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1.
Conical picks are the essential cutting tools used especially on roadheaders, continuous miners and shearers and their cutting performance affects directly the efficiency and the cost of rock/mineral excavation. In this study, in order to better understand the effects of dominant rock properties on cutter performance, 22 different rock specimens having compressive strength values varying from 10 to 170 MPa are first subjected to a wide range of mechanical tests. Then, laboratory full-scale linear cutting tests with different depth of cut and cutter spacing values are realized on large blocks of rock specimens using one type of conical pick. Specific energy, cutting and normal force values for relieved and unrelieved cutting modes are recorded using a triaxial force dynamometer with capacity of 50 tonnes and a data acquisition system. Cutter force and specific energy values are correlated with rock properties and theoretical force and specific energy values obtained from widely used theoretical approaches.The results indicate that uniaxial compressive strength among the rock properties investigated is best correlated with the measured cutter performance values, which is in good agreement with previous studies. However, it is also emphasized in this study that Brazilian tensile strength, Schmidt hammer rebound values, static and dynamic elasticity modulus are also dominant rock properties affecting cutter performance.Theoretical specific energy defined by different researchers has a meaningful relationship with the experimental specific energy, which is an essential parameter for predicting the instantaneous cutting rates of mechanical excavation systems. It is also demonstrated that the experimental cutter forces obtained for 5 mm depth of cut are in good agreement with theoretical force values, if the friction angle between rock and cutting tool is included in the theoretical formulation. It is emphasized that, to some extend, laboratory tests can help to minimize high cost of a trial–error approach in the field.  相似文献   
2.
Flame front surface area and enflamed volume (the volume enclosed with flame front) is theoretically analysed for a spark‐ignition engine, having cylindrical disc‐shaped combustion chamber with two spark plugs located axisymmetrically on cylinder head, between cylinder axis and cylinder wall. Spherical flame front assumption is used. A computer code is developed based on purely geometric consideration of the flame development process in combustion chamber, and is used to investigate the effects of variations of spark plugs' locations on geometric features of the flame front. A comparison has also been made with a spark‐ignition engine having one spark plug at the same location. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
3.
Two types of conventional kiln-drying schedules (mild and harsh) based on moisture content (MC) were compared with regard to time, drying quality, and energy cost. The results were evaluated according to the classification of the European Drying Group. Proper drying periods of mild and harsh schedules were found to be 550 and 514 h, respectively. Evaluations in terms of drying quality indicated that better results were achieved with the mild schedule, especially when comparing drying defects and final MC. From an energy efficiency point of view, the harsh schedule, by saving 36 h of drying time, reduced electricity by 594 KWh and was therefore found to be $65 more profitable in this trial.  相似文献   
4.
Many researchers studying examination timetabling problems focus on either benchmark problems or problems from practice encountered in their institutions. Hyperheuristics are proposed as generic optimisation methods which explore the search space of heuristics rather than direct solutions. In the present study, the performance of tournament-based hyperheuristics for the exam timetabling problem are investigated. The target instances include both the Toronto and ITC 2007 benchmarks and the examination timetabling problem at KAHO Sint-Lieven (Ghent, Belgium). The Toronto and ITC 2007 benchmarks are post-enrolment-based examination timetabling problems, whereas the KAHO Sint-Lieven case is a curriculum-based examination timetabling problem. We drastically improve the previous (manually created) solution for the KAHO Sint-Lieven problem by generating a timetable that satisfies all the hard and soft constraints. We also make improvements on the best known results in the examination timetabling literature for seven out of thirteen instances for the To ronto benchmarks. The results are competitive with those of the finalists of the examination timetabling track of the International Timetabling Competition.  相似文献   
5.
Bulletin of Engineering Geology and the Environment - The new Istanbul Airport is being constructed over an old coal field area, 35 km away from the city center. The construction of a rail link...  相似文献   
6.
In the present work, six new kinds of building composite PCMs (BCPCMs), PS/octadecane, BC/octadecane, PS/CA–MA, BC/CA–MA, PS/PEG1000, and BC/PEG1000 composites, were prepared by using vacuum impregnation method. The maximum percent of PCM in the composites was assigned to be 12, 13, 18, 23, 30, and 42 wt%, respectively. The form‐stable BCPCMs were characterized using SEM, FT‐IR, DSC, and TG analysis techniques. The characterization results showed the existence of homogenous dispersion of the PCM into the PBM matrixes. The DSC measurements indicated that the melting temperatures of the form‐stable BCPCMs are in the range of 20–33°C while they have latent heats of melting in the range of about 28–55 J/g. These results make them promising BCPCMs for low temperature‐passive TES applications in buildings. Thermal cycling test indicated that the prepared BCPCMs have good thermal reliability and chemical stability. TG analysis proved that the prepared BCPCMs have good thermal durability. In addition, the thermal conductivity of BCPCMs was enhanced considerably by addition of expanded graphite (EG). The improvement in thermal conductivity of the BCPCMs caused appreciably reduction in their melting times. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
7.
