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Dynamic properties of mode Ⅰ and mode Ⅱ fractures of shale under impact loading

Journal of Rock Mechanics and Geotechnical Engineering 2025年第2期17卷 1053-1067页

作者： Zelin Yan Linjuan Wang Jidong Jin Jianxiang Wang State Key Laboratory for Turbulence and Complex Systems Department of Mechanics and Engineering ScienceCollege of EngineeringPeking UniversityBeijing100871China School of Astronautics Beihang UniversityBeijing100191China

Controllable shock wave fracturing is an innovative engineering technique used for shale reservoir fracturing and *** the anisotropic fracture mechanism of shale under impact loading is vital for optimizing shock wave fracturing equipment and enhancing shale oil *** this study,using the well-known notched semi-circular bend(NSCB)sample and the novel double-edge notched flattened Brazilian disc(DNFBD)sample combined with a split Hopkinson pressure bar(SHPB),various dynamic anisotropic fracture properties of Lushan shale,including failure characteristics,fracture toughness,energy dissipation and crack propagation velocity,are comprehensively compared and discussed under mode Ⅰ and mode Ⅱ fracture ***,using a newly modified fracture criterion considering the strength anisotropy of shale,the DNFBD specimen is predicted to be a robust method for true mode Ⅱ fracture of anisotropic shale *** experimental results show that the dynamic mode Ⅱ fracture of shale induces a rougher and more complex fracture morphology and performs a higher fracture toughness or fracture energy compared to dynamic mode Ⅰ *** minimal fracture toughness or fracture energy occurs in the Short-transverse orientation,while the maximal ones occur in the Divider *** addition,it is interesting to find that the mode Ⅱ fracture toughness anisotropy index decreases more slowly than that in the mode Ⅰ fracture *** results provide significant insights for understanding the different dynamic fracture mechanisms of anisotropic shale rocks under impact loading and have some beneficial implications for the controllable shock wave fracturing technique.

关键词： Shale Controllable shock wave fracturing Dynamic fracture property Fracture toughness anisotropy Loading rate effect

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Toward Analytical Homogenized Relaxation Modulus for Fibrous Composite Material with Reduced Order Homogenization Method

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Computers, Materials & Continua 2025年第1期82卷 193-222页

作者： Huilin Jia Shanqiao Huang Zifeng Yuan HEDPS Center for Applied Physics and Technology(CAPT)Department of Mechanics and Engineering SciencePeking UniversityBeijing100871China State Key Laboratory for Turbulence and Complex Systems Peking UniversityBeijing100871China

In this manuscript,we propose an analytical equivalent linear viscoelastic constitutive model for fiber-reinforced composites,bypassing general computational *** method is based on the reduced-order homogenization(ROH)*** ROH method typically involves solving multiple finite element problems under periodic conditions to evaluate elastic strain and eigenstrain influence functions in an‘off-line’stage,which offers substantial cost savings compared to direct computational homogenization *** to the unique structure of the fibrous unit cell,“off-line”stage calculation can be eliminated by influence functions obtained *** the standard solid model to the ROH method enables the creation of a comprehensive analytical homogeneous viscoelastic constitutive *** method treats fibrous composite materials as homogeneous,anisotropic viscoelastic materials,significantly reducing computational time due to its analytical *** approach also enables precise determination of a homogenized anisotropic relaxation modulus and accurate capture of various viscoelastic responses under different loading *** sets of numerical examples,including unit cell tests,three-point beam bending tests,and torsion tests,are given to demonstrate the predictive performance of the homogenized viscoelastic ***,the model is validated against experimental measurements,confirming its accuracy and reliability.

