1,721,400 research outputs found
A hexagonal percolation model for zone-dependent pore interlinkage fraction and its application to the prediction of fission gas release
No full textA percolation model is proposed to determine the interlinkage fraction of intergranular pores in the restructured and cracked fuel. A fuel rod is simulated as a large hexagon which consists of many small hexagonal grains. The fuel rod is divided into four zones of which boundaries are determined depending on their morphological and thermal properties. Grain size grown during irradiation is calculated using the FASTGRASS code and is used to calculate the number of hexagonal rings in zones. It is assumed that there is a circumferential crack at each zone boundary and radial cracks dividing zones radially. The algorithm for calculation of the pore interlinkage fraction (PIF) includes several steps; checking the site-occupancy, labeling the occupied sites, checking the site's connectivity to the nearest occupied sites, and counting the number of sites in the cluster connected to the free space. The Monte Carlo method is used for checking site-occupancy and the Hoshen-Kopelman method is applied to labeling. The site occupation probability is assumed to be the ratio of the current swelling to the maximum fractional swelling of pores in the grain edge, which is approximately 8.7%. The proposed model provides zone-dependent PIFs as a function of the site occupation probability. Comparisons of the calculated results with experimental data including the AECL-2230,CBX fuel rod of fractional gas release are done by replacing the PIF function in the FASTGRASS code with the calculated zone-dependent PIFs. Restructuring with cracks is found to affect fission gas release significantly. The calculated fission gas release as a function of linear heat rate shows better fitting to the experimental data than the simple model in the FASTGRASS code. The fission gas release is also sensitive to the maximum fractional volume swelling. The main advantage of this model is to treat the interlinkage phenomena in the grain boundaries more realistically than the single PIF correlation and to take into account of grain growth and cracks parametrically. Copyright (C) 1996 Elsevier Science Ltd
An optimum 2.5D contour parallel tool path
No full textAlthough conventional contour parallel tool paths obtained from geometric information have successfully been used to produce desired shapes, they seldom consider physical process concerns such as cutting forces and chatter. In this paper we introduce an optimized contour parallel path that maintains a constant material removal rate at all times. The optimized tool path is based on a conventional contour parallel tool path. Additional tool path segments are appended to the basic path to achieve constant cutting forces and to avoid chatter vibrations over the entire machining area. The algorithm was implemented for two-dimensional contiguous end milling operations with flat end mills, and cutting tests were conducted to verify the performance of the proposed method
PREPARATION OF OXYGEN-ENRICHED AIR BY THE SELECTIVE ADSORPTION WITH PLATINUM CRYSTALLITES SUPPORTED ON GAMMA-ALUMINA
No full textDevelopment of a back propagation network for one-step transient DNBR calculations
No full textOne of the key safety parameters during the transient of pressurized water reactor is the departure from nucleate boiling ratio (DNBR). In the transient analysis caused by the anticipated operational occurrences or accidents, the DNBR is predicted by three steps: firstly, a system transient analysis code, secondly, a heat flux calculation code and finally a detailed DNBR calculation code should be used. This tandem procedure is time consuming and very cumbersome. In this paper, the back propagation network (BPN) algorithm is incorporated into the system transient analysis code for the one-step transient DNBR calculation, thus, to eliminate the tandem procedure and to increase calculation speed. The BPN is trained with the DNBR training data selected by latin hypercube sampling technique. After the completion of training, performance is evaluated. Results show that the system transient analysis code with a multi-layer BPN algorithm can quickly calculate the transient DNBR with the reasonable accuracy even in case of axial flux shape changes. (C) 1997 Elsevier Science Ltd
A DESIGN OF PIPELINED ARCHITECTURE FOR HIERARCHICAL BLOCK-MATCHING ALGORITHM
