Tech Briefs

Stress Testing of Data-Communication Networks

NetStress is a computer program that stress-tests a data-communication network and components thereof. NetStress comprises two components running, respectively, in a transmitting system and a receiving system connected to a network under test. The novelty of the program is that is has the capability to generate/receive varied network loading traffic profiles, which prior known programs were incapable of producing (i.e., various packet sizes and various packet rates all combined to make a pseudo-random traffic pattern). The transmitting-system component generates increasingly stressful data traffic for transmission via the network. The receiving- system component analyzes the resulting traffic arriving in the receiving system, generating such statistics as the number of data packets successfully received, the number of dropped packets, and the number of packets received out of order. The packet sizes must be configured before the transmitting-system component is started, but the packet frequencies, numbers of packets in bursts, and burst times can be configured during execution. Typically, a test begins with transmission of data at low sustained rates. Then the sustained rates are increased and burst rates are modified while monitoring to determine whether the receiving-system component reports any losses. When significant losses are reported, the user seeks to determine whether a malfunction or deficiency has been found or normal network saturation has been attained. NetStress was written for execution in the VxWorks real-time operating system, but could easily be ported to other operating systems.

Posted in: Briefs, Software

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Sizing Structures and Predicting Weight of a Spacecraft

EZDESIT is a computer program for choosing the sizes of structural components and predicting the weight of a spacecraft, aircraft, or other vehicle. In designing a vehicle, EZDESIT is used in conjunction with a finite-element structural- analysis program: Each structural component is sized within EZDESIT to withstand the loads expected to be encountered during operation, then the weights of all the structural finite elements are added to obtain the structural weight of the vehicle. The sizing of the structural components elements also alters the stiffness properties of the finite-element model. The finite-element analysis and structural component sizing are iterated until the weight of the vehicle converges to a prescribed iterative difference. The results of the sizing can be reviewed in two ways: 1. An interactive session of the EZDESIT program enables review of the results in a table that shows component types, component weights, and failure modes; and 2. The results are read into a finite-element preprocessing-and-postprocessing program and displayed on a graphical representation of the model.

Posted in: Briefs, TSP, Software

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Interferometer for Low Uncertainty Vector Metrology

Accuracy is increased; time and cost are reduced. The figure is a simplified schematic diagram of a tilt-sensing unequal-path interferometer set up to measure the orientation of the normal vector of one surface of a cube mounted on a structure under test. This interferometer has been named a “theoferometer” to express both its interferometric nature and the intention to use it instead of an autocollimating theodolite.

Posted in: Briefs, TSP, Test & Measurement

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Rayleigh Scattering for Measuring Flow in a Nozzle Testing Facility

The facility can test nozzles up to 8.75-in. (22.2-cm) in diameter. A molecular Rayleigh scattering based air density measurement system was built in a large nozzle and engine component test facility for surveying supersonic plumes from jet-engine exhaust. The facility (see Figure 1) can test nozzles up to 8.75 in. (22.2-cm) in diameter. It is enclosed in a 7.5-ft (2.3- m) diameter tank where ambient pressure is adjusted to simulate engine operation up to an altitude of 48,000 ft (14,630 m). The measurement technique depends on the light scattering by gas molecules present in the air; no artificial seeding is required. Commercially available particle-based techniques, such as laser Doppler velocimetry and particle image velocimetry, were avoided for such reasons as requirement of extremely large volume of seed particles; undesirable coating of every flow passages, model, and test windows with seed particles; and measurement errors from seed particles not following the flow. The molecular Rayleigh-scattering-based technique avoids all of these problems; however, a different set of obstacles associated with cleaning of dust particles, avoidance of stray light, and protection of the optical components from the facility vibration need to be addressed

Posted in: Briefs, TSP, Test & Measurement

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Improved Gear Shapes for Face Worm Gear Drives

These shapes offer potential for increasing precision and reducing vibration and noise. Shapes different from the traditional ones have been proposed for face worm gears and for conical and cylindrical worms that mesh with them. The proposed shapes are based on the concept of generating a face worm gear surface by use of a tilted head cutter instead of by the traditional use of a hob. (As used here, “head cutter” is also meant to signify, alternatively, a head grinding tool.)The gear-surface-generation equipment would be similar to that used for generation of spiral bevel and hypoid gears. In comparison with the corresponding traditional hob, a tilted head cutter according to the proposal would be larger, could be fabricated with greater precision, and would enable the generation of gear surfaces with greater precision and greater productivity.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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Lightweight Electronic Camera for Research on Clouds

This camera would rapidly acquire image data on aerosol particles. “Micro-CPI” (wherein “CPI” signifies “cloud-particle imager”) is the name of a small, lightweight electronic camera that has been proposed for use in research on clouds. The Micro-CPI would be incorporated into a small autonomous or remotely piloted airplane of a type that is now used in meteorological research and that is capable of remaining aloft for times long enough (typically about 30 hours) to collect statistically significant sets of data.

Posted in: Briefs, Electronics & Computers

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Optical Profilometers Using Adaptive Signal Processing

Sizes would be reduced, leading to development of hand-held profilometers. A method of adaptive signal processing has been proposed as the basis of a new generation of interferometric optical profilometers for measuring surfaces. Many current optical surface-measuring profilometers utilize white-light-interferometry and, because of optical and mechanical components essential to their operation, are comparable in size to desktop computers. In contrast, the proposed profilometers would be portable, hand-held units. Sizes could be thus reduced because the adaptive-signal-processing method would make it possible to substitute lower-power coherent light sources (e.g., laser diodes) for white light sources and would eliminate the need for most of the optical components of current white-light profilometers. Furthermore, whereas the height scanning ranges of current surface-measuring profilometers are of the order of millimeters, the adaptive-signal-processing method would make it possible to attain scanning ranges of the order of decimeters in the proposed profilometers.

Posted in: Briefs, Electronics & Computers

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