The Influence of Countermovements on Inter-Segmental Coordination and Mechanical Energy Transfer during Vertical Jumping

2020 ◽  
pp. 1-13
Author(s):  
Devon H. Frayne ◽  
John L. Zettel ◽  
Tyson A. C. Beach ◽  
Stephen H. M. Brown
Keyword(s):  
Energy Transfer ◽  
Mechanical Energy ◽  
Vertical Jumping ◽  
Segmental Coordination

Interphasial energy transfer and particle dissipation in particle-laden wall turbulence

2013 ◽  
Vol 715 ◽  
pp. 32-59 ◽  
Author(s):  
Lihao Zhao ◽  
Helge I. Andersson ◽  
Jurriaan J. J. Gillissen
Keyword(s):  
Energy Transfer ◽  
Kinetic Energy ◽  
Stokes Equations ◽  
Mechanical Energy ◽  
Wall Turbulence ◽  
Spherical Particles ◽  
Velocity Versus ◽  
Wall Region ◽  
Carrier Fluid ◽  
Stokes Force

AbstractTransfer of mechanical energy between solid spherical particles and a Newtonian carrier fluid has been explored in two-way coupled direct numerical simulations of turbulent channel flow. The inertial particles have been treated as individual point particles in a Lagrangian framework and their feedback on the fluid phase has been incorporated in the Navier–Stokes equations. At sufficiently large particle response times the Reynolds shear stress and the turbulence intensities in the spanwise and wall-normal directions were attenuated whereas the velocity fluctuations were augmented in the streamwise direction. The physical mechanisms involved in the particle–fluid interactions were analysed in detail, and it was observed that the fluid transferred energy to the particles in the core region of the channel whereas the fluid received kinetic energy from the particles in the wall region. A local imbalance in the work performed by the particles on the fluid and the work exerted by the fluid on the particles was observed. This imbalance gave rise to a particle-induced energy dissipation which represents a loss of mechanical energy from the fluid–particle suspension. An independent examination of the work associated with the different directional components of the Stokes force revealed that the dominating energy transfer was associated with the streamwise component. Both the mean and fluctuating parts of the Stokes force promoted streamwise fluctuations in the near-wall region. The kinetic energy associated with the cross-sectional velocity components was damped due to work done by the particles, and the energy was dissipated rather than recovered as particle kinetic energy. Componentwise scatter plots of the instantaneous velocity versus the instantaneous slip-velocity provided further insight into the energy transfer mechanisms, and the observed modulations of the flow field could thereby be explained.

scholarly journals Depressed Cardiac Mechanical Energetic Efficiency: A Contributor to Cardiovascular Risk in Common Metabolic Diseases—From Mechanisms to Clinical Applications

2020 ◽  
Vol 9 (9) ◽  
pp. 2681
Author(s):  
Albert Juszczyk ◽  
Karolina Jankowska ◽  
Barbara Zawiślak ◽  
Andrzej Surdacki ◽  
Bernadeta Chyrchel
Keyword(s):  
Heart Failure ◽  
Metabolic Syndrome ◽  
Energy Transfer ◽  
Metabolic Diseases ◽  
Mechanical Energy ◽  
Second Step ◽  
Energetic Efficiency ◽  
Preserved Ejection Fraction ◽  
The Third ◽  
Total Mechanical Energy

