• Transactions on Electrical and Electronic Materials
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• v.11 no.5
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• pp.216-221
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• 2010

The microstructure, electrical properties, and DC-accelerated aging behavior of the Zn-Pr-Co-Cr-Y-Er (ZPCC-YE) varistors were investigated for different amounts of erbium oxide ($Er_2O_3$). The microstructure consisted of zinc oxide grain and an intergranular layer ($Pr_6O_{11}$, $Y_2O_3$, and $Er_2O_3$-rich phase) as a secondary phase. The increase of $Er_2O_3$ amount decreased the average grain size and increased the sintered density. As the $Er_2O_3$ amount increased, the breakdown field increased from 5094 V/cm to 6966 V/cm and the nonlinear coefficient increased from 27.8 to 45.1. The ZPCC-YE varistors added with 0.5 to 1.0 mol% $Er_2O_3$ are appropriate for high voltage, with high nonlinearity and stability against DC-accelerated aging stress.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.3
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• pp.276-282
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• 2013

This paper proposes an ultrasonic method for measurement of linear and hysteretic interfacial stiffness of contacting surfaces between two steel plates subjected to nominal compression pressure. Interfacial stiffness was evaluated by the reflection and transmission coefficients obtained from three consecutive reflection waves from solid-solid surface using the shear wave. A nonlinear hysteretic spring model was proposed and used to define the quantitative interfacial stiffness of interface with the reflection and transmission coefficients. Acoustic model for 1-D wave propagation across interfaces is developed to formulate the reflection and transmission waves and to determine the linear and nonlinear hysteretic interfacial stiffness. Two identical plates are put together to form a contacting surface and pressed by bolt-fastening to measure interfacial stiffness at different states of contact pressure. It is found from experiment that the linear and hysteretic interfacial stiffness are successfully determined by the reflection and transmission coefficient at the contact surfaces through ultrasonic pulse-echo measurement.

• International Journal of Precision Engineering and Manufacturing
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• v.7 no.2
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• pp.56-59
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• 2006

A vibrational model of powder transfer equipment based on the lumped parameter method was developed, in which the operating motion consists of surging, bouncing, and pitching. After decoupling the equation of motion, the vibrational excitation source of the pitching motion was removed. So the designers are able to plan the optimum design to adjust the motion trajectory of the powder transfer equipment. That is, a procedure to adjust the motion trajectory of powder transfer equipment by changing design specifications such as the installation position, the direction of the motor, the driving speed, the mass unbalance, the stiffness coefficient, and the installation position of the support spring, is presented in this paper. The powder transfer equipment manufactured according to the results of this study did not suffer fatigue destruction, since the maximum stress on the basket structure was sufficiently small.

• Journal of Ocean Engineering and Technology
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• v.10 no.1
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• pp.108-118
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• 1996

This paper presents automatic reentry of a deepsea reser by adaptive control. Reentry is one of the major pro blems regarding a deepsea riser. In the reentry operation, the lower end of riser must be accurately positioned over the tarket point on the seabed. But the deepsea riser shows complex elastic response due to flexibility and nonlinearity of the riser dynamics and the required positioning accuracy is high. Moreover, elastic deformation must by controlled for securing structural integrity. In adaptive control, uncertainly known parameters like added mass and drag coefficient in the riser dynamics are identified and control forces at the floating body and the riser are calculated simultaneously. An Adaptive algorithm for MIMO linear discrete time system without requiring a persistent excitation is adopted in this study. The effectiveness of adaptive control logic is tested by numerical simulation and model experiment. The designed control system shows good overall performances, so that the present study can be applied to the control of the deepsea riser.

