Increasing Step Height Research Articles

Evaluating plantar biomechanics while descending a single step with different heights.

This study aims to investigate the plantar biomechanics of healthy young males as they descend a single transition step from varying heights. Thirty healthy young males participated the experiment using the F-scan insole plantar pressure system in which participants made single transition steps descent from four step heights (5, 15, 25, and 35cm), leading with their dominant or non-dominant foot. Plantar pressure data were collected for 5s during the period between landing touchdown and standing on the ground. Landing at each step height was repeated three times, with a five-minute rest between different height trials. At 5cm and 15cm steps, participants demonstrated a rearfoot landing strategy on both sides. However, forefoot contact was observed at heights of 25cm and 35cm. Parameters related to center of plantar pressure (COP) of the leading foot were significantly larger compared to the trailing foot (P < 0.001), increased with higher step heights. Vertical ground reaction forces for the biped, leading and trailing feet decreased with increasing step height (all P < 0.05). The leading foot had a higher proportion of overall and forefoot loads, and a lower proportion of rearfoot load compared to the trailing foot (P < 0.001). The overall load on the dominant side was lower than that on the non-dominant side for both the leading and trailing feet (P < 0.001). For the trailing foot, forefoot load on the dominant side was lower than that on the non-dominant side, however, the opposite result appeared in rearfoot load (P < 0.001). Upon the leading foot landing, forefoot load exceeded the rearfoot load for the dominant (P < 0.001) and non-dominant sides (P < 0.001). Upon the trailing foot landing, forefoot load was lower than the rearfoot load for the dominant (P < 0.001) and non-dominant sides (P = 0.019). When the characteristics of biomechanical stability are compromised by step height, landing foot, and footedness factors - due to altered foot landing strategies, changing COP, or uneven force distribution - ability to control motion efficiently and respond adaptively to the forces experienced during movement is challenged, increasing the likelihood of loss of dynamic balance, with a consequent increased risk of ankle sprains and falls.

Kinematics Analysis and Gait Study of Bionic Turtle Crawling Mechanism.

Longer distance water delivery culverts pose obstacles such as deposited silt, stones, and dead trees. In this paper, a crawling robot is designed to mimic the joint structure of a turtle using bionic design principles. The mechanism and gait of the robot are analyzed. The kinematics model of the robot is established using the D-H method and analytical approach, while the dynamics model is established using Lagrange's method. Based on kinematics and dynamics analysis theory, compound cycloid and cubic polynomial motion trajectories for the robot foot are planned along with a crawling gait resembling that of a turtle's abdomen. Simulation experiments and scale prototype experiments confirm that when gait parameters are identical, the energy consumption of compound cycloid trajectory exceeds that of cubic polynomial foot trajectory. When planning these two types of foot trajectories, it was observed that energy consumption ratio decreases with increasing step length but increases with increasing step height.

Low-frequency broadband characteristics of stepwise radial acoustical black holes

In this paper, a stepped radial acoustic black hole (SR-ABH) structure formed via a stepwise arrangement of two-dimensional radial acoustic black holes(ABH) is proposed. The finite element method is used to calculate the energy band and frequency response curve of the SR-ABH structure. It is found that the low-frequency bandgap accounts for 83.4% of the whole energy band region (0-2000 Hz) , which is 7.6 times broader than that of a horizontally arranged radial acoustic black hole (HR-ABH). On the basis of modal analysis at special points, the introduction of gradient arrays into radial ABH is confirmed, which reduces the cut-off frequency of ABH and leads to a low-frequency broadband coupling of local resonance and acoustic black hole effects. In addition, the influence of geometric parameters on the bandgap is explored. The results indicate that as the step height increases, the coupling relationship between local resonance and acoustic black hole effects shows a trend of first strengthening and then weakening, thereby affecting the movement of the low-frequency bandgap. In addition, the proposed structure provides a way to reduce the high cutoff frequency of ABH.

