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Letteratura scientifica selezionata sul tema "Oscillator flows"

Autore: Grafiati

Pubblicato: 12 aprile 2025

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Articoli di riviste sul tema "Oscillator flows"

Portillo, Daniel J., Eugene Hoffman, Matt Garcia, Elijah LaLonde, Christopher Combs e R. Lyle Hood. "The Effects of Compressibility on the Performance and Modal Structures of a Sweeping Jet Emitted from Various Scales of a Fluidic Oscillator". Fluids 7, n. 7 (21 luglio 2022): 251. http://dx.doi.org/10.3390/fluids7070251.

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Investigations of fluidic oscillators, or sweeping jet actuators, have primarily been conducted within the incompressible flow regime, which limits the accuracy of estimating fluidic oscillator performance for compressible flows. The objective of this study was to evaluate the effects of gas compressibility on the performance of a fluidic oscillator. A commonly used fluidic oscillator geometry (the Bray geometry) was scaled to five different sizes, 3D printed, and tested over a range of air flow rates. High-speed Schlieren images captured the sweeping jet exiting the fluidic oscillators, and custom MATLAB algorithms were used to calculate the oscillation frequencies and angles. A spectral proper orthogonal decomposition (SPOD) method was used to identify and compare the mode structures within the flow fields. All the results were compared using dimensionless parameters to observe performance trends. The results showed that the oscillation frequencies were directly proportional to the flow rate, while the oscillation angles were inversely proportional to the flow rate, regardless of scale size. The angular velocities were not proportional to the flow rate or scale size and exhibited maxima within the evaluated ranges. For all scale sizes, the mode structures were symmetric across the centerlines of the fluidic oscillators and extended further beyond the fluidic oscillators at higher flow rates. These results enable the prediction of fluidic oscillator performance, which can significantly improve the design process for an application where a fluidic oscillator may be used, such as aerospace applications, power generation, heat exchangers, or medical devices.

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Shardt, Orest, Hassan Masoud e Howard A. Stone. "Oscillatory Marangoni flows with inertia". Journal of Fluid Mechanics 803 (19 agosto 2016): 94–118. http://dx.doi.org/10.1017/jfm.2016.507.

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When the surface of a liquid has a non-uniform distribution of a surfactant that lowers surface tension, the resulting variation in surface tension drives a flow that spreads the surfactant towards a uniform distribution. We study the spreading dynamics of an insoluble and non-diffusing surfactant on an initially motionless liquid. We derive solutions for the evolution over time of sinusoidal variations in surfactant concentration with a small initial amplitude relative to the average concentration. In this limit, the coupled flow and surfactant transport equations are linear. In contrast to exponential decay when the inertia of the flow is negligible, the solution for unsteady Stokes flow exhibits oscillations when inertia is sufficient to spread the surfactant beyond a uniform distribution. This oscillatory behaviour exhibits two properties that distinguish it from that of a simple harmonic oscillator: the amplitude changes sign at most three times, and the decay at late times follows a power law with an exponent of $-3/2$. As the surface oscillates, the structure of the subsurface flow alternates between one and two rows of counter-rotating vortices, starting with one row and ending with two during the late-time monotonic decay. We also examine numerically the evolution of the surfactant distribution when the system is nonlinear due to a large initial amplitude.

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Kovacic, Ivana, Matthew Cartmell e Miodrag Zukovic. "Mixed-mode dynamics of certain bistable oscillators: behavioural mapping, approximations for motion and links with van der Pol oscillators". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 471, n. 2184 (dicembre 2015): 20150638. http://dx.doi.org/10.1098/rspa.2015.0638.

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This study is concerned with a new generalized mathematical model for single degree-of-freedom bistable oscillators with harmonic excitation of low-frequency, linear viscous damping and a restoring force that contains a negative linear term and a positive nonlinear term which is a power-form function of the generalized coordinate. Comprehensive numerical mapping of the range of bifurcatory behaviour shows that such non-autonomous systems can experience mixed-mode oscillations, including bursting oscillations (fast flow oscillations around the outer curves of a slow flow), and relaxation oscillations like a classical (autonomous) van der Pol oscillator. After studying the global system dynamics the focus of the investigations is on cubic oscillators of this type. Approximate techniques are presented to quantify their response, i.e. to determine approximations for both the slow and fast flows. In addition, a clear analogy between the behaviour of two archetypical oscillators—the non-autonomous bistable oscillator operating at low frequency and the strongly damped autonomous van der Pol oscillator—is established for the first time.

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LUO, ALBERT C. J., e MOZHDEH S. FARAJI MOSADMAN. "SINGULARITY, SWITCHABILITY AND BIFURCATIONS IN A 2-DOF, PERIODICALLY FORCED, FRICTIONAL OSCILLATOR". International Journal of Bifurcation and Chaos 23, n. 03 (marzo 2013): 1330009. http://dx.doi.org/10.1142/s0218127413300097.

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In this paper, the analytical dynamics for singularity, switchability, and bifurcations of a 2-DOF friction-induced oscillator is investigated. The analytical conditions of the domain flow switchability at the boundaries and edges are developed from the theory of discontinuous dynamical systems, and the switchability conditions of boundary flows from domain and edge flows are presented. From the singularity and switchability of flow to the boundary, grazing, sliding and edge bifurcations are obtained. For a better understanding of the motion complexity of such a frictional oscillator, switching sets and mappings are introduced, and mapping structures for periodic motions are adopted. Using an eigenvalue analysis, the stability and bifurcation analysis of periodic motions in the friction-induced system is carried out. Analytical predictions and parameter maps of periodic motions are performed. Illustrations of periodic motions and the analytical conditions are completed. The analytical conditions and methodology can be applied to the multi-degrees-of-freedom frictional oscillators in the same fashion.

