Dissipation Profiles Research Articles

An efficient numerical solver for highly compliant slender structures in waves: Application to marine vegetation

This paper presents a fully explicit coupled wave–vegetation interaction model capable of efficiently solving the coupled wave dynamics and flexible vegetation motion with large deflections. The flow model is formulated using the continuity equation and linearized momentum equations of an incompressible fluid, with additional terms within the canopy region accounting for the presence of vegetation. This linearized flow solver is unconditionally stable and second-order accurate. The flow model is validated and verified against experimental measurements and analytical solutions for waves over a rigid canopy, demonstrating its capability to accurately capture the wave dissipation and flow velocity profiles, even with a relatively coarse grid. A truss-spring model is proposed to capture vegetation motion with substantial deflections, and is proven to be mathematically consistent with the governing equation for the flexible vegetation motion. It allows for explicit time integration with large time steps when dealing with highly compliant vegetation. The truss-spring model is validated and verified by experimental and numerical results for large-amplitude motions of a single elastic blade subjected to waves and sinusoidal oscillatory flows. The coupled model, combining the linearized flow solver and the truss-spring model, is applied to investigate wave propagating over a heterogeneous, suspended, and flexible canopy, showing high efficiency and good agreement with the experiments concerning wave attenuation and the hydrodynamic loads on the vegetation.

Minimum mass-entransy dissipation profile for one-way isothermal diffusive mass-transfer process with mass-resistance and mass-leakage

Minimum mass-entransy dissipation profile for one-way isothermal diffusive mass-transfer process with mass-resistance and mass-leakage

Joint-mode diffusion analysis of discontinuous Galerkin methods: Towards superior dissipation estimates for nonlinear problems and implicit LES

We present a new linear eigensolution analysis technique that provides superior estimates of dissipation distribution in wavenumber space for the discontinuous Galerkin (DG) method. The technique builds upon traditional dispersion-diffusion analyses that have been applied to spectral/hp element methods, but in particular is an improvement upon the non-modal eigenanalysis approach proposed by Fernandez et al. in [1]. The present technique takes into account the indirect effects that dispersion may have on dissipation, as recently discussed by Moura et al. in [2], in order to better represent dissipation itself. Also, a concept often used with dynamic mode decomposition (DMD) techniques is invoked to weight the relative contribution of the multiple diffusion curves that stem from temporal eigenanalysis. This allows for obtaining a single dissipation profile in wavenumber space, so that the proposed technique is named joint-mode analysis. Although the non-modal approach also provides a single diffusion curve, the joint-mode dissipation curve is shown to correlate significantly better with the energy spectrum of Burgers' turbulence at large and intermediate scales, which is particularly relevant for implicit large-eddy simulation (LES). The proposed technique is readily extensible to other spectral/hp element methods.

Ultralight, Robust, Thermal Insulating Silica Nanolace Aerogels Derived from Pickering Emulsion Templates.

Synthesis of silica aerogel insulators with ultralight weight and strong mechanical properties using a simplified technique remains challenging for functional soft materials. This study introduces a promising method for the fabrication of mechanically reinforced ultralight silica aerogels by employing attractive silica nanolace (ASNLs)-armored Pickering emulsion templates. For this, silica nanolaces (SiNLs) are fabricated by surrounding a cellulose nanofiber with necklace-shaped silica nanospheres. In order to achieve amphiphilicity, which is crucial for the stabilization of oil-in-water Pickering emulsions, hydrophobic alkyl chains and hydrophilic amine groups are grafted onto the surface of SiNLs by silica coupling reactions. Freeze-drying of ASNLs-armored Pickering emulsions has established a new type of aerogel system. The ASNLs-supported mesoporous aerogel shows 3-fold greater compressive strength, 4-fold reduced heat transfer, and a swift heat dissipation profile compared to that of the bare ASNL aerogel. Additionally, the ASNL aerogel achieves an ultralow density of 8 mg cm-3, attributed to the pore architecture generated from closely jammed emulsion drops. These results show the potential of the ASNL aerogel system, which is ultralight, mechanically stable, and thermally insulating and could be used in building services, energy-saving technologies, and the aerospace industry.

