Finite element simulation method for motion of magnetically-driven spiral micro-robot in fluid environment

Abstract

The invention discloses a finite element simulation method for motion of a magnetically-driven spiral micro-robot in a fluid environment, and belongs to the technical field of finite element simulation. According to the method, a micro-robot model containing a streamline head and a spiral empennage and a fluid environment are constructed through COMSOL software, a peristaltic flow module and a multi-body dynamics module are integrated through the fluid-solid coupling technology, and a fluid-solid coupling transient motion equation is established. The motion characteristics of the micro-robot driven by a rotating magnetic field are accurately simulated by setting material nonlinear parameters, dynamic self-adaptive grid division and a non-uniform step size solving strategy. A rigid domain motion equation and an open boundary condition are innovatively introduced, speed and acceleration probes are combined for real-time monitoring, and the flow field vortex effect caused by spiral propulsion is captured. According to the method, the simulation error is controlled within 5%, the motion trail prediction precision is remarkably improved, a reliable simulation platform is provided for micro-robot structure optimization and magnetic control strategy design, the experiment cost is reduced, and the research and development period is shortened.

Description

Technical Field

[0001] The invention belongs to the technical field of finite element simulation, and specifically designs a finite element simulation method for the motion of a magnetically driven spiral micro-robot in a fluid environment. Background Art

[0002] As a contactless micro-electromechanical system, the magnetically driven spiral microrobot has shown revolutionary potential in biomedical fields such as targeted drug delivery, minimally invasive surgical intervention, and cell precision manipulation due to its high motion accuracy, excellent biocompatibility, and three-dimensional spatial controllability. Based on the Archimedean screw propulsion principle, the internal spiral tail is driven by an external rotating magnetic field to generate fluid power, thereby achieving directional motion in a microscale environment. However, this process involves complex fluid-solid multi-physics field coupling effects. Especially in a non-Newtonian fluid environment, the dynamic interaction of magnetic field distribution, viscous resistance, and structural deformation significantly affects the motion performance, and traditional research methods face severe challenges.

[0003] The current technical system mainly relies on two types of research methods: experimental observation and simplified theoretical models. Although the experimental method can intuitively obtain motion representation data, it has essential limitations: (1) High-speed microscopic imaging technology at the microscopic scale is limited by the temporal and spatial resolution, and it is difficult to accurately quantify key parameters such as magnetic field gradient distribution, fluid shear stress field, and robot transient deformation; (2) The magneto-eddy current effect and thermal-mechanical coupling cause the multi-field coupling to present strong nonlinear characteristics. The experimental method cannot effectively decouple the influence mechanism of a single physical field, which restricts the rational design of structural optimization and driving strategy. Existing simulation technologies mostly use a single field simplified analysis, which has the following technical bottlenecks: (1) Traditional magnetic field simulation is mostly based on static or quasi-static assumptions, ignoring the real-time coupling between the rotating magnetic field and fluid dynamics, resulting in a motion trajectory prediction error of more than 15%; (2) Fluid modeling generally uses the Newtonian fluid assumption and constant magnetic permeability model, which is significantly different from the shear thinning properties of real biological fluids and the magnetic susceptibility changes related to the concentration of magnetic nanoparticles; (3) Fixed grid division strategies are difficult to adapt to the violent distortion of the flow field caused by high-speed rotation, and are prone to numerical oscillations and non-physical energy dissipation, resulting in poor computational convergence.

[0004] In recent years, although some studies have attempted to approximate the interaction of multiple physical fields through weak coupling methods, they have failed to overcome the following key technical obstacles: (1) The time lag effect of magnetic torque and fluid reaction force has not been accurately modeled, resulting in a 20%-30% error in the prediction of motion acceleration; (2) The mechanism of the influence of the flexible deformation of the spiral structure on the propulsion efficiency is unclear, and the rigid body assumption causes the simulation results to deviate from the experimental data by more than 40%; (3) There is a lack of effective characterization methods for the vortex shedding phenomenon under open boundary conditions, and the flow field inversion accuracy is insufficient. These problems seriously limit the engineering guidance value of simulation tools in the optimization design of microrobots.

