Academic literature on the topic 'Potential flow theory'
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Journal articles on the topic "Potential flow theory"
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COLEMAN, S. E., and J. D. FENTON. "Potential-flow instability theory and alluvial stream bed forms." Journal of Fluid Mechanics 418 (September 10, 2000): 101–17. http://dx.doi.org/10.1017/s0022112000001099.
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The present work constitutes a reassessment of the role of potential-flow analyses in describing alluvial-bed instability. To facilitate the analyses, a new potential-flow description of unsteady alluvial flow is presented, with arbitrary phase lags between local flow conditions and sediment transport permitted implicitly in the flow model. Based on the present model, the explicit phase lag between local sediment transport rate and local flow conditions adopted for previous potential-flow models is shown to be an artificial measure that results in model predictions that are not consistent with observed flow system behaviour. Previous potential-flow models thus do not provide correct descriptions of alluvial flows, and the understanding of bed-wave mechanics inferred based upon these models needs to be reassessed. In contrast to previous potential-flow models, the present one, without the use of an explicit phase lag, predicts instability of flow systems of rippled or dune-covered equilibrium beds. Instability is shown to occur at finite growth rates for a range of wavelengths via a resonance mechanism occurring for surface waves and bed waves travelling at the same celerity. In addition, bed-wave speeds are predicted to decrease with increasing wavelength, and bed waves are predicted to grow and move at faster rates for flows of larger Froude numbers. All predictions of the present potential-flow model are consistent with observations of physical flow systems. Based on the predicted unstable wavelengths for a given alluvial flow, it is concluded that bed waves are not generated from plane bed conditions by any potential-flow instability mechanism. The predictions of instability are nevertheless consistent with instances of accelerated wave growth occurring for flow systems of larger finite developing waves. Potential-flow description of alluvial flows should, however, no longer form the basis of instability analyses describing bed-form (sand-wavelet) generation from flat bed conditions.
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Chadwick, Edmund. "A slender–wing theory in potential flow." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 461, no. 2054 (February 8, 2005): 415–32. http://dx.doi.org/10.1098/rspa.2004.1295.
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Consider uniform, steady potential flow past a slender wing. By considering a horseshoe vortex in the limit as γ / Us → ∞, where γ is the circulation, U is the uniform stream velocity and s is the span, a model representing a vortex sheet is obtained from which the lift on the slender wing can be determined. (This is in contrast to the textbook approach of Batchelor and Katz & Plotkin, who discretize the vortex sheet with horseshoe vortices in the limit as γ / Us → ∞, but then relate the vortex strength to lift by using the two–dimensional limit γ / Us → 0. We shall argue that using these different limits in the same analysis is inconsistent and leads to an incorrect result.) The resulting potential term is shown to be the same as the potential term of the lift Oseenlet in Oseen flow. In the limit of high–Reynolds–number flow, only half the contribution to the lift integral comes from the potential–velocity part of the lift Oseenlet. The other half comes from the vortex–wake–velocity part of the lift Oseenlet. We therefore assume potential flow everywhere except at the vortex sheet, along which we allow a singular vortex–wake–velocity term of the lift Oseenlet. From this, a slender–wing theory is presented together with integral expressions for the lift and change in lift over the wing surface. Applications to slender bodies and large–aspect–ratio wings, in particular, the Lanchester–Prandtl lifting line, are then considered.
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Dassios, G. "The Kelvin transformation in potential theory and Stokes flow." IMA Journal of Applied Mathematics 74, no. 3 (September 9, 2008): 427–38. http://dx.doi.org/10.1093/imamat/hxn027.
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VERHOFF, A. "Two-dimensional potential flow solutions with separation." Journal of Fluid Mechanics 657 (July 21, 2010): 238–64. http://dx.doi.org/10.1017/s0022112010001448.
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A procedure for constructing two-dimensional incompressible potential flowfield solutions with separation and a recirculation region is presented. It naturally makes use of complex variable theory and other analysis techniques such as conformal mapping and the generalized Poisson integral formula. Flowfield determination is reduced to solution of a boundary value problem in various simple domains. The entire velocity field is described analytically; stream function and velocity potential contour maps are readily constructed. Example solutions are presented. Solutions for sharp leading edge airfoils at arbitrary angle of attack are completely determined, including the limiting angle of attack for upper-surface flow re-attachment. For other configurations (e.g. circular cylinder, backward-facing step) the analytical solution contains one or more free parameters, whose values may be inferred from boundary layer theory or experiment.
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Ma, Chao, Yi Zhu, Jiayi He, Chenliang Zhang, Decheng Wan, Chi Yang, and Francis Noblesse. "Nonlinear corrections of linear potential-flow theory of ship waves." European Journal of Mechanics - B/Fluids 67 (January 2018): 1–14. http://dx.doi.org/10.1016/j.euromechflu.2017.07.006.
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Baddoo, Peter J. "Lightning Solvers for Potential Flows." Fluids 5, no. 4 (November 30, 2020): 227. http://dx.doi.org/10.3390/fluids5040227.
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We present a method for computing potential flows in planar domains. Our approach is based on a new class of techniques, known as “lightning solvers”, which exploit rational function approximation theory in order to achieve excellent convergence rates. The method is particularly suitable for flows in domains with corners where traditional numerical methods fail. We outline the mathematical basis for the method and establish the connection with potential flow theory. In particular, we apply the new solver to a range of classical problems including steady potential flows, vortex dynamics, and free-streamline flows. The solution method is extremely rapid and usually takes just a fraction of a second to converge to a high degree of accuracy. Numerical evaluations of the solutions are performed in a matter of microseconds and can be compressed further with novel algorithms.
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Stropky, D. M., N. Djilali, I. S. Gartshore, and M. Salcudean. "Application of Momentum Integral Methods and Linearized Potential Theory for Predicting Separation Bubble Characteristics." Journal of Fluids Engineering 112, no. 4 (December 1, 1990): 416–24. http://dx.doi.org/10.1115/1.2909419.
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A new viscous-inviscid interaction procedure of the semi-inverse type has been developed to predict two-dimensional separated flows. The method is applied to incompressible flow over an external backward-facing step, using linearized potential theory for the inviscid region and a simple modification of Pohlhausens’ momentum-integral method in the viscous region. The modified Pohlhausen method, which approximates the reverse flow region with a region of “dead-air,” is first tested without the viscous-inviscid procedure to predict fully developed laminar and turbulent flow in a plane symmetric sudden expansion. Comparisons are made with experimental data, other calculation methods, and finite difference predictions using a modified version of an elliptic code (TEACH-II). Reasonable predictions of the sudden expansion and backward-facing step flows are obtained, provided that the step-height to boundary-layer thickness ratio is large enough for the Pohlhausen type velocity profiles to be effective. The relative simplicity of the zonal equations coupled with the viscous-inviscid interaction procedure makes the present calculation method computationally attractive. The method should also prove useful in more complex separated flow situations, such as bluff-body aerodynamics.
