Torque Curves Research Articles

Interference torque of a three-floated gyroscope with gas-lubricated bearings subject to a sudden change of the specific force

A numerical study is carried out to investigate the influence of a sudden change of the specific force on a three-floated gyroscope with a rotor supported on gas-lubricated bearings. The interference torque is calculated to evaluate the influence by modeling the transient behavior of the rotor-bearing system. In combination with dynamic equations of the rotor displacement, the Reynolds equation is solved on the surface of spiral-grooved conical bearings. It is assumed that a steady state has been obtained with a constant specific force, and then the specific force is suddenly changed and maintained constant after that. Responses of the sudden change are obtained by solving the equations. Numerical results show that the direction of the sudden change of the specific force is the main factor which influences the interference torque curve. With a sudden change along the input direction, the interference torque fluctuation has a constant frequency and a decreasing amplitude. With a sudden change along the output direction, the interference torque fluctuates in a small range. With a sudden change along the spin direction, the change of the interference torque combines a fluctuation and a gradually-changing quasi-equilibrium value. This study provides a supplement to the steady-state error model of the three-floated gyroscope.

Star Shaped Long Chain Branched Poly (lactic acid) Prepared by Melt Transesterification with Trimethylolpropane Triacrylate and Nano-ZnO.

Long chain branched poly (lactic acid) (LCBPLA) was prepared via transesterification between high molecular weight poly (lactic acid) (PLA) and low molar mass monomer trimethylolpropane triacrylate (TMPTA) during melt blending in the presence of zinc oxide nanoparticles (nano-ZnO) as a transesterification accelerant in a torque rheometer. Compared with the traditional processing methods, this novel way is high-efficiency, environmentally friendly, and gel-free. The results revealed that chain restructuring reactions occurred and TMPTA was grafted onto the PLA backbone. The topological structures of LCBPLA were verified and investigated in detail. It was found that the concentration of the accelerants and the sampling occasion had very important roles in the occurrence of branching structures. When the nano-ZnO dosage was 0.4 phr and PLA was sampled at the time corresponding to the reaction peak in the torque curve, PLA exhibited a star-shaped topological structure with a high branching degree which could obviously affect the melt strength, extrusion foaming performances, and crystallization behaviors. Compared with pristine PLA, LCBPLA showed a higher melt strength, smaller cell diameter, and slower crystallization speed owing to the synergistic effects of nano-ZnO and the long chain branches introduced by the transesterification reaction in the system. However, severe degradation of the LCBPLAs would take place under a mixing time that was too long and lots of short linear chains generated due to the excessive transesterification reaction, with a sharp decline in melt strength.

Thixotropic Mechanics in Soft Hydrated Sliding Interfaces

Soft hydrated permeable surfaces exhibit unique lubrication behaviors, including recently discovered frictional hysteresis. This duration-dependent frictional effect can be analogous to the thixotropic fluid response under shear-driven Couette flow. We illustrate torque-speed hysteresis loops using tribo-rheometry measurements between an aluminum annulus and polyacrylamide surface. Frictional torque response was measured under stepwise sliding speed increments at five different step durations. The torque-sliding speed curves exhibit hysteresis loops and the shape of the hysteresis loops depends on step durations. Longer duration shows greater hysteresis with higher average friction. Torque curves at highest speeds converge to one line with a power law exponent of α = 0.7. Based on the experimental data, a hydrogel lubrication model was developed using a thixotropic fluid model, where viscosity change is described as a competition between structural buildup and breakdown. Simulation using the model correlates well with the experimental results, indicating the existence of effective structural change on the hydrogel surface.

3D-Dynamic Modelling and Performance Analysis of Service Behavior for Beam Pumping Unit

In consideration of the rod, the tube, and the liquid column, a 3D dynamic model was established, which could be expressed as a set of partial differential equations. A measured torque curve and a calculated torque curve of Nan1-2-22 oil-well in Daqing oilfield were contrasted with each other which improved the rationality of this model. At last, we researched the influence of the stroke and the frequency of stroke on the displacement of rod, suspension velocity, suspension acceleration, polish rod load, and net torque of gearbox. This 3D dynamic model has a higher calculated accuracy and veracity and could be used to design and optimize the structure of rod pumping and the working process of pumping wells.

Comparison of Isolated Lumbar Extension Strength in Competitive and Noncompetitive Powerlifters, and Recreationally Trained Men.

