This paper presents a novel volume of fluid ghost-cell immersed boundary (IB) method for two-phase free surface flow interacting with structures. To circumvent the disturbance occurring around the intersection area of the IB and free surface when using the interpolation method for variable reconstruction, the fluid-structure interaction is firstly considered with the orthogonal IB by mimicking the imposition of boundary conditions in the body-conformal grid method. Treatments are subsequently performed to account for the non-orthogonal effect in accurately simulating the FSI, including the newly proposed flux-scaling and IB velocity re-evaluation methods. Further, a variable smoothing process and a flux correction method are adapted to handle moving boundary cases. Based on OpenFOAM, a two-phase flow solver has been developed. Both stationary and moving immersed boundary cases are used for validations. The numerical results reasonably agree with the corresponding laboratory data and other numerical simulation results, demonstrating the disturbance being effectively depressed and the solver's accuracy in capturing fluid-structure interactions involving free surface flow.
{"title":"A novel volume of fluid ghost-cell immersed boundary method for free surface flow interacting with structures","authors":"Fan Chen, Jinghua Wang, Huan-Feng Duan","doi":"arxiv-2409.08810","DOIUrl":"https://doi.org/arxiv-2409.08810","url":null,"abstract":"This paper presents a novel volume of fluid ghost-cell immersed boundary (IB)\u0000method for two-phase free surface flow interacting with structures. To\u0000circumvent the disturbance occurring around the intersection area of the IB and\u0000free surface when using the interpolation method for variable reconstruction,\u0000the fluid-structure interaction is firstly considered with the orthogonal IB by\u0000mimicking the imposition of boundary conditions in the body-conformal grid\u0000method. Treatments are subsequently performed to account for the non-orthogonal\u0000effect in accurately simulating the FSI, including the newly proposed\u0000flux-scaling and IB velocity re-evaluation methods. Further, a variable\u0000smoothing process and a flux correction method are adapted to handle moving\u0000boundary cases. Based on OpenFOAM, a two-phase flow solver has been developed.\u0000Both stationary and moving immersed boundary cases are used for validations.\u0000The numerical results reasonably agree with the corresponding laboratory data\u0000and other numerical simulation results, demonstrating the disturbance being\u0000effectively depressed and the solver's accuracy in capturing fluid-structure\u0000interactions involving free surface flow.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"198 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267650","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Marco Artiano, Carlo De Michele, Francesco Capuano, Gennaro Coppola
The effects of kinetic-energy preservation errors due to Runge-Kutta (RK) temporal integrators have been analyzed for the case of large-eddy simulations of incompressible turbulent channel flow. Simulations have been run using the open-source solver Xcompact3D with an implicit spectral vanishing viscosity model and a variety of temporal Runge-Kutta integrators. Explicit pseudo-symplectic schemes, with improved energy preservation properties, have been compared to standard RK methods. The results show a marked decrease in the temporal error for higher-order pseudo-symplectic methods; on the other hand, an analysis of the energy spectra indicates that the dissipation introduced by the commonly used three-stage RK scheme can lead to significant distortion of the energy distribution within the inertial range. A cost-vs-accuracy analysis suggests that pseudo-symplectic schemes could be used to attain results comparable to traditional methods at a reduced computational cost.
