• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.9
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• pp.53-59
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• 2006

Need for agile satellite increases for performing various mission due to increase of satellite image applications and users. In high resolution satellite TDI (time delay and integration) method is adopted in order to improve SNR. But image quality can be degraded by satellite maneuver. In this paper requirements for remote sensing in high resolution satellite with agility are extracted and an approach to operate the agile satellite to perform the missions are proposed. The proposed approach in this paper will be applicable to system level design and analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.9
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• pp.60-66
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• 2006

Now, on developing COMS(Communication, Ocean and Meteorological Satellite) has solar panel on the south panel only. Therefore, the wheel off-loading has to be performed periodically to reduce a induced momentum energy by a asymmetric solar panel. One of two East/West station keeping maneuver to correct simultaneously longitude and eccentricity, orbit corrections may be performed during one of the two wheel off-loading manoeuvres per day to get enough observation time for meteorological and ocean sensor. In this paper, we applied a linearized orbit maneuver equation to acquire maneuver time and delta-V. Nonlinear simulation for the station keeping is performed and compared with general station keeping strategy for fuel reduction.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.4
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• pp.48-59
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• 1996

The numerical step in the unsteady viscous flow analysis can be divided in the space analysis step satisfying continuity equation and the time marching step. In this study the spectral method is applied to solve the pressure Poisson equation in the space analysis step. If the highest order differential term of the pressure Poisson equation is transformed by Fourier series, pressure arid its first derivatives can be expressed by the integral form of Fourier series. So Gibb's phenomena can be eliminated and the spectral method can be applied to non-periodic problems. The numerical analysis of unsteady viscous flow around 2-dimensional circular cylinder and wing is carried out and compared for verification.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.2
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• pp.22-28
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• 1999

Small amplitude in-phase oscillations of multi-cylinders are considered both numerically and experimentally. Flow field is separated into inner and outer regions. The basic unsteady solution is obtained analytically and the secondary flow, termed as steady streaming flow, can be obtained numerically by using Finite Volume Code with Panel Method. The Particle Induced Velocimetry, one of whole field measurements, is introduced for comparison with numerical flow visualization quantitatively. Among the algorithms for PIV, the Three Step Vector Searching Technique is applied to reduce CPU time. Small but non-zero damping coefficient, that is important in lightly damped system can be obtained with varying number of bodies and distances.

• Journal of the Korean Society for Railway
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• v.18 no.3
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• pp.194-202
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• 2015

In this paper, dynamic modeling with viscoelastic properties of a human body resting on a seat is presented to quantitatively analyze ride quality of passengers exposed to vertical vibrations. In describing the motions of a seated body, a 5 degree-of-freedom multibody model from the literature is investigated. The viscoelastic characteristics of seats used in railway vehicles are mathematically formulated with nonlinear stiffness characteristics and convolution integrals representing time delay terms. Transfer functions for the floor input are investigated and it is found that these are different in accordance with the input magnitude due to nonlinear characteristics of the seat. Measured floor input at the railway vehicle is used to analyze realistic human vibration characteristics. Frequency weighted RMS acceleration values are calculated and the effects of the seat design parameters on the frequency weighted RMS acceleration values are presented.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.2
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• pp.1-14
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• 2006

Present study examines the numerical issues of cell structure simulation for various regimes of detonation phenomena ranging from weakly unstable to highly unstable detonations. Inviscid fluid dynamics equations with $variable-{\gamma} $ formulation and one-step Arrhenius reaction model are solved by a MUSCL-type TVD scheme and 4th order accurate Runge-Kutta time integration scheme. A series of numerical studies are carried out for the different regimes of the detonation phenomena to investigate the computational requirements for the simulation of the detonation wave cell structure by varying the reaction constants and grid resolutions. The computational results are investigated by comparing the solution of steady ZND structure to draw out the minimum grid resolutions and the size of the computational domain for the capturing cell structures of the different regimes of the detonation phenomena.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.7
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• pp.1424-1428
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• 2004

In this paper, CMOS analog filters for use in the Analog front End of digital subscriber loop(DSL) chip set are proposed. Designed filters contain receiver continuous-time filters which are composed of lowpass and highpass functions. And their cutoff frequency are 138H1z and 1.1MHz respectively. A low-voltage gm-c integrator is improved and used to design filters. Desisned filters are verified by HSPICE simulation with the 0.25${\mu}m$ CMOS n-well parameter.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1333-1340
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• 2000

This paper shows that the Kronecker sequence, the rapid acquisition spreading code, can be used in packet wireless data communication systems. The general properties of the Kronecker sequence such as construction and correlation characteristics are described, and it is shown that the Kronecker sequence can use a partial-period correlation for a faster acquisition. Based on above Properties, it can be expected that the Kronecker sequence can be used in packet communication systems because the probability of false alarm for the Kronecker sequence is lower and flatter(that is, less sensitive to Ec/No variations) than that for the PN sequence under the assumption that both sequences have the same acquisition time.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.519-522
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• 2010

Flow-induced vibration analyses have been conducted for a 3D compressor blade model. Advanced computational analysis system based on computational fluid dynamics(CFD) and computational structural dynamics has been developed in order to investigate detailed dynamic responses of designed compressor blades. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D compressor blade for fluid-structure interaction problems. Detailed dynamic responses and instantaneous pressure contours on the blade surfaces considering flow-separation effects are presented to show the multi-physical phenomenon of the rotating compressor blade.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1555-1561
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• 2003

Finite element analysis using modern constitutive equation is one of the most general tools to simulate the deformation behavior and to predict the life of the structure. Constitutive equation becomes complicated so as to predict the material behavior more accurately than the classical models. Because of the complexity of constitutive model, numerical treatment becomes so difficult that the calculation should be verified carefully. One-element tests, simple tension or simple shear, are usually used to verify the accuracy of finite element analysis using complicated constitutive model. Since this test is mainly focused on the time integration scheme, it is also necessary to verify the equilibrium iteration using material stiffness matrix and to compare FE results with solution of structures. In this investigation, viscoplastic solution of thick walled cylinder was derived considering axial constraints and was compared with the finite element analysis. All the numerical solutions showed a good coincidence with FE results. This numerical solution can be used as a verification tool for newly developed FE code with complicated constitutive model.