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In vivo characterization of intracardiac blood velocity vector fields may provide new clinical information but is currently not available for bedside evaluation. In this paper, 4-D vector flow imaging for intracardiac flow assessment is demonstrated using a clinical ultrasound (US) system and a matrix array transducer, without the use of contrast agent. Two acquisition schemes were developed, one for full volumetric coverage of the left ventricle (LA) at 50 vps and a 3-D thick-slice setup with continuous frame acquisition (4000 vps), both utilizing ECG-gating. The 3-D vector velocity estimates were obtained using a novel method combining phase and envelope information. In vitro validation in a rotating tissue-mimicking phantom revealed velocity estimates in compliance with the ground truth, with a linear regression slope of 0.80, 0.77, and 1.03 for the ${x}$ , ${y}$ , and ${z}$ velocity components, and with standard deviations of 2.53, 3.19, and 0.95 cm/s, respectively. In vivo measurements in a healthy LV showed good agreement with PC-MRI. Quantitative analysis of energy loss (EL) and kinetic energy (KE) further showed similar trends, with peak KE at 1.5 and 2.4 mJ during systole and 3.6 and 3.1 mJ for diastole for US and PC-MRI. Similar for EL, 0.15– 0.2 and 0.7 mW was found during systole and 0.6 and 0.7 mW during diastole, for US and PC-MRI, respectively. Overall, a potential for US as a future modality for 4D cardiac vector flow imaging was demonstrated, which will be further evaluated in clinical studies. [ABSTRACT FROM AUTHOR]

Water ramps are one of the most conveyance structures for surface water, irrigation and drainage networks, as well as wastewater collection and discharge systems. To reduce the size of the dissipaters or completely eliminate it, it is required to decrease flow energy over the water ramps. In this paper, results from an experimental investigation into ramps with different slopes and roughened beds are presented. The effects of hemispherical roughness on the kinetic energy dissipation have been studied. The experimental studies were conducted into energy dissipation a ramps with three different slopes (15, 22.5 and 30 degrees), three different roughness height (0.043, 2.2 and 3.2 cm), five roughness arrangements on the bed, and discharge rates of 5 to 30 lit/s. Results show that the energy dissipation in two models with a rough bed and different arrangements increased by 10–32% higher than the control model with a smooth bed. In addition, the energy dissipation of flow in all slopes increased with increasing roughness height. According to the results, a slope at a 30-degree angle had the maximum energy dissipation. Finally, an energy dissipation equation was developed to predict the energy dissipation in any rough model. [ABSTRACT FROM AUTHOR]

In this paper, a novel method with good numerical stability is proposed from the perspective of energy preserving to alleviate the numerical dissipations in the advection step of Eulerian fluid simulation. The main idea is to measure the vorticity loss during advection, calculate the lost angular kinetic energy with a proposed scheme, and then synthesize a high-frequency incompressible details field to compensate the lost energy in a way that is consistent with Kolmogorov's theory, which prevents the synthetic details from interfering with the existing fluid flow. The method works independently of the advection scheme and can be easily combined with other advection schemes to enhance the effect. It adds only 5% to 10% of the computational overhead while producing convincing fluid details without changing the overall behavior of the original flow. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to calculate the Hugoniot relations of polyurea; also to investigate the atomic-scale energy change, the related chain conformation evolution and the hydrogen bond dissociation of polyurea under high-speed shock. Design/methodology/approach: The atomic-scale simulations are achieved by molecular dynamics (MD). Both non-equilibrium MD and multi-scale shock technique are used to simulate the high-speed shock. The energy dissipation is theoretically derived by the thermodynamic and the Hugoniot relations. The distributions of bond length, angle and dihedral angle are used to characterize the chain conformation evolution. The hydrogen bonds are determined by a geometrical criterion. Findings: The Hugoniot relations calculated are in good agreement with the experimental data. It is found that under the same impact pressure, polyurea with lower hard segment content has higher energy dissipation during the shock-release process. The primary energy dissipation way is the heat dissipation caused by the increase of kinetic energy. Unlike tensile simulation, the molecular potential increment is mainly divided into the increments of the bond energy, angle energy and dihedral angle energy under shock loading and is mostly stored in the soft segments. The hydrogen bond potential increment only accounts for about 1% of the internal energy increment under high-speed shock. Originality/value: The simulation results are meaningful for understanding and evaluating the energy dissipation mechanism of polyurea under shock loading, and could provide a reference for material design. [ABSTRACT FROM AUTHOR]

In mountainous areas, rock avalanches swarm downslope leading to large impact forces on structures. Baffle systems are usually set up in torrent channels to dissipate the flow energy and reduce the destructive effects. In this paper, a crown-like baffle system is proposed to better dissipate the flow energy. The energy dissipation mechanism of this system was investigated based on DEM. The results reveal more than 90% of the kinetic energy of the granular flow was dissipated by particle-particle interaction. Two effects, the impedance effect and the deflection effect, were identified. The influence of these effects leads to the formation and growth of cushions behind the baffles, and these cushions enhance the particle-particle interaction. Two crown-like baffle systems were compared with a conventional baffle system based on the typical avalanche model. The results reveal the cumulative residual kinetic energy of the crown-like baffle system with square baffles decreased by 18.75% with the same concrete consumption as the conventional baffle system. For the crown-like baffle system with triangular baffles, the cumulative residual kinetic energy decreased by 6.22% with 83.94% of the concrete consumption of the conventional baffle system. Hence, the proposed baffle system is more cost-effective compared with the conventional baffle system. [ABSTRACT FROM AUTHOR]