{"title":"On the performances of standard and kinetic energy preserving time-integration methods for incompressible-flow simulations","authors":"Marco Artiano, Carlo De Michele, Francesco Capuano, Gennaro Coppola","doi":"arxiv-2409.08851","DOIUrl":"https://doi.org/arxiv-2409.08851","url":null,"abstract":"The effects of kinetic-energy preservation errors due to Runge-Kutta (RK)\u0000temporal integrators have been analyzed for the case of large-eddy simulations\u0000of incompressible turbulent channel flow. Simulations have been run using the\u0000open-source solver Xcompact3D with an implicit spectral vanishing viscosity\u0000model and a variety of temporal Runge-Kutta integrators. Explicit\u0000pseudo-symplectic schemes, with improved energy preservation properties, have\u0000been compared to standard RK methods. The results show a marked decrease in the\u0000temporal error for higher-order pseudo-symplectic methods; on the other hand,\u0000an analysis of the energy spectra indicates that the dissipation introduced by\u0000the commonly used three-stage RK scheme can lead to significant distortion of\u0000the energy distribution within the inertial range. A cost-vs-accuracy analysis\u0000suggests that pseudo-symplectic schemes could be used to attain results\u0000comparable to traditional methods at a reduced computational cost.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267646","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wake and force characteristics of an oscillating cylinder in inline steady currents are investigated numerically over a wide parameter space of dimensionless oscillation amplitude ($A^* = 0.01 - 0.50$) and wavelength ($lambda^* = 0.4 - 25$) at a fixed Reynolds number $Re = 500$. Fundamental issues addressed in this study are the interactions of wakes induced by steady approaching flow and cylinder oscillations and the influences of the governing parameters of $A^$ and $lambda^$ on such interactions. Whilst the collinear flow is dominated by wakes induced by cylinder oscillation at $lambda^* leq 1.5$ and steady current at $lambda^* geq 10$, it exhibits characteristics of nonlinear interactions of wakes induced by the cylinder oscillation and steady current at $lambda^* = 1.5 - 10$, such as the formation of multiple synchronized modes interleaved with desynchronized modes. The synchronized mode varies with both $lambda^$ and $A^$, forming an inclined Arnold's tongue across $lambda^-A^$ space. There is a wide variability of the vortex shedding pattern in each synchronized mode. Variations of different hydrodynamic force coefficients with $lambda^$ and $A^$ are investigated with physical interpretations based on the wake characteristics. The applicability of the Morison equation in predicting inline force fluctuations is examined. We found that the Morison equation shows reasonable accuracy only for a small range of $lambda^* leq 1.5$. Beyond this range, its performance deteriorates due to the influence of steady current on wake characteristics.
{"title":"Hydrodynamics of an oscillating cylinder inline with steady current","authors":"Chengjiao Ren, Feifei Tong, Fei He, Liang Cheng","doi":"arxiv-2409.08528","DOIUrl":"https://doi.org/arxiv-2409.08528","url":null,"abstract":"Wake and force characteristics of an oscillating cylinder in inline steady\u0000currents are investigated numerically over a wide parameter space of\u0000dimensionless oscillation amplitude ($A^* = 0.01 - 0.50$) and wavelength\u0000($lambda^* = 0.4 - 25$) at a fixed Reynolds number $Re = 500$. Fundamental\u0000issues addressed in this study are the interactions of wakes induced by steady\u0000approaching flow and cylinder oscillations and the influences of the governing\u0000parameters of $A^$ and $lambda^$ on such interactions. Whilst the collinear\u0000flow is dominated by wakes induced by cylinder oscillation at $lambda^* leq\u00001.5$ and steady current at $lambda^* geq 10$, it exhibits characteristics of\u0000nonlinear interactions of wakes induced by the cylinder oscillation and steady\u0000current at $lambda^* = 1.5 - 10$, such as the formation of multiple\u0000synchronized modes interleaved with desynchronized modes. The synchronized mode\u0000varies with both $lambda^$ and $A^$, forming an inclined Arnold's tongue\u0000across $lambda^-A^$ space. There is a wide variability of the vortex shedding\u0000pattern in each synchronized mode. Variations of different hydrodynamic force\u0000coefficients with $lambda^$ and $A^$ are investigated with physical\u0000interpretations based on the wake characteristics. The applicability of the\u0000Morison equation in predicting inline force fluctuations is examined. We found\u0000that the Morison equation shows reasonable accuracy only for a small range of\u0000$lambda^* leq 1.5$. Beyond this range, its performance deteriorates due to\u0000the influence of steady current on wake characteristics.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267648","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We develop a deep reinforcement learning method for training a jellyfish-like swimmer to effectively track a moving target in a two-dimensional flow. This swimmer is a flexible object equipped with a muscle model based on torsional springs. We employ a deep Q-network (DQN) that takes the swimmer's geometry and dynamic parameters as inputs, and outputs actions which are the forces applied to the swimmer. In particular, we introduce an action regulation to mitigate the interference from complex fluid-structure interactions. The goal of these actions is to navigate the swimmer to a target point in the shortest possible time. In the DQN training, the data on the swimmer's motions are obtained from simulations conducted using the immersed boundary method. During tracking a moving target, there is an inherent delay between the application of forces and the corresponding response of the swimmer's body due to hydrodynamic interactions between the shedding vortices and the swimmer's own locomotion. Our tests demonstrate that the swimmer, with the DQN agent and action regulation, is able to dynamically adjust its course based on its instantaneous state. This work extends the application scope of machine learning in controlling flexible objects within fluid environments.
