Coupled resonance of FGM nanotubes transporting super-critical high-speed pulsatile flow under forced vibration: size-dependence and bifurcation topology

The combination resonance of size-dependent microbeams is investigated. Two harmonic forces act on the microbeam, and combination resonance is observed while the excitation frequencies differ from ...

Theoretical modeling on the combination resonance of size-dependent microbeams:

Aiming at the problem of large deformation geometric nonlinearity of high aspect ratio wing/multi external storage system affected by aerodynamic, multi external storage and gravity loads, the nonlinear aeroelastic motion equation of wing is established by using medium deformation beam theory and quasi steady aerodynamic model, and the effects of geometric nonlinear deformation of high aspect ratio wing/multi external storage system on structural modal frequency Influence of vibration mode and flutter characteristics.The analysis results show that the influence of geometric nonlinear effect is mainly reflected in the first-order mode of lead-lag, and its flutter mechanism is flexural torsional coupling flutter dominated by the first-order mode of lead-lag. The random wing/multi plug-in system changes from vertical downward bending state to horizontal state, the influence of geometric nonlinear effect is weakened, and the amplitude of the first-order mode shape of lead-lag increases, Moreover, the variation trend of the first-order lead-lag and torsional modal frequencies slows down, which correspondingly reduces the variation amplitude of flutter velocity at the corresponding angle of attack, which shows that it has a certain positive effect on the flutter velocity by slowing down the geometric nonlinearity of the wing/multi plug-in system.

Analysis of Nonlinear Aeroelastic and Structural Characteristics of Wing / Multi External Storage System with High Aspect Ratio

In order to improve the stability of ground resonance and air resonance of the bearingless rotor helicopter, especially the unstable phenomenon of air resonance may occur in the condition of large overload high-speed flight and maneuvering flight, how to broaden the flight envelope of air stability, the key is to study and master the design parameters or factors that significantly affect the dynamic instability. Based on the stability analysis of the bearingless rotor model test-bed and the compatibility design analysis of ground and air resonance of bearingless rotor prototype, some main factors affecting the ground and air resonance were summarized and found. The influence of these design parameters is mainly studied, such as natural frequency, aerodynamic damping, artificial damping, lift force, pitch control line stiffness and flight speed. The influence of these design parameters on the stability was analyzed to provide technical support for avoiding or eliminating the ground and air resonance instability. It provides important design measures for improving or eliminating the ground and air resonance of bearingless rotor.

Study on the influence of design parameters on the dynamic instability of bearingless rotor helicopter


Purpose
Computational fluid dynamics (CFD)/computational structural dynamics (CSD) coupling analysis is an important method in the research of helicopter aeroelasticity due to its high precision. However, this method still suffers from some problems, such as wake dissipation and large computational cost. In this study, a new coupling method and a new air load correction method that combine the free wake model with the CFD/CSD method are proposed to maintain computational efficiency whilst solving the wake dissipation problem of the prior coupling methods.


Design/methodology/approach
A new coupling method and a new air load correction method that combine the free wake model with the CFD/CSD method are proposed. With the introduction of the free wake model, the CFD solver can adopt two-order accuracy schemes and fewer aerodynamic grids, thus maintaining computational efficiency whilst solving the wake dissipation problem of the prior coupling methods.


Findings
Compared with the predictions of the prior methods and flight test data, those of the proposed method are more accurate and closer to the test data. The difference between the two methods in high-speed forward flight is minimal.


Research limitations/implications
Because of the chosen research approach, the research results may lack generalisability. Therefore, researchers are encouraged to test the proposed method further.


Originality/value
In this paper, a CFD/CSD/free wake coupling method is proposed to improve the computational accuracy of the traditional CFD/CSD coupled method and ensure the computational efficiency.


CFD-CSD method for rotor aeroelastic analysis with free wake model

In order to explore the influence mechanism of different parameters on Multi-rotor aircraft dynamic characteristics, Hamilton principle and the theory of medium deformation beam were used to derive the rotors/nacelle/wing coupling structure dynamic equation, and a solution method suitable for the analysis of coupled modal was established. By using literature as an example calculate rotor and wing modal, the error is less than 5% compared with the experimental results in the literature, indicating that the coupling model in this paper is accurate and effective. On this basis, the influences of, nacelle offset, rotor collective pitch, blade center of mass on the coupling modal are studied.

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Qiyou Cheng

Papers

Theoretical modeling on the combination resonance of size-dependent microbeams:

Analysis of Nonlinear Aeroelastic and Structural Characteristics of Wing / Multi External Storage System with High Aspect Ratio

Study on the influence of design parameters on the dynamic instability of bearingless rotor helicopter

CFD-CSD method for rotor aeroelastic analysis with free wake model

Distributed rotorcraft coupling modal parameters influence analysis