For more information on the Linear Perturbation procedure for rotating structures, see Considerations for Rotating Structures.
To generate the Campbell diagram of a prestressed structure, use one of the following procedures. If the prestress is dependent on the rotational velocity, use the procedure based on the CAMPBELL command described in Procedure for Campbell analysis of prestressed structure (CAMPBELL). Otherwise, you may use the procedure in Alternative procedure for rotational velocity independent prestress.
5.3.1. Procedure for Campbell analysis of prestressed structure (CAMPBELL)
To generate the Campbell diagram, multiple static and
perturbed modal solutions are calculated alternately. The Campbell action
(Action on the CAMPBELL command)
must be set to the results file name extension of the perturbed solution (RSTP) in
the first static analysis. Issue the command CORIOLIS,ON,,,ON in
the static prestress portion of the analysis to include the Coriolis effect.
The results of the modal analyses are appended to the Jobname.rstp file to accommodate a subsequent Campbell diagram analysis – see Campbell Diagram.
The example snippet below shows the commands used for a Campbell analysis of a prestressed structure.
Example 5.1: Commands used in a Campbell Diagram Analysis of a Prestressed Structure
! *** Define the rotational velocity array parameter ‘spins’ nbstep = 5 ! number of steps dspin = spin/(nbstep-1) ! increment *dim,spins,,nbstep *vfill,spins,ramp,0.,dspin spins(1) = 0.1 ! nonzero to ease the Campbell diagram sorting !*** Perform the multiple prestress modal analyses in a *do loop *do,iloop,1,nbstep /solu antype,static rescontrol,linear ! enable file writing for a subsequent linear perturbation coriolis,off ! de-activate Coriolis effect if needed (centrifugal force) omega,,,spins(iloop) ! set rotational velocity f,… ! define static loads campbell,rstp ! enable file handling for Campbell analysis solve fini /solu antype,static, restart,,,perturb perturb, modal coriolis,on,,,on ! activate Coriolis effect in stationary reference frame solve, elform modopt,… ! specify the eigensolver – only DAMP and QRDAMP are supported mxpand solve fini *enddo ! *** Post-process the Campbell diagram /post1 file,,rstp ! define the results file to be used plcamp finish
An alternative procedure for generating a Campbell diagram of a prestressed structure is demonstrated with the simple script below. The gyroscopic forces are of primary importance, and the linear perturbation analysis is performed in the stationary reference frame. The prestress effect in the static base analysis does not include centrifugal force from rotational velocity. In this case, a static analysis (without rotational velocity) can be performed, followed by a multistep perturbation modal analysis with varying spin speeds.
! *** Define the rotational velocity array parameter ‘spins’ nbstep = 5 ! number of steps dspin = spin/(nbstep-1) ! increment *dim,spins,,nbstep *vfill,spins,ramp,0.,dspin spins(1) = 0.1 ! nonzero to ease the Campbell diagram sorting /solu antype,static rescontrol,linear ! enable file writing for a subsequent linear perturbation coriolis,on,,on ! activate Coriolis effect in stationary reference frame f,… ! define static load solve fini /solu antype,static, restart,,,perturb perturb, modal coriolis,on,,,on solve, elform modopt,… ! specify the eigensolver – only DAMP and QRDAMP are supported mxpand omega,spins(1) solve omega,spins(2) solve .. .. .. .. omega,spins(5) solve fini ! *** Post-process the Campbell diagram /post1 file,,rstp ! define the results file to be used plcamp finish