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Injection pultrusion (IP) process is a manufacturing technique for producing advanced fiber reinforced polymers having constant cross-section. Unlike the traditional pultrusion process, in which fibers are impregnated passing through an open bath of liquid resin, in IP the uncured polymer is directly injected within the advancing reinforcement in a close chamber generally connected to the die. This paper investigates the resistant forces evolution in IP process at different pulling speeds. Resistant loads are mainly due to the interaction between the advancing material and the die cavity walls, inducing residual stress and, eventually, internal defects. These loads are typically classified in three main contributes, namely fiber collimation, viscous drag and solid friction. The latter two are directly related to the resin degree of cure, and, therefore, the overall resistant load is dramatically sensitive to the changes in operative parameters. In this paper, the resistant force acting along the die cavity has been measured using a dedicated experimental setup. Measurements were performed during the pultrusion of glass-reinforced polyester with different pulling speeds to evidence the variations in resistant load as a function of the process velocity.

Background: Recent studies suggest that blood flow in main arteries is intrinsically disturbed, even under healthy conditions. Despite this, many computational fluid dynamics (CFD) analyses of aortic haemodynamics make the assumption of laminar flow, and best practices surrounding appropriate modelling choices are lacking. This study aims to address this gap by evaluating different modelling and post-processing approaches in simulations of a patient-specific aorta.Methods: Magnetic resonance imaging (MRI) and 4D flow MRI from a patient with aortic valve stenosis were used to reconstruct the aortic geometry and derive patient-specific inlet and outlet boundary conditions. Three different computational approaches were considered based on assumed laminar or assumed disturbed flow states including low-resolution laminar (LR-Laminar), high-resolution laminar (HR-Laminar) and large-eddy simulation (LES). Each simulation was ran for 30 cardiac cycles and post-processing was conducted on either the final cardiac cycle, or using a phase-averaged approach which utilised all 30 simulated cycles. Model capabilities were evaluated in terms of mean and turbulence-based parameters.Results: All simulation types, regardless of post-processing approach could correctly predict velocity values and flow patterns throughout the aorta. Lower resolution simulations could not accurately predict gradient-derived parameters including wall shear stress and viscous energy loss (largest differences up to 44.6% and 130.3%, respectively), although phase-averaging these parameters improved predictions. The HR-Laminar simulation produced more comparable results to LES with largest differences in wall shear stress and viscous energy loss parameters up to 5.1% and 11.6%, respectively. Laminar-based parameters were better estimated than turbulence-based parameters.Conclusion: Our findings suggest that well-resolved laminar simulations can accurately predict many laminar-based parameters in disturbed flows, but there is no clear benefit to running a HR-Laminar simulation over an LES simulation based on their comparable computational cost. Additionally, post-processing “typical” laminar simulation results with a phase-averaged approach is a simple and cost-effective way to improve accuracy of lower-resolution simulation results.

In this study, we mathematically predict retinal vascular resistance (RVR) and retinal blood flow (RBF), we test predictions using laser speckle flowgraphy (LSFG), we estimate the range of vascular autoregulation, and we examine the relationship of RBF with the retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC). Fundus, optical coherence tomography (OCT), and OCT-angiography images, systolic/diastolic blood pressure (SBP/DBP), and intraocular pressure (IOP) measurements were obtained float 36 human subjects. We modeled two circulation markers (RVR and RBF) and estimated individualized lower/higher autoregula tion limits (LARL/HARL), using retinal vessel calibers, fractal dimen- sion, perfusion pressure, and population-based hematocrit values. Quantitative LSFG waveforms were extracted from vessels of the same eyes, before and during IOP elevation. LSFG metrics explained most variance in RVR (R-2 =0.77/P = 6.9.10(-9)) and RBF (R-2 =0.65/P = 1.0.10(-6)), suggesting that the markers strongly reflect blood flow physiology. Higher RBF was associated with thicker RNFL (P = 4.0.10(-4)) and GCC (P = 0.003), thus also verifying agreement with structural measurements. LARL was at SBP/DBP of 105/65 mmHg for the average subject without arterial hypertension and at 115/75 mmHg for the average hypertensive subject. Moreover, during IOP elevation, changes in RBF were more pronounced than changes in RVR. These observations physiologically imply that healthy subjects are already close to LARL, thus prone to hypoperfusion. In conclusion, we modeled two clinical markers and described a novel method to predict individualized autoregulation limits. These findings could improve understanding of retinal perfusion and pave the way for personalized intervention decisions, when treating patients with coexisting ophthalmic and cardiovascular pathologies.NEW & NOTEWORTHY We describe and test a new approach to quantify retinal blood flow, based on standard clinical examinations and imaging techniques, linked together with a physiological model. We use these findings to generate individualized estimates of the autoregulation range. We provide evidence that healthy subjects are closer to the lower autoregulation limit than thought before. This suggests that some retinas are less prepared to withstand hypoperfusion, even after small intraocular pressure rises or blood pressure drops.

We investigate the dynamic interfacial deformation induced by micrometric particles exerting a periodic force on a planar interface or on a bubble, and the resulting lateral capillary interactions. Assuming that the deformation of the interface is small, neglecting the effect of viscosity and assuming point particles, we derive analytical formulas for the dynamic deformation of the interface. For the case of a planar interface the dynamic point force simply generates capillary waves, while for the case of a bubble it excites shape oscillations, with a dominant deformation mode that depends on the bubble radius for a given forcing frequency. We evaluate the lateral capillary force acting between two particles, by superimposing the deformations induced by two point forces. We find that the lateral capillary forces experienced by dynamically forced particles are non-monotonic and can be repulsive. The results are applicable to micrometric particles driven by different dynamic forcing mechanisms such as magnetic, electric or acoustic fields.

