Institute Of Mechanics,Chinese Academy of Sciences
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Mass Flow Rate Measurement of Gas-Liquid Two-Phase Flow Using Multi-Sensor Data Fusion and Soft Computing Model
No full textThis article presents a novel method for measuring the mass flow rate of gas-liquid two-phase flow based on the multi-sensor data fusion and soft computing model. A multi-sensor system comprising a throat-extended Venturi tube (TEVT) and a dual-modality electrical sensor (DMES) has been developed for gas-liquid two-phase flow measurement. Soft computing models are employed to address the intricate non-linear mapping between the measurement data and flow parameters. Initially, flow regimes are identified based on the time-domain features of the multi-sensor data using a support vector machine (SVM). Subsequently, mass quality is derived from the multi-differential pressure fluctuations and the eigenvalue sequence of the normalized electrical matrices, employing a hybrid neural network comprising a convolution neural network and a deep neural network (DNN). Ultimately, gas/liquid over-reading (OR) is predicted via extreme gradient boosting (XGBoost) using multi-differential pressure ratios. The gas and liquid mass flow rates are subsequently derived from the preceding results. The proposed method addresses the issue that the parameters measurement of gas-liquid two-phase flow is significantly influenced by the flow regimes, and achieves accurate flow rate measurement under the diverse flow regimes. Experimental validation confirms the method's effectiveness and superior performance compared to conventional approaches
Experimental studies on flow noise interference mechanism of tandem shallow cavities with different spacings at subsonic speeds
No full textRegarding the flow noise interference mechanism of tandem shallow cavities, experimental research on the near-field flow field characteristics and far-field acoustic field characteristics of two cavities of the same size along the flow direction in tandem was carried out. The incoming flow velocity was adjusted from 60 to 80 m/s at the intervals of 5 m/s, which corresponded to Reynolds numbers from 6.6 x 10(5) to 8.8 x 10(5). A spacing distance between the tandem cavities is from 0.25 to 4 times the cavity length. The experimental results show that the variations of all the fluctuation characteristics basically occur below 500 Hz, both for the near-field wall pressure and for the far-field acoustic pressure. When the spacing distance is small, the near-field flow characteristics of the upstream cavity change very little, but the low-frequency broadband pressure fluctuation of the downstream cavity is excited; when the spacing distance is large, the low-order flow-acoustic feedback modes of the upstream cavity are excited, and the intensity of pressure fluctuation in the corresponding characteristic frequency as well as the nearby frequency bands increase significantly, while the intensity of pressure fluctuation in the downstream cavity decreases slightly. This leads to a significant increase in the far-field noise of the tandem cavities below 500 Hz, and the increase is larger in the upstream of the tandem-cavity system than in the downstream
An improved modeling approach for riblet effects based on Reynolds-averaged Navier-Stokes turbulence model
No full textMicro riblet surfaces have demonstrated significant potential for reducing skin-friction drag in turbulent boundary layers, making them attractive candidates for aerodynamic optimization in high-speed transportation. To address the high computational cost arising from the large disparity between riblet scale and engineering scale in numerical simulations, modeling riblet effects in Reynolds-averaged Navier-Stokes (RANS) computations has become an effective strategy. However, existing methods often suffer from excessive mesh sensitivity and overprediction of drag increases for oversized riblets, limiting their engineering applicability. The present study proposes an improved RANS-based modeling approach for simulating riblet effects. The core of the model involves a correction to the boundary condition of the specific dissipation rate (omega), extending a formulation previously introduced by other researchers. The modeling method consists of three key components. First, an empirical relation is established between riblet geometry and the riblet-induced velocity profile shift in the logarithmic region, accounting for variations in the aspect ratio of V-shaped riblets and accurately capturing both drag-reducing and drag-increasing regimes. Second, a boundary correction for omega is developed through numerical experiments to reproduce the velocity profile shift, incorporating a mesh-sensitivity analysis and introducing a correction factor related to grid resolution. Third, a pressure-gradient correction factor is introduced to simulate the influence of adverse pressure gradients on riblet performance. The proposed method is implemented in the OpenFOAM solver and validated through simulations of flat-plate boundary layers and a wind turbine airfoil, demonstrating good agreement with experimental results
In-situ impedance-infrared spectroscopy reveals the role of Br?nsted acid sites in NO reduction during high-concentration NH<sub>3</sub> combustion