Multi-objective reduced-order design optimization of single-phase liquid coolers for electronics

Thermal management using liquid cooled cold plates is a key enabler in modern electronic systems such as power converters and multi-chip arrays. Traditional cold plate designs are limited in their ability to handle the heterogeneous heat profiles in ever-larger modern multi-chip arrays requiring design optimization. This work demonstrates a design optimization method for liquid-cooled cold plates subjected to discrete heat dissipation profiles. We used reduced order performance modeling enabled by splitting the heat sink geometry onto a coarse grid with up to 50 elements each assigned with a simplified flow block such as a straight, elbow, or tee section. Correlations for thermal-fluidic performance metrics were used to obtain the pressure drop and surface temperature. Multi-objective design optimization focused on minimizing the pressure drop and temperature was broken down into layout and geometry optimization sub-steps. Layout optimization found the optimal flow path from inlet to outlet using a novel optimal path search method combining pathfinding algorithms with search on a random population. Geometry optimization solved for the dimensions of the coarse grid elements and the corresponding flow blocks using gradient based optimizers. We experimentally tested an aluminum water-cooled heat sink design generated by the reduced order optimization demonstrating a thermal resistance of 0.065 K/W. We compared the performance of our optimal designs with conventional and topology optimized cold plate designs to benchmark performance, computational cost, and computational time. Topology optimized designs showed a 22% reduction in average heated surface temperature for similar pressure drops. However, the computation time required to generate the topology optimized design was more than one order of magnitude higher than the reduced order method, requiring over 3,600 s to generate the optimal design. Our reduced order optimization in comparison provides optimal designs at computational timescales of 60 s.

Dissipation profile and risk assessment of diflubenzuron and novaluron in tomato fruits under greenhouse conditions

Dissipation profile and risk assessment of diflubenzuron and novaluron in tomato fruits under greenhouse conditions

Modelling smear effect of vertical drains using a diameter reduction method

Vertical drains are used to accelerate consolidation of clays in ground improvement projects. Smear zones exist around these drains, where permeability is reduced due to soil disturbance caused by the installation process. Hansbo solution is widely used in practice to consider the effects of drain discharge capacity and smear on the consolidation process. In this study, a computationally efficient diameter reduction method (DRM) obtained from the Hansbo solution is proposed to consider the smear effect without the need to model the smear zone physically. Validated by analytical and numerical results, a diameter reduction factor is analytically derived to reduce the diameter of the drain, while achieving similar solutions of pore pressure dissipation profile as the classical full model of the smear zone and drain. With the DRM, the excess pore pressure u obtained from the reduced drain in the original undisturbed soil zone is accurate enough for practical applications in numerical models. Such performance of DRM is independent of soil material property. Results also show equally accurate performance of DRM under conditions of multi-layered soils and coupled radial-vertical groundwater flow.

A scenario framework for electricity grid using Generative Adversarial Networks

This study proposes a synthetic data framework to decrease the cost of smart metering. It offers clustering of real-time buses based on their electricity consumption levels and synthetic data generated by Generative Adversarial Networks (GANs) to provide sufficient information and data in grid modeling. GANs can be used to predict the electrical dissipation profiles of buses and their total energy consumption since they replicate the distributional features of the recorded data. This study is expected to facilitate energy distribution companies and grid operators in the progress of efficient and intellectual modeling of smart grids by stimulating the bottom-up contribution of end-users. It aims to decrease the data collection cost while allowing realistic scenarios. Furthermore, it introduces a new metric to measure the accuracy of the GANs and illustrates some empirical analysis using single consumer data.

Striped Jets in Post–Neutron Star Merger Systems

Models invoking magnetic reconnection as the particle acceleration mechanism within relativistic jets often adopt a gradual energy dissipation profile within the jet. However, such a profile has yet to be reproduced in first-principles simulations. Here we perform a suite of 3D general relativistic magnetohydrodynamic simulations of post–neutron star merger disks with an initially purely toroidal magnetic field. We explore the variations in both the microphysics (e.g., nuclear recombination, neutrino emission) and system parameters (e.g, disk mass). In all of our simulations, we find the formation of magnetically striped jets. The stripes result from the reversals in the poloidal magnetic flux polarity generated in the accretion disk. The simulations display large variations in the distributions of stripe duration, τ, and power, 〈P Φ〉. We find that more massive disks produce more powerful stripes, the most powerful of which reaches 〈P Φ〉 ∼ 1049 erg s−1 at τ ∼ 20 ms. The power and variability that result from the magnetic reconnection of the stripes agree with those inferred in short-duration gamma-ray bursts. We find that the dissipation profile of the cumulative energy is roughly a power law in both radial distance, z, and τ, with a slope in the range of ∼1.7–3; more massive disks display larger slopes.

