The first seminar of the semester will be this Friday! MASc CandidateMajid Tanbakuei Kashani will be giving a talk on “Effect of Forming Process on the Deformational Behaviour of Steel Pipes”. The seminar abstract is below.
Date: Friday September 16th
Room: SITE J0106
Buried pipeline networks play a vital role in transportation of oil and natural gas from centers of productions to centers of consumptions. A common manufacturing technique for such pipes is the UOE process, where a flat plate is first formed into a U shape, then in an O shape, welded at the seam, and Expanded before being shipped on site. The UOE forming process induces residual strains in the pipe.
When buried pipelines cross the regions of discontinuous permafrost, they undergo differential frost heaving, inducing significant bending deformations, which potentially induce local buckling in the pipe wall. To control local buckling, design standards impose threshold limits on buckling strains. Such threshold values are primarily based on costly full-scale experimental results. Past nonlinear finite element analysis attempts aiming at determining the threshold buckling strains have neglected the presence of residual stresses induced by UOE forming and were thus found to grossly overestimate the buckling strains compared to those based experiments.
Within the above context, the present study focuses on developing a numeric technique to predict the residual stresses induced in UOE forming, and incorporating the residual stresses in 3D nonlinear FEA modeling to predict improved buckling strain limits. Comparisons against conventional analysis techniques that omit residual stresses reveal the importance of incorporating residual stresses when quantifying buckling strains.
Rym Mehri will present her PhD thesis seminar this coming Friday. She will be giving a talk on “Investigation and Characterization of Red Blood Cells Aggregation: Experimental and Numerical Study”. The talk abstract is below. All are welcome!
Date: Friday March 4
Room: CBY B205
Red blood cells (RBC) are the most abundant cells in human blood, representing 40 to 45% of the blood volume (hematocrit). These cells have the particularity to deform and bridge together to form aggregates under very low shear rates. Due to their unique mechanical properties, RBCs represent the focus of numerous experimental and numerical studies, especially, at the microscopic level. In fact, the theory and mechanics behind aggregation are not yet completely understood. Understanding the conditions of aggregate formation could provide a better understanding of the mechanics behind this phenomenon and could help to determine aggregate behaviour related to clinical application such as diabetes and heart disease.
The purpose of this work is to provide a novel method to analyze, understand and mimic blood behaviour in the microcirculation. The main objective is to develop a methodology in order to quantify and characterize RBC aggregates and hence comprehend the non-Newtonian behaviour of blood at the microscale. For this purpose, suspensions of porcine blood and human blood are tested in vitro in a Polydimethylsiloxane (PDMS) microchannel to characterize the RBC aggregates. These microchannels are fabricated using standard photolithography methods. Experiments are performed using a micro Particle Image Velocimetry (μPIV) system for shear rate measurements coupled with a high speed camera for the flow visualization. Corresponding numerical simulations are conducted using a research Computational Fluid Dynamic (CFD) Solver, Nek5000, based on the spectral element method.
RBC aggregate sizes are quantified in controlled and measurable shear rates environments for 5, 10 and 15% hematocrit. Aggregate sizes are determined using image processing techniques. Velocity fields of the blood flow are measured experimentally and compared to numerical simulations using simple non-Newtonian models (Power law and Carreau models).
This work establishes for the first time a relationship between RBC aggregate sizes and corresponding shear rates as well as one between RBC aggregate sizes and apparent blood viscosity at body temperature. The results of the investigation can be used to help develop new numerical models for non-Newtonian blood flow.
We have special guest seminar this Friday by Dr. Maurizio Porfiri. He will be giving a talk on “Modeling finite amplitude vibrations of flexible beams in viscous fluids”.
Modeling finite amplitude vibrations of flexible beams in viscous fluids
The analysis of mechanical vibrations of flexible slender structures immersed in viscous fluids is of fundamental importance in many technical fields, across a wide range of length and force scales, from atomic force microscopy to naval engineering. One of the main challenges in this class of problems involves the prediction of the forces exerted on the oscillating structure by the fluid. In this talk, I will present a comprehensive modeling framework to interpret and predict the steady-state response of flexible beams oscillating in viscous fluids. We will depart from unsteady Stokes hydrodynamics to consider finite-amplitude structural vibrations, for which vorticity generation and transport modulate the fluid-structure interaction. To illustrate the methodology, I will focus on harmonic bending vibrations of a thin cantilever beam in an unbounded fluid. Theoretical results will be validated against direct three-dimensional fluid dynamics simulations and experiments on centimeter-size beams undergoing low frequency and finite amplitude underwater vibrations. Then, I will briefly touch on torsional vibrations and discuss the role of finite beam thickness, interactions with side walls, polychromatic excitations, and application to biomimetic propulsion and energy harvesting. I will conclude with a series of open questions and possible research directions.
