Small Radial Displacement Research Articles

Temperature properties of passive magnetic bearing

The practical interest in passive magnetic bearings is due to the fact that they are not subject to wear and have insignificant dissipative energy losses. However, when the magnets are heated during operation, a reversible and irreversible decrease in the residual magnetization occurs and, consequently, the force of interaction between them changes. The thermal properties of passive magnetic bearings are adversely affected by the large demagnetizing fields from the coupled magnets. To predict the performance of passive magnetic bearings with regard to external temperature, an assessment of temperature changes in the bearing capacity of bearings with optimally shaped magnets is necessary. The optimum magnets were considered to be those with sizes, whose interaction force, reduced to a single volume of magnetic material, was the maximum. A magnetic system of two cylindrical magnets with equal radii and heights located coaxially or with some radial displacement was considered. The studies were carried out on cylindrical magnets made of SmCo5 alloy, capable of maintaining magnetically hard properties at temperatures up to 250°C. It was confirmed that irreversible changes in the magnetic force for bearings with optimally sized magnets are close to each other. The destabilizing (radial) magnetic force at small radial displacements of one of the magnets also irreversibly decreased. A temperature of 250°C defines the upper limit of the temperature range for the normal operation of magnetic bearings with SmCo5 magnets. It was found that as a result of the action of a demagnetizing field on magnets during heating, they develop a significant inhomogeneity of magnetization over the volume. After demagnetization of the magnets kept at a temperature of 260 °C, the force of their interaction reaches only 85 - 90% of the original, which is associated with microstructural changes in the magnets. Theoretically and experimentally, the numerical values of the temperature coefficients of changes in the bearing capacity and stiffness of bearings are determined.

Design and Evaluation of a Polymer Support Fluid in a Soil-Rock Mixture.

Soil–rock mixtures are commonly encountered in the construction of bored piles. Conventional bentonite support fluids have disadvantages, such as more significant environmental impacts, more complex mixing, bigger site footprint, weaker foundation performance, and overall low economies. The present study conducted a comprehensive investigation of partially hydrolyzed polyacrylamide (PHPA) polymer fluids, an alternative to bentonite ones, to drill into a soil-limestone mixture. The fluid flow pattern, aging behavior, and the influence of finer silty clay on polymer fluid were explored. The test results showed that polymer fluids were reasonably well fitted to the power-law model and were a good alternative to the conventional bentonite ones. In terms of their aging behavior, the remaining active viscosity of the polymer was at least 70% after a prolonged aging time of up to 30 days, showing the effective on-site use of polymer fluids. The mixing of silty clay significantly reduced the apparent viscosity of polymer fluids, with 10% silty clay causing a viscosity reduction of 76%, indicating the importance of fluid control in drilling these materials. A polymer formula, water + 0.08%PHPA + 0.1~0.5%Na2CO3, was proposed and was verified by drilling into a soil–limestone mixture. The polymer fluids led to small radial displacements around the boreholes with a high drilling quality. This work would be helpful for consultants and contractors designing and constructing bored piles in soil and rock mixtures utilizing polymer fluids.

Simulation and optimization design of fuel rod in pressurized water fuel assemblies

Since the working environment of the pressurized water reactor (PWR) fuel element is complex, the analysis and optimization of its performance involve many physical phenomena, such as thermic, mechanics and so on. In order to analyze and optimize the performance of PWR fuel element, the column fuel element (CFE), singular-cooled annular fuel element (SCAFE) and dual-cooled annular fuel element (DCAFE) are simulated based on the finite element analysis software called ABAQUS. For the DCAFE, the inner diameter is modified, and the concept of “normalized volume parameter” is proposed to eliminate the influence of volume change on the performance of the fuel element, and to accurately describe the thermodynamic performance of the fuel element under different inner and outer diameters. The results show that: The DCAFE has advantages of low von Mises stress, small radial displacement and low temperature. When the ratio of inner and outer diameters is about 0.67, thermodynamic properties are the best and the optimal size is achieved.

