Thomas R. Chase

Multiaxial cycle counting for critical plane methods

The critical plane method has proven to be a popular analytical tool for estimating multiaxial fatigue. Based on the strain-life approach to fatigue, the method relies on a cycle counting routine to identify cycles and a damage model to assess damage for each cycle. Researchers have traditionally borrowed cycle counting methods from established uniaxial methods. This work will show how uniaxial rainflow methods are inappropriate for cycle counting on the critical plane. A multiaxial cycle counting method, based on a simple uniaxial rainflow algorithm, is then presented.

The MINOS light-injection calibration system

A description is given of the light-injection calibration system that has been developed for the MINOS long-baseline neutrino oscillation experiment. The system is based upon pulsed blue LEDs monitored by PIN photodiodes. It is designed to measure non-linearities in the PMT gain curves, as well as monitoring any drifts in PMT gain, at the 1% level.

High Speed Rotary Pulse Width Modulated On/Off Valve

A key enabling technology to effective on/off valve based control of hydraulic systems is the high speed on/off valve. High speed valves improve system efficiency for a given PWM frequency, offer faster control bandwidth, and produce smaller output pressure ripples. Current valves rely on the linear translation of a spool or poppet to meter flow. The valve spool must reverse direction twice per PWM cycle. This constant acceleration and deceleration of the spool requires a power input proportional to the PWM frequency cubed. As a result, current linear valves are severely limited in their switching frequencies. In this paper, we present a novel fluid driven PWM on/off valve design that is based on a unidirectional rotary spool. The spool is rotated by capturing momentum from the fluid flow through the valve. The on/off functionality of our design is achieved via helical barriers that protrude from the surface of a cylindrical spool. As the spool rotates, the helical barriers selectively channel the flow to the application (on) or to tank (off). The duty ratio is controlled by altering the axial position of the spool. Since the spool no longer accelerates or decelerates during operation, the power input to drive the valve must only compensate for viscous friction, which is proportional to the PWM frequency squared. We predict that our current design, sized for a nominal flow rate of 40l/m, can achieve a PWM frequency of 84Hz. This paper presents our valve concept, design equations, and an analysis of predicted performance. A simulation of our design is also presented.Copyright

Design of a Solar Reactor to Split CO2 Via Isothermal Redox Cycling of Ceria

The design procedure for a 3 kWth prototype solar thermochemical reactor to implement isothermal redox cycling of ceria for CO2 splitting is presented. The reactor uses beds of mm-sized porous ceria particles contained in the annulus of concentric alumina tube assemblies that line the cylindrical wall of a solar cavity receiver. The porous particle beds provide high surface area for the heterogeneous reactions, rapid heat and mass transfer, and low pressure drop. Redox cycling is accomplished by alternating flows of inert sweep gas and CO2 through the bed. The gas flow rates and cycle step durations are selected by scaling the results from small-scale experiments. Thermal and thermo-mechanical models of the reactor and reactive element tubes are developed to predict the steady-state temperature and stress distributions for nominal operating conditions. The simulation results indicate that the target temperature of 1773K will be reached in the prototype reactor and that the Mohr-Coulomb static factor of safety is above two everywhere in the tubes, indicating that thermo-mechanical stresses in the tubes remain acceptably low.

Design, Modeling, and Validation of a High-Speed Rotary Pulse-Width-Modulation On/Off Hydraulic Valve

Efficient high-speed on/off valves are an enabling technology for applying digital control techniques such as pulse-width-modulation (PWM) to hydraulic systems. Virtually variable displacement pumps (VVDPs) are one application where variable displacement functionality is attained using a fixed-displacement pump paired with an on/off valve and an accumulator. High-speed valves increase system bandwidth and reduce output pressure ripple by enabling higher switching frequencies. In addition to fast switching, on/off valves should also have small pressure drop and low actuation power to be effective in these applications. In this paper, a new unidirectional rotary valve designed for PWM is proposed. The valve is unique in utilizing the hydraulic fluid flowing through it as a power source for rotation. An unoptimized prototype capable of high flow rate (40 lpm), high speed (2.8 ms transition time at 100 Hz PWM frequency), and low pressure drop (0.62 MPa), while consuming little actuation power (<0.5% full power or 30 W, scavenged from fluid stream), has been constructed and experimentally validated. This paper describes the valve design, analyzes its performance and losses, and develops mathematical models that can be used for design and simulation. The models are validated using experimental data from a proof-of-concept prototype. The valve efficiency is quantified and suggestions for improving the efficiency in future valves are provided. [DOI: 10.1115/1.4006621]

Circuit Rectification for Four Precision Position Synthesis of Stephenson Six-Bar Linkages

Circuit rectification ensures that a linkage may reach all precision positions without disassembly. Circuit rectification is crucial to the practical synthesis of Stephenson linkages, which have up to six circuits. Causes of circuit defects that may arise during synthesis are quantified first. A procedure is then developed to identify the segments of Burmester curves which produce mechanisms with all precision positions on the same circuit. The procedure is applicable to any Stephenson linkage.

