Instantaneous Load Research Articles

Role of cosmic-ray streaming and turbulent damping in driving galactic winds

ABSTRACT Large-scale galactic winds driven by stellar feedback are one phenomenon that influences the dynamical and chemical evolution of a galaxy, redistributing material throughout the circumgalatic medium. Non-thermal feedback from galactic cosmic rays (CRs) – high-energy charged particles accelerated in supernovae and young stars – can impact the efficiency of wind driving. The streaming instability limits the speed at which they can escape. However, in the presence of turbulence, the streaming instability is subject to suppression that depends on the magnetization of turbulence given by its Alfvén Mach number. While previous simulations that relied on a simplified model of CR transport have shown that super-Alfvénic streaming of CRs enhances galactic winds, in this paper we take into account a realistic model of streaming suppression. We perform three-dimensional magnetohydrodynamic simulations of a section of a galactic disc and find that turbulent damping dependent on local magnetization of turbulent interstellar medium (ISM) leads to more spatially extended gas and CR distributions compared to the earlier streaming calculations, and that scale heights of these distributions increase for stronger turbulence. Our results indicate that the star formation rate increases with the level of turbulence in the ISM. We also find that the instantaneous wind mass loading is sensitive to local streaming physics with the mass loading dropping significantly as the strength of turbulence increases.

A Study of the Strain Response of Stainless Steel 304 to Extreme Uniform Instantaneous Explosion Pressure Loads

Abstract The paper describes a new configuration using a gaseous detonation explosive blast source suitable for the studies of the instantaneous uniform pressure loading and mechanical response of materials. The capabilities of the configuration are illustrated by a preliminary series of experiments of the dynamic loading of clamped circular plates of 304 grade stainless steel with thicknesses ranging from 9.5 mm to 0.5 mm. The mechanical responses of the plates were monitored using strain gauges placed across the plate radius together with physical measurements of any permanent residual displacement of the center of the plate. The residual central deformations were analyzed using a well-established correlation involving nondimensional pressure load impulse. No universal correlation for the present data was found, but linear relationships for changes in two experimental parameters were identified, suggesting that the existing correlations have some deficiencies when applied to stainless steel 304.

Effects of basketball court construction and shoe stiffness on countermovement jump landings

Foot-ground contact upon landing from a jump results in an impulsive impact force. Parameters of impact including vertical ground reaction force (vGRF), loading rate, tibial acceleration, and impact attenuation have been associated with lower limb injury risk. Differences in shoe stiffness and surface construction may influence impact loading and attenuation, but evidence is limited. The purpose of this study was to quantify the influence of basketball court surface construction and shoe midsole stiffness on ground reaction force, joint work, and acceleration measures during countermovement jump landings. Twenty-nine male collegiate and high school basketball players performed maximal countermovement jumps in each of three basketball shoes and on three wood court surfaces with varying compressive stiffness. Peak vGRF, vertical instantaneous loading rate, tibial and head acceleration, impact attenuation, and joint work at the ankle and knee were quantified. No differences in peak vGRF, loading rate, impact attenuation, or knee joint work were observed between surface or shoe conditions (p ≥ 0.056). Eccentric ankle work was lowest on the stiffest surface (p ≤ 0.014). Peak resultant tibial acceleration in the time domain and axial tibial high frequency signal power magnitude in the frequency domain were lowest in the most compliant shoe (p = 0.005 and p = 0.046, respectively). The few significant findings for shoe stiffness and the somewhat counterintuitive finding for surface suggest that shoe and surface stiffness have minimal effects on parameters associated with impact during countermovement jump landings.

