• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.796-805
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• 2005

The tilting pad journal bearings have been widely used to support high pressure/high rotating turbine rotors owing to their inherent dynamic stability characteristics. However, fatigue damages in the upper unloaded pads and the break of locking pins etc. by pad fluttering are continuously taken place in the actual steam turbines. The purpose of this paper is to develop a new bearing model that can prevent bearing problems effectively by pad fluttering in a tilting pad journal bearing. A new bearing model which has a wedged groove is suggested from the studies of fluttering mechanism performed by previously research works. The fluttering characteristics of the upper unloaded pad are studied experimentally in order to verify the reliability of a new bearing model. It can be known that the phenomenon of pad fluttering nearly does not occurred in the new bearing model under the various experimental conditions. And it is observed that any kinds of bearing failures by pad fluttering does not detect in the application of acture steam turbines.

• Journal of Wellbeing Management and Applied Psychology
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• v.3 no.2
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• pp.21-26
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• 2020

The purpose of this article is to capture this situation within the changes that take place due to it, inside the Greek society where there is a great need for professional social workers who are able to work targeted and effectively with foreigners, both children and adults, who have or develop mental health problems for the very first time. Over the recent decades the increasing number of migration flows has exerted and continues to exert great pressure on the health system and on the welfare structures of Greece. The bases for the development of a rudimentary reception and integration system that still is in progress have been delayed, while there has been no happy medium, between the enormous pressure that foreigner users of this system put on, and the humanitarian obligation of a well-governed state towards all residents of the country. Straight through everyday clinical practice in the field of intercultural work, social work has the knowledge and techniques for a total management of emerging problems and at the same time provides a value system with an ethical background which approaches refugees and migrants in order to provide quality services, mostly to users of mental health services.

• Computers and Concrete
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• v.15 no.5
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• pp.833-845
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• 2015

In the world total boron reserve rating, Turkey is taken place on the first rank, meeting the demand of refined mineral and main boron chemicals. Development of the new boron products and production technologies, spreading the using area of the boron are the study topics which must be finically discussed. In this study, with the help of colemanite taken in ratio as (0%, 7.5%, 12.5%, and 17.5%) by being mixed by the cement, surfaces of the pumice aggregates have been covered. Permeability of the samples has been investigated by producing lightweight concrete with 400 dose with the help of aggregates covered with colemanite. For this, the experiments of water absorption, capillary water absorption, depth of penetration of water under pressure and rapid chloride permeability have been performed. In addition, analyses of the thin section of covered and uncovered pumice aggregates and SEM (Scanning Electron Microscope) have been investigated. When the control samples produced with the covered aggregates and concretes produced with colemanite covered aggregates are compared each other, it has been determined that special lightweight concretes whose values of capillary water absorption experiment, depth of penetration of water under pressure experiment and rapid chloride permeability are low can be produced.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.171-176
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• 2006

An experimental study on a fuel-rich gas generator was carried out. Thirty seven double-swirl injectors with recess number of 1.5 were distributed and installed in the injector head, which significantly influences the combustion performance. In the paper, the characteristics of combustion stability are inspected by the parametric varations such as changing length and diameter of a combustion chamber and installing a turbulence ring. The experimental results show that as a resonant frequency took place in a high region, the amplitude of the dynamic pressure generally diminished, however, the combustion instability could not be suppressed perfectly.

• The KSFM Journal of Fluid Machinery
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• v.8 no.5 s.32
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• pp.35-45
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• 2005

The tilting pad journal bearings have been widely used to support high pressure/high rotating turbine rotors owing to their inherent dynamic stability characteristics. However, fatigue damages in the upper unloaded pads and the break of locking pins etc. by pad fluttering are continuously taken place in the actual steam turbines. The purpose of this paper is to develop a new bearing model that can prevent bearing problems effectively by pad fluttering in a tilting pad journal bearing. A new bearing model which has a wedged groove is suggested from the studies of fluttering mechanism performed by previously research works. The fluttering characteristics of the upper unloaded pad are studied experimentally in order to verify the reliability of a new bearing model. It can be known that the phenomenon of pad fluttering nearly does not occurred in the new bearing model under the various experimental conditions. And it is observed that any kinds of bearing failures by pad fluttering does not detect in the application of acture steam turbines.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.5
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• pp.612-619
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• 2003

