The objective of this research is to present a theoretical study of the compressibility effects on the performance of an electric D/C motor driven synthetic jet actuator for flow separation control. Hot wire anemometer experiments were conducted to validate the jet exit velocities predicted by the theoretical model. The optimal jet exit velocity required to achieve maximum flow reattachment at reasonable blowing momentum coefficients is predicted. A dynamic electro-acoustic model of the D/C motor driven actuator is developed to accurately predict its performance and efficiency. This model should help formulate a feedback optimal control strategy for real-time flow control using an array of actuators. This model is validated by comparing with hot wire anemometer experiments conducted under similar conditions. The effects of geometric parameters like the slot width, slot geometry, and cavity volume on the performance of the actuator are also tested using this model.

A reflective type Fresnel lens using an array of micromirrors is designed and fabricated using the MUMPs?? surface micromachining process. The focal length of the lens can be rapidly changed by controlling both the rotation and translation of electrostatically actuated micromirrors. The suspension spring, pedestal and electrodes are located under the mirror to maximize the optical efficiency. The micromirror translation and rotation are plotted versus the applied voltage. Relations are provided for the fill-factor and the numerical aperture as functions of the lens diameter, the mirror size, and the tolerances specified by the MUMPs?? design rules. Linnik interferometry is used to measure the translation, rotation, and flatness of a fabricated micromirror. The reflective type Fresnel lens is controlled by independent DC voltages of 16 channels with a 0 to 50V range, and translational and torsional stiffness are calibrated with measured data. The spot diameter of the point source by the fabricated and electrostatically controlled reflective type Fresnel lens is measured to test focusing quality of the lens.

The annular-return flow and the utility of small-scale, combustion-based actuators for its control are investigated experimentally. The annular return flow is generated by an axial primary round jet, which impinges normally on a bounded end wall of a concentric tube, subsequently reverses direction, and exits the tube in a countercurrent flow to the primary jet. The combustion-based actuator generates a momentary (pulsed) jet that is produced by the ignition of a mixture of gaseous fuel and oxidizer in a small (cubic centimeter scale) combustion chamber. The operating frequency and the phase can be continuously varied by independently controlling the flow rate of the fuel/oxidizer and the ignition frequency. Two radially-opposing actuators are mounted on the wall of the annular return tube and are used to trigger flow transients that alter the global flow through strong feedback. The characteristics of the baseline flow and the effects of actuation are investigated using particle image velocimetry (PIV) as well as static and unsteady pressure measurements. The baseline flow is highly unstable, exhibiting very high rates of flow recirculation. The actuator jet acts as an azimuthal obstruction deflecting the primary jet and causing it to flow around the actuator jet. Furthermore, the interaction of the primary jet with the actuator jets generates large-scale circulation domains.

Earlier investigations of Combustion Powered Actuation (COMPACT) have demonstrated its utility for high-speed aerodynamic flow control. In this actuation approach, momentary (pulsed) actuation jets are produced by the ignition of a mixture of gaseous fuel and oxidizer within a cubic-centimeter scale chamber. The combustion process yields a high pressure burst and the ejection of a high-speed exhaust jet. The present thesis focuses on characterization of the effects of the internal flow (which is altered through the fuel and oxidizer inlet streams) on mixing and flame propagation within the actuator's combustion chamber, and thereby on actuator operation and performance. A test chamber with a grid of interchangeable air and fuel inlets was used for parametric investigations of the effects of inlet size and location. Actuator performance is characterized using dynamic pressure measurements and phase-locked Particle Image Velocimetry (PIV) of the combustor's internal flow field in the presence and absence of the active combustion process. Over the range tested, increased momentum of the air inlet jet for a given flow rate improves the actuator performance by increasing bulk velocities and small-scale motions within the chamber, thus yielding net higher flame propagation speed and subsequently faster pressure rise and higher pressure peak. Variation in inlet location that results in swirling flow within the chamber yields higher internal pressures while air flow over the spark ignition site yields lower internal pressures and erratic combustion. Improved refill and combustion processes will lead to enhanced performance combustor designs.

