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Automotive Noise and Vibration

Statistical Energy Analysis (SEA): The increasing demand for improved sound quality for passenger vehicles has reinforced the need for high frequency analysis. Modelling the internal noise of cars up to at least 1500 Hz is well beyond the capability of the finite element method (FEM), so it has been necessary to set up SEA models. These have already reached the stage where they can be used as a development tool by the manufacturers, although further research is still required to close the gap between the low frequency SEA limit and the high frequency FEM limit.

The SEA models so far developed have already proved extremely useful for analysing input (exciting) powers and power flows during normal operation of the vehicle. A minimum search algorithm has been coupled to the model so that the optimum values of damping and coupling loss factors can be found, for minimum noise. In parallel with this experimental research, significant progress has been achieved in the theoretical prediction of the SEA parameters.

These techniques have also been applied to engine noise prediction and control. Although FEM can be used over the complete frequency range of interest, SEA provides a valuable tool for the rapid assessment of the noise implications of design changes, thereby reducing the number of options requiring detailed analysis.

Finite Element Analysis (FEA): Working in conjunction with ISVR Consulting, the Group has gained extensive modelling experience with a wide variety of vibro-acoustic problems. For some time these models have been coupled with minimum search algorithms (as used with the SEA models) to find the optimum thickness variation, within weight constraints, for minimum noise. More recently the shape of the model has also been allowed to change, within profile limits. It has been found that in many cases this latter variable enables significantly larger noise reductions (up to 5 dBA) to be achieved, often with little or no weight increase.

Another recent development is the ability to calculate SEA coupling loss factors from a finite element model. The model is either created in-house or imported into the ISVR Consulting system, and two connected subsystems of interest are windowed out and the SEA analysis performed on them. Comparison with measured values is very encouraging.

Vehicle Refinement:  Vehicle manufacturers are continuously searching for ways in which vehicle refinement can be improved and its cost reduced.  This involves the study of a wide range of noise sources from engine structure-borne noise to airborne tyre noise. Consumers now expect high levels of comfort and refinement from all passenger cars and no longer just in executive class models. In response, car manufacturers are placing vehicle refinement at the heart of their product development strategies. ISVR is well placed to support this process, supplying training in NVH (Noise, Vibration and Harshness) engineering, research, and consultancy services to the automotive industry.

IC Engine Noise and Vibration Analysis:  Modelling and experimental techniques have been developed to assess combustion excitation propensities, (in both petrol and diesel engines), multi-valve train and high performance engine supercharger noise generation, and to investigate the effect of engine structural changes. Engine test bed, motoring and rig test facilities are available. Vehicle noise studies can be carried out under anechoic conditions.

Vehicle External Noise: The relations between engine surface vibration characteristics and radiated noise of IC engines have successfully been modelled and new methods to take account of the interaction of the vehicle body and engine space for external noise radiation are being developed.  Further work concerns the vibrational behaviour of tyres in the audio-frequency range, and the consequent radiation of noise.

Contact:

Dr T.P. Waters
Dynamics Group
Institute of Sound and Vibration Research
University of Southampton
Southampton  S017 1BJ

Telephone: +44 (0)23 8059 4979
Facsimilie: +44 (0)23 8059 3190

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