Investigation of Spanwise End Effects on Dynamic Stall of a Pitching Wing Section

An investigation of spanwise end effects on deep dynamic stall of a nominally two-dimensional pitching wing section is performed using high-fidelity large-eddy simulations (LES). This study was motivated by the need to reduce uncertainties in comparisons of computations and experiments. A NACA 0012 wing section was employed with freestream Mach number and chord Reynolds number . A harmonic pitching motion was prescribed with reduced frequency and minimum and maximum angles of attack of 4 and 22 deg, respectively. To characterize the effects of spanwise end conditions, several geometrical configurations are considered, including spanwise periodic, end walls, and end gaps. These configurations correspond to either spanwise-homogeneous LES or typical wind-tunnel installations. A comparison among various setups was performed in terms of instantaneous flow structure and aerodynamic loads. It was found that end effects can have a significant impact on the flow structure during the motion downstroke, which limits the agreement to be expected in computational/experimental comparisons. Although these effects are not unforeseen, this work provides a quantification of their magnitude. It is also confirmed that end walls are preferable to end gaps even if the latter are of the order of 1% chord. End-wall configurations with aspect ratio higher than 4 are preferable for improved comparisons.

Recovery of the natural grassland in a degraded native forest of the Argentine Espinal through aerial chemical control of shrubs

The stability of the ecosystems is directly related to a high value of biodiversity and, in this sense, the anthropic effects have generated negative conditions on the natural pastures. The aim of this work was to evaluate the recovery of the natural grassland of a degraded native forest of the Argentine Spinal with shrubs by means of an aerial chemical control in a cattle system with rotary grazing of low instantaneous load. The study was carried out in the Protected Natural Area Reserve of Multiple Uses Estancia El Caraya located in the north central of Entre Rios, Argentina.16 evaluations were carried out (between 2012 and 2015) on the chemically treated sector with Picloram+2,4-D and on three sectors without treatment. In each evaluation, the vegetation cover, the floristic composition of the most representative forage species, and the plant biomass, were quantified. The results of this work show that the use of an aerial chemical control technique increases significantly, by 44%, the coverage and biomass of the forage species in the treated areas with respect to the control. Chemical control over shrubs persisted over time with considerable effectiveness during the years of evaluation. Likewise, the floristic composition of the herbaceous species did not present significant differences between treatments.

Analytical study of transient thermo-mechanical responses in a fractional order generalized thermoelastic diffusion spherical shell with variable thermal conductivity and diffusivity

ABSTRACT With the great development of micro-electromechanical devices and wide application of subpicosecond/femtosecond ultrafast laser technology in micro-machining of micro-electromechanical devices, the investigations of interactions between thermodiffusion and deformation become significantly important. To accurate modeling the thermo-elasto-diffusive coupling, a new time fractional-order (i.e. memory-dependent derivative) based model of generalized thermoelastic diffusion for a perfect thermally and isotropic conducting medium which is assumed to have variable thermal conductivity and diffusivity is given in this work. This model is applied to investigate transient responses of a spherical shell subjected to instantaneous thermal and chemical shock loadings at external surface, whilst it is assumed that a permeating substance is in contact with the rigid surface at its internal surface. The solutions in the Laplace transform domain are obtained by using Kirchhoff and Laplace transform techniques and then the numerical inversion process based on fast Fourier transformation is carried out to derive the transient solutions in the time domain. Numerical computations for all the physical quantities considered are implemented and represented graphically. The results show that the variable thermal conductivity and diffusivity as well as memory-dependent parameters have the varying degrees of influences on the structural transient thermo-elasto-diffusive responses.

Running biomechanics before and after Pose® method gait retraining in distance runners

ABSTRACT Pose® Method gait retraining has been claimed to modify running form and prevent injury. This study examined the running biomechanics before and after Pose® Method gait retraining. Fourteen runners underwent a 4-week Pose® Method gait retraining program delivered by a certified coach. Paired t-tests were employed to compare vertical average (VALR) and instantaneous loading rates (VILR), lower limb kinematics, footstrike angle and trunk flexion in the sagittal plane before and after the training. Kinetically, there were no significant differences in the VALR (p= 0.693) and VILR (p= 0.782) before and after the training. Kinematically, participants exhibited greater peak hip flexion (p= 0.008) and knee flexion (p= 0.003) during swing. Footstrikeangle also reduced significantly (p= 0.008), indicating a footstrike pattern switch from rearfoot strike to midfoot strike. There was no significant difference in the trunk flexion in the sagittal plane after training (p= 0.658). After a course of Pose® Method gait retraining, runners demonstrated a footstrike pattern switch and some kinematics changes at the hip and knee joint during swing. However, injury-related biomechanical markers (e.g., VALR and VILR) and the trunk kinematics remained similar after training. Runners may consider other gait retraining programs for impact loading reduction.