{"title":"Deep reinforcement learning for tracking a moving target in jellyfish-like swimming","authors":"Yihao Chen, Yue Yang","doi":"arxiv-2409.08815","DOIUrl":"https://doi.org/arxiv-2409.08815","url":null,"abstract":"We develop a deep reinforcement learning method for training a jellyfish-like\u0000swimmer to effectively track a moving target in a two-dimensional flow. This\u0000swimmer is a flexible object equipped with a muscle model based on torsional\u0000springs. We employ a deep Q-network (DQN) that takes the swimmer's geometry and\u0000dynamic parameters as inputs, and outputs actions which are the forces applied\u0000to the swimmer. In particular, we introduce an action regulation to mitigate\u0000the interference from complex fluid-structure interactions. The goal of these\u0000actions is to navigate the swimmer to a target point in the shortest possible\u0000time. In the DQN training, the data on the swimmer's motions are obtained from\u0000simulations conducted using the immersed boundary method. During tracking a\u0000moving target, there is an inherent delay between the application of forces and\u0000the corresponding response of the swimmer's body due to hydrodynamic\u0000interactions between the shedding vortices and the swimmer's own locomotion.\u0000Our tests demonstrate that the swimmer, with the DQN agent and action\u0000regulation, is able to dynamically adjust its course based on its instantaneous\u0000state. This work extends the application scope of machine learning in\u0000controlling flexible objects within fluid environments.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"21 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267645","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Manipulation of small-scale particles across streamlines is the elementary task of microfluidic devices. Many such devices operate at very low Reynolds numbers and deflect particles using arrays of obstacles, but a systematic quantification of relevant hydrodynamic effects has been lacking. Here, we explore an alternate approach, rigorously modeling the displacement of force-free spherical particles in vortical Stokes flows under hydrodynamic particle-wall interaction. Certain Moffatt-like eddy geometries with broken symmetry allow for systematic deflection of particles across streamlines, leading to particle accumulation at either Faxen field fixed points or limit cycles. Moreover, particles can be forced onto trajectories approaching channel walls exponentially closely, making quantitative predictions of particle capture (sticking) by short-range forces possible. This rich, particle size-dependent behavior suggests the versatile use of inertial-less flow in devices with a long particle residence time for concentration, sorting, or filtering.