Developed log-wake law and turbulent behaviour of flow along a stepped spillway

Abstract The log-wake law for turbulent current has been developed and tested with laboratory data on turbulent flow in smooth pipes. However, flow with turbulence and vortices in a stepped spillway have not been described. Therefore, in this study, a log-wake law has been developed for use in stepped spillway systems. It can be divided into three parts. The first part, a logarithmic equation, describes the effect of shear stress between the flow layers with a von Kármán constant of 0.41. The second part, a third-degree polynomial, describes the effect of the shear stress on the wall. The last part, a fourth-degree polynomial, describes the effect of changing the flow pressure distribution, similar to the wall-free shear stress. Calibration tests (68 datasets) are used with a flow rate between 0.0233 and 3.285 m3/s, a spillway slope of 14–30°, and a step height of 0.0380–0.610 m. The developed log-wake law characterized the flow in a stepped spillway well. The limitation of the equation is a maximum flow velocity of 4 m/s; the accuracy of this equation decreases as the step height increases.

Research on thermochemical erosion and thermal protection properties of multiple interface nozzles in long-time working hybrid rocket motors

To improve the ablation resistance under long-time working conditions, a multiple interface nozzle with a carbon ceramic throat cap and a copper infiltrated tungsten throat insert is designed. Firstly, a transient numerical model on thermochemical erosion (considering surface reactions of carbon and tungsten) of the multiple interface nozzle in a hybrid rocket motor is established, and the regression of nozzle inner profile is simulated by adopting a dynamic grid technique. Then a 200 s firing test of the full-scale hybrid rocket motor with the multiple interface nozzle is conducted, and 98% hydrogen peroxide and hydroxyl-terminated polybutadiene based fuel are adopted. Erosion steps are formed at the interface of the carbon ceramic and copper infiltrated tungsten, and its formation mechanism is discussed. The erosion step height on the windward side of the throat insert is larger than that on the leeward side of the throat insert. The nozzle inner profile after the test agrees well with the simulation results, and the error of the nozzle throat diameter between the simulation results and test data is about 3.45%, which verifies the accuracy of numerical models. Finally, effects of erosion steps on the ablation characteristics and thermal protection properties are studied by numerical simulations. The results indicate that the erosion rate on the leeward side is much lower than that on the windward side. On the leeward side, the obvious radial diffusion of the gas occurs and the erosion rate increases with the increase of the erosion step height. Local vortices at the position of erosion steps will improve the heat transfer coefficient. When the erosion step height increases, the temperature on the outside surface of the nozzle shell improves, and it is increased by 38.3 K on the shell surface in the nozzle throat at t = 200 s. Research findings in this paper can provide important support for the engineering application of hybrid rocket motors with multiple interface nozzles.

Shaping Exploration: How Does the Constraint-Induced Movement Therapy Helps Patients Finding a New Movement Solution

Despite the relative success of constraint-induced movement therapy in the recovery of injury-/trauma-related populations, the mechanisms by which it promotes its results are still unknown. From a dynamical systems approach, we investigated whether the induced exploratory patterns within and between trials during an exercise in Shaping (the therapy's practice) could shed light on this process. We analyzed data from four chronic spinal-cord injury patients during a task of placing and removing their feet from a step. We assessed the within and between trial dynamics through recurrent quantification analyses and task-space analyses, respectively. From our results, individuals found movement patterns directed to modulate foot height (to accomplish the task). Additionally, when the task was manipulated (increasing step height), individuals increased coupling and coupling variability in the ankle, hip, and knee over trials. This pattern of findings is in consonance with the idea of Shaping inducing exploration of different movements. Such exploration might be an important factor affording the positive changes observed in the literature.

Turbulent Fluid Flow and Heat Transfer Enhancement Using Novel Vortex Generator

One of several effective methods for improving heat transfer in heat exchangers is the use of vortex generators in channels. The flow of fluid through a channel with a vortex generator is disrupted by the development of recirculation zones on the step wall, which improves fluid mixing and heat transmission. The current work investigates the flow and heat transfer of turbulent fluid flow through channels with various vortex generator designs mathematically (triangular, half-circle, and quarter circle). The finite volume method (FVM) is used to discretize and solve the continuity, momentum, and energy equations. The SIMPLE algorithm approach is used to connect the pressure and velocity fields within the domain. The effect of geometrical factors such as step height (2, 3, 4, 5, and 6 mm) on the flow and heat fields is demonstrated and analyzed, as is the effect of Reynolds number. As the step height increases, so do the surface Nusselt number and skin friction coefficient, which peak at 4 mm. According to the findings, as Re increases, so does the average Nusselt number. The quarter circle vortex generator has the best thermal-hydraulic performance at a 4 mm amplitude height, followed by the triangle vortex generator. The simulation results are consistent with those found in the literature.

