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The “flow” of electric currents and heat in standard metals is diffusive with electronic motion randomized by impurities. However, for ultraclean metals, electrons can flow like water with their flow being described by the equations of hydrodynamics. While theoretically postulated, this situation was highly elusive for decades. In the past decade, several experimental groups have found strong indications for this type of flow, especially in graphene-based devices. In this review, we give an overview of some of the recent key developments, on both the theoretical and experimental sides.

In this dissertation, I investigate the limits of the hydrodynamic approach to many-body systems. Due to the impracticality of solving equations of motion for individual particles, hydrodynamics provides an effective description, reducing complex systems to a few macroscopic variables, such as density, entropy, and velocity. However, the validity of hydrodynamic equations has to be carefully assessed when applied to small length scales comparable to the average interparticle distance. I explore this limitation by analyzing systems under extreme physical conditions in two scenarios.First, I study strongly coupled plasmas, where traditional hydrodynamic methods fail. In such plasmas, the electrostatic interaction is sufficiently strong to influence their equilibrium and out-of-equilibrium behavior. I use a variational approach to derive generalized hydrodynamic equations from first principles, where the effects of strong coupling are included using nonlocal terms. The obtained results are compared in the linear regime to numerical experiments, showing excellent agreement for a wide range of coupling strengths. This suggests exploring the developed framework for nonlinear problems and other long-range systems in the future. Second, I examine extreme bubble collapse when the bubble is surrounded by a compressible fluid. The goal is to evaluate the response of the compressible fluid when its motion reaches high Mach numbers. This is challenging to describe with existing numerical methods due to the presence of large gradients within the fluid. I implement a uniform density and pressure approximation inside the bubble, which allows for quick and accurate computations that include the effects of compressibility of the surrounding fluid. To check the accuracy of the created solver, I derive an asymptotic analytic benchmark for late stages of the collapse. This key limit was achieved in the simulations. The obtained results in the future can be coupled with molecular dynamic

As natural predators, owls fly with astonishing stealth due to the serrated feather morphology that produces advantageous flow characteristics. Traditionally, these serrations are tailored for airfoil edges with simple two-dimensional patterns, limiting their effect on noise reduction while negotiating tradeoffs in aerodynamic performance. Conversely, the intricately structured wings of cicadas have evolved for effective flapping, presenting a potential blueprint for alleviating these aerodynamic limitations. In this study, we formulate a synergistic design strategy that harmonizes noise suppression with aerodynamic efficiency by integrating the geometrical attributes of owl feathers and cicada forewings, culminating in a three-dimensional sinusoidal serration propeller topology that facilitates both silent and efficient flight. Experimental results show that our design yields a reduction in overall sound pressure levels by up to 5.5 dB and an increase in propulsive efficiency by over 20% compared to the current industry benchmark. Computational fluid dynamics simulations validate the efficacy of the bioinspired design in augmenting surface vorticity and suppressing noise generation across various flow regimes. This topology can advance the multifunctionality of aerodynamic surfaces for the development of quieter and more energy-saving aerial vehicles.

Aquest treball final d’estudis es basa en aprendre a fer l’anàlisi hidrodinàmic de carenes d’embarcacions submergibles per tal d’optimitzar la seva geometria i obtenir el disc d’estela. Per aconseguir-ho hi ha un procés d’aprenentatge que comença en entendre què és i com funciona un programa cad i un programa cae. Gran part d’aquest projecte ha estat invertit en estudiar les geometries dels submarins i en aprendre a utilitzar el software rhinoceros 7 (programa cad).L’altra part del treball ha estat invertit en adquirir coneixements del tdyn wind tunnel (programa cae) que és una eina que serveix per calcular, estudiar i simular fluids dinàmics cfd (computational fluid dynamics)

El riu Tormes al llarg del seu curs per la capçalera de la conca, des del seu naixement a la serra de Gredos fins l’embasament de San Fernando, té un règim de cabals molt variat, amb grans crescudes, avingudes ordinàries y durs estiatges. Això implica que estigui sotmès a episodis periòdics de gran mobilitat de sediments. Aquesta singularitat del riu Tormes en el seu tram alt és coneguda per l’administració competent que ha encarregat la realització d’un estudi per a la caracterització i estimació del transport sòlid amb origen a la llera que es produeix a la capçalera de la conca fins el embasament de San Fernando. Dintre de l’àmbit d’estudi mencionat es troba un delta interior de dimensions notables en la confluència del Tormes amb el seu tributari Corneja. Es creu que per la seva extensió pot causar una interferència amb la dinàmica del transport de sediments del Tormes, un riu de graves, i del Corneja, un riu de sorres. El present treball estudia el control que exerceix el delta sobre el subministrament de sediment cap a aigües avall mitjançant la modulació del transport sòlid procedent del Tormes i el Corneja. Desprès de realitzar l’estudi es va trobar que la forma en que interfereix el delta en el transport sòlid depèn dels cabals del Tormes i el Corneja. En condiciones de cabals ordinaris el delta actua com un embornal del cabal sòlid de fons provinent del Tormes, es a dir, que retè el material transportat pel Tormes des de aigües amunt. En canvi, amb cabals extraordinaris, en crescudes, actua com una font de material proporcionant sediment al tram d’aigües avall. Per altra banda, la interferència que causa el delta sobre el material transportat pel Corneja es molt menor. Únicament, en crescudes ordinàries en que el delta queda parcialment inundat retindria part de les fraccions granulomètriques més fines transportades pel Corneja., El río Tormes a lo largo de su curso por la cabecera de la cuenca, desde su nacimiento en la Sierra de Gredos hasta el embalse de San Fernando, tiene un régimen de caudales muy variado, con grandes crecidas, avenidas ordinarias y duros estiajes. Esto conlleva que esté sometido a episodios periódicos de gran movilidad de sedimentos. Esta singularidad del río Tormes en su tramo alto es conocida por la administración competente que ha encargado la realización de un estudio para la caracterización y estimación del transporte sólido con origen en el cauce que se produce en la cabecera de la cuenca hasta el embalse de San Fernando. Dentro del ámbito de estudio mencionado se halla un delta interior de dimensiones notables en la confluencia del Tormes con su tributario Corneja. Se cree que por su extensión el delta puede causar una interferencia en la dinámica del transporte de sedimentos del Tormes, un río de gravas, y del Corneja, un río de arenas. El presente trabajo estudia el control que ejerce el delta sobre el suministro de sedimento hacia aguas abajo a través de la modulación del transporte sólido procedente del Tormes y el Corneja. Tras realizar el estudio se encontró que la manera en que interfiere el delta en el transporte sólido depende de los caudales del Tormes y el Corneja. En condiciones de caudales ordinarios el delta actúa como un sumidero del caudal sólido de fondo proveniente del Tormes, es decir, que retiene el material transportado por el Tormes desde aguas arriba. En cambio, con caudales extraordinarios, en crecidas, actúa como una fuente de material proporcionando sedimentos al tramo de aguas abajo. Por otro lado, la interferencia que causa el delta sobre el material transportado por el Corneja es mucho menor. Únicamente, en crecidas ordinarias en que el delta queda parcialmente anegado retendría parte de las fracciones granulométricas más finas transportadas por el Corneja., The course of the Tormes River, from headwaters Sierra de Gredos down to the San Fernando reservoir, has a very varied flow regime, with large flood events, ordinary floods and severe low flows. As a result, the Tormes River is subjected to periodic high sediment mobility episodes. The singularity of the Tormes sediment transport regimen, especially in its uppermost reaches is well known by the water authority. This is the reason for CHD has commissioned a study to UPC aimed at characterizing and estimating the bed-load transport in those reaches from the headwaters down to the San Fernando reservoir (with a drainage area of 1500 km2, approximately). Within the aforementioned study reach, few kilometers upstream of the reservoir there is an inland delta of considerable size, in the order of 19 ha, at the confluence of the Tormes and one of its tributary, the Corneja River. It is believed that, due to the dimensions of the delta, may interfere with the sediment supplied from the upper Tormes, a gravel-bed river, and with that coming from the Corneja River, a sandy bed river. The present work studies the control exerted by the delta on sediment supply from Tormes and Corneja rivers to downstream reaches. The study has found the delta interferes with the sediment supplied from both Tormes and Corneja rivers depending on the flows conditions: magnitude and relative distribution. At ordinary flows conditions, the delta plays the role of a sink for bed-load transport from the Tormes, i.e. it contributes to stall sediment transport upper Tormes reaches. However, during extraordinary flows events, i.e. during floods, the delta exerts as a source for lower reaches, to which it interference is caused by the delta as far as the material supplied by the Corneja is concerned River: only at ordinary floods events, when the delta is just partially flooded, the delta contribute to accumulate part of the finer fractions transported by the Corneja.

