M.S.

The advancements made in technology over the past several decades have brought the field of humanoid robotics closer to integration into the everyday lives of humans. Despite these advances, the cost of these systems consistently remains high, thus limiting the environments in which these robots can be deployed. In this thesis, a pair of low-cost, bio-mimetic legs for a humanoid robot was developed with 12 degrees of freedom: three at the hip, one at the knee, and two at the ankle. Prior to developing the robot, a survey of the human-sized robotic legs released from 2006-2012 was conducted. The analysis included a summary of the key performance metrics and trends in series of human-sized robots. Recommendations were developed for future data reporting that will allow improved comparison of different prototypes. The design of the new robotic legs in this thesis utilized human anatomy data to devise performance parameters and select actuators. The developed system was able to achieve comparable ROM, size, weight, and torque to a six-foot tall human. Position and zero-moment point sensors were integrated for use in balancing, and a control architecture was developed. A model of the leg dynamics was created for designing balancing and walking algorithms. In addition, hydraulic actuators were evaluated for use in humanoid robotics, and testing was conducted in order to create a position control methodology. Finally, a predictive deadband controller was designed that was able to achieve accuracy of less than one degree using a valve with slow switching speed. / Master of Science

A nondimensional form of the basic differential equation for spatially varied flow with increasing discharge was developed in section VI. The main purpose of this thesis is the application of this nondimensional equation to rectangular channels of various roughness values. A rectangular channel with continuous flow was constructed in order to establish uniform flow. The channel roughness was altered by placing screen wire and wooden cubes in the channel. Manning roughness coefficients were determined from the observed values for uniform depth. The law of conservation of linear momentum was used to develop a differential equation for spatially varied flow with increasing discharge. By defining certain dimensionless parameters, this equation was altered to a dimensionless form. An IBM 7040 computer was used to solve this nondimensional equation for various conditions of slope, roughness, and discharge. When the channel slope and roughness were held constant, the theoretical profiles varied slightly over a wide range of discharge. / Master of Science

Call number: LD2668 .T4 1979 A28 / Master of Science

published_or_final_version / Mechanical Engineering / Master / Master of Science in Engineering

published_or_final_version / Civil Engineering / Master / Master of Philosophy

No description available.

Renewable marine energy has attracted considerable interest in recent years, especially in the UK due to its excellent location to take advantage of this sustainable energy source. Dierent types of device have been developed over several decades to capture the energy of sea waves but they all need to be able to convert this mechanical energy into electrical energy. The success of wave energy converters (WECs) depends on their eciency, reliability and their ability to react to the variable wave conditions. Although a number of simulation studies have been undertaken, these have used signicantly simplied models and any experimental data is scarce. This work considers a heaving point absorber with a hydraulic power takeo unit. It employs a common hydraulic power take-o design, which uses the heaving motion of the buoy to drive an actuator that behaves like a linear pump. Energy storage is used to provide power smoothing in an attempt to give a constant power output from a hydraulic motor coupled to a generator. Although this design has been presented before, the ineciencies and dynamics of the components have not been investigated in detail. The aim of this work is to create an understanding of the non-linear dynamics of a hydraulic power take-o unit and how these aect the hydrodynamic behaviour of the WEC. A further aim is to predict the eciency of the power take-o unit and determine tuning and control methods which will improve the power generation. In order to do this and test the device in dierent wave conditions, a full hydrodynamic and hydraulic model is developed using the Simulink and SimHydraulics software package. The model is initially tested with regular waves to determine the behaviour of the power take-o unit and a method for adjusting the hydraulic motor displacement depending on the frequency of the incoming wave is investigated. The optimal eective PTO damping to maximise power generation is found to be dependent on the signicant wave frequency and the values of PTO damping are signicantly dierent to previous work using a linear power take-o model which emphasises the importance of including the ineciencies of the hydraulic components. The model is then analysed with irregular waves to predict the behaviour and power levels in realistic wave conditions. Power generation reduces in comparison to regular waves but a similar tuning method to maximise power generation still exists. A hydraulic motor speed control method is shown to increase power generation in irregular waves by maintaining the motor speed within an acceptable working range. Wave data from the Atlantic Ocean is then used to investigate the benets of an adaptive tuning method which uses estimated wave parameters for a number of dierent sea conditions. Results show only minimal gains from using active tuning methods over a passive method. However, results revealed signicant power losses in both calm and rough sea conditions with the PTO most ecient, at approximately 60%, in an average sea power. A scaled experimental power take-o unit is developed to help validate the simulation results. The power take-o unit is tested using a hardware-in-the-loop system in which the hydrodynamic behaviour of the WEC is predicted by a realtime simulation model. The experimental results show good agreement to the simulation with the PTO showing similar characteristics and tuning trends for maximising power generation.

