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Geometrical structures and operating performance of volutes used in centrifugal pumps are assessed in cross sections. By a volute, we mean the wetted part surrounding the impeller in a pump that converts the kinetic energy of water into potential energy. It is important to develop improved design principles and approaches for volutes to reduce hydraulic loss and increase the efficiency of pumps. However, when designing volutes, pump designers often neglect a key factor related to pump efficiency, namely, the energy loss due to the friction at the volute sidewall is directly proportional to the wetted perimeter of the cross section. In this paper, we show that the length of the wetted perimeter of the cross section is mathematically proportional to the friction loss in the volute. In addition, we present the design principles and calculation process to minimize the wetted perimeters of two kinds of cross section based on the velocity coefficient method using the same statistical data. The structures and shapes of the new cross sections are completely different from those of traditional volutes. Moreover, two different volutes with different cross sections are numerically investigated using a verified computational fluid dynamics technique. Both the head and the efficiency of the pump with the new volute are higher than those of a conventional pump under all working conditions. This paper provides a new design approach for the energy-saving volutes of centrifugal pumps. [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]

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]

In Smoothed Particle Hydrodynamics (SPH), the motion of particles is based on symmetric inter-particle forces, such that the conservation of momentum is guaranteed. Inter-particle forces, however, can not prevent particle clustering. Clustering may occur for several reasons. A fundamental issue is the tensile instability, which is caused by the properties of the kernel gradient. Clustering may also be caused by discontinuities in the pressure (e.g. due to surface tension) and the pressure gradient (e.g. due to gravity), which may lead to instabilities around the interface between two fluids (Kruisbrink et al., 2018 [1]). Wall penetration is also a form of particle clustering. To suppress particle clustering, the use of kinematic conditions (motion) rather than dynamic conditions (forces) was previously explored in the concept of particle collisions by Kruisbrink et al. (2018) [1]. In this concept, the conservation of momentum is always satisfied, whilst the conservation of energy is only satisfied for fully elastic collisions. They conclude that inelastic collisions are more stable than elastic collisions, but that energy is dissipated. In the present paper, the particle collision model is further explored and extended to a particle collision shift model, which in itself is non-dissipative, i.e. it preserves kinetic energy as well as potential energy in a constant force field, like gravitation. This is achieved by changing the particle positions due to inter-particle collisions, but not their velocities. Other popular and commonly used particle shift methods, such as the Fickian shift method of Lind et al. (2012) [2] , are based on the particle concentration. They are non-conservative and as such dissipative to some extent. In this paper, the new particle collision shift model is introduced and explored in several case studies. This model is compared with another stabilization method, the Fickian Shift model of Lind et al. (2012) [2]. The particle collision shift model performs slightly better in terms of particle stability and reduction of energy dissipation in most of the case studies. However, it is simple (one algorithm only with few coefficients, no special treatment at the free surface) and efficient (no kernel approximation, less CPU time). This work is based on incompressible SPH (ISPH). The shift model may however also be applied to weakly compressible SPH. [ABSTRACT FROM AUTHOR]

