Underwater vehicle long cylindrical appendage drag reduction flow guide structure design method, program, equipment and storage medium

Abstract

The invention belongs to the technical field of hydrodynamic resistance calculation of underwater vehicles, and particularly relates to a design method, program and equipment for a long cylindrical appendage resistance reduction and flow guide structure of an underwater vehicle and a storage medium. According to the method, targeted resistance reduction optimization is carried out on the long cylindrical appendage on the outer side of the underwater vehicle by designing the fairing, viscous resistance and differential pressure resistance are comprehensively considered, a curve of the fairing is optimized through a multi-target optimization algorithm, verification is carried out through comparison calculation, and it is ensured that under different incoming flow velocities, the resistance of the long cylindrical appendage is reduced. Therefore, the resistance reduction performance of the air guide sleeve cannot be greatly attenuated due to environmental changes, and a powerful guarantee is provided for long-term stable operation of an underwater vehicle in a complex marine environment. Under various navigation working conditions, compared with a mode that only a long cylindrical appendage is configured, the flow guide cover designed by the invention has the advantages that the resistance borne by the underwater vehicle is obviously reduced, and the hydrodynamic performance of the underwater vehicle can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrodynamic drag calculation for underwater vehicles, and particularly relates to a method, program, device, and storage medium for designing a drag reduction and flow guiding structure for a long cylindrical appendage of an underwater vehicle. Background Art

[0002] Underwater vehicles are important devices and carriers for ocean monitoring. It is of great significance to carry out research and development on ocean monitoring technologies and equipment. With the rapid development of ocean technologies, the requirements for the speed, endurance, and maneuverability of underwater vehicles are continuously increasing. However, the problem of navigation resistance has become an important factor restricting their performance. Existing research has shown that, given a certain driving power and total energy capacity, when the resistance is reduced by 10%, the navigation speed and distance of the vehicle can increase by approximately 3.57% simultaneously. In addition, reducing the resistance of the vehicle is also of great significance for enhancing economic competitiveness and energy conservation and environmental protection.

[0003] A large amount of research has been carried out on the drag reduction of underwater vehicles, mainly focusing on two main directions. On the one hand, the overall shape of the vehicle is optimized. By simulating the flow characteristics of the fluid under different shapes, the shape scheme with the minimum resistance is sought. For example, the vehicle is designed in a droplet shape or a streamlined shape to reduce the separation of the water flow and the generation of vortices, thereby reducing the pressure drag. On the other hand, drag reduction materials or technologies are applied to the surface of the vehicle, such as low surface energy coatings, microstructured surfaces, etc., to reduce the friction between the fluid and the surface and lower the frictional drag. However, these existing drag reduction technologies have significant limitations. In terms of shape optimization, although theoretically certain shapes have lower resistance, in practical applications, underwater vehicles often need to carry various devices and instruments, which makes it difficult to design their shapes completely according to the ideal drag reduction shapes. Moreover, even with an optimized shape, the drag reduction effect will be greatly reduced under different navigation speeds, water flow conditions, and complex ocean environments. For surface drag reduction materials and technologies, the current drag reduction coatings have deficiencies in durability and stability. Under the influence of long-term seawater erosion, water flow scouring, and marine organism attachment, the drag reduction performance of the coatings will gradually decline or even fail. At the same time, the preparation processes of some microstructured surfaces for drag reduction are complex and costly, making it difficult to be widely applied to actual underwater vehicles.

[0004] The fairing of an underwater vehicle is a component installed on the surface of the underwater vehicle, aiming to guide the fluid flow. It reduces the resistance by optimizing the fluid flow, thereby improving the efficiency and performance of the vehicle. Summary of the Invention

[0005] The purpose of the present invention is to provide a design method, program, device and storage medium for a drag reduction and flow guiding structure of a long cylindrical appendage of an underwater vehicle. By integrating hydrodynamic simulation, parametric expression and optimization algorithm, and comprehensively considering viscous drag and pressure drag, a solution with both dynamic adaptability and high drag reduction performance is provided.

