Independent system displacement variables

[princejan7]

http://postimg.org/image/8jqk9q6rp/

Can someone explain what "independent system displacement variables" are?


http://postimg.org/image/eypl6edhh/

What are the independent system displacement variables in this diagram?


thanks

 

[haruspex]

I've not come across the term before, but since there is supposed to be a 1-1 correspondence with equilibrium equations, I deduce that it means a variable which would represent displacement from equilibrium. In two dimensions, you have X and Y displacement and angular displacement, giving three statics equations.