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• Impinging paper-thin sheets of liquids produces high energy dissipation rates. • The volume of energy dissipation is equal to the volume of the impingement zone. • A new expression for the energy dissipation rate was derived and compared with turbulence theory. • Large-eddy turnover time is approximately equal to liquid residence time in impingement zone. • Large-eddy kinetic energy decays exponentially in the impingement zone. The micromixing time of impinging thin liquid sheets depends upon the energy dissipation rate (∊). The kinetic energy released by the impingement has been previously studied and was found to be a function of the coefficient of restitution of the collision. In this work, the volume within which the released kinetic energy is dissipated was investigated. The volume of energy dissipation was determined by measuring the time required for the velocity of the liquid prior to the collision to be reduced to the velocity after the collision. High-speed video was used to measure the velocity of features, generated in the front single sheet, as they passed through the impingement zone and into the mixed sheet. The experimental results showed that the time required for the velocity change was approximately equal to the residence time of liquid in the impingement zone (t r). A new equation for ∊ was developed and compared with ∊ derived from turbulence energy-cascade theory. This comparison showed that the large-eddy turnover time (t Λ) was approximately equal to t r ; a result that is in accordance with the notion from turbulence energy-cascade theory that large, energy-containing eddies lose their energy within t Λ. Within the impingement zone, the large-eddy kinetic energy was found to decay exponentially with time. [ABSTRACT FROM AUTHOR]

In this paper, a heat generator with fluid agitation is developed and experimentally studied. This heat generator can convert kinetic energy from a wind turbine directly to thermal energy through the process of viscous dissipation—a process achieved through the agitation of the working fluid inside a container. In the experimental study, an electric motor (instead of a wind turbine) was used to provide the kinetic energy input to the heat generator. The torque, rotational speed, and temperature rise in the fluid were measured. Using the measured quantities, the efficiency of kinetic energy to sensible heat conversion was calculated. Experiments were conducted to investigate the effects of different impellers, rotational speeds, and working fluids, including distilled water, ethylene glycol (EG), and their respective nanofluids, with A l 2 O 3 nanoparticles at different concentrations. The study also found that the temperature rise in fluids due to viscous dissipation was influenced by the specific heat of the fluid, suggesting that the heat generator can be optimized for energy storage with high-specific-heat fluids, such as water, or for achieving a higher temperature rise with low-specific-heat fluids, such as ethylene glycol. The experimental results indicated that the heat generator was up to 90% efficient in converting kinetic energy to thermal energy. The study revealed that, for constant power input, the heat dissipation rate depends solely on the vessel's geometry, not the fluid properties. Optimizing the impeller design and baffles within the vessel is crucial for maximizing power input. For applications, a wind turbine can power this heat generator to provide heat to a house or a commercial building. [ABSTRACT FROM AUTHOR]

Rocking structures exhibit significant collapse resistance during earthquakes. In studies of rocking rigid bodies, the collision restitution coefficient is typically determined based on the classical model of the rocking rigid bodies. However, during the rocking process, the collision restitution coefficient, influenced by the uncontrollable error in collision energy dissipation between the rigid body and the ground, indirectly impacts the final results of the equations of motion. Therefore, the rationality and reliability of the collision restitution coefficient are crucial for seismic analysis of rocking rigid bodies and self-centering members. This paper introduces a phasic energy dissipation and kinetic energy redistribution model specifically designed for the rocking rigid body within the system of mass point. This model divides the collision into three distinct stages, incorporating energy dissipation considerations in the first two stages to calculate the total kinetic energy of the rigid body. In the third stage, the remaining kinetic energy is redistributed to precisely determine the analytical solution for the collision restitution coefficient of an ideal, homogeneous rectangular rigid body during collision. Lastly, the validity and reliability of the proposed model are confirmed through comparisons with experimental data. [ABSTRACT FROM AUTHOR]

Ultra‐low frequency (ULF) waves transfer energy and momentum into the ionosphere‐thermosphere system. To quantify this energy, this paper first presents a new method to quantitatively detect ULF waves in Incoherent Scatter Radar (ISR) data based on 2D fast‐Fourier transforms and subsequent reconstruction of the wave. In parallel with other data sets, including optical, magnetometer, satellite, and models, we present the first full ionospheric energy dissipation rates for a ULF wave, split into electromagnetic (EM) and kinetic fluxes. The EM energy deposition is calculated from the use of the Poynting theorem, looking at Joule and frictional heating rates, where both rates show the same order of magnitude (1.24 × 1013 and 7.3 × 1012 J) respectively when integrated over the wave lifetime of 2 hr 15 min and an area of 4° magnetic latitude × 74° magnetic longitude. However, contrary to the common assumption that the EM flux is dominant, we determined the kinetic flux, to be almost equal in magnitude (8.7 × 1012 J). This indicates that previous papers might have underestimated the total energy dissipation by ULF waves. Compared to the substorm energy budget, we find that locally, the ULF wave event studied here makes up approximately 10% of a typical substorm cycle budget. Plain Language Summary: The Earth's magnetic field lines can move back and forth regularly, like waves on a guitar string. When this happens on the time scale of minutes, we call these ultra‐low frequency (ULF) waves. ULF waves play an important role in the transfer of energy from the Earth's magnetic field to the Earth's upper atmosphere. In this study, we developed a new method to detect ULF waves in radar data to obtain information about the wave. By combining several data sets, such as radar, optical, satellite, and magnetic field measurements, we were then able to determine how much energy is being transferred in one ULF wave event. Both electromagnetic and kinetic energy are important in this transfer of energy. Key Points: We present a new method to detect and reconstruct ULF waves in ISR data with a 2D fast‐Fourier transformWe estimate ionospheric energy dissipation rates due to EM and kinetic energy sources using the new methodWe find that kinetic and EM energy rates are of similar magnitude and should both be included in ionospheric energy deposition by ULF waves [ABSTRACT FROM AUTHOR]

Mixing height is one of the key parameters in describing lower tropospheric dynamics, and capturing the diurnal variability is crucial, especially in interpreting surface observations. In this paper we introduce a method for identifying mixing heights below the vertical minimum range of a scanning Doppler lidar. The method we propose is based on velocity variance in low elevation angle conical scanning, and is applied to measurements in two very different coastal environments: Limassol, Cyprus during summer; and Loviisa, Finland during winter. At both locations, the new method agrees well with mixing heights derived from turbulent kinetic energy dissipation rate profiles obtained from vertically-pointing measurements. The low-level scanning routine frequently indicated non-zero mixing heights less than 100m above the surface. Such low mixing heights were more common at wintertime Loviisa on the Baltic Sea coast than during summertime in Mediterranean Limassol. [ABSTRACT FROM AUTHOR]

