Hydrodynamic Applications Research Articles

Invited perspectives: How machine learning will change flood risk and impact assessment

Abstract. Increasing amounts of data, together with more computing power and better machine learning algorithms to analyse the data, are causing changes in almost every aspect of our lives. This trend is expected to continue as more data keep becoming available, computing power keeps improving and machine learning algorithms keep improving as well. Flood risk and impact assessments are also being influenced by this trend, particularly in areas such as the development of mitigation measures, emergency response preparation and flood recovery planning. Machine learning methods have the potential to improve accuracy as well as reduce calculating time and model development cost. It is expected that in the future more applications will become feasible and many process models and traditional observation methods will be replaced by machine learning. Examples of this include the use of machine learning on remote sensing data to estimate exposure and on social media data to improve flood response. Some improvements may require new data collection efforts, such as for the modelling of flood damages or defence failures. In other components, machine learning may not always be suitable or should be applied complementary to process models, for example in hydrodynamic applications. Overall, machine learning is likely to drastically improve future flood risk and impact assessments, but issues such as applicability, bias and ethics must be considered carefully to avoid misuse. This paper presents some of the current developments on the application of machine learning in this field and highlights some key needs and challenges.

Hydrodynamic Performance of a Pitching Float Wave Energy Converter

This study analyzes the hydrodynamic performance and application of a pitching float-type wave energy conversion device under complex sea conditions in the South China Sea. Potential flow theory and ANSYS-AQWA software are used to establish a method for analyzing hydrodynamic performance in both time and frequency domains, as well as the various factors that influence hydrodynamic performance. The frequency domain characteristics of the conversion device are explored, as well as the time-domain characteristics when exposed to regular and irregular waves. The results show that the frequency domain of hydrodynamic performance conforms to the requirements of an offshore mobile platform. A mooring point that is closer to the center of mass leads to improved stability of the conversion device. The angle arrangement of the anchor-chain mooring method fully conforms to safety requirements. When the wave direction is 45°, the conversion device is highly stressed and its movement is the most strenuous; however, the device can operate safely and stably under all working conditions. These results provide a significant reference for expanding the wave-energy capture range and the hydrodynamic performance of floating wave-energy conversion devices.

On the Stability of Solitary Water Waves with a Point Vortex

This paper investigates the stability of traveling wave solutions to the free boundary Euler equations with a submerged point vortex. We prove that sufficiently small‐amplitude waves with small enough vortex strength are conditionally orbitally stable. In the process of obtaining this result, we develop a quite general stability/instability theory for bound state solutions of a large class of infinite‐dimensional Hamiltonian systems in the presence of symmetry. This is in the spirit of the seminal work of Grillakis, Shatah, and Strauss (GSS) , but with hypotheses that are relaxed in a number of ways necessary for the point vortex system, and for other hydrodynamical applications more broadly. In particular, we are able to allow the Poisson map to have merely dense range, as opposed to being surjective, and to be state‐dependent.As a second application of the general theory, we consider a family of nonlinear dispersive PDEs that includes the generalized Korteweg–de Vries (KdV) and Benjamin‐Ono equations. The stability or instability of solitary waves for these systems has been studied extensively, notably by Bona, Souganidis, and Strauss , who used a modification of the GSS method. We provide a new, more direct proof of these results, as a straightforward consequence of our abstract theory. At the same time, we allow fractional dispersion and obtain a new instability result for fractional KdV. © 2020 Wiley Periodicals, Inc.

Hydrodynamic processing application of heavy fuel oil and water fuel emulsions for two-stroke main marine diesel engines

Hydrodynamic processing application of heavy fuel oil and water fuel emulsions for two-stroke main marine diesel engines

