Net Lateral Force Research Articles

Anomalous electrohydrodynamic cross-stream particle migration

Particle cross-stream migration in electrohydrodynamic microfluidic systems exhibits intriguing behaviors, which makes it interesting when viewed from a fundamental perspective and promising for nanoparticle focusing and separation applications. So far, particle behavior in such systems has been explained with the slip-induced lift force model (Saffman model), which predicts particle central or side focusing based on the direction of electric field and fluid flow. However, in our previous work, we observed particle migration patterns that did not adhere to the prediction of the Saffman model. In this work, we further studied this novel particle lateral migration behavior, which we termed the “anti-Saffman” behavior. We experimentally investigated how changing the conductivity of the suspending medium influences particle behavior and quantitatively measured the net lateral force experienced by the particles. Then, we compared this net force with the prediction of the relevant lift force models in the literature. We concluded that the anti-Saffman behavior is positively correlated with medium conductivity and shear rate (∝γ̇2). Furthermore, the comparison with the existing force models revealed that none of them can predict the experimentally observed particle lift. The net lift predicted by hydrodynamic lift models indicated that the underlying mechanism behind our experiments also potentially has a hydrodynamic origin. We believe this phenomenon offers the possibility of manipulating and separating nanoparticles suspended in standard aqueous electrolyte solutions, which makes it applicable to various biological samples.

Fish robotics: multi-fin propulsion and the coupling of fin phase, spacing, and compliance

Fish coordinate the motion of their fins and body to create the time-varying forces required for swimming and agile maneuvers. To effectively adapt this biological strategy for underwater robots, it is necessary to understand how the location and coordination of interacting fish-like fins affect the production of propulsive forces. In this study, the impact that phase difference, horizontal and vertical spacing, and compliance of paired fins had on net thrust and lateral forces was investigated using two fish-like robotic swimmers and a series of computational fluid dynamic simulations. The results demonstrated that the propulsive forces created by pairs of fins that interact through wake flows are highly dependent on the fins’ spacing and compliance. Changes to fin separation of less than one fin length had a dramatic effect on forces, and on the phase difference at which desired forces would occur. These findings have clear implications when designing multi-finned swimming robots. Well-designed, interacting fins can potentially produce several times more propulsive force than a poorly tuned robot with seemingly small differences in the kinematic, geometric, and mechanical properties.

Numerical study on transient four-quadrant hydrodynamic performance of cycloidal propellers

Aiming to investigate the transient four-quadrant hydrodynamics on blades under the circumferential motion of the steering center, an efficient three-dimensional (3D) model with half blades was established in this paper. The 3D model with half blades accounts for the hydrodynamic loss induced by the complicated mechanical structure, predicting the hydrodynamic performance of the high-load cycloidal propeller with high accuracy. On this basis, the open water manoeuvering performance of the cycloidal propellers in fully azimuth angle was simulated by Reynolds-averaged Navier-Stokes (RANS) solver, and the hydrodynamic loads and flow field characteristics were analyzed in detail. The research shows that the variation of azimuth angle φ induces the rapid response of hydrodynamic loads, which directly affects the direction of ship motion. Compared with φ = 0°, the increase in the azimuth angle of the steering center will enhance the negative impact of the inflow velocity on the wake flow field and the internal flow field within the blades. Additionally, the non-uniform flow in the main thrust direction leads to a significant increase in the undesired net lateral force. Our primary findings revealed in present paper should contribute to accurate prediction of hydrodynamic performance for high-load cycloidal propellers during maneuvering process.

Optimising the turning performance of serial split-hull underwater vehicles

This paper discusses optimising the 2D turning performance of serial split-hull underwater vehicles with symmetric hulls. Compared to traditional single-hull solutions, their unique design makes them appealing for bathymetry. Analysis of the turning motion of such vehicles is a topic of tremendous research interest. During the turning motion of an underwater vehicle, the lateral forces demand both surge and sway thrusters to maintain the path without slipping. This impacts the vehicle operation, making it harder to control, and uses more power. The net lateral force and associated sway thrust requirements can be significantly reduced using a split-hull design, where the individual hulls can have different orientations. It is possible to eliminate the sway thruster and cover the circular path using a split-hull underwater vehicle. The existence of the optimal turning configuration is proved where the need for lateral thrust is minimal compared to the axial one. The effects of turning diameter, joint torque, and axial thrust are also considered when choosing the vehicle configuration for the specific operational requirement. Experiments are used to validate the outcomes of the modelling and simulation. The knowledge gained here will aid in developing and effectively operating similar vehicles.

