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Three-dimensional wave structure within the puff of pipe flow

PHYSICS OF FLUIDS 2025年第2期37卷

作者： Wu, Puyuan Gu, Dingwei Jiang, Xianyang Lee, Cunbiao Peking Univ Coll Engn State Key Lab Turbulence & Complex Syst Beijing 100871 Peoples R China

Direct numerical simulations are conducted to investigate the puff in pipe flow at various Reynolds numbers. Lagrangian approaches and vortex dynamics analysis are employed to examine the early-stage flow structures. The formation of low-speed streaks and the lift-up of three-dimensional (3D) waves (which is the same as soliton-like coherent structures in the boundary layer) upstream of the puff are observed in a pipe flow using timeline visualizations. The instantaneous vorticity deviation criterion reveals hairpin vortices surrounding 3D waves within the flow field. Vortex formation consistently follows 3D wave development, with the spatial delay influenced by the wave amplitude. The effects of the Reynolds number on the turbulence dynamics are assessed.

关键词： Reynolds number

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Internal structures of turbulent spots

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PHYSICS OF FLUIDS 2025年第2期37卷

作者： Hu, Ning Du, Bingyin Lee, Cunbiao Peking Univ State Key Lab Turbulence & Complex Syst Coll Engn Beijing Peoples R China

The evolution of turbulent spots over a flat plate is investigated using time-resolved tomographic particle image velocimetry. Timelines and material surfaces are used to visualize flow structures within the turbulent spots. The results reveal soliton-like coherent structures within the spots that act as three-dimensional (3D) waves, inducing wave-like peaks on material surfaces. The lift-up of these 3D waves and the downward movement of the surrounding fluid form high-shear layers, which serve as precursors to vortices at the edges of the turbulent spots. These findings suggest that 3D waves may serve as the fundamental structures of turbulent spots and play a dominant role in their development.

关键词： Shear flow

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MKDFusion: modality knowledge decoupled for infrared and visible image fusion

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APPLIED INTELLIGENCE 2025年第7期55卷 1-25页

作者： Zhang, Yucheng Ma, You Chai, Lin Southeast Univ Minist Educ Key Lab Measurement & Control Complex Syst Engn Nanjing 210096 Peoples R China

The purpose of infrared and visible fusion is to integrate useful information from both infrared and visible images into a single image. The fused image should possess rich texture details and salient target information of the two images. Current image fusion algorithms primarily face two limitations: 1) The lack of decoupling between modality-agnostic and modality-specific knowledge during the feature extraction stage hinders the alignment of modality-agnostic knowledge and the differentiation of modality-specific knowledge. 2) The interaction between modality features is not sufficiently explored in the feature fusion stage, which inhibits the exploitation of complementary information. To address the above challenges, we propose a Modality Knowledge Decoupled (MKD) module in the feature extraction stage and a Cross-Modality Mamba Fusion (CMF) module in the feature fusion stage. In MKD, we first utilize a dual-branch network to extract modality-agnostic and modality-specific knowledge separately. Then, a pair of Knowledge Discriminators (KD) is constructed to minimize inter-modality irrelevant knowledge and maximize inter-modality relevant knowledge. In CMF, the interactions between different modality knowledge are learnt in a hidden state space, which not only reduces the inter-modality knowledge differences but also enhances the texture information of the image. Experiments on three datasets demonstrate that our method outperforms existing methods, highlighting less salient targets and texture information more effectively. In addition, MKDFusion has demonstrated excellent generalization performance and enormous potential in high-level vision tasks in medical image fusion and object detection applications. The code is available at https://***/SEU-ZYC/MKDFusion.

关键词： Image fusion

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Leveraging multiple control codes for aspect-controllable related paper recommendation

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INFORMATION PROCESSING & MANAGEMENT 2025年第1期62卷

作者： Long, Kehan Li, Shasha Tang, Jintao Wang, Ting Natl Univ Def Technol Sch Comp Changsha 410000 Peoples R China Natl Univ Def Technol Key Lab Software Engn Complex Syst Changsha 410000 Peoples R China

Aspect-Controllable Related Papers Recommendation (ACRPR) aims to satisfy users' finegrained needs for specific aspects when finding related papers. Existing approaches rely on the segmentation of texts or aspects to independently learn multi-aspect representations of papers. However, different aspects of a paper are guided by its overall theme and interconnected with intrinsic relevance. In light of this, we propose a simple yet effective ACRPR framework called mCTRL, which leverages multiple control codes in Transformer to simultaneously learn multiple aspect-specific paper representations. Specifically, mCTRL incorporates a [CLS] control code to capture the overall theme and multiple [ASP] control codes to exploit fine-grained aspect information. Additionally, we introduce a hierarchical loss function to balance the overall theme and various aspects of a paper, enabling their mutual enhancement and alignment. Extensive comparative experiments on real-world datasets demonstrate the superiority of our proposed method over previous state-of-the-art approaches. Evaluations are conducted on 5 backbone models and 5 dimensions, which confirm the generalization ability of mCTRL. Moreover, ablation studies and further analyses prove the effectiveness and efficiency of mCTRL and the specialization across aspects of generated embeddings.

