• 대한기계학회논문집B
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• 제41권8호
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• pp.521-529
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• 2017

본 연구에서는 항공기 추진용 가스터빈 엔진의 고증속 터빈 제1단 정익 익렬을 새로이 구축하고, 이 정익의 기본 유동 특성에 대하여 연구하였다. 그 결과 본 연구에서 도입된 정익의 압력면에는 강한 순압력구배가 존재하는 반면, 흡입면에는 앞전에서 미드코드 근처까지 압력면보다 훨씬 더 심한 순압력구배가 존재하고 그 이후 역압력구배가 존재하였다. 두 종류의 유막법을 적용한 유동의 가시화 실험을 통하여, 정익 앞전 상류 영역에 4와류모델 말발굽와류 시스템이 존재함을 확인하였고, 입구 경계층 유동의 박리선과 재부착 유동의 박리선을 정확히 파악하였다. 이와 함께 이 고증속 정익 익렬 하류에서의 2차유동, 압력손실, 선회각, 등에 대한 데이터를 확보하였다.

• 대한치과보철학회지
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• 제57권4호
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• pp.364-373
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• 2019

2급 악간관계를 갖는 환자는 1급 악간관계인 환자와는 달리 불안정한 교합을 가질 수 있으며, 무치악인 경우 총의치를 사용할 때 불안정한 교합을 보이면서 의치의 움직임이 커질 가능성이 있다. 이런 환자에 있어 임플란트 피개의치를 사용함으로써 의치의 안정을 향상시킬 수 있다. 임플란트 피개의 치에서 attachment 종류는 크게 bar type과 solitary type으로 나눌 수 있는데 각각 적응증이 있어 상황에 따라 적용을 달리 하여야 한다. 본 증례는 2급 악간관계를 가진 하악 무치악 환자에서 임플란트 피개의치를 계획함에 있어 디지털 기술을 이용함으로써 더 적합한 attachment를 선택하고 임플란트의 위치 및 깊이를 미리 계획하여 계획한 위치에 식립하였다. 상악은 국소의치로 수복하였고 하악은 임플란트 피개의치로 수복하여 만족할만한 결과를 얻었기에 이를 보고하고자 한다.

• 한국시뮬레이션학회논문지
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• 제27권1호
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• pp.33-38
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• 2018

본 연구에서는 선유도 중어뢰의 전술 효과도 예측을 위하여 개발한 교전수준 시뮬레이터에 대해서 시뮬레이터 개발에 적용된 개념 및 구성요소 모델에 대해서 소개하고 있다. 특히 어뢰의 공격문제 해결을 위하여 기하학적 모델에 따른 해(Closed-form solution)를 도출하였고, 어뢰의 공격유도 방법에 비례항법 유도를 적용하여 구현하였다. 표적함에 대해서는 속도와 소음의 상충관계로 인한 피탐 가능성을 고려하였다. 어뢰의 초기위치에 따른 공격 소요 시간을 계산하고 이를 도시화하는 과정을 통하여 도출된 해의 정확성을 확인 할 수 있었고, 현실적인 공격유도 방법 및 소음원 모사를 통하여 시뮬레이터 충실도를 높일 수 있었다. 시뮬레이터는 다양한 전술상황을 가정하여 결과를 분석 할 수 있도록 자유도가 높게 개발되었으며, 구성요소 궤적 분석 및 전방위 요격 성공률 분석이 가능하여 전장 상황의 흐름을 파악하고 전술에 대한 이해를 높이는데 도움이 된다.

• 산업식품공학
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• 제21권3호
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• pp.233-241
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• 2017

Scaffolds of cell substrates are biophysical platforms for cell attachment, proliferation, and differentiation. They ultimately play a leading-edge role in the regeneration of tissues. Recent studies have shown the potential of bioactive scaffolds (i.e., osteo-inductive) through 3D printing. In this study, rice bran-derived biocomposite was fabricated for fused deposition modeling (FDM)-based 3D printing as a potential bone-graft analogue. Rice bran by-product was blended with poly caprolactone (PCL), a synthetic commercial biodegradable polymer. An extruder with extrusion process molding was adopted to manufacture the newly blended "green material." Processing conditions affected the performance of these blends. Bio-filament composite was characterized using field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDX). Mechanical characterization of bio-filament composite was carried out to determine stress-strain and compressive strength. Biological behaviors of bio-filament composites were also investigated by assessing cell cytotoxicity and water contact angle. EDX results of bio-filament composites indicated the presence of organic compounds. These bio-filament composites were found to have higher tensile strength than conventional PCL filament. They exhibited positive response in cytotoxicity. Biological analysis revealed better compatibility of r-PCL with rice bran. Such rice bran blended bio-filament composite was found to have higher elongation and strength compared to control PCL.

