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Abstract To optimize the magnetic fluid seal design, the single-factor method is usually used to study the effect of the rectangular pole teeth structure parameters on the sealing capacity of the magnetic fluid seal by current research, and the design formula is obtained. However, the supporting data is too few to make the results universalizable. In this paper, to obtain a wider range of applicable design formulas, a large number of modeling and simulation experiments are conducted using the co-simulation analysis experimental method of MATLAB and COMSOL. The influence of structure parameters of rectangular pole teeth and the coupling effects of the structure parameters on the sealing capacity of sealing devices has been studied under different lengths of pole piece (L p ) and seal gap (L g ). The results explain the influences of tooth height (L h ), tooth width (L t ), groove width (L s ), and their coupling effects on the theoretical sealing capacity of magnetic fluid seals, and more widely applicable design formulas for pole teeth structure parameters are given. The design formulas can help to obtain good design parameters directly or reduce the optimization range when the magnetic fluid seals need to be optimized to meet the miniaturization and lightweight requirements of magnetic fluid sealing devices or improve the sealing capacity under the same seal size.

Abstract Bronchopulmonary dysplasia (BPD) is the most common sequela of prematurity and is characterized by alveolar simplification and lung angiogenesis failure. The aim of this study was to explore the immune signatures of BPD. Differentially expressed gene analysis and immune infiltration analysis were conducted to identify key immune cell types and related genes by using the mRNA-seq dataset GSE25286. The expression patterns of key genes were validated in the scRNA-seq dataset GSE209664 and in experiments. The cell–cell crosstalk of key immune cells was explored with CellChat. We found that differentially expressed genes between BPD mice and controls were mostly enriched in leukocyte migration and M1 macrophages were highly enriched in BPD lungs. Hub genes (Cybb, Papss2, F7 and Fpr2) were validated at the single-cell level, among which the downregulation of Cybb was most closely related to macrophage infiltration. The reduced mRNA and protein levels of Cybb were further validated in animal experiments. Colocalization analysis of Cybb and macrophage markers demonstrated a significant decrease of Cybb in M1 macrophages. Cell–cell crosstalk found that alveolar epithelial cells interacted actively with macrophages through MIF-(CD74 + CD44) signalling. In conclusion, M1 macrophages played important roles in promoting BPD-like lung injury, which was correlated with a specific reduction of Cybb in macrophages and the potential activation of MIF signalling.

Abstract In this paper, we selected representative electric buses (EBs) and diesel buses as research cases, aiming to explore a localized method suitable for various vehicle types that can be implemented in any region to measure the carbon emissions of urban buses throughout the lifecycle. We take into account the influence of seasonal factors over the lifecycle. We fully consider the production, assembly, and recycling stages of vehicle systems. We construct a model for estimating CO2 emissions during the fuel cycle. We analyze and compare the impacts of the optimized power grid structure on the lifecycle CO2 emissions of the two types of buses. The results indicate that seasonal factors affect both bus types' energy consumption, with EBs being more sensitive. Carbon emissions primarily stem from manufacturing the body, chassis, and notably, the lithium‐ion batteries, with the latter having a pronounced impact on EBs. A decrease in coal power generation from 71% to 21% in the grid reduced EB fuel‐cycle emissions by 70.7%. Although EBs are sensitive to seasonal factors, they still have the greatest potential for carbon reduction, depending on the proportion of clean energy in the power grid and the production processes of vehicle components.

This paper reviews the current state of dynamic sealing technologies, examining the challenges faced by conventional sealing methods under complex working conditions, such as high temperature, high pressure, and corrosive environments. It also provides a concise overview of the status and developmental trends in sealing inspection technologies. From the perspective of obstruction mechanisms, this study reinterprets the concept of sealing science by redefining the classification of sealing types based on solid-phase medium obstruction, fluid hydrostatic and hydrodynamic obstruction, fluid pumping obstruction, fluid energy dissipation obstruction, and fluid impact obstruction. Comparative analyses of sealing structures across these obstruction mechanisms are presented. The sealing technology based on fluid impact medium obstruction, newly proposed by this paper, represents an innovative sealing approach. It offers distinct advantages such as zero wear, structural simplicity, and high stability, addressing longstanding issues in high-speed, large-clearance non-contact seals, including low leakage suppression efficiency, system complexity, and poor stability. Since its introduction, this novel sealing structure has garnered significant attention and recognition from both the academic and industrial sealing communities. With the potential to revolutionize the field, this groundbreaking sealing design is poised to lead the next wave of technological advancements in sealing science.

This paper introduces the prototype design, magnetic field analysis and experimental test of a double-rotating ferrofluid vane micropump with an embedded fixed magnet. The micropump is based on the working principle of a positive-displacement pump, as well as the magnetic characteristics and flow properties of magnetic fluid. Through the numerical analysis of the pump cavity magnetic field and the experimental test, the structural parameters of the micropump are optimized reasonably. The pumping flow and pumping height of the micropump were characterized at different driving speeds. The maximum pumping flow rate is approximately 410 μL/min, and the maximum pumping height is approximately 111.4 mm water column. The micropump retains the advantages of simple structure, easy manufacture, flexible control, self-sealing, self-lubrication, low heat production, etc., and can block the pumped liquid backflow. The resulting double-rotating ferrofluid blades can improve pumping efficiency and pumping capacity, and can improve pumping reliability and stability to a certain extent.