Androulakis-Korakakis, P, Gentil, P, Fisher, JP, and Steele, J. Comparison of isolated lumbar extension strength in competitive and noncompetitive powerlifters, and recreationally trained men. J Strength Cond Res 35(3): 652-658, 2021-Low-back strength has been shown to significantly impact performance in a plethora of sports. Aside from its effect on sport performance, low-back strength is strongly associated with low-back pain. A sport that heavily involves the lower-back musculature is powerlifting. This study looked to compare isolated lumbar extension (ILEX) strength in competitive and noncompetitive powerlifters, and recreationally trained men. Thirteen competitive powerlifters (CPL group; 31.9 ± 7.6 years; 173.4 ± 5.5 cm; 91.75 ± 18.7 kg), 10 noncompetitive powerlifters (NCPL group; 24 ± 3.5 years; 179 ± 4.8 cm; 92.39 ± 15.73 kg), and 36 recreationally trained men (RECT group; 24.9 ± 6.5 years; 178.5 ± 5.2 cm; 81.6 ± 10.0 kg) were tested for ILEX. Isolated lumbar extension strength was measured at every 12° throughout subject's full range of motion (ROM) and expressed as the following: "strength index (SI)" calculated as the area under a torque curve from multiple angle testing, average torque produced across each joint angle (AVG), and maximum torque produced at a single angle (MAX). Deadlift and squat strength were measured using 1 repetition maximum for the competitive and noncompetitive powerlifters. The following powerlifting characteristics were recorded for the competitive and noncompetitive powerlifters: primary deadlift stance, primary squat bar position, use of belt, use of performance-enhancing drugs, and use of exercises to target the lower-back musculature. Significant between-group effects were found for subject characteristics (age, stature, body mass, and ROM). However, analysis of covariance with subject characteristics as covariates found no significant between-group effects for SI (p = 0.824), AVG (p = 0.757), or MAX (p = 0.572). In conclusion, this study suggests that powerlifting training likely has little impact on conditioning of the lumbar extensors.

Torsional Vibration Analysis of Hydro-Generator Set Considered Electromagnetic and Hydraulic Vibration Resources Coupling

The torsional vibration characteristics of the hydro-generator set considering the electromagnetic and hydraulic vibration resources coupling are studied. The moment of rotation consists of water flow driving and magnetic torques caused by the air gap magnetic field in the generator rotor in the case of ignoring the mechanical friction. A coupling torque vibration model of hydro-generator shaft system was established. The model considered the coupling action of hydraulic and electromagnetic excitations, as well as the elastic effect of rotor spiders. The influences of the rotor moment inertia, rotor stiffness, and mass of turbine water added into the torsional natural vibration of the unit shaft system were studied. The effect of hydraulic excitation frequency on torsional vibration response was also investigated. The frequency response curves of shaft torque, torsional vibration angle, and electromagnetic torque were presented. The electromagnetic and hydraulic coupling resonance was studied when hydraulic excitation frequency was equal to zero and first-order frequencies. The excitation electric current and internal active power angle on torsional vibration was further analyzed. This study provides an analysis model and method considering the coupling of electromagnetic and hydraulic vibration resources for design and stable operation of water turbine generator sets.

Quadruped-imitating robot leg rod joint driving torque virtual prototype simulation

Based on the motion principle of the double-half-revolution mechanism, a new type of quadruped-imitating robot is designed. It mainly consists of body suspension, wheel leg support and walking-leg. In order to simplify its walking-leg mechanism, each leg rod joint is directly driven by a steering gear. The virtual prototype model of the robot is established based on SolidWorks. The motion constraint relationship of legs and the three-dimensional collision properties between the stride rod and the ground are set. According to the kinematic coupling relationship of the legs, the driving speed of each joint is set. For two typical working conditions of the robot: walking on flat ground and climbing over vertical obstacle, the driving torques of the leg joints, such as the first swivel arm, the second swivel arm and the stride rod, are simulated respectively. The driving torque curves of leg joints are obtained under different working conditions. The results provide a reference basis for the steering engine lectotype design in the future.

A general method for obtaining diffusion coefficients by inversion of measured torque from diffusion experiments under small amplitude oscillatory shear

A numerical approach based on Tikhonov regularization is developed to invert torque curves from time-dependent small amplitude oscillatory shear (SAOS) experiments in which diffusion occurs to determine the diffusion coefficient. Diffusion of a solvent into a polymer melt for example causes the measured torque to decrease over time and is thus dependent on diffusion kinetics and the concentration profile. Our numerical approach provides a general method for retrieving local viscosity profiles during diffusion with reasonable accuracy, depending only on the linear viscoelastic constitutive equation and a general power law dependency of the diffusion process on time. This approach also allows us to identify the type of diffusion (Fickian, pseudo-Fickian, anomalous, and glassy) and estimate the diffusion coefficient without the a priori identification of a specific diffusion model. Retrieving local viscosity profiles from torque measurements in the presence of a concentration gradient is an ill-posed problem of the second type and requires Tikhonov regularization. The robustness of our approach is demonstrated using a number of virtual experiments, with data sets from Fickian and non-Fickian theoretical concentration and torque profiles as well as real experimental data.

