• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.5
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• pp.668-676
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• 2003

The effect of nozzle height on heat transfer of a hot steel plate cooled by an impinging liquid jet is not well understood. Previous studies have been based on the dimensionless parameter z/d. To test the validity of this dimensionless parameter and to investigate gravitational effects on the jet, stagnation velocity of an impinging liquid jet were measured and the cooling experiments of a hot steel plate were conducted for z/d from 6.7 to 75, and an inverse heat conduction method is applied for the quantitative comparison. Also, the critical instability point of a liquid jet was examined over a range of flow rates. The experimental velocity data for the liquid jet were well correlated with the dimensionless number 1/F $r_{z}$$^2$based on distance. It was thought that the z/d parameter was not valid for heat transfer to an impinging liquid jet under gravitational forces. In the cooling experiments, heat transfer was independent of z when 1/F $r_{z}$$^2$< 0.187(z/d = 6.7). However, it was found that the heat transfer quantity for 1/F $r_{z}$$^2$=0.523(z/d = 70) is larger 11% than that in the region for 1/F $r_{z}$$^2$=0.187. The discrepancy between these results and previous research is likely due to the instability of liquid jet.uid jet.

• Structural Engineering and Mechanics
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• v.13 no.4
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• pp.369-385
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• 2002

Ductility capacity is comprehensively studied for steel moment-resisting frames. Local, story and global ductility are being considered. An appropriate measure of global ductility is suggested. A time domain nonlinear seismic response algorithm is used to evaluate several definitions of ductility. It is observed that for one-story structures, resembling a single degree of freedom (SDOF) system, all definitions of global ductility seem to give reasonable values. However, for complex structures it may give unreasonable values. It indicates that using SDOF systems to estimate the ductility capacity may be a very crude approximation. For multi degree of freedom (MDOF) systems some definitions may not be appropriate, even though they are used in the profession. Results also indicate that the structural global ductility of 4, commonly used for moment-resisting steel frames, cannot be justified based on this study. The ductility of MDOF structural systems and the corresponding equivalent SDOF systems is studied. The global ductility values are very different for the two representations. The ductility reduction factor $F_{\mu}$ is also estimated. For a given frame, the values of the $F_{\mu}$ parameter significantly vary from one earthquake to another, even though the maximum deformation in terms of the interstory displacement is roughly the same for all earthquakes. This is because the $F_{\mu}$ values depend on the amount of dissipated energy, which in turn depends on the plastic mechanism, formed in the frames as well as on the loading, unloading and reloading process at plastic hinges. Based on the results of this study, the Newmark and Hall procedure to relate the ductility reduction factor and the ductility parameter cannot be justified. The reason for this is that SDOF systems were used to model real frames in these studies. Higher mode effects were neglected and energy dissipation was not explicitly considered. In addition, it is not possible to observe the formation of a collapse mechanism in the equivalent SDOF systems. Therefore, the ductility parameter and the force reduction factor should be estimated by using the MDOF representation.

• Steel and Composite Structures
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• v.36 no.5
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• pp.603-615
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• 2020

The present manuscript focuses on the flow and heat transfer of the dusty fluid along exponentially stretching cylinder. Enormous attempts are made for fluid flow along cylinder but the study of fluid behavior along exponentially stretching cylinder is discussed lately. Using appropriate transformations, the governing partial differential equations are converted to non-dimensional ordinary differential equations. The transformed equations are solved numerically using Shooting technique with Runge-Kutta method. The influence of the physical parameters on the velocity and temperature profiles as well as the skin fraction coefficient and the local Nusselt number are examined in detail. The essential observations are as the fluid velocity decreases but temperature grows with rise in particle interaction parameter, and both the fluid velocity and temperature fall with increase in mass concentration parameter, Reynold number, Particle interaction parameter for temperature and the Prandtl number.

