• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.199-206
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• 2003

Particle-size distribution in soils is one of the most fundamental physical properties of soils. One of the latest developments in the study of particle-size distributions has focused on the use of fractal theories. In this study, the fragmentation fractals were used for determining the characteristics of the particle-size distribution curve. It was shown that the mass-size distribution method was more practical than the cumulative number-size distribution method. From the co-relation between fractal dimensions($D_{tot}$) and the coefficient of uniformity($C_{u}$), there was a sharp increase in fractal dimensions for $C_{u}$<4, but fractal dimension converged the single value for $D_{u}$$\geq$6. Fractal dimensions were affected by small sized particles for $C_{c}$$\geq$3 and large sized particles for $C_{c}$/<3. As a result of the analysis of the influence of the effective size($D_{10}$), it was observed that the changes of $D_{tot}$/ were nominal beyond the effective size.

• Bulletin of the Korean Mathematical Society
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• v.42 no.4
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• pp.855-867
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• 2005

Shattering or disintegration of mass is a well known phenomenon in fragmentation processes first introduced by Kol­mogorov and Filippop and extensively studied by many physicists. Though the mass is conserved in each break-up, the total mass decreases in finite time. We investigate this phenomenon in the n particle system. In this system, shattering can be interpreted such that, in uniformly bounded time on n, order n of mass is located in order o(n) of clusters. It turns out that the tagged particle processes associated with the systems are useful tools to analyze the phenomenon. For the newly defined stochastic shattering based on the above ideas, we derive far sharper conditions of fragmentation kernels which guarantee the occurrence of such a phenomenon than our previous work [9].

• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.193-204
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• 1999

Particle crushing is an important and essential factor in interpreting the strength and deformation properties of granular materials in the case of geotechnical problems related to soil crushability. As a recent field problem, the exploitation of offshore oil reserves in tropical and sub-tropical coastal shelf areas has shown that the behaviour of soils containing carbonates is markedly different from predominantly silica sands. In this study, as a first step in making a mechanical framework of granular materials incorporating the soil crushability, single particle fragmentation tests were carried out on four different types of sands in order to clarify the characteristics of the single particle fragmentation strength as related to soil crushability. The single particle strength was considered with the influence of the particle shapes, the amount of mineral components and the particle sizes. The soil particle strength corresponding $D_{50}$ of soil distribution curve has shown the lower value, the more the carbonate component and the more angular the particle shape.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.111-114
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• 2012

The ignition behavior of single coal particles of five kindes of coal with different ranks (low volatile bituminous, low volatile sub-bituminous, high volatile bituminous, lignite) with particle size of $150-200{\mu}m$ was investigated at high heating rate condition. Particles were injected into a laminar flow reactor and the ignition behavior was observed with high speed cinematography. Sub-bituminous were observed to ignite homogeneously; however, low volatile bituminous coal and lignite undergo fragmentation prior to igntion. The observation was analyzed with previous work.

• Nuclear Engineering and Technology
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• v.56 no.1
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• pp.283-291
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• 2024

Sodium cooled Fast Reactors (SFR) are built with several engineered safety features and hence a severe accident such as a core melt accident is hypothetical with a probability of <10^-6/ry. However, in case of such accidents, the mixture of the molten fuel and structural materials interacts with sodium. This phenomenon is known as Molten Fuel Coolant Interaction (MFCI) and results in fragmentation of the melt due to various instabilities. The fragmented particles settle as a debris bed on the core catcher at the bottom of the reactor vessel, and continue to generate decay heat. Characteristics of the debris particles play a vital role in heat transfer from the bed and need thorough investigation. The size, shape, and physical state of the debris depend on the associated fragmentation mechanism, superheating of the melt, and sodium temperature. Experiments have been conducted by releasing simulated corium, a molten mixture of alumina and iron generated by the aluminothermy process at ~2400 ℃ into liquid sodium, to study the fragmentation phenomena. After the experiment, the fragmented debris was retrieved and the particle size distribution was determined by sieve analysis. The debris was subjected to microscopic investigation for obtaining morphological characteristics. Based on the characteristics of debris, an attempt has been made to assess of fragmentation mechanism of simulated corium in sodium.

• Journal of the Korean Mathematical Society
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• v.39 no.4
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• pp.543-558
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• 2002

We investigate the fragmentation process developed by Kolmogorov and Filippov, which has been studied extensively by many physicists (independently for some time). One of the most interesting phenomena is the shattering (or disintegration of mass) transition which is considered a counterpart of the well known gelation phenomenon in the coagulation process. Though no masses are subtracted from the system during the break-up process, the total mass decreases in finite time. The occurrence of shattering transition is explained as due to the decomposition of the mass into an infinite number of particles of zero mass. It is known only that shattering phenomena occur for some special types of break-up rates. In this paper, by considering the n-particle system of stochastic fragmentation processes, we find general conditions of the rates which guarantee the occurrence of the shattering transition.

• Structural Engineering and Mechanics
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• v.82 no.6
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• pp.713-724
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• 2022

Effects of coal tensile strength and plow configuration on the coal fragmentation process was modeled by two-dimensional particles flow code (PFC2D). Three tensile strength values, 0.5, 1,5 and 3.5 MPa were considered in this numerical study. The cutters of plow penetrated in the coal for 4 mm at a rate of 0.016 m/s. According to the PFC manual, the local damping factor was 0.7. Three failure mechanism of coal during the fragmentation process by plow were modelled. The coal material beneath the cutters showed the elastic, plastic and fracturing behaviors in this analysis. In all the models, the plastic zone was fractured and some micro-cracks were induced but the elastic zone remained undamaged. It was observed that the tensile strength affected the failure mechanism of coal significantly and as it increased the extent of the fractured zone underneath the plow cutter decreased during the fragmentation process.

• 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.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.211-213
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• 2002

The purpose of this work is acquiring some parameters of therapeutic heavy ion beams after penetrating a thick target. The experiments were performed using a pencil-like $\^$12/C beam of about 3 mm in diameter from NIRS-HIMAC, and the data were taken at several points of the target thickness for $\^$12/C beam of 290 MeV/u and 400 MeV/u. By the simultaneous measurements using some detectors, the atomic number of each fragment particle was identified, and the beam profile, the dose distribution and the LET spectrum for each element were derived.

• Journal of the Korean Geotechnical Society
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• v.20 no.9
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• pp.47-56
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• 2004

A new fragmentation model, called the GRS (the generation model of weathered residual soils) model, was proposed in this study, This model could identify the formation of a residual soil. This model is based on the phenomena that as the soil was weathered more highly, soil particles were smaller and pores were more expanded simultaneously. The possibility of fragmentation, $P_F,$ which was based on the fractal theory, was introduced in this model. There were some fundamental notions in the GRS model that soil particles were generated as the rock is fragmented, and the fragmentation of the rock was performed step by step. The $P_F,$ of the rock was not constant at each fragmentation steps. As a result of application on the GRS model, there were more residue where $P_{Fi}s$ were small at any particle size. There was a S-shape of PSD curve at the concave shape of $P_{Fi},$ and the PSD curve goes to a gaped graded curve at the convex shape of $P_{Fi}.$ The shape of PSD curve was concave in the case of small $P_{Fi}s.$ The value of $P_{Fi}$ increased with the coefficient of uniformity $(C_u)$ and the fragmentation fractal dimension $(D_r),$ but had no relation with the coefficient of gradation $(C_C)$.