• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.534-541
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• 2010

A high-order accurate Euler flow solver based on a discontinuous Galerkin method has been developed for the numerical simulation of unsteady flows on unstructured meshes. A multi-level solution-adaptive mesh refinement/coarsening technique was adopted to enhance the resolution of numerical solutions efficiently by increasing mesh density in the high-gradient region. An acoustic wave scattering problem was investigated to assess the accuracy of the present discontinuous Galerkin solver, and a supersonic flow in a wind tunnel with a forward facing step was simulated by using the adaptive mesh refinement technique. It was shown that the present discontinuous Galerkin flow solver can capture unsteady flows including the propagation and scattering of the acoustic waves as well as the strong shock waves.

• Korean Journal of Construction Engineering and Management
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• v.5 no.5 s.21
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• pp.101-108
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• 2004

A construction process consists of value adding activities and non-value adding activities, necessary or unnecessary. If construction personnel can eliminate inefficient and/or unnecessary activities within the process, they may have a great opportunity to improve their construction process. The Product Process Analysis (PPA) technique, which was developed in the manufacturing industry, can be applied for identifying wastes in the construction process and ultimately improving the process itself. It provides useful tools, such as a process chart worksheet and flow diagram, for mapping the flow of construction activities with predetermined standardized symbols. These tools make people understand the flow of activities more easily, identify value adding/non-value adding activities within the process, and areas where the process can be improved. The example applications of PPA are demonstrated in the paper through the case studies implemented on the construction process of structural steel. The results of case studies indicate that PPA technique was effective at identifying and removing wastes in the steel construction process. It is also found that PPA technique is more effective for improving highly repetitive construction processes.

• International Journal of Air-Conditioning and Refrigeration
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• v.8 no.2
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• pp.11-22
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• 2000

Holographic interferometric tomography can provide reconstruction of instantaneous three-dimensional gross flow fields. The technique however confronts ill-posed reconstruction problems in practical applications. Experimental data are usually limited in projection and angular scanning when a field is captured instantaneously or under the obstruction of test models and test section enclosures. An algorithm, based on a series expansion method, has been developed to improve the reconstruction under the ill-posed conditions. A three-dimensional natural convection flow around two interacting isothermal cubes is experimentally investigated. The flow can provide a challenging reconstruction problem and lend itself to accurate numerical solution for comparison. The refractive index fields at two horizontal sections of the thermal plume with and without an opaque object are reconstructed at a limited view angle of 80$\circ$. The experimental reconstructions are then compared with those from numerical calculation and thermocouple thermometry. It confirms that the technique is applicable to reconstruction of reasonably complex, three-dimensional flow fields.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.35-38
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• 2002

Variations of temperature and velocity fields in a Hele-Shaw Convection Cell (HSC) were measured using a holographic interferometry and PIV technique with varying Rayleigh number. Experimental results show a steady flow pattern at low Rayleigh numbers and a time-dependent periodic flow at high Rayleigh numbers. Two different measurement methods of holographic interferometry, double-exposure method and real-time method, were employed to measure the temperature field variations of HSC convective flow. In the double-exposure method, unwanted waves can be eliminated and reconstruction images are clear, but transient flow structure cannot be observed clearly. On the other hand, transient flow can be observed and reconstructed well using the real-time method. PIV results show that flow inside the HSC is periodic and the oscillating state is well matched with the temperature field results. The holographic interferometry and PIV techniques employed in this study are useful for analyzing the unsteady convective thermal fluid flows.

• Journal of the Korean Society of Visualization
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• v.19 no.1
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• pp.94-99
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• 2021

In order to increase the efficiency of thermoelectric refrigerators using the Peltier effect, it is necessary to optimize the distribution of the flow of cold air from the fan. In this study, the flow flowing upwards and downwards while changing the area of the flow path was visualized using the PIV technique for the control of cold air in a thermoelectric refrigerator. From these results, the flow rate according to the change in the area of the flow path was confirmed, and design criteria for optimizing the distribution of cold air flowing to the top and bottom of the refrigerator were suggested.