A numerical study to reduce the drag effects in hypersonic flow over the backward facing step

A numerical simulation study of laminar hypersonic cold airflow over the backward-facing step (BFS) is performed at a freestream Knudsen number of 0.00009589 for resolving the flow field. The effects on the wall properties caused by the expansion of the flow and the separation of the boundary layer at the step corner have been investigated. The contributions of pressure and viscosity to the coefficients of lift and drag have been elucidated. It is seen that an increase in step height “nh” from n = 1 to 5 for a freestream flow at Mach 7.6 produces an incremental effect on the CL/CD ratio, whose range is between −1 to 1 for the variations in the step height simulated. The current study concludes that BFS yet remains a geometry that contributes to more drag than lift, however that effect can be minimized by increasing the step height during the design process of hypersonic vehicles for the above-mentioned Mach number.

Slope stability analysis in various Terraces model (case study: Sendangmulyo, Tirtomulyo District, Wonogiri Regency)

Wonogiri has various contours. Steep slopes dominate some areas. Hence it has a high possibility to occur landslides. There are still a lot of people living under the slopes. Therefore, this research is essential for disaster mitigation purposes. The study aims to know how the value of the slope safety factor changes with construction terraces design. The research was conducted by collecting secondary data and improving the Terraces construction carried out. The data was analyzed in the limit equilibrium method to provide conditions before and after the rain. The models were tried with several Terraces variations on the slope to obtain the most optimal design. The results used a simplified Bishop method. The design of terraces on the slopes of Sendangmulyo Wonogiri Village shows that the SF value increase is only for the conditions before a rain. In contrast, the states after the rain do not yield a safety condition. The SF value increases if the number of steps increases, whereas the more step height increases, the less the SF value will be.

Performance, metabolic, hemodynamic, and perceived exertion in the six-minute step test at different heights in a healthy population of different age groups

Abstract Aim: This study aimed to compare the performance, metabolic, hemodynamic, and perceived exertion during the 6-minute step test (6MST) conducted with different step heights in healthy subjects and also to compare the performance between different age groups for each step height. The association between age, body mass index, level of physical activity, and lower limb measurements with performance were also evaluated. Methods: This is a cross-sectional study. Anthropometric measures, physical performance, and cardiovascular stress were evaluated during a self-paced 6MST with different step heights in healthy subjects in the age group of 18-59. All the participants underwent three-step tests (15 cm, 20 cm, and 30 cm) on the same day, in a randomized order. Results: Forty participants (20 men and 20 women) performed the tests. The performance in the test for the highest step was significantly lower compared to the step with the lowest height (152 ± 24 vs. 173 ± 27 and 184 ± 33; p < 0,05). The estimated peak oxygen consumption (VO2peak) increased by ∼2.5 mL.kg−1·min−1 with the increase in step height. Hemodynamic variables, such as percent of maximum heart rate (%HRmax), and systolic blood pressure increased as the step height increased. There was a fair correlation between performance and the level of physical activity in the test with a step height of 15 cm and 20 cm. Conclusion: A higher step height caused greater cardiovascular stress, without exceeding the submaximal levels of the test, indicating that the 6MST can be used as an accurate instrument for evaluating aerobic capacity in healthy individuals.

