Radial Force Field Research Articles

Effect of the Guide Vane on the Hydraulic Stability of a Low-head, Large-discharge Industrial Hydraulic Turbine

The hydraulic turbine has been used extensively in the field of energy conservation. For turbines that have low heads and large discharge, improving recovery efficiency and stability is crucial due to their significant hydraulic impact. This paper provides a detailed analysis of the correlation between the influence of radial guide vanes on the stability of low-head, large-discharge turbines focusing on hydraulic performance and energy dissipation before and after the implementation of guide vanes. Moreover, in this paper, two types of turbines, with and without guide vanes, were designed considering the desulfurization scenario. Hydraulic efficiency, radial force, and internal flow field mechanics were numerically studied, and validated through experiments. The results reveal that the working range of the hydraulic turbine could be widened and the energy recovery efficiency improved by a maximum of 3.11% in the small flow rate under the action of guide vanes. Furthermore, it results in a substantial reduction in the radial force of the impeller. Subsequently, the variation in entropy production of different components under full flow rate conditions was compared between the models with and without guide vanes. The total energy consumption decreases sharply under overall working conditions due to the flow control ability of guide vanes affecting the flow state. The entropy production rate of the impeller remains the largest regardless of the presence of a guide vane in the turbine. The vortices inside the guide vanes increase obviously with the flow rate increase.

FINITE ELEMENT BIOMECHANICAL MODELING OF PAROTID GLAND MORPHING IN PATIENTS UNDERGOING RADIOTHERAPY FOR HEAD AND NECK TUMORS

Patients treated with radiation therapy (RT) for head and neck cancer are exposed during the course of several weeks of treatment (6–7 weeks) to several physiological processes that can induce inter-fraction deformation of the parotid salivary glands (PGs). Gland morphing tends to make them move towards the high dose region of the dose distribution. As a consequence, parotids may be irradiated more than initially planned, leading to increased toxicity. We implemented a biomechanical model of the parotid morphing process that can serve as the basis to optimize adaptive RT protocols, leading to further reductions of dose to these structures. Raystation[Formula: see text] hybrid deformation algorithms and 3DSlicer[Formula: see text] tools were employed to obtain a mesh representation of PG anatomy and deformation from CT-series of eight patients treated with highly modulated radiotherapy (Tomotherapy[Formula: see text]). The biomechanical model was computationally implemented with the finite element software COMSOL[Formula: see text] multiphysics. Gland tissue was modeled as a linear elastic material with a Poisson ratio of 0.49 and a density value of 1 g/cm3. A radial force field was introduced to mimic parotid shrinkage due to radiation exposure. Fixed constraints were placed taking into account the anatomical barrier effect of parotid-surrounding structures (mandible) during the shrinkage process. The implemented biomechanical model was able to predict PG morphing with a mean volume difference of 1.36% [0.9–2.0] % between real and modeled deformed anatomy for the first half of treatment and 1.5% [0.8–2.1]% for the second half of treatment. Prediction of geometric overlap of observed versus simulated geometry as quantified using DICE was acceptable for the first half of the treatment but still unsatisfactory for the second half. Adding model components taking into account other elements that define PG morphing (facial geometry changes due to general weight loss and — in patients with significant macroscopic tumor load - local tumor volume loss) may accurately predict parotid morphing and thus permit further optimization of frequency and timing of off-line ART protocols in patients undergoing radiotherapy for head and neck cancer. This may result in a further reduction of treatment toxicity and these approaches are becoming even more important as the use of particle therapy with its increased dosimetric sensitivity towards geometric changes of the patient is slowly increasing.

Computational analysis of optical trapping of transparent and reflecting micron-sized spherical particles

In the ray-optics regime, we calculated the radial and axial force field on a micron-sized spherical particle in an optical levitation trap. The momentum change in the photon-stream path of tightly focused incident laser beam causes the calculated force field in the optical trap. The computational results for the force field are compared with the literature and a good agreement is obtained. Utilizing the benchmarked force field, the optical trapping dynamics of (i) a transparent spherical particle with continuous-wave 〖TEM〗_00 Gaussian beam and (ii) a reflecting spherical particle with continuous-wave 〖TEM〗_01^* Laguerre-Gaussian beam under various conditions are simulated in Matlab.

