Kinematic Response Research Articles

Effects of an integrated safety system for swivel seat arrangements in frontal crash.

Objective: Autonomous vehicles (Avs) have paved the way for the arrangement of swivel seats in vehicles, which could pose a challenge to traditional safety systems. The integration of automated emergency braking (AEB) and pre-pretension (PPT) seatbelts improves protection for a vehicle's occupant. The objective of this study is to explore the control strategies of an integrated safety system for swiveled seating orientations. Methods: Occupant restraints were examined in various seating configurations using a single-seat model with a seat-mounted seatbelt. Seat orientation was set at different angles, from -45° to 45° with 15° increments. A pretension was used on the shoulder belt to represent an active belt force cooperating with AEB. A generic full frontal vehicle pulse of 20mph was applied to the sled. The occupant's kinematics response under various integrated safety system control strategies was analyzed by extracting a head pre-crash kinematics envelope. The injury values were calculated for various seating directions with or without an integrated safety system at the collision speed of 20mph. Results: In a lateral movement, the excursions of the dummy head were 100mm and 70mm in the global coordinate system for negative and positive seat orientations, respectively. In the axial movement, the head traveled 150mm and 180mm in the global coordinate system for positive and negative seating directions, respectively. The 3-point seatbelt did not restrain the occupant symmetrically. The occupant experienced greater y-axis excursion and smaller x-axis excursion in the negative seat position. Various integrated safety system control strategies led to significant differences in head movement in the y direction. The integrated safety system reduced the occupant's potential injury risks in different seating positions. When the AEB and PPT were activated, the absolute HIC15, brain injury criteria (BrIC), neck injury (Nij), and chest deflection were reduced in most seating directions. However, the pre-crash increased the injury risks at some seating positions. Conclusion: The pre-pretension seatbelt could reduce the occupant's forward movement in the rotating seat positions in a pre-crash period. The occupant's pre-crash motion envelope was generated, which could be beneficial to future restraint systems and vehicle interior design. The integrated safety system could reduce injuries in different seating orientations.

Kinematic Response of Subaerial Salt Diapirs to Geomorphic, Tectonic and Climatic Regimes: Insights From Space‐Based Observations in the Western Kuqa Fold‐Thrust Belt, NW China

AbstractEphemeral subaerial salt diapirs are gravitationally unstable and vulnerable to climate and tectonic activity due to the rheology and incompressibility of rock salt. Quantifying the kinematics of subaerial salt and clarifying the role of tectonics, surface processes, and climate in reshaping the surface salt morphology provides an invaluable opportunity to explore the interactions between Earth’s spheres on a much shorter timescale. With diverse exposed salt diapirs and potential motions, the Kuqa fold‐thrust belt (KFTB), NW China, represents an optimum natural laboratory to understand subaerial salt kinematics. Here, we integrated ascending and descending geometries of Sentinel‐1 synthetic aperture radar images with optical remote sensing data, seismic profiles, digital elevation models, and meteorological records to explore the potential correlation between subaerial salt motions and geomorphic, tectonic, and climatic factors. Using the interferometric synthetic aperture radar technique, we observed a maximum of 25 mm/yr in vertical and 40 mm/yr in horizontal surface salt deformation in the KFTB from 2014 to 2020. Our findings demonstrate a gravity spreading dominant system, where topography exerts a primary control on the surface displacement patterns of salt structures, while weather variables influence deformation mainly by softening salt and facilitating gravity‐driven salt flow.

Lateral kinematic response of offshore pipe piles to S‐wave seismic excitation

AbstractThis paper presents an analytical study on the lateral kinematic response of offshore pipe piles subjected to vertically propagating S‐wave seismic excitation. Both the kinematic interaction of the pipe pile with the soil and seawater are considered. The lateral resistances of the outer and inner soil are obtained based on the confined viscoelastic dynamic continuum models, while the hydrodynamic pressures of the seawater are based on the inviscid incompressible fluid theory. The pile response is then obtained by utilizing the continuity condition at the soil‐pile and seawater‐pile interfaces along the pile shaft. The derived solution is employed to investigate the sensitivity of the seismic response of pipe piles to certain key problem parameters, such as length of pile segment embedded in seawater, the relative stiffness of the pile and soil and the pile radius ratio. We demonstrate that the partially embedded piles are much more flexible compared with fully embedded piles when subjected to S‐wave excitation, resulting more strong motion transferred to the superstructures and the existence of seawater will amplify the seismic responses of offshore pipe piles.

