IA Scholar Query: Finite Difference Simulations of the Navier-Stokes Equations Using Parallel Distributed Computing.
https://scholar.archive.org/
Internet Archive Scholar query results feedeninfo@archive.orgSat, 31 Dec 2022 00:00:00 GMTfatcat-scholarhttps://scholar.archive.org/help1440The Effect of Nanoparticles on MHD Blood Flow in Stretching Arterial Porous Vessel with the Influence of Thermal Radiation, Chemical Reaction and Heat Generation/Absorption
https://scholar.archive.org/work/53qfuyys2nggjbdy37quvnohpq
Nanotechnology becomes significant field of study and has very wide applications in biology, chemistry, physics and engineering. Nanofluid is a new class of nanotechnology based on heat transfer fluids that enhances thermal properties compared with that of classical fluid particles. Nanofluid is the interaction of nanoparticles in a fluid. Nanoparticles used in nanofluids are consisted of base fluidsZigta Binyamwork_53qfuyys2nggjbdy37quvnohpqSat, 31 Dec 2022 00:00:00 GMTAn improved fringe-region technique for the representation of gravity waves in large-eddy simulation with application to wind farms
https://scholar.archive.org/work/kaquek6qzzf4rngw6hd4nzjqoi
Large-eddy simulations of the atmospheric boundary layer are often performed using pseudo-spectral methods, which adopt a fringe-region approach to introduce inflow boundary conditions. However, we notice that a standard fringe-region technique excites spurious gravity waves when stratified atmospheres are considered, therefore enhancing the amount of energy reflected from the top of the domain and perturbing the velocity and pressure fields downstream. In this work, we develop a new fringe-region method that imposes the inflow conditions while limiting spurious effects on the surrounding flow. This is achieved by locally damping the convective term in the vertical momentum equation. We first apply the standard and wave-free fringe-region techniques to two-dimensional inviscid-flow simulations subjected to 169 different atmospheric states. A similar study is performed on a three-dimensional domain using a couple of atmospheric states. In all cases, the new fringe-region technique outperforms the standard method, imposing the inflow conditions with a minimal impact on the surrounding flow. Moreover, we also investigate the performance of two already existing non-reflective upper boundary conditions, that is a Rayleigh damping layer (RDL) and a radiation condition (RC). Results highlight the importance of carefully tuning the RDL to limit the distortion of the numerical solution. Also, we find that the tuned RDL outperforms the RC in all cases. Finally, the tuned RDL together with the wave-free fringe-region method are applied to an LES of a wind farm operating in a conventionally neutral boundary layer, for which we measure a reflectivity of only 0.75%.Luca Lanzilao, Johan Meyerswork_kaquek6qzzf4rngw6hd4nzjqoiFri, 16 Sep 2022 00:00:00 GMTHow to train your solver: Verification of boundary conditions for smoothed particle hydrodynamics
https://scholar.archive.org/work/nkj67d4z7jgl5h3cqkbotscpcm
The weakly compressible smoothed particle hydrodynamics (WCSPH) method has been employed to simulate various physical phenomena involving fluids and solids. Various methods have been proposed to implement the solid wall, and inlet/outlet and other boundary conditions. However, error estimation and the formal rates of convergence for these methods have not been discussed or examined carefully. In this paper, we use the method of manufactured solution (MMS) to verify the convergence properties of a variety of commonly employed of various solid, inlet, and outlet boundary implementations. In order to perform this study, we propose various manufactured solutions for different domains. On the basis of the convergence offered by these methods, we systematically propose a convergent WCSPH scheme along with suitable methods for implementing the boundary conditions. Along with other recent developments in the use of adaptive resolution, this paves the way for accurate and efficient simulation of incompressible or weakly-compressible fluid flows using the SPH method.Pawan Negi, Prabhu Ramachandranwork_nkj67d4z7jgl5h3cqkbotscpcmFri, 16 Sep 2022 00:00:00 GMTNumerical Simulation of the Effect of a Single Gust on the Flow Pasta Square Cylinder
https://scholar.archive.org/work/ejqf3eih6fdxhjioah3okwkqpi