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Synthetic jet actuators for flow control applications have been an active topic of experimental research since the 90’s. Numerical simulations have become an important complement of that experimental work, providing detailed information of the dynamics of the controlled flow. This study is part of the AVOCET (Adaptive VOrticity Control Enabled flighT) project and is intended to provide computational support for the design and evaluation of closed-loop flow control with synthetic jet actuators for small scale Unmanned Aerial Vehicles (UAVs). The main objective is to analyze active flow control of a NACA4415 airfoil with tangential synthetic jets via computational modeling. A hybrid Reynolds-Averaged Navier-Stokes/Large Eddy Simulation (RANS/LES) turbulent model (called Delayed Detached-Eddy Simulation-DDES) was implemented in CDP, a kinetic energy conserving Computational Fluid Dynamics (CFD) code. CDP is a parallel unstructured grid incompressible flow solver, developed at the Center for Integrated Turbulence Simulations (CITS) at Stanford University. Two models of synthetic jet actuators have been developed and validated. The first is a detailed model in which the flow in and out of the actuator cavity is modeled. A second less costly model (RSSJ) was also developed in which the Reynolds stress produced by the actuator is modeled, based on information from the detailed model. Several static validation test cases at different angle of attack with modified NACA 4415 and Dragon Eye airfoils were performed. Numerical results show the effects of the actuators on the vortical structure of the flow, as well as on the aerodynamic properties. The main effect of the actuation on the time averaged vorticity field is a bending of the separation shear layer from the actuator toward the airfoil surface, resulting in changes in the aerodynamic properties. Full actuation of the suction side actuator reduces the pitching moment and increases the lift force, while the pressure side actuator increases the pitching moment and reduces the lift force. These observations are in agreement with experimental results. The effectiveness of the actuator is measured by the change in the aerodynamic properties of the airfoil in particular the lift ([Delta]C[subscript t]) and moment ([Delta]C[subscript m]) coefficients. Computational results for the actuator effectiveness show very good agreement with the experimental values (over the range of −2° to 10°). While the actuation modifies the global pressure distribution, the most pronounced effects are near the trailing edge in which a spike in the pressure coefficient (C[subscript p]) is observed. The local reduction of C[subscript p], for both the suction side and pressure side actuators, at x/c = 0.96 (the position of the actuators) is about 0.9 with respect to the unactuated case. This local reduction of the pressure is associated with the trapped vorticity and flow acceleration close to the trailing edge. The RSSJ model is designed to capture the synthetic jet time averaged behavior so that the high actuation frequencies are eliminated. This allows the time step to be increased by a factor of 5. This ad hoc model is also tested in dynamic simulations, in which its capacity to capture the detail model average performance was demonstrated. Finally, the RSSJ model was extended to a different airfoil profile (Dragon Eye) with good results. / text

