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Experimental and numerical investigations of near-field underwater explosions
Seunggyu Lee,Junghee Cho,Chaemin Lee,Seongpil Cho 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.77 No.3
Near-field underwater explosion (UNDEX) phenomena were investigated by experiments and numerical simulations. The UNDEX experiments were performed in a water tank using a ship-like model. One kilogram of TNT, one of the most widely used military high explosives, was used for the experiments. Numerical simulations were performed under the same conditions as in the experiments using the commercial software LS-DYNA. Underwater pressures, accelerations, velocities, and strains by shock waves were measured at multiple locations. Further, the bubble pulsation period and the whipping deformations of the ship-like model were explored. The experimental results are presented and examined through comparison with the results obtained from widely used empirical equations and numerical simulations.
Flexibility enhancement of poly(lactide-co-glycolide) for fused deposition modeling technology
Seunggyu Jeon,Jonghyeuk Han,Wonwoo Jeong,Jeonghyun Son,Hyun-Wook Kang 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.6 No.3
Poly(lactide-co-glycolide) (PLGA) is one of the most widely used bioplastics in bioengineering and has been actively applied to fused deposition modeling (FDM)-based 3D printing. However, the brittleness of PLGA remains a major obstacle to its application in FDM systems, because these systems can only process flexible materials. Here, we developed a new technique to enhance the flexibility of PLGA. A polymer drawing process involving bidirectional extension was applied to induce molecular alignment, which affects the flexibility of the material. Filamentous forms of PLGA with various draw ratios were prepared and their material properties were investigated in detail. The results showed that PLGA flexibility was markedly increased at the draw ratio of 3, which was identified as the brittle-to-ductile transition point. The elongation at break of the drawn PLGA at this draw ratio was approximately 14 times greater than that of the raw material. Printability tests showed that various complex 3D structures could be fabricated with the drawn PLGA using a FDM system. In addition, the drawn PLGA showed no cytotoxicity in culturing. The technique developed here shows potential for the preparation of long and flexible PLGA filaments for use in FDM technology with biological applicability.
Effect of Heating Rate on Microstructure and Mechanical Properties in Al 7055
Seunggyu Choi,Junhyub Jeon,Namhyuk Seo,Seung Bae Son,Seok‑Jae Lee 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.3
The effects of the heating rate during solid solution heat treatment on the mechanical properties and microstructure of the7055 aluminum alloy were investigated. The dissolution and formation kinetics of the precipitates in the sample before thesolid solution treatment vary depending on the heating rate. This is because the dissolution and formation of precipitateparticles are diffusion-controlled. Therefore, dilatometric tests were carried out to control the heating rates during the solidsolution treatment. Then, the mechanical properties were evaluated using hardness and compressive tests, while the microstructuralfeatures were observed using X-ray diffraction, optical microscopy, and scanning transmission electron microscopy. The characteristics of the precipitate for each heating rate were calculated using thermodynamic simulation, and a model topredict the mechanical properties was proposed based on the results.
A MODIFIED CAHN–HILLIARD EQUATION FOR 3D VOLUME RECONSTRUCTION FROM TWO PLANAR CROSS SECTIONS
SEUNGGYU LEE,YONGHO CHOI,DOYOON LEE,HONG-KWON JO,SEUNGHYUN LEE,SUNGHYUN MYUNG,JUNSEOK KIM 한국산업응용수학회 2015 Journal of the Korean Society for Industrial and A Vol.19 No.1
In this paper, we present an implicit method for reconstructing a 3D solid model from two 2D cross section images. The proposed method is based on the Cahn?Hilliard model for the image inpainting. Image inpainting is the process of reconstructing lost parts of images based on information from neighboring areas. We treat the empty region between the two cross sections as inpainting region and use two cross sections as neighboring information. We initialize the empty region by the linear interpolation. We perform numerical experiments demonstrating that our proposed method can generate a smooth 3D solid model from two cross section data.
Seunggyu Ji,Hyungtak Kim,Il Hwan Cho 대한전자공학회 2018 Journal of semiconductor technology and science Vol.18 No.3
A novel tunneling field effect transistor (TFET) with a recess channel is proposed. Proposed TFET has a thin intrinsic region and it is formed in the shape of surrounding the gate. The performance of the proposed device is analyzed through comparison with double gate thin intrinsic TFET (DGTI) TFET and double gate (DG) TFET structures. The comparison results of on-current (Ion) and subthreshold swing (S) with other devices shows that the proposed device has excellent characteristics. The effects of the structural parameters change of the device on the proposed device are analyzed and compared with the other two TFET structures. A guideline for the optimization of the proposed device is suggested.
