Force Mechanism Research Articles

Generation mechanism and empirical model of eddy current force and torque in drum-type eddy current separation

Enhancing the recovery efficiency of non-ferrous metals in eddy current separation is of great significance. In this study, the accuracy of the simulation model was verified by comparing the eddy current force. The transformation mechanism of the Lorentz forces into the eddy current force and torque in non-ferrous metal particles was revealed by analyzing various physical fields. Then, the influence of magnetic field parameters on eddy current, eddy current force, and torque was studied. It shows that the eddy current force and torque are affected by the vector gradient of the magnetic field and the magnetic flux density, respectively. Additionally, the time derivative of the magnetic field impacts the magnitude of the eddy current force and torque by controlling the eddy current. On this basis, the empirical models of eddy current force and torque were established by similarity theory. The results obtained can improve and expand the application of eddy current separation.

Finite Element Analysis of Combined Bearing Characteristics of Pile–Soil Interaction in Composite Foundation

Composite foundations have been widely used and promoted in practical engineering applications. However, research on the joint-bearing mechanism of piles and soil within composite foundations is still not comprehensive enough. This paper proposes a method for calculating the additional internal forces of piles and soil within composite foundations. Based on a three-dimensional finite element analysis, this study investigates the variation patterns of the stress, displacement, and additional internal forces of piles and soil in the depth direction under the action of upper loads when using friction piles and end-bearing piles. This research aims to reveal the bearing performance of piles and soil. The results showed that, under the same conditions and due to the presence of end-bearing effects, the internal forces experienced by the entire pile body of the end-bearing piles were more uniform, exhibiting significant advantages in resisting deformation and being able to withstand larger loads. Additionally, the diffusion mechanism of the vertical forces, stresses, and displacements of piles and soil is discussed. Due to the negative frictional resistance of soil and the influence of pile end-bearing effects, the distribution of internal forces and the displacements of piles and soil exhibited different characteristics. This study provides a scientific reference for the theoretical analysis and design of composite foundations.

A novel viscoelastic microfluidic platform for nanoparticle/small extracellular vesicle separation through viscosity gradient-induced migration.

Small extracellular vesicles (sEVs) are extracellular vesicles with diameters ranging from 30 to 150 nm, harboring proteins and nucleic acids that reflect their source cells and act as vital mediators of intercellular communication. The comprehensive analysis of sEVs is hindered by the complex composition of biofluids that contain various extracellular vesicles. Conventional separation methods, such as ultracentrifugation and immunoaffinity capture, face routine challenges in operation complexity, cost, and compromised recovery rates. Microfluidic technologies, particularly viscoelastic microfluidics, offer a promising alternative for sEV separation due to its field-free nature, fast and simple operation procedure, and minimal sample consumption. In this context, we here introduce an innovative viscoelastic approach designed to exploit the viscosity gradient-induced force with size-dependent characteristics, thereby enabling the efficient separation of nano-sized particles and sEVs from larger impurities. We first seek to illustrate the underlying mechanism of the viscosity gradient-induced force, followed by experimental validation with fluorescent nanoparticles demonstrating separation results consistent with qualitative analysis. We believe that this work is the first to report such viscosity gradient-induced phenomenon in the microfluidic context. The presented approach achieves ∼80% for both target purity and recovery rate. We further demonstrate effective sEV separation using our device to showcase its efficacy in the real biological context, highlighting its potential as a versatile, label-free platform for sEV analysis in both fundamental biological research and clinical applications.

Oscillatory instability of magneto-convection during the melting of non-Newtonian ferromagnetic nano-enhanced phase change materials at low Rayleigh number

