Riks Analysis-Arc length problem (Please help!)

[Ariyan1]

Hello,

I am trying to run GMNIA analysis for the wind turbine monopile. I have obtained the imperfection based on the the standard as 0.00538. Initially I did a linear buckling analysis in abaqus in order to get critical load. I have applied 1N force in y direction and obtained 2105000 as the load multiplier. Next I run Riks analysis and I have applied the load of 2105000 N, and also introduced the imperfection stated above for the first buckling mode to the keyword. My question is how to adjust to arc length increments and what to use as the stopping criteria? Am I following the right procedure?

My other question is about the load proportionality factor. Do I need to obtain this from the field history output when the simulation finish or this is something that I can obtained now prior to finishing the simulation?

Any help is greatly appreciated.

Regards,

Ariyan

 

[Mustaine3]

Just define the load with 1 and the look at the LPF history output to see the actual load.
When a certain displacement is passed you can end the Riks step. That's the easiest way to do it.

 

[Ariyan1]

Hi Mustaine3,

Thanks for your explanation.

I have found my own way to solve this issue and apparently it works. Here is the breakdown of my workflow,

1) I have run the linear buckling analysis to the perfect tower in order to get load multiplier.
2) I have changed the steps to riks and also introduce the material linearity to the software. I have used the load multiplier as the applied load. Beside this I have introduced the geometric non-linearity. I have run the simulation to get an estimate of my arc length and have carefully watch LPF. Once I have satisfied that there is not much changed for LPF, I have stopped the software.
3) In order to obtain the good results to let me plot the meaningful graphs, I have set the arc length of the programme according to my second step. For instance if arc length is 1, I have set the maximum arc length as 1, the minimum increment as 0.01 and maximum increment as 2.
4) I have let the software to run a good chuck of iteration i.e 136 and then stopped the simulation. I have plotted the LPF vs arc length and other information required. It is visible this way when the collapse occurs.

Have does it sound?

Thanks in advance.

Regards,
Ariyan

 

[Mustaine3]

If it works and the results are reasonable...