No full textMotion estimation is a major part of the video coding, which traces the motion of moving objects in video sequences. Among various motion estimation algorithms, the Hierarchical Block-Matching Algorithm (HBMA) that is a multilayered motion estimation algorithm is attractive in motion-compensated interpolation when accurate motion estimation is required. However, parallel processing of HBMA is necessary since the high computational complexity of HBMA prevents it from operating in real-time. Further, the repeated updates of vectors naturally lead to pipelined processing. In this paper, we present a pipelined architecture for HBMA. We investigate the data dependency of HBMA and the requirements of the pipeline to operate synchronously. Each pipeline stage of the proposed architecture consists of a systolic array for the block-matching algorithm, a bilinear interpolator, and a latch mechanism. The latch mechanism mainly resolves the data dependency and arranges the data flow in a synchronous way. The proposed architecture achieves nearly linear speedup without additional hardware cost over a non-pipelined one. It requires the clock of 2.70 ns to process a large size of frame (e.q. HDTV) in real-time, which is about to be available under the current VLSI technology
Multiplexed Fiber Optic Temperature Monitoring Sensor Using Hard-Polymer-Clad Fiber and An Optical Time-Domain Reflectometer
No full textShape design of channel flows for steady, incompressible flows
No full textA shape design problem for stationary, viscous, incompressible, two-dimensional channel flows is considered. The shape of part of the boundary is determined so that the viscous drag is minimized. The adjoint equation method is used to derive an optimality system and the shape gradient of the design functional
An independent assessment of Groeneveld et al.s 1995 CHF look-up table
No full textThe prediction capability of the 1995 CHF look-up table (Groeneveld D.C., et al., Nucl. Eng. Des. 163 (1996) 1-23) is independently assessed based on the KAIST data base consisting of 10 822 data for uniformly-heated, vertical, round tubes. This confirms the error statistics for the heat balance method reported by Groeneveld et al. and shows overall average and RMS errors of 4.2 and 36.7%, respectively, for the direct substitution method. The new 1995 table shows better prediction capability than the 1986 AECL-UO table (Groeneveld et al., 1986), especially for the low-pressure, low-flow region. The error analysis indicates the length effect even for significantly long tubes. (C) 1997 Elsevier Science S.A
Development of a rapid heat ablation (RHA) process using a hot tool
No full textRapid prototyping and manufacturing (RPM) technologies have played a crucial role in reducing the lead-time and development costs of new products since its birth in the late 1980s. As compared with laminating processes for RPM, the machining process has been more commonly used because it offers such practical advantages as precision and versatility. However, the traditional machining process requires a large amount of time for product cutting and the remaining material causes problem as inconvenience due to cleaning process. The objective of this paper is to propose a new rapid manufacturing process using a hot tool with tangential grooves, rapid heat ablation process (RHA), to overcome the limitations of traditional machining processes. In order to investigate the material removal zone according to process parameters, several experiments were carried out. From the results of experiments, the relationships between the radius of the material removal zone and the process parameters were obtained. Furthermore, the depth of cut was compared with the kerfwidth in order to verify the isotropy of the material removal zone. As a result, a method of toolpath generation for ball-end mill commercially used can be adopted into the RHA process because the geometry of material removal zone is equal to that of the ball-end mill. The practical applicability of the RHA process is then demonstrated by the results of these fabrications for a hemispherical shape and a standard test part for machining in terms of geometrical conformity, volume of remaining material, ablating time and dimensional accuracy. (C) 2006 Elsevier Ltd. All rights reserved
Toolpath planning algorithm for the ablation process using energy sources
No full textAblation processes using various energy sources such as lasers, electrical power and ultrasonic sources have been widely used in industry to ablate workpieces made of hard-to-cut and temperature resistive materials. Even though the cutting mechanism of the ablation process is different from that of the mechanical cutting process, an identical toolpath of the mechanical cutting process has been applied to the ablation process. An inappropriate toolpath for the ablation process may result in a lower dimensional accuracy of the ablated part. Therefore, a new toolpath planning algorithm considering the characteristics of the energy source is required. In this paper, a toolpath planning algorithm for the ablation process is proposed. The proposed algorithm consists of three steps: (1) The generation of a valid toolpath element, (2) the storage of toolpath elements and the creation of sub-groups, (3) the linking of sub-groups. New guidelines on the toolpath demanded by the ablation process are studied. A new idea involving the use of a storage matrix is applied to the storage of toolpath elements and the creation of sub-groups. In order to verify the applicability of the proposed algorithm, the proposed toolpath planning algorithm has been implemented and tested with practical examples. (C) 2009 Elsevier Ltd. All rights reserved
- …