This paper investigates the effect of initial volume fraction on the runout characteristics of collapse of granular columns on slopes in fluid. Two-dimensional sub-grain scale numerical simulations are performed to understand the flow dynamics of granular collapse in fluid. The Discrete Element (DEM) technique is coupled with the Lattice Boltzmann Method (LBM), for fluid-grain interactions, to understand the evolution of submerged granular flows. The fluid phase is simulated using Multiple- Relaxation-Time LBM (LBM-MRT) for numerical stability. In order to simulate interconnected pore space in 2D, a reduction in the radius of the grains (hydrodynamic radius) is assumed during LBM computations. The collapse of granular column in fluid is compared with the dry cases to understand the effect of fluid on the runout behaviour. A parametric analysis is performed to assess the influence of the granular characteristics (initial packing) on the evolution of flow and run-out distances for slope angles of 0{\deg}, 2.5{\deg}, 5{\deg} and 7.5{\deg}. The granular flow dynamics is investigated by analysing the effect of hydroplaning, water entrainment and viscous drag on the granular mass. The mechanism of energy dissipation, shape of the flow front, water entrainment and evolution of packing density is used to explain the difference in the flow characteristics of loose and dense granular column collapse in fluid.

International audience; Hypothesis: Rotational Brownian diffusions of colloidal particles at a fluid interface play important roles in particle self-assembly and in surface microrheology. Recent experiments on translational Brownian motion of spherical particles at the air-water interface show a significant slowing down of the translational diffusion with respect to the hydrodynamic predictions (Boniello et al., 2015). For the rotational diffusions of partially wetted colloids, slowing down of the particle dynamics can be also expected.Experiments: Here, the rotational dynamics of Janus colloids at the air-water interface have been experimentally investigated using optical microscopy. Bright field and fluorescent microscopies have been used to measure the in-plane and out-of-plane particle rotational diffusions exploiting the Janus geometry of the colloids we fabricated.Findings: Our results show a severe slowing down of the rotational diffusion Dr,⊥ connected to the contact line motion and wetting-dewetting dynamics occurring on particle regions located at opposite liquid wedges. A slowing down of the particle rotational diffusion about an axis parallel to the interfacial normal Dr,|| was also observed. Contact line fluctuations due to partial wetting dynamics lead to a rotational line friction that we have modelled in order to describe our results.

日本船舶海洋工学会 平成28年春季講演会（2016年5月26日～27日）にて講演 / 論文番号: 2016S-GS3-16

The present study aims to implement the software ANSYS AQWA to discuss the hydrodynamic analysis of the DeepCwind semi-submersible floating platform in waves based on the potential flow theory by considering the second-order wave exciting force. In this study, the linearized potential-flow hydrodynamic radiation and diffraction problems in the frequency domain were firstly solved by adopting the three-dimensional panel method. Subsequently, the hydrodynamic coefficients and wave loading data were transformed to time domain forms by the Cummins time domain equation as a system loading input. Furthermore, the quadratic transfer function (QTF) matrices with different frequencies and directions deduced based on the near field integration over the mean wetted hull surface were adopted for the calculation of slow-drift forces. In order to represent the damping in a real system for modeling potential flow without Morison&rsquo, s elements, an additional quadratic damping matrix was added to capture the viscous drag. Eventually, both of the dynamic mooring model based on the lump-mass (LM) approach and the quasi-static mooring model based on the multi-segmented, quasi-static (MSQS) approach are introduced to discuss the mooring effect on the platform hydrodynamics. The effect of wave heading angles on the platform motion is considered as an influential parameter as well.

Despite the relevance to environmental, biological and industrial processes, the motion of a colloidal particle close to a fluid interface and the way it interacts with the water surface are still largely elusive and intriguing physical phenomena.In this thesis, we explore the motion dynamics and the interaction of individual colloidal particles close to an air-water interface in thermal equilibrium.In order to investigate them without perturbing or altering the experimental system, we designed and built a dual-wave reflection interference microscope working with an air-water interface geometry. Contrary to other established experimental techniques, our set-up allows accurate measurements of the absolute particle-interface distance and thus does not require any calibration or assumption to know the location of the interface. Highly resolved 3D particle trajectories close to the interface were obtained, from which information on particle diffusion close to the interface and particle-interface interactions are obtained.The system shows two different potential energy landscapes resulting in two different equilibrium particle-interface distances. The larger one can be fairly explained by Van der Waals and electrostatic interactions combined with gravity. The shorter one highlights the existence of an unexpected additional attractive interaction. The possible origins of such an interaction are discussed.Using a method of analysis of the particle mean square displacements in a generic potential we developed, we were able to access to particle drag coefficients as a function of the distance from the interface. Peculiarly, the air-water interface acts as a slip boundary for the particle motion parallel to the interface and as a no-slip boundary for the particle motion perpendicular to the interface. This experimental result can be partially rationalized considering recent models based on surface incompressibility. However, some discrepancies between experiments and theories remain. Experimental drag coefficients are larger than the hydrodynamic predictions and depend on the particle electrical charge, pointing therefore to a possible role of electrokinetic phenomena.Finally, the particle trapping at the air-water interface and its contact angle were observed while tuning the ionic strength of the aqueous solution and varying the surface state of the colloids.; Malgré un rôle important en physique, biologie et dans les processus industriels tels l’agroalimentaire et la dépollution de l’eau, la dynamique d'une particule colloïdale à proximité d'une interface fluide et ses interactions avec l’interface sont des phénomènes physiques encore débattus.Dans cette thèse, nous explorons la dynamique et l'interaction de particules colloïdales individuelles à proximité d'une interface air-eau à l’équilibre thermique.Afin de mener cette étude sans perturber le système expérimental, nous avons conçu et construit un microscope interférentiel à double onde adapté à l'interface air-eau. Contrairement à d'autres techniques expérimentales, notre configuration permet la mesure précise de la distance absolue entre particule l'interface sans nécessiter d’étalonnage ou d’hypothèse sur l'emplacement de l'interface. Nous avons ainsi pu obtenir des trajectoires hautement résolues de particules en 3D proches de l'interface, permettant la mesure précise des diffusions proche de l’interface et des interactions particules-interface.Le système montre deux profils d’énergie potentielle différents. Deux distances d’équilibre particule-interface sont ainsi observées. La plus grande peut être expliquée par la compétition des interactions de Van der Waals et électrostatiques avec la pesanteur. La distance d’équilibre plus courte ne peut s’expliquer que par la présence d’une interaction attractive supplémentaire. Les origines possibles de cette interaction sont discutées.En utilisant une nouvelle méthode d'analyse des déplacements quadratiques moyens des particules dans un potentiel générique, nous avons pu accéder aux coefficients de friction visqueuse des particules en fonction de la distance à l'interface. De manière singulière, l’interface air-eau se comporte comme une paroi liquide pour le mouvement des particules parallèlement à l’interface et comme une paroi solide pour le mouvement des particules perpendiculaire à l’interface. Ce résultat expérimental peut être partiellement rationalisé en considérant des modèles récents basés sur l’incompressibilité de surface. Cependant, certaines différences entre les expériences et les théories demeurent. Les coefficients de friction visqueuse sont plus importants que les prédictions hydrodynamiques et dépendent de la charge électrique des particules, ce qui suggère un possible rôle des phénomènes électrocinétiques.Enfin, le piégeage des particules à l'interface air-eau et leur angle de contact ont été mesurés tout en modifiant la force ionique de la solution aqueuse et en faisant varier l‘état de surface des colloïdes.