{"title":"Principles of hydrodynamic particle manipulation in internal Stokes flow","authors":"Xuchen Liu, Partha Kumar Das, Sascha Hilgenfeldt","doi":"arxiv-2409.08452","DOIUrl":"https://doi.org/arxiv-2409.08452","url":null,"abstract":"Manipulation of small-scale particles across streamlines is the elementary\u0000task of microfluidic devices. Many such devices operate at very low Reynolds\u0000numbers and deflect particles using arrays of obstacles, but a systematic\u0000quantification of relevant hydrodynamic effects has been lacking. Here, we\u0000explore an alternate approach, rigorously modeling the displacement of\u0000force-free spherical particles in vortical Stokes flows under hydrodynamic\u0000particle-wall interaction. Certain Moffatt-like eddy geometries with broken\u0000symmetry allow for systematic deflection of particles across streamlines,\u0000leading to particle accumulation at either Faxen field fixed points or limit\u0000cycles. Moreover, particles can be forced onto trajectories approaching channel\u0000walls exponentially closely, making quantitative predictions of particle\u0000capture (sticking) by short-range forces possible. This rich, particle\u0000size-dependent behavior suggests the versatile use of inertial-less flow in\u0000devices with a long particle residence time for concentration, sorting, or\u0000filtering.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"119 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267651","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nearly constant mean angular momentum profiles are widely observed in curved turbulent flows, including the bulk region of Taylor--Couette (TC) flows, where the inner and outer cylinders have weakly counter-rotating and co-rotating conditions. For high-Reynolds-number TC flows under these conditions, both the bulk and boundary layers become turbulent without Taylor rolls, referred to as the featureless ultimate regime (UR). In this study, we examine Reynolds-averaged Navier--Stokes (RANS) models to predict the nearly constant mean angular velocity as a one-dimensional problem in the featureless UR of TC turbulence. High-Reynolds-number experiments of TC turbulence are performed for reference, where the radius ratio is $eta = r_mathrm{in}/r_mathrm{out} = 0.732$ and angular velocity ratio $a = -omega_mathrm{out}/omega_mathrm{in}$ is in the range $-0.5 le a le 0.1$. Verification of the RANS model using the algebraic Reynolds stress model (ARSM) suggests that convection of the Reynolds stress is essential for predicting the angular momentum profile. We introduce the Jaumann derivative as a covariant time derivative to develop ARSMs that incorporate the convection effect in a covariant manner. The proposed ARSM using the Jaumann derivative of the term composed of the strain and vorticity tensors successfully predicts the nearly constant mean angular momentum for a wide range of angular velocity ratios in the co-rotating case. The modelling approach incorporating time-derivative terms is a candidate for expressing curvature effects while satisfying the covariance of the Reynolds stress tensor.
在弯曲湍流（包括泰勒--库埃特（TC）流的主体区域）中广泛观察到近乎恒定的平均角动量剖面，其中内筒和外筒具有弱反转和共转条件。对于这些条件下的高雷诺数 TC 流，流体层和边界层都会变成没有泰勒卷的湍流，称为无特征终极制度（UR）。在本研究中，我们研究了雷诺数平均纳维-斯托克斯（RANS）模型，以预测 TC 湍流的无特征终极制度（UR）中作为一维问题的近恒定平均角速度。进行了TC湍流的高雷诺数实验作为参考，其中半径比为$ea = r_mathrm{in}/r_mathrm{out} =0.732$，角速度比$a = -omega_mathrm{out}/omega_mathrm{in}$ 的范围为$-0.5 le a le 0.1$。使用代数雷诺应力模型（ARSM）验证 RANS 模型表明，雷诺应力的对流对于预测角动量剖面至关重要。我们引入 Jaumann 导数作为协变时间导数，开发出以协变方式纳入对流效应的 ARSM。利用应变和涡度传感器组成的 Jaumann 导数项提出的 ARSM 成功地预测了共旋转情况下角速度比范围较大的近乎恒定的平均角动量。包含时间导数项的建模方法是一种既能表达曲率效应又能满足雷诺应变传感器协方差的候选方法。
{"title":"Covariant algebraic Reynolds stress modelling of curvature effects in high-Reynolds-number Taylor--Couette turbulence","authors":"Kazuhiro Inagaki, Yasufumi Horimoto","doi":"arxiv-2409.08471","DOIUrl":"https://doi.org/arxiv-2409.08471","url":null,"abstract":"Nearly constant mean angular momentum profiles are widely observed in curved\u0000turbulent flows, including the bulk region of Taylor--Couette (TC) flows, where\u0000the inner and outer cylinders have weakly counter-rotating and co-rotating\u0000conditions. For high-Reynolds-number TC flows under these conditions, both the\u0000bulk and boundary layers become turbulent without Taylor rolls, referred to as\u0000the featureless ultimate regime (UR). In this study, we examine\u0000Reynolds-averaged Navier--Stokes (RANS) models to predict the nearly constant\u0000mean angular velocity as a one-dimensional problem in the featureless UR of TC\u0000turbulence. High-Reynolds-number experiments of TC turbulence are