Structure-borne Noise at PWM Excitation using an Extended Field Reconstruction Method and Modal Decomposition

Pulse-Width Modulation (PWM) represents a carrier-frequency-dependent structural excitation. The PWM’s excitation harmonics are also reflected in the air gap’s electromagnetic forces, the vibration response and the resulting structure-borne noise. The last of these can be numerically predicted with a multiphysics finite-element-analysis (FEA) containing electronic, electromagnetic, mechanical and acoustic field problems. The multiphysics FEA are precise, but computationally inefficient and consequently inadequate for parametric studies. This paper introduces a method for a fast structure-borne noise prediction at PWM excitation. The presented approach contains the Extended Field Reconstruction Method (EFRM) to handle the magnetic saturation and slotting effects in magnetics, and the modal decomposition to couple the electromagnetic and mechanical domains. Finally, the structure-borne sound power level is calculated via the vibration-velocity response. Indeed, this approach demands a pre-calculation of the basis functions and modal parameters from the FEA, but afterwards the effect of the different PWM excitation cases can be evaluated in a few seconds. The proposed method can calculate the structure-borne noise at PWM excitation accurately and is more than 104 times faster than the conventional multiphysics FEA approach.

Evidencing the relationship between isomer spectra and melting: the 20- and 55-atom silver and gold cluster cases

The present work highlights the links between melting properties and structural excitation spectra of small gold and silver clusters.

Uncertainty in vision based modal analysis: probabilistic studies and experimental validation

This paper analyses the issues related with the application of photogrammetric methods in the context of modal analysis. In this field of mechanical testing, the vibrations of the measurand are monitored. The possibility to measure displacement of several monitored points without directly instrumenting those, pushes the interest toward the application of an image based measurement system. However, the process of acquiring a moving target with a camera is complex due to the motion blur phenomenon. The effects of this particular phenomenon on uncertainty generation and propagation are discussed in parallel with Monte Carlo simulation and experimental approach. The case study here proposed focuses on the estimation of the main modal parameters (first two resonant frequencies and amplitudes) of a structure with the help of 2D Blob Analysis, with particular focus in comparing the performances of photogrammetry with the ones of classic motion transducers. The results of both the approaches confirm that the choice of using photogrammetry as an input for modal analysis should be made carefully, since the actual behavior of a structure can be distorted. Nonetheless, the results show that particular care should be made in the choice of structural excitation when using vision based techniques.