• Journal of Korea Foundry Society
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• v.23 no.3
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• pp.137-146
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• 2003

The main purpose of this study is to investigate the effects of process parameter on alpha-case formation of Ti and TiAl castings. The previous studies showed that the molten titanium is excessively reactive to the refractory oxide mold, resulting in alpha-caes of the titanium castings regardless of composition of titanium alloys. However, the behavior of the alpha-case formation of TiAl alloy is not consistent with conventional titanium alloy. In order to investigate the alpha-case formation of Ti and TiAl castings with process parameter, especially the associated factors of investment mold such as mold material, binder and mold preheating temperature. An attempt has been made to characterize the alpha-case of titanium casting by using optical microscope, EDS, XRD, EMPA and hardness profiles. The formation of the alpha-case on the surface of pure titanium during investment casting was rather by that of solid solution with metallic element from mold material. The required mold strength was obtained with $CaZrO_3$ because of the possibility of using water soluble binder. However, the separation phenomenon between facing and back-up mold materials should be considered. The interfacial reaction of TiAl alloy showed different behavior from that of pure titanium and $Al_2O_3$ was best mold materials. The effect of binder as well as mold material on the formation of alpha-case was significant.

• Journal of The Korean Society of Agricultural Engineers
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• v.59 no.3
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• pp.63-70
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• 2017

The purpose of this study was to calibrate the hydrologic parameters of SWAT model and analyze the daily runoff for the study watershed using SWAT-CUP. The Hardware watershed is located in Virginia, USA. The watershed area is $356.15km^2$, and the land use accounts for 73.4 % of forest and 23.2 % of pasture. Input data for the SWAT model were obtained from the digital elevation map, landuse map, soil map and others. Water flow data from 1990 to 1994 was used for calibration and from 1997 to 2005 was for validation. The SUFI-2 module of the SWAT-CUP program was used to calibrate the hydrologic parameters. The parameters were calibrated for the highly sensitive parameters presented in previous studies. The P-factor, R-factor, $R^2$, Nash-Sutcliffe efficiency (NS), and average flow were used for the goodness-of-fit measures. The applicability of the model was evaluated by sequentially increasing the number of applied parameters from 4 to 11. In this study, 10-parameter set was accepted for calibration in consideration of goodness-of-fit measures. For the calibration period, P-factor was 0.85, R-factor was 1.76, $R^2$ was 0.51 and NS was 0.49. The model was validated using the adjusted ranges of selected parameters. For the validation period, P-factor was 0.78, R-factor was 1.60, $R^2$ was 0.60 and NS was 0.57.

• Journal of the Institute of Convergence Signal Processing
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• v.6 no.4
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• pp.176-181
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• 2005

This paper presents an equal bit rate control algorithm utilizing the statistical change between the previous frame and the current frame. The previous studies on the model-based rate control have focused on the models of bit rate and distortion in types of coders, in terms of the quantization parameter. The proposed algorithm improves the typical model-based rate control by updating a model parameter instead of modeling a better model of the rate and distortion. The proposed algorithm updates this model parameter by recognizing the change in statistics between the previous frame and the current frame. We implement the proposed algorithm in MPEG-4 coders and verify its performance while comparing it to the TMN8's approach (up to 0.6dB of improvement).

• Journal of Ocean Engineering and Technology
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• v.29 no.6
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• pp.445-453
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• 2015

The stress triaxiality and lode angle are known to be most dominant fracture parameters in ductile materials. This paper proposes a three-dimensional failure strain surface for a ductile steel, called a low-temperature high-tensile steel (EH36), using average stress triaxiality and average normalized lode parameter, along with briefly introducing their theoretical background. It is an extension of previous works by Choung et al. (2011; 2012; 2014a; 2014b) and Choung and Nam (2013), in which a two-dimensional failure strain locus was presented. A series of tests for specially designed specimens that were expected to fail in the shear mode, shear-tension mode, and compression mode was conducted to develop a three-dimensional fracture surface covering wide ranges for the two parameters. This paper discusses the test procedures for three different tests in detail. The tensile force versus stroke data are presented as the results of these tests and will be used for the verification of numerical simulations and fracture identifications in Part II.

