Method and device for obtaining viscous-pressure resistance of ocean vehicles based on equivalent ellipsoid assumption

Abstract

This application belongs to the field of ship viscous drag assessment and specifically discloses a method for obtaining the viscous-pressure drag of an ocean vehicle based on the equivalent ellipsoid hypothesis. The method comprises: establishing a geometric model of the ocean vehicle and gridding the geometric model to determine the geometric coordinates of the centroid, the area of the cell mesh, and the outer normal vector of the cell; dividing the flow separation zone of the geometric model according to the velocity vector of the distant unit incoming flow and the outer normal vector of the cell; calculating the projected perimeter, projected area, and shape factor of the flow separation zone, constructing an equivalent ellipsoid of the ocean vehicle, and determining the geometric dimensions of the equivalent ellipsoid; determining the characteristic length of the ocean vehicle based on the geometric dimensions, calculating the Reynolds number of the ocean vehicle, and obtaining the viscous-pressure drag coefficient of the equivalent ellipsoid by interpolation; and obtaining the viscous-pressure drag of the ocean vehicle based on the viscous-pressure drag coefficient, fluid density, incoming flow velocity, and wet projected area. This application can improve the accuracy and efficiency of viscous-pressure drag acquisition.

Description

Technical Field

[0001] The present application belongs to the technical field of ship viscous resistance evaluation, and more specifically, relates to a method and device for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid assumption. Background Art

[0002] The flow resistance (the force acting parallel to the incoming flow direction) experienced by ocean vehicles can be divided into viscous resistance and wave-making resistance, which is basically unrelated to viscosity, according to the properties of the fluid. The viscous resistance can be further divided into frictional resistance (shear stress) and viscous-pressure resistance (also known as shape resistance, pressure difference resistance, and compressive stress). Currently, potential flow theory and its boundary element method can quickly and accurately predict the wave-making resistance of structures such as ships and offshore wind turbines. The ship boundary layer theory combined with the equivalent flat plate assumption can quickly and accurately predict frictional resistance. However, due to the complexity of viscous-pressure resistance, there is currently no fast and accurate method to solve viscous-pressure resistance alone, except for the two universal but high-cost methods of ship model testing and numerical solution of viscous fluid mechanics equations.

[0003] Current state-of-the-art methods still suffer from issues such as large network training requirements, weak generalization capabilities, high costs, and insufficient precision, resulting in poor accuracy and efficiency in obtaining viscous and pressure resistance. Therefore, improving the accuracy and efficiency of obtaining viscous and pressure resistance is a pressing technical issue that needs to be addressed. Summary of the Invention

[0004] In view of the defects of the prior art, the purpose of this application is to provide a method and device for obtaining the viscous-pressure resistance of ocean vehicles based on the equivalent ellipsoid assumption, aiming to solve the problems of poor accuracy and efficiency of the viscous-pressure resistance.

[0005] To achieve the above objectives, the present application provides a method for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid assumption, comprising:

[0006] Establishing a geometric model of the ocean vehicle, and meshing the geometric model to determine the centroid geometric coordinates, the area of the panel, and the outward normal vector of the panel;

[0007] Dividing the flow separation area of the geometric model according to the velocity vector of the distant unit flow and the normal vector outside the surface element;

[0008] Calculating a projected perimeter, a projected area, and a shape factor based on the flow separation zone, constructing an equivalent ellipsoid of the ocean vehicle, and determining geometric dimensions of the equivalent ellipsoid;

[0009] Determine the characteristic length of the ocean vehicle according to the geometric dimensions, calculate the Reynolds number of the ocean vehicle according to the characteristic length of the ocean vehicle, the velocity vector, and the kinematic viscosity of seawater, and obtain the viscous-pressure drag coefficient of the equivalent ellipsoid by interpolation;

[0010] The viscous-pressure resistance of the ocean vehicle is obtained according to the viscous-pressure resistance coefficient, fluid density, incoming flow velocity and wet projected area; the wet projected area is the underwater area of the flow separation zone.

[0011] Optionally, the flow separation zone is an outer surface area of the ocean vehicle that meets the separation conditions;

[0012] The division conditions include:

[0013] Determine the velocity vector of the distant unit flow, and calculate the cosine value of the angle between the velocity vector and the outer normal vector of the object surface unit;

[0014] If the cosine value of the angle is greater than 0, the current surface position of the ocean vehicle belongs to the flow separation area; if the cosine value of the angle is less than or equal to 0, the current surface position of the ocean vehicle does not belong to the flow separation area.

