Method for calculating influence of non-uniformly attached netting on flow field distribution and water resistance

Abstract

The invention discloses a method for calculating the influence of a non-uniformly attached netting on flow field distribution and water resistance. The method comprises the following steps: establishing a non-uniformly attached netting numerical model and a water tank numerical model; the netting is arranged in the water tank in the transverse direction; grid division is carried out on the fluid domain and the nettings, and topological boundary sharing is carried out between the nettings with different attachment degrees and between the nettings with different attachment degrees and the fluid domain; simulating a fluid domain by adopting an SSTk-turbulence model; the nettings are simulated by adopting a porous medium, calculation areas where the nettings with different attachment degrees are located are set respectively, and water resistance coefficients and porous medium directions corresponding to the nettings with different attachment degrees are input; setting boundary conditions of an inlet, an outlet, a side wall and a water surface of the water tank; calculating flow velocity distribution and pressure distribution; and establishing different computational domain profiles, drawing a flow velocity distribution cloud chart according to the flow velocity distribution, and integrating the pressure to obtain the water resistance. According to the method, the influence of the non-uniformly attached netting on flow field distribution and water resistance can be quickly and accurately evaluated.

Description

Technical Field

[0001] This invention relates to a method for calculating the influence of non-uniformly attached netting on flow field distribution and water resistance. Background Technology

[0002] Severe adhesion of netting to deep-sea aquaculture cages significantly impacts water exchange within the cages and increases the risk of cage damage. Therefore, calculating the impact of adhered netting on velocity distribution and water resistance is essential. However, the degree of netting adhesion in deep-sea aquaculture cages is uneven, making numerical calculations complex. Existing methods assume uniform density to calculate the impact of uniformly adhered netting on velocity distribution and water resistance, failing to consider the varying degrees of adhesion at different locations within the aquaculture cages. Therefore, this method has the following drawbacks:

[0003] (1) The effect of non-uniformly attached netting on velocity distribution cannot be considered.

[0004] (2) It is impossible to consider the influence of different positions and different degrees of attachment of the netting on the amplitude of water resistance.

[0005] (3) It cannot handle the connection and data exchange between meshes with different positions and different degrees of attachment.

[0006] (4) It is impossible to consider the mutual influence between meshes with different positions and different degrees of attachment. Summary of the Invention

[0007] The purpose of this invention is to provide a method for calculating the influence of non-uniformly attached netting on flow field distribution and water resistance, which can quickly and accurately assess the influence of non-uniformly attached netting on flow field distribution and water resistance.

[0008] The objective of this invention is achieved through the following technical measures: a method for calculating the influence of non-uniformly attached netting on flow field distribution and water resistance, characterized by comprising the following steps:

[0009] S1. Establish a numerical model of non-uniformly attached netting, which is composed of netting with different degrees of attachment set sequentially along the water depth direction.

[0010] S2. Establish a numerical model of the water tank, with an inlet at one end and an outlet at the other end;

[0011] S3. The netting is placed horizontally in the water tank, with gaps between the netting and the inlet, outlet, side wall, and bottom of the water tank.

[0012] S4. Mesh the fluid domain and the mesh, and establish topological shared boundaries between meshes with different adhesion levels and between meshes with different adhesion levels and the fluid domain.

[0013] S5, using SSTk- Turbulence models simulate the fluid domain;

[0014] S6. The mesh is simulated using a porous medium. The calculation area where the mesh with different adhesion levels are located is set, and the water resistance coefficient and porous medium direction corresponding to the mesh with different adhesion levels are input.

[0015] S7. Set the boundary conditions for the tank inlet, outlet, sidewalls, and water surface;

[0016] S8. Calculate the velocity and pressure distribution;

[0017] S9. Establish different computational domain profiles, draw velocity distribution cloud maps based on the velocity distribution, and integrate the pressure to obtain water resistance.

