Development and characterization of warp knitted spacer fabrics for helmet comfort liner application

The inner padding layer of the motorcycle helmet is one of the important components that control the factors of comfort during wearing the helmet and provides a perfect fit and stability of the helmet on the head. The inner padding consists of a low-density flexible polyurethane layer attached to a soft fabric layer that is in direct contact with the head. The present study aims to replace foam in the comfort liner of a helmet with spacer fabrics to avoid the risk of heat stress during the use of the helmet. In this work, 9 warp-knitted spacer fabrics were produced by varying the course/cm (10, 12 & 14) and thickness (3, 3.5, and 4 mm). Air permeability, thermal, and water vapour resistance of the developed spacer fabrics were characterized along with compression properties and compared with commercially available standard liner. The results showed that warp-knitted spacer fabrics had better energy absorption compared to the standard liner. Also, the developed spacer fabrics had better breathability and evaporative heat transfer compared to the standard liner.

A New Implementation of the Extended Helmholtz Resonator Acoustic Liner Impedance Model in Time Domain CAA

The application of wall acoustic lining is a major factor in the reduction of aircraft engine noise. The extended Helmholtz Resonator (EHR) impedance model is widely used since it is representative of the behavior of realistic liners over a wide range of frequencies. Its application in time domain CAA methods by means of [Formula: see text]-transform has been the subject of several papers. In contrast to standard liner modeling in time domain CAA, which consists in imposing a boundary condition modeling both the cavities and the perforated sheet of the liner, an alternative approach involves adding the cavities to the computational domain and imposing a condition between these cavities and the duct domain to model the resistive sheet. However, the original method may not be used for broadband acoustics since it implements an impedance condition with frequency independent resistance. This paper describes an extension of this method to implement the EHR impedance model in a time domain CAA method.