Passive Bearings Research Articles

Analytical and numerical investigation of gravity anchors for floating photovoltaic systems

Gravity anchors are a widely used anchoring solution for floating photovoltaic systems but can be costly and difficult to transport and install. To address this issue, 3D printed concrete gravity anchors can be fabricated offsite into a custom shape that optimizes the bearing resistance then filled with ballast onsite. This study evaluates the performance of gravity anchors with novel geometries enabled by 3D printing in representative sandy (drained) and clayey (undrained) soil layers for mooring angles ranging from 0 to 70°. The failure modes of gravity anchors were explored using numerical simulations with the goal of validating simpler analytical methods suitable for design. Results indicate that sliding primarily affects anchor efficiency (pullout capacity divided by buoyant weight) at small mooring angles, while overturning and plowing become dominant at larger mooring angles. Greater anchor efficiency is gained when using a skirt to enhance the passive bearing resistance, but difficulties may arise in the penetration of the skirt into sand. A C-shaped anchor with a padeye close to the center of gravity promoted plowing at high mooring angles. Analytical models are suitable fat lower mooring angles, but numerical simulations are recommended when evaluating anchor performance at mooring angles greater than 30°.

5-axes Levitation of a Rotor by Active Magnetic Bearings Employing Direct Output Feedback Control

In recent years the application of active magnetic bearings (AMB), as supporting element as well as vibration controller for rotors, has attracted considerable attention from researchers. In this work an attempt has been made for the complete levitation of a rotor weighing 4 kg, supported on two radial active magnetic bearings and two axial passive magnetic bearings (PMB) resulting in 5-axes levitation. The active bearings working in the mode of attraction make the system inherently unstable. Herein, a direct output feedback control scheme based on proportional and derivative of position signal has been employed to achieve stability. The active magnetic bearings consist of electromagnetic actuators, proximity probes for position measurement, feedback controller and current feedback type power amplifier. The passive bearings consisting of axially magnetized circular permanent magnets work in the mode of repulsion. The design of the electromagnetic actuator has been carried out considering load carrying capacity of the AMB, core loss and the resistive loss in the coil, so that the temperature rise in the core as well as in the coil is within allowable limit. Design of the feedback controller is based on direct output feedback control scheme, which makes the controller design easier and implementation of the controller hardware becomes simpler. The feedback controller parameters have been selected appropriately to generate required stiffness and damping in the AMBs for stable levitation of the rotor. The rotor has been driven up to a speed of 2000 rpm.

HTS-Tape Magnetic Bearing for Ultra High-Speed Turbo Motor

This paper aims to design superconducting mag-netic bearing using HTS tape for a ultra high-speed turbo motor operating up to 120000rpm. Despite being a recent technology compared to conventional magnetic bearings, HTS passive bearings have many interesting features, such as re-duced dimensions, easy implementation and excellent dynamic response at high speed. The results of the finite element simulation are promising as the levitation forces and the stiffness of the superconductor bearing are compatible with the design requirements. The main contribution of this paper lies in the use of short-circuited HTS coils, unlike previous systems that used HTS bulk.

Passive Bearing Estimation Using a 2-D Acoustic Vector Sensor Mounted on a Hybrid Autonomous Underwater Vehicle

The bearing estimation problem of low-frequency underwater acoustic sources is of paramount importance in antisubmarine warfare and passive acoustic monitoring applications. Typical solutions require manned vessels and towed arrays characterized by high costs, risks, and deployment difficulties. An alternative solution for such applications is represented by acoustic vector sensors (AVSs), which are lightweight, compact, and moderate in cost, have promising performance in terms of bearing discrimination and the potential to operate from autonomous underwater platforms. This article presents an experimental assessment of a 2-D AVS derived from a sonobuoy and mounted on a hybrid autonomous underwater vehicle (AUV) for estimating the bearing of underwater sources. The sensor model, its technical characteristics, the installation onboard the vehicle, and the implementation of the passive signal processing chain are reported. Three different algorithms for bearing estimation have been tested on real data: one based on a time-domain representation, one based on the frequency domain, and one relying on joint time–frequency representation. Experimentation and data are presented, first from very shallow waters within the Italian Navy base of CSSN, La Spezia, and then from the Tyrrhenian Sea, in the context of a multiplatform exercise led by the NATO S&TO CMRE. Using an acoustic navigation system as ground truth, these experiments allow the assessment of bearing estimation capabilities in both AUV (by using propeller and pump jets) and gliding navigation modes. While the results of all the three processing methods are at least par to those recently reported in similar experiments with different vector sensors and processing, the time–frequency-domain method can identify multiple sources without prior knowledge of the source signal waveform or bandwidth.

