• 전기의세계
• /
• 제22권2호
• /
• pp.40-44
• /
• 1973

A method for obtaining state equation for nonlinear time-varying RLC networks is presented. The nonlinear time-varying RLC elements are decomposed by using Murata method to formulate nonlinear state equation. A nonlinear time-varying RLC network containing twin tunnel diode is solved as an example. In consequence of solving the examjple, simple methods are presented for revising the original network model so that the formulation of state equation is simplified.

• 대한토목학회논문집
• /
• 제31권5A호
• /
• pp.341-349
• /
• 2011

본 연구에서는 다양한 풍동실험을 통하여 기류 조건에 따른 트윈박스 거더 교량의 공기역학적 특성을 파악하는데 그 목적이 있다. 이를 위하여 자연적인 난류를 생성할 수 있는 능동 난류 발생장치를 개발하였고 검증하였다. 그리고 능동 난류 및 격자 난류 조건하에서 정적공기력, 비정상공기력 그리고 버페팅 응답 측정 실험을 수행하였다. 풍동실험 결과를 보면, 난류 적분길이는 교량의 정적공기력과 $A_1^*$를 제외한 플러터계수에는 영향을 주지 않는 것으로 나타났다. 그리고 난류 강도는 비정상공기력에 일부 영향을 미치고, 난류 적분길이 또한 일부 수직 방향 성분에 영향을 주는 것으로 나타났다.

• 대한조선학회논문집
• /
• 제52권3호
• /
• pp.236-247
• /
• 2015

In this paper, the experimental equipments for ventilated supercavitation in cavitation tunnel is constructed and the basic data of ventilated supercavitation regard to the entrainment coefficient and Froude number is fulfilled. The experiments are conducted for the disk cavitator with injecting air and the pressure inside cavity and the shape of cavity are measured. As the entrainment coefficient increases while the Froude number is kept constant, the ventilated cavitation number decreases to a minimum value which decreases no more even with increasing the air entrainment. The minimum value of ventilated cavitation number, caused by the blockage effect, decreases according to increasing the diameter ratio of test section to cavitator. The cavity length is rapidly enlarged near the minimum cavitation number. In low Froude numbers, the cavity tail is floating up due to buoyancy and the air inside the cavity is evacuated from its rear end with twin-vortex hollow tubes. However, in high Froude numbers, the buoyancy effect is almost negligible and there is no more twin-vortex tubes so that the cavity shape becomes close to axisymmetric. In order to measure the cavity length and width, the two methods, which are to be based on the cavity shapes and the maximum width of cavity, are applied. As the entrainment coefficient increases after the ventilated cavitation number gets down to the minimum cavitation number, the cavity length still increases gradually. These phenomenon can be confirmed by the measurement using the method based on the cavity shapes. On the other hand, when the method based on the maximum width of cavity is used, the length and width of the cavity agree well with a semi-empirical formular of natural cavity. So the method based on the maximum width of cavity can be a valid method for cavitator design.

• Wind and Structures
• /
• 제22권2호
• /
• pp.161-184
• /
• 2016

Long-span suspension bridges have evolved through the years and with them, the bridge girder decks improved as well, changing their shapes from standard box-deck girders to twin box and multi-box decks sections. The aerodynamic characteristics of the new generation of twin and multiple-decks are investigated nowadays, to provide the best design wind speeds and the optimum dimensions such bridges could achieve. The multi-box Megane bridge deck is one of the new generation bridge decks, consisting of two side decks for traffic lanes and two middle decks for railways, linked between them with connecting beams. Three-dimensional CFD simulations were performed by employing the Large Eddy Simulation (LES) algorithm with a standard Smagorinsky subgrid-scale model, for $Re=9.3{\times}10^7$ and angles of attack ${\alpha}=-4^{\circ}$, $-2^{\circ}$, $0^{\circ}$, $2^{\circ}$ and $4^{\circ}$. Also, a wind tunnel experiment was performed for a scaled model, 1:80 of the Megane bridge deck section, for $Re=5.1{\times}10^5$ and the aerodynamic static coefficients were found to be in good agreement with the results obtained from the CFD-LES model. However the aerodynamic coefficients determined individually, from the CFD-LES model, for each of the traffic and railway decks of the Megane bridge, varied significantly, especially for the downstream traffic deck. Also the pressure distribution and the effect of the spacing between the connecting beams, on the wind speed profiles showed a slight increase in turbulence above the downstream traffic and railway decks.