In this paper, we provide an analysis of turbulent mixing in stably stratified wall-bounded flows to highlight a number of important issues such as prediction of the turbulent viscosity, the turbulent diffusivity, and the irreversible flux Richardson number. By invoking the equilibrium assumption between the production rate of the turbulent kinetic energy (P), the dissipation rate of the turbulent kinetic energy (ϵ), and the turbulent potential energy dissipation rate (ϵPE) as P â ϵ + ϵPE and also assuming equilibrium between the buoyancy flux (B) and ϵPE as â'B â ϵPE, we first propose that the irreversible flux Richardson number (R*f=ϵPE/(ϵ+ϵPE)) can be approximated with the flux Richardson number (Rf = â' B/P), especially for low gradient Richardson numbers. Second, we propose that the turbulent viscosity ŷtâ(1â'Râ--f)â'1ϵ/S², where S is the mean shear rate. We then extend our analysis to propose appropriate velocity and length scales. Tests using the direct numerical simulation (DNS) data of turbulent channel flow of García-Villalba and del Álamo ["Turbulence modification by stable stratification in channel flow," Phys. Fluids 23, 045104 (2011)] are performed to evaluate our propositions. The comparisons between the exact turbulent viscosity, length and velocity scales, and the proposed formulations are excellent. Also, the agreement between Rf and Râ--f is reasonable for the bulk of the flow depth with differences of about 20% on average, except at depths very close to the flow boundaries. Finally, by invoking the equilibrium assumption between the buoyancy flux (B) and the dissipation rate of the turbulent potential energy (ϵPE) as â'B â ϵPE, we infer the turbulent diffusivity as ŷ°t â ϵPE /N², where N is the buoyancy frequency. The comparison of the proposed turbulent diffusivity with the exact turbulent diffusivity computed from DNS data is good especially close to the wall but the agreement deteriorates far away from the wall, indicating the breakdown of assuming equilibrium as â'B â ϵPE which is attributed to the presence of linear internal wave motions in this far-wall region. [ABSTRACT FROM AUTHOR]

This paper combines two strains in the literature on subgrid-scale parameterizations for eddying ocean models to develop six new parameterizations and test them in an idealized quasigeostrophic model. The first strain develops nonlinear, Smagorinsky-like Leith scalings for the viscous coefficient based on reasoning about the turbulent forward enstrophy cascade of geophysical turbulence. The second introduces backscatter whose amplitude is scaled to re-inject a portion of the energy dissipated by other parameterizations. In the new parameterizations developed here the backscatter and viscous coefficients depend on each other and are set to simultaneously absorb the forward enstrophy (or potential enstrophy) cascade and backscatter a portion of the dissipated energy. The addition of backscatter to Leith-scaled nonlinear viscosity improves the simulations at resolutions from 4 km to 24 km by increasing the total kinetic energy and by reducing the fraction of the total energy dissipation rate associated with the net effect of viscosity and backscatter. Versions that use biharmonic viscosity to absorb the enstrophy cascade perform better than versions using a harmonic viscosity, and purely viscous closures perform better than closures that dissipate both kinetic and potential energy. Stochastic and deterministic backscatter schemes are developed, and though similar, the deterministic schemes perform slightly better. • Developed backscattering Leith parameterizations. • Compared old and new parameterizations across resolutions. • Backscattering 2D Leith parameterizations perform well. [ABSTRACT FROM AUTHOR]

Purpose. Research of dynamics and pull-speed characteristics during the process of dump truck movement. Methods. There were used general scientific as well as special methods of research in current paper. They include scientific synthesis, integrated assessment methods of technical level, mathematical modeling and apparatus of linear programming. The solution of this problem is based on the composing of differential equation of motion, for which it was used the Lagrange equation of the second order, and appropriate expression of the kinetic, potential energy and dissipation function. The results are obtained by mathematical calculations in the software for mathematical analysis and calculation – "Wolfram Mathematica". Result. The article is going about the mathematical model of the linear movement of career dump truck as a multimass system with eight degrees of freedom on a linear track, accounting for the road covering conditions. The method for calculation pulling and dynamic characteristics of dump truck movement on the road with longitudinal gradient is obtained. It allows to receive required traction force. Originality. It was compiled a calculation scheme and equations of motion in rectilinear vehicle's motion, which includes elastic-dissipative characteristics of ties, longitudinal incline and road profile, changing of mechanical characteristics that are similar to real exploitation indexes of career dump truck and indexes of traction performance. Practical value. The evaluation method of the dynamical characteristics of the dump truck while driving regime is described. The analysis of dump truck design parameters, basing on which it is possible to give the recommendations on reduction of capital costs on development of the open mines. [ABSTRACT FROM AUTHOR]

