• Tunnel and Underground Space
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• v.24 no.1
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• pp.89-96
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• 2014

Rock joint surface roughness, which is known to be one of the most important factors for defining shear strength of rock mass, has been researched in various methods. However, approaches to separate a roughness into two groups (primary and secondary) for evaluating the roughness have been rarely performed. In this study, elements of secondary roughness were eliminated through direct shear testing with tensile joint specimen and they were quantified with joint parameters. It is revealed that roughness parameters decrease with increasing the normal stress and sampling intervals, except for the case in which the normal stress is larger than 1.5 MPa. Also it is analyzed that ratio of area reduction in the opposite direction of shearing decreases with increasing the roughness parameter.

• Structural Engineering and Mechanics
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• v.7 no.4
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• pp.377-386
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• 1999

The stress distribution in a symmetrically laminated composite plate subjected to in-plane compression are evaluated using finite element analysis. Six different finite element models are created for the study of stresses in the plate after buckling. Two finite element modelling approaches are adopted to obtain the stress distribution. The first approach starts with a full model of shell elements from which sub-models of solid elements are spin-off The second approach adopts a full model of solid elements at the beginning from which sub-models of solid elements are created. All sub-models have either 1-element thickness or 14-element thickness. Both techniques show high interlaminar direct and shear stresses at the free edges. The study also provides vital information of the distribution of all components of stresses along the unloaded edges in length direction and also in the thickness direction of the plate.

• Geomechanics and Engineering
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• v.12 no.3
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• pp.399-415
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• 2017

A series of direct shear tests were conducted to investigate the frictional properties of the interface between structures and the filling soil of Chongqing airport fourth stage expansion project. Two types of structures are investigated, one is low carbon steel and the other is the bedrock sampled from the site. The influence of soil water content, surface roughness and material types of structure were analyzed. The tests show that the interface friction and shear displacement curve has no softening stage and the curve shape is close to the Clough-Duncan hyperbola, while the soil is mainly shear contraction during testing. The interface frictional resistance and normal stress curve meets the Mohr-Coulomb criterion and the derived friction angle and frictional resistance of interface increase as surface roughness increases but is always lower than the internal friction angle and shear strength of soil respectively. When surface roughness is much larger than soil grain size, soil-structure interface is nearly shear surface in soil. In addition to the geometry of structural surface, the material types of structure also affects the performance of soil-structure interface. The wet interface frictional resistance will become lower than the natural one under specific conditions.

• Journal of computational fluids engineering
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• v.13 no.4
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• pp.96-106
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• 2008

We review a series of studies on turbulent skin friction drag reduction in wall-turbulence recently conducted in Japan. First, an identity equation relating the skin friction drag and the Reynolds shearstress (the FIK identity) is introduced. Based on the implication of the FIK identity, a new analytical suboptimal feedback control law requiring the streamwise wall-shear stress only is introduced and direct numerical simulation (DNS) results of turbulent pipe flow with that control is reported. We also introduce DNS of an anisotropic compliant surface and parameter optimization using an evolutionary optimization technique.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.149-152
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• 2008

In structural design provision, maximum punching shear stress of slabs is prescribed as combined stress of direct shear occurred by balanced gravity load and eccentric shear occurred by unbalanced moment. This means that the effect of unbalanced moment is considered to decide the punching shear stress. However, from the resistance capacity standpoint, the effect of unbalanced moment strength is not considered for deciding punching shear strength. For this problem, a model to show unbalanced moment-punching shear interrelation was proposed. In the model, the relation between load effect and resistance capacity in unbalanced moment-punching shear was two-dimensionally expressed. Using the interrelation model, a method how unbalanced moment strength should be considered to decide the punching shear strength was proposed. Additionally, a effective width enlargement factor for deciding the unbalanced moment strength of flat plates with shear reinforcements was proposed. The interrelation model proposed in this paper is very effective for the design because not only punching shear and unbalanced moment strengths but also failure modes of flat plates can be accurately predicted.

