Net Force Research Articles

Seismic resilient performance of code-designed, base-isolated slender steel buildings in firm soils

The seismic response of slender base-isolated structures can be significantly compromised during strong earthquakes, as significant tensional forces or uplifts can be demanded to exterior and corner base isolators. Nevertheless, there are few studies published in the literature where the expected seismic response of fully-designed base-isolated buildings according to a given base-isolation code or standard is shown and discussed when subjected to ground motions records related to the design earthquake scenario. In this paper, the authors present the results obtained from the cases of study of four code-designed base-isolated buildings, from 8 to 24 stories in height, with different global slenderness ratios H/L: 2.0, 2.5, 4.0 and 6.0. Subject buildings were assumed to be located at the city of Puebla, Mexico, in firm soil sites. Buildings were designed according to current base-isolation guidelines for the Manual of Civil Works (MOC) using the modal response spectrum analysis method while neglecting the vertical component in the design process. The base isolation system was composed of high-damping rubber bearings (HDRB). The considered structural system above the isolation system was a dual system composed of special concentrically steel braced frames (SCBFs) and special moment steel frames (SMFs). The resulting base-isolated (TI) to fixed-base (Tfb) natural periods ratio for the designed buildings was within the range 2.55 ≤ TI/Tfb ≤ 3.02. Nonlinear dynamic analyses were conducted for the designed buildings when subjected to five strongest pairs of orthogonal ground motions recorded during the September 19, 2017 Puebla-Morelos earthquake, which correspond to the design earthquake scenarios considered in MOC. In addition, the impact of the vertical ground motion component was evaluated for the most critical station. From the obtained results, it can be concluded that for the studied buildings, the modal response spectrum design method was safe enough to achieve resilient seismic designs. Nevertheless, net tensile forces and uplifts were triggered in corner base isolators, particularly for ground motion records which corresponding displacement spectra was close to the code displacement spectra for the target design base-isolated period TI. Tensile forces and uplifts in base isolators were slightly increased when considering the action of the vertical ground motion component of the critical station. In addition, peak accelerations at the floor levels were moderately increased when considering the vertical component, which may have detrimental effects in acceleration-sensitive non-structural components and the shear capacity of floor systems.

Small-scale measurement of the transition in fracture behavior of marine sediments

Bubbles grow and burrows extend through cohesive, muddy marine sediments by fracture. In contrast, sands are non-cohesive, granular materials. Natural sediments comprised of heterogeneous mixtures of muds and sands are common in coastal areas and provide important habitat for infaunal animals. To explore the transition from cohesive to non-cohesive mechanical behavior of natural sediments, we modified a probe designed for measuring fracture toughness (KIc). The helical probe is rotated and translated into sediment to grip a plug of sediment, then translated upward to break off the plug while force is measured. Fracture toughness is calculated from the peak net force. The probe shows clearly distinct results in muddier sediments, in which fracture occurs, and in sandier sediments, in which no fracture occurs. The modified probe is limited to near-surface sediments, but it provides a novel method for distinguishing cohesive sediments with tensile strength from non-cohesive sediments on scales relevant for burrowing animals or bubble growth. This measurement allows for comparison of surface and subsurface cohesion and for assessing how tensile strength depends on other properties of sediments.

Effect of inorganic cation on dynamic characteristics of bubble generation

Understanding the effect of inorganic cations on dynamic bubble generation is an important precursor for predicting the bubble characteristics in actual coal flotation. Using the high-speed motion acquisition system, we investigated the bubble growth in different inorganic salt solutions. The bubble generation process was divided into Formation, Expansion, and Contraction stages according to the contact angle between the bubble and the capillary as 90°. Na+, Mg2+, Ca2+, and Al3+ were found to promote bubble growth during the Formation and Expansion stages while restraining the growth during the Contraction stage. Al3+ roughly presented the most obvious promotion of the bubble generation. The dynamic bubble width and length during different bubble growth stages were analyzed to discuss the bubble pressure. The internal pressure increased as the bubble grew. The pressure difference inside and outside the bubble generally followed the order Na+ > Mg2+ > Ca2+ > Al3+. The forces acting on the bubble were attempted to be discussed. The net force acting on the bubble first kept constant and then decreased with the concentrations of Na+, Mg2+, and Ca2+, while it first decreased and then increased in the presence of Al3+. Our results can provide valuable insight into the development of the technology for mineral flotation.

