Institute Of Mechanics,Chinese Academy of Sciences
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A phenomenological model for predicting bedload transport in vegetated channels using near-bed turbulent kinetic energy
No full textAccurate prediction of bedload transport in vegetated riverbeds is critical for wetland protection and ecological restoration. This study develops a novel turbulence-based theoretical model for bedload transport in vegetated flows. The near-bed turbulent kinetic energy (TKE) is derived from the phenomenological theory of turbulence through quantitative analysis of multiscale turbulent eddy structures. For rigid vegetation, the proposed model provides a unified framework for estimating near-bed TKE across diverse configurations, including uniform distribution, patchy clusters, random arrangements with variable diameters, and vertically heterogeneous morphologies, improving upon previous empirical superposition approaches. The predicted near-bed TKE exhibits a robust correlation with measured bedload transport rates compiled from 358 experimental datasets, supporting its validity as a physically meaningful predictor. Following the operators of formulas developed for unvegetated beds, a refined TKE-based bedload transport formulation for vegetated flow is derived using symbolic regression, calibrated on datasets with uniformly distributed cylindrical vegetation. Validation demonstrates that the proposed transport model maintains high accuracy while effectively generalizing to more complex rigid vegetation scenarios. Compared to existing literature models, our formulation shows improved predictive precision and broader applicability
Initiation and motion of rainfall-induced loose fill slope failure: New insights from the MPM
No full textLoose fill slopes are prevalent worldwide, and their failure during rainstorms is frequently documented. While existing studies have primarily focused on the initiation of such failures, the post-failure motion of rainfallinduced loose fill slope failures has rarely been explored. This study addresses this knowledge gap by investigating both the initiation and subsequent motion of rainfall-induced loose fill slope failures. To achieve this goal, a hydro-mechanical coupled MPM model was utilized to back-analyze the catastrophic 1976 Sau Mau Ping landslide in Hong Kong and conduct parametric studies. From an engineering perspective, the contractive behaviour of loose coarse-grained soil, which induces positive excess pore water pressure and leads to Bishop's stress reduction and a drop in strength, is a major factor contributing to this landslide. The entire failure process can be classified into three phases with different failure modes: local slide, global slide, and flow-like slide, closely related to the soil stress path. The computed results closely match the field measurements on various aspects, including the landslide zone, mobilized volume, and runout distance. The parametric studies reveal that the landslide zone, mobilized soil volume, and final runout distance decrease with a lower value of dilation angle and a smaller critical state plastic deviatoric strain. Conversely, in the case of a constant SWRC, there tends to be an overestimation of these parameters. It is therefore important to consider soil contraction and its influence on hydro-mechanical behaviour
Coupled liquid-gas flow over a submerged cylinder: interface topology, wake structure and hydrodynamic lift
No full textWe perform simulations of a two-fluid-structure interaction problem involving liquid-gas flow past a fully submerged stationary circular cylinder. Interactions between the liquid-gas interface with finite surface tension and flow disturbances arising from the cylinder induce a variety of interfacial phenomena and wake structures. We map different interface regimes in a parameter space defined by the Bond number and the submergence depth of the cylinder while keeping the Reynolds (Re) and Weber (We) numbers fixed at 150 and 1000, respectively. The emerging interface features are classified into three distinct regimes: interfacial waves generated by Strouhal vortices, the entrainment of multi-scale gas bubbles and the reduced deformation state. In the interfacial wave regime, we demonstrate that the frequency of transverse interface fluctuations at a specific streamwise location is identical to the vortex shedding frequency. Additionally, the wavelength of interfacial waves is determined by the size of vortex pairs consisting of alternating Strouhal vortices. In the gas entrainment regime at , our bubble-size distributions reveal that the entrained bubbles have sizes ranging from one to two orders of magnitude smaller than the cylinder. These multi-scale bubbles are formed primarily through plunging and surfing breakers at . In contrast, at , smaller bubbles initially emerge from the breakup of a gas finger. Over time, some of these bubbles grow in size through coalescence cascades. The influence of and on gas entrainment is quantified in terms of mean bubble size and count. Lastly, we demonstrate how the deformability of the liquid-gas interface drives the hydrodynamic lift force acting on the cylinder. The net downward lift materializes only in the gas entrainment and reduced deformation regimes due to the broken symmetry of the front stagnation point. While our study focuses on two-dimensional simulations, we also provide insights into the three-dimensional gas entrainment mechanism for one of the extreme cases at
