• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.481-486
• /
• 2001

The hydrodynamic instability of the three-dimensional boundary layer on a rotating disk introduces a periodic modulation of the mean flow in the form of stationary cross flow vortices. Detailed numerical values of the growth rates, neutral curves and other characteristics have been calculated for the Type II-instabilities. Presented are the neutral stability results concerning the two instability modes by solving new linear stability equations reformulated not only by considering whole convective terms but by correcting some errors in the previous stability equations. The present stability results are agree with the previously known ones within reasonable limit. The spatial amplification contours have been calculated for the moving disturbance wave, whose azimuth angle is between $\varepsilon=-10^{\circ}$ and $-20^{\circ}$. The transition flow of the moving disturbance wave will be developed at $\varepsilon=-15^{\circ}$ and Re=352 corresponding at the growth rates n = 5.8 from the spatial amplification contours.

• Structural Engineering and Mechanics
• /
• v.36 no.1
• /
• pp.111-127
• /
• 2010

This paper studies the effects of spatially varying ground motions on the responses of a bridge frame located on a canyon site. Compared to the spatial ground motions on a uniform flat site, which is the usual assumptions in the analysis of spatial ground motion variation effects on structures, the spatial ground motions at different locations on surface of a canyon site have different intensities owing to local site amplifications, besides the loss of coherency and phase difference. In the proposed approach, the spatial ground motions are modelled in two steps. Firstly, the base rock motions are assumed to have the same intensity and are modelled with a filtered Tajimi-Kanai power spectral density function and an empirical spatial ground motion coherency loss function. Then, power spectral density function of ground motion on surface of the canyon site is derived by considering the site amplification effect based on the one dimensional seismic wave propagation theory. Dynamic, quasi-static and total responses of the model structure to various cases of spatially varying ground motions are estimated. For comparison, responses to uniform ground motion, to spatial ground motions without considering local site effects, to spatial ground motions without considering coherency loss or phase shift are also calculated. Discussions on the ground motion spatial variation and local soil site amplification effects on structural responses are made. In particular, the effects of neglecting the site amplifications in the analysis as adopted in most studies of spatial ground motion effect on structural responses are highlighted.

• Korean Journal of Optics and Photonics
• /
• v.8 no.4
• /
• pp.308-314
• /
• 1997

We have studied the generation of an array of dark spatial solitons in a self-deforcusing medium. Unlike a single fundamental dark spatial soliton, we show numerically that the generation of an array of dark spatial solitons from a spatially sinusoidal input beam needs an adiabatic amplification of nonlinear refractive index with the beam propagation distance. In experiment, we establish a Mach-Zehnder interferometer for making the sinusoidal input beam and use a cylindrical lens for the adiabatic amplification. We observe that the dark soliton's dip-width becomes narrower and the background intensity distribution becomes flatter with increasing the nonlinearity.

• Steel and Composite Structures
• /
• v.21 no.5
• /
• pp.1069-1084
• /
• 2016

This paper introduces a new and effective design amplification factor-based approach for reliable optimum design of trusses. This paper may be categorized as in the family of decoupled methods that aiming for a reliable optimum design based on a Design Amplification Factor (DAF). To reduce the computational expenses of reliability analysis, an improved version of Response Surface Method (RSM) was used. Having applied this approach to two planar and one spatial truss problems, it exhibited a satisfactory performance.

• Proceedings of the KSME Conference
• /
• 2000.11b
• /
• pp.585-590
• /
• 2000

The hydrodynamic instability of the three-dimensional boundary layer on a rotating disk introduces a periodic modulation of the mean flow in the form of stationary cross flow vortices. Detailed numerical values of the growth rates, neutral curves and other characteristics of the two instabilities have been calculated over a wide range of parameters. Presented are the neutral stability results concerning the two instability modes by solving new linear stability equations reformulated not only by considering whole convective terms but by correcting some errors in the previous stability equations. The present stability results are agree with the previously known ones within reasonable limit. The flow is found to be always stable for a disturbance whose dimensionless wave number at Re=1200 is greater than 0.75. Also, the spatial amplification contours have been calculated for the moving disturbance wave, whose azimuth angle is between ${\varepsilon}=15^{\circ}$ and $12.5^{\circ}$.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.23 no.6
• /
• pp.414-421
• /
• 2011

In determination of the crest height of a vertical structure against attacking of obliquely incident waves, most of existing studies have suggested to use the overtopping reduction factor due to incident angles. However, they have not considered the amplification of wave heights and the spatial distribution of wave overtopping. In this study, a spatial distribution of overtopping due to the amplification of wave heights along a vertical structure is investigated experimentally. It is recommended that the crest height can be determined by the same manner as that for normally incident waves up to 3 significant wave lengths from the one end of the structure. However, the rest part of the structure can be done by employing the overtopping reduction factor with considering the amplification of wave heights and the spatial distribution of wave overtopping.

