Wire network behaviour of superconducting films with lower symmetrical mesoscopic hole arrays

Superconducting films with the same hole density but different geometric symmetry have been designed and fabricated. The R(H) curves show obvious periodic oscillations with several dips at fractional matching fields. It is found that the period of the oscillations in the low field is not necessary equal to that derived from the hole density, but consistent with that from the corresponding wire networks when the large disk-like film regions are regarded as nodes. The experimental results of R(H), T c (H) and j c (H) at fractional matching fields within the first oscillation also support the rationality of considering films with large-diametered hole arrays as wire networks. Our results demonstrate that the connectivity of superconducting films with large-diametered hole arrays plays a more important role in the oscillations of R(H) curves.

Numerical Investigation of Rotor and Journal Bearing Parameters on Nonlinear Vibration of a Highly Flexible Rotor Considering Journal Angular Motion With Experimental Verification

In this study, the nonlinear vibration (bifurcation type) of a highly flexible rotor supported by a journal bearing (JB) and self-aligning rolling element bearing (REB) under various configurations of rotor large disk mass/position, bearing length-to-diameter (L/D) ratio, and preload was investigated using two different bearing models: the model that considers both lateral and angular motion (Model A) and the model that considers just lateral motion (Model B). The rotor was modelled by 1-D finite elements (FE), and its degrees-of-freedom (DOF) was reduced to the DOF of the JB’s node by real mode component mode synthesis (CMS). Then, the shooting method and arclength continuation were applied to the reduced rotor model to obtain nonlinear limit cycles. Also, parallel computing was applied to the shooting method to shorten the calculation time. The stability of the obtained limit cycles was then determined by Floquet multiplier analysis. The experiment on the test rig with the same rotor and bearing parameters utilized in the calculation was carried out to verify the bearing models in each configuration. The calculation and experimental results showed that the bifurcation type calculated by Model A agreed with experimental results in all configurations. In addition, if the L/D ratio was short or the large disk position was near the rotor midspan, the bifurcation type obtained from both Model A and B agreed with the experimental results. The discrepancy in bifurcation type obtained from both bearing models only occurred in the cases that the L/D ratio was long and the large disk position was near the JB. Lastly, decreasing the L/D ratio, increasing preload, and moving the large disk position closer to the JB tended to change the bifurcation type from subcritical to supercritical.

Nonlinear Vibration Analysis of a Flexible Rotor Supported by a Journal Bearing Considering Journal Angular Motion

The effect of bearing length to diameter (L/D) ratio and large disk position on nonlinear vibration of a flexible rotor-bearing system was investigated. The rotor consisted of a shaft modeled by one-dimensional finite elements (FEs) and disks. It was supported by a self-aligning ball bearing (BB) and an axial-groove journal bearing (JB). Two JB's L/D ratios of 0.4 and 0.6, two large disk positions of 340 and 575 mm measured from the BB, and two bearing models that consider both journal's lateral and angular motion (model A) and consider only journal's lateral motion (model B) were investigated. The degrees-of-freedom (DOF) of the equation of motion (EOM) were reduced to those of the boundary DOF by real mode component mode synthesis (CMS) that retains only the first forward and backward modes of the internal DOF. Shooting method and Floquet multiplier analysis were applied to the reduced EOM to obtain limit cycles and their stability, which indicates Hopf bifurcation type. Numerical results indicated that supercritical bifurcation only occurred in the case of L/D = 0.4 and large disk position 575 mm for both bearing models. Otherwise, the subcritical bifurcation occurred except the case of L/D = 0.6 with the large disk position 575 mm that supercritical bifurcation occurred if model B was used. The experiment with the same parameters used in the calculation was conducted as verification. The experimental results showed the same bifurcation type as calculated by using model A.

Nonlinear Vibration Prediction of a Highly Flexible Rotor Supported by an Axial Groove Journal Bearing Considering Journal Angular Whirling Motion

The difference in dynamic behavior of the rotor-bearing system supported by the bearing model that considers both lateral and angular whirling motions of the journal (model A), and the model that considers only lateral whirling motion (model B) is investigated. The rotor model consists of a slender shaft, a large disk, and two small disks supported by a self-aligning rolling element bearing (REB) and an axial groove journal bearing (JB) of length-to-diameter ratio (L/D) = 0.6. Three positions of the large disk: 410, 560, and 650 mm measured from the REB, are investigated. Numerical integration of the rotor-bearing system which is modally reduced to the first forward (FWD) mode is performed at above the onset speed of instability until either a steady-state journal orbit or contact between the journal and the bearing occurs to identify the bifurcation type. Numerical results using model A indicate subcritical bifurcation with the contact between the journal and the inboard (IB) side of the bearing in all three large disk positions, whereas those of model B indicate subcritical bifurcation when the large disk position is at 410 mm, and supercritical bifurcation is observed in the other two cases. Finally, the experiments at the same three large disk positions are performed. Subcritical bifurcation with the contact between the journal and the IB side of the bearing is observed in all large disk positions, which conforms with the calculation result of model A. Hence, model A is essential in nonlinear vibration analysis of a highly flexible rotor system.