Mode transition mechanisms in semi-passive flapping-wing propulsion or energy extraction

To facilitate the smooth transition of operational modes in self-sustaining micro-thrusters, this study focuses on a device employing semi-passive flapping wings. Transient numerical methods are used to analyze the variation of flap energy acquisition and propulsion characteristics with pitching frequency, and the relationship between the dominant vortex structure and the force characteristics is analyzed by using the integral momentum theorem and the dynamic mode decomposition (DMD) method. The results indicate that, under the investigated operational conditions, with an increase in the pitching frequency, distinct wake evolution characteristics were observed. In the energy harvesting operational regime, the wake patterns manifest as 2P + mS, 2S + mS, and mS types. During the transitional phase from energy harvesting to propulsion, the wake patterns shift from 2S + mS to 2S transitional types, eventually leading to the manifestation of a reverse Karman vortex street (2S RBVK). In the propulsion operational regime, the wake patterns consist of a reverse Karman vortex street and asymmetric reverse Karman vortex street phenomena. Simultaneously, it was observed that the transition of flapping-wing performance from energy harvesting to propulsion conditions delays behind the transformation of vortex street structures. This delay is attributed to the necessity for the flapping-wing device to overcome its own resistance before generating a net effective propulsive force. The contributions of unsteady wake to thrust primarily encompass vortex thrust, thrust due to localized fluid acceleration, induced momentum force, and induced pressure force. As the pitching frequency increases, the influence of wake vortices on propulsion also intensifies. The contribution of wake vortices to flapping-wing propulsion is determined by the spatial distribution of Lamb vectors and localized fluid accelerations. The conclusions drawn from the dynamic modal analysis and reconstructed flow field analysis of wake vortices align with the findings of the investigation of wake vortices based on the integral momentum theorem.

Powered Low-Speed Experimental Aerodynamic Investigation of an Over-Wing-Mounted Nacelle Configuration

Over-wing integration of ultrahigh bypass turbofan engines can be a solution for next-generation commercial transport aircraft since it eliminates the ground clearance issue and it has the potential to reduce ground noise due to acoustic shielding. Moreover, a unique characteristic of this installation type is the powered lift benefit at low-speed flight conditions. This paper aims to experimentally investigate the effect of the engine power setting on the low-speed aerodynamic performance of an over-wing-mounted nacelle configuration comprising a conventional tube-and-wing layout. Thus, low-speed wind tunnel tests were performed for a half-span powered scale model of the aforementioned configuration. The effect of the engine power setting on the wing lift and spanwise pressure distributions was investigated. The experiments were carried out for angles of attack varying from 0 to 6° and inlet mass flow ratios up to 2.4. The results were used to validate computational fluid dynamics simulations conducted for the same wind tunnel conditions. It has been shown that a significant powered lift benefit can be achieved for the studied configuration, without a penalty in the net propulsive force and that the lift increases linearly with the inlet mass flow ratio. Furthermore, it was observed that the engine power setting largely influences the pressure distributions along the wing, especially at the spanwise sections closer to the nacelle. The low-momentum zone created upstream of the engine at high power settings reduces the pressure at the wing’s upper surface, which is the main factor responsible for the increased lift. By taking advantage of such behavior, drag can potentially be reduced at takeoff and climb due to a lower flap setting required for the same lift.