Transition to forefoot strike reduces load rates more effectively than altered cadence

BackgroundExcessive vertical impacts at landing are associated with common running injuries. Two primary gait-retraining interventions aimed at reducing impact forces are transition to forefoot strike and increasing cadence. The objective of this study was to compare the short- and long-term effects of 2 gait-retraining interventions aimed at reducing landing impacts. MethodsA total of 39 healthy recreational runners using a rearfoot strike and a cadence of ≤170 steps/min were randomized into cadence (CAD) or forefoot strike (FFS) groups. All participants performed 4 weeks of strengthening followed by 8 sessions of gait-retraining using auditory feedback. Vertical average load rates (VALR) and vertical instantaneous load rates (VILR) were calculated from the vertical ground reaction force curve. Both cadence and foot strike angle were measured using 3D motion analysis and an instrumented treadmill at baseline and at 1 week, 1 month, and 6 months post retraining. ResultsANOVA revealed that the FFS group had significant reductions in VALR (49.7%) and VILR (41.7%), and changes were maintained long term. Foot strike angle in the FFS group changed from 14.2° dorsiflexion at baseline to 3.4° plantarflexion, with changes maintained long term. The CAD group exhibited significant reduction only in VALR (16%) and only at 6 months. Both groups had significant and similar increases in cadence at all follow-ups (CAD, +7.2% to 173 steps/min; and FFS, +6.1% to 172 steps/min). ConclusionForefoot strike gait-retraining resulted in significantly greater reductions in VALR and similar increases in cadence compared to cadence gait-retraining in the short and long term. Cadence gait-retraining resulted in small reductions in VALR at only the 6-month follow-up.

Degradation Analysis of SOFC Performance (2) - Severe Operation with an Instantaneous Load Fluctuation

Central Research Institute of Electric Power Industry (CRIEPI) has operated four types of SOFC stacks, which are developed by KYOCERA, NGK SPARK PLUG (NTK), NGK INSULATORS (NGK), and DENSO under NEDO’s project on high efficiency and toughness of SOFC cell-stacks (FY2018-FY2019). In order to evaluate the applicability of SOFC for an instantaneous load fluctuation, the load-fluctuation tests in this project have been carried out. It was determined as a test protocol that the periodic current fluctuations which are the waveform of triangular wave with the periods of time for 0.02-20 sec are applied to SOFC cell-stacks as a severe operating condition with the instantaneous load fluctuation. The durability with instantaneous load fluctuation for 2,000 h applying this test protocol was evaluated. As a result, the instantaneous response of cell voltage and power density, and the voltage decay rates of cell voltage of each SOFC cell-stack during the load fluctuation tests were clarified.

Effect of the Initial Stage of Strain on the Properties of Relaxation Curves Generated by the Rabotnov Nonlinear Relation for Viscoelastic Materials

An equation describing a family of stress relaxation curves with arbitrary strain programs at the initial stage generated by the Rabotnov nonlinear constitutive relation with two arbitrary material functions is derived and studied analytically. The effect of the initial stage duration and shape on the properties of relaxation curves is analyzed. Their deviations from each other and from the relaxation curves under instantaneous load are estimated in terms of material functions and strain programs. The convergence of deviations to zero is proved when the time tends to infinity or when the initial stage duration tends to zero.

