A method for calculating structural characteristic stress optimization under multi-load and out-of-phase loading

Abstract

The present application belongs to the field of helicopter rotor system strength design, and particularly relates to a structural characteristic stress optimization calculation method under multi-load different phase loading. The periodic load containing exact phase information is divided into analysis steps containing certain time interval points, a numerical fitting method is used to find the maximum stress of the structure in the period, and then the structural characteristic stress is obtained. The method can quickly and accurately extract the structural characteristic stress, avoid the phenomenon that the characteristic stress is too small due to unreasonable step setting, and has important significance for the strength design of the helicopter rotor system. Compared with the traditional different phase load loading, the method of loading all load maximums, the analysis is more accurate, and the stress change of the structure in the load loading period can be effectively simulated.

Description

Technical Field

[0001] This invention belongs to the field of strength design of helicopter rotor systems, and particularly relates to a method for optimizing the calculation of structural characteristic stress under multi-load and non-phase loading. Background Technology

[0002] The vibration environment of helicopters is quite complex, with the main vibration sources being the rotor system, transmission system, and engine. These vibrations, transmitted to the fuselage, create a complex environment dominated by periodic vibrations superimposed with random vibrations. While the load patterns on components within the rotor system are relatively simple, the extraction of characteristic stress results from these components becomes crucial as a key input for fatigue life analysis when multiple out-of-phase periodic loads act simultaneously.

[0003] Traditional characterization methods simplify the load input by extracting the maximum stress point from all load amplitudes as the characteristic stress. However, this ignores the load direction issue caused by the phase difference during loading, leading to high computational risk. Therefore, this invention provides a method for calculating the characteristic stress under the simultaneous application of multiple out-of-phase periodic loads, providing support for fatigue life analysis of propeller hub components. Summary of the Invention

[0004] The purpose of this invention is to extract structural characteristic stresses under different phases and multiple loads while reducing computational load.

[0005] Technical solution

[0006] The main idea is to load a periodic load containing precise phase information, divide it into analysis steps containing certain time intervals, use numerical fitting methods to find the maximum stress of the structural component within the period, and then obtain the structural characteristic stress.

[0007] A structural characteristic stress optimization calculation method under multi-load and out-of-phase loading is proposed, based on a helicopter rotor hub. The load categories on the helicopter rotor hub components include: rotor hub center load, rotor blade root section load, damper load, pitch control rod load, and elastic bearing load, all of which can be simplified into simple periodic loads. Taking the rotor hub connector as an example, the structural connection form is shown in the attached figure. Figure 1 As shown. If the blade root end is constrained, the forces are: load F at the elastic bearing. x F y F z Damper load F a and the load F of the variable pitch tie rod b There are three types of loads, and there is a phase difference between the three types of loads. Let the loads be:

[0008]

[0009] Where t is the loading time point, and ω1, ω2, and ω3 are the angular velocities of the load at the elastic bearing, the damper load, and the torque converter load, respectively. A1, A2, A3, A4, and A5 represent the initial phases of the loads at the elastic bearing, damper, and torque converter, respectively. A1, A2, A3, A4, and A5 represent the initial phases of the load F at the elastic bearing, respectively. x F y F z The amplitudes of damper load and torque converter load.

[0010] The aforementioned loads are simultaneously applied to the connector model, and the solution duration is set to twice the period of the longest-period load, i.e.

[0011]

[0012] Where T is the solution time.

[0013] The solution is performed in 2n analysis steps over time, and there are two methods for extracting characteristic stresses:

[0014] Method 1, Spline interpolation, the steps are as follows:

[0015] (5) Due to the influence of phase difference on the results, the results of the first to nth analysis steps are discarded, and the maximum stress point σ of each node in the results of the (n+1)th to 2nth analysis steps is selected. p ;

[0016] (6) Extract σ p-1 σ p σ p+1 As a fundamental point, the fitting time T is a quadratic function of the nodal stress σ, σ = AT. 2 +BT+C;

[0017] (7) The maximum stress σ at each node is calculated based on the function expression. max The minimum stress σ at each node is obtained in the same way. min ;

[0018] (8) At this point, the stress extrema of all nodes in the structure are obtained, and the maximum and minimum stresses among the extrema are selected as the characteristic stress output results.

