• Journal of the Korean Society for Railway
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• v.7 no.4
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• pp.312-318
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• 2004

The wall in a subway structure is easily subject to crack occurrence since its expansion and shrinkage associated with hydration heat reaction is constrained by the slab. The greater problem is that the crack in the wall may be developed to pass through thickness and eventually deteriorate the structure due to rusting of reinforced steel. Thus, this study aims at controlling thermal cracks as much as possible and determining an optimized size of concrete placement through hydration heat analysis. For this study, effects of placement height, length, temperature and types of cement on the thermal cracks were evaluated by temperature rise, thermal stress and crack index. As results of parametric study, it was found that placement height and length do not have an effect on the temperature rise but have significant one on thermal stress which relates to direct possibility of thermal crack occurrence. This means that proper selection of size balancing internal constraint with external one is much more important than reducing the placement height and length simply. In order to prevent from thermal cracks most effectively, in addition, it was noted to reduce placement temperature and to use the cement blended with mineral admixture.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.1
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• pp.281-287
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• 1991

This study was designed to investigate the influence of the clasp arm length on the change of retentive force with repeated placement or removal. The author measured the retentive force of Akers clasp and I-bar clasp in the depth of undercut 0.5mm, 0.25mm, respectively, varying the length of clasp arm, that is, 10mm, 14mm, 17mm in Akers clasp and 16mm, 18mm, 20mm in I-bar clasp. The retentive force was measured just before the placement of removal, after 100 times repeated placement or removal, after 300 times repeated placement or removal. The obtained results were as follows : 1. The shorter the clasp arm, the greater retention in Akers clasp and I-bar clasp(p<0.05). 2. There was decreased retentive force of Akers clasp and I-bar clasp after 300 times repeated placement or removal(p.<0.005). 3. The decreasing rate of retentive force in Akers clasp with 10mm was higher than that with 17mm, after 300 times repeated placement or removal, but there was no statistica difference(p>0.05).

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.1205-1210
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• 2004

Cracks in the underground structures are mainly observed due to internal ununiformity of thermal stresses or restraint of structural movement in associate with rapid temperature gradient. Especially, thermal cracks are known to occur easily in a massive structure, but possibility of these depend on the amount of cement applied and ratio of span to height of the structure even though the thickness is less than specification‘s. Thus, this study aims at how to control thermal cracks in a massive subway structure and figures out an optimized construction method and procedure. As results of parametric study for length, height and outer temperature for concrete placement, it is found that hydration heats were not affected by both length and height of concrete placement but thermal stresses were greatly dependent. Most effective ways of controling thermal cracks were to fit a proper ratio of length to height of concrete placement and to decrease temperature of concrete placement as much as possible.

• Journal of the Korean Institute of Telematics and Electronics
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• v.23 no.4
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• pp.557-564
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• 1986

This paper describes a standard cell placement strategy which consists of three kconsecutive steps` initial placement, iterative placement improvement, and string placement. In the initial placement step, cell placement was done by solving the linear ordering problem for a one-dimensional layout of standard cells and then zigzaging the resultant linear order width in the chip plane. The iterative placement improvement step is based on the iterative pairwise interchange using the estimated total routing length as a figure-or -merit. The string placement is used to reorder cells and terminals in each etandard cell row such that channel routing in the adjacent channels is not blocked by cyclic constraints and needs fewer routing tracks. The placement program is coded in PASCAL and kimplemented on a VAX-11/750 computer. Experimental results for several examples are included.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.11
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• pp.128-139
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• 1996

In this paper, we propose an algorithm to solve the problem of placement of rectangular blocks whose sizes and shpaes are pre-determined. The proposed method solves the placement of many retangular blocks of different sizes and shapes in a hierarchical manner, so as to minimize the chip area. The placement problem is divided into several sub-problems: hierarchical partioning, hierarchical area/shape estimation, hierarchical pattern pacement, overlap removal, and module rotation. After the circuit is recursively partitioned to build a hierarchy tree, the necessary wiring area and module shpaes are estimated using the resutls of the partitioning and the pin information before the placement is performed. The placement templaes are defined to represent the relative positions of the modules. The area and the connectivity are optimized separately at each level of hierachy using the placement templates, so the minimization of chip area and wire length can be achieved in a short execution time. Experiments are made on the MCNC building block benchmark circuits and the results are compared with those of other published methods. The proposed technique is shown to produce good figures in tems of execution time and chip area.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.539-545
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• 1997

Since the length of massive wall-structure is generally longer and larger than its thickness and a lift height of concrete of placement, cracks induced by hydration heat are governed by outer structural restriction rather than inner one. However, the degree of restriction control is expected to be affected by the sizes of wall thickness, length and a lift height. Thus, this analytical study aims at the development of relationship among those to minimize thermal cracks. In addition, the effect of types of cement on the thermal heats and stresses is evaluated for anti-sulphate and 2blended Portland cements concrete. It was found from analytical study that a lift height of concrete placement is the most important factor controlling thermal cracks, and the increase of lift heights is not always detrimental to structural safety.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.2
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• pp.104-115
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• 1994

This paper presents the design of a placement sysyem integrated in PCB design system. to get an optimal component positioning from part and net list. Unplaced components are placed in initial process using modified cluster development algorithm and are swapped in improvement process using the GFDR(Generalized Force Directed Relaxation) algorithm. The result is optimized in post process by component rotating or pin/gate swapping. Experimental results shwo that the placement system produces manufacturable layouts which are optimal in terms of total routing length.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.10
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• pp.1598-1605
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• 1989

This paper describes an efficient global cell (module) placement strategy called HALO (Hierarchical Alternating Linear Ordering)which generates global 2-D placement of circuit modules by hierarchical application of linear ordering in alternating direction. We tried, in principle, to explain why HALO should perform better than other typical, somehat successful, analytical approaches such as min-cut, force-directed relaxation(FDR)or its likes. We have implemented HALO as a program for standard cell placement. Experimental results on two benchmark circuits, primary and primary 2 consisting of 752 and 2907 cells, respectively have shown a decrease of half-perimeter routing length by 7% and 24%, respectively compared to the best available results obtained so far. Total CPU time including the following detailed placement was less than half of the earlier work.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.301-304
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• 2003

Nowadays, hydration heat analysis using FEM is common in thermal crack control of concrete structure. Many kinds of general FEM programs for hydration heat analysis are used in practice. But there are some problems in this using. In this study hydration heat analysis of wall according to placement length are performed. In this results we could get two conclusions. First, general structures like wall having general geometry and construction condition have similar behavior. So it is not necessary to analysis thermal crack in every case. Second, the results of 2D analysis is possible to be applied instead of those of 3D analysis because the results of 2D analysis is similar to 3D analysis in long wall having about 15~18m or over length at 3m height.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.7 no.2
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• pp.10-15
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• 2011

A ground loop heat exchanger for the ground source heat pump system is the core equipment determining the thermal performance and initial cost of the system The length and performance of the heat exchanger is dependent on the ground thermal conductivity, the operation hours, the ground loop diameter, the grout, the ground loop arrangement, the pipe placement and the design temperature. The result of this simulation shows that higher thermal conductivity of grouting materials leads to the decrease length of geothermal heat exchanger from 100.0 to 84.4%.