Implicit Solution

In this group keywords are used for implicit solution. Different implicit solver methods (linear, nonlinear, buckling or quasi-static), different options to control the implicit computation, different implicit time step method and implicit output messages are introduced.

Groups	Keywords	Description
Implicit Controls	/IMPL/AUTOSPC	Used to constrain zero stiffness DOF automatically during the computation.
	/IMPL/DIVERG/n	During implicit computation, when successive increasing residual number is greater than N, divergence is considered and iteration will be restarted with a smaller time step.
	/IMPL/DYNA/1	Describes the implicit dynamics with α-HHT method.
	/IMPL/DYNA/2	Describes the implicit dynamics with a general Newmark method.
	/IMPL/DYNA/DAMP	Defines Rayleigh structure damping with dynamic implicit analysis. Since /DAMP defined in Starter has no effect on implicit run.
	/IMPL/DYNA/FSI	Defines the settings for Fluid Structure Interaction Analysis with AcuSolve.
	/IMPL/GSTIF/OFF	Geometrical stiffness matrix will not be used for implicit nonlinear calculation.
	/IMPL/INTER/KCOMP	Describes the stiffness matrix; due to contact interfaces will be assembled completely (for SPMD).
	/IMPL/INTER/KNONL	Defines including some contact nonlinearities in PCG linear solver.
	/IMPL/LINEAR/INTER	Implicit linear analysis will take into account contact interfaces.
	/IMPL/LSEARCH/OFF	Deactivates line search for nonlinear analysis.
	/IMPL/LSEARCH/n	Defines different Line search methods for nonlinear analysis.
	/IMPL/MONVOL/OFF	Describes the stiffness of gas in monitored volume type 3 (tire modeling). This should be set when a direct solver is used, considering its stiffness negligible.
	/IMPL/NCYCLE/STOP	Stops the computation, if implicit maximum cycle Number is reached.
	/IMPL/PREPAT	Describes the implicit option for pre-conditioning.
	/IMPL/PSTIF/OFF	Deactivates load (pressure) stiffness matrix.
	/IMPL/RREF/INTERF/n	Defines different reference force residual computations used for stop criteria on nonlinear analysis with contact.
	/IMPL/RREF/LIMIT	Defines reference force residual limit values used in stop criteria for implicit nonlinear.
	/IMPL/RREF/OFF	Deactivation reference residual option and using the previous one in stop criteria for implicit nonlinear analysis.
	/IMPL/SBCS/MSGLV	Describes the message level for BCS (Boeing) solver.
	/IMPL/SBCS/ORDER	Defines different reordering method definition for BCS.
	/IMPL/SBCS/OUTCORE	Used to force BCS solver to use minimum in-core memory.
	/IMPL/SHPOFF	The full projection of QEPH shell element for warped elements will be deactivated to keep consistency between the stiffness matrix and the internal force computations.
	/IMPL/SHPON	The full projection of QEPH shell element for warped elements will be activated for stiffness matrix to keep consistency with the internal force computations.
	/IMPL/SINIT	Describes the initial stresses that will be imposed gradually.
	/IMPL/SPRBACK	Implicit spring-back will be run in this session. The force residual will be reduced to the input tolerance (/IMPL/NONLIN/N).
	/IMPL/SPRING	Describes the linear or nonlinear stiffness choices for nonlinear spring in implicit nonlinear analysis.
Implicit Solvers	/IMPL/BUCKL/1	Euler buckling modes will be computed.
	/IMPL/BUCKL/2	Euler buckling modes will be computed based on actual pre-stress stat.
	/IMPL/LBFGS/L	Change the maximum number of BFGS quasi-Newton method for implicit nonlinear.
	/IMPL/LINEAR	Linear implicit solution will be computed. Required for linear statics, normal modes and linear buckling solution.
	/IMPL/SOLVER	Used to select different linear solve methods.
	/IMPL/LRIGROT	Due to linearization used in geometrical nonlinear analysis, small time step has to be chosen to avoid accumulated errors under large rotation. In this case, this option improves the accuracy using usual time step.
	/IMPL/NONLIN	Nonlinear implicit methods.
	/IMPL/NONLIN/SMDISP	Only small displacement effects will be considered with this option, and it is for the applications where the large displacement effects are negligible.
	/IMPL/NONLIN/SOLVINFO	Outputs solving information for each iteration in nonlinear implicit methods.
	/IMPL/QSTAT	Quasi-static implicit solution will be computed. For nonlinear analysis, this will only modify the convergence speed without changing the result; for linear analysis, time step (one step) should be chosen carefully. This option is suitable for the model in which some free pieces are connected only by contact during simulation and failed with other analysis types.
	/IMPL/QSTAT/DTSCAL	Quasi-static implicit solution with a factor for inertia stiffness matrix.
	/IMPL/QSTAT/MRIGM	Rigid motion has been removed or minimized from quasi-static implicit solution. This option has been developed for spring-back computation after forming.
Implicit Time Step	/IMPL/DT/1	Used to control the Implicit time step.
	/IMPL/DT/2	The time step is determined by displacement norm control (arc-length). Arc-length method is used to accelerate and to control the convergence.
	/IMPL/DT/3	Implicit automatic time step control with Riks method. It is suitable for nonlinear static analysis of unstable problems like buckling, snap-through. It solves at the same time for the displacement vector and for a loading scale factor by adding a constraint equation.
	/IMPL/DT/FIXPOINT	You input fix time points where implicit nonlinear computation will not miss with automatic time step control.
	/IMPL/DT/STOP	Stops the computation, if specific minimum time step is reached.
	/IMPL/DTINI	Used to set Initial time step for nonlinear implicit analysis. It should be used in nonlinear implicit.
Implicit Model Check	/IMPL/CHECK	Implicit model checking will be run. Used to check the rigid body modes.
Implicit Output Messages	/IMPL/PRINT/LINEAR	Printout frequency for linear solvers.
Implicit Output Messages	/IMPL/PRINT/NONLIN	Printout frequency for nonlinear implicit iterations.

Comments

1.	The /IMPL keywords have one or two additional keywords. These keywords and the respective input data are defined in the following topics.