The dynamic response of floating horizontal axis wind turbines (FHWATs) are affected by the viscous and inertia effects. In free decay motion, viscous drag reduces the amplitude of pitch and roll fluctuation, the quasi-static mooring system overestimates the resonant amplitude values of pitch and roll. In this paper, the quasi-static mooring system is modified by introducing linear damping and quadratic damping. The dynamic response characteristics of the FHAWT modified model of the DTU 10 MW tension leg platform (TLP) were studied. Dynamic response of the blade was mainly caused by wind load, while the wave increased the blade short-term damage equivalent load. The tower base bending moment was affected by inclination of the tower and the misaligned angle &beta, wave between wind and wave. Except the yaw motion, other degrees of freedom motions of the TLP were substantially affected by &beta, wave. Ultimate tension of the mooring system was related to the displacement caused by pitch and roll motions, and standard deviation of the tension was significantly affected by the wave frequency response. Under the action of wave load, the viscous drag would stimulate the mooring system and increase the resonance of the platform motion.

Despite the relevance to environmental, biological and industrial processes, the motion of a colloidal particle close to a fluid interface and the way it interacts with the water surface are still largely elusive and intriguing physical phenomena.In this thesis, we explore the motion dynamics and the interaction of individual colloidal particles close to an air-water interface in thermal equilibrium.In order to investigate them without perturbing or altering the experimental system, we designed and built a dual-wave reflection interference microscope working with an air-water interface geometry. Contrary to other established experimental techniques, our set-up allows accurate measurements of the absolute particle-interface distance and thus does not require any calibration or assumption to know the location of the interface. Highly resolved 3D particle trajectories close to the interface were obtained, from which information on particle diffusion close to the interface and particle-interface interactions are obtained.The system shows two different potential energy landscapes resulting in two different equilibrium particle-interface distances. The larger one can be fairly explained by Van der Waals and electrostatic interactions combined with gravity. The shorter one highlights the existence of an unexpected additional attractive interaction. The possible origins of such an interaction are discussed.Using a method of analysis of the particle mean square displacements in a generic potential we developed, we were able to access to particle drag coefficients as a function of the distance from the interface. Peculiarly, the air-water interface acts as a slip boundary for the particle motion parallel to the interface and as a no-slip boundary for the particle motion perpendicular to the interface. This experimental result can be partially rationalized considering recent models based on surface incompressibility. However, some discrepancies between experiments and theories remain. Experimental drag coefficients are larger than the hydrodynamic predictions and depend on the particle electrical charge, pointing therefore to a possible role of electrokinetic phenomena.Finally, the particle trapping at the air-water interface and its contact angle were observed while tuning the ionic strength of the aqueous solution and varying the surface state of the colloids., Malgré un rôle important en physique, biologie et dans les processus industriels tels l’agroalimentaire et la dépollution de l’eau, la dynamique d'une particule colloïdale à proximité d'une interface fluide et ses interactions avec l’interface sont des phénomènes physiques encore débattus.Dans cette thèse, nous explorons la dynamique et l'interaction de particules colloïdales individuelles à proximité d'une interface air-eau à l’équilibre thermique.Afin de mener cette étude sans perturber le système expérimental, nous avons conçu et construit un microscope interférentiel à double onde adapté à l'interface air-eau. Contrairement à d'autres techniques expérimentales, notre configuration permet la mesure précise de la distance absolue entre particule l'interface sans nécessiter d’étalonnage ou d’hypothèse sur l'emplacement de l'interface. Nous avons ainsi pu obtenir des trajectoires hautement résolues de particules en 3D proches de l'interface, permettant la mesure précise des diffusions proche de l’interface et des interactions particules-interface.Le système montre deux profils d’énergie potentielle différents. Deux distances d’équilibre particule-interface sont ainsi observées. La plus grande peut être expliquée par la compétition des interactions de Van der Waals et électrostatiques avec la pesanteur. La distance d’équilibre plus courte ne peut s’expliquer que par la présence d’une interaction attractive supplémentaire. Les origines possibles de cette interaction sont discutées.En utilisant une nouvelle méthode d'analyse des déplacements quadratiques moyens des particules dans un potentiel générique, nous avons pu accéder aux coefficients de friction visqueuse des particules en fonction de la distance à l'interface. De manière singulière, l’interface air-eau se comporte comme une paroi liquide pour le mouvement des particules parallèlement à l’interface et comme une paroi solide pour le mouvement des particules perpendiculaire à l’interface. Ce résultat expérimental peut être partiellement rationalisé en considérant des modèles récents basés sur l’incompressibilité de surface. Cependant, certaines différences entre les expériences et les théories demeurent. Les coefficients de friction visqueuse sont plus importants que les prédictions hydrodynamiques et dépendent de la charge électrique des particules, ce qui suggère un possible rôle des phénomènes électrocinétiques.Enfin, le piégeage des particules à l'interface air-eau et leur angle de contact ont été mesurés tout en modifiant la force ionique de la solution aqueuse et en faisant varier l‘état de surface des colloïdes.

