Method for solving hydrodynamic coefficient of autonomous underwater vehicle based on multi-degree-of-freedom coupling driving

Abstract

The invention discloses an autonomous underwater vehicle hydrodynamic coefficient solving method based on multi-degree-of-freedom coupling driving, and provides a multi-degree-of-freedom dynamic coupling driving joint simulation strategy aiming at the limitations of low efficiency, step-by-step calculation error accumulation and the like of a traditional hydrodynamic coefficient calculation method. Through deep fusion of a system identification theory and a six-degree-of-freedom rigid body motion equation, a full-degree-of-freedom coupling simulation platform based on dynamic grid self-adaption is developed, transverse fluid power interference under plane constraint motion is decoupled, and synchronous iterative solution of six-degree-of-freedom hydrodynamic parameters of surging, swaying, heaving, pitching, rolling and yawing is achieved. According to the method, six-degree-of-freedom coupling motion numerical simulation is carried out by taking an independently researched and developed cheongfish series AUV (Autonomous Underwater Vehicle) as an example, and all hydrodynamic coefficients can be solved only through one-time example calculation. According to the method, the hydrodynamic coefficient of the autonomous underwater vehicle can be rapidly obtained, and the purpose of accurately controlling the autonomous underwater vehicle is achieved.

Description

Technical Field

[0001] This invention belongs to the fields of marine engineering and underwater robots, and specifically relates to a method for solving the hydrodynamic coefficients of autonomous underwater vehicles based on multi-degree-of-freedom coupled drive. Background Technology

[0002] To achieve precise control of autonomous underwater vehicles (AUVs), accurate hydrodynamic coefficients are required. However, obtaining these coefficients is time-consuming. To balance accuracy and computation time, some researchers use CFD simulations or experiments to obtain the hydrodynamic coefficients. While these methods yield relatively accurate results, they require multiple simulations or experiments to obtain all coefficients, wasting significant time and thus reducing computational efficiency. Other researchers, using parameter identification methods, can determine most hydrodynamic coefficients with fewer simulations, but they only consider the AUV / ship's hull, neglecting the influence of appendages on hydrodynamics. Studying the hydrodynamic coefficients of the AUV hull in isolation makes it difficult to obtain the optimal hydrodynamic performance of the AUV. Summary of the Invention

[0003] In view of this, the purpose of this invention is to overcome the defects in the prior art and provide a method for solving the hydrodynamic coefficients of autonomous underwater vehicles based on multi-degree-of-freedom coupled drive. This method can take into account the overall performance of the AUV, improve the control accuracy of the AUV, meet different requirements for hydrodynamic coefficient solving and calculation time, and is highly practical.

[0004] The present invention provides a method for solving the hydrodynamic coefficients of an autonomous underwater vehicle based on multi-degree-of-freedom coupled drive, comprising:

[0005] By deeply integrating system identification theory with the six-degree-of-freedom rigid body motion equations, a fully coupled simulation platform based on dynamic mesh adaptation was developed. This platform decouples lateral hydrodynamic disturbances under planar constrained motion, enabling simultaneous iterative solutions for six-degree-of-freedom hydrodynamic parameters (sway, heave, pitch, roll, and bow). Taking the independently developed Sailfish series AUV as an example, numerical simulations of the six-degree-of-freedom coupled motion were conducted, and all hydrodynamic coefficients could be obtained in a single calculation.

[0006] Furthermore, the fully free-degree-of-freedom coupled simulation platform includes a six-degree-of-freedom dynamic model of the AUV; the six degrees of freedom include sway, roll, heave, pitch, roll, and bow roll.

[0007] Furthermore, a fully free-degree-of-freedom simulation platform based on dynamic mesh adaptation was developed to decouple lateral hydrodynamic disturbances under planar constrained motion and realize synchronous iterative solution of six-degree-of-freedom hydrodynamic parameters.

[0008] Furthermore, the forces and moments of the AUV obtained through the simulation platform will be substituted into the dynamic model with six degrees of freedom, and the hydrodynamic coefficients of the AUV will be obtained through polynomial fitting.

[0009] Furthermore, the obtained hydrodynamic coefficients are parameterized, and the goodness-of-fit coefficient is used to reflect the degree of fit of the original data.

[0010] Furthermore, by developing the most commonly used PID control algorithm in engineering and a six-degree-of-freedom dynamic model for the AUV, and substituting the hydrodynamic coefficients obtained through numerical simulation of fully free-degree-of-freedom coupled motion using a dynamic mesh-adaptive fully free-degree-of-freedom coupled simulation platform into the dynamic model of the AUV, hydrodynamic simulation analysis of the AUV was performed.