Refined Model of a Groove Seal and Calculation of Angular Hydrodynamic Force Coefficients

We propose a solution to the problem of calculating the coefficients of the radial and angular forces in a groove seal (with the use of a refined model of a smooth groove seal) as functions of two independent variables, the eccentricity of the rotor and the angle of misalignment of the rotor axis in the seal. Unsteady turbulent flow of a viscous incompressible fluid in the channel of the seal, due to both the axial pressure drop in the seal and the nature of the travel of the inner channel wall, is investigated. The problem is solved under the assumption of small radial and angular displacements of the shaft. The coefficients for forces determined by the angular misalignments of the rotor are obtained here for the first time.

Approaching ITER PF Coil Manufacturing

The ITER poloidal field (PF) coil system provides a magnetic field for plasma shaping and position control together with the central solenoid coils; it needs to operate in a fast pulse mode, leading to induced voltages of up to 14 kV on the coil terminals during operation. The PF magnet system consists of six coils. The cable-in-conduit conductors with niobium-titanium (NbTi) superconducting material are used in the coils. All coils are fabricated by stacking six to nine double pancakes wound by two-in-hand winding scheme. The six PF coils (PF1 to PF6) are attached to the toroidal field coil cases through the flexible plates or sliding supports to allow small radial and vertical displacements. The PF coils will be procured by the European and Russian domestic agencies under separate procurement arrangements. To accelerate the PF6 coil schedule, which is one of the critical paths for the ITER schedule, a cooperation agreement has been placed between F4E and ASIPP in China in October 2013 with the CN-DA support. Before starting the manufacturing of the coil, the component qualification has been started, such as the 3 × 3 conductor mock-up, turn insulation, and helium inlet with the dummy conductors. Corresponding mechanical and electric tests were carried out at room temperature and 77 K. The PF dummy double pancake is also wound to demonstrate the winding. This paper presents the updated design for manufacturing of components. Their fabrication methods are also described. This paper concludes with a summary state report on PF1 dummy winding.

Steady flows excited by circular oscillations of a free inner core in a rotating spherical cavity

This research involves experimental studies of the fluid flow excited by a light free spherical core in a spherical cavity rapidly rotating around the horizontal axis. The gravity force, directed perpendicular to the axis, causes a small radial displacement of the light core from the rotation axis; the displacement is steady in the laboratory reference frame. This corresponds to circular oscillations of the core in the rotating reference frame with the frequency equal to the rotation rate of the cavity. As a result, steady flows are generated in the fluid, which are accompanied by a lagging differential rotation of the core. Inertial waves created by the oscillating core also contribute to the generation of steady flows. The velocity field of fluid flow is studied using the PIV method. It is demonstrated that the mean azimuthal flow of the fluid has a two-dimensional structure, which means the azimuthal velocity magnitude is virtually constant with respect to the axial coordinate. The azimuthal flow consists of several coaxial cylindrical surfaces, nested into each other, rotating at different angular frequencies. The radial distribution of the azimuthal velocity is characterized by a series of inflexion points and is qualitatively different from the known case of a flow caused by a differential rotation of the core, mounted on the axis of the rotating cavity. The inflexion points, in their turn, form the basis for the development of various unstable modes. It is discovered that, before the instability threshold, the axisymmetric azimuthal flow of fluid is fully determined by the lagging differential rotation rate of the core. It is shown that the azimuthal fluid flow is accompanied by relatively weak flows of axial circulation in the form of toroidal vortices.

Unsteady flow of an incompressible viscous fluid around a deformable spherical body

An unsteady flow of a viscous incompressible fluid around a deformable spherical body is considered in the approximation of low Reynolds numbers with a predetermined flow velocity. The hydrodynamic impact of the flow incoming onto the body is determined with allowance for small radial displacements of the body surface. The effect of spherical body surface deformation on the magnitude of the incoming flow impact force is taken into account, in particular, the dependence of small radial displacements of the body surface on the time is found, which makes it possible to minimize the physical impact of the incident flow.

Development of the ITER PF Coils

The ITER Poloidal Field (PF) magnet system consists of six coils. Niobium-Titanium (NbTi) is used as superconducting material and cable-in-conduit conductor(CICC) type are used as a conductor. All coils are fabricated by stacking 6 to 9 double-pancakes wound by two-in-hand winding scheme. The six PF coils (PF1 to PF6) are attached to the Toroidal Field (TF) coil cases through flexible plates or sliding supports to allow small radial and vertical displacements. The outer diameters of the coils vary between 8 m and 24 m. Since the PF coil system provides magnetic field for plasma shaping and position control together with the Central Solenoid (CS) coil, it needs to operate in fast pulse mode, leading to induced voltages of up to 14 kV on the coil terminals during operation.