[0006] A design method for a drag reduction and flow guiding structure of a long cylindrical appendage of an underwater vehicle includes the following steps:

[0007] Step 1: Establish a fluid calculation domain and construct an underwater vehicle model in the fluid calculation domain;

[0008] Step 2: Set boundary conditions and calculation conditions in the fluid calculation domain, and configure the CFD numerical solution method;

[0009] Step 3: Solve the straight-line resistance of the bare hull of the underwater vehicle under the calculation conditions;

[0010] Step 4: Configure a long cylindrical appendage on the underwater vehicle, and solve the straight-line resistance of the entire underwater vehicle with the long cylindrical appendage configured thereon and the straight-line resistance of the long cylindrical appendage itself under the calculation conditions;

[0011] Step 5: Configure a fairing on the underwater vehicle, and the fairing wraps the long cylindrical appendage; use a parametric method to express the fairing bus line type, and according to the fairing design constraints, use a multi-objective optimization algorithm to obtain the fairing bus line type with the best drag reduction and flow guiding effect;

[0012] Step 6: Change the calculation conditions, and repeat Steps 2 to 6 to obtain a solution set of the fairing bus line types with the best drag reduction and flow guiding effects corresponding to different calculation conditions, and complete the design of the drag reduction and flow guiding structure of the long cylindrical appendage of the underwater vehicle.

[0013] Further, in Step 5, the inner diameter of the fairing is slightly larger than the outer diameter of the long cylindrical appendage, the gap between the fairing and the long cylindrical appendage does not exceed a threshold value, the axial range of the fairing does not exceed the middle section of the bare hull of the underwater vehicle, and the radial length of the fairing is the same as that of the long cylindrical appendage; the fairing shape is axisymmetrically designed and the shape has a smooth transition.

[0014] Further, the parametric method used to express the fairing bus line type in Step 5 is specifically as follows:

[0015]

[0016] Among them, the parameter ω i is the control point weight factor, corresponding to n + 1 control vertices P i respectively; B i,k (u) is calculated by a recurrence formula:

[0017]

[0018] Among them, vi为 the i-th element in the knot vector V, and the knot vector V is:

[0019]

[0020] Given the control point coordinates P i (x, y, z), specifying the curve power, giving the weights of each control point, and generating the fairing busbar through the mathematical expression of the NURBS curve.

[0021] Furthermore, according to the straight-line resistance R1 of the bare hull obtained in step 3 under the calculation conditions, the straight-line resistance R2 of the entire underwater vehicle equipped with a long cylindrical appendage obtained in step 4 under the calculation conditions, and the straight-line resistance R3 of the long cylindrical appendage itself under the calculation conditions, calculate the appendage resistance coefficient C of the long cylindrical appendage as:

[0022]

[0023] Among them, ρ is the density of the fluid in the calculation domain, S is the wetted surface area of the long cylindrical appendage, and V is the oncoming flow velocity in the calculation conditions;

[0024] The percentage increase Δ in the straight-line resistance of the underwater vehicle after configuring the long cylindrical appendage is:

[0025]

[0026] After configuring the fairing on the underwater vehicle in step 5, calculate the appendage resistance coefficient of the fairing and the percentage increase in the straight-line resistance of the underwater vehicle after configuring the fairing. Taking the minimum appendage resistance coefficient and the lowest percentage increase in the straight-line resistance as the goals, use the multi-objective optimization algorithm to obtain the fairing busbar line type with the best drag reduction and flow guiding effect.

[0027] A computer device / system, including a memory, a processor, and a computer program stored on the memory, and the processor executes the computer program to implement the steps of the above-mentioned design method for the drag reduction and flow guiding structure of the long cylindrical appendage of the underwater vehicle.

[0028] A computer-readable storage medium, on which a computer program / instructions are stored, and when the computer program / instructions are executed by the processor, the steps of the above-mentioned design method for the drag reduction and flow guiding structure of the long cylindrical appendage of the underwater vehicle are implemented.

