• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2160-2164
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• 2008

Miniature Joule-Thomson cryocoolers have been widely used for rapid cooling of infrared detectors, probes of cryosurgery, thermal cameras, missile homing head and guidance system, due to their special features of simple configuration, compact structure and rapid cool-down characteristics. The cool-down time, the temperature at the cold end, the running time and the gas consumption are the important indicators of the performance of the J-T cryocooler. In this study, the initial cool-down stages of the J-T cryocooler were investigated by numerical simulations. The results show the effects of the initial charging pressures of gas on the cool-down time and the temperature at the cold end and the gas consumptions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.2 no.1
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• pp.63-73
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• 1990

A numerical analysis of initial unsteady state flow and heat transfer in an enclosed cavity has been performed by the Modified QUICK Scheme. The stable QUICK Scheme which modified the coefficient always to be positive is included in this numerical analysis. The implicit method is applied to solve the unsteady state flow; between iterations the PISO (Pressure - Implicit with Splitting of Operators) algorithm is employed to correct and update the velocity and pressure fields on a staggered grid. The accuracy of the Modified QUICK Scheme is proved by applying fewer grid systems than those which Ghia et al. and Davis applied. The initial unsteady mixed convection in an enclosed cavity is analyzed using the above numerical procedure. This study focuses on the development of the large main vortex and secondary vortex in forced convection, the effects of the Rayleigh Number in natural convection and the relative direction of the forced and natural convection.

• International Journal of Automotive Technology
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• v.6 no.2
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• pp.79-85
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• 2005

This work is to investigate the surface heat flux and combustion characteristics of premixed propane mixture in a constant volume chamber. The experiment of heat flux and combustion characteristics of premixed propane mixture are performed with various equivalence ratio and initial pressure conditions. Based on the experimental results, it is found that the maximum instantaneous temperature is increased with the increase of initial pressure in the chamber. There are significant differences in the burning velocity of premixed propane mixture at different measuring points in the constant volume combustion chamber. A]so, the trends of temperature difference at each measuring points are similar to the burning velocity in the combustion chamber. It is concluded that the total heat loss during the combustion period is affected by the equivalence ratio and the initial condition of fuel-air mixture.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.575-586
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• 2008

The main objective of this paper is to develop an improved model for the analysis of liquefaction potential and to predict excess pore pressure (EPP) using the proposed model that can simulate behavior of saturated sand under earthquake loading conditions. The damage concept is adopted for the development of the proposed model. For the development of the model, a general formulation based on experimental results and damage potential using cumulative absolute velocity (CAV) is proposed for a more realistic description of dynamic responses of saturated sand. Undrained dynamic triaxial tests are conducted using earthquake loading conditions. Based on test results, the NCER-NCW function in terms of $w_d$ and CAV is developed. Procedure for the evaluation of EPP and determination of model parameters for the proposed model is presented as well. For the determination of initial liquefaction, the minimum curvature method using the NCS-NCW curve is proposed. It is observed that predicted initial liquefaction using the proposed method agrees well with measured initial liquefaction. From results of additional undrained dynamic triaxial tests, it is seen that predicted EPP generation using the proposed model agrees well with measured results for earthquake loading cases.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1224-1227
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• 2006

It has been recognized unsaturated soil behaviour playing an important role in geomechanics. Up to now, only a few experimental data are available for the technical difficulties related to both volume changes and suction measurements. In this study, the volume changes of unsaturated compacted silty soil were monitored with proximeter (i.e. non-contactable transducer) during various triaxial compression tests, which gave a realistic estimation in the volume changes of unsaturated soil sample. The measurement of volume changes were performed with 0.5% of the maximum error under the axial strain ratio of less than 10%. The experimental results have revealed that the mechanical behaviour of unsaturated soil can be significantly affected by the matric suction. During the shearing processes, the level of maximum deviator stress under the initial suction pressure of 50kPa was higher than that under the initial suction pressure of 10kPa. On the other hand, the volume changes became smaller under the increase in the initial suction pressure.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.5
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• pp.747-753
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• 2006

