• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.1
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• pp.43-51
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• 1998

In this paper, the performance about the CDMA inital synchronization under the Rician fading channel, which is actively studied as a CAI for IMT2000(FPLMTS) is analyzed. Through the performance analysis with the double dwell serial search code acquisition, the minimum mean initial synchronization acquisition time vs signal detection threshold value and first dwell duration time respectively with parameters of false alarm probability, detection probability and test PN chips is presented and the results show the mean initial synchronization acquisition time is increased with lower slope than Rayleigh fading as the threshold value of the initial synchronization acquisition decision is increased.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.755-761
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• 2014

Internal or external restraint of concrete strain due to drying shrinkage and creep in concrete structures causes mechanical strain and becomes a source of persistent change in creep-causing stress conditions. Mathematical modeling to incorporate the persistent change of creep-inducing stress is generally achieved with consideration of the ages of concrete and concrete properties at the times of loadings, and stress history. This paper presents an incremental format of creep model based on parallel creep concept to depict the creep under time-varying stress history in developing creep strain. Laboratory experiments are carried out to validate the performance of the presented creep model. Typical creep phenomena are addressed through the comparisons between the measured and predicted creep strains.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.37.3-37.3
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• 2009

태양물리연구실에서는 춘 추분기를 전후한 일정 기간 사이에 수분 정도 발생하는 태양간섭 현상을 예측하기 위하여 프로그램을 개발하였다. TU 미디어에서 제공해준 3개의 통신위성 PAS-8, TELSTAR-10, MEASAT-1에 대한 2006, 2007년도 춘 추분기의 통신장애 자료와 계산한 자료를 비교 분석하였고, 이를 이용하여 2009년도 추분기의 태양간섭 현상 시간을 예측하였다. 태양위치변화 계산은 NASA/JPL에서 발행하는 DE406 역서 자료를 이용하여 정밀도를 높였으며, 지구 타원체 모델을 통해 기지국에서의 정확한 태양 및 위성의 고도, 방위각을 구하였다. 또한 기지국 안테나 이득률을 계산하여 기지국 안테나에서 예상 되는 태양 간섭 시간을 얻어 냈다. 기지국 안테나의 빔 패턴은 안테나의 중심 부근에서 가장 강하게 나타나며, 중심에서 멀어질수록 특수한 감쇄 형태를 보인다. 이러한 빔 패턴은 안테나의 이득률과 관련이 있으며, 빔 패턴의 적분을 통해 얻어진 이득률과 태양 디스크가 얼마나 안테나의 범위에 들어오는가에 따라 안테나에 수신되는 전파의 강도가 달라진다. 이러한 강도 변화량을 계산함으로써 태양 간섭 시간을 계산할 수 있다. 본래 안테나 빔 패턴은 개개의 안테나에 따라 다르며 직접 측정하여 얻을 수 있다. 사용한 빔 패턴 모델은 ITU에서 채택된 WARC-79 모델을 이용하였고 모든 위성 기지국 안테나의 빔 패턴은 이 모델에서 벗어나지 않는다. 이 연구에서는 빔 패턴 모델을 적용하여 기존의 TU미디어 성수기지국에서의 태양간섭 시간을 다시 계산하였다. 또한 새롭게 KT 용인 위성 관제센터의 자료를 추가하여 태양 간섭시간을 계산하고 예측하였다. 위성데이터는 기존의 PAS-8, TELSTAR-10, MEASAT-1 통신위성과 KT에서 운용하고 있는 무궁화 3호와 무궁화 5호 통신위성 자료를 사용하였다. 이러한 계산 방법은 전국 임의의 지역에서 춘 추분기에 발생할 수 있는 태양간섭 시간을 예측하고 적용할 수 있다.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.4
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• pp.39-47
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• 2001

In this paper, the hydroelastic behavior of a mat-type large floating structure is analyzed in time domain by using mode superposition method. The time-memory function is estimated by Fourier transforming the wave damping coefficients, which are computed by a higher-order boundary element method based on potential theory. Meanwhile, the structural response is obtained by time integrating the eigenmodes of the structure. Numerical examples are made for three test cases on the scaled model of a mat-type large floating structure ; weight pull-up case, weight drop case and weight moving case. In all three cases, the numerical results coincide well with experimental data.