Soldiers in the Unites States Army operate under uniquely demanding conditions with increasingly high performance expectations. Modern missions, including counter-insurgency operations in Iraq and Afghanistan, are complex operations. The Army expects this complexity to continue to increase. These conditions affect Soldier performance in combat. Despite spending billions of dollars to provide Soldiers with better equipment to meet the demands of the modern battlefield, the U.S. Army has dedicated comparatively little resources to measuring and improving individual Soldier performance in real-time. As a result, the Army does not objectively measure a Soldier’s performance at any point in their active duty career. The objective of this report is to demonstrate the utility and feasibility of monitoring Soldier performance in real-time by means of visual 3D performance maps supported by a Bayesian network model of Soldier performance. This work draws on techniques developed at the University of Texas’ Robotics Research Group for increasing performance in electro-mechanical systems. Humans and electro-mechanical systems are both complex and demonstrate non-linear performance trends which are often ignored by simplified analytical models. Therefore, application of empirical Bayesian models with visual presentation of data in 3D performance maps enables rapid understanding of important performance parameters for a specific Soldier. The performance maps can easily portray areas of non-linear performance that should be avoided or exploited, while presenting levels of uncertainty regarding the assessments, thus empowering the individual to make informed decisions regarding control and allocation of resources. The present work demonstrates the utility of visual performance maps by structuring 19 relatively mature 3D performance maps based on published empirical research data and analytical models related to human performance. Based on a broad review of the literature, the present research evaluated 10 potential physiological indicators, termed biomarkers that correlate with human responses to a select set of stressors, referred to as impact parameters. The 10 evaluated impact parameters affect various components of Soldier performance. The present research evaluated the documentation of these relationships in the existing literature with regard to 9 general Soldier performance measures. Identifying the research supported relationships from biomarkers to impact parameters to Soldier performance measures resulted in a preliminary Bayesian Soldier Performance Model, from which it is possible to create 70 distinct 3D performance maps. Based on the quality of the relationships identified in the reviewed literature, and a contemporary evaluation of existing sensor technology for the related biomarkers, the present research assessed 26 of the potential 70 performance maps as being achievable in the near-term. Continuing development of the Soldier Performance Model (SPM) as proposed in this report has the potential to increase Soldier performance while simultaneously improving Soldier well-being, reducing risk of physical and mental injury, and reducing downstream treatment cost. / text

Inspiration from biological systems suggests that robots should demonstrate same level of capabilities that are embedded in biological systems in performing safe and successful interaction with the humans. The major challenge in physical human robot interaction tasks in anthropic environment is the safe sharing of robot work space such that robot will not cause harm or injury to the human under any operating condition. Embedding human like adaptable compliance characteristics into robot manipulators can provide safe physical human robot interaction in constrained motion tasks. In robotics, this property can be achieved by using active, passive and semi active compliant actuation devices. Traditional methods of active and passive compliance lead to complex control systems and complex mechanical design. In this thesis we present compliant robot manipulator system with semi active compliant device having magneto rheological fluid based actuation mechanism. Human like adaptable compliance is achieved by controlling the properties of the magneto rheological fluid inside joint actuator. This method offers high operational accuracy, intrinsic safety and high absorption to impacts. Safety is assured by mechanism design rather than by conventional approach based on advance control. Control schemes for implementing adaptable compliance are implemented in parallel with the robot motion control that brings much simple interaction control strategy compared to other methods. Here we address two main issues: human robot collision safety and robot motion performance.We present existing human robot collision safety standards and evaluate the proposed actuation mechanism on the basis of static and dynamic collision tests. Static collision safety analysis is based on Yamada’s safety criterion and the adaptable compliance control scheme keeps the robot in the safe region of operation. For the dynamic collision safety analysis, Yamada’s impact force criterion and head injury criterion are employed. Experimental results validate the effectiveness of our solution. In addition, the results with head injury criterion showed the need to investigate human bio-mechanics in more details in order to acquire adequate knowledge for estimating the injury severity index for robots interacting with humans. We analyzed the robot motion performance in several physical human robot interaction tasks. Three interaction scenarios are studied to simulate human robot physical contact in direct and inadvertent contact situations. Respective control disciplines for the joint actuators are designed and implemented with much simplified adaptable compliance control scheme. The series of experimental tests in direct and inadvertent contact situations validate our solution of implementing human like adaptable compliance during robot motion and prove the safe interaction with humans in anthropic domains.

This thesis presents a general simulation framework used for evaluating the performance of bilateral teleoperation systems under consistent and controllable network conditions. A teleoperation system is where an operator uses a master device to control a slave robot through a communication link. The communication link between the master and slave has an important impact on the system performance. Network emulation using ns-2 has been proposed as a way of simulating the communication link. It allows for the network conditions to be controlled and for repeatable results. The proposed setup was used to test the performance of a hydraulic actuator under various conditions of wired and wireless networks. Three control schemes were evaluated using various combinations of time delay and packet loss. The system was also tested simulating wireless communication between the master and slave to determine the effects of transmission power and distance on the performance of the system.

No description available.