Unbalanced Force Research Articles

Design, static analysis, and dynamic system modeling of 3-PPRS parallel manipulator with load-balancing UPS leg

AbstractAs a heavy load is applied to the parallel manipulators, it causes inaccuracies while positioning the end-effector or unbalanced dynamic forces in the legs. Various load-balancing techniques overcome this. However, the disadvantage of most load-balancing mechanisms is that they add inertia to the assembly and decrease the speed of motion. This article studies a new load-balancing method (a passive damper mechanism). The passive balancing mechanism is proposed to negate the inertia effects while countering the static inaccuracies in the parallel mechanism. This is verified by the structural analysis of the mechanism. The impact of the damper element on the dynamics of the mechanism is unknown. Hence, a complete mathematical model for the balancing mechanism has been developed to study its impact on the dynamics of the entire structure. Laplace transformations characterize the system response. The inclusion of a passive damper in a 3-prismatic-prismatic-revolute-spherical system was examined and found to be stable and critically damped. Such a passive damper was envisaged to facilitate additional force transmission for the actuators, and the DC gain from the system response validates the torque support for the actuators.

Numerical Study of the Influence of the Spatial Distribution of Oversized Rock Blocks on the Stability of Soil-Rock Mixture Slopes

Soil-rock mixtures (S-RMs), as special engineering geological materials, are widely distributed in mountainous regions and are important hosts of slope disasters. Stability studies are very important for predicting S-RM slope safety during the construction and operation of engineering projects. To investigate S-RM slope stability considering the spatial distribution of oversized rock blocks in the slope, the distinct element method (DEM) program particle flow code in two dimensions (PFC2D) was used to analyse the stability of slopes composed of S-RMs. First, according to the stochastic approach, different numerical models of an S-RM slope were established with different oversized rock block spatial distributions. Then, the S-RM slope models were simulated, the safety factor and sliding characteristics of the slopes were analysed, and the unbalanced contact force and rotational characteristics of the oversized rock blocks were discussed. Finally, the concept of key rock blocks in S-RM slopes was proposed, and their spatial distribution characteristics and influence characteristics were summarized. The findings of this study suggest that oversized rock blocks have a certain influence on the stability of S-RM slopes.

Multi-Objective Optimal Design of μ–Controller for Active Magnetic Bearing in High-Speed Motor

In this paper, a control strategy based on the inverse system decoupling method and μ-synthesis is proposed to control vibration in a rigid rotor system with active magnetic bearings that are built into high-speed motors. First, the decoupling method is used to decouple the four-degrees-of-freedom state equation of the electromagnetic bearing rigid rotor system; the strongly coupled and nonlinear rotor system is thus decoupled into four independent subsystems, and the eigenvalues of the subsystems are then configured. The uncertain parametric perturbation method is used to model the subsystem, and the multi-objective ant colony algorithm is then used to optimize the sensitivity function and the pole positions to obtain the optimal μ-controller. The closed-loop system thus has the fastest possible response, the strongest internal stability, and the best disturbance rejection capability. Then, the unbalanced force compensation algorithm is used to compensate for the high-frequency eccentric vibration; this algorithm can attenuate the unbalanced eccentric vibration of the rotor to the greatest extent and improve the robust stability of the rotor system. Finally, simulations and experiments show that the proposed control strategy can allow the rotor to be suspended stably and suppress its low-frequency and high-frequency vibrations effectively, providing excellent internal and external stability.

Failure Analysis of Fatigue Failed M20 Class 8.8 Galvanized Steel Bolt

An M20 Class 8.8 galvanized steel bolt (derrick bolt) was found to fail after five years of service in an offshore drilling station. A comprehensive failure analysis investigation was carried out to reveal the root cause of the detected failure. Visual inspection coupled with complete microstructural characterization as well as mechanical testing were performed in the investigation. The results showed that the failure was mainly caused by fatigue failure. The initiation of the fatigue crack was supposedly promoted by the existence of non-metallic inclusions that were present at both the surface and the interior of the microstructure. Furthermore, unbalanced preload forces resulted in bolt loosening which caused fretting wear of the galvanized layer thickness. The detected drop in the galvanized layer thickness by 42.20% at the primary origin of the fatigue crack along with the presence of non-metallic inclusions were thought to be the reason for the initiation of the fatigue crack. The crack was then found to propagate through a transitional complete cleavage to quasi-cleavage fracture as appeared from fracture surface topography studied by scanning electron microscopy (SEM). The final stage of the fatigue failure was found to be caused by ductile fracture of the overloaded zone.

