• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.1
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• pp.8-18
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• 2012

In early constructed nuclear power plants, Ni-based Alloys 82/182 had been widely used for dissimilar metal welds (DMW) as a weld filler metal. However, Alloys 82/182 have been proven to be susceptible to primary water stress corrosion cracking (PWSCC) in the nuclear primary water environment. The formation of crack due to PWSCC is also influenced by weld residual stresses. Thus, the accurate estimation of weld residual stresses of DMW is crucial to investigate the possibility of PWSCC and instability behaviors of crack due to PWSCC. In this context, the present paper investigates weld residual stresses of nuclear reactor piping nozzles based on 2-D axi-symmetric finite element analyses based on layer-based approach using maximum molten bead temperature. In particular, the effect of analysis parameters, i.e., a thickness of weld layer, an initial molten bead temperature, convection heat transfer coefficient, and geometric constraints on predicted weld residual stresses was investigated.

• Communications of the Korean Mathematical Society
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• v.25 no.1
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• pp.119-128
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• 2010

Let ${X_n,\;n\geq1}$ be a sequence of independent identically distributed (i.i.d.) random variables (r.vs.), defined on a probability space ($\Omega$,A,P), and let ${N_n,\;n\geq1}$ be a sequence of positive integer-valued r.vs., defined on the same probability space ($\Omega$,A,P). Furthermore, we assume that the r.vs. $N_n$, $n\geq1$ are independent of all r.vs. $X_n$, $n\geq1$. In present paper we are interested in asymptotic behaviors of the random sum $S_{N_n}=X_1+X_2+\cdots+X_{N_n}$, $S_0=0$, where the r.vs. $N_n$, $n\geq1$ obey some defined probability laws. Since the appearance of the Robbins's results in 1948 ([8]), the random sums $S_{N_n}$ have been investigated in the theory probability and stochastic processes for quite some time (see [1], [4], [2], [3], [5]). Recently, the random sum approach is used in some applied problems of stochastic processes, stochastic modeling, random walk, queue theory, theory of network or theory of estimation (see [10], [12]). The main aim of this paper is to establish some results related to the asymptotic behaviors of the random sum $S_{N_n}$, in cases when the $N_n$, $n\geq1$ are assumed to follow concrete probability laws as Poisson, Bernoulli, binomial or geometry.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.34-40
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• 2016

In ventilated seats for cars, air flow is generated by a fan and passed through a foam pad, foam filter, and seat cover. There is a significant loss of air flow in this process, and it is not easy to analyze the amount delivered to the driver. Another difficulty is the geometric complexity of the air flow passage inside the seats. In this paper, the air flow through a foam pad was analyzed. Proper modeling of the bumps in the ventilation mat was found to be important in the analysis. Air flow is lost when it passes through the porous pad foam, which was measured and used to correct the analysis results. The corrected analysis results were in a good agreement with the experimental results. The amount of air flow delivered to a driver was measured using an airflow cone. Only 35.7% of the air flow from the fan was delivered.

• KIPS Transactions on Software and Data Engineering
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• v.4 no.4
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• pp.177-186
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• 2015

For data fusion of laser range finder (LRF) and vision camera, accurate calibration of external parameters which describe relative pose between two sensors is necessary. This paper proposes a new calibration method which can acquires more accurate external parameters between a LRF and a vision camera compared to other existing methods. The main motivation of the proposed method is that any corner data of a known 3D structure which is acquired by the LRF should be projected on a straight line in the camera image. To satisfy such constraint, we propose a 3D geometric model and a numerical solution to minimize the energy function of the model. In addition, we describe the implementation steps of the data acquisition of LRF and camera images which are necessary in accurate calibration results. In the experiment results, it is shown that the performance of the proposed method are better in terms of accuracy compared to other conventional methods.

• Journal of Korean Society of Transportation
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• v.25 no.3
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• pp.77-85
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• 2007

The number of accidents occurring at railway crossings is less than the accidents on other sections of roads but they cause enormous socio-economic damages. The geometric aspects of the railway crossing have to allow the drivers to recognize the crossings and take precautions against collisions. Therefore, ensuring visibility for the vehicle approaching the railway crossing is necessary for safe operation of the crossing. However, as there is little research related to railway crossing visibility in Korea. validating visibility and maintaining visibility based on the validation is badly needed. This research develops a visibility validation model to support improving visibility and to reduce accidents at railway crossings to improve safety for the crossing users.

• The Journal of the Acoustical Society of Korea
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• v.11 no.2
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• pp.59-67
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• 1992

Recently, the problem which actively control the unwanted noise propagated from the technical structure by the generated secondary sound has become considerable topic from the environmental preservation point of view. In most of these studies, active noise control deals with a plane wave propagation at low frequency using adaptive filtering techniques. On the other hand, in real acoustic systems are mostly short due to the limitation of geometric configuration. In this case, the acoustic properties such as reflections and resonances inside the acoustic system should be considered. In this paper, the acoustic modeling method for short length duct was introduced using the transfer matrix method, and the active noise control problem was investigated with \implementation of FIR filter for the transfer function of control system derived from this modeling method. The identification methods for the acoustic model of actual control system was proposed by numerical computation technique based on the estimation of optimal FIR filter coefficients. The acceptable attenuation on the real acoustic system and stability of the controller are predicted in this computational simulation.

