# Geometry and mesh / with sliding surface

## Introduction

This paragraph deals with rotation or translation motion with sliding motion of the moving part with respect to the fixed part.

## Technique used

The technique used consists in dissociating the different parts: fixed part and moving part. As in the previous case, these fixed and moving parts are not re-meshed.

This technique is detailed in the following blocks.

## Dissociation surfaces

The sliding surface is interposed between the volumes belonging to the two mechanical sets, which slide with respect to each other.

Sliding surface examples

## Separation of objects

To allow the moving part to slide with respect to the fixed one, a separation of geometric objects (points, lines and faces) and mesh objects (nodes, line elements and surface elements) is made at the level of the sliding surface. The mechanical sets become entirely independent from the geometric and meshing point of view.

When the moving part rotates, the nodes of the volume elements from the two sides of the sliding surface are not necessarily face to face. This is illustrated in the figure below.

Position 0° Position 35°

The mesh nodes of the fixed and moving part are face to face at the level of the sliding surface.

The mesh nodes of the fixed and moving part are not face to face at the level of the sliding surface.

In this situation, a non-conforming mesh is authorized at the level of the sliding surface.

## “Mesh connection” technical

The technique of “mesh connection” on the two sides of a sliding line consists of an interpolation of nodal values of the surface elements.

Each nodal value on each node of a surface element situated on one side of the sliding line is expressed as a linear function of the nodal values of the neighboring surface elements on the other side of the sliding line. This is done in order to ensure the continuity of state variable.

## Acceptable meshing

It is important that the areas of face to face surface elements be approximately the same for any rotating angle. This is illustrated in the figures below.

Recommended meshing
Non-recommended meshing (inhomogeneous density of nodes along the two circumferences)

## Geometry of the sliding surface

The sliding surface is:

• either a plane surface, for translating motion
• or a revolving surface, for rotating motion around an axis; it can be a cylindrical surface, a conical surface or a plane surface (see the following figure)

If the sliding surface is cylindrical, we are dealing with a sliding cylinder.