Bionic pectoral fin flexibility measurement and crack evaluation method based on near-field dynamics

Abstract

The invention discloses a bionic pectoral fin flexibility measurement and crack evaluation method based on near-field dynamics, which is different from a local method of continuum mechanics, and is characterized in that a near-field dynamics model considers the deformation characteristic and the mechanical characteristic of a certain substance point as the comprehensive influence of all substance points in a near-field range; through combination of a theoretical analysis model of near-field dynamics and a flexible bionic pectoral fin structure, the uniform flexibility after weighting in an overlook plane of the flexible bionic pectoral fin is determined, and represents the flexible deformation capability of a material point under the condition of no load, so that the flexibility measurement of the flexible bionic pectoral fin is realized; crack evaluation is realized by prefabricating cracks and performing scene simulation and simulation. According to the method, the flexible state and hydrodynamic characteristics of the pectoral fin when the bionic underwater vehicle is propelled and the crack propagation on the surface of the bionic pectoral fin after the bionic underwater vehicle is damaged can be rapidly estimated, so that the flexible design and optimization of bones and muscles of the bionic pectoral fin can be guided.

Description

Technical Field

[0001] The invention relates to the field of underwater bionic submersibles, and in particular to a bionic pectoral fin flexibility measurement and crack assessment method based on near-field dynamics. Technical Background

[0002] In nature, creatures with MPF (Median / Paired Fin) propulsion mode, such as manta rays and cownose rays, have good roll stability and pitch stability when swimming due to their wide and flat bodies and stable swimming postures, and are an excellent bionic prototype for bionic underwater submersibles. Compared with other bionic propulsion modes, the MPF propulsion mode has good stability and large load space, and is suitable for carrying sonar and cameras for stealth approach, bio-friendly underwater propulsion and acoustic and optical detection tasks. The propulsion structure of the application-type underwater bionic submersible based on the MPF propulsion mode is the bionic pectoral fin, which is mostly composed of bionic bones and bionic muscles. The driving source (such as a steering gear) inside the submersible is connected to the bionic skeleton, and the bionic muscle is coated on the bionic skeleton. The driving source outputs reciprocating rotational motion to drive the bionic skeleton to move, and the bionic skeleton drives the bionic muscle, so that it produces passive deformation under the dual action of the bionic skeleton and the water body, and the bionic muscle outputs momentum to the surrounding water body.

[0003] A deep understanding of the deformation and fracture characteristics of underwater bionic pectoral fins is of great significance for optimizing the design of bionic underwater submersibles. Existing studies have shown that bionic bones and bionic muscles with different flexibility distributions will make the bionic propulsion structure exhibit different hydrodynamic characteristics. Therefore, the flexibility of the bionic pectoral fins must be combined with the hydrodynamic analysis. However, there is currently no good method for measuring the flexibility of underwater bionic pectoral fins. At the same time, the application scenarios of bionic underwater submersibles are complex and changeable. For example, due to long-term movement or collision, cuts, etc., cracks expand on the surface of the bionic pectoral fins, and the mechanical properties change, making it impossible to normally output mechanical momentum to the water to drive itself. Most of the existing technologies focus on the design and control of flexible bionic structures. Therefore, in order to better analyze the quantitative relationship between the flexible deformation and hydrodynamic characteristics of the pectoral fins and the risk of propulsion failure caused by crack expansion of the bionic pectoral fins, an effective method for measuring the flexibility and crack expansion evaluation of underwater bionic pectoral fins is urgently needed. Summary of the invention

[0004] The present invention provides a bionic pectoral fin flexibility measurement and crack assessment method based on perifield dynamics by combining a perifield dynamics theoretical analysis model with a flexible bionic pectoral fin structure.

