• 대한수학회지
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• 제58권1호
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• pp.109-122
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• 2021

In this paper, we consider the problem of finding the hypersurface Mn in the Euclidean (n + 1)-space ℝn+1 that satisfies an equation of mean curvature type, called singular minimal hypersurface equation. Such an equation physically characterizes the surfaces in the upper half-space ℝ+3 (u) with lowest gravity center, for a fixed unit vector u ∈ ℝ3. We first state that a singular minimal cylinder Mn in ℝn+1 is either a hyperplane or a α-catenary cylinder. It is also shown that this result remains true when Mn is a translation hypersurface and u is a horizantal vector. As a further application, we prove that a singular minimal translation graph in ℝ3 of the form z = f(x) + g(y + cx), c ∈ ℝ - {0}, with respect to a certain horizantal vector u is either a plane or a α-catenary cylinder.

• 대한설비공학회지:설비저널
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• 제8권2호
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• pp.73-80
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• 1979

This study describes the conduction of heat in the discharge head of air compressor. It also gives a base for a finite elements analysis of two dimenional steady -state heat conduction in the cylinder head of air cooled type reciprocating compressor. Using a single cylinder compressor operated at a given speed, tests were made observing outside temperature, final pressure and discharge temperature of air in cylinder head. As a result, the following were obtained : (1) The rate oi heat flow from the inner surface of discharge head to outside wall reach 46. 328 kcal /h at a speed of 796rpm under the constant temperature of inlet air. (2) The compression work of air increase in accordance with temperature rise of inlet air.

• 한국의류산업학회지
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• 제21권5호
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• pp.677-686
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• 2019

This study helps out-size consumers purchase ready-made clothes and improve fitness by classifying the lower bodies of abdomen-obese adult males in their 20s and older; in addition, it creates a size system based on each size interval of obesity type. The criteria for the 559 male subjects surveyed in this study were over $25kg/m^2$ of BMI, over 90 cm of waist, and over 0.85 waist hip ratio. The results are as follows. First, the higher the age group, the higher the degree of abdominal obesity in each age group. The degree of obesity then decreases somewhat as their age increases; however, the risk of abdominal obesity also increases. Second, 3 clusters were categorized by cluster analysis, into abdominal obesity, larger oval-type, trapezoid-type and small cylinder-type. Third, the size system establishment according to lower-body types resulted in basic body sizes and reference body sizes being different according to types even in commonly-appeared size names in the sections of respective types. The above research findings show it is necessary to understand obesity types according to waist and hip sizes that represent basic sizes and to design patterns in consideration of the characteristics of obese body shapes when lower-half body clothes are designed among obesity groups.

• 한국의류산업학회지
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• 제25권5호
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• pp.615-625
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• 2023

This study aimed to analyze the characteristics of the lower-body shape of middle-aged males with abdominal obesity by type and consider dimensional distribution to present a suit-pants size. The criteria were having a waist circumference greater than 90 cm and a waist-to-hip ratio(WHR) greater than 0.90; a total of 566 middle-aged males were surveyed. The findings revealed that, first, compared to standard lower-body types, the average body size of abdomenobese middle-aged males was significantly larger, especially in the horizontal area than in the vertical ares. Second, through a cluster analysis, a total of three categories of abdominal obesity were defined: small oval, large cylinder, and trapezoid type. The coverage rates of each type were 93.8%, 75.9%, and 93.0%, respectively. Finally, the suit-pants size system established according to lower-body types indicated the basic body size and reference body size were different for each type and also for the KS K 0050 male adult's garments size system. According to the definition of abdominal obesity, the types of abdominal obesity and the dimensions of each area are different, even if they belong to the same obesity group, suggesting that it is necessary to develop a pattern based on the analysis of obesity types.

• 한국자동차공학회논문집
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• 제17권1호
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• pp.105-113
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• 2009

The performance of a direct-injection type diesel engine often depends on the strength of swirl or squish, shape of combustion chamber, the number of nozzle holes, etc. This is of course because the combustion in the cylinder was affected by the mixture formation process. In this paper, combustion process of biodiesel fuel was studied by employing the piston which has several grooves with inclined plane on the piston crown to generate swirl during the compression stroke in the cylinder in order to improve the atomization of high viscosity fuel such as biodiesel fuel and toroidal type piston generally used in high speed diesel engine. To take a photograph of flame, single cylinder, four stroke diesel engine was remodeled into two stroke visible engine and high speed video camera was used. The results obtained are summarized as follows; (1) In the case of toroidal piston, when biodiesel fuel was supplied to plunger type injection system which has very low injection pressure as compared with common-rail injection system, the flame propagation speed was slowed and the maximum combustion pressure became lower. These phenomena became further aggravated as the fuel viscosity gets higher. (2) In the case of swirl groove piston, early stage of combustion such as rapid ignition timing and flame propagation was activated by intensifying the air flow in the cylinder. (3) Combustion process of biodiesel fuel was improved by the reason mentioned in paragraph (2) above. Consequently, the swirl grooves would also function to improve the combustion of high viscosity fuel.

