ANSYS Tutorial: Spatially Varying Loads

Introduction

In previous versions, if the user wanted to define spatial varying loads, he/she had to turn to command snippets. For those who are not familiar with APDL, it could be a challenge.

ANSYS Workbench V12.1, as well as V12.0, brings us good news: it is now possible to directly define spatial varying loads which have a variable magnitude in a single coordinate direction (x, y, or z). If the expression of a spatial varying load cannot be decomposed to several expressions which are functions to a single coordinate variable, it cannot be defined directly. Furthermore, only four load types qualify as spatial varying load:

• Pressure (normal direction only)
• Line Pressure (tangential direction only)
• Temperature and Thermal Condition

Despite these two limitations, it is still highly valued and we can see possibilities for improvement in the futures versions.

1. Define by Tabular Data

Here we use a very simple structure and load type Pressure to demonstrate how to do it. After inserting a Pressure, go to Details of “Pressure” and set Define By: Normal To. With other two direction definitions we can only define time varying load. Then choose Magnitude to Tabular.

Now we can set Independent Variable from Time to X (or Y/Z if applicable). If necessary we can also set a local coordinate system instead of the global coordinate system.

Now we can fill tabular data to define the spatial varying load. Of course the more points we define the more precise curve we will get.

As shown in the following figure, the magnitude of the defined pressure is 0 as marked in the graphics window. It is a cheat. If we check carefully in Mechanical APDL, we will find that the pressure varies in the x-direction as we defined.

2. Define by Function

It is a little bit difficult to define a spatial varying load by tabular data. There must be a smarter way. Yes, that is by Function. First, set Magnitude to Function:

Second, fill the load function. Workbench V12.1 supports a lot of mathematical operations in load functions: operands with a constant (´+´, ´-´, ´*´, ´/´, ´^´), trigonometric functions, etc. We can also set minimum and maximum range for a spatial independent variable as well as Number of Segments. We can change the value to get a better visualized plot of the function. But the precision will be the same.

Now we get a more realistic contour plot for the spatial varying pressure.

3. Spatial Varying Displacement

We can also define spatial varying displacement beside loads. The definition is almost the same except both “Normal To” and “Components” work for Displacement object. If we need to define more than one direction component, we have to add additional Displacement object.

Displacements are shown as vectors instead of contours except if we choose Normal To the surface.

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