Energy Dissipation Rate Research Articles

Mechanical, microstructural, and fretting wear behaviour of Al2O3–ZrO2-CNT based bimodal composite coatings

In current work, bimodal thermal barrier coatings (TBC) were deposited via atmospheric plasma spraying (APS) using Al2O3 as matrix, reinforced with 20 wt% of ZrO2 and 4 wt% of carbon nanotubes (CNT) over Inconel 718 substrate. The objective is to study the effect of bimodality and reinforcements on mechanical and tribological behaviour of Al2O3 based thermal barrier coatings (TBC). Al2O3–ZrO2, Al2O3–ZrO2-CNT and micro-Al2O3 coatings named as AZ, AZC and μ-Al2O3, respectively. Presence of partially melted and solid-state sintered nanostructured region (NR) with fully melted and re-solidified microstructured regions (MR) showed bimodal microstructure. Reinforcements leads to enhance nano-hardness and plasticity index from (12.8 GPa, 0.12) for μ-Al2O3 to (14.7 GPa, 0.17) for MR of AZ and (14.1 GPa, 0.17) for AZC, which is attributed to higher amount of α-Al2O3 and t-ZrO2 present after coating deposition. Nanostructured regions reduce shear stress generation under 9.8 N load during fretting wear in AZ (293.8 MPa) and AZC (298.7 MPa), resulting in a more uniform surface and reduced wear rate. Additionally, the higher aspect ratio and lubrication effect of CNTs in AZC generates least energy dissipation (92.9 J) and wear rate (0.9 × 10−6 mm3N−1m−1). SEM and EDS analysis of worn surfaces in coatings and counter body revealed abrasive, adhesive wear is dominant in μ-Al2O3 than AZ and AZC coatings due to presence of larger wear debris and more material transfer from coating to Si3N4 body than AZ and AZC. Overall, the synergistic effect of bimodality and reinforcements leads to improved mechanical property, and reduced energy dissipation and shear stress generation during wear that makes APS-AZC coating a potential material for wear and high temperature environment.

Transmission Characteristics and Spatial Coherence of Partially Coherent Light-Emitting Diode Array in the Ocean

Underwater LED light sources are commonly implemented in array configurations with a wide-angle field of view, primarily catering to high-speed communication within a few meters. To increase transmission distance and mitigate oceanic turbulence effects, this paper focuses on the spatial coherence analysis of narrow-beam partially coherent light-emitting diode (PCLED) arrays, examining their average light intensity distribution, beam width, and spatial coherence during oceanic transmission. Based on the extended Huygens–Fresnel integral, the optical field models and spatial characteristics of the radial PCLED array are derived under oceanic conditions, considering parameters such as water attenuation coefficient, kinetic energy dissipation rate, temperature dissipation rate, temperature-to-salinity ratio, as well as the radial filling factor and the sub-beam spatial coherence length of the light source at different transmission distances. The simulations show that, as the spatial coherence length of the sub-beam decreases from hundreds to a few micrometers, the combining distance of the beam arrays also decreases. This reduction in coherence results in the average light intensity distribution degrading into a Gaussian-like distribution, with a significant five-fold decrease in peak intensity. Furthermore, the width of the array spreads, starting from distances of 7 m and 0 m, respectively. The radial PCLED beam array, with its sub-beam spatial coherence length inside micrometers, possesses inherent characteristics that suppress turbulence effects and has future extensive possibilities in the ocean.

