Transient Force Research Articles

Study on the tribo-dynamic performances of water-lubricated microgroove bearings during start-up

In the present works, a tribo-dynamic model considering the transient friction force is proposed to study the tribo-dynamic performances of the Water-Lubricated Microgroove Bearings (WLMB) during start-up under three acceleration modes. Based on the developed model, the tribo-dynamic performances of WLMB between three bottom shapes, i.e. triangle, left triangle, right triangle, are compared. In addition, the effects of the key factors, including the acceleration time, bearing shell thickness, surface parameters and dry friction coefficient, on the tribo-dynamic performances of WLMB are identified. Numerical results demonstrate that at the initial stage of start-up, the transient horizontal friction force drives the rotor along the opposite direction of rotation. The comparative analysis indicates that the sinusoidal acceleration mode and left triangle bottom shape may be recommended to yield the optimal tribo-dynamic performances of WLMB during start-up. The parametric studies reveal that during start-up, the acceleration time and the surface roughness significantly affect the tribo-dynamic performances, whereas the asperity curvature slightly affects the tribo-dynamic performances. Furthermore, the numerical results demonstrate that the dry friction coefficient plays an important role in tribo-dynamic analysis for WLMB during start-up.

Experimental investigation on the movement of triple-phase contact line during a droplet impacting on horizontal and inclined surface

The dynamic wetting process of a droplet impacting on a wall is a fascinating phenomenon relative to industrial application such as chemical engineering. However, the wetting detail, especially the characteristics of movement of the triple-phase contact line (TPCL) during impacting is not clear. In this paper, the dynamic behavior of the droplet during impacting was recorded by a high-speed camera, and the dynamic contact angle (DCA) of the droplet and the transient change of the velocity of the TPCL are mainly concerned. This paper will discuss the effects of droplet size, surface wettability, surface microstructure and the inclination angle of the plate on the TPCL movement, separately. Finally, a combined model of the transient force of the droplet on the inclined surface is proposed and verified by experimental data.

Collective intracellular cargo transport by multiple kinesins on multiple microtubules.

The transport of intracellular organelles is accomplished by groups of molecular motors, such as kinesin, myosin, and dynein. Previous studies have demonstrated that the cooperation between kinesins on a track is beneficial for long transport. However, within crowded three-dimensional (3D) cytoskeletal networks, surplus motors could impair transport and lead to traffic jams of cargos. Comprehensive understanding of the effects of the interactions among molecular motors, cargo, and tracks on the 3D cargo transport dynamics is still lack. In this work, a 3D stochastic multiphysics model is introduced to study the synergistic and antagonistic motions of kinesin motors walking on multiple mircotubules (MTs). Based on the model, we show that kinesins attaching to a common cargo can interact mechanically through the transient forces in their cargo linkers. Under different environmental conditions, such as different MT topologies and kinesin concentrations, the transient forces in the kinesins, the stepping frequency and the binding and unbinding probabilities of kinesins are changed substantially. Therefore, the macroscopic transport properties, specifically the stall force of the cargo, the transport direction at track intersections, and the mean-square displacement (MSD) of the cargo along the MT bundles vary over the environmental conditions. In general, conditions that improve the synergistic motion of kinesins increase the stall force of the cargo and the capability of maintaining the transport. In contrast, the antagonistic motion of kinesins temporarily traps the cargo and slows down the transport. Furthermore, this study predicts an optimal number of kinesins for the cargo transport at MT intersections and along MT bundles.

Interior Ballistic Characteristics of Electromagnetic Rail Launcher Considering the Dynamic Characteristics of Real Launcher

In this article, we have presented a three-dimensional transient electromagnetic (EM) force calculation model of the electromagnetic rail launcher (EMRL), which could quickly calculate the transient EM force of the armature and the rail through combining the finite-element method with experiment and proposed the model of structural stiffness nonlinearity of EMRL. To study the interior ballistic characteristics of the EMRL, through the self-programming and the development of commercial finite-element software for the second time, the article presents the first time that an interior ballistic simulation model (IBSM) of the EMRL with EM and structural coupling considering the structural stiffness nonlinearity of EMRL. The correction function is proposed to improve the prediction accuracy of armature dynamic parameters by IBSM and the calculation errors of displacement of IBSM can be guaranteed not to exceed 1% compared with the test results of magnetic probes array. A strain test platform with a demodulation frequency of 8000 Hz was established to verify the IBSM's ability to calculate dynamic characteristics of the armature and the rail. After considering the structural stiffness nonlinearity of EMRL, the simulation accuracy of IBSM has been greatly improved compared with that of linearity. The experimental test results show that the IBSM is ease of application and, meanwhile, performs satisfactorily in terms of high accuracy and low computation.

