• Nuclear Engineering and Technology
• /
• v.49 no.6
• /
• pp.1143-1156
• /
• 2017

This paper describes recent development activities of the GENESIS code, which is a transport code for heterogeneous three-dimensional geometry, focusing on applications to reactor core analysis. For the treatment of anisotropic scattering, the concept of the simplified Pn method is introduced in order to reduce storage of flux moments. The accuracy of the present method is verified through a benchmark problem. Next, the iteration stability of the GENESIS code for the highly voided condition, which would appear in a severe accident (e.g., design extension) conditions, is discussed. The efficiencies of the coarse mesh finite difference and generalized coarse mesh rebalance acceleration methods are verified with various stabilization techniques. Use of the effective diffusion coefficient and the artificial grid diffusion coefficients are found to be effective to stabilize the acceleration calculation in highly voided conditions.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.4
• /
• pp.247-256
• /
• 2003

FEM analyses which are based on modified Cam-clay theory have been generally used in such cases as analyses of stability and displacement fur embankment construction on soft clays. However, the Modified Cam Clay Model can generate some problems in anisotropic stress conditions of field because the critical state theory has been developed through many laboratory tests in isotropic conditions. Thus, the applicability on the prediction of undrained shear strength and pore water pressure which was based on the critical state theory was evaluated by triaxial tests and numerical analyses in isotropic and anisotropic conditions. Used samples often come out in domestic area, together with general low plastic clays which are showing dilatant behavior in shearing process. They were evaluated by laboratory tests and FEM based on MCCM. From the results of test and numerical analysis, the predictions of undrained strength in low plastic clays well coincided with each other in both isotropic and anisotropic conditions. However, the generation of porewater pressure was often overestimated during undrained shearing in anisotropic conditions. The results can generate the errors in the prediction of stress path of field sites during loading such as construction of embankment on soft clays because the field is subjected to anisotropic conditions during loading.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.7 no.1
• /
• pp.64-72
• /
• 1983

A method of numerical analysis is proposed for the pure stretch forming of A1 sheet by hemi-spherical punch. The analysis is performed by Woo's general method under the condition of variable friction and plastic yielding is based on the new anisotropic yield function proposed by Hill. A comparison of the calculated results with experiment shows good agreement for various lubrication when the initial values of the coefficient of coulomb friction at pole are less than 0.4.

• Journal of the Korean Geotechnical Society
• /
• v.21 no.5
• /
• pp.25-32
• /
• 2005

The coefficient of consolidation has been evaluated using the conventional oedometer tests based on the one-dimensional consolidation theory. In the field, however, the actual response of the soil will be subject to the three-dimensional condition during consolidation. In this research, a new method f3r estimating the coefficient of consolidation for various stress-deformation conditions was proposed. The good agreement between the computed dissipation of pore pressure and the measured data confirms the usefulness and the applicability of the proposed method to predict the exact rate of consolidation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.15 no.9
• /
• pp.794-797
• /
• 2002

Piezoelectric properties of PZT-PSN ceramics were investigated as a function of WO$_3$ addition from 0 wt% to 6.0 wt%. The dielectric and piezoelectric characteristics of PZT-PSN ceramics have been investigated at different calcination (80$0^{\circ}C$~90$0^{\circ}C$) and sintering (110$0^{\circ}C$~130$0^{\circ}C$) temperatures. The grain size was increased with the addition of WO$_3$and the sintering temperatures. Anisotropic properties of electromechanical coupling coefficient and piezoelectric coefficient are proven to be dependent on processing temperatures and amount of addition. At the specimen with 0.6 wt% WO$_3$ addition, using calcination temperature of 80$0^{\circ}C$ and sintering temperature of 110$0^{\circ}C$ , mechanical quality factor(Q$_{m}$) and electromechanical coupling coefficient(k$_{p}$) showed the excellent results of 1560 and 0.48, respectively Experimental results indicated that the PZT-PSN system ceramics with WO$_3$impurity could be effectively used for the microtransformer and actuator applications, etc.etc.

• Coupled systems mechanics
• /
• v.6 no.3
• /
• pp.317-333
• /
• 2017

The present paper is concerned with the investigation of Rayleigh waves in a homogeneous transversely isotropic magnetothermoelastic medium with two temperature, in the presence of Hall current and rotation. The formulation is applied to the thermoelasticity theories developed by Green-Naghdi theories of Type-II and Type-III. Secular equations are derived mathematically at the stress free and thermally insulated boundaries. The values of Determinant of secular equations, phase velocity and Attenuation coefficient with respect to wave number are computed numerically. Cobalt material has been chosen for transversely isotropic medium and magnesium material is chosen for isotropic solid. The effects of rotation, magnetic field and phase velocity on the resulting quantities and on particular case of isotropic solid are depicted graphically. Some special cases are also deduced from the present investigation.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.27 no.4
• /
• pp.563-570
• /
• 1990

