Working with Surface and Volume Regions
In some situations, you may want to isolate particular areas of your model to create a more refined mesh or to more closely simulate real world conditions. For example, if a portion of a surface on your model undergoes repeated force from a piston, you may want to apply a load only to the circular profile where the piston contacts the surface.
As another example, you may have a solid model that demonstrates poor mesh quality and singularities at a re-entrant corner. In this case, you can create a volume region around the re-entrant corner to ensure a better mesh outside of the volume region. You can then chose to disregard the results within the volume region, as the P-orders will be falsely high.
Creo Simulate enables you to isolate both surface areas and portions of a volume. To do so, you create surface regions and volume regions. By definition, a region is the child of the following:
• The geometry that describe the region
• The original surface or volume
As such, a region’s location can change if you apply design variables that change the shape of the original surface or volume.
A surface region is a contour that subdivides a part surface or volume to allow partial loading, constraining, or shell pairing of that surface. In situations where you want to constrain or load a specific portion of a part surface, you can create a region on the surface and apply the load or constraint to that region only.
A volume region is, essentially, a cut or protrusion that subdivides a volume into two distinct subvolumes. There are a variety of methods that you can use to define the contour of a volume region, including extruding the volume region, revolving the region, and developing the regions from a blend, sweep, or quilt surface. You can also use advanced volume region creation techniques such as helical sweeps, variable section sweeps, and sweeps based on blended sections retrieved from a file.
You use volume regions primarily if you want to refine your mesh in either native mode or FEM mode. You can apply materials to volume regions. Click > 
Material Assignment to assign material to a volume region. If your model has more than one volume region, you can assign different materials to each volume. However Creo Simulate processes the materials in the reverse order of creation of Material Assignment. You can also place loads, constraints, and other modeling entities on the surfaces that define the volume region, be they internal or external surfaces.
Material Assignment to assign material to a volume region. If your model has more than one volume region, you can assign different materials to each volume. However Creo Simulate processes the materials in the reverse order of creation of Material Assignment. You can also place loads, constraints, and other modeling entities on the surfaces that define the volume region, be they internal or external surfaces.Creating surface or volume regions can also prove handy if you want to define a small contact for contact analysis instead of using an entire part as the contact.