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Phase-field-based lattice Boltzmann method for containerless freezing

Physical Review E 2024年第3期110卷 035301页

作者： Jiangxu Huang Lei Wang Zhenhua Chai Baochang Shi School of Mathematics and Statistics School of Mathematics and Physics Institute of Interdisciplinary Research for Mathematics and Applied Science Hubei Key Laboratory of Engineering Modeling and Scientific Computing

In this paper we first propose a phase-field model for the containerless freezing problems, in which the volume expansion or shrinkage of the liquid caused by the density change during the phase change process is considered by adding a mass source term to the continuum equation. Then a phase-field-based lattice Boltzmann (LB) method is further developed to simulate solid-liquid phase change phenomena in multiphase systems. We test the developed LB method by the problem of conduction-induced freezing in a semi-infinite space, the three-phase Stefan problem, and the droplet solidification on a cold surface, and the numerical results are in agreement with the analytical and experimental solutions. In addition, the LB method is also used to study the rising bubbles with solidification. The results of the present method not only accurately capture the effect of bubbles on the solidification process, but also are in agreement with the previous work. Finally, a parametric study is carried out to examine the influences of some physical parameters on the sessile droplet solidification, and it is found that the time of droplet solidification increases with the increase of droplet volume and contact angle.

关键词： Drops & bubbles Liquid-solid phase transition

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A multidomain legendre pseudospectral frequency-domain method with penalty scheme for solving Maxwell's equations

A multidomain legendre pseudospectral frequency-domain metho...

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International Conference on Applications of Electromagnetism and Student Innovation Competition Awards

作者： Wang, Chih-Yu Chung, Shih-Yung Teng, Chun-Hao Chen, Chung-Ping Chang, Hung-Chun Graduate Institute of Electronics Engineering Department of Electrical Engineering National Taiwan University Taipei 10617 Taiwan Department of Applied Mathematics Center of Mathematical Modeling and Scientific Computing National Chiao Tung University Hsinchu 30010 Taiwan Department of Electrical Engineering Graduate Institute of Photonics and Optoelectronics National Taiwan University Taipei 10617 Taiwan

ISBN: (纸本)9781424464166

A new multidomain pseudospectral frequency-domain (PSFD) method based on Legendre polynomials with a penalty scheme for studying electromagnetic wave scattering is presented. Scattered field calculation with accuracy on the order of 9 10- is obtained for a circular plasmonic cylinder. The method is further applied to demonstrate the scattering by a dielectric rectangular cylinder with sharp corners and by multiple circular plasmonic cylinders. ©2010 IEEE.

关键词： Plasmonics

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Electromagnetic simulations of 2D optical microring resonators using the multidomain legendre pseudospectral time-domain method

Electromagnetic simulations of 2D optical microring resonato...

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International Conference on Applications of Electromagnetism and Student Innovation Competition Awards

作者： Chung, Shih-Yung Wang, Chih-Yu Teng, Chun-Hao Chen, Chung-Ping Chang, Hung-Chun Graduate Institute of Electronics Engineering Department of Electrical Engineering National Taiwan University Taipei 10617 Taiwan Department of Applied Mathematics Center of Mathematical Modeling and Scientific Computing National Chiao Tung University Hsinchu 30010 Taiwan Department of Electrical Engineering Graduate Institute of Photonics and Optoelectronics National Taiwan University Taipei 10617 Taiwan

ISBN: (纸本)9781424464166

The high-accuracy pseudospectral time-domain (PSTD) method is utilized to simulate electromagnetic responses of two-dimensional (2D) optical microring resonators. Besides its inherent spectral convergence in accuracy, the PSTD method using multidomain approach with curvilinear-quadrilateral subdomain partitioning possesses superior advantage in fulfilling field continuity conditions across material interfaces. And it should provide better results than the FDTD method simulations for optical waveguide resonators involving circular rings since the stair-casing approximation as often employed in the latter is avoided. ©2010 IEEE.