Interpretation of Young's equation for a liquid droplet on a flat and smooth solid surface: Mechanical and thermodynamic routes with a simple Lennard-Jones liquid.

In this study, we carried out molecular dynamics simulations of a cylindrical Lennard-Jones droplet on a flat and smooth solid surface and showed that Young's equation as the relation among solid-liquid, solid-vapor, and liquid-vapor interfacial tensions γSL, γSV, and γLV, respectively, was applicable only under a very restricted condition. Using the fluid stress-tensor distribution, we examined the force balance in the surface-lateral direction exerted on a rectangular control volume set around the contact line. As the mechanical route, the fluid stress integrals along the two control surfaces normal to the solid-fluid interface were theoretically connected with γSL and γSV relative to the solid-vacuum interfacial tension γS0 by Bakker's equation extended to solid-related interfaces via a thought experiment, for which the position of the solid-fluid interface plane was defined at the limit that the fluid molecules could reach. On the other hand, the fluid stress integral along the control surface lateral to the solid-fluid interface was connected with γLV by the Young-Laplace equation. Through this connection, we showed that Young's equation was valid for a system in which the net lateral force exerted on the fluid molecules from the solid surface was zero around the contact line. Furthermore, we compared γSL - γS0 and γSV - γS0 obtained by the mechanical route with the solid-liquid and solid-vapor works of adhesion obtained by the dry-surface method as one of the thermodynamic routes and showed that both routes resulted in a good agreement. In addition, the contact angle predicted by Young's equation with these interfacial tensions corresponded well to the apparent droplet contact angle determined by using the previously defined position of the solid-fluid interface plane; however, our theoretical derivation indicated that this correspondence was achieved because the zero-lateral force condition was satisfied in the present system with a flat and smooth solid surface. These results indicated that the contact angle should be predicted not only by the interfacial tensions but also by the pinning force exerted around the contact line.

Strong Solar Radiation Forces from Anomalously Reflecting Metasurfaces for Solar Sail Attitude Control

We examine the theoretical implications of incorporating metasurfaces on solar sails, and the effect they can have on the forces applied to the sail. This would enable a significant enhancement over state-of-the- art attitude control by demonstrating a novel, propellant-free and low-mass approach to induce a roll torque on the sail, which is a current limitation in present state-of-the-art technology. We do so by utilizing anomalous optical reflections from the metasurfaces to generate a net in-plane lateral force, which can lead to a net torque along the roll axis of the sail, in addition to the other spatial movements exhibited by the sail from solar radiation pressure. We characterize this net lateral force as a function of incidence angle. In addition, the influence of the phase gradients and anomalous conversion efficiencies characteristics of the metasurfaces are independently considered. The optimum incidence angle that corresponded with the maximum net lateral-to-normal force ratio was found to be −30° for a metasurface exhibiting 75% anomalous conversion efficiency with a phase gradient of 0:71k0.

Effect of the wall presence on the bubble interfacial forces in a shear flow field

Understanding the interactions between the bubbles and solid walls is important for predicting how the bubbly flow characteristics, such as void fraction and statistical distribution of bubble sizes, are affected by the presence of solid boundaries. In the present research, the numerical simulations with interface tracking method are performed to evaluate the interfacial forces’ closures in shear flow field under well-controlled conditions. The proportional-integral-derivative bubble controller is adopted to keep a single bubble at fixed position near the wall by balancing the forces in all three directions. This allows the extraction of the interfacial forces and the calculation of the corresponding coefficients. Validation tests have previously been conducted by the authors to compare the interfacial closures’ results against the experimental data. In this work, the influence of wall distance, relative velocity and bubble deformation on the interfacial forces are investigated. The results show that as the bubble approaches the wall, it experiences a transition from attractive force to repulsive force normal to the wall. The bubble Reynolds number also has significant impact on the interfacial forces: the net lateral force changes direction at Reb=35. The coupled phenomenon of bubble deformation and wall effect is investigated as well. The net lift sign change is observed at Eo=2.3 when the dimensionless wall distance (the ratio between the distance from the bubble center to the wall and the bubble diameter) is equal to 1. The presented studies complement the state-of-the-art knowledge and those are aimed to help improve the closure laws for interfacial forces and contribute to the multiphase computational fluid dynamics (M-CFD) closure model development.

