scholarly journals Sensitivity of Idealized Moist Baroclinic Waves to Environmental Temperature and Moisture Content

2018 ◽  
Vol 75 (1) ◽  
pp. 337-360 ◽  
Author(s):  
D. J. Kirshbaum ◽  
T. M. Merlis ◽  
J. R. Gyakum ◽  
R. McTaggart-Cowan
Keyword(s):  
Kinetic Energy ◽  
Moisture Content ◽  
Potential Energy ◽  
Diabatic Heating ◽  
Environmental Temperature ◽  
Mechanical Energy ◽  
Negative Relationship ◽  
Vertical Motion ◽  
Periodic Wave ◽  
Cloud Band

Idealized simulations are used to examine the sensitivity of moist baroclinic wave growth to environmental temperature and moisture content. With relative humidity held fixed, the surface temperature at 45°N, denoted T0, is varied from 275 to 290 K. As T0 increases, the atmospheric moisture content, moist instability, and moist available potential energy also increase. For the chosen initial configuration, moist waves develop larger eddy kinetic energy K e than corresponding dry waves, but enhanced diabatic heating at larger T0 does not further increase K e. This finding is linked to a warm-frontal cyclonic potential vorticity (PV) anomaly that strengthens and shifts downstream at larger T0 owing to increased diabatic heating along the frontal cloud band. This eastward shift feeds back negatively on the parent cyclone by increasing the downstream export of mechanical energy aloft and degrading the phasing between dry baroclinic vertical motion and buoyancy within the warm sector. The latter suppresses the conversion from eddy potential energy to K e [ C( P e, K e)], offsetting a direct enhancement of C( P e, K e) by diabatic heating. Compared to their dry counterparts, isolated moist waves (initiated by a single finite-amplitude PV anomaly) display a similar sensitivity to T0, while periodic wave trains (initiated by multiple such anomalies) exhibit a stronger negative relationship. The latter stems from anticyclonic diabatic PV anomalies aloft that originate along the warm front and recirculate through the system to interact with the upper-level trough. This interaction leads to a horizontal forward wave tilt that enhances the conversion of wave K e into zonal-mean kinetic energy.

scholarly journals Walking in simulated reduced gravity: mechanical energy fluctuations and exchange

1999 ◽  
Vol 86 (1) ◽  
pp. 383-390 ◽  
Author(s):  
Timothy M. Griffin ◽  
Neil A. Tolani ◽  
Rodger Kram
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Gravitational Potential ◽  
Inverted Pendulum ◽  
Mechanical Energy ◽  
Center Of Mass ◽  
Metabolic Cost ◽  
Metabolic Energy ◽  
Gravitational Potential Energy ◽  
Reduced Gravity

Walking humans conserve mechanical and, presumably, metabolic energy with an inverted pendulum-like exchange of gravitational potential energy and horizontal kinetic energy. Walking in simulated reduced gravity involves a relatively high metabolic cost, suggesting that the inverted-pendulum mechanism is disrupted because of a mismatch of potential and kinetic energy. We tested this hypothesis by measuring the fluctuations and exchange of mechanical energy of the center of mass at different combinations of velocity and simulated reduced gravity. Subjects walked with smaller fluctuations in horizontal velocity in lower gravity, such that the ratio of horizontal kinetic to gravitational potential energy fluctuations remained constant over a fourfold change in gravity. The amount of exchange, or percent recovery, at 1.00 m/s was not significantly different at 1.00, 0.75, and 0.50 G (average 64.4%), although it decreased to 48% at 0.25 G. As a result, the amount of work performed on the center of mass does not explain the relatively high metabolic cost of walking in simulated reduced gravity.

The structures and energetics of fully nonlinear symmetric baroclinic waves

1984 ◽  
Vol 142 ◽  
pp. 343-362 ◽  
Author(s):  
Timothy L. Miller
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Richardson Number ◽  
Vertical Plane ◽  
Vertical Motion ◽  
Zonal Flow ◽  
Meridional Flow ◽  
Average Kinetic Energy ◽  
Basic Solution ◽  
Baroclinic Waves

A finite-difference Navier-Stokes model has been used to study rotating baroclinic flow for Richardson number [lsim ] 1, assuming no variations except in the vertical plane wholly containing the density-gradient vector. A section of a horizontally infinite channel has been studied, assuming periodic boundary conditions at the vertical computational boundaries and no-slip conducting horizontal boundaries. Two configurations were studied, both of which have an analytic basic solution with no horizontal variations in the velocities or density gradients. Symmetric baroclinic waves developed in the flows, as long as the Richardson number was not too large and the thermal Rossby number was large enough (for fixed diffusion parameters), consistent with linear theory. The structures and energetics of the fully developed waves were found to be especially dependent upon the Prandtl number Pr. Potential energy was the ultimate wave-energy source in all cases, and the average zonal flow was never much affected by the waves. For Pr > 1 the conversion from potential energy to wave kinetic energy was direct, via temperature and vertical-motion correlation. For Pr < 1 the conversion was from potential energy, to average kinetic energy by virtue of an induced meridional flow, to wave kinetic energy. For Pr = 1 the energy conversion was by either or both of the above, depending upon the other parameters.