Summer bottom oxygen depletion dynamics and the associated physical structure in the Bohai Sea

Summertime oxygen depletion has been more and more frequently observed in the bottom water of the Bohai Sea in the last decade. Based on comprehensive hydrography and microstructure measurements in summer in the Bohai Sea, the physical structure and bottom dissolved oxygen (DO) dynamics were investigated. The study area is characterized by strong tidal currents and obvious horizontal temperature and DO gradients in the bottom boundary layer. The strong tidal forcing induces large near-bottom turbulent kinetic energy dissipation rates (ϵ ~ 5 × 10-5 W kg-1) which can be well parameterized by the law of the wall. Tidal horizontal advection effects dominate the short-term variations of bottom hydrography. Although the residual current is in a near-perpendicular direction with the horizontal DO gradient (~94°), the horizontal residual DO transport was calculated to be 67.4 mg m-2 d-1 which is ~ 33% of the magnitude of sediment oxygen demand. During the observation period, we observed an intense high-turbidity event leading to a severe drawdown of near-bottom DO concentration (0.16 mg L-1) in 1.5 hours. The DO consumption rate due to this event was then estimated to be ~ 33.3 g m-2 d-1 (1.39 g m-2 h-1) which is two orders of magnitude larger than the sediment oxygen demand. Rapid DO consumption can be induced by the great increase in bioavailable surface area in bottom water and seabed when benthic organic matter is resuspended. This process should be incorporated into the coupled physical-biogeochemical model to improve accuracy in simulating DO depletion.

Backscatter in energetically-constrained Leith parameterizations

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.

Study of the Failure Mechanism of Soft Rock Mining Roadways Based on Limit Analysis Theory

To study the deformation and failure mechanisms of soft rock mining roadways, the 1506 return airway of Anyang Coal Mine is taken as the engineering background. Based on limit analysis theory, a failure model based on a rigid slider system is constructed to assess the failure of the soft rock surrounding a roadway. The formulas for calculating the self-weight power of the slider in the velocity discontinuity line of the rock surrounding the roadway, the work power of the surrounding rock pressure, and the energy dissipation rate of the velocity discontinuity line are derived, and the upper limit objective function of the velocity discontinuity line height is obtained. The failure characteristics and fracture evolution process of the surrounding rock under different mining stresses are analyzed by means of physical similarity simulations. The simulation results show that shear failure occurs first on the roadway side due to stress concentration. The fissures expand along the bottom angle of the roadway to the blind support area and the low-intensity support area. The cracks weaken the support strength of the angled anchor cable and bolt in the roadway shoulder. Under the action of roof pressure, the status of the rock mass inside and outside the shear slip zone changes from static to dynamic. This causes deformation and failure of the roadway roof, side, and floor.

The influence of bandwidth on the energetics of intermediate to deep water laboratory breaking waves

An experimental investigation of two-dimensional dispersively focused laboratory breaking waves is presented. We describe the bandwidth effect on breaking wave energetics, including spectral energy evolution, characteristic group velocity, energy dissipation and its rate, and breaking strength parameter, $b$ . To evaluate the role of bandwidth, three definitions of wave group steepness are adopted where $S_s$ and $S_n$ are bandwidth-dependent and $S_p$ remains constant when bandwidth is changed. Our data show two regimes of spectral energy evolution in breaking wave groups, with both regimes bandwidth-dependent: energy dissipation and gain occur at $f > 0.95f_p$ ( $f_p$ is the peak frequency) and $f < 0.95f_p$ , respectively. The characteristic group velocity, which is used in energy dissipation calculations, increases by up to 7 % after wave breaking, being larger for higher bandwidth breaking waves. An unambiguous bandwidth dependence is found between $S_p$ and both the fractional and absolute wave energy dissipation. Wave groups of larger bandwidth break at a lower value of $S_p$ and consequently lose relatively more energy. The energy dissipation rate depends on the breaking duration which itself is bandwidth dependent. Consequently, no clear bandwidth effect is observed in energy dissipation rate when compared with either $S_p$ or $S_s$ . However, there is a systematic bandwidth dependence in the variation of $b$ when parameterised in terms of $S_p$ , with their relationship becoming increasingly nonlinear as bandwidth increases. When parameterised with $S_s$ , $b$ shows a markedly reduced bandwidth dependence. Finally, the numerical breaking onset and relationship between $b$ and $S_s$ in the numerical study of Derakhti & Kirby (J. Fluid Mech., vol. 790, 2016, pp. 553–581) is validated experimentally.