Generalized pseudo Bayesian algorithms for tracking of multiple model underwater maneuvering target

The strength of Generalized Pseudo Bayesian (GPB) algorithms is exploited in the presented study to enhance the target tracking precision, effective model approximation and rapid convergence of multimodel maneuvering object tracking. The GPB methods are considered to be suitable for approximating systems whose dynamics follow discrete-time and fixed state Markov process. Underwater maneuvering target tracking problems are usually solved with nonlinear Bayesian algorithms, in which kinetics of object are associated with passive bearings using state-space modeling. Here accuracy and convergence of GPB methods based on Interacting Multiple Model Extended Kalman Filter (IMMEKF), Interacting Multiple Model Extended Kalman Smoother (IMMEKS), Interacting Multiple Model Unscented Kalman Filter (IMMUKF) and Interacting Multiple Model Unscented Kalman Smoother (IMMUKS) are efficiently analyzed for tracking of multimodel maneuvering target in complex ocean environment. Application of these algorithms is systematically presented for estimating the real-time state of a maneuvering object that follows a coordinated turn trajectory. Performance analysis of IMM Kalman filters and smoothers is done with variations in the standard deviation of white Gaussian measurement noise by following Bearings Only Tracking (BOT) phenomena. Least Mean Square Error (MSE) between approximated and the real position of maneuvering target in rectangular coordinates is calculated for analyzing the performance of filtering and smoothing techniques. Simulation results of the Monte Carlo runs validate the effectiveness of IMMEKS and IMMUKS over IMMEKF and IMMUKF for scenario of given framework.

ЭКСПЕРИМЕНТАЛЬНЫЙ КОМПЛЕКС ДЛЯ ИССЛЕДОВАНИЯ ТРЕНИЯ В АКТИВНЫХ РАДИАЛЬНЫХ ПОДШИПНИКАХ СКОЛЬЖЕНИЯ

One of the most important characteristics taken into account when designing machines is their efficiency. Active fluid-film bearings are able to influence tribological processes and reduce frictional energy, which increases the efficiency of the machine. For experimental determination of friction and verification of simulation results, an experimental complex was created, which makes it possible to directly measure the moment of friction force in active journal bearings. The complex is based on a rotor-bearing system with a rigid rotor on one active and one passive bearing. The information-measuring system includes a set of sensors and has the ability to control servo valves of active hybrid bearings. The system interface is based on virtual devices and allows both monitoring the state of the rotor-bearing system in real time and recording signals for their subsequent processing. The article contains a description of design and the principle of operation of the complex, including the features of processing various sensor signals, as well as a description of measures to improve measurement quality.

A new hybrid observer based rotor imbalance vibration control via passive autobalancer and active bearing actuation

Many researchers have explored the use of active bearings, such as non-contact Active Magnetic Bearings (AMB), to control imbalance vibration in rotor systems. Meanwhile, the advantages of a passive Auto-balancer device (ABD) eliminating the imbalance effect of rotor without using other active means have been recently studied. This paper develops a new hybrid imbalance vibration control approach for an ABD-rotor system supported by a normal passive bearing in augmented with an AMB to enhance the balancing and vibration isolation capabilities. Essentially, an ABD consists of several freely moving eccentric balancing masses mounted on the rotor, which, at supercritical operating speeds, act to cancel the rotor's imbalance at steady-state. However, due to the inherent nonlinearity of the ABD, the potential for other, non-synchronous limit-cycle behavior exists resulting in increased rotor vibration. To address this, the algorithm of proposed hybrid control is designed to guarantee globally asymptotic stability of the synchronous balanced condition. This algorithm also incorporates with a “Luenberger-like” observer that continuously estimates the states of a balancer ball circulating around within ABD. In particular, it is shown that the balanced equilibrium can be made globally attractive under the hybrid control strategy, and that the control power levels of AMB are significantly reduced via the addition of the ABD because the control is designed such that it is only switched on for the abnormal operation of ABD and will be disengaged otherwise. Moreover, unlike other imbalance vibration control applications based upon ABD such as rotor speed regulator [21,22], this approach enables the controller to achieve the desirable performance without altering rotor speed once the rotor initially reaches the target speed. These applications are relevant to limited power applications such as in satellite reaction wheels, flywheel energy storage batteries or CD-ROM application.

