Peter Gajdatsy

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...

Effect of systematic FRF errors on matrix inversion based vibro-acoustic analysis methods

The establishment of a non-parametric system description in terms of a Frequency Response Function matrix is an essential step in many structural and vibro-acoustic analysis approaches such as Modal Analysis, Load Identification, Transfer Path Analysis and Substructuring. A crucial step in many of these applications is the inversion of a matrix of this FRF matrix. Several studies have been reported on the influence of stochastic FRF errors on this matrix inversion, leading to the use of a pseudo-inverse approach, SVD truncation, regularization etc. but little is known about the effect of systematic errors, such as amplitude or frequency shifts and inter-FRF inconsistencies on the matrix inversion result. The present paper investigates the effect of selected systematic FRF measurement errors on applications involving matrix inversion, with emphasis on the Transfer Path Analysis method. The subject is reviewed through analytical considerations and through simulations on a reference numerical model (the Garteur model). In particular, the sensitivity of two Transfer Path Analysis methods with respect to the studied systematic errors is analyzed and considerations on increasing the robustness of these methods are derived.

Active control of engine noise transmitted into cavities: simulation, experimental validation and sound quality assessment

Active control has been proposed as a possible solution to cope with low frequency noise reduction in vehicles. Active noise control systems tend to be designed with a target on the sound pressure level reduction. However, the perceived control efficiency for the occupants can be more accurately assessed if psychoacoustic metrics are taken into account. The aim of this paper is to evaluate, numerically and experimentally, the effect of a collocated velocity feedback controller on the sound quality of engine noise in a vehicle mockup. The simulation scheme is described and experimentally validated. The engine excitation is provided by a sound quality equivalent engine simulator, running on a real‐time platform that delivers harmonic excitation in function of the driving condition. The controller performance is evaluated in terms of sound quality metrics such as specific loudness and roughness. As a result of the control action, loudness is significantly reduced and roughness slightly spread, with an overal...