• Korean Journal of Materials Research
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• v.12 no.5
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• pp.398-406
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• 2002

VAR process is required to control its various operating parameters. Heat transfer simulation has been accomplished to understand development of solidification micro and macro-structures during VAR process in Ti alloys. Optimum VAR process parameters could be also estimated in this study. It was found that macro-structures were closely related to the shape and depth of liquid pool, and solidification parameters, such as temperature gradient, heat flux, solid fraction. The cooling rates were higher at bottom, top, and center part respectively. As cooling rates increased, the $\alpha$ phase decreased in length, width and fraction. In order to evaluate which parameter affects the result of heat transfer calculation most sensitively, the sensitivities of input parameters to the simulation result were examined. The pool depth and cooling rate showed more sensitive to the temperature of the molten metal, heat transfer coefficient, and liquidus respectively. Also, these thermal properties became more sensitive at higher temperatures.

• Journal of Ocean Engineering and Technology
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• v.36 no.4
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• pp.251-269
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• 2022

The process-based XBeach model has numerous empirical parameters because of insufficient understanding of hydrodynamics and sediment transport on the nearshore; hence, it is necessary to calibrate parameters to apply to various study areas and wave conditions. Therefore, the calibration process of parameters is essential for the improvement of model performance. Generally, the trial-and-error method is widely used; however, this method is passive and limited to various and comprehensive parameter ranges. In this study, the Generalized Likelihood Uncertainty Estimation (GLUE) method was used to estimate the optimal range of three parameters (gamma, facua, and gamma2) using morphological field data collected in Maengbang beach during the four typhoons that struck from September to October 2019. The model performance and optimal range of empirical parameters were evaluated using Brier Skill Score (BSS) along with the baseline profiles, sensitivity, and likelihood density analysis of BSS in the GLUE tools. Accordingly, the optimal parameter combinations were derived when facua was less than 0.15 and simulated well the shifting shape, from crescentic sand bar to alongshore uniform sand bars in the surf zone of Maengbang beach after storm impact. However, the erosion and accretion patterns nearby in the surf zone and shoreline remain challenges in the XBeach model.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.12
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• pp.4891-4895
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• 2010

RF coil is an important component of the Magnetic Resonance Imaging (MRI) system and the performance of RF coil is one of major factors for high SNR images. Sensitivity and RF field uniformity are parameters for evaluating RF coil performance. Since the B1 field is induced by RF coil, MR signal is strongly affected by RF coil structure and arrangement. In receiving MR signal, the RF coil sensitivity to MR Signal is also determined by the induced B1 field of RF coil. Therefore, the spatial distribution of B1 field must be verified. In this work, we performed computer simulation of the basic RF coil structures using Matlab and verified their sensitivity and uniformity through their B1 field distribution. This work will be useful for the advanced multi-channel RF coil design.

• Anxiety and mood
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• v.7 no.2
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• pp.107-112
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• 2011

Objective : This study aimed to ascertain the effect of interpersonal sensitivity/resilience on depression and anxiety in firefighters whose frequency of exposure to traumatic events is high. Method : A survey was performed and data related to 75 firefighters were analyzed. Questionnaires included the Beck Depression Inventory (BDI) and Impact of Event Scale-Revised (IES-R). To assess the susceptibility or protector roles with respect to psychopathology, the Interpersonal Sensitivity Measure (IPSM) and Conner-Davidson Resilience Scale (CD-RISC) were used. Results : The personality characteristic, interpersonal sensitivity (IPSM) showed a significant positive correlation with depression (BDI, r=0.557, p<0.001) and posttraumatic stress symptoms (IES-R, r=0.316 ; p<0.001). In contrast, resilience and symptom parameters (BDI, IES-R) were negatively correlated with each other, but not statistically significant. However, an adaptive factor for change, a third sub-factor of CD-RISC, had significant negative correlation with depression and anxiety symptoms (BDI, r=-0.275, p<0.005 ; IES-R, r=-0.254, p<0.005). Conclusion : The results of the present study showed that some personality traits may act as vulnerability or protective factors with respect to the psychopathologies of depression and anxiety.

• The Journal of the Acoustical Society of Korea
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• v.16 no.3
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• pp.73-80
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• 1997

This paper describes structural optimization of optical fiber-wound mandrel hydrophones with Finite Element Method (FEM). The hydrophone is supposed to have operation frequency range of up to 10 kHz and show omni-directional sensitivity pattern at 5 kHz. Studied parameters are mandrel geometry, molding thickness, and material properties of constitutional parts of the hydrophone. Theoretical calculation result shows that pressure sensitivity of the hydrophone increased as either mandrel length or molding thickness gets larger. Also higher pressure sensitivity requires a mandrel or molding material with relatively low Youngs modulus or Poissons ratio. Hydrophone bandwidth increases either as the mandrel length becomes shorter or as the mandrel becomes harder. The omni-directional characteristic is improved as the mandrel length becomes shorter, at 5 kHz. With the above results, we determine the structure of an optical fiber-wound mandrel hydrophone which has the pressure sensitivity of $30 {\times} 10_{-7}$ Rad./Pa, operation frequency range of up to 10 kHz, and shows omni-directional sensitivity pattern at 5 kHz.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.2
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• pp.162-168
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• 2008

