• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.6
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• pp.10-18
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• 2008

Metal stamping is widely used in the mass-production process of the automobile industry. During the stamping process, air may be trapped between the draw die and the panel. The high pressure of trapped air induces imperfections on the panel surface and creates a situation where an extremely high tonnage of punch is required. To prevent these problems, many air ventilation holes are drilled through the draw die and the punch. The present work has developed a simplified mathematical formulation for computing the pressure of the air pocket based on the ideal gas law and isentropic relation. The pressure of the air pocket was compared to the results by the commercial CFD code, Fluent, and experiments. The present work also used the Bisection method to calculate the optimum cross-sectional area of the air ventilation holes, which did not make the pressure of the air pocket exceed the prescribed maximum value.

• Journal of the Institute of Convergence Signal Processing
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• v.15 no.1
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• pp.1-8
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• 2014

Digital watermarking techniques are attracting attention as a proper solution to protect copyright for multimedia data. This paper proposes a new audio watermarking method based on Discrete Cosine Transformation (DCT) and Discrete Wavelet Transformation (DWT) for copyright protection. In our proposed watermarking method, the original audio is transformed into DCT domain and divided into two parts. Synchronization code is applied on the signal in first part and 2 levels DWT domain is applied on the signal in second part. The absolute value of DWT coefficient is divided into arbitrary number of segments and calculates the energy of each segment and middle peak. Watermarks are then embedded into each middle peak. Watermarks are extracted by performing the inverse operation of watermark embedding process. Experimental results show that the hidden watermark data is robust to re-sampling, low-pass filtering, re-quantization, MP3 compression, cropping, echo addition, delay, and pitch shifting, amplitude change. Performance analysis of the proposed scheme shows low error probability rates.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.12
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• pp.1725-1731
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• 2017

In hysteresis simulation, the Preisach model is most widely used as the reliability. However, since the first-order transition curves used in the conventional Preisach model are very inconvenient for actual measurement, many researches have been made to simplify them. In this study, the minor loops obtained along the initial magnetization curve are used to obtain the Everett function used in the Preisach model. In other words, The Everett table is constructed by using the minor loops, and are applied to the magnetization dependent Preisach model to reconstruct the Everett table. In order to minimize the error, the spline interpolation method is used to complete the final Everett table and the hysteresis loop simulation is performed with the Everett table. Furthermore, it is applied to the inductor analysis to perform not only sinusoidal wave and square wave drive but also PWM wave drive considering hysteresis. The validity of the proposed method is confirmed by comparison with simulation and experiment.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.1
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• pp.98-103
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• 2017

In this paper, determination method for drag force and drag coefficient from results of firing test is described. The drag force and drag coefficient are determined through inverse operation of 2-dimensional projectile equation of motion. Determination method was verified by comparing analytical drag coefficient with data from flight test. Analysis of drag coefficient and drag reduction was performed with the data of flight test using artillery projectiles with base bleed unit.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.16 no.3
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• pp.143-155
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• 2006

ARIA is a 128-bit block cipher, which became a Korean Standard in 2004. According to recent research, this cipher is attacked by first order DPA attack. In this paper, we propose a new masking technique as a countermeasure against first order DPA attack and apply it to the ARIA. The proposed method is suitable for low memory environment. By using this countermeasure, we verified that it is secure against first order DPA attack. In addition, our method based on precomputation of inverse table can reduce the computational cost as increasing the number of S-BOX masking.

• Structural Engineering and Mechanics
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• v.77 no.1
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• pp.103-114
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• 2021

Ultra high strength concrete (UHSC) originally proposed by Richards and Cheyrezy (1995) composed of cement, silica fume, quartz sand, quartz powder, steel fibers, superplasticizer etc. Later, other ingredients such as fly ash, GGBS, metakaoline, copper slag, fine aggregate of different sizes have been added to original UHSC. In the present investigation, the combined effect of coarse aggregate (6mm - 10mm) and steel fibers (0.50%, 1.0% and 1.5%) has been studied on UHSC mixes to evaluate mechanical and fracture properties. Compressive strength, split tensile strength and modulus of elasticity were determined for the three UHSC mixes. Size dependent fracture energy was evaluated by using RILEM work of fracture and size independent fracture energy was evaluated by using (i) RILEM work of fracture with tail correction to load - deflection plot (ii) boundary effect method. The constitutive relationship between the residual stress carrying capacity (σ) and the corresponding crack opening (w) has been constructed in an inverse manner based on the concept of a non-linear hinge from the load-crack mouth opening plots of notched three-point bend beams. It was found that (i) the size independent fracture energy obtained by using above two approaches yielded similar value and (ii) tensile stress increases with the increase of % of fibers. These two fracture properties will be very much useful for the analysis of cracked concrete structural components.

• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3205-3214
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• 2022

The aim of this study is to provide a clear and accessible method to obtain accurate true-stress strain data, and to extend the limited material data beyond the ultimate tensile strength (UTS) for AISI 304L. AISI 304L is used for the outer construction for some types of nuclear transport packages, due to its post-yield ductility and high failure strain. Material data for AISI 304L beyond UTS is limited throughout literature. 3D digital image correlation (DIC) was used during a series of uniaxial tensile experiments. Direct method extracted data such as true strain and instantaneous cross-sectional area throughout testing such that the true stress-strain response of the material up to failure could be created. Post processing of the DIC data has a considerable effect on the accuracy of the true stress-strain data produced. Influence of subset size and smoothing of data was investigated by using finite element analysis to inverse model the force displacement response in order to determine the true stress strain curve. The FE force displacement response was iteratively adapted, using subset size and smoothing of the DIC data. Results were validated by matching the force displacement response for the FE model and the experimental force displacement curve.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.781-786
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• 2009

The thesis shows that we gauged vibration of vehicular load regarding WPC girder bridge and researched into dynamic characteristics(natural frequency, vibration acceleration) of WPC girder bridge. By the basic of that, we researched on vibration serviceability by looking over and being compared to vibration criteria we had before. In the thesis, the gauged vibration made an analysis of vertical acceleration through FFT method and evaluated vibration serviceability about vibration sense the body feels by means of the standard of ISO assessment standard and Meister assessment standard by referring to analysis data. This research on bridge is WPC girder bridge of 90m span, width of 5.5m, and the experiment was gauged by a fluent which is right way and inverse way about dump truck of gross 270kN. Acceleration was located in the middle of 1st span, 2nd span, 3rd span. As a result of appraisal standard of Meister, the vibrations of the bridge have distributed between "Level C, Strongly Perceptible" and "Level B, Disturbing". Also the vibration can be attacked with unpleasant feeling. As a result of appraisal standard of ISO, from vibration influence didn't come to 60s, and reduced comfort boundary in part of most rigorous standard that such a case didn't happen.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.5
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• pp.460-469
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• 2010

This paper presents the analysis of a time reversal process for $A_0$ Lamb wave mode($A_0$ mode) on a rectangular plate. The dispersion characteristic equation of the $A_0$ mode is approximated using the Timoshenko beam theory. A virtual sensor array model is developed to consider the effects of reflections occurring on the plate boundary on the time reversal process. The time reversal process is formulated in the frequency domain using the virtual sensor array model. The reconstructed signal is obtained in the time domain through an inverse fast Fourier transform. The validity of the proposed method is demonstrated through the comparison to the numerical simulation results computed by the finite element analysis.

• Computers and Concrete
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• v.8 no.6
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• pp.735-755
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• 2011

The capability of a multi-directional fixed smeared crack constitutive model to simulate the flexural/punching failure modes of fiber reinforced concrete (FRC) laminar structures is discussed. The constitutive model is implemented in a computer program based on the finite element method, where the FRC laminar structures were simulated according to the Reissner-Mindlin shell theory. The shell is discretized into layers for the simulation of the membrane, bending and out-of-plane shear nonlinear behavior. A stress-strain softening diagram is proposed to reproduce, after crack initiation, the evolution of the normal crack component. The in-plane shear crack component is obtained using the concept of shear retention factor, defined by a crack-strain dependent law. To capture the punching failure mode, a softening diagram is proposed to simulate the decrease of the out-of-plane shear stress components with the increase of the corresponding shear strain components, after crack initiation. With this relatively simple approach, accurate predictions of the behavior of FRC structures failing in bending and in shear can be obtained. To assess the predictive performance of the model, a punching experimental test of a module of a façade panel fabricated with steel fiber reinforced self-compacting concrete is numerically simulated. The influence of some parameters defining the softening diagrams is discussed.