Free-form surface shell structure form creating method based on NURBS technology

Abstract

The invention belongs to the field of structural form creation, and particularly relates to a free-form surface shell structural form creation method based on an NURBS technology, and the method comprises the steps: S1, simulating and creating a smooth and continuous ruled surface initial model structure and a surface boundary; s2, after the initial model structure is created, a ruled surface shell structure form creation method is created; s3, creating the structural form of the combined ruled surface shell; s4, performing engineering simulation example calculation; a form creating mode in a traditional structural system is replaced, and the problem that the form structure of the free-form surface cannot be effectively created is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of structural morphology creation, and in particular to a free-form surface shell structural morphology creation method based on NURBS technology. Background Art

[0002] As people's material living standards improve, their requirements for the span of buildings are getting higher and higher, and the specific structural implementation methods are gradually becoming more diverse.

[0003] As an emerging structural form, free-form surface structure is different from traditional structure in that it does not have structural components such as beams, slabs and columns with clear primary and secondary structures, and its shape is free and diverse. In the past, the process of creating spatial structure forms was usually through simple geometric elements such as points, lines, surfaces, etc., which were arranged in a certain pattern, or generated according to a certain motion trajectory. For free-form surface spatial structures, since there is no unified regularity, each link from design to construction is relatively cumbersome, and due to its high construction cost, there are very few completed projects, and the research on the creation of free-form surface structure forms is relatively scarce. However, with the continuous improvement of people's requirements for functions and architectural performance, it has gradually attracted people's attention in recent years. Free-form surface building structures have injected fresh vitality into modern architectural design with their free and diverse forms. However, due to their shortcomings such as complex design variables, difficult modeling, cumbersome construction technology, and high cost, free-form surface structures are still subject to strong constraints in actual engineering applications, and many free-form surface building designs are still in the drawing stage. Summary of the invention

[0004] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0005] Therefore, the purpose of the present invention is to provide a free-form surface shell structure morphology creation method based on NURBS technology, which replaces the morphology creation method in the traditional structural system and avoids the problem of being unable to effectively create the morphology structure of the free-form surface.

[0006] To solve the above technical problems, according to one aspect of the present invention, the present invention provides the following technical solutions:

[0007] A free-form surface shell structure morphology creation method based on NURBS technology, comprising:

[0008] S1, simulate and create a smooth and continuous ruled surface initial model structure and surface boundary;

[0009] S2. after creating the initial model structure, creating a method for creating a ruled surface shell structure morphology;

[0010] S3, creating the structure of the combined ruled surface shell;

[0011] S4. Carry out engineering simulation examples.

[0012] As a preferred solution of the free-form surface shell structure morphology creation method based on NURBS technology described in the present invention, in S1, B-spline is referenced to define curves and surfaces, and curve construction is performed through 1k-order B-spline curves and spline functions of inversely calculated (k-1)-order B-spline curves.

[0013] As a preferred solution of the free-form surface shell structure morphology creation method based on NURBS technology described in the present invention, in S1, according to the aforementioned B-spline curve theory analogy, the B-spline curve function can be extended to three-dimensional space to form a B-spline surface, thereby constructing a B-spline free-form surface and a B-spline ruled surface.

[0014] As a preferred solution of the free-form surface shell structure morphology creation method based on NURBS technology described in the present invention, in S1, the in-plane deformation unit, out-of-plane deformation unit, in-plane torsion unit and coordinate transformation matrix in the triangular thin plate unit are specifically expanded through the finite element method, which provides a clear idea for the integration of unit stiffness and the specific implementation of programming. In S1, the objective function strain energy is optimized, and the sensitivity of the strain energy in the global coordinates to the key points of the ruled surface shell structure is derived in detail.

[0015] As a preferred solution of the free-form surface shell structure morphology creation method based on NURBS technology described in the present invention, in S2, (1) k-order B-spline curve function is used to construct multiple boundary curves of the ruled surface, thereby realizing the generation and connection of multiple boundary curves, and further realizing the creation of the initial structure of the ruled surface.

[0016] As a preferred solution of the free-form surface shell structure morphology creation method based on NURBS technology described in the present invention, in S2, a ruled surface shell structure morphology creation method is established according to the ruled surface structure morphology creation problem.