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Vodinchar, Gleb. "Hereditary Oscillator Associated with the Model of a Large-Scale αω-Dynamo". Mathematics 8, n. 11 (19 novembre 2020): 2065. http://dx.doi.org/10.3390/math8112065.

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Cosmic magnetic fields possess complex time dynamics. They are characterized by abrupt polarity changes (reversals), fluctuations of fixed polarity, bursts and attenuations. These dynamic conditions can replace each other, including both regular and chaotic components. Memory in dynamo systems manifests itself in a feedback mechanism when a strong magnetic field begins to change the properties of turbulent flows. A hereditary oscillator can be the simplest model of such complex oscillatory systems with memory. The article suggests the construction of such oscillator by means of two-mode approximation of magnetic field components in the αω-dynamo model. The hereditary member describes the suppression of a field turbulent generator by magnetic helicity and determines the shape of oscillator potential. The article describes the implicit difference scheme for numerical research of oscillator. It also describes the results of numerical simulation for two cases—instantaneous feedback and delay in feedback. The results of simulation are interpreted in terms of oscillator theory. It is shown that the observed dynamic regimes in the model go well with the change of potential shape.

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Serrar, Abderrahim, Mohamed El Khlifi e Azeddine Kourta. "Characterisation and comparison of unsteady actuators: a fluidic oscillator and a sweeping jet". International Journal of Numerical Methods for Heat & Fluid Flow 32, n. 4 (4 ottobre 2021): 1237–54. http://dx.doi.org/10.1108/hff-07-2021-0474.

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Purpose The purpose of this study is to compare two unsteady actuators: an oscillator and a sweeping jet. Both actuators can produce an oscillating jet of different amplitudes and frequencies without any moving parts, making them an attractive actuator concept. The Coanda effect phenomenon can explain the operating principles of these two unsteady actuators. Design/methodology/approach A numerical study was conducted to compare the amplitudes and frequencies of fluidic and sweeping jet (SJ) oscillators to obtain an efficient actuator to control separated flows at high Reynolds numbers. For this goal, two-dimensional unsteady Reynolds-averaged Navier-Stokes simulations were carried out using computational fluid dynamics (CFD) fluent code to evaluate the actuator performances. The discrete fast Fourier transform method determined the oscillation frequencies. Findings The oscillation frequencies gradually increase as the inlet pressure increases. The characteristics and dimensions of the vortices produced in the mixing chamber and feedback loops vary overtime when the injected fluid is swept sideways. The frequencies supplied by the SJ are stronger than those obtained by the fluidic oscillator, which may contribute to improving the aerodynamic performance at a lower power supply cost. Originality/value The existence of the splitter in the fluidic oscillator led to the production of separate pulses, which would be useful in various industrial applications, including active control of combustion and mixing processes while other applications such as flow separation control require SJs. With the latter actuator higher and interesting frequencies can be obtained, leading to efficient flow control.

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KHEIRANDISH, F., e M. AMOOSHAHI. "RADIATION REACTION AND QUANTUM DAMPED HARMONIC OSCILLATOR". Modern Physics Letters A 20, n. 39 (21 dicembre 2005): 3025–34. http://dx.doi.org/10.1142/s0217732305018384.

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By taking a Klein–Gordon field as the environment of a harmonic oscillator and using a new method for dealing with quantum dissipative systems (minimal coupling method), we find out the quantum dynamics and radiation reaction for a quantum damped harmonic oscillator. Applying perturbation method, we obtain some transition probabilities indicating the way energy flows between oscillator, reservoir and quantum vacuum.

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Ma, Zhao Wei, Tiang Jiang Hu, Han Zhou, Guang Ming Wang e Dai Bing Zhang. "Modeling of Fish Adaptive Behaviors in Unsteady Flows". Applied Mechanics and Materials 461 (novembre 2013): 313–19. http://dx.doi.org/10.4028/www.scientific.net/amm.461.313.

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Fish can swim swiftly in complicated flow environments, which conceives inspirations for man-made underwater vehicles. This paper concentrates on observation and modeling of fish adaptive behaviors in unsteady flows. A good representative of bony fish, crucian, is taken as the experimental specimen for investigating biological adaptation with response to alteration of surrounding flow patterns. Difference of swimming parameters is confirmed by recorded samples within several flow patterns. Furthermore, a bio-inspired gait model is constructed to stimulate fish adaptive behaviors, since the traditional model is hardly suitable. The model is inspired and supported by biological neural oscillators. By using the developed neural oscillator model, not only certain rhythmic motions under a steady flow pattern can be generated, but also behavioral transitions between multiple different patterns within unsteady flows come true. Experimental results validate the effectiveness of the developed neural model in continuously and smoothly regulating fish propulsive patterns within unsteady flows.

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BILLINGHAM, JOHN. "Modelling the response of a vibrating-element density meter in a two-phase mixture". Journal of Fluid Mechanics 340 (10 giugno 1997): 343–60. http://dx.doi.org/10.1017/s0022112097005600.

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A vibrating-element density meter is a mechanical oscillator with known properties, for example a tuning fork or a simple rod, driven to vibrate at a known frequency. The oscillator is immersed in a fluid and the resonant frequency measured. The density of the fluid can then be inferred. We consider an idealized meter immersed in two-phase flows of various types, and investigate whether a simple single-phase interpretation allows us to deduce the density of the mixture. We find that, when the density contrast between the two fluids is not great, the simple interpretation gives good results, for example in oil/water flows. However, when the density contrast is significant, for example in gas/liquid flows, the simple interpretation is highly inaccurate.

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Cang, Shijian, Yueyue Shan e Zenghui Wang. "Conservative dynamics in a novel class of 3D generalized thermostatted systems". Chaos: An Interdisciplinary Journal of Nonlinear Science 32, n. 8 (agosto 2022): 083143. http://dx.doi.org/10.1063/5.0101570.

