Mechanical Engineering
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Item INVESTIGATIONS INTO THE EFFECTS OF SECONDARY-FREQUENCY ADDITIONS ON SLENDER ROTATING STRUCTURES(2014) Meyer, Gregory William; Balachandran, Balakumar; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Drill strings are slender structures used extensively in drilling and mining operations. In this thesis work, secondary-frequency input additions to the drive speed input are considered and the resulting influence on system dynamics is examined. Experimental studies are conducted with a laboratory scale drill-string arrangement, and high-frequency and low-frequency additions are considered for cases in which the drive speed frequency is close to either a bending mode or torsion mode natural frequency. It is found that carefully chosen secondary-frequency additions can be used to attenuate undesirable system dynamics, especially, for rotary systems. To complement the experiments, numerical studies are conducted with a reduced-order model of the drill-string system. The obtained numerical results are found to be in reasonable agreement with the experimental results. Preliminary numerical results obtained in the presence of rotor-stator interactions are also included. In addition, areas in which the model construction will need further development are also discussed. The findings of this work can be useful for considering secondary-frequency addition based schemes for controlling bending and torsional motions of drill-string systems.Item Performance of Residential Heating and Cooling Control Strategies using Distributed Wireless Sensor Networks(2010) Siemann, Michael; Kim, Jungho; Chopra, Nikhil; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Previous work has suggested that residential space heating and cooling control strategies that partition the structure into individual zones using wireless sensor networks might result in lower energy consumption compared to systems using a single-sensor thermostat. Questions have been posed as to whether these strategies can achieve the same level of performance in a variety of geographic locations and climates. This study compared four control strategies that utilized a wireless temperature and humidity sensor network to regulate the comfort of a residence in the mid-Atlantic region of the United States during the summer and winter. In particular, the energy consumption and comfort levels of each multi-sensor strategy were compared to a baseline strategy that mimicked a single thermostat. The difference in energy usage measured by each control strategy was found to be statistically insignificant. However, experiments indicated that these strategies may nevertheless result in improvements in thermal comfort.Item DEVELOPMENT OF A DYNAMIC TEST FACILITY FOR ENVIRONMENTAL CONTROL SYSTEMS(2006-04-06) Gado, Amr El-Sayed Alaa El-Din; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Passenger cars and light trucks consume 80% of the total oil imported by U.S.A. Mobile air conditioners (MACs) increase vehicle fuel consumption and exhaust gas emissions. They operate most of the time in a transient state. It is currently impossible to test the performance of an air conditioner during transient operation without it being associated with its intended conditioned space, the car cabin. In this research work a new smart test facility is designed, built, and verified. This facility makes it possible to test the MAC independent of the vehicle, but yet under realistic dynamic conditions. The facility depends on simulation software that measures the conditions of the air supplied by the MAC and subsequently adjusts the conditions of the air returning to the MAC depending on the results of a thermal numerical model of the car cabin that takes into consideration sensible and latent loads, as well as passengers' control settings. It was successful in controlling the temperature and relative humidity within ±0.9°C and ±5% of their respective intended values. The test facility is used to investigate the dynamic performance of a typical R134a MAC system. The tests include pull-down, drive cycle, and cyclic on/off tests. The analysis focuses on the latent capacity and moisture removal due to the difficulty in measuring these variables during field tests. The results show that the most energy efficient method to pull-down the air temperature inside a hot-soaked cabin is to start with fresh air as long as the temperature in the cabin exceeds that of the ambient and then switch to recirculated air. The effect of re-evaporation is illustrated by showing the off-cycle latent capacity. Cyclic tests show that the net moisture removal rate has a minimum at around a 2 minute duty cycles. This implies a means of controlling the coil latent heat factor by varying duty cycle. The automotive air conditioning system is numerically modeled and used in cooperation with the cabin model to conduct numerical tests. The numerical simulation results are compared to the experimental results and the error is less than 1.5 K of cabin air temperature.