The discontinuous deformation analysis (DDA) is a numerical method for modeling discontinuous deformation behaviour of jointed rocks. In this paper, two basic problems are discussed related to kinetic energy dissipation and the convergence criterion for the DDA method when it is applied to geotechnical engineering. In view of the fact that the deformation and progressive failure can be treated as a quasi-static process with low kinetic energy dissipation rates, this paper introduces a viscous damping component to absorb discrete blocks' kinetic energy, establishes the global equations of motion of the discrete block system that take damping effects into account, investigates the energy dissipation mechanism when solving a static or quasi-static problem, and defines the convergence criteria of displacement, kinetic energy and unbalanced force for DDA solutions when the system arrives at a stable state. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the effects of the Reynolds number (Resj = 300, 600, and 900) and porosity (ϕ = 20%–85%) on synthetic jet vortex rings impinging onto a porous wall. Laser-induced fluorescence and particle image velocimetry are used to acquire flow information qualitatively and quantitatively. When Resj is low (Resj = 300), ϕ plays a key role in determining the formation of transmitted vortex rings downstream. For the first time, a row of individual small-scale vortex rings that form at the lowest porosity (ϕ = 20%) have been observed in the synthetic jet/porous wall interaction. As Resj increases to 900, the triggered Kelvin–Helmholtz instability promotes the vorticity cancellation at a low porosity (ϕ = 30%), and thus contributes to the formation of a transmitted vortex ring. It is concluded that the vorticity cancellation is the dominant factor affecting the generation of a transmitted vortex ring. Time-averaged characteristics indicate that for a low Resj, the incoherence of the vortex ring is mainly due to the viscous effects. However, for a high Resj, it is the transition that leads to a significant enhancement in the turbulent kinetic energy. Measurements of flow macroscopic parameters show that the loss of the momentum flux exhibits a linear relationship with ϕ for all Resj, while the loss of the kinetic energy transport is nonlinearly dependent on ϕ. Incorporating ϕ, this study presents a more comprehensive similarity parameter, ϕln(Resj2 d h * 3 ), to characterize the synthetic jet/porous wall interaction. [ABSTRACT FROM AUTHOR]

This paper studies the turbulent kinetic energy ( k ⊥ ) in 2D isothermal electrostatic interchange-dominated E × B drift turbulence in the scrape-off layer and its relation to particle transport. An evolution equation for the former is analytically derived from the underlying turbulence equations. Evaluating this equation shows that the dominant source for the turbulent kinetic energy is due to interchange drive, while the parallel current loss to the sheath constitutes the main sink. Perpendicular transport of the turbulent kinetic energy seems to play a minor role in the balance equation. Reynolds stress energy transfer also seems to be negligible, presumably because no significant shear flow develops under the given assumptions of isothermal sheath-limited conditions in the open field line region. The interchange source of the turbulence is analytically related to the average turbulent E × B energy flux, while a regression analysis of TOKAM2D data suggests a model that is linear in the turbulent kinetic energy for the sheath loss. A similar regression analysis yields a diffusive model for the average radial particle flux, in which the anomalous diffusion coefficient scales with the square root of the turbulent kinetic energy. Combining these three components, a closed set of equations for the mean-field particle transport is obtained, in which the source of the turbulence depends on mean flow gradients and k ⊥ through the particle flux, while the turbulence is saturated by parallel losses to the sheath. Implementation of this new model in a 1D mean-field code shows good agreement with the original TOKAM2D data over a range of model parameters. [ABSTRACT FROM AUTHOR]

Columnar dangerous rock mass is widely developed in many high and steep mountain areas around the world. It often collapses, disintegrates and produces debris flow, which is disastrous. The collapse process of the columnar dangerous rock mass is very similar to the collapse of granular column. In this paper, we report the results of an experimental investigation of the flow induced by the collapse of a column of granular material over a horizontal surface. Two different setups are used, namely, a channelized granular column collapse (i.e., two-dimensional) and an unchannelized granular column collapse (i.e., three-dimensional), allowing us to compare channelized and unchannelized collapses flows. The experimental data suggest that our experimental findings were markedly different from those reported by previous authors (i.e., include the channelized and unchannelized collapse flows showed differences in energy conversion and dissipation). In channelized collapse flows, the maximum vertical speed appears in the free fall regime, while, the maximum speed in the vertical direction of unchannelized collapse flows appears in the spreading regime. During the whole collapse process, i.e., in channelized and unchannelized collapse flows, the conversion of potential energy and kinetic energy does not occur uniformly, and the maximum kinetic energy of the channelized collapse flows is higher than that of the unchannelized collapse flows, and compared with the unchannelized collapse flows, the dissipation energy in the channelized collapse flows is lower. A series of experiments was performed to predict the behaviour of different granular columns (characterized by different initial aspect ratio (a), varying from 1 to 4). The data obtained from 2D experimental model and 3D experimental model have certain amount of difference, such as the particle runout distance (d1), the maximum central height (h2), and the deposition angle (i.e., β1, β2). These differences show that the 2D experimental model does not fully represent the 3D conditions (i.e., the role of side-walls on the channelized collapse flows characteristic is non-negligible). Accordingly, care must be taken when validating 3D models with 2D experimental data. The movement of the tower dangerous rock masses with collapse failure mode could be evaluated using this channelized and unchannelized granular column experimental results. [ABSTRACT FROM AUTHOR]

In this paper, we introduce the notion of an energy graph G of order n ∈ N. Energy graphs are simple, connected and finite directed graphs. The vertices, labelled u1, u2, . . . , un, are such that (ui, uj) ∉ A(G) for all arcs (ui, uj) with i > j. Initially, equal amount of potential energy is allocated to certain vertices. Then, at a point of time, these vertices transform the potential energy into kinetic energy and initiate transmission to head vertices. Upon reaching a head vertex, perfect elastic collisions with atomic particles take place and propagate energy further. Propagation rules apply which could result in energy dissipation. The total dissipated energy throughout the graph is called the black energy of the graph. The notion of the black arc number of a graph is also introduced in this paper. Mainly Jaco-type graphs are considered for the application of the new concepts. [ABSTRACT FROM AUTHOR]

Proper EMA-balance (balance of kinetic energy, linear momentum and angular momentum), pressure-robustness and Re-semi-robustness (Re: Reynolds number) are three important properties of Navier–Stokes simulations with exactly divergence-free elements. This EMA-balance makes a method conserve kinetic energy, linear momentum and angular momentum in an appropriate sense; pressure-robustness means that the velocity errors are independent of the pressure; Re-semi-robustness means that the constants appearing in the error bounds of kinetic and dissipation energies do not explicitly depend on inverse powers of the viscosity. In this paper, based on the pressure-robust reconstruction framework and certain suggested reconstruction operators in Linke and Merdon [Comput. Methods Appl. Mech. Eng.311 (2016) 304–326], we propose a reconstruction method for a class of non-divergence-free simplicial elements which admits almost all the above properties. The only exception is the energy balance, where kinetic energy should be replaced by a suitably redefined discrete energy. The lowest order case is the Bernardi–Raugel element on general shape-regular meshes. Some numerical comparisons with exactly divergence-free methods, the original pressure-robust reconstruction methods and the EMAC method are provided to confirm our theoretical results. [ABSTRACT FROM AUTHOR]

