• Journal of Mechanical Science and Technology
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• 제19권9호
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• pp.1790-1800
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• 2005

The examination on the operating mechanism of a pulsating heat pipe (PHP) using visualization revealed that the working fluid in the PHP oscillated to the axial direction by the contraction and expansion of vapor plugs. This contraction and expansion is due to the formation and extinction of bubbles in the evaporating and condensing section, respectively. In this paper, a theoretical model of PHP was presented. The theoretical model was based on the separated flow model with two liquid slugs and three vapor plugs. The results show that the diameter, surface tension and charge ratio of working fluid have significant effects on the performance of the PHP. The following conclusions were obtained. The periodic oscillations of liquid slugs and vapor plugs were obtained under specified parameters. When the hydraulic diameter of the PHP was increased to d=3mm, the frequency of oscillation decreased. By increasing the charging ratio from 40 to 60 by volume ratio, the pressure difference between the evaporating section and condensing section increased, the amplitude of oscillation reduced, and the oscillation frequency decreased. The working fluid with higher surface tension resulted in an increase in the amplitude and frequency of oscillation. Also the average temperature of vapor plugs decreased.

• Journal of Chest Surgery
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• 제21권2호
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• pp.246-253
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• 1988

An in vitro model providing with a recirculating perfusion apparatus using an isolated canine heart and its autogenous blood, which was prepared for study of myocardial protection method. This apparatus was easily used by quick connect system and maintained well heart function for about 2 hours. The Langendorff perfusion was initiated for a 10 minute period by introducing perfusate at 37` into the aorta from aortic reservoir located 100 cm above the heart. The isolated perfused working canine heart model was a left heart preparation in which oxygenated perfusion medium [at 37K] entered the cannulated left atrium at a constant flow rate [900ml/ min] under 20 mmHg overflow system and was spontaneously ejected[no electrical pacing] via an cannula against a hydrostatic pressure of 80 cm H2O. During this working period, various indices of cardiac function were measured. The cardiac functions were stable for over 2 hours with perfusion of Krebs-Henseleit solution and autologous blood[1:1] mixture in volume and maintained heart rate ]]3-122/bpm peak systolic pressure 109-113 mmHg, cardiac output 900 ml / min and left atrial mean pressure 8-9 mmHg. In this model, the efficiency of myocardia] protection could be easily measured by means of functional, enzymatic, biochemical and ultrastructural assessment. And also, we believe this model to be a useful assessment screening model of recovery state after long duration of myocardial preservation of donor heart without difficult transplantation procedures.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 한국항해항만학회 2023년도 춘계학술대회
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• pp.57-58
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• 2023

The working time for loading and transporting containers in the container terminal is one of the factors directly related to port productivity, and minimizing working time for these operations can maximize port productivity. Among working time for container operations, the working time of yard tractors(Y/T) responsible for the transportation of containers between berth and yard is a significant portion. However, it is difficult to estimate the working time of yard tractors quantitatively, although it is possible to estimate it based on the practical experience of terminal operators. Recently, a technology based on IoT(Internet of Things), one of the core technologies of the 4th industrial revolution, is being studied to monitoring and tracking logistics resources within the port in real-time and calculate working time, but it is challenging to commercialize this technology at the actual port site. Therefore, this study aims to develop yard tractor working time prediction model to enhance the operational efficiency of the container terminal. To develop the prediction model, we analyze actual port operation data to identify factors that affect the yard tractor's works and predict its working time accordingly.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제11권4호
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• pp.549-559
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• 1999

An experimental study was peformed to measure the viscosity of microencapsulated PCM slurries as the functions of its concentration and temperature, and also influence to its fluid dynamics. For the viscosity measurement, a rotary type viscometer, which was equipped with temperature control system, was adopted. The slurry was mixed with water and Sodium Lauryl Sulphate as a surfactant by which its suspended particles were dispersed well without the segregation of particles during the experiment. The viscosity was increased as the concentration of MicroPCM particle added. The surfactant increased 5% of the viscosity over the working fluid without particles. Experiments were proceeded by changing parameters such as PCM particles'concentration as well as the temperature of working fluid. As a result, a model to the functions of temperature for the working fluid and its particle concentration is proposed. The proposed model, for which its standard deviation shows 0.8068, is agreed well with the reference's data. The pressure drop was measured by U-tube manometer, and then the friction factor was obtained. It was noted that the pressure drop was not influenced by the state of PCM phase, that is solid or liquid in its core materials at their same concentration. On the other hand, it was described that the pressure drop of the slurry was much increased over the working fluid without particles. A friction factor was placed on a straight line in all working fluids of the laminar flow regardless of existing particles as we expected.

• Journal of the Korean Data and Information Science Society
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• 제24권3호
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• pp.651-658
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• 2013

For the marginal model and generalized estimating equations (GEE) method there is important full covariates conditional mean (FCCM) assumption which is pointed out by Pepe and Anderson (1994). With longitudinal data with time-varying stochastic covariates, this assumption may not necessarily hold. If this assumption is violated, the biased estimates of regression coefficients may result. But if a diagonal working correlation matrix is used, irrespective of whether the assumption is violated, the resulting estimates are (nearly) unbiased (Pan et al., 2000).The quadratic inference functions (QIF) method proposed by Qu et al. (2000) is the method based on generalized method of moment (GMM) using GEE. The QIF yields a substantial improvement in efficiency for the estimator of ${\beta}$ when the working correlation is misspecified, and equal efficiency to the GEE when the working correlation is correct (Qu et al., 2000).In this paper, we interest in whether the QIF can improve the results of the GEE method in the case of FCCM is violated. We show that the QIF with exchangeable and AR(1) working correlation matrix cannot be consistent and asymptotically normal in this case. Also it may not be efficient than GEE with independence working correlation. Our simulation studies verify the result.

