Effect of magnetic hysteresis on rotational losses in heteropolar magnetic bearings

This paper extends a method for predicting rotational losses for laminated rotors of heteropolar magnetic bearings by using an eddy-current model to include the effect of magnetic hysteresis in the rotor material. It compares the modeling results to the experimental data that were used earlier to assess the loss model neglecting hysteresis. The correction to the total electromagnetic loss in the rotor due to the hysteresis is significant at rotational speeds below 6000 revolutions per minute (RPM), where the model including hysteresis effects provides much better agreement with existing experimental data.     

Stable load-carrying and rotational loss Characteristics of diamagnetic bearings

We investigated the use of diamagnetic materials in magnetic bearings using an experimental apparatus to study the static equilibrium, load-carrying capacity, and dynamic characteristics of the bearings. The apparatus consisted of a 0.79-g NdFeB disk-shaped permanent-magnet rotor levitated by a ferrite magnet with a diamagnetic stabilizer made of either bismuth or graphite, all in a bell-jar vacuum chamber to eliminate air friction on the rotor. The equilibrium position of the rotor was statically and dynamically stable, according to theoretical calculations based on the magnetic-image method. In dynamic tests, the rotor of the diamagnetic bearing was spun up to 100 Hz by a tangential jet of nitrogen gas and then was allowed to spin down freely to measure the rotational losses. The rotational losses varied with the frequency of the rotation, indicating that most of the losses were mainly due to eddy currents. Minor losses due to magnetic inhomogeneities in the permanent magnets and diamagnetic parts were also observed over a small frequency range.     

Thermal effects in externally pressurized porous conical bearings with variable viscosity

Summary The present paper analyzes the porous constant gap externally pressurized conical bearings when the slider is rotating with uniform angular velocity. The lubricant is assumed to be incompressible, and its viscosity varies exponentially with temperature. The lubricant inertia due to rotation of the slider is considered but the convective inertia is neglected. The energy equation is used to determine the temperature generated in the lubricant film. The governing system of coupled momentum and energy equation is solved numerically, using finite difference method, to determine various bearing characteristics. It is observed that for the surfaces which are highly porous the inlet pressure decreases remarkably, resulting in reduced load capacity of the bearing, and the torque remains unaffected with respect to variation in the permeability.Notation c specific heat of the fluid - D dissipation parameter - E a type of Eckert number - h lubricant film thickness - h _p thickness of the porous matrix - H=h _p/h nondimensional thickness of the porous matrix - k thermal conductivity - permeability - L load capacity of the bearing - M torque on the bearing surface - p gauge pressure - p ^* pressure in the porous matrix - Pr Prandtl number - Q flow rate - R rotational parameter - Re Reynolds number - Re^* modified Reynolds number - T temperature of the lubricant - T _i, T_u temperature of the pad and the slider, respectively - u, v, w velocity components in thex, y and directions, respectively - u ^*, v^*, w^* velocity components in the porous matrix - U, V, W reference quantities for the velocity components - x, y, conical coordinate system - x _in, x₀ inlet, outlet positions - angle between stationary pad surface and a plane perpendicular to the bearing axis - viscosity-temperature exponent - viscosity of the lubricant - density of the lubricant - v ₀ kinematic viscosity of the lubricant - ₀ viscosity of the lubricant at pad temperature - angular velocity of the slider     

Experimental and simulation-based analysis of asymmetrical spherical roller bearings as main bearings for wind turbines

Symmetrical spherical roller bearings (SSRB) used as main bearings for wind turbines are known for their high load carrying capacity. Nevertheless, even designed after state-of-the-art guidelines premature failures of this bearing type occur. One promising solution to overcome this problem are asymmetrical spherical roller bearings (ASRB). Using ASRB the contact angles of the two bearing rows can be adjusted individually to the load situation occurring during operation. In this study the differences between symmetrical and asymmetrical spherical roller bearings are analyzed using the finite element method (FEM). Therefore, FEM models for a three point suspension system of a wind turbine including both bearings types are developed. These FEM models are validated with measurement data gained at a full-size wind turbine system test bench. Taking into account the design loads of the investigated wind turbine it is shown that the use of an ASRB leads to a more uniform load distribution on the individual bearing rows. Considering fatigue-induced damage an increase of the bearing life by 62% can be achieved. Regarding interactions with other components of the rotor suspension system it can be stated that the transfer of axial forces into the gearbox is decreased significantly.

