Dynamic load static equivalent coefficient determination method and structural parameter design method

Abstract

The invention belongs to the field of airplane structure dynamic strength design, and particularly relates to a dynamic load static equivalent coefficient determination method and a structure parameter design method.The method comprises the steps that S1, a relation curve of a water pressure load at the bottom of an airplane body and a time history is obtained according to a water forced landing dynamic load measurement test, and the peak value Ps of the water pressure load is determined according to the relation curve; s2, carrying out a fuselage bottom elastic model water forced landing test, and determining critical failure parameters of an elastic structure; s3, performing a static mechanical property test according to the critical failure parameters of the elastic structure to obtain the maximum static pressure Pd which can be borne by the elastic structure; and S4, calculating the static equivalent coefficient of the dynamic load of the forced landing on the water. The static equivalent coefficient of the dynamic load of the water pressure of the forced landing on the water is obtained through a scale model test. The objective of the invention is to solve the problem of lack of design load in airplane water forced landing performance design.

Description

Technical Field

[0001] The present application belongs to the field of aircraft structure dynamic strength design, and in particular relates to a method for determining a static equivalent coefficient of a dynamic load and a method for designing structural parameters. Background Art

[0002] The water pressure load on the bottom of the aircraft fuselage during forced landing is an impact dynamic load. If the peak value of the impact dynamic load during forced landing is used as the design input for the structural design, it will be very conservative. If the peak load is used as the design load for the damage source of the aircraft floatation test, it will not truly reflect the floatation performance of the aircraft. Summary of the invention

[0003] In order to solve the above problems, the present application provides a method for determining the static equivalent coefficient of the dynamic load of an aircraft forced landing on water, comprising:

[0004] Step S1: According to the forced landing dynamic load measurement test, obtain the relationship curve between the water pressure load at the bottom of the aircraft fuselage and the time history, and determine the peak value Ps of the water pressure load according to the relationship curve

[0005] Step S2: performing a forced landing test on the fuselage bottom elastic model to determine the critical failure parameters of the elastic structure;

[0006] Step S3: Perform static mechanical performance test with critical failure parameters of the elastic structure to obtain the maximum static pressure P that the elastic structure can withstand. d ;

[0007] Step S4: Calculate the static equivalent coefficient of the ditching dynamic load.

[0008] Preferably, the experimental site for the forced landing dynamic load measurement test is a towing pool or an open water pool, and the test model is a rigid pressure measurement model.

[0009] Preferably, the test model of the ditching test of the fuselage bottom elastic model is a rigid model, and the fuselage bottom is an elastic model.

[0010] Preferably, the elastic model of the fuselage bottom specifically includes: the ultimate strength of the skin material is less than that of the fuselage stringers, the skin material includes multiple layers of fiber paper, and the critical failure parameter is determined according to the fiber paper layer parameters and failure form of the skin after the test.

[0011] Preferably, the critical failure parameters include: skin thickness and skeleton stiffness.

[0012] Preferably, the most severely loaded part of the test model for the forced landing dynamic load measurement test is replaced with an elastic model based on the relationship curve and the most severely loaded part is determined, and a forced landing test of the fuselage bottom elastic model is carried out.

[0013] Preferably, the formula for calculating the static equivalent coefficient of the ditching dynamic load is:

[0014] η=P s / P d .

[0015] Preferably, the skin of the elastic model of the bottom of the fuselage is formed by coating waterproof, shape-enclosable multi-layer fiber paper with an organic solvent, and the thickness of the skin is adjusted by adjusting the number of layers of the fiber paper and the number of times the organic solvent is coated.

[0016] An aircraft fuselage bottom structure optimization design method, comprising:

[0017] Obtain the equivalent static load distribution under the ditching condition on the bottom of the aircraft fuselage;

[0018] Determine the initial values ​​of fuselage structural parameters;

[0019] Taking the initial values ​​of the fuselage structural parameters as input, satisfying the equivalent static load distribution at the bottom of the aircraft fuselage as a constraint, and minimizing the weight of the bottom of the aircraft fuselage as the optimization goal, the optimization is performed;

[0020] The fuselage structural parameters of different parts are optimized.

