• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.4
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• pp.73-80
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• 2005

In general, the performance of movable nozzle used for thrust vector control in solid rocket motor is estimated on the basis of the effective pivot of nozzle. However, it is nearly impossible to define the exact effective pivot by the mathematical model or experimental technique owing to pivot dynamics. In this paper, pivot dynamic properties were investigated by ADAMS simulation technique and trajectory of the exact effective pivot was modelled by the artificial neural network. Comparison of the proposed method was made with the virtual movable nozzle (computer simulation) to verify the method, and showed good agreement. Therefore, the proposed method will be applicable to predict the effective pivot of movable nozzle during bench or ground test.

• Geomechanics and Engineering
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• v.4 no.3
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• pp.191-208
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• 2012

Due to rapid industrialisation, large scale infrastructure development is taking place worldwide. This includes railways, high speed highways, elevated roads etc. To meet the demands of society and industry, many innovative techniques and materials are being developed. In developed nations like USA, Japan etc. for railways applications, new material like geocells, geogrids are being used successfully to enable fast movement of vehicles. The present research work was aimed to develop design methodologies for improvement of grounds subjected to cyclic loads caused by moving vehicles on roads, rail tracks etc. Deformation behavior of ballast under static and cyclic load tests was studied based on square footing test. The paper presents a study of the effect of geo-synthetic reinforcement on the (cumulative) plastic settlement, of point loaded square footing on a thick layer of granular base overlying different compressible bases. The research findings showed that inclusion of geo-synthetics significantly improves the performance of ballasted tracks and reduces the foundation area. If the area is kept same, higher speed trains can be allowed to pass through the same track with insertion of geosynthetics. Similarly, area of machine foundation may also be reduced where geosynthetics is provided in foundation. The model tests results have been validated by numerical modeling, using $FLAC^{3D}$.

• Journal of Electrical Engineering and Technology
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• v.3 no.4
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• pp.484-490
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• 2008

In this paper, an integrated fault section detection and isolation strategy is proposed based on the application of the Distribution Automation System(DAS) utilizing advanced IT and communication technologies. The Feeder Remote Terminal Unit(FRTU) has been widely used to collect data in the Korean distribution system. The achieved data is adopted in this method for detecting multiple fault types. Especially in the case of single phase-to-ground fault, the fault section is detected by comparison of the zero-sequence current phase angle. The test results have verified the effectiveness of the proposed method in a radial distribution system through extensive simulations in Matlab/Simulink. Furthermore, a communication-based demo system identical to the simulation model has been developed, and it can be applied as an online monitoring and control program for fault section detection and isolation.

• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.114-121
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• 1997

Helical anchors are foundation structure that designed to resist uplift loads are installed by applying in load to shaft while rotating it into the ground. These can be a cost effective means of proving tension anchorage for foundation where soil conditions permit their installation because of ease of installation. At present time, tapered helical anchors are commonly used to carry uplift loads. The uplift capacity includes the following factors : the height of overburden above the top helix, the resistant along a cylinder, the weight of the soil in the cylinder and suction force. In order to make clear behavior characteristics of helical anchors with pullout, model tests were conducted with respect to various embedment depth, space of helix, shape of helix. Based on the experimental study, the following conclusions are drawn. 1) The uplift capacity of multi helical anchors increase with embedment ratio of anchors The increase is smooth after critical uplift capacity. 2) Critical breakout factors and critical embedment ratio of multi helical anchor exist 7∼8, 4∼6 respectively. 3) Variation of uplift capacity with helix spaces show down after S/D=5. 4) Critical breakout factors of helical anchor in the laboratory test are similar to Das's theory.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.385-391
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• 2000

An analysis of the heat transfer in a PDP ventilation chamber has been conducted to investigate the required heat curve and temperature uniformity of the panels. Firstly, experiment in a test chamber has been carried out and compared with the unsteady 3D numerical simulation. Reasonable agreement was found, which suggested that the employed numerical model had its credibility in an actual PDP ventilation process. On this ground, tact-type heating/cooling system was analyzed. The panel temperature was more uniform in the $40^{\circ}C$ tact-type system than in the $80^{\circ}C$ one. Comparison of full simulation of a cart and simplified simulation of one panel shows the panel pitch, which is closely related to a production rate, can be also predicted.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.80.2-80.2
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• 2011

