Tutorial VSP Conference 2013, San Luis Obispo, CA

University of Texas VSP Structural
Analysis Module Update - Demonstration
http://vspsam.ae.utexas.edu/
VSP Workshop, San Luis Obispo, CA
Hersh Amin
Armand J. Chaput
Department of Aerospace Engineering and
Engineering Mechanics, University of Texas at Austin
7 August 2013

© 2012 Armand J. Chaput

Today’s Lineup
• Overview of VSP SAM Process
• VSP Model
• Grumman A6E Intruder Wing
• VSP SAM
• Version 1
• Overview
• Tutorial:
• Shrenk’s Approximation (Air Loads)
• Load Factor: 9.75 g
• Version 2
• Overview
• Tutorial:
• Shrenk’s Approximation (Air Loads)
• Load Factor: 9.75 g
• Wing fuel
• External stores (external fuel tanks)
• Note: corresponding files can be found at:
http://vspsam.ae.utexas.edu/archieve/VSPWorkshop2013

Overview of VSP SAM Process
Vehicle Sketch Pad
Parametric
Internal Geometry
Parametric
External Geometry
External and Internal Mesh
Generation
UT Convergence Executable
(Java)
Solution Files

UT Input Executable (Java)
Wing Trim
Thickness and
Material Properties
Boundary Conditions
and Load Cases
CalculiX Input File

CalculiX 
FEM Input
FEM Solution

Thickness Calculation
Mass Calculation

FEM Post Process
and Graphics

Stress Convergence

Output Files

Overview of VSP SAM Process – Vehicle Sketch Pad
Vehicle Sketch Pad
Parametric
Internal Geometry
Parametric
External Geometry
External and Internal Mesh
Generation

VSP process through mesh generation

Overview of VSP SAM Process – UT Input Executable
• Deletes non-primary load carrying structure
- Typically leading and trailing edge devices
• Deletes non-load carrying skin panels
- To represent typical fabric or film skin sections

Wing Trim
Thickness and
Material Properties
Boundary Conditions
and Load Cases
CalculiX Input File

Wing Trim

Spars, Ribs and Skins can be defined as different
materials

Thickness and
Material Properties
Boundary Conditions
and Load Cases
CalculiX Input File

Required Thickness
defined by input
Design Nominal
Stress (DNS)
objective and
Minimum Gauge

Executable
• 2D linear load – at defined constant chord fraction UT Input Wing Trim (Java)
- Input based on root and tip running load
Thickness and
Material Properties
• 2D elliptical and Schrenk approximations
Boundary Conditions
- Input based on flight design gross weight and nz
and Load Cases
• Discrete point loads (Fxx, Fyy, Fzz, Mxx, Myy, Mzz)
CalculiX Input File
- GUI inputs at defined % span and % chord locations
• Discrete mass loads (nz) (v2+ feature)
- GUI inputs at defined spar # and % span or rib # and % chord
locations with multiple attachment points on ribs and/or spars
• Multiple Load Cases (v2+ feature)
- GUI inputs for multiple 2D linear, elliptical or Schrenk
approximations with varying angle of attacks and varying load
distributions on spars
• Fuel Loads (v2+ feature)
- GUI inputs for adding fuel tanks between ribs and spars
- Applies pressure loads and inertial loads on the skin

Boundary conditions define which rib is fixed from
translation in the x, y and z axis

Overview of VSP SAM Process – CalculiX Solutions
Wing Trim
Thickness and
Material Properties
Boundary Conditions
and Load Cases
CalculiX Input File

CalculiX 

Users can see status messages while VSP SAM
is running. Messages can have information on
VSP SAM’s current stress convergence iteration,
Load cases and/or Wing trim operation.

