Bicycle technology is in constant evolution, and the industry is always looking for new designs and new technology. Understanding and mastering the dynamic behaviour of a bike is not an easy task and requires more fundamental and applied research. A bicycle is a light structure that has to support a much heavier weight (the cyclist). The components and the frame are subjected to time-varying force excitations imposed by the cyclist and by the road. Its dynamic behaviour becomes an important issue, because it is directly linked to the bike lifetime, maneuverability, efficiency and comfort. Researchers at the Universite de Sherbrooke research group VelUS have taken up the challenge in collaboration with the industry to develop know-how and knowledge in bicycle dynamics. The importance of teamwork, intellectual honesty and openness are essential ingredients in any relationship. The VelUS mechanical engineers, with expertise in modal analysis, metrology, material strength, and biomechanics, joined their efforts to address these challenges. To get a good idea of the dynamic behaviour of a bicycle structure, experimental modal analysis (EMA) can be used while considering different operating conditions in the lab with or without a cyclist or on the road. EMA allows input forces, natural frequencies, modal damping and scaled modal shapes to be obtained. SIMO (single input multiple output) and MIMO (multiple input multiple output) analyses were carried out using one or several shaker configurations. For SIMO, a single shaker is connected to the front wheel axle imposing forces in-plane and out-of-plane directions. For the MIMO configuration, an additional shaker is installed on the handlebars. For a better understanding of how the presence of a cyclist influences a bike's dynamic behaviour, tests were conducted with, and without the cyclist and the bike resting on a flat surface. The bike is resting on a steel table and is held vertically with a set of soft elastic bands. The stiffness of the bands is selected to adequately support a 160-lb rider resting statically on the bike. The results of the tests with a cyclist show that both SIMO and MIMO analyses give similar results for natural frequencies and mode shapes. However, damping ratios vary according to the technique employed. Also, the MIMO technique can extract one more mode than SIMO analysis. This can be explained by the fact that the there is a node of that mode at the reference location for the SIMO test.
Bicycle structural dynamics
Strukturdynamik von Fahrrädern
Sound and Vibration ; 41 , 7 ; 16-24
2007
9 Seiten, 20 Bilder, 4 Tabellen, 8 Quellen
Article (Journal)
English
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