Air flotation is a solid-liquid separation process that utilizes up-flow microbubbles to thicken activated sludge and enhance clarification efficiency. Continuous air flotation experiments were performed to investigate the effect of operation parameters such as initial MLSS (mixed liquor suspended solid) concentration, air pressure, surface loading rate, air to solid (A/S) ratio, and flotation time on thickening efficiency. An initial activated sludge concentration ranged from 3,000 to 12,000mgSS/L and thickened sludge concentration varied from 6,400 to 28,100mgSS/L. The result showed that the thickening efficiency was mainly dependent on surface loading rate, A/S ratio, and flotation time. The pressure did not affect the thickening efficiency when it kept in the range of 1.6 to 1.8 bar. Experimental results showed that the thickening efficiency of activated sludge was increased only when the feed sludge concentration exceeded 5,000mgSS/L and the thickened concentration was over 20,000mgSS/L. At this time, SS concentration in the clarified liquid was ranged from 5 to 10mg/L.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.4
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• pp.289-298
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• 2011

This paper provides procedures to effectively determine arrangement of hydraulic type top-bracings, which are popular for the main engine of the mid and large sized commercial vessels. Analyzing the operation mechanism of hydraulic top-bracing, ideal unified nonlinear stiffness curve is presented for linear frequency response analysis and nonlinear transient response analysis. Nonlinear stiffnesses of the curve are determined based on the regression analysis of test results. It is noted from linear frequency response analysis, initial setting pressure is most important among the setting values of the other stiffness intervals. From transient response analyses for two top-bracing arrangement scenarios, it is recognized that, as far as initial setting pressure is well controlled for the concerning vessels, only two top-bracings are enough to suppress H-mode excitation forces from main engine.

• Proceedings of the Korean Geotechical Society Conference
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• 1998.04a
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• pp.37-46
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• 1998

Several researchers have developed a number of theoretical time factors to determine the coefficient of consolidation by biezocone excess pore water dissipation test in soft clay deposits. However, depending on the assumptions and analytical techniques, the estimated coefficient of consolidation could be in a considerably wide range even for a specific degree of consolidation. These solutions are obtained from an initial excess porewater pressure distribution which can be determined from. either the cavity expansion theory or the strain path method. The 야ssipation of the initial excess porelvater pressure has been usally simulated by means of linear-uncoupled consolidation analysis and then the dissipation curve is normalized by the initial excess porewater pressure for easy use. However. since there is no guidelines or rules on which method gives the best solution for obtaining the coefficient of consolidation from the dissipation curve, the final selection was only based on engineer's extrience and Judgements. Thus, such an arbitrary selection might be inappropriate for a specific site to characterize the consolidation behavior. In this paper, we reviewed various theoretical time factors and, based on this consideration, we mentioned needs for researches in selecting a specific solution that is compatible for Korean clays. Also we listed some source of errors that can be encountered in the procedure of dissipation analysis.

• Journal of Korean Association for Spatial Structures
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• v.21 no.4
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• pp.49-56
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• 2021

This study aims to develop a form-finding algorithm for a single-layered pneumatic membrane. The initial shape of this pneumatic membrane, which is an air-supported type pneumatic membrane, is to find a state in which a given initial tension and internal pneumatic pressure are in equilibrium. The algorithm developed to satisfy these conditions is that a nonlinear optimization problem based on the force method considering the deformed shape is formulated, and, it's able to find the shape by iteratively repeating the process of obtaining a solution of the governing equations. An computational technique based on the Gauss-Newton method was used as a method for obtaining solutions of nonlinear equations. In order to verify the validity of the proposed form-finding algorithm, a single-curvature pneumatic membrane example and a double-curvature air pneumatic membrane example were adopted, respectively. In the results of these examples, it was possible to well observe the step-by-step convergence process of the shape of the pneumatic membrane, and it was also possible to confirm the change in shape according to the air pressure. In addition, the calculation results of the shape and internal force after deformation due to initial tension, air pressure, and self-weight were obtained.

• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4607-4616
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• 2023

We implement machine learning regression models to predict peak pressures of primary and secondary systems, a major safety concern in Loss Of Condenser Vacuum (LOCV) accident. We selected the Multi-dimensional Analysis of Reactor Safety-KINS standard (MARS-KS) code to analyze the LOCV accident, and the reference plant is the Korean Optimized Power Reactor 1000MWe (OPR1000). eXtreme Gradient Boosting (XGBoost) is selected as a machine learning tool. The MARS-KS code is used to generate LOCV accident data and the data is applied to train the machine learning model. Hyperparameter optimization is performed using a simulated annealing. The randomly generated combination of initial conditions within the operating range is put into the input of the XGBoost model to predict the peak pressure. These initial conditions that cause peak pressure with MARS-KS generate the results. After such a process, the error between the predicted value and the code output is calculated. Uncertainty about the machine learning model is also calculated to verify the model accuracy. The machine learning model presented in this paper successfully identifies a combination of initial conditions that produce a more conservative peak pressure than the values calculated with existing methodologies.