Heavy Load Conditions Research Articles

A Light-Load Efficiency Improvement Technique for an Inductive Power Transfer System through a Reconfigurable Circuit

Constant voltage (CV) charging and efficiency improvement are the most basic and main targets to be achieved in inductive power transfer (IPT) systems. However, efficiency may be jeopardized as battery charging progresses, especially under a light-load condition, which accounts for most of the charging time. Traditional maximum-efficiency tracking (MET) control provides an effective solution to the above issues. However, MET control not only brings the difficulties of complicated control and increased cost/volume, but also increases the additional power losses because of the introduction of additional converters or hard-switching in dual-shift phase control. To address the above difficulty, a light-load efficiency improvement (LLEI) technique is presented in this study. Under a heavy-load condition, both the inverter and rectifier operate in conventional full-bridge mode with satisfactory efficiency. Under a light-load condition, both the rectifier and inverter are reconfigured as a voltage-doubler rectifier and half-bridge inverter, respectively, to achieve two targets: one is to keep the charging voltage roughly unchanged, and the other is to force the equivalent load resistance (ELR) approach to the optimal point to improve system power transfer efficiency. A demonstrative experimental prototype with a charging voltage of 60 V is constructed and tested to validate the LLEI method proposed in this study. The experimental results show that the proposal can ensure stable CV charging and significantly improve the system efficiency under a light-load condition over the whole charging process.

Multi-stream domain adversarial prototype network for integrated smart roller TBM main bearing fault diagnosis across various low rotating speeds

The well-being of tunnel boring machines (TBM) heavily relies on the health status of main bearings, significantly impacting both safety and operational efficiency. Investigating the operation monitoring and diagnosis algorithms of TBM main bearings in practical scenarios with limited fault data and real-time variations in low-speed heavy-load operating conditions poses a research challenge. To solve these issues, a novel domain-adversarial prototype network diagnostic algorithm with a multi-stream fusion feature encoder (MDAPN) based on smart roller monitoring data is proposed. In contrast to existing external vibration monitoring schemes for bearings, monitoring data from smart rollers can mitigate complex external interference and greatly shorten the transmission path of fault sources. The algorithm encompasses a multi-stream fusion feature encoder, domain discriminator, and prototype network classifier. Specifically, the multi-stream fusion feature encoder adopts the two-stream convolutional network to deeply extract the axial-radial fused features of rollers, incorporating shallow statistical feature information. Domain-invariant features are generated based on domain adversarial learning strategies, and the prototype network classifier reduces dependence on target domain samples. An integrated smart roller main bearing fault simulation testbed was built, conducting 6 sets of cross-domain experiments. The proposed method reached an average accuracy of 98.41 % under 5-shot, surpassing the baseline method by 6.57 % at least. This validates that the MDAPN based on smart roller state exhibits excellent fault recognition performance for the main bearing under varying operational conditions with scarce available samples.

The optimization design for the journal-thrust couple bearing surface texture based on particle swarm algorithm

Journal-thrust coupled bearings (JTC bearings), unlike conventional journal or thrust bearings, require consideration of both reducing friction coefficient in the journal part while increasing the load-carrying capacity in the thrust part during lubrication design. This study established a thermal-elastohydrodynamic mixed lubrication model for JTC bearings considering flow, pressure, and thermal continuity conditions, validated through experiments. Based on this, the influence of texture parameters on lubrication under real heavy load conditions was preliminarily investigated. The orthogonal test design was then used to determine the texture parameter that had the greatest impact on optimization. Subsequently, particle swarm optimization (PSO) algorithm was employed for synchronous optimization design of textures for both journal and thrust parts.

A numerical research on the hydrodynamic performance of marine propellers with bionic coupled blade sections

ABSTRACT The propulsive efficiency and cavitation performance of marine propellers directly affect the operating costs and radiated noise of ships, warranting further research on the hydrodynamic performance. The blade sections' profile of the MAU 5-80 propeller has been modified to incorporate avian wing geometry and spacing ridge structures have been introduced between the leading edge and the thickest point. The numerical results indicate that the spacing ridge structures marginally impact the efficiency enhancement of the bionic blade sections with avian wing geometry, particularly under low advance speeds and heavy load conditions. However, the chordwise coordinate value at the thickest point of the bionic blade sections significantly influences the cavitation containment capability of the ridge structures. Compared with the original propeller, the redesigned propeller with bionic coupled blade sections shows a 2.37% improvement in open water efficiency at J = 0.2 and a 20.12% reduction in cavitation volume at J = 0.48.

