Underwater robot propeller layout optimization method based on CFD

Abstract

The invention discloses an underwater robot thruster layout optimization method based on CFD, and the method comprises the steps: firstly determining the offset angle of a thruster for an underwater robot with a front thruster and a rear thruster, and building a geometric model according to the offset angle; then performing grid division on the model and the flow field area, determining boundary conditions, and performing transient simulation by using a slip grid technology to obtain data; and further calculating a velocity flow field and a forward total thrust value, determining vorticity change, calculating a Q value by adopting a Q criterion, and finally realizing optimization of the propeller layout according to the parameters. According to the method, the multi-parameter influence is accurately analyzed by combining a vorticity calculation formula with the help of CFD simulation, the optimal layout is scientifically determined, the performance of the propeller is improved, and energy loss and unstable factors are reduced; multiple factors such as thrust, vorticity and a Q value are comprehensively considered, the performance of the propeller is comprehensively optimized, meanwhile, a large number of actual tests are replaced with analogue simulation, the design period is effectively shortened, and high efficiency and economical efficiency are achieved.

Description

Technical Field

[0001] This application belongs to the technical field of the design of underwater robot propulsion systems, and particularly relates to a method for optimizing the layout of underwater robot thrusters based on computational fluid dynamics (CFD). Background Art

[0002] Underwater cable laying robots are usually equipped with multiple thrusters to achieve multi-directional maneuverability. However, in complex sea conditions, an unreasonable thruster layout is likely to cause wake interference, resulting in thrust loss and efficiency decline. Existing research mainly focuses on ship propulsion systems or dynamic positioning fields, and there is relatively little research on the optimization of thruster layouts for underwater cable laying robots. In traditional layouts, the distance between the front and rear thrusters is fixed and there is no offset angle, resulting in the rear thruster being completely immersed in the wake of the front propeller, thereby reducing thrust output. In the prior art, most thrusters adopt a non-offset layout, and the rear thruster is prone to getting into the wake of the front thruster, leading to thrust loss and energy dissipation, and affecting the operation stability and efficiency of the robot. Therefore, a method for optimizing the thruster layout based on fluid mechanics analysis is needed to solve the above technical problems. Summary of the Invention

[0003] The technical objective of this application is to provide a method for optimizing the layout of underwater robot thrusters based on computational fluid dynamics (CFD) to solve the technical problem of thrust loss and energy dissipation caused by the non-offset layout commonly used in the design of underwater robot thrusters in the prior art. By accurately analyzing the flow field characteristics and vortex evolution laws, the optimal thruster offset angle is determined to reduce thrust interference and improve the total forward thrust and operation efficiency.

[0004] To achieve the above technical objective, the following technical solutions are adopted in this application.

[0005] An embodiment of this application provides a method for optimizing the layout of underwater robot thrusters based on CFD. The underwater robot has front and rear double thrusters. The layout optimization method includes:

[0006] Determine the offset angles of the front and rear thrusters respectively. Based on the offset angles, establish geometric models of the front and rear thrusters using computational fluid dynamics methods;

[0007] Perform mesh division on the geometric model and the flow field region under the current offset angle to obtain a mesh file, and create a computational domain mesh model under the adjusted offset angle;

[0008] Determine the boundary conditions of the computational domains of the front and rear thrusters according to the mesh file; based on the computational domain mesh model and the boundary conditions, use the sliding mesh technology to simulate the rotational motion of the front and rear double thrusters for transient simulation to obtain simulation data;

[0009] Based on the simulation data, determine the velocity flow field and the forward total thrust value of the thrusters before and after; based on the velocity flow field, combine with the vorticity calculation formula to determine the vorticity change of the thrusters at different offset angles, and use the Q-criterion calculation formula to determine the Q values of the front and rear thrusters at different offset angles.

[0010] According to the forward total thrust value, vorticity change and Q values of the front and rear thrusters at different offset angles, determine the optimal layout optimization of the thrusters.

[0011] Further, use the sliding mesh technique to simulate the rotational motion of the front and rear dual thrusters for transient simulation to obtain simulation data, specifically including:

[0012] Use the RNG K-ε turbulence model and the SIMPLE algorithm for transient simulation to obtain simulation data including the physical quantities in the flow field changing with time, and the physical quantities at least include velocity and / or pressure.

[0013] Further, the method further includes: creating a computational domain for the front and rear dual thrusters according to the actual size of the thrusters, including an external flow field and a duct forming a stationary domain and a rotating domain formed by the propellers.

