Browsing by Subject "hydraulic"

Now showing 1 - 3 of 3
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    High Speed Rotary PWM On/Off Valves for Digital Control of Hydraulic Pumps and Motors
    (2014-08) Tu, Haink
    The research described in this dissertation focuses on the development of innovative on/off valves for high performance, high efficiency control of fixed displacement hydraulic pumps and motors. On/off valves, the hydro-mechanical equivalent of transistors, enable the application of digital control techniques found in electrical systems to hydraulics. These techniques, such as pulse-width-modulation (PWM), have the potential of combining the low cost, high bandwidth characteristics of valve control with the efficiency of variable displacement machines. Effective control of hydraulic systems using PWM requires that the on/off valve simultaneously exhibits fast switching speed, large flow area, and low actuation power. The valves developed in this dissertation exploit continuous rotary motion to achieve the desired, and traditionally competing, operating characteristics. A helical land is used to mechanically embed the desired PWM functionality into the valve spool. The rotary motion of the valve performs the switching functionality while its axial motion determines the PWM duty ratio. Several unique rotary valve concepts are presented in this dissertation for switched-mode pump and pump/motor circuits. An analysis framework is developed that predicts valve performance and typical losses which can be used for design and optimization. Physics based dynamic models of switched-mode pump and motor circuits are also developed for simulating system pressures and flow rates and for validating the analytical models. In addition, guidelines for sizing the valve sleeve based on fatigue considerations are formulated to aid prototype design. Prototype hardware is fabricated and extensively tested to validate the analysis, performance, and predicted efficiency of the proposed valves. The research in this dissertation verifies that helical land rotary valves used in switched-mode hydraulic circuits are capable of exceeding the efficiency of comparable metering valve circuits at moderate PWM frequencies. In two comparable systems, the switched-mode circuit achieved 84% efficiency at 50% output flow compared to 50% efficiency in the bleed off circuit. Analysis also shows that substantial gains in efficiency and switching frequency can be attained with improvements in valve configuration, circuit configuration, and valve geometry. Additional suggestions for further improving efficiency in switched-mode hydraulic systems are also discussed.
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    Modeling And Design Of Hydraulic Power Take-Offs For Ocean Wave-Powered Reverse Osmosis Desalination
    (2024-04) Simmons, Jeremy
    Ocean wave-powered desalination of seawater using reverse osmosis (RO) presents an important opportunity for coastal communities as an economical and clean source of fresh water. However, the breadth and depth of study in the design of hydraulic power take-offs (PTOs) for ocean wave-powered RO is not sufficient for reliable high-performance. This work introduces several novel PTO architectures for wave-powered RO systems that take the approach of pressurizing seawater directly using a pump that is driven by the wave energy converter (WEC). These architectures include co-generation of electricity with fresh water to support the system without reliance on a local electrical grid. These architectures are modeled and compared in terms of the size of the WEC-driven pump, the RO membrane module, high-pressure accumulator volume, and the yearly average rate of permeate production. Results show that a parallel-type PTO architecture that closely resembles the state-of-the-art is consistently outperformed by series-type architectures. The series-type architecture, which is examined with and without an integrated switch-mode power transformer, produces as much fresh water as the parallel-type architecture while (1) using a WEC-driven pump that is 30–74 percent smaller without the switch-mode power transformer and 70–92 percent smaller with the switch-mode power transformer and (2) requiring 75 percent less high-pressure accumulator volume. Results also show that varying the active RO membrane area as a function of sea conditions can improve performance in terms of WEC-driven pump size, RO membrane module size, and permeate production, by 7–41 percent. Using model predictive control as an optimal load control method, this work also finds that a variable displacement WEC-driven pump can enhance productivity by 11–29 percent. Pipeline modeling methods are also examined for their use in wave energy systems and results show that a lumped parameter pipeline model that represents a pipeline in multiple segments is sufficient for the design of these systems, subject to a constraint on the length of pipe each segment represents. As a whole, this work provides guidance to the design of PTOs in future projects with insight into selecting the architecture of the PTO, formulation of multi-objective design problems, and models that can be usedeffectively for model-based design.
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    Multiphysics Topology Optimization of Small-Scale Hydraulic Conduits
    (2023) Bies, Jeffrey
    This dissertation focuses on the application of thermal-fluid-structure topology optimization to small-scale hydraulic systems for robotic exoskeletons. The primary goal was to develop optimization capabilities that can simultaneously consider fluid flow, heat transfer, and structural integrity under external loads while optimizing the design of these systems. The optimization methodology is based on the continuous adjoint method and the method of moving asymptotes and was implemented using the open-source computational fluid dynamics software OpenFOAM. The optimization approach was demonstrated through a series of two-dimensional case studies as well as a three-dimensional hydraulic system in a medical robotic exoskeleton focused on the knee-to-ankle region. The results show that topology optimization leads to significant improvements in the performance and efficiency of small-scale hydraulic systems. By optimizing for fluid flow, heat transfer, and structural integrity, the optimized designs are able to achieve a balance between thermal dissipation, structural strength, and pressure drop, resulting in designs that outperform traditional designs in terms of performance and efficiency. This work demonstrates how topology optimization can revolutionize the design and optimization of small-scale hydraulic systems.