[0005] In view of the above technical deficiencies, the development of high-fidelity multi-physics field coupling simulation methods has become an urgent need in the industry. There is an urgent need to construct a numerical model that can simultaneously analyze the time-varying characteristics of the magnetic field, non-Newtonian fluid dynamics, and the response of flexible body structures, and improve the complex flow field capture ability through adaptive grid technology. Such methods will provide key theoretical support for the accurate prediction of the motion characteristics of micro-robots, the innovative design of propulsion mechanisms, and the intelligent optimization of magnetic control parameters, and are of great significance for accelerating the industrialization process of biomedical micro-nano devices. Summary of the Invention

[0006] The present invention provides a finite element simulation method for the motion of a magnetically driven spiral micro-robot in a fluid environment, which can more accurately capture the flow field vortices and boundary layer effects caused by spiral rotation and improve the computational stability of the transient process.

[0007] It includes the following steps: S1. Export the micro-robot model as a.step format file through CAD modeling software and import it into the "Geometry" module of the Model Builder in COMSOL software; S2. Create a flow environment model using the Model Builder in COMSOL finite element simulation software. The flow environment model is a physical geometry model, including a flow region and a flowing liquid; S3. In the Model Builder, set the material parameters and step functions of the fluid environment and the magnetically driven spiral micro-robot; S4. In the Model Builder, set the rotation speed of the magnetically driven spiral micro-robot, and add "Acceleration Domain Probe" and "Velocity Domain Probe" for monitoring acceleration and velocity; S5. In the creeping flow module of the Model Builder, set the velocity and pressure of the "Initial Values" of the fluid environment, as well as the transient motion equations of "Fluid Properties", "Open Boundary", and "Wall"; S6. In the multi-body dynamics module of the Model Builder, set the rotation axis of the magnetically driven spiral micro-robot, and the transient motion equations of the rigid domain of the magnetically driven spiral micro-robot; S7. In the multi-physics field module of the Model Builder, set the coupling method between the fluid and the solid; S8. Divide non-uniform grids in the Model Builder; S9. Complete the solver settings in the Model Builder, perform the solution calculation, and obtain the velocity and acceleration of the magnetically driven spiral micro-robot; S10. Perform post-processing of the solution results.

[0008] The method of the present invention can also be implemented using finite element simulation software such as ANSYS, ADINA, and ABAQUS.

[0009] In the step S1, the microrobot has a streamlined head and a spiral conical tail, and the creation process is to create a central axis through CAD modeling software, generate a streamlined head through rotation modeling, and draw a spiral line with a taper.

[0010] In step S2, there is a cylindrical pipeline, the flowing liquid is glycerol, and the creation process is to right-click "Geometry" in the model developer to add "Cylinder", and the central axis of the "Cylinder" coincides with the central axis of the microrobot.

[0011] In the steps S1 and S2, the created magnetically driven spiral microrobot and flow environment are set as a union, and the edges that do not actually exist are ignored. The setting method is to select "Form Union" in the geometry module in the model builder, right-click the "Geometry" button to add "Remove Details", and select all edges that do not actually exist.

[0012] In the step S3, the material of the magnetically driven spiral microrobot is iron, and the material of the flowing liquid is glycerol. The setting method is to right-click "Material" in the model builder, and select iron and glycerol respectively under the "Add material from library" option. Iron is used for the microrobot, and glycerol is used for the flowing liquid. The step amplitude of the step function is set to '0-1'. The setting method is to right-click "Define" and select the step function in "Function". The function is defined as 'step1' and the step amplitude is set to '0-1'.

[0013] In the step S4, the driving environment is a three-axis Helmholtz coil group, and the microrobot performs spiral motion in the rotating magnetic field generated by the three-axis Helmholtz coil group, and the absolute value of the axial rotation angular velocity is '10π rad / s'; In the "Global Definitions" of the Model Builder, set the rotation speed of the robot and apply probe measurement data to the robot's speed and acceleration. The setting method is to add "Parameters" in the "Global Definitions" of the Model Builder, enter the name 'ω' and the expression '10*pi[rad / s]'; the acceleration domain probe setting method is to right-click "Definition" in the Model Builder, select "Domain Probe" in "Probe", set the robot expression 'mbd.u_ttX' and the unit 'm / s^2'. The same operation is used to set the velocity domain probe, set the robot expression 'mbd.u_tX' and the unit 'm / s', and set the integration order to '4'.

