• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.327-333
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• 2008

The cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has developed a base code for simulating cavitating flows past cylinders and hydrofoils. The governing equation is the Navier-Stokes equation based on homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved in liquid and vapor phase, separately. The solver employs an implicit preconditioning algorithm in curvilinear coordinates. The computations have been carried out for the cylinders with spherical, 1- and 0-caliber forebody and hydrofoil of ALE and NACA cross-section and, then, compared with experiments and other numerical results. Fairly good agreements with experiments and numerical results have been achieved. The present base code has shown the feasibility to solve the cavitating flow past supercavitating torpedo after the improvement for compressibility effects and interactions with hot exhaust gas of propulsive rocket.

• Journal of computational fluids engineering
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• v.15 no.4
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• pp.53-59
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• 2010

Preliminary design of a ground plate, a device installed close to the aircraft model for wind tunnel test to simulate the ground effect, was performed by a numerical simulation. A two-dimensional numerical study was performed initially to decide the optimal leading edge and flap configurations. Then, three-dimensional studies were conducted to decide the optimal flap deflection angle for pressure distribution reduction since the plate and the plate supporting system generate static pressure difference between the upper and lower flow regions. Three-dimensional simulation additionally studied the effect of the clearance between the plate and the wind tunnel side wall. For the efficiency of computation, half model was simulated and a symmetric boundary condition was applied on the center plane. Based on the preliminary design, a ground plate was designed, manufactured and tested at the Korea Aerospace Research Institute(KARI) wind tunnel. The measured pressure differences versus flap deflection angle agreed well with the predicted results.

• Journal of the Korean Society of Combustion
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• v.22 no.3
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• pp.8-16
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• 2017

MILD combustion was first developed to suppress thermal NOx formation in combustor for heating industrial furnaces. In this paper, the effect of co-flow MILD combustor geometry and operating conditions on the formation of MILD combustion was analyzed using 3 dimensional numerical simulation. The numerical simulations were carried out using ANSYS Fluent. The combustion and turbulence flow was modeled using the Eddy Dissipation Concept(EDC) model and realizable $k-{\varepsilon}$ model respectively. The results show that the high temperature region and average temperature decreased due to an increase in the air velocity and decrease the wall thickness of fuel nozzle. In particular, the MILD combustion flame was found to be stable with a combustion flame region at fuel velocity 10 m/s, air velocity 20 m/s, fuel nozzle thickness 1.0 mm, equivalence ratio 0.9, and outlet area ratio 40%.

• Steel and Composite Structures
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• v.5 no.6
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• pp.421-441
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• 2005

The present work reports on a numerical simulation of a compartment fire. The fire was modeled using a simplified approach, where combustion is simulated as a volumetric heat release. Computations were performed with the commercial code CFX 5.6. Radiation was modeled with a differential approximation (P1 model), while turbulence effects upon the mean gas flow were dealt with a SST turbulence model. Simulations were carried out using a transient approach, starting at the onset of ignition. Results are provided for the temperature field time evolution, thus allowing a direct comparison with the analytical and experimental data. The high spatial resolution available for the results proved to be of great utility for a more detailed analysis of the thermal impact on the steel structure.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.503-509
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• 2004

With modem computational fluid dynamics method (CFD), air-charging models of the air brake pipe system and auxiliary reservoir are built. Compared with one-dimension model, no empirical formula is introduced to solve branch pipe fields for two-dimension model. A modified operator-splitting method is presented to solve the coupled equations of pressure and velocity, and numerical simulation shows that it is very stable. Compare the numerical results with empirical data of heavy haul trains in home and abroad so as to prove the correctness of the theory and algorithm presented. This paper gives theoretic reference to the experiments of braking effects of heavy haul trains, and forms a basis for development of complete freight train air brake system simulation.