The sudden decrease of galactic cosmic ray (GCR) intensity observed by ground neutron monitor (NM) is called a Forbush decrease (FD) event. The intensity time profile of FD event looks like the geomagnetic storm visualized by geomagnetic storm index Dst. Oh et al. [2008] and Oh and Yi [2009] classified the FD events into two kinds by criteria of the overlapping simultaneity of main phase in universal time (UT). The FD event is defined simultaneous if the main phase parts observed by the stations distributed evenly around the Earth are overlapped in UT and non-simultaneous if ones are overlapped in each station's local time (LT). They suggested the occurrence mechanisms of two kind FD events related to the interplanetary magnetic structures such as the interplanetary shock (IP shock) and magnetic cloud. According to their model, the simultaneity of FD depends on the strength and propagation direction of interactive magnetic structures overtaking the Earth. Now the STEREO mission can visualize the emergence and propagation direction of the coronal mass ejection (CME) in 3-dimension in the heliosphere. Thus, it is possible to test the suggested mechanisms causing two different types of FD events. One simultaneous FD observed on February 17, 2011 may be caused by a CME heading directly toward the Earth observed on February 15, 2011 by the STEREO mission. The simultaneity of FD event is proved to be a useful analysis tool in figuring out the geo-effectiveness of solar events such as interplanetary CMEs and IP shocks.

• KIEAE Journal
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• v.16 no.2
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• pp.17-22
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• 2016

Purpose: Sensitivity analysis offers a good guideline for designing energy conscious buildings, which is fitted to a specific building configuration. Sensitivity analysis is, however, still too expensive to be a part of regular design process. The One-at-a-time (OAT) is the most common and simplest sensitivity analysis method. This study aims to propose a reasonable ground that the OAT can be an alternative method for the variance-based method in some early design scenarios, while the variance-based method is known adequate for dealing with nonlinear response and the effect of interactions between input variables, which are most cases in building energy simulations. Method: A test model representing the early design phase is built in the DOE2 energy simulations. Then sensitivity ranks between the OAT and the Variance-based methods are compared at three U.S. sites. Result: Parameters in the upper rank by the OAT do not much differ from those by the Main effect index. Considering design practices that designers would chose the most energy saving design option first, this rank similarity between two methods seems to be acceptable in the early design phase.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.308-327
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• 2004

As use of tunnels and subways increase there also are accidents proportionate to it. Daegu Subway Station fire, Hongjimoon tunnel fire led people to be conscious of disaster protection and as a result, there is a trend to adopt standards for fire protection. Accordingly, this thesis is focused on investigating various fire and water protection related issues for subaqueous tunnel under Ran river. The thesis developed evacuation and disaster prevention plan as fire level increases and have identified the suitability of disaster prevention through evacuation and fire simulation, countermeasure of a water leakage during construction and operation considering the subaqueous tunnel. And we selected EPB shield TBM equipment considering the ground condition and effect of boring hole, and accomplished reasonable water protection design through setting goals using event-tree method, as well as examining model test of boring hole and flooding in heavy rain. Also included structured total system consist of water leakage sensing system, water protection gate, pumping system and fire protection system to respond systematically in emergency.

• Journal of the Korean GEO-environmental Society
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• v.13 no.4
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• pp.61-69
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• 2012

A high rock embankment by means of phased dynamic compaction has hardly carried out in Korea. Settlement of each layer is measured in order to verify the settlement behavior of dynamically compacted high rock embankment. A high rock embankment is generally constructed by dividing into several sub-embankments. Such a sub-embankment and dynamic compaction may induce an increase of pressure at the lower part of embankment and cause a different behavior of ground from initial status. In this study, settlement of a high rock embankment is estimated using a hyperbolic model taking into construction history. The results from prediction are compared with those obtained from field measurements. And second creep settlement is predicted using pre-loading test.

• Journal of the Korean GEO-environmental Society
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• v.18 no.11
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• pp.19-26
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• 2017

When narrowly excavated in the urban area, the wall of backfill space is not only symmetrical but also asymmetrical. In this case, the horizontal stress induced by backfilling depends mostly on the wall asymmetry and the wall friction angle. Therefore, in this study, the model test in the laboratory was conducted to investigate horizontal earth pressure with depth considering various boundary conditions such as base width, wall friction, relative density of backfill, and wall angle. As the wall is smoother and wall angle is lower from the bottom, the results showed higher the horizontal stresses due to the increase of vertical stresses.