• Journal of Ocean Engineering and Technology
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• v.22 no.3
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• pp.41-46
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• 2008

It is a recent trend for advanced ships and submarines to incorporate composite structures with viscoelastically damping material. Much research has been done on curve-fitting techniquesto identify vibration characteristic parameters such as natural frequencies, modal damping ratios, and mode shapes of the composite structure. In this study, an advanced technique for accurately determining vibration characteristic of a circular cylindrical shell-attached viscoelastically damping material is used, based on a multi-degree of freedom (MDOF) curve-fitting method. First, an initial value is obtained by using a linear least square method. Next, using the initial value, the exact modal parameters of the composite circular cylindrical shell are obtained by using a nonlinear least square method. Results show computation time is greatly decreased and accurate results are obtained by the MDOF curve-fitting method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.296-303
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• 1987

The composite gear which is composed of involute curve and circular arc has been studied. In the vicinity of pitch point, its profile is an involute curve, and in the dedenum, a circular arc. The curve in the dedendum is generated by the circular arc of the mating gear. Though the available range between minimum and maximum radius of circular arc can be given by existing tooth profile equation, there was no formulation which relates design parameters to the desired radius. It is attempted to get the formula for the radius of circular arc as a function of design parameters, such as unwounded angle, number of teeth, module, and pressure angle. The radius of circular arc, the chordal tooth thickness at working root circle, nominal bending stress, Hertz stress and contact ratio obtained from derived formula are compared with those of the existing design criteria. And these are compared with those of involute gear.

• Journal of Welding and Joining
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• v.14 no.5
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• pp.78-86
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• 1996

Vision sensor was used to track the weld line of the compressor case. The compressor case was fixed in jig equipped with the rotating system, and two torches having one degree of freedom was applied in automatic welding system. The radius of rotation for the compressor case is varying with each rotating angle, while, the angle velocity is constant Therefore, an algorithm to extract the feature of the compressor case for varying rotation angle is needed. To over come the avove difficulties, the curve fitting and composite curve were used. The experiment to verify the proposed algorithm showed desirable results for tracking the welding line of compressor case.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.870-875
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• 1986

In this study, full-rounded tip curve of rack and its mating fillet curve of pinion in Involute-circular arc composite tooth profile are derived. Mechanical characteristics are calculated analytically, i.e., Specific sliding, Nominal bending stress at working root circle and the Contact factor of the arc of contact in circular arc part to the arc of double contact. These characteristics compared with standard involute tooth profile are improved in circular arc part of composite tooth profile. To obtain more efficient composite tooth profile, we studied these characteristics with regard to the changes of unwound angle and radius of circualr arc. And a design method of composite tooth profile is suggested. Composite tooth profile are compared with standard involute tooth profile.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.3
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• pp.389-395
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• 2011

Since Elliptic Curve Cryptosystems(ECCs) support the same security as RSA cryptosystem and ElGamal cryptosystem with 1/6 size key, ECCs are the most efficient to smart cards, cellular phone and small-size computers restricted by high memory capacity and power of process. In this paper, we explicitly explain methods for finite fields operations used in ECC, and then construct some composite fields over finite fields which are secure under Weil's decent attack and maximize the speed of operations. Lastly, we propose a fast multiplier over our composite fields.

• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.359-367
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• 2000

Particulate composites of Al2O3/SiC, Al2O3/ZrO2 and Al2O3/ZrO2/SiC have been fabricated to investigate their R-curve behaviors and toughening mechanisms. Al2O3 containing 30 vol% SiC particles of 3${\mu}{\textrm}{m}$ showed rising R-curve behavior owing to the strong crack bridging by SiC particles. The fracture toughness reached 9.1 MPa {{{{ SQRT {m} }} at the crack length of 1000${\mu}{\textrm}{m}$. On the other hand, ZrO2-toughened Al2O3 had a high flat R-curve since it rose steeply in the short crack region due to the well known transformation toughening. For Al2O3/ZrO2/SiC composites, the R-curve behavior was similar to that of Al2O3/SiC but with slightly higher toughness. The SiC particles in this composite decreased the amount of transformable tetragonal phase to reduce the effect of transformation toughening by 50%. It was also found that the fracture toughness of this composite with two different toughening mechanisms was markedly lower than that estimated by the simple addition of two contributions.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.2
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• pp.145-151
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• 2014

Recently, the growing demand for weight reduction and improved structure durabilityfor commercial vehicles has led to active research into the development and application of suitablecomposite materials. This studysuggests abimaterial composite frame produced by apultrusion process to replace steel frames. We focused on the development of a composite frameconsisting of two types of materialsby mixing anorthotropic material with anisotropic material. The inside layer consisted of an aluminum pipe, and the outside layer was composed of a glass fiber pipe. To determine the strength and failure mechanisms of the composite material, tensile tests, shear tests, and three-point bending tests were conducted, followed by fatigue tests. After static testing, the fatigue tests were conducted at a load frequency of 5 Hz, a stress ratio (R) of 0.1, and an endurance limit of $10^6$ for the S-N curve. The resultsshowed that the failure modes were related to both the core design and the laminating conditions.

• The KIPS Transactions:PartA
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• v.8A no.1
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• pp.42-47
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• 2001

In this paper, we present a curve fitting algorithm using a ball curve. Our algorithm is recursive method for fitting, which is not a traditional ball function but a continuous ball function. This algorithm consists of two steps. The first step, it is classified the composite corner points to joint points until selected from the given data set. The second step is the curve fitting. The basis function for curve fitting is use to ball function. Also, the weighted least square method, to insert knot, is an efficient method for piecewise ball curve and ball curve segments will be smoothly connected at all composit points. The proposed algorithm will be applied to represent image representation, like fonts, digital image and GIS.

• Water for future
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• v.24 no.2
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• pp.97-108
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• 1991

A number of different curve numbers are estimated, and three of them are the basin or composite curve numbers (CN-II and CN-III) evaluated from hydrologic soil cover complex, the observed curve numbers computed from rainfal1-runoff observations and the basin median curve numbers as a median of the observed curve numbers. Based on the observed runoff, CM-II underestimates the effective rainfall meanwhile CN-III overestimates. Hence, for the improvement in estimating effective rainfall, a modulating curve number may be defined as a value in between CN-II and CN-III. Basin median curve numbers produces the closest result to the observed runoff and therefore it can be adopted as a representative curve number for gaged basin.

• Progress in Superconductivity
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• v.6 no.1
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• pp.24-31
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• 2004

Magnetic $T_{c}$ of composite superconductors has been studied for providing a standard method. Various magnetization-temperature curves of NbTi, $Nb_3$Sn and Bi-2223 wires were measured using a SQUID magnetometer. Magnetization-temperature curve of zero-field-cooled procedure showed larger values than fie Id-cooled procedure. To obtain higher resolution near the onset temperature, we employed a two-field-direction method which measures a magnetization-temperature curve of a specimen first in positive and then negative fields. Analytical comparison of the magnetic $T_{c}$, with the resistive T$_{c}$ was accomplished for three specimens. The magnetic $T_{c}$/ mettled showed more detailed information on superconducting state of a specimen than the resistive$T_{c}$/ method. We have also studied the field dependence of the magnetic $T_{c}$ from 5 Oe to 120 Oe, however, no significant difference on field strength was found in our three specimensns