[0029] A computer program product includes a computer program / instructions. When the computer program / instructions are executed by a processor, the steps of the above-mentioned design method for the drag reduction and flow guiding structure of the long cylindrical appendage of the underwater vehicle are implemented.

[0030] The beneficial effects of the present invention are as follows:

[0031] The present invention optimizes the drag reduction of the long cylindrical appendage outside the underwater vehicle by designing a fairing. By comprehensively considering the viscous drag and pressure drag, the fairing curve is optimized using a multi-objective optimization algorithm, and verified through comparative calculations, ensuring that the drag reduction effect can be stably exerted at different oncoming flow velocities, so that the drag reduction performance of the fairing will not be significantly attenuated due to environmental changes, providing a strong guarantee for the long-term stable operation of the underwater vehicle in a complex marine environment. Under various navigation conditions, compared with only configuring the long cylindrical appendage, the drag force on the underwater vehicle is significantly reduced when using the fairing designed by the present invention, and the present invention can improve the hydrodynamic performance of the underwater vehicle. Description of the Drawings

[0032] Figure 1 It is a flowchart of the technical solution of the present invention.

[0033] Figure 2 It is a schematic diagram of the bare hull of the underwater vehicle in the embodiment of the present invention.

[0034] Figure 3 It is a schematic diagram of the CFD calculation domain setting in the embodiment of the present invention.

[0035] Figure 4 It is a schematic diagram of the CFD calculation domain grid in the embodiment of the present invention.

[0036] Figure 5 It is a schematic diagram of the underwater vehicle with a long cylindrical appendage in the embodiment of the present invention.

[0037] Figure 6 It is a schematic diagram of the fairing curve in the embodiment of the present invention.

[0038] Figure 7 It is a schematic diagram of the underwater vehicle with a fairing in the embodiment of the present invention. Detailed Embodiments

[0039] The following further describes the present invention with reference to the drawings.

[0040] The fairing of an underwater vehicle is a component installed on the surface of the underwater vehicle, aiming to guide the fluid flow. By optimizing the fluid flow and reducing resistance, it can improve the efficiency and performance of the vehicle. The present invention aims to develop a new fairing drag reduction method based on parametric design and multi-objective optimization. By integrating hydrodynamic simulation, parametric expression, and optimization algorithms, and comprehensively considering viscous drag and pressure drag, a solution with both dynamic adaptability and high drag reduction performance is provided.

[0041] The purpose of the present invention is to significantly reduce the resistance of the long cylindrical appendage to the underwater vehicle by installing a fairing and improve the hydrodynamic performance of the underwater vehicle. A design method for the drag reduction fairing structure of the long cylindrical appendage of an underwater vehicle comprises the following steps:

[0042] S1. Establish a three-dimensional model of the underwater vehicle and the fluid domain and perform mesh division;

[0043] Use SOLIDWORKS software to perform three-dimensional modeling of the underwater vehicle and the fluid domain. The geometric model of the underwater vehicle is the Suboff standard model without appendages; the fluid domain is cylindrical. The front end of the underwater vehicle is 2L away from the velocity inlet, the tail end is 4L away from the pressure outlet, and the diameter of the cylinder is 3L, where L is the total length of the bare hull, which is 4.356 meters. Import the three-dimensional models of the underwater vehicle and the fluid domain into StarCCM+ software for mesh division. The fluid domain uses hexahedral meshes, and the surface of the underwater vehicle uses tetrahedral meshes. In order to accurately capture the change of the navigation resistance, the mesh is encrypted around and on the surface area of the underwater vehicle. When encrypting the near-wall area, there are 5 prism layers, the total thickness is 0.01m, and the growth rate is 1.2.

[0044] Table 1 Underwater vehicle parameters

[0045]

[0046] S2. Select an equation solver, set the boundary conditions of the CFD calculation domain, and configure the CFD numerical solution method;

[0047] Use StarCCM+ software to perform CFD numerical calculations and solve the control equations. The control equations used are as follows:

[0048]

[0049] Among them, i, j = 1, 2, 3, representing the X, Y, and Z axis directions; u' is the time-averaged value and pulsation value of the flow velocity in the i direction; p' is the time-averaged value and pulsation value of the pressure received by the fluid microelement; f i =(F i +s i ) / ρ is the generalized momentum source term; Fi is the resultant external force acting on the fluid element in the i - direction; s i is a term that contributes less to the viscous stress.

