• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.2
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• pp.255-265
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• 2019

In the present study, the effect of opening patterns of a flow control valve on underwater discharge systems using a linear pump was investigated numerically. For that, a improved mathematical model was developed. The improvement is to separate a middle tank from a water cylinder because the cross-section area of the inlet of the middle tank is an important parameter. To validate the improved model, calculation results were compared with a previous study. The results showed that $2^{nd}$ order or more polynomial opening patterns had an advantage over ramp opening patterns. Higher an order of polynomial resulted in wider operating limits. An escape velocity and a maximum acceleration of underwater vehicle were affected by time derivative of the cross-section area of the flow control valve. Besides, as a velocity profile of the vehicle got closer to linearity, the escape velocity got faster and the maximum acceleration got smaller. And velocities of the vehicle and piston had similar variation trend.

• Journal of IKEEE
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• v.18 no.2
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• pp.220-227
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• 2014

This paper presents a control method of Single-Inductor Dual-Output DC-DC Converter using Common mode feedback and differential feedback loops. To generate duty used for differential mode feedback loop, this paper propose relative sawtooth circuit using current divider circuit which makes ramp signal with variable dead-time. Two outputs of the Single-Inductor Dual-Output DC-DC Converter are specified for 2.8 V and 4.2 V with input voltage 2.5 V. The maximum conversion efficiency of designed SIDO DC-DC Converter is 95% at total output power of 539mW. Cross regulations of Boost1 and Boost2 are 3.57% and 4% each, when increasing twice times output current.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.64-71
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• 2005

To achieve efficient supersonic combustion within a manageable length, a successful fuel injection scheme must provide rapid mixing between fuel and airstream. In former days, various injection concepts have been investigated. Cavity flow is the open type, that is, length-to-depth ratio L/D=4.8, aft ramp angle is $22.5^{\circ}$. An experimental study on a transverse cross jet injection into a Mach 1.92 supersonic main stream which flows over a cavity was carried out to investigate the effect of the momentum flux ratio(J), the jet interaction characteristics, and the pressure distribution in the combustor and using the primary diagnostics : schlieren visualization and wall static pressure measurements. Fuel penetration height and jet interaction characteristics depend strongly on the momentum flux ratio.

• Journal of Navigation and Port Research
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• v.30 no.8 s.114
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• pp.649-655
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• 2006

Waves progressing into the coastal area can be amplified, swashed and overtopped by a wave overtopping control structure, and it converts the kinetic energy of the waves to the potential energy with a hydraulic head above the mean sea level by conserving the overflow in a reservoir. Then the potential energy in the form of hydraulic head can be converted to electric power utilizing extremely low-head hydraulic turbine. This study aims to find the most optimal shape of wave overtopping structure which maximizes overtopping volume rate of sea water. Laboratory experiments for the performance evaluation of wave overtopping control structures were carried out in three dimensional wave tank, and the three dimensional structure models with planar wave concentration shapes(B/b) were manufactured into five classes, which were optimized by cross sectional parameters of the structure, ie, length of ramp(l), gradient of inclined ramp($cot{\phi}$) and freeboard height of the wave overtopping structure($h_e$) proposed by Shin and Hong(2005). The wave overtopping discharges were investigated with 20 incident wave conditions and wave directions of $0^{\circ},\;15^{\circ},\;30^{\circ}$.

• Steel and Composite Structures
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• v.37 no.2
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• pp.117-136
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• 2020

Curved steel-concrete composite box girder has been widely adopted in urban overpasses and ramp bridges. In order to investigate its mechanical behavior under complicated and combined bending, shear and torsion load, two large-curvature composite box girders with interior angles of 25° and 45° were tested under static hogging moment. Based on the strain and deflection measurement on critical cross-sections during the static loading test, the failure mode, cracking behavior, load-displacement relationship, and strain distribution in the steel plate and rebar were investigated in detail. The test result showed the large-curvature composite box girders exhibited notable shear lag in the concrete slab and steel girder. Also, the constraint torsion and distortion effect caused the stress measured at the inner side of the composite beam to be notably higher than that of the outer side. The strain distribution in the steel web was approximately linear; therefore, the assumption that the plane section remains plane was approximately validated based on strain measurement at steel web. Furthermore, the full-process non-linear elaborate finite element (FE) models of the two specimens were developed based on commercial FE software MSC.MARC. The modeling scheme and constitutive model were illustrated in detail. Based on the comparison between the FE model and test results, the FE model effectively simulated the failure mode, the load-displacement curve, and the strain development of longitudinal rebar and steel girder with sufficient accuracy. The comparison between the FE model and the test result validated the accuracy of the developed FE model.

• Journal of Korean Society of Transportation
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• v.26 no.4
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• pp.7-16
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• 2008

Severe congestion is happening at urban freeway off-ramps in Seoul. Major causes of congestion at off-ramps are a shortage of capacity and inefficient signal operations at the downstream intersection at off-ramps. It is necessary to control congestion by improving design or operations in the downstream intersection. In this study, the authors analyzed the case of the Jungdong interchange that was improved for design in the downstream intersection. When a freeway and an arterial road cross, diamond interchanges are usually selected with a single-point urban interchange (SPUI) as an alternative. To compare the effectiveness of a diamond interchange with a SPUI, the authors applied these two configurations to the Jungdong interchange using a simulation. The result of the analysis shows that congestion at off-ramps in diamond interchanges can be reduced by improving signal operations such as the application of "4 phase with overlaps" and that diamond interchanges are more efficient than a SPUI with a frontage road. Efficient operation of the downstream intersection by these findings can minimize congestion of not only the downstream intersection but also the freeway mainline.

