Modern Physics Letters B

Sedimentation immunity is one of the key features of magnetorheological (MR) dampers, which means the lifetime-long service without degradation under the sedimentation of MR fluid. In this paper, an active-dispersing mechanism is established with twin-tube configuration toward the sedimentation immunity, by adding a circulation channel powered by rotating blades between the tubes when the MR damper is not in operation. Finite element (FE) method is employed to reveal the re-dispersion process once the MR fluid settled to a specific degree, and the benefits of circulating channel and twin-tube sedimentation-immunity system for the MR fluid are discovered by the simulation. Ultimately, a self-adaptive system could be built to ensure the MR fluid in the damper keeping in a relative uniform and thus the sedimentation immunity is fulfilled.

Twisted string actuators (TSAs) are innovative linear soft actuators that can mimic natural muscle contraction. However, obtaining feedback on their stroke requires cumbersome external sensors that compromise their compliance. We addressed this by developing self-sensing strings using conductive polymer composites (CPCs). The CPC strings exhibit electrical resistance changes in response to strain, enabling stroke sensing by the strings themselves. We fabricated CPCs strings with varying concentrations of multi-walled carbon nanotubes (MWCNTs). Characterization revealed excellent conductivity, tensile strength exceeding 30 N, tunable strain sensitivity via MWCNTs concentration variation, as well as stable and repeatable strain-dependent resistance changes. Optimization via a high-strength core fiber enabled the CPCs strings to withstand over 6kg loading with enhanced stroke and minimal resistance variation. We achieved at least a 97.8% linear correlation between resistance change rate and contraction rate in twisting experiments. This research provides a self-contained stroke sensor compatible with high-load soft TSAs, overcoming limitations of external sensors. The simple yet effective sensing mechanism could spur adoption of TSA in robotics.

Considering the development of ultra-wideband detection technology, the effective attenuation performance of conventional electromagnetic absorbing materials prepared by component-morphology method is still affected by narrowband, which hinders its application. An effective strategy is to develop nanomagnetic metal absorbent that can effectively overcome skin effect through fine control based on nanotechnology. Mulberry-like Fe nanoparticles based on the self-assembly of spheroid blocks were synthesized in a simple chemical reduction process supplemented by a magnetic field. In view of synergistic loss of magnetic metal Fe, and unique physical properties of nanoparticles, the mulberry-like Fe nanoparticles exhibited attractive wave-absorbing properties. At a thickness of 3mm, the minimum reflection loss (RL) reaches −29.57dB, and the bandwidth less than −10dB reaches 8.38GHz, which covers the entire X-band, most of the C-band and part of the Ku-band. This will make it possible for electromagnetic protection and electromagnetic stealth. A possible growth mechanism was proposed to provide theoretical guidance for the subsequent preparation of nanomagnetic metal absorbent.

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.

Variable damping control technology based on intelligent materials of electromagnetic excitation has been widely used in the field of (semi-) active vibration control and fluid control. Unfortunately, a major drawback is the electromagnetic noise interference and low response speed. In this paper, a new optically controlled variable damping system based on PLZT ceramic/electrorheological fluid (ERF) is proposed. The mathematical models of the photovoltage generated by PLZT ceramics and the pressure difference between the two ends of the microchannel are established and verified by numerical simulation in COMSOL Multiphysics. Meanwhile, with the increase of light intensity, liquid flow rate and decrease of microchannel height and width, the pressure difference shows an uptrend. Optically controlled variable damping system based on PLZT ceramic/ERF is a control method with the advantages of a clean excitation source, remote control, no electromagnetic interference, and fast response speed, and has a good application prospect in the field of vibration control and fluid control.

The sedimentation measurement is of significant importance when designing and synthesizing magnetorheological (MR) fluid for engineering applications. Generally, visual observation is always used to discern the mud line position but knows nothing about the concentration distribution under the mud line. The method using electromagnetic scanning is limited by the position resolution because of the height of the inductor, and the method based on thermal conductivity is time-consuming and determines the sedimentation status at a specific location.

