Bearing and support representations

SDT-rotor Contents Functions

3.2 Bearing and support representations

3.2.1 Linear bearing

One can simply represent a support or a bearing by a linear spring that is to say a celas element (for more details see sdtweb('celas')). A celas element is announced in the model element matrix by the header [Inf abs('celas')] and format is as follow: [NodeId1 NodeId2 -DofID1 DofID2 ProID EltID Kv Mv Cv] NodeId1 and NodeId2 define between which nodes celas is connected (if NodeId2=0 celas is grounded), DofID1 and DofID2 which dof are connected, and Kv Mv and Cv give respectively stiffness mass and damping. A typical bearing for a rotor turning around x will then be defined by

Figure 3.5: Simple disk on long rod model.

The following generates a spring bearing connected to node n1, stiffness is 1e9 and damping 1e2 in the xy plane. The use of a spring property is necessary for non linear time domain applications

 model=d_rotor('TestDiskLongBeam');
 n1=feutil('findnode z==.71 & x==0 & y==0',model);
 model=feutil('AddElt',model,'celas',[n1 0   -12 0  100]);
 model.il=p_spring(model.il,'dbval 100 1e10 0 1e2');
 fe_simul('mode',model)

r1=struct('Origin',[20 10 0],'axis',[0 0 1],'radius',3, ...
          'planes',[1.5 1 111 1 3.1;
                    5.0 1 112 1 4;], ...
          'MasterCelas',[0 0 -123456 123456 10 0 1e14], ...
          'NewNode',0);
links={'connection','bearing',...
         struct('C1',1,'C2',r1,...
              'link',{{'celas',[0 0 23 0 103 0 1e5 0 0.1]}},...
              'NLdata',struct('type','RotCenter','lab','Bearing',...
                 'sel','ProId 1','JCoef',1,'drot',n1+.06))}
[model,RunOpt.idof]=nl_spring('ConnectionBuild',model,links)


[cf.mdl,RunOpt.idof]=nl_spring('ConnectionBuild',cf.mdl,links);

For 3d rotors, if there is no node on the axis of the shaft where one want to model the bearing, one can add a node whose displacement depends on displacements of nodes on a ring of the shaft using (see sdtweb('fe_case#connectionscrew')). Then one can connect a grounded celas to this node. xxx a full example is needed xxx

3.2.2 Non-linear bearings in the time domain

Documentation of nl_spring capabilities should go here.

One has a particular example, with a simple rotor (beam1+mass), non linear bearings (not the same in y and z direction), using the rotcenter non linearity, spurious mass for rotation DOF (no basis transformation). The strategy to have different NL according to Y and Z is to add a mass connected to the rotcenter extremity usually connected to stator, and to use this mass motion in global basis to apply NL bearing in the 2 different directions Y and Z. See sdtweb d_rotor rotcenter.