• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
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• pp.145-152
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• 2000

A turbopump system composed of two pumps and one turbine is considered. The turbine composed of a nozzle and a rotor is used to drive the pumps while gas passes through the nozzle, potential energy is converted to kinematic energy, which forces the rotor blades to spin. In this study, an aerodynamic design of turbine system is investigated using compressible fluid dynamic theories with some pre-determined design requirements (i.e., pressure ratio, rotational speed, required power etc.) obtained from liquid rocket engine (L.R.E.) system design. For simplicity of turbine system, impulse-type rotor blades for open type L.R.E. have been chosen. Usually, the open-type turbine system requires low mass flow rate compared to close-type system. In this study, a partial admission nozzle Is adopted to maximize the efficiency of the open-type turbine system. A design methodology of turbine system has been introduced. Especially, partial admission nozzle has been designed by means of simple empirical correlations between efficiency and configuration of the nozzle. Finally, a turbine system design for a 10 ton thrust level of L.R.E is presented.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.209-212
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• 2006

Insect and birds in nature flap their wings to generate fluid dynamic forces that are required for the locomotion. Most of the previous published papers discussed mainly on the effect of flapping parameters such as flapping frequency and amplitude on the thrust at a fixed Reynolds number. However, it is not much known on the values of the flapping parameters that the flapping wing requires to generate the thrust at the low Reynolds number flow. In this paper, the onset of the thrust generation is investigated using the lattice Boltzmann method. The wake patterns and velocity profiles behind a flat plate in heaving oscillation are investigated for the heaving amplitude of 0.5C. The time-averaged thrust coefficient value is investigated by changing the reduced frequency from 0.125 to 3.0 for three values of heaving amplitude (h/C=0.25, 0.325, 0.50). It is also found that the critical Strouhal number over which the flat plate starts to produce the thrust is around 0.1 and the thrust is an exponential function of the Strouhal number.

• 한국유체기계학회 논문집
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• 제14권5호
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• pp.48-54
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• 2011

Structural modifications of a ship may cause a fatal accident such as sinking and wrecking of ship. Especially, barge ship can be easily reconstructed to load more bulk cargo. In this study, for a real accident case, change of mooring force due to structural modification was analyzed to evaluate accident risk. A two dimensional dynamic model for the barge ship was constructed to compute mooring forces with related to floating motion. The equation of motion was established in Matlab code and buoyancy was calculated by using direct integration of submerged volume. The results showed that wind force, current force, and mooring force after rebuilding was approximately 4.3 kN, 14 kN, 1,561 kN respectively. The maximum force of mooring force according to the length of mooring cable were 1,614 kN at 30 m of mooring cable. Thus, an arbitrary modification of ship lead instability and unreliable result so that illegal rebuilding of ship should be avoided.

• Korea-Australia Rheology Journal
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• 제14권2호
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• pp.57-62
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• 2002

The sensitivity of the final filament to the ongoing sinusoidal disturbances has been Investigated in the viscoelastic spinning using frequency response method. Amplification ratios or gains of the spinline cross-sectional area at the take-up to any disturbances show resonant peaks along the frequency regime, where the frequencies at theme points directly correspond to the imaginary parts of the successive leading eigenvalues from the linear stability analysis. As shown in Jung et al. (1999) and Lee et al (2001), the sensitivity results on the effect of various process conditions such as spinline cooling and fluid viscoelasticity, obtained by dynamic transient simulation have been corroborated in this study. That is, increasing spinline cooling makes the system less sensitive to disturbances, thus stabilizes the spinning. Also, an increasing viscoelasticity for extension-thickening fluids decreases the sensitivity of the spinning. i.e., stabilizing the system, where, as it increases the sensitivity of the spinning of extension-thinning fluids. Furthermore, it has been found in the present study that the inertia force as one of secondary forces causes the system to be more stabile or less sensitive to process disturbances.

• 한국압력기기공학회 논문집
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• 제7권1호
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• pp.35-40
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• 2011

If a plugged tube in a steam generator is broken, it may damage nearby intact tubes. To prevent this damage, it is recommended that a stabilizer is installed into the plugged tube. However, the installation cost of a stabilizer is very high. So studies are required to determine the conditions on which the installation is necessary. For this purpose static loads and dynamic loads applied on a tube should be known to estimate the residual strength and remaining fatigue and wear life of a plugged tube. Two-dimensional and three-dimensional computational fluid dynamics (CFD) analyses are performed to obtain the drag coefficient for cross flow to a tube. Using the obtained drag coefficient, the static load can be estimated and the residual strength of a plugged tube can be calculated. An inclined flow problem is also analyzed and the vertical and horizontal forces are obtained and discussed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.381-387
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• 2002

In this work, the dynamic characteristics of an oil-lubricated, short SFD with a central feeding groove are derived based on a theoretical analysis considering the effect of a groove. The validity of the analysis is investigated experimentally using an Active Magnetic Bearing (AMB) system as an exciter. For the theoretical solution, the fluid film forces of a grooved SFD are analytically derived so that the dynamic coefficients of a SFD are expressed in terms of its design parameters. For the experimental validation of the analysis, a test rig using AMB as an exciter is proposed to identify the dynamic characteristics of a short SFD with a central groove. As an exciter, the AMB represents a mechatronic device to levitate and position the test journal without any mechanical contact, to generate relative motions of the journal inside the tested SFD and to measure the generated displacements during experiments with fairly high accuracy. Using this test rig, experiments are extensively conducted with different clearance, which is one of the most important design parameters, in order to investigate its effect on the dynamic characteristics and the performance of SFDs. Damping and inertia coefficients of the SFD that are experimentally identified are compared with the analytical results to demonstrate the effectiveness of the analysis. It is also shown that AMB is an ideal device for tests of SFDs.