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Zhang, Zhang, and Shang. "A Potential Flow Theory and Boundary Layer Theory Based Hybrid Method for Waterjet Propulsion." Journal of Marine Science and Engineering 7, no. 4 (April 21, 2019): 113. http://dx.doi.org/10.3390/jmse7040113.
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A hybrid method—coupled with the boundary element method (BEM) for wave-making resistance, the empirical method (EM) for viscous resistance, and the boundary layer theory (BLT) for capture of an area’s physical parameters—was proposed to predict waterjet propulsion performance. The waterjet propulsion iteration process was established from the force-balanced waterjet–hull system by applying the hybrid approach. Numerical validation of the present method was carried out using the 1/8.556 scale waterjet-propelled ITTC (International Towing Tank Conference) Athena ship model. Resistance, attitudes, wave cut profiles, waterjet thrust, and thrust deduction showed similar tendencies to the experimental curves and were in good agreement with the data. The application of the present hybrid method to the side-hull configuration research of a trimaran indicates that the side-hull arranged at the rear of the main hull contributed to energy-saving and high-efficiency propulsion. In addition, at high Froude numbers, the “fore-body trimaran” showed a local advantage in resistance and thrust deduction.
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Dillmann, Andreas. "Linear potential theory of steady internal supersonic flow with quasi-cylindrical geometry. Part 2. Free jet flow." Journal of Fluid Mechanics 286 (March 10, 1995): 327–57. http://dx.doi.org/10.1017/s0022112095000759.
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By extending the methods of Part 1, the general problem of steady cylindrical supersonic free jet flow is treated in a similar manner to the flow in quasi-cylindrical ducts. It is shown that the presence of a finite pressure jump at the nozzle lip gives rise to a periodic singularity pattern in the flow field. Basic examples of free jet flows are discussed, and for the case of a nearly ideally expanded axisymmetric jet, theoretical Mach—Zehnder interferograms are calculated by analytical integration of the density field. Excellent agreement with experiment proves the validity of linear theory even close to the singularities and far downstream of the nozzle orifice. Furthermore, it is shown that Pack's formula for the wavelength of the shock cell structure is inconsistent; the correct formula is derived and excellent agreement with Emden's empirical fit is found.
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Dowell, Earl H., and Donald B. Bliss. "New Look at Unsteady Supersonic Potential Flow Aerodynamics and Piston Theory." AIAA Journal 51, no. 9 (September 2013): 2278–81. http://dx.doi.org/10.2514/1.j052088.
Full textDissertations / Theses on the topic "Potential flow theory"
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Dodworth, Kieran. "The application of potential flow theory to damaged hull dynamics." Thesis, University of Strathclyde, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366890.
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Capanna, Roberto. "Modelling of fluid structure interaction by potential flow theory in a pwr under seismic excitation." Thesis, Ecole centrale de Marseille, 2018. http://www.theses.fr/2018ECDM0013/document.
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Une modélisation efficace et une connaissance précise du comportement mécanique du cœur du réacteur sont nécessaires pour estimer les effets de l'excitation sismique sur une centrale nucléaire. La présence d'un écoulement d'eau (dans les REP) engendre des phénomènes d'interaction fluide structure. La modélisation des interactions fluide structure sur les assemblages combustible revêt donc une importance fondamentale pour la sécurité des réacteurs nucléaires. L’objectif principal du projet de thèse présenté dans ce document est d’étudier les interactions fluide structure afin de mieux comprendre les phénomènes impliqués. La modélisation et l'approche expérimentale sont considérées. Un nouveau modèle linéaire simplifié pour les interactions fluide structure est développé en utilisant la théorie de l'écoulement potentiel pour la modélisation des forces fluide, tandis que le modèle de poutre d'Euler-Bernoulli est utilisé pour la partie structurelle. Le modèle est d'abord développé pour un seul cylindre et il est validé avec des ouvrages de référence dans la littérature. Les effets de la taille de confinement et du nombre d'onde sont examinés. Le modèle d'écoulement potentiel développé pour un seul cylindre est ainsi étendu à une géométrie multicylindre. La démarche expérimentale est donc nécessaire pour valider le modèle développé. Une nouvelle installation expérimentale, ICARE, a été conçue pour étudier les phénomènes d’interaction fluide structure sur des assemblages combustible à demi-échelle. Dans ce document, les résultats fournis par les mesures de déplacement et de LDV sont largement analysés. Le comportement dynamique de l'assemblage combustible et les effets de couplage sont étudiés. Les calculs sont comparés aux résultats expérimentaux afin de valider le modèle et d’en analyser ses limites. Le modèle est en accord avec les résultats expérimentaux concernant l'effet de masse ajouté. De plus, le modèle prédit qualitativement les effets des couplages dans différentes directions. Par contre, le modèle d'écoulement potentiel ne permet pas de prédire des effets d'amortissement ajouté, principalement dus aux forces visqueuses. Enfin, dans ce document, une autre application du modèle développé est décrite. Le modèle est utilisé afin de simuler des expériences réalisées sur une maquette d'assemblage combustible dans l'installation expérimentale installée à l'Université George Washington (GWU). Le modèle est capable de prédire et de fournir une interprétation valide de la perturbation du débit d'eau due au mouvement de l'ensemble excité. La thèse se termine par des perspectives d'amélioration du modèle, en intégrant des termes visqueux dans les équations. L'analyse des données de vélocimétrie par image de particules (PIV) recueillies au cours des campagnes expérimentales ICARE doit être poursuivieEfficient modelling and accurate knowledge of the mechanical behaviour of the reactorcore are needed to estimate the effects of seismic excitation on a nuclear power plant. Thepresence of cooling water flow (in PWRs) gives rise to fluid structure interaction phenomena.Modelling of fluid structure interactions on fuel assemblies is thus of fundamentalimportance in order to assure the safety of nuclear reactors. The main objective of thePhD project which is presented in this document is to investigate fluid structure interactionsin order to have a better understanding of the involved phenomena. Both modellingand experimental approach are considered. A new simplified linear model for fluid structureinteractions is developed by using the potential flow theory for fluid force modellingwhile the Euler-Bernoulli beam model is used for the structural part. The model, is firstdeveloped for a single cylinder and it is validated with reference works in literature. Theeffects of the confinement size and of the wavenumber are investigated. The potential flowmodel developed for a single cylinder, is thus extended to a multi cylinders geometry. Theexperimental approach is thus needed in order to validate the developed model. A newexperimental facility, ICARE, is designed in order to investigate fluid structure interactionphenomena on half scale fuel assemblies. In this document, the results provided bydisplacement and LDV measurements are widely analysed. The dynamical behaviour ofthe fuel assembly and coupling effects are investigated. Calculations are compared to theexperimental results in order to validate the model and to analyse its limits. The model isin agreement with experimental results regarding the added mass effect. In addition, themodel qualitatively predicts couplings effects on different directions. As a drawback, thepotential flow model cannot predict added damping effects, which are mainly due to viscousforces. Finally in this document another application of the developed model is described.The model is used in order to simulate experiments performed on a surrogate fuel assemblyin the experimental facility installed at George Washington University (GWU). The modelis able to predict and to provide a valid interpretation for the water flow perturbation dueto the motion of the excited assembly. The thesis concludes with perspectives for furtherimprovements of the model, by integrating viscous terms in the equations. Work needs tobe carried out on the analysis of Particle Image Velocimetry (PIV) data collected duringICARE experimental campaigns
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Karban, Ugur. "Three-dimensional Flow Solutions For Non-lifting Flows Using Fast Multipole Boundary Element Method." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615042/index.pdf.
