• Wind and Structures
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• v.22 no.2
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• pp.161-184
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• 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.

• Journal of Ocean Engineering and Technology
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• v.35 no.1
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• pp.24-37
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• 2021

As one of the development directions of high-performance ships to reduce greenhouse gas emissions, there is research on high-performance propellers. However, in the case of conventional screw propellers, as they have been studied for a long time, there is a limit to improving efficiency only by depending on the conventional design and analysis methods. In this study, we tried to solve the problems using the Coanda effect by spraying a jet on the surface of the hydrofoil. The Coanda hydrofoil consists of a tunnel and jet slit to make jet flow. The computation was performed for each tunnel and slit position, and the efficiency according to the geometry of the hydrofoil was analyzed. In addition, a study on the 3D geometry change was conducted to analyze the performance according to the span direction spraying range and hydrofoil shape. As the height of the slit and the diameter of the tip were lower, when the slit is located in the center of the hydrofoil, the lift force increased and the drag force decreased. The increase rate of lift-to-drag ratio was different according to the shape of the hydrofoil, and the efficiency of the spraying condition of 0.1S-0.5S, which had the least effect on the vortex at the tip of the blade, was high for all 3D hydrofoils. When the geometry of the slit was optimized, and also the shape and spray range of the hydrofoil in 3D was considered, the efficiency of the jet sprayed hydrofoil was increased.

• Tunnel and Underground Space
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• v.24 no.2
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• pp.155-165
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• 2014

Multiple thermal energy storage (TES) caverns can be used for storing thermal energy on a large scale and for a high-aspect-ratio heat storage design to provide good thermal performance. It may also be necessary to consider the use of multiple caverns with a reduced length when a single, long tunnel-shaped cavern is not suitable for connection to aboveground heat production and injection equipments. When using multiple TES caverns, the separation distance between the caverns is one of the significant factors that should be considered in the design of storage space, and the optimal separation distance should be determined based on a quantitative stability criterion. In this paper, we described a numerical approach for determining the optimal separation distance between multiple caverns for large-scale TES utilization. For reliable stability evaluation of multiple caverns, we employed a probabilistic method which can quantitatively take into account the uncertainty of input parameters by probability distributions, unlike conventional deterministic approaches. The present approach was applied to the design of a conceptual TES model to store hot water for district heating. The probabilistic stability results of this application demonstrated that the approach in our work can be effectively used as a decision-making tool to determine the optimal separation distance between multiple caverns. In addition, the probabilistic results were compared to those obtained through a deterministic analysis, and the comparison results suggested that care should taken in selecting the acceptable level of stability when using deterministic approaches.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.97-100
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• 2008

Various flyers in nature have attracted great interests with a recent need for developing versatile and small-size flight vehicles. In the present study, we focus on the flying fish which has been observed to glide a long distance just above a seawater surface. Since previous studies have depended on the field observation or measurement of the physical parameters only, quantitative data of the flying fish flight has not been provided so far. Therefore, we evaluate the wing performance of the flying fish in gliding flight by directly measuring the lift, drag and pitching moment on real flying fish models (Cypselurus hiraii) in a wind tunnel. In addition, we investigate the roles of wing morphology like the enlarged pectoral and pelvic fins, and lateral dihedral angle of pectoral fins. With both the pectoral and pelvic fins spread, the lift-to-drag ratio is larger and the longitudinal static stability is enhanced than those with the pelvic fins folded. From the glide polar, we find that the wing performance of flying fish is equivalent to those of medium-size birds like the petrel, hawk and wood duck. Finally, we examine the effect of water surface underneath the flying fish and find that the water surface reduces the drag and increases the lift-to-drag ratio.

• Tunnel and Underground Space
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• v.20 no.5
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• pp.390-398
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• 2010

The time-dependent behaviour of rock is very important characteristics which can be utilized as basic input data for underground mine design or in predicting a long-term stability of underground rock mass structures. In this study, creep tests under uniaxial compression were carried out for the granite specimens sampled in Gagok Mine. Burgers model, Griggs and Singh creep laws were used to simulate the measured creep strain. Through comparing the measured creep behaviour with the approximated creep behaviors from Burgers model, Griggs and Singh creep laws, it is shown that Griggs creep law results in the best approximation of granite in Gagok Mine.