Study on the influencing parameters of rough-strip energy dissipators of curved spillways based on orthogonal tests and numerical simulation

Abstract Rough-strip energy dissipators (R-SEDs) can be arranged at the bend bottom of curved spillways to dissipate energy and divert flow for bend flow. Using the entropy weight and TOPSIS methods, a multi-criteria evaluation system was established for comprehensive energy dissipation and flow diversion effects of R-SEDs. Orthogonal tests and numerical simulation were conducted to analyze factors affecting these effects (average R-SED height, R-SED angle, R-SED spacing, bend width, bend centerline radius and discharge flow rate). It was found that bend width and bend centerline radius significantly affected R-SEDs' energy dissipation effects. Average R-SED height, R-SED spacing and bend centerline radius significantly affected R-SEDs' flow diversion effects. Bend width, average R-SED height and bend centerline radius significantly affected R-SEDs' combined effects of energy dissipation and flow diversion. Their energy dissipation effects were larger than the flow diversion effects. R-SEDs can effectively alleviate adverse hydraulic phenomena in curved spillways. With the recommended parameters, R-SEDs showed the best performance, with the energy dissipation rate increasing by 18.67% and the water surface superelevation coefficient decreasing by 26.14%. The accuracy of the multi-criteria evaluation system was verified. This study can provide a reference for the R-SED design of similar curved spillways.

Turbulent kinetic energy dissipation rate in the lower troposphere using the 205 MHz radar at Kochi, India

The Stratosphere–Troposphere (S–T) radar at Kochi (10.04° N, 76.33° E), India is the first radar operating at 205 MHz. At this location, the atmospheric background parameters such as atmospheric wind, temperature, and humidity show distinct changes from monsoon to winter season in the lower atmosphere. The general wind patterns differ significantly during different seasons, giving rise to differences in the characteristics of atmospheric turbulence parameters. S–T radar estimates of the Turbulence Kinetic Energy dissipation rate (ɛ) from ∼0.35–5 km for 722 days (2017–2019) are presented in this study to explain the seasonal variability of turbulence in terms of the background atmospheric conditions. Doppler spectral width measurements made by the S–T Radar are utilized to estimate ɛ. Non-turbulent contributions to the spectral broadening are calculated and separated from the observed spectral width before estimating ɛ. Turbulence in the planetary boundary layer is stronger and it generally decreases with height. Turbulence is highest during the monsoon season and lowest during winter. Under strong wind conditions, turbulence is stronger, and it is highly variable under weak wind conditions. Stronger turbulence is observed during monsoon season and is associated with higher wind speeds.

Impacts of Biomimetic Mangrove Structures on Wave Attenuation in Kuala Sepetang, Perak

Biomimicry is introduced as an approach to develop an ecologically-informed design solution. The study proposes a regenerative design solution through hydrodynamic effects of the complex mangrove roots system that is applied to a biomimetic structural column design, with consideration on interactions between root porosity, water flows, and sediment transportation. Sangga Besar River, Perak is chosen as the key parameters of the flow. The roots are modelled with a circular array of cylinders (patch) with different porosities and varying spacing ratios. 15 patches are derived from 3 main sets where each set consisted of five patches with varying porosities. The simulation of each case to understand the impacts of different patch porosity on the flow structure is carried out using Ansys Fluent Student Version 2021. The study found that turbulence is impacted, but not directly proportional to the patch porosity where there could be an optimal porosity of the patch that generates maximum yield of turbulent kinetic energy dissipation rate with minimum sediment erosion for the onset of sediment deposition. The patch with φ=40% has the highest turbulence dissipation rate which relatively coherent with the range of porosity that would likely be encountered in natural mangrove ecosystem.

