Robertas Balevičius

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.

Model for Time-Dependent Stress and Strain Analysis of Layered Composite Element

The authors have proposed a relatively simple and convenient method for engineering purposes that allows one to simulate time-dependent viscoelastic properties of a multilayered composite element subjected to loading along layer joints. The method proposed is found to be of a good coincidence in comparison with the known analytical solution of a two-layered composite element. Numerical analysis is also performed adopting the model proposed for the deformational response of reinforced concrete elements.

Long‐term strength and deformational analysis of reinforced concrete columns

Abstract The paper presents a method of non‐linear analysis of load‐carrying capacity and deformations of reinforced concrete columns subjected to long‐term loads. Physical relationships expressing non‐linear relations between internal forces and stresses, strains and stiffness are derived on the basis of the fracture and creep theories for concrete and using non‐linear stress‐strain diagrams modified for time effects. Second‐order geometrical effects are taken into account by solving a second‐order differential equation for elements subjected to compression and bending. A number of numerical and test results are presented. The technique proposed is verified by comparison of analysis results with extensive experimental data.

Discrete Element Method in Simulation of Granular Materials

The discrete (or distinct) element method (DEM) has been recently recognized as efficient numerical tool for solving many scientific and technological problems in various fields of engineering. The method started in the 70-ies with its first application to simulate the dynamic behaviour of granular material in the work of Cundall and Strack [1]. Unlike the continuum approach, the DEM presents particulate material as an assemblage of discrete elements. It is based on the Lagrangian approach, according to which particles of granular material are treated as contacting bodies, while the dynamical parameters (i. e. position, velocity, orientation, etc.) of each body are tracked during the simulation. Some variations on the theme of DEM and granular materials may be found in [2]–[5].

DEM analysis of granular flow in pyramidal hoppers

The processes of granular material handling in the hoppers are of a great importance in pharmaceutical, chemical, food and other industries. Theoretical treatments of such problems are usually based on simplified continuum models, which are useful to predict the stress field within the hopper, especially, on the walls at the end of filling process. The Continuum approach has some drawbacks for discharge state modeling when description of transient flow is required. Consequently, discrete element method (DEM) based on the application Newton’s and contact mechanics laws predicting dynamical parameters, such as position, velocity, etc., of individual particles, have been adopted in numerical analysis of granular flow in hoppers.

SIMULATION OF THE POLY- AND MONODISPERSED GRANULAR MATERIAL. PART II: THE STABILITY STATE CHARACTERIZATION / DAUGIADISPERSIO IR VIENDISPERSIO DALELIŲ MIŠINIO ELGSENOS TYRIMAS. II DALIS: STABILUMO BŪSENŲ CHARAKTERIZAVIMAS

Santrauka Sioje straipsnio dalyje pagrindinis dėmesys skiriamas viendispersinio ir daugiadispersio sferinių dalelių misinio mikrobūsenai charakterizuoti, analizuojant atskirų misinio dalelių stabilumą esant kvazistatiniam būviui. Tiriamos ir vizualizuojamos atskirų dalelių greicio vektorių normalinių plokstumų formuojamos tekstūros, kurios esant kvazistatiniam būviui interpretuojamos kaip tam tikri rezonansinio poveikio dariniai, gaubiantys dalelių pavirsių.

Daugiadispersio ir viendispersio dalelių mišinio elgsenos tyrimas. I dalis: Struktūros charakterizavimas

Santrauka Diskreciųjų elementų metodu modeliuota viendispersio ir daugiadispersio sferinių dalelių misinio elgsena. Dėmesys skirtas misinio mikro- ir makrostruktūros charakterizavimui, pasitelkiant dalelių dinaminio modeliavimo rodiklius. Pirmojoje straipsnio dalyje aptarta modeliavimo metodika ir grindžiamas gautųjų rezultatų korektiskumas, remiantis kontroliuojamaisiais mechaniniais būvio parametrais. Dalelių misinio struktūrai charakterizuoti makrolygmeniu naudoti sie rodikliai: struktūros užimama tūrio dalis (tankumas), koordinacijos skaicius, dalelių kontaktinės jėgos. Aprasomas dalelių būsenų charakterizavimas taikant Hamiltono mechanikos principus.