[0017] As a preferred solution of the free-form surface shell structure morphology creation method based on NURBS technology described in the present invention, in S3, under the simulation scenario of multiple wires, a combined model of ruled surfaces of wires with irregular boundaries and a combined model of ruled surfaces of regular boundaries are constructed.

[0018] As a preferred solution of the free-form surface shell structure morphology creation method based on NURBS technology described in the present invention, in S3, the stress progressive change of the structure is obtained in the case of branch holes.

[0019] As a preferred solution of the free-form surface shell structure morphology creation method based on NURBS technology described in the present invention, in S3, the constructed model is repeatedly verified by varying the number of times and combining multiple situations.

[0020] As a preferred solution of the free-form surface shell structure morphology creation method based on NURBS technology described in the present invention, in S4, a single-piece ruled free-form surface example, a ruled surface structure simulation example, a free-form surface ruled surface approximation example and a ruled surface shell structure stability example are performed.

[0021] Compared with the prior art, the present invention has the beneficial effect that the free-form surface shell structure morphology creation method based on NURBS technology utilizes the geometric characteristics of ruled surfaces and combines computer-aided design methods to create a variety of ruled surface shell initial structures that meet the functional requirements and aesthetic requirements of buildings, and can achieve rich requirements such as different times of splicing, digging holes, and variable times, and has the versatility of programming and the requirements of architectural diversity. At the same time, it can take into account the requirements of architectural design and ensure that the ruled surface has the geometric characteristics of smooth and continuous free curves as guides and straight lines as generatrixes. The method should combine the initial structure establishment method and the structural optimization method to select reasonable design variables, and through iterative optimization, the method can significantly improve the overall mechanical properties and architectural aesthetic effects of the shell structure, create a ruled surface shell structure that organically integrates architecture, structure, and construction, and provide a useful reference for the determination of architectural form. Combined with mechanical theory, the objective function that can reflect the overall structural performance and is conducive to program iterative calculation is selected to replace the traditional structural system morphology creation method, avoiding the problem of being unable to effectively create the morphological structure of the free-form surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below in combination with the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0023] Figure 1 It is a schematic diagram of Formula 2-1 of a free-form surface shell structure morphology creation method based on NURBS technology of the present invention;

[0024] Figure 2It is a schematic diagram of Formula 2-2 of a free-form surface shell structure morphology creation method based on NURBS technology of the present invention;

[0025] Figure 3 It is a schematic diagram of formula 2-3 of a free-form surface shell structure morphology creation method based on NURBS technology of the present invention;

[0026] Figure 4 It is a schematic diagram of formula 2-5 of a free-form surface shell structure morphology creation method based on NURBS technology of the present invention;

[0027] Figure 5 It is a specific construction schematic diagram of the inverse calculation (k-1) order B-spline curve of a free-form surface shell structure morphology creation method based on NURBS technology of the present invention;

[0028] Figure 6 A schematic diagram of the generation process of a B-spline surface of a free-form surface shell structure morphology creation method based on NURBS technology of the present invention;

[0029] Figure 7 It is a schematic diagram of Formula 3-1 of a free-form surface shell structure morphology creation method based on NURBS technology of the present invention;

[0030] Figure 8 It is a schematic diagram of Formula 3-2 of a free-form surface shell structure morphology creation method based on NURBS technology of the present invention;

[0031] Fig. 9 It is a schematic diagram of the steps of a ruled surface shell structure morphology creation method of a free-form surface shell structure morphology creation method based on NURBS technology of the present invention. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0033] Secondly, the present invention is described in detail with reference to schematic diagrams. When describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0034] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0035] The present invention provides a free-form surface shell structure morphology creation method based on NURBS technology, which replaces the morphology creation method in the traditional structural system and avoids the problem of being unable to effectively create the morphology structure of the free-form surface.

[0036] Figure 1-Figure 9 The figure shows a schematic diagram of a free-form surface shell structure creation method based on NURBS technology in the present invention. Figure 1-Figure 9 A detailed introduction is given to this free-form shell structure creation method based on NURBS technology.