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Self-organized oblique waves upstream of the leading edge of a flat plate

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PHYSICS OF FLUIDS 2025年第2期37卷

作者： Yang, Congrui Feng, Zhenghao Lee, Cunbiao Peking Univ Coll Engn State Key Lab Turbulence & Complex Syst Beijing 100871 Peoples R China

In this paper, for the first time, we report the formation of self-organized oblique waves upstream of the leading edge of a flat plate. The flow structures are identified by a reflection method and a refraction method via the visualization of water waves. The results show that the interaction of oblique waves leads to the deformation of two-dimensional waves. The oblique waves propagate upstream from the leading edge at all flow velocity cases. As the flow velocity increases, the angle between the oblique waves and the leading edge decreases.

关键词： Water waves

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A fourth-order compact finite volume method on unstructured grids for simulation of two-dimensional incompressible flow

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JOURNAL OF COMPUTATIONAL PHYSICS 2025年 520卷

作者： Wen, Ling Yang, Yan-Tao Cai, Qing-Dong Peking Univ Coll Engn Dept Mech & Engn Sci State Key Lab Turbulence & Complex Syst Beijing 100871 Peoples R China

This paper introduces a novel and efficient compact reconstruction procedure for high-order finite volume methods applied to unstructured grids. In this procedure, we establish a set of constitutive relations that ensure the continuity of the reconstruction polynomial and its normal derivatives between adjacent elements at control points. The paper delves into the details of the fourth-order compact reconstruction method specifically designed for two-dimensional triangular grids. This method can be considered an extension of the one-dimensional compact scheme and cubic spline interpolation methods to two-dimensional triangular unstructured grids. In the cubic polynomial reconstruction, a two-dimensional cubic polynomial is reconstructed using the cell averages of elements in the standard stencil and the function values at control points. The determination of function values at control points is achieved by adhering to the constraint of normal derivative continuity. This reconstruction is solved using a relaxation iteration method and has been verified to be solvable for triangular grids. Compared to other fourth-order implicit compact polynomial reconstructions, our method requires solving a smaller number of unknowns, which means less computational cost in reconstruction. By applying this method to solve the Poisson equation, the linear convection equation, and incompressible flow benchmarks, it demonstrates that the proposed method exhibits the expected high-order accuracy and performs well in incompressible flow problems.

关键词： Unstructured triangular grids Finite volume method High order Compact reconstruction Incompressible flow

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Elastic sheets on Winkler foundations: Indentation stiffness and nonlinearities

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INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES 2025年 315卷

作者： Chen, Erteng Dai, Zhaohe Peking Univ Coll Engn Dept Mech & Engn Sci State Key Lab Turbulence & Complex Syst Beijing 100871 Peoples R China

The indentation of thin sheets on Winkler's mattress or elastic foundations offers valuable opportunities to gain quantitative insights into the mechanical properties of both the material and its interface. However, interpreting indentation data is complicated by the interplay of plate bending, sheet pre-tension, and foundation deformation. The challenges are further amplified in recently developed nanoindentation techniques for small-scale systems, such as 2D materials and cell membranes, where indenter size, shape, and foundation nonlinearity have been found to influence the results significantly. Here, we address these challenges by investigating a generalized indentation problem involving a pre-tensioned elastic sheet on a mattress foundation, considering both punch and spherical indenters. By linearizing the F & ouml;ppl-von K & aacute;rm & aacute;n equations and the elastic foundation under small indentation depth, we obtain a set of asymptotic solutions that quantify the effects of pre-tension and indenter geometry on indentation stiffness. These solutions show excellent agreement with numerical solutions in various parameter regimes that we classify. We also discuss sources of nonlinearities arising from the kinematics in sheet stretching and the evolving contact radius in spherical indentation. The results should be of direct use for the nanometrology of layered materials where indentation remains one of the most accessible techniques for characterizing mechanical properties at small scales.

