[Thesis]. Manchester, UK: The University of Manchester; 2018.
The fluid-structure interactions of wall-mounted slender structures, such as cilia,
filaments, flaps, and flags, play an important role in a broad range of physical processes:
from the coherent waving motion of vegetation, to the passive flow control capability
of hair-like surface coatings. While these systems are ubiquitous, their coupled nonlinear
response exhibits a wide variety of behaviours that is yet to be fully understood,
especially when multiple structures are considered. The purpose of this work is to
investigate, via numerical simulation, the fluid-structure interactions of arrays
of slender structures over a range of input conditions. A direct modelling approach,
whereby the individual structures and their dynamics are fully resolved, is realised
via a lattice Boltzmann-immersed boundary model, which is coupled to two different
structural solvers: an Euler-Bernoulli beam model, and a finite element model. Results
are presented for three selected test cases - which build in scale from a single flap
in a periodic array, to a small finite array of flaps, and finally to a large finite
array - and the key behaviour modes are characterised and quantified. Results show
a broad range of behaviours, which depend on the flow conditions and structural properties.
In particular, the emergence of coherent waving motions are shown to be closely related
to the natural frequency of the array. Furthermore, this behaviour is associated with
a lock-in between the natural frequency of the array and the predicted frequency of
the fluid instabilities. The original contributions of this work are: the development
and application of a numerical tool for direct modelling of large arrays of slender
structures; the characterisation of the behaviour of slender structures over a range
of input conditions; and the exposition of key behaviour modes of slender structures
and their relation to input conditions.