• Journal of Magnetics
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• v.13 no.2
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• pp.65-69
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• 2008

The magneto impedance (MI) behaviors of patterned $Co_{30}Fe_{34}Ni_{36}$ microwire were investigated with respect to its shape variation. After preparing $Co_{30}Fe_{34}Ni_{36}$ microwires using electrodeposition and photolithography methods, impedance measurements were conducted to compare the MI ratios of the devices with different aspect ratios. As a result, the anisotropy field and transverse permeability were found to be strongly affected by the aspect ratio of the device. The external field value at the maximum impedance and maximum sensitivity of the device was found to increase with increasing device width, which was attributed to the increased transverse anisotropy with decreasing aspect ratio. While an increase in the thickness also contributed to an increase in the MI ratio, a variation in the thickness not only increased the anisotropic field, but the variation in the MI ratio was as also affected by the skin effect. Conversely, the MI ratios of the present devices were hardly affected by variations in the length. Considering the typical aspect ratios of our devices, it was expected that the length effect would emerge when the aspect ratio was reduced to less than 10. Nevertheless, our results show that for the practical application of MI devices, the MI characteristics can be optimized by tailoring the aspect ratio of the devices.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.594-597
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• 2003

In the present study, the piezoelectricity and polarization of multilayer ceramic actuator, being designed to stack PMN-PZ-PT ceramic layers and Ag-Pd electrode layers alternatively, were investigated under a consideration of geometric factor, the volume ratio of the ceramic to the electrode layers. The actuators were fabricated by tape casting of 0.2Pb(Mg1/3Nb2/3)O3-0.38PbZrO3-0.42PbTiO3 followed by lamination and burnout & co-firing processes. The actuators of 10 10 0.62 nm3 in size were formed in a way that 60 200 m thick ceramics were stacked alternatively with 5 m thick electrode layer. Increases in polarization and electric field-induced displacement with thickness of the ceramic layer were attributed to change of 90o/180o domain ratio, which was affected by interlayer internal stress. The piezoelectricity and actuation behaviors were found to depend upon the volume ratio (or thickness ratio) of ceramic to electrode layers.

• Journal of the Korean Society of Visualization
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• v.18 no.2
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• pp.28-34
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• 2020

In this study, we numerically investigated the thermal stratification in solar seasonal thermal storage tanks. The vertical in/out flows were unsuitable for the thermal stratification in a large scale. The effect of an aspect ratio (AR) on the thermal stratification was investigated. When AR was less than 2, water adheres and flows along the upper wall due to buoyance and the surface effect. Thereafter, hot water flows down and a large scale vortex occurs in entire tank. For high AR, jet flows ejected from the inlet pipe impinges to the opposite wall and splits. The divided flows create two vortex flows in the upper and lower regions. These different flows strongly influence temperature and thermal stratification. The thermal stratification was evaluated in terms of the thermocline thickness and degree of stratification. Compared to ARs, the maximum degree of stratification was obtained with AR of 5 having the minimum thermocline thickness.

• Korea-Australia Rheology Journal
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• v.12 no.2
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• pp.107-117
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• 2000

Prediction of the product shape in sheet casting process is performed from the numerical simulation. A three-dimensional finite element method is used to investigate the flow behavior and to examine the effects of processing conditions on the sheet produced. Effects of inertia, gravity, surface tension and non-Newtonian viscosity on the thickness profile of the sheet are considered since the edge bead and the flow patterns in the chill roll region have great influence on the quality of the products. In the numerical simulation with free surface flows, the spine method is adopted to update the free surface, and the force-free boundary condition is imposed along the take-up plane to avoid severe singularity problems existing at the take-up plane. From the numerical results of steady isothermal flows of a generalized Newtonian fluid, it is shown that the draw ratio plays a major role in predicting the shape of the final sheet produced and the surface tension has considerable effect on the bead thickness ratio and the bead width fraction, while shear-thinning and/or tension-thickening viscosity affect the degree of neck-in.

• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.2
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• pp.32-39
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• 2015

So far, square concrete filled tubular(CFT) columns have been used in a limited width thickness ratio. The reason is that local buckling occurs in steel tube easily. Once the local buckling occurs, the confinement effect of steel tube on concrete disappears. In this study, we developed welded built-up square steel tube with reinforcement which are placed at the center of the tube width acts as an anchor. 3 specimens of slender welded built-up square CFT columns and 3 specimens of slender welded built-up square steel tube columns were manufactured with parameters of width(B) of steel tube, width thickness ratio(B/t). we conducted a experimental test on the 6 specimens under eccentric load, and evaluated the structural resistance and behavior of 6 specimens.

