• Structural Engineering and Mechanics
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• 제48권6호
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• pp.849-878
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• 2013

This paper consists of two parts, which broadly examines solution techniques abilities for the structures with geometrical nonlinear behavior. In part I of the article, formulations of several well-known approaches will be presented. These solution strategies include different groups, such as: residual load minimization, normal plane, updated normal plane, cylindrical arc length, work control, residual displacement minimization, generalized displacement control, modified normal flow, and three-parameter ellipsoidal, hyperbolic, and polynomial schemes. For better understanding and easier application of the solution techniques, a consistent mathematical notation is employed in all formulations for correction and predictor steps. Moreover, other features of these approaches and their algorithms will be investigated. Common methods of determining the amount and sign of load factor increment in the predictor step and choosing the correct root in predictor and corrector step will be reviewed. The way that these features are determined is very important for tracing of the structural equilibrium path. In the second part of article, robustness and efficiency of the solution schemes will be comprehensively evaluated by performing numerical analyses.

• Steel and Composite Structures
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• 제24권2호
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• pp.151-176
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• 2017

This paper deals with general equations of motion for free vibration analysis response of thick three-layer doubly curved sandwich panels (DCSP) under simply supported boundary conditions (BCs) using higher order shear deformation theory. In this model, the face sheets are orthotropic laminated composite that follow the first order shear deformation theory (FSDT) based on Rissners-Mindlin (RM) kinematics field. The core is made of orthotropic material and its in-plane transverse displacements are modeled using the third order of the Taylor's series extension. It provides the potentiality for considering both compressible and incompressible cores. To find these equations and boundary conditions, Hamilton's principle is used. Also, the effect of trapezoidal shape factor for cross-section of curved panel element ($1{\pm}z/R$) is considered. The natural frequency parameters of DCSP are obtained using Galerkin Method. Convergence studies are performed with the appropriate formulas in general form for three-layer sandwich plate, cylindrical and spherical shells (both deep and shallow). The influences of core stiffness, ratio of core to face sheets thickness and radii of curvatures are investigated. Finally, for the first time, an optimum range for the core to face sheet stiffness ratio by considering the existence of in-plane stress which significantly affects the natural frequencies of DCSP are presented.

• 공업화학
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• 제8권5호
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• pp.756-762
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• 1997

본 실험에서는 황산용액에서 전기화학적으로 금속 알루미늄판을 양극산화하여 원통형 세공구조를 갖고 있는 alumina막을 형성시켰다. 양극화에 사용된 알루미늄 시료는 전해연마, 화학연마 및 열산화와 같은 전처리 공정을 거쳐서 준비하였으며, 형성된 알루미나막의 세공분포와 두께 등을 SEM과 BET를 사용하여 조사하였다. 그 결과 산화피막이 Keller모델과 같은 기하 구조로 이루어져 있으며. 균일한 세공 분포를 지니고 있음을 볼 수 있었다. 그리고 산화막의 세공크기와 두께는 황산전해질의 농도, 반응온도 그리고 전류밀도와 같은 양극산화 공정변수에 의존함을 알수 있었다.

• 대한기계학회논문집B
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• 제27권12호
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• pp.1708-1715
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• 2003

An experimental study was made of turbulent separated and reattaching flow over a backward-facing step, where unsteady wake was generated by a spoked-wheel type wake generator with cylindrical rods in front of the separated flow. The influence of unsteady wake was scrutinized in terms of the rotating speed of the wake generator (0$\leq$S $t_{H}$$\leq$0.4). A conditional averaging technique in corporation with SBF was employed to elucidate the influence of the unsteady wake on the large-scale vortical structures of the separated flow. Special attention was made during two-dimensional measurements of wall-pressure with or without unsteady wake. The wall-pressure fluctuations were used to predict dipole sound source by Curie's integral formula. It was found that the reduction of the dipole sound source was due to the reduction of turbulent kinetic energy by unsteady wake in the recirculation region.n.

• Applied Microscopy
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• 제25권2호
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• pp.65-72
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• 1995

The interfacial structures of ZnSe/GaAs which were grown by single chamber MBE at $300^{\circ}C$ were investigated by high resolution transmission electron microscope working at 300 kV with resolution of 0.18 nm. The interfaces of ZnSe/GaAs whose thickness is 2,700 nm are wavy and extensive stacking faults were formed in ZnSe epilayer but the interfaces maintained the coherency with the substrate GaAs. The stacking faults are formed in {111} planes and their sizes are $10{\sim}20nm$ in length and two or three atomic layer in width with the density of $10^9/cm^2$. Micortwins and moire fringes are also observed. However. in 10 nm ZnSe epilayer, the interfaces are pseudomorphic and only moire fringes are observed in local areas. The cylindrical defects which are perpendicular to the interface with $50{\sim}60nm$ in length, were observed with the interval of 50 nm at ZnSe/GaAs interfaces in 2,700nm epilayer. The origin and character of these defects are unknown, however, they played a role of producing the structural defects at the interfaces.