[0011] Furthermore, by analyzing the experimental data, the relationship between the autonomous underwater vehicle's travel time and speed, underwater travel depth, pitch angle, and roll angle was determined, and the results were compared with simulation results.

[0012] The beneficial effects of this invention are as follows: This invention discloses a method for solving the hydrodynamic coefficients of an autonomous underwater vehicle based on multi-degree-of-freedom coupled drive. By deeply integrating system identification theory with the six-degree-of-freedom rigid body motion equations, a fully coupled simulation platform based on dynamic mesh adaptation is developed. This decouples lateral hydrodynamic disturbances under planar constrained motion, enabling the synchronous iterative solution of six-degree-of-freedom hydrodynamic parameters (sway, heave, pitch, roll, and bow). All hydrodynamic coefficients can be obtained through a single simulation example. The correctness of the proposed fully coupled motion numerical simulation method for obtaining hydrodynamic coefficients is verified through simulation analysis and experiments. Attached Figure Description

[0013] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0014] Figure 1 This is a schematic diagram illustrating the principle design of the present invention;

[0015] Figure 2 This is a comparison diagram of the simulation and fitting of forces in the X, Y, and Z directions of the present invention;

[0016] Figure 3 The simulation and fitting comparison diagrams show the torques in the X, Y, and Z directions of this invention.

[0017] Figure 4 The figure shows the simulation results after substituting the hydrodynamic coefficients into the six-degree-of-freedom model of the AUV. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings, such as... Figure 1 As shown:

[0019] The present invention provides a method for solving the hydrodynamic coefficients of an autonomous underwater vehicle based on multi-degree-of-freedom coupled drive, comprising:

[0020] By deeply integrating system identification theory with the six-degree-of-freedom rigid body motion equations, a fully coupled simulation platform based on dynamic mesh adaptation was developed. This platform decouples lateral hydrodynamic disturbances under planar constrained motion, enabling the synchronous iterative solution of six-degree-of-freedom hydrodynamic parameters (sway, heave, pitch, roll, and bow). Taking the independently developed Sailfish series AUV as an example, numerical simulations of six-degree-of-freedom coupled motion were conducted, and all hydrodynamic coefficients could be obtained in a single calculation. The system identification theory includes the least squares method; the six-degree-of-freedom rigid body motion equations include the translation and rotation of the AUV in the X, Y, and Z directions; and the fully coupled simulation platform allows for the solution of perturbations of the AUV in six directions with different rules, all of which can be solved in a single calculation.

[0021] In this embodiment, the fully free-degree-of-freedom coupled simulation platform includes a six-degree-of-freedom dynamic model of an AUV; the six degrees of freedom include the AUV's swaying motion, swaying motion, heave motion, pitching motion, rolling motion, and bowing motion; wherein, simulation software can be used to build the six-degree-of-freedom dynamic model.

[0022] In this embodiment, by considering the strong coupling effect between the hydrodynamic characteristics and motion control of the AUV, an accurate physical model of the AUV is constructed. The physical model is divided into a high-quality computational mesh, and the high-quality mesh is combined with dynamic mesh technology to perform high-fidelity numerical simulation. The key hydrodynamic coefficients and motion performance indicators of the AUV (such as drag, lift, pitching moment, displacement / velocity / acceleration of each degree of freedom) of each AUV are calculated by using existing computational fluid dynamics (CFD).

[0023] In this embodiment, the forces and torques of the AUV obtained through the simulation platform are substituted into the dynamic model with six degrees of freedom, and the hydrodynamic coefficients of the AUV are obtained through polynomial fitting.

[0024] In this embodiment, the hydrodynamic coefficients of the AUV simulated by the numerical simulation are parameter identified to verify the accuracy of the results; wherein, the numerical simulation can be performed using existing software, such as ANSYS Fluent, Star-CCM+, etc.

[0025] In this embodiment, the obtained hydrodynamic coefficients are input into a six-degree-of-freedom dynamic model to verify their correctness. The six-degree-of-freedom dynamic model is built using dynamic simulation software for simulation analysis. Existing software such as MATLAB / Simulink, Adams, and Carsim is used for the dynamic simulation analysis.

[0026] In this embodiment, the underwater motion of the AUV differs from planar constrained motion; it experiences irregular disturbances in all six degrees of freedom, with its velocity and acceleration in all directions being non-zero. The irregular motion experienced by the AUV is determined according to the following formula, and the motion parameters of the hull are set as follows:

[0027] γ=f(t)+y p sin(2πf γ1 t)sin(2πf γ2 t)sin(2πf γ3 t);

[0028] Where γ represents the speed u, v, w or angular velocity p, q, r set for the AUV's constrained motion. f(t) is the initial value; for motion in the x-direction, this value equals the hull's cruising speed; for speeds or angular velocities in other directions, this value equals 0. p The amplitude of the applied disturbance is denoted as . By applying the product of three sine functions to the AUV, an irregular motion is generated, ensuring that the motion state of the AUV hull approximates that of deep-sea motion.

