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Search Results: 1 - 10 of 20949 matches for " Seok Kim "
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Finite Element Analysis with Paraxial & Viscous Boundary Conditions for Elastic Wave Propagation  [PDF]
Hee Seok Kim
Engineering (ENG) , 2012, DOI: 10.4236/eng.2012.412107
Abstract: In this study, two studies are performed. One is to apply paraxial boundary conditions which are local boundary conditions based on paraxial approximations of the one-way wave equations to finite element analysis. To do this, a penalty functional is proposed and the existence and uniqueness of the extremum of the proposed functional is demonstrated. The other is to improve the capacity of viscous boundary conditions using dashpots. To do this, customary viscous boundary conditions are modified to maximize the efficiency according to angles of incidence and materials. For the numerical analysis of elasticity with paraxial boundary conditions and the modified viscous boundary conditions, the coding of the finite element models is implemented, and the efficiency of those boundary conditions is investigated.
A Study on the Characteristics for the Ground Vibration Due to the Travelling Tilting Train  [PDF]
Hee Seok Kim
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.59087
Abstract:

The development of the tilting train can contribute to solve the economic burden and enhance the transportation means of areas that did not share the benefits of the high speed railway. But the dynamic behavior caused by the interaction between the train and the track as well as the environmental vibrations along the railway should be evaluated to secure the safety of the train and riding comfort. In this paper a study on the characteristics for ground vibration due to the tilting train travelling in the conventional line are carried out. The transmitted load into the ground is computed through a study on the interrelation between the tilting car and the line. This load is applied into the numerical model which is one for the analysis of ground vibration due to the travelling tilting car. The far fields on the numerical model are formed by the absorbing boundary using dashpot, one of the most widely used absorbing boundary in finite element analysis. Using this numerical model, the analysis of the ground vibration characteristics caused by travelling tilting car is performed. From the analysis, it is shown that the transferred load due to the tilting train is larger than that of the conventional train.

A Study on the Performance of Absorbing Boundaries Using Dashpot  [PDF]
Hee Seok Kim
Engineering (ENG) , 2014, DOI: 10.4236/eng.2014.610060
Abstract: In this paper an analytical study is carried out to examine the effectiveness of absorbing boundaries using dashpot. Validity of the absorbing boundary conditions suggested by Lysmer-Kuhle- meyer and White et al. is investigated by adopting the solution of Miller and Pursey. The Miller and Pursey’s problem is then numerically simulated using the finite element method. The absorption ratios are calculated by comparing the displacements at the absorbing boundary to those at the free field without the absorbing boundary. The numerical verification is carried out through comparison of displacement at the boundary.
A Study on the Characteristics and the Effective Reduction Methods for the Ground Vibration Due to the Travelling Tilting Train  [PDF]
Hee Seok Kim
Engineering (ENG) , 2014, DOI: 10.4236/eng.2014.64024
Abstract:

In this paper, a study on the characteristics and the reduction methods of ground vibration due to the tilting train travelling in the conventional line is carried out. The load transmitted into the ground is computed considering the interaction between the tilting car and the line. This load is then applied in the numerical model for the analysis of ground vibration due to the travelling tilting car. The far-fields of the numerical model are modeled using the dashpot, as one of the most widely used absorbing boundaries in finite element analysis. Using this numerical model, the analysis of the ground vibration characteristics caused by the travelling tilting car and the analysis of the blocking effect of the ground vibration by wave barriers are performed. From the numerical analysis, it is shown that the blocking effect of the trench and the barrier filled with soft material is more effective than that of the barrier filled with hard material.

