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As an effort to solve high frequency brake squeals, increasing attentions have been placed on the relationship of the in-plane (IP) and the out-of-plane (OP) modes of a disc brake. However, there exists wide confusions between the frequency lineup and the mode coupling that largely hinders the efforts on correct solutions for brake squeals. This paper investigates the relationship between disc brake IP-OP modes interaction and brake squeal by both analytical and experimental approaches. It starts with a systematic discussion and categorization of the modal patterns of a typical disc brake rotor. Then, the relationship between IP-OP mode and high frequency squeal is evaluated by means of disc mode indicating function (DMIF) testing and dynamometer testing for three rotor designs. At last, comprehensive correlation study is performed for 19 different front and rear brake systems from the results of 60 dynamometer noise tests.

Lightweight spacecraft components such as reflectors are very sensitive to acoustic loading, and accurate prediction of peak stresses encountered in an acoustic test is critical to a successful design. A boundary element model (BEM) provides a very accurate means of representing the acoustic input into a finite element model (FEM) of the structure and has proven to be the method of choice for lightweight reflectors. Various aspects of accurate BEM modeling of acoustic input to a FEM of a lightweight reflector will be discussed. This includes choosing the portion of the structure that needs to be modeled to get correct boundary conditions and acoustic input, and also the modeling of the effect of a reverberant chamber on the acoustic response at low frequencies. Predictions will be compared with measured responses for both cases in order to illustrate the critical aspects of this modeling.

The perturbed boundary condition (PBC) model updating procedure has been developed to correct the finite element model [1]. The use of additional structural configurations adds more experimental information about the system and so better updating results can be expected. While it works well for simulated examples, practical limitations and additional requirements arise when it is used to update engineering structures. In this paper, the merits and the practical limitations of the techmques will be discussed in depth through the updating of a simulated system where the “measured” data is generated by computer and a real test structure where the experimentally measured data is noisy and distorted due to leakage. Useful suggestions and recommendations are drawn to guide the model updating of practical engineering structures.