• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.39 no.11
• /
• pp.1163-1173
• /
• 1990

In the stability analysis of a synchronous motor, the considerations of the initial conditions, that is, field application points and the determination techniques of stability regions to assure stable operations over four quadrants are very important. In this paper, Lyapunov stability regions obtained from a newly proposed algorithm with Lyapunov function of simple type on the basis of numerical analysis method are shown to be true stability regions which can accurately pull in within 2 (rad) after field application.

• 제어로봇시스템학회:학술대회논문집
• /
• 1988.10a
• /
• pp.210-213
• /
• 1988

By using Lyapunov method, sufficient conditions for linear time-varying continuous-time and discrete-time systems to be stable are presented under the assumption that the systems are slowly time-varying. Though it is not simple to find the stability regions immediately, one could find practical and large stability regions by constructing an appropriate algorithm.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.34 no.11
• /
• pp.430-435
• /
• 1985

Using the constructive algorithm proposed by Brayton and Tong, we analyze the stability of a modified coupled-form digital filter with quantization and overflow nonlinearities, and find the regions in the parameter plane where the filter is globally asymptotically stable. In these regions, the absence of zero-input limit cycles is ensured. This constructive algorithm gives less conservative stability results than the application of Jury-Lee stability criterion does.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.24 no.4
• /
• pp.430-437
• /
• 2018

For a ship navigating in waves, added resistance, sway force and yaw moment due to waves differ from still water conditions, which affects the maneuverability of the ship. Therefore, it is important to estimate the sway force and yaw moment generated by waves. In this study, numerical simulations were carried out to calculate the hydrodynamic forces acting on a barge in still water and waves using CFD. Based on the results, the characteristics of course stability of a barge were investigated and analyzed. The hydrodynamic forces acting on the barge in waves were stronger than in still water, and it was confirmed that hydrodynamic forces become greater as wavelength becomes longer. In long wavelength regions, the (-) value of the yaw damping lever was larger than in still water. However, in short wavelength regions and when wavelength coincided with the length of the ship, values were smaller than in still water. In this region, it can be assumed that course stability improved. In other words, in long wavelength regions, the course stability of the barge was worse than in still water and short wavelength regions. Therefore, attention is required for safe navigation in long wavelength regions.

• Journal of Mechanical Science and Technology
• /
• v.20 no.6
• /
• pp.874-881
• /
• 2006

Combustion stability characteristics in actual full-scale combustion chamber of a rocket engine are investigated by experimental tests with the model (sub-scale) chamber. The present hot-fire tests adopt the combustion chamber with three configurations of triplet impinging-jet injectors such as F-O-O-F, F-O-F, and O-F-O configurations. Combustion stability bound-aries are obtained and presented by the parameters of combustion-chamber pressure and mixture (oxidizer/fuel) ratio. From the experimental tests, two instability regions are observed and the pressure oscillations have the similar patterns irrespective of injector configuration. But, the O-F-O injector configuration shows broader upper-instability region than the other configurations. To verify the instability mechanism for the lower and upper instability regions, air-purge acoustic test is conducted and the photograph or the flames is taken. As a result, it is found that the pressure oscillations in the two regions can be characterized by the first impinging point of hydraulic jets and pre-blowout combustion, respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.05a
• /
• pp.877-882
• /
• 2005

Dynamic stability of an axially accelerating beam stucture is investigated in this paper. The equations of motion of a fixed-free beam are derived using the hybrid deformation variable method and the assumed mode method. Unstable regions due to periodical acceleration are obtained by using the Floquet's theory. Stability diagrams are presented to illustrate the influence of the dimensionless acceleration, amplitude, and frequency. Also, buckling occurs when the acceleration exceeds a certain value. It is found that relatively targe unstable regions exist around the first bending natural frequency, twice the first bending natural frequency, and twice the second bending natural frequency. The validity of the stability diagram is confirmed by direct numerical integration of the equations of motion.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.9 s.102
• /
• pp.1053-1059
• /
• 2005

Dynamic stability of an axially accelerating beam structure is investigated in this paper. The equations of motion of a fixed-free beam are derived using the hybrid deformation variable method and the assumed mode method. Unstable regions due to periodical acceleration are obtained by using the Floquet's theory. Stability diagrams are presented to illustrate the influence of the dimensionless acceleration, amplitude, and frequency. Also, buckling occurs when the acceleration exceeds a certain value. It is found that relatively large unstable regions exist around the first bending natural frequency, twice the first bending natural frequency, and twice the second bending natural frequency. The validity of the stability diagram is confirmed by direct numerical integration of the equations of motion.

• Mass Spectrometry Letters
• /
• v.6 no.3
• /
• pp.59-64
• /
• 2015

Quadrupole ion trap mass analyzer with a simplified geometry, namely, the cylindrical ion trap (CIT), has been shown to be well-suited using in miniature mass spectrometry and even in mass spectrometer arrays. Computation of stability regions is of particular importance in designing and assembling an ion trap. However, solving CIT equations are rather more difficult and complex than QIT equations, so, analytical and matrix methods have been widely used to calculate the stability regions. In this article we present the results of numerical simulations of the physical properties and the fractional mass resolutions m/Δm of the confined ions in the first stability region was analyzed by the fifth order Runge-Kutta method (RKM5) at the optimum radius size for both ion traps. Because of similarity the both results, having determining the optimum radius, we can make much easier to design CIT. Also, the simulated results has been performed a high precision in the resolution of trapped ions at the optimum radius size.

• Journal of the Korean Society of Combustion
• /
• v.22 no.1
• /
• pp.46-52
• /
• 2017

High-frequency combustion instabilities may occur during the development of feasible engine combustors. These instabilities can result in irreparable damages to the wall of combustors or the degradation of engine performance. So, it is essential to identify injectors that have high stability characteristics during the early stages of development. The objective of present study was to assess the stability of coaxial injectors and an impinging injector with different recess lengths in order to develop stable injectors optimally. Stability margin was evaluated based on the distance from operating condition to the unstable regions. A simulating combustion test method was used to analyze the stability of injectors. A small-scale combustion chamber was designed to simulate the first tangential acoustic mode of the actual combustor. Gaseous oxygen and a mixture of methane and propane were used as simulant propellants to satisfy their flow similarity to the actual propellants of a combustor in a liquid rocket combustor. The results indicated that injectors having small recess lengths showed relatively large combustion stability margins. For the injectors of large recess lengths, instability regions with large and super-large amplitude oscillations were observed. Thus, injector with shorter recess lengths had a higher stability than that of longer one due to the different mixing processes.

• International Journal of Control, Automation, and Systems
• /
• v.5 no.6
• /
• pp.707-711
• /
• 2007

An observer-based fault tolerant control (FTC) method is proposed for constrained switched systems (CSS) with input constraints. A family of Lyapunov-based bounded controllers are designed to ensure that, whenever actuator faults occur at the dwell time period of each continuous mode, the mode is always within its corresponding stability region. A set of switching laws are designed to guarantee the asymptotic stability of the overall CSS. The fixed stability regions on which the FTC method is based are also relaxed by the proposed variable stability regions. An example of CPU processing illustrates the effectiveness of proposed method.