workshop 1 – modal analysis of a flat plateforums.mscsoftware.com/patran/files/3164-workshop...
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Department of Aerospace EngineeringFaculty of Engineering
Universiti Putra Malaysia
Modal and Flutter Analysis of a Square Flat Plate Workshop
August 2005
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Workshop 1 – Modal Analysis of a Flat Plate
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Objective: to find the first five natural frequencies and mode shapes of the plate which is used in flutter analysis in M-k pair set definition.
Model Description:
For this example, we use Lanczos method to find the first five natural frequencies and mode shapes of a flat square plate (0.254m x 0.254 m). Figure 1 shows the plate geometry in MSC.Patran environment.
Figure 1 - Flat Square Plate Geometry
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Elastic properties of the aluminum plate are stated in Table 1:
Table 1 – Elastic Properties of Aluminum 6061
Elastic Modulus 6.8947e10 PaShear Modulus 2.6518e10 PaPoisson’s Ratio 0.3
Density 2643.4 kg/m3
Plate Thickness 0.000508 m
Figure 2 - Loads and Boundary Conditions
In this example at Nodes 1, 12, 23, 34, 45 we have neither translation nor rotation (T1, T2, T3, R1, R2, R3 = 0); at all other nodes of the plate the vertical component of the translation (T2) as well horizontal and lateral component of the rotation (R1 and R3) are zero.
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Exercise Procedure:
1. Create a new database named prob1.db.File/NewNew Database Name prob1OK
In the New Model Preferences form, set the following:Tolerance DefaultAnalysis Code: MSC/NASTRANOK
2. Activate the entity labels by selecting the Show Labels icon on the toolbar.
3. Create a surface.
Geometry
Action: Create
Object: Surface
Method XYZ
Vector Coordinates List <0.254, 0.254, 0>
Origin Coordinates List [0, 0, 0]
Apply
4. Create the finite element model and mesh the surface.
Finite Elements
Action: Create
Object: Mesh Seed
Type: Uniform
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Figure 3 - The surface should resemble the output below.
Number of Elements
Number = 10
Curve List Surface 1.4(See Figure 3)
Apply
5. Change the number of mesh seeds to 4 and select the right edge.
Finite Elements
Number = 4
Curve List Surface 1.1(See Figure 3)
Apply
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Surface 1.1
Surface 1.4
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6. Mesh the Surface
Action: Create
Object: Mesh
Type: Surface
Surface List Surface 1
Apply
Figure 4-The model should appear as below
7. Create a set of material properties for the plate.
MaterialsAction: Create
Object: Isotropic
Method: Manual Input
Material Name mat_1
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Input Properties...
Elastic Modulus = 6.8947e10
Poisson Ratio = 0.3
Shear Modulus = 2.6518e10
Density = 0.282
OK
Apply
8. Define the plate thickness.
Properties
Action: Create
Dimension: 2D
Type: Shell
Property Set Name plate
Input Properties...
Material Name m:mat_1(Select from Material Property Sets box.)
Thickness 0.100
OK
Select Members Surface 1
Add
Apply
9. Apply constraints to the model.
Load/BC’s
Action: Create
Object: Displacement
Type: Nodal
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New Set Name Seta
Input Data...
Translations <T1 T2 T3> <0, 0, 0>
Rotations <R1 R2 R3> <0, 0, 0>
Analysis Coordinate Frame Coord 0
OK
Select Application Region...
Geometry Filter FEM
Select Nodes Node 1:45:11
Add
OK
Apply
Repeat this action for Setb
Action: Create
Object: Displacement
Type: Nodal
New Set Name Setb
Input Data...
Translations <T1 T2 T3> <, 0,>
Rotations <R1 R2 R3> <0, , 0>
Analysis Coordinate Frame Coord 0
OK
Select Application Region...
Geometry Filter FEM
Select Nodes Node 2:11 13:22 24:33 35:44 46:55
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Add
OK
Apply
10. Run the analysis.
Due to the fact that only one full run can be done at a time so we analyze this job using analysis deck and after creation of *.bdf file students should queue to run their files and get the result.
