Propulsive Force Research Articles

Directional-Specific Modulation of Postural Control and Stepping Kinematics in Multidirectional Gait Initiation.

Daily living activities present a diverse array of task and environmental constraints, highlighting the critical role of adapting gait initiation (GI) for an individual's quality of life. This study investigated the effects of GI directions, obstacle negotiation, and leg dominance on anticipatory postural adjustments and stepping kinematics. Fourteen active, young, healthy individuals participated in GI across 4 directions-forward, medial 45°, lateral 45°, and lateral 90°-with variations in obstacle presence and leg dominance. Results revealed a consistent decreasing trend in maximum center of pressure displacement, anticipatory postural adjustment duration, step distance, and swing leg velocity with lateral shifts in GI directions, yet the step duration and swing leg heel trajectory were not affected by GI directions except in lateral 90° GI. Center of pressure displacements were intricately scaled to directional propulsive forces generation, and the stepping kinematics were influenced by the directional modifications in movements. With obstacles, modifications in anticipatory postural adjustment metrics and stepping kinematics reflected the obstacle clearance movements. The dominant leg GI exhibited longer step durations and greater movement variability in medial 45° GI. The current investigation of GI factors expands our existing understanding of GI dynamics and offers valuable insights applicable to fall prevention and gait rehabilitation strategies.

4D printing of liquid crystal elastomer composites with continuous fiber reinforcement

Multifunctional composites have been continuously developed for a myriad of applications with remarkable adaptability to external stimuli and dynamic responsiveness. This study introduces a 4D printing method for liquid crystal elastomer (LCE) composites with continuous fibers and unveils their multifunctional actuation and exciting mechanical responses. During the printing process, the relative motion between the continuous fiber and LCE resin generates shear force to align mesogens and enable the monodomain state of the matrix materials. The printed composite lamina exhibits reversible folding deformations that are programmable by controlling printing parameters. With the incorporation of fiber reinforcement, the LCE composites not only demonstrate high actuation forces but also improved energy absorption and protection capabilities. Diverse shape-changing configurations of 4D composite structures can be achieved by tuning the printing pathway. Moreover, the incorporation of conductive fibers into the LCE matrix enables electrically induced shape morphing in the printed composites. Overall, this cost-effective 4D printing method is poised to serve as an accessible and influential approach when designing diverse applications of LCE composites, particularly in the realms of soft robotics, wearable electronics, artificial muscles, and beyond.

We Will, We Will Shock You: Adaptive Versus Conventional Functional Electrical Stimulation in Individuals Post-Stroke.

Functional electrical stimulation (FES) is often used in poststroke gait rehabilitation to address decreased walking speed, foot drop, and decreased forward propulsion. However, not all individuals experience clinically meaningful improvements in gait function with stimulation. Previous research has developed adaptive functional electrical stimulation (AFES) systems that adjust stimulation timing and amplitude at every stride to deliver optimal stimulation. The purpose of this work was to determine the effects of a novel AFES system on functional gait outcomes and compare them to the effects of the existing FES system. Twenty-four individuals with chronic poststroke hemiparesis completed 64-min walking trials on an adaptive and fixed-speed treadmill with no stimulation, stimulation from the existing FES system, and stimulation from the AFES system. There was no significant effect of stimulation condition on walking speed, peak dorsiflexion angle, or peak propulsive force. Walking speed was significantly faster and peak propulsive force was significantly larger on the adaptive treadmill (ATM) than the fixed-speed treadmill (both p < 0.0001). Dorsiflexor stimulation timing was similar between stimulation conditions, but plantarflexor stimulation timing was significantly improved with the AFES system compared to the FES system (p = 0.0059). Variability between and within subjects was substantial, and some subjects experienced clinically meaningful improvements in walking speed, peak dorsiflexion angle, and peak propulsive force. However, not all subjects experienced benefits, suggesting that further research to characterize which subjects exhibit the best instantaneous response to FES is needed to optimize poststroke gait rehabilitation using FES.

