Under high torque and extended duty cycles, current-only control can become less effective as magnetic saturation limits further torque increase, temperature rise weakens the MR-fluid yield stress, and hysteresis affects repeatability. This study develops a coordinated gap-current torque control strategy for a variable-gap multi-disc MR brake, in which bracket displacement and coil current are scheduled together. The control framework integrates weighted multi-criteria gap allocation, feedforward torque-current mapping, and an improved golden jackal optimization (IGJO)-tuned PID loop used only for local current-loop correction. Bench and real-time implementation tests were conducted to evaluate the integrated strategy. For a 60 N & centerdot;m step command, relative to a current-only IGJO-PID baseline, the proposed controller reduced the time to 90% of the target from 0.942 s to 0.607 s, shortened the 2% settling time from 2.308 s to 0.848 s, and reduced the integral of time-weighted absolute error from 18.30 to 8.90. Step tests at 120, 240, and 360 rpm showed no monotonic dependence of the short-duration closed-loop response on rotational speed within the tested range. During loading-unloading staircase tracking over 0-70 N & centerdot;m, stable tracking was maintained, with directional asymmetry mainly concentrated in the 70-60 N & centerdot;m unloading transition. In 0.125 Hz sinusoidal tests, the delay remained about 0.336 s across the tested peak-to-peak torque levels, while amplitude attenuation increased moderately at higher loads. In a 300 s continuous braking test at 60 N & centerdot;m and 120 rpm, the controller maintained a mean torque of 59.923 N & centerdot;m over the main quasi-steady interval with 100% coverage within the 2% error band, although ripple increased toward the end as temperature rose. These results show that coordinated gap-current control improves transient response, tracking consistency, and thermal-drift compensation under the tested operating conditions, while the IGJO-tuned PID acts as a local current-loop corrector within the overall architecture.

BACKGROUND: Slow kVp switching technique is an important approach to realize dual-energy CT (DECT) imaging, but its performance has not been thoroughly investigated yet. OBJECTIVE: This study aims at comparing and evaluating the DECT imaging performance of different slow kVp switching protocols, and thus helps determining the optimal system settings. METHODS: To investigate the impact of energy separation, two different beam filtration schemes are compared: the stationary beam filtration and dynamic beam filtration. Moreover, uniform tube voltage modulation and weighted tube voltage modulation are compared along with various modulation frequencies. A model-based direct decomposition algorithm is employed to generate the water and iodine material bases. Both numerical and physical experiments are conducted to verify the slow kVp switching DECT imaging performance. RESULTS: Numerical and experimental results demonstrate that the material decomposition is less sensitive to beam filtration, voltage modulation type and modulation frequency. As a result, robust material-specific quantitative decomposition can be achieved in slow kVp switching DECT imaging. CONCLUSIONS: Quantitative DECT imaging can be implemented with slow kVp switching under a variety of system settings.

The staggered labyrinth seal is widely used in aerospace, transportation, mining, and other fields due to its advantages of adapting to high speed, reliable sealing performance, and low or even frictionless friction between dynamic and static rotors. The traditional calculation method of labyrinth seal leakage mostly focuses on the fact that the internal medium is an ideal gas and only considers a single effect, which cannot accurately describe the leakage of liquid medium lubricating oil in the labyrinth seal. Therefore, this study focuses on the leakage characteristics of labyrinth seals, and it proposes a leakage calculation method based on liquid medium in view of the shortcomings of existing calculation methods under liquid medium conditions. By considering the thermodynamic and frictional effects of the staggered labyrinth sealing, the resistance loss and thermodynamic effect of the lubricating oil in the sealing cavity were analyzed. The flow field analysis was used to reveal the leakage law of lubricating oil under different conditions, and the factors such as total inlet pressure, spindle speed, and sealing clearance were considered. Finally, the leakage characteristics of the staggered labyrinth seal and the accuracy of the calculation method of the leakage of the staggered labyrinth seal under multiple effects were revealed through experimental verification. This study provides useful guidance for the performance optimization of labyrinth seals in practical applications.

Magneto-rheological Brakes (MRBs) have attracted much attention because of their fast, controllable and adjustable braking performance. During the braking process, a lot of heat was generated by the excitation oil and the friction between magneto-rheological fluid and mechanical parts. The objective of this manuscript is to investigate the effect of temperature on the braking performance of MRB. The thermal distribution of MRB under different excitation current was analyzed through numerical simulation; The braking torque model based on temperature effect was established from microscopic point of view; The braking performance of MRB under different working conditions were tested through MR braking torque test platform, and the results not only revealed the influence of temperature, rotational speed and excitation current on the braking torque, but also verified the rationality and accuracy of the braking torque model. The research results fill the gap in the theoretical model and have important significance for the research on the braking performance of MRBs.

