Fluid-solid coupling model of bionic robotic fish based on MFC material

Abstract

The invention discloses a fluid-solid coupling model of a bionic robotic fish based on an MFC material. The fluid-solid coupling model comprises a bionic robotic fish structural body dynamic model, a bionic robotic fish fluid model and a fluid-solid coupling module, wherein the bionic robotic fish structural body kinetic model is used for simulating deformation of a bionic robotic fish to obtain structural body displacement data; the bionic robotic fish fluid model is used for simulating the movement of fluid around the bionic robotic fish to obtain fluid pressure data; the fluid-solid coupling module is used for inputting the structural body displacement data into the bionic robotic fish fluid model as a boundary condition, inputting the fluid pressure data into the bionic robotic fish structural body dynamic model as a load, and carrying out iterative calculation to obtain a dynamic model of the bionic robotic fish structural body; until the bionic robotic fish structural body dynamic model and the bionic robotic fish fluid model reach a balanced state. The fluid-solid coupling model is favorable for optimizing a bionic robotic fish structure model and improving the swimming efficiency of the bionic robotic fish.

Description

Technical Field

[0001] The invention relates to the technical field of underwater robots, and more particularly to a fluid-solid coupling model of a bionic robot fish based on MFC materials. Background Art

[0002] At present, the propulsion modes of fish can be summarized into two types: body-tail fin mode and central fin-opposite fin mode. The central fin-opposite fin propulsion mode is slow and inefficient, and cannot meet the driving requirements of underwater robots. Therefore, bionic robot fish mainly focus on the body-tail fin mode. The body-tail fin propulsion mode mainly uses the fluctuation of the fish body or the swing of the tail fin to push the water around the body obliquely backward, and use the reaction force of the water to obtain forward thrust.

[0003] Piezoelectric fiber composite (Marco Fiber Composite, MFC) is a composite of piezoelectric fibers and resin matrix through a specific ratio, spatial distribution and mutual connection method, combining the advantages of traditional piezoelectric polymers with resin matrices. Due to the protective effect of the resin matrix, piezoelectric fiber composites have a considerable improvement in strength, brittleness and other aspects compared to traditional piezoelectric polymers. The composite material has greatly improved its flexibility and piezoelectric properties due to the huge changes in the ratio and spatial distribution of the resin matrix compared to traditional piezoelectric materials. MFC can achieve complete piezoelectric control deformation and has the advantages of light weight and high efficiency.

[0004] Therefore, how to optimize the design and performance of bionic robotic fish based on piezoelectric fiber composites (MFC) is a problem that technicians in this field need to solve urgently. Summary of the invention

[0005] In view of the above problems, the present invention provides a fluid-solid coupling model of a bionic robotic fish based on MFC materials to at least solve some of the technical problems mentioned in the above background technology.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] The present invention provides a fluid-solid coupling model of a bionic robotic fish based on MFC materials, comprising: a bionic robotic fish structural dynamics model, a bionic robotic fish fluid model and a fluid-solid coupling module; wherein:

[0008] The bionic robotic fish structural dynamics model is used to simulate the deformation of the bionic robotic fish and obtain structural displacement data;

[0009] The bionic robotic fish fluid model is used to simulate the movement of the fluid around the bionic robotic fish to obtain fluid pressure data;

[0010] The fluid-solid coupling module is used to input the structural displacement data as boundary conditions into the bionic robotic fish fluid model, and to input the fluid pressure data as load into the bionic robotic fish structural dynamics model, and to perform iterative calculations until the bionic robotic fish structural dynamics model and the bionic robotic fish fluid model reach a state of equilibrium.

[0011] Furthermore, the steps of constructing the dynamic model of the bionic robotic fish structure include:

[0012] Design a bionic robotic fish based on MFC materials;

[0013] Performing modal analysis on the bionic robotic fish to obtain the first-order modal vibration shape and the first-order modal frequency of the driving voltage signal of the bionic robotic fish in the body-tail fin propulsion mode;

[0014] Based on the first-order modal vibration shape and the first-order modal frequency, the external force and external torque to which the bionic robotic fish is subjected during steady-state swimming motion are obtained through dynamic analysis and fluid dynamics;

[0015] A bionic robotic fish structural dynamics model is constructed based on the external force and external torque.

[0016] Furthermore, the main body of the bionic robotic fish is composed of two MFC flat plates sandwiching a CFRP substrate;

[0017] The two MFC plates are symmetrically distributed, and sinusoidal driving voltage signals with the same frequency and opposite phases are applied; while one MFC plate contracts, the other MFC plate stretches, so that the middle CFRP substrate produces periodic bending deformation.

