breaking length is 1L_pp.

[0023] Preferably, when the dimension of the side is 1.5L_pp, the damping wave-breaking length is 1L_pp.

[0024] Preferably, the size of the bottom is determined according to the Rudd number of the water depth at which the ship is sailing.

[0025] Preferably, the preset pressure measuring point position interval is 0-0.5L.

[0026] Preferably, the ship water pressure field prediction method based on the RANS method takes into account the viscosity of the fluid and the strong nonlinear effect of the free liquid surface.

[0027] The technical solution of the present invention proposes a ship water pressure field prediction method based on the RANS method, by obtaining the main scale parameter value corresponding to the ship, the ship speed at a preset water depth is obtained according to the main scale parameter value; the ship's sailing depth Froude number is calculated according to the preset water depth and the ship's speed; a virtual numerical water pool is constructed according to the ship's sailing depth Froude number; according to the main scale parameter value, the preset water depth and the ship's speed, the boundary conditions, scales and damping wave-breaking lengths corresponding to the top, bottom, side, outlet, inlet, symmetry surface and hull of the virtual numerical water pool are preset; the virtual numerical water pool is meshed to generate a computational domain mesh virtual numerical pool and a free surface mesh virtual numerical pool; the ship water pressure field is predicted according to the computational domain mesh virtual numerical pool and the free surface mesh virtual numerical pool, and a prediction result when the speed is the ship's sailing depth Froude number at a preset pressure measuring point position and a preset water depth is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flowchart provided for an embodiment of the present invention;

[0029] Figure 2 A schematic diagram of a virtual numerical water pool provided by an embodiment of the present invention;

[0030] Figure 3 A schematic diagram of mesh division of a virtual numerical calculation domain provided by an embodiment of the present invention;

[0031] Figure 4 A schematic diagram of meshing of a virtual numerical free surface provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0033] The relevant terms and concepts in this invention are as follows:

[0034] Water pressure field: When a ship sails in the water, the surrounding velocity field and pressure field will change. This change in flow field pressure caused by the movement of the ship is called the ship's water pressure field.

[0035] RANS method: Reynolds-averaged Navier-Stokes method.

[0036] like Figure 1 As shown, an embodiment of the present invention provides a ship water pressure field prediction method based on the RANS method, comprising the following steps:

[0037] Obtain the main scale parameter values ​​corresponding to the ship. Take ship model A as an example for example analysis. The main scales of the selected ship model A are shown in Table 1.

[0038] Table 1 Main dimensions of ship model A

[0039]

[0040] The Rude number of the ship's navigation depth is calculated according to the main scale parameter value. The calculation formula of the Rude number of the ship's navigation depth is as follows:

[0041]

[0042] Where V is the ship speed (m / s), g is the acceleration of gravity (m / s2), and h is the preset water depth (m).

[0043] According to the water depth, the Fu Rude number is constructed as follows Figure 2 Virtual numerical pool shown.

[0044] The boundary conditions and related parameters of the virtual numerical pool are set according to Table 2.

[0045] Table 2 Boundary conditions and parameters of virtual numerical pool

[0046]

[0047] The virtual numerical pool is meshed, and the generated computational domain mesh and free surface mesh are as follows: Figure 3 shown.

[0048] Conduct simulation and prediction of water pressure field during ship navigation.

[0049] The comparison between the numerical prediction results of the ship water pressure field prediction method proposed in the embodiment of the present invention and the experimental values ​​and the theoretical calculation method is shown in Table 3. The prediction accuracy is improved by 11% on average. Compared with the traditional theoretical calculation method, the numerical simulation prediction method proposed in the embodiment of the present invention can effectively improve the numerical prediction accuracy.

[0050]

[0051]

Claims

1. A ship water pressure field prediction method based on RANS method, characterized in that: The following steps are involved: Obtain the main scale parameter value corresponding to the ship, and obtain the ship speed at the preset water depth according to the main scale parameter value; Calculate the ship's navigation depth Fu Rude number according to the preset water depth and ship speed; According to the Froude number of the ship's navigation depth, a virtual numerical water pool with top, bottom, side, outlet, inlet, symmetry plane and hull is constructed; According to the main scale parameter values, preset water depth and ship speed, preset the boundary conditions, scales and damping wave-absorbing lengths corresponding to the top, bottom, sides, outlet, inlet, symmetry plane and hull of the virtual numerical water pool; Meshing the virtual numerical pool to generate a computational domain mesh virtual numerical pool and a free surface mesh virtual numerical pool; The ship water pressure field is predicted based on the computational domain grid virtual numerical pool and the free surface grid virtual numerical pool, and the prediction results are obtained when the speed is the Rude number of the ship's navigation depth at the preset pressure measuring point position and the preset water depth.

2. A ship water pressure field prediction method based on RANS method as claimed in claim 1, characterized in that: The main scale parameter values ​​include ship length, draft and ship width.

3. A ship water pressure field prediction method based on RANS method as claimed in claim 1, characterized in that: The calculation formula of the Rude number of the ship's navigation depth is as follows: Where: V represents the ship speed (m / s), g represents the acceleration of gravity (m / s2), and h represents the water depth (m).

4. A ship water pressure field prediction method based on RANS method as claimed in claim 1, characterized in that: The boundary condition of the inlet is the velocity inlet, the boundary condition of the outlet is the pressure outlet, the boundary condition of the side is the velocity inlet, the boundary condition of the bottom is the no-slip wall, the boundary condition of the top is the symmetry plane, the boundary condition of the symmetry plane is the symmetry plane, and the boundary condition of the hull is the no-slip wall.

5. A ship water pressure field prediction method based on RANS method as claimed in claim 1, characterized in that: The corresponding dimensions of the outlet and the side are greater than their corresponding damping and wave-breaking lengths.

6. A ship water pressure field prediction method based on RANS method as claimed in claim 5, characterized in that: When the outlet size is 2.5L pp When the damping length is 1L pp .

7. A ship water pressure field prediction method based on RANS method as claimed in claim 5, characterized in that: When the side dimension is 1.5L pp When the damping length is 1L pp .

8. A ship water pressure field prediction method based on RANS method as claimed in claim 1, characterized in that: The size of the bottom is determined according to the Rude number of the water depth in which the ship is sailing.

9. A ship water pressure field prediction method based on RANS method as claimed in claim 1, characterized in that: The preset pressure measuring point position interval is 0-0.5L.

10. A ship water pressure field prediction method based on RANS method as claimed in claim 1, characterized in that: The ship water pressure field prediction method based on the RANS method takes into account the viscosity of the fluid and the strong nonlinear effect of the free liquid surface.

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