[0021] Preferably, the fuselage structural parameters include: structural form, skin thickness, frame stiffness, energy absorbing structure configuration and arrangement.

[0022] Preferably, the influence weights of different fuselage structural parameters on the dynamic response of the bottom of the aircraft fuselage are analyzed, and the optimization of different fuselage structural parameters is sorted based on the influence weights.

[0023] Preferably, the number of optimizations of fuselage structural parameters with an earlier optimization sequence is greater than that of fuselage structural parameters with a later optimization sequence.

[0024] Preferably, the method for obtaining the equivalent static load distribution under the forced landing condition at the bottom of the aircraft fuselage includes: determining the dynamic water pressure load distribution at the bottom of the aircraft fuselage, and calculating the equivalent static load distribution under the forced landing condition at the bottom of the aircraft fuselage based on the static equivalent coefficient of the forced landing dynamic load.

[0025] The invention obtains the static equivalent coefficient of the hydrodynamic load of forced landing on water by a scaled model test, aiming to solve the problem of lack of design load in the forced landing performance design of the aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a flow chart of a method for determining a static equivalent coefficient of a dynamic load according to a preferred embodiment of the present application;

[0027] Figure 2This is a water pressure load-time curve diagram of a preferred embodiment of the present application

[0028] Figure 3 This is a peak pressure diagram of each part of the bottom of the aircraft in a preferred embodiment of the present application.

[0029] Figure 4 It is a curve diagram showing the relationship between the ultimate strength of the skin and the thickness of the skin in a preferred embodiment of the present application. DETAILED DESCRIPTION

[0030] In order to make the technical solution and advantages of the present application clearer, the technical solution of the present application will be further described in detail in detail and in detail in conjunction with the accompanying drawings. It can be understood that the specific embodiments described here are only partial embodiments of the present application, which are only used to explain the present application, not to limit the present application. It should be noted that, for the convenience of description, only the parts related to the present application are shown in the accompanying drawings, and other related parts can refer to the general design. In the absence of conflict, the embodiments in the present application and the technical features in the embodiments can be combined with each other to obtain new embodiments.

[0031] according to Figure 1 The static equivalent coefficient of the dynamic load of a certain type of aircraft forced landing on water was determined by the process. The specific implementation steps are as follows:

[0032] Step 1: Obtain the time history of the water pressure load at the bottom of the aircraft fuselage.

[0033] The time history of the water pressure load on the bottom of the aircraft fuselage is obtained through the water landing dynamic load measurement test. The test can generally be carried out in a towing pool or an open water pool, and the test model is a rigid pressure measurement model. The water pressure load test of a certain aircraft during water landing was completed in a towing pool. The water pressure load-time curve under a typical configuration is shown in Figure 2 , the peak pressure of each part is shown in Figure 3 , the maximum peak pressure is about 52kPa.

[0034] Step 2: Determine the critical parameters of elastic structure damage through the dynamic response test of the aircraft fuselage bottom elastic model forced landing.

[0035] The critical failure parameters of the elastic structure are determined by the forced landing test of the elastic model of the fuselage bottom. The test state must be consistent with the forced landing dynamic load measurement test. The structural failure parameters include skin thickness, frame stiffness, etc. The full aircraft test model is a rigid model, and the fuselage bottom is replaced by a designed elastic model.

[0036] For the bottom structure of the aircraft, since the skin and the long stringer are riveted together, under the action of out-of-plane loads, it can be considered that the strain of the skin is consistent with the strain of the long stringer contact surface. Under the action of water loads, the skin of the bottom structure of the fuselage generally fails before the stringer structure, so the equal-strength fuselage bottom is designed based on the skin failing before the fuselage stringers. The skin of the model uses a waterproof, shapeable, and low-limit strength skin material. The skin material is made of a special fiber paper, and the thickness of the skin can be adjusted by adjusting the number of paper layers and the number of times the organic solvent is applied.

[0037] During a forced landing test, the skin of the fuselage structure with three layers of fiber paper was partially torn due to the water pressure, while the fuselage structure with four layers of fiber paper was intact. This shows that the critical failure thickness of the skin is between three and four layers.

