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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

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.