Fluid Mechanics Research Articles

A systematic study of efficient sampling methods to quantify uncertainty in crack propagation and the Burgers equation

We present a systematic study of efficient sampling methods to quantify parametric uncertainty in stage II crack propagation and in a Burgers equation with random viscosity. The samplingmethods employed are Monte Carlo and quasi-Monte Carlo methods enhanced through variance reduction techniques including stratified sampling. We also present a recent variance reduction technique called sensitivity derivative enhanced sampling that utilizes sensitivity derivatives to make more efficient use of random samples. The crack propagation problem is a benchmark problem proposed by the Society of Automotive Engineers (SAE); this problem was selected because its large variance can hinder the already slow convergence of typical Monte Carlo methods and thus provides an ideal test for efficient sampling methods. We also examine a steady-state Burgers equation, a model equation of perennial interest for its connections with the equations of fluid mechanics, with uncertain viscosity. We demonstrate that sensitivity derivative enhanced sampling (SDES) can reduce the required number of samples by an order of magnitude to achieve the same accuracy as a traditionalMonte Carlo method. When SDES is coupled with other sampling techniques such as stratified sampling, the number of samples required can be reduced by as much as two orders of magnitude. In addition, we introduce an analogous approach that utilizes sensitivity derivatives which, under appropriate conditions, results in a more efficient quasi-Monte Carlo method.

Numerical Simulation of Drop Impact on Wetted and Dry Surfaces

first_page settings Order Article Reprints Font Type: Arial Georgia Verdana Font Size: Aa Aa Aa Line Spacing:    Column Width:    Background: Open AccessConference Report Numerical Simulation of Drop Impact on Wetted and Dry Surfaces by M. GATTRINGER and H. STEINER * Institute of Fluid mechanics and Heat transfer, Graz University of Technology, Graz, Austria * Author to whom correspondence should be addressed. Sci. Pharm. 2010, 78(3), 568; https://doi.org/10.3797/scipharm.cespt.8.LPES07 Received: 12 July 2010 / Accepted: 12 July 2010 / Published: 12 July 2010 Download Download PDF Versions Notes Abstract The impact of liquid drops on wetted and dry surfaces is a complex two-phase flow phenomenon with high technical relevance especially in surface coating. [...] Share and Cite MDPI and ACS Style GATTRINGER, M.; STEINER, H. Numerical Simulation of Drop Impact on Wetted and Dry Surfaces. Sci. Pharm. 2010, 78, 568. https://doi.org/10.3797/scipharm.cespt.8.LPES07 AMA Style GATTRINGER M, STEINER H. Numerical Simulation of Drop Impact on Wetted and Dry Surfaces. Scientia Pharmaceutica. 2010; 78(3):568. https://doi.org/10.3797/scipharm.cespt.8.LPES07 Chicago/Turabian Style GATTRINGER, M., and H. STEINER. 2010. "Numerical Simulation of Drop Impact on Wetted and Dry Surfaces" Scientia Pharmaceutica 78, no. 3: 568. https://doi.org/10.3797/scipharm.cespt.8.LPES07 Find Other Styles Article Metrics No No Article Access Statistics For more information on the journal statistics, click here. Multiple requests from the same IP address are counted as one view.