[0037] refer to Figure 1-9 The present invention discloses a free-form surface shell structure morphology creation method based on NURBS technology, comprising:

[0038] S1, simulate and create a smooth and continuous ruled surface initial model structure and surface boundary;

[0039] S2. after creating the initial model structure, creating a method for creating a ruled surface shell structure morphology;

[0040] S3, creating the structure of the combined ruled surface shell;

[0041] S4. Carry out engineering simulation examples.

[0042] In this embodiment, in S1, B-spline is used to define curves and surfaces, and the curve is constructed by using the 1k-order B-spline curve and the spline function of the inverse (k-1)-order B-spline curve. The recursive definition method is adopted here, and the node vector U = {u0, u1, ..., u m} is a monotonically non-decreasing real number sequence, and N, x(u) represents the i-th k-order B-spline basis function. Its de Boor-Cox recursion formula is as follows: Figure 1 ;

[0043] In this article, reference Figure 2 The quasi-uniform node vector in the formula in , to ensure the coincidence of the first and last points;

[0044] From this we can see that:

[0045] (1)N i，0 (u) is a step function, which is in the half-open interval (u i ,u i+k ) are all zero;

[0046] (2) When k>0, N i，k (u) is a linear combination of two k-1 basis functions;

[0047] (3) When calculating a set of basis functions, the node vector v and the number k need to be specified in advance;

[0048] (4) In formula (2-1), 0 / 0 may appear, so we stipulate that 0 / 0=0;

[0049] (5)N i，k (u) is a piecewise polynomial function defined on the entire real number axis, but we usually only use it in the interval [u o ,u m ] are of interest;

[0050] (6) Half-open interval [u i ,u i+1 ) is called the 7th node interval, and its length can be 0 because adjacent nodes can be the same:

[0051] (7) The process of calculating the k-th basis function can generate a triangular array of the following form:

[0052] Based on the B-spline basis function, the definition of k-order B-spline curve refers to Figure 3 Formula 2-3, where {NA,,(u)} is defined on the non-periodic (and non-uniform) node vector;

[0053] In this embodiment, the B-spline curve has:

[0054] (1) Strong convexity: The curve C(u) must be contained within its control polygon; this approximation can be improved by inserting nodes or increasing the degree. In general, the lower the degree k, the closer the B-spline curve is to its control polygon: when the degree is 1, the curve coincides with the control polygon, that is, the straight line segments of the control points are connected;

[0055] (2) Local modifiability: Moving P1 only changes the shape of C(u) in the interval [u1,u3,,n0);

[0056] (3) The continuity and differentiability of C(u) can be achieved by re-controlling nodes: by properly setting re-controlling points, it is possible to ensure that the B-spline curve passes through a certain point or generates straight line segments and cusps locally to meet the shape requirements of the building;

[0057] (4) It is possible (and sometimes useful) to use duplicate (coincident) control vertices.

[0058] In this embodiment, the (k-1)th degree B-spline curve is inversely calculated, given the known n data points

[0059] (x1,y1,z1),(x2,y2,z2),…,(x n ,y n ,z n)

[0060] The De Boor-Cox algorithm gives the i-th (k-1) degree B-spline basis function. i，k The recursive expression of (x) is as follows Figure 4 Formula 2-5 in the reference Figure 5 , which is a schematic diagram of the specific construction of the inverse calculation of the (k-1)th order B-spline curve.

[0061] In this embodiment, in S1, according to the aforementioned B-spline curve theory analogy, the B-spline curve function can be extended to three-dimensional space to form a B-spline surface, thereby constructing a B-spline free-form surface and a B-spline ruled surface;

[0062] According to the aforementioned B-spline curve theory analogy, the B-spline curve function can be extended to three-dimensional space to form a B-spline surface. Since the B-spline surface can be determined by the key point grid formed in the x and y directions, by multiplying the independent B-spline basis functions and control coefficients in the x and y directions and bringing them into the key points, assuming that m×n key points known in the x and y directions are given, the B-spline surface can be expressed as: Where: there are m and n key points in the x-direction and y-direction respectively, y,j is the coefficient, B,x(x) is the (k-1)th order B-spline basis function in the x-direction, and B,x(y) is the (ll)th order B-spline basis function in the y-direction;

[0063] A ruled surface is a curved surface generated by linear motion. The moving straight line is called a straight generatrix (referred to as a generatrix). Cylinders and cones are ruled surfaces. Simple straight surfaces such as single-leaf hyperboloids and hyperbolic paraboloids (saddle surfaces) in quadratic surfaces can be expressed by the following formula: f(u) and h(u) represent the two conductors of the ruled surface; u and v represent parameter variables.

