• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.3
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• pp.384-392
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• 2017

A linear explosively formed penetrator(LEFP) is a modification of the explosively formed penetrator(EFP). An EFP is axisymmetric and has a dish-shaped liner while LEFP has a rectangular-shaped liner with curved cross section. Upon detonating LEFP forms laterally wide projectile like blade, leaving a long penetration hole on the target. On the other hand, a long-rod tungsten heavy alloy(WHA) penetrator is one of the major threats against most of the ground armored vehicles. In this paper, the feasibility of using an LEFP in protecting against a long-rod WHA penetrator by colliding LEFP into the threat was investigated through a set of numerical simulations. In this study, a scale-down WHA penetrator with length to diameter ratio(L/D) of 10.7 and 7.0 mm diameter was used to represent a long-rod WHA penetrator. LS-DYNA and Multi-Material ALE technique were employed for the simulation. For estimation of the protection effect by LEFP, residual penetration depths into RHA by the threat were compared according to various impact locations against the threat.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.5
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• pp.583-591
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• 2012

In this paper, using a folded parasitic patch, a hybrid metamaterial antenna having the enhanced bandwidth is presented. To obtain a broad bandwidth of the antenna, a zeroth-order resonance(ZOR) mode of a mushroom antenna and a $TM_{010}$ mode of a conventional patch antenna are combined. By employing an etched rectangular hole and a folded parasitic patch in the conventional patch antenna, a resonance frequency of the $TM_{010}$ mode can be down-shifted toward that of the ZOR mode without changing the size of the antenna. Therefore, the proposed antenna has broad bandwidth which ranges from the ZOR mode to the $TM_{010}$ mode. As a result, a fractional bandwidth of the proposed antenna is measured as 12 % and a radiation efficiency is above 75 % in whole band.

• Smart Structures and Systems
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• v.28 no.6
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• pp.745-760
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• 2021

Dynamic buckling of structure is one of the failure modes that needs to be considered since it may result in catastrophic failure of the structure in a short period of time. For a thin fiber-reinforced polymer (FRP) plate under compression, buckling is an inherent hazard which will be intensified by the existence of defects like holes, cracks, and delamination. On the other hand, the growth of the delamination is another prime concern for thin FRP plates. In the current paper, reinforcing the plates against buckling is realized by using SMA wires in the form of stitches. A numerical framework is proposed to simulate the dynamic instability emphasizing the effect of the SMA stitches in suppressing delamination growth. The suggested algorithm is more accurate than the other methods when considering the transformation point of the SMA wires and the modeling of the cohesive zone using simple and yet reliable technique. The computational design of the method by producing the line by line orders leads to a simple algorithm for simulating the super-elastic behavior. The Lagoudas constitutive model of the SMA material is implemented in the form of user material subroutines (VUMAT). The normal bilinear spring model is used to reproduce the cohesive zone behavior. The nonlinear finite element formulation is programmed into FORTRAN using the Newmark-beta numerical time-integration approach. The obtained results are compared with the results obtained by the finite element method using ABAQUS/Explicit solver. The obtained results by the proposed algorithm and those by ABAQUS are in good agreement.

• Korean Journal of Heritage: History & Science
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• v.46 no.4
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• pp.126-143
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• 2013

Myeonghwalsanseong Fortress and Namsansinseong Fortress in Gyeongju are one of the few that have accurate records of when and who constructed the structures. Based on the monument commemorating the construction of Myeonghwalsanseong Fortress and the construction technique and structure of the fortresses confirmed through excavation survey, it can be induced that Myeonghwalsanseong Fortress was built prior to the 7th century. Meanwhile, Namsansinseong Fortress is believed to have been erected in 679, with the exception of one part of the wall found in the northwestern valley that was built during the first construction period of 591. Referring to the construction method of these fortresses in the royal capital, Gyeongju, various recentlystudied fortresses were reviewed to estimate the construction periods. As a result, Haman Seongsansanseong Fortress, which takes similar form with Myeonghwalsanseong Fortress, is believed to have been built during the mid-6th century based on the construction method and supplementary work method(i.e. Bochuk). Yangdongsanseong Fortress in Gimhae and Singisanseong Fortress, similar in their construction method, are also believed to be from the same period. Meanwhile, Jusanseong Fortress of Goryeong, despite the similar construction technique used, the construction technique used for Bochuk or limited Bochuk imply a time gap. Separately, most of the remaining walls of Namsansinseong Fortress appear to date back to the additional construction period, and Sageunsanseong Fortress in Hamyang and Dadaesanseong Fortress in Geoje that show similar construction method are set for the same period. Such conclusion was drawn from straight layer piling using the refined rectangular stones found in the fortress and the supplementary part remaining thereof. In addition, the study discovered a cross-section triangular water hole at Yangdongsanseong Fortress in Gimhae and Sageunsanseong Fortress in Hamyang and the trace of wooden fences constructed before the construction of stone-wall, reaping outcomes rarely found in this region.

• Conservation Science in Museum
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• v.29
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• pp.47-64
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• 2023

Daehye Bogakseonsaseo (Letters of Master Bogak) in the possession of the National Museum of Korea is a Goryeo-era book produced in 1387, which was acquired in 2005 in a state of severe general damage. Subsequently, its production techniques and materials were examined using bibliographical characteristics and scientific analysis, based on which an overall conservation treatment was carried out. Janghwang(mounting) in bibliographical characteristics is a five-hole-stitch binding (五針眼線裝本), a single-lined rectangular box (四周單邊), and no column lines. The conservation treatment was examined in two aspects: the basic form and the conservation treatment process. The book is composed of the outer cover, original cover, end paper, and inner paper of 0.04-0.07mm thick, which is significantly thinner than general book paper. The conservation treatment was applied after the entire book was disassembled, based on the assessment that both the cover and the inner sheets of paper were in a dire condition due to deterioration. The conservation treatment comprised of the process of disassembly, cleaning, reinforcement of defective parts, scanning, and binding, with a paulownia box made for its storage. At the time of disassembly, samples were made for the inner sheets and the book string in order to conduct fiber identification. The fibers were identified using Safranin and C-stains. Safranin staining identified a thick fiber wall, in addition to cross-marking, dislocation, and transparent membranes. C-stain staining identified the fiber as mulberry, given the dark red residue. The book strap has a flat, circular cross-section, and was identified as cotton fiber, since a lumen was observed in the center.