サッカーのナックルボールにおける非定常流体力

In this study, the unsteady aerodynamics of a knuckle ball in soccer were investigated. The characteristics of the fluid force, i.e. the magnitude and frequency acting on the knuckle ball, were analyzed through comparison with those of the straight ball using high-speed video cameras. Furthermore, the fluid flow around the knuckleball in flight was visualized using a smoke agent (titanium tetrachloride), and an attempt was made to clarify the fundamental fluid mechanics expressed by the knuckle ball as well as to analyze the vortex dynamics. It was found that the vertical acceleration of the knuckle ball tended to vary greatly (oscillate) in comparison with the acceleration of a straight ball, despite the fact that both are influenced by gravity. Moreover, in the case of the knuckle ball, the peak value of the vortex lift reached approximately 2.0 N, which was larger than the value of approximately 0.5 N for an instep kick. This vortex lift fluctuated greatly with time and was thought to be a highly unstable phenomenon. When the large-scale vortex structure of the knuckle ball was studied, successively shed vortex loops transformed and merged, and a few massive vortices formed an extended vortex street structure. Moreover, when the vertical fluctuation along the wake axis of the large-scale vortex structure was studied, evidence of unsteady wave oscillation (undulation) was observed. This large-scale structure of the far wake was conjectured to indicate traces of vortex motion at the time of vortex shedding, and the effect of this motion was thought to have a direct influence on the motion of the ball. Furthermore, the knuckle ball was observed to have an average vortex lift force frequency of approximately 3.5 Hz. A comparison of this vortex lift frequency and a vortex oscillation frequency indicated that these frequencies tended to act in unison with a high statistical correlation (r=0.83, p<0.01). Thus, it is considered that the oscillation of the large-scale vortex structures of the knuckle ball was the fundamental mechanism responsible for creating the fluctuating forces acting on the knuckle ball.

Streamline Simulation for Modern Reservoir-Engineering Workflows

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering. Abstract In this article, we present a high-level description of streamline-based flow simulation and focus on four areas in which the technology has proved valuable: reservoir-flow surveillance, flow simulation, history matching, and flood management. We highlight the advantages and disadvantages of streamline simulation (SLS) throughout the article and conclude with a look at possible SLS evolution. SLS re-emerged in the early 1990s to alleviate some computational problems faced by finite-difference (FD) simulation when confronted with high-resolution geological models characterized by heterogeneous spatial distributions of static properties. Since then, development and application of SLS has advanced the technology significantly, such that SLS complements conventional-modeling approaches in many reservoir-engineering (RE) workflows. What Is SLS? A streamline is defined as a line that is everywhere tangent to the local velocity field at a given instant in time. The smoke lines generated in a wind tunnel and shown in advertisements to demonstrate aerodynamic qualities of cars are a good representation of streamlines under the assumption of steady state. Modern SLS used in the oil and gas industry has its roots in the analytical and semianalytical streamline and streamtube methods that date back to the work of Muskat and Wyckoff (1934). Since then, important early contributions were made by several authors (see Datta-Gupta and King 2007 for a reference list). Streamlines also have a long history in the areas of fluid mechanics and groundwater flow, and petroleum literature has drawn heavily from those sources. In contrast to the early semianalytical streamtube work of the 1970s and 1980s, modern SLS generally is understood to be associated with work published after 1990 and is characterized by six important ideas: tracing 3D streamlines by use of the concept of ’time of flight?? (TOF) rather than arc length, expressing the mass-conservation equations in terms of TOF, periodic updating of the streamlines in time, solving the transport problems numerically along the streamlines rather than analytically, accounting for gravity effects, and extension to compressible flow. All of these improvements originated from the need to relax the limiting assumptions inherent in the early semianalytical streamtube methods and adapt the method to more-realistic and -complex reservoir scenarios (Batycky et al. 1997).

Regularity and Blow up for Active Scalars

We review some recent results for a class of fluid mechanics equations called active scalars, with fractional dissipation. Our main examples are the surface quasi-geostrophic equation, the Burgers equation, and the Cordoba-Cordoba-Fontelos model. We discuss nonlocal maximum principle methods which allow to prove existence of global regular solutions for the critical dissi- pation. We also recall what is known about the possibility of finite time blow up in the supercritical regime.

Introduction: Special issue on turbulent boundary layers at the AIAA 5th Theoretical Fluid Mechanics Conference

The articles included in this special issue represent some of the contributions, many of which were invited papers, presented at the 5th Theoretical Fluid Mechanics Conference of the American Insti...

