Heavy power-plant rotors are generally supported on journal bearings. However, hydrodynamic actions in journal bearings generate spin speed-dependent stiffness and damping forces, which induce ...instability beyond a spin speed limit called the stability limit speed. The presence of other rotating forces such as due to internal friction may further decrease the stability limit speed. Therefore, identification of journal bearing parameters and other rotating damping forces is important. This work extends Inverse eigen-sensitivity method to update a finite element model of a rotor-shaft system to identify journal bearing parameters and internal friction. Eccentricity ratio and coefficient of shaft material damping are updated in this process to identify bearing model and internal friction force at any speed. Updating of eccentricity ratio to identify journal bearing coefficients as proposed in this work is a novel approach that eliminates the need to update eight bearing coefficients per bearing and hence helps in effective parameterization in the model updating process.
•Updating of an FE model for a rotor system on short journal bearing is proposed.•For ease of parameterization, eccentricity ratio is updated for journal bearings.•Rotor-shaft material damping is also updated in this process.•Application of Inverse eigen-sensitivity approach is used and found very efficient.•The approach helps reducing bearing updating parameters from 8 to 1.
•Finite element rotor models are must to predict dynamic behaviour and rotor faults.•FE models need true boundary conditions, support and material properties as inputs.•Inverse eigen sensitivity ...method updates ball bearing stiffness, material damping.•Updated model results validated with measured frequency response.•Updated model predicts rotor unbalance accurately.
This work attempts experimental studies in finite element model updating of an actual rotor system mounted on ball bearings by using Inverse Eigen Sensitivity Method (IESM). The IESM is applied on state space representation of equations of motion and is used to identify bearing stiffness, damping and shaft material damping parameters. Non-proportional viscous damping model is used to model the bearing and shaft material damping. The experimental identification of viscous coefficient of shaft material damping was not found in the available literature and this work attempts the same as well. The updated model is validated for its accuracy by comparing the predicted frequency response with that obtained from the experiments. Finally, it is shown that the updated finite element model of the rotor system can be efficiently used to predict the unbalance in the rotor.
We study the zero temperature non-equilibrium dynamics of a fermionic superfluid in the BCS limit and in the presence of a drive leading to a time-dependent chemical potential μ(t). We choose a ...periodic driving protocol characterized by a frequency ω and compute the fermion density, the wavefunction overlap, and the residual energy of the system at the end of N periods of the drive. We demonstrate that the BCS self-consistency condition is crucial in shaping the long time behaviour of the fermions subjected to the drive and provide an analytical understanding of the behaviour of the fermion density nkF (where kF is the Fermi momentum vector) after a drive period and for large ω. We also show that the momentum distribution of the excitations generated due to such a drive bears the signature of the pairing symmetry and can be used, for example, to distinguish between s- and d-wave superfluids. We propose experiments to test our theory.