FEM Input
FEM Solution
FEM Post Process
and Graphics
Output Files

Overview of VSP SAM Process – CalculiX Solutions
CalculiX 
FEM Input

Left click in
white area
brings up menu
Menu provides
range of stress
& displacement
viewing options

FEM Solution
FEM Post Process
and Graphics

Solution
viewing
area

Output Files

Option shown
is von Mises
stress
Mouse commands
rotate and zoom
solution

Overview of VSP SAM Process – UT Convergence Executable
Simple Von Mises stress-based structural
UT Convergence Executable
Summary of theory and method used to back out required Nodal thicknesses
(Java)
thickness resizing algorithm developed
Solution Files
• Background
An enabling capability for FEM based
Thickness Calculation
structural the project to be able to determine the optimized thickness of each part of the Mass Calculation
Part of the objective ofmass isproperty estimation
wing for a given working stress. This backing out the thicknesses aims to do that. The procedure used
Stress Convergence
• by our team and the theory behind itresizing is based on
Node thickness is described.
user defined design nominal stress (DN)
Theory
or minimum gage, whichever larger
We begin with an arbitrary 3D element as shown below:

Thickness

t’i = (/DN)  ti

The SAM iterates stress principal axes, showing that the element can be
VSPblue plane represents a plane lying in one of the 3to mass convergence
arbitrarily oriented. We can then describe the stress acting on this plane as follows:
(1)
We know seek to find the required thickness for a given working stress as defined by the user:
(2)

Overview of VSP SAM Process – Mass Calibration Method

Build VSP Model
• Use actual Area, Taper Ratio, Dihedral, Thickness, and Span
• Model the actual Spar locations.
• Model the actual Rib locations.

Generate Mesh
• Choose mesh size depending on wing size. Typically 100
elements spanwise (Half-Span/100).
• Generate meshes.
• If mesh size > 5 Mb, increase mesh size.

Mass Convergence Minimum Gauges & DNS
• Constant Minimum Gauge
• Initial Design Nominal Stress (DNS) = Initial guess
• Vary DNS for ribs, spars and skins until final wing structure
weight matches expected value.

Overview of
VSP SAM

VSP Model
Information

VSP Model – A6E Intruder

Intermediate & Outer sections Only
No Center Section

VSP Model – Why A6E Intruder ?
• Available in Metal and Composite
• Good Mass Properties
• Internal Fuel and External Stores
• Larger Operating Flight Envelope
• Good for the purpose of Software Calibration

VSP Model – A6E Planform

All locations and linear
dimensions in inches
BL 38.9

Tip Chord (BL 305):
62.125” = 5.18

 BL 66
 BL 78

Root Chord (BL 66):
~156.53” = 13.04’

BL 144

Sweep: 29.5
29.5

BL 318

BL 305

 0.05 c

56”

 28

 0.70 c

33”

NOTE: Currently VSP SAM does not
support Multi-Section Wing which
limits this analysis to intermediate
and outer sections only which will be
combined into single wing section

VSP Model – A6E Airfoil

NACA-6 Series
Airfoil
t/c (BL 66):
~0.0885

t/c (BL 305):
~0.0612
NOTE: Only Root and Tip t/c ratios
will be used since adding additional
t/c ratios need multi-section wing
which is not currently supported by
VSP SAM

VSP Model – A6E Spars

 BL 78

 117”

All locations and linear
dimensions in inches

BL 144

BL 318

 BL 66

BL 38.9

BL 0

FS 0

29.5
BL 305

FS 228.2
 0.05 c

56”

0.15 c

182.6
FS 283.9

 28

33”

Drawing warped L/R

 0.70 c

0.83 c
0.70 c?
57”

318”

VSP Model – A6E Ribs

9 Ribs
including Root
Rib 0

and Tip Rib
Spar 1

Spar 0
NOTE: To further simply the
model, all ribs are placed parallel
to free stream.

Rib 8

VSP Model
Information

Build A6E
VSP Model

VSP Model – Adding a new wing
1

3
2

VSP Model – Modifying the new wing (A6E Planform)
1

5

2
6

3

4

2

4
Delete all sections
except section ID: 0

3

6
Set Tip Chord, Root
Chord, & Sweep

Set Span, &
Projected Span

VSP Model – Modifying the new wing (A6E Airfoil)
1
2

1

3

Airfoil ID:

0

2

Type:
(Dropdown
menu)

3

t/c ratio:
0.0885
(“Thick” slider)

1

NACA
NACA
6-series 6-series
0.0612

VSP Model – Modified A6E wing geometry

1

2

VSP Model – FEM Geometry

1
2

VSP Model – A6E FEM Geometry (Spars)

3

Spar ID:
1

0

1

Position:
(“Position:
Slider)

2

3

0.05

0.7

Sweep
Angle:
(“Rel”
checkbox)

Checked

Checked

Relative
Sweep
Angle:
(“Sweep”
Slider)

0.00

0.00

VSP Model – A6E FEM Geometry (Ribs)

3

Rib ID:

Position
(“Position” Slider)

1
0
1

3

0.1

2

2

0.0
0.231

3

0.322

4

0.457

5

0.611

6

0.751

7

0.892

8

1.0

VSP Model – Finished A6E FEM Geometry
1

2

Location of Ribs and Spars

VSP Model – Generate A6E Mesh
1
Bigger element
size yields bigger
mesh and faster
run time.