A silicon pressure sensor made of a full bridge of diffused resistors was designed and fabricated using semiconductor integrated circuit process. Thin diaphragms with 30\ulcorner thickness were obtained using anisotropic wet chemical etching technique. Our device showed strong temperature dependence. Compensation networks are used to compensate for the temperature dependence of the pressure sensor. The bridge supply voltage having positive temperature coefficient by compensation networks was utilized against the negative temperature coefficient of bridge output voltage. The sensitivity fluctuation of pressure sensor before temperature compensation was -1700 ppm/\ulcorner, while it reduced to -710ppm\ulcorner with temperature compensation. Our result shows that the we could develop accurate and reliable pressure sensor over a wide temperature range(-20\ulcorner~50\ulcorner).

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.9
• /
• pp.1408-1414
• /
• 2004

The use of flip-chip technology has many advantages over other approaches for high-density electronic packaging. ACF (anisotropic conductive film) is one of the major flip-chip technologies, which has short chip-to-chip interconnection length, high productivity, and miniaturization of package. In this study, thermal fatigue lift of ACF bonding flip-chip package has been predicted. Elastic and thermal properties of ACF were measured by using DMA and TMA. Temperature dependent nonlinear hi-thermal analysis was conducted and the result was compared with Moire interferometer experiment. Calculated displacement field was well matched with experimental result. Thermal fatigue analysis was also conducted. The maximum shear strain occurs at the outmost located bump. Shear stress-strain curve was obtained to calculate fatigue life. Fatigue model for electronic adhesives was used to predict thermal fatigue life of ACF bonding flip-chip packaging. DOE (Design of Experiment) technique was used to find important design factors. The results show that PCB CTE (Coefficient of Thermal Expansion) and elastic modulus of ACF material are important material parameters. And as important design parameters, chip width, bump pitch and bump width were chose. 2$^{nd}$ DOE was conducted to obtain RSM equation far the choose 3 design parameter. The coefficient of determination ($R^2$) for the calculated RSM equation is 0.99934. Optimum design is conducted using the RSM equation. MMFD (Modified Method for feasible Direction) algorithm is used to optimum design. The optimum value for chip width, bump pitch and bump width were 7.87mm, 430$\mu$m, and 78$\mu$m, respectively. Approximately, 1400 cycles have been expected under optimum conditions. Reliability analysis was conducted to find out guideline for control range of design parameter. Sigma value was calculated with changing standard deviation of design variable. To acquire 6 sigma level thermal fatigue reliability, the Std. Deviation of design parameter should be controlled within 3% of average value.

• Earthquakes and Structures
• /
• v.14 no.4
• /
• pp.313-322
• /
• 2018

The present study is dedicated to investigate the SH body-as well as Love-waves propagation effects in porous media with uncertain porosity and permeability. A unified formulation of the governing equations for one-dimensional (1-D) wave propagation in anisotropic porous layered media is presented deterministically. The uncertainties around the above two cited parameters are taken into account by random fields with the help of Monte Carlo Simulations (MCS). Random samples of the porosity and the permeability are generated according to the normal and lognormal distribution functions, respectively, with a mean value and a coefficient of variation for each one of the two parameters. After performing several thousands of samples, the mathematical expectation (mean) of the solution of the wave propagation equations in terms of amplification functions for SH waves and in terms of dispersion equation for Love-waves are obtained. The limits of the Love wave velocity in a porous soil layer overlaying a homogeneous half-space are obtained where it is found that random variations of porosity change the zeros of the wave equation. Also, the increase of uncertainties in the porosity (high coefficient of variation) decreases the mean amplification function amplitudes and shifts the fundamental frequencies. However, no effects are observed on both Love wave dispersion and amplification function for random variations of permeability. Lastly, the present approach is applied to a case study in the Adapazari town basin so that to estimate ground motion accelerations lacked in the fast-growing during the main shock of the damaging 1999 Kocaeli earthquake.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.6
• /
• pp.104-111
• /
• 2013

Deterioration is accelerated due to additional intrusion of chloride ion in crack width in cracked concrete. In this paper, modeling on equivalent diffusion coefficient in cracked concrete is performed for 1-D (Anisotropic) and 2-D (Isotropic) diffusion based on steady state condition. In the previous research, rectangular shape of crack was considered but the shape was modified to wedge shape with torturity. For verification of the proposed model, crack is induced in concrete sample and migration test in steady state is performed for 1-D diffusion. For 2-D diffusion, previous test results are adopted for verification. Through considering wedge shape of crack with torturity, diffusion coefficients in 1-D and 2-D diffusion are reduced, and the more reasonable prediction is obtained. The results from the proposed model with torturity of 0.10~0.15 are shown to be in the best agreement with the test results.