Force Profiles Research Articles

Three-Dimensional Finite Element Modeling of Drilling-Induced Damage in S2/FM94 Glass-Fiber-Reinforced Polymers (GFRPs).

Considering that the machining of composites particularly fiber-reinforced polymer composites (FRPCs) has remained a challenge associated with their heterogeneity and anisotropic nature, damage caused by drilling operations can be considerably mitigated by following optimum cutting parameters. In this work, we numerically evaluated the effects of cutting parameters, such as feed rate and spindle speed, on the thrust force and torque during the drilling of glass-fiber-reinforced polymers (GFRPs). A meso-scale, also known as unidirectional ply-level-based finite element modeling, was employed assuming an individual homogenized lamina with transversely isotropic material principal directions. To initiate the meso-scale damage in each lamina, 3D formulations of Hashin’s failure theory were used for fiber damage and Puck’s failure theory was implemented for matrix damage onset via user subroutine VUMAT in ABAQUS. The developed model accounted for the complex kinematics taking place at the drill–workpiece interface and accurately predicted the thrust force and torque profiles as compared with the experimental results. The thrust forces for various drilling parameters were predicted with a maximum of 10% error as compared with the experimental results. It was found that a combination of lower feed rates and higher spindle speeds reduced the thrust force, which in turn minimized the drilling-induced damage, thus providing useful guidelines for drilling operations with higher-quality products. Finally, the effect of coefficient of friction was also investigated. Accordingly, a higher coefficient of friction between the workpiece and drill-bit reduced the thrust force.

Flexible neural control of motor units.

Voluntary movement requires communication from cortex to the spinal cord, where a dedicated pool of motor units (MUs) activates each muscle. The canonical description of MU function rests upon two foundational tenets. First, cortex cannot control MUs independently but supplies each pool with a common drive. Second, MUs are recruited in a rigid fashion that largely accords with Henneman's size principle. Although this paradigm has considerable empirical support, a direct test requires simultaneous observations of many MUs across diverse force profiles. In this study, we developed an isometric task that allowed stable MU recordings, in a rhesus macaque, even during rapidly changing forces. Patterns of MU activity were surprisingly behavior-dependent and could be accurately described only by assuming multiple drives. Consistent with flexible descending control, microstimulation of neighboring cortical sites recruited different MUs. Furthermore, the cortical population response displayed sufficient degrees of freedom to potentially exert fine-grained control. Thus, MU activity is flexibly controlled to meet task demands, and cortex may contribute to this ability.

Molecular dynamics simulations of LiCl ion pairs in high temperature aqueous solutions by deep learning potential

Molecular dynamics simulation is an efficient method to study ion-pair association in high temperature supercritical fluid. Interatomic potentials based on neural-network machine learning shows outstanding ability of balancing the accuracy and the efficiency in molecular dynamics (MD) simulations. In present study, a neural-network potential (NNP) model for LiCl ion-pair in high temperature aqueous solutions was developed using database obtained by the first-principles density functional theory (DFT) calculations. With this NNP model, the structures of LiCl solution and the dissociation pathway of LiCl dissociation process were investigated. The results show that deep learning molecular dynamic (DPMD) simulations can accurately reproduce the radial distribution functions of ab initio MD simulations. And several metastable states were clearly identified from the dissociation 2D energy surfaces. In addition, the potential of mean force (PMF) profiles and corresponding association constants (Ka) were extensively investigated under a wide range of temperature-density (T = 330–1273 K and ρ = 0.45–1.0 g/cm3) conditions. The association constants calculated from DPMD are satisfactory compared with the experimental data. The study indicates that deep learning potential exhibits good capabilities to describe the association behavior of metal complex in high temperature aqueous solutions. This work also provides the microstructures and LiCl association constants in temperature aqueous solutions for which no experimental data exist.

