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Support for cyclic symmetry computations.


 model=fe_cyclic('build NSEC',model,LeftNodeSelect)
 def=fe_cyclic('eig NDIAM',model,EigOpt)


fe_cyclic groups all commands needed to compute responses assuming cyclic symmetry. For more details on the associated theory you can refer to [47].

Assemble [,-struct]

This command supports the computations linked to the assembly of gyroscopic coupling, gyroscopic stiffness and tangent stiffness in geometrically non-linear elasticity. The input arguments are the model and the rotation vector (in rad/s)

 model=demosdt('demo sector all');
 [K,model,Case]=fe_case('assemble -matdes 2 1 NoT -cell',model);
 SE=fe_cyclic('assemble -struct',model,[0 0 1000]); % 
 def=fe_eig({K{1:2},Case.T,model.DOF},[6 20 0]);% Non rotating modes
 def2=fe_eig({K{1},SE.K{4},Case.T,model.DOF},[6 20 0]); % Rotating mode shapes

Note that the rotation speed can also be specified using a stack entry model=stack_set(model, 'info', 'Omega',[0 0 1000]).

Build ...

model=fe_cyclic('build nsec epsl len',model,'LeftNodeSelect') adds a cyclic symmetry entry in the model case. It automatically rotates the nodes selected with LeftNodeSelect by 2π/nsec and finds the corresponding nodes on the other sector face. The default for LeftNodeSelect is 'GroupAll' which selects all nodes.

The alternate command model=fe_cyclic('build nsec epsl len -intersect',model,'LeftNodeSelect') is much faster but does not implement strict node tolerancing and may thus need an adjustement of epsl to higher values.

Command options are

model=demosdt('demo sector 5');
cf.model=fe_cyclic('build epsl 1e-6',model);


The command is used to build centrifugal loads based on an info,Omega stack entry in the form

data=struct('data',[0 0 1000],'unit','RPM');


def=fe_cyclic('eig ndiam',model,EigOpt) computes ndiam diameter modes using the cyclic symmetry assumption. For ndiam>0 these modes are complex to account for the inter-sector phase shifts. EigOpt are standard options passed to fe_eig.

This example computes the two diameter modes of a three bladed disk also used in the d_cms2 demo.

  model=demosdt('demo sector');
  model=fe_cyclic('build 3',model,'groupall');
  def=fe_cyclic('eig 2',model,[6 20 0 11]);
  fe_cyclic('display 3',model,def)

The basic functionality of this command is significantly extended in fe_cyclicb ShaftEig that is part of the SDT/Rotor toolbox.

See also


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