• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.591-604
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• 2008

In this study, two design examples of drilled shafts on soft ground in Ho-Chi-Minh City, Vietnam are introduced. One is for a 27-story apartment and the other is for a Arch bridge over Saigon river. Unlikely the normal cases in Korea, all of the bored pile foundations are supposed to be placed on soil layers. Therefore, skin friction between pile and ground is the most crucial design parameter. Three methods using SPT N value of sandy soil -Korean Road Bridge Code(1996), Reese and Wright (1977), and O'Neill and Reese (1988)- were adopted to obtain an ultimate axial bearing capacity. In order to verify the calculated bearing capacity, 3 sets of static load test and a Osterberg Cell test were performed at an apartment site and a bridge site respectively. LRFD (Load Resistance Factored Design) method was compared with ASD (Allowable Stress Design) method. On application of ASD method, safety factor for skin friction was adopted as 2 or 3 while safety factor for end bearing was 3. The design bearing capacities from ASD method matched well with those from LRFD method when safety factor for skin friction was adopted as 2.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.2
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• pp.67-76
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• 2017

In this study, the effect of caisson heel on the active earth pressure is investigated. Using limit analysis method, inclinations of slip surface developed above the heel with different lengths are analyzed. The shorter the heel length, the larger those of inside slip surface, however those of outside slip surface are not changed. According to the relative heel length, relationships of internal friction angle of backfill material - wall friction angle between caisson structure and backfill - friction angle acting on virtual section at the end of heel are presented. Earth pressures acting against caisson structure with relatively short heel are smaller than Rankine earth pressure but always greater than Coulomb earth pressure which does not consider the heel length.

• Tribology and Lubricants
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• v.27 no.6
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• pp.344-350
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• 2011

Friction and wear behavior of tungsten oxide nanorods (TONs) was investigated using friction force microscopy(FFM) employing colloidal probes instead of conventional sharp tips. Vertically well-ordered TONs with 40 nm diameter, 130 nm length and 100 nm pitch width were synthesized on an anodic aluminium oxide substrate using two step electrochemical anodizing processes. The colloidal probe (diameter 20 ${\mu}m$) attached at the free end of tipless cantilever was oscillated(scanned) against a stationary surface of vertically aligned TONs with various scan speeds (1.2 ${\mu}m/s$, 3.0 ${\mu}m/s$ and 6.0 ${\mu}m/s$) and sliding cycles (100, 200 and 400) under normal load of 800 nN. The friction force and wear depth decreased with the increase of the scan speed. Plastically deformed thin layers were formed and sparsely deposited on the worn nonorod surface. The lower wear rate of the TONs with the longer oscillating cycles was attributed to the decreased real contact pressure due to the increase of real contact area between the colloidal probe and the TONs.

• Coupled systems mechanics
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• v.11 no.3
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• pp.267-284
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• 2022

Due to the high usage of ABS in industries, such as aerospace, auto, recreational devices, boat, submarines, etc., the purpose of this project was to find a way to weld this material, which gives advantages, such as affordable, high speed, and good connection quality. In this experimental project, the friction welding method was applied with parameters such as numerical control (NC) machine with two different speeds and three cross-sections, including a flat surface, cone, and step. After the end of the welding process, samples were then applied for both tensile and bending tests of materials, and the results showed that, with increasing the machining velocity Considering of samples, the friction of the surface increased and then caused to increase in the surface temperature. Considering mentioned contents, the melting temperature of composite materials increased. This can give a chance to have a better combination of Nanomaterial to base melted materials. Thus, the result showed that, with increasing the weight percentage (wt %) of Nanomaterials contents, and machining velocity, the mechanical behavior of welded area for all three types of samples were just increased. This enhancement is due to the better melting process on the welded area of different Nano contents; also, the results showed that the shape of the welding area could play a significant role, and by changing the shape, the results also changed drastically.A better shape for the welding process was dedicated to the step surface.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.425-426
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• 2002

Lineal and angular movements of many engine components make the lubricant absorb air and the aerated lubricant greatly influences the clearance performance of contacting behaviors of engine components such as big-end bearing, cam and tappet, etc. This study investigates the behaviors of aerated lubricant in the gap between con-rod bearing and proceeding which is one of the most frictional energy consuming components in the engine. Our assumption for the analysis of aerated lubricant film is that the film formation is influenced by the two major factors. One is the density characteristics of the lubricant due to the volume change of lubricant by absorbing the bubbles and the other is the viscosity characteristics of the lubricant due to the surface tension of the bubble in the lubricant. In our investigation, it is found that these two major factors surprisingly increase the load capacity in certain ranges of bubble sizes and densities. Frictional forces are also influenced by the aerated bubble size and density, which eventually enlarge the shear resistance due the surface tension, Modified Reynolds' equation is developed for the computation of fluid film pressure with the effects of aeration ratio under the dynamic loading condition. From the calculated load capacity by solving modified Reynolds' equation, proceeding locus is computed with Mobility method at each time step.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.905-911
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• 2009

