Rotational Centrifugal Forces Research Articles

Modelling and characterisation of a magnetically coupled piezoelectric beam for energy harvesting gear meshing motion

Gear transmission systems are crucial components for transmitting power and motion in a host of engineering applications. Recently, the potential to embed sensors into transmission components has attracted significant attention for accurate condition monitoring of system health. As a result, embedded sensors must operate in a safe and stable manner, whilst being able to provide a continuous power-supply and ensure operational autonomy. In this work, a magnetically coupled beam-type piezoelectric energy harvester is developed for energy harvesting of rotational centrifugal forces and individual gear meshing excitation events. A new coupled electromechanical dynamic model is developed to explain the working principle and response of the harvester when excited by a combination of gear meshing excitation events, a centrifugal force, and a magnetic force. Since gear meshing events are observed to lead to an increased hardening nonlinearity of the energy harvester, and a decrease in power output, a novel variable-section cantilever structure was developed. Our detailed theoretical analysis demonstrates that the novel variable stiffness structure improves both the power output and bandwidth, with excellent agreement with experimental measurements. This work provides new theoretical insights into the application of magnetically coupled piezoelectric energy harvesters for self-powered sensing systems for critical gear transmission systems.

Dynamic instability of an eccentrically rotating ring-shaped structure

Ring-shaped structures are widely used in engineering. However, their rotation axes are typically not coincident with the geometric axes, thus resulting in a rotational centrifugal force and significant vibration. This study focuses on the dynamic instability caused by constant and time-varying eccentricities. An analytical model is established using Hamilton’s principle and the Galerkin method, in which the rotational centrifugal forces resulting from constant and time-varying eccentricities are incorporated. Based on this model, the effects of rotation, revolution, eccentricity ratio, and damping on instability behaviors are examined. The instabilities caused by constant eccentricity are predicted using eigensolutions, whereas those caused by time-varying eccentricity with single- and multifrequency components are estimated by applying the Floquét theory. The results show that the instability domains from the multifrequency eccentricity are not a simple superposition of those from the single-frequency eccentricity but contain more instability domains originating from their combinations. The instability suppressions imposed by damping and gyroscopic effects are compared. Finally, the instability domains from constant and time-varying eccentricities are verified via numerical calculations.

Effect of Rotational Control for Accelerating Water Discharge on the Performance of a Circular Polymer Electrolyte Membrane Fuel Cell

Polymer electrolyte membrane fuel cells are emerging as an important research topic owing to increasingly intensified environmental pollution. The flow field pattern of the fuel cell controls the electrochemically uniform distribution and water flooding in the reaction area between the anode and cathode. Water discharge management in the channel is an important factor influencing the efficiency of the fuel cell. In this paper, we propose a polymer electrolyte fuel cell with a rotatable circular spiral channel set to a constant size. The mass transfer behavior was analyzed numerically according to the number of channel passes. Numerical analysis showed that the production and behavior of water are closely associated with the performance of fuel cells. The circular spiral-pattern fuel cell with the greatest membrane water content was rotated through the experimental device to confirm the performance change of the fuel cell for each rotation speed. The performance improved as the internal water was ejected by the rotational centrifugal force. However, when excessive rotation was applied, the performance decreased because the water was forcibly drained out by a strong centrifugal force.

A New Approach in the Design of Microstructured Ultralight Components to Achieve Maximum Functional Performance.

In the energy and aeronautics industry, some components need to be very light but with high strength. For instance, turbine blades and structural components under rotational centrifugal forces, or internal supports, ask for low weight, and in general, all pieces in energy turbine devices will benefit from weight reductions. In space applications, a high ratio strength/weight is even more important. Light components imply new optimal design concepts, but to be able to be manufactured is the real key enable technology. Additive manufacturing can be an alternative, applying radical new approaches regarding part design and components’ internal structure. Here, a new approach is proposed using the replica of a small structure (cell) in two or three orders of magnitude. Laser Powder Bed Fusion (L-PBF) is one of the most well-known additive manufacturing methods of functional parts (and prototypes as well), for instance, starting from metal powders of heat-resistant alloys. The working conditions for such components demand high mechanical properties at high temperatures, Ni-Co superalloys are a choice. The work here presented proposes the use of “replicative” structures in different sizes and orders of magnitude, to manufacture parts with the minimum weight but achieving the required mechanical properties. Printing process parameters and mechanical performance are analyzed, along with several examples.

