ABSTRACT
A system may possess various physical characteristics that arise from its physical domains; particularly, mechanical, electrical, thermal, and fluid processes. The basic physical elements in an engineering system can be divided into two broad categories: energy storage elements and energy dissipation elements. The constitutive equations in a thermal system are the physical equations for thermal capacitors (A-type elements) and thermal resistors (D-type elements). There are no T-type thermal elements. In general, the conditions (and parameters) of heat transfer will change from location to location. Mechanical systems can produce natural (free) oscillatory responses (or, free vibrations) because they can possess two different types of energy (kinetic and potential energies). Oscillations are possible, however, when forced by external means or integrated with other types of systems that can produce natural oscillations (e.g., integrating with a fluid system resulting in a thermo-fluid system).
