• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.999-1004
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• 2004

A numerical method and algorithms is proposed to perform optimization of non-linear response structures. An analytical and numerical method based finite element method is also proposed for the transformation of non-linear response into linear response. Loads transformed from this method are defined as the equivalent linear loads. With the loads and the transformed response, linear static optimization is performed for nonlinear response structure with geometric and/or material non-linearity. The results of the optimization are compared with them of typical non-linear response optimization using finite difference method. The proposed method is very efficient and derives good solution.

• Structural Engineering and Mechanics
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• 제44권3호
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• pp.339-361
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• 2012

Large amplitude free vibration and thermal post-buckling of shear flexible Functionally Graded Material (FGM) beams is studied using finite element formulation based on first order Timoshenko beam theory. Classical boundary conditions are considered. The ends are assumed to be axially immovable. The von-Karman type strain-displacement relations are used to account for geometric non-linearity. For all the boundary conditions considered, hardening type of non-linearity is observed. For large amplitude vibration of FGM beams, a comprehensive study has been carried out with various lengths to height ratios, maximum lateral amplitude to radius of gyration ratios, volume fraction exponents and boundary conditions. It is observed that, for FGM beams, the non-linear frequencies are dependent on the sign of the vibration amplitudes. For thermal post-buckling of FGM beams, the effect of shear flexibility on the structural response is discussed in detail for different volume fraction exponents, length to height ratios and boundary conditions. The effect of shear flexibility is observed to be predominant for clamped beam as compared to simply supported beam.

• Structural Engineering and Mechanics
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• 제40권3호
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• pp.347-371
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• 2011

This paper focuses on post-buckling analysis of Timoshenko beams with various boundary conditions subjected to a non-uniform thermal loading by using the total Lagrangian Timoshenko beam element approximation. Six types of support conditions for the beams are considered. The considered highly non-linear problem is solved by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. As far as the authors know, there is no study on the post-buckling analysis of Timoshenko beams under uniform and non-uniform thermal loading considering full geometric non-linearity investigated by using finite element method. The convergence studies are made and the obtained results are compared with the published results. In the study, the relationships between deflections, end rotational angles, end constraint forces, thermal buckling configuration, stress distributions through the thickness of the beams and temperature rising are illustrated in detail in post-buckling case.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 I
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• pp.319-324
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• 2001

Free non-linear vibration of a rotating thin ring with a constant speed is analyzed when the ring has both the in-plane and out-of-plane motions. The geometric non-linearity of displacements is considered by adopting the Lagrange strain theory for the circumferential strain. By using Hamilton's principle, the coupled non-linear partial differential equations are derived, which describe the out-of-plane and in-plane bending, extensional and torsional motions. The natural frequencies are calculated from the linearized equations at various rotational speeds. Finally, the computation results from three non-linear models are compared with those from a linear model. Based on the comparison, this study recommends which model is appropriate to describe the non- linear behavior more precisely.

• 한국통신학회논문지
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• 제31권2C호
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• pp.191-199
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• 2006

본 논문에서는 OFDM 신호의 높은 PAPR과 전력 증폭기의 비선형성에 의한 신호의 왜곡과 스펙트럼의 확산을 방지하기 위하여 $rho$차 역필터 구조를 사용하는 전치 보상기를 구현하는 방안을 제시한다. 메모리가 없는 고전력 증폭기를 다항식으로 모델링 하고 전치 보상기로써 비선형 증폭기 특성의 역모델인 $rho$차 역필터 구조를 이용한다. $rho$차 역필터 구조는 비선형 시스템이 다항식으로 모델링 된다면 다항식의 계수만으로 구현될 수 있으므로 많은 메모리가 필요 없다. 비선형 전력 증폭기 모델의 계수 갱신을 위하여는 LMS, RLS 알고리듬을 모두 사용할 수 있으며 계수의 개수가 적어 수렴 속도가 빠르고 복소 계산이 필요 없으므로 계산도 간단하다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.87-90
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• 2004