Vortex-induced vibration (VIV) fatigue damage characteristics of submarine multispan pipelines
No full textIn offshore engineering, the free-spanning phenomenon frequently occurs in submarine pipelines. Multiple freespan pipelines are usually susceptible to more severe vortex-induced vibration (VIV) because of interactive effects between adjacent spans, resulting in potential fatigue damage. However, little attention has been given to the VIV fatigue damage characteristics of multispan pipelines. In this work, considering the pipe-sediment interaction, model experiments were carried out on multispan pipelines to investigate the VIV fatigue damage features of double-span and triple-span pipelines. The VIV fatigue damage of the pipeline models was calculated via the S-N curve method and the linear accumulative damage law. The effects of the span ratio, burial depth, and axial tension force on VIV fatigue characteristics were studied in terms of the fatigue damage distribution and maximum fatigue damage. The results indicated that neighboring interactions and pipe-sediment interactions considerably influence VIV fatigue damage in multispan pipelines. The variation in the span ratio significantly affects the fatigue damage distribution of adjacent spans. As the length difference between adjacentspan pipelines increases, the fatigue damage of the longer span greatly intensifies. However, with increasing burial depth, the VIV of the pipeline model decreases, and the fatigue damage is alleviated because the boundary constraint is strengthened. The increasing axial tension force can also somewhat reduce the maximum fatigue damage. Additionally, the suppression effect of the three-start helical strake on the VIV fatigue features of a multispan pipeline was also experimentally studied. The coverage rate of the helical strakes had a pronounced effect on the suppression efficiency. A coverage rate of 75% can have a more effective VIV suppression effect, with the maximum suppression efficiency exceeding 90%
Separator with high ionic conductivity enables electrochemical capacitors to line-filter at high power
No full textLine-filtering electrochemical capacitors (LFECs) are demonstrating advantages in line filtering over traditional electrolytic capacitors. However, they can only function at no-load or low-power conditions due to the limited high-frequency capacitance resulting from the excessive ionic resistance, despite much progress in electrode materials. Here, we show separators dominate both ion migration and capacitance in LFECs. A 3 mu m-thick thread-anchor structured separator is developed, featuring both accelerated ionic transport and reliability, leading to a low ionic resistance of 25 m Omega cm2. With a phase angle of -80 degrees at 120 Hz, the assembled device has an areal capacitance of 6.6 mF cm-2. Furthermore, stack integration in parallel breaks the trade-off between capacitance and frequency response, boosting the areal capacitance by two orders of magnitude without decay of frequency characteristics. The On-board field test demonstrates that voltage ripples are steadily suppressed below 5% even for practical high-power line filtering with a load power density of 2.5 W cm-2, three orders of magnitude higher than previous instances. This work opens up a perspective of separator engineering for the development of high-performance line-filtering electrochemical capacitors and promotes their applications in practical high-power scenarios
Lunar and Martian gravity alter immune cell interactions with endothelia in parabolic flight
No full textReturning to the moon and traveling to Mars represent the main targets of human space exploration missions within the upcoming decades. Comparable to microgravity, partial gravity in these destinations is assumed to dysregulate immune functions, thereby threatening astronauts health. To investigate the impact of partial gravity on immune cell attachment to vessel endothelia, THP-1 cells and HUVEC cell layers were monitored in a flow chamber system during parabolic flight in lunar (0.16 g) or Martian (0.38 g) gravity. Focus was set on floating speed, cell adhesion, surface molecule expression and cytoskeletal reorganization under basal and TNF-induced inflammatory environment. Floating speed of THP-1 cells was increased in partial gravity, which was accompanied by a successively lower adhesion to the endothelial HUVEC cells. Expression levels of the adhesion markers Mac-1 on THP-1 cells as well as ICAM-1 on HUVECs were found elevated in lunar and Martian gravity, which was aggravated by TNF. Analysis of cytoskeletal organization in HUVECs revealed reduced intracellular F-actin microfilament networks and a stronger cell directionality with stress fiber alignment at cell borders in partial gravity, which was intensified by TNF. In summary, altered immune cell - endothelium interactions as quantified in partial gravity conditions show similarities to cellular behavior in microgravity. However, the different magnitudes of effects in dependence of gravitational level still need to be assessed in further investigations
Liquid directional transport surface applied to the spacecraft fluid management system: Fundamentals and prospect analysis
