• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.7
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• pp.1013-1021
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• 1998

Various vortical structures are investigated by using three kinds of flow visualization methods in branch pipe flows. There are two typical flow patterns when a jet from the branch pipe with various angles is injected to the main pipe cross flow. The velocity range of cross flow of the main pipe is 0.2 m/s ~ 1.2 m/s and the corresponding Reynolds number, R$_{p}$ is of the range 1.5 * 10$^{3}$ ~ 9.02 * 10$^{3}$. The velocity ratio(R), jet velocity/cross flow velocity, is chosen from 1.3 to 4. The subsequent behavior and development of the ring vortices which are created at the jet boundary mainly depend on the velocity ratio. An empirical relation for the shedding frequency of the ring vortices is derived. It is also found that there are two different vortex shedding mechanism in the mixing of two fluid streams.s.

• Journal of Electrical Engineering and Technology
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• v.8 no.3
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• pp.478-489
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• 2013

The controllability and stability of power systems can be increased by Flexible AC Transmission Devices (FACTs). One of the FACTs devices is Interline Power-Flow Controller (IPFC) by which the voltage stability, dynamic stability and transient stability of power systems can be improved. In the present paper, the convenient operation and control of IPFC for transient stability improvement are considered. Considering that the system's Lyapunov energy function is a relevant tool to study the stability affair. IPFC energy function optimization has been used in order to access the maximum of transient stability margin. In order to control IPFC, a Brain Emotional Learning Based Intelligent Controller (BELBIC) and PI controller have been used. The utilization of the new controller is based on the emotion-processing mechanism in the brain and is essentially an action selection, which is based on sensory inputs and emotional cues. This intelligent control is based on the limbic system of the mammalian brain. Simulation confirms the ability of BELBIC controller compared with conventional PI controller. The designing results have been studied by the simulation of a single-machine system with infinite bus (SMIB) and another standard 9-buses system (Anderson and Fouad, 1977).

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.49 no.6
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• pp.259-265
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• 2000

The purpose of this paper is to detect and identify topological errors in order to maintain a reliable database for the state estimator. In this paper, a two stage estimation procedure is used to identify the topology errors. At the first stage, the WSAV state estimator which has characteristics to remove bad data during the estimation procedure is run for finding out the suspected branches at which topology errors take place. The resulting residuals are normalized and the measurements with significant normalized residuals are selected. A set of suspected branches is formed based on these selected measurements; if the selected measurement is a line flow, the corresponding branch is suspected; if it is an injection, then all the branches connecting the injection bus to its immediate neighbors are suspected. A new WLAV state estimator adding the branch flow errors in the state vector is developed to identify the branch topology errors. Sample cases of single topology error and topology error with a measurement error are applied to IEEE 14 bus test system.

• Journal of Power System Engineering
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• v.14 no.3
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• pp.5-12
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• 2010

The purpose of this study is to analyze heterogeneous distribution of branch-like structure at downstream region of inner spray. The previous many studies about diesel spray structure have yet stayed in the analysis of 2-D structure, and there are very few of informations which are concerned with 3-D analysis of the structure. The heterogeneous distribution of droplets in inner spray affects the mixture formation of diesel spray, and also the combustion characteristics of the diesel engines. Therefore, in order to investigate 3-D structure of evaporative spray the laser beam of 2-D plane was used in this study. Liquid fuel was injected from a single-hole nozzle (l/d=5) into a constant-volume vessel under high pressure and temperature in order to visualize the spray phenomena. The incident laser beam was offset on the central axis. From the images analysis taken by offset of laser beam, we examine formation mechanism of heterogeneous distribution by vortex flow at the downstream of the diesel spray. As the experimental results, the branch-like structure formed heterogeneous distribution of the droplets consists of high concentration of vapor phase in the periphery of droplets and spray tip of branch-like structure. Also the 3-D spatial structure of the evaporative diesel spray can be verified by images obtained from 2-D measurement methods.

• New & Renewable Energy
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• v.19 no.2
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• pp.23-30
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• 2023

Vortex-induced vibrations are a type of flow-induced vibrations caused by alternating lift forces. With increasing demand for renewable energy, the application of vortex-induced vibrations to renewable energy has been widely studied. Vortex-induced vibrations for aquatic clean energy (VIVACE) converter is a renewable energy device that generates electricity from rivers or oceans using vortex-induced vibrations. To increase the design life and power harnessing capacity of the VIVACE converter, the estimation of fluid forces due to vortex-induced vibrations is essential. Herein, vortex-induced vibrations were experimentally tested, and their amplitude and frequency response were measured. The amplitude results showed four different branches: initial branch, upper branch, lower branch, and desynchronization range. According to the fluid force coefficient results, the maximum lift coefficient occurred at the upper branch. Additionally, a mathematical model is proposed to estimate fluid forces due to vortex-induced vibrations without using measurement devices. This mathematical model enables the estimation of fluid force coefficients and phase lag using amplitude and frequency response of vortex-induced vibrations.

