Aircraft flexible thermal protection structure shape design method and system based on physical simulation

Abstract

The present invention relates to a method and system for designing the shape of an aircraft flexible thermal protection structure based on physical simulation. The method comprises: constructing a three-dimensional model based on characteristic parameters of the aircraft flexible thermal protection structure installation interface; setting sampling points in the model to form a plurality of connected strip-shaped four-sided curved surfaces, and splicing them onto the same plane; performing a swing simulation on the model based on the engine swing requirements to obtain the range of distance variation between all point pairs on the plane; treating the sampling points as mass points, setting a structural spring with a larger elastic coefficient connecting adjacent sampling points on the same curve, and setting a shear spring between two sampling points on different curves, wherein the minimum length of the shear spring is the maximum distance between corresponding point pairs during the swing simulation plus an additional design slack; iteratively calculating the force applied to each mass point and updating the position state, ultimately obtaining the optimal envelope space surface geometric unfolding shape of each mass point in a stable state. Compared with the existing technology, the present invention has the advantages of accuracy, versatility, and speed.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible heat-resistant structures for aircraft, and in particular to a shape design method and system for flexible heat-resistant structures for aircraft based on physical simulation. Background Art

[0002] Flexible thermal protection structures are a crucial component of the heat shielding near the engine. For example, a rocket heat shield, a component of this structure, is installed between the engine's tail section and the support arm's heat shield plate. It oscillates with the support arm's movement. During this oscillation, the heat shield can easily become locally stretched and pulled, making it unable to withstand the engine's swinging motion.

[0003] Existing thermal skirt structural designs approximate the actual, unexpandable "lantern-shaped" surface of the envelope as a truncated cone, and account for the deviations caused by the approximation by a width magnification factor λ. The specific value of λ requires repeated testing and modification, resulting in low accuracy, leading to repeated design iterations and low overall design efficiency. Furthermore, because the current design only considers the linear distance between corresponding points on either side of the connection and magnifies it by the conventional λ factor, the thermal skirt lacks margin during swinging, resulting in localized tension and pulling, which restricts engine swing. Material accumulation also occurs in some areas, resulting in large areas and high weight, increasing the risk of flexible structure damage. With the rapid development of new aircraft models, the thermal shielding envelope has become increasingly irregular. Different aircraft models, engine swing patterns, and amplitudes require different flexible thermal shielding structures, resulting in distinct flexible thermal shielding designs. Existing thermal skirt structural designs are also not universally applicable. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned existing technologies and provide a method and system for designing the shape of an aircraft flexible thermal protection structure based on physical simulation. It takes into account the diversity of aircraft engine models and can accurately and quickly design the optimal shape of the template of the aircraft flexible thermal protection structure, adapt to the complex engine spatial swing trajectory, optimize the area of ​​the thermal protection structure graphic, reduce the phenomenon of fabric tension and pulling or fabric accumulation, improve the overall reliability of the thermal protection structure, and shorten the development cycle of the thermal protection structure.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A method for designing the shape of an aircraft flexible thermal protection structure based on physical simulation includes the following steps:

[0007] Based on the characteristic parameters of the installation interface of the aircraft's flexible thermal protection structure, curve fitting of the upper and lower boundaries is performed to construct a three-dimensional model of the flexible thermal protection structure's envelope space.

[0008] A plurality of equally spaced sampling points are sampled on the upper and lower curves in the three-dimensional model of the flexible heat-protective structure envelope space, and the sampling points closest to each other on the two curves are formed into sampling point pairs, which are connected to each other to form a plurality of connected strip-shaped quadrilateral surfaces;

[0009] splicing the strip-shaped four-sided curved surfaces onto the same plane to obtain a two-dimensional unfolded figure as the geometric unfolding initial shape of the envelope space curved surface;

[0010] According to the engine swing requirements, a swing simulation is performed on the three-dimensional model of the flexible thermal protection structure envelope space, and during the swing simulation, the position coordinates of each sampling point in the corresponding two-dimensional unfolded graph are recorded to obtain the distance variation range between all point pairs;

[0011] Treating each sampling point as a mass point, a massless spring with a non-zero natural length connecting the two interacting sampling points is set between the two sampling points to construct a spring-mass system. The spring connecting two adjacent sampling points on the same curve is a structural spring with a larger elastic coefficient, and the spring connecting two sampling points on different curves is a shear spring. The minimum length of the shear spring is the maximum distance between the corresponding point pairs during the swing simulation plus an additional design slack.