Optimal design of power-split transmissions for hydraulic hybrid passenger vehicles

Hydraulic hybrid vehicles are inherently power dense. Power-split or hydro-mechanical transmissions (HMT) have advantages over series and parallel architectures. In this paper, an approach for optimizing the configuration and sizing of a hydraulic hybrid power-split transmission is proposed. Instead of considering each mechanical configuration consisting of combinations of gear ratios, a generalized kinematic relation is used to avoid redundant computation. This captures different architectures such as input coupled, output coupled and compound configurations. Generic kinematic relations are shown to be mechanically realizable. Modal operation of the transmission is introduced to reduce energy loss. The Lagrange multiplier method for computing the optimal energy management control is shown to be computationally efficient for use in transmission design iterations. An optimal design case study indicates improvement in fuel economy and smaller component sizes for the compound and input coupled power-split configurations.

SOFTWARE ENABLED VARIABLE DISPLACEMENT PUMPS - EXPERIMENTAL STUDIES ∗

The majority of hydraulic systems are controlled using a metering valve or the use of variable displacement pumps. Metering valve control is compact and has a high control bandwidth, but it is energy inefficient due to throttling losses. Variable displacement pumps are far more efficient as the pump only produces the required flow, but comes with the cost of additional bulk, sluggish response, and added cost. In a previous paper [1], a hydromechanical analog of an electronic switch-mode power supply was proposed to create the functional equivalent of a variable displacement pump. This approach combines a fixed displacement pump with a pulse-width-modulated (PWM) on/off valve, a check valve, and an accumulator. The effective pump displacement can be varied by adjusting the PWM duty ratio. Since on/off valves exhibit low loss when fully open or fully closed, the proposed system is potentially more energy efficient than metering valve control, while achieving this efficiency without many of the shortcomings of traditional variable displacement pumps. The system also allows for a host of programmable features that can be implemented via control of the PWM duty ratio. This paper presents initial experimental validation of the concept as well as an investigation of the system efficiency. The experimental apparatus was built using available off-the-shelf components and uses a linear proportional spindle valve as the PWM valve. Experimental results confirm that the proposed approach can achieve variable control function more efficiently than a valve controlled system, and that by increasing the PWM frequency and adding closed-loop control can decrease system response times and of the output ripple magnitude. Sources of inefficiency and their contributions are also investigated via modeling, simulation and are validated by experiments. These indicate design parameters for improving inefficiency.Copyright

MODELING AND VALIDATION OF A HIGH SPEED ROTARY PWM ON/OFF VALVE

Efficient high-speed on/off valves are a critical technology for enabling digital control of hydraulic systems via pulse-width-modulation (PWM). High-speed valves, when used in virtually variable displacement pumps (VVDP), increase system bandwidth and reduce output pressure ripple by enabling higher PWM frequencies. Our approach to achieving high speed and large flow area with low actuation power is a unidirectional rotary valve designed specifically for PWM. In comparison to conventional valves, the rotary valve reduces valve actuation power from a cubic dependence on PWM frequency to a square dependence by eliminating motion reversals during transition. This paper presents experimental data that validates the rotary valve concept, valve design equations, and dynamic model of a rotary valve based VVDP. Our unoptimized prototype exhibits 65 % efficiency at 50 % displacement and 15 Hz PWM frequency while the validated model projects that an optimized valve is capable of achieving 85 % efficiency at 15 Hz and 73 % at 75 Hz.Copyright

Circuit Rectification for Four Precision Position Synthesis of Four-Bar and Watt Six-Bar Linkages

The circuit defect arises in precision position based linkage synthesis when a potential solution linkage cannot be moved between all precision positions without disassembly. Circuit rectification consists of reducing the potential solution space to include only those linkages that are free of the circuit defect. Circuit rectification for four precision position synthesis of Watt six-bar linkages is developed here. Circuit rectification of four-bar linkages is refined in the process. An example demonstrates the synthesis of a new Watt I sofa bed linkage free of the circuit defect.