• 한국산업융합학회 논문집
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• 제25권2_2호
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• pp.279-287
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• 2022

Butterfly valves installed on ships use valves with up to triple offset to improve tightness. However, the triple offset valve has structural problems such as disc deformation and seat separation. Accordingly, interest in quadruple offset butterfly valves with added offset is increasing. In this study, the structural safety of the quadruple offset butterfly valve was examined through numerical analysis. In addition, we intend to evaluate the performance of the valve through flow coefficient analysis.

• Journal of Advanced Marine Engineering and Technology
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• 제22권1호
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• pp.52-66
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• 1998

An experimental study on the flow characteristics was performed for a two-dimensional turbulent wall attaching offset jet at different oblique angles to a surface. The flow characteristics were investigated by using a split film probe with the modified Stock's calibration method. The jet mean velocity, turbulent intensity, wall static pressure coefficient profiles, and time-averaged reattachment point were measured at the Reynolds number Re (based on the nozzle width, D) ranging from 17700 to 53200, the offset ratio H/D from 2.5 to 10, and the inclined angle .alpha. from 0.deg. C to 40.deg. C. The Correlations between the maximum pressure position, minimum pressure position, and reattachment point and offset ratios, and inclined angles are presented.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1237-1242
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• 2004

In this study, single-phase heat transfer experiments were conducted with oil cooler with offset strip fin using water. An experimental water loop has been developed to measure the single-phase heat transfer coefficient in a vertical oil cooler. Downflow of hot water in one channel receives heal from the cold water upflow of water in the other channel. Similar to the case of a plate heat exchanger, even at a very low Reynolds number, the flow in the on cooler with offset strip fin remains turbulent. The present data show that the heat transfer coefficient increases with the Reynolds number. Based. On the present data, empirical correlation of the heat transfer coefficient was proposed. Also, performance prediction analysis for oil cooler were executed and compared with experiments. ${\varepsilon}-NTU$ method was used in this prediction program. Independent variables are flow rates and inlet temperature. Compared with experimental data, the accuracy of the program is within the error bounds of ${\pm}5$% in the heat transfer rate.

• 대한조선학회논문집
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• 제59권4호
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• pp.243-250
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• 2022

In the design stage of hull forms, a fast prediction method of resistance performance is needed. In these days, large test matrix of candidate hull forms is tested using Computational Fluid Dynamics (CFD) in order to choose the best hull form before the model test. This process requires large computing times and resources. If there is a fast and reliable prediction method for hull form performance, it can be used as the first filter before applying CFD. In this paper, we suggest the offset-based performance prediction method. The hull form geometry information is applied in the form of 2D offset (non-dimensionalized by breadth and draft), and it is studied using Convolutional Neural Network (CNN) and adapted to the model test results (Residual Resistance Coefficient; C_R). Some additional variables which are not included in the offset data such as main dimensions are merged with the offset data in the process. The present model shows better performance comparing with the simple regression models.

• 센서학회지
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• 제7권5호
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• pp.300-305
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• 1998

본 논문에서는 옵셋전압 및 full scale 출력전압, 옵셋전압 및 full scale 출력전압의 온도특성이 보상된 집적화 된 실리콘 압력센서를 설계하였다. 신호처리회로는 옵셋전압 및 full scale 출력전압을 원하는 값으로 조정할 수 있고 옵셋전압의 온도 드리프트를 최소화할 수 있으며 출력전압이 양의 온도계수를 갖도록 하여 압저항계수의 온도계수와 상쇄되도록 설계하였다. 설계한 신호처리회로는 바이폴라 공정 파라미터를 이용하여 SPICE로 시뮬레이션하였다. 옵셋전압 및 full scale 출력전압의 조정을 위하여 온도계수가 서로 다른 이온주입저항을 이용하였다. 시뮬레이션결과 옵셋전압 및 옵셋전압의 온도계수 조정저항을 이용하여 옵셋전압을 0.133V로 조정하였고 온도 드리프트는 $42\;ppm/^{\circ}C$로 감소시킬 수 있었다. full scale 출력전압 조정저항을 이용하여 full scale 출력전압값을 4.65V로 조정하였고 온도보상을 통해 출력전압의 온도계수를 $40\;ppm/^{\circ}C$로 감소시킬 수 있었다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1999년도 추계종합학술대회 논문집
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• pp.51-54
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• 1999