• Journal of Mechanical Science and Technology
• /
• v.17 no.9
• /
• pp.1388-1396
• /
• 2003

The hydrodynamic instability of the three-dimensional boundary layer on a rotating disk introduces a periodic modulation of the mean flow in the form of stationary cross flow vortices. The instability labeled Type II by Faller occurs first at lower Reynolds number than that of well known Type I instability. Detailed numerical values of the amplification rates, neutral curves and other characteristics of the two instabilities have been calculated over a wide range of parameters. Presented are the neutral stability results concerning the two instability modes by solving the appropriate linear stability equations reformulated not only by considering whole convective terms but also by correcting some errors in the previous stability equations. The present stability results agree with the previously known ones within reasonable limit. Consequently, the flow is found to be always stable for a disturbance whose dimensionless wave number is greater than 0.75. Some spatial amplification contours have been computed for the stationary disturbance wave, whose azimuth angle $\varepsilon$= 11.29$^{\circ}$ to 15$^{\circ}$ and for the moving disturbance wave, whose azimuth angle $\varepsilon$ = 12.5$^{\circ}$ to 15$^{\circ}$. Also, some temporal amplification contours have been computed for the stationary disturbance wave, whose azimuth angle $\varepsilon$= 11.29$^{\circ}$ to 15$^{\circ}$ and for the moving disturbance wave, whose azimuth angle $\varepsilon$= 12$^{\circ}$ to 15$^{\circ}$. The flow instability was observed by using a white titanium tetrachloride gas over rotating disk system. When the numerical results are compared to the present experimental data, the numerical results agree quantitatively, indicating the existence of the selective frequency mechanism.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.14 no.4
• /
• pp.352-357
• /
• 2004

This paper studies the errors that associated with particle velocity and intensity in a space. We theoretically derived their bias error and random error. The analysis shows that the more samples do not always guarantee the better results. The random error of the velocity and intensity are increased when we have many samples. The characteristics of the amplification of the random error are analyzed in terms of the sample spacing. The amplification was found to be related to the spatial differential of random noise. The numerical simulations are performed to verify theoretical results.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.35 no.4
• /
• pp.759-768
• /
• 2015

The ground motions of large dimensional structures such as long span bridges at different stations during an earthquake, are inevitably different, which is known as the ground motion spatial variation effect. There are many causes that may result in the spatial variability in seismic ground motion, e.g., the wave passage effect due to the different arrival times of waves at different locations; the loss of coherency due to seismic waves scattering in the heterogeneous medium of the ground; the site amplification effect owing to different local soil properties. In previous researches, the site amplification effects have not been considered or considered by a single-layered soil model only. In this study, however, the ground motion amplification and filtering effects are evaluated by multi-layered soil model. Spatially varying ground motion at the sites with different number of layers, depths, and soil characteristics are generated and the variation characteristics of ground motion time histories according to the correlation of coherency loss function and soil conditions are evaluated. For the bridge system composed of two unit bridges, seismic behavior characteristics are analyzed using the generated seismic waves as input ground motion. Especially, relative displacement due to coherency loss and site effect which can cause the unseating and pounding between girders are evaluated. As a result, considering the soil conditions of each site are always important and should not be neglected for an accurate structural response analysis.

• Journal of the Korean earth science society
• /
• v.30 no.7
• /
• pp.810-823
• /
• 2009

One of the critical factors in accurate determination of earthquake source parameters, and in prediction of seismic hazards is the detailed information related to the site amplification characteristics. The site amplification characteristics of the broad-band seismic stations in Korea were estimated as a function of frequency in the range of 0.2 to 20 Hz. A total of 1275 seismograms recorded from 43 earthquakes observed from 2003 to 2008 in the southern Korean Peninsula were used. It was found that the site amplification ratios for 28 stations estimated from the inversion of the ground motion model were approximately concordant with those obtained from the horizontal-to-vertical (H/V) spectral ratio except for some stations. The spectral site amplification characteristics obtained in this study did not show any considerable spatial distribution. It revealed to be largely correlated with the degree of weathering rather than the basement rock type. Considering the spectral site amplification ratio, 28 broad-band stations were classified into four groups and the characteristics of each group were described in the text.