CFD simulation of an axial discharge rotor-stator mixer: LES versus RANS predictions

The large eddy simulation (LES) technique is used to model the turbulent flow of water in a two-stage, axial discharge, in-line rotor-stator mixer. The WALE sub-grid scale model is employed, and the resulting filtered velocity field is ensemble averaged to predict the mean velocity, turbulent kinetic energy, energy dissipation rate, and energy production rate. The results of these 3-D sliding mesh simulations are compared to analogous RANS predictions on similar meshes using the realizable k-ε turbulence model. Stator slot flow rate and rotor torque/power draw are also monitored. RANS and LES predict similar mean velocity profiles, flow rate and rotor torque. LES predicts higher turbulent kinetic energy, but lower dissipation rate compared to RANS. Results from a coarse and refined computational mesh are compared to discuss the significance of resolving smaller scales for LES. The effect of operating conditions on throughput, power draw, and other quantities of practical utility are also discussed. It was found that prediction of macroscopic quantities such as flow rate and power draw can be done efficiently using either RANS or LES on a relatively course mesh while capturing turbulence quantities requires a well refined LES simulation.

I‐beam to RHS‐column joints with welded studs under cyclic loading

AbstractThe design of removable beam‐column joints between open structural steel beams and rectangular hollow section (RHS) columns is not easy because of the inaccessibility to the tube interior from outside. I‐beam to RHS‐column joints with threaded welded studs are of great interest due to their low‐cost assembling technique and easy on‐site execution. This study examines the cyclic performance of these joints with welded studs. A quasi‐static experimental study on the cyclic response of eight joint specimens is described. The strength of the joint and the failure modes were revealed. The ductility of the joints was also evaluated according to the rotation capacity after yielding, classifying all of them as having intermediate ductility and, therefore, implying some capacity to withstand limited plastic deformations when subjected to seismic forces. Some equations were also used to classify the joints according to the components that mainly govern the deformation of the full joint. In addition, the energy dissipation rate was assessed for all the specimens, finding the highest energy dissipation rates in the most rigid joints.

WAVE TRANSMISSION OVER A WIDE NEARSHORE REEF

As a shoreline erosion mitigation measure, nearshore reefs have attracted increasing attention. Nearshore reefs are wide submerged porous structures with mild natural slopes constructed in shallow nearshore waters. These reefs mitigate shoreline erosion by managing wave energy through a variety of wave transformation processes (e.g., refraction and energy dissipation through breaking and internal turbulence and friction). Wave attenuation over solid impermeable structures have been widely studied (e.g., Gurley 1994; Chella et al., 2015; Lowe et al., 2022). On the other hand, details of wave transformation over wide porous reef structures and the corresponding rate of wave energy dissipation are yet to be understood. The goal of this study is to develop a better understanding of how waves interact with porous nearshore reefs using Computational Fluid Dynamics (CFD).

Scaling the Bubble Penetration Depth in the Ocean

AbstractBubble plume penetration depths have been identified as a key parameter linking subsurface turbulent kinetic energy (TKE) dissipation rates and whitecaps. From data collected in the Atlantic sector of the Southern Ocean, nominally 50°S 40°W, bubble plume penetration depths were estimated from Acoustic Doppler Current Profiler measurements of the acoustic backscatter anomaly. Bubble presence at depth was corroborated using independent measurements of optical scattering. Here, an effective wavelength, observations of significant wave height and atmospheric forcing were used to scale penetration depths of breaking waves under open ocean conditions. The parameterization was developed assuming a correlation between the observed penetration depth and an estimate of the TKE dissipation rate enhancement under breaking waves. The effective wavelength was defined from the effective phase speed based on a momentum and energy balance across the atmospheric wave boundary layer and was considered to be the largest actively wind‐coupled wave and representative of large‐scale breaking for wave ages ranging from 15 to 35 (i.e., 15 ≤ 〈cp/u*〉 ≤ 35). This yields a dimensional penetration depth parameterization in terms of inverse wave age and the length scales under consideration. The parameterization captures the bubble plume penetration depth with stronger forcing leading to deeper injections, reaching up to 9 m. Both length scales are effective at defining the depth of a wave‐affected layer in terms of bubble presence with the effective wavelength better collapsing the data under mixed conditions with deeper plumes associated to larger fractional whitecap coverage.