A model of racing kayak surge motion a numerical approach with realistic oscillating propulsion forces

This study presents a novel forward dynamics model of racing kayak surge motion. The model, driven by adjustable oscillating propulsion forces, replicates true paddle stroke forces. It is based on Newton’s second law of motion, with the net force comprising of propulsion force, skin friction drag, wave-making drag, form drag, and air drag. The total mass includes the kayak, paddler, and added mass. The fourth-order Runge–Kutta method is used to solve for speed and distance. The model incorporates a unique hull formulation for wetted surface area estimation, Michell’s integral for wave-making drag, and a log wind profile with allometric scaling for air drag. It accounts for varying stature height, body mass, kayak dimensions, wind speed, and stroke propulsion profiles. The model is a significant advancement in its domain, with broad applicability for the future. It aligns with existing data and analyses, but validation data is limited.

Coupling Dynamics Study on Multi-Body Separation Process of Underwater Vehicles

Based on the Newton-Euler method, a coupling rigid-body dynamics model of a Trans-Medium Vehicle (TMV) separating from an Unmanned Underwater Vehicle (UUV) has been established. The modeling is based on the “holistic method” and “Kane” ideas respectively, so that most of the equations can be derived without considering the internal forces between the two bodies. The separation propulsion force, which is an internal force, only appears in the relative glide dynamics equation of the TMV along the axis of the separation tube that is installed on the UUV. This greatly reduces the workload of modeling and derivation. The UUV works entirely underwater, while the hydrodynamic shape of the TMV changes continuously during the process of the TMV separating from the UUV. Therefore, accurate hydrodynamic calculations for the UUV and TMV are the basis of numerical resolution for the two rigid bodies’ coupling dynamics model in water. A large number of numerical simulations was conducted using CFD methods to investigate the hydrodynamic performance of the UUV and TMV under various conditions. These simulations aim to establish a hydrodynamic database, and accurate hydrodynamic models were developed through fitting methods and online interpolation. In the process of solving the coupling dynamics of two bodies, the hydrodynamic model is used to calculate the hydrodynamic force experienced by the UUV and TMV. This balances the accuracy and efficiency of a numerical simulation. Finally, numerous simulations and comparative analyses were conducted under various operational conditions and separation parameters. The simulation results indicate that the impact of TMV separation on the motion state of the UUV becomes more prominent with smaller UUV to TMV mass ratios or deeper TMV separation depths. This effect can further influence the stability control of the UUV. The coupling rigid body dynamics analysis method established in this paper provides a fast and effective prediction method for use during the scheme design and separation safety evaluation phases of creating UUV-TMV systems.

Heat and mass transfer in tri‐layer ependymal ciliary transport with diverse viscosity

AbstractSpecialized cilia known as ependymal cilia help the cerebrospinal fluid, which is important for nutrient delivery and waste elimination, to circulate in the brain. Many species rely on cilia and flagella for fluid movement and motility. Cilia and flagella, for instance, produce propulsive forces that allow unicellular creatures like Paramecium and Euglena to move through their surroundings. Ciliary transport plays a role in the flow of egg cells, or oocytes, via the fallopian tubes in the female reproductive system. The transfer of the egg towards the uterus is facilitated by the synchronized wave‐like motion produced by the cilia lining the fallopian tubes. Like this, ciliary transport in men aids in the passage of sperm cells via the epididymis. Many scientists and researchers are studying the mechanics of cilia motion and the properties of the viscoelastic fluid layer to develop new treatments and applications in biomedical engineering and for some diseases. Motivated by a wide range of biological applications, the objective of this study is to investigate the heat and mass transfer flow of tri‐layered Newtonian fluids flowing with the help of ciliary beating in a Cartesian coordinate. The fluid is incompressible, and fluid layers are not intermixed. The fluid flow with heat and mass transfer is first modelled in wave and then transmuted into fixed. Solutions for temperature profile, velocity distribution, stresses and concentration distribution are obtained. The influence of incipient parameters is displayed with graphs and plotted with the computational software MATHEMATICA 13.0 in the results section. The key findings obtained from graphs show that the maximum magnitude for temperature and velocity is achieved in the middle layer of fluid whereas in the outer layer concentration profile is maximum. It is predicted that this approach will make an essential contribution to the progress and enhancement of various types of drug delivery systems in the biomedical industry and biomechanics.

