• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.11-22
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• 2018

The safety of tunnels is quantified by quantitative risk assessment when planning the disaster prevention facilities of railway tunnels, and it is decided whether they are appropriate. The purpose of this study is to estimate the probability of the train stopping in the tunnels at train fire, which has a significant effect on the results of quantitative risk assessment for tunnel fires. For this purpose, a model was developed to calculate the coasting distance of the train considering the coefficient of train running resistance. The probability of stopping in case of train fire in the tunnel is predicted by the Monte Carlo simulation method with the coasting distance and the emergency braking distance as parameters of the tunnel lengths and slopes, train initial driving speeds. The kinetic equations for predicting the coasting distance were analyzed by reflecting the coefficient train running resistance of KTX II. In the case of KTX II trains, the coasting distance is reduced as the slope increases in a tunnel with an upward slope, but it is possible to continue driving without stopping in a slope downward. The probability of the train stopping in the case of train fire in tunnel decreases as the train speed increases and the slope of the tunnel decreases. If human error is not taken into account, the probability that a high-speed train traveling at a speed of 250 km/h or above will stop in a tunnel due to a fire is 0% when the slope of the tunnel is 0.5% or less, and the probability of stopping increases rapidly as the tunnel slope increases and the tunnel length increases.

• Journal of the Korean Society for Railway
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• v.13 no.2
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• pp.194-200
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• 2010

Recently, a longitudinal tunnel construction has increased because of subway construction extension, geomorphological effect and the development of construction Technologies etc. When the fire occurs in a tunnel and an underground structure, the many damage of human life and the economic losses are caused. In Korea, fire resistance character study of a tunnel and an underground structure is proceeding. However, when a concrete is exposed to high temperature, study of load carrying capacity reduction and stability evaluation for spalling of a concrete is not enough. Therefore in this study, fire resistance character of a concrete evaluated according to time heating temperature curve(RABT and RWS) and a result compared on virtual fire accident in order to apply fire scenario. Also this study performed thermo-mechanical coupled analysis of a FEM-based numerical technique and estimated fire-induced damage of a tunnel and an underground structure.

• Journal of Bio-Environment Control
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• v.5 no.2
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• pp.152-159
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• 1996

Experiment was performed in a newly developed wind tunnel with light system to determine the aerodynamic resistance and eddy diffusivity above the plug stand under artificial light. Maximum air temperature appeared near the top of the plug stand under artificial light. Since Richardson number was ranged from -0.07 to +0.01, the atmosphere above the plug stand in wind tunnel was in an unstable or near- neutral stability state. The average aerodynamic resistance at rear region of plug stand was 25 % higher than that at middle region. Eddy diffusivity($K_{M}$) linearly increased with the increasing air current speed. $K_{M}$ at air current speed of 0.9 m.$s^{-1}$ was about two times as many as that at air current speed of 0.3 m.$s^{-1}$. And average $K_{M}$ at the rear region was 15% lower than that at the middle region. These results indicated that the diffusion of heat and mass along the direction of air current inside the plug stand was different. It might cause the lack of uniformity in the growth and quality of plug seedlings. The wind tunnel developed in this study would be useful to investigate the effects of air current speed on microclimates and the growth of plug seedlings under artificial light in a semi- closed ecosystem.

• Proceedings of KOSOMES biannual meeting
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• 2017.04a
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• pp.260-260
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• 2017

• Journal of the Korean Geotechnical Society
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• v.23 no.11
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• pp.87-98
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• 2007

For the quick rehabilitation of a fire-damaged tunnel structure, it is the most important procedure to investigate the fire-induced damaged zone rapidly. This study aims to propose a new drilling resistance testing method by which mechanical properties of tunnel concrete lining altered by high temperature can be estimated easily and continuously. Especially, it alms to derive the relationships to estimate mechanical properties of mortar and concrete materials from drilling parameters. To obtain the optimum testing condition, a series of drilling resistance tests were carried out for mortar specimens. When the rotation per minute of drill bit, tile penetration rate and the bit diameter were 1,300 rpm, 1.40 mm/sec, and 10 mm respectively, the deviation of measured drilling resistance forces was minimal. Under the optimum testing condition, the relationships between drilling resistance and mechanical properties of mortar specimens were shown to be very favorable. The concept of replacing a mean value of resistance farces measured during drilling with the resistance energy was proposed to consider the effects of randomly distributed aggregates inside a concrete material on drilling resistance. When the concept was applied to concrete materials, a favorable relationship between actual compressive strength and drilling resistance energy was also successfully derived.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.485-488
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• 2008

