Heavy Load Conditions Research Articles

Research on the performance of frequency tracking methods for the ultrasonic machining system considering the influence of impedance matching unit

In power ultrasonic systems, impedance matching is a critical technique which enables electrical energy to be fully utilized by the transducer. However, the electrical parameters of the transducer will change when thermal-force loads are applied in the application scenario. Although the transducer can be operated at the optimum frequency point by using resonance frequency tracking (RFT), there is a certain tracking error when tracking the resonant frequency of the transducer in the loaded condition due to the impedance matching unit. To improve the RFT accuracy and the stability of the ultrasonic system, an ultrasonic system with RFT function was designed in this research. Then four commonly used matching topologies were introduced. Secondly, the electrical parameter drift patterns of the ultrasonic device were explored. Based on the patterns, the impedance characteristics of the transducer with four matching topologies after being loaded were revealed. Finally, the theory and experiments were combined to reveal the influence of matching topology and loading effect on the output characteristics of the transducer. The results showed that the Ls and LCL topologies have better resistance to load fluctuation. Meanwhile, after Ls and LCL matching, the phase-locked loop method still has good RFT performance under heavy load conditions. This study can guide the selection of the transducer’s matching topology and RFT methods.

PDCF-DRL: a contention window backoff scheme based on deep reinforcement learning for differentiating access categories

AbstractIn wireless networks, the Contention Window (CW) is a crucial parameter for wireless channel sharing among numerous stations, directly influencing overall network performance. With the rapid growth and increasing diversity of traffic in wireless networks, differentiating and serving various types of traffic to enhance network performance has become a pressing issue that needs to be addressed. Deep Reinforcement Learning (DRL) optimizes decision-making through the interaction between an agent and its environment, enabling it to handle complex state spaces and high-dimensional data, making it particularly suitable for dynamically adjusting the contention window and adapting to environmental changes in real time. Access Category (AC) is used to differentiate various types of traffic to support different quality of service (QoS) requirements. Therefore, this paper proposes the integration of DRL techniques into the EDCA mechanism, utilizing AC to differentiate network traffic, while the DRL technology adjusts the contention window to adequately ensure QoS for different types of traffic and enhance overall network performance. This paper proposes a CW back off scheme based on DRL for differentiating ACs. The scheme uses DRL technology to observe the channel collision rate and sense the current network conditions, thereby adaptively adjusting the CW size for ACs. In addition, it dynamically adjusts the back off strategy according to the perceived current network conditions to optimize the data transmission process. In the range of 20–120 stations, the scheme was tested in both single AC and multiple AC traffic scenarios, demonstrating excellent performance. The collision rate consistently remained below 18%, while the normalized throughput was maintained above 76%. Additionally, there is a significant improvement compared to existing deep reinforcement learning-based optimization schemes. Experimental results show that this scheme effectively discriminates between different ACs, resulting in lower latency and higher throughput for high-priority traffic. Furthermore, adaptively adjusting the CW size and improving the back off strategy maintains a low collision rate and stable throughput even under heavy load conditions, significantly improving the overall network performance.

Asperity interaction induced vibration excitation of cylindrical roller bearings with localized defect

Asperity interaction induced vibration excitation of cylindrical roller bearings with localized defect

Design and optimization of the jet cooling structure for permanent magnet synchronous motor

Permanent magnet synchronous motor (PMSM) is widely used in electric vehicles due to its high power density and wide speed range. However, when operating under long-term heavy load conditions, PMSM is prone to heat accumulation. It’s difficult to cool the motor with existing indirect cooling structures efficiently, which may lead to its high temperature and result in winding burnout or even permanent demagnetization of the magnets. In this paper, a novel cooling structure based on jet cooling is proposed to reduce the operating temperature of the PMSM efficiently and improve its stability. The temperature field model, which accounts for the influence of end windings, is developed to analyze and optimize the parameters of the jet cooling structure, leading to the determination of an optimal parameter set. By exploring the cooling effects of motors with different cooling structures under stable, extreme and mixed cycle operating conditions, it is proved that the jet cooling structure designed in this paper can effectively reduce the temperature of the motor and ensure its reliable operation. The results show that with the influence of the jet cooling structure designed in this paper, the maximum temperatures of the rotor and winding are reduced by 35.2℃ and 44.5℃ respectively.

