This study presents a new concept of gas bearings consisting of controllable gas foil bearings (C-GFBs) in which piezoelectric actuators are applied to the GFBs. The C-GFB consists of a laminated top foil, bump foil, and piezo stacks and can simply change the bearing shape or film thickness locally and globally by varying the thickness of the piezo stacks by adjusting the input voltage. The working method of C-GFBs is as follows. First, the bearing clearance is adjusted by changing the overall piezo stack thickness (clearance control). Second, the bearing preload (preload control) is modulated by the thickness expansion of several piezo stacks. Bearing lubrication performance is predicted for four cases of C-GFBs that controlled to have different bearing clearances and preloads. The piezo stack control generates meaningful differences in the fluid-film thickness and pressure. Clearance control has a great effect on the dynamic force coefficients, but preload control slightly increases the dynamic stiffness and damping coefficients. Furthermore, the rotordynamic prediction of a rotor supported on two journal C-GFBs is conducted. As a result, both control mode for C-GFB is found to have a positive effect on rotordynamic performance in terms of synchronous motions. Finally, the C-GFB is controlled to have a small bearing clearance and large preload at critical speeds to make it possible to stably pass through the critical speeds. Consequently, it turns out that the C-GFB can generate meaningful performance change in terms of bearing lubrication and ro-tordynamic performances by controlling only the input voltage of the piezo stacks. In addition, the C-GFB can be used to form various shapes to meet the operation conditions of an applied system.

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