Hypopharyngeal geometry impact on air-induced loads on the supraglottis

Exercise-induced laryngeal obstruction (EILO) describes paradoxical laryngeal closure during inspiration at high-intensity exercise. It is hypothesised that during intense activity, the air-induced loads on supraglottic walls overcome their internal stiffness, leading to the obstruction. Recent investigations have revealed that the air-induced loads on the supraglottic walls vary nonlinearly with increasing flow rate. It is, however, unclear whether certain geometric configurations of the hypopharynx and larynx may contribute to the predisposition to EILO. This study investigates the influence of hypopharyngeal and laryngeal geometry on upper respiratory tract airflow and air-induced forces. A computational fluid dynamics model is developed to study airflow through larynx. Four real, adult upper respiratory tracts with variable configurations are considered. Two steady, uniform inspiratory flow rates of 60 L/min and 180 L/min are considered. The analysis shows that geometries with a space lateral to the epiglottis (EpiS) and piriform fossae (PF) directs the hypopharyngeal and supraglottic pressure field to remain positive and increase with the flow rate. In geometries with EpiS and PF, pressure differential occurs around the aryepiglottic fold producing a net inward force over the region. The three-fold increase in flow rate induces near ten-fold increases in force over the region which may facilitate the closure. It is concluded that hypopharyngeal anatomy, particularly the piriform fossae, play a significant role in the obstruction of the supraglottic airway and should be considered in research and clinical assessment of EILO.

Assessment of Tractor Tires Used in Forest Conditions in Terms of Traction Performance and Impact on Ground

This paper presents the assessment of selected tractor tires used in forest conditions. The first element of this assessment is related to tractive properties, while the second part concerns the potential negative impact of the tires on the ground. The research was conducted on the skid trail located in a lowland pine stand in Poland (Lower Silesian District). The 9.5-24, 400/55-22.5 and 11.2R24 tires were used for the experiment, and the following tractive parameters were analyzed: traction force, pulling force and rolling resistance. These parameters were determined during the experiment using special measure stand mounted on a 3-point linkage of the tractor. In addition to the traction properties, the impact of the wheel on the ground was determined – this evaluation included measurements of footprint areas and calculation of contact pressures. Based on the obtained results, it was shown that the increase of the vertical load and reduction of the inflation pressure of tires can cause an increase in net traction force of as much as 35% and 16%, respectively. The analysis of contact areas and pressures showed that the widest tire (400/55-22.5) had the least negative impact on the ground. The reducing of inflation pressure allowed to obtain higher traction force, higher contact area and smaller contact pressures.

Individuals with rotator cuff tears unsuccessfully treated with exercise therapy have less inferiorly oriented net muscle forces during scapular plane abduction

Exercise therapy for individuals with rotator cuff tears fails in approximately 25.0 % of cases. One reason for failure of exercise therapy may be the inability to strengthen and balance the muscle forces crossing the glenohumeral joint that act to center the humeral head on the glenoid. The objective of the current study was to compare the magnitude and orientation of the net muscle force pre- and post-exercise therapy between subjects successfully and unsuccessfully (e.g. eventually underwent surgery) treated with a 12-week individualized exercise therapy program. Twelve computational musculoskeletal models (n = 6 successful, n = 6 unsuccessful) were developed in OpenSim (v4.0) that incorporated subject specific tear characteristics, muscle peak isometric force, in-vivo kinematics and bony morphology. The models were driven with experimental kinematics and the magnitude and orientation of the net muscle force was determined during scapular plane abduction at pre- and post-exercise therapy timepoints. Subjects unsuccessfully treated had less inferiorly oriented net muscle forces pre- and post-exercise therapy compared to subjects successfully treated (p = 0.039 & 0.045, respectively). No differences were observed in the magnitude of the net muscle force (p > 0.05). The current study developed novel computational musculoskeletal models with subject specific inputs capable of distinguishing between subjects successfully and unsuccessfully treated with exercise therapy. A less inferiorly oriented net muscle force in subjects unsuccessfully treated may increase the risk of superior migration leading to impingement. Adjustments to exercise therapy programs may be warranted to avoid surgery in subjects at risk of unsuccessful treatment.

