bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical simulation of blood flow in coronary bifurcation
Authors: Liu Changshuo , Xu Xingming 
Published: June 2024

Abstract
A numerical simulation of blood flow in a Y-shaped coronary artery was executed by constructing ideal geometric models. The influences of bifurcation angle, the initial velocity of inlet blood flow, and the diameter ratio of bifurcated vessels on the blood flow velocity field, wall shear stress, wall pressure, etc. were analyzed. The blood velocity at the bifurcation of the blood vessel was slower, while the wall shear stress and wall pressure value were higher. The wall shear stress and wall pressure increased with the increase of blood flow velocity at the entrance. Greater bifurcation angle led to higher wall shear stress. With the increase of the diameter ratio of the two branches, the maximum value of the shear stress became smaller. The probability of thrombosis formation increases as the diameter ratio increases. The numerical results showed that the bifurcation of the blood vessel is the optimal place to form the thrombosis.
Effect of finned configuration of circular tube based on fluid-structure coupling on hydrogen flow characteristics
Authors: Wu Xunliang , Shao Mingxue , Cai Kaiyuan , Li Xiaoliang , Feng Songjiang 
Published: June 2024

Abstract
Nuclear thermal propulsion has the characteristics of high specific impulse, large thrust, green and efficient, and is the primary choice of manned deep space exploration propulsion system. Because the circulating flow of propellant hydrogen in the internal pipeline of the engine is always affected by the harsh environment of high temperature and high pressure, it is very important to study the flow characteristics of hydrogen in the pipeline, the heat exchange characteristics of hydrogen and pipeline and the deformation characteristics of pipeline under heat stress. In this paper, the flow phenomena of hot hydrogen in round tubes in a laminar flow state were analyzed by numerical simulation with COMSOL Mulitiphisics6.0, and the fluid-structure coupling between hot hydrogen fluid and pipe was investigated by a multi-physics field. It is concluded that the smoother the inner wall of the pipeline is, the smaller the hydrogen flow velocity is, the smaller the surface pressure of the pipe wall is, and the smaller the fluid extrusion and impact deformation of the pipe in the typical pipe with the inner fin is. It inspires studying the application of hot hydrogen flow and pipeline configuration in nuclear thermal rocket engines, including improving heat transfer energy and uniformity.
Study on manufacturing process and load-bearing capacity of innovative GFRP composite sandwich panels with connecting grooves
Authors: Du Yanpin , Qi Yujun 
Published: June 2024

Abstract
Composite sandwich panels have been widely utilized in various fields, including civil engineering, wind turbine blades, and transportation engineering, due to their lightweight, high strength, corrosion resistance, and exceptional thermal and damping properties. This paper introduces a novel wood-core composite sandwich panel produced through pultrusion. It features connection grooves designed to fulfill lateral connection requirements. The production of this innovative composite sandwich panel has been completed. The bending load-bearing capacity of this panel is comprehensively studied through theoretical analysis, and a modeling approach utilizing the general finite element software ANSYS is introduced. Ultimately, the efficacy of both theoretical methods and finite element simulations is verified through rigorous experiments. The research findings presented in this paper are highly significant for optimizing the design and manufacturing of composite sandwich panels, ultimately enhancing their utilization in rail transit vehicles and other industries.
Sub-nanosecond magnetic vortex reversal induced by localized resonant strain field in doped nanomagnets
Authors: Cui Huanqing , Yang Xiaokuo , Zhang Mingliang , Wei Bo , Xia Yongshun , Dou Shuqing 
Published: June 2024

