Physical Sciences

Preparing and Analyzing Iced Airfoils

SmaggIce version 1.2 is a computer program for preparing and analyzing iced airfoils.It includes interactive tools for (1)measuring ice-shape characteris- tics,(2)controlled smoothing of ice shapes,(3)curve discretization,(4)gen- eration of artificial ice shapes,and (5)de- tection and correction of input errors. Measurements of ice shapes are essential for establishing relationships between characteristics of ice and effects of ice on airfoil performance.The shape-smoothing tool helps prepare ice shapes for use with already available grid-generation and computational-fluid-dynamics soft- ware for studying the aerodynamic effects of smoothed ice on airfoils.The artificial ice-shape generation tool supports para- metric studies since ice-shape parameters can easily be controlled with the artificial ice.In such studies,artificial shapes gen- erated by this program can supplement simulated ice obtained from icing re- search tunnels and real ice obtained from flight test under icing weather condition. SmaggIce also automatically detects geometry errors such as tangles or dupli- cate points in the boundary which may be introduced by digitization and provides tools to correct these.By use of interactive tools included in SmaggIce version 1.2,one can easily characterize ice shapes and prepare iced airfoils for grid genera- tion and flow simulations.

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Coronagraphic Notch Filter for Raman Spectroscopy

Design could be optimized for attenuating pump light and transmitting Raman-scattered light. A modified coronagraph has been proposed as a prototype of improved notch filters in Raman spectrometers. Corona-graphic notch filters could offer alternatives to both (1) the large and expensive double or triple monochromators in older Raman spectrometers and (2) holographic notch filters, which are less expensive but are subject to environmental degradation as well as to limitations of geometry and spectral range.

Posted in: Physical Sciences, Briefs, TSP

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On-the-Fly Mapping for Calibrating Directional Antennas

Source-size corrections are not necessary in this method.  An improved method of calibrating a large directional radio antenna of the type used in deep-space communication and radio astronomy has been developed. This method involves a raster-scanning-and-measurement technique denoted on-the-fly (OTF) mapping, applied in consideration of the results of a systematic analysis of the entire measurement procedure. Phenomena to which particular attention was paid in the analysis include (1) the noise characteristics of a total-power radiometer (TPR) that is used in the measurements and (2) tropospherically induced radiometer fluctuations. The method also involves the use of recently developed techniques for acquisition and reduction of data. In comparison with prior methods used to calibrate such antennas, this method yields an order-of-magnitude improvement in the precision of determinations of antenna aperture efficiency, and improvement by a factor of five or more in the precision of determination of pointing error and beam width. Prerequisite to a meaningful description of the present method is some background information concerning three aspects of the problem of calibrating an antenna of the type in question:

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Working Fluids for Increasing Capacities of Heat Pipes

Fluids are formulated to make surface tensions increase with temperature. A theoretical and experimental investigation has shown that the capacities of heat pipes can be increased through suitable reformulation of their working fluids. The surface tensions of all of the working fluids heretofore used in heat pipes decrease with temperature. As explained in more detail below, the limits on the performance of a heat pipe are associated with the decrease in the surface tension of the working fluid with temperature, and so one can enhance performance by reformulating the working fluid so that its surface tension increases with temperature.

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Hybrid Piezoelectric/Fiber-Optic Sensor Sheets

Multiple sensors of different types could be installed on or in structures.Hybrid piezoelectric/fiber-optic (HyPFO) sensor sheets are undergoing development. They are intended for use in nondestructive evaluation and long-term monitoring of the integrity of diverse structures, including aerospace, aeronautical, automotive, and large stationary ones. It is anticipated that the further development and subsequent commercialization of the HyPFO sensor systems will lead to economic benefits in the form of increased safety, reduction of life-cycle costs through real-time structural monitoring, increased structural reliability, reduction of maintenance costs, and increased readiness for service.

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Integrated-Optic Oxygen Sensors

Compact optical oxygen sensors with self-calibration capabilities are undergoing development. A sensor of this type features a single-chip, integrated-optic design implemented by photolithographic fabrication of optical waveguides in a photosensitive porous glass. The porosity serves as both a matrix for retention of an oxygensensitive fluorescent indicator chemical and a medium for diffusion of oxygen to the chemical from the ambient air to be monitored. Each sensor includes at least one such waveguide exposed to the atmosphere and at least one covered with metal for isolation from the atmosphere. The covered one serves as a reference channel. In operation, the concentration of oxygen is deduced from the intensity and lifetime of the fluorescence in the exposed channel, with the help of calibration data acquired via the reference channel. Because the sensory chemical is placed directly in and throughout the cross section of the light path, approximately 99 percent of the light in the waveguide is available for interaction with the chemical, in contradistinction to only about 1 percent of the light in an optical sensor that utilizes evanescentwave coupling. Hence, a sensor of this type is significantly more sensitive.

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Multisensor Arrays for Greater Reliability and Accuracy

Calibrations and replacements are needed less frequently than they are for single sensors.Arrays of multiple, nominally identical sensors with sensor-output-processing electronic hardware and software are being developed in order to obtain accuracy, reliability, and lifetime greater than those of single sensors. The conceptual basis of this development lies in the statistical behavior of multiple sensors and a multisensor-array (MSA) algorithm that exploits that behavior. In addition, advances in microelectromechanical systems (MEMS) and integrated circuits are exploited. A typical sensor unit according to this concept includes multiple MEMS sensors and sensor-readout circuitry fabricated together on a single chip and packaged compactly with a microprocessor that performs several functions, including execution of the MSA algorithm.

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