• Journal of Ship and Ocean Technology
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• v.12 no.2
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• pp.41-52
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• 2008

The development of a high-lift rudder is needed because low speed full ships such as the VLCC(Very Large Crude oil Carrier) have difficulty for obtaining enough lifting force from a common rudder. The rudder of a ship is generally positioned behind the hull and propeller. Therefore, rudder design should consider the interactions between hull, propeller, and rudder. In the present study, the FLUENT code and body fitted mesh systems generated by the GRIDGEN program are adopted for the numerical simulations of flow characteristics around a rudder that is interacting with hull and propeller. Sliding mesh model(SMM) is adopted to analyze the interaction between propeller rotation and wake flow behind hull. Several numerical simulations are performed to compare the interactions such as hull-rudder, propeller-rudder, and hull-propeller-rudder. Also, we consider relationships between the interactions. The results of present numerical simulations show the variation of flow characteristics by the interaction between hull, propeller, and rudder, and these results are compared with an existing experimental result. The present study demonstrates that numerical simulations can be used effectively in the design of high-lift rudder behind low speed full ship.

• Journal of Ocean Engineering and Technology
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• v.36 no.6
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• pp.364-379
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• 2022

Coastal communities have been vulnerable to extreme coastal flooding induced by hurricanes and tsunamis. Many studies solely focused on the overland flow hydrodynamic and loading mechanisms on individual inland structures or buildings. Only a few studies have investigated the effects of flooding mitigation measures to protect the coastal communities represented through a complex series of building arrays. This study numerically examined the performance of flood-mitigation measures from tsunami-like wave-induced overland flows. A computational fluid dynamic model was utilized to investigate the performance of mitigation structures such as submerged breakwaters and seawalls in reducing resultant forces on a series of building arrays. This study considered the effects of incident wave heights and four geometrically structural factors: the freeboard, crest width of submerged breakwaters, and the height and location of seawalls. The results showed that prevention structures reduced inundation flow depths, velocities, and maximum forces in the inland environment. The results also indicated that increasing the seawall height or reducing the freeboard of a submerged breakwater significantly reduces the maximum horizontal forces, especially in the first row of buildings. However, installing a low-lying seawall closer to the building rows amplifies the maximum forces compared to the original seawall at the shoreline.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4373-4391
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• 2022

Marine reactor systems experience platform movement, and therefore, the system thermal-hydraulic analysis code needs to reflect the motion effect on the fluid to evaluate reactor safety. A moving reactor model for MARS-KS was developed to simulate the hydrodynamic phenomena in the reactor under motion conditions; however, its applicability does not cover the MULTID component used in multidimensional flow analyses. In this study, a moving reactor model is implemented for the MULTID component to address the importance of multidimensional flow effects under dynamic motion. The concept of the volume connection is generalized to facilitate the handling of the junction of MULTID. Further, the accuracy in calculating the pressure head between volumes is enhanced to precisely evaluate the additional body force. Finally, the Coriolis force is modeled in the momentum equations in an acceleration form. The improvements are verified with conceptual problems; the modified model shows good agreement with the analytical solutions and the computational fluid dynamic (CFD) simulation results. Moreover, a simplified gravity-driven injection is simulated, and the model is validated against a ship flooding experiment. Throughout the verifications and validations, the model showed that the modification was well implemented to determine the capability of multidimensional flow analysis under ocean conditions.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.1002-1012
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• 2024

To remove insoluble fission products, which could possibly cause reactor instability and significantly reduce heat transfer efficiency from primary system of molten salt reactor, a helium bubbling method is employed into a passive molten salt fast reactor. In this regard, two-phase flow behavior of molten salt and helium bubbles was investigated experimentally because the helium bubbles highly affect the circulation performance of working fluid owing to an additional drag force. As the helium flow rate is controlled, the change of key thermal-hydraulic parameters was analyzed through a two-phase experiment. Simultaneously, to assess the applicability of numerical model for the analysis of two-phase flow behavior, the numerical calculation was performed using the OpenFOAM 9.0 code. The accuracy of the numerical analysis code was evaluated by comparing it with the experimental data. Generally, numerical results showed a good agreement with the experiment. However, at the high helium injection rates, the prediction capability for void fraction of helium bubbles was relatively low. This study suggests that the multiphaseEulerFoam solver in OpenFOAM code is effective for predicting the helium bubbling but there exists a room for further improvement by incorporating the appropriate drag flux model and the population balance equation.

• Molecules and Cells
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• v.37 no.6
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• pp.435-440
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• 2014

Hemodynamic shear stress, the frictional force acting on vascular endothelial cells, is crucial for endothelial homeostasis under normal physiological conditions. When discussing blood flow effects on various forms of endothelial (dys)function, one considers two flow patterns: steady laminar flow and disturbed flow because endothelial cells respond differently to these flow types both in vivo and in vitro. Laminar flow which exerts steady laminar shear stress is atheroprotective while disturbed flow creates an atheroprone environment. Emerging evidence has provided new insights into the cellular mechanisms of flowdependent regulation of vascular function that leads to cardiovascular events such as atherosclerosis, atherothrombosis, and myocardial infarction. In order to study effects of shear stress and different types of flow, various models have been used. In this review, we will summarize our current views on how disturbed flow-mediated signaling pathways are involved in the development of atherosclerosis.