[0014] Further, according to the forward total thrust value, vorticity change and Q values of the front and rear thrusters at different offset angles, determine the optimal layout optimization of the thrusters, including:

[0015] Select the offset angle that can make the vorticity change distribution in the flow field uniform and stable, the Q value is in the optimal range, and the forward total thrust value is the largest under the design constraint conditions as the final offset angle of the front and rear thrusters.

[0016] Further, determine the respective offset angles of the front and rear thrusters, including:

[0017] Taking the oncoming flow direction as the reference, set the angle obtained by rotating the oncoming flow direction clockwise by a set angle as the offset angle of the front thruster, and set the angle obtained by rotating the oncoming flow direction counterclockwise by the set angle as the offset angle of the rear thruster.

[0018] Further, the value range of the offset angle is 5° to 50°.

[0019] Further, the offset angle is 20°.

[0020] Further, the boundary conditions include: setting the inlet boundary as a velocity inlet boundary condition, setting the outlet boundary as a pressure outlet boundary condition, and setting the thruster wall as a no-slip wall boundary condition.

[0021] Further, the calculation formula of the Q value is as follows:

[0022]

[0023] where Ω is the anti-symmetric part of the velocity gradient tensor, S is the symmetric part of the velocity gradient tensor, ||·|| represents the Frobenius norm of the tensor, and the velocity gradient tensor.

[0024] Furthermore, the calculation formula for the total forward thrust value is:

[0025] T forward = T1·cosβ + T2cosβ;

[0026] where, T forward is the total forward thrust value, T1 is the thrust generated by the front thruster, T2 is the thrust generated by the rear thruster, and β is the offset angle.

[0027] Compared with the prior art, the underwater robot thruster layout method optimized based on computational fluid dynamics (CFD) provided by the embodiments of the present application determines the optimal thruster offset angle by accurately analyzing the flow field characteristics and the eddy evolution law, reduces the thrust interference, and improves the total forward thrust and operation efficiency. This method performs layout optimization based on CFD simulation data, comprehensively considers multiple factors such as thrust, vorticity, Q value, etc. Compared with the traditional empirical design method, it can more accurately determine the optimal layout of the thrusters; at the design stage, it can quickly screen out better layout parameters such as the offset angle by simulating different working conditions, avoid a large number of actual tests, shorten the design cycle, make the underwater robot thruster layout design more scientific and reasonable, and improve the overall performance of the equipment and the underwater operation adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the disclosure of the present application in any way. Additionally, the shapes and proportional dimensions of the components in the drawings are only schematic and are used to assist in understanding the present application, rather than specifically limiting the shapes and proportional dimensions of the components of the present application. Those skilled in the art can, under the teaching of the present application, select various possible shapes and proportional dimensions according to specific circumstances to implement the present application. In the drawings:

[0029] Figure 1 is a schematic flow chart of the underwater robot thruster layout method optimized based on computational fluid dynamics (CFD) according to an embodiment of the present invention;

[0030] Figure 2 is a schematic flow chart of the underwater robot thruster layout method optimized based on computational fluid dynamics (CFD) according to another embodiment of the present invention;

[0031] Figure 3It is a schematic diagram for comparing the front and rear dual - thruster layouts of an underwater robot. Among them, (a) is a schematic diagram of the conventional layout, and (b) is a schematic diagram of the bias optimization layout achieved by the method provided in the embodiment of the present application;

[0032] Figure 4 It is a schematic diagram for comparing the CFD calculation domain model and the polyhedral mesh division. Among them, (a) is a schematic diagram of the calculation domain model and the polyhedral mesh division of the conventional layout, and (b) is a schematic diagram of the calculation domain model and the polyhedral mesh division of the method provided in the embodiment of the present application;

[0033] Figure 5 It is a contour map of the flow field velocity distribution at different bias angles according to the embodiment of the present invention;

[0034] Figure 6 It is a schematic diagram of the thruster thrust at different bias angles according to the embodiment of the present invention;

[0035] Figure 7 It is a schematic diagram of the vorticity streamline at different bias angles according to the embodiment of the present invention;

[0036] Figure 8 It is a visualization distribution diagram of the thruster vortex structure at different bias angles according to the embodiment of the present invention. Detailed implementation manners

[0037] In order to enable those skilled in the art to better understand the technical solutions in this application, the following will clearly and completely describe the technical solutions in the embodiments of this application with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of this application.

