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Keywords: discrete element method, silo, discharge stage, interaction model, spatial sorting and searching, horizontal pressures, contact forces.

Summary

Silos are industrial structures which experience a significant percentage of damage and collapse in comparison with other engineering structures. Over 1000 silos, bins and hoppers fail in North America each year [1].

The Jansen-Koenen equations are used to model the filling of the silo and their exact or approximate solutions are available [2]. In the course of the discharge stages the usual state of the content is that of a non-uniform, relatively slow flow of material, characterized by arching and a large number of collisions between particles and therefore, by high dissipation of energy which leads to potential instabilities in solving the equations derived from thermo-dynamical or hydro-dynamical analogies [3]. In this paper, the discrete element method (DEM) has been used to model the discharge stage in a silo, and the emphasis has been be made on phenomena that occurs during the discharge stage rather than on algorithms used to model the problem.

The DEM is today widely used in modelling of multi-body granular systems [4]. These discrete numerical approaches comprise three main parts: (i) interaction model, (ii) determination of the interacting bodies, (iii) numerical integration of the governing equations.

Important results may be summarized as follows:

a): Depending on the regions of different ball velocities, the development of time stepping methods with different durations of time increments over these regions may increase the computational performance of these processes
b): Detecting and separating compressive forms from the heap provide a much better insight into the behaviour of the contents of asilo. Results obtained by discrete element procedures are not directly useful for practical purposes at present. Qualitative results and shapes of some phenomena are well identified, but quantitative values must be considered with great caution.

This situation presently exists because of two main problems with the DEM:

a): Time consuming numerical calculations of discrete systems, especially when numerous passes are required, changing different parameters of the system, finding an envelope of pressures and,
b): Knowledge about the shape, fraction distribution and micromechanics of the contact behaviour (especially friction) of tiny grains in the undisturbed contents is modest.

References

1: T.M. Knowlton, J.W. Carson, G.E. Klinzing, W.-C. Yang, "The importance of Storage, Transfer and Collection", Chemical Engineering Progress, 90, 44-54, 1994.
2: R.M. Nedderman, "Statics and Kinematics of Granular Materials", Cambridge University Press, Cambridge, New York, USA, 1992.
3: H.M. Jaeger, "Chicago Experiments on Convections, Compaction and Compression", in H.J. Herrmann, J.-P. Hovi, S. Luding, (Editors), "Physics of Dry Granular Media", Kluwer Academic Publishers, Dordrecht, 553-583, 1997.
4: E. Stein, R. de Borst, T.J.R. Hughes, "Encyclopedia of Computational Mechanics - Volume 1, Fundamentals", Wiley & Sons, Chichester, 313-337, 2004.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 94 PROCEEDINGS OF THE SEVENTH INTERNATIONAL CONFERENCE ON ENGINEERING COMPUTATIONAL TECHNOLOGY Edited by: Paper 133 Some Discrete Properties of the Granular Contents of Silos D. Lazarevic¹, K. Fresl¹ and B. Milovanovic² ¹Department of Engineering Mechanics, ²Department of Materials, Faculty of Civil Engineering, University of Zagreb, Croatia doi:10.4203/ccp.94.133 purchase the full-text of this paper Full Bibliographic Reference for this paper D. Lazarevic, K. Fresl, B. Milovanovic, "Some Discrete Properties of the Granular Contents of Silos", in , (Editors), "Proceedings of the Seventh International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 133, 2010. doi:10.4203/ccp.94.133 Keywords: discrete element method, silo, discharge stage, interaction model, spatial sorting and searching, horizontal pressures, contact forces. Summary Silos are industrial structures which experience a significant percentage of damage and collapse in comparison with other engineering structures. Over 1000 silos, bins and hoppers fail in North America each year [1]. The Jansen-Koenen equations are used to model the filling of the silo and their exact or approximate solutions are available [2]. In the course of the discharge stages the usual state of the content is that of a non-uniform, relatively slow flow of material, characterized by arching and a large number of collisions between particles and therefore, by high dissipation of energy which leads to potential instabilities in solving the equations derived from thermo-dynamical or hydro-dynamical analogies [3]. In this paper, the discrete element method (DEM) has been used to model the discharge stage in a silo, and the emphasis has been be made on phenomena that occurs during the discharge stage rather than on algorithms used to model the problem. The DEM is today widely used in modelling of multi-body granular systems [4]. These discrete numerical approaches comprise three main parts: (i) interaction model, (ii) determination of the interacting bodies, (iii) numerical integration of the governing equations. Important results may be summarized as follows: a) Depending on the regions of different ball velocities, the development of time stepping methods with different durations of time increments over these regions may increase the computational performance of these processes b) Detecting and separating compressive forms from the heap provide a much better insight into the behaviour of the contents of asilo. Results obtained by discrete element procedures are not directly useful for practical purposes at present. Qualitative results and shapes of some phenomena are well identified, but quantitative values must be considered with great caution. This situation presently exists because of two main problems with the DEM: a) Time consuming numerical calculations of discrete systems, especially when numerous passes are required, changing different parameters of the system, finding an envelope of pressures and, b) Knowledge about the shape, fraction distribution and micromechanics of the contact behaviour (especially friction) of tiny grains in the undisturbed contents is modest. References 1 T.M. Knowlton, J.W. Carson, G.E. Klinzing, W.-C. Yang, "The importance of Storage, Transfer and Collection", Chemical Engineering Progress, 90, 44-54, 1994. 2 R.M. Nedderman, "Statics and Kinematics of Granular Materials", Cambridge University Press, Cambridge, New York, USA, 1992. 3 H.M. Jaeger, "Chicago Experiments on Convections, Compaction and Compression", in H.J. Herrmann, J.-P. Hovi, S. Luding, (Editors), "Physics of Dry Granular Media", Kluwer Academic Publishers, Dordrecht, 553-583, 1997. 4 E. Stein, R. de Borst, T.J.R. Hughes, "Encyclopedia of Computational Mechanics - Volume 1, Fundamentals", Wiley & Sons, Chichester, 313-337, 2004. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £125 +P&P)
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