A finite element formulation is presented for the prediction of nonlinear response of thin plates under a steady-state non-uniform temperature change over the thin plate and band limited Gaussian white noise. Thermal buckling temperatures and thermal deflections are obtained to explain the stability of panels, and modal frequencies of thermally buckled plate are obtained to explain the stiffness characteristics of panels. The stress responses of panels under thermo-acoustic loadings exhibit complex nonlinear characteristics. Miner linear accumulation damage theory and improved Rainflow counting cycle method are used for estimation of fatigue life of panels under combined thermo-acoustic loadings. Results show that the fatigue life decreases till the end of snap-through and then gives a rise trend. Afterward, the fatigue life reaches a steady state at low peak temperature area. As the peak temperature goes up sequentially, the fatigue life rises suddenly, and then reaches a steady state at high peak temperature area.
Hypersonic aircrafts are facing increasingly severe aerodynamic heating, noise and so on, which will lead to nonlinear vibration characteristics for thin-walled structures of hypersonic aircrafts. Considering the influence of thermo-acoustic loadings, finite element formulation of simply supported plate under combined thermo-acoustic loadings are founded, and vibration characteristics of simply supported plate under thermal loadings with temperature gradient and random acoustic loadings are investigated. According to finite element numerical method, modal frequencies, critical thermal buckling temperature difference, dynamic stress response of simply supported plates with temperature gradient under combined thermo-acoustic loadings were calculated before and after thermal buckling. The results show that three types of motion: random vibrations around initial equilibrium position in pre-buckling region, snap-through oscillations between two post-buckling equilibrium positions, nonlinear vibrations around one of the two post-buckling equilibrium position, and The RMS of nodes for different locations of the simply plate are obtained in pre-buckling post-buckling region, and it is shown that different interaction of tensile bend stress, compressive stress and compressive thermal stress lead to different RMS trends.
Rotating instability can be observed in the tip flow region of axial compressor stage while stable operation. In order to investigate the noise characteristics in a multi-stage axial compressor, the noise inner compressor casing is measured simultaneously with the vibration of the rotor blades on a high pressure compressor component rig testing. An azimuthal mode analysis and theoretical formulation of the rotating source mechanism are applied to the unsteady pressure at the casing wall immediately upstream of the inlet plane of the rotor. It is shown that RIs might be described by a group of superimposed modes. This is the reason why RIs can be identified as an amplitude increase in a frequency band. The mode orders of RI are consecutively numbered riseing with frequency. The frequency in the source frame (ωN) closed to the frequency in the rotating frame (ωN) can be got well recovered. The results presented in this paper can be a reference for further understanding of the characteristics of unsteady flow field and the effects of the high intensity sound waves on the rotor blades.
Advanced materials and processes are required to meet the performance goals in the design of advanced turbofan engine, SiC/Ti composite is typically used in low pressure turbine shaft (LPTS). Firstly, establish the viability and effectiveness of composite cylinder assemblage (CCA) micro-mechanics model and representative volume element (RVE) micro-mechanics model which are utilized to calculate the mechanical parameter of continuous fiber reinforced metal matrix composite (CFRMMC), respectively. Results show that RVE model is more applicable to calculate continuous fiber reinforced LPTS. Secondly, parameters of mechanics performance calculated by RVE model are taken as input to build mechanics analysis model of fiber reinforced metal matrix composite shaft structure. The optimal solution will be got by design and analysis of CFRMMC shaft structure with 2 kinds of loads. Compared with deformation and stress of shaft structure with different material scheme, then an optimization scheme of SCS/Ti2AlNb composite of LPTS can be obtained.
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