Self-centric cyclic resistance of reinforced concrete shear wall with Shape Memory Alloy: Numerical and experimental large-scale model

Over several decades, numerous researches have been routed to forge ahead in enhancing the building performance against dynamic loads. Nowadays, smart materials such as Shape Memory Alloy (SMA) have found profound impact in many applications of civil engineering. Nickel titanium alloy (NiTi) is one of the most famous among types of SMA. The current paper studies the behavior of shear wall, representing one of the most efficient lateral bracing element, structured by NiTi subjected to cyclic loading. Due to the unique characteristics of NiTi particularly in capacity to restore its original shape after unloading, the improvement in shear wall displacement recovery, wall ductility, hysteric behavior and inter-story drift ratio is presented. For this purpose, experiment study on large scale shear walls with aspect ratio 1.9 is conducted to investigate the effect of the intensity of NiTi on cyclic response. Two ordinary walls, as reference structures, and two hybrid walls are set up in order to perform the study. In addition, the validation of numerical simulation is examined by comparing its results with that obtained by the experiments and a pretty much in agreement is found. Hence, three-dimensional modeling by mean of ANSYS19 is extended to study the effect of NiTi length throughout the wall height on the shear wall response. The results showed that the existing of NiTi controls the cracks propagation and confines the majority in the lower third of the wall. Furthermore, for NiTi-wall, the study showed remarkable enhancement in recover capacity by 77 % and significantly increase in drift capacity ratio by 16.5 % relies on the NiTi ratio. Besides, some significant observations like the profile of wall curvature and energy dissipation are analyzed in this paper.

Connecting the early afterglow to the prompt GRB and the central engine in the striped jet model

ABSTRACT Despite a generally accepted framework for describing the gamma-ray burst (GRB) afterglows, the nature of the compact object at the central engine and the mechanism behind the prompt emission remain debated. The striped jet model is a promising venue to connect the various GRB stages since it gives a robust prediction for the relation of jet bulk acceleration, magnetization, and dissipation profile as a function of distance. Here, we use the constraints of the magnetization and bulk Lorentz of the jet flow at the large scales, where the jet starts interacting with the ambient gas in a large sample of bursts to (i) test the striped jet model for the GRB flow and (ii) study its predictions for the prompt emission and the constraints on the nature of the central engine. We find that the peak of the photospheric component of the emission predicted by the model is in agreement with the observed prompt emission spectra in the majority of the bursts in our sample, with a radiative efficiency of about 10 per cent. Furthermore, we adopt two different approaches to correlate the peak energies of the bursts with the type of central engine to find that more bursts are compatible with a neutron star central engine compared to a black hole one. Lastly, we conclude that the model favours broader distribution of stripe length-scales which results in a more gradual dissipation profile in comparison to the case, where the jet stripes are characterized by a single length-scale.

Dissipation-optimized proper orthogonal decomposition

We present a formalism for dissipation-optimized decomposition of the strain rate tensor (SRT) of turbulent flow data using Proper Orthogonal Decomposition (POD). The formalism includes a novel inverse spectral SRT operator allowing the mapping of the resulting SRT modes to corresponding velocity fields, which enables a complete dissipation-optimized reconstruction of the velocity field. Flow data snapshots are obtained from a direct numerical simulation of a turbulent channel flow with friction Reynolds number Reτ=390. The lowest dissipation-optimized POD (d-POD) modes are compared to the lowest conventional turbulent kinetic energy (TKE)-optimized POD (e-POD) modes. The lowest d-POD modes show a richer small-scale structure, along with traces of the large-scale structure characteristic of e-POD modes, indicating that the former captures structures across a wider range of spatial scales. Profiles of both TKE and dissipation are reconstructed using both decompositions, and reconstruction convergences are compared in all cases. Both TKE and dissipation are reconstructed more efficiently in the dissipation-rich near-wall region using d-POD modes, and in the TKE-rich bulk using e-POD modes. Lower modes of either decomposition tend to contribute more to either reconstructed quantity. Separating each term into eigenvalues and factors relating to the inherent structures in each mode reveals that higher e-POD modes tend to encode more dissipative structures, whereas the structures encoded by d-POD modes have roughly constant inherent TKE content, supporting the hypothesis that structures encoded by d-POD modes tend to span a wide range of spatial scales.

