## Name

case — Analysis case block

## Synopsis

case id
attributes
end

## Description

The case command specifies all ingredients needed for the analysis case identified by id (a positive and unique integer number), in particular the boundary conditions, the initial conditions, and the solution strategy parameters.

The analysis case that will be solved must be specified by the case attribute of the adir command.

## Attributes

The attributes enumerated in this section pertain to most types of analyses and concern the specification of initial conditions, boundary conditions, and constraints. Solver-specific attributes are explained in the chapter Solvers.

analysis t

Specifies the type of analysis for the present analysis case. The string t is one of

linear

Linear static (stationary) analysis (default).

nonlinear

Non-linear static (stationary) analysis.

linearised_prebuckling

Bifurcation buckling analysis with linear prestress (solid mechanics).

free_vibration

Free vibration analysis (solid mechanics).

dynamic_nonlinear

Nonlinear dynamic (transient or non-stationary) analysis.

frequency_dependent_free_vibration
atemperatures id [sfactor s|sfunction "function_string"]

Specifies the ambient temperatures set id to be included for certain types of analysis, like heat analysis.

In linear analysis, the optional parameter sfactor specifies a scale factor s by which the set is multiplied, the default value being 1.0.

In nonlinear direct analysis and in incremental analysis, the set is scaled by the load factor (static analysis) or by the time (dynamic analysis). The optional parameter sfactor specifies an additional scale factor s by which the set is multiplied, the default value being 1.0. Alternatively, the optional parameter sfunction specifies a function which is being evaluated at each load or time increment and by which the set is multiplied.

component name type "argument" [sfactor s|sfunction "function_string"]

Specifies a component to be used in the current analysis case. Components are extensions to B2000++. They implement specific natural boundary conditions, essential boundary conditions, initial conditions, or sets of constraints.[4].

The name and type parameters are used to identify the component[5], while the argument parameter is given to the component at the start of the analysis (stage).

In linear analysis, the optional parameter sfactor specifies a scale factor s by which the values returned by the component are multiplied, the default value being 1.0.

In nonlinear direct analysis and in incremental analysis, the values returned by the component are scaled by the load factor (static analysis) or by the time (dynamic analysis). The optional parameter sfactor specifies an additional scale factor s by which the values returned by the component are multiplied, the default value being 1.0. Alternatively, the optional parameter sfunction specifies a function which is being evaluated at each load or time increment and by which the values returned by the component are multiplied.

dof_init|dofdot_init id

Specifies the initial conditions set id for the current analysis case.

ebc id [sfactor s|sfunction "function_string"]

Adds the essential boundary conditions set id to the current analysis case. Note that essential boundary conditions are not cumulative, i.e. if several essential boundary condition sets are specified, all values of common degrees-of-freedom must be equal.

In linear analysis, the optional parameter sfactor specifies a scale factor s by which the set is multiplied, the default value being 1.0.

In nonlinear direct analysis and in incremental analysis, the set is scaled by the load factor (static analysis) or by the time (dynamic analysis). The optional parameter sfactor specifies an additional scale factor s by which the set is multiplied, the default value being 1.0. Alternatively, the optional parameter sfunction specifies a function which is being evaluated at each load or time increment and by which the set is multiplied.

field_transfer id

Adds the field_transfer set id to the current analysis case. Note that a field_transfer set with an id of 0 is automatically added to all analysis cases.

Alternatively, several or all field_transfer sets may be specified:

field_transfer ilist field_transfer all

It is required to specify a constraint method other than the default reduction method for which the accuracy of the calculated solution cannot be always ensured when field_transfer conditions are active. See also Imposing Constraints.

join id

Adds the join set id to the current analysis case. Note that a join set with an id of 0 is automatically added to all analysis cases.

linc id

Adds the linear constraints set id to the current analysis case. Note that a linc set with an id of 0 is automatically added to all analysis cases.

nbc id [sfactor s|sfunction "function_string"]

Adds the natural boundary conditions set id to the current analysis case. Natural boundary conditions are cumulative, i.e. if several natural boundary condition sets are specified the resulting natural boundary condition for id is the sum of all natural boundary condition sets multiplied by their respective scaling.

