• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1560-1565
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• 2003

Tapping mode atomic force microscopy (TM-AFM) utilizes the dynamic response of a resonating probe tip as it approaches and retracts from a sample to measure the topography and material properties of a nanostructure. We present recent results based on nonlinear dynamical systems theory, computational continuation techniques and detailed experiments that yield new perspectives and insight into AFM. A dynamic model including van der Waals and Derjaguin-Muller-Toporov (DMT) contact forces demonstrates that periodic solutions can be represented with respect to the approach distance and excitation frequency. Turning points on the surface lead to hysteretic amplitude jumps as the tip nears/retracts from the sample. Experiments are performed using a tapping mode tip on a graphite sample to verify the predictions.

• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1246-1257
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• 2004

The objective of this paper is to characterize dynamic pressure traces measured at self-excited combustion instabilities occurring in two combustion systems of different hardware. One system is a model lean premixed gas turbine combustor and the other a fullscale bipropellant liquid rocket thrust chamber. It is commonly observed in both systems that low frequency waves at around 300㎐ are first excited at the onset of combustion instabilities and after a short duration, the instability mode becomes coupled to the resonant acoustic modes of the combustion chamber, the first longitudinal mode for the lean premixed combustor and the first tangential mode for the rocket thrust chamber. Low frequency waves seem to get excited at first since flame shows the higher heat release response on the lower frequency perturbations with the smaller phase differences between heat release and pressure fluctuations. Nonlinear time series analysis of pressure traces reveals that even stable combustion might have chaotic behavior with the positive maximum Lyapunov exponent. Also, pressure fluctuations under combustion instabilities reach a limit cycle or quasi-periodic oscillations at the very similar run conditions, which manifest that a self-excited high frequency instability has strong nonlinear characteristics.

• Journal of Korean Association for Spatial Structures
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• v.10 no.4
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• pp.133-140
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• 2010

This paper studies on the instability behaviour of the Seoul southwest baseball dome. The nonlinear Snapping phenomenon of the structure is investigated about the load mode by the design load of analysis structure and these combined loads. The initial imperfection obtains the buckling mode through the eigenvalue analysis of the tangential stiffness matrix and uses this for the nonlinear analysis. However, the buckling of members or the local buckling, and etc don't consider in the research range of this research task. Also it is limited the overall buckling phenomenon.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.2
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• pp.49-58
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• 1997

The objective of this study is to investigate effects of prebuckling on the bucking of laminated compostie cylindrical shells, Both axial compression and lateral pressure are considered for laminated composite cylindrical shells with length to radius ratios. The shell walls are made of a laminate with several symmetric ply orientations. The study was using finite difference energy method, utilizing the nonlinear bifurcation branch with nonlinear prebuckling displacements. The results are compared to the buckling loads determined when membrane prebuckling displacements are considered.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.693-696
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• 1999

This paper presents an analysis of the chaotic behavior in the discrete-time chaotic generator fabricated by CMOS technology. An approximated empirical equation is extracted from the measurement data of a nonlinear function block. Then the bifurcation diagram and Lyapunov exponent and time waveforms and frequency responses of the chaotic generator are calculated and simulated. And results of experiments in the chaotic circuit with the $\pm$2.5V power supply and clock rate of 10KHz are shown, and analysed.

• Journal of Korean Association for Spatial Structures
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• v.4 no.3 s.13
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• pp.103-109
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• 2004

The lowest load when the equilibrium condition becomes to be unstable is defined as the buckling load. The primary objective of this paper is to be analyse stability boundaries for star dome under combined loads and is to investigate the iteration diagram under the independent loading parameter. In numerical procedure of the geometrically nonlinear problems, Arc Length Method and Newton-Raphson iteration method is used to find accurate critical point(bifurcation point and limit point). In this paper independent loading vector is combined as proportional value and star dome was used as numerical analysis model to find stability boundary among load parameters and many other models as multi-star dome and arch were studied. Through this study we can find the type of buckling mode and the value of buckling load.

• Journal of the Korean Vacuum Society
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• v.21 no.5
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• pp.249-257
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• 2012

Nonlinear dynamical behaviors of plasma in the Pierce diode are investigated by a numerical code developed using a one dimensional fluid model. The plasma in Pierce diode is alternately stable and unstable as Pierce parameter is changed. The dynamical characteristics of neutral and non-neutral Pierce system is examined analytically and numerically. It alternately has growing and oscillatory mode as Pierce parameter varies. As Pierce parameter is decreased, each oscillatory mode undergoes a sequence of subharmonic period-doubling bifurcation and then culminate in a chaotic strange attractor. The analysis for this nonlinear behavior can be used as a model for understanding of beam-plasma interaction in more complex geometries and a data for chaos control.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.3
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• pp.55-62
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• 2000

This paper presents an analysis of the chaotic behavior in the discrete-time voltage mode chaotic generator fabricated using 0.8${\mu}{\textrm}{m}$ single poly CMOS technology. An approximated empirical equation is extracted from the measurement data of a nonlinear function block. Then the bifurcation diagram is simulated according to input variables and Lyapunov exponent λ which represent a dependence on an initial value is calculated. We show the interrelations among time waveforms, state transition, and power spectra for the state condition of chaotic circuit, such as equilibrium, periodic, and chaotic state. And results of experiments in the chaotic circuit with the $\pm$2.5V power supply and sampling clock frequency of 10KHz are shown and compared with the simulated results.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.1
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• pp.65-72
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• 1994

Collapse characteristics of thin-walled hatted section tubes are investigated. The square section members with flanges are substituted by the equivalent rectangular tube. The stiffening effects of flanges are transformed to the restraining plate with the equivalency of buckling strength. The square tubes of single-hatted and double-hatted sections are investigated. The double-hatted section members show symmetric and antisymmetric crushing modes depending on the stiffness of flanges. The single-hatted section members show only symmetric modes. The bifurcation point of the compact crushing modes are investigated by experiments and shown almost same thickness-width ratio of the rectangular tubes. A large maximum crippling strength can be obtained by double-hatted section members with proper flange dimensions.

• Journal of Power Electronics
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• v.4 no.4
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• pp.197-204
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• 2004

Two-stage Power-Factor-Correction (PFC) converters are the most common circuits for drawing sinusoidal and in phase current waveforms from an ac source with a good regulated output voltage. The first stage is a boost PFC converter with average-current-mode control for achieving the near-unity power factor and the second stage is a forward converter with voltage-mode control to regulate the output voltage. Stability analysis and design methods of two-stage PFC converters have previously been discussed using linear models. Recently, new nonlinear phenomena have been detected in pre-regulator boost PFC circuits and a new nonlinear model has been proposed for pre-regulated PFC converters. Therefore, investigation of two-stage PFC converters from the nonlinear viewpoint becomes important because the second stage DC/DC converter adds more complexity to the circuit. So, this paper introduces a study of the stability of two-stage PFC converters. A novel nonlinear model of two-stage PFC converters is proposed. Then, a stability analysis is made based upon this nonlinear model. The high correspondence between the simulated and experimental results confirms our analysis.