• Wind and Structures
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• v.17 no.4
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• pp.379-397
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• 2013

Large Eddy Simulations (LES) were carried out to investigate the aerodynamic characteristics of a rectangular cylinder with side ratio B/D=5 at Reynolds number Re=22,000 (based on cylinder thickness). Particular attention was devoted to the effects of velocity shear in the oncoming flow. Time-averaged and unsteady flow patterns around the cylinder were studied to enhance understanding of the effects of velocity shear. The simulation results showed that the Strouhal number has no significant variation with oncoming velocity shear, while the peak fluctuation frequency of the drag coefficient becomes identical to that of the lift coefficient with increase in velocity shear. The intermittently-reattached flow that features the aerodynamics of the 5:1 rectangular cylinder in non-shear flow becomes more stably reattached on the high-velocity side, and more stably separated on the low-velocity side. Both the mean and fluctuating drag coefficients increase slightly with increase in velocity shear. The mean and fluctuating lift and moment coefficients increase almost linearly with velocity shear. Lift force acts from the high-velocity side to the low-velocity side, which is similar to that of a circular cylinder but opposite to that of a square cylinder under the same oncoming shear flow.

• Journal of the Korean Geotechnical Society
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• v.35 no.2
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• pp.29-36
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• 2019

There always exist the spatial variations of material properties such as a shear wave velocity in a dam and between same type dams. These uncertainties cause those in evaluation of a shear wave velocity profile of a dam and should be considered in determining the shear wave velocity profile for a rockfill zone of a fill dam. In this paper, these uncertainties of a shear wave velocity in the rockfill zone of the fill dam in Korea are evaluated. And the shear wave velocity profile model considering these uncertainties in rockfillzone is proposed using the method based on Harmonic wavelet transform. The proposed shear wave velocity profile model is compared with Sawada-Takahashi model widely used for evaluation of a shear wave velocity profile of a rockfill zone of fill dams.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.318-326
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• 2008

Recently, a new seismic probe, called "MudFork", has been developed and can be utilized for accurate and easy measurements of shear wave velocities of soft soils. To expand its use to estimate undrained shear strength and density, correlations between those and shear wave velocity were being attempted. Cone penetration tests and a seismic test, using MudFork, were performed at a soft ground site near Incheon, Korea. Also, undisturbed samples were obtained and shear wave velocities of the samples were measured as well as undrained shear strength, using triaxial compression test and bender elements. A simple linear relationship between shear strength and shear wave velocity was obtained, and a tentative relationship between density and shear wave velocity was also defined.

• The Journal of the Acoustical Society of Korea
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• v.22 no.4E
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• pp.167-175
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• 2003

Shear wave velocity was measured and grain size analysis was conducted on two core samples obtained in unconsolidated marine sediments of the western continental margin, the East Sea. A pulse transmission technique based on the Hamilton frame was used to measure shear wave velocity. Duomorph ceramic bender transducer-receiver elements were used to generate and detect shear waves in sediment samples. Time delay was calculated by changing the sample length from the transducer-receiver element. Time delay is 43.18 μs and shear wave velocity (22.49 m/s) is calculated from the slope of regression line. Shear wave velocities of station 1 and 2 range from 8.9 to 19.0 m/s and from 8.8 to 22 mis, respectively. Shear wave velocities with depth in both cores are qualitatively in agreement with the compared model〔1〕, although the absolute value is different. The sediment type of two core samples is mud (mean grain size, 8-9Φ). Shear wave velocity generally increases with sediment depth, which is suggesting normally consolidated sediments. The complicated variation of velocity anisotropy with depth at station 2 is probably responsible for sediment disturbance by possible gas effect.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.402-413
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• 2006

Strength evaluation of soft soils is a formidable task because of difficulties in sampling, specimen preparation and setting in triaxial cells. In undrained triaxial testing, sampling disturbance, verticality of specimen and bedding effect give a great influence on shear strength measurements. In the other hand, shear wave measurements of specimens are less influenced by these factors. In this research, the bender elements were attached top cap and base pedestal of triaxial cell and shear wave velocities were measured. To initiate a methodology to evaluate shear strength indirectly by measuring shear wave velocity, a relationship between shear strength and shear wave velocity was developed with kaolinite specimens consolidated in the laboratory. Undrained shear strength turns out to increase linearly with shear wave velocity. Stress-strain curves can also be predicted with a hyperbolic model and shear wave measurements.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.121-131
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• 2007