关键词： Thin sheets Elastic foundation Indentation Indenter geometry Pretension

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Adhesion of elastic microbeams on thin deformable substrates

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ENGINEERING FRACTURE MECHANICS 2025年 313卷

作者： Li, Hang Dai, Zhaohe Peking Univ Coll Engn Dept Mech & Engn Sci State Key Lab Turbulence & Complex Syst Beijing 100871 Peoples R China

We revisit the adhesion problem of microbeams by considering thin elastic substrates and longrange interfacial forces, inspired by recent experiments in flexible electronics and micro/nano electromechanical systems (M/NEMS). Previously, this problem has been extensively analyzed for rigid substrates using a Johnson-Kendall-Roberts (JKR) or Griffith-type adhesion criterion, which involves applying a discontinuity condition across the adhesion front as a critical boundary condition. Our study demonstrates that this critical adhesion condition can be qualitatively altered when the substrate deformation is taken into account. We introduce a single parameter to determine when the effect of substrate elasticity should be considered or can be neglected. For structures at small scales, we replace the JKR-type jump conditions with a smoothed interfacial law, specifically the Lennard-Jones potential in this work. We then discuss the small-scale adhesion behavior of microbeams with thin deformable substrates and examine how this behavior transitions back to Griffith-type adhesion as the system's length scale increases. These findings have direct implications for the design and reliability of M/NEMS and microfluidic devices, especially those developed or encapsulated with deformable substrates.

关键词： Adhesion Stiction Thin elastic layer Delamination Van der Waals forces

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Data-Driven Design of Distributed Kalman Filter-Based Fault Diagnosis for Large-Scale systems

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IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS 2025年

作者： Ding, Shuyu Liang, Dingguo Li, Zhuyuan Yang, Ying Peking Univ Coll Engn Dept Mech & Engn Sci State Key Lab Turbulence & Complex Syst Beijing 100871 Peoples R China

This article presents a data-driven distributed Kalman filter (DKF)-based fault diagnosis scheme, which can successfully detect actuator and sensor faults in large-scale dynamic systems, with heterogeneous subsystems interconnected through the directed topological graph. In the developed distributed framework, a local computing model (LCM) is formulated for each individual subsystem. In each LCM, based on the subspace identification method, the data-driven distributed Luenberger observer-based residual generator is constructed for each subsystem using local and neighboring process data. This offers an alternative expression of subsystem dynamics, supporting the design of more practical functions, for example, integrated monitoring and control design. The totally unknown interaction term is decoupled in the local residual, preventing the effect of actuator faults from propagating through the diagnostic network, so that the actuator fault isolation can be realized in each LCM. Then, the local noise covariance matrices are identified, and thus the data-driven DKF-based residual generator is formed, attaining improved detection performance by attenuating the effect of strong noises. Moreover, the adaptive configuration is developed for each subsystem, where the detector does not require retraining for changes in operating points or interconnection parameters, ensuring the continuity of the diagnostic process. Finally, case studies on the hot strip mill process verify the effectiveness and performance of the proposed method.

关键词： Large-scale systems Generators Monitoring Fault diagnosis Fault detection Nickel Kalman filters Estimation Distributed databases Actuators Adaptive system data-driven method distributed fault diagnosis (FD) Kalman filter large-scale system

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A Particle Rearrangement Approach for Optimizing Planar and Surface Particle Distributions in Meshless Particle Methods

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INTERNATIONAL JOURNAL OF COMPUTATIONAL METHODS 2025年

作者： Xu, Haobin Sun, Shuli Peking Univ Coll Engn Dept Mech & Engn Sci State Key Lab Turbulence & Complex Syst R China Beijing Peoples R China Peking Univ Nanchang Innovat Inst Nanchang Key Lab Ind Software Res & Applicat Nanchang 330000 Peoples R China

Particle-based meshless methods are commonly used in fluid dynamics and solid mechanics involving finite deformations, owing to their ability to break through the limitations imposed by mesh topology. Particle distribution usually plays a crucial role in determining the accuracy of simulation results for them. In this study, an error estimation was first conducted to ascertain the requirements for particle distribution necessary for accurate simulations. It was revealed that the sawtooth and chaotic particle distributions can significantly reduce numerical accuracy and even cause numerical instability in simulations. To address this issue, we propose a particle rearrangement approach including a pseudo hydrostatic pressure treatment to achieve body-fitted particles and a geometric smoothing method based on the metric of a point cloud unit to optimize chaotic particle distributions for improved regularity. The particles are iteratively moved according to their proximity to neighboring particles. Notably, the number of particles remains constant throughout the smoothing procedure, neither particles inserted or removed, nor particles overflow or volume expansion. This new approach facilitates the generation of body-fitted and relatively regular planar and surface particle distributions, meeting the requirements for arbitrarily complex shape particle distributions. The effectiveness of this method has been demonstrated through two-dimensional SPH simulations for problems of the flow around a cylinder, dam break, and Taylor-Green vortex.

关键词： Particle method particle distribution error estimation particle rearrangement pseudo hydrostatic pressure body-fitted

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