Identification and Control of a Soft-Robotic Bladder Towards Impedance-Style Haptic Terrain Display

This letter evaluates the capabilities of a soft robotic pneumatic actuator derived from the terrain display haptic device, the “Smart Shoe.” The bladder design of the Smart Shoe is upgraded to include a pressure supply and greater output flow capabilities. Forcing characteristics are identified and incorporated as feedforward terms in a sliding-mode tracking controller to provide impedance control. A bench top setup is created to rigorously test this new type of actuator. The bandwidth and stiffness capability are evaluated relative to forces and displacements encountered during human gait. Four force vs. displacement profiles relevant to haptic terrain display are proposed and evaluated. It was found that the actuator could sustain a stiffness similar to a soft-soled shoe on concrete, as well as other terrain (sand, dirt, etc.). Compressions of the bladder done at 20 mm/s, which is similar to the speed of human gait, showed promising results in tracking a desired force trajectory. The results in this letter show this actuator can display haptic terrain trajectories, providing a basis for future wearable haptic terrain display devices.

Design of Pulse Forming Systems for Pulsed Electromagnetic Manufacturing Applications

Electromagnetic (EM) manufacturing techniques are currently being used to manufacture several industrial components with both tubular and sheet metal workpieces. The deformation behavior of the workpiece in an EM manufacturing process is governed by the spatial distribution and the temporal behavior of the magnetic pressure acting on it. This article considers the specific inverse problem of pulsed power source design from the output objective temporal force waveform required for final mechanical deformation in the workpiece. It presents a novel method using direct transcription formulation to calculate the necessary input needed to generate the desired temporal variation in the magnetic pressure on the workpiece. The required controlling parameters for the rise time control, the peak pressure control, and the fall time control are identified. A model waveform has been proposed for the temporal variations of the EM force on the workpiece, followed by the technique to synthesize the tooling coil current using direct collocation methods. The suitable pulsed power circuit topology is then identified, and a curve fitting method is proposed to exactly achieve the desired temporal features of the force profile. Without loss of generality, the technique is experimentally validated for the free-forming process of sheet metal using a uniform pressure tooling coil (UPTC).

Learning to Assemble Noncylindrical Parts Using Trajectory Learning and Force Tracking

The purpose of this article is to teach a robot assembly skills from demonstrations, and we attempt to train both the trajectory and the insertion force simultaneously. We encode human demonstrations data via motion primitives and, then, generate a reference trajectory and a prescribed force profile for a new assembly task using the combination of the motion primitives. We then propose an adaptive impedance controller to track the prescribed force with unknown environment stiffness, where the impedance parameters are estimated by the optimal solution of an equivalent linearization model. Our approach combines adaptive impedance control techniques with learning from demonstration on the same that makes it tractable and applicable to a real robot. Experiments on several typical noncylindrical parts illustrate the efficiency of the proposed method.

An Insight on Mud Behavior Upon Stepping

In this research we show a characterization of mud behavior under vertical stepping. We showed that mud stiffness can vary 45-fold and the energy spent to generate equivalent impulse can vary 2-fold depending on the mud water content, but also that stepping faster on mud leads to lower peak forces and higher energy consumption. Next, we showed that the peak force generated can be increased by 33% by changing the foot stiffness, but is reduced by 18% if stepping is repeated on the same spot. We then demonstrated how force control can be used to achieve identical force profiles on very different muds. These results will help to design mechanical parts or control strategies for legged robot locomotion on mud.

Predictability shapes movement kinematics and grip force regulation in human object handovers

In contrast to a self-generated action, a human-to-human object handover represents a semi-predictable task, due to a lack of exact knowledge about the partner's future movement behavior. Thus far, it has not been determined which behavioral characteristics result from dealing with this prevailing uncertainty, although this distinction would enhance the understanding of underlying motor control strategies in such semi-predictable situations. Behavioral effects of mutual interaction during object handovers were therefore investigated in the current study, by comparing grip force profiles and kinematic data from predictable solo-handovers (between the two hands of one person) with data from semi-predictable partner-handovers. There were significant decreases in passers' mean release rates as well as corresponding increases in handover durations in partner-handovers compared to solo-handovers. Likewise, receivers in partner-handovers employed lower mean grip force rates to take the object, which speaks for feedback reliance of both partners in the load transfer process of partner-handovers. Increased vertical object displacement in this phase might represent timing deficits due to the prediction uncertainties in partner-handovers. The data also provided first evidence that left-handed people serving as receivers in partner-handovers exhibit an altered take-over strategy compared to right-handed receivers.

