Force Hysteresis Research Articles

Facilitating water droplet removal from surfaces using air flow and wettability gradients

A new method is proposed to mitigate ice accretions on wind turbine blades via the creation of a microstructural gradient surface geometry that facilitates spontaneous water droplet motion along the surface. The wettability gradients are formed by laser etching 35 μm wide, 35 μm deep channels into aluminum to form a surface with a gradually increasing solid area fraction. Different design variations are then proposed and systematically evaluated on the merits of their performance. An analytical model is also derived based on a balance of hysteresis and drag forces to predict the critical airspeed necessary for droplet movement as a function of the droplet size and surface contact angle. Experimentation has shown good agreement with the model for both the baseline and fixed-pitch channel surfaces and has also demonstrated that, in certain cases, up to 70 % lower critical airspeeds are needed to initiate droplet motion on these microstructured surfaces.

Analytical modeling of capillary force hysteresis in liquid bridge between two spheres of unequal sizes

Analytical modeling of capillary force hysteresis in liquid bridge between two spheres of unequal sizes

Characterization of water-controlled shape memory alloys for solar tracking applications

Growing demands for cleaner energy sources lead to innovations that require investigations in solar energy harvesting. Though numerous organic and inorganic photovoltaic devices have been explored for the solar power conversion, achieving a high efficiency is still an open challenge for the researchers. In this context, an efficient, self-adjusting solar power panel coupled with low-cost and high reliability is of great significance and demand. In this study, we investigate the potential of Shape Memory Alloy (SMA) actuators for solar tracking applications. Three SMA configurations were considered containing one and up to three SMAs arranged in parallel. The temperature range for the displacement experiments was 40°–60°. Additionally, three levels of mass were used, namely, 500 g, 600 g, and 700 g. The displacement experiments revealed that the addition of more SMAs into the configuration provided a more consistent performance. The force experiment revealed that two-SMA configuration achieved 60% higher force production compared to the one-SMA configuration under the same conditions while the three-SMA configuration was 31% higher than in the two-SMA configuration and 110% compared to the one-SMA configuration. Additionally, the force hysteresis of the two-SMA setup was smaller and closer to that of single-SMA configuration. The two-SMA configuration force hysteresis exhibited a more linear trend as compared to that of the three-SMA configuration. The outcomes of this work highlight the potential of using SMAs as actuators in solar-powered applications and that optimization in terms of the needed number of SMAs is required to meet the displacement and/or force requirements.

3D modeling and measurement of HTS tape stacks in linear superconducting magnetic bearings

Superconducting magnetic bearings (SMBs) are among the possible new technologies to be incorporated in maglev vehicles. Stacks of high-temperature superconductor (HTS) tapes can be used as an alternative to bulks, because stacks offer better mechanical properties, a better thermal conductivity and a simpler production process. Numerical modeling has been employed as a cost-effective, fast and reliable tool for improving the performance of SMBs. Several scenarios can be simulated with fast and relatively simple 2D models; however, in some cases using 3D models is inevitable. In this study, we use a full 3D model to solve the problem of magnetization of the tape stacks and obtaining the hysteresis force loop between a permanent magnet and the tape stacks. For this purpose, we employ an energy minimization-based method called minimum electromagnetic entropy production in 3D, combined with a homogenization technique and the Jc(B,θ) dependence of the HTS tape as input. The modeling results agree very well with the experiment both in the zero-field cooled and field-cooled conditions. The presented approach offers significant computational advantages, delivering faster and more efficient results compared to previously proposed 3D methods.

Solidity effects and azimuth angles on flow field aerodynamics and performance of vertical axis wind turbines at low Reynolds number