©2024 American Physical Society., Wereveal and analyze an efficient magnetic dynamo action due to precession-driven hydrodynamic turbulence in the local model of a precessional flow, focusing on the kinematic stage of this dynamo. The growth rate of the magnetic field monotonically increases with the Poincaré number Po, characterizing precession strength, and the magnetic Prandtl number Pm, equal to the ratio of viscosity to resistivity, for the considered ranges of these parameters. The critical Poc for the dynamo onset decreases with increasing Pm. To understand the scale-byscale evolution (growth) of the precession dynamo and its driving processes, we perform spectral analysis by calculating the spectra of magnetic energy and of different terms in the induction equation in Fourier space. To this end, we decompose the velocity field of precession-driven turbulence into two-dimensional (2D) vortical and three-dimensional (3D) inertial wave modes. It is shown that the dynamo operates across a broad range of scales and exhibits a remarkable transition from a primarily vortex-driven regime at lower Po to a more complex regime at higher Po where it is driven jointly by vortices, inertial waves, and the shear of the background precessional f low. Vortices and shear drive the dynamo mostly at large scales comparable to the flow system size, and at intermediate scales, while at smaller scales it is mainly driven by inertial waves. This study can be important not only for understanding the magnetic dynamo action in precession-driven flows, but also in a general context of f lows where vortices emerge and govern the flow dynamics and evolution., This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No. 787544), Shota Rustaveli National Science Foundation of Georgia (SRNSFG) [Grant No. FR-23-1277] and EPSRC Grant No. EP/R014604/1. A.J.B. was funded by STFC Grants No. ST/S000275/1 and No. ST/W000873/1., Peer Reviewed, Postprint (author's final draft)

The development of quarries and underground mines is characterized by the need to expand their borders and resume the work of temporarily non-working sections of the countries, as well as maintain the capacity for ore production, the reduction of which is associated with a reduction in the active area of ore bodies. At the same time, work intensification is necessary, which is complicated by the limited size of the working area. Such complications can be largely compensated for by increasing the height of the exploding sill. At the same time, work intensification is necessary, which is complicated by the limited size of the working area. Such complications can be largely compensated for by increasing the height of the exploding sill. This is precisely the purpose of the present research, which was carried out by processing arrays of information that allows us to optimize this process. The study was carried out with machine processing of the information and change of the studied parameters.

The mass mortality event of the herbivorous sea urchin Diadema antillarum in 1983–1984 has been a major contributor to the diminished resilience of coral reefs throughout the Caribbean. The reduction in grazing pressure resulted in algae proliferation, which inhibited coral recruitment after disturbances such as disease, hurricanes, pollution and climatic change induced marine heat waves. Natural recovery of D. antillarum after the 1983–1984 die-off has been slow. However, the few locations with recovered populations exhibit signs of improvement in coral reef health, prompting interest in D. antillarum restoration. Current restoration strategies include translocation of wild individuals, the restocking of juveniles that are either cultured from gametes or collected as settlers and head-started in a nursery, and assisted natural recovery by providing suitable settlement substrate. Both the collection of wild settlers and assisted natural recovery necessitate an understanding of the local, spatiotemporal trends in settlement. In this study, which was carried out on the Dutch Caribbean Island of Saba, artificial turf settlement collectors were deployed at nine locations around the island and monitored from June 2019 till July 2020 (13 months). The primary objective was to identify trends in larval settlement in space and time, to be able to optimize restoration efforts. Additionally, the small size of Saba allowed us to deploy settlement collectors around the island and compare D. antillarum settlement between windward and leeward sides. Our study showed that on Saba, D. antillarum settlement peaked in June and July, following similar seasonal trends observed around other islands in the Northeastern Caribbean. By far the most settlement occurred at the leeward side of the island, suggesting that hydrodynamic forces entrained D. antillarum larvae in the lee of Saba and/or calmer waters facilitated settlement. Limited settlement occurred on the more exposed windward loca

Context. Traditional one-dimensional hydrostatic model atmospheres introduce systematic modelling errors into spectroscopic analyses of FGK-type stars. Aims. We present an updated version of the STAGGER-grid of three-dimensional model atmospheres, and explore the accuracy of postprocessing methods in preparation for spectral synthesis. Methods. New and old models were (re)computed following an updated workflow, including an updated opacity binning technique. Spectroscopic tests were performed in three-dimensional local thermodynamic equilibrium for a grid of 216 fictitious Fe I lines, spanning a wide range of oscillator strengths, excitation potentials, and central wavelengths, and eight model atmospheres that cover the stellar atmospheric parameter range (Teff, log g, and [Fe/H]) of FGK-type stars. Using this grid, the impact of vertical and horizontal resolutions, and temporal sampling of model atmospheres on spectroscopic diagnostics, was tested. Results. We find that downsampling the horizontal mesh from its original size of 240 × 240 grid cells to 80 × 80 cells, in other words, sampling every third grid cell, introduces minimal errors on the equivalent width and normalised line flux across the line and stellar parameter space. Regarding temporal sampling, we find that sampling ten statistically independent snapshots is sufficient to accurately model the shape of spectral line profiles. For equivalent widths, a subsample consisting of only two snapshots is sufficient, introducing an abundance error of less than 0.015 dex. Conclusions. We have computed 32 new model atmospheres and recomputed 116 old ones present in the original grid. The public release of the STAGGER-grid contains 243 models and the processed snapshots can be used to improve the accuracy of spectroscopic analyses.

System identification offers ways to obtain proper models describing a ship’s dynamics in real operational conditions but poses significant challenges, such as the multicollinearity and generality of the identified model. This paper proposes a new physics-informed ship manoeuvring model, where a deterministic semi-empirical rudder model has been added, to guide the identification towards a physically correct hydrodynamic model. This is an essential building block to distinguish the hydrodynamic modelling uncertainties from wind, waves, and currents – in real sea conditions – which is particularly important for ships with wind-assisted propulsion. In the physics-informed manoeuvring modelling framework, a systematical procedure is developed to establish various force/motion components within the manoeuvring system by inverse dynamics regression. The novel test case wind-powered pure car carrier (wPCC) assesses the physical correctness. First, a reference model, assumed to resemble the physically correct kinetics, is established via parameter identification on virtual captive tests. Then, the model tests are used to build both the physics-informed model and a physics-uninformed mathematical model for comparison. All models predicted the zigzag tests with satisfactory agreement. Thus, they can indeed be considered as being mathematically correct. However, introducing a semi-empirical rudder model seems to have guided the identification towards a more physically correct calm water hydrodynamic model, having lower multicollinearity and better generalization., The authors would like to acknowledge the financial support from Trafikverket/Lighthouse (grant id: FP4 2020) to prepare this paper. They would also thank all personnel at SSPA who have been involved in creating the model test results, building the ship models, and conducting the experiments.