The flow past a square cylinder under the influence of a one dimensional gust was investigated using computational fluid dynamics (CFD). The effect of upstream wind gusts of the same amplitude but different duration was investigated with respect to their effect on the flow, the vortex-shedding, and the pressure distribution around the square cylinder. For the computations, a very large eddy simulation (VLES) model was implemented in an in-house code and validated against numerical and experimental results from the literature. The gusts of different duration were found to have a distinctly different effect. The short-duration gust causes a lock-on behavior with cessation of the alternating vortex shedding, and a symmetric pair-vortex was created above and below the square cylinder. It was observed that the pressure distribution on the lateral sides of the cylinder has the same magnitude and phase, which resulted in a zero total lift coefficient. In terms of a free-standing structures, such as a building, this would lead to zero instantaneous forces and pressure difference in the lateral direction with obvious implications for dynamic response and cross ventilation.Maria Kotsiopoulou, Demetri Bouriswork_ejqf3eih6fdxhjioah3okwkqpiThu, 15 Sep 2022 00:00:00 GMTLimit Consistency of Lattice Boltzmann Equations
https://scholar.archive.org/work/tw3g2vvkrvg7nhkmcahrcmvl7u
We establish the notion of limit consistency as a modular part in proving the consistency of lattice Boltzmann equations (LBE) with respect to a given partial differential equation (PDE) system. The incompressible Navier-Stokes equations (NSE) are used as paragon. Based upon the diffusion limit [L. Saint-Raymond (2003), doi: 10.1016/S0012-9593(03)00010-7] of the Bhatnagar-Gross-Krook (BGK) Boltzmann equation towards the NSE, we provide a successive discretization by nesting conventional Taylor expansions and finite differences. Elaborating the work in [M. J. Krause (2010), doi: 10.5445/IR/1000019768], we track the discretization state of the domain for the particle distribution functions and measure truncation errors at all levels within the derivation procedure. Via parametrizing equations and proving the limit consistency of the respective sequences, we retain the path towards the targeted PDE at each step of discretization, i.e. for the discrete velocity BGK Boltzmann equation and the space-time discretized LBE. As a direct result, we unfold the discretization technique of lattice Boltzmann methods as chaining finite differences and provide a generic top-down derivation of the numerical scheme which upholds the continuous limit.Stephan Simonis, Mathias J. Krausework_tw3g2vvkrvg7nhkmcahrcmvl7uThu, 15 Sep 2022 00:00:00 GMTOn error-based step size control for discontinuous Galerkin methods for compressible fluid dynamics
https://scholar.archive.org/work/irtdqo5qn5dw5gjauo37m7oevi
We study temporal step size control of explicit Runge-Kutta methods for compressible computational fluid dynamics (CFD), including the Navier-Stokes equations and hyperbolic systems of conservation laws such as the Euler equations. We demonstrate that error-based approaches are convenient in a wide range of applications and compare them to more classical step size control based on a Courant-Friedrichs-Lewy (CFL) number. Our numerical examples show that error-based step size control is easy to use, robust, and efficient, e.g., for (initial) transient periods, complex geometries, nonlinear shock capturing approaches, and schemes that use nonlinear entropy projections. We demonstrate these properties for problems ranging from well-understood academic test cases to industrially relevant large-scale computations with two disjoint code bases, the open source Julia packages Trixi.jl with OrdinaryDiffEq.jl and the C/Fortran code SSDC based on PETSc.Hendrik Ranocha and Andrew R. Winters and Hugo Guillermo Castro and Lisandro Dalcin and Michael Schlottke-Lakemper and Gregor J. Gassner and Matteo Parsaniwork_irtdqo5qn5dw5gjauo37m7oeviThu, 15 Sep 2022 00:00:00 GMTRegime transitions in stratified shear flows: the link between horizontal and inclined ducts
https://scholar.archive.org/work/3xflbp2l2ndhxee2abaxuhx56y
We present the analytical solution for the two-dimensional velocity and density fields within an approximation for laminar stratified inclined duct (SID) flows where diffusion dominates over inertia in the along-channel momentum equation but it is negligible in the density transport equation. We refer to this approximation as the hydrostatic/gravitational/viscous in momentum and advective in density (HGV-A) approximation due to the leading balances in the governing equations. The analytical solution is valid for laminar flows in a two-layer configuration in the limit of long ducts. Under such conditions, the non-dimensional volume flux is given by the Froude number Fr^* =Re_g/(A K) with Re_g the gravitational Reynolds number, A the aspect