Creating Surface Force Densities

Surface Force Densities are intensive loads representing surface traction fields of uniform magnitude applied to surface geometries.
Surface Force Density objects belong to Loads objects sets.

The user specifies three components for the direction of the field, along with a magnitude information. Upon modification of any of these four values, the surface traction vector components and magnitude are updated based on the last data entry. The surface traction vector remains constant independently of the geometry selection.

Units are surface traction units (typically N/m2 in SI).

Surface Force Density can be applied to the following types of Supports:

Mechanical Feature	Geometrical Feature				Analysis Feature
Mechanical Feature	Point or Vertex	Curve or Edge	Surface or Face	Volume or Part	Analysis Feature

This task shows you how to create a Surface Force Density applied to a surface geometry.

You can use the sample00.CATAnalysis document from the samples directory for this task: Finite Element Model containing a Static Analysis Case and computed corresponding Static Solution.

Before You Begin:
Go to View -> Render Style -> Customize View and make sure the Shading, Outlines and Materials options are active in the Custom View Modes dialog box.

1. Click the Surface Force Density icon

.
The Surface Force Density dialog box is displayed.

2. You can change the identifier of the Surface Force Density by editing the Name field.

3. Set the Axis system.

The Axis System Type combo box allows you to choose between Global, Implicit and User Axis systems for entering components of the traction field vector:

	`Global`: if you select the `Global` Axis system, the components of the surface traction field will be interpreted as relative to the fixed global coordinate system.
	`Implicit`: if you select the Implicit Axis system, the components of the surface traction field will be interpreted as relative to a local variable coordinate system whose type depends on the support geometry.
	`User`: if you select a `User` Axis system, the components of the surface traction field will be relative to the specified Axis system. Their interpretation will further depend on your Axis Type choice.

To select a User Axis system, you must activate an existing Axis by clicking it in the specification tree. Its name will then be automatically displayed in the Current Axis field.

If you choose the User axis system, the Local orientation combo box further allows you to choose between Cartesian, Cylindrical and Spherical local axis orientations.

Cartesian: the components of the surface traction field are interpreted as relative to a fixed rectangular coordinate system aligned with the cartesian coordinate directions of the User-defined Axis.

Cylindrical: the components of the surface traction field are interpreted as relative to a local variable rectangular coordinate system aligned with the cylindrical coordinate directions of each point relative to the User-defined Axis.

Spherical: the components of the surface traction field are interpreted as relative to a a local variable rectangular coordinate system aligned with the spherical coordinate directions of each point relative to the User-defined Axis.

	You can define the surface traction direction by using the compass.
	You can modify the compass orientation either with the mouse or by editing the compass.
	By applying the compass to any part geometry, you can align the compass directions with the implicit axis directions of that geometry: drag the compass by handling the red square and drop it on the appropriate surface. The normal direction to this surface defines the new direction. Then, click on the Compass Direction button to take this new direction into account. You can now invert the direction if desired, editing the values of the three components.

4. Select the geometry support (a face) on which the surface traction is to be applied. Any selectable geometry is highlighted when you pass the cursor over it.

You can select several supports in sequence, to apply the Surface Force Density to all supports simultaneously.
Symbols representing the Surface Force Density are displayed on the support geometry to visualize the traction field.

5. Enter a new value for any one of the four fields. For example, enter values for the X, Y, Z components of the surface traction field as shown below

The corresponding Norm value is automatically computed and displayed.

The remaining three fields are automatically computed and displayed.

The visualized symbols orientation is also updated to reflect the modification.

You can re-use data (Data Mapping) that are external from this version (experimental data or data coming from in-house codes or procedures). For more details, see Creating Pressures.
This capability is only available if you installed the ELFINI Structural Analysis product.

6. Click OK in the Surface Force Density dialog box to create the Surface Force Density.

A Surface Force Density object appears in the features tree under the active Loads objects set.

	You can either select the surface and then set the Surface Force Density specifications, or set the Surface Force Density specifications and then select the surface.
	If you select other surfaces, you can create as many Surface Force Density loads as desired with the same dialog box. A series of Surface Force Densities can therefore be created quickly.
	Loads are required for Stress Analysis computations.
	If several Analysis Cases have been defined in the Finite Element Model, you must activate a Loads objects set in the features tree before creating a Surface Force Density object (only available if you installed the ELFINI Structural Analysis product).
	Surface Force Density objects can be edited by a double click on the corresponding object or icon in the specification tree.

Make sure the computation is finished before starting any of the below operations.

Products Available in Analysis Workbench

The ELFINI Structural Analysis product offers the following additional features with a right mouse click (key 3):

on a Surface Force Density object:

Surface load visualization on mesh: the translation of your Surface Force Density object specifications into solver specifications can be visualized symbolically at the impacted mesh elements, provided the mesh has been previously generated via a Compute action.

on a Loads objects set:

1) Generate Image: generates an image of the computed Load objects (along with translating all user-defined Loads specs into explicit solver commands on mesh entities), by generating symbols for the elementary loads imposed by the Loads objects set. The image can be edited to include part or all of the options available.

2) Report: the partial status and results of intermediate pre-processor computations are reported in HTML format. It represents a subset of the global Report capability and generates a partial report of the Loads objects set Computation.

See Creating Pressures for more details.

3) Double-clicking on the Loads set, you will display the Loads dialog box that lets you choose whether you wish to apply self-balancing to the load. Example of use: if this option is used with iso-static specifications, it will allow you to simulate free-body loading. If you make the option active, the center of inertia results null.