Rotating spherical gap convection in the GeoFlow International Space Station (ISS) experiment

The GeoFlow experiment on the International Space Station was the first experiment to investigate rotating convection in a radial gravitylike force field. This led to the first observation of the existence of global columnar cells in a microgravity environment. The flow structures are identified by a machine learning algorithm and complemented by numerical simulations.

Design and Property Analysis of a Performance Evaluation System for HTS Wind Power Generators

Large-scale High Temperature Superconducting (HTS) wind generators produce strong electromagnetic force and high torque due to the high magnetic load of the machines, which is produced by HTS coils with high excitation current. Therefore, in order to properly maintain the mechanical strength of the HTS coil part, the torque and Lorentz force of the HTS wind generator must be scrutinized and reflected in the design. The authors proposed a method for assessing mechanical and electrical stability of a large-scale HTS wind generator based on a Performance Evaluation System (PES) that has the same characteristics as some of the pole-pairs of the HTS generator. The generator and the PES were analyzed using 3D finite element method. The performance of the HTS coil was evaluated by comparing the tangential, radial force and magnetic field distribution of the 10 MW HTS generator with the PES. The tangential and radial forces of the 10 MW HTS generator were 73 kN and 11 kN, respectively. The tangential, radial forces and magnetic flux density of the HTS coils in the PES were equal to one pole in the 10 MW HTS generator. Therefore, the proposed PES-based generator characteristic evaluation method can be used to estimate the mechanical stability of the generator under a high magnetic field and high torque before manufacturing the HTS wind turbine.

Influence of dielectrical heating on convective flow in a radial force field.

We present results of numerical and experimental investigations of thermal convection induced by internal heating in both a nonrotating and a rotating spherical gap filled with dielectric fluid. The inner and outer surfaces are maintained at constant temperatures T_{in} and T_{out}, respectively. A radial force field is produced due to the dielectrophoretic effect. The buoyancy force in the Navier-Stokes equation and the source term in the energy equation depend on the imposed oscillating electric field according to V_{rms}^{2}r^{-5} and V_{rms}^{2}r^{-4}, respectively, where V_{rms} is the root mean squared value of the voltage between spherical surfaces and r is the radial distance. Beginning with the nonrotating case, we perform linear instability analysis in the case of purely internal heating, i.e., both surfaces are maintained at the same temperature ΔT=T_{in}-T_{out}=0. Next, we consider a situation in which there is not only internal heating but also a temperature difference ΔT>0. While the spherical gap rotated, the occurring two-dimensional steady basic flow was calculated numerically. The stability of the basic flow was investigated by means of linear instability theory. The critical Rayleigh numbers and the critical azimuthal wave numbers are presented in dependence on the Taylor number. We calculate supercritical three-dimensional flows for comparison with experimentally obtained patterns in frames of the GeoFlow experiment on the International Space Station.

Influence of the temperature-dependent viscosity on convective flow in the radial force field.

The numerical investigation of convective flows in the radial force field caused by an oscillating electric field between spherical surfaces has been performed. A temperature difference (T_{1}>T_{2}) as well as a radial force field triggers a fluid flow similar to the Rayleigh-Bénard convection. The onset of convective flow has been studied by means of the linear stability analysis as a function of the radius ratio η=R_{1}/R_{2}. The influence of the temperature-dependent viscosity has been investigated in detail. We found that a varying viscosity contrast β=ν(T_{2})/ν(T_{1}) between β=1 (constant viscosity) and β=50 decreases the critical Rayleigh number by a factor of 6. Additionally, we perform a bifurcation analysis based on numerical simulations which have been calculated using a modified pseudospectral code. Numerical results have been compared with the GeoFlow experiment which is located on the International Space Station (ISS). Nonturbulent three-dimensional structures are found in the numerically predicted parameter regime. Furthermore, we observed multiple stable solutions in both experiments and numerical simulations, respectively.

Pilot-wave dynamics in a harmonic potential: Quantization and stability of circular orbits.

