Deog Hee Doh

Unsteady MHD non-Darcian flow over a vertical stretching plate embedded in a porous medium with non-uniform heat generation

Abstract A numerical model is developed to study hydromagnetic unsteady laminar boundary layer flow of viscous, incompressible fluid over a vertical stretching plate embedded in a sparsely packed porous medium in the presence of non-uniform heat generation/absorption. The flow in the porous medium is governed by Brinkman–Forchheimer extended Darcy model. The variation of porosity and permeability is assumed. By applying similarity analysis, the governing partial differential equations are transformed into a set of time dependent non-linear coupled ordinary differential equations and they are solved numerically by Runge–Kutta Fehlberg method along with shooting technique. The effects of governing parameters on the dimensionless velocity and temperature distributions are studied in detail by considering uniform permeability (UP) and variable permeability (VP) of the porous medium and the results are discussed graphically. Besides, skin friction coefficient and the rate of heat transfer are also computed for various pertinent parameters governing the problem. Further, the numerical results obtained in this study is compared with the existing literature and found that they are in good agreement.

4D-PTV: Measurements of an Impinged Jet with a Dynamic 3D-PTV

Abstract4D-PTV system was constructed. The measurement system consists of three high-speed high-definition cameras (1k × 1k, 2000 fps), Nd-Yag laser (2000 Hz) and a host computer. The GA-3D-PTV algorithm was used for completing the measurement system. The 4D-PTV is capable of probing the spatial distribution of velocity vectors of the flow field overcoming the temporal resolution of the characteristic turbulence length scales of the measured flow fields. A horizontal impinged jet flow (H/D = 7) was measured. The Reynolds number is about 33,000. Spatial temporal evolution of the jet flow was examined and physical properties such as spatial distributions of vorticity and turbulent kinetic energy were obtained with the constructed system.

Measurements of Remote Micro Displacements of the Piping System and a Real Time Diagnosis on Their Working States Using a PIV and a Neural Network

Abstract >> Piping systems play an important role in gas and oil transferring system. In the piping system, thereare many elements, such as valves and flow meters. In order to check their normal operating conditions, eachsignal from each element is displayed on the monitor in the pipe control room. By the way, there are severalaccidental cases in the piping system even if all signals from the local elements are judged to be normal on themonitor in the control room. Further, opposite cases often happen even the monitor shows abnormal while the local elements work normal. To overcome this abnormal functions, it is not so easy to construct the environmentin which sensors detecting the working states of all elements installed in the piping system. In this paper, a newnon-contact measurement technique which can calculate the elements delicate displacements by using a PIV(particleimage velocimetry) and diagnose their working states by using a neural network is proposed. The measurementsystem consists of a host computer, a micro system, a telescope and a high-resolution camera. As a preliminarytest, the constructed measurement system was applied to measure delicate vibrations of mobile phones. For practical application, a pneumatic system was measured by the constructed system.

Visualizations of fluid flows in the TIG welding region for different shapes of the shield gas nozzle

The tungsten inert gas (TIG) welding enables to produce high welding qualities. However, it has some problems such as a large distortion and a shallow penetration into the welding parts. To overcome those problems, there have been many studies on A-TIG welding in which active flux and a shield gas are used. The shield gas pressure, velocity, and distribution area are dominant factors in producing better welding condition which can be evaluated by the gas penetration, the gap between the nozzle tip and welding plate and the nozzle shape of the shield gas. In this study, the influences of the shield gas distribution onto the melting efficiency and penetration shape in TIG welding were investigated using a numerical simulation. The gap distances between the nozzle tip and the welding plate were changed 3, 4, 5xa0mm and two nozzle shapes, convergent parallel (CP) and CDP, were tested. 100% Ar gas was used as the shield gas. CDP type nozzle showed deeper penetrations and higher melting efficiency compared to those of CD type and CP type nozzles.Graphical Abstract

Power generation characteristics of a novel horizontal tidal current power generation system installed in the Akashi Strait of Japan

Power generation characteristics of a horizontal tidal current power generation system have been investigated. At first, a model test had been carried out at laboratory level for finding more optimal shapes of the turbine of the generation system. Secondly, two tests had been carried out for two model sizes (medium size: 1.2m × 0.65m, large size: 6.0m × 3.0m). In the laboratory test, the constructed systems have been tested under three different current speeds, 1.35knot, 1.5knot and 2knot. Five different model shapes (A50, SE50, S50, S55, S65) have been tested. The width of the blade installed around the body is 50mm. To investigate the flow characteristics around the turbine blades, a PIV test had been carried out under electric load conditions. The power generation performances had been obtained from this model test. Among the models it had been verified that the S65 has the highest efficiency of power generation. The power generation characteristics of two model sizes that have the optimal shape had been investigated. The medium one had been tested under 1.5knot, 2.0knot, 2.5knot and 3.0knot. The large one was done under 4.28knot.

