• 한국지진공학회논문집
• /
• 제1권1호
• /
• pp.51-56
• /
• 1997

이 연구의 목적은 진동대를 사용한 지진모의 기술의 현상황을 살펴보고 그의 신뢰성을 검토하는 것이다. 1자유도 및 3자유도 알루미늄 전단구조 모델이 사용되었으며, $4m{\times}4m$ 6자유도 진동대가 1940 El centro 지진 가속도 기록(NS요소)를 재현하기 위해 수평 1방향으로 흔들어졌다. 진동대의 실제 가속도 이력과 목표 가속도 이력을 비교할 때, 전반적인 이력은 매우 흡사했으나 실제 진동의 저 주파수 영역은 목표치보다 후리에 변환 강도에서 낮은 값을 대체로 나타내고 있었다. 자유진동 및 백색파 실험은 고유주파수에 대해서는 거의 일치하는 값을 나타내고 있으나 감쇠계수에 대해서는 자유진동실험의 경우 1.4%, 백색파실험의 경우 14.8%를 나타내어 큰 차이를 보여주고 있다. 층 전단력 대 층간변위의 이력곡선으로부터 전제적으로 선형탄성거동을 나타내고 있으나 이 이력곡선의 모습이 층 강성을 한축으로 하는 타원형을 나타내어 점성감쇠의 영향을 암시하고 있다.

• 자원환경지질
• /
• 제34권4호
• /
• pp.417-422
• /
• 2001

계면활성제는 소수성 화합물로 오염된 토양과 대수층을 복원하는데 사용할 수 있다. 본 연구의 목적은 톨루엔으로 오염된 사질토양을 복원하는데 사용될 수 있는 적당한 계면활성제들의 선택과 선택된 계면활성제들이 얼마나 효과적으로 톨루엔을 제거하는가를 연구하는데 있다. 사용된 토양은 Ottawa 사질 토양이며, 이용된 유기오염물질은 톨루엔이었다. 6종의 계면활성제의 선택은 독성도, 용해도 등에 따라 이루어졌으며, 이들을 이용한 계면활성제들의 선택실험 방법은 separatory funnel 실험과 shaker table agitation and centrifugation 실험이다. HLB 및 표면장력과 본 연구의 실험 결과에 의하여 6종의 계면활성제 중 가장 효율적인 종으로 Sandopan JA36(an anionic surfactant)과 Pluronic L44(a nonionic surfactant)가 선택되었다. 최고의 톨루엔 회수율 96%는 Sandopan JA36를 사용한 shaker table agitation and centrifugation 실험에서 얻었다.

• 대한수학교육학회지:학교수학
• /
• 제15권4호
• /
• pp.833-846
• /
• 2013

본 논문에서는 우리나라 초등학교 1~2학년 수학 교과서/익힘책 <수와 연산> 영역에서 '곱', '자릿값', '구구', '숫자'라는 용어를 잘못 사용하거나 또는 비일관적으로 사용하고 있는 실태를 분석하고 있다. 이러한 분석을 바탕으로 다음 네 가지를 결론으로 제시한다. 첫째, ${\ll}$수학 3${\gg}$ 교과서에서 '곱'을 정의해야 한다. ${\ll}$수학 3${\gg}$ 교과서/익힘책에서 곱셈을 도입하지만, 그 계산 결과를 '곱'이라 하고 있지는 않다. 둘째, 초등학교 2학년 수학에서 '자릿값'이라는 용어의 사용을 재고할 필요가 있다. ${\ll}$수학 3${\gg}$과 ${\ll}$수학 4${\gg}$ 교과서/익힘책에서 사용하는 '자릿값'이라는 용어의 의미는 명료하지 않다. 셋째, ${\ll}$수학 2${\gg}$와 ${\ll}$수학 4${\gg}$ 교과서에서 '덧셈구구표'와 '뺄셈구구표'라는 표현을 사용하지 말아야한다. 넷째, 초등학교 1, 2학년 수학에서 '숫자'의 사용을 최소화하고, 가급적 '수'로 통일해서 사용하는 것을 고려할 필요가 있다.

• Journal of Chest Surgery
• /
• 제8권2호
• /
• pp.119-124
• /
• 1975

This is a case report of the rupture of the trachea and the esophagus following external blunt trauma without any associated injury. A 7 year old male patient was brought to the emergency room. Hanyang University Hospital, on 23 Jul, 1974 while he played under the pile of pingpong table A table was fall down over the patient accidentally. The patient was injured by the table and found lying in unconsciousness on the ground.There was subcutaneous emphysema on his anterior chest and neck. A contusion on the upper part of the sternum was noted. The breathing sound were diminished over the left side of the chest. Ronchi were heard over the right lung field. This patient was suffered from vomiting, dypsnea, and irritable mental state after this accident. On the chest roentgenogram in A-P view, hyperlucency at the mediastinum and parapericardiac area suggested the pneumomediastinum. On the next day, a diagnosis of the tracheal and esophageal rupture was confirmed by the esophagogram with Lipiodol swallowing. A right thoracotomy was performed and ruptured orifice of the trachea and the esophagus were closed with interrupted sutures. Postoperative course was uneventful and primary closure of the rupture of the trachea and the esophagus were succeeded.