This work experimentally studies the fundamental mechanisms by which the ultrasonic vibration enhances convection and pool boiling heat transfer. A thin platinum wire is used as both a heat source and a temperature sensor. A high speed video imaging system is employed to observe the behavior of cavitation and thermal bubbles. It is found that when the liquid temperature is below its boiling point, cavitation takes place due to ultrasonic vibration while cavitation disappears when the liquid reaches the boiling point. Moreover, when the gas dissolved in liquid is removed by pre-degassing, the cavitation arises only locally. Depending on the liquid temperature, heat transfer rates in convection, subcooled boiling and saturated boiling regimes are examined. In convection heat transfer regime, fully agitated cavitation is the most efficient heat transfer enhancement mechanism. Subcooled boiling is most enhanced when tile local cavitation is induced after degassing. In saturated boiling regime, acoustic pressure is shown to be a dominant heat transfer enhancement mechanism.

• Structural Engineering and Mechanics
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• v.61 no.5
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• pp.637-643
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• 2017

Carbon fiber reinforced polymers (CFRPs) have been recently investigated as an alternative material for Geosynthetics to improve soil properties. One of the factors influencing the fiber orientation and mechanical properties of CFRP is the effect of soil overburden pressure. This study investigates the tensile behavior of cast-in-place CFRP. During the curing time of specimens, a wide range of normal stress is applied on specimens sandwiched between the soils. Two different soil types are used to determine the effect of soil grain size on the mechanical properties of CFRP. Specimens are also prepared with different specifications such as curing time and mixing soil in to the epoxy. In this study, tensile tests are conducted to investigate the effect of such parameters on tensile behavior of CFRP. The experimental results indicate that by increasing the normal stress and soil grain size, the ultimate tensile strength and the corresponding strain of CFRP decrease; however, reduction in elastic modulus is not noticeable. It should be noted that, increasing the curing period of epoxy resin and mixing soil in to the epoxy have no significant effect on the tensile properties of CFRP.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1987.06a
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• pp.50-56
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• 1987

A mechanical face seal is most commonly used to seal liquids and gases at various speeds, pressures and temperatures. The primary seal ring is in sliding contact with the seal seat and as a result heat in the vicinity of the interface is generated. Local temperatures at points along the circumferential direction will fluctuate as asperities on the surfaces pass. This kind of fluctuation of temperature has been investigated to take place. This may lead to the hot spots phenomenon between the contacting asperities. Sibley and Allen showed photographic evidence of systemically moving hot spots in the contact zone. The appearance of such a temperature disturbance has been attributed to a kind of thermoelastic instabilities between two surfaces: This involves a feedback loop which comprises localized elevation of frictional heating, resultant localized thermal bulding, localized pressure increase as the result of the bulging and futher elevation of frictional heating as the result of the pressure increase. The heating of hot spots will be continued until the expanded material due to the frictional heating is worn off. Therefore to predict the speed of temperature propagation into the body is essential to the analysis of heat transfer on the edge of the seal.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.38.1-38.1
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• 2017

We report the results of three-dimensional radiation hydrodynamic simulations of star cluster formation in turbulent molecular clouds, with primary attention to how stellar radiation feedback controls the lifetime and net star formation efficiency (SFE) of their natal clouds. We examine the combined effects of photoionization and radiation pressure for a wide range of cloud masses (10^4 - 10^6 Msun) and radii (2 - 80 pc). In all simulations, stars form in densest regions of filaments until feedback becomes strong enough to clear the remaining gas out of the system. We find that the SFE is primarily a function of the initial cloud surface density, Sigma, (SFE increasing from ~7% to ~50% as Sigma increases from ~30 Msun/pc^2 to ~10^3 Msun/pc^2), with weak dependence on the initial cloud mass. Control runs with the same initial conditions but without either radiation pressure or photoionization show that photoionization is the dominant feedback mechanism for clouds typical in normal disk galaxies, while they are equally important for more dense, compact clouds. For low-Sigma clouds, more than 80% of the initial cloud mass is lost by photoevaporation flows off the surface of dense clumps. The cloud becomes unbound within ~0.5-2.5 initial free-fall times after the first star-formation event, implying that cloud dispersal is rapid once massive star formation takes place. We briefly discuss implications and limitations of our work in relation to observations.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.1-8
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• 2008

We analyzed the characteristics of water leakage from cooling components of the storage ring in the Pohang Light Source. The water leaks led localized pressure bumps and abnormal pressure changes. The leakage also changed the residual gas compositions depending not only on the position between leakage place to gas analyzer but also on on/off switching of ion pump and electron beam. We found that the residual gas analysis of $CH_4$, CO, NO was useful in determining water leaks.