Global Torque Research Articles

Performance Evaluation and Optimization of Flux-Regulated Axial-Radial Eddy Current Coupling

Abstract This paper proposes a novel axial-radial permanent magnet eddy-current coupling equipped with a mechanical magnetic adjuster. The innovative design integrates mechanical flux weakening technology with an enhanced magnetic method rooted in axial-radial hybrid flux topology. Concise analytical models for air-gap field and torque are developed, leveraging the magnetic equivalent circuit method and Faraday’s law. These models are subsequently validated using the 3D finite-element method. The results indicate that this device boasts an exceptionally broad torque adjustment range, reaching approximately 93% at a given slip. Furthermore, it exhibits a substantial optimal working area, spanning from 20% to 80% of the mechanical magnetic adjuster's movable distance. To comprehensively analyze the impact of structural parameters on overall performance, three novel metrics are defined. The analysis reveals that the pole pairs of the radial magnetic circuit (RMC) have the most significant influence on the device's comprehensive performance. In the end, a multi-objective optimization method to maximize the global torque regulation capabilities, local torque regulation abilities, and maximum torque potential is developed to enhance the overall performance of this innovative magnetic coupling design.

Development and Validation of a Self-Aligning Knee Exoskeleton With Hip Rotation Capability.

The self-aligning capability of an exoskeleton is important to ensure wearing comfort, and the delicate motion ability of the exoskeleton is essential for motion assistance. Designing a self-aligning exoskeleton that offers improved wearing comfort and enhanced motion-assistance functions remains a challenge. This paper proposes a novel spatial self-aligning mechanism for a knee exoskeleton to enable simultaneous assistance in the flexion and extension (FE) of the knee joint and the internal and external rotation (IER) of the hip joint. Additionally, considering the misalignment of the human-robot joint axes, a kinematic model of the knee exoskeleton is established and analyzed to demonstrate the kinematic compatibility of the exoskeleton. Furthermore, a global torque manipulability (GTM) index is proposed to evaluate the effects of dimensional parameters on the exoskeleton's performance, and then the knee exoskeleton is optimized according to the GTM index. Finally, experiments are conducted to validate the performance of the proposed exoskeleton. The experimental results show that during knee FE and hip IER, the proposed exoskeleton exhibits lower interaction forces and torques than existing exoskeletons.

Design, Fabrication, and Characterization of a Novel Optical Six-Axis Distributed Force and Displacement Tactile Sensor for Dexterous Robotic Manipulation.

Real-time multi-axis distributed tactile sensing is a critical capability if robots are to perform stable gripping and dexterous manipulation, as it provides crucial information about the sensor-object interface. In this paper, we present an optical-based six-axis tactile sensor designed in a fingertip shape for robotic dexterous manipulation. The distributed sensor can precisely estimate the local XYZ force and displacement at ten distinct locations and provide the global XYZ force and torque measurements. Its compact size, comparable to that of a human thumb, and minimal thickness allow seamless integration onto existing robotic fingers, eliminating the need for complex modifications to the gripper. The proposed sensor design uses a simple, low-cost fabrication method. Moreover, the optical transduction approach uses light angle and intensity sensing to infer force and displacement from deformations of the individual sensing units that form the overall sensor, providing distributed six-axis sensing. The local force precision at each sensing unit in the X, Y, and Z axes is 20.89 mN, 19.19 mN, and 43.22 mN, respectively, over a local force range of approximately ±1.5 N in X and Y and 0 to -2 N in Z. The local displacement precision in the X, Y, and Z axes is 56.70 μm, 50.18 μm, and 13.83 μm, respectively, over a local displacement range of ±2 mm in the XY directions and 0 to -1.5 mm in Z (i.e., compression). Additionally, the sensor can measure global torques, Tx, Ty, and Tz, with a precision of of 1.90 N-mm, 1.54 N-mm, and 1.26 N-mm, respectively. The fabricated design is showcased by integrating it with an OnRobot RG2 gripper and illustrating real-time measurements during in simple demonstration task, which generated changing global forces and torques.

Control of a Segmented Three-Phase Synchronous Motor With Highly Coupled Subwindings

This article addresses the control issue of a structure enabling the segmentation of three-phase electric drives. The proposed segmentation process offers an additional degree of freedom in terms of voltage rating for power electronics but results in a three-phase system with highly coupled sub-windings. Thus, for such a segmented motor, the true challenge lies in controlling the machine global electromagnetic torque while balancing the power among the different inverters. To tackle this issue, the dq standard synchronous frame is extended to common and differential modes. This approach enables to design a suitable control structure based on an analytical model and physical considerations. The developed model is calibrated with realistic numerical values obtained from a finite element analysis. Finally, an experimental setup allows developing a proof of concept which shows the interest of the proposed control method compared to a standard multiple dq-frame method. The key finding is that the above-mentioned control objective of the segmented synchronous motor can be achieved without additional inductors and despite the severe constraint imposed by such highly coupled segmentation.

