• 대한기계학회논문집A
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• 제36권4호
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• pp.451-455
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• 2012

수학적 방법에 기초한 점근해석기법은 이방성 보 구조물의 설계 및 해석에 있어 강력한 도구이다. 이러한 장점에도 불구하고, 점근해석 기법은 전단 변형에 상대적으로 취약한 복합재료 보의 고차해를 구함에 있어 점근적으로 정확한 경계조건을 필요로 한다. 생브낭의 원리를 적용하여 응력상태를 개선하는 방법은 등방성 보 및 판 구조물에 대하여 개발되었고, 외팔보 등의 예제를 통해 검증되었다. 이 방법은 점근적으로 정확한 경계조건을 요구하지 않으며, 반복계산도 필요로 하지 않는다는 장점이 있다. 본 논문에서는 이 방법을 일반 이방성 보 구조물에 대하여 확장 적용하여 생브낭의 원리를 적용하는 방법을 일반화 하고자 한다.

• Computers and Concrete
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• 제30권4호
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• pp.289-299
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• 2022

Based on the random cracking theory, the cylinder RVE model of reinforced concrete is established and the damage process is divided into three stages as the evolution of the cracks. The stress distribution along longitude direction of the concrete and the steel bar in the cylinder model are derived. The equivalent elastic modulus of the RVE are derived and the user-defined field variable subroutine (USDFLD) for the equivalent elastic modulus is well integrated into the ABAQUS. Regarding the tensile rebars and the concrete surrounding the rebars as the equivalent homogeneous transversely isotropic material, and the FEM analysis for the reinforced concrete beams is conducted with the USDFLD subroutine. Considering the concrete cracking and interfacial debonding, the macroscopic damage process of the reinforced concrete beam under four-point bending loading in the simulation. The volume fraction of rebar and the cracking degree are mainly discussed to reveal their influence on the macro-performance and they are calibrated with experimental results. Comparing with the bending experiment performed with 8 reinforced concrete beams, the bending stiffness of the second stage and the ultimate load simulated are in good agreement with the experimental values, which verifies the effectiveness and the accuracy of the improved finite element method for reinforced concrete beam.

• Advances in nano research
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• 제14권1호
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• pp.27-43
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• 2023

This article investigates the energy harvesting characteristics of a magneto-electro-elastic (MEE) cantilever beam reinforced with carbon nanotubes (CNT) under transverse vibration. To this end, the well-known lumped parameter model is used to represent the coupled multiphysics problem mathematically. The proposed system consists of the MEE-CNT layer on top and an inactive substrate layer at the bottom. The substrate is considered to be made of either an isotropic or composite material. Basic laws such as Gauss's Law, Newton's Law and Faraday's Law are used to arrive at the governing equations. Surface electrodes across the beam are used to harvest the electric potential produced, together with a wound coil, for the generated magnetic potential. The influence of various distributions of the CNT and its volume fraction, substrate material, length-to-thickness ratio, and thickness ratio of substrate to MEE layer on the energy harvesting behaviour is thoroughly discussed. Further, the effect of external resistances and changes in substrate material on the response is analysed and reported. The article aims to explore smart material-based energy harvesting systems, focusing on their behaviour when reinforced with carbon nanotubes. The results of this study may lead to an improved understanding of the design and analysis of CNT-based smart structures.

• Computers and Concrete
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• 제29권2호
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• pp.117-126
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• 2022

The vibrational characteristic of three-layered cylindrical shell (CS) submerged in fluid with the ring support has been studied. The inner and outer layer is supposed to construct by isotropic layer. The composition of central layer is of functionally graded material type. Acoustic Wave condition has been utilized to present the impact of fluid. The central layer of cylindrical shell (CS) varies by volume fraction law that has been expressed in terms of polynomial. The main shell frequency equation has been obtained by theory of Love's shell and Rayleigh-Ritz technique. The oscillation of natural frequency has been examined under a variety of end conditions. The dependence of axial model has been executed with the help of characteristic beam function. The natural frequencies (NFs) of functionally graded material (FGM) shell have been observed of cylindrical shell along the shell axial direction. Different physical parameters has been used to examine the vibration characteristics due to the effect of volume fraction law. MATLAB software has been used to get result.

