Method and device for acquiring viscous pressure resistance of marine vehicle based on considerable ellipsoid hypothesis

Abstract

The invention belongs to the field of ship viscous resistance evaluation, and particularly discloses a marine vehicle viscous pressure resistance acquisition method based on considerable ellipsoid hypothesis, which comprises the following steps: establishing a geometric model of a marine vehicle, gridding the geometric model, and determining centroid geometric coordinates, surface element area and surface element external normal vectors of a surface element grid; dividing a flow separation area of the geometric model according to a velocity vector of a remote unit incoming flow and a normal vector outside a surface element; calculating a projection perimeter, a projection area and a shape factor according to the flow separation area, constructing a considerable ellipsoid of the marine vehicle, and determining the geometric dimension of the considerable ellipsoid; the characteristic length of the marine vehicle is determined according to the geometric dimension, the Reynolds number of the marine vehicle is calculated, and the viscosity-pressure resistance coefficient of a considerable ellipsoid is obtained through an interpolation method; and acquiring the viscous pressure resistance of the marine vehicle according to the viscous pressure resistance coefficient, the fluid density, the incoming flow velocity and the wet projection area. According to the invention, the accuracy and efficiency of acquiring the viscous pressure resistance can be improved.

Description

Technical Field

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

[0002] The flow resistance (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 fluid properties. Among them, viscous resistance can be further divided into friction resistance (shear stress) and viscous-pressure resistance (also known as shape resistance, pressure difference resistance, and compressive stress). At present, 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, and ship boundary layer theory combined with the equivalent flat plate assumption can quickly and accurately predict friction 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] At present, the related existing technologies still have the problems of large network training volume, weak generalization ability, high cost and insufficient precision, which leads to poor accuracy and efficiency in obtaining the viscous-pressure resistance. Therefore, how to improve the accuracy and efficiency of obtaining the viscous-pressure resistance is a technical problem that needs to be solved urgently. Summary of the invention

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

[0005] To achieve the above purpose, 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 navigation body, and meshing the geometric model, determining the centroid geometric coordinates of the panel mesh, the panel area, and the panel external normal vector;

[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 the projected perimeter, projected area and shape factor according to the flow separation zone, constructing an equivalent ellipsoid of the ocean vehicle, and determining the geometric dimensions of the equivalent ellipsoid;

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

[0010] The viscous-pressure drag of the ocean vehicle is obtained according to 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.

[0011] Optionally, the flow separation zone is an outer surface area of ​​the ocean vehicle that satisfies the division 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, the projected area and the shape factor according to the flow separation zone includes:

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

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

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

[0019] Optionally, it also includes:

[0020] Determine 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] Among them, 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] Determine that the equivalent ellipsoid is a rotation ellipsoid, determine the circumference radius of the rotation ellipsoid perpendicular to the flow direction according to the projection area, and calculate 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 elliptical cylinder with an axis length perpendicular to the flow direction on the elliptical section is calculated according to the projected area and the projected perimeter, and the semi-axis length parallel to the flow direction on the elliptical section is calculated according to the principle of equal shape factors.

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

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

[0031] The shape factor is obtained by obtaining a weighted average value of all the facets according to the dot product result and the total area of ​​the facets.

[0032] Optionally, it also includes:

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

[0034] The geometric dimensions are normalized and 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 also provides a device for obtaining viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid assumption, comprising:

[0036] A model building module is used to build a geometric model of the ocean navigation body, and to grid the geometric model to determine the centroid geometric coordinates, the area of ​​the panel element, and the external normal vector of the panel element.

[0037] A separation zone division module, used for dividing 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, for calculating the projected perimeter, projected area and shape factor according to the flow separation zone, constructing an equivalent ellipsoid of the ocean vehicle, and determining the geometric size of the equivalent ellipsoid;

[0039] A coefficient acquisition module, used 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 method;

[0040] The viscous-pressure resistance acquisition module is used to obtain the viscous-pressure resistance of the ocean vehicle 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.

[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. When the computer program product runs on a processor, the processor executes 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 prior art:

[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 predictions under different speeds and fluid conditions.

[0047] (2) The present 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 obtain. Therefore, for the viscous-pressure resistance that is difficult to solve in ship resistance, the present application quantifies the mathematical description of the shape (the main factor causing the viscous-pressure resistance) and builds a "bridge" for its conversion with the resistance 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 the 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 the 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 the 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 the embodiment of the present application;

[0053] Figure 5 It is a structural schematic diagram of a device for obtaining the viscous-pressure resistance of an ocean vehicle based on the equivalent ellipsoid assumption provided in an embodiment of the present application;

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

[0055] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0056] The term "and / or" in this article is a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The symbol " / " in this article indicates that the associated objects are in an or relationship, for example, A / B means A or B.

