A new method for verifying resistance performance of penguin bionic AUV

Abstract

This invention discloses a method for verifying the drag performance of a penguin-shaped biomimetic AUV, comprising the following steps: establishing a computational domain for the penguin-shaped biomimetic AUV; meshing the computational domain of the penguin-shaped biomimetic AUV; setting boundary and physical conditions for the computational domain of the penguin-shaped biomimetic AUV; setting the outflow surface of the computational domain of the penguin-shaped biomimetic AUV as a pressure outlet, and the inflow surface, upper, lower, and side surfaces as velocity inlets, setting the mid-longitudinal section as a symmetry plane, and setting the AUV model surface as a wall surface; calculating the viscous drag of the penguin-shaped biomimetic AUV when it navigates in still water, and using the computational fluid dynamics software STAR-CCM+ to predict the drag at three modeling stages for three types of AUV models.

Description

Technical Field

[0001] This invention belongs to the field of underwater AUVs and relates to a novel method for verifying the drag performance of a penguin-inspired AUV. Background Technology

[0002] The ocean is one of the most valuable ecosystems, rich in biological and mineral resources. In recent decades, countries worldwide have actively developed marine science and technology, formulating various strategies for ocean development and exploration. The ocean is a treasure trove of resources for human survival and development, and my country's economy has achieved significant growth by leveraging marine resources and space. With the continuous depletion of non-renewable land resources, the role of marine resource development and utilization in promoting human development and social progress is becoming increasingly evident, and the pace of human exploration and development of marine resources is accelerating. Due to the development of marine-related industrial technologies, underwater robots, as an effective platform for marine development, have been widely researched and applied.

[0003] Bionics is an interdisciplinary field that combines life sciences with engineering technologies such as mechanics, materials, and information. Its aim is to study and simulate the structure, function, behavior, and machine control mechanisms of living organisms, providing new design concepts, working principles, and system compositions for engineering technologies. Bionic robots possess strong flexibility and excellent adaptability, enabling them to undertake complex, dangerous, and specific tasks. With the continuous development of bionic technology, underwater robots that mimic the forms and even locomotion of marine organisms such as fish, turtles, and manta rays will continue to increase, leading to the rapid development of bionic underwater robots.

[0004] Marine life is incredibly diverse, with a wide variety of appearances. After millions of years of evolution and development, many marine creatures, such as penguins, sea lions, and seals, can swim as fast as fish, and are more agile than any underwater vehicle made by humans. They consume less energy and produce less noise while swimming, and their near-perfect body structure is a key factor in their survival in the wild. Summary of the Invention

[0005] To address the above problems, the present invention provides the following technical solution: a method for verifying the drag performance of a penguin-shaped biomimetic AUV, comprising the following steps:

[0006] Establish the computational domain of a penguin-shaped biomimetic AUV;

[0007] The computational domain of the penguin-shaped biomimetic AUV is meshed;

[0008] Boundary and physical conditions are set for the computational domain of the penguin-shaped biomimetic AUV;

[0009] The computational domain of the penguin-shaped biomimetic AUV is set as the pressure outlet, the inlet surface, the upper, lower and side surfaces are set as the velocity inlet, the mid-longitudinal section is set as the symmetry plane, and the AUV model surface is set as the wall.

[0010] Calculation of the viscous resistance of water when a penguin-shaped biomimetic AUV navigates in still water.

[0011] Furthermore: the penguin-shaped biomimetic AUV pressure-resistant shell adopts a ring-ribbed cylindrical structure;

[0012] The ring-ribbed cylindrical structure is provided with two reinforcing rings;

[0013] The ring-ribbed cylindrical structure also has O-ring grooves on both sides to seal the pressure-resistant shell;

[0014] It also includes an intermediate liner plate with a circular hole for mounting through parts and axially fixing internal equipment.

[0015] Furthermore, the penguin-shaped biomimetic AUV pressure-resistant shell is made of 7075T6 aluminum alloy.

[0016] Furthermore: The hydrostatic pressure analysis of the pressure-resistant shell of the penguin-shaped biomimetic AUV includes the following steps:

[0017] The existing mesh can be refined or coarsened by dragging the slider or directly entering a value between -100 and +100 in the Defaults section of the software.

[0018] The Element Size option in the Sizing property window of the mesh control allows you to set the element size that applies to the entire model. This element size will be used for meshing all edges, faces, and volumes.

[0019] Given that the mesh generation is selected as a tetrahedral structure, and the transition is set to slow, a smooth transition is achieved.