[0012] Calculate the force on each mass point in the spring mass system and update the position state until the net force on each mass point is zero and it is in equilibrium and no longer moves. Based on the position of each mass point at this time, the optimal geometric unfolding shape of the envelope space surface after adding looseness is obtained.

[0013] Furthermore, for each minimum quadrilateral ABCD in the spring-mass system, the spring between mass A and mass B and the spring between mass C and mass D are structural springs; the spring between mass A and mass C, the spring between mass B and mass C, and the spring between mass B and mass D are shear springs.

[0014] Furthermore, the force and position state update process of each mass point in the spring mass system is specifically as follows: calculating the elastic forces in all directions on each mass point to form the resultant force on each mass point; calculating the corresponding acceleration and position change based on the resultant force on the mass point; and continuously updating the force and position state of each mass point at each time step.

[0015] Furthermore, the elastic force between mass point i and mass point j connected by the shear spring in the spring-mass system is calculated as follows:

[0016]

[0017] f j =-f i

[0018] Where, f i is the elastic force on particle i, f j is the elastic force on particle j, x i is the position of particle i, |x ij |=|x j -x i |, is the distance between mass point i and mass point j; is the unit direction vector from mass point i to mass point j; l0 is the natural length of the spring, k s is the elastic constant of the spring.

[0019] Furthermore, the updated expressions for the position, velocity and acceleration of the particle are:

[0020]

[0021] Where, X t+1 is the position of the particle at time t+1, X t is the position of the particle at time t, X t-1 is the position of the particle at time t-1, a t is the acceleration of the particle at time t, Δt is the time step, F t is the net force of the particle at time t, m is the mass of the particle, V t is the velocity of the particle at time t, V t+1 is the velocity of the particle at time t+1, F t+1 is the net force of the particle at time t+1, a t+1 is the acceleration of the particle at time t+1.

[0022] Furthermore, the method uses a numerical integration calculation method to solve the force and position state of the particle.

[0023] Furthermore, the strip-shaped four-sided curved surfaces are spliced ​​onto the same plane, specifically:

[0024] Approximate each strip-shaped quadrilateral surface to a ruled surface, and sequentially splice each ruled surface onto the same plane to obtain a two-dimensional unfolded figure;

[0025] Alternatively, each strip of four-sided curved surface is triangulated along the diagonal line and converted into two triangular faces. The first triangle is selected, and the position and angle of each triangle are adjusted in turn, and they are spliced ​​to one side of the previous triangle so that all triangles fall on the same plane to obtain a two-dimensional unfolded figure.

[0026] Furthermore, the sampling process of the sampling point includes:

[0027] The same number of sampling points are sampled on the two curves respectively. The sampling method is to sample the two curves at equal distances, and then match the corresponding relationship between the sampling point pairs on the two curves based on the minimum and maximum distances between the sampling point pairs.

[0028] Alternatively, one of the curves is sampled at equal distances first, and then the nearest points of each sampling point on the other curve are taken as sampling points on the other curve.

[0029] Furthermore, the swing simulation process is to simulate the swing of any trajectory by simulating the rotation combination of one or more swing axes, and the corresponding swing forms include circular swing, square swing and / or simple pendulum.

[0030] The present invention also provides a design system based on the above-mentioned physical simulation-based design method for the shape of an aircraft flexible thermal protection structure, comprising:

[0031] An input unit, used to input characteristic parameters of an aircraft flexible thermal protection structure installation interface;

[0032] A construction unit, used to construct a three-dimensional model of the flexible thermal protection structure envelope space according to characteristic parameters of the aircraft flexible thermal protection structure;

[0033] A sampling unit is used to sample required sampling points on the interface curve of the constructed three-dimensional model of the flexible thermal protection structure envelope space;

[0034] A connection unit is used to sequentially connect the sampling points on each curve into a closed polyline segment connected end to end, and to connect the closest sampling points on two curves to form a strip-shaped four-sided surface;

[0035] The surface unfolding unit is used to split the strip-shaped four-sided surface into triangular surfaces, flatten them one by one and splice them onto the same plane to obtain a two-dimensional unfolded figure as the geometric unfolding initial shape of the envelope space surface;

[0036] A swing simulation unit is used to perform a swing simulation on the three-dimensional model of the flexible heat protection structure envelope space according to the engine swing requirement, and record the position coordinates of each sampling point in the corresponding two-dimensional unfolded graph during the swing simulation process to obtain the distance variation range between all point pairs;

