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Thanks Mastro, GBor, and toog for your responses. GBor, thanks for trying it with a commericial package. Are you trying with ANSYS/NASTRAN ? Just curious. Do you have the test-case parameters so that I can see it working here ? Please don't be obligated to do this. I set-up a case in...

Dear Mastro, What I solve is a set of nonlinear beam equations derived based on no kinematic assumptions to the beam reference line as is done in our typical E-B/Timoshenko models. You were a bit off in the calculation of the fundamental mode. There is a factor of 3.52 after you take the...

Greg, Thanks. So, by choosing such a small time-step, am I applying a high frequency impulse ?? Also, what would shear waves have to do with the finite element discretization ? Please clarify if possible. Thanks, Aero^2

Oops.. forgot to mention that I do not have any structural damping in the model.

Hi, The EI (flat-wise) is 4x10^6 N-m^2 and the mass per unit length of the beam is 0.769 kg/m. Again, as mentioned, this is a cantilever beam with a sinusoidal force at the tip. And, I have a diagonal stiffness matrix which uncouples one motion from the other. It is definitely restrained out...

Hi Greg, I am applying a force at the tip as I mentioned (5sin30t). I get this singularity in my Newton-Raphson jacobian at the second time-step itself which is around 0.0002 s (when the time-step is 0.0001 s). Thanks, Satish

Hi Greg and Drej, Thanks for responding so promptly. Drej, let me correct myself. The forcing is 5sin30t and not 50sin20t. The problem does'nt seem to be the forcing frequency at all. It is with my finite-element discretization. There seems to be a connection between the number of beam finite...

Hi all, I am working on the geometrically nonlinear dynamic response of a cantilever beam using an in-house FEM code. I have a 16 m cantilever beam whose fundamental frequency is around 5 Hz. In a particular simulation, I discretized the beam into 50 elements and tried to use a time-step of...

Hi Jplot, Nice to know that you got the Shapiro's book. I think I will also order it from Alibris.com. Thanks, aero^2

Hi all, I have Red hat 7.3 on my system and would like to upgrade to a higher version preferably 9.0. I am wondering if I would lose my data if I do it. My hunch is that it should'nt. Can someone confirm this ? Thanks, aeroaero

Hi all, Can someone explain to me briefly as to what 4/rev hub loads mean exactly ?? I know that I will see 4 wavelengths in the response if it is 4/rev and similarly for other kinds of response. But, I don't understand the physical significance behind this. Why am I seeing 4 wavelengths in the...

Hi jplot, I will watch for your comments on that book. Surprisingly, very few books explain stuff figuratively while it is necessary for a complicated subject like helicopter theory. It's become simply hard to imagine many of those things having had no formal class in it.

Hello all, Can someone tell me if there is any really basic book on helicopter theory ? I was trying to understand concepts like 2/rev, 4/rev vibratory load variation/response and all that. There was no clear introduction of small things like this in books of Leishman and even Johnson too. I am...

Hi, Thanks for your response. What I have is a time-response of a certain deflection analysis and the idea is to fit the data only to an ARMA model. LINEST, as I see, is not meant to do that. It may help me do some kind of regression, but, it cannot simulate ARMA. I hope I am right at this...

Hi all, Did anyone ever use the ARMA function of MATLAB system identification toolbox to estimate parameters of an ARMA model fitted to a time-series data ?? Thanks in advance, aero

Hi all, Does anyone know of any good softwares (apart from MATLAB/MATHEMATICA) which could be used to estimate parameters of an ARMA model from time-series data ? Thanks in advance, aero

Hi, it is the stiffness matrix of a structure. The purpose is to see if matrices of this type could be assembled to form the global stiffness. Infact, the only thing that could prevent the latter is the rigid body motion which is clearly removed since this matrix is non-singular. The example of...

Hi all, I have a stiffness matrix sent to me and was asked to check the sanity of it and identify the physical process that it might have come from. I have gone through a number of FEM texts to get an idea about sanity, but was of no use. Can someone give me a clue atleast as to how I can do...