• Journal of Biosystems Engineering
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• 제17권1호
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• pp.37-44
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• 1992

This study was intended to develop the design program of the working surface of moldboard-plow by use of the computer-aided design. The mathematical model of the working surfaces of moldboard-plows by use of computer graphics was developed and plotted in two dimension on three major planes. The surfaces of moldboard-plows were represented with "B-spline surface fitting" by selecting the twenty-five three-dimensional data that could well describe the working surface of moldboard-plow. The shape of moldboard-plow on three major planes was drawn for varied design parameters. The representation of the mathematical model for the working surfaces of various types of moldboard-plows was manipulated by translation, rotation and scaling about arbitrary axes in space. By using three-dimensional graphics techique to describe moldboard-plows, it was capable of plotting the three-dimensional shape of moldboard-plow easily and quickly in comparison with the existing design methods that were difficult to grasp the shape of moldboard-plow as a whole. The design theories of moldboard plow and three-dimensional computer graphic technique were applied to find out the improved reversible Jaenggi bottom. It was resulted in the newly developed shape of Jaenggi which may be used for improving the performance compared to existing ones.

• Journal of Korean Society of Industrial and Systems Engineering
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• 제43권1호
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• pp.61-69
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• 2020

Systems such as database and socal network systems have been broadly used, and their unexpected failure, with great losses and sometimes a social confusion, has received attention in recent years. Therefore, it is an important issue to find optimal maintenance plans for such kind of systems from the points of system reliability and maintaining cost. However, it is difficult to maintain a system during its working cycle, since stopping works might incur users some troubles. From the above viewpoint, this paper discusses minimal repair maintenance policy with periodic replacement, while considering the random working cycles. The random working cycle and periodic replacement policies with minimal repair has been discussed in traditional literatures by usually analyzing cases for the nonstopping works. However, maintenance can be more conveniently done at discrete time and even during the working cycle in real applications. So, we propose that periodic replacement is planned at discrete times while considering the random working cycle, and moreover provide a model in which system, with a minimal repair at failures between replacements, is replaced at the minimum of discrete times KT and random cycles Y. The average cost rate model is used to determine the optimal number of periodic replacement.

• Journal of Mechanical Science and Technology
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• 제19권8호
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• pp.1662-1669
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• 2005

Boiling heat transfer characteristics of a two-phase closed thermosyphons with various helical grooves are studied experimentally and a mathematical correlation is developed to predict the performance of such thermosyphons. The study focuses on the boiling heat transfer characteristics of two-phase closed thermosyphons with copper tubes having 50, 60, 70, 80, 90 internal helical grooves. A two-phase closed thermosyphon with plain copper tube having the same inner and outer diameter as those of grooved tubes is also tested for comparison. Water, methanol and ethanol are used as working fluid. The effects of the number of grooves, various working fluids, operating temperature and heat flux are investigated experimentally. From these experimental results, a mathematical model is developed. In the present model, boiling of liquid pool in the evaporator is considered for the heat transfer mechanism of the thermosyphons. And also the effects of the number of grooves, the various working fluids, the operating temperature and the heat flux are brought into consideration. A good agreement between the boiling heat transfer coefficient of the thermosyphon estimated from experimental results and the predictions from the present mathematical correlation is obtained. The experimental results show that the number of grooves, the amount of the working fluid and the various working fluids are very important factors for the operation of thermosyphons. Also, the thermosyphons with internal helical grooves can be used to achieve some inexpensive and compact heat exchangers in low temperature.

• Special Issue of the Society of Naval Architects of Korea
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• 대한조선학회 2008년도 특별논문집
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• pp.112-117
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• 2008

The Insulation, which is consist of the glass wool, mineral wool or perforated SUS plate, installed on the wall or under ceiling for the protecting heat and the blocking the noise of engine room area. In our shipyard, designing the structure model of insulation is hard and difficult, Because designed the insulation model is considered of any factors which are hull model properties of panel shape, direction and thickness and service of area. In this paper, We issue the way to utilize shape and direction of the hull model information and specific character of working space in engine room.

• Journal of the Korean Society of Manufacturing Process Engineers
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• 제7권4호
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• pp.37-43
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• 2008

Working condition is one of the most important factors in precision working. In this study, we optimized the vibration acceleration level(VAL) of Al 2024 alloy to select optimum working condition of side wall end-milling using RSM(Response Surface Methodology). RSM was well adapted to make analytic model for minimizing vibration acceleration, created the objective function and saved a great deal of computational time. Therefore, it is expected that the proposed optimization procedure using RSM can be easily utilized to solve the optimization problem of working condition. The experimental results of the surface roughness and VAL showed the validity of the proposed working condition of side wall end-milling as it can be observed.