Acta Mechanica Sinica最新文献

{"title":"A new method for simultaneous measurement of flow velocity and temperature using phosphorescent particle tracking velocimetry","authors":"Rong Tian \u0000 (,&nbsp;),&nbsp;Yang Xu \u0000 (,&nbsp;),&nbsp;Yichen Zhu \u0000 (,&nbsp;),&nbsp;Yi Xu \u0000 (,&nbsp;),&nbsp;Jinjun Wang \u0000 (,&nbsp;)","doi":"10.1007/s10409-025-24691-x","DOIUrl":"10.1007/s10409-025-24691-x","url":null,"abstract":"<div><p>This study combines particle tracking velocimetry and thermographic phosphor thermometry to develop a new method for simultaneously measuring the flow field velocity and temperature based on the decay lifetime of phosphor particles. In this method, phosphor particles are used as tracer particles. Velocity is measured by tracking the position of the phosphor particles, and temperature is determined by obtaining the decay lifetime from multi-frame tracking of the particles’ luminescence information, achieving instantaneous and simultaneous measurements. This paper analyzes the influence of the intensity characteristics of the phosphor particles and the number of frames used in particle tracking on the temperature measurement precision. The findings indicate that using the mean intensity from a local window of the particle to calculate the temperature yields higher precision than the maximum intensity. Furthermore, increasing the number of frames used for particle tracking within a specified range enhances the precision of the temperature measurement. Calibration results over a temperature range of 20 °C–180 °C show that the uncertainty of the phosphorescence decay slope constant is 3.5%–4.4%, indicating high-precision temperature measurements. Finally, the proposed method is experimentally validated by capturing the instantaneous velocity and temperature field of a cold jet flow. Based on the simultaneous measurement results, the turbulent heat flux of the flow field is determined, revealing that the heat exchange is most intense near the jet shear layer. These results confirm the method’s feasibility and its potential in studying multi-physics complex flow problems.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 3","pages":""},"PeriodicalIF":4.6,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145169421","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Rate dependent fracture of hydrogels: from small to large-scale swelling","authors":"Yan Yang \u0000 (,&nbsp;),&nbsp;Tongqing Lu \u0000 (,&nbsp;),&nbsp;Tiejun Wang \u0000 (,&nbsp;)","doi":"10.1007/s10409-025-25166-x","DOIUrl":"10.1007/s10409-025-25166-x","url":null,"abstract":"<div><p>When a cracked hydrogel sample immersed in water is stretched, a swelling zone near the crack tip emerges. Within the swelling zone, water diffusion occurs and swells the hydrogel. Outside the swelling zone, water diffusion is negligible, and the material behaves like an incompressible elastomer. Since water diffusion is a time-dependent process, the size of the swelling zone changes with time. As time evolves, the size of the swelling zone grows until to the size of the hydrogel sample. There exists a competition between the size of the swelling zone and the size of the hydrogel sample, which results in complex rate-dependent fracture behavior of hydrogel. In this article, the competition effect is studied theoretically and numerically. We find that the hydrogel undergoes three stages gradually: small-scale swelling, large-scale swelling, and equilibrium as the size of the swelling zone approaches the size of the hydrogel sample. In the stage of small-scale swelling, the first invariant of stretch at the notch tip <i>I</i>_1notch increases with the decrease of the stretch rate. In the stage of large-scale swelling, <i>I</i>_1notch increases first and then decreases with the decrease of stretch rate. In the stage of equilibrium, the effect of water diffusion is negligible, and <i>I</i>_1notch is independent of stretch rate. This work reveals the connection between the stretch rate, the size of the swelling zone, and the crack tip quantity <i>I</i>_1notch, which is used to establish the fracture criterion and predict rate-dependent fracture of hydrogel. Particularly, the previous works on different trends of rate-dependent behavior of hydrogel can be unified in this work, when both small-scale swelling and large-scale swelling are considered.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"41 7","pages":""},"PeriodicalIF":4.6,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145169978","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Wake instability of a fixed spherical droplet with a high drop-to-fluid viscosity ratio","authors":"Pengyu Shi \u0000 (,&nbsp;),&nbsp;Éric Climent,&nbsp;Dominique Legendre","doi":"10.1007/s10409-025-25253-x","DOIUrl":"10.1007/s10409-025-25253-x","url":null,"abstract":"<div><p>Direct numerical simulations of a uniform flow past a fixed spherical droplet are performed to investigate the parameter range within which the axisymmetric flow becomes unstable due to an external flow bifurcation. The hydrodynamics is governed by three dimensionless parameters: the viscosity ratio <i>μ</i>*, the external Reynolds numbers <i>Re</i>^e, and internal Reynolds numbers <i>Re</i>ⁱ, respectively. The drop-to-fluid density ratio is related to these parameters as <i>ρ</i>* = <i>μ</i>*<i>Re</i>ⁱ/<i>Re</i>^e. This study focuses on highly viscous droplets with <i>μ</i>* ≥ 5, where wake instability is driven by the vorticity flux transferred from the droplet surface into the surrounding fluid. By analysing the wake structure, we confirm that the onset of the external bifurcation is linked to the tilting of the azimuthal vorticity <i>ω</i>_<i>ϕ</i>, in the wake and that the bifurcation occurs once the isocontours of <i>ω</i>_<i>ϕ</i> align nearly perpendicular to the symmetry axis. We propose an empirical criterion for predicting the onset of the external bifurcation, formulated in terms of the maximum vorticity on the external side of the droplet surface. This criterion is applicable for sufficiently high <i>Re</i>ⁱ and holds over a wide range of <i>μ</i>* and <i>Re</i>^e. Additionally, we examine the bifurcation sequence for two specific external Reynolds numbers, <i>Re</i>^e = 300 and <i>Re</i>^e = 500, and show that, beyond a critical viscosity ratio, the axisymmetric wake first transitions to a steady planar-symmetric state before undergoing a secondary Hopf bifurcation. Finally, we highlight the influence of <i>Re</i>ⁱ on external bifurcation and show that, at moderate <i>Re</i>ⁱ, wake instability may set in at a lower vorticity threshold than predicted by our criterion. These findings provide new insights into the external flow bifurcation of viscous droplets.</p></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"41 7","pages":""},"PeriodicalIF":4.6,"publicationDate":"2025-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145168697","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cluster globally, model locally: clusterwise modeling of nonlinear dynamics","authors":"Nan Deng \u0000 (,&nbsp;),&nbsp;Bernd R. Noack,&nbsp;Luc R. Pastur,&nbsp;Guy Y. Cornejo Maceda,&nbsp;Chang Hou \u0000 (,&nbsp;)","doi":"10.1007/s10409-024-24545-x","DOIUrl":"10.1007/s10409-024-24545-x","url":null,"abstract":"<div><p>Data-driven reduced-order modeling opens new avenues of understanding, predicting, controlling, and optimizing system behavior. Simple systems may have state spaces in which sparse human-interpretable dynamical systems can be identified. This approach has been pioneered by Brunton et al. (2016, PNAS) with sparse identification of nonlinear dynamics. Complex systems, however, cannot be expected to benefit from such simple analytical descriptions. Yet, smoothness may be exploited by analytical local descriptions. In this paper, we identify a clusterwise polynomial dynamics from time-resolved snapshot data. The full state space is partitioned into clusters with a reduced-order polynomial description for each cluster and a global patching strategy. The resulting clusterwise modeling is entirely data-driven and requires no prior knowledge of the system dynamics. We illustrate the approach on the well-known chaotic Lorenz and Rössler systems, on the more challenging chaotic fluid flow dynamics of higher state-space dimensions, on a noisy electrocardiogram signal, and finally on the time evolution of the monthly sunspot number. Clusterwise modeling offers a powerful and interpretable paradigm for dynamical modeling. Nonlinear dynamics can be approximated by assembling many simple local models of different resolutions, opening new paths to understand and control intricate nonlinearities.</p></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"41 8","pages":""},"PeriodicalIF":4.6,"publicationDate":"2025-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145144261","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New insights into cloud cavitation noise spectrum","authors":"Xincheng Wang \u0000 (,&nbsp;),&nbsp;Mingtai Song \u0000 (,&nbsp;),&nbsp;Huaiyu Cheng \u0000 (,&nbsp;),&nbsp;Bin Ji \u0000 (,&nbsp;),&nbsp;Mohamed Farhat","doi":"10.1007/s10409-025-25186-x","DOIUrl":"10.1007/s10409-025-25186-x","url":null,"abstract":"<div><p>Cloud cavitation induces intense underwater radiation noise, with complex spectral characteristics that remain insufficiently understood. This study explores the underlying mechanisms through experiments and simulations on a twisted hydrofoil. Beyond the well-known harmonic tones linked to cavity shedding frequency, two key spectral characteristics were identified: a series of lock-in frequency features and a consistent high-frequency decay rate. Experimental and numerical results reveal that tunnel acoustic modes and hydrofoil structural modes contribute to the lock-in features at their respective natural frequencies, while the collapse of cascaded microscale bubbles drives the regular high-frequency noise decay at a rate of −4 dB/octave. These findings contribute to a deeper understanding of cloud cavitation noise, and provide valuable insights for modifying existing cavitation noise prediction models.