• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.8
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• pp.1097-1104
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• 2003

The current study analyzes Langmuir slip boundary condition theoretically and it is tested in practical numerical analysis for separation-associated flow. Slip phenomenon at the channel wall is properly implemented by various numerical slip boundary conditions including Langmuir slip model. Compressible backward-facing step flow is compared to other analysis results with the purpose of diatomic gas Langmuir slip model validation. The numerical solutions of pressure and velocity distributions where separation occurs are in good agreement with other numerical results. Numerical analysis is conducted for Reynolds number from 10 to 60 for a prediction of separation at T-shaped micro manifold. Reattachment length of flows shows nonlinear distribution at the wall of side branch. The Langmuir slip model predicts fairly the physics in terms of slip effect and separation.

• Journal of the Korean Geotechnical Society
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• v.19 no.3
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• pp.65-74
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• 2003

The dragload on pile groups in consolidating ground was investigated based on a numerical analysis. The case of a single pile and subsequently the response of groups were analyzed by 2D and 3D finite element studies. Conventional continuum elements and special slip elements were used in the analyses for comparison. Based on a limited parametric study, it is shown that dragload for a single pile and group effect are normally overestimated by continuum analyses, compared with the predictions by the slip analyses. The group effect was examined from the slip analysis by considering various factors such as pile configurations, surface loading, interface friction coefficient, and axial loading on piles. An examplary analysis and one previous experimental observation of dragload and group effects were back-analysed. The case histories demonstrated that the slip analysis might predict a better estimate of dragload and group effect compared to the no-slip continuum analysis.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.3
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• pp.164-169
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• 2009

The slip velocity and the temperature jumps for low-speed flow in microchannels are investigated using Langmuir slip boundary condition. This slip boundary condition is suggested to simulate micro flow. The current study analyzes Langmuir slip boundary condition theoretically and it analyzed numerically micro-Couette flow, micro-Poiseuille flow and grooved microchannel flow. First, to prove validity for Langmuir slip condition, an analytical solution for micro-Couette flow is derived from Navier-Stokes equations with Langmuir slip conditions and is compared with DSMC and an analytical solution with Maxwell slip boundary condition. Second, the numerical analysis is performed for micro-Poiseuille flow and grooved microchannel flow. The slip velocity and temperature distribution are compared with results of DSMC or Maxwell slip condition and those are shown in good agreement.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2585-2596
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• 1994

Many particle filled materials like Poweder/Binder mixtures for poweder injection moldings, have complicated rheological behaviors such as an yield stress and slip phenomena. In the present study, numerical simulation programs via a finite element method and a finite difference method were developed for the quasi-three-dimensional flows and the two-dimensional flow models, respectively, with the slip phenomena taken into account in terms of a slip velocity. In order to qualitatively understand the slip effects, typical numerical results such as vector plots, pressure contours in the cross-channel plane, and isovelocity controus for the down-channel direction were discussed with respect to various slip coefficients. Slip velocities along the boudary surfaces were also investigated to find the effects of the slip coefficient and processing conditions on the overall flow behavior. Based on extensive numerical calculations varying the slip coefficients, pressure gradient, aspect ratio, and power law index, the screw characteristics of the extrusion process were studied in particular with comparisons between the slip model and non-slip model.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.18 no.2
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• pp.144-153
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• 2009

It is widely known that no-slip assumptions are often violated on regular basis in micrometer- or nanometer-scale fluid flow. In the case of cavity-filling process of nanoimprint lithography(NIL), slip phenomena take place naturally at the solid-to-liquid boundaries, that is, at the mold-to-polymer or polymer-to-substrate boundaries. If the slip or partial slip phenomena are promoted at the boundaries, the processing time of NIL, especially of thermal-NIL which consumes more tact time than that of UV-NIL, can be significantly improved. In this paper it is aimed to elucidate how the cavity-filling process of NIL can be influenced by the slip phenomena at boundaries and to what degree those phenomena increase the process rate. To do so, computational fluid dynamics(CFD) analysis of cavity filling process has been carried out. Also, the effect of mold pattern shape and initial thickness of polymer resist were considered in the analysis, as well.

