• 대한기계학회논문집B
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• 제27권4호
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• pp.458-465
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• 2003

The main objective of the research is to develop a research code solving transient incompressible Navier-Stokes equation. In this research code, Adams-Bashforth method was applied to the convective terms of the navier stokes equation and the splitted equations were discretized spatially by finite element methods to solve the complex geometry problems easily. To reduce the divergence on the boundaries of pressure poisson equation due to the unsuitable pressure boundary conditions, multi step approximation pressure boundary conditions derived from the boundary linear momentum equations were used. Simulations of Lid Driven Flow and Flow over Cylinder were conducted to prove the accuracy by means of the comparison with results of the previous workers.

• 한국해안·해양공학회논문집
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• 제21권2호
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• pp.91-107
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• 2009

단일 계단지형 위를 지나는 선형 파랑의 변형을 계산하기 위해 변분근사법과 고유함수 전개법을 사용하였다. 이들 수치해를 비교에서 반사율과 투과율 그리고 해면변위는 거의 일치한다. 그러나 계단 경계에서 유속 정합조건이 부여되었음에도 불구하고 계산된 x방향 유속의 수직구조는 차이를 보인다.

• 에너지공학
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• 제24권2호
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• pp.110-114
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• 2015

A numerical investigation has been carried out on recirculation zone formed downstream of a compressible flow over a backward facing step. The study has been performed by solving Two-Dimensional Navier-Stokes equations. The system of governing equations has been solved, using an explicit Harten-Yee Non- MUSCL Modified flux type TVD scheme and a zero-equation algebraic turbulence model to calculate the eddy viscosity coefficient. The recirculation region dimensions are characterized over a range of Mach numbers of fixed step height 5mmThe detail of recirculation zone such as pressure, temperature, recirculation length, strength etc are reported. The variations of these characteristics due to change of Mach number are also presented.

• 대한물리의학회지
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• 제9권1호
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• pp.69-74
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• 2014

PURPOSE: The aim of this study is to compare the spatio-temporal gait parameters between paretic and non-paretic limb while stepping over the different obstacle's heights in subjects with stroke. METHODS: Nine subjects with stroke were participated in this study. Subjects were asked to step over obstacles with a different height. 8 camera motion analysis system(Motion Analysis Corporation, Santa Rosa, USA) was used to measure spatio-temporal parameters. The two way repeated measurement ANOVA was used to compare spati-temporal gait parameters between paretic and non-paretic limbs while stepping over a different obstacle's height(0cm, 10cm, 20cm). RESULTS: Step width, velocity, single supoort time, and double support time were not different among obstacle's height(p>0.05) but stride length, step length, and cadence were significantly different(p>0.05). In stride length, cadence, and double support time, the interactions between obstacle's heights and limbs were not different(p>0.05) but it was significantly different in velocity, step length, and single support time(p<0.05). Velocity, stride length, cadence, and double support times were not different between paretic limb and non-paretic limb(p>0.05) but step length and single support times were significantly different between paretic limb and non-paretic limb(p<0.05). CONCLUSION: These results show that there are differences with spatio-temporal gait parameters among obstacle's heights and between paretic and non-paretic limb during obstacle crossing in subjects with stroke.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.525-526
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• 2007

Over-polishing is required to completely remove the material of top surface across whole wafer, in spite of a local dishing problem. This paper introduces the two-step CMP process using protective layer and high selectivity slurry, to reduce dishing amount and variation. The 30nm thick protective oxide layer was deposited on the pattern, and then polished with low selectivity slurry to partially remove the projected area while suppressing the removal rate of the recessed area. After the first step CMP process, high selectivity slurry was used to minimize the dishing amount and variation in pattern structure. Experimental result shows that two-step CMP process can be successfully applicable to reduce the dishing defect generated in over-polishing.

• 대한기계학회논문집
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• 제19권9호
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• pp.2328-2341
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• 1995

An experimental study on the flow over the axisymmetric backward-facing step was carried out. The purposes of the present study are to investigate the effect of the free stream turbulence intensity on the reattachment length and to understand the turbulence structure of the recirculating flows. Local mean and fluctuating velocity components were measured in the separated and reattaching axisymmetric turbulent boundary layer over the wall of convex cylinder placed in a water tunnel by using 2-color 4-beam fiber optics laser Doppler velocimetry. As the free stream turbulence intensity increased, the reattachment length became shorter due to the enhanced mixing in the separated shear layer. It was also observed that the reverse flow velocity and turbulent kinetic energy increase with increasing free stream turbulence intensity. Spectral data and flow visualization showed that low-frequency motions occur in the separated flow behind a backward-facing step. These motions have a significant effect on the time-averaged turbulence data.

