• 한국자동차공학회논문집
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• 제12권5호
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• pp.198-204
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• 2004

Dynamic fracture is investigated in plate applied by impacting bar. Numerical simulations of the experiments are made by using a finite element method(FEM) code, LS-DYNA. The eroding surface-to-surface contact allows between impacting bar and impacted plate. The occurrence of hourglass deformations in an analysis can invalidate results and hourglass energy is minimized to obtain the good accuracy of result. Total, internal and kinetic energies, von Mises plastic stress and X,Y,Z velocities of impacting bar are analyzed in this study.

• 한국분말재료학회지
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• 제13권2호
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• pp.108-111
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• 2006

Aluminum hydroxides were synthesized by a simple electrolytic reaction of aluminum plates. The aluminum hydroxide, boehmite (AlO(OH)), was predominantly formed in the application of electrical potential at and above 30V, while the mixture of bayerite ($Al(OH)_3$) and boehmite (AlO(OH)) phases were formed below 20V. The boehmite has a clear fibrous structure controlled on nanometer scale. On the contrary, the bayerite consists of the typical hourglass or semi-hourglass shaped coarse crystals as a result of aggregation of various crystals stacked together. The specific surface area of the boehmite nanofiber was markedly high, approaching at about $302\;m^2/g$.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.428-429
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• 2006

Aluminum hydroxides were synthesized by a simple electrolytic reaction of aluminum plates. The aluminum monohydroxide, boehmite(AlO(OH)), was predominantly formed by the application of an electrical potential above 30V, while the mixture of the bayerite$(Al(OH)_3)$ and boehmite(AlO(OH)) phases were formed below 20V. The boehmite has a clear fibrous structure which is controlled on a nanometer scale. On the contrary, the bayerite consists of the typical hourglass or semi-hourglass shaped coarse crystals as a result of an aggregation of the various crystals stacked together. The specific surface area of the boehmite nanofiber was remarkably high, reaching about $300m^2/g$.

• Smart Structures and Systems
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• 제14권5호
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• pp.883-900
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• 2014

Shape memory alloys (SMA) can dissipate energy through hysteresis cycles without significant residual deformation. This paper describes the fabrication and testing of copper-based SMA hourglass-shaped plates for use in energy dissipation devices and the development of a numerical model to reproduce the experiments. The plates were tested under cyclic flexural deformations, showing stable hysteresis cycles without strength degradation. A detailed nonlinear numerical model was developed and validated with the experimental data, using as input the constitutive relationship for the material determined from cyclic tests of material coupons under tension loading. The model adequately reproduces the experimental results. The study is focused on the exploitation of SMA in the martensite phase.

• Structural Engineering and Mechanics
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• 제21권5호
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• pp.539-551
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• 2005

Finite elements based on isoparametric formulation are known to suffer spurious stiffness properties and corresponding stress oscillations, even when care is taken to ensure that completeness and continuity requirements are enforced. This occurs frequently when the physics of the problem requires multiple strain components to be defined. This kind of error, commonly known as locking, can be circumvented by using reduced integration techniques to evaluate the element stiffness matrices instead of the full integration that is mathematically prescribed. However, the reduced integration technique itself can have a further drawback - rank deficiency, which physically implies that spurious energy modes (e.g., hourglass modes) are introduced because of reduced integration. Such instability in an existing stiffness matrix is generally detected by means of an eigenvalue test. In this paper we show that a knowledge of the dimension of the solution space spanned by the column vectors of the strain-displacement matrix can be used to identify the instabilities arising in an element due to reduced/selective integration techniques a priori, without having to complete the element stiffness matrix formulation and then test for zero eigenvalues.

• 셀메드
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• 제12권1호
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• pp.1.1-1.2
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• 2022

Mental health is attributed to person's well-being, abilities and productivity. The purpose of this study is to suggest the effects of K-culture to people in adversity. It is PungmulPanGut, represented by traditional Korean play culture. Pungmul is a performance with four percussion instruments, Janggu (Korean hourglass drum), Buk (barrel shaped drum), Jing (large gong), Kkwaenggwari (small gong), and play. In Korean, "pan" means that it's a place to do something. Gut means to make a wish. The ensemble Better Than Medicine (eBTM) is a team that has trained and worked with Gamuak (歌,舞,樂; singing, dancing, playing) for a long time, but is not perfect (we refer this as 2% lacking in music). The characteristic of our team is that we share joy while voluntarily participating and doing what we like. It is a combination of singing, dancing, playing musical instruments, and exciting people. There is wind-like energy and there is mutual cooperation, not competition. As we concentrate, we become immersed in each other's breathing and movement. So it makes us forget the hard situation, the hardships, the pain, and so on. In the meantime, our pleasures peak and share happy energy with each other. Even though we are two percent less skilled, our sense of happiness doubles. Music together is not competition but cooperative work and healing. Therefore, we suggest that PungmulPanGut can be better K-culture than medicine in promoting mental health.

