• Progress in Superconductivity and Cryogenics
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• v.20 no.2
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• pp.6-10
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• 2018

Removal of iron oxide scale from feed-water in thermal power plant can improve power generation efficiency. We have proposed a novel scale removal system utilizing High Gradient Magnetic Separation (HGMS). This system can be applied to high temperature and pressure area. We have conducted the lab-scale model experiments using ${\varphi}50mm$ filters and it demonstrated high removal efficiency in HGMS, but scale-up of the system is required toward practical use. In this study, we conducted a large scale mock-up HGMS experiment. We used the superconducting solenoidal magnet with ${\varphi}400mm$ bore and demonstrated that our HGMS system can achieve sufficient scale removal capacity that is required to introduce into both off-line and on-line system.

• Structural Engineering and Mechanics
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• v.77 no.3
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• pp.305-314
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• 2021

In order to reduce enormous cost of real-scale underwater explosion experiments on ships, the mechanical response of the ships have been analyzed by combining scaled-down experiments and Hopkinson's scaling law. However, the Hopkinson's scaling law is applicable only if all variables vary in an identical ratio; for example, thickness of ship, size of explosive, and distance between the explosive and the ship should vary with same ratio. Unfortunately, it is infeasible to meet such uniform scaling requirement because of environmental conditions and limitations in manufacturing scaled model systems. For the facile application of the scaling analysis, we propose a generalized scaling law that is applicable for non-uniform scaling cases in which different parts of the experiments are scaled in different ratios compared to the real-scale experiments. In order to establish such a generalized scaling law, we conducted a parametric study based on numerical simulations, and validated it with experiments and simulations. This study confirms that the initial peak value of response variables in a real-scale experiment can be predicted even when we perform a scaled experiment composed of different scaling ratios for each experimental variable.

• Wind and Structures
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• v.31 no.4
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• pp.287-298
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• 2020

This paper presents an experimental investigation on the surface pressures on the CAARC standard tall building model concerning the effects of freestream turbulence. Two groups of incidence turbulence are generated in the wind tunnel experiment. The first group has an approximately constant turbulence intensity of 10.3% but different turbulence integral scale varying from 0.141 m to 0.599 m or from 0.93 to 5.88 in terms of scale ratio (turbulence integral scale to building dimension). The second group presents similar turbulence integral scale but different turbulence intensity ranging from 7.2% to 13.5%. The experimental results show that the mean pressure coefficients on about half of the axial length of the side faces near the leading edge slightly decrease as the turbulence integral scale ratio that is larger than 4.25 increases, but respond markedly to the changes in turbulence intensity. The root-mean-square (RMS) and peak pressure coefficients depend on both turbulence integral scale and intensity. The RMS pressure coefficients increase with turbulence integral scale and intensity. As the turbulence integral scale increases from 0.141 m to 0.599 m, the mean peak pressure coefficient increases by 7%, 20% and 32% at most on the windward, side faces and leeward of the building model, respectively. As the turbulence intensity increases from 7.2% to 13.5%, the mean value of peak pressure coefficient increases by 47%, 69% and 23% at most on windward, side faces and leeward, respectively. The values of cross-correlations of fluctuating pressures increase as the turbulence integral scale increases, but decrease as turbulence intensity increases in most cases.

• Journal of the Korean Society of Hazard Mitigation
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• v.5 no.1 s.16
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• pp.63-68
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• 2005

LSIV (Large Scale Image Velocimetry), a technique of image analysis on velocity measurement, was applied to a hydraulic model experiment of river confluence. The surface velocities measured by using LSIV showed similar results with the mean velocities by using a traditional velocimeter, While a general velocimeter can measure only local point velocity, LSIV can measure whole velocity field with one shot. When it is applied to river confluence or around a bridge pier where local flow is dominant, LSIV may be a powerful tool to measure velocity field.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.303-314
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• 2009

The present paper shows the results of numerical and experimental modal analyses of Francis runners, which were executed in air and in still water. In its first part this paper is focused on the numerical prediction of the model parameters by means of FEM and the validation of the FEM method. Influences of different geometries on modal parameters and frequency reduction ratio (FRR), which is the ratio of the natural frequencies in water and the corresponding natural frequencies in air, are investigated for two different runners, one prototype and one model runner. The results of the analyses indicate very good agreement between experiment and simulation. Particularly the frequency reduction ratios derived from simulation are found to agree very well with the values derived from experiment. In order to identify sensitivity of the structural properties several parameters such as material properties, different model scale and different hub geometries are numerically investigated. In its second part, a harmonic response analysis is shown for a Francis runner by applying the time dependent pressure distribution resulting from an unsteady CFD simulation to the mechanical structure. Thus, the data gained by modern CFD simulation are being fully utilized for the structural design based on life time analysis. With this new approach a more precise prediction of turbine loading and its effect on turbine life cycle is possible allowing better turbine designs to be developed.