ratio of the duct, and K a geometrical parameter that depends on the tilt of the duct and is obtained from the analytical solution. The analytical solution in the HGV-A approximation is validated against results from laboratory experiments, and allows us to gain new insight into the dynamics and properties of SID flows. Most importantly, constant values of Fr^* describe, in both horizontal and inclined ducts, the transitions between increasingly turbulent flow regimes: from laminar flow, to interfacial waves, to intermittent turbulence and sustained turbulence.Matias Duran-Matute, Steven J. Kaptein, Herman J.H. Clercxwork_3xflbp2l2ndhxee2abaxuhx56yWed, 14 Sep 2022 00:00:00 GMTHow important are activation functions in regression and classification? A survey, performance comparison, and future directions
https://scholar.archive.org/work/sixlu7zrn5el3pghlaebu5g5ou
Inspired by biological neurons, the activation functions play an essential part in the learning process of any artificial neural network commonly used in many real-world problems. Various activation functions have been proposed in the literature for classification as well as regression tasks. In this work, we survey the activation functions that have been employed in the past as well as the current state-of-the-art. In particular, we present various developments in activation functions over the years and the advantages as well as disadvantages or limitations of these activation functions. We also discuss classical (fixed) activation functions, including rectifier units, and adaptive activation functions. In addition to presenting the taxonomy of activation functions based on characterization, a taxonomy of activation functions based on applications is also presented. To this end, the systematic comparison of various fixed and adaptive activation functions is performed for classification data sets such as the MNIST, CIFAR-10, and CIFAR-100. In recent years, a physics-informed machine learning framework has emerged for solving problems related to scientific computations. To this purpose, we also discuss various requirements for activation functions that have been used in the physics-informed machine learning framework. Furthermore, various comparisons are made among different fixed and adaptive activation functions using various machine learning libraries such as TensorFlow, Pytorch, and JAX.Ameya D. Jagtap, George Em Karniadakiswork_sixlu7zrn5el3pghlaebu5g5ouTue, 13 Sep 2022 00:00:00 GMTProceedings of the First International Conference and School on Radiation Imaging (ICSRI-2021), Ferhat Abbas-Setif1 University, Setif, September 26-30, 2021, Algeria
https://scholar.archive.org/work/gywyoztdenc4fjvctgywoid2xa
This publication presents the proceedings of the first international conference and school on radiation imaging (ICSRI-2021). The ICSRI-2021 is a biennial scientific event organized by the dosing, analysis, and characterisation with high-resolution laboratory of Ferhat Abbas-Sétif1 university. The ICSRI-2021 was held for the first time at the University of Setif1. Setif is one of the most active and beautiful cities of Algeria. Due to the COVID-19 pandemic, the conference took place virtually while the school was face-to-face. This year scientists met to explore the development and application of radiation imaging and image processing in the domains of medicine and industry. As it is well known, radiation imaging is a field of science that cover a wide variety of disciplines such as imaging principles and methodologies, development of applications, imaging technologies, design of imaging systems...The recent progress in radiation imaging has been accelerated by advances in computer technology. Some imaging techniques are replacing other less efficient in terms of examination capability while some are able to provide almost perfect internal details with high contrast and resolution. As an example from medical imaging, techniques using radioisotopes provide functional and metabolic information that can be used to complement the morphological information provided by X-ray CT-scan. Image processing has always played a major role in the development and use of radiation imaging techniques. Image processing in radiation imaging is, indeed, a science field presenting up-to-date detailed treatment techniques and algorithms for the registration, segmentation, reconstruction, and evaluation of imaging data. The ICSRI-2021 was focused on all above-mentioned radiation imaging topics and moreover on: non-medical radiation imaging, imaging methods and systems development, radiation imaging simulation and modelling, molecular imaging and nuclear medicine, medical radiation imaging, advanced imaging methods, image processing, and [...]KHARFI Faycalwork_gywyoztdenc4fjvctgywoid2xaMon, 12 Sep 2022 00:00:00 GMTOn the thermalization of the three-dimensional, incompressible, Galerkin-truncated Euler equation