[0018] Furthermore, a weight is fixed to the head of the bionic robotic fish to limit lateral displacement of the head.

[0019] Furthermore, the dynamic model of the bionic robotic fish structure is expressed as:

[0020]

[0021] Wherein, m represents the mass of the simulated robotic fish; represents the swimming acceleration of the simulated robot fish; F(t) represents the external force on the simulated robot fish; I c (t) represents the instantaneous moment of inertia of the simulated robotic fish relative to the center of mass; Represents the time rate of change of instantaneous moment of inertia; ω c (t) represents the control angular velocity of the simulated robotic fish; represents the control angular acceleration of the simulated robot fish; M c (t) represents the external torque acting on the simulated robotic fish.

[0022] Furthermore, the steps of constructing the bionic robotic fish fluid model include:

[0023] Determine the fluid calculation domain;

[0024] The Navier-Stokes equations are used to describe the fluid motion in the fluid calculation domain, and boundary conditions are considered to construct a bionic robotic fish fluid model;

[0025] Based on the bionic robotic fish fluid model, a dynamic mesh model is used to process moving or deformed objects in the fluid calculation domain.

[0026] Furthermore, the bionic robotic fish fluid model is expressed as:

[0027]

[0028] Where ρ represents the fluid density; V represents the fluid velocity; V x 、V y and V z They represent the components of fluid velocity on the x, y, and z axes respectively; P represents the fluid pressure; μ represents the dynamic viscosity of the fluid; F x 、F y 、F z Represent the pressure components on the x, y, and z axes respectively.

[0029] Furthermore, the use of a dynamic mesh model to process moving or deforming objects in a fluid computational domain includes:

[0030] Determine the boundary position of the object at the next moment according to the boundary position, velocity and its increment and time increment of the object at the current moment;

[0031] The grid of the area near the boundary position of the object is adjusted and modified, and the area with severe distortion is re-divided.

[0032] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a fluid-solid coupling model of a bionic robotic fish based on MFC materials, which has the following beneficial effects:

[0033] The fluid-solid coupling model provided by the present invention is helpful to optimize the structural model of the bionic robotic fish and improve the swimming efficiency of the bionic robotic fish.

[0034] The present invention improves the calculation method of the fluid-solid coupling model, thereby increasing the calculation efficiency and reducing the calculation complexity.

[0035] The present invention applies the dynamic mesh model to the flow-solid coupling analysis of the MFC robot fish, and re-divides the mesh based on the previous calculation data in each step to ensure the accuracy of the flow-solid coupling calculation.

[0036] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0038] Figure 1 A schematic diagram of the principle of a fluid-solid coupling model provided in an embodiment of the present invention.

[0039] Figure 2 A schematic diagram of the structure of a bionic robotic fish model provided in an embodiment of the present invention.

[0040] Figure 3 A schematic diagram of a coordinate system of a bionic robotic fish provided in an embodiment of the present invention.

[0041] Figure 4 Schematic diagram of the fluid domain boundary conditions of the bionic robotic fish provided in an embodiment of the present invention.

[0042] Figure 5 A schematic diagram of a mesh model of the fluid computational domain of a bionic robotic fish provided in an embodiment of the present invention.

[0043] Figure 6 A schematic diagram of a pressure cloud diagram for fluid-solid coupling analysis of a bionic robotic fish provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0044] 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 ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] See also Figure 1 As shown, the embodiment of the present invention discloses a fluid-solid coupling model of a bionic robotic fish based on MFC materials, including: a bionic robotic fish structure dynamics model, a bionic robotic fish fluid model and a fluid-solid coupling module; wherein:

[0046] The bionic robot fish structure dynamics model is used to simulate the deformation of the bionic robot fish and obtain the structure displacement data;

[0047] The bionic robotic fish fluid model is used to simulate the movement of the fluid around the bionic robotic fish and obtain fluid pressure data;

[0048] The fluid-solid coupling module is used to input the structural displacement data as boundary conditions into the bionic robotic fish fluid model, and to input the fluid pressure data as load into the bionic robotic fish structural dynamics model, and perform iterative calculations until the bionic robotic fish structural dynamics model and the bionic robotic fish fluid model reach a state of equilibrium.

[0049] Next, each of the above parts will be explained in detail.

