• Journal of Navigation and Port Research
• /
• v.48 no.4
• /
• pp.303-309
• /
• 2024

This study examines the effects of wave pressure on a vertical wall due to armor block failure at the front of a caisson, using a 2-D hydraulic model to simulate three types of armor block cross-sections. Additionally, the hydraulic characteristics of two cross-sections that replicated the armor blocks' failure, based on complete cross-sections, were compared. Moreover, quantitative analysis indicated that in the cross-section where the displacement of the armor block was recreated, wave run-up( ) increased by an average of 73%, the sum of dimensionless wave pressures increased by 28%, and converted wave force rose by 33%. These findings underscore the need for countermeasures in the event of armor block failure.

• Publications of The Korean Astronomical Society
• /
• v.12 no.1
• /
• pp.173-183
• /
• 1997

We have numerically simulated the evolution of supernova remnant VRO 42.05.01(G166.0+43) in order to understand its morphology m radio and X-ray observations as well as the dynamical interaction of the supernova remnant with the surrounding interstellar medium. The Radio and ROSAT observations suggest that the unusual morphology of VRO 42.05.01 is caused by a supernova blast wave breaking out of the cloud boundary where the supernova event occurred, and expanding into another cloud across a much less dense and presumably hot cavity. Our numerical results are consistent with the interactions of a passing supernova blast wave with the clouds across the cavity. We discuss the implications of our results on the dynamics of VRO 42.05.01 such as the reverse shocks, the rejuvenation of the hot cavity, and the reflected shocks formed by the reverse shock collisions. We have theoretically mapped the radio continuum(1.4 GHz) and X-ray(0.1~2 keV) morphology which are consistent with the observational ones.

• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.2
• /
• pp.45.1-45.1
• /
• 2010

Using SOHO particle and EUV detection and radio spectrograms from both ground-based and spaceborne instruments, we have studied the first phase of major solar energetic particle (SEP) events associated with wide and fast coronal mass ejections (CMEs) centered at different solar longitudes. Observations support the idea that acceleration of SEPs starts in the helium-rich plasma of the eruption's core well behind the CME leading edge, in association with coronal shocks and magnetic reconnection caused by the CME liftoff; and those "coronal" components dominate during the first ~1.5 hour of the SEP event, not yet being hidden by the CME-bow shock in solar wind. At magnetic connection to the eruption's periphery, onset of SEP emission is delayed for a time of the lateral expansion that is visualized by global coronal (EIT) wave. The first, "coronal" phase of SEP acceleration is followed by a second phase associated with CME-driven shock wave in solar wind, which accelerates high-energy ions from a helium-poor particle population until the interplanetary shock slows down to below 1000 km/s. Based on these and other SOHO observations, we discuss what findings can be expected from STEREO in the SOHO era perspective.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.1
• /
• pp.62.3-62.3
• /
• 2019

After first identification of electromagnetic counterpart of gravitational wave source (GW170817), era of multi-messenger astronomy has begun. For specifying coordinate, magnitude, and host galaxy information, optical follow-up observation of GW source becomes important. With following engineering run and O3 run of LIGO and VIRGO starting in March 2019, we present searching strategy for optical counterpart of GW source using KMTNet. 24 hours monitoring system and large field of view (4 square-degree) of KMTNet are advantage to discover a transient like GW event. By performing tiling observation of high probability area in GW localization map, we expect to observe early light-curve of GW optical counterpart. After identification, follow-up observation with various KMTNet bands and other telescopes like Gemini and UKIRT will also be performed. We will study collision mechanism, progenitor, and characteristics of host galaxy using observation data of GW source.

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.1
• /
• pp.61.2-61.2
• /
• 2021

SkyMapper is the largest-aperture optical wide-field telescope in Australia and can be used for transient detection in the Southern sky. Reference images from its Southern Survey cover the sky at δ <+10 deg to a depth of I ~ 20 mag. It has been used for surveys of extragalactic transients such as supernovae, optical counterparts to gravitational-wave (GW) and fast radio bursts. We adopt an ensemble-based machine learning technique and further filtering scheme that provides high completeness ~98% and purity ~91% across a wide magnitude range. Here we present an important use-case of our robotic transient search, which is the follow-up of GW event triggers from LIGO/Virgo. We discuss the facility's performance in the case of the second binary neutron star merger GW190425. In time for the LIGO/Virgo O4 run, we will have deeper reference images for galaxies within out to ~200 Mpc distance, allowing rapid transient detection to i ~ 21 mag.

