How reproducible are methods to measure the dynamic viscoelastic properties of poroelastic media?

There is a considerable number of research publications on the acoustical properties of porous media with an elastic frame. A simple search through the Web of Science™ (last accessed 21 March 2018) suggests that there are at least 819 publications which deal with the acoustics of poroelastic media. A majority of these researches require accurate knowledge of the elastic properties over a broad frequency range. However, the accuracy of the measurement of the dynamic elastic properties of poroelastic media has been a contentious issue. The novelty of this paper is that it studies the reproducibility of some popular experimental methods which are used routinely to measure the key elastic properties such as the dynamic Young's modulus, loss factor and Poisson ratio of poroelastic media. In this paper, fourteen independent sets of laboratory measurements were performed on specimens of the same porous materials. The results from these measurements suggest that the reproducibility of this type of experimental method is poor. This work can be helpful to suggest improvements which can be developed to harmonize the way the elastic properties of poroelastic media are measured worldwide

Numerieke methoden voor het oplossen van een eigenwaardeprobleem

Confidential

Acoustic excitation of mechatronic systems

Within the specialty mechatronics a plurality of disciplines such as mechanics, electronics, software and control are combined to develop extremely accurate precision machinery. Examples are ultra-precise measuring equipment with nanometer accuracy, stages for lithography applications and stages for electron microscopes. The accuracy of mechatronic systems is rapidly increasing. Key in the development of such highly precise machinery is to control the disturbances affecting the accuracy of the machine. A systematic way to do so, is to define a "dynamic error budget" which is divided amongst the different disturbances. Many different disturbances need to be considered. To mention a few: floor vibrations, vibrations generated internally by the machine, acoustic excitation due to flow and/or cleanroom air-conditioning systems, etc. The latter disturbance, acoustic excitation, claims a significant part to the error budget, especially for extremely accurate precision machinery.In order to estimate the contribution to the dynamic error budget already in the design phase of the machine, it is necessary to predict the response of the system to acoustic excitation. In the design phase of a machine only approximate dimensions are available, which calls for approximate estimates of the machines sensitivity to acoustic excitation. The paper discusses such an approximate method, which considers rigid body motion of the machine only, excited by plane acoustic waves. The method uses an analytical model. The analytical model is derived, and the theory is validated by means of experiments

Acoustic excitation of mechatronic systems

Within the specialty mechatronics a plurality of disciplines such as mechanics, electronics, software and control are combined to develop extremely accurate precision machinery. Examples are ultra-precise measuring equipment with nanometer accuracy, stages for lithography applications and stages for electron microscopes. The accuracy of mechatronic systems is rapidly increasing. Key in the development of such highly precise machinery is to control the disturbances affecting the accuracy of the machine. A systematic way to do so, is to define a "dynamic error budget" which is divided amongst the different disturbances. Many different disturbances need to be considered. To mention a few: floor vibrations, vibrations generated internally by the machine, acoustic excitation due to flow and/or cleanroom air-conditioning systems, etc. The latter disturbance, acoustic excitation, claims a significant part to the error budget, especially for extremely accurate precision machinery.In order to estimate the contribution to the dynamic error budget already in the design phase of the machine, it is necessary to predict the response of the system to acoustic excitation. In the design phase of a machine only approximate dimensions are available, which calls for approximate estimates of the machines sensitivity to acoustic excitation. The paper discusses such an approximate method, which considers rigid body motion of the machine only, excited by plane acoustic waves. The method uses an analytical model. The analytical model is derived, and the theory is validated by means of experiments