In this paper, the sedimentation behavior is revealed by the laser transmittance intensity (LTI) method which is based on scattering when the light passes through the MR fluid, the higher the concentration and the stronger the scattering, the weaker the received light intensity. Specifically, the laser diode and the photodiode were utilized as the light source and receiver, respectively.

MR fluid samples in a series of concentrations are used to obtain the correlation between volume fraction and photodiode output voltage, and that is taken as the calibration of the sensing method. In the experiments, the scanning with height and the sensing with time are jointly employed to characterize the settling process of a specific MR fluid.

In this study, electrorheological (ER) properties of biodegradable and conducting polyaniline-graft-chitosan (PAni-g-CS) copolymer particles were investigated. For this purpose, PAni and PAni-g-CS particles were synthesized by using in situ oxidative radicalic polymerization method. At first, PAni and PAni-g-CS/silicone oil (SO) ER suspensions (15% V/V) were subjected to external electric field and they exhibited low ER activity. When the external electric field strengths ($E)$ were increased, both the suspensions showed electrical breakdown. Therefore, virgin PAni and PAni-g-CS were first subjected to dedoping process by treating with 1.0 M NaOH(aq) and non-ionic surfactant Triton X-100 (T-X) surfactant to enhance the expected ER activity and prevent the electrical breakdown. But we observed that the addition of T-X as promoter had no significant effect on the ER activity. On the other hand, electric filed-induced viscosities of both the suspensions were observed to enhance after the dedoping (DD) process and electrical breakdown prohibited. After the DD process, DD PAni-g-CS/SO ER system exhibited the highest electric field-induced viscosity by reaching 400Pa⋅s at $E=4$kV/mm. The highest ER efficiency was also obtained for DD PAni-g-CS/SO system at 15% (V/V) as 79. Additionally, typical shear thinning non-Newtonian viscoelastic behavior was observed under externally applied E. The conduction model of DD PAni-g-CS/SO system was determined to well fit the conduction model by showing a slope of $m=1.5$ calculated from the E vb. yield stress graph. In conclusion, conducting and biodegradable-dedoped PAni-g-CS particles would be a good candidate for potential ER applications as dry-based ER materials having high colloidal stability of 76%.

Black carbon, a part of harmful PM2.5 air pollution, is the second largest contributor to global warming. Due to per unit of mass, black carbon has a warming impact on climate 460–1,500 times stronger than CO₂. UNEP emphasizes that the black carbon issue is more urgent than CO₂ now. Unfortunately, current technologies cannot help large factories in preventing emission of black carbon particles into air because they fail to catch them effectively. Therefore, a new technology, which can catch black carbon and other PM2.5 pollution effectively, is critically needed. Here we report that electrorheology is the solution we are looking for. Under a strong electric field, black carbon and other particles are polarized. When the polluted air flow becomes a special flow with pollution particles moving adjacent to the electrodes, black carbon and other particles are captured by the electrodes effectively. Our tests have confirmed that with this technology, more than 98% black carbon and other PM2.5 particles can be caught. Moreover, this technology is not only suitable as incoming air filters, but also appropriate for large factories in preventing emitting black carbon and pollution into air. We hope that electrorheology will improve our environment and reduce global warming effectively.

The sting support faces an issue of being prone to resonance due to its low-damping characteristics, which will compromise the accuracy of test data in wind tunnel experiments. Magnetorheological damper (MRD)-based tail support (MRSS) features varying stiffness and damping abilities, enabling it to suppress the vibration with random, time-variation characteristics in a self-adaptive way, and it also exhibits excellent fail–safe properties. This work aims to validate its controllability and fail–safe property in a wind tunnel environment. First, the natural frequency, root mean square (RMS), and power spectral density (PSD) of the designed MRSS’ response for random excitation were theoretically analyzed. Then, wind tunnel experiments were conducted to test the response under different attack angles, wind speeds, and test currents. Subsequently, the controllability and fail–safe property were demonstrated by analyzing the aircraft model response. Also, the variable stiffness and damping properties of MRD behind the observed phenomena were revealed based on the theoretical analysis. Results demonstrate that as the input current increases and the MRD’s stiffness continues to increase, the damping initially increases and then decreases. Increasing wind speed leads to a decrease in the MRD’s stiffness. Additionally, approximately 50% reduction in RMS and a multi-modal response attenuation was achieved.