Hot Super-Earths with Hydrogen Atmospheres: A Model Explaining Their Paradoxical Existence

Abstract In this paper, we propose a new mechanism that could explain the survival of hydrogen atmospheres on some hot super-Earths. We argue that on close-orbiting tidally locked super-Earths, the tidal forces, together with the orbital and rotational centrifugal forces, can partially confine the atmosphere on the nightside. Assuming a super-terran body with an atmosphere dominated by volcanic species and a large hydrogen component, the heavier molecules can be shown to be confined within latitudes of ≲80° while the volatile hydrogen is not. Because of this disparity, the hydrogen has to slowly diffuse out into the dayside where X-ray and ultraviolet irradiation destroys it. For this mechanism to take effect, it is necessary for the exoplanet to become tidally locked before losing the totality of its hydrogen envelope. Consequently, for super-Earths with this proposed configuration, it is possible to solve the tidal-locking and mass-loss timescales in order to constrain their formation “birth” masses. Our model predicts that 55 Cancri e formed with a day length between approximately 17−18.5 hr and an initial mass less than ∼12M ⊕, hence allowing it to become tidally locked before the complete destruction of its atmosphere. For comparison, CoRoT-7b, an exoplanet with very similar properties to 55 Cancri e but lacking an atmosphere, formed with a day length significantly different from ∼20.5 hr while also having an initial mass smaller than ∼9M ⊕.

Influence of sleeve thickness and various structures on eddy current losses of rotor parts and temperature field in surface mounted permanent‐magnet synchronous motor

For surface mounted permanent magnet synchronous motor (PMSM), due to the large rotor rotational centrifugal forces, a sleeve is often used to prevent damage to rotor permanent magnets. However, eddy current losses appearing in the sleeve can increase the temperature of surface mounted PMSM. If the rotor heat dissipation condition is poor, high temperature can influence the surface mounted PMSM performance and even result in thermal demagnetisation of the permanent magnets. Thus, a sleeve scheme designed with low eddy current loss is very necessary. In this study, taking a 12.5 kW, 2000 rpm PMSM with 0.2 mm thickness stainless steel sleeve as an example, first, the influences of sleeve thickness on the eddy current loss and temperature field are analysed. Then, sleeve various composition structures of carbon fibre and stainless steel are presented, and the influences of different composition percentages on the eddy current losses and temperature field are analysed in detail, which shows the effectiveness in reducing the eddy current losses and temperature in the rotor. The obtained conclusions can provide useful reference for the design and research of surface mounted PMSM.

Rotational Failure of Rubble-pile Bodies: Influences of Shear and Cohesive Strengths

Abstract The shear and cohesive strengths of a rubble-pile asteroid could influence the critical spin at which the body fails and its subsequent evolution. We present results using a soft-sphere discrete element method to explore the mechanical properties and dynamical behaviors of self-gravitating rubble piles experiencing increasing rotational centrifugal forces. A comprehensive contact model incorporating translational and rotational friction and van der Waals cohesive interactions is developed to simulate rubble-pile asteroids. It is observed that the critical spin depends strongly on both the frictional and cohesive forces between particles in contact; however, the failure behaviors only show dependence on the cohesive force. As cohesion increases, the deformation of the simulated body prior to disruption is diminished, the disruption process is more abrupt, and the component size of the fissioned material is increased. When the cohesive strength is high enough, the body can disaggregate into similar-size fragments, which could be a plausible mechanism to form asteroid pairs or active asteroids. The size distribution and velocity dispersion of the fragments in high-cohesion simulations show similarities to the disintegrating asteroid P/2013 R3, indicating that this asteroid may possess comparable cohesion in its structure and experience rotational fission in a similar manner. Additionally, we propose a method for estimating a rubble pile’s friction angle and bulk cohesion from spin-up numerical experiments, which provides the opportunity for making quantitative comparisons with continuum theory. The results show that the present technique has great potential for predicting the behaviors and estimating the material strengths of cohesive rubble-pile asteroids.

To Find Different Gravity Law Proof Gravity Wave Equations are Real and Generate Gravitational Waves

Various gravitational laws are examined. Binary pulsars imply unusual behavior as evidence for gravitational waves in contrast to Newtonian gravity. Gravity's intensity in the restricted three-body problem can significantly be reduced due to rotational centrifugal forces to explain shortcomings usually mentioned to invent dark matter. Although Libration Points are distinct, they represent a suitable testing ground. The Trojan asteroids at the Sun-Jupiter stable triangular points do not demonstrate that millions of asteroids reside at a singular point but with a very large scatter and do not asymptotically congeal due to attraction to create planetoids thereby suggesting Newtonian gravitation is not ample and has flaws. A phase-space trajectory methodology for an integral equation defines eigenvalues and a forcing function to test some different gravity laws. These findings indicate that a time-dependent law may not locally conserve energy and result in a celestial vibration, repulsive gravitation or produce gravitational waves. This provides insights for newer gravitational models possible suitable for using warp drive concepts. Furthermore, this effort warrants placing more space probes at the triangular Libration Points as cosmic anomalies.

