Journal of Fluids and Structures最新文献_第8页

Spanwise variations in membrane flutter dynamics 膜扑动态的跨度变化

IF 3.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Journal of Fluids and Structures

Pub Date : 2024-10-14 DOI: 10.1016/j.jfluidstructs.2024.104194

Christiana Mavroyiakoumou , Silas Alben

We study the large-amplitude flutter of rectangular membranes in 3-D inviscid flows. The membranes’ deformations vary significantly in both the chordwise and spanwise directions. Many previous studies used 2D flow models and neglected spanwise variations, so here we focus on cases with significant spanwise nonuniformity. We determine when such cases occur and how the dynamics vary over the parameter space of membrane mass and pretension for two sets of boundary conditions and two values of both the Poisson ratio and the membrane aspect ratio. With spanwise symmetric and asymmetric initial perturbations, the motions differ for long times but eventually reach the same steady state in most cases.

At large times, spanwise symmetric and asymmetric oscillations are seen, with the latter more common. Oscillations are often in the form of “side-to-side” and other standing wave motions along the span, as well as traveling wave motions, particularly with free side-edges. Motions are generally nonperiodic and more spatially complex with a large membrane mass, and sometimes periodic at small-to-moderate membrane mass. A large Poisson ratio gives somewhat smoother spatial and temporal features in the dynamics at a given pretension. Increasing the aspect ratio makes the deflection more uniform along the span. With different chordwise and spanwise pretensions we find motions that are qualitatively similar to cases with isotropic pretensions between the anisotropic values.

我们研究了矩形膜片在三维不粘性流中的大振幅飘动。膜片的变形在弦向和跨向都有显著变化。以前的许多研究使用二维流动模型，忽略了跨度方向的变化，因此我们在此重点研究跨度方向不均匀性显著的情况。我们确定了何时会出现这种情况，以及在两组边界条件和泊松比和膜长宽比的两个值下，膜质量和预拉伸参数空间的动态变化情况。在跨度对称和不对称的初始扰动下，运动在很长一段时间内是不同的，但在大多数情况下最终会达到相同的稳定状态。振荡的形式通常是沿跨度方向的 "侧向 "运动和其他驻波运动，以及行波运动，尤其是自由侧边的行波运动。当膜质量较大时，运动通常是非周期性的，而且在空间上更为复杂；当膜质量较小或中等时，运动有时是周期性的。泊松比越大，给定预拉力下的动态时空特征越平滑。增大纵横比会使挠度沿跨度方向更加均匀。在不同的弦向和跨度预拉力下，我们发现运动在各向异性值之间与各向同性预拉力的情况在性质上相似。

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引用次数: 0

Fluid-structure interaction among three tandem circular cylinders oscillating transversely at a low Reynolds number of 150 在低雷诺数（150）条件下横向摆动的三个串联圆柱体之间的流体与结构相互作用

IF 3.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Journal of Fluids and Structures

Pub Date : 2024-10-13 DOI: 10.1016/j.jfluidstructs.2024.104204

Hongjun Zhu , Jiawen Zhong , Ze Shao , Tongming Zhou , Md. Mahbub Alam

The flow-induced vibration (FIV) of three tandem circular cylinders is numerically investigated using OpenFOAM based on the finite-volume method. The one-degree-of-freedom dynamic response of three tandem circular cylinders with a spacing ratio ranging from 2 to 6 is analysed at a low Reynolds number of 150 over a reduced velocity range of 2–16. The results of hydrodynamic coefficients, response amplitude, vibration frequency, wake structure, and decomposition of vorticity are discussed in this study. Although the streamwise spacing ratio is constant, the dynamic evolution of the crossing angles among three cylinders leads to the switching of wake interference mode. The two-layered vortices are merged into secondary vortices in the far wake, and the energy of secondary vortices is higher than the two-layered vortices. The upstream cylinder exhibits a similar trend as an isolated cylinder in terms of the variations of hydrodynamic coefficients and response amplitude with the reduced velocity. In contrast, the middle and downstream cylinders experience a significantly lower drag due to the shielding effect. Particularly at small spacing ratios, the drag on the middle cylinder becomes negative. At the same time, the lift coefficient and response amplitude are higher than those of an isolated cylinder at high reduced velocities. The three tandem cylinders intermittently form a triangular configuration during the oscillation.