In this paper, the RCF(Resistive Companion Form) analysis method is applied to analyze small signal stability of power systems including thyristor controlled FACTS(Flexible AC Transmission System) equipments such as TCSC(Thyristor Controlled Series Capacitor). The eigenvalue sensitivity analysis algorithm in discrete systems based on the RCF analysis method is presented and applied to the power system including TCSC. As a result of simulation, the RCF analysis method is very useful to precisely calculate the variations of eigenvalues or newly generated unstable oscillation modes after periodic switching operations of TCSC. Also the eigenvalue sensitivity analysis method based on the RCF analysis method enabled to precisely calculate eigenvalue sensitivity coefficients of controller parameters about the dominant oscillation mode after periodic switching operations in discrete systems. These simulation results are different from those of the conventional continuous system analysis method such as the state space equation and showed that the RCF analysis method is very useful to analyze the discrete power systems including periodically operated switching equipments such as TCSC.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.8
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• pp.9-16
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• 2007

Currently, the measurement of RF parameters for a base station in operation is typically limited to easily measured forward path items. In this paper, the forward monitoring ports of base stations are used to measure the reverse RF performance. The system has been implemented and effectiveness has been proven on an operating base station. The receiver sensitivity is measured using an internal CDMA modem which is used to monitor the output power based on closed loop power control when the modem is connected to the base station via a voice call. In order to improve accuracy, in addition to the modem Tx adjust(TxAdj) parameter, the detector's actual measurement is used. For accurate receiver sensitivity, the measurement should be made when there is no traffic which is not possible on an operating base station. Therefore, pilot channel chip energy to received signal power spectral density ratio$(E_c/I_o)$ compensation method is used to offset the receiver sensitivity degradation with voice traffic increase.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.846-853
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• 2006

In this study, quantitative sensitivity analysis on rockfill material influencing the dam crest displacement of Concrete-Faced Rockfill Dam(CFRD) was carried out. The purpose of this study is to indicate the most important input parameter and to show the quantitative variation of displacement at the crest of CFR type dam with this input parameter. The rockfill material properties for parametric study were obtained from the results of large scale triaxial tests on 34 rockfill materials in the 22 different sites. From the statistical analysis on these data, some statistical characteristics of rockfill material properties such as property range, distribution characteristics, and correlation between the properties were investigated. based on these characteristics, 27 property combinations were constituted by Latin Hypercube sampling method. Dam crest displacements after construction, impounding, and earthquake loading were evaluated by static and dynamic numerical analysis on each combination. From the sensitivity analysis, it was found that the crest displacement of CFR type dam was absolutely affected by the shear modulus of rockfill material and the effect of friction angle of it was negligible. This relative difference of sensitivity was more outstanding in case of crest settlement than in case of crest horizontal displacement. Also, it was found that the settlement and horizontal displacement of dam crest logarithmically decreased as the shear modulus increased and the difference between the maximum value and the minimum vale amounted to about 9.5 times in case of settlement and about 10 times in case of horizontal displacement.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.2
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• pp.113-128
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• 2004

To investigate major influencing factors on earth pressure acting on an arch-shaped cut and cover tunnel, Monte Carlo simulation based quantitative sensitivity analysis was carried out for mechanical properties of ground as well as excavation configuration-related design factors. From the sensitivity analysis, it was intended that effects of earth pressures from different influencing factors on a cut and cover tunnel should be numerically identified. Output factors used in the sensitivity analysis such as vertical and horizontal earth pressures at different tunnel positions were obtained from the finite element analysis. In this study, it was revealed that depending upon positions where horizontal as well as vertical earth pressures were acting, they were differently influenced by the same input factors. In addition, earth pressures acting an cut and cover tunnel depended mainly on the embankment at crown and the inclination of cut slope.

• Journal of the Korean Geotechnical Society
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• v.36 no.8
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• pp.49-60
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• 2020

A fully coupled thermo-hydro-mechanical model is established to evaluate frost heave behaviour of saturated frost-susceptible soils. The method is based on mass conservation, energy conservation, and force equilibrium equations, which are fully coupled with each other. These equations consider various physical phenomena during one-dimensional soil freezing such as latent heat of phase change, thermal conductivity changes, pore water migration, and the accompanying mechanical deformation. Using the thermo-hydro-mechanical model, a sensitivity analysis study is conducted to examine the effects of the geotechnical parameters and external conditions on the amount of frost heave and frost heaving rate. According to the results of the sensitivity analysis, initial void ratio significantly affects each objective as an individual parameter, whereas soil particle thermal conductivity and temperature gradient affect frost heave behaviour to a greater degree when applied simultaneously. The factors considered in this study are the main factors affecting the frost heaving amount and rate, which may be used to determine the frostbite sensitivity of a new sample.