• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.15 no.7
• /
• pp.692-697
• /
• 2004

OFDM system is very useful for the multi-path channel and highly bandwidth-efficient system. However, OFDM signal shows the high PAPR so that nonlinear distortion can happen in the HPA(high power amplifier). This paper studies BER performance variation according to IBO(input back off) values when the predistorter is used fur the compensation for the HPA nonlinearity. In case of the SSPA(solid state power amplifier) of nonlinearity parameter p=0.5 and IBO=0㏈, the system with predistorter is poorer than the one without predistorter. But this situation is inverted, if IBO is increased from 0㏈ to 3㏈. So, we can find that there is a threshold value of IBO for the predistorter to effectively compensate for the nonlinear SSPA when the sub-carrier number and p value are changed.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.2
• /
• pp.463-477
• /
• 1991

This study proposed a new method to design a robot manipulator control system capable of tracking the trajectories of joint angles in a reasonable accuracy to cover with actual situation of varying payload, uncertain parameters, and time delay. The direct adaptive model following control method has been used to improve existing industrial robot manipulator control system design. The proposed robot manipulator controller is operated by adjusting its gains based on the response of the manipulator in such a way that the manipulator closely matches the reference model trajectories predefined by the designer. The manipulator control system studied has two loops: they are an inner loop on adaptive model following controller to compensate nonlinearity in the manipulator dynamic equation and to decouple the coupling terms and an outer loop of state feedback controller with integral action to guarantee the stability of the adaptive scheme. This adaptation algorithm is based on the hyperstability approach with an improved Lyapunov function. The coupling among joints and the nonlinearity in the dynamic equation are explicitly considered. The designed manipulator controller shows good tracking performance in various cases, load variation, parameter uncertainties. and time delay. Since the proposed adaptive control method requires only a small number of parameters to be estimated, the controller has a relatively simple structure compared to the other adaptive manipulator controllers. Therefore, the method used is expected to be well suited for a high performance robot controller under practical operation environments.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.31 no.1
• /
• pp.40-46
• /
• 2011

In the field application of the conventional acoustic nonlinear technique using through transmission of bulk waves to evaluate the contact acoustic nonlinearity(CAN) in solid-solid contact interfaces like as in the closed crack, it has difficulty to access inner position for attaching the pulsing or receiving transducer. In the present study, a new reflection technique has been suggested to measure the acoustic nonlinearity in solid-solid contact interfaces, which uses both of pulsing and receiving transducers on the same side of target and so that it will be very useful for the field application. For this, based on the linear and the nonlinear contact stiffness estimated by the power-model of the contacting pressure, the nonlinear parameter of the reflected ultrasonic wave at the interfaces has been theoretically calculated. Experimental results in contact interfaces of A1606l-T6 alloy specimens with loading pressure showed good agreement with the theoretical predictions, which proves the validity of the suggested reflection mode technique.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.49 no.7
• /
• pp.32-38
• /
• 2012

In this paper, to eliminate intersymbol interference of the received signal due to multipath propagation, a parallel equalization algorithm using two error estimation functions is proposed. In the proposed algorithm, multilevel two-dimensional signals are considered as equivalent binary signals, then error signals are estimated using the sigmoid nonlinearity effective at the initial phase equalization and threshold nonlinearity with high steady-state performance. The two errors are scaled by a weight depending on the relative accuracy of the two error estimations, then two filters are updated differentially. As a result, the combined output of two filters was to be the optimum value, fast convergence at initial stage of equalization and low steady-state error level were achieved at the same time thanks to the combining effect of two operation modes smoothly. Usefulness of the proposed algorithm was verified and compared with the conventional method through computer simulations.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.22 no.3
• /
• pp.267-272
• /
• 2012

This paper propose the implementation of robust fuzzy controller for controlling an active magnetic bearing (AMB) system with 6 degree of freedom (DOF). A basic model with 6 DOF rotor dynamics and electromagnetic force equations for conical magnetic bearings is proposed. The developed model has severe nonlinearity and uncertainty so that it is not easy to obtain the control objective. For solving this problem, we use the Takagi-Sugeno (T-S) fuzzy model which is suitable for designing fuzzy controller. The control object in the AMB system enables the rotor to rotate without any phsical contact by using magnetic force. In this paper, we analyze the nonlinearity of the active magnetic bearing system by using fuzzy control algorithm and desing the robust control algorithm for solving the parameter variation. Simulation results for AMB are demonstrated to visualize the feasibility of the proposed method.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.26 no.3
• /
• pp.92-102
• /
• 2022