[0050] The Reynolds - averaged Navier - Stokes equations (RANS equations) are the time - averaged equations of motion for fluid flow. The idea behind the equations is Reynolds decomposition, which decomposes the instantaneous quantity into its time - averaged quantity and fluctuating quantity.

[0051] In the Reynolds - averaging method, the solution variables in the instantaneous (exact) Navier - Stokes equations are decomposed into the mean value (ensemble - average or time - average) and the fluctuating component. For the velocity components:

[0052]

[0053] where, and u' i represent the mean velocity component and the fluctuating velocity component respectively (i = 1, 2, 3).

[0054] Similarly, for pressure and other scalars:

[0055]

[0056] where, represents scalars such as pressure, energy, or component concentration.

[0057] Substituting an expression of this form into the instantaneous continuity and momentum equations and performing a time (or ensemble) average yields the ensemble - averaged momentum equation, which in Cartesian tensor form is:

[0058]

[0059] The Reynolds - averaging method requires appropriate modeling of the Reynolds stress in turbulence modeling, relating the Reynolds stress to the mean velocity gradient:

[0060]

[0061] Referring to some mature underwater vehicle devices, except for special requirements, the maximum speed of an underwater vehicle with an approximate size generally does not exceed 8 kn. Therefore, the oncoming flow velocities are set to 1, 2, 3, and 4 m / s respectively, and the boundary conditions are set as follows: The inlet is set as a velocity inlet, and the normal inflow velocity is the fluid flow velocity; the outlet is set as a pressure outlet with a static pressure of 0; the wall of the underwater vehicle is set as a no - slip wall, and the wall of the fluid domain is set as a symmetry plane.

[0062] Select the RANS SST k - ω turbulence model, and the turbulent eddy viscosity μ t = ρkT, where ρ is the density and T is the turbulent time scale:

[0063]

[0064] where α * and a1 are model coefficients, and F2 is a mixing function, which is calculated as follows:

[0065]

[0066] where β * is a model coefficient; d is the distance from the wall;

[0067] The transport equations for kinetic energy k and specific dissipation rate ω are:

[0068]

[0069] where is the average velocity, μ is the dynamic viscosity; σ k and σ ω , C ε1 , C ε2 are model coefficients; P k and P ω are result terms; is the free shear correction factor; f β is the eddy extension correction factor; S k and S ω are user-specified source terms, and k0 and ω0 are ambient turbulence values that prevent turbulent decay.

[0070] S3. Solve the straight-line resistance of the bare hull under different navigation conditions;

[0071] The solution data is as follows:

[0072] The total resistance during underwater navigation is:

[0073] R = R F + R X

[0074] where R F is the frictional resistance; R x is the pressure drag;

[0075] R x = ∫ A pdAcosθ

[0076] R F = ∫ A τdAsinθ

[0077] Table 2 Straight-line resistance of the bare hull of the underwater vehicle

[0078] Speed / m / s Naked hull of underwater vehicle / N 1 10.775 2 38.540 3 81.981 4 140.229

[0079] S4. A long cylindrical appendage is configured on the underwater vehicle, and the total resistance of the underwater vehicle and the resistance received by the long cylindrical appendage itself are calculated under different navigation conditions;

[0080] The position X of the appendage is the position of the foremost end of the appendage, which is the axial position along the underwater vehicle. The origin is placed at the bow of the vehicle, and the positive direction is towards the stern. All appendages are considered to be in the middle parallel mid-body section. For the underwater vehicle, the middle section starts at 1.016 m and ends at 3.245 m. Compared with the total length L of the vehicle, x / L ∈ (0.234, 0.744). The selected position of the appendage for calculation is X / L = 0.26. The length-to-diameter ratio of the long cylindrical appendage is 8, and the diameter is 40 mm. The navigation conditions are the same as those of the bare hull. The total resistance of the underwater vehicle and the resistance received by the long cylindrical appendage itself (including viscous resistance and pressure difference resistance) are calculated under different navigation conditions.