[0020] Based on the edge refinement curvature target, a span angle center is set, which allows a single element to span across the angle, thereby refining the mesh in the curved region. The span angle center has three forms: coarse, medium, and refined, with corresponding span angles of 91°~60°, 75°~24°, and 36°~12°, respectively.

[0021] Furthermore, the physical conditions were numerically calculated using constant density, separated flow, RANS k-epsilon turbulence, and implicit unsteadiness.

[0022] Furthermore, the boundary conditions are as follows: the outflow surface of the computational domain is set as a pressure outlet, the inflow surface, upper, lower and side surfaces are set as velocity inlets, the mid-longitudinal section is set as a symmetry plane, and the surface of the penguin-shaped biomimetic AUV model is set as a wall.

[0023] This invention provides a novel method for verifying the drag performance of a penguin-inspired AUV, which has the following advantages: Penguins, known as the "ships of the sea," are among the oldest waterfowl, possessing a graceful streamlined profile. They are approximately 80-120cm in length, with a maximum cross-section of about 30cm × 25cm, making them quite robust. This design effectively solves the problem of small volume and limited payload in underwater robots. Furthermore, the penguin-shaped bionic AUV exhibits superior drag performance compared to common tuna-type and X-35-type AUVs, and has already attracted widespread attention.

[0024] The computational fluid dynamics software STAR-CCM+ was used to predict drag in three stages of three different AUV models. By utilizing symmetry, the flow field of only half of the AUV was considered, saving resources and improving computational efficiency. A ship coordinate system was established, with the stern of the AUV as the origin. The positive X-axis was defined along the length from stern to bow, the positive Z-axis along the height, and the positive Y-axis pointing from starboard to port. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is the computational domain diagram of a penguin-shaped biomimetic AUV;

[0027] Figure 2 (a) is the mesh division of the penguin-shaped biomimetic AUV. Figure 1 (b) shows the mesh division of the penguin-shaped biomimetic AUV. Figure 2 (c) shows the mesh division of the penguin-shaped biomimetic AUV. Figure 3 (d) is the mesh division of the penguin-shaped biomimetic AUV. Figure 4 ;

[0028] Figure 3 These are drag diagrams at different modeling stages for penguin-type, tuna-type, and X-35-type biomimetic AUVs;

[0029] Figure 4 These are drag diagrams for three types of biomimetic AUVs—the penguin-type, the tuna-type, and the X-35-type—at different speeds.

[0030] Figure 5 (a) is a penguin-type isomap, (b) is a tuna-type isomap, and (c) is an X-35-type isomap.

[0031] Figure 6 This is a cross-sectional view of the pressure-resistant shell of a penguin-shaped AUV.

[0032] Figure 7 (a) Enhanced front view of the ring; (b) Enhanced side view of the ring;

[0033] Figure 8 This is a bar chart;

[0034] Figure 9 (a) is a diagram of a penguin-type geometric AUV, (b) is a diagram of a tuna-type geometric AUV, and (c) is a diagram of an X-35-type geometric AUV.

[0035] Figure 10 It is a diagram of the ship's coordinate system. Detailed Implementation

[0036] It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0039] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0040] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0041] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0042] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0043] A method for verifying the drag performance of a penguin-shaped biomimetic AUV includes the following steps:

[0044] S1: Establish the computational domain for the penguin-shaped biomimetic AUV;

[0045] S2: Mesh the computational domain of the penguin-shaped biomimetic AUV;

[0046] S3: Set boundary and physical conditions for the computational domain of the penguin-shaped biomimetic AUV;

[0047] S4: The computational domain of the penguin-shaped biomimetic AUV is set as the pressure outlet, the inlet surface, upper, lower and side surfaces are set as the velocity inlet, the mid-longitudinal section is set as the symmetry plane, and the AUV model surface is set as the wall.

[0048] S5: Calculation of the viscous resistance of water when a penguin-shaped biomimetic AUV navigates in still water.

[0049] The process of establishing the computational domain for the penguin-shaped biomimetic AUV is as follows:

[0050] To make the numerical calculation results more approximate the three-dimensional flow around the source in infinite space, the computational domain should be sufficiently large. Therefore, the inflow boundary is twice the total length from the origin, the outflow boundary is twice the total length from the origin, and the upper, lower, and side boundaries are twice the total length from the axis. The resulting computational domain is as follows: Figure 1 As shown.