In this paper, geometrically non-linear finite element analyses were performed to study the mechanical behavior of the material system of the envelope of stratospheric airships. The microstructure of the load­bearing plain weave layer was identified and modeled. The Updated Lagrangian formulation was employed to consider the geometric non-linearity as well as the induced structural non-linearity for the fiber tows. The stress-strain behavior was predicted and the effective elastic modulus was calculated by numerical experiments. It was found the non-linear stress-strain curves were largely different from those by linear analysis with much higher non-linear elastic moduli. The difference was more distinguishable when the tow waviness was smaller.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.443-447
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• 1999

The AC drive systems of a voltage source inverter and an induction motor. The inverter non linearity caused by the turn on/off time dependency of the current level in the switching IGBT is described in the first part of this paper. To improve the low-speed drive characteristics, accurate applied voltage calculation is proposed under considerations of the compensations for the quantization error in the digital controller, the forward voltage drop of switching drives and the dead time of the inverter. The experimental studies show the improved drive characteristics.

• 한국군사과학기술학회지
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• 제10권1호
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• pp.107-115
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• 2007

In this paper we confirm the disappearance of dynamic lock-in simply by increasing the dither noise magnitude of the ring laser gyroscope by numerical and experimental method. After that, we numerically study the relation between the dither noise forms and scale factor non-linearities by comparing those of the two case outputs which are individually generated by operating with the two types of dither noise forms. The first one is the simple form composed of consecutive alternations of the random increasing and decreasing parts but maximum and minimum dither envelopes are scarcely changeable. And the second one is similar to the first one but maximum and minimum dither envelopes are randomly changable. As a result, we find that the scale factor non-linearity could be improved by the second one. And we confirm those results by experimental measurements.

• 대한전자공학회논문지SD
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• 제46권4호
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• pp.1-9
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• 2009

본 논문에서는 디스플레이 시스템을 위한 소면적 12-bit 300MSPS의 D/A 변화기(DAC)를 제안한다. 최근 SoC(System-On-Chip) 경향에 맞는 소면적 DAC를 구현하기 위한 전체적인 구조는 6-MSB(Most Significant Bit) + 6-LSB(Least Significant Bit)의 full matrix 구조로 설계 하였다. 고해상도 동작에 요구되는 output impedance을 만족하는 monitoring bias 구조, 고속 동작 및 소면적 디지털 회로 구성을 위하여 logic과 latch 및 deglitching 역할을 동시에 할 수 있는 self-clocked switching logic을 각각 제안하였다. 설계된 DAC는 Samsung $0.13{\mu}m$ thick gate 1-poly 6-metal N-well CMOS 공정으로 제작되었다. 제작된 DAC의 측정결과 INL (Integrated Non Linearity) / DNL (Differential Non Linearity)은 ${\pm}3LSB$ / ${\pm}1LSB$ 이하로 나타났으며, 300MHz 샘플링 속도와 15MHz의 출력신호에서 SFDR은 약 70dB로 측정되었다. DAC의 유효면적은 $0.26mm^2$ ($510{\mu}m{\times}510{\mu}m$)로 기존의 DAC에 비하여 최대 40% 감소된 초소면적으로 구현되었으며, 최대 전력 소모는 100mW로 측정되었다.

• Coupled systems mechanics
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• 제7권4호
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• pp.441-453
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• 2018

Longitudinal fracture in a functionally graded beam configuration was studied analytically with taking into account the non-linear behavior of the material. A cantilever beam with two longitudinal cracks located symmetrically with respect to the centroid was analyzed. The material was functionally graded along the beam width as well as along the beam length. The fracture was studied in terms of the strain energy release rate. The influence of material gradient, crack location along the beam width, crack length and material non-linearity on the fracture behavior was investigated. It was shown that the analytical solution derived is very useful for parametric analyses of the non-linear longitudinal fracture behavior. It was found that by using appropriate material gradients in width and length directions of the beam, the strain energy release rate can be reduced significantly. Thus, the results obtained in the present paper may be applied for optimization of functionally graded beam structure with respect to the longitudinal fracture performance.