Rimantas Kačianauskas

Parallel discrete element simulation of poly-dispersed granular material

The paper presents parallel 3D DEM simulation of poly-dispersed material described by the normal size distribution. Static domain decomposition and message passing inter-processor communication have been implemented in the DEM code. A novel algorithm for moving particles that exchange processors has been incorporated in the domain decomposition framework. Parallel performance of the developed algorithm and software has been investigated by a series of benchmark tests conducting tri-axial compaction of material with different numbers of particles, heterogeneity ratios and compaction durations. The speed-up equal to 8.81 has been obtained on 10 processors of the distributed memory PC cluster. It has been shown that a drastic increase of computational expenses of simulation for the poly-dispersed material in terms of CPU time is associated with the increase of its heterogeneity. A contribution of the temporal evolution of microscopic behaviour has also been illustrated.

Discrete element method and its application to the analysis of penetration into granular media

Abstract Application of discrete element method (DEM) to keel penetration in granular media is investigated. The basic relations for visco‐elastic granular media composed of spherical particles are presented, together with 5th order Gear predictor‐corrector scheme for time‐integration. The background version of DEM and numerical time integration algorithm are developed and implemented into DEMMAT code. The implementation of time‐integration algorithm is verified by simple tests concerning particle‐particle, particle‐wall interactions, for which analytical expressions exist. By limiting the size of the media domain, the three‐dimensional problem is reduced to particular case presented as two‐dimensional domain of spherical particles. The variation of keel reaction and distribution of the particle forces due to different material properties are investigated.

Investigation of performance of programming approaches and languages used for numerical simulation of granular material by the discrete element method

Abstract Performance of programming approaches and languages used for the development of software codes for numerical simulation of granular material dynamics by the discrete element method (DEM) is investigated. The granular material considered represents a space filled with discrete spherical visco-elastic particles, and the behaviour of material under imposed conditions is simulated using the DEM. The object-oriented programming approach (implemented via C++) was compared with the procedural approach (using FORTRAN 90 and OBJECT PASCAL) in order to test their efficiency. The identical neighbour-searching algorithm, contact forces model and time integration method were implemented in all versions of codes. Two identical representative examples of the dynamic behaviour of granular material on a personal computer (compatible with IBM PC) were solved. The results show that software based on procedural approach runs faster in compare with software based on OOP, and software developed by FORTRAN 90 runs faster in compare with software developed by OBJECT PASCAL.

COMPACTING OF PARTICLES FOR BIAXIAL COMPRESSION TEST BY THE DISCRETE ELEMENT METHOD

Numerical simulation of the compacting of particles for the biaxial compression test using the discrete element method is presented. Compacting is considered as the first independent step required for a proper simulation of the entire compression process. In terms of the continuum approach, compacting is regarded as generation of the initial conditions. Three different compacting scenarios with differently manipulated loading history on the boundaries, namely, compacting by using the moving rigid walls, by the static pressure using flexible membranes as well as combining the above two methods are considered. Discrete element methodology and basic relations, as well as formulation of the compacting problem and computational aspects of compacting are presented in detail. Each of the scenarios is illustrated by the numerical results. It has been found that the combined compacting scenario yields the required initial conditions exhibiting the best physically adjustable state of particles.

Maize grain shape approaches for DEM modelling

Display Omitted The shape of a grain of maize was approached using the multi-sphere method.Models with single-spherical particles and with rolling friction were also used.Results from two DEM software codes were compared.Recommendations on the shape approach for DEM modelling were provided. Granular materials are commonly stored in silos, and usually presented in a wide range of shapes and sizes. To understand its behaviour simulations based on the Discrete Element Method (DEM) are becoming widely used nowadays. The strength of this method lies in its ability to capture the discrete nature of particle assemblies in comparison with other methods that are based in continuum approaches. However, one of the challenges that still need to be tackled is the approximation of the shape of real particles in order to achieve more realistic simulations. In this paper, the shape of a grain of maize has been approached using the so-called multi-sphere method, and also as single-spherical particles with rolling friction. Furthermore, as it is already known that the use of different software codes can show differences, although good agreement in general, results from two DEM software codes were compared.