[0064] S(u,v)=(1-v)f(u)+vh(u)

[0065] h(u)=f(u)-h(u). On the one hand, the ruled surface is composed of only straight lines in the direction of the busbar, which has a certain regularity and greatly reduces the difficulty of construction. On the other hand, the ruled surface is a free curve in the direction of the conductor. Reasonable arrangement and connection of multiple ruled curves can also achieve diversified architectural expressions.

[0066] In this embodiment, in S1, the finite element method is used to form the specific expansion of the in-plane deformation unit, out-of-plane deformation unit, in-plane torsion unit, and coordinate transformation matrix in the triangular thin plate unit, which provides a clear idea for the integration of unit stiffness and the specific implementation of programming. In S1, the objective function strain energy is optimized, and the sensitivity of the strain energy in the global coordinates to the key points of the ruled surface shell structure is derived in detail.

[0067] In this embodiment, in S2, a (1) k-order B-spline curve function is used to construct multiple boundary curves of the ruled surface, thereby achieving the generation and connection of multiple boundary curves, and further achieving the creation of the initial structure of the ruled surface.

[0068] In this embodiment, in S2, a ruled surface shell structure morphology creation method is established according to the ruled surface structure morphology creation problem.

[0069] In this implementation, the composition of the (k-1)th order B-spline curve function is first introduced through the basic theory of B-spline function. Secondly, the method of inverse calculation of the (k-1)th order B-spline curve function is introduced to meet the architectural intention, so that the curve strictly passes through the known key points, which is convenient for program control and analysis, and provides conditions for subsequent optimization programming. On the basis of B-spline curve, the calculation method, composition steps and characteristics of B-spline surface, as well as the definition characteristics and generation method of ruled surface are introduced, which lays the foundation for the subsequent morphological creation of the initial structure of ruled surface. The differential equation of elastic surface and shape function are introduced in detail, and the specific development of in-plane deformation unit, out-of-plane deformation unit, in-plane torsion unit and coordinate transformation matrix in triangular thin plate unit provide a clear idea for the integration of unit stiffness and the specific implementation of programming, and also provide a theoretical basis for the subsequent derivation of strain energy sensitivity.

[0070] In this embodiment, in S3, in a simulation scenario of multiple wires, a model of a combination of ruled surfaces of wires with irregular boundaries and a model of a combination of ruled surfaces of wires with regular boundaries are constructed;

[0071] The (k-1)-order B-spline curve function is used to construct multiple boundary curves of the ruled surface. Assuming that the number of curves is N, the number of segments and the total number of branches of each curve are stored in an array, and the branch information is marked with a start number and an end number to achieve complex and diverse boundary conditions. The inverse calculation of the (k-1)-order B-spline curve function is referenced in Figure 7 ,refer to Figure 7 , where α i, β1, γ1 are combination coefficients. By substituting the coordinate values ​​of the known points into equation (2-8), the LU decomposition method is used to numerically calculate the coefficients. The information of different segmented curves of a curve can be stored in the form of an array to realize the variable degree processing of the segmented intervals of the curve, as well as the label processing of the overlapping and non-overlapping parts of the two curves, which lays the foundation for the subsequent branch processing of complex ruled surfaces. When the busbar direction connects two ruled surfaces, there are three conductors, among which f2 becomes the common conductor of ruled surfaces A1 and A2. At this time, for ruled surface A1, the two conductors of equation (2-10) are f(u) = f1, h(u) = f2, and for ruled surface A2, f(u) = f2, h(u) = f3. Similarly, when connecting multiple ruled surfaces, adjacent ruled surfaces can use common conductors. In actual engineering design, it is possible to encounter a conductor with different degrees or adjacent fingerprint surfaces separated in a certain part. In this regard, the corresponding B-spline curves are separated according to their degrees, and the end point conditions can be processed by using the feature that the end of the first interval wire overlaps with the beginning of the second interval wire. According to the B-spline curve, it is divided into f2 and f2 interval curves. The end b1 of curve f2 overlaps with the beginning a2 of curve f2. At the end b1, the first few nodes in f2 can be used as the end point conditions, and at the beginning a2, the adjacent nodes at the end of f2 can be used as the end point conditions, which can ensure the continuity of the connection. At this time, an odd number (2m-1) B-spline curve function is often used;