Transient solute drag and strain aging of dislocations

The transient drag force exerted by mobile solutes on a moving dislocation is computed using continuum theory. These mobile solutes form so-called Cottrell atmospheres around dislocations during static and dynamic strain aging. We evaluate the evolution of the drag force exerted by the atmosphere under two velocity time-histories: impulsive acceleration to a chosen velocity and a constant acceleration rate. A particular focus is on the conditions under which the stationary limit assumed by theories of dynamic strain aging is obeyed. According to our results, two conditions—one on the dislocation velocity and one on the acceleration rate—must be satisfied for the stationary limit to hold. Using the Orowan relation and a line tension model, we obtain estimates for the temperature, stress, strain rate, and dislocation density regimes where the stationary limit is valid, and compare these results with experiments for a few material systems.

Fault localization and analysis for a damaged hydrogenerator and a proposal to improve the standard for generator commissioning tests

Large power generators, especially hydropower generators with a few hundred megawatts power and a few ten kV voltages, have high inertial power while operating, so they must not only withstand the operating torques and forces during operation, but also the transient forces that may arise at the time of failures, while also taking into account economic considerations. It is worth mentioning that for a large hydroelectric generator, these transient electromagnetic forces are several times the operating forces.

Design and numerical simulation of a self-adaptive variable-diameter robot for in-pipe non-destructive inspection

This paper presents a design method and numerical simulation result of an smart in-pipe inspection robot with capability of adjusting its diameter to adapt to pipelines of non-constant inner diameter insensitive to non-smooth imperfect inner surface due to corrosion or erosion. A variable-diameter component consisting of a motor, gear wheels, a screw and nut drive system and a bar linkage is introduced to achieve this self-adaption. Moreover this paper presents a force-balance analysis by virtual displacement principle relating the normal force and internal spring force and conducts a numerical simulation of dynamic process of a 3D mechanical model across diameter-varying sections in horizontal, vertical manners and records transient inner spring force. The paper has significant reference merit for engineering application to ensure safe operation of pipelines.

Lift Regulation During Transverse Gust Encounters Using a Modified Goman–Khrabrov Model

This paper presents a framework for the estimated state regulation of the lift force for a maneuvering wing during a transverse gust encounter. An expression for the effective angle of attack of the wing is derived and used to construct a modified Goman–Khrabrov (GK) model for wing–gust encounters. Experiments were carried out in the University of Maryland water towing facility to identify parameters in the modified GK model and to evaluate its ability to represent gust encounters of varying gust strengths. Using this gust-encounter model, an observer-based feedback controller for pitch actuation is constructed to regulate the coefficient of lift of a wing during a transverse gust encounter. Closed-loop control simulations provided pitching kinematics that mitigated the transient force response. Gust encounter experiments were performed using the control signal from simulation as an open-loop control signal during an encounter with a known gust. The lift force time histories of the gust encounter experiments with control show effective mitigation of the peak lift force. The wing experienced transient forces that merit further investigation, including an initial transient peak and a later undershoot that may be due to uncertainty in the start of the gust region.