[0015] Optionally, calculating the projected perimeter, projected area, and shape factor according to the flow separation region includes:

[0016] Obtain the projected perimeter, projected area, and shape factor of the flow separation zone;

[0017] Determining that the occurrence area, impact area, and occurrence intensity of the flow separation zone are in a comparable relationship between the ocean vehicle and the comparable ellipsoid;

[0018] According to the equivalence of the occurrence area, the impact area and the occurrence intensity, the projection perimeter, the projection area and the shape factor of the equivalent ellipsoid are determined in combination with the principle of equal parameters to construct the equivalent ellipsoid of the ocean vehicle.

[0019] Optionally, it also includes:

[0020] Determining the shape of the equivalent ellipsoid according to the projected perimeter and projected area of the equivalent ellipsoid;

[0021] The judgment formula is as follows:

[0022] like Then the equivalent ellipsoid is an ellipsoid;

[0023] like Then the equivalent ellipsoid is an ellipsoid;

[0024] Where C is the projected perimeter and A is the projected area.

[0025] Optionally, when the equivalent ellipsoid is an ellipsoid, the method for obtaining the geometric dimensions of the equivalent ellipsoid includes:

[0026] Determining that the equivalent ellipsoid is a rotation ellipsoid, determining the circumferential radius of the rotation ellipsoid perpendicular to the flow direction according to the projected area, and calculating the semi-axis length of the rotation ellipsoid parallel to the flow direction according to the principle of equal shape factors;

[0027] When the equivalent ellipsoid is an ellipsoid, the method for obtaining the geometric dimensions of the equivalent ellipsoid includes:

[0028] The height of the ellipse with the axis perpendicular to the flow direction on the ellipse section is calculated according to the projected area and the projected perimeter, and the semi-axis length parallel to the flow direction on the ellipse section is calculated according to the principle of equal shape factors.

[0029] Optionally, the method for obtaining the shape factor includes:

[0030] Obtaining a dot product of the normal vector outside the surface element and the velocity vector of the distant unit flow, and integrating all the surface elements in the flow separation area to obtain the total surface element area;

[0031] A weighted average of all bins is obtained according to the dot product result and the total area of the bins to obtain the shape factor.

[0032] Optionally, it also includes:

[0033] Querying a constructed viscous-pressure resistance coefficient database to obtain the viscous-pressure resistance coefficient;

[0034] The geometric dimensions are normalized, and the normalized geometric dimensions are stored in the viscosity-pressure drag coefficient database, so as to search for relevant parameters of the equivalent ellipsoid from the viscosity-pressure drag coefficient database.

[0035] In a second aspect, the present application further provides a device for obtaining viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid hypothesis, comprising:

[0036] A model building module is used to build a geometric model of the ocean vehicle, grid the geometric model, and determine the centroid geometric coordinates, bin area, and bin external normal vector of the bin mesh;

[0037] A separation zone division module is used to divide the flow separation zone of the geometric model according to the velocity vector of the distant unit flow and the normal vector outside the surface element;

[0038] a size determination module, configured to calculate a projected perimeter, a projected area, and a shape factor based on the flow separation zone, construct an equivalent ellipsoid of the ocean vehicle, and determine geometric dimensions of the equivalent ellipsoid;

[0039] a coefficient acquisition module, configured to determine the characteristic length of the ocean vehicle according to the geometric dimensions, calculate the Reynolds number of the ocean vehicle according to the characteristic length of the ocean vehicle, the velocity vector, and the kinematic viscosity of seawater, and obtain the viscous-pressure drag coefficient of the equivalent ellipsoid by interpolation;

[0040] The viscous-pressure resistance acquisition module is used to obtain the viscous-pressure resistance of the ocean vehicle based on the viscous-pressure resistance coefficient, fluid density, incoming flow velocity and wet projected area; the wet projected area is the underwater area of the flow separation zone.

[0041] In a third aspect, the present application provides an electronic device comprising: at least one memory for storing programs; and at least one processor for executing the programs stored in the memory. When the program stored in the memory is executed, the processor is used to execute the method described in the first aspect or any possible implementation of the first aspect.

[0042] In a fourth aspect, the present application provides a computer-readable storage medium, which stores a computer program. When the computer program runs on a processor, the processor executes the method described in the first aspect or any possible implementation of the first aspect.

[0043] In a fifth aspect, the present application provides a computer program product, which, when executed on a processor, enables the processor to execute the method described in the first aspect or any possible implementation of the first aspect.

[0044] It can be understood that the beneficial effects of the second to fifth aspects mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here.

