• Journal of The Korean Astronomical Society
• /
• v.33 no.1
• /
• pp.47-55
• /
• 2000

Nonpotential characteristics of magnetic fields in AR 5747 are examined using Mees Solar Observatory magnetograms taken on Oct. 20, 1989 to Oct. 22, 1989. The active region showed such violent flaring activities during the observational span that strong X-ray flares took place including a 2B/X3 flare. The magnetogram data were obtained by the Haleakala Stokes Polarimeter which provides simultaneous Stokes profiles of the Fe I doublet 6301.5 and 6302.5. A nonlinear least square method was adopted to derive the magnetic field vectors from the observed Stokes profiles and a multi-step ambiguity solution method was employed to resolve the $180^{\circ}$ ambiguity. From the ambiguity-resolved vector magnetograms, we have derived a set of physical quantities characterizing the field configuration, which are magnetic flux, vertical current density, magnetic shear angle, angular shear, magnetic free energy density, a measure of magnetic field discontinuity MAD and linear force-free coefficient. Our results show that (1) magnetic nonpotentiality is concentrated near the inversion line in the flaring sites, (2) all the physical parameters decreased with time, which may imply that the active region was in a relaxation stage of its evolution, (3) 2-D MAD has similar patterns with other nonpotential parameters, demonstrating that it can be utilized as an useful parameter of flare producing active region, and (4) the linear force-free coefficient could be a evolutionary indicator with a merit as a global nonpotential parameter.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.48 no.12
• /
• pp.1520-1526
• /
• 1999

This paper presents a current feedback learning controller for dynamic control of DC motors. The proposed controller uses the full third-order dynamics model of DC motor system to drive stable learning rules for virtual current learning input, voltage learning input, and the coefficient of electromotive force. It is shown that the proposed learning controller drives the state of uncertain DC motor system with unknown system parameters and external load torque to the desired one globally asymptotically. Computer simulation and experimental results are given to demonstrate the effectiveness of the proposed adaptive learning controller.

• Proceedings of the KSR Conference
• /
• 2004.06a
• /
• pp.696-701
• /
• 2004

Electric vehicle that is manufactured present by development of electric vehicle technology were available automatic driving. Control of air breaking system for precision stopping is important at automatic driving. Current Electric vehicle is doing precision stopping using braking force control. Braking force control is difficult to take static deceleration by rail condition or change of friction coefficient. Therefore, Proposed the controller in this study is deceleration controller. Designed controller is a robust controller that take state control characteristic for modelling error.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.13 no.4
• /
• pp.511-519
• /
• 2010

This paper presents the modeling and validation of a pile-driver breech fatigue testing system model to replicate actual high pressure in a large caliber gun barrel. A hysteresis damping function was incorporated in the nonlinear impact force model. Test of real pile-driver breech fatigue testing system had been performed for model validation. Comparison of the experimental result and model simulation during impact were made. Numerical studies were performed to evaluate how the actual chamber pressure pattern in the live firing of gun barrel was affected by parameters' variation. Some of the parameters simulated included input velocity, damping coefficient and stiffness. As a result, a variety of actual chamber pressure pattern could be reproduced and controlled through current simulation model.

• 한국전산유체공학회:학술대회논문집
• /
• 2002.10a
• /
• pp.28-34
• /
• 2002

A computational study of supersonic flow around lateral jet controlled missile has been performed. For this study, three dimensional Navier-Stokes code(AADL3D) has been developed. Spalart-Allmaras one equation turbulence model has been implemented on the AADL3D code for relatively rapid computational time. For the validation of developed code, AADL3D, pressure distributions on an ogive-cylinder body has been compared with experimental data. Also, the shock structure of sonic jet on the flat plate in the supersonic flow field has been compared with experimental flow visualization result to see the analysis capability of freestream-jet interaction case. A case study has been performed through comparing the normal force coefficient and the moment coefficient of missile body for several jet flow conditions. Current results will be used to the optimum design of a lateral jet controlled missile.

