Unsteady Aeroelasticity

It is recommended that the user refer to the CFL3D Tutorial page for additional information on unsteady aeroelasticity capabilities.

CONTENTS

Description of Methodology
Sample Input and Parameter Definitions

DESCRIPTION OF METHODOLOGY

Acknowledgment: Thanks to Peter Hartwich of Boeing Phantom Works, Long Beach, for suggesting and providing the model routines for coupling the CAPTSD structural solver with CFL3D.

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SAMPLE INPUT AND PARAMETER DEFINITIONS

Notes:
1. Aeroelastic analysis can only be utilized in time-accurate mode, i.e. dt > 0
2. The mesh movement flag, iunst, must be set equal to 2.
3. If iunst=2, the following lines in the input file must appear after the control surface data section (line types LT31 through LT32 in the terminology of the Version 5 User Manual) in order to enable the aeroelastic option:
Example: Single-zone, 2D grid with one aeroelastic surface:
```
moving grid data - deforming surface (forced motion)
 ndefrm
      0
   lref
   grid idefrm      rfreqi  omegax  omegay  omegaz  xorig  yorig zorig
   grid   icsi   icsf     jcsi    jcsf     kcsi    kcsf
moving grid data - aeroelastic surface (aeroelastic motion)
 naesrf
      1
 iaesrf    ngrid    grefl      uinf      qinf    nmodes    iskyhk
      1       -1 1.333333      393.      155.         2         0
    freq   gmass     damp x0(2*n-1)   x0(2*n)   gf0(2*n)
  21.363      1.       0.        0.        0.         0.
  32.421      1.       0.        0.        0.         0.
  moddfl     amp     freq       t0
       0      0.       0.       0.
       0      0.       0.       0.
   grid     iaei     iaef     jaei    jaef      kaei      kaef
      1        0        0        0       0         0         0
moving grid data - skip data for field/multiblock mesh movement
   nskip   isktyp    beta1   alpha1    beta2   alpha2  nsprgit
       0       -1      1.0      1.0     1.0     0.05         0
   grid    iskip    jskip    kskip
```
In all deforming mesh applications, the additional input is broken up into three sections, as illustrated in the example above: 1) forced motion, 2) aeroelastic motion, and moving grid data.
For any problem in which the forced motion is not used, but the aeroelastic response of one or more surfaces is desired (which is the focus of this section), the forced-motion input section should appear as shown above - the only numerical value which should appear is the value of ndefrm, the number of surfaces undergoing forced motion - zero.
The following definitions apply for the aeroelastic section:

naesrf

number of aeroelastic surfaces; each aeroelastic surface is represented as a distinct set of modal shapes. Most typically, naesrf = 1, but for example, naesrf = 2 would allow the wing to be represented with one set of mode shapes, while the tail could be represented with a different set of mode shapes. All of the remaining data is repeated as a block for each of the aeroelastic surfaces from 1 to naesrf.

iaesrf

the aeroelastic surface for which the data is being set

ngrid

the number of grids which contain the aeroelastic surface iaesrf. If ngrid = -1, then the aeroelastic surface is assumed to be comprised of all solid surfaces (i.e. bc types 1005, 1006 or 2004) within the entire grid system. Thus, ngrid = -1 is appropriate only for naesrf = 1.

grefl

the reference length, in grid units, used to nondimensionalize the reduced frequency associated with the mode shapes of the aeroelastic surface.

uinf

reference flow speed used to nondimensionalize the reduced frequency.

qinf

reference dynamic pressure used to nondimensionalize the gneralized forces.

nmodes

number of modes used to represent the aeroelastic surface.

iskyhk

flag to indicate the use of the "skyhook" terms. NOT YET IMPLEMENTED. However, a value must still be input as a placeholder (any value will do).

The lines following freq gmass ... gf0 are repeated nmodes times, with data arranged from mode 1 to mode nmode:

freq

the wind-off natural freqency of the mode.

gmass

the generalized mass to include for the mode.

damp

the damping factor of the mode

x0(2*n-1)

the initial generalized displacement of the mode; if non-zero, will overide the value in the restart file (if restarting). this allows the mode to be perturbed for dynamic response studies

x0(2*n)

the initial generalized velocity of the mode; if non-zero, will overide the value in the restart file (if restarting). this allows the mode to be perturbed for dynamic response studies

gf0(2*n)

the generalized force to include for the mode.

The lines following moddfl amp ... t0 are repeated nmodes times, with data arranged from mode 1 to mode nmode:

moddfl

type of time-varying modal perturbation desired:

= 0, no perturbation

= 1, harmonic (sinusoidal) perturbation

= 2, Gassian pulse

= 3, step pulse

amp

amplitude of modal perturbation. use any value as a placeholder if moddfl = 0

freq

reduced frequncy of modal perturbation if moddfl = 1

half-width of Gaussian pulse if moddfl = 2

use any value as a placeholder for moddfl = 0 or 4

t0

time about which Gaussian pulse is centered if moddfl = 2

time at which step pulse starts is centered if moddfl = 3

use any value as a placeholder for moddfl = 0, 1, or 4

The lines following grid iaei ... kaef are repeated |ngrid| times:

grid

grid containing all or part of the current aeroelastic surface iaesrf. use any value as a placeholder if ngrid = -1.

iaei

starting i-index of the current aeroelastic surface in zone grid. use any value as a placeholder if ngrid = -1.

iaef

ending i-index of the current aeroelastic surface in zone grid. use any value as a placeholder if ngrid = -1.

jaei

starting j-index of the current aeroelastic surface in zone grid. use any value as a placeholder if ngrid = -1.

jaef

ending j-index of the current aeroelastic surface in zone grid. use any value as a placeholder if ngrid = -1.

kaei

starting k-index of the current aeroelastic surface in zone grid. use any value as a placeholder if ngrid = -1.

kaef

ending k-index of the current aeroelastic surface in zone grid. use any value as a placeholder if ngrid = -1.

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Responsible NASA Official: Christopher Rumsey
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Last Updated: 03/29/2013