New computer geometric modeling approach with filament assembly model for woven fabric structures

This paper presents a new computer geometric modeling approach for three-dimensional woven fabric structures. Pierce’s geometry of the weave fabric of yarn from an arc abscissa (Peirce’s) model is presented. Then, new algorithms with a filament assembly model for a single yarn composed of many filaments by twisting along the crimp shape in the warp/weft is developed. The concept of a virtual location is used to simulate the fiber distributions in the yarn cross-section. Each cross-section is rotated along the yarn length by a pre-determined amount to allow for the yarn twist. The curve of each filament in each two successive cross-sections is approximated by NURBS and then each curve is created by sweeping a closed curve along the centerline of the yarn path. The method described is demonstrated by the CAD model of woven fabrics with plain and twill weaves. The simulated woven fabrics using this approach can demonstrate a wider variety and improved visual simulations of real woven fabric and can then be further generalized for different and more complicated fabrics. The method is necessary as an input to many computational models, such as modeling the mechanical properties or the heat transfer of fabrics or composite parts.     

IEEE 802.11b based ad hoc networking and its performance in mobile channels

It is widely believed that IEEE 802.11 standard is aimed mainly for fixed indoor wireless local area networks and is not suited for mobile applications, even though the IEEE 802.11b systems may work in either infrastructure mode or ad hoc mode. The impact of node mobility on ad hoc network performance has already been studied intensively, but these studies mostly do not consider temporal fluctuations of the mobile wireless channel due to the Doppler shift. An investigation of the mobility impact on the performance of IEEE 802.11b ad hoc systems with Rician/Rayleigh fading under different node velocities is presented. A comprehensive and in-depth analysis of the impacts of a multitude of different signal distortions on an IEEE 802.11b system performance is also presented. Specifically, the authors study the bit-error rate performances with respect to node velocities for different modulation schemes. The simulation results show that, owing to its extremely low implementation and deployment cost, the current IEEE 802.11b standard has its potential to be deployed in a mobile ad hoc environment if the line-of-sight path between transmitter and receiver exists.     

Performance Study of a Mobile Multi-hop 802.11a/b Railway Network Using Passive Measurement

In this paper, we study the performance of IEEE 802.11a/b in a large-scale mobile railway networks and introduce our developed passive measurement approach. To provide a comprehensive evaluation, we built an outdoor multi-hop multi-interface railroad testbed (UNL-FRA Testbed), which consists of eight access points deployed along 3.5 mile of railroad track. We propose a novel large-scale passive measurement approach that synchronizes the system clocks of our monitoring systems, merges packet traces collected from multiple wireless channels across a multi-hop network, and enables a global performance view for the entire monitored network and across multiple layers. Based on the testing data collected from 15 field experiments carried out using BNSF locomotives and HyRail vehicles over a period of 18 months we conclude that in typical outdoor 802.11 railway environments the wireless link quality, the channel assignment scheme, and the handoff latency have much more significant impacts on the performance than the velocity. Furthermore, we discuss the implications of our conclusions on guaranteeing the quality of mobile services. We believe this is the first analysis on such a scale for 802.11-family railway networks.