2,523 research outputs found
An engineering methodology for kite design
No full textKites have seen substantial development in the last 10 years, going from mostly toys to high-performance sports-related equipment for e.g. kite surfing. The design process of these kites, however, is mostly a trial-and-error affair. Ten years after the sports-related kite revolution a new development is is emerging: Industrial applications for kites. Systems to propel ships and generate sustainable energy are now under development worldwide at over 40 companies and institutes. These new industrial applications will put strickter and more complex requirements on these kites. The current trial-and-error approach to the design of kites will not suffice. In this thesis a different design methodology is proposed. This methodology leans on three pillars. The first pillar is "Knowledge". As it turns out, there is still a lot unknown about the behavior of kites. This thesis further develops that knowledge. The seccond pillar is "Simulation". Nowadays, a large number of prototypes are produced and tested. So many in fact, that many designers do not even have the time to test them all. With the advance of complex industrial kites, this situation is expected to escalate. The capability of virtually testing kites will shrink the prototype phase into more managable proportions. Furthermore, it will contribute to the understanding of kites as well. This thesis proposes a number of models to simulate kites on a conventional desktop computer. These models include both rigid-body and multi-body models. The latter is capable of simulating a kite including its extreme flexibility. The third and last pillar is "Measurement". Controlled and reproducable measurements are essential for validation and evaluation. The thesis closes with a number of case studies which show the advantages and opportunities of this methodology.ASSETAerospace Engineerin
Feed velocity feedback for high speed fused deposition modelling machines
No full textAdditive manufacturing (AM) is a manufacturing method with two distinct advantages over traditional subtractive methods. First, it allows for much higher form freedom, allowing for shapes that are unobtainable by conventional techniques. Second, this method is also referred to 'rapid prototyping' given the fact that objects, and mainly prototype iterations, may be produced in a matter of hours instead of days. Fused deposition modelling (FDM) is the most ubiquitous and accessible AM technology, relying on the layer-by-layer deposition of molten thermoplastics. While FDM is very accessible and shows great potential as a future manufacturing technique, it is still inferior to traditional techniques due to the very low production capacity and limited speed. Print speed is mainly limited by volumetric ow rate through the nozzle, of which the counter pressure at high velocity causes filament slip in the extrusion mechanism. Therefore, the goals of this thesis are (1) to design an accurate extruder model to describe input-output behaviour of feed velocity. This may yield better understanding of FDM extrusion and form a basis for model-based design. (2) The synthesis of an anti-slip controller allowing for high print speed while retaining object quality. When a higher print speed could be attained, one of the largest disadvantages of FDM would be mitigated and a new step is made towards industrial application of this technology. To make the model of the extruder, the only known velocity input-output model available was taken and verified. This black-box transfer function model accurately describes low-speed behaviour of the extruder. This model, however, did not incorporate slip phenomena, making it an inaccurate model at high volume flow. Hence, a model from the automotive industry, also known as the 'Magic Formula' was combined with this known transfer function, producing a new black-box model covering all feed velocities. This new model has opportunity to be used as a basis for model-based design of 3D printers, which are now generally designed based on past experience and trial-and-error. For the future, it would be highly interesting to find an analytical model rather than a transfer-based one in order to gain physical understanding in the influence of extruder parameters. Regarding the synthesis of an anti-slip controller, we implemented a type of extremum seeking hybrid control which essentially finds an feasible maximum velocity for a limited amount of slip. The logic of the controller was based on Schmitt trigger logic, defining three control parameters that together define the switching behaviour of the controller. After tuning, if was found that the controller improved extrusion errors as well as completion time compared to open-loop control, achieving the set goals. The successful application of such a controller could mitigate the low velocity disadvantages of FDM and facilitate the acceptance of this technology. In the future, it is recommended to further investigate the practical applications of the controller, find the limitations of the controller in real printing and explore different control architectures.Mechanical, Maritime and Materials EngineeringBiomechanical Engineerin
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