• Magazine of korean Tunnelling and Underground Space Association
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• v.3 no.2
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• pp.32-44
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• 2001

Most of the major aspects of the high speed rail tunnels in Korea, including such items as the tunnel geometry, excavation methods, primary support, final lining, drainage and waterproofing, are similar to the practices followed in other countries. The tunnels in Korea provide the largest net internal area $(107\;m^2)$ as compared to the other counties addressed in this paper. The effective adaptation and modification of international practices and designs, combined with the integration of domestic practices, has resulted in the successful construction of these large tunnels. The experience gained from the completed work to date on the high speed line in Korea, combined with international technology input, will help to ensure future tunnels are constructed in an efficient manner with adequate design measures implemented for the long-term operational life of the tunnels. As has occurred in these other countries, further improvements and modifications to the Korea high-speed railway tunnels will occur as experience is gained and new technology develops.

• Wind and Structures
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• v.23 no.3
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• pp.253-273
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• 2016

Ice accretions on stay cables may result in the instable vibration of galloping, which would affect the safety of cable-stayed bridges. A large number of studies have investigated the galloping vibrations of transmission lines. However, the obtained aerodynamics in transmission lines cannot be directly applied to the stay cables on cable-stayed bridges. In this study, linear and nonlinear single degree-of-freedom models were introduced to obtain the critical galloping wind velocity of iced stay cables where the aerodynamic lift and drag coefficients were identified in the wind tunnel tests. Specifically, six ice shapes were discussed using section models with geometric scale 1:1. The results presented obvious sudden decrease regions of the aerodynamic lift coefficient for all six test models. Numerical analyses of iced stay cables associated to a medium-span cable-stayed bridge were carried out to evaluate the potential galloping instability. The obtained nonlinear critical wind velocity for a 243-meter-long stay cable is much lower than the design wind velocity. The calculated linear critical wind velocity is even lower. In addition, numerical analyses demonstrated that increasing structural damping could effectively mitigate the galloping vibrations of iced stay cables.

• Journal of Korean Society of Transportation
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• v.22 no.4 s.75
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• pp.97-106
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• 2004

It is a Known fact that driving through long tunnel increases possibility of traffic accident because of psychological feeling of insecurity and dispersion of drivers' concentration since driving in narrow and limited space for a longtime. It, therefore, results in raising transportation and environment problems, such as traffic accident difficult to be properly dealt with and ventilation. This study aims at proposing a method of augmenting driving amenity by improving the internal lighting facilities in the tunnel. The study is conducted by investigating internal landscapes of tunnels by lighting colors, which are currently being operated. The Color Planning System (CPS), developed by SHARP Co. Ltd, is exploited for selecting adjective that express the sensitivity image on lighting colors. The CPS is an example that applies to sensitivity of human body for products design development. The CPS takes the following process to define the color : 1) expressing "Pvoduct's Image" as "A Word (adjective)" and 2) referring "A Word" to "Image Scale", and 3) determining the color through this "Image Panel". The study is processed by making a questionnaire using the semantic differential (SD) scale, grasping the consciousness structure of experimental persons through the Factor Analysis, and building a model in which dependent variable is "Degree of Preference" about internal landscape in tunnel using LISREL(LInear Structural RELations).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.6
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• pp.955-967
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• 2016

As transportation systems for connecting lands and islands, oversea long-span bridges, underwater tunnels, and immersed tunnels have been mainly used so far. Submerged floating tunnels (SFTs) moored under specific water depth are one of the newest oversea transportation system. Compared to other existing systems, the new system requires relatively less construction cost and time. But, there is still no construction example. For reasonable design of the tunnel and mooring lines the rational structural analysis should be firstly performed. Unlike common transportation structures, the submerged tunnels are mainly affected by the wave, vary irregular excitation component. So, the analysis scheme might be difficult because of the characteristics of the submerged structures. This study aims to suggest the rational global performance analysis methodology for the submerged tunnels. Using ABAQUS the dynamic response of the experimental models studied by KIOST (2013) was investigated considering regular waves. By comparing the simulation results with the experimental results, the feasibility of the numerical simulation was verified. Using the suggested method, the effects of initial inclination of the tethers and draft of the tunnel on the dynamic behavior were studied. In addition, dynamic response of a SFT under the irregular wave was examined.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.6
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• pp.837-847
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• 2019

Korea's long underground roads are being promoted around the metropolitan city center to realize advanced transportation networks. Many disaster prevention facilities are applied to secure fire safety of the closed and long-distance underground roads. As the facility response and fire suppression subjects are unclear, additional human and material damages from fire spread are inevitable. Therefore, in this study, we developed a remote automatic fire extinguishing system that uses the fire extinguishing water inside the fire hydrant to monitor the CCTV in the management room and sprays it directly to the fire site through automatic control. The design application method was studied through the performance improvement that can be put into practical use.