基于有限体积法，使用 OpenFOAM 对三个串联圆柱体的流动诱发振动（FIV）进行了数值研究。分析了间距比从 2 到 6 的三个串联圆柱体在 150 低雷诺数和 2-16 的减速度范围内的一自由度动态响应。本研究讨论了流体力学系数、响应振幅、振动频率、尾流结构和涡度分解的结果。虽然流向间距比保持不变，但三个圆柱体之间交叉角的动态演变导致了唤醒干涉模式的切换。两层涡旋在远侧尾流中合并为二级涡旋，二级涡旋的能量高于两层涡旋。上游气缸的流体力学系数和响应振幅随速度降低的变化趋势与孤立气缸相似。相反，由于屏蔽效应，中间和下游圆柱体的阻力明显降低。特别是在间距比很小的情况下，中间圆筒的阻力变为负值。同时，在高速降低时，升力系数和响应振幅均高于孤立气缸。在振荡过程中，三个串联气缸间歇地形成一个三角形构型。

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引用次数: 0

Multistable dynamic behaviors of cantilevered curved pipes conveying fluid 输送流体的悬臂弯曲管道的多稳态动态行为

IF 3.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Journal of Fluids and Structures

Pub Date : 2024-10-10 DOI: 10.1016/j.jfluidstructs.2024.104196

Runqing Cao , Dilong Ma , Wei Chen , Mingwu Li , Huliang Dai , Lin Wang

The present study newly found multistable dynamic characteristics of cantilevered curved pipes conveying fluid due to the gravity. These multistable behaviors of the pipe offer a promising avenue for the development and deployment of fluid actuators. Three configurations of curved pipes, namely, one-quarter circular, semi-circular, and three-quarter circular, are considered. A nonlinear dynamic theoretical model is established based on the geometrically exact model to investigate the large deformation behaviors of the curved pipe conveying subcritical fluid flows. The theoretical model for predicting large deformations of the curved pipe is validated through the finite element method (FEM). Afterwards, linear dynamic characteristics for three configurations of curved pipes are explored. Strangely, the discontinuity phenomenon for natural frequencies of the curved pipe occurs with increasing the flow velocity, which has never been reported before. Meanwhile, it is demonstrated that the gravity parameter has a significant effect on the critical velocity for flutter. Large deformation responses of the curved pipe in three configurations are further investigated, multistable dynamic behaviors are detected for all considered curved pipes. It displays that for different gravity parameters, the dynamic behavior of curved pipe is varying from a single state to multiple states with increasing the flow velocity. Results indicate that when the dimensionless gravity parameter and fluid velocity are 15 and 2.5, the curved pipe exhibits three distinct displacements due to static deformations. These three displacements are in three equilibrium states, which helps to explain the interesting phenomenon of frequency discontinuity.

本研究新近发现，由于重力作用，输送流体的悬臂弯曲管道具有多稳动态特性。管道的这些多稳态行为为流体致动器的开发和应用提供了一个前景广阔的途径。本文考虑了四分之三圆、半圆和四分之三圆三种弯曲管道的配置。在几何精确模型的基础上建立了非线性动态理论模型，以研究输送亚临界流体的弯曲管道的大变形行为。通过有限元法（FEM）验证了预测弯曲管道大变形的理论模型。随后，探讨了三种配置的弯曲管道的线性动态特性。奇怪的是，随着流速的增加，弯曲管道的固有频率出现了不连续现象，这是以前从未报道过的。同时，研究还证明重力参数对飘移的临界速度有显著影响。进一步研究了三种配置的弯曲管道的大变形响应，发现所有考虑的弯曲管道都存在多稳动态行为。结果表明，对于不同的重力参数，随着流速的增加，弯管的动态行为从单一状态变为多重状态。结果表明，当无量纲重力参数和流体速度分别为 15 和 2.5 时，由于静态变形，弯曲管道会出现三种不同的位移。这三种位移处于三种平衡状态，有助于解释频率不连续这一有趣现象。