• Journal of KSNVE
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• v.9 no.6
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• pp.1218-1226
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• 1999

In this paper, the extended Biot's semilinear model was developed. Combining the extended Biot model with the dynamic equation yields the nonlinear wave equation in poproelastic sound absorbing materials. Both perturbation and matching techniques are used to find solutions for nonlinear wave equations. By comparing results between linear and nonlinear wave solutions, characteristics of nonlinear waves in poroelastic sound abosrbing materials have been studied. Nonlinear waves were found to be attenuated faster than the linear ones. A maximum amplitude of the nonlinear wave occurred near its surface boundaries and decay quickly with distance from the surface. It has also been found that, if the amplitudes of linear waves are known at the surface boundaries, those of nonlinear ones can be determined. This will be the basis of finding effects of nonlinearity on the absorption coefficient and the transmission loss.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.565-570
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• 2001

Vehicle dynamics control (VDC) system requires more information on driving conditions compared with ABS and/or TCS. In order to develop the VDC system, tire slip angles, vehicle side-slip angle, and vehicle lateral velocity as well as road friction coefficient are needed. Since there are not any cheap and reliable sensors, recent researches on parameter estimation have given rise to a number of parameter estimation techniques. This paper presents new vehicle model to estimate vehicle's yaw rate. This model is improved from the conventional 2 degrees of freedom vehicle model, so-called bicycle model, taking nonlinear effects into account. These nonlinear effects are: (i) tyre nonlinearity; (ii) lateral load transfer during cornering; (iii) variable gear ratio with respect to vehicle velocity. Estimation results are validated with the experimental results.

• Bulletin of the Society of Naval Architects of Korea
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• v.8 no.2
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• pp.25-34
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• 1971

The characters of linear response of ship among irregular waves were researched. But nonlinear characters of ship motion in irregular waves have not been considered. Then the author showed a method to linearize nonlinearity of damping coefficient of ship by making statistically equivalent linear theory and get equivalent gain K from the condition that the difference of variance between linear response and approximate response is minimum and show that the results of correlogram and spectrum, obtained from this method, for model 700 GT Ferry boat agree with the actual response. The author pays a particular attention not to the nonlinear element but to nonlinear system itself.

• Journal of Korea Water Resources Association
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• v.32 no.4
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• pp.447-455
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• 1999

In this study, the Bragg resonant of cnoidal waves propagating over a sinusoidally varying topography lying on a uniformly sloping beach is investigated. The governing equations derived from the Boussinesq equations are numerically integrated. The effects of fast varying terms and nonlinearity in reflection coefficients are also examined. Variation of reflection coefficient for different sloping beaches is studied. It is found that reflection coefficients are not strongly dependent on slopes of beaches.

• Journal of the Earthquake Engineering Society of Korea
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• v.19 no.4
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• pp.183-194
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• 2015

In this paper, Nonlinear Static Pushover analysis method(NSP) is proposed which apply to RC buildings reinforced by external retrofit for seismic performance. Based on previous analysis and research, NSP is more developed by connection nonlinearity according to shear resistance mechanism such as dowel and adhesive resistance as major shear resistance elements. According to the proposed method, structural analysis for example buildings was carried out to evaluate seismic performance of buildings. And, it was confirmed that depending on shear strain and characteristics of joint resistant of external retrofitting are different from internal retrofitting. Furthermore, the strength reduction coefficient of the anchor needs to be considered at the joint design.

• Bulletin of the Korean Chemical Society
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• v.19 no.7
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• pp.738-742
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• 1998

A new polyamide was prepared from 4,4'-(hexafluoroisopropylidene)di-aniline and 4-[NN-bis(2-carboxyethyl)] amino-4'-nitrostilbene. This polymer was cast into thin films by spin coating cyclohexanone solution. After being poled, the electro-optic coefficients of electrode poled polymer films were measured by the reflection measurement technique using an incident laser beam of 1.3 Jim. The film poled at the field strength of 1.2 V/μm exhibited the electro-optic coefficient (r33) of 5.9 pm/V. The relaxation behavior of the poled polymer film was compared with other reported polymers bearing the same NLO chromophores. Due to stiff and highly polar nature of the backbone and also due to formation of interchain hydrogen bonds, this polymer reveals a slower relaxation characteristics. The polymer is amorphous and soluble in various organic solvents.