• Journal of computational fluids engineering
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• v.19 no.4
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• pp.20-28
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• 2014

An efficient solution algorithm for simulating free surface problem is presented. Navier-Stokes equations for variable density incompressible flow are employed as the governing equation on Cartesian meshes. In order to describe the free surface motion efficiently, VOF(Volume Of Fluid) method utilizing THINC(Tangent of Hyperbola for Interface Capturing) scheme is employed. The most time-consuming part of the current free surface flow simulations is the solution step of the linear system, derived by the pressure Poisson equation. To solve a pressure Poisson equation efficiently, the PCG(Preconditioned Conjugate Gradient) method is utilized. This study showed that the proper application of the preconditioner is the key for the efficient solution of the free surface flow when its pressure Poisson equation is solved by the CG method. To demonstrate the efficiency of the current approach, we compared the convergence histories of different algorithms for solving the pressure Poisson equation.

• Journal of the Korean Society of Visualization
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• v.9 no.3
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• pp.65-70
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• 2011

Three major physiological functions of nose can be described as air-conditioning, filtering and smelling. Detailed knowledge of airflow characteristics in nasal cavities is essential to understanding of the physiological and pathological aspects of nasal breathing. In our laboratory, a series of experimental investigations have been conducted on the airflows in normal and abnormal nasal cavity models by means of PIV under both constant and periodic flow conditions. In this work, more specifically experimental and numerical results on the surgically modified inferior turbinate model were presented. With the high resolution CT data and a careful treatment of the model surface under the ENT doctor's advice yielded quite sophisticated cavity models for the PIV experiment. Physiological nature of the airflow was discussed in terms of velocity distribution and vortical structure for constant inspirational flow. Since the inferior and middle turbinate are key determinants of nasal airflow, the turbinectomy obviously altered the main stream direction. This phenomenon may cause local changes in physiological function and the flow resistance.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.4_2
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• pp.541-547
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• 2022

Before making a prototype, we predicted the inlet/outlet differential pressure and flow coefficient, which are the most basic design data for the valve through the design and numerical analysis of the trim, which is the most important in the localization development of the 1500Ib high differential pressure control valve used for boiler feed water. As a result, the design value and the analysis value were found to be about 98% similar. The flow field within the fluid velocity of 23m/s to prevent cavitation was also found. The result of the numerical analysis on thermal stress due to the characteristics of valves exposed to high temperatures showed that it was found to be about 18% less than the allowable stress of the bolt fixing the trim. When all loads such as pressure, self-weight, and vibration are applied, however, it is judged to go beyond the currently calculated thermal stress, exceeding the allowable stress.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1999-2007
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• 2013

The key characteristics of two-lane-and-two-way traffic flow are platoon and overtaking caused by low-speed vehicle such as truck. In order to develop two-way traffic flow model comprised of CF(car-following) and overtaking model, it is essential to develop a car-following model which is suitable to two-way traffic flow. Short distance between vehicles is caused when a high-speed vehicle tailgates and overtakes foregoing low-speed vehicle on two-way road system. And a vehicle following low-speed vehicle decides to overtake the front low-speed vehicle using suitable space within the headway distribution of opposite traffic flow. For this reason, a two-way CF model should describes not only running within short gap but also headway distribution. Additionally considering domestic two-way-road size, there is a on-going need for large-network simulation, but there are few studies for two-way CF model. In this paper, a two-way CA model is developed, which explains two-way CF behavior more realistic and can be applied for large road network. The experimental results show that the developed model mimics stop-and-go phenomenon, one of features of congested traffic flow, and efficiently generates the distribution of headway. When the CF model is integrated with overtaking model, it is, therefore, expected that two-way traffic flow can be explained more realistically than before.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.2
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• pp.75-85
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• 2016

A pyrotechnic system consisting of donor/acceptor pair separated by a gap relies on shock attenuation characteristics of the gap material and shock sensitivity of the donor and acceptor charges. Despite of its common use, numerical study of such pyrotechnic train configuration is seldom reported because proper modeling of the full process requires precise capturing of the shock wave attenuation in the gap prior to triggering a full detonation of high explosive and accurate description of the high strain rate dynamics of the explosively loaded inert confinements. We apply a Eulerian level-set based multimaterial hydrocode with reactive flow models for pentolite donor and heavily aluminized RDX as acceptor charge. The complex shock interaction, critical gap thickness, acoustic impedance, and go/no-go characteristics of the gap test are quantitatively investigated.

