Search

We present an Eulerian vortex method based on the theory of flow maps to simulate the complex vortical motions of incompressible fluids. Central to our method is the novel incorporation of the flow-map transport equations for line elements, which, in combination with a bi-directional marching scheme for flow maps, enables the high-fidelity Eulerian advection of vorticity variables. The fundamental motivation is that, compared to impulse m, which has been recently bridged with flow maps to encouraging results, vorticity ω promises to be preferable for its numerical stability and physical interpretability. To realize the full potential of this novel formulation, we develop a new Poisson solving scheme for vorticity-to-velocity reconstruction that is both efficient and able to accurately handle the coupling near solid boundaries. We demonstrate the efficacy of our approach with a range of vortex simulation examples, including leapfrog vortices, vortex collisions, cavity flow, and the formation of complex vortical structures due to solid-fluid interactions. [ABSTRACT FROM AUTHOR]

Accurately simulating turbulent wind fields is a significant challenge in wind engineering. This study proposes a novel block‐vorticity method aimed at overcoming the limitations of traditional turbulence generation methods. By superimposing a blocked vortex field at the inlet boundary of large eddy simulation (LES), the proposed method enables the generation of highly precise and anisotropic turbulent wind fields. To validate the effectiveness of the proposed method, the study investigates wind pressures on a high‐rise building structure and performs a comparative analysis with LES narrowband synthesis random flow generator (NSRFG), traditional LES, and SST k‐ω turbulence inlet models. The results demonstrate that the proposed method can effectively simulate turbulence characteristics of atmospheric boundary layer flow, including vortex structure and stochastic fluctuating wind field. Compared to traditional methods, the wind field characteristics of turbulence intensity, instantaneous vorticity, and turbulence self‐equilibrium had obvious advantages over traditional methods. Moreover, the LES vortex method is more accurate in simulating the mean wind pressure and fluctuating wind pressure of the high‐rise building compared to traditional models and is closer to the wind tunnel test results. The proposed method provides an effective approach for generating turbulent wind fields with anisotropic characteristics and can be used to predict the wind‐induced response of civil engineering structures. [ABSTRACT FROM AUTHOR]

A 2-D Lattice Boltzmann Method, designed to ensure stability at high Reynolds numbers, is combined with an Actuator Line Model to compute the loads on a two-bladed vertical axis wind turbine. Tests on the kernel size at a high mesh resolution reveal that a size equal to half of the full chord length yields the most accurate results. The aerodynamic load solution is validated against a fully resolved Scale-Adaptive Simulation (SAS) output, demonstrating high correlation, and enabling an assessment of near wake and downstream effects. The model's adaptability to various rotor operating conditions is confirmed through tests at high and low tip-speed ratios. Additionally, a Biot–Savart-based Vortex Model (VM) is employed for further comparison, showing good agreement with the Lattice Boltzmann output. The results indicate that the Highly Stable Lattice Boltzmann Method integrated with the Actuator Line Model enhances the accuracy of flow field resolution and effectively captures complex aerodynamic phenomena, making it a valuable tool for simulating vertical axis wind turbines. [ABSTRACT FROM AUTHOR]

The objective of the present study is to analyze the influence of various inflow turbulence generation techniques (ITGT) on the flow field and pollutant dispersion around a street canyon with perpendicular wind flow through the large eddy simulation approach. Vortex method (VM), internal mapping (IM), spectral method (SM) and no fluctuations (NF) are the four ITGTs under investigation. Results suggest that ventilation of the canyon is mainly due to corner eddies, canyon vortex and the flow passing over the top of the buildings. All ITGTs can capture the two important structures of canyon vortex and corner eddy, but IM underpredicts the corner eddies and SM and NF underpredict the canyon vortex. VM slightly overpredicts the canyon vortex. However, its accuracy in predicting the pollutant dispersion at both walls and low speed regions is higher than the other methods. The velocity fluctuation is also another important parameter for ventilating the low speed regions. The VM displays the most accurate results, and the NF shows the least accurate ones. In terms of relative error, computational cost, and the number of required input parameters, VM is the most optimized ITGT. [ABSTRACT FROM AUTHOR]