This paper presents an analytical investigation on the free vibration, static buckling and dynamic instability of channel-section beams when subjected to periodic loading. The analysis is carried out by using Bolotin's method. By assuming the instability modes, the kinetic energy and strain energy of the beam and the loss of the potential of the applied load are evaluated, from which the mass, stiffness and geometric stiffness matrices of the system are derived. These matrices are then used to carry out the analyses of free vibration, static buckling and dynamic instability of the beams. Theoretical formulae are derived for the free vibration frequency, critical buckling moment, and excitation frequency of the beam. The effects of the lateral restraint applied to the flange, the section size of the beam and the static part of the applied load on the variation of dynamic instability zones are also discussed. [ABSTRACT FROM AUTHOR]

In a series of papers, we investigate the effect of collisions between turbulent molecular clouds on their structure, evolution, and star formation activity. In this paper, we look into the role of the clouds' initial virial ratios. Three different scenarios were examined: both clouds initially bound, one cloud bound and one unbound, and both clouds initially unbound. Models in which one or both clouds are bound generate filamentary structures aligned along the collision axis and discernible in position–position and position–velocity space. If neither cloud is bound, no filaments result. Unlike in previous simulations of collisions between smooth clouds, owing to the substructure created in the clouds by turbulence before the collisions, dissipation of kinetic energy by the collision is very inefficient and in none of our simulations is sufficient bulk kinetic energy lost to render the clouds bound. Simulations where both clouds are bound created twice as much stellar mass than the bound–unbound model, and both these scenarios produced much more stellar mass than the simulation in which both clouds are unbound. Each simulation was also compared with a control run in which the clouds do not collide. We find the bound–bound collision increases the overall star formation efficiency by a factor of approximately two relative to the control, but that the bound–unbound collision produces a much smaller increase, and the collision has very little effect on the unbound–unbound cloud collision. [ABSTRACT FROM AUTHOR]

This paper presents a novel method of labyrinth seals design. This method is based on CFD calculations and consists in the analysis of the phenomenon of gas kinetic energy carry-over in the seal chambers between clearances. The design method is presented in two variants. The first variant is designed for seals for which it is impossible to change their external dimensions (length and height). The second variant enables designing the seal geometry without changing the seal length and with a slight change of the seal height. Apart from the optimal distribution of teeth, this variant provides for adjusting chambers geometry to flow conditions. As the result of using both variants such design of the seal geometry with respect to leakage is obtained which enables achieving kinetic energy dissipation as uniform as possible in each chamber of the seal. The method was developed based on numerical calculations and the analysis of the flow phenomena. Calculation examples included in this paper show that the obtained reduction of leakage for the first variant ranges from 3.4% to 15.5%, when compared with the initial geometry. The relation between the number of seal teeth and the leakage rate is also analyzed here. The second variant allows for reduction of leakage rate by 15.4%, when compared with the geometry with the same number of teeth. It is shown that the newly designed geometry reveals almost stable relative reduction of leakage rate irrespective of the pressure ratio upstream and downstream the seal. The efficiency of the used method is proved for various heights of the seal clearance. [ABSTRACT FROM AUTHOR]

Urban landslides always occur where development has taken place on pre-existing unstable land. Due to rapid urbanization, human activities expand onto sloping terrain and disturb the geological environment, increasing the urban landslide risk. When a rapid flow-like landslide occurs, the landslide mobility can be affected by the presence of buildings located along its flow path. In this paper, the effect of building blockage on landslide mobility and the associated energy dissipation mechanisms are evaluated based on a well-documented landslide, which happened on 20 December 2015 in Shenzhen, China. The landslide flow process is reproduced by three-dimensional terrain analyses using LS-DYNA, considering three scenarios; namely, green field, movable buildings, and fixed buildings. Simulations show that the presence of densely located buildings significantly affects flow pattern, travel distance, deposition, and energy transfer mechanism. A fully developed debris fan in the flat area is observed in the green field case. The buildings in the runout path decelerate the flow process, leading to lower landslide mobility and less volume deposited in the accumulation zone. The shortest runout distance and widest and thickest deposits are observed in the fixed buildings case. The debris fan in the movable buildings case is closer to reality. Fixed buildings pose more constraint on surface moving material, leading to the largest deformation, largest internal energy, and smallest kinetic energy of the soil mass. The dissipation of the largest frictional energy occurs in the movable buildings case due to the long sliding distance of the damaged buildings. The internal energy of the landslide mass dominates the energy transfer mechanism. The results presented here indicate the need to consider building clusters when conducting urban landslide hazard mapping and risk assessment. [ABSTRACT FROM AUTHOR]

Dipolarization fronts (DFs) are important for energy conversion, particle acceleration, and flux transport in the magnetotail. The partition of energy conversion between ions and electrons and the energy dissipation at DFs are not well understood. In this paper, we present a statistical study of energy conversion and dissipation of 122 DFs observed by Magnetospheric Multiscale mission in the magnetotail. Statistically, electromagnetic energy transfers to plasma at DF. The released energy is mainly transferred to ions rather than electrons. On average, ions gain energy across the whole DF, while electrons gain energy at the leading part but lose energy at the trailing part of DFs. Joule dissipation J · (E+ve × B) can be either positive or negative at DFs, and its average value is very small. The kinetic energy dissipation parameter Pi − D does not exhibit clear signatures at the DFs; hence, it is not suitable for quantifying the energy dissipation at DF. Key Points: Statistical study of the energy conversion and dissipation at DFs observed by MMSElectromagnetic energy released at DF mainly goes to heat and accelerate ionsAverage Joule dissipation across DF is very small, and the parameter Pi − D is not suitable for quantifying the energy dissipation at DF [ABSTRACT FROM AUTHOR]