[0018] This invention relates to a calculation method for the influence of different attachment degrees of a single piece of netting at different locations on flow velocity distribution and water resistance under water flow conditions. This invention is the first to consider the influence of different attachment degrees of a single piece of netting on flow velocity distribution and water resistance. By employing computational fluid dynamics methods and porous media theory, and introducing methods for data exchange and topological sharing boundaries between netting with different attachment degrees, this invention can quickly and accurately assess the influence of non-uniformly attached netting on flow field distribution and water resistance. This provides data support for exploring the influence mechanism of attached netting on water flow exchange and promotes the development of deep-sea aquaculture facilities.

[0019] In step S1 of this invention, the density of the mesh with different adhesion levels increases sequentially from top to bottom.

[0020] In step S4 of this invention, the fluid domain is divided into tetrahedral meshes, and the mesh is divided into hexahedral meshes.

[0021] In step S4 of this invention, the mesh in the contact area between the fluid domain and the mesh is densified to a density of 0.1m to 0.025m.

[0022] In step S6 of this invention, the inlet boundary of the water tank adopts a velocity inlet, the outlet boundary adopts a free outflow, the sidewall adopts a wall boundary condition, and the water surface adopts a shear stress-free boundary condition.

[0023] In step S7 of this invention, transient calculations are used and the influence of gravity is considered. The pressure and flow velocity variables are discretized using a second-order discretization method, and the flow velocity distribution and pressure distribution are obtained by using the SIMPLEC algorithm.

[0024] In step S2 of this invention, a numerical model of the water tank is established through Boolean operations.

[0025] Compared with the prior art, the present invention has the following significant effects:

[0026] (1) This invention can realize the transfer of data between different attached nets, the calculation of the influence of different positions and different degrees of attachment of a single net on the flow velocity distribution, the calculation of the influence of different positions and different degrees of attachment of a single net on water resistance, and the calculation of the mutual influence between nets attached at different positions. This invention can quickly and accurately evaluate the influence of non-uniformly attached nets on the flow field distribution and water resistance through numerical calculation methods, saving a lot of manpower, material resources and financial resources, and providing reference data for the design and optimization of aquaculture cages, which has practical engineering significance.

[0027] (2) This invention effectively solves the problems of non-uniformly attached nets affecting flow velocity distribution, water resistance amplitude, data exchange, and mutual influence. It provides strong technical support for promoting the transfer of marine aquaculture from nearshore to deep sea, making full use of the excellent water quality of the deep sea, and promoting the healthy and sustainable development of fisheries. Attached Figure Description

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] Figure 1 is a front view of the numerical model of the non-uniformly attached netting of the present invention;

[0030] Figure 2 This is a three-dimensional structural schematic diagram of the numerical model of the non-uniformly attached netting and the numerical model of the water tank of the present invention;

[0031] Figure 3 This is a top view of the numerical model of the non-uniformly attached netting and the numerical model of the water tank of the present invention;

[0032] Figure 4 This is a cross-sectional view of the numerical model of the non-uniformly attached netting and the numerical model of the water tank of the present invention;

[0033] Figure 5 This is a schematic diagram of the fluid domain mesh generation of the present invention;

[0034] Figure 6 This is a schematic diagram of the mesh partitioning of the numerical model of the non-uniformly attached netting of the present invention;

[0035] Figure 7 This is a schematic diagram of the velocity distribution plane based on the numerical calculation results of this invention;

[0036] Figure 8 This is a schematic diagram of the velocity distribution profile resulting from the numerical calculation of this invention.

[0037] In the figure: 1-first attached netting, 2-second attached netting, 3-third attached netting, 4-fourth attached netting, 5-non-uniform attached netting, 6-water tank, 7-inlet, 8-outlet, 9-side wall, 10-bottom surface. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the embodiments and accompanying drawings to help those skilled in the art better understand the inventive concept of the present invention. However, the scope of protection of the claims of the present invention is not limited to the following embodiments. For those skilled in the art, all other embodiments obtained without creative effort without departing from the inventive concept of the present invention are within the scope of protection of the present invention.

[0039] like Figures 1-8 As shown, the present invention provides a method for calculating the influence of non-uniformly attached netting on flow field distribution and water resistance, which specifically includes the following steps:

[0040] S1. Establish a numerical model of non-uniformly attached netting, which is composed of netting with different degrees of attachment set sequentially along the water depth direction.

