Forward Kinetic Energy Research Articles

Eddy–Internal Wave Interactions: Stimulated Cascades in Cross-Scale Kinetic Energy and Enstrophy Fluxes

Abstract The interactions between oceanic mesoscale eddies, submesoscale currents, and internal gravity waves (IWs) are investigated in submesoscale-resolving realistic simulations in the North Atlantic Ocean. Using a novel analysis framework that couples the coarse-graining method in space with temporal filtering and a Helmholtz decomposition, we quantify the effects of the interactions on the cross-scale kinetic energy (KE) and enstrophy fluxes. By systematically comparing solutions with and without IW forcing, we show that externally forced IWs stimulate a reduction in the KE inverse cascade associated with mesoscale rotational motions and an enhancement in the KE forward cascade associated with divergent submesoscale currents, i.e., a “stimulated cascade” process. The corresponding IW effects on the enstrophy fluxes are seasonally dependent, with a stimulated reduction (enhancement) in the forward enstrophy cascade during summer (winter). Direct KE and enstrophy transfers from currents to IWs are also found, albeit with weaker magnitudes compared with the stimulated cascades. We further find that the forward KE and enstrophy fluxes associated with IW motions are almost entirely driven by the scattering of the waves by the rotational eddy field, rather than by wave–wave interactions. This process is investigated in detail in a companion manuscript. Finally, we demonstrate that the stimulated cascades are spatially localized in coherent structures. Specifically, the magnitude and direction of the bidirectional KE fluxes at submesoscales are highly correlated with, and inversely proportional to, divergence-dominated circulations, and the inverse KE fluxes at mesoscales are highly correlated with strain-dominated circulations. The predominantly forward enstrophy fluxes in both seasons are also correlated with strain-dominated flow structures.

A New Quantitative Gait Analysis Method Based on Oscillatory Mechanical Energies Measured near Body Center of Mass.

Human locomotion involves the modulation of whole-body mechanical energy, which can be approximated by the motion dynamics at the body's center of mass (BCOM). This study introduces a new method to measure gait efficiency based on BCOM oscillatory kinetic energy patterns using a single inertia measurement unit (IMU). Forty-seven participants completed an overground walk test at a self-selected speed. The average oscillatory energy (OE) at BCOM during walking was derived from measured acceleration data. The total OE showed a positive correlation with forward-walking velocity. The ratio of total OE to constant forward kinetic energy for healthy adults varied from ~1-5%, which can be considered the percent of oscillatory energy required to maintain gait posture for a given forward-walking velocity. Mathematically, this ratio is proportional to the square of the periodic peak-to-peak displacement of BCOM. Individuals with gait impairments exhibited a higher percentage of oscillatory energy, typically >6%. This wearable IMU-based method has the potential to be an effective tool for the rapid, quantitative assessment of gait efficiency in clinical and rehabilitation settings.

Turbulence kinetic energy transfers in direct numerical simulation of shock-wave–turbulence interaction in a compression/expansion ramp

A direct numerical simulation is performed for a supersonic turbulent boundary layer interacting with a compression/expansion ramp at an angle $\alpha =24^{\circ }$ , matching the same operating conditions of the direct numerical simulation by Priebe & Martín (J. Fluid Mech., vol. 699, 2012, pp. 1–49). The adopted numerical method relies on the high-order spectral difference scheme coupled with a bulk-based, low-dissipative, artificial viscosity for shock-capturing purposes (Tonicello et al., Comput. Fluids, vol. 197, 2020, 104357). Filtered and averaged fields are evaluated to study total kinetic energy transfers in the presence of non-negligible compressibility effects. The compression motions are shown to promote forward transfer of kinetic energy down the energy cascade, whereas expansion regions are more likely to experience backscatter of kinetic energy. A standard decomposition of the subgrid scale tensor in deviatoric and spherical parts is proposed to study the compressible and incompressible contributions in the total kinetic energy transfers across scales. On average, the correlation between subgrid scale dissipation and large-scale dilatation is shown to be caused entirely by the spherical part of the Reynolds stresses (i.e. the turbulent kinetic energy). On the other hand, subtracting the spherical contribution, a mild correlation is still noticeable in the filtered fields. For compressible flows, it seems reasonable to assume that the eddy-viscosity approximation can be a suitable model for the deviatoric part of the subgrid scale tensor, which is exclusively causing forward kinetic energy cascade on average. Instead, more complex models are likely to be needed for the spherical part, which, even in statistical average, provides an important mechanism for backscatter.

