MEASUREMENT AND ANALYSIS OF SEA WAVES NEAR A REFLECTIVE STRUCTURE

Merged with duplicate record 10026.1/2047 on 06.20.2017 by CS (TIS)Methods and equipment for the measurement of ocean waves were reviewed and their suitability assessed for the aim of this project: field measurement of sea waves near a reflective coastal structure such as a breakwater. None was found to be suitable. The functional and performance objectives are set out for a new system. The evolution of the final design, based on an array of pressure sensors, is described. The whole system is intended to be deployed on the sea-bed. It is fully self contained and independent of shore based services. Located away from the surf zone it is well placed to survive storm conditions and unauthorised interference. Theoretical methods for the re-construction of surface elevation records from measured sub-surface pressures, and the experimental findings of other workers, are presented. Available methods of estimating the wave directional spectrum from a spatial array of surface elevation records are reviewed, and the most appropriate one implemented. The system has given extensive service at a number of coastal defence sites. The results of subsequent analysis of selected data sets are presented in detail. They show the pronounced nodal structure in amplitude expected in the presence of wave reflection, clearly demonstrating that a single point measurement is likely to give misleading estimates of incident wave height. For near-calm to moderate, shore-normal incident wave conditions the results were found to agree with theoretical predictions both of wave height as a function of distance offshore, and of the structure's frequency-dependent reflection coefficient. For rougher conditions, in which both theoretical and physical models are less applicable, the results agreed with visual observations

Development of limb volume measuring system

The mechanisms underlying the reductions in orthostatic tolerance associated with weightlessness are not well established. Contradictory results from measurements of leg volume changes suggest that altered venomotor tone and reduced blood flow may not be the only contributors to orthostatic intolerance. It is felt that a more accurate limb volume system which is insensitive to environmental factors will aid in better quantification of the hemodynamics of the leg. Of the varous limb volume techniques presently available, the ultrasonic limb volume system has proven to be the best choice. The system as described herein is free from environmental effects, safe, simple to operate and causes negligible radio frequency interference problems. The segmental ultrasonic ultrasonic plethysmograph is expected to provide a better measurement of limb volume change since it is based on cross-sectional area measurements

Preliminary candidate advanced avionics system for general aviation

An integrated avionics system design was carried out to the level which indicates subsystem function, and the methods of overall system integration. Sufficient detail was included to allow identification of possible system component technologies, and to perform reliability, modularity, maintainability, cost, and risk analysis upon the system design. Retrofit to older aircraft, availability of this system to the single engine two place aircraft, was considered

Planetary explorer liquid propulsion study

An analytical evaluation of several candidate monopropellant hydrazine propulsion system approaches is conducted in order to define the most suitable configuration for the combined velocity and attitude control system for the Planetary Explorer spacecraft. Both orbiter and probe-type missions to the planet Venus are considered. The spacecraft concept is that of a Delta launched spin-stabilized vehicle. Velocity control is obtained through preprogrammed pulse-mode firing of the thrusters in synchronism with the spacecraft spin rate. Configuration selection is found to be strongly influenced by the possible error torques induced by uncertainties in thruster operation and installation. The propulsion systems defined are based on maximum use of existing, qualified components. Ground support equipment requirements are defined and system development testing outlined

Advanced sensors technology survey

This project assesses the state-of-the-art in advanced or 'smart' sensors technology for NASA Life Sciences research applications with an emphasis on those sensors with potential applications on the space station freedom (SSF). The objectives are: (1) to conduct literature reviews on relevant advanced sensor technology; (2) to interview various scientists and engineers in industry, academia, and government who are knowledgeable on this topic; (3) to provide viewpoints and opinions regarding the potential applications of this technology on the SSF; and (4) to provide summary charts of relevant technologies and centers where these technologies are being developed

Development of techniques for detection and dissolution enhancement of mineral deposits in petroleum pipelines using ultrasound.