Residues of the Acaricides Abamectin, Hexythiazox, and Spiromesifen in Eggplant (Solanum melongena L.) Fruits Grown under Field Conditions in Najran, Saudi Arabia

The dissipation profiles of the acaricides abamectin, hexythiazox, and spiromesifen in the fruits of eggplant (Solanum melongena L.) grown under field conditions in Najran, Saudi Arabia, were studied. Extraction was performed with acetonitrile, and UPLC-MS/MS was used for quantification. Instead of conventional adsorbents, a 2-fold dilution of the sample extract quickly and efficiently reduced interfering co-extracts and matrix effects. The method was successfully validated according to EU regulations. The limit of quantification was set at 5 µg/kg for hexythiazox and spiromesifen and 20 µg/kg for abamectin. The mean recoveries and relative standard deviations were 88.6–98.7% and 5.2–12.4%, respectively. The method precision was evaluated at the LOQ level for each analyte and ranged from 6.7 to 15.7%, with good trueness (recovery) ranging from 85.7 to 97.2%. The matrix effect ranged from −2.2% to −4.6%, indicating negligible signal suppression. First-order kinetics were used to characterize the dissipation rates of abamectin, hexythiazox, and spiromesifen with half-lives (t1/2) of 2.11–2.42, 2.3–2.73, and 1.31–1.47 days, respectively, using the authorized and double authorized doses. Terminal residues were 0.028–0.331 mg/kg, 0.019–0.592 mg/kg, and 0.044–0.408 mg/kg, respectively, at 3, 7, and 10 days after the second treatment. According to the risk assessment results, the percentage of chronic dietary risk quotient was <100, meaning that abamectin, hexythiazox, and spiromesifen are not considered a risk to human health. The preharvest interval (PHI) should be 7, 7, and 3 days, respectively, if the authorized dose is used, and 10, 10, and 3 days, respectively, if double the authorized dose is used. The current study can be a helpful resource for the responsible and safe use of the tested acaricides on eggplant fruits.

Molecular Photothermal Effects on Time-Resolved IR Spectroscopy: Solute-Solvent Intermolecular Energy Transfer.

Time-resolved IR pump-probe (IR-PP) and two-dimensional IR (2D-IR) spectroscopy are valuable tools for studying ultrafast chemical and biological processes in solutions. However, the corresponding signals at long times are obscured by the molecular photothermal effects resulting from the heat dissipation of vibrationally photoexcited molecules to the surroundings. Recently, a phenomenology model was used to describe molecular photothermal effects on IR-PP signals and the diagonal and cross-peaks of 2D-IR spectra at long pump-probe delay times. Here, we consider the thermal diffusion equation with a time-dependent heat source term to describe the solute-solvent energy transfer process. An approximate solution to the nonhomogeneous differential equation shows that the molecular photothermal effect is determined by the mean intermolecular distance between IR-absorbing molecules. We show that the time profile of heat dissipation from a vibrationally excited molecule to the surroundings, which provides information about the mechanisms involved in the solute-solvent intermolecular energy transfer process in solutions, can be directly measured by analyzing the molecular photothermal IR-PP and 2D-IR signals. We anticipate that the present work can be used to interpret local heating-induced time-resolved IR spectroscopic signals and understand the rate of and the mechanisms involved in the conversion from high-frequency molecular vibrational energy to solvent kinetic energy in condensed phases.

