• Advances in aircraft and spacecraft science
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• v.4 no.2
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• pp.203-218
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• 2017

This paper focuses on the computational study of nonlinear effects of unsteady aerodynamics for non-classical aileron buzz. It aims at a comprehensive investigation of the aileron buzz phenomenon under varying flow parameters using the describing function technique with multiple inputs. The limit cycle oscillatory behavior of an asymmetrical airfoil is studied initially using a CFD-based numerical model and direct time marching. Sharp increases in limit cycle amplitude for varying Mach numbers and angles of attack are investigated. An aerodynamic describing function is developed in order to estimate the variation of limit cycle amplitude and frequency with Mach number and angle of attack directly, without time marching. The describing function results are compared to the amplitudes and frequencies predicted by the CFD calculations for validation purposes. Furthermore, a limited sensitivity analysis is presented to demonstrate the potential of the approach for aeroelastic design.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.89-96
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• 2002

A two-degree of freedom model is suggested to understand the basic dynamical behaviors of the interaction between two masses of the friction induced vibration system. The two masses may be considered as the pad and the disk of the brake, The phase space analysis is performed to understand complicated dynamics of the non-linear model. Attractors in the phase space are examined for various conditions of the parameters of the model especially by emphasizing on the damping parameters. In certain conditions, the attractor becomes a limit cycle showing the stick-slip phenomena. In this paper, not only the existence of the limit cycle but also the size of the limit cycle is examined to demonstrate the non-linear dynamics that leads the unstable state. For the two different cases of the system frequency ((1)two masses with same natural frequencies, (2) with different natural frequencies), the propensity of limit cycle is discussed in detail. The results show an important fact that it may make the system worse when too much damping is present in the only one part of the masses.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.7
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• pp.502-509
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• 2002

A two-degree of freedom model Is suggested to understand the basic dynamical behaviors of the interaction between two masses of the friction induced vibration system. The two masses may be considered as the pad and the dusk of the brake. The phase space analysis is performed to understand complicated dynamics of the non-linear model. Attractors in the phase space are examined for various conditions of the parameters of the model especially by emphasizing on the damping parameters. In certain conditions, the attractor becomes a limit cycle showing the stick-slip phenomena. In this Paper, not only titre existence of the limit cycle but also the sloe of the limit cycle is examined to demonstrate the non-linear dynamics that leads the unstable state. For the two different cases of the system frequency[(1) Two masses with same natural frequencies, (2) with different natural frequencies] . the propensity of limit cycle Is discussed In detail. The results show an important fact that it may make the system worse when too much damping Is present in the only one part of the masses.

• Journal of the Korea Institute of Military Science and Technology
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• v.11 no.4
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• pp.159-165
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• 2008

The purpose of this paper is to study the impact of concentrated nonlinearities, freeplays, on the aeroelastic behaviors of single- and double-folded control fins. The nonlinearities may cause limit cycle oscillation(LCO) below the linear flutter boundary. The effects of nonlinear hinges on LCO characteristics of the fins are examined as flight condition changes. Nonlinear time-domain flutter analyses are performed, using ZAERO. The results show that the aeroelastic stability boundaries of double-folded fin(DF) are higher than those of the single-folded fin(SF) and the lower hinge freeplay impact more critically on the stability than the upper hinge freeplay of the DF.