The Extrapolated Motion Protocol For Molecular Dynamics Simulations: Predicting Large-scale Conformational Transitions In Mechanosensitive Channels

Gating of ion channels involves large structural rearrangements and timescales posing challenges for conventional MD simulations. Forces imposed in steered MD protocols may lead to unnatural distortions, whereas near-physiological gradients produce small motions capturing just the local direction. We developed a new computationally efficient protocol allowing to ‘continue’ the observed small-scale motion and drive the protein along a self-chosen pathway. It was tested on bacterial channels MscL and MscS for which the initial outward motion of helices is pre-defined by membrane tension. The motion was initiated with a small (0.1-0.5 A) radial displacement of all atoms of the barrel away from the axis (step 1), followed by energy minimization (2), 1 ps relaxing MD simulation (3), and symmetry-restrained energy minimization (4). The conformational change resulting from this first cycle was linearly extrapolated with a small amplification coefficient and the three structure-relaxing steps (2-4) were repeated completing the next cycle. A sequence of 50-100 extrapolation/relaxation cycles produces a smooth pseudo-continuous trajectory revealing substantial conformational changes while preserving most of the secondary structure. The character of motion was sensitive to the amplification coefficient with 1.00 producing local oscillations, 1.05 - consistent moderate-scale motions, and 1.10 - larger transitions reaching instability. When applied to MscL, the method reproduced the characteristic iris-like gating supported by experiments. Extrapolations of the compact MscS model with reconstructed N-termini predicted barrel expansion with tilting and straightening of the kinked pore-lining helices. Extrapolations started with random thermal fluctuations produced trajectories similar to those started with a pre-conceived displacement. Open conformations of MscS reproducibly closed in extrapolations. Resting and open models of MscS based on families of extrapolated trajectories were refined in all-atom MD simulations, tested for conductance and received support by experiments.

Displacement amplification and resonance characteristics of the cymbal transducers

The cymbal transducer consists of an inner P-5 piezoelectric disk mechanically coupled to two thin brass end caps on each of its electrode faces by eccobond epoxy. The caps serve as mechanical transformers for converting and amplifying the small radial displacement and vibration velocity of the ceramic disk into a much larger axial displacement and vibration velocity normal to the surface of the caps. Based on previous studies of cymbal transducers, the displacement amplification and the properties of resonance of the cymbal were elevated by optimizing the fabrication technique. Several kinds of end caps were designed and some theoretical models were used for the cymbals to study their performances based on the cavity depth and caps thickness. They showed more than 14× to 38× amplification over the uncapped ceramic alone under the direct current (dc) mode. And under the alternating current (ac) mode, the cymbals showed much larger peak-to-peak displacement than dc displacement. Effective piezoelectric charge coefficient of the cymbal reached to 22,550 pm/V. The cymbals also showed the first resonance frequency from 28.54 to 58.53 kHz and faster resonance time about several tens of microseconds.

Some characteristics of entrainment at a cylindrical turbulence boundary

Over the last 30 years, turbulent entrainment has come to be viewed as a large-scale process, directed by coherent structures, and described as engulfing. With turbulence simulations, we examined the process of entrainment directly, as growth of vorticity and concentration along fluid particle pathlines which were computed simultaneously. Our results indicate that the process is more often small scale. Growth occurs close to the turbulence boundary, within small radial displacements, and in times which are smaller than local large-scale times. These observations can be cast into a model to show that overall rates can be predicted by large-scale quantities even though the process occurs at small scales; the only requirement is a fixed relationship across scales as in fully developed turbulent flows. So it is not inconsistent that engulfment can be a successful, and accepted, model for fully developed flows even if it is not the more frequent process.