[0038] The embodiment of the present application provides a method for optimizing the thruster layout of an underwater robot based on CFD. The underwater robot has front and rear dual thrusters, as Figure 1 shown, and includes:

[0039] Step S1: Determine the respective bias angles of the front and rear thrusters. Based on the bias angles, use the computational fluid dynamics method to establish the geometric models of the front and rear thrusters;

[0040] Step S2: Mesh the geometric model and the flow field region at the current bias angle to obtain a mesh file, and create a computational domain mesh model at the adjusted bias angle;

[0041] Step S3: Determine the boundary conditions of the front and rear thruster calculation domains according to the grid file; based on the computational domain grid model and boundary conditions, use the sliding grid technique to simulate the rotational motion of the front and rear dual thrusters for transient simulation to obtain simulation data;

[0042] Step S4: Based on the simulation data, determine the velocity flow field and the forward total thrust value of the front and rear thrusters; based on the velocity flow field, combine with the vorticity calculation formula to determine the vorticity change of the thruster at different offset angles, and use the Q-criterion calculation formula to determine the Q value of the front and rear thrusters at different offset angles;

[0043] Step S5: Determine the optimal layout optimization of the thrusters according to the forward total thrust value, vorticity change and Q value of the front and rear thrusters at different offset angles.

[0044] In some embodiments, it further includes constructing the visualization of the velocity flow field of the front and rear thrusters at different offset angles based on the simulation data and analyzing the change of the front and rear thrusts.

[0045] The embodiments of the present application combine the vorticity calculation and the Q-criterion vorticity structure identification method to quantitatively analyze the flow field stability, vorticity distribution and evolution mechanism, and determine the optimal layout scheme.

[0046] In practical embodiments, the underwater robot can be an underwater cable laying operation robot, etc.

[0047] In the embodiment, according to the actual size of the thruster, create the calculation domain of the front and rear dual thrusters, including the external flow field and the ducts that form the stationary domain and the rotating domain formed by the propellers.

[0048] As Figure 2 shown, in some embodiments, first establish the geometric model and computational domain grid model of the front and rear dual thrusters in the conventional layout based on the computational fluid dynamics method, specifically including: using SpaceCliam software to create the geometric model and computational domain of the front and rear dual thrusters in the conventional layout of the underwater robot, see Figure 3 shown in (a) of

[0049] Use the flunet meshing function in Fluent software to mesh the thruster computational domain in the conventional layout, adopt the polyhedral mesh division method, and create the thruster computational domain grid model in the conventional layout, see Figure 4 shown in (a) of

[0050] In some embodiments, based on the geometric model of the front and rear dual thrusters in the conventional layout, optimize and improve it, set it to different offset angles, and on this basis, create the computational domain grid model of the thruster at different offset angles, specifically including:

[0051] Use the SpaceClaim software to adjust the offset angles of the front and rear thrusters on the basis of the conventional layout, that is, the front propeller is offset upward and the rear propeller is offset downward, as shown in Figure 3 Figure (b) below. As shown in Figure 3 Figure (b) below, taking the oncoming flow direction as the reference, the offset angle of the front thruster is the set angle β rotated clockwise from the oncoming flow direction, and the offset angle of the rear thruster is the same set angle β rotated counterclockwise from the oncoming flow direction. The offset angle ranges from 5° to 50°, and can be incremented in steps of 5°.

[0052] Use the flunet meshing function in the Fluent software to mesh the thruster geometric model and the flow field area at different offset angles. Adopt the polyhedral meshing method to create the mesh model of the thruster calculation domain at different offset angles, as shown in Figure 4 Figure (b) below.

[0053] As an example, adopt the sliding mesh technology to simulate the rotational motion of the thrusters of the underwater cable laying operation robot and perform CFD simulation, specifically including: import the.msh mesh file of the thruster meshing at different offset angles in the Fluent software; set the boundary conditions (velocity inlet, pressure outlet, non-slip wall).

[0054] As an example, the boundary conditions include: set the inlet boundary as the velocity inlet boundary condition, the outlet boundary as the pressure outlet boundary condition, and the thruster wall as the non-slip wall boundary condition.

[0055] Adopt the RNG K-ε turbulence model and the SIMPLE algorithm for transient simulation; set the report definition to monitor the lift values of the thrusters at different offset angles; use the transient calculation method in Fluent to calculate the velocity flow field and thrust values of the front and rear thrusters at different offset angles, and combine the sliding mesh technology to achieve the CFD simulation of the thrusters at different offset angles.

