Three-dimensional Discretization Research Articles

Three-Dimensional Modeling of Green Sand and Squeeze Molding Simulation

The green sand mold with good mold properties are useful to obtain the sound cast iron castings. For example, the green sand mold with high density and uniform for compacting characteristics would be required. Molding simulation is indispensable to make a good sand mold. In recent years, the package software was released from software vendors of foundry CAE, and the demand for molding simulation is increasing. Fundamental algorithms of the green sand particulate model and the three-dimensional Discrete Element Method (DEM) were proposed. They take into consideration of the particle size distribution and the cohesion of green sand particles.In this study, the squeeze molding simulation is carried out and we execute the re-development of this method under the current computer environment. They are tried to simulate the dynamic behavior during molding and to predict the mold properties after squeeze molding. The characteristics of green sand with cohesion are reflected in the particle model called Hard-Core/Soft-Shell. The compacting behavior of squeeze molding is traced numerically, and the visualization by a three-dimensional model and comparison of dynamics molding are carried out. From the simulation with several kinds of particle distribution, it becomes clear the relationship between the void fraction and the squeeze pressure during molding. The effect of particle size distribution on sand compacting behavior is also clarified. Furthermore, the three-dimensional display of green sand with particle size distribution is very effective in the post-processing.

A novel framework for compressed sensing based scalable video coding

Considering high throughput values as specified by modern video processing standards, Scalable Video Coding (SVC) systems intended for such standards are generally implemented by means of dedicated hardware. However, the high computational complexity associated with the current Compressed Sensing (CS) based video coding schemes makes their hardware realization considerably challenging. In this paper, we present a novel CS based SVC framework that is amenable to real-time VLSI implementation. At the encoder, after applying the Three-Dimensional Discrete Wavelet Transform (3-D DWT) on the input video frames, a novel Adaptive Measurement Scheme (AMS) in CS is introduced, which is applied on the high frequency sub-bands of the 3-D DWT frames. The proposed AMS along with 3-D DWT not only achieves scalability and better compression ratio, but also reduces the overall computational complexity of the system. We have also proposed an Enhanced Approximate Message Passing (EAMP) algorithm to reconstruct the high frequency sub-bands from the CS measurements at the decoder. The proposed EAMP procedure combines the benefits of Approximate Message Passing (AMP) and Iterative Hard Thresholding (IHT) algorithms thereby simultaneously achieving sparsity measurement trade-off and good reconstruction quality. We have carried out the detailed complexity analysis and simulations to demonstrate the superiority of the proposed framework over the existing schemes.

Analysis of experimentally assessed EVA foams with mixed solid-shell elements capable of very large strains

We analyze, both experimentally and numerically, two EVA foam specimens with densities ρ=120kg/m3 and ρ=220kg/m3. In the numerical analysis, we use our recent finite strain element formulations based on least-squares strains (in both solid-shells and full three-dimensional discretizations). The Ogden–Hill hyperelastic model is coupled with a one-term standard solid containing a Maxwell element. Compression experiments are performed to evaluate the Ogden–Hill properties for the two EVA foams. Viscous properties are obtained from interpolation of creep results reported by R. Verdejo. An exponential integration of the internal variables (which have the role of back-stresses) is proposed along with the complete description of the constitutive system. The classical analysis of the acoustic tensor is also performed for the measured properties. Four benchmark examples are introduced.

Finite-difference time-domain analysis of the vibration characteristics of building structures using a dimension-reduced model

In order to accurately predict the vibration characteristics of buildings, wave-based numerical methods are effective from the viewpoint of the modeling accuracy of the physical mechanism and the detailed geometries of the simulated field. However, because of the performance of current PCs, the prediction of real-scale problems remains difficult. In order to address such problems, we herein propose a vibration simulation method for a beam-plate structure using a dimension-reduced modeling method. The target structure is modeled as a composite structure consisting of two-dimensional plate elements and one-dimensional beam elements, which are coupled based on the implicit finite-difference approximation scheme. By applying such a low-dimensional element, a faster simulation that requires less memory, as compared with a three-dimensional discretization scheme, is made available. To validate the method, the vibration characteristics obtained by the proposed scheme are compared to the measured results for model-scale and full-scale structure. The comparison of the measurement and simulation results suggest that the proposed method can be used to accurately simulate a multilayered building structure.

