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Realistic data-based bending models were developed for virtual DEM crop stems.The effect of plastic deformation and damage was incorporated in the models.The bending model was validated through comparison of simulations and measurements.The effect of stem length and support distance were also taken into account.Pendulum experiments showed that the deformation rate has no significant effect. A requirement for optimising crop processing machinery using DEM simulations is the application of virtual stems that behave realistically during deformation. In this study, data based bending models were developed for virtual segmented crop stems. These models combine realistic bending behaviour with a minimal number of model parameters. Also the effects of plastic deformation and damage were incorporated in the model. The bending model was successfully used to validate the bending behaviour of individual stems through comparison of simulations and validation measurements. It was also shown that the model is suitable for virtual stems with different numbers of segments. Moreover, based on a stem measurement it could be predicted what would happen to the same stem if it would have other dimensions or if it would be supported at different locations. Additional stem measurements were used to validate this. No significant difference ( α = 0.05 ) was observed between measurements and simulations. Finally, pendulum experiments showed that the deformation rate has no significant effect ( α = 0.05 ) on the deformation behaviour of individual crop stems.

© 2015 Elsevier Ltd.All rights reserved. Computer simulations are becoming increasingly important for the optimisation of various processes since they can significantly reduce the development time and costs. The discrete element method (DEM) offers a powerful tool for simulating the interactions of large numbers of particles. The method has proven its usefulness for many applications where granular and spherical particles are handled. Very recently DEM, was used to simulate the interactions of tubular particles. While the existing linear elastic models could describe the reversible bending and denting of these particles in a realistic way for small deformations, they are inadequate for describing the bending and compression behaviour at higher forces. In this region, buckling phenomena become important. Therefore, new phenomenological models, inspired by the collapse of steel tubes due to ovalisation of the cross section and the formation of plastic hinges, have been implemented for metal and synthetic plastic tubes. Using these models virtual, bendable tubes were created in the DEMeter++ software. The DEM parameters were calibrated for copper and PVC tubes based on combined bending and denting tests conducted using an Universal Testing System. The simulations were in good agreement with the measurements (R2>0.91). This realistic DEM model of bending can, in future research, be used to simulate the processing of large numbers of tubular particles (e.g. the processing of crop stems). publisher: Elsevier articletitle: Discrete element modelling of bendable tubes journaltitle: International Journal of Mechanical Sciences articlelink: http://dx.doi.org/10.1016/j.ijmecsci.2015.02.017 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved. ispartof: International Journal of Mechanical Sciences vol:94 pages:75-83 status: published

In order to optimise the processing of stem crops, insight into the deformation behaviour of the crop and the interaction between crop and machine is essential. Most research in the area of mechanical and physical properties of crop stems is focused on characterising the agricultural products to the point of failure using mechanical parameters and empirical relations. No studies have been conducted on the processes which lead to failure of stems and on the processes that take place after failure. In this paper it is shown that the bending behaviour of wheat and barley stalks is very similar to that of steel tubes. Two consecutive phases can be distinguished: ovalisation and buckling. During ovalisation the forces on the wall tend to flatten the cross-section. When this process continues the flexural stiffness is reduced until the structure becomes unstable and buckles. The cross-section locally completely flattens. This deformed cross-section offers virtually no resistance to bending. Mechanical models described in literature have successfully been adapted to describe the bending behaviour of crop stalks during both phases (R2>0.98 for ovalisation and R2>0.97 for buckling). The crop species, growing conditions, stem diameter and wall thickness were found to influence the bending process significantly. The presence of a core-rind structure increases the bending resistance of the stems. publisher: Elsevier articletitle: Mechanical analysis of the bending behaviour of plant stems journaltitle: Biosystems Engineering articlelink: http://dx.doi.org/10.1016/j.biosystemseng.2014.09.016 content_type: article copyright: Copyright © 2014 IAgrE. Published by Elsevier Ltd. All rights reserved. ispartof: Biosystems Engineering vol:129 pages:87-99 status: published

Generation IV (GEN IV) reactors promise higher safety levels compared to current generation II or III reactors, one of the most important safety aspects of any reactor is the ability to shutdown the reactor in any condition. The shutdown mechanism in current designs of liquid metal cooled Gen IV reactors is based on absorber rods. Although these rod based systems are duplicated to provide redundancy, they all have a common mode of failure as a consequence of their identical operating mechanism; possible causes being a largely deformed core or blockage of the rod guidance channel. To achieve the goal of higher safety, a complementary scram system is desirable. In this paper an overview of existing solutions of such a complementary system is given and a new concept based on absorber particles and the existing solutions is proposed. This original system, which is not rod based, is under investigation and its feasibility is verified both by experiments and simulations. © 2011 Elsevier B.V. All rights reserved.

One important safety aspect of any reactor is the ability to shutdown the reactor. A shutdown in an ADS can be done by stopping the accelerator or by lowering the multiplication factor of the reactor and thus by inserting negative reactivity. In current designs of liquid-metal-cooled GEN IV and ADS reactors reactivity insertion is based on absorber rods. Although these rod-based systems are duplicated to provide redundancy, they all have a common failure mode as a consequence of their identical operating mechanism, possible causes being a largely deformed core or blockage of the rod guidance channel. In this paper an overview of existing solutions for a complementary shut down system is given and a new concept is proposed. A tube is divided into two sections by means of aluminum seal. In the upper region, above the active core, spherical neutron-absorbing boron carbide particles are placed. In case of overpower and loss of coolant transients, the seal will melt. The absorber balls are then no longer supported and fall down into the active core region inserting a large negative reactivity. This system, which is not rod based, is under investigation, and its feasibility is verified both by experiments and simulations. © 2012 Simon Vanmaercke et al. ispartof: Science and Technology of Nuclear Installations vol:2012 status: published