• Nuclear Engineering and Technology
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• 제12권3호
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• pp.163-170
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• 1980

4KJ의 에너지 뱅크(16.5KV, 35nH)를 사용하여 Mather형의 플라즈마총을 1 torr이하의 낮은 기체압력에서 동작시키면서 플라즈마의 효율적인 집속조건을 구하였다. 중수소기체의 충전압력이 0.18torr, 저장에너지가 3.8KJ일때 방전전류의 최고치는 180KA이었고 플라즈마의 축방향 평균속도는 약 $7cm/\mu\textrm{s}$이었다. 이것은 snowplow모델에 의해 계산된 속도보다 작은 값인데 이는 절연재 표면을 통한 전류의 손실에 기인하는 것으로 생각된다. H. Bruzzone의 플라즈마 집속장치(1KJ, 16KV, $4.2\mu\textrm{s}$)에 비해 본 실험에서는 기체압력이 낮은 역역에서 플라즈마 접속이 일어났다. 이는 이 실험에서 사용한 플라즈마총의 크기가 저장에너지에 비해 크고 또 잔여기체의 함량이 비교적 높기 때문이다. 집속된 플라즈마로 부터 방출되는 중성자는 Long counter를 사용해서 계측했다.

• 융합신호처리학회논문지
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• 제24권2호
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• pp.97-102
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• 2023

방향타는 조선 분야에서 중요한 역할을 하기 때문에 방향타의 유체역학적 특성을 조사하기 위해 수치 시뮬레이션이 수행되었다. 유체역학적 힘과 같은 일부 값은 예인 탱크에서 쉽게 측정할 수 있지만, 실험을 통해 압력 분포, 속도 분포, 와류 발생과 같은 유동장에 대한 자세한 정보를 얻기는 어렵다. 본 연구에서는 전산유체역학(CFD)을 이용하여 방향타에 작용하는 유체역학 계수와 레이놀즈수가 미치는 영향을 연구하였다. 상용 전산유체역학 프로그램 Ansys Fluent를 이용하여 방향타 주위의 유동 특성을 연구하였고, 이때 k-epsilon 난류 모델이 사용되었다. 먼저 CFD 상용코드를 이용하여 KCS 방향타의 받음각에 따른 항력계수와 양력계수를 구하였다. 둘째, 동일한 조건에서 2차원 양력계수와 항력계수를 3차원 계수와 비교되었다. 셋째, 레이놀즈수가 유체역학적 힘에 미치는 영향이 연구되었다.

• 한국지진공학회논문집
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• 제24권6호
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• pp.253-266
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• 2020

The extended slip-weakening model was investigated by using a compiled set of source-spectrum-related parameters, i.e. seismic moment M_o, S-wave velocity V_s, corner-frequency f_c, and source-controlled high-cut frequency fmax, for 113 shallow crustal earthquakes (focal depth less than 25 km, M_W 3.0~7.5) that occurred in Japan from 1987 to 2016. The investigation was focused on the characteristics of stress drop, radiation energy-to-seismic moment ratio, radiation efficiency, and fracture energy release rate, G_c. The scaling relationships of those source parameters were also investigated and compared with those in previous studies, which were based on generally used singular models with the dimensionless numbers corresponding to f_c given by Brune and Madariaga. The results showed that the stress drop from the singular model with Madariaga's dimensionless number was equivalent to the breakdown stress drop, as well as Brune's effective stress, rather than to static stress drop as has been usually assumed. The scale dependence of stress drop showed a different tendency in accordance with the size category of the earthquakes, which may be divided into small-moderate earthquakes and moderate-large earthquakes by comparing to M_o = 10¹⁷~10¹⁸ Nm. The scale dependence was quite similar to that shown by Kanamori and Rivera. The scale dependence was not because of a poor dynamic range of recorded signals or missing data as asserted by Ide and Beroza, but rather it was because of the scale dependent V_r-induced local similarity of spectrum as shown in a previous study by the authors. The energy release rate G_c with respect to breakdown distance D_c from the extended slip-weakening model coincided with that given by Ellsworth and Beroza in a study on the rupture nucleation phase; and the empirical relationship given by Abercrombie and Rice can represent the results from the extended slip-weakening model, the results from laboratory stick-slip experiments by Ohnaka, and the results given by Ellsworth and Beroza simultaneously. Also the energy flux into the breakdown zone was well correlated with the breakdown stress drop, ${\tilde{e}}$ and peak slip velocity of the fault faces. Consequently, the investigation results indicate the appropriateness of the extended slip-weakening model.

• 한국산학기술학회논문지
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• 제14권3호
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• pp.1519-1526
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• 2013

본 연구에서는 현장조사를 통해 주물 제조 사업장의 일부 용해공정에 적용되고 있는 캐노피 후드(canopy hood)의 흡인 성능을 검토하였다. 또한, CFD model을 이용하여 유해대기오염물질 포집 능력을 향상시킬 수 있는 방안들을 대한 유동장 및 압력장을 비교 및 평가하였다. Case-2(플랜지 부착+이중 후드)의 경우 포집 성능 측면에서는 개선이 가능하지만 후드 정압이 기존 구조보다 약 70% 이상 증가할 것으로 예측되어 현장 적용성이 좋지 않을 것으로 나타났다. 흡인효율을 개선하기 위해서는 case-3(플랜지 부착+이중 콘 부착)의 형상이 가장 적합할 것으로 판단된다. 이는 개구부 중앙에 이중 콘(cone)이 설치되어 후드 가장자리로 유량을 집중시킬 수 있으며, 또한 후드 중앙으로 상승되는 흄(hume)은 콘의 기울기에 의해 정압 상승의 요인 없이 제어할 수 있기 때문이다.

