• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.1
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• pp.18-26
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• 2001

In this paper, the resonant characteristics and modes of the film bulk acoustic wave resonator (FBAR) used in 1~2 GHz frequency region are analyzed by it's input impedance which was calculated by three dimensional finite element method formulated as eigenvalue problem using electro-mechanical wave equation and boundary condition. It was extracted that the resonant and the spurious characteristics considering the effects of electrode area and shape variation and unsymmetry of upper and lower electrode. Those effects couldn't be analyzed by on dimensional analysis, e.g. Mason equivalent model. The simulation result was confirmed by comparing with the simulation data from Mason model analysis and the measured data of the ZnO FBAR fabricated using micro-machining technique. Also, through the simulation of the area variations of FBAR, it was obtained that the optimum ratio of length and thickness is 20:1 and the minimum ratio is 5:1 to operate thickness vibration mode.

• Journal of the Korean Institute of Gas
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• v.20 no.6
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• pp.58-64
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• 2016

Vibrational characteristics of curved pipe structures are investigated with respect to the change of inside flow velocities. Based upon the Hamilton's principle, the equations of motions are derived, and the finite element equation is constructed to solve the frequency equation for curved pipe structures. When the initial tension is neglected in cured pipes, the natural frequencies are reduced as flow velocity increases, and the rapid decreases of the natural frequencies take place. However, when the initial tension is taken into account, the natural frequencies are not changed with the change of the flow velocity. In free vibrational simulation of pipe systems, it is necessary to calculate the initial force due to the velocity and the pressure of the fluid flow from the equilibrium. The force should be included in the equation of motion of the systems to get more accurate natural frequencies. The mechanical properties like stiffness or the location of pipe support need to be changed to avoid resonance. The natural frequencies are to be isolated from the frequency range of dominant vibration modes. The angles of elbows do not affect the change of the fundamental natural frequency, but affect the change of the third or higher natural frequencies.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.5
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• pp.2617-2622
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• 2014

In this study, the critical frequency happened at system is analyzed when the motor of camera manufacturing system is working on the direction of Z axis. Configurations of modes at natural frequencies happened at two models are investigated by the study result through modal analysis. The range of natural frequency in this study system is from 100 Hz to 500 Hz. At this range, the maximum equivalent stress in case of 20 kg weight becomes 6.2335MPa and this stress is shown as 50 times more than in case of 10 kg weight. The working safety of system can be investigated through the analyses of natural frequency and harmonic response of this camera manufacturing system.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.4
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• pp.121-128
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• 2003

In recent years, various artificial neural network algorithms are used in the damage assessment of civil infrastructures. So far, many researchers have used the artificial neural network as a pattern classifier for the structural damage assessment but, in this paper, the neural network is used as a structural reanalysis tool not as a pattern classifier. For the model updating using the optimization algorithm, the summation of the absolute differences in the structural vibration modes between undamaged structures and damaged ones is considered as an objective function. The stiffness of structural components are treated as unknown parameters to be determined. The structural damage detection is achieved using model updating based on the optimization techniques which determine the estimated stiffness of components minimizing the objective function. For the verification of the proposed damage identification algorithm, it is numerically applied to a simply supported bridge model.

• Earthquakes and Structures
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• v.13 no.4
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• pp.377-386
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• 2017

Earthquake-induced pounding damages to building structures were repeatedly observed in many previous major earthquakes. Extensive researches have been carried out in this field. Previous studies mainly focused on the regular shaped buildings and each building was normally simplified as a single-degree-of-freedom (SDOF) system or a multi-degree-of-freedom (MDOF) system by assuming the masses of the building lumped at the floor levels. The researches on the pounding responses between irregular asymmetric buildings are rare. For the asymmetric buildings subjected to earthquake loading, torsional vibration modes of the structures are excited, which in turn may significantly change the structural responses. Moreover, contact element was normally used to consider the pounding phenomenon in previous studies, which may result in inaccurate estimations of the structural responses since this method is based on the point-to-point pounding assumption with the predetermined pounding locations. In reality, poundings may take place between any locations. In other words, the pounding locations cannot be predefined. To more realistically consider the arbitrary poundings between asymmetric structures, detailed three-dimensional (3D) finite element models (FEM) and arbitrary pounding algorithm are necessary. This paper carries out numerical simulations on the pounding responses between a symmetric rectangular-shaped building and an asymmetric L-shaped building by using the explicit finite element code LS-DYNA. The detailed 3D FEMs are developed and arbitrary 3D pounding locations between these two buildings under bi-directional earthquake ground motions are investigated. Special attention is paid to the relative locations of two adjacent buildings. The influences of the left-and-right, fore-and-aft relative locations and separation gap between the two buildings on the pounding responses are systematically investigated.

• Steel and Composite Structures
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• v.36 no.1
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• pp.1-16
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• 2020

In steel-concrete composite beams, to improve the cracking resistance of the concrete slab in the hogging moment region, a new type of connector in the interface, named uplift-restricted and slip-permitted screw-type (URSP-S) connector has been proposed. This paper focuses on the behavior of steel-concrete composite beams with URSP-S connectors. A total of three beam specimens including a simply supported beam with URSP-S connectors and two continuous composite beams with different connectors arrangements were designed and tested. More specifically, one continuous composite beam was equipped with URSP-S connectors in negative moment region and traditional shear studs in other regions. For comparison, the other one was designed with only traditional shear studs. The failure modes, crack evolution process, ultimate capacities, strain responses at different locations as well as the interface slip of the three tested specimens were measured and evaluated in-depth. Based on the experimental study, the research findings indicate that the larger slip deformation is allowed while using URSP-S connectors. Meanwhile, the tensile stress reduces and the cracking resistance of the concrete slab improves accordingly. In addition, the overall stiffness and strength of the composite beam become slightly lower than those of the composite beam using traditional shear studs. Moreover, the arrangement suggestion of URSP-S connectors in the composite beam is discussed in this paper for its practical design and application.

