• Steel and Composite Structures
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• v.19 no.4
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• pp.939-952
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• 2015

In this paper, brake pad performance of two organic matrix composites namely, Sample 1 (contains no brass filler) and Sample 2 (contains 1.5% brass filler), is studied based on tribological and squeal noise behavior. In the first stage, a pin-on-disc tribometer is used to evaluate the frictional behavior of the two pads. On the following stage, these pads are tested on squeal noise occurrence using a drag-type brake dynamometer. From the two type of tests, the results show that; (i) brass fillers play a dual role; firstly as reinforcing element of the brake pad providing primary contact sites, and secondly as solid lubricant by contributing to the formation of a layer of granular material providing velocity accommodation between the pad and the disc; (ii) brass fillers contribute to friction force stabilization and smooth sliding behavior; (iii) the presence of small weight quantity of brass filler strongly contributes to squeal occurrences; (iv) there is close correlation between pin-on-disc tribometer and brake dynamometer tests in terms of tribological aspect.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.652-655
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• 2008

Despite of the laminar-turbulent transition region co-exist with fully turbulence region around the leading edge of an airfoil, still lots of researchers apply to fully turbulence models to predict aerodynamic characteristics. It is well known that fully turbulent model such as standard k-${\varepsilon}$ model couldn't predict the complex stall and the separation behavior on an airfoil accurately, it usually leads to over prediction of the aerodynamic characteristics such as lift and drag forces. So, we apply correlation based transition model to predict aerodynamic performance of the NREL (National Renewable Energy Laboratory) Phase IV wind turbine. And also, compare the computed results from transition model with experimental measurement and fully turbulence results. Results are presented for a range of wind speed, for a NREL Phase IV wind turbine rotor. Low speed shaft torque, power, root bending moment, aerodynamic coefficients of 2D airfoil and several flow field figures results included in this study. As a result, the low speed shaft torque predicted by transitional turbulence model is very good agree with the experimental measurement in whole operating conditions but fully turbulent model(k-${\varepsilon}$) over predict the shaft torque after 7m/s. Root bending moment is also good agreement between the prediction and experiments for most of the operating conditions, especially with the transition model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2706-2711
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• 1994

In this work, an experimental type of torque converter has been constructed and its characteristics have been evaluated by adapting an electrorheological fluid(ERF) as an operating medium. The device was designed by using the equations which were proposed by Carlson et al. The correlation between the rheological behaviour of an ERF and mechanical parameters of the clutch has been investigated. The torque generated by an ERF in this device is sum of one due to the yield strength by polarizing dispersed particles in dielectric oil and one due to the viscous drag. The experimental results are presented in terms of torque and current density as a function of rotational speed at various electric field strength applied. Experimental results showed that the measured torque was rapidly increased with the increase of the electric field, generally being proportional to the rotational speed of the motor. The measured current was shown to be increased with the increased electric field. Also, the current was decreased with the increase of increased with the increased electric field. Also, the current was decreased with the increase of the rotational speed of the motor and reached plateau region after f = 5 Hz.

• Atmosphere
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• v.25 no.4
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• pp.591-600
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• 2015

We have analyzed wind and eddy covariance data collected within roughness sublayer over sloping terrain. The study site is located on non-flat terrain with slopes in both south-north and east-west directions. The surface elevation change is smaller than the height of roughness element such as building and tree. This study examines the directional wind shear for data collected at three levels in the lowest 10 m in the roughness sublayer. The wind direction shear is caused by drag of roughness element and terrain-induced motions at this site. Small directional shear occurs when wind speed at 10 m is strong and wind direction at 10 m is southerly which is the same direction as upslope flow near surface at this site during daytime. Correlation between vertical shear of lateral momentum and lateral momentum flux is smaller over steeply sloped surface compared to mildly sloped surface and lateral momentum flux is not down-gradient over steeply sloped surface. Quadrant analysis shows that the relative contribution of four quadrants to momentum flux depends on both surface slope and wind direction shear.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.1
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• pp.120-139
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• 1996

Experiment was performed to study the heat transfer characteristics in 27 kinds of 15 : 1 scale models of multi-louverred fin heat exchangers with a wide range of variables(R $e_{Lp}$ =100~1, 800, $L_p$/F$p$=0.3~0.9, $\theta$=20$^{\circ}$~40$^{\circ}$). Thermofoil heaters were used to heat the louver fins and the local average Nusselt number for each louver in the louver array was obtained at constant wall temperature conditions. Correlations are developed to predict the heat transfer characteristics and drag coefficients. Generally, the heat transfer characteristics in the multi-louvered fins is shown to be similar to those of the laminar heat transfer on a flat plate. As the Reynolds number, the louver pitch to fin pitch ratio$L_p$/F$p$and the louver angle($\theta$) increase respectively, the average Nusselt number increases, but the variation of average Nusselt number as a function of the louver angle is smaller than that as a function of the louver pitch to fin pitch ratio. In case of$L_p$/F$p$ <0.5, the average Nusselt number of the 3rd louver is especially lower than the others, it is expected that it is due to the flow structure such as a recirculation flow and a flow separation.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.1105-1117
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• 2023