On the forced oscillations of a small gas bubble in a spherical liquid-filled flask

A spherically-symmetric problem is considered in which a small gas bubble at the centre of a spherical flask filled with a compressible liquid is excited by small radial displacements of the flask wall. The bubble may be compressed, expanded and made to undergo periodic radial oscillations. Two asymptotic solutions have been found for the low-Mach-number stage. The first one is an asymptotic solution for the field far from the bubble, and it corresponds to the linear wave equation. The second one is an asymptotic solution for the field near the bubble, which corresponds to the Rayleigh–Plesset equation for an incompressible fluid. For the analytical solution of the low-Mach-number regime, matching of these asymptotic solutions is done, yielding a generalization of the Rayleigh–Plesset equation. This generalization takes into account liquid compressibility and includes ordinary differential equations (one of which is similar to the well-known Herring equation) and a difference equation with both lagging and leading time. These asymptotic solutions are used as boundary conditions for bubble implosion using numerical codes which are based on partial differential conservation equations. Both inverse and direct problems are considered in this study. The inverse problem is when the bubble radial motion is given and the evolution of the flask wall pressure and velocity is to be calculated. The inverse solution is important if one is to achieve superhigh gas temperatures using non-periodic forcing (Nigmatulin et al. 1996). In contrast, the direct problem is when the evolution of the flask wall pressure or velocity is given, and one wants to calculate the evolution of the bubble radius. Linear and nonlinear periodic bubble oscillations are analysed analytically. Nonlinear resonant and near-resonant periodic solutions for the bubble non-harmonic oscillations, which are excited by harmonic pressure oscillations on the flask wall, are obtained. The applicability of this approach bubble oscillations in experiments on single-bubble sonoluminescence is discussed.

3D magnetic analysis of the CMS magnet

The CMS magnetic system consists of a super-conducting solenoid coil, 12.5 m long and 6 m free bore diameter, and of an iron flux-return yoke, which includes the central barrel, two end-caps and the ferromagnetic parts of the hadronic forward calorimeter. The magnetic flux density in the center of the solenoid is 4 T. To carry out the magnetic analysis of the CMS magnetic system, several 3D models were developed to perform magnetic field and force calculations using the Vector Fields code TOSCA. The analysis includes a study of the general field behavior, the calculation of the forces on the coil generated by small axial, radial displacements and angular tilts, the calculation of the forces on the ferromagnetic parts, the calculation of the fringe field outside the magnetic system, and a study of the field level in the chimneys for the current leads and the cryogenic lines. A procedure to reconstruct the field inside a cylindrical volume starting from the values of the magnetic flux density on the cylinder surface is considered. Special TOSCA-GEANT interface tools have being developed to input the calculated magnetic field into the detector simulation package.

On the axial dispersion induced by vibrations of a flexible tube

The mechanism of shear-augmented longitudinal dispersion in a vibrating flexible thin-walled tube is investigated. An oscillatory flow in a long and longitudinally-tethered elastic tube is generated by small periodic radial displacements which form a standing-wave mode of wall vibrations. This mode of vibration arises in cylindrical shells, and for small radial displacements is consistent with the continuity equation for the fluid filling the tube. An order of magnitude analysis for the dispersion rate reveals that the effective dispersion depends on the fluid properties, the elastic and geometrical properties of the tube, and the oscillations frequency. Since no visco-elastic damping is accounted and, hence, there is no dispersion of the wave-length with the vibration frequency, the wave speed is independent of the constraining frequency. For this case (1) the dispersion induced by low-frequency wall vibrations of a gas-filled tube is almost unaffected by the frequency; (2) the effective dispersion decreases with frequency both for low-frequency wall vibrations of a liquid-filled tube, and for high-frequency wall vibrations of a tube filled with either gas or liquid. These results hold as long as dispersion induced by secondary streaming is negligible, which is true for the present long-wave mode of wall-vibrations induced flow. Monte–Carlo simulations were performed by tracking aerosol tracer point-particles in the flow field. Very high rates of dispersion were found relative to a spread resulting solely from molecular diffusion. For physiological systems as lungs and udders, enhancement of longitudinal transport by radial tube vibrations is limited due to the large wave-lengths associated with this mode of vibration.

