• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.539-542
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• 1997

We present a micro-positioning stage that has minimized geometrical error and can drive in the 4-axis. This stage divided into two parts: $Z\theta_x$ $\theta_y$, motion stage and$\theta_z$ motion stage. These stages are constructed in flexure hinges, piezoelectric actuators and displacement scnsors. The dynamic model for each stage is obtained and their FE (finite element) models are made. Using the Lagrange's equation, the motion of equation is found. Through the parametric analysis and FE analysis, sensitiv~ty of the design parameters is executed. Finally, fundamental frequencies, maximum stress, and displacement sensitivity for each stage are obtained. We expect that this micro-positioning stage be a useful micro-alignment device for various applications.

• 센서학회지
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• 제18권5호
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• pp.372-376
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• 2009

This paper describes the characteristics of piezoelectric micro power generators by the ANSYS FEA(finite element analysis). The micro power generator was designed to convert ambient vibration energy to electrical power as a ZnO piezoelectric material. To find optimal model in low vibration ambient, the shape of power generator was changed with different membrane width, thickness, length, and proof mass size. Using the ANSYS modal analysis, bending mode and stress distribution of optimal model were analyzed. Moreover, the displacement with the frequency range was analyzed by harmonic analysis. From the simulation results, the resonance frequency of optimal model is about 373 Hz and investigate the possibility of ZnO micro power generator for ambient vibration applications.

• 한국항공우주학회지
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• 제42권8호
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• pp.692-700
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• 2014

본 논문에서는 미소진동 영향성 예측을 위한 인공위성 유한요소모델 보정에 관해 기술한다. 최근 지구 저궤도에 발사되는 상업용 지구관측위성의 경우, 수요자의 요구로 인해 주어진 시간 안에 다양한 지역의 많은 영상을 공급해야 한다. 이를 구현하기 위해 고용량휠, 다축 김발을 탑재한 안테나 등 다양한 구동기를 사용한다. 그러나 이러한 구동기는 작동 시 미소진동을 유발할 수 있으며, 이러한 미소진동은 매우 작기는 하지만 지구관측 탑재체를 가진하여 영상품질을 저감시킬 수 있다. 이러한 미소진동에 의한 영향성을 살펴보기 위해서 유한요소모델과 미소진동원 시험결과를 결합한 연성해석을 실시하며, 해석에 앞서 유한요소모델 보정을 실시한다. 보정 전후의 주파수 차이, 모드형상 상관관계, 주파수응답함수 상관관계를 비교하여 개선된 유한요소모델의 품질을 평가하였다.

• Computers and Concrete
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• 제17권1호
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• pp.107-127
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• 2016

Concrete is a heterogeneous material containing many weaknesses such as micro-cracks, pores and grain boundaries. The crack growth mechanism and failure behavior of concrete structures depend on the plastic deformation created by these weaknesses. In this article the non-linear finite element method is used to analyze the effect of presence of micro pore near a crack tip on both of the characteristics of crack tip plastic zone (its shape and size) and crack growth properties (such as crack growth length and crack initiation angle) under pure shear loading. The FE Code Franc2D/L is used to carry out these objectives. The effects of the crack-pore configurations and the spacing between micro pore and pre-excising crack tip on the characteristics of crack tip plastic zone and crack growth properties is highlighted. Based on the obtained results, the relative distance between the crack tip and the micro pore affects in very significant way the shape and the size of the crack tip plastic zone. Furthermore, crack growth length and crack initiation angle are mostly influenced by size and shape of plastic zone ahead of crack tip. Also the effects of pore decrease on the crack tip by variation of pore situation from linear to perpendicular configuration. The critical position for a micro pore is in front of the crack tip.

• Structural Engineering and Mechanics
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• 제61권2호
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• pp.193-207
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• 2017

In this study, the vibration of an electrostatically actuated micro cantilever beam is analyzed in which a viscoelastic layer covers a portion of the micro beam length. This proposed model is considered as the main element of mass and pollutant micro sensors. The nonlinear motion equation is extracted by means of Hamilton principle, considering nonlinear shortening effect for Euler-Bernoulli beam. The non-linear effects of electrostatic excitation, geometry and inertia have been taken into account. The viscoelastic model is assumed as Kelvin-Voigt model. The motion equation is discretized by Galerkin approach. The linear free vibration mode shapes of non-uniform micro beam i.e. the linear mode shape of the system by considering the geometric and inertia effects of viscoelastic layer, have been employed as comparison function in the process of the motion equation discretization. The discretized equation of motion is solved by the use of multiple scale method of perturbation theory and the results are compared with the results of numerical Runge-Kutta approach. The frequency response variations for different lengths and thicknesses of the viscoelastic layer have been founded. The results indicate that if a constant volume of viscoelastic layer is to be deposited on the micro beam for mass or gas sensor applications, then a modified configuration may be found by using the analysis of this paper.

