W H I T E P A P E R
3
What if the fiber is anisotropic?
It is possible to define an elastic ratio individually for each joint deformation: normal, tangential,
bending, and torsion. By defining a ratio that multiplies the stiffness computed from the
particle material and geometrical properties, you can tune the effective stiffness for one or
more directions. Using the anisotropic model, the range of materials that can be modeled is
considerably wider.
In the example shown in Figure 4 below, similar flexible fibers are bending due to their own
weight. In purple, the fiber is isotropic, i.e., it has the same stiffness for bending as for traction.
In yellow, the fiber is anisotropic, and the bending resistance is almost null. The image on the
right shows how the yellow fiber's behavior matches an analytical catenary curve.
Figure 4. Anisotropy Influence: The purple fiber has the same bending stiffness for all deformations, whereas the yellow fiber has bending
stiffness less than other stiffnesses (Left). The yellow fiber anisotropic behavior closely matches a catenary curve (Right).
How do you compute the forces and moments?
For a flexible fiber, the forces and moments are computed (as is the case for any other particle
in Rocky) as functions of the linear and angular deformations. The different models available
in Rocky are described below.
The linear elastic model
This is the most basic model in Rocky. In this model, the forces (normal force, F
ⁿ
and tangential
force, F
τ
) and moments (bending moment, M
ben
and torsional moment, M
tor
) are directly
proportional to the deformations (normal deformation, s
n
rel
, tangential deformation, s
τ
rel
, angular
bending deformation, θ
ben
and angular torsional deformation, θ
tor
), as shown in Figure 5.