Maurizio Porfiri was born in Rome, Italy in 1976. He received M.Sc. and Ph.D. degrees in Engineering Mechanics from Virginia Tech, in 2000 and 2006; a “Laurea” in Electrical Engineering (with honours) and a Ph.D. in Theoretical and Applied Mechanics from the University of Rome “La Sapienza” and the University of Toulon (dual degree program), in 2001 and 2005, respectively. From 2005 to 2006 he held a Post-doctoral position with the Electrical and Computer Engineering Department at Virginia Tech. He has been a member of the Faculty of the Mechanical and Aerospace Engineering Department of New York University Polytechnic School of Engineering since 2006, where he is currently a Professor. He is engaged in conducting and supervising research on dynamical systems theory, multiphysics modeling, and underwater robotics. Maurizio Porfiri is the author of approximately 200 journal publications and the recipient of the National Science Foundation CAREER award (Dynamical Systems program) in 2008. He has been included in the “Brilliant 10” list of Popular Science in 2010 and his research featured in all the major media outlets, including CNN, NPR, Scientific American, and Discovery Channel. Other significant recognitions include invitations to the Frontiers of Engineering Symposium and the Japan-America Frontiers of Engineering Symposium organized by National Academy of Engineering in 2011 and 2014, respectively; the Outstanding Young Alumnus award by the college of Engineering of Virginia Tech in 2012; the ASME Gary Anderson Early Achievement Award in 2013; the ASME DSCD Young Investigator Award in 2013; and the ASME C.D. Mote, Jr. Early Career Award, 2015.
Juanjuan Shi will be presenting her PhD work on Tuesday May 26th at 10:00am in CB B012. She will give a talk on “Morphology-based feature extraction method and resampling-free fault identification technique for bearing condition monitoring”. Her supervisors are Dr. Ming Liang and Dr. Dan-Sorin Necsulescu. Abstract of the talk is below.
Date: May 26th, 2015
Location: CBY B012
The effectiveness of vibration-based bearing fault diagnosis is often handicapped by 1) background noise and compounded effects of interferences for constant speed case, and 2) non-stationarity plus the two aforementioned factors for time-varying speed case. To address these issues and overcome the shortcomings of filter-parameter-dependence and error-propagation of conventional methods, novel methods are proposed in this work.
Two morphology-based methods are first proposed to extract fault features without prefiltering for constant speed case. The first method, based on fractal dimension (FD), can suppress interferences and highlight fault-induced impulse envelope by mapping the signal into FD representation. Its effectiveness, however, deteriorates with the interference frequency increase. Hence, the second method, which isolates impulses from interferences and noise via resonance behaviors, is developed. Both methods are independent of frequency information and can reveal fault features without prefiltering.
For bearings under variable speed, since resampling propagates error and complicates the process substantially resampling-free methods are innovatively proposed. A resampling-free order spectrum is derived via the joint application of generalized demodulation and short time Fourier transform, from which not only the existence of faults but also the location of faults can be revealed. Nevertheless, the success of this method relies upon an effective envelope demodulation. Based on the proposed resampling-free order spectrum, a time-frequency analysis technique termed dual demodulation transform is devised and applied to bearing fault identification, without envelope procedure.
And coming up next on the 19th May at 10:00am is Charles Blouin. Again, we’ll be in CBY B012 and I’ve been told there will be master coffee making and expert cookie tasting to go along with the seminar.
Charles will be talking about “Trajectory Optimization for a Small Airship Using an Optimal Control Solver”.
Date: May 19th, 2015
Location: CBY B012
Presented by: Charles Blouin, M.A.Sc. Candidate
Supervisors: Eric Lanteigne, Wail Gueaieb
Airships demonstrate long endurance and long range capabilities. Those characteristics make them ideal for telecommunication, surveillance and long endurance missions. To maximize flight time or reduce the time required to attain an objective, optimal trajectories are computed before a dirigible performs a maneuver. This seminar will demonstrate how the optimal trajectory problem can be formulated as a general optimization problem, and how it can be solved with a pseudo-spectral optimal control solver. Experimental and simulation results will be presented and discussed. In general, optimal control solvers can be used to optimize dynamical systems with respect to a performance index and subject to time varying inputs.