[0050] 1. Dynamic model of the bionic robotic fish structure

[0051] The steps for constructing the dynamics model of the bionic robotic fish structure include:

[0052] (1) Design a bionic robotic fish based on MFC materials;

[0053] The bionic robot fish consists of three parts: the actuator, the substrate, and the adhesive layer. The actuator is two MFC plates, the substrate is a CFRP carbon fiber plate, and the CFRP substrate is sandwiched between the two MFC plates; the actuator is connected to the substrate through the adhesive layer. The deformation of the actuator is transmitted to the substrate through the adhesive layer to control the bending or torsional deformation of the substrate. The MFC material is selected as the M-8528-P1 model, the thickness of the central CFRP plate is 0.2mm, and the other structural parameters of the bionic robot fish are shown in Table 1; the bionic robot fish model is shown in Figure 2 shown.

[0054] Table 1: Structural parameters of the robotic fish model

[0055] name parameter Body length (mm) 167 Maximum body height (mm) 55 Tail fin height (mm) 50 Body thickness(mm) CFRP0.2 MFC size (mm) 112×40 Activity area size (mm) 85×28

[0056] The two MFCs of the robot fish are symmetrically distributed, and sinusoidal driving voltage signals with the same frequency and opposite phases are applied. When one MFC contracts, the other MFC stretches, causing the CFRP substrate in the middle to undergo periodic bending deformation. Adding a weight to the head of the robot fish to limit the lateral displacement of the head can increase the lateral deformation of the tail of the robot fish, strengthen the effect of the tail pushing out water flow, and increase propulsion.

[0057] (2) Performing modal analysis on the bionic robotic fish to obtain the first-order modal vibration shape and the first-order modal frequency of the driving voltage signal of the bionic robotic fish in the body-tail fin propulsion mode; specifically:

[0058] Modal analysis is a numerical analysis method for calculating the vibration characteristics of the bionic robotic fish structure. The dynamic equation of the MFC undamped modal analysis is expressed as:

[0059] [M]{x″}+[C]{x'}+[K]{x}={0}

[0060] Wherein, M represents the mass matrix of the bionic robot fish structure; C represents the damping matrix of the bionic robot fish structure; K represents the stiffness matrix of the bionic robot fish structure; x represents the displacement vector of the bionic robot fish;

[0061] The free vibration of the bionic robot fish structure is a simple harmonic vibration, and the displacement is a sinusoidal function, that is, x = x sin (ωt). Substituting into the above formula, we get:

[0062] ([K]-ω 2 [M]){x}={0}

[0063] In the formula, the eigenvalue ω i The corresponding eigenvector {x} i is the natural frequency The corresponding vibration mode.

[0064] The modal analysis of the robot fish structure was performed to obtain the first four vibration modes of the robot fish. The calculation results of the bending modal frequency of the robot fish are shown in Table 2.

[0065] Table 2 Calculation results of bending modal frequencies of robotic fish

[0066]

[0067] The bionic robot fish adopts the tunas propulsion mode in the body-tail fin mode, that is, the front end structure of the body maintains a small deformation, and the surrounding fluid is pushed backwards through the lateral swing of the tail fin at the rear end to obtain forward propulsion. The first-order vibration mode keeps the fixed end without lateral displacement, the lateral displacement of the front half of the body length direction is small, and the lateral displacement of the free end tail is large, which is consistent with the propulsion mode of tunas fish, so the vibration mode of the bionic robot fish is similar to the first-order modal vibration mode, and the frequency of the driving voltage signal is also near the first-order modal frequency.

[0068] (3) Based on the first-order modal vibration shape and the first-order modal frequency, the external forces and external torques on the bionic robotic fish during steady-state swimming motion are obtained through dynamic analysis and fluid dynamics; specifically:

[0069] Establish the fish body coordinate system at the center of the bionic robot fish head b x b y b , establish the center of mass coordinate system with the center of mass of the robot fish as the origin c x c y c , and the oxy is the inertial coordinate system. The robot fish coordinate system is defined as Figure 3 shown.

[0070] During the movement of the bionic robot fish, it is subjected to the independent effects of external forces (torques) and internal forces (torques). The external forces (torques) determine the macroscopic movement of the bionic robot fish in the inertial coordinate system oxy, and the internal forces (torques) such as the mass of the bionic robot fish determine the deformation of the robot fish itself. The movement includes the translation and rotation of the robot fish, and the speed generated includes the translation speed and rotation speed along the center of mass coordinate system.

[0071] (4) Based on external forces and external moments, a dynamic model of the bionic robotic fish structure is constructed. The model is expressed as:

[0072]

[0073] Wherein, m represents the mass of the simulated robotic fish; represents the swimming acceleration of the simulated robot fish; F(t) represents the external force on the simulated robot fish; I c (t) represents the instantaneous moment of inertia of the simulated robotic fish relative to the center of mass; Represents the time rate of change of instantaneous moment of inertia; ω c (t) represents the control angular velocity of the simulated robotic fish; represents the control angular acceleration of the simulated robot fish; M c (t) represents the external torque acting on the simulated robotic fish.

