• 한국지능시스템학회논문지
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• 제19권6호
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• pp.749-754
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• 2009

4족 보행로봇의 빠른 걸음새를 자동으로 생성하는 문제에 대해서 GP(Genetic Programming)와 CPG(Central Pattern Generator) 기반의 두 가지 방식을 비교한다. GP(Genetic Programming)를 이용한 관절좌표계 상에서의 걸음새 생성 기법은 발끝의 자취와 수 많은 자세 파라미터를 사용하는 대신에 적은수의 관절 궤적을 생성하므로 효율적이다. CPG는 뇌로부터의 입력을 받아서 진동적인 출력을 생성하는 신경회로로 고등생물의 걸음 원리를 수학적으로 모델링한 것이다. 바이올로이드로 구성된 4족 보행로봇에 대하여 Webots기반의 ODE 시뮬레이션을 통해 접근 기법들에 대한 최적화를 수행하고 결과를 비교 분석한다. 그리고, 구해진 시뮬레이션과 결과를 실제 로봇에 대해서 각 동작을 실행시켜 보면서 CPG와 GP 기반의 걸음새 방식의 실제적인 성능 및 특성을 고찰한다.

• 대한조선학회논문집
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• 제35권4호
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• pp.27-37
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• 1998

선박이 대형화되고, LNG선의 건조가 활발해지면서 액체화물탱크의 내부유동을 뜻하는 슬로싱에 대한 연구가 중요해지고 있다. 슬로싱에 의한 충격압력의 크기와 특성을 파악하기 위하여 직사각형 모델에 대한 체계적인 실험을 수행하여 회전각, 동요주파수, 적재수심에 따른 내부유동의 특성을 분석하였고, 충격압력이 가해지는 탱크벽면의 구조응답을 계측하여 유탄성효과를 고찰하였다. 탱크의 내부유동은 고차경계요소법을 이용하여 해석하였고, 평판의 진동에 의해 유기되는 유체력은 고유함수 전개법을 이용하여 부가질량과 감쇠력으로 표현하였다. 충격하중이 작용하는 경우 유탄성 효과를 고려한 탱크 벽면은 부가질량의 영향으로 그 때의 수심에 해당하는 접수진동수로 진동하였고, 벽면에서 압력은 유탄성효과를 고려하지 않은 경우에 비해 두 배 이상 크게 나타났다. 이를 실험과 계산에서 모두 확인하였고, 충격하중에 의한 평판의 거동에서 유탄성효과를 규명하였다

• 한국전산구조공학회논문집
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• 제28권5호
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• pp.477-483
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• 2015

본 논문에서는 Euler-Bernoulli Beam(EB-beam) 및 신속 Fourier 변환을 이용하여 수치분석적 빔 모델 및 Co-rotational plane beam EDISON program(CR-beam)을 이용한 빔 모델의 가진주파수 변화에 따른 외팔보의 자유단 진동 연구를 수행하였다. 위의 두 빔 모델에서의 끝단에서는 진동이 시간이 지남에 따라 감소하다가 정상상태에 이르는 것을 확인하였다. 끝단에서 가진주파수가 증가함에 따라 구조적 감쇠에 의해 변위이 감소하는 경향을 보인다. 감쇠를 고려한 EB-beam과 CR-beam가 정상상태로 진입하는 경향이 비슷하나, 가진주파수는 정상상태가 나타나는 시간과 독립적임을 제시한다.

• 천문학회지
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• 제28권2호
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• pp.245-253
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• 1995

We have analyzed the time series of Ca II H,K and ${\lambda}8498$ line profiles taken for a sunspot (SPO 5007) with the Echelle spectrograph attached to Vacuum Tower Telescope at Sacramento Peak Solar Observatory. Each set of spectra was taken simultaneously for 20 minutes at a time interval of 30 seconds. A total of 40 photographic films for each line was scanned by a PDS at Korea Astronomy Observatory. The central peak intensity of Ca II H ($I_{max}$), the intensity measured at ${\Delta}{\lambda}=-0.1{\AA}$ from the line center of ${\lambda}8498(I_{{\lambda}8489})$, the radial velocity ($V_r$) and the Doppler width (${\Delta}{\lambda}_D$) estimated from Ca II H have been measured to study the dynamical behaviors of the sunspot chromosphere. Fourier analysis has been carried out for these measured quantities. Our main results are as follows: (1) We have confirmed the 3-minute oscillation being dominant throughout the umbra. The period of oscillations jumps from 180 sec in the umbra to 500 to 1000 sec in the penumbra. (2) The nonlinear character of the umbral oscillation is noted from the observed sawtooth shaped radial velocity fluctuations with amplitudes reaching up to $5{\sim}6\;km/sec$. (3) The spatial distribution of the maximum powers shows that the power of oscillations is stronger in the umbra than in the penumbra. (4) The spatial distributions of the time averaged < $I_{max}$ > and < $V_r$ > across the spot are found to be nearly axially symmetric, implying that the physical quantities derived from the line profiles of Ca II H and ${\lambda}8498$ are inherently associated with the geometry of the magnetic field distribution of the spot. (5) The central peaks of the CaII H emission core lead the upward motions of the umbral atmosphere by $90^{\circ}$, while no phase delay is found in intensities between $I_{max}$ and $I_{{\lambda}8498}$, suggesting that the umbral oscillation is of standing waves.