New Equations for Rate of Energy Dissipation of a Stepped Spillway with Slope less than Critical and Specific Step Height

Stepped spillways disperse energy in floodwater by utilizing their stepping nature. Several researchers investigated the hydraulic and geometric relationships of the stepped spillway with a dam slope above 26.6o, which resulted in energy dissipation. But a few studied stepped spillways with a dam slope of 26.6o with a step height of 0.61 m. This move led to a lack of knowledge and rules for the designers of stepped spillways with slope of 26.6o and a step height of 0.61 m. The authors reviewed the researchers' publications on horizontal stepped spillways with dam slopes of 26.6o with step height of 0.61 m conducted in transition and skimming flows in large-size facilities with phase-detection intrusive probes. They retrieved data sets from them, which they took into account to create two novel equations for energy dissipation in stepped spillways: one for nappe flow and one for skimming flow. The results showed that the measured data sets compared well with the data sets calculated from the two empirical models.

DAMPING OF FINITE AMPLITUDE SOLITARY WAVES IN A FLUME

Solitary wave is a permanent wave when the dissipation is ignored. Many analytical solutions have been developed for finite amplitude solitary waves. In additional to the perturbation solutions, closed form solutions are also available (e.g., McCowan 1891, Clamond and Fructus 2003, being denoted as CF from hereon), which are more accuracy, especially for larger amplitude solitary waves which were discussed in Wang and Liu (2022). In Wang and Liu (2022) ’s laboratory experiments, solitary waves are slowly damped along the wave flume, which can be attributed to the energy dissipation inside the boundary layers on the bottom and sidewalls. Keulegan (1948) first derived an approximate solution to describe the wave damping in the wave flume for small amplitude solitary wave. The basic idea of calculating the damping effect is that the rate of energy dissipation inside the boundary layers must be the same as the rate of wave energy loss. In this work, the same principle of energy balance is adopted for calculating the wave damping for finite amplitude solitary waves in a wave flume. The closed form solutions provided in CF are employed here for analyses.

Signature of transition in granular flow through apertures

We employ computations to examine transition in granular flow, right above an aperture, in a silo draining under gravity. We show that the energy dissipation rate exhibits a well-defined peak near the aperture. Tracing locations of maximum dissipation rate describes an arch, signifying flow transition. We present a correlation between the transition boundary and outlet using the arguments of self-similarity and geometric similarity, suggesting the spatial non-monotonicity of the dissipation rate to be a signature of flow transition. Utilizing the aforementioned similarity criteria, we also explore the kinetic pressure as a marker of transition in granular flow.

THERMOPHYSICAL AND ENVIRONMENTAL ASSESSMENT OF NATURAL GAS UTILIZATION IN THE RECONSTRUCTION OF A PULVERIZED COAL-FIRED BOILER

Link for citation: Maltsev K.I., Gil A.V., Abramov N.V., Puzyrev S.A. Thermophysical and environmental assessment of natural gas utilization in the reconstruction of a pulverized coal-fired boiler. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 8, рр. 30-38 In Rus. The relevance of the investigation is caused by the need to assess the completeness of fuel combustion, harmful emissions, and temperature stress of the screen surfaces of a pulverized coal-fired boiler during its reconstruction for natural gas combustion. Currently, the conversion of solid fuel combustion installations to natural gas is highly relevant due to significantly lower emissions of carbon compounds. The main aim of this research is to study the physicochemical processes in the combustion chamber at various loads with flammable natural gas combustion and evaluate the effectiveness of combustion organization during the reconstruction of a pulverized coal-fired boiler. Objects: combustion chamber of a boiler unit with a steam capacity of 210 t/h, burners, parameters of the combustion chamber environment Methods: comparison of results obtained from analytical thermal calculations and numerical modeling. The numerical simulation of gas flare combustion was performed using the ANSYS Fluent software package. Reynolds Averaged Navier–Stokes approaches based on averaging the Navier–Stokes equations over the Reynolds number with additional equations for the turbulent kinetic energy k and the rate of turbulent kinetic energy dissipation ε were applied to describe the turbulent flow. Results. A numerical study of the physicochemical processes in the combustion chamber of a boiler unit was conducted after its reconstruction for natural gas combustion. Dependencies of temperature level changes, hydrodynamics, and concentrations of combustion products components in the volume of the combustion chamber at various loads were obtained. It was found that high-temperature combustion products are redistributed towards the front and rear walls, resulting in the formation of zones in the wall layer with a significant temperature gradient. The nozzles of the tertiary air contribute to the reduction of nitrogen oxide emissions in the combustion chamber by suppressing their formation due to oxygen deficiency in the combustion zone, as well as by lowering the temperature of the flame in the oxidizing zone.