Recently, high internal surfaces for titanium alloy pipes have been required due to the increment of various applications such as aerospace components. In this work, vertical magnetorheological polishing (VMRP) is carried out to achieve high polishing performance on the internal surface of the titanium alloy pipe. A series of comparative experiments were conducted to investigate the polishing mechanism of magnetorheological polishing (MRP) fluid and enhance the polishing performance. It is shown from the experimental results that the VMRP method under the opposite polarity arrangement improves the surface roughness from 47.85% to 83.34% by reducing unwanted vibration and noise during operation. This provides nanoscale surface polishing quality, while such a precision cannot be achieved from the previous horizontal MR polishing apparatus method. It is found that under a 2700 cycle polishing time, a polishing process combining a rough and fine polishing approach with a combination of different particle diameters results in an axial surface roughness of 0.05 μm and circumferential surface roughness of 0.038 μm, respectively. It is also identified that the axial surface roughness of 0.04 μm–0.041 μm is achieved through the combination of high- and low-speed polishing process after 1602 cycles.

Traditional surface polishing methods are no longer able to meet the ultra-precision requirements of the high-tech industry for the inner surface of the pipe, but magnetorheological polishing technology is very suitable due to its advantages of high precision, fast controllability and good deposition stability. However, there is even less investigation on the microforce analysis, chaining mechanism and micromodeling methods of magnetorheological polishing fluid (MRPF), and the polishing mechanism of MRPF has not been explored yet. As a step to completely develop the magnetorheological polishing (MRP) technique, this paper proposed the simulation method of MRPF based on particle dynamics, and the shear stress model of magnetorheological fluid (MRF) is optimized under the action of the magnetic field after performing the chain simulation. On the basis of the optimized shear stress model and the hexagonal close-packed structure of MRF, the holding mechanism of polishing abrasive particles is explored for the MRPF and the corresponding holding models are proposed. Then, the shear yield stress models and material removal model are also established for the inner surface polishing, respectively. Eventually, the above theoretical analysis and related models have been verified though the polishing experiment of the titanium alloy pipe.

This paper presents a novel design scheme of magnetorheological limited slip differential (MR LSD) and analyses its structure and principle. Compared with ordinary differential, the proposed magnetorheological limited slip differential overcomes the disadvantage of "Same torque but different speed" of common differential. The simulation analysis is used to analyse and optimise the damping model. The anti-slip control system of the vehicle model is established based on the fuzzy PID method, and the performance of magnetorheological limited slip differential is studied by using simulation softwares to simulate the vehicle's movement in typical road conditions. The simulation results show that the new magnetorheological limited slip differential proposed in this paper can redistribute the driving torque of the two driving wheels reasonably when the vehicle is skidding, so that the vehicle can overcome skidding and pass the low adhesion road surface.

In this paper, the friction and wear mechanisms of O-ring, commonly used sealing element of magnetorheological damper, were revealed, which has reference significance for seal design, fault diagnosis and life prediction of damper. A series of models of frictional force were established, through calculation and analysis, it was found that the piston rod velocity, particle size and particle mass fraction have certain rules that affect the friction coefficient and the film thickness. Subsequently, the friction and wear test bench of the sealing element of the magnetorheological damper was built, verifying the correctness of the theoretical model. In addition, through the observation of O-rings after the tests under different experimental conditions, the wear mechanism of O-ring is mainly abrasive wear.

The friction and wear characteristics of spike-tooth material (65Mn steel) of Spike-Tooth Harrow in a two-stage peanut harvester were studied in this paper. The friction and wear tests of pin and disc on 65 manganese steel were carried out on the tribometer, then the wear loss and the friction coefficient were studied. The wear loss of the pin was acquired by calculating the mass of the pin before and after the experiment using an electronic balance. According to the actual working environment of peanut spring-finger, four variable parameters are set up: load, speed, soil moisture and soil type. The friction and wear characteristics of pins were studied under different loads, speeds and different soil environments. After wearing, the worn surface of the material was observed by scanning microscope and the wear mechanism was studied. The experimental results show that the wear of the pin increases with the increase of load and decreases with the increase of rotational speed in the same rotation number. Especially in the case of the sandy soil with 20% in moisture, a maximum wear loss of the pin is achieved.