[0019] Method 2, Trigonometric Function Method, the steps are as follows:

[0020] (4) Due to the influence of phase difference on the results, the results of the first to nth analysis steps are discarded, and the maximum (or minimum) stress point σ of each node in the results of the (n+1)th to 2nth analysis steps is selected. p ;

[0021] (5) Extract σ p-1 σ p σ p+1 As a fundamental point, the trigonometric function of fitting time T and nodal stress σ

[0022] (6) According to the function expression, the maximum stress σ max and the minimum stress σ min of each node are calculated.

[0023] (4) The maximum stress and the minimum stress in the stress extreme value of all nodes in the structure are selected as the characteristic stress output results.

[0024] At this point, the maximum stress and the minimum stress in the stress extreme value of all nodes in the structure are selected as the characteristic stress output results.

[0025] Further, in the method, the angular velocity and the initial phase of the three-direction load at the elastic bearing are the same.

[0026] Further, in the method, the elastic bearing does not transmit the bending moment load, but only transmits the shear force load.

[0027] Further, in the method, the elastic bearing hinge point exists between the connecting piece and the central piece, that is, the ball flexible hub.

[0028] Further, in the method, the density of the analysis step should be as close to the slope change of the complex load as possible, and it is recommended that n>5.

[0029] Further, if the accuracy of the maximum stress and the minimum stress in the method is to be verified, the analysis step can be increased, and the more analysis steps, the closer the result is to the true value.

[0030] The beneficial effects of the application are:

[0031] A structure characteristic stress optimization calculation method under multi-load different phase loading, through a periodic load loading rule, a function method is used to extract the finite element structure analysis stress result, and the characteristic stress for fatigue life analysis is obtained after calculation, which provides an important input for structure fatigue design. The method can quickly and accurately extract the structure characteristic stress, avoid the phenomenon that the characteristic stress is too small due to unreasonable step length setting, and has important significance for the strength design of the helicopter rotor system. Compared with the method of loading all load maximum values when the traditional different phase load is loaded, the method is more accurate in analysis, and can effectively simulate the stress change of the structure piece in the load loading period. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A schematic view of a helicopter connecting piece structure;

[0033] Wherein: 01 elastic bearing, 02 connecting piece body, 03 damper connection, 04 variable pitch pull rod connection, 05 blade root connection. DETAILED DESCRIPTION

[0034] Example 1: Spline interpolation method

[0035] Step one: in the finite element model of the connector, input the load type in the format of (5)-(7) for finite element analysis, the solution time is ω = min{ω1, ω2, ω3}, the number of analysis steps is 2n;

[0036] Step two: for each node m, select the maximum stress σ p_m in the results of the n+1 to 2n analysis steps, and the results of the adjacent two analysis steps σ p-1_m and σ p+1_m , use the three-point method to fit the quadratic function σ m1 = AT 2 + BT + C of time T and node stress σ.

[0037] Step three: select the maximum value σ m1 in σ 2 = AT max_m + BT + C.

[0038] Step four: for each node m, select the minimum stress σ q_m in the results of the n+1 to 2n analysis steps, and the results of the adjacent two analysis steps σ q-1_m and σ q+1_m , use the three-point method to fit the quadratic function σ m2 = AT 2 + BT + C of time T and node stress σ.

[0039] Step five: select the minimum value σ m2 in σ 2 = AT min_m + BT + C.

[0040] Step six: select the maximum stress σ max and the minimum stress σ min of all nodes 1-m as the characteristic stress result output.

