• 동력기계공학회지
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• 제21권6호
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• pp.56-61
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• 2017

The check valves are mechanical valves that permit fluids to flow in only one direction, preventing flow from reversing. It is classified as one way directional valves. There are various types of check valves that used in a marine application. A lift type check valve uses the disc to open and close the passage of fluid. The disc lift up from seat as pressure below the disc increases, while drop in pressure on the inlet side or a build up of pressure on the outlet side causes the valve to close. An important concept in check valves is the cracking pressure which is the minimum upstream pressure at which the valve will operate. On the other hand, optimization is a process of finding the best set of parameters to reach a goal while not violating certain constraints. The AMESim software provides NLPQL(Nonlinear Programming by Quadratic Lagrangian) and genetic algorithm(GA) for optimization. NLPQL is the implementation of a SQP(sequential quadratic programming) algorithm. SQP is a standard method, based on the use of a gradient of objective functions and constraints to solve a non-linear optimization problem. A characteristic of the NLPQL is that it stops as soon as it finds a local minimum. Thus, the simulation results may be highly dependent on the starting point which user give to the algorithm. In this paper, we carried out optimization design of the check valve with NLPQL algorithm.

• Wind and Structures
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• 제9권2호
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• pp.109-124
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• 2006

This paper describes the characteristics of the fluctuating lift forces when a circular cylinder vibrates in the cross-flow direction. The response characteristics on elastically supported the circular cylinder was first examined by a free-vibration test. Next, flow-induced vibrations obtained by the free-vibration test were reproduced by a forced-vibration test, and then the characteristics of the fluctuating lift forces, the work done by the fluctuating lift, the behavior of the rolling-up of the separated shear layers were investigated on the basis of the visualized flow patterns. The main findings were that (i) the fluctuating lift forces become considerably large than those of a stationary circular cylinder, (ii) negative pressure generates on the surface of the circular cylinder when the rolling-up of separated shear layer begins, (iii) the phase between the fluctuating lift force and the cylinder displacement changes abruptly as the reduced velocity $U_r$ increases, and (iv) whether the generating cross-flow vibration becomes divergent or convergent can be described based on the work done by the fluctuating lift force. Furthermore, it was found that the generation of cross-flow vibration can be perfectly suppressed when the small tripping rods are installed on the surface of the circular cylinder.

• 한국지반환경공학회 논문집
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• 제21권2호
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• pp.5-13
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• 2020

감압정은 소규모 필댐과 같은 소규모 댐에서 침투수 관리에 효과가 있다고 보고되고 있지만 감압정의 효과에 대한 정량적인 연구는 드물고 설계기준 또한 전무한 실정이다. 이에 본 연구에서는 소규모 필댐의 침투수 처리 효과를 정량적으로 분석하고자 댐 제체와 기초지반의 조건에 따른 침투해석을 수행하여 침투수의 거동특성을 파악함으로써, 댐 제체 선단에 작용하는 양압력을 분석하였다. 감압정의 설치 여부에 따라 댐 하류부 제체 선단의 기초지반에 작용하는 양압력의 감소 효과를 분석하였으며, 분석결과 감압정은 기초지반에서 파이핑 및 제체 활동을 유발시킬 수 있는 간극수압을 저감시키는데 효과가 있는 것을 확인하였다.

• 오토저널
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• 제7권2호
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• pp.45-54
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• 1985

Recently, the problem of exhaust gas pollution is increasingly being aggravated by the active use of the Diesel engine. For the fuel-injection system which affects the composition of exhaust gas from the Bosch type single-hole nozzle in the Diesel engine, a mathematical model was set up to study pressure variations in the high pressure pipe, the injection rate, and the needle lift. The fundamental equations of the mathematical model have been solved by the Newton Raphson Method applying the Finite Diffrence Method. The effective stroke of the injection pump plunger due to a change in engine rpm was calculated by the measurement of Control Rack, Pinion, and Plunger sizes and by the use of Characteristic Curve of Governor. The computed results for the pressure variations in the high pressure pipe and needle lift at 800 rpm and 1000 rpm are in good agreement with experimental ones in general. By a developed program, the effects of other various parameters will by calculated for the performance of the fuel-injection system.

• Tribology and Lubricants
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• 제31권3호
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• pp.109-124
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• 2015

This paper presents a wear analysis procedure for the journal bearings on a stripped-down single-cylinder engine during start-up and coast-down by motoring. A journal bearing is in the mixed elastohydrodynamic (EHL) lubrication region when the shaft speed is less than the corresponding lift-off speed. Below the lift-off speed, a wear scar can form on bearing surfaces. In part 1 of this paper, we develop the appropriate formulations and the calculation procedure for the analysis. Specifically, we formulate an equation for modified film thickness in a journal bearing considering the additional wear volume. In order to obtain the modified specific wear rate induced by the modified Archard’s wear coefficient, we utilized the extended non-dimensional diagram for the specific wear rate, k, the fractional film defect coefficient, Ψ and the asperity load sharing factor, γ₂. This asperity load sharing factor is newly calculated by setting the Zhao-Maietta-Chang (ZMC) asperity contact pressure equation coupled with the central film thickness equation derived by using the ZMC asperity contact model equal to the modified central contact pressure derived by using the central (or maximum) contact pressure at the dry rough line-contact configuration. We can use the procedure introduced in this paper to determine the lifetime (or longterm) linear wear in radial journal bearings that is a result of repeated stop-start cycles.

