Not an energy storage element

Why are energy storage elements not independent?

Because the two energy storage elements in this model are not independent. Because of the one-junction, the velocity or momentum of one determines the velocity or momentum of the other; given the masses of both bodies, knowing the energy of one is sufficient to determine the energy of the other.

Why is Q a generalized potential energy storage element?

It is a generalized potential energy storage element. The displacement, q, plays the same role as the specific entropy and specific volume do for a pure thermodynamic substance: it is sufficient to define the energy in the system. By convention we will define Ep = 0 at q = 0 as shown in figure 4.1.

Is energy storage a static or memory-less function?

Note that although we will use energy storage elements to describe dynamic behavior, this constitutive equation is a static or memory-less function. The constitutive equation permits us to evaluate the generalized potential energy, Ep For this element, potential energy is a function of displacement alone.

Which energy storage element does not give rise to a state variable?

Conversely, any energy storage element which must be described using a derivative operation will not require an independent initial condition and therefore will not give rise to a state variable; energy storage elements which have derivative causality are dependent.

Why do we need to know about dependent energy storage elements?

This is a typical consequence of dependent energy storage elements and, as one might expect, in more complex systems the algebraic manipulations can become formidable, even prohibitively so. It would be useful to know about dependent energy-storage elements before attempting to derive equations. How may we do so?

What is inter-dependence of energy storage elements?

That is the true meaning of inter-dependence of energy storage elements: in the model they are not distinct energy storage elements, despite appearances to the contrary. These two modelling approximations — rigid-body models and time-derivative operations — are intimately related.