Magnetic and structural properties of L10 Mn-Ga epitaxially grown islands

Magnetic and structural properties of L10 Mn53Ga47 islands epitaxially grown onto MgO(1 0 0) substrates are discussed. The samples were fabricated by sputter-deposition at a substrate temperature Ts during deposition. The samples deposited at Ts above 500 °C were found to form the island structure of Volmer-Weber type. The average size of the islands fabricated at Ts = 600 °C is around 200 nm in width and 60 nm in height. The XRD and TEM analyses indicate that those islands are of the L10 phase with the 〈0 0 1〉 axis perpendicular to the substrate surface. The lattice constants a and c are 3.91 ± 0.01 Å and 3.65 ± 0.02 Å, respectively, which are larger by 0.8%, and smaller by 1.5% respectively, as compared to the bulk values of the same composition. The order parameter of these islands is found to increase from 0.7 to 0.8 for Ts = 450–500 °C, and then remains nearly constant (≈0.8) for higher Ts. The M-H hysteresis loops exhibit a high squareness for all the samples for Ts = 450–600 °C. The saturation magnetization Ms is about 220 and 350 emu/cm3 for Ts = 450 and 600 °C, respectively. The out-of-plane coercivity Hc is 5 and 13 kOe for Ts = 450 and 600 °C, respectively. The temperature dependence of Ms for the sample made at Ts = 600 °C was measured and fitted to an empirical relation in order to estimate Tc. The estimated Tc around 600 K is in reasonable agreement with the reported value of bulk L10 Mn53Ga47. The uniaxial perpendicular magnetic anisotropy constant Ku estimated by the out-of-plane torque curves is around 1.1 × 107 and 8.3 × 106 erg/cm3 at 5 and 300 K, respectively. The initial magnetization curves of these islands exhibit a typical pinning mode for the coercivity mechanism. A phenomenological discussion of the coercivity is presented on the basis of Kronmuller’s formula. It is found that the coefficient α and effective demagnetizing factor Neff in the formula by Kronmuller are approximately 0.38 and 12. For the magnetic anisotropy mechanism, the power law relation between Ku(T) and Ms(T) is examined. It is found that the exponent n for Ku(T)∝Ms(T)n varies from 2.3 to 3.5 for T from 350 to 5 K. However, the n in a whole temperature range from 5 to 350 K is 2.6. The n = 2.6 suggests a deviation from the single-ion mechanism, and is consistent with the theoretical predictions of Ga contribution.

Advantages and Characteristic Analysis of Slotless Rotary PM Machines in Comparison With Conventional Laminated Design Using Statistical Technique

Slotless permanent magnet (PM) machines have been the considerable research subject for electric vehicles application due to their obvious merits. As opposed to conventional laminated PM machines, such machines can offer zero cogging torque, sinusoidal torque curve angle yielding a machine with very smooth rotation, no laminated core loss, and negligible eddy current losses in rotor magnets. This paper presents the mathematical model and the characteristics analysis of slotless rotary PM machines compared to a conventional laminated design. An explicit analytical expression of slotless rotary machines is developed to calculate the electromagnetic torque on both the ${q}$ - and ${d}$ -axis current injections. The validity of an analytical calculation is confirmed by the finite element analysis. Subsequently, the performance comparisons of slotless and laminated designs are carried out using a statistical technique. The key results derived from the comparative study are expected to be a useful reference resource for decision makers who should make a comparative judgment.

Load Reduction in Wind Turbines with Bend-Twist Coupled Blades without Power Loss at Underrated Wind Speeds

Usage of composite materials in wind turbine blades is a passive mechanism to alleviate fatigue loads besides the reduction in the mass of the wind turbine system. Off-axis plies in bend-twist coupled (BTC) blades account for the passive fatigue load reduction by reducing the effective angle of attack of blade sections. Reduction in fatigue loads is generally represented by damage equivalent load ratios. In the present study, multibody aeroelastic analyses are performed for wind turbine systems for the underrated, rated and the overrated turbulent wind speeds. It is shown that load reduction can be achieved for the whole range of wind speeds with the usage of bend-twist coupled blades at the cost of power loss at underrated wind speeds which is unacceptable. Thus, the main concern of the present study is first to make performance study of wind turbines with bend-twist coupled blades at underrated wind speeds and then to overcome the power loss while still achieving reduction in damage equivalent loads by the proper modification of the pre-twist variation of the bend-twist coupled blades together with the generator torque curve across whole range of wind speeds. This study has been performed utilizing the same pitch control settings in region 2 to examine the mere effect of pretwist modification on the power performance of the wind turbine and on the damage equivalent loads.