[0081] Table 3 Total resistance of the underwater vehicle with a long cylindrical appendage

[0082] Speed / m / s Drag of underwater vehicle with long cylindrical appendage / N 1 13.842 2 49.966 3 106.935 4 183.881

[0083] Table 4 Resistance of the long cylindrical appendage

[0084]

[0085] S5. Define two indicators, the appendage resistance coefficient C and the resistance increase percentage Δ, to quantify the influence of the appendage on the resistance of the vehicle;

[0086] The geometric shape of the appendage is determined by the actual underwater vehicle fittings and is installed in the middle section of the bare hull of the underwater vehicle. Under different navigation conditions, the total resistance of the underwater vehicle and the resistance received by the long cylindrical appendage are calculated and the data is recorded.

[0087] Calculation formula for the appendage resistance coefficient C:

[0088]

[0089] where R is the appendage resistance, ρ is the water density, S is the wetted surface area of the appendage, and V is the oncoming flow velocity;

[0090] Calculation formula for the resistance increase percentage Δ:

[0091]

[0092] where R1 is the total resistance of the underwater vehicle with the appendage, and R2 is the resistance of the bare hull;

[0093] By calculating the values of the appendage resistance coefficient C and the resistance increase percentage Δ, the influence of the long cylindrical appendage on the resistance of the underwater vehicle is quantified, and the data is as follows:

[0094] Table 5 Appendage resistance coefficient of the long cylindrical appendage

[0095]

[0096] Table 6 Increased percentage of resistance of long cylindrical appendages Δ

[0097] Speed / m / s Underwater vehicle with long cylindrical appendage 1 28.46％ 2 29.65％ 3 30.44％ 4 31.13％

[0098] S6. Clarify the design constraints of the fairing, including the size, shape and smoothness requirements; the inner diameter of the fairing should be greater than or equal to the outer diameter of the cylindrical appendage, because if there is a large gap between the two, the fluid will form a complex secondary flow in the gap, which will produce additional energy dissipation and vortexes, thereby increasing unnecessary flow resistance. A design that is as close as possible can ensure that the fairing can guide the fluid more effectively, allowing the fluid to flow along the expected path, reducing local turbulence and separation caused by the gap, significantly reducing the additional resistance caused by the gap flow, and making the fluid flow between the fairing and the long cylindrical appendage smoother, which helps to achieve a better drag reduction effect.

[0099] The axial length is set in the middle section. The middle section of the bare hull is usually a relatively stable area for fluid flow. At this time, the fluid velocity is relatively uniform, and the turbulence and pressure difference are small. Therefore, setting a fairing in this area can more effectively guide the fluid flow and reduce resistance. The radial length of the fairing is consistent with the long cylindrical appendage, ensuring a smooth transition between the fairing and the appendage, ensuring a smoother transition of the fluid from the appendage to the fairing, and reducing local flow resistance or separation.

[0100] The axisymmetric design of the fairing ensures that the geometric shape and physical properties of the fairing are symmetrical in all directions. When the fluid flows around the axisymmetric object, the forces and moments generated are symmetrical on both sides of the axis of symmetry. This ensures that no additional lateral forces will be generated in the horizontal direction due to the asymmetry of the fairing shape, thereby preventing the underwater vehicle from deviating from the predetermined navigation trajectory. When the vehicle is turning or changing speed, the axisymmetric fairing also makes it easier to predict and control the forces and moments generated by the fluid on it.

[0101] The smoothly transitioned shape can prevent flow separation and turbulence caused by sharp edges and sudden curvatures. These undesirable flows will increase resistance and help the fluid flow evenly on the surface of the guide cover, thereby reducing flow instability. The smooth shape can reduce the pressure difference between the fluid and the guide cover, reducing flow turbulence and pressure loss.

