Analytical studies on the vibration and sound radiation characteristics of an asymmetric laminated rectangular plate are carried out in this paper. Theoretical formulations, in which the effects of thermal environments are taken into account, are derived for the vibration and sound radiation based on both first-order shear deformation plate theory and Rayleigh integral. It is found that the natural frequencies, the resonant amplitudes of vibration response and the sound pressure level decrease with the temperature rising. The natural frequencies of asym- metric plates are smaller than those of symmetric plates and the velocity responses of asymmetric plates are larger than those of symmetric plates.
Thermal and acoustic environments pose severe challenges to find optimal design that exhibits ideal acoustic characteristics the structural design of hypersonic vehicles. One of them is to in a frequency band, which is discussed in this paper through topology optimization aiming at resonance sound radiation in thermal environments. The sound radiation at resonance fre- quencies is the main component of response, minimization on which is likely to provide a satisfactory design. A bi-material plate subjected to uniform temperature rise and excited by harmonic loading is studied here. Thermal stress is first evaluated and considered as prestress in the following dynamic analysis; radiated sound power is then calculated through Rayleigh inte- gral. Sensitivity analysis is carried out through adjoint method considering the complicated relationship between stress-induced geometric stiffness and design variables. As the resonance frequency is constantly changing during the optimization, its sensi- tivity should be considered. It is also noticed that mode switching may occur, so mode tracking technique is employed in this work. Some numerical examples are finally discussed.
Experiments were carried out for a clamped rectangular aluminum plate to study the dynamic and acoustic behaviors in both pre-and post-buckling ranges under thermal loads.Plate temperature was elevated from ambient value to the level above the theoretical critical buckling temperature of the plate.In the whole test temperature range,the measured frequencies decreased to the minimum values in sequence,and then turned to increase as temperature rose.The softening effect of thermal stresses played the leading role in the decreasing stage and the stiffening effect of thermal buckling deflection became the major influence factor in the increasing stage.The later one could drive the temperature equilibrium point of the heated plate to move towards lower temperature range.All the frequencies would not drop to zero due to the inherent initial deflection which provides additional stiffness to the plate.Dynamic responses state two variation trends in different temperature ranges,shifting toward the lower frequency range and closing up in the mid-frequency range.The characters of spectrum responses changed gradually as the temperature was elevated.Numerical simulations gave predictions with same variation trend as the test results.
Traditional coupled multi-disciplinary design optimization based on computational fluid dynamics/computational structure dynamics(CFD/CSD)aims to optimize the jig shape of aircraft,and general multi-disciplinary design optimization methodology is adopted.No special consideration is given to the aircraft itself during the optimization.The main drawback of these methodologies is the huge expanse and the low efficiency.To solve this problem,we put forward to optimize the cruise shape directly based on the fact that the cruise shape can be transformed into jig shape,and a methodology named reverse iteration of structural model(RISM)is proposed to get the aero-structural performance of cruise shape.The main advantage of RISM is that the efficiency can be improved by at least four times compared with loosely-coupled aeroelastic analysis and it maintains almost the same fidelity of loosely-coupled aeroelastic analysis.An optimization framework based on RISM is proposed.The aerodynamic and structural performances can be optimized simultaneously in this framework,so it may lead to the true optimal solution.The aerodynamic performance was predicted by N-S solver in this paper.Test shows that RISM predicts the aerodynamic and structural performances very well.A wing-body configuration was optimized by the proposed optimization framework.The drag and weight of the aircraft are decreased after optimization,which shows the effectiveness of the proposed framework.
ZUO Ying TaoGAO Zheng HongCHEN GangWANG Xiao PengLI Yue Ming
Gust alleviation is very important to a large flexible aircraft.A nonlinear low-order aerodynamic state space model is required to model the nonlinear aeroelastic responses due to gust.Based on the proper orthogonal decomposition method,a reduced order modeling of gust loads was proposed.And then the open-loop and closed-loop reduced order state space model for the transonic aeroelastic system was developed.The static output feed back control scheme was used to design a simple multiple-in multiple-out(MIMO)gust alleviation control law.The control law was demonstrated with the Goland+wing model with four control surfaces.The simulation results of different discrete gusts show the capability and good performance of the designed MIMO controller in transonic gust alleviation.
