• Computational Structural Engineering
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• v.9 no.3
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• pp.169-177
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• 1996

The focus of this study is on the problem of the design of structure of undetermined topology. This problem has been regarded as being the most challenging of structural optimization problems, because of the difficulty of allowing topology to change. Conventional approaches break down when element sizes approach to zero, due to stiffness matrix singularity. In this study, a novel nonlinear programming formulation of the topology problem is presented. Its main feature is the ability to account for topology variation through zero element sizes. Stiffness matrix singularity is avoided by embedding the equilibrium equations as equality constraints in the optimization problem. Although the formulation is general, two dimensional plane elasticity examples are presented. The design problem is to find minimum weight of a plane structure of fixed geometry but variable topology, subject to constraints on stress and displacement. Variables are thicknesses of finite elements, and are permitted to assume zero sizes. The examples demonstrate that the formulation is effective for finding at least a locally minimal weight.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.2
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• pp.175-182
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• 2012

In this paper we are concerned with the performance of structural stability of torsion in square cross section of a beam with holes. The critical load is defined as the smallest load at which the equilibrium of the structure fails to be stable as the load is slowly increased from zero. The beams subjected to torsion are frequently encountered in general structures and these forces influence to the stability of structure. The boundary element method is found to be very efficient and accurate for the analysis of torsion problems including complex boundary conditions with respect to its simplicity and generality. In this paper, it is required to derive the boundary element formulation for torsion problem and integrate directly on the discrete boundary. To investigate the validity of the developed computer program, three distinctly solid cross-sections which are elliptical, rectangular and triangular one are analyzed, and comparisons are made with analytical approaches where these can also be used.

• Nuclear Engineering and Technology
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• v.47 no.1
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• pp.47-58
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• 2015

Four recycling scenarios involving pyroprocessing of spent fuel (SF) have been investigated for a 600-MWe transmutation sodium-cooled fast reactor (SFR), KALIMER. Performance evaluation was done with code system REBUS connected with TRANSX and TWODANT. Scenario Number 1 is the pyroprocessing of Canada deuterium uranium (CANDU) SF. Because the recycling of CANDU SF does not have any safety problems, the CANDU-Pyro-SFR system will be possible if the pyroprocessing capacity is large enough. Scenario Number 2 is a feasibility test of feed SF from a pressurized water reactor PWR. Thefsensitivity of cooling time before prior to pyro-processing was studied. As the cooling time sensitivity of cooling time before prior to pyro-processing was studied. As the cooling time increases, excess reactivity at the beginning of the equilibrium cycle (BOEC) decreases, thereby creating advantageous reactivity control and improving the transmutation performance of minor actinides. Scenario Number 3 is a case study for various levels of recovery factors of transuranic isotopes (TRUs). If long-lived fission products can be separated during pyroprocessing, the waste that is not recovered is classified as low- and intermediate-level waste, and it is sufficient to be disposed of in an underground site due to very low-heat-generation rate when the waste cooling time becomes >300 years at a TRU recovery factor of 99.9%. Scenario Number 4 is a case study for the recovery factor of rare earth (RE) isotopes. The RE isotope recovery factor should be lowered to ${\leq}20%$ in order to make sodium void reactivity less than <7$, which is the design limit of a metal fuel.

• Journal of Korean Society of Water and Wastewater
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• v.8 no.2
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• pp.12-24
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• 1994

The occurrence of objectionable tastes and odors in drinking water is a common and widespread problem. The most troublesome odors are usually those described as muddy or earthy-musty. Two organic compounds which have been implicated as the cause of earthy-musty odor problems in water are geosmin and 2-Methylisoborneol. These earthy-musty organics have been shown to be metabolites of actinomycetes and blue green algae. The purpose of this paper is to describe adsorbability in removing these two oder causing compounds(geosmin and 2-MIB) upon various conditions like pH variation, adding humic acid and different activated carbon. The conclusion of this study are as followings. In batch test, carbon dosage is 10mg/100ml for geosmin and 15mg/100ml for 2-MIB. Both were in equilibrium state after 60 hours. In model simulation, F-P model described experiment data and modelling data appropriately in geosmin but F-S model not. In case of 2-MIB, models didn't describe relation between experiment and modelling data well. Two causative agents of earthy-musty odor compounds, geosmin and 2-MIB, are strongly adsorbed by activated carbon either coconut or brown. There appears to be no effect of pH (3,7,9) on adsorption of these two organics. Activated carbon proved to be more effective for removing geosmin than for removing 2-MIB. When activated carbon is. used in removing these two organics, the removal of these appeared to be adversely affected by back ground organic compounds, such as humic substances, due to competitive adsorption.

• Environmental Engineering Research
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• v.25 no.3
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• pp.384-392
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• 2020

The presence of high fluoride concentration (> 1.5 mg/L) in water causes serious health problems such as fluorosis, infertility, brain damage, etc., which are endemic to many places in the world. This study has investigated the fluoride removal capacity of the novel activated biochar (BTS) and hydrochar (HTS) using Teff (Eragrostis tef) straw as a precursor. Activated biochar with mesoporous structures and large specific surface area of 627.7 ㎡/g were prepared via pyrolysis process. Low-cost carbonaceous hydrochar were also synthesized by an acid assisted hydrothermal carbonization process. Results obtained from both adsorbents show that the best local maximum fluoride removal was achieved at pH 2, contact time 120 min and agitation speed 200 rpm. The thermodynamic studies proved that the adsorption process was spontaneous and exothermic in nature. Both adsorbents equilibrium data fitted to Langmuir isotherm. However, Freundlich isotherm fitted best for BTS. The maximum fluoride loading capacity of BTS and HTS was found to be 212 and 88.7 mg/g, respectively. The variation could primarily be attributed to a relatively larger Surface area for BTS. Hence, to treat fluoride contaminated water, BTS can be promising as an effective adsorbent.

