• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2002년도 학술발표회 논문집(II)
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• pp.1187-1194
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• 2002

In this study, we have simulated regional climate over East Asia using dynamical downscaling For dynamic downscaling experiments for regional climate simulation, MM5method. with 27 km horizontal resolution and 18 layers of sigma-coordinate in vertical is nested within global-scale NCEP reanalysis data with 2.5。${\times}$2.5。 resolution in longitude and latitude. In regional simulation, January and July, 1979 monthly mean features have been obtained by both continuous integration and daily restart integration driven by updating the lateral boundary forcing at 6-hr intervals from the NCEP reanalysis data using a nudging scheme with the updating design of initial and boundary conditions in both continuous and restart integrations. In result, we may successfully generated regional detail features which might be forced by topography, lake, coastlines and land use distribution from a regional climate. There is no significant difference in monthly mean features either integrate continuously or integrate with daily restart. For climatologically long integration, the initial condition may not be significantly important. Accordingly, MM5 can be integrated for a long period without restart frequently, if a proper lateral boundary forcing is given.

• 한국정밀공학회지
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• 제18권8호
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• pp.116-121
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• 2001

The paper presents the dynamic characteristics of a rotor-bearing system supported by an actively controlled hydrodynamic journal bearing. The proportional. derivative and integral controls are adopted for the control algorithm to control the hydrodynamic journal bearing with an axial groove. Also, the cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film more accurately than conventional analysis, which uses the Reynolds condition. The speed at onset of instability of a rotor-bearing system is increased by both proportional and derivative control of the bearing. The proportional control increases the stability threshold without affecting the whirl ratio. However, for the derivative control of the bearing, increase of stability threshold speed is accompanied by a parallel reduction of the whirl ratio. The integral control has no effect on stability characteristics of hydrodynamic journal bearing. The PD-control is more effective than proportional or derivative control. Results 7how the active control of bearing can be adopted for the stability improvement of a rotor-bearing system.

• 대한조선학회논문집
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• 제55권5호
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• pp.421-430
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• 2018

The shape of a yacht sail made of thin fabric materials is easily deformed by wind speed and direction and it is affected by the deformation of the standing rig such as mast, boom, shrouds, stays and spreaders. This deformed sail shape changes the air flow over the sail, it makes the deformation of the sail and the rig again. To get a sail performance accurately these interactive behavior of sail system should be studied in aspects of the aerodynamics and the fluid-structure interaction. In this study aerodynamic analysis for the sail system of a 30 feet sloop is carried out and the obtained dynamic pressure on the sail surface is applied as the loading condition of the calculation to get the deformations of the sail shape and the rig. Supporting forces by rig are applied as boundary condition of the structure deformation calculations. And the characteristics of the air flow and the dynamic pressure over the deformed sail shape is investigated repeatedly including the lift force and the location of CE.

• 전자공학회논문지SC
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• 제43권5호
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• pp.10-18
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• 2006

본 논문에서는 다중 로봇 시스템에서 물체와 로봇 팔끝 간에 접촉 마찰이 존재할 때 이 로봇 시스템의 조작도를 해석하는 새로운 방법을 제안한다. 로봇이 물체를 떨어뜨리지 않고 잡고 있으려면, 로봇이 물체에 가하는 힘 벡터가 friction cone 내부에 존재 해야만 한다. 이러한 friction cone 내부를 나타내는 식은 일반적으로 비선형 형태로 되어 있기 때문에 기존의 조작도 분석 방법에 이 식을 구속 조건으로 적용하기가 쉽지 않다. 따라서 본 논문에서는 이러한 friction cone 내부를 다각뿔로 근사함으로써 선형적인 구속 조건으로 표현하였다. 또한 선행 연구에서 찾지 못했던 부분을 새롭게 찾아내었다. 그리고 다중 로봇 시스템에 조작도를 나타내는 물체 중심의 가속도를 구하기 위해서, 먼저 선형계획법을 통해서 허용 가능한 토크의 영역을 구하였다. 이 토크의 영역을 선형 변환을 통해 최종적으로 물체의 최대 가속도의 영역을 구하였다. 본 방법의 타당성을 입증하기 위해서 두 대로 구성 된 다중 로봇 시스템과 PUMA560 로봇 시스템에 적용하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제22권2호
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• pp.76-82
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• 2018

