• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.531-534
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• 2006

This study is concerned with radial turbine design and performance improvement of a turbo generator system, which is used for maximizing performance of a 250kW MCFC fuel cell system. A preliminary design of a radial turbine has been performed under the thermodynamic and fluid-dynamic conditions determined by a cycle analysis of the MCFC BOP system. Basic demensions are determined by a meanline analysis and calculation of radial variation at the exit of the turbine. The turbine impeller is designed and modified by iterative processes of three dimensional flow analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.1
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• pp.155-164
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• 2002

The journal bearings use in machine parts which move relative to each other and those reduce friction and wear of journals. The journal bearings are designed to operate in the hydyodynamic lubrication regime, but elastohydrodynamic lubrication nay occur if the pressures are too high or the running speeds are too low at machine elements. It is the phenomenon that the lubricant film is broken and some parts of surfaces are in rolling contact, so that wear will increase in mixed lubrication regime. The purpose of this study is to minimize the wear rate of journal bearings for extending machine life. The wear mate in mixed lubricated regime is selected as objective function because most of wear of the journal bearings develops in elastohydrodynamic lubrication. The journal bearings we represented by a bearing radius, shaft radius, and bearing width, but the bearing radius only is selected as design variables due to a bearing radius has an influence on friction loss, stability limit velocity, and film parameter, which are used as constraints. For numerical calculation, PLBA, that is a class of the RQP algorithm, is used.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.1
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• pp.43-53
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• 2020

The effect of the relative location between pre-swirl nozzle and receiver hole on the performance of radial on-board injection type pre-swirl system was analyzed. In this study, tendency of the change of discharge coefficient and temperature drop efficiency were analyzed for 20 design points through the combination of 5 pre-swirl nozzle location and 4 receiver hole location. Discharge coefficient of system tended to be similar to the pressure ratio of the pre-swirl nozzle. System performance variation occurred as the flow structure in the cavity was affected by the surface, and the influence of the stationary surface is greater than that of the rotating surface. Discharge coefficient of system changed -1.39% to 1.25% and temperature drop efficiency changed -5.41% to 2.94% refer to reference design point.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.1
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• pp.223-233
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• 2014

This study empirically analyzes the relationships among the road and traffic experts' personal characteristics, the driving behavior and factors being expected to have an effect on the satisfaction about roundabout operation. The factors are drawn and grouped through the principle component analysis to clarify driving environment satisfaction on roundabout operation. Each group is named as personal attribute, driving behavior attribute, and satisfaction. After the variables are refined by confirmatory factor analysis, satisfaction model is developed with personal attribute and driving behavior attributes as exogenous variables and roundabout driving awareness and emotion attributes as endogenous variables. As a result, driving satisfaction of roundabout operation is directly influenced by delay reduction, safety improvement, capacity increase, sight improvement, severity accident reduction, and bicycle convenience and indirectly gender, age, driving time, and driving experience. Law obeyance, driving concession, traffic sign obeyance, and interposition do not statistically shows significant on satisfaction. As a result of Analytical Hierarchy Process (AHP), the turning radius of geometry and the driving behavior are important elements for roundabout safety.

• Tunnel and Underground Space
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• v.12 no.4
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• pp.277-283
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• 2002

This experimental study concerns the characteristics of a helical flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one is rotating. The pressure losses and skin friction coefficients have been measured for the fully developed flow of Non-Newtonian fluid, aqueous solution of sodium carbomethyl cellulose (CMC) and bentonite with inner cylinder rotational speed of 0~400 prm. Also, the visualization of helical flows has been performed to observe the unstable waves. The results of present study reveal the relation of the Reynolds number Re and Rossby number Ro with respect to the skin friction coefficients. In somehow, they show the existence of flow instability mechanism. The pressure losses increase as the rotational speed increases, but the gradient of pressure losses decreases as the Reynolds number increases in the regime of transition and turbulence. And the increase of flow disturbance by Taylor vortex in a concentric annulus with rotating inner cylinder results in the decrease of the critical Reynolds number with the increase of skin friction coefficient.

