Hello,

Recently i have done a MSC NASTRAN Free-Free analysis for a FEM consisting of only one beam element (See Figure:1 in attached excel sheet). I could not get the all eigenvalue roots of the SOL 103 modal analysis. In fact I got only 6 modes eigenvalues as shown in Table 1: MSC NASTRAN SOL 103 Summary in the attached excel sheet.

As per theory, a beam element has 6 dof at each nodes. Hence a complete beam should have 6 eigenvalues for elastic modes and 6 rigid body modes (i.e., total of 12 eigenvalues). So my first question is why SOL 103 for this model is giving me only 6 modes even though i requested for 18 eigenvalue roots?

Generally in free-free analysis the first 6 modes should be rigid body modes (i.e., the eigenvalues for these 6 should be zero). But I have noticed that the 6th mode eigenvalue is non Zero. So my second question,  Could you please give me a justification for this 6th mode non zero eigenvalue?

I have attached my .bdf file and . F06 file for more details. Also an excel sheet highlighting the SOL 103 summary and model snap from MSC Patran.

Any help will be appreciated,

Thank You,

Paul

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