• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.159-160
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• 2002

New S-shaped aeroelastic mesoflaps are utilized to control normal shock/boundary-layer interactions. New generation of the mesoflaps is designed f3r a better rigidness and a good flow uniformity across the ulteractions. ,Major advantages of the mesoflap system can be a better total pressure recovery downstream of the interactions due to the lambda shock structure over the flap system, and a rehabilitation of the thickened boundary layer due to bleeding through a cavity underneath the flap system. Skin friction has been measured downstream of the interactions, using the laser interferometer skin friction (LISF) meter, which optically detects the rate of thinning of an oil film applied to the test surface. Various flap-thicknesses of the S-shaped mesoflap arrays are tested, and the results are compared to the solid-wall reference case. Overall, not much difference in the level of skin friction is noticed for the S-shaped flap arrays of various thicknesses, and its level is lower than the skin friction downstream of the solid-wall interaction

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.923-932
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• 2009

Generally most of pile foundations are constructed with group pile rather than single pile. The study on efficiency and bearing capacity which are major elements for rational design of this group pile has been actively progressed, whereas there are truly only a few studies of negative skin friction working on group pile due to the consolidation of ground. The purpose of this study is to determine, among the elements of negative skin friction applied to pile, the occurrence modality of negative skin friction at center, side, and corner of $3{\times}3$ group pile using model test and, based on those observations, to propose the effective design direction of group pile.

• 대한기계학회논문집B
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• 제21권1호
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• pp.140-152
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• 1997

A simultaneous measurement of the wall skin friction and near-wall streamwise velocity fluctuations is performed using hot film and hot wire anemometers to investigate the relation between them. Near-wall turbulence statistics measured with a hot-wire probe are in good agreement with previous results. Turbulence properties of the wall skin friction fluctuations measured with a hot film also show fairly good agreements with those measured by others except that rms level is lower in the present study. Long-time averaged space- time correlations show that the wall skin friction is highly correlated with a turbulence structure which is tilted from the wall in the streamwise direction. Tilting angles are obtained from the phase shifts between the wall skin-friction and streamwise velocity fluctuations. The convection velocity of the near-wall streamwise velocity obtained from the space-time correlation is in good agreement with that from the direct numerical simulation database.

• Geomechanics and Engineering
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• 제8권6호
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• pp.769-781
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• 2015

The skin friction of a pile foundation is important and essential for its design and analysis. More attention has been given to the softening behaviour of skin friction of a pile. In this study, to investigate the load-transfer mechanism in such a case, an analytical solution using a nonlinear softening model was derived. Subsequently, a load test on the pile was performed to verify the newly developed analytical solution. The comparison between the analytical solution and test results showed a good agreement in terms of the axial force of the pile and the stress-strain relationship of the pile-soil interface. The softening behaviour of the skin friction can be simulated well when the pile is subjected to large loads; however, such behaviour is generally ignored by most existing analytical solutions. Finally, the effects of the initial shear modulus and the ratio of the residual skin friction to peak skin friction on the load-settlement curve of a pile were investigated by a parametric analysis.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.631-636
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• 2000

The experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ration of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow have been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.

• 한국지반공학회지:지반
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• 제8권2호
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• pp.21-30
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• 1992

말뚝의 주면마찰력은 전체 지지력중 상당한 하중을 지지할 수 있으나 실제 설계시에는 무시되는 경우가 많이 있다. 주면마찰력을 설계에 반영할 경우에도 계산결과의 신뢰도는 매우 낮은 것이 현실이다. 국내의 사정은, 설계 자료로 활용할 수 있는 것은 표준관입시험 결과뿐인 경우가 대부분으로 빈곤하며 특히 국내에 많은 화강암, 편마암의 풍화잔류토에 관해서는 설계자료가 극히 희박해 외국에 비해 열악하다. 최근에 국내에서 개발된 간편한 말뚝재하시험(simple pile loading test: SPLT)의 사용은 선단지지력과 주면마찰력의 별도 측정이 가능하도록 하였다. 본 연구에서는 풍화잔류토 지반에서의 SPLT 결과를 분석하여 N값에 의한 새로운 설계관계식을 제안하였다.

