In this work the dynamic substructuring approach was applied to a noise, vibration and harshness problem within the automotive engineering field. In particular, a noise, vibration and harshness analysis was carried out on the body-in-white structure of a passenger car. The work focuses on the theory of component mode synthesis. Two component mode synthesis reduction methods, namely the Craig–Bampton method and the Craig–Chang method, were applied to the body-in-white structure of the Volvo V40. The influences of various parameters were investigated. In particular, the effect of the reduction basis on the response accuracy and on the reduction time was studied. Moreover, the effects of the connection properties between different parts of the model were examined. The simulation times of the reduced models and of the full finite element model were compared. The results showed that the Craig–Chang method performs better when the modes are retained for up to one and a half times the maximum frequency response studied. Additionally, the Craig–Chang method gives a very accurate representation of the system dynamics even when connections with a low stiffness are used. Finally, it is possible to reduce the simulation time by up to 90% if component mode synthesis methods are used instead of the full finite element model.
No abstract
Noise generated by low Mach number flow in duct networks is important in many industrial applications. In the automotive industry, the two most important are the ventilation duct network and the engine exhaust system. Traditionally, design is made based on rule-of thumb or slightly better by simple semi-empirical scaling laws for flow noise. In many cases, strong curvatures and local deviations from circular cross-sections are created due to outer geometry restrictions. This can result in local relatively high flow velocities and complex flow separation patterns and as a result, rule-of thumb and scaling law methods can become highly inaccurate and uncertain. More advanced techniques based on time domain modelling of the fluid dynamics equations together with acoustic analogies can offer a better understanding of the local noise generation, the propagation and interaction with the rest of the system. This investigation contains a study on flow noise generation in a circular duct with a 90-degree bend carrying a low Mach number flow. Experimental results are presented and compared to numerical simulations, based on a combination of computational fluid dynamics and the acoustic analogies by Lighthill and Möhring, as well as semi-empirical models.
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