No full textLiquid directional transport surfaces have the ability to control the movement of liquids in specific directions, making them highly applicable in various fields such as heat transfer, fluid management, microfluidics, and chemical engineering. This review aims to summarize the research progress on liquid directional transport surfaces and spacecraft fluid management devices. Among the different liquid control technologies available, certain surface design methods based on principles of fluid dynamics under microgravity show remarkable potential for space fluid management. Precise fluid management is crucial for the in-orbit operation of spacecraft. Utilizing surface tension effects represents the most direct and effective approach to achieve directional liquid transport in space. The intrinsic flow characteristics of the two-dimensional plane of directional transport surfaces are advantageous for managing fluids in the confined spaces of spacecraft. By analyzing the functional characteristics of these liquid directional transport surfaces, we assess their feasibility for integration into spacecraft fluid management devices. Considering the features of the space environment, this review also provides design guidelines for liquid directional transport surfaces suitable for use in spacecraft fluid management devices, serving as a significant reference for future research
Numerical simulation of crack surface contacting behavior with stress-induced martensitic phase transformation in very-high-cycle fatigue regime
No full textA modified kinetic model for the status of stress-induced martensitic phase transformation is developed, and the reliability of the resultant constitutive governing equations is verified by the experimental data of stainless steel AISI 348. Then, a numerical simulation, based on the established constitutive governing equations with martensitic phase transformation, is performed to address the process of microstructure refinement and nanograin formation due to the contact actions at crack surfaces in fine-granular-area (FGA) region in very-high-cycle fatigue (VHCF) process of metallic materials. A correlation between the calculated maximum contact stresses from the numerical model and the observed FGA thickness in experiments is confirmed for the stress ratios of -1, -0.5, 0.1 and 0.3 for a high-strength steel. The simulation results conform well to the FGA formation mechanism of numerous cyclic pressing (NCP) between originated crack surfaces, which causes grain refinement at originated crack wake and therefore induces the formation of FGA in high-strength alloys
Redox Oscillation Enhanced Water-Enabled Electric Generator
No full textThe energy crisis driven by the widespread use of fossil fuels highlights the urgent need for green energy solutions. A variety of green electric generators based on interfacial ion regulation have emerged in recent years. However, conventional electricity generation methods that rely solely on ion movement at interfaces suffer from a rapid decline in electrical signals due to poor ion-electron conversion at the interface. Inspired by the bioelectrical phenomena based on the variations in membrane potential and the glucose oxidation/reduction reactions, a redox oscillation enhanced water-enabled electric generator is herein proposed. The oscillating redox process not only boosts the ion-electron conversion at the interface but also enables the synergy between the non-Faraday current and the Faraday current. As a result, the generator achieves an impressive peak electric output of 1.20 mA cm-2 and 0.41 W m-2 for 60 days, outperforming various water-enabled electric generators. Furthermore, this generator can be integrated into a flexible unit for both portable and large-scale applications. This work presents a novel approach for enhancing the output of green energy devices based on interfacial ion migration
Study on the High-Speed Penetration and Shear Failure Mechanism of Beach Sand
No full textIn this paper, the contact parameters of beach sand are calibrated based on the discrete element method and the optimal design method, and the obtained parameters by calibration are used as input for the angle of repose simulation. The relative error between angle of repose simulation results and experimental results is 3.27%. Based on the penetration and shear tests, simulation models were constructed to study the pressure shear failure mechanism of beach sand under high-speed conditions. The high-speed penetration simulation shows that with the increase of the penetration rate, the influence area of the sinkage plate gradually increases, and the stress of sand particles also increases. When the penetration rate increased from 0.5 m/s to 8 m/s, the pressure on the plate increased 12.7 times, indicating that the bearing capacity of the sand increased significantly with the increase of the penetration rate. The high-speed shear simulation shows that in the stable shear stage, the average shear torque initially increases slightly with the increase of speed, and then decreases significantly when the speed exceeds 4 m/s. This is because as the shear rate increases, the disturbance of the soil by the shear plate increases, the velocity of soil particles increases, resulting in a decrease in the number of soil particles in contact with the shear plate, thereby reducing the shear torque