Dynamic Behavior of a Nanosized Water Droplet on the Stepped Surface with a Wetting Gradient

The present study investigated the dynamic behavior of a nanosized water droplet on a flat and stepped surface using molecular dynamics simulations. The effects of a wetting gradient associated with the surface and the step height of a stepped surface on the dynamic behavior of the water droplet were considered in this study. The dynamic behaviors of the water droplet were described quantitatively upon analyzing the transient variation of the adhesion energy and the position of the water droplet along with the time required to climb the step. The water droplet moved smoothly along the surface with an increasing wetting gradient. On the other hand, the step obstructed the water droplet from climbing the step as the step height increases. The dynamic behavior of the water droplet depending on the variation of the normalized step height and the differences in adhesion energies between the different surfaces was classified into three types, namely, (1) fully climbing the step, (2) partially climbing the step, and (3) being blocked by the step. In the case in which the water droplet fully climbs the step, the time taken for the water droplet to fully climb the step showed a non-monotonic pattern as the step height increases.

Experimental investigations of the evolution of step-pools in rills with heterogeneous soils in Yuanmou Dry-Hot Valley, SW China

As a common type of microtopography in rill channels, the formation and dynamics of step-pools are prerequisites for the occurrence of rills. However, the evolution of step-pools in a rill (SPRs) is still unclear. Scouring experiments in field plots were conducted to explore the dynamic evolution of SPRs and the effect of steps on pools under conditions of strong runoff and soil-like materials aggregated with gravels in Yuanmou Dry-Hot Valley (SW China). Using three-dimensional laser scanning, spatial analysis of a GIS (geographic information system), and statistical analysis, 11 parameters were used to characterize step-pool morphology. The results showed that SPRs formed after several scourings at particular locations, and some of them disappeared in the late stage. A diverse range of SPRs formed, with geometrical parameters initially increasing, then stabilizing, and finally decreasing. During scouring, pool shape transformed from a deep V-shape to a shallow V-shape and then to a U-shape. The evolution of a typical pool included initial, active, stable and fading stages. There were 59 oval-shaped pools (88.06% of the total number of pools) in plane form and 37 deep pools (55.22%) in cross-section, and significant differences in the plane form and profile morphology of a pool presented themselves during its evolution. SPRs developed more easily in dry red soil-like materials compared with vertisol-like materials. The geometrical parameters of pools correlated with step size; and pools became deeper with increasing step height, and longer with increasing step height and decreasing step slope. The spatial heterogeneity of soil-like materials, as well as hydraulic conditions, led to complex and nonlinear SPR evolution. It is helpful to further understand the mechanism of rill incision and evolution.

The effect of tempering temperatures on the surface swelling of helium-ion-implanted Ti/Ta-added reduced-activation ferritic/martensitic steel

The swelling of a newly developed Ti/Ta-added reduced-activation ferritic/martensitic (RAFM) steel is evaluated using helium ion implantation. He ions are injected into sample surfaces covered with a transmission electron microscopy (TEM) grid; subsequent post-implantation annealing (PIA) causes surface mounds to form where He ions are injected. The heights of surface mounds on Ti/Ta-RAFM steels tempered at three different temperatures are found to increase with increasing tempering temperature. TEM observation reveals that helium bubbles formed along lath/block boundaries, dislocations, and precipitate-matrix interfaces. The increased step height of the Ti/Ta-RAFM steel tempered at higher temperature can be attributed to increases in the block and precipitate sizes and a decrease in dislocation density. The mechanism of helium bubble evolution in RAFM steel after helium implantation at room temperature and subsequent PIA is illustrated schematically. The swelling of Ti/Ta-RAFM steel is compared to that of a reference steel with a composition similar to that of Eurofer97.

Snap behaviour in the upheaval buckling of subsea pipelines under topographic step imperfection

Pipelines exposed to high temperature and high pressure with a topographic step imperfection are susceptible to the phenomenon of upheaval buckling potentially leading to a hazard for the structural integrity of the pipeline. To analyse this problem we derive analytical upheaval buckling solutions and obtain the locations of maximum displacement and maximum axial compressive stress. We also analyse the typical post-buckling behaviour and its dependence on step height, axial soil resistance and wall thickness. The difference in behaviour between a pipeline with step imperfection and one with a symmetric prop imperfection is discussed. Our results show that a pipeline with a step imperfection is more prone to upheaval buckling than a perfect pipeline. For sufficiently small step heights the pipeline may suffer a snap-back instability under decreasing thermal loading, raising the possibility of hysteretic snap behaviour under cyclic thermal loading (for instance caused by periodic start-ups and shut-downs). The snap-back buckling disappears for large enough step height and the minimum critical temperature difference decreases with increasing step height and wall thickness or with decreasing axial soil resistance. The maximum compressive stress decreases with increasing step height and axial soil resistance or with decreasing wall thickness. A pipeline with step imperfection is safer than one with a symmetric prop imperfection.