针对传统被动隔振装置隔振效果较差、使用寿命较短的问题,本文以3-RPS并联机构为主体建立并联隔振平台,通过拉格朗日法求解并联隔振平台系统动力学方程,在Matlab/Simulink中设计基于天棚模型的半主动on-off控制器.为解决并联机构系统模型存在非线性化和理想化等问题,应用Sim Mechanics建立并联隔振平台系统物理模型,通过对并联隔振平台单个支链分别进行on-off控制,提高隔振平台的隔振性能.仿真结果表明:相比于被动隔振平台,含有on-off控制器的隔振平台可以有效抑制振幅,具有良好的隔振效果.

This paper presents a new constitutive model of high particles concentrated magnetorheological fluids (MRFs) that is based on the hexagonal close-packed structure, which can reflect the micro-structures of the particles under the magnetic field. Firstly, the particle dynamic simulations for the forces sustained by carbonyl iron powder (CIP) particles of MRFs are performed in order to investigate the particles chain-forming process at different time nodes. Subsequently, according to the force analyses, a hexagonal close-packed structure, which differs from the existing single-chain structure and body-cantered cubic structure, is adopted to formulate a constitutive model of MRFs with high concentration of the magnetic-responsive particles. Several experiments are performed while considering crucial factors that influence on the chain-forming mechanism and, hence, change the field-dependent shear yield stress in order to validate the proposed model. These factors include the magnetic induction intensity, volume fraction and radius of CIP particles, and surfactant coating thickness. It is shown that the proposed modeling approach can predict the field-dependent shear yield stress much better than the single-chain model. In addition, it is identified that the shear yield stress is increased as the particle volume fraction increases and surfactant coating thickness decreases. It is believed that the proposed constitutive model can be effectively used to estimate the field-dependent shear yield stress of MRFs with a high concentration of iron particles.

针对国内汽车悬架研发的需求,测试悬架在各种复杂多变负载下的响应性能是非常重要的一个环节.本文重点分析电液伺服式悬架模拟试验台中电液位置伺服系统的组成及原理,建立伺服系统的模型,并基于MATLAB/Simulink软件,建立1/4非独立悬架模型及伺服系统的仿真模型,根据结构不变性原理和最优控制理论分别设计前馈干扰补偿器和系统最优反馈控制器,并将两种控制器应用于伺服系统,构成基于前馈补偿与最优反馈的复合控制,并将B级和D级路面路谱作为电液伺服系统的输入进行仿真,在给定不同负载力的情况下提高系统的响应速度和跟随精度.仿真结果与PID控制作对比表明,采用该复合控制策略能在保证系统稳定性的前提下,有效提高系统的响应速度和跟随精度,从而使试验台能够精确复现路面激励,提高试验台测试精度.

This study investigates friction and wear properties of rod seals used to prevent leakage of base oil in magnetorheological (MR) dampers. As the first step, a non-piston MR damper (MRD) model is considered for the analysis of both the frictional force and three-body abrasive wear of seals in MRD. Three different seals; O-ring, step ring, and glyd ring seals are adopted for the analysis and experimental tests. In order to conduct the friction and wear testing, a new type of in-house experimental apparatus consisting of an electrical cylinder, pressure sensor and gravity sensor is established. Subsequently, the friction coefficients and wear losses of the seals are evaluated as a function of operation time to validate the feasibility of the derived friction and wear models. To investigate the variation of the seals within MR fluid domain, morphological scanning electron microscopy images such as contacting and worn surfaces are observed and discussed. In addition, the energy-dispersive spectroscopy images are investigated after wearing the seal to observe the changes in size and shape of iron particles which are randomly distributed in MR fluid.

The aim of this work is to develop a magneto-rheological brake control system based on the hardware-in-the-loop simulation to analyze braking performances such as time response characteristics of the desired torque with the input currents. As a first step, a mathematical model of the braking torque is formulated and the optimized structure parameters of magneto-rheological brake are determined. Subsequently, the hardware-in-the-loop simulation system associated with the braking bench is established in which the software controlling the braking performances is implemented by a proportional–integral–derivative controller. Several tests to evaluate control performances of magneto-rheological brake are undertaken focusing on the decrement and increment by the input current. In addition, a quarter vehicle model equipped with the antilock brake system is tested through the hardware-in-the-loop simulation. It is shown that the antilock brake system integrated with magneto-rheological brake quickly tracks the desired slip rate resulting in stable performances.