Computation of Energy Loss in an Induction Motor During Unsymmetrical Voltage Sags—A Graphical Method

Symmetrical and unsymmetrical voltage sags are a major cause of energy loss in induction motors affecting the efficiency and longevity of the motor. A comprehensive and novel graphical method to determine energy loss during unsymmetrical sags is proposed. The energy is computed using torque–speed characteristics of the induction motor. Due to unbalance in the voltages during unsymmetrical sags, oscillations are observed in torque–speed characteristics. Throughout these oscillations, motor torque and speed attain extreme values. Area under the curve of torque and speed during oscillation is computed using MATLAB/Simulink simulation, which is a measure of the output power during unsymmetrical sags. The sag duration is measured to compute the energy loss. The analytical expression to assess output power of an induction motor during unsymmetrical sag is derived. The graphical results are validated using analytical calculations. Graphical representation is easy and faster to construct than analytical methods; in addition, the graphical method proposed makes it easier to assess the comparative magnitudes. Assessment of energy loss provides a useful tool for optimal injection of energy for sag mitigation techniques.

Magnetocaloric Effect in Layered Organic Conductor λ-(BETS)2FeCl4

Magnetocaloric effect (MCE) and magnetic torque measurements have been carried out in the π–d system λ-(BETS)2FeCl4 [BETS = bis(ethylenedithio)tetraselenafulvalene], which shows an antiferromagnetic insulating (AFI) phase below ∼8.5 K. In the magnetic torque curve, a sharp structure at ∼1.2 T and a step at ∼10 T are observed at low temperatures, which are caused by the spin-flop (SF) transition and the transition from the AFI to paramagnetic metallic (PM) phase, respectively. The MCE, directly related to the magnetic entropy, shows a small sharp peak at the SF transition and a sharp dip at the AFI–PM transition. The overall feature above 3 K is qualitatively interpreted by a simple picture: antiferromagnetic (AF) π spins and paramagnetic 3d spins at the Fe sites. However, a broad dip in the MCE is additionally found at ∼5 T below ∼3 K, which is not explained by the above picture. The results are compared with those of κ-(BETS)2FeBr4, which shows an AF order of the 3d spins at the Fe sites.

Modelling the Thermal Degradation and Stabilisation of PVC in a Torque Rheometer

Abstract A novel method for simulating the torque and temperature curves from a torque rheometer thermal stability test on poly(vinyl chloride) (PVC) was developed. A mathematical model was proposed which combines the chemical kinetics involved in the thermal degradation and stabilisation process of PVC with heat transfer and viscosity relationships within the torque rheometer. The model coefficients were fitted to data obtained from previous experiments with a program written in the Python programming language using the Levenberg-Marquardt Algorithm (LMA) with multiple starts. The mathematical model fits the torque rheometer data successfully depending on the characteristics of the torque curve. The model fit is successful when the torque curve follows the expected behaviour. An unsuccessful model fit occurs when the torque curve deviates from the expected shape in a very specific way. In the degradation phase the torque curve increases to a local maximum, decreases to a local minimum and then increases again. The exact reason for the dip in torque is unknown.

A Simple Strategy for Parameters Identification of SRM Direct Instantaneous Torque Control

This paper proposed a simple strategy for parameters identification of switched reluctance motor (SRM) direct instantaneous torque control. This strategy without rotor locking includes measuring and calculating steps. In the measuring step, flux linkage curves with current at three critical positions are obtained. At the intermediate position, flux linkage curve is measured under current chopper control (CCC). At the aligned and unaligned position, flux linkage curves are measured when the winding is given a voltage pulse. In the calculating step, the whole flux-linkage characteristics with current and position can be calculated based on the measured critical curves. Then torque curves are calculated for direct instantaneous torque control. Meanwhile, the i-Ψ loci curves during CCC operation are analyzed for identifying adjusting advance angle. In this way, the entire flux linkage characteristics and adjusting advance angle parameters under different operating area are obtained. This strategy is applied to a 7.5 kW 12/8 SRM for direct instantaneous torque control (DITC). Experiments have been carried out to verify the effectiveness and accuracy of the proposed method.

