Mechanical & Fluid Systems

Mechanical Amplifier for a Piezoelectric Transducer

In addition to multiplication of stroke, the design affords momentum compensation.

A mechanical amplifier has been devised to multiply the stroke of a piezoelectric transducer (PZT) intended for use at liquid helium temperatures. Interferometry holds the key to high angular resolution imaging and astrometry in space. Future space missions that will detect planets around other solar systems and perform detailed studies of the evolution of stars and galaxies will use new interferometers that observe at mid- and far-infrared wavelengths. Phase-measurement interferometry is key to many aspects of astronomical interferometry, and PZTs are ideal modulators for most methods of phase measurement, but primarily at visible wavelengths. At far infrared wavelengths of 150 to 300 µm, background noise is a severe problem and all optics must be cooled to about 4 K. Under these conditions, piezos are ill-suited as modulators, because their throw is reduced by as much as a factor of 2, and even a wavelength or two of modulation is beyond their capability. The largest commercially available piezo stacks are about 5 in. (12.7 cm) long and have a throw of about 180 µm at room temperature and only 90 μm at 4 K. It would seem difficult or impossible to use PZTs for phase measurements in the far infrared were it not for the new mechanical amplifier that was designed and built.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Amplifiers, Imaging, Imaging and visualization, Lasers, Amplifiers, Imaging, Imaging and visualization, Lasers

Swell Sleeves for Testing Explosive Devices

A device is detonated in a sleeve and the resultant swelling is measured.

A method of testing explosive and pyrotechnic devices involves exploding the devices inside swell sleeves. Swell sleeves have been used previously for measuring forces. In the present method, they are used to obtain quantitative indications of the energy released in explosions of the devices under test.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Test equipment and instrumentation

Propulsion Flight-Test Fixture

Subscale engines can be flight-tested early in the development cycle.

NASA Dryden Flight Research Center's new Propulsion Flight Test Fixture (PFTF), designed in house, is an airborne engine-testing facility that enables engineers to gather flight data on small experimental engines. Without the PFTF, it would be necessary to obtain such data from traditional wind tunnels, ground test stands, or laboratory test rigs.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Jet engines, Flight tests, Test facilities

High-Temperature Switched-Reluctance Electric Motor

Motors like this one would be incorporated into gas turbines as starter/generators.

An eight-pole radial magnetic bearing has been modified into a switched-reluctance electric motor capable of operating at a speed as high as 8,000 rpm at a temperature as high as 1,000 °F (Å540 °C). The motor (see figure) is an experimental prototype of starter-motor/ generator units that have been proposed to be incorporated into advanced gas turbine engines and that could operate without need for lubrication or active cooling.

Posted in: Briefs, Mechanical Components, Mechanics, Bearings, Electric motors

Using ERF Devices To Control Deployments of Space Structures

A report proposes devices containing electrorheological fluids (ERFs) damper for controlling deployments of lightweight, flexible structures in outer space. The structures would include spring members that could be wound or compressed for compact stowage during transport. The ERF based damper would keep the structures compacted and/or regulate the speeds with which the structures would spring out for deployment. After deployment, ERF based dampening mechanism could be used to rigidize the structures or damp their vibrations. The report describes several potential variations on the basic concept of an ERF-controlled structural member, including compartmentalization of the interior volume to prevent total loss of the ERF in case of a leak and the use of multiple, individually addressable electrode pairs to enable more localized control.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Dampers and shock absorbers, Dampers or shock absorbers, Smart materials

Miniature Gas-Turbine Power Generator

Energy density would greatly exceed that of a typical battery system.

A proposed microelectromechanical system (MEMS) containing a closed- Brayton-cycle turbine would serve as a prototype of electric- power generators for special applications in which high energy densities are required and in which, heretofore, batteries have been used. The system would have a volume of about 6 cm3 and would operate with a thermal efficiency >30 percent, generating up to 50 W of electrical power. The energy density of the proposed system would be about 10 times that of the best battery-based systems now available, and, as such, would be comparable to that of a fuel cell.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Microelectricmechanical device, Microelectromechanical devices, Microelectricmechanical device, Microelectromechanical devices, Electric power, On-board energy sources, Gas turbines

Pneumatically Actuated Miniature Peristaltic Vacuum Pumps

Small, rugged, low-power pumps could be fabricated inexpensively.

Pneumatically actuated miniature peristaltic vacuum pumps have been proposed for incorporation into advanced miniature versions of scientific instruments that depend on vacuum for proper operation. These pumps are expected to be capable of reaching vacuum-side pressures in the torr to millitorr range (from ≈133 down to ≈0.13 Pa). Vacuum pumps that operate in this range are often denoted roughing pumps. In comparison with previously available roughing pumps, these pumps are expected to be an order of magnitude less massive and less power-hungry. In addition, they would be extremely robust, and would operate with little or no maintenance and without need for oil or other lubricants. Portable mass spectrometers are typical examples of instruments that could incorporate the proposed pumps. In addition, the proposed pumps could be used as roughing pumps in general laboratory applications in which low pumping rates could be tolerated.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Spectroscopy, Spectroscopy, Gases, Pumps, Pneumatic systems, Durability, Durability, Test equipment and instrumentation

Soft Landing of Spacecraft on Energy-Absorbing Self-Deployable Cushions

A report proposes the use of cold hibernated elastic memory (CHEM) foam structures to cushion impacts of small (1 to 50 kg) exploratory spacecraft on remote planets. Airbags, which are used on larger (800 to 1,000 kg) spacecraft have been found to (1) be too complex for smaller spacecraft; (2) provide insufficient thermal insulation between spacecraft and ground; (3) bounce on impact, thereby making it difficult to land spacecraft in precisely designated positions; and (4) be too unstable to serve as platforms for scientific observations. A CHEM foam pad according to the proposal would have a glass-transition temperature (Tg) well above ambient temperature. It would be compacted, at a temperature above Tg, to about a tenth or less of its original volume, then cooled below Tg, then installed on a spacecraft without compacting restraints. Upon entry of the spacecraft into a planetary atmosphere, the temperature would rise above Tg, causing the pad to expand to its original volume and shape. As the spacecraft decelerated and cooled, the temperature would fall below Tg, rigidifying the foam structure. The structure would absorb kinetic energy during ground impact by inelastic crushing, thus protecting the payload from damaging shocks. Thereafter, this pad would serve as a mechanically stable, thermally insulating platform for the landed spacecraft.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Elastomers, Foams, Insulation, Smart materials, Entry, descent, and landing, Spacecraft

Energy-Absorbing, Lightweight Wheels

Efficient structures would absorb impact energies and distribute contact loads.

Improved energy- absorbing wheels are under development for use on special-purpose vehicles that must traverse rough terrain under conditions (e.g., extreme cold) in which rubber pneumatic tires would fail. The designs of these wheels differ from those of prior non-pneumatic energy-absorbing wheels in ways that result in lighter weights and more effective reduction of stresses generated by ground/wheel contact forces. These wheels could be made of metals and/or composite materials to withstand the expected extreme operating conditions.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Wheels, Cold weather, Terrain, Composite materials, Metals

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, Mechanics, Fatigue, Exterior noise, Vibration, Exterior noise, Vibration, Mountings, Fans, Aerodynamics

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