Experimental and numerical study on thermodynamic performance in a designate pilot-ignition structure: Step

Reliable ignition and stable flame spreading were extremely important especially for the increasing expansion of flight envelope. A new pilot-ignition structure- step- was put forward with low resistance and developed to meet more critical challenges. To optimize structure parameters, thermodynamic performance with various step heights (30 mm, 40 mm, 50 mm, and 60 mm) was investigated in premixed combustion, such as ignition and blow-off loop measured by intelligent metal tube flowmeter, and flame development recorded by high-speed camera. Additionally, numerical simulation of flow field was performed to analyse the influence of flow pattern on thermodynamic characteristics. It was found that flow pattern occurred transition with the increase of step height, namely, couple-vortex recirculation in 30 mm-height step structure and single-vortex recirculation in the other three. Additionally, the four kinds of steps realised successful ignition and stability loop. Specially, ignition and blow-off performance of 30 mm-height step structure with particular couple-vortex recirculation was sensitive to temperature, and improved with the growing temperature; also its ignition limits were increasing with the growing velocity, especially up to 200 m/s, ignition limits were almost lower than the others. Once ignited, flame development rate had a convex-function relation to temperature and optimized temperature existed at an extreme point (at 800 K), it decreased progressively with growing velocity. Moreover, flame spreading height up to core flow increased first and then decreased with growing temperature, and it was monotone decreasing with the growing inlet velocity. The step structure conducted in this work was validated for its reliable ignition and broad stability loop. Low-resistance pilot ignition design was developed and employed for turbojet/ramjet.

The sensitivity of digital intraoral scanners at measuring early erosive wear

ObjectivesTo investigate the sensitivity of intraoral scanners to quantitatively detect early erosive tooth wear. MethodsNatural buccal enamel samples were mounted in acrylic and scanned at baseline with an intraoral scanner (3 M True Definition Scanner, 3 M, USA). Samples were then exposed to 0.3% citric acid pH 3.2 at intervals of 10 min up to a total of 120 min and scanned after each exposure resulting in analysis of 13 datapoints per sample. Each scan was aligned with the baseline and data points super-imposed using an iterative closest point (ICP) algorithm on the acrylic surfaces (Geomagic Control Software, 3Dsystems, Darmstadt, Germany). Wear was measured using maximum profile loss, average profile loss and volume change. Data were normally distributed and Pearson correlations between erosion time and wear measurements assessed. ResultsAfter each 10-minute exposure until 120 min, maximum profile loss (μm) increased from 33.4 to 72.8 μm, average profile loss from 9.1 to 18.6 μm. Wear correlated with increasing acid exposure for both maximum profile loss wear (r = 0.877 p < 0.001) and average profile loss (r = 0.663 p = 0.019) respectively. Volume measurements were inconsistent at this level of wear. ConclusionsUsing scan data obtained from the intra oral scanners (IOS), increasing step height changes were observed with increasing exposures to acid. This study indicates there is potential of scans taken with an IOS to be used to detect early erosive tooth wear. However, precision was low suggesting limitations for minimal changes. Clinical significanceAlthough sub-visual wear was detected by intra-oral scanners on natural enamel surfaces, the accuracy was not sufficient to reliably diagnose that wear had occurred and interpretation of measurements should be done with caution. However, these results may be promising for detecting wear at more advanced stages.

