• Journal of Power Electronics
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• v.9 no.5
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• pp.757-771
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• 2009

This paper proposes a systematic approach to the modeling of the small-signal characteristics of three-phase bridge boost rectifiers under non-sinusoidal conditions. The main obstacle to the conventional synchronous d-q frame modeling approach is that it is unable to identify a steady-state under non-sinusoidal conditions. However, for most applications under non-sinusoidal conditions, the current loops of boost rectifiers are designed to have a bandwidth that is much higher than typical harmonics frequencies in order to achieve good current control for these harmonic components. Therefore a quasi-static method is applied to the proposed modeling approach. The converter small-signal characteristics developed from conventional synchronous frame modeling under different operating points are investigated and a worst case point is then located for the current loop design. Both qualitative and quantitative analyses are presented. It is observed that operating points influence the converter low frequency characteristics but hardly affect the dominant poles. The relationship between power stage parameters, system poles and zeroes is also presented which offers good support for the system design. Both the simulation and experimental results verified the analysis and proposed modeling approach. Finally, the practical case of a parallel active power filter is studied to present the modeling approach and the resultant regulator design procedure. The system performance further verifies the whole analysis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4B
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• pp.405-411
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• 2008

The Nakdong River Estuary Barrage (NREB) was constructed in 1987 to prevent saltwater intrusion and to provide the sustainable water supply in the upstream channel. Sediment dredging has been conducted to eliminate deposited sediments in the approached upstream channel of the NREB. Fluvial changes and sedimentation problems have been continued due to urbanization and development in the watershed as well as construction of the NREB. However, the sufficient field monitoring and researches for sedimentation characteristics and bed changes have not been performed after construction of the NREB. Therefore, bed elevation changes and seasonal sediment concentration distribution were analyzed using the quasi-steady state model with historical field data in this study. The water surface elevation changes with and without sediment dredging operation were calculated using the developed quasi-steady state model and finally the sediment dredging effects were evaluated.

• Proceedings of the KIEE Conference
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• 2005.05a
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• pp.243-245
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• 2005

Condition monitoring is desirable for increasing machinery availability, reducing consequential damage, and improving operational efficiency. In this paper, a model-based method using neural network modeling of induction noter in vibration spectra is proposed for machine fault detection and diagnosis. The short-time Fourier transform (STFT) is used to process the quasi-steady vibration signals to continuous spectra so that the neural network model can be trained with vibration spectra. And the faults are detected from changes in the expectation of vibration spectra modeling error. The effectiveness of the proposed method is demonstrated through experimental results.

• International Journal of Vascular Biomedical Engineering
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• v.4 no.2
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• pp.13-18
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• 2006

Direct injection of a fibrinolytic agent to the intra-arterial thrombosis may increase the effectiveness of thrombolysis by enhancing the permeation of thrombolytic agents into the blood clot. Permeation of fibrinolytic agents into a clot is influenced by the surface pressure, which is determined by the injection velocity of fibrinolytic agents. Computational fluid dynamic methods were used in order to predict clot lysis for different jet velocities and nozzle arrangements. Firstly, thrombolysis of a clot was mathematically modeled based on the pressure and lysis front velocity relationship. Direct injection of a thrombolytic agent increased the speed of thrombolysis significantly and the effectiveness was increased as the ejecting velocity increased. The nine nozzles model showed about 20% increase of the lysed volume, and the one and seventeen nozzles models did not show significant differences. Secondly, thrombolysis was modeled based on the enzyme transport and the fluid flow equations, and quasi steady numerical analysis was performed. Clot lysis efficiency was also increased as injection velocity increased.

• Proceedings of the KIEE Conference
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• 1997.07b
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• pp.685-688
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• 1997

In this paper, we introduce a new adaptive controller for induction motor based on singular perturbation theory. The design of 5th induction motor was changed for the 3rd modeling using the singular perturbation method. The resulting boundary layer and quasi-steady-state systems are made exponentially stable. Therefore the statements of Tychonov's theorm are valid for an infinite time interval for induction motor, too.