Near-surface oceanic turbulence plays an important role in the exchange of mass, momentum, and energy between the atmosphere and the ocean. The climate modifying the air–sea CO 2 transfer rate varies linearly with the surface turbulent kinetic energy dissipation rate to the 1 / 4 power in a range of systems with different types of forcing, such as coastal oceans, river estuaries, large tidal freshwater rivers, and oceans. In the first part of this paper, we present a numerical study of the near-surface turbulent kinetic energy spectra deduced from a direct numerical simulation (DNS) compared to turbulent kinetic energy spectra deduced from idealized infrared (IR) images. The DNS temperature fields served as a surrogate for IR images from which we have calculated the underlying kinetic energy spectra. Despite the near-surface flow region being highly anisotropic, we demonstrated that modeled isotropic and homogeneous turbulence spectra can serve as an approximation to observed near-surface spectra within the inertial and dissipation ranges. The second part of this paper validates our numerical observations in a laboratory experiment. In this experiment, we compared the turbulent kinetic energy spectra near the surface, as measured using a submerged shear sensor with the spectra derived from infrared images collected from above the surface. The energy dissipation measured by the shear sensor was found to be within 20% of the dissipation value derived from the IR images. Numerically and experimentally, we have demonstrated that IR-based and remote measurement techniques of the aquatic near surface offer a potentially accurate and non-invasive way to measure near-surface turbulence, which is needed by the community to improve models of oceanic air–sea heat, momentum, and gas fluxes. [ABSTRACT FROM AUTHOR]

Microstructure measurements were collected using an autonomous freely rising profiler under a variety of different atmospheric forcing and sea states in the open ocean. Here, profiles of turbulent kinetic energy dissipation rate, ε, are compared with various proposed scalings. In the oceanic boundary layer, the depth dependence of ε was found to be consistent with that expected for a purely shear-driven wall layer. This is in contrast with many recent studies which suggest higher rates of turbulent kinetic energy dissipation in the near surface of the ocean. However, many dissipation profiles scaled with a Stokes drift-generated shear, suggesting there may be occasions where the shear in the mixed layer are dominated by wave-induced currents, which often causes turbulence to extend beyond the mixed layer depth. Integrating ε in the mixed layer yielded results that 1% of the wind power referenced to 10m is being dissipated here. [ABSTRACT FROM AUTHOR]

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]

The hydraulic engineering designers focus on shaping up the flow regime so that the greatest energy dissipation is ensured. On the other hand, the structural designers focus on load bearing capacity and durability of the structural components which may contradict the focus of the hydraulic experts. Such a case may occur when the spillway chute floor slab must be thin due to the limited spaces. Then, the dynamic load acting on the chute floor slab may compromise its long-term operation. The dynamic forces are created by the violent turbulences which may even coincide with the natural frequency of the reinforced concrete floor slab. Therefore, the objective of this paper is a complex approach to small-scale physical model testing which makes use of the latest rapid-prototyping techniques and the optical flow, and which in the end allows to estimate the magnitude of the dynamic hydraulic forces acting on the channel bed. The newly developed organic-shape energy dissipators play a key role in reducing the kinetic energy of water through its enhances aeration. The proposed method on a small scale can assist favorably the design process of real-scale hydraulic reinforced concrete structures. [ABSTRACT FROM AUTHOR]

This paper focuses on the response of reticulated shell structures under oblique impact loads, with a departure from the traditional emphasis on vertical impact loads. These structures are typically utilised in large-span spaces such as iconic buildings and large venues. The study begins by establishing a numerical simulation method for reticulated shell structures subjected to oblique impact loads, which is then validated against existing experimental results. Building on this verified method, the research delves into the effects of varying impactor mass, velocity, and initial kinetic energy on the reticulated shell structure under oblique impacts, as well as the influence of different oblique impact angles. The study extensively examines the failure modes of the structure, node displacements in the structure, and variations in member stress under different impactor parameters. It further investigates how these parameters influence the maximum impact bearing capacity, impact duration, energy dissipation capability, and response forms of the structures, analyzing the reasons behind these effects. The findings offer valuable insights for further research and practical engineering design of reticulated shell structures. [ABSTRACT FROM AUTHOR]

Purpose: This paper presents an experimental and numerical study to evaluate the impact energy dissipation, proposing a friction damper with the use of layers (LFD) for the dissipation of kinetic energy generated as a consequence of dynamic loads in an accidental fall due to work at heights. Methods: The study is performed by experimentation using a free-fall bench and numerical modeling using the finite element software Abaqus. The energy dissipation analysis is presented by comparing the system displacements for different impact masses. The geometry of the dissipator elements for a particular case of working at heights is proposed. Results: The results show the feasibility of applying the LFD for dynamic loads by dissipating 100% of the kinetic energy caused by an accidental fall for particular conditions. Conclusions: The use of layer elements as a preload mechanism allows the increase of the friction force with respect to the displacement of the system, increasing the energy dissipation capacity. In addition, the relationship of the geometrical parameters of the LFD allows the sizing of the layer elements and, in turn, the increase in the energy dissipation capacity according to the user's needs. [ABSTRACT FROM AUTHOR]

The non-cavitating and cavitating wake flow of a circular cylinder, which contains multiscale vortices, is numerically investigated by Large Eddy Simulation combined with the Schnerr-Sauer cavitation model in this paper. In order to investigate the spatiotemporal evolution of cavitation vortex structures, the Proper Orthogonal Decomposition (POD) method is employed to perform spatiotemporal decomposition on the cylinder wake flow field obtained by numerical simulation. The results reveal that the low-order Proper Orthogonal Decomposition modes correspond to large-scale flow structures with relatively high energy and predominantly single frequencies in both non-cavitating and cavitating conditions. The presence of cavitation bubbles in the flow field leads to a more pronounced deformation of the vortex structures in the low-order modes compared to the non-cavitating case. The dissipation of pressure energy in the cylinder non-cavitating wake occurs faster than the kinetic energy. While in the cavitating wake, the kinetic energy dissipates more rapidly than the pressure energy. [ABSTRACT FROM AUTHOR]

In order to solve the blockage effect and energy dissipation phenomenon caused by cavitation in the low-pressure vortex core region, this paper analyzes the spatial evolution of vorticity intensity and turbulent kinetic energy intensity under different cavitation conditions based on the Wray–Agarwal (WA) model. First, the tip leakage flow characteristics are studied, the evolution of vorticity and vorticity intensity is analyzed, then the distribution of turbulent kinetic energy distribution in the blade tip region is studied, and finally, the vorticity transport characteristics of the tip region are analyzed. It is found that the tip leakage rate is less affected by the vortex cavitation of the tip leakage, and there is a strong interaction between the leakage flow at the tip leading edge and the trailing edge, and the separation vortices and low-speed regions formed in the end-wall region cause blockage of the flow passage. Low pressure causes cavitation to cover most regions of the suction surface, inhibiting the formation and development of the tip leakage vortices. The distribution range of high turbulent kinetic energy region is almost the same as that of high-vorticity region, and there is a positive correlation between the two intensities. Severe cavitation causes the high turbulent kinetic energy region at the outlet of the flow passage to develop in the radial and axial directions of the impeller, which increases the turbulent dissipation and energy loss. The change of vorticity transport intensity caused by cavitation is mainly reflected in the expansion contraction term, and the Coriolis force term plays a dominant role in the vorticity transport process. This paper provides a reference for further improving the performance of mixed-flow pumps. [ABSTRACT FROM AUTHOR]