关键词： Electromagnetic simulation

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hN-adaptive spectral element discretization of optimal control problems for environmental applications

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SeMA Journal 2011年第1期53卷 55-69页

作者： Gaudio, L. Quarteroni, A. MOX- Modellistica e Calcolo Scientifico Dipartimento di Matematica “F. Brioschi” Politecnico di Milano Italy CMCS- Chair of Modeling and Scientific Computing Mathematics Institute of Computational Science and Engineering École Polytechnique Fédérale de Lausanne EPFL Switzerland

In this work, we propose an hN adaptive algorithm for optimal control problems whose space discretization is based on the spectral element method. We focus on a special class of problems described by quadratic cost functional and linear advection-diffusion state equation. This model has been employed to forecast and suitably reduce, by an optimization process, the pollutant concentration in air on a specific area of interest. Moreover, a local adaptive algorithm is employed to achieve a desired accuracy on the cost functional by reducing the computational cost of the problem. © 2011, Sociedad Española de Matemática Aplicada.

关键词： advection-diffusion equation hN-adaptive strategies Optimal control problems spectral element methods

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Mechanism reduction for hetero-/homogeneous combustion of syngas over platinum 12

Mechanism reduction for hetero-/homogeneous combustion of sy...

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12th Asia-Pacific Conference on Combustion, ASPACC 2019

作者： Sui, Ran Liang, Wenkai Mantzaras, John Law, Chung K. Department of Mechanical and Aerospace Engineering Princeton University PrincetonNJ08544 United States Laboratory for Scientific Computing and Modeling Paul Scherrer Institute Villigen PSICH-5232 Switzerland Center for Combustion Energy Tsinghua University Beijing100084 China

Detailed catalytic and gas-phase reaction mechanisms were reduced for the hetero-/homogeneous combustion of H2/CO/ O2/N2 mixtures using the directed relation graph (DRG) method. Simulations were performed in a Pt-coated planar channel using a 2-D steady Navier Stokes code with either detailed or reduced catalytic and gas-phase reaction mechanisms for a wide range of operating conditions. Catalytic and gas-phase reaction mechanisms were treated as a unit and reduced together for fuel-lean and low-pressure fuel-rich cases, while reduced separately for high-pressure fuel-rich cases. The reduced mechanisms well reproduced the major gaseous species concentrations, gas temperatures and homogeneous ignition distances obtained with the detailed mechanisms, thus demonstrating the capacity of DRG in reducing combined catalytic/gas-phase reaction mechanisms. As such, it can provide a quick indication of the important reactions and contributions of both reaction pathways prior to simulations, and is of main interest for large scale simulations used for the design and thermal management of practical catalytic combustion systems. © Asia-Pacific Conference on Combustion, ASPACC *** right reserved.

关键词： Fuels

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Homogeneous ignition of H2/CO/O2/N2 mixtures over palladium at pressures up to 8 bar 38th

Homogeneous ignition of H2/CO/O2/N2 mixtures over palladium ...

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38th International Symposium on Combustion, 2021

作者： Sui, Ran Mantzaras, John Law, Chung K. Bombach, Rolf Khatoonabadi, Meysam Paul Scherrer Institute Laboratory for Scientific Computing and Modeling Villigen PSI CH-5232 Switzerland Princeton University Department of Mechanical and Aerospace Engineering Princeton NJ 08544 United States Paul Scherrer Institute Energy System Integration Platform Villigen PSI CH-5232 Switzerland

The catalytic and gas-phase combustion of fuel-lean H2/CO/O2/N2 mixtures over palladium was studied experimentally and numerically at a global equivalence ratio Φ = 0.285, H2/CO volumetric ratios of 1-4, pressures of... 详细信息

