Seppe Rogge

A Geometrical Model Generator for Quasi-Axisymmetric Biological Products

A geometrical model generator for biological products is presented, which uses X-ray computed tomography images of quasi-axisymmetric biological products as input. It was tested with a dataset of 73 scanned Braeburn apples. For each sample, the generator constructed different cross sections. From these sections, contours were extracted and selected. The contours were expressed as a series of shape descriptors. For this purpose, elliptical Fourier descriptors were used. The obtained frequency distributions were transformed to standard normal distributions. On these transformed distributions, the covariance decomposition algorithm was applied. This algorithm generated new sets of descriptors, which opened up a large range of possibilities for generation of representative shape contours. After reverse transformation of the (generated) descriptor distributions, new contours were obtained from the new descriptors. These new contours were converted to 3D geometrical models of biological products by interpolation and revolving. By comparing the volumes of the generated models with those of the scanned fruit, it was shown that the resulting geometrical models have the same variability as the biological variability in the original dataset. This generator is a fast method, which requires minimal user intervention, and creates 3D models including the biological variability as observed in the scanned fruit. Because these 3D geometrical models are directly available as CAD models, they are useful for numerical modelling of transport phenomena in and around biological products.

Multiscale Modeling of Food Processes

Food unit operations involve complex transport phenomena. As experimental characterization of transport processes is not usually straightforward, mathematical models are often used to improve our understanding of them, and, more importantly, to design and optimize food processes. Contrary to typical engineering materials such as steel or brick, food tissues are intrinsically multiscale assemblies with different characteristics at each spatial scale. As a consequence, multiscale modeling is required. This article gives a systematic introduction to multiscale modeling in food processes, including imaging techniques for food microstructure, model formulation, and numerical solution techniques. Several applications in food process engineering will be presented. The article concludes with a discussion on future prospects for the use of multiscale modeling.

Down-regulation of respiration in pear fruit depends on temperature

The respiration rate inside plant organs such as pear fruit is controlled both by diffusion limitation of oxygen and through additional regulatory processes in a temperature-dependent manner.

Modelling Cooling of Packaged Fruit Using 3D Shape Models

This study presents a novel methodology to model the cooling processes of horticultural produce using realistic product shapes rather than commonly used simplified 3D shapes, such as spheres. Variable 3D apple and pear models were created by means of a validated geometric model generator based on X-ray computed tomography images. The fruit were randomly stacked into a geometrical model of a corrugated fibreboard box using the Discrete Element Method. A forced-air cooling process was simulated for three such apple filling patterns using CFD and the results were compared to those obtained with fruit represented by equivalent spheres. No significant difference in average aerodynamic resistance between the real apple shape and its spherical representation was found. The main contributor to the overall pressure drop was the package design rather than product shape. However, large differences in local air velocity and convective heat transfer coefficients were found between the two representations. The degree of cooling uniformity between individual fruit was overestimated when using simplified product shapes: real apple fruit shapes cooled less uniform. This difference between real and simplified product shapes was even larger for a box filled with pear fruit that are more different from a spherical shape. These results demonstrate that improved computer-aided design approaches help in simulating more accurate convective cooling processes. In a next step, such simulations will be used for multi-objective optimization of packaging in terms of cold chain efficiency and cooling uniformity.

Online Tomato Inspection Using X-ray Radiographies and 3-dimensional Shape Models

A method is proposed that fits a 3-dimensional shape model (SM) on X-ray radiographies of tomatoes on a conveyor belt to allow for inspection of internal tomato quality using X-ray. For the training of the SM a set of computed tomography (CT) scans is used. From these scans, the surfaces of the fruits are extracted. Corresponding points on all these surfaces are located after which the variation in position of every point can be determined using principal component analysis (PCA). The result of this process is a mean shape with various modes of variation, which represent the variability of the shape. Any shape can then be reconstructed through a linear combination of the mean shape and its modes of variation. During runtime, the contour of every tomato is extracted onto which the SM is fitted. This allows us to accurately estimate tomato volume and 3-dimensional shape, and assess the presence of defects and other unwanted properties from X-ray radiographies in an online application. Results are promising, but show that improvement can be made by simulating radiographs from the shape model and fitting these directly to the measured radiograph.