Nonlinear Force and Vibration Analysis of an Interior Permanent Magnet Synchronous Generator With Eccentricity Detection

In this article, an in-depth study on eccentricities and their resultant vibration characteristics of an interior permanent magnet synchronous generator (IPMSG) for portable power generation is proposed. Also, this article introduces the eccentricity detection through vibration tests, since the vibration patterns caused by eccentricities are unique. Three basic eccentricity cases are investigated, namely the static, dynamic, and elliptical. Air-gap radial flux density and radial force density profiles are theoretically analyzed through mathematical modeling. With the help of finite-element analysis, the unique force profiles are verified for IPMSG of different cases, and the tooth force chopping process is studied. With modal analysis and testing, the harmonic vibration responses are predicted. An IPMSG prototype is fabricated and an overall eccentricity evaluation is reported through vibration tests.

Characterizing the separation behavior of photocurable PDMS on a hydrogel film during vat photopolymerization: A benchmark study

The separation between printed part and vat floor in constrained surface vat photopolymerization (VP) is a long-standing challenge, which limits the printability of soft materials like polydimethylsiloxane (PDMS). This study aims to characterize the separation behavior of a photocurable PDMS resin on a hydrogel film whose high-water content is expected to minimize the separation force. For this benchmark study, a commercially available polytetrafluoroethylene (PTFE) and an acrylate-based photopolymer are used as the baselines. Along with two printing speeds, a total of eight cases (two films, two resins, and two speeds) are used in the design of the experiment. A modified digital light processing (DLP) printing with a built-in force sensor is used to sample the force profile during the printing. The results show that PDMS has a lower separation force but longer separation distance than those of the acrylate-based resin. The hydrogel film can further minimize the separation force and distance; those values are under 0.5 N in PDMS printing. A lower speed can further reduce the separation force, but increase separation distance, likely due to the rate-dependent material properties. These results suggest a potential solution to print PDMS fast with small and fragile features.

Simultaneous monitoring of mouse grip strength, force profile, and cumulative force profile distinguishes muscle physiology following surgical, pharmacologic and diet interventions

Grip strength is a valuable preclinical assay to study muscle physiology in disease and aging by directly determining changes in muscle force generation in active laboratory mice. Existing methods to statistically evaluate grip strength, however, have limitations in the power and scope of the physiological features that are assessed. We therefore designed a microcontroller whose serial measure of resistance-based force enables the simultaneous readout of (1) peak grip strength, (2) force profile (the non-linear progress of force exerted throughout a standard grip strength trial), and (3) cumulative force profile (the integral of force with respect to time of a single grip strength trial). We hypothesized that muscle pathologies of different etiologies have distinct effects on these parameters. To test this, we used our apparatus to assess the three muscle parameters in mice with impaired muscle function resulting from surgically induced peripheral pain, genetic peripheral neuropathy, adverse muscle effects induced by statin drug, and metabolic alterations induced by a high-fat diet. Both surgically induced peripheral nerve injury and statin-associated muscle damage diminished grip strength and force profile, without affecting cumulative force profile. Conversely, genetic peripheral neuropathy resulting from lipin 1 deficiency led to a marked reduction to all three parameters. A chronic high-fat diet led to reduced grip strength and force profile when normalized to body weight. In high-fat fed mice that were exerted aerobically and allowed to recover for 30 min, male mice exhibited impaired force profile parameters, which female mice were more resilient. Thus, simultaneous analysis of peak grip strength, force profile and cumulative force profile distinguishes the muscle impairments that result from distinct perturbations and may reflect distinct motor unit recruitment strategies.

