In this study, water meter accuracy in response to short, intermittent flows was tested. Burst flows have short durations (a few seconds or less), and occur at a variety of flow rates. For some types of meters, it is difficult to accurately measure short, intermittent flow rates. Depending on the meter type, an intermittent flow can result in either under-registering or over-registering of the actual throughput. During the testing for this research, water was passed through meters for various time combinations, test setups, and flows. It should be understood that realistically, a household setting will not see burst flows occurring in a repeated manner. For the purposes of laboratory testing, however, time-on and condensed time-off combinations were used. The reduced time off allowed for a controlled test procedure and efficient data collection. Ultrasonic, electromagnetic, nutating disc, and oscillating piston meters were tested. The meter types were found to perform differently under the varying test setups, time combinations, and flow rates. The electromagnetic meters were generally unaffected by burst flows. Burst flows caused one of the ultrasonic meter models to have decreased accuracies, while the other model remained mostly unaffected. Nutating disc and oscillating piston meters were generally affected by burst flows only at the lowest flow.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1982. / Supervised by Nelson Hogg. Includes bibliographical references (leaves 108-109).

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1982. / Bibliography: p. 139-140.

This thesis proposes a new type of hydraulic valve: an adjustable-ratio flow divider. This valve attempts to split one input flow into two output flows in a predetermined ratio, independent of load pressure or total flow. The valve uses a two dimensional structure to form a two-stage valve with only one moving part; the pilot stage uses the spool s rotary position, and the main stage uses its linear position. This arrangement allows for a cheaper, simpler valve with smaller volumes (translating into faster response). The ratio of outlet flows can be set on the fly by the angular position of the spool, driven by a stepper motor or other low-power input. In order to evaluate the initial feasibility of the concept, steady state and dynamic models were developed and the effects of the physical parameters were studied. Two non-linear non-derivative multiobjective optimization strategies were used to determine the optimum parameters for a prototype. Finally, the prototype s performance was experimentally examined and appears to work as expected.

This thesis proposes a new type of hydraulic valve: an adjustable-ratio flow divider. This valve attempts to split one input flow into two output flows in a predetermined ratio, independent of load pressure or total flow. The valve uses a two dimensional structure to form a two-stage valve with only one moving part; the pilot stage uses the spool s rotary position, and the main stage uses its linear position. This arrangement allows for a cheaper, simpler valve with smaller volumes (translating into faster response). The ratio of outlet flows can be set on the fly by the angular position of the spool, driven by a stepper motor or other low-power input. In order to evaluate the initial feasibility of the concept, steady state and dynamic models were developed and the effects of the physical parameters were studied. Two non-linear non-derivative multiobjective optimization strategies were used to determine the optimum parameters for a prototype. Finally, the prototype s performance was experimentally examined and appears to work as expected.

Control design for flexible robots is a challenging problem. Part of the difficulty comes from a lack of controls-focused modeling tools. Practical flexible robots have several aspects that make them difficult to model: continuous elements, complicated actuators, multiple feedback loops, non-collocated sensors and actuators, and the ability to take on arbitrary three-dimensional poses. Even if existing techniques for modeling flexible structures could model the closed-loop response of a hydraulically-actuated flexible robot with a vibration suppression controller, how would such a model be used for control design? This work presents the development of a modeling approach that meets the needs of a controls engineer. The approach is based on the transfer matrix method (TMM). The TMM has been expanded in several ways to enable it to accurately model practical flexible robots. Quantitative agreement is shown between model and experiment for the interaction of a hydraulic actuator and a flexible structure as well as for the closed-loop response of a system with vibration suppression. Once the ability to model the closed-loop response of the system has been demonstrated, this work focuses on using the model for control design. Control design is facilitated by symbolic implementation of the TMM, which allows closed-form expressions for the closed-loop response of the system to be found without discretization. These closed-form expressions will be transcendental transfer functions for systems with continuous elements. These transfer functions can then be used in various optimization approaches for designing the closed-loop system response.

The aim of this study is to develop a dynamic model of the loader system of a backhoe-loader. Rigid bodies and joints in the loader mechanism and loader hydraulic system components are modelled and analyzed in the same environment using the physical modelling toolboxes inside the commercially available simulation software, MATLAB/Simulink. Interaction between the bodies and response of the hydraulic system are obtained by co-operating the mechanical and hydraulic analyses. System variables such as pressure, flow and displacement are measured on a physical machine and then compared with the simulation results. Simulation results are consistent with the measurement results. The main result of this work is the ability to determine the dynamic loads on the joints and attachments of the backhoe-loader. In addition to that, prototyping time and costs can be highly reduced by implementing this model in the design process.

published_or_final_version / Civil and Structural Engineering / Master / Master of Philosophy

This three part study attempted to enhance our understanding of vegetation change and its potential effects on ecohydrology in drylands. The first study developed a method to measure the velocity of shallow overland flow. Under rainfall simulation, dye tracers were applied to runoff and photographed to calculate mean surface velocity. Results showed this approach was a significant improvement explaining 13% more of the variation in mean velocity compared to traditional methods. Results from the first study were used to compare hydraulic parameters on shrub- and grass-dominated plots in the second study. Previous research has suggested microtopography in shrublands acts to concentrate flow, leading to increased runoff velocity compared to grasslands. However, present findings showed that flow velocities were similar on many grass and shrub plots; only plots with ground cover > 90% exhibited significantly lower flow velocities, and some shrub-dominated plots had lower flow velocities than grass-dominated plots implying that horizontal water flux is reduced under certain states of woody plant encroachment. In terms of ground cover characteristics, velocity increased rapidly with increases in the fraction of bare soil, up to a value of ~20% bare soil. Above ~20% bare soil, basal gap became a dominant factor suggesting a possible threshold where spatial metrics related to the distance between plants become important indicator of shallow flow velocity. The third study tested an approach to quantify woody plant canopy metrics over large areas. Radar has been used to map biomass in forests but few studies have examined open canopy ecosystems. Field measurements of shrublands were compared to satellite images to identify the relationship between radar signal and height and cover of woody vegetation. Results indicated that radar signal increased positively with shrub height or shrub volume explaining 74% and 90% of the variation, respectively. The effect of surface roughness and sub-canopy species on radar signal appears reduced when images are collected at large incidence angles.

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