Neutron star (NS) mergers where both stars have negligible spins are commonly considered as the most likely 'standard' case. In globular clusters, however, the majority of NSs have been spun up to millisecond (ms) periods and, based on observed systems, we estimate that a non-negligible fraction of all double NS mergers ($\sim 4\pm 2\, {{\ \rm per\ cent}}$) contains one component with a spin of a (few) ms. We use the Lagrangian numerical relativity code SPHINCS_BSSN to simulate mergers where one star has no spin and the other has a dimensionless spin parameter of chi = 0.5. Such mergers exhibit several distinct signatures compared to irrotational cases. They form only one, very pronounced spiral arm and they dynamically eject an order of magnitude more mass of unshocked material at the original, very low electron fraction. One can therefore expect particularly bright, red kilonovae. Overall, the spinning case collisions are substantially less violent and they eject smaller amounts of shock-generated semirelativistic material. Therefore, the ejecta produce a weaker blue/ultraviolet kilonova precursor signal, but - since the total amount is larger - brighter kilonova afterglows months after the merger. The spinning cases also have significantly more fallback accretion and thus could power late-time X-ray flares. Since the post-merger remnant loses energy and angular momentum significantly less efficiently to gravitational waves, such systems can delay a potential collapse to a black hole and are therefore candidates for merger-triggered gamma-ray bursts with longer emission time-scales., QC 20240524

Context. Traditional one-dimensional hydrostatic model atmospheres introduce systematic modelling errors into spectroscopic analyses of FGK-type stars. Aims. We present an updated version of the STAGGER-grid of three-dimensional model atmospheres, and explore the accuracy of postprocessing methods in preparation for spectral synthesis. Methods. New and old models were (re)computed following an updated workflow, including an updated opacity binning technique. Spectroscopic tests were performed in three-dimensional local thermodynamic equilibrium for a grid of 216 fictitious Fe I lines, spanning a wide range of oscillator strengths, excitation potentials, and central wavelengths, and eight model atmospheres that cover the stellar atmospheric parameter range (Teff, log g, and [Fe/H]) of FGK-type stars. Using this grid, the impact of vertical and horizontal resolutions, and temporal sampling of model atmospheres on spectroscopic diagnostics, was tested. Results. We find that downsampling the horizontal mesh from its original size of 240 × 240 grid cells to 80 × 80 cells, in other words, sampling every third grid cell, introduces minimal errors on the equivalent width and normalised line flux across the line and stellar parameter space. Regarding temporal sampling, we find that sampling ten statistically independent snapshots is sufficient to accurately model the shape of spectral line profiles. For equivalent widths, a subsample consisting of only two snapshots is sufficient, introducing an abundance error of less than 0.015 dex. Conclusions. We have computed 32 new model atmospheres and recomputed 116 old ones present in the original grid. The public release of the STAGGER-grid contains 243 models and the processed snapshots can be used to improve the accuracy of spectroscopic analyses.

This work proposes a modified interfacial tension model based on the continuum surface force (M-CSF) in the context of smoothed particle hydrodynamics. This correction aims to enhance computational stability, improve force evaluation precision, and increase symmetry around the interface. Several two-phase flow benchmarks are solved using both the conventional and proposed CSF models, and the results are compared with each other and with the available literature. The results indicate that the modified model can efficiently increase the force evaluation accuracy in the pressure field at the interface. For instance, the relative error in pressure calculation using the proposed and conventional CSF models is 0.05% and 3.5%, respectively, when compared to the analytical solution, with both models having the same particle resolutions for the droplet deformation problem. In predicting the critical surface tension for hydrodynamic instabilities, such as the Rayleigh-Taylor instability, the M-CSF methodology exhibits much better alignment with existing theories, showing less than 5% deviation, while conventionally used CSF models can deviate up to 15% for the same problem. These findings confirm the superiority of the proposed methodology in evaluating interfacial forces, even in complex hydrodynamic instabilities.

System identification offers ways to obtain proper models describing a ship’s dynamics in real operational conditions but poses significant challenges, such as the multicollinearity and generality of the identified model. This paper proposes a new physics-informed ship manoeuvring model, where a deterministic semi-empirical rudder model has been added, to guide the identification towards a physically correct hydrodynamic model. This is an essential building block to distinguish the hydrodynamic modelling uncertainties from wind, waves, and currents – in real sea conditions – which is particularly important for ships with wind-assisted propulsion. In the physics-informed manoeuvring modelling framework, a systematical procedure is developed to establish various force/motion components within the manoeuvring system by inverse dynamics regression. The novel test case wind-powered pure car carrier (wPCC) assesses the physical correctness. First, a reference model, assumed to resemble the physically correct kinetics, is established via parameter identification on virtual captive tests. Then, the model tests are used to build both the physics-informed model and a physics-uninformed mathematical model for comparison. All models predicted the zigzag tests with satisfactory agreement. Thus, they can indeed be considered as being mathematically correct. However, introducing a semi-empirical rudder model seems to have guided the identification towards a more physically correct calm water hydrodynamic model, having lower multicollinearity and better generalization., The authors would like to acknowledge the financial support from Trafikverket/Lighthouse (grant id: FP4 2020) to prepare this paper. They would also thank all personnel at SSPA who have been involved in creating the model test results, building the ship models, and conducting the experiments.

Context. Traditional one-dimensional hydrostatic model atmospheres introduce systematic modelling errors into spectroscopic analyses of FGK-type stars. Aims. We present an updated version of the STAGGER-grid of three-dimensional model atmospheres, and explore the accuracy of postprocessing methods in preparation for spectral synthesis. Methods. New and old models were (re)computed following an updated workflow, including an updated opacity binning technique. Spectroscopic tests were performed in three-dimensional local thermodynamic equilibrium for a grid of 216 fictitious Fe I lines, spanning a wide range of oscillator strengths, excitation potentials, and central wavelengths, and eight model atmospheres that cover the stellar atmospheric parameter range (Teff, log g, and [Fe/H]) of FGK-type stars. Using this grid, the impact of vertical and horizontal resolutions, and temporal sampling of model atmospheres on spectroscopic diagnostics, was tested. Results. We find that downsampling the horizontal mesh from its original size of 240 × 240 grid cells to 80 × 80 cells, in other words, sampling every third grid cell, introduces minimal errors on the equivalent width and normalised line flux across the line and stellar parameter space. Regarding temporal sampling, we find that sampling ten statistically independent snapshots is sufficient to accurately model the shape of spectral line profiles. For equivalent widths, a subsample consisting of only two snapshots is sufficient, introducing an abundance error of less than 0.015 dex. Conclusions. We have computed 32 new model atmospheres and recomputed 116 old ones present in the original grid. The public release of the STAGGER-grid contains 243 models and the processed snapshots can be used to improve the accuracy of spectroscopic analyses.

The global transition to renewable energy has put pressure on wind turbine installation vessels (WTIV), thus creating an urgent demand for optimizing their operation. This includes more accurate predictions of the ship motions at sea, at which roll motion is of particular interest. For accurate prediction of the roll motion, roll damping is important to consider and is commonly found from empirical methods if experimental data are not available. Since the hull geometry and loading conditions of WTIVs are significantly different from conventional ships the validity of existing empirical methods has not been justified. This paper studies an alternative approach of determining the roll damping, by utilizing CFD to simulate free roll decay of a WTIV, from which the roll damping can be extracted. A WTIV is simulated under different loading conditions, varying the vertical center of gravity and adding a bilge keel to study the influence on the roll damping. Model tests are carried out to validate the CFD simulations. CFD simulations are performed in both model scale and full scale. The implied extreme roll motions in irregular waves are compared with empirical methods. It is found that CFD can predict roll damping accurately and that roll damping decreases for high centers of gravity. The viscous scaling effects for a 2 m long model is significant, causing too large damping in model scale. The investigated bilge keel reduced roll motions significantly. The empirical methods consistently overestimated the roll damping, especially near the resonant frequency.