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This paper reports a method to derive a novel class of 3D generalized thermostatted oscillators from a simple damped harmonic oscillator. Its detailed procedure is obtained through a mathematical derivation. Then, we propose an example system to show the effectiveness of the method. Furthermore, the numerical analysis is performed to investigate its rich conservative dynamics, including chaotic sea, hierarchical invariant tori, and the coexistence of chaotic seas and invariant tori with islands-around-islands hierarchy, even if there are three dissipative terms in the example system. To verify the existence of conservative chaos at the physical level, an analog circuit is presented to observe the existing conservative chaotic flows in National Instruments multisim. We finally provide two systems, which can produce conservative chaotic flows with more complicated topologies, and draw our conclusions.

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Tesi sul tema "Oscillator flows"

Barbagallo, Alexandre. "Model reduction and closed-loop control of oscillator and noise-amplifier flows". Palaiseau, Ecole polytechnique, 2011. https://pastel.hal.science/docs/00/65/49/30/PDF/Barbagallo_PhDThesis.pdf.

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This work deals with the closed-loop control of disturbances which develop linearly in laminar and incompressible flows. The control of both oscillator and amplifier flows is assessed. We consider a LQG control strategy in which the control law is computed using a reduced-order model of the flow. This reduced-order model is obtained by a Petrov-Galerkin projection. The first part is devoted to the stabilization of an open cavity flow which behaves as an oscillator. It is shown that the unstable subspace of the flow (the unstable global modes) and the input-output behaviour between the actuator and the sensor of the stable subspace must be captured by the reduced-order model to stabilize the system. Global modes, POD modes and BPOD modes are successively evaluated as projection bases to construct a reduced-order model of the stable part of the flow. It appears that global modes are not able to reproduce the input-output behaviour of the stable part of the flow and subsequently may only stabilize the flow if the instability is very weak (close to the criticality). On the contrary, reduced-order models based on POD modes and BPOD modes efficiently extract the input-output dynamic of the stable subspace and are successful to stabilize the flow. The second part of this work is dedicated to the reduction of the disturbances' amplification on a backward facing step. The influence of the sensor's location and of the cost functional on the performance of the compensator is studied. It is shown that the truncation of the reduced-order model may lead to an unstable closed-loop system. Finally, the possibility to control a non-linear simulation using a linear compensator is evaluated
Ce travail est consacré au contrôle en boucle fermée des perturbations se développant linéairement dans des écoulements laminaires et incompressibles de types oscillateurs et amplificateurs de bruit. La loi de contrôle, calculée selon la théorie du contrôle LQG, est basée sur un modèle d'ordre réduit de l'écoulement obtenu par projection de Petrov-Galerkin. La stabilisation d'un écoulement de cavité de type oscillateur est traitée dans une première partie. Il est montré que la totalité de la partie instable de l'écoulement (les modes globaux instables) ainsi que la relation entrée-sortie (action de l'actionneur sur le capteur) de la partie stable doivent être captées par le modèle réduit afin de stabiliser le système. Les modes globaux, modes POD et modes BPOD sont successivement évalués comme bases de projection pour modéliser la partie stable. Les modes globaux ne parviennent pas à reproduire le comportement entrée-sortie de la partie stable et par conséquent ne peuvent stabiliser l'écoulement que lorsque l'instabilité du système est initialement faible (nombre de Reynolds proche de la criticité). En revanche, les modes POD et plus particulièrement BPOD sont capable d'extraire la dynamique entrée-sortie stable et permettent de stabiliser efficacement l'écoulement. La seconde partie de ce travail est consacrée à la réduction de l'amplification des perturbations sur une marche descendante. L'influence de la localisation du capteur et de la fonctionnelle de coût sur la performance du compensateur est étudiée. Il est montré que la troncature du modèle réduit peut rendre le système bouclé instable. Finalement, la possibilité de contrôler une simulation non-linéaire avec un modèle linéaire est évaluée

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Salmon, Mathieu. "closed-loop control of finite amplitude perturbations : application to sub- and super-critical flow-bifurcations". Electronic Thesis or Diss., Paris, ENSAM, 2024. http://www.theses.fr/2024ENAME072.

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Les méthodes de contrôle actuelles rencontrent des difficultés pour stabiliser un champ de base soumis à des perturbations d’amplitude finie. Une frontière appelée ”edge of chaos” sépare en deux zones distinctes le portrait de phase d’un écoulement qui transitionne de façon sous-critique à la turbulence. Le bassin d’attraction turbulent rassemble les perturbations capables de faire transitionner l’écoulement, le bassin d’attraction laminaire est l’ensemble des perturbations qui sont relaminarisées. La situation précédente caractérisée par deux attracteurs locaux qui coexistent peut être rencontrée en dehors du cadre de la transition à la turbulence. Un écoulement de type cylindre à Re = 100 possède un champ de base globalement instable ainsi qu’un cycle limite stable. Deux bassins d’attraction émergent lors de la stabilisation du champ de base par un contrôleur linéaire optimisé sur les équations de Navier-Stokes linéarisées. Nous cherchons dans cette étude à augmenter la taille du bassin d’attraction du champ de base. La nouveauté de ce travail réside dans le choix de la fonctionnelle qui est optimisée avec contrôle. En effet, l’optimisation vise l’énergie d’une perturbation située sur la frontière des deux bassins d’attraction. La transition sous-critique à la turbulence est étudiée par le biais du modèle SSP de Waleffe, un modèle d’ordre réduit des équations de Navier-Stokes avec seulement quatre degrés de liberté. Les méthodes de contrôle élaborées dans ce travail sont efficaces pour induire une croissance du bassin d’attraction ”laminaire”. Dans l’écoulement de type cylindre, la robustesse d’un contrôleur initial à des perturbations d’amplitude finie est augmentée avec succès dans une direction du portrait de phase
Current control optimisation methods struggle to stabilize a base flow in the case of finite amplitude perturbations. A boundary called edge of chaos separates into two regions the phase space of a flow which transitions subcritically to turbulence. The turbulent basin of attraction incorporates the perturbations whose energy is sufficient to trigger transition to turbulence, the laminar basin of attraction is the set of initial perturbations which are relaminarized. Such situation with two coexisting local attractors can also be encountered in flow cases outside the scope of transition to turbulence. A cylinder flow at Re = 100 exhibits a globally unstable base flow and a stable limit-cycle. Two basins of attraction emerge from the local stabilization of the base flow by a linear controller optimized on the linearized Navier-Stokes equations. We seek in this study to increase the basin of attraction of the base flow. The novelty of this work lies in the choice of the functional to be optimised with control. Indeed, the optimisation targets the energy of a perturbation located on the boundary of the two basins of attraction. We consider subcritical transition to turbulence using the well-known SSP model of Waleffe, a reduced-order model of the Navier-Stokes equations with only four degrees of freedom. The control methods elaboratored in this work are effective to induce a growth of the ”laminar” basin of attraction. In the cylinder flow, the robustness of an initial controller to finite amplitude perturbations is increased in a chosen direction of the phase space