[0045] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the existing technologies:

[0046] (1) This application uses a gridded geometric model and divides the flow separation zone, and proposes to construct an equivalent ellipsoid based on the principle of three equal parameters in the flow separation zone. The three parameters are the projected perimeter, the projected area, and the shape factor, which physically correspond to the equivalent flow separation occurrence area, the equivalent flow separation influence area, and the equivalent flow separation influence intensity. By accurately calculating the projected perimeter and projected area of the flow separation zone, the accuracy of the calculation of the flow resistance can be further improved. Under the shape factor, a better approximation of the shape and flow characteristics can be constructed. In ocean vehicles of different shapes, the shape factor can be used to systematically adjust and optimize the model to ensure the accuracy of prediction under different speed and fluid conditions.

[0047] (2) This application proposes that the equivalent ellipsoid formed based on this principle has a viscous-pressure resistance similar to that of the original object. The equivalent ellipsoids are all simple standard objects such as cylinders, spheres, and ellipses, and their viscous-pressure resistance coefficients are either easy to find or easy to calculate. Therefore, for the viscous-pressure resistance that is difficult to solve in ship resistance, this application quantifies the mathematical description of the shape (the main factor causing the viscous-pressure resistance) and builds a "bridge" between it and the resistance conversion of simple objects, thereby reducing the complexity of solving the viscous-pressure resistance and improving the efficiency of solving the viscous-pressure resistance.

[0048] (3) This application improves the rapid evaluation method of ship resistance, and together with the existing equivalent plate method for calculating friction resistance, it constitutes an evaluation method for ship viscous resistance, which improves the calculation accuracy of viscous pressure resistance while maintaining the same solution time. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is one of the flow charts of the method for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid assumption provided in an embodiment of the present application;

[0050] Figure 2 This is the second flow chart of the method for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid assumption provided in an embodiment of the present application;

[0051] Figure 3 This is the third flow chart of the method for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid assumption provided in an embodiment of the present application;

[0052] Figure 4 This is the fourth flow chart of the method for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid assumption provided in an embodiment of the present application;

[0053] Figure 5 Schematic diagram of the structure of a device for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid hypothesis provided in an embodiment of the present application;

[0054] Figure 6 It is a structural diagram of an electronic device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0056] The term "and / or" as used herein describes an association between related objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. The symbol " / " as used herein indicates that the related objects are in an "or" relationship, for example, A / B means either A or B.

[0057] The terms "first" and "second" in this specification and claims are used to distinguish different objects rather than to describe a specific order of objects. For example, "first response message" and "second response message" are used to distinguish different response messages rather than to describe a specific order of response messages.

[0058] In the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0059] In the description of the embodiments of the present application, unless otherwise specified, "multiple" means two or more, for example, multiple processing units means two or more processing units, etc.; multiple elements means two or more elements, etc.

[0060] Next, the technical solutions provided in the embodiments of this application are introduced.

[0061] Reference Figure 1 The present application provides a method for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid assumption, comprising:

[0062] S101. Establish a geometric model of the ocean navigation body, and mesh the geometric model to determine the centroid geometric coordinates, the area of the panel, and the normal vector outside the panel;

[0063] S102. Divide the flow separation area of the geometric model according to the velocity vector of the distant unit flow and the normal vector outside the surface element;

[0064] S103. Calculate the projected perimeter, projected area, and shape factor of the flow separation zone, construct an equivalent ellipsoid of the ocean vehicle, and determine the geometric dimensions of the equivalent ellipsoid;

[0065] S104. Determine the characteristic length of the ocean vehicle based on the geometric dimensions, calculate the Reynolds number of the ocean vehicle based on the characteristic length, velocity vector, and kinematic viscosity of the seawater, and obtain the viscous-pressure drag coefficient of the equivalent ellipsoid by interpolation;

[0066] S105. Obtain the viscous-pressure resistance of the ocean vehicle based on the viscous-pressure resistance coefficient, fluid density, incoming flow velocity, and wet projected area; the wet projected area is the underwater area of the flow separation zone.

[0067] First, a geometric model of the ocean vehicle is constructed through S101. The geometric model of the ocean vehicle can be created by using modeling software such as SolidWorks, AutoCAD or Rhino, and then the geometric model is meshed using a mesh generation tool.

[0068] Determine the geometric parameters of the surface element grid, including but not limited to: calculating the geometric center coordinates of each surface element; calculating the area dS of each surface element; for each surface element, calculating its unit external normal vector n, which points to the outside of the fluid flow direction.

[0069] Next, in step S102, the flow separation zone is delineated based on the velocity vector of the distant unit flow and the bin's outer normal vector. The unit flow velocity vector v is determined. Its direction is typically the vehicle's forward direction, and its magnitude is set based on the design speed. For each bin, the calculated unit flow velocity vector v is dot-producted with the bin's outer normal vector n to obtain the cosine of the angle between the velocity vector v and the object surface unit's outer normal vector n.