Slender-body theory for transient heat conduction: theoretical basis, numerical implementation and case studies

Slender-body theory (SBT) for transient heat transfer from bodies whose lengths are much larger than their radius into a conductive medium is derived. SBT uses matched asymptotic expansions of inner and outer solutions. An analytical inner solution for heat transfer from a circular cross section is matched to an outer solution obtained using Green’s functions. An efficient numerical implementation is obtained based on a judicious choice of the discrete elements used to represent the body and implementation of the fast multipole method (FMM). The SBT requires a one-dimensional spatial discretization only along the axis of the body in contrast to the three-dimensional discretization for finite-element models. Two case studies, heat transfer from two parallel cylinders and heat transfer from a slinky-coil heat exchanger, are used to show the speed and accuracy of the SBT model and its ability to model interacting slender bodies of finite length and bodies with centreline curvature and internal advective heat flow.

THREE-DIMENSIONAL DISCRETE ELEMENT ANALYSIS OF RAILWAY BALLAST’S SHEAR PROCESS BASED ON PARTICLES’ REAL GEOMETRY

Ballast beds are made up of particles with diverse sizes and shapes. Particle shape plays a fairly important role in affecting ballast aggregate’s mechanical behaviors; however, conventional grading curves indicating particle unidirectional size distribution cannot describe ballast particle shape characteristics comprehensively. Computer-vision technology is applied to obtaining three orthogonal views of a ballast particle, then extracting outlines of these three views to compute particle shape characteristic parameters. Three dimensional discrete element numerical simulations of ballast aggregate are processed by a self-developed program using elements which are built based on a particle’s three orthogonal views and identical in shape characteristics to realistic ballast particles. The computer-vision based discrete element method is validated with predictions from discrete element simulations matching closely with laboratory direct shear test results. Ballast aggregate’s deformation features and micro-scale mechanical behaviors in direct shear tests are investigated in depth based on the validated discrete element method

Finite-difference time-domain analysis of the vibration characteristics of a beam-plate structure using a dimension-reduced model

In order to accurately predict the vibration characteristics of structure-borne sound transmission in buildings, wave-based numerical methods are effective from the viewpoint of the modeling accuracy of the physical mechanism and the detailed geometries of the simulated field. However, because of the performance of current PCs, the prediction of real-scale problems remains difficult. In order to address such problems, we herein propose a vibration simulation method for a beam-plate structure using a dimension-reduced modeling method. The target structure is modeled as a composite structure consisting of two-dimensional plate elements and one-dimensional beam elements, which are coupled based on the implicit finite-difference approximation scheme. By applying such a low-dimensional element, a faster simulation that requires less memory, as compared with a three-dimensional discretization scheme, is made available. Good agreement between the measured and simulated results for the vibration characteristics of acrylic beam-plate models indicates the validity of the proposed method.

Study of the internal mechanical response of an asphalt mixture by 3-D discrete element modeling

In this paper the viscoelastic behavior of asphalt mixture was investigated by employing a three-dimensional Discrete Element Method (DEM). The cylinder model was filled with cubic array of spheres with a specified radius, and was considered as a whole mixture with uniform contact properties for all the distinct elements. The dynamic modulus and phase angle from uniaxial complex modulus tests of the asphalt mixtures in the laboratory have been collected. A macro-scale Burger’s model was first established and the input parameters of Burger’s contact model were calibrated by fitting with the lab test data of the complex modulus of the asphalt mixture. The Burger’s contact model parameters are usually calibrated for each frequency. While in this research a constant set of Burger’s parameters has been calibrated and used for all the test frequencies, the calibration procedure and the reliability of which have been validated. The dynamic modulus of asphalt mixtures were predicted by conducting Discrete Element simulation under dynamic strain control loading. In order to reduce the calculation time, a method based on frequency–temperature superposition principle has been implemented. The ball density effect on the internal stress distribution of the asphalt mixture model has been studied when using this method. Furthermore, the internal stresses under dynamic loading have been studied. The agreement between the predicted and the laboratory test results of the complex modulus shows the reliability of DEM for capturing the viscoelastic properties of asphalt mixtures.