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Driving aim of this study was to develop a solver which is accurate enough to be used in analysis and fast enough to be used in optimization purposes. As a first step, a three-dimensional potential flow solver is developed using Fast Multipole Boundary Element (FMBEM) for calculating the pressure distributions in non-lifting flows.
It is a steady state solver which uses planar triangular unstructured mesh. After the geometry is introduced, the program creates a prescribed wake surface attached to the trailing edge(s), obtains a solution using panel elements on which the doublet and source strengths vary linearly. The reason for using FMBEM instead of classical BEM is the availability of solutions of systems having DOFs up to several millions within a few hours using a standard computer which is impossible to accomplish with classical BEM. Solutions obtained for different test cases are compared with the analytical solution (if applicable), the experimental data or the results obtained by JavaFoil.
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Goparaju, Kalyan. "Flow and Acoustic Characteristics of Complex Supersonic Jets." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1510933315034965.
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Aggarwal, Aditya Mohan. "B-Spline Boundary Element Method for Ships." ScholarWorks@UNO, 2008. http://scholarworks.uno.edu/td/853.
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The development of a three dimensional B-Spline based method, which is suitable for the steady-state potential flow analysis of free surface piercing bodies in hydrodynamics, is presented. The method requires the B-Spline or Non Uniform Rational B-Spline (NURBS) representation of the body as an input. In order to solve for the unknown potential, the source surface, both for the body as well as the free surface, is represented by NURBS surfaces. The method does not require the body surface to be discritized into flat panels. Therefore, instead of a mere panel approximation, the exact body geometry is utilized for the computation. The technique does not use a free surface Green's function, which already satisfies the linear free surface boundary conditions, but uses a separate source patch for the free surface. By eliminating the use of a free surface Green's function, the method can be extended to considering non-linear free surface conditions, thus providing the possibility for wave resistance calculations. The method is first applied to the double body flow problem around a sphere and a Wigley hull. Some comparisons are made with exact solutions to validate the accuracy of the method. Results of linear free surface conditions are then presented.
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Fogagnolo, Mattia. "Geometric Applications of Linear and Nonlinear Potential Theory." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/252169.
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We provide geometric inequalities on $R^n$ and on general manifolds with nonnegative Ricci curvature by employing suitable monotone quantities along the flow of capacitary and $p$-capacitary potentials, as well as through related boundary value problems. Among the main achievements, we cite
[(i)] a Willmore-type inequality on manifolds with nonnegative Ricci curvature leading in turn to the sharp Isoperimetric Inequality on $3$-manifolds with nonnegative Ricci curvature ;
[(ii)] enhanced Kasue/Croke-Kleiner splitting theorems ;
[(iii)] a generalised Minkowski-type inequality in $R^n$ holding with no assumptions on the boundary of the domain considered except for smoothness ;
[(iv)] a complete discussion of maximal volume solutions to the least area problem with obstacle on Riemannian manifolds and its relation
with the variational $p$-capacity.
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Nakanishi, Humberto de Carvalho. "Modelo computacional para avaliação do desempenho hidrodinâmico de embarcações de planeio em águas calmas." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/3/3135/tde-11072016-155508/.
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Em geral, uma embarcação de planeio é projetada para atingir elevados níveis de velocidade. Esse atributo de desempenho está diretamente relacionado ao porte da embarcação e à potência instalada em sua planta propulsiva. Tradicionalmente, durante o projeto de uma embarcação, as análises de desempenho são realizadas através de resultados de embarcações já existentes, retirados de séries sistemáticas ou de embarcações já desenvolvidas pelo estaleiro e/ou projetista. Além disso, a determinação dos atributos de desempenho pode ser feita através de métodos empíricos e/ou estatísticos, onde a embarcação é representada através de seus parâmetros geométricos principais; ou a partir de testes em modelos em escala reduzida ou protótipos. No caso específico de embarcações de planeio, o custo dos testes em escala reduzida é muito elevado em relação ao custo de projeto. Isso faz com que a maioria dos projetistas não opte por ensaios experimentais das novas embarcações em desenvolvimento. Ao longo dos últimos anos, o método de Savitsky foi largamente utilizado para se realizar estimativas de potência instalada de uma embarcação de planeio. Esse método utiliza um conjunto de equações semi-empíricas para determinar os esforços atuantes na embarcação, a partir dos quais é possível determinar a posição de equilíbrio de operação e a força propulsora necessária para navegar em uma dada velocidade. O método de Savitsky é muito utilizado nas fases iniciais de projeto, onde a geometria do casco ainda não foi totalmente definida, pois utiliza apenas as características geométricas principais da embarcação para realização das estimativas de esforços. À medida que se avança nas etapas de projeto, aumenta o detalhamento necessário das estimativas de desempenho. Para a realização, por exemplo, do projeto estrutural é necessária uma estimativa do campo de pressão atuante no fundo do casco, o qual não pode ser determinado pelo método de Savitsky. O método computacional implementado nesta dissertação, tem o objetivo de determinar as características do escoamento e o campo de pressão atuante no casco de uma embarcação de planeio navegando em águas calmas. O escoamento é determinado através de um problema de valor de contorno, no qual a superfície molhada no casco é considerada um corpo esbelto. Devido ao uso da teoria de corpo esbelto o problema pode ser tratado, separadamente, em cada seção, onde as condições de contorno são forçadamente respeitadas através de uma distribuição de vórtices.Generally, a planing craft is designed to achieve high speed levels. This performance attribute is directly related to the boat size and to the propeller plant power. Traditionally, during a boat design, performance analyses are carried out using results taken from systematic series or from others boat previously build by the shipyard and/or designer. Furthermore, performance attributes can be calculated by semi-empirical and/or statistic methods or by tests of reduced scale models. In the specific case of planing boats, the costs of reduced scale tests are too high compared to the design cost itself. Because of this, most designers do not perform experimental tests during the development of new boats. During the last years, the Savitsky method was extensively used to estimate planing craft effective power. The method uses a set of semi-empirical equations to calculate the forces acting on the boat, from which the equilibrium position and the required propeller thrust are determined. During the preliminary phases of planing craft design, the hull geometry hasn\'t been fully defined. Therefore, the Savitsky method is widely used during this phase, because it uses only the main geometrical characteristics to estimate the forces acting on the hull. Advancing toward the final phases of the design process, more detailed information is required. To execute the structural design, for example, the pressure field acting on the hull must be known, which can\'t be estimate using the Savitsky method. The main objective of the present study is to implement a computer method that can be used to estimate the fluid flow and pressure field acting on the hull of a boat moving with forward speed constant in calm water. The fluid flow around the hull is treated as a boundary value problem, in which the wetted hull surface is considered a slender body. The slender body theory enables to solve the problem separately, in each transverse section, where boundary conditions are respected by a sheet of vortices.
