• Journal of the Korean Institute of Telematics and Electronics
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• v.8 no.3
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• pp.1-14
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• 1971

A relay servo, one of the nonlinear sytsems, is inherently compact compared to a linear system for an equivalent control problem. The power element or actuator is not adjusted proportionally in accordance with an error signals but rather is switched abruptly between several discrete conditions. Usually switched conditions are off, full, forward or full reverse. The relay system is a particularly simple and compact one, but probably more effort has been expended on its analysis and design than on all other systems together. Early studies in the art were made by Goldfarb, austin, Oppelt and Kochenburger on the describing function method, which can be used as an approximate check on the stability of the system. The describing function method is based on the assumption that any periodic wave could be approximated as a fundamental one in wide ranges of practical applications. A relay servo system usually operates on a limit cycle condition as the loop gain increases. The stability analysis compensation or any improvement effort based on the describing function method sometimes may present considerable discrepancies on physically realized practical systems. An approach to exact periodic solutions of a relay servo system is much important for the analysis, design and system improvement. This paper dells with periodic solutions of a relay servo system on the basis of describing function and generalized chopper wave form which is composed of infinite number of harmonic series. Various ways of graphical representation were attempted to get periodic solutions, some of which have shown its validity in rapid approach to exact solutions and also in judgement of system behavior.

• Journal of Pharmaceutical Investigation
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• v.39 no.3
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• pp.185-199
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• 2009

Using a strain-controlled rheometer [Advanced Rheometric Expansion System (ARES)], the steady shear flow properties and the dynamic viscoelastic properties of $Antiphlamine-S^{(R)}$ lotion have been measured at $20^{\circ}C$ (storage temperature) and $37^{\circ}C$ (body temperature). In this article, the temperature dependence of the linear viscoelastic behavior was firstly reported from the experimental data obtained from a temperature-sweep test. The steady shear flow behavior was secondly reported and then the effect of shear rate on this behavior was discussed in detail. In addition, several inelastic-viscoplastic flow models including a yield stress parameter were employed to make a quantitative evaluation of the steady shear flow behavior, and then the applicability of these models was examined by calculating the various material parameters. The angular frequency dependence of the linear viscoelastic behavior was nextly explained and quantitatively predicted using a fractional derivative model. Finally, the strain amplitude dependence of the dynamic viscoelastic behavior was discussed in full to elucidate a nonlinear rheological behavior in large amplitude oscillatory shear flow fields. Main findings obtained from this study can be summarized as follows : (1) The linear viscoelastic behavior is almostly independent of temperature over a temperature range of $15{\sim}40^{circ}C$. (2) The steady shear viscosity is sharply decreased as an increase in shear rate, demonstrating a pronounced Non-Newtonian shear-thinning flow behavior. (3) The shear stress tends to approach a limiting constant value as a decrease in shear rate, exhibiting an existence of a yield stress. (4) The Herschel-Bulkley, Mizrahi-Berk and Heinz-Casson models are all applicable and have an equivalent validity to quantitatively describe the steady shear flow behavior of $Antiphlamine-S^{(R)}$ lotion whereas both the Bingham and Casson models do not give a good applicability. (5) In small amplitude oscillatory shear flow fields, the storage modulus is always greater than the loss modulus over an entire range of angular frequencies tested and both moduli show a slight dependence on angular frequency. This means that the linear viscoelastic behavior of $Antiphlamine-S^{(R)}$ lotion is dominated by an elastic nature rather than a viscous feature and that a gel-like structure is present in this system. (6) In large amplitude oscillatory shear flow fields, the storage modulus shows a nonlinear strain-thinning behavior at strain amplitude range larger than 10 % while the loss modulus exhibits a weak strain-overshoot behavior up to a strain amplitude of 50 % beyond which followed by a decrease in loss modulus with an increase in strain amplitude. (7) At sufficiently large strain amplitude range (${\gamma}_0$>100 %), the loss modulus is found to be greater than the storage modulus, indicating that a viscous property becomes superior to an elastic character in large shear deformations.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.1
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• pp.39-58
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• 2024

