• Wind and Structures
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• v.38 no.5
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• pp.367-379
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• 2024

Compared with traditional transmission towers, T-shaped angle towers have long cross-arms and are specially used for ultrahigh-voltage direct-current (UHVDC) transmission. Nevertheless, the wind loads of T-shaped towers have not received much attention in previous studies. Consequently, a series of wind tunnel tests on the T-shaped towers featuring cross-arms of varying lengths were conducted using the high-frequency force balance (HFFB) technique. The test results reveal that the T-shaped tower's drag coefficients nearly remain constant at different testing velocities, demonstrating that Reynolds number effects are negligible in the test range of 1.26 × 10⁴-2.30 × 10⁴. The maximum values of the longitudinal base shear and torsion of the T-shaped tower are reached at 15° and 25° of wind incidence, respectively. In the yaw angle, the crosswind coefficients of the tower body are quite small, whereas those of the cross-arms are significant, and as a result, the assumption in some load codes (such as ASCE 74-2020, IEC 60826-2017 and EN 50341-1:2012) that the resultant force direction is the same as the wind direction may be inappropriate for the cross-arm situation. The fitting formulas for the wind load-distribution factors of the tower body and cross-arms are developed, respectively, which would greatly facilitate the determination of the wind loads on T-shaped angle towers.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.2
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• pp.251-259
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• 1999

A computer simulation was conducted for heat and momentum transfer in a roller kiln. Time-averaged Navier-Stokes equation conjugated with energy balance equation was numerically solved to predict the temperature distribution and fluid flow field in the roller kiln. A computer simulation was performed for a roller kiln for three cases. Firstly, when there are no ceramic materials in the roller kiln, the effect of natural convection was studied on the temperature distribution and fluid flow field. From the result, it was observed that air takes the heat of wall away from the roller kiln by natural convection and the heat was not transferred effectively. Secondly, with ceramic materials temperature difference of ceramic material from the borrom to the top of a ceramic material was about 255K in 5th zone and this is because the heat is transferred from the surface of a ceramic material to flowing air with relatively low temperature. Finally, we considered effect of radiation heat transfer. Temperature difference of ceramic material in 5th zone was about 300 K, due to radiation heat transfer on the ceramic material surfaces.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4B
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• pp.335-344
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• 2006

In this study, sequential mixing model (SMM) was proposed based on the Taylor's theory which can be summarized as the fact that longitudinal advection and transverse diffusion occur independently and then the balance between the longitudinal shear and transverse mixing maintains. The numerical simulation of the model were performed for cases of different mixing time and transverse velocity distribution, and the results were compared with the solutions of 1-D longitudinal dispersion model (1-D LDM) and 2-D advection-dispersion model (2-D ADM). As a result it was confirmed that SMM embodies the Taylor's theory well. By the comparison between SMM and 2-D ADM, the relationship between the mixing time and the transverse diffusion coefficient was evaluated, and thus SMM can integrate 2-D ADM model as well as 1-D LDM model and be an explanatory model which can represents the shear flow dispersion in a visible way. In this study, the predicting equation of the longitudinal dispersion coefficient was developed by fitting the simulation results of SMM to the solution of 1-D LDM. The verification of the proposed equation was performed by the application to the 38 sets of field data. The proposed equation can predict the longitudinal dispersion coefficient within reliable accuracy, especially for the river with small width-to-depth ratio.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.10
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• pp.1213-1222
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• 1999

A finite element method is developed for calculating the temperature and enthalpy distribution and accordingly the solid, liquid and mushy zone in a three-dimensional body subjected to any heat boundary conditions. The method concurrently consider both temperature and enthalpy for consideration of the latent heat effect, differently from other methods of using a special energy balance equation for solving a mushy zone. The developed brick element has eight nodes with one degree of freedom at each node. The numerical method and procedure are verified using the results of one and two dimensional analytic solutions and by other researchers. It is shown that the present method presents a consistent and stable results in either abrupt or ranged phase change problems. Moreover, the numerical results by the present method are hardly effected by the calculation time steps which otherwise are difficult to determine in most phase change problems. Finally, as a three-dimensional application, a T-shaped body of a phase change is presented and the temperature and enthalpy variation along the time are solved.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
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• 2003.04a
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• pp.517-522
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• 2003

Exact estimation of evapotranspiration is important to understand natural phenomena and social issues associated with the climate such as irrigation scheme, reservoir water management, and many other meteorological and climatological problems. To overcome limits of point measurement of evapotranspiration, several models have been developed through the techniques of remote sensing and Geographical Information System. SEBAL model is one of them, based on the energy balance equation, and it has a lot of advantages such as that it requires relatively small empirical relations. In this study, the SEBAL model has been calibrated and validated in Geumgang upper basin, Bochung-stream basin, Korea with 5 satellite images Landsat 5 TM. In validation, the results of SEBAL model were compared with those by Merton method. After validation, the spatial and temporal characteristics of the distribution of evapotranspiration within the basin were analyzed with 3 factors, the aspect of slope, the angle of slope, and the land cover.