Two of the most common modes of oscillation of single degree of freedom wave energy converters are heave and surge, which are, respectively, exploited by heaving point absorbers (HPAs), and oscillating wave surge converters (OWSCs). Given major hydrodynamic differences between HPAs and OWSC, different nonlinear forces may be more or less relevant. Likewise, the scaling properties of such nonlinear forces may be different, according to the type of device, introducing uncertainties. This paper studies different nonlinear effects, and the relevance of different hydrodynamic force components, in HPAs and OWSCs. Nonlinear Froude–Krylov forces, as well as viscous drag effects, are represented and both prototype and full-scale device sizing are considered. Results show that HPAs are predominantly affected by nonlinear Froude–Krylov forces, while the most important hydrodynamic forces in OWSCs are diffraction and radiation effects. In addition, viscous drag appears to have little relevance in HPAs, but a significant influence in OWSCs. Finally, nonlinearities are shown to significantly affect the phase of the different force components.

Designing, optimizing and controlling a wave energy converter requires the construction of a mathematical model in order to simulate the behaviour of the device. Given the nonlinear nature of fluid-structure interactions, the definition of the model is not straightforward and should take into account the specific application it is intended for. Two of the most important characteristics of a model are the computational time and the expected accuracy, which usually are mutually conflicting. The inclusion of nonlinearities potentially increases the model accuracy, but at a higher computational price. Considering a heaving wave energy converter with and without the application of latching control, this paper studies and compares nine different modelling options, eight of which are based on potential theory and consider nonlinear Froude-Krylov and viscous drag forces, while one is based on fully-nonlinear computational fluid dynamics. The value of including nonlinearities in the hydrodynamic model is discussed in relation to the computational cost of the eventual accuracy benefits, under a range of scenarios.

The disc pump operates using boundary layer principle and viscous drag with a relatively low efficiency. There are methods to increase head and efficiency, one of them is the placing of blades sector sor splitter blades in disc. This method has been applied only in the low viscosity fluids pumping (v

Boundary layer akan terbentuk apabila aliran viscous melewati suatu kontur permukaan. Hal ini menyebabkan terjadinya gaya drag di kontur permukaan, oleh karena itu boundary layer yang terbentuk perlu dikontrol. Salah satu cara untuk mengkontrol boundary layer yang terbentuk adalah dengan memberi alur permukaan yang dilalui aliran. Pada penelitian ini, aliran yang dikaji adalah aliran boundary layer turbulen yang melintasi suatu pelat datar dengan alur melintang tipe-D. Alur tipe-D adalah tipe alur berbentuk persegi dengan kedalaman dan jarak antar alur yang sama, diletakan normal terhadap arah aliran. Penelitian ini dilakukan secara simulasi numerik. Terdapat 4 model yang disimulasikan yaitu pelat datar (smooth-wall), pelat beralur tipe-D ukuran 4mm, 10mm, dan 30mm . Bilangan Reynolds berdasarkan panjang pelat yaitu Rel = 2.16 x 106 dan kecepatan freestream pada inlet sebesar 10 m/s. Pemodelan numerik dilakukan menggunakan software Gambit 2.4.6 dan Fluent 6.3.26 dengan model 2ddp unsteady, viscous model standart k-epsilon. Berdasarkan hasil penelitian, penambahan alur tipe-D berbagai ukuran meningkatkan koefisien drag total dibanding pelat datar (smooth-wall). Pressure-gradient yang terbentuk didalam alur berkontribusi pada peningkatan ini walaupun nilai koefisien skin-friction mengalami penurunan. Tidak hanya koefisien drag total, tapi nilai intensitas turbulensi juga mengalami peningkatan dibanding pelat datar (smooth-wall). Didalam alur juga terbentuk vortex yang berkontribusi dalam penurunan koefisien skin-friction. Dari ketiga ukuran alur yang berbeda, ditemukan ukuran alur tipe-D ukuran 4mm memiliki nilai koefisien drag total yang lebih rendah daripada lainya.

This paper analyses the nonlinear forces on a moored point-absorbing wave energy converter (WEC) in resonance at prototype scale (1:1) and at model scale (1:16). Three simulation types were used: Reynolds Averaged Navier&ndash, Stokes (RANS), Euler and the linear radiation-diffraction method (linear). Results show that when the wave steepness is doubled, the response reduction is: (i) 3% due to the nonlinear mooring response and the Froude&ndash, Krylov force, (ii) 1&ndash, 4% due to viscous forces, and (iii) 18&ndash, 19% due to induced drag and non-linear added mass and radiation forces. The effect of the induced drag is shown to be largely scale-independent. It is caused by local pressure variations due to vortex generation below the body, which reduce the total pressure force on the hull. Euler simulations are shown to be scale-independent and the scale effects of the WEC are limited by the purely viscous contribution (1&ndash, 4%) for the two waves studied. We recommend that experimental model scale test campaigns of WECs should be accompanied by RANS simulations, and the analysis complemented by scale-independent Euler simulations to quantify the scale-dependent part of the nonlinear effects.