Scale formation in petroleum pipelines causes progressive flow reductions, leading to large production losses and operating costs. The composition and thickness of the scale deposits vary widely, but with present technology they cannot be accurately quantified or monitored. Remedial treatments such as chemical de-scaling etc. are therefore largely based on guesswork, which can lead to expensive chemical wastage and production shutdowns. This project is intended to address some of the above problems using ultrasonic techniques. Work presented in this thesis branches out into two main areas of interest, namely: (a) developments concerning location of deposits from both top-side and down-hole locations; and (b) developments relating to enhancement of scale removal, using ultrasound. With regard to top-side scale detection, the major challenge in this work was to develop a technique by which acoustic signatures are synthetically generated, which can be used with the techniques previously developed for pipeline inspection. This required the determination of a suitable type of transducer and the study of its radiation characteristics in developing comprehensive mathematical models for artificially generating reference echoes. The model allowed the first three multiple echoes (in steel objects) to be computed for given test parameters. Close agreement of the synthesised echoes with practical measurements was demonstrated with good repeatability. An essential requirement for the detection of deposits in down-hole is the accurate alignment of the test probes with respect to the pipe-wall. In this regard, a novel technique for remote alignment of the transducers was successfully formulated. It is based on identifying symmetrical properties of the signals received from the test probe itself when scanned around the correct angular position with respect to the target. However, through extensive practical measurements, it was found that an important requirement for applying this technique is to know in advance whether a particular combination of probe, target diameter and separation distance would give satisfactory angular resolution. Extensive practical examination of these factors showed that no general conclusion can easily be drawn with respect to this requirement. Therefore a mathematical model was successfully developed, which would predict the suitability of given probe/target parameters. It has been reported in previous studies that ultrasonic irradiation could greatly enhance the chemical dissolution of localised deposits during de-scaling operations. In this regard, a major challenge was to improve the efficiency of power transducers radiating into confined spaces at elevated temperatures. That required the study of radiation characteristics of ultrasonic power transducers and compensation techniques to regain loss of efficiency at elevated temperatures. Alternative types of transducers - based on flexural-horn designs - were also investigated and their relative merits presented. Significant findings related to the performance variations of ultrasonic transducers and transmission cables at elevated temperatures have been made. After examining the transducer efficiency drop with temperature, a closed-loop compensation strategy was proposed for maintaining optimal performance. The matching requirements of the cables transmitting power from top-side to down-hole power transducers were also investigated as part of optimisation of ultrasonic power output. From this study it was found that, within the temperature range of interest, the cable in itself does not require changes to the matching requirements as the environmental temperature fluctuates. However, it was noted that the transducer impedance changes rapidly with temperature and therefore a unified compensation strategy incorporating both cable and transducer impedances was proposed as a better solution. Overall, the main objectives of the project concerning pipeline scale detection were well achieved, namely: (a) modelling of a suitable type of ultrasonic transducer to synthesise the reference multiple echoes to aid top-side scale detection; and (b) development of a remote sensing technique for ultrasonic probe alignment in downhole pipes. With regard to dissolution enhancement, techniques for enhancing power output of ultrasonic transducers to aid dissolution enhancement of scale deposits have been determined. Further work includes the improvements to software algorithms developed and hardware integration to achieve the expected performance of the techniques presented

Portable inshoe gait analysis device

Gait analysers are devices or systems that quantify the planter /' pressures as they occur under the foot. The data obtained, be it. in visual or digital format, assists the medical practitioner in the diagnosis of an abnormality of gait. This thesis describes the development of a low-cost, portable, inshoe gait analysis device which overcomes all the limitations experienced by other systems currently in use. The non-availability of .robust, yet small pressure transducers, required the design and manufacture of these components. Capable of being embedded within an insole environment, it allows for the unobtrusive monitoring of localised planter pressures associated with all modes of gait. The transducer output, being analogy and continuous in nature, allows for the production of a real-time pressure display an important requirement for the therapeutic assessment and treatment of patients. The flexibility and accuracy of this system surpasses that of other systems. Its configuration provides for operation in remote environments, allowing for gait measurements under specific ambulation conditions. Use of a new transducer monitoring technique, in addition to a new video mixing technique, has enabled this device to compete with those systems making use of expensive processing and display equipment. Two prototype gait analysis systems have been built and extensively tested under clinical conditions. The results obtained provide unique, hitherto unavailable data, which can now be used for a more precise classification of gait disorders. It is already clear that the data will provide the basis for more accurate diagnosis and therefore more appropriate treatment of a variety of gait

Magnetic sensors and gradiometers for detection of objects

Disertační práce popisuje vývoj nových detekčních zařízení s anizotropními magnetorezistoryThis thesis describes development of innovative sensor systems based on anisotropi

An Opto-Electronic Stand-Off Sensor for Robotics

This thesis presents an optoelectronic stand-off sensor and actuation system developed for robotic applications. The measuring principle is based on an on-axis method of detecting variation in a beam reflected from a surface. The sensor utilizes two photodiodes to measure the difference in beam power falling through two pinholes, to estimate the distance between the workpiece surface and incident focused beam waist. The output voltage from the differential stage is normalized to negate the effects of surface reflectivity, colour, and texture. Two mathematical models are presented which simulate the device. The first depends only on the theory of propagation of gaussian beams, whilst the second relies upon simulating the reflected beam using geometrical optics to calculate the radiometric distribution at the detecting pinholes. A set of experiments were performed to analyze and optimize the performance of a number of sensor configurations. The experimental results are bounded between gaussian and radiometric model results. A comparison of the results of the three models, conclusions regarding sensor performance and principles for optimally designing such systems are given. A proportional control circuit for one sensor servo combination was designed and tested using a solenoid as an actuator. The predicted performance of the complete servo system was modelled utilizing the ACSL language. While an experimental rig was built and experiments designed to analyze the output of the system in response to a step input. The results of this show that the stand-off system gives varying response to different materials indicating that the electronic method of normalizing the sensor output is insufficient. The results also show that the device is sensitive to controller gain and behaves in a non-linear fashion as predicted. The actual response is generally faster than the predicted response. Conclusions and recommendations for further work and development are given