Browsing by Subject "Hydraulic"

Now showing 1 - 6 of 6
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    Configuration and Performance of Hydraulic Transformer Power Distribution Systems
    (2016-09) Gagnon, Pieter
    Hydraulic transformers implemented in a common pressure rail architecture have been suggested as a means to efficiently distribute hydraulic power to a system of actuators. This thesis explores the role that the configuration of the system plays in the operating region and efficiency performance of the power distribution system. The primary tool used in this thesis is a dynamic loss model of a hydraulic transformer. Full mathematical documentation and experimental parameter tuning are described. Six configurations for distributing power with a hydraulic transformer are presented, and it is shown that each configuration has a unique operating region and efficiency trend. The hydraulic circuit is given for a port switching transformer that utilizes valves to switch between configurations during operation, and experimental tests demonstrate successful switching on a prototype machine. The maximum displacements of the two rotating groups within a set of hydraulic transformers distributing power to linear actuators driving the hip, knee, and ankle joints of a humanoid robot are optimized to maximize efficiency over a walking gait duty cycle. The resulting size ratios of the groups vary from a 1:1 ratio to a 1:2.4 ratio for the three duty cycles investigated. A comparison of the hydraulic transformer architecture against a throttling valve architecture for the humanoid robot indicates that the transformer system can achieve a distribution efficiency of 47.6%, which is a 31.9% increase over the throttling architecture distribution efficiency of 16.0%. The transformer system consumes 142 J to drive a single step of the walking gait, which is a decrease of 281 J from the 422 J required by the throttling architecture. This thesis thoroughly captures the efficiency performance and operating region of hydraulic transformers, and demonstrates how system configurations can improve the performance of the system beyond what has been generally considered in previous literature. These factors can then be weighed along with complexity, size, control performance, production cost, and other such metrics to enable a decision as to whether transformers are an appropriate power distribution architecture for a given application.
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    Modeling, Optimization, and Detailed Design of a Hydraulic Flywheel-Accumulator
    (2014-07) Strohmaier, Kyle Glenn
    Improving mobile energy storage technology is an important means of addressing concerns over fossil fuel scarcity and energy independence. Traditional hydraulic accumulator energy storage, though favorable in power density, durability, cost, and environmental impact, suffers from relatively low energy density and a pressure-dependent state of charge. The hydraulic flywheel-accumulator concept utilizes both the hydro-pneumatic and rotating kinetic energy domains by employing a rotating pressure vessel. This thesis provides an in-depth analysis of the hydraulic flywheel-accumulator concept and an assessment of the advantages it offers over traditional static accumulator energy storage.After specifying a practical architecture for the hydraulic flywheel-accumulator, this thesis addresses the complex fluid phenomena and control implications associated with multi-domain energy storage. To facilitate rapid selection of the hydraulic flywheel-accumulator dimensions, computationally inexpensive material stress models are developed for each component. A drive cycle simulation strategy is also developed to assess the dynamic performance of the device. The stress models and performance simulation are combined to form a toolset that facilitates computationally-efficient model-based design.The aforementioned toolset has been embedded into a multi-objective optimization algorithm that aims to minimize the mass of the hydraulic flywheel-accumulator system and to minimize the losses it incurs over the course of a drive cycle. Two optimizations have been performed - one with constraints that reflect a vehicle-scale application, and one with constraints that reflect a laboratory application. At both scales, the optimization results suggest that the hydraulic flywheel-accumulator offers at least an order of magnitude improvement over traditional static accumulator energy storage, while operating at efficiencies between 75% and 93%. A particular hydraulic flywheel-accumulator design has been selected from the set of laboratory-scale optimization results and subjected to a detailed design process. It is recommended that this selection be constructed and tested as a laboratory prototype.
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    A Numerical and Experimental Study of Flywheel Energy Storage in Hydraulic Systems, with Particular Emphasis on the Hydraulic Flywheel Accumulator
    (2023) Cronk, Paul
    Hydraulic power transmission is preferred in many industries where power density, ruggedness, and reliability in challenging environments are important characteristics. Two major deficiencies of hydraulic power are energy efficiency and energy storage density. Several avenues for rectifying the low energy storage density of hydraulic systems have attracted research interest.One such avenue is the application of kinetic energy storage, or flywheels, to hydraulic systems, and another is a specific and unique instance of the flywheel known as the Hydraulic Flywheel Accumulator (HFA).This study reviews the current research into the application of kinetic energy storage to hydraulic systems. It then explores various mobile hydraulic flywheel topologies and their control strategies when applied to a hydraulic hybrid truck. To understand and model the HFA this study presents an experimental analysis of power loss in the viscous spin-up of hydraulic fluid in a HFA, in a form useful for HFA design optimization. Then this loss is included in a much broader HFA model to optimize the design of the HFA for vehicle-scale and laboratory applications. Finally, this study presents the results of the construction of the optimized laboratory-scale HFA design and its use in a hydraulic circuit simulating a mobile hydraulic drivetrain. The contributions of this work include the direct comparison of two different hydraulic system topologies previously proposed in the literature, analysis revealing the positive effect on efficiency of allowing increased hydraulic system pressure ranges, an empirical approximation of viscous spin-up loss appropriate for optimization, the development of a detailed model of the HFA, and the first construction and testing of an HFA prototype. This study confirms the presented HFA model through the construction and implementation of this prototype and demonstrates the feasibility of the HFA concept, taking it from a concept on paper to a device, operating at industry standard pressures and application-realistic flywheel speeds, and increasing the boundary of knowledge not only of the HFA, but of the implications of flywheel energy storage for hydraulic systems in general.