AZ91E, a magnesium alloy, shows promise in vehicle technology with its lightweight properties and potential for hybrid metal matrix composites. This study focuses on investigating compression properties using statistical analysis and finite element method simulations. However, experimental measurements reveal a density decrease compared to theoretical values, impacting weight optimization and structural integrity in vehicles. Incorporating strengthening agents like ZrO2 and fly ash enhances mechanical properties, though fracture toughness reduces due to grain refinement. Overall, this research provides valuable insights for integrating AZ91E-based composites in the automotive industry to achieve weight reduction and improved performance. As vehicles aim for lighter materials to improve fuel efficiency and reduce emissions, magnesium alloys have emerged as promising candidates for various components. AZ91E, composed mainly of magnesium (Mg), along with aluminum (Al) and zinc (Zn) as primary alloying elements, offers excellent lightweight characteristics. However, the experimental measurements in this study revealed a decrease in density compared to theoretical values, which may have implications for vehicle weight optimization and structural integrity. Decreasing deformation height reduced compressive strength for (H/D = 1 and 1.5) of AZ91E and composites, but composites showed higher compressive strength despite slightly higher density, indicating their superior performance. Analytical equations and ANSYS software provided closely matched results for axial, compressive and hydrostatic stress, while the strength coefficient and the exponent of strain hardening revealed plastic behavior of the samples. Incorporation of FA particles improved the ultimate yield and tensile strengths, as well as the tensile characteristics and hardness with underlying processes for strengthening were discussed. The investigation of AZ91E-ZrO2-fly ash hybrid metal matrix offers valuable insights into potential applications of magnesium alloys in the automotive industry. Understanding the compression attributes and mechanical behavior of these composites, its crucial for their successful integration into vehicle components, where weight reduction and improved performance are essential goals. [ABSTRACT FROM AUTHOR]

Pseudothrombocytopenia (PTCP) refers to the aggregation of platelets in anticoagulant blood in vitro and causes a false lower platelet count (PLT). For the purpose to achieve an accurate PLT, we presented an alternative vortex method to disaggregate platelet clumps and consequently generate a reliable PLT without a second venous puncture for patients. PLT, mean-platelet-volume (MPV), red blood cells (RBCs), hematoglobin (Hb), hematocrit (Hct) and white blood cells (WBCs) were evaluated before and after vortex in 221 specimens with PTCP using vortex method, and the PLT was also compared with 85 specimens disaggregated by citrate method. Twenty control samples were used to investigate mixing effect on complete blood counts in normal samples. One thrombocytopenia specimen was used to evaluate reproducibility of vortex. The mean PLT, MPV, RBCs, Hb, Hct and WBCs of 20 control specimens pre-vortex were 260.7 ± 53.4 × 109/L, 11.65 ± 0.85, 4.87 ± 0.46 × 1012/L, 147.6 ± 13.8 g/L, 45.31 ± 4.04, 6.46 ± 1.41 × 109/L, and results of post-vortex were 252.9 ± 50.2 × 109/L, 11.66 ± 0.92, 4.95 ± 0.48 × 1012/L, 149.1 ± 13.8 g/L, 45.19 ± 4.03, 6.35 ± 1.36 × 109/L respectively. Specimens with platelet clumps using vortex mixer had higher PLT after mixing, the mean pre-vortex PLT was 54.3 ± 35.2 × 109/L, and after vortexing PLT increased to 157.5 ± 58.8 × 109/L (p < 0.05). MPV, RBCs, Hb, Hct and WBCs in 221 specimens were comparable before and after vortex mixing (all p > 0.05). Vortex method might disaggregate platelet clumps sufficiently in most PTCP specimens, and obtain a relatively reliable PLT without the need of a second venous puncture. [ABSTRACT FROM AUTHOR]