Double-cone ignition scheme for inertial confinement fusion.

While major progress has been made in the research of inertial confinement fusion, significant challenges remain in the pursuit of ignition. To tackle the challenges, we propose a double-cone ignition (DCI) scheme, in which two head-on gold cones are used to confine deuterium–tritium (DT) shells imploded by high-power laser pulses. The scheme is composed of four progressive controllable processes: quasi-isentropic compression, acceleration, head-on collision and fast heating of the compressed fuel. The quasi-isentropic compression is performed inside two head-on cones. At the later stage of the compression, the DT shells in the cones are accelerated to forward velocities of hundreds of km s–1. The head-on collision of the compressed and accelerated fuels from the cone tips transfer the forward kinetic energy to the thermal energy of the colliding fuel with an increased density. The preheated high-density fuel can keep its status for a period of approximately 200 ps. Within this period, MeV electrons generated by ps heating laser pulses, guided by a ns laser-produced strong magnetic field further heat the fuel efficiently. Our simulations show that the implosion inside the head-on cones can greatly mitigate the energy requirement for compression; the collision can preheat the compressed fuel of approximately 300 g cm−3 to a temperature above keV. The fuel can then reach an ignition temperature of greater than 5 keV with magnetically assisted heating of MeV electrons generated by the heating laser pulses. Experimental campaigns to demonstrate the scheme have already begun.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 1)’.

Regime transition in the energy cascade of rotating turbulence.

Transition from a split to a forward kinetic energy cascade system is explored in the context of rotating turbulence using direct numerical simulations with a three-dimensional isotropic random force uncorrelated with the velocity field. Our parametric study covers confinement effects in high-aspect-ratio domains and a broad range of rotation rates. The data presented here add substantially to previous works, which, in contrast, focused on smaller and shallower domains. Results indicate that for fixed geometrical dimensions the Rossby number acts as a control parameter, whereas for a fixed Rossby number the product of the domain size along the rotation axis and the forcing wave number governs the amount of energy that cascades inversely. The regime transition criterion hence depends on both control parameters.

Kinetic Gait Analysis of Agility Dogs Entering the A-Frame.

The main purpose of this study was to investigate the effect of a decrease in the A-frame angle of incline on the vertical and cranio-caudal ground reaction forces observed in a homogeneous cohort of agility dogs during entrance and contact with the A-frame. A crossover study design was applied to eight large breed dogs to compare the vertical and cranio-caudal ground reaction forces entering the A-frame at three angles of incline: 40° (standard), 35° and 30°. The peak vertical force, passive impact peak, peak propulsive force, peak braking force, the time point (percentile) in the stance phase at which these events occurred and the proportion of time for limb contact spent in braking (% braking) and propulsion (% propulsion) were examined.The variables measured from three trials at each incline were evaluated for a significant effect of A-frame angle with height and velocity included as covariates. The peak propulsive force and the % propulsion were significantly higher at the 40° angle of incline compared with 30° (p = 0.013, p = 0.0165 respectively) and the % braking was significantly lower at the 40° angle of incline compared with 30° (p = 0.0165). There was no significant effect of A-frame angle on the vertical ground reaction forces measured. Compared with 30° incline, ascent up the A-frame at a 40° incline requires a higher propulsive force and extended time in propulsion to maintain forward movement and convert potential energy into forward kinetic energy.

Field Electron Emission Images Far Away from a Semi-Infinitely Long Emitter: A Multiscale Simulation

Ab initio calculations reveal that in cold field electron emission from nanostructures, the electron state of top priority not necessarily the occupied state with largest forward kinetic energy but depends on the applied field. We show that single-walled carbon nanotube emission at low fields is dominated by the states with highest forward kinetic energy. On the other hand, high field emission is dominated by states that extend deeply into the potential barrier. We find that the distribution of the local density of states is an important factor for emission, in addition to the forward kinetic energy. We have calculated the wave functions of such states for semi-infinitely long single-walled carbon nanotubes by combining time-dependent density functional theory (TDDFT) with a reactant– product decoupling method. The emission image on a distant screen is found by matching the analytical solution of the wave function calculated with TDDFT on a plane which is a few nanometers away from the apex of the nanostr...