• Journal of Biomedical Engineering Research
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• v.26 no.3
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• pp.157-161
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• 2005

Direct injection of a fibrinolytic agent to the intraarterial thrombosis may increase the effectiveness of thrombolysis by enhancing the permeation of thrombolytic agents into the blood clot. Permeation of fibrinolytic agents into a clot is influenced by the surface pressure, which is determined by the injection velocity of fibrinolytic agents. In order to calculate the pressure distribution on the clot surface for different jet velocities (1, 3, 5 m/sec) and nozzle arrangements (1, 9, 17 nozzles), computational fluid dynamic methods were used. Thrombolysis of a clot was mathematically modeled based on the pressure and lysis front velocity relationship. Direct injection of a thrombolytic agent increased the speed of thrombolysis significantly and the effectiveness was increased as the ejecting velocity increased. The nine nozzles model showed about $20\%$ increase of the lysed volume, and the one and seventeen nozzles models did not show significant differences. The wall shear stress decreased as the number of nozzles increased, and the wall shear stress in most vessel wall was lower than 25 Pa. The results implied that thrombolysis could be accelerated by direct injection of a drug with the moderate velocity without damaging the blood vessel wall.

• Journal of the Korean Geotechnical Society
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• v.18 no.1
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• pp.79-89
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• 2002

Various geosynthetics used as liners or protection layers are installed in the solid waste landfills. The interface shear strength between geosynthetics installed at the slope of the landfill is a very important variable for the safe design of the bottom and cover systems in the solid waste landfills. The interface shear strength between Geomembrane and Geotexile is estimated by a large direct shear test in this study, The effects of normal stress, water existing between geosynthetics and surface condition of Geomembrae, i.e. smooth or textured, were investigated. The test results show that the effect varied depending on the level of normal stress and the type of geosynthetic combinations. The shear strength was evaluated by the Mohr-Coulomb failure criterion in this research. The shear strength parameters obtained from tests considering the site specific conditions such as normal stress, dry or wet, and surface condition of geosynthetic should be applied to the design of geosynthetics installed at the slope of the landfill to construct a safe solid waste landfill.

• Journal of computational fluids engineering
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• v.14 no.4
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• pp.101-108
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• 2009

We present a new finite-element scheme for direct numerical simulation of particle suspensions in simple shear flow of a viscoelastic fluid in 3D. The sliding tri-periodic representative cell concept has been combined with DEVSS/DG finite element scheme by introducing constraint equations along the domain boundary. Rigid body motion of the freely suspended particle is described by the rigid-shell description and implemented by Lagrangian multipliers on particle boundaries. We present the bulk rheology of suspensions through the numerical examples of single-, two- and many-particle problems, which represent a large number of such systems in simple shear flow. We report the steady bulk viscosity and the first normal stress coefficient, which show shear-thickening behavior for both properties.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1181-1192
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• 2008

A laboratory investigation was carried out into effects of strain rate on undrained shear behavior of Holocene clay underneath Kobe Airport with an objective to evaluate the factor of safety of the retaining structure built on it. It was examined in a series of triaxial compression and extension tests performed using different rate of axial straining. A comparative compression test in which the strain rate was changed in steps was also carried out. Similar tests were performed in constant-volume direct shear box (DSB) test. And, the deformation characteristics of the clay were also examined in order to evaluate the variation of stiffness during undrained shearing. It was found that the undrained strength increased with not only the shear rate but also the consolidation period. ISOTACH properties seemed a key to govern the undrained shear behavior.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.285-298
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• 2003

Shear properies of geosynthetic/geosynthetic and geosynthetic/soil interfaces which are widely met in landfill sites were evaluated from the inclined board tests. The inclined board testing apparatus is known to reproduce the shear behavior on the low normal stress most accurately. In this study, the friction angle of each interface was estimated and the tensile force mobilized at the geosynthetic was measured as well. The test results showed that the friction angle of each interface and the tensile force of the geosynthetics depended on the amount of normal stress, the type of the geosynthetics used, and the combinations of geosynthetics and soils. In addition, the sand/geotextile/geomembrane interface system was simulated in this study, and it was observed that the tensile force developed at the geomembrane decreased due to the protection effect of the geotextile located above the geomembrane. The test results of this research was compared with those of direct shear tests published, too. Finally, by comparing the measured tensile force of the geosynthetics when the initial displacement of the box occurs, when the slope is called as the critical slope, with suggested analytic solution, the accuracy of analytic solution and the applicability to design were identified.