Software handles complex numbers

While FEA and CFD packages are now plentiful, real world engineering design problems involve many different variables such as heat, electric current, fluid flow and distorting structures – which all affect one other. For highly complex problems such as these, conventional modelling packages cannot produce an accurate answer. Take RocTool’s Cage process, described in Eureka’s November 2006 edition. It uses induction heating of mould surfaces to speed the production of composite parts. Because of the high frequency, current is only induced – and heat produced – in the surface of the mould and not throughout its depth. However, the mould surface shape influences the magnetic field and thus the induced currents. This problem was worked through using a range of ‘multiphysics’ software tools from Comsol – which, while able to solve fiendishly difficult problems, are also fiendishly difficult to use. These tools allow the modelling of complex problems that are almost impossible to study any other way – with consequent benefits to final system performance. At a recent Comsol users’ conference in Paris, Roland Ernst of the EPM Laboratory in Saint-Martin d'Hères said of the RocTool system: “The more the coil windings have space between them, the more the heating is homogeneous along the moulding surfaces – until an optimal value corresponding to a covering rate of about 35%.” For this inductor covering rate, there was still a ‘cold area’ located on the mould extremities – as the magnetic field density is stronger near the coil. To reduce this phenomenon, the inductor configuration is changed so that the inductor is longer than the mould. As a result, the heating is homogeneous in the inlet/outlet magnetic field. Eureka understands that various other enhancements were also achieved as a result of the study, with the bottom line result that the process is a commercial success and expected to shortly go into mass production making car parts. At the same event, Frederic Thiebaud from the Institute Femto-ST in Besancon talked about using Comsol to predict the dynamic behaviour of shape memory alloys. These have great potential to be used as actuators and dampers. Used as dampers, they absorb energy by changing their crystalline state under load, but cannot be simply analysed using conventional finite element analysis. Another novel material is Aerogel, invented by NASA and 95% porous. It has great potential for insulation – and, sandwiched between layers of glass, is already used as such. But for wider use, this highly porous and fragile material needs to be coated. Joel Plawsky of the Rensselaer Polytechnic Institute in Troy, New York, has studied the design and simulation of a spout fluid bed coating system. Because the material is so different from conventional foam beads, it is not possible to base a design on what has been done before. The problem involved not only fluid flow but the behaviour of solid particles moving through it under their own inertia and weight. This is beyond the capability of conventional CFD. The first idea for the design was modelled in 2D, but found not to work. A better design was then considered and modelled in 3D. This could not easily be drawn using Comsol tools so was modelled in SolidWorks and imported into Comsol. The resulting coater apparently does work, although Plawsky says: “The ultimate goal is to compare the Comsol simulations with experimental measurements and modify the model to match.” It is to be assumed that, once the model has been tweaked, it can be used to improve the experimental coater. Other engineering applications that benefited from this type of modelling include magnetically levitated trains, electronic heat sinks, Mems (Micro Electro Mechanical Systems) and micro fluidic pumps – which involve surface double layer effects, electric conduction, and viscous flow. Comsol Ltd Pointers * Software can be used in 2D or 3D to model multi-physics problems that are beyond the scope of other commercial offerings * 3D models can be imported from SolidWorks, SolidEdge, NX, Catia V4 and V5, Autodesk Inventor and Pro/Engineer