[0037] Add units to add extra design flexibility;

[0038] The simulation deformation unit is used to treat each sampling point as a mass point, and set a massless spring with a non-zero natural length connecting the two sampling points between two adjacent sampling points to construct a spring-mass system. The spring connecting two adjacent sampling points on the same curve is a structural spring with a larger elastic coefficient, and the spring connecting two sampling points on different curves is a shear spring. The minimum length of the shear spring is the maximum distance between corresponding points during the swing simulation plus an additional design slack. The force on each mass point in the spring-mass system is calculated and the position state is updated until the resultant force on each mass point is zero and the mass point is in equilibrium and no longer moves. Based on the position of each mass point at this time, the optimal geometric unfolding shape of the envelope space surface after adding slack is obtained.

[0039] The display unit is used to output and display the optimal geometric unfolding shape of the envelope space surface obtained by the simulation deformation unit.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] (1) The present invention constructs a three-dimensional envelope space model based on the characteristic parameters of the installation interface of the aircraft flexible thermal protection structure, and performs a two-dimensional unfolding of the outer surface of the model by setting sampling points for uniform discretization of the surface; performs a swing simulation on the three-dimensional envelope space model according to the engine swing requirements, and records the distance variation range of each sampling point pair in the corresponding two-dimensional unfolding graph during the swing simulation process. This method can obtain the minimum length requirement of each sampling point pair in the envelope space surface of the aircraft flexible thermal protection structure;

[0042] Based on the above minimum length requirement, each sampling point on the flattened plane figure of the envelope space surface of the aircraft's flexible thermal protection structure is regarded as a mass point, and springs are set according to the interaction between the sampling points. For two adjacent sampling points on the same curve, a structural spring with a large elastic coefficient is used to keep its length relatively fixed during motion. For two sampling points on different curves, a shear spring that can be stretched or compressed with the motion of the mass point is used. The minimum length of the shear spring is set to the maximum distance between the corresponding point pairs during the swing simulation plus an additional design slack, so that it can meet the distance change requirements of each sampling point pair during the swing simulation. Finally, a numerical integration method is used to achieve the calculation and solution, resulting in a stable and area-optimized plane clipping figure.

[0043] (2) Accuracy: The present invention obtains the distance variation range of each sampling point pair on the plane through the swing simulation process, which serves as the minimum length constraint of the shear spring in the spring-mass system. The optimal plane cutting pattern finally obtained can prevent the occurrence of local tightness and oblique pulling, reduce the area and weight of the thermal soft skirt, have good follow-up adaptability and low additional damping, and ensure the accuracy and stability of the aircraft's flight attitude adjustment.

[0044] (3) Universal: The universal flexible thermal protection structure design method of the present invention has no requirements on the shape of the installation interface of the aircraft flexible thermal protection structure, can adapt to different models, effectively save design costs and improve design efficiency, reduce material consumption and cost expenditure, shorten the research and development cycle of the thermal protection structure, and respond to the cost reduction and efficiency improvement policy.

[0045] (4) Fast: This solution can be implemented by developing software. By inputting relevant parameters, the optimal expansion diagram of the heat protection structure can be obtained in a short time, and the design is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A schematic flow chart of a method for designing the shape of a flexible thermal protection structure of an aircraft based on physical simulation provided in an embodiment of the present invention;

[0047] Figure 2 A schematic diagram of the shape change process of the minimum unit of a heat protection structure of a spring-mass system constructed by physical simulation provided in an embodiment of the present invention;

[0048] Figure 3 A schematic diagram of a shear spring between a mass point and the mass points on the corresponding edges of a spring mass point system constructed through physical simulation provided in an embodiment of the present invention;

[0049] Figure 4 A schematic diagram of a shear spring formed between points on a curve provided in an embodiment of the present invention;

[0050] Figure 5 The figure is a schematic diagram of a framework of a physical simulation-based aircraft flexible thermal protection structure shape design system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0052] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0053] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0054] Example 1

[0055] like Figure 1 As shown, this embodiment provides a method for designing the shape of an aircraft flexible thermal protection structure based on physical simulation, comprising the following steps:

[0056] S1: Based on the characteristic parameters of the installation interface of the aircraft's flexible thermal protection structure, curve fitting of the upper and lower boundaries is performed to construct a three-dimensional model of the flexible thermal protection structure envelope space;

[0057] S2: Sample a number of equally spaced sampling points on the upper and lower curves in the three-dimensional model of the flexible thermal protection structure envelope space. The sampling points closest to each other on the two curves form sampling point pairs, which are then connected to form a number of connected strip-shaped quadrilateral surfaces.

