• 한국초전도학회:학술대회논문집
• /
• v.9
• /
• pp.222-222
• /
• 1999

From extensive measurements of the resistance and the dynamic resistance as functions of magnetic field and temperature, we find that the transport in the insulating state beyond the superconductor-insulator (S-I) transition is dominated by bosons(Cooper pairs and/or vortices) and cannot be described by the theory of the fermionic insulating phase. The maximum of the magnetoresistance at B = B$_m$ and the following negative slope in R(B) with increasing field can be explained by the crossover from the "Bose-glass" to the "Fermi-glass" phase as suggested by Paalanen, Hebard, and Ruel. The zero bias peak in dv/dl for biases below the characteristic voltage V$_c$ (or current $I_c$), gives a clue for the assumption of the "dirty boson" model which states that the insulating state above the critical magnetic field is the phase where Cooper pairs are localized due to the Coulomb blockade with a nonvanishing order parameter. The shift to a lower value of the critical magnetic field by overlaying thin Au layer, which is known as a strong spin-orbit scatterer, also supports the bosonic nature of the S-I transition.

• Korea-Australia Rheology Journal
• /
• v.18 no.2
• /
• pp.99-102
• /
• 2006

Primitive chain network model for block copolymers is used here to simulate molecular dynamics in the entangled state with acceptable computational cost. It was found that i) the hooking procedure rearranging the topology of the entangled network is critical for the equilibrium structure of the system, and ii) simulations accounting for the different chemistry, i.e., with a biased hooking probability based on interaction parameter ${\chi}$ for selection of the hooked partner, generates a reasonable phase diagram.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 2001.02a
• /
• pp.61-64
• /
• 2001

Levitation force of a new magnetic levitation system using a super-conducting bulk magnet(SBM) and a permanent magnet(PM) was numerically calculated. The non-linear J-E relation of a SBM was modeled using a critical state model and iteration method, and demagnetization of a PM was considered using a demagnetization curve of a real PM. The maximum limitation of levitation force was found according to increasing the trapped field in a SBM. Finite element method was used for numerical calculation.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 2001.02a
• /
• pp.185-188
• /
• 2001

Magnetization loss of a Bi-2223 tape in magnetic fields parallel to the tape surface was measured by a magnetization method. The results indicate that the magnetization loss is hysteretic because the measured loss agrees well with calculated one from a critical state model. In the full field penetration case the magnetization loss increases with the frequency but in the partial field penetration case the influence of the frequency is opposite.

• Journal of Magnetics
• /
• v.2 no.3
• /
• pp.93-95
• /
• 1997

We investigated the temperature dependence of magnetization of Fe/Al multilayers fabricated by dc magnetron sputtering system. As the temperature increased from 5 K in a low magnetic field (100G) the magnetization of the samples increased and made a broad peak at some critical temperature. Further increase of temperature decresed the magnetization as an ardinary ferromagnetic curve. Part of samples show rapid increase of magnetization at low temperature. A model developed in this study suggests that the biquadratic coupling yields such a rapidly increasing behavior of magnetization at low temperature.

• Proceedings of the KSR Conference
• /
• 1998.11a
• /
• pp.413-420
• /
• 1998

In this study, optimum design methodology for rail vehicle suspension characteristics is suggested. Three parameters, primary lateral/longitunal stiffness and secondary lateral stiffness, are selected as design parameters. critical speed, suspension stroke trade-off and derailment coefficient are selectee as performance constraints. The optimum parameters to maximize ride quality are evaluated under the constraints. Steady-state curiving model to be able to evaluate derailment coefficient is developed. The combined design procedure is developed to evaluate Three parameters at the same time.