https://scholar.archive.org/work/nnw6e5eux5hlvbyxjrvmeh3ody
The long-time solutions of the Galerkin-truncated three-dimensional, incompressible Euler equation relax to an absolute equilibrium as a consequence of phase space and kinetic energy conservation in such a finite-dimensional system. These thermalized solutions are characterised by a Gibbs distribution of the velocity field and kinetic energy equipartition amongst its (finite) Fourier modes. We now show, through detailed numerical simulations, the triggers for the inevitable thermalization in physical space and how the problem is reducible to an effective one-dimensional problem making comparisons with the more studied Burgers equation feasible. We also discuss how our understanding of the mechanism of thermalization can be exploited to numerically obtain dissipative solutions of the Euler equations and evidence for or against finite-time blow-up in computer simulations.Sugan Durai Murugan, Samriddhi Sankar Raywork_nnw6e5eux5hlvbyxjrvmeh3odyMon, 12 Sep 2022 00:00:00 GMTRiccati-feedback Control of a Two-dimensional Two-phase Stefan Problem
https://scholar.archive.org/work/scr27h2uabddnpbwz3aahynucm
We discuss the feedback control problem for a two-dimensional two-phase Stefan problem. In our approach, we use a sharp interface representation in combination with mesh-movement to track the interface position. To attain a feedback control, we apply the linear-quadratic regulator approach to a suitable linearization of the problem. We address details regarding the discretization and the interface representation therein. Further, we document the matrix assembly to generate a non-autonomous generalized differential Riccati equation. To numerically solve the Riccati equation, we use low-rank factored and matrix-valued versions of the non-autonomous backward differentiation formulas, which incorporate implicit index reduction techniques. For the numerical simulation of the feedback controlled Stefan problem, we use a time-adaptive fractional-step-theta scheme. We provide the implementations for the developed methods and test these in several numerical experiments. With these experiments we show that our feedback control approach is applicable to the Stefan control problem and makes this large-scale problem computable. Also, we discuss the influence of several controller design parameters, such as the choice of inputs and outputs.Björn Baran, Peter Benner, Jens Saakwork_scr27h2uabddnpbwz3aahynucmMon, 12 Sep 2022 00:00:00 GMTVariational Quantum Algorithms for Computational Fluid Dynamics
https://scholar.archive.org/work/yb7uvvedcbfqloegyk7rp7tnsq
Quantum computing uses the physical principles of very small systems to develop computing platforms which can solve problems that are intractable on conventional supercomputers. There are challenges not only in building the required hardware, but also in identifying the most promising application areas and developing the corresponding quantum algorithms. The availability of intermediate-scale noisy quantum computers is now propelling the developments of novel algorithms, with applications across a variety of domains, including in aeroscience. Variational quantum algorithms are particularly promising since they are comparatively noise tolerant and aim to achieve a quantum advantage with only a few hundred qubits. Furthermore, they are applicable to a wide range of optimization problems arising throughout the natural sciences and industry. To demonstrate the possibilities for the aeroscience community, we give a perspective on how variational quantum algorithms can be utilized in computational fluid dynamics. We discuss how classical problems are translated into quantum algorithms and their logarithmic scaling with problem size. As an explicit example we apply this method to Burgers' Equation in one spatial dimension. We argue that a quantum advantage over classical computing methods could be achieved by the end of this decade if quantum hardware progresses as currently envisaged and emphasize the importance of joining up development of quantum algorithms with application-specific expertise to achieve real-world impact.Dieter Jaksch, Peyman Givi, Andrew J. Daley, Thomas Rungwork_yb7uvvedcbfqloegyk7rp7tnsqSun, 11 Sep 2022 00:00:00 GMTLow Reynolds Number Flow Past Square Cylinder in the Vicinity of a Plane Wall
https://scholar.archive.org/work/e2gk5symvzh4do7swnzoa3br3a
