Complex Resonance Structures
Last week we attempted to do some simplistic modal analysis on some plant geometries, pruned from local shrubbery and these are our findings!
__Premise Prior to the experiment, we had been looking at the potential for using digital design tools to inform the design of multi-tonal resonance objects. Specifically we are interested in being able to design percussive objects that can resonate with not only one, but many fundamental resonant modes, with no harmonic relation. Imagine a specified planar metal geometry which when struck vibrates with a C-Minor 7.
We set out to answer the question of whether or not this would be possible by observing the resonance properties of existing complex structures. Trees and shrub structures seemed like a good place to start for a number of reasons. They contain extremely complex geometric structures, ultimately giving rise to a multitude of resonant modes. They also oscillate at very low frequencies (less than 10Hz), which enabled us to use a low cost camera to capture video of the motion for vibration analysis.
Experiment__ Just as an initial investigation, we did some simplistic estimates of the resonant frequencies of plant off-cuts by manually calculating the frequency of vibration through observation of a slow motion video (100fps). The video below demonstrates the vibration of each of the plant off-cuts, after some initial disturbance. The observed resonant frequency can also be seen, as well as an audible sound representation of the vibration.
Results__ From the footage it is clear that it is possible to have multiple resonant modes with no harmonic relation in a single rigid body. It is also maybe interesting that these organic structures do not grow to resonate in harmony. Perhaps this is beneficial for the structural stability of the plant? There is a commonly used technique in Civil Engineering to design buildings to not resonate at specific frequencies, so as to ensure robustness to various dynamic load cases. Maybe this one factor in the generative design of an organic structure! Hopefully more on this soon…
Next__ We would like to next look at how we can digitally design rigid bodies to have pre-designed resonant modes, allowing us to design objects with polyphonic vibration response. To do so we will look into the potential of using Finite Element methods to simulate the vibration of rigid bodies.