• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.10a
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• pp.45-51
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• 1999

The attenuations of peak vertical displacements are studies using a conventional least squeare regression technique for microearthquakes occurred in the Kyungsang Basin southeastern Korea. The regression model applied to bandpass-fitered ground motion data includes parameters to account for geometric spreading anelastic attenuation depending on frequency source size and station site effects. Thirty nine displacement traces obtained by integrating velocity records for six shallow local microearthquakes are used to determine attenuation characteristics in the Basin. The regression result of the peak amplitude data leads to Q(f)=59.9 {{{{ {f }^{0.955 } }} for 1.5Hz$\leq$ f $\leq$ 25 Hz. It appears that the anelastic attenuation in the Kyungsang Basin is greater than that in the Western North America Area.

• Steel and Composite Structures
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• v.38 no.2
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• pp.141-150
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• 2021

In the present paper we have investigated the Stoneley wave propagation at the interface of two dissimilar homogeneous nonlocal magneto-thermoelastic media under the effect of hall current applied to multi-dual-phase lag heat transfer. The secular equations of Stoneley waves have been derived by using appropriate boundary conditions. The wave characteristics such as attenuation coefficients, temperature distribution and phase velocity are computed and have been depicted graphically. Effect of nonlocal parameter and hall effect are studied on the attenuation coefficient, phase velocity, temperature distribution change, stress component and displacement component. Also, some particular cases have been discussed from the present study.

• Computers and Concrete
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• v.34 no.5
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• pp.519-534
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• 2024

Metaconcrete is a relatively new concept of concrete where traditional aggregates are partially replaced by resonant aggregates which consist of solid core coated with a relatively soft material. In this research, a mass-spring-mass analytical simplified model is used to predict the bandgap characteristics of metaconcrete firstly, then the bandgap characteristics of metaconcrete unit cell are numerically investigated by using finite element software COMSOL Multiphysics, the numerical model is built and verified by the analytical solution in terms of predicting bandgap frequency region. The effect of the parameters such as the modulus of coating, the density and radius of heavy core and resonant aggregate volume fraction on the characteristics of bandgap are studied based on validated finite element model. The vibration attenuation property of metaconcrete slab is studied by using the finite element code LS-DYNA and the effect of the parameters such as the modulus of coating, the density and radius of heavy core and resonant aggregate volume fraction. Metaconcrete slab exhibit prominent vibration attenuation capacity in the predicted bandgap. Finally, a frequency sweeping experiment is carried out to verify the theoretical model. The experimental results show that metaconcrete specimens exhibit excellent vibration attenuation ability in the predicting bandgap. The results can be used for designing engineered aggregates for better structural protection.

• Wind and Structures
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• v.35 no.6
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• pp.395-403
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• 2022

The present research is concerned with the study of Stoneley wave propagation at the interface of two dissimilar homogeneous orthotropic magneto-thermoelastic solids with fractional order theory of type GN-III with three phase-lags and combined effect of hall current and rotation. With the help of appropriate boundary conditions the secular equations of Stoneley waves are obtained in the form of determinant. The characteristics of wave such as phase velocity, attenuation coefficient and specific loss are computed numerically. The effect of rotation on the Stoneley wave's phase velocity, attenuation coefficient, specific loss, displacement components, stress components and temperature change has been depicted graphically. Some particular cases are also derived in this problem.

• Journal of the Korean Geotechnical Society
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• v.37 no.12
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• pp.7-23
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• 2021

Underground utility tunnels, which contribute to supply of electricity, communication, water and heat, are critical lifelines of an urban area. In case service is discontinued or functional disruption happens, there will be a huge socio-economic impact. For the improved seismic design and evaluation of underground structures, this study proposes a ground displacement measure when the site is subjected to a scenario earthquake based on hazard-consistent source spectra and site amplification/attenuation. This measure provides a rational estimation of ground displacement and can be an alternative to existing response displacement methods.