[0072] The shape of the ruled surface structure depends on the position of the control points of the wires arranged when creating the initial structure. This study uses the control points of the ruled surface B-spline curve as the design variables and the structural strain energy as the design target to establish a mathematical model for the ruled surface structure morphology problem. Figure 8 , where Z is the ordinate parameter vector of the key points on the B-spline model surface; C is the strain energy; S is the surface shape; Ω0 is the allowed adjustment space; δ max , σ m x Represent the maximum displacement and maximum stress respectively; δ0 and σ0 represent the allowable displacement and allowable stress respectively. In general, it is allowed to adjust the upper and lower limits of the given design variable Ω0 to express it. As the strain energy decreases, δ m m x , σ m n x It also decreases synchronously, so the maximum displacement and maximum stress conditions do not need to be considered in the shape optimization process, but the final structure obtained should be verified. The work done by the external force is converted into the strain energy inside the structure. For convenience, the strain energy C is replaced by the work done by the external force, that is;

[0073]

[0074] In the formula, P and U represent the load vector and the displacement vector generated by the load, respectively;

[0075] The basic steps of the ruled surface shell structure creation method can be summarized as follows:

[0076] 1) Use B-spline curve to establish the initial model, and divide the initial model into regular triangular meshes suitable for ruled surfaces:

[0077] 2) The Fortran finite element method is used to obtain the displacement expression of any node of the structure, which is substituted into the strain energy formula to determine the sensitivity of the structure to the strain energy of the key points;

[0078] 3) Determine the increment of the ordinate of the key point of the independent variable through strain energy sensitivity to control whether it is movable and the step size information:

[0079] 4) Adjust the vertical coordinates of key points on the surface to form a new structural model;

[0080] 5) Repeat steps 2), 3), and 4) until a certain convergence condition is met.

[0081] In this embodiment, in S3, a stress progression change of the structure is obtained in the presence of branch holes.

[0082] In this embodiment, in S3, the constructed model is repeatedly verified by varying the number of times and the combination of various situations, so that the design variables are determined according to the geometric characteristics of the ruled surface and the expression characteristics of the ruled surface B-spline function, and the minimization of strain energy is taken as the design goal. A mathematical model of the ruled surface shell structure morphology creation problem is established, and the relationship between the design variables and the strain energy is further studied. The morphology creation of the ruled surface shell structure is proposed, and the morphology creation steps using this method are summarized. On the basis of the above research, through simple examples, the changes in the mechanical properties of tension, compression, bending, etc. in the shape and structure before and after optimization are compared, the characteristics of the evolution are summarized, and finally a reasonable and ruled surface structure that maximizes the suppression of bending stress and transfers loads mainly by the internal force of the film is obtained.

[0083] In this embodiment, in S4, a single-piece ruled free-form surface calculation example, a ruled surface structure simulation calculation example, a ruled surface approximation calculation example of a free-form surface, and a ruled surface shell structure stability calculation example are performed;

[0084] The method of creating the structure of the ruled surface shell mainly guides the initial selection of the scheme. The program is completed by using Fortran with the assumption of small linear elastic deformation. However, for the ruled surface shell structure, due to the large amount of in-plane compressive stress, stability is also particularly important in the mechanical indicators of the shell structure. Therefore, it is necessary to summarize the instability law of the ruled surface shell structure by comparing different initial structures and the differences before and after optimization.