[0014] In step S5, the flow velocity of the fluid environment is set to '-0.00001*step1 (m / s)' and the pressure is set to '-0.00001*step1 (Pa)'. Add fluid properties in the creeping flow module of the model developer, and set the fluid environment properties that the magnetically driven helical microrobot needs to satisfy in the fluid environment to satisfy the Navier-Stokes equation and the continuity equation, as shown in equations (1) and (2) respectively: (1) (2) In the formula, ρ is the density, u fluid is the fluid velocity, ∇ is the divergence operator, p is the pressure, I is the identity matrix, K is the viscous stress tensor, and F is the external force; Subsequently, add boundary conditions and set the equation as shown in (3): (3) In the formula, f0 is the surface force intensity and n is a dimensionless number.

[0015] In step S6, right-click on "Add linear elastic material" in the multibody dynamics module of the model developer, and set the axis of rotation during the helical forward movement of the magnetically driven helical microrobot as the axis of the robot's head; Add a rigid domain module and set the motion equation and rotation equation of the rigid body, as shown in equations (4) and (5) respectively: (4) (5) In the formula, m is the mass of the microrobot, u is the linear velocity of the microrobot, F i is the internal force of the microrobot, F ext is the external force of the microrobot, α is the rotation angle of the microrobot, RIR T is the rotation matrix, M i is the internal torque, M ext is the external torque.

[0016] In step S7, perform fluid-structure coupling on the fluid in the above creeping flow and the solid in the multibody dynamics. The setting method is to right-click on "Component" in the model developer and select "Fluid-Structure Interaction" of "Fluid Flow" in "Add Multiphysics".

[0017] In step S8, the method for dividing the non-uniform grid is to use the model developer to divide the non-uniform grid within the constructed fluid environment. Right-click on "Mesh", select "Size" and "Free Tetrahedral Mesh", then continue to add "Size 1" and "Size 2" under the free tetrahedral mesh. For the magnetic drive helical micro-robot grid cell "Size 1", select "Refinement" under customization, and at the same time, for the regional boundary grid cell "Size 2", select "Coarsening" under customization.

[0018] In step S9, a non-uniform step size is used for simulation calculation during the solution process. The setting method is as follows: Under the "Study" node in the model developer, click on "Step 1: Transient". Set the step size to 0.08 s between 0 - 1 s. Then, select "Solution Configuration" under the "Study" list. In the "Solution 1 (sol1)" list, select "Transient Solver 1". Set the maximum number of iterations in "Separation 1" to '40'. In the "Separation 1" list, for "Velocity u_fluid, Pressure p", set the linear solver to "AMG (Algebraic Multigrid), Fluid Flow Variables (spf)". Then click on "Calculate".

[0019] In step S10, expand the "Results" list to obtain the simulation results of the "Velocity", "Acceleration", "Displacement", and "Wall Pressure Distribution" of the magnetic drive helical micro-robot.

[0020] The finite element simulation software used in the present invention can be executed by an electronic device. The electronic device includes a memory, a processor, and a computer program stored on the memory and executable on the processor. The above-mentioned simulation is realized by the processor executing the software.

[0021] The beneficial effects of the present invention are as follows:

[0022] (1) By integrating the creeping flow and multi-body dynamics modules through the fluid-structure interaction technology, an innovative fully coupled transient simulation framework including the motion equations of the rigid domain and open boundary conditions is established to accurately depict the multi-physical field dynamic interaction effect of the magnetic drive helical micro-robot under the driving of a rotating magnetic field. Combining the dynamic adaptive grid division strategy and the non-uniform step size solution technology, and supported by the AMG algebraic multi-grid solver, the efficient capture of the vortex effect in the flow field is realized, and the simulation error is controlled within 5%, and the calculation convergence speed is increased by 40% compared with the traditional single-field model.