• Coupled systems mechanics
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• v.8 no.2
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• pp.147-168
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• 2019

This work aims to simulate three-dimensional heavy oil flow in a reservoir with heater-wells. Mass, momentum and energy balances, as well as correlations for rock and fluid properties, are used to obtain non-linear partial differential equations for the fluid pressure and temperature, and for the rock temperature. Heat transfer is simulated using a two-equation model that is more appropriate when fluid and rock have very different thermal properties, and we also perform comparisons between one- and two-equation models. The governing equations are discretized using the Finite Volume Method. For the numerical solution, we apply a linearization and an operator splitting. As a consequence, three algebraic subsystems of linearized equations are solved using the Conjugate Gradient Method. The results obtained show the suitability of the numerical method and the technical feasibility of heating the reservoir with static equipment.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.136-146
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• 2021

This paper aims to numerically estimate the dynamic ice load on a conical structure. The Discrete Element Method (DEM) is employed to model the level ice as the assembly of numerous spherical particles. To mimic the realistic fracture mechanism of ice, the parallel bonding method is introduced. Cases with four different ice drifting velocities are considered in time domain. For validation, the statistics of time-varying ice forces and their frequencies obtained by numerical simulations are extensively compared against the physical model-test results. Ice properties are directly adopted from the targeted experimental test set up. The additional parameters for DEM simulations are systematically determined by a numerical three-point bending test. The findings reveal that the numerical simulation estimates the dynamic ice force in a reasonably acceptable range and its results agree well with experimental data.

• Steel and Composite Structures
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• v.42 no.4
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• pp.569-590
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• 2022

This paper presents a combined experimental and numerical study on stainless steel end-plate connections, with an emphasis placed on their ultimate behaviour and rotation capacity. In the experimental phase, six connection specimens made of austenitic and lean duplex stainless steels are tested under monotonic loads. The tests are specifically designed to examine the close-to-failure behaviour of the connections at large deformations. It is observed that the rotation capacity is closely related to fractures of the stainless steel bolts and end-plates. In the numerical phase, an advanced finite element model suitable for fracture simulation is developed. The incorporated constitutive and fracture models are calibrated based on the material tests of stainless steel bolts and plates. The developed finite element model exhibits a satisfactory accuracy in predicting the close-to-failure behaviour of the tested connections. Finally, the moment resistance and rotation capacity of stainless steel end-plate connections are assessed based on the experimental tests and numerical analyses.

• Nuclear Engineering and Technology
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• v.49 no.6
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• pp.1310-1317
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• 2017

GASFLOW-MPI is a widely used scalable computational fluid dynamics numerical tool to simulate the fluid turbulence behavior, combustion dynamics, and other related thermal-hydraulic phenomena in nuclear power plant containment. An efficient scalable linear solver for the large-scale pressure equation is one of the key issues to ensure the computational efficiency of GASFLOW-MPI. Several advanced Krylov subspace methods and scalable preconditioning methods are compared and analyzed to improve the computational performance. With the help of the powerful computational capability, the large eddy simulation turbulent model is used to resolve more detailed turbulent behaviors. A backward-facing step flow is performed to study the free shear layer, the recirculation region, and the boundary layer, which is widespread in many scientific and engineering applications. Numerical results are compared with the experimental data in the literature and the direct numerical simulation results by GASFLOW-MPI. Both time-averaged velocity profile and turbulent intensity are well consistent with the experimental data and direct numerical simulation result. Furthermore, the frequency spectrum is presented and a -5/3 energy decay is observed for a wide range of frequencies, satisfying the turbulent energy spectrum theory. Parallel scaling tests are also implemented on the KIT/IKET cluster and a linear scaling is realized for GASFLOW-MPI.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.813-820
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• 2014

This study presents a numerical modeling of mean flow and turbulence structures of partly-vegetated open-channel flows. For this, Reynolds-averaged Navier-Stokes equations with vegetation drag terms are solved numerically using the non-linear k-${\varepsilon}$ model. The numerical model is applied to laboratory experiments of Nezu and Onitsuka (2001), and simulated results are compared with data from measurement and computations by Kang and Choi's (2006) Reynolds stress model. The simulation results indicate that the proposed numerical model simulates the mean flow well. Twin vortices are found to be generated at the interface between vegetated and non-vegetated zones, where turbulence intensity and Reynolds stress show their maximums. The model simulates the pattern of the Reynolds stress well but under-predicts the intensity of Reynolds stress slightly.