In this paper, large-eddy simulation of the interaction between a shock wave and the hypersonic turbulent boundary layer in a compression corner with a fixed 34° deflection angle at Ma = 6 for different Reynolds number cases is conducted. For investigating the effects of the Reynolds number for hypersonic cases, three cases where the free-stream Reynolds numbers are 14000, 20000, and 30000/mm are selected. The averaged statistics, such as the mean velocity, the skin friction, the heat flux, and the wall pressure, are used in this paper. The flow structures in the compression ramp including the shock wave and interaction region are discussed. The decomposition of the mean skin-friction drag for the flat flow is extended to be used in the compression corner. In addition, the turbulent kinetic energy is studied through the decomposition of the mean skin-friction drag for the flat-plate region and the corner region. It is found that higher Reynolds numbers would increase the turbulent kinetic energy by turbulent dissipation at the interaction region, while higher Reynolds numbers would decrease the turbulent kinetic energy by turbulent dissipation after reattachment. In addition, it is also found that the turbulent kinetic energy is larger with a higher Reynolds number and higher turbulent kinetic energy inhibits the movement from the separation point to the inflection point (x = 0 mm), which deduces larger separation bubbles. [ABSTRACT FROM AUTHOR]

In a seminal paper in the Philosophical Transactions of the Royal Society (A244, 87–112). Eshelby (Eshelby 1951 Phil. Trans. R. Soc. Lond. A 244, 87–112. (doi:10.1098/rsta.1951.0016)) introduced the concept of 'the force on an elastic singularity' and suggested that the extensions to dynamics include the application of the momentum flux. In this direction, it is shown that, in the non-uniformly motion of a dislocation there is a loss in quasi-momentum (or pseudo-momentum) across the scales ε to ε2, which induces an effective mass of the dislocation, and a loss in kinetic energy across the scales. It is shown through Noether's theorem that the rate of change of quasi-momentum in the volume enclosing the dislocation is equal to the flux of it through the surface minus a quasi-force, which is the dynamic J integral. The connection between the variation in the Hamiltonian and in the Lagrangian relates the quasi-force to the energy-release rate, yielding the same effective mass, while providing physical meaning both through momentum and energy. The effective mass of a dislocation is important in relating the energetics of defects from the micro to the macro scales, and the loss of quasi-momentum can have wider applications in continua. This article is part of the theme issue 'Foundational issues, analysis and geometry in continuum mechanics'. [ABSTRACT FROM AUTHOR]

In the impinging region of opposing jets, strong mixing and significant energy dissipation are observed, but the mixing parameters invariably change with the opposed impinging strength (OIS). In this paper, the ratio of the turbulent kinetic energy (TKE) intensity at the theoretical impinging point to the nozzle exit is defined as the opposed impinging strength. To examine the mixing properties of opposed impinging jets (OIJs) in a limited field under various OIS, a renormalization group k-ε turbulence model is employed to calculate three-dimensional OIJs under various OIS. The nozzle exit diameter is set to 0.6 m, and the inlet velocity is between 0.08 and 8 m/s, so the simulations are performed at Re between 4.8 × 104 and 4.8 × 106. This work focuses on the radial and vertical jets produced after impinging as well as the distribution of the TKE, flow field, and vortices. A thorough investigation reveals that although the OIS of the jets is primarily determined by the degree of jet development, it increases with the Reynolds number. A low OIS results in less mixing in the surrounding water and relatively unconstrained jet generation; however, it also results in limited energy extraction from the fluid. Once the OIS is high, there is more mixing in the surrounding water, and more energy is also lost during impinging. The distribution of vortices in the vortex field is not only influenced by the OIS but is also very closely related to the scale of the limited mixing field. [ABSTRACT FROM AUTHOR]

The opposite side vertical joint fishway has the characteristics of better adaptation to water level changes, obvious energy dissipation effect and better flow pattern of water. According to the design guidelines, the fish passage in the study area is designed in body shape. In this paper, the effect of different vertical slit positions on the flow structure of the chamber is investigated by numerical simulation, including the hydraulic characteristics of the main flow area, the hydraulic characteristics of the return flow area and the flow velocity distribution of the vertical slit position, and the vertical slit position of the fish passage suitable for the fish in the study area is analyzed. The simulation results show that: the vertical slit position has almost no effect on the maximum flow velocity in the pool chamber of the opposite side vertical slit, and has less effect on the change of the maximum flow velocity along the main flow area. As the center of the vertical slit gradually approaches the center of the pool chamber, the decay of the maximum flow velocity along the main flow area takes the lead in gradually becoming larger and then tends to saturate. Most of the flow velocity in the return area of the upper left part of the main flow area gradually decreases and then increases, and most of the flow velocity in the return area of the lower right part gradually increases. The area ratio of the two sides of the reflux zone gradually decreases. The vertical slit position on the pool room mainstream area flow pattern and the flow velocity distribution of the return area has a significant impact, when 0.23≤l/B≤0.40, the pool room flow pattern is the best; when l/B≥0.37, the mainstream area along the maximum flow decay rate tends to saturate, when 0.37≤l/B≤0.40, the maximum turbulent kinetic energy in the pool room at l/B =0.40 minimum, and the area of the return area on the left and right sides. Therefore, when l/B=0.40, the migratory effect of semi-migratory fish in the study area can be significantly improved. The maximum variation of turbulent energy in the pool is between 0.074 and 0.116 m²/s² when the vertical slit is located at 0.13-0.50 of the width of the pool chamber from the side wall, and the flow pattern in the pool is the best when the vertical slit is located at 0.23-0.40 of the width of the pool chamber, which can significantly improve the migratory effect of semimigratory fish in the study area. The results of the study clarify the influence of the center position of the vertical joints on the water flow structure of the pool chamber and provide a reference for the subsequent design and research work of other related fish passage projects. [ABSTRACT FROM AUTHOR]

Purpose: The paper aims to build a finite element simulation model for pilling of polyester hairiness on the fabric to study the effects of hairiness performance on pilling and reveal pilling mechanisms. Design/methodology/approach: The finite element simulation model of pilling of polyester hairiness was established by ABAQUS. Polyester hairiness was treated as elastic thin rod, which was divided by two-node linear three-dimensional truss element. The effects of hairiness elastic modulus, hairiness friction coefficient and hairiness diameter on frictional dissipation energy, strain energy and kinetic energy produced by pilling have been studied. The analysis solution values were compared with the finite element simulation results, which was used to verify finite element simulation. Findings: The paper provides new insights about how to reveal pilling mechanisms of polyester hairiness with different performance. Comparing finite element simulation results with analysis solutions shows that the fitness is greater than 0.96, which verifies finite element simulation. Larger hairiness elastic modulus gives rise to higher friction dissipation energy and strain energy of hairiness but lower kinetic energy. Increasing friction coefficient enhances friction dissipation and strain energy of hairiness. However, kinetic energy decreases with the increase of friction coefficient. Hairiness diameter also has an important effect on hairiness entanglement and pilling. Increasing hairiness diameter can decrease friction dissipation energy but enhance strain energy and kinetic energy. Research limitations/implications: Finite element simulation was verified by analysis solutions. The solutions include friction dissipation energy, strain energy and kinetic energy, which cannot measured b experiment. Therefore, researchers are encouraged to simulate pilling to obtain pilling grades, which be compared with experiment results. Originality/value: Pilling of polyester hairiness was simulated by ABAQUS. This method makes pilling process visualization, and pilling mechanisms was revealed from non-linear dynamics. [ABSTRACT FROM AUTHOR]