• 대한금속재료학회지
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• 제46권7호
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• pp.427-436
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• 2008

The effect of dewpoints on annealing behavior and coating characteristics such as wettability and galvannealing kinetics was studied by annealing 0.3wt%Si - 0.1~0.4wt% Mn added interstitial-free high strength steels(IF-HSS). The 0.3wt%Si-0.1wt%Mn steel exhibited good wettability with molten zinc and galvannealing kinetics after annealing when the dewpoint of $H_2-N_2$ mixed gas was above $-20^{\circ}C$. It is shown that the wettability and galvannealing kinetics are directly related to the coverage of the external(surface) oxide formed by selective oxidation during annealing. At $N_2-15%H_2$ annealing atmosphere, the increase of dewpoint results in a gradual transition from external to internal selective oxidation. The decrease of external oxidation of alloying elements with a concurrent increase of their subsurface enrichment in the substrate, showing a larger surface area that was free of oxide particles, contributed to the improved wettability and galvannealing kinetics. On the other hand, the corresponding wettability and galvannealing kinetics were deteriorated with the dewpoints below $-20^{\circ}C$. The continuous oxide layer of network and/or film type was formed on the steel surface, leading to the poor wettability and galvannealing kinetics. It causes a high contact angle between annealed surface and molten zinc and plays an interrupting role in interdiffusion of Zn and Fe during galvannealing process.

• 대한금속재료학회지
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• 제47권9호
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• pp.523-532
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• 2009

In this study, four API X80 linepipe steel specimens were fabricated with varying cooling rates and finish cooling temperatures, and their microstructures and crystallographic orientations were analyzed to investigate the effects of cooling conditions on their tensile and Charpy impact properties. All the specimens consisted of acicular ferrite, granular bainite, and secondary phases such as martensite and martensiteaustenite constituent. The volume fraction of secondary phases increased with increasing cooling rate, and the higher finish cooling temperature resulted in the reduction in volume fraction and grain size of secondary phases. According to the crystallographic orientation analysis data, the effective grain size and unit crack path decreased as fine acicular ferrites having a large amount of high-angle grain boundaries were homogeneously formed, thereby leading to the improvement of Charpy impact properties. The specimen fabricated with the higher cooling rate and lower finish cooling temperature had the highest upper shelf energy and the lowest energy transition temperature because it contained a large amount of fine secondary phases homogeneously distributed inside fine acicular ferrites, while its tensile properties well maintained.

• 한국지반공학회논문집
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• 제24권11호
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• pp.17-24
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• 2008

하천 교각에서 유발되는 국부세굴은 교량의 붕괴를 유발하는 요인들 가운데 하나로 알려져 있다. 그러나, 교각주위 하천 흐름은 매우 복잡하기 때문에 국부세굴을 정확하게 산정하는 경험식을 도출하기가 쉽지 않다. 따라서, 기존의 경험식들은 특정 세굴 자료에는 좋은 상관 관계를 보이지만 다양한 현장 세굴자료들에 대해 신뢰성 있는 예측 정도를 갖기는 어렵다. 본 연구에서는 많은 현장 계측자료를 바탕으로 국부세굴심을 산정할 수 있는 인공신경망 모델을 제안하고자 하였다. 제안된 산정식은 교각 형상, 교각 폭, 교각 길이, 흐름 입사각, 흐름 속도, 수심 및 $D_{50}$의 총 7개의 변수의 함수로 구성되었다. 인공신경망 모델의 학습과 검증에 총 426개의 현장 계측자료들이 사용되었으며, 인공신경망 모델이 기존 경험 식들에 비하여 개선된 예측정도를 보임을 확인하였다.

