Marine propeller tip geometric fairing modeling method
By inserting control points into the propeller blade tip area and introducing the tangent cylindrical surface normal vector for correction, the problem of difficult modeling of the propeller blade tip and sharp configuration is solved, smooth tip geometry is achieved, and performance simulation and processing accuracy are improved.
Patent Information
- Application Number
- CN202510218437.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-26
- Publication Date
- 2025-06-13
AI Technical Summary
Geometric modeling of the tip of the propeller blade is difficult. The existing methods lead to the sharp configuration of the tip, which cannot effectively express geometric details, affecting performance simulation and processing accuracy.
By obtaining the propeller blade type scatter and its coordinate values, an initial NURBS surface is established, and additional control points are inserted in the tip area, the tangent cylindrical surface normal vector is introduced for radial derivative correction, and the surface is reconstructed to achieve smooth tip geometry.
It realizes the smooth characteristics of the tips of the propeller blades, improves the quality of model automation generation, improves performance simulation and processing accuracy, and has great engineering practical value.
Smart Images
Figure CN120145548A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of ships, and in particular to a geometric fairing modeling method for the tip of a marine propeller. Background Art
[0002] The geometric modeling accuracy of a propeller has an important impact on both its performance simulation and the machining accuracy of the model. However, the three-dimensional surface of the propeller is severely distorted, making geometric modeling difficult, especially in the tip region where there are limited design control parameters. In existing modeling methods, due to the chord length being zero at the tip of the blade, the parametric surface has only one direction (lacking the chord direction), that is, there is only one profile point at the tip of the blade, and the position of this point is the surface convergence point. There is no continuity relationship between different parameters in the same direction at the convergence part. Therefore, the tip of the established propeller model is often a sharp configuration rather than a smooth one, which cannot well express the geometric details of this region. Thus, it is difficult to generate high-quality tip geometry, which is not conducive to the design control of the tip vortex cavitation performance and the improvement of the comprehensive performance of the propeller. In summary, it is necessary to further improve the generation algorithm for the geometry of the propeller blade tip. Summary of the Invention
[0003] In view of the above problems and technical requirements, the inventor of the present invention has proposed a geometric fairing modeling method for the tip of a marine propeller. The technical solution of the present invention is as follows:
[0004] A geometric fairing modeling method for the tip of a marine propeller includes the following steps:
[0005] 1) Obtain the scattered profile points of the propeller blade and their coordinate values. The position parameters of the scattered points in the radial and chord directions are u and v respectively. The u value is usually r / R, and the v value is usually x / C, where r is the radial station radius, R is the propeller radius, x is the chordwise station position, and C is the section chord length. The blade surface is discretized into m layers of scattered points in the radial direction. Each of the first to the m - 1 layers has n scattered points in the chord direction, and the mth layer is the tip of the blade, having only 1 scattered point (this application only performs tip fairing modeling for propellers with a zero chord length at the tip, so there is only 1 scattered point at the tip). Denote the kth scattered point in the radial direction and the lth scattered point in the chord direction as P kl .
[0006] 2) Based on the scattered points, establish an initial NURBS surface for the blade and obtain the coordinate values of each control point of the surface. The surface equation is:
[0007]
[0008] 3) To ensure that the original design parameters are not affected when performing fairing processing on the tip region, an additional layer of control points is inserted between the control points of the mth and m - 1th layers in the radial direction, denoted as K m-0.5,j . The position value of this control point can be taken as u m-0.5 = u m-1+0.5(u m -u m-1 ), then the control point is represented as:
[0009]
[0010] K m-0.5,j =(1 - a m-0.5 )K m-1,j +a m-0.5 K m,j (2)
[0011] where a m-0.5 is the radial position coefficient of the inserted control point, u m-2 , u m are the radial position values of the control points on the (m - 2)-th and m-th layers in the radial direction respectively, K m-1,j , K m,j are the coordinate values of the control points on the (m - 1)-th / m-th layer in the radial direction and the j-th control point in the chordal direction respectively. Note that K m-1,j here is the coordinate value of the control point before correction.
