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Mechanical Systems Engineering Research

Thayer School's single, unified department of engineering is uniquely suited for in-depth studies in mechanical systems engineering—one of the broadest engineering disciplines. Current research integrates concepts from chemistry, electrical and computer engineering, and materials science. At the smallest scales mechanical engineering becomes molecular engineering within the growing field of nanotechnology.

Control Systems & Intelligent Systems

See also Microelectromechanical Systems

Distributed and/or complex systems are characterized by: 1) sensors and actuators that are distributed spatially over a large volume, and whose locations can be changed dynamically; 2) system dynamics that are poorly known, time-varying, have complex connectivity and interdependencies, or are embodied by multiple modalities; or 3) systems with a large number of individual components whose collective behavior cannot be anticipated. These systems are found in a multitude of engineering and life science applications, such as sensor networks, manufacturing systems, large-scale infrastructure monitoring systems, and autonomous underwater, land, air, and space vehicle networks. Such multiple-component systems have a degree of complexity that renders traditional single-component-based control methods inadequate. Our goal is to conduct cross-disciplinary research in intelligent control of distributed systems in order to develop new methods of modeling and control. More specific research topics are described below.

Cooperative control of multi-robot systems focuses on modeling and control of groups of high-speed mobile robots while accommodating communication latencies and nonlinear vehicle dynamics. In distributed cooperative control, robots communicate information about their state to each other; communication latencies and error depends on the amount of information communicated and the number of robots. We are developing distributed control system modeling and design tools that seek to maximize control bandwidth for a given information set. These tools will also assist in assessing the value of information transmitted in maintaining stability and performance of group dynamics. Both potential function path planning and control and predictive control methods are being developed.
(Faculty contacts: Ray, Phan)

Robot design and smart navigation focuses on developing affordable robot designs that employ "smart navigation" for path planning and mobility in extreme terrain, rather than complex and expensive vision systems. We are developing solar-powered robotic platforms for deploying scientific instrumentation over hundreds of kilometers in Arctic and Antarctic regions. These robots employ proprioceptive sensors to determine whether difficult terrain is passable, and if not, to navigate around such terrain.
(Faculty contact: Ray)

Terrain identification research focuses on using small, lightweight robots to classify, characterize, and identify terrain properties necessary to predict mobility of these vehicles on the terrain. Terramechanics models for heavy vehicles are well understood, but similar comprehensive models do not exist for lightweight (sub-500 kg) vehicles. We are developing terrain models and modeling tools that can be used to asses mobility on a given terrain, while avoiding maneuvers that cause immobilization. We seek to integrate terrain identification and traction/stability control of the robots in order to allow autonomous or remote control of these robots at the maximum attainable speeds and accelerations achievable on the terrain.
(Faculty contact: Ray)

Active Control, Model Predictive Control & Iterative Learning Control

Active noise control has applications for communication headsets, hearing protection systems, and hearing aids. These applications blend mechatronics—the design of mechanical and electrical systems—with high performance control algorithms to improve active noise attenuation.
(Faculty contact: Ray)

Model predictive control is control action based on a prediction of the system output a number of time steps into the future. Originated from chemical process engineering, model predictive control has found its way into virtually all areas of control engineering. Our research focuses on the development of a general formulation of predictive control that subsumes both the input-output and state-space perspectives. We seek comprehensive answers to questions such as: What is the simplest way to justify the existence and structures of various input-output predictive models? How does one arrive at an input-output controller if the starting point of the derivation is a state-space model? Can explicit state-space model identification be avoided? What is an efficient strategy to synthesize a predictive controller from input-output data directly without having to resort to model identification? What is the role of predictive control in the disturbance rejection problem? How can we design model predictive controllers for a swarm of robots?
(Faculty contact: Phan)