SST-CFD Workshop. International CFD Workshops for Super-sonic Transport Design 航空宇宙技術研究所 19980316-19980317 東京 日本, SST-CFD Workshop. International CFD Workshops for Super-sonic Transport Design National Aerospace Laboratory 19980316-19980317 Tokyo Japan, Most current turbulence models involve explicit wall distance in their formulation. However, wall distance is ambiguous in all but the simplest topologies. Besides, it is not at all evident that it bears a relationship to the structure of turbulence. Thus it is desirable to base modeling practice on wall proximity indicators which are local (pointwise) in nature and convey the influence of walls indirectly, based on parameters that 'measure' this proximity. Examples are the turbulence Reynolds number, k(exp 2)/(nu x epsilon), and various dot products of gradients such as (delta tau/delta x(sub j))(delta k/delta x(sub j)) where tau = k/epsilon, the turbulence time scale. Adhering to this modeling practice retains full generality of the model, since the entire formulation is local. Thus wall-distance-free models are tensorially invariant and frame-indifferent, applicable to arbitrary topologies and moving boundaries. They are also usable in conjunction with solvers based on either unstructured or structured book-keeping, executed on any computer architecture, including massively parallel processors. This paper illustrates the pointwise approach to turbulence modeling by introducing several such models of both linear and nonlinear types, and by demonstrating their performance in 2D and 3D flow eases., 資料番号: AA0063609008, レポート番号: JAXA-SP-06-029E

In order to evaluate the strain rate dependence of the dynamic flow stress of 6061-T6 aluminum alloy, strain rate reduction tests are conducted in the strain rate range from about 2×10^4 to 4×10^4s^, which is the strain rate range before reduction, and the reduction in strain rate is 58.6%. To eliminate an effect of elastic wave dispersion produced in a bar on the measured flow stress, a output bar being 2mm in diameter is employed. A steep increase in the flow stress was observed at the strain rate of about 2×10^4s^. A simplified model for dislocation kinetics under dynamic plastic deformation is used which can represent a transition in the rate controlling mechanism of dislocation motion from a thermally activated process to a viscous drag. It is comfirmed that the steep increase in the flow stress of 6061-T6 observed at the strain rate of about 2×10^4s^ is attributed to the rate dependence of the viscous drag on the dislocation motion and furthermore, the increase in the mobile dislocation density lowers a velocity of moving dislocations and shifts the transition region, or the strain rates in which the steep increase in the flow stress becomes to appear, to the higher strain rate side.

In the previous paper, in order to evaluate the strain rate dependence of the dynamic flow stress of aluminum alloys, 6061-O and -T6, high strain rate tests were performed at strain rates ranging from 1×10^3_> to 3×10^4_>, and strain rate reduction tests were also conducted in the strain rate range from about 1×10^4_> to 2×10^4_>, which is the strain rate range before reduction. A steep increase in the flow stress was observed for 6061-0 at the strain rate of about 5×10^3_>. The above phenomenon, however, was not observed for 6061-T6 in the strain rate range where the strain rate reduction tests were conducted and also the strain rate dependence of the flow stress was negligibly small. In this paper, to clarify the difference between the above-mentioned phenomenon for 6061-0 and -T6, a simplified model for dislocation kinetics under dynamic plastic deformation is used which can represent a transition in the rate controlling mechanism of dislocation motion from a thermally activated process to a viscous drag. The equation derived from the kinetic model reveals that the steep increase in the flow stress of 6061-0 observed at the strain rate of about 5×10^3_> is attributed to the rate dependence of the viscous drag on the dislocation motion and furthermore, the increase in the mobile dislocation density lowers a velocity of moving dislocations and shifts the transition region, or the strain rates in which the steep increase in the flow stress becomes to appear, to the higher strain rate side. It is expected that the flow stress of 6061-T6 increases abruptly in the strain rate region above about 2×10^4_>.

Bu tez çalışmasında, dairesel silindir etrafındaki akışın kontrolü için pasif akış kontrol yöntemi (ayırıcı plaka) ve aktif akış kontrol yöntemi (plazma aktuatör) birlikte kullanılmıştır. Tek dairesel silindir, dairesel silindir ile ayırıcı plaka, dairesel silindir ile plazma aktüatür ve ayırıcı plaka konfigürasyon durumları için deneyler yapılmıştır. Yapılan çalışmalarda elektrohidrodinamik yöntemlerin önemli üç faktörü olan uygulanan voltajın etkisi, plazma oluşumu için frekansın etkisi ve di-elektrik malzeme kalınlığının etkisine bağlı olarak akış yapısı incelenmiştir. Rüzgar tünelinde Reynolds sayısının 2000 ile 12500 değerleri arasında gerçekleştirilen bu çalışmada, test modeli olarak D=40mm olan dairesel silindir ve L=3.75D uzunluğunda ayırıcı plaka kullanılmıştır. Simetrik elektrot çifti dairesel silindir üzerine θ=±90º açıda olacak şekilde yerleştirilmiştir. Yük hücresi ile kuvvet ölçümlerinin ve kızgın-tel anemometresi ile hız ve girdap kopma frekansı ölçümlerinin yanı sıra duman-tel yöntemiyle akış görüntülemesi yapılmıştır. Aktif akış kontrol yöntemi, hem tek dairesel silindirle hem de pasif kontrol yöntemi ile birlikte kullanıldığında iz bölgesi genişliğini daraltarak sürükleme kuvvetinde önemli azalmalar sağlamıştır., In this master thesis, passive (splitter plate) and active (plasma actuator) flow control methods were used together to control the flow around circular cylinder. Experiments accomplished in the case of single circular cylinder, circular cylinder with splitter plate, circular cylinder with splitter plate and plasma actuator configurations. The effect of plasma actuator to the flow structure were investigated. Also, the applied voltage, frequency and the dielectric thickness which effects the performance of plasma actuator were examined. Experiments were conducted at wind tunnel in the range of Reynolds number between 2000 to 12500, the circular cylinder of 40mm with splitter plate of 3.75D were used as a test model. The simetrical electrode pair was placed on the cylinder with θ=±90º angle. Drag force measurements by load cell and the velocity profiles and vortex shedding frequency in the wake by the hot-wire anemometer were conducted as well as the flow visualization by smoke-wire method. By using active flow control with the circular cylinder both only and the splitter plate, the drag force is reduced dramatically due to contraction in the wake region.