关键词： Homogenized relaxation modulus viscoelastic standard solid model reduced order homogenization fibrous composite material

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Bioinspired Sensing of Undulatory Flow Fields Generated by Leg Kicks in Swimming

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IEEE Transactions on Automation Science and Engineering 2025年 22卷 13895-13906页

作者： Wang, Jun Shen, Tongsheng Zhao, Dexin Zhang, Feitian Peking University State Key Laboratory of Turbulence and Complex Systems College of Engineering Department of Advanced Manufacturing and Robotics Beijing100871 China National Innovation Institute of Defense Technology Beijing100071 China

The artificial lateral line (ALL) is a bioinspired flow sensing system for underwater robots, comprising of distributed flow sensors. The ALL has been successfully applied to detect the undulatory flow fields generated by body undulation and tail-flapping of bioinspired robotic fish. However, its feasibility and performance in sensing the undulatory flow fields produced by human leg kicks during swimming have not been systematically tested and studied. This paper presents a novel sensing framework to investigate the undulatory flow field generated by swimmer’s leg kicks, leveraging bioinspired ALL sensing. To evaluate the feasibility of using the ALL system for sensing the undulatory flow fields generated by swimmer leg kicks, this paper designs an experimental platform integrating an ALL system and a lab-fabricated human leg model. To enhance the accuracy of flow sensing, this paper proposes a feature extraction method that dynamically fuses time-domain and time-frequency characteristics. Specifically, time-domain features are extracted using one-dimensional convolutional neural networks and bidirectional long short-term memory networks (1DCNN-BiLSTM), while time-frequency features are extracted using short-term Fourier transform and two-dimensional convolutional neural networks (STFT-2DCNN). These features are then dynamically fused based on attention mechanisms to achieve accurate sensing of the undulatory flow field. Furthermore, extensive experiments are conducted to test various scenarios inspired by human swimming, such as leg kick pattern recognition and kicking leg localization, achieving satisfactory results. © 2004-2012 IEEE.

关键词： Long short-term memory

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Unveiling the confined dispersion mechanism of nanomaterials by stereocomplex cross-linked networks in polylactic acid

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Journal of Materials Science and Technology 2025年 235卷 293-301页

作者： Su, Xiaolong Pan, Qingchun Zhai, Yaling Jia, Chao Wang, Jinqi Xu, Zhe Li, Jiaxin Zhao, Jian Xiang, Hengxue Wei, Xiaoding Zhu, Meifang State Key Laboratory of Advanced Fiber Materials College of Material Science and Engineering Donghua University Shanghai201620 China State Key Laboratory for Turbulence and Complex System Department of Mechanics and Engineering Science College of Engineering Beijing Innovation Center for Engineering Science and Advanced Technology Peking University Beijing100871 China College of Material Science and Engineering Xinjiang University Urumqi830046 China

Nanomaterials are extensively utilized in a multitude of sectors, but their propensity to aggregate can considerably diminish the efficacy of functional materials. A pivotal challenge in this domain is achieving a homogenous distribution of nanomaterials, which is essential for enhancing their performance while also reducing production costs. In this work, we achieve uniform and stable dispersion of various nanomaterials through the confinement effect generated by the stereocomplex cross-linked network formed by the combination of poly (L-lactic) acid and poly (D-lactic) acid. The unique confinement effect of polylactic acid (PLA) isomers is universal and significantly enhances the dispersion of nanomaterials in both PLA solutions and films. To demonstrate the efficacy of our approach, we disperse aggregation-induced emission (AIE) molecules within PLA, which leads to the production of PLA films exhibiting improved fluorescence property. This work provides an effective solution for the preparation of nanocomposite materials that are both high-performing and cost-efficient. © 2025

关键词： Nanoclay

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Planar Pose Control of Robotic Fish Based on Deep Reinforcement Learning

Planar Pose Control of Robotic Fish Based on Deep Reinforcem...

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International Conference on Artificial Intelligence and Autonomous Transportation, AIAT 2024

作者： Hongqi, Yang Xie, Guangming 96037 PLA Troops Baoji721000 China State Key Laboratory for Turbulence and Complex Systems Intelligent Biomimetic Design Lab College of Engineering Peking University Beijing100871 China

ISBN: (纸本)9789819639762

With the development of computational fluid dynamics and deep reinforcement learning, it has become possible to combine deep reinforcement learning with computational fluid dynamics to study the control problem of underwater robots. This article uses Computational Fluid Dynamics (CFD) and Deep Reinforcement Learning to study planar pose control of robotic fish. A two-dimensional model of the robotic fish is built in CFD, and the surrogate model environment is built based on CFD simulation results. Actor-Critic method is used to train the pose control in surrogate model environment. Sparse reward problem is solved by using course learning method during training. Finally, pose control experiment of robotic fish is carried out. The experimental results show that this pose control method is effective and feasible, control accuracy is higher. © Beijing Paike Culture Commu. Co., Ltd. 2025.

