Medicine Hat, Canada
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Hsieh K.-J.,University of Waterloo | Lien F.-S.,University of Waterloo | Yee E.,Defence RandD Canada Suffield
Flow, Turbulence and Combustion | Year: 2010

A hybrid Reynolds-averaged Navier-Stokes/Large-Eddy Simulation (RANS/LES) methodology has received considerable attention in recent years, especially in its application to wall-bounded flows at high-Reynolds numbers. In the conventional zonal hybrid approach, eddy-viscosity-type RANS and subgrid scale models are applied in the RANS and LES zones, respectively. In contrast, the non-zonal hybrid approach uses only a generalized turbulence model, which provides a unified simulation approach that spans the continuous spectrum of modeling/simulation schemes from RANS to LES. A particular realization of the non-zonal approach, known as partially resolved numerical simulation (PRNS), uses a generalized turbulence model obtained from a rescaling of a conventional RANS model through the introduction of a resolution control function F R, where F R is used to characterize the degree of modeling required to represent the unresolved scales of turbulent motion. A new generalized functional form for F R in PRNS is proposed in this study, and its performance is compared with unsteady RANS (URANS) and LES computations for attached and separated wall-bounded turbulent flows. It is demonstrated that PRNS behaves similarly to LES, but outperforms URANS in general. © 2009 Springer Science+Business Media B.V.

Smith J.A.,Ryerson University | Poulakakis I.,Princeton University | Trentini M.,Defence RandD Canada Suffield | Sharf I.,McGill University
International Journal of Robotics Research | Year: 2010

The bounding gait for the Platform for Ambulating Wheels (PAW), a new and unique hybrid wheeled-leg system is presented. Two hypotheses are tested and discussed: first, that the robot's forward speed can be increased by increasing the leg liftoff angles and, second, that the addition of distally mounted actuated wheels can be used in running gaits such as the bound. Both hypotheses were tested experimentally and found to be valid. © The Author(s), 2010.

Yee E.,Defence RandD Canada Suffield | Skvortsov A.,Defence Science and Technology Organisation, Australia
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

The downstream development of the concentration probability distribution along the mean-plume centerline of a dispersing plume in the wake of a ground-level continuous point source in a neutrally stratified wall-shear layer is studied. It is shown that the concentration distribution is well described by a family of one-parameter gamma distributions, as first suggested by Villermaux and Duplat in the context of confined mixing. A prediction of the downstream evolution of the parameter k (which specifies the gamma distribution) is obtained. This prediction includes explicitly the effects of mean shear on the mean-square concentration. © Published by the American Physical Society.

McFee J.E.,Defence RandD Canada Suffield | Faust A.A.,Defence RandD Canada Suffield | Pastor K.A.,McMaster University
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2013

To date, the most successful nuclear methods to confirm the presence of bulk explosives have been radiative thermal neutron capture (thermal neutron activation) and prompt radiative emission following inelastic fast neutron scattering (fast neutron analysis). This paper proposes an alternative: photoneutron spectroscopy using monoenergetic gamma rays. If monoenergetic gamma rays whose energies exceed the threshold for neutron production are incident on a given isotope, the emitted neutrons have a spectrum consisting of one or more discrete energies and the spectrum can be used as a fingerprint to identify the isotope. A prototype compact gamma-ray generator is proposed as a suitable source and a commercially available 3He ionization chamber is proposed as a suitable spectrometer. Advantages of the method with respect to the previously mentioned ones may include simpler spectra and low inherent natural neutron background. Its drawbacks include a present lack of suitable commercially available photon sources, induced neutron backgrounds and low detection rates. This paper describes the method, including kinematics, sources, detectors and geometries. Simulations using a modified Geant4 Monte Carlo modelling code are described and results are presented to support feasibility. Further experiments are recommended. © 2013 Published by Elsevier B.V.

Postma J.V.,University of Alberta | Yee E.,Defence RandD Canada Suffield | Wilson J.D.,University of Alberta
Boundary-Layer Meteorology | Year: 2012

A theoretical requirement of the Interaction by Exchange with the Conditional Mean (IECM) micromixing model is that the mean concentration field produced by it must be consistent with the mean concentration field produced by a traditional Lagrangian stochastic (LS) marked particle model. We examine the violation of this requirement that occurs in a coupled LS-IECM model when unrealistically high particle velocities occur. No successful strategy was found to mitigate the effects of these rogue trajectories. It is our hope that this work will provide renewed impetus for investigation into rogue trajectories and methods to eliminate them from LS models. © 2012 Springer Science+Business Media B.V.