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 4","pages":""},"PeriodicalIF":4.6,"publicationDate":"2025-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145166892","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Prediction of mechanical properties of cross-linked polymer interface by graph convolution network","authors":"Xintianyang Wang \u0000 (,&nbsp;),&nbsp;Lijuan Liao \u0000 (,&nbsp;),&nbsp;Chenguang Huang \u0000 (,&nbsp;),&nbsp;Xianqian Wu \u0000 (,&nbsp;)","doi":"10.1007/s10409-024-24627-x","DOIUrl":"10.1007/s10409-024-24627-x","url":null,"abstract":"<div><p>Machine learning models have made significant advances in the establishment of structure-property relationships. However, it is still a challenge to predict the mechanical properties of the adhesive interface due to the complexity and randomness of the polymer topologies. In this paper, we employed a graph convolutional network (GCN) model to predict the mechanical properties of a specific cross-linked polymer interfacial system, including yield strength (<i>σ</i>_<i>y</i>), ultimate strength (<i>σ</i>_<i>u</i>), failure strain (<i>ε</i>_<i>u</i>), and fracture toughness (<i>Γ</i>) utilizing molecular dynamics simulations. The results showed that the adopted GCN model can predict the mechanical properties with over 88% accuracy. Furthermore, the prediction performances for <i>ε</i>_<i>u</i> and <i>σ</i>_<i>u</i> are better than those for <i>Γ</i> and <i>σ</i>_<i>y</i>, with <i>R</i>² ∼ 0.73 for <i>ε</i>_<i>u</i>, <i>R</i>² ∼ 0.64 for <i>σ</i>_<i>u</i>, <i>R</i>² ∼ 0.51 for <i>Γ</i>, and <i>R</i>²<i>∼</i> 0.43 for <i>σ</i>_<i>y</i>. It is worth noting that the GCN model with the sum aggregator slightly outperforms that with the mean aggregator, and that models with linear regression and fully connected neural network regression provide similar predictions. The influence of input node features on prediction performance was also investigated. It was observed that the node closeness centrality is an important graph parameter in prediction. Specifically, node closeness centrality presents a more significant influence on the global mechanical properties of the adhesive interface, such as <i>ε</i>_<i>u</i>, <i>σ</i>_<i>u</i>, and <i>Γ</i>. Additionally, sensitivity analysis demonstrated that appropriate hyperparameters can improve computational efficiency without losing accuracy on a restricted set of data. This paper demonstrated the capacity of the GCN model to predict the mechanical properties of the adhesive interface with diverse topologies and provided a possible pathway for improving the mechanical properties of the adhesive interface by tailoring polymer structures in the future.\u0000</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 3","pages":""},"PeriodicalIF":4.6,"publicationDate":"2025-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145168112","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dynamics of molten droplet/pool fusion in additive manufacturing","authors":"Zhiyuan Niu \u0000 (,&nbsp;),&nbsp;Chengming He \u0000 (,&nbsp;),&nbsp;Zhengmao Yang \u0000 (,&nbsp;),&nbsp;Zhixia He \u0000 (,&nbsp;)","doi":"10.1007/s10409-025-25020-x","DOIUrl":"10.1007/s10409-025-25020-x","url":null,"abstract":"<div><p>This mini-review first clarifies a very basic process of the fusion-solidification between molten droplet/pool in additive manufacturing (AM) from its technical principle and various experimental observations on the material defects, such as porosity, separation and splashing, erosion and surface concave, and balling effects. Then, the dynamical similarities between the droplet/pool coalescence at normal temperature and the molten droplet/pool fusion at high temperature are illustrated to reveal the fusion-solidification-induced mechanism of material defects, where the droplet/pool fusion phenomena in the early stage have significant influences on the solidification of molten pool in the late stage for the AM process. Finally, some thoughts on the modeling of the fusion-solidification process between molten droplet/pool are stated by referring to the droplet-pool dynamics, which is benefit to the Eulerian-Lagrangian simulation on the prediction of AM process, so as to change the traditional trial-and-error methodology and improve the manufacturing technique.\u0000</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 3","pages":""},"PeriodicalIF":4.6,"publicationDate":"2025-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145167016","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Development of a novel electrotaxis tweezer for enhancement of droplet manipulation","authors":"Mohammad Amin Mohammadi,&nbsp;Yousef Hojjat,&nbsp;Mohammad Reza Karafi,&nbsp;Behzad Ghavami Namin","doi":"10.1007/s10409-025-24923-x","DOIUrl":"10.1007/s10409-025-24923-x","url":null,"abstract":"<div><p>Electrotaxis, a method that utilizes an electric field to direct the motion of particles or droplets, typically involves a droplet on a flat surface being guided by an electrically charged tweezer above it. Traditional electrotaxis methods have relied on voltages over 1.5 kV for droplet control, but this has several disadvantages, such as high voltage demands, the danger of electric discharge to the droplet, possible adhesion of the droplet to the