Increased muscle responses to balance perturbations in children with cerebral palsy can be explained by increased sensitivity to center of mass movement

BackgroundBalance impairments are common in children with cerebral palsy (CP). Muscle activity during perturbed standing is higher in children with CP than in typically developing (TD) children, but we know surprisingly little about how sensorimotor processes for balance control are altered in CP. Sensorimotor processing refers to how the nervous system translates incoming sensory information about body motion into motor commands to activate muscles. In healthy adults, muscle activity in response to backward support-surface translations during standing can be reconstructed by center of mass (CoM) feedback, i.e., by a linear combination of delayed (due to neural transmission times) CoM displacement, velocity, and acceleration. The level of muscle activity in relation to changes in CoM kinematics, i.e., the feedback gains, provides a metric of the sensitivity of the muscle response to CoM perturbations. Research questionCan CoM feedback explain reactive muscle activity in children with CP, yet with higher feedback gains than in TD children? MethodsWe perturbed standing balance by backward support-surface translations of different magnitudes in 20 children with CP and 20 age-matched TD children and investigated CoM feedback pathways underlying reactive muscle activity in the triceps surae and tibialis anterior. ResultsReactive muscle activity could be reconstructed by delayed feedback of CoM kinematics and hence similar sensorimotor pathways might underlie balance control in children with CP and TD children. However, sensitivities of both agonistic and antagonistic muscle activity to CoM displacement and velocity were higher in children with CP than in TD children. The increased sensitivity of balance correcting responses to CoM movement might explain the stiffer kinematic response, i.e., smaller CoM movement, observed in children with CP. SignificanceThe sensorimotor model used here provided unique insights into how CP affects neural processing underlying balance control. Sensorimotor sensitivities might be a useful metric to diagnose balance impairments.

Biomechanical comparisons of dynamic fixators with rod-rod and screw-spacer joints on lumbar hybrid fixation

BackgroundHybrid fixators with quite different joint design concepts have been widely to suppress adjacent segment degeneration problems. The kinematic and kinetic responses of the adjacent and transition segments and contact behaviors at the bone-screw interfaces served as the objective of this study. MethodsThe moderately degenerated L4/L5 and mildly degenerative L3/L4 segments were respectively immobilized by a static fixator and further bridged by the rod-rod (Isobar) and screw-spacer (Dynesys) fixator. The joint stiffness and mobility of the rod-rod system and the cable pretension of the screw-spacer system were systematically varied. FindingsThe flexion of the screw-spacer system provided higher mobility to the transition segment, reducing adjacent-segment problems. The cable pretension had a minor effect on the construct behavior. However, due to limited joint mobility, the rod-rod system showed higher constraints to the transition segment and induced more adjacent-segment compensations. The increased mobility of the rod-rod joint caused it to behave as a more dynamic fixator that increased adjacent-segment compensations at the transition segment. Comparatively, increasing the joint mobility showed more significant effects on the construct behaviors than decreasing the joint stiffness. Furthermore, increased constraint by the rod-rod joint induced higher stress and risk of loosening at the bone-screw interfaces InterpretationIf the protection of the transition segment is the major concern, the rod-rod system can be used to constrain the intervertebral motion and share the higher loads through the fixator. Otherwise, the screw-spacer system is recommended in situations where higher loads onto the transition disc are allowable.