Structural Strength Analysis and Optimization of Commercial Aircraft Nose Landing Gear under Towing Taxi-Out Conditions Using Finite Element Simulation and Modal Testing

In the field of civil aviation, the nose landing gear is a critical component that is prone to damage during taxiing. With the advent of new technologies such as towing taxi-out and hub motors, the nose landing gear faces increasingly complex operational environments, thereby imposing higher performance demands. Ensuring the structural safety of the nose landing gear is fundamental for the successful application of these technologies. However, current research on aircraft nose landing gear under these new conditions is somewhat lacking, particularly in terms of reliable analysis models for real-world scenarios. This study focuses on a typical Class C aircraft, specifically the B-727 model, for which a finite element model of the nose landing gear is developed. Modal testing of the aircraft’s nose landing gear is conducted using the impact hammer method, and the results are compared with those from the simulations. The experimental data indicate that the error range for the first seven natural frequencies is between 0.23% and 9.27%, confirming the high accuracy of the developed landing gear model. Furthermore, with towing taxi-out as the primary scenario, a dynamic model of the aircraft towing system is established, and an analysis on the structural strength and topological optimization of the nose landing gear under various conditions, including high speeds and heavy loads, is performed. The results show that the developed model can effectively support the analysis and prediction of the mechanical behavior of the nose landing gear. Under high-speed, heavy-load conditions, the nose landing gear experiences significantly increased loads, with the maximum deformation primarily occurring at the lower section of the shock strut’s outer cylinder. However, no damage occurred. Additionally, under these conditions, an optimized structural design for the landing gear was identified, which, while ensuring structural strength, achieves a 22.32% reduction in the mass of the outer cylinder, also ensuring safety in towing taxi-out conditions.

Insight into the tribological properties of cylinder liner-piston ring under the nano BNNs/Cu composite additive lubrication

To improve the tribological properties of the cylinder liner-piston ring, a two-dimensional hexagonal boron nitride/copper composite lubricant additive was prepared and characterized in detail. The tribological properties and lubrication mechanism of nano hexagonal boron nitride composites with different concentrations were studied through the reciprocating friction test on the Rtec friction and wear tester. The results show that copper is successfully reduced and attached to the surface of h-BN nanosheets through the self-polymerization of dopamine, and the spherical structure promotes the interlayer slip of the nanosheets during the reciprocating friction process. The appropriate concentration of nano composite additives has excellent anti-friction and anti-wear properties. At 1 Hz and 100 N, the friction coefficient and wear quality of the nano composite additive with a concentration of 2 wt% were reduced by 29.07% and 76%, respectively. The surface Sq value and Sz value of the cylinder liner sample decreased by 68.06% and 74.47%. At the same time, under the condition of high speed and heavy load, the average wear depth of the cylinder liner sample is reduced by 61.3%. The nano composite material additive forms an excellent friction protective film on the wear surface of the cylinder liner, which can better enter the wear surface of the cylinder liner and produce a filling and repairing effect. The research results provide a method for the use of nano hexagonal boron nitride composite additives to inhibit the wear of cylinder liner-piston ring of Marine diesel engines.

Friction and Wear Performances of Materials for Wind Turbine Sliding Bearing Bushes

This study aimed to enhance the friction and wear characteristics of materials for wind turbine sliding-bearing bushes operating under low-speed and heavy-load conditions. To this end, a high-entropy CoCrFeNiMo alloy coating was applied to the surface of 9Cr18 bearing steel, and Ni-Cr-Mo-Si alloy coating was applied to MTCrMoCu30 wear-resistant cast iron using laser cladding. The effects of varying loads on the friction and wear properties of these coatings were investigated, and the friction and wear properties were compared. Furthermore, the overall priority indices for both groups of bearing bush coatings were assessed. The findings indicated that the friction coefficient, wear quality, and wear rate of CoCrFeNiMo high-entropy alloy coating initially decreased and then increased with the increase in applied load, dominated by abrasive wear. By contrast, the friction coefficient of the Ni-Cr-Mo-Si alloy coating increased, and wear quality and wear rate initially increased and then decreased, indicating the coexistence of adhesive wear and abrasive wear. Therefore, Ni-Cr-Mo-Si alloy coating exhibited a high overall priority index and favorable friction and wear properties.

