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Numerical contact parameters

The Contacts tab is to specify the different contacts to be managed during the simulation. The tab consists in three general parameters, plus a table which details the various possible contacts and related parameters.

Warning

At least one contact type must have been defined in the Types > Contact Types folder in the model browser before defining the numerical parameters to be used to handle the contact.

General parameters : there are three values to be defined, as follows :

  • Iterations on contact location : may be increased for complex contact problem. Iteration on contact location defines the number of allowable iteration to check for the proximity zone and direction of friction loads.

  • Iterations on contact normal direction: may be increased when friction with high velocity motion is implied. Iteration on contact normal direction defines the number of allowable iteration to check for the proximity zone and direction of friction loads.

  • Tolerance on penetration: length of the quadratic penetration zone

Table of contacts: this table defines which contacts are to be considered during the analysis, and further contains all the related numerical parameters. Each row from the table allows to define one type of contact. For example, one row may be used to define how contact should occur between a riser and the seabed, or between two adjacent risers.

Note

In case a line is linked to a connection point from the Sea & Ground object, the contact is automatically defined by default but can be removed. Contact between two lines or between a line and a surface (defined in a Rigid Body object) can be added.

You can create new contacts by clicking the New contact button in the tab. Clicking this button will add a new row into the table. Similarly, you can remove any existing contact by clicking the Delete selected contact button, which will remove the active row from the table.

Each contact is characterized by a number of parameters, as listed below :

  • Line: use the drop down list to select which line will be considered when handling this contact. In case the contact is an internal lines contact type (for instance a guide, or PIP), this line will be considered as the internal one.

  • Name: use the drop down list to select either the whole line or selected segment from the line that will be considered when handling this contact.

  • Object2: use the drop down list to select which object from your analysis will be considered to contact with the line selected in the previous cell. This object may either be a line or a surface meshed with triangle elements. In case the contact is an internal lines contact type (for instance a guide, or PIP), the line selected in this cell will be considered as the external one.

  • Name2: In case where Object2 is a line, use the drop down list to select either the whole line or selected segment from the line that will be considered when handling this contact.

  • Density of contact elements (elts/m): this defines the number of contact elements per unit length along the contact zone.

Note

The density of contact elements is a parameter that controls the number of contact springs to be distributed along a contact zone. It is recommended to set this value equal to the inverse of the beam elements length for simple contacts like a pipe resting on the seabed - which requires that you calculate the optimum density of contact elements for every line segments. Setting the density of contact elements to zero in the contact input data automatically asks the FE engine to consider the optimum density of contact elements, so that each node is in average - supported by a single contact spring.

Warning

The density of contact elements defaults to 1 so that in average one contact element is created per unit length along the contact zone. This default value is generally too high for simple contact patterns such as line to seabed, as the length of the beam elements is generally larger than 1m. Considering high density of contact elements may slow down your calculation.

Note

Special contact patterns like orthogonal contact between two lines may require large densities of contact elements. This is because highly localized contact zones (for instance point contact) requires that the total contact force capacity is high enough to prevent the 2 lines to go through each other.

  • Criteria on proximity zone (m): this is the radial distance below which a contact zone will be created. In other words, contact elements will be created to simulate possible contact between two objects in case the distance between these objects becomes lower than the value you have input in this cell.

  • Minimum proximity zone (m): this is the minimum length of a contact zone - where length should be thought of as an axial length along the line.

  • Contact property: specify the contact property that will be used for this contact. At least one contact property must have been defined in the Types > Contact Types folder of the model browser. Contact properties may be either line-to-line contact type or line-to-surface type.

  • Friction induced moment: You may specify whether to consider the turning moment induced on the line by lateral friction forces or not. The turning moment results from the lateral friction force being applied at the contact point on the circumference bottom instead of the center line. Set the box to Yes if you wish to consider this moment in the analysis and No otherwise. Default value is No.

Note

When dealing with friction problems, it is often better to increase the iteration on contact location (to 100 for instance) and decrease the number of iterations in the Newton-Raphson loop in Static/Advanced