[0041] See Figure 1 In this embodiment, the non-uniformly attached netting 5 is a rectangular single-piece netting, 1.0m long and 0.4m high. It is composed of netting with different degrees of attachment arranged sequentially along the water depth direction. The netting with different degrees of attachment includes the first attached netting 1 (density Sn=0.15), the second attached netting 2 (density Sn=0.25), the third attached netting 3 (density Sn=0.35), and the fourth attached netting 4 (density Sn=0.45). The height of each attached netting is 0.1m, and the density of each attached netting increases sequentially from top to bottom.

[0042] This invention uses a variable density method to calculate the influence of non-uniformly attached netting on flow field distribution and water resistance. The overall netting has a low density at the top and a high density at the bottom, which can more realistically reflect the attachment status of the netting.

[0043] S2. Establish a numerical model of the water tank through Boolean operations. It is a cuboid with an inlet 7 at one end and an outlet 8 at the other end.

[0044] S3. The mesh 5 is placed horizontally in the water tank 6, with the mesh 5 having a gap between it and the inlet 7, outlet 8, side walls 9 and bottom surface 10 of the water tank 6 respectively.

[0045] See Figures 2-4 In this embodiment, the water tank 6 is 10m long, 2m wide, and 0.7m high. The mesh 5 is 3m from the inlet of the water tank 6, 7m from the outlet, 0.5m from each of the two side walls, and 0.3m from the bottom of the water tank. The top edge of the mesh is flush with the top edge of the side wall. The fluid flows in direction A.

[0046] S4. Mesh the fluid domain (water tank) and the mesh, and refine the mesh of the fluid domain in contact with the mesh, with a refinement range of 0.1m to 0.025m. Topologically share boundaries between meshes with different adhesion levels and between meshes with different adhesion levels and the fluid domain. That is, the feature nodes and boundaries at the contact positions between meshes with different adhesion levels and between meshes with different adhesion levels and the fluid domain are kept consistent and shared. The method of sharing topology ensures the connection of mesh nodes and realizes the transmission of data between meshes with different adhesion levels.

[0047] See Figure 5 and Figure 6 In this embodiment, the fluid domain is meshed with a tetrahedral grid with a grid size of 0.1m; the mesh is meshed with a hexahedral grid with a grid size of 0.025m. The mesh in the contact area between the fluid and the porous media mesh is refined.

[0048] To realize the effect of different attachment degrees at different locations of a single mesh on flow velocity and water resistance, flow velocity data is exchanged between mesh sections with different attachment degrees using a topologically shared boundary method.

[0049] S5. Based on the Reynolds average method, using SSTk- Turbulence models simulate the fluid domain;

[0050] Continuity equation:

[0051] ;

[0052] Momentum equation:

[0053] ;

[0054] SST k- Turbulence equations:

[0055] ;

[0056] ;

[0057] ;

[0058] in, For fluid density, For time, For velocity components, For coordinate components, For pressure, It is the acceleration due to gravity. For fluid viscosity, Eddy viscosity, For source terms, Kinematic viscosity, =0.31, For turbulent kinetic energy, For turbulent dissipation rate, This is the absolute value of vorticity. For the second mixing function, Let Reynolds stress tensor be the stress tensor. =9 / 100, For turbulent kinetic energy diffusion term, and These are model constants. For the specific dissipation rate diffusion term, " is the first mixing function", =0.856.

[0059] S6. The mesh is simulated using a porous medium. The calculation regions where meshes with different adhesion levels are located are set, and the water resistance coefficients and porous medium directions corresponding to meshes with different adhesion levels are input. The influence of the attached mesh on the flow field and water resistance is considered.

[0060] This invention is based on porous media theory and considers the damping effect of mesh with different degrees of adhesion on water flow and the amplitude of water resistance.

[0061] Control equations for porous media:

[0062] ;

[0063] in, The coefficient of viscosity resistance. The inertial drag coefficient, Number the different attached mesh garments. For the first attached netting source item, For the second attached netting source item, For the third attached netting source item, This is the fourth attachment web source term. Similarly... to These represent the adhesive resistance coefficients of the first to fourth attached mesh layers, respectively. to These represent the inertial drag coefficients of the first to fourth attached netting, respectively.