[0038] Step 3: Determine the critical capacity of the structure to withstand static pressure loads through load-bearing capacity tests.

[0039] The bearing capacity of the elastic structure is obtained through the static mechanical properties test of the structure, and the structural parameters of the elastic structure are consistent with the structural parameters in step 2. The static bearing limit of the structure is obtained through the static test.

[0040] The model used in the static pressure test is consistent with the dynamic model. The thickness of the skin laid in the maximum stress area is 3 layers of fiber paper and 4 layers of fiber paper. The relationship curve between the ultimate strength of the skin and the thickness of the skin shows that the ultimate strength of the skin and the thickness of the skin are not strictly linear. As the thickness of the skin increases, the elastic modulus of the material decreases slightly. The ultimate static pressure corresponding to the 3-layer and 4-layer skin of the aircraft bottom scale model is 31.04kPa and 37.4kPa respectively.

[0041] Step 4: Obtain the static equivalent coefficient of the dynamic load of forced landing on water by comprehensive evaluation of structural damage. Applying formula (1), the static equivalent coefficient of the dynamic load of forced landing on water of a certain aircraft is obtained as η = 0.60 ~ 0.72.

[0042] A method for optimizing the design of the bottom structure of an aircraft fuselage, using the coefficients determined in the method for determining the static equivalent coefficients of the dynamic loads of an aircraft forced landing,

[0043] An aircraft fuselage bottom structure optimization design method, comprising:

[0044] Obtain the equivalent static load distribution under the ditching condition on the bottom of the aircraft fuselage;

[0045] Determine the initial values ​​of fuselage structural parameters;

[0046] Taking the initial values ​​of the fuselage structural parameters as input, satisfying the equivalent static load distribution at the bottom of the aircraft fuselage as a constraint, and minimizing the weight of the bottom of the aircraft fuselage as the optimization goal, the optimization is performed;

[0047] The fuselage structural parameters of different parts are optimized.

[0048] In some optional embodiments, the fuselage structural parameters include: structural form, skin thickness, skeleton stiffness, energy absorbing structure configuration and layout.

[0049] In some optional implementations, the influence weights of different fuselage structural parameters on the dynamic response of the bottom of the aircraft fuselage are analyzed, and the optimization of different fuselage structural parameters is ranked based on the influence weights.

[0050] In some optional implementations, the number of optimizations of fuselage structural parameters with an earlier optimization order is greater than that of fuselage structural parameters with a later optimization order.

[0051] In some optional embodiments, a method for obtaining an equivalent static load distribution under a forced landing condition at the bottom of an aircraft fuselage includes: determining a dynamic water pressure load distribution at the bottom of the aircraft fuselage, and calculating an equivalent static load distribution under a forced landing condition at the bottom of the aircraft fuselage based on a static equivalent coefficient of the forced landing dynamic load.

[0052] The static equivalent coefficient of the dynamic load of the aircraft forced landing determined by the present invention is mainly used for the design of the aircraft forced landing performance, so as to improve the optimization and iterative design efficiency of the aircraft fuselage structure under the forced landing load condition. The water pressure load borne by the bottom of the fuselage when the aircraft makes an emergency landing is an impact dynamic load. The conventional method uses the peak value of the forced landing impact dynamic load as the design load for the structure design, which leads to a very conservative design result. The use of the impact dynamic load for the optimization design of the structure will make the design iteration efficiency relatively low. The static equivalent coefficient of the dynamic load of the aircraft forced landing determined by the present invention can quickly obtain the equivalent static load of the structural optimization design under the condition of the aircraft forced landing. This static load is used to optimize the parameters such as the structural form, skin thickness, skeleton stiffness, energy absorption structure configuration and layout of the fuselage structure, so as to achieve rapid iteration of structural parameters and improve design efficiency.