Cardiac mechanical energetic efficiency is the ratio of external work (EW) to the total energy consumption. EW performed by the left ventricle (LV) during a single beat is represented by LV stroke work and may be calculated from the pressure–volume loop area (PVLA), while energy consumption corresponds to myocardial oxygen consumption (MVO2) expressed on a per-beat basis. Classical early human studies estimated total mechanical LV efficiency at 20–30%, whereas the remaining energy is dissipated as heat. Total mechanical efficiency is a joint effect of the efficiency of energy transfer at three sequential stages. The first step, from MVO2 to adenosine triphosphate (ATP), reflects the yield of oxidative phosphorylation (i.e., phosphate-to-oxygen ratio). The second step, from ATP split to pressure–volume area, represents the proportion of the energy liberated during ATP hydrolysis which is converted to total mechanical energy. Total mechanical energy generated per beat—represented by pressure–volume area—consists of EW (corresponding to PVLA) and potential energy, which is needed to develop tension during isovolumic contraction. The efficiency of the third step of energy transfer, i.e., from pressure–volume area to EW, decreases with depressed LV contractility, increased afterload, more concentric LV geometry with diastolic dysfunction and lower LV preload reserve. As practical assessment of LV efficiency poses methodological problems, De Simone et al. proposed a simple surrogate measure of myocardial efficiency, i.e., mechano-energetic efficiency index (MEEi) calculated from LV stroke volume, heart rate and LV mass. In two independent cohorts, including a large group of hypertensive subjects and a population-based cohort (both free of prevalent cardiovascular disease and with preserved ejection fraction), low MEEi independently predicted composite adverse cardiovascular events and incident heart failure. It was hypothesized that the prognostic ability of low MEEi can result from its association with both metabolic and hemodynamic alterations, i.e., metabolic syndrome components, the degree of insulin resistance, concentric LV geometry, LV diastolic and discrete systolic dysfunction. On the one part, an increased reliance of cardiomyocytes on the oxidation of free fatty acids, typical for insulin-resistant states, is associated with both a lower yield of ATP per oxygen molecule and lesser availability of ATP for contraction, which might decrease energetic efficiency of the first and second step of energy transfer from MVO2 to EW. On the other part, concentric LV remodeling and LV dysfunction despite preserved ejection fraction can impair the efficiency of the third energy transfer step. In conclusion, the association of low MEEi with adverse cardiovascular outcome might be related to a multi-step impairment of energy transfer from MVO2 to EW in various clinical settings, including metabolic syndrome, diabetes, hypertension and heart failure. Irrespective of theoretical considerations, MEEi appears an attractive simple tool which couldt improve risk stratification in hypertensive and diabetic patients for primary prevention purposes. Further clinical studies are warranted to estimate the predictive ability of MEEi and its post-treatment changes, especially in patients on novel antidiabetic drugs and subjects with common metabolic diseases and concomitant chronic coronary syndromes, in whom the potential relevance of MEE can be potentiated by myocardial ischemia.

scholarly journals Metabolic to mechanical energy transfer after regional and global myocardial ischemia

1991 ◽  
Vol 17 (2) ◽  
pp. A44
Author(s):  
John C Lucke ◽  
Joseph R Elbeery ◽  
Theodore C Koutlas ◽  
Stan A Gall ◽  
Thomas A D'Amico ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Myocardial Ischemia ◽  
Mechanical Energy

scholarly journals Optimisation of Energy Transfer in Reluctance Coil Guns: Application to Soccer Ball Launchers

2020 ◽  
Vol 10 (9) ◽  
pp. 3137 ◽  
Author(s):  
Valentin Gies ◽  
Thierry Soriano ◽  
Sebastian Marzetti ◽  
Valentin Barchasz ◽  
Herve Barthelemy ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Energy Conversion ◽  
Mechanical Energy ◽  
Optimization Technique ◽  
Good Choice ◽  
Storage Capacitor ◽  
Trade Off ◽  
Electromagnetic Launchers ◽  
Mechanical Models ◽  
Structure Splitting

Reluctance coil guns are electromagnetic launchers having a good ratio of energy transmitted to actuator volume, making them a good choice for propelling objects with a limited actuator space. In this paper, we focus on an application, which is launching real size soccer balls with a size constrained robot. As the size of the actuator cannot be increased, kicking strength can only be improved by enhancing electrical to mechanical energy conversion, compared to existing systems. For this, we propose to modify its inner structure, splitting the coil and the energy storage capacitor into several ones, and triggering the coils successively for propagating the magnetic force in order to improve efficiency. This article first presents a model of reluctance electromagnetic coil guns using a coupled electromagnetic, electrical and mechanical models. Four different coil gun structures are then simulated, concluding that splitting the kicking coil into two half size ones is the best trade-off for optimizing energy transfer, while maintaining an acceptable system complexity and controllability. This optimization results in robust enhancement and leads to an increase by 104 % of the energy conversion compared to a reference launcher used. This result has been validated experimentally on our RoboCup robots. This paper also proves that splitting the coil into a higher number of coils is not an interesting trade-off. Beyond results on the chosen case study, this paper presents an optimization technique based on mixed mechanic, electric and electromagnetic modelling that can be applied to any reluctance coil gun.

