Feature extraction of separation and attachment lines

Separation and attachment lines are topologically significant curves that e xist on 2D surfaces in 3D vector fields. Two algorithms are presented, one point-based and one element-based, that extract separation and attachment l ines using eigenvalue analysis of a locally linear function. Unlike prior t echniques based on piecewise numerical integration, these algorithms use ro bust analytical tests that can be applied independently to any point in a v ector field. The feature extraction is fully automatic and suited to the an alysis of large-scale numerical simulations. The strengths and weaknesses o f the two algorithms are evaluated using analytic vector fields and also re sults from computational fluid dynamics (CFD) simulations. We show that bot h algorithms detect open separation lines-a type of separation that is not captured by conventional vector field topology algorithms.