3D rotor

SDT-rotor Contents Functions

4.4 3D rotor

The same rotor as described in lalanne (see fig 4.3) is meshed using hexa8 elements. Use model=d_rotor('TestVolShaftDiskMdl').

Figure 4.11: 3d model of Lalanne rotor.

Matrices are defined in the local rotating frame. We described the unbalanced load by a static load, and we use in following example the same procedure as for local frame 1d rotor, at w=0.

 model=d_rotor('testvolshaftdiskmdl')
 % Assemble nominal matrices:
 model.DOF=[];model=fe_caseg('assemble -se -matdes 2 1 7 8',model);
 model.DOF=fe_case('gettdof',model);
 % Campbell diagram:
 model=stack_set(model,'info','eigopt',[5 20 1e3]);
 fe_rotor('campbell -critical',model,linspace(0,20000,30));
    
 % Unbalanced mass or asynchronous load :
 mb=1e-4; db=0.15; % mass, distance to axis
 s=0; f0=1; % s=1, unbalanced load. s<>1, asynchronous load
 om=sort([2789 2750:10:2820 11760:10:11840 linspace(0,20000,101)]); % RPM

   
  model=fe_rotor(sprintf('rotatingload 180 %.15g 0 2',f0),model);

  r1=struct('Omega',om/60*2*pi,'w',s*om/60*2*pi); % Range
  model=stack_set(model,'info','Range',r1);
  R1=fe_rotor('forcedresponse',model); % compute forced response
  iiplot(R1) % plot response
  % Post (radial deformation):  
  Q=abs(R1.Y(:,1)); % unbalanced along x 
  figure;semilogy(om,Q);
  xlabel('Rotation speed [RPM]'); ylabel('radial def amplitude [m]')
  if s==0; title('Unbalanced mass')
  else;    title(sprintf('Asynchronous load %.15g\\Omega',s))
  end

Figure 4.12: Left: Campbell diagram. Right: Response to unbalanced mass.

Unbalanced mass excites the forward whirl modes. Maximum response is found at critical speeds (rotation speeds that induce a complex mode of 0 Hz frequency in the rotating frame). Campbell critical speed (2789 RPM) matches computed frequency response.