[0005] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0006] A bionic pectoral fin flexibility measurement and crack assessment method based on peri-field dynamics, comprising:

[0007] Step 1, scanning the three-dimensional shape of the physical manta ray to obtain a three-dimensional model of the manta ray composed of a three-dimensional point set on the surface of the manta ray;

[0008] Step 2, based on the manta ray three-dimensional model, delete the facial fin structure of the manta ray head on the model and use different curve optimization schemes to optimize the manta ray three-dimensional model; based on the Euclidean distance between the optimized three-dimensional point set and the three-dimensional point set on the manta ray surface, determine the final manta ray-simulating submersible three-dimensional model;

[0009] Step 3, the three-dimensional model of the manta ray-like submersible includes a rigid bionic main compartment in the middle and flexible bionic pectoral fins on both sides; the flexible bionic pectoral fins are composed of an internal carbon fiber bionic skeleton and an elastic bionic muscle wrapped on the bionic skeleton, and the bionic skeleton is driven by a motor set at the fin root; the rigid bionic main compartment is regarded as a rigid material, and motion deformation is not considered, and the deformation form of the flexible bionic pectoral fin is bending deformation, and tensile deformation is ignored;

[0010] Step 4, setting the flexible bionic pectoral fin of the manta ray submersible to a double fin structure, and the flexibility of the bionic skeleton in the flexible bionic pectoral fin gradually increases along the direction from head to tail and from center to two wings;

[0011] Step 5, applying the peridynamic analysis method, using a rigid material model to characterize the rigid bionic main compartment of the manta ray submersible; selecting the near-field range of the material point, the engineering material constants of the bionic bone material and the bionic muscle material, and dividing the material points of the flexible bionic pectoral fin in the manta ray submersible; using the carbon fiber material model in the unconventional state-based peridynamics to characterize the material properties of the bionic bone, and using the hyperelastic material model to characterize the material properties of the bionic muscle;

[0012] Step 6, based on the peridynamic model, describe the deformation state and force state of the bionic skeleton and bionic muscle, calculate the Jacobian matrix of all material points in the flexible bionic pectoral fin, and then obtain the material stiffness matrix characterized by the peridynamic method based on the parameter relationship between the Jacobian matrix and the peridynamic model, and based on this, obtain the bending stiffness of the bionic skeleton and the bending stiffness of the bionic muscle and update them;

[0013] Step 7, establish the distance-based coupling weight function of the bionic skeleton and bionic muscle, take the material point at the root of the front fin as the current reference material point, and perform weighted summation on the inverse of the bending stiffness of the material points in other parts of the flexible bionic pectoral fin along the chord direction and the span direction to obtain the weighted uniform flexibility of the flexible bionic pectoral fin in the top-view plane, which represents the ability of the material point to flexibly deform under no-load conditions, thereby realizing the flexibility measurement of the flexible bionic pectoral fin;

[0014] Step 8, applying a periodic reciprocating rotational motion to the root of the front fin of the manta ray-like submersible to determine the deformation of the material points on the flexible bionic pectoral fin;

[0015] Step 9, pre-set initial cracks on the bionic bones or bionic surface skin in the flexible bionic pectoral fin, determine the critical stretching rate, and simulate different impact and scratch scenarios, and delete the material points corresponding to the damaged parts; start the solid simulation calculation program based on the near-field dynamics method, set different motion properties of bionic bones, record the mechanical parameters of the bionic pectoral fin material points at each moment, the crack extension and solid loss on the surface of the bionic bones or bionic muscles, so as to realize crack evaluation.

[0016] Furthermore, the optimization result of each curve optimization scheme is a three-dimensional model of a manta ray-like submersible, and its corresponding three-dimensional point set is S (x, y, z);

[0017] For the optimization results of each curve optimization scheme, the Euclidean distance d between the three-dimensional point set S (x, y, z) and the three-dimensional point set S0 (x, y, z) on the manta ray surface is calculated, and the three-dimensional model corresponding to the curve optimization scheme with the smallest Euclidean distance is taken as the final three-dimensional model of the manta ray-like submersible.

[0018]

[0019] Where, d i represents the distance between the i-th corresponding point in the three-dimensional point set S0(x,y,z) and S(x,y,z), S 0xi , S 0yi , S 0zi is the coordinate of the i-th 3D point in the 3D point set S0(x,y,z), S x , S y , S z is the coordinate of the i-th material point in the three-dimensional point set S(x,y,z).

[0020] Furthermore, in the process of bionic bone design, spanwise and chordwise sections with different widths are designed so that the overall flexibility distribution of the fin rays conforms to the biological flexibility characteristics.

