Creating Distributed Forces

Distributed Forces are force systems statically equivalent to a given pure force resultant at a given point, distributed on a virtual part or on a geometric selection.
Distributed Force objects belong to Loads objects sets.

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

The point of application of the force resultant is automatically defined as follows:

	For extended geometries, this point is the centroid of the geometry.
	For virtual parts, this point is the handler of the virtual part.

The given single-force system is processed by the program as follows:

	In the case of extended geometries, it is transformed into an equivalent force system distributed over the selected support.
	In the case of virtual parts connected to deformable bodies, it is transmitted as a force system collectively to the entire connected geometry.

Units are force units (typically N in SI).

Distributed Forces 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
					virtual part

This task shows you how to create a Distributed Force applied to a virtual part or to a geometry selection.

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 Distributed Force icon

The Distributed Force dialog box is displayed.

2. If needed, change the identifier of the Distributed Force by editing the Name field.

3. Set the Axis System Type.

The Axis System Type combo box allows you to choose between Global and User Axis systems, for entering components of the resultant force vector.

Global: if you select the Global Axis system, the components of the resultant force vector will be interpreted as relative to the fixed global rectangular coordinate system.

User: if you select a User Axis system, the components of the resultant force vector will be interpreted as relative to the specified rectangular coordinate system.

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.

	You can define the resultant force vector 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. Enter values for the X, Y, Z components of the resultant force vector. For example, enter -50N as Z value.

The remaining three fields are automatically computed and displayed.

The visualized symbols orientation will also reflect the modification, once the support will be selected.

5. Select the support (a virtual part or a geometry) on which the resultant force vector is applied at the pre-defined point. Any selectable geometry is highlighted when you pass the cursor over it.

You can select several supports in sequence, to apply the Distributed Force to all supports simultaneously.
A symbol representing the resultant force equivalent to the Distributed Force is displayed at the application point of the support to visualize the input force system.

The Distributed Force dialog box now appears as shown here:

6. Click OK in the Distributed Force dialog box to create the Distributed Force.
A Distributed Force object appears in the specification tree under the active Loads objects set.

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

Be aware that the Distributed Force, as the Distributed Moment, applies directly to the nodes of the selected entity, whereas a Surface Density Force, or a Pressure, applies to the element faces of the selected entity. The latter type of forces is far more accurate and should be used whenever equivalent to the Distributed Force.

As an example, consider a coarsely meshed cylinder whose top surface has been submitted to a Distributed Force and whose bottom surface is clamped. As the nodes on the edges have less neighbors that inner nodes, they are pulled a lot further than the inner nodes, thus leading to an erroneous result near the edges. Mesh refinement is needed to get proper results. On the contrary, the Surface Density Force leads to a smoother and more accurate displacement.

Open DistribForce.CATAnalysis in this particular case.

Applying a Distributed Force results as shown here:

Applying a Surface Density Force results as shown here:

	You can either select the support and then set the Distributed Force specifications, or set the Distributed Force specifications and then select the support.
	If you select several geometric supports, you can create as many Distributed Forces as desired with the same dialog box. A series of Distributed Forces can therefore be created quickly. The point of application is automatically assumed to be the centroid of the system of individual supports centroids.
	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 Distributed Force object.
	Distributed Force objects can be edited by a double click on the corresponding object or icon in the features tree.

Products Available in Analysis Workbench

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

on a Body Force object:

Distributed Force Visualization on Mesh: the translation of your Distributed Force object specifications into solver specifications can be visualized symbolically at the impacted mesh nodes, 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.