• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.4
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• pp.376-387
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• 2012

Based on the nonlinear spring model coupled with perturbation method, 2nd harmonic waves generated by oblique incident ultrasound on nonlinear crack interface were calculated and investigated. Reflected and transmitted waves from the interface were determined and analyzed at various angle of incidence for the cracks with different interfacial stiffness in order to estimate the 2nd harmonic generation of incident ultrasound. It was shown in computer simulation that the 2nd harmonic components changed much with the increase of incidence angle in both reflected and transmitted wave, but became very small when the incident angle approached toward 90 degree. It can be concluded that the 2nd harmonic component of reflected wave has a meaningful amplitude as much as the transmitted 2nd harmonic wave from partly closed crack.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.2
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• pp.214-217
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• 2013

In this paper, a waveguide-type resonator with a slot is proposed to measure permittivity of thin film from resonant frequency shifting by an attached MUT(Material Under Test). The MUT on the slot shifts resonant frequency by perturbation of electromagnetic field. Amount of shifting resonance frequency is dependent on the permittivity of MUT, and that relation is obtained from numerical simulation. The measured relative permittivity of a thin film with thickness of $65{\mu}m$ is 3.3492 with standard error of ${\pm}0.0605$ in the frequency range of 2 GHz to 3 GHz. Also the proposed method is compared with other measuring methods such as dielectric resonator and waveguide probe systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.857-864
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• 1998

The infuluence of Doppler effects on the tracking performance of a noncoherent second-order delay locked loop (DLL) operating on a data modulated signal is investigated. For the perfoermance analysis we consider the tracking accuracy (steady state error and jitter) of the linear DLL and the reliability of the nonlinear loop. The nonlinear analysis concerning the loop reliability makes use of an asympototic expansion for the MTLL(mean time to lose lock) which has been derived by applying the singular perturbation method. In particular, we give optimal loop parameters and the optimal bandwidth of the bandpass filter in the loop arms to achieve a maximum MTLL. Since Doppler effects can be producesd comparatively in LEO system, we can espect the more reliable DLL loop design. by using the results of the circuit simulation, the delay lock loop is synthesized in FPGA, and verified to get the GPS data from the STR-2770 GPS simulator system. So, the synthesized logic circuit is shown be accurately performed.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.5
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• pp.418-426
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• 2019

To derive a simplified analytic solution which can be utilized as a fundamental solution for the wave maker design, a segment of the wave board has been idealized as a submerged line segment in a two dimensional domain of a wave flume. The lower end of the line segment could be located at arbitrary depth of the wave flume and the upper end of the board could be also submerged to any depth from the free surface. The freely oscillating motion of the wave board is assumed to be defined by determining the condition of horizontal oscillation on both ends differently. The submerged wave board oscillating in horizontal direction could be specified by selecting the amplitude, frequency and the phase lag differently on lower and upper ends of the board. The simplified two dimensional wave generated by the wave board segment has been obtained by the first order perturbation method. It is found that the general solution of the freely oscillating wave board in two dimensional domain could be decomposed into the solution of flap motion with lower end hinge and swing motion with upper end hinge. The case study of the analytic solutions has been carried out to evaluate the effect on the wave height due to the difference of oscillation frequency, phase difference and variation of stroke between for the motion of both ends. It is found that the solution of the freely oscillating wave board could be utilized for the development of high performance wavemaker especially for irregular waves.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.4
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• pp.395-404
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• 2000

A damage detection and assessment algorithm is developed by measuring accelerations at limited locations of a structure under forced vibrations. The developed algorithm applies a time-domain system identification (SI) method that identifies a structure by solving a linearly constrained nonlinear optimization problem for optimal structural parameters. An equation error of the dynamic equilibrium of motion is minimized to estimate optimal parameters. An adaptive parameter grouping scheme is applied to localize damaged members with sparse measured accelerations. Damage is assessed in a statistical manner by applying a time-windowing technique to the measured time history of acceleration. Displacements and velocities at the measured degrees of freedom (DOF) are computed by integrating the measured accelerations. The displacements at the unmeasured DOF are estimated as additional unknowns to the unknown structural parameters, and the corresponding velocities and accelerations we computed by a numerical differentiation. A numerical simulation study with a truss structure is carried out to examine the efficiency of the algorithm. A data perturbation scheme is applied to determine the thresholds lot damage indices and to compute the damage possibility of each member.

• Journal of the Korean Dietetic Association
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• v.19 no.1
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• pp.1-13
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• 2013

The purpose of this study was to determine the optimal mixing condition of tomato powder and sugar for producing chiffon cake. The experiment was designed according to the central composite design of response surface, which yielded ten experimental points, including two replicates. Physiochemical and sensory properties were measured, and theses values applied to mechanical models. A canonical form and perturbation plot showed the influence of each ingredient on the final product mixture. The results of the physiochemical analysis of each sample showed significant differences in sweetness (P<0.01), color L (P<0.001), color a (P<0.001), color b (P<0.05), hardness (P<0.05), and cohesiveness (P<0.01). The sensory measurements were significantly different in color (P<0.05), appearance (P<0.05), flavor (P<0.05), sweetness (P<0.01), moistness (P<0.05), and overall acceptability (P<0.05). The optimal formulation, calculated using the numerical and graphical method, was determined to be 59.27 g tomato powder and 285.66 g sugar. The sensory evaluation showed significantly higher preferences in the color, flavor, appearance, texture, sweetness, tenderness, moistness and overall quality of the optimized chiffon cake compared to the controlled chiffon cake. The optimized chiffon cake also showed a high antioxidative activity compared to the controlled chiffon cake. Our results show that chiffon cake prepared with tomato powder enhances sensory characteristics and antioxidative activity.