Numerical modeling of heating tomato pulp in continuous flow microwave‐assisted thermal processing: Estimation of quality parameters

AbstractContinuous thermal treatment of tomato pulp aims for microbial and enzyme inactivation with minimal quality degradation. The objective of this work was to model the thermal treatment of tomato pulp flowing continuously inside a microwave cavity and a holding tube. The three‐dimensional model considers the Navier–Stokes, thermal energy conservation, Fourier's law of heat conduction, and Maxwell's equations of electromagnetism. The tomato pulp was pseudoplastic, and the phase change during heating was considered using an equivalent specific heat capacity. The model calculated the effect of diameter of the applicator tube (Dt), volumetric flow rate (), and processing temperature () on Bacillus coagulans inactivation, lycopene and color degradation, and furan formation for a thermal treatment sufficient to reduce six logarithmic cycles of the spoilage microorganism. The results revealed that tomato pulp flowing in a tube with 38 mm diameter absorbed 98% of the electromagnetic power input. However, in terms of the food nutritional and sensory quality attributes, the better design parameter was the microwave system operating with a 42 mm diameter tube. Furthermore, the tomato pulp quality also was improved when the processing temperature increased from 100°C to 120°C (reduction of 77% of furan, and reduction of 88% and 90% of lycopene and color degradation, respectively), and in this process condition, the effect of the tube diameter on the quality attributes ceased to be important.Practical applicationsThis work presented a numerical simulation‐based study to enhance the microwave‐assisted thermal processing design for liquid foods. The mathematical tool developed here allows a detailed evaluation of the electromagnetic power dissipation and temperature profiles in the tomato pulp and how these parameters affect microbial inactivation and the food's nutritional and sensory quality attributes. These results contribute to understanding the microwave heating system and guide microwave equipment manufacturers. Furthermore, the model can be useful for optimizing and controlling microwave‐assisted pasteurization/sterilization processes.

Residue analysis and effect of preharvest forchlorfenuron (CPPU) application on quality formation of kiwifruit

Forchlorfenuron (CPPU) is widely used as a growth regulator in kiwifruit production to improve fruit yield. However, little is known about the dissipation profile of CPPU and the effect of pre-harvest CPPU treatment on fruit aroma formation during storage. Here, high (0.02 g L−1) and low (0.005 g L−1) dosages of CPPU were applied to ‘Biyu’ kiwifruit at twenty days after anthesis (DAA). The results revealed that 4-OH-CPPU was the main metabolite from CPPU and the 75 d after treatment is a key period for the conversion of CPPU into 4-OH-CPPU. Pre-harvest CPPU treatment reduced fruit hardness, respiratory rate, fatty acids, fatty-acid derived volatiles (FA-VOCs) and activities of ROS scavenging enzymes such as SOD, POD and CAT, but evidently increased the levels of malondialdehyde (MDA), hydrogen peroxide (H2O2), total soluble solids (TSS), some sugars and amino acids during storage, especially in fruit under high-dosage CPPU treatment. Therefore, we concluded that pre-harvest CPPU treatment might inhibit fatty acid biosynthesis, reduce membrane integrity and further decrease fruit storage ability and aroma quality, and therefore pre-harvest application of high-dose CPPU on kiwifruit is not recommended. These results would help to clarify the action mechanism of preharvest CPPU treatment on aroma formation and provide reference for the rational application of CPPU on kiwifruit.

Upper‐Ocean Turbulence Structure and Ocean‐Ice Drag Coefficient Estimates Using an Ascending Microstructure Profiler During the MOSAiC Drift

AbstractSea ice mediates the transfer of momentum, heat, and gas between the atmosphere and the ocean. However, the under‐ice boundary layer is not sufficiently constrained by observations. During the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), we collected profiles in the upper 50–80 m using a new ascending vertical microstructure profiler, resolving the turbulent structure within 1 m to the ice. We analyzed 167 dissipation rate profiles collected between February and mid‐September 2020, from 89°N to 79°30′N through the Amundsen Basin, Nansen Basin, Yermak Plateau, and Fram Strait. Measurements covered a broad range of forcing (0–15 m s−1 wind and 0–0.4 m s−1 drift speeds) and sea ice conditions (pack ice, thin ice, and leads). Dissipation rates varied by over 4 orders of magnitude from 10−9 W kg−1 below 40 m to above 10−5 W kg−1 at 1 m. Following wind events, layers with dissipation W kg−1 extended down to 20 m depth under pack ice. In leads in the central Arctic, turbulence was enhanced 2–10 times relative to thin ice profiles. Under‐ice dissipation profiles allowed us to estimate the boundary layer thickness (4 ± 2 m), and the friction velocity (1–15 mm s−1, 4.7 mm s−1 on average). A representative range of drag coefficient for the MOSAiC sampling site was estimated to (4–6) × 10−3, which is a typical value for Arctic floe observations. The average ratio of drift speed to wind speed was close to the free‐drift ratio of 2% with no clear seasonal or regional variability.