Analytical analysis of sleeve permeability for output performance of high speed permanent magnet generators driven by micro gas turbines

An alloy sleeve is often used to prevent the damage to rotor magnets caused by the large rotational centrifugal forces within a high speed permanent magnet generator (HSPMG). It should be thick enough to satisfy the mechanical strength needed. The generator main reluctance mainly focuses on the rotor sleeve, so sleeve permeability has much influence on the magnetic circuit and generator performance. Since a finite element simulation for every machine is time consuming and complicated, a simple analytical model of general surface-mounted permanent magnet machines has been established within this paper. Additionally, an analytical method is also given in full, so that optimal sleeve permeability can be obtained for a set of parameters for a given machine. In order to accurately establish the variation of the pole-to-pole leakage flux in the air gap and rotor sleeve of the generator with different permeability sleeves, an iterative method is proposed. The leakage flux, main flux, magnet performance and their relationships with the generator have been studied further, and the influence mechanism of sleeve permeability on the generator performance has been determined. Based on the research of the above influence factors, the optimal sleeve permeability is obtained by using the analytical method. Comparing the results of the analytical method and finite element method, they are in close agreement; hence the rotor sleeve with optimal permeability can improve the generator performance.

Aeroelastic Responses of Ultra Large Wind Turbine Tower-Blade Coupled Structures with SSI Effect

By a case study on a new-generation 5MW ultra large wind turbine system, the finite element model of the blade-nacelle-tower-foundation coupled structure with soil-structure interaction (SSI) and blade rotational centrifugal force is established. The harmonic superposition method and modified blade-element momentum theory are used to predict the aerodynamic loads with the consideration of tower-blade aerodynamic and model interaction, and modification of steady wind. Then the modal superposition method is adopted to solve the wind turbine coupling dynamic equation, in which the blade speed and aerodynamic force were updated though iteration to obtain the aeroelastic loads. At last, based on the previous work of “consistent coupling method”, which can fully consider the structure background mode, resonant mode, and the coupling effect between them, the aeroelastic responses of the wind turbine-blade coupled system are investigated. For completeness, the action mechanism of SSI effect and aeroelastic effect on the wind-induced responses are discussed through parameter analysis. The research conclusions can provide a scientific foundation for wind-resistance design of the ultra large wind turbine systems.

The processing and application of a zirconia ceramic shaft

In some ways, conventional steel shafts are not appropriate for high-speed operation because of their high rotational inertia; however, the application of ceramic materials can solve this problem. The use of ceramic shafts in high-speed spindles can reduce the high-speed rotational centrifugal force and inertial force, and realise good operation of the spindle system. Zirconia has characteristics of high hardness, heavy brittleness, high-temperature resistance and high chemical resistance. However, its hard brittleness also involves some difficulties in processing. This paper studied the processing of zirconia ceramic shafts on the basis of the characteristics of zirconia ceramics. A MK2710 grinder was used for grinding the zirconia ceramic material, and a surface roughness measuring instrument was used to measure the roughness of the shafts under different parameters. Finally, the processing of the zirconia ceramic shaft was put forward. This paper can provide a theoretical basis and technical support for the development and design of high-speed motorised ceramic spindles.

G0900205 リング型粉砕媒体を持つ乾式微粉砕機の木質バイオマス粉砕特性の検討

We examined the pulverizing characteristics of woody biomass by three defferent sizes of dry mills with ring-type pulverizing media. This type of mills have many pulverizing rings in the inside of the pulverizing cylindrical chambers and these rings roll and rotate in me chambers by external vibration. Woody biomass are pulverized by this high rotational centrifugal force. Two kinds of woody biomass: cedar and douglas fir were used for pulverizing tests of these mills. Pulverizing energy consumption of each of mills was inversely proportional to the amount of input materials. When the amount was too large, the pulverizing was no longer proceeding. The study of the pulverizing characteristics of small and large dry mills leaded to the definite relationship between the pulverizing energy consumption and saccharification efficiency of woody biomass. The relationship was independent of the physical size of mills. Input power per area of pulverizing chamber is about 15 kw/m^2. Then, it was estimated that woody powder was heated by large pressure from pulverizing rings and the average temperature of this woody powder layer achieved at about 300 centigrade.

Research on Application of Advanced Ceramics in Machine Tool Spindles

One important demand on spindle systems in modern machine tools is to realize higher rotational speed in order to increase the machining efficiency. So, the low rotational inertia and high fundamental natural frequency are indispensable. Because of advanced ceramics' extraordinary physical properties such as high hardness, low thermal expansion, light weight, abrasion resistant and good chemical and thermal stability, it accommodates very well the high-speed and precision requirements of machine tool spindles. In this study, a high-speed ceramic spindle system equipped with high-performance structural ceramic shaft and fully-ceramic ball bearings was designed and developed. The high-speed ceramic motorized spindle prototype was assembled with high precision successfully, and its performance test and analysis were finished. The test results show that ceramic motorized spindle can reduce the high-speed rotational centrifugal force and inertia force and increase the stiffness and rotation accuracy of spindle-bearing system greatly.