Static voltage stability considering reactive power limit of salient synchronous generator and active power loss of exciter

With increasing load, it is difficult to maintain power system static voltage stability (SVS). The existing SVS analysis based on the reactive power limit (RPL) of the non-salient synchronous generator (SG) and ignoring the exciter’s loss is inaccurate. This paper proposes an SVS model with exact description to the SG. The novelties are: (1) Seeing that the SVS is deteriorated when the SG reaches the RPL, a solution to the RPL of the salient SG with different reactances along the direct and quadrature axis is newly proposed. (2) The active power loss of the exciter of the SG is newly included in the power flow and the SVS analysis. (3) By deriving the sensitivity of the L index with respect to the load, an index is newly defined to quantify the dependency of the SVS on the RPL. The simulation results show that the RPL of the salient SG considering the stator resistance is narrower. The active power loss of the exciter has more obvious impact on the power flow under heavier loading conditions. When the proposed index is positive, the RPL instead of the L index is more critical to maintain the SVS.

Mesh stiffness calculation of defective gear system under lubrication with automated assessment of surface defects using convolutional neural networks

As typical failure mode of gear system, the tooth surface pitting, spalling can be detected in most long-running gear system, especially under heavy-load and high-speed condition, or under lubricant-starvation condition, the tooth pitting is characterized by irregular contour and random distribution. Most previous study on the defective gear system mainly based on manually detection of defective region, or just rely on geometric simplification of defects, leading to inaccurate results with low-efficient method, therefore, the machine-vision-based defect inspection method is proposed in the study of defective gear system. First, the pitting defects on gear tooth surface is detected and segmented based on involutional neural network U-net, then the tooth surface with segmented defective region is mapped to the elastohydrodynamic lubrication model of spur gear system, finally, the tribological behavior in addition to the mesh stiffness under lubrication condition of defective spur gear system are investigated and discussed. The results reveal that the machine-vision-based defects inspection could improve the accuracy and efficiency of the failure study for gear system.

Cat paw-inspired magnetorheological elastomer embedded mechanical metamaterials with active sensing and switching stiffness for vibration isolator

Real-time vibration monitoring, assessment, and isolation play critical roles in the safety and maintenance of engineering industries and traffic facilities. Recently, magnetorheological elastomers (MRE) with tunable stiffness have been considered promising solutions for vibration isolation. However, for some heavy-load conditions, such as motors or machine tools, MRE vibration isolators are insufficient for realizing vibration sensing and high bearing capacity. Therefore, it is critical to design a novel MRE isolator system that enables real-time vibration monitoring, isolation, and bearing capacity. Herein, we propose a cat's paw-inspired oct-MRE vibration isolator coupled with a soft MRE for energy buffering embedded in octet metamaterials to support the load. For vibration sensing, a sliding triboelectric nanogenerator (TENG) was constructed using polytetrafluoroethylene (PTFE) and a copper foil around the oct-MRE inside a vibration isolator to monitor and evaluate the vibration state in real-time. Experimental tests show that our all-in-one vibration isolator can monitor motor vibration accurately and actively modulate it under resonant conditions, the vibration acceleration can be reduced from 17.0 m/s2 to 12.9 m/s2. This study provides an ideal solution for intelligent health monitoring of motors and other autonomous, smart, and long-term engineering tasks.

