• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 봄 학술발표회 논문집
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• pp.41-48
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• 2002

The fact that nonlinearity and anisotropy of soil should be considered for the proper estimation of soil deformation has been recongnized for a long time. In this study, a new stiffness model which can reflect both nonlinearity and anisotropy is proposed. Nonlinearity is simulated by Ramberg-Osgood model and anisotropy is modeled with the cross-anisotropic elasticity. Analysis results with the developed model compared with those from analyses using linear isotropic model, linear anisotropic model, and nonlinear isotropic model. In the triaxial compression like condition, the effects of nonlinearity on the vertical strain are significant, but soil anisotropy does not affect the vertical strain. In 1-dimensional deformation condition, however, both nonlinearity and anisotropy of soil influence the final magnitude of the vertical strain. Also the increase of poisson's ratio magnifies the effect of anisotropy on the vertical strain in this condition.

• 통합자연과학논문집
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• 제6권3호
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• pp.181-182
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• 2013

In this note, we are concerned with a class of semi-linear elliptic pdes with exponential nonlinearity in a bounded domain. Here, the nonlinearity is more or less growing exponentially with power p. We consider the problem under two types of Dirichlet boundary condition. We give existence and non-existence of solutions for those problems and some asymptotics.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.389.2-389
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• 2002

Nonlinear aeroelastic characteristics of a missile control surface are investigated in this study. The wing model has freeplay structural nonlinearity at its pitch axis. Nonlinear aerodynamic flows with unsteady shock waves are also considered in high-speed flow region. To effectively consider a freeplay structural nonlinearity, the fictitious mass method (FMM) is applied to structural vibration analysis based on finite element method (FEM). (omitted)

• 비파괴검사학회지
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• 제33권1호
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• pp.14-19
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• 2013

금속 재료의 비선형 파라미터는 고유한 물성치로서 기본주파수의 음압의 크기($A_1$)과 2차고조파의 음압의 크기($A_2$)을 측정하면 산정할 수 있다. 하지만, 실험적으로 $A_1$과 $A_2$를 측정하는 것은 매우 복잡한 변환 과정이 필요하기 때문에 현재 많은 연구자들이 비선형 파라미터의 절대값을 측정하지 않고, 전압 변화를 관찰하는 비선형 파라미터의 상대값을 측정하고 있다. 하지만, 비선형 파라미터 상대값으로는 재료의 물성치를 대변할 수가 없기 때문에, 열화도에 따른 시편 측정에만 사용할 수 있는 제약이 있다. 따라서 본 연구에서는 정전용량 측정기법(capacitive detector)보다는 비용이 적게 소모되고 현장 적용이 가능한 압전형 수신기법(piezoelectric detection)을 이용하여 비선형 파라미터의 절대값을 측정하기 위한 시스템을 구축하였다. $A_1^2vsA_2$ 그래프로 시스템의 선형성을 검증하고 시험편인 fused silica와 Al2024-T4에 대한 비선형 파라미터를 측정하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 Proceedings of the Korea Automatic Control Conference, 11th (KACC); Pohang, Korea; 24-26 Oct. 1996
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• pp.177-180
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• 1996

The purpose of this paper is to design a robust adaptive control algorithm for a class of systems having continuous relay nonlinearity. This continuous relay nonlinearity can be defined as an analytic nonlinear function having unknown parameters and bounded unmodeling part. By this mathematical modeling, the whole system can be considered as a nonlinear system having unknown parameters and bounded perturbation. The control algorithm of this paper, RALC, can be constructed by robust adaptive law, feedback linearization, and indirect robust adaptive control. By this RALC, we can obtain that the output of given system can follow that of a stable reference linear model made by designer and the boundedness of all signals in closed-loop system can be maintained. Therefore, we can confirm a robust adaptive control for a class of systems having continuous relay nonlinearity.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.349-352
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• 1997