Methodology for assessing and reducing the aerodynamic imbalance of the impellers of GTE fans

The reasons for the occurrence of increased vibration of the engine rotor due to aerodynamic imbalance of the fan of the first stage of the impeller are determined. A method for estimating the aerodynamic imbalance of the gas turbine engine fan is proposed, taking into account the influence of the following factors: geometric errors in the manufacture of blade airfoils and their positioning in the disk; deformation of the blade airfoil during the assembly of the impeller, as well as the factors of the working process occurring in the impeller. The use of the technique makes it possible to evaluate the aerodynamic imbalance of the impeller at the stage of its balancing and significantly reduce the amount of aerodynamic imbalance by determining the parameters for removing a layer of material or adding corrective masses. The influence of geometric errors of the blades on the value of the aerodynamic imbalance of the impeller was analyzed. Based on the results of the research, the type of dependence of unbalanced gas forces on the influence of technological and operational factors of the impeller under consideration was determined.

A novel triple-diameter pulsating heat pipe: Flow regimes and heat transfer performance

A single-turn triple-diameter pulsating heat pipe (TD-PHP) with a total length of 250 mm (the evaporation, adiabatic, and condensation lengths were 25 mm, 125 mm, and 100 mm, respectively) made of a transparent Pyrex glass was designed and fabricated for the first time. The thermal performance and flow characteristics of the TD-PHP were compared with two other fabricated PHPs, the single-diameter (SD) and dual-diameter (DD) PHPs, to determine the effect of non-uniform channel diameters. The PHPs were mounted on a tilting frame, and their thermal performances were tested with various heat inputs, inclination angles, and filling ratios. The temperatures of the evaporation, condensation, and adiabatic sections and flow behaviors were monitored. Results indicated that circulating flow was enhanced by using TD-PHP, and thermal resistance was reduced considerably. The visualization results showed that the bubbles' generation, growth, and breakage leading to enlarged vapor plugs were enhanced because of the unbalanced gravitational forces owning to the channel with non-uniform diameter. Hence, the TD-PHP was functional even at inclination angles near the horizontal angle.

An adaptive morphological filtering and feature enhancement method for spindle motor bearing fault diagnosis

The unbalanced electromagnetic force and unqualified assembly of the spindle motor lead to weak vibration energy and the difference in fault features in different life cycles and different bearing individuals. Compared with single fault diagnosis and the datasets that come from the test bench, compound faults diagnosis of the spindle motor is a challenging task. To solve it, an improved filtering and feature enhancement method combined with the merits of AMF and TEO is proposed. Firstly, the adaptive morphological filtering (AMF) method is developed by adaptively constructing the size of the structural element (SE) for remaining in corresponding SE with the component of interest, which can reduce interference from background noise. Still, the periodic fault impulse, especially the incipient fault signals, is easily modulated by other fault-unrelated harmonic components. Thus, the filtered signals are processed by the Teager energy operator (TEO) for enhancing the faint transient impact compositions. Finally, the effectiveness of the method is verified by simulation and fault motor matched with NTN ceramic bearing and FAG metal bearing respectively, where the motor matched with NTN ceramic bearing is an early failure case and the other is a late failure case. Besides, compared with some traditional methods, the result proves that the proposed method has better performance under the actual engineering scenarios for different degrees of fault feature identification.