• 마이크로전자및패키징학회지
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• 제16권4호
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• pp.33-39
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• 2009

마스크리스 리소그래피(maskless lithography)에 응용하기 위한 마이크로렌즈 어레이(microlens array, MLA)가 석영의 습식 식각과 UV 접착제(UV adhesive)의 코팅을 바탕으로 개발되었다. 제작된 MLA의 초점거리는 ${\sim}45\;{\mu}m$ 정도였으며, 집광되는 광선의 초점은 ${\sim}1\;{\mu}m$로 측정되었다. MLA를 통과하며 초점을 맺은 빔(beam)의 크기 및 세기가 charge coupled device (CCD) 카메라와 빔 프로파일러(beam profiler)를 이용하여 각각 측정되었으며, 일정한 세기의 점들이 초점면에서 고르게 관찰되었다. 초점거리는 코팅된 UV 접착제의 두께에 따라 변화하였으며, UV 접착제의 두께가 두꺼울수록 짧아지는 경향을 보였다. 일반적인 마스크 얼라이너(mask aligner)를 이용한 MLA의 UV 포커싱(UV focusing)이 감광막(photoresist, PR) 상에서 실시되었으며, MLA를 통과한 빛이 감광막 위에 일정하게 집광되었다. 마스크 얼라이너와 MLA 사이의 거리 변화에 따라 감광막에 구현된 패턴 사이즈가 조절 되었다. 고온에서 오랜 시간이 지난 후에도 소자의 특성은 전혀 변함이 없었다.

• Steel and Composite Structures
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• 제26권2호
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• pp.241-253
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• 2018

Mode II fracture toughness, $K_{IIC}$, of single-ply triaxially woven fabric (TWF) composite due to tow waviness and anisotropy effects were numerically and experimentally studied. The numerical wavy beam network model with anisotropic material description denoted as TWF anisotropic was first validated with experimental Mode II fracture toughness test employing the modified compact tensile shear specimen configuration. 2D planar Kagome and TWF isotropic models were additionally constructed for various relative densities, crack lengths, and cell size parameters for examining effects due to tow waviness and anisotropy. $K_{IIC}$ generally increased with relative density, the inverse of cell size, and crack length. It was found that both the waviness and anisotropy of tow inflict a drop in $K_{IIC}$ of TWF. These effects were more adverse due to the waviness of tow compared to anisotropy.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.637-642
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• 2004

This paper presents a new shape design method for the multi-mode sensor that can detect selected multiple modes for the active vibration control of mechanical structures. The structure used for this study is an isotropic cantilever beam type with a PVDF(polyvinylidene fluoride) which is bonded onto the structure as a sensor. Characteristic behaviors of the sensor are related with the electrode shapes of PVDF. The shape optimization problem is solved by defining a new multi-objective function and using the genetic algorithm. Resulting electrode shape functions have good performances to detect the multiple vibration modes. The results of analytical simulations are compared with those of experiment works. The results agree well each other. Hence, the obtained experimental results give evidence for the validity of the presented theoretical analysis of the electrode shape design problem.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.927-931
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• 2005

Carbon nanotube actuator, working under physical conditions (in aqueous solution) and converting electrical energy into mechanical energy directly, can be a good substitute for artificial muscle. The carbon nanotube actuator simulated in this paper is an isotropic cantilever type with an adhesive tape which is sandwiched between two single-walled carbon nanotubes. For predicting the static and dynamic characteristic parameters, the analytical model for a 3 layer bimorph carbon nanotube actuator is developed by using Euler-Bernoulli beam theory. The governing equation and boundary conditions are derived from energy principles. The induced displacements of the theoretical model are presented in order to investigate the performance of the carbon nanotube actuator with different control voltages. The developed model presents invaluable means for designing and predicting the performance of carbon nanotube actuator that can be used in artificial muscle applications.

• 대한기계학회논문집
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• 제1권3호
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• pp.141-145
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• 1977

In this paper, approximate solutions of the von Karman equations for the free flexural vibration of a transversely isotropic thin rectangular plate with two simply supported edges and two clamped edges are obtained. Applying one term Ritz-Galerkin procedure, the spatial dependent part of the equation is separated and time dependent function is found to be the Duffing's equation. Then the relation between nonlinear period and amplitude of the vibration is obtained by using averaging method which is a method of the perturbation procedure. It can be seen that averaging method is easy and agrees well with prior results.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 1999년도 춘계종합학술대회
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• pp.43-46
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• 1999

소나 array의 기능을 최대로 활용하기 위한 다양한 기법들이 논의되고 있다. 기존에는 지향성을 최대화하거나 제한조건을 갖는 빔 형성 기법들이 연구되었다. 그러나 이러한 연구들은 대부분 등간격 선형 array문제에 적용되었다. 본 논문에는 이러한 기법을 Conformal array에 응용한 후에 발생하는 문제점에 대해 고찰하고, 이에 따른 해결책으로 보상된 가중 벡터를 적용하여 원하는 빔 패턴을 형성하는 방법을 제시한다.