• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.548-553
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• 2016

본 연구는 타원형 물체가 유체 중에서 침강할 때 물체의 형상과 밀도에 따른 침강특성을 분석하는 것이며, 이로 인해 종단속도에 미치는 영향을 평가하는 것이다. 복잡한 형태의 물체를 타원기둥으로 단순화하였고, 낮은 Reynolds 수(=0.5~100)에 대하여 연구를 진행하였다. 또한 침강형태가 종단속도에 미치는 영향을 연구하였다. 수치해석 검증을 통해 정확하고 효율적인 격자 크기를 결정하였다. 정확한 분석을 위해 단순히 종단속도의 변화를 본 것이 아니라 진동하지 않은 물체의 이론적 속도와 비교하여 이와 얼마나 차이가 있는지를 확인하였다. 수치해석 결과 장단축비에 따라 물체의 침강특성이 크게 변하였고 그 경향은 밀도비에 따라 다른 양상을 보였다. 또한 각의 진동에 대한 진폭과 진동수가 물체의 침강속도에 영향을 주는 것을 확인하고 그 원인에 대해서도 연구하였다.

• Journal of Korean Society of Transportation
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• v.23 no.8 s.86
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• pp.153-162
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• 2005

This study is carried out to evaluate the sight distance change due to construction errors of vertical crest curves. Various design speeds and grades as well as various size of construction errors are incorporated in this study. After showing theoretical methodology numerical results are compared and analysed for the given ranges of parameters. New vertical curve change rate(m/%) is suggested to guarantee minimum sight distance under construction errors. As to the results, the reduction of sight distance are $2.8{\sim}21.3m$ at 120km/h, $2.0{\sim}15.1m$ at 100km/h, $1.4{\sim}10.6m$ at 80km/h, $1.0{\sim}7.5m$ at 60km/h $0.5{\sim}3.9m$ at 40km/h. Vortical curve change rates need to be increased about $6{\sim}25%$ to provide minimum stopping sight distance according to design speed.

• Explosives and Blasting
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• v.37 no.3
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• pp.13-24
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• 2019

This paper was prepared to investigate the behavior of fragments in underwater torpedo explosion beneath a frigate or surface ship by using an explicit finite element analysis. In this study, a fluid-structure interaction (FSI) methodology, called the multi-material arbitrary Lagrangian-Eulerian (MM-ALE) approach in LS-DYNA, was employed to obtain the responses of the torpedo fragments and frigate hull to the explosion. The Euler models for the analysis were comprised of air, water, and explosive, while the Lagrange models consisted of the fragment and the hull. The focus of this modeling was to examine whether a worst-case fragment could penetrate the frigate hull located close (4.5 m) to the exploding torpedo. The simulation was performed in two separate steps. At first, with the assumption that the expanding skin of the torpedo had been torn apart by consuming 30% of the explosive energy, the initial velocity of the worst-case fragment was sought based on a well-known experimental result concerning the fragment velocity in underwater bomb explosion. Then, the terminal velocity of the worst-case fragment that is expected to occur before the fragment hit the frigate hull was sought in the second step. Under the given conditions, the possible initial velocities of the worst-case fragment were found to be very fast (400 and 1000 m/s). But, the velocity difference between the fragment and the hull was merely 4 m/s at the instant of collision. This result was likely to be due to both the tremendous drag force exerted by the water and the non-failure condition given to the frigate hull. Anyway, at least under the given conditions, it is thought that the worst-case fragment seldom penetrate the frigate hull because there is no significant velocity difference between them.

• International Journal of Highway Engineering
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• v.14 no.1
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• pp.95-102
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• 2012

This study has been conducted to characterize the relations between the accident rate and the overlap section elements where the horizontal alignment and vertical alignment are overlapped. The researches were performed on Horizontal curve sections of 4-lane highways with 100km/h of design speed and speed limit. Korea Highway Corporation's Geographic Figurative Information System was adopted for geometric organization and Highway Traffic Accident Statistics was used. The results reveal that sections made of a single slope without vertical curve has greater accident rate than those with vertical curve, and that sections with 1 vertical curve are higher in the accident rate than those with over 2 vertical curve. For the sections with 1 vertical curve, SAG sections are higher than CREST sections and for the previous straight section of horizontal curve are higher than curved ones. In particular, when the road surface is wet, the accident rate is closely related with SAG vertical curves or leftward horizontal curved sections. This study will have meanings that it proposes the importance of design of road alignment by taking consideration of 3D synthetic alignment conditions for improvement of the road safety.

