A System for Unsteady Pressure Measurements Revisited

An overview is presented of some recent developments in the field of the design of effective sound absorbers. The first part deals with the application of socalled coupled tubes. For this purpose use is made of a system originally applied for unsteady pressure measurements on oscillating wind tunnel models. The second part deals with an extension of the theory of tubing systems to thin air layers, trapped between flexible walls

A finite element approach to the prediction of sound transmission through panels with acoustic resonators

Previous research by the authors has shown that sound radiated by a vibrating panel can be reduced considerably by using tuned acoustic resonators. The length of the tube resonators determines the frequency range in which sound is reduced. The shape of the spectrum is determined by the ratio of the cross-sectional areas of the resonators to the area of the panel. Maximum sound reduction is achieved if the volume velocities at the surface of the vibrating panel and those at the entrance of the resonators are equal in magnitude but opposite in phase. Up to now, the effect of the resonators on the radiated sound has been studied with a one-dimensional analytical model. In this paper, a three-dimensional acousto-elastic model is developed using the finite element method. The purpose of this model is to study the influence of the flexibility and the boundaries of the panel, as well as the presence of rooms behind and in front of the panel on the sound transmission. Modelling the complete structure, including the resonators and the interaction with the air inside the resonators, is computationally expensive. Therefore, an alternative approach is developed. Because of the repetitive pattern of resonators in the panel, the structural part of the panel is modelled with superelements. To enable coupling between the structural part of the model and the air behind and in front of the panel, a new interface element is derived. The formulation of this interface element also includes the acoustic behaviour of the resonators. Sound transmission loss calculations are made for one configuration and the results are compared with the results obtained with a one-dimensional analytical model

Investigation of stress-concentration factors in tensile strips

A photoelastic and a numerical investigation has been carried out to determine the stress-concentration factors at the edge of a central circular hole in a tensile strip for different ratios of hole diameter to width of the strip. The photoelastic data and the numerical results indicate that the stress-concentration factor at the minimum cross-sectional area tends to a value of two if the ratio of the hole diameter to the strip-width approaches a value of one

Air loads on a rigid plate oscillating normal to a fixed surface

This paper deals with the theoretical and experimental investigation on a rigid, rectangular plate oscillating in the proximity of a fixed surface. The plate is suspended by springs. The airloads generated by the oscillating motion of the plate are determined. Due to the fact that the plate is rigid, the system is modelled as a 1-DOF system. The influence of the surrounding air is detected by changes in the plate's natural frequency and damping. For the behaviour of the air in the gap between the plate and the fixed surface an analytical solution is presented. This solution includes the effects of inertia, viscosity, compressibility and thermal conductivity. It is shown that the main parameters governing the motion of the air in the gap are the shear wave number, the reduced frequency, the narrowness of the gap and the aspect ratio of the plate. With these parameters the validity of several simplifications can easily be demonstrated and solutions, given in the literature, can be put in perspective. Special experiments were carried out with an oscillating solar panel in order to verify the analytical model. The analytical results and the experimental results show fair agreement. The solutions shows that for low shear wave numbers the effects of viscosity cannot be discarded. \u

On-chip decoupling zone for package-stress reduction

A mathematical analysis is presented of the reduction of package stresses by introducing an on-chip decoupling zone. Different configurations of the zones are compared, using the finite-element method (FEM) and analytical models. A reduction of several orders of magnitude is obtained when a deep and thin axisymmetrical corrugation with a V-shaped cross section (a V-zone) is applied as the decoupling zone. Approximate expressions for the stiffness and the force reduction are derived. The application of a membrane pressure sensor with a V-zone as decoupling zone is evaluated. It is shown that the sensitivity of the sensor is not reduced by the addition of the V-zone

On-chip Decoupling Zone For Package-Stress Reduction

The authors report the reduction of package stresses by introducing a decoupling zone directly around a sensor structure. Different geometries of the decoupling zones are compared, using the finite element method (FEM) and analytical models. Reduction factors over 1000 and higher can be realized by using an axisymmetrical V-corrugation. A design rule to optimize the reduction for the V-corrugation is given. This rule is based on analytical calculations and verified by FEM-simulations. Finally, it is shown that the thickness of a backplate, mounted to the sensor chip, can be optimized for minimal thermal stresses in the senso

Sound attenuation: implementation of the Biot Theory

Sound absorption can be modelled as a surface boundary condition by means of the impedance elements in B2000 or as a volume by means of the Limp elements. Both methods are simplifications of a porous material. The Biot theory allows a more complete description of the sound absorbing material and models the acousto-elastic interaction of the elastic frame (skeleton) and the fluid inside. This theory is implemented in B2000 and the first results are presented. A short overview of the experimental sound reduction techniques at the laboratory is presented as well