Abstract The manuscript presents a novel numerical investigation on the impact of the wake of a floating IEA wind 15‐MW reference wind turbine (RWT) on downstream machines using a state‐of‐the‐art vortex solver coupled to a multi‐body code. The coupling enables to account for the flexibility of the different turbine components as well as to include the effect of the controller and the dynamics of the floating support structure. First, the turbine is mounted on the WindCrete spar‐buoy platform, and the wake impact on a second turbine positioned at different downstream positions is investigated and compared with the impact of the wake generated by a bottom‐fixed machine. It is found that the faster breakdown of the vortex structures triggered by the motion of the floater in the upstream turbine increases the power production of a downstream machine, as well as its mean thrust level relative to normal operation downstream a bottom‐fixed machine. It is demonstrated that this effect is drastically reduced with the increase of the turbulence intensity (TI). Further, simulations with a prescribed harmonic motion of the upstream turbine in surge and pitch under different turbulence levels are presented. It is found that the motion of the floater has a strong impact in the generated wake and consequently in the operation of downstream machines. In particular, downstream turbines experienced considerably higher blade loading that led to an increase of the aerodynamic power. Finally, aero‐hydro‐servo‐elastic simulations of five turbines in a row have shown that the interaction between multiple floating machines is more dynamic than between bottom‐fixed turbines. This has been mainly observed at high wind speeds, where the pitch and surge motions of the floater in turbines located deep inside the farm can be resonantly excited by the interaction with the wind farm flow. In practice, this means that the power and thrust variations increase with the turbine location depth inside the farm. Overall, the study highlights the importance of an accurate flow and wake modeling for the prediction of turbine‐to‐turbine interaction in a floating context.

Abstract Floating wind turbines have the potential to enable global exploitation of offshore wind energy, but there is a need to further understand the complex aerodynamic phenomena they can encounter due to floater induced rotor motion. Aerodynamic models traditionally used in the wind energy sector, like the Blade Element Momentum (BEM) theory, may not be capable of capturing the dynamic phenomena that occur when the rotor moves in and out of its own wake. In the present paper, we therefore compare an industry standard BEM‐based code to a state of the art vortex solver, to investigate the phenomena in detail and further clarify the capabilities and limitations of both methods. An initial benchmark of the two codes using the IEA Wind 15 MW RWT mounted on the WindCrete spar‐buoy floater is carried out. Three different scenarios are taken into account: a bottom‐fixed, a floating case, and a floating case subject to regular waves. Growing discrepancies between the codes have been observed with the increasing complexity of the simulations. Moreover, large differences between the wake generated by a bottom fixed and a floating turbine have been observed, with the latter one experiencing a faster recovery. To further explore the floating turbines behaviors that can affect the rotor performance and wake, a systematic investigation of the mean tilt angle influence in the wake development has been carried out. Further, to account for the oscillatory motion of a floating turbine, a parametric study where the floater motion is prescribed in both pitch and surge degrees of freedom (DoF) is designed. The study covers a large variety of scenarios; a wide range of relevant frequencies and amplitudes are taken into account in under and above‐rated wind conditions. A total of more than 28 unique cases have been defined and simulated with both fidelity models. The results include the downstream evolution of the wake recovery and intensity of the turbulent disturbances induced by the rotor. The generic nature of the study allows to characterize the flow and performance effects and enables subsequent generalization to floater designs of given natural frequency and motion amplitude. It has been found that the BEM and LL predictions of the maximum loading in the blade root and tower bottom compare quite well, except for the case of large oscillation frequency in above rated conditions, where the BEM method under‐predicts the loads. Moreover, the use of a vortex solver makes it possible to look in depth into the wake characteristics, in which large differences are observed between the bottom‐fixed and the floating case in non‐turbulent inflow conditions. It has been found that the frequency and amplitude of the turbine oscillations can have a strong impact on the recovery of the wake. Moreover, we have found a link between short time intervals of large FA blade tip displacements and a faster break down of the wake. Finally it has been shown that a floating wind turbine with large and fast oscillations can transition between the different rotor states, including the non‐conventional propeller and vortex ring states, which are identified and characterized.