performed for\u0000reference, where the radius ratio is $eta = r_mathrm{in}/r_mathrm{out} =\u00000.732$ and angular velocity ratio $a = -omega_mathrm{out}/omega_mathrm{in}$\u0000is in the range $-0.5 le a le 0.1$. Verification of the RANS model using the\u0000algebraic Reynolds stress model (ARSM) suggests that convection of the Reynolds\u0000stress is essential for predicting the angular momentum profile. We introduce\u0000the Jaumann derivative as a covariant time derivative to develop ARSMs that\u0000incorporate the convection effect in a covariant manner. The proposed ARSM\u0000using the Jaumann derivative of the term composed of the strain and vorticity\u0000tensors successfully predicts the nearly constant mean angular momentum for a\u0000wide range of angular velocity ratios in the co-rotating case. The modelling\u0000approach incorporating time-derivative terms is a candidate for expressing\u0000curvature effects while satisfying the covariance of the Reynolds stress\u0000tensor.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267649","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jonas R. Naujoks, Aleksander Krasowski, Moritz Weckbecker, Thomas Wiegand, Sebastian Lapuschkin, Wojciech Samek, René P. Klausen
Recently, physics-informed neural networks (PINNs) have emerged as a flexible and promising application of deep learning to partial differential equations in the physical sciences. While offering strong performance and competitive inference speeds on forward and inverse problems, their black-box nature limits interpretability, particularly regarding alignment with expected physical behavior. In the present work, we explore the application of influence functions (IFs) to validate and debug PINNs post-hoc. Specifically, we apply variations of IF-based indicators to gauge the influence of different types of collocation points on the prediction of PINNs applied to a 2D Navier-Stokes fluid flow problem. Our results demonstrate how IFs can be adapted to PINNs to reveal the potential for further studies.
最近，物理信息神经网络（PINNs）作为深度学习在物理科学偏微分方程中的一种灵活而有前途的应用而崭露头角。虽然它们在正演和反演问题上具有强大的性能和极具竞争力的推理速度，但其黑箱性质限制了其可解释性，尤其是在与预期物理行为的一致性方面。在本研究中，我们探索了如何应用影响函数（IF）来验证和调试 PINN。具体来说，我们应用基于影响函数的指标变量来衡量不同类型的定位点对应用于二维纳维-斯托克斯流体流动问题的 PINN 预测的影响。我们的结果表明了 IF 如何适用于 PINN，从而揭示了进一步研究的潜力。
{"title":"PINNfluence: Influence Functions for Physics-Informed Neural Networks","authors":"Jonas R. Naujoks, Aleksander Krasowski, Moritz Weckbecker, Thomas Wiegand, Sebastian Lapuschkin, Wojciech Samek, René P. Klausen","doi":"arxiv-2409.08958","DOIUrl":"https://doi.org/arxiv-2409.08958","url":null,"abstract":"Recently, physics-informed neural networks (PINNs) have emerged as a flexible\u0000and promising application of deep learning to partial differential equations in\u0000the physical sciences. While offering strong performance and competitive\u0000inference speeds on forward and inverse problems, their black-box nature limits\u0000interpretability, particularly regarding alignment with expected physical\u0000behavior. In the present work, we explore the application of influence\u0000functions (IFs) to validate and debug PINNs post-hoc. Specifically, we apply\u0000variations of IF-based indicators to gauge the influence of different types of\u0000collocation points on the prediction of PINNs applied to a 2D Navier-Stokes\u0000fluid flow problem. Our results demonstrate how IFs can be adapted to PINNs to\u0000reveal the potential for further studies.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267652","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Duowen Chen, Zhiqi Li, Junwei Zhou, Fan Feng, Tao Du, Bo Zhu
We propose a novel solid-fluid interaction method for coupling elastic solids with impulse flow maps. Our key idea is to unify the representation of fluid and solid components as particle flow maps with different lengths and dynamics. The solid-fluid coupling is enabled by implementing two novel mechanisms: first, we developed an impulse-to-velocity transfer mechanism to unify the exchanged physical quantities; second, we devised a particle path integral mechanism to accumulate coupling forces along each flow-map trajectory. Our framework integrates these two mechanisms into an Eulerian-Lagrangian impulse fluid simulator to accommodate traditional coupling models, exemplified by the Material Point Method (MPM) and Immersed Boundary Method (IBM), within a particle flow map framework. We demonstrate our method's efficacy by simulating solid-fluid interactions exhibiting strong vortical dynamics, including various vortex shedding and interaction examples across swimming, falling, breezing, and combustion.