• Geophysics and Geophysical Exploration
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• v.23 no.4
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• pp.243-252
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• 2020

To share an understanding of trajectory measurement in surveys using borehole, this tutorial summarizes the relevant mathematical principles of the borehole deviation survey based on coordinate transform. For uncased or open holes, calculations of the azimuth-deviation-tool face rotation using three-component accelerometer and magnetometer measurements are summarized. For the steel-cased holes, calculations are based on the time-derivative formula of the coordinate transform matrix; yaw-pitch-roll angles through time are mathematically determined by integrating the threecomponent angular velocity measurements from the gyroscope while also removing the Earth's rotation effect. Sensor and data fusion to increase the accuracy of borehole deviation survey is explained with an example of the method. These principles of borehole deviation surveys can be adapted for attitude estimation in air-borne surveys or for positioning in tunnels where global positioning system (GPS) signals cannot be accessed. Information on the optimization filter that must be incorporated in sensor fusion is introduced to help future research.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.5
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• pp.51-57
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• 2015

In this paper, in order to design the A / D converter with a high resolution of 14 bits or more for the biological signal processing, CMOS delta sigma modulator that is a 1.8V power supply voltage - were designed. we propose a new structure of The fourth order delta-sigma modulator that needs four op amps but we use only two op amps. By using a time -interleaving technique, we can re-construct the circuit and reuse the op amps. Also, we proposed a KT/C noise reduction circuit to reduce the thermal noise from a noisy resistor. We adjust the size of sampling capacitor between sampling time and integrating time, so we can reduce almost a half of KT/C noise. The measurement results of the chip is fabricated using a Magna 0.18um CMOS n-well1 poly 6 metal process. Power consumption is $828{\mu}W$ from a 1.8V supply voltage. The peak SNDR is measured as a 75.7dB and 81.3dB of DR at 1kHz input frequency and 256kHz sampling frequency. Measurement results show that KT/C noise reduction circuit enhance the 3dB of SNDR. FOM of the circuit is calculated to be 142dB and 41pJ / step.

• Journal of the Korean Society of Safety
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• v.11 no.4
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• pp.143-150
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• 1996

This is an explicit-Implicit, finite element analysis for linear as well as nonlinear hygrothermal stress problems. Additional features, such as moisture diffusion equation, crack element and virtual crack extension(VCE ) method for evaluating J-integral are implemented in this program. The Linear Elastic Fracture Mechanics(LEFM) Theory is employed to estimate the crack driving force under the transient condition for and existing crack. Pores in materials are assumed to be saturated with moisture in the liquid form at the room temperature, which may vaporize as the temperature increases. The vaporization effects on the crack driving force are also studied. The Ideal gas equation is employed to estimate the thermodynamic pressure due to vaporization at each time step after solving basic nodal values. A set of field equations governing the time dependent response of porous media are derived from balance laws based on the mixture theory Darcy's law Is assumed for the fluid flow through the porous media. Perzyna's viscoplastic model incorporating the Von-Mises yield criterion are implemented. The Green-Naghdi stress rate is used for the invariant of stress tensor under superposed rigid body motion. Isotropic elements are used for the spatial discretization and an iterative scheme based on the full newton-Raphson method is used for solving the nonlinear governing equations.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1084-1094
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• 1993

An efficient method for determining forced responses of a general linear structural system in time domain using subtructure modes and Lagrange multipliers is presented. Compared with the conventional mode synthesis methods, the suggested method does not construct the equations of motion of the combined whole structure and thus the modal parameters of the whole structure are not required. Only modal parameters of each substructure and geometric compatibility conditions are needed. Both the loaded interface free-free modes and free interface modes can be employed as the modal bases of each substructure. Recurrence discrete-time state equations based upon state transition matrix are formulated for the transient analysis of a parameter-changing system. It is shown form numerical examples that the suggested method is very accurate and efficient to calculate transient responses compares with the direct numerical integration method.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.4
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• pp.141-150
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• 1990

Numerical experiments of sballow water equations are performed under various boundary conditions by finite element method to simulate the circulation in estuaries and coastal areas. Galerkin method is employed to discretize spatial domain, and for time integration, finite difference method (Crank-Nicolson scheme) is used. This method is tested in five problems, in which first four cases have analytic solutions. The computed values are well in agreement with the analytic solutions in four experiments and the result of the last 2-dimensional ease is resonable. Implicit and two step Lax-Wendroff schemes in time domain are compared, and the results when using four node bilinear and triangular elements are presented. Consequently it takes very long time for complex problems requiring many elements to integrate all the time steps using the implicit schemes. And the explicit scheme requires careful consideration in selecting the time step and the grid size to obtain the desired accuracy.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.3
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• pp.62-71
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• 1995

In the numerical analysis of incompressible unsteady Navier-stokes equation, large time is required for solving the pressure Poisson equation of the elliptic type at each time step. In this paper, a numerical analysis by the direct method is carried out to solve the pressure Poisson equation and the computing time is analyzed as mesh size increases. The pressure Poisson equation can be transformed to the boundary value problem by the Green theorem. The computing time for the convolution type of the domain integral can be reduced by using F.F.T. and the computing time in the direct method depends entirely on obtaining the solution of the boundary value problem. The numerical analysis on the known solutions is carried out and compared for the verification of the direct method. And the numerical analysis on the body boundary and domain decomposition problem are carried out with the computing time less than O($n^{3}$) in the (n.n) mesh.