Study of a hybrid pneumatic-combustion engine under steady-state and transient conditions for transport application

In this study, a new form of hybrid pneumatic combustion engine based on compressed air injection boosting is proposed. The hybrid pneumatic combustion engine regenerates the wasted energy during engine brake to improve the engine performance achieving better fuel economy. The mathematic model of the hybrid pneumatic combustion engine including a supercharged engine and the compressed air tank has been established. The steady-state and transient performance of the engine are analysed. Results show that the air injection boosting system can effectively improve the steady-state performance. Under the speed of 1900 r/min and 100% load, the engine torque and power can be increased from 1039 N m, 206.9 kW to 1057 N m, 210 kW by adopting air injection boosting with the injection pressure of 0.5 MPa. Effects of air injection parameters are also studied, showing that better performance can be achieved under higher air tank pressure and larger injection hole diameter. In addition, a transient analysis is completed under the speed of 1100 r/min. The result shows that when air injection boosting is used, the responding time of the engine to an instant load increase can be potentially reduced from 5.5 to 3.5 s under the injection pressure and duration of 0.5 MPa and 3 s. Meanwhile, the tank pressure has limited influence on the transient performance of the engine.

Validating theta power as an objective measure of cognitive load in educational video

We know from the literature that high cognitive load can impede performance and educational outcomes. Previous measures of cognitive load have largely relied on subjective scales but few have explored more objective measures. This paper aims to address this issue by examining the validity of electroencephalography (or EEG) as an objective measure of cognitive load in the context of educational video. EEG is an online brain measure of the electrical activity that a population of neurons elicits when they are activated. Theta power is a brain oscillation ranging from 4 to 7 Hz that has been linked to cognitive and memory performance. We manipulated the linguistic complexity of three texts delivered by a speaker on video to induce a simple, a moderate and a complex level of cognitive load amongst a sample of students pursuing postgraduate studies through the medium of English as a second language (n = 35). We specifically measured intrinsic cognitive load via a subjective scale, a recall test, and theta power as an objective measure (average cognitive load). Our results show that the subjective scale was significantly different across the three levels of linguistic complexity. However, theta power and recall were only significantly different between the two most distinct levels of linguistic complexity. Although, this finding suggests theta power may not be as sensitive for average cognitive load as the subjective scale for intrinsic cognitive load, a correlation analysis shows that theta power was correlated with self-reported cognitive load. However, it may need more power compared to the subjective scale. These findings suggest that theta power may be developed into a valid objective measure of average cognitive load although its true potential lies in the possibility to measure online fluctuations in cognitive load or instantaneous cognitive load.

Aeration effects on water-structure impacts: Part 2. Wave impacts on a truncated vertical wall

Aeration effects on wave loading are of considerable importance for offshore design. This paper describes experimental work to investigate four types of wave impact on a truncated vertical wall (representative of a plate in an FPSO vessel), in pure and aerated water. Investigations showed that high aeration and flip-through wave impacts are the most severe impact types and should therefore be considered for offshore structure design. It was also observed that there is a significant reduction in peak impact loads (both pressure and force) for impacts in aerated water compared to those in pure water. However, there was almost no reduction in impulsive loadings in aerated water compared to those in pure water, and therefore maximum instantaneous loads may be conservative in the presence of aerated water, in the implementation for offshore structure design. This paper is a companion paper to “Aeration effects on water-structure impacts: Part 1. Drop plate impacts”.

Experimental study on crack propagation of stainless steel 304 material under amplitude overloads

Fatigue mechanisms caused by dynamic loadings starts with cracks that occurred in a material. Under conditions such as transient conditions, an earthquake or instantaneous external loads, some parts of nuclear reactor that initially receive operating loads can be overloaded. The purpose of this research is to investigate the change of crack propagation in stainless steel 304 material related with amplitude overloads. The crack propagation test used the axial dynamic testing with the maximum stress (σ max) of 145 MPa, stress ratio R = 0.1 and over loading ratio (OVR) of 1.5, 1.75, 2. The results showed that the amplitude overloads caused the crack to propagate slowly as the crack tip formed a branch. The higher crack growth rate also showed the higher stress intensity factors in the crack tip.