[0056] As an example, based on the simulation data, construct the visualization of the velocity flow field of the front and rear thrusters at different offset angles, analyze the change of the front and rear thrusts, and calculate the total forward thrust. The simulation data is the velocity flow field and lift values of the front and rear thrusters at different offset angles after the simulation calculation is completed; the calculation formula for the total forward thrust is where T1 is the thrust generated by the front thruster, T2 is the thrust generated by the rear thruster, and β is the offset angle. Specifically, it includes:

[0057] T forward = T1·cosβ + T2·cosβ;

[0058] where, T forward is the total forward thrust value, T1 is the thrust generated by the front thruster, T2 is the thrust generated by the rear thruster, and β is the offset angle.

[0059] After the simulation calculation is completed, use the post-processing function of Fluent software to construct the visualization of the velocity flow field according to the velocities of the front and rear thrusters at different offset angles, as shown in Figure 5 . Figure 5 It is the distribution diagram of the thruster velocity flow field at different offset angles, from which the changes in the wake can be observed. As Figure 5 can be seen, at different offset angles, there are significant differences in the influence of the wake of the front thruster on the rear thruster: when the deflection angle is small, the rear thruster is completely within the wake area of the front; as the offset angle increases (when it exceeds 15°), the rear thruster gradually moves out of the wake area, and the influence it receives continues to weaken until it disappears. It should be noted that under different offset angle conditions, the oncoming flow conditions of the front thruster remain basically stable.

[0060] According to the thrust values of the thrusters at different offset angles monitored as defined in the report, use the calculation formula of the forward total thrust to calculate the forward total thrust of the thrusters at different offset angles. The specific thrust values are shown in Figure 6 . As Figure 6 can be known, at different offset angles, the thrust of the front thruster remains basically constant, while the thrust of the rear thruster increases with the increase of the offset angle. Before about 15°, the thrust change of the rear thruster is relatively large. After 15°, the thrust change of the rear thruster is relatively gentle. After about 20°, the thrust of the rear thruster maintains a relatively stable state. From the change of the forward total thrust, it can be seen that when the offset angle is 20°, the forward total thrust is the largest, which is 17% higher than that under the conventional layout.

[0061] In the embodiment, combined with the vorticity calculation and the Q-criterion vortex structure identification method, quantitatively analyze the flow field stability, vorticity distribution and energy loss to determine the optimal layout scheme, specifically including:

[0062] Import the.cas and.dat simulation files of the thruster simulation results under different offset angle layouts into Tecplot software;

[0063] Define the calculation formulas of vorticity calculation and Q-criterion through the Analyze function in Tecplot software;

[0064] The vorticity calculation formula is: where wx, wy, and wz represent the vorticity components in the x, y, and z directions respectively. In the research of the present invention, the oncoming flow direction of the thruster is the z-axis direction, and the direction of vorticity needs to be perpendicular to the oncoming flow direction. Therefore, it is necessary to calculate the vorticity in the x direction (x vorticity).

[0065] As an example, the formula for calculating the Q value of the Q-criterion is as follows:

[0066]

[0067] where Ω is the anti-symmetric part (rotation tensor) of the velocity gradient tensor, representing the rotational characteristics of the fluid; S is the symmetric part (strain rate tensor) of the velocity gradient tensor, representing the deformation characteristics of the fluid; ||·|| represents the Frobenius norm of the tensor (i.e., the square root of the sum of the squares of each component), is the velocity gradient tensor.

[0068] According to the vorticity calculation formula and the Q-criterion, the eddy current field generated by the thruster and the evolution law of the vortex structure at different bias angles are calculated and analyzed, and the vorticity streamline diagram and the visualization of the vortex structure are constructed;

[0069] The vorticity calculation and analysis are as follows: First, the velocity field data are extracted from the simulation results, and then the vorticity components of the front and rear thrusters at different bias angles are calculated using the vorticity calculation formula. Based on this, the vorticity streamline diagrams at different bias angles are constructed, as shown in Figure 7 . From Figure 7 , it can be seen that when the bias angle is 15° - 25°, the flow field shows high orderliness, the streamline directions are roughly the same, the vorticity is evenly distributed, the fluid is efficiently accelerated, the energy loss is minimized, and the thrust performance is relatively ideal; while when the angle is too small (5° - 10°) or too large (30° - 50°), the flow field disorder intensifies, the high vorticity regions are scattered, the streamlines flow back, resulting in significant energy dissipation and a large reduction in efficiency.