Resonance mode detuning in rotor systems employing active and passive magnetic bearings with controlled stiffness

In the paper, the investigator offered a method of reducing the amplitude of vibrations of turbo machinery rotors with passive and active magnetic bearings in resonances and resonance zones corresponding to one of the critical speeds ranging from zero to operating rotational ones. The method was based on the ability to vary the nonlinear force characteristic and the damping properties of active magnetic bearings and passive magnetic bearings of a novel design by changing the electric parameters of electromagnet circuits. The offered design of a passive magnetic bearing with permanent ring magnets and a control winding enabled a short-time change of rotor bearing stiffness. Such rotor bearings can realise the method of detuning from critical speeds during rotor speed-up and run-down. Earlier, this method was feasible only when active magnetic bearings were used. However, a complete magnetic suspension of a rotor with the employment of two radial passive bearings and one axial active magnetic bearing was advantageous as compared to three active magnetic bearings. The feasibility of the detuning method had been substantiated by study results. The study presented the results of numerical analysis, which simulated the process of transition through resonances of the initial system with a significant reduction of vibration amplitudes. The nonlinear system of differential magnetic-mechanical equations was solved using the 5th-order Runge-Kutta method with a validation for the duality of solutions. The results were shown as 3-dimensional spectra of displacement of bearing points and amplitude-frequency responses. These results had been confirmed by experimental data obtained for a laboratory setup that implemented a combined passive-active magnetic suspension of a rotor. The overall total relative error of measurements was maintained at less than 0.5%. The discrepancy between the experimental and design data for amplitudes was within 2-3%, and for resonance frequencies, it was less than 0.2%. Hence, these studies substantiated the feasibility of passive magnetic bearings with controlled stiffness. They also confirmed the possibility of using passive-active magnetic suspensions for lightweight rotors (e.g., expanders and compressors) with the implementation of the suggested method of detuning from resonance modes.

Tests with a hybrid bearing for a flywheel energy storage system

This paper describes the design and experimental test of a passive magnetic bearing system composed by a superconductor magnetic bearing (SMB) and a permanent magnet bearing (PMB). This bearing setup is part of a flywheel energy storage system. The advantage of using a passive bearing system is that it offers low friction without the need of a magnetic bearing controller, increasing the reliability and decreasing the energy consumption. The first set of tests were quasi-static radial and axial force measurements of the PMB operating alone and together with the SMB. As the PMB is intrinsically unstable in one degree of freedom, the operation of the SMB together with the PMB is necessary to stabilize the system. After that, dynamic measurements were made for the SMB operating alone and together with the PMB. The resonant speeds were identified and the bearing radial and axial forces were also measured for the SMB and SMB + PMB operation. These results indicate that the studied bearing set is technologically feasible to be used in flywheel energy storage systems.

A Bilateral Traumatic Hip Obturator Dislocation.

A case of a bilateral simultaneous traumatic obturator dislocation of both hip joints in an 18-year-old young man following a traffic accident is presented. We reduced the dislocated femoral heads immediately under general anesthesia followed by passive and active exercises and early full-weight bearing mobilization. After 5 years, the result was excellent.

Designing, simulations and experiments of a passive permanent magnet bearing

This paper presents simulations and experimental results for two types of Passive Permanent Magnet Bearings. The bearing system under investigation consists of two permanent magnet rings opposing to each other in two different config- urations. The influence of parameters, such as thickness and radius of permanent magnets, in the force is presented through FEM calculations. Two setups of passive magnetic bearings have been built. Static measurements of radial and axial forces are reported and results compared with simulations. Also, dynamic tests show the behavior of the bearing and the magnitudes of force in the foothold. The results are presented to show trends in the parameters, so the conclusions are applicable for other sizes and applications. As an example, the application as a top bearing for a 12 kW vertical axis wind turbine is considered.