Investigation of inertial focusing of micro- and nanoparticles in spiral microchannels using computational fluid dynamics

Inertial microfluidics utilize hydrodynamic forces for particle manipulation and require precise trajectory estimation for efficiency. This study examines parameters affecting micro- and nanoparticle inertial focusing in microchannels by introducing a novel sunflower geometry through asymmetric serpentine segments. This design enhances inertial focusing and particle separation through the Dean effect and continuous acceleration modulation, bolstering operational efficiency. Dynamic variations in lift (FL) and drag forces (FD) within the sunflower geometry augment their ratio, improving particle separation. Asymmetric serpentine attribute enhances lift force by adapting the coefficients (G1 and G2) along the channel and amplifies the net lift force. The varying FL in different sunflower zones concentrates particles of different sizes, while the channel curvature influences FD. While the traditional spiral microchannel only provides global forces due to its radius of curvature, the sunflower microchannel gives rise to the superposition of local forces induced by the expanding and narrowing changing of the serpentine shape and the global forces caused by the spiral shape. The study also examines the differences between local and global force effects on particle focusing. Ultimately, a passive separation of 500 nm particle is achieved by collecting the nanoparticle on the inner surface, while 1 μm particle locates at the central axis and 3.3 μm particle clusters on the outer surface. The significance of the study is that the effective passive particle separation could be managed even for sub micrometer particles without any auxiliary external forces but with inertial forces thanks to the novel sunflower microchannel design.

Exploring molecular interactions of potential inhibitors against the spleen tyrosine kinase implicated in autoimmune disorders via virtual screening and molecular dynamics simulations

ABSTRACT The spleen tyrosine kinase (Syk) plays a pivotal role in immune cells’ signal transduction mechanism. While fostamatinib, an FDA-approved Syk inhibitor, is currently used to treat immune thrombocytopenia, the search for improved Syk-targeted medications to treat autoimmune diseases is still underway. Herein, we screened 38,493 compounds against Syk and selected eight leads based on the docking score and ADMET properties, and performed 3200 ns long molecular dynamics simulations of the apo and Syk-ligand complexes. We considered R406, the active component of fostamatinib, as a control. The molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) calculations demonstrated the lead1 ( = -30.35 kcal/mol) exhibited a similar binding free energy as the control (= −29.82 kcal/mol). The Syk stabilizing effect of lead1 was also indicated in its network features, sampling space, and residual correlation motion analysis. We further generated 100 structural analogues of lead1 using deep learning, and one of the analogues displayed a better binding free energy (= −47.58 kcal/mol) compared to the control or lead1, facilitated by more favourable van der Waals interactions and lesser binding-opposing net polar forces. This analogue may be further exploited to develop effective therapeutics against Syk-associated diseases after validation in vitro and in vivo.

Design optimisation of non-axisymmetric exhausts for installed civil aero-engines

Future civil aero-engines are likely to operate with higher bypass-ratios (BPR) than current power-plants to improve propulsive efficiency and reduce specific thrust. This will probably be accompanied by an increase of fan diameter and size of the power plant. Consequently, future configurations are likely to require more close-coupled installations with the airframe due to structural and ground clearance requirements. This tendency may lead to an increase in the adverse installation effects which could be mitigated with non-axisymmetric exhausts. However, due to the prohibitive computational cost, limited regions of the design space have been studied. For this reason, a relatively low-cost design approach for the integrated system is required. The aim of this work is to establish a method to map the non-axisymmetric exhaust design space where the effects of the propulsion system installation are taken into account. The methodology relies on the generation of a design database using inviscid computational fluid dynamics (CFD) methods. This is used to characterise the design space, identify the dominant design parameters and build response surface models for optimisation. The candidate designs that arise from the optimisation are assessed with viscous CFD simulations to assess the aerodynamic mechanisms and performance characteristics. The result is a set of design recommendations for installed configurations with non-axisymmetric exhausts. The method is an enabler for the optimisation of installed propulsion systems and has provided an exhaust design with a 0.7% improvement on net vehicle force relative to an axisymmetric exhaust, for a close coupled configuration where the fan cowl is overlapped with the wing. A reduction in net vehicle force is expected to lead to a similar reduction in cruise fuel burn.

