• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.1
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• pp.73-79
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• 2001

In this study, a submerged plate-type breakwater is considered, which is supported by elastic foundation. This breakwater makes use of wave phase interaction among the incident, diffracted and radiated waves. We apply a three-dimensional singularity distribution method within the linear potential theory in order to describe the wave field. The submerged plate is assumed to be rigid and the elastic support be a linear spring with constant stiffness. A typical rectangle plate is exemplified for numerical calculation. The thickness of the plate is carefully selected in order to guarantee the solution to be stable by checking the condition number of the system matrix. A parametric study is carried out for examining the effect of the stiffness of the elastic support on performance of the breakwater. We also examine the effect of the submerged depth.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.11
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• pp.1075-1080
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• 2010

For the aeroelastic analysis of a wing with friction damping, coupled time integration method was used to obtain time responses in the subsonic and transonic regions. To take into account aerodynamic nonlinearity induced by shock wave on the lifting surface, transonic small disturbance equation with in-phase periodic boundary condition was used for unsteady aerodynamic calculation. For 2-DOF airfoil system with displace-dependent friction dampers, the effects of normal load slope and Mach number on flutter boundary were investigated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.19-22
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• 2004

In the future engine with high performance, the gas-liquid scheme injectors will be adopted and the role of the injector as an acoustic resonator is investigated as an advanced study The injector can play a significant role in acoustic damping and the optimum length of the injector to maximize the damping capacity is calculated as a function of baffle length.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.5
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• pp.79-86
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• 2005

The role of the injector as an acoustic resonator is studied for the high performance rocket engine adopting the gas-liquid scheme injector. Acoustic behavior in the combustor with single injector is investigated numerically adopting linear acoustic analysis for cold condition. Acoustic-damping effect of the injector is evaluated by damping factor as a function of the injector length. From the numerical results, it is found that the injector can play a significant role in acoustic damping and the optimum length of the injector corresponds to half of a full wavelength of the longitudinal mode with the acoustic frequency to be damped in the chamber. In baffled chamber, the optimum lengths of the injector are calculated as a function of baffle length for both cold and hot conditions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.73-76
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• 2006

Acoustic cavity as a stabilization device to control high-frequency combustion instabilities in liquid rocket engine is adopted and its damping capacity is verified in atmospheric temperature. Geometric effects of acoustic cavity on damping characteristics are analyzed and compared quantitatively. Satisfactory agreements have been achieved with linear acoustic analysis and experimental approach. Results show that the acoustic cavity of the largest orifice area or the shortest orifice length was the most effective in acoustic damping of the harmful resonant frequency finally, it is proved that an optimal design process is indispensable for the effective control of combustion instabilities.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.3 s.55
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• pp.217-224
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• 2009

Many engineering researches are performed to ensuring structural safety from earthquake. In this study, the damping capacity of LRB(lead rubber bearing) with high lead-plug area ratio was examined by hysteresis loop from experiments. The displacement controlled tests were performed for 12 specimens designed in 2 types by lead-plug area ratio as main parameter. Each coupled specimens were tested by 3 times sinusoidal loads with different loading velocities. From the experimental results, LRB with high lead-plug area ratio has sufficient damping ratio for reducing horizontal seismic load to structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.2A
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• pp.89-96
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• 2011

The damping ratio as an index of bridge vibration could be considered as one of the important dynamic characteristics of a suspension bridge. But estimating of damping ratio on an existing suspension bridge under ambient vibration condition could be a laborious task. Moreover, it is not simple to directly distinguish aerodynamic damping and friction damping from apparent damping. According to previous studies, the aerodynamic damping properties can be linearly affected by wind speed level, and apparent damping ratio can be affected by amplitude of vibration. Therefore, in this article, the relationships among damping ratio, wind speed level and amplitude of acceleration were studied for separating extract aerodynamic damping and friction damping from apparent damping. Damping ratios on Sorok Bridge, a suspension bridge which is a located in Go-Heung, Korea, were estimated by two different methods as using Hilbert transform and extended Kalman filter which were well known as effective estimation methods for non-linear state. It was possible to distinguish aerodynamic damping and friction damping from apparent damping using averaged normal components of wind speed, RMQ values of acceleration, and estimated damping ratios from wind-induced vibration responses and vehicle loading responses.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.5
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• pp.438-445
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• 2007

A Helmholtz resonator as a stabilization device to control high-frequency combustion instabilities in liquid rocket engine is adopted and its damping capacity is verified by linear acoustic analysis and atmospheric acoustic tests. To compare the results of acoustic attenuation effect in accordance with uni-resonator's geometry, quantitative analyses were made in the cases of various orifice diameters and lengths. Next, in the experiments to compare the results of acoustic attenuation effect by a difference in the number of resonators, damping capacity of harmful resonant frequency was improved by the increase of the number of resonators. On the other hand, attenuation efficiency of the frequency tended rather to lower due to over damping from the point of view of absorption coefficient. As the result, tuning the suitable geometry for the resonator to the resonant frequency is required for the control using the resonator. Also, the design of resonator's geometry and the choice of its number are important to put up the optimal efficiency in consideration of restriction of its volume.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.9
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• pp.838-844
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• 2015

This paper includes summarization and analysis of previous research results on acoustic attenuation due to particles and flow turning in rocket motors among various damping parameters. Particle damping is the most effective mechanism in suppressing high-frequency combustion instabilities occurring in rocket combustion chambers, which is dependent on the size and the mass fraction of particles. Relatively weak attenuation by flow turning compared to particle damping depends on the geometry of propellant and a combustion chamber. Pumping driving effects need to be taken into account when realizing vorticity generation on the propellant surface. However, its driving effects become cancelled out by flow turning loss when the propellant geometry is cylindrical.

• Journal of KSNVE
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• v.5 no.2
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• pp.207-213
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• 1995

A new predictor-corrector explicit time integration algorithm is presented for solving structural dynamics problems. The basis of the algorithm is the implicit generalized-.alpha. method recently developed by the authors. Like its implicit parent, the explicit generalized-$\alpha$ method is a one- parameter family of algorithms in which the parameter defines the high-frequency numerical dissipation. The algorithm can be utilized effectively for linear and nonlinear structural dynamics calculations is which numerical dissipation is needed to reduce spurious oscillations inherent in non-dissipative time integration methods used to solve wave propagation problems.