AbstractIn this paper, the statistical properties of the kinetic εu and thermal εθ dissipation rates in two-dimensional (2D) turbulent Rayleigh–Bénard convection (RBC) are studied by using the thermal lattice Boltzmann method (LBM). A series of direct numerical simulations (DNS) are implemented in a square cell with the unit aspect ratio for the Rayleigh number Ra = 108 and Prandtl number Pr = 4.38. The roughness height h* and vary the vibration frequency ω* from 0 to 1000 are fixed in the vibrational RBC with rough plates to explore their effect on the kinetic and thermal dissipation rates. The global features indicate that the εu and εθ are more intense in the regions with high gradients of velocity and temperature, which is in good agreement with the previous work. The scalings of Nu∼ω*0.55±0.1 and Re∼0.59±0.2 are proposed between the ensemble averaged Nusselt number Nu and Reynolds number Re. The probability density functions (PDFs) of both logarithmic kinetic dissipation rate lg εu and thermal dissipation rate lg εθ are not conformed to the log-normal distributions. Through the analysis of the time-averaged εu and εθ vertical profiles, it is further demonstrated that the local dissipation rates from the boundary layer region are still the major contribution in the vibrational RBC with rough plates. [ABSTRACT FROM AUTHOR]

The Tesla valve has a special structural form that can guide the flow entering from the reverse port into two sets of straight/curved channels, and dissipate energy through friction and collision at the end of the guide column, greatly weakening the flow velocity in the pool. This unique flow characteristic is very suitable for designing fishways. However, direct applying the original structure of Tesla valves as a fishway has been proven to have significant limitations. The original structure of the Tesla valve fishway is optimized in this paper. By adjusting the aspect ratio of the straight/curved channel in the fishway pool, hollowing out the guide column, and increasing the length of the opening end, a new Tesla valve fishway with relatively independent energy dissipation channels and fish upstream channels has been obtained. The hydraulic characteristics parameters of the optimized Tesla valve fishway are compared with the original structure using numerical simulation, with a focus on analyzing the flow velocity variation, flow field, and turbulent energy distribution of the new Tesla valve fishway. The results show that the new Tesla valve fishway has significant advantages compared to the original structure. While maintaining the same energy dissipation efficiency, it effectively improves the flow pattern in the pool, and the overall flow velocity and turbulent kinetic energy are smaller than the original structure. The new structure significantly increases the proportion of rest areas. When the pool bottom slope gradient from 1% to 3%, the proportion of rest areas in the original Tesla valve fishway is 8.5% to 1.2%, while the proportion of rest areas in the new Tesla valve fishway is 44.7% to 25.8%, increasing the possibility of successful fish upstream migration. The flow velocity and turbulent kinetic energy of the new structure increase with the increase of the bottom slope gradient, but the flow velocity remains low in the fish upstream channels, while the high flow velocity mainly occurs in the energy dissipation passage. The maximum flow rate increase rate in the energy dissipation channel of the first two stages of the pool is relatively high, while after the third stage of the pool, the increase rate tends to slow down. The overall turbulent kinetic energy in the fish upstream channels is relatively low. When the bottom slope gradient is less than 2.5%, the upstream conditions and economy of the fishway are better. [ABSTRACT FROM AUTHOR]

This paper presents the results of a hydrodynamic experimental study of the hydraulic characteristics of flow in different vertical slot fishway (VSF) designs with L-shaped, polygonal, and semicircular baffles. A biological experiment was conducted using endemic fish to analyze the efficiency of the upstream passage of different VSF designs. Based on the results, a significant difference in water depth, slot velocity, turbulence kinetic energy, and efficiency of the upstream passage was observed. The L-shaped baffle had better energy dissipation; however, the fishway with a polygonal baffle had better efficiency of the upstream passage. The results indicated that the present VSFs are all fish-friendly for Chinese endemic fish, but VSFs with polygonal baffles may be a better choice. [ABSTRACT FROM AUTHOR]

The current advanced aero-engine fan rotors are usually integrally-bladed rotor discs, and the root of the fan blade has irregular curved surface, which brings technical difficulties and challenges to achieve the blade releasing. In this paper, the dynamic response and energy dissipation process of the titanium alloy blade under shaped charge jet explosion were analyzed by numerical model, and the explosion damage mechanism of titanium alloy fan blades was clarified. Finally, a FBO test was conducted to verify the blade explosion release method in rotating state. Through the energy dissipation analysis of the whole explosion process, it can be seen that the overall residual kinetic energy of the blade is about 15.7 J, which is only 0.02 % of the initial kinetic energy of the releasing blade in rotating. It is indicated that the explosion separation method will not generate additional kinetic energy to the released blade. [ABSTRACT FROM AUTHOR]

The process of a submillimeter sphere eccentric impacting a single droplet under electric field is experimentally investigated by using high-speed micrographic techniques in this paper. The spheres are released at a fixed height to impact different positions of droplets. With the increase in electric field intensity, the impact behavior evolves from oscillation mode to submergence mode. The trajectory of the sphere deviates from the impact direction affected by the eccentric impact. Each mode can be divided into three stages: slamming, cavity developing, and reverting. In the slamming stage, the sphere is decelerated by hydrodynamic forces where the kinetic energy loss increases with the increase in Weber number We. Surface tension becomes the dominant force in the cavity developing stage due to the expanding cavity. The impact angle α and We show little influence on the expanding speed; thereinto We has a significant effect on the limit diameter of the cavity. The cavity with different α and We reaches a peak value near the critical state of the impact angle of 90 degrees. A scaling law is constructed to obtain the transitional boundary between the impact modes based on dimensional analysis and data rearrangement. The electric force is mainly used to accelerate the sphere in the gas phase and has little influence on the solid–liquid interaction behavior after contacting the droplet. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to present an innovative insight into the behavior and energy dissipation mechanism of a single‐degree‐of‐freedom (SDOF) structure controlled by pounding tuned mass damper (PTMD). In this study, a shake table test was conducted to investigate energy response of the SDOF structure incorporated with PTMD and subjected to seismic excitations. Moreover, SDOF structure and the updated analytical structural pounding force model based on viscoelasticity of materials have been investigated for parametric studies, including dynamic parameters of the primary structure, properties of PTMD, and characteristics of the earthquake records. The influence of these parameters has been discussed in details in this paper. The results showed that energy can be dissipated by PTMD as well as via the three traditional ways of TMD. The energy dissipated by PTMD keeps increasing during excitation, which is similar to the process of energy dissipated by damping mechanism. Furthermore, energy dissipated by damping and PTMD are nearly equal, and the two types of energy dissipation predominate the behavior of the system. Hysteretic, recoverable elastic strain and kinetic energy of the controlled structure diminish to very low level during earthquakes. [ABSTRACT FROM AUTHOR]