• International Journal of Aeronautical and Space Sciences
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• 제15권4호
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• pp.366-373
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• 2014

A conceptual design of a three-surface strike fighter was studied and stealth performance was taken into account to enhance survivability and battle effectiveness. CATIA was used to design the aircraft's three-dimensional prototype model and the weapon carriage arrangement was also studied. The aircraft's RCS characteristics and distributions under X, S, C, and L bands were simulated using the RCSPlus software, which is based on the PO method. Pressure and velocity distributions of the flow field were also simulated using CFD. A turbulence model was based on standard $k-{\varepsilon}$ function and N-S functions were used during the CFD computation. Lift coefficients, drag coefficients, and lift-to-drag ratio were obtained by aerodynamic simulation. The results showed that: (1) the average value of head-on RCS between ${\pm}30^{\circ}$ is below -3.197 dBsm, and (2) the lift coefficient is 0.34674, the drag coefficient is 0.04275, and the lift-to-drag ratio is 8.11087 when the attack angle is $2.5^{\circ}$.

• JSTS:Journal of Semiconductor Technology and Science
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• 제12권4호
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• pp.458-466
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• 2012

A Dual metal gate stack cylindrical/ surrounded gate MOSFET (DMGSA CGT/SGT MOSFET) has been proposed and an analytical model has been developed to examine the impact of this structure in suppressing short channel effects and in enhancing the device performance. It is demonstrated that incorporation of gate stack along with dual metal gate architecture results in improvement in short channel immunity. It is also examined that for DMGSA CGT/SGT the minimum surface potential in the channel reduces, resulting increase in electron velocity and thereby improving the carrier transport efficiency. Furthermore, the device has been analyzed at different bias point for both single material gate stack architecture (SMGSA) and dual material gate stack architecture (DMGSA) and found that DMGSA has superior characteristics as compared to SMGSA devices. The analytical results obtained from the proposed model agree well with the simulated results obtained from 3D ATLAS Device simulator.

• 한국자동차공학회논문집
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• 제6권3호
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• pp.123-137
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• 1998

The finite deformation with self contact problem of C. V. joint boots is analysed by using the implicit finite element code ABAQUS/Standard. It is shown that analysis results have a good agreement with experimental ones to the degree of maximum rotation angle. As an application of design modification, the effects of thickness change of the rounded part of boot model on the bending and the contact situation of deformed geometry are investigated. In this paper, the effect of the design modification in the end on the leakage is examined using 2-D finite element simulation. To solve the leakage problem of grease, the length of the small end is enlarged. From this study, it is confirmed that we can save the cost and time by applying FEM techniques to analyze and design the boot model.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.765-770
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• 2010

In this study, the behavior of underground pipeline subjected to pile driving is examined using the verified finite element model based on the field experiment. Young's modules of surface soil is varied and elastic modulus of the other soil layer is fixed. The pile driving force model proposed by Mounir E. Mabsout in 1999 was used and it was functions of time and of force. The forcing function applied on this study considers the kinetic energy of ram located at 1.2m height with 7 tonf. The 3-layered pipeline is composed of steel(inner) pipe, PUR(Polyurethane Resin, filler) and HDPE(outer) pipe, and the length/diameter of main steel pipe is 20m/0.8m(O.D). It is used for district heating pipes in Korea. The results are expressed in terms of Von Mises stress, displacement, and vibration velocity for each soil condition. From the results of the analyses, PUR which is originally intended as a thermal insulation of inner pipe shows performance as a structural member which distributes external pressure.

• 드라이브 ㆍ 컨트롤
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• 제14권1호
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• pp.14-22
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• 2017

Flow force is the additional unbalanced force acting on the valve spool by fluid flow, excluding the static pressure force that is offset on the spool land wall at the same magnitude. When designing the valve spool, it is assumed that the same average value of static pressure is applied to the inlet and outlet spool land wall in one chamber. However, the high velocity of the fluid flow by the inlet or outlet metering orifice creates unbalanced pressure distribution and generates additional force in the opposite direction to that of the solenoid attraction force. This flow force has a negative effect on the control performance of the EPPR valve, which needs to develop uniform output pressure along the entire spool control range. In this study, we developed a 3D model of the EPPR valve and conducted flow force characteristic analysis using CFD S/W (ANSYS FLUENT). The alleviated flow force model was derived by adjusting the design parameters of the spool notch.

• 제어로봇시스템학회논문지
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• 제17권10호
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• pp.1029-1036
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• 2011

An energy-efficient reference walking trajectory generation algorithm is suggested utilizing allowable ZMP (Zero-Moment-Point) region, which maxmizes the energy efficiency for cyclic gaits, based on three-dimensional LIPM (Linear Inverted Pendulum Model) for biped robots. As observed in natural human walking, variable ZMP manipulation is suggested, in which ZMP moves within the allowable region to reduce the joint stress (i.e., rapid acceleration and deceleration of body), and hence to reduce the consumed energy. In addition, opimization of footstep planning is conducted to decide the optimal step-length and body height for a given forward mean velocity to minimize a suitable energy performance - amount of energy required to carry a unit weight a unit distance. In this planning, in order to ensure physically realizable walking trajectory, we also considered geometrical constraints, ZMP stability condition, friction constraint, and yawing moment constraint. Simulations are performed with a 12-DOF 3D biped robot model to verify the effectiveness of the proposed method.