• 설비공학논문집
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• 제16권11호
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• pp.1092-1100
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• 2004

This paper presents the effect of opening configuration on the thermal behavior and air pattern of earth tube system. The earth tube system is a fresh air load reduction system by using underground double floor space for air-conditioning. In order to analyze the effect of opening configuration on thermal performance of this system and air pattern in underground double floor space quantitatively, we used a model dealing with tree-dimensional profile of wind velocity and temperature in underground double floor space. In conclusion, it is confirmed that heat exchange of a fresh air is mainly performed with upper and lower wall in underground double floor space, and that heat exchange area increased by installing the opening near the wall.

• 대한조선학회논문집
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• 제58권3호
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• pp.144-157
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• 2021

Brake Horse Power (BHP) reduction ratios by air injection to the underside of the hull surface in an actual ship are predicted using an unstructured finite-volume CFD solver and compared with the sea trial results. In addition, air lubrication system installed on the existing vessel is investigated to find a good solution for additional drag reduction. As a results, it is found that the thickness of the air layer should be minimized within a stable range while securing the area covered by the air layer as much as possible. Furthermore, the amount of frictional drag reduced by air injection is found to be independent of surface roughness and still effective on rough surface. Based on the results of this study, it is expected that systematic and reliable air lubrication system can be designed and evaluated using the proposed method.

• 한국정밀공학회지
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• 제11권1호
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• pp.123-128
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• 1994

A high speed spindle system for machine tools can be used to reduce the machining time, to improve the machining accuracy, to perform the machining of light metals and hard materials, and to unite the cutting and grinding processes. In this study, a high speed spindle system is developed by applying the oil-air lubrication method, angular contact ball bearings, injection nozzles with dual orifices, cooling jacket and so on. And an air cooling experiment for evaluating the performance of the spindle system is carried out. Especially, in ofder to establish the air cooling conditions related to the development of a high speed spindle system, the effects of cooling air pressure, oil supply rate, air supply rate and rotational spindle speed are studied and discussed on the bearing temperature rise and frictional torque. Also the effects of cooling air pressure, rotational spindle speed and spindle system structure is investigated on the bearing temperature distribution. The experiment on the test model reveals the usefulness of the air cooling method.

• 무역학회지
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• 제46권1호
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• pp.135-154
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• 2021

This study aims to investigate the difference in the perception of shippers on the quality of air freight service between air express and air freight forwarders. This study suggests hypothesis verification and implications on importance-performance between two groups of air express and air freight forwarders. In this study, we find that important variables through paired t-test and importance-performance analysis. As a result of paired t-test, there was a difference in the use variables of the document work variables through computerization in the importance area. In the satisfaction area, there was a difference between the groups in the response to customer request and the response to accidents. The variables that need to improve the focus derived from the importance-performance analysis are document work through computer and response to accidents. It is necessary to observe and manage the response of shippers continuously by holding various transportation schedules in the schedule area, possibility of adjustment of transportation schedule, regular freight and schedule provision.

• 한국정밀공학회지
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• 제25권1호
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• pp.72-78
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• 2008

Metal stamping is widely used in the mass-production process of the automobile. During the stamping process, air may be trapped between the draw die and the panel and/or between the punch and the panel. Air pocket rapidly not only increases forming load in the final stage, but also deforms the product just formed by compressive air inside the air pocket in knockout process. To prevent these problems air bent holes are drilled in the die to exhaust the trapped air but all processes associated with air bent holes are performed by empirical know-how of workers in the field due to lack of researches. Therefore this study developed an automated design system for predicting the shape and position, and volume of air pocket on the draw die by using the AutoLISP language under AutoCAD circumstance. The system is able to display the shape of air pocket occurred in the draw die and to calculate automatically its volume by strokes. So it makes a stepping stone to calculate theoretical size of an air bent hole and numbers according to it by predicting and analyzing the position and volume of air pocket. Results obtained from the system enable the designers or manufacturers of the stamping die to be more efficient in this field.

• 한국분무공학회지
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• 제28권4호
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• pp.198-206
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• 2023

In this study, visualization of in-cylinder spray behavior and spark channel stretching by air flow characteristics depending on engine operating conditions were investigated. For in-cylinder spray behavior, increase in engine rpm did not alter the counter-clockwise air flow direction and location of in-cylinder dominant air flow but increased average air flow velocity, which hindered spray propagation parallel to the piston surface. When injection timing was retarded, direction of in-cylinder dominant air flow was changed, and average air flow velocity was reduced resulting in an increase in spray penetration length and change in direction. For spark channel stretching, increase in air flow speed did not affect spark channel stretch direction but affected length due to increase in spark channel resistance and limitation of energy ignition coil can handle. Change in air flow direction affected spark channel stretch direction where the air flow was obstructed by ground electrode which caused spark channel direction to occur in the opposing direction of air flow. It also affected spark channel stretch length due to change in air flow speed around the spark plug electrode from the interaction between the air flow and ground electrode.

