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An efficient multi-resolution SPH framework for multi-phase fluid-structure interactions

Science China(Physics,Mechanics & Astronomy) 2023年第10期66卷 92-113页

作者： Chi Zhang Yujie Zhu xiangyu hu TUM School of Engineering and Design Technical University of MunichGarching 85748Germany huawei Technologies Munich Research Center Munich 80992Germany Xi'an Research Institute of Hi-Tech Xi'an 710025China

Applying different spatial and temporal resolutions for different sub-systems is an effective approach to increase computational efficiency for particle-based methods. However, it still has many challenges in terms of achieving an optimized computational efficiency and maintaining good numerical robustness and accuracy for the simulation of multi-phase flows involving large density ratio and interacting with rigid or flexible structures. In the present work, based on the multi-resolution smoothed particle hydrodynamics(SPH) method [Zhang et al., JCP 429, 110028(2021)], an efficient multi-resolution SPH framework for multi-phase fluid-structure interactions(FSI) is proposed. First, an efficient multi-phase model, exploiting different density reinitialization strategies instead of applying different formulations to implement mass conservation to the light and heavy phases, respectively,is developed and the same artificial speed of sound for both phases can be used. Then, the transport velocity formulation is rewritten by applying temporal local flow state dependent background pressure to eliminate the unnatural voids, unrealistic phase separation and decrease the numerical dissipation. Finally, the one-sided Riemann-based solid boundary condition is modified to handle the FSI coupling in both single-and multi-resolution scenarios in the triple point. A set of examples involving multi-phase flows with high density ratio, complex interface and multi-phase FSI are studied to demonstrate the efficiency, accuracy and robustness of the present method.

关键词： multi-resolution method smoothed particle hydrodynamics multi-phase flows multi-phase FSI

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An Eulerian SPH method with WENO reconstruction for compressible and incompressible flows

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Journal of Hydrodynamics 2023年第2期35卷 210-221页

作者： Zhentong Wang Chi Zhang Oskar J.Haidn xiangyu hu TUM School of Engineering and Design Technical University of MunichMunichGermany huawei Technologies Munich Research Center MunichGermany

While Eulerian smoothed particle hydrodynamics(SPH)method has received increasing attention in scientific and industrial communities owing to its high spatial accuracy,it exhibits excessive numerical dissipation due to the fact that the flux is derived in particle pair pattern.In this paper,we adopt a one-dimensional weighted essentially non-oscillatory(WENO)reconstruction to reduce the numerical dissipation and improve the overall accuracy particularly in capturing the contact discontinuity.The underlying principle is to construct a 4-point stencil along the interacting line of each particle pair and then the WENO scheme is applied to reconstruct the initial states of the Riemann problem which determines the flow flux.A set of benchmark tests for both compressible and incompressible flows are studied to investigate the accuracy,robustness and versatility of the proposed Eulerian SPH method with the WENO reconstruction(ESPH-WENO).

关键词： Eulerian smoothed particle hydrodynamics(SPH) compressible flows incompressible flows Riemann problem

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Smoothed particle hydrodynamics:Methodology development and recent achievement

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Journal of Hydrodynamics 2022年第5期34卷 767-805页

作者： Chi Zhang Yu-jie Zhu Dong Wu Nikolaus A.Adams xiangyu hu TUM School of Engineering and Design Technical University of MunichMunichGermany Xi’an Research Institute of High Technology Xi’an 710025China

Since its inception,the full Lagrangian meshless smoothed particle hydrodynamics(SPH)has experienced a tremendous enhancement in methodology and impacted a range of multi-physics applications in science and engineering.This review presents a concise survey on latest developments and achievements of the SPH method,including:(1)Brief review of theory and fundamental with kernel corrections,(2)The Riemann-based SPH method with dissipation limiting and high-order data reconstruction by using MUSCL,WENO and MOOD schemes,(3)Particle neighbor searching with particle sorting and efficient dual-criteria time stepping schemes,(4)Total Lagrangian formulation with stablized,dynamics relaxation and hourglass control schemes,(5)Fluid-structure interaction scheme with interface treatments and multi-resolution discretizations,(6)Novel applications of particle relaxation in SPH methodology for mesh and particle generations.Last but not least,benchmark tests for validating computational accuracy,convergence,robustness and efficiency are also supplied accordingly.

