Learning Forum

[vbb96vbb]

the flag still working.mp4

[Karthik Remella]

Hello,nInstead of attaching videos, could you post some screenshots or embed a gif into your post? Ansys employees are not able to download attachments from the forum.nAlso, are you running a transient structural analysis in this problem? I just want to confirm if there is not Fluid flow involved at this time. Please let me know.nKarthikn

[vbb96vbb]

Thank you so muchnHere are the screenshots,nAnd affrimative - I am running this simulation as a transient structural analysis now...There is not Fluid flow involved at this time.nn

[Karthik Remella]

Hello,nLet me check on this with a Mechanical expert and get back to you.nKarthikn

[Ashish Khemka]

nnHow is the fluid connected to the pole? I do not see any contact between flag and pole.nnRegards,nAshish Khemkan

[vbb96vbb]

Thank you - there is no established contact but that side of the flag (fabric) is fixed... so the pole is a representation: but idle.nI am only focused on the flag (materials); Intending to make it drop under gravity.nn

[vbb96vbb]

Thank you so much nI am looking forward to hearing from you soon.n

[Karthik Remella]

Hi,nSince I'm don't have a deep knowledge of structural mechanics, is going to be helping you with this one.nKarthikn

[Ashish Khemka]

nnI think you have defined the Elastomer Sample model for the cloth. Do you think that the fabric of Young's modulus of ~ 1342 MPa? Also, how is the flag deforming when applying standard earth gravity? Can you please share a snapshot of the same?.Regards,nAshish Khemkan

[vbb96vbb]

Thank you

[vbb96vbb]

Thank you nYes, I did define the material model appropriately and I will share some reference extract.nnBurnett, B . Coupled fluid-structure interaction modeling of a parafoil. PhD Dissertations and Master’s Theses, 2016, p. 74nnYes, I think that the fabric of Young's modulus of ~ 1342 MPa, and please kindly find attached the imagery from a work.n nAccardo, Giampiero & Eugeni, Marco & Mastroddi, Franco & Romano, Giovanni. (2013). Experimental and numerical modelling for flag flutter. pg. 9nnAnd - this is the deformation of the fabric under gravity.nn

[vbb96vbb]

please I wanted to follow up to know if there is any update thanksn

[Ashish Khemka]

nnI think you want the flag to be dropped to a position something like this -nnn(Image snip from google search)nnIf this is the case then I do not think that elastomer is the material to model it.nnRegards,nAshish Khemka

[vbb96vbb]

Thank you for the response, your time, and the information.nnYes, correct - I need the flag to be at rest at the Imaged position, under gravity.nIf I can't use elastomer as the material, please what can I change it to in order to get successful at this?.Thank you so much. n

[Ashish Khemka]

nnI think composites can be used to model fabric but I have limited knowledge on the same. I will check if someone can comment on the use of composites.nnRegards,nAshish Khemka n

[vbb96vbb]

Thank you n

[mrife]

Hi @vbb96vbb nYou have run into a classic issue with Finite Element models being too perfect. The flag is modeled as a perfectly flat surface with gravity acting in the plane of the surface. Our instincts are to expect the FEA result to show the flag droop, since that is our real-world experience. But in the real world the flag is not perfectly flat. There are really ripples in the fabric. nTo overcome this try a static-linear buckling-transient linked system approach like so:nSet the scale factor to a value where the flag looks like it it has ripples or slight waves. Note the mode number and the scale factor.nIn Workbench select View -> Properties and select the Solution cell of the buckling; you will see a scale factor and mode number you can apply. Pick/set the values to match the deformation plot in buckling. Now the Transient model should have geometry that looks like a flag in the wind. Define the same boundary condition and gravity load as the static case. Then solve for 1-2 seconds with initial/minimum/maximum time steps set to 1e-5/1e-5/5e-2. For potential troubleshooting I find it easier to start with a small time step and see how the solve progresses. You can always stop the solve early on and reset the time step controls as needed. Be sure to turn on large deformation in the analysis settings. nSince the structure (flag) is so thin using a membrane formulation for the shell element will be useful. Inserted a Commands Object to the part and entered the command:nkeyopt,matid,1,1nSee the Mechanical APDL element help section on shell 181 for a list of its keyopts. And the MAPDL command help section on the keyopt command if there are any questions on its use.nMiken

[peteroznewman]

Awesome!n

[vbb96vbb]

This is great ...`I am going to do this and inform you of the outcome.nThank you so muchn

[Sean Harvey]

Nice! I was going to suggest perturbing, but you beat me by a few hours hours. Well done.nnRegards,nSeann

[vbb96vbb]

I can't connect my Model on the Static to the Bucklingn

[mrife]

Drag and drop the whole Eigenvalue buckling onto the Solution cell of the Static structural system. Miken

[vbb96vbb]

Great, it worked...I would finish upnThank you so much n