Transmissionlosssimulation of acoustic elements in LS-DYNA®

This paper presents validated simulations of transmission loss in LS-DYNA for basic acoustic elements in exhaust systems. According to [1] there are several indicators available that describe the acoustic performance of an exhaust system and its components. These mainly include transmission loss (TL), insertion loss (IL) and noise reduction (NR). The TL is a ratio of sound power level between the inlet wave entering and the transmitted wave exiting the element. Acoustic element termination has to be anechoic, since the TL is a property of the acoustic element only. The NR is sound pressure level difference across the element. The IL is the loss of sound power from the insertion of an arbitrary acoustic element. In this paper we will focus on the TL only. There are several applicable methods in use to measure the TL. The most common and popular approach for measuring transmission loss is decomposition method or VRPHWLPHV FDOOHG 3WKUHH-pole PHWKRG ́ The method is based on the decomposition theory. The basic idea of the method is that the sound pressure may be decomposed in its incident and reflected waves. When the pressure wave is decomposed, the TL can be calculated. 6RXQG LV RQH RI WKH NH\ WULJJHU HOHPHQWV WKDW PDNH FXVWRPHU ZDQW WR EX\ DQ $NUDSRYLþ H[KDXVW system. Well-done sound solutions have been so far developed with the testing of different exhaust system prototype configurations. This demands time and costs to build and test every new configuration. Therefore, we had been always looking for faster solutions. The goal in our company was to create measurement-validated probational simulation models in LS-DYNA to examine the acoustic performance of such parts. Acoustic component performance prediction is a good example of the use of simulation software in industrial applications. LS-DYNA is one of the widely used finite element codes for solving complex mechanical problems. One of the recent developments is the addition of a vibro-acoustic solver, which enables users to perform a number of vibro-acoustic analyses in the frequency domain. In order to obtain a numerical solution in our case we have used the recently implemented *FREQUENCY_DOMAIN_ACOUSTIC_BEM keyword in LS-DYNA. This new keyword allows users to run acoustic computations based on boundary element method (BEM).