• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.1
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• pp.267-277
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• 2003

The purpose of this study makes a retrofit and rehabilitation practice trough the analysis and the improvement for the underlying problem of current retrofit and rehabilitation methods. Therefore, the deterioration process, the damage cause, the condition classification, the fatigue mechanism and the applied quantity of strengthening methods for slab bridge decks were analysed. Artificial neural networks are efficient computing techniqures that are widely used to solve complex problems in many fields. In this study, a back-propagation neural network model for estimating a management on existing slab bridge decks from damage cause, damage type, and integrity assessment at the initial stsge is need. The training and testing of the network were based on a database of 36. Four different network models werw used to study the ability of the neural network to predict the desirable output of increasing degree of accuracy. The neural networks is trained by modifying the weights of the neurons in response to the errors between the actual output values and the target output value. Training was done iteratively until the average sum squared errors over all the training patterms were minimized. This generally occurred after about 5,000 cycles of training.

• Nuclear Engineering and Technology
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• v.48 no.5
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• pp.1264-1272
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• 2016

The accurate estimation of leak rate through cracks is crucial in applying the leak before break (LBB) concept to pipeline design in nuclear power plants. Because of its importance, several programs were developed based on the several proposed flow models, and used in nuclear power industries. As the flow models were developed for a homogeneous pipe material, however, some difficulties were encountered in estimating leak rates for bimaterial pipes. In this paper, a flow model is proposed to estimate leak rate in bimaterial pipes based on the modified Henry-Fauske flow model. In the new flow model, different crack morphology parameters can be considered in two parts of a flow path. In addition, based on the proposed flow model, a program was developed to estimate leak rate for a crack with linearly varying cross-sectional area. Using the program, leak rates were calculated for through-thickness cracks with constant or linearly varying cross-sectional areas in a bimaterial pipe. The leak rate results were then compared and discussed in comparison with the results for a homogeneous pipe. The effects of the crack morphology parameters and the variation in cross-sectional area on the leak rate were examined and discussed.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.10a
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• pp.227-236
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• 2002

The purpose of this study makes a retrofit and rehabilitation practice trough the analysis and the improvement for the underlying problem of current retrofit and rehabilitation methods. Therefore, the deterioration process, the damage cause, the condition classification, the fatigue mechanism and the applied quantity of strengthening methods for RC deck slabs were analyzed. Artificial neural networks are efficient computing techniques that are widely used to solve complex problems in many fields. In this study, a back-propagation neural network model for estimating a management on existing reinforced concrete bridge decks from damage cause, damage type, and integrity assessment at the initial stage is need. The training and testing of the network were based on a database of 36. Four different network models were used to study the ability of the neural network to predict the desirable output of increasing degree of accuracy. The neural networks is trained by modifying the weights of the neurons in response to the errors between the actual output values and the target output value. Training was done iteratively until the average sum squared errors over all the training patterns were minimized. This generally occurred after about 5,000 cycles of training.

• Ocean and Polar Research
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• v.29 no.4
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• pp.367-378
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• 2007

A sediment quality index (SQI) and a mean sediment quality guideline quotient (M-SQGQ) were applied for the assessment of sediment quality in Masan Bay, Korea where metals and organic pollutants are of concern. The SQI was calculated by two functions, 'scope' (the number of variables that do not meet guideline objective) and 'amplitude' (the magnitude by which variables exceed guideline objective), with six different sediment quality guideline values from Canada, USA and Australia/New Zealand. Categorization of sediment quality was on the basis of SQI scores. The SQI values were compared with six guideline values applied as well as with the M-SQGQs. The SQI values were severely influenced by a few variables of high exceedance in the degree of non-compliance. The SQI values were very dependent on both the numbers and values of guideline variables used in index caluculation. Nevertheless, the SQI could provide integrated and simplified information from a large number of chemical data set. It is required to further evaluate protocols and guideline applied for deriving SQI and to compare it with field based sediment toxicity test and ecosystem integrity.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.1
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• pp.8-14
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• 2015

Transmission of a tracked vehicle designed for multiple functions such as steering, gear-shifting, and braking is a core component of heavy vehicle to which the power is transferred based on combined technology of various gears, bearing, and fluid machineries. Robustness and durability of transmission, however, have been issued due to a large number of driving units and sub-components inside its body. Particularly, transmission housing is important structure which supports the transmission, and is made of aluminum alloy. Thus, structural robustness against such mechanical loading or vibration must be attained. Structural reliability evaluation through FEM analysis can save time and cost of the actual tests. In this study, structural evaluation is conducted on output housing of transmission, which is core component of tracked vehicle, using the simulation program. In addition, transmission dynamo test is performed to evaluate structural robustness of the output housing against the vibration which can be produced during the transmission operation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1469-1476
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• 2003

