Adrian Bejan | Canopy and Branches, from Design in Nature
The video explains how the design of vegetation, from roots to canopy and branches, can be understood by starting with very simple shapes and rules and then seeing how diversity grows around a common structure. The root behaves like a conical pump, sending water upward, with a larger diameter at ground level, meaning more water flows into the trunk. The trunk itself is also roughly conical and acts as a main elevator, supporting many different canopy shapes, so behind the visible variety lies a simple pillar that organizes the flow. Vegetation is seen as protuberances rising from flat ground that return water to the dry wind, just as engineers design fluid-flow structures for heat transfer enhancement and thermal insulation that look different but serve a common purpose. Inside the canopy, there are branches, each with its own stem and personal canopy, and the relations between branch size, length, and canopy size follow simple power laws that connect the trunk, the canopy diameter at ground level, and the water mass flow rate that the tree puts into the air. At the end, the speaker links all this to the constructal or constructor law and shows, with the example of rivulets and cataracts on gravel during a downpour, how questioning an idea can lead to the discovery that the patterned flow down a rough path can be faster than smooth flow, confirming rather than refuting the original principle.
The root is treated as a simple conical object that pumps water upward, and the analysis shows that a larger diameter at ground level gives a larger water flow rate into the trunk, so the size of the root at the surface matters for how much water reaches the tree.
The trunk, with its canopy, is modeled in a similarly simple way, with the trunk roughly conical or triangular in profile, despite the visible diversity of canopy shapes, so the trunk acts like a pillar or main elevator that supports many different architectural bodies.
Vegetation is described as protuberances rising from flat ground that naturally return water to the dry wind, and this activity is compared with engineering work in heat transfer augmentation using fins and dendritic shapes, and with thermal insulation using hair or thick layers that separate hot from cold.
The canopy is filled with branches, each branch having its own trunk-like stem and its own narrow to fat personal canopy, and by using ratios of diameter to length for both branch and canopy, and power law variations from the top coordinate, the analysis leads to a link between overall canopy diameter at ground level and water mass flow rate.
Big trees, with larger projected canopy discs seen from above, put more water into the air than small plants. This result becomes a kind of fruit of the journey that supports the constructor law, which is then tested by looking at rivulets and cataracts on gravel during torrential rain and finding that the sequence of pools and free fall can, in fact, flow faster than down a smooth incline, giving joy in being proven right by first trying to prove oneself wrong.
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