This work complements mechanism of the oscillatory instability of magneto-convection in the process of melting heat transfer controlled by magnetic field at low Rayleigh number (Ra), aiming to provide a theoretical basis for improving the stability of energy storage system and melting manufacturing process. A latent heat storage cavity unit exposed in uniform magnetic field is designed to reveal the magnetic-controlled heat transfer in solid–liquid phase change process. The volume average method is used to describe porous media composite nano-enhanced phase change materials in latent heat unit. Special attentions are paid to the key parameters of Magnetic number (Mn) and Ra, and coupling flow heat transfer mechanism of magnetic force and natural convection effect is numerically studied. The evolution stages of different flow patterns are divided according to the Kelvin force, vorticity, velocity, flow field and isotherm distributions of characteristic points. Main results show that the magnetic field-modulated phase change process at low Ra can be divided into three stages, of which the second stage is characterized by periodic oscillations. Increasing Mn at fixed Ra accelerates the second stage of oscillatory convection heat transfer coming earlier and promotes melting. When Mn increase to 5 × 106, the full melting time is reduced to the greatest extent, resulting in 11.6 % reduction in heat storage but 17.4 % increase in heat storage efficiency. Three mechanisms of magnetic forced convection coupled with natural convection are found during the increase of Ra: synergistic (Ra < 2 × 103), antagonistic (2 × 103≤ Ra < 1 × 104), and natural convection-dominated (Ra = 1 × 104). Finally, the mode distribution map of Ra-Mn regulation is obtained, in which the unstable transformation mechanism of steady-state, periodic oscillation and chaotic oscillation heat transfer in the melting process under the control of magnetic field is described.

Performance of Steel Fiber Reinforced Concrete under Different Cooling Methods at High Temperature

Performance of Steel Fiber Reinforced Concrete under Different Cooling Methods at High Temperature

A Comprehensive Review on Cutting Tool Material in Hard Turning Performance

The work presents a comprehensive review on the influences of cutting tool material on the efficiency of hard turning process. Major trends in tool use and coating innovations are specified. The results of the hard turning process are evaluated through a number of main parameters such as surface roughness, cutting force, cutting heat, and wear mechanism. These results show that high cutting forces and cutting temperatures are still the huge challenges in choosing cutting tool materials in hard turning. This also limits the applicability of these materials and increases tooling costs due to the need to move towards using cutting tools with higher grades and hardness. The analysis results also point out the necessity of using appropriate cooling lubrication technology to support the hard turning process, helping to improve tool usage efficiency and the effectiveness of the hard turning process.

Effect of interfacial treatments on wet joints performance in steel-UHTCC composite bridge decks

Using Ultra-High Toughness Cementitious Composite (UHTCC) to the wet joints of composite bridge decks (CBDs) is a new solution to the cracking issue under hogging moments. Interfacial treatments and reinforcement details play a critical role in enhancing the crack resistance performance of wet joints in CBDs, while the quantitative impact of these factors on wet joints utilizing UHTCC materials remains uncertain. In this study, three different wet joint interfacial treatments (surface roughening, smearing epoxy adhesive, applying both) were proposed and the crack resistance performance were investigated through hogging moment tests on CBDs. During the tests, failure modes, flexural capacity, deformation behavior, force mechanism, crack propagation process and strain development of the CBD specimens with different wet joint details were discussed. To investigate the crack resistance performance of different wet joint interfaces, theoretical model for calculating nominal UHTCC tensile stress considering steel/UHTCC interfacial slip was constructed. Subsequently, the development curves of maximum crack width with nominal UHTCC tensile stress at wet joint interfaces were plotted. Test results indicated that interfacial treatment methods exert a distinct influence on the crack resistance performance of wet joints in steel-UHTCC CBDs. For reinforcement-enhanced wet joints, wet joint interfaces can be treated only with surface roughening, and the crack resistance performance was comparable to that treated with the combination of surface roughening and epoxy adhesive. Wet joint interfaces treated with the combination of surface roughening and epoxy adhesive exhibit a smaller value and growth rate of maximum crack width compared to those treated only with epoxy adhesive, and the cracking stresses σ0.05, σ0.1, and σ0.2 at wet joint interfaces were improved by 41.1%, 35.7%, and 232.6%, respectively. The wet joint interfaces in conventional wet joints are recommended to be treated with a combination of surface roughening and epoxy adhesive, resulting in smaller growth rates of interfacial maximum crack width. Moreover, the cracking stresses σ0.1 and σ0.2 at these interfaces were respectively improved by 577.4% and 400% compared to those treated only with surface roughening.

