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우수한 기구학 특성을 가지는 새로운 병렬형 구형 3자유도 메커니즘의 구현
이석희(S. H. Lee),김희국(W. K. Kim),오세민(S. M. Oh),이병주(B. J. Yi) 한국정밀공학회 2004 한국정밀공학회 학술발표대회 논문집 Vol.2004 No.10월
In our pervious paper, a new parallel-type spherical 3-degree-of-freedom mechanism consisting of a two-degree-of-freedom parallel module and a serial RRR subchain was proposed[1]. In this paper, its improved version is suggested and implemented. Differently from the previous 3-dof spherical mechanism, gear chains are incorporated into the current version of the mechanism to drive the distal revolute joint of the serial subchain from the base of the mechanism and in fact, the modification significantly improves kinematic characteristics of the mechanism within its workspace. Firstly, after a brief description on its structure, the closed-form solutions of both the forward and the reverse position analysis are derived. Secondly, the first-order kinematic model of the mechanism for the inputs which are assumed to be located at the base is derived. Thirdly, through the simulations of the kinematic analysis via. kinematic isotropic index, it is confirmed that the mechanism has much more improved isotropic properties throughout the workspace of the mechanism than the previous mechanism in [1]. Lastly, the proposed mechanism is implemented to verify the results from this analysis.
조장근(J.K. Cho),오상욱(S.W. Oh),박원규(W.G. Park),오세민(S.M. Oh),이수원(S.W. Lee) 한국전산유체공학회 1996 한국전산유체공학회 학술대회논문집 Vol.1996 No.-
The jet pump is being used in many fields for several purposes because of its simple construction and easy operation. The characteristics of the geometrical variables, pressure gradient and velocity distribution of the jet pump are studied using the CFD technique. The flow calculations through a bended nozzle, a mixing chamber and a venturi are presented and phenomenological aspects are discussed. This study solve 3-D steady incompressible Navier-Stokes equations using the Iterative time marching scheme. The governing equations are differenced with 1st-order accurate backward difference scheme for the time derivatives and 3rd-order accurate QUICK scheme for the convective terms, The Mark-and-cell concept was applied efficiently to solve continuity equation. which is differenced 2nd-order accurate central differenced scheme. The 4th-order artificial damping is added to the continuity equation for numerical stability. A O-type of grid system is generated inside a nozzle and venturi of the jet pump. It has concluded that the results of present study properly agree with physical flow phenomena.
일부 영세 도금사업장의 국소배기성능과 공기중 총크롬 , 6가 크롬 및 니켈농도와의 관계분석
박동욱,박두용,신용철,오세민,정규철 한국산업위생학회 1993 한국산업보건학회지 Vol.3 No.1
To evaluate efficiencies of the local exhaust systems installed in chromium and nickel electroplating tanks, specifications of each tank and general performances of the local exhaust systems were measured in 16 electroplating plants from July 3 to November 24, 1992. Airborne concentrations of total chromium, hexa-chromium and nickel were also measured. Most of the local exhaust systems installed in electroplating plants were inadequately designed. Average capture velocities of local exhaust systems in chromium and nickel tanks were 0.45 m/sec and 0.29 m/sec. Average slot velocities in chromium and nickel tanks were 7.30 m/sec and 2.87 m/sec respectively. Both average capture and slot velocities were in noncompliance with the standards recommended by American Conference of Governmental Industrial Hygienists (ACGIH) and National Institute for Occupational Safety and Health (NIOSH). Exhausted air volume was insufficient in all local exhaust systems surveyed. Worker exposure levels to total chromium, hexa-chromium and nickel were 43.0 ㎍/㎥, 1.7 ㎍/㎥ and 9.3 ㎍/㎥, which were below the Korean Standard and U.S. Occupational Health and Safety Administration (OHSA) Permissible Exposure Limit (PEL). However, Worker exposure level to hexa-chromium exceeded the NIOSH Recommended Exposure Limit(REL) of 1 ㎍/㎥. As the result of Scheffee's multiple comparions, worker exposure levels to all metals were significantly different between two groups by the management state of existing local exhaust systems (p$lt;0.05). However, Difference between a group with local exhaust systems which were poorly managed and another group without local exhaust system was satatistically non-significant.