Effect of bionic shield texture on friction behavior of silicon carbide under water lubrication condition

Abstract Reasonable texture parameters can effectively generate local dynamic pressure effects and promote the formation of lubrication film. The synergistic friction reduction mechanism of the shield-shaped texture on the Silicon Carbide (SiC) surface under water-based lubrication conditions between the flow pressure effect and the ‘rolling ball’ effect is investigated by combining simulation analysis and friction experiments. The effects of shield textured surface on the friction and wear characteristics of SiC surface and the characteristics of interfacial polarization electric field under different rotational speeds and different load conditions were analyzed. The results display that synergistic texture lubrication has a beneficial effect on improving tribological properties. The surface with 6% texture area occupancy showed the best tribological characteristics. The surface with a textured area occupancy of 6% displays the optimal tribological properties. Moreover, the friction reduction mechanisms under different working conditions are discussed, with the textured uniformly arranged surfaces being more suitable for high-speed and heavy load (140 N, 2000 rpm) conditions and the textured non-uniformly arranged surfaces being more suitable for low-speed and light load (40 N, 400 rpm) conditions.

The investigation of nonlinear dynamic characteristics of spur gear with angular misalignment error based on an improved dynamic model

Angular misalignment error is a prevalent occurrence in gear systems, mainly caused by manufacturing and installation errors in gearbox components. This significantly impacts the meshing characteristics of the system, making it necessary to carry out the nonlinear dynamic analysis of spur gear pairs with angular misalignment errors. In this study, a meshing stiffness model for a spur gear pair with angular misalignment error is established based on the Load Teeth Contact Analysis (LTCA) method. The effect of misalignment errors on the distribution of tooth surface stiffness are analyzed. Additionally, an improved dynamic model considering angular misalignment errors and variable backlash along the tooth width direction was proposed based on the lumped mass method and the slicing method. The effects of angular misalignment errors parallel and perpendicular to the meshing plane on the nonlinear dynamics of the system were studied. Frequency domain diagrams, Poincaré diagrams, and bifurcation diagrams were employed to comprehensively analyze the nonlinear characteristics of the system. The results indicate that with light loads, the system experiences a sequence of periodic and chaotic motions as θa increases, eventually returning to periodic motion. Conversely, θv shows minimal influence on the gear backlash, with the system exhibiting periodic motion when θv is small. As θv increases, the system transitions to chaotic motion before ultimately returning to periodic motion. Under heavy load conditions, as θa increases, the system transitions gradually from chaotic to periodic motion. However, regardless of the variations in θv, the system consistently remains in periodic motion.

Analysis of tooth root three-dimensional fatigue crack initiation, propagation, and fatigue life for spur gear transmission

The gears in aviation gear systems are susceptible to fatigue fracture due to high-speed, heavy-load, and load alternation operating conditions. Therefore, a numerical calculation model with multiple mesh positions loading form has been proposed in this paper to analyze the fatigue crack initiation and propagation behavior, and to estimate the fatigue life of these gears. The fatigue life of the gear is determined by separately calculating the fatigue crack initiation life and the fatigue crack propagation life. The tooth root fatigue stress and the fatigue initiation life are calculated by the multi-axial fatigue life prediction method with the Smith-Watson-Topper criterion and the critical plane method. Afterwards, the tooth root stress–strain field is calculated in Finite element (FE) software and the stress intensity factors of the crack tip are calculated in three-dimensional (3D) crack analysis software. Then, the tooth root fatigue crack propagation trajectory and the fatigue crack propagation life are obtained separately. Finally, the influence mechanism of the loading conditions, the geometry parameters of gears, and the initial crack positions on the tooth root fatigue crack initiation life, propagation life, and fatigue crack propagation trajectory are analyzed, and a tooth fatigue test bench is built for verifying the crack propagation trajectory.