关键词： Deep reinforcement learning

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Quantum-enriched large-eddy simulation with the incompressible Schrodinger flow

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Acta Mechanica Sinica 2025年第1期41卷 95-105页

作者： Zishuo Han Yue Yang State Key Laboratory for Turbulence and Complex Systems College of EngineeringPeking UniversityBeijing 100871China Key Laboratory of High Energy Density Physics Simulations Center for Applied Physics and TechnologyPeking UniversityBeijing 100871China Received January 282024

We propose a hybrid quantum-classical method,the quantum-enriched large eddy simulation(QELES),for simulating *** QELES combines the large-scale motion of the large eddy simulation(LES)and the subgrid motion of the incompressible Schrodinger flow(ISF).The ISF is a possible way to be simulated on a quantum computer,and it generates subgrid scale turbu-lent structures to enrich the LES *** enriched LES field can be further used in turbulent combustion and multi-phase flows in which the subgrid scale motion plays an important *** a conceptual study,we perform the simulations of ISF and LES separately on a classical computer to simulate decaying homogeneous isotropic ***,the QEI ES velocity is obtained by the time matching and the spectral blending *** QEL ES achieves significant improvement in predicting the energy spectrum,probaility density functions of velocity and vorticity components,and velocity structure functions,and reconstructs coherent small-scales vortices in the direct numerical simulation(DNS).On the other hand,the vortices in the QELES are less elongated and tangled than those in the DNS,and the magnitude of the third-order structure function in the QELES is less than that in the DNS,due to the diferent constitutive relations in the viscous flow and ISE.

关键词： Quantum computing Large-eddy simulation Subgrid motion

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Distributed Task Allocation With Minimum Makespan for Heterogeneous Multiplayer Pursuit–Evasion Games

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IEEE Transactions on Automatic Control 2025年第5期70卷 2827-2842页

作者： Li, Shuai Wang, Chen Sun, Jinan Zhang, Shikun Xie, Guangming Peking University State Key Laboratory of Turbulence and Complex Systems Intelligent Biomimetic Design Lab College of Engineering Beijing100871 China Peking University National Engineering Research Center of Software Engineering Beijing100871 China Peking University Center for Multi-Agent Research Institute for Artificial Intelligence Beijing100871 China

In the domain of multiplayer pursuit–evasion games, it is crucial to address the practical aspects of the players' heterogeneity, the distributed control manner, and the pursuers' goal of minimum makespan. However, the three topics have received limited attention in existing literature, both separately and in combination. In this article, we address the multiplayer pursuit–evasion game integrating these key topics, where the pursuers with simple motions strive to capture as many evaders, characterized by damped double integrators, as possible, meanwhile minimizing the task makespan. To this end, we establish an overall framework and sequentially tackle four key issues, leading to an effective solution to the entire problem. We first propose a novel isochron-based method to derive the capture condition and acquire the optimal pursuit and evasion strategies. Then, we enhance the usability of the capture condition by geometrically deriving the analytical form of the pursuer's winning region with respect to a given evader. Third, leveraging the concept of winning regions, we determine the lower boundary of pursuers' sensing range, ensuring sufficient information acquisition for evader allocation while avoiding selection conflicts. Finally, we propose a fully distributed allocation algorithm for each pursuer allowing the pursuer team to converge to the optimal evader allocation. By combining these contributions, we successfully provide an effective solution to the entire problem. Various simulations are conducted to show the effectiveness of our proposed methods. © 1963-2012 IEEE.