• Tribology and Lubricants
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• 제30권1호
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• pp.36-45
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• 2014

Understanding steel/skin contact phenomena is important for the study of object manipulation in robotics and has been a topic of great interest. In this study, pig skin was taken as a surrogate model for human skin, and its adhesive, friction, and deformation behaviors were measured under various exposure times to air. Indentation, friction, and scratch tests were performed at $25^{\circ}C$ and 45% relative humidity. The influences of adhesion and deformation on the coefficient of friction were characterized; the pig skin was found to be sensitive to the sliding velocity and normal load under the controlled experimental conditions.

• Tribology and Lubricants
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• 제29권3호
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• pp.167-170
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• 2013

The friction behavior of human skin is determined by the complex interplay of the material and surface properties of the skin, as well as the contacting material, and strongly depends on the contact parameters (e.g., pressure and sliding velocity) and the presence of substances such as water, sweat, or skin surface lipids at the interface. Including a study on the effect of a surface's physical roughness for skin sliding over the surface, various studies have been conducted to understand human tactile sensibility. However, to investigate products in relation to human tactile sensibility, more objective research is needed. This study performed sliding experiments between the skin and the surfaces of phone cases to understand how the texture, friction, and stick-slip characteristics are related. Eight phone case surfaces with different topologies and chemical (or mechanical) compatibilities with skin were prepared and tested multiple times.

• 한국지반공학회논문집
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• 제20권4호
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• pp.15-27
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• 2004

본 연구에서는 현재까지 연구된 깊은 기초의 주면마찰력 산정법에 의해 제안된 방법들을 검토하여 대형기초인 케이슨(우물통)기초에 대하여 주면마찰력을 적절히 산정할 수 있는 산정법을 제시하였다. 특히 홍원표(1987)가 제안안 주면마찰력 산정법을 기본 토대로 하여 새로운 주면마찰력 산정방법(Kn계수법)을 제시하였다. 그리고 깊은기초인 말뚝의 주면마찰력을 합리적으로 산정할 수 있다고 알려진 $\lambda$법을 이용한 케이슨의 주면마찰력 산정에 대해서도 검토하였다. 이를 위해 영종대교 주탑하부구조인 뉴매틱케이슨 기초의 시공시 계측된 주면마찰력 데이터를 이용하였다. 주면마찰력은 침설속도에 비례하며 주면마찰력의 분포양상은 직선분포보다 포물선분포에 가깝다. 저부가 확대되는 대규모 케이슨기초 침설시 발생하는 주면마찰력 산정결과 일반적인 말뚝기초의 주면마찰력과는 상이하다. 제안된 Kn계수법과 $\lambda$법을 각각 사용하여 산정한 케이슨의 주면마찰력을 실제 케이슨의 계측값으로부터 산정한 주면마찰력과 비교한 결과, Kn계수법를 이용하여 산정한 케이슨의 주면마찰력은 $\lambda$법에 의해 산정된 주면마찰력보다 실측값에 훨씬 근접하다. 즉, 저부가 확대된 형상의 대형의 케이슨기초의 주면마찰력을 산정하기에는 홍원표가 제안한 식을 이용한 Kn계수법이 $\lambda$법보다 더 적절한 방법임을 알 수 있다.

• 한국지반신소재학회논문집
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• 제21권4호
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• pp.13-20
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• 2022

본 연구에서는 바렛말뚝의 형상비 및 말뚝 주변 지반 강성 변화가 주면마찰력에 미치는 영향을 분석하였다. 유한요소 프로그램을 활용하여 부산 OO현장의 바렛말뚝 정재하시험 결과를 역해석 하였으며 이를 바탕으로 형상비 및 말뚝 주변 지반의 강성을 달리하여 총 36개의 수치해석을 수행하였다. 그 결과, 바렛말뚝의 형상비가 커질수록 주면마찰력은 증가하였으며 극한상태에 다다를수록 그 영향이 커짐을 확인할 수 있었다. 또한 말뚝 주변 지반 강성 변화에 따른 형상비 및 주면마찰력의 상관관계를 분석하였다.