• Journal of the Korea Computer Graphics Society
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• v.25 no.1
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• pp.13-22
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• 2019

In this paper, we propose a new method to improve the details of the fluid surface by removing liquid sheets that are over-preserved in particle-based water simulation. A variety of anisotropic approaches have been proposed to address the surface noise problem, one of the chronic problems in particle-based fluid simulation. However, a method of stably expressing the preservation and breakup of the liquid sheet has not been proposed. We propose a new framework that can dynamically add and remove the water particles based on anisotropic kernel and density to simultaneously represent two features of liquid sheet preservation and breakup in particle-based fluid simulations. The proposed technique well represented the characteristics of a fluid sheet that was breakup by removing the excessively preserved liquid sheet in a particle-based fluid simulation approach. As a result, the quality of the liquid sheet was improved without noise.

• Journal of Ocean Engineering and Technology
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• v.31 no.6
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• pp.388-396
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• 2017

A Lagrangian approach based computational fluid dynamics (CFD) was used to simulate large and/or sharp deformations and fragmentations of interfaces, including free surfaces, through tracing each particle with physical quantities. According to the concept of the particle-based CFD method, it is possible to apply it to both fluid particles and solid particles such as sand, gravel, and rock. However, the presence of more than two different phases in the same domain can make it complicated to calculate the interaction between different phases. In order to solve multiphase problems, particle interaction models for multiphase problems, including surface tension, buoyancy-correction, and interface boundary condition models, were newly adopted into the moving particle semi-implicit (MPS) method. The newly developed MPS method was used to simulate a typical validation problem involving dam breaking. Because the soil and other particles, excluding the water, may have different viscosities, various viscosity coefficients were applied in the simulations for validation. The newly developed and validated MPS method was used to simulate the mobile beds induced by broken dam flows. The effects of the viscosity on soil particles were also investigated.

• International Journal of Highway Engineering
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• v.15 no.5
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• pp.31-45
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• 2013

PURPOSES : Determination of particle packing model variables that can be used for formulation of new DEM based particle packing model by examining existing particle packing models METHODS : Existing particle packing models are thoroughly examined by analytical reformulation and sensitivity analysis in order to set up DEM based new particle packing model and to determine its variables. All model equations considered in this examination are represented with consistent expressions and are compared to each others to find mathematical and conceptual similarity in expressions. RESULTS : From the examination of existing models, it is observed that the models are very similar in their shapes although the derivation of the models may be different. As well, it is observed that variables used in some existing models are comprehensive enough to estimate particle packing but not applicable to DEM simulation. CONCLUSIONS : A set of variables that can be used in DEM based particle packing model is determined.

• Journal of Ocean Engineering and Technology
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• v.28 no.2
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• pp.93-101
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• 2014

In general, particle simulation methods such as the MPS(Moving Particle Simulation) or SPH(Smoothed Particle Hydrodynamics) methods have some serious drawbacks for pressure solutions. The pressure field shows spurious high fluctuations both temporally and spatially. It is well known that pressure fluctuation primarily occurs because of the numerical approximation of the partial differential operators. The MPS and SPH methods employ a pre-defined kernel function in the approximation of the gradient and Laplacian operators. Because this kernel function is constructed artificially, an accurate solution cannot be guaranteed, especially when the distribution of particles is irregular. In this paper, we propose a particle simulation method based on the moving least-square technique for solving the partial differential operators using a Taylor-series expansion. The developed method was applied to the hydro-static pressure and dam-broken problems to validate it.

• The Journal of Korean Institute of Next Generation Computing
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• v.15 no.4
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• pp.51-61
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• 2019

In this paper, we have implemented soil simulation using fluid simulation technology. A widely used NVIDIA FleX was used to represent the soil generated by excavation work. FleX is a particle-based physics simulation library that combines SPH (Smoothed-particle hydrodynamics) and Position Based Dynamics techniques. However, since the soil has not only fluid properties but also non-fluid properties, it is difficult to simulate with the functions provided by conventional FleX. In this study, we added a technique to simulate non-fluid behavior using existing Flex. This can lead to effective results improvement at low cost.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.559-564
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• 2003

Recently, particle filters have attracted attentions for nonlinear state estimation. They evaluate a posterior probability distribution of the state variable based on observations in simulation using so-called importance sampling. However, degeneracy phenomena in the importance weights deteriorate the filter performance. A new filter, Evolution Strategies Based Particle Filter, is proposed to circumvent this difficulty and to improve the performance. Numerical simulation results illustrate the applicability of the proposed idea.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1765-1770
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• 2005

Recently, particle filters have attracted attentions for nonlinear state estimation. In this approaches, a posterior probability distribution of the state variable is evaluated based on observations in simulation using so-called importance sampling. We proposed a new filter, Evolution Strategies based particle (ESP) filter to circumvent degeneracy phenomena in the importance weights, which deteriorates the filter performance, and apply it to simultaneous state and parameter estimation of nonlinear state space models. Results of numerical simulation studies illustrate the applicability of this approach.

• Journal of the Korea Computer Graphics Society
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• v.14 no.4
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• pp.1-5
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• 2008

In this paper, we propose an efficient technique for improving the grid based fluid simulation by sub-grid visuals. The detailed turbulency generated efficiently by Vortex Particle Method are blended with the flow fields coming from the traditional incompressible Navier-Stokes solver. The algorithm enables large- and small- scale detail to be edited separately.

• Journal of the Korean Society of Visualization
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• v.15 no.1
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• pp.32-40
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• 2017

Interaction between fluid and a rigid object is frequently observed in everyday life. However, it is difficult to simulate their interaction as the medium and the object have different representations. One of the challenging issues arises especially in handling deformation of the object visually as well as rendering haptic feedback. In this paper, we propose a real-time simulation technique for multimodal interaction between particle-based fluids and soluble solids. We have developed the dissolution behavior model of solids, which is discretized based on the idea of smoothed particle hydrodynamics, and the changes in physical properties accompanying dissolution is immediately reflected to the object. The user is allowed to intervene in the simulation environment anytime by manipulating the solid object, where both visual and haptic feedback are delivered to the user on the fly. For immersive visualization, we also adopt the screen space fluid rendering technique which can balance realism and performance.

• 한국전산유체공학회:학술대회논문집
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• 2006.05a
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• pp.27-34
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• 2006

In this paper, a recently proposed parallel hybrid particle-continuum (DSMC-NS) scheme employing 3D unstructured grid for solving steady-state gas flows involving continuum and rarefied regions is described [1]. Substitution of a density-based NS solver to a pressure-based one that greatly enhances the capability of the proposed hybrid scheme and several practical experiences of implementation learned from the development and verifications are highlighted. At the end, we present some simulation results of a realistic RCS nozzle plume, which is considered very challenging using either a continuum or particle solver alone, to demonstrate the capability of the proposed hybrid DSMC-NS method.