• Water for future
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• v.27 no.2
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• pp.129-137
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• 1994

The surface hydrology of large land areas is susceptible to several preferred stable states with transitions between stable states induced y stochastic fluctuation. This comes about due to the close coupling of land surface and atmospheric interaction. An interesting and important issue is the duration of residence in each mode. Mean transtion times between the stable modes are analyzed for different model parameters or climatic types. In an example situation of this differential equation exhibits a bimodal probability distribution of soil moisture states. Uncertainty analysis regarding the model parameters is performed using a Monte-Carlo simulation method. The method developed in this research may reveal some important characteristics of soil moisture or precipitation over a large area, in particular, those relating to abrupt changes in soil moisture or precipitation having extremely variable duration.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.6
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• pp.408-414
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• 2018

Given that lithium-ion batteries are expected to be used as power sources for electric and hybrid vehicles, thermodynamics experimentation and prediction based on experimental data were performed. Thermal, electrochemical, and electrochemical/electrical-thermal models were used for accurate battery modeling. Various applications of different battery packs were demonstrated, and thermal analysis was performed using the same experimental conditions for square and rectangular battery packs. Accurate thermal analysis for a single cell should be prioritized to determine the thermal behavior of the battery pack. The energy balance equation, which contains heat generation and heat transfer factors, defines the thermal behavior of the battery pack. By comparing battery packs of different shapes tested under the same condition, this study revealed that the rectangular battery pack is superior to the square battery pack in terms of the maximum temperature of inner cells and temperature variation between cells.

• Geomechanics and Engineering
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• v.25 no.2
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• pp.111-121
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• 2021

Large deformation and rapid pressure propagation take place inside the rock mass under the dynamic loads caused by the explosives, on quarry faces in order to extract aggregate material. The complexity of the science of rock blasting is due to a number of factors that affect the phenomenon. However, blasting engineering computations could be facilitated by innovative software algorithms in order to determine the results of the violent explosion, since field experiments are particularly difficult to be conducted. The present research focuses on the design of a Finite Element Analysis (FEA) code, for investigating in detail the behavior of limestone under the blasting effect of Ammonium Nitrate & Fuel Oil (ANFO). Specifically, the manuscript presents the FEA models and the relevant transient analysis results, simulating the blasting process for three types of limestone, ranging from poor to very good quality. The Finite Element code was developed by applying the Jones-Wilkins-Lee (JWL) equation of state to describe the thermodynamic state of ANFO and the pressure dependent Drucker-Prager failure criterion to define the limestone plasticity behavior, under blasting induced, high rate stress. A progressive damage model was also used in order to define the stiffness degradation and destruction of the material. This paper performs a comparative analysis and quantifies the phenomena regarding pressure, stress distribution and energy balance, for three types of limestone. The ultimate goal of this research is to provide an answer for a number of scientific questions, considering various phenomena taking place during the explosion event, using advanced computational tools.

• Health Policy and Management
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• v.18 no.2
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• pp.19-38
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• 2008

Financial ratios are key indicators of an organization's financial and business conditions. Among various financial indicators, profitability, financial structure, financial activity and liquidity ratios are frequently used and analyzed. Using the structural equation modeling(SEM) technique, this study examines the structural causal relationships among key financial indicators. Data for this study are taken from complete financial statements from 142 hospitals that passed the standardization audit undertaken by the Korean Hospital Association from 1998 to 2001 for the purpose of accrediting teaching hospitals. In order to improve comparability, ratio values are standardized using the Blom's normal distribution. The final model of the SEM has four latent constructs: financial activity(total asset turnover, fixed asset turnover), liquidity(current ratio, quick ratio, collection period), financial structure(total debt to equity, long-term debt to equity, fixed assets to fund balance), and profitability(return on assets, normal profit to total assets, operating margin to gross revenue, normal profit to gross revenue). While examining several model fit indices(Chi-square (df) = 178.661 (40), likelihood ratio=4.467, RMR=.11, GFI=.849, RMSEA=.157), the final SEM we employed shows a relatively good fit. After examining the path coefficient of the constructs, the financial structure of the hospital affects the hospital's profitability in a statistically significant way. A hospital which utilizes its liabilities, more specifically fixed liabilities, and makes a stable investment decision for fixed assets was found to have a higher profitability than other hospitals. Then, the standard path coefficients were examined to directly compare the influence of variables. It was found that there were no statistically significant path coefficients among constructs. When it comes to variables, however, statistically significant relationships were found. between. financial activity and. fixed. asset turnover, and between profitability and normal profit to gross revenue. These results show that the observed variables of fixed asset turnover and normal profit to gross revenue can be used as indicators representing financial activity and profitability.

• Korean Journal of Food Science and Technology
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• v.18 no.1
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• pp.61-65
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• 1986

This study was performed to examine the drying characteristics of apples at various drying conditions. Air velocity has no effect on the drying rate except the constant rate period. In this experiment the diffusion coefficients of moisture in the apple tissue were in the range of $1.1470-2.2148{\times}10cm^2/sec$. As a result of balance of heat and mass transfer during the falling rate period. an empirical equation based on Fick's law was obtained as follows; $log{\Delta}t\;=\;log\;t_o\;-\;D{\frac{{\pi}^2{\theta}}{4d.}}$ This equation can be used to calculate the temperature of apples during the falling rate period, provided the diffusion coefficients of apple are known. The experimental values of the internal moisture distribution during apple dehydration were nearly in accord with the theoretical values.