Travis Wiens

A Multisodar Approach to Wind Profiling

Abstract This paper presents the development of a multisodar mode from a five-beam sodar whereby a wind speed vector is found for sets of three acoustic beams. If the vertical beam is used, this mode enables the profiling of four wind speed measurements around the sodar. These multisodars can be used to investigate the spatial and temporal nature of winds in both flat and complex terrain. The spatial, temporal, and signal-to-noise qualities of the sodar signal in this mode are analyzed, and a metric for understanding the inhomogeneity of the atmosphere through cross-correlating opposing multisodars is developed. A driving factor for this work is developing the use of such sodar systems in complex terrain, where experimental measurements are traditionally difficult and expensive.

Analysis and Mitigation of Valve Switching Losses in Switched Inertance Converters

Switched inertance converters use digital valves to exploit the inertia of a flow in order to trade flow for pressure or vice versa. These components can be used to efficiently match load and supply pressures, avoiding the energy wasted by using resistive valves. While theoretical switched inertance converters can be highly efficient, practical implementations suffer from a number of energy losses. One of these losses is the valve switching loss: the energy wasted due to the flow experiencing a pressure drop across the partially open valve as the digital valve shifts from one position to the other. This paper quantifies the effect of this loss on the valve’s overall performance. Two novel strategies for mitigating this effect are introduced: a shaped inertance tube design and positioning of the tank-flow valve along the length of the inertance tube.Copyright

Optimization and Experimental Verification of a Variable Ratio Flow Divider Valve

Abstract A common problem in fluid power control systems is the synchronization of two loads. A frequent solution to this problem is to use a flow divider valve. Typical flow divider valves can deliver flow to two circuits such that the ratio of flows is independent of the load pressures, but it is not possible to easily change the ratio after manufacturing. In this paper, the design process used to develop a new variable ratio flow divider valve is introduced. As the first step, a preliminary model was used to optimize the physical parameters for a prototype. In the second step, a valve was subsequently constructed and the performance experimentally determined. The prototype constructed exhibits low dynamic and steady state error with low pressure losses in experimental tests. This novel valve shows sufficient feasibility to warrant future study and development for commercialization.

An Efficient, High Performance and Low-Cost Energy Recovering Hydrostatic Linear Actuator Concept

Hydrostatic or closed-circuit pump-controlled hydraulic systems are attractive due to their high energy efficiency; their lack of throttling losses and ability to recover energy onto the pump shaft have made them a common design choice in systems using rotary actuators such as ground drive transmissions. However, the natural asymmetrical flow of typical hydraulic cylinders have prevented the widespread adoption of closed-circuit systems for linear actuators. Some hydrostatic linear actuator systems have been developed, but these suffer from a large dead volume and reduced force if using a symmetrical dual rod cylinder, or increased cost and complexity if using a specialized cylinder geometry or flow balancing circuits. This paper presents a concept system which uses a pair of common single-rod hydraulic cylinders to achieve the efficiency of a pump-controlled hydrostatic system with the opportunity for energy recovery. The system’s available force is equal to a standard valve-controlled system with a greater maximum velocity. This is achieved using only commercially-available components. The paper will present an analysis of the theoretical energy recovery potential over a representative work cycle for a hydraulic excavator. It will also present a controller design analysis and experimental verification.Copyright

An efficient, compact and low-cost Dual Cylinder Hydrostatic Actuator (DCHA)

Abstract Pump-controlled systems are highly efficient alternatives to the high throttling losses of valve-controlled systems. Closed-circuit systems have been widely adopted for rotary loads, but the asymmetrical nature of linear actuators has limited their acceptance. Hydrostatic linear actuators typically are costly or complex, inefficient or exhibit low force density. This paper presents a Dual Cylinder Hydrostatic Actuator, which is highly efficient for both resistive and overrunning loads, uses commercially available low-cost components, and provides the same high force of a conventional system in a similarly sized system. A steady-state model is presented, along with an experimental validation on a small-scale apparatus. An analysis of a full-scale application is performed, including strategies for mitigation of energy losses.