COMPUTER MODELLING SOFTWARE | MACHINERY
Modelling buried pipe Australian researchers have used numerical modelling to investigate load distributions on PVC and HDPE pipe that is buried under geosynthetic covers. The researchers, from Edith Cowan University
in Perth, say that a geosynthetic layer helps to reduce the load over the buried structure. “Some small-scale studies have indicated that the geosynthetic layer can reduce the load over the buried structure, the investigation on a large scale is limited,” said the researchers, in a paper pub- lished in Geotechnical and Geological Engineering. “A realistic estimation of load distribution over buried structures is necessary for proper analysis of pipes, conduit, culverts and tunnel lining.” The study was carried out by developing a numerical model of the problem using Plaxis 3D software from Bentley Systems. Comparing HDPE and PVC pipes showed that the pressure around the PVC pipe was greater than that around HDPE pipe, while pressure around the larger diameter HDPE pipe was lower than that around the smaller diameter HDPE pipe. Pressure on the top of the pipe decreased with
presence of the geosynthetic reinforcement layer. The optimal distance between the geosynthetic reinforcement layer and the pipe was equal to the diameter of the pipe. The pressure reduction on the top of the HDPE and PVC pipes – which had a diameter of 914mm – are 31% and 27%, respectively.
Flight simulation Researchers in Germany and Austria have devel- oped a modelling approach to predict flow when using wave dispersion screws. “Wave-dispersion screws have been used industri- ally in many types of extrusion processes,” said the researchers, from Johannes Kepler University in Linz, Austria, and Paderborn University in Germany Their design replaces the metering section of a conventional screw with a melt-conveying zone comprising two or more parallel flow channels that oscillate periodically over multiple cycles. This can help extruders to run at higher output without excessive temperature rise. Despite their industrial relevance, few scientific studies have investigated the flow in wave-dispersion sections in detail, say the researchers. “As a result, current screw designs are often based on traditional trial-and-error procedures rather than on the principles of extrusion theory,” they said – aiming to address this in a two-part study that was published in the journal Polymers. The first paper deliberately reduced the com-
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plexity of the problem by ignoring the influence of screw rotation on conveying characteristics. This helped to understand the underlying physics, said the researchers. Experiments were performed on a novel extrusion die, which had a dual wave-channel system with alternating channel depth profiles. The researchers say that their semi-numerical model- ling approach – backed up by three-dimensional, non-Newtonian CFD simulations -- enabled “fast, stable prediction of the flows and pressure de- mands of wave systems”. The second part of the study extended this model by considering the drag flow imposed by the screw. Two main modifications were made to the original model: first, melt conveying models for shear-thinning polymer melts were combined, using a novel correction factor; and second, the structure of the flow network was adapted to include both transverse flow over the barrier flight and leakage flow over the main flight. The accuracy of the modelling was confirmed by experimental data. “Due to its efficient solving process, the model-
ling approach is expected to be particularly useful in design and optimisation studies, and in the process troubleshooting of wave-dispersion screws,” said the researchers. “In both cases, fast and accurate analysis of the screw concept is crucial.”
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.plasticflow.com �
www.plasticpipe.org �
www.borealisgroup.com �
www.borouge.com �
www.ansys.com �
www.ecu.edu.au �
www.bentley.com �
www.jku.at �
https://ktp.uni-paderborn.de
March 2021 | PIPE & PROFILE EXTRUSION 37
Above: Australian researchers have used numerical modelling to investigate load distributions on buried pipe
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