It has been considered that two close vortex sheets become unstable and evolve simultaneously when sufficiently strong uniform shears exist. However, Moore (Mathematika, 1976) suggested in his linear analysis that a vortex sheet evolves just as if the other vortex sheet were absent under certain conditions. In the current study, we investigate how the two vortex sheets evolve in the nonlinear region when they satisfy Moore's condition. We also consider density stratification, which is not included in Moore's analysis. Moore's estimate is only valid within linear theory; however, a motion suggested by Moore appears even in the nonlinear regime when Moore's condition is satisfied. We found that there is a case that a vortex sheet hardly deforms, even though the other sheet becomes unstable and largely deforms. We also show that there is a case that Moore's analysis is not effective even the condition is satisfied when a density instability exists in the system.

In this paper, we present a novel, closed, three-dimensional random vortex dynamics system, which is equivalent to the Navier–Stokes equations for incompressible viscous fluid flows. The new random vortex dynamics system consists of a stochastic differential equation which is, in contrast with the two-dimensional random vortex dynamics equations, coupled to a finite-dimensional ordinary functional differential equation. This new random vortex system paves the way for devising new numerical schemes (random vortex methods) for solving three-dimensional incompressible fluid flow equations by Monte Carlo simulations. In order to derive the three-dimensional random vortex dynamics equations, we have developed two powerful tools: the first is the duality of the conditional distributions of a couple of Taylor diffusions, which provides a path space version of integration by parts; the second is a forward type Feynman–Kac formula representing solutions to nonlinear parabolic equations in terms of functional integration. These technical tools and the underlying ideas are likely to be useful in treating other nonlinear problems. [ABSTRACT FROM AUTHOR]

It has been considered that two close vortex sheets become unstable and evolve simultaneously when sufficiently strong uniform shears exist. However, Moore (Mathematika, 1976) suggested in his linear analysis that a vortex sheet evolves just as if the other vortex sheet were absent under certain conditions. In the current study, we investigate how the two vortex sheets evolve in the nonlinear region when they satisfy Moore's condition. We also consider density stratification, which is not included in Moore's analysis. Moore's estimate is only valid within linear theory; however, a motion suggested by Moore appears even in the nonlinear regime when Moore's condition is satisfied. We found that there is a case that a vortex sheet hardly deforms, even though the other sheet becomes unstable and largely deforms. We also show that there is a case that Moore's analysis is not effective even the condition is satisfied when a density instability exists in the system. [ABSTRACT FROM AUTHOR]

In marine firefighting, a realistic virtual ship fire scenario is crucial for enhancing the effectiveness of simulation training and the firefighting capabilities of the crew. Given that fluid simulation is a key and challenging aspect of virtual scenarios, we propose a unified particle method based on vortex dynamics for real-time fluid simulation in ship fire scenarios. We introduce a hybrid discrete structure, utilizing vortex segments and vortex particles, to represent the vorticity and the velocity. The vortex segments are primarily used to construct an accurate velocity field, while the vortex particles enhance the stability of the simulation. To improve the efficiency, we devise a local summation operation to reduce the time complexity of computing the velocity field, which is the most computationally expensive part of the simulation. By adjusting the radius of the summation operation, we can control the scale of the vortices, thereby influencing the flow characteristics of the fluid. We demonstrate the efficiency and effectiveness of our real-time fluid simulation through various challenging scenarios involving smoke, gaseous carbon dioxide, and water mist. Our method is valuable for practical applications to improve the efficiency of ship fire simulation training. • A hybrid structure of vorticity field to simulate the fluid in ship fire scenario. • A local summation operation to improve the efficiency and efficacy of the simulation. • A real-time fluid simulation framework based on the hybrid structure. [ABSTRACT FROM AUTHOR]

