conditions along the axis of symmetry unknown. The z-direction boundary conditions
also make it impossible to use an axis of symmetry along an axis 45 degrees from the x or
y axis. The cable element controlling the z-direction boundary condition lies along this
axis of symmetry and can not be split.
4.3.1 Applied Loading Conditions
Since external fluid flows over the entire cage, the total fluid drag force on the
cage is calculated based on its total cross-sectional area perpendicular to the direction of
flow. The total force is then divided equally and applied to all nodes of the eight caps
and eight tubes. Referring to the coordinate system defined in Figure 4.23, all drag forces
act in the negative z-direction for the top-down flow model.
4.3.2 Boundary Conditions
Boundary conditions are applied to simulate the conditions acting on the cage as
simply as possible while minimizing solution time. The two locations labeled A in
Figure 4.23 describe two single nodes at the top and bottom of the cage. These points are
placed to obtain a cage diameter-to-height ratio of 8:5. Both points are constrained to
zero deflection in the x,y, and z directions. Cables on the underside of the cage are slack
and do not affect the system, but were included for aesthetics along with the fixed node at
the bottom of the cage.
Locations labeled B and C in Figure 4.23 describe all nodes around the
circumference of a tube at the center of its length. Nodes at location B are constrained to
zero deflection in the y-direction. Nodes at location C are constrained to zero deflection
in the x-direction. Constraining locations B and C prevents rotational rigid body motion
while allowing the individual tubes and cage to expand symmetrically.