Free surface effect when tank is empty?

The free surface effect occurs in tanks when they are partially filled with liquid, but it can also be relevant when a tank is empty. In an empty tank, there may still be residual liquid or sloshing from previous fills that can create a shifting mass. This shifting can affect the tank's stability and cause dynamic forces on the structure when the tank is in motion or subjected to external forces. Thus, even in an empty tank, considerations for the free surface effect are crucial for safety and structural integrity.