Mechanical & Fluid Systems

Measuring Dynamic Transfer Functions of Cavitating Pumps

Flow and pressure perturbations are imposed; transfer functions are computed from responses. A water-flow test facility has been built to enable measurement of dynamic transfer functions (DTFs) of cavitating pumps and of inducers in such pumps. Originally, the facility was intended for use in an investigation of the effects of cavitation in a rocket-engine low-pressure oxygen turbopump. The facility can also be used to measure DTFs of cavitating pumps in general.

Posted in: Briefs

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Robot Would Climb Steep Terrain

This walking robot could even climb under overhangs. The figure depicts the steep terrain access robot (STAR) — a walking robot that has been proposed for exploring steep terrain on remote planets. Robots based on the STAR concept could also be used on steep terrain on Earth for diverse purposes that could include not only scientific exploration but also military reconnaissance and search-and-rescue operations.

Posted in: Briefs, TSP

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First-Order Theory of Control of Motion of a Crane and Load

Suitably modulated motion of the crane could prevent swinging of the load. A first-order mathematical model has been developed in a theoretical study of the dynamics of a load suspended by a cable from a crane that moves along a straight track. The model is the basis of a proposed method of computer control of the velocity as well as the position of the crane to minimize or prevent swinging of the load. (Traditionally, only the position of the crane is controlled; there is no engineering provision against swinging of the load.) Velocity and position control to prevent swinging would be highly desirable, especially in situations in which there are requirements for precise placement of large loads and/or the delays incurred in waiting for damping of pendulum oscillations of loads are unacceptable. Because most modern cranes are already controlled by computers and include position-indicating control subsystems, the implementation of this method of control would entail little or no additional equipment and thus should be relatively inexpensive.

Posted in: Briefs, TSP

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Hollow Shaft Actuators with Harmonic Drive Gearing

They can be used in demanding applications such as industrial robots and servo systems. Harmonic drive gearing is recognized by designers for its zero backlash, high gear ratios, and compact design features. A recent development by HD Systems incorporates a large hollow shaft through the actuator, offering many benefits to the machine designer. The FHA hollow shaft actuator series allows cables, shafts, or tubing to be passed concentrically through the center of the actuator. Through this innovation, the series provides precision motion control and high torque capacity in very compact packages.

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Actuated Ball-and-Socket Joints

These joints would be relatively compact, lightweight, simple, and inexpensive. The term "actuated ball-and-socket" (ABS) characterizes a proposed class of ball-and-socket joints that would incorporate ultrasonic motors and other piezoelectric actuators to generate multidimensional actuation. In some applications, ABS joints could supplant traditional joint-and-actuator assemblies that include passive rotary joints actuated by electromagnetic motors via gears. In comparison with such assemblies, ABS joints offer potential advantages of compactness, relative mechanical simplicity, higher torque-to-weight ratios, no backlash, self-braking with power turned off, and lower cost. ABS joints are expected to be particularly attractive for use as robot joints and as general low-power orienting actuators for diverse applications that could include robot hands, tools, and mechanisms for aiming scientific instruments.

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Laser Anemometer Measures Flow in a Centrifugal Compressor

High-resolution data are representative of flows in practical centrifugal compressors. Detailed measurements of complex flow fields within the NASA Low Speed Centrifugal Compressor (LSCC) have been acquired. The measurement data provide insight into the fundamental physics of flow in centrifugal compressors, and can be used to assess computational fluid dynamics codes and to develop flow-physics models. The resultant benefit is better predictive computational tools and shorter design cycle times.

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High-Altitude Flight Test of the Perseus B Airplane

Flawless aerodynamic, propulsion, and control performance was observed. The Perseus B remotely piloted vehicle (RPV) has achieved a record altitude for a single-engine, propeller-driven airplane of 60,260 ft (18,367 m) on June 27, 1998. The Perseus B is one of the test-bed aircraft developed under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program for use in conducting high-altitude, long-duration missions carrying atmospheric sampling and sensing payloads for the scientific community within NASA and other agencies.

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