The present paper examines failure in discrete granular media with respect to its mode and nature based on energetic considerations through a comprehensive discrete element modelling computational analysis. The mode of failure refers to whether deformations will localize into an intense shear band or be diffuse. More subtly, a given failure mode can be effective with a burst of kinetic energy, or non-effective with a more controlled release of kinetic energy, depending on the control parameter. Physical quantities based on energy considerations with elementary decompositions of externally applied energy into elastic, plastic and kinetic contributions at the particle level are computed for a number of granular assemblies under a variety of failure scenarios. With the picture of a particle system experiencing macroscopic deformations according to underlying micro- and meso-mechanisms, it is concluded that computed grain-energy components depend on the microstructural detail that emerges as a function of loading program and control parameter. The relationship between elastic unloading outside a shear band and plastic dissipation inside it under both strain and stress control modes determines the genesis of shear banding in terms of plastic work dissipation minimization. Most interestingly, it is found that the energy signature inside the shear band in a dense granular packing is germane to energy characteristics of diffuse failure in a loose assembly, suggesting some similarities in microscopic failure processes between shear banding and diffuse failure. [ABSTRACT FROM AUTHOR]

The hump characteristic is one of the unique hydraulic instability of the large vertical volute centrifugal pump (LVVCP) under part-load conditions, which is extremely detrimental to the safe and stable unit operation. To suppress the hump characteristic of LVVCP, a passive suppression method with a combined diffuser vane structure is proposed in this paper. This diffuser vane structure consists of a combination of large and small hydrofoil vanes, with the special 6 small hydrofoil vane B are arranged within 150° range of the small volute section side. To investigate the key reasons for suppression, detached eddy simulations are performed for LVVCP with original diffuser vane (Diffuser A) and combined diffuser vane (Diffuser B), and the energy loss and flow patterns are analyzed. The hump region of LVVCP with Diffuser B is narrower, the positive slope of Q - H curve is decreased and the hump margin is increased. The reduced conversion of kinetic energy to turbulent kinetic energy and the decreased Reynolds stress diffusion loss in the Diffuser B and volute are main reasons for the hump characteristic suppression. The energy loss in the volute small section side region and its corresponding diffuser region increases significantly under hump conditions, and Diffuser B can obviously reduce the energy loss in these regions. The flow pattern analysis in the diffuser shows that the weakened rotating stall in Diffuser B leads to a more regular Q m variation with time in D1∼D6. The reduced chord length and thickness of vane B results in a significant decrease of pressure surface separation vortex (PSV) and suction surface separation vortex (SSV) scales and a weakened vortex merging phenomenon, which causes a considerable drop of Δ S PRO in the Diffuser B. The Diffuser B provides a more uniform α distribution to the volute inlet, and decreases the vortex scale and vortex-induced energy loss on the volute small section side. • A passive suppression method is proposed for the hump characteristic: combined diffuser vane arrangement strategy. • A combined energy loss evaluation methodology with entropy production theory and energy balance equations is applied. • The entropy production and Omega vortex identification technology are combined to analyze the flow pattern on the hump characteristic suppression. • The smaller chord length and thickness of vane B can alleviate flow separations and vortices merging in the diffuser and provide better inlet conditions for the volute. [ABSTRACT FROM AUTHOR]

Background: The perinatal transition's impact on systemic right ventricle (SRV) cardiac hemodynamics is not fully understood. Standard clinical image analysis tools fall short of capturing comprehensive diastolic and systolic measures of these hemodynamics. Objectives: Compare standard and novel hemodynamic echocardiogram (echo) parameters to quantify perinatal changes in SRV and healthy controls. Methods: We performed a retrospective study of 10 SRV patients with echocardiograms at 33-weeks gestation and at day of birth and 12 age-matched controls. We used in-house developed analysis algorithms to quantify ventricular biomechanics from four-chamber B-mode and color Doppler scans. Cardiac morphology, hemodynamics, tissue motion, deformation, and flow parameters were measured. Results: Tissue motion, deformation, and index measurements did not reliably capture biomechanical changes. Stroke volume and cardiac output were nearly twice as large for the SRV compared to the control RV and left ventricle (LV) due to RV enlargement. The enlarged RV exhibited disordered flow with higher energy loss (EL) compared to prenatal control LV and postnatal control RV and LV. Furthermore, the enlarged RV demonstrated elevated vortex strength (VS) and kinetic energy (KE) compared to both the control RV and LV, prenatally and postnatally. The SRV showed reduced relaxation with increased early filling velocity (E) compared prenatally to the LV and postnatally to the control RV and LV. Furthermore, increased recovery pressure (ΔP) was observed between the SRV and control RV and LV, prenatally and postnatally. Conclusions: The novel hydrodynamic parameters more reliably capture the SRV alterations than traditional parameters. [ABSTRACT FROM AUTHOR]

Chromospheric condensations (CCs) are a prominent feature of flare footpoint heating in the solar flare standard model, yet their timescales and velocities are not well understood. Fisher derived several important analytical relationships, which have rarely been examined with modern spectral observations. The Interface Region Imaging Spectrograph (IRIS) provides a wealth of flare data with a high enough cadence to sufficiently capture CC evolution. We analyzed Doppler shifts in Mg ii 2791 and Fe ii 2814 from a sample of flare footpoint pixels observed by IRIS to compare with Fisher's analytics and recent flare models. We found a detection lifetime of 1 minute occurs in 50% of the sample, with Mg ii showing several pixels with longer values and Fe ii almost categorically shorter, and both growing with the maximum velocity, v max. The shifts' half-life is commonly <40 s and is inversely related to v max, indicating that the first half of the CC evolution has more efficient kinetic energy loss. The lifetime's wide range and growth with v max indicate that the footpoint atmospherics and heating scenarios can vary more widely than first postulated in Fisher. Around 90% of the sample had observable acceleration periods, lasting an average of 38 and 32 s for Mg ii and Fe ii, respectively. These acceleration periods, as well as serving as flare model diagnostics themselves, could potentially be used to calculate other model diagnostics such as the initially accelerated mass. [ABSTRACT FROM AUTHOR]