Assessment of machining performance parameters of nanofluid-based MQL-turning: An experimental analysis and CFD modelling

Nano-cutting fluids as a coolant are often used in modern days manufacturing industry. These nano-cutting fluids have certain advantages over conventional coolants in terms of heat transferability and lubricity. The present focused study investigates the machining performance in Minimum quantity lubrications (MQL) turning operation using MoO3/water nano-cutting fluid. The machining performance parameters (like friction coefficient, cutting forces, surface roughness and wear) are investigated experimentally using MoO3/water nano-cutting fluid. Also, a computational fluid dynamics (CFD) model was developed to investigate the heat dissipation and temperature profile at rake and flank surface of the carbide cutting tool. The experimental outcomes of the present study illustrate the enhancement in machining performance in terms of reduction in friction coefficient, cutting forces, surface roughness and wear. Heat transfer analysis and a numerical model based on the notion of a CFD tool were used to explore the temperature propagation along with the flank and rake surface of tungsten carbide cutting inserts in order to properly measure tool tip temperature while turning. The simulation study demonstrated the reduction in tool tip temperature at rake face from 1031 K to 824.98 K for the cutting fluid velocity of 25 m/s, while for 2 bar cutting fluid pressure the temperature at rake face reduces to 874.37 K.

Sobre la disipación de energía cinética turbulenta asociada con olas que aún no rompen

The turbulent kinetic energy dissipation is an essential quantity in the study of turbulence in fluids. In particular, on the transference of turbulent energy from large to small scales and determining its state of equilibrium and stationarity. This work has the purpose of understanding turbulence generation by non-breaking waves from turbulent kinetic energy dissipation analysis. Different groups of nonbreaking monochromatic waves with different slopes were mechanically constructed in a laboratory, whereby an acoustic device, the wave orbitals velocities were measure in various depths. Considering the inertial subrange in the power spectrum of components of turbulence velocity, a turbulent kinetic energy dissipation rate was quantified. It was detected that the magnitude of the turbulent kinetic energy dissipation rate increases with the wave slope and that deeper is invariant to axis rotations. It was distinguished that most of the profiles of the turbulent kinetic energy dissipation agree with an atypical logarithmic layer. Finally, a term of turbulence production was introduced, relative to nonbreaking wave orbital velocities. Unlike other turbulence production terms or approximations, it adequately reproduces the values of the turbulent kinetic energy dissipation rate regardless of wave slope, which established that the wave orbitals velocities shear is the generator mechanism of turbulence in a fluid under nonbreaking waves.

Stabilization of spatiotemporal dissipative solitons in multimode fiber lasers by external phase modulation

In this work, we introduce a method for the stabilization of spatiotemporal (ST) solitons. These solitons correspond to light bullets in multimode optical fiber lasers, energy-scalable waveguide oscillators and amplifiers, localized coherent patterns in Bose–Einstein condensates, etc. We show that a three-dimensional confinement potential, formed by a spatial transverse (radial) parabolic graded refractive index and dissipation profile, in combination with quadratic temporal phase modulation, may permit the generation of stable ST dissipative solitons. This corresponds to combining phase mode-locking with the distributed Kerr-lens mode-locking. Our study of the soliton characteristics and stability is based on analytical and numerical solutions of the generalized dissipative Gross–Pitaevskii equation. This approach could lead to higher energy (or condensate mass) harvesting in coherent spatio-temporal beam structures formed in multimode fiber lasers, waveguide oscillators, and weakly-dissipative Bose–Einstein condensates.