Friction is the dominant factor restricting tracking accuracy and machining surface quality in mechanical systems such as machine tool feed-drive. Hence, friction modeling and compensation is an important method in accurate tracking control of CNC machine tools used for welding, 3D printing, and milling, etc. Many static and dynamic friction models have been proposed to compensate for frictional effects to reduce the tracking error in the desired trajectory and to improve the surface quality. However, most of them focus on the friction characteristics of the pre-sliding zone and low-speed sliding regions. These models do not fully describe friction in the case of insufficient lubrication or high acceleration and deceleration in machine tool systems. This paper presents a new nonlinear friction model that includes the typical Coulomb-Viscous friction, a nonlinear periodic harmonic friction term for describing the lead screw property in insufficient lubrication, and a functional component of acceleration for describing the friction lag caused by the acceleration and deceleration of the system. Experiments were conducted to compare the friction compensation performance between the proposed and the conventional friction models. Experimental results indicate that the root mean square and maximum absolute tracking error can be significantly reduced after applying the proposed friction model.

Bronchopulmonary dysplasia (BPD) is the most common chronic respiratory disease in preterm infants. Little is known about the regulatory effect of lung Lactobacillus and its mechanism in BPD. This study explored the effect of L. reuteri on hyperoxia-induced mice lung injuries and examined whether L. reuteri played a role via the IL-22/STAT3 pathway. We found that the intranasal administration of L. reuteri and its tryptophan metabolite indole-3-aldehyde (3-IAld) ameliorated hyperoxia-induced mice lung BPD-like changes, deceased proinflammatory cytokines (IL-1β, IL-6, and TNF-α), and increased the levels of surfactant-associated protein C (SPC), aquaporin 5 (AQP5), and vascular endothelial growth factor receptor 2 (VEGFR2, also known as FLK-1). Furthermore, L. reuteri and 3-IAld increased the expression of IL-22. IL-22 was also confirmed to ameliorate hyperoxia-induced mice lung pathological changes, and the protective effects of L. reuteri could be inhibited by anti-IL-22 neutralizing antibody. Finally, we confirmed STAT3 activation by IL-22 in MLE-12 cells. In summary, our study confirmed L. reuteri alleviated hyperoxia-induced lung BPD-like changes in mice by activating the IL-22/STAT3 signaling pathway via IL-22 production. Probiotics Lactobacillus is a potential treatment for hyperoxia-induced lung injury in newborns.

Objectives As a common and frequently occurring disease, heart failure has been paid more and more attention, but the mechanism of its occurrence and development is still unclear. This study investigated that PGAM5 expression levels in heart failure and its underlying mechanisms in vivo and in vitro. Methods The inhibition of PGAM5 mRNA expression levels in patients with heart failure was compared with the normal group. Results The serum of PGAM5 mRNA expression was negative correlation with collagen I and collagen III in patients with heart failure. PGAM5 mRNA and protein expression in the heart tissue of mice with heart failure were down-regulated at a time-dependent rate. The inhibition of PGAM5 presented heart failure in the model. PGAM5 reduced inflammation and inhibited ROS-induced oxidative stress in models of heart failure. PGAM5 reduced Ferroptosis in models of heart failure. PGAM5 regulated Keap1/Nrf2 signaling pathway. IP also showed that PGAM5 protein combined with the Keap1 protein. PGAM5 could increase Keap1 protein ubiquitination. Keap1 inhibition affected the effects of PGAM5 in model of heart failure. Conclusions We conclude that the protection of PGAM5 reduced ROS-induced oxidative stress and ferroptosis by the Keap1/Nrf2 signaling pathway in heart failure, suggesting that targeting this mechanism of PGAM5 may be a feasible strategy to treat heart failure.

Abstract Magnetic fluids are the suspensions composed of magnetic nanoparticles, surfactants, and non-magnetic carrier liquids. Magnetic fluids are widely used in various fields, especially in sealing, because of their excellent features, including rapid magnetic response, flexible flow ability, tunable magneto-viscous effect, and reliable self-repairing capability. Here, we provide an in-depth, comprehensive insight into the theoretical analyses and diverse applications of magnetic fluids in sealing from three categories: static sealing, rotary sealing, and reciprocating sealing. We summarize the magnetic fluid sealing mechanisms and the development of magnetic fluid seals from 1960s to the present, particularly focusing on the recent progress of magnetic fluid seals. Although magnetic fluid sealing technology has been commercialized and industrialized, many difficulties still exist in its applications. At the end of the review, the present challenges and future prospects in the progress of magnetic fluid seals are also outlined.

Unmanned surface vehicles (USVs) have garnered significant attention across various application fields. A sufficiently accurate kinetic model is essential for achieving high-performance navigation and control of USVs. However, time-varying unobservable internal states and external disturbances pose challenges in accurately modeling the USV’s kinetics, and existing methods face difficulties in accurately estimating unknown time-varying disturbances online while ensuring precise mechanism modeling. To address this issue, a novel grey-box modeling method based on incremental learning and mechanisms (GBM-ILM) is proposed. Its union structure combines the advantages of both incremental learning networks and physical mechanisms for estimating the USV’s full kinetics. Depending on the linear parameter-varying (LPV) mechanism, it not only adheres to physical laws but also calculates the unstructured model errors. An incremental learning network is implemented to continuously refine model errors, by accounting for the USV’s time-varying characteristics and iteratively updating the network parameters and structures to adapt to different USV states and environmental disturbances. To validate this method, we developed the ‘Salmon’ USV and conducted identification experiments in a lake. Compared to tests of other state-of-the-art methods, our method has better adaptability, with 46.34%, 14.86%, and 6.87% accuracy improvements when estimating the USV’s forward, turning, and sideslip dynamic model, respectively.