[0070] The Q-criterion calculation and analysis are as follows: The Q values of the front and rear thrusters at different bias angles are calculated using the Q-criterion calculation formula. Usually, the region where Q > 0 is selected to identify the vortex core, and the visualization of the vortex structure is constructed, as shown in Figure 8 . Combining Figure 8 and Figure 6 analysis shows that when the bias angle is small, the rear thruster is immersed in the wake vortex structure of the front thruster, and its flow field characteristics are significantly disturbed, resulting in a decrease in thrust performance; as the bias angle increases to 20°, the rear thruster gradually moves out of the vortex influence region of the front thruster, and the thrust shows a continuous increasing trend. The flow field visualization results show that when the bias angle is 20°, the proportion of the rotation-dominated region (red region) where Q > 0 in the flow field is the largest, and the corresponding total forward thrust of the thruster reaches the peak value. When the bias angle exceeds 20°, the Q value shows a monotonic decreasing characteristic with the increase of the angle, and the thrust of the thruster also decays synchronously.

[0071] Through the combined analysis of vorticity and the Q-criterion, from the mechanism of the evolution of the eddy current field, the influence of the eddy current interaction at different bias angles on the vortex stability is revealed. Combining with the Flunet simulation results shows that in the bias angle range of 0° - 50°, when the bias angle between the front and rear thrusters is 20°, the maximum total forward thrust and the peak Q value are achieved simultaneously. This layout improves the forward propulsion efficiency and operation stability of the robot, providing a theoretical basis for the layout optimization research of the propulsion system of the underwater cable laying robot

[0072] An example of the present invention provides a method for optimizing the propeller layout of an underwater robot (such as an underwater cable laying operation robot) based on computational fluid dynamics numerical analysis. A geometric model and a computational domain model of the front and rear propellers in the horizontal plane under a conventional layout (without front-to-back offset) are established based on SpaceClaim software; the computational domain model of the propellers under the conventional layout is meshed based on the fluent-meshing function in Fluent software; on the basis of the conventional propeller layout, the deflection angles of the front and rear propellers are changed using SpaceClaim software, that is, the front propeller is offset upward (that is, taking the oncoming flow direction as the reference, rotating clockwise by a set angle from the oncoming flow direction), and the rear propeller is offset downward (that is, rotating counterclockwise by a set angle from the oncoming flow direction), with the range from 5° to 50°, increasing in steps of 5°, and a computational domain model of the propellers under different offset angles is created; then, the fluent-meshing function in Fluent software is used again to mesh the flow field model of the propellers under different offset angle layouts; based on the RNG k- ε turbulence model, transient simulation is used to analyze the flow field characteristics of the double-ducted propellers under different offset angles (5° - 50°), and the thrust values of the front and rear propellers under different offset angles are monitored through report definition; the data obtained from the simulation is processed through the post-processing function of Fluent software to obtain the thrust and the velocity flow field distribution nephogram generated by the movement of the front and rear propellers under different offset angles, and based on the thrust values of the front and rear propellers, the total forward thrust of the propellers under different offset angles is calculated; through Tecplot software, the vorticity calculation and Q-criterion vortex structure identification method are used to construct vorticity streamlines and visualize the vortex structure, and the evolution law of the vortex flow field and vortex structure generated by the propellers under different offset angles is analyzed; on this basis, by comprehensively considering the flow field characteristics of the propellers under different offset angles, the thrust changes of the front and rear propellers under different offset angles, and the total forward thrust, the optimal layout scheme is obtained. By adopting the above technical solution, the example of the present invention solves the problem of optimizing the propeller layout of the underwater cable laying operation robot, improves the total forward thrust and operation efficiency of the robot, and provides a theoretical basis for the layout optimization of the propulsion system of the underwater cable laying operation robot.

[0073] In the embodiment, the propeller layout optimization method provided by the present application is applied to the propeller layout optimization work of the underwater cable laying operation robot. After optimization, the total forward thrust is increased, which is 17% higher than the traditional layout, enhancing the operation ability of the robot; by optimizing the offset angle, the hydrodynamic interference between the propellers is reduced, the energy loss is lowered, and the propulsion efficiency is improved; by combining vorticity analysis and Q-criterion, the flow field stability is accurately identified to ensure the reliability of the robot's underwater movement; using CFD simulation to replace traditional experiments reduces the R & D cost and shortens the design cycle.