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Wang, Liguo. "Modelling and Advanced Control of Fully Coupled Wave Energy Converters Subject to Constraints: the Wave-to-wire Approach." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-320906.
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Ocean wave energy is a promising renewable source to contribute to supplying the world’s energy demand. The Division of Electricity at Uppsala University is developing a technology to capture energy from ocean waves with a wave energy converter (WEC) consisting of a linear permanent magnet generator and a point absorber. The linear generator is placed on sea bed and is driven directly by the floating absorber. Since March 2006, multiple wave energy converters have been deployed on the Swedish west coast outside the town of Lysekil. The technology is verified by long-term operation during at sea and satisfactory reliability of the electricity generation. This thesis focuses on developing advanced control strategies for fully coupled wave energy converters subject to constraints. A nonlinear control strategy is studied in detail for a single WEC subject to constraints under regular and irregular waves. Besides, two coordinated control strategies are developed to investigate the performance of a wave energy farm subject to constraints. The performance of the WECs using these control strategies are investigated in case studies, and optimal PTO damping coefficients are found to maximize the output power. The results show that these control strategies can significantly improve the performance of the WECs, in terms of mean power, compared to a conventional control. Besides these control strategies, a wave-to-wire simulation platform is built to study the power generation control of the WEC subject to constraints. The wave-to-wire simulation platform allows both nonlinear and linear control force. The results show that there is a good agreement between the desired value and the actual value after advanced control.
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Gundermann, Julia. "The Crooks Fluctuation Theorem Derived for Two-Dimensional Fluid Flow and its Potential to Improve Predictions." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-156748.
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The weather dynamics are significantly determined by the motion of the atmosphere and the ocean. This motion is often turbulent, characterized by fluctuations of the flow velocity over wide spatial and temporal scales. This fact, besides limited observability and inaccurate models, impedes the predictability of quantities such as the velocity of winds, which are relevant for the everyday life. One is always interested in improving such predictions - by employing better models or obtaining more information about the system.
The Crooks fluctuation theorem is a relation from nonequilibrium thermodynamics, which has its typical applications in nanoscale systems. It quantifies the distribution of imposed work in a process, where the system is pushed out of thermal equilibrium. This distribution is broadened due to the fluctuations of the microscopic degrees of freedom in the system.
The fluctuations of the velocity field in turbulent flow suggest the derivation of an analogy of Crooks' theorem for this macroscopic system. The knowledge about the validity of such a relation is additional information, which one in reverse could use to improve predictions about the system. In this thesis both issues are addressed: the derivation of the theorem, and the improvement of predictions.
We illustrate the application of Crooks' theorem to hydrodynamic flow within a model of a two-dimensional inviscid and incompressible fluid field, when pushed out of dynamical equilibrium. The flow on a rectangular domain is approximated by the two-dimensional vorticity equation with spectral truncation. In this setting, the equilibrium statistics of the flow can be described through a canonical ensemble with two conserved quantities, kinetic energy and enstrophy. To perturb the system out of equilibrium, we change the shape of the domain according to a protocol, which changes the kinetic energy but leaves the enstrophy constant. This is interpreted as doing work to the system. Evolving along a forward and its corresponding backward process, we find that the distributions of the work performed in these processes satisfy the Crooks relation with parameters derived from the canonical ensembles.
We address the issue of prediction in this thesis in a concrete setting: There are examples where the distributions of a variable in the forward and the backward process collapse into one, hence Crooks' theorem relates the distribution of one variable with itself. For a finite data set drawn from such a distribution, we are interested in an estimate of this variable to exceed a certain threshold. We demonstrate that, using the knowledge about Crooks' relation, forecast schemes can be proposed which improve compared to a pure frequency estimate on the data set. The findings are illustrated in three examples, studies of parameters such as exceedance threshold and data set size are presented.
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Gundermann, Julia. "The Crooks Fluctuation Theorem Derived for Two-Dimensional Fluid Flow and its Potential to Improve Predictions." Doctoral thesis, Technische Universität Dresden, 2014. https://tud.qucosa.de/id/qucosa%3A28433.
Full textAbstract:
The weather dynamics are significantly determined by the motion of the atmosphere and the ocean. This motion is often turbulent, characterized by fluctuations of the flow velocity over wide spatial and temporal scales. This fact, besides limited observability and inaccurate models, impedes the predictability of quantities such as the velocity of winds, which are relevant for the everyday life. One is always interested in improving such predictions - by employing better models or obtaining more information about the system.
The Crooks fluctuation theorem is a relation from nonequilibrium thermodynamics, which has its typical applications in nanoscale systems. It quantifies the distribution of imposed work in a process, where the system is pushed out of thermal equilibrium. This distribution is broadened due to the fluctuations of the microscopic degrees of freedom in the system.
The fluctuations of the velocity field in turbulent flow suggest the derivation of an analogy of Crooks' theorem for this macroscopic system. The knowledge about the validity of such a relation is additional information, which one in reverse could use to improve predictions about the system. In this thesis both issues are addressed: the derivation of the theorem, and the improvement of predictions.
We illustrate the application of Crooks' theorem to hydrodynamic flow within a model of a two-dimensional inviscid and incompressible fluid field, when pushed out of dynamical equilibrium. The flow on a rectangular domain is approximated by the two-dimensional vorticity equation with spectral truncation. In this setting, the equilibrium statistics of the flow can be described through a canonical ensemble with two conserved quantities, kinetic energy and enstrophy. To perturb the system out of equilibrium, we change the shape of the domain according to a protocol, which changes the kinetic energy but leaves the enstrophy constant. This is interpreted as doing work to the system. Evolving along a forward and its corresponding backward process, we find that the distributions of the work performed in these processes satisfy the Crooks relation with parameters derived from the canonical ensembles.
We address the issue of prediction in this thesis in a concrete setting: There are examples where the distributions of a variable in the forward and the backward process collapse into one, hence Crooks' theorem relates the distribution of one variable with itself. For a finite data set drawn from such a distribution, we are interested in an estimate of this variable to exceed a certain threshold. We demonstrate that, using the knowledge about Crooks' relation, forecast schemes can be proposed which improve compared to a pure frequency estimate on the data set. The findings are illustrated in three examples, studies of parameters such as exceedance threshold and data set size are presented.
Books on the topic "Potential flow theory"
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Dulikravich, George S. Theory of unsteady compressible irrotational flows including heat conductivity and longitudinal viscosity. New York: American Institute of Aeronautics and Astronautics, 1988.
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Chaffin, Mark S. Navier-Stokes and potential theory solutions for a helicopter fuselage and comparison with experiment. Hampton, Va: Langley Research Center, 1994.
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Wenyang, Duan, ed. Chuan bo zai bo lang zhong yun dong de shi liu li lun: Potential flow theory of ship motions in waves. Beijing Shi: Guo fang gong ye chu ban she, 2008.