Nonstationary convection forced by distributed buoyancy sources is a fundamental environmental fluid mechanics process, particularly in ice-covered freshwater waterbodies. In this paper, we present novel field-based results that characterise the diurnal evolution of the main energetics of radiatively-driven convection in ice-covered lakes that is the radiatively-induced buoyancy flux, B, and the kinetic energy dissipation rate, ε . To estimate the spatiotemporal distribution of ε , we applied scale similarity of the velocity structure functions to identify the fine turbulence scales from high-frequency velocity measurements. The field study was carried out at Lake Vendyurskoe, Russia, in April 2016. Small-scale velocity fluctuations were measured using acoustic Doppler current profiler in a 2 m layer beneath the ice cover. The method was proven to be valid for low-energy convection without mean shear. The inertial subrange, covering order of magnitude in the spatial domain, was identified by fitting the 2 / 3 scaling power law to the structure function method, thus confirming the regime of fully developed turbulence. The calculated rate of dissipation of turbulent kinetic energy ε reaches values up to 3 × 10 - 9 m 2 s - 3 . Although a strong correlation between ε and B was observed, ε picks up about 1 h later after the onset of the heating-phase. This delay roughly corresponds to the turnover time of the energy containing eddies. We finally observed a decay of ε at night, during the relaxation-phase, but, interestingly, the level remained above the statistical error. [ABSTRACT FROM AUTHOR]

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Kinetic energy loss during the impact between two vehicles is an essential parameter to assess the impact severity and for road accident reconstruction, since knowledge of this value allows us to estimate the collision closing speed. In this paper, an activity for the evaluation of the kinetic energy loss in collisions between two-wheeler vehicles and cars by means of semi-empirical methods is presented. Often in this field, as remarked in literature, the main difficulty lies in the evaluation of the energy loss for the car, on which usually localised deformations are produced, involving zones, near the wheels, for instance, having stiffness completely different from those on which crash tests are normally carried out. The work provides an initial analysis of crash tests between motorcycles and rigid barriers present in literature and a subsequent experimental work aimed at extending the records and assessing the influence on the impact of a braking motorcycle. Subsequently, a method is developed for the assessment of the energy loss of the car–motorcycle system and a campaign of crash tests conducted between the two types of vehicle for the validation of the model. [ABSTRACT FROM AUTHOR]

In this paper computational modeling was conducted on a single cylinder four valve pent-roof spark ignition (SI) engine at a speed of 1000rpm. The model was validated against experimental data available in the literature. To study the effect of intake port configuration two designs of ports were incorporated into the intake of base model. The parameter of SI engine at cold start condition by motoring revealed the betterment of engine performance for different port runner configuration. The turbulence character of average temporal fluctuation velocity along the cylinder axis of an engine is high for model-2. It is more around 54% than other models. The forward tumble is 1.73 for model-2. This ratio is higher than model-1 and model-3 by 2.9% and 90.17% respectively whereas cross tumble is 55.56% and 33.33%. Now the model-3 has maximum positive swirl than the other models with 16.67% and 33.33% for model-1 and model-2 respectively in which negative direction has attain maximum value at model-1 than model-2 and model-3 as 6.25% and 82.5%. The strength of vortices is defined by its length scale of turbulence parameter. The model-2 has 16.05% and 22.9% higher length scale strength than other models. Also it has maximum kinetic energy and dissipation rate at around 66% and 83% than other two models. Model-2 has better than other models for good preparation of mixture and combustion to meet out recent norms and regulation which gets greener engine. [ABSTRACT FROM AUTHOR]

SUMMARY This paper focuses on the assessment of a discontinuous Galerkin method for the simulation of vortical flows at high Reynolds number. The Taylor-Green vortex at Re = 1600 is considered. The results are compared with those obtained using a pseudo-spectral solver, converged on a 5123 grid and taken as the reference. The temporal evolution of the dissipation rate, visualisations of the vortical structures and the kinetic energy spectrum at the instant of maximal dissipation are compared to assess the results. At an effective resolution of 2883, the fourth-order accurate discontinuous Galerkin method (DGM) solution ( p = 3) is already very close to the pseudo-spectral reference; the error on the dissipation rate is then essentially less than a percent, and the vorticity contours at times around the dissipation peak overlap everywhere. At a resolution of 3843, the solutions are indistinguishable. Then, an order convergence study is performed on the slightly under-resolved grid (resolution of 1923). From the fourth order, the decrease of the error is no longer significant when going to a higher order. The fourth-order DGM is also compared with an energy conserving fourth-order finite difference method (FD4). The results show that, for the same number of DOF and the same order of accuracy, the errors of the DGM computation are significantly smaller. In particular, it takes 7683 DOF to converge the FD4 solution. Finally, the method is also successfully applied on unstructured high quality meshes. It is found that the dissipation rate captured is not significantly impacted by the element type. However, the element type impacts the energy spectrum in the large wavenumber range and thus the small vortical structures. In particular, at the same resolution, the results obtained using a tetrahedral mesh are much noisier than those obtained using a hexahedral mesh. Those obtained using a prismatic mesh are already much better, yet still slightly noisier. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Triply Periodic Minimal Surface (TPMS)-based cellular structures are widely adopted due to their high surface-to-volume area, superior mechanical characteristics, and adaptive properties. This paper is dedicated to deriving a new semi-empirical equation for pressure drop in TPMS-based structures (specifically Schwarz-P, Schoen I-WP, Neovius). Both numerical and experimental tests were conducted to analyze the impact of TPMS parameters on pressure drop and velocity distribution. It was determined that flow through the Schwarz-P structure exhibits a tubular flow pattern, flow through the Neovius structure demonstrates active flow mixing, and flow through the Schoen I-WP structure does not have stagnant (dead) zones. A novel semi-empirical equation was formulated to calculate pressure drop as a function of flow parameters and TPMS-based structure parameters. This equation incorporates both viscous resistance (Δ p = f (v)) and kinetic energy loss (Δ p = f (v 2)) , enabling its application for predicting pressure drop across a wide range of practically interesting operational parameters. • Fluid flow through TMPS-based structures is numerically and experimentally investigated. • Schwarz-P, Schoen I-WP, and Neovius TPMS-based structures are tested. • Tubular flow pattern for Schwarz-P; active flow mixing for Neovius; no stagnant (dead) zones for Schoen I-WP. • A novel equation was formulated for the calculation of pressure drop through TMPS-based structure. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the Cauchy problem for the three dimensional inviscid Boussinesq system in the periodic setting. For 1 ≤ p ≤ ∞ , we show that the threshold regularity exponent for L p -norm conservation of temperature of this system is 1/3, consistent with Onsager exponent. More precisely, for 1 ≤ p ≤ ∞ , every weak solution (v , θ) ∈ C t C x β to the inviscid Boussinesq equations satisfies that ‖ θ (t) ‖ L p (T 3) = ‖ θ 0 ‖ L p (T 3) if β > 1 3 , while if β < 1 3 , there exist infinitely many weak solutions (v , θ) ∈ C t C x β such that the L p -norm of temperature is not conserved. As a byproduct, we are able to construct many weak solutions in C t C x β for β < 1 3 displaying wild behavior, such as fast kinetic energy dissipation and high oscillation of velocity. Moreover, we also show that if a weak solution (v , θ) of this system has at least one interval of regularity, then this weak solution (v , θ) is not unique in C t C x β for β < 1 3. [ABSTRACT FROM AUTHOR]