Performance evaluation of a tactile and kinesthetic finger feedback system for teleoperation

Teleoperation during a catastrophic event requires an interface that can perform under frequently changing circumstances caused by unpredictable and dangerous conditions. Thus, teleoperation interfaces are under active development to provide both visual and haptic feedback to the fingers. However, studies of teleoperation systems with finger haptic feedback based on force profiles are difficult to conduct because of interface limitations. Therefore, in this paper, we introduce an intuitive teleoperation interface, an anthropomorphic teleoperated robot, and a hand-wearable force-feedback system that provides various feedbacks to the fingers. We combined these systems to compare and evaluated the performance of tactile and kinesthetic finger feedback using two experiments: maintaining appropriate grip force for variably fragile objects and following a force trajectory that changed in real time. Ten subjects participated in the experiments. The results were analyzed using repeated measures analysis of variance. Feedback factors differed significantly. Provision of force feedback to the user’s finger was most effective in both teleoperation experiments.

A WaveNet-based fully stochastic dynamic stall model

Abstract. Accurate modeling of the dynamic stall remains a challenge for the design and construction of turbine blades and helicopter rotors. At the same time, wind turbines, for instance, are becoming steadily larger, further increasing the demands on their structure and necessitating even more detailed modeling of the forces at hand. The primarily used (semi-)empirical models today have a long research history and are invariably based on phase-averaged data from oscillating blade pitch experiments. However, much potential for more accurate modeling of uncertainties and force peaks is wasted here, since averaging blurs many features of the response signals. Even computational fluid dynamics can help little in this regard, since the Reynolds-averaged Navier–Stokes equations used in practice cannot account for cycle variations, and scale-resolving models require extremely large amounts of computational resources. This paper presents an approach for a fully stochastic machine learning model that can nevertheless simulate these critical properties. Aerodynamic coefficients are compared with experimental data for different test cases. It is shown that synthetic force profiles which cannot be distinguished from the experimental data visually and are very close to them in the frequency spectrum can be generated. Additionally, attention is drawn to the difficulty of evaluating such a model, as traditional error metrics are of little use. A combination of dynamic time warping and the Earth mover's distance provides a robust solution for this problem.

The attraction between like-charged oil-in-water emulsion droplets induced by ionic micelles

Although extensive work has been reported that micelles can induce depletion attraction between two solid spheres or a sphere and a plate, the effect of different micelles on the depletion between two soft surfaces has been rarely reported. Optical tweezers were used to measure the forces between two oil-in-water emulsions in solutions of sodium dodecylbenzenesulfonate (SDBS), cetyltrimethylammonium bromide (CTAB), and octylphenol polyoxyethylene ether with ten oxyethylene glycol ether (OP-10) at varying concentrations. When the concentration of surfactant below their critical micelle concentration (cmc), force profiles between two emulsion droplets were purely repulsive. As the concentration of SDBS or CTAB above its cmc, the attraction between like-charged O/W emulsion droplets was dominant. The coalescence of the like-charged O/W emulsion droplets is observed. For nonionic surfactants OP-10, even if the cmc had been reached, the attractive force between O/W emulsion droplets couldn’t be measured. Results shows that attractive forces between two like-charged emulsion droplets of several microns in solution can also be induced by ionic micelles and the depletion was enhanced by counterion osmotic pressure. Our work suggests that the effect of micelle-induced depletion on the force between two solid surfaces can be used to predict forces between several micrometers of emulsion droplets.

Foot arch rigidity in walking: In vivo evidence for the contribution of metatarsophalangeal joint dorsiflexion

Human foot rigidity is thought to provide a more effective lever with which to push against the ground. Tension of the plantar aponeurosis (PA) with increased metatarsophalangeal (MTP) joint dorsiflexion (i.e., the windlass mechanism) has been credited with providing some of this rigidity. However, there is growing debate on whether MTP joint dorsiflexion indeed increases arch rigidity. Further, the arch can be made more rigid independent of additional MTP joint dorsiflexion (e.g., when walking with added mass). The purpose of the present study was therefore to compare the influence of increased MTP joint dorsiflexion with the influence of added mass on the quasi-stiffness of the midtarsal joint in walking. Participants walked with a rounded wedge under their toes to increase MTP joint dorsiflexion in the toe-wedge condition, and wore a weighted vest with 15% of their body mass in the added mass condition. Plantar aponeurosis behavior, foot joint energetics, and midtarsal joint quasi-stiffness were compared between conditions to analyze the mechanisms and effects of arch rigidity differences. Midtarsal joint quasi-stiffness was increased in the toe-wedge and added mass conditions compared with the control condition (both p < 0.001). In the toe-wedge condition, the time-series profiles of MTP joint dorsiflexion and PA strain and force were increased throughout mid-stance (p < 0.001). When walking with added mass, the time-series profile of force in the PA did not increase compared with the control condition although quasi-stiffness did, supporting previous evidence that the rigidity of the foot can be actively modulated. Finally, more mechanical power was absorbed (p = 0.006) and negative work was performed (p < 0.001) by structures distal to the rearfoot in the toe-wedge condition, a condition which displayed increased midtarsal joint quasi-stiffness. This indicates that a more rigid foot may not necessarily transfer power to the ground more efficiently.