[0058] S3: Splice the strip-shaped four-sided surfaces onto the same plane to obtain a two-dimensional unfolded figure, which serves as the initial geometric unfolding shape of the enveloping spatial surface;

[0059] S4: Based on the engine swing requirements, perform a swing simulation on the three-dimensional model of the flexible thermal protection structure envelope space. During the swing simulation, record the position coordinates of each sampling point in the corresponding two-dimensional unfolded graph to obtain the distance variation range between all point pairs.

[0060] S5: Consider each sampling point as a mass point, and set a massless spring with a non-zero natural length between two interacting sampling points to connect the two sampling points to construct a spring-mass system. The spring connecting two adjacent sampling points on the same curve is a structural spring with a larger elastic coefficient to keep the distance unchanged. The spring connecting two sampling points on different curves is a shear spring. The minimum length of the shear spring is the maximum distance between the corresponding point pairs during the swing simulation plus an additional design slack.

[0061] S6: Calculate the force on each mass point in the spring mass system and update the position state until the net force on each mass point is zero and the mass point is in equilibrium and no longer moves. Based on the position of each mass point at this time, the optimal geometric unfolding shape of the envelope space surface after adding looseness is obtained.

[0062] Each step is described in detail below.

[0063] In step S1, this embodiment specifically uses spline curves to fit the boundaries of relevant parts of the aircraft flexible thermal protection structure interface model, extracts characteristic parameters such as the curve coordinates, swing axis axis coordinates, swing axis vector, and swing angle at the aircraft pressure plate interface hole position, and constructs a three-dimensional model of the flexible thermal protection structure envelope space based on the flexible thermal protection structure interface model.

[0064] The curves of the flexible heat protection structure of the aircraft are: the hole position curve of the heat protection plate on the base connection side and the edge curve of the pressure plate on the support arm connection side.

[0065] In step S2, the sampling process of the sampling point includes:

[0066] The same number of sampling points are sampled on the two curves respectively; the sampling method is to sample the two curves at equal distances respectively, and then match the corresponding relationship of the point pairs based on the minimum and maximum distances between the sampling point pairs on the two curves.

[0067] Alternatively, one of the curves is sampled at equal distances first, and then the nearest points of each sampling point on the other curve are taken as sampling points on the other curve, and corresponding sampling point pairs are formed.

[0068] After the sampling of the sampling point pairs is completed, the three-dimensional model of the flexible thermal protection structure envelope space is expressed as several connected strip-shaped quadrilateral surfaces by connecting the sampling point pairs, and the triangular mesh discrete surface is constructed using the surface uniform discretization method.

[0069] In step S3, the strip-shaped four-sided curved surfaces are spliced ​​onto the same plane, specifically:

[0070] Approximate each strip-shaped quadrilateral surface to a ruled surface, and sequentially splice each ruled surface onto the same plane to obtain a two-dimensional unfolded figure;

[0071] If unfolding to a ruled surface is not possible, each strip of four-sided surfaces is triangulated along its diagonal lines, transforming it into a mesh surface consisting of two tightly connected triangles. The first triangle is selected from the mesh surface and unfolded onto a plane without deformation. Based on the initial unfolded triangle, the positions and angles of the triangles are adjusted, and each triangle is sequentially spliced ​​next to the previous one, ensuring that all triangles fall on the same plane. This is done until the entire surface is unfolded onto the plane. The resulting two-dimensional unfolded shape is used as the initial geometric unfolding shape for the enveloping spatial surface.

[0072] In step S4, various swing forms such as circular swing, square swing, and simple pendulum are simulated according to the engine swing requirements, and swing simulation is performed. During this process, the shape of the two-dimensional unfolded graph of the envelope space surface changes accordingly. The position coordinates of each sampling point on the two-dimensional unfolded graph at each moment are recorded, and the lengths between all point pairs are calculated to obtain the length constraints between the point pairs.