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引用次数: 0

Numerical study on three-dimensional self-induced inverted flag 三维自诱导倒旗的数值研究

IF 3.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Journal of Fluids and Structures

Pub Date : 2024-10-07 DOI: 10.1016/j.jfluidstructs.2024.104198

Novi Andria , Lavi Rizki Zuhal , Pramudita Satria Palar , Duong Viet Dung , Leonardo Gunawan , Hari Muhammad

The current study aims to investigate the fluid–structure interaction (FSI) of flexible thin structures undergoing large displacements using numerical simulations. The primary case of interest is the self-induced inverted flag problem, which exhibits a rich set of coupled fluid–structure behavior and flapping dynamics. To achieve this, a new FSI algorithm is proposed via a partitioned approach. The proposed algorithm uses the remeshed-Vortex Particle Method (VPM) to resolve the flow and a finite element method-based elastodynamics solver to evaluate the response of the flexible structure. The remeshed-VPM algorithm is modified and extended in this study with new developments to enhance its applicability for complex FSI simulations of thin flexible structures. A multiresolution scheme is developed and applied in combination with the iterative Brinkman penalization method for remeshed-VPM. A new force formulation is introduced that is based on corrected penalization velocity, which can generate distributed body forces for the iterative Brinkman penalization method. Finally, the fully 3D remeshed-VPM is applied in conjunction with corotational beam formulation for FSI simulations of the inverted flag system. The FSI solver is utilized to conduct a series of simulations on the 2D and 3D inverted flag model, aiming to gain insights into the intricate dynamics of these fluid–structure interactions.

目前的研究旨在通过数值模拟来研究承受大位移的柔性薄结构的流固耦合（FSI）问题。主要研究对象是自诱导倒旗问题，该问题表现出丰富的流固耦合行为和拍击动力学。为此，我们通过分区方法提出了一种新的 FSI 算法。所提出的算法使用重置涡粒法（VPM）来解决流动问题，并使用基于有限元法的弹性动力学求解器来评估柔性结构的响应。本研究对重置涡粒子法进行了新的修改和扩展，以提高其在薄柔性结构的复杂 FSI 模拟中的适用性。我们开发了一种多分辨率方案，并将其与布林克曼迭代惩罚法结合应用于重置-VPM。此外，还引入了一种基于校正惩罚速度的新受力公式，可为迭代布林克曼惩罚法生成分布式体力。最后，将全三维重置-VPM 与惯性梁公式相结合，用于倒旗系统的 FSI 仿真。利用 FSI 求解器对二维和三维倒旗模型进行了一系列模拟，旨在深入了解这些流体与结构相互作用的复杂动力学。

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引用次数: 0

Genetic algorithm LQG and neural network controllers for gust response alleviation of flying wing unmanned aerial vehicles 用于减轻飞翼无人飞行器阵风响应的遗传算法 LQG 和神经网络控制器

IF 3.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Journal of Fluids and Structures