Low-mass planets migrate in the type-I regime. In the inviscid limit, the contrast between the vortensity trapped inside the planet's corotating region and the background disc vortensity leads to a dynamical corotation torque, which is thought to slow down inward migration. We investigate the effect of radiative cooling on low-mass planet migration using inviscid 2D hydrodynamical simulations. We find that cooling induces a baroclinic forcing on material U-turning near the planet, resulting in vortensity growth in the corotating region, which in turn weakens the dynamical corotation torque and leads to 2-3 × faster inw ard migration. This mechanism is most efficient when cooling acts on a time-scale similar to the U-turn time of material inside the corotating region, but is none the less rele v ant for a substantial radial range in a typical disc ( R ~5-50 au). As the planet migrates inwards, the contrast between the vortensity inside and outside the corotating region increases and partially regulates the effect of baroclinic forcing. As a secondary ef fect, we sho w that radiati ve damping can further weaken the vortensity barrier created by the planet's spiral shocks, supporting inward migration. Finally, we highlight that a self-consistent treatment of radiative diffusion as opposed to local cooling is critical in order to avoid overestimating the vortensity growth and the resulting migration rate., Planetary Exploration

Dust rings in protoplanetary discs are often observed in thermal dust emission and could be fa v ourable environments for planet formation. While dust rings readily form in gas pressure maxima, their long-term stability is key to both their observability and potential to assist in planet formation. We investigate the stability of the dust ring generated by interactions of a protoplanetary disc with a Neptune-sized planet and consider its possible long-term evolution using the FARGO3D Multifluid code. We look at the onset of the Rossby Wave Instability (RWI) and compare how the addition of dust in a disc can alter the stability of the gas phase. We find that with the addition of dust, the rings generated by planet-disc interactions are more prone to RWI and can cause the gas phase to become unstable. The instability is shown to occur more easily for higher Stokes number dust, as it accumulates into a more narrow ring which triggers the RWI, while the initial dust fraction plays a more minor role in the stability properties. We show that the dusty RWI generates vortices that collect dust in their cores, which could be sites for further planetesimal formation. We conclude that the addition of dust can cause a ring in a protoplanetary disc to become more prone to instability leading to a different long-term evolution compared to gas-only simulations of the RWI., Planetary Exploration

In this paper, Magnetic Resonance Imaging (MRI) and a Pore Network Model (PNM) are used to characterize the flow in packed beds of spherocylindrical particles. PNM is chosen as it is a relatively fast numerical approach, which provides local information on the bed flow pattern. MRI scans of packed bed reactors provide detailed information on the bed structure and the flow. In this study, the packed beds are reconstructed from the MRI images. The impact of the image quality on the PNM’s flow field prediction is assessed. It is shown that improved image quality significantly enhances prediction accuracy. With a sufficient image quality, PNM is able to closely match MRI in predicting the flow fields and capture important characteristics such as wall channeling.

In this work, the hydrodynamics inside packed beds of particles with different shapes are investigated: spherical, cylindrical, and cubical particles. The cylindrical and cubical geometries contain sharp ridges, which give rise to complicated pore geometries. In this study, Pore Network Modeling (PNM) validated with the Particle-Resolved Computational Fluid Dynamics (PR-CFD) simulations of packed beds with these non-spherical particles will be reported. The results show that the PNM predicts the same average flow behavior and pore pressure variations as PR-CFD. However, the PNM prediction of the pressure values is less accurate at the pore level compared to the PR-CFD for the cubical particles.

For many fishes, their early life stages are transported (passively) by currents between spawning areas and coastal nurseries, but also potential dispersal towards new habitats. Therefore, species have developed strategies to enhance the recruitment success, including the selection of appropriate spawning grounds. However, increased temperature due to climate change may lead to changes in hydrodynamics, shorter larval drifts, and earlier spawning, and consequently the location of the most suitable spawning grounds may change. We investigated whether the location of the most favourable spawning areas (allowing higher rates of larvae reaching coastal nurseries) was stable over time, and if differences could be found between environmentally contrasted years. We used a larval drift model taking into account hydrodynamics, larval characteristics and behaviour for three commercially exploited fish species (sole Solea solea, flounder Platichthys flesus and seabass Dicentrarchus labrax) in the Western Europe (encompassing the Bay of Biscay, the Celtic Sea and the English Channel). According to our model, we conclude that despite contrasting environmental conditions, the location of spawning grounds allowing the best chance of recruitment to nurseries for the offspring was fairly similar. However, even if the location of the main spawning grounds is stable over time, their relative effectiveness varies greatly between years. This would suggest that natural selection may favour the emergence of homing behaviour. This stability in this fish essential habitat location could facilitate protection measures. Going further, it could be interesting to study the variations occurring in spawning grounds (in terms of recruitment success, and retention/dispersion) during the course of a spawning season.

The growing global population and heightened concern for climate change leads to increased interest in utilizing microbial fermentations to replace polluting production processes for e.g., plastics, fuels, and animal proteins. Computational fluid dynamics (CFD) is a valuable tool for accelerating the scale-up and optimization of large-scale bioprocesses. However, the design correlations underlying most of these CFD models are validated with air-water systems, not accounting for the distinct hydrodynamic properties of microbial fermentation broth. In this review, we provide an extensive overview of the current understanding of how various biotechnologically relevant solutes impact the hydrodynamics of bubble columns. We examine the effects of components found in fermentation broths, including salts, surfactants, viscoelastic solutes, alcohols, acids, ketones, sugars, biomass, and proteins, on mass transfer, bubble formation, bubble interactions, and flow regime transitions. These components all exhibit unique effects, yet their combined influences remain poorly understood. Future research should prioritize identifying the concentration at which coalescence inhibition occurs for different compounds, especially in mixtures, and exploring the role of proteins in bubble column hydrodynamics from micro- to macroscale., BT/Bioprocess Engineering

This paper presents a novel computational approach for modelling fluid-driven fracturing in quasi-brittle solids using peridynamics. The approach leverages a rigorous coupling of the total- and semi-Lagrangian formulations of peridynamics. Specifically, the total-Lagrangian formulation, whch is based on classical peridynamics theory used for modelling fractures in solids, is combined with the semi-Lagrangian formulation to solve the Navier-Stokes equation using a non-local differential operator for weakly compressible fluid flow. The proposed approach offers a unified peridynamics-based framework that enables simulations of a wide range of fluid-driven fracturing problems in solids. The framework can model the solid as either an ordinary or non-ordinary material and quantify the fluid with different equations of state. To prevent unphysical inter-penetration, a fluid-solid interaction scheme that assumes fictitious fluid points in the solid domain is proposed to quantify the forces at the fluid-solid interface. The proposed computational approach is validated through simulations of several classic problems, including the dam break and the Kristianovich-Geertsma-de Klerk (KGD) problem. The predictive capability of the proposed approach is further demonstrated by numerical examples of fractures induced by fluid injection in sandstone, which reasonably capture the fracture patterns compared to experimental results. The presented approach offers an alternative to explicit modelling of fluid-driven fracturing processes and may find wide and useful applications to a variety of industrial and geophysical processes. © 2023 Elsevier B.V.

