ICCS 2018 Main Track (MT) Session 8

Time and Date: 15:45 - 17:25 on 11th June 2018

Room: M2

Chair: Stefano Casarin

68 Elucidation of Mechanism for Reducing Porosity in Electric Arc Spraying through CFD [abstract]
Abstract: We elucidated the mechanism for reducing the porosity (a means for achieving smaller globules) through Computational Fluid Dynamics while focusing on the flow of compressed air. A simulation study revealed that a spray gun nozzle comprising a flow splitting plate located upstream of the arc point in the nozzle produces compression waves whereby the flow field made in the nozzle differs substantially from that made in a conventional, plate-less nozzle. Observation using a high-speed camera showed that smaller particles of the molten metal (globules) were made due to the plate, which means that the compression waves generated upstream of the arc point affect the formation of globules at the arc point.
Ryoji Tamaki and Masashi Yamakawa
159 nSharma: Numerical Simulation Heterogeneity Aware Runtime Manager for OpenFOAM [abstract]
Abstract: CFD simulations are a fundamental engineering application, implying huge workloads, often with dynamic behaviour due to runtime mesh refinement. Parallel processing over heterogeneous distributed memory clusters is often used to process such workloads. The execution of dynamic workloads over a set of heterogeneous resources leads to load imbalances that severely impacts execution time, when static uniform load distribution is used. This paper proposes applying dynamic, heterogeneity aware, load balancing techniques within CFD simulations. nSharma, a software package that fully integrates with OpenFOAM, is presented and assessed. Performance gains are demonstrated, achieved by reducing busy times standard deviation among resources, i.e. heterogeneous computing resources are kept busy with useful work due to an effective workload distribution. To best of authors' knowledge, nSharma is the first implementation and integration of heterogeneity aware load balancing in OpenFOAM and will be made publicly available in order to foster its adoption by the large community of OpenFOAM users.
Roberto Ribeiro, Luís Paulo Santos and João Miguel Nóbrega
213 High Performance Computational Hydrodynamic Simulations: UPC Parallel Architecture as a Future Alternative [abstract]
Abstract: Developments in high-performance computing (HPC) has today transformed the manner of how computational hydrodynamic (CHD) simulations are performed. Till now, the message passing interface (MPI) remains the common parallelism architecture and has been adopted widely in CHD simulations. However, its bottleneck problem remains for some large-scale cases due to delays in message passing whereby the total communication time may exceed the total simulation runtime with an increasing number of processes. In this study, we utilise an alter-native parallelism architecture, known as PGAS-UPC, to develop our own UPC-CHD model with a 2-step explicit scheme from Lax-Wendroff family of predictors-correctors. The model is evaluated on three incompressible, adiabatic viscous 2D flow cases having moderate flow velocities. Model validation is achieved by the good agreement between the predicted and respective analytical values. We then compare the computational performance between UPC-CHD and that of MPI in its base design in an SGI UV-2000 server with 100 cores. The former achieves a near 1:1 speedup which demonstrates its efficiency potential for very large-scale CHD simulations, while the later experiences bottleneck at some point. Extension of UPC-CHD remains our main objective which can be achieved by the following additions: (a) inclusions of other numerical schemes to accommodate for varying flow conditions, and (b) coupling UPC-CHD with Amazon Web Service (AWS) to further exploit its parallelism efficiency as the viable alternative.
Alvin Wei Ze Chew, Tung Thanh Vu and Adrian Wing-Keung Law
373 On Parametric Excitation for Exploration of Lava Tubes and Caves [abstract]
Abstract: Huge lava tubes with an approximate diameter of 65-225m were found on the surfaces of Moon and Mars in the late 2000's. It has been argued that the interior of the caves are spacious, and are suitable to build artificial bases with habitable features such as constant temperature, as well as protection from both meteorites and harmful radiation. In line of the above, a number of studies which regard the soft landing mechanisms on the bottom of the lava tubes have been proposed. In this paper, aiming to extend the ability to explore arbitrary surface caves, we propose a mechanism which is able to reach the ceiling of lava tubes. The basic concept of our proposed mechanism consists of a rover connected to an oscillating sample-gatherer, wherein the rover is able to adjust the length of the rope parametrically to increase the deflection angle by considering periodic changes in the pivot, and thus to ease the collection of samples by hitting against the ceiling of the cave. Relevant simulations confirmed our theoretical observations which predict the increase of deflection angle by periodically winding and rewinding the rope according to pivotal variations. We believe our proposed approach brings the building blocks to enable finer control of exploration mechanisms of lava tubes and narrow environments.
Victor Parque, Masato Kumai, Satoshi Miura and Miyashita Tomoyuki