Recently, the probability of rock joints being exposed to free faces is getting higher for the scale of rock mass structures gets larger. Also, the frequency of occurring dynamic events such as earthquakes and blasting has been increasing. Thus, the shear behavior of rock joints under different conditions needs to be investigated. In this study, a series of direct shear tests were carried out under various conditions to examine the velocity-dependent shear behavior of saw-cut rock joints. Two types of direct shear test were carried out. The first was to examine the velocity-dependent shear behavior of saw-cut rock joints at seven different shear velocities, each with three different normal stresses. The second was to examine the shear behavior of saw-cut rock joints when three different instantaneous shear velocities changed. As a result, the coefficient of friction was affected by normal stress. The breakpoint velocity, the point when the change of shear velocity starts to affect the frictional behavior, became lower as normal stress increased. Also, as the shear velocity became lower, the degree of stress-drop on stick-slip behavior became larger. As a result of examining the changes of friction coefficient, velocity weakening (decrease of friction coefficient) was observed. The decrement of friction coefficient due to the changes of shear velocity under slow shear velocity was larger than that under fast shear velocity.

• Geomechanics and Engineering
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• v.11 no.5
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• pp.713-723
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• 2016

Shear wave velocities of three selected sandy soils subject to drained triaxial compression test were continuously measured using the bender elements. The shear wave velocity during isotropic compression, as widely recognized, increased as confining pressure increased and they were correlated well. However, during drained shearing, the mean effective stress could no further provide a suitable correlation. The shear wave velocity during this stage was almost constant with respect to the mean effective stress. The vertical stress was found to be more favorable at this stage (since confining stress was kept constant). When sample was attained its peak stress, the shear wave velocity reduced and deviated from the previously existed trend line. This was probably caused by the non-uniformity induced by the formation of shear band. Subsequently, void ratios computed based on external measurements could not provide reasonable fitting to the initial stage of post-peak shear wave velocity. At very large strain levels after shear band formation, the digital images revealed that sample may internally re-arrange itself to be in a more uniform loose stage. This final stage void ratio estimated based on the proposed correlation derived during pre-peak state was close to the value of the maximum void ratio.

• Journal of the Korean Geotechnical Society
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• v.31 no.9
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• pp.17-27
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• 2015

We perform a series of experimental tests to evaluate whether the shear strength of clean sands can be reliably predicted from shear wave velocity. Isotropic drained triaxial tests on clean sands reconstituted at different relative densities are performed to measure the shear strength and bender elements are used to measure the shear wave velocity. Laboratory tests reveal that a correlation between shear wave velocity, void ratio, and confining pressure can be made. The correlation can be used to determine the void ratio from measured shear wave velocity, from which the shear strength is predicted. We also show that a unique relationship exists between maximum shear modulus and effective axial stress at failure. The accuracy of the equation can be enhanced by including the normalized confining pressure in the equation. Comparisons between measured and predicted effective friction angle demonstrate that the proposed equation can accurately predict the internal friction angle of granular soils, accounting for the effect of the relative density, from shear wave velocity.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.656-665
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• 2010

Shear modulus has been recognized as one of the important soil properties in dynamic analysis of ground and can be calculated from in situ measurement of shear wave velocity. Field seismic tests are the most accurate but expensive methods to investigate dynamic ground characteristics. Due to that reason, empirical equations for estimating the shear wave velocity are widely used rather than conducting in-situ tests. The most common equations are based on the N value obtained in conjuctions with a standard penetration test. In this paper, the field datas of standard penetration test and suspension PS logging measured in 126 sites of Korea were summarized and the correlation equations between N value and shear wave velocity are suggested.

• Journal of Mechanical Science and Technology
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• v.17 no.2
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• pp.296-309
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• 2003

The periodicity of the physiological flow has been the major interest of analytic research in this field up to now Among the mechanical forces stimulating the biochemical reaction of endothelial cells on the wall, the wall shear stresses show the strongest effect to the biochemical product. The objective of present study is to find the effects of velocity waveform on the wall shear stresses and pressure distribution along the artery and to present some correlation of the velocity waveform with the clinical observations. In order to investigate the complex flow phenomena in the bifurcated tube, constitutive equations, which are suitable to describe the rheological properties of the non-Newtonian fluids, are determined, and pulsatile momemtum equations are solved by the finite volume prediction. The results show that pressure and wall shear stresses are related to the velocity waveform of the physiological flow and the blood viscosity. And the variational tendency of the wall shear stresses along the flow direction is very similar to the applied sinusoidal and physiological velocity waveforms, but the stress values are quite different depending on the local region. Under the sinusoidal velocity waveform, a Newtonian fluid and blood show big differences in velocity. pressure, and wall shear stress as a function of time, but the differences under the physiological velocity waveform are negligibly small.