[0051] The process of meshing the computational domain of the penguin-shaped biomimetic AUV is as follows:

[0052] The computational domain was meshed using STAR-CCM+ software. The surface mesh was reconstructed using surface mesh, and the volume mesh was constructed using cut volume mesh and prism layer mesh.

[0053] The mesh distribution should be sparse and reasonable to ensure both the accuracy of the calculation results and the improvement of computational efficiency. The flow field edges are minimally affected by ship motion, so the mesh is sparse to reduce the overall computational workload. Near the hull, parameters vary greatly, and the flow field is complex, containing phenomena such as separation, vortices, and detachment. Therefore, a denser mesh is needed in this region to facilitate the analysis of the flow field at the bow and stern of the AUV. Figure 2 (a) is the mesh division of the penguin-shaped biomimetic AUV. Figure 1 (b) shows the mesh division of the penguin-shaped biomimetic AUV. Figure 2 (c) shows the mesh division of the penguin-shaped biomimetic AUV. Figure 3 (d) is the mesh division of the penguin-shaped biomimetic AUV. Figure 4 ;

[0054] The process of setting boundary and physical conditions for the computational domain of the penguin-shaped biomimetic AUV is as follows:

[0055] In STAR-CCM+, the outflow surface of the computational domain is set as the pressure outlet, the inflow surface, upper surface, lower surface and side surface are set as the velocity inlet, the mid-longitudinal section is set as the symmetry plane, and the AUV model surface is set as the wall.

[0056] The physical conditions were numerically calculated using constant density, separated flow, RANS k-epsilon turbulence, and implicit unsteadiness.

[0057] When an AUV navigates in still water, it is primarily subject to viscous drag. Generally, viscous drag is decomposed into frictional drag and viscous pressure drag. Frictional drag is generated by the viscosity of the fluid. A boundary layer forms on the surface of an object; although the boundary layer is very thin, the velocity gradient within it is large. According to Newton's law of internal friction, this creates frictional shear stress along the tangential direction on the object's surface.

[0058]

[0059] In the formula: τ is the frictional shear stress; μ is the hydrodynamic viscosity coefficient; Velocity gradient within the boundary layer.

[0060] Viscous drag is caused by the separation of the boundary layer at the stern of the AUV, which creates many unstable vortices, leading to a decrease in stern pressure and resulting in drag due to the pressure difference between the front and rear ends.

[0061] When an AUV navigates in still water, neglecting the effects of fluid gravity, in order to compare the drag performance of AUVs with different drag coefficients, they should satisfy Reynolds' similarity law.

[0062]

[0063] Where: u—velocity of the object relative to the fluid; L—effective longitudinal length of the model; kinematic viscosity coefficient.

[0064] Calculations show that the Reynolds numbers for the three AUVs at a speed of 1 m / s are as follows: Penguin AUV – 2.444 × 10⁵; Tuna AUV – 2.702 × 10⁵; X-35 AUV – 2.642 × 10⁵. These AUVs have relatively similar Reynolds numbers and can be compared.

[0065] The formula for calculating resistance is:

[0066]

[0067] In the formula: Cf is the drag coefficient; ρ is the liquid density; v is the speed; S is the wetted surface area.

[0068] By predicting drag using models established for the three stages of three different AUVs, we can see that...

[0069] The model established in the first stage is a perfect streamlined shape with minimal resistance;

[0070] After the second stage added a stern section with a propulsion device, the drag increased by about 10%.

[0071] After the third stage added an effective load area, the drag increased by about 15% compared to the first stage.

[0072] like Figure 3 As shown;

[0073] like Figure 4 As shown, a comparison of the drag of the three types of AUVs at different speeds reveals that the Penguin-type AUV consistently experiences the least drag, followed by the X-35 AUV, while the Tuna-type AUV experiences the greatest drag. In actual AUV operation, appendages such as the propulsion system, rudder, and communication equipment also generate significant drag. However, in general, other AUV types require similar arrangements, thus the Penguin-type AUV still holds a considerable advantage.

[0074] S5: Post-processing of the calculated flow field

[0075] The drag study of the penguin-inspired AUV model mainly reflects the overall characteristics of the surrounding flow field. Visualizing the flow field around the penguin-inspired AUV model using STAR-CCM+ provides a direct visual representation of the flow field conditions. At a velocity of 3.0 m / s, the velocity contour maps of the longitudinal profiles for the three AUVs are shown below. Figure 5 As shown, Figure 5 (a) is a penguin-type isomap, (b) is a tuna-type isomap, and (c) is an X-35-type isomap.