We present the results of a theoretical investigation of the dynamics of a droplet walking on a vibrating fluid bath under the influence of a harmonic potential. The walking droplet's horizontal motion is described by an integro-differential trajectory equation, which is found to admit steady orbital solutions. Predictions for the dependence of the orbital radius and frequency on the strength of the radial harmonic force field agree favorably with experimental data. The orbital quantization is rationalized through an analysis of the orbital solutions. The predicted dependence of the orbital stability on system parameters is compared with experimental data and the limitations of the model are discussed.

Operationally Complete Work Done Suggests Presence of Extra Potentials Corresponding to Repulsive Forces

Operationally complete representation of work done and the corresponding to it potential energy within the usual radial/center-bound, nonrotating gravitational force fields comprises two extra terms: linear nonradial and angular nonradial, in addition to the usual radial term. Since these nonradial terms have negative signs, they suggest presence of potentials corresponding to repulsive forces generated by the very same, usual radial attractive force field. The extra linear nonradial term depends on exposure of an orbiting satellite to the distribution of mass within the field, whereas the extra angular nonradial term also depends on that as well as on exposure of the satellite to density of matter of the mass source that generates the usual, locally dominant radial/center-bound attractive gravitational force field.

Operationally Complete Work Done Suggests Presence of Extra Potentials Corresponding to Repulsive Forces

Operationally complete representation of work done and the corresponding to it potential energy within the usual radial/center-bound, nonrotating gravitational force fields comprises two extra terms: linear nonradial and angular nonradial, in addition to the usual radial term. Since these nonradial terms have negative signs, they suggest presence of potentials corresponding to repulsive forces generated by the very same, usual radial attractive force field. The extra linear nonradial term depends on exposure of an orbiting satellite to the distribution of mass within the field, whereas the extra angular nonradial term also depends on that as well as on exposure of the satellite to density of matter of the mass source that generates the usual, locally dominant radial/center-bound attractive gravitational force field.

Air-Gap Magnetic Field Optimization to Reduce Losses in High Speed Bearingless Permanent Magnet Synchronous Motor

In this paper, the high speed motor hybrids with a radial-axial 3 degree of freedom hybrid magnetic bearing unit and BPMSM unit is proposed. The radial suspension force and magnetic field distributions with different magnetized mode are calculated. The losses are calculated and compared using time-stepping finite element method. The research results have shown that the high-speed BPMSM with Halbach array permanent magnet rotor has sinusoidal air-gap magnetic field, minimum losses.

Characteristics Analysis of a Novel Detent-Force-Based Magnetic Suspension System

A novel Detent-force-based Magnetic Suspension System (DMSS) is presented. The topological structure and operating principle of DMSS are analyzed. The characteristics of the axial, radial force and magnetic field and torsion moment are studied with FEA method respectively. Simulation results show that the DMSS can generate larger levitation force than common levitation systems, and its levitation mode is a passive suspension in the axial direction and torsion without external control.

Dust Diffusion in Protoplanetary Disks by Magnetorotational Turbulence

We measure the turbulent diffusion coefficient of dust grains embedded in magnetorotational turbulence in a protoplanetary disk directly from numerical simulations and compare it to the turbulent viscosity of the flow. The simulations are done in a local coordinate frame comoving with the gas in Keplerian rotation. Periodic boundary conditions are used in all directions, and vertical gravity is not applied to the gas. Using a two-fluid approach, small dust grains of various sizes (with friction times up to Ω0τf = 0.02) are allowed to move under the influence of friction with the turbulent gas. We measure the turbulent diffusion coefficient of the dust grains by applying an external sinusoidal force field acting in the vertical direction on the dust component only. This concentrates the dust around the midplane of the disk, and an equilibrium distribution of the dust density is achieved when the vertical settling is counteracted by the turbulent diffusion away from the midplane. Comparing with analytical expressions for the equilibrium concentration, we deduce the vertical turbulent diffusion coefficient. The vertical diffusion coefficient is found to be lower than the turbulent viscosity and to have an associated vertical Schmidt number (vertical diffusion Prandtl number) of about 1.5. A similar radial force field also allows us to measure the radial turbulent diffusion coefficient. We find a radial Schmidt number of about 0.85 and also find that the radial turbulent diffusion coefficient is around 70% higher than the vertical. As most angular momentum transport happens through magnetic Maxwell stresses, both the vertical and the radial diffusion coefficients are found to be significantly higher than suggested by the angular momentum transport by Reynolds stresses alone. We also find evidence for trapping of dust grains of intermediate friction time in turbulent eddies.

