• The Transactions of the Korean Institute of Electrical Engineers D
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• v.53 no.5
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• pp.315-322
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• 2004

A direct adaptive state-feedback controller for highly nonlinear systems is proposed. This paper considers uncertain or ill-defined nonaffine nonlinear systems and employs a static fuzzy logic system (FLS). The employed FLS estimates. and adaptively cancels an unknown plant nonlinearity using its proved universal approximation property. A control law and adaptive laws for unknown fuzzy parameters and bounding constant are established so that the whole closed-loop system is stable in the sense of Lyapunov. The tracking error is guaranteed to be uniformly asymptotically stable rather than uniformly ultimately bounded with the aid of an additional robustifying control term. No a priori knowledge of an upper bound on an lumped uncertainty is required.

• Korean Journal of Optics and Photonics
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• v.4 no.3
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• pp.317-322
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• 1993

In this paper we propose a method to analyze the nonlinear behavior of an integrated-mirror etalon by the characteristic matrix method. If the dependence of the refractive index and the absorption coefficient upon the light intensity are known, we can couple this with an equation by which we can evaluate the light intensity distribution inside an etalon for the given values of the refractive index and the absorption coefficient. By solving these coupled equations by the iteration method, we evaluate the transmission characteristics of a nonlinear integrated-mirror etalon. By the characteristic matrix method, we have demonstrated the static and dynamic bistable behavior of a nonlinear integrated-mirror etalon.

• Advances in Computational Design
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• v.4 no.4
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• pp.397-413
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• 2019

In this paper, static nonlinear analysis of gable frame is performed using OpenSees software. Both geometric and material nonlinearities are considered in analyses. To consider large displacements, co-rotational coordinate transformation is used in software. The effects of symmetric and asymmetric support conditions including clamped and simple supports are studied. On the other hand, the material nonlinearity is reflected on analyses using Giuffre-Menegotto-Pinto steel material. Note that strain hardening characteristics are also considered in this model. Moreover, I-shaped cross-section is assumed for all members. The results are provided for different geometry properties of gable frame including shallow and deep inclined roof. It should be added that buckling and post-buckling behaviors of gable frame are investigated using related equilibrium paths. A comparison study is also implemented on the responses of buckling loads obtained for different support and geometry conditions. To trace snap-through paths completely, a displacement control method entitled arc-length is utilized. Findings show the capability of proposed model in nonlinear analysis of gable frames.

• Geomechanics and Engineering
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• v.11 no.1
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• pp.95-116
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• 2016

A novel higher order shear-deformable beam model, which provides linear variation of transversal normal strain and quadratic variation of shearing strain, is proposed to describe the beam resting on foundation. Then, the traditional two-parameter Pasternak foundation model is modified to capture the effects of the axial deformation of beam. The Masing's friction law is incorporated to deal with nonlinear interaction between the foundation and the beam bottom, and the nonlinear properties of the beam material are also considered. To solve the mathematical problem, a displacement-based finite element is formulated, and the reliability of the proposed model is verified. Finally, numerical examples are presented to study the effects of the interfacial friction between the beam and foundation, and the mechanical behavior due to the tensionless characteristics of the foundation is also examined. Numerical results indicate that the effects of tensionless characteristics of foundation and the interfacial friction have significant influences on the mechanical behavior of the beam-foundation system.

• Structural Engineering and Mechanics
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• v.34 no.1
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• pp.97-107
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• 2010

Nonlinear thermoelastic static response characteristics of laminated composite conical panels are studied employing finite element approach based on first-order shear deformation theory and field consistency principle. The nonlinear governing equations, considering moderately large deformation, are solved using Newton-Raphson iterative technique coupled with the adaptive displacement control method to efficiently trace the equilibrium path. The validation of the formulation for mechanical and thermal loading cases is carried out. The present results are found to be in good agreement with those available in the literature. The adaptive displacement control method is found to be capable of handling problems with multiple snapping responses. Detailed parametric study is carried out to highlight the influence of semicone angle, boundary conditions, radius-to-thickness ratio and lamination scheme on the nonlinear thremoelastic response of laminated cylindrical and conical panels.

• Structural Engineering and Mechanics
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• v.72 no.4
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• pp.525-540
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• 2019

The purpose of the present work was to study the dynamic instability of a three-layered, symmetric sandwich beam subjected to a periodic axial load resting on nonlinear elastic foundation. A higher-order theory was used for analysis of sandwich beams with soft core on elastic foundations. In the higher-order theory, the Reddy's third-order theory was used for the face sheets and quadratic and cubic functions were assumed for transverse and in-plane displacements of the core, respectively. The elastic foundation was modeled as nonlinear's type. The dynamic instability regions and free vibration were investigated for simply supported conditions by Bolotin's method. The results showed that the responses of the dynamic instability of the system were influenced by the excitation frequency, the coefficients of foundation, the core thickness, the dynamic and static load factor. Comparison of the present results with the published results in the literature for the special case confirmed the accuracy of the proposed theory.

