Nonlinear dynamic behavior of a water-lubricated hybrid bearing-rotor system
In this study, the stability analysis is carried out on a water-lubricated hybrid bearings used as the support of a high-speed motorized spindle. A two-dimension finite element method considering turbulence effect has been developed to solve the nonlinear oil film force. This paper mainly studies the influence of the water supply pressure, rotating speed, and unbalance mass on the axis orbit of the rotor-bearing system. The results of the axis orbit indicate that the effect of nonlinear for the hybrid bearing studied in this paper is not obvious, and the bearing-rotor system can run safely and stably at the rotating speed not more than 30000 rpm.
Nonlinear Dynamic Behaviors of an Imbalance Rotor on Multi-Lobe Bearings
Based on the free boundary theory and the variational method,a fast and accurate model for the calculation of the fluid-film forces under the Renolds boundary condition is presented.The model has been applied to the nonlinear dynamic behavior analysis of an imbalanced rigid rotor with two three-lobe bearing supports.Numerical simulation shows that the imbalanced rotor undergoes a bifurcation from synchronous motion to double period motion and at last loses its stability as chaotic motion. This paper also studied the influences of the rotor mass and the mass eccentricity. It is found that the threshold speed at which the rotor will lose stability decreases with the increase of rotor mass.The eccentricity influences the motion of the rotor seriously.The rotor threshold speed increases rapidly with the increase of mass eccentricity.Study of the elliptical bearing shows that the threshold speed of rotor supported by three-lobe bearings is higher than that of the elliptical bearings.
Complications of motility peg placement for porous hydroxyapatite orbital implants
Aim: To evaluate the complications associated with pegging of porous hydroxyapatite orbital implants. Methods: Complications associated with pegging were retrospectively reviewed from the charts of 100 of 133 patients with hydroxyapatite implantation from 1993 to 2000. Results: 48 (48%) of the 100 hydroxyapatite implanted patients who had undergone pegging were found to have problems with their pegs, including discharge (45.8%), peg falling out (20.8%), pyogenic granulomas (16.7%), popping peg (14.6%), hydroxyapatite visible around peg hole (8.3%), part of peg shaft visible (6.2%), peg drilled off centre (6.2%), peg drilled at an angle (4.2%), and excess movement of peg (4.2%). The standard peg fell out statistically more often than the peg and sleeve system (Yates's corrected χ2, p=0.038). There was a trend towards complications of the peg with use of a standard peg (versus sleeved peg) (p=0.226). Conclusions: There are several potential complications of pegging. Most complications are minor and can be managed successfully.