Abstract Rheological properties are the theoretical basis and the key to common problems in ferrofluid applications, therefore they are expected to be adjustable to satisfy different technical requirements through altering the microstructure of ferrofluid during the process of preparation. In this paper, Four ferrofluid samples with different magnetic particle size were prepared by controlling the concentration of precursor solution during co-precipitation process and the rheological properties of these samples were investigated. These samples exhibited field-controlled rheological properties. Eternal magnetic field would enhance the formation of microstructures, resulting in an increase of viscosity. While with the increase of shear rate, microstructures tended to be destroyed, causing viscosity to decrease. There were two opposing mechanisms of the influence of precursor solution concentration. On one hand, the reduction of the precursor solution concentration would produce primary magnetic particles of smaller size. But on the other hand, the surfactant became insufficient to completely coat the magnetic particles because of an increased specific surface area, causing the magnetic particles to aggregate and form secondary clustering structures which strongly enhanced the magnetoviscous effect and weakened the viscoelastic effect.

Abstract The current research on the evaporation of ferrofluids mainly focuses on the characterization of ultra-low vapor pressure ferrofluids in vacuum and the theoretical analysis of the evaporation process. Few studies have focused on the experimental validation of the proposed evaporation rate equations and on the comparison of the differences in ferrofluid evaporation. In this study, based on the Bolotov’s model, an evaporation rate equation is deduced from the experimental model. The experimental study included a comparison of the evaporation, magnetic particle volume fraction, temperature, height of the fluid surface from the outlet, and magnetic field of a kerosene-based ferrofluid and its base carrier liquid. The prepared sample was evaporated in a test tube, and the evaporation rate was calculated by measuring the weight loss of the sample. The experimental results show that the evaporation rate of the base carrier liquid is higher than that of the ferrofluid. The smaller the volume fraction of the magnetic particles, the greater the evaporation rate. The magnetic particles play a key role in preventing evaporation of the base liquid. The higher the temperature, the smaller the deviation of the evaporation rate from the predicted value. The evaporation rates obtained by the two control groups at the height of the fluid surface from the outlet were lower than the predict value. The magnetic field had a certain promotional effect on the evaporation of the ferrofluid. The experimental results were consistent with the results obtained using Bolotov’s model. This research validates Bolotov’s model and shows that the model is somewhat biased but still responds well to different variables.

Abstract It is a difficult task to root the cause of the failure of a gas face seal because different causes may result in similar observations. In the work being presented, the discrimination of multiple types of abnormities in a spiral groove gas face seal is studied. A dynamic model is employed to analyze groups of cases in order to uncover the dynamic behaviors when the face contact is induced by different mixtures of abnormities, whose discriminative features when motion and contact are monitored are studied and uncovered. A circumferential-pattern-related oscillation phenomenon is discovered, which is extracted from contact information and implies the relative magnitude of the moment on stator and the rotor tilt. The experimental observation shows consistent results. It means that the grooves (or other circumferential patterns) generate useful informative features for monitoring. These results provide guidance for designing a monitored gas face seal system.

Magnetic fluids, a new type of energy transfer fluid with tunable properties, have garnered significant interest from researchers worldwide. Hybrid magnetic fluids prepared by adding different types of nanoparticles exhibit superior thermophysical properties and functional characteristics. In this paper, we prepared a water-based magnetic fluid loaded with multi-walled carbon nanotubes (MCNTs), silver (Ag), and copper (Cu) to enhance thermal conductivity. Using a transient double hot-wire method, we designed and built an experimental measurement system for the thermal conductivity of magnetic fluids with an average measurement error of less than 5%. We studied the thermal conductivity of hybrid magnetic fluids under different conditions and evaluated the advantages and disadvantages of various models, including the Maxwell model, H&C model, Tim model, Y&C model, and Evans model. Our results show that MF+MCNTs, MF+Ag, and MF+Cu nanofluids can all improve the thermal conductivity of the carrier fluid, with MF+MCNTs exhibiting the best improvement effect of 10.93%. Among the five models evaluated, the Evans model had the best predictive effect with a deviation range within 5%. This work provides theoretical and practical reference for enhancing the thermal conductivity of magnetic fluids and provides a more accurate theoretical model for calculating the thermal conductivity of hybrid magnetic fluids.

With the rapid development of aerospace technology, the vibration problem of the spacecraft flexible structure urgently needs to be solved. Magnetic fluids are a type of multi-functional smart materials, which can be employed in shock absorbers to eliminate these vibrations. Referring to the calculation methods of stiffness coefficients of other passive dampers, the stiffness coefficient formula of magnetic fluid shock absorbers (MFSAs) was derived and refined. Meanwhile, a series of varying stiffness magnetic fluid shock absorbers (VS-MFSAs) were proposed and fabricated based on the second-order buoyancy principle. The range of stiffness coefficients covered by these VS-MFSAs contains the optimal stiffness coefficient estimated by formulas. The repulsive force measurement and vibration attenuation experiments were conducted on these VS-MFSAs. In the case of small amplitude, the relationship between the repulsive force and the offset distance was linear, which means the stiffness was linear. The simulation and experiment curves of the stiffness were in good agreement. The results of vibration attenuation experiments demonstrated that the rod length and the magnetic fluid mass influence the damping efficiency of VS-MFSAs. In addition, these results verified that the VS-MFSA with the optimal stiffness coefficient performed best. Therefore, the stiffness coefficient formula can guide the design of MFSAs.