Pub Date : 2024-10-07 DOI: 10.1016/j.jfluidstructs.2024.104199

Elijah Hao Wei Ang, Bing Feng Ng

In this paper, a genetic algorithm linear quadratic Gaussian controller (GA-LQG) and an artificial neural network (ANN) controller are implemented for gust response alleviation of lightweight flying wings undergoing body-freedom oscillations. A state–space aeroelastic model has been formulated by coupling the unsteady vortex lattice method for aerodynamics with finite-element based structural dynamics. The model is subsequently reduced using balanced truncation to improve computational efficiency during controller synthesis. Open-loop simulations show that the flying wing experiences large changes in pitching angles during gusts. For GA-LQG controller, the LQG weights are optimised using a genetic algorithm, maximising a defined fitness function. Generally, the GA-LQG controller reduces the plunge displacements by up to 94.2% while damping out wingtip displacements for discrete and continuous gusts. Similarly, the ANN controller effectively regulates both the plunge displacements and wingtip displacements, including gust cases that are not presented during the ANN training phase. The ANN controller is more effective in correcting wingtip displacements during discrete gusts than the GA-LQG controller, while the opposite is true for the continuous gust cases. The ANN controller offers several advantages over the GA-LQG controller, including the elimination of the need for a Kalman filter for full state estimation and offers a non-linear control solution.

本文采用遗传算法线性二次高斯控制器（GA-LQG）和人工神经网络控制器（ANN）来减轻轻质飞翼在体自由度振荡下的阵风响应。通过将空气动力学的非稳态涡流晶格法与基于有限元的结构动力学相结合，建立了一个状态空间气动弹性模型。随后采用平衡截断法对该模型进行缩减，以提高控制器合成过程中的计算效率。开环仿真显示，飞行翼在阵风时俯仰角变化很大。对于 GA-LQG 控制器，LQG 权重是通过遗传算法优化的，最大化定义的适应度函数。一般来说，GA-LQG 控制器可减少高达 94.2% 的俯仰位移，同时抑制离散和连续阵风的翼尖位移。同样，ANN 控制器也能有效调节垂尾位移和翼尖位移，包括在 ANN 训练阶段未出现的阵风情况。与 GA-LQG 控制器相比，ANN 控制器能更有效地修正离散阵风时的翼尖位移，而在连续阵风情况下则相反。与 GA-LQG 控制器相比，ANN 控制器具有多项优势，包括无需使用卡尔曼滤波器进行全状态估计，并提供了非线性控制解决方案。

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引用次数: 0

High lift devices using compliant surfaces 使用兼容表面的高提升装置

IF 3.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Journal of Fluids and Structures

Pub Date : 2024-10-04 DOI: 10.1016/j.jfluidstructs.2024.104192

Junchen Tan, Zhijin Wang, Ismet Gursul

Stall delay and lift enhancement play a crucial role in modern aircraft performance. This is commonly achieved by devices such as slats or flaps located at the leading edge or trailing edge of an aircraft's wing. In this paper, we report a feasibility study of using light-weight compliant surfaces for novel high lift devices. The effects of compliant flags with one end fixed or both ends fixed near the leading edge and trailing edge of an airfoil were studied by force, flag deformation, and flow field measurements in a wind tunnel. When a flag is placed near the leading edge, the excitation of the separated shear layer from the leading edge is the main mechanism in increasing the lift at the post-stall angles of attack. In contrast, the trailing-edge flag with an excess length and both ends fixed could increase the effective camber and the circulation around the airfoil in a time-averaged sense. The mechanism is similar to that of the conventional Gurney flap effect, and equally effective at pre-stall and post-stall angles of attack. When used together, the compliant flags can delay stall angle by 8° and increase the maximum lift coefficient by 67% in the parameter range tested presently. Compliant surfaces require no external power as a passive method. If they are to be used as active methods, they are light weight, and can be stored and deployed easily.