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Wang, Jianhong. "Oscillatory flows round combinations of cylinders". Thesis, University of Edinburgh, 1998. http://hdl.handle.net/1842/13196.

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Comprehensive experimental and computer simulational studies have been carried out to measure the velocity fields in oscillatory flows around combinations of cylinders and also the forces acting on the cylinders in oscillatory flow. Particle Image Velocimetry (PIV) has been used to measure the instantaneous velocity flow fields. Simultaneous measurements have also been made of both inline force and lift force using a transducer installed at the end of one of the cylinders. The strengths of the vortices in the immediate vicinity of the cylinders were calculated. The numerical simulation study used a random vortex method with three overlapping meshes. Forces on the cylinders, together with the corresponding velocity vector fields, were simulated and comparisons made with the experimental results. The combinations of cylinders were (a) a square array of four cylinders with the dimensions chosen so that the array was an approximate scale model of the Heidrun Tension Leg Platform , (b) two cylinders in tandem with different distances between them, (c) a single cylinder. The Keulegan-Carpenter numbers (KC) were 5.8, 10, 13, 20, the Reynolds numbers (Re) were 2500, 4000, 5000, 6500 and 10000 and the viscous parameter (β = R_e/KC) was set at 500. A comparison of the experimental results with the numerical simulations showed good agreement. For the single cylinder the main frequency component of the lift force shifted from the first harmonic, to the second, and then the third harmonic of the oscillatory flow when the KC number and oscillatory velocity increases. For the four cylinder array, in which the distance between two cylinder was greater than 2.5 times the cylinder diameter, the main frequency component of the lift force shifted from the first harmonic to the second as the KC number and oscillatory velocity increased; the third harmonic was relatively small. The strength and fundamental frequency of the force both increased faster than for the single cylinder case.

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Wybrow, M. F. "Oscillatory flows about elliptic and circular cylinders". Thesis, University of East Anglia, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389229.

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Wijetunge, Janaka Jayasekera. "Velocity measurements in oscillatory and steady flows". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627385.

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Al-Asmi, Khalfan. "Vortex shedding in oscillatory flow". Thesis, University of Surrey, 1992. http://epubs.surrey.ac.uk/842864/.

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Measurements of the response to inline flow oscillations of vortex shedding from certain bluff bodies have been made. Four cylinders with fixed separation points were exposed to a mean stream with controlled sinusoidal oscillations at defined frequency ratios and amplitudes. Attention was concentrated on the highly sensitive reduced velocity regime around the inverse of twice the Strouhal number, 1/2S. Synchronisation of vortex formation was first established; then, for conditions at which synchronisation occured, threshold amplitude was measured. In order to determine the common and distinguishing features of bluff body shape the response from cylinders having 'zero' and finite afterbody were investigated. Finally, for a selected cylinder, the influence, in the presence of oscillations, of turbulence intensity (of defined scale), solid blockage and aspect ratio to the synchronous range were examined. Of particular interest were the changes that occur in the characteristic period of vortex formation and base pressure, relevant to the design and application of vortex flowmeters and self induced excitations of structures in general. The experiments were carried out in two separate blower tunnels under various oscillatory flow conditions in the Reynolds number range (0.5-5.0) X 104 and amplitudes of velocity fluctuation (+/-AU/U) of up to 0.3. It was found that amplitudes of oscillations of the order of 0.025 were sufficient to induce frequency lock-in when the reduced velocity was close to 1/2S and, provided the amplitude was sufficiently large, limited synchronisation could also be induced near the upper and lower reduced velocities of 1/S and 1/4S. Synchronisation is accompanied by enhanced vortex shedding which, in turn, can lead to increased base suction (and therefore increase in drag force). Flow visualisation revealed that the near wake vortex arrangement can vary a great deal depending on the ratio of Strouhal numbers at the forced and self-excited frequencies (N/no). It was concluded that the behaviour of the base pressure reflected this situation and that the range of synchronisation depended strongly on the stability of the prevailing mode of vortex shedding. The precise details of the flow were found to be highly dependent on body geometry and the frequency ratio N/no. The production of oscillatory flow in the wind tunnels did not proved to be an easy task. A review of the various methods that have been used in the past is presented. The advantages and disadvantages of different techniques are highlighted and details are given of a further method developed for use with the present open circuit blower tunnels of differing sizes. In the smaller tunnel, having a working section size of 0.3x0.3m, it was possible to produce sinusoidal variations of the working section flow, having peak to peak amplitude of up to 60% of the mean flow speed and frequencies up to, typically, that corresponding to the acoustic quarter-wavelength frequency determined by the tunnel length. Over the viable working range, the device is shown to produce high quality periodic flow with negligible harmonic distortion or acoustic noise difficulties.

