• Journal of Advanced Marine Engineering and Technology
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• v.25 no.6
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• pp.1291-1297
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• 2001

The commercial viability of heat exchanger is mainly dependent on their long-term fouling characteristics because the feeling increases the pressure loss and degrades the thermal performance of a heat exchanger An experimental study was performed to investigate the characteristics of fluid flow in a fluidized bed heat exchanger with circulating various solid particles. The present work showed that the drag force coefficients of particles in the internal flow were higher than in the external flow, in addition, they were lower with the shapes of particles being closer to the spherical geometries.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.4
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• pp.315-323
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• 2002

The commercial viability of heat exchanger is mainly dependent on their long-term fouling characteristics because the fouling increases the pressure loss and degrades the thermal performance of a heat exchanger. An experimental study was performed to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with circulating various solid particles. The present work showed that the drag force coefficients of particles in the internal flow were higher than those in the external flow, in addition, the solid particle periodically hitting the tube wall broke the thermal boundary layer, and increased the rate of heat transfer. Particularly when the flow velocity was low, the effect was more pronounced.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.705-710
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• 2001

The commercial viability of heat exchanger is mainly dependent on their long-term fouling characteristics because the fouling increases the pressure loss and degrades the thermal performance of a heat exchanger. An experimental study was performed to investigate the characteristics of fluid flow in a fluidized bed heat exchanger with circulating various solid particles. The present work showed that the drag force coefficients of particles in the internal flow were higher than in the external flow, in addition, they were lower with the shapes of particles being closer to the spherical geometries.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.16 no.2
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• pp.61-67
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• 1980

Previously, we had experimented on the model of stow net under the various combination including water velocity, spherical floats and elevating floats with the shearing hoods instead of the upper beam, however we couldn't concern with their characteristics. Spherical floats maintain their buoyancy at the same level when the speed increases, only the drag increases and effects some reduction in the fishing height. To eliminate this shortcoming, floats have to some hydrodynamic lifting force which increases with increasing speed. Phillips float with a dish-shaped metal plate welded on at the lower part and synthetic upthrusting float were used for the experiment to compare with their characteristics. Six kinds of model shearing hood depend on the angle of attack were used to test the characteristic of the shearing hood. According to their results, when the angle of attack is 30\ulcorner, the lift and drag coefficient reveal 1. 36, 0.84 respectively. And also experimented on the 5X8cm shearing hood to investigate the suitability for the model stow net.

• Journal of ILASS-Korea
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• v.7 no.2
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• pp.22-30
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• 2002

A number of droplet breakup models have been developed to predict the diesel spray. The capabilities of droplet deformation and breakup models such as TAB, ETAB, DDB and APTAB models are evaluated in modeling the non-evaporating diesel sprays injected into atmosphere. New methods are also suggested that take into account the non- spherical shape of droplets and the reduced drag force by the presence of neighbouring droplets. The KIVA calculations with standard ETAB, DDB, and APTAB models predict well the spray tip penetrations of the experiment, but overestimate the Sauter mean Diameter(SMD) of droplets. The calculation with non spherical droplets injected from the nozzle shows very similar results to the calculation with spherical droplets. The drag coefficient which is linearly increased with the time after start of injection during the breakup time gives the smaller SMD that agrees well with the experimental result.

• Ecology and Resilient Infrastructure
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• v.10 no.3
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• pp.51-63
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• 2023

Riverine tree management is crucial in realizing a balance between flood control and ecological preservation, which requires an accurate assessment of the impact of trees on river water elevations. In this study, eight different formulas for evaluating vegetation roughness considering the drag force acting on trees, were reviewed, and the characteristics and applicability of these methods were evaluated from a practical engineering perspective. The study compared the characteristics of vegetation roughness measurement methods for calculated roughness coefficients at different water depths and analyzed factors such as effects of tree canopy width, tree density and diameter, and tree stiffness coefficient, and water level estimation results. A comparison of roughness coefficients at the same water depths revealed that the Kouwen and Fathi-Moghadam formulas and the Fischenich formula yield excessive drag coefficients compared to other formulas. Factors such as channel geometry, tree diameter, and tree density showed varying trends depending on the formula but did not exhibit excessive outliers. Formulas considering the tree stiffness coefficient, such as the Freeman et al.'s formula and the Whittaker et al.'s formula, showed significant variations in drag coefficients depending on the stiffness coefficient. When applied to small- and medium-sized virtual rivers in South Korea using the drag coefficient results from the eight formulas, the results indicated a maximum increase in water level of approximately 0.2 to 0.4 meters. Based on this review, it was concluded that the Baptist et al., Huthoff et al., Cheng, Luhar, and Nepf's formulas, which exhibit similar characteristics and low input data uncertainties, are suitable for practical engineering applications.