[0073] In step S5, the process of performing physical simulation to construct the spring-mass system is specifically as follows:

[0074] The sampling points on the two-dimensional unfolded graph are considered particle points. Between each sampling point, there exists a massless spring with a non-zero natural length that is interconnected. The parameters of the mass points and springs are set to construct a spring-mass system. The springs are differentiated: Structural springs with large elastic coefficients are set between adjacent sampling points on the same curve, keeping their lengths relatively fixed during motion. Springs between sampling points on different curves are shear springs. In the spring-mass system, they stretch or compress as the mass points move. The maximum length between the pair of points is taken as the minimum length of the spring at that location. When the spring reaches its minimum length, a reaction force is applied to release the compression.

[0075] The minimum length of the shear spring is the maximum distance between corresponding point pairs during the swing simulation plus an additional design slack. The additional design slack is defined and input by the user to ensure that the flexible thermal protection structure still has a certain safety margin when the engine swings to the extreme position.

[0076] Specifically, if Figure 2 As shown, for each minimum quadrilateral ABCD in the spring-mass system, the spring between mass A and mass B and the spring between mass C and mass D are structural springs with large elastic coefficients and constant lengths; the spring between mass A and mass C, the spring between mass A and mass D, the spring between mass B and mass C, and the spring between mass B and mass D are shear springs, which will exert a certain elastic force on the masses and stretch or compress as the masses move until they stabilize.

[0077] like Figure 3 The figure shows a schematic diagram of the shear spring formed by a point on the outer curve and the points on the inner curve.

[0078] like Figure 4 The figure shows the shear spring formed between the points on the curve.

[0079] In step S6, the force and position state of each mass point are preferably solved using a numerical integration calculation method, and the specific process is as follows:

[0080] Based on the initial two-dimensional unfolded figure, the spring length does not meet the constraint conditions at this time, so there is an elastic force between the particles, causing the particles to move outward.

[0081] The elastic force of the spring obeys Hooke's law. The elastic force between mass i and mass j can be expressed as:

[0082]

[0083] fj =-f s (x i ,x j )=-f i

[0084] Where, f i is the elastic force on particle i, f j is the elastic force on particle j, x i is the position of particle i, |x ij |=|x j -x i |, is the distance between mass point i and mass point j; is the unit direction vector from mass point i to mass point j; l0 is the natural length of the spring, that is, the original length between mass point i and mass point j, k s is the elastic constant of the spring.

[0085] The particle is subjected to elastic forces in multiple directions, forming a net force F. According to Newton's second law, the acceleration of an object is proportional to the net force acting on the object:

[0086] F=ma

[0087] Therefore, acceleration a = 1 / m*F, and the magnitude of the acceleration determines the magnitude of the velocity. It is known that:

[0088]

[0089] but,

[0090] V t =V0+at

[0091] This solution takes the Verlet integration method as an example. The Verlet integration method uses the state of the previous moment to infer the state of the next moment:

[0092]

[0093] Where, X t+1 is the position of the particle at time t+1, X t is the position of the particle at time t, X t-1 is the position of the particle at time t-1, a t is the acceleration of the particle at time t, Δt is the time step, F t is the net force of the particle at time t, m is the mass of the particle, V t is the velocity of the particle at time t, V t+1 is the velocity of the particle at time t+1, F t+1 is the net force of the particle at time t+1, a t+1 is the acceleration of the particle at time t+1.

[0094] According to each time step, the force on the mass point is calculated, the state of the mass point, such as velocity, acceleration, position, etc., is updated, and the spring length at each step is calculated.

[0095] When all spring lengths meet the constraints, the net force on the mass point is zero, the mass point is in equilibrium and no longer moves, the two-dimensional unfolded figure gradually stabilizes, and finally forms a stable and optimal area plane clipping figure.

[0096] like Figure 5 As shown, this embodiment further provides a design system based on the above-mentioned physical simulation-based design method for the shape of an aircraft flexible thermal protection structure, including:

[0097] An input unit, used to input characteristic parameters of an aircraft flexible thermal protection structure installation interface;

[0098] A construction unit, used to construct a three-dimensional model of the flexible thermal protection structure envelope space according to characteristic parameters of the aircraft flexible thermal protection structure;

[0099] A sampling unit is used to sample required sampling points on the interface curve of the constructed three-dimensional model of the flexible thermal protection structure envelope space;

[0100] A connection unit is used to sequentially connect the sampling points on each curve into a closed polyline segment connected end to end, and to connect the closest sampling points on two curves to form a strip-shaped four-sided surface;