Polycarboxylate superplasticizer modified 3D graphene as long-term-efficient water-based lubricating additive under heavy load conditions

At present, due to the excellent properties of graphene, which can significantly enhance the performance of lubricants, researchers are conducting extensive studies on it. However, the poor dispersion of graphene limits its application in lubrication, which becomes an urgent problem for researchers to solve. Moreover, with the concept of green environmental protection becoming more and more popular, the research on water-based lubricants is of great significance. Therefore, we modify three-dimensional graphene (3DG) by polycarboxylate superplasticizer (PCE) to prepare a water-based lubrication nano-additive with long-term dispersion stability, named PCEG. PCEG nanomaterials can stably disperse in water for more than three months, which effectively solves this problem. Tests show that friction coefficient and wear volume of the lubricant with 0.5 wt% PCEG are reduced by 31.1 % and 23.1 %, respectively, compared to the base fluid at 20 N (2.7 GPa) heavy load conditions. The enhanced lubrication performance is attributed to the fact that PCEG, which has excellent dispersion stability, forms a strong adsorption and continuous dense lubrication film on the friction surface. In addition, it fills and polishes the grooves and pits, thus improving the friction-reduction and anti-wear properties. This study not only greatly solves the problem of poor dispersion stability of graphene and develops a nano-lubricant that is consistently effective under heavy load conditions, but also provides an important reference value for the subsequent development of high-performance and stable graphene-based lubricants.

Research on Bearing Mechanism of Spherical Valve Pairs of Axial Piston Pumps

The hydraulic system drives the cutter head mechanism to realize the excavation of large tunnel boring equipment, which puts forward the technical requirements of high pressure and large flow to the pump source. The traditional small displacement axial piston pump uses a planar valve plate. However, under high flow and heavy load conditions, the planar valve plate configuration is prone to uneven wear due to the high-pressure and -velocity (PV) value and pressure shock, which ultimately affects the reliability of the system. A simulation analysis of the load-bearing characteristics of the spherical valve plate mechanism is conducted. The Computational Fluid Dynamics (CFD) method was used to construct flow field models for different valve plate oil film structures to calculate differences in their load-bearing capacities. Additionally, the reasons for variations in load-bearing characteristics based on the curvature radius of the spherical valve plate were analyzed. The simulation results demonstrate that the spherical valve plate exhibits superior leak and load-bearing performance compared to the traditional flat valve plate. Furthermore, the curvature radius of the spherical valve plate directly affects the pulsation characteristics of the piston pump. Smaller curvature radii increase the contact area of the oil film, resulting in greater fluctuation in oil film load-bearing, whereas larger curvature radii lead to increased oil film leakage. Using simulation calculations on heavy-load, high-displacement axial piston pumps, it is determined that the optimal curvature radius for stable load-bearing is 350 mm.

Analyzing the age of information in prioritized status update systems under an interruption-based hybrid discipline

Motivated by real-life applications, a special research-work interest has been recently directed towards the prioritized status update systems, which prioritize the update streams according to their timeliness constraints. The preferential service treatment between priority classes is commonly based on classical disciplines, preemption and non-preemption. However, both disciplines fail to give an even satisfaction between all classes. In our work, an interruption-based hybrid preemptive/non-preemptive discipline is proposed under a single-buffer system modeled as an M/M/1/2 priority queueing system. Each class being served (resp. buffered) can be preempted unless its recorded number of service preemptions reaches the predetermined in-service (resp. in-waiting) threshold. All thresholds between classes are the controlling parameters of the whole system’s performance. Using the stochastic hybrid system approach, the age of information (AoI) performance metric is analyzed in terms of its statistical average along with the higher-order moments, considering a general number of priority classes. Closed-form results are also obtained for some special cases, giving analytical insights about the AoI stability in heavy loading conditions. The average AoI and its dispersion are numerically investigated for the case of a three-class network. The significance of the proposed model is manifested in achieving a compromise satisfaction between all priority classes by a thorough adjustment of its threshold parameters. Two approaches are proposed to clarify the adjustment of these parameters. It turned out that the proposed hybrid discipline compensates for the limited buffer resource, achieving more promising performance with low design complexity and low cost. Moreover, the proposed scheme can operate under a wider span of the total offered load, through which the whole network satisfaction can be optimized under some legitimate constraints on the age-sensitive classes.

