Application of multi-layered polyurethane foams for flat-walled anechoic linings

Previous work demonstrated that a multi-objective evolutionary algorithm could be successfully employed as an optimiser to make the design of flat-walled multi-layered anechoic linings more efficient. In the present work, such an algorithm is employed to investigate the practical aspects of the application of multi-layered polyurethane foams as the flat-walled anechoic lining. The investigation includes aspects such as the efficacy of a single layer of material, the minimum number of layers of linings to achieve the minimum overall thickness for low (100 Hz), mid (250 Hz) and high (500 Hz) cut-off frequencies, the use of the three-layered lining composite for low to mid cut-off frequencies and the effect of air gaps.