A Study On Sound Insulation Optimization Of Sandwich Plates Considering Manufacturability

Metallic sandwich plates with corrugated cores have attracted much attention in the engineering field for their high specific strength and stiffness. Effective methods for numerical modeling of sound transmission through this kind of structure and efficient tools for computing the sound transmission loss(STL) are needed to predict the interior noise level of those vehicles such as airplanes and high speed trains with the restrict stiffness.In this thesis, the sound transmission loss(STL) through sandwich plates with typical corrugated cores under the excitation of plane wave of acoustic pressure has been studied. The analysis is implemented by using conventional finite element method. In this part, the influence of the structure-acoustic coupling effect has been studied by comparing the sound transmmited loss of the coupling case and the uncoupling case.The obtained result indicates that the STLs of the two different models are almost the same when the acoustic media is air.Next, the structure- acoustic coupling theory is employed to investigate the coupling effect on the vibro-acoustic response of metallic sandwich plates whose dip angle is 45 degree. Although the sound radiation powers of the coupled and uncoupled model are almost the same under a wide frequency band. However the evident differences show in the partial frequency band. To explain the reason, the thesis analysed the structure-cavity coupling modals of the sandwich plate. The obtained result indicates that the interaction of the cavity’s nature sound modal and the structure-cavity coupling modal is the reason that why there are evident differences between the structure sound transmission model and the structure-cavity coupled model. At the same time, the cavity’s nature sound modal and the structure-cavity coupling modal will change as various topological shape of sandwich plates, which will change the frequency’s location of peak and valley values of the transmission sound power. And the evident differences of the transmission sound powers of the structure sound transmission model and the structure-cavity coupled model occured at the different frequency band because of the various topological structure of sandwich plates.At last, this thesis presents an optimization study of sandwich plates with corrugated cores for high sound transmission loss(STL), considering the manufacturability of the structure, and subject to the constraints on the weight and fundamental frequency. A theoretical study on the vibration response of sandwich plates is firstly presented by using spectral element method(SEM). The numerical result shows that SEM has a higher computational efficiency than the traditional FEM under the same accuracy condition. Then a genetic algorithm-based penalty method is employed to search for the optimal corrugated core topology and structural parameters with objective to maximize the STL at a tonal frequency and in a specific narrow frequency band. The obtained results indicate that higher STL can be achieved with optimal inclined angle of trapezoidal core under the condition of same weight of whole sandwich structure and without deterioration of its bending stiffness.