Page 58 - Computational Modeling in Biomedical Engineering and Medical Physics

Shape and structure morphing of systems with internal flows 45

the shape and structure of systems that emerge naturally under known constraints, and
it points out physics out to extend over all naturally organized flow systems as well as
in biology.
The constructal law, in its early exposure states that “For a finite-size open system
to persist in time (to survive) it must evolve in such a way that is provides easier access
to the currents (fluxes) that flow through it” (Bejan and Errera, 1997). It emerged
from the optimization work performed on engineered heat transfer systems with a
purpose (optimal heat transfer rates), with minimum entropy generation (or finite
time, or endoreversible thermodynamics): compact and efficient shapes and structures
(Novikov, 1958; Hoffman et al., 1997; Bejan, 1980, 1996, 2001a,b; Ledezma et al.,
1996; Morega and Bejan, 2005; Hoffman, 2008) aimed to enhance the thermody-
namic efficiency of an engineered structure subject to global constraints by physically
modifying its design. These studies led to arborescent heat transfer networks where
each feature is a natural consequence and not an axiom. Relating this result with the
tree networks in nature is a natural reflection of the invocated principle of global max-
imization in volume (territory) to point flows. The same principle should act every-
where where trees occur.

2.2 Biomimetics, bionics, fractal geometry, constructal theory

Nature provides answers to all problems encountered throughout our existence, and
new technologies are more than often inspired by biological realizations that evolved
through natural selection into too well adapted, developed structures and materials.
Engineering objectives such as self-healing abilities, tolerance to environmental expo-
sure, hydrophobicity, self-assembly, solar energy usage, have thus been addressed.
3
2
Closely related to bionics, or biologically inspired engineering, biomimetics or biomimicry
terms the replication of elements, functionalities, models, and systems of nature with
the aim to solve convoluted human problems, which means the application of biologi-
cal means and systems found in nature to the study and planning of engineering sys-
tems and modern technology (Vincent et al., 2006). For instance, the design of the
aircraft wing profile and the flying techniques, physiology and methods of locomotion
transferred to biorobots, etc. The Schmitt trigger device (Schmitt, 1938, 1969) repli-
cates the squid nerve propagation in “a thermionic trigger” that allows a constant elec-
tronic signal to be changed to an on/off state, and makes the basis of analog to digital

2
Biology & electronics; “the use of electronically operated artificial body parts”; the science of systems
which have some function copied from nature, or which represent characteristics of natural systems or
their analogs—largely abandoned in English speaking countries (Vincent, 2009).
3
Ancient Greek: β ιoς (bios), life, and μ ιμησις (mīm¯ esis), imitation.