• 신재생에너지
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• 제9권1호
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• pp.6-11
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• 2013

Jeollabuk-do has announced a future plan for the Saemangeum Wind Farm which includes the installation of fourteen wind turbines in a single line, located 500m back from the Saemangeum Seawall. It is anticipated as a positive effect that, for sea breeze blowing toward land, the average wind speed could be accelerated and the wind speed distribution could be uniformized by dint of the seawall, an upstream structure of the turbines. At the same time it is also anticipated as a negative effect that the strength of wind turbulence could be increased due to the flow separation generated at the back end of the seawall. According to the results of the computational fluid dynamics analysis of this paper, it has been observed that, at the 50m zone on the road surface located at the uppermost part of the Saemangeum Seawall, the average wind speed has been accelerated by approximately 6~7% and that wind shear has been decreased by 70%, but this positive effect disappears in the zone situated beyond the 100m from the back end of the seawall. It has also been observed that flow separation exists to a limited extent only below the bottom of the blade-sweeping circle and, furthermore, does not extend very far downstream of the wind. As a conclusion, it can be said that the seawall neither positively nor negatively affects the proposed Saemangeum Seawall Wind Farm layout.

• 한국소음진동공학회논문집
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• 제24권3호
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• pp.213-218
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• 2014

썬루프 버페팅 소음의 고유특성을 의미하는 속도에 따른 소음강도의 증-감쇠 현상을 살펴보고자, HSM(Hyundai simplified model) 형상에 대해서 유동소음 해석 프로그램인 STAR-CCM+을 통하여 전체 차속 범위에 걸쳐 시험과 비교 검토하였다. 차량 내부의 재질에 따른 압축성 효과 및 감쇠효과는 인공 압축성과 감쇠 보정 기법인 FRET(frequency response test)를 이용하였다. 시뮬레이션 결과는 특정 속도에서 나타나는 소음 강도의 증-감쇠 시험결과를 매우 잘 예측하였으며 최대 SPL 수치도 정확히 예측하였다. 이는 썬루프 개방에 의해 발생하는 전단면에서의 유동 박리 주파수를 유동 소음 해석인 STAR-CCM+가 전 차속에 걸쳐서 매우 잘 예측하고 있음을 나타낸다.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2001년도 Proceedings of 2001 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.86-99
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• 2001

Vortex lock-on or resonance in the flow behind a circular cylinder is investigated from a time-resolved PIV when a single frequency oscillation is superimposed on the mean incident velocity. Measurements are made of the $K\acute{a}rm\acute{a}n$ and streamwise vortices in the wake-transition regime at the Reynolds number 360. Streamwise vortices at the lock-on and natural shedding states are observed, as well as the changes in the wake region with the change of the shedding frequency of lock-on state. When lock-on occurs, the vortex shedding frequency is found to be half the oscillation frequency as expected from previous experiments. At the lock-on state, the $K\acute{a}rm\acute{a}n$ vortices are observed to be more disordered by the increased strength and spanwise wavelength of the streamwise vortices, which leads to a strong three-dimensional motion. Recirculation and vortex formation region at the lock-on state is reduced as the oscillating frequency is increased. By comparing the Reynolds stresses at the lock-on and natural shedding states, $\bar{u'u'}\;and \;\bar{u'u'}$ at the lock-on state are concentrated on the shear layer around the cylinder. The $\bar{u'u'}\;at\;f_o/f_n=2.0$ has a large value near the centerline, compared with that of other cases. Considering the traces of maximum of u', in the wake region near the cylinder, wake width at the lock-on state is wider than that at the natural shedding state.

• Asian Journal of Atmospheric Environment
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• 제12권1호
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• pp.47-58
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• 2018

The aim of this work is to investigate the effect of atmospheric stability on near-field pollutant dispersion from rooftop emissions of a single cubic building using computational fluid dynamics (CFD). This paper used the shear stress transport (here after SST) k-${\omega}$ model for predicting the flow and pollutant dispersion around an isolated cubic building. CFD simulations were performed with two emission rates and six atmospheric stability conditions. The results of the simulations were compared with the data from wind tunnel experiments and the result of simulations obtained by previous studies in neutral atmospheric condition. The results indicate that the reattachment length on the roof ($X_R$) obtained by computations show good agreement with the experimental results. However, the reattachment length of the rooftop of the building ($X_F$) is greatly overestimated compared to the findings of wind tunnel test. The result also shows that the general distribution of dimensionless concentration given by SST k-${\omega}$ at the side and leeward wall surfaces is similar to that of the experiment. In unstable conditions, the length of the rooftop cavity was decreased. In stable conditions, the horizontal velocity in the lower part around the building was increased and the vertical velocity around the building was decreased. Stratification increased the horizontal cavity length and width near surface and unstable stratification decreased the horizontal cavity length and width near surface. Maintained stability increases the lateral spread of the plume on the leeward surface. The concentration levels close to the ground's surface under stable conditions were higher than under unstable and neutral conditions.

