Neil A. Kelson

Effect of surface conditions on flow of a micropolar fluid driven by a porous stretching sheet

Abstract Self-similar boundary layer flow of a micropolar fluid driven by a stretching sheet with uniform suction or blowing through the surface is considered. A perturbation analysis is used to derive closed form solutions, and a number of numerical solutions are used to validate the analysis. In order to investigate the effects of different microrotation boundary conditions, results are obtained here which prescribe a fixed ratio between the microrotation and the shear stress at the surface.

Micropolar flow over a porous stretching sheet with strong suction or injection

We consider self-similar boundary layer flow of a micropolar fluid driven by a porous stretching sheet. For the limiting cases of large suction or injection, an order of magnitude analysis is used to obtain analytic results for the shear stress and the microrotation at the surface. Our analysis reveals how the wall shear stress is significantly affected by two of the parameters in the micropolar model and we indicate how our findings may be of use in technological applications involving micropolar flow.

FPGA Implementation of an Evolutionary Algorithm for Autonomous Unmanned Aerial Vehicle On-Board Path Planning

In this paper, a hardware-based path planning architecture for unmanned aerial vehicle (UAV) adaptation is proposed. The architecture aims to provide UAVs with higher autonomy using an application-specific evolutionary algorithm (EA) implemented entirely on a field-programmable gate array (FPGA) chip. The physical attributes of an FPGA chip, being compact in size and low in power consumption, makes it an ideal platform for UAV applications. The design, which is implemented entirely in hardware, consists of EA modules, population storage resources, and 3-D terrain information necessary to the path planning process, subject to constraints accounted for separately via UAV, environment, and mission profiles. The architecture has been successfully synthesized for a target Xilinx Virtex-4 FPGA platform with 32% logic slice utilization. Results obtained from case studies for a small UAV helicopter with environment derived from light-detection and ranging data verify the effectiveness of the proposed FPGA-based pathplanner, and demonstrate convergence at rates above the typical 10 Hz update frequency of an autopilot system.

Computational fluid dynamic analysis of intracranial aneurysmal bleb formation

BACKGROUND The management of unruptured aneurysms is controversial, with the decision to treat influenced by aneurysm characteristics including size and morphology. Aneurysmal bleb formation is thought to be associated with an increased risk of rupture. OBJECTIVE To correlate computational fluid dynamic (CFD) indices with bleb formation. METHODS Anatomic models were constructed from 3-dimensional rotational angiography data in 27 patients with cerebral aneurysms harboring a single bleb. Additional models representing the aneurysm before bleb formation were constructed by digitally removing the bleb. We characterized hemodynamic features of models both with and without the blebs using CFDs. Flow structure, wall shear stress (WSS), pressure, and oscillatory shear index (OSI) were analyzed. RESULTS There was a statistically significant association between bleb location at or adjacent to the point of maximal WSS (74%, P = .019), irrespective of rupture status. Aneurysmal blebs were related to the inflow or outflow jet in 89% of cases (P < .001), whereas 11% were unrelated. Maximal wall pressure and OSI were not significantly related to bleb location. The bleb region attained a lower WSS after its formation in 96% of cases (P < .001) and was also lower than the average aneurysm WSS in 86% of cases (P < .001). CONCLUSION Cerebral aneurysm blebs generally form at or adjacent to the point of maximal WSS and are aligned with major flow structures. Wall pressure and OSI do not contribute to determining bleb location. The measurement of WSS using CFD models may potentially predict bleb formation and thus improve the assessment of rupture risk in unruptured aneurysms.

An experimental and theoretical investigation of flow in a gross pollutant trap.

Flow through a gross pollutant trap (GPT) with fully blocked screens is investigated experimentally and theoretically using computational fluid dynamics (CFD). Due to the wide range of possible flow regimes, an experimental approach is developed which uses a downstream weir arrangement to control the nature of the flow and the variation in free surface height. To determine the overall flow structure, measurements are taken at a fixed depth throughout the trap with an Acoustic Doppler Velocimeter (ADV), including velocity profile data across three cross sections of the GPT suitable for more detailed comparison with simulations. Observations of the near-wall flow features at the free surface are also taken, due to their likely importance for understanding litter capture and retention in the GPT. Complementary CFD modelling (using Fluent 6.3) is performed using a two-dimensional k-epsilon turbulence model along with either standard wall law boundary conditions or enhanced near-wall modelling approaches. Comparison with experiments suggest that neither CFD modelling approach could be considered as clearly superior to the other, despite the significant difference in near-wall mesh refinement and modelling that is involved. The experimental approach taken here is found useful to control the flow regime in the GPT and further experiments are recommended to study a greater range of flow conditions.

Computation of ECG Signal Features Using MCMC Modelling in Software and FPGA Reconfigurable Hardware

Computational optimisation of clinically important electrocardiogram signal features, within a single heart beat, using a Markov-chain Monte Carlo (MCMC) method is undertaken. A detailed, efficient data-driven software implementation of an MCMC algorithm has been shown. Initially software parallelisation is explored and has been shown that despite the large amount of model parameter inter-dependency that parallelisation is possible. Also, an initial reconfigurable hardware approach is explored for future applicability to real-time computation on a portable ECG device, under continuous extended use.

Comparison of high level FPGA hardware design for solving tri-diagonal linear systems

Abstract Reconfigurable computing devices can increase the performance of compute intensive algorithms by implementing application specific co-processor architectures. The power cost for this performance gain is often an order of magnitude less than that of modern CPUs and GPUs. Exploiting the potential of reconfigurable devices such as Field-Programmable Gate Arrays (FPGAs) is typically a complex and tedious hardware engineering task. Recently the major FPGA vendors (Altera, and Xilinx) have released their own high-level design tools, which have great potential for rapid development of FPGA based custom accelerators. In this paper, we will evaluate Alteras OpenCL Software Development Kit, and Xilinxs Vivado High Level Sythesis tool. These tools will be compared for their performance, logic utilisation, and ease of development for the test case of a tri-diagonal linear system solver.

Calculation of engine parameters using reconfigurable hardware

The feasibility of real-time calculation of parameters for an internal combustion engine via reconfigurable hardware implementation is investigated as an alternative to software computation. A detailed in-hardware field programmable gate array (FPGA)-based design is developed and evaluated using input crank angle and in-cylinder pressure data from fully instrumented diesel engines in the QUT Biofuel Engine Research Facility (BERF). Results indicate the feasibility of employing a hardware-based implementation for real-time processing for speeds comparable to the data sampling rate currently used in the facility, with acceptably low level of discrepancies between hardware and software-based calculation of key engine parameters.