[0074] 2. Bionic Robot Fish Fluid Model

[0075] The steps for constructing the bionic robotic fish fluid model include:

[0076] (1) Determine the fluid calculation domain;

[0077] In the embodiment of the present invention, the fluid calculation domain in the fluid-solid coupling analysis of the bionic robotic fish is designed as a cuboid with dimensions of 590×133×440 mm, and the robotic fish structure model is located in the center of the fluid calculation domain.

[0078] (2) The Navier-Stokes equations are used to describe the fluid motion in the fluid computational domain, and boundary conditions are considered to construct a bionic robotic fish fluid model; specifically:

[0079] The Navier-Stokes equation is a motion equation that describes the conservation of momentum of a viscous incompressible fluid. The incompressible viscous fluid equation of the MFC robot fish is expressed as:

[0080]

[0081] Where ρ represents the fluid density; V represents the fluid velocity; V x 、V y and V zThey represent the components of fluid velocity on the x, y, and z axes respectively; P represents the fluid pressure; μ represents the dynamic viscosity of the fluid; F x 、F y 、F z Represent the pressure components on the x, y, and z axes respectively.

[0082] Due to the large deformation effect and nonlinear characteristics of the robot fish structure, the Navier-Stokes equation is used to calculate the fluid domain, which can more completely reflect the coupling characteristics. Figure 4 shown.

[0083] (3) Based on the bionic robotic fish fluid model, a dynamic mesh model is used to handle moving or deforming objects in the fluid calculation domain.

[0084] When the calculation boundary is in motion and the objects in the calculation area are moving or deformed, a dynamic mesh model is required. The mesh distribution at the moving boundary moves with the movement of the boundary. The boundary position of the object at the next moment is determined based on the boundary position, velocity, increment and time increment of the object at the current moment; the mesh is adjusted and modified in the area near the boundary position of the object, and the severely distorted area is re-divided to eliminate the mesh units distorted by the movement of the boundary. The mesh model of the fluid calculation domain is as follows: Figure 5 shown.

[0085] 3. Fluid-Structure Interaction Module

[0086] In the transient analysis of the robotic fish, the solid domain and the fluid domain have their own meshing and boundary conditions, and data exchange occurs at the interface. In each calculation step, the fluid domain solver obtains data from itself and the solid domain's previous calculation results, and substitutes them for the new calculation step, and the solid domain solver does the same.

[0087] In order to determine the performance of the fluid dynamics of the robotic fish, the forward propulsion force of the robotic fish is analyzed. The length direction of the robotic fish represents the x-axis, and the tail fin swings in the z-axis direction. It is necessary to calculate the fluid pressure along the x-axis direction, and the integral of the fluid pressure and the viscous pressure gives the following formula.

[0088]

[0089] Among them, dA represents the infinitesimal surface element of the robotic fish structure; Represents the direction vector of the unit surface element dA on the x-axis; represents the i-th order normal vector of the surface element dA; Indicates fluid pressure; represents the viscosity stress tensor on the x-axis.

[0090] As one of the coupling data of the interface, fluid pressure plays a great role in the propulsion process of the bionic robot fish. The deformation effect of the robot fish is different when the frequency and amplitude of the driving signal are different, resulting in different fluid pressures in the fluid-solid coupling analysis. The working principle of the bionic robot fish is to push the fluid backward by swinging the tail fin, and use the reaction force of the fluid on the tail fin to generate forward propulsion. The pressure of the fluid domain around the robot fish structure determines the size of the reaction force and directly affects the propulsion effect. Figure 6 It represents the fluid pressure cloud diagram generated when the driving voltage signal is a 3Hz sine wave. During the bending deformation of the robot fish, the liquid flow near the robot fish structure is significantly disturbed, and the fluid pressure is affected by the deformation, speed and speed increment of the robot fish.

[0091] The absolute value of fluid pressure is the largest around the robot fish structure, and the closer to the fish body, the greater the pressure; in the flow field far away from the structure, the pressure does not change much during the deformation of the robot fish structure. The peak value of fluid pressure appears near the tail of the robot fish. Comparing the pressure cloud diagrams at different times, when the tail fin deformation reaches the peak value, the pressure of the corresponding surrounding fluid calculation domain reaches the maximum value. The robot fish tail fin swings along the z-axis, so the fluid pressure difference on both sides of the robot fish along the z-axis is large. The propulsion effect of the bionic robot fish can be represented by the sum of the fluid pressure in a cycle. The greater the pressure, the greater the driving force generated and the better the propulsion effect.