[0102] S7. Use parametric method to express the busbar line shape of the air deflector;

[0103] Parameterized expression using NURBS curves:

[0104]

[0105] The mathematical expression of a k - degree NURBS curve represented by parameter u is as follows:

[0106]

[0107] where the parameter ω i is the control point weight factor, corresponding to n + 1 control vertices P i (i = 0, 1, 2,..., n) respectively. B i,k (u) is a k - degree B - spline basis function determined by the knot vector V according to the recurrence formula. The recurrence relation of B i,k (u) is as follows, where v i is a set of non - decreasing real numbers, called knot values, which constitute the knot vector V. i = 0, 1, 2,..., n + k + 1. A uniform knot vector is adopted, that is, the non - repeating knot values are in arithmetic progression.

[0108]

[0109]

[0110] Given the control point coordinates P i (x, y, z) (i = 0, 1, 2,..., n), specifying the curve degree, giving the weights of each control point, the bus bar of the fairing is generated through the mathematical expression of the NURBS curve.

[0111] S8. Use the multi - objective optimization algorithm to optimize the fairing curve, generate the optimal solution set of the bus bar line type, and complete the fairing design based on the optimal solution;

[0112] According to the clear fairing design constraints, optimize the fairing bus bar line type through the genetic algorithm to obtain the optimal solution set; compare all the results in the solution set, select the solution set with the highest stability, and complete the fairing mechanism design.

[0113] The optimization design process first takes the parameters of the generated fairing bus bar as the initial scheme and uses the multi - objective optimization algorithm to search for the globally better solution. The optimization algorithm adopted is the genetic algorithm. The genetic algorithm is a random search optimization algorithm that draws on the natural selection and genetic mechanisms of biology. By simulating the phenomena of reproduction, gene crossover, and mutation that occur in the natural selection and natural genetic processes, a group of candidate solutions is retained in each iteration, and better individuals are selected from the solution set according to a certain index. The genetic operators (selection, crossover, and mutation) are used to perform arithmetic recombination on the individuals to generate a new generation of candidate solution groups, and this process is repeated until a certain convergence index is met.

[0114] The basic implementation process of the genetic algorithm is as follows:

[0115] The genetic algorithm is an optimization search algorithm based on the principles of natural selection and genetic genetics. Its basic implementation process mainly includes the following steps:

[0116] 1. Encoding: Map the solution space of the problem to the encoding space that the genetic algorithm can handle, and represent the solution as a combination of genetic materials, that is, chromosomes. Using binary encoding, each solution is represented by a string of binary digits.

[0117] 2. Population initialization: Randomly generate an initial population. The population consists of multiple individuals, and each individual is a coded solution. The population size is generally determined according to the complexity of the problem and computing resources, usually between dozens and hundreds.

[0118] 3. Fitness evaluation: Define a fitness function to measure the fitness or superiority of each individual in the current problem. The larger the value of the fitness function, the better the individual.

[0119] 4. Selection: According to the fitness of the individuals, select some better individuals from the current population, so that they have the opportunity to produce offspring and enter the next generation population. Taking the roulette wheel selection method as an example, the probability of each individual being selected is proportional to its fitness value. The higher the fitness of the individual, the greater the probability of being selected.

[0120] 5. Crossover: Perform a crossover operation on the selected individuals to simulate the gene recombination process in the biological world. According to a certain crossover probability, randomly select two individuals, randomly select one or more crossover points on their chromosomes, and exchange the gene segments on both sides of the crossover points to generate two new individuals.

[0121] 6. Mutation: Perform a mutation operation on the chromosomes of the individuals with a certain mutation probability to simulate gene mutations in the biological world. Randomly select one or more gene positions on the chromosomes of the individuals and change their gene values. In binary encoding, change 0 to 1 or 1 to 0.

[0122] 7. Population update: Put the new individuals generated after selection, crossover, and mutation operations into a new population, replacing some or all of the individuals in the original population to form a new generation population.

