• 한국생산제조학회지
• /
• 제25권2호
• /
• pp.118-123
• /
• 2016

Overlap cutting is a fundamental method of applying abrasive water jet (AWJ) machining to milling to produce a wider surface because the nozzle outlet is approximately 1.0 mm wide. In this study, the effects of overlap cutting on the depth profile and surface roughness are investigated. The overlapping area depends on the amount of step over, which is controlled in the pick-feed direction. If the step over is equal to or larger than the diameter of the nozzle, no overlap cut occurs but large cusps remain between the cut paths. A step over as small as one-thirds of the nozzle diameter may lead to triple-overlap cutting resulting in an extraordinary depth. By using pocket milling experiments with a step over of 0.46 (or 0.47), it is verified that AWJ can produce a milled surface of titanium, one of the hard-to-cut materials, with $76{\mu}m$ Ra.

• 대한기계학회논문집B
• /
• 제21권6호
• /
• pp.735-746
• /
• 1997

A nonlinear low-Reynolds-number k-.epsilon. model of Park and Sung was extended to predict the flows over a step with inclined wall, where a boundary layer flow without separation and a separated and reattaching flow coexist. For a better prediction of the flows, a slight modification was made on the function of the wall damping( $f_{\mu}$) and the model constant ( $C_{{\epsilon}1}$) in the .epsilon.-equation. The model performance was validated by comparing the model predictions with the experiment. It was shown that the flows over a step with inclined wall are simulated successfully with the present model.ent model.

• 대한산업공학회지
• /
• 제23권3호
• /
• pp.597-608
• /
• 1997

Life cycle product data is very important yet difficult to handle for manufacturing companies. Shoring and exchanging product data over world-wide-web is a part of key technology to implement PDM or CALS. STEP is widely accepted as a standard to represent the life-cycle product model data. Described in this paper is a web browser plug-in that can graphically display and explore product data represented by STEP over internet. By the use of the plug-in (named "npSTEP"), a product model data stored in STEP format on a web server can be displayed on a commonly used web client (browser), such as Netscape navigator, without any format conversion process. Furthermore one can explore the components or attributes of the product model data in hierarchical manner.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2007년도 추계 학술대회논문집
• /
• pp.194-199
• /
• 2007

IB (immersed boundary) method is one of the prominent tool in computational fluid dynamics for the analysis of flows over complex geometries. The IB technique simplyfies the solution procedure by eliminating the requirement of complex body fitted grids and it is also superior in terms of memory requirement. In this study we have developed numerical code (FOTRAN) for the analysis of 2D flow over a cylinder using IB technique. The code is validated by comparing the wake lengths and separation angles given by Guo et. al. We employed fractional-step procedure for solving the Navier-Stokes equations governing the flow and discrete forcing IB technique for imposing boundary conditions. Also we have developed a 3D code for the backward-facing-step flow and flow over a sphere. The reattachment length in backward-facing-step flow was compared with the one given by Nie and Armaly, which has proven the validity of our code.

• 대한토목학회논문집
• /
• 제34권2호
• /
• pp.479-492
• /
• 2014

이 연구에서는 계단과 같이 불연속 횡단 구조물을 지나는 천수 흐름에 대해 내부 경계조건으로서 정확해를 부여하는 기법을 제안하였다. 제안된 기법의 검토를 위해 MUSCL이 적용된 HLLL 근사 Riemann 해법을 이용하였다. 계단을 지나는 천수 흐름에 대한 다양한 문제에서 모의 결과는 정확해와 잘 일치하였다. 또한, 계단에서 댐 붕괴 실험 및 급경사 수로 실험의 결과와 부합되었다. 개발된 모형으로 낙차공과 같이 불연속 바닥을 지나는 천수 흐름에 대해 별도의 수위-유량 관계나 지형의 완화 없이 모의가 가능하다. 향후, 계단에 의한 흐름 저항과 수맥에 의한 에너지 손실에 대해 적절한 평가가 이루어진다면, 보나 옹벽(강변 도로)과 같은 불연속 지형을 넘나드는 천수 흐름에 대한 수치모의가 가능할 것으로 기대된다.

