• 대한조선학회논문집
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• 제52권3호
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• pp.222-235
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• 2015

The purpose of this study is to suggest guidelines for riser fatigue analysis in terms of selection of reasonable analysis method. Three analysis methods (spectral, regular wave, rain-flow counting) are introduced and compared. As the riser systems give non-linear response, the time-domain analysis method is more preferred than frequency-domain analysis method. The spectral fatigue analysis method, however, is still useful for identifying fatigue prone areas. Once stress RAO is established, fatigue damage can be calculated very quickly. The regular wave method and the rain-flow counting method are more time consuming but give more exact results compare to spectral method. In case of regular wave method, a set of regular waves which represent random sea states is considered for dynamic analysis. The rain-flow counting method is the most intuitive and exact method because it refers time history stresses containing most of non-linear effects of the riser system. However, it is not common for early design stage to use rain-flow counting method because of its high cost. In this study, it was confirmed that the regular wave method is the most cost effective way in specific cases. However, if the system is highly non-linear, it seems that the regular wave method gives less accurate results than rain-flow counting method. Therefore, it is imperative that the engineers select appropriate analysis method based on design stage and given engineering period. This paper also discusses the theoretical background of each calculation method and hydrodynamic aspects of marine riser systems. A steel catenary riser (SCR) line on FPSO was considered and marine dynamic program (OrcaFlex) was used for static and dynamic analysis.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 합동 추계학술대회 논문집 정보 및 제어부문
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• pp.22-25
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• 2001

In this paper, a fuzzy advance angle control method is described to drive an industrial low voltage SRM (Switched Reluctance Motor) for 10kW forklift truck. SRM has a highly non-linear characteristic that is due to change the rotor and stator. And low voltage SRM is designed that its phase resistance and phase inductance is very low to inject high current into the phase windings. In this reason, the proper current control is necessary to drive the low voltage SRM efficiently. SRM has positive torque at increasing inductance region and negative torque at decreasing inductance region. Due to this reason, the current has to be built up in the increasing phase inductance part as soon as possible. Therefore, the phase switch must be turned on before the phase inductance increases, and this angle is called as the advance angle. Also, the phase current has to be dropped before the phase inductance decreases. Fuzzy logic is a flexible and general-purposed method of implementing non-linear functions and as such it is useful in control applications. Consequently, we designed a fuzzy advance angle controller to control the phase current appropriately.

• Journal of Advanced Marine Engineering and Technology
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• 제36권4호
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• pp.527-532
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• 2012

최근 복잡해지고 다양해지는 전력계통의 고신뢰성 운용을 위하여 근래에는 고속 고기능이 첨가된 지능형 보호 IED의 적용이 확산되고 있다. 이와 같이 전력계통의 운용에 있어서 보호 IED의 필요성이 증대되고 있으나, 실제 보호 IED의 운용에 있어서는 몇 가지 문제점이 노출되어 있는데, 과부하 상태가 일정하지 않은 상태에서 동작특성의 문제점 즉, 과부하상태에서 그 크기가 변동될 경우 트립 직전의 크기로만 동작시간을 판별하고, 과부하 상태와 정상상태가 반복되는 상태에서는 경우에 따라 부동작하는 기존 보호 IED의 문제점과 비선형 부하의 사용 증가로 전원 계통에서 유입되는 다양한 고조파에 대한 대책을 요구하고 있다. 그러므로 본 연구에서는 이러한 문제점들에 대한 해결 방안을 제시하고자 한다.

• 생명과학회지
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• 제13권5호
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• pp.751-755
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• 2003

Cyclic AMP receptor proteins(CRP) activate many genes in Escherichia coli by binding of cAMP with not fully known mechanism. CRP existed as apo-CRP in the absence of cAMP, $CRP;(cAMP)_2$$_2$ at low(micromolar) cAMP concentration, or $CRP;(cAMP)_4$ at high(millimolar) concentration of cAMP. This study is designed to measure the thermal stability of S83G CRP, which substituted glycine for serine at amino acid 83 position, with CD spectrapolarimeter at 222nm by the constant elevation of temperature from $20^{\circ]C\; to\; 90^{\circ}C\; at\; 1^{\circ}C/min$. The non-linear regression analysis showed that melting temperatures were 68.4, 72.0, and $82.3^{\circ}C$ for no cAMP, 0.1mM cAMP, and 5mM cAMP, respectively. Result showed the strong thermal stability of CRP by binding of additional cAMP molecules to region between the hinge region and helix-turn-helix(HTH) motif at 5mM cAMP concentration.

• Bulletin of the Korean Chemical Society
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• 제34권8호
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• pp.2358-2366
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• 2013

Iron oxide (ferrihydrite, hematite, and magnetite) coated silica gels were prepared using a low-cost, easily-scalable and straightforward method as the adsorbent material for arsenic removal application. Adsorption of the anionic form of arsenic oxyacids, arsenite ($AsO^{2-}$) and arsenate ($AsO{_4}^{3-}$), onto hematite coated silica gel was fitted against non-linear 3-parameter-model Sips isotherm and 2-parameter-model Langmuir and Freundlich isotherm. Adsorption kinetics of arsenic could be well described by pseudo-second-order kinetic model and value of adsorption energy derived from non-linear Dubinin-Radushkevich isotherm suggests chemical adsorption. Although arsenic adsorption process was not affected by the presence of sulfate, chloride, and nitrate anions, as expected, bicarbonate and silicate gave moderate negative effects while the presence of phosphate anions significantly inhibited adsorption process of both arsenite and arsenate. When the actual efficiency to remove arsenic was tested against 1 L of artificial arsenic-contaminated groundwater (0.6 mg/L) in the presence competing anions, the reasonable amount (20 g) of hematite coated silica gel could reduce arsenic concentration to below the WHO permissible safety limit of drinking water of $10{\mu}g/L$ without adjusting pH and temperature, which would be highly advantageous for practical field application.

