Cameron is right, .2dm files typically contain triangular or quadrilateral elements, however, using the SMS software developed by Aquaveo, you can convert .2dm files to the RAS geometry format and load that into RAS 5.0. It works well and does preserve the triangular or quadrilateral cell configuration, you just have to be careful not to make any changes to the “2D flow areas” options after importing it into RAS, as RAS will regenerate the mesh and build a different configuration of cell edges.