• Journal of the Korean Society for Precision Engineering
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• v.34 no.4
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• pp.253-258
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• 2017

This paper presents a numerical study on the thermal characteristics of a milling process of titanium alloy with nanofluid minimum-quantity lubrication (MQL). The computational fluid dynamics (CFD) approach is introduced for establishing the numerical model for the nanofluid MQL milling process, and estimated temperatures for pure MQL and for nanofluid MQL using both hexagonal boron nitride (hBN) and nanodiamond particles are compared with the temperatures measured by thermocouples in the titanium alloy workpiece. The estimated workpiece temperatures are similar to experimental ones, and the model is validated.

• The KSFM Journal of Fluid Machinery
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• v.7 no.4 s.25
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• pp.40-46
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• 2004

This paper is concerned with the numerical analyses of an S-shaped duct for the inter-channel between compressor spools. For the compactness and lightweight of an engine, the length of the S-shaped duct is desired to be minimized. Shortening the S-shaped duct, however, flow separation is likely to occur. Numerical investigation using a three-dimensional Navier-Stokes flow solver was performed to determine the availability of the minimization of an S-shaped duct. Computations were performed introducing the experimental data as the inlet flow condition of the OGV in determining the minimum length of the S-shaped duct. Also, the leaning effect of the OGV which assists the flow to turn radially inward was studied adopting mixing-plane method to consider the rotor/OGV interaction.

• 한국전산유체공학회:학술대회논문집
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• 1999.05a
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• pp.113-123
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• 1999

In this study a pure vector potential method (PVPM) for a three dimensional, unsteady, incompressible flow is proposed. A simplified version for a two dimensional problem is described in detail, and a method to prescribe appropriate boundary conditions is also presented. The resulting numerical algorithm is applied to the cavity flow driven by an impulsively started wall and also to the Stokes' first problem. Some important unsteady/steady features are captured for these two flows, and quantitative agreements of flow variables with available reference database are good.

• Journal of computational fluids engineering
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• v.14 no.4
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• pp.101-108
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• 2009

We present a new finite-element scheme for direct numerical simulation of particle suspensions in simple shear flow of a viscoelastic fluid in 3D. The sliding tri-periodic representative cell concept has been combined with DEVSS/DG finite element scheme by introducing constraint equations along the domain boundary. Rigid body motion of the freely suspended particle is described by the rigid-shell description and implemented by Lagrangian multipliers on particle boundaries. We present the bulk rheology of suspensions through the numerical examples of single-, two- and many-particle problems, which represent a large number of such systems in simple shear flow. We report the steady bulk viscosity and the first normal stress coefficient, which show shear-thickening behavior for both properties.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.548-553
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• 2016

본 연구는 타원형 물체가 유체 중에서 침강할 때 물체의 형상과 밀도에 따른 침강특성을 분석하는 것이며, 이로 인해 종단속도에 미치는 영향을 평가하는 것이다. 복잡한 형태의 물체를 타원기둥으로 단순화하였고, 낮은 Reynolds 수(=0.5~100)에 대하여 연구를 진행하였다. 또한 침강형태가 종단속도에 미치는 영향을 연구하였다. 수치해석 검증을 통해 정확하고 효율적인 격자 크기를 결정하였다. 정확한 분석을 위해 단순히 종단속도의 변화를 본 것이 아니라 진동하지 않은 물체의 이론적 속도와 비교하여 이와 얼마나 차이가 있는지를 확인하였다. 수치해석 결과 장단축비에 따라 물체의 침강특성이 크게 변하였고 그 경향은 밀도비에 따라 다른 양상을 보였다. 또한 각의 진동에 대한 진폭과 진동수가 물체의 침강속도에 영향을 주는 것을 확인하고 그 원인에 대해서도 연구하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.1
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• pp.69-76
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• 2003

Low-tension cables have been increasingly used in recent years due to deep-sea developments and the advent of synthetic cables. In the case of low-tension cables, large displacements may happen due to relatively small restoring forces of tension and thus the effects of fluid and geometric non-linearities and bending stiffness. A Fortran program is developed by employing a finite difference method. In the algorithm, an implicit time integration and Newton-Raphson iteration are adopted. For the calculation of huge size of matrices, block tri-diagonal matrix method is applied, which is much faster than the well-known Gauss-Jordan method in two point boundary value problems. Some case studies are carried out and the results of numerical simulations are compared with a in-house program of WHOI Cable with good agreements.

• Tunnel and Underground Space
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• v.33 no.2
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• pp.83-94
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• 2023

Unlike the conventional triaxial test cells for cylindrical specimens, which impose uniform lateral confining pressures, the GREAT (Geo-Reservoir Experimental Analogue Technology) cell can exert differential radial stresses using eight independently-controlled pairs of lateral loading elements and thereby generate horizontal stress fields with various magnitudes and orientations. In the preceding companion paper, GREAT cell tests were numerically simulated under different mechanical loading conditions and the validity of the numerical model was investigated by comparing experimental and numerical results for circumferential strain. In the present study, we simulated GREAT cell tests for an artificial sample containing a fracture under both mechanical loading and fluid flow conditions. The numerical simulation was carried out by varying the mechanical properties of the fracture surface, which were unknown. The numerical responses (circumferential strains) of the sample were compared with experimental data and a good match was found between the numerical and experimental results under certain mechanical conditions of the fracture surface. Additionally, the effect of fluid flow conditions on the mechanical behavior of the sample was investigated and discussed.

• Journal of Korea Water Resources Association
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• v.50 no.5
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• pp.325-334
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• 2017

In this study, the numerical investigation of the non-linear behavior of the fluid flow with physical properties, such as porosity and intrinsic permeability of a porous medium, and kinematic viscosity of a fluid, are carried out. The applied numerical model is ANSYS CFX which is the three-dimensional fluid dynamics model and this model is verified through the application of existing physical and numerical results. As a result of the verification, the results of the pressure gradient-velocity relationship and the friction coefficient-Reynolds number relationship produced from this study show relatively good agreement with those from existing physical and numerical experiments. As a result of the simulation by changing the porosity and intrinsic permeability of a porous medium and the kinematic viscosity of a fluid, the kinematic viscosity has the biggest effect on the non-linear behavior of the fluid flow in the porous medium.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1910-1913
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• 2006

To solve the interaction of incident monochromatic waves with a bottom-fixed vertical circular cylinder, a numerical analysis by boundary element method is developed using three-dimensional linear potential theory. A numerical analysis by boundary element method is based on Green's theorem and introduce to an integral equation for the fluid velocity potential around the vertical circular cylinder. These numerical results are compared with those of ManCamy and Fuchs(1954) and Williams and Mansour(2002), and it has shown good relationship with their results. This numerical analysis developed by boundary element method will be applied for various offshore structures to be constructed in coastal zones in the future.

• Aerospace Engineering and Technology
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• v.4 no.1
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• pp.39-44
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• 2005

To validate the rotor performance analysis, 3D Computational Fluid Dynamics(CFD) analysis was performed for tilt rotor aeroacoustic model(TRAM). Also, 3D vehicle with rotating rotors was simulated for rotor power effect analysis. Multiple reference frame(MRF) and sliding mesh techniques were implemented to capture the effect of rotor revolution. CFD results were compared with the wind tunnel test results to validate their accuracy. At helicopter mode, CFD analysis predicted lower thrust than the wind tunnel test but CFD results showed good agreement with the test result at cruise mode. Rotor power effect decreased the lift but did not change drag and pitching moment.