Fire intensity in tunnel fire is very severe, which might cause the spalling on the surface of shotcrete and concrete lining exposed to the heat as well as rapidly-reducing stress due to heat transfer by steel material such as anchor embedded in tunnel which plays the critical role in securing the stability of the tunnel. In this study, a fire test to identity the heat intensity(Modifired Hydrocarbon Curve) and the fire resistance of steel materials embedded as parameters, was carried out. And the evaluation to identify the thermal damage, which was based on critical temperature range for thermal damage of steel materials determined according to the road tunnel fire resistance standard established by ITA(International Tunneling Association).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.8
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• pp.688-693
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• 2001

A series of Fe/CeO$_2$/Fe$_{75}$Co$_{25}$ tunnel junctions (Magnetic Tunnel Junction, MTJ) having CeO$_2$ barrier layers from 30 to 90$\AA$ in thickness were prepared by ion beam sputtering (IBS) method. In order to compare the properties of MTJs, Fe/Al oxide/Fe-Co tunnel junctions were also prepared. Some junctions with a CeO$_2$ barrier layer showed the ferromagnetic tunneling effect and the highest MR ratio at room temperature was 5%. The electric resistance of junctions with a CeO$_2$ barrier layer was higher that that of junctions with an Al oxide barrier. On the other hand, The interface analysis of the Fe/CeO$_2$ bilayer was conducted by means of X-ray photoelectron spectroscopy (XPS). It was found that CeO$_2$ was decomposed to Ce and $O_2$ during sputtering, and Fe was oxidized with these decomposed $O_2$ molecules. The reduction of both electric resistance and MR ratio may be associated with the decomposed Ce in the barrier layer.r.r.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.119-125
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• 2007

The equation of Resistance to motion of the Korean high-speed train has been calculated and evaluated using train speed measurements gathered from coasting tests in the speed range from 30km/h to 300km/h and wind tunnel test of 1/25th scale model. The factors of resistance to motion have been decomposed into various coefficients which compose the coefficients of Davis equation referring the general resistance to motion equation of KTX train. The coefficients of Korean high-speed train has been calculated using the measurements of coasting tests and the results of wind tunnel test has been implemented to consider the minor shape modification after the coasting tests.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2017.11a
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• pp.232-233
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• 2017

In this research, tunnel stern was applied on the asymmetric high-speed catamaran to evaluate vessel's hydrodynamic performance by numerical method, and the tunnel stern types are distinguished by angle of inclination of tunnel exit region into 3cases ($0^{\circ}$, $3^{\circ}$ and $6^{\circ}$). Consequently, it is confirmed that the total resistances of tunnel stern which have $0^{\circ}$ of inclination are lower about 4.8-17.9% than the bare hull in the wide speed range, but those of $3^{\circ}$ and $6^{\circ}$ of inclination tunnel stern are higher than bare hull about 5-14% and 5-29%, respectively. On the other hand, trim angles of $0^{\circ}$ of inclination tunnel stern show similar trend with those of bare hull in whole ranges of FnV but those of $3^{\circ}$ and $6^{\circ}$ of inclination tunnel stern are stabilized and declined respectively after FnV=1.54. These phenomena indicated that increasing angle of inclination of tunnel exit region had negative influence on resistance performance, however, it could make vessel's operation performance better than bare hull.

• Journal of Bio-Environment Control
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• v.17 no.2
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• pp.83-89
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• 2008

A wind tunnel test was conducted at Protected Horticulture Experiment Station of National Horticultural Research Institute in Busan to find the aerodynamic resistance and quadratic resistance coefficient of chrysanthemum in greenhouse. The internal plants of the CFD model has been designed as a porous media because of the complexity of its physical shapes. Then the aerodynamic resistance value should be input for analyzing CFD model that crop is considered while the value varies by crops. In this study, the aerodynamic resistance value of chrysanthemum canopy was preliminarily found through wind tunnel test. The static pressure at windward increased as wind velocity and planting density increased. The static pressure at leeward decreased as wind velocity increased but was not significantly affected by planting density. The difference of static pressure between windward and leeward increased as wind velocity and planting density increased. The aerodynamic resistance value of chrysanthemum canopy was found to be 0.22 which will be used later as the input data of Fluent CFD model. When the planting distances were $9{\times}9\;cm$, $11{\times}11\;cm$, and $13{\times}13\;cm$, the quadratic resistance coefficients of porous media were found to be 2.22, 1.81, and 1.07, respectively. These values will be used later as the input data of CFX CFD model.