A new friction–slip brace damper to improve seismic performance of braced frames

Global buckling in compression braces results in compression strength degradation, compression stiffness degradation, brace local buckling, and finally brace fracture. Consequently, the braces cannot achieve high energy dissipation capacity. The current study proposes a novel friction−slip damper employed in the middle of square−Hollow Structural Section (square−HSS) and H−shaped braces to prevent the strength and stiffness degradation of braces and improve their seismic responses. In these braces, slip prevents the global buckling of brace and friction dissipates a large portion of energy. To assess the performance of proposed damper, the hysteresis behaviors of square−HSS and H−shaped braces with the proposed friction−slip damper were compared with those of conventional braces both in bracing elements and in diagonal and chevron Special Concentrically Braced Frames (SCBFs) through modeling the numerical models in ABAQUS finite element software validated with two experimental studies. The study findings showed that in the models equipped with the friction−slip damper, the braces experienced no global buckling, local buckling, yielding, plastic hinge, damage, and fracture. Additionally, the obtained results indicated that no degradation was observed in the strength and stiffness of the models with the friction−slip damper than the conventional models. Consequently, a 186.3% increase in energy dissipation capacity was experienced by installing the proposed damper in the middle of braces. Moreover, the results showed that the beams of chevron SCBFs with the friction−slip damper experienced no unbalanced force and thus, no deflection resulting in the stiffness and strength degradation in the tension and compression braces was observed in the chevron beams.

A Deep Learning-Based Unbalanced Force Identification of the Hypergravity Centrifuge.

Accurate and quantitative identification of unbalanced force during operation is of utmost importance to reduce the impact of unbalanced force on a hypergravity centrifuge, guarantee the safe operation of a unit, and improve the accuracy of a hypergravity model test. Therefore, this paper proposes a deep learning-based unbalanced force identification model, then establishes a feature fusion framework incorporating the Residual Network (ResNet) with meaningful handcrafted features in this model, followed by loss function optimization for the imbalanced dataset. Finally, after an artificially added, unbalanced mass was used to build a shaft oscillation dataset based on the ZJU-400 hypergravity centrifuge, we used this dataset to train the unbalanced force identification model. The analysis showed that the proposed identification model performed considerably better than other benchmark models based on accuracy and stability, reducing the mean absolute error (MAE) by 15% to 51% and the root mean square error (RMSE) by 22% to 55% in the test dataset. Simultaneously, the proposed method showed high accuracy and strong stability in continuous identification during the speed-up process, surpassing the current traditional method by 75% in the MAE and by 85% in the median error, which provided guidance for counterweight and guaranteed the unit's stability.

Mean stress tensor of discrete particle systems in submerged conditions

The mean stress tensor is essential to investigate the dynamics of granular material. In this paper, we use Hamilton’s principle of least action to derive the averaged stress tensor of discrete granular assemblies subjected to hydraulic force fields, as well as rigorous conditions for a proper definition of the Representative Volume Element (RVE). The main goal behind our efforts is to upscale particle physics into a sound stress tensor for systems involving the complex interaction between grains and water. We identify the contributions from the unbalanced forces, hydraulic forces, gravity, external forces, and particle fluctuation to the mean stress tensor. In doing so, it is convenient to separate the influence of different force fields when the granular system is subjected to complex environments, e.g., subaqueous conditions. The obtained formula is then validated by triaxial test simulations of dry and saturated granular systems using the Discrete Element Method (DEM) and the Lattice-Boltzmann Method (LBM). The results show that the deduced formula can accurately calculate the stress tensor of discrete assemblies with various body-force fields. We used validated DEM-LBM simulations of submerged granular column collapses to explore the physics happening at the grain scale with this mathematical formalism and showcase its potential. We provide a new perspective based on the granular assembly scale to pursue the fluid–solid interaction. Due to the importance of stress analysis in the constitutive modeling of granular materials, this work could help to better obtain the stress–strain relationship of saturated or submerged granular systems.