Due to the distinctive working environment of high precision machining and manufacturing field, it poses challenges in meeting the isolation requirements, including limited installation space, multi-dimensional vibration, and a wide range of vibration frequencies. To tackle these obstacles, this paper introduces a magnetorheological (MR) isolator that offers adjustable vertical damping characteristics while guaranteeing three-axis vibration isolation through an inclined cone structure. First, the structure of the isolator was designed by combining a flow valve damper with a conical rubber structure. Second, in pursuit of lightweight design and enhanced magnetic field strength, collaborative simulations using ANSYS and Maxwell are conducted to subject the critical components of the isolator to multi-objective optimization. The optimization results demonstrate that the mass of the isolator has been reduced by approximately 27.7%, while the magnetic field intensity has increased by around 20%. Finally, the performance of the MR isolator was verified through static testing and dynamic testing, respectively. The experimental results demonstrate that the isolator can generate a maximum damping force of approximately 778N when exposed to a current of 1.5A. Compared to the initial value of 445.06N at 0A, there has been an approximate increase of 1.74 times.

This study examines the analytical study of magnetic hydrodynamic stagnation point flow with the impact variable viscosity on a movable surface along with the impact of thermal radiation. The problem is modeled with the help of momentum and energy conservation laws in the form of NLPDEs. The novelty of this study is the combined impact of variable viscosity and thermal radiation with the analytical method. Aluminum oxide nanoparticles and water are used as base fluids in this research work. The authors applied appropriate transformations to convert a collection of dimension forms of NLPDEs to dimensionless forms of NODEs. The transformed NODEs are solved with the help of an approximate analytical method known as the HAM. The effects of different parameters, including electric field, magnetic field, stagnation point flow, thermal radiation PN, and EN on energy and momentum profiles intended, and the results are planned with the help of graphs.

A computational investigation is furnished to explore the responses of a Darcy–Forchheimer EMHD Williamson flow of a Sodium Alginate $({\mathrm{\text{C}}}_6{\mathrm{\text{H}}}_9{\mathrm{\text{NaO}}}_7)$-based Ag-Al₂O₃ hybrid nanofluid passing over a vertically exponentially stretching cylinder emerged through a porous region. The prime focus of this research is to encompass the inclusion of nonlinear variations in heat distribution, Newtonian boundary heating (NBH) effects, and the influence of thermo-convection alongside suction effects. Key parameters, including thermal buoyancy, Darcy porous medium effects, heat source/sink effects, Biot number, variable thermal index, and thermal convection factor, are comprehensively analyzed as these combining factors can play a crucial role in optimizing the efficacy of several systems such as heat exchanger, material processing and geothermal system that involve the concept of thermo-transportation mechanism. The physical flow dynamics are modeled, employing suitable similarity transformations, and subsequently translated into a dimensionless form. The ensuing collection of modified nonlinear ordinary differential equations is solved by employing the Bvp4c solver bundled into the MATLAB program. Several parameters are scrutinized through graphical presentations to elucidate their impacts on the velocity curve, temperature curve, skin friction coefficient, and Nusselt index. It is worth mentioning that the heat distribution profile significantly escalated for the rising values of several factors such as electric field parameter, varying thermal index, Biot number and shape factor, but the reverse is the pattern with suction and thermo-convection effect. Also, the thermal transportation rate at the proximity of the vertical cylindrical wall appears to exhibit an increment of about an average of 47% in SA-based Williamson hybrid nanofluid compared to Williamson fluid for thermo-convective effect, NBH, and thermal buoyancy. Furthermore, the proximate shear stress rate appears to be amplified by approximately 39% in Williamson hybrid nanofluid when contrasted with Williamson fluid for electric field parameter and thermo-convection effect alongside the raised Darcy–Forchheimer factor.