baran.ze
27th September 2011, 07:31 AM
ANSYS Tutorial: Non Linear Buckling
ANSYS Workbench Tutorial: Learn how to perform Non Linear Buckling simulations with initial imperfections included. In ANSYS Workbench in V12, we can update the geometry based on the calculated results from a previous analysis and import the finite element model of the updated and deformed geometry into a new analysis. This article shows how to do it.
Buckling
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image001.gif
"Buckling (http://en.wikipedia.org/wiki/Buckling)" is a failure mode characterized by a sudden failure of a structural member subjected to high compressive stresses, where the actual compressive stress at the point of failure is less than the ultimate compressive stresses that the material is capable of withstanding. This mode of failure is also described as failure due to elastic instability. Mathematical analysis of buckling makes use of an axial load eccentricity that introduces a moment, which does not form part of the primary forces to which the member is subjected.
Introduction
ANSYS Mechanical APDL (previously called ANSYS Classic etc…) has been integrated into Workbench as a module in ANSYS Release 12. The integration creates a tighter connection between Workbench and Mechanical APDL which in its turn gives us more possibilities to handle difficult analysis procedures, such as running DesignXplorer with an analysis calculated in Mechanical APDL.
In this tutorial we will take a look on how we can update geometry depending on results of a previous analysis and import the finite element model of the updated and deformed geometry into a new analysis.
In the current tutorial we will run a non-linear buckling analysis of a tower (could be a crane or a wind turbine foundation) with geometry defects. Initially, the geometry of the structure is perfect and we don’t know where geometry defects are located. A reasonable and conservative suggestion is that the geometry defects fit to the first mode shape of a linear buckling analysis. Therefore, the analysis procedure is first to run a linear buckling analysis and then to run a non-linear analysis with geometry defects depending on the first buckling mode shape.
---
Step 1: Setup linear buckling analysis
In this step we setup a linear buckling analysis as usually as shown in the following figure:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image002.png
After solving the model we get the first buckling mode shape and a maximum total deformation 1.098 mm.
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image004.png
Step 2: Update Geometry by Mechanical APDL
We create an input file “uppgeom.inp”. UPGEOM adds displacements from a previous analysis and updates the geometry of the finite element model to the deformed configuration. 20 in the command means we want to enlarge deformation of the first shape mode 20 times. Do not forget save the updated finite element model as a CDB file by command CDWRITE.
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image006.png
Now we can attach the input file to Mechanical APDL:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image008.png
After update the project take a look of Outline of Schematic to make sure the input file is correctly attached:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image010.png
Step 3: Recreate the deformed Model in FE Modeler
Now we have updated the geometry of the finite element model to the deformed configuration and saved it in a CDB file. We cannot import directly the model into Mechanical but via FE Modeler:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image012.png
In FE Modeler we can see clearly the deformed configuration, in which the deformation is enlarged 20 times:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image014.png
Step 4: Import the Deformed Model into Mechanical
From FE Modeler we can now import the deformed model into Mechanical:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image016.png
The following figure shows the recreated geometry depending on the first mode shape of a linear buckling analysis. We define a Fixed Support on its foot as in the previous analysis and a large Remote Displacement on its top. The displacement is so large that the structure could not sustain it. This is done in order to model the full collapse, and the post-buckling behavior of the structure.
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image018.png
The mesh is the same but the model is updated with geometry defects:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image020.png
In post-processing, we check the relationship between the applied displacement and the reaction force. At time=0.38, the reaction force reaches its maximum point. After the time point, the reaction force decreases while the applied displacement increases. It is obvious that nonlinear buckling happens at time=0.38.
From this result we can also extract the total collapse load for the structure, in this case 120 kN.
http://www.civilbaran.blogfa.com
ANSYS Workbench Tutorial: Learn how to perform Non Linear Buckling simulations with initial imperfections included. In ANSYS Workbench in V12, we can update the geometry based on the calculated results from a previous analysis and import the finite element model of the updated and deformed geometry into a new analysis. This article shows how to do it.
Buckling
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image001.gif
"Buckling (http://en.wikipedia.org/wiki/Buckling)" is a failure mode characterized by a sudden failure of a structural member subjected to high compressive stresses, where the actual compressive stress at the point of failure is less than the ultimate compressive stresses that the material is capable of withstanding. This mode of failure is also described as failure due to elastic instability. Mathematical analysis of buckling makes use of an axial load eccentricity that introduces a moment, which does not form part of the primary forces to which the member is subjected.
Introduction
ANSYS Mechanical APDL (previously called ANSYS Classic etc…) has been integrated into Workbench as a module in ANSYS Release 12. The integration creates a tighter connection between Workbench and Mechanical APDL which in its turn gives us more possibilities to handle difficult analysis procedures, such as running DesignXplorer with an analysis calculated in Mechanical APDL.
In this tutorial we will take a look on how we can update geometry depending on results of a previous analysis and import the finite element model of the updated and deformed geometry into a new analysis.
In the current tutorial we will run a non-linear buckling analysis of a tower (could be a crane or a wind turbine foundation) with geometry defects. Initially, the geometry of the structure is perfect and we don’t know where geometry defects are located. A reasonable and conservative suggestion is that the geometry defects fit to the first mode shape of a linear buckling analysis. Therefore, the analysis procedure is first to run a linear buckling analysis and then to run a non-linear analysis with geometry defects depending on the first buckling mode shape.
---
Step 1: Setup linear buckling analysis
In this step we setup a linear buckling analysis as usually as shown in the following figure:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image002.png
After solving the model we get the first buckling mode shape and a maximum total deformation 1.098 mm.
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image004.png
Step 2: Update Geometry by Mechanical APDL
We create an input file “uppgeom.inp”. UPGEOM adds displacements from a previous analysis and updates the geometry of the finite element model to the deformed configuration. 20 in the command means we want to enlarge deformation of the first shape mode 20 times. Do not forget save the updated finite element model as a CDB file by command CDWRITE.
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image006.png
Now we can attach the input file to Mechanical APDL:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image008.png
After update the project take a look of Outline of Schematic to make sure the input file is correctly attached:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image010.png
Step 3: Recreate the deformed Model in FE Modeler
Now we have updated the geometry of the finite element model to the deformed configuration and saved it in a CDB file. We cannot import directly the model into Mechanical but via FE Modeler:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image012.png
In FE Modeler we can see clearly the deformed configuration, in which the deformation is enlarged 20 times:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image014.png
Step 4: Import the Deformed Model into Mechanical
From FE Modeler we can now import the deformed model into Mechanical:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image016.png
The following figure shows the recreated geometry depending on the first mode shape of a linear buckling analysis. We define a Fixed Support on its foot as in the previous analysis and a large Remote Displacement on its top. The displacement is so large that the structure could not sustain it. This is done in order to model the full collapse, and the post-buckling behavior of the structure.
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image018.png
The mesh is the same but the model is updated with geometry defects:
file:///C:/DOCUME~1/baran/LOCALS~1/Temp/msohtmlclip1/01/clip_image020.png
In post-processing, we check the relationship between the applied displacement and the reaction force. At time=0.38, the reaction force reaches its maximum point. After the time point, the reaction force decreases while the applied displacement increases. It is obvious that nonlinear buckling happens at time=0.38.
From this result we can also extract the total collapse load for the structure, in this case 120 kN.
http://www.civilbaran.blogfa.com