Flow excitation mechanisms of unbalanced impeller forces after pump power-trip of ultra-high head pump-turbines

Flow excitation mechanisms of unbalanced impeller forces after pump power-trip of ultra-high head pump-turbines

Seismic performance verification and theoretical stiffness calculation for a novel assembled concrete dry-connected beam-column node

This paper proposes a novel assembled concrete dry-connected beam-column node, which consists of a precast concrete beam with steel haunch plates at the end and a precast concrete column connected by ordinary strength long bolts. The quasi-static test study and finite element numerical simulation of the node are used to analyze the hysteresis curve, skeleton curve, and other performance indexes and investigate mechanical properties under low-cycle reciprocating load. The results demonstrate that the overall stress performance of the column specimen is outstanding; the specimen node possesses large deformation and good ductility, presenting semi-rigid characteristics; the damage of the specimen mainly includes the bending deformation of the connecting bolts. By analyzing the damage and force mechanisms of the node, an "equivalence method" for the initial rotational stiffness calculation of the beam-column combination node is established. Moreover, the formula for calculating the stiffness of this semi-rigid node is deduced.

Design of constant-force mechanisms using origami

The origami mechanisms possess numerous unique advantages, including folding, reconfigurability, and multi-stability. The presence of multi-stability introduces a novel concept for the design of constant force mechanisms (CFM). In this study, we present a CFM with multi-segment constant-force regions by leveraging the multi-stable characteristics of the origami mechanism. The design principle behind this CFM involves combining an accordion origami structure with positive stiffness and a Kresling origami structure with multi-segment negative stiffness regions. To achieve zero stiffness, the Kresling origami structure is aligned parallel to the accordion origami. To effectively utilize both the Kresling and accordion origamis, we have established a mechanical model that describes their respective stiffness characteristics to establish design rules for the constant-force mechanism. By carefully designing the parameters of these two origami structures, we evaluate how variations in the structural parameters of Kresling influence the constant force properties of our proposed multi-segment CFM. To illustrate its inherent property of providing constant force across multiple segments, we employ finite element analysis and experiments to obtain force-displacement curves for our mechanism. The results demonstrate the feasibility of our presented design method which paves the way for constructing a simple CFM.

Behavior of Modified Strut-and-Tie Model (STM) on Concrete Beams

Reinforced concrete components are generally designed to withhold shear and bending based on the assumption at strain varies linearly in a section where the applied force is a combination of shear with bending, torsion, or normal forces. The behavior of shear failure in reinforced concrete beams is very different from that in flexural failure. Shear failure is brittle without warning in the form of significant deflection, resulting in diagonal cracks in the beam then the shear force mechanism will be contributed by an arching action where this action can provide a reserve capacity large enough for the beam to carry the load. Nonlinear analysis using the strut-and-tie method is particularly useful for shear-critical structures where classical beam theory is not valid due to significant shear deformations. Strut-and-Tie Model research which is applied to concrete (25 MPa), also uses the optimal configuration FEM software tool from Strut-and-Tie which leads to the efficiency of Strut-and-Tie. The results of the optimization and modification of the Strut-and-Tie Model on concrete will also be applied to the experimental models tested until they fail so that the optimal conditions for numerical models will be obtained.Based on the analysis result of element model using ANSYS computational assistance program, the ultimate flexural capacity of the beam model will increase depending on the used STM model and inclination angle (Φ), at the STM type 2 high < 1000 mm, inclination angle (Φ) 45° having a decrease in ultimate shear capacity (Vu) of 49,31% against type 1, at the STM model 3 high < 1000 mm, with inclination angle (Φ) 45° having an increase ultimate shear (Vu) of 4,14% against type 1. Stress pattern performed bottle shape in line with diagonal strut. Ductility capacity will be decreased at inclination angle <45° of 27,11%, at inclination angle >45° will be decreased of 55,67%,

Mechanical analysis of mud return on deepwater drilling riser system

The process of mud return generates complex forces on the deepwater drilling riser system. However, the specific mechanism and effect of these mud forces on the deepwater drilling riser system remain unclear. To address this gap, an analysis methodology is proposed to investigate the mechanism and effects of mud forces. Mechanical and numerical models of the deepwater drilling riser system, taking into account mud return, are established based on the analysis methodology. The mechanical model incorporates centrifugal force, Coriolis force, inertial force, and friction force. Both the individual and comprehensive effects of these mud forces are thoroughly examined. The results show that centrifugal force and Coriolis force contribute to an increase in the lateral displacement of the riser. Friction force can decrease the lateral displacement of the riser. Inertial force can change the amplitude of riser vibration. Among these forces, friction force emerges as the most significant factor. The analysis results indicate that the maximum effect of friction force is 5.15%.