Iterative learning control refers to the mechanism by which the necessary control can be synthesized by repeated trials—based on the fundamental recognition that repeated practice is a common mode of human learning. Learning control is most suitable for operations where the same task is to be performed over and over again, e.g., robots in a manufacturing line. Available learning techniques range from those requiring no knowledge of the system dynamics to more sophisticated methods involving system identification to make the learning process efficient and successful on difficult problems. Our research finds ways to design optimal iterative learning controllers that are robust to model uncertainty, and capable of producing monotonic convergence.
(Faculty contact: Phan)

System Identification

System identification refers to the general process of extracting information about a system from measured input-output data. A typical outcome is an input-output model which may be static or dynamic, deterministic or stochastic, linear or nonlinear. One can use such an input-output model for simulation, controller design, or analysis. System identification can extract the physical properties of a system such as its mass, stiffness, and damping distribution. System identification methods can also be applied to obtain information other than a model of a system. For example, it can be used to identify an observer or Kalman filter gain, existing feedback controller gain, disturbance environment, or to detect actuator and sensor failure. The same theory can even be used to synthesize feedback or feedforward controller gains directly from input-output data without having to obtain an intermediate model of the system first. System identification has widespread applications in virtually all areas of engineering including chemical, electrical, mechanical, biomedical, aerospace engineering, and economics.
(Faculty contact: Phan)

Soft Computing

Recent years have seen major advances in actuator and sensor technology, computing technology, and the emergence of a collection of new tools that can solve problems in an unconventional yet effective way:

Artificial neural networks are constructed from identical data processing elements arranged in some regular pattern. These networks exhibit surprising abilities to capture non-linear relationships among variables, perform pattern classification and feature extraction, and encode associate memory, among others.
Fuzzy logic can emulate human-like rule-based operations using linguistic terms such as "if it starts to become hot, turn the temperature down a little bit."
Genetic algorithms give us a new way to perform optimization without actually solving equations in the traditional sense.

Other soft computing techniques such as DNA computing and simulated annealing are also very intriguing. Our research finds ways to apply these tools to problems such as the control of a magneto-hydrodynamic power generators for hypersonic aircraft, and the evolution of a robot's rule base for obstacle avoidance and target acquisition.
(Faculty contact: Phan)

Fluid Mechanics

Magnetohydrodynamics (MHD) is a combination of fluid mechanics and electromagnetics concerned with the motion of electrically-conducting liquids and gases in the presence of a magnetic field. Examples of technical applications are electric power generation, electromagnetic pumping and propulsion as well as control of moving molten metals. MHD research at Thayer School is concerned with the high-speed flow of tenuous, ionized gas from the Sun past the Earth's magnetic field. The research is fundamental in nature but also contributes to the development of a national space-weather forecasting capability. This capability is important for the safe operation of manned spacecraft and a variety of communications, global-positioning, and defense satellite systems, as well as for protection against geomagnetically-induced electric power outages on Earth.
(Faculty contact: Lotko)

Solid Mechanics & Mechanical Design

Thermal Science & Heat Transfer

Pulse electro-thermal de-icing (PETD) is a new method of ice removal and prevention that uses short pulses of electricity applied directly to an ice-material interface. PETD uses a thin, electrically-conductive film applied to the substrate. The film is then heated with a milliseconds-long pulse of electricity. Because only a micrometer-thin layer of ice is melted, PETD achieves nearly perfect efficiency even in extreme cold. Regular pulsing can keep surfaces consistently ice-free while maintaining low overall power consumption. Research is ongoing for the extensive applications of PETD such as de-icing of airplanes, ships, refrigeration systems, windshields, power lines, bridges and buildings, roads and walkways, and windmill turbines.
(Faculty contact: Petrenko)

Thermal spraying involves particles less than 100 microns in diameter. Particles are accelerated and heated while exposed to a supersonic hot gas stream forming a gas dynamic shock upstream of each particle. Current research aims to solve the heat transfer in this complex flow with computational fluid dynamics.
(Faculty contact: Richter)

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