• Journal of the korean Society of Automotive Engineers
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• v.12 no.3
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• pp.53-62
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• 1990

A wind tunnel experiment for the flow around a 1/5 scale passenger vehicle model has been carried out. A 5-hole Pitot tube is used for measuring velocity distributions around the model and a scanivalve with 48 ports is used for measuring surface pressure distribution at various Reynolds numbers. In order to observe the flow on the surface and in the wake region, a flow visualization experiment has been performed using wool tuft with and without paper cones. In addition, a 2-dimensional viscous calculation considering only the mid-plane section of the model has been performed. A complex wake structure in the immediate rear of the model has been confirmed. The distributions of the surface pressure coefficient are not sensitively dependent on the Reynolds Number. In the first half of the model, they do not seem to vary form section to section. However, in the second half, they do vary from section to section, especially at the bottom surface, which indicates that the cross flow vortex is more affected by the bottom surface than the top surface. The qualitative agreement of the measured and calculated velocity field also explains the usefulness of the 2-dimensional calculation in the limited sense.

• International Journal of Railway
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• v.3 no.2
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• pp.60-67
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• 2010

This paper deals with an experimental study on the wheel flange climbing of railway vehicles, which is a major factor leading to derailment. An experiment is carried out on a 1/5-scale model wheelset of a truck used on a standard-gauge track, which is placed on a roller rig. The lateral external force acting on the wheelset is ramped up until derailment occurs under the condition of a fixed attack angle and wheel-load unbalance ratio. Three parameters, the height of wheel lift, the lateral force, and the wheel load acting on the outer rail, are measured until derailment occurs. From these measurements, it is possible to observe the behavior of the wheelset and to elucidate how the attack angle, the wheel-load unbalance ratio and the lateral external force affect flange-climb derailment. Then, a numerical simulation is carried out using an analytical model based on a single wheelset. As a result, the flange-climb behavior observed in the experiment can be explained theoretically on the bases of the analytical results, although further improvement of the model is desired.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.5 no.3
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• pp.186-194
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• 2000

In this study, the oceanic responses to given atmospheric boundary conditions are investigated using a mesoscale ocean circulation model. The numerical experiments are divided into two parts: One is, so called, spin-up experiment and the other is reproduction experiment. The spin-up experiment simulates climatic state of ocean by integrating the ocean model with upper boundary conditions of the monthly mean atmospheric climate data. In the reproduction experiment, for the reproduction of major oceanic changes around Korean Peninsula during the period of 1980-1998 (19 years), the model has been integrated under the boundary condition of the 19year monthly mean atmosphere data. The spined-up state of ocean generated from the spin-up experiment is assigned to the initial boundary condition of the reproduction experiment. In the spin-up experiment, the model properly simulates the major features of circulation structure around Korean Peninsula; such as separation of East Korean Warm Current (EKWC), formation of the polar front, cold water band associated with the small scale eddies in the East Sea, the formation of front along west coast, and the seasonal variation of circulation pattern caused by changing upwind current in the West Sea. In the reproduction experiment, the model has shown the interannual sea surface temperature variations and a warming trend of about 0.5$^{\circ}$C during the period around Korean Peninsula, as in the case of the observation. Therefore, it is concluded that the model is capable of simulating not only the mean states but also the variabilities of ocean under the given atmosphere boundary conditions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.2030-2038
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• 1995

In this study, three turbulent flame propagation models are compared using experimentally measured data of a 4 valves/cylinder spark-ignition engine. First two conventional models are B.K model and GESIM combustion model. The burning rates calculated from the two models are compared with the burning rates calculated from measured pressure data using the one-zone heat release analysis. GESIM combustion model predicts burning rates closer to the data acquired from the experiment in wide operating ranges than B-K model does. The third model is refined based on GESIM combustion model by including the effect of flame stretch, turbulent length scale band pass filter and a variable that considers flame size and the area of flame contacting the cylinder wall surface. The refined combustion model predicts burning rates closer to experimental results than GESIM combustion model does. Also, the refined combustion model predicts flame radius close to the experimental result measured by using optical fiber technique.

• Journal of Environmental Impact Assessment
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• v.10 no.2
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• pp.123-133
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• 2001

Gaussian dispersion model is the most widely used tool for the ground level air pollution simulation. Though in spite of the convenience there are important problems on the Pasquill- Gifford' stability classification scheme which was used to define the turbulent state of the atmosphere or to describe the dispersion capabilities of the atmosphere which was each covers a broad range of stability conditions, and that they were very site specific, and the vertical dispersion calculation formula on the case of the unstable atmospheric condition. This paper was carried out to revise the Gaussian dispension model for the purposed of increase the modeling performance and propose the revised model, which was composed of the turbulent characteristics in the unstable atmospheric conditions. The proposed models in this study were composed of the profile method, Monin-Obukhove length, the probability density function model and the lateral dispersion function which was composed of the turbulent parameters, $u_*$(friction velocity), $w_*$(convective velocity scale), $T_L$(lagrangian time scale) for the model specific. There were very good performance results compare with the tracer experiment result on the case of the short distance (<1415m) from the source, but increase the simulation error(%) to stand off the source in the all models. In conclusion, the revised Gaussian dispersion model using the turbulent characteristics may be a good contribution for the development of the air pollution simulation model.