No full textThe utilization of carbon-free NH3 gas can be extended from low-concentration environmental applications to high-concentration energy applications. To achieve this, minimizing NO formation while maximizing energy release is essential. In this study, we investigated the catalytic performance of catalysts with different acid site characteristics, including a non-acidic catalyst, CuO-CeO2 supported on TiO2 providing only Lewis acid (LA) sites, and a catalyst with both Br & Oslash;nsted acid (BA) and LA sites at the same active sites. These catalysts were used to examine the synergistic effects of BA and LA sites in NH3 catalytic combustion. Results show that proton transfer at BA sites, where H+ protonates NH3 to form NH+4, stabilizes NH3, reducing reactive NHx intermediates and enhancing NO reduction efficiency by interacting with N2O.In-situ impedance spectroscopy and diffuse reflectance infrared spectroscopy reveal that NH+4 formed on BA sites migrates, interacting with reductive NO species to prevent nitrate decomposition and limit NHx formation. The 18O2 isotope tracing of O species in NO reveals that NH+4 promotes NO conversion to N2 via an internal selective catalytic reduction (i-SCR) mechanism, maintaining NO concentrations below 50 ppm at temperatures below 550 degrees C. Based on this specially designed catalyst, the combination of advanced in-situ analytical techniques and isotopic tracing highlights a crucial pathway for NH+4-mediated NOx reduction at acidic sites. The utilization of carbon-free NH3 gas can be extended from low-concentration environmental applications to high-concentration energy applications, requiring minimized NO formation alongside maximized energy release
In-situ impedance-infrared spectroscopy reveals the role of Br?nsted acid sites in NO reduction during high-concentration NH<sub>3</sub> combustion
No full textThe utilization of carbon-free NH3 gas can be extended from low-concentration environmental applications to high-concentration energy applications. To achieve this, minimizing NO formation while maximizing energy release is essential. In this study, we investigated the catalytic performance of catalysts with different acid site characteristics, including a non-acidic catalyst, CuO-CeO2 supported on TiO2 providing only Lewis acid (LA) sites, and a catalyst with both Br & Oslash;nsted acid (BA) and LA sites at the same active sites. These catalysts were used to examine the synergistic effects of BA and LA sites in NH3 catalytic combustion. Results show that proton transfer at BA sites, where H+ protonates NH3 to form NH+4, stabilizes NH3, reducing reactive NHx intermediates and enhancing NO reduction efficiency by interacting with N2O.In-situ impedance spectroscopy and diffuse reflectance infrared spectroscopy reveal that NH+4 formed on BA sites migrates, interacting with reductive NO species to prevent nitrate decomposition and limit NHx formation. The 18O2 isotope tracing of O species in NO reveals that NH+4 promotes NO conversion to N2 via an internal selective catalytic reduction (i-SCR) mechanism, maintaining NO concentrations below 50 ppm at temperatures below 550 degrees C. Based on this specially designed catalyst, the combination of advanced in-situ analytical techniques and isotopic tracing highlights a crucial pathway for NH+4-mediated NOx reduction at acidic sites. The utilization of carbon-free NH3 gas can be extended from low-concentration environmental applications to high-concentration energy applications, requiring minimized NO formation alongside maximized energy release
A Study of the Correlation Between English Academic Exchanges and Academic Influence
No full textTo measure the international scholarly impact of researchers and institutions and develop effective predictive models, this study assesses the impact of English-language scholarly exchanges (English-language publication opportunities, international collaborations, and international tenure) on academic impact in non-native English-speaking countries through data analysis. Data were obtained from a database of academic exchanges published by a national research institution in China that focuses on science and engineering research, and the English-language exchange records of 1,889 researchers were statistically analyzed. The guiding research questions aimed to explore the extent to which the subcomponents included in English-language academic exchanges affect academic impact, and the correlations and principal component weights among the components. The statistical results show that the degree and frequency of English academic communication significantly impact influence the academic impact of researchers/institutions. An evaluation model of academic impact based on English academic exchanges (English academic publication opportunities, international academic cooperation, and international academic tenure) was further developed, and the weights and contributions of each influential element were characterized using a normalized evaluation index. The evaluation model is of reference significance for optimizing the evaluation of the academic influence of scholars/research institutes from non-native English-speaking countries and enhancing international exchanges. It further provides necessary solutions for sustainable academic innovation
Solving continuum and rarefied flows using differentiable programming