A 96-well culture platform enables longitudinal analyses of engineered human skeletal muscle microtissue strength

Three-dimensional (3D) in vitro models of human skeletal muscle mimic aspects of native tissue structure and function, thereby providing a promising system for disease modeling, drug discovery or pre-clinical validation, and toxicity testing. Widespread adoption of this research approach is hindered by the lack of easy-to-use platforms that are simple to fabricate and that yield arrays of human skeletal muscle micro-tissues (hMMTs) in culture with reproducible physiological responses that can be assayed non-invasively. Here, we describe a design and methods to generate a reusable mold to fabricate a 96-well platform, referred to as MyoTACTIC, that enables bulk production of 3D hMMTs. All 96-wells and all well features are cast in a single step from the reusable mold. Non-invasive calcium transient and contractile force measurements are performed on hMMTs directly in MyoTACTIC, and unbiased force analysis occurs by a custom automated algorithm, allowing for longitudinal studies of function. Characterizations of MyoTACTIC and resulting hMMTs confirms the capability of the device to support formation of hMMTs that recapitulate biological responses. We show that hMMT contractile force mirrors expected responses to compounds shown by others to decrease (dexamethasone, cerivastatin) or increase (IGF-1) skeletal muscle strength. Since MyoTACTIC supports hMMT long-term culture, we evaluated direct influences of pancreatic cancer chemotherapeutics agents on contraction competent human skeletal muscle myotubes. A single application of a clinically relevant dose of Irinotecan decreased hMMT contractile force generation, while clear effects on myotube atrophy were observed histologically only at a higher dose. This suggests an off-target effect that may contribute to cancer associated muscle wasting, and highlights the value of the MyoTACTIC platform to non-invasively predict modulators of human skeletal muscle function.

A cortical bone milling force model based on orthogonal cutting distribution method

In orthopedic surgery, the bone milling force has attracted attention owing to its significant influence on bone cracks and the breaking of tools. It is necessary to build a milling force model to improve the process of bone milling. This paper proposes a cortical bone milling force model based on the orthogonal cutting distribution method (OCDM), explaining the effect of anisotropic bone materials on milling force. According to the model, the bone milling force could be represented by the equivalent effect of a transient cutting force in a rotating period, and the transient milling force could be calculated by the transient milling force coefficients, cutting thickness, and cutting width. Based on the OCDM, the change in transient cutting force coefficients during slotting can be described by using a quadratic polynomial. Subsequently, the force model is updated for robotic bone milling, considering the low stiffness of the robot arm. Next, an experimental platform for robotic bone milling is built to simulate the milling process in clinical operation, and the machining signal is employed to calculate the milling force. Finally, according to the experimental result, the rationality of the force model is verified by the contrast between the measured and predicted forces. The milling force model can satisfy the accuracy requirement for predicting the milling force in the different processing directions, and it could promote the development of force control in orthopedic surgery.

TRPV4 channel opening mediates pressure-induced pancreatitis initiated by Piezo1 activation.

Elevated pressure in the pancreatic gland is the central cause of pancreatitis following abdominal trauma, surgery, endoscopic retrograde cholangiopancreatography, and gallstones. In the pancreas, excessive intracellular calcium causes mitochondrial dysfunction, premature zymogen activation, and necrosis, ultimately leading to pancreatitis. Although stimulation of the mechanically activated, calcium-permeable ion channel Piezo1 in the pancreatic acinar cell is the initial step in pressure-induced pancreatitis, activation of Piezo1 produces only transient elevation in intracellular calcium that is insufficient to cause pancreatitis. Therefore, how pressure produces a prolonged calcium elevation necessary to induce pancreatitis is unknown. We demonstrate that Piezo1 activation in pancreatic acinar cells caused a prolonged elevation in intracellular calcium levels, mitochondrial depolarization, intracellular trypsin activation, and cell death. Notably, these effects were dependent on the degree and duration of force applied to the cell. Low or transient force was insufficient to activate these pathological changes, whereas higher and prolonged application of force triggered sustained elevation in intracellular calcium, leading to enzyme activation and cell death. All of these pathological events were rescued in acinar cells treated with a Piezo1 antagonist and in acinar cells from mice with genetic deletion of Piezo1. We discovered that Piezo1 stimulation triggered transient receptor potential vanilloid subfamily 4 (TRPV4) channel opening, which was responsible for the sustained elevation in intracellular calcium that caused intracellular organelle dysfunction. Moreover, TRPV4 gene-KO mice were protected from Piezo1 agonist- and pressure-induced pancreatitis. These studies unveil a calcium signaling pathway in which a Piezo1-induced TRPV4 channel opening causes pancreatitis.