[0123] 8. Termination condition judgment: Check whether the termination conditions are met, such as reaching the preset maximum number of iterations, the fitness value reaching a certain threshold, and the fitness value not improving significantly for several consecutive generations. If the termination conditions are met, the algorithm stops and outputs the individual with the highest fitness in the current population as the optimal solution; otherwise, return to step 4 and continue the next round of genetic operations.

[0124] The genetic algorithm continuously iterates and evolves, making the individuals in the population gradually approach the optimal solution set. By comparing all the results in the solution set, the solution set with the highest stability is selected to complete the design of the fairing mechanism.

[0125] S9. Through comparative calculations, the drag reduction effect of the fairing under different navigation conditions is effectively verified.

[0126] The calculation results of the underwater vehicle with a fairing are as follows:

[0127] Table 7 Total drag of the underwater vehicle with a fairing

[0128] Speed / m / s Total drag of underwater vehicle with fairing / N 1 12.225 2 43.622 3 92.667 4 158.471

[0129] Table 8 Appendage drag of the fairing

[0130]

[0131] Table 9 Appendage drag coefficient of the fairing

[0132]

[0133] Table 10 Percentage increase in drag of the underwater vehicle with a fairing

[0134] Speed / m / s Underwater vehicle with fairing 1 13.46％ 2 13.19％ 3 13.03％ 4 13.01％

[0135] Specifically, when the underwater vehicle appendage is a long cylinder, for different navigation conditions (inflow velocities of 1, 2, 3, and 4 m / s), the calculated drag coefficients C of the appendage are 0.1416, 0.1310, 0.1268, and 0.1246 respectively, the drag increases are 28.46%, 29.65%, 30.44%, and 31.13% respectively, the viscous drags are 0.130 N, 0.423 N, 0.845 N, and 1.387 N respectively, the pressure drags are 2.892 N, 10.753 N, 23.512 N, and 41.159 N respectively, and the total drags are 13.842 N, 49.966 N, 106.935 N, and 183.881 N respectively. When the underwater vehicle is equipped with a fairing, for different navigation conditions (inflow velocities of 1, 2, 3, and 4 m / s), the calculated drag coefficients C of the appendage are 0.0183, 0.0158, 0.0147, and 0.0141 respectively, the drag increases are 13.46%, 13.19%, 13.03%, and 13.01% respectively, the viscous drags are 0.455 N, 1.580 N, 3.286 N, and 5.529 N respectively, the pressure drags are 0.906 N, 3.133 N, 6.571 N, and 11.243 N respectively, and the total drags are 12.225 N, 43.622 N, 92.667 N, and 158.471 N respectively. The drags under different navigation conditions (inflow velocities of 1, 2, 3, and 4 m / s) are reduced by 1.617 N, 6.344 N, 14.268 N, and 25.41 N respectively.

[0136] By comparing the performance of the fairing and the long-cylindrical appendage, although the wetted surface area of the fairing is about 3 times that of the long-cylindrical appendage, its drag coefficient is reduced by 5.27 times, 6 times, 6.48 times, and 6.76 times respectively at different inflow velocities, indicating that the fairing has a good drag reduction effect.

[0137] From the data, it can be seen that the drag of the underwater vehicle with a long-cylindrical appendage mainly comes from the pressure drag, accounting for more than 90% of the total drag of the appendage; while for the underwater vehicle equipped with a fairing, the pressure drag only accounts for about two-thirds. The viscous drag of the fairing increases slightly, mainly because its wetted surface area is slightly larger than that of the long-cylindrical appendage. However, the fairing significantly reduces the pressure drag by optimizing fluid flow, reducing fluid separation, and reducing local negative pressure, thereby reducing the total drag as a whole. Based on these results, the design scheme of using a fairing to replace the long-cylindrical appendage is reasonable and effective.