{"title":"Solid-Fluid Interaction on Particle Flow Maps","authors":"Duowen Chen, Zhiqi Li, Junwei Zhou, Fan Feng, Tao Du, Bo Zhu","doi":"arxiv-2409.09225","DOIUrl":"https://doi.org/arxiv-2409.09225","url":null,"abstract":"We propose a novel solid-fluid interaction method for coupling elastic solids\u0000with impulse flow maps. Our key idea is to unify the representation of fluid\u0000and solid components as particle flow maps with different lengths and dynamics.\u0000The solid-fluid coupling is enabled by implementing two novel mechanisms:\u0000first, we developed an impulse-to-velocity transfer mechanism to unify the\u0000exchanged physical quantities; second, we devised a particle path integral\u0000mechanism to accumulate coupling forces along each flow-map trajectory. Our\u0000framework integrates these two mechanisms into an Eulerian-Lagrangian impulse\u0000fluid simulator to accommodate traditional coupling models, exemplified by the\u0000Material Point Method (MPM) and Immersed Boundary Method (IBM), within a\u0000particle flow map framework. We demonstrate our method's efficacy by simulating\u0000solid-fluid interactions exhibiting strong vortical dynamics, including various\u0000vortex shedding and interaction examples across swimming, falling, breezing,\u0000and combustion.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267543","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High-speed imaging is central to the experimental investigation of fast phenomena, like flapping flags. Event-based cameras use new types of sensors that address typical challenges such as low illumination conditions, large data transfer, and the trade-off between increasing repetition rate and measurement duration more efficiently and at reduced costs compared to classical frame-based fast cameras. Event-based cameras output unstructured data that frame-based algorithms can not process. This paper proposes a general method to reconstruct the motion of a slender object similar to the centreline of a flapping flag from raw streams of event data. Our algorithm relies on a coarse chain-like structure that encodes the current state of the line and is updated by the occurrence of new events. The algorithm is applied to synthetic data, generated from known motions, to demonstrate that the method is accurate up to one percent of error for tip-based, shape-based, and modal decomposition metrics. Degradation of the reconstruction accuracy due to simulated defects only occurs when the defect intensities become more than two orders of magnitude larger than the values expected in experiments. The algorithm is then applied to experimental data of flapping flags, and we obtain relative errors below one percent when comparing the results with the data from laser distance sensors. The reconstruction of line deformation from event-based data is accurate and robust, and unlocks the ability to perform autonomous measurements in experimental mechanics.
