Define unstressed length at reference temperature X instead of 0°C

[adriengoeller]

Implementation part

The unstressed length of the cable must be defined using span parameters, sagging parameter, and sagging temperature.

The physics parameters of the cable given in documentation > Physics-based cable model >Cable's physics properties has to be implemented in a different class with abstract interface (name suggestion: PhysicsCableModel).

Documentation part (from a bug report)

Describe the issue linked to the documentation

In cable modelling, the unstressed length is defined as L_0 which means L at reference temperature 0°C.
It could be another temperature modifying the following equation

$$\varepsilon_{therm} = \theta \cdot \alpha_{th}$$

Suggest a potential alternative/fix

Suggested changes :

$$\varepsilon_{therm} = (\theta - \theta_{ref}) \cdot \alpha_{th}$$

$$L_{ref} = \frac{L}{1+\varepsilon_{total}}$$

Extra

L_ref should be implemented:

• inside the SpacePositionCableModel. Then it uses L from model but it has dependencies to a PhysicsCableModel for alpha_th and epsilon_total
• inside the PhysicsCableModel. Then it uses alpha_th and epsilon_total from model but it has dependencies to a SpacePositionCableModelfor L.

[adriengoeller]

Conception CR:

• A CableArray is needed
• The physics-based part is inside a separate class which need SPCableModel and CableArray
• For the moment the tension are inside the SPCableModel.