/SLIPRING/SPRING
Block Format Keyword Define 1D slipring for seatbelt elements defined with /MAT/LAW114 and /PROP/TYPE23.
Format
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

/SLIPRING/SPRING/slipring_ID/unit_ID  
slipring_title  
El_ID1  El_ID2  node_ID_{1}  node_ID_{2}  sens_ID  Fl_flag  A  Ed_factor  
fct_ID_{1}  fct_ID_{2}  Fric_d  Xscale_{1}  Yscale_{2}  Xscale_{2}  
fct_ID_{3}  fct_ID_{4}  Fric_s  Xscale_{3}  Yscale_{4}  Xscale_{4} 
Definitions
Field  Contents  SI Unit Example 

slipring_ID  Slipring identifier. (Integer, maximum 10 digits) 

unit_ID  (Optional) Unit
identifier. (Integer, maximum 10 digits) 

slipring_title  Slipring title title. (Character, maximum 100 characters) 

El_ID1  ID of first element in
slipring. (Integer, maximum 10 digits) 

El_ID2  ID of second element in
slipring. (Integer, maximum 10 digits) 

node_ID_{1}  ID of anchorage node.
(Integer, maximum 10 digits) 

node_ID_{2}  Optional ID of node for the
orientation of the slipring. (Integer, maximum 10 digits) 

sens_ID  Sensor identifier used for slipring
locking.
(Integer) 

Fl_flag  Sliding direction control flag
(Integer) 

A  Coulomb friction scale
factor. (Real) 

Ed_factor  Exponential decay factor for
Coulomb friction. (Real) 
$\left[\frac{\text{s}}{\text{m}}\right]$ 
fct_ID_{1}  Function identifier defining
dynamic Coulomb friction coefficient as a function of
time. (Integer) 

fct_ID_{2}  Function identifier defining
dynamic Coulomb friction coefficient as a function of normal
force. (Integer) 

Fric_d  Dynamic Coulomb friction
coefficient. If fct_ID_{1} = 0: constant value (Default = 0). If fct_ID_{1} > 0: ordinate scaling factor for function fct_ID_{1 } (Default = 1). (Real) 

Xscale_{1}  Abcissa scaling factor for function
fct_ID_{1}. Default = 1 (Real) 

Yscale_{2}  Ordinate scaling factor for
function fct_ID_{2}. Default = 1 (Real) 

Xscale_{2}  Abcissa scaling factor for function
fct_ID_{2}. Default = 1 (Real) 

fct_ID_{3}  Function identifier defining static
Coulomb friction coefficient as a function of
time. (Integer) 

fct_ID_{4}  Function identifier defining static
Coulomb friction coefficient as a function of normal
force. (Integer) 
$\left[\text{s}\right]$ 
Fric_s  Static Coulomb friction
coefficient. If fct_ID_{3}= 0: constant value (Default = 0). If fct_ID_{3}> 0: ordinate scaling factor for function fct_ID_{2} (Default = 1). (Real) 
$\left[\text{N}\right]$ 
Xscale_{3}  Abcissa scaling factor for function
fct_ID_{3}. Default = 1 (Real) 

Yscale_{4}  Ordinate scaling factor for
function fct_ID_{4}. Default = 1 (Real) 
$\left[\text{s}\right]$ 
Xscale_{4}  Abcissa scaling factor for function
fct_ID_{4}. Default = 1 (Real) 
$\left[\text{N}\right]$ 
Comments
 The slipring is defined by the 2 spring seatbelt elements initially connected to the slipring, El_ID1, El_ID2 and the node node_ID_{1} are used to define the position of the slipring. The common node between the 2 elements El_ID1 and EL_ID2 must be at the same coordinates as node_ID_{1}.
 node_ID_{1} and node_ID_{2} must not be nodes of the seatbelt spring component.
 By default, the
rotation axis of the slipring is defined by
$\overrightarrow{{n}_{def}}$
, the normal direction to the plane defined
by the two connected elements. Additionally, the rotation axis of the slipring can be defined by the direction of node_ID_{1} and node_ID_{2}. the angle $\gamma $ between the direction of node_ID_{1} and node_ID_{2} and $\overrightarrow{{n}_{def}}$ is used to compute the friction.
 The Coulomb friction
coefficient is computed with:
(1) $$\mu =\left(1+A{\gamma}^{2}\right)\left({\mu}_{dyn}+\left({\mu}_{stat}{\mu}_{dyn}\right){e}^{Ed\_factor.\left{V}_{rel}\right}\right)$$Where, ${\mu}_{stat}$
 Static friction coefficient
 ${\mu}_{dyn}$
 Dynamic friction coefficient
 ${V}_{rel}$
 Relative slip velocity
They are respectively computed with:(2) $${\mu}_{dyn}=Fric\_d.fct\_I{D}_{1}\left(\frac{t}{Xscal{e}_{1}}\right)+Yscal{e}_{2}.fct\_I{D}_{2}\left(\frac{Fn}{Xscal{e}_{2}}\right)$$(3) $${\mu}_{stat}=Fric\_s.fct\_I{D}_{3}\left(\frac{t}{Xscal{e}_{3}}\right)+Yscal{e}_{4}.fct\_I{D}_{4}\left(\frac{Fn}{Xscal{e}_{4}}\right)$$  When the slipring is
unlocked, sliding is activated if the difference of force after flow (marked
with *) is lower than the difference of force obtained without flow, and
material flow
$\delta {L}_{0}$
is computed accordingly:
$\left{F}_{k}{}^{*}{F}_{k1}{}^{*}\right<\left{F}_{k}{F}_{k1}\right$ with $\frac{{F}_{k}^{*}}{{F}_{k1}^{*}}={e}^{\mu \theta .sign({F}_{k}^{*}{F}_{k1}^{*})}$
 The common node of the 2 strands of the slipring is kinematically attached to the anchorage node of the slipring node_ID_{1}. No other kinematic condition can be applied to any node of a seatbelt element which can enter the slipring.
 When the length of one
strand reaches zero, the slipring is updated. This strand reappears on the
other side of the slipring and the previously connected strand on that side
leaves the slipring. At the same time, a new spring enters the slipring
replacing the one that has moved. The kinematic condition with the anchorage
node is also switched to the new common node of the strands. The previous
common node is released with an initial velocity computed from the material
flow and direction of the released element, such that the two directions of
the slipring
$\overrightarrow{{n}_{1}}$
and
$\overrightarrow{{n}_{2}}$
and the angle
$\theta $
are not modified by the update.
(4) $$\overrightarrow{{V}_{ini}}=\frac{\delta {L}_{0}}{dt}\overrightarrow{{n}_{k}}$$  To ensure element and
time step stability, maximum stiffness value is computed from
${L}_{\mathrm{min}}$
defined in seatbelt
material (/MAT/LAW114) and spring element reference
length
${L}_{0}$
.
(5) $$K=\frac{k}{\mathrm{max}\left({L}_{\mathrm{min}},{L}_{0}\right)}$$  When a spring element is in the slipring, viscosity is deactivated.