Effect of generator torque ripple optimization on a geared wind turbine drivetrain

In this paper, the load effect of torque ripple reduction of a wind turbine generator is analyzed on the high-speed shaft gear stage and high-speed shaft bearings, which are the nearest components to the generator. Two generator designs with different torque ripples for the NREL 5‑MW reference wind turbine are considered. A decoupled analysis method is used, where global loads and torque ripple loads are used as input to a multibody model of the drivetrain in order to analyze the gear and bearing load response. Two different multibody models are considered in this work; one traditional decoupled model without generator inertia and one model with additional coupling and generator. For the model without generator inertia, statistical changes are observed for the load case with the largest torque ripple. This subsequently causes a limited increase in gear root bending damage and bearing fatigue damage. For the load case with the smallest torque ripple a limited statistical change and no damage increase is observed. For the model that includes the coupling and the generator, no statistical changes are observed between the simulation with the largest torque ripple and the smallest torque ripple. This is due to the torque ripple load that is expended to overcome the large inertia of the generator.

Static Model of Athlete's Upper Limb Posture Rehabilitation Training Indexes.

With the gradual expansion of the development of sports, the level of sports has been rapidly improved. Athletes have to carry out high-intensity and systemic technical movements in training and competition. Some sports have the greatest burden on the shoulder joint. From the observation and investigation of the injured parts of athletes, it is found that the shoulder joint is the most common sports injury, which is the most typical sports injury. Based on the problem of insufficient strength and endurance reserve after rehabilitation of shoulder external rotator injury, it will cause muscle tension and poor extensibility. To prove the improvement effect of functional training and posture index calibration on the poor posture of the shoulder, considering the measurement of global passive torque, this paper uses a limited set of joint angles and corresponding passive torque data in the upper arm lifting trajectory to train the neural network and uses the trained network to predict the passive torque in other upper arm trajectories. The kinematics model of the shoulder joint is established, and the human-computer interaction experiment is designed on the platform of the gesture index manipulator. The passive and active torque components of the shoulder joint in the human-computer interaction process are calculated by measuring the man-machine interaction force of the subjects in the motion state, which is used as the basis for evaluating the active motion intention of the subjects. Surface electromyography (SEMG) was used to calibrate and verify the attitude index of shoulder active torque. The method proposed in this paper is helpful to achieve more efficient on-demand assisted rehabilitation training exercises, which is of great significance to improve the level of rehabilitation training.

Comparative Analysis of Torque Ripple for Direct Torque Control based Induction Motor Drive with different strategies

ABSTRACT Direct Torque Control (DTC) method is one of the most outstanding and proficient control techniques of the induction motor. The foremost drawback of DTC induction motor drive is high torque pulsation, variable frequency of inverter switching. The main reason of torque pulsation is torque and flux hysteresis band utilised in DTC. DTC method is utilising hysteresis comparators which produce high torque pulsation and unpredictable switching frequency. In this paper, torque ripple analysis of fuzzy logic controller (FLC) based Direct Torque Control (DTC) of three-phase induction motor drive has been discussed. The space vector pulse width modulation (SVPWM) based DTC technique, which operates with the regular switching frequency, helps to solve the fundamental issues of torque pulsation. In addition to this, literature proposes different solutions like a prediction scheme, fuzzy logic controller technique, global minimum torque ripple strategy, constant frequency torque controller (CFTC) Technique, optimal switching instant scheme, duty cycle control scheme, SVPWM DTC for torque ripple reduction. The fuzzy logic controller capabilities for DTC technique are applied with the induction motor (IM) drive for high-performance applications. The simulation results of Conventional DTC, SVPWM DTC, Carrier SVPWM DTC and FLC-DTC method for the induction motor are illustrated. Fuzzy-based DTC technique compared with CSVPWM DTC method and conventional DTC method are presented. The torque ripple of 7.4% for 5 HP induction motor is achieved by FLC-based DTC method. Hardware results for DTC induction motor drive are also demonstrated and discussed. This paper presents improvement in torque ripple reduction with the help of carrier space vector pulse width modulation (CSVPWM) and FLC-based DTC.