Academician CAIUS IACOB – a Brilliant Mathematician Fascinated by Mechanics

The paper presents some interesting aspects related to the biography and works of Romanian mathematician Caius Iacob (1912–1992). He was famous for his works in the fields of mathematical analysis, fluid mechanics, classical hydrodynamics and compressible-flow theory. At the age of 19, he graduated from the Mathematics Faculty in Bucharest, and then he went to Paris to continue his studies at the Faculty of Sciences, where he worked on a PhD thesis under the advice of famous French mathematician Henri Villat. On 24 June 1935, Caius Iacob successfully presented to the Sorbonne committee his PhD thesis about “Determination of conjugated harmonic functions with some limit conditions, and their applications in hydrodynamics”. Returning to Romania, Caius Iacob had a long and successful career teaching mathematics and mechanics at the universities of Timişoara, Cluj and Bucharest. His most important work is considered the “Mathematical introduction to the mechanics of fluids”. This book, providing original ways to work with classical hydrodynamics and compressible-flow theory, was published in Romanian in 1952 and in French in 1959. In 1955, he was elected a Corresponding Member of the Romanian Academy, becoming a titular Member in 1963. He was also President of the Mathematics Section of the Romanian Academy from 1980 until the end of his life, in 1992. In 1991, he initiated the foundation of the “Romanian Academy Institute of Applied Mathematics”. In 2001 the institute merged with the “Centre for Mathematical Statistics”, which had been created in 1964 by mathematician Gheorghe Mihoc, thus creating the “Gheorghe Mihoc – Caius Iacob Institute of Mathematical Statistics and Applied Mathematics” of the Romanian Academy.

Ultimate Image Singularities in Oblate Spheroidal Coordinates with Applications in Hydrodynamics

This study exploits the Touvia Miloh oblate spheroid theorem with a special focus on hydrodynamical applications. The theorem provides explicit relations that express the oblate spheroidal harmonics, given in terms of the fundamental solutions of the Laplace equation. Here, the theorem is employed to transform the underlying Green’s function into the relevant coordinate system and, consequently, to formulate the diffraction potential. The case considered refers to the axisymmetric placement of the spheroid, namely, symmetrical axis perpendicular to the free surface. The mathematical formulations have been implemented numerically providing exceptionally accurate computations, which manifests the consistency and robustness of the relevant formulas.

Breaking Wave Height Estimation from Timex Images: Two Methods for Coastal Video Monitoring Systems

The breaking wave height is a crucial parameter for coastal studies but direct measurements constitute a difficult task due to logistical and technical constraints. This paper presents two new practical methods for estimating the breaking wave height from digital images collected by shore-based video monitoring systems. Both methods use time-exposure (Timex) images and exploit the cross-shore length ( L H s ) of the typical time-averaged signature of breaking wave foam. The first method ( H s b , v ) combines L H s and a series of video-derived parameters with the beach profile elevation to obtain the breaking wave height through an empirical formulation. The second method ( H s b , v 24 ) is based on the empirical finding that L H s can be associated with the local water depth at breaking, thus it can be used to estimate the breaking wave height without the requirement of local bathymetry. Both methods were applied and verified against field data collected at the Portuguese Atlantic coast over two days using video acquired by an online-streaming surfcam. Furthermore, H s b , v 24 was applied on coastal images acquired at four additional field sites during distinct hydrodynamic conditions, and the results were compared to a series of different wave sources. Achievements suggest that H s b , v method represents a good alternative to numerical hydrodynamic modeling when local bathymetry is available. In fact, the differences against modeled breaking wave height, ranging from 1 to 3 m at the case study, returned a root-mean-square-error of 0.2 m. The H s b , v 24 method, when applied on video data collected at five sites, assessed a normalized root-mean-square-error of 18% on average, for dataset of about 900 records and breaking wave height ranging between 0.1 and 3.8 m. These differences demonstrate the potential of H s b , v 24 in estimating breaking wave height merely using Timex images, with the main advantage of not requiring the beach profile. Both methods can be easily implemented as cost-effective tools for hydrodynamic applications in the operational coastal video systems worldwide. In addition, the methods have the potential to be coupled to the numerous other Timex applications for morphodynamic studies.

Boundary Layer Transition Models for Naval Applications: Capabilities and Limitations

