• Geomechanics and Engineering
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• 제32권6호
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• pp.553-566
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• 2023

A circular tank foundation resting on the ground and subjected to axisymmetric horizontal and vertical loads and moments is analyzed using the variational principles of mechanics. The circular foundation is assumed to behave as a Kirchhoff plate with in-plane and transverse displacements. The soil beneath the foundation is assumed to be a multi-layered continuum in which the horizontal and vertical displacements are expressed as products of separable functions. The differential equations of plate and soil displacements are obtained by minimizing the total potential energy of the plate-soil system and are solved using the finite element and finite difference methods following an iterative algorithm. Comparisons with the results of equivalent two-dimensional finite element analysis and other researchers establish the accuracy of the method.

• 산업융합연구
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• 제20권12호
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• pp.59-70
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• 2022

본 연구는 동일한 시장정보에 대하여 이익과 손실이라는 회계정보의 특성차이에 따라 회계이익에 반영되는 민감도가 차별적인지를 검증하였다. 이를 위해 Basu의 조건부 보수주의 측정치 및 Ball and Shivakumar의 보수주의 측정치를 활용하여 2012년부터 2020년까지 유가증권시장 및 코스닥시장에 상장된 비금융 상장기업 11,462개의 기업-연도별 자료를 분석대상으로 시장정보와 회계정보의 조합에 따라 회계이익 민감도를 분석하였다. 연구결과 경제적 이익에 대하여 이익기업과 손실기업 모두 지연 인식하는 것으로 나타난 반면, 경제적 손실에 대하여 손실기업은 신속하게 인식하고, 이익기업은 지연 인식하는 경향이 있음을 확인하였다. 이익기업과 비교하여 손실기업은 경제적 이익을 지연 인식하는 반면, 경제적 손실은 조기 인식함으로써 더욱 엄격한 보수주의가 적용되는 것을 확인하였다. 손실기업은 시장정보에 민감하게 반응하는 반면, 이익기업은 시장정보에 민감하게 반응하지 않음을 검증함으로써 시장정보와 회계정보의 결합효과와 비대칭적 적시성 간의 인과성에 대한 실증자료를 제공하고 있다.

• 한국융합학회논문지
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• 제13권1호
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• pp.341-348
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• 2022

본 연구는 KONEX에 상장된 기업의 회계 보수성을 분석하였다. 기존의 회계 보수성에 관해 분석한 연구는 유가증권시장(KOSPI)이나 코스닥시장(KOSDAQ)을 대상으로 한 분석 결과를 제시한다. 그러나 2013년 7월, 우리나라는 KONEX라는 새로운 상장시장을 개설하였고, 이후 KONEX는 중소기업의 자금조달 가능성을 높이고자 운영되고 있다. 그러나 KONEX에 관한 연구는 상대적으로 활발하게 이뤄지지 않고, 현재 진행된 선행연구 역시 이익조정에 초점을 맞추어 있는 실정에, 본 연구는 회계정책의 하나인 회계 보수성을 분석한다는 점에서 선행연구와 차별성이 있다. 이를 위해 2014년부터 2020년까지를 분석 기간으로 설정하고 회계 보수성을 측정하기 위해 비대칭적 적시성 모형인 Basu(1997)와 Ball and Shivakumar(2005)의 연구모형을 이용하여 실증 분석하였다. 분석 결과, KONEX 시장에서도 조건적 보수주의가 확인되었다. 즉, 호재와 비교하여 악재의 적시성이 높음을 확인할 수 있었다. 이에 더하여 실시한 감사인의 규모에 따라 KONEX 기업의 보수성의 차이에 관한 분석 결과에서는 유의한 차이를 확인할 수 없었다. 본 연구는 KONEX 시장을 대상으로 회계정책을 분석하였다는 데 기존 연구를 확대하였다.

• 대한화학회지
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• 제56권6호
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• pp.720-724
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• 2012

Under pseudo-first order conditions, the monomeric species of Cr(VI) was found to be kinetically active in the absence of phenanthroline (phen) whereas in the phen-promoted path, the Cr(VI)-phen complex undergoes a nucleophilic attack by etane-1,2-diol to form a ternary complex which subsequently experience a redox decomposition leading to hydroxy ethanal and Cr(III)-phen complex. The effect of the cationic surfactant (CPC), anionic surfactant (SDS) and neutral surfactant (TX-100) on the unpromoted and phen-promoted path have been studied. Micellar effects have been explained by considering the preferential partitioning of reactants between the micellar and aqueous phase. Combination of TX-100 and phenanthroline will be the ideal for chromic acid oxidation of ethane-1,2-diol in aqueous media.

• Smart Structures and Systems
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• 제16권4호
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• pp.593-606
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• 2015

This paper presents a novel concept of healing some of the damages in wind turbine blades (WTBs) such as cracks and delamination. This is achieved through an inherent functioning autonomous repairing system. Such wind turbine blades have the benefit of reduced maintenance cost and increased operational period. Previous techniques of developing autonomous healing systems uses hollow glass fibres (HGFs) to deliver repairing fluids to damaged sites. HGFs have been reported with some limitations like, failure to fracture, which undermines their further usage. The self-healing technique described in this paper represents an advancement in the engineering of the delivery mechanism of a self-healing system. It is analogous to the HGF system but without the HGFs, which are replaced by multiple hollow channels created within the composite, inherently in the FRP matrix at fabrication. An in-house fabricated NACA 4412 WTB incorporating this array of network hollow channels was damaged in flexure and then autonomously repaired using the vascular channels. The blade was re-tested under flexure to ascertain the efficiency of the recovered mechanical properties.