• Journal of the Korean Society for Railway
• /
• v.7 no.3
• /
• pp.193-199
• /
• 2004

Numerical analysis of aerodynamic characteristics was differently performed according to the running situation of the Korean Tilting Train eXpress(TTX) that would be introduced for an improvement in efficiency of the used railroad track. Fluent 6.0 was used for the analysis of Non-tilting case, Tilting case and Passing-by case with the model of TTX. As a result, the aerodynamic drag had little difference between Tilting and Non-tilting case. However, pressure contour under the train of Tilting case was not symmetry because the gap between a train and the ground was different at both sides. In Passing-by case attraction and counterattraction occurred alternately and affected to the opposite train. When two trains were side by side, the maximum attraction was generated especially. Through an analysis of pressure wave in tunnel a large variation of pressure was generated by the bluff nose of TTX. The results in this study would be good data for the aerodynamic characteristic on TTX and provide important information to judgment of running safety.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.34 no.6
• /
• pp.177-187
• /
• 2022

This study estimates the design wave in the event of a typhoon attack at Busan new port using the wind field, the revised shallow water design wave estimation method proposed by the Ministry of Oceans and Fisheries in 2020, and proposed a reliable method of calculating the shallow water design through verification with the wave observation data. As a result of estimating typhoon wave using the wind field and SWAN numerical model, which are commonly used in the field work, for typhoon that affected Busan new port, it was found that reproducibility was not good except typhoons KONG-REY(1825) and MAYSAK(2009). In particular, in the case of typhoon MAEMI(0314), which had the greatest impact on Busan new port, the maximum significant wave height was estimated to be about 35.0% smaller than that of the observed wave data. Therefore, a plan to improve the reproducibility of typhoon wave was reviewed by applying the method of correcting the wind field and the method of using the Boussinesq equation numerical model, respectively. As a result of the review, it was found that the reproducibility of the wind field was not good as before when the wind field correction. However as a method of linking wind field data, SWAN model results, and Boussinesq numerical model, typhoon wave was estimated during typhoon MAEMI(0314), and the maximum significant wave was similar to the wave observations, so it was reviewed to have good reproducibility.

• Journal of Power System Engineering
• /
• v.21 no.3
• /
• pp.102-107
• /
• 2017

A tungsten inert gas (TIG) welding method was used for the bonding of stainless steel. TIG welding using inert gas (He or Ar gas) is a method to prevent oxidation and nitriding of materials and to combine non-ferrous metals. This method has the advantage of obtaining a smooth weld surface. In this study, the welding characteristics of 304 stainless steel welded by TIG welding method were analyzed by using nondestructive technique. Ultrasonic and Acoustic Emission (AE) was applied to evaluate the micro-damage of TIG welded 304 stainless steel. The velocity and damping coefficient of ultrasonic wave showed a slight difference in HAZ, which is the welding part of stainless steel. The AE parameters of average frequency, rise time and event were analyzed for the dynamic behavior of stainless steel during loading. Optimal AE parameters for evaluating the degree of damage to the specimen have been derived. Fractograph and metal structures of 304 stainless steel using SEM and optical microscope were discussed.

• The Bulletin of The Korean Astronomical Society
• /
• v.43 no.1
• /
• pp.54.4-55
• /
• 2018

Propagating speeds of coronal mass ejections (CMEs) have been calculated by several geometrical models based on multi-view observations (STEREO/SECCHI and SOHO/LASCO). But in 2015, we were unable to obtain radial velocity of a CME because the STEREO satellites were located near the backside of the sun. As an alternative to resolve this problem, we propose a method to combine a coronal shock front, which appears on the outermost of the CME, and an EUV-wave that occurs on the solar disk. According to recent studies, EUV-wave occurs as a footprint of the coronal shockwave on the lower solar atmosphere. In this study, the shock, observed as a bubble shape, is assumed as a perfect sphere. This assumption makes it possible to determine the height of a coronal shock, by matching the position of an EUV-wave on the solar disk and a coronal shock front in coronagraph. The radial velocity of Halo-CME is calculated from the rate of coronal shock position shift. For an event happened on 2011 February 15, the calculated speed in this method is a little slower than the real velocity but faster than the apparent one. And these results and the efficiency of this approach are discussed.

• Journal of the korean society of oceanography
• /
• v.37 no.3
• /
• pp.144-153
• /
• 2002

This is a review paper, assessing progress reported in a Special Issue (Prandle and Lane, 2000) of Coastal Engineering focusing on simulation of SPM in the North Sea, against issues over a diverse range of shelf seas and their coastal margins. The broad objectives of reproducing the characteristics of sediment fluxes off an open coast and relating these to tidal and wave forcing were achieved. However, accurate computation of these fluxes remains sensitive to largely empirical coefficients used in determining erosion and deposition rates. Bed roughness strongly influences both these coefficients and the associated near-bed current magnitudes (including wave impact thereon). Bed roughness can change significantly over a tidal cycle and dramatically over seasons or in the course of a major event. Accurate simulation of sediment fluxes on a day-to-day basis is constrained by dependency on the initial distribution of mobile sediments. The latter depends on rates and locations of original sources and the time history of preceding events. Remote sensing via aircraft could provide data for assimilation into such models to circumvent these constraints. The approaches described here can be readily applied to other coastal regions to indicate the likely distributions and pathways of known sediment sources. However quantitative simulations will require an associated observational programme. A subsequent stage is to understand the evolving balance between the forecasted sediment movement - the resulting morphological adjustments and thence modifications to the prevailing tidal current and wave regimes.