본 논문에서는 지점부 경계조건을 고려하여 단순보의 유한요소모델을 개선하는 기법을 제안하였다. 기존의 유한요소모델개선 기법은 주로 가속도 응답으로부터 추정된 동특성(고유진동수, 모드형상)을 이용하여 유한요소모델을 개선하였다. 이렇게 개선된 유한요소모델은 실제 구조물의 정적응답을 예측하기 어렵고, 잘못된 구조물의 물성치를 추정하는 문제가 발생한다. 제안된 기법은 먼저, 구조물의 처짐과 지점부 회전변위를 계측하여 지점부 경계조건을 간략화한 유한요소모델의 회전 스프링 강성을 정량적으로 추정한다. 회전 스프링 강성이 개선된 유한요소모델과 구조물의 동특성을 사용하여 구조물의 물성치를 추정함으로써 최종 개선된 유한요소모델을 구축된다. 제안된 유한요소모델 개선 기법과 기존 유한요소모델개선 기법을 수치해석 시뮬레이션을 통하여 비교 및 검증하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.273-276
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• 2004

Dynamic model of the Korea standardized rubber-tired AGT light rail vehicle, and boundary conditions between vehicle and infrastructures (running track, guidance rail) were defined to analyze vehicular vibration behaviors occurred at the worst condition for straight running track. Using the commercialized software RecurDyn, resultant forces and vibration accelerations of car body and bogies were analyzed. Based on the Korea performance test criteria for urban transit, vertical and lateral vibration of car body were calculated and evaluated as wearing condition of guide wheels. And resultant forces between bogie guidance frame and guide rail in straight running track were analyzed. As the results, the Korea standardized rubber-tired AGT light rail vehicle satisfied the performance criteria and design requirement .

• Tribology and Lubricants
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• 제14권3호
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• pp.51-58
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• 1998

This paper considers analysis of the lubrication between the piston ring and the cylinder liner. Piston ring lubrication analysis considering oil transport is important because oil consumption is an essential factor to design the piston assembly. To develop the lubrication analysis program for the piston ring, oil continuity condition and open-end boundary assumption are used for computational boundaries. Results show that oil continuity can be almost satisfied at any crank angle in and out of the piston ring clearance. Therefore the amount of oil consumption and the dynamic behavior of ring pack can be estimated using this algorithm. And it can be known that the effective width may be smaller than the full width of the piston ring, so oil starvation condition should be considered for the lubrication analysis of the piston ring.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제33회 춘계학술대회 개최
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• pp.212-217
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• 2001

This paper presents the stability characteristics of a rotor-bearing system supported by actively controlled hydrodynamic journal bearing. The proportional and derivative controls including coupled motion are adopted for the control algorithm to control the hydrodynamic journal bearing with a circumferentially groove. Also, the cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film more accurately than conventional analysis which uses the Reynolds condition. The stability characteristics are investigated with the Routh-Hurwitz criteria using the linear dynamic coefficients which are obtained from the perturbation method. The stability characteristics of the rotor-bearing system supported by active controlled hydrodynamic journal bearing are investigated for various control gain. It is found that the speed at onset of instability is increased for both proportional and derivative control of the bearing, and the proportional and derivative control of coupled motion is more effective than proportional and derivative control of uncoupled motion.

• Tribology and Lubricants
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• 제17권4호
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• pp.283-289
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• 2001

The paper presents the stability characteristics of a rotor-bearing system supported by actively controlled hydrodynamic journal bearing. The proportional and derivative controls including coupled motion are adopted for the control algorithm to control the hydrodynamic journal bearing with a circumferentially groove. Also, the cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film more accurately than a conventional analysis which uses the Reynolds condition. The stability characteristics of a rotor-bearing system supported by actively controlled hydrodynamic journal bearing are investigated for various control gains with the Routh-Hurwitz criteria using the linear dynamic coefficients which are obtained from the perturbation method. It is found that the speed at onset of the instability is increased for both proportional and derivative control of the bearing. It is also found that the proportional and derivative control of the coupled motion is more effective than that of the uncoupled motion.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제33회 춘계학술대회 개최
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• pp.334-339
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• 2001

The nonlinear vibration characteristics of hydrodynamic journal bearings with a circumferentially groove are analyzed numerically when the external sinusoidal disturbances are given to the rotor-bearing system continuously. Also, the cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film more accurately than conventional analysis which uses the Reynolds condition. It is found that the difference between linear and nonlinear analysis is much more remarkable as the amplitude of external disturbance increases, and it depends upon the excitation frequency of external disturbance. It is also shown that the cavity region in the fluid film is increased as the amplitude or excitation frequency of external disturbance increases. The whirling center of the steady state orbit moves closer to the bearing center as the amplitude or the excitation frequency of the external disturbance increases because of smaller range of full film region.