Regime Map of Dry Neutralization Agglomeration Process Containing Non-Reactive Ingredient on a Laboratory Scale

This study described a regime map for dry neutralization agglomeration. Based on the map, the effects of selected key parameters, such as ingredient composition, operation temperature, agitation speed, and size of Na2CO3 particles, were investigated using a laboratory-scale mixer, and properties of the agglomeration product were analyzed, including particle size distribution, Hunter color, and flowability. Torque curves evolving during the process were correlated with the system flowability. Three distinguishable regimes were indicated, dry, wet, and transitional, and the agitation speed was found to have a different influence on the agglomeration process for the three regimes. Furthermore, the influence of temperature on reactive agglomeration significantly differed from that in agglomeration processes in which the binder was non-reactive.

Reactive processing preparation of sustainable composites from canola meal reinforced by chemical modification

Canola meal (CM), a by-product of canola oil extraction, was modified by poly (styrene-co-glycidyl methacrylate) (PSG) and could potentially be used as a sustainable natural composite. Infrared analysis indicated that PSG could efficiently react with the proteins in CM and become covalently bonded. DSC results revealed that the modified CM composites showed new glass transition temperatures (Tg) decreasing with the introduction of PSG, which were attributed to the disruption of intermolecular association. Torque curves and melt flow index tests showed the flow property of the modified CM composites increased due to interference by PSG of the hydrogen and disulfide bonding among the protein species. DMA results showed greater amorphous character for the modified CM composites and new glassy plateaus with increased storage moduli, indicating a change in molecular structure and enhancement in mechanical property and usability below Tg. Furthermore, the thermostability, the tensile strength, and the elastic moduli of the modified CM composites increased because of the formation of cross-linked proteins in the CM composites, which will potentially increase the application value in some fields, such as single-use agricultural planting containers replacing high-impact polystyrene (HIPS) containers, and food or coffee trays.

Space-Time Kriging Surrogate Model to Consider Uncertainty of Time Interval of Torque Curve for Electric Power Steering Motor

In rotating motors, an electromagnetic analysis using finite-element analysis is performed according to the time interval such as the steps of the rotation angle. If the uncertainty of time variable is necessary to be handled, the time interval should become smaller than uncertainty values. It causes an increase of the cost even if the surrogate model is applied. Thus, space-time kriging surrogate model is proposed to consider time variable as well as space variable in the design stage. The proposed model handles time variable and predicts responses between time intervals to obtain outputs for the tiny uncertainty of time variable. The performance of prediction is verified with simulation data and then the reliability estimated by the proposed model is compared with measured data from manufactured prototypes.

Dynamic Testing Characterization of a Synchronous Reluctance Machine

The dynamic testing method (DTM) has been shown to accurately characterize the electromagnetic model of permanent magnet synchronous machines by describing the relationship between the phase currents and the linked magnetic flux with minimal amount of test equipment as compared with traditional methods. Within this paper, a performance evaluation of the DTM applied to a synchronous reluctance machine is presented. This paper discusses the challenges of a dynamic test of a nonlinear synchronous machine and suggests a fuzzy proportional, derivative and integral controller (PD + I) controller for improved control performance and measurements. Finally, the DTM measurements are compared with the results of the constant speed method (CSM). The CSM measurements of flux linkage and torque curves confirm the validity of the DTM measurements for this machine.

Numerical validation of a subject-specific parameter identification approach of a quadriceps femoris EMG-driven model

Muscle models can be used to estimate muscle forces in motor tasks. Muscle model parameters can be estimated by optimizing cost functions based on error between measured and model-estimated joint torques. This paper is a numerical simulation study addressing whether this approach can accurately identify the parameters of the quadriceps femoris. The simulated identification task is a single joint maximum voluntary knee concentric–eccentric extension in an isokinetic dynamometer, keeping the hip fixed at a neutral position. A curve considered as the nominal torque was obtained by simulating the quadriceps femoris model exerting a maximum knee extension torque using a set of known parameter values. Three parameters, with different expected sensitivities of force estimations by Hill-type muscle models, were studied: very sensitive, sensitive and not sensitive, corresponding to slack tendon length, maximum isometric force, and pennation angle, respectively. The initial values of the parameters were randomly changed, simulating an ignorance of nominal values. EMG generation and torque measurement error models were used to obtain realistic simulated data corrupted by noise. Simulated annealing was chosen as the optimization algorithm. Different sequences of parameter identification and cost functions were tested. The best nominal torque curve reconstruction was obtained by optimizing the parameters sequentially, starting from slack tendon length using the Euclidean norm cost function. However, the simultaneous estimation of all parameters resulted in the most accurate values for the parameters, although dispersion was relatively large. In conclusion, in the present simulation study using realistic synthetic torque and EMG data, the optimization approach based on torque error curve was able to closely approximate the parameter values of the model's quadriceps femoris muscle.