Dynamic and Isometric Force-Time Curve Characteristics Influencing Change of Direction Performance of State-Level Netball Players.

Smolarek, T, Haff, GG, Poon, WCK, Nagatani, T, Barley, OR, and Guppy, SN. Dynamic and isometric force-time curve characteristics influencing change of direction performance of state-level netball players. J Strength Cond Res 37(12): 2397-2404, 2023-Although multiple lower-body strength capacities are required to change direction rapidly, there is limited knowledge about the relative importance of these factors. Therefore, the purpose of this study was to assess the relationship between dynamic and isometric lower-body strength capacities and change of direction (COD) time in state-league netball players. Seventeen female athletes completed maximal isometric midthigh pull (IMTP), countermovement jump (CMJ), and modified 5-0-5 COD tests. Pearson's product moment correlations were used to determine the relationship between COD time and several IMTP and CMJ force-time curve characteristics. To assess the level of contribution of each force-time curve characteristic to COD time, multivariate-linear stepwise regression analyses were performed. A significant moderate correlation was noted between net relative peak force (PF) during the IMTP and COD time ( r = 0.488, p = 0.047), accounting for 23.8% of the variance in COD time. Moreover, concentric relative impulse during the CMJ was strongly correlated with COD time ( r = 0.718; p = 0.001), explaining 81.9% of the variance in COD time when combined with net relative braking PF in a stepwise regression. Based on these findings, female netball players who display higher concentric and isometric strength, as well as the ability to express higher impulses during the concentric phase of the CMJ, are likely to perform CODs faster. This may occur because COD requires the generation of greater propulsive forces, as well as reduced braking and contact times, along with greater isometric strength enabling effective repositioning of center of mass during COD tasks.

3D‐Architected low melting point alloys foam microstructure‐reinforced polymer composite with superior stiffness‐switchable for soft actuator

AbstractStiffness variable materials have aroused extensive research interest in smart devices, especially in soft actuators. However, achieving materials with high stiffness switch range remains challenging. Here, a novel three‐dimensional (3D) lightweight Field's metal (FM) foam was developed. Meanwhile, the polymer composite (SUFF) with superior stiffness switchable capacity was fabricated by embedding FM foam into a kind of designed stiffness variable polymer. The SUFF shows outstanding conductivity under relatively low FM volume fraction of 20.6%. Impressively, because of the extremely high modulus and fast transition of FM foam, the stiffness switch ratio of the SUFF are able to reach an ultra‐high value of 6987.5‐folds. Apart from its exceptional stiffness switchable capacity, the SUFF also possesses remarkable shape memory and self‐healing characteristics. Next, the SUFF was then fastened to a soft actuator as the stiffness changing units. The obtained actuator was able to exhibit a short heating–cooling cycle time of 44 s while using 10 A of current and 4°C water for cooling. Moreover, the actuator can reach remarkable values of 973 mN/mm and 4729 mN, respectively, for its stiffness and net force. Then, a soft robot gripper made up of three obtained actuators mounted on a base demonstrates its excellent load and stiffness switchable ability. It can lift a variety of objects with various forms with weights up to more than 3 kg. This study might provide a reference for application of stiffness variable materials in soft actuators.Highlights The FM foam were designed and synthetized by lost‐wax casting method. The polymer composite exhibits large stiffness switching range. The polymer composite achieves 6987.5‐folds rigid/soft stiffness ratio. A 3D‐printing soft actuator was fabricated using obtained polymer composite. The assembled robotic gripper can lift weights up to more than 3 kg.