关键词： Smoothed particle hydrodynamics(SPH) Riemann-based SPH update and total Lagrangian formulations fluid-structure interaction mesh and particle generation

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A microfluidic bleeding model to investigate the effects of blood flow shear on microvascular hemostasis

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Friction 2022年第1期10卷 128-141页

作者： xiangyu hu Haosheng CHEN Jiang LI Kuilin MENG Yuming WANG Yongjian LI State Key Laboratory of Tribology.Tsinghua University Beijing 100084China School of Mechanical Engineering.University of Science and Technology Beijing Beijing 100083China

Hemorrhage is the phenomenon of blood loss caused by vascular trauma or other pathological reasons,which is life-threatening in severe cases.Because microhemorrhage is difficult to visually monitor and pre-treat in vivo,it is necessary to establish in vitro prediction methods to study the hemostasis mechanism in different physiological environments.In this study,a microfluidic bleeding model was developed to investigate the effect of blood flow shear on microvascular hemostasis.The results indicated that the regulation of blood shear rate on platelet aggregation affected the growth and morphology of hemostatic thrombus,and finally regulated the process of hemostasis.This in vitro model is significant to studies on hemostatic mechanisms,a reliable prediction of microhemorrhages,and an adjustment of the treatment scheme.

关键词： stasis fluid bleeding

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Physics-Driven Learning of the Steady Navier-Stokes Equations using Deep Convolutional Neural Networks

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Communications in Computational Physics 2022年第8期32卷 715-736页

作者： Hao Ma Yuxuan Zhang Nils Thuerey xiangyu hu Oskar J.Haidn Department of Aerospace and Geodesy Technical University of Munich85748 GarchingGermany Beijing Aerospace Propulsion Institute 100076BeijingChina Technical University of Munich 85748GarchingGermany Department of Mechanical Engineering Technical University of Munich85748 GarchingGermany

Recently,physics-driven deep learning methods have shown particular promise for the prediction of physical fields,especially to reduce the dependency on large amounts of pre-computed training data.In this work,we target the physicsdriven learning of complex flow fields with high resolutions.We propose the use of Convolutional neural networks(CNN)based U-net architectures to efficiently represent and reconstruct the input and output fields,respectively.By introducingNavier-Stokes equations and boundary conditions into loss functions,the physics-driven CNN is designed to predict corresponding steady flow fields directly.In particular,this prevents many of the difficulties associated with approaches employing fully connected neural networks.Several numerical experiments are conducted to investigate the behavior of the CNN approach,and the results indicate that a first-order accuracy has been achieved.Specifically for the case of a flow around a cylinder,different flow regimes can be learned and the adhered“twin-vortices”are predicted correctly.The numerical results also show that the training for multiple cases is accelerated significantly,especially for the difficult cases at low Reynolds numbers,and when limited reference solutions are used as supplementary learning targets.

关键词： Deep learning physics-drivenmethod convolutional neural networks Navier-Stokes equations

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SPH modeling of fluid-structure interaction

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Journal of Hydrodynamics 2018年第1期30卷 62-69页

作者： Luhui Han xiangyu hu Department of Mechanical Engineering Technical University of Munich

This work concerns numerical modeling of fluid-structure interaction（FSI） problems in a uniform smoothed particle hydrodynamics（SPH） framework. It combines a transport-velocity SPH scheme, advancing fluid motions, with a total Lagrangian SPH formulation dealing with the structure deformations. Since both fluid and solid governing equations are solved in SPH framework, while coupling becomes straightforward, the momentum conservation of the FSI system is satisfied strictly. A well-known FSI benchmark test case has been performed to validate the modeling and to demonstrate its potential.

关键词： Fluid-structure interaction（FSI） smoothed particle hydrodynamics（SPH） total Lagrangian formulation

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A CAD-compatible body-fitted particle generator for arbitrarily complex geo-metry and its application to wave-structure interaction

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Journal of Hydrodynamics 2021年第2期33卷 195-206页

作者： Yujie Zhu Chi Zhang Yongchuan Yu xiangyu hu Department of Mechanical Engineering Technical University of MunichGarchingGermany Department of Aerospace and Geodesy Technical University of MunichTaufkirchenGermany