Calculation and analysis of the unbalanced magnetic thrust for the linear motor drive motion system

AbstractThe unbalanced magnetic thrust caused by the mover eccentricity for the linear motor drive motion system is analytically represented. Firstly, the relative complex magnetic permeability function is introduced to represent the effects of the mechanical installation errors and vibrations on the mover eccentricity. Then, the distortion of the magnetic field caused by the mover eccentricity is represented based on the Maxwell equation. The spectrum characteristics of the unbalanced magnetic thrust force is analytically calculated taking into account the harmonics in the drive circuit. Finally, the validity of the theoretically analysis is verified by the experiments. The results show that the static eccentricity caused by the mechanical installation error will produce the unbalanced magnetic thrust, affecting the thrust characteristics of the linear motor. In particular, the dynamic mover eccentricity caused by the mechanical vibration will produce paired unbalanced magnetic thrust harmonics on both sides of the original thrust harmonics, deteriorating the dynamic precision and efficiency of the direct drive motion system.

Effect of Unbalanced Magnetic Pull of Generator Rotor on the Dynamic Characteristics of a Pump—Turbine Rotor System

In pumped storage units, the rotor-bearing electromagnetic system is under the joint influence of hydraulics, mechanics, and electromagnetics, and the mechanism of unit vibration problems is very complex to investigate. ANSYS software is used to establish a three-dimensional model of a pumped storage power plant’s rotor-bearing electromagnetic system, and the stiffness coefficient of the unbalanced magnetic traction forces is calculated using the Fourier series of the magnetic conductivity of the air gap. This shows that the nonequilibrium magnetic attraction increases non-linearly with increasing excitation current and eccentricity of the rotor. At each order, the critical velocity of the rotor system increases as the stiffness factor of the bearing increases, with the greatest increase in critical velocity at the third and fourth orders. In the first-order mode-oscillation pattern, the unbalanced magnetic attraction has an effect on the intrinsic frequency of the transverse oscillation, with a reduction in the amplitude of the intrinsic frequency by 34.65%. Axial and transverse modal vibrations manifest themselves as upward and downward motions and transverse oscillations in different portions of the rotor system, respectively, whereas torsional modal vibrations manifest as a radial broadening or reduction in the generator rotor, runner, and coupling portions of the rotor system. The results of the study provide a theoretical foundation and a computational method for the dynamic analysis and design of the rotor system of pumped storage power stations.

Biomimetic fabrication of PET composite membranes with enhanced stability and demulsibility for emulsion separation

Membrane separation of highly emulsified oily wastewater is a critical requirement, but still challenging due to the poor demulsibility, unstable wettability, and low recyclability of oil/water separation membranes. Herein, inspired by beetles capturing water from the air, an inverse desert beetle-like membrane with excellent demulsibility and significant stability was fabricated using waste poly(ethylene terephthalate) (PET) bottles as building blocks for enhanced emulsion separation. Due to the unbalanced force formed by the surface energy gradient, the small tiny oil droplets of the oil-in-water emulsion can be captured by the superhydrophobic bumps (hierarchical Al2O3 clusters), thus strengthening the demulsification ability of the membrane. Interestingly, the membrane exhibits excellent emulsion separation efficiency (99.91%) and flux (2193.5 L m−2h−1) for surfactant-stabilized oil-in-water emulsions, as well as sustained and stable separation performance, which outperforms conventional single superhydrophilic PDA/PET membrane without superhydrophobic bumps structure. Moreover, a two-stages“growing-jumping” model for the water droplet discharge mechanism was revealed to depict the enhanced stable separation of APP3 membrane, avoiding sticky Wenzel states to destroy the superhydrophobicity of bumps. Thus, the as-designed membrane achieved stable emulsion separation performance in continuous operation, as well as good recyclability. This biomimetic membrane not only shows emergent application potential for emulsion separation, but also provides insights into designing advanced membrane-based separation technology.

Investigation of Flux-Modulating Consequent Pole Motors

This article investigates the electromagnetic performance of a novel variable-flux permanent magnet (PM) motor, named the “flux-modulating consequent pole motor (FCM),” through finite element analysis (FEA) and experiments. The FCM is a combination of a flux-modulating (FM) motor and a consequent-pole PM motor, whose torque can be generated from both the FM and PM motors without causing unbalanced magnetic forces (UMFs). Two models with 16 and 20 poles are used to analyze the torque, efficiency, and power factor of the FCM. Moreover, efficiency maps of the FCM are compared with those of the conventional PM synchronous motors. It is revealed that the torque of the FCM depends on the values of winding factors of the FM and PM motors. Finally, experimental results on a 20-pole prototype machine are presented to validate the operating principle of the FCM and the FEA simulations.