Patterns of change in propulsion force and late braking force in patients with stroke walking at comfortable and fast speeds

Increased propulsion force (PF) in the paretic limb is associated with improved walking speed in patients with stroke. However, late braking force (LBF), an additional braking force occurring between PF onset and toe-off, is present in a subset of stroke patients. Few studies have investigated the changes in LBF and walking speed in these patients. This study aimed to elucidate the patterns of change in PF and LBF during fast gait in hemiplegics and identify potential compensatory strategies based on the LBF patterns. Data from 100 patients with stroke walking at both comfortable (mean, 0.79 ± 024 m/s) and fast speeds (mean, 1.06 ± 0.35 m/s) were analyzed retrospectively stroke using a 3D motion analyzer. PF was higher during fast-speed walking than that during comfortable-speed walking in all patients, while LBF showed both decreasing and increasing trends during fast-speed walking. In the LBF increasing pattern, a reduction in in-phase coordination of the shank and foot during the pre-swing phase was observed, along with an increase in pelvic hike during fast-speed walking compared to those in the decreasing LBF pattern. Our findings demonstrate that alterations in LBF patterns are associated with gait deviations in patients with stroke at fast speeds.

Design and performance analysis of a composite flexure hinge based on micro-ultrasonic powder molding

This paper presents a new type of flexure hinge and its fabrication method based on micro-ultrasonic powder molding (micro-UPM). A right-circular notch-type flexure hinge (RFR-RC hinge) comprising an aluminum alloy 7075 (Al 7075) rigid structure and a polypropylene (PP) flexible structure was designed and fabricated. This composite RFR-RC hinge was experimentally studied, and the results helped confirm that the hinge could be considered a complete single structure; the flexible structure had a good forming quality, and the interlocking performance met normal use requirements. The RFR-RC hinge was evaluated in terms of its motion range, stiffness, and stiffness ratio through finite element analysis (FEA) and then compared with a single-material right-circular flexure hinge (RC hinge). The RFR-RC hinge provided a significantly wider operation range with a lower actuation force than the Al 7075-RC hinge and a higher motion pureness and accuracy than the PP-RC hinge. The motion stiffness obtained from the FEA was in agreement with the bending test results, thus validating the FEA results to some extent. From the bending tests, the elastic and total motion ranges of the RFR-RC hinge were found to be 0.068 rad and 0.202 rad, respectively. Finally, the fabrication of a 3-RRR compliant parallel mechanism and four typical applications were taken as examples to demonstrate that the RFR-RC hinge and its fabrication method have a wide range of applications.

Understanding the Actuation Point Stiffness of Electromechanical Drum Brakes

&lt;div&gt;Electromechanically actuated drum brakes are one interesting option for the realization of brake-by-wire systems for future electric vehicles. A key characteristic for the design and control of electromechanical brake actuators is the actuation point stiffness, as this quantity relates the actuation force to the required actuator position. The various known approaches for the control of electromechanical brakes, which primarily focus on disc foundation brakes, typically rely on the stiffness curve at least to some extent. A transfer of these approaches to drum brakes is not straightforward, because the actuation point stiffness for drum brakes is much more complex compared to disc brakes. In particular, a strong hysteretic behavior is observed for the standing drum and a considerable change of the stiffness and hysteresis can be observed for the rotating drum. Although drum brakes have been used for decades these effects have not been thoroughly discussed in literature, yet. Hence, this article proposes a minimal model, which gives a fundamental understanding of the stiffness characteristics of drum brakes. The relation to measured stiffness curves is discussed in detail to provide an in-depth understanding of the drum brake behavior. Additionally, prospect is given to a reduced complexity model that is suitable for online identification and control.&lt;/div&gt;

Escape of an active ring from an attractive surface: Behaving like a self-propelled Brownian particle.

