• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.05a
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• pp.1-4
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• 1995

The most of conventional ultrasonic transducers are constructed to generate either longitudinal or shear waves, but not both of them. We investigated the mechanism of dual mode transducers that generates both of the longitudinal and shear waves simultaneously with a single PZT element. The study has been aimed to find the desired cut by the examining the piezoelectric properties. Theory predicts that a mixed P/S mode transducer can be constructed using a related Z-cut of a PZT ceramics. We studied the performance of a PZT element as a function of its rotation angle so that its efficiency is optimized to excite the two waves equally strongly. The results are verified by checking the impedance variation of the element with Finite Element Methods, and chocking the wave form by pulse-echo test simulation. Based upon the theory a rotated Z-cut was prepared and a transducer were fabricated. Validity of the theory calculation is verified through the

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.4
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• pp.410-420
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• 1999

The value of the mode I interlamina fracture toughness, GIC, is calculated by experimental compliance method, modified compliance method and beam theory. The value of the mode II interlamina fracture toughness, GIC, is evaluated by beam method, theory beam theory and compliance method. This paper describes the effect of load pint displacement rate and speicimen geometries for mode I and II interlaminar fracture toughness of glass fiber reinforced plastic composites by using double cantilever beam (DCB) and end notched flexure (ENF) specimen. For the load point displacement rate of increases whereas the value of 2,6 and 10 mm/min the value of GIC decrease as load point displacement rate increases whereas the value of GIC is found to be no significant effect. The value of GIC decreases as initial crack length increases. The fractured surface of the DCB and ENF samples are examined by scanning electron microscopy (SEM).

• New & Renewable Energy
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• v.7 no.3
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• pp.74-82
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• 2011

Because concern on the problem of the limited energy is growing and the wind energy is considered as one of the biggest solutions, the researches on the wind energy and turbine are accomplished vigorously. The simulation tools on the non-linear characteristics of wind turbine system are various and it could describe the non-linear characteristics well but, the tool and methodology to apply non-linear control theory rarely exist. In this paper, the application procedure of sliding mode control theory to 2-DOF non-linear wind turbine system is suggested and the application results of it are also shown as compared with a torque loop control theory.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.2040-2049
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• 1999

The Rayleigh-Ritz method is used to investigate the natural frequencies and mode shapes of the ring stiffened cylindrical shells with a rectangular cutout. The cutout is located on the center of the shell. The Love's thin shell theory combined with the discrete stiffener theory is adopted to formulate the analytical model of the shell. The effect of stiffener eccentricity, number, and position on vibration characteristics of the shell is examined. Also the effect of cutout size is examined. By comparison with previously published analytical and new FEM results, it is shown that natural frequencies and mode shapes can be determined with adequate accuracy.

• Proceedings of the KIEE Conference
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• 1996.11a
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• pp.401-403
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• 1996

In this paper, a new control strategy is presented that combines sliding mode control theory with a neural network. Sliding mode control theory requires the complete knowledge of the dynamics of the controlled system. However, in practice, one often bas only a small number of state measurements. This could be a serious limitation on the practical usefulness of sliding mode control theory. A multilayer neural network is employed to solve this kind of problem. The neural network serves as a compensator without a prior knowledge about the system. The proposed control algorithm is applied to a class of uncertain nonlinear system. The robustness against parameter uncertainty, nonlinearity and external disturbances, and the effectiveness is verified by the simulation results.

• International Area Studies Review
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• v.22 no.1
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• pp.61-78
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• 2018

Foreign subsidiary operation modes can be broadly divided into horizontal subsidiaries and vertical subsidiaries. According to institutional theory, foreign subsidiary operation mode differs depending on the host country institution. This study examines the effects of formal and informal institution on the foreign subsidiary operational mode of Korean firms. As a result of the empirical analysis, the higher the cultural distance and the lower political risks, the more favored the vertical foreign operation mode than the horizontal foreign operation mode. On the other hand, the higher the economic freedom and the lower corruption, the more favored the horizontal foreign operation mode than the vertical foreign operation mode.

• Steel and Composite Structures
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• v.25 no.1
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• pp.67-78
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• 2017

In this study, free vibration of functionally graded (FG) micro/nanobeams based on nonlocal third-order shear deformation theory and under different boundary conditions is investigated by applying the differential quadrature method. Third-order shear deformation theory can consider the both small-scale effects and quadratic variation of shear strain and hence shear stress along the FG nanobeam thickness. The governing equations are obtained by using the Hamilton's principle, based on third-order shear deformation beam theory. The differential quadrature (DQ) method is used to discretize the model and attain the natural frequencies and mode shapes. The properties of FG micro/nanobeam are assumed to be chanfged along the thickness direction based on the simple power law distribution. The effects of various parameters such as the nonlocal parameter, gradient index, boundary conditions and mode number on the vibration characteristics of FG micro/nanobeams are discussed in detail.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.2
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• pp.289-295
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• 2001

The aim of this study is to investigate the ductile fracture behaviour under pure Mode II loading using A533B pressure vessel steel. Single punch shear(SPS) test was performed to obtain the J-R curve under pure Mode II loading which was compared with that of the Model I loading. Simulation using Rousellier Ductile Damage Theory(RDDT) was carried out with 4-node quadrilateral element(L(sub)c=0.25mm). For the crack advance, the failed element removal technique was adopted with a $\beta$ criterion. Through the $\beta$ value tuning-up procedures, $\beta$(sub)crit(sup)II was determined as 1.5 in contrast with $\beta$(sub)crit(sup)I=5.5. In conclusion, it was found that the J-R curve under Mode II loading was located at lower part than that under Mode I loading obtained from the previous study and that the $\beta$ values strongly depended on the loading type. In addition, the predicted result using RDDT showed a good agreement with the SPS experimental one under pure Mode II loading.

• Journal of the Korean Institute of Intelligent Systems
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• v.12 no.1
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• pp.39-43
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• 2002

In the frequency response analysis using a modal method, it is very important to determine the number of modes involved with the formulation of a frequency response function. Most engineers are inclined to determine mode truncation with their experience. But it is difficult for non-experts to decide the mode truncation reasonably in many problems of dynamic analyses. In this study, fuzzy theory is used to standardize the empirical determination of mode truncation so that not only the experts but also non-experts can decide a Proper mode truncation easily. Fuzzy rule base is based on the simulation results using finite element method. Numerical simulations show that the developed mode truncation method is a very effective method to choose the number of the considered modes.

• Journal of Welding and Joining
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• v.27 no.5
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• pp.88-93
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• 2009

While the pinch instability theory (PIT) has been widely employed to analyze the spray transfer mode in the gas metal arc welding (GMAW), it cannot predict the detaching drop size accurately. The PIT is modified in this work to increase the accuracy of prediction and to simulate the molten tip geometry to be more physically acceptable. Since the molten tip becomes a cone shape in the spray mode, the effective wire diameter is formulated that the effective diameter is inversely proportional to current square. Modifications are also made to consider the finite length of the liquid column and current leakage through the arc. While the effective diameter influences drop transfer significantly, the current leakage has negligible effects. The effects of modifications on drop transfer are analyzed, and the predicted drop diameters show good agreements with the experimental data of the steel wire.