关键词： Games Resource management Sensors Robot sensing systems Mathematical models Heuristic algorithms Decentralized control Usability Biomimetics Topology

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An Isochron-Based Solution to Pursuit–Evasion Games of Two Heterogeneous Players

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IEEE Transactions on Automatic Control 2025年第5期70卷 2811-2826页

作者： Li, Shuai Wang, Chen Xie, Guangming Peking University State Key Laboratory of Turbulence and Complex Systems Intelligent Biomimetic Design Lab College of Engineering Beijing100871 China Peking University National Engineering Research Center of Software Engineering Beijing100871 China Peking University Center for Multi-Agent Research Institute for Artificial Intelligence Beijing100871 China

In this article, we study a pursuit–evasion game between two players with heterogeneous kinematics, where the pursuer is with damped double-integrator dynamics and the evader is with single-integrator dynamics. The pursuer aims at capturing the evader as soon as possible, while the evader wants to avoid or delay the capture. Traditional methods to solve pursuit–evasion games rely on the Hamilton–Jacobi–Isaacs (HJI) equations and retrogressive path equations, which are very complicated and nonintuitive, thus failing to obtain a complete solution. To overcome these challenges, we develop an intuitive isochron-based method to thoroughly analyze all possible situations of the game and a concise geometric approach to calculate the optimal strategies, providing a complete solution to this game. Specifically, the isochron-based method effectively leverages three main factors: the players' motion capability, the pursuer's capture capability, and the players' states. Based on these, we analyze the players' superiority and the geometrical features of their isochrones and the intersections, thus acquiring concise conditions that determine the game's outcome. For the success-capture cases, we propose a new geometric approach to calculate the target points of the players and then obtain the closed-loop state feedback optimal pursuit and evasion strategies. We then get the corresponding value function and provide a validation using the HJI equation. For the success-evasion cases, we exploit the intersection of the players' isochrones to design some effective evasion strategies, which ensure that the evader can always avoid or delay the capture. Finally, some numerical simulations are carried out to validate the effectiveness and applicability of our results. © 1963-2012 IEEE.

关键词： state feedback

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Universal pull-off force for separating a rigid sphere from a membrane

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Journal of the Mechanics and Physics of Solids 2025年 201卷

作者： Zheng, Wanying Dai, Zhaohe Department of Mechanics and Engineering Science State Key Laboratory for Turbulence and Complex Systems College of Engineering Peking University Beijing100871 China

A pull-off force Fc is required to separate two objects in adhesive contact. For a rigid sphere on an elastic slab, the classic Johnson–Kendall–Roberts (JKR) theory predicts Fc=[Formula presented]πγRs, where γ represents the interface adhesion or toughness and Rs is the radius of the sphere. Here, we investigate an alternative, extreme scenario: the pull-off force required to detach a rigid, frictionless sphere from a thin membrane, a scenario observed in a wide range of nature and engineering systems, such as nanoparticles on cell membranes, atomic force microscopy probes on atomically thin 2D material sheets, and electronic devices on flexible films. We show that, within the JKR framework, the pull-off forces in axisymmetric soap films, linearly elastic membranes, and nonlinear hyperelastic membranes are all given by Fc=πγRs. This result is remarkable as it indicates that the pull-off force for membranes is independent of the material's constitutive law, size, pretension, and solid surface tension. © 2025 Elsevier Ltd

关键词： Cell engineering

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Distributed Kalman Filter with Ultimately Accurate Fused Measurement Covariance

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IEEE Transactions on Automatic Control 2025年

作者： Yang, Tuo Qian, Jiachen Duan, Zhisheng Sun, Zhiyong Peking University State Key Laboratory for Turbulence and Complex Systems Department of Mechanics and Engineering Science College of Engineering Beijing100871 China

This paper investigates the distributed Kalman filter (DKF) for linear systems, with specific attention on measurement fusion, which is a typical way of information sharing and is vital for enhancing stability and improving estimation accuracy. We show that it is the mismatch between the fused measurement and the fused covariance that leads to performance degradation or inconsistency in previous consensus-based DKF algorithms. To address this issue, we introduce two fully distributed approaches for calculating the exact covariance of the fused measurements, building upon which the modified DKF algorithms are proposed. Moreover, the performance analysis of the modified algorithms is also provided under rather mild conditions, including the steady-state value of the estimation error covariance. We also show that due to the guaranteed consistency in the modified DKF algorithms, the steady-state estimation accuracy is significantly improved compared to classical DKF algorithms. Numerical experiments are carried out to validate the theoretical analysis and show the advantages of the proposed methods. © 1963-2012 IEEE.

关键词： Wiener filtering

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