• Wind and Structures
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• 제24권5호
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• pp.501-528
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• 2017

In this work, wind tunnel tests of pressure measurements are carried out to assess the global aerodynamic interference factors, the local wind pressure interference factors, and the local lift spectra of an square high-rise building interfered by an identical cross-sections but lower height building arranged in various relative positions. The results show that, when the interfering building is located in an area of oblique upstream, the RMS of the along-wind, across-wind, and torsional aerodynamic forces on the test building increase significantly, and when it is located to a side, the mean across-wind and torsional aerodynamic forces increase; In addition, when the interfering building is located upstream or staggered upstream, the mean wind pressures on the sheltered windward side turn form positive to negative and with a maximum absolute value of up to 1.75 times, and the fluctuating wind pressures on the sheltered windward side and leading edge of the side increase significantly with decreasing spacing ratio (up to a maximum of 3.5 times). When it is located to a side, the mean and fluctuating wind pressures on the leading edge of inner side are significantly increased. The three-dimensional flow around a slightly-shorter disturbing building has a great effect on the average and fluctuating wind pressures on the windward or cross-wind faces. When the disturbing building is near to the test building, the vortex shedding peak in the lift spectra decreases and there are no obvious signs of periodicity, however, the energies of the high frequency components undergo an obvious increase.

• 한국지반환경공학회 논문집
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• 제23권2호
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• pp.25-36
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• 2022

본 연구에서는 감압정의 침투수 처리 효과를 정량적으로 분석하여 소규모 필댐과 하천제방에서 제체를 통과하는 침투수의 처리 효과를 확인하였다. 이를 위해 댐과 제방에서의 제체와 기초지반의 투수 특성에 따른 침투해석을 수행하여 침투수의 거동특성을 파악하여 댐 제체 선단에 작용하는 양압력을 분석하였다. 또한 감압정의 설치 조건을 변수로 분석하여 댐 또는 제방의 제체 선단에 작용하는 양압력의 감소 효과를 분석함으로써 침투수 처리 효과를 분석하였다. 감압정은 파이핑 현상 또는 양압력을 유발하는 제체의 선단 하부 기초지반에서의 작용 간극수압을 감소시키는 효과가 있는 것으로 평가되었으며, 제체의 높이 및 비탈면 기울기와 같은 기하학적 조건에 크게 영향을 받지 않고 간극수압을 관리할 수 있는 것으로 확인되었다. 투수성이 상대적으로 큰 조립토 지반에 비해 세립토 지반에서 감압정의 간극수압 저감 효과는 상대적으로 저하되지만 감압정이 설치되지 않은 조건에 비해서 간극수압 저감 효과를 기대할 수 있는 것으로 확인되었다. 감압정의 직경, 설치 깊이에 따라서 감압정의 저감 효과는 상대적으로 차이가 발생하지만 감압정의 설치 깊이가 침투수 관리에 가장 효과적인 것으로 확인되었다.

• 한국전산유체공학회지
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• 제13권4호
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• pp.66-71
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• 2008

This research computes the viscous flow field and aerodynamics around the model of a commercial passenger airplane, Boeing 747-400, which cruises in transonic speed. The configuration was realized through the reverse engineering based on the photo scanning measurement. In results, the pressure coefficients at the several wing section on the wing surface of the airplane was described and discussed to obtain the physical meaning. The lift coefficient increased almost linearly up to $17^{\circ}$. Here the maximum lift occurred at $18^{\circ}$ according to the angle of attack. And the minimum drag is expected at $-2^{\circ}$. The maximum lift coefficient occurred at the Mach number 0.89, and the drag coefficient rapidly increased after the Mach number of 0.92. Also shear-stress transport model predicts slightly lower aerodynamic coefficients than other models and Chen's model shows the highest aerodynamic values. The aerodynamic performance of the airplane elements was presented.

• Journal of Biosystems Engineering
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• 제31권4호
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• pp.342-348
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• 2006

Aerial application using an unmanned agricultural helicopter became necessary for both labor saving and timely spraying. In the previous paper, a rotor system was developed and lift capability was evaluated. The experimental results were compared with simulated predictions using the CFD-ACE program. From the simulation, the relative velocity on the top surface of the blade airfoil increased, resulting in the pressure drop. The CFD analyses were revealed that a drag resistance on the leading edge of the airfoil, a wake at the trailing edge, and a positive pressure underneath the bottom surface were observed. As the results of the simulation, total lifts of 56.8, 74.4 and $95.0kg_f$ were obtained at the 6, 8 and $10^{\circ}$ of AAT (angle of attack), respectively. The simulation results agreed reasonably up to $10^{\circ}$ of AAT. However, at a greater AAT $(<12^{\circ})$ the simulated total lift continuously increased to $105kg_f$, comparing with a decreasing experimental total lift due to the lack of engine power. At a stiff angle of $18^{\circ}$ AAT, a wake was observed at the trailing edge of the airfoil. A rated operating condition determined from the previous paper was also verified through the simulation.

• 해양환경안전학회지
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• 제5권2호
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• pp.35-44
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• 1999

High negative pressure coefficient is formed in the corner of the bluff body structures. For many curtain wall designers this phenomena is of interest because this high negative pressure coefficient is adopted in structural calculation. The present study is aimed to investigate shedding vortex characteristics of two-dimensional rectangular prism flow. Unsteady calculation by finite difference method based upon SOLA is carried out for three aspect ratios(1:1, 1:2, 1:3) of Re=10$^4$ in viscous incompressible flow within infinite domain. Fluctuation of velocity components at various pick-up points and time variation of drag and lift coefficients are analysed by FFT method to reveal shedding vortex frequency patterns. At aspect ratio 1:1, one primary Strouhal number appears for about all pick-up points. At aspect ratio 1:2, two representative Strouhal numbers are classified by pick-up positions and their flows show two different reattachment patterns. For aspect ratio 1:3, frequency spectrum maintains multiple peaks.