Kinematic response of end-bearing piles in saturated soil to seismic SH-waves

This paper presents a mathematical model for the seismic analysis of end-bearing piles founded in a homogeneous saturated soil of finite thickness. Seismic loading is modelled as harmonic horizontal strong motion of the rigid bedrock, that generates vertically-propagating shear SH-waves. The transfer function of the soil layer is first established, considering soil as uniform isotropic poroelastic medium that obeys Biot’s governing equations. Accordingly, free-field and scattered soil displacements are co-evaluated, to establish a series-form expression that provides the dynamic lateral force acting on an Euler-Bernoulli elastic beam representing the pile. We employ the model to show that energy dissipation due to relative movement between the pore fluid and the solid matrix may have a noteworthy effect on the amplitude of high-frequency components of the strong motion in high permeability soils, and this in turn affects the kinematic response of piles. Finally, we use arithmetic examples to identify the soil permeability threshold, beyond which simpler single-phase soil models will produce reliable results for piles embedded in saturated two-phase soil.

Analytical Modeling of Posttensioned C-Shaped CLT Core Walls

Post-tensioned (PT) timber technology, also referred to as Pres-Lam (prestressed laminated timber) provides a low damage seismic design solution. So far PT timber research and practical implementation have focused on moment resisting frames, planar shear walls and coupled planar shear wall—or column-wall-column—systems and their analytical prediction models were adapted and extended from precast concrete to account for the unique characteristics of engineered timber. Following a recent experimental study on a PT cross-laminated timber (CLT) C-shaped core-wall system aiming to enhance lateral strength and stiffness, this paper presents an analytical framework/model to capture three unique kinematic rocking mechanisms for a PT C-shaped CLT core-wall system connected primarily with self-tapping screws. Depending on the relative stiffness of the screwed connections to the PT and the energy dissipaters, the model considers different kinematic responses, and that a staged kinematic response could occur at different imposed core-wall base connection rotations. It also accounts for the material inhomogeneity of CLT with nonedge glued lamella and implements a nonlinear spring model for the screwed connections calibrated from component testing and expected elastic core-wall deformations. The study showed that, for the given specimen configurations presented, the compressive flange wall could be neglected for a PT C-shaped CLT core wall. The analytical model was verified against three large-scale 8.6 m high PT C-shaped core-wall experimental tests and the model prediction error was within 10%. The analytical model was limited to capturing the envelope (push-over) curve of a four wall PT C-shaped CLT core-wall system.

Mechanical energy on anaerobic capacity during a supramaximal treadmill running in men: Is there influence between runners and active individuals?

This study verified whether mechanical variables influence the anaerobic capacity outcome on treadmill running and whether these likely influences were dependent of running experience. Seventeen physical active and 18 amateur runners, males, performed a graded exercise test and constant load exhaustive running efforts at 115% of intensity associated to maximal oxygen consumption. During the constant load were determined the metabolic responses (i.e., gas exchange and blood lactate) to estimate the energetic contribution and anaerobic capacity as well as kinematic responses. The runners showed higher anaerobic capacity (16.6%; p=0.005), but lesser time to exercise failure (-18.8%; p=0.03) than active subjects. In addition, the stride length (21.4%; p=0.00001), contact phase duration (-11.3%; p=0.005), and vertical work (-29.9%; p=0.015). For actives, the anaerobic capacity did not correlate significantly with any physiologic, kinematic, and mechanical variables and no regression model was fitted using the stepwise multiple regression, while to runners the anaerobic capacity was significantly correlated with phosphagen energetic contribution (r=0.47; p=0.047), external power (r=-0.51; p=0.031), total work (r=-0.54; p=0.020), external work (r=-0.62; p=0.006), vertical work (r=-0.63; p=0.008), and horizontal work (r=-0.61; p=0.008), and the vertical work and phosphagen energetic contribution presented a coefficient of determination of 62% (p=0.001). Based on findings, it is possible to assume that for active subjects, the mechanical variables have no influence over the anaerobic capacity, however, for experienced runners, the vertical work and phosphagen energetic contribution have relevant effect over anaerobic capacity output.

Identification and focusing of edge diffractions using wavefront attributes

Edge diffractions are more common in 3D seismic data than point diffractions; however, most current studies on processing and imaging diffractions consider point diffractions. We find that the 3D kinematic response of an edge diffractor manifests itself locally as a 2D diffraction for a specific azimuth, which can be uniquely determined using the local characteristics of the wavefronts. This applies to arbitrarily oriented curvilinear edges embedded in inhomogeneous anisotropic media. We further establish a novel 3D time-domain event classification, generalizing the existing 2D technique. A new criterion based on data-derived wavefront curvature matrices allows the unambiguous zero-offset identification of the wave scatterer types: point diffractors, edge diffractors, and reflecting boundaries. We further develop a new data-driven technique of receiver grouping to focus edge diffractions, which contributes to diffraction imaging and tomography. Both proposed methods do not rely on a priori knowledge of the subsurface. Synthetic examples validate these findings.