This paper provides plastic limit load solutions of cylinders with circumferential part-through surface cracks under combined axial tension, internal pressure and global bending. Such solutions are developed based on detailed three-dimensional (3-D) finite element (FE) limit analyses using elastic-perfectly-plastic material behaviour, together with analytical solutions based on equilibrium stress fields. For the crack location, both external and internal cracks are considered. Furthermore, in terms of the crack shape, both semi-elliptical and constant-depth surface cracks are considered. The resulting limit load solutions are given in a closed form, and thus can be easily used in practical situations. Being based on detailed 3-D FE limit analysis, the present solutions are believed to most reliable, and thus to be valuable information for integrity assessment of piping.

• Nuclear Engineering and Technology
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• v.48 no.1
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• pp.218-227
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• 2016

Background: Steam explosions may occur in nuclear power plants by molten fuel-coolant interactions when the external reactor vessel cooling strategy fails. Since this phenomenon can threaten structural barriers as well as major components, extensive integrity assessment research is necessary to ensure their safety. Method: In this study, the influence of yield criteria was investigated to predict the failure of a reactor cavity under a typical postulated condition through detailed parametric finite element analyses. Further analyses using a geometrically simplified equivalent model with homogeneous concrete properties were also performed to examine its effectiveness as an alternative to the detailed reinforcement concrete model. Results: By comparing finite element analysis results such as cracking, crushing, stresses, and displacements, the Willam-Warnke model was derived for practical use, and failure criteria applicable to the reactor cavity under the severe accident condition were discussed. Conclusion: It was proved that the reactor cavity sustained its intended function as a barrier to avoid release of radioactive materials, irrespective of the different yield criteria that were adopted. In addition, from a conservative viewpoint, it seems possible to employ the simplified equivalent model to determine the damage extent and weakest points during the preliminary evaluation stage.

• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.160-167
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• 2014

To determine a proper ASIL for each hazardous event with a proper safety goal, the right classes should first be determined for the three properties of the hazardous event; (i) severity of harm from the resultant accident, (ii) exposure to the relevant operational situation, and (iii) controllability to avoid the induced risks. ASIL can be clearly determined with right classes of these three properties. But no specific methodologies or processes for their classification can be found in ISO 26262, except only a rough guideline with a simplified set of illustrative tables. In this paper, we try to present a systematic model for classifying the three properties of the hazardous event and suggest a refined procedure of ASIL determination. The proposed model provides a specific method to get a more objective ASIL compared with that in the standard. Scrutinizing the current methodology, we develop a refined method and also provide an illustrative example.

• Journal of the Korean Institute of Landscape Architecture
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• v.31 no.1
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• pp.34-41
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• 2003

Connectivity is a quantitative indicator of landscape structure, and connectivity of urban green areas is an indicator of ecological integrity in urban landscapes. The purposes of this study are to assess the connectivity of urban green areas in Seoul, and to develop a method of siting new green areas for better connectivity. Diverse methods for connectivity assessment and indices of connectivity are reviewed and applied to the connectivity assesment of green areas in Seoul. The indices of connectivity of green areas in Seoul turned out to be higher than expected, maybe because many of them are rather evenly distributed, serving as stepping stones, and because there are many riparian corridors, including the Han River. Analysis also shows the optimum location of new green space patches or corridors will be those spots that would link the mainland, or large green areas outside the city, and existing green areas in the city. Restoration of urban streams as ecological corridors will significantly enhance connectivity. Three different scenarios with increasing numbers of new green areas in the city were then prepared. The changes of connectivity were measured and the possible success rates of animal dispersal were simulated. The results revealed that restoration of streams will increase the connectivity and success rates of animal dispersal.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.6
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• pp.40-52
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• 1998

A good grasp of the failure mechanisms of resistance spot weld, widely used in joining the auto-panels, in essential to the structural/crashworthy analyses and integrity assessment of the whole auto-body. In this study, We provide an estimative model describing the failure behavior of resistance spotf weld, and apply the model to the finite element analysis of crashworthiness. First, in "Part 1-Failure Criteria", to be used for the finite element analysis of spot-welded structural panels of an auto-body, (i) a methodology for quantifying the spot weld failure and the accompanying failure criteria are presented, and (ii) the coefficients of the failure equation are determined by a munimum number of appropriate experimental tests. To achieve these, we derive the functional form of the failure envelop by limit analysis, and correlate it with the form in PAM-$CRASH^{TM}$ code, and also investigate the effect of the failure coefficients on the failure envelop form. An estimative model obtained in this Part1, as spot weld failure criteria is applied to the Macroscopic finite element analysis of autobody structural panels using PAM-$CRASH^{TM}$ code in Part 2.