Helicopter pneumatic surface non-uniformly distributed load fine loading method

Abstract

The invention belongs to the technical field of structural strength design in a helicopter development stage, and particularly relates to a refined loading method for non-uniformly distributed loads of a helicopter pneumatic surface. By means of the method, the evenly-distributed aerodynamic loads of the helicopter can be accurately and rapidly distributed and applied to finite element nodes, then full-helicopter balance load calculation and finite element model load loading are conducted, and input is provided for structural strength design of the helicopter. According to the method, the non-uniform pneumatic distribution load is accurately loaded and refined to each unit area under the condition that the loading efficiency is not influenced, and the whole-aircraft inertia balance load calculation is efficiently completed through mass distribution and finite element node load, so that the loading efficiency and accuracy of the load are improved.

Description

Technical Field

[0001] This invention belongs to the field of structural strength design technology in the helicopter development stage, and specifically relates to a method for finely loading non-uniformly distributed loads on the aerodynamic surfaces of a helicopter. Background Technology

[0002] During helicopter flight, the fuselage surface is typically subjected to non-uniform aerodynamic loads. In the design phase, these aerodynamic loads are usually calculated by load specialists through simulation and provided to strength specialists as load inputs in the form of pressure coefficients at each aerodynamic mesh point. Strength specialists then simulate and apply these loads to the nodes of the finite element model during the finite element method (FEM) preprocessing. However, the fuselage has millions of aerodynamic mesh points, and their locations do not correspond to the finite element mesh nodes in the overall aircraft FEM model. Therefore, applying the non-uniformly distributed aerodynamic loads to the finite element nodes is a very tedious but crucial task, directly impacting the computational accuracy and efficiency of the overall aircraft model.

[0003] Currently, finite element analysis software widely used in the aerospace industry, such as PATRAN / NASTRAN, while providing powerful finite element analysis calculation capabilities, cannot automatically apply loads to non-uniformly distributed surface loads. Although PATRAN software offers the ability to directly import aerodynamic pressure, this method has two drawbacks: firstly, when the mesh size is large, the load may be lost when importing pressure using PATRAN's Field function; secondly, the pressure imported using PATRAN's Field function cannot generate external loads for finite element nodes, which is incompatible with the loading process of helicopter finite element models. Manually loading finite element nodes or elements one by one cannot meet the needs of actual engineering design, because helicopter structural strength design involves numerous load cases, and the number of nodes in the finite element detailed model is extremely large. Loading elements or nodes one by one severely affects the efficiency and quality of load application. Therefore, in engineering, for ease of loading, non-uniformly distributed loads are usually approximated as several concentrated forces, which improves efficiency but introduces significant errors. Summary of the Invention

[0004] Purpose of the invention: To provide a method for finely applying non-uniformly distributed aerodynamic loads on helicopter aerodynamic surfaces. This method can accurately and quickly distribute uniformly distributed aerodynamic loads on the helicopter to the finite element nodes, and then perform full-aircraft balance load calculation and finite element model load loading, providing input for helicopter structural strength design.

[0005] To address the aforementioned technical issues, according to a first aspect of the present invention, a method for finely applying non-uniformly distributed loads on helicopter aerodynamic surfaces is proposed, specifically comprising the following steps: Step 1: Obtain aerodynamic non-uniform load data for helicopter aerodynamic surfaces. The aerodynamic non-uniform load data includes the aerodynamic node number, aerodynamic node coordinates, and corresponding loads. Step 2: Obtain the finite element element division of the helicopter's aerodynamic surfaces and the mesh node data of each finite element element; Step 3: Based on the principle of proximity, find the finite element closest to each aerodynamic node and use it as the load distribution element; Step 4: Using the load distribution method, the corresponding load of the aerodynamic node is distributed to the grid nodes of the load distribution unit to ensure that the force and torque of each load distribution unit after distribution are in balance.