[0012] 4) Introduce the outer normal vector of the circumscribed cylindrical surface of the tip point to correct the coordinate values of the additionally inserted control points;
[0013] 5) Substitute the corrected coordinate values of the control points back into the initial NURBS surface (1) of the blade generated in step 2) to obtain a smooth propeller blade surface at the tip. The method proposed in this application only smooths the surface between P m and P m-1 without changing the rest of the surface.
[0014] A further technical solution thereof is that in step 2), obtaining the coordinate values of each control point of the surface includes:
[0015] Solve the following system of linear equations for K ij :
[0016]
[0017] where: N i,p and N j,p are both p-order basis functions, represents the tensor product operation, u k , v l are the position values corresponding to the scatter point P kl , K ij is the coordinate value of the control point on the i-th layer in the radial direction and the j-th control point in the chordal direction, and is the unknown to be solved, and U kl is the coordinate value of P kl .
[0018] All the existing propeller blade profile value scatter points should be on the surface, so they can be expressed by the surface equation. And for each scatter point P kl A linear equation (3) can be listed through the interpolation algorithm, and the control points K of the surface equation can be obtained by joint solution ij , and substituting it back into the surface equation (1) realizes the NURBS surface expression of the propeller surface.
[0019] Its further technical solution is that in step 4), the outer normal vector of the circumscribed cylindrical surface of the tip point is introduced to correct the coordinate values of the additionally inserted control points, including:
[0020] 41) Obtain the unit outer normal vector of the circumscribed cylindrical surface S of the tip point P mn , denoted as T;
[0021] 42) Calculate the projection value of the radial position derivative of the propeller tip point on T as the radial correction amount;
[0022] 43) Use the radial correction amount to correct the coordinate values K of the additionally inserted control points m-0.5,j .
[0023] Its further technical solution is that step 42) specifically includes:
[0024] First, since the tip is a single point, only the derivative values of all radial positions u of the propeller tip point need to be obtained:
[0025]
[0026] The method for obtaining the derivative values of the basis functions is:
[0027]
[0028] Where N i ′ ,p (u k ) is calculated through the derivative recurrence formula with p = 2:
[0029]
[0030] Here, t refers to the derivative direction variable, which is equivalent to u.
[0031] Secondly, project the obtained derivative value D u S onto the unit outer normal vector T of the circumscribed cylindrical surface S to obtain:
[0032] D ml = D u S(u m , v l ) - (T · D u S(u m , vl ))·T(5)
[0033] where u m , v l are the position values corresponding to the m-th radial layer and the l-th chordal scatter point.
[0034] Its further technical solution is that step 43) specifically includes:
[0035] Substitute the radial correction amount D ml into the following linear equations and solve for K ij :
[0036]
[0037] Here, K ij is the coordinate value of the control point of the extra inserted layer K m-0.5,j and is the unknown to be solved.
[0038] Its further technical solution is that the method further includes:
[0039] After inserting an extra layer of control points (i.e., adding basis functions) in step 3), it is necessary to correct the coordinate values of the control points in the affected area, that is, recalculate the coordinate values of the control point K m-1,j of the (m - 1)-th layer, which will not change the original surface shape and blade design parameters.
[0040] Then the modified K m-1,j is expressed as:
[0041]
[0042] K m-1,j =(1 - a m-1 )K m-2,j + a m-1 K m-1,j (7)
[0043] where a m-1 is the radial position coefficient of the control point of the (m - 1)-th layer, u m-1 , u m-3 are the radial position values of the control points of the (m - 1)-th and (m - 3)-th radial layers respectively, and K m-2,j is the coordinate value of the control point of the (m - 2)-th radial layer and the j-th chordal layer. It should be noted that K m-1,j on the left side of the equation represents the modified value, and K m-1,j on the right side of the equation represents the value obtained by solving before modification.
[0044] Its further technical solution is that the general value ranges of m and n are m≥11 and n≥12 respectively.