This paper presents an estimate of the oceanic Lorenz energy cycle derived from a simulation forced by 6-hourly fluxes obtained from NCEP-NCAR reanalysis-1. The total rate of energy generation amounts to 6.6 TW, of which 1.9 TW is generated by the time-mean winds and 2.2 TW by the time-varying winds. The dissipation of kinetic energy amounts to 4.4 TW, of which 3 TW originate from the dissipation of eddy kinetic energy. The energy exchange between reservoirs is dominated by the baroclinic pathway and the pathway that distributes the energy generated by the time-mean winds. The former converts 0.7 to 0.8 TW mean available potential energy to eddy available potential energy and finally to eddy kinetic energy, whereas the latter converts 0.5 TW mean kinetic energy to mean available potential energy. This energy cycle differs from the atmospheric one in two aspects. First, the generation of the mean kinetic and mean available potential energy is each, to a first approximation, balanced by the dissipation. The interaction of the oceanic general circulation with mesoscale eddies is hence less crucial than the corresponding interaction in the atmosphere. Second, the baroclinic pathway in the ocean is facilitated not only by the surface buoyancy flux but also by the winds through a conversion of 0.5 TW mean kinetic energy to mean available potential energy. In the atmosphere, the respective conversion is almost absent and the baroclinic energy pathway is driven solely by the differential heating. [ABSTRACT FROM AUTHOR]

The article discusses various aspects of the interaction of vortices with the barotropic flow. Vortex interaction with a flow results in rotation variants, nutational oscillations, and unlimited stretching of its core. The vortex remains in a localized formation, with the semi-axes of the ellipse experiencing fluctuations near an average value in the first two cases. In the third case, the vortex is significantly elongated, and its shape in the horizontal plane changes as follows: one axis of the ellipse increases, and the other decreases. In this case, the vortex, when viewed from above, stretches into a thread, while remaining ellipsoidal. These vortex formations are called filaments. The latter arise from initially almost circular vortices in the horizontal plane and represent structures with non-zero vorticity elongated in one direction. Here, we aim to study the energy transformation of a vortex during its evolution process, mainly due to changes in its shape by stretching. The energy evolution of a mesoscale vortex located in the Norwegian Sea is analyzed using GLORYS12V1 ocean reanalysis data to verify the theoretical conclusions. During the evolution, the vortex is found to transform from a round shape and becomes elongated, and after three weeks its longitudinal scale becomes 4 times larger than the transverse one. During the transformation of a vortex, the kinetic energy and available potential energy decrease respectively by 3 times and 1.7 times. Concurrently, the total energy of the vortex is found to decrease by 2.3 times. We argue that the stretching of vortices results in a loss of energy as well as its redistribution from mesoscale to submesoscale. The lost part of the energy returns to the flow and results in the occurrence of the reverse energy cascade phenomenon. [ABSTRACT FROM AUTHOR]

In this paper, kinetic and potential energy transfers around a spectral test filter scale in direct numerical simulations of decaying stratified turbulence are studied in both physical and spectral domains. It is shown that while the domain-averaged effective subgrid scale energy transfer in physical space is a net downscale cascade, it is actually a combination of large values of downscale and upscale transfer, i.e. forward- and backscatter, in which the forward scatter is slightly dominant. Our results suggest that spectral backscatter in stratified turbulence depends on the buoyancy Reynolds number R e b and the filtering scale Δ t e s t . When the test filter scale Δ t e s t is around the dissipation scale L d , transfer spectra show spectral backscatter from sub-filter to intermediate scales, as reported elsewhere. However, we find that this spectral backscatter is due to viscous effects at vertical scales around the test filter. It is also shown that there is a non-local energy transfer from scales larger than the buoyancy scale L b to small scales. The effective turbulent Prandtl number spectra demonstrate that the assumption P r t ≈ 1 is reasonable for the local energy transfer. [ABSTRACT FROM AUTHOR]

