Mechanical & Fluid Systems

Improved Lightweight Freeze-Tolerant Tubes

Improved designs have been conceived for lightweight tubes that can withstand the large (as much as 8 or 9 volume percent) freeze/thaw expansions and contractions of typical heat-transfer fluids like water and ammonia. Intended originally for radiators for rejecting waste heat from spacecraft, these designs may also be suitable for such terrestrial applications as freeze-tolerant water pipes in houses and sprinkler systems. Typical prior freeze-tolerant-tube designs are characterized by short operating lives because they rely on compressible polymeric inserts that are degraded by permeability and by embrittlement at low temperatures. The improved designs call for thin tube walls with noncircular (typically oval) cross sections and solid or hollow metal inserts of various shapes, all selected together to obtain specific combinations of limited volume expansion and mechanical advantage such that the stresses in the tube walls remain sufficiently low under all anticipated freeze/thaw conditions.

Posted in: Mechanics, Briefs, TSP

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Mechanisms Facilitate Blowdown of Large Diesel Engines

Blowdown can be performed faster, more easily, and more safely. Simple mechanisms have been devised to facilitate the blowdown of large diesel engines. As explained below, these mechanisms reduce the amount of time and effort that must be expended to test engines before operating them.

Posted in: Mechanics, Briefs, TSP

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Uncertainty Models From Ground Vibration Testing

Test data indicate least conservative errors in model. Structural dynamics are often an important consideration when evaluating system characteristics. A concern related to structural dynamics is the analysis of flutter for a flight vehicle. The instability associated with flutter can be quite sensitive to the structural dynamics; therefore, analysis of robustness with respect to error, or uncertainty, is becoming increasingly important for the flight test community. In particular, uncertainty models are needed for μ-method analysis as described in "Characterizing Worst-Case Flutter Margins From Flight Data'' (DRC-97-03), NASA Tech Briefs, Vol. 21, No. 4 (April 1997), page 62.

Posted in: Mechanics, Briefs

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Spacecraft Nuclear Reactor Would Be Fueled in Orbit

Two reports summarize progress thus far in the continuing development of a spacecraft nuclear reactor, some or all of the fuel rods of which would not be loaded until the spacecraft was in orbit. (Keeping the fuel rods out of the reactor core before and during launch is intended to minimize the risk of release of radioactive material in the event of a launch accident.) The report describes the design and operation of the fueling mechanism, and problems in the design and fabrication of the core. The fuel rods include uranium oxide in rhenium sleeves. The core includes niobium star-cross-section inserts and molybdenum tubes, into which the fuel rods are to be inserted.

Posted in: Mechanics, Briefs

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Designs for Safer Launching of Spacecraft Fission System

A report proposes the development of two different mechanisms that would prevent inadvertent startup of reactors in nuclear-fission-based propulsion and power systems in future spacecraft. The purpose of this development is to contribute to safety by ensuring that radioactivity is kept to normal negligible levels before and during launch and in the event of a launch accident. Once the spacecraft was safely in outer space, a motor would actuate a linear screw that would move the fuel section of the rods into the core, enabling the reactor.

Posted in: Mechanics, Briefs

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Saturation Technique for Rapid Binary Image Processing

This technique is fundamentally different from truncation of least-significant bits. An improved technique of limited-precision arithmetic has been devised for use in convolutional filtering of image data prior to conversion of the data to binary form. Both limited-precision arithmetic and conversion to binary form reduce the volume of data, thereby contributing to processing speed and reducing the sizes of circuits needed to perform, and store the results of, intermediate stages of processing. Applications in which these techniques are or could be helpful include robotic vision, recognizing and tracking moving targets, stabilizing images in hand-held video cameras, and general enhancement of images.

Posted in: Mechanics, Briefs, TSP

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Breathing-Air and Cooling Apparatus for Protective Suit

Applications can include diving, space, and firefighting suits. The figure schematically illustrates a portable life-support apparatus for any of a variety of protective suits to be worn in hostile environments. A prototype of the apparatus has been fitted to space suits for use underwater. Astronauts wear these suits during training dives in a tank of warm water, using the neutral buoyancy available in the underwater environment to simulate aspects of the zero gravitation of outer space. The apparatus provides breathing air and adjustable cooling in the suit, while maintaining overall neutral buoyancy. The apparatus is readily adaptable to such related applications as conventional diving and space suits, firefighting suits, and protective garments to be worn in hot, toxic, and/or radioactive environments.

Posted in: Mechanics, Briefs, TSP

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