When applying a 0.59-N force, the contours of the stress were typically similar to the model with the larger crown-root angle that received 0.5 N of the force.
In addition to the internal and external forces, the active contour model can be extended by including a balloon force λ that acts perpendicular to the contour.
The internal force Fint forces the snake contour to be smooth while the external force Fext attracts the snake to the desired image features.
In particular, this proposed prediction model allows accurate design verifications for high-speed machines because it reflects the influences of the high inertia forces and the contour errors caused by high feed rate.
If λ is positive, the VVF term, acting as a shrinkable force, will penalize the arc length of the curve along vessel boundaries and force the evolving contour to shrink to thick vessel boundaries, while the weak vessels may be neglected.
Balloon force allows the contour curve to expand or to shrink in order to fit to the target boundaries.
By creating an energy functional that penalises deviations of the candidate model from the target model, one is able to force the candidate contour around objects appearing similar to those surrounded by the target contour in the original frame.
Furthermore, there is lack of a force pushing the contour to evolve along the centerline of weak vessels, which makes the energy function tend to trap into a local minimum.
These peaks are deformed under compression forces and form 'contact spots.' Isolated valleys with lubricant are formed between the compressed peaks forming closed contour lines (Figure 2).
We can generalise for forces applied along the contour.
