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Fascinated by an ingenious habitation structure

The mounds of the African termite, Macrotermes michaelseni, which are common through sub-Saharan Africa, may hold the key for a major breakthrough in eco-architecture. Many entomologists, physiologists and engineers agree that this construction is one of the most fascinating and ingenious ventilation structures in nature. The termite colony, which resides in a subterranean nest, builds these mounds from the surrounding soil. The mound powers ventilation of the subterranean nest by capturing the wind’s energy. The mounds are organs of colony physiology, in the broadest sense, shaped to accommodate and regulate the exchange of respiratory gases between the nest and the atmosphere (see figure 1).

Fascinated by this natural ventilation system, a group of researchers became convinced it could be applied to human habitation. But in order to make that possible, they first needed a closer look at the complex architecture of these mounds.

Understanding the thermoregulation of the termite mound requires knowledge of how its complex architecture integrates structure and function. Once its 3D geometry has been captured, the entire interior structure can be analyzed.

Digitally capturing the termite mound by the world’s largest slice-and-scan machine

As the mound is best investigated on-site in Africa, the researchers opted for a digital slice-and-scan technique to capture the geometry of the termite mounds. Consequently, the team at Loughborough University built the world’s largest custom-built, slice-and-scan machine and shipped it to Namibia (see figure 2). To maintain the mound’s structural integrity, the researchers first infiltrated the structure with plaster of Paris. The plaster also improves the contrast between the mound material and its internal voids.

Digital reconstruction provides insight

The slice-and-scan machine operated continuously day and night over a two-month period. Since the 2D scanning could not be performed in a constantly illuminated environment, different lighting levels occurred throughout the images as the sun passed overhead. This prevented the researchers from using a single threshold value to translate the scanner images into a 3D reconstruction.
However, thanks to Mimics' powerful threshold editing tool, they easily overcame this obstacle. The tool allowed them to add unselected areas to the applied mask (see figure 3).

Because of the vast amounts of image data, the mound was reconstructed in Mimics in separate segments, converted to STL format (see figure 4 ) and subsequently assembled in Materialise’ Magics software. In Magics, the team then recreated the complete termite mound digitally by concatenating and aligning the segments (see figure 5).

The researchers used the 3D model to gain insight to how the ventilation in this mound works. Thanks to the model’s accuracy, they were able to analyze the mound’s internal structure easily, obtaining the dimensions of the various channels and conduits and how they are interconnected. The model’s great size and high level of detail coupled with the current limitations in computational power make computational fluid dynamics (CFD) simulations on the complete mound impossible. This means the researchers are still limited to a simplified model of the wind’s flow pattern through the porous skin of the mound (see figure 6).