[0076] The comparison shows that, because the bow of the penguin-type AUV is sharper than that of the tuna-type AUV and the X-35-type AUV, the velocity variation of the penguin-type AUV is smaller.

[0077] At the bow, the fluid velocity drops to zero, forming a stagnation point, which is also the point of highest pressure. After the stagnation point, the fluid velocity gradually increases while the pressure decreases, a phenomenon known as the pressure gradient with respect to pressure. After the point of highest velocity, the pressure continuously increases along the flow direction while the fluid velocity decreases, a phenomenon known as the pressure gradient against pressure. During the flow along the pressure gradient (decompression and acceleration), some of the pressure energy is converted into kinetic energy. In the region of the pressure gradient against pressure (pressure increase and decompression), not only is some of the fluid's kinetic energy converted into pressure energy, but the viscous forces also continue to consume kinetic energy, resulting in energy loss and a continuous decrease in velocity.

[0078] Furthermore, the penguin-inspired AUV pressure-resistant shell design:

[0079] The pressure hull is the most important pressure-bearing component of an AUV. With the increasing demands for modern exploration depth, the requirements for the structural performance of the pressure hull are also becoming higher. Modern pressure hulls are developing towards miniaturization, lightweighting, and high depth to improve the controllability, flexibility, high depth, and high load capacity of AUVs.

[0080] S21: Establishment of the pressure hull model

[0081] The penguin-shaped AUV pressure hull is a ring-ribbed cylindrical structure. Due to the need to install equipment inside, it is divided into three sections, with preliminary lengths of 180mm, 200mm, and 160mm, and an outer diameter of 210mm. Two reinforcing rings are installed, which not only provide secure support to the hull but also have O-ring grooves on both sides for sealing the pressure hull. The central liner has circular holes for installing through-holes and axially securing internal equipment.

[0082] The AUV pressure hull is initially designed using 7075T6 aluminum alloy. The hull and reinforcing ribs are all made of 7075T6 with a yield strength of 505 MPa and a working water depth of 1000 m.

[0083] Figure 6 This is a cross-sectional view of the pressure-resistant shell of a penguin-shaped AUV.

[0084] Figure 7 (a) Enhanced front view of the ring; (b) Enhanced side view of the ring;

[0085] S22: Hydrostatic Pressure Analysis of Pressure Tank

[0086] S221: Grid generation

[0087] Mesh generation is one of the most important steps in structural analysis. The quality of the mesh generation directly affects the accuracy of the analysis results, and the higher the quality of the mesh, the better.

[0088] (1) Correlation and correlation center can be adjusted in the Defaults section of the properties window by dragging the slider or directly entering a value between -100 and +100 to refine or coarse the existing mesh. In this application, the correlation is set to 100;

[0089] (2) The global element size can be set in the Element Size option in the Sizing property window of the mesh control to apply to the penguin-shaped bionic model AUV. This element size will be applied to the meshing of all edges, faces and volumes. Given that the shell, walls and ribs of the thin solid created are relatively thin and the size of the geometry is not large, this application sets the global element size to 2 mm.

[0090] (3) Given that the mesh is selected as a tetrahedral structure, the transition is set to slow to make the transition smooth;

[0091] (4) Span Angle Center: Based on the edge refinement curvature target, a span angle center is set, allowing a single element to span this angle, thus refining the mesh in curved regions. There are three forms of span angle center: coarse, medium, and fine, with corresponding span angles of 91°–60°, 75°–24°, and 36°–12°, respectively. The pressure shell analyzed in this paper is composed of tubular bodies. The transitions between components are not perfect curves; therefore, this application sets the span angle center to fine.

[0092] S222: Check Mesh Quality. To check the final mesh, click Mesh, open the Statistic sub-window in the Properties window, and select the Element Quality option to view the current mesh quality. The current mesh has 3,429,517 nodes and 2,268,228 elements, with an average quality of 0.83748 (defined as acceptable at 0.7). Therefore, the current mesh meets the accuracy requirements. If the average quality of the mesh is lower than 0.7, such as... Figure 8 View the mass distribution of the mesh in the Mesh Metric chart below the plotting area. Clicking on the bar chart will show the distribution of that mass mesh across the structure, such as... Figure 8 As shown.

