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© 2017 Elsevier B.V. A non-destructive methodology was developed to automatically detect and quantify bruise volumes in the equatorial region of apples, using X-ray CT images. Grey level threshold values were calculated to segment bruises in ‘Jonagold’, ‘Joly Red’ and ‘Kanzi’ apple fruit using the multi-level Otsu's threshold method. Comparisons were made between the CT-based bruise volume estimates and bruise volume estimates that were based on destructive measurements in combination with simple geometric assumptions. Visualisation of the bruises in both 2 and 3D showed that bruises, resulting from a pendulum impact with a spherical impactor, can be highly irregularly shaped which implies that the bruise volume estimations based on simple geometric assumptions cannot deliver accurate results. publisher: Elsevier articletitle: Assessment of bruise volumes in apples using X-ray computed tomography journaltitle: Postharvest Biology and Technology articlelink: http://dx.doi.org/10.1016/j.postharvbio.2017.01.013 content_type: article copyright: © 2017 Elsevier B.V. All rights reserved. ispartof: Postharvest Biology and Technology vol:128 pages:24-32 status: published

A contact force model was developed to model the visco-elastoplastic (VEP) behaviour of apples. The model is based on the elastoplastic Thornton model and has been written in a pressure-based formulation to extend the application of the model to Discrete Element Method (DEM) simulations with arbitrary rounded shapes. The parameters of the new developed VEP contact force model were determined by fitting the experimental data acquired from Jonagold, Joly Red and Kanzi apples impacted by a pendulum. With only one parameter set per cultivar and for a large impact range (impact velocity range: 0.3-1.5 m/s), the VEP-model (R2=0.90±0.13) provides a better description of the force-deformation profiles than the viscoelastic Kono and Kuwabara (KK) model (R2=0.71±0.20). The equivalent Young’s modulus (E*) was also determined under quasi-static conditions, which resulted in measured E*-values for Jonagold, Joly Red and Kanzi apples of respectively 4.24±0.96 MPa , 5.09±1.27 MPa and 7.82±0.41 MPa. The novel VEP-model has the potential to help predict and understand bruise damage in apples as well as other horticultural products. publisher: Elsevier articletitle: Development of a visco-elastoplastic contact force model and its parameter determination for apples journaltitle: Postharvest Biology and Technology articlelink: http://dx.doi.org/10.1016/j.postharvbio.2016.06.003 content_type: article copyright: © 2016 Elsevier B.V. All rights reserved. ispartof: Postharvest Biology and Technology vol:120 pages:157-166 status: published

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.

Advancing front packing algorithms have proven to be very efficient in 2D for obtaining high density sets of particles, especially disks. However, the extension of these algorithms to 3D is not a trivial task. In the present paper, an advancing front algorithm for obtaining highly dense sphere packings is presented. It is simpler than other advancing front packing methods in 3D and can also be used with other types of particles. Comparison with respect to other packing methods have been carried out and a significant improvement in the volume fraction (VF) has been observed. Moreover, the quality of packings was evaluated with indicators other than VF. As additional advantage, the number of generated particles with the algorithm is linear with respect to time.

© 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

We propose viscoelastic smoothed particle hydrodynamics (SPH) with extended boundary conditions as a new method to model the extracellular matrix (ECM) in contact with a migrating cell. The contact mechanics between a cell and ECM is modeled based on an existing boundary method in SPH that corrects for the well-known missing kernel support problem in Fluid Structure Interactions (FSI). This boundary method is here extended to allow the modeling of moving boundaries in contact with a viscoelastic solid. To validate the method, simulations are performed of tractions applied to a viscoelastic solid, Stokes flow around an array of square pillars, and indentation of a viscoelastic material with a circular indenter. By drop out of the inertial terms in the SPH equations of motion, the new SPH formulation allows to solve problems in a low Reynolds environment with a timestep independent of the particle spacing, permitting to model processes at the cellular scale (i.e. μm-scale). The potential of the method to capture cell-ECM interactions is demonstrated by simulation of a self propelling object that locally degrades the ECM by fluidizing it to permit migration. This should enable us to model and understand realistic cellâ matrix interactions in the future. ispartof: Computer Methods in Applied Mechanics and Engineering vol:322 pages:515-540 status: published

A new shutdown system that does not rely on absorber rods, is being developed at SCK.CEN and UCL for application in Liquid Metal Reactors (LMR). The system consists of tubes filled with absorber particles. During normal operation, these particles are kept above the active core by means of a metallic melt seal. In case of an accident, the system is activated by the temperature increase in the coolant. This leads to melting of the metal seal, releasing the absorber particles into the core. The resulting flow of the particles has been studied both experimentally, and with Discrete Element Method (DEM) simulations. This paper focuses on the second important aspect of the safety system, being the melting and flowing of the metallic seal in interaction with the solid absorber particles moving through the molten seal.

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.

The paper aims at developing a validated model that can accurately predict the flow of a particulate material. This model will serve as a virtual design tool for the design of a novel passive safety system for nuclear reactors. Therefore an experimental setup consisting of a vertical glass tube is filled with 500±30 μmspherical glass particles. The experiment is then placed in a vacuum and the particles are released by opening a valve. The velocity of the particles is recorded during their fall at three different heights using a non invasive optical tracking technique with an original implementation. The same experiment is then simulated using the Discrete Element Method and results are compared. A good agreement between the simulation and the experiment was found. The sensitivity of the simulation to a change in the contact stiffness, dynamic Coulomb coefficient of friction and tangential contact force model was investigated. The influence of the initial position of the simulated particles on the packing factor was shown to be very important. Finally the experiment proved to be extremely sensitive to a perturbation of the outflow section of the tube, something that was predicted by the simulations.

It is widely recognized that the control of the activity of dissolved oxygen is essential for the use of lead–bismuth eutectic (LBE) as primary coolant for nuclear systems. A lead oxide mass exchanger (PbO MX) comprised of a packed bed of lead oxide spheres is a promising solution to regulate the dissolved oxygen activity in the LBE. In order to design and operate a PbO MX properly, the dissolution kinetics of PbO in flowing LBE should be determined. A high-fidelity Computational Fluid Dynamic (CFD) model of solid-to-liquid mass transfer has been developed to determine the mass transfer coefficient of a PbO MX in flowing LBE. We validated the developed CFD model against experimental data obtained from the LBE test loop CRAFT, at SCK•CEN. The model is in good agreement with the experimental data. The effect of the channel to particle diameter ratio ( R ) on the mass transfer coefficient was evaluated by using the validated model. A mass transfer correlation for PbO MX was obtained, in terms of the Sherwood number, by fitting the simulation results for the general case of a random packed bed with a porosity of about 0.4.

Calculating contact forces between complex shapes for performing Discrete Element Method (DEM) simulations is a long standing problem with no unique ideal solution. In this work, a new method to calculate interactions between arbitrary rounded bodies is presented. Each body is represented by a triangulated surface mesh, in which each triangle is associated with a unique radius of curvature. Then, normal contact forces are calculated by numerically integrating a (Hertz) contact pressure formulation over the contact area between two contacting particles. This results in a mechanistic contact description that is converging with refinement of a given triangulation and directly uses physical material properties as parameters of the contact model. After showing convergence upon mesh refinement towards the Hertzian solution, the error for non-spherical curvatures is investigated and the new model is compared with an indentation experiment of a pear-shaped object. Finally, the method is demonstrated in a simulation of gravitational packing by simulating packing of spheres, pear-shaped as well as gummy bear-shaped objects. ⃝c 2014 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