Master's thesis in Petroleum engineering As the modern day extended reached wells are getting longer and more complex, the torque and drag is one of the restraining aspects for achieving the target depth. Torque and drag becomes a precarious issue, for example it can be difficult to land the long completion string. Therefore, understanding the friction in the wellbore and how it affects hook load and torque is essential for well path design in planning phase as well as for real time monitoring analysis and post analysis. In planning phase the offset well torque and drag profiles will be used to better well planning. In real time monitoring the torque and drag roadmaps will be used as the well is drilling in order to warn us about upcoming potential drilling problems. In post analysis the torque and drag profiles will be analyzed in order to optimize the well path and drillstring design of new wells in the same area. There are some confusion about torque and drag software and validity of models that are used to characterize drilling operation, especially as the well trajectory is getting more complex. The objective of this study is to perform a sensitivity analysis on different parameters that affect torque and drag in drilling wellbores. The parameters that will be investigated in this project are those which are place of negotiation among individuals; in a way that some of them believe the effect of such parameters are negligible whereas some have opinion that effects of these parameters must be taken into account. These parameters are: Extra friction due to sheave Friction due to hydrodynamic viscous drag force Effect of weight on bit (WOB) on torque In order to carry out this study Landmark WellPlan software has been used. For the effect of viscous drag forces Kristian Gjesrstad’s medium-order flow model for dynamic pressure surges (Gjerstad, March 2013) was used to compare the results obtained from WellPlan. The Gjerstad’s model takes into account the effects of combined axial and rotational movement of pipe as well as the flow regimes.

The input of energy by wind to water waves is compared with the observed growth of the waves using a suite of microphysical measurement techniques in the laboratory. These include measured tangential stresses in the water and air immediately adjacent to the interface with corresponding form drag measurements above wind-forced freely propagating waves. The drag data sets are consistent but the comparison has highlighted important issues in relation to the measurement of fluctuating pressures above freely propagating waves. Derived normalized wind input values show good collapse as a function of mean wave steepness and are significantly in excess of the assembly of net wave growth measurements by Peirson & Garcia (J. Fluid Mech., vol. 608, 2008, pp. 243–274) at low steepness. Sheltering coefficients in the form of Jeffreys (Proc. R. Soc. Lond. Ser. A, vol. 107, 1925, pp. 189–206) are derived that are consistent with values previously obtained by Donelan & Pierson (J. Geophys. Res., vol. 92, 1987, pp. 4971–5029), Donelan (Wind-over-Wave Couplings: Perspectives and Prospects, Clarendon, 1999, pp. 183–194) and Donelan et al. (J. Phys. Oceanogr., vol. 36, 2006, pp. 1672–1689). The sheltering coefficients exhibit substantial scatter. By carefully measuring the associated growth of the surface wave fields, systematic energy budgets for the interaction between wind and waves are obtained. For non-breaking waves, there is a significant and systematic misclose in the radiative transfer equation if wave–turbulence interactions are not included. Significantly higher levels of turbulent wave attenuation are found in comparison with the theoretical estimates by Teixeira & Belcher (J. Fluid Mech., vol. 458, 2002, pp. 229–267) and Ardhuin & Jenkins (J. Phys. Oceanogr., vol. 36, 2006, pp. 551–557). Suitable normalizations of attenuation for wind-forced wave fields exhibit consistent behaviour in the presence and absence of wave breaking. Closure of the surface energy flux budget is obtained by comparing the normalized energy loss rates due to breaking with the values previously determined by Banner & Peirson (J. Fluid Mech., vol. 585, 2007, pp. 93–115) and Drazen et al.(J. Fluid Mech., vol. 611, 2008, pp. 307–332) when expressed as a function of mean wave steepness. Their normalized energy loss rates obtained for non-wind forced breaking wave groups are remarkably consistent with the levels found during this present study when breaking waves are subject to wind forcing.

A novel method similar to marching technique was used to model wind tunnel tests. ► Sail trim criteria based on their interactive effect are identified. ► Areas of separated flow were characterised. ► Local flow field was correlated with sail surface pressures. ► An aerodynamic model based on potential flow with viscous correction is proposed. The aerodynamics of a sailing yacht with different sail trims are presented, derived from simulations performed using Computational Fluid Dynamics. A Reynolds-averaged Navier-Stokes approach was used to model sixteen sail trims first tested in a wind tunnel, where thepressure distributions on the sails were measured. An original approach was employed byusing two successive simulations: the first one on a large domain to model the blockage due to the wind tunnel walls and the sails model, and a second one on a smaller domain to model the flow around the sails model. A verification and validation of the computed aerodynamic forces and pressure distributions was performed. The computed pressure distribution is shown to agree well with the measured pressures. The sail surface pressure was correlated with the increase of turbulent viscosity in the laminar separation bubble, the flow reattachment and the trailing edge separation. The drive force distribution on both sails showed that the fore part of the genoa (fore sail) provides the majority of the drive force and that the effect of the aft sail is mostly to produce an upwash effect on the genoa. An aerodynamic model based on potential flow theory and a viscous correction is proposed. This model, with one free parameter to be determined, is shown to fit the results better than the usual form drag and induced drag only, even if no friction drag is explicitly considered. the third author received a financial support from Brest Métropole Océane and the ERASMUS scholarship

The aim of this work is to develop a simple nonlinear model of a wave energy converter (WEC) for capturing power from ocean waves and converting it into electrical power. A generic axisymmetric device is considered, which consists of a vertical circular cylinder surrounded by a circular annulus. The nonlinear system of equations of motion of this generic WEC are derived; these include the nonlinear term arising from viscous drag due to boundary layer separation. The expressions for radiation damping and added mass are determined by dimensional analysis. These equations are then solved numerically and the results are displayed graphically in a number of figures. Consideration of these graphs leads to conclusions that should be taken into account by the design engineer.