Magnetic seals as a class of non-contact sealing technology have been a research focus. In these seals, magnetic materials, usually ferrofluids or magnetorheological fluids are attracted in sealing gaps as sealing medium. Recently, a novel sealing method using nano-micron sized magnetic powders has been raised up as well. However, the working performance of these magnetic seals has not been studied thoroughly and comparatively yet. Here, we provide a comparative study of magnetic seals by ferrofluid, magnetorheological fluid and magnetic powder theoretically and experimentally. The formulas of pressure capability are derived based on their different properties. A modified empirical formula of magnetic powder seals is proposed, taking the frictional effect into consideration. The magnetic field distribution is calculated by the finite element method. Finally, a test bench for static magnetic seals is established. The pressure capability and leakage rate of three materials are measured by sealing experiments. The differences in mechanism of pressure transfer and the ability of self-recovery are discussed. This research summarizes the characteristics of different magnetic seals, and provides a guidance for sealing medium selection and structure design.

In this article, a full-scale computational model for fluid–particle interaction under a magnetic field is developed. In this model, the fluid field is solved by the lattice Boltzmann method, and the hydrodynamic force acting on the particle is computed by the immersed boundary method . The numerical solutions of the magnetic field in the fluid–solid domain are achieved by the immersed interface method with a finite difference scheme, in which the normal and tangential jump conditions of the magnetic field intensity are applied to modify the standard finite difference scheme. The magnetic stress tensor along the fluid–particle interface can be calculated accurately. Unlike the widely used point–dipole model, the magnetic force acting on the particle is determined by the stress integration method. Numerical simulation of several numerical tests are carried out to validate the proposed model. The numerical results demonstrate the validity of the present model. Moreover, the magnetoviscous effect is studied by simulating the motion of elliptical particles under the uniform magnetic field in shear flow.

In response to the requirement of high vacuum and leakage rate of a small-diameter low-speed device of an enterprise, a double magnet multistage magnetic fluid sealing device is designed by analyzing the advantages and disadvantages of four different vacuum magnetic fluid sealing devices. The Ansys simulation software is used to analyze and calculate the magnetic field strength and distribution of this magnetic fluid sealing device, discuss the influence of the number of intermediate section pole teeth and the seal gap size on the pressure resistance of the magnetic fluid seal, and summarize the law. The proposed structure of the double magnet multistage magnetic fluid sealing device is optimized and determined by the influence law of structural parameters. Compared with traditional sealing forms, the advantages of the sealing device proposed in this article can be summarized as low processing difficulty, good reliability, and high pressure resistance. The reliability and rationality of this magnetic fluid sealing device are demonstrated by Ansys simulation results, which provide a reference for the structural design and analysis of small-diameter low-speed vacuum magnetic fluid sealing devices.

A magnetic fluid seal is often used in complex working conditions with harsh environmental requirements. Timely and accurate identification of the seal status can help avoid the major economic losses and even casualties caused by the seal failure. However, research on the recognition of magnetic fluid seal status is still at the exploratory stage internationally. Aiming at the problem of inclusion of other components and Gaussian noise when using acoustic emission nondestructive testing technology to detect the magnetic fluid seal status, a new recognition method based on the combination of high-order cumulant image and VGG16 convolutional neural network is proposed to identify the magnetic fluid seal status in this paper. In this method, high-order cumulant images are used for the denoising and feature selecting of detected signals, and the VGG16 convolutional neural network is trained to automatically learn image features to classify and recognize high-order cumulant images representing different sealing states. Experiments show that the accuracy of image recognition using VGG16 is significantly higher than that of other methods. The VGG16 method can identify the magnetic fluid seal state accurately and effectively, with strong robustness and Gaussian noise suppression ability.

The aim of the study was to analyze acoustic emission (AE) signals generated in different magnetic fluid sealing processes to estimate the status of the seal. Based on a magnetic fluid rotary sealing experimental setup, the AE sensor is respectively attached to the shell at the corresponding position of the seal, and the external pressure is applied to the magnetic fluid seal by a gas supply system. As the pressure gradually increases, the magnetic fluid sealing rings under different pole teeth are gradually broken, and processes such as pressure transfer between the seal stages occur. These processes generate different AE signals, which are collected by the sensors. The results show that the root-mean-square values of AE signals generated at the moment of sealing failure are different from those generated before and after. At the same time, by analyzing the characteristic values of AE signals generated in the whole process, we can infer the time when the rupture begins under different pole pieces and further estimate the status of the magnetic fluid seal. For the first time, this research demonstrates the experimental and data analysis procedures of AE technology for magnetic fluid seals.

Magnetic fluid seal is a new type of sealing method, which has been applied in many fields. For some fields, such as aviation and aerospace, high sealing performance, large shaft diameter, and small design space are required, which brings difficulties to the sealing design. Therefore, it is necessary to study a large diameter magnetic fluid seal with thin-wall parts. In this article, the effects of seal clearance and shaft deflection on the magnetic field distribution of magnetic fluid seal are analyzed by the finite element method. At the same time, the force of seal shaft in the assembly process is also simulated. The influence of the amount of magnetic fluid on the pressure resistance is analyzed. The low-temperature starting torque and high-temperature pressure resistance of magnetic fluid seal are experimentally studied, and the optimal injection amount of magnetic fluid is obtained. The research content of this article can be used as a reference for the design of a large diameter magnetic fluid seal with thin-wall parts.

