Multi-robot hunting in dynamic environments

This paper is concerned with multi-robot hunting in dynamic environments. A BCSLA approach is proposed to allow mobile robots to capture an intelligent evader. During the process of hunting, four states including dispersion-random-search, surrounding, catch and prediction are employed. In order to ensure each robot appropriate movement in each state, a series of strategies are developed in this paper. The dispersion-search strategy enables the robots to find the evader effectively. The leader-adjusting strategy aims to improve the hunting robots&rsquo; response to environmental changes and the outflank strategy is proposed for the hunting robots to force the evader to enter a besieging circle. The catch strategy is designed for shrinking the besieging circle to catch the evader. The predict strategy allows the robots to predict the evader&rsquo;s position when they lose the tracking information about the evader. A novel collision-free motion strategy is also presented in this paper, which is called the direction-optimization strategy. To test the effect of cooperative hunting, the target to be captured owns a safety-motion strategy, which helps it to escape being captured. The computer simulations support the rationality of the approach.<br /

Crystallographic Disorder and Strong Magnetic Anisotropy in Dy3.1Pt2.0Sb3.8

We report the crystal growth and characterization of a rare-earth-containing ternary material, Dy3.1(3)Pt2.0(7)Sb3.8(4). This compound possesses a similar structure to the previously reported Y3Pt4Ge6, but lacks two layers of Pt atoms. Crystallographic disorder was found in Dy3.1Pt2.0Sb3.8. Additionally, the Dy-Dy framework was found to have both square net and triangular lattices. Dy3.1Pt2.0Sb3.8 was determined to be antiferromagnetically ordered around ~15 K while a competing antiferromagnetic sublattice also exists at lower temperature. Strong magnetic anisotropy was observed and several metamagnetic transitions were seen in the hysteresis loops. Furthermore, the Curie-Weiss fitting revealed unusually small effective moment of Dy, which is far below the expected value of Dy2+ (10.6 muB), Dy3+ (10.65 muB) and Dy4+ (9.72 muB). This novel material might provide a new platform to study the relation between crystallographic disorder and magnetism.Comment: 26 pages, 8 figure

Selected papers from the 17th IAHR (International Association for Hydro-Environment Engineering and Research) International Conference on Cooling Tower and Heat Exchanger

The special issue of Heat Transfer Engineering published selected papers from the 17th International Association for Hydro-Environment Engineering and Research (IAHR) International Conference on Cooling Tower and Heat Exchanger, held in Gold Coast, Australia from September 7–11, 2015. The authors were invited to revise/upgrade their manuscripts and resubmit them according to the reviewers’ comments and the journal requirements. The special issue started with a paper on heat exchanger performance by Dai and others from Xi’an Jiaotong University, China. The authors reported the results of a thermoeconomic comparison of a basic organic Rankine cycle (ORC) with a parallel double-evaporator organic Rankine cycle

Dragline Field Testing

Draglines are the most expensive pieces of equipment used in coal mines at a cost of $50 M to$100M each. Improving their productivity will produce major benefits to the coal mining industry. The dynamic behaviour of the dragline structure has a significant effect on the fatigue life of the main components of a dragline and related maintenance costs. This paper describes the field tests conducted on the dragline DRE23 at the Peak Down coal mine, Queensland, Australia. Sixteen accelerometers were installed on the dragline boom and mast. Three different excitation methods were used in the test: 5.4-kg impact hammer, dragline bucket impulse and ambient excitations produced during normal operation. The aim of the modal testing was set to explore the six global modes for the dragline boom structure. The results showed that the impact hammer excitation was not adequate to excite any of the global modes. The excitation produced by bucket impulse was powerful but was difficult to control. The output-only identification using the response to the ambient excitation was promising but it was difficult to identify all targeted global modes

Experimental study of cold inflow effect on a small natural draft dry cooling tower

The heat rejection rate of natural draft dry cooling tower, as well as the operating performance of a power plant, can be affected by numerous ambient factors. The cold inflow is an unfavourable air turbulence at the top of the cooling tower and has a significant negative effect on the performance of natural draft cooling towers. In the present research, results are given for a 20 m high natural draft dry cooling tower experimental system tested at different ambient conditions. Several events of cold air incursion into the top of the cooling tower are identified and the detailed experimental data are presented. The experimental data show that this effect could seriously impair the thermal performance of the cooling tower. The water outlet temperature of the cooling tower has increased by as much as to 3 °C in these tests because of the cold inflow effect. The mechanism and the solution are discussed based on the experimental data. The findings in this paper can lay an important foundation for future small natural draft cooling tower design and operation

