• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.11a
• /
• pp.356-359
• /
• 2007

In this paper, the stability of a rotating cantilever pipe conveying fluid with a crack is investigated by the numerical method. That is, the influences of the rotating angular velocity, mass ratio and crack severity on the critical flow velocity for flutter instability of system are studied. The equations of motion of rotating pipe are derived using the Euler beam theory and the Lagrange's equation. The crack section of pipe is represented by a local flexibility matrix connecting two undamaged pipe segments. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. Generally, the critical flow velocity for flutter is proportional to the angular velocity and the depth of crack. Also, the critical flow velocity and stability maps of the rotating pipe system as a function of mass ratio for the changing each parameter are obtained.

• Korea-Australia Rheology Journal
• /
• v.16 no.3
• /
• pp.153-160
• /
• 2004

Open microcellular foams having small-sized cell and good mechanical properties are desirable for many practical applications. As an effort to reduce the cell size, the microcellular foams combining viscosity improvers into the conventional formulation of styrene and water system were prepared via high internal phase emulsion polymerization. Since the material properties of foam are closely related to the solution properties of emulsion state before polymerization, the flow behavior of emulsions was investigated using a controlled stress rheometer. The yield stress and the storage modulus increased as viscosity improver concentration and agitation speed increased, due to the reduced cell size reflecting both a competition between the continuous phase viscosity and the viscosity ratio and an increase of shear force. Appreciable tendency was found between the rheological data of emulsions and the cell sizes of polymerized foams. Cell size reduction with the concentration of viscosity improver could be explained by the relation between capillary number and viscosity ratio. A correlative study for the cell size reduction with agitation speed was also attempted and the result was in a good accordance with the hydrodynamic theory.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.19 no.4
• /
• pp.24-29
• /
• 2011

Conceptual study of an open-circuit type low-speed wind tunnel for performance test of wind turbine blade and airfoil is conducted. The tunnel is constituted of a settling chamber, a contraction, closed test section, a diffuser, two corners, a cross leg and a fan and motor. For the performance test, the closed test section width of 1.8 m, height of 1.8 m and length of 5.25 m is selected. The contraction ratio is 9 to 1 and maximum speed in the test section is 67 m/sec. Input power in the tunnel is about 238 kW and its energy ratio is 3.6. The wind tunnel designed in present study will be an effective tool in research and development of wind turbine and airfoil.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.04a
• /
• pp.46-49
• /
• 2008

This paper deals with the free vibrations of elastica shaped arches with constant arc length. The elastica shaped arches are formed by the post-buckled column whose arc length is always constant. The equations governing free, in-plane vibration of general arch in open literature are modified for applying the free vibrations of elastica shaped arch and solved numerically to obtain frequencies and mode shapes for hinged-hinged end constraints. The effects of rotatory inertia, rise to span length ratio and slenderness ratio on natural frequencies are presented. The frequencies of elastica and parabolic shaped arches are compared. Also, typical mode shapes are presented in figures.

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 1996.04a
• /
• pp.333-336
• /
• 1996

This paper is an exploratory study aimed at finding factors that influence the penetration of cellular mobile telecommunications which have seen rapid development since 1980s. The paper tries to find economy and policy variables to influence the penetration by means of the multiple regression analysis. This paper shows a model that explain the penetration ratio of cellular service. The model is based on data from 39 upper middle income and 39 high income countries. The result shows that GDP per capita and the service period of the cellular mobile telecommunication have influenced on the penetration ratio positively, and the tariff of the service negatively. But, it is the open area to study the impact of the telecommunications policy changes on penetration, and to set a model which could explain the nation-specific characteristics.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.1434-1437
• /
• 2003

Sometimes open holes are required for the function and the weight reduction of structure and machinery. However, the serious stress concentration occurs because of the geometric discontinuity caused by the holes and cutting section. In this study, it is attempted to obtain the stress concentration coefficients of the inner surface of the hole boundary by changing the position and the shape of holes on the homogeneous isotropic plate. And the effects on the plate are investigated. The results show that the stress level becomes low and the distribution area widens the position of stress concentration changes as the ratio a/b increases and change to a circle. And as the ratio a/l decreases, the stress concentration reduces. As the plate with three holes. the stress $\sigma$$\_$x/ and $\tau$$\_$xy/ of hole 1,3 becomes high, especially $\sigma$$\_$x/ dominant and high.