Bilateral traumatic C6-C7 facet dislocation with C6 spondyloptosis and large disk sequestration in a neurologically intact patient

Traumatic cervical spondyloptosis is an uncommon and severe form of facet joint dislocation that commonly leads to severe neurological damage. Decision making regarding the reduction and fixation technique is challenging, especially when a patient is neurologically intact, since an undiagnosed prolapsed disk at the involved level may lead to severe neurological consequences during reduction. A 24-year-old male was admitted after sustaining a severe direct axial blow to his head. Computed tomographic and magnetic resonance imaging scans revealed an acute C6C7 fracture dislocation with spondyloptosis of C6 vertebra and a large disk fragment posterior to C6 vertebral body. The patient was neurologically intact, apart from mild bilateral numbness over C6 distribution. The patient underwent C6 corpectomy to avoid acute cord compression related to the large sequestered disk behind C6 vertebra. Following C6 corpectomy, we were unable to exert enough axial pull to reduce the facet dislocation through the anterior approach. Therefore, the reduction was performed through a posterior approach with C5T1 posterior fusion, followed by anterior cage placement and C5-7 anterior fusion (front-back-front approach). At postoperative follow-up of 24 months, the patient demonstrated a full and pain-free cervical range-of-motion and remained neurologically intact. Follow-up radiographs of the cervical spine demonstrated good instrumental alignment with solid fusion at 6-month follow-up.

Nonlinear Vibration Analysis of a Flexible Rotor Supported by a Journal Bearing Considering Journal Angular Motion

The effect of bearing length to diameter (L/D) ratio and large disk position on nonlinear vibration (limit cycle and bifurcation type) of a flexible rotor-bearing system is investigated. The rotor consists of a shaft modeled by 1-D finite elements (FE), two small disks and a large disk. It is supported by a self-aligning ball bearing and an axial-groove journal bearing with L/D ratio of 0.4 and 0.6. Two large disk positions: 340 and 575 mm measured from the ball bearing are investigated. The journal angular motion, which is essential for the highly flexible rotor but typically not considered in the previous nonlinear vibration literature; is considered in nonlinear bearing force calculation. The degrees of freedom (DOF) of the rotor-bearing system are reduced to those of the node that the nonlinear journal bearing force and moment act on by real mode component mode synthesis (CMS) that retains only the 1st forward and backward modes. Shooting method and Floquet multiplier analysis are applied to the reduced rotor-bearing system to obtain limit cycles and their stability of each bearing L/D ratio and large disk position case. Numerical results indicate that supercritical Hopf bifurcation only occurs in the case of L/D = 0.4 and large disk position 575 mm, otherwise subcritical occurs. However, if the typical bearing model that does not consider journal angular motion is used, the bifurcation type for the case of L/D = 0.6 with large disk position 575 mm will change to supercritical. Lastly, the experiments with the same L/D ratio and large disk position investigated in the calculation are performed as a validation. The experimental result of each case shows the same bifurcation type as the calculation result using the bearing model that considers the journal angular motion.

Nonlinear Vibration Prediction of a Highly Flexible Rotor Supported by an Axial Groove Journal Bearing Considering Journal Angular Whirling Motion

In this study, the difference in dynamic behavior of the rotor-bearing system supported by the bearing model that considers both lateral and angular whirling motions of the journal (model A), and the model that considers only lateral whirling motion (model B) is investigated. The rotor model consists of a slender shaft, a large disk and two small disks supported by a self-aligning ball bearing and an axial groove journal bearing of L/D = 0.6. Three positions of the large disk: 410, 560, and 650 mm measured from the ball bearing, are investigated. Numerical integration of the rotor-bearing system which is modally reduced to the 1st forward mode is performed at above the onset speed of instability until either a steady state journal orbit or contact between the journal and the bearing occurs to identify the bifurcation type. Numerical results using model A indicate subcritical bifurcation with the contact between the journal and the inboard side of the bearing in all three large disk positions, whereas those of model B indicate subcritical bifurcation when the large disk position is at 410 mm, and supercritical bifurcation is observed in the other two cases. Lastly, the experiments at the same three large disk positions are performed. Subcritical bifurcation with the contact between the journal and the inboard side of the bearing is observed in all large disk positions, which conforms with the calculation result of model A. As a result, model A is essential in nonlinear vibration analysis of a highly flexible rotor system.