Multi-objective Optimization and Sensitivity Analysis of the Parameters Affecting Sealing Performance of the Piston Rings Face through the Validated Model for the Four-stroke Bi-fuel Engine

A multi-objective optimization study and sensitivity analysis of a SI engine piston-rings pack using dynamics analysis software (AVLExcite Piston&Rings) and optimizer software (modeFRONTIER) are presented. The effects of changing the piston rings' tangential force and face profile on the oil and gas flow behavior inside the piston-rings pack are investigated by calculating the lubrication oil consumption, blow-by, and power losses. The feasibility of the simulation model was determined by comparing it to empirical data obtained from experimental testing of the engine to estimate the amount of oil consumption and blow-by gas flow. Using the statistical modeling algorithm SS-ANOVA, multi-objective optimization investigates the individual and interaction effects of the three rings' tangential forces. This method significantly reduces the time and cost required to find the optimal design, an approach not reported in previous studies. The results showed a strong correlation between simulation and experimental test results, indicating an acceptable match during model validation. Furthermore, the predictions show that tangential forces affect sealing performance; thus, modifying the tangential force resulted in a 30% reduction in oil consumption and less than a 0.8 percent increase in friction. Furthermore, the LKZ oil control ring model efficiently reduces oil consumption by 25% while slightly increasing friction (about 10 percent without face coating).

Binding of human serum albumin with uranyl ion at various pH: an all atom molecular dynamics study

Uranium is routinely handled in various stages of nuclear fuel cycle and its association with human serum albumin (HSA) has been reported in literature, however, their binding characteristics still remains obscure. The present study aims to understand interaction of uranium with HSA by employing all atom molecular dynamics simulation of the HSA-metal ion complex. His67, His247 and Asp249 residues constitute the major binding site of HSA, which capture the uranyl ion (UO2 2+). A total of six sets of initial coordinates are used for Zn2+-HSA and UO2 2+-HSA system at pH = 4, 7.4 and 9, respectively. Enhance sampling method, namely, well-tempered meta-dynamics (WT-MtD) is employed to study the binding and un-binding processes of UO2 2+ and Zn2+ ions. Potential of mean force (PMF) profiles are generated for all the six sets of complexes from the converged WT-MtD run. Various basins and barriers are observed along the (un)binding pathways. Hydrogen bond dynamics and short-range Coulomb interactions are evaluated from the equilibrium run at each basins and barriers for both the ions at all pH values. The binding of UO2 2+ ion with HSA is the result of the dynamical balance between UO2 2+-HSA and UO2 2+-water short range Coulomb interactions. Zn2+ ion interact more strongly than UO2 2+ at all pH through short range Coulomb interactions. PMF values further concludes that UO2 2+ cannot associate to the Zn2+ bound HSA protein but can be captured by free HSA at all pH values i.e. endosomal, alkaline and physiological pH. Communicated by Ramaswamy H. Sarma

Dynamic force and stability prediction for milling using feed rate scheduling software and time-domain simulation

This paper describes: 1) the use of feed rate scheduling software to predict the radial depth of cut variation for three-axis milling toolpaths and; 2) the use of the radial depth profile in a time-domain simulation to predict dynamic cutting forces. The time-domain simulation, which also includes the tool tip frequency response functions and force model (which relates the cutting force components to the chip geometry) as inputs, enables dynamic force profiles to be predicted and parameter combinations that cause chatter to be identified. A ramp geometry is selected that provides constantly varying radial depth and force predictions are completed at multiple axial depths for comparison to measured forces. Both stable and unstable (chatter) milling conditions were observed with good agreement between time-domain simulation and measurement results. The value of combining the feed rate scheduling software and time-domain simulation is demonstrated.