Using magnetic fluids to simulate convection in a central force field in the laboratory

Abstract. Large-scale convection in planetary or stellar interiors plays a significant role but it is difficult to reproduce the central force field of those systems in experimental studies. A technique to approximate a central force field through the magnetic field from magnets acting on a magnetic liquid is presented. The thermomagnetic convection in a spherical shell filled with a magnetic liquid is analyzed in the context of a terrestrial laboratory using a 2D Finite Element model. Two configurations of magnetic fields were investigated, one resulting in a radially decreasing force field, and the other in a radially increasing force field. The results suggest that, while the actual force field does not reproduce the central gravity in planetary interiors accurately, it captures the essential qualitative character of the flow unlike other terrestrial experiments, which were either dominated by gravity or by a cylindrical radial force field. It is therefore suggested that such an experiment would provide a useful tool to investigate thermal convection in planetary interiors.

The geoflow-experiment on ISS (Part II): Numerical simulation

Convection in spherical shells under the influence of a radial force field is an important problem in classical convection theory. It is difficult to reproduce in a terrestrial laboratory though, because there gravity is everywhere downwards rather than radially inwards. It turns out that one can produce a radial force field, by applying a high voltage difference between the inner and outer spheres. The combination of the electric field and the temperature-dependence of the fluid's dielectric coefficient then produces an r −5 central force field. Of course, in a terrestrial laboratory one still has the external gravity as well. In order to eliminate this effect and produce a purely radial force field, an experiment is planned on the International Space Station. In this paper we will present the results of numerical simulations intended to assist in the design of this experiment, for example in choosing the optimal radius ratios. We solve for the onset of convection in such an r −5 force field, as a function of the radius ratio (varying between 0.3 and 0.6), the Prandtl number (varying between 1 and 100), and the Taylor number (measuring an overall rotation of the whole shell, which will also be possible in the experiment).

Bar strengths in spiral galaxies estimated from 2MASS images

Non-axisymmetric forces are presented for a sample of 107 spiral galaxies, of which 31 are barred (SB) and 53 show nuclear activity. As a data base we use JHK images from the 2 Micron All-sky Survey, and the non-axisymmetries are characterized by the ratio of the tangential force to the mean axisymmetric radial force field, following Buta & Block. Bar strengths have an important role in many extragalactic problems and therefore it is important to verify that the different numerical methods applied for calculating the forces give mutually consistent results. We apply both direct Cartesian integration and a polar grid integration utilizing a limited number of azimuthal Fourier components of density. We find that the bar strength is independent of the method used to evaluate the gravitational potential. However, because of the distance-dependent smoothing by Fourier decomposition, the polar method is more suitable for weak and noisy images. The largest source of uncertainty in the derived bar strength appears to be the uncertainty in the vertical scaleheight, which is difficult to measure directly for most galaxies. On the other hand, the derived bar strength is rather insensitive to the possible gradient in the vertical scaleheight of the disc or to the exact model of the vertical density distribution, provided that the same effective vertical dispersion is assumed in all models. In comparison with the pioneering study by Buta & Block, the bar strength estimate is improved here by taking into account the dependence of the vertical scaleheight on the Hubble type: we find that for thin discs bar strengths are stronger than for thick discs by an amount that may correspond to as much as one bar strength class. We confirm the previous result by Buta and co-workers showing that the dispersion in bar strength is large among all the de Vaucouleurs optical bar classes. In the near-infrared 40 per cent of the galaxies in our sample have bars (showing constant phases in the m = 2 Fourier amplitudes in the bar region), while in the optical band one-third of these bars are obscured by dust. Significant non-axisymmetric forces can also be induced by the spiral arms, generally in the outer parts of the galactic discs, which may have important implications on galaxy evolution. Possible biases of the selected sample are also studied: we find that the number of bars identified drops rapidly when the inclination of the galactic disc is larger than 50 ◦ .A similar bias is found in the Third Reference Catalogue of Bright Galaxies, which might be of interest when comparing bar frequencies at high and low redshifts.

