ANTYPE,HARM to specify a harmonic analysis.

HROPT,HBM,NH to specify an HBM harmonic analysis and the number of harmonics NH retained for the solution. In most cases, it is good practice to start with NH = 1, then check the solution accuracy with higher harmonics at a few frequency points closer to resonance.

HBMOPT,CONTSET,CorrMeth,DS,DSMIN,DSMAX to set up a numerical continuation solution. Continuation is necessary for problems with complex nonlinearities where turning points or bifurcations are expected. Turning continuation off (by issuing HBMOPT,CONTSET,OFF) is not recommended. If you leave CorrMeth blank on HBMOPT,CONTSET, the corrector method is set to the arc-length method by default. You must specify a value for the step size of the first substep (DS) unless CorrMeth = OFF. The initial continuation step size DS can be estimated from the expected order of magnitude of DOF values and the frequency.

Default values are set for DSMIN and DSMAX, but if you want to change them, keep the following points in mind. Since the minimum step size DSMIN is a stopping criteria, it is recommended to set its value several orders of magnitude lower than the initial step size. The maximum step size DSMAX is not a stopping criteria, but rather a setting that acts on the frequency resolution.

HARFRQ,FREQB,FREQE command to specify the beginning and ending simulation frequencies. The beginning frequency can be larger than the ending frequency to run a simulation in a decreasing frequency direction. Note that if continuation is on (CorrMeth has any setting except OFF on HBMOPT,CONTSET), the simulation may be allowed to go beyond these frequencies, depending on the values specified on the HBMOPT, CONTTERM command.

HBMOPT,CYCLIC,CYCkey,EO,SEPrefix to specify if the HBM analysis is an HBM cyclic analysis solving for spatial harmonic indicies greater than 0 (CYCkey=1). Also defines the fundamental engine order (EO) and the prefix for all single stage cyclic superelement names (SEPrefix).

HBMOPT, NR, MAXITER, MAXINITITER to specify the maximum number of iterations allowed for the nonlinear equation solver at a frequency point (MAXITER) and the maximum number of iterations for the initial continuation step (MAXINITITER). If continuation is used, a lower MAXITER value (10-30) is recommended under most circumstances. The lower number means that the solver has less iterations to converge to the solution, but it also means that continuation will adjust the step size from the previous solution to be faster and waste less time iterating at a larger step-size when convergence is unlikely. If continuation is off, a larger number (MAXITER = 50-500) is recommended and may be decided based on the frequency resolution and tolerances specified, to allow the solver to reach convergence at each frequency. The maximum number of iterations at the initial step (MAXINITITER) should be much higher than the number specified for the following steps (MAXITER).

HBMOPT,TRTOL,UTOL,RTOL.GTOL to specify tolerances for the trust-region nonlinear equation solver. The residual tolerance (RTOL) is a convergence criteria and may be used to adjust the desired solution accuracy. Since the step (UTOL) and gradient (GTOL) tolerances are additional stopping criteria, set their values sufficiently low so that they are not encountered during a normal solution.

HBMOPT,CONTTERM,MAXSTEPS, FREQMIN, FREQMAX to specify the termination criteria when continuation is on. Set the maximum number of successful continuation steps (MAXSTEPS) high enough to allow the solver to finish simulation over the frequency range. Also, use this command to specify the minimum and maximum allowed simulation frequencies (FREQMIN and FREQMAX) if turning points beyond the simulation range specified via HARFRQ are expected.

HBMOPT,AFT,NP,NT to specify the maximum number of time periods (NP) and time-points (NT) within a period of simulation for the AFT procedure. Set NP high enough to allow the nonlinear transient force calculation to converge. For closed-form nonlinearities (without internal states) such as polynomial stiffness nonlinearity, two periods are sufficient. Nonlinearities with internal states such as friction may require more than two periods for convergence. An internal check is done after each computed period to verify if convergence is reached. So, the actual number of periods used by the solver might be lower than NP. The number of time points per periods should ideally be ten times the highest harmonic. For example, a cubic nonlinearity may have significant contributions from components up to the third harmonic, so a minimum of 30 points should be used.

HBMOPT,UINIT to provide a solution guess at the beginning frequency of solution. Usually, this guess is obtained from a previously performed HBM analysis.

HBMOPT,SCAL to linearly scale the solution vector to improve the convergence rate by a either a constant value or values contained in a user-defined array. For example usage of this scaling command, see Scaling the solution vector and VM320: Nonlinear Harmonic Analysis of a Frictional Damper in the Mechanical APDL Verification Manual.

HBMOPT,LINEAR to turn off the nonlinearity and enforce zero nonlinear forces from the AFT procedure. This will solve the corresponding linear problem and can be used to understand the system dynamics or build up an initial solution guess.

HBMOPT,LIST and HBMOPT,CONTLIST to list parameters associated with the current HBM solution. This is useful for checking if the default settings have been changed by previously issued commands or automatically due to missing inputs or procedures.