Wave Impact Pressures on Stepped Revetments

The wave impacts on horizontal and vertical step fronts of stepped revetments is investigated by means of hydraulic model tests conducted with wave spectra in a wave flume. Wave impacts on revetments with relative step heights of 0.3 &lt; Hm0/Sh &lt; 3.5 and a constant slope of 1:2 are analyzed with respect to (1) the probability distribution of the impacts, (2) the time evolution of impacts including a classification of load cases, and (3) a special distribution of the position of the maximum impact. The validity of the approved log-normal probability distribution for the largest wave impacts is experimentally verified for stepped revetments. The wave impact properties for stepped revetments are compared with those of vertical seawalls, showing that their impact rising times are within the same range. The impact duration for stepped revetments is shorter and decreases with increasing step height. Maximum horizontal wave impact loads are about two times larger than the corresponding maximum vertical wave impact loads. Horizontal and vertical impact loads increase with a decreasing step height. Data are compared with findings from literature for stepped revetments and vertical walls. A prediction formula is provided to calculate the maximum horizontal wave impact at stepped revetments along its vertical axis.

Influence of a Backward-Facing Step on Swept-Wing Boundary-Layer Transition

Experimental measurements were performed on a swept flat-plate model with an airfoil leading edge and imposed chordwise pressure gradient to determine the effects of a backward-facing step on transition in a low-speed stationary crossflow-dominated boundary layer. Detailed hot-wire measurements were performed for three step heights ranging from 36 to 49% of the boundary-layer thickness at the step and corresponding to subcritical, nearly critical, and critical cases. In general, the step had a small localized effect on the growth of the stationary crossflow vortex, whereas the unsteady disturbance amplitudes increased with increasing step height. Intermittent spikes in instantaneous velocity began to appear for the two larger step heights. A physical explanation was provided for the mechanism leading to transition and the sudden movement in the transition front due to the critical steps. The large localized velocity spikes, which ultimately led to an intermittent breakdown of the boundary layer, were the result of nonlinear interactions of the different types of unsteady instabilities with each other and with the stationary crossflow vortices. Thus, the unsteady disturbances played the most important role in transition, but the stationary crossflow vortices also had a significant role via the modulation and the increased amplitude of the unsteady disturbances.

Retraining of Human Gait - Are Lightweight Cable-Driven Leg Exoskeleton Designs Effective?

Exoskeletons for gait training commonly use a rigid-linked "skeleton" which makes them heavy and bulky. Cable-driven exoskeletons eliminate the rigid-linked skeleton, providing a lighter and transparent design. Current cable-driven exoskeletons are aimed only at gait assistance by providing short bursts of forces to the leg during walking. It has not yet been shown if these designs are suitable for gait retraining, where rehabilitative forces need to be continuously applied to the leg in response to errors from a desired movement. The goal of this study is to investigate if a cable-driven leg exoskeleton can retrain the gait of human users. Nine healthy subjects were trained by a cable-driven leg exoskeleton to walk in a new gait pattern with 30% increase in step height from their natural gait. After 40 min of training, the gait of the subjects became significantly closer to the target gait than before the training. In three different post-training sessions, the step height of the subjects increased by 22%, 29%, and 31% on an average. In a fourth post-training session, when the subjects were instructed to ignore the training and walk naturally, the step height remained increased by 11%. These results confirm the potential of cable-driven designs in gait training applications.

Foot and Ankle Kinematics During Descent From Varying Step Heights.

In the general population, one-third of incidences during step negotiation occur during the transition to level walking. Furthermore, falls during curb negotiation are a common cause of injury in older adults. Distal foot kinematics may be an important factor in determining injury risk associated with transition step negotiation. The purpose of this study was to identify foot and ankle kinematics of uninjured individuals during descent from varying step heights. A 7-segment foot model was used to quantify kinematics as participants walked on a level walkway, stepped down a single step (heights: 5cm, 15cm, 25cm), and continued walking. As step height increased, landing strategy transitioned from the rearfoot to the forefoot, and the rearfoot, lateral and medial midfoot, and medial forefoot became more plantar flexed. During weight acceptance, sagittal plane range of motion of the rearfoot, lateral midfoot, and medial and lateral forefoot increased as step height increased. The changes in landing strategy and distal foot function suggest a less stable ankle position at initial contact and increased demand on the distal foot at initial contact and through the weight acceptance phase of transition step negotiation as step height increases.