• Steel and Composite Structures
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• v.50 no.1
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• pp.45-61
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• 2024

This research explores the domain of organic solar cells, a photovoltaic technology employing organic electronics, which encompasses small organic molecules and conductive polymers for efficient light absorption and charge transport, leading to electricity generation from sunlight. A computer simulation is employed to scrutinize resonance and dynamic stability in OSCs, with a focus on size effects introduced by nonlocal strain gradient theory, incorporating additional terms in the governing equations related to displacement and time. Initially, the Navier method serves as an analytical solver to delve into the dynamics of design points. The accuracy of this initial step is verified through a meticulous comparison with high-quality literature. The findings underscore the substantial impact of viscoelastic foundations, size-dependent parameters, and geometric factors on the stability and dynamic deflection of OSCs, with a noteworthy emphasis on the amplified influence of size-dependent parameters in higher values of the different layers' thicknesses.

• Wind and Structures
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• v.19 no.4
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• pp.443-465
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• 2014

Hyperbolic thin-shell cooling towers have complicated vibration modes, and are very sensitive to the effects of group towers and wind-induced vibrations. Traditional aero-elastic models of cooling towers are usually designed based on the method of stiffness simulation by continuous medium thin shell materials. However, the method has some shortages in actual engineering applications, so the so-called "equivalent beam-net design method" of aero-elastic models of cooling towers is proposed in the paper and an aero-elastic model with a proportion of 1: 200 based on the method above with integrated pressure measurements and vibration measurements has been designed and carried out in TJ-3 wind tunnel of Tongji university. According to the wind tunnel test, this paper discusses the impacts of self-excited force effect on the surface wind pressure of a large-scale cooling tower and the results show that the impact of self-excited force on the distribution characteristics of average surface wind pressure is very small, but the impact on the form of distribution and numerical value of fluctuating wind pressure is relatively large. Combing with the Complete Quadratic Combination method (hereafter referred to as CQC method), the paper further studies the numerical sizes and distribution characteristics of background components, resonant components, cross-term components and total fluctuating wind-induced vibration responses of some typical nodes which indicate that the resonance response is dominant in the fluctuating wind-induced vibration response and cross-term components are not negligible for wind-induced vibration responses of super-large cooling towers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.3
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• pp.30-36
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• 2004

As fiber reinforced composite materials are widely used in aircraft, space structures and robot arms, the study on the non-destructive testing methods of the composite materials has become an important research area for improving their reliability and safety. In this paper, the AE signal analyzer with the resonance circuit to extract the specified frequency of the acoustic emission signal were designed and fabricated. The noise levels of the fabricated AE signal analyzer by the disturbance such as impact or mechanical vibration had a very small value comparable to those of the conventional AE signal analyzer. Also, the fabricated AE signal analyzer was proved to have about the same crack detection capabilities with the conventional AE signal analyzer under the static and dynamic tensile tests of the composite materials.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.7
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• pp.275-280
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• 2013

This paper presents an optimizing method for wireless charging system, specifically focused on the capsule endoscope applications. In order to increase the wireless power transfer efficiency of electro-magnetic resonance coupled coils, this paper investigates the impact factors of the power transfer efficiency in small battery capacity system and proposes a efficiency optimizing method based on frequency control. Simulation results show that the proposed efficiency optimal control method can effectively stabilize the wireless power transfer efficiency so as to successfully solve the main issue of transfer efficiency variation with distance and as well as parasitic element.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1996.10a
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• pp.167-172
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• 1996

A Dual Mass Flywheel system is a evolution to the reduction of torsional vibration and impact noise occuring in powertrain when a vehicle is eit-her moving or idling. The name already explains what it is : The mass of the conventional single mass flywheel is divided. One section continues to belong to the mass moment of inertia of the engine-side. The ot-her section increass the mass moment of inertia of the transmission-side. The two masses are connected via a spring /damping system. This reduces the speed at which the dreaded resonance occurs to below idle speed. Since 1984 Dual Mass Flywheel has been de-veloped again and again. But the prosidures of de-velopment of D.M.F system didn't have had differe-nce from conventional clutch system's trial and err-or This paper presents the method for systematical design of D.M.F system with demensionless design variables of D.M.F system mass ratio between two flywheels λ. natual frequency rate of two flywheel s, ${\gamma}$and viscosity coefficient ζ. And experimental re-sults are used to prove these theoretical results.

