• International Journal of Control, Automation, and Systems
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• v.4 no.4
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• pp.506-515
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• 2006

This paper studies an intelligent digital control for nonlinear systems with multirate sampling. It is worth noting that the multirate control design is addressed for a given nonlinear system represented by Takagi-Sugeno (T-S) fuzzy models. The main features of the proposed method are that i) it is provided that the sufficient conditions for stabilization of the discrete-time T-S fuzzy system in the sense of Lyapunov stability criterion, which is can be formulated in the linear matrix inequalities (LMIs); and ii) the stability properties of the trivial solution of the digital control system can be deduced from that of the solution of its discretized versions. An example is provided for showing the feasibility of the proposed method.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.2 no.1
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• pp.78-82
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• 2002

In this paper, we have studied a numerical stability analysis method for the robust fuzzy feedback linearization regulator using Takagi-Sugeno fuzzy model. To analyze the robust stability, we assume that uncertainty is included in the model structure with known bounds. For these structured uncertainty, the robust stability of the closed system is analyzed by applying Linear Matrix Inequalities theory following a transformation of the closed loop systems into Lur'e systems.

• Transactions on Control, Automation and Systems Engineering
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• v.4 no.4
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• pp.356-362
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• 2002

In this paper, well-known Takagi-Sugeno fuzzy model is used as the nonlinear plant model and uncertainty is assumed to be included in the model structure with known bounds. Based on the fuzzy models, a numerical robust stability analysis for the fuzzy feedback linearization regulator is presented using Linear Matrix Inequalities (LMI) Theory. For these structured uncertainty, the closed system can be cast into Lur'e system by simple transformation. From the LMI stability condition for Lur'e system, we can derive the robust stability condition for the fuzzy feedback linearization regulator based on Takagi-Sugeno fuzzy model. The effectiveness of the proposed analysis is illustrated by a simple example.

• International Journal of Aeronautical and Space Sciences
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• v.2 no.2
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• pp.82-94
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• 2001

The purpose of this paper is to analyze the static and dynamic stability-of the unmanned airship under development ; the target airship's over-all length of hull is 50m and the maximum diameter is 12.5m. For the analysis, the dynamic model of an airship was defined and both the nonlinear and linear dynamic equations of motion were derived. Two different configuration models (KA002Y and KA003Y) of the airship were used for the target model of the static stability analysis and the dynamic stability analysis. From the result of analyses, though the airship is unstable in static stability, dynamic characteristics of the airship can provide the stable dynamic stability. All of the results, airship models and dynamic flight equations will be an important basement and basic information for the next step of developing the automatic flight control system(AFCS) and the stability augmentation system(SAS) for the unmanned airship as well as for the stratospheric airship in the future.

• Nuclear Engineering and Technology
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• v.31 no.6
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• pp.572-585
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• 1999

The characteristics of two-phase flow instability in a vertical boiling channel connecting with an unheated riser are investigated through the linear stability analysis model. Various two-phase flow models, including thermal non-equilibrium effects, are taken into account for establishing a physical model in the time domain. A classical approach to the frequency response method is adopted for the stability analysis by employing the D-partition method. The adequacy of the linear model is verified by evaluating experimental data at high quality conditions. It reveals that the flow-pattern-dependent drift velocity model enhances the prediction accuracy while the homogeneous equilibrium model shows the most conservative predictions. The characteristics of density wave oscillations under low-power and low-quality conditions are investigated by devising a simple model which accounts for the gravitational and frictional pressure losses along the channel. The necessary conditions for the occurrences of type-I instability and flow excursion are deduced from the one-dimensional D-partition analysis. The parametric effects of some design variables on low quality oscillations are also investigated.

• International Journal of Control, Automation, and Systems
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• v.6 no.4
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• pp.495-505
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• 2008

This paper describes modeling Voltage Sourced Inverter (VSI) type Flexible AC Transmission System (FACTS) controllers and control methods for power system dynamic stability studies. The considered FACTS controllers are the Static Compensator (STATCOM), the Static Synchronous Series Compensator (SSSC), and the Unified Power Flow Controller (UPFC). In this paper, these FACTS controllers are derived in the current injection model, and it is applied to the linear and nonlinear analysis algorithm for power system dynamics studies. The parameters of the FACTS controllers are set to damp the inter-area oscillations, and the supplementary damping controllers and its control schemes are proposed to increase damping abilities of the FACTS controllers. For these works, the linear analysis for each FACTS controller with or without damping controller is executed, and the dynamic characteristics of each FACTS controller are analyzed. The results are verified by the nonlinear analysis using the time-domain simulation.

• Journal of the Korean Mathematical Society
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• v.35 no.2
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• pp.259-268
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• 1998

In this paper the stochastic multiple objective programming problems where the right-hand-side of the constraints is stochastic are considered. We define the equivalent scalar-valued problem and study the stability of the equivalent scalar-valued problem with respect to the weight parameters and probability mesures under reasonable assumptions.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.4
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• pp.29-37
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• 2008

Vehicle stability is a very important subject in vehicle design and control, because vehicle safety is closely dependent upon its dynamic stability. For the vehicle stability analysis, the nonlinear vehicle model of a mid-size car with three DOF - longitudinal, lateral and yaw - is employed. A rigorous method is used to determine the vehicle stability region in plane motion. An algorithm is used to materialize a topology theorem, which enables to find the exact stability region. A stability criterion for the critical cornering is proposed.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.788-791
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• 1999

In recent years, many studies have been conducted on fuzzy control since it can surpass the conventional control in several respects. In this paper, numerical stability analysis methodology for the singleton-type linguistic fuzzy control systems is proposed. The Proposed stability analysis is not the analytical method but the numerical method using the convex optimization technique of Quadratic Programming (QP) and Linear Matrix Inequalities (LMI).

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.33 no.4
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• pp.455-463
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• 2023

Objectives: The aim of this study was to develop an air sampling and analytical method for estimating worker exposure to linear carbonate solvents and to evaluate the method. Methods: The target substances were three linear carbonates: DMC, DEC, EMC. GC/FID was used for sample analysis. Laboratory experiments were conducted to determine desorption solvents and sample capacity, and to evaluate storage stability, accuracy, and precision. Results: Coconut Shell Charcoal (CSC, 100/50 mg) was used as the air sampling media, and a desorption solvent of 5% methanol/95% dichloromethane was selected. Recommended sampling capacities were 1~11 ℓ for DMC, 1~18 ℓ for DEC, and 1~24 ℓ for EMC. The stability of three linear carbonates was demonstrated over 30 days in a refrigerator (4℃). Detection limits were determined as follows: DMC 0.26 ㎍/sample, DEC 0.24 ㎍/sample, and EMC 0.25 ㎍/sample. The total coefficient of variation was calculated as DMC 0.064, DEC 0.079, and EMC 0.07. Conclusions: This sampling and analysis method is suitable for estimating personal exposure to linear carbonates in the workplace.