A dynamical understanding of the physical process of surface gravity wave breaking remains an unresolved problem in fluid dynamics. Conceptually, breaking can be described by inception and onset, where breaking inception is the initiation of unknown irreversible processes within a wave crest that precede the visible manifestation of breaking onset. In the search for an energetic indicator of breaking inception, we use an ensemble of non-breaking and breaking crests evolving within unsteady wave packets simulated in a numerical wave tank to investigate the evolution of each term in the kinetic energy balance equation. We observe that breaking onset is preceded by around one quarter of a wave period by a rapid increase in the rate of convergence of kinetic energy that triggers an irreversible acceleration of the kinetic energy growth rate. This energetic signature, which is present only for crests that subsequently break, arises when the kinetic energy growth rate exceeds a critical threshold. At this point the additional kinetic energy convergence cannot be offset by converting excess kinetic energy to potential energy or by dissipation through friction. Our results suggest that the ratio of the leading terms of the kinetic energy balance equation at the time of this energetic signature is proportional to the strength of the breaking crest. Hence this energetic inception point both predicts the occurrence of breaking onset and indicates the strength of the breaking event. [ABSTRACT FROM AUTHOR]

Focusing on the effect of the meandering planform, two functions are investigated by a numerical experiment: the first represents the ratio between the intensities of the resisting forces acting on a meandering flow and its corresponding straight flow; and the second represents the ratio between the intensities of the resisted meandering flow itself and its corresponding straight flow. Both functions depend on the sinuosity (or relative curvature) and the width-to-depth ratio. The two functions and their numerical results are thoroughly analyzed, showing the following: (1) meandering causes an increase in the resistance to flow, with a greater resistance occurring in the stream having an "intermediate" sinuosity (or "large" relative curvature) and a "small" width-to-depth ratio; (2) there is an imbalance between the driving and resisting forces in a meandering stream, and the degree of this imbalance has a direct interrelation with the intensity of the "kinetic-energy-weighted" convergence of flow; and (3) the ratio of kinetic to potential energy of a meandering flow cannot be reflected by the square of the (Chézy) resistance factor alone, and the two things manifest different variation patterns versus the sinuosity and the width-to-depth ratio. These findings are likely to advance the understanding of the resistance to flow in meandering channels. [ABSTRACT FROM AUTHOR]

• The principle design of a tri-stable system is presented. • The energy trapping capacity of TEEH under a single impulse is studied. • The energy harvesting and bifurcation of TEEH under harmonic vibration are conducted. • A prototype of TEEH composed of a linear spring and magnetic spring is proposed. Multi-stable energy harvesters have emerged as the most attractive candidates for vibration-based energy harvesting recently. Energy trapping and energy conversion are the main characteristics of a vibration-based energy harvester, similarly, energy absorption and damping dissipation are the main features of a conventional dynamic vibration absorber (DVA). Therefore, combination of vibration absorption and energy conversion is a potential strategy for vibration control and self-powered wireless sensors. This paper presents the principle design of tri-stable systems and mathematical modeling of a 2-dof tri-stable DVA and energy harvester. The energy harvesting performances of multi-stable energy harvesters in terms of tri-stable electromagnetic energy harvester (TEEH) and bi-stable electromagnetic energy harvester (BEEH) are evaluated under impulsive excitations and harmonic vibrations, respectively. The energy trapping capacity of TEEH is calculated under single impulsive excitation and compared with its counterpart of BEEH. Furthermore, the dynamic characteristics of the multi-stable DVA (tri-stable and bi-stable) are studied. Simulation results show that TEEH induces a more rapid attenuation in the residual kinetic energy of the primary system excited by a weak impulse than its counterpart of BEEH, and the trapped energy in TEEH increases remarkably with the application of a weak impulse. Compared with BEEH, the energy dissipation and harvesting performances of TEEH are more satisfactory under low-amplitude impulse and low mass ratio conditions. Additionally, the snap-through motion can be more easily triggered in TEEH under broadband and low-amplitude vibrations. With the increase in vibration amplitude, the multi-stable mechanism of TEEH can be readily understood through observing phase portrait and Poincaré mapping, from which tri-stable state, chaotic attractors and bi-stable state are presented successively. Moreover, the energy harvesting efficiency of TEEH is more advanced under broadband ambient vibrations in comparison with BEEH. Finally, a prototype of tunable tri-stable system composed of a linear spring and magnetic spring is proposed. [ABSTRACT FROM AUTHOR]

