AUV (Autonomous Underwater Vehicle) reversing numerical simulation method and system under dynamic grid

Abstract

The invention discloses an AUV (Autonomous Underwater Vehicle) reversing numerical simulation method and system under a dynamic grid. The method comprises the following steps: pre-processing an AUV model according to a reversing working condition of an underwater vehicle in a deep sea; building reversing drainage basins in blocks, and performing grid division on each drainage basin; according to an AUV reversing working condition, compiling a related parameter file of a force required by reversing; setting each drainage basin by adopting a moving grid method; solving conditions are set, AUV backing is simulated, backing numerical values are simulated and analyzed, and related numerical values in the backing process are obtained.

Description

Technical Field

[0001] The present invention relates to the field of AUV simulation, and in particular to a method and system for numerical simulation of AUV reversing under dynamic grid. Background Art

[0002] The demand for autonomous underwater vehicles (AUVs) in scientific research and military fields is increasing, and the motion control and navigation performance of AUVs in complex underwater environments has become one of the key technologies. Dynamic simulation and path planning of AUVs are the core parts of their performance optimization and operational safety. In recent years, computational fluid dynamics (CFD) combined with AUV dynamic simulation has become an important means of studying AUV motion and control. Fluent, as a widely used CFD software in the industry, can accurately simulate underwater fluid fields. However, although Fluent's powerful fluid dynamics simulation function is widely used in AUV research, it still has some shortcomings in complex scenarios, especially in the simulation of special actions such as AUV reversing.

[0003] Defects and shortcomings of the existing technology: 1. Insufficient reversing simulation: Existing AUV simulation technologies mostly focus on motion control in forward mode, and there are relatively few reversing simulation technologies.

[0004] 2. Currently, most numerical simulations use overlapping grids to realize the dynamic behavior of AUV. However, when overlapping grid areas are connected, it will cause numerical accuracy and interface problems, resulting in low calculation data accuracy. Summary of the invention

[0005] To achieve the above-mentioned purpose and other related purposes, the present invention discloses a numerical simulation method of AUV reversing under dynamic grid, comprising: The AUV model is pre-processed according to the reversing conditions of the underwater vehicle in the deep sea; Build the reverse watershed in blocks, and divide each watershed into grids; According to the AUV reversing working conditions, compile the relevant parameter files of the force required for reversing; The moving grid method is used to set each watershed; Set the solution conditions, simulate the AUV reversing, and simulate and analyze the reversing values ​​to obtain the relevant values ​​in the reversing process.

[0006] Furthermore, the step of constructing the reverse watershed in blocks includes: The reversing flow area includes an AUV area, an area A, an area B, an area C, an area D, an area E and an area F, wherein the AUV area is a central area including an AUV model, an area A and an area B are reversing navigation areas, an area A is located in a backward direction of the AUV area, an area B is located in a forward direction of the AUV area, an area C and an area D are located above and below the AUV area, respectively, an area E and an area F are located on the left and right of the AUV area, respectively, and the AUV area, an area A, an area B, an area C, an area D, an area E and an area F together form a flow area in the shape of a rectangular parallelepiped.

[0007] Furthermore, the step of dividing each watershed into grids comprises: The surface size of the AUV area model is encrypted and the volume is encrypted using the BOI block method, and the overall mesh of the AUV area adopts a hybrid mesh of polyhedron and hexahedron; Region A, region B, region C, region D, region E and region F are meshed using hexahedral meshes.

[0008] Furthermore, the properties of Region A, Region B and AUV Region are set to Rigid Body, and the motion mode is set to Translation; The properties of area C, area D, area E, and area F are set to Stationary, and the motion mode is set to Stationary.

[0009] Furthermore, the grids between the AUV area, area A, area B, area C, area D, area E and area F are combined through interfaces.

[0010] Furthermore, the step of setting the solution conditions and simulating the AUV reversing includes: The k-ω SST turbulence model is used for simulation, in which all the walls except the interfaces between the regions are no-slip walls; The SIMPLE algorithm is used as the solution method, the pressure term uses the second-order iteration, and the momentum and turbulent kinetic energy both use the second-order upwind format; After initializing the data, import the date of steady direct flight, set the time step, and perform numerical calculations for unsteady reverse flight.

[0011] Furthermore, the method for setting the time step includes: Δt=CFL×Δx / U; where Δx is the characteristic scale of the grid cell, U is the characteristic velocity of the flow field, and CFL is the Courant-Friedrichs-Lewy number, where CFL<1.