Abstract
The strain-induced magnetic vortex dynamics in nanomagnets with ring-shaped impurities are investigated by means of micromagnetic simulations. It is found that the type and location of impurities can modulate the strain-stimulated spin wave spectrum of the magnetic vortex. Compared with pure nanomagnets without doping, the scattering impurities make the eigenfrequency of nanomagnets higher, while the pinning impurities lead to lower eigenfrequency. Moreover, the spin wave oscillation amplitude in a doped nanomagnet is strengthened by the gradient of exchange energy at the interface between the impurity ring and nanomagnet. The magnetic vortex polarity in a nanomagnet with specific doping schemes can be reversed in a sub-nanosecond scale by a localized resonant strain signal. Besides the switching efficiency improvement, the threshold stress of sub-nanosecond polarity reversal in nanomagnets with specific doping schemes is also reduced compared to the counterpart of nanomagnets without impurities. These results indicate that doping engineering of nanomagnets is a significant method to achieve straintronic devices with higher operating frequency and lower energy consumption.
Design and research on ultra-high pressure sealing structure based on tight plug ring
Authors: Li Guiyuan , Li Jiaxing , Wu Yong , Liu Haoxuan , Niu Tianhong , Zhang Long 
Published: June 2024

Abstract
A new ultra-high pressure sealing structure was designed based on the sealing requirements of ultra-high pressure vessels, using a tight plug ring. The finite element method was used for simulation analysis. The results show that the contact pressure on the sealing surface of the tight plug ring is linear with the vessel pressure, which is always greater than the vessel pressure. To further verify its sealing performance, a semi-closed bomb test device was designed based on the principle of the semi-closed bomb, which can generate a pressure of 300 MPa. The test pressure exceeded 300 MPa multiple times, but no gas leakage was observed. The comprehensive research results indicate that the sealing structure has good performance and can meet the sealing requirements of 300 MPa ultra-high pressure.
Efficient geometric parametrization of blades cross-sections by means of B-splines
Authors: Llamazares G , San Miguel U , Plaza A 
Published: June 2024

Abstract
Optimization and enhancement of rotor blade design are critical to improving the productivity of the wind energy industry. Airfoil geometry is a key factor that makes airfoil design and optimization a common task for aerodynamicists. Ensuring proper airfoil parametrization is essential. It serves as the first step in aerodynamic optimization, where the efficiency is directly related to the geometric complexity. This research presents a cost-effective and robust method for fitting airfoils using B-splines. We take into account factors such as computational cost, resource requirements, and accuracy. In this work, we present a method for minimizing the geometric distances between target points and a B-spline curve. We streamline the fitting process, create a computational Python package, and explore different approaches, objective functions, algorithms, and error tolerance settings. The work concludes that it is highly recommended to use an iterative fitting process, to adequately represent common airfoils with B-splines. Moreover, the accuracy and the computational cost can be managed subject to the minimization algorithm used, and the technique utilized for the objective cost calculation. The fitting procedure we develop in this study gives the smallest number of variables capable of accurately representing a desired airfoil.
Computational investigation of the effect of the trailing edge thickness on the wind turbine performance
Authors: Echenique Daniel , Puertolas Aitor Plaza , Amo Rubén Gutierrez 
Published: June 2024

Abstract
Trailing edge (TE) thickness is a manufacturing constraint in blade design, especially for airfoils with a sharp TE. To achieve a specific TE thickness, blade geometry is often modified during the design process, typically in the outer zone of the blade where the airfoil’s TE is thinner. This area has a significant impact on energy production and loads. Quantifying the effect of TE thickness modifications is crucial for making informed design decisions.
Therefore, this study quantifies and compares the impact of linear and polynomial geometry modifications on airfoil aerodynamics and turbine performance. Xfoil and OpenFAST were used to calculate these performance variations in the well-known NREL 5 MW wind turbine. The TE thickness of the model was modified to meet various manufacturing constraints, ranging from no restriction to a limit of 12mm TE thickness.
In terms of the aerodynamic behavior of the airfoils, the maximum efficiency of airfoils with low relative thickness decreases as the TE thickness increases. Annual Energy Production shows a reduction of up to 0.42% for the worst case, while blade root loads increase by up to 20%. For low relative thickness airfoils, the linear method has proven to be a better option with less impact on performance.
Partitioned time couplings of an aero-mechanical wind turbine problem.
Authors: Guern Caroline Le , Blondel Frédéric , Pfister Jean-Lou , Guy Nicolas , Bergmann Michel 
Published: June 2024