We describe the implementation of several recently developed boundary layer transition models into the overset computational fluid dynamics code, REX, developed at the University of Iowa, together with an evaluation of its capabilities and limitations for naval hydrodynamics applications. Models based on correlations and on amplification factor transport were implemented in one- and two-equation Reynolds-averaged Navier-Stokes turbulence models, including modifications to operate in crossflow. Extensive validation of the transition models implemented in REX is performed for several 2- and 3-dimensional geometries of naval relevance. Standard tests with extensive available experimental data include flat plates in zero pressure gradient, an airfoil, and sickle wing. More complex test cases include the propeller, P4119, with some experimental data available, and the generic submersible, Joubert BB2, with no relevant experimental data available, to validate the transition models. Simulations for these last two cases show that extensive regions of laminar flow can be present on the bodies at laboratory scale and field scale for small vessels, and the potential effects on resistance and propulsion can be significant. 1. Introduction Progress for prediction of attached, fully turbulent flows for practical aerodynamic and hydrodynamic applications has reached a relatively mature plateau. However, according to a recent comprehensive review of pacing items (Slotnick et al. 2014), the single largest hurdle for incorporating computational fluid dynamics (CFD) into the design process in the near future is the ability to accurately predict turbulent flows with boundary layer transition and separation. Transition can impact skin friction, heat transfer, noise, propulsion efficiency, and maneuverability. This is especially true at model scale and for small craft such as unmanned or autonomous surface and underwater vehicles.

The impact of distributed landuse information in hydrodynamic model application in storm surge inundation

The depth-integrated hydrodynamic models have wide application in coastal management. These models have been extensively used in modelling storm surges and related inundation, coastal engineering, tidal forecasting and vulnerability assessments over continental selves across the world. However, there is a general paucity in storm surge modelling studies where an integration of distributed land use information with depth-integrated hydrodynamic models had been tested. The landuse plays a vital role as far as the overland flow is concerned as it determines the flow velocity and travel time vis-à-vis the extent and depth. Therefore, it is essential to test the storm surge inundation models with inclusion of distributed land use land cover. In order to understand the impact of land use land cover inclusion in the storm surge model, a severe cyclone AILA is considered in this study for the assessment over the Bay of Bengal of North Indian Ocean region. Four decades of land use information are fed in the model to test the impact in storm surge inundation extent and depth. The results suggest a significant change in water depth and inundation extent when distributed land use information is included in the simulation. Five landuse scenarios were tested in the model to examine which land use class has the maximum and minimum reduction potential for storm surge inundation. The results provide valuable information for land use based coastal flood management as well as will be useful in enhancing the skill of storm surge forecast.

Why the hydrodynamics is valid at early stage of heavy-ion collisions?

Evolution of hot and dense nuclear matter produced in central Au+Au collisions at energies of NICA, FAIR, and SPS is studied within two transport models. Two interesting features in the matter behaviour are observed almost from the very beginning of the collisions, at t ≥ 2 fm/c, for all studied reactions. (i) Expansion of the system proceeds with constant entropy-per-baryon ratio. (ii) Effective equation of state has a linear form, P = aε, a ≃ const. Both observations support the formal application of hydrodynamics at the early stages of heavy- ion collisions, when the system is very far from the equilibrium.

Blood flow through arteries in presence of transverse magnetics field

The aim of the study of this paper is the application of magneto hydrodynamics in physiological problems to develop a mathematical model for the study of blood flow in the presence of magnetic effect through stenosis arterial segment. Herschel-Bulkley equation has been taken to the non-Newtonian character of blood flow in the presence of applied magnetics effect. The mathematical model is analyzed through graphically and numerically. As blood is an electrically conducting the magneto hydrodynamic principle may be used to decelerate the flowing blood in a human arterial system and treatment of certain cardiovascular disease.

SPH Modeling of Water-Related Natural Hazards

This paper collects some recent smoothed particle hydrodynamic (SPH) applications in the field of natural hazards connected to rapidly varied flows of both water and dense granular mixtures including sediment erosion and bed load transport. The paper gathers together and outlines the basic aspects of some relevant works dealing with flooding on complex topography, sediment scouring, fast landslide dynamics, and induced surge wave. Additionally, the preliminary results of a new study regarding the post-failure dynamics of rainfall-induced shallow landslide are presented. The paper also shows the latest advances in the use of high performance computing (HPC) techniques to accelerate computational fluid dynamic (CFD) codes through the efficient use of current computational resources. This aspect is extremely important when simulating complex three-dimensional problems that require a high computational cost and are generally involved in the modeling of water-related natural hazards of practical interest. The paper provides an overview of some widespread SPH free open source software (FOSS) codes applied to multiphase problems of theoretical and practical interest in the field of hydraulic engineering. The paper aims to provide insight into the SPH modeling of some relevant physical aspects involved in water-related natural hazards (e.g., sediment erosion and non-Newtonian rheology). The future perspectives of SPH in this application field are finally pointed out.