A novel RuP2-infused heteroatom-doped porous carbon for high-durability lithium-sulfur batteries

Nitrogen and phosphorus co-doped three-dimensional porous carbon encapsulated ruthenium diphosphide (PCS900@RuP2-2) is successfully synthesized via a phytic acid-assisted phosphating process. The resulting RuP2 nanoparticles, ranging in size from 10 to 50 nm, are encapsulated within a carbon matrix, providing a stable catalytic structure. Nitrogen adsorption and desorption tests reveal that PCS900@RuP2-2/S possesses a high specific surface area and a rich micro/mesoporous structure. This high porosity facilitates multi-directional ion diffusion and offers ample buffer space to accommodate sulfur volume expansion during cycling. Density functional theory (DFT) calculations confirm that PCS900@RuP2-2/S enables efficient adsorption of soluble polysulfides, thereby minimizing the notorious "shuttle effect." Electrochemical testing demonstrates the remarkable durability of PCS900@RuP2-2/S. After 500 cycles at a 1 C current density, the reversible capacity remains at 511.6 mAh g⁻¹, with an average capacity decay rate of just 0.047 % per cycle. Even under heavy sulfur loading conditions (4.2 mg cm⁻²), the composite maintains a high reversible capacity of 386.6 mAh g⁻¹ after 500 cycles. The combination of high porosity, stable catalytic structure, and efficient redox reaction facilitation contributes to the exceptional performance and longevity of PCS900@RuP2–2/S.

Predictive Model for Scuffing Temperature Field Rise of Spiral Bevel Gears under Different Machining Conditions

Spiral bevel gears are extensively employed in mechanical transmissions; however, they are prone to adhesive wear when operating under high-speed and heavy-load conditions. Research indicates that the tooth surface roughness of gears significantly influences the friction and wear of the meshing gears. The present study delves into the origins of tooth surface roughness through the integration of the W-M function and fractal theory. Utilizing an involute helical gear with surface roughness for tooth cutting, a three-dimensional model is established with roughened tooth surfaces. This paper introduces an approach to developing three-dimensional gear models with roughness and applies the finite element method to perform thermodynamic analysis on gears exhibiting diverse levels of surface roughness. The thermal analysis of gears with varying degrees of roughness was conducted using the finite element method. Comparative analysis of the results under specific operating conditions elucidated the impact of roughness on tooth surface temperature rise. In order to validate the simulation model, an experimental test platform for spiral bevel gears of identical size was established. This model integrates tooth surface roughness with thermodynamic analysis, allowing for the rapid assessment of tooth surface temperature rise under different machining conditions, and reducing the cost of validating predicted tooth surface load-carrying capacity.

Study on the Influence Law of Micro-Scale Abrasive Wear on a Wind Turbine Brake Pad

The hard particles in the copper-based powder metallurgic material of a brake pad for a wind turbine brake falls off and presses into the surface of the brake disc to form abrasive particles under high-speed and heavy-load working conditions. The presence of abrasive particles will produce abrasive wear with micro-scratch and micro-scribe on the copper-based material of the brake pad. The critical scratch depth effect in the abrasive wear process is proposed based on the critical depth effect of the metal removal process at the micro-scale. The abrasive wear is divided into two types: scratch wear and scratch wear, which is proposed according to the comparison of the actual scratch depth and the critical scratch depth. The range of braking speeds and friction coefficients in abrasive wear is determined by the recommended parameters of the disc brake. The ABAQUS2020 software is used to simulate and analyze the micro-scale abrasive wear of a brake pad. The brake strain/stress curves of the brake pad under different brake speeds and friction coefficients are compared and analyzed for two abrasive wear types based on the range of braking parameters, and the key factors affecting abrasive wear are proposed.