AbstractWind turbine developments have led to more powerful offshore rotor systems, creating complex aero-hydro-servo-elastic behaviors that require numerical analysis. A mutliphysics problem can be modelled using several approaches: a “monolithic” method where the systems are considered as a unique block or a “partitioned coupling” where the different domains are solved sequentially. The latter is the retained technique for this work in which different solvers are related to distinct equations that require independent time discretisations. The focus is set on coupling a wind turbine’s mechanical solver with an aerodynamic code, the latter being modelled through an inviscid vortex method and the structural aspect using a finite element method. The study aims to present the implementation process and comparison of different time integration coupling schemes within a large wind turbine simulation framework where aeroelastic effects are studied on the IEA 15MW wind turbine. A ”Conventional Serial Staggered” (CSS) scheme is used as a reference coupling technique, allowing independent time integration while limiting coupling to a single time step. Alternatively, a resembling “subcycling” architecture is proposed and implemented to remedy cases with different temporal discretisations and reduce computational costs of CSS when using the inviscid vortex method.
Numerical analysis of static and dynamic wind turbine airfoil characteristics in transonic flow
Authors: Vitulano M C , De Tavernier D , De Stefano G , Von Terzi D 
Published: June 2024

AbstractThis study performed an aerodynamic characterization of the FFA-W3-211 wind turbine tip airfoil in transonic flow using Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations, for both steady and dynamic operational conditions. First, the boundary between subsonic and supersonic flow in static conditions was identified, depending on the angle of attack, the approach flow Mach number, and the Reynolds number. The analysis points out that higher Reynolds numbers promote the occurrence of local supersonic flow. Thereafter, to investigate the dynamic behavior in the transonic flow regime, a sinusoidal pitching motion with representative values was imposed. A hysteresis, similar to but distinct from dynamic stall, was observed for entering and leaving the supersonic and subsonic regions. Elevated reduced frequencies widened the hysteresis loop, resulting in increased normal forces on the airfoil. The study indicated that an increase in reduced frequency leads to an earlier onset of transonic flow. In conclusion, the risk of transonic flow occurring during normal operation of the next generation wind turbines predicted in earlier studies could be corroborated. Moreover, dynamic effects and Reynolds number dependencies can be significant.
CFD investigation of flatback airfoils and swallow tail for wind turbine blades
Authors: Solombrino C , Ravishankara A Koodly , Özdemir H , Venner C H 
Published: June 2024

Abstract
Modern wind turbines use longer blades to improve annual energy production. Longer blades require thicker airfoils for structural integrity. Thicker airfoils are susceptible to issues like erosion, abrupt stalls, and early boundary layer transition, leading to increased drag and decreased lift, affecting overall performance. Flatback airfoils offer structural and aerodynamic advantages, being stiffer, less sensitive to surface roughness. However, this comes with a drag penalty, mainly due to the increase in base drag. Swallow tail add-on has been proposed to overcome these challenges. URANS simulations are used to analyze the aerodynamic performance of the different airfoils and hybrid RANS/LES simulations are used to study the flow features in more detail. The swallow tail airfoil was found to maintain many of the advantages of the flatback airfoils while reducing the drag penalty.
Numerical investigation of vortex induced vibrations on cylinders
Authors: Vlastos D , Riziotis V A , Papadakis G , Manolas D I , Chaviaropoulos P K 
Published: June 2024

Abstract
The paper addresses Vortex Induced Vibrations (VIV) caused by tower vortex shedding through LES simulations of a wind tunnel experiment. A high-fidelity (HiFi), Fluid Structure Interaction (FSI) framework for aeroelastic analysis of 3D flexible cylinders is established, based on the open-source Computational Fluid Dynamics (CFD) code OpenFOAM and the coupling library preCICE. In the present study, the FSI framework is employed with the aim to replicate a low Reynolds (Re=26000) forced vibrations wind tunnel experiment of a circular cross-section rigid cylinder. The paper compares predictions of the aerodynamic damping of the oscillating cylinder for different oscillation frequencies within the lock-in range and amplitudes against experimental results. While the model consistently predicts the lock-in range of frequencies and the trends in the variation of the aerodynamic damping with the oscillation amplitude, it falls short of accurately capturing the maximum value of the aerodynamic damping at the onset of lock-in.
Hierarchical sensitivity study on the aeroelastic stability of the IEA 15 MW reference wind turbine
Authors: Verdonck Hendrik , Hach Oliver 
Published: June 2024

