• Nuclear Engineering and Technology
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• v.55 no.9
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• pp.3367-3382
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• 2023

Smoothed Particle Hydrodynamics (SPH) is a Lagrangian computational fluid dynamics method that has been widely used in the analysis of physical phenomena characterized by large deformation or multi-phase flow analysis, including free surface. Despite the recent implementation of eddy-viscosity models in SPH methodology, sophisticated turbulent analysis using Lagrangian methodology has been limited due to the lack of computational performance and numerical consistency. In this study, we implement the standard and dynamic Smagorinsky model and dynamic Vreman model as sub-particle scale models based on a weakly compressible SPH solver. The large eddy simulation method is numerically identical to the spatial discretization method of smoothed particle dynamics, enabling the intuitive implementation of the turbulence model. Furthermore, there is no additional filtering process required for physical variables since the sub-grid scale filtering is inherently processed in the kernel interpolation. We simulate lid-driven flow under transition and turbulent conditions as a benchmark. The simulation results show that the dynamic Vreman model produces consistent results with experimental and numerical research regarding Reynolds averaged physical quantities and flow structure. Spectral analysis also confirms that it is possible to analyze turbulent eddies with a smaller length scale using the dynamic Vreman model with the same particle size.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.7
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• pp.665-670
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• 2010

The effect of a particle's spin is investigated numerically by taking into account the effect of lift forces originating due to difference between the rotations of a particle and of a fluid, such as the Saffman and Magnus lift forces. These lift forces have been ignored in many previous studies on particle-laden turbulence. The trajectory of the particles can be changed by the lift forces, resulting in a significant modification of the stochastic characteristics of heavy particles. Probability density functions and autocorrelations are evaluated from the velocity of solid particle, acceleration of solid particles, and acceleration of fluid at the position of solid particle. Changes in velocity statistics are negligible but statistics related with acceleration are affected by the rotation of particle. When a laden particle encounters coherent structures during its motion, the particle's rotation might significantly affects the motion due to intermittently large fluid acceleration near the coherent structures.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.11
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• pp.824-831
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• 2008

We present a continuous size-dependent particle separator using a negative dielectrophoretic (DEP) virtual pillar array. Two major problems in the previous size-dependent particle separators include the particle clogging in the mechanical sieving structures and the fixed range of separable particle sizes. The present particle separator uses the virtual pillar array generated by negative DEP force instead of the mechanical pillar array, thus eliminating the clogging problems. It is also possible to adjust the size of separable particles since the size of virtual pillars is a function of a particle diameter and applied voltage. At an applied voltage of 500 kHz $10\;V_{rms}$ (root mean sqaure voltage) sinusidal wave and a flow rate of $0.40\;{\mu}l\;min^{-1}$, we separate $5.7\;{\mu}m$-, $8.0\;{\mu}m$-, $10.5\;{\mu}m$-, and $11.9\;{\mu}m$-diameter polystyrene (PS) beads with separation purity of 95%, 92%, 50%, and 63%, respectively. The $10.5\;{\mu}m$- and $11.9\;{\mu}m$-diameter PS beads have relatively low separation purity of 50% and 63%. However, at an applied voltage of $8\;V_{rms}$, we separate $11.9\;{\mu}m$-diameter PS beads with separation purity over 99%. Therefore, the present particle separator achieves clog-free size-dependent particle separation, which is capable of size tuning of separable particles.

• Journal of the Korean Ceramic Society
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• v.15 no.4
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• pp.193-198
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• 1978

Test-bricks were prepared from an artifically graded Ham Kang sand and a commercial CaO and autoclaved for 6 hours at $16 kg/cm^2$ pressure $(203^{\circ}C)$. Bricks were tested for compressive strength, free lime, saluble silica and amount of water absorption. Physical properties of bricks were very much depended on the size distribution of sand particle and the amount of soluble silica in bricks.

• Computers and Concrete
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• v.16 no.6
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• pp.933-961
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• 2015

Damage by high-speed impact fracture is a dominant mode of failure in several applications of concrete structures. Numerical modelling can play a crucial role in understanding and predicting complex fracture processes. The commonly used mesh-based Finite Element Method has difficulties in accurately modelling the high deformation and disintegration associated with fracture, as this often distorts the mesh. Even with careful re-meshing FEM often fails to handle extreme deformations and results in poor accuracy. Moreover, simulating the mechanism of fragmentation requires detachment of elements along their boundaries, and this needs a fine mesh to allow the natural propagation of damage/cracks. Smoothed Particle Hydrodynamics (SPH) is an alternative particle based (mesh-less) Lagrangian method that is particularly suitable for analysing fracture because of its capability to model large deformation and to track free surfaces generated due to fracturing. Here we demonstrate the capabilities of SPH for predicting brittle fracture by studying a slender concrete structure (column) under the impact of a high-speed projectile. To explore the effect of the projectile material behaviour on the fracture process, the projectile is assumed to be either perfectly-elastic or elastoplastic in two separate cases. The transient stress field and the resulting evolution of damage under impact are investigated. The nature of the collision and the constitutive behaviour are found to considerably affect the fracture process for the structure including the crack propagation rates, and the size and motion of the fragments. The progress of fracture is tracked by measuring the average damage level of the structure and the extent of energy dissipation, which depend strongly on the type of collision. The effect of fracture property (failure strain) of the concrete due to its various compositions is found to have a profound effect on the damage and fragmentation pattern of the structure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.10
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• pp.1408-1416
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• 2001