• Bulletin of the Korean Chemical Society
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• v.31 no.6
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• pp.1469-1473
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• 2010

Influences of alrylamino (R) substituents on the herbicidal activity ($pI_{50}$) of 1-(4-chloro-2-fluoro-5-propargyloxypheny)-3-(R)-thiourea analogues (1 ~ 35) against the barnyard grass (Echinochloa crusgalli) in the pre-emergence step were discussed quantitatively using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) as the three dimensional quantitative structure-activity relationship (3D-QSAR) method. The statistically most satisfactory CoMFA models for the herbicidal activity against the barnyard grass had the better predictability ($r^2{_{cv.}}$) and correlativity ($r^2{_{ncv.}}$) than those of CoMSIA models. The optimized CoMFA model 1($r^2{_{cv.}}$ = 0.531 & $r^2{_{ncv.}}$ = 0.931) with the sensitivity to the perturbation (${d_q}^{2'}{dr^2}_{yy'}$ = 1.081) and the prediction ($q^2$ = 0.475) produced by a progressive scrambling analyses were not dependent on chance correlation. And statistical qualities with the atom based fit alignment (AF) were slightly higher than those of the field fit alignment (FF). According to the optimized CoMFA model 1, the contribution ratio (%) of the steric field (76.9%) on the herbicidal activity of the Thioureas was three-fold higher than that of the electrostatic field (20.1%) and the hydrophobic field (3.0%) had the least influence. A steric favor group is on the vicinity of the nitrogen atom in alrylamino (R) substituent, and a steric disfavor group is on the outer side of alrylamino (R) substituent. Thus, as the size of alrylamino (R) substituent increases, so does the herbicidal activity of the substituent.

• Journal of the Korean Chemical Society
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• v.40 no.12
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• pp.748-755
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• 1996

The effects of temperature on the conformational properties of poly(ethylene oxide) (PEO) in aqueous and aqueous urea solutions are reported. The values of intrinsic viscosity and Huggins coefficients for the PEO dissolved in water and urea/water mixtures (urea concentration 0.2, 1, and 2 M) were obtained using a viscometry method and discussed with respect to the change of water structure. At low temperatures (below 22 $^{\circ}C)$, the PEO-water interaction is favorable and the chain can be extended, whereas at higher temperatures (above 24 $^{\circ}C)$, it is less favorable and the chain can be contracted by a hydrophobic hydration, i.e., the PEO-water interaction becomes to be unfavorable with the increase in temperature. As the urea is added to the system, the PEO chain can be more extended and huged by the perturbation of the structured water originating from the unfavorable PEO-water interaction. The effect of temperature on the intrinsic viscosity values shows an Arrhenius behavior. The activation energies of the viscous flow were obtained and discussed.

• Structural Engineering and Mechanics
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• v.40 no.5
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• pp.637-654
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• 2011

The present paper studies the variation of the natural frequencies and mode shapes of rectangular plates carrying a three degree-of-freedom spring-mass system (subsystem), when the subsystem changes (stiffness, mass, moment of inertia, location). An analytical approach based on Lagrange multipliers as well as a finite element formulation are employed and compared. Numerically reliable results are presented for the first time, illustrating the convenience of using the present analytical method which requires only the solution of a linear eigenvalue problem. Results obtained through the variation of the mass, stiffness and moment of inertia of the 3-DOF system can be understood under the effective mass concept or Rayleigh's statement. The analysis of frequency values of the whole system, when the 3-DOF system approaches or moves away from the center, shows that the variations depend on each particular mode of vibration. When the 3-DOF system is placed in the center of the plate, "new" modes are found to be a combination of the subsystem's modes (two rotations, traslation) and the bare plate's modes that possess the same symmetry. This situation no longer exists as the 3-DOF system moves away from the center of the plate, since different bare plate's modes enable distinct motions of the 3-DOF system contributing differently to the "new' modes as its location is modified. Also the natural frequencies of the compound system are nearly uncoupled have been calculated by means of a first order eigenvalue perturbation analysis.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.12
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• pp.29-35
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• 2008

In this paper, The author present a load current feed-forward compensator by method that improve voltage controller of Step-down Chopper to get stable output voltage to sudden change of load current. To confirm the characteristics of a presented load current feed-forward compensator compared each transfer function of whole system that load current feed-forward compensator is added with transfer function of whole system that existent voltage controller is included using Mason gains formula in Root locus and Bode diagram. As a result the pole of system is improved, extreme point of the wave and system improves, and size of peak value and phase margin of break frequency in resonance frequency confirmed that is good. Therefore, presented control technique could confirm that reduce influence by perturbation and improves stationary state and dynamic characteristics in output of Step-down Chopper.