191 Discrete Element Simulation of Apple Vibration Damage M. Van Zeebroeck, E. Tijskens, E. Dintwa, J. Loodts, J. De Baerdemaeker and H. Ramon Laboratory for Agro Machinery and Processing, Catholic University Leuven Kasteelpark Arenberg 30, B-3001 Leuven Belgium Keywords: Malus × domestica, bruise, simulation, particle, DEMeter++ Abstract Making use of the Discrete Element Method (DEM) a study is presented of the influence of mechanical parameters (vibration frequency and acceleration amplitude, apple size, stacking height) on vibration damage of apples (Malus × domestica) during bulk transport. As acceleration input a sinus in the vertical direction was applied. Realistic parameters of the Kuwabara and Kono (1987) contact force model for apples and bruise prediction models have been applied. Major influences of mechanical parameters on the vibration damage were identified, in particular stacking height and fruit size. A study was performed to investigate the relation between apple positions in the stacking and bruise damage. The existence of damage chains within the core of the apple stacking was also identified, that is in accordance with the well-known force chains in bulk materials. INTRODUCTION For most fruit types, bruising is the common type of post harvest mechanical injury. Not only a direct effect of fruit bruising exists, the quality appreciation by the consumer, but bruises, even small ones, can open the way for pathogen attack. Bruising due to impact and vibration, to which this paper is restricted, is a more important cause than static compression damage (Mohsenin, 1986). In order to improve the control of mechanical processes of fruit handling with respect to bruising, efforts have been made to develop a generic computer model for these processes based on the Discrete Element Method (DEM). Such models rely on the basic laws of classical mechanics (Newton’s law of motion) and a contact force model to simulate the trajectory and the impact history of each fruit throughout the process. The impact history is coupled to a bruise prediction model to provide temporal and spatial information on the occurrence of bruises in the process. DEM computer models must allow for identification of critical parts of the process, to provide guidelines for an improved control of the mechanical system, and ultimately to aid the design of harvesting, handling and transport systems that minimize the risk of damaging the fruit (Tijskens et al., 2003). DEM has been validated for its applicability in predicting the bruise damage of apples (Malus × domestica)(Van Zeebroeck et al., 2004b). The validation was an evaluation of the developed software DEMeter++3.1, the applied contact force and bruise prediction models incorporating the measured parameters. This validation step was necessary to proceed to the next step: the execution of simulations without experimental validation to gain insight in the process of bruising. In this paper the apple bruise damage due to continuous vibrations during transport is discussed. MATERIALS AND METHODS The materials and methods to obtain the normal and tangential contact force model parameters are previously described (Van Zeebroeck et al., 2003; 2004ab). The bruise prediction model with the bruise depth as dependent variable and peak contact force and effective radius of curvature as independent variable were applied (Van Zeebroeck et al., 2004b). A ‘shaking box’ application program was compiled from the DEMeter++ library (Van Zeebroeck et al., 2004b). As acceleration input a sinus in the vertical direction was applied. The maximum bruise depth of an individual particle (apple) contracted during the total simulation time was taken as the evaluation parameter Proc. 3 rd IS on Model IT Eds.: M.L.A.T.M. Hertog and B.M. Nicolaï Acta Hort. 674, ISHS 2005