Abstract
Increased rotor size and blade flexibility are leading to new stability characteristics for current and future wind turbines. Numerical aeroelastic models are an essential tool to understand these new mechanisms and to design next-generation wind turbines suitably. A comprehensive understanding of how model input parameters influence the stability analysis will enhance the confidence in these simulations. This article presents a study on the sensitivity of uncertain parameters on aeroelastic stability predictions of the IEA 15 MW turbine model in HAWCStab2. It uses a hierarchical approach to handle the large number of investigated model parameters. Relevant uncertainties are identified through one-at-a-time and elementary effects analyses first. The remaining parameters are fed into a variance-based uncertainty quantification (UQ), that employs polynomial chaos expansion representations as surrogates for a full nonlinear description of the sensitivities. A robust post-processing of the stability analysis results is the main challenge of the presented methodology, but it is shown how the UQ process can still be used to explore the parameter space effectively. The presented study shows that the structural blade properties have the highest sensitivity and that a set of relatively small parameter variations can lead to unstable behavior of the reference model.
Machine Learning Based Predictions of Airfoil Aerodynamic Coefficients for Reynolds Number Extrapolations
Authors: Özgören Ahmet Can , Acar Deniz Alper , Kamrak Recep , Eriş Görkem Mahir , Özdemir Yasin , Uzol Nilay Sezer , Uzol Oğuz 
Published: June 2024

Abstract
This study investigates the application of various machine learning (ML) algorithms for predicting two critical aerodynamic coefficients, i.e. the maximum lift coefficient (C

l max
) and the minimum drag coefficient (C

d min
), for wind turbine airfoils at any given Reynolds number. We propose to use clustering techniques to group similar airfoil shapes and use the created partitions to predict unseen airfoil properties utilizing their similarity. Here, we also represent airfoils in the PARSEC low dimensional space, rather than high dimensional airfoil points space, to remedy the small number of training data. For this purpose, an extended experimental airfoil database is created and used for training models based on five different ML algorithms. We observe that the Decision Tree Ensemble (DTE), Random Forest (RF) and multi-layer perceptron (MLP) models emerge as the most effective predictors for C

l max
and C

d min
. Testing these two ML models on three additional airfoil cases not included in the training database shows that the C

l max
prediction performance is generally reasonable, with error levels being around 5% on average. In contrast, the prediction error levels for C

d min
are usually higher, with an average of around 15%.
Study of surface roughness on flow past a wind turbine tower section
Authors: VimalKumar Shyam , De Tavernier Delphine , Von Terzi Dominic , Belloli Marco , Viré Axelle 
Published: June 2024

Abstract
The flow around wind turbine towers usually reaches very high Reynolds numbers greater than a million. Understanding the flow around the towers under these conditions is crucial, as it may lead to vibrations due to the vortices formed. Investigating aerodynamic characteristics at such high Reynolds numbers, both numerically and experimentally, is challenging. The current study validates such an experimental study, where a rough surface is employed to increase the effective Reynolds numbers and accelerate the laminar-turbulent transition in the boundary layer. Unsteady Reynolds-Averaged Navier-Stokes (RANS) simulations are carried out using OpenFOAM for a Reynolds number range of 1.36·105 to 6.8·105. The constant (a
1) used to calculate the eddy viscosity is varied to simulate the flow separation during adverse pressure gradients. A force partitioning method is implemented in OpenFOAM and various force contributions are analysed for this Reynolds number range. It is seen that the RANS simulations overpredict the aerodynamic characteristics and the extent of flow separation unless the value of a
1 is varied as a function of the Reynolds number. Furthermore, it is observed that the only force contributor is the vorticity-induced force, as the simulations are performed for a fixed cylinder.
Norm-Optimal Iterative Learning Control for Wind Turbines During Grid Faults
Authors: Spijkerman D. , Navalkar S.T. , Solberg B. , Mulders S.P. 
Published: June 2024