Microalgae are vital microorganisms due to their role in oxygen production, marine ecosystems, and as a source of various high-value products such as vitamins, biofuel, livestock feed, cosmetics, and more. Within some applications, challenges arise in large-scale microalgae production, characterized by high costs and growth rates that fall short of meeting commercial production demands. Therefore, there is still a need for further research to be conducted on microalgae strains and cultivation systems to improve costs and production rates. The focus of this study was to research a novel, patent-pending 360 Air-Loop Series Bioreactor (360-ASBR) and compare it to a Bubble Column Bioreactor (BCBR) that serves as the control. The specific objectives were to (1) determine and compare the hydrodynamic variables of the 360-ASBR and the BCBR including mixing time, residence time, and oxygen liquid mass transfer coefficient (KLa) and (2) determine the effect of the amount and placement of spargers in the BCBR. The results of this study showed that: (1) the mixing time of 198 seconds for the high flow rate and 247 seconds for the low flow rate for the ASBR significantly exceeded that of 25.1 seconds and 38.7 seconds respectively for the BCBR (2) the average residence time of 829 seconds was not significantly less than 1048 seconds for the BCBR at the high flow rate whereas the average residence time of 698 seconds for the ASBR was significantly less than 1053 seconds for the BCBR at the low flow rate, (3) the KLa of 0.012 s-1 for the ASBR was not significantly higher than 0.011 s-1 for the BCBR at the high flow rate whereas 0.009 s-1 for the ASBR significantly exceeded the KLa of 0.002 s-1 for the BCBR at the low flow rate, and (4) the mixing times of 25.1, 25.0, and 29.5 s for each sparger arrangement at the high flow rate and 38.7, 29.8, and 39.2 s for each sparger arrangement at the low flow rate did not result in significant differences. The principal conclusions drawn fro

Over the years, various technologies have been developed to produce and separate advanced biomolecules. These technologies range from complex terpenoids for pharmaceuticals and flavors to commodity chemicals and fuels via the fermentative route. These compounds are often poorly water soluble, phase splitting organic compounds or inhibitory and unstable necessitating addition of an extractive, second liquid phase for product removal. The turbulent conditions in the multiphasic fermentation coupled with the presence of surface-active compounds in the medium create a stable emulsion that is difficult to separate in conventional systems. Technologies such as centrifugation and de-emulsifiers have been used to separate the emulsion and recover the product. However, these type of recovery processes are expensive, drastically increase the final product’s environmental footprint and often hamper cell recycling.

The smoothed particle hydrodynamic technique is strongly based on the proper choice of interpolation functions. This statement is particularly relevant for the study of subsonic fluxes and turbulence, where inherent small errors in the averaging procedures introduce excessive damping on the smallest scales. To mitigate these errors, we can increase both the number of interpolating points and the order of the interpolating kernel function. However, this approach leads to a higher computational burden across all fluid regions. Ideally, the development of a single kernel function capable of effectively accommodating varying numbers of interpolating points in different fluid regions, providing good resolution and minimal errors would be highly desirable. In this work, we revisit and extend the main properties of a family of interpolators called Sinc kernels and compare them with the widely used family of Wendland kernels. We show that a linear combination of low- and high-order Sinc kernels generates good-quality interpolators, which are resistant to pairing instability while maintaining good sampling properties in a wide range of neighbour interpolating points, 60 ≤ nb ≤ 400. We show that a particular case of this linear mix of Sincs produces a well-balanced and robust kernel that improves previous results in the Gresho–Chan vortex experiment even when the number of neighbours is not large, while yielding a good convergence rate. Although such a mixing technique is ideally suited for Sinc kernels owing to their excellent flexibility, it can be easily applied to other interpolating families such as the B-splines and Wendland kernels.

The expansion of floating offshore wind brings the industry closer to achieving commercial viability. However, the challenging environment characterised by strong winds, waves, and currents, along with the growing size of wind turbines and the dynamic behaviour of floaters, introduces concerns about power production efficiency and system durability due to increased fatigue loads, which subsequently impacts overall costs. In an attempt to mitigate the financial implications coming from alterations made to control strategies and structural elements during the initial design phase, this paper propounds an all-encompassing simulation framework for offshore wind turbines. The current study thoroughly explores the various capabilities of the tool, with a focus on its simulation models. Importantly, the paper highlights the complex interactions between tool models and different controllers. Carefully designed, this tool offers users a variety of functions to enhance system design, fine-tune control strategies, and thoroughly assess performance metrics. The paper elaborates on these aspects, providing an explanation of the tool's capabilities and enhancing the dynamic comparison between the models.

The rise of animals across the Ediacaran–Cambrian transition marked a step-change in the history of life, from a microbially dominated world to the complex macroscopic biosphere we see today.1,2,3 While the importance of bioturbation and swimming in altering the structure and function of Earth systems is well established,4,5,6 the influence of epifaunal animals on the hydrodynamics of marine environments is not well understood. Of particular interest are the oldest “marine animal forests,”7 which comprise a diversity of sessile soft-bodied organisms dominated by the fractally branching rangeomorphs.8,9 Typified by fossil assemblages from the Ediacaran of Mistaken Point, Newfoundland,8,10,11 these ancient communities might have played a pivotal role in structuring marine environments, similar to modern ecosystems,7,12,13 but our understanding of how they impacted fluid flow in the water column is limited. Here, we use ecological modeling and computational flow simulations to explore how Ediacaran marine animal forests influenced their surrounding environment. Our results reveal how organism morphology and community structure and composition combined to impact vertical mixing of the surrounding water. We find that Mistaken Point communities were capable of generating high-mixing conditions, thereby likely promoting gas and nutrient transport within the “canopy.” This mixing could have served to enhance local-scale oxygen concentrations and redistribute resources like dissolved organic carbon. Our work suggests that Ediacaran marine animal forests may have contributed to the ventilation of the oceans over 560 million years ago, well before the Cambrian explosion of animals., Copyright © 2024 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). The linked document is the published version of the article., NHM Repository

Two rectangular-shaped lakes, Lake Hulun and Lake Buir, located at the boundary between China and Mongolia, only c. 75 km apart and therefore experiencing similar wind fields, have been studied based on satellite images and field surveys in order to compare their geomorphological and sedimentological characteristics. The wind-driven hydrodynamics, which have a significant effect on the development of littoral landforms and on sediment distribution, have been discussed for the two similar lakes that experienced a prevailing wind perpendicular to their long axis. A conceptual model related to wind-driven water bodies and sediment distribution is proposed. Wave-influenced to wave-dominated deltas, beaches, spits, and eolian dune deposits develop around these two lakes, with a strikingly similar distribution pattern. These features locally inform the longshore drift and help reconstruct the water circulation induced by wind forcing. Under the NW prevailing wind regime, the spits developed on the SW coast with a NW–SE extension, which was influenced by the NW–SE longshore currents. The same influence was observed in the delta extension in the NE area. The differences lie in the presence of fan deltas in the NW region of Lake Hulun, but not in Lake Buir. Additionally, the width of the beach and eolian deposits on the downwind coast of Lake Hulun is three times greater than that of Lake Buir which were caused by the differences in sediment supply and wind fetch between the two lakes. Lake Hulun and Lake Buir provide two reliable examples to understand the relationship among the wind field, provenance, hydrodynamics, landforms, and asymmetrical distribution of clastics in elongated lakes. They also represent relevant modern analogs, which may also be of guiding significance to wind-driven sand body prediction in lacustrine basins., Applied Geology

Multitubular reactors are commonly used in industry for processes involving highly exothermic chemical reactions. This reactor type consists of individual tubes, with a small diameter compared to the particle size. These slender beds facilitate heat management, but also give rise to flow maldistribution, which decreases the reactor efficiency. The aim of this article is to validate particle-resolved simulations using Magnetic Resonance Imaging experiments while focusing on the flow maldistribution. The packing structure used in the simulations is reconstructed from the experimental images to facilitate a one-to-one comparison. A good match between experiments and simulations is found for the averaged flow profile, probability density function of the velocity in axial direction and even the local velocity distributions. However, a correction of the experimental results for magnetic susceptibility artifacts is necessary to obtain a similar match in the probability density functions and the local profiles.

Dynamics and astrochemistry in the cosmos frequently, and sometimes strongly, feedback on one another. Therefore, the most predictive simulations of the cosmos should include coupled dynamics + chemistry. The technical details of this coupling are worth considering, in part, because maintaining the conservation of charge and atomic species in a dynamical model requires care, but also because simulating chemistry at every location in a large, multidimensional dynamical model is generally prohibitively expensive. Here, we review how to ensure conservation of species and charge in the most common hydrodynamical numerical methods, how chemistry commonly feeds back onto the dynamics, and present guidelines for how to minimize the cost of modeling coupled chemistry + dynamics.