Magnetic fluid seals have the advantages of zero leakage, long life, simple structure and high reliability, and have become one of the most widely used applications of magnetic fluids. In this paper, the effect of magnetic fluid evaporation on the pressure resistance of magnetic fluid seals is studied. In terms of theory, through theoretical calculation and simulation analysis, a calculation method for the pressure resistance of magnetic fluid seals is established. In terms of experiments, firstly, five groups of control groups were set up to conduct evaporation experiments under the same conditions, and magnetic fluids with different evaporation rates were obtained; Secondly, the performance of magnetic fluids with different evaporation rates was tested, and the flow curves, viscosity-temperature curves, and magnetic-viscosity curves of magnetic fluids were obtained respectively, and the effect of evaporation on the performance of magnetic fluids was analyzed; Finally, magnetic fluid sealing experiments with different evaporation rates were carried out. It is found that evaporation increases the pressure resistance of static seal to a certain extent, which is of great significance.

At present, most research studies on the changing process of the magnetic fluid seal are analyzed with the pressure signal of each chamber or the magnetic fluid flow photos taken by a camera, which need to change the seal structure. Based on nondestructive acoustic emission technology, a flow-state identification model of the oil-based magnetic fluid seal using the grey wolf optimizer and random forest is proposed in this study. The acoustic emission signal and pressure signal are collected at the same time under static conditions in the two-stage pole shoes oil-based magnetic fluid seal experiment. Through power spectrum analysis of the acoustic emission signal with the aid of pressure signal, the changing process before seal failure is divided into three states: no magnetic fluid flow, the first pole shoe magnetic fluid flow, and two pole shoes magnetic fluid flow together. Then, the time- and frequency-domain features of acoustic emission signal samples are extracted to form feature vectors as inputs, and the flow-state identification model is established based on the grey wolf optimizer and random forest. The experimental results show that the testing accuracy and F1 scores (the index representing the precision and recall at the same weight) of three states are close to or higher than 90%. The effectiveness of oil-based magnetic fluid seal flow-state identification model based on non-destructive acoustic emission technology is proved.

Three types of surfactants (oleic acid, linoleic acid, and a mixture of oleic acid and linoleic acid) were coated on ferromagnetic particles, which were dispersed in kerosene to prepare magnetic fluids, to study the effect of different fatty acids as surfactants on the rheological properties of magnetic fluids. The particles were analyzed by XRD, TEM, FT-IR, and VSM. Furthermore, a rheometer was used to examine the rheological properties of kerosene-based magnetic fluids dispersed with various surfactants. The yield stress at different magnetic fields was calculated by fitting the Herschel–Bulkley model. The fitted curve and the observed values of mixed fatty acids are identical. The graphs of viscosity increase with the shear rate for each magnetic fluid were measured at constant magnetic field strengths. At constant shear rates, the curves of viscosity increase with magnetic field intensity were measured. In the absence of a magnetic field, the relative change in viscosity from 40°C to 0°C was observed. The rheological measurements of the mixed fatty acid-dispersed ferrofluid with a rising magnetic field at a constant shear rate are smoother than the single-fatty-acid-dispersed ferrofluid, indicating that it is more stable. As the temperature is dropped, the viscosity–temperature curve evidence that mixed fatty acids as surfactants can lower the proportion of magnetic fluid viscosity rise.

Magnetic fluid is a typical type of functional fluid which can be magnetized and controlled by an external magnetic field. In magnetic fluid seals, magnetic fluid is attracted in sealing gaps by a magnetic field gradient to form non-contact sealing. Compared to traditional sealing methods, they possess unique advantages such as zero leakage, long lifetime, low friction torque, and high reliability. Although the design and performance estimation of magnetic fluid seals rely mostly on numerical simulation, a number of simplifications or even mistakes during the simulation process exist in previous studies. The error caused by simplifications and mistakes has not been studied, leading to a possible problem of simulation results in reliability and consistency with experimental data. Here, we examined the influence of common simplifications and mistakes in numerical simulation of the static pressure capability of magnetic fluid seals, including material properties, geometric modeling, and theoretical formulas. A novel method of structure optimization based on a derivative-free multiparameter algorithm is also presented. A test bench for magnetic fluid seals is established, and the difference between simulation and experimental results is discussed. This research provides a precise, efficient, and standard procedure for numerical simulation of magnetic fluid seals.

In order to understand the factors affecting the colloidal stability in the carrier liquids of different ferrofluids, magnetite nanoparticles coated by surfactants 3-(N,N-dimethylmyristylammonio)propanesulfonate (DP) and oleic acid (OA) were fabricated as dispersions in diverse colloidal systems. The OA-coated magnetite could only be dispersed in the apolar carrier liquid (εr < 5), while DP-coated magnetite particles could establish a stable colloidal system in the polar base liquid (εr > 5) such as water and ethanol. The colloidal stability of OA-coated particles in the apolar solvents was mainly attributed to the steric repulsion of its outer thick liquid shell (∼3 nm). Due to the absence of steric repulsion on the solid thin shell (∼1 nm) on DP-coated magnetite, DP-coated particles could not be dispersed in the apolar liquid. In the polar liquid-based ferrofluids, DP-coated magnetite could form an electric double layer (EDL). The total Gibbs interfacial energy was analyzed based on Van Oss-Chaudhry-Good and DLVO theory to describe the behaviors of coated particles in solvents. In the case of neutral (pH = 7) water-based colloidal, DP-coated magnetite could establish an energy barrier of ∼2.2 kBT to prevent the particles from precipitation. Bare magnetite particles could form a relatively fragile colloid in a water system with an energy repulsion of ∼1.2 kBT. In contrast, OA-coated magnetite exhibited a severe phase separation in a water-based colloidal system due to its net attraction ∼ −1.3 kBT.

