A Graphics Processing Unit (GPU) Approach to Large Eddy Simulation (LES) for Transport and Contaminant Dispersion

Recent advances in the development of large eddy simulation (LES) atmospheric models with corresponding atmospheric transport and dispersion (AT&D) modeling capabilities have made it possible to simulate short, time-averaged, single realizations of pollutant dispersion at the spatial and temporal resolution necessary for common atmospheric dispersion needs, such as designing air sampling networks, assessing pollutant sensor system performance, and characterizing the impact of airborne materials on human health. The high computational burden required to form an ensemble of single-realization dispersion solutions using an LES and coupled AT&D model has, until recently, limited its use to a few proof-of-concept studies. An example of an LES model that can meet the temporal and spatial resolution and computational requirements of these applications is the joint outdoor-indoor urban large eddy simulation (JOULES). A key enabling element within JOULES is the computationally efficient graphics processing unit (GPU)-based LES, which is on the order of 150 times faster than if the LES contaminant dispersion simulations were executed on a central processing unit (CPU) computing platform. JOULES is capable of resolving the turbulence components at a suitable scale for both open terrain and urban landscapes, e.g., owing to varying environmental conditions and a diverse building topology. In this paper, we describe the JOULES modeling system, prior efforts to validate the accuracy of its meteorological simulations, and current results from an evaluation that uses ensembles of dispersion solutions for unstable, neutral, and stable static stability conditions in an open terrain environment.

Oklahoma City Contaminant Dispersion: Concentration Data Processing and Analysis for a Scaled Puff Release Experiment

Magnetic resonance techniques were leveraged to obtain velocity and concentration measurements for a puff release contaminant dispersion study. The study involved a scaled model of downtown Oklahoma City as it was in 2003, and sought to provide a high fidelity, three-dimensional data set for comparison with JU2003 and subsequent studies. The scaled model was placed in a water channel with fully turbulent flow (Re = 36,000), and an MRI system was used to take scans at 12 time-specific measurement phases throughout the puff injection cycle. The present work details processing methods applied to the nearly 650 million magnetic resonance concentration (MRC) data points obtained from the study. Processing entailed the calculation of a concentration field through background subtraction and normalization involving several distinct scan types. Uncertainty was reduced through the scaling and combination of high molarity scans. Processing methods are followed by a preliminary investigation of the results, which highlights noteworthy elements of scalar transport within the data set and the need for further investigation of the complex flow field. The study ultimately demonstrates the applicability of magnetic resonance techniques to puff release and dynamic experimental conditions, as well as a method for working with data from phase-locked experiments.

Contamination of Coupling Glass and Performance Evaluation of Protective System in Vacuum Laser Beam Welding

Vacuum laser beam welding enables deeper penetration depth and welding stability than atmospheric pressure laser welding. However, contaminated coupling glass caused by welding fumes in the vacuum space reduces laser transmittance, leading to inconsistent penetration depth. Therefore, a well-designed protective system is indispensable. Before designing the protective system, the contamination phenomenon was quantified and represented by a contamination index, based on the coupling glass transmittance. The contamination index and penetration depth behavior were determined to be inversely proportional. A cylindrical protective system with a shielding gas supply was proposed and tested. The shielding gas jet provides pressure-driven contaminant suppression and gas momentum-driven contaminant dispersion. The influence of the shielding gas flow rate and gas nozzle diameter on the performance of the protective system was evaluated. When the shielding gas flow was 2.0 L/min or higher, the pressure-driven contaminant suppression dominated for all nozzle diameters. When the shielding gas flow was 1.0 L/min or lower, gas momentum-driven contaminant dispersion was observed. A correlation between the gas nozzle diameter and the contamination index was determined. It was confirmed that contamination can be controlled by selecting the proper gas flow rate and supply nozzle diameter.