• Steel and Composite Structures
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• 제32권5호
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• pp.657-670
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• 2019

This paper proposes a one-dimensional fiber beam element model taking account of materially non-linear behavior, benefiting the highly efficient elastic-plastic analysis of girders with shear-lag effects. Based on the displacement-based fiber beam-column element, two additional degrees of freedom (DOFs) are added into the proposed model to consider the shear-lag warping deformations of the slabs. The new finite element (FE) formulations of the tangent stiffness matrix and resisting force vector are deduced with the variational principle of the minimum potential energy. Then the proposed element is implemented in the OpenSees computational framework as a newly developed element, and the full Newton iteration method is adopted for an iterative solution. The typical materially non-linear behaviors, including the cracking and crushing of concrete, as well as the plasticity of the reinforcement and steel girder, are all considered in the model. The proposed model is applied to several test cases under elastic or plastic loading states and compared with the solutions of theoretical models, tests, and shell/solid refined FE models. The results of these comparisons indicate the accuracy and applicability of the proposed model for the analysis of both concrete box girders and steel-concrete composite girders, under either elastic or plastic states.

• Computers and Concrete
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• 제23권2호
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• pp.81-95
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• 2019

The unexpected seismic interaction of dry-assembled precast concrete frame structures typical of the European heritage with their precast cladding panels brought to extensive failures of the panels during recent earthquakes due to the inadequateness of their connection systems. Following this recognition, an experimental campaign of cyclic and pseudo-dynamic tests has been performed at ELSA laboratory of the Joint Research Centre of the European Commission on a full-scale prototype of precast structure with vertical and horizontal cladding panels within the framework of the Safecladding project. The panels were connected to the frame structure by means of innovative arrangements of fastening systems including isostatic, integrated and dissipative. Many of the investigated configurations involved a strong frame-cladding interaction, modifying the structural behaviour of the frame turning it into highly non-linear since small deformation. In such cases, properly modelling the connections becomes fundamental in the framework of a design by non-linear dynamic analysis. This paper presents the peculiarities of the numerical models of precast frame structures equipped with the various cladding connection systems which have been set to predict and simulate the experimental results from pseudo-dynamic tests. The comparison allows to validate the structural models and to derive recommendations for a proper modelling of the different types of existing and innovative cladding connection systems.

• Geomechanics and Engineering
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• 제32권3호
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• pp.335-346
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• 2023

For structures with underground basement walls, the soil-structure-interaction between the side soil and the walls affects the response of the system. There is interest in quantifying the relationship between the lateral earth pressure and the wall displacement using p-y curves. To date, passive p-y curves in available limited studies were assumed elastic-perfectly plastic. In reality, the relationship between earth pressure and wall displacement is complex. This paper focuses on studying the development of passive p-y curves behind rigid walls supporting granular soils. The study aims at identifying the different components of the passive p-y relationship and proposing a rigorous non-linear p-y model in place of simplified elastic-plastic models. The results of the study show that (1) the p-y relationship that models the stress-displacement response behind a rigid basement wall is highly non-linear, (2) passive p-y curves are affected by the height of the wall, relative density, and depth below the ground surface, and (3) passive p-y curves can be expressed using a truncated hyperbolic model that is defined by a limit state passive pressure that is determined using available logarithmic spiral methods and an initial slope that is expressed using a depth-dependent soil stiffness model.

• Steel and Composite Structures
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• 제44권6호
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• pp.867-882
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• 2022

Predicting the compressive strength of concrete (CSoC) is of high significance in civil engineering. The CSoC is a highly dependent and non-linear parameter that requires powerful models for its simulation. In this work, two novel optimization techniques, namely evaporation rate-based water cycle algorithm (ER-WCA) and equilibrium optimizer (EO) are employed for optimally finding the parameters of a multi-layer perceptron (MLP) neural processor. The efficiency of these techniques is examined by comparing the results of the ensembles to a conventionally trained MLP. It was observed that the ER-WCA and EO optimizers can enhance the training accuracy of the MLP by 11.18 and 3.12% (in terms of reducing the root mean square error), respectively. Also, the correlation of the testing results climbed from 78.80% to 82.59 and 80.71%. From there, it can be deduced that both ER-WCA-MLP and EO-MLP can be promising alternatives to the traditional approaches. Moreover, although the ER-WCA enjoys a larger accuracy, the EO was more efficient in terms of complexity, and consequently, time-effectiveness.

• 한국멀티미디어학회논문지
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• 제17권2호
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• pp.113-123
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• 2014

Electrophysiological recordings are considered a reliable method of assessing a person's alertness. Sleep medicine is asked to offer objective methods to measure daytime alertness, tiredness and sleepiness. As EEG signals are non-stationary, the conventional method of frequency analysis is not highly successful in recognition of alertness level. In this paper, EEG signals have been analyzed using wavelet transform as well as discrete wavelet transform and classification using statistical classifiers such as euclidean and mahalanobis distance classifiers and a promising method SVM (Support Vector Machine). As a result of simulation, the average values of accuracies for the Linear Discriminant Analysis (LDA)-Quadratic, k-Nearest Neighbors (k-NN)-Euclidean, and Linear SVM were 48%, 34.2%, and 86%, respectively. The experimental results show that SVM classification method offer the better performance for reliable classification of the EEG signal in comparison with the other classification methods.