Context. A growing planet embedded in a protoplanetary disk induces three-dimensional gas flow, which exhibits a midplane outflow that can suppress dust accretion onto the planet and form global dust substructures (rings and gaps). Aims. Because analytic formulae for the planet-induced outflow are useful for modeling its influences on local and global dust surface densities and planet accretion, we derived analytic formulae that describe the morphology and velocity of the planet-induced outflow. Methods. We first performed three-dimensional, nonisothermal hydrodynamical simulations of the gas flow past a planet, which enabled us to introduce a fitting formula that describes the morphology of the outflow. We then derived an analytic formula for the outflow speed using Bernoulli’s theorem. Results. We successfully derived a fitting formula for the midplane outflow morphology (the shape of the streamline), which is valid when the dimensionless thermal mass falls below m ≲ 0.6. The obtained analytic formulae for the outflow, such as the maximum outflow speed and the velocity distributions of the outflow in the radial and vertical directions to the disk, show good agreement with the numerical results. We find the following trends: (1) the maximum outflow speed increases with the planetary mass and has a peak of ∼30–40% of the sound speed when the dimensionless thermal mass is m ∼ 0.3, corresponding to a super-Earth mass planet at 1 au for the typical steady accretion disk model, and (2) the presence of the headwind (namely, the global pressure force acting in the positive radial direction of the disk) enhances (reduces) the outflow toward the outside (inside) of the planetary orbit. Conclusions. The planet-induced outflow of the gas affects the dust motion when the dimensionless stopping time of dust falls below St ≲ min(10 m2, 0.1), which can be used to model the dust velocity influenced by the outflow.

Context. A growing planet embedded in a protoplanetary disk induces three-dimensional gas flow, which exhibits a midplane outflow that can suppress dust accretion onto the planet and form global dust substructures (rings and gaps). Aims. Because analytic formulae for the planet-induced outflow are useful for modeling its influences on local and global dust surface densities and planet accretion, we derived analytic formulae that describe the morphology and velocity of the planet-induced outflow. Methods. We first performed three-dimensional, nonisothermal hydrodynamical simulations of the gas flow past a planet, which enabled us to introduce a fitting formula that describes the morphology of the outflow. We then derived an analytic formula for the outflow speed using Bernoulli’s theorem. Results. We successfully derived a fitting formula for the midplane outflow morphology (the shape of the streamline), which is valid when the dimensionless thermal mass falls below m ≲ 0.6. The obtained analytic formulae for the outflow, such as the maximum outflow speed and the velocity distributions of the outflow in the radial and vertical directions to the disk, show good agreement with the numerical results. We find the following trends: (1) the maximum outflow speed increases with the planetary mass and has a peak of ∼30–40% of the sound speed when the dimensionless thermal mass is m ∼ 0.3, corresponding to a super-Earth mass planet at 1 au for the typical steady accretion disk model, and (2) the presence of the headwind (namely, the global pressure force acting in the positive radial direction of the disk) enhances (reduces) the outflow toward the outside (inside) of the planetary orbit. Conclusions. The planet-induced outflow of the gas affects the dust motion when the dimensionless stopping time of dust falls below St ≲ min(10 m2, 0.1), which can be used to model the dust velocity influenced by the outflow.

The Hollandsche IJssel plays an important role in the freshwater provision of the province Zuid-Holland. Consequently, for Rijkswaterstaat it is key that salt intrusion is minimal in the Hollandsche IJssel. Recent studies noted that salt intrusion in the Hollandsche IJssel is limited due to a phase difference between tidal velocities in the main channel, the Nieuwe Maas, and the side channel, the Hollandsche IJssel. Earlier research investigated the impact of phase differences between branches and found it can lead to increased dispersion in the main channel, through a process known as tidal trapping. At the same time, this phase difference can prevent the saltiest water from entering the side channel, as was found at the Hollandsche IJssel. Because of this role, it is relevant to find out how this phase difference may be influenced by sea level rise, more extreme river discharges and particularly how it depends on the geometry of the main and the side channels. Especially the latter could help Rijkswaterstaat to minimize salt intrusion at locations relevant to freshwater intake, such as the Hollandsche IJssel. The main objective of this thesis is to investigate how the geometry of the side and main channel influences the tidal phase difference between these two channels, and how this may impact the salt dispersion in the side channel. For this, an analytical model is developed describing harmonic wave propagation in multi-branch systems and this is used next to results from a 3D numerical model for the Rhine Meuse Delta (RMM3D). First, the influence of changes in geometry and forcing is systematically investigated for a network containing a single junction. This shows that the length and depth of the side channel are the most significant variables. The depth is one of the main variables impacting friction, which governs the type of wave which can form in the system. A decrease in friction allows a wave to transform into a standing wave pattern as the retur, Civil Engineering | Hydraulic Engineering

The sandfish Holothuria (Metriatyla) scabra, is a high-value tropical sea cucumber harvested from wild stocks for over four centuries in multi-species fisheries across its Indo-Pacific distribution, for the global bêche-de-mer (BDM) trade. Within Southeast Asia, the Philippines is an important centre of the BDM trade, however overharvesting and largely open fishery management have resulted in declining catch volumes. Sandfish mariculture has been developed to supplement BDM supply and assist restocking efforts; however, it is heavily reliant on wild populations for broodstock supply. Consequently, to inform fishery, mariculture, germplasm and translocation management policies for both wild and captive resources, a high-resolution genomic audit of 16 wild sandfish populations was conducted, employing a proven genotyping-by-sequencing approach for this species (DArTseq). Genomic data (8,266 selectively-neutral and 117 putatively-adaptive SNPs) were used to assess fine-scale genetic structure, diversity, relatedness, population connectivity and local adaptation at both broad (biogeographic region) and local (within-biogeographic region) scales. An independent hydrodynamic particle dispersal model was also used to assess population connectivity. The overall pattern of population differentiation at the country level for H. scabra in the Philippines is complex, with nine genetic stocks and respective management units delineated across 5 biogeographic regions: (1) Celebes Sea, (2) North and (3) South Philippine Seas, (4) South China and Internal Seas and (5) Sulu Sea. Genetic connectivity is highest within proximate marine biogeographic regions (mean Fst=0.016), with greater separation evident between geographically distant sites (Fst range=0.041–0.045). Signatures of local adaptation were detected among six biogeographic regions, with genetic bottlenecks at 5 sites, particularly within historically heavily-exploited locati

Flow based deformation cytometry has shown potential for cell classification. We demonstrate the principle with an injection moulded microfluidic chip from which we capture videos of adult and fetal red blood cells, as they are being deformed in a microfluidic chip. Using a deep neural network - SlowFast - that takes the temporal behavior into account, we are able to discriminate between the cells with high accuracy. The accuracy was larger for adult blood cells than for fetal blood cells. However, no significant difference was observed between donors of the two types.