• 천문학회보
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• 제37권2호
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• pp.121.1-121.1
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• 2012

It has been suggested that oscillatory earthward bursty bulk flows (BBFs) in the magnetotail are driving Pi2 oscillations on the ground. However, only a few studies examined the BBF-driven Pi2 model. The goal of this study is to establish the relation between BBFs and Pi2s. In order to examine BBF-drive model, we will conduct the timing analysis between BBFs and Pi2s for the intervals during which both Pi2 and BBF are present. In our study BBFs are identified with earthward flow speeds up to 200 km/s from THEMIS probes with a geocentric distance between 7 and 12 RE in the nightside magnetosphere for the interval from January 2008 to March 2008. Pi2 pulsations are identified at three low/mid-latitude ground stations having different local times; Bohyun (L = 1.35, LT ~ UT +9 hr), Hermanus (L = 1.83, LT ~ UT +2 hr) and Carson city (L = 2.00, LT ~ UT -2 hr). It is found that ~28% of BBFs have onset timing nearly identical to Pi2 onset. To investigate whether there is high similarity in the waveform between BBF and Pi2 oscillations, the coherence analysis is applied to the time series of BBF and Pi2 events. We found that there is no high coherence between BBF and Pi2 oscillations. Thus our observations suggest that low-latitude Pi2 oscillations are not directly driven by earthward flow bursts.

• 폴리머
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• 제38권6호
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• pp.735-743
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• 2014

폴리프로필렌의 분자량 및 분자량 분포를 예측하기 위해 레오메터, 고유점도측정기 및 MI(melt index) 기기 등을 이용하여 유변 물성을 측정하였고, 분자구조해석에는 GPC가 사용되었다. 기존에 사용되어온 동적진동측정을 이용한 교차 모듈러스에서 결정된 유변학적 PI(다분산 지표)와 변형된 Carreau 모델을 이용하여 계산된 분포 폭 매개변수(distribution broadness parameter)를 분자량 분포와의 관계를 비교해보았다. 유변학적 PI의 경우 이론적 근거가 부족하고, 압출에 의해 재 생성된 폴리프로필렌 시료에 대해서는 분자량 분포와 잘 일치하지만 반응기에서 중합된 시료 즉, 분자량 분포가 넓거나 다른 경우 잘 일치하지 않는다는 보고가 지배적인데 비해 분포 폭 매개변수는 폴리프로필렌의 전단담화의 정도를 직접적으로 측정하는 것으로 분자량 분포를 잘 예측할 수 있음을 알았다.

• 한국수자원학회논문집
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• 제44권6호
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• pp.429-438
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• 2011

In order to simulate a free surface flow in a trench channel, a three-dimensional incompressible unsteady Reynolds-averaged Navier-Stokes (RANS) equations are closed with the ${\kappa}-{\epsilon}$ model. The artificial compressibility (AC) method is used. Because the pressure fields can be coupled directly with the velocity fields, the incompressible Navier-Stokes (INS) equations can be solved for the unknown variables such as velocity components and pressure. The governing equations are discretized in a conservation form using a second order accurate finite volume method on non-staggered grids. In order to prevent the oscillatory behavior of computed solutions known as odd-even decoupling, an artificial dissipation using the flux-difference splitting upwind scheme is applied. To enhance the efficiency and robustness of the numerical algorithm, the implicit method of the Beam and Warming method is employed. The treatment of the free surface, so-called interface-tracking method, is proposed using the free surface evolution equation and the kinematic free surface boundary conditions at the free surface instead of the dynamic free surface boundary condition. AC method in this paper can be applied only to the hydrodynamic pressure using the decomposition into hydrostatic pressure and hydrodynamic pressure components. In this study, the boundary-fitted grids are used and advanced each time the free surface moved. The accuracy of our RANS solver is compared with the laboratory experimental and numerical data for a fully turbulent shallow-water trench flow. The algorithm yields practically identical velocity profiles that are in good overall agreement with the laboratory experimental measurement for the turbulent flow.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2010년도 학술발표회
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• pp.268-272
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• 2010

