• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.33-36
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• 2010

터빈손실에 관해서 다양한 연구가 진행되어 왔다. 특히 팁 누수에 의한 손실은 주로 블레이드 높이의 5% 이하에 대해 연구되었다. 그러나 터보펌프 등 소형 터빈은 작은 크기로 인해 상대적으로 큰 팁 간극을 가지며 그에 대한 연구결과는 발표된 것을 찾기 힘들다. 본 연구는 입구유속 30m/s, 코드길이 기준 레이놀즈 수 210,000의 조건의 선형 터빈 캐스케이드에서 진행되었으며, 팁 간극은 코드길이의 1%에서 20%까지 총 6가지에 대해 손실을 측정하였다. 실험결과 팁 간극 10%에서 손실계수 최대 0.113으로 측정되었으며, 더 이상 손실이 선형적으로 증가하지 않는 것을 확인하였다.

• Structural Engineering and Mechanics
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• 제63권5호
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• pp.691-702
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• 2017

Clearances are essential for the assemblage of mechanisms to allow the relative motion between the joined bodies. This clearance exists due to machining tolerances, wear, material deformations, and imperfections, and it can worsen the mechanism performance when the precision and smoothly-working are intended. Energy is a subject which is less paid attention in the area of clearance. The effect of the clearance on the energy of a flexible slider-crank mechanism is investigated in this paper. A clearance exists in the joint between the slider and the coupler. The contact force model is based on the Lankarani and Nikravesh model and the friction force is calculated using the modified Coulomb's friction law. The hysteresis damping which has been included in the contact force model dissipates energy in clearance joints. The other source for the energy loss is the friction between the journal and the bearing. Initial configuration and crank angular velocity are changed to see their effects on the energy of the system. Energy diagrams are plotted for different coefficients of friction to see its influence. Finally, considering the coupler as a flexible body, the effect of flexibility on the energy of the system is investigated.

• 약학회지
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• 제27권4호
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• pp.271-282
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• 1983

This study is an attempt to study the influence of clonidine, which has a central sympatholytic action, on the renal function in dogs and to elucidate its mechanism of action. Clonidine ($15\mu$g/kg) injected into a cephalic vein of the dog produced a marked increase in urine flow and in amounts of $Na^{+}$ and $K^{+}$ excreted in urine, and clearances of free water and osmolar substance, the reabsorption rates of $Na^{+}$ and $K^{+}$ in renal tubules were significantly decreased. Clonidine ($50.0]mu$g/kg) administered intravenouly elicited a transient reduction in urine flow, along with inhibition of all renal functions. Intravenous clonidine-induced diuretic effect was completely blocked by pretreatment with reserpine, and was lessened by water diuresis. Clonidine ($3.0\mu$g/kg) injected tnto a carotid artery revealed a transient diuresis with a increase in clearance of free water. Clonidine injected into a renal artery showed a significant antidiuretic effect and all functions of an experimental kidney were reduced. Antidiuretic action induced by clonidine given into a renal artery markedly suppressed by pretreatment with reserpine. The above results suggest that clonidine has dual mechanisms: 1) diuretic effect due to the central sympatholytic action and inhibition of release of antidiuretic hormone, and 2) antidiutetic effect indued by indirect symptheic stimulation in the periphery.

• 대한기계학회논문집
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• 제13권4호
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• pp.583-594
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• 1989

본 연구는 기계적 간극의 존재로 양면 접촉에 의한 강성 및 감쇠가 대칭적 으로 두번 생기는 강제 대칭 편적 선형(forced symmetric piecewise-linear vibarti- on)에 대하여 비선형진동의 분수조화 정상해 과정을 설명한 Stoker 가설로부터 분수조화진동을 포함한 복수의 정상해를 구하고 피로, 마멸 연구를 위한 접촉시간 및 접촉력을 계산하였다. 또한 강제 대칭 편적 선형진동자의 운동방정식을 무차원화 하고 각 무차원 시스템 변수에 따른 주파수응답특성을 살펴보았다.

• 한국유체기계학회 논문집
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• 제12권2호
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• pp.39-45
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• 2009

Leakage flow through turbine blade tip gap causes strong leakage vortex near the blade suction side and induces large aerodynamic losses. In this study, the conventional plane tip and various squealer tip blades were tested in a linear cascade in order to measure the effect of the tip shape on the total pressure loss. Three tip gap clearances of 0.6%, 1.3%, and 2.0% of blade span were tested. Flow measurement was conducted at one chord downstream from the trailing edge with a five-hole probe. Results showed that the leakage vortex was stronger than passage vortex and the mass averaged overall total pressure loss through the cascade was the lowest for suction side blade tip case. For all tested cases, the area averaged overall total pressure loss was increased as the tip clearance increased.