[0093] S23: Load and solve

[0094] First, in the Properties window, select the outer surface of the pressure hull under Scope-Geometry, and then set the Fluid Density to 1025 kg / m³. 3 Select the coordinate axis and set the hydrostatic acceleration to 9.81 m / s². 2 The free surface height is set to 1000 meters. The load settings are shown in the table below:

[0095] Right-click the Solution button and double-click the Solve command, or click Solve directly in the menu bar to perform iterative calculations. Its maximum stress is 442.96 MPa, which is less than the material's yield strength of 505 MPa, leaving some margin. This means that even if the pressure hull continues to sink a little further in special circumstances, it will not be damaged.

[0096] The maximum deformation is 0.10697 mm. Based on the main dimensions determined above, its height is 210 mm in diameter, meaning the deformation is only 0.05% of the dimensions, which meets the requirements.

[0097] At this point, the structure and dimensions of the biomimetic penguin AUV pressure shell under static load conditions have been completed.

[0098] To verify that the penguin-inspired AUV has superior drag performance, we compared it with common tuna-type AUVs and X-35-type AUVs. These three types of hulls have the same surface area but differ in shape, overall length, volume, and cross-sectional shape.

[0099] We used the 3D modeling software Rhino for model building, and each ship type was modeled in three stages. The first stage was a perfect streamlined shape without any expansion modules. The second stage added a stern section for installing the propulsion system. The third stage, based on the second stage, added a payload area amidships. The main dimensions of these three models in the third stage are shown in Table 1. Figure 9 The images shown are the exterior designs of three stage models of the AUV: Penguin, Tuna, and X-35. Figure 9 (a) is a diagram of a penguin-type geometric AUV, (b) is a diagram of a tuna-type geometric AUV, and (c) is a diagram of an X-35-type geometric AUV.

[0100] Table 1. Main Scales of AUV

[0101] Penguin type X-35 Tuna type Overall length (mm) 1230 1330 1360 Outer diameter (mm) 280 275 250 Payload area length (mm) 110 135 145

[0102] We used the computational fluid dynamics software STAR-CCM+ to predict drag in three stages of the modeling process for three different types of AUV models. Utilizing symmetry, we considered only half of the AUV's flow field, saving resources and improving computational efficiency. We established a ship coordinate system, taking the stern of the AUV as the origin. The length direction from stern to bow was defined as the positive X-axis, the height direction as the positive Z-axis, and the direction from starboard to port as the positive Y-axis. Figure 10 As shown.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for verifying the drag performance of a penguin-shaped biomimetic AUV, characterized by: Includes the following steps: Establish the computational domain of a penguin-shaped biomimetic AUV; The computational domain of the penguin-shaped biomimetic AUV is meshed; Boundary and physical conditions are set for the computational domain of the penguin-shaped biomimetic AUV; The computational domain of the penguin-shaped biomimetic AUV is set as the pressure outlet, the inlet surface, the upper, lower and side surfaces are set as the velocity inlet, the mid-longitudinal section is set as the symmetry plane, and the AUV model surface is set as the wall. Calculation of the viscous drag of water on a penguin-shaped biomimetic AUV when it navigates in still water; The penguin-shaped biomimetic AUV pressure-resistant shell adopts a ring-ribbed cylindrical structure; The ring-ribbed cylindrical structure is provided with two reinforcing rings; The ring-ribbed cylindrical structure also has O-ring grooves on both sides to seal the pressure-resistant shell; It also includes an intermediate liner plate with a circular hole for mounting a through-hole and axially fixing internal equipment; The hydrostatic pressure analysis of the penguin-shaped biomimetic AUV pressure-resistant shell includes the following steps: The existing mesh can be refined or coarsened by dragging the slider or directly entering a value between -100 and +100 in the Defaults section of the software. The Element Size option in the Sizing property window of the mesh control allows you to set the element size that applies to the entire model. This element size will be used for meshing all edges, faces, and volumes. Given that the mesh generation is selected as a tetrahedral structure, and the transition is set to slow, a smooth transition is achieved. Based on the edge refinement curvature target, a span angle center is set, which allows a single element to span across the angle, thereby refining the mesh in the curved region. The span angle center has three forms: coarse, medium, and refined, with corresponding span angles of 91°~60°, 75°~24°, and 36°~12°, respectively.

2. The method for verifying the drag performance of a penguin-shaped biomimetic AUV according to claim 1, characterized in that: The penguin-shaped biomimetic AUV pressure-resistant shell is made of 7075T6 aluminum alloy.

3. The method for verifying the drag performance of a penguin-shaped biomimetic AUV according to claim 1, characterized in that: The physical conditions were numerically calculated using constant density, separated flow, RANS k-epsilon turbulence, and implicit unsteadiness.

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