失速延迟和升力增强对现代飞机的性能起着至关重要的作用。这通常是通过位于飞机机翼前缘或后缘的板条或襟翼等装置来实现的。在本文中，我们报告了利用轻质顺应面制造新型高升力装置的可行性研究。我们在风洞中通过力、旗帜变形和流场测量，研究了一端固定或两端固定在机翼前缘和后缘附近的顺应性旗帜的效果。当旗帜靠近前缘时，前缘分离剪切层的激励是增加滞后攻角升力的主要机制。相比之下，两端固定且长度过长的后缘旗可以增加有效外倾，并在时间平均意义上增加机翼周围的环流。这种机制与传统的古尼襟翼效应类似，在失速前和失速后攻角下同样有效。配合使用时，在目前测试的参数范围内，顺应式襟翼可将失速角推迟 8°，并将最大升力系数提高 67%。作为一种被动方法，兼容表面不需要外部动力。如果作为主动方法使用，它们重量轻，易于储存和展开。

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引用次数: 0

Omnidirectional control of the wake of a circular cylinder with spinning rods subject to a turbulent flow 对带有旋转杆的圆形圆筒在湍流中的尾流进行全方位控制

IF 3.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Journal of Fluids and Structures

Pub Date : 2024-09-30 DOI: 10.1016/j.jfluidstructs.2024.104191

I.A. Carvalho , G.R.S. Assi

We numerically investigate the attribute of omnidirectionality of the flow-control system comprised of a large circular cylinder equipped with eight spinning rods of smaller diameter, subject to an incoming flow that adopts different angles of attack. Detached-eddy simulations are employed to compute hydrodynamic loads and to provide flow topology at a Reynolds number of 1000. Two cases are assessed regarding the rods angular velocities. In case 0, all rods spun with the same angular velocity. In case 1, velocities were inspired by potential-flow theory. The two systems have the same input kinetic energy in common. To assess the system response, the velocities were increased proportionally. Both cases succeeded in reducing the mean drag. However, while case 1 proved to become ever “more omnidirectional” with increasing angular velocities, case 0 demonstrated to be prone to the angle of attack as it was unable to suppress vortex shedding for sufficiently large slopes of the incoming flow, and in such circumstances, unable to reduce hydrodynamic forces. We verify that the lift is mitigated in case 1, in contrast to case 0. Even for a vortex-free downstream flow resulting from configurations of high velocities and high angle of attack, the latter produces asymmetric recirculation regions downstream of the system that drive a pressure imbalance. The different outcomes of the two systems are also explored from the viewpoint of power consumption, and it is revealed that the omnidirectionality of case 1 is intrinsically related to the emphasis imposed on rotation rates of a subset of the eight rods.

我们用数值方法研究了流动控制系统的全向性属性，该系统由一个装有八根直径较小的旋转杆的大型圆柱体组成，受采用不同攻击角的入流影响。采用离散涡流模拟计算流体动力负荷，并提供雷诺数为 1000 的流动拓扑结构。对两种情况下的棒角速度进行了评估。在情况 0 中，所有棒都以相同的角速度旋转。在情况 1 中，速度受势能流理论启发。这两个系统具有相同的输入动能。为评估系统响应，速度按比例增加。两种情况都成功地减少了平均阻力。然而，情况 1 随着角速度的增加而变得 "更加全向"，而情况 0 则容易受到攻角的影响，因为它无法抑制足够大的入流斜率的涡流脱落，在这种情况下，也无法减少流体动力。我们证实，与情况 0 相比，情况 1 的升力得到了缓解。即使是高流速和高攻角配置所产生的无涡下游流，后者也会在系统下游产生不对称的再循环区域，从而导致压力失衡。此外，还从功耗的角度探讨了两种系统的不同结果，结果表明，情况 1 的全向性与强调八根杆中一个子集的旋转率有内在联系。

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引用次数: 0

Multiphysics critical flow dynamics involving moving/deformable structures with design applications 涉及移动/可变形结构的多物理场临界流动动力学设计应用

IF 3.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Journal of Fluids and Structures

Pub Date : 2024-09-28 DOI: 10.1016/j.jfluidstructs.2024.104197

Marianna Braza , Ian Eames , Yannick Hoarau

引用次数: 0

Wave energy extraction from rigid rectangular compound floating plates 从刚性矩形复合浮板提取波能

IF 3.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Journal of Fluids and Structures