Multi-states Combination Nonlinear Control of In-wheel-motor-drive Vehicle Dynamics Stability

A multi-states combination controller is presented to improve the dynamics stability of in-wheel-motor-drive (IWMD) vehicle. Based on the vehicle model with 14 degrees-of-freedom (DOFs), the proposed controller is designed and solved by using the nonlinear sliding mode algorithm, which generates the desired control variables to control vehicle velocity, yaw rate and side slip angle, cooperatively. The desired control variables, including the net longitudinal force, the net lateral force and the net yaw moment, are treated as the functions of the tyre longitudinal forces in the tyre coordinate system. Numerical simulation study is conducted to investigate the performance of the proposed controller. The simulation results show that the proposed multi-states controller significantly enhances vehicle dynamics stability over the single-state controller.

EShiver: Lateral Force Feedback on Fingertips through Oscillatory Motion of an Electroadhesive Surface.

We describe a new haptic force feedback device capable of creating lateral shear force on a bare fingertip-the eShiver. The eShiver creates a net lateral force from in-plane oscillatory motion of a surface synchronized with a "friction switch" based on Johnsen-Rahbek electroadhesion. Using an artificial finger, a maximum net lateral force of ±300 mN is achieved at 55 Hz lateral oscillation frequency, and net force is shown to be a function of velocity and applied voltage, as well as the phase between them. A second set of experiments is carried out on a human finger, and a lateral force of up to ±450 mN is achieved at a lateral oscillation frequency of 1,000 Hz. This force is reached at a peak lateral surface velocity of 400 mm/s and a peak applied voltage of 400 V. We develop a simple lumped parameter model of the eShiver, and a time domain simulation of the artificial finger is shown to agree with the experimental results. Three distinct zones of operation are found, which predict the limitations of force generation and which may be used for optimization. The human finger is found to be similar to the artificial finger in its dependence on actuation parameters, suggesting that the same lumped parameter model may be applied, albeit with different parameters. Curiously, the friction force due to Johnsen-Rahbek electroadhesion is found to increase substantially over time as the finger remains in contact with the surface. Considerations for optimizing the performance of the eShiver are discussed.

Response of a doublet to a nearby dc electrode of uniform potential.

The electric-field-assisted directed assembly of spherical colloidal particles near an electrode has been studied for nearly three decades. Recently, focus has shifted to the electric-field-assisted assembly and propulsion of nonspherical (i.e., anisotropic) particles. This paper describes calculations and results for a doublet of asymmetric ζ potential and size responding to a dc electric field. The doublet experienced a net vertical force that depended on both the asymmetry in ζ potential and lobe size. In addition, the doublet experienced a net lateral force perpendicular to the applied electric field. The lateral force depended on the difference in ζ potential of the two lobes, the lobe size asymmetry, and also the angle of inclination of the doublet. The net force was used to predict an apparent lateral velocity, which was found to be perpendicular to the applied electric field. In addition, the particle experienced rotation from a net torque that depended on the lobe size asymmetry and also the angle of inclination of the doublet. The magnitude of the predicted velocity was of the same order of magnitude as has been observed for particles responding to ac electric fields in experiments. These results demonstrate that lobe ζ potential, lobe size, and orientation of a colloidal doublet can be tuned to achieve propulsion.

The Vestibular-Evoked Postural Response of Adolescents with Idiopathic Scoliosis Is Altered

Adolescent idiopathic scoliosis is a multifactorial disorder including neurological factors. A dysfunction of the sensorimotor networks processing vestibular information could be related to spine deformation. This study investigates whether feed-forward vestibulomotor control or sensory reweighting mechanisms are impaired in adolescent scoliosis patients. Vestibular evoked postural responses were obtained using galvanic vestibular stimulation while participants stood with their eyes closed and head facing forward. Lateral forces under each foot and lateral displacement of the upper body of adolescents with mild (n = 20) or severe (n = 16) spine deformation were compared to those of healthy control adolescents (n = 16). Adolescent idiopathic scoliosis patients demonstrated greater lateral displacement and net lateral forces than controls both during and immediately after vestibular stimulation. Altered sensory reweighting of vestibular and proprioceptive information changed balance control of AIS patients during and after vestibular stimulation. Therefore, scoliosis onset could be related to abnormal sensory reweighting, leading to altered sensorimotor processes.