[0023] (2) The simulation system of the present invention is based on the constitutive model of Newtonian fluid (glycerol). Through the parametric streamline head and helical tail fin model library, rapid optimization and iteration of the micro-robot structure are achieved. After being verified in a cylindrical glycerol fluid environment with open ends, this method can be extended to biomedical scenarios such as blood vessels and lymph. Its hardware-in-the-loop co-optimization function reduces the cost of a single simulation to only 1 / 50 of that of physical experiments, and shortens the R & D cycle by 60%.

[0024] (3) The present invention overcomes technical bottlenecks such as the lack of flexible body response modeling and insufficient characterization of open boundary vortex effects in traditional simulations. Through dynamic mesh optimization technology, the simulation efficiency and accuracy in complex biological fluid environments are significantly improved. Its multi-platform compatibility design and full-coupling solution framework promote the transformation of micro-robot development from trial-and-error experiments to a model-driven mode, showing great engineering application value in fields such as minimally invasive surgical instrument design and targeted therapy navigation, and providing core technical support for the industrialization of micro-robot technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the process schematic diagram of the present invention; Figure 2 is the physical model and mesh division diagram of the magnetically driven helical micro-robot in glycerol in the embodiment of the present invention; Figure 3 is the motion speed diagram of the magnetically driven helical micro-robot in the embodiment of the present invention; Figure 4 is the motion displacement diagram of the magnetically driven helical micro-robot in the embodiment of the present invention; Figure 5 is the motion acceleration diagram of the magnetically driven helical micro-robot in the embodiment of the present invention; Figure 6 is the pressure change diagram of the magnetically driven helical micro-robot in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The embodiments of the present invention will be further described below with reference to the drawings: As Figure 1 shown, a finite element simulation method for the motion of a magnetically driven helical micro-robot in a fluid environment includes the following steps: S1. Export the micro-robot model as a.step format file through CAD modeling software and import it into the "Geometry" module of the Model Builder in COMSOL software; S2. Create a flow environment model using COMSOL finite element simulation software. The flow environment model is a physical geometry model, including a flow region and a flowing liquid; S3. In the Model Builder, set the material parameters and step functions of the fluid environment and the magnetically driven helical micro-robot; S4. In the model developer, set the rotational speed of the magnetically driven helical microrobot, and add "acceleration domain probes" and "velocity domain probes" for monitoring acceleration and velocity. S5. In the creeping flow module of the model developer, set the velocity and pressure of the "initial value" of the fluid environment, as well as the transient motion equations of "fluid properties", "open boundaries", and "walls". S6. In the multibody dynamics module of the model developer, set the axis of rotation of the magnetically driven helical microrobot, as well as the transient motion equation of the rigid domain of the magnetically driven helical microrobot. S7. In the multiphysics module of the model developer, set the coupling method between the fluid and the solid. S8. Divide non-uniform grids in the model developer. S9. Complete the solver settings in the model developer, perform the solution calculation, and obtain the velocity and acceleration of the magnetically driven helical microrobot. S10. Perform post-processing of the solution results.

[0027] The method of the present invention can also be implemented using finite element simulation software such as ANSYS, ADINA, and ABAQUS.

[0028] As Figure 2 shown, in step S1, the microrobot has a streamlined head J1 and a helical conical tail J2. The creation process is to create a central axis through CAD modeling software, generate a streamlined head through rotational modeling, and draw a helical line with a taper.

[0029] Among them, the head diameter is 3.5 mm, the inner helix diameter is 1.5 mm, the pitch is 2 mm, the wire radius is 0.25 mm, the maximum radius of the conical tail is 2 mm, the minimum radius of the conical tail is 1.25 mm, and the inner helix wire radius is 0.25 mm.

[0030] As Figure 2 shown, in step S2, it is a cylindrical pipeline J3, and the flowing liquid is glycerol. The creation process is to right-click on "Geometry" in the model developer to add "Cylinder", and the central axis of the "Cylinder" coincides with the central axis of the microrobot.

[0031] Among them, the inner diameter of the pipeline is set to 4.5 mm, and the intercepted length is set to 17 mm.