[0006] In one possible embodiment, in step three, it is assumed that the pneumatic node is Point0 ( x p ,y p ,z p ), the centroid of the finite element is Node0 ( x n ,y n ,z n If we calculate the distance between Point0 and Node0, we can find the finite element with the smallest distance and use it as the load distribution element.

[0007] In one possible embodiment, the specific process of solving the distance between Point0 and Node0 includes: .

[0008] In one possible embodiment, step four specifically includes the following steps: 1) Force distribution. Assume the load corresponding to a certain aerodynamic node is... The corresponding load distribution unit nodes are Node1, Node2, ..., Nodem, where m Let be the number of nodes. Then, the load obtained by each node of this load distribution unit from the force distribution is:

[0009] 2) Torque Distribution. After the aerodynamic nodal forces are evenly distributed to the finite element nodes, additional unbalanced torques will be generated, which need to be counteracted again by the nodal forces. The specific distribution process is as follows: Assume the distance from the aerodynamic node to the centroid of the finite element is The magnitude of the resultant torque at the centroid is , among them for and The angle between directions, Direction from direction and The direction is determined by the right-hand rule; calculate the inertia tensor matrix of the corresponding load distribution element: In the formula , The remaining components can be represented by their subscripts; in the formula , , Let x, y, and z represent the x-axis, y-axis, and z-axis coordinates of the i-th node of the element; solve for the eigenvectors of the above inertia tensor matrix to obtain three eigenvectors; the three axes along the directions of the three eigenvectors and passing through the centroid are the three principal axes of inertia. , , The resultant moment at the centroid is decomposed into moments along the three principal axes of inertia, calculated using the following formulas:

[0010] In the formula, , , They are respectively direction and , , The angle between directions; , and The sizes are respectively the main axis , , Torque on; The torques along each principal axis of inertia are decomposed into forces at each node of the finite element method, and the calculation formulas are as follows: , ,

[0011] In the formula , , Indicates torque , , The force distributed to node i; For node i to the principal axis of inertia The vertical distance. The force distribution result is summed with the torque distribution results of the three principal inertial axes to obtain the force at the element node; Based on the above steps, all external loads applied to the finite element nodes can be obtained.

[0012] In one possible embodiment, the method further includes step five: acquiring the overall mass distribution data, which includes the coordinates of mass points and their corresponding masses; and calculating the inertial force of each mass point based on the finite element nodal loads of the allocated loads and the coordinates and corresponding masses of the mass points obtained in step four.

[0013] In one possible embodiment, step five specifically includes the calculation of the inertial forces of all mass points: Assumption , , For load F i Along x, y, z The load components in the directional direction are concentrated at the center of gravity of the entire machine in a statically equivalent manner, as follows:

[0014]

[0015] , , Along the center of gravity x, y, z Directional coordinates , , For the first i The load application point along x、 y, z Directional coordinates , , For the first i The load application point along x, y, z Torque in direction, , , Along the center of gravity x, y, z Directional force, , , Along the center of gravity x, y, z Torque in direction; Calculating the inertial force generated by the distributed mass: When calculating the overall inertial balance load of the aircraft, the loads of the aircraft include not only active external loads (such as flight, landing, ship landing, water landing, etc.), but also the inertial force generated by the distributed mass of the entire aircraft; the steps for calculating the inertial force are as follows: 1) Sum of all mass points: ,in m For total mass, m j For the first j The quality of each quality point n (Number of quality points); 2) Calculate the coordinates of the centroid:

[0016] In the formula x c、 y c、 z c The center of gravity x, y, z coordinate, x cj、 y cj、 z cj The first j mass point x, y, z coordinate; 3) Calculate the moment of inertia of all mass points: No. j The formulas for calculating the moment of inertia and product of inertia of a point mass relative to the center of gravity are as follows: Moment of inertia:

[0017]

[0018]

[0019] Product of inertia:

[0020]

[0021]

[0022] Total moment of inertia of the structure: , ,

[0023] , ,

[0024] 4) Calculate the overload at the center of gravity: The formula for calculating translational overload is:

[0025] In the formula ，n xc , n yc、 n zc Center of gravity x, y, z Directional overload,g It is the acceleration due to gravity; Rotational acceleration is calculated using the following set of equations:

[0026] in , , They are respectively around the center of gravity x, y, z Overload of shaft rotation.