[0021] Furthermore, considering the surface effect of the material points near the boundary and interface in the flexible bionic pectoral fin, the material point force state is re-characterized according to the set near-field range and the material point distribution on the surface of the bionic bone and muscle, and the material stiffness matrix based on the perifield dynamics characterization is updated to obtain the updated bending stiffness K of the bionic bone. F (x,y) and the bending stiffness K of bionic muscle M (x,y).

[0022] Furthermore, the distance-based coupling weight function g of the bionic skeleton and bionic muscle is F (x,y,d),g M (x,y,d) is represented as follows:

[0023]

[0024] Among them, the projection coordinates of the current reference material point in the top-down plane of the flexible bionic pectoral fin are (x0, y0, z0), the projection coordinates of a material point in other parts of the flexible bionic pectoral fin are (x, y), and the distance between the two is d; δ represents the near-field range of the preset material point, SL is the unilateral span length of the flexible bionic pectoral fin, and BL is the body length of the manta ray submersible.

[0025] Furthermore, a periodic reciprocating rotational motion R(t) is applied to the root of the front fin of the manta ray-like submersible, and there is a time lag between the movement of the root of the rear fin and the root of the front fin, namely R(t-dt); then:

[0026] R(t)=Asinωt

[0027] A is the maximum amplitude angle, ω is the periodic angular frequency, and dt is the lag time of the rear fin relative to the front fin. According to the Morrison equation, the force F on the surface of the moving object in the flow field satisfies:

[0028]

[0029] X=F·Flex

[0030] Where ρ is the fluid density, V is the velocity of the material point on the flexible bionic pectoral fin, S is the set microelement area, C is the fluid coefficient, y is the spanwise coordinate of the microelement, and Flex is the weighted uniform flexibility in the top-down plane of the flexible bionic pectoral fin. The microelement size is matched with the material point spacing, and the deformation X of the material point of the flexible bionic pectoral fin is calculated.

[0031] Furthermore, the deformation at the wing tip where the deformation is the largest in the deformation field of the flexible bionic pectoral fin is taken as the eigenvalue; the deformation field on the pectoral fin is dimensionlessly processed to obtain a dimensionless number set, which characterizes the flexible deformation ability of the bionic pectoral fin after the fluid load is applied.

[0032] Furthermore, during the simulation process, a material point loss monitoring function is set to monitor the development of the crack throughout the entire process, forming a spatial coordinate evolution data set of the material points in the crack zone based on the time axis advancement, so as to evaluate the crack propagation of the pectoral fin of the manta ray submersible.

[0033] Compared with the prior art, the present invention has the following technical features:

[0034] The present invention can realize the flexibility measurement and crack propagation prediction of underwater bionic pectoral fins, solving the problem of the lack of flexibility measurement technology and crack propagation prediction technology. Based on this technology, the flexibility state and hydrodynamic characteristics of the pectoral fins during the propulsion of the bionic underwater submersible, as well as the crack propagation on the surface of the bionic pectoral fins after damage can be quickly estimated, and this can guide the flexibility design and optimization of the bionic pectoral fin bones and muscles. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is divided into a rigid body and flexible pectoral fins for a manta ray-like submersible;

[0036] Figure 2 Design and movement of variable stiffness fins for manta ray-like submersibles;

[0037] Figure 3 It is the bionic pectoral fin material point and chord-direction traveling wave;

[0038] Figure 4 Initial crack settings for bionic bones or bionic surface skins. DETAILED DESCRIPTION

[0039] In view of the technical deficiency mentioned in the technical background, the present invention proposes a method for measuring the flexibility of underwater bionic pectoral fins and evaluating crack propagation based on a peri-field dynamics model. Different from the local method of continuum mechanics, the peri-field dynamics model considers the deformation and mechanical properties of a certain material point as the comprehensive influence of all material points within the near field.

[0040] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0041] A bionic pectoral fin flexibility measurement and crack assessment method based on peri-field dynamics is proposed. Taking a manta ray-like underwater submersible as an example, the specific steps are as follows:

[0042] Step 1, scan the three-dimensional shape of the physical manta ray, and obtain a three-dimensional model of the manta ray composed of a three-dimensional point set S0 (x, y, z) on the manta ray surface, where the x direction is the wingspan direction, the y direction is the head-tail axis direction, and the z direction conforms to the right-hand screw rule.

