• Journal of the Korean Solar Energy Society
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• v.35 no.3
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• pp.9-16
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• 2015

In order to support various studies for assessment of onshore and offshore wind turbine system including foundations, the land-based version of 2MW PMSG direct drive wind turbine has been analyzed using HAWC2 that account for the coupled dynamics of the wind inflow, elasticity, and controls of the turbine. this work presents the steady-state response of the system and natural frequency of the first thirteen structure turbine modes as a function of wind speed. Rotor, generator speeds, pitch angle, power production, thrust force, deflections of tower and blade are compared for one case below and one case above the rated wind speed.

• Structural Engineering and Mechanics
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• v.70 no.3
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• pp.289-301
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• 2019

Hysteretic energy is defined as energy dissipated through inelastic deformations during a ground motion by the system. It includes frequency content and duration of ground motion as two remarkable parameters, while these characteristics are not seen in displacement spectrum. Since maximum displacement individually cannot be the appropriate criterion for damage assessment, hysteretic energy has been evaluated in this research as a more comprehensive seismic demand parameter. An innovative methodology has been proposed to establish a new equivalent linear model to estimate hysteretic energy spectrum for bilinear SDOF models under two different sets of earthquake excitations. Error minimization has been defined in the space of equivalent linearization concept, which resulted in equivalent damping and equivalent period as representative parameters of the linear model. Nonlinear regression analysis was carried out for predicting these equivalent parameter as a function of ductility. The results also indicate differences between seismic demand characteristics of far-field and near-field ground motions, which are not identified by most of previous equations presented for predicting seismic energy. The main advantage of the proposed model is its independency on parameters related to earthquake and response characteristics, which has led to more efficiency as well as simplicity. The capability of providing a practical energy based seismic performance evaluation is another outstanding feature of the proposed model.

• Advances in concrete construction
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• v.11 no.1
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• pp.1-9
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• 2021

This article discusses the issue of optimizing controller design issues, in which the artificial intelligence (AI) evolutionary bat (EB) optimization algorithm is combined with the fuzzy controller in the practical application of the building. The controller of the system design includes different sub-parts such as system initial condition parameters, EB optimal algorithm, fuzzy controller, stability analysis and sensor actuator. The advantage of the design is that for continuous systems with polytypic uncertainties, the integrated H2/H∞ robust output strategy with modified criterion is derived by asymptotically adjusting design parameters. Numerical verification of the time domain and the frequency domain shows that the novel system design provides precise prediction and control of the structural displacement response, which is necessary for the active control structure in the fuzzy model. Due to genetic algorithm (GA), we use a hierarchical conditions of the Hurwitz matrix test technique and the limits of average performance, Hierarchical Fitness Function Structure (HFFS). The dynamic fuzzy controller proposed in this paper is used to find the optimal control force required for active nonlinear control of building structures. This method has achieved successful results in closed system design from the example.

• Structural Engineering and Mechanics
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• v.77 no.3
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• pp.369-381
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• 2021

The seismic responses of elevated tanks considering liquid-structure interaction are presented under horizontal earthquake. The scaled model tank is fabricated to study the dynamic responses of anchored tank and newly designed uplift tank with replaced dampers. The natural frequencies for structural mode are obtained by modal analysis. The dynamic responses of tanks are completed by finite element method, which are compared with the results from experiment. The displacement parallel and perpendicular to the excitation direction are both gained as well as structural acceleration. The strain of tank walls and the axial strain of columns are also obtained afterwards. The seismic responses of liquid storage tank can be calculated by the finite element model effectively and the results match well with the one measured by experiment. The aim is to provide a new type of tank system with vertical constraint relaxed which leads to lower stress level. With the liquid volume increasing, the structural fundamental frequency has a great reduction and the one of uplift tank are even smaller. Compared with anchored tank, the displacement of uplift tank is magnified, the strain for tank walls and columns parallel to excitation direction reduces obviously, while the one perpendicular to earthquake direction increases a lot, but the values are still small. The stress level of new tank seems to be more even due to uplift effect. The new type of tank can realize recoverable function by replacing dampers after earthquake.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.6
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• pp.498-506
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• 2022

This study proposes a design methodology for bidirectional, series-resonant, dual-active bridge (SRDAB) converters. The circuit parameters of the SRDAB converters are designed by considering the output power and efficiency of the converter. The proposed method can be used to design a high-power, high-efficiency SRDAB converter. A voltage controller is employed to manipulate the output voltage of the converter, and the controller gains are selected using the transfer function and frequency response of the controller. Simulation results show that the output power of the designed SRDAB converter is 2 kW per converter module as designed. In addition, the performance of the voltage controller is evaluated using the simulation and experimental results. The output voltage follows the reference voltage within 10 ms under the step change of the reference command. The output voltage also follows the reference voltage under the step load change. The efficiency of the designed SRDAB converter is 95.6%.

• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.6
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• pp.237-246
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• 2022

Based on the random-vibration-theory methodology, dynamic responses of nuclear facilities subjected to obliquely incidental and incoherent earthquake ground motions are calculated. The spectral power density functions of the 6-degree-of-freedom motions of a rigid foundation due to the incoherent ground motions are obtained with the local wave scattering and wave passage effects taken into consideration. The spectral power density function for the pseudo-acceleration of equipment installed on a structural floor is derived. The spectral acceleration of the equipment or the in-structure response spectrum is then estimated using the peak factors of random vibration. The approach is applied to nuclear power plant structures installed on half-spaces, and the reduction of high-frequency earthquake responses due to obliquely incident incoherent earthquake ground motions is examined. The influences of local wave scattering and wave passage effects are investigated for three half-spaces with different shear-wave velocities. When the shear-wave velocity is sufficiently large like hard rock, the local wave scattering significantly affects the reduction of the earthquake responses. In the cases of rock or soft rock, the earthquake responses of structures are further affected by the incident angles of seismic waves or the wave passage effects.

• ETRI Journal
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• v.45 no.2
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• pp.338-345
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• 2023

A filtering power divider based on air-filled substrate-integrated waveguide (AFSIW) technology is proposed in this study. The AFSIW structure is used in the proposed filtering power divider for substantially reducing the transmission losses. This structure occupies a large area because of the use of air as a dielectric instead of typical dielectric materials. A filtering power divider provides power division and frequency selectivity simultaneously in a single device. The proposed filtering power divider comprises three AFSIW cavities. The filtering function is achieved using symmetrical inductive posts. The input and output ports of the proposed circuit are realized by directly connecting coaxial lines to the AFSIW cavities. This transition from the coaxial line to the AFSIW cavity eliminates the additional transitions, such as AFSIW-SIW and SIW-conductor-backed coplanar waveguide, applied in existing AFSIW circuits. The proposed power divider with a second-order bandpass filtering response is fabricated and measured at 5.5 GHz. The measurement results show that this circuit has a minimum insertion loss of 1 dB, 3-dB fractional bandwidth of 11.2%, and return loss exceeding 11 dB.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.947-957
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• 2023

Curved cylindrical structures such as elbows have a non-uniform thickness distribution due to their fabrication process, and as a result have a number of complex mode shapes, including circumferential and axial nodal patterns. In nuclear power plants, material degradation is induced in pipes by flow accelerated erosion and corrosion, causing the wall thickness of carbon steel elbows to gradually thin. The corresponding frequencies of each mode shape vary according to the wall thinning state. Therefore, the thinning state can be estimated by monitoring the varying modal characteristics of the elbow. This study investigated the varying modal characteristics of artificially thinned carbon steel elbows for each thinning state using numerical simulation and experimental methods (MRIT, Multiple Reference Impact Test). The natural frequencies of specified mode shapes were extracted, and results confirmed they linearly decreased with increasing thinning. In addition, by comparing single FRF (Frequency Response Function) data with the results of MRIT, a concise and cost effective thinning estimation method was suggested.

• Journal of the Korean Ceramic Society
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• v.55 no.3
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• pp.244-260
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• 2018

Issues in the electrical characterization of semiconducting photoanodes in a photoelectrochemical (PEC) cell, such as the cell geometry dependence, scan rate dependence in DC measurements, and the frequency dependence in AC measurements, are addressed, using the example of a $TiO_2$ photoanode. Contrary to conventional constant phase element (CPE) modeling, the capacitive behavior associated with Mott-Schottky (MS) response was successfully modeled by a Havriliak-Negami (HN) capacitance function-which allowed the determination of frequency-independent Schottky capacitance parameters to be explained by a trapping mechanism. Additional polarization can be successfully described by the parallel connection of a Bisquert transmission line (TL) model for the diffusion-recombination process in the nanostructured $TiO_2$ electrode. Instead of shunt CPEs generally employed for the non-ideal TL feature, TL models with ideal shunt capacitors can describe the experimental data in the presence of an infinite-length Warburg element as internal interfacial impedance - a characteristic suggested to be a generic feature of many electrochemical cells. Fully parametrized impedance spectra finally allow in-depth physicochemical interpretations.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.1
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• pp.49-53
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• 2000

Sodium borate silicate glass of composition $10Na_2O-39B_2O_3-50SiO_2-CoO$ and $20Na_2O-14B_2O_3-65SiO_2-CoO$ were prepared by melting oxide mixtures in alumina crucible at $1210^{\circ}C$ in an electric furance in air for 2h, and then quenching in air. The dielectric behavior of the quenched glasses are the subject of the present work. Properties such as dielectric constant and resistivity as a function frequency and temperature are reported. From the dielectric spectra, the glass phase transition temperature has been found to decrease at a rate $Na_2O$ 20 mol% and the dielectric constants increase with increasing $Na_2O$ content. The frequency dependent resistivity response of glass exhibits a non-Debye type relaxation.