• Structural Engineering and Mechanics
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• v.86 no.2
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• pp.181-195
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• 2023

To predict the rheological behaviours along with the compressive strength of self-compacting concrete that incorporates environmentally friendly ingredients as cement substitutes, a comparative evaluation of machine learning methods is conducted. To model four parameters, slump flow diameter, L-box ratio, V-funnel time, as well as compressive strength at 28 days-a complete mix design dataset from available pieces of literature is gathered and used to construct the suggested machine learning standards, SVM, MARS, and Mp5-MT. Six input variables-the amount of binder, the percentage of SCMs, the proportion of water to the binder, the amount of fine and coarse aggregates, and the amount of superplasticizer are grouped in a particular pattern. For optimizing the hyper-parameters of the MARS model with the lowest possible prediction error, a gravitational search algorithm (GSA) is required. In terms of the correlation coefficient for modelling slump flow diameter, L-box ratio, V-funnel duration, and compressive strength, the prediction results showed that MARS combined with GSA could improve the accuracy of the solo MARS model with 1.35%, 11.1%, 2.3%, as well as 1.07%. By contrast, Mp5-MT often demonstrates greater identification capability and more accurate prediction in comparison to MARS-GSA, and it may be regarded as an efficient approach to forecasting the rheological behaviors and compressive strength of SCC in infrastructure practice.

• Structural Engineering and Mechanics
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• v.68 no.3
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• pp.359-368
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• 2018

This paper deals with the dynamic stability of nanocomposite pipes conveying pulsating ferrofluid. The pipe is reinforced by carbon nanotubes (CNTs) where the agglomeration of CNTs are considered based on Mori-Tanaka model. Due to the existence of CNTs and ferrofluid flow, the structure and fluid are subjected to axial magnetic field. Based on Navier-Stokes equation and considering the body forced induced by magnetic field, the external force of fluid to the pipe is derived. For mathematical modeling of the pipe, the first order shear deformation theory (FSDT) is used where the energy method and Hamilton's principle are used for obtaining the motion equations. Using harmonic differential quadrature method (HDQM) and Bolotin's method, the motion equations are solved for calculating the excitation frequency and dynamic instability region (DIR) of the structure. The influences of different parameters such as volume fraction and agglomeration of CNTs, magnetic field, structural damping, viscoelastic medium, fluid velocity and boundary conditions are shown on the DIR of the structure. Results show that with considering agglomeration of CNTs, the DIR shifts to the lower excitation frequencies. In addition, the DIR of the structure will be happened at higher excitation frequencies with increasing the magnetic field.

• Korea-Australia Rheology Journal
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• v.16 no.2
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• pp.75-83
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• 2004

The purpose of the present study is to investigate fluid mechanical interactions between two major abdominal aortic branches under both steady and pulsatile flow conditions. Two model branching systems are considered: two branches emerging off the same side of the aorta (model 1) and two branches emerging off the opposite sides of the aorta (model 2). At higher Reynolds numbers, the velocity profiles within the branches in model 1 are M-shaped due to the strong skewness, while the loss of momentum in model 2 due to turning effects at the first branch leads to the absence of a reversed flow region at the entrance of the second branch. The wall shear stresses are considerably higher along the anterior wall of the abdominal aorta than along the posterior wall, opposite the celiac-superior mesenteric arteries. The wall shear stresses are higher in the immediate vicinity of the daughter branches. The peak wall shear stress in model 2 is considerably lower than that in the model 1. Although quantitative comparisons of our results with the physiological data have not been possible, our results provide useful information for the localization of early atherosclerotic lesions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.732-736
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• 2008

The traditional method to calculate the gravity feed is to assume that only one tank in fuel system supplies the needed fuel to the engine, and then calculated for the single branch. Actually, all fuel tanks compete for supplying oil. Our method takes into consideration all fuel tanks and therefore, we believe, our method is intrinsically superior to traditional methods and is closer to understanding the real seriousness of the oil supply situation. Firstly, the thesis gives the mathematical model for fuel flow pipe, pump, check valve and the simulation model for fuel tank. On the basis of flow network theory and time difference method, we established a new calculation method for gravity feed oil of aeroplane fuel system, secondly. This model can solve the multiple-branch and transient process simulation of gravity feed oil. Finally, we give a numerical example for a certain type of aircraft, achieved the variations of oil level and flow mass per second of each oil tanks. In addition, we also obtained the variations of the oil pressure of the engine inlet, and predicted the maximum time that the aeroplane could fly safely under gravity feed. These variations show that our proposed method of calculations is satisfactory.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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• pp.1464-1471
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• 2003

In order to investigate the flows with shock wave in branch, 108$^{\circ}$ elbow and T-junction of the IRWST system of standard Korean nuclear reactor, detail time dependent behaviors of unsteady flow with shock wave, vortex and so on are obtained by numerical method using compressible three-dimensional Navier-Stokes equations. At first, the complex flow including the incident and reflected shock waves, vortex and expansion waves which are generated at the corner of T-junction is calculated by the commercial code of FLUENT6 and is compared with the experimental result to obtain the validation of numerical method. Then the flow fields in above mentioned units are analyzed by numerical method of [mite volume method. In numerical analysis, the distributions of flow properties with the moving of shock wave and the forces acting on the wall of each unit which can be used to calculate the size of supporting structure in future are calculated specially. It is found that the initial shock wave of normal type is re-established its type from an oblique one having the same strength of the initial shock wave at the 4 times hydraulic diameters of downstream from the branch point of each unit. Finally, it is turned out that the maximum force acting on the pipe wall becomes in order of the T-junction, 108$^{\circ}$ elbow and branch in magnitude, respectively.