3

4

2

VSP SAM – Required Files

1

• Geom File: <Wing_Name>_calculix_geom.dat
• Thick File: <Wing_Name>_calculix_thick.dat
• Copy the “Geom File” and the “Thick File” in a separate directory to run
SAM
• NOTE: SAM working directory (next slide) must not have any spaces in its
path.

VSP SAM – Import VSP Mesh
1
1

2

Set directory for VSP Mesh Files.
You can choose either
calculix_geom or calculix_thick file.

3

1
NOTE: having spaces in the
directory path will result in crash.

2
3

Open

2
Set the directory of the CalculiX
folder
(use default with typical installation)
3

Save

3
Open GUI inputs from previous
session or Save GUI inputs for
future sessions

VSP SAM – Sign Conventions
Origin is always at wing Apex
and parallel to the VSP
coordinate system.

Z

NOTE: All Axis are parallel or
perpendicular to the Datum
regardless of wing sweep,
dihedral or angle of attack

Y
X

X axis goes
chordwise

Y axis
goes into
the page

Y axis goes
spanwise

α

Datum

Applies to all the load factors including nx, ny, and nz

Z axis goes
normal to the
Datum

Build A6E
VSP Model

VSP SAM
Version 1

VSP SAM – Version 1
Features:
• Skin Trim Feature
• Load Spar Approximations
• Boundary Condition
• Separate FEM Models
• Special Case: “Zero” Node Thickness
• Stress Convergence and Node Sizing
• Mass Calculation

VSP SAM – Skin Trim Feature

Remove non-load carrying skin
panels which can be fabric
sections of the skin, landing
gear hatches, etc.

Skin trim must be defined by
Inboard/Outboard rib and
Forward/Aft spar

VSP SAM – Load Spar Approximations
Planform Shape, Elliptical and Schrenk’s Approximations:

Schrenk’s Load distribution is equivalent to average of elliptical load distribution
and the actual planform shape distribution of the wing.

VSP SAM – Boundary Condition
Rib 0 is fixed from
translation in the x,y and
z axis as shown in the
CalculiX results file.
As a result, this particular
wing structure is a
cantilever beam with Rib
0 as the stationary plane.
Any Rib can be defined
as a fixed rib such as a
“Body Rib” as shown in
the figure below.

Rib 0

Body Rib

VSP SAM – Separate FEM Models
Version 0 contains Single FEM model results from original VSP’s output files
When node thickness is
resized to meet user defined
DNS objective, different node
thickness requirements at
intersections distort elements
which results in CalculiX error

Version 1 Splits FEM into separate Skin, Rib, and Spar FEM models using “Rigid
Body Elements” to make connections at rib-skin, spar-skin, and rib-spar intersections

Thicker
elements at ribskin, spar-skin,
and rib-spar
intersections

VSP SAM – Special Case: “Zero” Node Thickness
Set of vertical nodes from a spar, with the horizontal lines representing the
thickness of each node and the Red Arrow represents the force applied to this set

Thickness of
some nodes
approaches at
nearly zero after
convergence

Solution: Apply average
thickness of the adjacent
nodes to the affected node

z

y
Before

After

NOTE: Set of nodes from a
spar is only used as an
example, The same method
applies to any affected node
within the FEM model

Summary of theory and method used to back out required Nodal thicknesses

VSP SAM – Stress Convergence and Node Sizing
Background
Part of the objective of the project is to be able to determine the optimized thickness of each part of the
wing for a given working stress. This backing out the thicknesses aims to do that. The procedure used
by our team and the theory behind it is described.

1 and Thickness1 corresponds to each node

Theory

We begin with an arbitrary 3D element as shown below:

Thickness

t’i = (/DNS)  ti

The blue plane represents a plane lying in one of the 3 principal axes, showing that the element can be
arbitrarily oriented. We can then describe the stress acting on this plane as follows:
(1)
We know seek to find the required thickness for a given working stress as defined by the user:
(2)

Solving equation (1) for the force, and plugging into equation (2) it can be shown that we get:

By using the max principal stress in any given element for we can ensure that the element is sized for
the worst case scenario. This is the theory behind the procedure used.