• Journal of KSNVE
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• v.8 no.6
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• pp.1144-1149
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• 1998

A two degree-of-freedom model of suspended cables is studied for forced resonant response. The method of averaging is used to obtain first-order approximations to the response of the system. A bifurcation analysis of the averaged system is performed in the case of 2-to-1 internal resonance. Nonlinear coupled-mode motions are found to bifurcate from single-mode responses and further bifurcate to limit cycle motions via Hopf bifurcations. The limit cycle solutions undergo period doubling bifurcations to chaos.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.21 no.4
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• pp.47-52
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• 2013

In this paper, limit cycle flutter induced by Hopf bifurcation is studied with nonlinear system analysis approach and observed for the critical slowing down phenomenon. Considering an attractor of the dynamics of a system, when a small perturbation is applied to the system, the dynamics converge toward the attractor at some rate. The critical slowing down means that this recovery rate approaches zero as a parameter of the system varies and the size of the basin of attraction shrinks to nil. Consequently, in the pre-bifurcation regime, the recovery rates decrease as the system approaches the bifurcation. This phenomenon is one of the features used to forecast bifurcation before they actually occur. Therefore, studying the critical slowing down for limit cycle flutter behavior would have potential applicability for forecasting those types of flutter. Herein, modeling and nonlinear system analysis of the 2D airfoil with torsional nonlinearity have been discussed, followed by observation of the critical slowing down phenomenon.

• Journal of Electrical Engineering and Technology
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• v.1 no.1
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• pp.80-84
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• 2006

The sustained oscillation of rotor speed is often experienced in PWM inverter induction motor (IM) drive systems. In this paper the oscillation is investigated from the point of view of Hopf bifurcation theory. The sufficient and necessary conditions for existence of limit cycle are introduced to determine the bifurcation set in the stator voltage versus stator frequency plane. According to the conditions it is clarified that the bifurcation set inherently exists in the instable operation of IM. Moreover, it is numerically shown that the V/f curve can be adjusted to stabilize the sustained oscillation of rotor speed.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.98.1-98
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• 2002

In principle, a resonance type sensor generally has an oscillation characteristic. Thus, an analysis on transient oscillation response takes a great interest since it is related to the performance of resonant sensor. In particular, system bandwidth has tradeoff with oscillation accuracy, i.e. quality factor. For an efficient analysis of the oscillation characteristic, several analytic methods are introduced and summarized. The results are fundamentally based on the classical describing function method, but can explain the transient oscillation by introducing time varying concept about the predicted limit cycle. After introducing those methods, the application results to the specified system...

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.255-261
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• 2002

A four-degree of freedom model is suggested to understand the basic dynamical behaviors of the normal interaction between two masses of the friction induced normal vibration system. The two masses may be considered as the pad and the disk of the brake. The phase space analysis is performed to understand complicated in-plane dynamics of the non-linear model. Attractors in the phase space are examined for various conditions of the parameters. In certain conditions, the attractor becomes a limit cycle showing the stick-slip phenomena. In this paper, on the basis of the in-plane motion not only the existence of the limit cycle but also the size of the limit cycle is examined o demonstrate the non-linear dynamics that leads the unstable state and then the normal vibration is investigated as the state of the in-plane motion For only one case of the system frequency(two masses with same natural frequencies), the propensity of the normal vibration is discussed in detail. The results show an important fact that it may be not effective when too much damping is present in the only one part of the masses.

• Journal of Power Electronics
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• v.17 no.3
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• pp.686-694
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• 2017

Due to the wide use of electronic products, digitally controlled DC-DC converters are attracting more and more attention in recent years. However, digital control strategies may introduce undesirable Limit Cycle Oscillation (LCO) due to quantization effects in the Analog-to-Digital Converter (ADC) and Digital Pulse Width Modulator (DPWM). This results in decreases in the quality of the output voltage and the efficiency of the system. Meanwhile, even if the resolution of the DPWM is finer than that of the ADC, LCO may still exist due to improper parameters of the digital compensator. In order to discover how LCO is generated, the state space averaging model is applied to derive equilibrium equations of a digital PID controlled DC-DC converter in this paper. Furthermore, the influences of the parameters of the digital PID compensator, and the resolutions of the ADC and DPWM on LCO are studied in detail. The amplitude together with the period of LCO as well as the corresponding PID parameters are obtained. Finally, MATLAB/Simulink simulations and FPGA verifications are carried out and no-LCO conditions are obtained.