[0043] Step 2, based on the manta ray three-dimensional model, delete the facial fin structure of the manta ray head on the model and use different curve optimization schemes to optimize the manta ray three-dimensional model. The optimization result of each curve optimization scheme is a three-dimensional model of a manta ray-like submersible, and its corresponding three-dimensional point set is S (x, y, z); during the optimization, the shape of the manta ray-like submersible should achieve a balance between fluid dynamics and structural design.

[0044] For the optimization results of each curve optimization scheme, the Euclidean distance d between the three-dimensional point set S (x, y, z) and the three-dimensional point set S0 (x, y, z) on the manta ray surface is calculated, and the three-dimensional model corresponding to the curve optimization scheme with the smallest Euclidean distance is taken as the final three-dimensional model of the manta ray-like submersible.

[0045]

[0046] Where, d irepresents the distance between the i-th corresponding point in the three-dimensional point set S0(x,y,z) and S(x,y,z), S 0xi , S 0yi , S 0zi is the coordinate of the i-th 3D point in the 3D point set S0(x,y,z), S x , S y , S z is the coordinate of the i-th material point in the three-dimensional point set S (x, y, z), is the shape deviation threshold, which is taken as 0.1 in this scheme, that is, the shape similarity based on Euclidean distance at any point is greater than 0.9.

[0047] Step 3, the three-dimensional model of the manta ray submersible includes a rigid bionic main cabin in the middle and flexible bionic pectoral fins on both sides, and the corresponding three-dimensional point sets are S1(x, y, z) and S2(x, y, z) respectively; the outer shell of the rigid bionic main cabin is usually made of hard, highly buoyant and lightweight materials, and the interior is a control and energy module; the flexible bionic pectoral fins on both sides are composed of an internal carbon fiber bionic skeleton and a super-elastic bionic muscle coated on the skeleton, such as silicone, hydrogel, etc., and the bionic skeleton is driven by a motor set at the root of the fin.

[0048] Since the rigid bionic main compartment is regarded as a rigid material, the motion deformation of the S1 (x, y, z) part is not considered; the flexible bionic pectoral fin is driven by a motor to reciprocate, and considering the fluid-solid coupling effect of the flexible bionic pectoral fin, the main deformation form of the material point on S2 (x, y, z) is bending deformation, and the tensile deformation is ignored.

[0049] Step 4, setting the flexible bionic pectoral fin of the manta ray submersible to a double fin ray structure, and at the same time, the flexibility of the bionic skeleton in the flexible bionic pectoral fin gradually increases along the direction from head to tail and from center to two wings; specifically, in the process of designing the bionic skeleton, spanwise and chordwise sections with different widths can be designed so that the overall flexibility distribution of the fin rays conforms to the biological flexibility characteristics.

[0050] According to biological research on manta rays, the flexibility of manta ray skeletons gradually increases from head to tail and from center to wings, which is conducive to the thrust on the pectoral fin surface gathering to the trailing edge, thereby improving propulsion performance; therefore, the bionic skeleton of manta ray submersibles should be designed according to this law. For the bionic skeleton in a single fin ray, the groove structure is designed on the fin plate to make the overall flexibility distribution of the fin plate conform to the biological flexibility characteristics; for the bionic skeleton in a double fin ray, the spanwise and chordwise sections with different widths are designed to make the overall flexibility distribution of the fin ray conform to the biological flexibility characteristics. This scheme adopts a double fin ray design.

[0051] Step 5, applying the peridynamic analysis method, using a rigid material model to characterize the rigid bionic main compartment of the manta ray-like submersible; selecting the near-field range δ of the material point, the engineering material constants of the carbon fiber material and the hydrogel material, and dividing the material points of the flexible bionic pectoral fin (including bionic bones and bionic muscles) in the manta ray-like submersible; using the existing carbon fiber material model in unconventional state-based peridynamics to characterize the material properties of the bionic bone, and using the existing hyperelastic material model in unconventional state-based peridynamics to characterize the material properties of the bionic muscle.