• Journal of the Korean institute of surface engineering
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• v.49 no.2
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• pp.159-165
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• 2016

The hydrogen has been recognized as a clean, nonpolluting and unlimited energy source that can solve fossil fuel depletion and environmental pollution problems at the same time. Water electrolysis has been the most attractive technology in a way to produce hydrogen because it does not emit any pollutants compared to other method such as natural gas steam reforming and coal gasification etc. In order to improve efficiency and durability of the water electrolysis, comprehensive studies for highly active and stable electrocatalysts have been performed. The platinum group metal (PGM; Pt, Ru, Pd, Rh, etc.) electrocatalysts indicated a higher activity and stability compared with other transition metals in harsh condition such as acid solution. It is necessary to develop inexpensive non-noble metal catalysts such as transition metal oxides because the PGM catalysts is expensive materials with insufficient it's reserves. The optimization of operating parameter and the components is also important factor to develop an efficient water electrolysis cell. In this study, we optimized the operating parameter and components such as the type of AEM and density of gas diffusion layer (GDL) and the temperature/concentration of the electrolyte solution for the anion exchange membrane water electrolysis cell (AEMWEC) with the transition metal oxide alloy anode and cathode electrocatalysts. The maximum current density was $345.8mA/cm^2$ with parameter and component optimization.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.1
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• pp.13-18
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• 2015

This study presents the structure design of antenna to have the dual band characteristics in a desired frequency band through the structural modification of an antenna structure. For the experiment, a wideband crossed planar monopole antenna was used. The target frequency band was set to ISM 2.45GHz/5.8GHz. To give the properties, an additional antenna element was added to the crossed planar monopole antenna, which is a main body of the antenna. And then structural adjustment parameter was set to change the length(shape) of the antenna. Various simulations were conducted to find the dual band characteristics in the desired frequency band. The simulations brought forth the antenna bandwidth above the normal values for ISM 2.45GHz/5.8GHz. The structural adjustment parameter introduced in this study for structural modification of an antenna can be useful in developing an antenna featured with dual band(multiband) characteristics.

• Nuclear Engineering and Technology
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• v.54 no.10
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• pp.3855-3863
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• 2022

An evaluation of the radiation shielding performance of high-Z-particle-loaded polylactic acid (PLA) composite materials was pursued. Specimens were produced via fused deposition modeling (FDM) using copper-PLA, steel-PLA, and BaSO₄-PLA composite filaments containing 82.7, 75.2, and 44.6 wt% particulate phase contents, respectively, and were tested under broad-band flash x-ray conditions at the Sandia National Laboratories HERMES III facility. The experimental results for the mass attenuation coefficients of the composites were found to be in good agreement with GEANT4 simulations carried out using the same exposure conditions and an atomistic mixture as a model for the composite materials. Further simulation studies, focusing on the Cu-PLA composite system, were used to explore a shield design parameter space (in this case, defined by Cu-particle loading and shield areal density) to assess performance under both high-energy photon and electron fluxes over an incident energy range of 0.5-15 MeV. Based on these results, a method is proposed that can assist in the visualization and isolation of shield parameter coordinate sets that optimize performance under targeted radiation characteristics (type, energy). For electron flux shielding, an empirical relationship was found between areal density (AD), electron energy (E), composition and performance. In cases where ${\frac{E}{AD}}{\geq}2MeV{\bullet}cm{\bullet}g^{-1}$, a shield composed of >85 wt% Cu results in optimal performance. In contrast, a shield composed of <10 wt% Cu is anticipated to perform best against electron irradiation when ${\frac{E}{AD}}<2MeV{\bullet}cm{\bullet}g^{-1}$.