0414 噴流法による二段環境下のキャビテーション損傷研究(OS4-3 キャビテーションおよびマイクロバブル効果とその応用技術,オーガナイズドセッション)

Two-stage cavitation erosion tests were performed using carbon steel S15C with a cavitating jet apparatus in seawater and tap water. The mass loss of carbon steel S15C by cavitation erosion is reduced remarkably when the test solution is changed to tap water from seawater. However, the mass loss rate that occurs when the experimental environment is changed to seawater from tap water is markedly higher because of corrosive action and mechanical disruption, and their synergistic effects. Changes in the environment demand consideration of the fluid mechanics because mass loss increases remarkably when the environment is changed repeatedly to seawater from tap water.

High Performance Computing on New Accelerated Hardware Architectures

This paper presents recent work that has been performed in the context of high performance computing and hybrid architectures at Poznan Supercomputing and Networking Center. Three algorithms: JPEG2000 – compression/decompression, computational fluid mechanics and motion tracking have been parallelized on various architectures and compared to reference sequential applications. The performance results, implementation issues and best practices are discussed as well.

Progress in Direct Noise Computation

The needs for accurate and efficient numerical solvers in computational aeroacoustics have motivated the development of low-dispersion and low-dissipation schemes as an alternative to more classical methods of applied mathematics for computational fluid mechanics over the last two decades. These numerical methods have now reached maturity, even if progress is still necessary to take account of specific physics. The paper provides a short overview of some recent developments and applications involving the direct computation of aerodynamic noise with applications to subsonic and supersonic jet noise, to cavity noise and to self-excited internal flows.

English

Blades are the most critical component of a wind turbine which is responsible for conversion of wind energy into kinetic energy. Aerodynamics is a science and study of physical laws of the behavior of objects in airflow and the forces that are produced by airflows. In the early stage, the research on wind turbine blade design was limited on theoretical study, field testing and wind tunnel testing which need a lot of efforts and resources. Due to the development of computer aided design codes, they provide another way to design and analyzed the wind turbine blades. Aerodynamic performance of wind turbine blades can be analyzed using computational fluid dynamics (CFD), which is one of the branches of fluid mechanics. In this paper an effort is made to study the Lift and Drag forces in a wind turbine blade at numerous sections and the effect of angle of attack on these forces. In this paper airfoil profile is considered for analysis of wind turbine blade. The wind turbine blade is modeled and several sections are produced from root to tip. The Lift and Drag forces are calculated at different sections for different angle of attack (AoA) for varied Reynolds numbers. The pressure and velocity distributions are also conspired. The cross sectional of blade is analyzed based on computational fluid dynamics to identify its suitability for its application on wind turbine blades and good agreement is made between conclusions

Simulation Analysis and Experimental Research on the Movements of Biomimetic Fin

Researchers Pay more and more attention to the biomimetic underwater propulsive technologies,especially to the research on the robotic fish.To improve the performances of the propulsion system based on long flexible undulating fin,a method of combination of caudal fin and long flexible fin is proposed.The propulsive model of long flexible undulating fin and the propulsive model of composite fin are introduced.Comparison and analysis of the results obtained by using a two-dimensional computational fluid dynamics method for rigid caudal fin oscillating model and for long flexible undulating model are emphasized.Experiments which use a simplified particle image velocity method are done for better understanding the fluid mechanism and validating the simulation results.It provides the foundation for further research on the performance of this propulsive system.

Introduction to nonlinear acoustics

A brief review of the basic principles of fluid mechanics needed for development of linear and nonlinear ultrasonic concepts will be given. The fundamental equations of nonlinear ultrasonics will be derived and their physical properties explained. It will be shown how an originally monochromatic finite-amplitude ultrasonic wave, due to nonlinear effects, will distort during its propagation in time and space to form higher harmonics to its fundamental frequency. The concepts of shock formation will be presented. The material nonlinearity, described by the nonlinearity parameter B/A of the material, and the convective nonlinearity, described by the ultrasonic Mach Number, will be explained. Two procedures for determination of B/A will briefly be described and some B/A-values characterizing biological materials will be presented. Shock formation, described by use of the Goldberg Number,and Ultrasonic Saturation will be discussed.. An introduction to focused ultrasonic fields will be given and it will be shown how the ultrasonic intensity will vary axially and laterally in and near the focal region and how the field parameters of interest to biomedical applications may be described by use of the KZK-Model. Finally, an introduction will be given to the parametric acoustic array formed by mixing and interaction of two monochromatic, finite-amplitude ultrasonic waves in a liquid and the potentials of this mixing process in biomedical ultrasound will briefly be mentioned.