[0052] The peridynamics method is based on the non-local idea and divides the structure into material points with equal spatial spacing. The deformation state and force state of a single material point are affected by all other material points in the near-field range. The dimensionless near-field range δ=3 is selected, that is, the material point is affected by other material points within 3 unit lengths in any direction of space.

[0053] Step 6, based on the peridynamic model, describe the deformation state and force state of the bionic skeleton and bionic muscle, calculate the Jacobian matrix K of all material points in the flexible bionic pectoral fin, and then obtain the material stiffness matrix characterized by the peridynamic method based on the parameter relationship between the Jacobian matrix and the peridynamic model, and based on this, obtain the bending stiffness of the bionic skeleton and the bending stiffness of the bionic muscle;

[0054] Considering the surface effect of the material near the boundary and interface of the material points in the flexible bionic pectoral fin (such as the connection between the surface of the bionic pectoral fin and the water body, and the connection between the bionic bone and the bionic muscle), the material point force state is re-characterized according to the set near-field range and the material point distribution on the surface of the bionic bone and muscle, and the material stiffness matrix based on the perifield dynamics characterization is updated to obtain the updated bending stiffness K of the bionic bone. F (x,y) and the bending stiffness K of bionic muscle M (x,y).

[0055] Step 7: Establish the distance-based coupling weight function g between bionic skeleton and bionic muscle F (x,y,d),g M (x,y,d), such as Figure 3 As shown in the figure, the material point at the root of the front fin ray (the front edge of the bone for a single fin ray bone) is taken as the current reference material point, and the inverse of the bending stiffness of the material points in other parts of the flexible bionic pectoral fin is weighted and summed along the chord direction and the span direction to obtain the weighted unified flexibility Flex(x,y) of the flexible bionic pectoral fin in the top-view plane, which represents the ability of the material point to flexibly deform under no load, thereby realizing the flexibility measurement of the flexible bionic pectoral fin.

[0056]

[0057] Among them, the coordinates of the current reference material point are (x0, y0, z0), the coordinates of a material point in other parts of the flexible bionic pectoral fin are (x, y, z), and the distance between the two is d; since this is the projection calculation in the top-down plane of the flexible bionic pectoral fin, z0 and z are not considered; δ represents the near-field range of the preset material point, SL is the unilateral span length of the flexible bionic pectoral fin, and BL is the body length of the manta ray submersible.

[0058] Step 8, a periodic reciprocating rotational motion R(t) is applied to the root of the front fin of the manta ray submersible, and there is a time lag between the movement of the root of the rear fin and the root of the front fin, namely R(t-dt); the deformation of the material points on the flexible bionic pectoral fin is determined by calculation.

[0059] R(t)=Asinωt

[0060] A is the maximum amplitude angle, ω is the periodic angular frequency, dt is the lag time of the rear fin ray relative to the front fin ray, and the lag time depends on the number of chord-wise traveling waves on the flexible bionic pectoral fin. According to the Morrison equation, the force on the surface of the moving object in the flow field satisfies:

[0061]

[0062] X=F·Flex

[0063] Where ρ is the fluid density, V is the velocity of the material point on the flexible bionic pectoral fin, S is the set microelement area, C is the fluid coefficient, and y is the spanwise coordinate of the microelement. The microelement size is matched with the material point spacing, and the deformation X of the material point on the flexible bionic pectoral fin is calculated.

[0064] Step 9, pre-set initial cracks on the bionic skeleton or bionic surface skin in the flexible bionic pectoral fin, determine the critical stretching rate, and simulate different impact and scratch scenarios, and delete the material points corresponding to the damaged parts; start the solid simulation calculation program based on the near-field dynamics method, set different motion properties of the bionic skeleton, such as motion cycle, amplitude, lag time, etc., and record the mechanical parameters of the bionic pectoral fin material points at each moment, including the force vector set F, the deformation field X (composed of the deformation at each material point), the deformation gradient tensor, the crack extension and solid loss on the bionic skeleton or bionic muscle surface skin, such as Figure 4 shown.