Under the current background of navigation education, students generally lack a comprehensive grasp of ship firefighting equipment's operation. Therefore, we develop a novel ship firefighting training simulator with a multi-sensory human–computer interaction function for teaching and training marine students. In the simulator, we consider a container ship of 1.8w containers as the prototype ship, and the entire ship models are built using three-dimensional modeling technology. We design various interactive modes and realize a full-process operation simulation of several standard ship firefighting equipment. Furthermore, we propose a purely Lagrangian vortex dynamics framework to simulate smoke and flame in fire scenarios. In this framework, we model fluids using velocity and vorticity fields discretized on discrete vortex segments. The main components of the framework include a stable geometric stretching solution and particle strength exchange method for solving the diffusion term. The simulation results show that the simulator has good behavioral realism and scene immersion and can be applied to ship firefighting training. To the best of our knowledge, this is the first study on real-time smoke simulation using a physics-based method in a firefighting training simulator. [ABSTRACT FROM AUTHOR]

The manuscript presents a novel numerical investigation on the impact of the wake of a floating IEA wind 15‐MW reference wind turbine (RWT) on downstream machines using a state‐of‐the‐art vortex solver coupled to a multi‐body code. The coupling enables to account for the flexibility of the different turbine components as well as to include the effect of the controller and the dynamics of the floating support structure. First, the turbine is mounted on the WindCrete spar‐buoy platform, and the wake impact on a second turbine positioned at different downstream positions is investigated and compared with the impact of the wake generated by a bottom‐fixed machine. It is found that the faster breakdown of the vortex structures triggered by the motion of the floater in the upstream turbine increases the power production of a downstream machine, as well as its mean thrust level relative to normal operation downstream a bottom‐fixed machine. It is demonstrated that this effect is drastically reduced with the increase of the turbulence intensity (TI). Further, simulations with a prescribed harmonic motion of the upstream turbine in surge and pitch under different turbulence levels are presented. It is found that the motion of the floater has a strong impact in the generated wake and consequently in the operation of downstream machines. In particular, downstream turbines experienced considerably higher blade loading that led to an increase of the aerodynamic power. Finally, aero‐hydro‐servo‐elastic simulations of five turbines in a row have shown that the interaction between multiple floating machines is more dynamic than between bottom‐fixed turbines. This has been mainly observed at high wind speeds, where the pitch and surge motions of the floater in turbines located deep inside the farm can be resonantly excited by the interaction with the wind farm flow. In practice, this means that the power and thrust variations increase with the turbine location depth inside the farm. Overall, the study highlights the importance of an accurate flow and wake modeling for the prediction of turbine‐to‐turbine interaction in a floating context. [ABSTRACT FROM AUTHOR]

This paper compares three different numerical models to evaluate their accuracy for predicting the performance of an H-rotor vertical-axis wind turbine (VAWT) considering the influence of struts. The strut of VAWTs is one factor that makes the flow feature around the turbine more complex and thus influences the rotor performance. The focus of this study is placed on analyzing how accurately three different numerical approaches are able to reproduce the force distribution and the resulting power, taking the strut effect into account. For the 12 kW straight-bladed VAWT, the blade force is simulated at three tip speed ratios by the full computational fluid dynamics (CFD) model based on the Reynolds-averaged Navier–Stokes (RANS) equations, the actuator line model (ALM), and the vortex model. The results show that all the models do not indicate a significant influence of the struts in the total force over one revolution at low tip speed ratio. However, at middle and high tip speed ratio, the RANS model reproduces the significant decrease of the total tangential force that is caused due to the strut. Additionally, the RANS and vortex models present a clear influence of the struts in the force distribution along the blade at all three tip speed ratios investigated. The prediction by the ALM does not show such distinctive features of the strut impact. The RANS model is superior to the other two models for predicting the power coefficient considering the strut effect, especially at high tip speed ratio. [ABSTRACT FROM AUTHOR]