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Dick, Jennifer Ellen. "Sediment transport in oscillatory flow". Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235836.

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The effect of non-cohesive sediment on wave-induced bottom boundary layers was examined experimentally. Fluid velocity and sediment concentration were measured simultaneously in a sheet regime generated in a u-shaped oscillating water tunnel. A major obstacle to the understanding of fluid-grain flow has been the absence of suitable measuring devices. Thus, previous experimental investigations have been concerned primarily with low sediment concentration flows. For this study, a probe was developed to measure the instantaneous variations in sediment concentration based on the electrical conductivity of the fluid-grain mixture. Unlike earlier concentration devices, this probe is non-intrusive and is capable of measuring a wide range of sediment concentrations; from close packing within the bed to low concentration suspended load. Horizontal fluid velocities were measured simultaneously using Laser Doppler Anemometry in backscatter mode. Height and time-dependent velocity and concentration profiles were obtained for differing wave and sediment conditions. Values of the shear stress calculated from the momentum integral were found to be an order of magnitude larger than in sediment-free flows. The variation in shear stress with distance from the bed is clearly dependent on the thickness of the movable bed and also on the sediment flow regime. As expected, the eddy viscosity varied significantly during the wave cycle. The time-mean eddy viscosity decreases with height above the movable bed and at large distances from the bed, fluctuates about the mean. The sediment concentration measurements provide a comprehensive data set for sediment transport in sheet flow and near sheet flow regimes. The sediment concentration was found to be time-dependent with the amplitude and form of the temporal variation dependent on distance from the bed, wave amplitude and velocity, and sediment characteristics. With increasing wave amplitude and velocity, the number of peaks in the concentration profile increased while the magnitude of the peaks decreased. Fluid velocity and sediment concentration measurements were used to calculate rates of sediment transport which were compared with predictions from existing models.

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Stephens, Gerard Groves. "Suspension polymerisation in oscillatory flow". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627184.

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Tait, Nicole Lynn. "Recovery factors in zero-mean internal oscillatory flows". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA306233.

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Thesis (M.S. in Mechanical Engineering and M.S. in Astronautical Engineering) Naval Postgraduate School, December 1995.
"December 1995." Thesis advisor(s): Ashok Gopinath, Oscar Biblarz. Bibliography: p. 61. Also available online.

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Krishna, Vikas. "Numerical simulation of vortex shedding in oscillatory flows". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1995. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq25859.pdf.

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Libri sul tema "Oscillator flows"

G, Friedman, Simon T. W e United States. National Aeronautics and Space Administration., a cura di. Fluid mechanics experiments in oscillatory flow. [Washington, DC]: National Aeronautics and Space Administration, 1992.

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Amin, Norsarahaida. Oscillation-induced mean flows and heat transfer. Norwich: University of East Anglia, 1989.

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Coward, Adrian V. Stability of oscillatory two phase Couette flow. Hampton, Va: Institute for Computer Applications in Science and Engineering, 1993.

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T, Papageorgiou Demetrios, e Langley Research Center, a cura di. Stability of oscillatory two phase coutette flow. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1993.

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Cobbin, Adrian Matthew. Viscous forces on cylindrical bodies in attached turbulent oscillatory flows. Manchester: University of Manchester, 1996.

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G, Allan Brian, e Institute for Computer Applications in Science and Engineering., a cura di. Closed-loop separation control using oscillatory flow excitation. Hampton, Va: ICASE, National Aeronautics and Science Administration, Langley Research Center, 2000.

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G, Allan Brian, Institute for Computer Applications in Science and Engineering. e Langley Research Center, a cura di. Closed-loop separation control using oscillatory flow excitation. Hampton, Va: Institute for Computer Applications in Science and Engineering, Langley Research Center, 2000.

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Cirovic, Srdjan. Characterizing flow-induced oscillation in a mechanical trachea. Ottawa: National Library of Canada, 1996.

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Sarpkaya, Turgut. In-line and transverse forces on smooth and rough cylinders in oscillatory flow at high Reynolds numbers. Monterey, Calif: Naval Postgraduate School, 1986.

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Capitoli di libri sul tema "Oscillator flows"

James, J., G. Joseph, A. Magaña e B. Mena. "Oscillatory Granular Flows". In Progress and Trends in Rheology V, 276–77. Heidelberg: Steinkopff, 1998. http://dx.doi.org/10.1007/978-3-642-51062-5_128.

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Li, Sicheng, e Jinjun Wang. "Frequency Effect on Properties of Turbulent/Non-turbulent Interface in Separated and Reattaching Flows Past an Oscillating Fence". In IUTAM Bookseries, 182–93. Cham: Springer Nature Switzerland, 2024. https://doi.org/10.1007/978-3-031-78151-3_14.

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AbstractThe turbulent/non-turbulent interface (TNTI) in the separated and reattaching flows induced by an oscillating fence is experimentally study using particle image velocimetry in this paper. The oscillation frequency of fence is varied spanning subcritical, transitional, critical and supercritical flow regimes, respectively. In the subcritical case, the flow pattern and the TNTI properties are very similar to that in the static case, except in the vicinity of the fence where the actuated low-frequency flapping of the separated shear layer causes larger TNTI height fluctuations. The strongest conditional averaged vorticity is observed in the critical case. However, the faster transition to turbulence is induced by the higher oscillation frequency rather than the critical one. Higher oscillation frequency results in the slower decrease and less fluctuations in the TNTI height normalized by the boundary thickness. Additionally, the greatest TNTI height fluctuation in the recirculation zone is observed in the transitional case, where the vortex shedding frequency is locked to the oscillation frequency resulting in larger shedding vortices.

