# DESIGN VARIABLES FIELD

Specifies design optimization variables field for topology optimization.

## Type

AcuSolve Command

## Syntax

DESIGN_VARIABLES_FIELD {parameters}

## Qualifier

This command has no qualifier.

## Parameters

- default_value (real) [=1.0]
- Initial constant value assigned to the design variables field.
- max_update_factor (real) [=0.05]
- Max relative step change allowed for the design variables to change between iterations.
- design_topology_interpolation (enumerated) [=simp]
- The interpolation used at the interface of the two different material regions. The two different materials are specified using the ELEMENT_SET command. For topology optimization of flow, the material_model parameter is equal to a fluid material without a porosity model, and the parameter design_material_model is equal to a fluid material model with a specified porosity model and darcy coefficient. With the material model of type fluid and the design material model of type design, representing the solid, the interface is the region between the fluid and the solid.
- min_filter_radius (real) [=0.0]
- By setting the min_filter_radius parameter to a dimensional value, the topology optimizer prevents the creation of narrow topological passages whose width dimension falls below the specified min_filter_radius parameter value. The radius must be at least the size of the element mesh size. The minimum resolved design features correspond to two times the given radius. The minimum filter radius used by laplacian topology defined in the EQUATION command.
- filter_wall_type (enumerated) [=free]
- Type of the design topology level for walls.
- free
- Automatically computes the design value for all wall surfaces using the solution algorithm.
- constant
- Assign a constant value (either 1 or 0) on the wall, determined by the types specified in the topology_design_wall parameter in the SIMPLE_BOUNDARY_CONDITION. When topology_design_wall = on, the design value at the wall is set to 1. Conversely, when topology_design_wall = off, it is set to 0. This option is the preferred method to solve topology problems with obstructions. Requires topology_design_wall in the SIMPLE_BOUNDARY_CONDITION command.

- project_design_topology (enumerated) [=step]
- Type of projection used with laplacian_topology filtering
defined in the EQUATION command.
- step
- Stepwise increase of the projection, every 20
^{th}case. - continuous
- Continuous increase of the projection; every case.

- project_design_topology_factor_max (real) [=32]
- The maximum value of the projection used with
laplacian_topology defined in the
EQUATION command. A higher value gives a sharper
interface between the fluid and solid regions.Note: A too high value may give convergence problems.

## Description

The shape of the geometry is controlled by the design variables field. For topology
flow optimization, the field value of zero represents the fluid and the field value
of one represents the solid. The default initial value is equal to one, that is, the
optimization starts from solid domain everywhere by default. To start from fluid
domain default_value should be set to zero.
Modifying max_update_factor will act as a relaxation factor to
the convergence of the optimization cycles. There is a single option for the design
topology interpolation, and a single design variables field is supported in this
version.

```
DESIGN_VARIABLES_FIELD(“design topology”) {
default_value = 1.0
max_update_factor = 0.05
design_topology_interpolation = simp
}
```

If the laplacian topology filtering is used, the command can be given
by:

```
DESIGN_VARIABLES_FIELD( "topology" ) {
default_value = 0.0
project_design_topology = step
filter_radius = 0.02
project_design_topology_factor_max = 32
filter_wall_type = constant
}
```

Here, design_topology_filter =
laplacian_topology must be set in the
EQUATION command. Further, to specify a "solid" wall
condition for the design topology, when filter_wall_type =
constant,
use:

```
SIMPLE_BOUNDARY_CONDITION( "Wall with solid design topology boundary condition" ) {
...
topology_design_wall = on
}
```