Droplet capture and release are very significant for droplet manipulation on a superhydrophobic surface. Once the aqueous droplets impact the stiff superhydrophobic surface, they easily detach from the surface and generate chaotic motion without much energy loss. Thus, it is difficult to catch and manipulate the droplets falling on these kinds of surfaces. In this study, a droplet was captured after impacting the superhydrophobic porous sponge. Most of the kinetic energy of a falling droplet is transferred into the elastic potential energy of a sponge. The absorbed energy in the deformation process and the elastic modulus of sponge were adjusted by the porosity of the sponge. With the decrease in density, the elastic modulus of the sponge decreases, and the energy loss increases. During the droplet impacting process, the sponge with smaller elastic modulus can obtain much more energy from the droplet, which makes it easy to drag and capture the droplet. This new design also has other potential applications, such as water collection and fog harvest. [ABSTRACT FROM AUTHOR]

Double diffusion refers to a variety of turbulent processes in which potential energy is released into kinetic energy, made possible in the ocean by the difference in molecular diffusivities between salinity and temperature. Here, we present a new method for estimating the kinetic energy dissipation rates forced by double‐diffusive convection using temperature and salinity data alone. The method estimates the up‐gradient diapycnal buoyancy flux associated with double diffusion, which is hypothesized to balance the dissipation rate. To calculate the temperature and salinity gradients on small scales we apply a canonical scaling for compensated thermohaline variance (or 'spice') on sub‐measurement scales with a fixed buoyancy gradient. Our predicted dissipation rates compare favorably with microstructure measurements collected in the Chukchi Sea. Fine et al. (2018), https://doi.org/10.1175/jpo-d-18-0028.1, showed that dissipation rates provide good estimates for heat fluxes in this region. Finally, we show the method maintains predictive skill when applied to a sub‐sampling of the Conductivity, Temperature, Depth (CTD) data. Plain Language Summary: Understanding the transport of heat in the Arctic Ocean is vital for predicting the fate of sea‐ice in the decades to come. Small‐scale turbulence is an important driver of heat transport and one of the major forms of this turbulence is known as 'double‐diffusive convection'. This is where gradients in temperature and salinity drive turbulence. It is only possible because salinity diffuses significantly slower than temperature, hence the name 'double‐diffusive'. The most direct measurements of ocean mixing require sampling velocity or temperature gradients on scales <1 mm, so‐called microstructure measurements. Here we present a new method for estimating the energy dissipated by double‐diffusive convection using temperature and salinity measurements on larger scales (100s–1000s of metres). We apply the method to a high‐resolution survey of temperature and salinity through a subsurface Arctic eddy and compare the results with simultaneous microstructure measurements. The new technique can reproduce up to 72% of the observed dissipation rates to within the measurement uncertainty. This suggests the method could be used to estimate the dissipation and so heat fluxes associated with double‐diffusive convection in regions without microstructure measurements. The method also performs well when applied to data sub‐sampled on larger scales. Key Points: We develop a method for estimating dissipation rates due to double‐diffusive convection from temperature and salinity data using an energetic argumentThe method reproduces the patterns and magnitude of dissipation rates and heat fluxes from microstructure measurements across an arctic eddyThe technique performs well even when applied to lower resolution Conductivity, Temperature, Depth (CTD) data [ABSTRACT FROM AUTHOR]

Based on daily data from the Japanese 55-year Reanalysis (JRA-55) covering the spring seasons from 1958 to 2018, this study examines the formation mechanisms and climate impacts of the springtime western Pacific (WP) pattern as subseasonal climate variability over North Pacific. Results suggest that the springtime WP pattern arises from a weak dipole-like disturbance over North Pacific and disturbances over East Asia. The energetic analysis suggests that the baroclinic energy conversion acts as an important energy source to balance the available potential energy loss caused by transient eddies and diabatic heating and acts as a kinetic energy (KE) source for the WP pattern. For the feedback forcing by total transient eddies, it acts as a major KE source for the WP pattern before day 0 and acts as a strong KE sink after day 0. It turns out that the barotropic energy conversion makes only weak KE contribution to the WP pattern. Once the WP pattern forms, East Asia and North America experience strong surface air temperature anomalies of opposite signs, while strong sea surface temperature anomalies are found to occur over midlatitude and tropical North Pacific at the same time. Concurrently, the Pacific jet and the storm track shift northward or southward around their climatological position. In addition, a dipole-like shallow convective anomaly appears over midlatitude North Pacific, and a band of anomalous deep convection tends to occur in the tropics as the energy of the WP pattern propagates into the region. [ABSTRACT FROM AUTHOR]