An ion chromatographic method for the quantitative determination of free cyanide in bottled natural mineral waters were measured in terms of selectivity, linearity, the limit of detection, limit of quantification, repeatability, precision, and accuracy. Chromatographic separation of free cyanide ions was accomplished with an anion-exchange column and detected by pulsed amperometric detection with a silver working electrode. The method was found to be selective, linear (r2 = 0.999) at a concentration range of 0.5 to 134 μg L?1, precise, and accurate. Recovery values of free cyanide in all classes of natural mineral water varied from 65.9 ± 1.6 to 95.2 ± 0.7 at different spiking levels (5–70 μg L?1). Parameters (total dissolved solids, mineral interferences, and added sodium hydroxide) affecting the recovery values were studied in this project. The limit of detection and limit of quantification were found to be 0.295 and 0.983 μg L?1, respectively. The proposed method was applied to 27 different brands of commercially available bottled natural mineral water products sold in Turkish markets. These natural mineral waters were classified as: (i) very low mineral concentration, (ii) low mineral concentration, (iii) intermediate mineral concentration, and (iv) high mineral concentration based on their total dissolved solids contents according to European Union Directive (Directive 80/777/EEC). Levels of free cyanide residues in the samples ranged from > limit of detection to 6.12 μg L?1. The highest average concentration of free cyanide residues was found in the class of “high mineral concentration waters.” However, the determined free cyanide values in all of the tested natural mineral water samples were found to be within the limits of European Union legislation.  相似文献   
8.
Current design practice of reinforced soil retaining walls is based on the limit equilibrium approach. The walls are designed for both external and internal stability criteria. Design reinforcement length should be such that minimum required safety factors are fulfilled for all failure modes. Most agencies require minimum reinforcement length equal to 70 percent of wall height. However, it is not always possible to have enough space behind a wall to accommodate these required reinforcement lengths due to an existing natural rock formation, man-made shoring system, or the presence of another reinforced soil retaining wall. This study was performed to investigate governing failure mode in determining the required minimum reinforcement length and also to investigate the possibility of shortening the specified minimum reinforcement lengths. Effect of different parameters involved in the design of reinforced soil retaining walls on the required minimum reinforcement length and the governing failure mode were studied. Parameters considered included wall height, surcharge, reinforcement vertical spacing, reinforced soil properties, backfill/retained soil properties, and foundation soil properties. Results indicated that both external and internal failure modes can be governing criteria in determining the required minimum reinforcement length depending on the parameters involved for a specific wall. In addition, it may be possible to use reinforcement lengths as low as almost 50 percent of the wall height, instead of 70 percent as required by many agencies around the world. This paper presents the results of parametric studies conducted, including the effect of different parameters on the required minimum reinforcement length and the governing failure criteria.  相似文献   
9.
Polyethylene pipes are commonly used in pipeline systems. Current methods used to determine the pipe pullout capacity do not consider the effects of diameter changes and cyclic movements that the pipelines may experience. Laboratory tests were performed to study the interface shearing resistance of polyethylene pipes under varying conditions. The tests were performed in a temperature-controlled room, where properties were investigated for thermal variations expected in the field. Two types of tests were performed: pull/push tests and cyclic tests. Test results indicated that reductions in pipe diameter affect the interface shear resistance that develops between the pipe and soil. As the pipe diameter gets smaller, the normal contact stresses at the interface decreases, causing a reduction in the interface shearing resistance directly proportional to the normal stress changes. Cyclic pipe movements also cause significant reduction in pipe pullout resistance. The test results indicated that the polyethylene pipe interface shear resistance can be significantly lower than the one determined using the current methods. This paper presents the test results, findings, and design recommendations for the pullout resistance of buried polyethylene pipes.  相似文献   
10.
Remote visualization of volumetric images has gained importance over the past few years in medical and industrial applications. Volume visualization is a computationally intensive process, often requiring hardware acceleration to achieve a real time viewing experience. One remote visualization model that can accomplish this would transmit rendered images from a server, based on viewpoint requests from a client. For constrained server-client bandwidth, an efficient compression scheme is vital for transmitting high quality rendered images. In this paper, we present a new view compensation scheme that utilizes the geometric relationship between viewpoints to exploit the correlation between successive rendered images. The proposed method obviates motion estimation between rendered images, enabling significant reduction to the complexity of a compressor. Additionally, the view compensation scheme, in conjuction with JPEG2000 performs better than AVC, the state of the art video compression standard.  相似文献   
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