• Geophysics and Geophysical Exploration
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• v.10 no.1
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• pp.19-28
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• 2007

In this study, we propose a joint inversion method, using genetic algorithms, to estimate an S-wave velocity structure for deep sedimentary layers from receiver functions and surface-wave phase velocity observed at several sites. The method takes layer continuity over a target area into consideration by assuming that each layer has uniform physical properties, especially an S-wave velocity, at all the sites in a target area in order to invert datasets acquired at different sites simultaneously. Numerical experiments with synthetic data indicate that the proposed method is effective in reducing uncertainty in deep structure parameters when modelling only surface-wave dispersion data over a limited period range. We then apply the method to receiver functions derived from earthquake records at one site and two datasets of Rayleigh-wave phase velocity obtained from microtremor array surveys performed in central Tokyo, Japan. The estimated subsurface structure is in good agreement with the results of previous seismic refraction surveys and deep borehole data. We also conclude that the proposed method can provide a more accurate and reliable model than individual inversions of either receiver function data only or surface-wave dispersion data only.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.2
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• pp.349-356
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• 2018

This paper attempts to develop a connection model based on FE analysis that can be applied to the evaluation of earthquake fragility of Steel Storage Racks lacking research in Korea. In order to accomplish this goal, shaking table tests, modal tests, and various member tests (8 case, push-over test) for structural members have been conducted to understand the behavior of steel storage racks. Based on the experimental results, detailed modeling of the joints was conducted using the NX-Nastran program in order to develop a connection model for Steel storage racks to be applied to the seismic vulnerability assessment. Especially, surface to surface contact element and spring element are applied to simulate the connection between the column member and the beam member connected by the simple latch method. Spring element model developed and applied ARX (Auto Regressive eXogenous) based mathematical model. The simulation results based on the FE model showed excellent reliability with a mutual error rate of less than 8% when compared with the member test results. As a result, it was confirmed that the FE model based connection model developed in the study can be applied to the analytical model for the seismic vulnerability assessment of Steel storage racks.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.2
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• pp.114-120
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• 2011

The characteristics of a helical turbine to be used for tidal stream energy conversion have been numerically studied with varying a few design parameters. The helical turbines were proposed aiming at mitgating the well known poor cut-in characteristics and the structural vibration caused by the fluctuating torque, and the basic concept is introducing some twisting angle of the vertical blade along the rotation axis of the turbine. Among many potential controling parameters, we focused, in this paper, on the twisting angle and the height to diameter ratio of the turbine, and, based on the numerical experiment, We tried to propose a configuration of such turbine for which better performance can be expected. The three-dimensional unsteady RANS equations were solved by using the commercial CFD software, FLUENT with k-${\omega}$ SST turbulence model, and the grid was generated by GAMBIT. It is shown that there are a range of the twisting angle producing better efficiency with less vibration and the minimum height to diameter ratio above which the efficiency does not improve considerably.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.1
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• pp.143-157
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• 1992

For the design of structural systems having the prescribed or optimum dynamic characteristics, some design changes of the initially designed system are required. In these cases, if the sensitivity analysis which can predict the changes of dynamic characteristics due to the changes of design variables is applied, the design changes can be carried out rationally and very efficiently. For many structural systems, it is well known that the analysis by the transfer matrix method(TMM) and the combined finite element-transfer matrix method(FETMM) is more efficient than the analysis by the finite element method. However, most known studies on the sensitivity analysis of structural systems premise using the finite element method. In this paper, the sensitivity analysis methods by the TMM and the FETMM are presented and some numerical investigations on the beam-column with elastically restrained ends and intermediate contraints and the stiffened plate having subsystems are carried out. The results of the numerical examples show good accuracy and computational efficiency of the presented methods, and show that the application of sensitivity analysis in the dynamic characteristic reanalysis give good results within the practically changeable range of design variables.

• Journal of the Korean Society for Railway
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• v.19 no.1
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• pp.20-28
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• 2016

Curved squeal noise may result when railway vehicles run on curved tracks. Contact between the wheels and the rails causes a stick-slip phenomenon, which generates squeal noise. In order to identify the mechanism of the squeal noise systematically, a scaled test rig has been fabricated. Knowledge of the contact forces between the wheels and the rail rollers is essential for investigating the squeal noise characteristics; however, it is difficult to measure there contact force. In this study, contact forces have been calculated indirectly according to the modal behavior of the subframe that supports the rail roller and the responses at specific positions of that subframe. In order to verify the estimated contact forces, the displacements at the contact points between the wheels and rail rollers have been calculated from the estimated forces; the resulting values have been compared with the measured displacement values. The SPL at the specific location has been calculated using the estimated contact forces and this also has been compared with the SPL, measured in a semi-anechoic chamber. The comparisons in displacements and SPLs show good correlation.