As one of the most mature applications of ferrofluid, the pole shoes of a ferrofluid seal are easily damaged under the situation of the large radial beating of the main shaft. Meanwhile, due to the small size, the pole teeth commonly used in pole shoes harbor problems such as poor processability and low seal pressure under a large gap. In order to solve the aforementioned problems, we proposed a new structure of the ferrofluid seal that uses a radial-charged ring magnet as the magnetic source. Then, considering that the ring magnets have problems of uneven magnetization and installation difficulties, we used split magnets to take the place of ring magnets and proposed the second new structure. According to the study on the distribution of magnetic field in seal gap axially and circumferentially, we obtained the simulation results of the two new structures’ seal pressure. The results revealed that the new structure of the ferrofluid seal with rectangular magnets can solve the aforementioned problems and exhibited a certain amount of sealing pressure.

Magnetic fluid seals have long been thought to be a successful sealing form while sealing liquids are always a challenge. The instability of the liquid–liquid interface under the washout has become the key technical problem that hinders the realization of sealing liquid. This work mainly presents an experimental study about the influence of high viscosity and magnetoviscous effects on washout resistance. Three engine oil-based magnetic fluids of different viscosities were prepared with two kinds of surfactants. The magnetoviscous effects of the prepared magnetic fluids under different working conditions were found through rheological experiments. The viscosity of the three samples decreased at most by about 100 times with the shear rate increasing. An experimental platform was designed and built for the washout tests. The entire process of magnetic fluids being washed away was obtained experimentally. The magnetic fluid of higher viscosity can remain stationary with lower magnetic force. The quantitative results show that the viscosity of the magnetic fluid has a significant influence on washout resistance under a magnetic field.

Magnetic fluids, as smart nanomaterials, have been successfully used in sealing applications and other fields. However, the temperature of magnetic fluids in the sealing gap is a key factor affecting sealing performances, limiting their application in high-speed sealing fields. Since obtaining a direct measurement of the magnetic fluid’s temperature is difficult, due to the small clearance, accurately calculating the maximum temperature of the magnetic fluid layer in high-speed seals is crucial. Herein, a mathematical model for calculating the maximum temperature of the magnetic fluid layer was established, by using a reasonable simplification of high-speed sealing conditions, and the calculation formula was modified by studying the rheological properties of the diester-based magnetic fluid. The results suggest that the calculation of the maximum temperature is influenced by viscous dissipation, and both are related to the rheological characteristics of magnetic fluids. When the influence of rheological properties is ignored, the calculation results are not accurate for higher-velocity seals, but the calculation model applies to lower-velocity seals. When the influence of rheological properties is considered, the calculation results obtained by the corrected formula are more accurate, and they are applicable to both lower- and higher-velocity seals. This work can help us more accurately and conveniently estimate the maximum temperature of magnetic fluids in high-speed seal applications, which is of theoretical and practical research significance for determining sealing performances and thermal designs.

As a novel functional nanomaterial, Fe3O4 magnetic nanoparticles (MNPs) modified by different surfactants have attracted and are attracting worldwide interest. In this research, we introduced two different silane coupling agents to modify Fe3O4 MNPs instead of a single surfactant to achieve complete coating and functionalization. The modification mechanism was also explained. Techniques such as TEM, XRD, FT-IR, TG-DSC, and VSM were applied to characterize the obtained modified Fe3O4 sample. From these techniques, the following information is obtained: The characteristic bands of TEOS and KH-792 were present in the FT-IR spectra and in the XPS plots of modified Fe3O4 MNPs, demonstrating that the silane coupling agents were present in the sample obtained after the modification. The TG analysis of the modified sample showed complete decomposition at 228 °C. The mass ratio of the sample obtained before and after the modification was close to 29:65. The XRD patterns show that the modified Fe3O4 MNPs possessed an identical reverse spinel crystal structure as an unmodified Fe3O4 sample. The modification decreased the saturation magnetization of Fe3O4 MNPs from 70.04 emu/g to 57.41 emu/g and the coating did not change the superparamagnetism of Fe3O4 MNPs.

Most denoising methods are designed to deal standard images with specific type noise, which do not perform well when denoising real noisy images contain uncertain types of noise. However, underwater image is a typical uncertain type noise image. To solve this problem, this paper presents a method using spatial feature classification jointing nonsubsampled shearlet transform (NSST) for denoising uncertain type noise images. Justifiable granule is employed to solve the problem of parameter selection. The raw image was decomposed by using the NSST to get one low frequency subband and several high frequency subbands. Then, the preliminary binary map is built, the binary map is employed to decide whether a coefficient contains spatial feature or not. And we employ justifiable granule to solve the difficulty of parameter selection. The high subbands coefficients are classified into two classes by fuzzy support vector machine classification: the texture class and the noise class. At last, the adaptive Bayesian threshold is used to shrink the coefficients. Simulation results show the proposed method is effective in uncertain type noise images(also have good performance in specific type noise). The method we proposed has been compared with other popular denoising methods and get excellent subjective performance and PSNR improvement.

Accurate measurement of the flow curves of magnetic fluid under a uniform field has always been a challenge. In this article, a novel method is proposed to measure the flow curve of magnetic fluids based on plane Poiseuille flow. The measuring system was built and its performance was compared with that of a commercial rheometer. Flow curves of magnetic fluid with different zero-field viscosity were tested under various field strengths. This novel method facilitates direct observation of the flowing behaviors of magnetic fluid under different stresses. By examining the variation trend of viscosity under certain constant stress, a more reliable method to determine the dynamic yield stress of magnetic fluid was used. The dynamic yield stress of the magnetic fluid measured by the new method was larger than the value obtained by the fitting, which is more reliable from an engineering point of view.