Postma J.V.,University of Alberta | Yee E.,Defence RandD Canada Suffield | Wilson J.D.,University of Alberta
Agricultural and Forest Meteorology | Year: 2012

A Lagrangian stochastic (LS) implementation of an interaction by exchange with the conditional mean (IECM) micromixing model is used to estimate concentration fluctuations in plumes dispersing from an in-canopy, localized source into a model plant canopy flow. The sensitivity of the LS-IECM model to the underlying Eulerian flow statistics is investigated by comparing model predictions from simulations driven by two interpolations of the same water-channel flow data. The two simulations showed minor differences in the predicted mean concentration but marked differences in the standard deviation, skewness and kurtosis of concentration. This is shown to be caused by differences in the turbulent kinetic energy (TKE) dissipation rates between the two interpolations and their effects on the IECM model. The LS-IECM model predictions of the first four moments of the scalar concentration field showed fair to good conformance (depending on which TKE dissipation rate is used) with experimental water-channel dispersion data. © 2012 Elsevier B.V.

Irvine S.E.,Defence RandD Canada Suffield
IEEE Geoscience and Remote Sensing Letters | Year: 2012

The experimental results of the response of a single-transmitter-single- receiver electromagnetic induction sensor to a linear conductor are reported. First, the sensor geometry is given, and a simple model is derived to predict the survey profile of the instrument as it moves over a linear conductor. Next, the experimental apparatus is described, and the acquired results are compared with those predicted by the model. As part of this analysis, various orientations of the transmitter and receiver dipoles are considered, as well as different tilt angles of the sensor head. The variation of peak signal strength with height above the linear conductor is also investigated. In all cases, excellent agreement between experiment and theory is achieved. These results demonstrate the potential for implementing simple sensors for detecting linear conductors or buried utilities and are important for verification of theoretical analyses. © 2012 IEEE.

McFee J.E.,Defence RandD Canada Suffield | Mosquera C.M.,Defence RandD Canada Suffield | Faust A.A.,Defence RandD Canada Suffield
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2016

An analysis of digitized pulse waveforms from experiments with LaBr3(Ce) and LaCl3(Ce) detectors is presented. Pulse waveforms from both scintillator types were captured in the presence of 22Na and 60Co sources and also background alone. Two methods to extract pulse shape discrimination (PSD) parameters and estimate energy spectra were compared. The first involved least squares fitting of the pulse waveforms to a physics-based model of one or two exponentially modified Gaussian functions. The second was the conventional gated integration method. The model fitting method produced better PSD than gated integration for LaCl3(Ce) and higher resolution energy spectra for both scintillator types. A disadvantage to the model fitting approach is that it is more computationally complex and about 5 times slower. LaBr3(Ce) waveforms had a single decay component and showed no ability for alpha/electron PSD. LaCl3(Ce) was observed to have short and long decay components and alpha/electron discrimination was observed. © 2016 Published by Elsevier B.V.

Pedersen D.B.,Defence RandD Canada Suffield | Wang S.,Defence RandD Canada Suffield
Journal of Physical Chemistry C | Year: 2012

Naked (i.e., ligand-free) Ag nanoparticle anions, 6.5 ± 0.5 nm in diameter, have been synthesized in the gas phase and deposited as monodispersed monolayers. By tuning the average interparticle separation in these assemblies, the monodispersed structure was found to be stable only when the average edge-to-edge distance between nanoparticle anions was greater than 3.5 ± 0.5 nm. This separation was found to mark a fundamental limit where the integrity of the monodispersed structure is compromised due to a spontaneous coalescence process. Conductivity measurements taken in real time, as the interparticle separation was steadily decreased, clearly show a dramatic transition at an interparticle separation of 3.5 ± 0.5 nm that manifests itself as a near complete change in conduction mechanism from tunneling to percolation. The observation of a fundamental 3.5 ± 0.5 nm limit, below which monodispersions of nanoparticles are not stable, has significant consequences in the field of nanofabrication. These results suggest that it is not possible to place two small naked metal nanoparticles any closer than this. To provide some context and understanding of the forces controlling this fundamental limit, a diatomic model is helpful. Much of the chemistry and physics of the nanoparticle anion assemblies can be understood in terms of the classical forces acting between two particles (i.e., a pseudodiatomic). In this context, the coalescence limit is the result of a curve-crossing process that occurs at a 3.5 nm edge-to-edge distance. © 2011 American Chemical Society.

Yee E.,Defence RandD Canada Suffield
International Journal of Environment and Pollution | Year: 2012

A Bayesian inference scheme is used to address the problem of general source reconstruction. To this purpose, starting from a simple, physically motivated structure-based representation for a general source distribution, Bayesian probability theory is used to formulate the full joint posterior probability density function for the parameters in this representation. The exploration of the high-dimensional parameter space using simulated annealing and a Markov chain Monte Carlo sampler is described. The explicit linkage between the computational tools used for posterior sampling and concepts in statistical mechanics is emphasised. The proposed methodology is validated using a real dispersion experiment involving a multiple source release. Copyright © 2012 Inderscience Enterprises Ltd.

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