THEORY, METHOD, AND APPLICATION OF A NUMERICAL SIMULATIONINAN OIL RESOURCES BASIN METHODS OF NUMERICAL SOLUTIONS OF AERODYNAMIC PROBLEMS

This paper considers the theory, method, and application of a numerical simulation of an oil-gas basin. From geological science, geochemistry, permeation fluid mechanics, and computer technology, it puts forward the mechanical model, mathematical model, careful parallel upwind fractional steps implicit iterative finite difference scheme, parallel arithmetic program, parallel arithmetic information, and alternating direction mesh subdivision. Our work has realized a highly accurate numerical simulation in hundreds of meters with millions of nodes and during an extra long period of time. It has produced a first-at-home-and-abroad software system of resources evaluation and multilayer oil resources migration and accumulation. This system has successfully been applied in oil-gas resources evaluation in Jiyang Dongying Hollow, Huimin Hollow, Tanhai Region, and Yangxin Hollow, and has gotten good practical results. Thus, an important problem on oil resources is solved.

Heat Transfer and Fluid Flows in Gas Springs

Thermodynamical processes and fluid mechanics phenomena occurring in an unlubricated piston-cylinder gas spring are investigated. Existing instantaneous heat transfer correlations are not applicable to the piston-cylinder compressed volumes. Accurate prediction of the transient thermal properties, heat transfer and fluid flows for the high performance, tight tolerance and lubricant-free gas compressors (e.g. cryo-cooling industry) is of high industrial importance. Research is here done with the use of ANSYS CFX finite-volume numerical package, modelling the closed fluid domain in a valveless non-lubricated one-piston-cylinder gas spring. Obtained numerically simulated values are compared to experimentally measured pressure and heat-flux data; very good agreement is observed. Broad discussion and conclusions with regard to thermodynamic and fluid-flow phenomena occurring are presented.

Analysis of cyclic events in turbulent flows using recurrence plots

A new technique for extracting information about cyclic and periodic features in turbulent-flow fields is proposed. This is based on a combination of proper orthogonal decomposition, applied to DNS and LES flow data, and the use of ‘recurrence plots’, the latter being a tool often adopted for analysing dynamical systems outside the field of fluid mechanics. The principal premise underpinning the technique is that the properties of a flow, viewed as a dynamical system, can be characterised by the temporal coefficients of the related proper orthogonal decomposition analysis of the flow. While such an analysis, on its own, yields useful information on the mode shapes, ordered according to their energy content, and on the temporal variation of these modes, it is not suited to the identification of ‘cyclicity’, here understood to be recurrent, as opposed to periodic, events that characterise drastic changes in the flow when this is viewed as a dynamical system. Following illustration with reference to a classi...

New method of predicting surge pressure apply to horizontal well based on casson flow*

In order to predict the surge pressure caused in the horizontal well drilling process, a new simple and applicable method has been established. It is based on the general theory of hydrostatic drilling fluid mechanics, and specifically described the flowing physical model towards surge pressure in horizontal well annulus, taking the effect of string eccentricity on the flowing law of drilling fluid into consideration. According to the constitutive equation of casson-mode under one-dimensional steady flow and the equations of annular flow rate under different drill string working conditions, this paper introduced the flow rate computation models of axial laminar flow in eccentric annulus apply to horizontal well, of which the numerical model was calculated by the program called Mathematica, ultimately, a new model for surge pressure prediction towards each interval in horizontal well was put forward. Application examples indicated that it can solve questions easily and precisely, which presents important meaning of guidance to the safety control while horizontal well drilling.