Drop manholes are hydraulic devices typically employed to dissipate flow energy in high slope, urban drainage systems. The use of several drops of small height placed in series (drop manhole cascade) is a more economical and effective method for controlling velocity and kinetic energy than a single drop of large height. An experimental campaign was specifically designed to investigate hydraulics of drop manhole cascades at the LIA Laboratory, University of Cassino and Southern Lazio. Results were summarized in equations that quantify overall dissipation performance and describe the hydraulics of the downstream flow in terms of outflow depth and energy head. The performance of single drops and a three-drop cascade are compared. The data show how the energy of the stream passing through the dropshaft cascade quickly achieves a new equilibrium condition downstream from the second manhole. Finally, the energy dissipation of a drop manhole cascade was compared with that of smooth and roughened chutes to highlight similarities and differences between different dissipation structures. [ABSTRACT FROM AUTHOR]

Flood management is fundamentally unresolved in nature due to several sources of unreliability including parameter uncertainty. Applying inappropriate values for the kinetic energy and momentum correction coefficients (usually named α and β, respectively) can lead to considerable error in the calculation of water surface profiles, critical depth and energy losses in rivers. Due to the strong variations in the streamwise velocity, the values of α and β across compound open channels differ from those in a simple open channel. In this paper, the variations of α and β coefficients are investigated across the main channel and floodplain of two different shapes of compound open channel (rectangular and trapezoidal). Also, variations of these coefficients against the relative flow depth (the ratio of floodplain to main channel flow depths) are discussed. The results show that the values of α and β in the main channel are always lower than those over the floodplain. As flow relative depth increases, the hydraulic behavior of the compound channel tends to that of a simple channel. [ABSTRACT FROM AUTHOR]

The global dissipation caused by bottom boundary layer drag is one of the major pathways for the consumption of kinetic energy in the deep ocean. However, the spatial distribution and global integral of the drag dissipation are still debatable. This paper presents an updated estimate of the dissipation rate, using the barotropic component of surface geostrophic currents and 632 in situ velocity measurements. Also, the seafloor roughness is proposed as a parameter of drag efficiency in the parameterized method. The results provide a map of the drag dissipation rate with a global integral of ~0.26 TW. Approximately 66% of this dissipation occurs in the Southern Ocean, which is consistent with the proportion of wind power input into this region. Building upon the work in previous studies on the bottom boundary layer drag, more long-period observations are used, eliminating the influence of the baroclinic contribution to the surface geostrophic currents in the construction of the bottom velocity, and taking topographic roughness into account. The estimates have implications for the maintenance of density structure in the deep ocean and understanding of the kinetic energy budget. [ABSTRACT FROM AUTHOR]

Shi, J.; Zhang, C.; Zheng, J.; Tong, C.; Wang, P., and Chen, S., 2018. Modelling Wave Breaking across Coral Reefs Using a Non-Hydrostatic Model. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 501–505. Coconut Creek (Florida), ISSN 0749-0208. Wave breaking is the main mechanism to drive flow across shallow reef flats. The breaking process is more complex than on continental shelves due to the extreme geometries. This paper describes a non-hydrostatic model with shock-capturing capability to simulate the wave breaking process over two reef profiles. The two cases with and without ridge at the edge of reef crest are simulated, and the results are compared with data measured from laboratory experiment. The results show that the model can predict the surface elevation and mean sea level with good accuracy. The existence of a ridge can narrow the width of surfzone and increase wave-induced setup of sea level. The turbulent intensity and energy dissipation rate during wave breaking in the two reef profiles are analyzed. The comparison shows that the near-surface turbulence, energy dissipation rate and spanwise vortex are greatly enhanced by the existence of ridge, and the maximum value of turbulent kinetic energy at the breaking point can be two times larger than the case without the reef ridge. Moreover, the reef ridge decreases water depth in the surfzone, which makes the role of bottom friction in energy dissipation more significant. The interaction between breaking induced turbulence and the bed becomes more intense. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamics of warm logamediate inflation for flat isotropic and homogeneous universe in Einstein frame representation of gravity. In this scenario, we study dissipative effects for weak and strong interactions of inflaton field via constant and generalized dissipative coefficient. In both interacting regimes, we find inflaton solution corresponding to scalar potential and radiation density of dissipating inflaton. Under slow-roll approximation, we formulate scalar and tensor power spectra, their spectral indices and tensor-scalar ratio for Starobinsky inflationary model and construct graphical analysis of these observational parameters. It is concluded that this model remains compatible with Planck 2015 constraints in weak and strong regimes for constant dissipative coefficient. For generalized dissipative coefficient, the inflationary model yields consistent results for and in strong regime while condition of warm inflation is violated for in weak regime. [ABSTRACT FROM AUTHOR]

