Mechanical & Fluid Systems

Viscoelastic Vibration Dampers for Turbomachine Blades

These dampers can be retrofitted to existing machines. Simple viscoelastic dampers have been invented for use on the root attachments of turbomachine blades. These dampers suppress bending- and torsion-mode blade vibrations, which are excited by unsteady aerodynamic forces during operation. In suppressing vibrations, these dampers reduce fatigue (thereby prolonging blade lifetimes) while reducing noise. These dampers can be installed in new turbomachines or in previously constructed turbomachines, without need for structural modifications. Moreover, because these dampers are not exposed to flows, they do not affect the aerodynamic performances of turbomachines.

Posted in: Briefs, Mechanical Components

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Optimization of Orientations of Spacecraft Reaction Wheels

A report presents a method of optimizing the orientations of three reaction wheels used to regulate the angular momentum of a spacecraft. The method yields an orientation matrix that minimizes mass, torque, and power demand of the reaction wheels while maximizing the allowable duration between successive angular-momentum dumps. Each reaction wheel is parameterized with its own unit vector, and a quadratic cost function is defined based on requirements for torque, storage of angular momentum, and power demand. Because management of angular momentum is a major issue in designing and operating an orbiting spacecraft, an angular-momentum-management strategy is parameterized and included as part of the overall optimization process. The report describes several case studies, including one of a spacecraft proposed to be placed in orbit around Europa (the fourth largest moon of Jupiter).

Posted in: Briefs, TSP, Mechanical Components

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Flexure Rings for Centering Lenses

The rings accommodate fabrication tolerances and thermal-expansion mismatches. Specially shaped mounting rings keep lenses precisely centered, regardless of temperature, in the lens housings of cameras and other optical systems. These rings feature (1) well-defined contact spots for alignment, plus (2) relieved surfaces that form flexures to accommodate small manufacturing tolerances and differences among the thermal expansions of lenses, lens housings, and the rings themselves. These rings are made by numerically controlled machining of recently developed clean, strong, machinable plastics.

Posted in: Briefs, TSP, Mechanical Components

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Variable Submillimeter-Wave Delay Line for Cryogenic Use

Stiffness, size, vacuum adhesion, range, and number of parts were considered in designing this device. A variable delay line is being developed as part of a far-infrared or submillimeter- wavelength interferometer that would operate in a vacuum in the cryogenic temperature range. No such delay line for spatial interferometry has previously been built for operation under these conditions.

Posted in: Briefs, TSP, Mechanical Components

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Precise Air Bearings Redesigned

A simplified design affords low friction at minimum airflow. Highly precise air bearings for suspending objects over an epoxy flat floor in a laboratory have been developed. These bearings float on airgaps 3 to 5 mil (about 0.08 to 0.13 mm) thick. They are modern versions of precise air bearings, developed during the 1960s, that offer a working coefficient of friction of only 1/16,000. The basic design of these bearings can be scaled easily for different loads and airflows.

Posted in: Briefs, TSP, Mechanical Components

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User’s Guide for ENSAERO

A report summarizes the development, applications, and procedures for use of ENSAERO, a computer program for simulating aeroelastic phenomena (e.g., wing flutter) of aircraft and spacecraft. ENSAERO computes aeroelastic responses by simultaneously numerically integrating Euler and/or Navier-Stokes equations of airflow and modal finite-element equations of structural dynamics on aeroelastically adaptive dynamic grids. The numerical integrations are performed by time-accurate finitedifference schemes. The report describes the coupling of the governing equations of flow with the governing equations of structural dynamics and with equations that describe active controls and thermal loads. The criteria and procedures for generation of zonal adaptive grids are discussed. Results of simulations performed by use of ENSAERO are presented for examples that involve, variously, steady or unsteady flow about rigid full aircraft or elastic wing/body assemblies. This work was done by Guru P. Guruswamy of Ames Research Center. This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, Ames Research Center, (650) 604-5104. Refer to ARC-14239.

Posted in: Briefs, TSP, Mechanical Components

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Minimally Actuated Hopping Robot

This robot can traverse terrain that is too cluttered for wheeled vehicles. A small robot that travels by hopping has been built and tested. This is a prototype of hopping robots that would carry video cameras and possibly other sensory devices and that are under consideration for use in exploring cluttered, unpredictable terrain on distant planets. On Earth, robots like this one might have value for entertainment and civilian and military reconnoitering of hazardous areas.

Posted in: Briefs, TSP, Mechanical Components

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