In this paper, we consider a simplified model of turbulence for large Reynolds numbers driven by a constant power energy input on large scales. In the statistical stationary regime, the behaviour of the kinetic energy is characterized by two well-defined phases: a laminar phase where the kinetic energy grows linearly for a (random) time tw followed by abrupt avalanche-like energy drops of sizes S due to strong intermittent fluctuations of energy dissipation. We study the probability distribution P[tw] and P[S] which both exhibit a quite well-defined scaling behaviour. Although tw and S are not statistically correlated, we suggest and numerically checked that their scaling properties are related based on a simple, but non-trivial, scaling argument. We propose that the same approach can be used for other systems showing avalanche-like behaviour such as amorphous solids and seismic events. This article is part of the theme issue 'Scaling the turbulence edifice (part 1)'. [ABSTRACT FROM AUTHOR]

In this paper, we put forward a hypothesis for turbulent kinetic energy, Reynolds stresses and scalar variance in wall-bounded turbulent flows, whereby these quantities, when normalized with the kinematic viscosity, mean turbulent energy dissipation rate and scalar dissipation rate, are independent of the Reynolds and Péclet numbers when they are sufficiently large. In particular, there exist two scaling ranges: (i) an inertial-convective range at sufficiently large distance from the wall over which a $2/3$ power-law scaling emerges for all quantities mentioned above; (ii) a viscous-convective range between the viscous-diffusive and inertial-convective ranges at large Prandtl number over which the normalized scalar variance is constant. The relatively large amount of available wall turbulence data either provides reasonably good support for this hypothesis or at least exhibits a trend that is consistent with the predictions of this hypothesis. The relationship between the proposed scaling and the traditional wall scaling is discussed. Possible ultimate statistical states of wall turbulence are also proposed. [ABSTRACT FROM AUTHOR]

Purpose It is significant to know the real-time indexes about the turbulence flow of the ocean system, which has a deep influence on ocean productivity, distribution of the ocean populations and transmission of the ocean energy, especially the measurement of turbulence flow velocity. So, it is particularly urgent to provide a high-sensitivity, low-cost and reliable fluid flow sensor for industry and consumer product application. This paper aims to design a micro fluid flow sensor with a cross beam membrane structure. The designed sensor can detect the fluid flow velocity and has a low kinetic energy dissipation rate.Design/methodology/approach In this paper, a micro fluid flow sensor with a cross beam membrane structure is designed to measure the ocean turbulence flow velocity. The design, simulation, fabrication and measurement of the designed sensor are discussed. By testing the simply packaged sensor in the fluid flow and analyzing the experiments data, the results show that the designed sensor has favorable performance.Findings The paper describes the tests of the designed sensor, and the experimental results show that the designed sensor can measure the fluid flow velocity and has a sensitivity of 11.12 mV/V/(m/s)2 and a low kinetic energy dissipation rate in the range of 10-6-10-4 W/kg.Originality/value This paper provides a micro-electro-mechanical systems fluid flow sensor used to measure ocean turbulence flow velocity. [ABSTRACT FROM AUTHOR]

The ever increasing need to extend battery life in IoT devices, self-powered sensors, and autonomous nodes highlights the need to reduce energy consumption as much as possible. One of the main issues still not fully addressed is the reduction of power consumption of sensors and measurement systems in standby mode, which represents a significant amount of the total power dissipation. In fact, nowadays, despite the continuous efforts, standby power is still far from being negligible. This paper exploits a new approach named “zero-current standby” to tackle this issue; moreover, due to the fact that the transducer implements kinetic-to-electrical energy conversion, a sensor that performs kinetic energy measurements is obtained and characterized. The proposed solution goes beyond the concept of the standby state itself, as it can actually be applied to appliances turned OFF. The design of a piezoelectric-based sensor able to measure kinetic energy is discussed in this paper. The proposed device will also allow zero-energy standby operation, with vibrations acting as trigger for sensor activation and data transmission via Wi-Fi. Numerical analysis, laboratory characterization, and experimental results of a complete working prototype are presented here, demonstrating both the suitability of the approach proposed and the improvement with respect to conventional strategies. [ABSTRACT FROM AUTHOR]

Baffles and check-dam systems are often used as granular flow (rock avalanches, debris flows, etc.) control structures in regions prone to dangerous geological hazards leading to massive landslides. This paper explores the use of numerical modelling to simulate large volume granular flow and the effect of the presence of baffles and check dam systems on granular flow. In particular, the paper offers a solution based on the smoothed particle hydrodynamics numerical method, combined with a modified Bingham model with Mohr–Coulomb yield stress for granular flows. This method is parallelised at a large scale to perform high-resolution simulations of sand flowing down an inclined flume, obstructed by rigid control structures. We found that to maximise the flow deceleration ability of baffle arrays, the design of baffle height ought to reach a minimum critical value, which can be quantified from the flow depth without baffles (e.g. 2.7 times for frictional flows with friction angle of 27.5°). Also, the check-dam system was found to minimise run-out distances more effectively but experiences substantially higher forces compared to baffles. Finally, flow-control structures that resulted in lower run-out distances were associated with lower total energy dissipation, but faster kinetic energy dissipation in the granular flows; as well as lower downstream peak flow rates. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation of the liquefaction behavior of granular materials considering the initial static shear effects. Two typical cyclic failure modes were identified: cyclic liquefaction and residual deformation accumulation. During the simulation processes, the evolution of the applied work, strain energy, frictional dissipation, and kinetic energy was examined and interpreted by the law of thermodynamics. The relative magnitudes of the applied work and dissipation were found to be significantly different for the two distinct cyclic failure modes. For cyclic liquefaction, the applied work was smaller than the frictional dissipation, accompanied by continuous liberation of the strain energy. In contrast, for residual deformation accumulation, the applied work was nearly the same as dissipation, and the strain energy appeared to be stable and periodically varying in each cycle, indicating the attainment of a steady internal structure and thus a strong resistance to liquefaction. These observations can be interpreted by correlating the energy transfer and dissipation with the contact-normal-based fabric evolution of the granular system at microscale. [ABSTRACT FROM AUTHOR]

Precise prediction of ventilation flow is essential to create a comfortable, economical, and healthy indoor environment. In the past three decades, the computational fluid dynamics (CFD) method has been used more often, and it is now one of the primary methods for studying building ventilation. The most common CFD method is RANS simulation because of the low cost of computational resources and good accuracy. This paper presents a numerical investigation of a transitional ventilation flow with the Coanda effect, which makes the initial free jet transform into a wall jet. Six low-Reynolds number k-ε models proposed by Abid (AB), Lam and Bremhorst (LB), Launder and Sharma (LS), Yang and Shih (YS), Abe Kondoh and Nagano (AKN), and Chang, Hsieh and Chen (CHC) are applied. The performance of the six models is evaluated by comparing the computational results with the PIV measurements of Van Hooff et al. The predictions revealed that the LS model has a good approximation of velocity profiles because of its two extra terms in k and ε equations, and the AB model is in good agreement with experimental results for predicting the Coanda effect. The LB model provides the worst agreement with experimental data on account of the wrong prediction of turbulent kinetic energy and dissipation rate. [ABSTRACT FROM AUTHOR]

