• International Journal of Control, Automation, and Systems
• /
• v.5 no.1
• /
• pp.1-7
• /
• 2007

In this paper, the necessary and sufficient conditions for strict positive realness of the rational transfer functions directly from basic definitions in the frequency domain are studied. A new frequency domain approach is used to check if a rational transfer function is a strictly positive real or not. This approach is based on the Taylor expansion and the Maximum Modulus Principle which are the fundamental tools in the complex functions analysis. Four related common statements in the strict positive realness literature which is appeared in the control theory are discussed. The drawback of these common statements is analyzed through some counter examples. Moreover a new necessary condition for strict positive realness is obtained from high frequency behavior of the Nyquist diagram of the transfer function. Finally a more simplified and completed conditions for strict positive realness of single-input single-output linear time-invariant systems are presented based on the complex functions analysis approach.

• Korean System Dynamics Review
• /
• v.15 no.4
• /
• pp.29-60
• /
• 2014

As every commentators has noted, bureaucratic corruption, which has complicated causes, is prevalent phenomenon in Korean society. Especially, most people realize that systemic corruption has a strong negative effect on society; however, only few studies reflect on the nature of 'systemic corruption' and it seems that no established theory explains the phenomenon. Thus, this study suggest that we look more carefully into the nature and mechanisms of 'systemic corruption'. Interdisciplinary approach based on the integrated model of structure-behavior to analyse the nature of bureaucratic corruption. The system dynamics method can test the mechanisms of 'systemic corruption'. With this way, the factors generating systemic corruption represent the relationships reinforcing and balancing within system dynamics model. This paper also consider 'isomorphism' and 'dominance' as control mechanisms to systemic corruption. From the CLD(Causal Loop Diagram), three main areas(rent in organization, networking, control mechanisms) are overlapped and it indicates dynamic relationships of systemic corruption in organizations.

• Journal of the Korean Society for Precision Engineering
• /
• v.20 no.8
• /
• pp.194-204
• /
• 2003

A Web-based dynamic simulation system, called O-DYN, for multibody dynamic systems is developed. All the interfaces of the system are accessible via Web browsers, such as Netscape or Explorer. The system uses a block-diagram type O-DYN/Modeler developed in JAVA Applet as a preprocessor. The O-DYN postprocessor composed of O-DYN/Plotter and O-DYN/Animator is developed in JAVA Applet. The O-DYN/Solver for predicting the dynamic behavior is run on the server. Anyone who wants to simulate the dynamics of multibody systems or share results data can access the analysis system over the Internet regardless of their OS, platform, or location.

• Proceedings of the KWS Conference
• /
• 2004.05a
• /
• pp.249-251
• /
• 2004

According to our fatigue tests carried out at 20 ㎐, R=0.1 on transversely butt-welded joints, fatigue strengths of as-welded specimens, that is, specimens having residual stress are higher than those of annealed specimens in short hie range, but vice verse in long life range. This behavior seems to be concerned mainly with residual stress relaxation by applied loading. After analyzing the welding process, we conducted finite element analysis to quantify the degree of residual stress relaxation. By taking into account residual stress relaxation, modified Goodman diagram, and nominal stress, we evaluated the fatigue life of the welded joint from the S-N curve for the parent material. The estimated results are in a good agreement with the experimental results.

• Computers and Concrete
• /
• v.12 no.4
• /
• pp.431-442
• /
• 2013

This study attempted to find a proper method applicable to simulating practical equifield lines of two-dimensional Accelerate Lithium Migration Technique (ALMT), and evaluate the feasibility of using the theoretical ion migration model of one-dimensional ALMT to predict the ion migration behavior of two-dimensional ALMT. The result showed that the electrolyte or carbon plate can be used as matrix to draw equifield line graph similar to that by using mortar as matrix. Using electrolyte electrode module for simulation has advantages of simple production, easy measurement, rapidness, and economy. The electrolyte module can be used to simulate the equifield line distribution diagram in practical two-dimensional electrode configuration firstly. Then, several equifield line zones were marked, and several subzones under one-dimensional ALMT were separated from various equifield line zones. The theoretical free content distribution of alkali in concrete under two-dimensional electric field effect could be obtained from duration analysis.

• Proceedings of the KSME Conference
• /
• 2000.11a
• /
• pp.274-279
• /
• 2000

The overhead transmission wires operating both at warm temperature and tighten state for a long period of time in a power transmission plant are degraded by air pollution, wind, creep and slip between steel wire and aluminium conductor. The objective of this study is to investigate a high carbon steel wire. We tested for basic mechanical properties and 3 types fatigue behavior, tension-tension, 4 points bending and 3 points bending fatigues. In this study, a conventional fatigue strengths between 4 points bending and tension-tension fatigue were determined by Gerber, Sorderberg and Goodman's theory and we investigated S-N diagram for bending and tensile loading.

• Transactions of Materials Processing
• /
• v.19 no.7
• /
• pp.393-398
• /
• 2010

This paper investigates the effect of material properties on the formability of sheet metals based on the Marciniak-Kuczynski model (M-K model). The hardening behavior of the material is modeled as the Hollomon model with the strain rate effect. The yield surfaces are constructed with Hosford79 yield function. The material properties considered in this study include the R-value, the strain hardening exponent, the strain rate hardening exponent, and the crystal structure of the material. The effect of the crystal structure on formability is roughly expressed as the change of the yield surface by varying the value of the exponent in Hosford79 yield function. Results show that the R-value affects neither the magnitude nor the shape of right hand side of forming limit diagrams (FLDs). Higher strain hardening exponent and higher strain rate hardening exponent improve the formability of sheet metals because they stabilize the forming processes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.11a
• /
• pp.498-503
• /
• 2003

Dynamic analysis of a plate with non-linearity due to large deformation is performed in the study. There have been many researches about the non-linear dynamic behavior of plates examining by means of theoretical or numerical analyses. But it is important how exactly model the actual system. In this respect, the Continuous-Time system identification technique is used to generate non-linear models, for stiffness and damping terms, to explain the observed behaviors with single mode assumptions for the simplicity after comparing the experimental results with the numerical results of a linear plate model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2011.10a
• /
• pp.602-606
• /
• 2011

In this study, operational vibration experiment and analysis have been conducted for the 4-blade small vertical-axis wind turbine (VAWT) including the effect of tower elastic behavior. Computational structural dynamics analysis method is applied to obtain Campbell diagram for the VAWT with elastic tower. An open type wind-tunnel is used to change and keep the wind velocity during the ground test. Equivalent reduced elastic tower is supported to the VAWT so that the elastic stiffness effect of the tower can be reflected to the present vibration experiment. Various excitation sources with aerodynamic forces are considered and the dominant operating vibration phenomena are physically investigated in detail.

• International Journal of Precision Engineering and Manufacturing
• /
• v.4 no.6
• /
• pp.50-60
• /
• 2003

A web-based dynamic simulation system, called O-DYN, for multibody systems is developed. All the interfaces of the system are accessible via web browsers, such as Netscape or Explorer. The system uses a block-diagram type O-DYN/Modeler developed in JAVA Applet as a preprocessor. The O-DYN postprocessor composed of O-DYN/Plotter and O-DYN/Animator is developed in JAVA Applet. The O-DYN/Solver for predicting the dynamic behavior is run on the web server. Anyone who wants to simulate the dynamics of multibody systems or share results data can access the analysis system over the internet regardless of their OS, platform, or location.