• 한국지반공학회논문집
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• 제20권4호
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• pp.75-88
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• 2004

사질토 지반의 원형수직구에 설치된 흙막이벽에 작용하는 토압은 축대칭 아칭효과로 인하여 평면변형조건의 옹벽에 작용하는 토압보다는 작은 토압이 작용한다. 따라서, 수평 및 연직방향 아칭효과에 의한 토압감소를 고려하고 상재하중, 벽면마찰, 파괴면의 경사각 등 각종 인자의 영향을 적절히 반영하여 원통형 벽체에 작용하는 토압을 예측할 수 있는 토압산정공식이 제안되었다. 제안된 토압공식의 적용성 확인을 위하여 모형실험이 수행되었다. 벽체변위, 벽면마찰, 벽체 형상비 등을 조절할 수 있는 모형실험장치가 개발되었으며, 건조한 모래지반에서 깊이에 따른 벽체변형이 일정한 조건의 모형실험을 통하여 각각의 영향인자가 원통형 벽체에 작용하는 주동토압에 미치는 영향이 분석되었다. 제안된 토압공식은 모형실험에 의한 토압분포와 유사한 경향을 예측하여 만족스러운 결과를 주는 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제42권2호
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• pp.247-267
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• 2012

Calculating the displacements of retaining walls under seismic loads is a crucial part in optimum design of these structures and unfortunately the techniques based on active seismic pressure are not sufficient alone for an appropriate design of the wall. Using limit analysis concepts, the seismic displacements of retaining walls are studied in present research. In this regard, applying limit analysis method and upper bound theorem, a new procedure is proposed for calculating the yield acceleration, critical angle of failure wedge, and permanent displacements of retaining walls in seismic conditions for two failure mechanisms, namely sliding and sliding-rotational modes. Also, the effect of internal friction angle of soil, the friction angle between wall and soil, maximum acceleration of the earthquake and height of the wall all in the magnitude of seismic displacements has been investigated by the suggested method. Two sets of ground acceleration records related to near-field and far-field domains are employed in analyses and eventually the results obtained from the suggested method are compared with those from other techniques.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.578-581
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• 2007

In this study, the seismic control performance of energy dissipation devices installed in a shear all-frame structure is investigated through nonlinear time history analysis of a 12-story building. Inelastic shear walls are modeled using the multiple vertical line element model (MVLEM) and inelastic columns and girders were modeled using fiber beam elements. For a seismic load increased by 38% compared to the design load, the seismic control performance was analyzed based on the results of a nonlinear time history analysis in terms of the inter-story drift, the story shear and the flexural strain. Friction type dampers was found to performs best if they are installed in the form of a brace adjacent to the shear wall with the friction force of 15 % of the maximum story shear force induced in the original building structure without dampers.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1084-1089
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• 2000

The basic equations are derived for the analysis of a stepped labyrinth gas seal which are generally used in high performance compressors, gas turbines, and steam turbines. The Bulk-flow is assumed for a single cavity control volume and the flow is assumed to be completely turbulent in circumferential direction. Moody's wall-friction-factor formula is used for the calculation of wall shear stresses in the single cavity control volume. For the reaction force developed by the seal, linearized zeroth-order and first-order perturbation equations are developed for small motion about a centered position. Integration of the resultant first-order pressure distribution along and around the seal defines the rotordynamic coefficients of the stepped labyrinth gas seal. The leakage and rotordynamic characteristic results of the stepped labyrinth gas seal are presented and compared with Scharrer's theoretical analysis using Blasius' wall-friction-factor formula.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1996년도 춘계학술대회논문집
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• pp.23-30
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• 1996

The purpose of this study was to investigate changes in thewall thickness of tube sinking and working forces by the upper bound method and ABAQUS code. The independent variables were : Workpiece material, original wall thickness of tube, die angle, friction, and diameter reduction. The results indicated that of these five variables were a factor in wall-thickness increase and working forces. Three variables, a inner tube wall angle and two angles of the velocity discontinuous surfaces, are optimized in this proposed velocity field by the upper bound method. In this method, we can estimate the working forces and final tube thicknesses whcih are similar to acturla forming process. Optimized process variables which are obtained by upper bound method are used in ABAQUS pre-model . In ABAQUS analysis, the stress and the strain contours which are considered to be heat generation occured by the friction during forming process are observed.