Mathematical modelling for investigating the function of anatomical structures
Seunggyu Lee,Mi-Sun Hur,Chang-Seok Oh 대한체질인류학회 2021 대한체질인류학회 학술대회 연제 초록 Vol.64 No.-
Mathematics is considered as a useful scientific tool in various fields such as multiphase fluid dynamics, image processing, dendrite growth, and cell dynamics. Since Allen Turing (1952) proposed a concept of the reaction-diffusion equation for pattern formation, the mathematical and computational biology has been actively studied in many areas of both basic and clinical medicines. In this talk, we discuss some mathematical models used in our recent studies of anatomical structures and their corresponding numerical simulation results. It is presented how mathematics and 21st century anatomy meet to investigate the function of human organs; the longitudinal muscular column in the prostatic urethral wall (Prostate 80(6), 2020), the facial muscles acting on the nasolabial fold (PLoS One 15(8), 2020), the channels in the interatrial septum of the heart (PLoS One 16(2), 2021), and the structure and function of pyloric sphincter in preparation. The immersed boundary and phase-field methods, which are coupled systems of the Navier-Stokes and transport equations have been mainly applied for the research.
( SeungGyu Shin ),( JungJae Lee ),( ChangHee Do ) 한국축산학회(구 한국동물자원과학회) 2021 한국축산학회지 Vol.63 No.4
This study was performed to investigate genetic relationship of age at first calving (AFC) with body development and reproduction capacity in female Hanwoo. The data sets of 52,299 reproduction records of 19,566 heads calved from 2011 to 2019 and conformation records of 19565 heads born from 1997 to 2017 were analyzed by separating them based on age at first calving. In the analysis, conformation traits included the body condition score (BCS), height (HT), body width (BW), hip bone length (HL), hip bone width (HW), and final score (FS). The heritability and genetic correlation of AFC with conformation traits and calving interval (CI) were analyzed. The heritability for AFC was 0.716, 0.087, and 0.097 for the before and after 24 months and combined data, respectively. The genetic correlation of AFC before 24 months with BCS was -0.778, -0.600 with BW, and 0.442 with HT. The genetic correlation of AFC after 24 months with HT was -0.826, -0.706 with BW, -0.623 with HL, -0.456 with HW, and -0.675 with FS. When the first calving age of young heifers approached 24 months, BCS and BW decreased, and HT increased. When first calving is delayed to after 24 months, the conformation traits become smaller, which indicates that conformation to some extent affects the delay in AFC. The genetic correlation between CI and AFC was -0.116, 0.307, and 0.250 for the before and after 24 month of AFC and combined data, respectively. When first calving date approached 24 months, CI was reduced. The obtained results suggest that it is important that first calving occurs at an appropriate age. Additional research is needed to perform proper genetic evaluation of first calving age in Hanwoo cattle in Korea.
COMPARISON OF NUMERICAL METHODS FOR TERNARY FLUID FLOWS
SEUNGGYU LEE,DARAE JEONG,YONGHO CHOI,JUNSEOK KIM 한국산업응용수학회 2016 Journal of the Korean Society for Industrial and A Vol.20 No.1
This paper reviews and compares three different methods for modeling incompressible and immiscible ternary fluid flows: the immersed boundary, level set, and phase-field methods. The immersed boundary method represents the moving interface by tracking the Lagrangian particles. In the level set method, an interface is defined implicitly by using the signed distance function, and its evolution is governed by a transport equation. In the phase-field method, the advective Cahn–Hilliard equation is used as the evolution equation, and its order parameter also implicitly defines an interface. Each method has its merits and demerits. We perform the several simulations under different conditions to examine the merits and demerits of each method. Based on the results, we determine the most suitable method depending on the specific modeling needs of different situations.
ACCURATE AND EFFICIENT COMPUTATIONS FOR THE GREEKS OF EUROPEAN MULTI-ASSET OPTIONS
SEUNGGYU LEE,YIBAO LI,YONGHO CHOI,HYOUNGSEOK HWANG,JUNSEOK KIM 한국산업응용수학회 2014 Journal of the Korean Society for Industrial and A Vol.18 No.1
This paper presents accurate and efficient numerical methods for calculating the sensitivities of two-asset European options, the Greeks. The Greeks are important financial instruments in management of economic value at risk due to changing market conditions. The option pricing model is based on the Black-Scholes partial differential equation. The model is discretized by using a finite difference method and resulting discrete equations are solved by means of an operator splitting method. For Delta, Gamma, and Theta, we investigate the effect of high-order discretizations. For Rho and Vega, we develop an accurate and robust automatic algorithm for finding an optimal value. A cash-or-nothing option is taken to demonstrate the performance of the proposed algorithm for calculating the Greeks. The results show that the new treatment gives automatic and robust calculations for the Greeks.