[0092] It can be seen that constructing a good fluid-solid coupling model can help obtain the optimal driving voltage amplitude and frequency, and optimize the design and performance of the bionic robotic fish.

[0093] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0094] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A fluid-solid coupling model of a bionic robotic fish based on MFC material, characterized in that: include: Bionic robotic fish structural dynamics model, bionic robotic fish fluid model and fluid-solid coupling module; among which: The bionic robotic fish structural dynamics model is used to simulate the deformation of the bionic robotic fish and obtain structural displacement data; The bionic robotic fish fluid model is used to simulate the movement of the fluid around the bionic robotic fish to obtain fluid pressure data; The fluid-solid coupling module is used to input the structural displacement data as boundary conditions into the bionic robotic fish fluid model, and to input the fluid pressure data as load into the bionic robotic fish structural dynamics model, and to perform iterative calculations until the bionic robotic fish structural dynamics model and the bionic robotic fish fluid model reach a state of equilibrium.

2. According to the fluid-solid coupling model of a bionic robotic fish based on MFC material according to claim 1, it is characterized in that: The steps of constructing the bionic robotic fish structure dynamics model include: Design a bionic robotic fish based on MFC materials; Performing modal analysis on the bionic robotic fish to obtain the first-order modal vibration shape and the first-order modal frequency of the driving voltage signal of the bionic robotic fish in the body-tail fin propulsion mode; Based on the first-order modal vibration shape and the first-order modal frequency, the external force and external torque to which the bionic robotic fish is subjected during steady-state swimming motion are obtained through dynamic analysis and fluid dynamics; A bionic robotic fish structural dynamics model is constructed based on the external force and external torque.

3. The fluid-solid coupling model of a bionic robotic fish based on MFC material according to claim 2 is characterized in that: The main body of the bionic robotic fish is composed of two MFC flat plates sandwiching a CFRP substrate; The two MFC plates are symmetrically distributed, and sinusoidal driving voltage signals with the same frequency and opposite phases are applied; while one MFC plate contracts, the other MFC plate stretches, so that the middle CFRP substrate produces periodic bending deformation.

4. The fluid-solid coupling model of a bionic robotic fish based on MFC material according to claim 2, characterized in that: A weight is fixed to the head of the bionic robotic fish to limit lateral displacement of the head.

5. The fluid-solid coupling model of a bionic robotic fish based on MFC material according to claim 2, characterized in that: The dynamic model of the bionic robotic fish structure is expressed as: Wherein, m represents the mass of the simulated robotic fish; represents the swimming acceleration of the simulated robot fish; F(t) represents the external force on the simulated robot fish; I c (t) represents the instantaneous moment of inertia of the simulated robotic fish relative to the center of mass; Indicates the time rate of change of instantaneous moment of inertia; ω c (t) represents the control angular velocity of the simulated robotic fish; represents the control angular acceleration of the simulated robot fish; M c (t) represents the external torque acting on the simulated robotic fish.

6. The fluid-solid coupling model of a bionic robotic fish based on MFC material according to claim 1, characterized in that: The steps of constructing the bionic robotic fish fluid model include: Determine the fluid calculation domain; The Navier-Stokes equations are used to describe the fluid motion in the fluid calculation domain, and boundary conditions are considered to construct a bionic robotic fish fluid model; Based on the bionic robotic fish fluid model, a dynamic mesh model is used to process moving or deformed objects in the fluid calculation domain.

7. The fluid-solid coupling model of a bionic robotic fish based on MFC material according to claim 1, characterized in that: The bionic robotic fish fluid model is expressed as: Where ρ represents the fluid density; V represents the fluid velocity; V x 、V y and V z They represent the components of fluid velocity on the x, y, and z axes respectively; P represents the fluid pressure; μ represents the dynamic viscosity of the fluid; F x 、F y 、F z Represent the pressure components on the x, y, and z axes respectively.

8. The fluid-solid coupling model of a bionic robotic fish based on MFC material according to claim 6, characterized in that: The method of using a dynamic mesh model to process moving or deforming objects in a fluid computational domain includes: Determine the boundary position of the object at the next moment according to the boundary position, velocity and its increment and time increment of the object at the current moment; The grid of the area near the boundary position of the object is adjusted and modified, and the area with severe distortion is re-divided.

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