Mechanics of locomotion in lizards.

1997 ◽  
Vol 200 (16) ◽  
pp. 2177-2188 ◽  
Author(s):  
C T Farley ◽  
T C Ko
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Gravitational Potential ◽  
Inverted Pendulum ◽  
Mechanical Energy ◽  
Center Of Mass ◽  
Gravitational Potential Energy ◽  
Lateral Bending ◽  
Walking Gait ◽  
Bending Force

Lizards bend their trunks laterally with each step of locomotion and, as a result, their locomotion appears to be fundamentally different from mammalian locomotion. The goal of the present study was to determine whether lizards use the same two basic gaits as other legged animals or whether they use a mechanically unique gait due to lateral trunk bending. Force platform and kinematic measurements revealed that two species of lizards, Coleonyx variegatus and Eumeces skiltonianus, used two basic gaits similar to mammalian walking and trotting gaits. In both gaits, the kinetic energy fluctuations due to lateral movements of the center of mass were less than 5% of the total external mechanical energy fluctuations. In the walking gait, both species vaulted over their stance limbs like inverted pendulums. The fluctuations in kinetic energy and gravitational potential energy of the center of mass were approximately 180 degrees out of phase. The lizards conserved as much as 51% of the external mechanical energy required for locomotion by the inverted pendulum mechanism. Both species also used a bouncing gait, similar to mammalian trotting, in which the fluctuations in kinetic energy and gravitational potential energy of the center of mass were nearly exactly in phase. The mass-specific external mechanical work required to travel 1 m (1.5 J kg-1) was similar to that for other legged animals. Thus, in spite of marked lateral bending of the trunk, the mechanics of lizard locomotion is similar to the mechanics of locomotion in other legged animals.

scholarly journals Gravitational Potential Energy Balance for the Thermal Circulation in a Model Ocean

2006 ◽  
Vol 36 (7) ◽  
pp. 1420-1429 ◽  
Author(s):  
Rui Xin Huang ◽  
Xingze Jin
Keyword(s):  
Energy Balance ◽  
Equation Of State ◽  
Kinetic Energy ◽  
Potential Energy ◽  
Gravitational Potential ◽  
Mechanical Energy ◽  
Vertical Mixing ◽  
Gravitational Potential Energy ◽  
Thermal Circulation ◽  
Model Ocean

Abstract The gravitational potential energy balance of the thermal circulation in a simple rectangular model basin is diagnosed from numerical experiments based on a mass-conserving oceanic general circulation model. The vertical mixing coefficient is assumed to be a given constant. The model ocean is heated/cooled from the upper surface or bottom, and the equation of state is linear or nonlinear. Although the circulation patterns obtained from these cases look rather similar, the energetics of the circulation may be very different. For cases of differential heating from the bottom with a nonlinear equation of state, the circulation is driven by mechanical energy generated by heating from the bottom. On the other hand, circulation for three other cases is driven by external mechanical energy, which is implicitly provided by tidal dissipation and wind stress. The major balance of gravitational energy in this model ocean is between the source of energy due to vertical mixing and the conversion from kinetic energy at low latitudes and the sink of energy due to convection adjustment and conversion to kinetic energy at high latitudes.

scholarly journals A Cascade-Type Global Energy Conversion Diagram Based on Wave–Mean Flow Interactions

2006 ◽  
Vol 63 (12) ◽  
pp. 3277-3295 ◽  
Author(s):  
Sachiyo Uno ◽  
Toshiki Iwasaki
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Wave Energy ◽  
General Circulation ◽  
Diabatic Heating ◽  
Mean Flow ◽  
Available Potential Energy ◽  
Flow Interactions ◽  
Northern Hemispheric ◽  
Cascade Type

