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--- doc:user:conditions:displacements [2013/07/12 13:26] – created joris
+++ doc:user:conditions:displacements [2016/03/30 15:23] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
+====== Prescribed Displacements ======
+===== Basic usage =====
+{{:doc:user:ico-beginner.png?40 |Beginner}}
+A displacement can be prescribed to a set of nodes with an evolution function and the object ''LoadingSet'':
+  loadingset.define(target, field, ampl=0.0, fct=None,
+                    incr=INCREMENTAL_LOAD)
+  loadingset.define(target, field, ampl, fctMulti, fieldList,
+                    incr=INCREMENTAL_LOAD)
+with
+|< 100% 8em - - >|
+|''target''          | ''GObject''  | meshed geometric entity where the displacement is prescribed |
+|''field''           | ''Field1D''  | variable to be prescribed              |
+|''ampl''            | ''float''    | amplitude                              |
+|''fct''             | ''[[doc:user:general:fonctions|Function]]'' | function for time dependence |
+|''fctMulti'' {{:doc:user:ico-advanced.png?18|Advanced}}        | ''[[doc:user:general:fonctions|Function]]'' | (spatiotemporal dependency) |
+|''fieldList'' {{:doc:user:ico-advanced.png?18|Advanced}}       |              | list of dependency fields  |
+|''incr'' {{:doc:user:ico-advanced.png?18|Advanced}}            | ''enum''     | = ''INCREMENTAL_LOAD'' : incremental (default)\\ = ''TOTAL_LOAD'' : total (useful to apply initial displacement or for unreliable integration schemes)|
+The displacement is then given by
+  * ''INCREMENTAL_LOAD'':  ''u(t1) = u(t0) + ampl * (fct(t1)-fct(t0))''
+  * ''TOTAL_LOAD'':        ''u(t) = ampl * fct(t)''
+__Example:__ FIXME
+\\
+=====  Activation/Deactivation of boundary conditions =====
+{{:doc:user:ico-advanced.png?40 |Advanced}}
+Prescribed displacements can be added or removed during the computation.
+It is useful to add some prescribed displacements for example when we want to avoid numerical vibrations or rigid body modes. Conversely, it is sometimes useful to drive a workpiece to a desired position, then to remove the prescribed displacements and let the workpiece deform freely.
+For any calculation, the simulation time is automatically divided into several stages (''Stage'' objects) using the ''setNextTime()'' method of the ''[[doc:user:integration:general:time_step|TimeStepManager]]''.
+For each stage, it is possible to activate (''activate()'') and deactivate (''deactivate()'') any ''Loading'' (including prescribed displacements).
+After the configuration of the ''[[doc:user:integration:general:time_step|TimeStepManager]]'', all the defined stages can be retrieved using:
+  stages = metafor.getStageManager()
+==== Example ====
+Definition of a prescribed displacement on ''Curve'' #4 and deactivation during stage #1 (corresponding to the second stage since numbering starts with 0):
+  load1 = loadingset.define(curveset(4), Field1D(TY,RE), 1.0, fct2)
+  load1.deactivate(stages[1])
+Definition of a load on ''Curve'' #1, deactivated during stage #1 and activated for the next ones:
+  load2 = loadingset.define(curveset(1), Field1D(TY,RE), -0.1, fct1)
+  load2.deactivate(stages[0])
+  load2.activate(stages[1])
+These two loads are represented schematically as:
+|          ^  load1  ^  load2  ^
+^ stage #0 |  ACTIVE    |  INACTIVE  |
+^ stage #1 |  INACTIVE  |  ACTIVE    |
+^ stage #2 |  INACTIVE  |  ACTIVE    |
+<note important>Order of operations: Activation surpasses deactivation: A node can indeed be part of two entities, one activated, one deactivated. But the operation of deactivation will be done first, then the activation, so such a node will be activated.</note>