Various numerical analysis models can be used to evaluate the behavior characteristics of tunnel facilities which are representative underground structures. In general, the Mohr-Coulomb model, which is most often used for numerical analysis, is an elastic-perfect plastic behavior model. And the deformation characteristics are the same during the load increase-load reduction phase. So there is a problem that the displacement may appear different from the field situation in the case of excavation analysis. In contrast, the HS-small strain stability model has a wide range of applications for each ground. And it is known that soil deformation characteristics can be analyzed according to field conditions by enabling input of initial elastic modulus and nonlinear curve parameter and so on. However, civil engineers are having difficulty using nonlinear models that can apply material nonlinear properties due to difficulties in estimating ground property coefficients. In this study, the necessity of rational model selection was reviewed by comparing the results of seismic performance evaluation using the Mohr-Coulomb model, which civil engineers generally apply for numerical analysis of tunnels, and the HS Small strain Stiffness model, which can consider ground nonlinearity.

• Journal of Mechanical Science and Technology
• /
• v.16 no.12
• /
• pp.1613-1626
• /
• 2002

This paper presents hybrid control of an active suspension system with a full-car model by using H$\sub$$\infty$/ and nonlinear adaptive control methods. The full-car model has seven degrees of freedom including heaving, pitching and rolling motions. In the active suspension system, the controller shows good performance: small gains from the road disturbances to the heaving, pitching and rolling accelerations of the car body. Also the controlled system must be robust to system parameter variations. As the control method, H$\sub$$\infty$/ controller is designed so as to guarantee the robustness of a closed-loop system in the presence of uncertainties and disturbances. The system parameter variations are taken into account by multiplicative uncertainty model and the system robustness is guaranteed by small gain theorem. The active system with H$\sub$$\infty$/ controller can reduce the accelerations of the car body in the heaving, pitching and rolling directions. The nonlinearity of a hydraulic actuator is handled by nonlinear adaptive control based on the back-stepping method. The effectiveness of the controllers is verified through simulation results in both frequency and time domains.

• Aerospace Engineering and Technology
• /
• v.8 no.1
• /
• pp.58-65
• /
• 2009

The paper identifies noise characteristics of a nonliner image sensor model which reflects a saturation effect of each detector pixel and extends the result to estimate an image SNR (Signla-to-Noise Ratio) distribution over all the pixels in a detector. In particular, nonlinearity of a pixel is studied from two perspectives of including asymmetry of a noise PDF (Probability Distribution Function) and enhancing a pixel SNR value, in comparison to a linear model. It is noted that the proposed image SNR distribution function is useful to effectively select new optimal operation parameter values: an integration time and an pixel-summing number, even after a launch campaign, assuming sensor gain degradation in orbit or inevitable modification of some operation parameter values due to space contingency.

• Structural Engineering and Mechanics
• /
• v.66 no.3
• /
• pp.295-303
• /
• 2018

The semi-analytical method to study the nonlinear dynamic behavior of simply supported spiral stiffened functionally graded (FG) cylindrical shells subjected to an axial compression is presented. The FG shell is surrounded by damping and linear/nonlinear elastic foundation. The proposed linear model is based on the two-parameter elastic foundation (Winkler and Pasternak). A three-parameter elastic foundation with hardening/softening cubic nonlinearity is used for nonlinear model. The material properties of the shell and stiffeners are assumed to be FG. Based on the classical plate theory of shells and von $K{\acute{a}}rm{\acute{a}}n$ nonlinear equations, smeared stiffeners technique and Galerkin method, this paper solves the nonlinear vibration problem. The fourth order Runge-Kutta method is used to find the nonlinear dynamic responses. Results are given to consider effects of spiral stiffeners with various angles, elastic foundation and damping coefficients on the nonlinear dynamic response of spiral stiffened simply supported FG cylindrical shells.

• Journal of information and communication convergence engineering
• /
• v.5 no.1
• /
• pp.17-22
• /
• 2007

In this paper, the optimal value of optical phase conjugator (OPC) position and the optimal values of dispersion coefficients of fiber sections for the best compensation of the distorted WDM signals with frequency chirp of -1 are induced to alternate with the symmetrical distributions of power and local dispersion with respect to OPC, which is difficult to form in real optical link due to fiber attenuation in mid-span spectral inversion (MSSI) technique. It is confirmed that the Q-factors of total channels of -18.5 dBm launching light power exceed 16.9 dB, which value corresponds to 10-12 BER, by applying the induced optimal parameter values into 16 channels ${\times}$ 40 Gbps WDM system, on the other hand the Q-factors of only 9 channels exceed that value in WDM system with the conventional MSSI technique. Thus, it is expected to expand the availability of OPC in WDM system through the using of the optimal parameter values that are induced by the proposed method in this paper, without the symmetrical distributions of power and local dispersion.