• Wind and Structures
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• v.29 no.6
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• pp.431-440
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• 2019

The aim of this study was to explore the influence of structure coupling effect on structural damping of blade based on the blade vibration characteristic. For this purpose, the scaled blade model of NREL 5 MW offshore wind turbine was processed and employed in the wind tunnel test to validate the reliability of theoretical and numerical models. The attenuation curves of maximum displacement and the varying curves of equivalent damping coefficient of the blade under the rated condition were respectively compared and analyzed by constructing single blade model and whole machine model. The attenuation law of blade dynamic response was obtained and the structure coupling effect was proved to exert a significant influence on the equivalent damping coefficient. The results indicate that the attenuation trend of the maximum displacement response curve of the single blade varies more obviously with the increase of elastic modulus as compared to that under the structure coupling effect. In contrast to the single blade model, the varying curve of equivalent damping coefficient with the period is relatively steep for the whole machine model. The findings are of great significance to guide the structure design and material selection for wind turbine blades.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.211-216
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• 2008

In this study, we have developed a program which can calculate phase and group velocities, attenuation and wave structures of each mode in multi-layered plates. The wave structures of each mode are obtained, varying material properties and number of layers. The key in the success of guided wave NDE is how to optimize the mode selection scheme by minimizing energy loss when a structure is in contact with liquid. In this study, the normalized out-of-plane displacements at the surface of a free plate are used to predict the variation of modal attenuation and verily the correlation between attenuation and wave structure. It turns out that the guided wave attenuation can be efficiently obtain from the out-of-plane displacement variation of a free wave guide alleviating such mathematical difficulties in extracting complex roots for the eigenvalue problem of a liquid loaded wave guide. Through this study, the concert to optimize guided wave mode selection is accomplished to enhance sensitivity and efficiency in nondestructive evaluation for multi-layered structures.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.2
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• pp.78-86
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• 1990

The vertical attenuation of structureborne noise in a ship structure is studied by means of the wave guide theory. When modeling a ship structure as an acoustic wave guide system the cross mode is derived from the assumption about the boundary of the system, i.e. the constraint due to transverse frames. In this paper, the constraint is relaxed so that the displacement at the boundaries could take place. The numerical result shows better agreement with the measured one than that of the previous assumption of fixed boundary condition in the low frequency region. The effect of local changes of mass and damping factors on the attenuation losses are also investigated numerically.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.3
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• pp.33-38
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• 2002

This paper deals with pressure ripple attenuation far separated-type Hydrostatic Transmission (HST) consisting ova variable axial piston pump connected in an open loop to a fried displacement axial piston motor. Pressure ripples in HST is major source of vibration which can lead to fatigue failure of components and cause noise. In order to reduce the pressure ripple, an annular tube tripe hydraulic filter is proposed to attenuate pressure ripples with the high frequencies components to achieve better noise reduction in HST. The basic principle of a hydraulic filter is allied to propagation of pressure wave, reflection, absorption in cross section of discontinuity and resonance in the hydraulic pipeline. It is experimentally shown that the hydraulic filter attenuates about 30∼40dB of pressure ripple with high frequencies. These results will assist in modeling and design of noise reduction in hydraulic control systems, and provide a means of designing a quieter HST.

• Korean Journal of Applied Biomechanics
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• v.15 no.4
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• pp.117-129
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• 2005

The purpose of this study was to characterize the impact shock wave and its attenuation, and the kinematic response of the lower extremity's joints to the impact shock during downhill running in which the lower extremity's extensor acts dominantly. For this study, fifteen subjects(mean age:$27.08{\pm}4.39$; mass:$76.30{\pm}6.60$; height:$177.25{\pm}4.11$) were required to run on the 0% grade treadmill and downhill grades of 7%, and 15% in random at speed of their preference. When the participant run, acceleration at the tibia and the sacrum and kinematic data of the lower extremity were collected for 20s so as to provide at least 5 strides for analysis at each grade. Peak impact accelerations were used to calculate shock attenuation between the tibia and sacrum in time domain at each grade. Fast Fourier transformation(FFT) and power spectral density(PSD) techniques were used to analyze impact shock factors and its attenuation in the frequency domain. Joint coordinate system technique was used to compute angular displacement of the ankle and knee joint in three dimension. The conclusions were drawn as fellows: 1. Peak impact accelerations of the tibia and sacrum in downhill run were greater than that of 0% grade run, but no significant between conditions. Peak shock of PSD resembled also in pattern of peak impact acceleration. The wave of impact shock attenuation between the tibia and sacrum decreased with increasing grade, but didn't find a significant difference between grade conditions. 2. Adduction/abduction, flexion/extention, and internal/external rotation of the ankle and knee joints at support phase between grade conditions didn't make much difference. 3. At grade of 7% and 15%, there were relationship between the knee of the flexion/extension movement and peak impact acceleration during heel strike and found also it in the ankle of plantar/dorsiflexion at grade of 15%.