Three‐dimensional transient rip currents: Bathymetric excitation of low‐frequency intrinsic variability

AbstractThe ROMS‐WEC model [Uchiyama et al., 2010] based on an Eulerian wave‐averaged vortex‐force asymptotic theory of McWilliams et al. (2004) is applied to analyze 3‐D transient wave‐driven rip currents and associated intrinsic very low‐frequency (VLF) variability in the surf zone on a surveyed bathymetry under spatiotemporally uniform offshore incident waves. The 3‐D rip currents are substantially depth‐dependent due to the vertical recirculation, composed of pairs of counter‐rotating longitudinal overturning roll cells that promote surface convergence. The vortex force plays an important role in vorticity budget, preconditioning overall vorticity reduction. These rip currents are intrinsically unstable and contribute about 70% to kinetic energy (KE) as eddy kinetic energy (EKE), consistent with observations. The dominant fluctuation period fits the VLF band, at about 18 min. The current effect on waves (CEW) alters not only the mean rip structure, but also the associated turbulence as the modified cross‐shore EKE profile with considerable accentuation in the inner surf zone. Increased alongshore bathymetric variability proportionally intensifies KE and intrinsic EKE, whereas it reduces the VLF period. With a guide of a pseudo 2D model, we reveal that vortex tilting effect due to the horizontal vorticity inherent in the 3‐D rip currents promotes collapse of the 3‐D eddies through an enhanced forward kinetic energy cascade, leading to short‐lived, laterally‐stretched 3‐D eddies resulting in elongated filaments that decay more quickly than coherent, long‐lived, circular 2‐D eddies.

Abstract 17388: Cardiac MRI Derived Forward Stroke Energy is a Better Index of Left Ventricular Pump Function over Ejection Fraction in Mitral Regurgitation

Introduction: Mitral regurgitation (MR) into the low impedance left atrium (LA) enables a pop off valve effect and enables a false low end-diastolic volume and increased ejection fraction (EF). EF in these patients seems falsely high even though their ventricular contraction seems impaired, thus better indices that represent ventricular contraction are required in this lesion. Hypothesis: In this study we sought to investigate if forward stroke energy (FSE), which represents the forward kinetic energy of the blood through the aortic valve is a better indicator of ventricular contraction than EF. Methods: Phase-contrast MRI was performed in patients with MR (n=63; Mild MR =23; Moderate-severe MR=40), at the aortic and mitral valve planes, to compute the transvalvular through-plane flow. EF was measured as ((end-diastolic volume- end systolic volume)/end-diastolic volume), and FSE as (forward aortic stroke volume X mean arterial pressure). LV contractility was computed as the dynamic myocardial wall thickening over the cardiac cycle. Results: Regional peak wall thickening was significantly reduced in the moderate-severe MR groups - equatorial sector (5.9±0.6mm vs. 4.3±0.4mm, p=0.02) and apical sector (6.4±0.5mm vs. 4.5±0.3mm, p=0.003), indicating LV dysfunction with higher MR severity. EF did not capture this difference in LV contraction between the groups (50.1±3.7% vs. 48.3±3.2%, p=0.72). However, FSE demonstrated a significant difference between the two groups and a significant negative correlation (6527±483 mmHg.mL vs. 4895±282 mmHg.mL, p=0.002, r(MRfraction)=-0.42, p=0.0007). Conclusions: Forward stroke energy may better capture reduced myocardial contractility in the setting of MR, than EF - the current clinical gold standard.

Balanced and unbalanced routes to dissipation in an equilibrated Eady flow

The oceanic general circulation is forced at large scales and is unstable to mesoscale eddies. Large-scale currents and eddy flows are approximately in geostrophic balance. Geostrophic dynamics is characterized by an inverse energy cascade except for dissipation near the boundaries. In this paper, we confront the dilemma of how the general circulation may achieve dynamical equilibrium in the presence of continuous large-scale forcing and the absence of boundary dissipation. We do this with a forced horizontal flow with spatially uniform rotation, vertical stratification and vertical shear in a horizontally periodic domain, i.e. a version of Eady's flow carried to turbulent equilibrium. A direct route to interior dissipation is presented that is essentially non-geostrophic in its dynamics, with significant submesoscale frontogenesis, frontal instability and breakdown, and forward kinetic energy cascade to dissipation. To support this conclusion, a series of simulations is made with both quasigeostrophic and Boussinesq models. The quasigeostrophic model is shown as increasingly inefficient in achieving equilibration through viscous dissipation at increasingly higher numerical resolution (hence Reynolds number), whereas the non-geostrophic Boussinesq model equilibrates with only weak dependence on resolution and Rossby number.