In linear analysis, the optional parameter sfactor specifies a scale factor s by which the set is multiplied, the default value being 1.0.

In nonlinear direct analysis and incremental analysis, the set is scaled by the load factor (static analysis) or by the time (dynamic analysis). The optional parameter sfactor specifies an additional scale factor s by which the set is multiplied, the default value being 1.0. Alternatively, the optional parameter sfunction specifies a function which is being evaluated at each load or time increment and by which the set is multiplied.

rcfo_restrict list

Specifies to which nodes the calculation of reaction forces shall be restricted in post-processing (this directive is ignored by the b2000++ processor). If not specified, b2browser and baspl++ will loop over all nodes of the model to calculate the reaction forces.

epatch id p1-p8|e1-e12|f1-f6|b

When the discretization of a part of the discretization was created by means of the epatch command, a number of pre-defined nodelists are available. The epatch is identified by id.

Individual patch vertex nodes are specified with p1 to p8.

The collection of nodes that are located at a patch edge are specified with e1 to e12.

The collection of nodes that are located at a patch face are specified with f1 to f6.

The collection of nodes of the whole patch body are specified with b.

nodelist name

Specifies the name of the node list.

nodeset name

Specifies the name of the node set.

stage id [sfactor s|sfunction "function_string"]

Specifies the analysis stage id to be activated for the current analysis case. One or more stages can be defined for the current case. If more than one stage is specified, the solver will solve for one stage after the other in the order stages have been entered. If stage is specified for a given analysis case, no boundary conditions (such as ebc or nbc), no constraints, and no initial conditions that analysis case.

In linear analysis, the optional parameter sfactor specifies a scale factor s by which the conditions of the referenced stage are multiplied, the default value being 1.0.

In nonlinear direct analysis and in incremental analysis, the conditions of the referenced stage are scaled by the load factor (static analysis) or by the time (dynamic analysis). The optional parameter sfactor specifies an additional scale factor s by which the set is multiplied, the default value being 1.0. Alternatively, the optional parameter sfunction specifies a function which is being evaluated at each load or time increment and by which the set is multiplied.

temperatures id [sfactor s|sfunction "function_string"]

Specifies the temperatures set id to be included for certain types of analysis, like thermal stress analysis.

In linear analysis, the optional parameter sfactor specifies a scale factor s by which the set is multiplied, the default value being 1.0.

In nonlinear direct analysis and in incremental analysis, the set is scaled by the load factor (static analysis) or by the time (dynamic analysis). The optional parameter sfactor specifies an additional scale factor s by which the set is multiplied, the default value being 1.0. Alternatively, the optional parameter sfunction specifies a function which is being evaluated at each load or time increment and by which the set is multiplied.

title '...text...'

Optional title describing the case.

## Per-Stage Commands in Multi-stage analysis

In nonlinear analysis, it is often necessary to split the loading path into a series of stages. Example:

stage 1
ebc                   1
nbc                   1
end

stage 2
ebc                   2
step_size_init        0.05
step_size_max         0.05
end

case 3
analysis              nonlinear
residue_function_type artificial_damping
stage                 1
stage                 2
end

case 3
end

In this example, case 3 is executed, which consists of two stages (defined by stages 1 and 2). To ensure convergence of the nonlinear solver in the presence of buckling (load-controlled by default), artificial damping is performed to stabilise the problem.

The b2000++ program initializes many of its internal procedures and data structures on a per-case basis, not on a per-stage basis. The commands for the various methods are interpreted only during this initialization phase. Specification of commands like residue_function_type inside of stages 1 or 2 will be ignored. Instead, they must be placed in the definition of case 3 and, consequently, they will be active for both stages.

On the other hand, commands controlling the step size and the tolerances for the residual, solution, etc., can be defined inside a stage.

[4] For example, a component can implement a weakly-coupled fully-nonlinear aero-elastic tool-chain. In this case, the values taken by the component are the current (nodal) displacements (calculated by B2000++), and the values returned by the component are the (nodal) forces. To this end, at each Newton iteration (or each xth Newton iteration), the component invokes the spatial coupling tool, the CFD mesh deformation tool, the CFD solver, and again the spatial coupling tool.

[5] Under this identifier, the component is registered.