[0074] Based on the computational fluid dynamics method, the example determines the optimal angle of 20° by simulating and analyzing the flow field characteristics at different offset angles; combines vorticity calculation and Q-criterion to quantitatively analyze the stability of vortex structures, providing a scientific basis for layout optimization; adopts sliding mesh and polyhedral mesh technologies to efficiently simulate the rotational motion of the thruster, improving the simulation accuracy and computational efficiency. This invention provides a theoretical support for optimizing the layout of the propulsion system of an underwater cable-laying operation robot.

[0075] The above has introduced in detail the method for optimizing the layout of the underwater robot thruster based on CFD. Specific examples are used in this article to elaborate on the principle and implementation manner of this application. The description of the above embodiments is only used to help understand the concept of this application and should not be construed as a limitation on the protection scope of this application.

Claims

1. A method for optimizing the propeller layout of an underwater robot based on CFD, characterized in that, The underwater robot has front and rear double thrusters, and the layout optimization method includes: Determine the offset angles of the front and rear thrusters respectively. Based on the offset angles, establish the geometric models of the front and rear thrusters by using the computational fluid dynamics method. Perform mesh division on the geometric model and the flow field region under the current offset angle to obtain a mesh file, and create a computational domain mesh model under the adjusted offset angle. Determine the boundary conditions of the computational domains of the front and rear thrusters according to the mesh file; based on the computational domain mesh model and the boundary conditions, use the sliding mesh technique to simulate the rotational motion of the front and rear double thrusters for transient simulation to obtain simulation data. Based on the simulation data, determine the velocity flow field and the forward total thrust value of the front and rear thrusters; based on the velocity flow field, combine the vorticity calculation formula to determine the vorticity change situation generated by the thrusters under different offset angles, and use the Q-criterion calculation formula to determine the Q values of the front and rear thrusters under different offset angles. Determine the optimal layout optimization of the thrusters according to the forward total thrust values, vorticity change situations, and Q values of the front and rear thrusters under different offset angles.

2. The CFD-based underwater robot thruster layout optimization method according to claim 1, characterized in that Use the sliding mesh technique to simulate the rotational motion of the front and rear double thrusters for transient simulation to obtain simulation data, specifically including: Perform transient simulation by using the RNG K-ε turbulence model and the SIMPLE algorithm to obtain simulation data including the physical quantities in the flow field changing with time, and the physical quantities include at least velocity and / or pressure.

3. The CFD-based underwater robot thruster layout optimization method according to claim 1, wherein Determine the optimal layout optimization of the thrusters according to the forward total thrust values, vorticity change situations, and Q values of the front and rear thrusters under different offset angles, including: Select the offset angle that can make the vorticity change situation in the flow field evenly distributed and stable, the Q value is within the optimal range, and the forward total thrust value is the largest under the design constraint conditions as the final offset angle of the front and rear thrusters.

4. The CFD-based underwater robot thruster layout optimization method according to claim 1, wherein Determine the offset angles of the front and rear thrusters respectively, including: Taking the oncoming flow direction as the reference, rotating the oncoming flow direction clockwise by a set angle is set as the offset angle of the front thruster, and rotating the oncoming flow direction counterclockwise by the set angle is set as the offset angle of the rear thruster.

5. The CFD-based underwater robot propeller layout optimization method according to claim 4, characterized in that The value range of the offset angle is 5° to 50°.

6. The CFD-based underwater robot thruster layout optimization method according to claim 4, wherein The offset angle is 20°.

7. The CFD-based underwater robot thruster layout optimization method according to claim 1, wherein The boundary conditions include: the inlet boundary is set as the velocity inlet boundary condition, the outlet boundary is set as the pressure outlet boundary condition, and the thruster wall surface is set as the no-slip wall boundary condition.

8. The CFD-based underwater robot thruster layout optimization method according to claim 1, characterized in that The calculation formula of the Q value is as follows: where Ω is the anti-symmetric part of the velocity gradient tensor, S is the symmetric part of the velocity gradient tensor, and ||·|| denotes the Frobenius norm of the tensor, is the velocity gradient tensor.

9. The CFD-based underwater robot thruster layout optimization method according to claim 4, characterized in that The calculation formula of the forward total thrust value is: T forward = T1·cosβ + T2·cosβ; Among them, T forward is the total forward thrust value, T1 is the thrust generated by the front thruster, T2 is the thrust generated by the rear thruster, and β is the offset angle.

10. The CFD-based underwater robot propeller layout optimization method according to claim 1, wherein The method further includes: creating the computational domains of the front and rear double thrusters according to the actual sizes of the thrusters, including the external flow field and the ducts forming the stationary domain and the rotating domain formed by the propellers.

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