• Transactions on Control, Automation and Systems Engineering
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• v.2 no.4
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• pp.235-243
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• 2000

The probabilistic data association filter(PDAF) is known to provide better tracking performance than the standard Kalman filter(KF) in a cluttered environment. In this paper, the stability of the PDAF of Fortmann et al[7], in the presence of uncertainties with regard to the origin of measurement, is investigated. The modified Riccati equation derived by approximating two random terms with their expectations is used to prove the stability of the PDAF. A new Lyapunov function based approach, which is different from the quantitative evaluation of Li and Bar-Shalom[7], is pursued. With the assumption that the system and observation noises are bounded, specific tracking error bounds are established.

• Journal of the Korean Ceramic Society
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• v.30 no.1
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• pp.78-84
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• 1993

In PMN-pyrochlore phase mixtures, dielectric constant was measured as a function of the volume fraction of pyrochlore phase and considered with general effective media(GEM) equation. For the application of GEM equation to this system, the critical volume fraction(Vc) where connectivity between the perovskite PMN and pyrochlore phase changed from 0-3 to 3-3, was determined based on the each particle size ratio of two phases with microstructural observation. And then the t value was determined from modified percolation powder-law dependence ( K-Kc (V-Vc)t). In the case of applying such values of t and Vc to the GEM equation, which provided a reasonable fit to the measured dielectric constant within the experimental error range.

• Smart Structures and Systems
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• v.26 no.6
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• pp.693-701
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• 2020

The conventional Kalman Filter (KF) provides a promising way for structural state estimation. However, the physical parameters of structural systems or models should be available for the estimation. Moreover, it is not applicable when the loadings applied to the structures are unknown. To circumvent the aforementioned limitations, a two-stage KF with unknown input approach is proposed for the simultaneous identification of structural parameters and unknown loadings. In stage 1, a modified observation equation is employed. The structural state vector is estimated by KF on the basis of structural parameters identified at the previous time-step. Then, the unknown input is identified by Least Squares Estimation (LSE). In stage 2, based on the concept of sensitivity matrix, the structural parameters are updated at the current time-step by using the estimated structural states obtained from stage 1. The effectiveness of the proposed approach is numerically validated via a five-story shearing model under random and earthquake excitations. Shaking table tests on a five-story structure are also employed to demonstrate the performance of the proposed approach. It is demonstrated from numerical and experimental results that the proposed approach can be used for the identification of parameters of structure and the external force applied to it with acceptable accuracy.

• Journal of Korea Foundry Society
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• v.31 no.4
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• pp.198-204
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• 2011

The present study was aimed to investigate the dependence of fatigue property on microporosity variation of low-pressure die-cast (LPDC) A356 alloy. The fatigue property of A356 alloy was evaluated through high cycle fatigue test, and the microporosity-terms used were the fractographic porosity measured from SEM observation on fractured surface and the volumetric porosity obtained through the density measurement using Archimedes's principle. The number of cycles to failure of A356 alloys depends obviously upon the variation of fractographic porosity, and can describe in terms of the defect susceptibility which depends on the microporosity variation at a given value of stress amplitude. The modified Basquin's equation was suggested through the combination of microporosity variation and static maximum tensile stress to fatigue strength coefficient. Using modified Basquin's equation, it could suggest that the maximum values of fatigue strength coefficient and exponent achievable in defect-free condition of A356 alloy are 265 MPa, -0.07, respectively.

• Journal of Wetlands Research
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• v.21 no.2
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• pp.152-156
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• 2019

The removal property of magnetic zeolite for the adsorption of aqueous ammonium ion was examined in this work. The surface modified magnetic zeolite was produced by hydrothermal synthesis. The complex of zeolite and $Fe_3O_4$ was established by the observation of SEM and XRD analysis and less than 12.6% of $Fe_3O_4$ content in magnetic zeolite was observed in the form of $Fe_3O_4$ particles. The optimum pH of adsorption was shown around 8 and the maximum adsorption linearly decreased with the increase of $Fe_3O_4$ content. The adsorption isotherm for aqueous ammonium ion was approximated by Langmuir equation. The developed surface modified magnetic zeolite adsorbent was recommended to control the nitrogen pollution for wetland environment system.

