• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.1
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• pp.53-64
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• 2011

The present study considers multi-level approach for the analysis of parametric roll phenomena. Three kinds of computation method, GM variation, impulse response function (IRF), and Rankine panel method, are applied for the multi-level approach. IRF and Rankine panel method are based on the weakly nonlinear formulation which includes nonlinear Froude-Krylov and restoring forces. In the computation result of parametric roll occurrence test in regular waves, IRF and Rankine panel method show similar tendency. Although the GM variation approach predicts the occurrence of parametric roll at twice roll natural frequency, its frequency criteria shows a little difference. Nonlinear roll motion in bichromatic wave is also considered in this study. To prove the unstable roll motion in bichromatic waves, theoretical and numerical approaches are applied. The occurrence of parametric roll is theoretically examined by introducing the quasi-periodic Mathieu equation. Instability criteria are well predicted from stability analysis in theoretical approach. From the Fourier analysis, it has been verified that difference-frequency effects create the unstable roll motion. The occurrence of unstable roll motion in bichromatic wave is also observed in the experiment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.9
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• pp.776-782
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• 2002

The microstructure, V-Ι characteristics, and stability of ZnO-P $r_{6}$ $O_{11}$ CoO-C $r_2$ $O_3$- $Y_2$ $O_3$-based varistor ceramics were investigated with cooling rate in the range of 2~8$^{\circ}C$/min. The cooling rate relatively weakly affected the microstructure, the varistor voltage, and the leakage current in the V-Ι characteristics. But the nonlinear exponent relatively strongly affected by cooling rate. The cooling rate also greatly affected the stability of V-Ιand dielectric characteristics for DC accelerated aging stress. On the whole, the varistors cooled with 4$^{\circ}C$/fin exhibited the highest performance in the densification, nonlinearity, and stability. Especially, they exhibited a high stability, in which the variation rate of the varistor voltage( $V_{1㎃}$), the nonlinear exponent($\alpha$), and the dissipation factor(tan $\delta$) is -1.4%, -4.9%, and ＋60.0%, respectively, under DC accelerated aging stress such as 0.95 $V_{1㎃}$15$0^{\circ}C$/12 h)

• Nuclear Engineering and Technology
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• v.53 no.12
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• pp.4179-4188
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• 2021

This study identifies efficient earthquake intensity measures (IMs) for seismic performances and fragility evaluations of the reactor containment building (RCB) in the advanced power reactor 1400 (APR1400) nuclear power plant (NPP). The computational model of RCB is constructed using the beam-truss model (BTM) for nonlinear analyses. A total of 90 ground motion records and 20 different IMs are employed for numerical analyses. A series of nonlinear time-history analyses are performed to monitor maximum floor displacements and accelerations of RCB. Then, probabilistic seismic demand models of RCB are developed for each IM. Statistical parameters including coefficient of determination (R²), dispersion (i.e. standard deviation), practicality, and proficiency are calculated to recognize strongly correlated IMs with the seismic performance of the NPP structure. The numerical results show that the optimal IMs are spectral acceleration, spectral velocity, spectral displacement at the fundamental period, acceleration spectrum intensity, effective peak acceleration, peak ground acceleration, A95, and sustained maximum acceleration. Moreover, weakly related IMs to the seismic performance of RCB are peak ground displacement, root-mean-square of displacement, specific energy density, root-mean-square of velocity, peak ground velocity, Housner intensity, velocity spectrum intensity, and sustained maximum velocity. Finally, a set of fragility curves of RCB are developed for optimal IMs.

• Bulletin of the Korean Chemical Society
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• v.32 no.5
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• pp.1625-1629
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• 2011

Kinetic studies of the reactions of O,O-diphenyl Z-S-aryl phosphorothioates with X-benzylamines have been carried out in dimethyl sulfoxide at 55.0 $^{\circ}C$. The Hammett (log $k_2$ vs ${\sigma}_X$) and Bronsted [log $k_2$ vs $pK_a(X)$] plots for substituent X variations in the nucleophiles are biphasic concave downwards with a maximum point at X = H, and the unusual positive ${\rho}_X$ and negative ${\beta}_X$ values are obtained for the strongly basic benzylamines. The sign of the cross-interaction constant (${\rho}_{XZ}$) is negative for both the strongly and weakly basic nucleophiles. Greater magnitude of ${\rho}_{XZ}$ value is observed with the weakly basic nucleophiles (${\rho}_{XZ}$ = -2.35) compared to with the strongly basic nucleophiles (${\rho}_{XZ}$ = -0.03). The deuterium kinetic isotope effects ($k_H/k_D$) involving deuterated benzylamines [$XC_6H_4CH_2ND_2$] are primary normal ($k_H/k_D$ > 1). The proposed mechanism is a concerted $S_N2$ involving a frontside nucleophilic attack with a hydrogen bonded, four-center-type transition state for both the strongly and weakly basic nucleophiles. The unusual positive ${\rho}_X$ and negative ${\beta}_X$ values with the strongly basic benzylamines are rationalized by through-space interaction between the ${\pi}$-clouds of the electron-rich phenyl ring of benzylamine and the phenyl ring of the leaving group thiophenoxide.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.6
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• pp.459-479
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• 2014

