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(2006)Conference PaperRecent localization systems do not effectively estimate the location of a target in the presence of dynamic obstacles. This paper presents nonline- of-sight (NLOS) localization technique and system for a quiet and known environment based on the measured time-of-arrival (ToA) of first arrival low-frequency acoustic signals. The true ToA is estimated using the modelled map, and then compared with the detected ToA to update the target position. The strength of the proposed technique is that the positioning accuracy is not corrupted by small or known obstacles. The performance of the system was investigated using different techniques and experimental setups. The numerical results show successful localization of a target in various situations, demonstrating the effectiveness of the technique and the system as a possible solution to the NLOS localization problem.
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(2006)Conference PaperThere are few numerical methods available for the prediction of resistance of hullforms with fine entrances and broad, flat sterns, typical of tugs, trawlers and offshore supply vessels. The field narrows even further for those hullforms having high displacement/length ratios. Ridgeley-Nevitt’s trawler series data caters for high displacement-length ratios up to 500, but the residuary resistance data are only available in the form of two-dimensional contour plots at each speed/length ratio, and determination is time consuming. Data were therefore lifted from each of the contour plots and regression analyses completed, resulting in polynomial expressions for the residuary resistance at each of the speed/length ratios. The expressions are in terms of the prismatic coefficient and displacement/length ratio, giving good results compared to the contour plots and providing fast evaluation of the residuary resistance component.
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(2006)Conference PaperTwo very different styles of practicals have been introduced into a conventional engineering vibrations course. This was a reintroduction of practical work into a class where it had been deleted for resource reasons. The first of the reinstated practicals demonstrated rotating out of balance and with it the use of common instrumentation such as FFT analysers. It was a conventional style of practical. The second demonstrated modal frequencies and mode-shapes for a multiple degree of freedom system using innovative simple experimental equipment that required extensive hands-on activities from the students. In this second practical the students explored the phenomena for themselves. Surveys of students revealed that they saw value in both styles of activity. Further, they would not as a group have preferred more lecture or tutorial time instead, or even private study time. This paper describes the aims of including experiments again in the course, how the experiments were constructed, and how the practical periods were organised. It also explains how the activities were assessed and gives full details of the student reactions.
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(2006)Journal ArticleTwo kinds of Al2O3/Ti(C0.7N0.3) nanocomposites were fabricated with traditional hot pressed sintering and repetitious-hot-pressing technology, one is added with nano-scale SiC, and the other is without SiC. The results showed that the mechanical properties of the former are higher than that of the latter, especially the fracture toughness can reach up to 8.3 MPa m1/2. Although the fracture toughness remains high, repetitious-hot-pressing results in the reduction of flexural strength. The improvement of the mechanical properties is interpreted from the different microstructure and fracture mode. The microstructure shows that the addition of nano-scale Ti(C0.7N0.3) and nano-scale SiC lead to the refinement of matrix grain, and the inter/intragranular microstructure can be formed instead of the intergranular microstructure in monolithic alumina. The higher fracture toughness resulted mainly from the transgranular fracture mode.
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(2006)Journal Article20 wt% TiN/3Y-TZP mixed with an amount of less than 15 wt% Al2O3 particles has been fabricated by hot-pressing techniques, and the mechanical properties and microstructure were investigated. There is a good chemical compatibility among ZrO2, TiN and Al2O3 and the addition of 5 wt% Al2O3 can improve the densification of composites. Al2O3 particles have little effect on improving flexural strength but have a distinct effect on toughening for 20 wt% TiN/3Y-TZP, which may be due to the residual stresses and microcracks resulting from the mismatch between the expansion coefficients of Al2O3 and ZrO2. An amount of 5 wt% Al2O3 in 20 wt% TiN/3Y-TZP can improve the bonding strength among grains and change the fracture pattern from intergranular to transgranular fracture.
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(2006)Journal ArticleReal-time parametric interpolation has played a key role in the computer control of machine tools. To achieve highest quality parts, generated trajectories not only describe the desired toolpath accurately, but also have smooth dynamics profiles. This paper presents a novel parametric interpolator based on guide curve. The relationships between geometric properties and kinematic properties are firstly discussed. Then, with a consideration of the important effect of the curvature of curvilinear path on the machining dynamics, a corresponding formula, which describes the relation of the maximum allowed feed acceleration/deceleration and the maximum allowed rate of change of curvature radius of paths, is built. Thus, based on a near arc parameterization and through modifying the curvature radius curve to deal with corners, key regions and other cases, adaptive feedrate schedule is completed according to the reconstructed smooth curvature radius curve. Consequently, confined chord errors, corners on the path and the acceleration/deceleration capabilities of the machine tool are simultaneously considered and incorporated into the guide curve based parametric interpolation system without using look-ahead scheme. Simulation results indicate the feasibility and precision of the proposed interpolation method.
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(2006)Journal ArticleAn experimental investigation of abrasive waterjet (AWJ) cutting of alumina ceramics with controlled nozzle oscillation is presented and discussed. Particular attention is paid to the effect of small oscillation angles on the various cutting performance measures. It is found that nozzle oscillation at small angles can equally improve the major cutting performance measures if the cutting parameters are correctly selected. However, under high water pressures, high nozzle traverse speeds and large oscillation frequencies, nozzle oscillation may cause a decrease in some major cutting performance measures such as surface finish. Plausible trends of cutting performance with respect to the process parameters are amply discussed. Finally, a predictive mathematical model for the depth of cut is developed and verified.
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