Numerical Simulation of Two Phase Change Materials Melting Process

Phase change thermal control technology has gained increasing focus as an emerging technology for the thermal control of spacecraft. This literature focused on melting process inside a latent heat energy storage filled with phase change material (PCM) by numerical simulation. A matrix-based enthalpy porosity theory in a three-dimensional finite volume discretization is simulated. The temperature distribution during the melting process of PCM Cerrolow-136 and CH3COONa·3H2O is obtained, based on which the thermal control function and energy storage capacity is compared. The results show that Cerrolow-136 has better performance. In different states of phase change, the temperature distribution of Cerrolow-136 is fairly uniform. Thermal control face's temperature of Cerrolow-136 is closer to phase transition temperature. In the same heat flux of 3000 W/m2, The whole process of thermal control temperature getting to 80°C for Cerrolow-136 is longer. Cerrolow-136, for its excellent characteristics, has potentially broad application in the fields of latent heat energy storage and space vehicle electronics.

Prediction of low-frequency structure-borne sound in concrete structures using the finite-difference time-domain method.

Due to limitations of computers, prediction of structure-borne sound remains difficult for large-scale problems. Herein a prediction method for low-frequency structure-borne sound transmissions on concrete structures using the finite-difference time-domain scheme is proposed. The target structure is modeled as a composition of multiple plate elements to reduce the dimensions of the simulated vibration field from three-dimensional discretization by solid elements to two-dimensional discretization. This scheme reduces both the calculation time and the amount of required memory. To validate the proposed method, the vibration characteristics using the numerical results of the proposed scheme are compared to those measured for a two-level concrete structure. Comparison of the measured and simulated results suggests that the proposed method can be used to simulate real-scale structures.

Rotational resistance and shear-induced anisotropy in granular media

This paper presents a micromechanical study on the behavior of granular materials under confined shear using a three-dimensional Discrete Element Method (DEM). We consider rotational resistance among spherical particles in the DEM code as an approximate way to account for the effect of particle shape. Under undrained shear, it is found rotational resistance may help to increase the shear strength of a granular system and to enhance its resistance to liquefaction. The evolution of internal structure and anisotropy in granular systems with different initial conditions depict a clear bimodal character which distinguishes two contact subnetworks. In the presence of rotational resistance, a good correlation is found between an analytical stress-force-fabric relation and the DEM results, in which the normal force anisotropy plays a dominant role. The unique properties of critical state and liquefaction state in relation to granular anisotropy are also explored and discussed.

Editorial: Special Issue on Stochastic Modelling of Reaction–Diffusion Processes in Biology

Editorial: Special Issue on Stochastic Modelling of Reaction–Diffusion Processes in Biology

106 RC構造物における固体伝搬音を対象としたFDTD解析(音響・構造の連成解析)

Due to limitations of computes, prediction of structure-borne sound remain difficult for large-scale problems. Herein a prediction method for low-frequency structure-borne sound transmissions on concrete structures using the finite-difference time-domain scheme is proposed. The target structure is modeled as a composition of multiple plate elements to reduce the dimensions of the simulated vibration field from three-dimensional discretization by solid elements to two-dimensional discretization. This scheme reduces both the calculation time and the amount of required memory. To validate the proposed method, the vibration characteristics using the numerical results of the proposed scheme are compared to those measured for a two-level concrete structure. Comparison of the measured and simulated results suggests that the proposed method can be used to simulate real-scale structures.

A study into extraction of geothermal energy from tailings ponds

Assessing the performance of ground-coupled heat exchangers (GCHE) of closed-loop geothermal systems installed in tailings ponds is studied. A heat transfer model is constructed, taking into account heat conduction as well as groundwater advection. A three-dimensional finite volume discretisation method over a structured mesh with variable grid size is used to solve the governing equations. The performance of a GCHE system installed in tailings ponds is assessed based on the rate of energy extraction and the outlet fluid temperature. The geothermal capacity of mine tailings ponds and its sustainable rate of heat extraction are estimated. Effects of tube network configuration and horizontal and vertical underground advection on the performance of the system are investigated. It is found that two-dimensional heat transfer models may lead to over-designed systems and the effect of advection cannot be neglected in highly pervious tailings.