Exact solutions and attractors of higher-order viscous fluid dynamics for Bjorken flow

We consider causal higher order theories of relativistic viscous hydrodynamics in the limit of one-dimensional boost-invariant expansion and study the associated dynamical attractor. We obtain evolution equations for the inverse Reynolds number as a function of Knudsen number. The solutions of these equations exhibit attractor behavior which we analyze in terms of Lyapunov exponents using several different techniques. We compare the attractors of the second-order M\"uller-Israel-Stewart (MIS), transient Denicol-Niemi-Molnar-Rischke (DNMR), and third-order theories with the exact solution of the Boltzmann equation in the relaxation-time approximation. It is shown that for Bjorken flow the third-order theory provides a better approximation to the exact kinetic theory attractor than both MIS and DNMR theories. For three different choices of the time dependence of the shear relaxation rate we find analytical solutions for the energy density and shear stress and use these to study the attractors analytically. By studying these analytical solutions at both small and large Knudsen numbers we characterize and uniquely determine the attractors and Lyapunov exponents. While for small Knudsen numbers the approach to the attractor is exponential, strong power-law decay of deviations from the attractor and rapid loss of initial state memory are found even for large Knudsen numbers. Implications for the applicability of hydrodynamics in far-off-equilibrium situations are discussed.

Application of smooth particle hydrodynamics (SPH) method in gravity casting shrinkage cavity prediction

Gravity casting has been applied extensively. Cavity will occur in the casting and form shrinkage cavity in solidification due to volume reduction and lowering of liquid metal level, which will affect casting quality. The formation process of shrinkage cavity cannot be directly observed and needs to be displayed by using the numerical simulation method. The smoothed particle hydrodynamics (SPH) method is a pure Lagrange method with no grids and has now been applied in casting numerical simulation, but the prediction model of the shrinkage cavity in gravity casting solidification based on the SPH method has not been reported. In this paper, the mathematical model for temperature field (including latent heat treatment) and shrinkage cavity prediction in solidification is established based on the SPH method. The correctness for the temperature field (including latent heat treatment) is validated by computing temperature field in the solidification of an L-shaped aluminum alloy casting, and correctness for the prediction of shrinkage cavity is validated by computing the shrinkage cavity in the solidification of a cylindrical steel casting.

High-order discontinuous Galerkin methods for coastal hydrodynamics applications

This paper applies high-order discontinuous Galerkin finite element solutions of the shallow water equations to realistic coastal hydrodynamics problems. The goal is to obtain results on par with the accuracy of current low-order models, while significantly surpassing their performance. Accomplishing this requires developing mesh discretizations with boundary and parameter field representations that are consistent with the high-order accuracy of the numerical methods. These developments allow coarse-mesh, high-order, solutions to provide comparable accuracy to today’s state-of-the-art high-resolution, low-order coastal models at reduced computational expense.

On the application of SPH to solid mechanics

We analyze the applicability of the smooth particle hydrodynamics (SPH) to the solution of boundary value problems involving large deformation of solids. The main focus is set on such issues as the reduction of artificial edge effects by implementing corrected kernels and their gradients, accurate and efficient computation of the deformation gradient tensor, evaluation of the internal forces from the given stress field. For demonstration purposes, a hyperelastic body of neo-Hookean type and a visco-elastic body of Maxwell type are considered; the formulation of the Maxwell material is based on the approach of Simo and Miehe (1992). For the implementation of constitutive relations efficient and robust numerical schemes are used. A solution for a series of test problems is presented. The performance of the implemented algorithms is assessed by checking the preservation of the total energy of the system. As a result, a functional combination of SPH-techniques is identified, which is suitable for problems involving large strains, rotations and displacements coupled to inelastic material behaviour. The accuracy of the SPH-computations is assessed using nonlinear FEM as a benchmark.