Energy-saving cruise control method for heavy-duty transport vehicle based on pump-valve coordinated drive

In order to realize the dual-goal of the improvement in the cruise performance and fuel economy of the heavy-duty transport vehicle (HDTV) for the transfer of the prefabricated box-girder in the construction of high-speed railway, a pump-valve parallel coordinated drive scheme is designed on the basis of the hydrostatic drive system of the HDTV, which combines the load-sensing valve control system and hydrostatic pump control system. Furthermore, the pump-valve coordinated controller (PVC) is also proposed to ensure the cooperation of the two systems, which adopts power following control strategy to control engine speed, the pump and motor displacement respectively, thus achieving the rough adjustment of the cruise velocity. The linear quadratic regulator (LQR) based on the full-state closed-loop feedback is introduced in PVC to control the proportional direction-valve (EPDV) and compensate for the velocity errors, thus realizing the fine adjustment of cruise velocity. A semi-physical experimental test-platform for the HDTV is established to conduct contrast tests between the rule-based controller (RBC) and the proposed PVC under different operating conditions. The results indicate that the PVC effectively reduces the velocity error, the total error is decreased by 80.6% and that of the maximum error is 43.4% under empty-load conditions, and under heavy load conditions, the total error is lowered by 82.1% and that of the maximum error is 46.8%. Moreover, the PVC also brings down the fuel consumption rate of the HDTV, with a maximum reduction of 27.6% and a minimum of 11.4%.

Effects of propeller cavitation on ship propulsion performance in off-design operating conditions

The propeller cavitation is closely related with its hydrodynamic performance. When the propeller works in the cavitating flow, the propeller hydrodynamic performance, in terms of thrust and torque coefficients, is reduced due to the propeller cavitation. When the high-speed and high-power ship sails in adverse sea, the varying loads on propeller will cause severer cavitation on propeller. The reduction in propulsion performance caused by cavitation will further affect the propulsion system, impacting the ship sailing performance and safety. The VP1304 propeller cavitation CFD simulation are conducted to validate the CFD method. Furthermore, the influence of propeller advance ratio and cavitation numbers on the performance of low-speed high-power series propeller in cavitating flow are studied and illustrated. This influence of cavitation has also been transferred to the propulsion system and this process are calculated by the ship propulsion system numerical model. Additionally, the sailing performance of ship propulsion system under off-design conditions, where the cavitation is more likely to occur, has been investigated in this article. Under severe heavy load conditions, it can even result in a complete loss of propulsion capability, posing significant risks. Therefore, it is necessary to further optimize control strategies for the propulsion system to mitigate the hazards caused by cavitation.

A wideband high-PSR OCL LDO using a gain-relaxed OTA featuring dynamic complex zeros frequency compensation

This article proposes an Output-Capacitor-Less (OCL) Low-Dropout (LDO) regulator with an assisted positive feedback loop technique, which mimics a negative resistance, along with a single common-gate stage. Conventional techniques utilize multistage high-gain OTA to achieve a high DC loop gain. However, such an OTA suffers from high power consumption and sophisticated frequency compensation mechanisms. Instead, the use of a single-stage relatively low-gain OTA helps to extend the bandwidth. Then, the overall DC loop gain is maximized by the proposal of a novel negative resistance circuit. To further improve the PSR, a bulk-driven ripple canceling path that is insensitive to process corners is proposed making the LDO suitable for high-PSR applications. Stability is another challenge in the design of OCL LDOs due to its associated complex poles. We propose a new frequency compensation technique by introducing two complex zeros to eliminate these complex poles. Hence, the overall stability is improved. Since these complex poles location vary from light to heavy loads, the proposed zeros dynamically change accordingly. Besides, this suggested mechanism has been analyzed using the generalized time-and-transfer constants (TTCs) circuit analysis technique. Under heavy load conditions, the suggested LDO has attained phase and gain margins of 62.8° and 29 dB, respectively. Moreover, Monte Carlo simulations along with process and temperature variations have been investigated to prove the reliability of such a frequency compensation technique. The proposed LDO has been implemented in 65 nm CMOS technology node with a short pass transistor length of 100nm. The simulation results reveals that the LDO draws 299.4μA of quiescent current under light load conditions and 296.8μA under heavy load conditions (including the bandgap voltage reference). The suggested LDO functions at 1.2V supply voltage, delivers 0.93V output voltage and can handle a load current up to 10mA with load regulation of 17μV/mA, line regulation of 2.22mV/V, and PSR of −48.7dB at low frequencies. The PSR at 1MHz is at least −32.5dB which is superior to the reported recent LDOs.

