• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.546-551
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• 2001

In this paper, an algorithm to improve the optimal engine operation is suggested by increasing the CVT shift speed. By rearranging the CVT shift dynamic equation, it is found that the CVT shift speed depends on the line pressure as well as the primary pressure. Based on the shift dynamics, an algorithm to accomplish a faster shift speed is presented by increasing the line pressure. In order to apply the algorithm, dynamic models of the line pressure control valve and the ratio control valve are obtained by considering the CVT shift dynamics and model based controllers are designed. It is found from the simulation results that fuel economy can be improved by 2% in spite of the increased hydraulic loss due to the increased line pressure.

• 한국정밀공학회지
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• 제32권3호
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• pp.269-277
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• 2015

Compressed natural gas (CNG) composite vessels for vehicles have been generally made of 34CrMo4 for a inner liner part and E-glass/epoxy for a composite layer part. But, there is a problem of material loss of CNG composite vessels used in vehicles due to the design of excessive thickness of the liner. And, light weight of the CNG composite vessel is required for improving fuel efficiency. In this study, optimal design for CNG composite pressure vessel was performed by using basalt fiber, which is the environment-friendly material having a good mechanical strength. The optimal thickness of each part (inner liner and composite layer) was determined by theoretical analysis and FEA for satisfying structural safety and lightweight of the vessel. Also, for improving fatigue life, optimal autofrettage pressure was derived from FEA results.

• 대한물리의학회지
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• 제9권3호
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• pp.301-305
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• 2014

PURPOSE: The purpose of this study was to determine the optimal thresholds of serum lipid level related to hypertension according to age in Korean adults. METHODS: In total, 564 adults who visited the health examine center in general hospital were included. The blood pressure and lipid profiles of low density lipoprotein cholesterol(LDL), high density lipoprotein cholesterol (HDL), triglyceride(TG) were measured. Receiver operating characteristic (ROC) curve were used to establish optimal thresholds between blood pressure and lipid profiles. RESULTS: The optimal TG cutoff value were 110.50(mg/dl) in the 18-39 and 81.50(mg/dl) in the 40-59 age group, and optimal cutoff value of LDL were 126.50(mg/dl) in the 40-59 age group and 111.00(mg/dl) in the 60 and over age group. There was a negative correlation between HDL and hypertension, a higher HDL decreased hypertension. The optimal cutoff value of HDL was 49.50(mg/dl) in the 18-39 age group. CONCLUSION: The thresholds of hypertension were lower in LDL and TG with aging. This result indicated that elderly people needs to concern more about their lipid profiles to maintain healthy cardiovascular function.

• 소성∙가공
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• 제19권5호
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• pp.277-282
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• 2010

Magnesium alloy has been known as lightweight material in automobile and electronic industry with aluminum alloy, titanium alloy and plastic material. Friction welding is useful to join various metals and nonferrous metals that are difficult to join by such as gas welding, resistance welding and electronic beam welding. In this study, friction joining was performed to investigate mechanical properties of Mg alloy with 20mm diameter solid bar. Also the optimal joining conditions for its application were determined on the basis of tensile test, and hardness survey. The joining parameters were chosen as heating pressure, heating time, upsetting pressure, and upsetting time. Heating and upsetting pressure were executed under the range of 10~40MPa and 20~80MPa, respectively. From the experimental results, optimal joining conditions were determined as follows; rotating speed=2000rpm, heating pressure=35MPa, upsetting pressure=70MPa, heating time=1sec, upsetting time=5sec. Also the hardness of jointed boundary showed as HV50 which was similar to that of base metal at the optimal condition, and it was supposed that zone of HAZ was 8mm. Finally two materials were strongly mixed at interface part to show a well-combined microstructure without particle growth or any defect.

• 설비공학논문집
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• 제21권6호
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• pp.333-339
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• 2009

The objective of this study is to predict optimal intermediate pressure of a 2-stage compression heat pump system using river water. To determine the maximum performance of the 2-stage compression heat pump system, the experimental evaluations on the 2-stage compression cycle were carried out under various operating conditions. Electronic expansion valves were applied to control intermediate pressure and superheat. Based on the experimental data, an empirical correlation for predicting optimal intermediate pressure which considering cycle operating parameters was developed. The present correlation was verified by comparing the predicted data with the measured data. The predictions showed a good agreement with the measured data within a relative deviation of ${\pm}4%$ at various operating conditions.