Ground force kinetic adaptations associated with canine boots

Dog boots are being utilized to improve performance and welfare of dogs exposed to a range of adverse conditions; however, there is a lack of empirical evidence establishing the impact of these on gait characteristics. The aim of this research was to quantify alterations to ground force kinetics associated with the introduction of canine boots. Six clinically sound beagles were analyzed on two separate occasions using a cross-over study design to enable randomization between barefoot and shod conditions. During each session, dogs were trotted by an experienced handler over an AMTI force plate sampling at 1,000 Hz to quantify stance time, peak vertical force, peak vertical instantaneous loading rate, and vertical impulse. Although there was no significant difference found between footwear conditions for stance time, peak vertical force, and vertical impulse, peak vertical instantaneous loading rate was significantly greater in shod when compared to barefoot. Findings suggest that while canine boots may provide environmental protection, increases in loading rate are indicative of alterations in foot strike that may result in overloading of musculoskeletal structures. Therefore, caution must be taken when introducing footwear to ensure an adequate adjustment period.

Overview of Hysteresis Current Controller Application in Renewable Energy Based Power Systems

This paper presents an overview of the Hysteresis Current Controller (HCC) application in Renewable Energy Based Power System. The beginning concept of HCC is considered to be formally introduced by Thomas M. Freederiksen and Ronald W. Russel in 1971 that was registered in US Patent No. US3725673. The fundamental principle of HCC is based on the comparison of the instantaneous load current to the instantaneous sine wave reference where the difference between the two is maintained within the defined upper and lower band. There are some advantages of using HCC including simple, insensitivity to load parameters variations, fast dynamic response and inherent maximum current limiting characteristics. Therefore, based on its robustness, HCC has currently applied also in renewable energy based power plants such as PV converter system, Power Electronics System of Wind Energy, and in SMES control system for Wind Energy Application. However, the drawback of HCC system was also discussed in some papers compared with other control systems, for instant HCC is giving high chattering in torque in IM drive test. Therefore the combination of HCC with other controllers also becomes a new trend to improve the applied system that involving HCC as the main controller.

Impact Mechanics in Female Runners with Single and Multiple Stress Fractures Following Fatigue

Stress fractures are common injuries in runners and military recruits, with females at greater risk than their male counterparts. Impact variables including peak axial tibial shock and vertical average load rate during running have been shown to be higher in females with a history of tibial stress fractures and increase with fatigue. However, the relationship between mechanics and injury in those with multiple lower extremity stress fractures has not been examined. PURPOSE: To investigate whether impacts increase with fatigue in runners with no history of stress fractures (CON), one (1SFX), and 3 or more (3SFX) stress fractures. METHODS: Impact variables were calculated for 43 females (14 CON, 14 1SFX, and 15 3SFX) at a speed of 2.67 m/s before and after a fatigue run. Variables included peak axial and resultant tibial shock (VTA, RTA) and vertical average and instantaneous loading rates (VALR, VILR). The fatigue run was performed at a 5 km predicted pace and stopped when a RPE reached ≥ 18. Absolute change comparisons were made using one-way ANOVAs and post-hoc tests. RESULTS: 3SFX had larger changes (i.e. increased values) after fatigue than CON or 1SFX for all variables (Table 1), although after post-hoc tests only VILR for 3SFX was statistically higher than 1SFX (p<0.05), with VALR, VTA, and RTA not reaching significance. Additionally, subjects with the largest changes in these variables exhibited a change in their foot strike towards a more posterior strike pattern. CONCLUSION: Females with multiple stress fractures showed larger changes in load rates after fatigue, compared to those with history of one stress fracture. Change in foot strike pattern greatly influences impact mechanics before and after fatigue. Supported by U.S. Department of Defense, Defense Health Program, and Joint Program Committee W81XWH-16-1-0652 The views expressed are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government

Biomechanical effects of a lightweight, sock-style minimalist footwear design during running: a musculoskeletal simulation and statistical parametric mapping approach

