Mohamed Khalid

Hello, I would like to perform a modal analysis of a helicopter blade while it is rotating at a constant RPM. I have created two steps in hyper-mesh, first is a linear static with boundary conditions and applied a centrifugal force with the RFORCE card. Second step is a normal modes step with the previous step linked through the STATSUB card and no boundary conditions or forces selected (free-free) modal analysis. Whenever i run this, the first step works, however i get an error: *** ERROR # 15 *** CTETRA element 252760 is distorted (zero or negative Jacobian). I checked my mesh and i have no issues with the Jacobian or mesh at those indicated elements. As a check, i've run both steps separately and both work and give good results. I don't know if this is the right way to perform such an analysis where the blade stiffness is changed by the centrifugal loading due to rotation. Your help is appreciated. Kind Regards, Mohamed FinalModel_01-12-2016_Finalzed_model_Pre_stressed_modal.hm

Hi Prakash, I currently have the model, with a boundary condition at the root. No other inputs. I want to find at what RPM if this blade spins, will it reach one of it's natural modes. Thanks

Hello Guys, I have a working model of a composite helicopter blade. I have extracted the modal frequencies of the blade. I want to know if there is a way to find out at what rotational speeds will the blade reach any of those modal frequencies? is there a way to do this on hyperworks? Kind Regards, Mohamed

Thank you very much man! Really appreciate it!

Another question i had, Can i open and use a model i created in the student edition in a full license edition that the university has? Thanks

Hi Prakash, Yes i do get results when i run the model, however in the model it does not allow me to set the ply material type to 'orthotropic'. I see the text "Cannot compute material normal" on the bottom left on the 'Status bar' when i click ok after changing the material type to orthotropic. When i open the ply definition, i find it has changed the material type to 'All' I am not sure if using the material type 'All' is accurate for composites. Correct, I am using HW 14.0 Student Edition. Thanks, Mohamed

Hello, Yes i want to determine inter-laminar shear stress. I also want to know what allowable values for this shear stress would be, for example for carbon fiber with epoxy. Thannks

Hi Prakash, Thanks for replying, i have attached my model file. Hope that helps Please note that the blade is 600mm long with a chord length of ~54mm. Thanks

Hi everyone, I am trying to model a helicopter blade, i have imported the CAD model.. etc until i created Plys. whenever i set the material type to orthotropic and hit update, at the bottom left it says "cannot compute material normal" and when i go back into the ply, the material type is back again to "all". would you be able to help me with this issue? Kind Regards, Mohamed

I am modelling a helicopter blade, with a leading edge mass ballast. I am not sure how to get a standard value for the inter laminar allowable shear stress value for unidirectional carbon fibre. Additionally, how would i model the allowable shear between the metallic mass ballast and the carbon fibre ontop of it? Kind Regards, Mohamed