All are cordially invited to a graduate seminar talk to be given by Mostafa Fallah. He will give talk titled “Coordinated Deployment of Multiple Autonomous Agents in Area Coverage Problems with Evolving Risk.”
Date: Friday March 20th
Room: CBY D207
Coordinated missions with platoons of autonomous agents are rapidly becoming popular because of technological advances in computing, networking, miniaturization and combination of electromechanical systems. These multi-agents networks coordinate their actions to perform challenging spatially-distributed tasks such as search, survey, exploration, and mapping. Environmental monitoring and locational optimization are among the main applications of the emerging technology of wireless sensor networks where the optimality refers to the assignment of sub-regions to each agent, in such a way that a suitable coverage metric is maximized. Usually the coverage metric encodes a distribution of risk defined on the area, and a measure of the performance of individual robots with respect to points inside the region of interest. The risk density can be used to quantify spatial distributions of risk in the domain.
The solution of the optimal control problem in which the risk measures are not time varying is well known in the literature, with the optimal configuration of the robots given by the centroids of the Voronoi regions forming a centroidal Voronoi tessellation of the area. In other words, when the set of mobile robots converge to the corresponding centroids of the Voronoi tessellation dictated by the coverage metric, the coverage itself is maximized.
In this work, we consider a time-varying risk density function evolving according to a diffusion equation with varying boundary conditions that quantify a time-varying risk on the border of the workspace. Boundary conditions model a time varying flux of external threats coming into the area, averaged over the boundary length, so that we do not consider the individual kinematics of incoming threats but rather their averaged, distributed effect. This approach is similar to the one commonly adopted in continuum physics, in which kinematic descriptors are averaged over spatial domain and suitable continuum fields are introduced to describe their evolution. By adopting a first gradient constitutive relation between the flux and the density, we obtain a simple diffusion equation. Asymptotic convergenceand optimality of the non-autonomous system are studied by means of Barbalat’s Lemma and connections with varying boundary conditions are established. Some criteria on time-varying boundary conditions and its evolution are established to guarantee the stabilities of agents’ trajectories. A set of numerical simulations illustrate the theoretical results.
Everyone is cordially invited to hear Arian Panah present a talk on his MASc work: “Nonuniform Coverage with Time-Varying Risk Density Function”. The abstract of the talk is attached. The talk will start promptly at 2:30pm.
Date: Friday February 27
Room: CBY D207
Multi-agent systems are extensively used in several civilian and military applications, such as surveillance, space exploration, cooperative classification, and search and rescue, to name a few. An important class of applications involves the optimal spatial distribution of a group of mobile robots on a given area, where the optimality refers to the assignment of subregions to the robots, in such a way that a suitable coverage metric is maximized. Typically the coverage metric encodes a risk distribution defined on the area, and a measure of the performance of individual robots with respect to points inside the region of interest. The risk density can be used to assign spatial distributions of risk in the region, as for example typically happens in surveillance applications in which high value units have to be protected against external threats coming into a given area surrounding them.
The solution of the optimal control problem in which the metric is autonomous (a function of time only through the state of the robots) is well known in the literature, with the optimal location of the robots given by the centroids of the Voronoi regions forming a Voronoi tessellation of the area. In other words, when the set of mobile robots configure themselves as the centroids of the Voronoi tessellation dictated by the coverage metric, the coverage itself is maximized.
In this work we advance on this result by considering a generalized area control problem in which the coverage metric is non-autonomous, that is the coverage metric is time varying independently of the states of the robots. This generalization is motivated by the study of coverage control problems in which the coordinated motion of a set of mobile robots accounts for the kinematics of objects penetrating from the outside. Asymptotic convergence and optimality of the non-autonmous system are studied by means of Barbalat’s Lemma, and connections with the kinematics of the moving intruders is established. Several numerical simulation results are used to illustrate theoretical predictions.
Special Seminar! Speaker: Professor Dan Henningson, Royal Institute of Technology, Sweden
DATE: Friday February 6th, 2015
Location: University of Ottawa
Colonel By Pavilion, Room D207, 161 Louis Pasteur
2:30-‐3:30 pm: Presentation
3:30-‐4:00: Question and Answer Session
Abstract: Recent work within a number of EU-‐projects have shown that laminar flow can significantly reduce drag and fuel consumption of modern transport aircraft. Methods include the application of suction on the wing surface and the modification of the wing geometry in order to minimize growth of disturbances that causes laminar-‐turbulent transition. Efficient optimization of suction distributions and wing shapes can be performed using so called adjoint methods from optimal control theory. It is shown that such suction distributions and wing shapes significantly increases the laminar regions of wings on transport aircraft. Such optimization tools are now used in the next generation of laminar flow projects, such as the EU Joint Technology Initiative Clean Sky. Showstoppers and an outlook for future work will also be presented.