• 한국산업융합학회 논문집
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• 제25권1호
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• pp.131-139
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• 2022

The exchange of goods over the sea is a situation in which the amount of trade between countries is gradually increasing. In order to maintain the optimal operating condition, the ship maintains stability and optimal operating conditions by inserting or withdrawing ballast water from the ballast tank according to the loading condition of cargo capacity is also increasing. Control valves play an important role in controlling fluid flow in these pipes. When the flow rate is controlled using a control valve, problems such as cavitation, flashing, and suffocating flow may occur due to high differential pressure, and in particular, damage to valves and pipes due to cavitation is a major problem. Therefore, in this study, the cavitation phenomenon is reduced by installing orifices at the front and rear ends of the high differential pressure control butterfly valve to reduce the sudden pressure drop at the limiting part of the butterfly valve step by step. The flow coefficient according to the shape of the orifice, the degree of cavitation occurrence, and the correlation were analyzed using a CFD(Cumputational Fluid Dynamics), and an optimal orifice design for reducing cavitation is derived.

• 한국식품조리과학회지
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• 제24권2호
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• pp.188-197
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• 2008

This study was carried out to determine the optimal cooking conditions for various rice cultivars (Ilpoom, Saechucheong, Sindongjin, and Sura-top rice) using trial preparations with different soaking times (0, 30, and l20min) and cooking equipment (electric pressure cookers, electric cookers, gas pressure cookers, iron pots, and stone pots). In adddition, the texture and sensory characteristics of the rice prepared with the electric pressure cookers, gas pressure cookers, and stone pots were analyed. The results showed that the moisture, amylose and physicochemical compositions of the four rice varieties were similar. According to RVA, the Sura, cultivar had generally high viscosity, and the Ilpoom, cultivar presented the highest hot and peak viscosities. Saechucung had the highest initial gelatinizing temperature and Sindongjin showed the greatest setback. The optimal amounts of added water as well as heating conditons were dependent on the rice varieties, soaking times, and cooking equipment. A longer soaking time reduced the hardness of the cooked rice, amount of added water, and the heating time. The pressure cooking equipment provided the best cooked rice texture, reduced the affect of the soaking time, and decreased the heating time. In general, all the variaties of cooked rice had high overall acceptability, which tended to increase when the rice was soaked for 30min prior to cooking, had a 1.2-fold amount of water to rice added, and was cooked in the pressure equipment.

• Journal of Advanced Marine Engineering and Technology
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• 제35권7호
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• pp.891-898
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• 2011

The present work was conducted to get the best geometric information for the optimum design of the complex heat exchanger. The objective function for optimal design was expressed as a combination of pressure drop and heat transfer rate. The geometric parameters for the variables of louver pitch and height, tube width, etc., were limited to ranges set by manufacturing conditions. The optimum geometric parameters were calculated by using empirical correlations and theory. The sensitivity of the parameters and optimum values are shown and discussed. The weighting factor in the objective function is important in the selection of the louver fin-tube heat exchanger.

• Journal of Welding and Joining
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• 제4권1호
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• pp.32-39
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• 1986

This paper was studied about the influence of oxidized films on workability in cold pressure welding. In preceding studies, the principal foci of the studies about pressure welding were considered several factors(surface manufacturing methods, surface roughness, pressure welding speed and surface temperature). But the influence to the growth of oxidation have hardly known well. So the purpose of this paper consists in solving the question above and proposing the optimal states of the pressure welding. Therefore the results obtained is as the following; When the oxidation time is within about 2 minutes, the bonding strength is very good after surface manufacturing of the neighboring to be bonded. The more surfaces are fine the more bonding strength is excellent. Above all, the optimal condition of cold pressure welding is the state that the characteristic value is 38% with smooth surface and without oxidation.

• 한국유체기계학회 논문집
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• 제13권2호
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• pp.30-35
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• 2010

Pressure characteristics according to the duct shapes of turbo blowers connected in serial have been performed to reduce pressure loss in the piping system. To analyze three-dimensional flow field in the turbo blower system, general analysis code, CFX, is introduced in the present work. SST turbulence model is applied to estimate the eddy viscosity. Throughout the numerical simulation for the turbo blower system having a various shape of a inlet guide, optimal inlet guide can be selected. It is found that the pressure loss in the piping system having the optimal inlet guide can be reduced by minimizing the inflow distortion at the upstream of the impeller. Detailed flow analysis of the blower system serially connected is also performed and analyzed.