Mechanical Components

Axial Field Electric Motor

An axial field electric motor comprises one or more elements such as a rotor mounted for rotation and multiple axial flux permanent magnets carried by the rotor. The axial flux permanent magnets are oriented such that an associated magnetic flux produced thereby is at least substantially axially oriented. The axial flux permanent magnets are positioned around the rotor with alternating orientations of flux direction so that a flux direction of adjacent magnets is at least substantially axially oriented but opposite in direction. The radial flux permanent magnets are also carried by the rotor and oriented so that an associated magnetic flux produced is at least substantially radially oriented.

Posted in: Briefs, Mechanical Components
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SparkJet Actuators for Controlling Flows

SparkJet actuators are under investigation as means of controlling flows — especially supersonic and hypersonic flows. In one important class of potential applications, SparkJet actuators would be used to effect rapid and flexible steering of advanced aerospace vehicles. Effective manipulation of flow fields in aerospace systems could afford significant benefits, including increases in performance, maneuverability, payload, and range, as well as reductions in overall costs. These macro-scale benefits would be achieved through the use of SparkJet actuators to alter such phenomena as laminar-to-turbulent transition, turbulence, and flow separation on a micro scale.

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Stability of Rotors Supported by Hydrodynamic Film Bearings

The document, "Hydrodynamic Fluid Film Bearings and Their Effect on the Stability of Rotating Machinery" represents a lecture in a series "Design and Analysis of High-Speed Pumps," held in 2006 under the auspices of the North Atlantic Treaty Organization. The document introduces the basic principles of hydrodynamic lubrication and the fundamental equation of classical lubrication theory, then proceeds through derivation of the static and dynamic performance characteristics of short cylindrical journal bearings, with application to the dynamic forced performance of a rigid rotor supported on plain bearings. The Sommerfeld number is introduced and shown to define the relation among load, speed, and equilibrium eccentricity of a journal within a radial bearing. Rotordynamic force coefficients (direct and cross-coupled stiffnesses) are introduced and the relationships between them and instabilities of the rotor-and-bearing system are thoroughly discussed. The relationship between the whirl frequency ratio (the ratio between the frequency of undesired orbital rotor motion about the nominal journal axis and the frequency of rotation) and the threshold rotational frequency for instability is discussed. The document concludes with a review of practical journal-bearing configurations, including summaries of their major advantages and disadvantages and brief descriptions of typical applications.

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Prototype Rocket Engine for a Nanosat Launch Vehicle

A paper discusses a prototype rocket engine for a suborbital Reusable Nanosat Launch Vehicle (RNLV). The engine must operate with thrust levels from 3,000 to 5,000 lbf. The engine is comprised of three major subassemblies: the injector, igniter, and the combustion chamber nozzle. Propellants are introduced and mixed in the combustion chamber utilizing a combination of triplet and unlike doublet injector elements. In addition, film cooling is provided in order to extend the life of the ablative chamber. Ignition is accomplished with solid propellant ports mounted on the side of the chamber.

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Biaxial and Shear Testing Apparatus With Force Controls

An apparatus for in-plane biaxial tension/compression and in-plane shear testing of fabrics, other flexible sheet materials, or relatively rigid thin plate materials has been invented. The apparatus is capable of applying, to a sheet material specimen, a controlled tensile or compressive force along each of two directions in the plane of the specimen. The force along each direction can differ from the force along the other direction. The directions of the applied forces can be orthogonal or can be set at an oblique angle, depending on the combination of stresses required to be applied to the specimen. Thus, depending on the angle between the applied-force directions, the sense (tensile or compressive) of each applied force, and the magnitude of each force, the specimen can be subjected to almost any combination of in-plane shear and biaxial tension/compression loading.

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MEMS Offset-Beam Torsional Electrothermal Actuators

Prototypes of microelectromechanical system (MEMS) rotational actuators based on a principle of torsion induced by thermal expansion of electrically heated offset beams have been designed, fabricated, and tested. It is envisioned that after further development, these actuators might be used to satisfy stringent competing requirements for smaller, larger-force, largerdisplacement actuators in increasingly complex MEMS systems. Until now, MEMS thermal actuators have been regarded as inefficient and capable of producing, variously, either large forces and small displacements or small forces and large displacements. The actuators of the present type are intended to overcome some of the deficiencies heretofore attributed to MEMS thermal actuators by producing medium displacements and medium forces.

Posted in: Briefs, Mechanical Components, Microelectricmechanical device, Sensors and actuators
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Tethered, Remotely Operated Miniature Submarine

A tethered, remotely operated, armed underwater vehicle has been conceived to satisfy a need for an uninhabited vehicle for Navy missions in which positive identification of targets is needed. Examples of such missions include those involving detection of swimmers and neutralization of mines. Unarmed versions of the vehicle might also be useful in civilian applications involving underwater inspections under hazardous conditions.

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The Future of Space Propulsion

A paper presents an overview of state of the art of space propulsion, oriented toward attempting to understand recent history in order to make some predictions about future developments. As used here, "space propulsion" refers generally to what are now called "spacelift" and "spacecraft propulsion." Further, as used here, "spacelift" refers generally to large rockets, associated equipment, and other resources for launching spacecraft into outer space, while "spacecraft propulsion" refers generally only to systems for propelling spacecraft once they are in outer space. The paper includes a summary of recent history of spacecraft propulsion, with greatest emphasis on spacelift systems, from the perspective of striving to maintain the military superiority and economic competitiveness of the United States in the face of the rapid international evolution of space technology. Advantages and disadvantages of various engine designs and propellant substances, and considerations of cost and development time, are discussed. Trends in spacelift (and, to a lesser extent, trends in spacecraft propulsion) are discussed. An attempt is made to predict the general nature of future developments by extrapolating the trends into the foreseeable future.

This work was done by John F. Remen and Glenn Liston of the Air Force Research Laboratory.

Posted in: Briefs, Mechanical Components, Technical reference, Rocket engines, Launch vehicles, Spacecraft
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Miniature Wheel-Leg Mobile Robots

Mini-Whegs™ are small mobile robots, designed according to abstracted cockroach locomotion principles, that can run and can climb obstacles taller than themselves. Mini-Whegs are derived from larger mobile robots denoted Whegs™, with modifications to reduce size, reduce the number of mechanisms, and increase relative mobility. The name "Whegs" originated as a contraction of "wheel-legs," referring to three-spoke appendages by means of which these robots move, as described below.

Posted in: Briefs, Mechanical Components, Wheels, Downsizing, Robotics
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Simulations of Brush Contacts of Homopolar Motor/Generators

A computational- simulation study of distributions of electric current and temperature in brushes and slip rings in two model homopolar- motor/generator configurations was performed in support of the development, by the U.S. Navy, of a superconducting homopolar motor/generator (SCHPMG) machine for ship propulsion. Electrical-contact performance (more specifically, brush/slip-ring contact performance) is a limiting factor in the performance of an SCHPMG machine. The present study and similar studies are needed to gain understanding of brush/slip-ring contact performance in order to enable optimal design of brushes for homopolar machines.

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