[0101] The surface unfolding unit is used to split the strip-shaped four-sided surface into triangular surfaces, flatten them one by one and splice them onto the same plane to obtain a two-dimensional unfolded figure as the geometric unfolding initial shape of the envelope space surface;

[0102] The swing simulation unit is used to perform swing simulation on the three-dimensional model of the flexible thermal protection structure envelope space according to the engine swing requirements, and record the position coordinates of each sampling point in the corresponding two-dimensional unfolded graph during the swing simulation process to obtain the distance variation range between all point pairs;

[0103] Add units to add extra design flexibility;

[0104] The simulation deformation unit is used to treat each sampling point as a mass point, and set a massless spring with a non-zero natural length connecting the two sampling points between two adjacent sampling points to construct a spring-mass system. The spring connecting two adjacent sampling points on the same curve is a structural spring with a larger elastic coefficient, and the spring connecting two sampling points on different curves is a shear spring. The minimum length of the shear spring is the maximum distance between corresponding point pairs during the swing simulation plus the design slack of the added unit. The force on each mass point in the spring-mass system is calculated and the position state is updated until the resultant force on each mass point is zero and the mass point is in a state of equilibrium and no longer moves. Based on the position of each mass point at this time, the optimal geometric unfolding shape of the envelope space surface after adding slack is obtained.

[0105] The display unit is used to output and display the optimal geometric unfolding shape of the envelope space surface obtained by the simulation deformation unit.

[0106] It should be noted that the specific content and beneficial effects of the system of this application can be found in the above-mentioned method embodiment and will not be repeated here.

[0107] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for designing the shape of an aircraft flexible thermal protection structure based on physical simulation, characterized in that: The following steps are involved: Based on the characteristic parameters of the installation interface of the aircraft's flexible thermal protection structure, curve fitting of the upper and lower boundaries is performed to construct a three-dimensional model of the flexible thermal protection structure's envelope space. A plurality of equally spaced sampling points are sampled on the upper and lower curves in the three-dimensional model of the flexible heat-protective structure envelope space, and the sampling points closest to each other on the two curves are formed into sampling point pairs, which are connected to each other to form a plurality of connected strip-shaped quadrilateral surfaces; splicing the strip-shaped four-sided curved surfaces onto the same plane to obtain a two-dimensional unfolded figure as the geometric unfolding initial shape of the envelope space curved surface; According to the engine swing requirements, a swing simulation is performed on the three-dimensional model of the flexible thermal protection structure envelope space, and during the swing simulation, the position coordinates of each sampling point in the corresponding two-dimensional unfolded graph are recorded to obtain the distance variation range between all point pairs; Treating each sampling point as a mass point, a massless spring with a non-zero natural length connecting the two interacting sampling points is set between the two sampling points to construct a spring-mass system. The spring connecting two adjacent sampling points on the same curve is a structural spring with a large elastic coefficient to keep the distance constant. The spring connecting two sampling points on different curves is a shear spring. The minimum length of the shear spring is the maximum distance between the corresponding point pairs during the swing simulation plus an additional design slack. Calculate the force on each mass point in the spring mass system and update the position state until the net force on each mass point is zero and it is in equilibrium and no longer moves. Based on the position of each mass point at this time, the optimal geometric unfolding shape of the envelope space surface after adding looseness is obtained.

2. The method for designing the shape of an aircraft flexible thermal protection structure based on physical simulation according to claim 1, characterized in that: For each minimum quadrilateral ABCD in the spring-mass system, the spring between mass A and mass B and the spring between mass C and mass D are structural springs; the spring between mass A and mass C, the spring between mass A and mass D, the spring between mass B and mass C, and the spring between mass B and mass D are shear springs.

3. The method for designing the shape of an aircraft flexible thermal protection structure based on physical simulation according to claim 1, characterized in that: The force and position state updating process of each mass point in the spring mass system is specifically as follows: calculating the elastic forces in all directions on each mass point to form the resultant force on each mass point; calculating the corresponding acceleration, velocity and displacement based on the resultant force on the mass point; and continuously updating the force and position state of each mass point at each time step.

4. The method for designing the shape of an aircraft flexible thermal protection structure based on physical simulation according to claim 3, characterized in that: The calculation expression of the elastic force between mass point i and mass point j connected by the shear spring in the spring-mass system is: f j =-f i Where, f i is the elastic force on particle i, f j is the elastic force on particle j, x i is the position of particle i, |x ij |=|x j -x i |, is the distance between mass point i and mass point j; is the unit direction vector from mass point i to mass point j; l0 is the natural length of the spring, k s is the elastic constant of the spring.

