MEAM Seminar Series Summer 2009

Seminars are held on Thursdays at 2:00 p.m. in 337 Towne Building (220 South 33rd Street), unless otherwise noted. Click the date of each seminar to find out additional information about the speaker and topic.

May 14
Anuj Chaudhri, PhD Candidate
"Dissipative particle dynamics for mesoscopic particle-based thermal-fluid simulations"

Speaker: Anuj Chaudhri
PhD Candidate
Advisor: Jennifer R. Lukes
Mechanical Engineering and Applied Mechanics, University of Pennsylvania

Abstract:
The primary objective of this dissertation is to develop theoretical and computational tools to simulate engineering problems in fluid mechanics and heat transfer using a mesoscopic framework. Phase change phenomena are ubiquitous in day to day technological and engineering applications. They are amongst the most complex transport processes and involve the interplay of multiple time and length scales, nonequilibrium and interfacial effects. Previous work on phase change phenomena at the continuum level has focused mainly on semi-theoretical models and correlations with experiments. Studies at the atomistic level using molecular dynamics have been limited to smaller nanoscopic length and time scales. Grid-based mesoscopic methods such as lattice Boltzmann have been very useful for problems in fluid mechanics but suffer from an inadequate multiphase thermal model. The focus of this work will be on the dissipative particle dynamics mesoscopic method and its use in modeling problems in the thermal-fluids area. Previous work on dissipative particle dynamics has focused primarily on an isothermal model and had inconsistencies in notation and nondimensionalization. In this work, a new and consistent notation is introduced for multicomponent systems and scaling factors for unknown parameters are determined. The dynamic properties of an ideal dissipative particle dynamics fluid are characterized by varying the integration algorithm, time step and friction factor. The energy-conserving model is analyzed in great depth and is shown to work very well for higher dimensional heat conduction problems for the first time. The model is further extended to investigate the Rayleigh B´enard convective instability problem in a single phase fluid for the first time and can easily be used to study other problems in convection. To develop a multiphase thermal framework, a phase change model is incorporated into the energy-conserving model and is being used to study vapor nucleation phenomena at mesoscopic length and time scales.

July 8
Mustafa-Ali Arat, MSE Student
"Brushless DC motor position controller for modular robotics applications"

Speaker: Mustafa-Ali Arat
MSE Student
Advisor: Mark Yim
Mechanical Engineering and Applied Mechanics, University of Pennsylvania

Abstract:
Modular Robotics has been a very appealing research field since the late 1980s. Many modular systems have been developed and today even commercial systems are available. The most significant feature of the modular systems, which separates them from other robotic systems, is that they are designed to be reconfigurable so that they can easily adapt themselves to perform varying tasks. Actuators in modular robots therefore need high torque performance, and brushless direct current (BLDC) motors have become the actuator of choice for modular robot applications due to their high torque capacities and lower weight. Although certain custom-made BLDC motors have the advantage of delivering higher torques while remaining cheaper than their commercial counterparts, they have proven to be more difficult to control because they suffer from cogging, which is an undesirable torque that opposes or assists the motion of the rotor. This study aims to reduce the cogging in such motors by developing a precise position controller, which employs an algorithm that uses the proportional-derivative (PD) control, to overcome the cogging effect. The results of this study will serve as a first step in developing a complete actuator for a new modular system to be designed in the Modular Robotics Laboratory at the University of Pennsylvania.

August 6
Kevin C. Galloway, PhD Candidate
"Developments toward passive variable compliance for dynamic legged robots"

Speaker: Kevin C. Galloway
PhD Candidate
Advisor: Mark Yim
Mechanical Engineering and Applied Mechanics, University of Pennsylvania

Abstract:
Recent developments in dynamic legged locomotion have focused on encoding a substantial component of leg intelligence into passive compliant mechanisms. One of the limitations of this approach is reduced adaptability: the final leg mechanism usually performs optimally for a small range of conditions (i.e. a certain robot weight, terrain, speed, gait, and so forth). For many situations in which a small locomotion system experiences a change in any of these conditions, it is desirable to have a variable stiffness leg to tune the natural frequency of the system for effective gait control.

To date, the mechanical complexities of designing usefully robust tunable passive compliance into legs has precluded their implementation on practical running robots. In this seminar, we present an overview of variable stiffness legs, and introduce new run-time tuning methods specifically for autonomous dynamic legged locomotion. We also introduce a simple leg model that captures the spatial compliance of the unable leg and present preliminary experimental data on the advantages of variable passive compliant legs. Lastly, we will discuss design rules, materials, and manufacturing methods that lead to robust passive compliant legs.

August 7
Ethan Stump, PhD Candidate
"Control for localization and visibility maintenance of an independent agent using robotic teams "

Speaker: Ethan Stump
PhD Candidate
Advisor: Vijay Kumar
Mechanical Engineering and Applied Mechanics, University of Pennsylvania

Abstract:
Given a non-cooperative agent, we seek to formulate a control strategy to enable a team of robots to localize and track the agent in a complex but known environment while maintaining a continuously optimized line-of-sight communication chain to a fixed base station. We focus on two aspects of the problem. First, we investigate the estimation of the agent's location by using nonlinear sensing modalities, in particular that of range-only sensing, and formulate a control strategy based on improving this estimation using one or more robots working to independently gather information. Second, we develop methods to plan and sequence robot deployments that will establish and maintain line-of-sight chains between the independent agent and the fixed base station. These methods will lead to feedback control laws that can realize this plan and ensure proper navigation and collision avoidance.

August 24
Anuj Chaudhri, PhD Candidate
"Dissipative particle dynamics for mesoscopic particle-based thermal-fluid simulations"

Speaker: Anuj Chaudhri
PhD Candidate
Advisor: Jennifer R. Lukes
Mechanical Engineering and Applied Mechanics, University of Pennsylvania

Abstract:
The primary objective of this dissertation is to develop theoretical and computational tools to simulate engineering problems in fluid mechanics and heat transfer using a mesoscopic framework. Phase change phenomena are ubiquitous in day to day technological and engineering applications. They are amongst the most complex transport processes and involve the interplay of multiple time and length scales, nonequilibrium and interfacial effects. Previous work on phase change phenomena at the continuum level has focused mainly on semi-theoretical models and correlations with experiments. Studies at the atomistic level using molecular dynamics have been limited to smaller nanoscopic length and time scales. Grid-based mesoscopic methods such as lattice Boltzmann have been very useful for problems in fluid mechanics but suffer from an inadequate multiphase thermal model. The focus of this work will be on the dissipative particle dynamics mesoscopic method and its use in modeling problems in the thermal-fluids area. Previous work on dissipative particle dynamics has focused primarily on an isothermal model and had inconsistencies in notation and nondimensionalization. In this work, a new and consistent notation is introduced for multicomponent systems and scaling factors for unknown parameters are determined. The dynamic properties of an ideal dissipative particle dynamics fluid are characterized by varying the integration algorithm, time step and friction factor. The energy-conserving model is analyzed in great depth and is shown to work very well for higher dimensional heat conduction problems for the first time. The model is further extended to investigate the Rayleigh B´enard convective instability problem in a single phase fluid for the first time and can easily be used to study other problems in convection. To develop a multiphase thermal framework, a phase change model is incorporated into the energy-conserving model and is being used to study vapor nucleation phenomena at mesoscopic length and time scales.