Index to nasa tech briefs, issue number 2

Annotated bibliography on technological innovations in NASA space program

Cumulative index to NASA Tech Briefs, 1963-1965

Annotated bibliography of NASA technical briefs on electrical, energy sources, materials, life sciences, and mechanical informatio

Performance analysis for a shaded-pole linear induction motor

Bibliography: pages 129-148.The induction motor remains the prime mover of present day industry with it's associated components in drive applications. In many such applications, fractional horse-power motors find ready use in small mechanisms where three-phase power supply is not available. In Southern Africa, these motors can be used is rural areas with simple reticulation systems, hence the renewed interest in the development of these low-power electrical motors, especially specialised models such as linear versions of such motors for special applications. This research is in the area of single-phase LIMs. The objective has been to model the shaded-pole LIM, in an attempt to enhance it's performance through improved design methods. This was carried out using an integrated analysis approach, involving circuital and field theory in the analysis of the practical motor, and computer simulation of it's equivalent model using the finite element method. Linear counterparts are possible for all the various forms of rotating electrical machines. All cylindrical machines can be 'cut' along a radial plane and 'unrolled' [32]. LIMs convert electrical energy directly into mechanical energy of translatory motion. Some advantages of linear version of induction motors are: they are gearless and often require minimal material thus minimising cost. While their scope of application are somewhat limited when compared to rotary versions, they do however give excellent performance in special situations where translator motion is required. However, the output power-to-mass and output power-to-volume of active materials ratio is reduced compared to rotary induction motors[45]. These disadvantages are caused by the large air-gap and the open magnetic circuit, which produces parasitical effects

Transducers for measuring acoustic transients

This thesis is concerned with the design and development of measuring devices for the characterisation of acoustic transients with high temporal and spatial resolution. Three new techniques are demonstrated characterising acoustic transients generated by Nd-YAG laser (1060nm, 30ns, 55mJ) assisted breakdown of water and air. The first technique demonstrates the use of a high power semiconductor laser in a high speed multiple exposure imaging system. This system developed is capable of illuminating an event with up to 10 pulses of light at a maximum repetition rate of 5MHz, with a timing accuracy of ≈5ns. Each semiconductor laser light pulse has a FWHM duration of 50ns, peak power of 30W, and a wavelength of 860nm. Images of individual acoustic transients are displayed on the same CCD camera frame, and it was found that this is best achieved using a dark field imaging technique such as Schlieren imaging. [Continues.

Energy Harvesting for Tire Pressure Monitoring Systems

Tire pressure monitoring systems (TPMSs) predict over- and underinflated tires, and warn the driver in critical situations. Today, battery powered TPMSs suffer from limited energy. New sensor features such as friction determination or aquaplaning detection require even more energy and would significantly decrease the TPMS lifetime. Harvesting electrical energy inside the tire of a vehicle has been considered as a promising alternative to overcome the limited lifetime of a battery. However, it is a real challenge to design a system, that generates electrical energy at low velocities while being robust at 200 km/h where radial accelerations up to 20000 m/s2 occur. This work focusses on developing different electromechanical energy transducers that meet the high requirements of the automotive sector. Different approaches are addressed on how the change of acceleration and strain within the tire can be used to provide mechanical energy to the energy harvester. The energy harvester converts the mechanical energy into electrical energy. In this thesis, piezoelectric and electromagnetic transducers are discussed in depth, modelled as electromechanical networks. Since the transducers provide energy in the form of an AC voltage, but sensors require a DC voltage, various common interface circuits are compared, using LTspice and applying method of the stochastic signal analysis. Furthermore, a buck-boost converter concept for the electromagnetic energy harvester is optimized and improved. Experiments on a tire test rig validate the theoretically determined output and confirm that well designed energy harvesters in the tire can generate much more energy than required by an TPMS not only at high velocities but also at velocities as low as 20 km/h

Modeling of Bearing Voltage in Electric Machines Based on Electromagnetic FEA and Measured Bearing Capacitance

Bearing voltages and associated bearing currents in electric machines driven by pulsewidth modulation converters with high switching frequencies and high dv/dt can cause premature bearing failures. This article proposes a new modeling approach for the prediction of steady-state and transient bearing voltages based on two-dimensional (2-D) electromagnetic finite element analysis with coupled external circuits using measured bearing capacitance values. The distributed-element external circuit was employed mainly to take into account the influence of wire distribution and frequency dependency, which are typically neglected by traditional equivalent circuits. The developed model was then used to simulate bearing voltages for various scenarios and evaluate the effectiveness of several easy-to-implement bearing voltage reduction methods from the perspective of machine design and manufacturing, such as using the insulated shaft and/or bearings, introducing additional insulation in the rotor, and changing the material of machine components. Experimental measurements are also provided to facilitate the analysis and validate the proposed approach

Transducer applications, a compilation

The characteristics and applications of transducers are discussed. Subjects presented are: (1) thermal measurements, (2) liquid level and fluid flow measurements, (3) pressure transducers, (4) stress-strain measurements, (5) acceleration and velocity measurements, (6) displacement and angular rotation, and (7) transducer test and calibration methods

Cumulative Index to NASA Tech Briefs, 1963 - 1966

Cumulative index of NASA Tech Briefs dealing with electrical and electronic, physical science and energy sources, materials and chemistry, life science, and mechanical innovation

KPK Lecture notes Mechanics (Der Karlsruher Physikkurs)

Skriptum zur Experimentalphysikvorlesung Mechani