[0070] Furthermore, the flow separation zone is an outer surface area of the ocean vehicle that meets the separation conditions;

[0071] The division conditions include:

[0072] Determine the velocity vector of the distant unit flow, and calculate the cosine value of the angle between the velocity vector and the outer normal vector of the object surface unit;

[0073] If the cosine value of the angle is greater than 0, the current surface position of the ocean vehicle belongs to the flow separation area; if the cosine value of the angle is less than or equal to 0, the current surface position of the ocean vehicle does not belong to the flow separation area.

[0074] The flow separation area refers to the outer surface area of the ocean vehicle that meets the following conditions, that is, the cosine value of the angle between the distant unit incoming flow velocity vector v and the outer normal vector n of the object surface unit is cosine:<v,n> The area is greater than zero. When cos<v,n> If it is greater than 0, the surface of the ocean vehicle belongs to the flow separation area, otherwise it does not belong to the flow separation area.

[0075] Reference Figure 2 , the flow separation zone of the embodiment of the present application should be the underwater wet surface part.

[0076] Through S103 above, the projected perimeter, projected area, and shape factor of the equivalent ellipsoid are calculated. This calculation is based on the principles of equivalent occurrence areas, equivalent impact areas, equivalent occurrence intensities, and equal parameters. The projected perimeter, projected area, and shape factor of the equivalent ellipsoid are obtained, denoted as C, A, and δ, respectively. Based on C, A, and δ, the equivalent ellipsoid is constructed, and its geometric dimensions, including the major axis a and minor axis b, are obtained to ensure that its shape characteristics conform to the geometric characteristics of the flow separation zone.

[0077] The Reynolds number and the viscous-pressure drag coefficient of the ocean vehicle are further calculated by the above S104. First, a characteristic length d is selected from the constructed equivalent ellipsoid, usually the short axis or a more representative length is selected, and the characteristic length is determined based on the major axis and the minor axis.

[0078] Then calculate the motion Reynolds number according to the following formula:

[0079]

[0080] Where v is the velocity vector of the distant oncoming flow, d is the characteristic length of the ocean vehicle, and nu is the kinematic viscosity of seawater.

[0081] The viscous-pressure drag coefficient and Reynolds number in the collected database are interpolated to obtain the viscous-pressure drag coefficient at a specific Reynolds number.

[0082] Finally, the viscous pressure resistance is calculated in step S105. It should be noted that the wet projected area generally refers to the underwater area of the flow separation zone, which can be obtained by extracting the portion intersecting the water surface from the flow separation zone.

[0083] The formula for obtaining the viscous pressure resistance is as follows:

[0084] F=0.5ρv 2 A.C. pv

[0085] Where F is the viscous pressure resistance, ρ is the fluid density (i.e., seawater density), v is the velocity vector of the distant flow, A is the wetted projected area of the flow separation zone, and C is the average flow velocity. pv is the viscous pressure resistance coefficient.

[0086] This application uses a gridded geometric model and divides the flow separation zone, and proposes to construct an equivalent ellipsoid based on the principle of three equal parameters in the flow separation zone. The three parameters are the projected perimeter, the projected area, and the shape factor, which physically correspond to the equivalent flow separation occurrence area, the equivalent flow separation influence area, and the equivalent flow separation influence intensity. By accurately calculating the projected perimeter and projected area of the flow separation zone, the accuracy of the calculation of the flow resistance can be further improved. Under the shape factor, a better approximation of the shape and flow characteristics can be constructed. In ocean vehicles of different shapes, the shape factor can be used to systematically adjust and optimize the model to ensure the accuracy of predictions under different speed and fluid conditions.

[0087] Optionally, calculating the projected perimeter, projected area, and shape factor according to the flow separation region includes:

[0088] Obtain the projected perimeter, projected area, and shape factor of the flow separation zone;

[0089] Determining that the occurrence area, impact area, and occurrence intensity of the flow separation zone are in a comparable relationship between the ocean vehicle and the comparable ellipsoid;

[0090] According to the equivalence of the occurrence area, the impact area and the occurrence intensity, the projection perimeter, the projection area and the shape factor of the equivalent ellipsoid are determined in combination with the principle of equal parameters to construct the equivalent ellipsoid of the ocean vehicle.

[0091] Specifically, refer to Figure 3 Calculate the projected perimeter, projected area, and shape factor of the flow separation zone. The projected perimeter is obtained by accumulating edge boundary segments based on the flow separation zone's occurrence area. The underwater projected area is obtained based on the area of all facets in the flow separation zone's impact region. The shape factor is calculated based on the flow separation zone's occurrence intensity.