• Wind and Structures
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• v.12 no.5
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• pp.441-455
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• 2009

Studying the spatial distribution in coherent fields such as turbulence and turbulence-induced force is important to model and evaluate turbulence-induced forces and response of structures in the turbulent flows. Turbulence field-based coherence function is commonly used for the spatial distribution characteristic of the turbulence-induced forces in the frequency domain so far. This paper will focus to study spectral coherent structure of the turbulence and induced forces in not only the frequency domain using conventional Fourier transform-based coherence, but also temporo-spectral coherence one in the time-frequency plane thanks to wavelet transform-based coherence for better understanding of the turbulence and force coherences and their spatial distributions. Effects of spanwise separations, bluff body flow, flow conditions and Karman vortex on coherent structures of the turbulence and induced pressure, comparison between turbulence and pressure coherences as well as intermittency of the coherent structure in the time-frequency plane will be investigated here. Some new findings are that not only the force coherence is higher than the turbulence coherence, the coherences of turbulence and forces depend on the spanwise separation as previous studies, but also the coherent structures of turbulence and forces relate to the ongoing turbulence flow and bluff body flow, moreover, intermittency in the time domain and low spectral band is considered as the nature of the coherent structure. Simultaneous measurements of the surface pressure and turbulence have been carried out on some typical rectangular cylinders with slenderness ratios B/D=1 (without and with splitter plate) and B/D=5 under the artificial turbulent flows in the wind tunnel.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.12
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• pp.1-8
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• 2005

A parametric study has been accomplished to figure out the effects of the elliptic cylinder thickness, angle of attack, and Reynolds number on the lift and drag forces exerted on the elliptic cylinder. A two-dimensional incompressible Navier-Stokes flow solver is developed using SIMPLER method to analyze the unsteady viscous flow over elliptic cylinder. Thickness-to-chord ratios of 0.2, 0.4, and 0.6 elliptic cylinders are simulated at different Reynolds numbers of 400 and 600, and angles of attack of $10^{\circ}$, $20^{\circ}$, and $30^{\circ}$. Through this study, it is observed that the elliptic cylinder thickness, angle of attack, and Reynolds number affect significantly not only the time-mean values and the amplitudes of the drag and lift forces but also the frequencies of the force oscillations.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1621-1632
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• 1993

A numerical simulation is carried out on flows in a rotating serpentine flow passage, which models a cooling passage in a gas turbine blade, by using a 3-D FVM based TURBO-D program. When it is rotating, the flow field exhibits quite different aspects due to the effect of the Coriolis force. Especially the secondary flow field appearing in the cross-sectional area is very complex because of the combined effect of the Coriolis force and the centrifugal force in the curved area. Local Nusselt numbers are also obtained based on the Reynolds analogy and compared with the published experimental data showing a good agreement. The results of the present study can be applied to the design of cooling passages of a gas turbine blade.

• The KSFM Journal of Fluid Machinery
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• v.10 no.6
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• pp.32-37
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• 2007

Aerodynamic forces and moments have been used to control rocket propelled vehicles. If control is required at very low speed, Those systems only provide a limited capability because aerodynamic control force is proportional to the air density and low dynamic pressure. But thrust vector control(TVC) can overcome the disadvantages. TVC is the method which generates the side force and roll moment by controlling exhausted gas directly in a rocket nozzle. TVC is classified by mechanical and fluid dynamic methods. Mechanical methods can change the flow direction by several objects installed in a rocket nozzle exhaust such as tapered ramp tabs and jet vane. Fluid dynamic methods control the flight direction with the injection of secondary gaseous flows into the rocket nozzle. The tapered ramp tabs of mechanical methods are used in this paper. They installed at the rear in the rocket nozzle could be freely moved along axial and radial direction on the mounting ring to provide the mass flow rate which is injected from the rocket nozzle. In this paper, the conceptual design and the study on the tapered ramp tabs of the thurst vector control has been carried out using the supersonic cold flow system and schlieren system. This paper provides the thrust spoilage, three directional forces and moments and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.10
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• pp.898-906
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• 2005

The present study has been conducted to investigate convective heat/mass transfer in the cooling passage with bleed holes. The rotating square channel has 40.0 mm hydraulic diameter and the bleed holes on the leading surface of the channel. The hole diameter of bleed hole is 4.5mm and its spacing is ( p/d:4.9) about five times of hole diameter. Exit mass flow rate through bleed holes is $10\%$ of the main mass flow rate and relation number is changed form 0.0 to 0.4. A naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy The cooling performance is influenced by exit mass flow rate through bleed holes and Coriolis force of rotating channel for fixed Reynolds number. The heat transfer on the leading surface is decreased due to Coriolis force. However the total heat transfer is enhanced around holes on the leading surface because of trapping flow by bleeding.