• Journal of ILASS-Korea
• /
• v.17 no.1
• /
• pp.9-13
• /
• 2012

This study investigates experimentally evaporation characteristics of nanofluid droplets containing 50 nm alumina($Al_2O_3$) particles and the wettability changes on a hydrophilic glass surfaces. From the captured digital images by using a CMOS camera and a magnifying lens, we examined the effect of particle concentration on droplet evaporation rate which can be indirectly deduced from the measured droplet volumes varying with time. In particular, with the use of a digital image analysis technique, the present study measured droplet perimeters and the contact angles to study the wetting dynamics during evaporating process. In addition, we compared the measured total evaporation time with theoretically estimated values. It was found that as the volume fractions of nanofluid increased, the total evaporation time and the initial contact angles decreased, while the droplet perimeters increased.

• Bulletin of the Korean Chemical Society
• /
• v.20 no.12
• /
• pp.1501-1505
• /
• 1999

Expansion dynamics of C$^{+}$ ions ejected from 355-nm laser ablation of graphite target in vacuum has been investigated by pulsed-field time-of-flight (TOF) mass spectrometry. A strong nonlinear dependence of the amount of desorbed C$^{+}$ ions on laser fluence is interpreted by the mechanism that C$^{+}$ ions are produced directly from the graphite via conversion of the multiphoton energy into thermal energy. The temporal evolution of C$^{+}$ ions was measured by varying the delay time of the ion repelling pulse with respect to the laser irradiation, which provides significant information on the ablated plume characterization. The TOF distributions of ablated ions showed a bimodal shape and could be fitted by shifted Maxwell-Boltzmann distributions. The velocity of the fast component increases with the delay time, whereas the slow component (< 500 m/s) exhibits a constant velocity. Also studied were the effects of the laser fluence on the energetics of C$^{+}$ ions.

• Journal of the Institute of Convergence Signal Processing
• /
• v.9 no.1
• /
• pp.89-97
• /
• 2008

Chaotic behavior in motor systems is undesired dynamics in real-time implementation since the speed is oscillated in a wide range and the torque is changed by a random manner. We present an adaptive control approach for time-varying permanent-magnet synchronous motors (PMSM) with chaotic phenomenon. We consider that its parameters are changed randomly within certain bounds. First, a nonlinear system model of a PMSM is transformed to derive a nominal linear control strategy. Then, an auxiliary control for compensating real-time control error occurred by system perturbation due to parameter change is designed by using Lyapunov stability theory. Numerical simulation is accomplished for evaluating its efficiency and reliability comparing with the traditional control method. Additionally, we test our control method in real-time motor experiment including a PSoC based drive system to demonstrate its practical applicability.

• Journal of the Korean Society for Precision Engineering
• /
• v.12 no.4
• /
• pp.55-66
• /
• 1995

This paper presents an explicit pole-assignment adaptive servocontrol shceme and its application to cutting force regulation for feedrate maximization. The controller structure of the suggested adaptive control scheme is based on robust control theory. This controller structure is then combined with an on-line model estimation algorithm. The whole scheme is applied to a milling process control. The results of real time cutting experimental studies show that the asymptotic regulation of milling peak cutting forces can be achieved with robust- ness against the time varying perturbations to the process model parameters, which are caused by nonlinear cutting dynamics.

• 제어로봇시스템학회:학술대회논문집
• /
• 1996.10b
• /
• pp.482-485
• /
• 1996

We design a homing guidance law based on the proportional navigation for the fast-rolling, single-axis control missiles and analyse the misdistance of the designed guidance system. The guidance law includes a compensation scheme which compensates for the phase-shift between the commanded and achieved acceleration which is peculiar to the fast rolling airframe with single-axis control. In the error analysis of the guidance system, we calculate the misdistance with respect to the target maneuver on the 3-dimensional space via direct simulations. Also, we conduct adjoint simulation on the 2-dimensional plane in case that phase-shift is perfectly compensated. Finally we approximate the linear time-varying dynamics of the missile with autopilot to a linear time-invarient system, and as a result we can find the misdistance as a closed-form.

• Journal of Institute of Control, Robotics and Systems
• /
• v.18 no.5
• /
• pp.439-444
• /
• 2012

In this study, we address the formation control problem of coupled unicycle-type mobile robots, each of which can interact with its neighboring robots by communicating their position outputs. Each communication link between two mobile robots is assumed to be established according to the given time-varying interconnection topology that switches within a finite set of connected fixed undirected networks and has a non-vanishing dwell time. Under this setup, we propose a distributed formation control algorithm by using the dynamics extension and feedback linearization methods, and by employing a consensus algorithm for linear multi-agent systems which provides arbitrary fast convergence rate to the agreement of the multi-agent system. Finally, the proposed result is demonstrated through a computer simulation.

• International Journal of Control, Automation, and Systems
• /
• v.6 no.3
• /
• pp.460-466
• /
• 2008

This paper deals with the stability analysis of a missile guidance loop employing an integrated proportional navigation guidance law. The missile guidance loop is formulated as a closed-loop control system consisting of a linear time-invariant feed-forward block and a time-varying feedback gain. Based on the circle criterion, we have defined the concept of absolute stability margins and obtained the gain and phase margins for the system assuming 1 st order missile/autopilot dynamics. The correlation between the absolute stability margins and the margins derived from the frozen system analysis is also discussed.

• 한국전산유체공학회:학술대회논문집
• /
• 2011.05a
• /
• pp.458-464
• /
• 2011

A new method identifies coupled fluid-structure system with a reduced set of state variables is presented. Assuming that the structural model is known a priori either from an analysis or a test and using linear transformations between structural and aeroelastic states, it is possible to deduce aerodynamic information from sampled time histories of the aeroelastic system. More specifically given a finite set of structural modes the method extracts generalized aerodynamic force matrix corresponding to these mode shapes. Once the aerodynamic forces are known, an aeroelastic reduced-order model can be constructed in discrete-time, state-space format by coupling the structural model and the aerodynamic system. The resulting reduced-order model is suitable for constant Mach, varying density analysis.

• Journal of Mechanical Science and Technology
• /
• v.18 no.1
• /
• pp.1-11
• /
• 2004

The ionic Polymer Metal Composite (IPMC) is one of the electroactive polymers (EAP) that was shown to have potential application as an actuator It bends by applying a low voltage current (1∼3 V) to its surfaces when containing water In this paper, the basic characteristics and the static ＆ dynamic modeling of IPMC is discussed. In modeling and analysis, the equations of motion, which describe the total dynamics of the system, are driven. To control the position of the IPMC actuator, an adaptive fuzzy algorithm is used. IPMC is a time varying system because the some parameters vary with the passage of time. In this paper, the modeling and control of IPMC is introduced.

• Proceedings of the KIEE Conference
• /
• 1997.07b
• /
• pp.672-674
• /
• 1997

In this paper, we study the idle speed control of the spark ignition engine. Engine idle speed control is a difficult problem because of troublesome characteristics such as severe process nonlinearities, variable time delays, time-varying dynamics and unobservable internal system states and disturbances. We investigate the intelligent control algorithms such as neural network controller and fuzzy controller for 4-cylinder 4-stroke engine.