In this paper a physical-based constitutive relation for defining the thermo-viscoplastic behaviour of FCC metals with dependence on strain on thermal activation processes is presented. The model, based on previous considerations reported by Rusinek and Klepaczko [Rusinek A, Klepaczko JR. Shear testing of sheet steel at wide range of strain rates and a constitutive relation with strain-rate and temperature dependence of the flow stress. Int J Plasticity 2001;17:87-115], is founded on physical aspects of the material behaviour. The proposed constitutive relation is applied to define the behaviour of oxygen-free high conductivity (OFHC) copper using the experimental data reported in Nemat-Nasser and Li [Nemat-Nasser S, Li Y. Flow stress of FCC polycrystals with application to OFHC copper. Acta Mater 1998;46:565-77]. The description of the material behaviour provided by the model gets satisfactory agreement with the experiments. The analytical predictions of this constitutive description are compared with those obtained from the models due to Voyiadjis and Almasri [Voyiadjis GZ, Almasri AH. A physically based constitutive model for fcc metals with applications to dynamic hardness. Mech Mater 2008;40:549-63], and Nemat-Nasser and Li. This comparison reveals that the original formulation proposed in this paper is a suitable alternative to other physically based relations for modeling OFHC copper. The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (ProjectCCG08UC3M/MAT4464) and to the Ministerio de Ciencia e Innovación de España (ProjectDPI/200806408) Publicado

Spacers are designed to generate significant secondary flow structures and create directional changes in the flow through membrane modules. Shape of the spacers used in membrane modules strongly influences the resulting flow and therefore performance of the module. In this work fluid dynamics of rectangular channels similar to membrane modules and containing different spacers was simulated using a three-dimensional computational fluid dynamics (CFD) model. A ‘unit cell’ approach was evaluated and used for this purpose. In addition to predicting the pressure drop, the simulated results provided significant insight into fluid dynamics of spacer filled channels. The validated CFD model was used to evaluate performance of different spacer shapes and understand the role of spacer shape and resulting fluid dynamics. The models were extended for the first time to simulate flow in spacer filled curvilinear channels, which could be useful in understanding the fluid behavior in spiral modules. The results were compared with those obtained with the flat channel. The approach and results presented in this work will have significant implications for identifying improved spacers with higher propensities to reduce fouling in membrane modules.

Many pump slippage formulas have been developed over the years. Most of these formulas over predict the pump slippage and a more accurate formula is needed. A slippage formula is required for plunger lubrication, pump efficiency and plunger pump production calculations to maximize production. Historical models are discussed and compared, which include Robinson (1935), Davis and Steams (1944), Robinson and Reekstin (1960), Davis, Steams, and Reekstin (1960), and the ARCOHarbinson Fisher (2000). A new method for calculating slippage is introduced. This method involves calculating a velocity profile for an annulus with the inner wall moving parallel to the outer wall. An average velocity is determined for the annular fluid flow, which in turn is used to calculate the fluid slippage. Eccentricity is also considered in the slippage calculation method. The method is compared to the historical formulas. A formula to calculate viscous drag on the pump plunger, which takes into account eccentricity, is also derived from the velocity profile.

We report here the collective behavior of droplets in the scale ${10}^{\ensuremath{-}6}--{10}^{\ensuremath{-}5}\mathrm{m}$ made of a concentrated magnetic fluid elongated and oriented by a magnetic field while rotating synchronously with respect to the carrier liquid. Distribution of droplet sizes is studied as a function of a magnetoviscous number ${N}_{\mathrm{mv}}$ that quantifies the competition between magnetic field and local vorticity. The liquid state and very low interfacial tension enable both breakup and coalescence processes, which are undergone by the droplet population to reach dynamic equilibrium. Theoretical analysis of a single drop motion is extended to the case of the drop assembly. Experiments combining rotation and field modulation show a regime of nonsteady rotation in good agreement with theory.

Experimental and theoretical developments in the study of turbulence have revealed several surface roughness geometries that reduce viscous drag. The interaction between structures in turbulent flow and patterns of structures of similar size on the surface can reduce global viscous drag. Experiments are shown that begin to map the combinations of water speed, groove size and spacing that accomplish this., 18th International Conference on Offshore Mechanics and Arctic Engineering, 11-16 July 1999, St. John's, Newfoundland

This paper investigates the accuracy of three aerodynamic models to compute loads on wind turbine rotors under turbulent inflow: Blade Element Momentum (BEM), Unsteady Vortex Lattice Method (UVLM), and Large Eddy Simulation with Actuator Line (LES‐AL). Turbulent inflow conditions are numerically generated with a new approach that combines control of turbulence and realistic velocity spectrum by using Mann boxes and LES simulations, respectively. Several deficiencies of the tested models are found and overcome through proposed improvements. First, the BEM assumption of independent radial sections does not hold in turbulent cases with long blades. Thus, a spatial filter to account for the interaction of radial sections in BEM is designed through the analysis of these interactions with UVLM. Second, the absence of viscous drag in UVLM is observed to lead to a very high rotor power coefficient, and it is shown that this can be mitigated by including drag in UVLM with a BEM‐like‐approach through look‐up tables. Third, the free wake model in UVLM, required to accurately capture rotor thrust, significantly increases computational cost. For this reason, a new wake discretisation scheme for the wake convection equation in UVLM is proposed, in which a coarse discretisation is employed far from the solid surfaces, which significantly reduces the computational time. Finally, these improvements and the performance of the three fidelities are analysed in a reference 10 MW wind turbine rotor demonstrating, in general, good agreement.