A cycloidal magnetic gear with a novel flux shield (“moon”) achieving higher torque density and lower unbalanced electromagnetic forces

Magnetic gears’ numerous potential advantages, such as contactless operation, reduced maintenance requirements, lack of lubrication, and inherent overload protection, have led to significant interest in the technology. The cycloidal magnetic gear (CyMG) is an enticing option for applications requiring high gear ratios. CyMGs do not require the modulators used in coaxial magnetic gears, but CyMGs have disadvantages, including counterproductive torque developed in the larger air gap region and unbalanced magnetic forces, which must be supported by the bearings. This paper introduces a novel “moon” structure, which serves as a flux shield, for CyMGs. The moon is made out of ferromagnetic material and is located in the larger region of the air gap. The moon increases torque density by providing a leakage path for the flux that would otherwise create counterproductive torque. The moon also reduces the unbalanced magnetic forces. This structure’s benefits are investigated using finite element analysis. The results show that, within the evaluated design space, the proposed moon can increase the maximum achievable active volumetric torque density (VTD) by 7.6% to 8.6% for each of the considered gear ratios or it can reduce the no-load eccentric force of the maximum VTD moon-free 20:1 CyMG by as much as ∼86% without decreasing the VTD.

Vertical-Longitudinal Coupling Effect Investigation and System Optimization for a Suspension-In-Wheel-Motor System in Electric Vehicle Applications

In-wheel-motor-drive electric vehicles have attracted enormous attention due to its potentials of improving vehicle performance and safety. Road surface roughness results in forced vibration of in-wheel-motor (IWM) and thus aggravates the unbalanced electric magnetic force (UEMF) between its rotor and stator. This can further compromise vertical and longitudinal vehicle dynamics. This paper presents a comprehensive study to reveal the coupled vertical–longitudinal effect on suspension-in-wheel-motor systems (SIWMS) along with a viable optimization procedure to improve ride comfort and handling performance. First, a UEMF model is established to analyze the mechanical–electrical–magnetic coupling relationship inside an IWM. Then a road–tire–ring force (RTR) model that can capture the transient tire–road contact patch and tire belt deformation is established to accurately describe the road–tire and tire–rotor forces. The UEMF and the RTRF model are incorporated into the quarter-SIWMS model to investigate the coupled vertical–longitudinal vehicle dynamics. Through simulation studies, a comprehensive evaluation system is put forward to quantitatively assess the effects during braking maneuvers under various road conditions. The key parameters of the SIWMS are optimized via a multi-optimization method to reduce the adverse impact of UEMF. Finally, the multi-optimization method is validated in a virtual prototype which contains a high-fidelity multi-body model. The results show that the longitudinal acceleration fluctuation rate and the slip ratio signal-to-noise ratio are reduced by 5.07% and 6.13%, respectively, while the UEMF in the vertical and longitudinal directions varies from 22.2% to 34.7%, respectively, and is reduced after optimization. Thus, the negative coupling effects of UEMF are minimized while improving the ride comfort and handling performance.

An Integrated Vibration Elimination System with Mechanical-Electrical-Magnetic Coupling Effects for In-Wheel-Motor-Driven Electric Vehicles

This study aims to improve the vehicle vertical dynamics performance in the sprung and unsprung state for in-wheel-motor-driven electric vehicles (IWMD EVs) while considering the unbalanced electric magnetic force effects. An integrated vibration elimination system (IVES) is developed, containing a dynamic vibration-absorbing structure between the IWM and the suspension. It also includes an active suspension system based on a delay-dependent H∞ controller. Further, a novel frequency-compatible tire (FCT) model is constructed to improve IVES accuracy. The mechanical-electrical-magnetic coupling effects of IWMD EVs are theoretically analyzed. A virtual prototype for the IVES is created by combining the CATIA, ADAMS, and MatLab/Simulink, resulting in a high-fidelity multi-body model, validating the IVES accuracy and practicability. Simulations for the IVES considered three different suspension structure types and time delay considerations were performed. Analyses in frequency and time domains for the simulation results have shown that the root mean square of sprung mass acceleration and the eccentricity are significantly reduced via the IVES, indicating an improvement in ride comfort and IWM vibration suppression.