Generating body-fitted particle distribution for arbitrarily complex geometry underpins the applications of particle-based method to engineering and bioengineering and is highly challenging,and thus hinders the potential of particle methods.In this paper,we present a new computer-aided design(CAD)compatible body-fitted particle generator,termed as CAD-BPG,for arbitrarily complex 3-D geometry.By parsing a CAD model,the present method can accurately tackle arbitrarily complex geometry representation and describe the corresponding geometry surface by constructing an implicit zero level-set function on Cartesian background mesh.To achieve a body-fitted and isotropic particle distribution,physics-driven relaxation process with surface bounding governed by the transport-velocity formulation of smoothed particle hydrodynamics(SPH)methodology is conducted to characterize the particle evolution.A set of examples,ranging from propeller,stent structures and anatomical heart models,show simplicity,accuracy and versatility of the present CAD-BPG for generating body-fitted particle distribution of arbitrarily complex 3-D geometry.Last but not least,the present CAD-BPG is applied for modeling wave-structure interaction,where wave interaction with an oscillating wave surge converter is studied,and the results show that the present method not only provides an efficient and easy-to-implement pre-processing tool for particle-based simulation but also improves the numerical accuracy compared with lattice particle distribution.Consequently,the propose CAD-BPG sheds light on simulating real-world applications by particle-based methods for researchers and engineers.

关键词： CAD-compatible body-fitted particle distribution level-set

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A Differentially Private Auction Mechanism in Online Social Networks

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Journal of Systems Science and Systems Engineering 2021年第4期30卷 386-399页

作者： xiangyu hu Dayong Ye Tianqing Zhu huan huo University of Technology SydneyAustralia

The growing popularity of users in online social network gives a big opportunity for online auction.The famous Information Diffusion Mechanism(IDM)is an excellent method even meet the incentive compatibility and individual rationality.Although the existing auction in online social network has considered the buyers’information which is not known by the seller,current mechanism still can not preserve the privacy information of users in online social network.In this paper,we propose a novel mechanism based on the IDM and differential privacy.Our mechanism can successfully process the auction and at the same time preserve clients’price information from neighbours.We achieved these by adding virtual nodes to each node and Laplace noise for its price in the auction process.We also formulate this mechanism on the real network and the random network,scale-free network to show the feasibility and effectiveness of the proposed mechanism.The evaluation shows that the result of our methods only depend on the noise added to the agents.It is independent from the agents’original price.

关键词： Online social network auction privacy preserving differential privacy

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过程评价及其在针刺临床研究中应用的思考与建议

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中国针灸 2024年第3期44卷 327-332,366页

作者：陈欢岗卫娟欧阳梦璐胡晓艺田紫煜修文萃明恬妤胡翔昱景向红中国中医科学院针灸研究所北京100700 乔治全球健康研究院新南威尔士大学医学院澳大利亚悉尼2000

过程评价(PE)通过评估复杂干预的实施情况以及与结果密切相关的背景影响因素等,帮助充分解释干预的效果,是随机对照试验的重要方法学补充,但尚未在针刺临床研究中充分应用。本研究通过梳理中英文文献,总结了PE的主要方法学框架,以及在... 详细信息

过程评价(PE)通过评估复杂干预的实施情况以及与结果密切相关的背景影响因素等,帮助充分解释干预的效果,是随机对照试验的重要方法学补充,但尚未在针刺临床研究中充分应用。本研究通过梳理中英文文献,总结了PE的主要方法学框架,以及在针刺临床研究中的应用现状;在此基础上结合针刺干预和实施的特点,初步探讨在针刺临床研究中开展PE的角度以及针刺干预实施过程中的相关影响因素;随后从规划、设计和实施、分析及报告等多个阶段着手,就关键研究内容提出初步的建议,为今后开展针刺临床研究的过程评价提供可借鉴的思路,为全面评价和解释针刺干预的疗效探索新的方法和路径。

关键词：过程评价复杂干预针刺随机对照试验实施

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On Relationship between Pediatric Shi Ji and Fever

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Open Journal of Pediatrics 2015年第3期5卷 236-239页

作者： xiangyu hu Lina hu Pingdingshang City Hospital of Traditional Chinese Medicine Pingdingshan China

Based on the clinical effect of the treatment on 546 Pediatric Shi Ji fever cases, the thesis tries to explore the effectiveness of Traditional Chinese Medicine(TCM) treatment on Pediatric Shi Ji and the relationship between Pediatric Shi Ji and fever. The methodology applied is a retrospective analysis on the clinical curative effect of TCM treatment on Shi Ji fever cases in our hospital from January 2008 to December 2012. And the results show that a total effective rate of 96.3% could be guaranteed through either oral Chinese Medicinal Herbs, Chinese Medicine Enema, Massage Therapy, or navel administration with TCM. The thesis holds that Pediatric Shi Ji may cause fever, which could be cured simply by applying TCM treatment (promoting digestion to eliminate stagnation) with less or no use of antibiotics.

关键词： TCM Pediatric Shi Ji Fever Retrospective Analysis

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