• 에너지공학
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• 제22권2호
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• pp.205-210
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• 2013

Cycle-to-cycle variation has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under lean and highly diluted operation conditions. At a part load, some of the cycles tend to knock, while others may have incomplete combustion by the time the exhaust valve opens. An experimental study has been performed in order to evaluate the relative contribution of several relevant parameters on the cyclic variability in spark ignition engines. In general, the stability of engine operation is improved with fuel injector according to the optimal injection timing, but the stability of engine operation at idle is not improved compared with a practical gasoline engine. In this study, we investigated the relationship of the effect of operating conditions for the stability at low speed and load.

• Structural Engineering and Mechanics
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• 제13권1호
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• pp.17-34
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• 2002

The use of local two-sided and three-sided jacketing for the repair and strengthening of reinforced concrete beam-column joints damaged by severe earthquakes is investigated experimentally and analytically. Two exterior beam-column joint specimens ($O_1$ and $O_2$) were submitted to a series of cyclic lateral loads to simulate severe earthquake damage. The specimens were typical of existing older structures built in the 1960s and 1970s. The specimens were then repaired and strengthened by local two-sided or three-sided jacketing according to UNIDO Manual guidelines. The strengthened specimens ($RO_1$ and $RO_2$) were then subjected to the same displacement history as that imposed on the original specimens. The repaired and strengthened specimens exhibited significantly higher strength, stiffness and better energy dissipation capacity than the original specimens.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 춘계학술대회 논문집
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• pp.1033-1040
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• 2004

Utilizing of the geotextile container shows several advantages such as standardized construction, factory manufactured products, the control of quality, workability. and economical point of view. Recently this technique can be applied to rehabilitate the loss of rail roadbed due to the heavy rainfall. In this study, a large-scale laboratory test were conducted with simulation of static performance on the geotextile container reinforced rail roadbed. Based on the laboratory test results, the vertical pressure distribution with respect to the depth, and settlement of rail roadbed were measured and compared test results between geotextile container reinforced case and unrein forced case. Thus, the effectiveness of reinforcement was evaluated in terms of its performance and stability.

• Structural Engineering and Mechanics
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• 제5권5호
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• pp.541-552
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• 1997

In this paper the ultimate strength of the R/C cooling towers, which have initial imperfection and pre-cracked elements, is analyzed. The initial geometric imperfections arise from the unavoidable inaccuracies under the construction and the pre-cracks are assumed to be produced by the temperature stress gradients or cyclic loading under wind pressure and/or earthquake load. Both effects are strongly influenced on the strength of the R/C cooling tower shell structures. The reinforcing ratio is also the important factor to evaluate the ultimate strength of the R/C cooling tower shells. However we could not analyze these structures experimentally because of their large, analyses are the powerful schemes to evaluate the safety and reliability of these structures. The analyzed model is Port Gibson cooling tower shell. In the numerical analysis the geometric and material nonlinearities are taken into account.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.852-855
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• 2010

Numerical simulations for large scale triaxial tests with large diameter rockfill materials are conducted using distinct element method. For generation of compacted assembly with specific grain size distribution and initial material porosity, the clump logic method and expansion of generated particles are adapted. With micro parameters which are chosen by calibration process, discrete particle modelling of triaxial test in case of other confining stress and cyclic loading condition were conducted. Also numerical simulations of fluid injection into particulate materials were conducted to observe cavity initiation and propagation using distinct element method. The fluid scheme solves the continuity and Navior-Stokes equations numerically, then derives pressure and velocity vectors for fixed grid by considering the existence of particles within the fluid cell.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.51-58
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• 2008

The George Massey immersed tunnel passes the Fraser River near Vancouver, Western Canada. In this paper, dynamic analysis of the tunnel on sandy soils was performed using an effective stress constitutive model called UBCSAND. This model is able to calculate pore pressure rise and resulting tunnel deformation due to cyclic loading. Centrifuge tests conducted at RPI are used to verify the model performance. Centrifuge tests consist of 3 models: Model 1 is designed for an original ground condition, Model 2 for a ground improvement by compaction method, Model 3 for a ground improvement by gravel drainage. The results of centrifuge Model 1 are presented and compared with predictions of UBCSAND model. This model well captured the results of centrifuge test and therefore can be used to predict dynamic behavior of similar tunnels or underground structures on sandy soils.

• 한국수소및신에너지학회논문집
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• 제5권1호
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• pp.51-57
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• 1994

Compaction techniques of hydrogen storage alloy 'powders, to solve the problems due to disintegration during the cyclic hydriding and dehydriding, by using polytetrafluoroethylene (PTFE) and silicon sealant as a polymer binder were studied. Optimum conditions of compaction were as follows. Binder content, 10 % for PTFE and 5 % for silicon sealant ; particle size of alloy powders, $-25{\mu}m$ ; compacting pressure, $4ton/cm^2$. Compacts obtained were easily activated and had a good strength even after 30 cycles of hydriding and dehydriding. PTFE added compacts showed very good rate capability, however, in the silicon added compacts hydrogen absorption rate was somewhat slow because of higher elasticity and adhesiveness of the binder.

• Journal of Mechanical Science and Technology
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• 제15권7호
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• pp.859-865
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• 2001

This paper reports on the theoretical analysis of mixed lubrication for the piston ring. The analytical model is presented by using the average flow and asperity contact model. The cyclic variations of the nominal minimum oil film thickness are obtained by numerical iterative method. The total friction is calculated by using the hydrodynamic and asperity contact theory. The effect of the roughness height, pattern, and engine speed on the nominal minimum film thickness, friction force, ad frictional power losses are investigated. As the roughness height increases, the nominal oil film thickness and total friction force increase. Also, the effect of the surface roughness on the boundary friction is dominant at low engine speed and high asperity height. The longitudinal roughness pattern shows lower mean oil film pressure and thinner oil film thickness compared to the case of the isotropic and transverse roughness patterns.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.778-783
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• 2001

Turbine blade is subject to cyclic bending force by steam pressure. Stress analysis by fractography is already established technology as means for seeking cause of fracture and has been widely employed. In the X-ray fractography, plastic deformation and residual stress near the fracture surface can by determined and information of internal structure of material can be obtained. Therefore, to find a fracture mechanism of torsion-mounted blade in nuclear power plant, based on the information from the fracture surface obtained by fatigue test, the correlation of X-ray parameter and fracture mechanics parameter was determined and then the load applied to actual broken turbine blade was predicted.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.891-897
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• 2006

The volume control method which utilize a pressure node added into a finite shell element can overcome the drawbacks of conventional load control method and displacement control method. In this study, an improved volume control method is introduced for effective analysis of path-dependant behaviors of RC structures subjected to cyclic loading. RC shell structures including RC hollow columns are anlayized by discretizing the structures with layered shell elements and by applying in-plane two dimensional constitutive equations for concrete layers and reinforcement layers of the shell elements. The so-called path dependant volume control method is verified by comparing analysis results with other data including experimental results.