[0045] The beneficial technical effects of the present invention are as follows:
[0046] By setting the additional cutting plane constraint at the tip, that is, introducing the normal vector of the circumscribed cylinder surface to correct the radial derivative, the original NURBS surface is reconstructed, thus avoiding the sharp shape presented at the tip during the blade modeling and realizing the smooth characteristic of the blade tip. The overall process of the method is clear, the operation is simple and easy to implement. Only the geometric surface between the tip points and K m-1,j is modified, and the remaining part of the blade is not modified, and the existing blade design parameters will not be changed. Using this method can improve the quality of automatic generation of the propeller model, which is beneficial to improving the performance simulation and machining accuracy of the propeller, and has great engineering practical value. Description of the Drawings
[0047] Figure 1 is a flowchart of a method for geometric fairing modeling of the tip of a marine propeller provided by this application.
[0048] Figure 2 is a schematic diagram of the spatial offset coordinate points of the propeller generated in an embodiment of this application.
[0049] Figure 3 is a schematic diagram of the control points of the blade surface generated in an embodiment of this application.
[0050] Figure 4 is a schematic diagram of inserting an additional layer of surface control points between the tip points and the control points of the second-to-last layer in an embodiment of this application.
[0051] Figure 5 is a schematic diagram of the outer normal of the circumscribed cylinder of the blade tip points in an embodiment of this application.
[0052] Figure 6 (a) and (b) are comparison diagrams of the surfaces before and after the tip fairing treatment in an embodiment of this application. Detailed Embodiments
[0053] The following further describes the detailed embodiments of the present invention with reference to the drawings.
[0054] An embodiment of this application discloses a method for geometric fairing modeling of the tip of a marine propeller. Referring to Figure 1 the flow shown, the method includes the following steps:
[0055] Step 1, according to the spatial offset table of the propeller, obtain the blade offset scatter points and their coordinate values. The blade surface is discretized into 13 layers of offset points in the radial direction. Among them, the first 12 layers each have 19 offset points in the chord direction. The 13th layer is the tip of the propeller blade, and the chord length of the section is zero. Therefore, it only contains 1 tip point, as Figure 2 shown.
[0056] Step 2: Use the interpolation algorithm to establish the initial NURBS surface (1) of the blade, and obtain the coordinates of each control point on the surface according to formula (3), as follows: Figure 3 shown.
[0057] Step 3: Insert an extra layer of control points between the 13th and 12th radial control points, denoted as K 12.5,j ,like Figure 4 As shown, its expression is shown in formula (2). Then, the coordinates of the control points of the 12th layer are recalculated according to formula (7).
[0058] Step 4: Get the blade tip point P mn The unit external normal vector of the circumscribed cylindrical surface S is denoted by T, such as Figure 5 shown.
[0059] Step 5: Obtain the u parameter derivative value of the blade tip parameter surface according to formula (4), and calculate the projection value of the derivative on T according to formula (5) as the radial correction value D ml .
[0060] Step 6, using D ml And formula (6) corrects all K of the surface 12.5,j The coordinate value of .
[0061] Step 7: K 12.5,j Substitute the coordinate values of into the parametric surface equation (1) generated in step 2 to obtain the blade surface with smooth tip.
[0062] In one embodiment, the method provided in this application is used to test and verify a propeller blade of a ship. The model of the propeller blade of the ship before the smoothing treatment is obtained as follows: Figure 6 As shown in (a), it can be seen that the tip of the propeller model is a sharp configuration rather than a smooth configuration, while the model constructed using this method is as follows Figure 6 As shown in (b), it is proved that this method can achieve the smooth characteristics of the blade tip.
[0063] The above is only a preferred embodiment of the present application, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.