• 한국염색가공학회지
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• 제22권3호
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• pp.187-193
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• 2010

The effects of molecular weight (MW) and concentration on the rheological properties of poly(vinyl alcohol) (PVA) solutions in dimethyl sulfoxide (DMSO) were investigated at $30^{\circ}C$. Ubbelohde viscometer and rotational rheometer were employed for dilute and concentrated regime, respectively. In the dilute regime, the Mark-Houwink exponent ($\alpha$) of the solutions determined from three different MWs proved 0.73. The critical concentration (C*), in which the entanglement and overlap of polymer molecules began to take place, decreased with increasing the MW of PVA. Huggins constant ($K_H$) values ranged from 0.33 to 0.45 over the MW examined. In the log-log plot of $\eta_{sp}$ versus [$\eta$]C, the PVA with higher degree of polymerization (DP) gave a greater slope exhibiting the inflection point in the vicinity of C*. In the dynamic viscosity ($\eta'$) curve, the PVA solutions of DP 1700 presented Newtonian fluid behavior over most of the frequency range examined. However, the lower Newtonian flow region reduced with increasing the DP. As the PVA concentration increased, $\eta'$ was increased and the onset shear rate for pseudoplasticity was decreased. In the Cole-Cole plot, PVA solutions showed almost a single master curve in a slope of ca. 1.65 regardless of the DP. However, the increase of the concentration from 8 to 12 wt% for PVA solutions of DP 5000 decreased the slope from 1.73 to 1.57. In the tan $\delta$ curve, the onset frequency for sol-gel transition was shifted from 154 to 92 rad/s with increasing the DP from 3300 to 5000 and from 192 to 46 rad/s with increasing the concentration from 8 to 12 wt%. In addition, longer relaxation time ($\lambda$) was observed with increasing the DP and concentration.

• 한국항공우주학회지
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• 제31권10호
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• pp.10-20
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• 2003

본 논문에서는 임의의 방향각을 가지고 적층된 평직 복합재료에 대하여 미세구조를 모델링하고 수치실험을 통하여 등가물성치를 계산하였다. 층간 상호이동에 의한 평직복합재료의 섬유다발의 배열의 경우의 수는 무한대에 이르므로 여기서는 몬테 카를로법을 이용하여 지정된 경우의 수에 대하여 모델링과 해석을 수행하는 전략을 채택하였다. 또한 평직복합재료의 미세구조를 효과적으로 고려하고 모델링 및 계산시간을 절감하기 위하여 수정된 분할영역 적분에 의한 단일변위장 마크로요소를 사용하였다. 계산결과, 평직복합재료 적층판의 등가물성치는 적층간에 따라서 편차가 크게 나타날 수 있음을 확인하였다. 또한 고전적층판 이론으로 계산한 값과 비교하였을 때 $0^{\circ}$, $45^{\circ}$ 이외의 적층각에서 값의 차이가 크게 났는데, 이로부터 평직복합재료 구조물의 경우 고전적층판이론으로 계산한 등가물성치를 사용할 때 주의가 필요함을 알 수 있었다.

• 기술발표회
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• 통권2006호
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• pp.320-328
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• 2006

In this test, there was two dimensional model loading test implemented for analysis with respect to the problem of evaluating bearing capacity and the application range on the dredged and reclaimed ground. It was got following conclusion through comparison of button's and Brown&Meyerhof"s equation with experimental result that was obtained by 2 dimensions model loading test. For the difference between average undrained shear strength by 2/3B of loading board width and under 2/3B is more than ${\pm}$ 50%, application of Nc(coefficient of bearing capacity was used in that case $\phi$=0 analysis is considered in the single layer) was declined. Brown&Meyerhof(1969)'s equation was underestimated comparing with loading test result, while Button(1953)'s equation was overestimated comparing with loading test result applied dividing as double layers of upper dessication layer and lower soft layer about dredged and reclaimed ground. Also, bearing capacity factors, Nc that was calculated by using button's equation was estimated greatly about 1.7 times more than bearing capacity factors, Nc that was calculated by using Brown&Meyerhof's equation. Bearing capacity factors, Nc that was calcuated by using Brown&Meyerhof's and Button's equation was evaluated each 2.3-3.6 times, 1.3-2.1 times smaller than bearing capacity factors, Nc5.14 that was calcuated by using Meyerhof's equation in case of unit layer.