• Journal of Advanced Marine Engineering and Technology
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• 제32권8호
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• pp.1221-1230
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• 2008

Inflatable rubber dams are used for controlling flood, impounding water for recreations, preventing beach erosions, diverting water for irrigations, and generating hydropower. They are long, flexible, inflated with air, cylindrical structures on a rigid horizontal foundation such as concrete. The dam is modeled as an elastic shell inflated with air. The mechanical behaviors of the inflated dam model were investigated by using the finite element method. The analysis process such as One Way Coupling Fluid-Structure Interaction consists of two steps. First, the influences of the fluid side were investigated, viz, the shape changes of the inflated rubber dam due to the fluid motions was captured when the height of the dam was 30cm with air pressure 0.01MPa, at which the pressure distributions over the surface of the dam were calculated. And next, the structural deformations were calculated using the pressure distributions. The initial inlet velocity for flow field was set to 0.1m/s. The structural deformation behaviors were investigated. The final research goal is to develop a Korean Inflatable Rubber Dam to be used for generating small hydropower.

• Composites Research
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• 제13권1호
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• pp.69-77
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• 2000

본 논문에서는 크기가 일정한 비증분 하중과 크기가 커서 증분이론을 사용해야만 하는 증분하중이 동시에 가해지는 구조물의 비선형 해석을 위한 수정 호길이법을 제시한다. 수정된 호길이법에서는 비선형 계산을 수행할 때 증분하중에 의한 변위와 비증분 하중에 의한 변위를 구분하여 처리하게 된다. 제안된 방법의 타당성은 내압, 외압 및 압축하중을 받는 쉘 구조물의 비선형 거동에 대한 기존 결과와의 비교를 통해 검토하였다. 또한 비증분 하중과 증분하중이 함께 가해지는 대표적인 경우로서, 일정 횡압력과 축방향 증분 압축하중을 동시에 받는 쉘 구조물의 비선형 좌굴거동에 대한 인자연구를 수행하였다.

• International Journal of Concrete Structures and Materials
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• 제4권2호
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• pp.113-118
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• 2010

This article aims to study the effects of adding steel fibers to concrete on the mechanical behavior of steel fiber concrete (SFC) slabs. After formulating the SFC, an experimental work was, first, conducted on $160\;{\times}\;320$ mm cylindrical specimens and $70\;{\times}\;70\;{\times}\;280$ mm prisms. Then, this study was carried out on 20 rectangular $1,100\;{\times}\;1,100\;{\times}\;60$ mm small slabs submitted to a distributed load. Two types of fibers with hooked ends were used: long fibers (LF) of a length of 50 mm and short fibers (SF) of a length of 35 mm. The studied parameters are compressive and tensile strengths and Young's modulus. Plain concrete (PC) small slabs were also prepared to be compared to the SFC specimens. The results showed that the compressive strength of SFC increased up to 25% while the splitting tests showed an improvement of the SFC reaching 45%. Tests on SFC small slabs also showed that a smaller deflection is obtained with respect to PC, which indicates an improvement in strength (up to 100%), in ductility and in resistance to cracking. The LF gives a better improvement in strength than the SF for a 70% $kg/m^3$ of steel proportioning.

• 한국음향학회지
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• 제19권2호
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• pp.8-12
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• 2000

본 논문은 주위 환경인 수압 및 수온변화에 따른 맨드릴형 광-음향센서의 감도특성을 분석한 것에 관한 것이다. 음향감지부의 구조로는 실린더형, 중공 층상복합체형 및 air cavity가 삽입된 중공 층상복합체를 선정하고, 주위 수압과 수온변화에 따른 광-음향센서의 감도특성을 분석하였다. 맨드릴형 광-음향센서는 주위 정수압의 변화에 대해 0.15dB 미만의 음향감도 변화를 나타내고, 수압변화에 대해 안정적인 특성을 보유하고 있다. 주위 수온변화에 대한 음향감도의 상대적인 안정성은 air cavity가 삽입된 중공 나일론 층상복합체를 이용한 맨드릴형 광-음향센서가 가장 우수한 것으로 나타났다.

• 대한토목학회논문집
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• 제10권4호
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• pp.103-112
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• 1990

본 연구는 실제크기의 첨성대 모형을 피사체로 선정하여 측정용 카메라에 의해 원형 strip과 Block을 형성한 후, bundle조성으로 촬영거리와 기준점 배치에 따른 정확도를 다양하게 분석하고 strip조합해석의 특성을 규명하므로써 전면(全面)해석을 요하는 각종 문화재 특히 원통형 구조물에 대한 최적 해석기법을 제시한 것이다. 연구결과 어느 일면에 배치된 기준점 만으로도 전면해석이 가능하며, 기준점수에 비해 그 배치가 정도에 보다 큰 영향을 미침을 알 수 있었다. 또한 구조물의 전면해석시 기준점은 X, Y, Z축 평면상에 고루 배치하는 것이 이상적이며, 근접촬영하여 strip조합수에 증가시킴에 따라 정확도가 현저히 향상되었다.