[0012] On the other hand, the present invention provides a numerical simulation system for AUV reversing under dynamic grid, comprising: A pre-processing module is used to pre-process the AUV model according to the reversing condition of the underwater vehicle in the deep sea; The reverse watershed construction module is used to build the reverse watershed in blocks and divide each watershed into grids; The force field definition module is used to compile the relevant parameter files of the force required for reversing according to the AUV reversing working conditions; The moving grid setting module is used to set each basin using the moving grid method; The simulation module is used to set the solution conditions, simulate the AUV reversing, and simulate and analyze the reversing values ​​to obtain relevant values ​​during the reversing process.

[0013] By adopting the above technical solution, the present invention reads the parameter file, sets the dynamic grid for each watershed, and uses the moving grid method to set each area to complete the simulation of the AUV reversing. Through sophisticated fluid mechanics simulation and dynamic grid technology, the mutual influence of fluid force and rigid body motion during the AUV reversing process can be accurately captured. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and other features, advantages and aspects of the embodiments of the present disclosure will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. The accompanying drawings are used to better understand the present solution and do not constitute a limitation of the present disclosure. In the accompanying drawings, the same or similar reference numerals represent the same or similar elements, among which: Figure 1 Flowchart of this application. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0016] Reference Figure 1 The embodiment of the present invention provides a numerical simulation method for AUV reversing under dynamic grid, comprising the following steps: S1: Pre-process the AUV model according to the reversing condition of the underwater vehicle in the deep sea.

[0017] As mentioned above, the AUV model and the places with high curvature such as rudder wings, as well as the gaps in the model, are simplified to facilitate meshing.

[0018] S2: Build the reverse watershed in blocks and divide each watershed into grids.

[0019] Specifically, the block-by-block construction of the reverse watershed includes: The reversing flow area includes an AUV area, an area A, an area B, an area C, an area D, an area E and an area F, wherein the AUV area is a central area including an AUV model, an area A and an area B are reversing navigation areas, an area A is located in a backward direction of the AUV area, an area B is located in a forward direction of the AUV area, an area C and an area D are located above and below the AUV area, respectively, an area E and an area F are located on the left and right of the AUV area, respectively, and the AUV area, an area A, an area B, an area C, an area D, an area E and an area F together form a flow area in the shape of a rectangular parallelepiped.

[0020] Among them, the rectangular basin composed of AUV area, area A, area B, area C, area D, area E and area F has a total length of 10L, a width of 19D and a height of 29D, where L represents the length of the AUV and D represents the diameter of the AUV. The AUV area is the central area, which contains the AUV model, with a total length of 2L, a width of 5D and a height of 5D. Area A and area B are the reversing navigation areas. To ensure that the reversing channel is sufficient, area A is 6L long, 5D wide and 5D high. Area B is the reversing deceleration channel, with a length of 2L, a width of 5D and a height of 5D. To ensure that the AUV has no wall effect when reversing and improve the calculation accuracy, area C and area D are 11L long, 5D wide and 12D high, and area E and area F are 10L long, 7D wide and 29D high. The fluid properties of each basin are water.

[0021] The steps of meshing each watershed include: The surface size of the AUV area model is encrypted and the volume is encrypted using the BOI block method, and the overall grid of the AUV area adopts a mixed grid of polyhedron and hexahedron; Region A, Region B, Region C, Region D, Region E and Region F are meshed using hexahedral grids.

[0022] As mentioned above, meshing is performed after watershed division. Hexahedral meshes are used to encrypt areas A and B of the reversing channel to accurately capture the wake and flow field characteristics of the AUV when it is reversing. The AUV area contains the calculation model. During meshing, the model surface size is encrypted and the volume is encrypted using the BOI block method. The overall mesh uses a mixed mesh of polyhedron and hexahedron to adapt to the complex surface of the AUV and improve the calculation accuracy. The meshes of other watersheds are all divided by hexahedral meshes. The meshes between the AUV area, area A, area B, area C, area D, area E and area F are combined through interface surfaces.

[0023] S3: According to the AUV reversing condition, write the relevant parameter file of the force required for reversing.

