• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.193-198
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• 2003

A gas turbine blade has an internal cooling passage equipped with ribs, which can be modeled as a ribbed channel. We have studied a flow inside a ribbed channel using large eddy simulaton (LES) with a dynamic subgrid-scale model. The simulation results are compared with the experimental ones. The turbulence intensity and local heat transfer near the rib have not been well captured by the conventional Reynolds averaged Navier-Stokes simulation (RANS). However, these variables obtained by the present LES agree well with those from experiments. From the instantaneous velocity and temperature fields, we explain the mechanisms responsible for the local peaks in the heat transfer distribution along the channel wall. We have also investigated the effect of rotation on the flow and heat transfer in the ribbed channel.

• 한국농공학회지
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• 제40권1호
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• pp.78-87
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• 1998

In this study, semi-rigid light-weight framed structures analysis model (SERIFS) was developed by advancing the LEIFS model. This model enables us to analyze simultaneous effects of large deflection and semi-rigid connection by computing unbalanced load occurring in the process of repeated loading through equalization of bending moments and torsion. This model is also able to handle the effect of the semi-rigid connection and large deflection by modifying the elastic stiffness matrix using moment-rotation behavior of connection. Moment-rotation behavior of the semi-rigid connection was adopted from the experimental results of load-vertical displacement of frame element In conclusion, this model achieves to analyze the nonlinear and large deflection behavior on the semi-rigid and light-weight steel frame connection.

• 한국운동역학회지
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• 제16권3호
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• pp.149-163
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• 2006

The purpose of this study was to compare the lower extremity's joint and segment coupling patterns between forward and backward running in subjects who were twelve healthy males. Three-dimensional kinematic data were collected with Qualisys system while subjects ran to forward and backward. The thigh internal/external rotation and tibia internal/external rotation, thigh flexion/extension and tibia flexion/extension, tibia internal/external rotation and foot inversion/eversion, knee internal/external rotation and ankle inversion/eversion, knee flexion/extension and ankle inversion/eversion, knee flexion/extension and ankle flexion/extension, and knee flexion/extension and tibia internal/external rotation coupling patterns were determined using a vector coding technique. The comparison for each coupling between forward and backward running were conducted using a dependent, two-tailed t-test at a significant level of .05 for the mean of each of five stride regions, midstance(1l-30%), toe-off(31-50%), swing acceleration(51-70%), swing deceleration(71-90), and heel-strike(91-10%), respectively. 1. The knee flexion/extension and ankle flexion/extension coupling pattern of both foreward and backward running over the stride was converged on a complete coordination. However, the ankle flexion/extension to knee flexion/extension was relatively greater at heel-strike in backward running compared with forward running. At the swing deceleration, backward running was dominantly led by the ankle flexion/extension, but forward running done by the knee flexion/extension. 2. The knee flexion/extension and ankle inversion/eversion coupling pattern for both running was also converged on a complete coordination. At the mid-stance. the ankle movement in the frontal plane was large during forward running, but the knee movement in the sagital plane was large during backward running and vice versa at the swing deceleration. 3. The knee flexion/extension and tibia internal/external rotation coupling while forward and backward run was also centered on the angle of 45 degrees, which indicate a complete coordination. However, tibia internal/external rotation dominated the knee flexion/extension at heel strike phase in forward running and vice versa in backward running. It was diametrically opposed to the swing deceleration for each running. 4. Both running was governed by the ankle movement in the frontal plane across the stride cycle within the knee internal/external rotation and tibia internal/external rotation. The knee internal/external rotation of backward running was greater than that of forward running at the swing deceleration. 5. The tibia internal/external rotation in coupling between the tibia internal/external rotation and foot inversion/eversion was relatively great compared with the foot inversion/eversion over a stride for both running. At heel strike, the tibia internal/external rotation of backward running was shown greater than that of forward(p<.05). 6. The thigh internal/external rotation took the lead for both running in the thigh internal/external rotation and tibia internal/external rotation coupling. In comparison of phase, the thigh internal/external rotation movement at the swing acceleration phase in backward running worked greater in comparison with forward running(p<.05). However, it was greater at the swing deceleration in forward running(p<.05). 7. With the exception of the swing deceleration phase in forward running, the tibia flexion/extension surpassed the thigh flexion/extension across the stride cycle in both running. Analysis of the specific stride phases revealed the forward running had greater tibia flexion/extension movement at the heel strike than backward running(p<.05). In addition, the thigh flexion/extension and tibia flexion/extension coupling displayed almost coordination at the heel strike phase in backward running. On the other hand the thigh flexion/extension of forward running at the swing deceleration phase was greater than the tibia flexion/extension, but it was opposite from backward running. In summary, coupling which were the knee flexion/extension and ankle flexion/extension, the knee flexion/extension and ankle inversion/eversion, the knee internal/external rotation and ankle inversion/eversion, the tibia internal/external rotation and foot inversion/eversion, the thigh internal/external rotation and tibia internal/external rotation, and the thigh flexion/extension and tibia flexion/extension patterns were most similar across the strike cycle in both running, but it showed that coupling patterns in the specific stride phases were different from average point of view between two running types.