• 한국가시화정보학회지
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• 제12권3호
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• pp.15-20
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• 2014

Direct numerical simulation (DNS) dataset of a turbulent boundary layer (TBL) with a step change from smooth to rough surface is analyzed to examine spatially developing flow characteristics. The roughness elements are periodically arranged two-dimensional (2-D) spanwise rods with a streamwise pitch of ${\lambda}=8k$ ($=12{\theta}_{in}$), and the roughness height is $k=15{\theta}_{in}$, where ${\theta}_{in}$ is the inlet momentum thickness. The step change is introduced $80{\theta}_{in}$ downstream from the inlet. For the first time, full images from the DNS data with the step change from the smooth to rough walls is present to get some idea of the geometry of turbulent coherent structures over rough wall, especially focusing on their existence and partial dynamics over the rough wall. The results show predominance of hairpin vortices over the rough wall and their spanwise scale growth mechanism by merging.

• International Journal of CAD/CAM
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• 제7권1호
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• pp.21-30
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• 2007

The inverse offset method (IOM) is widely used for generating cutter paths from the point-based surface where the surface is characterised by a set of surface points rather than parametric polynomial surface equations. In the IOM, cutter path planning is carried out by specifying the grid sizes, called the step-forward and step-interval distances respectively in the forward and transverse cutting directions. The step-forward distance causes the chordal deviation and the step-forward distance produces the cusp. The chordal deviation and cusp are also functions of local surface slopes and curvatures. As the slopes and curvatures vary over the surface, different step-forward and step-interval distances are appropriate in different areas for obtaining the machined surface accurately and efficiently. In this paper, the chordal deviation and cusp height are calculated in consideration with the surface slopes and curvatures, and their combined effect is used to estimate the machined surface error. An adaptive grid generation algorithm is proposed, which enables the IOM to generate cutter paths adaptively using different step-forward and step-interval distances in different regions rather than constant step-forward and step-interval distances for entire surface.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2011년도 추계학술대회
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• pp.237-240
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• 2011

행정기관 인터넷전화를 구축하여 사용하는 국가정보통신서비스 'C'그룹 사업자에는 KT, SK브로드밴드, LG유플러스, 삼성SDS 4개 사업자가 있다. 행정기관 인터넷전화에 대한 공격을 대비하여 보안 대응 모델에 대한 연구가 필요하다. 본 논문에서는 행정기관 인터넷전화 사업자 별로 보안 대응 대책을 내용으로 조사 분석한다. 행정기관 인터넷전화 보안 침해 모델 개발 연구를 위해 국정원의 5가지 보안 위협에 대해 기밀성을 중심으로 우선순위를 설정하여 (1)불법 도청 (2)호 가로채기 (3)서비스 오용 (4)서비스거부 공격 (5)인터넷전화 스팸 공격에 대한 공격 시나리오 작성하여 분석한다. 행정기관 인터넷전화 보안 대응 모델 개발 연구는 보안 위협별 보호 기술 분석과 보안 침해 단계별 대응 체계 연구를 통해 단계별 대응 모델 개발 연구를 한다.

• 한국전문물리치료학회지
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• 제14권4호
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• pp.66-74
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• 2007

The aim of the present study was to investigate age-related differences in stepping behavior in response to sensory perturbations of postural balance. The participants for this study were 2 healthy elderly adults (mean age=76.0) and 2 younger adults (mean age=25.5). Subjects were asked to step over a 10 cm high obstacle at self-paced speed with the right limb to land on the primary target (normal step length) that is 10 cm in diameter. However, if, during movement, the light was illuminated, then the subject had to step on the secondary target (long step length). It was planned that the onset of the light would be prior to peak Fx of swing limb, between swing peak Fx and swing toe-off, and after swing toe-off. In the younger adults these secondary visual cues were provided at mean times of 240 ms (standard deviation (SD)=11), 402 ms (SD=13), and 476 ms (SD=88) following the movement onset. Corresponding mean times for the healthy elderly were 150 ms (SD=67), 352 ms (SD=39), and 562 ms (SD=115). Results showed great changes in both group and visual cue condition in Fx ground reaction forces and temporal events following the swing toe-off. Swing limb acceleration force (Fx) and stance peak Fx1 was much greater in the young adults compared to the older adults. Both young and older adults increased stance peak Fx2 in the visual cue condition compared to normal stepping. There was no difference in stance peak Fx2 between the visual cue conditions in both groups. Similarly, the time to stance peak Fx2 was much longer for the visual cue condition than for the normal stepping. It was not different between the visual cue conditions in the young adults, but in the elderly mid and late cue was much greater than early cue. In addition, time to stance peak Fx2 and swing and stance time were much longer in the older adults compared to the young adults for the visual cue conditions. These results suggest that unlike young adults, elderly adults did not flexibly modify their responses to unexpected changes in step length while stepping over obstacles.