Influence of Copper Plating on Electromagnetic and Temperature Fields in a High-Speed Permanent-Magnet Generator

In a high-speed permanent-magnet generator (HSPMG), an alloy sleeve is often used to prevent damage to rotor magnets caused by the large rotational centrifugal forces. However, eddy-current losses appearing in the sleeve increase the generator working temperature, which may reduce the generator performance and even cause thermal demagnetization of the magnets. Thus, a sleeve scheme designed with low eddy current losses is necessary, and a rotor structure with copper plating is presented in this paper. The two-dimensional mathematical model of a 117 kW, 60 000 rpm HSPMG is established, and the electromagnetic field in the generator is calculated using the finite element method. The results show the effectiveness of the copper plating in reducing the eddy current losses in the rotor, and the influences of the sleeve thickness and the copper layer thickness on rotor eddy current losses are analyzed. Using the fluid-thermal coupling method, the temperature distribution of the generator with different copper layer thicknesses is comparatively analyzed based on the theories of fluid mechanics and heat transfer. The relationship between the temperature and the copper layer thickness is obtained, and finally the temperature of the permanent magnets, which is the part most seriously affected by the temperature, is given with different copper layer thicknesses. The obtained conclusions may provide useful reference for the design and research of HSPMG.

Mild method for bulk enrichment of high‐aspect ratio SWNTs

AbstractThis manuscript presents an effective method for the removal of amorphous carbon, metal catalyst particles and bundled SWNTs, while leaving long/undamaged SWNTs in aqueous suspension. This involves multiple centrifuge cycles at low rotational centrifugal force (RCF), facilitating the formation of suspensions of pristine SWNTs with lengths up to 5 μm. Electrical characterization of deposits formed from these suspensions demonstrates the efficacy of this purification technique for creation of thin‐film semiconductive materials.magnified image(© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Design and Manufacture of a Composite Flywheel Press-Fit Multi-Rim Rotor

The pre-compression that develops in a press-fit multi-rim rotor suppresses tensile stresses caused by the curing process and high speed rotational centrifugal forces, increasing the overall performance of the flywheel rotor. In this study, the interferences and the rim thickness of up to five rims of graphite/Ep and glass/Ep are analyzed to maximize the specific energy density (SED) of a multi-rim composite flywheel rotor. Three states are considered: (a) cured rims with residual stress prior to press-fitting; (b) a stationary press-fitted rotor; (c) a rotor at maximum rotational speed. Two methods of press-fitting rims are presented. One method has each rim machined with tapered inner and outer rim surfaces. The other method uses a guiding rim to expand the outer rim and guide the inner rim into the expanded outer rim. An optimized multi-rim rotor, composed of one glass/Ep rim and one graphite/Ep rim, is scaled to have energy storage capability of 5 kWh, and is successfully manufactured by machining tapered rims and hydraulic pressing.

Axisymmetric collapse simulations of rotating massive stellar cores in full general relativity: Numerical study for prompt black hole formation

We perform axisymmetric simulations for gravitational collapse of a massive iron core to a black hole in full general relativity. The iron cores are modeled by $\ensuremath{\Gamma}=4/3$ equilibrium polytrope for simplicity. The hydrodynamic equations are solved using a high-resolution shock-capturing scheme with a parametric equation of state. The Cartoon method is adopted for solving the Einstein equations. Simulations are performed for a wide variety of initial conditions changing the mass ($\ensuremath{\approx}2.0--3.0{M}_{\ensuremath{\bigodot}}$), the angular momentum, the rotational velocity profile of the core, and the parameters of the equations of state which are chosen so that the maximum mass of the cold spherical polytrope is $\ensuremath{\approx}1.6{M}_{\ensuremath{\bigodot}}$. Then, the criterion for the prompt black hole formation is clarified in terms of the mass and the angular momentum for several rotational velocity profile of the core and equations of state. It is found that (i) with the increase of the thermal energy generated by shocks, the threshold mass for the prompt black hole formation is increased by 20--40%, (ii) the rotational centrifugal force increases the threshold mass by $\ensuremath{\lesssim}25%$, (iii) with the increase of the degree of differential rotation, the threshold mass is also increased, and (iv) the amplification factors shown in the results (i)--(iii) depend sensitively on the equation of state. We also find that the collapse dynamics and the structure of the shock formed at the bounce depend strongly on the stiffness of the adopted equation of state. In particular, as a new feature, a strong bipolar explosion is observed for the collapse of rapidly rotating iron cores with an equation of state which is stiff in subnuclear density and soft in supranuclear density. Gravitational waves are computed in terms of a quadrupole formula. It is also found that the waveform depends sensitively on the equations of state.