During all the assembly stages of a polymer electrolyte membrane fuel cell (PEMFC) stack, gas diffusion layers (GDLs) endure clamping loads in the through-plane direction several times. Under such complicated assembly conditions, GDLs have to deform with the changes in structure, surface roughness, pore size, etc. A comprehensive understanding of the compressive performance of GDLs at different clamping phases is crucial to the assembly process improvement of PEMFCs. Two typical clamping compression was designed and performed to get close to the actual assembly conditions of PEMFCs. The results indicate that the initial clamping compression and the magnitude of the maximum clamping load have great impacts on the segmented compressive properties of GDLs. The nonlinear compressive performance of the GDL is mainly attributed to the unique microstructural information. The rough surface morphology contributes to the initial compressive characteristics where the big strain along with the small stress occurs, and the irreversible failures such as carbon fiber breakages and adhesive failures between fibers and binders account for the hysteresis between different compression stages. Importantly, it is found that the clamping compression hardly influences the small pore distribution below 175 μm but affects the large pore distribution over 200 μm.

Two-dimensional material nanosheets have always been a research hotspot because of their unique structure and properties. We report mode-locked operation in ytterbium-doped fiber laser (YDFL) for the first time by adopting Fe3O4 nanosheets as a saturable absorber (SA). The laser is capable of generating 456 ps pulses, centered around 1039 nm. Our results manifest that Fe3O4 nanosheets are expected to become a new type of saturable absorber, which can better promote the development of mode-locked lasers.

The electro-optical features of the PDLC films applied with a low-frequency square wave voltage were investigated. The transmittance curves indicated the double frequency of the applied voltage at 0–50 Hz, which resulted from the relaxation of an internal electric field polarized by ions in LC droplets. When the local electric field was reversed, the internal polarization electric field could be maintained and superimposed on the local electric field. The relaxation of the internal polarized electric field resulted in the relaxation of the transmittance. Furthermore, the transmittance curves changed with the frequency of the applied voltage.

This article describes the development of an unmanned aerial vehicle system that had a remarkable performance in the 6th International Unmanned Aerial Vehicle Innovation Grand Prix, which was held on November 2–4, 2018, in Anji, China. The main mission of the competition was to build a simulated tower using prefabricated components by an unmanned rotorcraft, which could be decomposed into the following four subtasks: (1) navigation and control, (2) recognition and location, (3) grasp and construction, and (4) task planning and scheduling. All the tasks were required to perform autonomously without human intervention. According to the requirement of the mission, the unmanned aerial vehicle system was designed and implemented with high degree of autonomy and reliability, whose hardware was developed on a quadrotor platform by integrating various system components, including sensors, computers, power, and grasp mechanism. Software algorithms were exploited, and executable computer codes were implemented and integrated with the developed unmanned aerial vehicle hardware system. Integration of the two provided onboard intelligence to complete the mission. This article addresses the major components and development process of the unmanned aerial vehicle system and describes its applications to the competition mission.

A numerical investigation of two-phase natural convection of Cu-water nanofluid in a square cavity is conducted by using a novel volume fraction-thermal lattice Boltzmann method to solve the governing equations of the flow field, temperature field, and nanoparticle volume fraction distribution field. The study explores the effects of the variable nanoparticle volume fraction at different Rayleigh numbers (103≤Ra≤106) and initial nanoparticle volume fractions (0.01≤ϕinitial≤0.05) on streamlines, isotherms and the Nusselt number. The results have shown that the Nusselt number along side walls would decrease when the Rayleigh number is large, with the opposite effects on parts of the side walls when the Rayleigh number is small. The relative difference of Nusselt number has a positive correlation with both the Rayleigh number and the initial nanoparticle volume fraction. When the Rayleigh number or the initial nanoparticle volume fraction is relatively large, the slip mechanisms of nanoparticles play an important role, and the two-phase model should be adopted instead of the conventional homogeneous one-phase model. Keywords: Natural convection, Nanofluid, Two-phase flow, Lattice Boltzmann method (LBM)

Compressed air energy storage is a well-used technology for application in high voltage power systems, but researchers are also investing efforts to minimize the cost of this technology in medium and low voltage power systems. Integration of this energy storage requires a robust control of the power electronic converter to control the power injection due to the dynamic behavior of the system. The conventional linear control design requires a thorough knowledge of the system parameters, but the uncertain disturbances caused by the mechanical properties of the energy storage is neglected in the design and the system fails in presence of such instances. In this paper an adaptive control-based boost converter and sliding mode control-based three phase inverter for a grid integrated compressed air energy storage system of up to 1 kW has been presented that can mitigate any uncertain disturbances in the system without prior knowledge of the system parameters. The experimental results along with the simulation results are also presented to validate the efficiency of the system.

Sterling seal is a commonly used reciprocating seal, in which the PTFE ring of the seal and the surface material of the piston rod play an important role in the reciprocating sealing process. In this paper, a reciprocating sealing test bench was built, four sets of carbon fiber PTFE sealing rings were used to perform reciprocating sealing bench experiments with Cr-coated piston rods and DLC-coated piston rods. After the experiment, the used four sets of seals were taken as experimental samples, and a new, unused carbon fiber PTFE seal was taken as a reference sample. The surface topography, surface wear, and wear surface elements of the test specimens were measured by three-dimensional white light interference surface topography instrument, field emission environment scanning electron microscope, and field emission scanning electron microscope. Through experimental determination, it is found that the coating material is detached to form abrasive grains, which causes the surface of the sealing ring to wear. This paper also proposes optimization suggestions for the processing method of the sealing ring and the selection of the material of the piston rod coating.