Pub Date : 2024-09-27 DOI: 10.1016/j.jfluidstructs.2024.104193

S. Michele , S. Zheng , E. Renzi , J. Guichard , A.G.L. Borthwick , D.M. Greaves

We present a theoretical model to analyse the hydrodynamics of wave energy converters (WECs) comprised of three-dimensional, rigid, floating, compound rectangular plates in the open sea. The hydrodynamic problem is solved by means of Green’s theorem and a free-surface Green’s function. Plate motion is predicted through decomposition into rigid natural modes. We first analyse the case of a single rectangular plate and validate our model against experimental results from physical model tests undertaken in the COAST laboratory at the University of Plymouth. Then we extend our theory to complex shapes and arrays of plates and examine how the geometry, incident wave direction and power take-off (PTO) coefficient affect the response of the platform and the consequent absorbed energy.

我们提出了一个理论模型，用于分析公海中由三维、刚性、浮动、复合矩形板组成的波浪能转换器（WECs）的流体力学。流体力学问题通过格林定理和自由表面格林函数来解决。通过将板块分解为刚性自然模态来预测板块运动。我们首先分析了单个矩形板的情况，并根据普利茅斯大学 COAST 实验室进行的物理模型试验结果验证了我们的模型。然后，我们将理论扩展到复杂形状和板阵列，并研究几何形状、入射波方向和功率起飞 (PTO) 系数如何影响平台响应以及由此产生的吸收能量。

引用次数: 0

Development of Reduced-Order-Discrete-Module method for hydroelastic analysis of floating flexible structures 开发用于浮动柔性结构水弹性分析的减阶离散模块法

IF 3.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Journal of Fluids and Structures

Pub Date : 2024-09-24 DOI: 10.1016/j.jfluidstructs.2024.104188

Yongkang Shi , Yanji Wei , Zuogang Chen

The present study proposes a novel method for analyzing the hydroelastic response of floating flexible structures based on Reduced-Order-Discrete-Module (RODM) model. In this model, the floating flexible structure is discretized into a finite number of modules. The hydrodynamic problem is simplified as the interaction between waves and multiple modules. The hydroelastic response is approximated by solving the motion equation of the multibody system, in which the mass and stiffness of the structure are obtained from the reduced-order matrices by the finite element method with a system equivalent reduction expansion process. By using the transformation matrix, the detailed floating structure response can be reconstructed from the multibody dynamics. The validity of the proposed method was demonstrated by comparing the results with the experimental data and other existing methods. The results show that this study has developed an accurate hydroelastic model to analyze the hydroelastic response of floating flexible structures. A module number selection formula is proposed to select the appropriate number of modules based on the exciting force frequency. This model is relatively easy to implement for the hydroelastic problem of interconnection modules and take into account the spatial inhomogeneity of wind/wave field. The proposed model can offer a useful tool for analyzing the hydroelastic response of the offshore floating photovoltaic systems.

本研究提出了一种基于降序离散模块（RODM）模型分析浮动柔性结构水弹性响应的新方法。在该模型中，浮动柔性结构被离散为有限数量的模块。水动力问题被简化为波浪与多个模块之间的相互作用。水弹性响应是通过求解多体系统的运动方程近似得到的，其中结构的质量和刚度是通过有限元法的系统等效缩减扩展过程从缩减阶矩阵中得到的。通过使用变换矩阵，可以从多体动力学中重建详细的浮动结构响应。通过将结果与实验数据和其他现有方法进行比较，证明了所提方法的有效性。结果表明，本研究建立了一个精确的水弹性模型来分析浮动柔性结构的水弹性响应。提出了模块数量选择公式，可根据激振力频率选择合适的模块数量。该模型对于互联模块的水弹性问题相对容易实现，并考虑了风场/波场的空间不均匀性。所提出的模型可为分析海上浮动光伏系统的水弹性响应提供有用的工具。

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引用次数: 0