Axial kinematic response of single floating pipe piles to vertically propagating P waves

This paper presents a rigorous analytical solution for predicting the axial kinematic response of single floating pipe piles subjected to vertically-propagating seismic P waves, by means of a refined Tajimi-type continuum elastodynamic model. The outer and inner soil motion are decomposed as the sum of free-field motion and the scattered soil motion due to the existence of the pipe pile, and their solutions are derived from the governing equations separately. Closed-form expressions for the responses of the pipe pile and soil are obtained by utilizing the continuity conditions at the interfaces between outer and inner soil and the pile shaft as well as its underlying soil column. The effects of key problem parameters on the seismic responses of the pipe pile and soil are discussed.

Extracting angle-domain common-image gathers in VTI media using ansiotropic-Helmholtz P/S wave-mode decomposition

Common-image gathers are extensively used in amplitude versus angle (AVA) and migration velocity analysis (MVA). The current state of methods for anisotropic angle gathers extraction use slant-stack, local Fourier transform or low-rank approximation, which requires much computation. Based on an anisotropic-Helmholtz P/S wave-mode decomposition method, we propose a novel and efficient approach to produce angle-domain common-image gathers (ADCIGs) in the elastic reverse time migration (ERTM) of VTI media. To start with, we derive an anisotropic-Helmholtz decomposition operator from the Christoffel equation in VTI media, and use this operator to derive the decomposed formulations for anisotropic P/S waves. Second, we employ the first-order Taylor expansion to calculate the normalized term of decomposed formulations and obtain the anisotropic-Helmholtz decomposition method, which generates the separated P/S wavefields with correct amplitudes and phases. Third, we develop a novel way that uses the anisotropic-Helmholtz decomposition operator to define the polarization angles for anisotropic P/S waves and substitute these angles to decomposing formulations. The polarization angles are then calculated directly from the separated vector P- and S-wavefields and converted to the phase angles. The ADCIGs are thusly produced by applying the phase angles to VTI ERTM. In addition, we develop a concise approximate expression of residual moveout (RMO) for PP-reflections of flat reflectors in VTI media, which avoids the complex transformations between the group angles and the phase angles. The approximate RMO curves show a good agreement with the exact solution and can be used as a tool to assess the migration velocity errors. As demonstrated by two selected examples, our ADCIGs not only produce the correct kinematic responses with regards to different velocity pertubatation, but also generate the reliable amplitude responses versus different angle. The final stacking images of ADCIGs data exhibit the identical imaging effect as that of VTI ERTM.

The prediction of autonomous vehicle occupants’ pre-crash motion during emergency braking scenarios

This research investigates a computational method, which can assist the development of occupants’ passive safety in future autonomous vehicles, more particularly in the definition of head kinematics in rotated seat arrangement during emergency braking. To capture these head motions, the methodology utilised an Active Human Model, whose head kinematics were validated in a previous work in three-point and lap-belt restraint configuration scenarios. A sled model was then built where the seat backrest angle (SBA) and the seat orientation, modelled by rotating the acceleration angle (AA), could be adjusted to represent various ‘living room’ seating conditions. A Design of Experiments study was then performed by varying AA from 0° to 360° in steps of 22.5° and SBA from 20° to 60° in steps of 8°. The responses were subsequently converted into a Reduced Order Model (ROM), which was then successfully validated through a comparison with the kinematic responses predicted with simulations. In terms of simulation time, it was found that the ROM was able to calculate the head kinematics in 3 s instead of the 1.5 h taken using Simcenter Madymo, without compromising predicted responses accuracy. This research has provided a unique method to define head kinematics corridors for seated occupants in autonomous vehicle interiors, including maximum head excursion, head kinematics as a function of time and define for the first time (a) the safe “or’ but not both head envelope within the cabin interior, and (b) capture the seated scenarios where head proximity to airbag systems could be of concern, following emergency braking.