• 한국컴퓨터정보학회논문지
• /
• 제29권5호
• /
• pp.123-129
• /
• 2024

구급대원에게 심폐소생술은 매우 중요하나 이동하는 주들것에서 수행하는 가슴압박은 정확도가 떨어진다. 이 연구의 목적은 이동 중 주들것에서 수행하는 심폐소생술 효과를 높이기 위하여 C-step을 이용하여 주들것의 측면에서 가슴압박을 수행하는 것과 환자의 복부 위에 위치하여 가슴 압박을 수행하는 것에 대하여 차이를 알아보고자 수행되었다. 연구는 C-step 군 20명과 복부 위군 20명을 대상으로 이동 중 주들것에서 2분간 연속된 가슴압박을 수행하였다. 연구결과 C-step을 적용한 군에서 적정한 깊이(t=4.132, p=.000)와 속도(t=7.177, p=.000)를 나타내었으며 정확도가 더 높은 것으로 나타났다(t=6.774, p=.000). 또한 C-step을 적용한 군에서 위치불량(t=-5.197, p=.008)과 너무 얕은 오류가 적은 것으로 나타났다. 결론적으로 C-step을 장착한 주들것에서의 가슴압박은 심폐소생술의 질을 높이고 병원 전 환자의 생존율을 높이는데 도움을 줄 것으로 판단된다.

• Journal of Positioning, Navigation, and Timing
• /
• 제10권4호
• /
• pp.387-393
• /
• 2021

This paper proposes a system to synchronize the time of computers over an unmanned aerial vehicle (UAV) network. With the proposed system, the UAVs can perform missions that require precise relative time. Also, data collected by UAVs can be fused precisely with synchronized time. In the system, to synchronize the time of all computers over the UAV network, two-step synchronization is performed. In the first step, the mission computers of the UAVs are synchronized through the server of the system. After the first step, the mission computers measure time offset between the time of the mission computers and the flight computers. The offset values are delivered to the server. In the second step, virtual time is determined by the server from the collected time offset. The measured offset is compensated by moving the synchronized time of mission computers to the reasonable virtual time. Since only the time of mission computers are controlled, any flight computers that use micro air vehicle link (MAVLink) protocol can be synchronized in the proposed system.

• 산업기술연구
• /
• 제19권
• /
• pp.59-65
• /
• 1999

This study is to analyze turbulent flow over a backward-facing step in a rectangular duct. The side wall effects on the internal flow were determined by varying the aspect ratio(defined as the step span-to-height ratio) from 1 to 20. In the flow behind a backward-facing step, separation, recirculation and redeveloping is occurred frequently. These phenomena appear in a particular variation by varying the aspect ratio. The results show that the aspect ratio has an influence on the velocity and reattachment length. When the AR is increased, the reattachment length is increased. For 6 over aspect ration, the rate of increase is decreased. The length of recirculation in the upper corner is increased, as the increase of aspect ration. It's width is not changed in the variation of aspect ration. The transverse, streamwise and spanwise velocities were decreased along the flow down stream of the step.

• 대한산업공학회지
• /
• 제27권1호
• /
• pp.69-88
• /
• 2001

In the zigzag milling operation, an important issue is to design a machining strategy which minimizes the cutting time. An important variable for minimization of cutting time is the tool path length. The tool path is divided into cutting path and non-cutting path. Cutting path can be subdivided into tool path segment and step-over, and non-cutting path can be regarded as the tool retraction. We propose a new method to determine the cutting direction which minimizes the length of tool path in a convex or concave polygonal shape including islands. For the minimization of tool path length, we consider two factors such as step-over and tool retraction. Step-over is defined as the tool path length which is parallel to the boundary edges for machining area and the tool retraction is a non-cutting path for machining any remaining regions. In the determination of cutting direction, we propose a mathematical model and an algorithm which minimizes tool retraction length in complex shapes. With the proposed methods, we can generate a tool path for the minimization of cutting time in a convex or concave polygonal shapes including islands.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2000년도 춘계학술대회 논문집
• /
• pp.944-947
• /
• 2000

Sculptured surface machining plays a vital role in the process of bring new products to the market place. A great variety of products rely on this technology for the production of the dies and moulds used in manufacturing. And, the use of CNC machines and CAD/CAM system has become a vital parts of product development process. The propose of this study is to investigate the effect of cutting parameters on the machinability such as surface roughness and cusp generated in the machining of sculptured surface on a three-axis CNC machining center using the CAD/CAM system. Experimental result showed that: In step down cutting, as the inclined angle of surface became smaller, the cusp height appeared higher. On the other hand, in step over cutting, as the inclined angle of surface became larger, the cusp height appeared higher. In the point of precision machining, step over cutting was more effective. For the minimization of cusp height, step down cutting was effective in larger inclined surface, but step over cutting in smaller inclined surface.