[0027] 5) Calculate the overload and inertial load at each mass point. The overload calculation formulas for each mass point are as follows:

[0028] The formula for calculating the inertial force at each mass point is:

[0029] The formula for calculating the moment of inertia at each mass point is: .

[0030] Establishing the equilibrium equations: According to d'Alembert's principle, for the helicopter to achieve formal equilibrium, an inertial force must be applied to it. The direction of the inertial force is opposite to the direction of acceleration, and its magnitude is equal to the mass of the object under study multiplied by the corresponding acceleration, i.e. Therefore, the following equilibrium equation can be obtained:

[0031] Solving the above equations yields the overload at each mass point. n xi , n yi 、n zi Based on the above formula for calculating inertial force, the inertial force at each mass point can be further obtained.

[0032] According to a second aspect of the present invention, a computer-readable storage medium is provided, wherein a program or instructions are stored therein, and when the program or instructions are executed, the loading method described above is implemented.

[0033] According to a third aspect of the present invention, a computer program product is provided, wherein a program or instructions are stored therein, and when the program or instructions are run, the above-described loading method is implemented.

[0034] In summary, the beneficial effects of the present invention are as follows: This paper presents a refined loading method for non-uniformly distributed aerodynamic loads on helicopter aerodynamic surfaces. It ensures accurate loading of non-uniformly distributed aerodynamic loads without compromising loading efficiency, refining the loading to each individual element region. Furthermore, by utilizing mass distribution and finite element nodal loads, it efficiently calculates the overall aircraft inertial balance load, thereby improving both loading efficiency and accuracy. Attached Figure Description

[0035] Figure 1 This is a flowchart of a preferred embodiment of the present invention; Figure 2 This is a schematic diagram of the aerodynamic non-uniform load distribution in step one of the preferred embodiments of the present invention; Figure 3 This is a schematic diagram of the finite element division of the helicopter aerodynamic surface in step two of the preferred embodiment of the present invention; Figure 4 This is a schematic diagram of the finite element mesh node of the aerodynamic node in step three of the preferred embodiment of the present invention; Figure 5 This is a schematic diagram of load distribution in step four of a preferred embodiment of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setups and methods set forth below, but covers any improvements, substitutions, and modifications to structures, methods, and devices without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description to avoid unnecessarily obscuring the invention.

[0038] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] Example 1 like Figure 1 As shown, a method for fine-grained loading of non-uniformly distributed loads on the aerodynamic surface of a helicopter includes the following steps: [1] Import aerodynamic non-uniform load data. The helicopter's non-uniform aerodynamic loads act on the structural surface, such as... Figure 2 Skin aerodynamic loads. Aerodynamic non-uniform load data includes node numbers, node coordinates, and pressure coefficients, in *.txt or *xlsx format, as shown in Table 1.

[0040] Table 1. Aerodynamic load input format

[0041] [2] Import finite element and node data. In the full-machine finite element model, the structural surface is generally simulated using three-node or four-node shell elements. Each element consists of three or four nodes, such as... Figure 3 As shown in Tables 2 and 3, the information used in the finite element model, including element and node data, is in *.txt or *xlsx format.

[0042] Table 2 Finite element information

[0043] Table 3 Finite element node information

[0044] [3] Import the mass and centroid coordinates of each mass point, as shown in Table 4.

[0045] Table 4 Quality Point Information

[0046] [4] Use the proximity principle to find the element closest to the aerodynamic node, such as Figure 4 As shown. Assuming the aerodynamic node is Point0, the finite element type is a quadrilateral element with four nodes: Node1, Node2, Node3, and Node4, and the centroid of the element is Node0, then the distance between Point0 and Node0 is calculated to find the element with the smallest distance.

