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A study was conducted on the measurement of skin friction, the least under-stood component of drag. Skin friction is considered the "last frontier" in drag reduction for supersonic flight, but to understand skin friction, it must be accurately measured. This study utilized the direct measuring technique for skin friction. A small de-vice, termed a skin friction gage, measures the stress on a cantilever beam topped with a movable surface piece as a shear flow passes over the flush surface. The improvement of these devices for various flow fields is ongoing. A problem that arose with many designs was leakage of a gap-filling liquid. The typical direct measuring skin friction gage uses oil in a gap between the cantilever beam and the encasement to dampen vibrations, to create an even flow over the surface, and for temperature compensation. In high speed testing the oil leaks out; therefore, a gage with rubber to fill the gap instead of oil was introduced This study employed a finite element method model to fully understand the strains involved with the rubber and the skin friction gage. The development of a calibration device, called the Calibration Rig, for the rubber skin friction gages was constructed. The Calibration Rig was successful, but deemed to be more cumbersome than initially expected. This led to the development of a thin rubber sheet to cover the face of the gage instead of rubber filling the entire gap. More finite element method modeling was done to finalize the design of a gage with a rubber sheet. The design consisted of a plastic skin friction gage with an approximately 0.015 in. thick rubber sheet, a 0.0625 in. wide gap between the floating head on the cantilever beam and the encasement to be filled with oil, and semi-conductor strain gages to measure the beam deflection. Vibration tests were performed to determine if the rubber sheet produced the required damping. These tests were successful, and so much so, that the oil for damping was not necessary. However, supersonic wind tunnel tests at Mach 2.4 which were done at Virginia Polytechnic Institute and State University, initially yielded unfavorable results. The rubber sheet failed during the violent process of starting and unstarting of the tunnel. More study on the adhesive mounting of the rubber sheet to the skin friction gage face is needed. / Master of Science

Research report to School of Electrical and Information Engineering / An investigation was conducted into how a variable speed drive can provide a damping torque when mechanical oscillations are present. The modeling of mechanical oscillations via an analogous electrical circuit was performed. Simulation was used to demonstrate how a variable speed drive is able to damp speed oscillations using Direct Torque Control (DTC). Damping of mechanical oscillations is done by means of the variable speed drive providing a damping torque component that is in-phase with the speed deviation. The simulation showed that by applying a small torque component with the speed variation results in torque oscillations being damped by 60% after the initial disturbance. Damping is further improved by applying a torque component equal to the speed variation resulting in the oscillations being damped by 80% when compared to the initial disturbance. / MT2017

abstract: Admittance control with fixed damping has been a successful control strategy in previous human-robotic interaction research. This research implements a variable damping admittance controller in a 7-DOF robotic arm coupled with a human subject’s arm at the end effector to study the trade-off of agility and stability and aims to produce a control scheme which displays both fast rise time and stability. The variable damping controller uses a measure of intent of movement to vary damping to aid the user’s movement to a target. The range of damping values is bounded by incorporating knowledge of a human arm to ensure the stability of the coupled human-robot system. Human subjects completed experiments with fixed positive, fixed negative, and variable damping controllers to evaluate the variable damping controller’s ability to increase agility and stability. Comparisons of the two fixed damping controllers showed as fixed damping increased, the coupled human-robot system reacted with less overshoot at the expense of rise time, which is used as a measure of agility. The inverse was also true; as damping became increasingly negative, the overshoot and stability of the system was compromised, while the rise time became faster. Analysis of the variable damping controller demonstrated humans could extract the benefits of the variable damping controller in its ability to increase agility in comparison to a positive damping controller and increase stability in comparison to a negative damping controller. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019

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This research will compare the transient response characteristics of a four-degree-of-freedom, roll-plane model, representing a class 8 truck, using passive and semiactive dampers. The semiactive damper control policies that are examined include the previously developed policies of on-off skyhook, continuous skyhook, and on-off groundhook control, along with a newly developed method of fuzzy logic semiactive control. The model input will include body forces and torques, as well as transient displacements at the tires. The model outputs include the vehicle body heave and roll displacements, the vertical displacement of the tire (wheel hop) and the vertical acceleration of the vehicle body. For each output, the maximum peak-to-peak and RMS values of the response are examined. The results of the study show that semiactive dampers have minimal effect on improving the vehicle body and tire transients due to forces or torques applied to the body, as compared to passive dampers. For road inputs, however, semiactive dampers are able to provide a more favorable compromise between the body and axle transient dynamics, when compared to passive dampers. The fuzzy logic semiactive control policy that is proposed in this research is better able to balance the body and axle dynamics than the conventional semiactive damping control policies that are investigated. Further research on the application of fuzzy logic semiactive control concepts is suggested, in order to fully investigate the potential of such control schemes for vehicle suspensions. / Master of Science

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