The Effects of Ankle Restriction on the Multijoint Coordination of Vertical Jumping

2013 ◽  
Vol 29 (4) ◽  
pp. 468-473 ◽  
Author(s):  
Hiroshi Arakawa ◽  
Akinori Nagano ◽  
Dean C. Hay ◽  
Hiroaki Kanehisa
Keyword(s):  
Energy Transfer ◽  
Knee Joint ◽  
Ankle Joint ◽  
Energy Transport ◽  
Inverse Dynamics ◽  
Plantar Flexion ◽  
Joint Movement ◽  
Squat Jump ◽  
Vertical Jumping ◽  
Custom Made

The current study aimed to investigate the effect of ankle restriction on the coordination of vertical jumping and discuss the influence of energy transfer through m. gastrocnemius on the multijoint movement. Eight participants performed two types of vertical jumps: a normal squat jump, and a squat jump with restricted ankle joint movement. Mechanical outputs were calculated using an inverse dynamics analysis. Custom-made shoes were used to restrict plantar flexion, resulting in significantly (P < .001) reduced maximum power and work at the ankle joint to below 2% and 3%, while maintaining natural range of motion at the hip and knee. Based on the comparison between the two types of jumps, we determined that the ankle restriction increased (P < .001) the power (827 ± 346 W vs. 1276 ± 326 W) and work (92 ± 34 J vs. 144 ± 36 J) at the knee joint. A large part of the enhanced output at the knee is assumed to be due to ankle restriction, which results in the nullification of energy transport via m. gastrocnemius; that is, reduced contribution of the energy transfer with ankle restriction appeared as augmentation at the knee joint.

A New Turbomachine for Clean and Sustainable Hydrocarbon Cracking

2021 ◽  
Author(s):  
Dylan Rubini ◽  
Liping Xu ◽  
Budimir Rosic ◽  
Harri Johannesdahl
Keyword(s):  
Energy Transfer ◽  
Mechanical Energy ◽  
Coke Deposition ◽  
Industrial Processes ◽  
Energy Transfer Mechanism ◽  
The Novel ◽  
Hydrocarbon Cracking ◽  
Surface Heat Exchange ◽  
Work Input ◽  
Novel Concept

Abstract Decarbonising highly energy-intensive industrial processes is imperative if nations are to comply with 2050 greenhouse gas emissions. This is a significant challenge for high-temperature industrial processes, such as hydrocarbon cracking, and there have been limited developments thus far. The novel concept presented in this study aims to replace the radiant section of a hydrocarbon cracking plant with a novel turbo-reactor. Rather than using heat from the combustion of natural gas, the novel turbo-reactor can be driven by an electric motor powered by renewable electricity. Switching the fundamental energy transfer mechanism from surface heat exchange to mechanical energy transfer significantly increases the exergy efficiency of the process. Theoretical analysis and numerical simulations show that the ultra-high aerodynamic loading rotor is able to impart substantial mechanical energy into the feedstock without excess temperature difference and metal temperature magnitude. The required enthalpy rise can be supplied within a reactor volume 500 times smaller than that for a conventional furnace. A significantly lower wall surface temperature, supersonic gas velocities and a shorter primary gas path enable a controlled reduction in the residence time for chemical reactions, which optimises the yield. For the same reasons the conditions for coke deposition on the turbo-reactor surfaces are unfavourable, leading to an increase in plant availability. This study demonstrates that the mechanical work input into the feedstock can be dissipated through an intense turbulent mixing process which maintains an ideal and controlled pressure level for cracking.

Sign in / Sign up

Export Citation Format

Share Document