It is well known that the OFDM transmission is weak against the frequency offset. We evaluate the BER performance of the OFDM system with guard interval and simple one-tap equalizer bank. For the small frequency offset, the loss in $E_{b}$ $N_{o}$ is about 1㏈ at required BER = 10$^{-5}$ , when the mean value of the second-ray's attenuation coefficient is 0.25 and the normalized frequency offset, which is normalized about OFDM symbol time, is 5%.%.%.

• Journal of Advanced Marine Engineering and Technology
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• 제22권2호
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• pp.200-209
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• 1998

Experiments have been conducted to determine heat transfer characteristics for a two-dimen-sional turbulent wall attaching offset jet at different oblique angles to a flat surface. The local Nusselt number distributions were measured using liquid crystal as a temperature sensor. Wall static pressure coefficient profiles were measured at the Reynolds number Re 53200(based on the nozzle width, D) the offset ratio H/D from 2.5 to 10 and the oblique angle a from $0^{\circ}$, to $40^{\circ}$ It is observed that the maximum Nusselt number point occurs slightly upstream of time-averaged reattachment point for all oblique angles. The correlations between the maximum Nusselt number and Reynolds number offset ration and oblique angle are presented.

• 설비공학논문집
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• 제14권9호
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• pp.734-740
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• 2002

In the present study, heat transfer characteristics of oil flow over offset strip fins are predicted by the numerical methods. Oil flow in the plate-fin passage is idealized by 2 dimensions. Inlet velocity, Prandtl number and fin pitch ratio are chosen as parameters which affect the heat transfer of offset strip fins. The effect of parameters on pressure drops and convective heat transfer coefficients are described. Characteristic length is derived in case of 2 dimensional flow situation. Correlations for friction factor and convective heat transfer coefficient are derived.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.545-548
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• 2002

Turbines have been known to be particularly susceptible to flow-induced self-excited vibration. In such vibrations, direct damping and cross stiffness effects of aerodynamic forces determine rotordynamic stability. In axial turbines with eccentric shrouded rotors, the non-uniform sealing gap causes azimuthal non-uniformities in the seal gland pressure and the turbine torque which destabilize the rotor system. Previously, research efforts focused solely on either the seal flow or the unshrouded turbine passge flow. Recently, a model for flow in a turbine with a statically offset shrouded rotor has been developed and some stiffness predictions have been obtained. The model couples the seal flow to the passage flow and uses a small perturbation approach to determine nonaxiymmetric flow conditions. The model uses basic conservation laws. Input parameters include aerodynamic parameters (e.g. flow coefficient, reaction, and work coefficient); geometric parameters (e.g. sealing gap, depth of seal gland, seal pitch, annulus height); and a prescribed rotor offset. Thus, aerodynamic stiffness predictions have been obtained. However, aerodynamic damping (i.e. unsteady aerodynamic) effects caused by a whirling turbine has not yet been examined. Therefore, this paper presents a new unsteady model to predict the unsteady flow field due to a whirling shrouded rotor in turbines. From unsteady perturbations in velocity and pressure at various whirling frequencies, not only stiffness but also damping effects of aerodynamic forces can be obtained. Furthermore, relative contributions of seal gland pressure asymmetry and turbine torque asymmetry are presented.

• 한국자동차공학회논문집
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• 제1권3호
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• pp.22-33
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• 1993

A theoretical analysis of predicting the detailed motion of a piston-crank mechanism within piston-guide clearance is presented, and the analysis is applied to the piston motion in a gasoline engine. A piston movement program is developed to calculate the piston attitude relative to the bore, the piston to bore impact velocity and kinetic energy loss and the net transverse force acting on the piston. This paper presents the formulation of a set of differential equations governing the transverse and rotational motion of a piston. These equations of motion were solved by well established Runge-Kutta method. As a result of this study, it is possible to predict the effects of piston geometry and piston pin offset on a piston motion and kinetic energy loss.