Velocity profiles with swirling flow in a vertical circular tube

Experiments are performed on swirling water flow in a vertical circular tube. This kind of flow is used in heat exchangers, combustion chambers, thermal power plants, and other mechanical equipment to move slurries or to convey materials. However, limited information on swirling flow in vertical circular tubes is available. In this paper, three-dimensional particle image velocimetry technique has been employed to measure velocities profiles in water along the vertical circular tube and then compared those of without swirl.Graphical Abstract

Measurements of 3D Model Shapes for Reverse Designs

Abstract. Reverse Design(RD) plays an important role in simulation engineering, such as CFD (Com-putational Fluid Dynamics) and Virtual Engineering and Design. RD becomes much more valuable whenthere is no shape data of the practical models for CFD grid generations. In this study, two-camera basedrapid prototyping(RP) system is proposed. 3D-PTV based measurement algorithm was adopted. Thedeveloped system was applied to reconstruct three-dimensional data of a human face, a motorcycle model,a cylindrical body and a triangular pyramid.Key Words:Reverse Designs(역설계), 3D-Shape Measurement(3차원 형상측정), CFD(전산유체역학 ),Rapid Prototyping(쾌속조형기술) 1. 서론 전산유체역학(CFD)의 급속한 발전에 따라 유체기기 등에 대한 성능평가 및 개발기술이 빠른 속도로 발전되고 있다. 전산유체역학(CFD)에 의한 산업분야에의 응용이 증가할수록 적용되는 대상의 (2)형상데이터의확보는 수치모사에 있어서 필수요인으로 대두될 것으로 예상되고 있다. 산업기기들의 형상데이터는 업체의기밀사항으로 간주되는 바 이들 데이터 확보는 용이하지 않다. 이는 수치모사분야에 종사하는 연구자들에게는 모델데이터의 확보 어려움으로 인한 연구개발의 의욕 혹은 동기부여의 결여로 이어질 수 있다.본 연구는 산업의 다양한 분야에 적용되고 있는 열유체기기들의 복잡한 형상을 용이하게 확보할 수 있는3차원 형상측정시스템의 구현함으로써 CFD분야의 발전에 기여하고자 함에 있다. 한편, 산업분야에 적용되고 있는 열유체기기들의 모델에 대한 형상측정은 1대카메라와 1대 레이저스캐너(laser scanner)에 의한 것

Hybrid Particle Image Velocimetry Based on Affine Transformation

Key Words: PIV(입자영상유속계), PTV(입자추적유속계), Virtual Image(가상영상), Cross-Correlation PIV(상호상관PIV), 2F-Match Probability Method(2프레임확률일치법), Affine Transformation(어파인변환)초록:입자추적유속계(PTV)는나노및바이오분야의유체유동장에서는각입자들을추적하여속도측정을하는관계로많은강점이있다. 그러나측정원리상보간에의한속도장측정오차를피할수없는관계로PTV기술을사용함에있어서제한적이었다. 본연구에서는어파인변환알고리듬을PIV 및PTV측정에도입함으로써보간에의한오차를줄일수있는어파인변환기반하이브리드PIV알고리듬을구축하였다. 구축된알고리듬에대한성능평가를위하여Green-Taylor와유동의수치적데이터를이용한가상영상에대한시험을실시하였으며,이로부터입자수가2000개이상일때최적의측정성능임을확인하였으며상호상관PIV법및확률일치PTV법보다우수한측정성능임을확인하였다. 나아가길이비2:1(6cm x 3cm)인장방형물체후류(Re=5,300)에대한실험영상에대한실제계산을통하여구축된알고리듬에대한측정성능의우수성을확인하였다.Abstract: Since PTV (particle tracking velocimetry) provides velocity vectors by tracking each particle in afluid flow, it has significant benefits when used for nano- and bio-fluid flows. However, PTV has only beenused for limited flow fields because interpolation data loss is inevitable in PTV in principle. In this paper, ahybrid particle image velocimetry (PIV) algorithm that eliminates interpolation data loss was constructed byusing an affine transformation. For the evaluation of the performance of the constructed hybrid PIV algorithm,an artificial image test was performed using Green–Taylor vortex data. The constructed algorithm was testedon experimental images of the wake flow (Re = 5,300) of a rectangular body (6 cm × 3 cm), and wasdemonstrated to provide excellent results.

Visualizations of the Transitional Flow Patterns at the Mid-Span between Shrouded Co-Rotating Disks

Transitional air flow patterns at the mid-plane of gap between co-rotating disks in a stationary cylindrical enclosure are visualized under the acceleration condition of disks. The flow visualization is performed using olive oil particles with a laser sheet and CCD camera. On disk spinning-up, the transition flow patterns are clearly observed. The affect of magnitude of acceleration on the onset of transition and the relations of the number of vortex cells in fully turbulent regime of the flow in an outer region of the flow field to the rotating speed are also investigated. The centrifugal effect of particle is evaluated from the comparison with visualization results using hollow glass spheres.

Non-Contact 3D Flow-Structure Interaction Measurement (FSIM) System for Motion and Flow Fields: Interactions of a Vertical Cylinder Motion

A simultaneous measurement system that can analyze the flow-structure interactions has been developed. This system consists of four CCD cameras, two for capturing instantaneous flow fields and two for tracking a solid body. The three-dimensional vector fields around a cylinder are measured while the motion of the cylinder forced by the flow field is measured simultaneously with the constructed system. The cylinder is suspended in the circulating water channel and the surface of the working fluid is forced sinusoidal to make the cylinder bounced. Reynolds number for the mean main stream is about 3500. The interaction between the flow fields and the cylinder motion is examined quantitatively.