A slender footbridge can suffer from a large vibration under vertical human-induced excitation. To improve its serviceability, a tuned mass damper (TMD) has a wide application. However, considering the randomness and synchronization of crowd-induced excitation and the effect of crowd-structure interaction (CSI), the control robustness of a passive TMD needs to be improved. To achieve a better performance, a semi-active TMD (STMD) with variable mass and damping (VMD-STMD) is presented in this paper, which can not only adjust the own mass and frequency in real time to adapt to the dynamic characteristics of the footbridge through the water pump and electromagnetic valve, but also adjust its damping to improve the effect of energy dissipation through changing the eddy current damping. The proposed VMD-STMD can maximize the absorption of structural kinetic energy and dissipate. The working mechanism and control algorithm of VMD-STMD are introduced first, and then, a Euler-Bernoulli simply supported beam is studied. To highlight the best control effect and robustness of VMD-STMD, an optimized passive TMD, variable mass STMD (VM-STMD) and variable damping STMD (VD-STMD) are compared, 100 calculations of them based on crowd probabilistic models are proposed. The influence of CSI is investigated and different crowd density and synergy rate are discussed in detail. Through the maximum, mean and standard deviation of the three comfort evaluation indexes of the 100 groups of acceleration, the control effect and robustness of different TMDs are analyzed. Results show that structural dynamic responses and TMD's performance vary greatly due to the randomness of CSI. In general, VMD-STMD has the best control effect, and its standard deviation is also the smallest, indicating the best control robustness. ● A semi-active tuned mass damper (STMD) with variable mass and damping and its control algorithm are proposed. ● The randomness and synchronization of crowd and the crowd-structure interaction effect are investigated. ● STMDs with different control strategies are compared based on multiple calculations according to crowd probabilistic models. ● Combined variable mass and damping STMD has the best control effect and robustness. [ABSTRACT FROM AUTHOR]

[Display omitted] • Flow characteristics of high shear mixer was studied by Particle Image Velocimetry. • Strain rate was studied under different structures. • Turbulence kinetic energy dissipation rate was studied under different structures. • Two dimensionless correlations were established to predict hydrodynamics performance. The in-line teethed high shear mixers (HSMs) have been widely used in the chemical industry. However, there is still a lack of comprehensive understanding of the hydrodynamics characteristics about the attractive process equipment. In this paper, the effects of rotor and stator structures and rotor speed on flow characteristics of in-line teethed HSM are systematically studied by the particle image velocimetry experiment for the first time. The results show that increasing the rotor speed can significantly increase the strain rate (S xy) and turbulence kinetic energy dissipation rate (ε). Especially, when the shear gap width is reduced from 1.5 mm to 0.5 mm, the mean ε increases by 96.8 %. Furthermore, two dimensionless correlations are established between the maximum value of the S xy , ε and rotor and stator geometrical parameters to provide a valuable guidance for the geometrical design and optimization of in-line teethed HSM. [ABSTRACT FROM AUTHOR]

In this paper we propose two approaches to estimating the turbulent kinetic energy (TKE) dissipation rate, based on the zero-crossing method by Sreenivasan et al. (1983). The original formulation requires a fine resolution of the measured signal, down to the smallest dissipative scales. However, due to finite sampling frequency, as well as measurement errors, velocity time series obtained from airborne experiments are characterized by the presence of effective spectral cutoffs. In contrast to the original formulation the new approaches are suitable for use with signals originating from airborne experiments. The suitability of the new approaches is tested using measurement data obtained during the Physics of Stratocumulus Top (POST) airborne research campaign as well as synthetic turbulence data. They appear useful and complementary to existing methods. We show the number-of-crossings-based approaches respond differently to errors due to finite sampling and finite averaging than the classical power spectral method. Hence, their application for the case of short signals and small sampling frequencies is particularly interesting, as it can increase the robustness of turbulent kinetic energy dissipation rate retrieval. [ABSTRACT FROM AUTHOR]

In this paper, we present an overview of concepts and data concerning inverse cascades of excitation towards scales larger than the forcing scale in a variety of contexts, from two-dimensional fluids and wave turbulence to geophysical flows in the presence of rotation and stratification. We briefly discuss the role of anisotropy in the occurrence and properties of such cascades. We then show that the cascade of some invariant, for example, the total energy, may be transferred through nonlinear interactions to both the small scales and the large scales, with in each case a constant flux. This is in contrast to the classical picture, and we illustrate such a dual cascade in the context of atmospheric and oceanic observations, direct numerical simulations, and modeling. We also show that this dual cascade of total energy can in fact be decomposed in some cases into separate cascades of the kinetic and potential energies, provided the Froude and Rossby numbers are small enough. In all cases, the potential energy flux remains small, of the order of 10% or less relative to the kinetic energy flux. Finally, we demonstrate that, in the small-scale inertial range, approximate equipartition between potential and kinetic modes is obtained, leading to an energy ratio close to one, with strong departure at large scales due to the dominant kinetic energy inverse cascade and piling-up at the lowest spatial frequency and at small scales due to unbalanced dissipation processes, even though the Prandtl number is equal to one. [ABSTRACT FROM AUTHOR]

This paper shows the results of the numerical modelling of the transition from supercritical to subcritical flow at an abrupt drop, which can be characterised by the occurrence of oscillatory flow conditions between two different jump types. Weakly-Compressible Smoothed Particle (WCSPH) model was employed and both an algebraic mixing-length model and a two-equation model were used to represent turbulent stresses. The purpose of this paper is to obtain through the SPH model a deeper understanding of the physical features of a flow, which is, in general, difficult to be reproduced numerically, owing to its unstable character. In particular, the experience already gained in SPH simulations of vorticity-dominated flows allows one to assess the fluctuations of hydrodynamic characteristics of the flow field, (e.g., free surface profile downstream of the jump, velocity, pressure and vorticity). Numerical results showed satisfactory agreement with measurements and most of the peculiar features of the flow were qualitatively and quantitatively reproduced. [ABSTRACT FROM AUTHOR]