[0029] In this embodiment, the axial force acting on the autonomous underwater vehicle is determined according to the following formula:

[0030]

[0031] Where X is the axial force acting on the autonomous underwater vehicle, ρ is the density of water, l is the dimensionless characteristic length, q is the angular velocity in the Y-axis direction, and X′ qq X′ is the dimensionless force coefficient caused by the velocity component in the Y direction. rr Let be the dimensionless force coefficient caused by the velocity component in the Z direction, p be the angular velocity in the X-axis direction, q be the angular velocity in the Y-axis direction, r be the angular velocity in the Z-axis direction, and X′ be the angular velocity in the Z-axis direction. uu is the dimensionless coefficient of the force caused by the velocity component in the X-axis direction. Let be the dimensionless coefficient of the force caused by the acceleration component in the X-axis direction, u be the velocity in the X-direction, v be the velocity in the Y-direction, and w be the velocity in the Z-direction. This is the acceleration in the X direction;

[0032] The lateral force acting on an autonomous underwater vehicle is determined using the following formula:

[0033]

[0034] Where Y is the lateral force acting on the autonomous underwater vehicle. Y′ is the dimensionless coefficient of the force caused by the Y-axis acceleration component. v The dimensionless coefficient of the force caused by the velocity component in the Y-axis direction. is the dimensionless coefficient of the force caused by the acceleration component in the Y-axis direction;

[0035] The vertical force acting on an autonomous underwater vehicle is determined using the following formula:

[0036]

[0037] Where Z is the vertical force acting on the autonomous underwater vehicle, Z′ w Z′ is the dimensionless coefficient of the force caused by the velocity component in the Z-axis direction. w is the dimensionless coefficient of the force caused by the acceleration component in the X-axis direction;

[0038] The rolling moment acting on an autonomous underwater vehicle is determined using the following formula:

[0039]

[0040] Where K is the rolling torque acting on the autonomous underwater vehicle, and K' is the dimensionless torque about the X-axis. p The dimensionless coefficient of the torque caused by the X-axis velocity component. The dimensionless coefficient of the torque caused by the X-axis acceleration component;

[0041] The pitching moment acting on an autonomous underwater vehicle is determined using the following formula:

[0042]

[0043] Where M is the pitching moment acting on the autonomous underwater vehicle, and M' is the dimensionless moment about the Y-axis. q The dimensionless coefficient of the torque caused by the Y-axis velocity component. The dimensionless coefficient of the torque caused by the Y-axis acceleration component;

[0044] The yaw moment acting on the autonomous underwater vehicle is determined using the following formula:

[0045]

[0046] Where N is the yaw torque acting on the autonomous underwater vehicle, and N' is the dimensionless torque about the Z-axis. r The dimensionless coefficient of the torque caused by the Z-axis velocity component. The dimensionless coefficient of the torque caused by the Z-axis acceleration component;

[0047] In this embodiment, the sum of squared residuals during parameter identification is determined according to the following formula:

[0048]

[0049] Where SSE is the sum of squared residuals, yi and The original data and its average value. The data is for model prediction, where n is the number of samples;

[0050] The sum of squares returned during parameter identification is determined using the following formula:

[0051]

[0052] SSR stands for Sum of Squares.

[0053] The total sum of squared deviations during parameter identification is determined using the following formula:

[0054]

[0055] Where SST is the sum of squares of total deviations;

[0056] The final determination coefficients for parameter identification are determined using the following formula:

[0057]

[0058] Among them, R 2 The coefficient of determination;

[0059] To better understand this invention, the results obtained using existing methods are analyzed as follows:

[0060] Figure 2 and Figure 3 The CFD simulations and fitting results for forces and moments in the X, Y, and Z directions are compared. Table 1 shows the goodness-of-fit coefficients. Figure 2 and Figure 3 It can be seen that the mathematical model obtained using this invention has excellent adaptability to all forces and moments. Goodness-of-fit coefficient R0 2 The closer the value is to 1, the better the equation matches the simulation results. The goodness-of-fit coefficient R1 in Table 1... 2 The values ​​show that the goodness-of-fit coefficient R obtained by linear fitting of the forces and torques X, Y, Z, K, M, and N generated by the AUV is... 2 The values ​​are all greater than 0.94, indicating that the hydrodynamic coefficients obtained by the full-degree-of-freedom coupled motion numerical simulation method meet the accuracy requirements.