• Physical Therapy Rehabilitation Science
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• v.1 no.1
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• pp.33-39
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• 2012

Objective: The objective of this study is to investigate the effect of treadmill training with real optic flow scene on functional recovery of balance and balance self-efficacy in stroke patients. Design: Single blind, Randomized controlled trial. Methods: Nine patients following stroke were divided randomly into the treadmill with optic flow group (n=3), treadmill with virtual reality group (n=3), and control group (n=3). Subjects in the treadmill with optic flow group wore a head-mounted display in order to receive a speed modulated real optic flow scene during treadmill training for 30 minutes, while those in the treadmill with virtual reality group and control group received treadmill training with virtual reality and regular therapy for the same amount of time, five times per week for a period of three weeks. Timed up and go test (TUG) and activities-specific balance confidence scale (ABC scale) were evaluated before and after the intervention. Results: TUG in the treadmill training with optic flow group showed significantly greater improvement, compared with the treadmill training with virtual reality group and control group (p<0.05). Significantly greater improvement in the ABC scale was observed in the treadmill training with optic flow group and the tread mill training with virtual reality group, compared with the control group (p<0.05). Conclusions: Findings of this study demonstrate that treadmill training with real optic flow scene can be helpful in improving balance and balance self-efficacy of patients with chronic stroke and may be used as a practical adjunct to routine rehabilitation therapy.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.28 no.2
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• pp.132-143
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• 1992

This paper presents a method in order to calculate the vortex distribution, the streak-line and the time-line around the flat and the cambered otter board in two dimensional flow using the discrete vortex method, and to calculate C sub(L) and C sub(D) of the otter boards varied with the passage of time by the numerical simulation using the Blasu's formula. The results obtained are summarized as follows: 1. Flow pattern around the otter boards calculated by the discrete vortex method was resembled closely that of the visualized photograph. 2. C sub(L) and C sub(D) calculated by the numerical simulation was very similar to the model test. 3. The circulation direction around the otter boards and the action direction of the shearing force can be recognized from the time-line around the otter boards. 4. Flow speed in the back side of the otter boards was faster than that in the front side, and the difference of the flow speed in both side of the cambered otter boards was about 1.3 times greater than that of the flat otter boards. 5. The clockwise vortex was generated in the trailing edge, and the counter-clockwise vortex was generated the leading edge of the otter boards. And they were shown the shape of Karman's vortex varied with the passage of time.

• Journal of the Institute of Convergence Signal Processing
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• v.15 no.4
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• pp.112-118
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• 2014

This paper deals with a color-based tracking of a moving object. Firstly, existing Camshift algorithm is complemented to improve the tracking weakness in the brightness change of an image which occurs in every frame. The complemented Camshift still shows unstable tracking when the objects with same color of the tracking object exist in background. In order to overcome the drawback this paper proposes the Camshift combined with KLT algorithm based on optical flow. The KLT algorithm performing the pixel-based feature tracking can complement the shortcoming of Camshift. Experimental results show that the merged tracking method makes up for the drawback of the Camshit algorithm and also improves tracking performance.

• Nuclear Engineering and Technology
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• v.33 no.6
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• pp.619-625
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• 2001

An axial-flow-induced vibration model was proposed for a rod supported by two translational springs at both ends. For developing the model, a one-mode approximation was made based on the assumption that the first mode was dominant in vibration behavior of the single span rod. The first natural frequency and mode shape functions for the flow-induced vibration, called the FIV model were derived by using Lagrange＇s method. The vibration displacements at reactor conditions were calculated by the proposed model for the spring-supported rod and by the previous model for the simple-supported(55) rod. As a result, the vibration displacement for the spring-supported rod was larger than that of the 55 rod, and the discrepancy between both displacements became much larger as flow velocity increased. The vibration displacement for the spring-supported rod appeared to decrease with the increase of the spring constant. AS flow velocity increased, the increase rate of vibration displacement was calculated to go linearly up, and that of the rod having the short span length was larger than that of the rod having the long span length although the displacement value itself of the long span rod was larger than that of the short one.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.11
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• pp.363-367
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• 1996

In general, the physiological systems have shown nonlinear complex phenomena. This study analyzes nonlinear characteristics of the flow of peripheral blood vessel dynamics in physiological systems using chaos theory. We performed this study by means of several quantity methods and power spectrum. The quantity methods are a phase space reconstruction and a poincare's map. And the power spectrum method is a conventional linear analysis. Experimental data have been acquired from examining 10 diabetic patients, and 10 control subjects in initial stable state. In acquisition experminetal data, we anlysized the differences of nonlinear characteristics between diabetic group and control group. The results of quality analysis methods showed the flow of peripheral blood vessel had the nonlinear and chaotic characteristics, screening a strange attractor on reconstructed phase space. In conclusion, the flow dynamics of peripheral blood vessel had a chaotic behavior of nonlinear dynamic systems, dynamic system, and differences of characteristic of nonlinear dynamic system.