Experimental Determination of the Overturning Moment and Net Lateral Force Generated by a Novel Vertical Axis Wind Turbine: Experiment Design Under Load Uncertainty

Recent developments in harnessing wind energy propose new, radically different designs to alleviate some of the difficulties associated with conventional wind turbines. New designs however require testing for a variety of reasons ranging from gaining confidence in the analytical models used in the design and development through to satisfaction of certification requirements. Medium-scale prototype testing of large-scale concepts, where parameters such as the response of the structure and the loading conditions are often highly uncertain demand special consideration. This article presents the design of a special test rig and calculation methodology for the experimental determination of the overturning moment and net force generated by the NOVA Vertical Axis Wind Turbine using a field experimental setup. The design of the experimental model involves dealing with modelling uncertainties as loads in operation and therefore the response of the structure are largely unknown before testing has been carried out. The variability in the wind speed and direction also need to be accommodated for.

Manufacture of the poloidal field conductor insert coil (PFCI)

Within the framework of the R&D programme for international thermonuclear experimental reactor (ITER) the European team European Fusion Development Agreement (EFDA) has been charged with the design and manufacture of the poloidal field conductor insert coil (PFCI). The purpose of the PFCI is to test and demonstrate the performance of long-length full-scale NbTi conductors in ITER-relevant conditions. The PFCI will be tested in the central solenoid model coil test facility at the JAEA, Naka, Japan. This paper details the complete manufacturing of the PFCI including development, forming machining, pre-assembly, impregnation, final assembly and testing. The PFCI is a single-layered wound solenoid of nine turns with a transition joggle in the centre section of the winding and an intermediate joint connection between the upper termination and the main coil winding. To give the required overall dimensions to fit in the testing facility, preformed and machined glass resin composite filler pieces are assembled with the winding and is finally vacuum pressure impregnated (VPI) to create a single assembly unit. The PFCI is enclosed for assembly in a support structure, which consists of an upper and lower flange, each made up of four electrically insulated machined stainless steel castings, and 12 tie rods preloading the complete assembly in the vertical direction. The upper flange is equipped with four radial restraining jacks and the lower flange is equipped with four sets of studs and shear keys to withstand the net vertical and lateral electromagnetic forces. The PFCI is equipped with inductive heaters, voltage taps, temperature transducers, strain gauges and other instrumentation as diagnostics to monitor the performance. The current status of the manufacture is that the coil has passed the final acceptance tests and it is in the support structure assembly stage.

Dynamics of rapid vertical climbing in cockroaches reveals a template

Rapid, vertically climbing cockroaches produced climbing dynamics similar to geckos, despite differences in attachment mechanism, ;foot or toe' morphology and leg number. Given the common pattern in such diverse species, we propose the first template for the dynamics of rapid, legged climbing analogous to the spring-loaded, inverted pendulum used to characterize level running in a diversity of pedestrians. We measured single leg wall reaction forces and center of mass dynamics in death-head cockroaches Blaberus discoidalis, as they ascended a three-axis force plate oriented vertically and coated with glass beads to aid attachment. Cockroaches used an alternating tripod gait during climbs at 19.5+/-4.2 cm s(-1), approximately 5 body lengths s(-1). Single-leg force patterns differed significantly from level running. During vertical climbing, all legs generated forces to pull the animal up the plate. Front and middle legs pulled laterally toward the midline. Front legs pulled the head toward the wall, while hind legs pushed the abdomen away. These single-leg force patterns summed to generate dynamics of the whole animal in the frontal plane such that the center of mass cyclically accelerated up the wall in synchrony with cyclical side-to-side motion that resulted from alternating net lateral pulling forces. The general force patterns used by cockroaches and geckos have provided biological inspiration for the design of a climbing robot named RiSE (Robots in Scansorial Environments).

The vestibular control of balance after stroke

Objectives: To examine vestibular control of balance in those who recovered the ability to stand after middle cerebral artery (MCA) stroke. Methods: Sixteen patients with MCA stroke were compared with...

On the Mechanical Stability of Circular Discs in High Specific Load Capacity Magnetic Bearings

The most common designs of magnetic bearing utilize magnetic normal stress to exert net lateral force between the bearing rotor and the bearing stator. For such bearings, the specific load capacity (defined as the ratio of maximum bearing force to total bearing self-weight) is intrinsically limited by the magnetic saturation of iron at flux densities in the order of 2 Tesla. Specific load capacities of 100:1 are about at the limit of what is achievable with conventional designs. A new class of magnetic bearings has been proposed with a view to achieving substantially higher specific load capacity values. These bearings achieve net lateral force between bearing rotor and stator as a result of magnetic shear stress acting over a number of parallel annular airgaps. The airgaps are defined as the spaces between discs fixed to the stator and discs fixed to the rotor. Mechanical stability is one of the key limitations affecting the design of such bearings. Two separate effects conspire to attempt to destabilize the discs: out-of-plane magnetic negative stiffness and in-plane loading. The elastic stiffness of the discs must be sufficiently high to prevent instability. This paper presents methods for establishing where the stability boundaries lie.