Effects of the Shaft Speed on Stiffness and Damping Coefficients of Hydrodynamic Bearing-Shaft System under Variable Viscosity

The rotating shaft-hydrodynamic bearings systems operated with high speed and/or heavy load conditions expose serious rotor-dynamics instability problems due to characteristics of the supporting bearings. The stability and the dynamics of these systems, directly relate to the lubricant properties that are directly affect by the heat generation. In this study, the dynamic characteristics of a shaft-hydrodynamic journal bearing and its stability were investigated under variable viscosity. The equations of lubricant flow were derived by Dowson’s equation under variable viscosity, and the perturbation equations were obtained for 2 degrees-of-freedom system. The heat transfers between oil and the journal surface was modelled in a 3-dimensional energy equation, and the heat transfer on the journal structure was also modelled with heat conduction equation. An algorithm based on finite difference scheme with successive over relaxation method was developed to solve the theoretical models, simultaneously, and a serial simulation was performed to investigate the variations of the dynamic coefficients of the bearing-shaft system concerning the rotating speed for different radial clearance values. It was determined that the high speed increases the lubricant temperature, and so the static and dynamic performance characteristics decrease, moreover, this effect is more dominant for the smaller radial clearance.

Numerical and experimental analysis on the whirl orbit with inner loop in cracked rotor system

Cracks in rotor systems are generated because of internal as well as external heavy loading conditions. The external loading conditions could be attributed to thermal gradients (such as in turbomachinery) or other environmental conditions that result in cracks developments. The internal loading conditions can be attributed to cyclic fatigue loading during continuous and recurrent shaft's running which is the most common cause for cracks propagation. The presence of cracks in rotor systems induces nonlinearities into the system which affects its whirl response. Many published literature on cracked rotors have indicated that when the rotational speed is at sub-critical resonance of order 1/n (1/2, 1/3,1/4, etc.…) of the critical rotational speed, the fundamental whirl orbit takes patterns including inner loop/loops of order (n-1) or outer loop/loops of order (n+1) depending on the critical whirling direction. The present study investigates the strong impact of the magnitude of unbalance force on whirling pattern with inner loop in a cracked rotor. Numerical analysis is carried out on the mathematical model of the considered cracked rotor. The unbalance force magnitude is observed to be the main factor affecting the inner loop pattern in the whirl orbit rather than the ½ of the critical resonance speed. Accordingly, the appearance of inner loop in shaft's whirl orbit due to crack propagation in the rotor system is found here to be present before and after passing through resonance speed. This inner loop whirl orbit pattern is not restricted to be associated with ½ of the critical rotational speed as believed in plenty of literature. This kind of whirling is observed to be strongly depending on the unbalance force magnitude rather than the subcritical resonance speed. The experimental results also validate the numerical simulation findings. Therefore, the whirl orbits of the cracked rotor can be categorized into pre-resonance whirl orbit (Pr-WO), resonance whirl orbit (R-WO) and post-resonance whirl orbit (Po-WO) based on the magnitude of the unbalance force. The resultant numerical and experimental findings on the whirl orbit with inner loop can provide a robust insight into the cracked rotor whirl behavior.

Modal and fatigue characteristics analysis of key components of tower crane

In order to ensure good stability and safety of the tower crane under long-term heavy load conditions, modal analysis and fatigue analysis were conducted on its key components, including standard section and frame section. The connection points of each truss structure were regarded as indivisible common nodes, and the model was simplified and parameterized, resulting in improved mesh quality and computational efficiency. Based on Pro/E, standard section and frame section models were established and imported into Workbench through intermediate data formats for simulation calculations in modal and static structural modules. By calculation, the natural frequency and modal shape of the standard section, as well as the lifespan, damage, and safety factor of the frame section, were obtained. It can be seen that the standard section has good structural stability and can maintain relative balance under excitation in different directions and degrees of freedom. If the safety factor of the web components is high and the service life is improved from a structural perspective, it can be considered to increase the thickness of the chord members.

