Application of Bond Graph Method for Determining the Nonlinear Mathematical Model for a Thermostat in a Thermo Hydraulic System
by
Hamed Hossein Afshari
Aerospace Department, K.N.Toosi University of Technology, Tehran, Iran
Coauthors: Iman Shafiee Nejad, Dr. Alireza Novinzadeh, Amir Zanj

In this paper, a system viewpoint method has been investigated to study and analyze the complex system using bond graph technique. Bond graph technique is a useful methodology for modeling multidisciplinary dynamic systems. Especially, for systems which have nonlinear and time-variant behaviors. In this way, a nonlinear dynamic model of a thermo hydraulic circuit utilized for cooling an engine is established and analyzed. This cooling system is composed of three subsystems include thermal, hydraulic and mechanical subsystem. The major elements of this system are a centrifugal pump, two heat exchangers and a mechanical thermostat. The mechanical thermostat has a mass-spring structure which its elasticity module is variable. It should be noted that the mentioned elements can transmit, transform, store and consume the hydraulic energy. Finally, by obtaining the mathematical model, the state-space equations could be derived and solved to determine the dynamic response curve of the operating system under various conditions. By considering the several complexities due to the modeling process, the advantages of bond graph method for nonlinear modeling are proven appropriately.

Date received: March 15, 2008