A Study on the Wave Screening Effectiveness According to Trench Dimensions Using Ultrasonic Waves  [PDF]
Hee Seok Kim, Won Jong Chin
Engineering (ENG) , 2014, DOI: 10.4236/eng.2014.610061
Abstract: In this study numerical and experimental studies are conducted to examine the wave screening effectiveness of trenches. The numerical study relies on the finite element model of a sandbox with Lysmer-Kuhlemeyer absorbing boundaries. This model is used to examine the screening ef-fectiveness of trench studied for different trench dimensions and distances from the source and receiver to the trench. The results of the numerical analysis are compared with the results of the ultrasonic experiment performed on an acrylic block drilled with a rectangular cut. The comparison shows that the screening effectiveness of the trench is nearly equal if the depth of trench is larger than 60% of the surface wave length. It is also shown that if the distance between the trench and the source is longer than twice the surface wave length, the thickness of the trench does not affect the screening effectiveness.
Study on Stack Effect of Stairwell by Numerical Model of Leakage Flow through Gap of Door  [PDF]
Jung-Yup Kim, Ji-Seok Kim
Open Journal of Fluid Dynamics (OJFD) , 2013, DOI: 10.4236/ojfd.2013.34029
Abstract: Since stack effect that occurs in high-rise buildings has an effect on the indoor environment of the buildings, energy loss and smoke control in case of a fire, there is a need to conduct research on this. For an analysis of the stack effect, analysis methods on the leakage flow through gap of interior door shall be formulated. Until now, studies related to the gap leakage flow in buildings have mainly analyzed flow field and pressure in the buildings one-dimensionally using pressure difference-leakage flowrate relations of Orifice Equation and a network numerical analysis algorithm that as- sumes each compartment in the buildings as a single point. In this study, the Momentum Loss Model which enables pressure drop to be proportional to the flow velocity through the gap of door in computational domain of 3-dimensional numerical analysis was proposed to reflect the gap flow phenomenon effectively in 3-dimensional numerical analysis. Using the proposed model, 3-dimensional numerical analysis of the stack effect on the stairs in buildings was performed, and the effects of separation door and lobby between stair and accommodation on the stack effect were investigated.
An Efficient Scheduling Scheme to Enhance the Capacity of VoIP Services in Evolved UTRA Uplink
Yong-Seok Kim
Lecture Notes in Engineering and Computer Science , 2008,
Abstract:
An Efficient Scheduling Scheme to Enhance the Capacity of VoIP Services in Evolved UTRA Uplink
Yong-Seok Kim
EURASIP Journal on Wireless Communications and Networking , 2008, DOI: 10.1155/2008/732418
Abstract: An efficient scheduling scheme is proposed to increase the available capacity of VoIP services over evolved UTRA uplink. On top of the advantages of persistent scheduling, the proposed scheme adaptively share the resources of two VoIP users to get early-termination gain of dynamic scheduler. Through system-level simulations, the performance of the proposed algorithm is evaluated in terms of the capacity enhancement of VoIP services. Comparisons with the original persistent scheduling and the HSUPA scheduler reveal that the proposed scheme increases the capacity of VoIP services up to 20%.
An Efficient Scheduling Scheme to Enhance the Capacity of VoIP Services in Evolved UTRA Uplink
Kim Yong-Seok
EURASIP Journal on Wireless Communications and Networking , 2008,
Abstract: An efficient scheduling scheme is proposed to increase the available capacity of VoIP services over evolved UTRA uplink. On top of the advantages of persistent scheduling, the proposed scheme adaptively share the resources of two VoIP users to get early-termination gain of dynamic scheduler. Through system-level simulations, the performance of the proposed algorithm is evaluated in terms of the capacity enhancement of VoIP services. Comparisons with the original persistent scheduling and the HSUPA scheduler reveal that the proposed scheme increases the capacity of VoIP services up to 20%.
Fermionization for charge degrees of freedom and bosonization of spin degrees of freedom in the SU(2) slave-boson theory
Ki-Seok Kim
Physics , 2008, DOI: 10.1103/PhysRevB.78.195113
Abstract: Fermionizing the charge sector and bosonizing the spin part in the SU(2) slave-boson theory, we derive an effective field theory for dynamics of doped holes in the antiferromagnetically correlated spin background, where spin fluctuations are described by an SO(5) Wess-Zumino-Witten (WZW) theory while dynamics of doped holes is characterized by QED$_{3}$ with a chemical potential term. An important feature of our effective field theory is the coupling term between valance bond fluctuations and doped holes. Considering that valance bond fluctuations are deeply related with monopole excitations of staggered U(1) gauge fields in the bosonic field theory for spin fluctuations, we demonstrate that hole dynamics helps deconfinement of bosonic spinons near the quantum critical point of the SO(5) WZW theory. We solve this effective field theory in the Eliashberg framework, and find non-Fermi liquid physics in thermodynamics and transport, where $z = 3$ criticality with dynamical exponent $z$ plays an important role for hole dynamics. We discuss validity of our field theory, applying it to a doped spin chain and comparing it with the slave-fermion framework. Furthermore, we discuss instability of the anomalous metallic phase against superconductivity and density waves of doped holes, resulting from competition between gauge and valance bond fluctuations.
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