• 대한치과보철학회지
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• 제14권1호
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• pp.47-54
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• 1976

Pulpal temperature is changed in response for various conditions which were mechanical, thermal, chemical and biological stimuli. This study was performed to determine the pulpal temperature changes which were using air turbine with air-water coolant, water coolant, and conventional dental engine with water coolant and no coolant on 28 canine of dogs. In order to record pulpal temperature, pulp chamber was opened on the labiocervical area of canine. Thermocouple was inserted into pulp chamber and was fixed with filling material(dycal). Changes of pulpal temperature were recorded on the physiograph, which had been standardized temperature degree, through thermocouple to thermistor bridge and carrier preamplifier. The amount of experimental temperature change to that of control was interpreted in the pulpal cavity. The obtained results were as followings: 1. The mean normal temperature was 33.07 centigrade. 2. The temperature was decreased than normal pulpal temperature. It was 12.04 centigrade in reduction by air turbine with air-water coolant, 7.17 centigrade in reduction by air turbine with air coolant, 5.54 centigrade in reduction by conventional engine with water coolant, and 1.26 centigrade in reduction by conventional engine with no coolant. 3. The time for maximal temperature change was 53.3 seconds in reduction by air turbine with air-water coolant, 73.4 seconds in reduction by air turbine with air coolant, 50.9 seconds in reduction by conventional engine with water coolant, and 27.1 seconds in reduction by conventional engine with no coolant. 4.. After reduction was ceased, the recovery time to normal pulp temperature was 287.1 seconds in air turbine with air-water coolant, 189.0 seconds in air turbine with air coolant, 86.9 seconds in conventional engine with water coolant, and 52.9 seconds in conventional engine with no coolant respectively.

• 설비공학논문집
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• 제26권12호
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• pp.553-558
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• 2014

Geothermal energy can be used with a geothermal heat pump or an earth-to-air heat exchange system (EAHES), which is referred to as a "cooling tube" in Korea. In this study, we suggest EAHES burial guidelines in terms of the parameters of buried pipe length and air velocity regarding the exit air temperature of EAHES. The exit air temperature for EAHES in three regions (Changwon, Busan and Seoul) was calculated with variation in buried pipe length and air velocity at ${\Phi}100mm$ and ${\Phi}200mm$. In conclusion, variation in the buried pipe length is more effective than that of air velocity to achieve the required exit air temperature.

• 환경영향평가
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• 제16권4호
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• pp.267-275
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• 2007

In this study, relationship between the air pollution of Siheung city and the relative contribution of automobiles to the city's pollution was evaluated for the first time. Then, new air pollution exposure index was developed through simulation. Using the newly developed index, two different urban development scenarios were compared to present a sustainable urban development plan to reduce air pollution from the land utilization point of view. According to the result of this simulation, air quality of the city was found to be affected significantly by human activities. More populated area showed worse level of air quality. Any development in the city resulted in more automobile activity and deterioration of air quality. This simulation result thus explains that a rapid increase of automobiles accompanied by the land development near local roadsides in the city is the major cause of air pollution in Siheung city. In this study, if urban activities are vigorous in an area with high air pollution, people are more likely to be exposed to air pollutant under the bad environmental conditions. On the other hand, if urban activities are less vigorous in an area with high pollution or if urban activities are vigorous in an area with less pollution, the environmental condition was positive. The APEI (Air Pollution Exposure Index) was developed based on these considerations. Scenarios 1 and 2 were compared and analyzed using APEI. In result, scenario 1 is the case in which land is developed and used in an environmentally favorable manner. From this study, it was proved that the impact of air pollution on human health can be minimized with proper land use. The result form the current study can be used as the basic information to solve problems from improper land utilization and air pollution (by road traffic). It also can be utilized to evaluate air pollution level according to land use and road characteristics and to help to choose the best location of land use to comply with the road function and status.

• 대한조선학회논문집
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• 제48권5호
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• pp.396-403
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• 2011

The concept of an air lubrication has long been an object of attention since it can be utilized to reduce the frictional resistance, and what is more, it is eco-friendly. The present study examines the basic characteristics of an air cavity with intention of applying the air lubrication technology to the reduction of the resistance of a ship without excessive power increment. For the purpose, an air cavity was created at the bottom of a flat plate by injecting air behind a backward step and the hydrodynamic properties of the air cavity and the surrounding flow has been investigated experimentally and numerically. The influence of the step height and the air flow rate have been more carefully studied since they are presumed to be the main parameters affecting the characteristics of an air cavity. The results indicates that the shapes of the air cavities attached on the flat plate become "U" or "V" type depending on the incoming flow velocity and air flow rate. The study also confirms that the length of the air cavity increases with increase in air flow rate but there is a certain critical limit in the flow rate above which increase in the air cavity length is no more evident.