Hydrodynamic theory of chiral angular momentum generation in metals

We present a hydrodynamic theory to describe a chiral electron system with a Weyl spin-orbit interaction on a field-theoretic basis. Evaluating the momentum flux density as a linear response to a driving electric field, we derive an equation of motion for the orbital angular momentum. It is shown that the chiral nature leads to a dynamic bulk angular momentum generation by inducing a global torque as a response to the applied field. The steady state angular momentum is calculated taking account of rotational viscosity.

Coefficient of friction random field modelling and analysis in planar sliding

In this paper, we investigate inherent mesoscale spatial fluctuations of the coefficient of friction (COF) in dry frictional phenomena by modelling it as a random field. The statistical properties of the resulting global random forces and torque are derived for three types of interface motion: pure translation, pure rotation and general planar motion. Closed-form formulas are derived for the case where the interface has a square geometry and a numerical simulation method is developed for more complex shapes. The analysis of these results shows that the statistical properties of the global forces and torque are functions of the ratio of the correlation length of the random field to the characteristic length of the interface, which enables limit analyses to be performed with respect to this ratio. These analyses provide guidance regarding whether the coefficient of friction should be modelled as a random field, a random variable or a deterministic variable. The concepts developed in this paper are illustrated through a simple crank-slider model for which the statistics of energy dissipated (because of the friction) are analysed concerning the value of the ratio of the correlation length to the sliding surface size.

Catastrophic Phase Inversion in High-Reynolds-Number Turbulent Taylor-Couette Flow.

Emulsions are omnipresent in the food industry, health care, and chemical synthesis. In this Letter the dynamics of metastable oil-water emulsions in highly turbulent (10^{11}≤Ta≤3×10^{13}) Taylor-Couette flow, far from equilibrium, is investigated. By varying the oil-in-water void fraction, catastrophic phase inversion between oil-in-water and water-in-oil emulsions can be triggered, changing the morphology, including droplet sizes, and rheological properties of the mixture, dramatically. The manifestation of these different states is exemplified by combining global torque measurements and local insitu laser induced fluorescence microscopy imaging. Despite the turbulent state of the flow and the dynamic equilibrium of the oil-water mixture, the global torque response of the system is found to be as if the fluid were Newtonian, and the effective viscosity of the mixture was found to be several times bigger or smaller than either of its constituents.

Halt Optimization Strategy for a Space Manipulator with a Joint-Locked Failure

Aiming at a space manipulator with a joint-locked failure, a halt optimization strategy is proposed in this paper. Firstly, a halt configuration optimization model (HCOM) is constructed, to select an optimal configuration where the kinematic ability of the manipulator is the best. Secondly, considering the constraint of joint running parameters and the disturbance torque of the base, we construct and solve the halt motion optimization model (HMOM), which can achieve a steady halt and ensure the safety of the manipulator. The correctness and effectiveness of the proposed strategy in this paper are verified with a 7-DOF space manipulator. This strategy firstly puts forward the idea of halt configuration optimization and realizes the minimum global disturbance torque of the base in the halt process.

A numerical study of Vertical Axis Wind Turbine performances in twin-rotor configurations

Placing two counter-rotating rotors of a Vertical Axis Wind Turbine (VAWT) can lead to a significant power enhancement and a faster wake resorption. This global power output is directly related to the spacing between both rotors permitting a mutual confinement effect. In addition, the relative direction of angular velocity of both rotors can strongly impact the overall performances of the machine. A range of two-dimensional (2D) Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations has been managed in order to study the aerodynamic interactions occurring in a pair of VAWT. By comparing with a single-rotor of VAWT, it has been shown than the global power enhancement of a double-rotor VAWT is linked with an extension of the lift production range in one of the two first quartiles of the upwind path. Moreover, the region of the extra power generation seems to be dependant on the relative rotational directions of counter-rotating rotors. In all cases, the extent of lift generation can be associated with a suppression of the cross-stream velocity induced by the confinement of the neighbouring turbine. This local flow perturbation, closed to the inner region, leads to an augmentation of the incidence experienced by the blades in the upwind path, increasing the global lift and torque recovered by the turbine.