Solidity is an important parameter in the design, manufacture, and operation concerning energy yield and performance efficiency of VAWTs. This paper examined detailed aerodynamic analysis of solidity effects at constant Re and at low Reynolds numbers, the flow field and forces (lift, drag, and Torque coefficients) aerodynamics at various azimuth positions, and the changes in the performance and the flow field of VAWTs at a wide range of TSR. The simulation of two three-bladed VAWT configurations, σ = 0.26 (C = 0.03 m) and σ = 0.34 C = 0.04 m) over 1.5 ≤ λ ≤ 5.5 tip speed ratios on the CL, CD, CM, and speed were monitored and extracted, and the blades surrounding flow field is plotted from the CFD simulations. Performance (Cp -λ) curves, force hysteresis, and plots of the flow field for the turbines are matched at low λ = 2 5, high λ = 4, and Reynolds number to explain solidity effects on the VAWTs performance and aerodynamics thus providing good insight into the underlying aerodynamics for the differences in power coefficient between the two rotors in detail. This allowed the linking of the performance to the detailed force and flow field aerodynamics at various azimuth angles. It has been shown that the initiation of blade stall and stall vortices shedding started earlier on the σ = 0.26 VAWT than the σ =0.34 VAWT, thus affecting the force attained and ultimately limiting the rotor efficiency of σ = 0.26 compared with the σ =0.34 rotor and provided an improved understanding of solidity phenomenon that will help in the design, production and operation of VAWTs.

Experimental and numerical investigation of the hysteretic behavior of reinforced concrete column-steel beam interior joints under low seismic intensity levels

For the composite frame structure of concrete column and steel beam, a connection structure based on ribbed angle steel connector (RASC) is proposed, and the hysteresis performance and force transmission mechanism of this new type of composite joint are studied. Through quasi-static experimental research, the influence of beam and column cross-sectional dimensions on the bearing capacity, energy dissipation capacity, stiffness degradation, ductility, and failure form of the frame structure was analyzed. The results of experimental and finite element analysis show that the failure forms of this joint under low-cycle repeated loading are mainly manifested as the shear failure of concrete in the core area of beams and columns and sliding failure between angle steel connectors and steel beams, and the hysteresis curves of the joints are similar to those of frame beams and columns, respectively.

Quantitative analysis on resistant forces at oil-surfactant-rock interfaces with dynamic wettability characterization

Adhesion of oil at rock surface plays an important role in the liberation of oil from micro-/nano-pores, especially for heavy oil that has extremely high viscosity. Although molecular dynamics simulation is widely used to study the interfacial interaction for some specific oil-water-rock systems, experimental measurements provide more realistic and reliable evidence. In this work, we propose a dynamic wettability characterization method to indirectly measure resistant forces at oil-surfactant-rock interfaces, including frictional force, wettability hysteresis force, and viscous force, which are parallel with the oil-solid interface. The adhesive force, which is normal to the oil-solid interface is calculated through measurement of work of adhesion. The results show that work of adhesion instead of contact angle can better describe the adhesion of oil at solid surface. The effect of surfactant concentration on work of adhesion is different for water-wet and oil-wet surfaces. Moreover, average viscous forces are calculated through force analysis on oil drops moving along solid surface in different surfactant environments. It is found that viscous force has a magnitude comparable to the frictional force during the movement, while the wettability hysteresis force is negligible. On the other hand, the adhesive force calculated from the work of adhesion is also comparable to the viscous force. Therefore, both the resistant forces parallel with and normal to the oil-solid interface should be minimized for the liberation of oil from rock surface. This work proposes a simple method to evaluate the wetting capability of different surfactants and measure the adhesive force between heavy oil and rock surfaces indirectly, which provides insight into the adhesion of heavy oil at rock surface and would be valuable for the development of surfactant-based oil recovery methods.

Asynchronous propagation of atomic force and excited electronic charge in GaAs under proton irradiation

The studies for the interaction of energetic particles with matter have greatly contributed to the exploration of material properties under irradiation conditions, such as nuclear safety, medical physics and aerospace applications. In this work, we theoretically simulate the non-adiabatic process for GaAs upon proton irradiation using time-dependent density functional theory, and find that the radial propagation of force on atoms and the excitation of electron in GaAs are non-synchronous process. We calculated the electronic stopping power on proton with the velocity of 0.1–0.6 a.u., agreement with the previous empirical results. After further analyzing the force on atoms and the population of excited electrons, we find that under proton irradiation, the electrons around the host atoms at different distances from the proton trajectories are excited almost simultaneously, especially those regions with relatively high charge density. However, the distant atoms have a significant hysteresis in force, which occurs after the surrounding electrons are excited. In addition, hysteresis in force and electron excitation behavior at different positions are closely related to the velocity of proton. This non-synchronous propagation reveals the microscopic dynamic mechanism of energy deposition into the target material under ion irradiation.