Escape of active agents from metastable states is of great interest in statistical and biological physics. In this paper, we investigate the escape of a flexible active ring, composed of active Brownian particles, from a flat attractive surface using Brownian dynamics simulations. To systematically explore the effects of activity, persistence time, and the shape of attractive potentials, we calculate escape time τ_{e} and effective temperature T_{eff}. We observe two distinct escape mechanisms: Kramers-like thermal activation at small persistence times, where ln(τ_{e})∼1/(k_{B}T_{eff}), and the maximal force problem at large persistence time, where τ_{e} is determined by persistence time. The escape time explicitly depends on the shape of the potential barrier at high activity and large persistence time. Moreover, when the propulsion force is biased along the ring's contour, escape becomes more difficult and is primarily driven by thermal noise. Our findings highlight that, despite its intricate configuration, the active ring can be effectively modeled as a self-propelled Brownian particle when studying its escape from a smooth surface.

Programming Hydrogen Bonds for Reversible Elastic‐Plastic Phase Transition in a Conductive Stretchable Hydrogel Actuator with Rapid Ultra‐High‐Density Energy Conversion and Multiple Sensory Properties

AbstractSmart hydrogels have recently garnered significant attention in the fields of actuators, human‐machine interaction, and soft robotics. However, when constructing large‐scale actuated systems, they usually exhibit limited actuation forces (≈2 kPa) and actuation speeds. Drawing inspiration from hairspring energy conversion mechanism, an elasticity‐plasticity‐controllable composite hydrogel (PCTA) with robust contraction capabilities is developed. By precisely manipulating intermolecular and intramolecular hydrogen‐bonding interactions, the material's elasticity and plasticity can be programmed to facilitate efficient energy storage and release. The proposed mechanism enables rapid generation of high contraction forces (900 kPa) at ultra‐high working densities (0.96 MJ m−3). Molecular dynamics simulations reveal that modifications in the number and nature of hydrogen bonds lead to a distinct elastic‐plastic transition in hydrogels. Furthermore, the conductive PCTA hydrogel exhibits multimodal sensing capabilities including stretchable strain sensing with a wide sensing range (1–200%), fast response time (180 ms), and excellent linearity of the output signal. Moreover, it demonstrates exceptional temperature and humidity sensing capabilities with high detection accuracy. The strong actuation power and real‐time sensory feedback from the composite hydrogels are expected to inspire novel flexible driving materials and intelligent sensing systems.

Comparison Study of Hydrodynamic Characteristics in Different Swimming Modes of Carassius auratus

This study utilized particle image velocimetry (PIV) to analyze the kinematic and hydrodynamic characteristics of juvenile goldfish across three swimming modes: forward swimming, burst and coast, and turning. The results demonstrated that C-shaped turning exhibited the highest speed, enabling rapid and agile maneuvers for predator evasion. Meanwhile, forward swimming was optimal for sustained locomotion, and burst-and-coast swimming was suited for predatory behaviors. A vorticity analysis revealed that vorticity around the tail fin was the primary source of propulsive force, corroborating the correlation between vorticity magnitude and propulsion found in previous research. The findings emphasize the crucial role of the tail fin in swimming efficiency and performance. Future research should integrate ethology, biomechanics, and physiology to deepen the understanding of fish locomotion, potentially informing the design of efficient biomimetic underwater robots and contributing to fish conservation efforts.

Enhanced phasic calf muscle activation with swing resistance enhances propulsion of the paretic leg in people post-stroke.

Reduced propulsion of the paretic leg contributes to impaired walking in people post-stroke. The goal of this study was to determine whether phasic electrical stimulation to the paretic gastrocnemius muscle combined with resistance applied to the non-paretic leg during swing phase while walking would enhance muscle activation of the paretic gastrocnemius and propulsive force of the paretic leg. Fifteen individuals who had a stroke visited the lab once to complete two experimental sessions (i.e., cross-over design; session order randomized). Each session consisted of 1) treadmill walking with either "motor stimulation and swing resistance" or "swing resistance only" (10-min walking: 1-min baseline, 7-min adaptation to intervention, & 2-min post-adaptation) and 2) instrumented treadmill walking before and after treadmill walking. Results: Participants showed enhanced muscle activation of the paretic gastrocnemius (P=0.03) and improved anteroposterior ground reaction force of the paretic leg (P=0.01) immediately after the treadmill walking with "motor stimulation and swing resistance", whereas no improvements after the walking with "swing resistance only". Those enhanced gastrocnemius muscle activation (P=0.02) and improved ground reaction force (P=0.03) were retained until the late post-adaptation period and 10 min after treadmill walking, respectively. Conclusion: Walking with "motor stimulation and swing resistance" may enhance forced use of the paretic leg and improve propulsive force of the paretic leg. Applying phasic electrical stimulation to the paretic gastrocnemius muscle and swing resistance to the non-paretic leg during walking can be used as a novel intervention strategy to improve motor control of the paretic leg and walking in people post-stroke.