• Earthquakes and Structures
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• v.17 no.2
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• pp.175-189
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• 2019

The aim of the study is to show the results of complex shaking table experimental investigation focused on the response of two models of cylindrical steel tanks under mining tremors and moderate earthquakes, including the aspects of diagnosis of structural damage. Firstly, the impact and the sweep-sine tests have been carried out, so as to determine the dynamic properties of models filled with different levels of liquid. Then, the models have been subjected to seismic and paraseismic excitations. Finally, one fully filled structure has been tested after introducing two different types of damages, so as to verify the method of damage diagnosis. The results of the impact and the sweep-sine tests show that filling the models with liquid leads to substantial reduction in natural frequencies, due to gradually increasing overall mass. Moreover, the results of sweep-sine tests clearly indicate that the increase in the liquid level results in significant increase in the damping structural ratio, which is the effect of damping properties of liquid due to its sloshing. The results of seismic and paraseismic tests indicate that filling the tank with liquid leads initially to considerable reduction in values of acceleration (damping effect of liquid sloshing); however, beyond a certain level of water filling, this regularity is inverted and acceleration values increase (effect of increasing total mass of the structure). Moreover, comparison of the responses under mining tremors and moderate earthquakes indicate that the power amplification factor of the mining tremors may be larger than the seismic power amplification factor. Finally, the results of damage diagnosis of fully filled steel tank model indicate that the forms of the Fourier spectra, together with the frequency and power spectral density values, can be directly related to the specific type of structural damage. They show a decrease in the natural frequencies for the model with unscrewed support bolts (global type of damage), while cutting the welds (local type of damage) has resulted in significant increase in values of the power spectral density for higher vibration modes.

• Smart Structures and Systems
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• v.23 no.6
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• pp.653-667
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• 2019

Using cross-ties to connect cables together when forming a cable network is regarded as an efficient method of mitigating cable vibrations. Cross-ties have been extended and fixed on bridge decks or towers in some engineering applications. However, the dynamics of this kind of system need to be further studied, and the effects of extending cross-links to bridge decks/towers on the modal response of the system should be assessed in detail. In this paper, a system of two cables connected by an inter-supported cross-link with another lower cross-link extended to the ground is proposed and analyzed. The characteristic equation of the system is derived, and some limiting solutions in closed form of the system are derived. Roots of cable system with special configurations are also discussed, attention being given to the case when the two cables are identical. A predictable mode behavior was found when the stiffness of inter-connection cross-link and the cross-link extended to the ground were the same. The vector of mode energy distribution and the degree of mode localization index are proposed so as to distinguish global and local modes. The change of mode behaviors is further discussed in the case when the two cables are not identical. Effects of cross-link stiffness, cross-link location, mass-tension ratio, cable length ratio and frequency ratio on $1^{st}$ mode frequency and mode shape are addressed.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.1
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• pp.1-8
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• 2019

In this study, a maximum power point tracking (MPPT) algorithm based on the perturb and observe (P&O) method with variable step size is proposed to improve the dynamic response characteristic of MPPT, using the existing P&O method. The proposed algorithm, which we verified by simulation and experiment, can track the maximum power point (MPP) through duty control and consisted of three operation modes, namely, constant voltage mode, fast mode, and variable step mode. When the insolation is constant, the voltage variation of the operating point at the MPP is reduced through the step size reduction of the duty in the variable step mode. Consequently, the vibration of the operating point is reduced, and the power generation efficiency is increased. When the insolation changes, the duty and the photovoltaic (PV) voltage are kept constant through the constant voltage mode. The operating point then rapidly tracks the new MPP through the fast-mode operation at the end of the insolation change. When the MPP is reached, the operation is changed to the variable step mode to reduce the duty step size and track the MPP. The validity of the proposed algorithm is verified by simulation and experiment of a PV system composed of a PV panel and a boost converter.

• Advances in concrete construction
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• v.7 no.2
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• pp.87-96
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• 2019

Self-compacting concretes (SCC) are highly fluid concrete which can flow without any vibration. Their composition requires a large quantity of fines to limit the risk of bleeding and segregation. The use of crushed sand rich in limestone fines could be an adequate solution for both economic and environmental reasons. This paper investigates the influence of quarry limestone fines from manufactured crushed sand on rheological, mechanical and durability properties of SCC. For this purpose, five mixtures of SCC with different limestone fines content as substitution of crushed sand (0, 5, 10, 15 and 20%) were prepared at constant water-to-cement ratio of 0.40 and $490kg/m^3$ of cement content. Fresh SCC mixtures were tested by slump flow test, V-funnel flow time test, L-box height ratio, segregation resistance and rheological test using a rheometer. Compressive and flexural strengths of SCC mixtures were evaluated at 28 days. Regarding durability properties, total porosity, capillary water absorption and chloride-ion migration were studied at 180 days. For the two test modes in fresh state, the results indicated compatibility between slump flow/yield stress (${\tau}_0$) and V-funnel flow time/plastic viscosity (${\mu}$). Increasing the substitution level of limestone fines in SCC mixtures, contributes to the decrease of the slump flow and the yield stress. All SCC mixtures investigated achieved adequate filling, adequate passing ability and exhibit no segregation. Moreover, the inclusion of limestone fines as crushed sand substitution reduces the capillary water absorption, chloride-ion migration and consequently enhances the durability performance.