• Ocean Systems Engineering
• /
• v.7 no.2
• /
• pp.143-155
• /
• 2017

For complex flexible structures such as nets, the determination of drag forces and its deformation is a challenging task. The accurate prediction of loads on cages is one of the key steps in designing fish farm facilities. The basic physics with a simple cage, can be addressed by the use of experimental studies. However, to design more complex cage system for various environmental conditions, a reliable numerical simulation tool is essential. In this work, the current load on a cage is calculated using a Morison-force model applied at instantaneous positions of equivalent-net modeling. Variations of solidity ratio ($S_n$) of the net and current speed are considered. An equivalent array of cylinders is built to represent the physical netting. Based on the systematic comparisons between the published experimental data for Raschel nets and the current numerical simulations, carried out using the commercial software OrcaFlex, a new formulation for $C_d$ values, used in the equivalent-net model, is presented. The similar approach can also be applied to other netting materials following the same procedure. In case of high solidity ratio and current speed, the hybrid model defines $C_d$ as a function of Re (Reynolds number) and $S_n$ to better represent the corresponding weak diffraction effects. Otherwise, the conventional $C_d$ values depending only on Re can be used with including shielding effects for downstream elements. This new methodology significantly improves the agreement between numerical and experimental data.

• Journal of the Korea Concrete Institute
• /
• v.14 no.4
• /
• pp.521-529
• /
• 2002

A restraint coefficient for creep and dry shrinkage deformation of concrete in a composite section was derived to calculate the residual stress, and an equation for the loss rate of the pre-compression force was proposed. The derived restraint coefficient was computed by using the transformed section properties for the age-adjusted effective modulus of elasticity. The long-term behavior of complicate composite sections could be analyzed easily with the restraint coefficient. The articles of the current design code was examined for PSC and steel composite sections. The dry shrinkage strains of $150 ~ 200$\times$10^{-6}$ for the computations of the statically indeterminate force and the expansion joint could be under-estimated for less restrained sections such as the reinforced concrete. The dry shrinkage strain of $180$\times$10^{-6}$ for the computation of residual stress in the steel composite section was unreasonably less value. The loss rate of 16.3% of the design code for the PSC composite section in this study was conservative for the long-term deformation of the ACI 205 but could not be used safely for that of the Eurocode 2. For pre-compressed concrete slab in the steel composite section, the loss rate of prestressed force with low strength reinforcement was much larger than that with high strength tendon. The loss rate of concrete pre-compression increased, while that of pre-tension decreased due to the restraint of the steel girder.

• Current Optics and Photonics
• /
• v.7 no.4
• /
• pp.449-456
• /
• 2023

The localized surface-plasmon resonance has drawn great attention, due to its unique optical properties. In this work a general theoretical description of the dipole mode is proposed, using the forced damped harmonic oscillator model of free charges in an ellipsoid. The restoring force and driving force are derived in the quasistatic approximation under general conditions. In this model, metal is regarded as composed of free charges and bound charges. The bound charges form the dielectric background which has a dielectric function. Those free charges undergo a collective motion in the dielectric background under the driving force. The response of free charges will not be included in the dielectric function like the Drude model. The extinction and scattering cross sections as well as the damping coefficient from our model are verified to be consistent with those based on the Drude model. We introduce size effects and modify the restoring and driving forces by adding the dynamic depolarization factor and the radiation damping term to the depolarization factor. This model provides an intuitive physical picture as well as a simple theoretical description of the dipole mode of the localized surface-plasmon resonance based on free-charge collective motion.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.48 no.11
• /
• pp.611-616
• /
• 1999

The introduction of the eddy current braking(ECB) system in HSRT(high speed railway train) is known to be advantageous, in that the system is independent on wheel-rail adhesion coefficient which is greatly affected by weather condition. It also minimize the maintenance of the brake system and does not require any additional electric energy because it is powered form the regenerated power at the time of the braking. In this study, the braking and attraction forces of the ECB are simulated by 2-D FEM and are experimentally verified on a down-scaled prototype. A control algorithm of the ECB is proposed to generate constant braking torque using linear variation of the reference current according to speed. Experimental results shows that the constant torque is generated over all operating speed region by developed control algorithm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.21 no.7
• /
• pp.669-673
• /
• 2008

ITO thin film was deposited on PC substrate in Facing Targets Sputtering (FTS) system with various sputtering conditions. After it is applied to external bending force, we investigated how change the surface and electrical property of as-deposited ITO thin film. As the L(face-plate distance) of substrate decreases, it found that the maximum crack density is increasing at the center position and decreasing crack density as goes to the edge. So to apply same curvature (r) and bending force to PC substrate with ITO thin film, we fixed the L that is equal to curvature radius (2r). Before bending test, ITO thin films that deposited in the input current of 0.4 A and thickness of 200 nm already had biaxial tensile failure because of each different CTE (Coefficient of Thermal Expansion) and Others had been shown no bending or crack. After bending test, all samples had been shown cracks at about 200 times and as increasing the crack density, resistivity increased.