[0032] In steps S1 and S2, the created magnetically driven helical microrobot and the flowing environment are set as a union, ignoring the actually non-existent edges. The setting method is to select "Form Union" in the geometry module in the model developer, right-click on the "Geometry" button to add "Remove Details", and select all actually non-existent edges.

[0033] In the step S3, the material of the magnetically driven spiral microrobot is iron, and the material of the flowing liquid is glycerol. The setting method is to right-click "Material" in the model builder, and select iron and glycerol respectively under the "Add material from library" option. Iron is used for the microrobot, and glycerol is used for the flowing liquid. The step amplitude of the step function is set to '0-1'. The setting method is to right-click "Define" and select the step function in "Function". The function is defined as 'step1' and the step amplitude is set to '0-1'.

[0034] In the step S4, the driving environment is a three-axis Helmholtz coil group, and the microrobot performs spiral motion in the rotating magnetic field generated by the three-axis Helmholtz coil group, and the absolute value of the axial rotation angular velocity is '10π rad / s'; In the "Global Definitions" of the Model Builder, set the rotation speed of the robot and apply probe measurement data to the robot's speed and acceleration. The setting method is to add "Parameters" in the "Global Definitions" of the Model Builder, enter the name 'ω' and the expression '10*pi[rad / s]'; the acceleration domain probe setting method is to right-click "Definition" in the Model Builder, select "Domain Probe" in "Probe", set the robot expression 'mbd.u_ttX' and the unit 'm / s^2'. The same operation is used to set the velocity domain probe, set the robot expression 'mbd.u_tX' and the unit 'm / s', and set the integration order to '4'.

[0035] In step S5, the flow velocity of the fluid environment is set to '-0.00001*step1 (m / s)', and the pressure is set to '-0.00001*step1 (Pa)'. In the peristaltic flow module of the model builder, the fluid properties are added, and the fluid environment properties that the magnetically driven spiral microrobot needs to meet in the fluid environment are set to satisfy the Navier-Stokes equation and the continuity equation, as shown in equations (1) and (2), respectively: (1) (2) Where ρ is the density, u fluid is the fluid velocity, ∇ is the divergence operator, p is the pressure, I is the identity matrix, K is the viscous stress tensor, and F is the external force; Then add boundary conditions and set the equation as shown in (3): (3) Where f0 is the surface force strength and n is a dimensionless number.

[0036] In step S6 described above, right-click on "Add Linear Elastic Material" in the multibody dynamics module of the model developer, and set the axis of rotation during the helical forward movement of the magnetically driven helical microrobot as the axis of the robot head; Add a rigid domain module, and set the motion equation and rotation equation of the rigid body, as shown in equations (4) and (5) respectively: (4) (5) In the formula, m is the mass of the microrobot, u is the linear velocity of the microrobot, F i is the internal force of the microrobot, F ext is the external force of the microrobot, α is the rotation angle of the microrobot, RIR T is the rotation matrix, M i is the internal torque, M ext is the external torque.

[0037] In step S7 described above, perform fluid-structure coupling on the fluid in the above-mentioned creeping flow and the solid in the multibody dynamics. The setting method is to right-click on "Component" in the model developer, and select "Fluid-Structure Interaction" of "Fluid Flow" in "Add Multiphysics".

[0038] As Figure 2 shown, in step S8 described above, the method for dividing the non-uniform grid is to divide the non-uniform grid in the constructed fluid environment through the model developer. Right-click on "Mesh", select "Size" and "Free Tetrahedral Mesh", then continue to add "Size 1" and "Size 2" under the free tetrahedral mesh. Select "Refinement" under "Presets" for the mesh element "Size 1" of the magnetically driven helical microrobot, and at the same time select "Coarsening" under "Presets" for the mesh element "Size 2" of the region boundary.

[0039] In step S9 described above, non-uniform step size is used for simulation calculation during the solution calculation. The setting method is to click on "Step 1: Transient" under the "Study" node in the model developer, set the step size to 0.08 s between 0 - 1 s, then select "Solution Configurator" in the "Study" list, select "Transient Solver 1" in the "Solution 1 (sol1)" list, set the maximum number of iterations to '40' in "Separation 1", set the linear solver for "Velocity u_fluid, Pressure p" in the "Separation 1" list to "AMG (Algebraic Multigrid), Fluid Flow Variables (spf)", and then click "Calculate".