The research presented here represents a collaborative effort with the SFWMD on developing scenarios for future climate for the SFWMD area. The project focuses on developing methodology for simulating precipitation representing both natural quasi-oscillatory modes of variability in these climate variables and also the secular trends projected by the IPCC scenarios that are publicly available. This study specifically provides the results for precipitation modeling. The starting point for the modeling was the work of Tebaldi et al that is considered one of the benchmarks for bias correction and model combination in this context. This model was extended in the framework of a Hierarchical Bayesian Model (HBM) to formally and simultaneously consider biases between the models and observations over the historical period and trends in the observations and models out to the end of the 21st century in line with the different ensemble model simulations from the IPCC scenarios. The low frequency variability is modeled using the previously developed Wavelet Autoregressive Model (WARM), with a correction to preserve the variance associated with the full series from the HBM projections. The assumption here is that there is no useful information in the IPCC models as to the change in the low frequency variability of the regional, seasonal precipitation. This assumption is based on a preliminary analysis of these models historical and future output. Thus, preserving the low frequency structure from the historical series into the future emerges as a pragmatic goal. We find that there are significant biases between the observations and the base case scenarios for precipitation. The biases vary across models, and are shrunk using posterior maximum likelihood to allow some models to depart from the central tendency while allowing others to cluster and reduce biases by averaging. The projected changes in the future precipitation are small compared to the bias between model base run and observations and also relative to the inter-annual and decadal variability in the precipitation.

• Molecules and Cells
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• 제38권10호
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• pp.851-858
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• 2015

Disturbed blood flow with low-oscillatory shear stress (OSS) is a predominant atherogenic factor leading to dysfunctional endothelial cells (ECs). Recently, it was found that disturbed flow can directly induce endoplasmic reticulum (ER) stress in ECs, thereby playing a critical role in the development and progression of atherosclerosis. Ursodeoxycholic acid (UDCA), a naturally occurring bile acid, has long been used to treat chronic cholestatic liver disease and is known to alleviate endoplasmic reticulum (ER) stress at the cellular level. However, its role in atherosclerosis remains unexplored. In this study, we demonstrated the anti-atherogenic activity of UDCA via inhibition of disturbed flow-induced ER stress in atherosclerosis. UDCA effectively reduced ER stress, resulting in a reduction in expression of X-box binding protein-1 (XBP-1) and CEBP-homologous protein (CHOP) in ECs. UDCA also inhibits the disturbed flow-induced inflammatory responses such as increases in adhesion molecules, monocyte adhesion to ECs, and apoptosis of ECs. In a mouse model of disturbed flow-induced atherosclerosis, UDCA inhibits atheromatous plaque formation through the alleviation of ER stress and a decrease in adhesion molecules. Taken together, our results revealed that UDCA exerts anti-atherogenic activity in disturbed flow-induced atherosclerosis by inhibiting ER stress and the inflammatory response. This study suggests that UDCA may be a therapeutic agent for prevention or treatment of atherosclerosis.

• 한국항해항만학회지
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• 제37권2호
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• pp.173-179
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• 2013

파랑과 해저지반 그리고 해안 해양 구조물과의 상호작용은 지반공학뿐만 아니라 해안공학 분야에서도 중요한 이슈중의 하나이며, 파랑에 의해 해저지반 내부에 발생하는 응력 및 간극수압 거동의 파악은 다양한 해안 해양 구조물의 기초 설계 및 해저 연안 지반의 불안정성 검토에 있어서 중요한 과제이다. 해저지반의 불안정에 대한 문제 중, 파랑에 의한 해저지반의 액상화는 기존의 연구를 통하여, 두개의 메커니즘이 존재한다는 것이 밝혀졌으며, 이는 각각 파랑에 의해 해저지반 내부에 발생하는 과잉간극수압의 변동 특성 및 잔류 특성에 따른 것이다. 본 연구에서는 일본 시코쿠 코치(高知)현에 위치하고 있는 코치항에서 채취한 토사에 대한 동적 특성을 고려하여, 파랑에 의해 해저지반 내부에 발생하는 침투류에 의한 잔류과잉간극수압에 대하여 해석을 하였으며, 더 나아가, 코치항에서 계측된 값과 비교 분석을 하였다.