/CLUSTER
Block Format Keyword Describes an assembly of brick or spring elements for postprocessing and failure control.
Format
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

/CLUSTER/ELEM_TYPE/cluster_ID/unit_ID  
cluster_title  
group_ID  skew_ID  Ifail  
Fn_fail1  a1  b1  
Fs_fail  a2  b2  
Mt_fail  a3  b3  
Mb_fail  a4  b4 
Definition
Field  Contents  SI Unit Example 

ELEM_TYPE  Cluster element type.


cluster_ID  Cluster
identifier. (Integer, maximum 10 digits) 

unit_ID  Unit Identifier. (Integer, maximum 10 digits) 

cluster_title  Cluster block
title. (Character, maximum 100 characters) 

group_ID  Element group
identifier. (Integer) 

skew_ID  Skew
identifier. (Integer) 

Ifail  Failure model option.
(Integer) 

Fn_fail  Failure force in normal
direction (tension). Default = 1.0e30 (Real) 
$\left[\text{N}\right]$ 
Fs_fail  Failure force in tangent
direction (shear). Default = 1.0e30 (Real) 
$\left[\text{N}\right]$ 
Mt_fail  Failure moment in normal
direction (torsion). Default = 1.0e30 (Real) 
$\left[\mathrm{N}\cdot \mathrm{m}\right]$ 
Mb_fail  Failure moment in tangent
direction (bending). Default = 1.0e30 (Real) 
$\left[\mathrm{N}\cdot \mathrm{m}\right]$ 
a1  a4  Multidirectional failure
scale factors (only used if Ifail
=3). Default = 1.0 (Real) 

b1  b4  Multidirectional failure
exponents (only used if Ifail
=3). Default = 1.0 (Real) 
Comments
 The cluster of elements are used for connection (spotweld, welding line, glue, and so on).
 The cluster of elements may only be defined with groups of solid (8 node bricks) or spring elements.
 For bricks, cluster of elements works with LAW59 and LAW83 only. Solid elements of cluster should be interconnected.
 For springs, cluster of elements works with TYPE13.
 The number of elements in cluster group is limited to 500.
 All cluster elements must have the same orientation (Z local coordinate for solids, X local coordinate for springs, or direction from first to second node).
 Only one layer of element in the normal (thickness direction) is allowed to define a cluster.
 When force/moment failure criterion is reached (see cluster failure definition below), then all elements in the cluster are deleted. Force and moment are always calculated in local cluster coordinate system or in skew system specified in /CLUSTER card.
 Cluster elements may have material referring to /FAIL/CONNECT or /FAIL/SNCONNECT, or to a failure spring property. These criteria are independent from the cluster failure criterion defined in /CLUSTER. Single elements may be deleted according to these failure criteria, but this will not affect the cluster failure.
 Failure criterion
FAIL is calculated, as follows:Unidirectional local, Ifail=1:
(1) $$FAIL=\mathrm{max}\left(\left\frac{Fn}{Fn\_fail}\right,\left\frac{Fs}{Fs\_fail}\right,\left\frac{Mt}{Mt\_fail}\right,\left\frac{Mb}{Mb\_fail}\right\right)$$Unidirectional general, Ifail=2:(2) $$FAIL=\mathrm{min}\left(\left\frac{Fn}{Fn\_fail}\right,\left\frac{Fs}{Fs\_fail}\right,\left\frac{Mt}{Mt\_fail}\right,\left\frac{Mb}{Mb\_fail}\right\right)$$Multidirectional, Ifail=3:(3) $$FAIL={a}_{1}{\left(\frac{Fn}{Fn\_fail}\right)}^{{b}_{1}}+{a}_{2}{\left(\frac{Fs}{Fs\_fail}\right)}^{{b}_{2}}+{a}_{3}{\left(\frac{Mt}{Mt\_fail}\right)}^{{b}_{3}}+{a}_{4}{\left(\frac{Mb}{Mb\_fail}\right)}^{{b}_{4}}>1$$  Local coordinate system is defined as:
 If skew_ID > 0, the skew Zaxis defines normal direction in the local coordinate system, tangent plane will be defined by skew X and Y axis.
 If skew_ID = 0, the normal direction in the local coordinate system is defined by the vector between geometrical centers of nodes on bottom and top side.
 Available
postprocessing options:
 /ANIM/VECT/CLUST/FORCE  force vector in global coordinates
 /ANIM/VECT/CLUST/MOM  moment vector in global coordinates
 /TH/CLUSTER  forces and moments in global or local coordinates
 Output for TH: Forces and moments in global and local coordinate system, failure criterion FAIL.
 True thickness parameter which accounts for virtual height of the cluster in /PROP/CONNECT is active only when skew_ID = 0.