[0065] The maximum deformation of a certain point or area in the deformation field X of the flexible bionic pectoral fin is taken as the eigenvalue. In this scheme, the deformation at the wing tip with the largest deformation is used as the eigenvalue. The deformation field on the pectoral fin is dimensionlessly processed to obtain a dimensionless number set, which characterizes the flexible deformation ability of the bionic pectoral fin after the fluid load is applied. During the calculation process, a material point loss monitoring function is set to monitor the development of the crack throughout the process, forming a spatial coordinate evolution data set of the material points in the crack zone based on the time axis advancement, so as to evaluate the crack propagation of the pectoral fin of the manta ray submersible.

[0066] Based on the above steps, the flexibility measurement and crack extension evaluation of the flexible pectoral fin of the manta ray are realized. It should be noted that the specific implementation methods described above are not used to limit the present invention. Any modifications, replacements, improvements, etc. made within the spirit and principles of the present invention, including but not limited to the flexible area division method, the overall stiffness distribution of the bionic skeleton, the coupling weight function form, the initial crack setting method, etc., should be within the scope of protection of the present invention.

[0067] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A bionic pectoral fin flexibility measurement and crack assessment method based on peri-field dynamics, characterized in that: include: Step 1, scanning the three-dimensional shape of the physical manta ray to obtain a three-dimensional model of the manta ray composed of a three-dimensional point set on the surface of the manta ray; Step 2, based on the manta ray three-dimensional model, delete the facial fin structure of the manta ray head on the model and use different curve optimization schemes to optimize the manta ray three-dimensional model; based on the Euclidean distance between the optimized three-dimensional point set and the three-dimensional point set on the manta ray surface, determine the final manta ray-simulating submersible three-dimensional model; Step 3, the three-dimensional model of the manta ray-like submersible includes a rigid bionic main cabin in the middle and flexible bionic pectoral fins on both sides; the flexible bionic pectoral fins are composed of an internal carbon fiber bionic skeleton and elastic bionic muscles coated on the bionic skeleton, and the bionic skeleton is driven by a motor set at the root of the fin; The rigid bionic main compartment is considered as a rigid material, and the motion deformation is not considered. The deformation form of the flexible bionic pectoral fin is bending deformation, and the tensile deformation is ignored. Step 4, setting the flexible bionic pectoral fin of the manta ray-like submersible to a double-fin structure, and the flexibility of the bionic skeleton in the flexible bionic pectoral fin gradually increases along the direction from head to tail and from center to two wings; Step 5, applying the peridynamic analysis method, using a rigid material model to characterize the rigid bionic main compartment of the manta ray submersible; selecting the near-field range of the material point, the engineering material constants of the bionic bone material and the bionic muscle material, and dividing the material points of the flexible bionic pectoral fin in the manta ray submersible; using the carbon fiber material model in the unconventional state-based peridynamics to characterize the material properties of the bionic bone, and using the hyperelastic material model to characterize the material properties of the bionic muscle; Step 6, based on the peridynamic model, describe the deformation state and force state of the bionic skeleton and bionic muscle, calculate the Jacobian matrix of all material points in the flexible bionic pectoral fin, and then obtain the material stiffness matrix characterized by the peridynamic method based on the parameter relationship between the Jacobian matrix and the peridynamic model, and based on this, obtain the bending stiffness of the bionic skeleton and the bending stiffness of the bionic muscle and update them; Step 7, establish the distance-based coupling weight function of the bionic skeleton and bionic muscle, take the material point at the root of the front fin as the current reference material point, and perform weighted summation on the inverse of the bending stiffness of the material points in other parts of the flexible bionic pectoral fin along the chord direction and the span direction to obtain the weighted uniform flexibility of the flexible bionic pectoral fin in the top-view plane, which represents the ability of the material point to flexibly deform under no-load conditions, thereby realizing the flexibility measurement of the flexible bionic pectoral fin; Step 8, applying a periodic reciprocating rotational motion to the root of the front fin of the manta ray-like submersible to determine the deformation of the material points on the flexible bionic pectoral fin; Step 9, presetting initial cracks on the bionic skeleton or bionic surface skin in the flexible bionic pectoral fin, determining the critical stretching rate, and performing different impact and scratch scene simulations, and deleting material points corresponding to the damaged parts; Start the solid simulation calculation program based on the peri-field dynamics method, set the motion properties of different bionic bones, record the mechanical parameters of the bionic pectoral fin material points at each moment, the crack extension and solid loss on the surface of the bionic bone or bionic muscle, so as to realize crack assessment.