[0061] Table 1 Goodness-of-fit coefficients

[0062]

[0063] Table 2 shows some of the calculated hydrodynamic coefficients. Figure 4 The simulation results after substituting the hydrodynamic coefficients into the AUV six-degree-of-freedom model also show that the hydrodynamic coefficients obtained using this invention are correct and reliable. From Figure 4(a) It can be seen that the underwater working depth of the AUV, after fluctuating for 300 seconds, eventually stabilized at 10 meters, with the simulation time set at 4000 seconds. From Figure 4 (b) It can be seen that the AUV's sailing speed was 2 m / s, at which point no speed fluctuation occurred. From Figure 4 (c) and Figure 4 (d) It can be seen that after a brief fluctuation, the pitch and roll angles of the AUV eventually converge at 0 degrees and remain stable. Therefore, the simulation proves that the hydrodynamic coefficients obtained using the fully free-degree-of-freedom coupled motion numerical simulation method are feasible, and verifies that the developed fully free-degree-of-freedom coupled simulation platform is correct.

[0064] Table 2 Partial Hydrodynamic Coefficients

[0065]

[0066] Based on the above analysis, it can be seen that the hydrodynamic coefficients of the fully attached AUV obtained by numerical simulation of coupled motion with full degrees of freedom in this invention are more comprehensive than those obtained by calculating the hydrodynamic coefficients of a light-body AUV. Compared with planar constrained motion, this method pays more attention to the overall accuracy of the dynamic model, can better calculate the force situation of the autonomous underwater vehicle under complex working conditions, and can obtain all the hydrodynamic coefficients in the motion equations of the autonomous underwater vehicle through only a single simulation, thus avoiding the increase in dynamic model error caused by using multiple methods to obtain hydrodynamic coefficients, and shortening the calculation cycle while ensuring accuracy.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for solving the hydrodynamic coefficients of an autonomous underwater vehicle based on multi-degree-of-freedom coupled drive, characterized in that: By deeply integrating system identification theory with the six-degree-of-freedom rigid body motion equations, a fully coupled simulation platform based on dynamic mesh adaptation was developed. This platform decouples lateral hydrodynamic disturbances under planar constrained motion, enabling simultaneous iterative solutions for six-degree-of-freedom hydrodynamic parameters (sway, heave, pitch, roll, and bow). Taking the independently developed Sailfish series AUV as an example, numerical simulations of the six-degree-of-freedom coupled motion were conducted, and all hydrodynamic coefficients could be obtained in a single calculation.

2. The method for solving the hydrodynamic coefficients of an autonomous underwater vehicle based on multi-degree-of-freedom coupled drive as described in claim 1, characterized in that: The fully free-degree-of-freedom coupled simulation platform includes a six-degree-of-freedom dynamic model of the AUV; the six degrees of freedom include sway, roll, heave, pitch, roll, and bow roll.

3. The method for solving the hydrodynamic coefficients of an autonomous underwater vehicle based on multi-degree-of-freedom coupled drive as described in claim 1, characterized in that: A fully free-degree-of-freedom simulation platform based on dynamic mesh adaptation was developed to decouple lateral hydrodynamic disturbances under planar constrained motion and achieve synchronous iterative solution of six-degree-of-freedom hydrodynamic parameters.

4. The method for solving the hydrodynamic coefficients of an autonomous underwater vehicle based on multi-degree-of-freedom coupled drive as described in claim 1, characterized in that: The forces and moments of the AUV obtained through the simulation platform are substituted into the dynamic model with six degrees of freedom, and the hydrodynamic coefficients of the AUV are obtained through polynomial fitting.

5. The method for solving the hydrodynamic coefficients of an autonomous underwater vehicle based on multi-degree-of-freedom coupled drive according to claim 1, characterized in that: The obtained hydrodynamic coefficients are parameterized, and the goodness-of-fit coefficient is used to reflect the degree of fit of the original data.

6. The method for solving the hydrodynamic coefficients of an autonomous underwater vehicle based on multi-degree-of-freedom coupled drive according to claim 1, characterized in that: By developing the most commonly used PID control algorithm in engineering and a six-degree-of-freedom dynamic model of an AUV, and substituting the hydrodynamic coefficients obtained through numerical simulation of fully free-degree-of-freedom coupled motion using a dynamic mesh-adaptive fully free-degree-of-freedom coupled simulation platform into the dynamic model of the AUV, hydrodynamic simulation analysis of the AUV is performed.

7. The method for solving the hydrodynamic coefficients of an autonomous underwater vehicle based on multi-degree-of-freedom coupled drive according to claim 1, characterized in that: By analyzing the experimental data, the relationship between the autonomous underwater vehicle's travel time and speed, underwater travel depth, pitch angle, and roll angle was determined, and the results were compared with simulation results.

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