Thermal and viscoelastic coupled influences analysis on mixed lubrication in dynamic journal bearings

The interaction of temperature variations and viscoelastic deformation is critical in dynamically loaded journal bearings, especially under fluctuating heavy load conditions. Previous studies have not fully explored the coupling of these two factors. Addressing this gap, this research introduces a novel transient mixed lubrication model that simultaneously considers thermal and viscoelastic effects. This model reveals intricate dynamics influencing the lubrication performance of journal bearings. The findings show that the combined impact of thermal and viscoelastic factors significantly alters the amplitude and phase of lubrication performance parameters. Notably, thermal effects tend to decrease oil film pressure while increasing asperity contact pressure, whereas viscoelastic effects enhance the oil film pressure peak and adjust its phase, concurrently reducing asperity contact pressure. Moreover, varying the eccentric speed profoundly influences the interplay between bearing thermal and viscoelastic effects. This study contributes to a deeper understanding of mixed lubrication in journal bearings and provides technical support for more accurate and predictive reliability improvement in complex mechanical systems.

Investigation of the interfacial bonding of new and old pavement materials for pothole applications: Bonding materials optimization, mechanical properties and structural performance

Under the combined effects of heavy traffic loading and extreme environmental conditions, the failure issues of repaired potholes caused by insufficient interfacial bonding strength between the new and old pavement materials occur frequently, which severely impairs the durability of the repaired structure. This study aims to improve the interfacial bonding strength between the new and old pavement materials and prolong the service life of repair pothole materials. Firstly, the mechanical analysis was carried out using finite element simulation, and a technical measure was proposed to ensure improved interfacial bonding strength between new and old pavement materials. Secondly, emulsified asphalt (EA), light asphalt (LA), waterborne epoxy resin-modified emulsified asphalt (WER-EA) and silicone penetrant (SP) were selected to investigate the paving workability, viscosity changing and curing times of bonding materials at different temperatures. On this basis, the interlaminar shear and pull-out tests were performed under different paving mass, temperatures and humidity conditions, and the shear and pull-out strengths of four bonding materials were compared to optimize the type and paving mass of interface bonding material. The results show that an increase in bonding coefficient (BC) significantly reduces the values of pressure stress (σy) and pressure strain (εy), even the bucking depth of the pothole sides, thus decreasing the risk of pothole repair failure. Under normal or low-temperature conditions and field construction, SP has exceptional paving workability, and its shear and pull-out strengths are much higher than other bonding materials, with an optimum paving mass rate being 0.3 kg/m2 ∼ 0.4 kg/m2. The research results are of great significance in improving the pothole repairing level, standardizing the repair process and extending the service life of pavements.

A new fault component selection strategy based on statistical detection for slewing bearing weak signal de-noising

Slewing bearing is a critical transmission component in large-size construction machinery due to its low-speed and heavy-load conditions. Fault prognostics and health management of slewing bearing are crucial for ensuring their high availability and profitable operation. However, the presence of background noise in construction machinery signals restricts the applicability of existing signal processing approaches in prognostics and health management. To address this challenge, a novel signal de-noising method is proposed based on adaptive decomposition, along with a new strategy for recognizing fault components using statistic detection through kernel principal component analysis (KPCA). First, robust local mean decomposition is utilized to adaptively decompose the fault and normal vibration signal over the entire service life. Then, product functions (PFs) decomposed by fault and normal vibration signal are used for KPCA anomaly detection. Finally, the fault PFs are reconstructed to obtain the de-noised signal. The effectiveness of the proposed method is validated through the use of both simulated and experimental vibration signals obtained from a slewing-bearing life-cycle test. The results illustrate that the proposed method has superior de-noising capability and decomposition efficiency, making it an effective signal preprocessing technique for prognostics and health management.

Composite thermal oil film lubrication model for hybrid journal bearings

Hybrid journal bearings are crucial components in many equipment, such as nuclear reactor cooling pumps and hydraulic motors. However, there exists a significant challenge to understand the lubrication behaviors of hybrid bearings with multiple thermal effects at low-speed, heavy-load conditions. Therefore, a composite thermal lubrication model is proposed, which includes four thermal effects: edge suction heat, hydrostatic pressure loss heat, oil viscous friction heat, and asperity friction heat. The lubrication and contact model are modified by actual rough surfaces to evaluate friction heat accurately. The experiments from a homemade testing rig verify the model well. Friction and temperature characteristics of the hybrid bearing are obtained, and the influence of hydraulic pressure and speed on four types of heat are analyzed.