In this study, the pressure drop behavior of single- and two-phase flows of air and water through the porous beds filled with uniform and non-uniform sized spherical particles was examined. The pressure drop data in the single-phase flow experiments for the uniform particle beds agreed well with the original Ergun correlation. The results from the two-phase flow experiments were analyzed using numerical results based on three types of previous models. In the experiments for the uniform particle beds, the data on the two-phase pressure drop clearly showed the effect of the flow regime transition with a variation in the gas flow rate under stagnant liquid condition. The numerical analyses indicated that the predictability of the previous models for the experimental data relied mainly on the sub-models of the flow regime transitions and interfacial drag. In the experiments for the non-uniform particle beds, the two-phase pressure loss could be predicted well with numerical calculations based on the effective particle diameter. However, the previous models failed to accurately predict the counter-current flooding limit observed in the experiments. Finally, we propose a relation of falling liquid velocity into the particle bed by gravity to appropriately simulate the CCFL phenomenon.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.7
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• pp.945-952
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• 2018

Recently, bass fishing has become a marine leisure sport in Korea. There are 4 major fishing associations in Korea, and each association holds 10-15 tournaments each year. However, supply of 17 ft bass boats, which are preferred in leagues, depends 100 % on imports. In this study, we have derived the main specifications to develop the initial hull forms of a 18.5ft bass boat through statistical analysis based on mothership data. In addition, CFD numerical analysis was carried out according to deadrise angle and longitudinal center of gravity, which strongly influenced the resistance and planing performance. For numerical analysis, design speed was set to $Fn=3.284 (Re=9.858{\times}10^7)$, the deadrise angle was set from 12 to $20^{\circ}$, and the longitudinal center of gravity was set in the range of 0 to $8%L_{wL}$ from the center of buoyancy to the stern. Based on the numerical results, we first set the range of these factors by resistance performance and immersion keel length. Furthermore, using a correlation graph of Savitsky's Drag-Lift ratio, we derived the deadrise angle ($14-16^{\circ}$) and longitudinal center of gravity ($4-6%L_{wL}$).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.7
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• pp.549-557
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• 2008

Despite of the laminar-turbulent transition region co-exist with fully turbulence region around the leading edge of an airfoil, still lots of researchers apply to fully turbulence models to predict aerodynamic characteristics. It is well known that fully turbulent model such as standard k-model couldn't predict the complex stall and the separation behavior on an airfoil accurately, it usually leads to over prediction of the aerodynamic characteristics such as lift and drag forces. So, we apply correlation based transition model to predict aerodynamic performance of the NREL (National Renewable Energy Laboratory) Phase IV wind turbine. And also, compare the computed results from transition model with experimental measurement and fully turbulence results. Results are presented for a range of wind speed, for a NREL Phase IV wind turbine rotor. Low speed shaft torque, power, root bending moment, aerodynamic coefficients of 2D airfoil and several flow field figures results included in this study. As a result, the low speed shaft torque predicted by transitional turbulence model is very good agree with the experimental measurement in whole operating conditions but fully turbulent model(${\kappa}-\;{\varepsilon}$) over predict the shaft torque after 7m/s. Root bending moment is also good agreement between the prediction and experiments for most of the operating conditions, especially with the transition model.

• Wind and Structures
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• v.30 no.2
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• pp.181-198
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• 2020

In the traditional buffeting response analysis method, the spanwise incomplete correlation of buffeting forces is always assumed to be same as that of the incident wind turbulence and the action of the signature turbulence is ignored. In this paper, three typical bridge decks usually adopted in the real bridge engineering, a single flat box deck, a central slotted box deck and a two-separated paralleled box deck, were employed as the investigated objects. The wind induced pressure on these bridge decks were measured via a series of wind tunnel pressure tests of the sectional models. The influences of the wind speed in the tests, the angle of attack, the turbulence intensity and the characteristic distance were taken into account and discussed. The spanwise root coherence of buffeting forces was also compared with that of the incidence turbulence. The signature turbulence effect on the spanwise root coherence function was decomposed and explained by a new empirical method with a double-variable model. Finally, the formula of a sum of rational fractions that accounted for the signature turbulence effect was proposed in order to fit the results of the spanwise root coherence function. The results show that, the spanwise root coherence of the drag force agrees with that of incidence turbulence in some range of the reduced frequency but disagree in the mostly reduced frequency. The spanwise root coherence of the lift force and the torsional moment is much larger than that of the incidence turbulence. The influences of the wind speed and the angle of attack are slight, and they can be ignored in the wind tunnel test. The spanwise coherence function often involves several narrow peaks due to the signature turbulence effect in the high reduced frequency zone. The spanwise coherence function is related to the spanwise separation distance and the spanwise integral length scales, and the signature turbulence effect is related to the deck-width-related reduced frequency.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.12
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• pp.1681-1691
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• 2002

The heat transfer and pressure drop characteristics of heat exchangers with louver fins were experimentally investigated. The samples had small fin pitches (1.0 mm to 1.4 mm), and experiments were conducted up to a very low frontal air velocity (as low as 0.3 m/s). At a certain Reynolds number (critical Reynolds number), the flattening of the heat transfer coefficient curve was observed. The critical Reynolds number was insensitive to the louver angle, and decreased as the louver pitch to fin pitch ratio (L$_{p}$F$_{p}$) decreased. Existing correlations on the critical Reynolds number did not adequately predict the data. It is suggested that, for proper assessment of the heat transfer behavior, the louver pattern in addition to the flow characterization need to be considered. The heat transfer coefficient increased as the fin pitch decreased. At low Reynolds numbers, however, the trend was reversed. Possible explanation is provided considering the louver pattern between neighboring fins. Different from the heat transfer coefficient, the friction factor did not show the flattening characteristic. The reason may be attributed to the form drag by louvers, which offsets the decreased skin friction at a low Reynolds number. The friction factor increased as the fin pitch decreased and the louver angle increased. A new correlation predicted 92% of the heat transfer coefficient and 90% of the friction factor within $\pm$10%.10%.