Abaqus shell element model - extract beam section properties

[xlxc34]

Hi,

I have modelled a wind turbine blade in Abaqus/CAE. It is made from a variety of different composite lay ups, so I have used composite shell elements to model it. I have some wind turbine specific simulation software, but it requires beam section properties (bending stiffnesses, shear stiffnesses, location of elastic and shear centres, torsional stiffness, mass per unit length, inertia etc) to be defined at a series of points along the blade length. The blade is then modelled as a series of beam elements connected end to end in the wind turbine analysis software.

A number of people have told me that it is possible to extract the beam properties from the shell element model somehow, but no one has told me how!

I have managed to get the mass properties using tools->query->mass properties but I can't find the stiffness properties anywhere.

I will be very grateful if anyone can shed any light on this!

Best regards,

Peter Greaves

 

[mlamping]

Peter,

Help me get this straight in my mind. To keep things simple, assume you have a straight cylindrical pipe meshed with shells at the pipe's midsurface. Are you looking for a way to extract beam cross section data at any given location along the pipe's axis? Essentially this is creating a cross section from chain of shell elements that intersect the cross section and the shell element thickness.

Doing this with CAD data as input is straight forward, but not so much with shells or solid elements as your starting point. Am I reading this correctly?

Regards,
Mark

Mark Lamping
CAE Technical Consultant
Siemens PLM Software

 

[xlxc34]

Hi Mark,

That's exactly right. At the moment I have the .inp file (the company I'm working with uses Patran) but I could probably get a hold of the CAD model if necessary - although I have no idea how a CAD model of a composite structure manifests itself; is it just a surface with layup information defined in regions over its surface? Ideally I'd prefer to do it just with the FE model as it is quite time consuming getting information out of them.

 

[mlamping]

Peter,

Thanks for the clarification. I have to admit this is a new one for me, but I can see how it could be done conceptually in a variety of ways. We have the building blocks in NX to do this sort of cross section extraction, but nothing that strings them together automatically. I used a manual approach. Maybe you could do something similar in PATRAN. This isn't a perfect solution, but food for thought that did get the job done.

The attached ZIP contains a set of JPG that illustrate the steps. I took advantage of the following items in NX Advanced Simulation:

1. Display of shell elements as solids based upon shell element thickness

2. Create curves (graphical, point to point) – could have skipped this and created nodes as in the next step
If NX supported 1D section creation from a closed loop of curves (that didn't come from a Modeling Sketch), I’d be done… that’s a good enhancement!

3. Create nodes (on curve end points)

4. Create shell elements using the planar nodes

5. Create a polygon face (NX CAE geometry similar to CAD) from the planar shells

At this point NX could have created a beam cross section from the polygon face. BUT when selecting a polygon face, it filters for faces from a solid body!!! So I went further than I think would be necessary assuming some enhancements to the product.

6. Use an NX Open program to create a CAD face from the planar polygon face

7. Use the CAD face to extrude a solid

8. Select the cross section face from the solid for the beam cross section

This process could be repeated for each cross section along the blade. A little automation and user interaction (to define cross section points (steps 2-3 combined) and to create elements in 4) would help.

The images are summarized next:

1. Variable thickness shells displayed as solids on the left, the original solid geometry on the right

2. Planar set of curves created manually from graphical selection

3. Shell elements defining the cross section

4. Polygon face from the cross section shell elements

5. Sheet body (CAD) from the polygon face along with the original solid body and midsurface

6. Solid body from the sheet body

7. Definition of the cross section from a solid body face

8. Resulting beam mesh

9. Overlay of the beam mesh and shell mesh used to create the beam cross section

I definitely can see a couple enhancements from the workflow above. PATRAN may be able to do something similar. For me the key was being able to display the shells as solids and then generate cross section curves. Ideally that's as far as I should have had to go.

Regards,
Mark

Mark Lamping
CAE Technical Consultant
Siemens PLM Software

 

[xlxc34]

Hi Mark,

Thanks for that, it's definitely an idea. I'm not sure if Abaqus can display shell thicknesses... I haven't found it yet if it can(still very much a novice). However I do know them so I could get the beam properties by doing something like what you suggest. The only problem I can foresee is that the element stiffnesses can be different around the cross section (because of different lay ups) which this method won't pick up. I'll definitely use it where I can though. I might see if I can find a helicopter forum, I know they have to do this sort of thing with composite shells.

Thanks,

Peter

 

[corus]

If you have a shell model then why use that to input data into a beam model, which will be less accurate? You should be able to interpret the results to satisfy the design standard you have, and a bit more.

Tara

http://tinyurl.com/4ydjg7m

 

[mechfeeney]

Abaqus can display shell thicknesses (although I'm not sure how this would help you as it's just a visualization feature). View --> 'Name' Display Options --> Render Shell Thickness. Where 'Name' is either Part, Assembly, ODB, etc depending on what module you are in. If there is a way to import this model in a CAD package like SW then this task would be relatively simple.

 

[loki3000]

familiarize yourself with abaqus scripting.
also, do you work in europe (germany, austria) by any chance?

 

[xlxc34]

corus, I need the beam elements as shell elements cannot be used as an input to the wind turbine simulation tool I am using.

loki3000, How would I work this out with scripting? And I am based in the UK.

 

[RenuWind]

Hello Everyone,

Just read this discussion and I am having the exact same problem.

I am trying to use ABAQUS to produce equivilant beam properties to that of a wind turbine blade for use in a simplified analysis involving beam elements as aposed to shells&solids.

"Meshed beam cross-sections" has been highlighted as a method to obtain this information, but ABAQUS fails to give enough information on how to achieve this in the GUI (Graphical User Interface) or by Python scripts?

Please could anyone shed some light on this issue?

Thanks in advance.

 

[xlxc34]

I never found out how to do this in Abaqus I'm afraid... I ended up writing a MATLAB code based on stuff in this book:

http://books.google.co.uk/books?id=...ge&q=analysis of aerospace structures&f=false

There is also some software called VABS which is the state of the art for obtaining beam properties.

 

[RenuWind]

Thank you for your time xlxc34, I will look into your that. Will respond again if I do manage to figure out the Abaqus issue via meshed beam cross sections approach.

Regards.

 

[rb1957]

are you looking for I values for a stick model ?

 

[RenuWind]

Yes I am, along with the appropriate modulii for the different directions (being as the blade is a composite structure this varies over the cross section).