Correlation of Planetary Bearing Outer Ring Creep and Gear Load Distribution in a Full-Size Wind Turbine

In this work, bearing outer ring creep in the planetary gear of a gear wind turbine gearbox is investigated. So far, gear creep has only been investigated experimentally on very small bearings under simplified load conditions. This paper presents experimental measurement results from a full-size 2.75 MW wind turbine. The test were performed on a system test bench capable of applying loads in all six degrees of freedom at the rotor hub. The objectives of this investigation are to provoke and measure bearing outer ring creep and to identify correlations to the gear load distributions acting on the planetary gear. After a motivation, a literature overview on bearing ring creep is given. Influences on and occurrences of ring creep are described and the two mechanisms roller-induced creep and gear creep explained. Then, the test setup and the evaluated experiments are presented. The influence of torque, rotational speed and additional non-torque loads on gear load distribution and bearing outer ring creep is shown, discussed and put in relation to findings from literature. Key findings are that outer ring creep speed increases with global rotational speed and torque. Also, gear creep – acting in the opposite direction of roller-induced creep – was found at the generator-sided bearing ring for loads below 40% nominal torque. The planet gear load distributions with sun and ring gear were highly uneven and opposed to each other at low torques while leveling out at high torques due to the load-dependent deformations of sun gear, planet carrier and ring gear. The average gear load distribution over all ring gear positions showed to be influenced only by torque and to be independent of non-torque loads. In accordance, even extreme non-torque loads were found to not influence the creep behavior of the two planetary bearing outer rings.

A numerical study on the interaction between forward and aft propellers of hybrid CRP pod propulsion systems

This paper presents a numerical study on the interaction between the forward and aft propellers of hybrid CRP pod propulsion systems (CRP-POD) in open water with a focus on both global quantities, that is, thrust and torque, and flow details, such as vortical structure, slipstream evolution, and lateral load on the pod unit. Improved delayed detached eddy simulation (IDDES) method is adopted and combined with the γ−Reθ transition model. The open-water characteristics of CRP-POD obtained by CFD are in satisfactory agreement with model test data. Two sets of CRP-PODs with different propeller geometries are considered. It is found independently of propeller geometry that (i) in terms of thrust and torque, the forward propeller is slightly affected by the aft propeller, while it has a large effect on the aft propeller; (ii) the wake of the forward propeller is accelerated in the axial direction and weakened in the tangential direction by the aft propeller; and (iii) the time-averaged lateral force on the pod unit is reduced remarkably by the propeller-propeller interaction. However, the vortex interaction between the forward and aft propellers depends significantly on the propeller geometry. In the case when the tip vortices shed by the forward and aft propellers can directly collide with each other, the vortical structure in the wake becomes unstable and rapidly breaks down.

Multilayer air gap winding designs for electric machines: theory, design, and characterisation

Here, the authors present a magnetic circuit design with a multilayer air gap winding. This design provides a new degree of freedom in the design process. The approach is based on a single layer air gap winding, which demonstrates the ability to scale, permitting application in small and large electric machines. A meandering structure with coils arranged parallel to the rotation axis are mounted in several layers on a slotless magnetic core. The authors consider a fixed ohmic power loss boundary condition to compare this approach with an existing validated machine design. Machine current is reduced with each winding layer, while self-inductance and induced voltage are increased. Since the air gap height is increased with every additional layer, the useable magnetic flux density decreases. Accordingly, an utilisable range in which optimal torque output is obtained can be described analytically. The authors provide comparison between a single-layer winding design, which achieves the global optimum torque, and a four-layer winding design, which gives a 16-fold increase in the phase self-inductance. Additional thermal simulations prove that the multilayer design give the same ohmic power losses as the single layer design, without having any thermal issues and hot spots.

Multiple states in turbulence

Turbulence is ubiquitous in nature, and is known as one of the unresolved problems in classical physics. The classical theory of turbulence assumed that turbulence is ergodic, which means that when turbulence is in a stationary state, even though the instantaneous properties are sensitive to initial conditions, the statistical averages of the instantaneous properties, such as the mean profiles and the skin friction in wall-bounded turbulence, are unique at any fixed set of parameters. This classical ergodic theory is the foundation of turbulence theory and modeling, and makes it possible to extrapolate data from lower Reynolds number turbulence to higher ones. However, in recent years, a few experimental and numerical evidences showed that multiple states exist in several flow problems. That is, the turbulent statistics and flow structures are not the same even at the same control parameters. In this paper, several published flow problems with multiple states are reviewed, including Rayleigh-Benard convection (RBC), von Karman flow (VKF), Taylor-Couette flow (TCF), spherical Couette flow (SCF), rotating homogeneous turbulence with Taylor-Green forcing (TGF), and the spanwise rotating plane Couette flows (RPCF). Two different categories of multiple states can be observed from these flow problems. One is in RBC, where several research groups found that the system will have different flow states and it will switch between different states as time evolves. The other can be generally seen from other five flows, where initial conditions or hysteresis effect can be observed. For example, hysteresis loops were reported in the experiments of TCF for global torque and local velocities at very high Reynolds numbers, while in RPCF, different flow statistics and flow structures were obtained with different initial flow fields based on the same code, the same computational domain and the same grid resolution at the same control parameters. Whether the second type of multiple states will finally turn into the first one in a long enough time is an open question which deserves further investigations. The underlying mechanism of multiple states is not clear at the present moment, which also demands continued effort and studies. In the six flow problems mentioned above, large-scale flow structures persist, which may highlight the importance of the coherent structures and their selectability in turbulence, as concluded by Huisman et al. Another possible guess from myself is the multiple competing flow mechanisms in the flow problems with multiple states. For example, in rotating homogeneous turbulence with Taylor-Green forcing (TGF), there are two competing mechanisms, one is the viscosity dissipation which causes the forward cascade, the other is the system rotation which results in the inverse cascade. The two competing mechanisms will make the system has more equilibrium points and multiple states. I believe that there will be more and more flow problems with multiple states reported in the future, together with a better understanding of the underling mechanism.