Experimental investigation of transition composite connections in historic style buildings

Historic timber buildings possess immense historical, artistic, and scientific value, but a few of them have survived after thousands of years of natural disasters and wars. Historic style buildings with modern construction material, imitating historic timber buildings forms, have emerged to inherit and promote traditional culture. To investigate the seismic performance of transition columns commonly used in historic style buildings, two full-scaled composite column transition (CCT) connections between steel reinforced concrete (SRC) square column and reinforced concrete (RC) circular column were designed and tested under invariable axial load and cyclic lateral load. Both failure patterns and force mechanism were studied based on the test process of the CCT connections. Then, the influence of axial compressive ratio on the mechanical behaviour of the CCT connections was assessed by looking at the hysteretic curves, backbone curves, characteristic loads, ductility, energy dissipation capacity and strength degradation. The results demonstrated that the failure patterns of the CCT connections were typical flexural failure, with the failure zone occurring at the upper column-root. The CCT connections exhibited excellent capacities of deformation and energy dissipation. As axial compression ratio increases, the failure of the CCT connection becomes more severe, leading to enhanced energy dissipation capacity. However, the strength and ductility of the CCT connection decrease. Based on the experimental results, an equation for calculating the lateral stiffness of CCT connections between SRC square column and RC circular column in historic style buildings was proposed, and verified to be accurate. The findings can provide necessary basis for the rational design and widespread application of historic style buildings.

Research on seedling sowing method based on high voltage electrostatic characteristics

In response to the difficult problem of high leakage rate and low seed pick-up rate of traditional air-suction seed dischargers. This study proposes a new high-voltage electrostatic vegetable seedling sowing method and system based on phase sucking of opposite charges and repulsive seeding of same charges. This method does away with small orifices and long conductance suction holes. It can solve the technical bottleneck of the traditional air-suction seed rower at the source, which causes a decrease in seed rowing accuracy due to clogging of the suction holes when facing irregular small vegetable seeds that are not pelleted. Combining high voltage electrostatic polarisation for seed vigour with precision seeding technology. Improving seed vigour and crop yield while precision sowing. Modelling the mechanics of adsorption seeding and repulsive seeding systems. Identify the main factors affecting electrostatic adsorption and phase repulsion forces and their interrelationships; Analysis of the decay mechanism of the electrostatic adsorption force upon repeated action. Proposing measures for the rapid restoration of the original equilibrium state of the dielectric insulation by reverse electric field polarization; Analysis of the migration pattern of electric particles during polarisation. Solving the equations for seed dynamics during sowing; At positive input voltages of 16 kV and negative input voltages of 0, 4, 8, 12, 16 and 20 kV. Separate dielectric insulation layer adsorption seeding tests. The test results show that: The reverse electric field polarisation of the dielectric insulating layer is effective in containing the electrostatic adsorption decay. The best containment was achieved at a positive input voltage of 16 kV and a negative input voltage of 16 kV; Seeding performance verification tests at a positive input voltage of 16 kV and a negative input voltage of 16 kV. The test results show that: The sowing conformity index was 90.25 %, the reseeding index 3.40 % and the missed sowing index 6.35 %. In the evaluation of applied research, the multi-objective optimization design with the objective function of maximum seed discharge qualification index, minimum leakage index and replanting index, the optimal parameter combinations of the test factors can be obtained as follows: the size of the type hole is 5.977 mm, and the output voltage of the positive high-voltage electrostatic generator is 16.423 kV, and at this time, the seeding machine's seed discharge qualification index is 90.78 %, the replanting index is 3.05 %, and the leakage index is 6.17 %. To verify the reliability of the optimal design of structural parameters, the seeding performance verification test is carried out, which can be obtained: the qualified index of row seeding is 90.54 %, the index of reseeding is 2.86 %, and the index of leakage is 6.60 %, which meets the technical requirements of precision seeding. The research not only provides a reference for the development of precision sowing machinery and equipment for irregular small-grain vegetable seeds. It also provides an academic reference for the research of quantitative adsorption and rapid separation methods and theories for irregular small particle materials.

