• Bulletin of the Korean Chemical Society
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• v.30 no.5
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• pp.1080-1084
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• 2009

Methyl 2,4-di-(2'-hydroxyethoxy)benzylidenecyanoacetate (3) was prepared and polymerized with terephthaloyl chloride to yield a novel Y-type polyester 4 containing 2,4-dioxybenzylidenecyanoacetate groups as NLOchromophores, which constituted parts of the polymer backbone. The resulting polymer 4 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. Polymer 4 showed thermal stability up to 280 ${^{\circ}C}$ in thermogravimetric analysis with glass-transition temperature obtained from differential scanning calorimetry near 108 ${^{\circ}C}$. The second harmonic generation (SHG) coefficient ($d_{33}$) of poled polymer films at the 1064 nm fundamental wavelength was around $3.54\;{\time}\;10^{-9}$ esu. The dipole alignment exhibited a thermal stability up to near $T_g$ and no significant SHG decay was observed below 100 ${^{\circ}C}$ due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.

• Earthquakes and Structures
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• v.9 no.5
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• pp.1029-1044
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• 2015

To investigate the seismic pounding response of long-span bridges with high-piers under strong ground motions, shaking table tests were performed on a 1/10-scaled bridge model consisting of three continuous spans with rigid frames and one simply-supported span. The seismic pounding responses of this bridge model under different earthquake excitations including the uniform excitation and the traveling wave excitations were experimentally studied. The influence of dampers to the seismic pounding effects at the expansion joints was analyzed through nonlinear dynamic analyses in this research. The seismic pounding effects obtained from numerical analyses of the bridge model are in favorable agreement with the experimental results. Seismic pounding effect of bridge superstructures is dependent on the structural dynamic properties of the adjacent spans and characteristics of ground motions. Moreover, supplemental damping can effectively mitigate pounding effects of the bridge superstructures, and reduce the base shear forces of the bridge piers.

• Journal of the Korean Institute of Gas
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• v.13 no.6
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• pp.1-8
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• 2009

This study pertains to damping device to reduce vibrational responses and shocks in multi-directions. To enhance the capability of disk spring damper which works for vertical vibration and shock, a multi-directional damper is proposed, which contains wedge system as well as disk spring stack. Wedge system converts horizontal load into vertical load. A mathematical model is proposed and investigated for the nonlinear behaviors of the disc spring damper containing wedge system. The results accord with the experimental results. Equivalent viscous damping in vertical and horizontal directions are found based upon energy dissipated.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1480-1482
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• 2005

The major causes of power quality deterioration are harmonic current through semiconductor switching device, due to use of nonlinear loads such as diodes rectifier or thyristor rectifiers. In response to this concerns, this paper presents a new control method of single-phase active power filter(APF) for the compensation of harmonic current components in nonlinear loads. In order to make the complex calculation to be possible, the single-phase system that has two phases was made by constructing a imaginary second-phase giving time delay to load currents. In the conventional method, a imaginary-phase lagged to the load current T/4(here T is the fundamental cycle) was made. But in this proposed method, the new signal, which has the delayed phase through the filter, using the phase-delay property of low-pass filter, was used as the second phase. As this control method is applied to the system of single phase, an instantaneous calculation was done rather by using the rotating reference frames that synchronizes with source-frequency than by applying instantaneous reactive power theory that uses the conventional fixed reference frames.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.764-774
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• 2002

Dynamic behaviors are analyzed for an automatic ball balancer (ABB) with triple races, which is a device to reduce the unbalanced mass of optical disk drives (ODD) such as CD-ROM or DVD drives. The nonlinear equations of motion are derived by using Lagrange's equations with the polar coordinate system. It is shown that the polar coordinate system provides the complete stability analysis while the rectangular coordinate system used in other previous studies has limitations on the stability analysis. For the stability analysis, the equilibrium positions and the linearized perturbation equations are obtained by the perturbation method. Based on the linearized equations, the stability of the system is analyzed around the equilibrium positions; furthermore, to confirm the stability, the time responses for the nonlinear equations of motion are computed by using a time integration method and experimental analyses are performed. Theoretical and experimental results show a superiority of the ABB with triple races.

