A Hybrid Model For Mid-Frequency Vibroacoustic Analysis

The work of this thesis was supported by National Natural Science Foundation of China "Computation and analysis of structural-acoustic coupled problems in the medium frequency range for thin wall structures"(No.10872075).Based on wave based method and hybrid method, theoretical analysis and numerical simulation for three-dimensional structural acoustic analysis, sound radiation analysis in unbounded domain and buid-up structures are investigated respectively, and the experiment analysis of vibration for built-up structures is studied. The low and mid frequency models for complex structural vibration systems and coupled structural-acoustic systems are introduced, the theory about mid frequency analysis has investigated. Research include following sections:wave based modeling for multi-domain structural acoustic; wave based modeling for sound radiation in unbounded domains; hybrid method modeling for acoustic,structural acoustic and built-up structures; experiments of vibration analysis for built-up structures. Taking into account the requirements for practical engineering, provide a reliable calculating method for vibration analysis or structural acoustic analysis of practical thin-wall structures.Proposing complete definition for mid-frequency analysis and hybrid model. Discussing the requirements for mid-frequency method,exhibition for mid-frequency unique dynamics behavior and uncertainty for mid-frequency analysis. Provides a theoretical basis and research ideas for mid-frequency vibro-acoustic analysis.A new set of continuity conditions for multi-domain wave based modeling is introduced. The impedance coupling approach introduces artificial damping into the numerical model, which has a beneficial effect on the method's efficiency as compared to the conventional pressure and velocity coupling approach.A generally applicable selection criterium for the impedance coupling factor is proposed. The characteristic impedance of the considered fluid gives the best results. By applied the proposed method, the cavity model and thin plate and cavity coupled model are buit. It shows that the proposed method is more efficient than the element based method and better convergence properties.Wave based method applies similar methodologies as for the FE schemes for tackling problems in unbounded domains. After an initial truncation and partitioning into a number of bounded convex subdomains and one unbounded subdomain, separated by a truncation curve, novel wave function sets are defined. These wave function sets are able to represent the acoustic pressure field within the unbounded subdomain, exterior to the truncation surface. Wave function sets for circular truncation curves are defined and validated. The wave function sets defined for the unbounded subdomains allow the introduction of rigid baffle planes implicitly in the wave function definitions. Selection of appropriate wave functions within subdomains and enforcement of continuity conditions over the truncation surface between the bounded and unbounded region, yields a WB model which can be solved for the associated wave function contribution factors. Application of the proposed approach to various validation examples illustrates an enhanced computational efficiency as compared with element-based methods.The applicability of the WBM is limited since the high computational efficiency only appears for moderate geometrical complexity. In order to take advantage of the wide application range of the FEM and the high convergence rate of the WBM, the coupling between both prediction tools is proposed. The basic idea is to replace parts of the finite element model with simple geometrical shapes by much smaller wave models. The resulting hybrid model has fewer degrees of freedom (DOF's). The hybrid modeling concept is demonstrated for structural-acoustic systems. Results show that because of the finite element method part existing in hybrid model, therefore hybrid model also has numerical pollution. The use of modal reduction techniques for the structural part results in a significant gain in CPU time.Considering the hybrid model concept for vibration analysis of buit-up structures.The coupling between the non-conforming approximation fields is created by enforcing continuity conditions. In this case the continuity conditions are enforced directly to the subdomains as boundary conditions. For a pure FE model, the main portion of the computational load is spent in modelling the plate domains. In the hybrid approach the plates can be modelled very efficiently by the WBM, leaving only the stiff frame to be modelled by the FEM.The number of FE dofs required to accurately model the stiff frame is relatively small. Consequently, the accuracy of the hybrid model is mainly determined by the accuracy of the WB models. The convergence analysis and predicted frequency response functions show that the newly developped hybrid method has an enhanced computational efficiency over the FEM.The vibration analysis of built-up structures is studied by experiment. The models of thin plate, bending plate, built-up structures are designed. Calculation model confirmed the validity of proposed method in this paper. The uncertainty in mid frequency vibration analysis is also discussed. The vibration analysis of thin wall structures and built-up structures used in practical engineering is studied. The theory analysis models of wave based method and hybrid model are proposed.The vibration analysis of structures is also studied by experiment. Afte improving and developing, provide a reliable computation and analysis method of complex structural-acoustic systems.