VSP SAM
Version 1

A6E Tutorial
for v1

VSP SAM (version 1) – A6E Wing Geometry
2

1
2

Initial Thickness definitions

3

3

Set boundary conditions
(Fixed Rib) which indicates
which Rib is fixed from
translation in x, y, and z
direction and Convergence
Tolerance which ends the
iterative process when the
mass difference between
previous iteration and
current iteration converges
to the user defined
tolerance

VSP SAM (version 1) – A6E Wing Trim

Before Trim

After Trim
Wing Box of the A6E Intruder Wing

VSP SAM (version 1) – A6E Wing Trim (cont’d)
1
2

1
2

4

4

3

3

Leading Edge Trim

Trailing Edge Trim

Device Trim definition to reveal the Wing Box of the A6E Intruder Wing

VSP SAM (version 1) – A6E Material Properties
Set Material Properties such as
Young’s Modulus, Poisson’s
Ratio, Yield Stress and Ultimate
Stress

1
2

3

3

NOTE: Throughout VSP
SAM, ft and lbm will be the
nominal units.

Assign materials defined (2) to
each component and set the
Design Nominal Stress (DNS)
as well as Density and Minimum
Gauge (minimum thickness) for
each component

For this case, properties of 2024 T3
Aluminum Alloy is used which is a
nominal material for metal wings,
and Minimum gauge of typical
military aircraft wing is used.
MIL-HDBK-5, Table 3.2.3.0(d)

VSP SAM (version 1) – A6E Aircraft Weight
Running Load p
Fuel inertia relief

Wing External Loads (distributed)
12000

NOTE: Only 73 % of the
Flight DGW will be used
since this analysis only
involves the intermediate
and outer sections of the
A6E Wing

10000

lbf/ft

8000

6000

4000

2000

0
0.000

0.100

0.200

0.300

0.400

0.500

y/b

External load
Inertia relief

Wing External Load Fraction
1.00
0.90
0.80

Load fraction

0.70

Flight Design Gross
Weight (DGW):
36526 lbm

0.60
0.50
0.40
0.30
0.20
0.10
0.00
0.00

0.10

0.20

0.30
y/b

0.40

0.50

Load Fraction at BL66 (root):
0.73 of Flight DGW
26664 lbm

VSP SAM (version 1) – A6E Load Case
1

2

NOTE: All of the Aircraft
Load will be placed on
Spar 0 Only due to VSP
SAM version 1 limitation

3

4

http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/airfoil.html

VSP SAM – Running SAM

1
Press Run button to initialize SAM

2
Press Stop button to quit SAM

1

2

A6E Tutorial
for v1

A6E v1
Results

VSP SAM – Viewing CalculiX Results

NOTE:
These files can be
found in the same
directory where VSP
Mesh files are located
1
In version 2, “Wing1_N” represents
CalculiX results for Case ID 1 set
in “Load Case” tab at iteration N.
Highest “N” represents the final
iteration.

NOTE: In version 1, “Wing1” from “WingN” is used where “N”
represents the iteration number. “Wing_initial” represents the
initial iteration and “Wing_final” represents the final iteration.

VSP SAM – Viewing CalculiX Results (cont’d)

1

Translate Model:
Use Right Mouse
Button

2

3

Rotate Model:
Use Left Mouse
Button
Zoom in/out Model:
Hold scroll wheel
while dragging the
mouse

VSP SAM – Mass Results File

NOTE:
These files can be
found in the same
directory where VSP
Mesh files are located

“mass.csv” consists of mass values of each
component as well as volume and surface
area at each iteration.

NOTE: VSP SAM only outputs the mass
values in “mass.csv” file. It does not plot any
values as of right now.