• Journal of Electrical Engineering and Technology
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• 제13권3호
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• pp.1326-1336
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• 2018

This paper proposes a numerical approach to predict the critical flashover voltages of air gaps under lightning impulses. For an air gap, the impulse voltage waveform features and electric field features are defined to characterize its energy storage status before the initiation of breakdown. These features are taken as the input parameters of the predictive model established by support vector machine (SVM). Given an applied voltage range, the golden section search method is used to compute the prediction results efficiently. This method was applied to predict the critical flashover voltages of rod-rod, rod-plane and sphere-plane gaps over a wide range of gap lengths and impulse voltage waveshapes. The predicted results coincide well with the experimental data, with the same trends and acceptable errors. The mean absolute percentage errors of 6 groups of test samples are within 4.6%, which demonstrates the validity and accuracy of the predictive model. This method provides an effectual way to obtain the critical flashover voltage and might be helpful to estimate the safe clearances of air gaps for insulation design.

• 한국전기전자재료학회논문지
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• 제22권10호
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• pp.870-878
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• 2009

The large increase in the use of electricity has resulted in an ever-growing electric power demand. It has created the need for the construction of power transmission facility located close to the load centers and it also has to require wide right-of-way and large lots, that are not always available, for especially the installation of the towers. The difficulties in acquiring right-of-way have put pressure on energy companies to either upgrade a line on an existing right-of-way to higher voltage or build a new line on a narrow right-of-way. This paper presents the design of a compact tower with polymer Insulation arm, in order to reduce the separation between phases. the compact tower can be built on a narrow right-of-way. the compact tower can be designed based on 345 kV Tower regarding electrical clearances and right of way, therefore the conventional 154 kV Tower can be upgrading transmission line voltages have moved to 345 kV levels.

• Tribology and Lubricants
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• 제16권3호
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• pp.157-165
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• 2000

A discharge free Electro-Rheological Squeeze Film Damper (ER-SFD) with predetermined-clearances at leakage ends can inherently eliminate electric discharge problems while still supplying stable leakage control. Test results show that the damping force of the slotted-ring ER-SFD is mainly affected by electric voltage, oil supply pressure, position of the damper and ratio of effective surface area of slotted-rings. As the supply voltage is larger, the amplitudes of both slotted ER-SFD and rotor are decreased at first and second critical speeds. The influence of the oil supply pressure and the effective surface area ratio was shown mainly near the first critical speed. The effective surface area ratio of slotted-rings influences the reduction of flexible rotor vibration. As a result, experimental results confirm that the slotted-ring ER-SFD satisfactorily controls the flexible rotor vibration, while eliminates the inherent electric discharge problems in conventional ER-SFDs.

• Tribology and Lubricants
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• 제31권6호
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• pp.245-250
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• 2015

This study investigates the lubrication characteristics of fuel injection pumps with reference to different fuel oils. Medium-speed diesel engines use fuel oils with various viscosities, such as heavy fuel oil (HFO, which is a high-viscosity fuel oil) and light diesel oil (LDO, which is a low-viscosity fuel oil). When fuel oil with a low viscosity is used, both fuel oil and lubricating oil lubricate the system. Thus, the lubrication of the fuel injection pump is in a multi-viscosity condition when the fuel oil in use changes. We suggest three cases of multi-viscosity models, and divide the fuel injection pump into three lubrication sections: a, the new oil section; b, the mixed oil section; and c, the used oil section. This study compares the lubrication characteristics with variation of the multi-viscosity model, clearance. The volume of Section b does not affect the lubrication characteristics. The lubrication characteristics of the fuel injection pump are poor when high-viscosity fuel oil transfers to low-viscosity fuel oil. This occurs because the viscosity in the new oil section (i.e., Section a) dominates the lubrication characteristics of the fuel injection pump. However, the lubricant oil supply in the used oil section (i.e., Section c) can improve the lubrication characteristics in this condition. Moreover, the clearances of the stem and head significantly influence the lubrication characteristics when the fuel oil changes.

• Tribology and Lubricants
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• 제27권6호
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• pp.314-320
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• 2011

Although swash-plate type axial piston pumps have the merits of wide operating conditions and high efficiency, the characteristics of pressure pulsation and flow ripple which result in system noise generation are on-going problems. This research examined the analytic models of the dynamic oil pressure and flow characteristics in the pump. A new mathematical model which considered the pressure behaviors of each cylinder and discharge piping was developed to analyze the pump pressure and flow. This model also considered the leakages in the clearances which many researchers have ignored so far. Using the developed model, numerical calculations were implemented. The results showed that widely used simple model which considered only a single cylinder can not predict actual discrete flow dynamics and that fluid inertia effect has to be considered in the mathematical model. Several critical parameters were discussed such as port volume and discharge resistance on the assumption that the pipe length is not so long. The effect of leakages was studied on the final stage.