• Journal of Astronomy and Space Sciences
• /
• 제31권3호
• /
• pp.241-246
• /
• 2014

The Amon-Ra instrument is the main optical payload of the proposed EARTHSHINE satellite. It consists of a visible wavelength instrument and an IR energy channel instrument to measure a global Earth albedo. We report a new sensitivity technique for efficient alignment of the visible channel instrument. Whilst the sensitivity table method has been widely used in the alignment process, the straightforward application of the method tends to produce slow process convergence because of shop floor alignment practice uncertainties. We investigated the error sources commonly associated with alignment practices and used them when estimating the Zernike polynomial coefficients. Aided with single center field wavefront error (WFE) measurements and their corresponding Zernike polynomial coefficients, the method involves the construction and use of an experimental, instead of simulated, sensitivity table to be used for alignment state estimations. A trial alignment experiment for the Amon Ra optical system was performed and the results show that 71.28 nm in rms WFE was achieved only after two alignment iterations. This tends to demonstrate its superior performance to the conventional method.

• Smart Structures and Systems
• /
• 제15권4호
• /
• pp.963-995
• /
• 2015

The effectiveness of the various control algorithms for semi-active structural control systems proposed in the literature is highly questionable when dealing with earthquake actions, which never reach a steady state. From this perspective, the paper summarizes the results of an experimental activity aimed to compare the effectiveness of four different semi-active control algorithms on a structural mock up representative of a class of structural systems particularly prone to seismic actions. The controlled structure is a near full scale 2-story steel frame, equipped with two semi-active bracing systems including two magnetorheological dampers designed and manufactured in Europe. A set of earthquake records has been applied at the base of the structure, by utilizing a shaking table facility. Experimental results are compared in terms of displacements, absolute accelerations and energy dissipation capability. A further analysis on the percentage incidence of undesired and/or unpredictable operations corresponding to each algorithm gives an insight on some factors affecting the reliability and, in turn, the real effectiveness of semi-active structural control systems.

• Steel and Composite Structures
• /
• 제28권4호
• /
• pp.427-438
• /
• 2018

Static stability is a decisive factor in the design of domes. Stability-related external factors, such as load and supports, are incorporated into structural vulnerability theory by the definition of a relative rate of joint well-formedness ($r_r$). Hence, the instability mechanism of domes can be revealed. To improve stability, an optimization model against instability, which takes the maximization of the lowest $r_r$ ($r_{r,min}$) as the objective and the discrete member sections as the variables, is established with constraints on the design requirements and steel consumption. Optimizations are performed on two real-life Kiewitt-6 model domes with a span of 23.4 m and rise of 11.7 m, which are initially constructed for shaking table collapse test. Well-formedness analyses and stability calculation (via arc-length method) of the models throughout the optimization history demonstrate that this proposed method can effectively enhance $r_{r,min}$ and optimize the static stability of shell-like structures. Additionally, seismic performance of the optimum models subjected to the same earthquake as in the shaking table test is checked. The supplemental simulations prove that the optimum models are superior to the original models under earthquake load as well.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2010년도 춘계 학술발표회
• /
• pp.213-220
• /
• 2010

This study presents a numerical simulation model of vertical ground heat exchangers, considering unsaturated hydro static ground conditions induced by the ground water table fluctuation. Heat transfer in ground and grout is modeled by a 3-D FEM transient conductive heat transfer model, where heat transfer between circulating fluid and heat exchanging pipe is treated as 1-D quasi steady state forced convective elements. To take into account the unsaturated ground condition, soil thermal conductivity and heat capacity which are dependent on the matric suction are applied to ground elements. Parametric studies considering various ground water table conditions are conducted to investigate the influence of unsaturated hydro static ground condition on the mean heat exchange rate of ground heat exchanger. Simulation results considering water table fluctuation show 60~100% of mean heat exchange rate for a saturated soil condition and 125~208% of that for a dry soil condition. Thus consideration of unsaturated soil condition is substantially recommended for more accurate design and performance evaluation for ground heat exchangers.

• 한국지반공학회논문집
• /
• 제20권3호
• /
• pp.141-150
• /
• 2004

1995년 고베지진에 의해 피해를 입었던 중력식 안벽구조물과 잔교식 안벽구조물의 동적 거동을 재현하고, 분석하기 위하여 소규모 1-g 진동대 모형시험을 수행하였다. 1989년 Iai가 제안한 상사법칙을 이용하여 진동대 모형시험 결과를 원형크기의 것으로 환산하여 현장계측 결과와 비교하였다. 그 결과, 중력식 안벽구조물의 변위는 현장계측 결과의 약 1/3 정도 발생하였고, 벽체의 변형 형상은 원형과 유사하였다. 잔교식 안벽구조물의 변위는 현장계측 결과의 약 2/3 가 발생하였고, 말뚝에 발생하는 최대모멘트의 위치와 원형말뚝의 파괴위치는 잘 일치하였다.

• Geomechanics and Engineering
• /
• 제18권3호
• /
• pp.235-245
• /
• 2019

This paper presents a novel methodology for face stability assessment of rock tunnels under water table by combining the kinematical approach of limit analysis and numerical simulation. The tunnels considered in this paper are excavated in fractured rock masses characterized by the Hoek-Brown failure criterion. In terms of natural rock deposition, a more convincing case of depth-dependent mi, GSI, D and ${\sigma}_c$ is taken into account by proposing the horizontally layered discretization technique, which enables us to generate the failure surface of tunnel face point by point. The vertical distance between any two adjacent points is fixed, which is beneficial to deal with stability problems involving depth-dependent rock parameters. The pore water pressure is numerically computed by means of 3D steady-state flow analyses. Accordingly, the pore water pressure for each discretized point on the failure surface is obtained by interpolation. The parametric analysis is performed to show the influence of depth-dependent parameters of $m_i$, GSI, D, ${\sigma}_c$ and the variation of water table elevation on tunnel face stability. Finally, several design charts for an undisturbed tunnel are presented for quick calculations of critical support pressures against face failure.