/CLUSTER

Block Format Keyword Describes an assembly of brick or spring elements for post-processing and failure control.

Format

(1)	(2)	(3)	(5)
/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. BRICK Cluster of brick elements SPRING Cluster of spring elements
`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. = 0 (Default) No global failure criterion. = 1 Unidirectional failure, element is deleted if force or moment in one direction reaches the limit value. = 2 Unidirectional failure, element is deleted if forces and moments in all directions reach the limit values. = 3 Multi-directional failure. 8 (Integer)
`Fn_fail`	Failure force in normal direction (tension). Default = 1.0e30 (Real)	$[N]$
`Fs_fail`	Failure force in tangent direction (shear). Default = 1.0e30 (Real)	$[N]$
`Mt_fail`	Failure moment in normal direction (torsion). Default = 1.0e30 (Real)	$[N \cdot m]$
`Mb_fail`	Failure moment in tangent direction (bending). Default = 1.0e30 (Real)	$[N \cdot m]$
`a1` - `a4`	Multi-directional failure scale factors (only used if `Ifail` =3). Default = 1.0 (Real)
`b1` - `b4`	Multi-directional 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)
$F A I L = \max (| \frac{F n}{F n_f a i l} |, | \frac{F s}{F s_f a i l} |, | \frac{M t}{M t_f a i l} |, | \frac{M b}{M b_f a i l} |)$

Unidirectional general, Ifail=2:(2)
$F A I L = \min (| \frac{F n}{F n_f a i l} |, | \frac{F s}{F s_f a i l} |, | \frac{M t}{M t_f a i l} |, | \frac{M b}{M b_f a i l} |)$

Multi-directional, Ifail=3:(3)
$F A I L = a_{1} {(\frac{F n}{F n_f a i l})}^{b_{1}} + a_{2} {(\frac{F s}{F s_f a i l})}^{b_{2}} + a_{3} {(\frac{M t}{M t_f a i l})}^{b_{3}} + a_{4} {(\frac{M b}{M b_f a i l})}^{b_{4}} > 1$
Local coordinate system is defined as:
- If skew_ID > 0, the skew Z-axis 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 post-processing 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.