• Korean Journal of Computational Design and Engineering
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• v.1 no.1
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• pp.56-64
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• 1996

A quadrilateral-triangular mixed grid method for the solution of incompressible viscous flow is presented. The solution domain near the body surface is meshed using elliptic grid geneator to acculately simulate the viscous flow. On the other hand, we used unstructured triangular grid system generated by advancing front technique of a simple automatic grid generation algorithm in the rest of the computational domain. The present method thus is capable of not only handling complex geometries but providing accurate solutions near body surface. The numerical technique adopted here is PISO type finite element method which was developed by the present author. Investigations have been made of two-dimensional unsteady flow of Re=550 past a circular cylinder. In the case of use of the unstructured grid only, there exists a considerable amount of difference with the existing results in drag coefficient and vorticity at the cylinder surface; this may be because of the lack of the grid clustering to the surface that is a inevitable requirement to resolve the viscous flow. However, numerical results on the mixed grid show good agreements with the earlier computations and experimental data.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.1
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• pp.118-125
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• 2004

The experimental study on flow and heat transfer characteristics was conducted to investigate and to compare the performance of swirl jet by a twisted tape as a swirl generator with the performance of impinging single circular jet in fully developed flow tube. The effects of jet Reynolds number(Re=8700, 13800, 20000, 26500), dimensionless distance of nozzle-to-plate(H/d=2, 4, 6, 8) and swirl ratio(S=0.11, 0.23, 0.30) of the jet on the local and average Nusselt number have been examined. Measurements of local heat transfer rate and flow patterns on the jet impinging plate were used naphthalene sublimation technique and flow visualization technique respectively. Mean velocity and turbulence intensity of the jet along the centerline were measured. With a twisted tape in the nozzle exit, average Nusselt number at the around area of stagnation point were higher than those without the twisted tape at H/d=2, 4 and with the increase of Reynolds number. With a twisted tape in the nozzle, in the case of H/d=2, Re=26500 and S=0.11, maximum local Nusselt number at the region of y/d=0 and x/d=0.44 was obtained.

• Journal of Sensor Science and Technology
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• v.13 no.2
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• pp.79-84
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• 2004

Asthma is one of the important respiratory diseases requiring home self care usually performed by commercialized peak expiratory flow meter (PEFM). However, this simple device can measure only single parameter, PEF, due to its purely mechanical principle, significantly limiting desease management quality. The present study introduced a new expiratory flow measurement technique by miniatured air expansion chamber easily installed within PEFM. Continuous pressure signal obtained from the chamber demonstrated an accurate quadratic relationship with flow. The volume measurement error was $<{\pm}1%$ well within the American Thoracic Society (ATS) criteria of 3%. Important spirometric parameters of FVC, PEF, and FEF25-75% were all accurately estimated with correlation coefficients > 0.95. The present technique obtains continuous expiratory air flow signal, making possible and convenient to perform spirometric test at home. Electronic interface capability would be also useful for remote asthma management.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.2 s.245
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• pp.110-116
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• 2006

A syringe pump or a device using high electric voltage has been used for controlling flows inside a LOC (lab-on-a-chip). Compared to LOC, however, these microfluidic devices are large and heavy that they are burdensome for a portable ${\mu}-TAS$ (micro total analysis system). In this study, a new flow control technique employing pressure regulators and pressure chambers was developed. This technique utilizes compressed air to control the micro-scale flow inside a LOC, instead of a mechanical actuator or an electric power supply. The pressure regulator controls the output air pressure by adjusting the variable resistor attached. We checked the feasibility of this system by measuring the flow rate inside a capillary tube of $100{\mu}m$ diameter in the Re numbers ranged from 0.5 to 50. In addition, the performance of this flow control system was compared with that of a conventional syringe pump. The developed flow control system was found to show superior performance, compared with the syringe pump. It maintains automatically the: air pressure inside a pressure chamber whether the flow inside the capillary tube is on or off. Since the flow rate is nearly proportional to the resistance, we can control flow in multiple microchannels precisely. However, the syringe pump shows large variation of flow rate when the fluid flow is blocked in the microchannel.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.3
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• pp.933-944
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• 1996

In this paper, two new techniques, the pattern filling and the refined flow field regeneration, based on the finite element method and Eulerian mesh advancement approach have been developed to analyze incompressible viscous flow with free surfaces. The gorerning equation for flow analysis is Navier-Stokes equation including inertia and gravity effects. The penalty and Newton-Raphson methods are used effectively for finite element formulation. The flow front surface and the volume inflow rate are calculated using the pattern filling technique to select an adequate pattern among five filling patterns at each quadrilateral control volume. By the refined flow field regeneration technique, the new flow field which renders better prediction in flow surface shape is generated and the velocity field at the flow front part is calculated more exactly. Using the new thchniques to be developed, the dam-breaking problem has been analyzed to predict flow phenomenon of fluid and the predicted front positions versus time have been compared with the reported experimental result.