Simulation of the process of landslide occurrence, including deformation and failure, material movement and energy dissipation of slopes, can help in predicting the features, affected area and risk of potential landslides induced by earthquakes, thus providing support to decision-makers, which is of great practical significance in hazard prevention and mitigation. Taking the Chenjiaying potential landslide in Mian County, Shaanxi Province, China, as the scenario, this study used the discrete element method to develop a numerical simulation. The results showed that deformation of the slope started from the trailing edge, then gradually extended to the middle and leading edge until the failure occurred, via a progressive process. With the increase of the friction coefficient, the movement distance, velocity and failure time of the landslide were shortened, reduced and delayed, respectively, but the peak velocity remained at about 7.5 s after the seismic loading. The proportions of kinetic energy and collision energy in the total energy dissipation also decreased as the friction coefficient increased, but friction energy increased gradually, becoming dominant. The simulation also suggested that the landslide could not only bury houses to a depth of more than 3.8 m but also generate an impact of between 1.18 × 105 and 5.50 × 105 kN on the unit width of houses at the leading edge, which would pose a major threat to life and property safety for more than 50 households. These findings will aid in the assessment of landside risk caused by earthquakes. [ABSTRACT FROM AUTHOR]

Some high-resolution CTD data collected in the spring of 2017 are analyzed using Thorpe sorting and scale analyses, including both the commonly used "Thorpe scale" method and a lesser-used method that is based on directly estimating the "available overturn potential energy" (AOPE): the difference between potential energies of the raw versus sorted density profiles in a mixing "turbulent patch." The speed of the profiler varied, so the spatial (vertical) sampling is uneven. A method is developed and described to apply the Thorpe scaling and the AOPE approaches to such unevenly sampled data. The AOPE approach appears to be less sensitive to the (poorly constrained) estimate of the "background" buoyancy frequency N. Although these approaches are typically used to first estimate the dissipation rate εK of turbulent kinetic energy, the real goal is to estimate the diffusivity of density Kρ and hence the net alteration of the density profile by mixing. Two easily measured dimensionless parameters are presented as possible metrics of the "age" or "state" of the mixing patch, which might help to resolve the question of how the total turbulent energy and dissipation are apportioned between kinetic and potential components and hence how much of the measured AOPE ends up changing the background stratification. A speculative example as to how this might work is presented. [ABSTRACT FROM AUTHOR]

The high-density gravitational collapse of granular columns is very similar to the movements of large collapsing columns in nature. Based on the development of dangerous columnar rock mass in fields, granular column collapse boundary condition in the physical experiments of this study is a new type of boundary conditions with a single free face and a three-dimensional deposit. Physical experiments have shown that the mobility of small particles during the collapse of granular columns was greater than that of large particles. For example, when particle size was increased from 5 to 15 mm, deposit runout was decreased by about 16.4%. When a column consisted of two particle types with different sizes, these particles could mix in the vicinity of layer interfaces and small particles might increase the mobility of large particles. In the process of collapse, potential and kinetic energy conversion rate is fluctuated. By increasing initial aspect ratio a, the ratio of the initial height of column to its length along flow direction, potential and kinetic energy conversion rate is decreased. For example, as a was increased from 0.5 to 4, the ratio of maximum kinetic energy obtained and total potential energy loss was decreased from 47.6% to 7.4%. After movement stopped, an almost trapezoidal body remained in the column and a fanlike or fan-shaped accumulation was formed on the periphery of column. Using multiple exponential functions of the aspect ratio a, the planar morphology of the collapse deposit of granular columns could be quantitatively characterized. The movement of pillar dangerous rock masses with collapse failure mode could be evaluated using this granular column experimental results. [ABSTRACT FROM AUTHOR]