Claims
1. A method for geometric smoothing modeling of a marine propeller tip, characterized in that: The method comprises: Obtain the propeller blade profile scatter points and their coordinate values, where the blade surface is discretized into m layers of scatter points in the radial direction, the first layer to the m-1th layer each have n scatter points in the chord direction, and the mth layer is the blade tip, which has only one scatter point; Establishing an initial NURBS surface of the blade based on the scattered points, and obtaining coordinate values of each control point of the surface; Insert an extra layer of control points between the radial m-th layer and the m-1-th layer of control points; The outer normal vector of the circumscribed cylindrical surface of the tip point is introduced to correct the coordinate value of the additional inserted control point; Substitute the corrected control point coordinate values back into the initial NURBS surface of the blade to obtain a smooth tip propeller blade surface.
2. The method for geometrically smoothing modeling of a marine propeller tip according to claim 1, characterized in that: The step of obtaining the coordinate values of each control point on the surface includes: Solve the following about K ij The linear equations are: Where: N i,p and N j,p are all p-order basis functions, represents the tensor product operation, u k 、v l is the kth radial and lth chordal scattered point P kl The corresponding position value, K ij is the coordinate value of the i-th control point in the radial direction and the j-th control point in the chord direction, and is the unknown number to be determined, U kl For the P kl The coordinate value of .
3. The method for geometrically smoothing modeling of a marine propeller tip according to claim 1, characterized in that: The method of introducing the outer normal vector of the circumscribed cylindrical surface of the tip point to correct the coordinate value of the additionally inserted control point includes: Get the unit external normal vector of the circumscribed cylindrical surface S of the tip point, denoted as T; Calculate the projection value of the radial position derivative of the blade tip point on T as the radial correction value; The radial correction amount is used to correct the coordinate values of the additionally inserted control points.
4. The method for geometrically smoothing modeling of a marine propeller tip according to claim 3, characterized in that: The step of calculating the projection value of the radial position derivative of the blade tip point on T includes: Get the derivative value of the radial position u of the blade tip point: The derivative value D u Projecting S onto the unit external normal vector T of the circumscribed cylindrical surface S yields: D ml =D u S(u m ,v l )-(T·D u S(u m ,v l ))·T Where N i,p and N j,p are all p-order basis functions, represents the tensor product operation, K ij is the coordinate value of the i-th control point in the radial direction and the j-th control point in the chord direction, u m 、v l It is the position value corresponding to the mth radial layer and the lth scatter point in the chord direction.
5. The method for geometrically smoothing modeling of a marine propeller tip according to claim 4, characterized in that: For the derivative value of the radial position u of the blade tip point, the derivative value of the basis function is obtained as follows: Where N i ' ,p (u k ) is calculated by the derivative recursion formula with p = 2: Here t refers to the derivative direction variable, which is equivalent to u.
6. The method for geometrically smoothing modeling of a marine propeller tip according to claim 3, characterized in that: The radial correction amount is used to correct the coordinate value of the additionally inserted control point, including: Substitute the radial correction into the following linear equations and solve for K ij : Among them, N ij,p is the p-order basis function, u m 、v l K is the position value corresponding to the mth radial layer and the lth scatter point in the chord direction, ij is the coordinate value of the i-th control point in the radial direction and the j-th control point in the chord direction in the additional insertion layer, and is the unknown number to be calculated, D ml is the radial correction amount.
7. The method for geometrically smoothing modeling of a marine propeller tip according to claim 1, characterized in that: The method further comprises: After inserting an extra layer of control points, the coordinate values of the control points in the m-1th layer are corrected.
8. The method for geometrically smoothing modeling of a marine propeller tip according to claim 7, characterized in that: The step of correcting the coordinate values of the control points of the m-1th layer includes: K m-1,j =(1-a m-1 )K m-2,j +a m-1 K m-1,j Among them, a m-1 is the radial position coefficient of the control point at the m-1th layer, u m-0.5 is the radial position value of the additional inserted control point, u m-1 、u m-3 are the radial position values of the control points at the m-1th and m-3th layers, respectively, and K m-1,j , K m-2,j They are the coordinate values of the m-1th layer / m-2th layer in the radial direction and the jth control point in the chord direction respectively.
9. The method for geometrically smoothing modeling of a marine propeller tip according to any one of claims 1 to 8, characterized in that: The value ranges of m and n are m≥11 and n≥12 respectively.