• Advances in aircraft and spacecraft science
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• v.10 no.4
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• pp.369-391
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• 2023

In our research we have offered a solid solution for aeronautical analysis. which can guarantee the asymptotic stability of coupled nonlinear facilities. According to the theoretical solutions and methods presented, the engine of this aircraft is a small high-bypass turbofan engine. using the non-linear aero-motor control approach and this paper focuses on the power management function of the aero-motor control system. These include static controls and transient controls. A mathematical model of the high-bypass-ratio two-spool unmixed-flow aeroengine was developed through a set of nonlinear dynamic equations verified by experimental data. A single actuator using the displacement method is designed to maintain a certain level of thrust under steady-state conditions. and maintains repeatable performance during transient operation from the requested thrust phase to the next. A single controller can compensate for the effects of noise and harmonic noise at many performance points. And the dynamic performance of a single controller is satisfactory during the transient. for fairness Numerical and computer experiments are described in the perfection of the methods we offer in research.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.119-124
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• 2008

Space structure is a appropriate shape that resists external force only with in-plane force by reducing the influence of bending moment, and it maximizes the effectiveness of structure system. The space structure should be analized by nonlinear analysis regardless static and dynamic analysis because it accompanies large deflection for member. To analyze the structure of the space structure exactly generally geometrically nonlinear and material nonlinear, complex nonlinear analysis are considered. To settle the weakness that geometric nonlinear problem does not consider nonlinear as per trait and position of the structure material and that the nonlinear matter of structure material also does not consider nonlinear as per geometric form. Therefore, In this paper, analysis is considered geometric nonlinear and material nonlinear simultaneous conditioning, and traced load-deflection curve by using ABAQUS which is the general purpose of the finite element program.

• Wind and Structures
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• v.27 no.6
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• pp.381-397
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• 2018

Nonlinear behavior in fluid-structure interaction (FSI) of bridge decks becomes increasingly significant for modern bridges with increasing spans, larger flexibility and new aerodynamic deck configurations. Better understanding of the nonlinear aeroelasticity of bridge decks and further development of reduced-order nonlinear models for the aeroelastic forces become necessary. In this paper, the amplitude-dependent and neutral angle dependent nonlinearities of the motion-induced loads are further highlighted by series of computational fluid dynamics (CFD) simulations. An effort has been made to investigate a semi-analytical time-domain model of the nonlinear motion induced loads on the deck, which enables nonlinear time domain simulations of the aeroelastic responses of the bridge deck. First, the computational schemes used here are validated through theoretically well-known cases. Then, static aerodynamic coefficients of the Great Belt East Bridge (GBEB) cross section are evaluated at various angles of attack, leading to the so-called nonlinear backbone curves. Flutter derivatives of the bridge are identified by CFD simulations using forced harmonic motion of the cross-section with various frequencies. By varying the amplitude of the forced motion, it is observed that the identified flutter derivatives are amplitude-dependent, especially for $A^*_2$ and $H^*_2$ parameters. Another nonlinear feature is observed from the change of hysteresis loop (between angle of attack and lift/moment) when the neutral angles of the cross-section are changed. Based on the CFD results, a semi-analytical time-domain model for describing the nonlinear motion-induced loads is proposed and calibrated. This model is based on accounting for the delay effect with respect to the nonlinear backbone curve and is established in the state-space form. Reasonable agreement between the results from the semi-analytical model and CFD demonstrates the potential application of the proposed model for nonlinear aeroelastic analysis of bridge decks.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.5
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• pp.1543-1551
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• 1996

The static tensile load bearing capability of as adhesively-bonded tubular single lap jint that is calculated usign the linear mechanical properties of adhesive is usually far from the experimentally determined because the majority of the load transfer of the adhesively-bonded jointd is accomplished by the nonlinear behavior of the rubber-toughened eoxy adhesive. In this paper, both the nonlinear mechanical properties and the fabrication residual thermal stresses of adhesive were included in the calculation of the stresses of adhesively-bonded joints. The onlinear tensile properties of adhesive were approximated by an exponential form which was represented by the initial tensile modulus and ultimate tensile stength of adhesive. The stress distribution in the adhesive were calculated by applying the load obtained from the tensile tests. From the tensile tests and the stress analysis of adhesively-bonded hoints, the failure model for adhesively-bonded tubular single lap joints was proposed.