Tunnel Boring Machines (TBM) use multiple disc cutters to excavate tunnels through rock. These cutters wear out due to continuous contact and friction with the rock, leading to decreased cutting efficiency and reduced excavation performance. The rock's abrasivity significantly affects cutter wear, with highly abrasive rocks causing more wear and reducing the cutter's lifespan. The Cerchar Abrasivity Index (CAI) is a key indicator for assessing rock abrasivity, essential for predicting disc cutter life and performance. This study aims to develop a new method for effectively estimating CAI using rock strength, petrological characteristics, linear regression, and machine learning. A database including CAI, uniaxial compressive strength, Brazilian tensile strength, and equivalent quartz content was created, with additional derived variables. Variables for multiple linear regression were selected considering statistical significance and multicollinearity, while machine learning model inputs were chosen based on variable importance. Among the machine learning prediction models, the Gradient Boosting model showed the highest predictive performance. Finally, the predictive performance of the multiple linear regression analysis and the Gradient Boosting model derived in this study were compared with the CAI prediction models of previous studies to validate the results of this research.

• Journal of the Korean Geosynthetics Society
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• v.10 no.2
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• pp.21-28
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• 2011

Several theoretical soil nonlinear models to predict damping ratio, which is one of the typical dynamic properties of soils, it is impractical to predict damping ratio. The resonant column and torsional shear test(RC-TS) is used to represent the dynamic behavior of soils from intermediate to medium shear strains. A limitation of RC-TS is measure precise shear strain in large strains and the modified equivalent radius($R_{eq}$) was obtained using both modified hyperbolic model and Ramberg-Osgood model. Bonneville clays were tested using RC-TS test to obtain rotation and torque. The measured rotation and torque were then compared with calculated rotation and torque using curve-fitting method. Then, the nonlinear soil model parameters were obtained and the equivalent radius was calculated using the model parameters.

• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.1
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• pp.62-68
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• 2012

Steady-State Visually Evoked Potentials (SSVEP) are natural response signal associated with the visual stimuli with specific frequency. By using SSVEP, occipital lobe region is electrically activated as frequency form equivalent to stimuli frequency with bandwidth from 3.5Hz to 75Hz. In this paper, we propose an experimental paradigm for analyzing EEGs based on the properties of SSVEP. At first, an experiment is performed to extract frequency feature of EEGs that is measured from the image-based visual stimuli associated with specific objective with affordance and object-related affordance is measured by using mirror neuron system based on the frequency feature. And then, linear discriminant analysis (LDA) method is applied to perform the online classification of the objective pattern associated with the EEG-based affordance data. By using the SSVEP measurement experiment, we propose a Brain-Computer Interface (BCI) system for recognizing user's inherent intentions. The existing SSVEP application system, such as speller, is able to classify the EEG pattern based on grid image patterns and their variations. However, our proposed SSVEP-based BCI system performs object pattern classification based on the matters with a variety of shapes in input images and has higher generality than existing system.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.5
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• pp.18-29
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• 2007

The main objective of this paper is to propose a new stability analysis method for a networked control system with multiple packet transmission. The new scheduling method that can guarantee the maximum time delay and discrete switch state equation model which represent a network data loss is proposed. The equivalent model of a MIMO(multi-input multi-output) networked control system is derived from a state space model of linear time invariant interconnected systems in the form of asynchronous dynamical system. Using this model, this paper presents new stability theorems that can determine stability of the networked control system with regard to time delay, data loss, and the number of transmission packets. Simulation results verify the effectiveness of proposed stability analysis method.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.11
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• pp.1543-1550
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• 2015