• 천문학회보
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• 제46권1호
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• pp.43.1-43.1
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• 2021

In this study, we suggest a new method to estimate the mass of a halo coronal mass ejection (CME) using synthetic CMEs. For this, we generate synthetic CMEs based on two assumptions: (1) the CME structure is a full ice-cream cone, (2) the CME electron density follows a power-law distribution (ρ_cme=ρ₀r^-n). The power-law exponent n is obtained by minimizing the root mean square error between the electron number density distributions of an observed CME and the corresponding synthetic CME at a position angle of the CME leading edge. By applying this methodology to 57 halo CMEs, we estimate two kinds of synthetic CME mass. One is a synthetic CME mass which considers only the observed CME region (M_cme1), the other is a synthetic CME mass which includes both the observed CME region and the occulted area larger than 4 solar radii (M_cme2). From these two cases, we derive conversion factors which are the ratio of a synthetic CME mass to an observed CME mass. The conversion factor for M_cme1 ranges from 1.4 to 3.0 and its average is 2.0. For M_cme2, the factor ranges from 1.8 to 5.0 with the average of 3.0. These results imply that the observed halo CME mass can be underestimated by about 2 times when we consider the observed CME region, and about 3 times when we consider the region including the occulted area. Interestingly these conversion factors have a very strong negative correlation with angular widths of halo CMEs.We also compare the results with the CME mass estimated from STEREO observations.

• 로봇학회논문지
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• 제18권4호
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• pp.385-391
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• 2023

In the elderly population, sarcopenia occurs due to physical aging, leading to movement restrictions and loss of function. This results in dependence on daily activities and limitations in participation, ultimately decreasing the overall quality of life. In this study, we propose an algorithm designed to enable patients with sarcopenia to perform sit-to-stand and stand-to-sit movements seamlessly in their daily lives. The algorithm incorporates a wearable robot for muscle support and includes algorithms for standing and seated muscle strength support. To validate the algorithm's performance, EMG sensors were attached to the Rectus Femoris and Biceps Femoris muscles. The participants underwent two scenarios: one without wearing the device and one with the device providing muscle strength support, performing sit-to-stand and stand-to-sit motions for one minute in each case. The results showed a 16% increase in the EMG peak value of the Rectus Femoris muscle during standing motion (p=0.009). On the right side, there was a roughly 20% decrease (p=0.018) during standing and a 21% decrease (p=0.014) during sitting motion. In the future, we aim to gather additional data to further refine the algorithm. Our goal is to develop an optimal muscle strength support algorithm based on this data, making it applicable for real-life use by patients with sarcopenia.

• Wind and Structures
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• 제38권1호
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• pp.59-74
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• 2024

Large Eddy Simulation (LES) is used to explore the influence of vibration frequency and amplitude on the aerodynamic performance of a rectangular cylinder with an aspect ratio of B/D=5 (B: breadth; D: depth of cylinder) at a Reynolds number of 22,000 near resonance frequency. In smooth flow conditions, the research employs a sequence of three-dimensional simulations under forced vibration with diverse frequency ratios f_e / f_o = 0.8-1.2 (f_e : oscillation frequency; f_o : Strouhal frequency when the rectangular cylinder is stationary ) and oscillation amplitudes A_h/D = 0.05 - 0.3. The individual influences of f_e / f_o and A_h/D on the characteristics of integrated and distributed aerodynamic forces are the focal points of discussion. For the integrated aerodynamic force, particular emphasis is placed on the analysis of the dependence of velocity-proportional component C₁ and displacement-proportional component C₂ of unsteady aerodynamic force on amplitude and frequency ratio. Near the resonance frequency, the dependencies of C₁ and C₂ on amplitude are stronger than that of frequency ratio. For the distributed aerodynamic force, the increase in frequency and amplitude promotes the position of the main vortex core and reattachment to the leading edge in the streamwise direction. In the spanwise direction, vibration enhances the spanwise correlation of aerodynamic force to weaken the three-dimensional effect of the flow field, and a lower frequency ratio and larger amplitude amplify this effect.