Kinematics characteristics analysis of a 3-UPS/S parallel airborne stabilized platform

In this paper, a kind of parallel airborne stabilized platform (ASP) is designed based on a 3-UPS/S mechanism, and a forward kinematics (FK) method named Finite-Step-Integration (FSI) is proposed, which can determine the pose of the moving platform and the consecutive kinematic responses without any sensor. In order to quantify and evaluate the precision of the FSI method, the error model is established between the computational and the real results. Meanwhile, the operation time is recorded during the precision test to reflect the FSI method's speed. To apply the method more widely, the mechanical restraint and accessible workspace are analyzed. An actual prototype was designed and fabricated to illustrate the effect of motion tracking on the FSI method. The outcomes presented in the research allow to observe that: the FSI method possesses excellent arithmetic accuracy and speed for consecutive FK analysis, the sufficiency of the ASP's workspace is proved with the application of the method, and the FSI method is accurate and timely on the motion tracking. The FSI method proposed in this paper can be well applied to the kinematics characteristics analysis of general parallel mechanisms.

Characterizing the response of the coastal Rio Grande to upstream damming

Dams are major obstructions to the flow of water and the transport of sediment in rivers. Much work has shown the construction of dams, and storage of sediment in reservoirs, can lead to significant changes in the morphodynamic behavior of alluvial rivers; however, in most cases, the effect of damming has a finite downstream limit as sediment is supplied back to the river through channel bed/bank erosion and/or tributary inputs. Here we present a study of a natural experiment that isolates one source of sediment downstream of a dam – the lower Rio Grande, which has no major tributary inputs of sediment over a ~450 km reach, from Falcon Dam to the coast. Analysis of the morphology and topography of the Rio Grande shows that prior to damming in the 1950s the coastal Rio Grande was a kinematically active channel with large, subaerial point bars. Subsequent to damming, lateral migration of the river shut down and exposed point bars shrunk in size, becoming static and vegetated. Bathymetric survey data show meter-scale incision of the channel bed for hundreds of kilometers downstream of the dam. Entrenchment of the river is also evidenced by the development of steep banks on the inner portions of channel bends. Damming also impacted the interaction between the river and the floodplain, resulting in the formation of persistent gullies incised into the channel banks, suggesting transport of water and sediment is net positive into, not out of, the channel. Based on all of these observations we conclude that the full ~450 km reach of the Rio Grande, from Falcon Dam to the coast, became net degradational following dam closure. We conclude that the presence of such a long degrading reach is caused by the exposure of bedrock in the Rio Grande channel for nearly 100 km downstream of the dam, which, combined with the lack of tributaries, limits downstream sediment supply to the river. Our results provide new insights into the response to damming for rivers with no tributary sediment input and thin alluvial cover, and more broadly to the kinematic and channel geometry responses to a major drop in water discharge and sediment supply for coastal meandering rivers.

Testing the acceptability of motorcycle-AEB system: Use of unanticipated interventions as a reliable surrogate of genuinely unexpected events

