## Grid3D Basics

### Terms and Definitions

The main purpose of Grid3D is to be an editor for FEATFLOW and FEAST models. In these models an area is defined and partitioned into finite elements. For every single element a solution is calculated which reflects the state of this element at a given time in a defined environment. On application of this methods is the simulation of a car in a wind tunnel as used by the automobile industry.

In terms of Grid, a model is a domain or a grid. The area which describes the physical environment is a combination of boundaries. Boundaries come in several flavours. In 2D there are

- segment lists -- a kind of high level polygon: the sides of the polygon can be
  - straight lines,
  - circle segments or
  - NURBS.
- circles

The direction of the boundaries is important. Boundaries which are anticlockwise enclose an area. Clockwise boundaries exclude an area. In these terms, the boundary in the picture describes a channel with a pillar within. Only the area between the two boundaries is important for the calculations.

The supported boundary types for 3D are triangle meshes (which can be loaded from DXF files) and spheres.

The finite elements are either triangles and quadrangles in 2D or tetraeders and hexaeders in 3D. Throughout this manual we usually use the short forms (tri, quad, tetra, hexa). Those are consisting of faces (3D), edges, and points. There are different types of points in use:

- Inner Nodes are points which have 3D coordinates. The usually are inside the boundaries and therefore are called innner.
- Parameterized Boundary Nodes are 2D points whose position depends on the boundary which is assigned to them and on a parameter t. For example, a position of t=0.5 on a circle corresponds to the six o'clock position. That is, if you do not redefine the parameter intervals for the boundary.
- Cartesian Nodes are only for 3D domains. They, too, have 3D coordinates and are assigned to a boundary. So when the assigned boundary changes (for example the radius of a sphere), their position in space is adapted accordingly.

### Interface Overview

The main window of Grid3D consists of a desktop window with a menu and a toolbar. As usual for this type of application the toolbar provides easy access to the most used function. Both the menu and the toolbars are customizable with the Key Bindings Editor, which is accessable from the Domain Menu. Additionally there is a statusbar on the bottom of the main window which provides information about the status of Grid.

The usual procedure is to create a new domain or load an existing domain by click the corresponding button or menu entry. Every created or loaded domain opens up its own view on the desktop. There may even be several views for the same domain. The different views can be maximized, minimized and closed.

As some of the views allow quite complex operations on the domain, they may open up new toolbars which allow the user easy access to the operations they provide. Do not be disturbed if the toolbar disappears. This is usually only a sign that the view which it belongs to is not active. Just click inside of the view and the toolbar will reappear.

Along with the toolbar some menu entries change too, because they provide access to operations which are unique for or dependent on the currently active view.

To prevent working with multiple views to become too complicated, there is some support integrated in the interface.

To make it easier to distinguish the diffent views, every view has a colored border. For every new view, a button appears in the main toolbar and in the View menu. This button has the same color as the border of the associated view. Clicking on the button make that view become active at once.

Furthermore the View menu provides some functions to arrange the views on the desktop and to hide toolbars if the desktop gets too cluttered.

### Different Views

Grid3d support different views of the same domain. A view is a visualization of the domain data. Currently these views are supported:

- the domain editor
- the domain browser
- the domain validator
- the explode view

All these views have diffent purposes. Every time you load a domain, a domain editor appears on the desktop. The domain editor is the default edit facility and allows the manipulation of the domain with mouse and keyboard. The other views can be opened from the menu or by using the toolbar buttons.

The domain browser provides dialog based access to the domain structure. All items of the domain are sorted by the type into a tree structure. Whenever an item is selected the browser window updates and shows the item's data in the main area. After clicking the Apply button, the item data is updated and the changes are broadcasted to all views of that domain.

To change multiple items at the same time, they must be selected from the tree while holding Ctrl or Shift. All items have to be of the same type. Those properties which should be changed have to be selected by clicking into the checkboxes.

The domain validator has not editing function but allows the user to find faults in the domain. On the first page of the dialog, one can choose which tests shall be performed on the domain. The second page holds a list containing the test results. The elements from the list entries can be focused in the other views by double clicking on them.

The explode view does not provide any editing facilities as well but visualizes the distribution of the parallel- and matrixblocks. To do this the domain is broken up in parts. Every part consists of elements which have the same parallel- or matrixblock number. Then these parts are moved apart as if the domain exploded and the parts fly away in different directions (therefore the name).