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World Bank. Global Development Finance 2006 (Complete Print Edition): The Development Potential of Surging Capital Flows. Washington, D.C: The World Bank, 2006.
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Wentworth, Richard A., Duong H. Phong, Paul M. N. Feehan, Jian Song, and Ben Weinkove. Analysis, complex geometry, and mathematical physics: In honor of Duong H. Phong : May 7-11, 2013, Columbia University, New York, New York. Providence, Rhode Island: American Mathematical Society, 2015.
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L, Ashby Dale, and Ames Research Center, eds. Potential flow theory and operation guide for the panel code PMARC. Moffett Field, Calif: National Aeronautics and Space Administration, Ames Research Center, 1991.
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Kuo-Yen, Szema, and Langley Research Center, eds. Nonlinear potential analysis techniques for supersonic aerodynamic design. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1985.
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1934-, Jameson Antony, and United States. National Aeronautics and Space Administration., eds. Control theory based airfoil design for potential flow and a finite volume discretization. [Washington, DC: National Aeronautics and Space Administration, 1995.
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Control theory based airfoil design for potential flow and a finite volume discretization. [Washington, DC: National Aeronautics and Space Administration, 1995.
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Research Institute for Advanced Computer Science (U.S.), ed. Control theory based airfoil design using the Euler equations. [Moffett Field, Calif.]: Research Institute for Advanced Computer Science, NASA Ames Research Center, 1994.
Find full textBook chapters on the topic "Potential flow theory"
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Kaushik, Mrinal. "Potential Flow Theory." In Theoretical and Experimental Aerodynamics, 107–26. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-13-1678-4_4.
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Kreul, R., and H. Kretzschmar. "On Mathematical Modelling of Non-Newtonian Flow by Perturbation Methods." In Potential Theory, 197–200. Boston, MA: Springer US, 1988. http://dx.doi.org/10.1007/978-1-4613-0981-9_25.
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Pai, Shih-I., and Shijun Luo. "Linearized Theory of Three-Dimensional Potential Flow." In Theoretical and Computational Dynamics of a Compressible Flow, 345–94. Boston, MA: Springer US, 1991. http://dx.doi.org/10.1007/978-1-4757-1619-1_12.
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Kim, Sung Jae, and Jongyoon Han. "Nonlinear Electrokinetic Flow: Theory, Experiment, and Potential Applications." In IUTAM Symposium on Advances in Micro- and Nanofluidics, 3–17. Dordrecht: Springer Netherlands, 2009. http://dx.doi.org/10.1007/978-90-481-2626-2_1.
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Joseph, Daniel D. "The Role of Potential Flow in the Theory of the Navier-Stokes Equations." In Advances in Mathematical Fluid Mechanics, 311–17. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-04068-9_19.
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Zhang, Bao-Ji, and Sheng-Long Zhang. "The Optimization of the Hull Form with the Minimum Wave-Making Resistance Based on Potential Flow Theory." In Research on Ship Design and Optimization Based on Simulation-Based Design (SBD) Technique, 143–95. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-10-8423-2_5.
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Hall, Heather M., and Kelly Vodden. "Learning, knowledge flows, and innovation in Canadian regions." In The Theory, Practice, and Potential of Regional Development, 183–211. Abingdon, Oxon ; New York, NY : Routledge, 2019. | Series: Regions and cities ; 136: Routledge, 2019. http://dx.doi.org/10.4324/9781351262163-9.
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Harris, T. E. "Isotropic stochastic flows and a related property of non-random potential flows." In Stochastic Processes and Their Applications, 66–74. Berlin, Heidelberg: Springer Berlin Heidelberg, 1986. http://dx.doi.org/10.1007/bfb0076873.
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Scholle, Markus, Marcel Mellmann, Philip H. Gaskell, Lena Westerkamp, and Florian Marner. "Multilayer Modelling of Lubricated Contacts: A New Approach Based on a Potential Field Description." In Springer Tracts in Mechanical Engineering, 359–75. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-60124-9_16.
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AbstractA first integral approach, derived in an analogous fashion to Maxwell’s use of potential fields, is employed to investigate the flow characteristics, with a view to minimising friction, of shear-driven fluid motion between rigid surfaces in parallel alignment as a model for a lubricated joint, whether naturally occurring or engineered replacement. For a viscous bilayer arrangement comprised of immiscible liquids, it is shown how the flow and the shear stress along the separating interface is influenced by the mean thickness of the layers and the ratio of their respective viscosities. Considered in addition, is how the method can be extended for application to the more challenging problem of when one, or both, of the layers is a viscoelastic material.
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Jasminská, Natália. "Mesurement of Energy Flows and CO2 Emissions Balance of the Low-Potential Heat Source in Combination with a Cogeneration Unit." In Aspects of Computational Intelligence: Theory and Applications, 63–82. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-30668-6_5.
Full textConference papers on the topic "Potential flow theory"
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Shi, Zeyu, Xiongliang Yao, Jiaolong Zhao, Longquan Sun, and Yue Tian. "Research on Trailing Cavity of Underwater Vehicles Based on Potential Flow Theory." In ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/omae2018-78676.
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In the exceeding water process of underwater vehicles, the existing of trailing cavity will have distinct effects on the hydrodynamic characteristics of vehicles. Recent researches mostly leave gravity effect out of consideration, while the gravity will affect trailing cavity characteristics and then affect the hydrodynamic characteristics of vehicles. In this study, we research the effect of gravity on the trailing cavity of underwater vehicles. Firstly, a complex boundary model which taken partial cavity into consideration is established based on potential flow theory and a program according to this model is written. Because all flow parameter has nothing to do with the radial location, the research problem can be simplified as a two-dimensional problem and studied in polar coordinates. With regularization of the length of the navigation calculation model, infinity to flow velocity and the distance pressure, research domain can be represented by plane in the containing slit. The program is proved to be effective by comparison the results with the data in existing papers. Finally, we calculate the trailing cavity forms of a cone and an underwater vehicle under different cavitation numbers and Froude numbers to study the rules of trailing cavity forms changing with cavitation number and Froude number. Under the same number of Froude, the cavity size of the rear part of vehicle gradually decreases with the increasing cavitation number, and the maximum radius of the cavity equals to the biggest size of the tail radius of the vehicle. Under the same cavitation number bodies, vehicle trailing cavity length gradually increases with the increase of Froude number, but radius of the cavity of the vehicle changed little, the largest radius is equivalent to the tail radius of the vehicle.
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Li, Wang-Long. "Effects of Electrokinetic Slip Flow on Lubrication Theory." In ASME/STLE 2007 International Joint Tribology Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ijtc2007-44167.