[0092] Furthermore, based on the projection characteristics, the projection perimeter, projection area and shape factor of the flow separation region are matched with the corresponding parameters of the equivalent ellipsoid using the equality relation:

[0093] C equivalent ellipsoid = C flow separation zone;

[0094] A is equivalent to an ellipsoid = A flow separation area;

[0095] δ equivalent ellipsoid = δ flow separation zone;

[0096] Based on the perimeter and area of the flow separation zone, these parameters of the equivalent ellipsoid are calculated by the similarity principle. According to the determination of the projected perimeter C and the projected area A, the final geometric dimensions of the equivalent ellipsoid (such as the major axis a and the minor axis b) can be defined by the shape parameters.

[0097] The embodiments of the present application can obtain corresponding geometric features through detailed analysis and quantification of the flow separation zone, ensuring that when the equivalent ellipsoid assumption is applied, the performance of the ocean vehicle in the fluid can be more realistically reflected.

[0098] Optionally, it also includes:

[0099] Determining the shape of the equivalent ellipsoid according to the projected perimeter and projected area of the equivalent ellipsoid;

[0100] The judgment formula is as follows:

[0101] like Then the equivalent ellipsoid is an ellipsoid;

[0102] like Then the equivalent ellipsoid is an ellipsoid;

[0103] Where C is the projected perimeter and A is the projected area.

[0104] Optionally, when the equivalent ellipsoid is an ellipsoid, the method for obtaining the geometric dimensions of the equivalent ellipsoid includes:

[0105] Determining that the equivalent ellipsoid is a rotation ellipsoid, determining the circumferential radius of the rotation ellipsoid perpendicular to the flow direction according to the projected area, and calculating the semi-axis length of the rotation ellipsoid parallel to the flow direction according to the principle of equal shape factors;

[0106] When the equivalent ellipsoid is an ellipsoid, the method for obtaining the geometric dimensions of the equivalent ellipsoid includes:

[0107] The height of the ellipse with the axis perpendicular to the flow direction on the ellipse section is calculated according to the projected area and the projected perimeter, and the semi-axis length parallel to the flow direction on the ellipse section is calculated according to the principle of equal shape factors.

[0108] Specifically, the steps of calculating the geometric dimensions of the equivalent ellipsoid are as follows: for the ellipsoid, it is a rotating ellipsoid, and the radius of its axis perpendicular to the flow direction is The length of its semi-axis parallel to the flow direction is calculated according to the principle of equal shape factors; for an elliptical column, the length of the axis perpendicular to the flow direction on its elliptical section is The height (i.e., the extension) of the ellipse is The length of the semi-axis parallel to the flow direction on its elliptical cross section is calculated according to the principle of equal shape factors.

[0109] The semi-axis length parallel to the flow direction is calculated according to the principle of equal shape factors by iterative solution. Specifically, the shape factor of the equivalent ellipsoid is an implicit function of the semi-axis length perpendicular to the flow direction and the semi-axis length parallel to the flow direction:

[0110] δ=f(b,a)

[0111] Where a is the semi-axis length parallel to the flow direction, and b is the semi-axis length perpendicular to the flow direction.

[0112] When the axis length perpendicular to the flow direction and the shape factor of the flow separation zone are known, the shape factor of the equivalent ellipsoid is set equal to the shape factor of the flow separation zone. The semi-axis length parallel to the flow direction can be iteratively solved according to the bisection method, and then all the geometric parameters of the equivalent ellipsoid are obtained.

[0113] Optionally, the method for obtaining the shape factor includes:

[0114] Obtaining a dot product of the normal vector outside the surface element and the velocity vector of the distant unit flow, and integrating all the surface elements in the flow separation area to obtain the total area of the surface element;

[0115] A weighted average of all bins is obtained according to the dot product result and the total area of the bins to obtain the shape factor.

[0116] Specifically, the formula for the shape factor is as follows:

[0117]

[0118] For the ellipsoid, the specific calculation formula is:

[0119]

[0120] Among them, x, y, z are the coordinates of the centroid of the face element grid, e1, e2, e3 are the unit vectors in the x, y, z directions of the coordinate system respectively, a is the length of the semi-axis parallel to the flow direction, b and c are the lengths of the semi-axis perpendicular to the flow direction. It should be noted that since the equivalent ellipsoid is a rotating ellipsoid, b = c.

[0121] Optionally, it also includes:

[0122] Querying a constructed viscous-pressure resistance coefficient database to obtain the viscous-pressure resistance coefficient;

[0123] The geometric dimensions are normalized, and the normalized geometric dimensions are stored in the viscosity-pressure drag coefficient database, so as to search for relevant parameters of the equivalent ellipsoid from the viscosity-pressure drag coefficient database.

[0124] This embodiment of the application queries and references a database of viscous-pressure drag coefficients to obtain the viscous-pressure drag coefficients under specific geometric conditions and normalizes the relevant geometric dimensions to facilitate subsequent data management and rapid search. Normalized parameters will help unify the data format within the database and improve search efficiency, providing immediate and reliable data support for ocean vehicle design and fluid dynamics research.

