• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.25-30
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• 2009

The present study deals with numerical investigation for smoke behavior in rescue station by using the commercial CFD code (FLUENT Ver 6.3). With the use of the MVHS(Modify Volumetric Heat Source) model modified from the original VHS(Volumetric Heat Source) model, a 10 MW mode was adopted for simulation and the MVHS model can describe the generation of product and the oxygen consumption at the stoichiometric state. In addition, the present simulation includes the species conservation equations for the materialization of heat source and the estimation of smoke movement. From the results, the smoke flows are moving along the ceiling because of thermal buoyancy force and as time goes, the smoke gradually moves downward at the vicinity of the entrance. Moreover, without using ventilation, it is found that the smoke flows no longer spread across the cross-passages because the pressure in the non-accident tunnel is higher than that in the accident tunnel.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.5
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• pp.77-83
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• 2016

A considerable amount of researches has been performed to investigate the flow characteristics produced in the cavity system over straight wall. However, many practical applications of the cavity flows are found on curved walls, which are strongly subject to the centrifugal force effects. No work has been made on the cavity flows on the curved wall to date. In the present study, a computational fluid dynamics method has been applied to investigate the cavity flows over curved walls at Mach numbers in range of 0.4 to 0.8. The aspect ratio of the cavity was fixed at L/H=3, but the radius of curvature of the curved wall is changed in considering the real engineering practice. The results reveal that the pressure oscillations in the curved walls are stronger than those in the straight wall. It is found that the ratio of curvature of the curved wall significantly affects the unsteady flow characteristics inside the cavity.

• Journal of the Korean Geotechnical Society
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• v.29 no.6
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• pp.77-86
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• 2013

Embankments on soft ground experience significant deformation during time-dependent consolidation settlement, as well as an initial undrained settlement. Since infinitesimal strain theory assumes no configuration change and minute strain during deformation, finite strain analysis is required for better prediction of geotechnical problems involving large strain and geometric change induced by imposed loadings. Updated Lagrangian formulation is developed for time-dependent consolidation combining both force equilibrium and mass conservation of fluid, and mechanical constitutive equation is written in Janumann stress rate. Numerical convergence during Newton's iteration in large deformation analysis is improved by Nagtegaal's approach of considering the effect of rotation in mechanical constitutive relationship. Numerical simulations are conducted to discuss numerical reliability and applicability of developed numerical code: deformation of cantilever beam, two-dimensional consolidation. The numerical results show that developed formulation can efficiently describe large deformation problems. Proposed formulation is expected to facilitate the upgrading of a numerical code based on infinitesimal strain theory to that based on finite strain analysis.

• Journal of Korean Association for Spatial Structures
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• v.11 no.2
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• pp.101-110
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• 2011

Many researchers have attempted to apply semi-active control systems in the civil engineering structures. Recently, magneto-rheological(MR) fluid dampers have been developed. This MR damper is one of semi-active dampers as a new class of smart dampers. This paper discusses the application of MR damper for seismic response control of adjacent buildings subjected to earthquake. Here, a controllable damping force of MR damper that is installed between adjacent buildings is applied to seismic response control. A hybrid model combines skyhook and groundhook control algorithm so that the benefits of each can be combined together. In this paper, hybrid control model are applied to the multi degree of freedom system representative of buildings in order to reduce seismic response of adjacent buildings. And the performance of hybrid control model is compared with that of others. It was demonstrated that hybrid control model or adjacent buildings with MR damper was effective for seismic response control of two adjacent buildings reciprocally.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.217-220
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• 2006

The lift and drag forces produced by a wing of a given cross-sectional profile are dependent on the wing planform and the angle of attack. Aspect ratio is the ratio of the wing span to the average chord. For conventional fixed wing aircrafts, high aspect ratio wings produce a higher lift to drag ratio than low ones for flight at subsonic speeds. Therefore, high aspect ratio wings are used on aircraft intended for long endurance. However, birds and insects flap their wings to fly in the air and they can change their wing motions. Their wing motions are made up of translation and rotation. Therefore, we tested flapping motions with parameters which affect rotational motion such as the angle of attack and the wing beat frequency. The half elliptic shaped wings were designed with the variation of aspect ratio from 4 to 11. The flapping device was operated in the water to reduce the wing beat frequency according to Reynolds similarity. In this study, the aerodynamic forces, the time-averaged force coefficients and the lift to drag ratio were measured at Reynolds number 15,000 to explore the aerodynamic characteristics with the variation of aspect ratio. The maximum lift coefficient was turned up at AR=8. The mean drag coefficients were almost same values at angle of attack from $10^{\circ}$ to $40^{\circ}$ regardless of aspect ratio, and the mean drag coefficients above angle of attack $50^{\circ}$ were decreased according to the increase of aspect ratio. For flapping motion the maximum mean lift to drag ratio appeared at AR=8.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.46 no.2
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• pp.108-115
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• 2020