Floating wind turbines have the potential to enable global exploitation of offshore wind energy, but there is a need to further understand the complex aerodynamic phenomena they can encounter due to floater induced rotor motion. Aerodynamic models traditionally used in the wind energy sector, like the Blade Element Momentum (BEM) theory, may not be capable of capturing the dynamic phenomena that occur when the rotor moves in and out of its own wake. In the present paper, we therefore compare an industry standard BEM‐based code to a state of the art vortex solver, to investigate the phenomena in detail and further clarify the capabilities and limitations of both methods. An initial benchmark of the two codes using the IEA Wind 15 MW RWT mounted on the WindCrete spar‐buoy floater is carried out. Three different scenarios are taken into account: a bottom‐fixed, a floating case, and a floating case subject to regular waves. Growing discrepancies between the codes have been observed with the increasing complexity of the simulations. Moreover, large differences between the wake generated by a bottom fixed and a floating turbine have been observed, with the latter one experiencing a faster recovery. To further explore the floating turbines behaviors that can affect the rotor performance and wake, a systematic investigation of the mean tilt angle influence in the wake development has been carried out. Further, to account for the oscillatory motion of a floating turbine, a parametric study where the floater motion is prescribed in both pitch and surge degrees of freedom (DoF) is designed. The study covers a large variety of scenarios; a wide range of relevant frequencies and amplitudes are taken into account in under and above‐rated wind conditions. A total of more than 28 unique cases have been defined and simulated with both fidelity models. The results include the downstream evolution of the wake recovery and intensity of the turbulent disturbances induced by the rotor. The generic nature of the study allows to characterize the flow and performance effects and enables subsequent generalization to floater designs of given natural frequency and motion amplitude. It has been found that the BEM and LL predictions of the maximum loading in the blade root and tower bottom compare quite well, except for the case of large oscillation frequency in above rated conditions, where the BEM method under‐predicts the loads. Moreover, the use of a vortex solver makes it possible to look in depth into the wake characteristics, in which large differences are observed between the bottom‐fixed and the floating case in non‐turbulent inflow conditions. It has been found that the frequency and amplitude of the turbine oscillations can have a strong impact on the recovery of the wake. Moreover, we have found a link between short time intervals of large FA blade tip displacements and a faster break down of the wake. Finally it has been shown that a floating wind turbine with large and fast oscillations can transition between the different rotor states, including the non‐conventional propeller and vortex ring states, which are identified and characterized. [ABSTRACT FROM AUTHOR]

The flutter of thin elastic plates (sheets) in a fluid flow is an interesting nonlinear problem, as well as an important engineering problem, because the sheets are used in many industrial applications. A detailed understanding of flutter characteristics and sustaining mechanism of limit cycle oscillation (LCO) is important to suppress the flutter. In this study, a nonlinear analysis on a LCO of rectangular sheets in a three-dimensional uniform fluid flow using the nonlinear beam model and vortex-lattice method is performed. The influence of the vortex element model of the vortex-lattice method on the post-critical behavior is investigated in detail. Moreover, fluid–structure interaction simulations are performed using computational fluid dynamics and computational structural dynamics to examine the flow field and pressure distributions acting on a sheet surface in detail. It is found that flow separation around the side edges of a fluttering sheet can affect the post-critical behavior. [ABSTRACT FROM AUTHOR]

In the present study, AA2024-SiO2np nanocomposites were prepared by the vortex method and effects of SiO2 content on resulting microstructural and mechanical properties were investigated. The results indicate that the addition of 0.5vol% of nanoparticles decreased the size of the dendrite cell intervals by about 16%. The observed mechanical properties exhibited an improvement of about 17, 28, 10, 157, 8 and 13%, in hardness, ultimate tensile strength, yield strength, tensile elongation, flexural and shear strengths, respectively. With more considerable additions of nanoparticles, scanning electron microscopy investigations confirm that there were more significant amounts of nanoparticle agglomerates in the microstructure, which reduced the mechanical properties of 1vol% SiO2np reinforced nanocomposite. The primary strengthening mechanisms evaluated appeared to be the effect of grain refinement (Hall–Petch), Orowan strengthening and the mismatch in coefficient of thermal expansion of the reinforcements and the matrix alloy. Evidence of some agglomerations of nanoparticles was recognized on the tensile fractured surfaces of the nanocomposites. [ABSTRACT FROM AUTHOR]