Influence of interface inclination angle and load impact velocity on dynamic splitting tensile behavior and dissipated energy of geopolymer-concrete composites

The application of geopolymer has great potential in repairing damaged concrete. In engineering construction, the repaired structure is often affected by dynamic loading. Experimental research on the dynamic mechanical behavior and energy dissipation of geopolymer-concrete composites (GCC) is of great significance for understanding the bonding performance between geopolymer and concrete. In this paper, dynamic splitting experiment was performed on GCC under different interface inclination angles and load impact velocities by using the split Hopkinson pressure bar (SHPB). Then, the influence of interface inclination angle and load impact velocity on dynamic splitting tensile behavior and dissipated energy of GCC were discussed. Finally, the failure modes and strain field were analyzed based on digital image correlation (DIC) technique. The results indicate that the static peak load of GCC is roughly distributed around 26.0 kN and the dynamic peak load is 263.0 kN. The dynamic peak load measured by GCC is more than 10 times the static peak load. As the interface inclination angle increases from 0° to 90°, the dynamic peak load, static peak load and energy dissipation rate increase linearly, while the tensile sensitivity coefficient decreases. The energy dissipation ratio of GCC is kept between 0.30 and 0.40. In addition, the dynamic peak load, tensile sensitivity coefficient and dissipated energy increase gradually as the load impact velocity increases. A transition from interface failure to tensile failure can be found in GCC with the inclination angle increases.

Image‐based measurement of engulfment vortex to quantitatively assess micromixing efficiency in a gas–liquid stirred tank

AbstractMicromixing in reactors is typically characterized by chemical test reactions. A novel image‐based measurement system of engulfment vortex (IMEV system) is developed to assess the micromixing efficiency. Over 2000 vortices were recognized from images captured under various experimental cases, and key frames for their formation, engulfment and dissipation were identified. Inspired by the engulfment model (i.e., E model), this work quantified the micromixing time and local turbulent energy dissipation rate with the vortex lifetimes. The micromixing time obtained through the IMEV method is comparable to its value estimated by the micromixing model and segregation index of the test reaction, with a deviation of less than 20%. In turbulent gas–liquid systems, bubbles play a dual role on the local micromixing due to frequent disturbance and phase interface limitation. To summarize, this work offers an alternative approach for micromixing studies and provides valuable insights into dispersed phase effects on the micromixing efficiency.

The energy dissipation property in bioinspired staggered composites with the viscoelastic matrix

Many biological materials, such as bone and nacre, exhibit remarkable combinations of stiffness, strength, toughness, and impact resistance over millions of years of evolution. They provide prototypes for designing high-performance artificial composites. However, the dynamic properties of biological materials under impact loading are still not clear. In this study, we establish a dynamic shear-lag model to explore the dynamic response and the energy dissipation capacity of bioinspired staggered composites with a viscoelastic matrix under impact loading. The time domain solution of the dynamic shear-lag model is derived. Then, the model is verified by comparing it with the results from the finite element method. The results demonstrate that matrix viscosity plays a significant role in dissipating the impact energy and enhances the wave transformation between adjacent tablets. Furthermore, there exists an optimal viscosity coefficient to achieve an excellent balance between the rate and efficiency of energy dissipation. The model and the results can not only reveal the energy dissipation property of biological materials but also provide guidelines for the design and optimization of high-performance composites.