The characteristics of flow over a square cylinder in the vicinity of a plane stationary wall have been numerically investigated. 2D time-dependent incompressible flow at low-Reynolds numbers of 100 and 200 has been calculated using the finite volume method. CFRUNS scheme is used for pressure-velocity coupling in numerical calculation. The authors have tried to make an attempt to analyze the features of the complex flow field through flow streamlines and the vorticity contours. The impact of the gap between the cylinder and the plane wall upon flow pattern behavior is also studied. An intense interaction between vorticity in the boundary layer generated over the plane wall and the vorticity associated with the shear layer emanating from the separation points on the cylinder surface has been observed producing a very complex flow field in the cylinder wake and the gap between the cylinder and the wall.Biranchi Narayana DAS, Manoj UKAMANAL, Atal Bihari HARICHANDANwork_e2gk5symvzh4do7swnzoa3br3aFri, 09 Sep 2022 00:00:00 GMTA predictive hemodynamic model based on risk factors for ruptured mirror aneurysms
https://scholar.archive.org/work/y7vdd7go3vhspfmultp2we2twq
ObjectivesTo identify hemodynamic risk factors for intracranial aneurysm rupture and establish a predictive model to aid evaluation.MethodsWe analyzed the hemodynamic parameters of 91 pairs of ruptured mirror aneurysms. A conditional univariate analysis was used for the continuous variables. A conditional multivariate logistic regression analysis was performed to identify the independent risk factors. Differences where p < 0.05 were statistically significant. A predictive model was established based on independent risk factors. Odds ratios (ORs) were used to score points. The validation cohort consisted of 189 aneurysms. Receiver operating characteristic curves were generated to determine the cutoff values and area under the curves (AUCs) of the predictive model and independent risk factors.ResultsThe conditional multivariate logistic analysis showed that the low shear area (LSA) (OR = 70.322, p = 0.044, CI = 1.112–4,445.256), mean combined hemodynamic parameter (CHP) (>0.087) (OR = 3.171, p = 0.034, CI = 1.089–9.236), and wall shear stress gradient (WSSG) ratio (>893.180) (OR = 5.740, p = 0.003, CI = 1.950–16.898) were independent risk factors. A prediction model was established: 23*LSA + 1*CHP mean (>0.087: yes = 1, no = 0) + 2 * WSSG ratio (>893.180: yes = 1, no = 0). The AUC values of the predictive model, LSA, mean CHP (>0.087), and WSSG ratio (>893.180) were 0.748, 0.700, 0.654, and 0.703, respectively. The predictive model and LSA cutoff values were 1.283 and 0.016, respectively. In the validation cohort, the predictive model, LSA, CHP (>0.087), and WSSG ratio (>893.180) were 0.736, 0.702, 0.689, and 0.706, respectively.ConclusionsLSA, CHP (>0.087), and WSSG ratio (>893.180) were independent risk factors for aneurysm rupture. Our predictive model could aid practical evaluation.Sheng-qi Hu, Ru-dong Chen, Wei-dong Xu, Hua Li, Jia-sheng Yuwork_y7vdd7go3vhspfmultp2we2twqFri, 09 Sep 2022 00:00:00 GMTLaser Polishing Die Steel Assisted by Steady Magnetic Field
https://scholar.archive.org/work/rksno4cmyneqjbfiqyrgq6aumi
To improve the surface roughness of SKD61 die steel and reduce the secondary overflow of the molten pool, a steady magnetic field-assisted laser polishing method is proposed to study the effect of steady magnetic field on the surface morphology and melt pool flow behavior of SKD61 die steel. Firstly, a low-energy pulsed laser is used for the removal of impurities from the material surface; then, the CW laser, assisted by steady magnetic field, is used to polish the rough surface of SKD61 die steel to reduce the material surface roughness. The results show that the steady magnetic field-assisted laser polishing can reduce the surface roughness of SKD61 die steel from 6.1 μm to 0.607 μm, which is a 90.05% reduction compared with the initial surface roughness. Furthermore, a multi-physical-field numerical transient model involving heat transfer, laminar flow and electromagnetic field is established to simulate the flow state of the molten pool on the surface of the SKD61 die steel. This revealed that the steady magnetic field is able to inhibit the secondary overflow of the molten pool to improve the surface roughness of SKD61 slightly by reducing the velocity of the molten pool. Compared with the molten pool depth obtained experimentally, the molten pool depth simulation was 65 μm, representing an error 15.0%, thus effectively demonstrating the accuracy of the simulation model.Zhenyu Zhao, Junyong Zeng, Zhouyi Lai, Jie Yin, Ting Guowork_rksno4cmyneqjbfiqyrgq6aumiThu, 08 Sep 2022 00:00:00 GMTScan strategies for wind profiling with Doppler lidar – an large-eddy simulation (LES)-based evaluation