Lubrication Film Generation with Limited Lubricant Supply and Its Tuned Oil Replenishment in a Cylinder-on-Disc Contact

Limited lubricant supply (LLS) with tuned dosage is an emerging approach to reduce friction and energy consumption. However, LLS can cause severe starvation when the oil supply is insufficient. Therefore, how to effectively replenish oil to the lubricated contact in LLS operation is very important. Using a custom-made optical slider bearing test rig, this work experimentally revealed some characteristics of LLS lubrication in a cylinder-on-disc contact, and proposed two wettability gradient patterns, namely stripe wettability and interlaced wettability, to regulate the lubricant supply to improve the lubricating properties of LLS. The effect of these two wettability patterns was evaluated experimentally according to the lubricating film thickness. The interferograms of the bearing contact under LLS show that the two patterns can augment the oil replenishment through unidirectional lubricant transport by the unbalanced interfacial force via the wettability gradient. Moreover, the interlaced wettability pattern is more effective due to the discontinuous distribution of lubricant from its hydrophilic/hydrophobic region intervals and the transfer of the hydrophobic film to the hydrophilic regions.

Study on Stator-Rotor Misalignment in Modular Permanent Magnet Synchronous Machines with Different Slot/Pole Combinations

Addressing stator-rotor misalignment, usually called eccentricity, is critical in permanent magnet (PM) machines since significantly high radial forces can be developed on the bearings, which can trigger a major fault and compromise the structural integrity of the machine. In this regard, this paper aims to provide insight into the unaddressed identification and analysis of the impact of eccentric tolerances on relevant performance indices of permanent magnet synchronous machines (PMSMs) with modular stator core. Static and dynamic eccentricity are assessed for different slot/pole combinations through the finite element method (FEM), and the results are compared with those of PMSMs with a conventional stator core. The unbalanced magnetic forces (UMF), cogging torque, back-emf, and mean torque variations are described and related to the eccentricity magnitude and classification. The main findings indicate that severe radial forces and significant additional cogging torque harmonics are generated because of eccentricity. Additionally, it is found that the main differences between modular PMSMs and conventional PMSMs rely on the value of slots per pole per phase.

Design and Simulation of Hydraulic Winch Tension Control for Trawler

The trawler winch is a main winching tool in the fishing operation of trawler. The disturbing influence of various factors such as sea wind and waves, change in the size of the catch and the turning of the fishing vessel during the operation of the trawler will cause unbalanced force on the wire rope of the two winches, which will easily cause the deformation and damage of the fishing net facilities and directly affect the improvement of the fishing yield and increase the harvest. In order to compensate for the change of the tension of the winch tractor during the operation of the trawler, the change of the load tension caused by the wave, or the rotation direction of the fishing vessel, and to ensure the good shape of the net opening, an electro-hydraulic control technology was used to design an automatic trawler tension controller. The tension control method of the trawler is investigated. The tension sensor is used as the input information of the electrical signal of the trawler's left and right trawler, which is measured indirectly and transmitted to the controller for logical operation, and the output torque of the hydraulic motor is changed by controlling the pilot overflow, which drives the trawler winch to adjust the tension of the left and right trawler to achieve the dynamic balance of the control system. In order to solve the problem of the tension of the trawl and the influence of the length change on the trawl, we designed an intelligent control system combining PLC control system and hydraulic system and used AMEsim hydraulic simulation software system to model and simulate it, the results show that without PLC control the torque of hydraulic motor 1 is 2387.7NM, the torque of hydraulic motor 9 is 2148.64NM the difference is 239.06 NM uneven force on both sides of the trailing platform, after adding PLC adjustment torque is obviously controlled torque to maintain about 2300NM, within a certain range to play a reliable adjustment effect.