[0041] Example 2: trigonometric function method

[0042] Step one: in the finite element model of the connector, input the load type in the format of (5)-(7) for finite element analysis, the solution time is ω = min{ω1, ω2, ω3}, the number of analysis steps is 2n;

[0043] Step two: for each node m, select the maximum (or minimum) stress σ p_m in the results of the n+1 to 2n analysis steps, and the results of the adjacent two analysis steps σ p-1_m and σ p+1_m , use the trigonometric function method to fit the function of time T and node stress σ

[0044] Step three: select the maximum stress σ max_m and the minimum stress σ min_m in the node i.

[0045] Step four: select the maximum stress σ max and the minimum stress σ min in all nodes 1-m as the characteristic stress results output.

[0046] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting, unless otherwise defined herein. It will be further understood that any terms used herein that are not previously defined, in particular technical terms, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and claims and that they should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. The specific embodiments described above have been chosen for purposes of illustration and not limitation. Those skilled in the art will readily and unconstrainedly apply the teachings of the specification to other embodiments falling within the scope of the inventive concept.​

Claims

1. A method for calculating the stress optimization of a structural feature under multiple loadings with different phase loads, characterized in that, Based on the helicopter hub, the helicopter hub components are loaded, including: hub center load, blade root section load, damper load, variable pitch pull rod load, elastic bearing load, which can be simplified as a simple periodic load, if the blade root end is constrained, the force is: elastic bearing load , damper load and variable pitch pull rod load Three categories, and there is a phase difference between the three loads; record the load respectively: (1) (2) (3) wherein, is the load time point, , , are the angular velocities of the load at the elastic bearing, the damper load, the variable moment tie rod load, respectively, , , are the initial phases of the load at the elastic bearing, the damper load, the variable moment tie rod load, respectively, , , , , are the amplitudes of the load at the elastic bearing , the damper load, the variable moment tie rod load, respectively. The above load is simultaneously loaded into the connecting piece model, and the solution time length is set to 2 times the cycle of the longest load, that is (4) wherein, t is the time duration; The solution along time is divided into two analysis steps, and there are two methods for extracting characteristic stress. Method one, spline interpolation method, the steps are as follows: (1) Discard the results of the first to nth analysis steps, and select the maximum stress point σ of each node in the results of the (n+1)th to 2nth analysis steps due to the influence of the phase difference on the results p ; (2) Extract σ p-1 , σ p , σ p+1 As a base point, fit a quadratic function of time T and nodal stress σ, σ = AT 2 + BT + C; (3) The maximum stress σ of each node is calculated according to the function expression max The minimum stress σ of each node is obtained in the same way min ; (4) At this point, the maximum and minimum stresses in the extreme values of all nodes in the structure are selected as the characteristic stress output results. Method two, trigonometric function method, the steps are as follows: (1) Discard the results of the first to nth analysis steps, and select the maximum or minimum stress point σ of each node in the results of the nth+1 to 2nth analysis steps due to the influence of the phase difference on the results p ; (2) Extract σ p-1 , σ p , σ p+1 As a base point, fit the trigonometric function of time T and node stress σ ； (3) The maximum stress σ at each node is calculated based on the function expression. max and minimum stress σ min ; (4) At this point, the maximum and minimum stresses in the extreme values of all nodes in the structure are selected as the characteristic stress output results.

2. The method according to claim 1, characterized in that, At this point, the maximum and minimum stresses in the extreme values of all nodes in the structure are selected as the characteristic stress output results.

3. The method according to claim 2, characterized in that, The angular velocity and initial phase of the three-direction load at the elastic bearing are the same.

4. The method according to claim 3, characterized in that, The elastic bearing does not transmit bending moment load, but only transmits shear force load.

5. The method according to claim 4, characterized in that, There is an elastic bearing hinge point between the connecting piece and the central piece, that is, a ball flexible hub.

6. The method according to claim 5, characterized in that, The density of the analysis step should conform to the slope change of the load, n>5.

7. The method according to claim 6, characterized in that, If you want to verify the accuracy of the maximum and minimum stresses in this method, increase the analysis steps, the more analysis steps, the closer the result is to the true value.

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