• Journal of the Korea Concrete Institute
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• v.12 no.6
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• pp.67-74
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• 2000

The usage of nondestructive testing on early-aged concrete leads to enhacned safty and allows effective scheduling of construction, thus making it possible to maximize the time and cost efficiencies. In this study, a reliable nondestructive strength evaluation method for early-aged concrete using the longitudinal wave velocity is proposed. Compression tests were performed to examine factors influencing the velocity-strength relationship of concrete, such as water-cement (w/c) ratio, fine aggregate ratio, curing temperature, and curing condition. The test results show that a change in the w/c ratio and curing temperature has minor effect on the velocity-strength relationship/ However, curing condition significantly influences the velocity-strength relationship of early-aged concrete. Moreover, the longitudinal wave velocity increases with decreasing fine aggregate ratio. It is concluded from this study that the strength evaluation of early-age concrete can be achieved by a nonlinear equation which considers the effects of curing condition and fine aggregate ratio.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.6
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• pp.193-199
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• 2001

Active control of forced vibration of the cantilevered laminated composite plates using collocated piezoceramic sensor/actuator is analyzed numerically and verified experimentally for various fiber orientations. Impact on the stiffness and the damping properties is studied by varying stacking sequence of [$\theta$$_{4}$O$_{2}$90$_{2}$]s for the laminated composite plate. For the forced vibration control, the plate is excited by one pair of collocated PZT exciters in resonance and its vibrational response is suppressed by the other collocated PZT sensor/actuator using direct negative velocity feedback. It is shown that the active control of forced vibration is more effective for the smart laminated plate with higher modal damped stiffness(2ζ$\omega$/aup 2/) .

• Journal of Ocean Engineering and Technology
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• v.38 no.1
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• pp.1-9
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• 2024

The vertical center of gravity (VCG) has a significant impact on the roll motion response of a surface ship, particularly oil tankers based on the oil level in the tanker after discharging oil at several stations or positional changes, such as changes in the superstructure and deck structure. This study examined the motion response of the Korea very large crude carrier 2 (KVLCC2) at various VCGs, especially roll motion when the VCG changed. The potential theory in the Ansys AQWA program was used as a numerical simulation method to calculate the motion response. On the other hand, the calculations obtained through potential theory overestimated the roll amplitudes during resonance and lacked precision. Therefore, roll damping is a necessary parameter that accounts for the viscosity effect by performing an experimental roll decay. The roll decay test estimated the roll damping coefficients for various VCGs using Froude's method. The motion response of the ship in regular waves was evaluated for various VCGs using the estimated roll-damping coefficients. In addition, the reliability of the numerical simulation in motion response was verified with those of the experiment method reported elsewhere. The simulation results showed that the responses of the surge, sway, heave, pitch, and yaw motion were not affected by changing the VCG, but the natural frequency and magnitude of the peak value of the roll motion response varied with the VCG.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.1
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• pp.90-98
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• 1998

A Dual Mass Flywheel(D.M.F.) system is an evolution to the reduction of torsional vibration and impact noise occurring in powertrain when a vehicle is either moving or idling. The D.M.F. system has two flywh-eels, which is different from the conventional clutch system. One section belongs to the mass moment of in-ertia of the engine-side. The other section increases the mass moment of inertia of the transmission-side. These two masses are connected via a spring/damping system. This reduces the speed at which the dreaded resonance occurs to below idle speed. Since 1984m D.M.F. system has been developed. However, the processes of development of D.M.F. system don't have any difference from the trial and error method of conventional clutch system. This paper present the method for systematical design of D.M.F. system with dimensionless design varia-bles of D.M.F. system, mass ratio between two flywheels, natural frequency rate of two flywheels, and visc-osity coefficient. And expermental results are used to prove these theoretical results.

• Structural Engineering and Mechanics
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• v.56 no.1
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• pp.49-56
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• 2015

Dynamic compaction (DC) is a useful method for improvement of granular soils. The method is based on falling a tamper (weighting 5 to 40 ton) from the height of 15 to 30 meters on loose soil that results in stress distribution, vibration of soil particles and desirable compaction of the soil. Propagation of the waves during tamping affects adjacent structures and causes structural damage or loss of performance. Therefore, determination of the safe or critical distance from tamping point to prevent structural hazards is necessary. According to FHWA, the critical distance is defined as the limit of a particle velocity of 76 mm/s. In present study, the ABAQUS software was used for numerical modeling of DC process and determination of the safe distance based on particle velocity criterion. Different variables like alluvium depth, relative density, and impact energy were considered in finite element modeling. It was concluded that for alluvium depths less than 10 m, reflection of the body waves from lower boundaries back to the soil and resonance phenomenon increases the critical distance. However, the critical distance decreases for alluvium depths more than 10 m. Moreover, it was observed that relative density of the alluvium does not significantly influence the critical distance value.