Simulative investigation of rubber damper elements for planetary touch-down bearings

Designing touch-down bearings (TDB) for outer rotor flywheels operated under high vacuum conditions constitutes a challenging task. Due to their large diameters, conventional TDB cannot suited well, and a planetary design is applied, consisting of a number of small rolling elements distributed around the stator. Since the amplitude of the peak loads during a drop-down lies close to the static load rating of the bearings, it is expected that their service life can be increased by reducing the maximum forces. Therefore, this paper investigates the influence of elastomer rings around the outer rings in the TDB using simulations. For this purpose, the structure and the models used for contact force calculation in the ANEAS simulation software are presented, especially the modelling of the elastomers. Based on the requirements for a TDB in a flywheel application, three different elastomers (FKM, VMQ, EPDM) are selected for the investigation. The results of the simulations show that stiffness and the type of material strongly influence the maximum force. The best results are obtained using FKM, leading to a reduction of the force amplitude in a wide stiffness range

Drop-Downs of an Outer Rotor Flywheel in Different Planetary Touch-Down Bearing Designs

With an increase in renewable energy in the electricity grid, more storage capacity for grid stabilization and energy flexibilization is necessary. Dynamic grid stabilization is one possible application for flywheels. To increase the energy density of flywheels, they can be built as highly integrated outer rotor systems. The losses of the flywheel are reduced by magnetic levitation and operation under vacuum conditions. In the case of the failure or overload of the active magnetic bearings, the system needs touch-down bearings to prevent system destruction. Planetary touch-down bearings consisting of several small bearing units circumferentially distributed around the stator are especially suited for these systems. In the literature, these planetary touch-down bearings are rarely investigated, especially the number of bearing units. Therefore, this paper investigates the influence of the number of touch-down bearing elements in simulations and experiments for an 8-element and a 6-element touch-down bearing arrangement. For the investigation, drop-downs at four different speeds were performed. Simulation and experimental results showed that, for the 6-element touch-down bearing, in contrast to the 8-element touch-down bearing, maximal velocity did not increase with the drop-down speed. Therefore, the touch-down bearing arrangement with fewer elements is preferrable

Control Strategies for Highly Gyroscopic Outer Rotors with Diametral Enlargement in Active Magnetic Bearings

Flywheels are used for peak shaving or load smoothing to generate a higher efficiency and a more stable power supply. Therefore, this paper investigates highly integrated outer rotor flywheels levitated by active magnetic bearings (AMB). Due to the highly gyroscopic behavior and the diametrical enlargement under rotation, the system behavior changes with the speed, leading to a significant decrease in the maximum force and maximum force slew rate of the AMB. Thus, the speed range in which a decentralized feedback control stabilizes the system is reduced. In the literature, there are numerous approaches for coping with gyroscopic behavior. However, there are far fewer investigations for explicit consideration of the change in the air gap in the control structure. Therefore, the goal of this work is to find a control strategy to reduce the effect of the gyroscopic behavior as well as the change of the air gap. The authors propose a control strategy combining a cross feedback control with a decentralized variable feedback control. With this combination, the drawbacks of the previously described effects are compensated, leading to a higher operating range of the system and a reduced utilization of the amplifier without overcompensation at lower rotational speeds