The Bromeliaceae is one of the largest and most ecologically diverse angiosperm families in the Neotropics. In recent years, this family has begun to emerge as a model system for the study of plant evolutionary ecology and physiology, and major advances have been made in understanding the factors involved in episodes of rapid diversification and adaptive radiation in specific bromeliad lineages. However, despite a long tradition of ecophysiological research on the Bromeliaceae, an integrative, evolutionarily-contextualised synthesis of the links between anatomical) physiological, and ecological aspects of bromeliad biology has hitherto been lacking. The overarching aim of this research project was therefore to use new quantitative data representing a wide range of bromeliad taxonomic and functional groups to elucidate how variation in leaf traits connected by structure-function relationships influences ecological differentiation among bromeliad taxa. Special emphasis was placed on hydraulic and water relations traits because of fast-paced contemporary developments in these fields. The methodologies employed included an assessment of the diversity of bromeliad hydrological habitat occupancy, quantification of key anatomical and physiological traits and their correlations, investigation of the links between vascular and extra-xylary anatomy and hydraulic efficiency and vulnerability, quantification of stomatal sensitivity to leaf-air vapour pressure deficit and stomatal kinetics, and a case study of trait-mediated niche segregation among congeneric epiphytic bromeliad species on the Caribbean island of Trinidad. The results highlight how divergences in a range of continuous and categorical anatomical traits underpin differences in physiological capacities and sensitivities, which in turn determine environmental relations and ecological distinctiveness. This research project therefore provides critical insights into the mechanistic basis of evolutionary diversification in a highly ecologically important family. It also represents the most comprehensive analysis of the significance of trait variation for ecological differentiation across any major radiation of herbaceous angiosperms.

Seasonality in the Amazon Rainforest is predicted to become more extreme, with dry seasons increasing in length and severity, while severe episodic droughts are expected to occur with greater frequency. Drought stress can reduce the capacity of the rainforest to sequester carbon, and severe drought events can switch the region from being a net sink to a temporary source of carbon to the atmosphere. A key component in the drought-induced carbon flux is tree mortality, and there is evidence of strong feedbacks globally and regionally in the Amazon with climate change. Although the exact cause of drought-induced mortality in trees is difficult to ascertain, recent data suggests that reduced functionality of the water transport pathway (hydraulic failure) is an important factor. Hydraulic vulnerability in trees is often assessed using measurements of the capacity of stems and branches to cope with the strongly negative internal water pressures associated with drought. However, leaves play a vital role in protecting the integrity of the ‘upstream’ hydraulic pathway by influencing the rate of transpiration and thus the tension in the water column. Therefore, the physiology of leaves can be informative of, and influence, tree species’ sensitivity to drought. This thesis uses a long-term large-scale rainfall exclusion experiment in the Eastern Amazon to examine the possible link between leaf physiology and drought sensitivity (or tolerance) by different taxa, and the capacity of mature, upper canopy Amazonian trees to respond to drought via plastic changes in leaf physiology. The plasticity in response to experimental drought and the differences between taxa classed as drought-sensitive and drought-resistant based on drought induced mortality records were tested by the study of leaf water relations (Chapter 2), leaf anatomy (Chapter 3) and foliar water uptake (Chapter 4). No consistent differences were found between drought-resistant and drought-sensitive species suggesting that the sensitivity of these species to drought may be due to other aspects of plant physiology. However, a limited response to the imposed drought conditions was detected across all taxa and included reductions of osmotic potential at full turgor and turgor loss point (Chapter 2), and increases in the thickness of the upper epidermis and the leaf internal cavity volume (Chapter 3). Interestingly, drought-sensitive taxa showed more seasonal osmotic adjustment than drought-resistant taxa, indicating that short-term responses to drought (e.g. season) are not representative of the capacity for adjustment in response to long-term water deficits. No significant changes occurred in leaf size, thickness, stomatal and vein density, the quantity of the inner leaf tissues (i.e. the palisade and spongy mesophyll) and mesophyll cell size, in response to the experimental drought. The experiments on foliar water uptake in Chapter 4 revealed that this rarely-considered process occurs in all taxa, but the response to the drought treatment differed among taxa. Using a simple model, foliar water uptake was scaled up to canopy level. Under normal conditions (i.e. no drought) canopy foliar uptake was calculated to be 29.9 ± 2.3 mm year-1 from rainfall alone, but this increased to a maximum of 51.9 ± 2.3 mm year-1 when including the input of dew in the dry season. However, lower water potential in the drought plot causing increased rates of foliar water uptake, led to estimates of 38.7 ± 3.0 mm year-1 (rainfall only) and 68.9 ± 2.9 mm year-1 (including dry season dew). Taken together, these results demonstrate that Amazonian trees show some limited capacity for acclimation to drought through the changes in leaf physiology measured in this thesis. Low turgor loss point is associated with dry climate-adapted plants, so the finding that this parameter reduced in response to the drought reveals some potential for Amazonian trees to acclimate with the predicted changes in moisture availability. However, the limited response of leaf anatomy to long-term drought might suggest that acclimation may only occur within a narrow range. The finding that six common Amazonian tree genera can take water up through their leaves has considerable implications for understanding the Amazon water budget, in terms of the contribution of dew and light rainfall to canopy water status, but also the implications it has for the hydraulic vulnerability of trees in rainforests right across the Amazon basin.