• 대한조선학회논문집
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• 제40권3호
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• pp.9-15
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• 2003

An experimental study has been carried out as a basic research for development of the friction drag reduction technology for ships by polymer injection. Experimental apparatus and procedures have been devised and prepared to measure the changes of the wall friction with injection of a polymer solution and basic experimental data on the friction drag reduction are obtained for a turbulent fiat-plate boundary layer and fully-developed channel flows. Variations of the friction drag reduction with some important parameters of polymer injection, such as the concentration of polymer solution, its injection flow rate and the measuring position downstream from the injection slot, are also investigated. Important experimental data and results obtained in the present study are presented. The amount of friction drag reduction up to 50% is observed.

• 설비공학논문집
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• 제26권4호
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• pp.175-180
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• 2014

Experimental investigations of the heat transfer and friction factors in the ribbed divergent rectangular channel with the channel exit hydraulic diameter to inlet hydraulic diameter ratio of 1.16 were performed. The surface heaters were mounted onto the two opposite walls. The main experimental parameter is the ratio of rib pitch (p) to height (e), at which the ratios (p/e) of 6, 10, and 14 are considered in the channel with ribs on one wall only. The straight ribbed square channel is also considered as a comparison. The major findings are that the ratio of p/e = 6 shows the highest values in the heat transfer and the ratio of p/e = 10 indicates the greatest friction factor in the ribbed divergent channel. Editor's note:No major changes or corrections needed. Well written.

• Tribology and Lubricants
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• 제12권4호
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• pp.7-12
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• 1996

Present study was undertaken to investigate the leakage and friction of self-lubricating piston seal rings. A crank-piston type gas leakage test set-up was constructed. The piston rings were made of PTFE-polyimide composite. The free gap configurations of the seal rings were butt and step types. Eccentric tension rings were used to give the seal rings prepressure between the seal rings and cylinder wall. Two sizes of the tension rings were installed to investigate their effect on the gas leakage and friction of the seal rings. The results showed that step type seal rings are superior than the butt types. High tension spring rings resulted in low leakage and high friction loss. In order to reduce the gas leakage and friction loss of the piston seal rings, there should be compromise between the number of ring stages and prepressure of the tension rings.

• 대한조선학회논문집
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• 제40권3호
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• pp.1-8
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• 2003

For the experiment of the friction drag reduction by microbubble injection, a drag reduction water tunnel was specifically designed and made. Experimental apparatus and procedures were devised and developed for measuring the change of wall friction drag with microbubble injection. For fully-developed channel flows. the change of friction drag with important parameters of microbubble injection is investigated and the experimental data and results obtained are presented. The amount of friction drag reduction up to 25% is observed in the present study.

• 한국지반공학회논문집
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• 제28권9호
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• pp.31-45
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• 2012

본 연구에서는 월파시 해안안벽에 작용하는 지진과 지진해일의 영향에 대하여 한계평형상태해석법을 적용하여 안정성을 검토하였다. 지진해일파력에 대하여 TWOPM-3D를 적용하였으며, 특히 안벽의 뒷채움재를 투과성재료로 가정하여 지진해일파가 월파 후에 안벽배후에 작용하는 파력을 산정하였다. 그리고, 수동상태와 주동상태 조건에서 해안안벽의 안정성에 영향을 주는 요인인 지진해일파고, 뒷채움재의 수위, 수평 수직지진가속도계수, 내부마찰각, 벽마찰각, 간극수압비 등을 변화하여 활동과 전도에 대한 안벽 안전율의 변화특성을 시간에 따라 검토하였다. 이로부터 지진과 지진해일파의 작용하에 지진해일파가 안벽을 월파하는 경우 수동상태에 대한 안전율은 결과적으로 안전율을 증가시키는 요인으로 작용하는 반면, 주동상태에 대하여 결과적으로 안전율을 감소시키는 요인으로 작용함을 확인할 수 있었다.