A cascade-type energy conversion diagram is proposed for the purpose of diagnosing the atmospheric general circulation based on wave–mean flow interactions. Mass-weighted isentropic zonal means facilitate the expression of nongeostrophic wave effects, conservation properties, and lower boundary conditions. To gain physical insights into energetics based on the nonacceleration theorem, the wave energy W is defined as the sum of the eddy available potential energy PE and the eddy kinetic energy KE. The mainstream of the energy cascade is as follows: The diabatic heating produces the zonal mean available potential energy PZ, which is converted into the zonal mean kinetic energy KZ through the mean meridional circulation. The KZ is mainly converted to W through zonal wave–mean flow interactions and the rest is dissipated through friction. Not only the dynamical conversion but also the diabatic heating generates W, which is dissipated through friction. A diagnosis package is designed to analyze actual atmospheric data on the standard pressure surfaces. A validation study of the package is made by using the output from a general circulation model. The scheme accurately expresses tendencies of the zonal mean and eddy available potential energy equations, showing the diagnosis capability. On shorter time scales, PE changes in accordance with KE, good correlation indicating the relevance of the definition of wave energy. A preliminary study is made of the climate in December–February (DJF), and June–August (JJA), using the NCEP–NCAR reanalysis. The dynamical wave energy generation rate C(KZ, W) is about 60% of the conversion rate C(PZ, KZ), which means that KZ is dissipated through friction at a rate of about 40%. In the extratropics, C(KZ, W) is almost equal to C(PZ, KZ), as is expected from quasigeostrophic balance. In the subtropics, however, C(KZ, W) is much smaller than C(PZ, KZ), which suggests the importance of nongeostrophic effects on the energetics. The energetics is substantially different between the two solstices. Both C(PZ, KZ) and C(KZ, W) are about 30% larger in DJF than those in JJA, reflecting differences in wave activity. Stationary waves contribute considerably to energy conversions in the Northern Hemispheric winter, while baroclinic instability waves do more in the Southern Hemispheric winter than in the Northern Hemispheric winter.

scholarly journals How Does Latent Cooling Affect Baroclinic Development in an Idealized Framework?

2019 ◽  
Vol 76 (9) ◽  
pp. 2701-2714 ◽  
Author(s):  
Kristine F. Haualand ◽  
Thomas Spengler
Keyword(s):  
Potential Energy ◽  
Potential Vorticity ◽  
Diabatic Heating ◽  
Vertical Motion ◽  
Latent Heating ◽  
Low Level ◽  
Available Potential Energy ◽  
Relative Contribution ◽  
Heating And Cooling

Abstract Latent cooling by evaporating or melting hydrometeors has recently been shown to contribute to the positive low-level potential vorticity (PV) anomaly below the layer of latent heating in midlatitude cyclones. While the low-level PV anomaly might be intensified by latent cooling, the influence on the overall baroclinic development remains unclear. Including both latent heating and cooling in the Eady model, this study finds that latent cooling reduces baroclinic growth. While the PV anomaly between the layers of latent cooling and heating increases for realistic heating intensities, the PV anomaly at the top of the heating layer decreases, as latent heating is weakened because of reduced vertical motion within the cyclone. Consequently, the relative contribution from diabatic heating to the generation of eddy available potential energy decreases when latent cooling is included. Thus, despite the recently emphasized role of evaporation for the low-level PV anomaly in developing cyclones, the overall effect of latent cooling is detrimental to baroclinic growth.

Mechanical Energy Expenditures and Movement Efficiency in Full Body Reaching Movements

2010 ◽  
Vol 26 (1) ◽  
pp. 32-44 ◽  
Author(s):  
Daohang Sha ◽  
Christopher R. France ◽  
James S. Thomas
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Target Location ◽  
Mechanical Energy ◽  
The Body ◽  
Reaching Movements ◽  
Whole Body ◽  
Joint Power ◽  
Total Mechanical Energy ◽  
Full Body

The effect of target location, speed, and handedness on the average total mechanical energy and movement efficiency is studied in 15 healthy subjects (7 males and 8 females with age 22.9 ± 1.79 years old) performing full body reaching movements. The average total mechanical energy is measured as the time average of integration of joint power, potential energy, and kinetic energy respectively. Movement efficiency is calculated as the ratio of total kinetic energy to the total joint power and potential energy. Results show that speed and target location have significant effects on total mechanical energy and movement efficiency, but reaching hand only effects kinetic energy. From our findings we conclude that (1) efficiency in whole body reaching is dependent on whether the height of the body center of mass is raised or lowered during the task; (2) efficiency is increased as movement speed is increased, in part because of greater changes in potential energy; and (3) the CNS does not appear to use movement efficiency as a primary planning variable in full body reaching. It may be dependent on a combination of other factors or constraints.

scholarly journals Energy absorption at lower limb joints in different foot contact strategies while descending stairs

2021 ◽  
Vol 29 ◽  
pp. 433-440
Author(s):  
Hyeong-Min Jeon ◽  
Ki-Kwang Lee ◽  
Jun-Young Lee ◽  
Ju-Hwan Shin ◽  
Gwang-Moon Eom
Keyword(s):  
Knee Joint ◽  
Potential Energy ◽  
Energy Absorption ◽  
Lower Limb ◽  
Mechanical Energy ◽  
Connective Tissues ◽  
Stair Descent ◽  
Young Subjects ◽  
Power And Energy ◽  
Joint Loads

