• 한국기계가공학회지
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• 제21권4호
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• pp.53-59
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• 2022

In this study, an enhanced first-order shear deformation theory is proposed to efficiently and accurately predict the thermo-mechanical-viscoelastic coupled behavior of laminated composite structures. To this end, transverse shearstress and displacement fields are independently assumed, and the strain-energy relationship between these fields issystematically established using the mixed variational theorem (MVT). In MVT, the transverse shear stress fields are obtained from the third-order zigzag model, whereas the displacement fields of the conventional first-order model are considered to amplify the benefits of numerical efficiency. Additionally, a transverse displacement field with a smooth parabolic distribution is introduced to accurately predict the thermal behavior of composite structures. Furthermore, the concept of Laplace transformation is newly employed to simplify the viscoelastic problem, similar to the linear-elastic problem. To demonstrate the performance of the proposed theory, the numerical results obtained herein were compared with those available in the literature.

• Smart Structures and Systems
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• 제21권1호
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• pp.113-122
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• 2018

In this article, an exact analytical solution for mechanical buckling analysis of magnetoelectroelastic plate resting on pasternak foundation is investigated based on the third-order shear deformation plate theory. The in-plane electric and magnetic fields can be ignored for plates. According to Maxwell equation and magnetoelectric boundary condition, the variation of electric and magnetic potentials along the thickness direction of the plate is determined. The von Karman model is exploited to capture the effect of nonlinearity. Navier's approach has been used to solve the governing equations for all edges simply supported boundary conditions. Numerical results reveal the effects of (i) lateral load, (ii) electric load, (iii) magnetic load and (iv) higher order shear deformation theory on the critical buckling load have been investigated. These results must be the analysis of intelligent structures constructed from magnetoelectroelastic materials.

• Journal of Mechanical Science and Technology
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• 제17권12호
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• pp.1867-1875
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• 2003

In exhaust pipes of automotive engines, the pulsating pressure waves are composed of fundamental frequency and high order harmonics. The nonlinearities in the exhaust pipe is caused by their interactions. The error between prediction and measurement is induced by the nonlinearities. We can not explain this phenomenon using linear acoustics theory. So power spectrum, which is used in linear theory, is not useful. This paper is concerned with the development of useful engineering techniques to detect and analyze nonlinearity in exhaust pipe of automotive engines. The study of higher order statistics has been dominated by work on the bispectrum. The bispectrum can be viewed as a decomposition of the third moment (skewness) of a signal over frequency and as such is blind to symmetric nonlinearities. The phenomenon of quadratic phase coupling (QPC) can be analyzed by the bicoherence function. Finally the application of these techniques to data from actual exhaust pipe systems is performed.

• 제어로봇시스템학회논문지
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• 제4권5호
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• pp.630-635
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• 1998

The objective of this paper is to propose a new efficient technique for the estimation of time-delay parameters using wavelet theory and third-order cumulants, yielding good performance even in the case of low SNR. In particular, band-limited non-Gaussian signals with non-zero skewness and spatially correlated Gaussian noises are considered here. The approach is based on the fact that the effects of spatially correlated Gaussian noises on time-delay estimation can be reduced by using the projection sequences (based on the redundant wavelet decomposition) of given measurements in the higher-order cumulant domain. Finally, the performance of the proposed approach is demonstrated using simulations.

• 한국구조물진단유지관리공학회 논문집
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• 제8권4호
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• pp.107-114
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• 2004

본 논문에서는 복합적층판의 유한요소해석을 위해 직접수정법으로 간단히 개선된 8절점 유한요소를 제안하였다. 우선, 9절점 등매개변수 요소와 동일한 조건하에서 이차다항식을 표현할 수 있도록 형상함수를 수정하며, 이를 외시적(explicit)으로 표현하였다. 전단보정계수를 갖는 1차전단변형이론을 고차전단변형이론에 근거하여 간단히 개선함으로써 두께방향으로 전단응력 및 변형률이 포물선 분포를 가지도록 하였다. 더 이상의 전단보정계수가 필요하지 않다. 따라서 간단한 직접수정법 즉, 형상함수의 수정, 1차전단변형이론의 개선 및 가정변형률을 조합함으로써 8절점 유한요소의 성능을 개선하였다. 제안된 유한요소를 이용하여 복합적층판의 정적, 좌굴 및 자유진동 수치해석을 실시하여 비교 검증하였다.

• 한국전자통신학회논문지
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• 제15권5호
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• pp.827-834
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• 2020

본 연구는 주파수 체배기 이론을 이용하여 초고주파 항공용 레이다를 위한 3차 고조파 믹서 설계에 대한 연구이다. 기본 믹서 설계 방법과는 달리 주파수 체배기 이론을 이용하여 국부 주파수(LO)의 3차 고조파 성분이 최대가 되는 게이트 바이어스 전압을 선택하여 중간주파수(IF)에서 3차 고조파 혼합(mixing) 성분이 최대가 되도록 하였다. 제안한 고조파 믹서는 플라스틱 패키지의 상용 GaAs MESFET 소자를 이용하여 설계 및 제작하여 기존 초고주파 믹서의 높은 변환손실, 회로 복잡성, 높은 가격 및 제작 복잡도를 개선할 수 있었다. 제안한 설계 방법을 이용한 3차 고조파 믹서는 33 GHz ~ 36 GHz 대역에서 8 ~10 dB 변환손실 특성 및 0 dBm 선형성 (P1dB) 특성을 나타내었다.