THE RESONANT SUPERCOMPRESSION AND SONOLUMINESCENCE OF A GAS BUBBLE IN A LIQUID-FILLED FLASK

The spherically-symmetric problem of the oscillations of a small gas bubble in the center of a spherical flask filled with a compressible liquid that is excited by small radial displacement of the flask's wall is considered. Two asymptotic solutions have been found for the low Mach number stage. The first one is an asymptotic solution for the field far from the bubble, and it corresponds to linear wave theory. The second one is an asymptotic solution for the boundary layer near the bubble and it corresponds to an incompressible fluid. In the analytical solution of the low Mach number step matching of these asymptotic solutions is done. A generalization of the Rayleigh = Plesset equation for a compressible liquid is given in the form of two ordinary difference-differential equations that take into account the pressure waves which are reflecting from the bubble and those that are incident on the bubble from the flask wall. The initial value problem for the initiation of the bubble oscillations due to flask wall excitation and for the evolution of these oscillations was considered. Linear and non-linear periodic bubble oscillations were analyzed analytically, and resonant frequencies were identified. Non-linear resonant and near-resonant solutions for the bubble's non-harmonic oscillations, which are excited by harmonic pressure or velocity oscillations on the flask wall, are obtained.

Interaction of C with Ni(100): Atom-resolved studies of the "clock" reconstruction.

The interaction of C with Ni(100) has been studied by scanning tunneling microscopy (STM). The C atoms, imaged as \ensuremath{\approxeq}0.3 \AA{} deep depressions consistent with theoretical predictions, are at low C coverages located in the fourfold hollow sites, causing a small radial displacement of the surrounding Ni atoms. Above a local critical coverage, C induces a disorder-order transition to a reconstruced phase, and the STM images reveal a coordinated 0.55 \AA{} lateral clockwise-counterclockwise displacement of the topmost Ni atoms. A simple model for the driving force for this ``clock'' reconstruction is proposed.

Elastic characteristics of the self-expanding metallic stents.

We measured elastic properties of the self-expanding metallic (Gianturco) stent using Hooke's law to characterize the stent with respect to its caliber, length, and radius by a coefficient of stiffness. Although this coefficient was independent of the radius of the stent, we found that it was directly dependent on caliber. For a stent of a particular caliber and length, the fractional change in radius determined the force exerted by the stent. For small radial displacements of the stent, the force required to compress it was directly proportional to the radial displacements; for large displacements, the force depended on a power series of the fractional radial displacement. A hyperbolic function was empirically introduced to approximate this type of relationship between force and radial displacement. We calculated tension and pressure exerted by the stent and suggest the use of our findings with normal vessels.

Stability Against Radial Perturbations of Slowly Rotating Neutron Stars

The dynamical equations governing pulsation in rotating neutron stars are derived in the framework of general relativity. Stellar models are constructed by using a realistic equation of state for cold neutron matter. Small radial displacement and slow rotation are treated as perturbations on spherically symmetric body. In these models the maximum masses are 1.761 M⊙ at the central density 3.461 × 1015 g cm−3 for a sequence of nonrotating configurations and 2.165 M⊙ for rotating models with the critical angular velocity (GM/R3)½.

Forced vibrations of a circular muscle ring.

We consider the small radial displacement of a circular ring of cardiac muscle subjected to periodic forcing. The ring in question is that in the middle layer, at the transverse midsection, of the left ventricle. We show that the ring reacts in a periodic manner when forced in a periodic manner. This is accomplished by writing the differential equation for the ring and solving it for two cases-one for constant and one for variable ring thickness.

Calculanion of hydraulic radial and angular forces of a smooth gap seal

The physical nature of the forces arising in the thin gaps of slotted seals of hydraulic machines has been studied quite fully. At the same time, various authors repeatedly studied the hydrodynamic characteristics of gap seals, however, the current methods for their analytical calculation for a number of parameters do not give a sufficiently accurate match. The inconsistencies in the conclusions of the researchers are due to assumptions that were made when solving the nonlinear equations of the unsteady flow of a viscous fluid in annular channels. The task of calculating radial forces includes an analysis of the law of the distribution of velocities and pressures in the flow of the fluid being sealed through an annular channel, one of the walls of which forms a rotating and vibrating rotor. In this case, the fluid flow in the gap is caused by both the axial pressure difference throttled at the seal and the nature of the movement of the inner channel wall. The problem is solved under the assumption of small radial and angular displacements of the shaft relative to the position of its static equilibrium.