[0047] [5] According to step four, the load distribution method is used to distribute the aerodynamic node loads in Table 1 to the finite element nodes in Table 3 to obtain the external loads of each finite element node, and it is necessary to ensure that the force and torque are balanced after distribution.

[0048] [6] According to step five, the external loads of each node of the finite element are equivalent to the center of gravity to obtain the resultant force and resultant moment at the center of gravity.

[0049] [7] Based on the mass point information in Table 4 and the calculation formula in step 5, the inertial force generated by the distributed mass is obtained.

[0050] [8] The obtained finite element nodal external loads and inertial forces at each mass point were applied to the finite element model using the software PATRAN. The specific implementation process is as follows: 1) Finite element nodal load loading: Based on the finite element nodal loads and corresponding node numbers obtained in step four, create a load loading command for the creation point *.ses, save it as a .ses file, click session in PATRAN, play, select the .ses file, and the load will be automatically loaded into the finite element model.

[0051] 2) Inertial force loading: Create points based on the coordinates of the mass points. Save the point creation command (ses) as a .ses file. In PATRAN, click session, play, and select the .ses file. This will automatically create the mass point coordinates and groups, and place the Nodes to be associated with each mass point into their corresponding groups. Then, use RBE3 to distribute the corresponding inertial loads to the associated Nodes. For example... Figure 5 As shown, the inertial force acts at Point0, and the associated finite element nodes are Node1 to Node5. The inertial force at Point0 is distributed to nodes Node1 to Node5 through RBE3.

Claims

1. A method for finely applying non-uniformly distributed loads on the aerodynamic surfaces of a helicopter, characterized in that, Specifically, the steps are as follows: Step 1: Obtain aerodynamic non-uniform load data for the helicopter's aerodynamic surfaces, including aerodynamic node numbers, aerodynamic node coordinates, and corresponding loads; Step 2: Obtain the finite element element division of the helicopter's aerodynamic surfaces and the mesh node data of each finite element element; Step 3: Find the finite element closest to each aerodynamic node according to the proximity principle, and use it as the load distribution unit; Step 4: Use the load distribution method to distribute the corresponding loads of the aerodynamic nodes to the mesh nodes of the load distribution unit, ensuring that the force and torque of each load distribution unit after distribution are in balance.

2. The method for fine-grained loading of non-uniformly distributed loads on helicopter aerodynamic surfaces according to claim 1, characterized in that: In step three, assume the aerodynamic node is Point0 ( x p ,y p ,z p ), the centroid of the finite element is Node0 ( x n ,y n , z n If we calculate the distance between Point0 and Node0, we can find the finite element with the smallest distance and use it as the load distribution element.

3. The method for fine-grained loading of non-uniformly distributed loads on helicopter aerodynamic surfaces according to claim 2, characterized in that: The distance between Point0 and Node0 can be calculated using the following formula: 。 4. The method for fine-grained loading of non-uniformly distributed loads on helicopter aerodynamic surfaces according to claim 1, characterized in that: Step four specifically includes the following steps: Based on the number of grid nodes in the load distribution unit, the loads corresponding to the aerodynamic nodes are assigned. Distribute evenly among the grid nodes; The additional torque is countered by nodal forces, and the specific distribution process is as follows: Assume the distance from the aerodynamic node to the centroid of the load distribution unit is The magnitude of the resultant moment at the centroid is , among them for and The angle between directions, Direction from direction and The right-hand rule determines the direction; Calculate the inertia tensor matrix of the corresponding load distribution element: In the formula , The remaining components can be represented by their subscripts; in the formula , , Let x, y, and z represent the x-axis, y-axis, and z-axis coordinates of the i-th node of the element; solve for the eigenvectors of the above inertia tensor matrix to obtain three eigenvectors; the three axes along the directions of the three eigenvectors and passing through the centroid are the three principal axes of inertia. , , The resultant moment at the centroid is decomposed into moments along the three principal axes of inertia, and the calculation formulas are as follows: In the formula, , , They are respectively direction and , , The angle between directions; , and The sizes are respectively the main axis , , Torque on; The torques along each principal axis of inertia are decomposed into forces at each node of the finite element method, and the calculation formulas are as follows: ， ， In the formula , , Indicates torque , , The force distributed to node i; For node i to the principal axis of inertia The vertical distance. The force distribution result is summed with the torque distribution results of the three principal inertial axes to obtain the force at the element node; Based on the above steps, all external loads applied to the finite element nodes can be obtained.