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

[0058] In the embodiments of the present 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 the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

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

[0060] Next, the technical solutions provided in the embodiments of the present 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 element, and the normal vector outside the panel element;

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

[0066] S105. Obtain the viscous-pressure resistance of the ocean vehicle 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.

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

[0069] Secondly, through the above S102, the flow separation area is divided according to the velocity vector of the distant unit flow and the outer normal vector of the surface element. The unit flow velocity vector v is determined, and its direction is usually the direction of the aircraft's advance, and its magnitude is set according to the design speed. For each surface element, the calculated unit flow velocity vector v is multiplied by the outer normal vector n of the surface element to obtain the cosine value of the angle between the velocity vector v and the outer normal vector n of the object surface unit.

[0070] Furthermore, the flow separation zone is an outer surface area of ​​the ocean vehicle that satisfies the division 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 cos<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 zone, otherwise it does not belong to the flow separation zone.

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

[0076] Through the above S103, the projection perimeter, projection area and shape factor of the equivalent ellipsoid are calculated. The calculation basis is based on the principle of equivalent occurrence area, equivalent impact area, equivalent occurrence intensity and equal parameters, so as to obtain the projection perimeter, projection area and shape factor of the equivalent ellipsoid, which are recorded as C, A and δ respectively. The equivalent ellipsoid is constructed according to C, A and δ to obtain the geometric dimensions of the equivalent ellipsoid, including the major axis a and the minor axis b, to ensure that the shape characteristics meet 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 through 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 according to the major axis and the minor axis.

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

[0079]

[0080] Among them, 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] And 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 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 part intersecting with 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 velocity vector of the distant flow. 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 speeds and fluid conditions.

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

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

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

[0090] According to the equivalence of occurrence area, impact area and occurrence intensity, combined with the principle of equal parameters, the projection perimeter, projection area and shape factor of the equivalent ellipsoid are determined 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. According to the occurrence area of ​​the flow separation zone, the edge boundary line segments are accumulated to obtain the projected perimeter; according to the area of ​​all facets in the impact area of ​​the flow separation zone, the underwater projected area is obtained; and the shape factor is calculated according to the occurrence intensity of the flow separation zone.

[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 an equal relationship:

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

[0094] A equivalent ellipsoid = A flow separation zone;

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

[0096] Based on the perimeter and area of ​​the flow separation zone, these parameters of the equivalent ellipsoid are calculated by 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 major axis a and minor axis b) can be defined by 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] Determine 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] Among them, 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] Determine that the equivalent ellipsoid is a rotation ellipsoid, determine the circumference radius of the rotation ellipsoid perpendicular to the flow direction according to the projection area, and calculate 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 elliptical cylinder with an axis length perpendicular to the flow direction on the elliptical section is calculated according to the projected area and the projected perimeter, and the semi-axis length parallel to the flow direction on the elliptical section is calculated according to the principle of equal shape factors.

[0108] Specifically, the steps of calculating the equivalent ellipsoid geometric dimensions 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 based on 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 length of the semi-axis parallel to the flow direction, and b is the length of the semi-axis 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, and the semi-axis length parallel to the flow direction can be iteratively solved according to the bisection method to obtain all the geometric parameters of the equivalent ellipsoid.

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

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

[0115] The shape factor is obtained by obtaining a weighted average value of all the facets according to the dot product result and the total area of ​​the facets.

[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 three directions of the coordinate system x, y, z 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 the constructed viscosity-pressure resistance coefficient database to obtain the viscosity-pressure resistance coefficient;

[0123] The geometric dimensions are normalized and 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] The embodiment of the present application obtains the viscous-pressure drag coefficient under specific geometric conditions by querying and referencing the viscous-pressure drag coefficient database, and normalizes the relevant geometric dimensions to facilitate subsequent data management and quick search. The normalized parameters will help unify the data format in the database and improve search efficiency, providing instant and reliable data support for ocean vehicle design and fluid mechanics 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 model: obtaining geometric parameters such as centroid geometric coordinates, surface element area, and surface unit external normal vector;

[0128] Divide the flow separation zone: 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] Calculate the projected area: The flow separation affected area is equivalent;

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

[0132] The calculated 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 finding the equivalent ellipsoid;

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

[0137] Calculate the piezoresistance 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 velocity vector of the distant flow. 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 assumption, comprising:

[0142] The model building module 510 is used to build a geometric model of the ocean navigation body, and to grid the geometric model to determine the centroid geometric coordinates, the area of ​​the panel, and the outer normal vector of the panel;

[0143] A separation zone division module 520 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;

[0144] A size determination module 530 is used to calculate the projected perimeter, projected area and shape factor according to the flow separation zone, construct an equivalent ellipsoid of the ocean vehicle, and determine the geometric size of the equivalent ellipsoid;