The aim of this study is to evaluate the applicability and suitability of the Smoothed Particle Hydrodynamics (SPH) method in modelling a flexible flat net in currents. SPH is a meshless Lagrangian method that discretises the system into particles, making it particularly suitable for modelling turbulent and highly nonlinear flows with the presence of a free surface. For the modelling of the flexible net, a methodology is proposed that uses fluid-driven elements (spheres) and dynamic links to discretise the geometry of the net within the SPH framework. This numerical approach allows the determination of the deformation of the net elements in the numerical model, the analysis of the fluid velocity field through the discrete elements and the calculation of the drag forces on the system under different flow regimes. The proposed method for the numerical modelling of the net is based on the coupling of DualSPHysics and MoorDyn+. DualSPHysics is a fully Lagrangian and meshless open-source code based on weakly compressible SPH that solves the fluid-structure interaction. MoorDyn+ is a dynamic library based on a lumped-mass numerical model, which solves tensions in the lines and allows the establishment of connections between the floating elements. In addition, an in-house algorithm is used to generate the configuration of the net in the numerical model, preserving the hydrodynamic and structural properties of the studied net. The proposed method for the discretisation of the net is validated by a comparative analysis of the drag forces obtained in the numerical model for a flat net fixed in a rigid frame, with different solidity values and those obtained by analytical solutions. Then, the method is applied to simulate a flexible flat net in steady currents with different velocities. The results are compared with those obtained from physical modelling tests and show a satisfactory agreement of the proposed method in the majority of the cases analysed, with a difference of l, Postprint (published version)

Lagrangian numerical methods are particularly suitable to reproduce flows involving large and rapid deformation of the domain, fluid splitting and coalescence, jets and sprays. The absence of the convective terms in the governing equations avoids numerical diffusion. This paper provides a comparative study between two Lagrangian particle models based on the Smoothed Particle Hydrodynamics (SPH) and the Particle Finite Element Method (PFEM). The description of the methods is provided; features and drawbacks of each method are compared and discussed. The introduced models, which represent widely used advanced analysis tools, are compared and validated in the simulation of five test cases: Two solitary waves, two regular wave trains and a non-linear wave-structure impact. Results from each model are similar and quite close to reference data. Therefore, both models have been validated against new test cases never simulated before, showing that these models can be effectively used for the analysis of regular and non-linear wave with structure impact., Peer Reviewed, Postprint (published version)

In the context of modeling solute transport through heterogeneous porous media, particle methods possess inherent advantages with respect to mesh-based (Eulerian) methods. In Smoothed Particle Hydrodynamics (SPH), particles represent fluid volumes exchanging concentrations with their neighbors to emulate hydrodynamic dispersion, and advection is simulated by the particles’ displacement. This crucially prevents problems that are otherwise typically associated with Eulerian advection schemes (especially at high grid-Péclet numbers), such as numerical diffusion. Despite the advantages of SPH, modeling dispersion with anisotropic coefficients remains a challenge for the approach, with studies reporting unphysical negative concentrations in conservative problems. This has likely hindered its practical use because dispersion is intrinsically anisotropic in porous media. This article provides a review and numerical evaluation of SPH for simulating dispersion, focusing on three formulations compatible with anisotropic dispersion coefficients. The analysis includes a scheme for which negative concentrations have been formerly reported, plus two more recently developed methods which are applied here for the first time to the problem of anisotropic dispersion in heterogeneous porous media. The SPH schemes are tested under different degrees of dispersion anisotropy for both homogeneous and heterogeneous velocity fields. The results indicate that the newer SPH schemes can produce accurate results without negative concentrations while considering anisotropic dispersion, providing a valid alternative to simulate solute transport through heterogeneous domains., To Escola Tècnica Superior d’Enginyers de Camins, Canals i Ports de Barcelona for granting computational resources in the cluster Titani, which contributed to the results presented in this article. The research leading to these results has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska - Curie grant agreement no. 814066 (Managed Aquifer Recharge Solutions Training Network – MARSoluT) and project GRADIENT (reference no. PID2021-127911OB-I00) from the Ministry of Science and Innovation of Spain ., Peer Reviewed, Postprint (published version)

Stellar winds of cool and pulsating asymptotic giant branch (AGB) stars enrich the interstellar medium with large amounts of processed elements and various types of dust. We present the first study on the influence of gas-to-dust drift on ab initio simulations of stellar winds of M-type stars driven by radiation pressure on forsterite particles. Our study is based on our radiation hydrodynamic model code T-800 that includes frequency-dependent radiative transfer, dust extinction based on Mie scattering, grain growth and ablation, gas-to-dust drift using one mean grain size, a piston that simulates stellar pulsations, and an accurate high spatial resolution numerical scheme. To enable this study, we calculated new gas opacities based on the EXOMOL database, and we extended the model code to handle the formation of minerals that may form in M-type stars. We determine the effects of drift by comparing drift models to our new and extant non-drift models. Three out of four new drift models show high drift velocities, 87- 310 km s-1. Our new drift model mass-loss rates are 1.7- 13 per cent of the corresponding values of our non-drift models, but compared to the results of two extant non-drift models that use the same stellar parameters, these same values are 0.33- 1.5 per cent. Meanwhile, a comparison of other properties such as the expansion velocity and grain size show similar values. Our results, which are based on single-component forsterite particles, show that the inclusion of gas-to-drift is of fundamental importance in stellar wind models driven by such transparent grains. Assuming that the drift velocity is insignificant, properties such as the mass-loss rate may be off from more realistic values by a factor of 50 or more., QC 20231115

Porous metallic structures play a critical role in mass and heat transfer processes due to their high surface areas, fixed porosity, and high stiffness – so understanding their fluid flow behaviour is crucial in designing materials that perform efficiently in mass and heat transfer. In view of this, a multi-disciplinary approach is employed to study the hydrodynamics of aluminium foams produced by a liquid melt infiltration technique using experimental, computational fluid dynamics (CFD) modelling and simulation, as well as artificial neural network (ANN) machine learning backpropagation. X-ray computed tomography datasets were used to characterize pore-structure-related properties of replicated materials, followed by three-dimensional advanced imaging of workable representative volume elements. Hydraulic flow information was acquired for the porous matrices using the constant-head permeameter technique. Experiments showed the permeability and Forchheimer coefficient dependence on pore-structure-related properties for fluid-flowing within the pre-Forchheimer and fully developed Forchheimer regimes. Flow permeability of 8.479 × 10−09m2 was highest in the material with the widest mean pore openings (0.212 mm) and lowest (1.291 × 10−09m2) in the material with the narrowest mean pore openings (0.106 mm). Conversely, Forchheimer coefficients were higher for materials with lower porosities and lower for materials with higher porosities. CFD calculations accurately predicted the fluid properties of metallic foams, as well as the influence of intrinsic foam properties on permeability and the Forchheimer coefficient. The ANN model framework was also able to provide valuable information about the hydrodynamics of these materials. Convolution and non-linearity of the ANN model were improved by adding supplementary neurons to the hidden layers allowing deviations within 0.3 and 9.0 percent to be attained., CC BY 4.0

Stellar winds of cool and pulsating asymptotic giant branch (AGB) stars enrich the interstellar medium with large amounts of processed elements and various types of dust. We present the first study on the influence of gas-to-dust drift on ab initio simulations of stellar winds of M-type stars driven by radiation pressure on forsterite particles. Our study is based on our radiation hydrodynamic model code T-800 that includes frequency-dependent radiative transfer, dust extinction based on Mie scattering, grain growth and ablation, gas-to-dust drift using one mean grain size, a piston that simulates stellar pulsations, and an accurate high spatial resolution numerical scheme. To enable this study, we calculated new gas opacities based on the EXOMOL database, and we extended the model code to handle the formation of minerals that may form in M-type stars. We determine the effects of drift by comparing drift models to our new and extant non-drift models. Three out of four new drift models show high drift velocities, 87–310 km s−1. Our new drift model mass-loss rates are 1.7–13 per cent of the corresponding values of our non-drift models, but compared to the results of two extant non-drift models that use the same stellar parameters, these same values are 0.33–1.5 per cent. Meanwhile, a comparison of other properties such as the expansion velocity and grain size show similar values. Our results, which are based on single-component forsterite particles, show that the inclusion of gas-to-drift is of fundamental importance in stellar wind models driven by such transparent grains. Assuming that the drift velocity is insignificant, properties such as the mass-loss rate may be off from more realistic values by a factor of 50 or more.