• Wind and Structures
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• 제13권6호
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• pp.557-580
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• 2010

A new inflow turbulence generation method and a combined dynamic SGS model recently developed by the authors were applied to evaluate the wind effects on 508 m high Taipei 101 Tower. Unlike the majority of the past studies on large eddy simulation (LES) of wind effects on tall buildings, the present numerical simulations were conducted for the full-scale tall building with Reynolds number greater than $10^8$. The inflow turbulent flow field was generated based on the new method called discretizing and synthesizing of random flow generation technique (DSRFG) with a prominent feature that the generated wind velocity fluctuations satisfy any target spectrum and target profiles of turbulence intensity and turbulence integral length scale. The new dynamic SGS model takes both advantages of one-equation SGS model and a dynamic production term without test-filtering operation, which is particular suitable to relative coarse grid situations and high Reynolds number flows. The results of comparative investigations with and without generation of inflow turbulence show that: (1) proper simulation of an inflow turbulent field is essential in accurate evaluation of dynamic wind loads on a tall building and the prescribed inflow turbulence characteristics can be adequately imposed on the inflow boundary by the DSRFG method; (2) the DSRFG can generate a large number of random vortex-like patterns in oncoming flow, leading to good agreements of both mean and dynamic forces with wind tunnel test results; (3) The dynamic mechanism of the adopted SGS model behaves adequately in the present LES and its integration with the DSRFG technique can provide satisfactory predictions of the wind effects on the super-tall building.

• 한국해안해양공학회지
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• 제3권3호
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• pp.126-136
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• 1991

본 논문에서는 파랑하중을 받는 Guyed Tower의 비선형 동적거동에 대하여 연구하였다. Guyed Tower를 효율적으로 해석하기 위하여 Tower는 등가의 기둥으로 모형화 하였으며, 계유장치는 수평방향의 비선형 경계요소로 이상화하였다. 또한 파일 기초부는 회전방향의 선형경계요소로 대치하였다. Tower에 작용하는 파랑하중은 Morison 방정식에 의한 산정하였다. 계유장치와 유체의 점성에 기인된 항력 등의 비선형성을 적절히 고려하기 위하여 시간영역에서 해석을 수행하였으며, 비선형 운동방정식을 효율적으로 풀기 위해 Newmark 적분기법에 기초한 모우드 중첩법을 사용하였다. Guyed Tower의 중요한 설계변수인 계유선의 Clump weight 중량 조건과 파일 기초부 조건의 변화에 대한 수치해석을 수행하였다.

• Nuclear Engineering and Technology
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• 제26권2호
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• pp.197-204
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• 1994

원자로운전정지시 사용되는 제어봉집합체는 제어봉구동장치에서 분리되어 핵연료집합체의 안내관으로 자유낙하한다. 이 제어봉집합체의 주요변수로는 낙하시간과 충격속도가 있는데, 낙하시간은 원자로 안전정지와 관계가 있으며, 충격속도는 핵연료집합체의 건전성과 관계가 있다. 따라서, 제어봉 낙하시간과 충격속도의 적절한 결정은 제어봉집합체와 핵연료집합체의 설계에 매우 중요하다. 제어봉집합체는 낙하도중 유체저항이나 마찰력 및 부력과 같은 여러 힘들에 의해 낙하시간이 감소하게 되는데, 이러한 여러가지 힘의 복잡한 결합으로 인해 낙하시간과 충격속도를 해석적으로 유추하는 것은 매우 어렵다. 본 논문에서는 국산핵연료집합체에 적용되는 해석적인 방정식을 포함하고 있는 프로그램을 개발하였고, 이 프로그램을 단일제어봉 낙하시험과 비교하였다. 비교결과 시험 및 해석결과가 잘일치하고 있음으로써 개발된 프로그램의 검증을 확인할 수 있었고, 따라서 이 프로그램이 제어봉및 안내관의 설계변경시 매우 유용하게 사용할 수 있게 되었다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.990-994
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• 2004

This paper presents a method to predict the transient characteristic of the air lubricated slider head in a hard disk drive by using optimization technique. The time dependent modified Reynolds equation based on the molecular slip flow approximation equations was used to describe the fluid flow within the air bearing and the implicit finite difference scheme is applied to calculate the pressure distribution under the slider head. The exhaustive search combined with the Broyden-Fletcher-Goldfarb-Shanno method were employed to obtain optimum design variables which are taper angle, rail width and taper length in order to keep the forces and moments acting on the slider head in dynamic equilibrium. The results show that the optimal head slider of the magnetic head has good stability characteristic that can reach the steady state within 0.5 microsecond.