[0125] Reference Figure 4 , Figure 4 : is a flow chart of a method for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid assumption provided in an embodiment of the present application, comprising the following steps:

[0126] Establish the geometric model of ocean navigation body;

[0127] Meshing of ocean navigation body geometric models: obtaining geometric parameters such as centroid coordinates, surface element area, and surface element external normal vectors;

[0128] The flow separation zone is divided into two parts: the cosine value of the angle between the velocity direction of the far front flow and the outer normal vector of the object surface unit is greater than zero;

[0129] Calculate the projected perimeter: the area where flow separation occurs is equivalent;

[0130] Calculation of projected area: The area affected by flow separation is equivalent;

[0131] Calculation of shape factor: Flow separation occurs with comparable intensity;

[0132] The calculation results are used to form an equivalent ellipsoid;

[0133] Calculate geometric dimensions;

[0134] Normalization of geometric dimensions and calculation of geometric dimensions;

[0135] Let the thickness semi-axis length be equal to 1 to facilitate the search for the equivalent ellipsoid;

[0136] Calculate the Reynolds number based on geometric dimensions and flow characteristics;

[0137] Calculate the piezoresistive coefficient based on the Reynolds number;

[0138] Finally, the viscous-pressure resistance is calculated according to the formula.

[0139] F=0.5ρv 2 A.C. pv

[0140] Where F is the viscous pressure resistance, ρ is the fluid density (i.e., seawater density), v is the velocity vector of the distant flow, A is the wetted projected area of the flow separation zone, and C is the average flow velocity. pv is the viscous pressure resistance coefficient.

[0141] Reference Figure 5 The present application also provides a device for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid hypothesis, comprising:

[0142] The model building module 510 is used to build a geometric model of the ocean vehicle, grid the geometric model, and determine the centroid geometric coordinates, bin area, and bin external normal vector of the bin mesh;

[0143] A separation zone division module 520 is configured to divide the flow separation zone of the geometric model according to the velocity vector of the remote unit flow and the normal vector outside the panel element;

[0144] a size determination module 530 for calculating a projected perimeter, a projected area, and a shape factor based on the flow separation zone, constructing an equivalent ellipsoid of the ocean vehicle, and determining geometric dimensions of the equivalent ellipsoid;

[0145] a coefficient acquisition module 540 for determining the characteristic length of the ocean vehicle based on the geometric dimensions, calculating the Reynolds number of the ocean vehicle based on the characteristic length of the ocean vehicle, the velocity vector, and the kinematic viscosity of the seawater, and obtaining the viscous-pressure drag coefficient of the equivalent ellipsoid by interpolation;

[0146] The viscous-pressure drag acquisition module 550 is used to obtain the viscous-pressure drag of the ocean vehicle based on the viscous-pressure drag coefficient, fluid density, incoming flow velocity and wet projected area; the wet projected area is the underwater area of the flow separation zone.

[0147] Optionally, the flow separation zone is an outer surface area of the ocean vehicle that meets the separation conditions;

[0148] The division conditions include:

[0149] Determine the velocity vector of the distant unit flow, and calculate the cosine value of the angle between the velocity vector and the outer normal vector of the object surface unit;

[0150] If the cosine value of the angle is greater than 0, the current surface position of the ocean vehicle belongs to the flow separation area; if the cosine value of the angle is less than or equal to 0, the current surface position of the ocean vehicle does not belong to the flow separation area.

[0151] Optionally, calculating the projected perimeter, projected area, and shape factor according to the flow separation region includes:

[0152] Obtain the projected perimeter, projected area, and shape factor of the flow separation zone;

[0153] Determining that the occurrence area, impact area, and occurrence intensity of the flow separation zone are in a comparable relationship between the ocean vehicle and the comparable ellipsoid;

[0154] According to the equivalence of the occurrence area, the impact area and the occurrence intensity, the projection perimeter, the projection area and the shape factor of the equivalent ellipsoid are determined in combination with the principle of equal parameters to construct the equivalent ellipsoid of the ocean vehicle.

[0155] Optionally, it also includes:

[0156] Determining the shape of the equivalent ellipsoid according to the projected perimeter and projected area of the equivalent ellipsoid;

[0157] The judgment formula is as follows:

[0158] like Then the equivalent ellipsoid is an ellipsoid;

[0159] like Then the equivalent ellipsoid is an ellipsoid;

[0160] Where C is the projected perimeter and A is the projected area.

