Investigation of rice grain flow by multi-sphere particle model with rolling resistance

A multi-sphere (MS) model combined with rolling friction was considered for modelling elongated particles of irregular shape. The performance of the model was investigated by numerical simulations of the rice grain flow. A set of 5000 poly-dispersed milled rice grains were selected for the investigation purposes. They were characterised by a constant aspect ratio 3.5, while their maximum size was ranging from 6.4 to 7.3 mm. Filling and discharge flow as well as piling were simulated numerically with and without rolling resistance of particles. Simulation results were validated on the basis of experimental results. Good agreement of numerical and experimental results in terms of the discharge time and repose angle of the pile was reached simultaneously, when rolling resistance was introduced

Investigation of symmetric non-spherical particle shapes by applying low-resolution spherical harmonics

The issue of mathematical modelling of non-spherical shapes of particles is considered. Thus, application of the spherical harmonics (SH) technique in modelling the simplest symmetric star-shaped particles is demonstrated by applying low-resolution functions. The investigation was restricted to a circular cylinder and a rectangular parallelepiped, geometrically primitive, but widespread oblate industrial shapes. The modelling quality was studied by considering selected error norms and the most important integral characteristics of a particle geometry, including the surface area and volume. The presented results discovered new features of the spherical harmonic technique and enhanced understanding of their applicability to describe non-spherical shapes

Investigation of armature-rail interaction in linear electromagnetic launcher

The behavior of the electromagnetic (EM) launcher depends on the structure of the construction. The dynamics of the EM construction and the local effects of the EM forces are topical issue in exploring and designing EM launcher device. This paper is aimed to refine mechanical behavior of the open barrel design EM launcher structure due to EM force evaluated by EM analysis based on three different shapes of armatures. The 3D finite element EM model was generated and the J×B force density distribution in the rail volume was calculated. The results of EM model calculations were applied further as input for structural mechanics model. The results of the finite element EM and mechanical analysis of the armatures influence are presented

The investigation of load carrying capacity of elastic-plastic strain hardening bisteel i-section beams

In the present study, CPT is modelled by static elastic-plastic small strain finite element method (FEM) analysis of axi-symmetric problem. Undrained soil properties and Tresca yield criterion is used for determining cone resistance of clay. Sand is modelled by using drained soil properties and Mohr-Coulomb yield criterion. Cone penetration problem is formulated as a collapse load problem. Associated and non-associated flow rules were used for modelling. A number of numerical experiments were performed to determine rational size of discrete region. Received dimensions of region were used for further research. Cone factor Nc for clay was obtained and the comparison of Nc values with other theoretical solutions is presented. A conclusion may be made that the limit of the validity of geometrically linear systems has been reached. The evaluation of the effect of cone penetration requires the analysis of large strains to be made. First Published Online: 30 Jul 201

Investigation of adequacy of multi-sphere approximation of elliptical particles for DEM simulations

Adequacy of approximation of ellipsoidal particles composed of a set of sub-spheres for numerical Discrete Element Method (DEM) simulations is examined. The algorithm of adaptive hierarchical multi-sphere (MS) model is suggested for composing elliptical particles. Numerical simulation of the piling problem is used as a test problem for evaluating the adequacy of MS model approximation in comparison to the model of smooth ellipses for multiparticle system. The accuracy of MS approximation with the increasing number of sub-spheres is examined in detail by comparison of macroscopic and microscopic parameters of granular dynamics. It was determined that the data on macroscopic parameters yielded by the MS model tend to converge to those of the smooth ellipsoid with the increasing number of the constituent sub-spheres, and the MS model approximates the smooth perfect ellipsoid with a reasonable number of sub-spheres within the limits of the appropriate tolerance. It can be concluded that a multi-sphere model remains a realistic and relatively simple particle model applicable to DEM simulations of the behaviour of the real smooth and rough elliptically shaped particles

Investigation of armature-rail interaction in linear electromagnetic launcher

The behavior of the electromagnetic (EM) launcher depends on the structure of the construction. The dynamics of the EM construction and the local effects of the EM forces are topical issue in exploring and designing EM launcher device. This paper is aimed to refine mechanical behavior of the open barrel design EM launcher structure due to EM force evaluated by EM analysis based on three different shapes of armatures. The 3D finite element EM model was generated and the J×B force density distribution in the rail volume was calculated. The results of EM model calculations were applied further as input for structural mechanics model. The results of the finite element EM and mechanical analysis of the armatures influence are presented

Investigation of traffic‐induced vibration in Vilnius Arch‐Cathedral Belfry

The influence of city traffic‐induced vibration on Vilnius Arch‐Cathedral Belfry is investigated. Two sources of dynamic excitation are studied. Conventional city traffic is considered to be a natural source of excitation while excitation imposed artificially by moving a heavily loaded truck is considered to be the source of increased risk excitation. The influence of induced vibrations is recorded by accelerometers located in various positions of the Belfry's structures and shown by accelerograms. Dynamic effects are evaluated by considering acceleration magnitudes and response spectra. A comparative analysis of both effects is presented and conclusions and recommendations are provided. First published online: 27 Oct 201

Numerical analysis of asphalt mixture and comparison with physical Marshall test

This paper addresses simulation of asphalt on the macroscopic scale, using the Discrete Element Model (DEM). Asphalt mixture is considered as a particulate solid composed of relatively stiff deformable layered spherical particles embedded into a homogenised matrix. The discrete model presents a 3D network of one-dimensional elements connecting particle's centres and comprising mutual interaction of particles. The contribution of the film layer and the interface thickness for normal stiffness is described analytically and illustrated by simulation results. Development of the normal interaction model of layered particles contacting via interface on the meso scale is the key point of the current development. The model applied aiming to simulate deformation of asphalt mixture is able to capture properties of the weaker matrix interface while layered particle comprises of bitumen film in meso scale. The developed technique is applied for simulation of Marshall test, i.e. diametric compression of cylindrical specimen, widely used for characterisation of asphalt mixtures. Finally, suitability of the model is illustrated by comparison with the available experimental results

A life dedicated to science: on the occasion of the 70th birthday of Editor-in-Chief Edmundas Kazimieras Zavadskas

„A life dedicated to science: on the occasion of the 70thbirthday of Editor-in-Chief Edmundas Kazimieras Zavadskas" Journal of Civil Engineering and Management, 20(3), p. 311-31

Comparison study of spherical and multi-spherical particles under cyclic uniaxial compression

Numerical simulation of cyclic compression of granular material by performing oedometric test has been performed. Discrete Element Method (DEM) has been employed for simulation. A comparison study has aimed to examine the differences in macroscopic behaviour of material discretized by spherical (S) and non-spherical shape models of a particle. During the study, microscopic data of sand from Klaipėda were used for modelling the shape of particles. The nonspherical particles were described by multi-spherical (MS) models retaining distributions for size and aspect ratios. Two DE models of tested specimens were developed and the deformation behaviour under cyclic uniaxial compression was simulated numerically by applying the commercial EDEM code. The variation of the oedometric elasticity modulus was investigated and influence of particle shape on void ratio changes was demonstrated. It was clearly shown that application of S particles is much more sensitive to rearrangement of particles during densification DEM. Simulations illustrated that the elasticity modulus of material corresponding to MS particles is approximately 1.9 times larger comparing with material corresponding to S particles. Therefore, one must improve the magnitude of elasticity modulus by introducing a respective correction factor