Numerical study of the effect of wind above irregular waves on the wave-induced load statistics

A wind-forcing model is implemented into a fully nonlinear potential flow solver for water wave propagation. The model is suited for simulations of a large number of waves and for generation of fully nonlinear wave kinematics. The direct effect of wind is achieved through Jeffreys sheltering mechanism, which models the form drag on steep waves by a varying surface pressure. We detail the implementation and examine the effect of the model parameters, which consist of a sheltering coefficient and a threshold of the spatial slope of the wave for activation of the wind model. Next, we present the calibration and application of the model for reproduction of a test campaign for the effect of wind over waves on the wave-induced loads on a vertical surface piercing cylinder. The experimental study has been reported in ( Kristoffersen et al., 2021 ) and consisted of four storm sea states, each run with a duration equivalent to 30 h (full scale), with and without a simultaneous scaled wind field above the waves in the flume. After calibration, the numerical model is able to reproduce many of the findings from the experimental study. When wind forcing is added and the significant wave height is kept fixed, the crest statistics are slightly suppressed in the tail by the presence of wind. The wind, however, leads to a pronounced increase in the wave steepness and to a larger number of breaking waves. Despite the increased number of breaking waves, the depth integrated inline force was only found to increase slightly for the most extreme events at small exceedance probabilities. In contrast, the local force in the vicinity of the free surface was found to increase significantly, at short term exceedance probabilities up to 10 −2 , which is consistent with the measured pressures. For the numerical force profile along the vertical direction of the pile, we found that the altitude of maximum wave force is lowered with the introduction of wind. All of these findings are consistent with the experimental observations. Further for the numerical wave-induced local force at short term exceedance probability of 10 −4 , an increase by a factor of 1.8 was found from the introduction of wind. Although the effect on the global inline force was less strong, this local effect is important for design. The present numerical approach offers a direct way to establish such design loads.

Motion state-dependent motor learning based on explicit visual feedback is quickly recalled, but is less stable than adaptation to physical perturbations.

Recent studies have shown that adaptation to visual feedback perturbations during arm reaching movements involves implicit and explicit learning components. Evidence also suggests that explicit, intentional learning mechanisms are largely responsible for savings-a faster recalibration compared with initial training. However, the extent explicit learning mechanisms facilitate learning and early savings (i.e., the rapid recall of previous performance) for motion state-dependent learning is generally unknown. To address this question, we compared the early savings/recall achieved by two groups of human subjects. One experienced physical perturbations (a velocity-dependent force-field, vFF) to promote adaptation that is thought to be a largely implicit process. The second was only given visual feedback of the required force-velocity relationship; subjects moved in force channels and we provided visual feedback of the lateral force exerted during the movement, as well as the required force pattern based on the movement velocity. Thus, subjects were shown explicit information on the extent the applied temporal pattern of force matched the required velocity-dependent force profile if the force-field perturbation had been applied. After training, both groups experienced a decay and washout period, which was followed by a reexposure block to assess early savings/recall. Although decay was faster for the explicit visual feedback group, the single-trial recall was similar to the physical perturbation group. Thus, compared with visual feedback perturbations, conscious modification of motor output based on motion state-dependent feedback demonstrates rapid recall, but this adjustment is less stable than adaptation based on experiencing the multisensory errors that accompany physical perturbations.NEW & NOTEWORTHY The extent explicit feedback facilitates motion state-dependent changes to motor output is largely unknown. Here, we examined motor adaptation for subjects that experienced physical perturbations and another that made adjustments based on explicit visual feedback information of the required force-velocity relationship. Our results suggest that adjustment of motor output can be based on explicit motion state-dependent information and demonstrates rapid recall, but this learning is less stable than adaptation based on physical perturbations to movement.