Claus Claeys

A wave based method to predict the absorption, reflection and transmission coefficient of two-dimensional rigid frame porous structures with periodic inclusions

This paper presents an extension to the Wave Based Method to predict the absorption, reflection and transmission coefficients of a porous material with an embedded periodic set of inclusions. The porous unit cell is described using the Multi-Level methodology and by embedding Bloch-Floquet periodicity conditions in the weighted residual scheme. The dynamic pressure field in the semi-infinite acoustic domains is approximated using a novel wave function set that fulfils the Helmholtz equation, the Bloch-Floquet periodicity conditions and the Sommerfeld radiation condition. The method is meshless and computationally efficient, which makes it well suited for optimisation studies.

Experimental validation of numerical structural dynamic models for metal plate joining techniques

Joined structures are of great industrial relevance. The dynamic effects of joints are, however, often practically difficult to accurately account for in numerical models, as they often lead to local changes in stiffness and damping. This paper discusses the comparison between measurements and simulations of joined panels considering four different joining techniques: adhesive bonding, metal inert gas welding, resistance spot welding and flow drill screwing. An experimental modal analysis is performed on the different systems and the power injection method is applied to determine the loss factors of single plate systems and their joined counterparts. The joined panels are modeled in a holistic simulation environment with particular focus on the joining region, by the application of predefined and generic joint models. A very good agreement is obtained between the simulated dynamic behavior and the experimental results, showing that an accurate representation of the joints has been obtained.

Prediction of transmission, reflection and absorption coefficients of periodic structures using a hybrid Wave Based – Finite Element unit cell method

Abstract This paper presents a hybrid Wave Based Method – Finite Element unit cell method to predict the absorption, reflection and transmission properties of arbitrary, two-dimensional periodic structures. The planar periodic structure, represented by its unit cell combined with Bloch–Floquet periodicity boundary conditions, is modelled within the Finite Element Method, allowing to represent complex geometries and to include any type of physics. The planar periodic structure is coupled to semi-infinite acoustic domains above and/or below, in which the dynamic pressure field is modelled with the Wave Based Method, applying a wave function set that fulfills the Helmholtz equation and satisfies the Sommerfeld radiation condition and the Bloch–Floquet periodicity conditions inherently. The dynamic fields described within both frameworks are coupled using a direct coupling strategy, accounting for the mutual dynamic interactions via a weighted residual formulation. The method explicitly accounts for the interaction between the unit cell and the surrounding acoustic domain, also accounting for higher order periodic waves. The convergence of the method is analysed and its applicability is shown for a variety of problems, proving it to be a useful tool combining the strengths of two methods.

Numerical and Experimental Study of Local Cell Resonators to Obtain Low-Frequency Vibrational Stopbands in Periodic Lightweight Structures

Periodic lightweight structures, such as honeycomb core panels, combine excellent mechanical properties with a low mass, becoming attractive for application in transport and machine design. However, the high stiffness to mass ratio of these lightweight structures may result in unsatisfactory dynamic behaviour in that it may impair the panels’ ability to reduce noise and vibration levels. Liu et al. demonstrated that inclusions of high density spheres with a rubber coating in a matrix material result in low-frequency sound isolation, breaking the mass law [1]. These locally resonant sonic materials require a high density of local resonators throughout the matrix material, either spread randomly or periodically. In this paper, resonating structures are introduced into the cavities of a honeycomb structure, leading to a material with excellent mechanical properties and strong structural attenuation in a low-frequency region. By means of both numerical models and experimental measurements, the potential of local cell resonators for periodic panels is shown.