Action: Analyze
Object: Entire Model
Method Analysis Deck
Job Name plate
Translation Parameters...
Data Output: XDB and Print
OK
Solution Type...
Solution Type: NORMAL MODES
Subcase Create...
Available Subcases Default
Subcase Parameters...
Number of Desired Roots = 5 OK
Apply
An MSC.Nastran input file called plate.bdf will be generated. The process of translating your model into an input file is called Forward Translation. The Forward Translation is complete when the Heartbeat turns green.
Submitting the input file for analysis:
On these computers the *.bdf files usually will be created in C:\Windows\Temp folder. After the analysis is completed try to locate this file in that folder. Now you have to submit this file which should be named as plate.bdf to Nastran for analysis. From Start
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Menu find this path: All Programs/MSC.Softeware/ MSC.Nastran NONE/ MSC.Nastran 2005. Run this application. In the dialogue box which will be popped up select plate.bdf as the input file and select open. Now on another dialogue box select run and wait until the beep which demonstrates that the analysis is complete. Go to the same folder (C:\Windows\Temp) and try to find plate.f06 file. Open this file with Notepad and search for the term FATAL. If there is no FATAL in your file, most probably you have done this analysis correctly. Now go back to Patran environment and invoke the analysis button. And follow this procedure:
Action: Analyze
Object: Access Results
Method Attach XDB
Job Name Results Entities
Select Result File …(Try to find plate.xdb in C:\Windows\Temp folder)
Apply
Now go to Result Menu, you can see the 5 natural frequencies of this plate.
Results
Action: Create
Object: Deformation
Select Results Cases Default, A1: Mode 1: Freq. = 6.7767
Select Deformation Result Eigenvectors, Translational
Apply
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Figure 6 – The First Mode Shape
The first five natural frequencies should be the same as following:
1- 6.7767 Hz
2- 42.003 Hz
3- 101.14 Hz
4- 116.44 Hz
5- 185.23 Hz
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Workshop 2 – Flutter Analysis of the Flat Plate
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Objectives:
Obtaining the flutter speed and frequency using MSC.Nastran PK-method. Getting the V-g graph using Microsoft Excel. Getting the V-F graph using Microsoft Excel.
Here we can use either the Graphical User Interface (GUI) or Input file for flutter analysis. The GUI for aeroelastic analysis is MSC.FlighLoads and Dynamics whose environment is actually MSC.Patran with aeroelasticity analysis module added to its analysis preference. Regardless of what method you opt there are three general steps for aeroelastic analysis using MSC.Nastran.
1. Defining the structural geometry and elements.2. Defining the aerodynamic geometry and boxes.3. Creating the appropriate splines to interpolate between structural elements and
aerodynamic boxes.
The structural geometry and elements have been defined in the previous workshop so we will leave it to the user to work with the same structure or create a new one following the procedure elaborated in the aforementioned exercise. Thus we start our exercise with aerodynamic geometry definition.
Exercise Procedure:
1. From the Preference Menu, select Analysis and change the analysis type to Aeroelasticity.
2. Create Aerodynamic Surface
Geometry
Action: Create
Object: Surface
Method XYZ
Vector Coordinates List <0.254, 0.254, 0>
Origin Coordinates List [0.01, 0.01, 0.01](The origin coordinates list should be different from structural geometry)
Apply
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3. Create the Aerodynamic Model
Flight Loads/Aero Modeling/Model Management
Action: Create
Object: SuperGroup
Type: Flat Plate
SuperGroup Name (8 chars)
Aeroelas
Apply
Cancel
Remark: If you don’t assign any name to the SuperGroup the Flight Load will automatically assign AeroSG2D for it as a default
Flight Loads/Aero Modeling/Flat Plate Aero Modeling…
Action: Create
Object: Lifting Surface
Method: Existing Surface
Surface Name
aero
Select Existing Surface Surface 2
Mesh Control
Span Mesh: Uniform
Number = 10
Chord Mesh: Uniform
Number = 4
Ok
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Apply
Cancel
4. Define the Aerodynamic Parameters
Flight Loads/Aerodynamic/Global Data
Aero Model: Aeroelas
Full Model Half Model(We will select full model for this exercise)
Reference Span: 0.254
Reference Chord: 0.254
Densities: SL kg/m3
Reference Density
1.226
OK
Flight Loads/Aerodynamic/Unsteady Aerodynamics…
Action: Create
Create: MK Pair Set
MK Pair Set Name
MK-Flutter
Mach Frequency Pairs…
Mach Set: Uniform
Mach: 0.09
Frequency Set: UniformDimensional
Fmin: 6.7767
Vmax: 50
Fmax: 185.23
Vmin: 10
Number: 8
Add
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OK
Apply
Cancel
1. Fmax and Fmin are referred to first and fifth natural frequencies of the plate respectively.2. Vmax and Vmin are referred to maximum speed and minimum speed of the plate respectively.
