Peter Mas

Critical assessment of operational path analysis: mathematical problems of transmissibility estimation

Classical transfer path analysis (TPA) is a widely used and reliable method for tackling noise and vibration problems. But due to its complexity and time‐consuming measurement procedure there is an ongoing research for simpler and faster methods. One such method, most often referred to as operational path analysis (OPA), was presented two years ago and has quickly gained popularity in the NVH field for its speed and ease of use. To estimate path contributions transmissibilities are calculated from the measured operational reference and target accelerations and sound pressures. This new method is now critically examined and compared to a reliable classical TPA measurement. The results of this examination reveal three significant weaknesses. This paper focuses on the problems related to the estimation of transmissibilities which mostly arise from the limited amount of orders present in the signal and the coherence between inputs. It is shown that despite the advantages of the method, it is not applicable in...

Critical assessment of operational path analysis: effect of coupling between path inputs

Classical transfer path analysis (TPA) is a widely used and reliable method for tackling noise and vibration problems. But due to its complexity and time‐consuming procedure the industry is constantly seeking for simpler and faster methods. One such method, often referred to as operational path analysis (OPA), was presented in 2006 and has quickly gained popularity in the NVH field. The method works with measured operational input and output accelerations and sound pressures and the transmissibilities calculated from these. The claim for its accuracy is based on being able to reproduce the original output signal by summing the calculated partial contributions but it has not yet been compared to other TPA methods. This new method is now critically examined and compared to a reliable classical TPA measurement. The results of this examination reveal three significant weaknesses. This paper deals with the effect of the cross‐coupling between the input signals. Due to modal behavior a single force will cause v...

Predicting and measuring flexural power flow in plates

Structural power flow is an alternative way of analyzing vibrations, where, differently from traditional techniques, the emphasis is put on the active part of the vibration energy instead of the total. The active vibration energy is directly related to the injection and dissipation of energy in the structure and can, therefore, be a valuable tool for solving vibroacoustical problems. However, measuring the active part of the vibration energy in the presence of a highly reverberant field is often impractical. This paper presents an experimental method especially adapted for the computation of structural power flow using spatially dense vibration data measured with scanning laser Doppler vibrometers. In the proposed method, an operational deflection shape measured over the surface of the structure is curve-fitted using a 2D discrete Fourier series approximation. This approximation minimizes the effects of spatial leakage. From the wavenumber-frequency domain data thus obtained, it is straightforward to compute the spatial derivatives that are necessary to determine the structural power flow. An example consisting of a rectangular aluminum plate supported by four rubber mounts and excited by an electrodynamic shakes is used to appraise the proposed method. Both numerically simulated data and experimental data are used.

Multi-Disciplinary Optimization of an Active Suspension System in the Vehicle Concept Design Stage

The automotive industry represents a significant part of the economic activity, in Europe and globally. Common drivers are the improvement of customer satisfaction (performance, personalization, safety, comfort, brand values,) and the adherence to increasingly strict environmental and safety regulations, while at the same time reducing design and manufacturing costs and reducing the time to market. The product evolution is dominated by pushing the envelope on these conflicting demands.

Modal and path contribution models from in-operation data: Review and new approaches

In several cases, laboratory-based modelling approaches such as Experimental Modal Analysis and Transfer Path Analysis run into limitations with respect to technical and economical feasibility (accessibility of the structure, excitation feasibility, measurement time, accuracy, ...) as well as model representativity. Therefore, approaches such as in-operation modal analysis (OMA) have been developed and are reaching a similar degree of acceptability as standard EMA, with all limitations regarding accuracy and observability of the structural dynamics. In the same line of reasoning fits the question of system characterization and identification using (or based on) other operation data types such as transmissibility functions and coherence functions and data analysis procedures such as principal component analysis. Using these testing and analysis paradigms instead of the classical load-FRF-response one, key analysis techniques such as transfer path and contribution analysis can be reconsidered.

Vibration pattern of sound-radiating structures using laser vibrometer measurements

The need to predict the dynamic behavior of a structure is of paramount importance in many engineering applications. To achieve this goal a certain number of measurements of the structure under study are needed. Unfortunately, not all the measuring problems can be solved with traditional techniques: on small and light structures the mass loading effect of the instrumentation can yield to incorrect estimation; similarly, in case of high temperature surfaces and magnetically or electrically noisy environment the use of normal sensors, like accelerometers, might be unmanageable. The use of a non-contacting technique, like the Laser Doppler Vibrometer seems to be a way to overcome efficiently and elegantly these problems.

Near field acoustic source identification based on numerical models and operational pressure data

When pressure measurements are taken in the near field of possible sources, a global inversion of an input–output model of the acoustic medium can be accomplished to calculate the source velocities, and thus to identify the main noise radiating parts. The acoustic medium can be represented by a frequency response function (FRF) matrix which can either be derived analytically based on a point source assumption, or experimentally under laboratory conditions, as well as numerically using a finite or a boundary element model. The operational source velocities can be calculated by multiplying the inverted FRF matrix with the vector of operational pressure measurements. The inversion process, however, is usually an ill‐conditioned problem. Regularization techniques based on a singular value decomposition can be used to solve for the ill‐conditioned nature of the inverse acoustic problem. In this paper, the applicability of numerically derived FRF models using the boundary element modeling technique, is shown fo...