• Proceedings of the KSME Conference
• /
• 2002.08a
• /
• pp.743-746
• /
• 2002

Experimental investigation of the flow field of supersonic cavity is described. In this research, supersonic cavity is used in chemical laser system. For efficient laser, downstream flow after cavity need to be uniform and clear for pressure recovery system. In previous research, it's known that there's oscillation In cavity and is due to Mach number and L/D ratio. A strong recompression occurs at the after wall and the flow is visibly unsteady. Cavity flow in this research is of the open type, that is, length-to-depth ratio $L/D<10\;at\;M\;=\;3$. Experiment is done with pressure measurement by piezo-type sensor and visualization by Schlirern method. The time-dependent experimental result is compared with computation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1995.10a
• /
• pp.157-166
• /
• 1995

A large crank shaft for ship engine consists of several components, such as throw, jornal, pin and flange. These compoents are individually made by open-die forging followed by machining and they are thermally fitted to form the crankshaft. In the present investigation, it was attempted to design an optimum preform for the throw by use of the spread coefficient. The spread coefficient found in the literature was confirmed by comparison with experimental results using plasticine. However, the preform designed by the spread coefficient was unable to produce the final product. The reason was found that the spread coefficient differs distinctly for the magnitude of bite ratio. Therefore, another spread coefficient, especially for low bite ratios, was proposed and the preform was redesigned. It was found that the new preform was able to produce the final product.

• Journal of Chest Surgery
• /
• v.26 no.12
• /
• pp.944-949
• /
• 1993

Clinical analysis were performed on 247 cases of thoracic trauma, those were admitted & treated at the department of thoracic & cardiovascular surgery,Hanyang University Hospital during the period from Jan,1989 to June,1992. Age distribution of those was from 2 to 80 years old & mean age was 38 years old. The ratio of male to female patient was 186:61 [3:1].This ratio revealed high incidence in male patient. The most common cause of trauma was traffic accident in this series.The modes of injury were as follows: traffic accident 124 cases[50.2%],fall down 52 cases[21.05%], stab wound 47 cases[19.03%] and gun-shut wound 1 case.Ellapse time from accident to admission were 141 cases [57.09%] under 6 hr.Rib fracture were observed in 159 cases[64.37%], hemo or pneumothorax were observed 134 cases[54.25%] of total cases and location distributed Right:Left:Both[74:112:37], in left predominant. Conservative,non-operative treatment were performed in 128 cases and operation[open thoracotomy] 32 cases.Mortality was 1.6%[4 cases] & most common cause of death were due to irreversible shock with brain edema. Conclusively, more evaluation & co-operation of other department were expected treatment & better prognosis.

• Journal of the Korea Safety Management & Science
• /
• v.18 no.2
• /
• pp.119-125
• /
• 2016

The ratio which we usually use in producing products is nonconforming proportion or percent defective. As our modern society develops, we cannot but meet another proportion in legal, managerial, and medical areas where our human beings might commit various kinds of errors though they do not want them. In this paper we will generally call the ratio 'proportion.' When the size of such proportion as percent defective is observed by persons, it is not true proportion but apparent proportion because it has been observed with human or situational errors. Past studies have not systematically covered the analysis of relations between such proportions and type 1 and 2 error, but this paper analyses and derives such various relations, and it suggests the guideline as sixteen properties for utilization and sensitive analysis of the relations. Current paper's consideration of apparent proportion in addition to true proportion as our familiar concept will open and widen existing academic and application areas where people have mainly built societal, scientific and engineering rules and methods based only on true proportion.