5. Define Splines
Flight Loads/Aeroelasticity/Aero-Structure Coupling…
Action: Create
Object: Surface
Method: General
Spline Name
spline
Structural Points
Nodes Groups
Select Groups…
Existing Groups: default_group
Close
Aero Boxes
Elements Surface
Existing Surface…
Existing Surfaces: aero
Close
Apply
Flight Loads/Aeroelasticity/Aeroelastic Model…
Auto Select Splines
Ok
6. Aeroelastic Analysis
Flight Loads/Aeroelasticity/Analysis…
Solution Type: Flutter
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Subcase Create…
Action: Create
Subcase Name
Flutter
Mach-Frequency Paris…
Mach-Frequency Sets: MK-Flutter
Ok
Flutter Parameters…
XZ Symmetry: Symmetry
XY Symmetry: Symmetry
Method: PK
Mach: 0.09
Density Ratio Sets…
Action: Create
Density Ratio Set Name
Density
Input
1
Enter
Apply
Action: Select
Density Ratio Set:
Density
Apply
Velocity Sets…
Action: Create
Velocity Set Name
Velocity
Input
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1
Enter
10
Enter
15
.
.
.
50
Enter
Apply
Action: Select
Velocity Set:
Velocity
Apply
OK
Subcase Select…
Subcases for Solution Sequence 145:
Flutter
OK
Job Name
Flutter
Job Parameters…
Run Type: Analysis Deck
(like previous exercise you can choose between Analysis Deck or Full run, but due to the same reason it is strongly advised to choose Analysis Deck and apply *.bdf file which is generated afterward to MSC.Nastran for Analysis).
OK
Run
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After the run is complete try to find flutter.bdf in C:\Windows\Temp folder and do the upcoming procedure as previously stated in the modal analysis exercise. Now find flutter.f06 file in the same folder, open it u with Notepad and search for the term FATAL, if you didn’t find any FATAL error messages your procedure is most probably correct. In this file you can find these data for the Mach-Frequency Pairs that you have defined: KFREQ, 1./KFREQ, VELOCITY, DAMPING, FREQUENCY, COMPLEX EIGENVALUE.
Take a quick look at the results, your flutter will normally occur at the first points. Try to plot velocity against damping for the first 4 points using Microsoft Excel. Flutter will occur when the damping is tending to zero. So the flutter speed value is the point where the graph crosses the velocity axis. This graph is called V-g graph. A Typical V-g graph should resemble this:
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
0.20
1 10 20 30 40 50 60 70 80 90 100 110 120 130 135 140 145 150 160
V- Velocity
g- D
ampi
ng
In the above graph Flutter occurs at 151 m/s and the corresponding frequency is the Flutter Frequency.
For the square flat plate the V-g and V-F (Velocity – Frequency) graph would be as following; for this example the flutter speed is around 29 m/s and flutter frequency is 35.8356 Hz.
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-0.20
0.00
0.20
0.40
0.60
0.80
1.00
1 10 20 30 40 50 60
V - Velocity
g - D
ampi
ng
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
1 10 20 30 40 50 60
V - Velocity
F - F
requ
ency
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