Magneto-rheological (MR) damper is a specific type of semi active suspension component which have the nature of rapidly and reversibly changing the damping characteristics. During working process, magnetic particles in MR fluid would inevitably friction with cylinder and seal component. This paper aims to study the effect of initial surface roughness on tribological characteristics of MR fluid based on damper design. Los steel specimens with three different initial surface roughness were prepared and tested by using a pin-on-disc tribometer at various magnetic current, normal load and rotating speed. Friction coefficient was measured and recorded through the modified vertical universal friction and wear tester. Wear loss was calculated by measuring the weight of the pin before and after test. Three dimensional laser microscope was utilized to characterize the surface profile curves, surface roughness values and surface morphology of the specimens before and after tests. The wear mechanisms were analyzed and demonstrated through scanning electron microscope (SEM), coupled with an energy-dispersive X-ray spectroscope (EDS). The experimental results showed that the friction coefficient and wear loss of MR fluids not only affected by current, load and rotating speed, but also depended on the initial surface roughness. Because of the micro-size carbonyl iron particles in the MR fluid, the effect of initial surface roughness of specimens is more important.

In investigating magnetorheological (MR) brakes, it is well known that the braking torque is the important factor in the structure's design and the temperature of MR fluid in the brake is required to be within the operating range. In addition, the stress condition of the component changes obviously in the combined effects of force and thermal load which may result in structural damage. This study aims to propose a multi-cylindrical MR brake with a high-torque and investigate it more comprehensively in multi-field simulation. To achieve this goal, the mathematical model of the braking torque and the computing platforms of Maxwell and Ansys workbench are adopted to explore the influence of the exciting current and the number of braking cylinders on the braking performance, as well as the temperature and structural stress distribution of the braking cylinder during braking. The magnetic analysis shows that the proposed magnetic circuit is reasonable. The relationship between braking torque and exciting excitation current is nonlinear. The thermal simulation analysis shows that the temperature of MR brake remains within operating range of MR fluid after braking. The structural stress analysis shows that the contact position of braking cylinder and magnetism-insulator is the easiest place to break.

In this article, thermal characteristics and tribological properties of a disk-type magnetorheological fluid–based brake are investigated under various brake operating conditions such as different working gaps. In order to achieve this goal, a theoretical analysis of the heating and heat dissipation of the magnetorheological brake is first performed and then the transient temperature behaviors of the magnetorheological brake are investigated through simulation works associated with the finite element method. Subsequently, an experimental apparatus is established to measure temperature distributions of the magnetorheological brake as a function of the operating time. Thereafter, several heating and wear tests are conducted on the magnetorheological brake, and worn surfaces of the friction plates are observed using a scanning electron microscope to understand tribological characteristics of the magnetorheological brake. It is shown that the smaller working gap causes the higher temperature compared with the larger gap under the same magnitude of the input current applied to the magnetorheological fluid domain. This thermal behavior consequently results in the reduction of the braking torque. It is also demonstrated from the wear test that the small working gap significantly affects both wear and tribological characteristics showing the large ridges and deep grooves on the worn surfaces of the friction plate.

In this paper, the effect of the surface textures of braking disc on the braking performance is experimentally investigated under the conditions of different working gaps and applied currents. For this purpose, a new configuration of magnetorheological fluid brake (MRB) with adjustable working gap is developed to improve the manufacturing accuracy and cost, and to reduce the problem of replacing the braking disc. In addition, the braking discs with three types of surface texture are designed and machined. Based on the test bed developed for the proposed MRB, a series of experiments are carried out on the manufactured prototype and the results are presented to obtain the relationship among the surface texture of the braking disc, applied current, working gap and the braking performance. The results show that the braking torque is significantly influenced by the working gap and surface texture of the braking disc, and the maximum braking torque is obtained on the conditions of 0.25 mm working gap and the braking disc with square surface texture.

Wind turbine blade, which was made of composite materials, is one of the most important parts for wind turbine. The better design, higher reliability and superior performance of wind turbine blade are the decisive factors for normal and stable operation of wind turbine. In this paper, the influence of beam structure on the modal characteristics of wind turbine blades under static and rotating states were studied by using ANSYS finite element method software. Comparing the simulation results it can be found that although working conditions has little effect on vibration modes, natural frequencies are depended on the working conditions and beam structures.

The aim of this work is to investigate the effect of the small magnetorheological fluid gap on the braking performance of the magnetorheological brake. In this article, theoretical analyses of the output torque are given first, and then the operating principle and design details of the magnetorheological brake whose magnetorheological fluid gap can be altered are presented and discussed. Next, the magnetic circuit of the proposed magnetorheological brake is conducted and further followed by a magnetostatic simulation of the magnetorheological brakes with different sizes of fluid gap. A prototype of the magnetorheological brake is fabricated and a series of tests are carried out to evaluate the braking performance and torque stability, as well as the verification of the simulation results. Experimental results show that the braking torque increases with the increase in the current, and the difference for the impact of the fluid gap on braking performance is huge under different currents. The rules, which the experimental results show, have an important significance on both the improvement of structure design for magnetorheological brake and the investigation of the wear property under different fluid gaps.