압축기 적용 고속열차의 터널 통과 시 공기력 저감 효과 연구

A series of CFD simulation have been conducted to evaluate the effect of the Hyperloop-type compressor adapted to a high-speed train to reduce the aerodynamic drag, the pressure transient and the micro-pressure during tunnel passage. Unsteady axi-symmetric Navier-Stokes equation has been employed to calculate the unsteady flow field induced by the KTX-Shancheon train through the Honam high-speed line tunnel. By comparing the calculation results with and without compressor, the effect of compressor to the reduction of tunnel transient forces has been analyzed. It is concluded that the adaption of compressor of 30% inlet area relative to the train cross-sectional area reduces the mean aerodynamic drag to 15.9%, the pressure change in the cabin up to 24.9%, and the micro-pressure wave to 40.3%.

Enriched continuum for multi-scale transient diffusion coupled to mechanics

In this article, we present a computationally efficient homogenization technique for linear coupled diffusion–mechanics problems. It considers a linear chemo-mechanical material model at the fine scale, and relies on a full separation of scales between the time scales governing diffusion and mechanical phenomena, and a relaxed separation of scales for diffusion between the matrix and the inclusion. When the characteristic time scales associated with mass diffusion are large compared to those linked to the deformation, the mechanical problem can be considered to be quasi-static, and a full separation of scales can be assumed, whereas the diffusion problem remains transient. Using equivalence of the sum of virtual powers of internal and transient forces between the microscale and the macroscale, a homogenization framework is derived for the mass diffusion, while for the mechanical case, considering its quasi-static nature, the classical equivalence of the virtual work of internal forces is used instead. Model reduction is then applied at the microscale. Assuming a relaxed separation of scales for diffusion phenomena, the microscopic fields are split into steady-state and transient parts, for which distinct reduced bases are extracted, using static condensation for the steady-state part and the solution of an eigenvalue problem for the transient part. The model reduction at the microscale results in emergent macroscopic enriched field variables, evolution of which is described with a set of ordinary differential equations which are inexpensive to solve. The net result is a coupled diffusion–mechanics enriched continuum at the macroscale. Numerical examples are conducted for the cathode–electrolyte system characteristic of a lithium ion battery. The proposed reduced order homogenization method is shown to be able to capture the coupled behavior of this system, whereby high computational gains are obtained relative to a full computational homogenization method.

Microneedle manipulation of the mammalian spindle reveals specialized, short-lived reinforcement near chromosomes.

The spindle generates force to segregate chromosomes at cell division. In mammalian cells, kinetochore-fibers connect chromosomes to the spindle. The dynamic spindle anchors kinetochore-fibers in space and time to move chromosomes. Yet, how it does so remains poorly understood as we lack tools to directly challenge this anchorage. Here, we adapt microneedle manipulation to exert local forces on the spindle with spatiotemporal control. Pulling on kinetochore-fibers reveals the preservation of local architecture in the spindle-center over seconds. Sister, but not neighbor, kinetochore-fibers remain tightly coupled, restricting chromosome stretching. Further, pulled kinetochore-fibers pivot around poles but not chromosomes, retaining their orientation within 3 μm of chromosomes. This local reinforcement has a 20 s lifetime, and requires the microtubule crosslinker PRC1. Together, these observations indicate short-lived, specialized reinforcement in the spindle center. This could help protect chromosome attachments from transient forces while allowing spindle remodeling, and chromosome movements, over longer timescales.

Magnetic Field Expulsion From a Conducting Projectile in a Pulsed Serial Augmented Railgun

The bore of a railgun is a harsh environment with high transient magnetic fields, temperature gradients, and forces. Most common payloads in railgun launch are made from conductive materials. In this article, we consider the effects of the transient magnetic field on a conducting payload during an electromagnetic launch by a serial augmented hexagonal railgun. The magnetic field distribution in the proximity of a solid aluminum payload was investigated by numerical calculations and experimentally by using a CMR-B-scalar sensor array.

