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Chapter 2: Guide to Use

Chapter 2: Guide to Use

Concept and Terminology

ACE/gredit is an evolving tool for the generation of two-dimensional triangular finite element grids for coastal and land-margin applications. The user retains full control of the final grid design, while letting the computer perform the mechanical, time-consuming tasks. ACE/gredit has automatic grid generation features, but we recommend that grids be generated semi-automatically, with substantial user control.

"Cast"

Grids

  • Background grid

    This is a non-modifiable grid that contains baseline information on bathymetry. This grid is composed of 3-node triangular elements. If the user starts ACE/gredit directly from a set of soundings, a background grid is formed automatically by triangulation of the sounding points.

  • Edit grid

    This is the grid that we want to construct. By definition, the edit grid is modifiable during the operation of ACE/gredit; when ACE/gredit is started the edit and background grids coincide. This grid is composed of 3-node triangular elements. Nodal bathymetry is obtained by interpolation from the background grid, an operation that requires a specific request by the user.

  • Auxiliary grid

    This is a uniform quadrangular grid, formed occasionally to assist specific operations. In particular, this grid is formed to support the automatic placement of build points (see below).

    Outlines

  • Coastal outline

    This outline represents the shape of land boundaries (coast, islands, etc.). This is an optional and non-binding feature, which is intended only as a reference for visual quality control by the user.

  • Boundary (or "edit-grid boundary")

    The boundary represents the actual limit of the "meshable" domain. It is a binding and extremely important feature within ACE/gredit. Whenever build points are assembled in the form of an edit grid, elements can be formed only within this boundary. The edit-grid boundary is not automatically updated every time that a triangulation occurs; hence the edit-grid boundary may at times be non-coincident with the actual outline of the edit grid.

    Miscellaneous

  • Elements

    Elements are the grid "cells". In ACE/gredit they can 3 or 6 node triangles, or 4 node quadrangles.

  • Nodes

    Nodes are the "key points" of the elements. They support the shape functions that will be used to define geometric mapping and/or the space distribution of variables of interest. In the current version of ACE/gredit the nodes are the vertices of the elements.

  • Build points

    Build points are potential nodes, but are not formally connected as a grid. Build points are used to build edit grids by "triangulation", and they will effectively coincide with nodes immediately after a triangulation. However, nodes and build points will often be non-coincident, as the user can independently modify the number and locations of either set.

    Last Modified: January 19, 1997
    Copyright © 1999 Center for Coastal and Land-Margin Research