Porous metallic structures play a critical role in mass and heat transfer processes due to their high surface areas, fixed porosity, and high stiffness – so understanding their fluid flow behaviour is crucial in designing materials that perform efficiently in mass and heat transfer. In view of this, a multi-disciplinary approach is employed to study the hydrodynamics of aluminium foams produced by a liquid melt infiltration technique using experimental, computational fluid dynamics (CFD) modelling and simulation, as well as artificial neural network (ANN) machine learning backpropagation. X-ray computed tomography datasets were used to characterize pore-structure-related properties of replicated materials, followed by three-dimensional advanced imaging of workable representative volume elements. Hydraulic flow information was acquired for the porous matrices using the constant-head permeameter technique. Experiments showed the permeability and Forchheimer coefficient dependence on pore-structure-related properties for fluid-flowing within the pre-Forchheimer and fully developed Forchheimer regimes. Flow permeability of 8.479 × 10−09m2 was highest in the material with the widest mean pore openings (0.212 mm) and lowest (1.291 × 10−09m2) in the material with the narrowest mean pore openings (0.106 mm). Conversely, Forchheimer coefficients were higher for materials with lower porosities and lower for materials with higher porosities. CFD calculations accurately predicted the fluid properties of metallic foams, as well as the influence of intrinsic foam properties on permeability and the Forchheimer coefficient. The ANN model framework was also able to provide valuable information about the hydrodynamics of these materials. Convolution and non-linearity of the ANN model were improved by adding supplementary neurons to the hidden layers allowing deviations within 0.3 and 9.0 percent to be attained., CC BY 4.0

Process intensification is one of the key branches of process engineering. High gravity equipment achieves intensification by substituting gravity with much higher centrifugal force. Rotating Packed Bed is the leading example of high gravity solutions, strongly facilitating gas-liquid mass transfer. However, cylindrical packings come with certain drawbacks, such as dry spots, that can be overcome with new solutions, such as baffle-based packing geometries. However, when baffles are arranged too close to each other, liquid bridges are formed between them, which may lead to decrease in mass transfer efficiency. This work is concerned with improvement of a Zickzack-like internal by the means of visual studies with the use of high-speed camera. According to measured ligament break-up length, two new packings were designed for particular rotational speeds and tested experimentally for effective mass transfer area and wet pressure drop.

The modeling of large wood (LW) transport in rivers has received increasing interest from researchers in the last decade due to the widely recognized role of LW concerning flooding risk. For this purpose, few 2D depth-averaged hydraulic models have been coupled with LW transport models. However, such models usually neglect the effects of secondary currents on LW trajectories in river bends. In this work, the model Iber-Wood was enhanced to simulate the effects of secondary currents in river bends on LW trajectories. The proposed methodology presents a new formulation for considering secondary current effects on the flow field derived from the Manning formula and considers a new approach for reproducing the surface flow field that develops at channel bends. The enhanced model was tested to reproduce a series of laboratory experiments on wood transport in a sharp channel bend. The methodology introduces two new parameters in the model related to the secondary current effects, that is, the secondary current intensity and the adaptation length. These parameters were calibrated using available data from laboratory experiments. The good agreement between observed and simulated dowel trajectories in a sharp channel bend validated the proposed approach to simulate LW transport in the case of secondary currents, Peer Reviewed, Postprint (published version)

The version of record of this article, first published in Computational particle mechanics, is available online at Publisher’s website: https://doi.org/10.1007/s40571-023-00673-z, This paper presents a set of novel refined schemes to enhance the accuracy and stability of the updated Lagrangian SPH (ULSPH) for structural modelling. The original ULSPH structure model was first proposed by Gray et al. (Comput Methods Appl Mech Eng 190:6641–6662, 2001) and has been utilised for a wide range of structural analyses including metal, soil, rubber, ice, etc., although the model often faces several drawbacks including unphysical numerical damping, high-frequency noise in reproduced stress fields, presence of several artificial terms requiring ad hoc tunings and numerical instability in the presence of tensile stresses. In these regards, this study presents a set of enhanced schemes corresponding to (1) consistency correction on discretisation schemes for differential operators, (2) a numerical diffusive term incorporated in the continuity or the density rate equation, (3) tuning-free stabilising term based on Riemann solution and (4) careful control/switch of stress divergence differential operator model under tensile stresses. Qualitative/quantitative validations are conducted through several well-known benchmark tests., This study was supported by JSPS (Japan Society for the Promotion of Science) KAKENHI Grants Number JP21H01433, JP18K04368, JP21K14250 and JP22H01599. Antonio Gil and Chun Hean Lee would like to acknowledge the financial support received through the project Marie Sklodowska-Curie ITN-EJD ProTechTion, funded by the European Union Horizon 2020 research and innovation program with grant number 764636. The first author acknowledges the contribution of Mr. Kazuhiro Kinuta and Mr. Kazunori Yunoki, students of Applied Mechanics Laboratory, Kyoto University, in conducting several preliminary simulations corresponding to this study back in 2021 and 2022, respectively., Peer Reviewed, Postprint (author's final draft)

This paper presents a study on the falling film characteristics of vertical tubes and inclined plates, focusing on film thickness and wave frequency. A numerical modelling approach was employed using OpenFOAM’s InterFOAM solver to calculate the fluid dynamic characteristics of the falling film. The experiments were conducted using a variety of liquids, including water, ethylene glycol, and LiBr solution, and in the range of Reynolds numbers (Re) up to 1000. The film thickness was measured using two methods i. e., the contact point method and the holding method. Besides, a laser distance sensor was employed to detect the wave frequency of the falling film. The results indicated that the numerical model was able to accurately predict the mean film thickness in the complete turbulent film regime. The film thickness measured in this study was in the 0.3-1.0 mm range, with the average film thickness of the horizontal falling film being higher than that of the vertical falling film., Research project PID2020-115837RB-I0 funded by MCIN/AEI/10.13039/501100011033. J. Zheng holds a China Scholarship Council Studentship with the Polytechnical University of Catalonia., Postprint (published version)

Background Computational Fluid Dynamics (CFD) are usually carried out with the rigid walls assumption. In some cases, this is a valid approach however, blood does not flow inside rigid vessels instead, they have some degree of elasticity. This elasticity is vital in some studies into the stiffness of the walls due to either natural aging or some cardiovascular disease. Materials and methods Parting with an already prepared 3D simVascular model of an healthy pulmonary artery, we started with deciding the characteristics of the mesh. Later, we decided the boundary conditions and the wall properties. Results Results show us the differences of a rigid wall simulation compared to one with deformable walls. At first glance, there might seem that the difference is negligible but, the reality is, that the values like wall shear stress (WSS) or the vorticity held great importance in the ambit of cardiovascular disease. Conclusions CFD is a powerful tool to investigate flow patterns in blood vessels and in the prediction of dangerous situations. Even though all the simulations have many assumptions and are not perfect, their advanced techniques that are continuously being introduced and improved are essential for the betterment of our life.

The goal of this study was to test if CFD-based virtual angiograms could be used to automatically discriminate between intracranial aneurysms (IAs) with and without flow stagnation. Time density curves (TDC) were extracted from patient digital subtraction angiography (DSA) image sequences by computing the average gray level intensity inside the aneurysm region and used to define injection profiles for each subject. Subject-specific 3D models were reconstructed from 3D rotational angiography (3DRA) and computational fluid dynamics (CFD) simulations were performed to simulate the blood flow inside IAs. Transport equations were solved numerically to simulate the dynamics of contrast injection into the parent arteries and IAs and then the contrast retention time (RET) was calculated. The importance of gravitational pooling of contrast agent within the aneurysm was evaluated by modeling contrast agent and blood as a mixture of two fluids with different densities and viscosities. Virtual angiograms can reproduce DSA sequences if the correct injection profile is used. RET can identify aneurysms with significant flow stagnation even when the injection profile is not known. Using a small sample of 14 IAs of which seven were previously classified as having flow stagnation, it was found that a threshold RET value of 0.46 s can successfully identify flow stagnation. CFD-based prediction of stagnation was in more than 90% agreement with independent visual DSA assessment of stagnation in a second sample of 34 IAs. While gravitational pooling prolonged contrast retention time it did not affect the predictive capabilities of RET. CFD-based virtual angiograms can detect flow stagnation in IAs and can be used to automatically identify aneurysms with flow stagnation even without including gravitational effects on contrast agents.