A Piezoelectric actuator yields hysteresis effect due to its composed ferroelectric. Hysteresis nonlinearity is neglected when a piezoelectric actuator moves with short stroke. However when it moves with long stroke and high frequency, the hysteresis nonlinearity can not be neglected. The hysteresis nonlinearity of piezoelectric actuator degrades the control performance in precision position control. In this paper, in order to improve the control performance of piezoelectric actuator, an inverse modeling scheme is proposed to compensate the hysteresis nonlinearity problem. And feedforward-feedforward-feedback controller is proposed to give a good tracking performance. The Feedforward controller is inverse hysteresis model, and PID control is sued as a feedback controller. To show the feasibility of the proposed controller and hysteresis modeling, some experiments have been carried out. It is concluded hat the proposed control scheme gives good tracking performance.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1638-1642
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• 2003

Piezoactuator using a flexure hinge mechanism is often used in the precision stages. When the total size of the hinge mechanism become small compared with the deformation of the hinge mechanism, the geometrical nonlinearity makes a considerable error in the output displacement. In this research, the incremental method based on the matrix method is developed to model the effect of the geometrical nonlinearity. Developed modeling method is applied to derive the error of output displacement of the bridge-type hinge mechanism and its results are derived with respect to the design parameters. This method can be easily used to the design optimization of the hinge mechanism and analysis results show that the geometrical nonlinearity error should be considered to achieve a high accuracy to the piezoactuators.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.419-424
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• 1996

As track density increases, the effects of nonlinearity in pivot bearing of hard disk drive on the servo performance are becoming more important in considering the range of inertia force and the input torque during settling and tracking mode. Recently, an increasing attention is given to more precise experimental observations and modelings of pivot nonlinearity for achieving higher performance of servo control. In this paper, we propose a new model that shows an improved prediction of the pivot nonlinearity than existing preload-plus-two-slope model at matching simulations and experimental results in both time and frequency domains. Experimental measurements are carried out to validate and identify the specific nonlinearity presents in the pivot bearing when its in fine motion. Using the experimental results new model along with the existing one are characterized and compared for relevancies.

• Journal of Ship and Ocean Technology
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• 제9권4호
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• pp.11-22
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• 2005

This paper addresses details of wave load nonlinearity effect on stress RAO and damage ratio using component stochastic fatigue analysis. Traditional spectral fatigue analysis for ship structure is based on linear theory; however, there are a number of nonlinearity sources. Especially loading nonlinearity, such as hydrodynamic pressure applying to ship side and gravity changes due to roll and pitch motion, is thought to critically violate the linearity assumption of spectral fatigue analysis, which involves stress RAO as linear parameter. The main focus is placed on how to idealize complicated characteristics of loading nonlinearity and how to implement the nonlinear bias to linear spectral fatigue analysis.

• 비파괴검사학회지
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• 제36권1호
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• pp.53-59
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• 2016

초음파 비선형 진단을 이용한 기법의 경우 재료의 단순 결함 검출뿐만 아니라 부식, 소성변형과 같은 미세손상을 평가할 때 주로 이용된다. 1차 조화파(primary wave)와 2차 조화파(second harmonic wave)의 진폭의 비를 이용하여 비선형성을 나타내며, 이러한 비선형성의 비교 결과를 진단에 사용한다. 실험 특성상 비선형성은 재료의 비선형성뿐만 아니라 장비의 비선형성 또한 포함하게 된다. 장비 비선형성은 사용자가 측정하고자 하는 값이 아니므로 오차로 작용하여 분석을 방해한다. 본 연구에서는 오차로 작용하는 장비의 비선형성을 감소시켜 보다 정확한 진단을 위해 체적파 혼합기법을 사용하였다. 체적파 혼합기법의 가장 큰 특징은 기존의 초음파 비선형 진단보다 장비의 비선형성을 줄일 수 있다는 점이다. 본 연구에서는 체적파 혼합기법을 이론 및 실험적으로 검증하였으며, 기존의 초음파 비선형 진단기법의 결과와 체적파 혼합기법의 결과를 비교하여 장단점 및 적용 가능성 분석에 초점을 두었다.