• 천문학회보
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• 제41권1호
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• pp.40.1-40.1
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• 2016

Recent integral-field spectrograph surveys have found that similar-looking early type galaxies have wide range of rotational properties (Emsellem et al. 2007). This finding initiated a new point of view to the galaxies; rotation of galaxy as the first parameter of galaxy classification (Emsellem et al. 2011, Cappellari et al. 2011, for example). Some theoretical studies tried to address the origin of galaxy rotation. Idealized galaxy merger simulations have shown that galaxy-galaxy interactions have significant effects on the rotation of galaxies. Cosmological simulations by Naab et al. 2014 also added some more insights to the rotation of galaxies. However, previous studies either lack cosmological background or have not enough number of samples. Running a set of cosmological hydrodynamic zoom-in simulations using the AMR code RAMSES(Teyssier 2002). we have constructed a sample of thousands of galaxies in 20 clusters. Here we present a kinematic analysis of a large sample of galaxies in the cosmological context. The overall distribution of rotation parameter of simulated galaxies suggests a single peak corresponding to fast rotating galaxies. But when divided by mass, we find a strong mass dependency of galaxy rotation, and massive galaxies are distinctively slow rotating. The cumulated effective of mergers seems to neutralize galaxy rotation as suggested by previous studies (Khochfar et al. 2011, Naab et al. 2014, and Moody et al. 2014). This is consistent with the fact that massive galaxies tend to rotate more slowly after numerous mergers. However, if seen individually, merger can either increase or decrease galaxy rotation depending on mass ratio, orbital parameter, and relative rotation axis of the two galaxies. This explains the existence of some non-slow rotating massive early type galaxies.

• 국제초고층학회논문집
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• 제4권1호
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• pp.45-55
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• 2015

The rotation capacity of the moment connections could significantly influence on the seismic performance of steel moment resisting frames. Current seismic provisions require that beam-to-column connections in Intermediate Moment Frames (IMF) should have a drift capacity as large as 0.02 radian. The objective of this study was to evaluate the effect of the rotation capacity of moment connections on the seismic performance of high-rise IMFs. For this purpose, thirty- and forty-story high-rise IMFs were designed according to the current seismic design provisions. The seismic performance of designed model frames was evaluated according to FEMA P695. This study showed that the forty-story IMF satisfied the seismic performance objective specified in FEMA P695 when the rotation capacity of the connections was larger than 0.02. However, thirty-story IMFs satisfied the performance objective when the connection rotation capacity is larger than 0.03.

• 한국정밀공학회지
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• 제24권12호
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• pp.88-94
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• 2007

A flexure hinge-based compliant stage driven by stack-type piezoelectric elements has high precision motion but small operational range due to the characteristics of the piezoelectric element. Since the common flexure hinges can be broken by excessive deflection when the displacement is amplified by a high amplification ratio, a flexure hinge mechanism for large deflection is required. A cartwheel-type flexure hinge has an advantage of larger deflection compared with the common flexure hinges. This study presents a rotation stage with cartwheel-type flexure hinges driven by a stack-type piezoelectric element. The characteristics and the performance of the rotation stage are described by the terms of principal resonance frequency, amplification ratio of rotational displacement, maximum rotational displacement and block moment, in which the terms are analyzed by geometric parameters of the rotation stage. The analyzed results will be used as the guideline of the design of the rotation stage.

• 전자공학회논문지C
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• 제36C권2호
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• pp.62-67
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• 1999

변조된 Passband 신호의 동기 검파 방식의 복조(Coherent Demodulation)에서 대부분의 수신 신호 decision에서 나타나는 실제적인 문제는 그 성상도가 회전하는 경우이다. 일단 성상도가 회전하는 경우이다. 일단 성상도가 회전하게 되면 수신단에서는 유효한 성상도와 구별해 낼 수 있는 방법이 없다. 그러나 수신기는 회전된 성상도에 의해 수신된 위상을 결정하므로 이러한 문제를 극복해 낼 수 없다면 그 결과는 계속되는 에러로 나타나게 된다. 본 논문에서는 먼저 QPSK 복조기에서의 주파수 옵셋과 위상 오차를 극복하기 위한 Carrier Recovery Loop에 대해서 살펴보고 나서 위상 Rotation을 방지하기 위한 방법을 제시하였다. 검출된 위상 오차를 주파수 옵셋 교정에 선별적으로 적용함으로써 Phase rotation의 발생을 줄일 수 있다. 시뮬레이션을 통해 제시한 방법의 타당성을 검증하였다.

• 천문학회지
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• 제37권5호
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• pp.337-342
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• 2004

The presence of magnetic fields in the intracluster medium in clusters of galaxies has been revealed through several different observational techniques. These fields may be dynamically important in clusters as they will provide additional pressure support to the intracluster medium as well as inhibit transport mechanisms such as thermal conduction. Here, we review the current observational state of Faraday rotation measure studies of the cluster fields. The fields are generally found to be a few to 10 $\mu$G in non-cooling core clusters and ordered on scales of 10 - 20 kpc. Studies of sources at large impact parameters show that the magnetic fields extend from cluster cores to radii of at least 500 kpc. In central regions of cooling core systems the field strengths are often somewhat higher (10 - 40 $\mu$G) and appear to be ordered on smaller scales of a few to 10 kpc. We also review some of the recent work on interpreting Faraday rotation measure observations through theory and numerical simulations. These techniques allow us to build up a much more detailed view of the strength and topology of the fields.

• 소성∙가공
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• 제19권8호
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• pp.480-485
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• 2010

In this work, the closing behavior of cylindrical-shaped voids was experimentally investigated according to various parameters such as reduction ratio in height, initial void size and billet rotation during hot open die forging process. The reduction ratio in height, number of path, and billet rotation were chosen as key process parameters which influence the void closing behavior including the change of void shape and size. On the other hand, values of die overlapping and die width ratio were set to be constant. Void closing behavior was estimated by microscopic observation. Based on the observations, it was confirmed that application of billet rotation is more efficient to eliminate the void with less reduction ratio in height. The experimental results obtained from this study could be helpful to establish the optimum path schedule of open die forging process.

• 전기저널
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• 7호통권115호
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• pp.28-32
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• 1986