https://scholar.archive.org/work/5q5c3ynnkbeppoqfmz4kjx2dsu
Doppler-lidar scan techniques for wind profiling rely on the assumption of a horizontally homogeneous wind field and stationarity for the duration of the scan. As this condition is mostly violated in reality, detailed knowledge of the resulting measurement error is required. The objective of this study is to quantify and compare the expected error associated with Doppler-lidar wind profiling for different scan strategies and meteorological conditions by performing virtual Doppler-lidar measurements implemented in a large-eddy simulation (LES) model. Various factors influencing the lidar retrieval error are analyzed through comparison of the wind measured by the virtual lidar with the "true" value generated by the LES. These factors include averaging interval length, zenith angle configuration, scan technique and instrument orientation (cardinal direction). For the first time, ensemble simulations are used to determine the statistically expected uncertainty of the lidar error. The analysis reveals a root-mean-square deviation (RMSD) of less than 1 m s−1 for 10 min averages of wind speed measurements in a moderately convective boundary layer, while RMSD exceeds 2 m s−1 in strongly convective conditions. Unlike instrument orientation with respect to the main flow and scanning scheme, the zenith angle configuration proved to have significant effect on the retrieval error. Horizontal wind speed error is reduced when a larger zenith angle configuration is used but is increased for measurements of vertical wind. Furthermore, we find that extending the averaging interval length of lidar measurements reduces the error. In addition, a longer duration of a full scan cycle and hence a smaller number of scans per averaging interval increases the error. Results suggest that the scan strategy has a measurable impact on the lidar retrieval error and that instrument configuration should be chosen depending on the quantity of interest and the flow conditions in which the measurement is performed.Charlotte Rahlves, Frank Beyrich, Siegfried Raasch, Technische Informationsbibliothek (TIB)work_5q5c3ynnkbeppoqfmz4kjx2dsuThu, 08 Sep 2022 00:00:00 GMTPatient-specific modelling, simulation and real-time processing for respiratory diseases
https://scholar.archive.org/work/nqmcvjoakrcitlsqrjbsduzqca
Asthma is a common chronic disease of the respiratory system causing significant disability and societal burden. It affects more than 300 million people worldwide, while more than 100 million people will likely have asthma by 2025. The price of asthma varies greatly from nation to nation. Mean yearly cost can be estimated to 1900 EUR in Europe and 3100 in the United States. Managing asthma involves controlling symptoms, preventing exacerbations, and maintaining lung function. Improved asthma control is reduces the risk of exacerbations and lung function impairment while reducing the direct costs of asthma care and indirect costs associated with reduced productivity. Understanding the complex dynamics of the pulmonary system and the lung's response to disease is fundamental to the advancement of Asthma treatment. Computational models of the respiratory system seek to provide a theoretical framework to understand the interaction between structure and function. Their application can improve pulmonary medicine by a patient-specific approach to medicinal methodologies optimizing the delivery given the personalized geometry and personalized ventilation patterns. A three-fold objective is addressed within this dissertation. The first part refers to the comprehension of pulmonary pathophysiology and the mechanics of Asthma and subsequently of constrictive pulmonary conditions in general. The second part refers to the design and implementation of tools that facilitate personalized medicine to improve delivery and effectiveness. Finally, the third part refers to the self-management of the condition, meaning that medical personnel and patients have access to tools and methods that allow the first party to easily track the course of the condition and the second party, i.e. the patient to easily self-manage it alleviating the significant burden from the health system.Stavros Nousiaswork_nqmcvjoakrcitlsqrjbsduzqcaThu, 08 Sep 2022 00:00:00 GMTA geometrically intrinsic Lagrangian-Eulerian scheme for 2D Shallow Water Equations with variable topography and discontinuous data
https://scholar.archive.org/work/artnehpb3rd3xhm7mej3gfa4pm