[0064] S7. Set the boundary conditions for the inlet, outlet, sidewall, and water surface of the water tank; in this embodiment, the inlet boundary adopts a velocity inlet with a velocity of 0.159 m / s, the outlet boundary adopts free outflow, the sidewall adopts a wall boundary condition, the water surface adopts a shear stress-free boundary condition, and data exchange is achieved between meshes with different adhesion levels and between meshes with different adhesion levels and the fluid domain by sharing a topological boundary.

[0065] S8. Calculate the velocity and pressure distribution; This embodiment uses transient calculation and considers the influence of gravity. The pressure and velocity variables are discretized using a second-order discretization method, and the SIMPLEC algorithm is used to solve the problem, finally obtaining the velocity and pressure distribution.

[0066] S9. Establish different computational domain profiles, draw velocity distribution cloud maps based on the velocity distribution, and integrate the pressure to obtain water resistance.

[0067] Specifically, the water resistance of the mesh at different locations and with varying degrees of adhesion is obtained by integrating the pressure, and then the total water resistance F is obtained by summing the results. t :

[0068] ;

[0069] in, For non-uniformly attached mesh, the total force is... For the force on the first attached mesh, For the stress on the second attached mesh, For the stress on the third attached mesh, The force on the fourth attached mesh.

[0070] The numerical calculation results of this embodiment are as follows: Figure 7 and Figure 8 As shown, the effect of the attached netting on the velocity distribution is visualized. The calculated water resistance acting on the attached netting is 8.573 N, which is about three times that of the netting without attachment.

[0071] Therefore, the present invention can be used to evaluate the impact of non-uniformly attached netting on flow velocity distribution and water resistance amplitude.

Claims

1. A method for calculating the influence of non-uniform attached boundary layer on the convection field distribution and water resistance, characterized in that The method comprises the following steps: S1, establishing a non-uniform attached net model, which is connected by nets with different attachment degrees arranged in sequence along the water depth direction; S2, establishing a water tank numerical model, one end of the water tank is provided with an inlet, and the other end is provided with an outlet; S3, the net is arranged in the water tank along the transverse direction, and the net is spaced apart from the inlet, outlet, side wall and bottom surface of the water tank; S4, the fluid domain and the net are meshed, and the topological shared boundary is performed between different attachment degree nets and between different attachment degree nets and the fluid domain; S5, take SSTk- Turbulence models simulate the fluid domain; S6, the net is simulated by using a porous medium, the calculation area of the net with different attachment degrees is set, and the water resistance coefficient and the porous medium direction corresponding to the net with different attachment degrees are input; S7, setting the boundary conditions of the inlet, outlet, side wall and water surface of the water tank; S8, calculating the flow velocity distribution and pressure distribution; S9, establishing different calculation domain profiles, drawing a flow velocity distribution cloud chart according to the flow velocity distribution, and integrating the pressure to obtain the water resistance.

2. The computational method of claim 1, wherein: In the step S1, the density of the nets with different attachment degrees increases from top to bottom.

3. The computational method of claim 2, wherein: In the step S4, the fluid domain is divided by tetrahedral mesh, and the net is divided by hexahedral mesh.

4. The computational method of claim 3, wherein: In the step S4, the mesh of the contact area between the fluid domain and the net is encrypted.

5. The computational method of claim 4, wherein: The mesh encryption is 0.1m~0.025m.

6. The computational method of claim 5, wherein: In the step S7, the inlet boundary of the water tank adopts velocity inlet, the outlet boundary adopts free outflow, the side wall adopts wall boundary condition, and the water surface adopts no-shear stress boundary condition.

7. The computational method of claim 6, wherein: In the step S8, the transient calculation is adopted, the influence of gravity is considered, the pressure and flow velocity variables are discretized by using the second-order discrete method, and the flow velocity distribution and pressure distribution are obtained by using the SIMPLEC algorithm.

8. The computational method of claim 7, wherein: In the step S2, the water tank numerical model is established by using Boolean operation.

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