Objective Active safety systems such as motorcycle autonomous emergency braking (MAEB) capable of ensuring effectiveness and safe rider–vehicle interaction present many potential benefits to reduce road fatalities but also many challenges. The whole development cycle of MAEB requires research through extensive field tests that reproduce unexpected interventions or real-life driving situation before the system can be available to the end-user. This study aims to better understand the rider’s kinematic response required to control the stability of the rider-motorcycle system, as well as the extent of unexpectedness perceived by participants under different degrees of awareness of automatic braking (AB) activation. Methods We compared responses to AB in anticipated and (un)anticipated conditions and in a condition that was intended to be genuinely unexpected (Out of the Blue). Twenty men and women, wearing an inertial measurement unit on their upper-back, rode a scooter-type motorcycle with two front wheels simulating urban riding maneuvers on a closed test-track. Three automatic braking (AB) profiles were tested in different sessions, ranged from 3 to 5 m/s2 deceleration and 15 to 25 m/s3 braking-jerk. Differences between AB conditions were analyzed using linear mixed models. Results The unanticipated condition was perceived as fairly unexpected (rated between Quite Unexpected and Very Unexpected). Out of the Blue condition was on average close to the highest level of unexpectedness (Completely Unexpected). The exposure to unanticipated AB events resulted in upper-body response with larger peaks of pitch rate (0.20 to 0.77 rad/s higher) and acceleration (1.0 to 2.3 m/s2 higher) than those of anticipated. Participants showed less postural stability during unanticipated events taking longer both to start correcting the initial forward lean and to fully stabilize balance. Unanticipated and Out of the Blue conditions did not differ in either the amplitude of the kinematic variables or the time-to-peak pitch rate. Conclusions The kinematic response of the rider’s upper-body was found to be a reliable estimator of unexpectedness in AB. The findings suggest that unanticipated AB events while the rider engages in riding tasks can enable testing aimed at designing MAEB systems and assessing end-user acceptance in a reliable manner and within ethical safety limits.

Validation of cognitive and neuromuscular latencies using an iPad-based tool to quantify simple reaction times in asymptomatic subjects.

Simple reaction times (SRTs), measured in milliseconds (msec), are equal to the sum of subject-dependent latencies that occur during cognitive processing and neuromuscular responses to a preprogrammed stimulus presented to a subject. SRTs have the advantage of being a relatively pure, neurologically driven motor/sensory task that provides a clinician with a generalized assessment of functional deficits. SRTs are easily obtained, and studies have reported that the average number of finger-taps during a 10-s interval can be utilized to distinguish between patients with mild traumatic brain injury (TBI) and healthy controls. A stimulus/response SRT protocol, utilizing an iPad-based tool, was utilized to see if differentiation andquantification of individual components of cognitive latency (CL) and neuromuscular latency (NL) from a subject's total SRT could be accomplished. The study hypothesis was that cognitive latencies, related to a specific cognitive challenge, would remain constant even as latencies due to neuromuscular challenges changed. Two categories of SRT tests were utilized. The first was a simple finger tapping test (FTT), without any cognitive involvement, that was designed to quantify pureNL. The second test was a choice test (CT) that was characterized by the addition of a cognitive task to the FTT. The objective of the FTT was for the subject to simply tap a single target positioned on the iPad screen as fast as possible over an interval of 10s. Measurement of the SRT began when a target was displayed and ended when the target was tapped. Two levels of challenge for the FTT and CT tests were presented to the subjects: a small random displacement (SD) of the target of up to 6mm, and a large random displacement (LD) of the target of up to 24mm. It was expected that the magnitude of the SRT (FTT) would be directly related to the magnitude of the displacement of the target due to kinematic response characteristics of the hand and arm. To validate the study hypothesis, CL for both small and large displacements was calculated by subtracting the respective NL from the total SRT. Utilizing a repeated measures t-test analysis utilizing SPSS, a significant difference between CL (SD) and CL (LD) at p=0.696 was not observed. Differentiation and quantification of individual components of CL and NL from a subject's total SRTwas accomplished. An Apple iPad Pro was selected asa platform for our study because: (1) it is readily available, affordable, and programmable; (2) it meets a requirement for portability; and (3) it allows the modification/addition of test parameters to meet future needs. The ability to quantify the extent of cognitive andneuromuscular dysfunction in the TBI patient is an essential component of developing an effective treatment plan.

Effects of simulated hypo-gravity on lower limb kinematic and electromyographic variables during anti-gravitational treadmill walking.