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Westerhof, Nicolaas, Nikolaos Stergiopulos e Mark I. M. Noble. "Oscillatory Flow Theory". In Snapshots of Hemodynamics, 41–43. Boston, MA: Springer US, 2010. http://dx.doi.org/10.1007/978-1-4419-6363-5_8.

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Westerhof, Nicolaas, Nikolaos Stergiopulos, Mark I. M. Noble e Berend E. Westerhof. "Oscillatory Flow Theory". In Snapshots of Hemodynamics, 47–50. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-91932-4_8.

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Holzbecher, Ekkehard O. "Oscillatory Convection". In Modeling Density-Driven Flow in Porous Media, 129–45. Berlin, Heidelberg: Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/978-3-642-58767-2_7.

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Bearman, P. W., X. W. Lin e P. R. Mackwood. "Prediction of vortex-induced oscillation of cylinders in oscillatory flow". In Hydroelasticity in Marine Technology, 3–16. London: Routledge, 2022. http://dx.doi.org/10.1201/9780203751503-2.

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Mottaghi, Sohrob, Rene Gabbai e Haym Benaroya. "Lagrangian Flow-Oscillator Models". In An Analytical Mechanics Framework for Flow-Oscillator Modeling of Vortex-Induced Bluff-Body Oscillations, 95–142. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-26133-7_5.

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Mottaghi, Sohrob, Rene Gabbai e Haym Benaroya. "Eulerian Flow-Oscillator Models". In An Analytical Mechanics Framework for Flow-Oscillator Modeling of Vortex-Induced Bluff-Body Oscillations, 189–240. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-26133-7_7.

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Ribberink, Jan S., Jebbe J. van der Werf e Tom O’Donoghue. "Sand motion induced by oscillatory flows: sheet flow and vortex ripples". In ERCOFTAC Series, 3–14. Dordrecht: Springer Netherlands, 2007. http://dx.doi.org/10.1007/978-1-4020-6218-6_1.

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Arwatz, Gilad, Ilan Fono e Avi Seifert. "Suction and Oscillatory Blowing Actuator". In IUTAM Symposium on Flow Control and MEMS, 33–44. Dordrecht: Springer Netherlands, 2008. http://dx.doi.org/10.1007/978-1-4020-6858-4_4.

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Atti di convegni sul tema "Oscillator flows"

Shakouchi, Toshihiko. "Gas Absorption, Aeration, by Fluidic Oscillator Operated by Gas-Liquid Two-Phase Flow". In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45132.

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It is known that a conventional feedback type and other type of fluidic oscillators can be operated not only by gas or liquid single phase flow but also by gas(air)-liquid(water) two-phase flow (Shakouchi, 1989, 2001). The two-phase jet flow oscillates periodically of the oscillator under some conditions, and then the gas, air bubble, and liquid flows are mixed and stirred forcibly. The contact area and time between gas and liquid flows increase considerably and then the much increasing of mass transfer, the diffusion or absorption of gas into liquid, will be expected. It may be able to construct an entirely new compact type gas-absorber, aerator, with a simple construction. In this paper, first the performance of fluidic oscillator operated by gas-liquid two-phase flow is made clear experimentally. Next, the aeration performance of the oscillator, namely the diffusion or absorption rate of air, dissolved oxygen, into water under various kind of operation conditions are examined experimentally. The following major results will be shown. (1) The oscillatory frequency f increases linearly with increasing the Re number (= udf/ν, u: mean velocity of water flow at the nozzle exit, df: nozzle width, ν: kinematic viscosity) and the void fraction α. (2) The pressure loss, flow resistance, Δp of the oscillator or increases rapidly with increasing Ref and linearly increasing α. (3) Dissolved oxygen in water can be increased considerably by fluidic oscillator operated by air-water two-phase flow, and it was well known that a new compact type aerator can be constructed by fluidic oscillator.

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Chen, Chiko, Jing-Tang Yang e Chien-Hung Ho. "A Novel Asymmetric Microfluidic Oscillator". In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-79269.

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In this work we present an asymmetric microfluidics oscillator of innovative design and systematically investigated it with both numerical and experimental methods. The design of both entrance nozzle and asymmetric feedback channels enable the oscillator to stably oscillate in very small range of Reynolds number 1~100, whereas the Strouhal number remained as 1 × 10−3. The results reveal that improvement of the performance was resulted from the augmented periodic impingement of the flows from the feedback channels. The analysis also indicates that dynamic phenomena in the working fluid of this novel oscillator were distinctive and appropriately appraised.

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Mozgovoi, Yury D., e Sergei A. Khritkin. "Radiation of multibeam microwave generator on electron-oscillator flows". In 2017 Eighteenth International Vacuum Electronics Conference (IVEC). IEEE, 2017. http://dx.doi.org/10.1109/ivec.2017.8289678.

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Morimoto, Yuichiro, Kenji Kawamata, Haruki Madarame e Koji Okamoto. "Bifurcation of Water Column Oscillator Behavior Simulating Reactor Safety System: 1st Report, Experiment". In ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-32555.

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The non-periodical oscillation was reported in Water Column Oscillator, which simulates a passive safety system of a future nuclear reactor, however, the mechanism of the oscillation is not clarified. The objective of this study is to elucidate the mechanism of non-periodical oscillation in Water Column Oscillator experimentally and analytically. The U-type rectangular duct is filled with the water in a certain degree of height. An end of the duct is sealed and the other is open to the atmosphere. The electromagnetic valve is installed at the top of the sealed side. A cover gas simulating vapor generation by residual heat is injected constantly into the gas phase of the sealed side. The water column oscillation with its natural frequency continues until the free surface in the sealed side, pushed by the gas, reaches at a certain height. When the height of the water level reaches HL, the electromagnetic valve is open and the cover gas flows out from the U-type duct. The gas is ejected rapidly, and thus, the cover gas pressure decreases almost to the atmospheric pressure. The water level in the sealed side of the duct rises with water supply from the open side and reaches a certain height HU. Then the valve is closed again and the increasing gas pressure pushes down the water surface of the sealed side. The water level oscillates repeating the above process. The analytical model which agrees well with the experiment is derived. The bifurcation-like phenomenon is shown in experiment, however, it can be clear that the phenomenon is not bifurcation but noise effects by the numerical simulation with noise effects. The variation of characteristics of oscillation are investigated in detail by using Poincare´ section (Y2(N), U2(N)), which indicate cover gas pressure and water level velocity at the beginning of the Nth valve-open instant. The parameter region where the system shows bifurcation can be discovered by the numerical simulation. The bifurcation is confirmed in the experiment.