Hybrid force-position coordinated control of a parallel mechanism with the number of redundant actuators equal to its DOF

To address the demands for precision and load-bearing capacity in the installation of building panels, a hybrid force-position driven robot with redundant actuation has been developed. The mechanical performance of this robot is primarily governed by its central parallel mechanism, which is equipped with redundant actuators matching the degrees of freedom. Non-redundant and redundant actuators are respectively responsible for position and force control. The inclusion of redundant force-driven joints has increased the internal coupling within the mechanism. To enhance the coordination between position and force control, a hybrid synchronized control method based on cross-coupling has been proposed. Initially, kinematic and dynamic models of the parallel structure were established. Under predefined trajectories, the theoretical inputs for each actuator were calculated using inverse kinematics and dynamics. Subsequently, employing the principle of cross-coupling, the torque output from the position actuators was used as feedback. This feedback was processed by a synchronized coordination controller to adjust the output force of the redundant force-driven joints. By adjusting the output force of the redundant actuators, the torque burden on the position actuators was effectively reduced, thereby enhancing the precision of position control. Additionally, under the same load conditions, smaller power actuators could be utilized for position control, reducing the overall weight of the robot and improving its load-to-weight ratio. To validate the effectiveness of the proposed control strategy, a robotic simulation environment was established. The simulation results demonstrated significant reductions in the average torque required by the position actuators across three different trajectories, with reductions of 91.43%, 54.56%, and 80.6% respectively. Finally, the load-bearing capacity and the load-to-weight ratio of the prototype were assessed. Experimental results confirmed that the prototype achieved a load-to-weight ratio of 15.83%, validating the effectiveness of the hybrid synchronized control method based on cross-coupling.

Kinematic and aerodynamic analysis of a Microraptor-inspired foldable wing mechanism

Bio-inspired mechanisms have opened new avenues of research to understand the flying capabilities of birds. While extensive studies have explored the aerodynamics and kinematics of bird flapping motions, limited attention has been given to the folding motion. This paper introduces a foldable wing mechanism inspired by avian anatomy, specifically drawing inspiration from Microraptor aerodynamics. Employing the screw theory approach, we analyze the kinematics of the mechanism and conduct parametric calculations. By segmenting the mechanism and integrating the solutions, we develop an algorithm that demonstrates favorable power transmission, enabling the wing to remain extended with minimal actuation forces. We further employ position analysis to investigate the system’s functionality analytically. To optimize the mechanism, we utilize the gradient descent method. We validate the achieved momentum and velocities through an illustrative example by solving individual four-bar segments and transmitting the outputs to adjacent segments. The study utilizes detailed 3D modeling techniques employing SolidWorks software to accurately represent the wing designs. The results obtained provide valuable insights into the aerodynamic behavior of Microraptor, by comparing the coefficients of lift and drag in graphical form and contribute to the advancement of micro-aerial vehicle design.

Modeling of Actuation Force, Pressure and Contraction of Fluidic Muscles Based on Machine Learning

Modeling of Actuation Force, Pressure and Contraction of Fluidic Muscles Based on Machine Learning

Selective actuation of higher-order modes of an electromagnetically driven micro drum

In this paper, we experimentally investigate selective actuation of the first few higher-order modes of a micromachined silicon nitride circular membrane (micro drum), which is actuated by electromagnetic forces. A novel design of electrodes is proposed to enable selective actuation for portions of the membrane with the Lorentz force, which excites efficiently the higher-order modes. With different electrode configurations, we show that the (0, 1) mode, the degenerate (1, 1) modes, and the (2, 1) mode can be selectively activated or deactivated using the orthogonality between the actuation force and the mode shapes. A reduced-order model for the circular membrane is established and used to explain the results.

