TSTEPNL

Bulk Data Entry

TSTEPNL – Parameters for Geometric Nonlinear Implicit Dynamic Analysis Control

Description

Defines parameters for geometric nonlinear implicit dynamic analysis strategy.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
TSTEPNL	ID	NDT	DT			KSTEP		CONV
	EPSU	EPSP	EPSW			MAXLS		LSTOL

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
TSTEPNL	99		0.01

Field	Contents
ID	TSTEPNL bulk data cards must have a unique identification number. No default (Integer > 0)
NDT	Number of implicit load sub-increments. No default (Integer > 0)
DT	Initial time step. No default (Real > 0)
KSTEP	Number of iterations before stiffness update. See comment 3. Default = 6 for BCS solver Default = 3 for PCG solver (Integer > 0)
CONV	Flags to select implicit convergence criteria. Default = UPW (Any combination of U, P and W)
EPSU	Error tolerance for displacement (U) criterion. Default = 1.0E-2 (Real > 0.0)
EPSP	Error tolerance for load (P) criterion. Default = 1.0E-2 (Real > 0.0)
EPSW	Error tolerance for work (W) criterion. Default = 1.0E-3 (Real > 0.0)
MAXLS	Maximum number of line searches allowed for each iteration. Default = 20 (Integer > 0)
LSTOL	Line search tolerance. Default = 1.0E-3 (Real > 0.0)

Comments

1.	The TSTEPNL bulk data entry is selected by the Subcase Information command TSTEPNL = option. Each subcase for which nonlinear implicit dynamic analysis is desired requires a TSTEPNL command.

2.	Additional control for geometric nonlinear implicit dynamic solution schemes (ANALYSIS = IMPDYN) can be defined using TSTEPNX bulk data entry. Defaults will be used if TSTEPNX is not present.

The solution method for geometric nonlinear implicit dynamic analysis (ANALYSIS = IMPDYN) is modified or Quasi-Newton. The frequency of stiffness matrix updates is controlled by KSTEP. For highly nonlinear problems, it is recommended to reduce KSTEP for better performance. KSTEP = 1 means full Newton. The initial implicit time step is DT. All subsequent time steps will be determined automatically. Termination time, TTERM, is defined by a TTERM subcase entry or computed from TTERM = NDT*DT. TTERM takes precedence.

4.	The time integration scheme for implicit transient is defined on TSTEPNX. The default method is α-HHT.

5.	For more information about geometric nonlinear analysis, refer to Geometric Nonlinear Analysis in the User's Guide.

In Nonlinear Direct Transient Analysis, TSTEPNL may be utilized as a replacement for some parameters in the NLPARM bulk data entry. However, not all entries of the TSTEPNL bulk data entry will be effective. Specifically, when TSTEPNL is used, instead of NLPARM, the fields DT, KTSTEP, MAXITER, CONV, EPSU, EPSP, EPSW, and LSTOL will be used with the same meaning of the corresponding entries of NLPARM. Additionally, NDT will be used as NINC of NLPARM. The rest of the values of NLPARM and TSTEP that are not issued by TSTEPNL, will assume default values. Using both TSTEPNL and NLPARM in a subcase is not supported.

7.	This card is represented as a loadcollector in HyperMesh.