# zone relax command

Syntax

zone relax keyword

Primary keywords:

Creates and modifies a special apply condition on the zones in the range. This condition gradually ‘excavates’ the material by reducing the stiffness, stresses, and densities of the zones. This keeps spurious inertial effects in the static solution process from causing unrealistic damage to the region around the excavation.

The values of these quantities are systematically reduced by applying a multiplier (the reduction factor) that varies from 1.0 to 0.0 over time. The precise time taken and shape of the curve is controllable by the user, but defaults to a servo controlled by the current mechanical force ratio (see zone ratio ).

When the reduction factor for a given zone is brought to zero, the mechanical constitutive model for the zone is set to null and the apply condition for that zone is removed. When all the zones involved in a given condition are nulled by the apply condition, the apply condition itself is destroyed.

The constitutive model of all zones included are set to elastic, preserving the bulk and shear modulus of the original model.

Since the density and stiffness of the material is reduced over time, in small strain mode a periodic recalculation of some parameters (body force due to gravity, inertial mass) will take place. This will happen when the reduction factor changes, but no more frequently than the current zone geometry-update setting.

Note that while the total stress is reduced to zero, any pore-pressures in the gridpoints attached to the zones will remain unaffected.

delete s

Finds a previously created zone relax apply condition with name s, and deletes it. If the reduction factor has reached 0, the material has been nulled and thus its relax condition has been deleted. For this case, no need to delete it once more.

excavate keyword <range>

Creates and initializes an excavation condition on all zones in the range. The following keywords are available to customize how the excavation progresses.

fish s

Specify a FISH function that determines the multiplier to use as the excavation progresses. This should return a value of 1.0 at the start, and 0.0 and the end. If this keyword is used, the default servo is not used.

fish-local s

Specify a FISH function that determines the multiplier to use as the excavation progresses. This function is called separately for each individual zone taking part in the apply condition. If this keyword is used, the default servo is not used.

The function is assumed to take two arguments. The first argument is a pointer to the zone in question. The second argument is unused.

minimum f

Sets the minimum reduction factor that will be allowed. The default value is 0.0. This should be a number between 0.0 and 1.0. This value can be used to solve to a specific reduction factor before installing reinforcement or other operation. Then the zone relax modify command can be used to lower the minimum.

Note changing the minimum when using the table, fish, or fish-local options to control the reduction factor may result in unexpected behavior, as the time index used for those options will not stop advancing after reaching the minimum value.

name s

Assigns the apply condition an identifying name s. If a name is not specified one will be created automatically based on the internally assigned ID number.

servo-bound f

If the current mechanical force ratio (see the zone ratio) is lower than this value, the reduction factor is reduced by the increment. The default value is 1e-3

servo-increment f

If the current mechanical force ratio is less than servo-bound, then the reduction factor is reduced by subtracting f from it. This number should be less than 1.0, and greater than 0.0. The default value is 0.005.

step i

If set to a positive value, then any FISH, table, or servo parameters are ignored and the reduction factor is reduced linearly from 1.0 to 0.0 over the course of i steps.

table s <time keyword>

If specified, then the reduction factor is given by table s. A lookup is performed every step. By default the x value used to lookup a table y value will be the accumulated mechanical time, which for a purely static analysis is the same as the number of steps. The time index used can be changed by using the optional time keyword, with the following options.

step

Use the total cycle count.

mechanical

Use the accumulated mechanical time (the default)

fluid

Use the accumulated fluid flow time.

thermal

Use the accumulated thermal time.

creep

Use the accumulated creep time.

dynamic

Use the accumulated dynamic time.

list

List all relax conditions, including their name and settings.

modify s keyword

Finds the previously created zone relax apply condition with name s, and modify its settings. The following keywords are available:

fish s

Specify a FISH function that determines the multiplier to use as the excavation progresses. This should return a value of 1.0 at the start, and 0.0 and the end. If this keyword is used, the default servo is not used.

fish-local s

Specify a FISH function that determines the multiplier to use as the excavation progresses. This function is called separately for each individual zone taking part in the apply condition. If this keyword is used, the default servo is not used.

The function is assumed to take two arguments. The first argument is a pointer to the zone in question. The second argument is unused.

name s

Assigns the apply condition an identifying name s. If a name is not specified one will be created automatically based on the internally assigned ID number.

servo-bound f

If the current mechanical force ratio (see the zone ratio) is lower than this value, the reduction factor is reduced by the increment. The default value is 1e-3

servo-increment f

If the current mechanical force ratio is less than servo-bound, then the reduction factor is reduced by subtracting f from it. This number should be less than 1.0, and greater than 0.0. The default value is 0.005.

step i

If set to a positive value, then any FISH, table, or servo parameters are ignored and the reduction factor is reduced linearly from the current value (which is at start 0.99) to minimum (by default 0.0) over the course of i steps.

table s <time keyword>

If specified, then the reduction factor is given by table s. A lookup is performed every step. By default the x value used to lookup a table y value will be the accumulated mechanical time, which for a purely static analysis is the same as the number of steps. The time index used can be changed by using the optional time keyword, with the following options.

step

Use the total cycle count.

mechanical

Use the accumulated mechanical time (the default)

fluid

Use the accumulated fluid flow time.

thermal

Use the accumulated thermal time.

creep

Use the accumulated creep time.

dynamic

Use the accumulated dynamic time.