• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.8-14
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• 2003

The particle dispersion in the turbulent mixing layer has been numerically investigated to clarify the effect of the velocity ratio in the large-scale vortical structures. In this study the LES with subgrid-scale model is employed. The Lagrangian method to predict the particle motion is applied. The particles of 10, 50, 150, 200${\mu}m$ in mean diameter were loaded into the origin of the mixing layer. It is shown that the characteristics of flow and growth rate are strongly dependent on the variation of the velocity ratio. It is also shown the relationship between the Stokes number and the particle dispersion. As a result, in the case of St~1 the particle dispersion is faster than the diffustion of the flow field while in the cases of both St<<1 and St>>1 it is shown that the particle dispersion in lower than the diffusion of the flow filed.

• International Journal of Highway Engineering
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• v.10 no.4
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• pp.19-29
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• 2008

To produce asphalt mixtures at temperature significantly below $135^{\circ}C$, called "Warm Mix Asphalt (WMA)", new technologies are currently being developed worldwide. To produce WMA mixtures in this research, foaming technology is adopted to effectively disperse asphalt binder at lower temperature than hot mix asphalt (HMA) in the field. The main objectives of this study are to develop WMA process using foaming technology (WMA-foam) and evaluate its performance characteristics under various temperatures and loading conditions. WMA-foam mixtures were produced by injecting PO 64-22 foamed asphalt into warm aggregates whereas WMA mixtures were produced by adding PO 64-22 asphalt (without foaming) in the warm aggregates. Both dynamic modulus and flow number of WMA-foam mixtures were higher than those of WMA mixtures. Based on the limited dynamic modulus and repeated load test results, it is concluded that the WMA-foam mixtures using warm aggregates at $100^{\circ}C$ are more resistant to fatigue cracking and rutting than WMA mixtures.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.396-401
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• 2004

In this paper, a 1MW HAWT(FIL-1000) rotor blade has been designed by BEMT(Blade Element Momentum Theory) with Prandtl's tip loss. Also, a 3-D flow and performance analysis on the FIL-1000 rotor blade has been carried out by using the 3-D Navier-Stokes commercial solver (CFX-5.7) to provide more efficient design techniques to the large-scale HAWT engineers. The rated power and itsapproaching wind velocity at design point (TSR=7.5) are 1MW and 9.99m/s respectively. The rotor diameter is 54.5m and the rotating speed is 26.28rpm. Airfoils such as FFA W-301, DU91-W-250, DU93-W-210, NACA 63418, NACA 63415 consist of the rotor blade from hub to tip. Recent CFX version, 5.7 was adopted to simulate 3-D flow field and to analyze the performance characteristics of the rotor blade. Entire mesh node number is about 730,000 and it is generated by ICEM-CFD to achieve better mesh quality The predicted maximum power occurringat the design tip speed ratio is 931.45kW. Approaching to the root, the inflow angle becomes large, which causesthe blade to be stalled in the region. Therefore, k-$\omega$ SST turbulence model was used to predict the quantitative flow information more accurately. Application of commercial CFD code to optimum blade design and performance analysis was proved to be more effective environment to HAWT blade designers.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.281-285
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• 2007

The flow characteristics in the thruster should be analyzed considering its geometry and the pressure ratio to estimate its performance and etc. This paper suggests the computational result of an axisymmetric real nozzle for the altitude control of a satellite to find out the application limit that the assumption of continuum mechanics holds. The steady non-reacted compressible flow field in the unstructured grid system is computed and analyzed with varying the environmental pressure (or the degree of vacuum) under the fixed pressure ratio in a real thruster of which the area ratio of exit to throat is 56. The assumption of the continuum mechanics is not approved when the environmental pressure is reduced less than $10^{-3}$ atm.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.717-722
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• 2010

Supersonic/Hypersonic wind tunnel is a facility which is intended to test and to observe the physical phenomena around a model by creating supersonic flow in the test section. In designing an airplane, the wind tunnel test is demanded to analyzing aerodynamic characteristics of the model without making a prototype. In this research, the model aerodynamic facility(MAF) is modified for the purpose of increasing running time and its functionality. New pneumatic valves for remote control was installed for safety requirement, and new air tanks was installed on MAF as well. A pipe system is also modified to use those new valves and tanks, and the ceiling and side glasses of the test section are switched to ones with the larger surface area. After the MAF modification, a test is performed at Mach 2, 3 and 4. In this test, shadow graph technique, one of the flow visualization methods, is used to visualize supersonic flow field. The pressure in the settling chamber and working section at Mach 2, 3 and 4 was measured in each case. As a result, the possible model size and running time are obtained.

