• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.22 no.4
• /
• pp.230-234
• /
• 2010

This study examined the effect of wall friction on deformation characteristics of the cellular bulkhead, in terms of artificial wall friction based on the results of model tests according to the existing penetration ratio and loading height. 1. The effect of wall friction on deformation characteristics of the cellular bulkhead turned out to be less as the loading height decreases and the penetration ratio increases. The yield load also becomes less as wall friction decreases. 2. The ratio of the rotational displacement to the horizontal displacement of the cellular bulkhead becomes less as the loading height decreases and the penetration ratio increases. Hence it is concluded that the effect of wall friction has close relationship with the rotational displacement.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.20 no.2
• /
• pp.405-421
• /
• 2018

In most of cases, the wall friction coefficients applied for local tunnel design are quoted directly from foreign data or local design guideline. In the previous studies, the wall friction coefficient was estimated using the velocity decay method. However, it is difficult to estimate the wall friction coefficient when the convergence wind velocity in the tunnel is negative (-) or if there is a change in the natural wind. Therefore, in this study, the wall friction coefficient is estimated by applying the dynamic simulation technique in addition to the conventional the velocity decay method. As a result of the analysis, the coefficient of wall friction in the tunnels for the total of 9 tunnels (18 tubes both directions) was 0.011~0.025, and the mean value was estimated to be 0.020. In addition, the wall friction coefficient obtained quantitatively through this study was compared with the current design criteria.

• Journal of Power System Engineering
• /
• v.13 no.2
• /
• pp.18-29
• /
• 2009

미세유동에 대한 폭발적인 관심에 의해 이 분야의 연구는 다양한 측면에서 이루어지고 있다. 본 연구는 사각 미세채널에서의 슬립유동에 관한 연구 중 아직 제대로 이루어져 있지 않은 마찰특성에 관한 종횡비의 영향에 초점을 맞추어 3차원 수치해석을 행하였다. 그 결과 종횡비가 1.0 일 때 상하 벽면 및 좌우측 벽면에서의 전단음력은 동일하나, 종횡비가 감소함에 따라 전단응력은 상하 벽면과 좌우측 벽면이 상이한 강도로 증가함을 보였다. 또한 Knudsen 수의 증가에 따라서는 전단응력이 감소함을 알 수 있었다. 따라서 벽면에서의 전단응력은 종횡비를 증가시키거나 혹은 Knudsen 수를 증가시키면 감소시킬 수 있으며, 마찰계수(fRe)도 종횡비를 증가시키거나 혹은 Knudsen 수를 증가시키면 감소됨을 밝혔다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.8
• /
• pp.1545-1551
• /
• 1992

This work is concerned with the prediction of turbulent friction factors in rod bundles. In this study, the Law of the Wall is assumed to be valid over the entire flow area. The flow channel is divided into element channels, and the algebraic form of the "Law of the Wall" is integrated over each element channel to yield an analytic expression for the pressure drop in the rod bundle. The method is applied to rod bundles with 1.2

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.20 no.1
• /
• pp.39-53
• /
• 2018

Generally, the total ventilation resistance coefficient in a tunnel consists of inlet/outlet loss coefficient, wall friction coefficient, and other loss coefficient caused by sudden expansion and contraction of cross-section, etc. For the tunnel before opening, when the running ventilation fan is stopped, the wind speed in the tunnel is reduced by the total ventilation resistance drag. The velocity decay method is comparatively stable and easy to estimate the wall friction coefficient in the pre-opening tunnel. However, the existing study reported that when the converging wind speed is a negative value after the ventilation fan stops, it is difficult to estimate the wall friction coefficient according to the velocity decay method. On the other hand, for the operating tunnel in which the piston effect acts, a more complex process is performed; however, a reasonable wall friction coefficient can be estimated. This paper aims at suggesting a method to minimize the measurement variables of the piston effect and reviewing a method that can be applied to the operating tunnel. Also, in this study, a new method has been developed, which enables to calculate an variation of the piston effect if the piston effect is constant with a sudden change of external natural wind occurring while the wind speed in the tunnel decreases after the ventilation fan stops, and a programming logic has been also developed, which enables dynamic simulation analysis in order to estimate the wall friction coefficient in a tunnel.

• Journal of the Korean Geotechnical Society
• /
• v.35 no.12
• /
• pp.7-13
• /
• 2019

In the case of the drilled shaft, one of the methods for calculating unit skin friction stress of rock socket parts is to measure the roughness of the excavated face. This method is to estimate the unit skin frictional resistance using a device which measures the roughness shape of the excavated face in the excavation step. In this study, the roughness shapes of the face of the rock socket part in the drilled shaft were measured directly in the perforated hole and the results are used to identify the characteristics of the unit skin friction of the bedrock. In addition, the static load test and the load transfer test were performed on the same pile to verify the result of the roughness test.

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

• Journal of the Korean Geotechnical Society
• /
• v.17 no.5
• /
• pp.147-155
• /
• 2001

좁은 되메움 공간의 벽체가 연직 또는 한쪽 벽체만이 경사진 경우 수평토압에 관한 연구는 국내외에서 상당히 진전되어 왔으나, 대칭으로 경사진 경우의 연구는 미흡한 실정이다. 본 연구는 되메움 공간의 벽체가 대칭으로 경사지고 벽체간 하부폭이 다를 때 발생되는 수평토압에 관한 거동을 구명하기 위하여 시도되었다. 이를 위하여 모형토조를 사용하여 되메움 공간의 벽체가 대칭으로 경사진 경우 벽체의 경사각, 하부폭, 벽마찰각, 상대밀도를 변화시켜 총 24종류의 모형실험을 수행하였고, 이 결과를 Kellogg(1993)제안식, 벽면경사를 고려한 수정 제안식 및 벽면마찰반력으로부터 구한 수평토압과 비교, 분석하였다. 연구 결과 벽면마찰반력을 고려한 경우 평균연직토압을 적용하였음에도 Arching 효과가 발휘된 실험결과와 가장 근소한 차이를 나타내었다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.10
• /
• pp.2630-2636
• /
• 1995

A theoretically based prediction for the determination of the subchannel friction factor at low pitch to the rod diameter ratio (P/D < 1.2) in the bare rod bundle flow has been developed. The present model assumes the validity of the Law of Wall over the entire flow area. The algebraic form of the Law of the Wall is integrated over the entire flow area and the local friction velocity variation along the rod periphery is considered in this study. The present method is applied to the rod bundles with P/D < 1.2, and the prediction results show good agreement with the available experimental data.

• Journal of the Korean GEO-environmental Society
• /
• v.18 no.11
• /
• pp.19-26
• /
• 2017

When narrowly excavated in the urban area, the wall of backfill space is not only symmetrical but also asymmetrical. In this case, the horizontal stress induced by backfilling depends mostly on the wall asymmetry and the wall friction angle. Therefore, in this study, the model test in the laboratory was conducted to investigate horizontal earth pressure with depth considering various boundary conditions such as base width, wall friction, relative density of backfill, and wall angle. As the wall is smoother and wall angle is lower from the bottom, the results showed higher the horizontal stresses due to the increase of vertical stresses.