Rocking bodies can be found at all structural scales, from small museum exhibits to uplifting buildings. These structures, whose dynamic stability springs from the difficulty of mobilizing their rotational inertia, are ideal candidates for benefiting from the supplemental inertia provided by inerters. This benefit can be limited, however, if the inerter drives the structural response towards potentially undesirable motions by transferring back the kinetic energy accumulated within it at inconvenient times. To control this phenomenon, a clutching system can be employed to direct the interaction between the interter and the structure improving further its dynamic behaviour. To date, however, most of the studies dealing with clutching inerto-elastic or inerto-rocking systems under seismic excitation have adopted a rather simplistic idealisation of the clutch engagement-disengagement response. In this paper, we re-visit the impact effects on inerto-rocking structures and propose an improved mechanistic model of the clutching system. First, the effects of the inerter on the transition upon impact and the impact effects on the acceleration response of rocking blocks are analysed. Then, a set of original analytical expressions for rigid and flexible rocking structures equipped with a pair of clutched inerters are derived. The newly proposed models are used to examine the evolution of the energy dissipation in the device and the influence of key parameters like the clutch stiffness, gears play, viscous damping and dry friction on its response. We conclude by evaluating the behaviour of the detailed rocking model with clutched inerters to a set of realistic earthquake ground motions. Although important differences are observed in the evolution of energy dissipation and engagement response depending on the type and characteristics of the clutch model, largely comparable peak values of displacement are obtained. On the other hand, a more accurate representation of the clutch behaviour leads to potentially larger acceleration demands. Our analyses also show that, in general, the inclusion of the inerter results in higher coefficients of restitution, indicating lower energy dissipation during impact and that the infinite acceleration spikes predicted by Housner's model can be ignored if impact forces are sufficiently distributed over time as to cause continuous velocity transitions, but sharp enough not to appreciably affect the rotation response. [ABSTRACT FROM AUTHOR]

Fragmentation of blocks upon impact is commonly observed during rockfall events. Nevertheless, fragmentation is not properly taken into account in the design of protection structures because it is still poorly understood. This paper presents an extensive and rigorous experimental campaign that aims at bringing insights into the understanding of the complex phenomenon of rock fragmentation upon impact. A total of 114 drop tests were conducted with four diameters (50, 75, 100, and 200 mm) of rock-like spheres (made of mortar) of three different strengths (34, 23 and 13 MPa), falling on a horizontal concrete slab, with the objective to gather high-quality fragmentation data. The analysis focuses on the fragment size distribution, the energy dissipation mechanisms at impact and the distribution of energy amongst fragments after impact. The results show that the fragment size distributions obtained in this campaign are not linear on a logarithmic scale. The total normalised amount of energy loss during the impact increases with impact velocity, and consequently the total kinetic energy after impact decreases. It was also found that energy loss to create the fracture surfaces is a constant fraction of the kinetic energy before impact. The trajectories of fragments are related to the impact velocity. At low impact velocity, the fragments tend to bounce but, as the impact velocity increases, they tend to be ejected sideways. Although testing mortar spheres in normal impact is a simplification, the series of tests presented in this work has brought some valuable understanding into the fragmentation phenomenon of rockfalls. Highlights: Data of 114 controlled drop tests of mortar spheres are analysed. Fragment size distributions obtained in this campaign are not linear on a logarithmic scale. The total amount of energy loss during the impact increases with impact velocity, and consequently the total kinetic energy after impact decreases. Energy loss to create fracture surfaces is a constant fraction of the kinetic energy before impact. At low impact velocity, the fragments tend to bounce but, as the impact velocity increases, they tend to be ejected sideways. [ABSTRACT FROM AUTHOR]

Cohesion and rolling friction play key roles in governing the behavior of soil; however, only a limited number of studies have been able to assess the simultaneous contributions of these two microparameters on the macroproperties of soil. In this respect, the innovation of the current study includes an attempt to examine the interplay of these two primary parameters on the angle of repose (AoR) based on the discrete-element method (DEM). Lifting cylinder tests on cohesive wet sand have been carried out in DEM, while the cohesion and rolling friction are captured through proposed computational models. In this paper, macroparameters, such as the geometry and developmental stages of sand piles obtained in DEM simulation, are compared with experimental data, while their microevolution is quantified in detail. The results show that a large AoR can only be obtained when the cohesive and rotational frictional forces work in tandem. Increasing the cohesion and rolling friction results in smaller contact numbers, with increasing chain-like connections between particles and larger pore spaces to account for a larger AoR. For the first time, this study distinctly identifies three major stages that contribute to the AoR, based on the development of contact numbers and the transformation of energy. Accordingly, the linkage between macroscale AoR and the microstructural coordination number is formulated with varying levels of cohesion and rolling friction. The DEM results prove that the more cohesive the particles are, the greater the delay in the dissipation of kinetic energy. [ABSTRACT FROM AUTHOR]

Dry coal separation is the key technology for coal separation in arid and water-scarce areas. The content of −6 + 1 mm coal gradually increases, and the weak gravity affect of this part of coal restricts the separation effect, causing serious resource waste and environmental pollution. In this paper, a process intensification method for compound dry separation based on high-frequency vibration was proposed to improve the separation effect of fine coal. The kinematic characteristics of the bed surface with high-frequency vibration was captured by the three-channels acceleration sensor, and the motion trajectories of different regions on bed surface were reconstructed. The separation area was located at the front end of the vibrating bed, and the elliptical trajectory promoted the material to roll. However, the tail of the bed showed a linear trajectory, the main team to the transport of the material. And then the force characteristics of various density particles were studied by using spherical inertial sensors. Compared with low-density particle swarm, the collision between high-density particles was more obvious, causing serious loss of kinetic energy, which increased the motion difference of particles with different densities. Furthermore, the significance of the effects of vibration frequency, bed inclination and air velocity on the separation effect of −6 + 1 mm coal and the interaction between the factors were investigated. Furthermore, the influence of vibration frequency, inclination, and air velocity on the separation effect and the interaction among various factors were explored. The influence of frequency and inclination was more obvious than that of gas velocity. And then a mathematical model was established to predict the calorific value of clean coal. The results illustrated that at a vibration frequency of 37.52 Hz, a bed inclination angle of 13.69°, and an air velocity of 2.26 m/s, the calorific of product was increased from 4306 kcal/kg to 5868 kcal/kg, and the heat efficiency reached 90.18%. The results provide a referable way to realize the large-scale and high-efficiency dry separation of fine coal. [ABSTRACT FROM AUTHOR]