Efficient parallelization of geostatistical inversion using the quasi-linear approach

Hydraulic conductivity is a key parameter for the simulation of groundwater flow and transport. Typically, it is highly variable in space and difficult to determine by direct methods. The most common approach is to infer hydraulic-conductivity values from measurements of dependent quantities, such as hydraulic head and concentration. In geostatistical inversion, the parameters are estimated as continuous, spatially auto-correlated fields, the most likely values of which are obtained by conditioning on the indirect data. In order to identify small-scaled features, a fine three-dimensional discretization of the domain is needed. This leads to high computational demands in the solution of the forward problem and the calculation of sensitivities. In realistic three-dimensional settings with many measurements parallel computing becomes mandatory.In the present study, we investigate how parallelization of the quasi-linear geostatistical approach of inversion can be made most efficient. We suggest a two-level approach of parallelization, in which the computational domain is subdivided and the evaluation of sensitivities is also parallelized. We analyze how these two levels of parallelization should be balanced to optimally exploit a given number of computing nodes.

Polymeric particle dampers under steady-state vertical vibrations

Numerical and experimental studies are made of the power dissipated by a granular medium as it undergoes sinusoidal vibrations in the same direction as gravity. The granular medium consists of spherical elastomeric particles that partially fill a box with rectangular cross section whose walls are made of thick blocks of Perspex. Simulations are obtained using a three-dimensional Discrete Element Method code. In order to find input parameters for use in the simulation studies, a specially designed test rig is used to measure the loss factor and dynamic stiffness of the particles. The power dissipation of the granular medium obtained from simulation is compared with that from a physical experiment and found to be in good agreement. The sensitivity of power dissipation to amplitude, frequency of excitation and friction coefficient is investigated.

Three-Dimensional Discrete Element Simulations of Round Hopper in Thermal Power Plant

Three-dimensional discrete element process was adopted to simulate the discharge of hopper and the change of flow pattern of particles and dynamic lateral pressure of walls were analyzed in process of discharge. The results showed that three-dimensional discrete element simulation can obtain much more information. Discrete element method can simulate dynamic discharge problems. The dynamic force of vertical direction is much greater than dynamic force of horizontal direction in the process of discharge in the cone section of hopper. When the stored materials in hopper generate arches in the course of discharge, the inertia of floating stored materials will make the pressure of particles above arches hoist, so the walls of hopper may crack.

Highly Efficient, Exact Quadratures for Three-Dimensional Discrete Ordinates Transport Calculations

Since the introduction of the angular segmentation or Sn method some 60 years ago, there have been many advances in the understanding of the method and many improvements to it. Indeed, the Sn method is now a widely used technique for deterministic solution of the transport equation. For three-dimensional (3-D) calculations, the method relies on numerical quadratures for the sphere, which integrate certain subspaces of spherical harmonics. The construction of such quadratures can be difficult. Here we report the development of new, highly efficient quadratures for the sphere that are invariant under the icosahedral rotation group. We compare the efficiency of the standard level-symmetric quadratures commonly used for 3-D Sn calculations and see that the new quadratures can be as much as 70% more efficient than the standard quadratures.

Parallel three-dimensional full-time domain applied to photonic structures

A new vector simulator to analyse time-domain electromagnetic field propagation in optical structures is thoroughly presented. The formulation is based on a three-dimensional discretisation by the finite element method. The linear system of equations is solved by parallel processing, allowing the analysis of hundreds of thousands unknowns.

Single particle fragmentation in ultrasound assisted impact comminution

Impact fragmentation is the underlying principle of comminution milling of dry, bulk solids. Unfortunately the outcome of the fragmentation process is more or less determined by the dimensionality of the impactor and its impact velocity. Since fragmentation is dominated by interfering shock waves, manipulating traveling shock waves and adding energy to the system during its fragmentation could be a promising approach to manipulate fragment mass distributions and energy input. In a former study we explored mechanisms in impact fragmentation of spheres, using a three-dimensional Discrete Element Model (DEM) Carmona et al. (Phys Rev E 77:051302, 2008). This work is focused on studying how single spheres fragment when impacted on a planar vibrating target.