tweezer, and issues with droplet oscillation and overshoot, which impede its broader application. The present study proposes an innovative tweezer design that not only operates at reduced voltages but also reduces droplet oscillation relative to traditional tweezers. This tweezer features a coaxial tubular sheath encircling the electrode, which modifies the electric field’s influence on the droplet. Numerical simulations were employed to obtain the tweezer’s ideal dimensions and shape. The empirical evidence indicates that the new tweezer can adeptly steer droplets at a markedly lower voltage of 620 V, ensuring a more stable trajectory and significantly diminishing overshoot. The tweezer’s distinctive design also decreases the possibility of electric discharge to the droplet, thus improving the safety of the system for managing delicate droplets. In the experiment, the maximum droplet translation speed attained was 105 mm/s at an applied voltage of 1.2 kV. This represents a 29.6% increase in speed and a 70% decrease in the required voltage compared to the previously highest reported droplet speed.</p></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"41 8","pages":""},"PeriodicalIF":4.6,"publicationDate":"2025-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145143833","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Some topics on Nanofluid Mechanics and Heat Transfer","authors":"Dia Zeidan,&nbsp;Xinliang Li,&nbsp;Eric Goncalves,&nbsp;Jochen Merker","doi":"10.1007/s10409-025-25515-x","DOIUrl":"10.1007/s10409-025-25515-x","url":null,"abstract":"","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"41 6","pages":""},"PeriodicalIF":4.6,"publicationDate":"2025-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145166594","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Surprises due to new elastoplastic equations of Prandtl-Reuss type","authors":"Heng Xiao \u0000 (,&nbsp;),&nbsp;Otto Bruhns,&nbsp;Albert Meyers","doi":"10.1007/s10409-025-25087-x","DOIUrl":"10.1007/s10409-025-25087-x","url":null,"abstract":"<div><p>New and perhaps unexpected progress in rate-independent elastoplastic modeling is reported with a unified approach toward simulating widely ranging non-elastic effects of various advanced engineering materials such as metals, shape memory alloys, granular materials, fiber-reinforced composites, as well as crystalline solids, etc. This progress originates from a simple idea of bypassing inherent limitations of usual elastoplastic formulations centered on the notion of yielding. With no reference to any yield criteria, the plastic strain-rate should be induced at all stress levels in a more realistic sense that it is small for stresses within a classical yield surface and becomes appreciable for stresses close to and on this surface. A new and unified flow rule for the plastic strain-rate is then proposed of the same smooth form for all cases of both the stress level and the stress rate. Without imposing the ad hoc simplified conditions introduced in usual Prandtl-Reuss equations, new elastoplastic equations are then established by incorporating such small deviations from realistic behaviors as neglected just by postulating these conditions. It turns out that the new equations are not only essentially simpler in both conceptual and structural formulations, but can automatically as inherent response features incorporate significant effects excluded from usual Prandtl-Reuss equations, such as the yielding and unloading behaviors with smooth transitions, the pseudo-elastic effect with hysteresis loops, the non-elastic recovery during unloading as well as failure effects under either monotone or cyclic loading conditions, etc. Since such effects not only go beyond the scope of usual elastoplastic equations but can be only partially simulated even if augmented constitutive equations are postulated toward further characterizing damaging and fracturing effects resulting from evolving micro-defects and macro-cracks, it may be probably surprising that now the new equations of essentially simpler structure not only can in a unified manner simulate all these effects but also can bypass numerical complexities in integrating various rate constitutive equations of complex structures. New results in treating long-standing issues in a few respects are presented, including (i) the yielding and the unloading behaviors with smooth transitions, (ii) the non-elastic recovery during unloading, (iii) the pseudo-elastic effect as extraordinary Bauschinger effect, (iv) failure effects under monotone and cyclic loading, (v) anisotropic multi-mode failure effects of unidirectional composites, (vi) new formulation of crystal elastoplasticity without involving non-uniqueness and singularity issues, (vii) non-normality effects for non-proportional multi-axial loading cases, and (viii) high efficiency algorithms for simulating multi-axial fatigue effects.\u0000</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"41 7","pages":""},"PeriodicalIF":4.6,"publicationDate":"2025-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145162076","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}