Segregated

The node (

) is an attribute that handles parameters for a segregated solution approach. This attribute makes it possible to split the solution process into substeps. Each substep uses a damped version of Newton’s method.

The attribute can be used together with the Stationary Solver and Time-Dependent Solver nodes. An alternative to the segregated approach is given by the coupled solver, which is handled with the Fully Coupled attribute node. Although several and attribute nodes can be attached to an operation node, only one can be active at any given time.

To add substeps to a segregated iteration, right-click the node. One segregated iteration consists of executing each active Segregated Step in the order shown in the model tree.

	The convergence properties of a model might depend on the order of the segregated steps. You can move the Segregated Step nodes to change the order in which the solver runs each step.

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Termination Criterion for the Fully Coupled and Segregated Attribute Nodes

Select a to control how the segregated iterations are terminated. Select:

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(the default) to terminate the segregated iterations when the estimated relative error is smaller than a specified tolerance.

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to terminate the segregated iterations when the estimated tolerance is smaller than a specified tolerance or after a specified number of iterations, whichever comes first.

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to terminate the segregated iterations after a fixed number of iterations.

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If is selected, enter a to limit the number of segregated iterations (default: 10). When the maximum number of iterations has been performed, the segregated method is terminated even if the tolerance is not fulfilled.

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If or is selected, enter a to modify the tolerance used for termination of the segregated iterations. The actual tolerance used is this factor times the value specified in the field in the sections of the and nodes.

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If or is selected, choose a to control how the Newton iterations are terminated for stationary problems. Select:

to terminate the Newton iterations on a solution-based estimated relative error.

to terminate the Newton iterations on a residual-based estimated relative error.

to terminate the Newton iterations on the minimum of the solution-based and residual-based estimated relative errors. Then enter a scalar (default: 1000) that multiplies the residual error estimate.

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If or is selected, enter a to specify a fixed number of iterations to perform. The default is 1.

With a Time-Dependent Solver, also select the check box to force the nonlinear solver to terminate as soon as the convergence is estimated to be too slow. Enter a limit on the convergence rate in the accompanying field.

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to use a pseudo time-stepping method to stabilize convergence toward steady state for a stationary solver. Pseudo time stepping is not available for time-dependent solvers. See Pseudo Time Stepping for more information. For the pseudo time-stepping method, specify the following regulator parameters:

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, which is a nonlinear convergence acceleration method that uses information from previous Newton iterates to accelerate convergence. The Anderson acceleration method is primarily intended for acceleration of nonlinear iterations in transport problems involving, for example, crosswind diffusion stabilization. You can control the number of iteration increments to store using the field (default: 10).