THE TEMPERATURE RESPONSE OF COMPACT TUBULAR MICROALGAE PHOTOBIOREACTORS

A mathematical and computational modeling of a photobioreactor for the determination of the transient temperature behavior in compact tubular microalgae photobioreactors is presented. The model combines theoretical concepts of thermodynamics with classical theoretical and empirical correlations of Fluid Mechanics and Heat Transfer. The physical domain is discretized with the Volume Element Model (VEM) through which the physical system (reactor pipes) is divided into lumped volumes, such that only one time dependent ordinary differential equation, ODE, results for temperature, based on the first law of thermodynamics. The energetic interactions between the volumes are established through heat transfer empirical correlations for convection, conduction and radiation. Within this context, the main goal of this study is to present a numerical methodology to calculate the mixture (algae + water + nutrients) temperature inside the compact photobioreactor. A pilot plant is under construction, in the Center of Research and Development for Self-Sustainable Energy (NPDEAS), located at UFPR, and the experimental data obtained from this research unit will be used to validate the present numerical solution. Temperature is one of the most important parameters to be controlled in microalgae growth. Microalgae that are cultivated outside their growth temperature range may have a low growth rate or die. For this reason a numerical simulation of the system based on the operating conditions and environmental factors is desirable, in order to predict the transient algae growth temperature distribution along the reactor pipes. The VEM creates an “artificial” spatial dependence in the system or process under analysis by dividing the space (physical domain) into smaller sub domains, namely Volume Elements (VE). Each VE interacts with its neighbors by exchanging energy and/or mass. Thus, each VE is treated as a control volume from classical thermodynamics, i.e., with uniform properties and exchanging mass and energy with its neighbors. The problem is then formulated with the energy equation applied to the fluid VE and to the wall VE. These equations form a system of time dependent ODE’s, which are not dependent on space, therefore eliminating the need for the solution of a system of partial differential equations, PDE’s, depend on time and space, as is the case of traditional numerical methods (e.g., finite element, finite volume and finite differences). The resulting ODE’s were solved using a fourth order Runge-Kutta method with adaptive time step.

ELIE CARAFOLI – PROFESSOR, ENTREPRENEUR and PATRIOT SCIENTIST

Nicolae Enache de la Olt – professor of mathematics and astronomy at the Dealu Monastery. The first Romanian who obtained a doctorate degree in aerodynamics at the Sorbonne (1908) Ion Ionescu Bizet – professor of strength of materials and metal structures at the Polytechnic School of Bucharest, one of the founders of the Mathematical Gazette Paul Painleve – professor of mathematics and fluid mechanics at the Faculty of Sciences in Paris Albert Toussaint – professor of experimental aerodynamics and director of the Institute of Saint Cyr

