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Browsing by Subject "Experimental validation"

Now showing 1 - 2 of 2
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    Modeling and Experimental Validation of Disc and Reed Style Check Valves for Hydraulic Applications
    (2016-08) Knutson, Anthony
    The goal of this thesis is to develop a computationally inexpensive, accurate, and practical mathematical model of a hydraulic reed style check valve. While the modeling of disc style check valves is well represented in literature, reed valve modeling research has focused on applications in air compressors and internal combustion engines, where the working fluid has low density, viscosity, and bulk modulus. However, in a hydraulic system, the fluid – namely oil – is dense, viscous, and stiff, contributing additional physical effects that must be considered. Furthermore, the operating pressure in hydraulic systems is higher than in pneumatic systems, creating additional challenges from a structural perspective. In this thesis, a one degree of freedom hydraulic disc and reed style check valve model were developed using a hybrid analytical, computational, and experimental approach. The disc valve equation of motion was derived from Newton’s second law applied to the disc considering forces including pressure, spring reaction, and drag. Euler- Bernoulli beam theory was used to derive the reed valve equation of motion. In each case, the valve flow rate was modeled as quasi-steady orifice flow using an empirical discharge coefficient. A non-contact method of experimentally measuring check valve position during operation using a laser triangulation sensor (LTS) was developed. An acrylic viewing window was installed in the check valve manifold to allow optical access. To precisely measure position through air, acrylic, and oil, refraction of the laser light was accounted for using Snell’s law. Finally, the disc and reed valve models were validated in the context of a single cylinder hydraulic piston pump across a range of operating conditions. Pump delivery, which is a measure of volumetric efficiency, and check valve position were chosen as the validation metrics. Experimental results showed that both the disc and reed check valve model accurately predicted the timing of valve opening and closing. The disc valve model predicted pump delivery within 5% of measured values for all cases while the reed valve model predicted pump delivery within 3% of measured values for all cases.
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    Modeling, Robust Control, and Experimental Validation of a Supercavitating Vehicle
    (2015-06) Escobar Sanabria, David
    This dissertation considers the mathematical modeling, control under uncertainty, and experimental validation of an underwater supercavitating vehicle. By traveling inside a gas cavity, a supercavitating vehicle reduces hydrodynamic drag, increases speed, and minimizes power consumption. The attainable speed and power efficiency make these vehicles attractive for undersea exploration, high-speed transportation, and defense. However, the benefits of traveling inside a cavity come with difficulties in controlling the vehicle dynamics. The main challenge is the nonlinear force that arises when the back-end of the vehicle pierces the cavity. This force, referred to as planing, leads to oscillatory motion and instability. Control technologies that are robust to planing and suited for practical implementation need to be developed. To enable these technologies, a low-order vehicle model that accounts for inaccuracy in the characterization of planing is required. Additionally, an experimental method to evaluate possible pitfalls in the models and controllers is necessary before undersea testing. The major contribution of this dissertation is a unified framework for mathematical modeling, robust control synthesis, and experimental validation of a supercavitating vehicle. First, we introduce affordable experimental methods for mathematical modeling and controller testing under planing and realistic flow conditions. Then, using experimental observations and physical principles, we create a low-order nonlinear model of the longitudinal vehicle motion. This model quantifies the planing uncertainty and is suitable for robust controller synthesis. Next, based on the vehicle model, we develop automated tools for synthesizing controllers that deliver a certificate of performance in the face of nonlinear and uncertain planing forces. We demonstrate theoretically and experimentally that the proposed controllers ensure higher performance when the uncertain planing dynamics are considered. Finally, we discuss future directions in supercavitating vehicle control.