Mean flow fields in the near wake of a square cylinder have been studied experimentally using a Particle Image Velocimetry (PIV). Ensemble-averaged velocity fields are successfully measured fur the square cylinder wake including the reverse flow region which arises many difficulties in accurate measurement by using conventional techniques, Experiments are performed at two free stream velocities of U$\_$$\infty$/ = 1.27m/s and 3.03m/s. The corresponding Reynolds numbers based on the free-stream velocity and cylinder diameter are 1600 and 3900, respectively. The intensity of free-stream turbulence is less than 1%, the blockage ratio (D/H) is 6.6% and the aspect ratio (W/D) is 40. The effect of Reynolds number on the near wake of a square cylinder has been investigated by the global mean velocity and instantaneous velocity fields. The most striking feature is that the length of the recirculating region increases with increasing Reynolds number, which turns out totally reverse trend compared with those observed in the circular cylinder wake at the same range of Reynolds number. Fer the case of higher Reynolds number, the mean velocity data agree well with those of relevant existing data obtained at much higher Reynolds numbers, which reflects the general aspect of sharp-edged bluff body wake.

• Polymer(Korea)
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• v.28 no.6
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• pp.524-530
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• 2004

Polystyrene particles (PS) with poly(ethylene glycol) units on surface were formed by an emulsifier-free emulsion polymerization using styrene, poly(ethylene glycol) methacrylate (PEG-MMA) or poly(ethylene glycol) dimethacrylate (PEG-diMMA) at pH 7, and followed by freeze-drying to give the corresponding powders. The structures of PS particles were confirmed by FT-IR spectroscopy, and the particle size and distribution the PS particle were observed by scanning electron microscopy and particle analyzer. Monodisperse polymer particles were obtained at a concentration of PEG-MMA 2∼5 mol% or PEG-diMMA 1 mol% relative to styrene. The highest zeta potential of polymer surface was measured to be 183 mV at a polymer of PEG-MMA 5 mol%, which was measured in dielectric medium by means of ELS-8000 dynamic light scattering.

• YAKHAK HOEJI
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• v.40 no.5
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• pp.522-531
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• 1996

5-fluorouracil(5-FU) derivatives synthesized with four N-acyloxycarbonyl group such as 1-(N-t-butyloxycarbonyl)glycyloxymethyl-5-FU(BGFU), 1-(N-t-butyloxycarbonyl)leucyloxymethy l-5-FU(BLFU), 1-(N-t-carbobenzyloxymethyl)glycyoxymethyl-5-FU(CGFU) and 1-(N-t-carbobenzyloxymethyl)leucyloxymethyl-5-FU(CLFU) were entrapped into liposomes with different lipid compositions. The entrapment efficiency and release rate of drugs from each liposomes were evaluated. The particle size of liposomes, cytotoxicity and stability of drug-entrapped in liposomes were evaluated. The entrapment efficiency in 5-FU derivatives liposomes was dependent on the lipophilicity of N-acyloxymethyl derivatives. The drug entrapment efficiency also increased on the content of lipid increased up to 200mcmol of lipid per milliliter of liposomal solution. However, inclusion of additives such as cholesterol, dicetylphosphate and stearylamine decreased the entrapment efficiency. The mean particle size and size distribution were varied with lipid compositions and lipophilicity of prodrugs. The release rates of drugs from liposomes were not affected by additives, but those of BGFU and CGFU entrapped in liposomes with cholesterol decreased. Cytotoxicity of BLFU and CLFU entrapped in liposomes decreased by 3~5 fold compared with those of free two prodrugs. Liposome-entrapped 5-FU prodrugs were more stable either at pH 7.4 or in human plasma. Especially, 5-FU prodrugs entrapped in liposome with dipalmitoylphosphatidylcholine(DMPC) was the most stable in human plasma. Compared with free BLFU, BLFU entrapped in DMPC liposome showed a superior antitumor activity at all doses used. In contrast, CLFU entapped in liposomes were more toxic than free prodrug.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10c
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• pp.151-156
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• 1998

Concrete structures is appeared the shrinkage after being harden of the hydration effect of cement. To overcome this disadvantage, expansive additives are used. In our country, the most popular expansive additives are hauyne(CSA) or free lime(free-CaO) systems. These expansive additives are used to expansive cement mortar or concrete materials. In this study, we analyzed the expansive property mechanism about the hydration reaction of the free lime systems and in particular we convinced size distributions of the free lime size affect the expansion ratio with expansion ratio with experiments. We carried out the experiment for the expansive properties by using the soundness molds and with various the humidity and dry setting conditions. The hydration reactions of the free lime affect the reaction properties according to the relative humidity by laboratory experiments.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.6
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• pp.7-12
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• 2005

In order to analyze the microscopic spray characteristics of free spray in ultra high pressure region, the droplets size and velocity of free spray injected under atmosphere condition were measured by PDPA. As injection pressure became ultra high pressure, the droplets size was decreased continuously due to the increase of mutual reaction between droplets and air. But the decreasing rate became moderate. The velocity was increased until 250 MPa, and then decreased over that of injection pressure. It was seemed that the droplet size was similar in range of $280\~350\;MPa$, but increased in 414 MPa, even though injection pressure was increased. The microscopic spray characteristics of free spray got worse in 414 MPa.