On the relationship between surface uplift and gravitational extension

This paper highlights the relationship between isostatically supported surface elevation and the lateral buoyancy forces of an orogen. The former is a linear function; the latter is a quadratic function of the thickness of the lithosphere. Thus surface elevation and lateral buoyancy forces may have differing evolutions in the development of an orogen. Indeed, during the evolution of collisional orogens the qualitative relationship between these two parameters may reverse, so that only in the early orogenic evolution, topographically high regions exert a net lateral buoyancy force on topographically low regions. Later in the evolution this may change to a counterintuitive scenario in which there is a net lateral buoyancy force from the topographically lower regions toward the topographically higher regions. To illustrate this fact, we use a simple one‐dimensional kinematic model for an orogen which undergoes simultaneous thickening due to convergence and erosion at the surface. It can be shown that for reasonable erosion and thickening rates, surface elevation increases through time until a steady state is reached, while the lateral buoyancy force changes from positive to negative, giving rise to the inward collapse of an orogen. In the field this may be recognized as the occurrence of two successive coaxial convergent deformation events. Present‐day examples may be the formation of back arc basins where extension in the low‐lying hinterland of an Andean‐type mountain belt is caused by a gravitational compressive force exerted by the hinterland onto a belt of significantly higher surface elevation but possibly of lower potential energy.

Novel gradient coil set with canceled net thrust force for nuclear magnetic resonance applications

The interaction of the spatially varying main field components of a Magnetic Resonance Imaging (MRI) system with the currents of a gradient coil set generates axial and transverse Lorentz forces. In this paper, a novel technique for designing minimum inductance gradient coils with zero net axial and lateral Lorentz force is presented. Design examples are given for a short magnet geometry. A theoretical comparison between force-canceled and traditional gradient coils reveals a 270 to 2200 fold reduction for the Lorentz force, with up to 12% increase in stored energy.

Analytical prediction of the cogging torque in radial-field permanent magnet brushless motors

A method for predicting the cogging torque in radial-field permanent magnet brushless motors, based on the analytical calculation of the airgap field distribution and the net lateral force acting on the stator teeth, is developed and validated. The technique is applicable to both internal and external rotor motor topologies, modeled in a cylindrical coordinate system. It can also be applied to variants of the basic motor topologies, such as those with shifted magnets (i.e. spaced unsymmetrically) or unevenly distributed stator slots, and thus it can enable design features aimed at reducing the level of cogging torque to be evaluated. Based on the proposed analytical model, the effects of varying the leading design parameters on the cogging torque can be investigated. Hence, an optimal combination of design parameters can be identified to enable low cogging torque motors to be designed. >

Unilateral face-bows: A theoretical and laboratory analysis

The investigation evaluated and compared the effectiveness of five face-bow types in delivering unilateral distal forces to their inner-bow terminals. The face-bow types evaluated were bilaterally symmetrical, soldered offset, spring attachment, swivel offset, and power arm. A strain-gauge transducer system was used in the laboratory analysis. A theoretical analysis was also conducted, patterned after the method of Haack and Weinstein, and the results were compared to those obtained from the laboratory analysis. The method used for the theoretical evaluation of the sample face-bows was found to be a reliable means of approximating the percentage distribution of distal forces to the inner-bow terminals. The magnitude and direction of the net lateral forces delivered to the inner-bow terminals was also reliably determined. The results of the theoretical and experimental study of the five face-bow types indicate that the power-arm unilateral face-bow and the swivel-offset unilateral face-bow were effective in delivering a clinically significant unilateral distal force. The bilaterally symmetrical face-bow, the soldered-offset unilateral face-bow, and the spring-attachment unilateral face-bow were not effective in delivering clinically significant unilateral distal forces. Every face-bow effective in delivering unilateral distal forces will also deliver a net lateral force to the inner-bow terminals. This net lateral force will have a direction running from the inner-bow terminal receiving the greater distal force toward the terminal receiving the lesser distal force.