CNN–AUPI-Based Force Hysteresis Modeling for Soft Joint Actuator

CNN–AUPI-Based Force Hysteresis Modeling for Soft Joint Actuator

Magnetically driven droplet manipulation on a smart surface prepared by electrospinning

Droplet manipulation using a magnetic field has vital applications in nanomaterials synthesis, lab-on-a-chip, and other domains. To address the separation issue between the droplet and the magnetic particle following the manipulation process, electrospinning technology was used to create a thermosensitive surface with changeable hydrophilicity. The droplet manipulation in this investigation could be divided into three steps: Step 1, the iron shot entered the droplet; Step 2, the iron shot carried the droplet forward; Step 3, the iron shot exited the droplet. The experimental findings revealed that a part of the iron shots could carry droplets with varying sizes when a magnetic field was activated. At the same time, droplet manipulation would be difficult employing high velocity iron shot movement or in a low temperature environment. Further investigation revealed two conditions for successful droplet manipulation. Firstly, the diameter of the iron shot had to be large enough to create adequate capillary force. Secondly, the hysteresis force between the droplet and the smart surface changed with the alteration of the hydrophilicity of the smart surface. More experiments indicated that the proposed droplet manipulation approach was also capable of achieving droplet transport on a slope, multi-droplets transport, and multi-droplets synthesis.

Reinforcement Learning-Based Adaptive Optimal Control for Nonlinear Systems With Asymmetric Hysteresis.

This article investigates the adaptive optimal tracking problem for a class of nonlinear affine systems with asymmetric Prandtl-Ishlinskii (PI) hysteresis nonlinearities based on actor-critic (A-C) learning mechanisms. Considering the huge obstacles arising from the uncertainty of hysteresis nonlinearity in actuators, we develop a scheme for the conflict between the construction of Hamilton functions and hysteresis nonlinearity. The actuator hysteresis forces the input into a hysteresis delay, thus preventing the Hamilton function from getting the current moment's input instantly and thus making optimization impossible. In the first step, an inverse model is constructed to compensate for the hysteresis model with a shift factor. In the second step, we compensate for the control input by designing a feedback controller and incorporating the estimation and approximation errors into the Hamilton error. Optimal control, the other part of the actual control input, is obtained by taking partial derivatives of the Hamiltonian function after the nonlinearities have been circumvented. At the end, a simulation is given to validate the developed solution.

The possible effect of surface barriers on the magnetic levitation of cylindrical superconductors

Abstract Superconducting magnetic levitation force measurements on large field cooled cylindrical MgB2 bulks with different diameters and thicknesses are reported. For these experiments, a special set-up permitting one to measure forces up to 500 N was used. In contradiction to previous measurements, the obtained force hysteresis cycles could not be reproduced with the analytical mean field model proposed by Bernstein et al (2017 Supercond. Sci. Technol. 30 065007). The failure of the model has been attributed to surface barriers effects which were not taken into account in the model. This last one was accordingly modified in order that the measured force cycles could be reproduced. Contrary to most other models describing surface barriers effects, the modified model suggests that above a threshold field anti-vortices and not vortices enter the superconductor. This behaviour is related to the storage by the superconductor of the mechanical work done by the operator. In addition, it has turned out that the threshold field is a decreasing function of the critical surface current density of the samples. As a consequence, the surface barriers effects occur only if this quantity and the critical current density are large enough. Otherwise, the internal magnetic field of the superconductor could be computed and was seen to be a decreasing function of the thickness of the superconductors.

Artificial magnetic disclination through local stress engineering

Magnetic disclination, characterized by the orientation of domain-wall arrangement rotating by π along a closed loop, is a type of topological spin texture. This study demonstrates the creation of artificial magnetic disclination through local stress engineering. By patterning nanotrenches in permalloy/poly(methyl methacrylate) bilayers, the tensile stress is relieved in a directional manner through the formation of boundaries. This orients the domain distributions at the microscale through magnetoelastic coupling. Two-dimensional (2D) closed boundaries induce curved stripe domains, which are ultimately converted into disclinations. The geometric configuration and arrangement of the disclination can be spatially adjusted via 2D boundary designation. The combination of in-situ magnetic force microscopy and hysteresis loop measurements links the microscopic domain configuration to the macroscopic magnetic properties of the system. Simulations reveal that the magnetic disclination is critically dominated by the local stress distribution within the topographic confinement.

How does roughness kill adhesion?