[0024] The relevant parameter file in this embodiment is a profile file. When writing it, it should be noted that the time variable must be arranged in ascending order. In addition to defining force, variables can also be defined for physical properties such as angular velocity, temperature, and speed. The defined variables all use the International System of Units. The specific writing method is the existing technology known to those skilled in the art and will not be repeated here.

[0025] By applying force distribution to the AUV boundary in the Profile file, the various physical environmental influences encountered by the AUV when reversing in the water can be simulated. The distribution of these forces will change with the motion state of the AUV (such as speed, posture), thereby more realistically reflecting the dynamic characteristics of the reversing process. In this process, the Profile file is not only used to define fixed boundary conditions, but also to dynamically adjust the magnitude and direction of the force to respond to changes in the AUV motion in real time. The introduction of the Profile file avoids readjusting the AUV motion parameters every time the simulation is performed, reduces unnecessary computational overhead, and improves the simulation speed.

[0026] S4: Use the moving grid method to set each watershed.

[0027] As mentioned above, this embodiment uses fluent software to read the grid and compile the Profile file, sets the dynamic grid for each watershed, and uses the moving grid method to set each area, where the area A, area B and AUV area attributes are set to Rigid Body, and the movement mode is set to Translation; Area C, area D, area E and area F attributes are set to Stationary, and the movement mode is set to Static. According to the settings, the force field information in the profile can be applied to the AUV, so that the AUV can perform dynamic reversing according to the defined force.

[0028] S5: Set the solution conditions, simulate the AUV reversing, and simulate and analyze the reversing values ​​to obtain relevant values ​​in the reversing process.

[0029] Specifically, after the dynamic grid flow domain is set, the k-ω SST turbulence model is used. The rightmost side is the inlet velocity, the leftmost side is the pressure outlet, and the remaining walls except the interfaces between the regions are all no-slip walls. The solution method uses the SIMPLE algorithm, the pressure term uses the second-order iteration, and the momentum and turbulent kinetic energy both use the second-order headwind format to increase the calculation accuracy. After initialization, the date of steady direct flight is imported, a reasonable time step is set, and the unsteady reverse numerical calculation is started.

[0030] Methods for setting the time step include: Δt=CFL×Δx / U; where Δx is the characteristic scale of the grid cell, U is the characteristic velocity of the flow field, and CFL is the Courant-Friedrichs-Lewy number, where CFL<1.

[0031] When the calculation and solution are started, the resistance, torque, speed and pressure characteristics of the AUV when reversing are monitored. After the calculation, the numerical simulation of reversing is analyzed, and the resistance change, speed change, flow field information, etc. of the AUV in the process are output. The above calculation method does not belong to the key content to be protected by the present invention and will not be repeated here.

[0032] The present invention uses Fluent software to simulate the fluid mechanics of the AUV in the reversing process in detail. During the reversing process, the propeller direction of the AUV is reversed, resulting in changes in the fluid field. By setting a dynamic grid model in the CFD simulation software, the interaction between the AUV and the water flow during the reversing process can be accurately simulated, and the force and torque generated by the fluid on the AUV can be captured, so as to achieve high-precision fluid-structure coupling analysis during the AUV reversing process. The Profile file provides accurate motion state data, while Fluent simulates the real-time interaction between the AUV and the fluid, effectively improving the accuracy of the reversing simulation results. The flow field simulation not only takes into account the thrust and movement of the AUV itself, but also includes complex fluid phenomena such as turbulence and eddy currents in the water flow environment. Combined with the dynamic grid function in Fluent and the rigid body dynamics model of the AUV, a high degree of coupling between the rigid body and the fluid is achieved during the simulation process. When the AUV is reversing, as the AUV moves, the grid of the simulation area will be adaptively adjusted to ensure accurate capture of the fluid field. In addition, the rigid body motion of the AUV interacts with the changes in the dynamic grid, which can more accurately simulate the real behavior of the AUV during the reversing process. The simulation results can not only help optimize the AUV's reversing trajectory, but also provide support for the AUV's control system, especially in a dynamic and complex marine environment, which can effectively improve the AUV's operational performance and reliability during the reversing process. Through numerical simulation methods, the fluid mechanics problems that may be encountered during the AUV's reversing process can be simulated and predicted, avoiding the high costs and high risks that may exist in traditional experiments, and greatly reducing the complexity of the AUV's reversing operation.