The viscosity drive method by the wheel which is widely used in the conventional railway systems needs a large friction force between the wheel and the guide-rail, which brings on a thrust force for a quick acceleration and a high-speed travelling. In addition, the viscosity drive method needs an increase of the vehicle weight for a large friction force. However, a maglev train is possible to be driven by the electro-magnet instead of the wheel, which produces a levitation and thrust force without any contact. In general, low-speed maglev train uses a linear induction motor(LIM) for propulsion that is operated under 300[km/h] due to the power-collecting and end-effect problems of LIM. In case of high-speed maglev train, a linear synchronous motor(LSM) is more suitable than LIM because of a high-efficiency and high-output properties. LSM has a driving principle as same as a conventional rotary synchronous motor(RSM), and the torque of RSM becomes the thrust force of LSM. A conventional LSM has relatively large air-gap compared with a conventional RSM. So, it must be achieved a design that is considered normal force by finite-asymmetric structure, end-effect on the entry and exit part, and support structure of a moving part. Therefore, in this research, authors accomplish a conceptualizing and basic design of a small-scaled LSM, and characteristics analysis using FEM.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.407-426
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• 2008

The bentonite slurry has been used as the stabilize suspension for wet process bored pile construction in Thailand. The bentonite suspension has benefit on filtration in the sand layer, but it creates thick cake film along pile shaft and loose sedimentation at pile toe. The base grouting technique was widely used to rectify the soft base or loose sedimentation problem of bored pile. The base grouting technique was not increased only end bearing capacity, but was also more increase in skin friction capacity of the bored piles. The comprehensive researches on base grouting was carried out by installing PVC casing inside the shaft to allow the drilling through the pile base in order to collect the soil sample below the pile tip. The polymer based slurry recently was used to replace the bentonite slurry to overcome the thick cake film along pile shaft as well as loose sedimentation at pile toe. The extent research on polymer slurry by physical model was performed to verify the real behavior of polymer. The appropriate mixing ratio of polymer was proposed. The design skin friction coefficient, $\beta$ and end bearing coefficient, Nq, for sand layer base on fully instrumented tested pile were proposed. The application on remedial of the lose capacity bored pile with large displacement in Bangladesh was proposed and discussed.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.43 no.5 s.311
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• pp.10-18
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• 2006

We propose a new approach to compute possible acceleration boundary, so is called dynamic manipulability, for multiple robotic systems with frictional contacts between robot end-effectors and object. As the frictional contact condition which requires each contact force to lie within a friction cone is based on the nonlinear inequality formalism is not easy to handle the constraint in manipulability analysis. To include the frictional contact condition into the conventional manipulability analysis we approximate the friction cone to a pyramid which is described by linear inequality constraints. And then achievable acceleration boundaries of manipulated object are calculated conventional linear programming technique under constraints for torque capability of each robot and the approximated contact condition. With the proposed method we find some solution to which conventional approaches did not reach. Also, case studies are Presented to illustrate the correctness of the proposed approach for two robot systems of simple planar robots and PUMA560 robots.

• Geotechnical Engineering
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• v.9 no.1
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• pp.31-44
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• 1993

Model tests in calibration chamber with open -ended steel pipe pile have been performed in sand deposit to clarify effect of soil plug on bearing capacity, load transfer mechanisms in soil plug, and behavior of soil plug under dynamic and static conditions. Model piles were devised so that bearing capacity of open -ended pile could be measured separately into outside skin friction, inside skin friction due to soil plug -pile interaction and end bearing force on the section of steel pipe pile. It may be concluded, form the test results, that the plugging level of open -ended pile is more correctily defined by specific recovery ratio, y, rather than by plug length ratio, PLR, and the major part of inside skin friction is generated within the range of three times as long as the inner diameter of the pile from the pile tip. The ratio of inside skin friction to total bearing capacity is much larger than that of outside skin friction to total bearing capacity. Therefore, the bearing capacity of pile could not be well predicted, unless the inside skin friction is properly taken into account.

• Journal of the Korean Geotechnical Society
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• v.28 no.3
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• pp.15-23
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• 2012

An internal friction angle, which is one of strength parameters of granular soils, can be obtained from direct shear tests or triaxial tests. The result of traixial tests can be influenced by various experimental conditions such as confining pressure, shearing rate, specimen diameter and height, and end constraint. In this study, undrained and drained shearing behaviors of Nakdong River sand were investigated for loose (Dr = 40%) and dense (Dr = 80%) specimens with 5, 7, and 10 cm in diameter. Friction angles such as undrained total stress friction angle, undrained effective stress friction angle, and drained friction angle obtained from Mohr's stress circle slightly increased and then decreased as a diameter of a specimen increased from 5, 7 to 10 cm, regardless of relative densities. The difference between friction angles caused by different specimen size was at maximum 4.5 degrees for undrained total stress friction angle of dense specimen. In most cases, there was little difference between friction angles of large and small specimens, which was less than 2 degrees. The difference between an effective friction angle from undrained tests and a drained friction angle from drained tests was at maximum 7 degrees for loose samples but negligible for dense samples.