We propose a novel Lagrangian geometric representation using segment clouds to simulate incompressible fluid exhibiting strong anisotropic vortical features. The central component of our approach is a cloud of discrete segments enhanced by a set of local segment reseeding operations to facilitate both the geometrical evolution and the topological updates of vortical flow. We build a vortex dynamics solver with the support for dynamic solid boundaries based on discrete segment primitives. We demonstrate the efficacy of our approach by simulating a broad range of challenging flow phenomena, such as reconnection of non-closed vortex tubes and vortex shedding behind a rotating object. [ABSTRACT FROM AUTHOR]

Under the current background of navigation education, students generally lack a comprehensive grasp of ship firefighting equipment’s operation. Therefore, we develop a novel ship firefighting training simulator with a multi-sensory human–computer interaction function for teaching and training marine students. In the simulator, we consider a container ship of 1.8w containers as the prototype ship, and the entire ship models are built using three-dimensional modeling technology. We design various interactive modes and realize a full-process operation simulation of several standard ship firefighting equipment. Furthermore, we propose a purely Lagrangian vortex dynamics framework to simulate smoke and flame in fire scenarios. In this framework, we model fluids using velocity and vorticity fields discretized on discrete vortex segments. The main components of the framework include a stable geometric stretching solution and particle strength exchange method for solving the diffusion term. The simulation results show that the simulator has good behavioral realism and scene immersion and can be applied to ship firefighting training. To the best of our knowledge, this is the first study on real-time smoke simulation using a physics-based method in a firefighting training simulator.

The manuscript presents a novel aero‐hydro‐servo‐elastic coupling framework, MIRAS‐HAWC2. In this coupling, the wind turbine blades and rotor‐wake aerodynamics are modeled using a modified lifting‐line theory which accounts for blade curvature, combined with a hybrid vortex method. The wind turbine structure and foundation are modeled using a finite‐element and multi‐body system approach. Last, hydrodynamics are modeled using Airy wave theory together with Morison's equation. An initial assessment of the performance of the aeroelastic coupling framework has been performed for steady rotor‐only cases, assuming laminar inflow without shear. This included a comparison against fully resolved computational fluid dynamics, for both stiff and flexible blades showing an excellent agreement. In a second stage, the aero‐hydro‐servo‐elastic coupling is used, comparing MIRAS‐HAWC2 as well as blade‐element momentum‐based simulations with selected results from the Offshore Code Comparison Collaboration projects (OC3 and OC4), which study the NREL 5 MW turbine mounted on different offshore support structures. A good agreement has been obtained for the simulations of a monopile with rigid foundation, a tripod, and jacket support structures. [ABSTRACT FROM AUTHOR]

The undulating membrane tidal energy converter is a device that uses the flutter instabilities occurring from the interaction between a slender body and a fluid flow. A new numerical model has been developed using a 2D corotational finite element method to represent the structure and the unsteady point-vortex method to compute the flow. These methods as well as the interaction process are presented. Trajectory and frequency of the undulating motion, hydrodynamic forces on the structure and velocity field in the wake are presented. Comparison shows a good agreement with experimental results obtained from a 1/20th scale prototype without power take off tested in flume tank.

The aim of the presents study was to investigates the influence of different sliding velocity 1.4, 2.8, 4.2 m/sec, applied load 5, 10, N and time 10, 20, 30 min on wear rate of Al-Mg-Si alloy reinforced with varying weight fraction of TiO₂/SiC 1.5:0 ,3:0 , 4.5:0 , 0:1.5 , 0:3 , 0:4.5 , 1.5:1.5 , 3:3 , 4.5:4.5 wt.% with the same particle size (>75μm) by using pin-on-disk techniques. In this research Al-Mg-Si alloy TiO₂/SiC hybrid composites was prepared by vortex technique. The primary objective is to use taguchi method for predicting the better parameter that give the highest wear resistance. A L9 orthogonal array was selected for each present to analysis of data and use ANOVA to determine parameters significantly influencing the wear rate of hybrid composite. Optical microscope and SEM with EDS examination were utilized to study the worn surface. The experimental and analytical results showed that the taguchi method was successful in predicting the parameters that give the highest properties and the volume fraction was the most influential parameter on the wear rate. The results demonstrated that when the applied load and time increased the wear rate increasing, but when the sliding velocity increased the wear rate decreasing and showed the minimum wear in hybrid composite with 4.5% reinforcement this observed with highest ratio of S/N 156.787.