The role of neuronavigation in intracranial endoscopic procedures

In occlusive hydrocephalus, cysts and some ventricular tumours, neuroendoscopy has replaced shunt operations and microsurgery. There is an ongoing discussion if neuronavigation should routinely accompany neuroendoscopy or if its use should be limited to selected cases. In this prospective clinical series, the role of neuronavigation during intracranial endoscopic procedures was investigated. In 126 consecutive endoscopic procedures (endoscopic third ventriculostomy, ETV, n = 65; tumour biopsy/resection, n = 36; non-tumourous cyst fenestration, n = 23; abscess aspiration and hematoma removal, n = 1 each), performed in 121 patients, neuronavigation was made available. After operation and videotape review, the surgeon had to categorize the role of neuronavigation: not beneficial; beneficial, but not essential; essential. Overall, neuronavigation was of value in more than 50% of the operations, but its value depended on the type of the procedure. Neuronavigation was beneficial, but not essential in 16 ETVs (24.6%), 19 tumour biopsies/resections (52.7%) and 14 cyst fenestrations (60.9%). Neuronavigation was essential in 1 ETV (2%), 11 tumour biopsies/resections (30.6%) and 8 cyst fenestrations (34.8%). Neuronavigation was not needed/not used in 48 ETVs (73.9%), 6 endoscopic tumour operations (16.7%) and 1 cyst fenestration (4.3%). For ETV, neuronavigation mostly is not required. In the majority of the remaining endoscopic procedures, however, neuronavigation is at least beneficial. This finding suggests integrating neuronavigation into the operative routine in endoscopic tumour operations and cyst fenestrations

Drop-Downs of an Outer Rotor Flywheel in Different Planetary Touch-Down Bearing Designs

With an increase in renewable energy in the electricity grid, more storage capacity for grid stabilization and energy flexibilization is necessary. Dynamic grid stabilization is one possible application for flywheels. To increase the energy density of flywheels, they can be built as highly integrated outer rotor systems. The losses of the flywheel are reduced by magnetic levitation and operation under vacuum conditions. In the case of the failure or overload of the active magnetic bearings, the system needs touch-down bearings to prevent system destruction. Planetary touch-down bearings consisting of several small bearing units circumferentially distributed around the stator are especially suited for these systems. In the literature, these planetary touch-down bearings are rarely investigated, especially the number of bearing units. Therefore, this paper investigates the influence of the number of touch-down bearing elements in simulations and experiments for an 8-element and a 6-element touch-down bearing arrangement. For the investigation, drop-downs at four different speeds were performed. Simulation and experimental results showed that, for the 6-element touch-down bearing, in contrast to the 8-element touch-down bearing, maximal velocity did not increase with the drop-down speed. Therefore, the touch-down bearing arrangement with fewer elements is preferrable

Simulative Investigation of Rubber Damper Elements for Planetary Touch-Down Bearings

Designing touch-down bearings (TDB) for outer rotor flywheels operated under high vacuum conditions are a challenging task. Due to the big diameters conventional TDB are not suited and a planetary design is applied consisting of a number of small rolling elements distributed around the stator. Since the amplitude of the peak loads during a drop-down lies close to the static load rating of the bearings, it is expected that the service life can be increased by reducing the maximal forces. Therefore, this paper investigates the influence of elastomer rings around the outer rings in the TDB using simulations. For this purpose, the structure and the models used for the contact force calculation in the simulation software ANEAS are presented, especially the modelling of the elastomers. Based on the requirements for a TDB in a flywheel application three different elastomers (FKM, VMQ, EPDM) are selected for the investigation. The results of the simulations show that stiffness and material strongly influence the maximum force. The best results are obtained using the material FKM. Leading to a reduction of the force amplitude in a wide stiffness range

Control Strategies for Highly Gyroscopic Outer Rotors with Diametral Enlargement in Active Magnetic Bearings

Flywheels are used for peak shaving or load smoothing to generate a higher efficiency and a more stable power supply. Therefore, this paper investigates highly integrated outer rotor flywheels levitated by active magnetic bearings (AMB). Due to the highly gyroscopic behavior and the diametrical enlargement under rotation, the system behavior changes with the speed, leading to a significant decrease in the maximum force and maximum force slew rate of the AMB. Thus, the speed range in which a decentralized feedback control stabilizes the system is reduced. In the literature, there are numerous approaches for coping with gyroscopic behavior. However, there are far fewer investigations for explicit consideration of the change in the air gap in the control structure. Therefore, the goal of this work is to find a control strategy to reduce the effect of the gyroscopic behavior as well as the change of the air gap. The authors propose a control strategy combining a cross feedback control with a decentralized variable feedback control. With this combination, the drawbacks of the previously described effects are compensated, leading to a higher operating range of the system and a reduced utilization of the amplifier without overcompensation at lower rotational speeds