• Journal of Korean Society of Transportation
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• v.23 no.5 s.83
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• pp.73-81
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• 2005

Triangle-shaped island was been used for the exclusive separation between the right-turn and the through flow. However, in case that existing Triangle-Shaped Island is built at the intersection of narrow road. there are more possibilities of traffic collision trespassing into the opposite lane. Accordingly, separation of the opposite lane is required so as to prevent the intrusion of the large-sized (a heavy) vehicle into the opposite lane turning at the intersection. This study showed the comparison between intersection composed of existing Triangle-Shaped Island and the intersection with Drop Island is added. First of all, in the safety aspect, a method to decide location and shape of Drop Island considering turning trajectory of the large-sized (the heavy vehicle) is addressed. The guideline on the placement of drop island install location and method to decide form the consider heavy truck's turn trajectory in safety side. As a conclusion. we analyzed that drop island is relatively superior to existing Triangle-Shaped Island in terms of driver, ease of driving, driving pleasantness, pedestrian, widening and economic performance aspect.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.891-898
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• 1992

When catilever beams rotate about axes perpendicular to the underformed beam's longitudinal axis, their bending stiffnesses change due to the stretching caused by centrifugal inertia forces. Such phenomena result in variations of natural frequencies and mode shapes associated with constant speed rotational motions of the beams. These variations are important in many practical applications such as helicopter blades, turbomachines, and space structures. This paper presents the formulation of a set of linear equations governing the lateral motion of rotating cantilever beams. These equations can be used to provide accurate predictions of the variations of natural frequencies and mode shapes associated with constant speed rotational motions of the beams. These variations are important in many practical applications such as helicopter blades, turbomachines, and space structures. This paper presents the formulation of a set of linear equations governing the lateral motion of rotating cantilever beams. These equations can be used to provide accurate predictions of the variations of natural frequencies and mode shapes due to rotation. This technique is simpler and more consistent than other conventional techniques which are commonly used in the literature.

• Journal of the Korean Institute of Intelligent Systems
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• v.26 no.6
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• pp.505-510
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• 2016

This paper presents a searching method of corresponding points robust to rotational error for scan-matching used for SLAM(Simultaneous Localization and Mapping) in mobile robot. A differential driving mechanism is one of the most popular type for mobile robot. For driving curved path, this type controls the velocities of each two wheels independently. This case increases a wheel slip of the mobile robot more than the case of straight path driving. And this is the reason of a drifting problem. To handle this problem and improves the performance of scan-matching, this paper proposes a searching method of corresponding points using extraction of a closest point based on rotational radius of the mobile robot. To verify the proposed method, the experiment was conducted using LRF(Laser Range Finder). Then the proposed method is compared with an existing method, which is an existing method based on euclidian closest point. The result of our study reflects that the proposed method can improve the performance of searching corresponding points.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1992.10a
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• pp.59-64
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• 1992