Numerical analysis of the flapping flight of insects has attracted great attention because of the expectation for insect-inspired micro air vehicles. A lot of numerical methods for the insect flight have been proposed, and they can be classified into two categories: inviscid flow solvers and viscous flow solvers. The discrete vortex method (DVM) has been regarded as a successful method in the first category, and the immersed boundary–lattice Boltzmann method (IB-LBM) has recently been developed as an efficient method in the second category. However, a detailed comparative study between these methods has not been sufficiently performed. In this study, we compare the DVM with the IB-LBM in two-dimensional flapping flight analysis. As a result, it is found that the aerodynamic forces obtained by the DVM are comparable to those by the IB-LBM, when the effect of separated vortices is not so accumulated, and when the forward speed of the model is smaller than the flapping speed. In addition, the DVM has a difficulty in estimating the aerodynamic torque. In terms of the computational time, the DVM is much faster than the IB-LBM. This result suggests that the DVM can be used for massive parametric studies or optimizations in flapping flight analysis, although there remain many issues in its accuracy. [ABSTRACT FROM AUTHOR]

• Implementation of the Synthetic Eddy Method into the purely Lagrangian Vortex framework. • To the author knowledge, one of the first attempt to model ambient turbulence in Lagrangian Vortex simulation. • The use of variable size structures enable a better representation of the obtained Power Spectral Density. • A linear relation is found between the mean structure size and the Taylor macro-scale. • Applications to the computation of (Tidal or Wind) turbine wake are presented as an illustration of the method. This paper describes a detailed implementation of the Synthetic Eddy Method (SEM) initially presented in Jarrin et al. (2006) applied to the Lagrangian Vortex simulation. While the treatment of turbulent diffusion is already extensively covered in scientific literature, this is one of the first attempts to represent ambient turbulence in a fully Lagrangian framework. This implementation is well suited to the integration of PSE (Particle Strength Exchange) or DVM (Diffusion Velocity Method), often used to account for molecular and turbulent diffusion in Lagrangian simulations. The adaptation and implementation of the SEM into a Lagrangian method using the PSE diffusion model is presented, and the turbulent velocity fields produced by this method are then analysed. In this adaptation, SEM turbulent structures are simply advected, without stretching or diffusion of their own, over the flow domain. This implementation proves its ability to produce turbulent velocity fields in accordance with any desired turbulent flow parameters. As the SEM is a purely mathematical and stochastic model, turbulent spectra and turbulent length scales are also investigated. With the addition of variation in the turbulent structures sizes, a satisfying representation of turbulent spectra is recovered, and a linear relation is obtained between the turbulent structures sizes and the Taylor macroscale. Lastly, the model is applied to the computation of a tidal turbine wake for different ambient turbulence levels, demonstrating the ability of this new implementation to emulate experimentally observed tendencies. [ABSTRACT FROM AUTHOR]

This study is concerned with the numerical simulations of the flow and performance of a rotor of a hydraulic Savonius turbine. The flow was simulated using the vortex in cell (VIC) method in combination with the volume penalization (VP) method. The torque acting on the rotor was computed using a custom method, which can accurately calculate the fluid forces on solid bodies in flows simulated by the VIC-VP method, to analyze the rotational speed and power output of the rotor. The simulated flow around the rotating blades agreed qualitatively with the experimentally visualized flow, and the analyzed relation between the rotor's rotational speed and power output agreed with the experimentally measured relation. These demonstrate that the VIC-VP method in combined with the authors' method for calculating fluid forces is applicable for the simulations of flow and performance of hydraulic Savonius turbines. • The flow through a hydraulic Savonius turbine is successfully simulated. • The performance of the rotor is calculated from the flow. • The unsteady flow around the rotor is studied by the simulation. • The relation between the rotor performance and the flow is reconfirmed. [ABSTRACT FROM AUTHOR]