During substructure formation in magnetized astrophysical plasma, dissipation of magnetic energy facilitated by magnetic reconnection affects the system dynamics by heating and accelerating the ejected plasmoids. Numerical simulations are a crucial tool for investigating such systems. In astrophysical simulations, the energy dissipation, reconnection rate, and substructure formation critically depend on the onset of reconnection of numerical or physical origin. In this paper, we hope to assess the reliability of the state-of-the-art numerical codes, pluto and koral by quantifying and discussing the impact of dimensionality, resolution, and code accuracy on magnetic energy dissipation, reconnection rate, and substructure formation. We quantitatively compare results obtained with relativistic and non-relativistic, resistive and non-resistive, as well as two- and three-dimensional set-ups performing the Orszag–Tang test problem. We find sufficient resolution in each model, for which numerical error is negligible and the resolution does not significantly affect the magnetic energy dissipation and reconnection rate. The non-relativistic simulations show that at sufficient resolution, magnetic and kinetic energies convert to internal energy and heat the plasma. In the relativistic system, energy components undergo mutual conversion during the simulation time, which leads to a substantial increase in magnetic energy at 20 per cent and 90 per cent of the total simulation time of 10 light-crossing times – the magnetic field is amplified by a factor of 5 due to relativistic shocks. We also show that the reconnection rate in all our simulations is higher than 0.1, indicating plasmoid-mediated regime. It is shown that in koral simulations more substructures are captured than in pluto simulations. [ABSTRACT FROM AUTHOR]

The annual increase in demand for electrical power is accompanied by a significant combustion of hydrocarbon fuels and, accordingly, significant CO2 emissions into the atmosphere, which, in turn, result in increasing the surface temperature of our planet. In addition, hydrocarbon fuel reserves are also depleted every year, which raises the question of the efficient use of fossil fuels. One of the promising solutions to this problem is introducing a technology that allows using the excess gas pressure at gas distribution points in order to generate additional electrical energy. As a rule, a radial turboexpander is used to convert the kinetic energy of natural gas at low power. In this paper, we study a method to reduce losses in a volute inlet of a radial expander. Based on our research, we could find that the use of two symmetrical fins in the volute inlet pipe makes it possible to decrease the turbulent kinetic energy by 1.29% and to reduce the energy losses in the inlet pipe by 2.18%. [ABSTRACT FROM AUTHOR]

The paper presents the results of the numerical calculation of the flow around hybrid unmanned aircraft with X-tail stabilizers. This aircraft design is an innovative combination of a gyroplane and a multirotor. The aerodynamic properties of the two-part X-tail stabilizer were analysed. The aerodynamic forces and moments on this element of the aircraft were specified from the CFD simulation calculations for the defined values of the angle of attack and the slip angle, and particular attention was paid to the differences between the upper and lower parts of the stabilizer. In addition, the turbulence kinetic energy on the surface of the vortex core region were analysed to conduct a qualitative and quantitative analysis of energy losses in flow, resulting from local separation and vortices. The obtained results allow for conducting further aerodynamic comparative analyses on other types of stabilizers. [ABSTRACT FROM AUTHOR]

Slit dams can eliminate the risk of particle overload accumulation, which can be safer in controlling debris flow compared with a completely closed dam. In attempting to better use the energy dissipation effect of particle collision and reduce the impact of the dam body, referring to the traditional slit dam, this paper proposed one with tilted baffles in the downstream direction. Discrete element simulation and several flume model experiments were carried out herein to verify the advantages and explore the applicable conditions of this tilted baffle slit dam, in which the particle trapping efficiency and the change law of impact force of the tilted baffles under the conditions of different inclined angles, opening sizes, and particle sizes were studied. The results show that: 1. when the inclination angle is 30° ≤ θ ≤ 45°, the tilted baffles can dissipate more particle kinetic energy than the transverse baffles; 2. the maximum impact force and trapping efficiency of the tilted baffles decrease with the increase in the width diameter ratio b/d, with the opening width b of the slit to the particle diameter d; 3. with the given particle size of 6 mm ≤ d ≤ 14 mm, the range that the tilted baffles can effectively intercept the particles flowing down is 0 ≤ b/d ≤ 4, and it reaches the ideal interception state near 1 ≤ b/d ≤ 2, where, relatively, the impact force is weak, and the interception efficiency is high. [ABSTRACT FROM AUTHOR]

This paper is concerned with limits on kinetic and magnetic energies and dissipation rates in forced flows that lead to dynamo action and a finite amplitude magnetic field. Rigorous results are presented giving upper and lower limits on the values of these quantities, in a simple cubic geometry with periodic boundary conditions, using standard inequalities. In addition to the general case, results in the special case of the Archontis dynamo are presented, in which fields and flows are closely similar in much of the domain. [ABSTRACT FROM AUTHOR]

This paper presents a quantitative analysis of system dynamic response, rockfall trajectory control, and kinetic energy evolution of the tests on the guiding flexible protection system (GFPS) based on 4D energy dissipation. The system achieves 4D protection against rockfall hazards on high and steep slopes, with 3D spatial motion and energy evolution control of rockfall trajectories in time history. After clarifying the structural principle of the system, analyzing the kinetic energy characteristics of the rockfall along the hill, and defining the multistage energy-dissipation control principle of the system, an evaluation method for rockfall energy evolution for quantitative back analysis was established for the whole course of system protection. Furthermore, the rockfall's energy decay characteristics in the guiding section were analyzed. Accordingly, a full-scale model of this system was constructed, and six in situ tests with and without the protection system were conducted. The system model was laid on a slope with a gradient of over 60°, a width of 130 m, and a height of 82 m, where the crushed rock developed. The maximum impacting energy was 2500 kJ. Quantitative back analysis of the experiment was carried out, and the results revealed that, compared with the unprotected tests, after the construction of the protection system, the motion duration of the falling block was extended by over 80%, the impact times increased by approximately five times, the bounce height reduced by roughly 80%, the transverse motion distance reduced by around 50%, and, for blocks that reached the bottom, the residual kinetic energy and the rolling distance away from the slope toe were both decreased by 70%. The combined energy-dissipation ratio was as high as 89%. [ABSTRACT FROM AUTHOR]

In this paper, the energy losses in big band saw machines are investigated. These losses are caused by the geometric and angular inaccuracies with which the leading wheels are made. Expressions for calculating the kinetic energy of the mechanical system in the ideal and the real cases are obtained. For this purpose, expressions for calculating the velocities of the centers of the masses in two mutually perpendicular planes are obtained. A dependence for calculation of the kinetic energy losses of the mechanical system in final form is received. Optimization procedure is used to determine the values of the parameters at which these losses have minimum values. The proposed study can be used to minimize energy losses in other classes ofwoodworking machines. [ABSTRACT FROM AUTHOR]