Dr. Henningson’s research and professional activities include Research on linear and nonlinear hydrodynamic stability and numerical simulation of transitional and turbulent flow. His academic background is Civ.Ing KTH 1983, M.Eng MIT 1985, PhD KTH 1988, Docent KTH 1992, while his professional history incudes Research Scientist FFA 1985-‐. Ass. Prof. Appl. Math. MIT 1988-‐1992. Adj. Prof. Mechanics (20%) KTH 1992-‐1998. Lektor Mechanics (50%) 1998-‐1999.
References: http://www.e-‐science.se/, http://www.cleansky.eu/
This event is being organized in collaboration with the University of Ottawa and the Carleton Mechanical and Aerospace Society (CMAS).
In the final instalment of our seminar series for 2014, Maha Manoubi will present a talk on her MASc work: “Criteria for a Flame to Propagate Between Neighboring Pockets of Reactive Gas”. The abstract of the talk is below. The talk will start promptly at 2:30pm.
**Kindly note the change of venue** since exams are now in full swing, we have to relocate our seminar to STE C0136
Friday December 12th, 2:30pm, Room STE C0136 (the glass engineering building next to CBY).
Criteria for a Flame to Propagate Between Neighboring Pockets of Reactive Gas
Maha Manoubi (M.A.Sc. Candidate), Supervisor: Dr. Matei. I. Radulescu
During severe accidents in water-cooled nuclear power plants, large amounts of hydrogen could be generated and released to form large composition heterogeneities. In fact, when leaks occur at several locations, or in the presence of complex geometries, multiple pockets of reactive gases may accumulate in certain locations, surrounded by inert gases. The focus of the present study is to determine the conditions for a flame to propagate between pockets of reactive mixtures separated by air and develop the scaling laws governing this phenomenon. The soap bubble technique was used to isolate pockets of reactive gas. The experiments were performed in hydrogen-air mixtures of different compositions. A largescale shadowgraph technique was implemented to visualize the events over length scales of almost 2 meters by 2 meters.
The high-speed visualization permitted to determine the transition mechanism and its influence on the critical separation distance between the pockets. The results have revealed that for mixtures characterized by high flame speed (at near stoichiometric compositions), where the effect of buoyancy is negligible, the propagation condition is related to the volumetric expansion. When the expansion of the gas kernel of the first pocket is sufficient for the hot products to reach the original position of the gas of the second pocket, the gas in the boundary layer of the second bubble ignites, permitting transition. However, for lean mixtures, or for bubbles sufficiently large, buoyancy effects become important and the spherical flame rises before it can reach the second bubble. Thus the critical separation distance becomes much smaller and is no longer determined by the expansion ratio. The critical radius of the flame that will rise due to buoyancy is presented as function of the mixture properties.
Hassan Shaban will present his PhD seminar talk this Friday on “Application of Machine Learning Techniques to Measurements in Gas-liquid Flows”. The abstract of the talk is below. Hassan is working on his PhD under the supervision of Dr. Stavros Tavoularis.
Date: Friday November 14th
Room: CBY B205.
Application of Machine Learning Techniques to Measurements in Gas-liquid Flows
Gas-liquid flows are found in the environment, as for example in clouds and breaking water waves, as well as in many industrial settings, as for example in heat exchangers containing boiling liquids and in petroleum pipelines in which oil flows mixed with gases. In this seminar, novel experimental methods will be presented for the identification of the flow regime and measurement of the flow rates of both phases in gas-liquid pipe flow using simple instrumentation. The differential pressure was measured in vertical upward air-water pipe flow, and the probability density function (PDF) of normalized differential pressure, was found to be indicative of the flow regime. The Elastic Maps algorithm was used to project this PDF onto a two-dimensional map, which when appropriately calibrated, allowed a user to identify the flow regime from the co-ordinates of the projected point. Also, the flow rates of the two phases in vertical upward air-water flow were found to have consistent effects on the PDF and power spectral density of normalized differential pressure. Artificial neural networks were used to correlate these features extracted from the differential pressure signal to the flow rates of both phases. Compared to other methods of flow regime identification and two-phase flow rate measurement, the developed methods had the advantages of being automated, non-intrusive and economical, such that their use was feasible in industrial as well as laboratory settings. To conclude the talk, other examples of the integration of machine learning with fluid flow instrumentation, as well as a practical application of similar methods in a header-feeder system will be briefly described.
