On the relation between energy conserving low-order models and Hamiltonian systems

In this paper we examine the relation between the energy conserving finite dimensional or low-order models obtained by the application of the Galerkin projection methods to infinite dimensional model, and the class of finite dimensional non-canonical Hamiltonian systems with quadratic Hamiltonian functions and structure matrix whose elements are linear function of the state. We also examine the conditions for the conservation of the phase volume.