An investigation on cooling performance of air-cooled heat exchangers used in coal seam gas production

This paper reports an investigation into a practical cooling issue on a type of fan-forced finned-tube heat exchangers used in Queensland's coal seam gas (CSG) industry. CSG compression facilities in some production sites suffered underproduction in recent summers because of frequent automatic engine shutdowns. The problem is not expected by the manufacturer's design. However, it is suspected of being related to the control systems on the compression facilities triggering the overheating-protection shutdowns due to possible deficiencies in one or some water/gas cooling loops in the facilities’ air-cooled heat exchangers. Therefore, to understand which heat exchangers and what exact reasons cause the unexpected cooling issue, an investigation has been carried out on the cooler units of the gas compression facilities. A field instrumentation measurement on one operating cooler unit has been done, followed by an analysis using a one-dimensional analytical model and a three-dimensional computational fluid dynamics model. The experimental results are used to validate both the models. Then the cooling performance of the cooler unit under the summer peak condition is predicted by the verified models. The prediction suggests that the water inlet temperature in one particular cooler section is higher than its upper limit defined by the manufacturer, due to poor cooling at high ambient temperatures. The lower cooling performance is caused by large reductions in the cooler air speed and total heat transfer coefficient, which are related to less efficiency of the cooler fans, more airflow resistance, and fouling on both sides of the finned tubes

Precision Measurement of M1 Optical Clock Transition in Ni12+

Highly charged ions (HCIs) have drawn significant interest in quantum metrology and in search for new physics. Among these, Ni12+ is considered as one of the most promising candidates for the next generation of HCI optical clocks, due to its two E1-forbidden transitions M1 and E2, which occur in the visible spectral range. In this work, we used the Shanghai-Wuhan Electron Beam Ion Trap to perform a high-precision measurement of the M1 transition wavelength. Our approach involved an improved calibration scheme for the spectra, utilizing auxiliary Ar+ lines for calibration and correction. Our final measured result of the M1 transition wavelength demonstrates a five-fold improvement in accuracy compared to our previous findings, reaching the sub-picometer level accuracy. In combination with our rigorous atomic-structure calculations to capture the electron correlations and relativistic effects, the quantum electrodynamic (QED) corrections were extracted. Moreover, comparing with an estimate of the one-electron QED contributions by using the GRASP2018 package, we found that the present experimental accuracy is high enough for testing the higher-order QED corrections for such a complex system with four electrons in the p subshell.Comment: 15 pages, 5 figure

Simulation of the UQ Gatton natural draft dry cooling tower

Natural draft dry cooling tower (NDDCT) is an effective cooling technology which can be utilized in most of geothermal and concentrated solar thermal (CST) power plants. The experimental studies of the full scale cooling tower, especially the small size NDDCTs, are still not extensive. To fill this gap, Queensland Geothermal Energy Centre of Excellence (QGECE) at The University of Queensland has built a 20m high NDDCT. In this paper, the 1D analytical model and the 3D CFD model of this cooling tower were developed and its cooling performance was investigated at different ambient temperatures, hot water temperatures and velocities of cross wind. The result shows that the small size NDDCT is suitable for 2~3MW CST power plants. The cooling performance decreases with the increase in the ambient temperature and the decrease in the hot water temperature. In terms of the cross wind, the heat rejection ratio decreases with the increase of the cross wind velocity when cross wind velocity is low. However, when velocities of the cross wind become large enough, the heat dumped at the bottom of the tower can compensate some loss caused by cross wind. The results found in the present paper give reference for planed future experiments

Influence of ambient conditions and water flow on the performance of pre-cooled natural draft dry cooling towers

A simplified heat and mass transfer model in cellulose medium was developed to predict the air outlet temperature and humidity after evaporative cooling. The model was used to simulate the operation of pre-cooled Natural Draft Dry Cooling Towers (NDDCTs) by a validated MATLAB code. The effects of supplied water flow rate to the media, ambient temperature and humidity on the performance of pre-cooled NDDCTs were investigated. It was found that the effect of the selected water flow rates on tower performance is negligible. Both ambient temperature and humidity affect the tower performance