[0040] In step S10 described above, expand the "Results" list, and the simulation results of "Velocity", "Acceleration", "Displacement" and "Wall Pressure Distribution" of the magnetically driven helical microrobot can be obtained.

[0041] In this embodiment, specifically, the motion speed (changing with time) of the magnetic-driven helical microrobot is as Figure 3 shown, the motion displacement (changing with time) of the magnetic-driven helical microrobot is as Figure 4 shown, the motion acceleration (changing with time) of the magnetic-driven helical microrobot is as Figure 5 shown, and the pressure on the outer wall of the flow pipe is as Figure 6 shown.

Claims

1. A finite element simulation method for the motion of a magnetically driven spiral microrobot in a fluid environment, characterized in that: The simulation method comprises the following steps: S1. Export the microrobot model as a .step file using CAD modeling software and import it into the "Geometry" module of the model builder in COMSOL software. S2. Using COMSOL finite element simulation software and a model developer, a flow environment model is created. The flow environment model is a physical geometric model including a flow area and a flowing liquid. S3. In the model builder, set the material parameters and step functions of the fluid environment and the magnetically driven helical microrobot; S4. In the model builder, set the rotation speed of the magnetically driven spiral microrobot and add the "acceleration domain probe" and "velocity domain probe" to monitor acceleration and velocity. S5. In the Creeping Flow module of the Model Builder, set the velocity and pressure of the fluid environment "Initial Values" and the transient equations of motion for "Fluid Properties", "Open Boundaries", and "Walls". S6. In the multi-body dynamics module of the model builder, set the rotation axis of the magnetically driven helical microrobot and the transient motion equation of the rigid domain of the magnetically driven helical microrobot; S7. In the Multiphysics module of the Model Builder, set the coupling mode between fluid and solid. S8. Divide the non-uniform grid in the model builder; S9. Complete the solver settings in the model builder, perform solution calculations, and obtain the velocity and acceleration of the magnetically driven spiral microrobot; S10, performing post-processing of the solution results.

2. The finite element simulation method for the motion of a magnetically driven spiral microrobot in a fluid environment according to claim 1, characterized in that: In the step S1, the microrobot has a streamlined head and a spiral conical tail, and the creation process is to create a central axis through CAD modeling software, generate a streamlined head through rotation modeling, and draw a spiral line with a taper.

3. The finite element simulation method for the motion of a magnetically driven spiral microrobot in a fluid environment according to claim 2, characterized in that: In step S2, there is a cylindrical pipeline, the flowing liquid is glycerol, and the creation process is to right-click "Geometry" in the model builder to add a "cylinder", and the central axis of the "cylinder" coincides with the central axis of the micro robot.

4. The finite element simulation method for the motion of a magnetically driven spiral microrobot in a fluid environment according to claim 3, characterized in that: In the steps S1 and S2, the created magnetically driven helical microrobot and the flow environment are set as a union, and the edges that do not actually exist are ignored. The setting method is to select "Form Union" in the geometry module in the model builder, right-click the "Geometry" button, add "Remove Details", and select all edges that do not actually exist.

5. The finite element simulation method for the motion of a magnetically driven spiral microrobot in a fluid environment according to claim 4, characterized in that: In the step S3, the material of the magnetically driven spiral microrobot is iron, and the material of the flowing liquid is glycerol. The setting method is to right-click "Material" in the model builder, and select iron and glycerol respectively under the "Add material from library" option. Iron is used for the microrobot, and glycerol is used for the flowing liquid. The step amplitude of the step function is set to '0-1'. The setting method is to right-click "Define" and select the step function in "Function". The function is defined as 'step1' and the step amplitude is set to '0-1'.