The Borg Cube Simulation: Cosmological Hydrodynamics with CRK-SPH

Abstract A challenging requirement posed by next-generation observations is a firm theoretical grasp of the impact of baryons on structure formation. Cosmological hydrodynamic simulations modeling gas physics are vital in this regard. A high degree of modeling flexibility exists in this space, making it important to explore a range of methods in order to gauge the accuracy of simulation predictions. We present results from the first cosmological simulation using Conservative Reproducing Kernel Smoothed Particle Hydrodynamics (CRK-SPH). We employ two simulations: one evolved purely under gravity, and the other with nonradiative hydrodynamics. Each contains 2 × 23043 cold dark matter plus baryon particles in an box. We compare statistics to previous nonradiative simulations including power spectra, mass functions, baryon fractions, and concentration. We find self-similar radial profiles of gas temperature, entropy, and pressure and show that a simple analytic model recovers these results to better than 40% over two orders of magnitude in mass. We quantify the level of nonthermal pressure support in halos and demonstrate that hydrostatic mass estimates are biased low by 24% (10%) for halos of mass . We compute angular power spectra for the thermal and kinematic Sunyaev–Zel’dovich effects and find good agreement with the low-ℓ Planck measurements. Finally, artificial scattering between particles of unequal mass is shown to have a large impact on the gravity-only run, and we highlight the importance of better understanding this issue in hydrodynamic applications. This is the first in a simulation campaign using CRK-SPH, with future work including subresolution gas treatments.

Analysis of Implementation Effectiveness of Two Working Fluids Characterized by Different Viscoelastic Characteristics at Hydrodynamic Impact on the Borehole Bottom Zone

Combination of hydrodynamic impact on the formation with acid treatment may be seen as a promising direction in the field of well development and repair in complex geological conditions. With multiple repetition of hydraulic shocks in conjunction with the injection of acid solution, the depth and opening of cracks gradually increases, which contributes to a deeper penetration of the acid solution into the reservoir. The article presents analytical studies, which are aimed at determining the effectiveness of applying the technology of hydrodynamic impact on the bottomhole zone of an oil reservoir when using two fluids with different viscoelastic characteristics as a working fluid. They are devoted to determining the pressure drop at the borehole bottom depending on the initial applied pressure at the wellhead, the velocity of the shock wave, the viscosity of the working and well fluid, and their quantity. These studies were based on the well-known models of Thomson – Tаt and Maxwell, considering viscous liquid flow. The dependence obtained proves that with an increase in the pressure pulse generated at the wellhead, the development of pressure pulses at the borehole bottom is a power-law dependence, and with significant volumes of fluid in contact with the bottomhole formation zone, the pressure drop generated at the borehole bottom does not depend only on pressure pulses generated at the wellhead, but also on the dynamic viscosity of this fluid. Conducted studies have shown the effectiveness of hydrodynamic impact technology application when using two liquids with different viscoelastic characteristics and obtaining a synergistic effect during the development and repair of wells in low-permeable reservoirs. Analytical studies were based on data from previously conducted experimental industrial tests on the operating injection well.

Matching the Nonequilibrium Initial Stage of Heavy Ion Collisions to Hydrodynamics with QCD Kinetic Theory.

High-energy nuclear collisions produce a nonequilibrium plasma of quarks and gluons which thermalizes and exhibits hydrodynamic flow. There are currently no practical frameworks to connect the early particle production in classical field simulations to the subsequent hydrodynamic evolution. We build such a framework using nonequilibrium Green's functions, calculated in QCD kinetic theory, to propagate the initial energy-momentum tensor to the hydrodynamic phase. We demonstrate that this approach can be easily incorporated into existing hydrodynamic simulations, leading to stronger constraints on the energy density at early times and the transport properties of the QCD medium. Based on (conformal) scaling properties of the Green's functions, we further obtain pragmatic bounds for the applicability of hydrodynamics in nuclear collisions.

Potential and limitations of scale resolved simulations for ship hydrodynamics applications

ABSTRACTThe paper gives an overview of experience gathered by the authors in development and application of hybrid URANS/LES methods for the solution of ship hydrodynamic problems. Difficulties arising at the interface between URANS and LES are discussed and illustrated for a channel flow benchmark. A hybrid model developed by the authors is described. It was shown that pure LES has advantages over hybrid models provided a sufficient resolution can be attained for a given Re number. Advantages of hybrid models over RANS-based ones is demonstrated for the determination of wake parameters behind models of full bottomed ships JBC and KVLCC2. Difficulties with prediction of the ship resistance by hybrid methods are discussed.