# BEM computed at the hub and the tip

Dear @Jason.Jonkman,

Sorry for opening a new task I’m workin on several things at the same time

i wanna ask you about the BEM implemented In AeroDyn using Ning method:

I obtained singularities at two positions:

at the tip, kappa equals infinity due to the fact that F (hub/tip loss correction) is equal to zero.
at the hub, where fhub<0 and therefore exp(-fhub)>0 and hence inverse cosine will be a complex number.

What do you think ? If i was right, what do you suggest in order to solve this problem ?

Best Regards,

Actually, at the hub, r=R_hub, and so, f_hub = 0.

In the present version of AeroDyn, there is a special case defined at the hub and tip where the hub and tip loss are zero. That is, at the hub and tip where the hub and tip loss are zero, a=1 and a’=0.

Best regards,

Dear @Jason.Jonkman ,

I am sorry, i would say at the hub, f_hub = 0.

If i understand well, at the tip and the hub, we consider that a=1 and a’=0 which leads us to an indeterminate case of the residual function. We are sure that a solution exists in ]0:pi/2] but due to the fact that R(pi/2)>0 and R(0)<=0 and hence in this case, phi is taken equals to zero right ?

In case of Vx=0 or Vy=0, BEM makes no sense and hence a=0, a’=0 and phi=0 right ?

Best Regards,