• 한국의류산업학회지
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• 제14권2호
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• pp.269-276
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• 2012

The aim of this study is to develop clothing size system according to each size interval for obese girls aged 10~12 by classifying the upper bodies. The criteria for subjects in this study were girls who had over 1.46 of the R$\ddot{o}$hrer Index. A total of 229 schoolgirls who met these criteria were enrolled. Results are as follows; 1st, 5 factors were extracted by factor analysis and 3 clusters were categorized by cluster analysis, cylinder-type, inverted triangle-type and inverted trapezoid-type. And 2nd, as a consequence of size system establishment, the basic body sizes and reference body sizes were different according to types even in commonly-appeared size names at sections of respective types. The research findings above suggest that it is necessary to figure out the obesity types according to height and bust girth sizes representing basic sizes and to design the patterns in consideration of the characteristics of obese body shapes. And it may be used as a basic data to decide the desirable output of production according to respective body types.

• Tribology and Lubricants
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• 제28권1호
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• pp.12-18
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• 2012

This application study of a swash-plate type axial piston pump was concerned about the lubrication characteristics between cylinder barrel and valve plate which are the main rotating body and its opposite sliding part respectively. A computer simulation was implemented to assess bearing and sealing functions of the fluid film between cylinder barrel and valve plate. A numerical algorithm was developed to facilitate simultaneous calculations of dynamic cylinder pressure, 3 degree-of-freedom barrel motions considering inertia effect, and fluid film pressure assuming full fluid film lubrication regime. Central clearance, tilt angle, and azimuth angle of the rotating body were calculated for each time step. Surface waviness was found to be an influential factor due to the small fluid film thickness which can appear in flat land bearings. Five surface lays which can form on the lubrication surface in accordance with machining process were defined and analyzed using the simulation tool. Oil leakage flow and frictional torque in the fluid film between cylinder barrel and valve plate were also calculated to discuss in the viewpoint of energy loss. The simulation results showed that in actual sliding conditions proper surface non-flatness can make a positive effect on the energy efficiency and reliability of the thrust bearing.

• 한국자동차공학회논문집
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• 제19권2호
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• pp.26-34
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• 2011

Hybrid powertrain systems have been developed to improve the fuel efficiency of internal combustion engines. In the case of a parallel hybrid powertrain system, an engine and a motor are directly coupled. Because of the hardware configuration of the parallel hybrid system, friction and the pumping losses of internal combustion engines always exists. Such losses are the primary factors that result in the deterioration of fuel efficiency in the parallel-type hybrid powertrain system. In particular, the engine operates as a power consumption device during the fuel-cut condition. In order to improve the fuel efficiency for the parallel-type hybrid system, cylinder deactivation (CDA) technology was developed. Cylinder deactivation technology can improve fuel efficiency by reducing pumping losses during the fuel-cut driving condition. In a CDA engine, there are two operating modes: a CDA mode and an SI mode according to the vehicle operating condition. However, during the mode change from CDA to SI, a serious fluctuation of the air-fuel ratio can occur without adequate control. In this study, an air-fuel ratio control algorithm during the mode transition from CDA to SI was proposed. The control algorithm was developed based on the mean value CDA engine model. Finally, the performance of the control algorithm was validated by various engine experiments.

• KIEE International Transactions on Electrophysics and Applications
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• 제11C권4호
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• pp.113-119
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• 2001

This paper presents a model for a pin-to-cylinder discharge type ozonizer, which utilizes the superposition of surface discharge and corona discharge operation. By changing the gas flow rate, the discharge power and the number of SDO units, the characteristics of ozone concentration ( $O_{3con}$), ozone generation ( $O_{3g}$) and ozone yield ( $O_{3Y}$) were investigated. Using one SDO unit the maximum values of $O_{3con}$, $O_{3g}$ and $O_{3Y}$ were found as 8100[ppm], 1623[mg/h] and 213[g/kWh] respectively. With two SDO units the corresponding values were found as 12800[ppm], 2893[mg/h] and 248[g/kWh] respectively. Hence using two SDO units the efficiency was improved by 16[%].y 16[%].

• 오토저널
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• 제13권2호
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• pp.50-66
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• 1991

There are many factors which influence on the performance of a diesel engine. The piston bowl shape and swirl ratio are important factors to enhance the fuel-air mixing and flame propagation. In this study, calculations of the flow field in the cylinder of the diesel engine were carried out using the CONCHAS-SPRAY code for different bowl shapes and swirl ratios. In the case of constant swirl ratio, vortices which affect fuel-air mixing, evaporation and flame propagation are generated more strongly and consistently in the bowl-piston type combustion chamber than in the flat piston type. With this strong squish effect, injected fuel droplets are widely diffused and rapidly evaporated in the bowl-piston type combustion chamber. Especially a strong squish is developed and large and strong vortices are generated in the edge cutted bowl piston chamber. As the swirl ratio increases, it is found that a large and strong squish and vortices are generated in the combustion chamber and also fuel droplets are diffused into the entire combustion chamber.