{"title":"Event-based reconstruction of time-resolved centreline deformation of flapping flags","authors":"Gaetan Raynaud, Karen Mulleners","doi":"arxiv-2409.08939","DOIUrl":"https://doi.org/arxiv-2409.08939","url":null,"abstract":"High-speed imaging is central to the experimental investigation of fast\u0000phenomena, like flapping flags. Event-based cameras use new types of sensors\u0000that address typical challenges such as low illumination conditions, large data\u0000transfer, and the trade-off between increasing repetition rate and measurement\u0000duration more efficiently and at reduced costs compared to classical\u0000frame-based fast cameras. Event-based cameras output unstructured data that\u0000frame-based algorithms can not process. This paper proposes a general method to\u0000reconstruct the motion of a slender object similar to the centreline of a\u0000flapping flag from raw streams of event data. Our algorithm relies on a coarse\u0000chain-like structure that encodes the current state of the line and is updated\u0000by the occurrence of new events. The algorithm is applied to synthetic data,\u0000generated from known motions, to demonstrate that the method is accurate up to\u0000one percent of error for tip-based, shape-based, and modal decomposition\u0000metrics. Degradation of the reconstruction accuracy due to simulated defects\u0000only occurs when the defect intensities become more than two orders of\u0000magnitude larger than the values expected in experiments. The algorithm is then\u0000applied to experimental data of flapping flags, and we obtain relative errors\u0000below one percent when comparing the results with the data from laser distance\u0000sensors. The reconstruction of line deformation from event-based data is\u0000accurate and robust, and unlocks the ability to perform autonomous measurements\u0000in experimental mechanics.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267644","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fluids at supercritical pressures exhibit large variations in density near the pseudo critical line, such that buoyancy plays a crucial role in their fluid dynamics. Here, we experimentally investigate heat transfer and turbulence in horizontal hydrodynamically developed channel flows of carbon dioxide at 88.5 bar and 32.6{deg}C, heated at either the top or bottom surface to induce a strong vertical density gradient. In order to visualise the flow and evaluate its heat transfer, shadowgraphy is used concurrently with surface temperature measurements. With moderate heating, the flow is found to strongly stratify for both heating configurations, with bulk Richardson numbers Ri reaching up to 100. When the carbon dioxide is heated from the bottom upwards, the resulting unstably stratified flow is found to be dominated by the increasingly prevalent secondary motion of thermal plumes, enhancing vertical mixing and progressively improving heat transfer compared to a neutrally buoyant setting. Conversely, stable stratification, induced by heating from the top, suppresses the vertical motion leading to deteriorated heat transfer that becomes invariant to the Reynolds number. The optical results provide novel insights into the complex dynamics of the directionally dependent heat transfer in the near-pseudo-critical region. These insights contribute to the reliable design of heat exchangers with highly property-variant fluids, which are critical for the decarbonisation of power and industrial heat. However, the results also highlight the need for further progress in the development of experimental techniques to generate reliable reference data for a broader range of non-ideal supercritical conditions.
{"title":"The stability of stratified horizontal flows of carbon dioxide at supercritical pressures","authors":"Marko Draskic, Jerry Westerweel, Rene Pecnik","doi":"arxiv-2409.08804","DOIUrl":"https://doi.org/arxiv-2409.08804","url":null,"abstract":"Fluids at supercritical pressures exhibit large variations in density near\u0000the pseudo critical line, such that buoyancy plays a crucial role in their\u0000fluid dynamics. Here, we experimentally investigate heat transfer and\u0000turbulence in horizontal hydrodynamically developed channel flows of carbon\u0000dioxide at 88.5 bar and 32.6{deg}C, heated at either the top or bottom surface\u0000to induce a strong vertical density gradient. In order to visualise the flow\u0000and evaluate its heat transfer, shadowgraphy is used concurrently with surface\u0000temperature measurements. With moderate heating, the flow is found to strongly\u0000stratify for both heating configurations, with bulk Richardson numbers Ri\u0000reaching up to 100. When the carbon dioxide is heated from the bottom upwards,\u0000the resulting unstably stratified flow is found to be dominated by the\u0000increasingly prevalent secondary motion of thermal plumes, enhancing vertical\u0000mixing and progressively improving heat transfer compared to a neutrally\u0000buoyant setting. Conversely, stable stratification, induced by heating from the\u0000top, suppresses the vertical motion leading to deteriorated heat transfer that\u0000becomes invariant to the Reynolds number. The optical results provide novel\u0000insights into the complex dynamics of the directionally dependent heat transfer\u0000in the near-pseudo-critical region. These insights contribute to the reliable\u0000design of heat exchangers with highly property-variant fluids, which are\u0000critical for the decarbonisation of power and industrial heat. However, the\u0000results also highlight the need for further progress in the development of\u0000experimental techniques to generate reliable reference data for a broader range\u0000of non-ideal supercritical conditions.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"102 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142267647","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：