BACKGROUND: Joint loads in different walking strategies during stair descent have been investigated in terms of the joint moment in association with the risk of osteoarthritis. However, the absorption mechanisms of the potential energy loss are not known. OBJECTIVE: This study aims to compare the mechanical energy absorptions in lower limb joints in different initial foot contact strategies. METHODS: Nineteen young subjects walked down on instrumented stairs with two different strategies, i.e., forefoot and rearfoot strike. Power and energy at lower limb joints during stance phase were compared between strategies. RESULTS: Lower limb joints absorbed 73 ± 11% of the potential energy released by descending stairs and there was no difference between strategies. Rearfoot strategy absorbed less energy than forefoot strategy at the ankle joint in the 1st phase, which was compensated mainly by more energy absorption at the knee in the 2nd phase and less energy generation at the hip joints in the 3rd phase. CONCLUSION: The results suggest that a leg absorbs most of the potential energy while descending stairs irrespective of the walking strategies and that any reduction of energy absorption at one joint is compensated by other joints. Greater energy absorption at the knee joint compared to the other joints suggests high burden of knee joint muscles and connective tissues during stair-descent, which is even more significant for the rearfoot strike strategy.

scholarly journals Hydrodynamic constraints on the energy efficiency of droplet electricity generators

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Antoine Riaud ◽  
Cui Wang ◽  
Jia Zhou ◽  
Wanghuai Xu ◽  
Zuankai Wang
Keyword(s):  
Energy Efficiency ◽  
Kinetic Energy ◽  
Total Energy ◽  
Viscous Dissipation ◽  
Shear Force ◽  
Mechanical Energy ◽  
Electric Energy ◽  
The Past ◽  
Viscous Shear ◽  
Impingement Velocity

AbstractElectric energy generation from falling droplets has seen a hundred-fold rise in efficiency over the past few years. However, even these newest devices can only extract a small portion of the droplet energy. In this paper, we theoretically investigate the contributions of hydrodynamic and electric losses in limiting the efficiency of droplet electricity generators (DEG). We restrict our analysis to cases where the droplet contacts the electrode at maximum spread, which was observed to maximize the DEG efficiency. Herein, the electro-mechanical energy conversion occurs during the recoil that immediately follows droplet impact. We then identify three limits on existing droplet electric generators: (i) the impingement velocity is limited in order to maintain the droplet integrity; (ii) much of droplet mechanical energy is squandered in overcoming viscous shear force with the substrate; (iii) insufficient electrical charge of the substrate. Of all these effects, we found that up to 83% of the total energy available was lost by viscous dissipation during spreading. Minimizing this loss by using cascaded DEG devices to reduce the droplet kinetic energy may increase future devices efficiency beyond 10%.

scholarly journals Systematic Variation in Wintertime Precipitation in East Asia by MJO-Induced Extratropical Vertical Motion

2008 ◽  
Vol 21 (4) ◽  
pp. 788-801 ◽  
Author(s):  
Jee-Hoon Jeong ◽  
Baek-Min Kim ◽  
Chang-Hoi Ho ◽  
Yeon-Hee Noh
Keyword(s):  
East Asia ◽  
Large Scale ◽  
Diabatic Heating ◽  
Daily Precipitation ◽  
Lower Troposphere ◽  
Vertical Motion ◽  
Mean Value ◽  
Asian Countries ◽  
The Indian Ocean ◽  
Omega Equation

Abstract The variations in the wintertime precipitation over East Asia and the related large-scale circulation associated with the Madden–Julian oscillation (MJO) are examined. By analyzing the observed daily precipitation for the period 1974–2000, it is found that the MJO significantly modulates the distribution of precipitation over four East Asian countries; the precipitation rate difference between wet and dry periods over East Asia, when the centers of MJO convective activities are located over the Indian Ocean and western Pacific, respectively, reaches 3–4 mm day−1, which corresponds to the climatological winter-mean value. Composite analysis with respect to the MJO suggests that the MJO–precipitation relation is mostly explained by the strong vertical motion anomalies near an entrance region of the East Asia upper-tropospheric jet and moisture supply in the lower troposphere. To elucidate different dynamic origins of the vertical motion generated by the MJO, diagnostic analysis of a generalized omega equation is adopted. It is revealed that about half of the vertical motion anomalies in East Asia are induced by the quasigeostrophic forcings by the MJO, while diabatic heating forcings explain a very small fraction, less than 10% of total anomalies.

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