Mechanical & Fluid Systems

Optimization of Synthetic Jet Actuators

A report presents a study oriented toward optimization of synthetic jet actuators. [A syn- thetic jet actuator is a fluidic control device that partly resembles a loudspeaker. It typically comprises a piezo- electric actuator/ diaphragm situated in a cavity, facing an orifice or nozzle at the opposite end of the cavity.] The instant report describes an experimental synthetic jet actuator equipped for tuning through variation of some of its cavity dimensions and its excitation frequency and for selection of either (1) clamping of the edge of the diaphragm between flat surfaces or (2) pinning of the edge of the diaphragm between steel O rings. The report goes on to discuss the effects of the cavity and nozzle geometry, diaphragm design, excitation frequency, and other design features on the vibrational resonance of the diaphragm, the acoustic resonance of the cavity, the coupling (or lack thereof) of these resonances, and the overall performance as characterized by the displacement at the center of the diaphragm or the speed of the jet at a specified distance from the orifice. Conclusions reached in this study are that (1) the pinning configuration results in better performance than does the clamping configuration and (2) the maximum performance is achieved by matching the resonant frequencies of the diaphragm and the cavity.

Posted in: Briefs, TSP, Mechanical Components

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Hexfoil Rotary Flexures

These devices would afford high accuracy of centration. Hexfoil rotary flexures have been proposed as pivots suitable for use in precise optical instruments. In the application that inspired the hexfoil concept, there is a requirement for a limited-rotation mirror gimbal that would maintain, with unprecedented accuracy, coincidence among the axes of rotation and a fiducial mark on the mirror, over the entire range of rotation. Theoretically, a hexfoil rotary flexure could satisfy this requirement.

Posted in: Briefs, TSP, Mechanical Components

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Improvements in the Use of Water Washes in Testing for NVR

Effectiveness of washing and sensitivity of detection are increased. Some improvements have been made to enhance the role of water as a test solvent for determining the amount of hydrocarbon nonvolatile residue (NVR) present on an item of hardware that is required to be totally or nearly devoid of such residue. Water is now used as an NVR-testing solvent because (1) even highmolecular- weight hydrocarbon greases are at least slightly soluble in water, (2) water is safer and less expensive than are chlorofluorocarbon solvents [in particular, 1,1,2- trichloro-1,2,2-trifluoroethane (also known as CFC-113), which was used previously in testing for hydrocarbon NVR], and (3) CFC solvents are expensive and are now recognized as environmentally harmful.

Posted in: Briefs, TSP, Mechanical Components

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Flight Research on Supersonic Laminar Flow

Flow over a suitably designed airfoil can remain largely laminar, even at supersonic speed. Some airfoil designs have been shown by theory and small-scale tests to be capable of passively maintaining laminar flow at super -sonic speeds. More recently, flight tests have proven that these designs can maintain large runs of laminar flow at higher Reynolds numbers in harsh flight environments. The flight tests were conducted for the purposes of observing laminar flow at speeds up to mach 2.0 and determining the conditions under which laminar flow breaks down.

Posted in: Briefs, Mechanical Components

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Improved Flange Design for Cryogenic Vacuum O-Ring Seals

Spring-loaded joints could be made less bulky. A compact spring-loading design has been proposed to increase the reliability of seals in the joints of vacuum cryogenic systems. Heretofore, such joints have been, variously, compact or reliable, but not both, for the following reasons: In all such joints, sealing is effected by compression of soft metal (typically, indium or alloys of indium) O rings between flanges. Over time, the soft O-ring metal flows, with consequent reduction of preload, sometimes leading to loss of seal. To ensure reliable seals, it is necessary to spring-load the flanges to maintain compression of the O rings. However, spring-loaded joints of traditional design are not compact.

Posted in: Briefs, TSP, Mechanical Components

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Algorithm Computes Kinematics of a Rover on Rocky Terrain

This algorithm is efficient enough for use in a real-time simulation. The Rover Analysis Modeling and Simulation (ROAMS) algorithm is to solve the kinematics of a wheeled mo- bile robot (rover) traversing on a rocky terrain. The rover is constructed using a “rocker-bogey-differential” type suspension and steering system as shown in the figure. By exploring the mechanical symmetry and the wheeled-terrain contact characteristics on a rough terrain profile, we developed a novel algorithm to carry out the rover’s configuration, including the vehicle’s wheels, steering and suspension linkages, and the position and orientation of the chassis. Because of its efficient and reliable numerical results, the ROAMS algorithm is well suited for the real-time simulation test bed, e.g., a simulation software system, of the mobile robotic vehicles in the planetary surface exploration missions. Currently, it is used to support the development of simulation and operation tools for the Mars Exploration Rover (MER) in the Mars ‘03 mission.

Posted in: Briefs, TSP, Mechanical Components

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Crowned Races for Crossed Roller Bearings

Scuffing would be reduced. Crowned races have been proposed for crossed roller bearings. Crowning of the races   is expected to reduce scuffing of the cylindrical rollers. Crowning of the races is expected to be especially beneficial in bearings made of polymers (instead of metals) to reduce weight.

Posted in: Briefs, TSP, Mechanical Components

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