Vortex Studio 2017b Feature – Stable Cable Simulation with Geometric Stiffness

Stable simulation of cables is a challenge, since they often involve very small compliances and large mass ratios. Instability manifests as vibrations in the cable with motion perpendicular to the stiff axes of the cable constraints. For example, this typically occurs during instances of high tension: the image below shows the cable constraints, direction of tension in blue, and the direction of vibration in green.

Stable Cable Simulation

A method for preventing such instability is to apply damping to all cable constraints based on the amount of tension in the cable. This approach corresponds to the “internal damping” feature that was in previous Vortex Studio releases. It tends to dampen in directions that aren’t necessary for cable stability. However, the high-frequency dynamics of the cable are reduced as a result.

Cables may now be stabilized using a new adaptive technique based on geometric stiffness. The geometric stiffness encodes the directions where instability may occur. This allows the cable to be automatically dampened during instances of high tension or when the simulation involves large constraint forces. However, damping only occurs in directions that require it. This improves the overall quality of the cable simulation and provides better dynamical behaviour.

Starting from Vortex Studio 2017b, you can enable geometric stiffness by selecting Dynamics Generic Cable and checking the Definition->Parameters Definition->Geometric Stiffness Enabled parameter (see image below). There are two parameters available for further tuning: Geometric Stiffness Stability Threshold (controls when dampening is applied), and Geometric Stiffness Scale (scales the computation of the geometric stiffness, which increases the frequency of damping being used to stabilize the simulation as constraint forces grow).

Stable Cable Simulation

Note that the Geometric Stiffness technology is patent pending. For more details, consult the Vortex Studio documentation — and please do feel free to ask questions in the Vortex Studio user community forum!