• Geomechanics and Engineering
• /
• 제9권6호
• /
• pp.775-791
• /
• 2015

Due to the extension of communication ways (metro, highways, railways), hence, to improve traffic flow imposes often the difficult crossing that generally drive to the construction of underground works (tunnel, water conveyance tunnel...) plays a major role in the redevelopment of urban areas. This study is focused on the assessment of the interaction response of parallel tunnels, so this study uses the results from the simulation of two tunnels to illustrate a few observations that may aid in practical designs. In this article, simultaneous drilling of highway's twin tunnels is simulated by means of Finite Element Method (FEM) implemented in Plaxis program. So the treated subject appears in a setting of geotechnical where one can be to construct several tunnels sometimes in a ground of weak mechanical characteristics. The objective of this study is to simulate numerically the interaction effects caused by construction of two parallels tunnels. This is an important factor in the study of the total answer of the problem interaction between parallels underground works. The importance of the effects transmitted is function of several parameters as the type of the works, and the mechanical characteristics (tunnel size, depth, and the relative position between two tunnels, lining thickness...). This article describes numerical analyses of two parallels tunnels interaction. This study will be applied to a real case of a section tunnel T4 of the highway East-West (Algeria); the study presented below comprises a series of numerical simulations of two tunnels using the computer program Plaxis which is used in the analyses is based on Finite Element Method.

• 한국터널지하공간학회 논문집
• /
• 제4권1호
• /
• pp.3-12
• /
• 2002

본 연구는 우면산터널 시공에 따른 예술의 전당내의 오페라극장 구조물에 대한 영향을 검토하고 필요시에는 적절한 대책을 조기에 강구하기 위하여 3차원 유한요소해석을 실시하였다. 쌍굴터널 굴진시 지반거동의 영향범위내에 있는 오페라극장은 문화재급의 건축물로써 그 기초형식 또한 다양하다. 그러므로, 건물구조의 3차원적인 특성과 기초형태의 변화를 이상적으로 모델링하고, 3차원해석 결과에 따른 시공전 예측과 시공중 안정성확인을 평가할 수 있도록 검토하였다. 문제발생시 신속한 대처를 할 수 있고, 터널굴진시 정보화 시공이 적용될 수 있도록 관리기준치를 단계적으로 변화 설정하였다.

• Wind and Structures
• /
• 제17권3호
• /
• pp.245-262
• /
• 2013

The flow interaction between two identical neighboring twin square prisms in a staggered arrangement in an open terrain was investigated experimentally. The downwind prism was mounted on a rigid-aeroelastic setup in an open-terrain boundary layer flow to measure its acrosswind root-mean-square responses and aerodynamic damping ratios. By varying the relative location of the upwind prism and the Scruton number associated with the downwind prism, the acrosswind aeroelastic behavior of the downwind prism was analyzed and compared to that of an isolated one. Results showed that the acrosswind root-mean-square response of the downwind prism could be either suppressed or enhanced by the wake flow produced by the neighboring upwind prism. Besides the assessment of the wake effect of the downwind prism, finally, regressed relationships were presented to describe the variation of the aerodynamic damping ratio so as to predict its acrosswind fluctuating response numerically.