It is well-known that adhesion is strongly influenced by surface roughness. Nevertheless, the literature currently contains an ongoing debate regarding which roughness scales are primarily responsible for adhesion loss. In this study, we aim to contribute to this debate by conducting numerical simulations on self-affine fractal profiles with varying fractal dimensions.Our results reveal that the long-wavelength portion of the roughness spectrum plays a crucial role in killing adhesion when considering profiles with Hurst exponent H>0.5. Conversely, for profiles with H<0.5, results show a different trend, indicating that adhesive stickiness is also influenced by short wavelength roughness. These findings are corroborated by our recent experimental observations. In such case, adhesive hysteresis and pull-off force exhibit a continuous decrease with increasing roughness scales. However, for H>0.5, the pull-off force converges towards a finite value as the magnification increases.

Investigation of the ability of steel plate shear walls against designed cyclic loadings: Benchmarking and parametric study

Abstract Shear wall structure is one of the options as an appropriate lateral load-bearing system for new structures or as a means of retrofitting existing buildings. There are many types of shear walls, including steel plate shear walls (SPSWs). In enhancing its function, a thin SPSW is added with a stiffener. However, steel shear walls with stiffeners increase construction costs due to the time-consuming factor and the high cost of welding thin plates. Therefore, the infill shape was modified to increase the energy dissipation capacity of the SPSW. This study conducted simulations by varying the geometry, mesh, load factor, and materials used in SPSW. The specimen was modeled and tested using the ABAQUS application’s finite element analysis. The simulation was done by ignoring welded joints, fish plates, and bolts. The result that was the output of the simulation was hysteresis behavior. In addition, the contours that occurred were also observed in this study. The H1 shape had the best hysteresis force–displacement graphics among the nine other geometric shapes. Ten mesh sizes were tested, starting from 25 mm and increasing by multiples of 10 up to 115 mm. The results showed significant differences, with a 33.3% increase at the 115 mm size, which was considered irrational. The load factor represented the applied load in each substep, and a load factor of 2 means the load was doubled compared to a load factor of 1. Seven materials were tested, and high carbon steel outperformed others as it can handle loads up to 1,000 kN, demonstrating excellent energy dissipation capabilities.

Batch-Arrangement of Droplets on Silica Surface Based on Laser Wettability Modification

The laser wettability modification method for a silica surface was applied to the liquid batch-arrangement process. The droplets on the contact angle boundary produced by the modification moved to the more hydrophilic modified area because of the driving force of the surface energy hysteresis. Based on this phenomenon, a substrate with an array of 1-mm square modified areas was dip-coated with different concentrations of glycerin solution to align the droplets in batches. The experimental and analytical results showed that when the amount of liquid adhering to the hydrophilic area was small, the droplet shape became round owing to surface tension, and the reproduction of the modified rectangular shape was difficult. To increase the amount of the adhered liquid, the arrangement was conducted under conditions that increased the capillary number, such as high viscosity and high pull-out speed. The reproducibility of the intended shape was found to increase with an increase in the capillary number. Although the spatial resolution of the arrangement was limited by the laser spot size, it was demonstrated that the proposed method could align droplets onto a silica surface in a batch with the intended geometry.

Magnetic-Field Mediated Active Propulsion of Ferrofluid Droplets on a Wire.

Droplet actuation on wires or fibers is highly relevant to digital microfluidics applications. Several different passive or active actuation mechanisms have been studied, including capillary pressure, thermal gradient, tilting, acoustics, and electrowetting, to name a few. However, the lack of precise control and accurate droplet positioning during its actuation on a wire limits the use of earlier methods. On the other hand, using a nonuniform magnetic field to actuate a droplet on a micrometer-size wire helps overcome the above limitations. In this context, we elucidate the motion of microliter-size ferrofluid droplets, smaller than the capillary length, in the presence of a permanent magnet using a simple yet robust experimental setup, wherein the clamshell shape droplets hang on a wire at a predetermined distance from the magnet. Beyond a critical volume, the droplet starts moving toward the magnet while exhibiting shape evolution continuously. Using a high-speed videography technique, we uncover the intricate relationship between the magnetowetting, favoring continuous shape evolution of droplets of different sizes, and their actuation dynamics (velocity) on a wire, which has scarcely been explored. The most significant contribution of this study is the detailed evaluation of the shape factor (k), relating the shape evolution of the droplet to its velocity through the contact angle hysteresis force. A theoretical framework has also been proposed, comprising different forces in action, which is found to set forth a good match with the experimental results. The results from this study are expected to open up new avenues in digital microfluidics, specifically in drug delivery, ferrobotics, and droplet logic gates, to name a few.