• 한국정밀공학회지
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• 제31권3호
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• pp.181-187
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• 2014

Micro patterns are used to maximize the performance and efficiency of the product in many industries such as energy, display, printing, biology, etc. Nowadays, the fabrication technology for micro patterns has been developed in various ways such as photolithography, laser machining, electrical discharge machining and mechanical machining. Recently, mechanical machining the size of smaller than 1 micrometer could be tried, because the technology related to the machining was developed brilliantly. This paper shows the experiments using cutting processes in order to fabricate the micro pattern. Micro patterns of the size of several micrometers were machined by the diamond tools of two different shape, the deformation and generation of burr were investigated.

• Structural Engineering and Mechanics
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• 제71권5호
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• pp.485-502
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• 2019

In this research, the nonlinear static, buckling and vibration analysis of viscoelastic micro-composite beam reinforced by various distributions of boron nitrid nanotube (BNNT) with initial geometrical imperfection by modified strain gradient theory (MSGT) using finite element method (FEM) are presented. The various distributions of BNNT are considered as UD, FG-V and FG-X and also, the extended rule of mixture is used to estimate the properties of micro-composite beam. The components of stress are dependent to mechanical, electrical and thermal terms and calculated using piezoelasticity theory. Then, the kinematic equations of micro-composite beam using the displacement fields are obtained. The governing equations of motion are derived using energy method and Hamilton's principle based on MSGT. Then, using FEM, these equations are solved. Finally the effects of different parameters such as initial geometrical imperfection, various distributions of nanotube, damping coefficient, piezoelectric constant, slenderness ratio, Winkler spring constant, Pasternak shear constant, various boundary conditions and three material length scale parameters on the behavior of nonlinear static, buckling and vibration of micro-composite beam are investigated. The results indicate that with an increase in the geometrical imperfection parameter, the stiffness of micro-composite beam increases and thus the non-dimensional nonlinear frequency of the micro structure reduces gradually.

• 한국음향학회지
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• 제37권4호
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• pp.181-187
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• 2018

본 논문은 원형 단면 임피던스 튜브내에 고정된 미세천공 탄성판의 흡음을 해석적으로 구하는 방법을 다루었다. 판의 진동과 덕트 내부 음장을 모드 함수의 무한 급수의 합으로 전개하였는데 반경방향으로는 Bessel 함수를 포함한다. 평면파 가정하에서 저주파수 대역의 근사식을 판의 처음 몇 개의 모드만 고려하여 흡음율을 유도하였으며 등가 임피던스를 갖는 단일 표면의 형태로 제시하였다. 본 논문에서 제안한 공식과 FEM(Finite Element Method)을 이용한 결과는 잘 일치 하였는데 탄성의 효과는 판의 고유진동수에 해당하는 골 또는 피크의 형태로 나타난다. 천공율이 매우 작으면 진동의 영향이 지배적이나 천공율이 어느 한계이상 되면 박판의 탄성거동은 매우 작게 나타나고 강체 MPP(Micro-Perforated Plate)의 흡음 특성이 지배적이 된다.

• 한국항공우주학회지
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• 제39권10호
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• pp.905-911
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• 2011

초소형 작동기 기술의 발전과 함께, 초소형 플랩핑 날개짓 비행체 개발 연구가 활발히 진행중이다. 본 연구에서는 경계요소법을 사용하여 히브진동운동하는 3차원 날개의 운동학적 매개변수인 진동 주파수 및 진폭과 기하학적 변수인 테이퍼 및 종횡비의 변화에 따른 양력 및 추력 특성을 연구했다. 날개짓 주파수가 1Hz 보다 작은 경우 진폭과 무관하게 양력이 발생하지 않았다. 추력계수 값은 날개짓 주파수와 히빙진폭이 클수록 값의 크기가 증가했다. 테이퍼 비와 종횡비가 큰 날개일수록 양력 및 추력 값이 크게 나타났다. 향후 피칭 및 플랩핑 운동 날개의 공력특성변화에 대한 연구를 수행할 예정이다.

• 한국지능시스템학회논문지
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• 제14권4호
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• pp.445-450
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• 2004

본 논문은 실질적인 최적화 구조물의 설계를 위한 시스템에 대한 것으로 퍼지이론에 바탕을 둔 자동 유한요소 생성 망 기술과 계산 기하학적 기술, 해석코드 및 솔리드모델러를 시스템에 통합시켰다. 최적해 또는 만족해는 자동해석 시스템과 함께 탐색공간을 위한 유전자 알고리즘을 이용하여 자동적으로 탐색되어 진다. 또한, 유전자 알고리즘을 이용함으로써 본 설계 시스템은 다차원 해를 얻을 수 있다. 개발된 시스템은 터널전류에 바탕을 둔 마이크로 가속도계의 형상설계에 적용하였다.