Static Aeroelastic
Analysis
The interpolation from the structural
to aerodynamic degrees of freedom is based upon the theory of splines.
High aspect ratio wings, bodies, or other beam-like structures should
use linear splines. Low aspect ratio wings, where the structural grid
points are distributed over an area, should use surface splines. Several
splines can be used to interpolate to the boxes on a panel or elements
on a body; however, each aerodynamic box or element can be referenced
by only one spline. Any box or body element not referenced by a spline
will be "fixed" and have no motion, and forces on these boxes
or elements will not be applied to the structure. A linear relationship
may be specified for any aerodynamic point using the entry. This is
particularly useful for control surface rotations. For all types of
splines, it must be specified the structural degrees of freedom and
the aerodynamic points involved. The given structural points can be
specified by a list or by specifying a volume in space and determining
all the grid points in the volume. The degrees of freedom utilized at
the grid points include only the normal displacements for surface splines.
For linear splines, the normal displacement is always used and, by user
option, torsional rotations and/or slopes may be included.
Static aeroelastic analysis is intended
to obtain both structural and aerodynamic data. The structural data
of interest include loads, deflections, and stresses. The aerodynamic
data include stability and control derivatives, trim conditions, 0and
pressures and forces. The analysis presupposes a structural model (both
stiffness and inertial data), an aerodynamic model, and the interconnection
between the two. The requirements for static aeroelastic analysis beyond
those for the structural and aerodynamic models are nominal. The stability
derivatives are obtained as part of the solution process.
Divergence Analysis
The static aeroelastic solution sequence
can also perform a divergence analysis. Hence, LDP performs an eigenanalysis
of the aerostructural matrices, carried out using a complex eigensolver.
Data entry specifies the attributes for the eigenanalysis. LDP then
extract a desired number of divergence pressures (typically one, since
the second and higher pressures are not of practical interest) for the
Mach numbers given on the entry. A complex Lanczos eigenanalysis can
also be performed, and in that case the model asks for five roots to
be extracted. This is suitable for i compressible aerodynamics (Mach
= 0.0).
|