• The KSFM Journal of Fluid Machinery
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• v.2 no.3 s.4
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• pp.17-23
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• 1999

In the present numerical analysis, investigation of the effect of blade loadings from design shape on the slip factor variation was studied. Both the Eckardt radial bladed impeller and the backswept impeller were analyzed. In addition, a new design of the blade profile was arbitrarily attempted to generate a center-loading pattern in the original backswept impeller. Three dimensional compressible Navier-Stokes flow analysis with the Baldwin-Lomax turbulence model was applied to get the numerical slip factor at each impeller exit plane using the mass-averaging technique. The numerical slip (actors are in good agreement with the experimental ones and the Wiesner's slip factors deviate further from the numerical and experimental ones in both backswept impellers. Deviation angles and meridional channel loadings are found in no relation with the trend of change of the slip factor. Blade-to-blade loadings in midspan location are, however, found to have a direct relationship, especially at the sections where maximum loadings we to be expected. That information can be utilized in establishing an improved expression for slip factors in the future.

• Journal of the Korean Society of Safety
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• v.27 no.5
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• pp.185-189
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• 2012

While there is no standards on slip risk for contaminants on surface, glycerol is described in standard contaminant for measuring coefficient of friction(COF) and slip resistance such as ISO 13287. But that is just used to measure the slip resistance of surface materials and shoes not to evaluate the contaminant materials. Therefore the objective of this study was to find out the relationship between standard contaminant and the contaminants used usually at the workplaces. For this, some measurement criteria were acquired from the analysis based on biomechanics and kinetics of human gait during slips. The slip resistance according to viscosity of the contaminants was measured applying the criteria and slip probability was determined by the gait analysis. Some factors which should be considered when measuring the slip resistance were identified. The velocity, acceleration, contact time and contact pressure should be 1 m/sec, 10 $m/sec^2$, 350 kPa and less than 0.5sec respectively. The variation of viscosity according to temperature for working oils was different from that of standard contaminant. The static coefficient of friction (SCOF) of working oils was almost 0.5 times as large as the SCOF of standard contaminant. So it was assumed to be difficult to compare the contaminants at the workplaces with the glycerol as a standard contaminant for estimating the slip risk.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.127-134
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• 2015

Recently, the external bonding of carbon fiber reinforced polymer (CFRP) sheets has come to be regarded as a very effective method for strengthening of reinforced concrete structures. The behavior of CFRP-strengthened RC structure is mainly governed by the interfacial behavior, which represents the stress transfer and relative slip between concrete and the CFRP sheet. In this study, the effects of bonded length, width and concrete strength on the interfacial behavior are verified and a bond-slip model is proposed. The proposed bond-slip model has nonlinear ascending regions and exponential descending regions, facilitated by modifying the conventional bilinear bond-slip model. Finite element analysis results of interface element implemented with bond-slip model have shown good agreement with the experimental results performed in this study. It is found that the failure load and strain distribution predicted by finite element analysis with the proposed bond-slip are in good agreement with results of experiments.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.91-96
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• 2006

Presently, cycle-slip detection is done between adjacent two points in many cycle-slip methods. Inherently, it is simple wavelet analysis. A new idea is put forward that the number of difference point can adjust by a parameter factor; we study this method to smooth raw data and detect cycle-slip with wavelet analysis. Taking CHAMP satellite data for example, we get some significant conclusions. It is showed that it is valid to detect cycle-slip in GPS phase measurement based on this wavelet function, and it is helpful to improve the precision of GPS data pre-processing and positioning.

• Structural Engineering and Mechanics
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• v.56 no.2
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• pp.275-291
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• 2015

Adherence between reinforcement and the surrounding concrete is usually ignored in finite element analysis (FEA) of reinforced concrete (RC) members. However, load transition between the reinforcement and surrounding concrete effects RC members' behavior a great deal. In this study, the effects of bond-slip on the FEA of RC members are examined. In the analyses, three types of bond-slip modeling methods (perfect bond, contact elements and spring elements) and three types of reinforcement modeling methods (smeared, one dimensional line and three dimensional solid elements) were used. Bond-slip behavior between the reinforcement and surrounding concrete was simulated with cohesive zone materials (CZM) for the first time. The bond-slip relationship was identified experimentally using a beam bending test as suggested by RILEM. The results obtained from FEA were compared with the results of four RC beams that were tested experimentally. Results showed that, in FE analyses, because of the perfect bond occurrence between the reinforcement and surrounding concrete, unrealistic strains occurred in the longitudinal reinforcement. This situation greatly affected the load deflection relationship because the longitudinal reinforcements dominated the failure mode. In addition to the spring elements, the combination of a bonded contact option with CZM also gave closer results to the experimental models. However, modeling of the bond-slip relationship with a contact element was quite difficult and time consuming. Therefore bond-slip modeling is more suitable with spring elements.