Multidirectional Mobilities - Advanced Measurement Techniques and Applications
Doctoral thesis, 2001
Today high noise-and-vibration comfort has become a quality sign of products in sectors such as the automotive industry, aircraft, components, households and manufacturing. Consequently, already in the design phase of products, tools are required to predict the final vibration and noise levels. These tools have to be applicable over a wide frequency range with sufficient accuracy. During recent decades a variety of tools have been developed such as transfer path analysis (TPA), input force estimation, substructuring, coupling by frequency response functions (FRF) and hybrid modelling. While these methods have a well-developed theoretical basis, their application combined with experimental data often suffers from a lack of information concerning rotational DOFs.
In order to measure response in all 6 DOFs (including rotation), a sensor has been developed, whose special features are discussed in the thesis. This transducer simplifies the response measurements, although in practice the excitation of moments appears to be more difficult. Several excitation techniques have been developed to enable measurement of multidirectional mobilities. For rapid and simple measurement of the loaded mobility matrix, a MIMO (Multiple Input Multiple Output) technique is used. The technique has been tested and validated on several structures of different complexity.
A second technique for measuring the loaded 6-by-6 mobility matrix has been developed. This technique employs a model of the excitation set-up, and with this model the mobility matrix is determined from sequential measurements. Measurements on "real" structures show that both techniques give results of similar quality, and both are recommended for practical use.
As a further step, a technique for measuring the unloaded mobilities is presented. It employs the measured loaded mobility matrix in order to calculate compensation forces and moments, which are later applied in order to compensate for the loading of the measurement equipment.
The developed measurement techniques have been used in a hybrid coupling of a plate-and-beam structure to study different aspects of the coupling technique. Results show that R-DOFs are crucial and have to be included in this case. The importance of stiffness residuals when mobilities are estimated from modal superposition is demonstrated. Finally it is shown that proper curve fitting can correct errors from inconsistently measured data.
multidirectional mechanical mobility