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Mozgovoi, Yury D., e Sergei A. Khritkin. "Phase focusing and synchronization of microwave generator with electron-oscillator flows". In 2017 Eighteenth International Vacuum Electronics Conference (IVEC). IEEE, 2017. http://dx.doi.org/10.1109/ivec.2017.8289645.

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Civrais, Clément H. B., Craig White e René Steijl. "Influence of anharmonic oscillator model for flows over a cylindrical body". In 2ND INTERNATIONAL CONFERENCE ON ADVANCED EARTH SCIENCE AND FOUNDATION ENGINEERING (ICASF 2023): Advanced Earth Science and Foundation Engineering. AIP Publishing, 2024. http://dx.doi.org/10.1063/5.0187445.

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Gomez, Mateo, Mikhail N. Slipchenko, Steven F. Son e Terrence R. Meyer. "Burst-Mode Noncollinear Optical Parametric Oscillator". In Laser Applications to Chemical, Security and Environmental Analysis. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/lacsea.2022.ltu5b.3.

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Laser illumination is preferred for visualization of hypersonic flows, but coherent speckle typically limits the spatial resolution. This work develops a burst-mode non-collinear optical parametric oscillator to realize a broadband signal for speckle-free imaging.

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Mudunuru, M. K., M. Shabouei e K. B. Nakshatrala. "On Local and Global Species Conservation Errors for Nonlinear Ecological Models and Chemical Reacting Flows". In ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-52760.

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Advection-controlled and diffusion-controlled oscillatory chemical reactions appear in various areas of life sciences, hydrogeological systems, and contaminant transport. In this conference paper, we analyze whether the existing numerical formulations and commercial packages provide physically meaningful values for concentration of the chemical species for two popular oscillatory chemical kinetic schemes. The first one corresponds to the chlorine dioxide-iodine-malonic acid reaction while the second one is a simplified version of Belousov-Zhabotinsky reaction of a non-linear chemical oscillator. The governing equations for species balance are presented based on the theory of interacting continua. This results in a set of coupled non-linear partial differential equations. Obtaining analytical solutions is not practically viable. Moreover, it is well-known in literature that if the local dynamics becomes complex, the range of possible dynamic behavior in the presence of diffusion and advection becomes practically unlimited. We resort to numerical solutions, which are obtained using two popular stabilized formulations: Streamline Upwind/Petrov Galerkin and Galerkin/Least Squares. In order to make the computational analysis tractable, an estimate on the range of system-dependent parameters is obtained based on model reduction performed on the strong-form of the governing equations. Finally, we quantify the errors in satisfying the local and global species balance for various realistic benchmark problems. Through these representative numerical examples, we shall demonstrate the need and importance of developing locally conservative non-negative numerical formulations for chaotic and oscillatory chemically reacting systems.

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Fuchiwaki, Masaki, e Surya Raghu. "Flow Structure Formed by a Sweeping Jet Ejected Into a Main Flow". In ASME 2018 5th Joint US-European Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/fedsm2018-83045.

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Various methods of controlling flow separation have been proposed and many studies have been performed on active separation control in correspondence with the flow state. However, their efficiency has been hampered by the requirement of electric power for the added stream. Recently, an active flow separation control device based on a fluidic oscillator that does not require electric power has been reported. This device is able to generate a sweeping jet over a wide spatial range as well as fluid oscillations, and its internal structure eliminates the need for a drive unit. The studies of the flow separation control techniques using the fluidic oscillator have been reported. However, most of these results are mainly contribution of the dynamic forces from the viewpoint of the flow control and the study on the flow mechanism for the separation flow control using the fluidic oscillator have not been understood. Especially, it is not known the interaction between the sweeping jet from the fluidic oscillator and the main flow and the flow structure due to the interaction. In order to make a flow separation control devise with high efficiency using the fluidic oscillator, it is require to be understood the complex flow structure by the interaction between the sweeping jet from the fluidic oscillator and the main flow. The purpose of the present study is to investigate the flow structure by the interaction between the sweeping jet from the fluidic oscillator and the main flow quantitatively by the stereo PIV measurement. The sweeping jet ejected from a fluidic oscillator evidently disrupts the main flow at high velocity ratios, leading to a significant change in flow structure. A high-speed jet appears at the center part of the structure, accompanied by low-speed flow at the outside, producing a 3D distribution. The sweeping jet ejected from the fluidic oscillator maintains the spreading angleas a result of the interaction between the two flows at high velocity ratios.

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Luo, Albert C. J., e Mehul T. Patel. "Complex Motions in a Periodically Forced Oscillator With Multiple Discontinuities". In ASME 2007 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/detc2007-34872.

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The complex motions in periodically forced oscillator with multiple discontinuities are investigated in this paper. From the local singularity theory in discontinuous systems, the passability condition of motion flow from one domain to the adjacent one in phase space is presented, and the sliding and grazing conditions of motion flows to discontinuous boundaries are given to understand the mechanism of such complex motions. From the separation boundary, the generic mappings are defined for mapping structures. A generalized mapping structure is introduced for all complex periodic motions, and the local stability and bifurcations of periodic motions in such a discontinuous system are discussed. The passability of motion flow to the discontinuous boundary is used for motion continuity, and the grazing condition of flow to the discontinuous boundary is employed for the vanishing of complex motion. Complex periodic motions with sliding and grazing in such a discontinuous system are predicted analytically and chaotic motions are also illustrated.