• Journal of the Korean Society for Railway
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• v.18 no.3
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• pp.175-185
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• 2015

Generally, in the train area, switch tracks have required high reliability because this system is directly associated with derailment. Especially, switch tracks of Maglev vehicles must be moved in terms of the whole geometric characteristics, in which the bogies are encased in the switch track. For this reason, switch track was constructed with steel lighter than concrete girders. But, the steel switch track was weak because of structural vibration as well as structural deformation. Therefore, it is important to predict the levitation stability when a vehicle passes over flexible switch track. The aims of this paper are to develop a coupled dynamic model to describe the relationship between a Maglev vehicle and switch track and to predict the levitation stability. In order to develop the coupled dynamic model, a three dimensional vehicle model was developed based on multibody dynamics; a switch model was made using the modal superposition method. And, the developed model was verified using comparison measured data.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.319-323
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• 1996

\ulcorner\ulcorner\ulcorner\ulcorner 80,000 rpm \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner(ultra-centrifuge)\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner. \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner(critical speed)\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner(separation margin)\ulcorner \ulcorner\ulcorner, \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner \ulcorner\ulcorner-\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner \ulcorner\ulcorner\ulcorner. \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner \ulcorner \ulcorner\ulcorner\ulcorner, \ulcorner\ulcorner \ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner(extra slender shaft)\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner. \ulcorner\ulcorner \ulcorner\ulcorner\ulcorner, \ulcorner\ulcorner 1\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner \ulcorner\ulcorner\ulcorner(bumper ring) \ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner(guide bearing)\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner. \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner(finite element method)\ulcorner \ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner, \ulcorner\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner\ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner \ulcorner\ulcorner\ulcorner \ulcorner\ulcorner(damping)\ulcorner \ulcorner\ulcorner\ulcorner\ulcorner.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.4
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• pp.355-364
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• 2010

Filiform hairs that respond to movements of the surrounding medium are the mechanoreceptors commonly found in arthropods and vertebrates. In these creatures, the filiform hairs function as a sensory system for raider detection. Parametric analyses of the motion response of filiform hairs are conducted by using a mathematical model of an artificial flow sensor to understand the possible operating ranges of a microfabricated device. It is found that the length and diameter of the sensory hair are the major parameters that determine the mechanical sensitivities and responses in a mean flow with an oscillating component. By changing the hair length, the angular displacement, velocity, and acceleration could be detected in a wide range of frequencies. Although the torques due to drag and virtual mass are very small, they are also very influential factors on the hair motion. The resonance frequency of the hair decreases as the length and diameter of the hair increase.

• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.2
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• pp.371-377
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• 1995

By using ultrasonic waves, we obtained conclusion from the experiment for measuring joint axial force of high tension bolt. The conclusion is followed. : From the high tension bolts used at turbine of Thermoelectric Power Plant, we obtained the equation of calculating joint axial force that is ${\sigma}=\frac{{\Delta}BPD}{j{\times}{\Sigma}{\delta}}$. By using IBM PC, which is inputed by the equation for calculating joint axial force of high tension bolts, we got joint axial force of high tension bolts form beam path of ultrasonic waves. Furrther, we can identify that constitution of plant safety inspection system is possible.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.3
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• pp.295-304
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• 2000

To evaluate the structural integrity for the strainer under seismic loading the seismic analysis and design were performed for T-type strainer in accordance with ASME, Section Ⅲ, Class 3(ND). Since there are no specified design requirements for the strainer in ASME Code, the strainer body was analysed according to ND-3500, valve design. Flanged joints connected with PCS piping were designed according to ND-3658.3. And the criteria for the cover flange was governed by the Appendix XI. Both a frequency analysis and an equivalent static seismic analysis of the strainer were carried out using the finite element computer program, ANSYS. The frequency analysis results show the fundamental natural frequency is greater than 33Hz, thus justifying the use of the equivalent static analysis through which membrane and bending stresses are obtained in the critical points near the branch connection area. The results of the seismic evaluation fully satisfied with the structural acceptance criteria of the ASME Code. Accordingly the structural integrity on the strainer body and flanges were proved.