• The Journal of the Petrological Society of Korea
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• v.25 no.3
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• pp.283-298
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• 2016

Sangumburi crater, designated as Natural Monument No. 63, recognized as a maar, but precise geological mapping and geological characteristics in the field indicate that Sangumburi crater is a pit crater. Two stages of volcanic activities created Sangumburi pit crater. Lava flow (aphanitic pyroxene basalt I) and associated pyroclastic deposit (pyroclast I), composed of ash and lapilli, were formed at the stage 1. In the stage 2, lava flow (feldspar olivine basalt) was overlain by lava flow (aphanitic pyroxene basalt II) and associated pyroclastic deposit (pyroclast II), composed of agglomerate. Sangumburi pit crater formed at $0.073{\pm}0.036Ma$, determined by Ar-Ar age dating for the feldspar olivine basalt at the stage 2. It is not clear the preferred migration direction of subsurface magma after Sangumburi pit crater formed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.2
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• pp.81-89
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• 2019

In this study, wind tunnel test on Quad-Tilt Propeller which has tandem wings is carried out to analyze the aerodynamic interference effect of front wing and propeller on rear wing during forward flight. Using 6-axis balance system, forces and moments of whole aircraft were measured and using strain gauge at wing root, bending moments were measured to observe change of aerodynamic force of each wings. A 12-hole probe was used to measure the flow field in the wing and propeller wake. Flow characteristics were observed qualitatively through flow visualization experiment using tuft and smoke. To measure the aerodynamic interference by elements, the influence of front wing and propeller on rear wing was analyzed by changing the wings and propellers mount combination.

• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1487-1503
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• 2019

The methods and performance of a pin-level nuclear reactor core thermal-hydraulics (T/H) code ESCOT employing the drift-flux model are presented. This code aims at providing an accurate yet fast core thermal-hydraulics solution capability to high-fidelity multiphysics core analysis systems targeting massively parallel computing platforms. The four equation drift-flux model is adopted for two-phase calculations, and numerical solutions are obtained by applying the Finite Volume Method (FVM) and the Semi-Implicit Method for Pressure-Linked Equation (SIMPLE)-like algorithm in a staggered grid system. Constitutive models involving turbulent mixing, pressure drop, and vapor generation are employed to simulate key phenomena in subchannel-scale analyses. ESCOT is parallelized by a domain decomposition scheme that involves both radial and axial decomposition to enable highly parallelized execution. The ESCOT solutions are validated through the applications to various experiments which include CNEN $4{\times}4$, Weiss et al. two assemblies, PNNL $2{\times}6$, RPI $2{\times}2$ air-water, and PSBT covering single/two-phase and unheated/heated conditions. The parameters of interest for validation include various flow characteristics such as turbulent mixing, spacer grid pressure drop, cross-flow, reverse flow, buoyancy effect, void drift, and bubble generation. For all the validation tests, ESCOT shows good agreements with measured data in the extent comparable to those of other subchannel-scale codes: COBRA-TF, MATRA and/or CUPID. The execution performance is examined with a mini-sized whole core consisting of 89 fuel assemblies and for an OPR1000 core. It turns out that it is about 1.5 times faster than a subchannel code based on the two-fluid three field model and the axial domain decomposition scheme works as well as the radial one yielding a steady-state solution for the OPR1000 core within 30 s with 104 processors.

• Geomechanics and Engineering
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• v.29 no.4
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• pp.391-405
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• 2022

A newly proposed grouting simulation method, the sequential diffusion solidification method was introduced into the numerical simulation of combined bi-borehole grouting. The traditional, critical and difficult numerical problem for the temporal and spatial variation simulation of the slurry is solved. Thus, numerical simulation of grouting and blocking of flowing water in karst conduits is realized and the mechanism understanding of the combined bi-borehole technology is promoted. The sensitivity analysis of the influence factors of combined bi-borehole grouting was investigated. Through orthogonal experiment, the influences of proximal and distal slurry properties, the initial flow velocity of the conduit and the proximal and distal slurry injection rate on the blocking efficiency are compared. The velocity variation, pressure variation and slurry deposition phenomenon were monitored, and the flow field characteristics and slurry outflow behavior were analyzed. The interaction mechanism between the proximal and distal slurries in the combined bi-borehole grouting is revealed. The results show that, under the orthogonal experiment conditions, the slurry injection rate has the greatest impact on blocking. With a constant slurry injection rate, the blocking efficiency can be increased by more than 30% when using slurry with weak time-dependent viscosity behavior in the distal borehole and slurry with strong time-dependent viscosity behavior in the proximal borehole respectively. According to the results of numerical simulation, the grouting scheme of "intercept the flow from the proximal borehole by quick-setting slurry, and grout cement slurry from the distal borehole" is put forward and successfully applied to the water inflow treatment project of China Resources Cement (Pingnan) Limestone Mine.

• Resources Recycling
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• v.33 no.1
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• pp.37-47
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• 2024

In grouting, the LW method is commonly employed to induce the gelation of cementitious material using water glass, thereby restricting the extent of material injection. Nevertheless, challenges manifest when materials are lost before gelation, particularly in regions with high groundwater flow rates or significant subsurface voids. This study developed a thixotropic grout material using LFS and GGBFS to mitigate material loss during injection, with an assessment of its flow characteristics, durability in marine exposure, strength, and injection properties. The outcomes revealed that the thixotropic grout material exhibited flow ranging from 105 to 143 mm and enhanced strength and durability compared to the LW method. Furthermore, field tests substantiated that applying vibration and impact improved impermeability.