Force decomposition on flapping flexible plate via impulse theory and dynamic mode decomposition

Dynamic mode decomposition (DMD) is a widely used method to extract dynamic information from sequential flow data, aiding our comprehension of fluid dynamics and transport processes. While DMD can unveil internal system laws and predict unsteady flow phenomena, the connection between DMD modes and the nonlinear hydrodynamic behavior of solid bodies remains unexplored. This study investigated the internal relationship between DMD modes and their impact on hydrodynamic forces. We employed a penalty-immersed boundary method to simulate the behavior of a flapping flexible plate in a uniform incoming flow, generating extensive datasets of vorticity fields. By applying DMD to these datasets, we identified key modes governing the flow dynamics, including the shear layer, symmetric vortex street, and antisymmetric vortex street. Furthermore, we utilized the impulse theory to analyze the force characteristics of the plate based on the corresponding DMD modes. The net force is determined by the combined contributions of the impulse force and the vortex force. Our findings reveal that the net horizontal force is primarily influenced by the first two modes. Specifically, mode 1, characterized by a dimensionless frequency of f*=0, contributes to thrust, whereas mode 2, with f*=1, contributes to drag. This physical investigation holds relevance for fluid–structure systems involving the interaction dynamics of flexible structures with unsteady wake vortex systems.

The Force-freeness of the Solar Photosphere: Revisit with New Approach and Large Data Sets

Although it is generally believed that the solar photosphere is not magnetically force-free owing to its high plasma β, the estimations of force-freeness using observed magnetograms have produced disputable results. Some studies confirmed that the photosphere is largely not force-free whereas some authors argued that the photosphere is not far away from being force-free. In a previous paper of ours we demonstrated that, due to the fact that the noise levels of the transverse field in the magnetograms are much larger than those of the vertical field, wrong judgments on the force-freeness could be made: a truly force-free field could be judged as being not-force-free and a truly not-force-free field could be judged as being force-free. Here in this Letter, we propose an approach to overcome this serious problem. By reducing the spatial resolution to lower the noise level, the heavy influence of the measurement noise on the force-freeness judgment can be significantly suppressed. We first use two analytical solutions to show the success and effectiveness of this approach. Then, we apply this new approach to two large data sets of active region magnetograms, obtained with the Helioseismic and Magnetic Imager/Solar Dynamics Observatory and Spectro-Polarimeter (SP)/Hinode, respectively. Our analysis shows that the photospheric magnetic fields are actually far away from being force-free. Particularly, and most notably, the mean value of F z /F p (where F z is the net Lorentz force in the vertical direction and F p the total Lorentz force) is as low as −0.47, with more than 98% of the active regions having ∣F z /F p ∣ > 0.1 when using the SP/Hinode magnetograms of true field strength.

Asymptotic profile for the interaction of a rigid ball and an incompressible viscous fluid

In this paper, we study the large time behavior of the solutions of the Stokes fluid-solid system. We compute the asymptotic expansion of the solution for Lq integrable initial data U0. We show that the asymptotic profile of the solution is a linear combination of the Stokes fundamental solution for the data with extra condition |x|U0∈L1. We also show that L1 integrability of the solution is strongly related to the net force exerted by the fluid on the boundary of the solid.

A self-loading suction cup driven by a resonant dielectric elastomer actuator

Suction cups are widely utilized in industries and robotics fields for object manipulation and robotic positioning. Conventional vacuum pumps can remove fluid from the suction cup continuously, enabling reliable adhesion. However, the bulky and rigid nature limits their integration with soft robotics. On the other hand, suction cups driven by soft smart materials offer better integration with soft robots but face challenges in achieving continuous fluid removal, resulting in potential suction failures in case of seal breaks. Aiming to address this limitation, a novel self-loading suction cup driven by a resonant dielectric elastomer actuator is proposed. This mechanism allows for continuous and efficient removal of the enclosed fluid in the sucker, thereby achieving successful and sustained adhesion. The structure design is presented and its fundamental working principles are revealed through theoretical analysis and experiments. The effects of several key design parameters (i.e., actuation electric field amplitude, moving mass, substrate roughness) on the performance of the suction cup are experimentally characterized to achieve performance optimization. This design demonstrates a maximum net suction force of 24.9 N (12.7 kPa), which is equivalent to 80 times its body weight. The suction cup design holds potential application values in soft robots, surveillance and environmental monitoring.