Performance study of eccentrically braced steel frames with core tube flange connection

This paper proposes a kind of assembly brace connections adapted to the core tube flanged column connection joint of the frame-brace structure, starting from the eccentrically braced frame structure in the steel frame system and designing and completing a set of proposed static tests of the eccentrically braced frame with the core tube flanged column connection joint. By conducting in-depth analysis and research at three levels, namely the seismic performance of the eccentrically braced frame system, the performance characteristics of the core tube type flanged column connection joints, and the performance of assembled brace connections, the study has yielded insights into the force mechanism and failure modes of the core tube type flanged column connection joints within the eccentrically braced frame system; the eccentrically braced frame system has been validated to possess good seismic performance by analyzing hysteresis curves, typical section strains, and bolt forces. These analyses have shown that the system can meet the seismic requirements. Moreover, the assembled brace joints were destroyed later than the braces, indicating that the assembled brace connection joints could fulfill the requirement of “strong joints.”

Design and fabrication of a soft wearable robot using a novel pleated fabric pneumatic artificial muscle (pfPAM) to assist walking

Defects in walking can substantially impact individuals' quality of life. Utilizing wearable robots is one of the known methods to improve this daily activity for individuals with disabilities or limited mobility. In recent years, one of the challenges confronting researchers has been improving these devices' comfort and efficacy. This research aims to provide a lower-limb exosuit that aids in walking while being more comfortable and efficient than previous models in some certain respects. One factor that reduces the usability of these active wearables is the heavy and rigid structure of the force interaction mechanism and their inflexible actuators. This study's wearable robot benefits from a new Pneumatic Artificial Muscle (PAM) and a skeletal-free force mechanism, which, due to their innovative design and garment-like structure, when combined with a sensor network, weigh only 536 g. Also, the compressed air system is designed so that the user can quickly wear or remove it. The developed exosuit considerably improves the wearer's walking ability while remaining lightweight and comfortable. This claim has been checked and validated through numerous tests. The final results reveal that the user's posterior thigh muscles had an activity reduction of 7.4% in each complete gate cycle and 22.7% at peak time when using the exosuit compared with walking without the exosuit. Additionally, compared with the state where the exosuit was worn but inactive, the reduction was 16.2% overall and 63.9% at peak time. The motion cycle analysis also indicated that the system caused the user to take longer and more frequent steps than when walking without the exosuit. One of the reasons that has caused the performance of wearable robots to drop significantly as they become softer is the weakness of their actuators. In pursuit of this study's primary objective, a functional PAM was devised, which may have some of the most suitable features for such wearable robots. A contraction of up to 40%, a force-to-weight ratio of one thousand (with a weight of 44 g), a fabric-based structure for use alongside the body, low-cost production, contractibility at low pressures, and high controllability compared to its peer actuators are some of the soft contractile actuator features developed in this research.

Disentangling influences of driving forces on intra-annual variability in sediment discharge in karst watersheds

The intra-annual variability in sediment discharge was considerably influenced by the climate variability and vegetation dynamics. Because of the coupled or relationships between climatic and vegetation variables, it is still challenging to decouple the direct and indirect effects of climate variability and vegetation dynamics on hydrological and sediment transport processes. The purpose of this study is to decouple influences of individual driving force on intra-annual distribution of sediment discharge during 2003–2017 using the partial least squares structural equation model (PLS-SEM) method in four typical karst watersheds of Southwest China. The coefficient of variation (Cv), Completely regulation coefficient (Cr), Lorenz asymmetry coefficient and Gini coefficient were used to represent the intra-annual sediment discharge variability. Results showed that the monthly sediment discharge (190 % < Cv < 353 %) exhibited greater variability than its potential affecting factors (18 % < Cv < 101 %). From the PLS-SEM analysis, the water discharge, climate, and vegetation together explain 57 %–75 %, 64 %–79 %, and 53 %–80 % of the total variance in Cv, Cr, and Gini coefficient, respectively. Specifically, water discharge exerts the largest influence on sediment discharge variability (0.65 ≤ direct effect ≤0.97, P < 0.05), while vegetation dynamic mainly indirectly affects sediment discharge variability (−0.88 ≤ indirect effect ≤ −0.01) through influencing water discharge. The climate factors also principally indirectly affect the sediment discharge variability (−0.47 ≤ indirect effect ≤0.19) by affecting water discharge and vegetation. The PLS-SEM can effectively reveal the driving force and influencing mechanism of intra-annual sediment discharge changes, and provide an important reference for regional soil and water resources management in karst watersheds. Future studies can decouple the influences of the extreme climate, unique lithology, discontinuous soil, heterogeneous landscape, and special geomorphology on spatial variability in sediment discharge across different karst watersheds.