• Journal of the Korean Association of Geographic Information Studies
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• v.6 no.3
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• pp.11-20
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• 2003

Many-sided approach methods are being demanded to solve environmental problems in urban areas. One of these methods will be to manage forests scattered in urban areas efficiently. This paper is to grasp the change of land use and landscape indices in Mt. Ap, Daegu, and to analyze the change of landscape structure. Mt. Ap is near Daegu Metropolitan, so under unnatural interferences of human activity persistently. The results of above analysis run as follows: First, the north of the case area is connected to forest, and keeps stable equilibrium ecologically, while the other parts of it suffer from rural exodus and side effects of urbanization which has been completed since 1980. Second, according to the area-rate change of each landscape element, a cultivated areas has been converted into urban one, especially Pinus densiflora forests and paddy fields into mixed forests and urban areas. Finally, most of plantations have been converted into deciduous forests and mixed forests in failure of adaption of plants in burned areas rather than owing to factitious interference.

• Journal of the Korean GEO-environmental Society
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• v.6 no.2
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• pp.39-49
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• 2005

In this study, the fifteen month behavior of two geosynthetic reinforced walls which was constructed on the shallow weak ground was measured and analyzed. The walls were backfilled with clayey soil obtained from the construction site nearby, and the safety factors obtained from general limit equilibrium analysis were less than 1.3 in both wall. The measured and analyzed data were horizontal earth pressures, strain of reinforcements, and excess pore water pressures. The used reinforcements were nonwoven geotextile, woven geotextile and geogrid. Although the length of reinforcement was only 30% of wall height and the safety factors of the walls were less than 1.3, the walls were constructed without any problems on the such weak ground. The analysis results showed that the maximum strain of reinforcements were negligible and the strain was between 2.3 and 6.0% according to tensile characteristic of the reinforcements. The excess pore water pressure was not changed due to the rainfall and the horizontal earth pressures in upper and lower part of the walls were larger than the active and the rest pressure.

• Environmental and Resource Economics Review
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• v.20 no.4
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• pp.689-733
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• 2011

This study evaluates a novel scheme to trade sulfur dioxide emission permits subject to non-uniform rates. These rates are based on generators' marginal costs of compliance with environmental policy in a hypothesized least social-cost solution. This scheme is compared against the existing trading program used by the U.S. Environmental Protection Agency, featuring permits tradable one for one. Both policies are modeled to yield identical aggregate emissions. A numerical partial-equilibrium model of the U.S. energy industry is used to infer sulfur dioxide concentrations and health damages, as well as producer and consumer surplus, under the two policies. Regional pollution levels are found to vary across the two policies significantly. The system of exchange rates is estimated to outperform the uniform-trading scheme by $2.2 billion in industry profits and $2.1 billion in health damages, but to reduce consumer surplus by $6.7 billion. Paradoxically, exchange rates are thus estimated to lower total welfare by $2.5 billion. This is due to conceptual mechanism-design problems, as well as empirical issues.

• Journal of the Korean association of regional geographers
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• v.8 no.1
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• pp.40-64
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• 2002

The locational characteristics of ceramic industry in Miryang city, Kyongnam province, were clarified by means of examining the process of its formation, spatial variation, locations and their changes. The government policy on industry and the business fluctuation are important in the quantitative changes of the industry. The spatial variation of industry toward the outer part of area are the results of equilibrium between the decrease of firms in inner city and the increase of firms in outer part. The births and deaths of firms played important role in the processes of spatial variations. The industry location has lasted by the accumulation of location decision of 'potential entrepreneurs' who learned knowledges on the industry and had personal contacts with the business-related persons for long time. The main factors on the locational decision of firms are personal factor, raw materials, land, water and market. The locational problems have mainly related with plant expansion, land, marketing, labour and capital. They caused investment changes and caused relocations of firms. Such disadvantages as raw material exhaustion, shortage of land and congestion within the agglomeration area, development of road transportation and local government policy on industry location, induced recent decentralization of industry to outer part.

• Journal of Navigation and Port Research
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• v.27 no.4
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• pp.397-402
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• 2003

Generally, container arrangement has been carried out based on the Classification guidelines. However, guidelines provide only container securing forces for the given container arrangement and Classification requirements of the forces. In order to design container arrangement additional information is needed such as container securing forces and arrangement that accounts for lashing bridges, vertical lashing, vertical center of gravity (VCG), and maximum stack weight. Trial and error method using the existing guidelines requires excessive amount of calculation time and cannot provide accurate results of the calculations. In order to fulfill this need, a new container securing system has been established based on the equilibrium conditions that include lashing bridges and vertical lashing. An optimization algorithm has been developed for the new system since current optimization methods such as genetic algorithms and evolution strategies are unsuitable for the container securing problems, which involve equality constraint. Design variables are container weights of tier and objective function is either total container weight or VCG of a stack. The newly developed system provides optimum arrangement of containers for both maximum stack weight and maximum VCG. It also greatly reduces time for designing container arrangement.