No full textAccurate and efficient prediction of multi-scale flows remains a formidable challenge. Constructing theoretical models and numerical methods often involves the design and optimization of parameters. While gradient descent methods have been mainly manifested to shine in the wave of deep learning, composable automatic differentiation can advance scientific computing where the application of classical adjoint methods alone is infeasible or cumbersome. Differentiable programming provides a novel paradigm that unifies data structures and control flows and facilitates gradient-based optimization of parameters in a computer program. This paper addresses the notion and implementation of the first solution algorithm for multi-scale flow physics across continuum and rarefied regimes based on differentiable programming. The fully differentiable simulator provides a unified framework for the convergence of computational fluid dynamics and machine learning, i.e., scientific machine learning. Specifically, parameterized flow models and numerical methods can be constructed for forward physical processes, while the parameters can be trained on the fly with the help of the gradients that are taken through the backward passes of the whole simulation program, a.k.a., end-to-end optimization. As a result, versatile data-augmented modeling and simulation can be achieved for physics discovery, surrogate modeling, and simulation acceleration. The fundamentals and implementation of the solution algorithm are demonstrated in detail. Numerical experiments, including forward and inverse problems for hydrodynamic and kinetic equations, are presented to demonstrate the performance of the numerical method. The open-source codes to reproduce the numerical results are available under the MIT license
Solving continuum and rarefied flows using differentiable programming
No full textAccurate and efficient prediction of multi-scale flows remains a formidable challenge. Constructing theoretical models and numerical methods often involves the design and optimization of parameters. While gradient descent methods have been mainly manifested to shine in the wave of deep learning, composable automatic differentiation can advance scientific computing where the application of classical adjoint methods alone is infeasible or cumbersome. Differentiable programming provides a novel paradigm that unifies data structures and control flows and facilitates gradient-based optimization of parameters in a computer program. This paper addresses the notion and implementation of the first solution algorithm for multi-scale flow physics across continuum and rarefied regimes based on differentiable programming. The fully differentiable simulator provides a unified framework for the convergence of computational fluid dynamics and machine learning, i.e., scientific machine learning. Specifically, parameterized flow models and numerical methods can be constructed for forward physical processes, while the parameters can be trained on the fly with the help of the gradients that are taken through the backward passes of the whole simulation program, a.k.a., end-to-end optimization. As a result, versatile data-augmented modeling and simulation can be achieved for physics discovery, surrogate modeling, and simulation acceleration. The fundamentals and implementation of the solution algorithm are demonstrated in detail. Numerical experiments, including forward and inverse problems for hydrodynamic and kinetic equations, are presented to demonstrate the performance of the numerical method. The open-source codes to reproduce the numerical results are available under the MIT license
Coupled discrete element-particle analysis of single-wheel and four-wheel off-road vehicle on soft ground
No full textConventional numerical studies on off-road vehicle performance typically focus on single wheel-soil interactions, overlooking the influence of multiple wheels in soft ground. This research introduces a novel continuous-discontinuous element method (CDEM) that couples discrete element models for both block and particle phases to analyze the behavior of a four-wheel off-road vehicle moving through soft soil. The full vehicle's motion is considered. It examines how varying sinkage depths and different soil parameters-such as cohesion and friction-affect the vehicle's forward resistance. The comprehensive analysis reveals key patterns in how soil properties and sinkage depth influence vehicle performance. This study offers valuable insights for improving off-road vehicle design and performance in challenging terrain conditions
Spotting structural defects in crystals from the topology of vibrational modes
No full textBecause of the inevitably disordered background, structural defects are not well-defined concepts in amorphous solids. In order to overcome this difficulty, it has been recently proposed that topological defects can be still identified in the pattern of vibrational modes, by looking at the corresponding eigenvector field at low frequency. Moreover, it has been verified that these defects strongly correlate with the location of soft spots in glasses, that are the regions more prone to plastic rearrangements. Here, we show that the topology of vibrational modes predicts the location of structural defects in crystals as well, including the cases of dislocations, disclinations and Eshelby inclusions. Our results suggest that in crystalline solids topological defects in the vibrational modes are directly connected to the well-established structural defects governing plastic deformations and present characteristics very similar to those observed in amorphous solids