Yokeless radial electrodynamic bearing

When null-flux, passive electrodynamic bearings include a ferromagnetic yoke in front of the permanent magnets, the stiffness associated with the radial centering force becomes negative under a critical speed. This yields a strong instability and the necessity of using mechanical launch bearings at low speeds. In this paper, an electrodynamic bearing without ferromagnetic yoke is proposed. An analytical 2D model of the bearing is presented and some hypotheses are validated. The model is then used to perform a first analysis of the bearing performance. The force predictions correspond to expectations: the stiffness never reaches negative values. It is also shown that for given geometrical parameters, the performance of the studied bearing can be improved by choosing the appropriate number of phases and number of pole pairs of the winding.

Superconducting Magnetic Bearing as Twist Element in Textile Machines

Superconducting magnetic bearings (SMBs) enable the levitation of a magnet in a stable position over a cooled superconductor without the need for an additional positioning system. These passive bearings are being investigated for applications wherever a stationary levitation or a contact-free rotary or linear motion is desired and cannot be realized by simpler means. Ring spinning is the most widely used technique for the production of short staple yarn in the textile industry. The productivity of the ring-spinning process depends on the rotational speed of the spindle. It is limited by friction in the so-called ring-traveler twist element. During the spinning process, the traveler is dragged along the ring by the yarn with up to 30000 r/min. The resulting friction causes wear of the twist element and melting of synthetic yarn at high spindle speeds due to strong heat generation. Recently, an SMB was implemented as a contact-free twist element in a ring-spinning machine up to 11000 r/min. This prototype SMB consists of a rotating permanent-magnetic (PM) NdFeB ring acting as a yarn-driven traveler and a stationary bulk YBCO ring at 77 K in an open LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> bath. In this paper, we investigate the bearing properties of this SMB with regard to the special requirements of the ring-spinning process. Dynamics of the spatially vibrating and rotating PM ring are analyzed including the forced vibration due to interaction with the yarn. For the expected yarn forces, the displacement amplitude at the resonance frequency remains below the field-cooling height. In addition, the possibility of realizing higher rotational speeds by mechanically reinforcing the NdFeB ring with a shrunk-on steel shell is discussed.

An Appraisal of Power-Minimizing Control Algorithms for Active Magnetic Bearings

Active magnetic bearings consume much less power than conventional passive bearings, especially when power-minimizing controllers are employed. Several power-minimizing controllers have been proposed, such as variable bias controllers and switching controllers. In this paper, we present an appraisal of the power-minimizing control algorithms for active magnetic bearings in an attempt to provide an objective guideline on the merits of the control algorithms. In order for the appraisal, we develop an unified and consistent model of active magnetic bearing systems. The performances of the power-minimizing controllers are assessed through this model. The results show that the power-minimizing controllers indeed save considerable power when the machine state is relatively steady. However, a simple proportional-derivative type controller is on a par with the much more complex power-minimizing controllers in terms of power consumption when the machine is experiencing transient loads.

Bearings-only constant velocity target maneuver detection via expected likelihood

This work addresses the problem of target maneuver detection using passive bearing measurements when the target motion dynamics can be described by a discrete constant velocity (CV) model. The proposed expected likelihood (EL) maneuver detector (ELMD) extends the EL approach from a direction of arrival estimation framework to maneuver detection of targets governed by a CV model. As a result of its array signal processing nature, and in contrast to measurement residual-based maneuver detectors, ELMD does not require statistical assumptions of the bearing measurements, and its maneuver detection performance improves with increasing signal-to-noise ratio and sample support. Maneuver detection performance of ELMD and two conventional maneuver detectors for the passive bearings-only target tracking problem are evaluated in this work via simulations using mean detection delay, detection delay standard deviation, and probability of false alarm criteria. ELMD is shown to outperform the other two evaluated algorithms in all tested practical scenarios.