[0161] Optionally, when the equivalent ellipsoid is an ellipsoid, the method for obtaining the geometric dimensions of the equivalent ellipsoid includes:

[0162] Determining that the equivalent ellipsoid is a rotation ellipsoid, determining the circumferential radius of the rotation ellipsoid perpendicular to the flow direction according to the projected area, and calculating the semi-axis length of the rotation ellipsoid parallel to the flow direction according to the principle of equal shape factors;

[0163] When the equivalent ellipsoid is an ellipsoid, the method for obtaining the geometric dimensions of the equivalent ellipsoid includes:

[0164] The height of the ellipse with the axis perpendicular to the flow direction on the ellipse section is calculated according to the projected area and the projected perimeter, and the semi-axis length parallel to the flow direction on the ellipse section is calculated according to the principle of equal shape factors.

[0165] Optionally, the method for obtaining the shape factor includes:

[0166] Obtaining a dot product of the normal vector outside the surface element and the velocity vector of the distant unit flow, and integrating all the surface elements in the flow separation area to obtain the total surface element area;

[0167] A weighted average of all bins is obtained according to the dot product result and the total area of the bins to obtain the shape factor.

[0168] Optionally, a database query module is further included, and the database query module is used to:

[0169] Querying a constructed viscous-pressure resistance coefficient database to obtain the viscous-pressure resistance coefficient;

[0170] The geometric dimensions are normalized, and the normalized geometric dimensions are stored in the viscosity-pressure drag coefficient database, so as to search for relevant parameters of the equivalent ellipsoid from the viscosity-pressure drag coefficient database.

[0171] It is understandable that the detailed functional implementation of each of the above units / modules can be found in the introduction of the aforementioned method embodiment, and will not be repeated here.

[0172] It should be understood that the above-mentioned device is used to execute the method in the above-mentioned embodiment. The implementation principle and technical effect of the corresponding program module in the device are similar to those described in the above-mentioned method. The working process of the device can refer to the corresponding process in the above-mentioned method and will not be repeated here.

[0173] Reference Figure 6 Based on the method in the above embodiment, an embodiment of the present application provides an electronic device, which may include: a processor (processor) 610, a communication interface (Communications Interface) 620, a memory (memory) 630 and a communication bus 640, wherein the processor 610, the communication interface 620, and the memory 630 communicate with each other via the communication bus 640. The processor 610 can call the logic instructions in the memory 630 to execute the method in the above embodiment.

[0174] In addition, the logic instructions in the above-mentioned memory 630 can be implemented in the form of a software functional unit and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application.

[0175] Based on the method in the above embodiment, an embodiment of the present application provides a computer-readable storage medium, which stores a computer program. When the computer program runs on a processor, the processor executes the method in the above embodiment.

[0176] Based on the method in the above embodiment, an embodiment of the present application provides a computer program product. When the computer program product runs on a processor, the processor executes the method in the above embodiment.

[0177] It is understood that the processor in the embodiments of the present application may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field programmable gate arrays (FPGA), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. The general-purpose processor may be a microprocessor or any conventional processor.

[0178] The method steps in the embodiments of the present application can be implemented by hardware or by a processor executing software instructions. The software instructions can be composed of corresponding software modules, which can be stored in random access memory (RAM), flash memory, read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disks, mobile hard disks, CD-ROMs or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor so that the processor can read information from the storage medium and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and the storage medium can be located in an ASIC.

[0179] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted via the computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server or data center to another website, computer, server or data center via a wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) method. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated. The available medium can be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid state drive (SSD)).

[0180] It will be understood that the various numerical numbers involved in the embodiments of the present application are merely distinctions for the convenience of description and are not intended to limit the scope of the embodiments of the present application.

[0181] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid assumption, characterized in that: include: Establishing a geometric model of the ocean vehicle, and meshing the geometric model to determine the centroid geometric coordinates, the area of the panel, and the outward normal vector of the panel; Dividing the flow separation area of the geometric model according to the velocity vector of the distant unit flow and the normal vector outside the surface element; Calculating a projected perimeter, a projected area, and a shape factor based on the flow separation zone, constructing an equivalent ellipsoid of the ocean vehicle, and determining geometric dimensions of the equivalent ellipsoid; Determine the characteristic length of the ocean vehicle according to the geometric dimensions, calculate the Reynolds number of the ocean vehicle according to the characteristic length of the ocean vehicle, the velocity vector, and the kinematic viscosity of seawater, and obtain the viscous-pressure drag coefficient of the equivalent ellipsoid by interpolation; The viscous-pressure resistance of the ocean vehicle is obtained according to the viscous-pressure resistance coefficient, fluid density, incoming flow velocity and wet projected area; the wet projected area is the underwater area of the flow separation zone.