• 한국음향학회지
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• 제24권3호
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• pp.160-165
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• 2005

본 연구에서는 DNA의 고정화 및 DNA 혼성화 반응을 감지할 수 있는 SH형 SAW 센서를 개발하였다. 고정화 및 혼성화 반응에 사용된 탐침 DNA 및 표적 DNA는 상보적 결합이 일어날 수 있는 염기서열을 가진 15-mer의 올리고뉴클레 오티드를 사용하였다. SH형 SAW 센서는 압전 단결정 $36^{\circ}\;YX\;LiTaO_3$를 사용하여 100 MHz로 발진되는 이중 지연선 형태로 제작하였다. 제작된 센서는 Au가 증착된 박막위에 고정화된 탐침 DNA와 표적 DNA와의 혼성화 반응을 시키고 난 후 센서의 주파수 변화를 측정하였으며, DNA 고정화 및 혼성화 반응은 pH 7.4의 PBS 완충용액상에서 수행하였다. 개발된 SH형 SAW센서는 $1.55 {\cal}ng/{\cal}ml/Hz$의 민감도를 가지며, DNA 혼성화 특성에 기인한 질량하중 효과에 따른 안정적인 주파수 변화를 나타내었다.

• Steel and Composite Structures
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• 제1권1호
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• pp.17-32
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• 2001

The Rosette-joining system is a completely new press-joining method for cold-formed steel structures. One Rosette-joint has a shear capacity equal to that of approximately four screws or rivets. The Rosette thin-walled steel truss system presents a new fully integrated prefabricated alternative to light-weight roof truss structures. The trusses are built up on special industrial production lines from modified top hat sections used as top and bottom chords and channel sections used as webs which are joined together with the Rosette press-joining technique to form a completed structure easy to transport and install. A single web section is used when sufficient but can be strengthened by double-nesting two separate sections or by using two lateral profiles where greater compressive axial forces are met. An individual joint in the truss can be strengthened by introducing a hollow bolt into the joint hole. The bolt gives the connection capacity a boost of approximately 20%. A series of laboratory tests have been carried out in order to verify the Rosette truss system in practice. In addition to compression tests on individual sections of different lengths, tests have also been done on small structural assemblies and on actual full-scale trusses of a span of 10 metres. Design calculations have been performed on selected roof truss geometries based on the test results, FE-analysis and on the Eurocode 3 and U.S.(AISI) design codes.

• Earthquakes and Structures
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• 제1권4호
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• pp.371-390
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• 2010

Historical buildings in seismically active regions are severely damaged by earthquakes, since they certainly were not designed by the original builders to withstand seismic effects. In particular the reports after major ground motions indicate that earthquake-induced pounding between buildings may lead to substantial damage or even collapse of colliding structures. The research on structural pounding during earthquakes has been recently much advanced, although most of the studies are conducted on simplified single degree of freedom systems. In this paper a detailed pounding-involved response analysis of three adjacent structures is performed, concerning the main bodies of the "Quinto Orazio Flacco" school. The construction includes a main masonry building, with an M-shaped plan, and a reinforced concrete building, separated from the masonry one and realized along its free perimeter. By the analysis of the capacity curves obtained by suitable pushover procedures performed separately for each building, it emerges that masonry and reinforced concrete buildings are vulnerable to earthquake-induced structural pounding in the longitudinal direction. In particular, due to the geometric configuration of the school, a special case of impact between the reinforced concrete structure and two parts of the masonry building occurs. In order to evaluate the pounding-involved response of three adjacent structures, in this paper a numerical procedure is proposed, programmed using MATLAB software. Both a non-linear viscoelastic model to simulate impact and an elastic-perfectly plastic approximation of the storey shear force-drift relation are assumed, differently from many commercial softwares which admit just one non-linearity.