Perspective on Afterglows: Numerically Computed Views, Light Curves, and the Analysis of Homogeneous and Structured Jets with Lateral Expansion

Herein I present numerical calculations of lightcurves of homogeneous and structured afterglows with various lateral expansion rates as seen from any vantage point. Such calculations allow for direct simulation of observable quantities for complex afterglows with arbitrary energy distributions and lateral expansion paradigms. A simple, causal model is suggested for lateral expansion of the jet as it evolves; namely, that the lateral expansion kinetic energy derives from the forward kinetic energy. As such the homogeneous jet model shows that lateral expansion is important at all times in the afterglow evolution and that analytical scaling laws do a poor job at describing the afterglow decay before and after the break. In particular, I find that lateral expansion does not cause a break in the lightcurve as had been predicted. A primary purpose of this paper is to study structured afterglows, which do a good job of reproducing global relationships and correlations in the data and thus suggest the possibility of a universal afterglow model. Simulations of structured jets show a general trend in which jet breaks become more pronounced with increasing viewing angle with respect to the jet axis. In fact, under certain conditions a bump can occur in the lightcurve at the jet break time. I derive scaling relations for this bump and suggest that it may be a source of some bumps in observed lightcurves such as that of GRB 000301C. A couple of lateral expansion models are tested over a range of efficiencies and viewing angles and it is found that lateral expansion can, in some cases, substantially sharpen the jet break. I show flux surface contour maps and simulated images of the afterglows which give insight into how they evolve and determine their lightcurves.

The role of ankle plantar flexor muscle work during walking.

Impaired ankle plantar flexor (APF) function is a frequent cause of gait limitations, but the role of the APF in the forward propulsion of the body remains controversial. To better understand both the direct and indirect effects of the APF during push-off and through advancement of the leg, mechanical work and inverse dynamic analyses were performed on 8 normal subjects during level walking. During push-off, 23.1 joules (J) of energy were generated, primarily by the APF, but only 4.2 J of this energy is transferred into the trunk. Ankle plantar flexor work is primarily used to accelerate the leg into swing. Most of the energy, 18.6 J, is recovered by transfer into the trunk at the end of swing. The timing of the energy transfers relative to the trunk motion imply that the APF contributes to the forward kinetic energy of the trunk but that other mechanisms likely account for the work used to raise the trunk against gravity.

Displacement of the pelvis during human walking: experimental data and model predictions

Displacements of the pelvis during treadmill walking were studied in dependence of walking speed, stride frequency and stride length. Displacement curves per stride cycle were described by means of harmonic analysis. Simple mechanical, or geometrical models of the body's center of mass (COM) tajectory during walking were used to predict amplitude and timing of pelvic displacements. As predicted by inverted pendulum models, the amplitude of pelvic displacement in vertical direction depended on stride length. Anterior-posterior displacements were predicted by assuming equal maxima of potential and forward kinetic energy of the body. Predictions for left-right displacements were based upon a model that assumed a constant stride width and a sinusoidal movement pattern. In agreement with this model, the amplitude of pelvic displacement in left-right direction depended on stride frequency. The presented models give insight into mechanical mechanisms which determine the pelvic trajectory during walking. The presented data may be useful in the clinical evaluation of gait disturbances.

Centrality dependence of K + and π+ multiplicities from Si + A collisions at 14.6 A GeV/ c

K + and π + multiplicities have been measured in magnetic spectrometer for Si++ Al, Si+ Cu and Si + Au collisions at 14.6 A GeV/ c incident momentum. The multiplicities were obtained for five different windows of forward kinetic energy as detected in a zero degree calorimeter. The K +/ π + multiplicity ratio ranges from ≈9% in peripheral interactions to 19% in central Si+Au. The largest K + / π + ratios are observed for those events for each target that leave the least energy in the zero degree calorimeter and the ratio increases with target mass. The observations suggest that multiple interactions are important in the particle production mechanism.