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A lubrication theory that includes the effects of electric double layer (EDL) and boundary slip is developed. Both effects are important in microflow, and thus in lubrication problems. They have opposite effects on velocity distributions between lubricating surfaces. Also, the velocity distribution induced by the EDL stream potential (electroviscous effect) is affected by the boundary slip. Under the usual assumptions of lubrication and Debye-Hu¨ckel approximation for low surface potential, the Navier-Stokes equation with body force due to the electrical potential as well as the widely accepted Navier slip boundary conditions is utilized on deriving the modified Reynolds equation. Effects of EDL and boundary slip on the 1-D bearing performance are discussed by solving the modified Reynolds equation numerically.
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Reuter, J., and A. Jameson. "Control theory based airfoil design for potential flow and a finite volume discretization." In 32nd Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1994. http://dx.doi.org/10.2514/6.1994-499.
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Mughal, Umair Najeeb. "Using potential flow theory and conformal mapping technique to measure pressure differential on airfoil." In ICNPAA 2016 WORLD CONGRESS: 11th International Conference on Mathematical Problems in Engineering, Aerospace and Sciences. Author(s), 2017. http://dx.doi.org/10.1063/1.4972692.
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Valentine, Daniel T., and Farshad Madhi. "Unsteady Potential Flow Theory and Numerical Analysis of Forces on Cylinders Induced by Nearby Oscillating Disturbances." In ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/omae2009-80124.
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The complete solution of several two-dimensional potential flow problems are reported that deal with the unsteady flow around circular cylinders. Three of the flows considered are induced by an oscillating disturbance near the cylinder. The three elemental disturbances examined are (1) a pulsating source, (2) a pulsating doublet and (3) a pulsating vortex. The formulas for the force acting on the cylinder due to each of the elemental disturbances were derived by applying the method of images and checked by deriving the equivalent surface distribution of sources to model the cylinder starting with Green’s second identity. The theory helped direct the development of a boundary-integral numerical model described and applied in this paper to solve the unsteady flow around a circular cylinder due to an arbitrarily specified oscillatory disturbance near the cylinder. The numerical method is validated by comparing predictions of the force with the exact solutions.
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Toulouse, Michael M., Guislain Doljac, Van P. Carey, and Cullen Bash. "Exploration of a Potential-Flow-Based Compact Model of Air-Flow Transport in Data Centers." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-10806.
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This paper summarizes an exploration of a compact model of air flow and transport in data centers developed from potential flow theory. Boundaries for the airflow in the data center are often complex due to the numerous rows of servers and other equipment in the facility, and there are generally multiple air inlets and outlets, which produce a fairly complex three-dimensional flow field in the air space in the data center. The general problem of airflow and convective transport in a data center requires accurate treatment of a turbulent flow in a complex flow passage with some buoyancy effects. As a result, full CFD thermofluidic models tend to be time-consuming and tedious to set up for such complex flow circumstances. In this initial study, we formulated an approximate model that retains only the most basic physical mechanisms of the flow. The resulting model of air flow in the data center is based on potential flow theory, which is exact for irrotational inviscid flow. The temperature field resulting from server heat input is determined by solving the convective energy transport equation along potential flow streamlines. This innovative approach, which takes advantage of the irrotational character of the modeled flow, provides a fast computational method for determining the temperature field and convective transport of thermal energy in the data center. Computations to predict the three-dimensional flow and temperature fields with the model typically require less than 60 seconds to complete on a laptop computer. Flow and temperature field results predicted by the model for typical data center flow circumstances are presented and limitations of the model are assessed. Features of an intuitive graphical user interface for the model that simplifies input of the data center design parameters are also described. Results for case studies indicate low sensitivity to mesh size and convergence criteria. Although the flow and temperature field models developed here are more approximate than full CFD methods, they are good first approximations that provide the means to rapidly explore the parameter space for the data center design. This model can be used to quickly identify the optimal region of the design space, whereupon a more detailed CFD modeling can be used to fine-tune an optimal design. The results of this investigation demonstrate that this type of fast compact model can be a very useful tool when used as a precursor to full CFD modeling in data center design optimization.
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Plagnard, T., C. Béguin, and S. Étienne. "Predicting Fluidelastic Instability in Tube Array With Potential Theory." In ASME 2014 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/pvp2014-28459.
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This paper studies the possibility to use potential theory to predict fluidelastic instability critical velocity in tube bundles. Potential flow is calculated semi analytically using Laurent expansions with the addition of discrete vortices behind the tube. The only experimental criterion used in this approach is the location of vortices behind the tubes. Using the linearized unsteady Bernoulli theorem we are able to model fluid forces as added mass, damping and stiffness effects. Fluid forces include coupling terms; that is the force on another tube induced by tube acceleration, velocity and location. The tube array is then described by a mass, damping and stiffness. The fluidelastic instability critical velocity becomes the solution of a linear eigenvalue problem. This approach has been compared with several experimental values of mass, damping and stiffness measurements, as well as the critical velocity. Mass matrix is in a very good agreement with experimental values, however damping and stiffness models still need some improvement. In the end, the model is able to predict the critical velocity within 20% of experimental values. This approach does not need stiffness experimental values (stability derivative) nor time delay as the stiffness, damping and mass matrices are calculated independently. The main purpose of this work is to understand the effect of induced forces involved in the fluidelastic instability.
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Jianjun, Wu. "Potential Theory Based Blank Design for Deep Drawing Irregular Shaped Components." In ASME 2008 International Manufacturing Science and Engineering Conference collocated with the 3rd JSME/ASME International Conference on Materials and Processing. ASMEDC, 2008. http://dx.doi.org/10.1115/msec_icmp2008-72544.
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A computer aided blank design method based on the potential theory and boundary element methods is presented. The potential theory approximately describes the material flow involved in deep drawing processes. Using the CAD model of an irregular shaped component, a specific number of cross sections at different heights can be generated. In order to obtain the blank shape, the outermost contour is determined by developing these sections gradually. This blank design procedure is like an imaginary reverse material flow governed by the potential theory. In addition, the boundary element method provides a good computational efficiency. This computer aided design method has been found effective by a manufacturer and the proposed approach can be used for a wide variety of complicated deep drawing components.
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Shao, Yan-Lin, and Odd M. Faltinsen. "Towards Efficient Fully-Nonlinear Potential-Flow Solvers in Marine Hydrodynamics." In ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/omae2012-83319.
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Solving potential-flow problems using the Boundary Element Method (BEM) is a strong tradition in marine hydrodynamics. An early example of the application of BEM is by Bai & Yeung [1]. The bottleneck of the conventional BEM in terms of CPU time and computer memory arises as the number of unknowns increases. Wu & Eatock Taylor [2] suggested that the Finite Element Method (FEM) field solver is much faster than the BEM based on their comparisons in a wave making problem. In this paper, we aim to find a highly efficient method to solve fully-nonlinear wave-body interaction problems based on potential-flow theory. We compare the efficiency and the accuracy of five different methods for the potential flows in two dimensions (2D), two of which are BEM-based while the other three are field solvers. The comparisons indicate that it is beneficial to use either an accelerated matrix-free BEM, e.g. Fast Multipole Method accelerated BEM (FMM-BEM), or any field solvers whose resulting matrix are sparse. Another highlight of this paper is that an efficient numerical potential-flow method named the harmonic polynomial cell (HPC) method is developed. The flow in each cell is described by a set of harmonic polynomials. The presented procedure has approximately 4th order accuracy, while its resulting matrix is sparse similarly as the other field solvers, e.g. Finite Element Method (FEM), Finite Difference Method (FDM) and Finite Volume Method (FVM). The method is verified by a linear wave making problem for which the steady-state analytical solution is available, and the forced oscillation of a semi-submerged circular cylinder for which the frequency-domain added mass and damping coefficients are compared. The fully-nonlinear wave making problem and nonlinear propagating waves over a submerged bar are also studied for validation purposes. Only 2D cases are studied in this paper.