The aim of this study was to examine the effects of existing minimalist footwear, new sock-style minimalist footwear and conventional running footwear on lower extremity biomechanics, using a musculoskeletal simulation and statistical parametric mapping (SPM) approach. Thirteen male participants ran over an embedded force plate at 4.0 m/s, in (1) existing minimalist footwear, (2) new sock-style minimalist footwear and (3) conventional running shoes. Kinematics of the lower extremities was collected using an eight-camera motion analysis system and lower extremity joint loading was also explored using a musculoskeletal simulation approach. Differences between footwear conditions were examined using SPM and one-way repeated measures ANOVA. The strike index indicated that the foot contact position was significantly more anterior in existing minimalist footwear (44.19%) and new sock-style minimalist footwear (42.33%) compared to conventional running shoes (29.00%). The instantaneous loading rate was also significantly larger in existing minimalist footwear (271.68 BW/s) and new sock-style minimalist footwear (299.26 BW/s) in relation to conventional running shoes (122.48 BW/s). In addition, during the late stance phase compressive hip joint loading was significantly larger in both minimalist footwear. Similarly, Achilles tendon loading was statistically greater in both minimalist footwear compared to the conventional running shoe during the early and middle aspects of the stance phase. The observations from this analysis show that minimalist footwear may place non-habituated runners at greater risk from the mechanical factors linked to the aetiology of chronic lower limb running-related injuries.

Grounded Running Reduces Musculoskeletal Loading.

Recent observations demonstrate that a sizeable proportion of the recreational running population runs at rather slow speeds and does not always show a clear flight phase. This study determined the key biomechanical and physiological characteristics of this running pattern, i.e., grounded running (GR), and compared these characteristics with slow aerial running (SAR) and reference data on walking at the same slow running speed. Thirty male subjects performed instructed GR and SAR at 2.10 m·s on a treadmill. Ground reaction forces, tibial accelerations, and metabolic rate were measured to estimate general musculoskeletal loading (external power and maximal vertical ground reaction force), impact intensity (vertical instantaneous loading rate and tibial acceleration), and energy expenditure. More explicit measures of muscular loading (muscle stresses and peak eccentric power) were calculated based on a representative subsample, in which detailed kinematics and kinetics were recorded. We hypothesized that all measures would be lower for the GR condition. Subjects successfully altered their running pattern upon a simple instruction toward a GR pattern by increasing their duty factor from 41.5% to 51.2%. As hypothesized, impact intensity, general measures for musculoskeletal, and the more explicit measures for muscular loading decreased by up to 35.0%, 20.3%, and 34.0%, respectively, compared with SAR. Contrary to our hypothesis, metabolic rate showed an increase of 4.8%. Changing running style from SAR to GR reduces musculoskeletal loading without lowering the metabolic energy requirements. As such, GR might be beneficial for most runners as it has the potential to reduce the risk of running-related injuries while remaining a moderate to vigorous form of physical activity, contributing to fulfillment of the recommendations concerning physical activity and public health.

Influence of thickness and initial groove angle in M–K model on limit strain of 7B04 by considering through-thickness stress

Marciniack–Kuczinski (M–K) model is widely used to predict material’s forming limit curve (FLC). The prediction of FLC traditionally neglected through-thickness normal stress. However, it cannot be neglected in some forming processes. Much work has been done to study the effect of through-thickness normal stress on FLC with constant through-thickness normal stress or constant ratio of through-thickness normal stress and maximum principal stress. In addition, based on Nakazima test process, the ratio of through-thickness normal stress and maximum principal stress has been derived, which was a function of instantaneous thickness and loading path. Here, initial groove angle in M–K model was not considered. In this paper, uniaxial tension tests and Nakazima tests were performed on 7B04 aluminum alloy. Based on Hill 48 yield criterion and M–K model, the prediction model of FLC was established. The increase of thickness can enhance FLC. Meanwhile, it is necessary to consider through-thickness normal stress and initial groove angle in prediction model. On the left side of FLC, the effect of initial groove angle on FLC is weakened by increasing sheet thickness. On the right side of FLC, the effect of initial groove angle on FLC is strengthened by increasing sheet thickness. On the right side of FLC, the relation between limit strain points with different thicknesses is linear under one certain loading path. Thickness has decisive effect on through-thickness normal stress level and the changing trendy of through-thickness normal stress during calculation is different under different stress condition.