• Journal of Astronomy and Space Sciences
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• v.28 no.4
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• pp.267-271
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• 2011

I developed an enhanced correction method for Ricean bias which occurs in linear polarization measurement. Two known methods for Ricean bias correction are reviewed. In low signal-to-noise area, the method based on the mode of the equation gives better representation of the fractional polarization. But a caution should be given that the accurate estimation of noise level, i.e. ${\sigma}$ of the polarized flux, is important. The maximum likelihood method is better choice for high signal-to-noise area. I suggest a hybrid method which uses the mode of the equation at the low signal-to-noise area and takes the maximum likelihood method at the high signal-to-noise area. A modified correction coefficient for the mode solution is proposed. The impact on the depolarization measure analysis is discussed.

• Journal of the Korean Society of Groundwater Environment
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• v.4 no.2
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• pp.95-102
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• 1997

So far, several fractal models of fluid flow in a fractured aquifer have been developed. In this study, a new fractal model is derived that considers transient flow in the dual-porosity aquifer with the fracture skin between the fissure and the block, and the storage capacity and the wellbore skin on the pumping well. Constant-head upper boundary is specified in the block. This model is a generalized one which comprises both modified Hantush equation (1960) and Boulton-Streltsova equation (1978). Type curves are plotted for different flow dimensions (0.5, 1, 1.5, 2, 2.5 and 3) with various values of the leakage factor and the fracture skin. They show dimensionless drawdown in the pumping well and observation wells located either in the fissure system or in the matrix block.

• Journal of KSNVE
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• v.7 no.2
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• pp.215-222
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• 1997

The flow and acoustic fields due to a vortex ring interaction with a rigid sphere are simulated numerically. The flow field is regarded as three-dimensional inviscid and incompressible. The vorticity is assumed to be concentrated inside the finite core of vortex filament. The vortex filament curve, described by parabolic blending curve function, is used to effectively solve the modified Biot-Savart equation. The interaction between a vortex ring and a rigid sphere using the parabolic blending curve is calculated. The trajectory of the vortex ring is obtained with several different initial positions between the ring and the sphere. The force variations acting on the sphere are calculated by using the boundary integral method. Finally, we can also obtain the acoustic signals at the far field observation positions from the force variations acting on the rigid surface. We can find that the dipole axis of the directivity patterns are rotated during the interacting phenomena.

• Geophysics and Geophysical Exploration
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• v.20 no.4
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• pp.199-206
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• 2017

Field data obtained from marine exploration are influenced by various environmental factors such as wind, waves, tidal current and flow velocity of a background medium. Most environmental factors except for the flow velocity are properly corrected in the data processing stage. In this study, the wave equation modeling considering flow velocity is used to generate observation data, and numerical experiments using the observation data were conducted to analyze the effect of flow velocity on waveform inversion. The numerical examples include the results with unrealistic flow velocities. In addition, an algorithm is suggested to numerically extract flow velocity for waveform inversion. The proposed algorithm was applied to the modified Marmousi2 model to obtain the results depending on the flow velocity. The effect of flow velocity on updated physical properties was verified by comparing the inversion results without considering flow velocity and those obtained from the proposed algorithm.

• Journal of computational fluids engineering
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• v.17 no.1
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• pp.94-100
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• 2012

In this paper, the cavitating flows around a hydrofoil have been numerically investigated by using a 2-d multi-phase RANS flow solver based on pseudo-compressibility and a homogeneous mixture model on unstructured meshes. For this purpose, a vertex-centered finite-volume method was utilized in conjunction with 2nd-order Roe's FDS to discretize the inviscid fluxes. The viscous fluxes were computed based on central differencing. The Spalart-Allmaras one equation model was employed for the closure of turbulence. A dual-time stepping method and the Gauss-Seidel iteration were used for unsteady time integration. The phase change rate between the liquid and vapor phases was determined by Merkle's cavitation model based on the difference between local and vapor pressure. Steady state calculations were made for the modified NACA66 hydrofoil at several flow conditions. Good agreements were obtained between the present results and the experiment for the pressure coefficient on a hydrofoil surface. Additional calculation was made for cloud cavitation around the hydrofoil. The observation of the vapor structure, such as cavity size and shape, was made, and the flow characteristics around the cavity were analyzed. Good agreements were obtained between the present results and the experiment for the frequency and the Strouhal number of cavity oscillation.