Substructured formulations of nonlinear structure problems - influence of the interface condition

We investigate the use of non-overlapping domain decomposition (DD) methods for nonlinear structure problems. The classic techniques would combine a global Newton solver with a linear DD solver for the tangent systems. We propose a framework where we can swap Newton and DD, so that we solve independent nonlinear problems for each substructure and linear condensed interface problems. The objective is to decrease the number of communications between subdomains and to improve parallelism. Depending on the interface condition, we derive several formulations which are not equivalent, contrarily to the linear case. Primal, dual and mixed variants are described and assessed on a simple plasticity problem.Comment: in International Journal for Numerical Methods in Engineering, Wiley, 201

Performance Improvements for a Large-scale Geological Simulation

AbstractGeological models have been successfully used to identify and study geothermal energy resources. Many computer simulations based on these models are data-intensive applications. Large-scale geological simulations require high performance computing (HPC) techniques to run within reasonable time constraints and performance levels. One research area that can benefit greatly from HPC techniques is the modeling of heat flow beneath the Earth's surface. This paper describes the application of HPC techniques to increase the scale of research with a well-established geological model. Recently, a serial C++ application based on this geological model was ported to a parallel HPC applications using MPI. An area of focus was to increase the performance of the MPI version to enable state or regional scale simulations using large numbers of processors. First, synchronous communications among MPI processes was replaced by overlapping communication and computation (asynchronous communication). Asynchronous communication improved performance over synchronous communications by averages of 28% using 56 cores in one environment and 46% using 56 cores in another. Second, an approach for load balancing involving repartitioning the data at the start of the program resulted in runtime performance improvements of 32% using 48 cores in the first environment and 14% using 24 cores in the second when compared to the asynchronous version. An additional feature, modeling of erosion, was also added to the MPI code base. The performance improvement techniques under erosion were less effective

Optimal job splitting in parallel processor sharing queues

The main barrier to the sustained growth of wireless communications is the Shannon limit that applies to the channel capacity. A promising means to realize high-capacity enhancements is the use of multi-path communication solutions to improve reliability and network performance in areas that are covered by a multitude of overlapping wireless access networks. Despite the enormous potential for capacity enhancements offered by multi-path communication techniques, little is known about how to effectively exploit this. Motivated by this, we study a model where jobs are split and downloaded over N multiple parallel networks, each of which is modeled as a processor sharing (PS) queue. Each job is fragmented, according to a fixed splitting rule α=

Application of Expurgated PPM to Indoor Visible Light Communications - Part I: Single-User Systems

Visible light communications (VLC) in indoor environments suffer from the limited bandwidth of LEDs as well as from the inter-symbol interference (ISI) imposed by multipath. In this work, transmission schemes to improve the performance of indoor optical wireless communication (OWC) systems are introduced. Expurgated pulse-position modulation (EPPM) is proposed for this application since it can provide a wide range of peak to average power ratios (PAPR) needed for dimming of the indoor illumination. A correlation decoder used at the receiver is shown to be optimal for indoor VLC systems, which are shot noise and background-light limited. Interleaving applied on EPPM in order to decrease the ISI effect in dispersive VLC channels can significantly decrease the error probability. The proposed interleaving technique makes EPPM a better modulation option compared to PPM for VLC systems or any other dispersive OWC system. An overlapped EPPM pulse technique is proposed to increase the transmission rate when bandwidth-limited white LEDs are used as sources.Comment: Journal of Lightwave Technolog

A context for error: using conversation analysis to represent and analyse recorded voice data

Recorded voice data, such as from cockpit voice recorders (CVRs) or air traffic control tapes, can be an important source of evidence for accident investigation, as well as for human factors research. During accident investigations, the extent of analysis of these recordings depends on the nature and severity of the accident. However, most of the analysis has been based on subjective interpretation rather than the use of systematic methods, particularly when dealing with the analysis of crew interactions. This paper presents a methodology, called conversation analysis, which involves the detailed examination of interaction as it develops moment-to-moment between the participants, in context. Conversation analysis uses highly detailed and revealing transcriptions of recorded voice (or video) data that can allow deeper analyses of how people interact. The paper uses conversation analysis as a technique to examine CVR data from an accident flight. The focus accident was a controlled flight into terrain event involving an Israel Aircraft Industries Westwind 1124 jet aircraft, which impacted terrain near Alice Springs on 27 April 1995. The conversation analysis methodology provided a structured means for analysing the crew’s interaction. The error that contributed directly to the accident, an incorrectly set minimum descent altitude, can be seen as not the responsibility of one pilot, but at least in part as the outcome of the way the two pilots communicated with one another. The analysis considered the following aspects in particular: the significance of overlapping talk (when both pilots spoke at the same time); the copilot’s silence after talk from the pilot in command; instances when the pilot in command corrected (repaired) the copilot’s talk or conduct; and lastly, a range of aspects for how the two pilots communicated to perform routine tasks. In summary, the conversation analysis methodology showed how specific processes of interaction between crew members helped to create a working environment conducive to making, and not detecting, an error. By not interacting to work together as a team, pilots can create a context for error. When analysing recorded voice data, and especially for understanding instances of human error, often a great deal rests on investigators’ or analysts’ interpretations of what a pilot said, or what was meant by what was said, or how talk was understood, or how the mood in the cockpit or the pilots’ working relationship could best be described. Conversation analysis can be a tool for making such interpretations.This report was commisioned by Australian Transport Safety Burea