• Journal of the Korean Magnetics Society
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• v.14 no.1
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• pp.25-28
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• 2004

The dependence of sensitivity, MR ratio, coercivity (Hc) and switching fields as a function of thickness of each magnetic layers(Co, NiFe and Cu) were investigated in pseudo spin valves with a structure of Ta/NiFe/Cu/Co. As measured results dependence of the thickness of each magnetic layer, we obtained MR ratio of 7.26% for Ta(4 nm)/NiFe(7.5 nm)/Cu(3 nm)/Co(5 nm) pseudo spin valves. Also, we could control properties of magnetoresistance for independent magnetization courses of each magnetic layer. Especially, we found that we could control coercivity as constant MR ratio dependence of Co thickness.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.568-572
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• 2000

A numerical investigation was performed to determine the effect of airfoil thickness on the optimum Gurney flap height using NACA 00XX series airfoils. Seven airfoils which have 3% chord thickness difference were used. These were NACA 0006, 0009, 0012, 0015, 0018, 0021, and 0024. A Navier-Stokes code, FLUENT, was used to calculate the flow field about airfoil. The fully turbulent results were obtained using the standard $k-{\varepsilon}$ two-equation turbulence model. To provide a check case fur our computational method, numerical studies for NACA 4412 airfoil were made and compared with already existing experimental data for this airfoil by Wadcock. For every NACA 00XX airfoil, Gurney flap heights ranging from 0.5% to 2.0% chord were changed by 0.5% chord interval and their effects were studied. With the numerical solutions, the relationship between $(L/D)_{max}$ and airfoil thickness as a function of flap height and the relationship between $(L/D)_{max}$ and flap height as a function of airfoil thickness were investigated. The same relationship for $(C_l)_{max}$ also were shown. From these results, the optimum flap size for each airfoil thickness can be determined and vice versa.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.11
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• pp.1949-1957
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• 2003

A hybrid finite element analysis was used to analyze the influence of ring gear rim thickness and spline number on the static properties of a planetary gear system with manufacturing errors. Both of these parameters affected the bearing force and critical stress. The effect of changes in the rim thickness on the load sharing between the gears depended on the type of manufacturing error. Ring flexibility improved the load sharing between planetary gears only in systems with planet tooth thickness or planet tangential errors; for other types of error, ring flexibility worsened the load sharing. To improve load sharing, rim thickness and spline number should be controlled within a specific range. The minimum rim thickness limit should be determined considering not only the critical stress but also the load sharing. The effect of the ring gear boundary condition was more apparent in a system with errors than in a normal system.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.841-844
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• 1997

Sandwich structure is widely used in various fields of industry due to its excellent strength and stiffness compared with weight. We studied the buckling and bending behavior with respect to the variation of design parameters such as length, height, and thickness of honeycomb sandwich core. We found that as the density and the thickness of core become higher, the value of critical bucking load increased significantly. We found that the effect of bending stress due to critical buckling load resulted in high bending stress and the value of bending stress decreased in half according to the increase of length of core. The effect by bending stress is dominant above the portion of the intersection line between bending stress and the effect of buckling is dominant below the potion of it. We could get proper thickness ratio and density of core according to applied load conditions.

• Journal of Magnetics
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• v.6 no.1
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• pp.9-12
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• 2001

The dependence of the magnetoimpedance effect (MI) on magnetic properties has been investigated in mumetal thin films prepared by rf magnetron sputtering. Coercivity of thin films prepared at 400 W was about 0.4 Oe, and the magnetic anisotropy field of films deposited under a uniaxial magnetic field decreased with increasing film thickness. The saturation magnetization of mumetal films increased with rising input power and thickness and was smaller than that of permalloy films. Transverse incremental Permeability (TPR) of films of 1$\mu m$ thick increased with increasing effective permeability. The magneto impedance ratio (MIR) was proportional to TPR in films 1$\mu m$ thick but in spite of lower effective permeability at higher thicknesses, MIR increased due to skin effect. The height of the double peaks in the MIR curves decreased with decreasing anisotropy and thickness. The maximum MIR value for a 4$\mu m$ thick 75% at 36.5 MHz.