/PROP/TYPE27 (SPR_BDAMP)
Block Format Keyword Describes a damper spring property with one translational DOF. Damper force is bounded by stiffness force.
Format
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

/PROP/TYPE27/prop_ID/unit_ID or /PROP/SPR_BDAMP/prop_ID/unit_ID  
prop_title  
Mass  sens_ID  I_{sflag}  I_{leng}  I_{tens}  I_{fail}  
K  C  n  ${\delta}_{\mathrm{min}}^{1}$  ${\delta}_{\mathrm{max}}^{1}$  
gap  F_{smooth}  F_{cut}  
fct_ID_{1}  fct_ID_{2}  Ascale_{1}  Fscale_{1}  Ascale_{2}  Fscale_{2} 
Definition
Field  Contents  SI Unit Example 

prop_ID  Property identifier. (Integer, maximum 10 digits) 

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

prop_title  Property title. (Character, maximum 100 characters) 

Mass  Mass. (Real) 
$\left[\text{kg}\right]$
(I_{leng} = 0) $\left[\frac{\text{kg}}{\text{m}}\right]$ (I_{leng} = 1) 
sens_ID  Sensor identifier.
(Integer) 

I_{sflag}  Sensor flag.
(Integer) 

I_{leng}  Input per unit length flag.
(Integer) 

I_{tens}  Tensile behavior flag.
(Integer) 

I_{fail}  Failure model flag.
(Integer) 

K  Linear loading and unloading
stiffness. (Real) 
$\left[\frac{\text{N}}{\text{m}}\right]$
(I_{leng} = 0) $\left[\frac{N}{{m}^{2}}\right]$ (I_{leng} = 1) 
C  Linear damping
coefficient. Default = 0.0 (Real) 
$\left[\frac{\text{Ns}}{\text{m}}\right]$
(I_{leng} = 0) $\left[\frac{Ns}{{m}^{2}}\right]$ (I_{leng} = 1) 
n  Exponent for nonlinear stiffness
force. Default = 1.0 (Real) 

${\delta}_{\mathrm{min}}^{1}$  Negative failure limit. Default = 10^{20} (Real) 

I_{fail} = 1: Failure displacement (I_{leng} = 0) Failure strain (I_{leng} = 1) 
$\left[\text{m}\right]$ (I_{leng} = 0)  
I_{fail} = 2: Failure force.  $\left[\text{N}\right]$  
${\delta}_{\mathrm{max}}^{1}$  Positive failure limit. Default = 10^{20} (Real) 

I_{fail} = 1: Failure displacement (I_{leng} = 0) Failure strain (I_{leng} = 1) 
$\left[\text{m}\right]$ (I_{leng} = 0)  
I_{fail} = 2: Failure force.  $\left[\text{N}\right]$  
gap  Minimum gap before
activation. Default = 0.0 (Real) 
$\left[\text{m}\right]$ (I_{leng} = 0) 
F_{smooth}  Spring force filtering flag.
(Integer) 

F_{cut}  Cutoff frequency for spring force
filtering. Default = 100 kHz (Real) 
$\text{[Hz]}$ 
fct_ID_{1}  Nonlinear stiffness force function
identifier:
(Integer) 

fct_ID_{2}  Damping force function identifier:
(Integer) 