Stiffness and damping coefficients for rubber mounted hybrid bearing

ABSTRACTA non‐contact passive magnetic bearing has a low friction compared with other passive (journal or ball) bearings. But these bearings have negligible damping due to which even small rotor vibration impacts the bearing magnet. It results in breakage of brittle magnetic materials. To overcome this problem, a hybrid bearing (passive magnet + elastomer) has been proposed in the present manuscript. To select an appropriate rubber, a step‐by‐step approach, using pendulum and hysteresis tests, has been followed. A parametric study on thickness of selected rubber was carried out. Experiments were conducted on three configurations: (i) a stand‐alone magnetic bearing, (ii) magnetic bearing with a butyl rubber having a thickness of 1 mm, and (iii) magnetic bearing with a butyl rubber having a thickness of 1.5 mm. To investigate the effect of rubber Young's modulus on the damping, rubber was made softer by immersing in aromatic liquid, and the experiments were repeated using softer rubber. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Parameter Optimization Experiment of Magnetorheological Bearing

The active bearings with variable damping and stiffness are important for vibration isolation in wide frequency excitation. A model of vertical isoaltion system via magnetorheological (MR) bearings was built. Based on analyzing the characteristics of MR grease and MR elastomer, an MR parallel-isolator was designed to instead the passive bearing.Then an adaptive particle swarm optimization (PSO) was adopted to adjust the parameters of MR bearing. A vertical MR isoaltion experiment was proposed. Results demonstrate that MR bearings have better performance than passive bearing in concurrently restraining force transmissibility and vibration acceleration.

Numerical simulation and experimental research on passive hydrodynamic bearing in a blood pump

The current research of hydrodynamic bearing in blood pump mainly focuses on the bearing structure design. Compared with the typical plane slider bearing and Rayleigh step bearing, spiral groove bearing has excellent performance in load-carrying capacity. However, the load-carrying capacity would decrease significantly with increasing flow rate in conventional designs. In this paper, the special treatment is made to the upper spiral groove bearing to make sure that both the circulatory flowing and load-carrying capacity are high. Three-dimensional computational fluid dynamics(CFD) models in the space between rotor and shaft are developed by using FLUENT software. Effects of groove number, film height and groove depth on load-carrying capacity of the spiral groove bearings are investigated by orthogonal experiment design. The experimental results show that film height is the most remarkable factor to the load-carrying capacity. The variation tendency of load-carrying capacity reveals that the best combination of geometry is the one with groove number of 8, film height 0.03 mm and groove depth 0.08 mm. The velocity and pressure distributions in spiral groove bearings are also analyzed, and the analysis result shows that the distributions are in conformity with the design of the blood pump based on the principle of hydrodynamic bearing. The displacement of the rotor with the best combination parameters is tested by using laser displacement sensors, the testing result shows that the suspending performance is satisfactory both in axial and radial directions. This research proposes a bearing design method which has sufficient load-carrying capacity to support rotor as an effective passive hydrodynamic bearing.

Analysis and Design of Passive Magnetic Bearing and Damping System for High-Speed Compressor

To provide a more reliable and low power consumption rotor support system for a high-speed compressor, a novel and compact magnetic bearing and damping system is proposed. It is composed of a cup-shaped rotor, an axial passive bearing of reluctance type outside the rotor cup, and a passive damper with Halbach magnet array inside the rotor cup, which not only can provide adequate stiffness, but also good damping ability for the rotor. To enhance the load and stability of the system, an analytical model, which can calculate the system stiffness and damping coefficient with significantly less computing time than the finite element method (FEM), is established. The effects of some important structure parameters on the system performance are discussed. Then, an optimal design method is proposed based on the above analysis. At last, an experimental setup has been developed and both static and dynamic performances have been tested. The experimental results show that the proposed system is capable of producing high axial stiffness and effective in suppressing the rotor vibration. The results also verify the validity of the analysis and design method.

Damping Optimization on Magnetorheological Grease Isolator of Floating Slab Track

The bearings with variable damping characteristics are very important for floating slab track (FST) to restrain vibration in low frequency. A model with single degree of freedom of FST is built. Based on analyzing the characteristic of the magnetorheological grease (MRG) materials, a MRG isolator is proposed to instead of passive bearings of FST. For attenuating the vertical vibration, the method of adaptive particle swarm optimization (PSO) with variable inertial parameter is proposed to adjust the damping. The results simulated in MATLAB show that MRG isolators with the adaptive PSO algorithm can optimize damping at different excitations effectively and conspicuously decrease the low frequency vibration energy of FST.