터빈 블레이드와 같이 회전하는 구조물의 파단은 공진 근처에서 진동이 발 생할 때에 이에 기인하는 피로에 의하여 발생한다. 그러므로 이와 같은 파단 을 피하기 위해서는 설계 단계에서 이론적인 계산에 의하여 구조물의 고유 진동수를 결정하는 것이 상당히 중요하다. 판이 회전을 받게 되면 원심력에 의하여 판의 강성이 증가하므로 고유진동수가 회전하지 않는 판의 고유진동 수보다는 상당히 증가하게 된다. 이에 대한 연구가 국내외에서 상당수 행하 여졌지만, 연구의 대부분이 회전의 영향을 고려하지 않은 정지판(stationary plate)에 대한 것이며 뢰전을 고려한 연구는 극히 제한되어 있다. 또한 회전 의 영향을 고려한 연구의 대부분이 해석 대상을 보로서 단순화 시켰고 해법 으로는 유한요소법과 Ritz법 등을 사용하였다. 이는 블레이드가 지니고 있는 기하학적인 형상과 진동 특성이 해석적인 방법으로 해결하는 데에는 상당한 어려움이 있기 때문이다. 실제적으로는 터빈 블레이드와 같은 회전체의 진동 특성이 설치각이나 비틀림각, 판의 형상비, 회전속도 등의 변화에 의하여 영 향을 받기 때문에 보와 같은 진동 거동을 보이기보다는 판이나 셀과 같은 진동 거동을 보이므로 보다 정확한 해석을 수행하기 위해서는 해석 대상을 판이나 셀로서 취급하는 것이 타당하다. 따라서 본 연구에서는 위와 같은 이 유 때문에 해석 대상을 등방성 사각판과 직교이방성 복합재료 사각판으로 선택하였으며, 구조물의 고유진동수에 영향을 미치는 다음과 같은 인자들을 해석에 고려하였다. 1. 회전속도 (rotational speed) 2. 설치각 (setting angle) 3. 허브의 반경 (hub radius) 4. 판의 형상비 (aspect ratio) 5. 적층순서 (stacking sequence)구조물에 대한 동적실험(dynamic test)을 통하여 단기간에 동적특성을 결정하고 SDM(structure dynamic modification)이나 FRS(force response simulation)를 수행하여 임의의 좌표 공간에 대한 진동수준을 해석적으로 예측할 뿐만 아니라 구조물의 진동제어 를 위한 동적인자를 변경시킬 수 있는 정보를 제공하며 장비를 방진할 경우 신뢰성 있는 전달률을 결정할 수 있다. 실험적으로 철교, 교량이나 건물의 철골구조 및 2층 바닥 등 대,중형의 복잡한 구조물에 대항 동특성을 나타내 는 모빌리티를 결정할 경우 충격 가진 실험이 사용되는 실험장비 측면에서 나 실험을 수행하는 과정이 대체적으로 간편하다. 그러나 이 경우 대상 구조 물을 충분히 가진시킬수 있는 용량의 대형 충격기(large impact hammer)가 필요하게 된다. 이러한 동적실험은 약 길이 61m, 폭 16m의 4경간 교량에 대 하여 동적실험을 수행하여 가능성을 확인하였다. 여기서는 실험실 수준의 평 판모델을 제작하고 실제 현장에서 이루어질 수 있는 진동제어 구조물에 대 한 동적실험 및 FRS를 수행하는 과정과 동일하게 따름으로써 실제 발생할 수 있는 오차나 error를 실험실내의 차원에서 파악하여 진동원을 있는 구조 물에 대한 진동제어기술을 보유하고자 한다. 이용한 해마의 부피측정은 해마경화증 환자의 진단에 있어 육안적인 MR 진단이 어려운 제한된 경우에만 실제적 도움을 줄 수 있는 보조적인 방법으로 생각된다.ofile whereas relaxivity at high field is not affected by τS. On the other hand, the change in τV does not affect low field profile but stron

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.851-860
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• 2020

With an increase in the aging population and a rising social interest in health and welfare, studies to improve healthcare in the elderly are being actively conducted. This study attempted to improve the current design and manufacture of elevating electric wheelchairs to enhance user safety and convenience. Seat design based on the user's body shape, convenience while boarding or alighting, caster turning radius and, safety and stability features that prevent shaking when the user gets up or sits down were improved. A driving experiment was conducted to evaluate the operation of the indoor electric wheelchair designed and manufactured with these additional functionalities. During the test, the performance parameters evaluated were continuous driving time, turning radius, maximum lifting and lowering load, maximum lifting height, noise level, minimum distance sensing by the driving auxiliary sensor, ability to interact with server and app programs, and the duty cycle maximum error rate. The test confirmed that this improved electric wheelchair successfully met target parameters. In a future study, we will evaluate this improved electric wheelchair from a user's perspective for its usability parameters, such as satisfaction, convenience and stability.