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Contact between lines and surfaces

Some new specific features have been introduced into DeepLines for the so called generalized contact. Clashes between risers may be taken into account as well as line to surface contacts. During the calculations, the distances between risers are automatically checked and when proximity zones are detected, contact elements are automatically created to handle the normal reaction forces. A specific feature to model a riser sliding into another has also been introduced. The user must be aware that for this version no friction is taken into account.

• Clashing between lines

  A global method has been developed to deal with clashes between lines. This approach may be divided into two steps i.e. the detection of the contact and the contact forces evaluation. In 3D, it is difficult to determine the contact between two slender structures. To do so, it is necessary to define series of planes separating both structures and to prevent each of them to pass through. Of course, these planes need to be up-dated by the time the structures are moving.

  Thus, the calculations follow three iterative phases:

  1. Contact detection

  2. Contact elements definition

  3. Global resolution of the Virtual Work Principle, accounting for contact reactions.

• Contact detection

  An area of neighborhood consists in two parts of the seabed connections, which are close to each other. The area is defined by the abscissa (a1,b1) and (a2,b2) giving the beginning and the end of each part. In a first step, control points are equally displayed along the first mean line. Their orthogonal projection on the second line is determined. This gives a first assessment of the distance between the structures. Every first time the distance is lower than the criterion, an area of neighborhood is entered. The abscissa a1 and a2 are stored. By the time, the criterion is no longer respected, the area of neighborhood is excited.

  In each area, a control mean line is created. This line is defined by a series of points and tangential vectors. The positions and vectors are the mean of the positions and the tangent vectors on both lines.

  These planes are composed of a point on the control mean line and a normal vector tangent to the mean line.

• Contact element definition

  A contact element is a couple of points, each point belonging to one of the neighboring structures. These points are the intersections of each structure with a control detector plane. These directions are necessary to calculate the gap between the particles of a contact element. They finally define different planes through which both risers cannot pass.

• Virtual work principle

  Following the relative positions of these two particles, each contact element generates reaction and friction forces. The evaluation of their intensity follows the same process as described in Section which presents basics about related theory. Every contact element contribution is included in the global system of equations thanks to the interpolation functions.