High-strength and wear-resistant Babbitt alloy coatings prepared through in-situ alloying

Babbitt alloy, a commonly used wear-resistant coating material, has a low hardness. This causes severe plastic deformation, detachment or heavy wear to easily occur under low speed and heavy-load service conditions, reducing its service life. To solve these problems and improve the bonding strength and wear resistance of the tin-based Babbitt alloy coating, a higher laser cladding power was adopted to achieve in-situ alloying of the cladding layer and enhance the strength of the coating. The increase in strength was verified through the Fleischer theory and Orowan empirical formula to mainly result from the enhancement of solid solution strengthening and dispersion strengthening. Meanwhile, due to dispersion strengthening and the presence of dendritic FeSn, the occurrence of delamination wear was effectively prevented. The bonding strength of the final sample reached 147 MPa, and the wear rate was as low as 4.24 × 10–5 mm3/N・m. Thus, a high-strength and wear-resistant Babbitt alloy cladding layer was obtained.

Frictional Wear Behavior of Water-Lubrication Resin Matrix Composites under Low Speed and Heavy Load Conditions.

Resin matrix composites are commonly utilized in water-lubricated stern tube bearings for warship propulsion systems. Low-speed and high-load conditions are significant factors influencing the tribological properties of stern tube bearings. The wear characteristics of resin-based laminated composites (RLCs), resin-based winding composites (RWCs), and resin-based homogeneous polymer (RHP) blocks were investigated under simulated environmental conditions using a ring-on-block wear tester. Simulated seawater was prepared by combining sodium chloride with distilled water. The wetting angle, coefficient of friction (COF), and mass loss were measured and compared. Additionally, their surface morphologies were examined. The results indicate a significant increase in the COFs for the three materials with an increased speed or load under dry conditions. The COF of the RLCs is the lowest, indicating that it has superior self-lubricating properties. In wet conditions, the COFs of the three materials decrease with an increasing speed or load, exhibiting a pronounced hydrodynamic effect. The COF and mass loss of RWCs are the highest, while RLCs and RHP exhibit lower COFs and mass loss values. The reticulated texture and flocculent fibers on the surface of RLC enhance the heat diffusion and improve the material wettability and water storage capacity. The surface of RWC is dense, and the friction area under dry conditions is melted and brightened. The surface of RHP is smooth, while the worn material forms an agglomerate and exhibits susceptibility to burning and blackening under dry conditions. The laminated formation method demonstrates superior tribological performance throughout the wear evolution process.

Enhancement of tribological performance of PTFE/aramid fabric liner under high-temperature and heavy-load through incorporation of microcapsule/CF multilayer composite structure

Liners suffer from low service life under high-temperature and heavy-load conditions, hindering their widespread use in aerospace applications. A novel strategy of incorporating polyaryl ether sulfone/polymethylphenlsiloxane (PES/PMPS) microcapsules and carbon fibers (CFs) into the polytetrafluoroethylene (PTFE)/aramid fabric liner was used. At the micro-scale level, the worn surface morphology and the transfer film morphology were analyzed to reveal the tribological mechanisms. At the nano-scale level, molecular dynamics simulation was used to analyze the formation mechanism of the transfer film. The results showed that the friction coefficient and wear rate of the liner with microcapsule/CF multilayer structure were reduced by 17 % and 24 %, respectively. The incorporation of microcapsule/CF multilayer structure can be effectively applied to enhance the tribological performance of liners in harsh operating conditions.