[0053] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for determining the static equivalent coefficient of dynamic load of an aircraft forced landing, characterized in that: include: Step S1: According to the forced landing dynamic load measurement test, obtain the relationship curve between the water pressure load at the bottom of the aircraft fuselage and the time history, and determine the peak value Ps of the water pressure load according to the relationship curve Step S2: performing a forced landing test on the fuselage bottom elastic model to determine the critical failure parameters of the elastic structure; Step S3: Perform static mechanical performance test with critical failure parameters of the elastic structure to obtain the maximum static pressure P that the elastic structure can withstand. d ; Step S4: Calculate the static equivalent coefficient of the ditching dynamic load.

2. The method for determining the static equivalent coefficient of the aircraft ditching dynamic load according to claim 1, characterized in that: The experimental site for the forced landing dynamic load measurement test is a towing pool or an open water pool, and the test model is a rigid pressure measurement model.

3. The method for determining the static equivalent coefficient of the aircraft ditching dynamic load according to claim 1, characterized in that: The test model of the ditching test with the elastic model of the fuselage bottom is a rigid model, and the fuselage bottom is an elastic model.

4. The method for determining the static equivalent coefficient of the aircraft ditching dynamic load according to claim 3, characterized in that: The elastic model of the fuselage bottom specifically includes: the ultimate strength of the skin material is less than that of the fuselage truss, the skin material includes multiple layers of fiber paper, and the critical failure parameter is determined according to the fiber paper layer parameters and failure mode of the skin after the test.

5. The method for determining the static equivalent coefficient of the aircraft ditching dynamic load according to claim 4, characterized in that: The critical failure parameters include: skin thickness and skeleton stiffness.

6. The method for determining the static equivalent coefficient of the aircraft ditching dynamic load according to claim 5, characterized in that: According to the relationship curve, the most severely loaded part is determined, the most severely loaded part of the test model of the forced landing dynamic load measurement test is replaced with an elastic model, and a forced landing test of the elastic model of the fuselage bottom is carried out.

7. The method for determining the static equivalent coefficient of the aircraft ditching dynamic load according to claim 5, characterized in that: The formula for calculating the static equivalent coefficient of the dynamic load for forced landing on water is: η6P s / P d 。 。 8. The method for determining the static equivalent coefficient of the aircraft ditching dynamic load according to claim 5, characterized in that: The skin of the elastic model at the bottom of the fuselage is made by coating waterproof, shape-enclosable multi-layer fiber paper with an organic solvent, and the thickness of the skin is adjusted by adjusting the number of layers of the fiber paper and the number of times the organic solvent is coated.

9. A method for optimizing the design of the bottom structure of an aircraft fuselage, using the coefficients determined in the method for determining the static equivalent coefficients of the dynamic loads of an aircraft ditching as claimed in any one of claims 1 to 8, characterized in that: Obtain the equivalent static load distribution under the ditching condition on the bottom of the aircraft fuselage; Determine the initial values ​​of fuselage structural parameters; Taking the initial values ​​of the fuselage structural parameters as input, satisfying the equivalent static load distribution at the bottom of the aircraft fuselage as a constraint, and minimizing the weight of the bottom of the aircraft fuselage as the optimization goal, the optimization is performed; The fuselage structural parameters of different parts are optimized.

10. The method for determining the static equivalent coefficient of the aircraft ditching dynamic load according to claim 9, characterized in that: The fuselage structural parameters include: structural form, skin thickness, frame stiffness, energy absorption structure configuration and layout.

11. The method for determining the static equivalent coefficient of the aircraft ditching dynamic load according to claim 10, characterized in that: The influence weights of different fuselage structural parameters on the dynamic response of the bottom of the aircraft fuselage are analyzed, and the optimization of different fuselage structural parameters is ranked based on the influence weights.

12. The method for determining the static equivalent coefficient of the aircraft ditching dynamic load according to claim 11, characterized in that: The optimization times of the fuselage structural parameters with an earlier optimization order are greater than those with a later optimization order.

13. The method for determining the static equivalent coefficient of the aircraft ditching dynamic load according to claim 11, characterized in that: The method for obtaining the equivalent static load distribution under the forced landing condition at the bottom of the aircraft fuselage includes: determining the dynamic water pressure load distribution at the bottom of the aircraft fuselage, and calculating the equivalent static load distribution under the forced landing condition at the bottom of the aircraft fuselage based on the static equivalent coefficient of the forced landing dynamic load.

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