Structure and Condition

Fixed

The animation on the left depicts an image of a leaf swaying in the wind.
Notice that the polygon is collapsed since a standard square polygon has been modeled straight into an elastic body (without using substructures). For this reason, the achieved motion appears unnatural suggesting that this leaf has no thickness. (The one on the right is the original object and the section shown in yellow is the polygon that remains stationary by setting Fixed to ON.)

Hold-Structure

This polygon needs to be reinforced in order to prevent it from collapsing. One way to do this is to use the hold-structure function. Specifying this
structure for a surface gives the points the ability to remain at their original positions. This power prevents the polygon from collapsing. However, the strength of this power is uniform throughout the entire polygon. So it results in the same motion and creates a leaf whose
motion is similar to that of an underwater plant. This kind of motion is not acceptable yet.

Sub-Structure

Instead of using the hold-structure parameter, we are going to use the substructure function. To do this, create an auxiliary structure in the surface where the polygon is specified and then add it to the elastic body model. This method allows the tip of the leaf to move freely. This model appears more natural than the model previously created using the hold-structure. However, the leaf still looks unnatural since reshaping concentrates heavily at the base of the leaf, which is still fixed in place. (The black line in the right figure is the substructure which has been created.)

Thus, we must also create a substructure for the surface of the fixed base. There is no meaningful difference created in the surface of the base; however, a clearly visible difference appears at the boundary between the fixed section and the leaf section. The substructure is created at the boundary extending into both of its sides and makes that section the same as the others. This prevents reshaping from being mostly applied at the leaf base and makes the bending effect nearly the same throughout the leaf. (The figure on the right side contains the substructure while the figure on the left side does not.)

Smoothing

Finally, we must use the Smoothing function. Increase the spring (coefficient) for the fixed section and then reflect this effect as many times as specified using the smoothing on the section that is in motion. This allows the base to remain stiff and the rest to be gradually more pliant. Notice that setting Smoothing has created a base firmly in place and the soft tip of the leaf in a naturalistic motion.

Reference Object

Also, define a different surface for the tip of the leaf and create a NULL and make it the Reference Object. Creating a motion for this NULL object allows the tip of the leaf to make a different motion.