Ferroresonance is a non-linear vibrational phenomenon that is generated by the electrical interaction of the inductance component with the capacitor component of a certain capacitance as the device of the inductance component such as a transformer is saturated due to the degradation, the waveform distortion of current and voltage, and the oscillation of overcurrent and overvoltage in a system. Recently, ferroresonance was generated from the waveform distortion of current and voltage, or the overvoltage or undervoltage phenomenon caused by the nature of an electrical power system and design technology of the transformer in the three phase transformer system. Hence, in general, ferroresonance analyzed by converting to the LC equivalent circuit. However, in general, the aforementioned analytical method only applies to the resonance phenomenon that is generated by the interaction of the capacitance of bussbar and grounding, and switching as the capacitor component with PT and the transformer as the inductance component in a system. Subsequently, the condition where ferroresonance was generated since overvoltage was supplied as line voltage to the phase voltage and thus the iron core is saturated due to the interconnection between grounded and ungrounded systems could not be analyzed when single phase PT was connected in a ${\Delta}$/Y connection system. In this study, voltage swell in the configuration of grounded circuit of a step-up transformer with the ${\Delta}-{\Delta}$ connection linked to PT for control power and the ferroresonance generated by overvoltage when the line voltage of the ${\Delta}-{\Delta}$ connection was connected to the phase voltage of the grounded Y-Y connection were analyzed using PSCAD / EMTDC through the failure case of the transformer caused by ferroresonance in the system with the ${\Delta}-{\Delta}$/Y-Y connection, and subsequently, the preventive measure of ferroresonance was proposed.

• Composites Research
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• v.18 no.4
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• pp.14-20
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• 2005

To determine the effect of chemical structure of aromatic amino curing agents on thermal and mechanical properties, standard epoxy resin DGEBF (diglycidylether of bisphenol F) was cured with diaminodiphenyl methane (DDM) and diaminodiphenyl sulphone (DDS) in a stoichiometrically equivalent ratio. From this work the effect of aromatic amino curing agents on the thermal and mechanical properties is significantly influenced by the chemical structure of curing agents. In contrast, the results show that the DGEBF/DDS system having the sulfone structure between the benzene rings had higher values in the thermal stability, density, shrinkage ($\%$), thermal expansion coefficient, tensile modulus and strength, flexural modulus and strength than the DGEBF/DDM system having methylene structure between the benzene rings, whereas the DGEBF/DDS system presented low values in maximum exothermic temperature, conversion of epoxide, and grass transition temperature. These results are caused by the relative effects of sulfone group having strong electronegativity and methylene group having (+) repulsive property. The result of fractography shows that the grain distribution of DGEBF/DDS system is more irregular than that of the DGEBF/DDM system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.1
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• pp.82-90
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• 2013

In this paper, conducted emission from the MDS(Motor Drive System) of a HEV/EV was analyzed using high- frequency circuit modeling in system-level approach. The conducted emission by PWM process can cause RFI(radio- frequency interference) problems in the AM/FM frequency range. In order to mitigate this conducted emission, a high-frequency equivalent circuit model is proposed by analyzing the fundamental circuits, parasitic components in their parts and connections and non-linear characteristics of IGBTs, high-power capacitors, inverters, motors, high-power cables, and bus bars which are composed of the MDS. It is confirmed that the simulated result by the proposed model is well agreed with measured results in spite of a large-scaled analysis in system level. We are looking forward that this approach can be effectively used in the EMC design of HEV/EV.

• Journal of Navigation and Port Research
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• v.26 no.3
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• pp.281-288
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• 2002

It might be true that both experimental and analytic techniques have been developed in the vibration analysis end engineering. It could not be said, however, that the experimental method has been also developed as much as analytic method, such as Finite Element Method One of the reason is that computation time becomes longer and that the solution often diverges depending on the choice of initial value in solving nonlinear equation. The equation in experimental modal analysis is usually composed of the nonlinear term of natural frequency and modal damping ratio, and the linear one of equivalent stiffness. In this study, the nonlinear terms were solved first, and then the linear term was obtained. The experimental modal parameters were estimated, applying the developed experimental modal analysis curve-fitting method to the super-structure model. In addition, the number of modes and modal damping ratio could be easily determined by the developed program with the application of graphical techniques and with easy handling button.