[0145] A coefficient acquisition module 540 is used 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 method;

[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 satisfies the division 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, the projected area and the shape factor according to the flow separation zone includes:

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

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

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

[0155] Optionally, it also includes:

[0156] Determine 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] Among them, 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] Determine that the equivalent ellipsoid is a rotation ellipsoid, determine the circumference radius of the rotation ellipsoid perpendicular to the flow direction according to the projection area, and calculate 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 elliptical cylinder with an axis length perpendicular to the flow direction on the elliptical section is calculated according to the projected area and the projected perimeter, and the semi-axis length parallel to the flow direction on the elliptical section is calculated according to the principle of equal shape factors.

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

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

[0167] The shape factor is obtained by obtaining a weighted average value of all the facets according to the dot product result and the total area of ​​the facets.

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

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

[0170] The geometric dimensions are normalized and 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 can be understood that the detailed functional implementation of each of the above-mentioned 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, which will not be repeated here.

[0173] Reference Figure 6 Based on the method in the above embodiment, the embodiment of the present application provides an electronic device, which may include: a processor (processor) 610, a communication interface (CommunicationsInterface) 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 through 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 it is 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, which is stored in a storage medium and includes a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform 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 understandable that the processor in the embodiment of the present application can be a central processing unit (CPU), or 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 can 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, and the software modules 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 a 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 may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted through the computer-readable storage medium. The computer instructions may be transmitted from a website site, a computer, a server or a data center to another website site, a computer, a server or a data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium may be any available medium that a computer can access or a data storage device such as a server or a data center that includes one or more available media integrated. The available medium may 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 disk (SSD)), etc.

[0180] It should be understood that the various numerical numbers involved in the embodiments of the present application are only used for the convenience of description and are not used to limit the scope of the embodiments of the present application.

[0181] It will be easily understood by those skilled in the art that the above description 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 shall 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 navigation body, and meshing the geometric model, determining the centroid geometric coordinates of the panel mesh, the panel area, and the panel external normal vector; 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 the projected perimeter, projected area and shape factor according to the flow separation zone, constructing an equivalent ellipsoid of the ocean vehicle, and determining the geometric dimensions of the equivalent ellipsoid; Determine the characteristic length of the ocean craft according to the geometric dimensions, calculate the Reynolds number of the ocean craft according to the characteristic length of the ocean craft, the velocity vector, and the kinematic viscosity of seawater, and obtain the viscous-pressure drag coefficient of the equivalent ellipsoid by interpolation method; The viscous-pressure drag of the ocean vehicle is obtained according to 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.

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 division 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 according to the flow separation region includes: Obtaining the projected perimeter, projected area and shape factor of the flow separation zone; Determining that the occurrence area, the impact area and the occurrence intensity of the flow separation zone are in a comparable relationship between the ocean navigation body and the comparable ellipsoid; According to the equivalence of occurrence area, impact area and occurrence intensity, combined with the principle of equal parameters, the projection perimeter, projection area and shape factor of the equivalent ellipsoid are determined 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: Determine 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: Determine that the equivalent ellipsoid is a rotation ellipsoid, determine the circumference radius of the rotation ellipsoid perpendicular to the flow direction according to the projection area, and calculate 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 elliptical cylinder with an axis length perpendicular to the flow direction on the elliptical section is calculated according to the projected area and the projected perimeter, and the semi-axis length parallel to the flow direction on the elliptical 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 the dot product result of the normal vector outside the surface element and the velocity vector of the distant unit flow, integrating all the surface elements of the flow separation area to obtain the total area of ​​the surface element; The shape factor is obtained by obtaining a weighted average value of all the facets according to the dot product result and the total area of ​​the facets.

7. The method for obtaining the viscous-pressure resistance of an ocean vehicle according to claim 1, characterized in that: Also includes: Querying the constructed viscous-pressure resistance coefficient database to obtain the viscous-pressure resistance coefficient; The geometric dimensions are normalized and 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 assumption, characterized in that: include: A model building module is used to build a geometric model of the ocean navigation body, and to grid the geometric model to determine the centroid geometric coordinates of the surface element grid, the surface element area, and the surface element external normal vector; A separation zone division module, used for dividing 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, for calculating the projected perimeter, projected area and shape factor according to the flow separation zone, constructing an equivalent ellipsoid of the ocean vehicle, and determining the geometric size of the equivalent ellipsoid; A coefficient acquisition module, used 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 method; The viscous-pressure resistance acquisition module is used to obtain the viscous-pressure resistance of the ocean vehicle 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.

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 runs on a processor, the processor is caused to execute the method according to any one of claims 1 to 7.

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