• Wind and Structures
• /
• 제28권4호
• /
• pp.255-270
• /
• 2019

Aerodynamic configurations of bridge decks have significant effects on the aerostatic torsional divergence and flutter forsuper long-span bridges, which are onset for selection of suitable bridge decksfor those bridges. Based on a cable-stayed bridge with double main spans of 1500 m, considering typical twin-box, stiffening truss and closed-box section, which are the most commonly used form of bridge decks and assumed that the rigidity of those section is completely equivalent, are utilized to investigate the effects of aerodynamic configurations of bridge decks on aerodynamic instability performance comprised of the aerostatic torsional divergence and flutter, by means of wind tunnel tests and numerical calculations, including three-dimensional (3D) multimode flutter analysis and nonlinear aerostatic analysis. Regarding the aerostatic torsional divergence, the results obtained in this study show twin-box section is the best, closed-box section the second-best, and the stiffening truss section the worst. Regarding the flutter, the flutter stability of the twin-box section is far better than that of the stiffening truss and closed-box section. Furthermore, wind-resistance design depends on the torsional divergence for the twin-box and stiffening truss section. However, there are obvious competitive relationships between the aerostatic torsional divergence and flutter for the closed-box section. Flutter occur before aerostatic instability at initial attack angle of $+3^{\circ}$ and $0^{\circ}$, while the aerostatic torsional divergence occur before flutter at initial attack angle of $-3^{\circ}$. The twin-box section is the best in terms of both aerostatic and flutter stability among those bridge decks. Then mechanisms of aerostatic torsional divergence are revealed by tracking the cable forces synchronous with deformation of the bridge decksin the instability process. It was also found that the onset wind velocities of these bridge decks are very similar at attack angle of $-3^{\circ}$. This indicatesthat a stable triangular structure made up of the cable planes, the tower, and the bridge deck greatly improves the aerostatic stability of the structure, while the aerodynamic effects associated with the aerodynamic configurations of the bridge decks have little effects on the aerostatic stability at initial attack angle of $-3^{\circ}$. In addition, instability patterns of the bridge depend on both the initial attack angles and aerodynamic configurations of the bridge decks. This study is helpful in determining bridge decksfor super long-span bridges in future.

• 한국터널지하공간학회 논문집
• /
• 제5권4호
• /
• pp.313-322
• /
• 2003

본 연구는 도심지터널 시공시 막장진행에 따라 다양하게 계측된 현장의 계측치 분석을 통하여 막장 진행에 따른 터널 주변지반의 거동 및 인접구조물의 3차원 거동을 상호 규명하였으며, 일반적으로 터널설계시 적용되는 Mohr-Coulomb 모델 및 막강관찰 자료를 바탕으로 한 Hoek-Brown 현장암반모델을 적용한 3차원 유한요소해석을 실시하여 각각의 결과를 비교 검토하여 이들 지반 및 구조물 거동을 규명하였다. 막장 진행에 따른 침하 양상은 greenfield 상태에서의 거동과는 차이를 보이고 있으며 구조물의 위치와 강성 그리고 하중에 큰 영향을 받는 것으로 나타났다.

• Wind and Structures
• /
• 제31권1호
• /
• pp.31-41
• /
• 2020

A new type of bridge deck section consisting of four-box decks, two side decks for vehicular traffic lanes and two middle decks for railway traffic, has been experimentally investigated for determining its aerodynamic properties. The eight flutter derivatives were determined by the Iterative Least Squares (ILS) method for this new type of four-box deck model, with two windshields of 30 mm and 50 mm height respectively. Wind tunnel experiments were performed for angles of attack α = ±6°, ±4°, ±2° and 0° and Re numbers of 4.85×105 to 6.06×105 and it was found that the four-box deck with the 50 mm windshields had a better aerodynamic performance. Also, the results showed that the installation of the windshields reduced the values of the lift coefficient CL for the negative angles attack in the range of -6° to 0°, but the drag coefficient CD increased in the positive angle of attack range. However, galloping instability was not encountered for the tested reduced wind speeds, of up to 9.8. The aerodynamic force coefficients and the flutter derivatives for the four-box deck model were consistent with the results reported for the Messina triple-box bridge deck, but were different from those reported for the twin-box bridge decks.