[0138] The above description is only the preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A design method for a drag reduction and flow guiding structure of a long cylindrical appendage of an underwater vehicle, characterized in that, It includes the following steps: Step 1: Establish a fluid calculation domain and construct an underwater vehicle model in the fluid calculation domain; Step 2: Set boundary conditions and calculation conditions in the fluid calculation domain and configure the CFD numerical solution method; Step 3: Solve the straight-line resistance suffered by the bare hull of the underwater vehicle under the calculation conditions; Step 4: Configure a long cylindrical appendage on the underwater vehicle and solve the straight-line resistance suffered by the whole underwater vehicle equipped with the long cylindrical appendage under the calculation conditions and the straight-line resistance suffered by the long cylindrical appendage itself under the calculation conditions; Step 5: Configure a fairing on the underwater vehicle, and the fairing wraps the long cylindrical appendage; Use a parameterization method to express the bus line type of the fairing, and according to the design constraints of the fairing, use a multi-objective optimization algorithm to obtain the bus line type of the fairing with the best drag reduction and flow guiding effect; Step 6: Change the calculation conditions and repeat steps 2 to 6 to obtain a set of bus line types of the fairing with the best drag reduction and flow guiding effect corresponding to different calculation conditions, and complete the design of the drag reduction and flow guiding structure of the long cylindrical appendage of the underwater vehicle.

2. A design method for a drag reduction and flow guiding structure of a long cylindrical appendage of an underwater vehicle, characterized in that: In step 5, the inner diameter of the fairing is slightly larger than the outer diameter of the long cylindrical appendage, the gap between the fairing and the long cylindrical appendage does not exceed the threshold, the axial range of the fairing does not exceed the middle section of the bare hull of the underwater vehicle, and the radial length of the fairing is the same as that of the long cylindrical appendage; The fairing is designed with axial symmetry and has a smooth transition in shape.

3. A method for designing a drag reduction and flow guiding structure for a long cylindrical appendage of an underwater vehicle according to claim 2, characterized in that: In step 5, the parameterization method is used to express the bus line type of the fairing, specifically: Among them, the parameter ω i is the control point weight factor, corresponding to n + 1 control vertices P i respectively; B i,k (u) is calculated by the recurrence formula: where v i is the i-th element in the node vector V, and the node vector V is: Give the coordinates of the control points P i (x, y, z), specify the curve power, give the weights of each control point, and generate the fairing bus line through the mathematical expression of the NURBS curve.

4. A design method for a drag reduction and flow guiding structure of a long cylindrical appendage of an underwater vehicle according to claim 3, characterized in that: According to the straight-line resistance R1 suffered by the bare hull under the calculation conditions obtained in step 3, the straight-line resistance R2 suffered by the whole underwater vehicle equipped with the long cylindrical appendage under the calculation conditions obtained in step 4, and the straight-line resistance R3 suffered by the long cylindrical appendage itself under the calculation conditions, calculate the appendage resistance coefficient C of the long cylindrical appendage as: Where ρ is the density of the fluid in the calculation domain, S is the wetted surface area of the long cylindrical appendage, and V is the oncoming flow velocity in the calculation conditions; The percentage increase Δ in the straight-line resistance suffered by the underwater vehicle after configuring the long cylindrical appendage is: In step 5, after configuring the fairing on the underwater vehicle, calculate the appendage resistance coefficient of the fairing and the percentage increase in the straight-line resistance suffered by the underwater vehicle after configuring the fairing. With the minimum appendage resistance coefficient and the lowest percentage increase in the straight-line resistance as the goals, use a multi-objective optimization algorithm to obtain the bus line type of the fairing with the best drag reduction and flow guiding effect.

5. A computer device / equipment / system, comprising a memory, a processor, and a computer program stored on the memory, characterized in that: The processor executes the computer program to implement the steps of the method described in any one of claims 1 to 4.

6. A computer-readable storage medium having computer programs / instructions stored thereon, characterized in that: When the computer program / instructions are executed by the processor, the steps of the method described in any one of claims 1 to 4 are implemented.

7. A computer program product, comprising a computer program / instructions, characterized in that: When the computer program / instructions are executed by the processor, the steps of the method described in any one of claims 1 to 4 are implemented.

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