For understanding characteristics of polymethylmetacrylate (PMMA) under impact, the damage behavior of PMMA plates with various thicknesses (1.5 to 6.0 mm) subjected to ballistic impacts with various velocities (63 to 180 m/s) is experimentally investigated using a specialized testing apparatus. Moreover, numerical simulations using FEM are conducted for the corresponding experimentally studied cases. Ductile response and brittle tensile failure behavior are considered in the FEM to describe the nonlinear response and the failure mode of the PMMA plates. The numerical simulations effectively describe the shape of cracks and perforations of the PMMA plates for all studied 25 cases, verifying the validity of the numerical model. Although the PMMA plates are generally brittle in the selected range of impact velocity, it was found that these plates exhibit ductile behavior under low-velocity impacts. Moreover, the numerical simulations imply that the kinetic energy loss of the projectile is linearly dependent on the plate thickness, whereas the impact velocity hardly affects this loss. This behavior obtained experimentally and numerically illustrates the usefulness of the PMMA material for the use as a protective layer in many applications involving ballistic (high-velocity) impacts. This study delves into the impact behavior of PMMA plates, offering insights with a range of practical implications. This research positions PMMA as a promising protective material for applications exposed to high-velocity impacts. The comprehensive understanding of failure modes aids in designing resilient PMMA structures. By subjecting PMMA plates of varying thicknesses (1.5 to 6.0 mm) to ballistic impacts at different velocities (63 to 180 m/s), this research reveals a nuanced interplay between ductile and brittle behavior within the material. The study uncovers a ductile response of the PMMA plates under low-velocity impacts, expanding the material's potential use in scenarios with lower impact velocities. Moreover, the linear relationship established between plate thickness and kinetic energy loss of the projectile, independent of the impact velocity, provides a practical basis for designing impact-resistant PMMA structures. The practical applications of the study extend to fields such as architectural glazing, automotive safety, and aerospace engineering, where protective materials play a crucial role in safeguarding against unexpected impacts. In summary, this study empowers practical decision-making by uncovering the PMMA's impact response, thereby contributing to optimized protective solutions across various domains. [ABSTRACT FROM AUTHOR]

Turbulent mixing in the ocean, lakes and reservoirs facilitates the transport of momentum, heat, nutrients, and other passive tracers. Turbulent fluxes are proportional to the rate of turbulent kinetic energy dissipation per unit mass, ε. A common method for ε measurements is using microstructure profilers with shear probes. Such measurements are now widespread, and a non-expert practitioner will benefit from best practice guidelines and benchmark datasets. As a part of the Scientific Committee on Oceanographic Research (SCOR) working group on "Analysing ocean turbulence observations to quantify mixing" (ATOMIX), we compiled a collection of five benchmark data of ε from measurements of turbulence shear using shear probes. The datasets are processed using the ATOMIX recommendations for best practices documented separately. Here, we describe and validate the datasets. The benchmark collection is from different types of instruments and covers a wide range of environmental conditions. These datasets serve to guide the users to test their ε estimation methods and quality-assurance metrics, and to standardize their data for archiving. [ABSTRACT FROM AUTHOR]

As a part of the Scientific Committee on Oceanographic Research (SCOR) Working Group #160 "Analyzing ocean turbulence observations to quantify mixing" (ATOMIX), we have developed recommendations on best practices for estimating the rate of dissipation of kinetic energy, ε, from measurements of turbulence shear using shear probes. The recommendations provided here are platform-independent and cover the conceivable range of dissipation rates in the ocean, seas, and other natural waters. They are applicable to commonly deployed platforms that include vertical profilers, fixed and moored instruments, towed profilers, submarines, selfpropelled ocean gliders, and other autonomous underwater vehicles. The procedure for preparing the shear data for spectral estimation is discussed in detail, as are the quality control metrics that should accompany each estimate of ε. The methods are illustrated using a high-quality 'benchmark' dataset, while potential pitfalls are demonstrated with a second dataset containing common faults. [ABSTRACT FROM AUTHOR]

Raco is a local wind occurring in central Chile where the Maipo River Canyon exits into the Santiago valley. The intensification of the easterly down-canyon flow starts at any time during some cold season nights, accompanied by increases in temperature and drops in humidity. The hypothesis of the raco being a gap wind controlled by the narrowest section in the 12-km canyon exit corridor is tested with data from two events in July 2018 and July 2019. The data are analyzed in the framework of hydraulic theory, and a subcritical-to-supercritical transition is documented to occur at the narrows of the gap where the Froude number is close to unity, confirmed by radiosondes launched in the narrows in 2019. For the raco flow, the sum of potential and kinetic energy is conserved upstream of the narrows, while the acceleration occurring farther downstream loses a large fraction of energy to frictional dissipation. The raco events occur under the influence of regional subsidence, but a differential nocturnal warming of the in-canyon air mass is responsible for a pressure gradient driving the raco. In the 2019 case, a ceilometer mounted on an instrumented pickup truck documented the structure and movement of the interface between the raco air and the cold-air pool (CAP) existing over the valley to the west. Together with a radiosonde launched near the CAP–raco surface front, the observations reveal the intense shear-driven mixing taking place at the interface and the factors supporting the establishment of a stationary front. [ABSTRACT FROM AUTHOR]

The theory of stratified turbulent flow developed earlier by the authors is applied to data from different areas of the ocean. It is shown that turbulence can be amplified and supported even at large gradient Richardson numbers. The cause of that is the exchange between kinetic and potential energies of turbulence. Using the profiles of Brunt–Väisälä frequency and vertical current shear given in , the profiles of the kinetic energy dissipation rate are calculated. The results are in reasonable agreement with the experimental data. [ABSTRACT FROM AUTHOR]

This paper introduces a method for achieving stable periodic walking for legged robots. This method is based on producing a type of odd-even symmetry in the system. A hybrid system with such symmetries is called a symmetric hybrid system (SHS). We discuss the properties of an SHS and, in particular, will show that an SHS can have an infinite number of synchronized periodic orbits. We describe how controllers can be obtained to make a legged robot an SHS. Then the stability of the synchronized periodic orbits of this SHS is studied, where the notion of self-synchronization is introduced. We show that such self-synchronized periodic orbits are neutrally stable in kinetic energy. As the final step in the process of achieving asymptotically stable periodic walking, we show how by introducing asymmetries (such as energy loss at impact) in the system, the synchronized periodic orbits of this SHS can be turned into asymptotically stable periodic orbits. Many numerical examples, including an 8-DOF 3D biped with 2 degrees of underactuation, are studied to demonstrate the effectiveness of the method. [ABSTRACT FROM AUTHOR]