• Geomechanics and Engineering
• /
• v.14 no.5
• /
• pp.467-477
• /
• 2018

Estimation of hydraulic parameters is a critical step during design of foundation dewatering works. When many piles are installed in an aquifer, estimation of the hydraulic conductivity should consider the blocking of groundwater seepage by the piles. Based on field observations during a dewatering project in Shanghai, hydraulic conductivities are back-calculated using a numerical model considering the actual position of each pile. However, it is difficult to apply the aforementioned model directly in field due to requirement to input each pile geometry into the model. To develop a simple numerical model and find the optimal hydraulic conductivity, three scenarios are examined, in which the soil mass containing the piles is considered to be a uniform porous media. In these three scenarios, different sub-regions with different hydraulic conductivities, based on either automatic inverted calculation, or on effective medium theory (EMT), are established. The results indicate that the error, in the case which determines the hydraulic conductivity based on EMT, is less than that determined in the automatic inversion case. With the application of EMT, only the hydraulic conductivity of the soil outside the pit should be inverted. The soil inside the pit with its piles is divided into sub-regions with different hydraulic conductivities, and the hydraulic conductivity is calculated according to the volume ratio of the piles. Thus, the use of EMT in numerical modelling makes it easier to consider the effect of piles installed in an aquifer.

• Proceedings of the Korean Institute of Intelligent Systems Conference
• /
• 1998.06a
• /
• pp.320-325
• /
• 1998

Underwater robotic vehicles (URVs) have been an important tool for various underwater tasks because they have greater speed, endurance, depth capability, and safety than human divers. As the use of such vehicles increases, the vehicle control system becomes one of the most critical subsytems to increase autonomy of the vehicle. The vehicle dynamics are nonlinear and their hydrodynamic coefficients are often difficult to estimate accurately. In this paper a new type of fuzzy model-based controller based on Takagi-Sugeno-Kang fuzzy model is designed and applied to the control of of an underwater robotic vehicle. The proposed fuzzy controller : 1) is a nonlinear controller, but a linear state feedback controller in the consequent of each local fuzzy control rule ; 2) can guarantee the stability of the closed-loop fuzzy system ; 3) is relatively easy to implement. Its good performance as well as its robustness to the change of parameters have been shown and compared with the re ults of conventional linear controller by simulation.

• Journal of Theoretical and Applied Mechanics
• /
• v.2 no.1
• /
• pp.31-50
• /
• 1996

In this paper, a finite element analysis based on the local approach concept to fracture in the continuum damage mechanics is performed to analyze ductile fracture in two dimensional quasi-static state. First an isotropic damage model based on the generalized concept of effective stress is proposed for structural materials in the context of large deformation. In this model, the stiffness degradation is taken as a measure of damage and so, the fracture phenomenon can be explained as the critical deterioration of stiffness at a material point. The modified Riks' continuation technique is used to solve incremental iterative equations. Crack propagation is achieved by removing critically damaged elements. The mesh size sensitivity analysis and the simulation of the well known shearing mode failure in plane strain state are carried out to verify the present formulation. As numerical examples, an edge cracked plate and the specimen with a circular hole under plane stress are taken. Load-displacement curves and successively fractured shapes are shown. From the results, it can be concluded that the proposed model based on the local approach concept in the continuum damage mechanics may be stated as a reasonable tool to explain ductile fracture initiation and crack propagation.

• Wind and Structures
• /
• v.29 no.3
• /
• pp.177-194
• /
• 2019

While establishing adequate load paths in the light-frame wood structures is critical to maintain the overall structural integrity and avoid significant damage under extreme wind events, the understanding of the load paths is limited by the high redundant nature of this building type. The objective of the current study is to evaluate the system effects and investigate the load paths in the wood structures especially the older buildings for a better performance assessment of the existing building stock under high winds, which will provide guidance for building constructions in the future. This is done by developing building models with configurations that are suspicious to induce failure per post damage reconnaissance. The effect of each configuration to the structural integrity is evaluated by the first failure wind speed, amajor indicator beyond the linear to the nonlinear range. A 3D finite-element (FE) building model is adopted as a control case that is modeled using a validated methodology in a highly-detailed fashion where the nonlinearity of connections is explicitly simulated. This model is then altered systematically to analyze the effects of configuration variations in the model such as the gable end sheathing continuity and the gable end truss stiffness, etc. The resolution of the wind loads from scaled wind tunnel tests is also discussed by comparing the effects to wind loads derived from large-scale wind tests.