• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.34 no.4
• /
• pp.213-219
• /
• 2021

Polytetrafluoroethylene (PTFE) is a commercialized friction material in friction pendulum systems used for earthquake hazard mitigation in structures, and it has excellent chemical resistance and frictional performance. However, PTFE has a relatively low wear resistance for the friction pendulum systems in service. As an alternative to PTFE, a cost-effective frictional material, polyvinylidene fluoride (PVDF) strengthened by magnesium oxide (MgO), with enhanced wear resistance performance is proposed in this study. The frictional performance of the developed PVDF/MgO was evaluated through experiments and compared with that of PTFE. Accordingly, a friction pendulum system was designed using the measured friction coefficient. The performance of this friction pendulum system was evaluated via nonlinear time history analyses of bridges. Subsequently, the plausibility of using PVDF/MgO as an alternative to PTFE as a friction material for friction pendulum systems was discussed.

• Journal of the Korean Geotechnical Society
• /
• v.26 no.8
• /
• pp.5-14
• /
• 2010

To simulate two-dimensional plane-strain conditions in the laboratory model test, the side frictional resistance between the soil and thick glass or plastic sheet of the soil container should be reduced as much as possible. However, in fact this side friction cannot be removed completely. In this paper, the ground model simulated as a multi-sized aluminium rod mixture was introduced to get rid of the side frictional resistance and applied to the laboratory shear box test. In addition, an application of the close range photogrammetric technique to the shear box test was validated. As a result, it was found that a mean value of dilation angle from the close range photogrammetry was close to the dilation angle defined by the curve of shear strain vs. volumetric strain.

• Journal of the Korean Geosynthetics Society
• /
• v.12 no.4
• /
• pp.77-86
• /
• 2013

Laboratory pullout tests were conducted to evaluate pullout performance of steel strip reinforcements with deformed steel bars as transverse members. The steel strip reinforcement has an installation hole to assemble a deformed steel bar. Jumunjin standard sand is used to form a relative density of ground model to 80%. Frictional resistance of steel strip reinforcement without transverse member increases sharply at the initial displacement and quickly decreases with displacement. Maximum frictional resistance increases linearly as normal pressure increasing, and soil-reinforcement interaction friction angle(${\rho}_{peak}$) of a steel strip reinforcement is estimated to $14.64^{\circ}$. Passive resistance increases with displacement and converge into maximum passive resistance in most cases. Maximum passive resistance increases linearly as normal pressure increasing irrespective of shape of the steel reinforcement. Pullout force of steel strip reinforcements with installation holes or transverse members largely increases about 4 to 7 times compared to frictional resistance force of steel strip reinforcements when embedment length($L_e$) of steel strip reinforcements is 500 mm. In the case of using 2 transverse members, interference effect is observed due to the spacing of 2 transverse members and location of assembly holes and transverse members.

• Elastomers and Composites
• /
• v.55 no.3
• /
• pp.161-166
• /
• 2020

On the basis of the use of shoes, the outsole, which is mainly made of rubber, has various characteristics. The most important of these characteristics is abrasion resistance and friction. Generally, the abrasion resistance can be improved by adding more reinforcing filler such as silica to the rubber; however, the friction force drops. Owing to these problems, rubber having excellent abrasion resistance and rubber having excellent frictional force are blended. In this study, various characteristics, including wear resistance and friction, were evaluated by blending NBR/SBR or NBR/BR mixture with high wear resistance and CIIR with high friction. The CIIR was increased up to 60 phr, whereas the friction wear characteristics were rapidly changed in the NBR/CIIR blend ratio from 75:15 to 60:30.

• Journal of Korea Water Resources Association
• /
• v.47 no.11
• /
• pp.1077-1086
• /
• 2014

The flood wave generated due to dam break is affected by initial depth upstream since it is related with hydraulic characteristics propagating downstream, and flow resistance stress has influence on the celerity, travel distance, and approaching depth of shock wave in implementing numerical simulation. In this study, a shallow water flow model employing SU/PG scheme was developed and verified by analytic solutions; propagation characteristics of dam break according to flow resistance and initial depth were analyzed. When bottom frictional stress was applied, the flow depth was relatively higher while the travel distance of shock wave was shorter. In the case of Coulomb stress, the flow velocity behind the location of dam break became lower compared with other cases, and showed values between no stress and turbulent stress at the reach of shock wave. The value of Froude number obtained by no frictional stress at the discontinuous boundary was the closest to 1.0 regardless of initial depth. The adaption of Coulomb stress gave more appropriate results compared with turbulent stress at low initial depth. However, as the initial depth became increased, the dominance of flow resistance terms was weakened and the opposite result was observed.

• 한국전산유체공학회:학술대회논문집
• /
• 2003.10a
• /
• pp.193-193
• /
• 2003

• Journal of the Society of Naval Architects of Korea
• /
• v.40 no.4
• /
• pp.8-15
• /
• 2003

This paper presents the method for developing an optimum hull form with minimum wave resistance using SQP(sequential quadratic programming) as an optimization technique. The wave resistance is evaluated by a Rankine source panel method with non-linear free surface conditions and the ITTC 1957 friction line is used to predict the frictional resistance coefficient. The geometry of the hull surface is represented and modified using B-spline surface patches. The optimization method is applied to Series 60 hull and KCS(KRISO 3600 TEU Container Ship). The obtained results prove that the method is appropriate for preliminary hull form design.

• International Journal of Ocean System Engineering
• /
• v.3 no.1
• /
• pp.1-9
• /
• 2013

A design procedure for a ship with minimum resistance had been developed using a numerical optimization method called SQP (Sequential Quadratic Programming) combined with computational fluid dynamics (CFD) technique. The frictional resistance coefficient was estimated by the ITTC 1957 model-ship correlation line formula and the wave-making resistance coefficient was evaluated by the potential-flow panel method with the nonlinear free surface boundary conditions. The geometry of the hull surface was represented and modified by B-spline surface modeling technique during the optimization process. The Series 60 ($C_B$=0.60) hull was selected as a parent hull to obtain an optimized hull that produces minimum resistance. The models of the parent and optimized hull forms were tested at calm water condition in order to demonstrate the validity of the proposed methodolgy.

• Proceedings of the Korean Geotechical Society Conference
• /
• 1999.10a
• /
• pp.389-396
• /
• 1999

In this study compressive and tensile load tests have been performed to investigate reinforcing effect and load transfer mechanism of small diameter piles installed in the foundation soil for the marine suspension bridge. Load tests were carried out on steel plate with diameters of 50cm, 100cm and 150cm varying loads starting from 39 tons up to 314 tons. Small diameter piles were proved to behavior like as friction piles and loads were not transmitted to the bottom of piles. From pull-out tests, the uplift capacity of small diameter piles was largely influenced by reinforcing materials compared to frictional resistance between piles and adjacent soils. The bearing capacity of small diameter piles appeared to be higher than the ultimate bearing capacity evaluated using static formulae. The load carrying capacity of small diameter piles was superior to the bored piles with a similar size. Thus, ultimate bearing capacity estimated from static formulae can provide conservative designs and thereby resulting in economic disadvantages. A further study to accumulate data regarding various soil conditions is recommended for an improved estimation of bearing capacity of piles with small diameter.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2017.11a
• /
• pp.234-235
• /
• 2017

In order to improve the frictional resistance of existing high-speed planning hull, a step-like linear transformation has been researched which forms an air layer on the bottom. However, there is a lack of research on the proper position to confirm the effect of Running Attitude and step on each position. In this study, we confirmed the change of the Running Attitude, the effect of the step and the change of the frictional resistance when the step was applied in the longitudinal location.