Structural-acoustic interaction modeling with passive damping materials for interior noise abatement

Abstract

Introduction The main objective of this paper is to develop a general procedure for structural-acoustic interaction modeling for passive cabin interior noise abatement with commercial computational tools. The ultimate goal is to help improve the future design process for cabin noise abatement The procedures described in this paper exhibit the steps of incorporating existing computational tools in structural acoustics for passive noise abatement and evaluating the interior noise level reduction with various sound damping materials. Based on a twin turboprop aircraft model, simplified finite element structural and acoustic models were created and used in the development process. Normal mode analyses were conducted for both structural and acoustic models. Subsequently, structural-acoustic interaction frequency response analyses based on the finite element method (FEM) were conducted with and without sound damping materials. These frequency response analyses were conducted using the modal superposition approach. Also, an impedance tube modeling using a FEM model was performed based on the impedance tube geometry. This modeling work was conducted to validate the analytical modeling process of treating damping material with measured sound absorbing properties. The structural-acoustic modeling process developed in this paper represents a first step to solve complicated, realistic interior noise abatement problems. Further examination of the process is underway to identify the benefits and shortcomings. 1. Graduate Research Assistant Aerospace Engineering Department 2. Assistant Professor, Member AIAA, Aerospace Engineering Department 3. Associate Professor, Member AIAA, Aerospace Engineering Department 4. Assistant Professor, Member AIAA, Mechanical Engineering Department Copyright © 1998 by Lim, Ewing, and Swearingen. Published by the Confederation of European Aerospace Societies, with permission. In many practical situations, sound-structure, or structural-acoustic interactions are frequently encountered between the acoustic medium in me cavity and the flexible structure on the boundary. One typical example is an aircraft cabin interacting with its fuselage structure subject to structure-borne excitation, such as engine vibration transmitted from the engine mount or air-borne excitation like pressure fields generated from the propellers. The resulting vibration and noise produce not only passenger discomfort but also fatigue and damage in the structure. Many approaches' have been proposed and conducted to abate mis unwanted by-product noise. In this paper, a procedure of modeling the structuralacoustic interaction is presented using a commercial computational tool. The objective of this study is to develop a capability of predicting interior noise levels when various sound absorbing materials are used for noise abatement To achieve mis, a structural-acoustic interaction problem was investigated for a simplified cabin model based on the geometry of a regional twin turboprop aircraft To model accurately the damping material properties in the analysis, an impedance tube was employed to get the admittance values needed in the analysis. The procedure developed and the results obtained will be presented in the paper. Generation of a FEM/FEM structural-acoustic interaction model In order to develop a structural-acoustic interaction modeling procedure, simplified finite element acoustic cavity and structural models were generated based on the geometry and construction of a typical regional turboprop aircraft. Beam elements and quadrilateral plate elements were used to construct the model. The structure consists of skins, bulkheads, longerons, and stringers. Figure 1 shows the structural model of the fuselage. The fuselage interior cavity model was also created using the same geometry. The nodes on the fuselage walls were shared between the two models to