Finite-sized rigid spheres in turbulent Taylor–Couette flow: effect on the overall drag

We report on the modification of drag by neutrally buoyant spherical finite-sized particles in highly turbulent Taylor–Couette (TC) flow. These particles are used to disentangle the effects of size, deformability and volume fraction on the drag, and are contrasted to the drag in bubbly TC flow. From global torque measurements, we find that rigid spheres hardly decrease or increase the torque needed to drive the system. The size of the particles under investigation has a marginal effect on the drag, with smaller diameter particles showing only slightly lower drag. Increase of the particle volume fraction shows a net drag increase. However, this increase is much smaller than can be explained by the increase in apparent viscosity due to the particles. The increase in drag for increasing particle volume fraction is corroborated by performing laser Doppler anemometry, where we find that the turbulent velocity fluctuations also increase with increasing volume fraction. In contrast to rigid spheres, for bubbles, the effective drag reduction also increases with increasing Reynolds number. Bubbles are also much more effective in reducing the overall drag.

Optimal distribution width for ALM in LES for (NEW) MEXICO experiment

The Actuator Line Method exists for more than a decade and has become a well established choice for simulating wind rotors in computational fluid dynamics. Numerous implementations exist and are used in the wind energy research community. A crucial parameter of this method is the distribution width used to distribute the blade forces in the domain in order to attain numerical stability but also to apply the force term over a length which makes physically sense. In this work the implementation is verified with results from the (NEW) MEXICO experiment and the optimal distribution width is found by setting the global torque as target variable.

Experimental Study on Momentum Transfer of Surface Texture in Taylor-Couette Flow

The behavior of Taylor-Couette (TC) flow has been extensively studied. However, no suitable torque prediction models exist for high-capacity fluid machinery. The Eckhardt-Grossmann-Lohse (EGL) theory, derived based on the Navier–Stokes equations, is proposed to model torque behavior. This theory suggests that surfaces are the significant energy transfer interfaces between cylinders and annular flow. This study mainly focuses on the effects of surface texture on momentum transfer behavior through global torque measurement. First, a power-law torque behavior model is built to reveal the relationship between dimensionless torque and the Taylor number based on the EGL theory. Second, TC flow apparatus is designed and built based on the CNC machine tool to verify the torque behavior model. Third, four surface texture films are tested to check the effects of surface texture on momentum transfer. A stereo microscope and three-dimensional topography instrument are employed to analyze surface morphology. Global torque behavior is measured by rotating a multi component dynamometer, and the effects of surface texture on the annular flow behavior are observed via images obtained using a high-speed camera. Finally, torque behaviors under four different surface conditions are fitted and compared. The experimental results indicate that surface textures have a remarkable influence on torque behavior, and that the peak roughness of surface texture enhances the momentum transfer by strengthening the fluctuation in the TC flow.

Experimental investigation of a helicopter rotor with Gurney flaps

ABSTRACTThe present work describes an experimental activity carried out to investigate the performance of Gurney flaps on a helicopter rotor model in hovering. The four blades of the articulated rotor model were equipped with Gurney flaps positioned at 95% of the aerofoil chord, spanning 14% of the rotor radius. The global aerodynamic loads and torque were measured for three Gurney flap configurations characterised by different heights. The global measurements showed an apparent benefit produced by Gurney flaps in terms of rotor performance with respect to the clean blade configuration. Particle image velocimetry surveys were also performed on the blade section at 65% of the rotor radius with and without the Gurney flaps. The local velocity data was used to complete the characterisation of the blade aerodynamic performance through the evaluation of the sectional aerodynamic loads using the the control volume approach.