5. The method for designing the shape of an aircraft flexible thermal protection structure based on physical simulation according to claim 3, characterized in that: The updated expressions for the position, velocity and acceleration of the particle are: Where, X t+1 is the position of the particle at time t+1, X t is the position of the particle at time t, X t-1 is the position of the particle at time t-1, a t is the acceleration of the particle at time t, Δt is the time step, F t is the net force of the particle at time t, m is the mass of the particle, V t is the velocity of the particle at time t, V t+1 is the velocity of the particle at time t+1, F t+1 is the net force of the particle at time t+1, a t+1 is the acceleration of the particle at time t+1.

6. The method for designing the shape of an aircraft flexible thermal protection structure based on physical simulation according to claim 1, characterized in that: The method adopts a numerical integration calculation method to solve the force and position state of the particle.

7. The method for designing the shape of an aircraft flexible thermal protection structure based on physical simulation according to claim 1, characterized in that: Flatten the strip-shaped four-sided curved surfaces and splice them onto the same plane, specifically: Approximate each strip-shaped quadrilateral surface to a ruled surface, and sequentially splice each ruled surface onto the same plane to obtain a two-dimensional unfolded figure; Alternatively, each strip of four-sided curved surface is triangulated along the diagonal line and converted into two triangular faces. The first triangle is selected, and the position and angle of each triangle are adjusted in turn, and they are spliced ​​to one side of the previous triangle so that all triangles fall on the same plane to obtain a two-dimensional unfolded figure.

8. The method for designing the shape of an aircraft flexible thermal protection structure based on physical simulation according to claim 1, characterized in that: The sampling process of the sampling point includes: The same number of sampling points are sampled on the two curves respectively. The sampling method is to sample the two curves at equal distances, and then match the corresponding relationship between the sampling point pairs on the two curves based on the minimum and maximum distances between the sampling point pairs. Alternatively, one of the curves is sampled at equal distances first, and then the nearest points of each sampling point on the other curve are taken as sampling points on the other curve.

9. The method for designing the shape of an aircraft flexible thermal protection structure based on physical simulation according to claim 1, characterized in that: The swing simulation process simulates the rotation combination of one or more swing axes to perform simulated swing of any trajectory, and the corresponding swing forms include circular swing, square swing and / or simple pendulum.

10. A design system based on the aircraft flexible thermal protection structure shape design method based on physical simulation according to any one of claims 1 to 9, characterized in that: include: An input unit, used to input characteristic parameters of an aircraft flexible thermal protection structure installation interface; A construction unit, used to construct a three-dimensional model of the flexible thermal protection structure envelope space according to characteristic parameters of the aircraft flexible thermal protection structure; A sampling unit is used to sample required sampling points on the interface curve of the constructed three-dimensional model of the flexible thermal protection structure envelope space; A connection unit is used to sequentially connect the sampling points on each curve into a closed polyline segment connected end to end, and to connect the closest sampling points on two curves to form a strip-shaped four-sided surface; The surface unfolding unit is used to split the strip-shaped four-sided surface into triangular surfaces, flatten them one by one and splice them onto the same plane to obtain a two-dimensional unfolded figure as the geometric unfolding initial shape of the envelope space surface; A swing simulation unit is used to perform a swing simulation on the three-dimensional model of the flexible heat protection structure envelope space according to the engine swing requirement, and record the position coordinates of each sampling point in the corresponding two-dimensional unfolded graph during the swing simulation process to obtain the distance variation range between all point pairs; Add units to add extra design slack; The simulation deformation unit is used to treat each sampling point as a mass point, and set a massless spring with a non-zero natural length connecting the two sampling points between two adjacent sampling points to construct a spring-mass system. The spring connecting two adjacent sampling points on the same curve is a structural spring with a larger elastic coefficient, and the spring connecting two sampling points on different curves is a shear spring. The minimum length of the shear spring is the maximum distance between corresponding point pairs during the swing simulation plus the design slack of the added unit. The force on each mass point in the spring-mass system is calculated and the position state is updated until the resultant force on each mass point is zero and the mass point is in a state of equilibrium and no longer moves. Based on the position of each mass point at this time, the optimal geometric unfolding shape of the envelope space surface after adding slack is obtained. The display unit is used to output and display the optimal geometric unfolding shape of the envelope space surface obtained by the simulation deformation unit.

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