Enhanced buoyancy and propulsion in 3D printed swimming micro-robots based on a hydrophobic nano-fibrillated cellulose aerogel and porous lead-free piezoelectric ceramics

This paper provides the first demonstration of additively manufactured swimming micro-robots which combine a hydrophobic nanofibrillated cellulose aerogel, to provide long-term buoyancy, with a low acoustic impedance porous piezoelectric ceramic for improved propulsion. The hydrophobic nanocellulose aerogel is shown to exhibit a high and stable contact angle that was maintained for extended periods of time, which facilitates long-term and stable buoyancy of the micro-robot. To quantify the benefits of introducing porosity into the active piezoelectric element, a new analysis model was developed to inform material design and maximize the acoustic propulsion force. Detailed characterisation and modelling of the swimming robots demonstrated that a swimming robot based on a lead-free porous Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramic exhibited a higher acoustic radiation propulsion force and a faster swimming speed compared to a robot fabricated using a dense ceramic element. These benefits were associated with the lower elastic modulus, density and acoustic impedance of the porous piezoelectric material. The lower dielectric constant, reduced device capacitance, and lower resonant frequency of the porous piezoelectric element also significantly reduced the driving current and power requirements of the robot. This work therefore provides new insights on the impact of hydrophobic and acoustically matched piezoelectric materials on the performance of swimming micro-robots, and successfully demonstrates the use of porosity to improve acoustic impedance matching of resonant piezoelectric devices, such as micro-robots and ultrasonic transducers.

Dynamic model of the UC San Diego NHERI six‐degree‐of‐freedom large high‐performance outdoor shake table

AbstractThe UC San Diego large high‐performance outdoor shake table (LHPOST), which was commissioned on October 1, 2004 as a shared‐use experimental facility of the National Science Foundation (NSF) Network for Earthquake Engineering Simulation (NEES) program, was upgraded from its original one degree‐of‐freedom (LHPOST) to a six‐degree‐of‐freedom configuration (LHPOST6) between October 2019 and April 2022. A mechanics‐based numerical model of the LHPOST6 able to capture the dynamics of the upgraded 6‐DOF shake table system under bare table condition is presented in this paper. The model includes: (i) a rigid body kinematic model that relates the platen motion to the motions of the components attached to the platen, (ii) a hydraulic dynamic model that calculates the hydraulic actuator forces based on all fourth‐stage servovalve spool positions, (iii) a hold‐down strut model that determines the pull‐down forces produced by the three hold‐down struts, (iv) Bouc‐Wen models utilized to represent the dissipative forces in the shake table system, and (v) a rigid body dynamic model borrowed from robotic analysis governing the translational and rotational motions of the platen subjected to the forces from the various components attached to the platen. Extensive validation against experimental data shows excellent agreement for tri‐axial and six‐axial earthquake shake table tests. This validated model can be coupled with finite element models of test specimens to study the interaction between the shake table system and the specimens, and it offers potential for enhancing motion tracking performance through off‐line controller tuning or advanced control algorithm development.

Data-physics hybrid-driven external forces estimation method on excavators

To enhance the accuracy of excavator external forces estimation, a data-physics hybrid-driven excavator external forces estimation method is proposed. MultiLayer Perceptron (MLP) model is applied for nonlinear component modeling and is used to compensate for Rigid Body Dynamics (RBD) models. Gaussian Process Regression (GPR) model is developed to estimate the external forces and uncertainties based on the joint angles, angular velocities, cylinder actuation forces, and actuation end velocities of the excavator. The external forces estimated by the GPR models are used as a new measurement in the Disturbance Kalman Filter (DKF), and the uncertainty is incorporated into the covariance of the process noise. The constructed GPR-DKF estimator is validated on a scaled-down excavator. The results demonstrate the robustness and effectiveness of the proposed method in estimating out-of-distribution samples.