     

Carbon microspheres as ball bearings in aqueous-based lubrication

We present an exploratory study on a suspension of uniform carbon microspheres as a new class of aqueous-based lubricants. The surfactant-functionalized carbon microspheres (～0.1 wt %) employ a rolling mechanism similar to ball bearings to provide low friction coefficients (μ ≈ 0.03) and minimize surface wear in shear experiments between various surfaces, even at high loads and high contact pressures. The size range, high monodispersity, and large yield stress of the C(μsphere), as well as the minimal environmental impact, are all desirable characteristics for the use of a C(μsphere)-SDS suspension as an alternative to oil-based lubricants in compatible devices and machinery.     

Methodology for the systematic design of conical plain bearings for use as main bearings in wind turbines

With the possibility to replace sliding segments on the tower without disassembling the drivetrain, the use of segmented plain bearings with conical sliding surfaces as main bearing in wind turbines has a great potential to reduce the maintenance costs and thus the levelized cost of energy (LCOE). Furthermore, the short axial design leads to lower investment costs. Since this design is totally new and no design guidelines are available so far, the objective of this paper is to investigate the influence of the geometric parameters on the hydrodynamic pressure distribution of the bearing. In this context a parameter screening is performed using a suitable test field according to Plackett and Burman in order to determine the most relevant parameters. With the help of the simulations carried out after this test field, correlations between the geometric parameters and the hydrodynamic pressure distribution are evaluated. To be able to quantitatively analyze the three-dimensional pressure distribution, several key values are defined in this paper that describe the pressure distribution. The content of this paper is part of a methodology with the goal of developing a design guideline for conical plain bearings.

     

Key features of flexure hinges used as rotational joints

This article is supposed to serve as a guide for the design of flexure hinges that act as rotational joints. Firstly, flexure hinges with concentrated and distributed compliance are reviewed. They can be modeled by linear beam theories or by the theory of Elastica, respectively. Secondly, the transition between these limit cases is investigated by finite element methods (FEM). A planar symmetric flexure hinge with a circular notch serves as an exemplary geometry. By extending the notch the compliance is distributed. The deflection curves and the kinetics of desired and parasitic motions are chosen as key features to be studied. The corresponding results are compressed into a pseudo-rigid-body model (PRBM) approximation for a range of geometries. It turned out that the concentrated compliance matches best with an ideal rotational joint, but even for small displacements large stresses occur so that its range of operation is small. Distributing the compliance increases the range of operation, however stiffness within the task space decreases dramatically so that the design of a flexure hinge becomes a tradeoff between the two concurring goals large stiffness and large range of operation.     

Thermal effect of an electrical current on contacts

The temperature field within a contact is calculated analytically, with consideration of real current distribution within the contact body. The possibility of replacing the volume heat source by an equivalent surface heat source is demonstrated.     

The effect of phosphate additives on the lubrication of rolling element bearings in a refrigerant environment

Chlorine free replacement refrigerants, HFC (hydrofluorocarbons) and HC (hydrocarbons), have shown less lubricating properties. Phosphate based additives were used to improve the lubricity with refrigerant R-134a, demonstrating positive effects. In the present paper, the ability to form lubricating film and wear of two additives, phosphate ester and acid phosphate, was investigated in a bearing test apparatus.The results show that phosphate additive in polyolester oil, in an R-134a environment, increases the lubricating film and reduce wear. Surface topography during the initial run-in changes to a more favorable profile with lower RMS angle and longer wavelengths that promote load-carrying capacity and film build-up.     

Thermal effect of nitrogen implantation on high carbon steels

Quenched and annealed samples of a high carbon steel implanted with 105 keV nitrogen at a nominal dose of 3 × 10¹⁷ ions cm^-2 and current densities of 50, 100 and 200 μA cm^-2 were analysed by a nuclear technique to measure the retained dose. The dose thus measured depends on the beam current density as well as on the initial steel structure: it decreases with the beam current density and is systematically lower in quenched steel than that in the annealed steel. Microhardness measurements and conversion electron Mössbauer scattering were used to study the structural modifications induced by various implantation conditions. The mean implantation temperature of the samples, as evaluated on the basis of the microhardness values and checked by a thermocouple, lies in the tempering range of hardened structures at the above implantation current densities. The metallurgical transformations observed can account for the different amount of retained implanted ions in the first 200 nm below the surface.     