2. The method for obtaining the viscous-pressure resistance of an ocean vehicle according to claim 1, characterized in that: The flow separation zone is the outer surface area of the ocean vehicle that meets the separation conditions; The division conditions include: Determine the velocity vector of the distant unit flow, and calculate the cosine value of the angle between the velocity vector and the outer normal vector of the object surface unit; If the cosine value of the angle is greater than 0, the current surface position of the ocean vehicle belongs to the flow separation area; if the cosine value of the angle is less than or equal to 0, the current surface position of the ocean vehicle does not belong to the flow separation area.

3. The method for obtaining the viscous-pressure resistance of an ocean vehicle according to claim 1, characterized in that: Calculating a projected perimeter, a projected area, and a shape factor based on the flow separation region includes: Obtain the projected perimeter, projected area, and shape factor of the flow separation region; Determining that the occurrence area, impact area, and occurrence intensity of the flow separation zone are in a comparable relationship between the ocean vehicle and the comparable ellipsoid; According to the equivalence of the occurrence area, the impact area and the occurrence intensity, the projection perimeter, the projection area and the shape factor of the equivalent ellipsoid are determined in combination with the principle of equal parameters to construct the equivalent ellipsoid of the ocean vehicle.

4. The method for obtaining the viscous-pressure resistance of an ocean vehicle according to claim 1, characterized in that: Also includes: Determining the shape of the equivalent ellipsoid according to the projected perimeter and projected area of the equivalent ellipsoid; The judgment formula is as follows: like Then the equivalent ellipsoid is an ellipsoid; like Then the equivalent ellipsoid is an ellipsoid; Where c is the projected perimeter and A is the projected area.

5. The method for obtaining the viscous-pressure resistance of an ocean vehicle according to claim 4, characterized in that: When the equivalent ellipsoid is an ellipsoid, the method for obtaining the geometric dimensions of the equivalent ellipsoid includes: Determining that the equivalent ellipsoid is a rotation ellipsoid, determining the circumferential radius of the rotation ellipsoid perpendicular to the flow direction according to the projected area, and calculating the semi-axis length of the rotation ellipsoid parallel to the flow direction according to the principle of equal shape factors; When the equivalent ellipsoid is an ellipsoid, the method for obtaining the geometric dimensions of the equivalent ellipsoid includes: The height of the ellipse with the axis perpendicular to the flow direction on the ellipse section is calculated according to the projected area and the projected perimeter, and the semi-axis length parallel to the flow direction on the ellipse section is calculated according to the principle of equal shape factors.

6. The method for obtaining the viscous-pressure resistance of an ocean vehicle according to claim 1, characterized in that: The method for obtaining the shape factor includes: Obtaining a dot product of the normal vector outside the surface element and the velocity vector of the distant unit flow, and integrating all the surface elements in the flow separation area to obtain the total area of the surface element; A weighted average of all bins is obtained according to the dot product result and the total area of the bins to obtain the shape factor.

7. The method for obtaining the viscous-pressure resistance of an ocean vehicle according to claim 1, characterized in that: Also includes: Querying a constructed viscous-pressure resistance coefficient database to obtain the viscous-pressure resistance coefficient; The geometric dimensions are normalized, and the normalized geometric dimensions are stored in the viscosity-pressure drag coefficient database, so as to search for relevant parameters of the equivalent ellipsoid from the viscosity-pressure drag coefficient database.

8. A device for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid hypothesis, characterized in that: include: A model building module is used to build a geometric model of the ocean vehicle, grid the geometric model, and determine the centroid geometric coordinates, bin area, and bin external normal vector of the bin mesh; A separation zone division module is used to divide the flow separation zone of the geometric model according to the velocity vector of the distant unit flow and the normal vector outside the surface element; a size determination module, configured to calculate a projected perimeter, a projected area, and a shape factor based on the flow separation zone, construct an equivalent ellipsoid of the ocean vehicle, and determine geometric dimensions of the equivalent ellipsoid; a coefficient acquisition module, configured to determine the characteristic length of the ocean vehicle according to the geometric dimensions, calculate the Reynolds number of the ocean vehicle according to the characteristic length of the ocean vehicle, the velocity vector, and the kinematic viscosity of seawater, and obtain the viscous-pressure drag coefficient of the equivalent ellipsoid by interpolation; The viscous-pressure resistance acquisition module is used to obtain the viscous-pressure resistance of the ocean vehicle based on the viscous-pressure resistance coefficient, fluid density, incoming flow velocity and wet projected area; the wet projected area is the underwater area of the flow separation zone.

9. An electronic device, characterized in that: include: at least one memory for storing a computer program; At least one processor is used to execute the program stored in the memory. When the program stored in the memory is executed, the processor is used to execute the method according to any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed on a processor, the processor is caused to execute the method according to any one of claims 1 to 7.

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