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    Optimization and Design Principles of a Minimal-Weight, Wearable Hydraulic Power Supply
    (2017-12) Nath, Jonathan
    The field of wearable hydraulics for human-assistive devices is expanding. One of the major challenges facing development of these systems is creating lightweight, portable power units. This project’s goal was to develop design strategies and guidelines with the use of analytical modeling to minimize the weight of portable hydraulic power supplies in the range of 50-350 W. Steady-state, analytical models were developed and validated for a system containing a lithium-polymer battery, brushless DC motor, and axial-piston pump. Component parameters such as motor size, pump size, and swashplate angle were varied to develop four design guidelines that can be used by designers to minimize system weight. First, the smallest electric motor that can provide the required torque and speed may not result in minimum system weight. Second, cooling systems do not reduce overall system weight. Third, the gearbox between the electric motor and pump should be eliminated to reduce system weight. Fourth, iterative modeling is necessary to determine the various range of component parameters necessary to result in a minimal-weight system. The analytical model developed takes inputs of desired flowrate, pressure, and runtime, and outputs the combination of pump size, swashplate angle, and motor size that results in a minimal-weight system. The four design principles and the computer simulation are tools that can be used to either design a fully-custom, weight-optimized power supply or to aid in the selection of commercially available components for a low-weight power supply.
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    The performance and efficiency of hydraulic pumps and motors.
    (2010-01) Grandall, David Rossing
    This research consists of predicting the performance and efficiency of hydraulic pumps and motors, both with experiments and modeling. A pump and motor test stand is constructed to measure the efficiency of an axial piston swashplate pump/motor unit. A regenerative loop hydraulic system is used to reduce the power requirements of the test stand. The test stand uses an xPC Target data acquisition system. Test conditions focused on low displacement and low speed regimes. Efficiency values ranged from less than 0% to 82%. An existing efficiency model in the literature is fit to the data. Several improvements to the model are suggested. The correlation was satisfactory, but room for improvement still exists. Displacement sensors are recommended in the pump/motor units being tested. This is to avoid the significant uncertainty associated with calculating the derived volume based on the data.
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    Thermodynamic and heat transfer models of an open accumulator.
    (2009-12) Hafvenstein, David James
    A conventional accumulator stores energy for hydraulic systems by compressing an enclosed mass of air, but this air takes up too much volume at low pressure to be practical in applications such as a hydraulic hybrid passenger vehicle. An open accumulator compresses air from the atmosphere to store energy, eliminating the need to store low-pressure air but creating large temperature swings if the heat transfer during compression and expansion is poor. This thesis investigates thermodynamic and heat transfer aspects of an open accumulator to assist in its design. A thermodynamic model was created to determine the efficiency and required heat transfer for open accumulator designs with a volume 1/5th that of a comparable conventional, or “closed,” accumulator. A heat transfer parameter, Z = hA/V, describes how easy it would be to implement the required heat transfer, with low required values of Z being desirable. A design with only one stage of compression and high wall temperature had a lower required value for Z than the high pressure stages in multi-stage designs. For an open accumulator that provides 20 kW of power in expansion and 840 kJ of energy storage at a pressure of 350 times atmospheric conditions, the volume target was 15.7 ℓ and the required Z values for compression and expansion were approximately 6.2×104 W/m3K. A computational fluid dynamics model using the program FLUENT was created to investigate whether the required Z could be achieved in a more practical, three-stage open accumulator design. The expansion case of the lowest-pressure stage was simulated, with a required Z value from the thermodynamic model of 3.83×104 W/m3K. The iv computational domain was a symmetrical, 3-D, diaphragm-bounded chamber of approximately 0.5 ℓ displaced volume, and a realizable k-ε model was used to model the effects of turbulence. The flow pattern generated during the air intake period dominated the flow during expansion, and peak local heat fluxes occurred where the intake flow patterns drew cold fluid next to the walls. The peak heat transfer for the simulation was 386 W. The mean Z value calculated was 9.79×103 W/m3K, around 1/4th of the required value.