• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.5
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• pp.414-422
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• 2005

This paper shows the results of atomistic modeling for the Interaction between spherical nano abrasive and substrate In chemical mechanical polishing processes. Atomistic modeling was achieved from 2-dimensional molecular dynamics simulations using the Lennard-jones 12-6 potentials. We proposed and investigated three mechanical models: (1) Constant Force Model; (2) Constant Depth Model, (3) Variable Force Model, and three chemical models, such as (1) Chemically Reactive Surface Model, (2) Chemically Passivating Surface Model, and (3) Chemically Passivating-reactive Surface Model. From the results obtained from classical molecular dynamics simulations for these models, we concluded that atomistic chemical mechanical polishing model based on both Variable Force Model and Chemically Passivating-reactive Surface Model were the most suitable for realistic simulation of chemical mechanical polishing in the atomic scale. The proposed model can be extended to investigate the 3-dimensional chemical mechanical polishing processes in the atomic scale.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.11a
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• pp.39-47
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• 2002

Heat is always the root of stress acting upon the electronic package, regardless of the heat due to the device itself during operation or working under the adverse environment. Due to the significant mismatch in coefficient of thermal expansion (CTE) and the thermal conductivity (K) of the packaging components, on one hand intensive research has been conducted in order to enhance the device reliability by minimizing the mechanical stressing and deformation within the package. On the other hand the effectiveness of different thermal enhancements are pursued to dissipate the heat to avoid the overheating of the device. However, the interactions between the thermal-mechanical loading has not yet been address fully. in articular when the temperature gradient is considered within the package. To address the interactions between the thermal loading upon the mechanical stressing condition. coupled-field analysis is performed to account the interaction between the thermal and mechanical stress distribution. Furthermore, process induced defects are also incorporated into the analysis to determine the effects on thermal conducting path as well as the mechanical stress distribution. It is concluded that it feasible to consider the thermal gradient within the package accompanied with the mechanical analysis, and the subsequent effects of the inherent defects on the overall structural integrity of the package are discussed.

• Journal of Mechanical Science and Technology
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• v.16 no.11
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• pp.1440-1447
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• 2002

Adhesion of a hemispherical tip to the flat surface in nano-structures is simulated using the molecular dynamics technique. The tip and plates are modeled with the Lennard-Jones molecules. The simulation focuses on the deformation of the tip. Detailed descriptions on the evolution of interaction force, the energy dissipation due to adhesion hysteresis, the forma- tion-growth-breakage of adhesive junction as well as the evolution of molecular distribution during the process are presented. The effects of the tip size, the maximum tip approach, the tip temperature, and the affinity between the tip and the mating plate are also discussed.

• Journal of Mechanical Science and Technology
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• v.16 no.8
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• pp.1144-1153
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• 2002

A hybrid performance prediction method is proposed in the present study. A channel diffuser is divided into four subregions: vaneless space, semi-vaneless space, channel, and channel exit region. One-dimensional compressible core flow and boundary layer calculation of each region with an incidence loss model and empirical correlation of residuary pressure recovery coefficient of a channel predict the performance of diffusers. Three channel diffusers are designed and tested for validating the developed prediction method. The pressure distributions from an impeller exit to the channel diffuser exit are measured and discussed for various operating conditions from choke to nearly surge conditions. The strong non-uniform pressure distribution which is caused by impeller-diffuser interaction is obtained over the vaneless and semi-vaneless spaces. The predicted performance shows good agreement with the measured performance of diffusers at a design condition as well as at off-design conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.275-284
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• 1997

Thermodynamic behavior of a composite system which is composed of two simple thermal subsystems with constant heat capacities is analyzed, and several thermodynamic phenomena are investigated. The changes of the states and the potential work of the composite system are shown as the interaction between the subsystems in the composite system. The potential work is defined as the possible maximum available work from the composite system, and it is a thermodynamic property of the composite system. The decrease of the potential work is the same as the available work output from the composite system in reversible processes. The dissipation of available work is directly connected to the generation of entropy. The concepts of exergy and internal energy can be explained as a special case of the potential work.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.80-86
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• 2005

In order to control the transonic flow field with a shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock-boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically. The result showed that the flow fields might be effectively controlled by the suitable combination between non-equilibrium condensation and the position of porous wall.

• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.1042-1051
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• 2004

The vortex flow characteristics of a sharp-edged delta wing at high angles of attack were studied using a computational technique. Three dimensional, compressible Reynolds-averaged Navier-Stokes equations were solved to understand the effects of the angle of yaw, angle of attack, and free stream velocity on the development and interaction of vortices and the relationship between suction pressure distributions and vortex flow characteristics. The present computations gave qualitatively reasonable predictions of vortical flows over a delta wing, compared with past wind tunnel measurements. With an increase in the angle of yaw, the symmetry of the pair of leading edge vortices was broken and the vortex strength was decreased on both windward and leeward sides. An increase in the free stream velocity resulted in stronger leading edge vortices with an outboard movement.

• International Journal of Automotive Technology
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• v.5 no.2
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• pp.95-108
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• 2004

Lanekeeping assistance has the potential to save thousands of lives every year by preventing accidental road departure. This paper presents experimental validation of a potential field lanekeeping assistance system with quantitative performance guarantees. The lanekeeping system is implemented on a 1997 Corvette modified for steer-by-wire capability. With no mechanical connection between the hand wheel and road wheels the lanekeeping system can add steering inputs independently from the driver. Implementation of the lanekeeping system uses a novel combination of a multi-antenna Global Positioning System (GPS) and precision road maps. Preliminary experimental data shows that this control scheme performs extremely well for driver assistance and closely matches simulation results, verifying previous theoretical guarantees for safety. These results also motivate future work which will focus on interaction with the driver.

• Interaction and multiscale mechanics
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• v.4 no.2
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• pp.107-122
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• 2011

Mechanical behavior in nano-sized structures differs from those in macro sized structures due to surface effect. As the ratio of surface to volume increases, surface effect is not negligible and causes size-dependent mechanical behavior. In order to identify this size effect, atomistic simulations are required; however, it has many limitations because too much computational resource and time are needed. To overcome the restrictions of the atomistic simulations and graft the well-established continuum theories, the continuum model considering surface effect, which is based on the bridging technique between atomistic and continuum simulations, is introduced. Because it reflects the size effect, it is possible to carry out a variety of analysis which is intractable in the atomistic simulations. As a part of the application examples, the homogenization method is applied to micro/nano thin films with porosity and the homogenized elastic coefficients of the nano scale thickness porous films are computed in this paper.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.271-273
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• 2006

This paper focuses on the developed empirical models for the prediction on top-bead width in GMA(Gas Metal Arc) welding process. Three empirical models have been developed: linear, curvilinear and an intelligent model. Regression analysis was employed fur optimization of the coefficients of linear and curvilinear model, while Genetic Algorithm(GA) was utilized to estimate the coefficients of intelligent model. Not only the fitting of these models were checked, but also the prediction on top-bead width was carried out. ANOVA analysis and contour plots were respectively employed to represent main and interaction effects between process parameters on top-bead width.