Ball-To-Hand Contact Forces Increase Modeled Shoulder Torques during a Volleyball Spike.

The volleyball spike is repeated many times in practices and games, presenting a high risk of overuse injury. Previous biomechanical analyses estimating forces on the shoulder during spiking have not included the force exerted on the arm by the ball, because no practical method exists to estimate the contact force between the ball and the hand. The objective of the study was to model the internal shoulder joint reactions while including the measured ball contact force. Ten adolescent female volleyball players performed spikes while we recorded 3D motion capture data for both ball and player. Using an impulse-momentum analysis, we estimated the ball contact force, then included the force in a computational simulation model to estimate the torques produced by the shoulder. The study found that post-contact ball velocities range from 8.6 m/s - 18.2 m/s with net forces between 238 N - 672 N. Most notably, when the ball contact force was included, the average modeled internal shoulder torque to internally rotate the arm increased from -26 N-m to +44 N-m (p < 0.001). These data suggest that neglecting the contact force may risk misinterpreting connections between biomechanics and injury due to spiking. More accurate joint mechanics models will lead to better injury prevention recommendations for volleyball players of all ages.

Deformation transients of confined droplets within interacting electric and magnetic field environment

A theoretical exploration and an analytical model for the electro-magneto-hydrodynamics (EMHD) of leaky dielectric liquid droplets suspended in an immiscible confined fluid domain have been presented. The analytical solution for the system, under small deformation approximation in the creeping flow regime, has been put forward. The study of droplet deformation suggests that its temporal evolution is exponential and dependent on the electric and magnetic field interaction. Furthermore, the direction of the applied magnetic field relative to the electric field determines whether the magnetic force opposes or facilitates the interfacial net electrical force caused by the electric field. Validation of the proposed model at the asymptotic limits of vanishing magnetic field shows that the model accurately reduces to the case of the transient electrohydrodynamic model. We also propose a magnetic discriminating function (ϕM) to quantify the steady-state droplet deformation in the presence of interacting electric and magnetic fields. The change of droplets from a spherical shape to prolate and oblate spheroids corresponds to ϕM&amp;gt; 0 and &amp;lt; 0 regimes, respectively. It is shown that a substantial augmentation in the deformation parameter and the associated EMHD circulation within and around the droplet is achieved when aided by a low-magnitude magnetic field. The analysis also reveals the deformation lag and specific critical parameters that aid or suppress this lag behavior, discussed in terms of relevant non-dimensional parameters.

Transition phase in the static thrust generation of the biomimetic fin with low oscillating frequency

Biomimetic fin propulsion could be a promising solution for an efficient underwater propulsion mechanism. It could be designed to generate thrust for underwater locomotion efficiently. Many studies have proposed that the flexibility characteristics of the fin affect its effectiveness in thrust generation; for example, a flexible fin generates more thrust than a rigid fin. In this regard, the rigid fin may suffer a mechanical disadvantage in thrust generation. This study introduces the presence of thrust generation phases in biomimetic fins. The phases could be caused by the interaction of the fins and the surrounding fluid. To distinguish the phases clearly, the experimental setup in this study was designed for no-flow conditions. This study presents three phases of thrust generation: negative, transition, and positive. The existence of the negative and transition phases explains the mechanical disadvantages of the rigid fin. Within the range of evaluated fin frequencies, approximately 80% of the average net force of the rigid fin is in the negative and transition phases, compared to only 20% in flexible fins. In comparison to less flexible and rigid fins, a flexible fin could maximize positive thrust production three times higher at high frequency. The vector composition analysis and dye-injection flow visualization reveal the transition phase by emphasizing the balancing process between the surface friction of the fin and the inertial component of the force of the fluid and fin interaction. This study demonstrates the independence of the transition phase from the flexibility characteristics of the biomimetic fin. Because the bending characteristic of the flexible fin could direct more vectors in thrust generation, the fin could act as a thrust vectoring agent. The findings of this study could be used as a guide in designing and implementing high-performance fin propulsion in low-speed underwater locomotion.