[0085] By simulating actual projects, we can accumulate experience for the actual engineering application of the ruled surface shell structure morphology creation method. In actual projects, the following process can be used to complete it:

[0086] (1) According to the architectural expression requirements, determine the position, quantity, and frequency of the wires, arrange the position and height of the control points, and locate the supports;

[0087] (2) Create the initial structure of the ruled surface shell and determine the design variables;

[0088] (3) Create an initial structure of a ruled surface shell with reasonable mechanical properties according to the method proposed in this paper;

[0089] (4) Comprehensively evaluate the structural form. If all indicators are met, proceed to detailed design. If not, adjust the wire position, quantity, number of times, position and height of the control points, and adjust the support position back to (2). If the free-form surface is approximated by the ruled surface, determine the wire position, quantity, number of times, and position and height of the control points according to the determined free-form surface shape, and then start the operation from the above step (2).

[0090] Although the present invention has been described above with reference to the embodiments, various modifications may be made thereto and parts thereof may be replaced by equivalents without departing from the scope of the present invention. In particular, as long as there is no structural conflict, the various features in the embodiments disclosed in the present invention may be used in combination with each other in any manner, and the fact that these combinations are not exhaustively described in this specification is only for the sake of omitting space and saving resources. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0091] Although the present invention has been described above with reference to the embodiments, various modifications may be made thereto and parts thereof may be replaced by equivalents without departing from the scope of the present invention. In particular, as long as there is no structural conflict, the various features in the embodiments disclosed in the present invention may be used in combination with each other in any manner, and the fact that these combinations are not exhaustively described in this specification is only for the sake of omitting space and saving resources. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for creating a free-form shell structure based on NURBS technology, characterized in that: include: S1, simulate and create a smooth and continuous ruled surface initial model structure and surface boundary; S2. after creating the initial model structure, creating a method for creating a ruled surface shell structure morphology; S3, creating the structure of the combined ruled surface shell; S4. Carry out engineering simulation examples.

2. According to claim 1, a free-form surface shell structure creation method based on NURBS technology is characterized in that: In S1, B-spline is used to define curves and surfaces, and curves are constructed by using 1k-order B-spline curves and spline functions that inversely calculate (k-1)-order B-spline curves.

3. According to claim 2, a free-form surface shell structure creation method based on NURBS technology is characterized in that: In S1, according to the aforementioned B-spline curve theory analogy, the B-spline curve function can be extended to three-dimensional space to form a B-spline surface, thereby constructing a B-spline free-form surface and a B-spline ruled surface.

4. According to claim 3, a free-form surface shell structure creation method based on NURBS technology is characterized in that: In S1, the finite element method is used to form the specific expansion of the in-plane deformation unit, out-of-plane deformation unit, in-plane torsion unit, and coordinate transformation matrix in the triangular thin plate unit, which provides a clear idea for the integration of unit stiffness and the specific implementation of programming. In S1, the objective function strain energy is optimized, and the sensitivity of the strain energy in the global coordinates to the key points of the ruled surface shell structure is derived in detail.

5. The method for creating a free-form surface shell structure based on NURBS technology according to claim 4 is characterized in that: In S2, (1) k-order B-spline curve function is used to construct multiple boundary curves of the ruled surface, thereby realizing the generation and connection of multiple boundary curves, and further realizing the creation of the initial structure of the ruled surface.

6. The method for creating a free-form surface shell structure based on NURBS technology according to claim 5, characterized in that: In S2, a method for constructing the structure of ruled surface shell is established based on the problem of constructing the structure of ruled surface.

7. The method for creating a free-form surface shell structure based on NURBS technology according to claim 6, characterized in that: In S3, in the simulation scenario of multiple wires, a model of the combined ruled surfaces of wires with irregular boundaries and a model of the combined ruled surfaces of wires with regular boundaries are constructed.

8. The method for creating a free-form surface shell structure based on NURBS technology according to claim 7, characterized in that: In S3, the stress evolution of the structure is obtained in the presence of branched holes.

9. The method for creating a free-form surface shell structure based on NURBS technology according to claim 8, characterized in that: In S3, the constructed model is repeatedly verified by varying the number of times and the combination of multiple situations.

10. The method for creating a free-form surface shell structure based on NURBS technology according to claim 9, characterized in that: In S4, a single-piece ruled free-form surface example, a ruled surface structure simulation example, a ruled surface approximation example of a free-form surface, and a ruled surface shell structure stability example are performed.

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