Samuel Leblanc Robert will present his MASc seminar talk this Friday on “Restoration of damaged aluminum parts on aircrafts”. The abstract of the talk is below.
Date: Friday November 7th
Room: CBY B205.
Restoration of damaged aluminum parts on aircrafts
The aerospace industry is growing at a fast pace and aircrafts manufacturers consistently keep improving the performance and efficiency of their airplanes in order to reduce the operation cost. Aircrafts have become tremendously technological and a lot more emphasis has been accorded to details these days in order to get the edge over the competition. A field that is often forgotten is the restoration of damaged parts on airplanes. These gigantic flying mechanical devices are subjected to high structural and aerodynamic loads during their life. They are also exposed to rough environmental conditions that can enhance corrosion formation. These circumstances will eventually damage parts on aircrafts and results in high replacement costs. The aerospace industry has shown interest in several methods used to restore damaged aircraft parts.
One of these methods is cold gas dynamic spray. The process consists of accelerating particles (ranging from 1 to 100 μm typically) to high velocities and produce coatings. The purpose of the coating is to protect a surface from wear, oxidation and corrosion. It can also be used to restore cracks and missing material on a component. This research project focuses on the feasibility of producing pure aluminum and aluminum 7075 coatings to meet industry standards.
You are all cordially invited to hear Christian Poupart present his MASc seminar talk on “Control of ignition temperature in hybrid thermite-intermetallic reactive materials”. The abstract of the talk is below. The talk will start promptly at 2:30pm – the seminar form will not be available to late-comers.
Date: Friday October 31st
Room: CBY B205
Thermite and intermetallic mixtures have received renewed interest in recent years. Such reactive materials have been used since the early 1900s as welding agents for railway tracks. New technologies have recently made these compounds more attractive. This work focuses on a thermite mixture of Aluminum Copper-oxide. This reactive mixture is largely popular due to its ability to create a substantial amount of gaseous products, and a reaction front that can propagate at supersonic speeds. This compound can be used in many applications involving propellants, pyrotechnics and military. Ignition temperatures for this mixture have been reported to be approximately 660oC. This study will focus on lowering the ignition temperature of Al-CuO.
Studies have shown that by reducing particle size, and increasing surface contact of constituents, reaction kinetics can be improved dramatically. In this work we investigate the effects of arrested reactive milling (ARM) on the reaction kinetics of mixtures of Aluminum Copper-Oxide and Nickel-Aluminum. Ni-Al is a mixture called an intermetallic. Intermetallic reactions are usually gasless, and highly exothermic. Previous reports have shown that ARM significantly reduces the ignition temperature of Ni-Al. The microstructure of these compounds becomes dependent on the duration of the milling process. Mechanical milling of powders reduces the particle size, and creates a constituent interface at the sub-micron level. Ignition temperatures of Al-CuO and Ni-Al are strongly dependent on the milling time. The ignition temperature of Al-CuO was reduced to 600oC for milling time of 16 minutes. The ignition temperature of Ni-Al was reduced from 660oC down to 207oC for a milling time of 40 minutes. Hybrid mixtures of Al-CuO-Ni are then created with the milled constituents, at different concentrations. Results show that the ignition temperature of a hybrid system is dependent on the concentration of constituents. The lowest ignition temperature observed was approximately 250oC for a milled hybrid mixture containing 25% (by mass) of 16 minute milled Al-CuO and 75% milled Ni-Al.
After many decades lost in the darkness of the CBY dungeon known as B08D, a mythical creature of mediocre proportions emerges in order to present his thesis. No one really knows how he got to work on guitars. But one thing is certain; his thesis might be a little easier to understand than most… Many unconfirmed sightings have been reported over the years by students who may or may not have had him as a TA in their undergrad, which just reinforces the timeless nature of the beast. Some say that that sightings are even rarer in the summer months when strange phone calls to the dungeon are received asking for favours. Nobody really knows how any other human being agreed to work on a project similar to his own but many feel uneasy at the sight of the blue Maple code sprawled across his computer screen. Interestingly, some rumours have it that the creature’s keeper is the new department chair, waiting to unleash the beast on a new, unsuspecting group of students. Only time will tell what ravages await…
Yesterday, Amir Behnamian gave his Ph.D. ’s thesis seminar.
Yesterday, Scott Audette gave his M.A.Sc.’s thesis seminar.