• Journal of Mechanical Science and Technology
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• 제19권6호
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• pp.1229-1242
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• 2005

When natural rubber is used for a long period of time, it becomes aged; it usually becomes hardened and loses its damping capability. This aging process affects not only the material property but also the (fatigue) life of natural rubber. In this paper the aging effects on the material property and the fatigue life were experimentally investigated. In addition, several fatigue life prediction equations for natural rubber were proposed. In order to investigate the aging effects on the material property, the load-stretch ratio curves were plotted from the results of the tensile test, the compression test and the simple shear test for virgin and heat-aged rubber specimens. Rubber specimens were heat-aged in an oven at a temperature ranging from $50^{\circ}C$ to $90^{\circ}C$ for a period ranging from 2 days to 16 days. In order to investigate the aging effects on the fatigue life, fatigue tests were conducted for differently heat-aged hourglass-shaped and simple shear specimens. Moreover, finite element simulations were conducted for the specimens to calculate physical quantities occurring in the specimens such as the maximum value of the effective stress, the strain energy density, the first invariant of the Cauchy-Green deformation tensor and the maximum principal nominal strain. Then, four fatigue life prediction equations based on one of the physical quantities could be obtained by fitting the equations to the test data. Finally, the fatigue life of a rubber bush used in an automobile was predicted by using the prediction equations, and it was compared with the test data of the bush to evaluate the reliability of those equations.

• 대한조선학회지
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• 제26권3호
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• pp.51-61
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• 1989

최근(最近)의 배는 에너지 절약(節約)을 도모하기 위하여 프로펠러 회전수(回轉數)의 저속화(低速化)와 더불어 대형화(大型化)되고 있다. 이와 같은 결과(結果)로 선미관(船尾管)의 후부(後部) 베어링에는 집중하중(集中荷重)이 작용(作用)하게 되어 선박(船舶)의 운항능력(運航能力)을 상실할 정도의 대형사고(大型事故)가 일어나고 있는 예(例)가 많다. 이와 관련하여 최근(最近) 유막(油膜)을 고려한 선미관(船尾管) 베어링 해석(解析)에 관(關)한 연구(硏究)가 활발하게 이루워지고 있다. 본(本) 연구(硏究)에서는 지금까지 연구발표(硏究發表)된 유막(油膜)을 고려한 선미관(船尾管) 베어링에 대한 축(軸)의 위치(位置)를 추정(推定)하는 방법(方法)을 수정보완(修正補完)한 새로운 방법(方法)을 제시(提示)하였다. 즉 축계(軸系)에 대해서는 유한요소법(有限要素法)에 의한 삼차원(三次元) 구조해석방법(構造解析方法), 베어링 유막(油膜)은 유한요소법(有限要素法)에 의한 이차원(二次元) 유체역학해석방법(流體力學解析方法), 그리고 축계(軸系)와 베어링 유막간(油膜間)의 준정적(準靜的) 평형점(平衡點)을 구하기 위해서는 최적화(最適化) 기법(技法)이 사용된다. 본(本) 해석방법(解析方法)의 타당성(妥當性) 여부(與否)를 확인(確認)하기 위하여 Vorus 등이 사용(使用)한 시산대상선(試算對象船)에 대한 일련의 수치계산(數値計算)을 수행하고 동(同) 결과(結果)를 Vorus등의 연구 결과와 비교검토(比較檢討)하여 본 결과(結果), 비교적(比較的) 잘 일치(一致)하고 있음을 미루어 보아 본(本) 해석방법(解析方法)의 타당성(妥當性)이 확인(確認)되었다.

• 한국전산구조공학회논문집
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• 제36권2호
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• pp.113-120
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• 2023

본 논문에서는 LS-DYNA를 활용한 원자력발전소 설치 로드블록 차량 시뮬레이션 방법을 소개한다. 차량 강습 위협이 원자력 발전소의 설계기준위협으로 포함된 이후로 차량 강습을 대비하기 위한 차량 방벽(Anti-ram barrier)의 성능 평가 소요가 커지고 있다. 차량 방벽은 일반적으로 충돌 실험을 통하여 성능을 인증 받는다. 하지만 국내에서는 차량 방벽에 대한 성능 시험 시설이 마련되어 있지 않아, 시뮬레이션을 통한 차량 방벽 성능 검증이 필요하다. LS-DYNA는 충돌 시뮬레이션에 특화되어 있으며, NCAC를 비롯한 여러 기관에서 충돌 시험과의 타당성 검증을 완료한 수치 모델을 배포하고 있다. 본 논문에서는 로드블록의 가장 핵심적인 차량 차단막 모듈의 FE 모델을 구축하여 충돌 시뮬레이션을 수행하였다. 계산된 결과는 NCHRP 179의 차량 안전 시설 충돌 시뮬레이션 검증 기준을 준용하여 검증하였다. 그 결과 모래시계 에너지(hourglass energy)가 총 에너지의 5%를 넘지 않고 내부 에너지의 10%를 넘지 않는 것을 확인하였으며, added mass가 1% 미만으로 기준인 10%를 넘지 않는 것을 확인하였다. 향후 FE 모델을 활용하여 물리적 방벽의 성능을 평가하여 데이터 베이스를 구축할 예정이다.