• Journal of Korean Society of Transportation
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• v.25 no.5
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• pp.79-90
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• 2007

In determining vertical grades in highway alignment design, engineers usually consider heavy vehicle performances on the upgrade. Heavy vehicles usually experience speed reduction on the upgrade and with recent years weight/horsepower improvements for heavy vehicles the speed reduction shows some change. However, in spite of the weight to horsepower improvements for the design vehicles from 300lb/HP to 200lb/HP in the AASHTO, there was no change in the maximum vertical grades. Therefore, a review of the maximum vertical grade reflecting existing heavy vehicle performances is required. In particular, in South Korea where highways pass through lots of mountaineous terrain, the maximum vertical grades must be reviewed throughly. In this study the amount of heavy vehicle performances during past decades were investigated and their expected impacts on highway vertical alignment designs were subsequently analyzed. A worldwide terrain analysis and international design standards were compared to set South Korean vertical grade standards. Traffic flow simulation Vissim was utilized to simulate vehicular flows on the upgrade and new truck performance curves on the grades were developed. Based on the new curve, it was decided that $1{\sim}2%$ increase of the maximum vertical grades could be allowed.

• Journal of Korean Society of Transportation
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• v.24 no.5 s.91
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• pp.109-121
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• 2006

The road should be designed in the consistent alignment which the driver can drive safely. Also, proper highway environments in order to maintain optimal operational speeds on highway sections should be provided In design stage, for highway environments, it is essential for an operational speed estimation model to different highway environments. If a method which could evaluate the status of the road safety is developed through this operational speed estimation model, it is possible to provide safe and more comfortable highways to road users. In the study factors to effect on operational speeds are classified into three groups horizontal & vertical alignments and traffic operation characteristic factors. Factors are chosen to effect on operational speeds by using collation analysis as classifications of tangent sections, horizontal curve sections and vertical curve sections. In order to develop operational speed estimation models in express highways, multi-regression analysis has been used in this study using the selected factors. This study has meaning that the developed estimation models for operational speeds and evaluation of degree of safety to horizontal and vortical alignments simultaneous. In order to represent whole area of the country with the developed models, the models should be re-analyzed with vast data related with road alignment factors in the near future.

• International Journal of Highway Engineering
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• v.10 no.2
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• pp.125-133
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• 2008

Achieving consistent geometric design is an important goal in highway design to ensure obtaining safe, economical and smooth traffic operation. Most evaluation of consistency is based on 'speed change' in speed profile. According to literature, the speed depends on geometric elements, speed on tangent section prior to a curve, and background around roads. Especially, the radius is the most main element mentioned in various literature. Therefore, this paper shows two ways of calculating horizontal radius on real road, that is, three-dimensional road. First of all, the radius of horizontal curve is calculated based on physical method. The calculated radius contains not only superelevation but also longitudinal grade while the current minimum radius is calculated by considering superelevation and side friction according to the point-mass equation. Secondly, the problem of composed curves with distorted appearance by overlaying sag or crest vertical alignment has been known. To quantify the extent of distortion effects, the method of calculation of real seen so called 'Perspective Radius' is developed. The paper presents the perspective radius and recommended perspective radius.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04d
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• pp.530-532
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• 2003

이 논문에서는 Semi-lightpath를 이용한 복구 경로의 준-동적 조합에 의한 WDM 망 복구 기법을 제안한다. 제안된 기법에서는 광파장 채널의 종단 노드간에 여러 개의 부분적인 대체 광파장 채널을 연결함으로써 복구를 수행한다. 이 방법은 정적인 복구 기법과 동적인 복구 기법의 장점을 모두 수용하여 빠른 복구 속도와 복구 동작의 유연성을 동시에 제공하며, 종단간 대체 경로를 여러개의 부분적인 대체 경로로 분할함으로써 복구 경로 및 예비 대역폭의 공유 정도를 높여 통신망 자원 이용의 효율성을 높일 수 있다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.3
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• pp.450-460
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• 1995

A modified circulating fluidized bed heat exchanger under severe fouling condition is developed. The effects of fouling deposits on the performance of a heat exchanger are investigated. The principle and operating characteristics of a circulating fluidized bed heat exchanger are dicussed. A modified circulating fluidized bed heat exchanger shows more stable operating than the other circulating fluidized bed heat exchanger. The characteristics of self cleaning and heat transfer enhancement of a circulating fluidized bed heat exchanger are studied. The movement of spherical particles in a tube is visualized and heat transfer enhancement and scale reduction mechanism by particles are investigated.

• Proceedings of the Korean Information Science Society Conference
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• 1999.10c
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• pp.241-243
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• 1999

인터넷이 급속도로 성장함에 따라 대형화된 망을 효과적으로 운용하기 위해서는 망 상태를 정확하게 파악하는 일이 매우 중요하다. 망 상태를 파악하기 위한 한 방법으로 능동적 측정 방법을 이용한 종단간 성능 측정 방법이 있다. 본 연구에서는 지금까지 능동적 측정 인자로 사용되던 양방향 인자들의 문제점들을 보완한 새로운 측정 대상인 단방향 인자들을 측정하기 위한 측정 도구를 구현하였다. 단방향 측정에서는 무엇보다 측정 대상인 종단간의 시간 동기화가 가장 중요하다. 본 연구에서는 GPS 위성 신호를 이용하여 정확한 시간 동기화를 하였으며, 실제 망에 적용하여 단방향 인자들을 측정한 결과를 분석하였다.