1. | is the difference between the current length and the initial length of the spring element. |
2. | In case of Ileng =0 (flag Ileng is defined in Line 3), the force in the spring is computed as: |
Linear spring:

Nonlinear spring:

with 

Linear spring
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Nonlinear elastic spring, H1=0
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Nonlinear elastic plastic spring, H1=1
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Nonlinear elasto-plastic spring with decoupled hardening in tension and compression, H1=2
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Nonlinear elasto-plastic spring with isotropic hardening and nonlinear unloading, H1=6
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Nonlinear spring with elastic hystersis, H1=7
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3. | If Ileng = 1, all input are per unit length: |
• | Spring mass = Spring stiffness = Spring damping = Spring inertia =  |
Where, l0 is the spring reference length.
• | The value of force in the spring is computed as: |
- Linear spring:

- Nonlinear spring:

Where, is the engineering strain:

- Force functions are given versus engineering strain and engineering strain rate.
- Failure criteria are defined with respect to strain. Input of negative/positive failure limit should be related to initial length l0
4. | If (resp ) is 0, no failure in the direction. The must be negative. For linear springs, and are null functions and A1, B1 and E1 are not taken into account. |
5. | Spring is activated and/or deactivated by sensor: |
• | If sens_ID ≠ 0 and Isflag = 0, the spring element is activated by the sens_ID. |
• | If sens_ID ≠ 0 and Isflag = 1, the spring element is deactivated by the sens_ID. |
• | If sens_ID ≠ 0 and Isflag = 2, then: |
• | The spring is activated and/or, deactivated by sens_ID.
(if sensor is ON, spring is ON; if sensor is OFF, spring is OFF). |
• | The spring reference length (l0) is the distance between spring node N1 and N2 at the time of the sensor’s activation. |
6. | If a sensor is used for activating or deactivating a spring, the reference length of the spring at sensor activation (or deactivation) is equal to the nodal distance at time =0; except if sensor flag is equal to 2. |

8. | If fct_IDfr and Fric = 0 (no friction), then . |
9. | If fct_IDfr = 0 and Fric > 0, then constant Coulomb friction coefficient used:  |
If fct_IDfr > 0, then variable friction is calculated as a function on relative force between two pulley branches:



Where, is the angle (radians unit) and ffr is the function of fct_IDfr.
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