We present a Lagrangian-Eulerian scheme to solve the shallow water equations in the case of spatially variable bottom geometry. Using a local curvilinear reference system anchored on the bottom surface, we develop an effective first-order and high-resolution space-time discretization of the no-flow surfaces and solve a Lagrangian initial value problem that describes the evolution of the balance laws governing the geometrically intrinsic shallow water equations. The evolved solution set is then projected back to the original surface grid to complete the proposed Lagrangian-Eulerian formulation. The resulting scheme maintains monotonicity and captures shocks without providing excessive numerical dissipation also in the presence of non-autonomous fluxes such as those arising from the geometrically intrinsic shallow water equation on variable topographies. We provide a representative set of numerical examples to illustrate the accuracy and robustness of the proposed Lagrangian-Eulerian formulation for two-dimensional surfaces with general curvatures and discontinuous initial conditions.Eduardo Abreu, Elena Bachini, John Perez, Mario Puttiwork_artnehpb3rd3xhm7mej3gfa4pmThu, 08 Sep 2022 00:00:00 GMTAssessment of a Hybrid Eulerian–Lagrangian CFD Solver for Wind Turbine Applications and Comparison with the New MEXICO Experiment
https://scholar.archive.org/work/le2obku7yjbc5bcv4xnhtgn67e
In this paper, the hybrid Lagrangian–Eulerian solver HoPFlow is presented and evaluated against wind tunnel measurements from the New MEXICO experiment. In the paper, the distinct solvers that assemble the HoPFlow solver are presented, alongside with details on their mutual coupling and interaction. The Eulerian solver, MaPFlow, solves the compressible Navier–Stokes equations under a cell-centered finite-volume discretization scheme, while the Lagrangian solver uses numerical particles that carry mass, pressure, dilatation and vorticity as flow markers in order to represent the flow-field by following their trajectories. The velocity field is calculated with the use of the decomposition theorem introduced by Helmholtz. Computational performance is enhanced by utilizing the particle mesh (PM) methodology in order to solve the Poisson equations for the scalar potential ϕ and the stream function ψ→. The hybrid solver is tested in 3-D unsteady simulations concerning the axial flow around the wind turbine (WT) model rotor tested in the New MEXICO experimental campaign. Simulation results are presented as integrated rotor loads, radial distribution of aerodynamic forces and moments and pressure distributions at various span-wise positions along the rotor blades. Comparison is made against experimental data and computational results produced by the pure Eulerian solver. A total of 5 PM nodes per chord length of the blade section at 75% have been found to be sufficient to predict the loading at the tip region of the blade with great accuracy. Discrepancies with respect to measurements, observed at the root and middle sections of the blade, are attributed to the omission of the spinner geometry in the simulations.Nikos Spyropoulos, George Papadakis, John M. Prospathopoulos, Vasilis A. Riziotiswork_le2obku7yjbc5bcv4xnhtgn67eThu, 08 Sep 2022 00:00:00 GMTModelling and Estimation of Vanadium Redox Flow Batteries: A Review
https://scholar.archive.org/work/x5ttkp2ljnc2vkmdkfvrtukpj4
Redox flow batteries are one of the most promising technologies for large-scale energy storage, especially in applications based on renewable energies. In this context, considerable efforts have been made in the last few years to overcome the limitations and optimise the performance of this technology, aiming to make it commercially competitive. From the monitoring point of view, one of the biggest challenges is the estimation of the system internal states, such as the state of charge and the state of health, given the complexity of obtaining such information directly from experimental measures. Therefore, many proposals have been recently developed to get rid of such inconvenient measurements and, instead, utilise an algorithm that makes use of a mathematical model in order to rely only on easily measurable variables such as the system's voltage and current. This review provides a comprehensive study of the different types of dynamic models available in the literature, together with an analysis of the existing model-based estimation strategies. Finally, a discussion about the remaining challenges and possible future research lines on this field is presented.Thomas Puleston, Alejandro Clemente, Ramon Costa-Castelló, Maria Serrawork_x5ttkp2ljnc2vkmdkfvrtukpj4Thu, 08 Sep 2022 00:00:00 GMT