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Kerboua, Y., A. A. Lakis, M. Thomas, L. Marcouiller, and M. H. Toorani. "Critical Velocity of Potential Flow in Interaction With a System of Plates." In 17th International Conference on Nuclear Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/icone17-76059.
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The elastic structures subjected to flowing flow can undergo the excessive vibrations and consequently a considerable change in their dynamic behavior, and they may lose their stability. A fluid-solid finite element model is developed to model a set of plates subjected to flowing fluid under various boundary conditions, fluid level, and fluid velocity that strongly influence the dynamic behavior of the plates. A hybrid method, which combines the finite element approach with the classical theory of plates, is used to derive the dynamic equations of the coupled fluid-structure system. The membrane and the transversal displacement fields are modeled, respectively, using the bilinear polynomials and the exponential function. The structural mass and rigidity matrices are derived by exact integration of developed displacement field. The fluid pressure is expressed by inertial, Coriolis and centrifugal fluid forces written, respectively, as a function of acceleration, velocity and transversal displacement. The fluid dynamic pressure is determined using the potential flow equation. Integrating this dynamic pressure in conjunction with the structural element results in the flow-induced mass, damping, and stiffness matrices, hence, one can establish the dynamic equations of coupled fluid-structure system. The impermeability condition that ensures the permanent contact between the shell and the fluid is applied at the contact surface. A parametric study has been performed to investigate the effect of physical and geometrical parameters (e.g. boundary conditions, fluid level, and flow velocity) on the dynamic response of the coupled system. The results are in satisfactorily agreement with those of experiments and other theories.
Reports on the topic "Potential flow theory"
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Melanie, Haupt, and Hellweg Stefanie. Synthesis of the NRP 70 joint project “Waste management to support the energy turnaround (wastEturn)”. Swiss National Science Foundation (SNSF), January 2020. http://dx.doi.org/10.46446/publication_nrp70_nrp71.2020.2.en.
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A great deal of energy can be sourced both directly and indirectly from waste. For example, municipal waste with an energy content of around 60 petajoules is incinerated in Switzerland every year. The energy recovered directly from this waste covers around 4 % of the Swiss energy demand. However, the greatest potential offered by waste management lies in the recovery of secondary raw materials during the recycling process, thus indirectly avoiding the energy-intensive production of primary raw materials. In order to optimise the contribution to the energy turnaround made by waste management, as a first step, improvements need to be made with respect to the transparent documentation of material and cash flows, in particular. On the basis of this, prioritisation according to the energy efficiency of various recycling and disposal channels is required. Paper and cardboard as well as plastic have been identified as the waste fractions with the greatest potential for improvement. In the case of paper and cardboard, the large quantities involved result in considerable impact. With the exception of PET drinks bottles, plastic waste is often not separately collected and therefore offers substantial improvement potential. Significant optimisation potential has also been identified with regard to the energy efficiency of incineration plants. To allow municipal solid waste incineration (MSWI) plants to use the heat they generate more effectively, however, consumers of the recovered steam and heat need to be located close by. A decisive success factor when transitioning towards an energy-efficient waste management system will be the cooperation between the many stakeholders of the federally organised sector. On the one hand, the sector needs to be increasingly organised along the value chains. On the other hand, however, there is also a need to utilise the freedom that comes with federal diversity in order to test different solutions.
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Rusk, Todd, Ryan Siegel, Linda Larsen, Tim Lindsey, and Brian Deal. Technical and Financial Feasibility Study for Installation of Solar Panels at IDOT-owned Facilities. Illinois Center for Transportation, August 2021. http://dx.doi.org/10.36501/0197-9191/21-024.
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The Smart Energy Design Assistance Center assessed the administrative, technical, and economic aspects of feasibility related to the procurement and installation of photovoltaic solar systems on IDOT-owned buildings and lands. To address administrative feasibility, we explored three main ways in which IDOT could procure solar projects: power purchase agreement (PPA), direct purchase, and land lease development. Of the three methods, PPA and direct purchase are most applicable for IDOT. While solar development is not free of obstacles for IDOT, it is administratively feasible, and regulatory hurdles can be adequately met given suitable planning and implementation. To evaluate IDOT assets for solar feasibility, more than 1,000 IDOT sites were screened and narrowed using spatial analytic tools. A stakeholder feedback process was used to select five case study sites that allowed for a range of solar development types, from large utility-scale projects to small rooftop systems. To evaluate financial feasibility, discussions with developers and datapoints from the literature were used to create financial models. A large solar project request by IDOT can be expected to generate considerable attention from developers and potentially attractive PPA pricing that would generate immediate cash flow savings for IDOT. Procurement partnerships with other state agencies will create opportunities for even larger projects with better pricing. However, in the near term, it may be difficult for IDOT to identify small rooftop or other small on-site solar projects that are financially feasible. This project identified two especially promising solar sites so that IDOT can evaluate other solar site development opportunities in the future. This project also developed a web-based decision-support tool so IDOT can identify potential sites and develop preliminary indications of feasibility. We recommend that IDOT begin the process of developing at least one of their large sites to support solar electric power generation.
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Winkler-Portmann, Simon. Umsetzung einer wirksamen Compliance in globalen Lieferketten am Beispiel der Anforderungen aus der europäischen Chemikalien-Regulierung an die Automobilindustrie. Sonderforschungsgruppe Institutionenanalyse, August 2020. http://dx.doi.org/10.46850/sofia.9783941627796.
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This publication based on a master thesis explores the challenges of the automotive industry regarding the European chemical regulations REACH and CLP, as well as potential improvements of the current compliance activities and the related incentives and barriers. It answers the research question: "To what extent should the compliance activities of actors in the automotive supply chain be extended in order to meet the requirements of European chemicals regulation; and where would it help to strengthen incentives in enforcement and the legal framework?“. The study’s structure is based on the transdisciplinary delta analysis of the Society for Institutional Analysis at the Darmstadt University of Applied Sciences. It compares the target state of the legal requirements and the requirements for corresponding compliance with the actual state of the actual compliance measures of the automotive players and attempts to identify their weak points (the delta). The main sources for the analysis are the legal texts and relevant court decisions as well as guideline-based expert interviews with automotive players based on Gläser & Laudel. As objects of the analysis, there are in addition answers to random enquiries according to Article 33 (2) REACH as well as the recommendations and guidelines of the industry associations. The analysis identifies the transmission of material information in the supply chain as a key problem. The global database system used for this purpose, the IMDS, shows gaps in the framework conditions. This results in compliance risk due to the dynamically developing regulation. In addition, the study identifies an incompliance of the investigated automobile manufacturers with regard to Art. 33 REACH. In answering the research question, the study recommends solutions to the automotive players that extend the current compliance activities. In addition, it offers tables and process flow diagrams, which structure the duties and required compliance measures and may serve as basic audit criteria. The analysis is carried out from an external perspective and looks at the entire industry. It therefore cannot cover all the individual peculiarities of each automotive player. As a result, the identified gaps serve only as indications for possible further compliance risks.