Structural Mechanics of Railguns in the Case of Discrete Supports

In this paper, numerical calculations concerning the dynamic behavior of a railgun are presented. At the first stage, the structural problem can be decoupled from electromagnetic phenomena as well as from the local projectile behavior. The magnetic pressure repelling the rails from each other and expanding with the speed of the projectile serves as a boundary condition for purely mechanical calculations. The particularity of the investigation is represented by the type of railgun housing. For some years, the ISL has been using laboratory housings of an open design allowing, for instance, to take flash radiographs during launch. The repelling forces are mainly taken by discrete supports in the form of steel bolts. These bolts are connected to bars made of glass fiber-reinforced plastics, while the rails are mounted on these bars. A 2-D finite-element model of a complex housing was developed in this paper. Bars, including rails, are described by plane-stress elements, while bolts, playing the role of discrete elastic supports, are presented by truss elements. The model is implemented using the ANSYS code. Deformation properties of the rail section and elastic supports are examined by considering a static solution, assuming constant loading. Differences between 2-D and conventional beam models being of importance for this kind of problem are briefly discussed. Transient analysis was performed for a set of constant loading velocities (600-1600 m/s) and for the experimentally derived transient-loading profile. The latter was obtained in the railgun experiments performed using the ISL-railgun EMA3 with a caliber of 15times30 mm2 and typical muzzle velocities up to 1600 m/s as well as peak currents of about 600 kA.

Simulation of Normal Impact of Ultrafine Silica Particle on Substrate

The normal impact of an ultrafine spherical silica particle with radius R = 0.6 μm on the plane surface substrate was simulated numerically by applying DEM. The variation of the coefficient of restitution for a wide range of impact velocities up to 30 m/s was investigated. The interaction model comprising both elastic and elastic-plastic contact with short-range van der Waals attraction was applied to capture the entire approach-rebound path. The study aims to evaluate the influence of various dissipation mechanisms during elastic and elastic-plastic contact with adhesion, with emphasis is placed on the role of the prescribed absorbed energy during rebound. The above approach was implemented into the discrete element method code DEMMAT. The numerical results are compared with the available solutions and employed for reasonable explanation of the impact experiment conducted by Poppe, Blum, and Henning (2000a). It is shown that experimentally observed scattering of the coefficient of restitution may be enveloped by curves related to various dissipation mechanisms.

A monument of historical heritage ‐ Vilnius archcathedral belfry: The dynamic investigation

Abstract The dynamic investigation of a monument of historical heritage ‐ Vilnius Archcathedral Belfry ‐ is investigated. In 2002 six new bells were installed in Vilnius Archcathedral Belfry according to a modern location scheme and their ringing order was changed. Evidently, they caused different dynamic loads which were not completely controlled and their effect on historical buildings of the Old Town of Vilnius could hardly be predictable. The paper presents the results of dynamic investigation of the Archcathedral Belfry, subject to the influence of the bell system operation. The dynamic impact was evaluated by measuring the acceleration history under the conditions, when different combinations of bells were used. A contribution of the dynamic effects was assessed in terms of response spectra. The obtained results have been thoroughly analysed and the appropriate findings and conclusions provided.

Manganite Sensor for Measurements of Magnetic Field Disturbances of Pulsed Actuators

Magnetic field sensors based on polycrystalline La0.83Sr0.17MnO3 films were used to measure the magnetic field distribution and disturbances during the operation of an electromagnetic launcher. Hollow cylinders made from dural aluminum and iron were used as propelled objects inside the solenoidal coil. The obtained results revealed the ability of manganite sensors to rapidly measure changing high magnetic fields of arbitrary waveforms.

Computation and visualization of discrete particle systems on gLite-based grid

Three-dimensional simulation of discrete particle systems is performed by the discrete element method (DEM) software on the gLite-based BalticGrid infrastructure. The performance of a parallel algorithm for particles exchanging processors is investigated by using a number of benchmarks. Polydispersed particle systems are visualized by a novel grid e-service VizLitG designed for convenient access and interactive visualization of remote data files located on the grid. Partial dataset transfer from the storage element is implemented in the visualization e-service. The efficiency tests of VizLitG are performed on the datasets of different sizes. Two granular problems associated with triaxial compaction and hopper discharge are solved.