Plasticized poly (lactic acid) (PPLA) was prepared by melt blending poly (lactic acid) (PLA) with 10 wt% of poly (ethylene glycol) (PEG), with varied molecular weights range from 400 to 4000. The structure, thermal property, morphology, and surface free energy of the PPLA were investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and contact angles (CA). The resulting PPLA results indicated that the introduction of PEG to the blend systems resulted in a ductile fracture, a decrease in the melt temperature (Tm) and glass transfer temperature (Tg), and an increase in the degree of crystallization (χc), which indicated an improved flexibility. In addition, the polarity of the PPLA increased and the surface free energy decreased. The resulting PPLA was subsequently used as matrix to blend with wood flour to prepare composites. The mechanical strength, melting behavior, thermal stability, and microscopy of the PPLA/wood flour composites were also evaluated. These results illustrated that the plasticized PPLA matrix was beneficial to the interfacial compatibility between the polar filler and the substrate.

Heterogeneous unmanned systems consisting of unmanned aerial vehicles (UAVs) and unmanned surface vehicles (USVs) have great application potential in marine environments. At present, the fully autonomous recovery of UAVs is a key problem that restricts any significant application of a heterogeneous unmanned system. This paper presents a novel fully autonomous recovery system, covering the entire process of recovery of small fixed-wing UAVs on mobile platforms at sea. We describe methods or solutions for the key problems encountered by the current system, including active modeling of the UAV−USV heterogeneous platform motion model, accurate estimation of the highly dynamic relative motion of the heterogeneous platform, dynamic analysis of the arresting cable system, and compliance control of the manipulator recovery system. Based on these methods, a physical simulation platform for the fully autonomous recovery system, including an actively adjustable arresting cable, manipulator compliance recovery system, and other subsystems, is developed and verified through experiments. The experiments show that the system proposed in this study can achieve full autonomous recovery of a small ship-based fixed-wing UAV with a high success rate in a short period. This system is the foundation for practical applications of UAV−USV heterogeneous unmanned systems in the marine environment.

We propose an intelligent human−unmanned aerial vehicle (UAV) interaction system, in which, instead of using the conventional remote controller, the UAV flight actions are controlled by a deep learning-based action−gesture joint detection system. The Resnet-based scene-understanding algorithm is introduced into the proposed system to enable the UAV to adjust its flight strategy automatically, according to the flying conditions. Meanwhile, both the deep learning-based action detection and multi-feature cascade gesture recognition methods are employed by a cross-validation process to create the corresponding flight action. The effectiveness and efficiency of the proposed system are confirmed by its application to controlling the flight action of a real flying UAV for more than 3 h.

To ensure the stability and reliability of the power network operation, a number of Grid Codes have been used to specify the technical boundary requirements for different countries and areas. With the fast propagation of the usage of Electrical Energy Storage (EES), it is quite important to study how the EES technology with its development can help the Grid Code realization. The paper provides a comprehensive study of Great Britain (GB) Grid Code mainly on its voltage and frequency relevant specifications, with a comparison of other countries’ grid operation regulations. The different types of EES technologies with their technical characteristics in relation to meeting Grid Codes have been analysed. From the study, apart from direct grid-connection to provide grid services on meeting Grid Codes, EES devices with different technologies can be used as auxiliary units in fossil-fuelled power plants and renewable generation to support the whole systems’ operation. The paper also evaluates the potentials of different types of EES technologies for implementing the relevant applications based on the Grid Codes. Some recommendations are given at the end, for the EES technology development to help the Grid Code realization and to support the relevant applications.

During the synthesis of the γ-Fe2O3 nanoparticles via the chemically induced transition method, Cu(I) modification has been attempted by adding CuCl/NaOH to the treatment solution. The experimental results showed that, under the condition of a NaOH content equal to 0.04 moles, when the content of CuCl is as low as 1.25×10-3 or 2.50×10-3 moles, the products are single γ-Fe2O3/Cu(I)FeO2/FeCl3·6H2O composite nanoparticles, whereas when the content of CuCl is higher, 5×10-2 moles, the product is a mixture consisting of γ-Fe2O3/Cu(I)FeO2/FeCl3·6H2O nanoparticles and Cu(II)(OH)Cl nanoparticles. For the γ-Fe2O3/Cu(I)FeO2/FeCl3·6H2O composite nanoparticles, the Cu(I)FeO2 interface layer is not thick enough to form one unit cell, but it can modify the formation of a FeCl3·6H2O surface layer and the effective magnetization of the γ-Fe2O3 core.

Using FeOOH/Mg(OH)2 as precursor and FeCl2 as the treating solution, we prepared γ-Fe2O3 based nanoparticles. The FeCl2 treating solution catalyzes the chemical reactions, dismutation and oxygenation, leading to the formation of products FeCl3 and Fe2O3, respectively. The treating solution (FeCl2) accelerates dehydration of the FeOOH compound in the precursor and transforms it into the initial seed crystallite γ-Fe2O3. Fe2O3 grows epitaxially on the initial seed crystallite γ-Fe2O3. The epitaxial layer has a magnetically silent surface, which does not have any magnetization contribution toward the breaking of crystal symmetry. FeCl3 would be absorbed to form the FeCl3·6H2O surface layer outside the particles to form γ-Fe2O3/FeCl3·6H2O nanoparticles. When the treating solution’s temperature is below 70 °C, the dehydration reaction of FeOOH is incomplete and the as-prepared samples are a mixture of both FeOOH and γ-Fe2O3/FeCl3·6H2O nanoparticles. As the treating solution’s temperature increases from 70 to 90 °C, the contents of both FeCl3·6H2O and the epitaxial Fe2O3 increased in totality.