Ascale_{1} 
Default = 1.0 (Real) 
$\left[\text{m}\right]$ (I_{leng} = 0) 
Fscale_{1}  Ordinate scale factor for the
stiffness function
$f$
. Default = 1.0 (Real) 
$\left[\text{N}\right]$ 
Ascale_{2} 
Default = 1.0 (Real) 
$\left[\frac{m}{s}\right]$
(I_{leng} = 0) $\left[\frac{\text{1}}{\text{s}}\right]$ (I_{leng} = 1) 
Fscale_{2}  Ordinate scale factor for the
stiffness function
$g$
. Default = 1.0 (Real) 
$\left[\text{N}\right]$ 
Comments
 The spring has one translational degree of freedom in the local x direction which is defined between node N1 and N2 of the spring.
 Force
computation is activated by default in compression (
$\delta $
< 0), and in tension only if
I_{tens} = 1. The
spring force value is obtained as follows, where I_{leng} = 0:
 Stiffness part:
$\{\begin{array}{ccc}{F}_{K}(\delta )=sign(\delta )\cdot K\cdot {\left\delta \right}^{n}& \text{if}& fct\_I{D}_{1}=0\\ {F}_{K}(\delta )=Fscale1\cdot f\left(\frac{\delta}{Ascale1}\right)& \text{otherwise}& \end{array}$
Where, $n\ge 1$ .
 Damping
part:
$\{\begin{array}{ccc}{F}_{D}(\dot{\delta})=C\cdot \dot{\delta}& \text{if}& fct\_I{D}_{2}=0\\ {F}_{D}(\dot{\delta})=Fscale2\cdot g\left(\frac{\dot{\delta}}{Ascale2}\right)& \text{otherwise}& \end{array}$
 Global
force:
$\{\begin{array}{ccc}F(\delta ,\dot{\delta})={F}_{K}(\delta )+{F}_{D}(\dot{\delta})& \text{if}& \left{F}_{D}(\dot{\delta})\right<\left{F}_{K}(\delta )\right\\ F(\delta )=2\cdot {F}_{K}(\delta )& \text{otherwise}& \end{array}$
 Stiffness part:
 If the I_{leng} flag is activated (I_{leng} = 1), the above computations become:
 Stiffness part:
$\{\begin{array}{ccc}{F}_{K}(\epsilon )=sign(\epsilon )\cdot K\cdot {\left\epsilon \right}^{n}& \text{if}& fct\_I{D}_{1}=0\\ {F}_{K}(\epsilon )=Fscale1\cdot f\left(\frac{\epsilon}{Ascale1}\right)& \text{otherwise}& \end{array}$
 Damping part:
$\{\begin{array}{ccc}{F}_{D}(\dot{\epsilon})=C\cdot \dot{\epsilon}& \text{if}& fct\_I{D}_{2}=0\\ {F}_{D}(\dot{\epsilon})=Fscale2\cdot g\left(\frac{\dot{\epsilon}}{Ascale2}\right)& \text{otherwise}& \end{array}$
 Global force:
$\{\begin{array}{ccc}F(\epsilon ,\dot{\epsilon})={F}_{K}(\epsilon )+{F}_{D}(\dot{\epsilon})& \text{if}& \left{F}_{D}(\dot{\epsilon})\right<\left{F}_{K}(\epsilon )\right\\ F(\epsilon )=2\cdot {F}_{K}(\epsilon )& \text{otherwise}& \end{array}$
 Stiffness part:
 You can define a
compression gap activation as defined on the following scheme:If the gap is defined (gap ≠ 0.0) the force computation is activated once the spring compression is bigger than the specified gap.$$\{\begin{array}{ccc}F(\delta +\leftgap\right,\dot{\delta})\ne 0& \text{if}& \delta <\leftgap\right\\ F(\delta +\leftgap\right,\dot{\delta})=0& \text{otherwise}& \end{array}$$Note: Defining a gap value implies that the spring only works in compression and thus, I_{tens} = 0, if the gap is defined. If I_{leng} = 1, the gap is homogeneous to a compressive strain.
 The switching
between the two forces computation’s formula can lead to a noisy spring
response. To address this issue, you can use filtering on the spring force
computation, allowing a smooth transition between the two spring states
(damped and undamped). To do so, the force filtering flag F_{smooth} and the cutoff frequency F_{cut} can be used as:
 If F_{cut} ≠ 0.0, the filtering is activated (F_{smooth} is automatically set to 1), and the filtering uses the cutoff frequency you provide.
 If F_{smooth} =1 and F_{cut} = 0.0, the filtering is activated and a default cutoff frequency of 100 kHz is used.
 If F_{smooth} =0 and F_{cut} = 0.0, no filtering is used.
If the filtering is activated, the spring force is computed as:
$${F}_{n}{}^{filter}=\alpha {F}_{n}+(1\alpha ){F}_{n1}$$Where, $\begin{array}{c}\alpha =2\pi \cdot \text{\Delta}t\end{array}\cdot Fcut$ .