5. The method for fine-grained loading of non-uniformly distributed loads on helicopter aerodynamic surfaces according to claim 1, characterized in that: The method further includes step five: obtaining the mass distribution data of the entire machine, the mass distribution data including the coordinates of mass points and their corresponding masses, and calculating the inertial force of each mass point based on the finite element nodal loads of the allocated loads and the coordinates and corresponding masses of the mass points obtained in step four.

6. The method for fine-grained loading of non-uniformly distributed loads on the aerodynamic surface of a helicopter according to claim 1, characterized in that: In step five, the calculation process for the inertial force of all mass points specifically includes: Assumption , , For load F i Along x, y, z The load components in the directional direction are concentrated at the center of gravity of the entire machine in a statically equivalent manner, as follows: , , Along the center of gravity x, y, z Directional coordinates , , For the first i The load application point along x, y, z Directional coordinates , , For the first i The load application point along x, y, z Torque in direction, , , Along the center of gravity x, y, z Directional force, , , Along the center of gravity x, y, z Torque in a direction.

7. The method for fine-grained loading of non-uniformly distributed loads on helicopter aerodynamic surfaces according to claim 1, characterized in that: In step five, the inertial force generated by the distributed mass is calculated. The calculation steps are as follows: 1) Sum of all mass points: ,in m For total mass, m j For the first j The quality of each quality point n The number of quality points; 2) Calculate the coordinates of the centroid: In the formula x c、 y c、 z c The center of gravity x, y, z coordinate, x cj、 y cj、 z cj The first j mass point x, y, z coordinate; 3) Calculate the moment of inertia of all mass points: No. j The formulas for calculating the moment of inertia and product of inertia of a point mass relative to the center of gravity are as follows: Moment of inertia: Product of inertia: Total moment of inertia of the structure: ， ， ， ， 4) Calculate the overload at the center of gravity: The formula for calculating translational overload is: In the formula ，n xc , n yc、 n zc Center of gravity x, y, z Directional overload, g It is the acceleration due to gravity; Rotational acceleration is calculated using the following set of equations: in , , They are respectively around the center of gravity x, y, z Shaft rotational overload; 5) Calculate the overload and inertial load at each mass point. The overload calculation formulas for each mass point are as follows: The formula for calculating the inertial force at each mass point is: The formula for calculating the moment of inertia at each mass point is: 。 8. The method for fine-grained loading of non-uniformly distributed loads on helicopter aerodynamic surfaces according to claim 7, characterized in that: In step five, according to d'Alembert's principle, for the helicopter to achieve formal equilibrium, an inertial force must be applied to it; the direction of the inertial force is opposite to the direction of acceleration, and its magnitude is equal to the mass of the object under study multiplied by the corresponding acceleration, i.e. ; This leads to the following equilibrium equation: Solving the above equations yields the overload at each mass point. n xi , n yi 、n zi and the inertial forces at each mass point.

9. A computer-readable storage medium, characterized in that, The storage medium stores a program or instructions, which, when executed, implement the loading method according to any one of claims 1-8.

10. A computer program product, characterized in that, The computer program product stores a program or instructions, which, when executed, implement the loading method according to any one of claims 1-8.

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