• Journal of Ocean Engineering and Technology
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• v.27 no.1
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• pp.85-92
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• 2013

This paper deals with the resonant type of a WEC (wave energy converter) and the determination method of its geometric parameters which were obtained to construct the robust and optimal structure, respectively. In detail, the optimization problem is formulated with the constraints composed of the response surfaces which stand for the resonance period(heave, pitch) and the meta center height of the buoy. Use of a signal-to-noise ratio calculated from normalized multi-objective results with the weight factor can help to select the robust design level. In order to get the sample data set, the motion responses of the power buoy were analyzed using the BEM (boundary element method)-based commercial code. Also, the optimization result is compared with a robust design for a feasibility study. Finally, the power efficiency of the WEC with the optimum design variables is estimated as the captured wave ratio resulting from absorbed power which mainly related to PTO (power take off) damping. It could be said that the resultant of the WEC design is the economical optimal design which satisfy the given constraints.

• Journal of Environmental Health Sciences
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• v.39 no.4
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• pp.346-353
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• 2013

Objectives: The goal of this study is to identify the distribution of the foliar fluorine content of vegetation surrounding the area where hydrofluoric acid was accidently released in Gumi, Gyeongsangbuk-do on September 27, 2012. In addition, it also aims to estimate the concentration of hydrogen fluoride in the air on the day of the accident. Methods: Samples of plant leaves were collected on October 7, 2012 within 1 km from the site where the accident occurred. These samples were analyzed for soluble fluorine ion with an ion selective electrode. The ambient concentration of hydrogen fluoride was calculated using the fluoride content in the plant via the dose-rate equation (${\Delta}F$=KCT). Results: The arithmetic and geometric means of the concentrations were 2158.2 and 1183.7mg F $kg^{-1}$ for leaves and, 2.4 and 1.1 ppm HF for the air, respectively. The highest concentration of hydrogen fluoride in the air was 14.7 ppm, which is higher than the maximum concentration reported by the government (1 ppm) and the exposure limit (ceiling, 3 ppm). The concentrations of both fluorine and hydrogen fluoride decreased with increasing distance from the accident site and showed a significant decrease outside of a 500m radius from the site (p <0.05). Conclusions: The area around the accident site was highly polluted with hydrogen fluoride according to the results of this study. Considering the persistency of hydrogen fluoride in the environment, long-term monitoring and environmental impact assessment should be pursued.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.66.2-66.2
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• 2017

The Korea Astronomy and Space Science Institute plans to develop a coronagraph in collaboration with National Aeronautics and Space Administrative (NASA) and install it on the International Space Station (ISS). The coronagraph is an externally occulted one stage coronagraph with a field of view from 2.5 to 15 solar radii. The observation wavelength is approximately 400 nm where strong Fraunhofer absorption lines from the photosphere are scattered by coronal electrons. Photometric filter observation around this band enables the estimation of 2D electron temperature and electron velocity distribution in the corona. Together with the high time cadence (< 12 min) of corona images to determine the geometric and kinematic parameters of coronal mass ejections, the coronagraph will yield the spatial distribution of electron density by measuring the polarized brightness. For the purpose of technical demonstration, we intend to observe the total solar eclipse in 2017 August for the filter system and to perform a stratospheric balloon experiment in 2019 for the engineering model of the coronagraph. The coronagraph is planned to be installed on the ISS in 2021 for addressing a number of questions (e.g. coronal heating and solar wind acceleration) that are both fundamental and practically important in the physics of the solar corona and of the heliosphere.

• Journal of the Korean Society of Safety
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• v.15 no.1
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• pp.140-145
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• 2000

This paper was composed with fatigue test of the cruciform specimens, as load carrying and non-load carrying type. It also has performed computational analyses for geometric condition of the fillet welding bead. As test results, the effect of stress ratio in the specimen was insignificant. Stress ranges were varied with R=0.1~0.2. The fatigue cracks that were found in the load carrying type specimens and most specimens welded with contact were developed at the end of welds. The fatigue strength of specimen that have fractured in maternal plate was found about ${\Delta}\sigma_c$=63.5MPa. It's about 24% less than that of the non-load carrying type specimens having about ${\Delta}\sigma_c$=83.8MPa. A category of the Fatigue design specifications which provide for cruciform details was defined grade C as a stress of the maternal member. And then, the fatigue strength to be transformed into the maternal stress was found about 78.27 MPa, it tends to be less than that of allowable fatigue strength.