2. The bionic pectoral fin flexibility measurement and crack assessment method based on peri-field dynamics according to claim 1 is characterized in that: The optimization result of each curve optimization scheme is a three-dimensional model of a manta ray-like submersible, and its corresponding three-dimensional point set is S (x, y, z); For the optimization results of each curve optimization scheme, the Euclidean distance d between the three-dimensional point set S (x, y, z) and the three-dimensional point set S0 (x, y, z) on the manta ray surface is calculated, and the three-dimensional model corresponding to the curve optimization scheme with the smallest Euclidean distance is taken as the final three-dimensional model of the manta ray-like submersible. Where, d i represents the distance between the i-th corresponding point in the three-dimensional point set S0(x,y,z) and S(x,y,z), S 0xi , S 0yi , S 0zi is the coordinate of the i-th 3D point in the 3D point set S0(x, y, z), S x , S y , S z is the coordinate of the i-th material point in the three-dimensional point set S(x,y,z).

3. The bionic pectoral fin flexibility measurement and crack assessment method based on peri-field dynamics according to claim 1 is characterized in that: In the process of bionic bone design, spanwise and chordwise sections with different widths are designed so that the overall flexibility distribution of the fin rays conforms to the biological flexibility characteristics.

4. The bionic pectoral fin flexibility measurement and crack assessment method based on peri-field dynamics according to claim 1 is characterized in that: Considering the surface effect of the material points near the boundary and interface in the flexible bionic pectoral fin, the material point force state is re-characterized according to the set near-field range and the material point distribution on the surface of the bionic bone and muscle, and the material stiffness matrix based on the perifield dynamics characterization is updated to obtain the updated bending stiffness K of the bionic bone. F (x,y) and the bending stiffness K of bionic muscle M (x,y).

5. The bionic pectoral fin flexibility measurement and crack assessment method based on peri-field dynamics according to claim 1 is characterized in that: Distance-based coupling weight function g between bionic skeleton and bionic muscle F (x,y,d),g M (x,y,d) is represented as follows: Among them, the projection coordinates of the current reference material point in the top-down plane of the flexible bionic pectoral fin are (x0, y0, z0), the projection coordinates of a material point in other parts of the flexible bionic pectoral fin are (x, y), and the distance between the two is d; δ represents the near-field range of the preset material point, SL is the unilateral span length of the flexible bionic pectoral fin, and BL is the body length of the manta ray submersible.

6. The bionic pectoral fin flexibility measurement and crack assessment method based on peri-field dynamics according to claim 1, characterized in that: A periodic reciprocating rotational motion R(t) is applied to the root of the front fin of the manta ray submersible. There is a time lag between the movement of the root of the rear fin and the root of the front fin, namely R(t-dt); then: R(t)=Asinωt A is the maximum amplitude angle, ω is the periodic angular frequency, and dt is the lag time of the rear fin relative to the front fin. According to the Morrison equation, the force F on the surface of the moving object in the flow field satisfies: Where ρ is the fluid density, V is the velocity of the material point on the flexible bionic pectoral fin, S is the set microelement area, C is the fluid coefficient, y is the spanwise coordinate of the microelement, and Flex is the weighted unified flexibility in the top-down plane of the flexible bionic pectoral fin; The microelement size is matched with the material point spacing, and the deformation X of the material points of the flexible bionic pectoral fin is calculated.

7. The bionic pectoral fin flexibility measurement and crack assessment method based on peri-field dynamics according to claim 1 is characterized in that: The deformation at the wing tip where the deformation is the largest in the deformation field of the flexible bionic pectoral fin is taken as the characteristic value; The dimensionless processing of the deformation field on the pectoral fins resulted in a dimensionless number set, which characterizes the flexible deformation ability of the bionic pectoral fins after the fluid load is applied.

8. The bionic pectoral fin flexibility measurement and crack assessment method based on peri-field dynamics according to claim 1 is characterized in that: During the simulation process, a material point loss monitoring function is set to monitor the development of the crack throughout the whole process, forming a spatial coordinate evolution data set of the material points in the crack zone based on the time axis advancement, so as to evaluate the crack propagation of the pectoral fin of the manta ray submersible.

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