• Journal of the Korean earth science society
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• v.28 no.4
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• pp.478-490
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• 2007

With groundwater data of seawater intrusion monitoring network in coastal areas of Korea's main land, we analyzed types of seawater intrusion through the coastal aquifer. The data including groundwater level, temperature and electrical conductivity obtained from 45 monitoring wells at 25 watershed regions were evaluated. Based on statistical analysis, correlation analysis and variation type analysis, groundwater levels were mainly affected by rainfall and artificial pumping. About 78% of the monitoring wells showed average temperature higher than $15^{\circ}C$ and about 58% of them showed minimum variations less than $0.2^{\circ}C$. Electrical conductivities showed a large magnitude of variation and irregular characteristics compared with groundwater levels and temperatures. Average electrical conductivities lower than $2,000\;{\mu}S/cm$ were observed at 28 monitoring wells while those of higher than $10,000\;{\mu}S/cm$ were done at 9 monitoring wells. From the cross-correlation analysis, groundwater levels were mostly affected by precipitation while temperature and electrical conductivity showed very low correlation. Meanwhile tidal variations strongly affected the groundwater levels comparing to precipitation. We classified the long-term monitoring data according to variation types such as constant process, linear trend, cyclic variation, impulse, step function and ramp. Impulse type was dominant for variations of groundwater level, which was largely affected by rainfall or artificial pumping, the constant process was dominant for temperature. Compared with groundwater level and temperature, electrical conductivities showed various types like linear trend, step function and ramp. According to the discrepancy of variation characteristics for monitoring data at each well in the same region, periodical analysis of monitoring data is essentially required.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.2
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• pp.213-229
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• 2017

Recently, in urban areas there is a tendency to construct more complex network-type tunnels including entrance and exit ramps. At the same time, various one-dimensional programs based on the network theory have been proposed for tunnel ventilation analysis. This paper aims at developing a program that can analyze the ventilation flow rate and pollutants concentration in complex network-type tunnels based on the none hardy-cross method. The flow analysis in the branch was carried out on the basis of the Gradient method, while for the concentration analysis a new logic has been developed to calculate the inflow and outflow concentration automatically in a complex network-type structure. Additionally, in the tunnel segments showing low flow rate, proper grid interval sizes were proposed to reduce numerical error. To verify the applicability of the program, flow rates predicted in the straight tunnels were compared with the classical velocity-diagram method by Stokic and the TVSDM program. The results showed that the errors were within 1%. In addition, the program was applied to the recent ventilation system adopted in the complex network-type urban tunnels.

• Journal of the Korean Institute of Landscape Architecture
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• v.40 no.4
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• pp.51-61
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• 2012

Kyong-Eui Railway used to be one of the major cross-country railways connecting Busan and Shineuiju. Being the central axis of logistics and transportation in Korea, it also signifies a symbolic meaning of the people's desire for the unification of divided Korean peninsula. A steam locomotive that had stopped in Jangdan Station was bombed out during the Korean War. The locomotive has been neglected and covered with rust in DMZ over a half century, and now is becoming a historic reminder of divided Korea. The initial design approach was based on the three main perspectives of the relocation plan of the steam locomotive in Jangdan Station which is designated as the registered cultural asset no. 78: historical significance, role of a monumental space, and influence on and from the local culture and tourism. Three design subjects were especially highlighted which would represent the identity of the cultural asset, the stream locomotive. First, a vertical watching deck was installed to provide various view points toward the locomotive while ensuring the security of visitors as well as the cultural asset. Second, the Dokgae bride area has good design potentials being on the railway. However, the site is too narrow. Thus, a new ramp and a stairway were placed responding to the existing topography so that the pedestrian environment could be secured last, to respect the local context where the locomotive was originally located, mulberry trees in the locomotive were transplanted as well. Flowering plants were planted around the display area for better ventilation to minimize the negative impact on the locomotive.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.6
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• pp.1731-1741
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• 2014

Recently, many overpasses, highway, and advanced transit systems have been constructed to distribute the traffic congestion, thus small size of curved bridges with small curvature such as ramp structures have been increasing. Many of early curved bridges had been constructed by using straight beams with curved slabs, but curved steel beams have replaced them due to the cost, aesthetic and the advantage in building the section form and manipulating the curvature of beams, thereby large portion of curved bridges were applied with steel box girders. However, steel box girder bridges needs comparatively high initial costs and continuous maintenance such as repainting, which is the one of the reason for increasing the cost. Moreover, I-type steel plate girder which is being studied by many researchers recently, seem to have problems in stability due to the low torsional stiffness, resulting from the section characteristics with thin plate used for web and open section forms. Therefore, in recent studies, researchers have proposed curved precast PSC girders with low cost and could secured safety which could replace the curved steel girder type bridges. Hence, this study developed a Smart Mold system to manufacture efficient curved precast PSC girders. And by using this mold system a 40 m 2-girder bridge was constructed for a static flexural test, to evaluate the safety and performance under ultimate load. At the manufacturing stage, each single girder showed problems in the stability due to the torsional moment, but after the girders were connected by cross beams and decks, the bridge successfully distributed the stress, thereby the stability was confirmed. The static loading test results show that the initial crack was observed at 1,400 kN when the design load was 450 kN, and the load at the allowable deflection by code was 1,800 kN, which shows that the safety and usability of the curved precast PSC bridge manufactured by Smart Mold system is secured.