• 한국강구조학회 논문집
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• 제13권5호
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• pp.443-455
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• 2001

전단 층을 갖는 2개 매개변수 탄성지반 위에 놓인 복합재료 적층판에서 휨 진동 및 좌굴해석을 위해 에너지 방법을 사용해 탄성해를 구하였다. 복합재료 적층판의 점탄성 해석은 유사-탄성방법을 사용해 탄성해를 구하였다. 전단에 의한 효과는 3창 전단변형이론을 적용하여 고려하였다. 유도된 식들을 검증하기 위해 LUSAS 프로그램에 의한 탄성지반위에 놓인 이방성 판의 처짐과 비교하였다. 점탄성 휨 진동 및 좌굴해석에 관한 수치해석결과들은 적층순서, 적층 수 재료 비등방성과 전단지반계수 등에 따른 효과를 보여 준다.

• Steel and Composite Structures
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• 제39권3호
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• pp.275-290
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• 2021

The main purpose of this research work is to investigate the critical buckling load of functionally graded (FG) porous plates with graphene platelets (GPLs) reinforcement using generalized differential quadrature (GDQ) method at thermal condition. It is supposed that the GPL nanofillers and the porosity coefficient vary continuously along the plate thickness direction. Generally, the thermal distribution is considered to be nonlinear and the temperature changing continuously through the thickness of the nanocomposite plates according to the power-law distribution. To model closed cell FG porous material reinforced with GPLs, Halpin-Tsai micromechanical modeling in conjunction with Gaussian-Random field scheme are used, through which mechanical properties of the structures can be extracted. Based on the third order shear deformation theory (TSDT) and the Hamilton's principle, the equations of motion are established and solved for various boundary conditions (B.Cs). The fast rate of convergence and accuracy of the method are investigated through the different solved examples and validity of the present study is evaluated by comparing its numerical results with those available in the literature. A special attention is drawn to the role of GPLs weight fraction, GPLs patterns through the thickness, porosity coefficient and distribution of porosity on critical buckling load. Results reveal that the importance of thermal condition on of the critical load of FGP-GPL reinforced nanocomposite plates.

• Structural Engineering and Mechanics
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• 제70권6호
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• pp.683-702
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• 2019

The present study aims to analyze the magneto-electro-elastic (MEE) vibration of a functionally graded carbon nanotubes reinforced composites (FG-CNTRC) cylindrical shell. Electro-magnetic loads are applied to the structure and it is located on an elastic foundation which is simulated by visco-Pasternak type. The properties of the nano-composite shell are assumed to be varied by temperature changes. The third-order shear deformation shells theory is used to describe the displacement components and Hamilton's principle is employed to derive the motion differential equations. To obtain the results, Navier's method is used as an analytical solution for simply supported boundary condition and the effect of different parameters such as temperature variations, orientation angle, volume fraction of CNTs, different types of elastic foundation and other prominent parameters on the natural frequencies of the structure are considered and discussed in details. Design more functional structures subjected to multi-physical fields is of applications of this study results.

• 한국실내디자인학회논문집
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• 제26권6호
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• pp.81-96
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• 2017

This study aims at establishing a basic theory for the combination of architecture and movies by comparing the long-take technique of movies and the continuity of space, one of space composition principles, which is important in digital architecture based on Jacques Lacan's visual-art theory and finding common features and differences of them. The following is a summary of the conclusions. First, analyzing the long-take technique on the basis of Lacan's visual-art theory found that the subject of representation is scenes of movies and that staring shows features of narrative. Second, the long-take technique can be thought as a cinematic technique which tries to realize the real order beyond the symbolic order in real life through the process of continuous replication of replication of replication of a scene in one shot. Third, in contemporary architecture, which is compared to the long-take technique in the past, the inclined space of opened gaze is similar to the method which tries to realize architectural space of the reality which belongs to the symbolic order close to the real order which belong to significant in human unconsciousness. Fourth, the freeform continuous space of closed gaze, which can be compared to contemporary long take combined with computer graphic technology, has more difficulty in realizing the real order than the long-take technique in the past and inclined, continuous space as the feature which belongs to $signifi{\acute{e}}$ in human consciousness has been strengthened through the circulation which repeats and expands along an observer's movement. Fifth, when the contemporary long-take technique and freeform continuous space expand gaze which opens from the inside to the outside, it is considered that the space which is closer to the real order than the classic long-take technique and inclined continuous space can be created.