Abstract
Due to the increasing share of (offshore) wind turbines, more stringent requirements on power quality have been established. Importantly, the low-voltage ride-through grid requirement states that a wind turbine must remain connected to the electrical grid after a short intermittent grid fault. In the industry mainly gain-scheduled PID-controllers are used to mitigate the effects of grid faults on turbine operation, whereas more advanced solutions have been proposed in the literature such as model predictive control or multiple parallel PI-controllers. Remarkably, all controller implementations mentioned earlier are based on feedback control, where no feedforward strategies have been discussed in the literature. However, feedforward control could improve grid fault recovery performance by exploiting the relatively known fault characteristics by virtue of the specification in the Transmission System Operator requirements. Therefore, for the first time, a norm-optimal Iterative Learning Control (NO-ILC) algorithm is presented that solves these issues by learning the feedforward signal that optimally mitigates the effects of a grid fault. The NO-ILC algorithm applies model-free learning based on iterations, in which the framework of NO-ILC has been extended to include explicit input constraints. The goal of the NO-ILC is to reduce a (quadratic) cost function on specific input and output channels whilst conforming to specific input constraints by solving an optimisation problem, with, for this study blade pitch and rotor speed as respective input and output channels. It is shown that the NO-ILC algorithm can yield improved performance on a high-fidelity model, with a 45% decrease in the cost function used by NO-ILC compared to the nominal feedback control. The optimised feedforward signals resulting from NO-ILC can be used as an analysis tool to closer match the nominal grid fault feedback controllers response with that of NO-ILC, or directly applied as a library that can supplement the feedback controllers output during a grid fault.
UNICO: an open-source controller optimized for stall-regulated wind turbines
Authors: Cioni Stefano , Papi Francesco , Cocchi Emanuele , Bianchini Alessandro 
Published: June 2024

Abstract
Stall regulation turbines still represent the preferred solution for small wind turbines. In stall-controlled rotors the controller plays a key role but, differently from pitch-based ones, no open-source controller was available to date. The study presents the UNICO (UNIfi research COntroller) controller, which has been specifically developed for variable speed stall-regulated turbines. The controller has been developed in MATLAB® Simulink® and a dynamic link library (.dll) has been generated, which can be coupled with common simulation codes such as OpenFAST and QBlade using a Bladed-style interface. UNICO includes features that are specifically tailored to variable-speed stall-regulated turbines. For below-rated conditions, the controller employs either the commonly used k-ω2 law or a tracking of the optimal tip speed ratio. For above-rated conditions, a PI controller is used to track a user-imposed reference speed. The reference speed is set to decrease linearly with wind speed, providing a safety margin for turbine operation at higher wind speeds. UNICO has been tested on a 50-kW stall-regulated reference turbine. Preliminary results show how the proposed controller can achieve better overall performance in comparison to the simplified control laws implemented in state-of-the-art codes. Additionally, the rotor speed can be controlled in above-rated conditions, providing an increased run away safety margin.
Model predictive control of wakes for wind farm power tracking
Authors: Sterle Arnold , Hans Christian A. , Raisch Jörg 
Published: June 2024

Abstract
In this paper, a model predictive control scheme for wind farms is presented. Our approach considers wake dynamics including their influence on local wind conditions and allows the tracking of a given power reference. In detail, a Gaussian wake model is used in combination with observation points that carry wind condition information. This allows the estimation of the rotor effective wind speeds at downstream turbines, based on which we deduce their power output. Through different approximation methods, the associated finite horizon nonlinear optimization problem is reformulated in a mixed-integer quadratically-constrained quadratic program fashion. By solving the reformulated problem online, optimal yaw angles and axial induction factors are found. Closed-loop simulations indicate good power tracking capabilities over a wide range of power setpoints while distributing wind turbine infeed evenly among all units. Additionally, the simulation results underline real time capabilities of our approach.