Objectives: Kinesiology tape (KT) creates a pulling force on the skin, thus improving blood and lymph flow by alleviating hemorrhage and congestion of lymphatic fluid. The authors hypothesized that the use of KT could be beneficial for the management of complications after head and neck surgery and designed this study to evaluate the effects of KT on swelling, pain, and trismus after enucleation of mandibular dentigerous cysts with third molar extraction. Materials and Methods: Forty patients who underwent enucleation of a dentigerous cyst with extraction of the mandibular third molar were selected. The patients were randomized into two groups (n=20 each): a KT group, where KT was applied after surgery in addition to basic postoperative care, and a control group, where patients received basic postoperative care without KT application. Swelling, pain, and trismus were evaluated before surgery (T0) and on postoperative days 1 (T1), 2 (T2), and 3 (T3). Cyst volume, gauze weight for assessing bleeding, and operation time were recorded. Results: There was a significant difference between the two groups in the change in swelling up to T1 and the change in swelling between T1 and T2. The maximum swelling in the KT group was significantly less than that in the No-KT group and maximum swelling appeared faster in the KT group than in the No-KT group. Both groups showed a mild pain response but there was no significant difference between the two groups. There was no significant difference on interincisal distance change between the two groups. There were no correlations between cyst volume, bleeding, operation time, and maximum swelling. Conclusion: KT can effectively manage facial swelling after oral and maxillofacial surgeries such as cyst enucleation and third molar extraction, thus improving postoperative patient satisfaction levels and quality of life.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.241-251
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• 2017

Computational fluid dynamics analysis was performed for the case 3 of the EFD-CFD workshop. Solvers were used for three commercial CFD codes(Star-CCM+, Fluent and CFX) and an open source CFD code(SU2). The grid were generated four types depending on the total cells using commercial grid generation code(Pointwise). Mach number of 0.4 and 0.8, 2 degree angle of attack and Mach number of 0.9, 1 degree angle of attack were calculated. Similar pressure coefficient curve and normal force coefficient were showed from the coarse grid to fine grid of four codes. But there is a difference in the drag coefficient. The position of the shock wave was predicted forward as the discretization order increased in calculations using Star-CCM+ and Fluent. The computation time to converge, Fluent, Star-CCM +, CFX are in order, and SU2 takes much time to converge.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.6
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• pp.869-876
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• 2008

A thermocompressor is the equipment which compresses a vapor to a desired discharge pressure. Since it was first used as the evacuation pump for a surface condenser, it has been widely adopted for energy saving systems due to its high working confidence. In the present study, the geometrical analysis of the shape between the jet nozzle and the diffuser inlet, the drag force was calculated by means of the integrated equation of motion and the computational fluid dynamic (CFD) package called FLUENT. The computer simulations were performed to investigate the effects by the various suction flow rates, the distance from jet nozzle outlet to the diffuser inlet and the dimensions of the diffuser inlet section through the iterative calculation. In addition, the results from the CFD analysis on the thermocompressor and the experiments were compared for the verification of the CFD results. In the case of a jet nozzle, the results from the CFD analysis showed a good agreement with the experimental results. Furthermore, in this study, a special attention was paid on the performance of the thermocompressor by varying the diffuser convergence angle of $0.0^{\circ}$, $0.5^{\circ}$, $1.0^{\circ}$, $2.0^{\circ}$, $3.5^{\circ}$ and $4.5^{\circ}$. With the increase of the diffuser convergence angle. the suction capacity was improved up to the degree of $1.0^{\circ}$ while it was decreased over the degree of $1.0^{\circ}$.

• Atmosphere
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• v.25 no.3
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• pp.501-510
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• 2015

In this study, the characteristics of flows around building groups are investigated using a computational fluid dynamics (CFD) model. For this, building groups with different volumetric ratios in a fixed area are considered. As the volumetric ratio of the building group increases, the region affected by the building group is widened. However, the wind-speed reduced area rather decreases with the volumetric ratio near the ground bottom (z ${\lesssim}$ 0.7H, here, H is the height of the building group) and, above 0.7H, it increases. As the volumetric ratio decreases (that is, space between buildings was widened), the size of recirculation region decreases but flow recovery is delayed, resulting in the wider wind-speed reduced area. The increase in the volumetric ratio results in larger drag force on the flow above the roof level, consequently reducing wind speed above the roof level. However, above z ${\gtrsim}$ 1.7H, wind speed increases with the volumetric ratio for satisfying mass conservation, resultantly increasing turbulent kinetic energy there. Inside the building groups, wind speed decreased with the volumetric ratio and averaged wind speed is parameterized in terms of the volumetric ratio and background flow speed. The parameterization method is applied to producing averaged wind speed for 80 urban areas in 7 cities in Korea, showing relatively good performance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.347-355
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• 2016

This study presents a Lattice Boltzmann Method (LBM) coupled with a momentum-exchange approach/fictitious domain (MEA/FD) method for the simulation of particle suspensions. The method combines the advantages of the LB and the FD methods by using two unrelated meshes, namely, a Eulerian mesh for the flow domain and a Lagrangian mesh for the solid domain. The rigid body conditions are enforced by the momentum-exchange scheme in which the desired value of velocity is imposed directly in the particle inner domain by introducing a pseudo body force to satisfy the constraint of rigid body motion, which is the key idea of a fictitious domain (FD) method. The LB-MEA/FD method has been validated by simulating two different cases, and the results have been compared with those through other methods. The numerical evidence illustrated the capability and robustness of the present method for simulating particle suspensions.