Comparison of bar strengths in active and non-active galaxies

ABSTRA C T From an original sample of 107 spiral galaxies, the bar strengths of 21 active galaxies are compared with those of 22 non-active galaxies. Our identifications of bars are inferred from near-IR images using Fourier methods. The bar torques are determined using a new technique due to Buta & Block, in which tangential forces are calculated in the bar region normalized to the axisymmetric radial force field. As a data base we use the JHK images of the 2 Micron All Sky Survey. The ellipticities e of the bars are also estimated with an isophotal fitting algorithm and the bar lengths from the phases of ma 2 and ma 4 Fourier components of density. We show a first clear indication that the ellipticity of a bar, generally used as a measure of the bar strength, is quite well correlated with the maximum relative tangential force, Qb, in the bar region. Most surprisingly, the galaxies with the strongest bars are non-active. A possible understanding of this unusual result is that previous gaseous inflow in such cases may have been so efficient that fuelling of the active nuclei may simply have ceased. We find that nuclear activity occurs preferentially in those barred early-type galaxies in which the maximal bar torques are weakOkQbla 0:21U and appear at quite large distances from the galactic centre when scaled with the radial scalelength of the disc OkrQb /hla 1:24U. For comparison, for the non-active galaxies kQbla 0:37 and krQb /hla 0:59. The force maximum in the active late-type galaxies also appears at rather large distances, but the difference from the non-active galaxies is smaller. These results imply that the bulges may be important for the onset of nuclear activity, but it is not clear why nuclear activity appears in some early-type galaxies but is missing from some others. We also find that for active early-type galaxies, bar length is not correlated with bar strength, although a weak correlation appears for the other barred galaxies studied.

Two-dimensional ferrofluid foam in an external force field: Gravity arches and topological defects

When subjected to an external force field, a two-dimension ferrofluid foam (whose cell boundaries are made of ferrofluid) becomes deformed. New morphologies are then observed. If the foam is tilted with respect to the horizontal position, the cells rearrange in arches whose base is the bottom of the system. Furthermore, when submitted to a radial force field, the structure can be described as a topological defect of the hexagonal lattice in the centre of the system. In all these patterns, which characterize the response of systems whose elements repel via forces of infinite range, the order remains locally hexagonal. We depict these experimental structures, and we suggest that they could be described theoretically as conformal transformations of the hexagonal lattice.

Speculation on the Mechanism of Unilateral Hydrodynamic Distribution of Two Immiscible Solvent Phases in the Rotating Coil

Abstract The proposed hypothesis is based on the interplay between two force components acting on the fluid in the rotating coil. The tangential force component generates the Archimedean screw effect to move two solvent phases toward the head of the coil whereas the radial force component acts against the Archimedean force to establish a hydrostatic distribution of the two phases throughout the coil. The unilateral hydrodynamic distribution of the two phases is governed by the degree of asymmetry in the radial force field on the coil in both simple rotation and synchronous planetary motion. The present hypothesis successfully explains all the observed hydrodynamic phenomena reported in the past.

The elastic resilience of DNA can induce all‐or‐none structural transitions in the nucleosome core particle

DNA on the surface of the histone octamer in the native nucleosome core particle is modeled as a circumferentially wound elastic line on the surface of a cylinder. In a model for the radial transition, the line is allowed to straighten, and thus lose energy, by swinging off the surface, but it is impeded in such an excursion by a radial force field representing the attractive interaction between DNA and histone octamer. In a model for the axial transition, the line may straighten by becoming more parallel to a generator of the cylinder while remaining on the surface. In this mode of straightening, dimer-tetramer or tetramer-tetramer interfaces are disrupted, and the resulting energy gain impedes the transition. Both radial and axial transitions are predicted to occur in all-or-none fashion. We propose that these models are related to the abrupt transitions actually observed in the nucleosome core particle.