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Rapporti di organizzazioni sul tema "Oscillator flows"

Ayoul-Guilmard, Q., F. Nobile, S. Ganesh, M. Nuñez, R. Tosi, C. Soriano e R. Rosi. D5.5 Report on the application of multi-level Monte Carlo to wind engineering. Scipedia, 2022. http://dx.doi.org/10.23967/exaqute.2022.3.03.

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We study the use of multi-level Monte Carlo methods for wind engineering. This report brings together methodological research on uncertainty quantification and work on target applications of the ExaQUte project in wind and civil engineering. First, a multi-level Monte Carlo for the estimation of the conditional value at risk and an adaptive algorithm are presented. Their reliability and performance are shown on the time-average of a non-linear oscillator and on the lift coefficient of an airfoil, with both preset and adaptively refined meshes. Then, we propose an adaptive multi-fidelity Monte Carlo algorithm for turbulent fluid flows where multilevel Monte Carlo methods were found to be inefficient. Its efficiency is studied and demonstrated on the benchmark problem of quantifying the uncertainty on the drag force of a tall building under random turbulent wind conditions. All numerical experiments showcase the open-source software stack of the ExaQUte project for large-scale computing in a distributed environment.

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Telionis, D. P., e T. E. Diller. Heat transfer in oscillatory flow: Final report. Office of Scientific and Technical Information (OSTI), novembre 1986. http://dx.doi.org/10.2172/6908819.

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Restrepo, Juan M. Particle and Blood Cell Dynamics in Oscillatory Flows Final Report. Office of Scientific and Technical Information (OSTI), settembre 2008. http://dx.doi.org/10.2172/953697.

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Seume, J., G. Friedman e T. W. Simon. Fluid mechanics experiments in oscillatory flow. Volume 1. Office of Scientific and Technical Information (OSTI), marzo 1992. http://dx.doi.org/10.2172/10181069.

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Howle, Laurens E. Enhancement of Oscillatory Flap Propulsors for Low Speed Flows in Water. Fort Belvoir, VA: Defense Technical Information Center, luglio 2010. http://dx.doi.org/10.21236/ada545931.

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Inc., Kellogg Brown and Root. L51989 Submarine Pipeline On-Bottom Stability-Volume 1-Analysis and Design Guidelines. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), dicembre 2002. http://dx.doi.org/10.55274/r0011168.

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The state-of-the-art in Pipeline stability design has been changing very rapidly recently. The physics governing on-bottom stability are much better understood now than they were eight years ago. This is due largely because of research and large scale model tests sponsored by PRCI. Analysis tools utilizing this new knowledge have been developed. These tools provide the design engineer with a rational approach for weight coating design, which he can use with confidence because the tools have been developed based on full scale and near full scale model tests. These tools represent the state-of-the-art in stability design and model the complex behavior of pipes subjected to both wave and current loads. These include; hydrodynamic forces which account for the effect of the wake (generated by flow over the pipe) washing back and forth over the pipe in oscillatory flow; and, the embedment (digging) which occurs as a pipe resting on the seabed is exposed to oscillatory loadings and small oscillatory deflections. This report has been developed as a reference handbook for use in on-bottom pipeline stability analysis and design. It consists of two volumes. Volume one is devoted to descriptions of the various aspects of the problem: the pipeline design process ocean physics, wave mechanics, hydrodynamic forces, and meteorological data determination geotechnical data collection and soil mechanics stability design procedures. Volume two describes, lists, and illustrates the analysis software. Diskettes containing the software and examples of the software are also included in Volume two. This publication was formally titled: AGA On Bottom Stability Software.

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Schilling, O., e M. Latini. Weighted Essentially Non-Oscillatory Simulations and Modeling of Complex Hydrodynamic Flows Part 1. Regular Shock Refraction. Office of Scientific and Technical Information (OSTI), giugno 2004. http://dx.doi.org/10.2172/15014460.

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Rosa, M. P., e M. Z. Podowski. Modeling and numerical simulation of oscillatory two-phase flows, with application to boiling water nuclear reactors. Office of Scientific and Technical Information (OSTI), settembre 1995. http://dx.doi.org/10.2172/107760.

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Latini, M., e O. Schilling. Weighted Essentially Non-Oscillatory Simulations and Modeling of Complex Hydrodynamic Flows. Part 1. Regular Shock Refraction. Office of Scientific and Technical Information (OSTI), gennaio 2005. http://dx.doi.org/10.2172/875932.

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Nobile, F., Q. Ayoul-Guilmard, S. Ganesh, M. Nuñez, A. Kodakkal, C. Soriano e R. Rossi. D6.5 Report on stochastic optimisation for wind engineering. Scipedia, 2022. http://dx.doi.org/10.23967/exaqute.2022.3.04.

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This report presents the latest methods of optimisation under uncertainties investigated in the ExaQUte project, and their applications to problems related to civil and wind engineering. The measure of risk throughout the report is the conditional value at risk. First, the reference method is presented: the derivation of sensitivities of the risk measure; their accurate computation; and lastly, a practical optimisation algorithm with adaptive statistical estimation. Second, this method is directly applied to a nonlinear relaxation oscillator (FitzHugh–Nagumo model) with numerical experiments to demonstrate its performance. Third, the optimisation method is adapted to the shape optimisation of an airfoil and illustrated by a large-scale experiment on a computing cluster. Finally, the benchmark of the shape optimisation of a tall building under a turbulent flow is presented, followed by an adaptation of the optimisation method. All numerical experiments showcase the open-source software stack of the ExaQUte project for large-scale computing in a distributed environment.

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