ÖZET Bu çalışmada, serbest su yüzeyinden sonsuz derinlikte sabit hızla ilerleyen bir çift-modelin viskoz direncini. belirle mek amacıyla, Stokes yaklaşımı çerçevesinde matematiksel bir yöntem geliştirilmiştir. I. Bölümde konunun önemi vurgulanmış ve ilgili çalışmalar sıralanarak, temel denklemlere sınır koşulları ortaya konulmuştur. II. Bölümde direncin sonlu kalması gerektiği fiziksel gerçeğinden hareketle, orijinal problemin kısmi türevli diferansiyel denklemleri, Hilbert uzayında açılım yoluyla sonsuz boyutlu adi türevli diferansiyel denklem takımına indirgenmiştir. Ayrıca, sınır koşulları da geliştirilen yönteme uygun olarak düzenlenerek, problemin seri çözümlerinin yakınsama kriterlerine ilişkin önermeler ispatlanmıştır. III. Bölümde sonlu boyutlu alt uzaylarda seri çözümlerin nasıl bulunacağı gösterilmiş ve bir boyutlu alt uzaydaki çözümler kapalı formda elde edilmiştir. Çalışmanın ilgili literatüre getirdiği en önemli yenilik, cismin geometrisine bağlı olmaksızın süreklilik ve dönel simetri koşulları altında, her türlü cisim için geçerliliğidir. Cismin yüzeyini karakterize etmek üzere önerilen şekil fonksiyonunun parametrik yapısı nedeniyle yöntem, belirli dizayn şartlarını sağlatmanın dışında, parametrelerin uygun şekilde seçilmesiyle direnci minimum olacak formların belirlenmesi için de elverişli dir. Bir boyutlu alt uzaydaki kapalı çözümler kullanılarak bulunan sayısal sonuçlar, literatürle karşılaştırıldığında oldukça yeterli olup paket bilgisayar programları yardımıyla hesaplanmış optimum formlar da gerçekçi ve kabul edilebilir niteliktedir. Çalışmanın, bundan sonra, hangi yönlerde geliştirileceği konusundaki görüş ve öneriler ise son bölümde tartışılmıştır. Buna göre, sonlu alt uzaylarda yakınsaklığı gösterilmiş çözümler kullanılarak geliştirilecek bilgisayar programıyla, sadece bir boyutlu alt uzay için verilmiş sayısal sonuçlar uzayın boyutu artırılarak test edilebilecektir, öte yandan uzayın boyutu sonsuza götürüldüğünde, çözüm serilerinin her biri teker teker yakınsak olmakla birlikte, bunların lineer bileşiminden oluşacak genel ' çözüm sonsuz eleman içereceğinden yakınsaması garanti değildir. Gelecekte çalışmaların sürdürüleceği bir diğer alan ise, sabit hacim koşulu halinde çıkacak optimum formlar dışında başka dizayn koşullarının da dikkate alınarak optimizasyon tekniklerinin geliştirilmesi olacaktır. -iv- SUMMARY VISCOUS-DRAG EVALUATION VIA A THEORETICAL METHOD AND SHAPE OPTIMIZATION IN AX I SYMMETRIC STOKES FLOW The classical Stokes-flow problem describing the creeping motion of a single body, without rotation, has been studied for more than a century. The importance of solving the problem is its applications for instance drag evaluation of a double-ship model. Moreover, in some cases', the solution of Stokes equation is used as a first approximation of Navier-Stokes equation in full form. First explicit analytic solutions are due to Stokes [33] for a sphere, and Oberbeck [34] for an ellipsoid. General solution of the Stokes equation in spherical co-ordinates is given by Sampson [35] in terms of stream functions as an infinite series of Legendre polynomials by separation of variables. However, both analytical and numerical implementation of this exact solution is extremely difficult for a treatment of the problem of an arbitrary axisymmetrical body, except for some special geometries. For example, the classical theory has been developed for slightly deformed spheres [ 32], lens-shaped bodies [37] and spherical caps [38], mainly, based upon the use of seperability of a special orthogonal co-ordinate system. The Green's function technique can be applied in order to attain an alternative approach, which is an integral representa tion, for the solution of the problem [39], [40]. The main concepts of the theory and detailed discussions on the advantages of the solution in integral form may be found in the literature [41], [42], [43]. On the other hand, various numerical methods have been proposed for the approximate solutions of such problems using the general integral form or, in the axisymmetrical case of flow, the serial expansion of the stream function. In this work, we show an exact theory can be constructed to determine Stokes-flow past an axisymmetrical arbitrary body. In Section 1.4 the statement of the problem is given. The govern ing equations valid in the fluid domain, V, are Stokes equations, (SI) V2v=Vp -v-and the equations of continuity, (S2) V.v=0, where v and p are velocity vector and pressure function respect ively. For an axisymmetrical fluid motion, the mathematical problem is reduced to search for a scalar function called stream function, y, which must satisfy the fourth-order equation, e'^O. This may be. written in the form (S3) E2$=0, E2*^. Here E2 is a second order partial differential operator defined by (S4) E2= İİ + £İE6 _3_ ( _J__ _8_ } )t2 r2 86 sine 3* in spherical co-ordinates and then all flow characteristics can be expressed in terms of $ and ¥. If F(9) denotes the equation of axisymmetric body surface, the boundary conditions are (S5a) r=F(6) + v =v =0 r 8 (S5b) v =cos6, Vg=-sin8 as r-*°°, and drag will be evaluated by R-l //` ljdrde V 3 0 F(6)SinG In chapter II, a general systematic method for solving -vi-the equations (S3) is presented. By performing the co-ordinate transformations (S7) n=cose, Ç=r-F(n), ne [-1,1], Çe.[0,«0 drag is expressible as (S8) r = 1 // *İ

For aircraft design, drag optimization is very important for having better flight performance and less fuel consumption. In this study, drag effects of fuselage, wing and tail section are separately analyzed using a generic F-16 fighter aircraft model in ANSYS Fluent CFD tool with polyhedral mesh. Pressure drag and viscous drag effects are shown on different section of the aircraft as fuselage, wing, vertical tail and horizontal tail. Drag values are presented on subsonic, transonic and supersonic flights. © 2016 9th International Conference on Computational Fluid Dynamics, ICCFD 2016 - Proceedings. All rights reserved.