温度对水饱和孔隙介质压缩波速度的影响

温度作用使孔隙介质密度、弹性模量等参数发生改变,从而影响声波传播性质。文章基于变形体能量守恒定律,考虑热机耦合和两相介质热耦合,推导水饱和孔隙介质的热传导方程;考虑孔隙水和固相孔隙介质存在的三种耦合性,基于热作用下应力应变关系分析,建立了热机耦合声波传播模型;设计温度变化沉积物样品声学测量实验,当温度由2℃增加到27℃时,压缩波速度平均增大88m·s^-1运用热机耦合声波传播模型解释了实验测量结果的上升趋势,获得理论计算值与测量值相对偏差范围为-3．03％～1．19％。     

The effect of a special hardening law on continuity in elastic-plastic problems with rotational symmetry

Subject of the investigation are the implications of a special nonlinear hardening law on the continuity of the slopes of stresses and strains at the elastic-plastic border in plane problems with rotational symmetry. The hardening law under consideration is a nonlinear generalization of linear hardening frequently used by experimenters. The general results are illustrated by means of the cylindrical vessel under internal pressure and the shrink fit.     

Thermal blooming effect on particle sizing with photon correlation spectroscopy

Photon correlation spectroscopy autocorrelation spectra were measured for gold nanocrystal superlattice colloids under several intensities of an incident laser beam. Thermal blooming in the colloid shifted the correlation spectra toward smaller times. A second cumulant term in the fitting curve proved effective to correct for the thermal blooming effect to yield the correct particle size.     

Thermal effect on anode during field electron emission from cathode

It is demonstrated that, during field electron emission from the cathode, the amount of heat evolved in the anode can differ from the classical value, provided that the translational energy of electrons reaching the anode does not exceed the Fermi energies of electrons in the dissimilar electrode pair. This effect is related to the fact that each electron emitted from the cathode brings the corresponding Fermi energy to the anode, in addition to the energy of the applied field. Therefore, under-or overheating of the anode is possible due to a difference between the Fermi energies.     

Advanced biomaterials in hip joint arthroplasty. A review on polymer and ceramics composites as alternative bearings

Wear of total hip prosthesis is a significant clinical problem that nowadays involves a growing number of patients. To acquire further knowledge on the tribological phenomena that involve hip prosthesis, wear tests are conducted on new biomaterials to increase materials life in orthopaedic implants. Advances in biomaterials for biomedical purposes have enhanced in the last years evolving in new improved ceramic and polymeric materials producing the so-called composite materials.This paper aims to review the evolution and the current state of the art of the ceramics composites and polymers commonly used in orthopaedic field as hip joint implants. This is specified through a schematic overview by describing, in particular, the evolution of various composites materials. The authors propose commentary on the evolution and current use of biomaterials for orthopaedic application on the evolution and actually used biomaterials for orthopaedic applications.     

基于小波的滚动轴承故障诊断

滚动轴承是机械设备中极易损坏的零部件.旋转机械的故障有百分之三十是由轴承故障引起的,因此引入轴承故障诊断对于机械化生产和作业来说是十分必要的.在对轴承故障的机理和特征全面了解的基础上,利用了离散小波变换对不同工矿下的原始信号进行分解,然后对小波分解出的近似和细节信号进行Hilbert变换,利用得出的信号可以较好地提取故障特征.     

Thermal effect limits in ultrahigh-density magnetic recording

In current longitudinal magnetic recording media, high areal density and low noise are achieved by statistical averaging over several hundred weakly coupled ferromagnetic grains per bit cell. Continued scaling to smaller bit and grain sizes, however, may prompt spontaneous magnetization reversal processes when the stored energy per particle starts competing with thermal energy, thereby limiting the achievable areal density. Charap et al. have predicted this to occur at about 40 Gbits/in². This paper discusses thermal effects in the framework of basic Arrhenius-Neel statistical switching models. It is emphasized that magnetization decay is intimately related to high-speed-switching phenomena. Thickness-, temperature- and bit-density dependent recording experiments reveal the onset of thermal decay at “stability ratios” (K_uV/K_BT)₀ ≃35 ± 2. The stability requirement is grain size dispersion dependent and shifts to about 60 for projected 40 Gbits/in ² conditions and ten-year storage times. Higher anisotropy and coercivity media with reduced grain sizes are logical extensions of the current technology until write field limitations are reached. Future advancements will rely on deviations from traditional scaling. Squarer bits may reduce destabilizing stray fields inside the bit transitions. Perpendicular recording may shift the onset of thermal effects to higher bit densities. Enhanced signal processing may allow signal retrieval with fewer grains per bit. Finally, single grain per bit recording may be envisioned in patterned media, with lithographically defined bits