Enforced displacement with NASTRAN modes

Question I want to used NASTRAN computed modes to generate an enforced displacement model.

Answer This answer assumes that you are using NASTRAN 2004 or later where residual vectors are properly supported with RESVEC. Since NASTRAN only allows for residual vectors associated to DOF loads, this solution is only applicable for cases with enforced motion at DOF (which is less general that enforced displacement shapes supported in DofSet case entries).

In your SOL 103 (eigenvalue) NASTRAN run, you need to have the specific entries

 $ In the case control - - - - - - - - - - - - - - - - - - - -
$ Ask to use residual vectors. With or without inertia relief (as shown here)
RESVEC(NOINRL)= YES
 ...

$ input locations
$ In the bulk - - - - - - - - - - - - - - - - - - - -
$ Define DOFS for residual vectors at force AND displacement
$ input locations
RVDOF1  123     4131
RVDOF1  123456  9999
$ Put stiff springs at locations of displacement inputs
CELAS2,6001,1.e9,9999,1
CELAS2,6002,1.e9,9999,2
CELAS2,6003,1.e9,9999,3
CELAS2,6004,1.e13,9999,4
CELAS2,6005,1.e13,9999,5
CELAS2,6006,1.e13,9999,6

 Case=fe_case(fe_case,'DofSet','Base',9999, ...
    'DofLoad','Force',4131+[1:3]'/100, ...
    'SensDof','Sensors',4131);
sys=nor2ss(DEF,.03,Case);
iiplot;
IIw=linspace(DEF.data(1),DEF.data(end,1),1024)'*2*pi;
RESP=qbode(sys,IIw,'struct');
XF(1).w=RESP.w;XF(1).xf=RESP.xf;XF(1).lab=RESP.lab;
iicom(';submagpha;titopt116')