Results are presented from highly resolved three-dimensional simulations of turbidity currents down a shallow slope into a stratified saline ambient, for various stratifications and particle settling velocity configurations. The front velocity is computed and the results are compared directly to experimental data by Snow and Sutherland (J Fluid Mech 755:251–273, 2014) and to an existing scaling law for gravity currents in stratified environments but on flat bottoms, with close agreement. The entrainment velocity of the ambient fluid into the current is computed from the DNS data and shows strong space time variability. The intrusion of the current into the ambient fluid is computed and compared to the experimental results of Snow and Sutherland (2014), an existing scaling law proposed by those authors, and a new model with increasing levels of complexity. The numerical results highlight the sensitivity of scaling tools to the choice of entrainment coefficient and their limitations in low entrainment but high settling rate scenarios. The new, simpler scaling relation for the intrusion depth is shown to be more robust and predictive in such cases. The energy budget of the flow is analysed in order to explain the governing processes in terms of energy transfers, with a focus on energy losses and potential to kinetic energy transfers. Particular attention is given to the Stokes losses with varying settling velocities, which validates the prediction of the concentration in the intrusion depth model introduced. [ABSTRACT FROM AUTHOR]

The seminal work of Lorenz on global atmospheric energetics has allowed understanding much on the physical processes responsible for the general circulation, its maintenance and the development of synoptic-scale weather systems. In mid-latitudes, potential energy generated by the differential heating of the planet by the Sun is converted into kinetic energy by the weather systems and eventually dissipated by friction. While a corresponding study of atmospheric energetics over a limited region would have the advantage of focusing on the details of individual storms and the processes taking place over a domain of interest, such study has encountered several pitfalls and has been challenging. Here we build upon our earlier work on the energy cycle of inter-member variability in ensembles of limited-area model simulations to develop a regional-scale atmospheric energy cycle formulated in terms of available enthalpy and kinetic energy. The approach is then applied to study the energetics of a short simulation made with the fifth-generation of the Canadian Regional Climate Model (CRCM5) over an eastern North American domain for December 2004. The results obtained for a specific storm and monthly mean climatology confirm the current understanding that available enthalpy of the atmospheric time-mean state is mainly generated by the covariance of diabatic heating and temperature, and that the most important conversions of energy are found to correspond to baroclinic processes that take place along the storm track, where perturbations of temperature and wind are important. Finally, transient-eddy kinetic energy is mainly dissipated by friction in the boundary layer. [ABSTRACT FROM AUTHOR]

Stratification in the Southern Ocean is determined primarily by a competition between westerly wind-driven upwelling and baroclinic eddy transport. This study investigates the time scales of equilibration of the Southern Ocean in response to changing winds through an idealized channel model. An analytical framework describing the energetic pathways between wind input, available potential energy (APE), eddy kinetic energy (EKE), and dissipation provides a simple theory of the phase and amplitude response to oscillating wind stress. The transient ocean response to variable winds lies between the two limits of Ekman response (high frequency), characterized by the isopycnal slope responding directly to wind stress, and 'eddy saturation' (low frequency), wherein a large fraction of the anomalous wind work goes into mesoscale eddies. The crossover time scale is the time scale of meridional eddy diffusive transport across the Antarctic Circumpolar Current (ACC) front. For wind variability with a period of 3 months (high-frequency forcing), the relative conversion of wind work to APE/EKE is 11, while for a period of 16 years (low-frequency forcing), the relative conversion to APE/EKE reduces to 3. The system's frequency response is characterized by a complex transfer function. Both the phase and amplitude response of EKE and APE predicted by the linear analytic framework are verified using multiple ensemble experiments in an eddy-resolving (4-km horizontal resolution) isopycnal coordinate model. The results from the numerical experiments show agreement with the linear theory and can be used to explain certain features observed in previous modeling studies and observations. [ABSTRACT FROM AUTHOR]