Studying Porosity Effect on Sound Transmission Loss for Firewall Insulator Design

Abstract

Noise, vibration, and harshness (NVH) attributes are considered crucial aspects of passenger comfort by automotive manufacturers. Reducing noise and vibration in each of the three sections (source, path, and receiver) can significantly improve passenger comfort. The engine system, in particular, is identified as one of the most challenging vehicle noise sources. Reducing the radiated engine sound in the cabin plays a significant role in decreasing the perceived noise level by occupants. The firewall, as the bulkhead part between the engine and passenger compartment, plays a dominant role in transferring engine noise to the cabin. To prevent this, an optimal design of the firewall structure and related insulator specifications are the most challenging problems from an automotive NVH point of view. Proper design of the firewall insulator requires vast knowledge in material science and acoustics. The composite nature of the insulator, along with many acoustically dependent material parameters, increases the complexity of this component. In this work, the effect of porosity magnitude on the acoustic behavior of the fiber part is investigated. For this purpose, numerical simulation is utilized to achieve significant cost and time reduction. A hybrid finite element-statistical energy analysis (FE-SEA) methodology is applied to simulate the acoustic behavior of materials. The aim is to find the effect of porosity magnitude on the transferred airborne noise in different frequency domains, from low to high range.