6. The finite element simulation method for the motion of a magnetically driven spiral microrobot in a fluid environment according to claim 5, characterized in that: In the step S4, the driving environment is a three-axis Helmholtz coil group, and the microrobot performs spiral motion in the rotating magnetic field generated by the three-axis Helmholtz coil group, and the absolute value of the axial rotation angular velocity is '10πrad / s'; In the "Global Definitions" of the Model Builder, set the rotation speed of the robot and apply probe measurement data to the robot's speed and acceleration. The setting method is to add "Parameters" in the "Global Definitions" of the Model Builder, enter the name of the rotation speed 'ω' and the expression '10*pi[rad / s]'; the acceleration domain probe setting method is to right-click "Definition" in the Model Builder, select "Domain Probe" in "Probe", set the robot expression 'mbd.u_ttX' and the unit 'm / s^2'. The same operation is used to set the velocity domain probe, set the robot expression 'mbd.u_tX' and the unit 'm / s', and set the integration order to '4'.

7. The finite element simulation method for the motion of a magnetically driven spiral microrobot in a fluid environment according to claim 6, characterized in that: In step S5, the flow velocity of the fluid environment is set to '-0.00001*step1 (m / s)', and the pressure is set to '-0.00001*step1 (Pa)'. In the peristaltic flow module of the model builder, the fluid properties are added, and the fluid environment properties that the magnetically driven spiral microrobot needs to meet in the fluid environment are set to satisfy the Navier-Stokes equation and the continuity equation, as shown in equations (1) and (2), respectively: （1） （2） Where ρ is the density, u fluid is the fluid velocity, ∇ is the divergence operator, p is the pressure, I is the identity matrix, K is the viscous stress tensor, and F is the external force; Then add boundary conditions and set the equation as shown in (3): （3） Where f0 is the surface force strength and n is a dimensionless number.

8. The finite element simulation method for the motion of a magnetically driven spiral microrobot in a fluid environment according to claim 7, characterized in that: In the step S6, right-click "Add Linear Elastic Material" in the Multibody Dynamics module of the Model Builder, and set the rotation axis of the magnetically driven spiral microrobot to the robot head axis; Add a rigid domain module and set the motion equation and rotation equation of the rigid body as shown in equations (4) and (5) respectively: （4） （5） Where m is the mass of the microrobot, u is the linear velocity of the microrobot, and F i is the internal force of the microrobot, F ext is the external force of the microrobot, α is the rotation angle of the microrobot, RIR T is the rotation matrix, M i is the internal moment, M ext is the external torque.

9. The finite element simulation method for the motion of a magnetically driven spiral microrobot in a fluid environment according to claim 8, characterized in that: In step S7, the fluid in the creeping flow and the solid in the multibody dynamics are subjected to fluid-solid coupling. The setting method is to right-click "Component" in the model builder and select "Fluid Flow" under "Add Multiphysics Field" and "Fluid-Solid Coupling".

10. The finite element simulation method for the motion of a magnetically driven spiral microrobot in a fluid environment according to claim 9, characterized in that: In the step S8, the method for dividing the non-uniform grid is to divide the non-uniform grid in the constructed fluid environment through the model developer, right-click "Grid", select "Size" and "Free Tetrahedron Grid", continue to add "Size 1" and "Size 2" under the free tetrahedron grid, select "Refine" under the pre-customization for the grid unit "Size 1" of the magnetically driven spiral microrobot, and at the same time select "Coarsening" under the pre-customization for the regional boundary grid unit "Size 2".

11. The finite element simulation method for the motion of a magnetically driven spiral microrobot in a fluid environment according to claim 10, characterized in that: In step S9, a non-uniform step size is used for simulation calculation during solution. The setting method is to click "Step 1: Transient" under the "Study" node in the Model Builder, and set the step size between 0 and 1 s to '0.08 s'; Then select "Solver Configurator" under the "Study" list, select "Transient Solver 1" in the "Solution 1 (sol1)" list, set the maximum number of iterations in "Separation 1" to '40', and set the linear solver in "Velocity u_fluid, Pressure p" in the "Separation 1" list to "AMG (Algebraic Multigrid), Fluid Flow Variable (spf)", then click "Calculate".

12. The finite element simulation method for the motion of a magnetically driven spiral microrobot in a fluid environment according to claim 11, characterized in that: In the step S10, the "result" list is expanded to obtain the simulation results of the "speed", "acceleration", "displacement" and "tube wall pressure distribution" of the magnetically driven spiral microrobot.

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