Smart materials' ability to deliver large block forces in a small package while operating at high frequencies makes them extremely attractive for converting electrical to mechanical power. This has led to the development of hybrid actuators consisting of co-located
smart material actuated pumps and hydraulic cylinders that are connected by a set of fast-acting valves. The overall success of the hybrid concept hinges on the effectiveness of the coupling between the smart material and the fluid. This, in turn, is strongly dependent on the resistance to fluid flow in the device. This paper presents results from three-dimensional unsteady simulations of fluid flow in the pumping chamber of a prototype hybrid actuator powered by a piezo-electric stack. The results show that the forces
associated with moving the fluid into and out of the pumping chamber
already exceed 10% of the piezo stack blocked force at relatively low frequencies ~120 Hz and approach 40% of the blocked force at 800 Hz. This reduces the amplitude of the piston motion in such a way that the volume flow rate remains approximately constant above operating frequencies of 500 Hz while the efficiency of the pump decreases rapidly.
Magnetorheological (MR) fluids can be used in a variety of smart semi-active systems. MR dampers have especially great potential to mitigate environmentally induced vibration and shocks. MR fluid can be used effectively in valve networks to control the flow from a hydraulic source to enable a fully active actuator. These devices are simple, have few moving parts and can be easily miniaturized to provide a compact, high energy density pressure source. The present study describes a prototype MR-piezo hybrid actuator that combines the piezo-pump and MR valve actuator concepts, resulting in a self-contained hydraulic actuation device without active electro-mechanical valves. Durability and miniaturization of the hybrid device are major advantages due to its low part count and few moving parts. An additional advantage is the ability to use the MR valve network in the actuator to achieve controllable damping. The design, construction and testing of a prototype MR-piezo hybrid actuator is described. The performance and efficiency of the device is derived using ideal, biviscous and Bingham-plastic representations of MR fluid behavior. Unidirectional performance, or constant velocity actuator shaft motion, is assessed analytically and compared to experimental data. A experimental assessment of the magnetorheological birectional flow control capability is also provided.
Smart materials' ability to deliver large block forces in a small package while operating at high frequencies makes them extremely
attractive for converting electrical to mechanical power. This has led to the development of hybrid actuators consisting of co-located
smart material actuated pumps and hydraulic cylinders that are connected by a set of fast-acting valves. The overall success of the hybrid concept hinges on the effectiveness of the coupling between the smart material and the fluid. This, in turn, is strongly dependent on the resistance to fluid flow in the device. This paper presents the results of two and three dimensional simulations of fluid flow in a prototpype hybrid actuator being developed for aerospace applications. The steady simulations show that losses in the device result primarily from three dimensional effects and that two dimensional approaches can underestimate losses by approximately a factor of 40. The effects of varying design parameters like the pumping chamber height, discharge port location, and discharge port chamfer are also explored and are found to have significant impacts on performance. Three dimensional, unsteady simulations demonstrate how resistance to fluid flow in the pump reduces the amplitude of the piezo displacement and thus limits the flow rate of the device.
Optical diagnostics play a key role in the development of a unique, high volumetric heat release rate incinerator
design at UCLA. In the device, a derivative of an aerospace dump combustor, a pre-mixed flame is stabilized within a rectangular
duct by a sudden expansion in cross section at the dump plane. Wastes injected into hot, oxidative recirculation
regions downstream of the dump plane experience much larger residence times than those of the bulk flow. Particle Image
Velocimetry is used to study the velocity field in the combustion cavity. The results confirm the existence of the recirculation
regions and illustrate the effect of waste injection on them. Planar Laser-Induced Fluorescence of the OH radical illustrates the propagation of a vortical reaction zone (flame) into the combustion cavity and its interaction with the recirculation
zones.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.