• Wind and Structures
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• v.6 no.1
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• pp.41-52
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• 2003

Rain-wind induced vibrations of cables are a challenging problem in the design of cable-stayed bridges. The precise excitation mechanism of the complex interaction between structure, wind and rain is still unknown. A theoretical model that is able to accurately simulate the observed phenomena is not available. This paper presents a mathematical model describing rain-wind induced vibrations as movement-induced vibrations using the quasi-steady strip theory. Both, the vibrations of the cable and the movement of the water rivulet on the cable surface can be described by the model including all geometrical and physical nonlinearities. The analysis using the stability and bifurcation theory shows that the model is capable of simulating the basic phenomena of the vibrations, such as dependence of wind velocity and cable damping. The results agree well with field data and wind tunnel tests. An extensive experimental study is currently performed to calibrate the parameters of the model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.256-263
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• 2008

The assumed modes method is developed to derive a set of linear differential equations describing the motion of a flexible wind turbine blade and to propose an approach to investigate the forced responses result from various wind excitations. In this work, we have adopted Euler beam theory and considered that the root of the blade is clamped at the rigid hub. And the aerodynamic parameters and forces are determined based on Blade Element Momentum (BEM) theory and quasi-steady airfoil aerodynamics. Numerical calculations show that this method gives good results and it can be used fur modeling and the forced vibration analysis including the coupling effect of wind-turbine blades, as well as turbo-machinery blades, aircraft propellers or helicopter rotor blades which may be considered as straight non-uniform beams with built-in pre-twist.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.120-124
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• 2007

Helicopters and rotary-wing vehicles encounter a wide variety of complex aerodynamic phenomena and these phenomena present substantial challenges for computational fluid dynamics(CFD) models. This investigation presents the rotor aerodynamic analysis items for the helicopter development and variety aerodynamic analysis methods to provide the better solution to researchers and helicopter developers between aerodynamic problems and numerical aerodynamic analysis methods. The numerical methods to make an analysis of helicopter rotor are as below - CFD Modelling : actuator disk model, BET model, fully rotor model,... - Grid : sliding mesh, chimera mesh / structure mesh, unstructure mesh,... - etc. : panel method periodic boundary, quasi-steady simulation, incompressible,... The choice of CFD methodology and the numerical resolution for the overall problem have been driven mostly by available computer speed and memory at any point in time. The combination of the knowledge of aerodynamic analysis items, available computing power and choice of CFD methods now allows the solution of a number of important rotorcraft aerodynamics design problems.

• Journal of computational fluids engineering
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• v.14 no.1
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• pp.70-77
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• 2009

In this study, time-dependent numerical analysis was carried out to investigate the plasma jet impingement on a flat plate, and a compressible form of two-dimensional inviscid gas dynamics equations were solved using the flux corrected transport algorithm. The mathematical modeling of Joule heating in the polycarbonate capillary bore and the mass ablation from the bore wall was incorporated in the numerical analysis and the series of computation was performed for three cases depending on the distance of the opposing plate from the capillary exit. The computational results reveal that the presence of the opposing plate does not affect the flow conditions inside the capillary when compared to the case of open-air plasma discharge. In the exterior region, the flow structure shows the typical supersonic underexpanded jet which consists of the strong Mach disk in front of the opposing plate and the barrel shock at the side of the jet. It is found that the shock evolution becomes more quasi-steady when the plate distance decreases. Also, the effects of the distance between the capillary bore exit and the opposing plate on the flow conditions along the opposing plate are investigated and the pressure variation on the plate shows more complicated interaction between the plasma discharge and the opposing plate when the location of plate becomes closer to the capillary exit.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.1
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• pp.100-113
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• 2017

Snap rolling during hard turning and instability during emergency rising are important features of submarine operation. Hydrodynamics modeling using a high incidence flow angle is required to predict these phenomena. In the present study, a quasi-steady dynamics model of a submarine suitable for high-incidence-angle maneuvering applications is developed. To determine the hydrodynamic coefficients of the model, static tests, dynamic tests, and control surface tests were conducted in a towing tank and wind tunnel. The towing tank test is conducted utilizing a Reynolds number of $3.12{\times}10^6$, and the wind tunnel test is performed utilizing a Reynolds number of $5.11{\times}10^6$. In addition, least squares, golden section search, and surface fitting using polynomial models were used to analyze the experimental results. The obtained coefficients are presented in tabular form and can be used for various purposes such as hard turning simulation, emergency rising simulation, and controller design.