Smooth adaptive hybrid impedance control for robotic contact force tracking in dynamic environments

PurposeThe purpose of this paper is to take transient contact force response, overshoots and steady-state force tracking error problems into account to form an excellent force controller.Design/methodology/approachThe basic impedance function with a pre-PID tuner is designed to improve the force response. A dynamic adaptive adjustment function that combines the advantages of hybrid impedance and adaptive hybrid impedance control is presented to achieve both force overshoots suppressing and tracking ability.FindingsThe introduced pre-PID tuner impedance function can achieve more than the pure impedance function in aspects of converging to the desired value and reducing the force overshoots. The performance of force overshoots suppression and force tracking error are maintained by introducing the dynamic adaptive sigma adjustment function. The simulation and experimental results both show the achieved control performance by comparing with the previous control methods.Practical implicationsThe implementation of the controller is easy and convenient in practical manufacture scenes that require force control using industrial robots.Originality/valueA superior robot controller adapting to a variety of complex tasks owing to the following characteristics: maintenance of high-accuracy position tracking capability in free-space (basic capabilities of modern industrial robots); maintenance of high speed, stability and smooth contact performance in collision stage; and presentation of high-precision force tracking capability in steady contact.

Quantitative Analysis of Attachment Time of Air Bubbles to Solid Surfaces in Water.

The attachment of air bubbles to solid surfaces in water is encountered in many natural processes and industrial applications. It has been established that the attachment can occur between hydrophobic surfaces and air bubbles. In this paper, we present novel experimental results to quantify the attachment in terms of the attachment time. We show that the attachment time can be determined from either the transient force curve or the transient film thickness. These techniques for determining the attachment time are based on the fact that the rupture of a thin liquid film produces a large attachment force and a rapid expansion of the three-phase contact radius in comparison with the expansion of the film radius. The experimental results are quantitatively analyzed using thin-film drainage theory and intermolecular forces, which include the advanced multilayer van der Waals force and the electrical double-layer force. The advanced van der Waals force theory allows us to incorporate the effect of interfacial gas enrichment (IGE) of dissolved gas in water at hydrophobic surfaces on the bubble-surface attachment. Critically, if the presence of IGE is ignored, the experimental results do not agree with the theory. Finally, IGE is shown to be a significant factor in controlling hydrophobic attraction between an air bubble and a hydrophobic surface and their attachment.

Formation of stable aggregates by fluid-assembled solid bridges

When a colloidal suspension is dried, capillary pressure may overwhelm repulsive electrostatic forces, assembling aggregates that are out of thermal equilibrium. This poorly understood process confers cohesive strength to many geological and industrial materials. Here we observe evaporation-driven aggregation of natural and synthesized particulates, probe their stability under rewetting, and measure bonding strength using an atomic force microscope. Cohesion arises at a common length scale (∼5 μm), where interparticle attractive forces exceed particle weight. In polydisperse mixtures, smaller particles condense within shrinking capillary bridges to build stabilizing "solid bridges" among larger grains. This dynamic repeats across scales, forming remarkably strong, hierarchical clusters, whose cohesion derives from grain size rather than mineralogy. These results may help toward understanding the strength and erodibility of natural soils, and other polydisperse particulates that experience transient hydrodynamic forces.

Single photon pulse induced transient entanglement force

We show that a single photon pulse incident on two interacting two-level atoms induces a transient entanglement force between them. After absorption of a multi-mode Fock state pulse, the time-dependent atomic interaction mediated by the vacuum fluctuations changes from the van der Waals interaction to the resonant dipole–dipole interaction (RDDI). We explicitly show that the RDDI force induced by the single photon pulse fundamentally arises from the two-body transient entanglement between the atoms. This single photon pulse induced entanglement force can be continuously tuned from being repulsive to attractive by varying the polarization of the pulse. We further demonstrate that the entanglement force can be enhanced by more than three orders of magnitude if the atomic interactions are mediated by graphene plasmons. These results demonstrate the potential of shaped single photon pulses as a powerful tool to manipulate this entanglement force and also provides a new approach to witness transient atom–atom entanglement.

Step Stretches and Shortenings Elicit Similar Transient Force Overshoots

Step Stretches and Shortenings Elicit Similar Transient Force Overshoots