VSP SAM (version 1) – A6E Mass Results

Skin
Mass (lbm):

Rib

Spar

Total

652.9

162.8

237.5

1052.8

VSP SAM (version 1) – A6E Stress Results (Iteration 0)
DNS
Skin: 46.181 ksi
Spars: 16.875 ksi
Ribs: 12.361 ksi

DNS
Skin: 46.181 ksi
Spars: 16.875 ksi
Ribs: 12.361 ksi

A6E v1
Results

VSP SAM
Version 2

VSP SAM – Version 2
Features:
• Multiple Load Spars & Angle of Attack
• Multiple Load Cases
• Wing Fuel Loads
• Discrete Mass Loads

VSP SAM – Multiple Load Spars & Angle of Attack
• Based on Angle of Attack (α), loads are split in x and z directions.
• Each spar can be assigned a load fraction of the Total Load in order to get
the resultant force applied on the wing.

Red Arrow
represents
the resultant
force applied
on the wing

α>0
α=0

z
x

http://www.pilotfriend.com/training/flight_training/aero/pres_pat.htm

VSP SAM – Multiple Load Cases
• More than one Load case can be assigned with varying Angles of Attack
and varying Load Spar Distributions.
• Constructs new FEM model from using Max Stress on each node and Max
Thickness of each node out of all the user-defined load cases.
• The new FEM model is used to calculate final mass estimate.
All 4 points of the flight envelope
can be analyzed
1
1

2

Positive High Alpha
2
Positive Low Alpha
3
Negative Low Alpha

4
4

3

Negative High Alpha

VSP SAM – Wing Fuel Loads

•

Fuel Tanks are defined by forward/aft spar and inboard/outboard rib

VSP SAM – Discrete Mass Loads
• Adds inertial loads on the spars and/or ribs with multiple
attachment points.
• User defines spanwise/chordwise fraction along with spar/rib
numbers and load fraction of the Total Load for a given attachment
point.
• Adds load along the neutral axis of the rib or spar (figure 2).
• Distributes loads based on the distance from user-defined spar/rib
location (figure 1).
Node 1

D1

D2

Node 2

figure 2

Location

figure 1

Loads are applied in the nz direction

VSP SAM
Version 2

A6E Tutorial
for v2

VSP SAM (version 2) – A6E Initial Inputs
1

1
Same inputs as version 1:
Wing Trim (Devices Tab)
Wing Geometry

VSP SAM (version 2) – A6E Material Properties
1

2
Same inputs as version 1

Different DNS for each
component. Same Minimum
Gauge and Density as version 1
3

VSP SAM (version 2) – A6E Load Case
4

1

2

Load
Parameters:
4

5

0

1

Spar #:

0

1

% of Load:

3

0.75

0.25

Fixed End
Moment:

0.0

0.0

6

7

http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/airfoil.html

VSP SAM (version 2) – A6E Wing Fuel Tanks
78. Starboard Wing
Integral Fuel Tank

Fuel Tanks

91. Outer Panel
Integral Fuel Tank

84. Outer Wing
Missile Pylon

201. Inboard Wing
Pylon

VSP SAM (version 2) – A6E External Stores
Rib 0

Rib 1

Rib 4

Rib 8

Rear View

z

Pylon

Outboard Fuel Tank

Outboard:

96.3

91.7

199

199

Fuel (lbm):

2005

2005

Total Mass (lbm):

Inboard Fuel Tank

Inboard:

Tank w/adapter (lbm):

y

External Stores:
Pylon (lbm):

Tank w/adapter

2300.3

2295.7

Spar 0
Top View

Attachment
Points

x
Spar 1

y

VSP SAM (version 2) – Adding A6E External Stores
1
3

4

2

Mass ID:

3

5
4

0

1

Mass(lbm):

2300.3

2295.7

Load Factor
(nz):

-9.75

-9.75

Rib #:

1

4

Chordwise
Fraction:

0.5

0.5

4

6

Note: All masses are
attached at ribs

VSP SAM (version 2) – Adding A6E Wing Fuel
1
3

4

2

Tank Inboard Outboard FWD Aft
Rib
Rib
Spar Spar
ID:
4

0

1

0

1

1
5

0

1

2

0

1

2

4

5

0

1

3

5

6

0

1

4

6

7

0

1

5

7

8

0

1

A6E Tutorial
for v2

A6E v2
Results

VSP SAM (version 2) – A6E Mass Results

Skin
Mass (lbm):

Rib

Spar

Total

651.8

162.3

235.9

1050.0

DNS
Skin: 42.569 ksi
Spars: 15.069 ksi
Ribs:
9.028 ksi

Tutorial VSP Conference 2013, San Luis Obispo, CA

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