• Structural Engineering and Mechanics
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• v.81 no.6
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• pp.677-689
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• 2022

Generally, the goal of seismic retrofit design of an existing structure using energy dissipation devices is to determine the optimum design parameters of a retrofit device to satisfy a specified limit state with minimum cost. However, the presence of multiple parameters to be optimized and the computational complexity of performing non-linear analysis make it difficult to find the optimal design parameters in the realistic 3D structure. In this study, genetic algorithm-based optimal seismic retrofit methods for determining the required number, yield strength, and location of steel slit dampers are proposed to retrofit an asymmetric soft first-story structure. These methods use a multi-objective and single-objective evolutionary algorithms, each of which varies in computational complexity and incorporates nonlinear time-history analysis to determine seismic performance. Pareto-optimal solutions of the multi-objective optimization are found using a non-dominated sorting genetic algorithm (NSGA-II). It is demonstrated that the developed multi-objective optimization methods can determine the optimum number, yield strength, and location of dampers that satisfy the given limit state of a three-dimensional asymmetric soft first-story structure. It is also shown that the single-objective distribution method based on minimizing plan-wise stiffness eccentricity turns out to produce similar number of dampers in optimum locations without time consuming nonlinear dynamic analysis.

• Advances in concrete construction
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• v.17 no.4
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• pp.221-232
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• 2024

As a supplemental energy dissipation device, friction dampers are widely employed to augment the behaviour of buildings under seismic forces. In the current work, a methodology for the design of the friction damping system of RC frame buildings is offered using performance-based plastic design (PBPD) method. Here 2% of maximum interstorey drift ratio for life safety (LS) level is taken into account as a target drift to estimate the design base shear. In this approach, the distribution of friction damper is determined based on the hysteretic energy demand of that storey. Two frames, five storey three bay (5S3B) and eight storey three bay (8S3B) RC frame building with and without friction damping systems are also taken up for the investigation. The suggested design approach is validated by the nonlinear time history analysis (NLTHA) procedure. Inter story drift ratio (ISDR) and storey displacement, which are the more closely related to structural damage during seismic excitation are evaluated. The results show that the friction damping system on a retrofitted RC frame building performs effectively under seismic excitations and that storey displacement and ISDR are within the limit at moderate and high seismic intensities.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.4
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• pp.353-362
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• 2020

Korea was recognized as a relatively safe area for earthquake. However, due to considerable damage to facilities caused by the earthquake in Gyeongju and Pohang, interest in the maintenance and repair of structures is increasing. So interest in vibration damping technology applicable to existing structures is also increasing. However, vibration damping technology has a problem in that its usability is reduced due to damage of the damping device when a strong earthquake occurs. Recently, in order to solve such a problem, study is being conducted to apply a superelastic shape memory alloys (SSMA) capable of recentering bracing. Therefore, in this study, nonlinear dynamic analysis is performed to evaluate the seismic performance of the buckling-restrained braced frame (BRBF) applied SSMA to bracing.

• Journal of the Korea Computer Industry Society
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• v.2 no.4
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• pp.565-572
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• 2001

At the most recent years, laser medical instruments, laser applications and laser nuclear fusion need strong visible light and ultraviolet rays. Nonlinear optical devices, such as harmonic generators and parametric oscillators, provide a means of extending the frequency range of available laser sources. Frequency conversion is a useful technique for extending the utility of high-power lasers. It utilizes the nonlinear optical response of an optical medium in intense radiation fields to generate new frequencies. These progresses have been used to generate high-power radiation in all spectral regions, from the ultraviolet to the far infrared. Optical parametric oscillators and amplifiers generate two waves of lower frequency They are capable of generating a range of wavelengths from a single frequency source, in some cases spanning the entire visible and near infrared regions. Consequently, in order to obtain the green light, the pulsed Nd:YAG laser using multiple-mesh PFN(Pulsed Forming Network) method with Nonlinear optical device was adopted. We compared the current pulseshapes with the laser output energy, and conversion efficiency.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.6
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• pp.137-146
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• 1998

Recently many devices print electronic images in a variety of ways. The reproduced color, however, is different from the original color because of the difference of hardware characteristics. To maintain device independent color, gamut mapping method is proposed. The proposed color gamut mapping uses nonlinear intensity mapping and clipping for saturation mapping on HSI color space. In the dithering operation, expanded nonlinear ordered dithering and modified error diffusion are proposed. The proposed ordered dithering uses expanded nonlinear quantization which considers overlapping phenomena of neighbored printing dots. In the modified error diffusion, quantization errors to be diffused are adjusted to improve both image blur and color change produced in the error diffusion. So, the printed image is similar to the image of monitor. Our results indicate that proposed algorithm can produce high quality image in the low bit color devices.