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Cooper, Christopher, Jacob McDonald, and Eric Starkey. Wadeable stream habitat monitoring at Congaree National Park: 2018 baseline report. National Park Service, June 2021. http://dx.doi.org/10.36967/nrr-2286621.
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The Southeast Coast Network (SECN) Wadeable Stream Habitat Monitoring Protocol collects data to give park resource managers insight into the status of and trends in stream and near-channel habitat conditions (McDonald et al. 2018a). Wadeable stream monitoring is currently implemented at the five SECN inland parks with wadeable streams. These parks include Horseshoe Bend National Military Park (HOBE), Kennesaw Mountain National Battlefield Park (KEMO), Ocmulgee Mounds National Historical Park (OCMU), Chattahoochee River National Recreation Area (CHAT), and Congaree National Park (CONG). Streams at Congaree National Park chosen for monitoring were specifically targeted for management interest (e.g., upstream development and land use change, visitor use of streams as canoe trails, and potential social walking trail erosion) or to provide a context for similar-sized stream(s) within the park or network (McDonald and Starkey 2018a). The objectives of the SECN wadeable stream habitat monitoring protocol are to: Determine status of upstream watershed characteristics (basin morphology) and trends in land cover that may affect stream habitat, Determine the status of and trends in benthic and near-channel habitat in selected wadeable stream reaches (e.g., bed sediment, geomorphic channel units, and large woody debris), Determine the status of and trends in cross-sectional morphology, longitudinal gradient, and sinuosity of selected wadeable stream reaches. Between June 11 and 14, 2018, data were collected at Congaree National Park to characterize the in-stream and near-channel habitat within stream reaches on Cedar Creek (CONG001, CONG002, and CONG003) and McKenzie Creek (CONG004). These data, along with the analysis of remotely sensed geographic information system (GIS) data, are presented in this report to describe and compare the watershed-, reach-, and transect-scale characteristics of these four stream reaches to each other and to selected similar-sized stream reaches at Ocmulgee Mounds National Historical Park, Kennesaw Mountain National Battlefield Park, and Chattahoochee National Recreation Area. Surveyed stream reaches at Congaree NP were compared to those previously surveyed in other parks in order to provide regional context and aid in interpretation of results. edar Creek’s watershed (CONG001, CONG002, and CONG003) drains nearly 200 square kilometers (77.22 square miles [mi2]) of the Congaree River Valley Terrace complex and upper Coastal Plain to the north of the park (Shelley 2007a, 2007b). Cedar Creek’s watershed has low slope and is covered mainly by forests and grasslands. Cedar Creek is designated an “Outstanding Resource Water” by the state of South Carolina (S.C. Code Regs. 61–68 [2014] and S.C. Code Regs. 61–69 [2012]) from the boundary of the park downstream to Wise Lake. Cedar Creek ‘upstream’ (CONG001) is located just downstream (south) of the park’s Bannister Bridge canoe landing, which is located off Old Bluff Road and south of the confluence with Meyers Creek. Cedar Creek ‘middle’ and Cedar Creek ‘downstream’ (CONG002 and CONG003, respectively) are located downstream of Cedar Creek ‘upstream’ where Cedar Creek flows into the relatively flat backswamp of the Congaree River flood plain. Based on the geomorphic and land cover characteristics of the watershed, monitored reaches on Cedar Creek are likely to flood often and drain slowly. Flooding is more likely at Cedar Creek ‘middle’ and Cedar Creek ‘downstream’ than at Cedar Creek ‘upstream.’ This is due to the higher (relative to CONG001) connectivity between the channels of the lower reaches and their out-of-channel areas. Based on bed sediment characteristics, the heterogeneity of geomorphic channel units (GCUs) within each reach, and the abundance of large woody debris (LWD), in-stream habitat within each of the surveyed reaches on Cedar Creek (CONG001–003) was classified as ‘fair to good.’ Although, there is extensive evidence of animal activity...
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Financial Stability Report - First Semester of 2020. Banco de la República de Colombia, March 2021. http://dx.doi.org/10.32468/rept-estab-fin.1sem.eng-2020.
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In the face of the multiple shocks currently experienced by the domestic economy (resulting from the drop in oil prices and the appearance of a global pandemic), the Colombian financial system is in a position of sound solvency and adequate liquidity. At the same time, credit quality has been recovering and the exposure of credit institutions to firms with currency mismatches has declined relative to previous episodes of sudden drops in oil prices. These trends are reflected in the recent fading of red and blue tonalities in the performance and credit risk segments of the risk heatmaps in Graphs A and B.1 Naturally, the sudden, unanticipated change in macroeconomic conditions has caused the appearance of vulnerabilities for short-term financial stability. These vulnerabilities require close and continuous monitoring on the part of economic authorities. The main vulnerability is the response of credit and credit risk to a potential, temporarily extreme macroeconomic situation in the context of: (i) recently increased exposure of some banks to household sector, and (ii) reductions in net interest income that have led to a decline in the profitability of the banking business in the recent past. Furthermore, as a consequence of greater uncertainty and risk aversion, occasional problems may arise in the distribution of liquidity between agents and financial markets. With regards to local markets, spikes have been registered in the volatility of public and private fixed income securities in recent weeks that are consistent with the behavior of the international markets and have had a significant impact on the liquidity of those instruments (red portions in the most recent past of some market risk items on the map in Graph A). In order to adopt a forward-looking approach to those vulnerabilities, this Report presents a stress test that evaluates the resilience of credit institutions in the event of a hypothetical scenario thatseeks to simulate an extreme version of current macroeconomic conditions. The scenario assumes a hypothetical negative growth that is temporarily strong but recovers going into the middle of the coming year and has extreme effects on credit quality. The results suggest that credit institutions have the ability to withstand a significant deterioration in economic conditions in the short term. Even though there could be a strong impact on credit, liquidity, and profitability under the scenario being considered, aggregate capital ratios would probably remain at above their regulatory limits over the horizon of a year. In this context, the recent measures taken by both Banco de la República and the Office of the Financial Superintendent of Colombia that are intended to help preserve the financial stability of the Colombian economy become highly relevant. In compliance with its constitutional objectives and in coordination with the financial system’s security network, Banco de la República will continue to closely monitor the outlook for financial stability at this juncture and will make the decisions that are necessary to ensure the proper functioning of the economy, facilitate the flow of sufficient credit and liquidity resources, and further the smooth functioning of the payment system. Juan José Echavarría Governor