The Galilean invariant thermodynamically compatible conservation laws that admit a class of generalized solutions is analyzed. The main feature of the generalized solutions considered in this paper is that they describe smooth solutions with the kinetic energy and total pressure loss, which accompany the dynamic process of heat supply. The principal properties of the generalized solutions analyzed in Godunov's works are the Galilean invariance and thermodynamic compatibilty of the original conservation laws under the closed mathematical formulation of the thermal gas-dynamic process. [ABSTRACT FROM AUTHOR]

With the purpose of solving the problems of uneven velocity and energy loss of the foreign fiber sorters, this paper has analyzed the nozzle distribution and structure in the foreign fiber sorting system, and presented the design of a nozzle with the circular distribution contraction–expansion structure. The turbulent kinetic energy was optimized through a circular distribution of the nozzle to improve nozzle velocity uniformity, according to the effect of air flow on wall surface distance. Meanwhile, the nozzle was optimized with the contraction–expansion structure based on the relationship between the Mach number and the nozzle's cross-sectional area. The stepped cross-section of the nozzle was replaced by a transition curve cross-section to restrain the sudden change of the air flow velocity in the nozzle. The optimized nozzle structure was discussed in terms of the velocity, the pressure, and the energy loss. It was found that the velocity increases by 9.2%, the required pressure decreases, and the energy loss decreases. So the effectiveness and practicability of the proposed method were illustrated. [ABSTRACT FROM AUTHOR]

Finescale strain parameterization (FSP) of turbulent kinetic energy dissipation rate has become a widely used method for observing ocean mixing, solving a coverage problem where direct turbulence measurements are absent but CTD profiles are available. This method can offer significant value, but there are limitations in its broad application to the global ocean. FSP often fails to produce reliable results in frontal zones where temperature–salinity (T/S) intrusive features contaminate the CTD strain spectrum, as well as where the aspect ratio of the internal wave spectrum is known to vary greatly with depth, as frequently occurs in the Southern Ocean. In this study we use direct turbulence measurements from Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) and glider microstructure measurements from Autonomous Sampling of Southern Ocean Mixing (AUSSOM) to show that FSP can have large biases (compared to direct turbulence measurement) below the mixed layer when physics associated with T/S fronts are meaningfully present. We propose that the FSP methodology be modified to 1) include a density ratio (Rρ)-based data exclusion rule to avoid contamination by double diffusive instabilities in frontal zones such as the Antarctic Circumpolar Current, the Gulf Stream, and the Kuroshio, and 2) conduct (or leverage available) microstructure measurements of the depth-varying shear-to-strain ratio Rω(z) prior to performing FSP in each dynamically unique region of the global ocean. Significance Statement: Internal waves travel through the ocean and collide, turbulently mixing the interior ocean and homogenizing its waters. In the absence of actual turbulence measurements, oceanographers count the ripples associated with these internal waves and use them estimate the amount of turbulence that will transpire from their collisions. In this paper we show that the ripples in temperature and salinity that naturally occur at sharp fronts masquerade as internal waves and trick oceanographers into thinking there is up to 100 000 000 times more turbulence than there actually is in these frontal regions. [ABSTRACT FROM AUTHOR]

In porous media, non-wetting phase droplets snapping off in a constricted microchannel are one of the most common phenomena in two-phase flow processes. In this paper, the application range of the classic quasi-static criterion in rectangular cross section microchannels is obtained. For three different droplet breakup phenomena—total breakup, partial breakup, and non-breakup—observed in experiments when a non-wetting phase droplet passes through a microchannel constriction, the breakup is caused by the droplet neck snapping off in a channel constriction. A critical criterion for the dynamic snap-off event in a two-phase flow is proposed considering the effect of viscous dissipation by mechanical analysis, energy dissipation analysis, and many microfluidic experiments. When the droplet front flows out of the constriction, snap-off will occur if the surface energy release exceeds the required energy for viscous dissipation and kinetic energy conversion. The unique partial breakup phenomenon is affected by droplet surfactant distribution and the acceleration effect in the constriction center. This partial breakup phenomenon in experiments is an essential evidence for the non-uniform distribution of surfactants in the droplet surface. The results of this study contribute to understanding pore-scale mass transfer and flow pattern changes within porous media. [ABSTRACT FROM AUTHOR]

Bird strikes are one of the most dangerous incidents occurring to aircraft engines and can inflict heavy casualties and economic losses. In this study, a smoothed particle hydrodynamics (SPH) mallard bird model has been used to simulate bird impact to rotary aero-engine fan blades. The simulations were performed using the finite element method (FEM) by means of LS-DYNA. The reliability of the material model and numerical method was verified by comparing the numerical results with Wilbeck's experimental results. The effects of impact and bearing parameters, including bird impact location, bird impact orientation, initial bird velocity, fan rotational speed, stiffness of the bearing, and the damping of the bearing on the bird impact to aero-engine fan blade are studied and discussed. The results show that both the impact location and bird orientation have significant effects on the bird strike results. Bird impact to blade roots is the most dangerous scenario causing the impact force to reach 390 kN. The most dangerous orientation is the case where the bird's head is tilted 45° horizontally, which leads to huge fan kinetic energy loss as high as 64.73 kJ. The bird's initial velocity affects blade deformations. The von Mises stress during the bird strike process can reach 1238 MPa for an initial bird velocity of 225 m/s. The fan's rotational speed and the bearing stiffness affect the rotor stability significantly. The value of bearing damping has little effect on the bird strike process. This paper presents a procedure for evaluating the strength of fan blades against bird strike in the design stage. [ABSTRACT FROM AUTHOR]

In this paper, the possibility of utilizing a wind turbine to recapture a portion of the kinetic energy losses of a car, irrespective of being a traditional car that is propelled by an internal combustion engine or an electric vehicle (EV) that is propelled by an electric motor, is appraised. To investigate the topic, a small wind turbine has been inserted at the back of the condenser of a car to recover a portion of the kinetic energy of wind passing through the condenser's crisscrossed bars. A portion of this wind is caused by wind existing outside the car, and the main portion is caused by the kinetic energy originating from the car movement. In the absence of the wind turbine, the wind passing through the condenser's crisscrossed bars hits the middle part of the car's chassis and loses its energy. Thus, not only the wind turbine uses a portion of the kinetic energy losses of the car to produce electricity but also, since it has been embedded at the back of the condenser, it has no impact on the aerodynamic coefficient of the car, i.e., it does not produce any extra resistive force. When the car is parked, and there is no kinetic energy resulting from the car movement, a small flow of wind available outside the car is converted into electricity stored in the car's battery. To realize the proposed scheme, a 100-W wind turbine, a permanent-magnet synchronous generator coupled to the turbine, and a novel built hybrid power generation system combining the wind-driven generator's output power with that of the car's battery have been embedded in an EV having a total weight of 1855 kg. Experimental measurements conducted under realistic operation of the EV are given that prove the traveling range of the EV and the power efficiency of the EV's power supply are enhanced by, 6.4 km and 0.2% respectively, by recovering only a portion of the kinetic energy losses of the EV. These two benefits also prove the novelty and contributions of this work in successfully recovering a portion of the kinetic energy losses of a car by using a small wind turbine embedded in the car. [ABSTRACT FROM AUTHOR]

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]