This paper considers experimental and numerical studies on added resistance in waves. As the numerical methods, three different methods, strip method, Rankine panel method and Cartesian-grid method, are applied. The computational results of vertical motion response and added resistance are compared with the experimental data of Series 60($C_B=0.8$) hull, S175 containership and KVLCC2 hull. To investigate the influence of above-still water hull form, a Rankine panel method is extended to two nonlinear methods: weakly-nonlinear and weak-scatterer approaches. As nonlinear computational models, three ships are considered: original KVLCC2 hull, 'Ax-bow' and 'Leadge-bow' hulls. Two of the three models are modified hull forms of original KVLCC2 hull, aiming the reduction of added resistance. The nonlinear computational results are compared with linear results, and the improvement of computational result is discussed. As experimental approach, a series of towing-tank experiment for ship motions and added resistance on the three models (original KVLCC2 hull, 'Ax-bow' and 'Leadge-bow') are carried out. For the original KVLCC2 hull, uncertainty analysis in the measurement of vertical motion response and added resistance is performed in three waves conditions: ${\lambda}/L=0.5$, 1.1, 2.0. From the experimental results, the effects of hull form on added resistance are discussed.

• Earthquakes and Structures
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• v.9 no.1
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• pp.73-91
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• 2015

The effectiveness of tuned mass dampers (TMDs) in reducing the seismic response of civil structures is still a debated issue. The few studies regarding TMDs on inelastic structures indicate that they would perform well under moderate earthquake loading, when the structure remains linear or weakly nonlinear, while tending to fail under severe ground shaking, when the structure experiences strong nonlinearities. TMD seismic efficiency should be therefore rationally assessed by considering to which extent moderate and severe earthquakes respectively contribute to the expected cost of damages and losses over the lifespan of the structure. In this paper, a method for evaluating, in a life-cycle cost (LCC) perspective, the seismic effectiveness of TMDs on inelastic building structures is presented and exemplified on the SAC LA 9-storey steel moment-resisting frame benchmark building. Results show that the LCC concept may provide an appropriate alternative to traditional performance criteria for the evaluation of the effectiveness of TMDs and that TMD installation on typical existing middle-rise buildings in high seismic hazard regions may significantly reduce building lifetime cost despite the poor control performance observed under the most severe seismic events.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.51.2-51.2
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• 2016

Hayabusa, the Japanese asteroid sample returning mission, acquired more than 1400 scientific images of its target asteroid (25143) Itokawa using the Asteroid Multi-band Imaging Camera (AMICA). It took images at a wide coverage of the phase angle a (Sun-Itokawa-Hayabusa) from $a{\sim}0^{\circ}$ to ${\sim}35^{\circ}$, providing a unique opportunity for studying the opposition effect (a sharp surge in brightness of asteroidal surface). Here we present a study of the opposition effect on Itokawa using the AMICA multi-band data. We found that (1) the opposition strength near the opposition is independent of the incident/emission angles of the light, also (2) it weakly depends on the wavelength showing the strongest surge around 0.7 um, and (3) the reflectance increases linearly at a>$1.5^{\circ}$ while nonlinearly at a<$1.5^{\circ}$ as approaching the opposition point. In particular, we noticed that the increasing rate has a correlation with the reflectance in the nonlinear domain whereas no detectable correlation with the reflectance in the linear domain. From these results, we conjecture that the coherent backscattering opposition effect is a dominant mechanism for the nonlinear opposition surge at a<$1.5^{\circ}$ while shadow hiding opposition effect is responsible for the linear opposition surge at a>$1.5^{\circ}$.

• Journal of Korea Water Resources Association
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• v.38 no.6 s.155
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• pp.429-438
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• 2005

In this study, a couple of ordinary differential equations which can describe random waves are derived from the Boussinesq equations. Incident random waves are generated by using the TMA(TEXEL storm, MARSEN, ARSLOE) shallow-water spectrum. The governing equations are integrated with the 4-th order Runge-Kutta method. By using newly derived wave equations, nonlinear energy interaction of propagating waves in constant depth is studied. The characteristics of random waves propagate over a sinusoidally varying topography lying on a sloping beach are also investigated numerically. Transmission and reflection of random waves are considerably affected by nonlinearity.

• Communications of the Korean Mathematical Society
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• v.26 no.4
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• pp.695-708
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• 2011

Based on the multiple-time-scale (MTS) method, a general formula has been presented for solving an n-th, n = 2, 3, ${\ldots}$, order ordinary differential equation with strong linear damping forces. Like the solution of the unified Krylov-Bogoliubov-Mitropolskii (KBM) method or the general Struble's method, the new solution covers the un-damped, under-damped and over-damped cases. The solutions are identical to those obtained by the unified KBM method and the general Struble's method. The technique is a new form of the classical MTS method. The formulation as well as the determination of the solution from the derived formula is very simple. The method is illustrated by several examples. The general MTS solution reduces to its classical form when the real parts of eigen-values of the unperturbed equation vanish.

• Journal of applied mathematics & informatics
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• v.27 no.1_2
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• pp.59-68
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• 2009

In this paper we present an iterative scheme for finding a common element of the set of zero points of accretive mappings and the set of fixed points of nonexpansive mappings in Banach spaces. By using viscosity approximation methods and under suitable conditions, some strong convergence theorems for approximating to this common elements are proved. The results presented in the paper improve and extend the corresponding results of Kim and Xu [Nonlinear Anal. TMA 61 (2005), 51-60], Xu [J. Math. Anal. Appl., 314 (2006), 631-643] and some others.