Seismic isolation effect of a new type of friction pendulum bearing in high-speed railway girder bridge

Residual displacement exists in the traditional friction pendulum bearings (FPB) under the action of earthquakes, which makes them fail to self-reset. In view of this, a new type of FPB called double concave friction pendulum with spring (DCFPS) is proposed. Firstly, the restoring force model and hysteresis characteristics of the theoretical DCFPS are derived. Then, the seismic isolation effect of the high-speed railway simply supported girder bridges (HRSB) equipped with the DCFPS is evaluated. Finally, the optimal spring parameters of the DCFPS are determined in terms of the efficiency coefficient and the optimal order method. The results show that the DCFPS has superior self-reset performance, and the hysteresis curve is “S” shaped. The stiffness of the DCFPS gradually increases with the swing displacement, which heightens the overall stiffness of the structure equipped with DCFPS. After HRSB is installed DCFPS, the displacement of the girder and the residual displacement of the DCFPS itself are reduced. The optimal stiffness and the initial tension of spring for the bridges exemplified in the paper are suggested as 3000 kN/m and 9 kN, respectively, through the efficiency coefficient method and the optimal order method. This research proposes a feasible solution for reducing the maximum displacement and residual displacement of bearings under an earthquake.

Temperature- and Frequency-Dependent Nonlinearities of an Integrated Hydro-Pneumatic Suspension with Mixed Gas-Oil Emulsion Flow

Hydro-pneumatic suspension (HPS) systems are increasingly being implemented in commercial vehicles and various industrial equipment, which is mainly attributed to the integration of adaptable nonlinear pneumatic stiffness and hydraulic damping properties. The integrated HPS design with a shared gas-oil chamber, however, leads to gas-oil emulsion flow within the suspension chambers, which intricately affects the internal and external properties of the HPS, especially under variations in temperature and excitation frequency. This study experimentally and analytically investigated the temperature- and frequency-dependent properties of the hydro-pneumatic suspension with the gas-oil emulsion. Laboratory experiments were performed under three different near-constant temperatures (30, 40, and 50 °C) in the 0.5–8 Hz frequency range. An analytical model of the HPS was formulated considering the effects of temperature on internal fluid properties, gas-oil emulsion flow between the coupled chambers, the dynamic seal friction, and polytropic change in the gas state. The internal parameters, including the gas volume fraction, the discharge coefficient of the emulsion, and the dynamic friction components, as well as the external stiffness and damping characteristics, were determined. The relationships between these properties and the system temperature, velocity, and excitation frequency were further investigated. The simulated responses obtained under different excitations showed reasonably good agreement with the experimental results of the HPS. The results suggested that increased temperature yielded greater equivalent stiffness and comparable damping properties of the system. The gas volume fraction, discharge coefficient, and magnitude of seal friction generally tended to increase with increasing temperature. Increased excitation frequency led to greater hysteresis in hydraulic damping force and seal friction, and reduced seal friction magnitude and Stribeck effect.

Strong Influence of Pressure on the Magnetic Properties of MgB2 Bulk Superconductors

The influence of the pressure on the magnetic and superconducting properties of polycrystalline MgB2 bulks was studied. Bulk MgB2 samples were prepared using conventional in-situ solid state reaction and hot-pressing methods. The structural and electromagnetic properties of MgB2 samples were studied by using x-ray diffraction (XRD), scanning electronic microscope (SEM), magnetic hysteresis (M-H) and magnetic levitation force (Fz, Fx) measurements. XRD measurements proved high quality of MgB2 bulks with only small traces of MgO impurity phase. The zero-field Jc value reached 240 kA/cm2 for MgB2 sample produced by hot-press while 23 kA/cm2 for MgB2 sample produced by conventional in-situ at measurement temperature of 25 K. The max. levitation force values were obtained as 11.60 N and 15.42 N for MgB2 bulk samples produced by in-situ and hot-press methods at 25 K, respectively. All these magnetic measurements result indicate that pressure acts like driving force for manufacturing highly dense and high levitation capability MgB2 bulk superconductors.