Introduction: This study investigated kinematic and EMG changes in gait across simulated gravitational unloading levels between 100% and 20% of normal body weight. This study sought to identify if each level of unloading elicited consistent changes-particular to that percentage of normal body weight-or if the changes seen with unloading could be influenced by the previous level(s) of unloading. Methods: 15 healthy adult participants (26.3 2.5years; 53% female) walked in an Alter-G anti-gravity treadmill unloading system (mean speed: 1.49 mph) for 1min each at 100%, 80%, 60%, 40% and 20% of normal body weight, before loading back to 100% in reverse order. Lower-body kinematic data were captured by inertial measurement units, and EMG data were collected from the rectus femoris, biceps femoris, medial gastrocnemius, and anterior tibialis. Data were compared across like levels of load using repeated measures ANOVA and statistical parametric mapping. Difference waveforms for adjacent levels were created to examine the rate of change between different unloading levels. Results: This study found hip, knee, and ankle kinematics as well as activity in the rectus femoris, and medial gastrocnemius were significantly different at the same level of unloading, having arrived from a higher, or lower level of unloading. There were no significant changes in the kinematic difference waveforms, however the waveform representing the change in EMG between 100% and 80% load was significantly different from all other levels. Discussion: This study found that body weight unloading from 100% to 20% elicited distinct responses in the medial gastrocnemius, as well as partly in the rectus femoris. Hip, knee, and ankle kinematics were also affected differentially by loading and unloading, especially at 40% of normal body weight. These findings suggest the previous level of gravitational load is an important factor to consider in determining kinematic and EMG responses to the current level during loading and unloading below standard g. Similarly, the rate of change in kinematics from 100% to 20% appears to be linear, while the rate of change in EMG was non-linear. This is of particular interest, as it suggests that kinematic and EMG measures decouple with unloading and may react to unloading uniquely.

Treadmill Belt Accelerations Do Not Replicate Kinematic Responses to Trips on a Walkway in Older People

Treadmill Belt Accelerations Do Not Replicate Kinematic Responses to Trips on a Walkway in Older People

A probabilistic study on impedances and kinematic response factors of square pile groups in homogeneous soils

The complexity of the Soil-Structure Interaction (SSI) problem is mainly due to difficulties related to the modelling of the soil-foundation behaviour, which is not only frequency-dependent, but is also largely influenced by uncertainties related to soil properties and stratigraphic conditions. According to a sub-structuring scheme for the analysis of SSI problems, a deterministic approach is usually adopted for the analysis of the soil-foundation system assuming properties and geotechnical models based on the expert judgment, despite the fact that uncertainties related to the intrinsic variability of soil parameters are widely recognised and confirmed by experimental campaigns and laboratory tests.This paper presents a probabilistic study on the dynamic behaviour of square pile group foundations in homogeneous soils, focusing on the effects of the uncertainties related to (i) the frequency-dependent impedance functions and (ii) the kinematic response factors. Above quantities are required to define compliant restraints for the modelling of the soil-foundation system in performing inertial soil-structure interaction analysis, and for the definition of the foundation input motion starting from the free-field motion. Square pile groups are considered, and uncertainties are described through probabilistic distributions of parameters governing the soil-foundation dynamic response. The probabilistic analyses are performed through a numerical model developed by the Authors and some results are presented to show and discuss the variability of the results. In addition, a sensitivity analysis is performed to assess the influence of each variable uncertainty on the system response. Overall, response quantities are found to be very sensitive to shear wave velocity, although soil density and pile elastic modulus may often play a significant role.

Muscle activity on head-first compression responses of a finite element neck model

Effects of muscle activation on human neck kinematic responses under compressive loads have not been understood empirically due to the limitation of testing on in vivo test specimens. Advanced computational models can potentially provide information to improve our understanding of such responses. This study used a previously developed ligamentous finite element (FE) neck model, further integrated with muscles, fleshy tissue, and skin of the neck to predict the influence of passive and active muscles on responses to neck compression. For validation, post-mortem human subject (PMHS) and volunteer responses in frontal sled impacts were used to compare the dynamic response of the model with passive and active muscles, respectively. An objective evaluation of the validation responses suggested the ‘fair’ to ‘good’ biofidelity rating of the muscular system model. The compressive impacts, used to validate the ligamentous FE neck, were methodologically applied in the current study including the muscles with various activation states, flesh, and skin. The contribution of muscles (passive or active) resulted in an increase in the peak lower neck compression and shear forces and in a reduction in the upper neck forces on average; the role of active state dynamics of the muscles was crucial on the magnitude of the forces. Therefore, modeling of the muscles in a computational neck model may not be neglected to study a head-first compressive impact.