The PVT limit for gear scuffing assessment

The growing interest in gear scuffing research primarily stems from the escalating standards and operation requirements in aero-engines and electric vehicles, particularly under high-temperature, high-speed, and heavy-load conditions. Existing calculation standards for gear scuffing often deviate when evaluating the load-carrying capacity under different rotational speeds or oil temperatures, thus undermining the reliability of gear scuffing assessments. To address this, thirty-five sets of gear scuffing experiments were conducted with different materials, manufacturing processes, and lubrication conditions. A new evaluation method based on the pressure-velocity-temperature (PVT) limit was proposed for assessing gear scuffing resistance. Using a non-dominated genetic algorithm, exponent coefficients for the contact pressure P, sliding velocity V, and lubricant temperature T were determined. The results demonstrated that the proposed PVT limit effectively evaluates gear scuffing resistance across various conditions. The PVT limits across different operating scenarios, under the same material, manufacturing process, and lubrication conditions, showed a maximum deviation of 6.6%. Conversely, the scuffing temperatures calculated using ISO 6336-20-2017 and AGMA 925-A03-2003 standards deviate from experimental results by up to 36.7% and 32.8%, respectively. Further application of the PVT limit to an aero-engine accessory gearbox confirmed the practical applicability of the proposed method.

Effect of Cu content on the microstructure and properties of sintered Fe-0.8C-xCu antifriction materials

Abstract Ferrous antifriction materials (FAMs) play a crucial role in powder metallurgy. Previous studies have primarily focused on exploring the antifriction properties of Fe-C-Cu materials with low copper content (0–5 wt%), while there have been fewer studies on high copper content FAMs. In this study, to investigate the effect of Cu content on the microstructure and properties of sintered FAMs, Fe-0.8C-xCu (x = 5–25 wt%) materials were prepared by powder metallurgy method. The density, microstructure, mechanical performance, friction and wear properties of the samples were analyzed. The results demonstrated a significant change in the relative density, hardness, friction and wear properties of sintered Fe-0.8C-xCu samples with increasing Cu content. Particularly, the Fe-0.8C-15Cu samples exhibited outstanding properties, with a relative density of 77.8%, a hardness of 43 HRB, crushing strength of 380 MPa, an average friction coefficient of 0.21, and a wear rate of 1.36 × 10−8 mm3 N·mm−1. The primary wear mechanisms of the Fe-0.8C-xCu specimens include abrasive wear, adhesion wear, chafing fatigue, pitting, and oxidation. This study aims to provide an experimental and theoretical basis for the development of ferrous antifriction materials suitable for heavy-load conditions.

Assessment of the Uniform Wear Bending Strength of Large Modulus Rack and Pinion Pair: Theoretical vs. Experimental Results

Due to long-term operation under low-speed and heavy-load conditions, large module gears and racks are inevitably subject to tooth surface wear. To investigate the changes in gear tooth bending strength, the Three Gorges ship lift was taken as the research object and a simulation test bench was established. An analytical method, a finite element method, and an experimental method were utilized to analyze the bending stress of gears under normal and various uniform wear conditions. The obtained results revealed that with the increase in wear degree and load, the bending stress of single-tooth meshing was significantly higher than that of double-tooth meshing, and the single-tooth meshing time also increased, which indicates that gear wear accelerated the process of performance degradation. Furthermore, the relative errors obtained by the three calculation methods were all at a low level. This investigation aims to provide a solid theoretical and experimental basis for the dynamic analysis of large module gear and rack transmission.

Influences of Surface Texture on the Friction Characteristics of Powder Metallurgy Clutch Disks

Many studies have consistently demonstrated the positive effects of surface texture on the performance of friction couples. Circular dimple textures are made on the flat surfaces of the copper-based powder metallurgy friction disk samples from a multi-disk clutch with five different circular densities. Long-term pin-on-disk sliding experiments under different loads are conducted. Surface morphology analysis is also conducted to evaluate the wear characteristics of the sample disks. Results show that the working load does not significantly affect the coefficient of friction (COF) of the flat surface samples, but there exist significant differences of the COF at different radii with the same rotation speed. Compared with the flat surface samples, the textured samples have a 20–65% decrease of COF under light load conditions but have a more than 30% increase under heavy load conditions. Furthermore, the wear of the textured samples is substantially reduced by more than 19% and 40% respectively. Therefore, the circular dimple texture can significantly enhance the friction and wear performances of the copper-based powder metallurgy friction disks, especially under heavy load working conditions.