• 비파괴검사학회지
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• 제26권6호
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• pp.390-402
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• 2006

The elastic properties and thickness of mullite environmental barrier coatings grown through chemical vapor deposition (CVD) on silicon carbide substrates were measured using frequency domain photoacoustic microscopy. In this technique, extremely narrow bandwidth surface acoustic waves are generated with an amplitude modulated laser source. A photorefractive crystal based interferometer is used to detect the resulting surface displacement. The complex displacement field is mapped as a function of source-to-receiver distance in order to extract the wavelength of the surface acoustic wave at a given excitation frequency, and the phase velocity is determined. The coatings tested exhibited spatial variations in thickness and mechanical properties. The measured surface wave dispersion curves were used to extract an effective value for the elastic modulus and the coating thickness. Nanoindentation was used to validate the measurements of the effective elastic modulus. The average elastic modulus measured through the coating thickness using nanoindentation is compared to the effective modulus found using the photoacoustic system. Optical microscopy is used to validate the thickness measurements. The results indicate that the photoacoustic microscopy technique can be used to estimate the effective elastic properties in coatings exhibiting spatial inhomogeneities, potentially providing valuable feedback for the optimization of the CVD growth process.

• Plant Biotechnology Reports
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• 제4권2호
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• pp.173-178
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• 2010

An efficient protocol for shoot regeneration was developed for sesame (Sesamum indicum L.) internodes using the transverse thin cell layer (tTCL) culture method. The frequency of shoot regeneration and the number of adventitious buds produced from regenerated shoots depend significantly on explant age, thickness of the tTCL sections, and the phytohormones supplemented to the culture medium. A combination of 6-benzyladenine (2.0 $mg\;l^{-1}$) and a-naphthaleneacetic acid (0.5 $mg\;l^{-1}$) was found to be the best phytohormone combination for shoot bud induction, with the maximum number of shoots obtained when the tTCL sections were 0.5-1.0 mm thick and derived from 4- to 6-week-old seedlings of sesame. Well-developed shoots were rooted on MS medium without phytohormones, and 80% of the regenerated plantlets were successfully established in soil.

• Smart Structures and Systems
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• 제3권1호
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• pp.23-49
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• 2007

Wavelet transforms are the emerging signal-processing tools for damage identification and time-frequency localization. A small perturbation in a static or dynamic displacement profile could be captured using multi-resolution technique of wavelet analysis. The paper presents the wavelet analysis of damaged linear structural elements using DB4 or BIOR6.8 family of wavelets. Starting with a localized reduction of EI at the mid-span of a simply supported beam, damage modeling is done for a typical steel and reinforced concrete beam element. Rotation and curvature mode shapes are found to be the improved indicators of damage and when these are coupled with wavelet analysis, a clear picture of damage singularity emerges. In the steel beam, the damage is modeled as a rotational spring and for an RC section, moment curvature relationship is used to compute the effective EI. Wavelet analysis is performed for these damage models for displacement, rotation and curvature mode shapes as well as static deformation profiles. It is shown that all the damage indicators like displacement, slope and curvature are magnified under higher modes. A localization scheme with arbitrary location of curvature nodes within a pseudo span is developed for steady state dynamic loads, such that curvature response and damages are maximized and the scheme is numerically tested and proved.

• Structural Monitoring and Maintenance
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• 제4권2호
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• pp.115-131
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• 2017

Classical flutter of wind turbine blades indicates a type of aeroelastic instability with fully attached boundary layer where a torsional blade mode couples to a flapwise bending mode, resulting in a mutual rapid growth of the amplitudes. In this paper the monitoring problem of onset of flutter is investigated from a detection point of view. The criterion is stated in terms of the exceeding of a defined envelope process of a specific maximum torsional vibration threshold. At a certain instant of time, a limited part of the previously measured torsional vibration signal at the tip of blade is decomposed through the Empirical Mode Decomposition (EMD) method, and the 1st Intrinsic Mode Function (IMF) is assumed to represent the response in the flutter mode. Next, an envelope time series of the indicated modal response is obtained in terms of a Hilbert transform. Finally, a flutter onset criterion is proposed, based on the indicated envelope process. The proposed online flutter monitoring method provided a practical and direct way to detect onset of flutter during operation. The algorithm has been illustrated by a 907-DOFs aeroelastic model for wind turbines, where the tower and the drive train is modelled by 7 DOFs, and each blade by means of 50 3-D Bernoulli-Euler beam elements.

• Smart Structures and Systems
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• 제18권4호
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• pp.683-705
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• 2016

A semi-active algorithm for edgewise vibration control of the spar-type floating offshore wind turbine (SFOWT) blades, nacelle and spar platform is developed in this paper. A tuned mass damper (TMD) is placed in each blade, in the nacelle and on the spar to control the vibrations for these components. A Short Time Fourier Transform algorithm is used for semi-active control of the TMDs. The mathematical formulation of the integrated SFOWT-TMDs system is derived by using Euler-Lagrangian equations. The theoretical model derived is a time-varying system considering the aerodynamic properties of the blade, variable mass and stiffness per unit length, gravity, the interactions among the blades, nacelle, spar, mooring system and the TMDs, the hydrodynamic effects, the restoring moment and the buoyancy force. The aerodynamic loads on the nacelle and the spar due to their coupling with the blades are also considered. The effectiveness of the semi-active TMDs is investigated in the numerical examples where the mooring cable tension, rotor speed and the blade stiffness are varying over time. Except for excessively large strokes of the nacelle TMD, the semi-active algorithm is considerably more effective than the passive one in all cases and its effectiveness is restricted by the low-frequency nature of the nacelle and the spar responses.