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This study conducts a nonlinear numerical analysis of the stability and the unbalance response of spherical spiral-grooved bearings (SSGBs) using a nonlinear orbit simulation method. This method is more accurate than the linear method, especially at high bearing loads. Parametric analyses are also performed with respect to nominal clearance and groove depth to optimize groove parameters. Shaft trajectories reflect the nonlinear characters of SSGBs when mass unbalance increases. Fast Fourier transform analyses of rotor orbit responses facilitate identification of the subsynchronous whirling and unbalance response in rotor vibration behavior. Results show that optimum dimensionless groove depths vary for different nominal clearances or rotational speeds. The static performance and stability characteristics of spherical bearings can be significantly influenced by the spiral grooves on the journal surface. [ABSTRACT FROM AUTHOR]

Orbit design for KufaSat Nano-satellites is presented. Polar orbit is selected for the KufaSat mission. The orbit was designed with an Inclination which enables the satellite to see every part of the earth. KufaSat has a payload for imaging purposes which require a large amount of power, so the orbit is determined to be sun synchronous in order to provide the power through solar panels. The KufaSat mission is designed for the low earth orbit. The six initial Keplerian Elements of KufaSat are calculated. The orbit design of KufaSat according to the calculated Keplerian elements has been simulated and analyzed by using MATLAB first and then by using General Mission Analysis Tool. [ABSTRACT FROM AUTHOR]

Airfoil bearings (AFBs) have been explored for various micro- to midsized turbomachinery for decades, and many successful applications of the AFBs to small turbomachinery were also reported. As machine size increases, however, one of the critical technical challenges of AFBs is a wear on the top foil and rotor during starts/stops due to relatively heavy rotor weight compared with the size of the bearing. The wear on the foil increases with greater loading during starts/stops as a function of the coating performance. The hybrid airfoil bearing (HAFB), which combines hydrodynamic pressure with hydrostatic lift, can help to minimize/eliminate the wear problem during the start/stops. This paper reports design and preliminary test results of hydrodynamically preloaded three-pad HAFB aimed for midsized airborne turbomachinery applications. Designed HAFB was manufactured and comprehensive parametric design simulations were performed using time-domain orbit simulations and frequency-domain linear perturbation analyses to predict performances of manufactured bearing. Static stiffness was measured at zero running speed to investigate the load capacity of hydrostatic operation when rotor is at stationary. The measured static stiffness showed good agreement with predictions. [ABSTRACT FROM AUTHOR]

A new estimate method is proposed, which takes advantage of the unscented transform method, thus the true mean and covariance are approximated more accurately. The new method can be applied to nonlinear systems without the linearization process necessary for the EKF, and it does not demand a Gaussian distribution of noise and what's more, its ease of implementation and more accurate estimation features enables it to demonstrate its good performance in the experiment of satellite orbit simulation. Numerical experiments show that the application of the unscented Kalman filter is more effective than the EKF. [ABSTRACT FROM AUTHOR]