[0033] An embodiment of the present invention further provides a numerical simulation system for AUV reversing under a dynamic grid, comprising: A pre-processing module is used to pre-process the AUV model according to the reversing condition of the underwater vehicle in the deep sea; The reverse watershed construction module is used to build the reverse watershed in blocks and divide each watershed into grids; The force field definition module is used to compile the relevant parameter files of the force required for reversing according to the AUV reversing working conditions; The moving grid setting module is used to set each basin using the moving grid method; The simulation module is used to set the solution conditions, simulate the AUV reversing, and simulate and analyze the reversing values ​​to obtain relevant values ​​during the reversing process.

[0034] Those skilled in the art will appreciate that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined.

[0035] For the method embodiments, for the sake of simplicity, they are all described as a series of action combinations, but those skilled in the art should know that the embodiments of the present invention are not limited by the order of the actions described, because according to the embodiments of the present invention, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions involved are not necessarily required by the embodiments of the present invention.

[0036] It can be known from the description of the above implementation modes that those skilled in the art can clearly understand that the present application can be implemented by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solution of the present application can be essentially or partly contributed to the prior art in the form of a software product, which can be stored in a storage medium such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes several instructions for enabling a computer device (which can be a personal computer, a server or a network device, etc.) to execute the methods described in the various implementation modes of the present application or certain parts of the implementation modes.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A numerical simulation method for AUV reversing under dynamic grid, characterized in that: include: The AUV model is pre-processed according to the reversing conditions of the underwater vehicle in the deep sea; Build the reverse watershed in blocks and divide each watershed into grids; According to the AUV reversing working conditions, compile the relevant parameter files of the force required for reversing; The moving grid method is used to set each watershed; Set the solution conditions, simulate the AUV reversing, and simulate and analyze the reversing values ​​to obtain the relevant values ​​in the reversing process.

2. The method according to claim 1, characterized in that: The steps of constructing the reverse watershed in blocks include: The reversing flow area includes an AUV area, an area A, an area B, an area C, an area D, an area E and an area F, wherein the AUV area is a central area including an AUV model, an area A and an area B are reversing navigation areas, an area A is located in a backward direction of the AUV area, an area B is located in a forward direction of the AUV area, an area C and an area D are located above and below the AUV area, respectively, an area E and an area F are located on the left and right of the AUV area, respectively, and the AUV area, an area A, an area B, an area C, an area D, an area E and an area F together form a flow area in the shape of a rectangular parallelepiped.

3. The method according to claim 2, characterized in that The step of dividing each watershed into grids comprises: The surface size of the AUV area model is encrypted and the volume is encrypted using the BOI block method, and the overall mesh of the AUV area adopts a hybrid mesh of polyhedron and hexahedron; Region A, region B, region C, region D, region E and region F are meshed using hexahedral meshes.

4. The method according to claim 2, characterized in that: The properties of area A, area B and AUV area are set to RigidBody, and the motion mode is set to translation; The properties of area C, area D, area E, and area F are set to Stationary, and the motion mode is set to Stationary.

5. The method according to claim 2, characterized in that: The grids between the AUV area, area A, area B, area C, area D, area E and area F are combined through interfaces.

6. The method according to claim 5, characterized in that The steps of setting the solution conditions and simulating the AUV reversing include: The k-ω SST turbulence model is used for simulation, in which all the walls except the interfaces between the regions are no-slip walls; The SIMPLE algorithm is used as the solution method, the pressure term uses the second-order iteration, and the momentum and turbulent kinetic energy both use the second-order upwind format; After initializing the data, import the date of steady direct flight, set the time step, and perform numerical calculations for unsteady reverse flight.

7. The method according to claim 6, characterized in that The method for setting the time step includes: Δt=CFL×Δx / U; where Δx is the characteristic scale of the grid cell, U is the characteristic velocity of the flow field, and CFL is the Courant-Friedrichs-Lewy number, where CFL<1.

8. A numerical simulation system for AUV reversing under dynamic grid, characterized in that: include: A pre-processing module is used to pre-process the AUV model according to the reversing condition of the underwater vehicle in the deep sea; The reverse watershed construction module is used to build the reverse watershed in blocks and divide each watershed into grids; The force field definition module is used to compile the relevant parameter files of the force required for reversing according to the AUV reversing working conditions; The moving grid setting module is used to set each basin using the moving grid method; The simulation module is used to set the solution conditions, simulate the AUV reversing, and simulate and analyze the reversing values ​​to obtain relevant values ​​during the reversing process.

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