• Wind and Structures
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• v.38 no.5
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• pp.367-379
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• 2024

Compared with traditional transmission towers, T-shaped angle towers have long cross-arms and are specially used for ultrahigh-voltage direct-current (UHVDC) transmission. Nevertheless, the wind loads of T-shaped towers have not received much attention in previous studies. Consequently, a series of wind tunnel tests on the T-shaped towers featuring cross-arms of varying lengths were conducted using the high-frequency force balance (HFFB) technique. The test results reveal that the T-shaped tower's drag coefficients nearly remain constant at different testing velocities, demonstrating that Reynolds number effects are negligible in the test range of 1.26 × 10⁴-2.30 × 10⁴. The maximum values of the longitudinal base shear and torsion of the T-shaped tower are reached at 15° and 25° of wind incidence, respectively. In the yaw angle, the crosswind coefficients of the tower body are quite small, whereas those of the cross-arms are significant, and as a result, the assumption in some load codes (such as ASCE 74-2020, IEC 60826-2017 and EN 50341-1:2012) that the resultant force direction is the same as the wind direction may be inappropriate for the cross-arm situation. The fitting formulas for the wind load-distribution factors of the tower body and cross-arms are developed, respectively, which would greatly facilitate the determination of the wind loads on T-shaped angle towers.

• Wind and Structures
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• v.25 no.5
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• pp.475-492
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• 2017

Inclined and yawed circular cylinder is an essential element in the widespread range of structures. As one of the applications, cables on bridges were reported to have the possibility of suffering a kind of large amplitude vibration called dry galloping. In order to have a detailed understanding of the aerodynamics related to dry galloping, this study carried out a set of wind tunnel tests for the inclined and yawed circular cylinders. The aerodynamic coefficients of circular cylinders with three surface configurations, including smooth, dimpled pattern and helical fillet are tested using the force balance under a wide range of inclination and yaw angles in the wind tunnel. The Reynolds number ranges from $2{\times}10^5$ to $7{\times}10^5$ during the test. The influence of turbulence intensity on the drag and lift coefficients is corrected. The effects of inclination angle yaw angle and surface configurations on the aerodynamic coefficients are discussed. Adopting the existed the quasi-steady model, the nondimensional aerodynamic damping parameters for the cylinders with three kinds of surface configurations are evaluated. It is found that surface with helical fillet or dimpled pattern have the potential to suppress the dry galloping, while the latter one is more effective.

• Journal of Advanced Research in Ocean Engineering
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• v.3 no.2
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• pp.59-65
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• 2017

When an anchor is dropped into the sea, there exists a danger of collision on the pipeline and subsea cables in the seabed. This collision could cause huge environmental disasters and serious economic losses. In order to secure the safety of subsea structures such as pipelines and subsea cables from the external impact, it is necessary to estimate the exact external force through the anchor's terminal velocity on the water. FLUENT, a computational fluid dynamic program, was used to acquire the terminal velocity and drag coefficient computation. A half-symmetry condition was used in order to reduce the computational time and a moving deforming mesh technique also adapted to present hydrostatic pressure. The results were examined with the equation based on Newton's Second Law to check the error rate. In this study, three example cases were calculated by stockless anchors of 5.25 ton, 10.5 ton, and 15.4 ton, and for the onshore experiment dropped height was back calculated with the anchor's terminal velocity in the water.

• Wind and Structures
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• v.17 no.4
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• pp.379-397
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• 2013

Large Eddy Simulations (LES) were carried out to investigate the aerodynamic characteristics of a rectangular cylinder with side ratio B/D=5 at Reynolds number Re=22,000 (based on cylinder thickness). Particular attention was devoted to the effects of velocity shear in the oncoming flow. Time-averaged and unsteady flow patterns around the cylinder were studied to enhance understanding of the effects of velocity shear. The simulation results showed that the Strouhal number has no significant variation with oncoming velocity shear, while the peak fluctuation frequency of the drag coefficient becomes identical to that of the lift coefficient with increase in velocity shear. The intermittently-reattached flow that features the aerodynamics of the 5:1 rectangular cylinder in non-shear flow becomes more stably reattached on the high-velocity side, and more stably separated on the low-velocity side. Both the mean and fluctuating drag coefficients increase slightly with increase in velocity shear. The mean and fluctuating lift and moment coefficients increase almost linearly with velocity shear. Lift force acts from the high-velocity side to the low-velocity side, which is similar to that of a circular cylinder but opposite to that of a square cylinder under the same oncoming shear flow.