• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.9
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• pp.1795-1805
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• 2002

A position controller which can achieve a specified dynamic performance irrespective of the different operating position of the pneumatic cylinder is proposed. The position controller developed in this paper is composed of a nonlinear compensator and a disturbance observer. The nonlinear compensator which feeds back position, velocity and acceleration is derived from the nonlinear dominating equations of the position control system to compensate for variation of dynamic characteristics of a pneumatic cylinder according to the change of the operating position. The disturbance observer including a simplified linear model is designed to reduce the effect of model discrepancy in the low frequency range which cannot be suppressed by the nonlinear compensator. The results of the experiments show that the position control performance maintains a designed performance regardless of the variations of an operating position of the pneumatic cylinder.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.838-843
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• 2005

The nonlinear characteristics of a suspension is directly related to the ride quality of a passenger car. In this study, a dynamic experiment for a spring and a damper of a passenger car is performed to analyze the nonlinear characteristics using MTS 1-axial testing machine and a mathematical nonlinear dynamic suspension model based on experimental data is devised to estimate the ride quality using Billings' method. The devised nonlinear model is applied to the ride quality analysis using K factor and the effect of suspension parameters is examined. As a result, the friction between the cylinder and the piston of a damper is the most effective parameter for the ride quality of a passenger car.

• Structural Engineering and Mechanics
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• v.83 no.3
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• pp.377-386
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• 2022

This paper considers dynamic impedance functions and presents a detailed analysis of the soil plasticity influence on the pile-group foundation dynamic response. A three-dimensional finite element model is proposed, and a calculation method considering the time domain is detailed for the nonlinear dynamic impedance functions. The soil mass is modeled as continuum elastoplastic solid using the Mohr-Coulomb shear failure criterion. The piles are modeled as continuum solids and the slab as a structural plate-type element. Quiet boundaries are implemented to avoid wave reflection on the boundaries. The model and method of analysis are validated by comparison with those published on literature. Numerical results are presented in terms of horizontal and vertical nonlinear dynamic impedances as a function of the shear soil parameters (cohesion and internal friction angle), pile spacing ratio and frequencies of the dynamic signal.

• Tribology and Lubricants
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• v.29 no.4
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• pp.248-254
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• 2013

This paper presents a numerical model for investigating the structural dynamic response of an unbalanced rotor system supported on deep groove ball bearings. The aim of this work is to develop a numerical model for investigating the effect of the number of balls on the dynamic characteristics of the rotor ball bearing system. The fourth-order Runge-Kutta numerical integration technique has been applied. The results are presented in the form of time displacement responses and frequency spectra. The analysis demonstrates that the model can be used as a tool for predicting the nonlinear dynamic behavior of the rotor ball bearing system under different operating conditions. Moreover, the study may contribute to a further understanding of the nonlinear dynamics of rotor bearing systems.

• Tribology and Lubricants
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• v.30 no.1
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• pp.64-70
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• 2014

This paper presents a numerical model for investigating the structural dynamics response of a rigid rotor supported on deep-groove ball bearings. The numerical model was used to investigate the influence of race waviness on the dynamic characteristics of a rotor ball bearing system, which is very important from a design viewpoint. The forth-order Runge-Kutta numerical integration technique was applied to determine the time displacement response, Poincare map, and frequency spectra. The analysis demonstrated that the model can be used as a tool for predicting the nonlinear dynamic behavior of a rotor ball bearing system under different operating conditions. The results of this study may help further understanding of the nonlinear dynamics of a rotor bearing system.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.31B no.10
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• pp.44-52
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• 1994

In this paper, we assume that the dynamics of DC motor and nonlinear load are unknown. We propose an inverse dynamic model of DC motor and nonlinear load using the artificial neural network and construck speed control system based on the proposed dynamic model. We also propose another dynamic model with speed prediction scheme using the artificial neural network that removes the undesirable time delay effect caused by the computation time during the real-time control. We suggest a dynamic model which has arbitrary number of speed arguments and is especially effective when the motor and load has large moment of inertia. Next, we suggest a controller that combine the neurocontrol and PID control with constant gain. We show that the proposed neurocontrol systems have capabilities of noise rejection and generalization to have good velocity tracking through computer simulations and experiments.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.5
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• pp.157-165
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• 1995

In this paper the comparison between the neural networks and traditional approaches as nonlinear system identification methods are considered. Two model structures of neural networks are the state space model and the input output model neural networks. The traditional methods are the AutoRegressive eXogeneous Input model and the Nonlinear AutoRegressive eXogeneous Input model. Computer simulation for an analytic dynamic model of a single input single output nonlinear system has been done for all the chosen models. Model validation for the obtained models also has been done with testing inputs of the sinusoidal, ramp and the noise ramp.

• Computers and Concrete
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• v.16 no.4
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• pp.643-667
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• 2015

3-dimentional precast recycled aggregate concrete (RAC) finite element models were developed by means of the platform OpenSees to implement sophisticated nonlinear model subjected to seismic loads. Efforts were devoted to the dynamic responses (including dynamic characteristics, acceleration amplifications, displacements, story drifts) and capacity curve. In addition, this study extended the prediction on dynamic response of precast RAC model by parametric study of material properties that represent the replacement percentage of recycled coarse aggregate (RCA). Principles and assumptions that represent characteristics of precast structure and influence of the interface between head of column and cast-in-place (CIP) joint on the stiffness of the joints was put forward and validated by test results. The comparison between simulated and tested results of the precast RAC frame shows a good correlation with most of the relative errors about 25% in general. Therefore, the adopted assumptions and the platform OpenSees are a viable approach to simulate the dynamic response of precast frames made of RAC.

• Smart Structures and Systems
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• v.15 no.2
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• pp.409-424
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• 2015

Structural nonlinearity is a common phenomenon encountered in engineering structures under severe dynamic loading. It is necessary to localize and identify structural nonlinearities using structural dynamic measurements for damage detection and performance evaluation of structures. However, identification of nonlinear structural systems is a difficult task, especially when proper mathematical models for structural nonlinear behaviors are not available. In prior studies on nonparametric identification of nonlinear structures, the locations of structural nonlinearities are usually assumed known and all structural responses are measured. In this paper, an identification algorithm is proposed for locating and identifying model-free structural nonlinearities and systems using incomplete measurements of structural responses. First, equivalent linear structural systems are established and identified by the extended Kalman filter (EKF). The locations of structural nonlinearities are identified. Then, the model-free structural nonlinear restoring forces are approximated by power series polynomial models. The unscented Kalman filter (UKF) is utilized to identify structural nonlinear restoring forces and structural systems. Both numerical simulation examples and experimental test of a multi-story shear building with a MR damper are used to validate the proposed algorithm.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1132-1133
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• 2007

A circuit-domain model of PWM inverter provides accurate simulation results in consideration of detail switching characteristics. Although, a huge amount of computation time is demanded for the simulation results of several ten seconds, which is the required time to analyze system behaviors or control performances of Electric Power Steering(EPS) on real drive condition. This paper describes the nonlinear inverter model for fast dynamic simulation of EPS without the PWM concept through analyzing the effect of nonlinear switching characteristics like dead time, forward voltage drop and conduction resistance. Some inverter models including proposed model are compared from two standpoints which are computation time and accuracy. The comparison results show the usefulness of the developed model in order to develop the control algorithm through the fast prediction of system behaviors.