Structure-borne sound transmission on frameworks of beams

Wang, Xing (2015) Structure-borne sound transmission on frameworks of beams. PhD thesis, University of Liverpool.

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Abstract

Many engineering structures are built from frameworks of beams, particularly lightweight structures. For the purpose of noise control from airborne and structure-borne sources, it is useful to be able to predict vibration transmission across these frameworks. This thesis investigates the potential use of Advanced Statistical Energy Analysis (ASEA) to predict structure-borne sound transmission when the beams support multiple wave types due to wave conversion at the junction. In contrast to Statistical Energy Analysis (SEA), ASEA is able to account for high propagation losses and indirect coupling through the use of ray tracing. SEA and ASEA were validated through comparison with measurements and numerical experiments with Finite Element Methods (FEM). When each beam supports at least two local modes for each wave type in the frequency band of interest and the modal overlap factor is at least 0.1, FEM and measurement data tend to have average values which form smooth curves such as those predicted by SEA and ASEA. It was shown that SEA and ASEA models could incorporate Euler-Bernoulli and Timoshenko theory by changing over from Euler-Bernoulli to Timoshenko group velocity when calculating the coupling loss factors. However, comparisons with measurements were not conclusive although there were indications that a suitable crossover frequency could be when Timoshenko and Euler-Bernoulli group velocities differ by at least 26%. Agreement between FEM and ASEA indicates that it is appropriate to ignore phase effects in the ray tracing approach used with ASEA. This was particularly noteworthy for the three-bay and five-bay truss beams as these were perfectly periodic for which phase effects could be important. Results for an L-junction, a rectangular beam frame and a five-bay truss with relatively long beams and relatively high internal loss factors demonstrated that ASEA was able to incorporate high propagation losses. This was not possible with SEA. For a three-bay truss beam with relatively short beams ASEA showed close agreement with FEM and measurements confirming that there was significant indirect coupling rather than high propagation losses. There are indications from the five-bay truss beams that ASEA may no longer be accurate in predicting the response on beams that are at least three structural junctions away from the source beam, particularly when ASEA predicts high propagation losses on the receiving beam.

Item Type:	Thesis (PhD)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Depositing User:	Symplectic Admin
Date Deposited:	31 Mar 2016 10:03
Last Modified:	31 Mar 2016 10:03
URI:	http://livrepository.liverpool.ac.uk/id/eprint/2022425

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