Retinal hemorrhages and damages from tractional forces associated with infantile abusive head trauma evaluated by wide-field fundus photography

We evaluated the distribution and types of retinal hemorrhages (RHs) and other damages in eyes with abusive head trauma (AHT). This retrospective, consecutive case series of AHT and non-AHT conditions involved 54 children with AHT, 43 children with head bruises, and 49 children with blunt eye trauma, each of non-AHT supported by reliable witness accounts. RHs and other damage were evaluated using ophthalmoscopy and wide-field fundus photography. A variety of RH types and other damage were identified in the AHT group but not in the non-AHT group. RHs in AHT extended from the posterior pole to the far periphery in 77% of eyes and on/near the veins in 86% and arteries in 85%, most of which were in the far periphery. Retinoschisis, white-dot lesions, and retinal folds were seen even in the far periphery. RHs on/near the veins and arteries, retinoschisis, and retinal folds suggest a traumatic mechanism of the tractional force of the vitreous that is attached to the entire retinal surface. Identifying the distribution and arterio and venous origins of RHs is a key factor in determining the association with trauma. Thus, wide-field fundus photography is useful to record and evaluate the origin of the RHs and other retinal damage.

Analysis of axial force and pressure pulsation of centrifugal pump as turbine impeller based on dynamic mode decomposition

To investigate the spatiotemporal evolution mechanism of the axial force on a centrifugal pump acting as a turbine, this study focuses on a single-stage single-suction centrifugal pump and applies dynamic mode decomposition (DMD) to decompose the flow field of the turbine impeller's axial force. The axial force of the impeller under three flow conditions, namely, 1.0Qd, 1.3Qd, and 1.6Qd, is extracted and analyzed. Results show that the DMD method can accurately extract the spatiotemporal coherent structural characteristics of the main modes of axial force, with the first five modes accounting for more than 99.97% of the total mode energy. Under the 1.3Qd condition, the flow field is stable, and the axial force remains constant over time with a very small degree of pressure pulsation. However, under the 1.6Qd condition, the flow field inside the pump becomes complex and unstable, leading to larger changes in axial force compared to the 1.0Qd condition, with an increase in 2.13 times. The amplitude of the pressure pulsation gradually decreases from the impeller inlet to the outlet under both 1.0Qd and 1.6Qd conditions, with vibration caused by the axial force mainly occurring at the impeller inlet. These findings provide a reference basis for improving the stability of centrifugal pumps acting as turbines.

Biomimetic Structure and Surface for Grasping Tasks.

Under water, on land, or in the air, creatures use a variety of grasping methods to hunt, avoid predators, or carry food. Numerous studies have been conducted to construct a bionic surface for grasping tasks. This paper reviews the typical biomimetic structures and surfaces (wedge-shaped surface, suction cup surface and thorn claw surface) for grasping scenarios. Initially, progress in gecko-inspired wedge-shaped adhesive surfaces is reviewed, encompassing the underlying mechanisms that involve tuning the contact area and peeling behavior. The applications of grippers utilizing this adhesive technology are also discussed. Subsequently, the suction force mechanisms and applications of surfaces inspired by octopus and remora suction cups are outlined. Moreover, this paper introduces the applications of robots incorporating the principles of beetle-inspired and bird-inspired thorn claw structures. Lastly, inspired by remoras' adhesive discs, a composite biomimetic adhesive surface is proposed. It integrates features from wedge-shaped, suction cup, and claw thorn surfaces, potentially surpassing the adaptability of basic bioinspired surfaces. This surface construction method offers a potential avenue to enhance adhesion capabilities with superior adaptability to surface roughness and curvature.