FLEXURAL OSCILLATIONS OF FLEXIBLE AIRFOILS IN SUBSONIC COMPRESSIBLE FLOWS

This paper presents simple and efficient analytical solutions for unsteady subsonic compressible flows past flexible airfoils executing low frequency oscillations. These analytical solutions are obtained with a method using velocity singularities related to the airfoil leading edge and ridges. The method has been validated for the pitching and plunging oscillations of the rigid airfoils by comparison with results based on Jordan’s data for compressible flows and by comparison with the solutions obtained by Theodorsen, Postel & Leppert and Mateescu & Abdo for incompressible flows. The method has been applied to obtain efficient analytical solutions for the flexural oscillations of airfoils in compressible flows, which can be efficiently used in solving aeroelastic problems. Professor Carafoli’s contributions to the aerodynamics of airfoils and wings Starting from 1924, in Paris, Elie Carafoli made significant contributions to the aerodynamic studies of wings and airfoils, included in Aerodynamics of airplane wings [5], Theory of lifting airfoils [6], in which he presented the aerodynamics of airfoils with rounded trailing edge, named later Carafoli airfoils, Influence of ailerons on the aerodynamic characteristics of lifting surfaces [7], and in Experimental studies on monoplane wings [8]. After 1928, he continued his research and academic activity in Romania, bringing new contributions to the aerodynamics of wings and airfoils in incompressible flows, which were mostly included in Aerodynamics [9], book also translated from Romanian into German and Russian. After 1950, Elie Carafoli developed a special interest for compressible flows and published High Speed Aerodynamics [10], initially in Romanian and then translated in English. He made, together with his collaborators, important contributions on the aerodynamics of wings and airfoils in supersonic flows, most of them included in the monograph Wing Theory in Supersonic Flow [11] published by Pergamon Press, to which the present author also collaborated. INCAS BULLETIN No. 2/ 2009 51 DOI: 10.13111/2066-8201.2009.1.2.11 For his outstanding achievements in aerodynamics, Elie Carafoli received very numerous international distinctions and awards, such as Diploma “Paul Tisandier” of the International Aeronautical Federation, Gauss Medal attributed yearly to the best scientist in the world by the Scientific Society Braunschweig, Germany, Apollo 11 Medal, Tsiolkovski Medal and many others distinctions which can not be listed here due to the space limitation. Elie Carafoli was one of the few Honorary Fellows of the Royal Aeronautical Society, Great Britain, and one of the first members of the International Academy of Astronautics (proposed by Theodor von Karman), and he was elected first Vice-President and then President of the International Astronautic Federation. In Romania, Carafoli was elected member of the Romanian Academy in 1948, and later named President of the Technical Sciences Section of the Academy, and he received the greatest Romanian medals, prizes and awards. One of the important realizations of Academician Carafoli was the foundation in 1949 of a research institute of the Romanian Academy, known as the Institute of Fluid Mechanics, which is presently named the National Institute for Aerospace Research “Elie Carafoli”. This institute contributed to the scientific formation of numerous former students and collaborators of Professor Carafoli, who distinguished themselves by contributions in aerodynamics and other related aerospace domains. Many of the former students and collaborators of Professor Carafoli became professors at their turn in Romania, as well as in other countries, such as Canada, France, Germany and United States of America, to name only a few. The present author had the privilege to study Aerodynamics with Professor Carafoli, who was also the Ph. D. supervisor, and to be his close collaborator for more than two decades. He is indebted to Professor Carafoli for many research advices, which materialized not only in many publications resulted from their direct scientific collaboration, but also in his further research and academic activity, first in Romania, and since 1982 in Canada. This author, together with his Masters’ and Ph. D. students, aims to continue the best scientific tradition of Professor Carafoli, with new contributions to the aerodynamics of wings and airfoils in steady and unsteady flows in incompressible, compressible subsonic and supersonic regimes and at low Reynolds numbers, in addition to other contributions in related aerospace domains (a few selected examples from the last ten years are included in references [20–37, 43].

Methods for measuring pedestrian density, flow, speed and direction with minimal scatter

The progress of image processing during recent years allows the measurement of pedestrian characteristics on a “microscopic” scale with low costs. However, density and flow are concepts of fluid mechanics defined for the limit of infinitely many particles. Standard methods of measuring these quantities locally (e.g. counting heads within a rectangle) suffer from large data scatter. The remedy of averaging over large spaces or long times reduces the possible resolution and inhibits the gain obtained by the new technologies. In this contribution we introduce a concept for measuring microscopic characteristics on the basis of pedestrian trajectories. Assigning a personal space to every pedestrian via a Voronoi diagram reduces the density scatter. Similarly, calculating direction and speed from position differences between times with identical phases of movement gives low-scatter sequences for speed and direction. Finally we discuss the methods to obtain reliable values for derived quantities and new possibilities of an in-depth analysis of experiments. The resolution obtained indicates the limits of stationary state theory.