The catalytic and gas-phase combustion of fuel-lean H₂/CO/O₂/N₂ mixtures over palladium was studied experimentally and numerically at a global equivalence ratio Φ = 0.285, H₂/CO volumetric ratios of 1-4, pressures of 1-8 bar and catalyst surface temperatures of 950-1200 K. In situ planar laser induced fluorescence (PLIF) of the OH radical was used to monitor homogeneous combustion inside a channel-flow catalytic reactor, while 1-D Raman measurements of main gas-phase species concentrations across the channel boundary layer were conducted to evaluate the heterogeneous processes. Simulations were carried out with a 2-D numerical code using detailed heterogeneous and homogeneous chemical reaction mechanisms and realistic transport. The simulated and measured transverse species profiles attested to a transport-limited catalytic conversion of H₂ and CO at all operating conditions. The OH-PLIF measurements and the simulations confirmed the establishment of appreciable homogeneous combustion only for p < 4 bar, with progressively diminishing gas-phase contribution as the pressure increased from 4 to 8 bar. This strong pressure dependence reflected the complex pressure/temperature dependence of the homogeneous ignition chemistry as well as the competition between the catalytic and gaseous reaction pathways for H₂ and CO consumption. Over the gaseous induction zones, the wall temperatures were below the pressure-dependent upper temperature limit for the decomposition of PdO to metallic Pd. Although palladium catalysts exhibited a “self-regulating” temperature effect due to PdO decomposition, the attained temperatures were still sufficient to ignite homogeneous combustion of the H₂/CO/O₂/N₂ mixtures. This was contrary to hydrocarbon fuels for which gas-phase combustion was largely suppressed over PdO in the pressure range of 1-8 bar. The results suggested that for the elevated p

关键词： Palladium

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Heterogeneous and homogeneous combustion of fuel-lean C3H8/O2/N2 mixtures over rhodium at pressures up to 6 bar 38th

Heterogeneous and homogeneous combustion of fuel-lean C3H8/O...

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38th International Symposium on Combustion, 2021

作者： Mantzaras, John Sui, Ran Law, Chung K. Bombach, Rolf Laboratory for Scientific Computing and Modeling Paul Scherrer Institute Villigen PSI CH-5232 Switzerland Department of Mechanical and Aerospace Engineering Princeton University Princeton NJ 08544 United States Energy System Integration Platform Paul Scherrer Institute Villigen PSI CH-5232 Switzerland

The heterogeneous and homogeneous combustion of C3H8/O2/N2 mixtures over Rh was studied at pressures 1-6 bar, catalyst surface temperatures 680-1100 K and C3H8-to-O2 equivalence ratios 0.25-0.52. Non-intrusive laser-b... 详细信息

The heterogeneous and homogeneous combustion of C₃H₈/O₂/N₂ mixtures over Rh was studied at pressures 1-6 bar, catalyst surface temperatures 680-1100 K and C₃H₈-to-O₂ equivalence ratios 0.25-0.52. Non-intrusive laser-based measurements were applied in a channel-flow catalytic reactor and involved 1-D Raman spectroscopy of major gas-phase species across the channel boundary layer for assessing the catalytic reactivity and planar laser induced fluorescence (PLIF) of the OH radical for monitoring homogeneous combustion. Simulations were performed using a 2-D CFD code with detailed heterogeneous and homogeneous chemical reaction mechanisms. By comparing the Raman-measured and predicted transverse profiles of the limiting C₃H₈ reactant, the suitability of a detailed surface reaction mechanism was initially evaluated and subsequently a one-step reaction was constructed, which was applicable for the C₃H₈ total oxidation over Rh at 1-6 bar. The catalytic reactivity of C₃H₈ over Rh displayed a ∼p^0.14 pressure dependence, which was substantially lower than a previously reported ∼p^0.70 dependence over Pt. The weak pressure dependence of the C₃H₈ reactivity on Rh suggested caution when selecting catalysts for high-pressure power systems (recuperative microreactors, small-scale turbines) fueled with C₃H₈ or LPG. Comparisons of PLIF-measured and predicted distributions of the OH radical indicated that the employed gas-phase reaction mechanism captured the onset of homogeneous ignition at pressures ≥ 3 bar as well as the ensuing flame shapes. Predicted and measured homogeneous ignition distances agreed within 2.5% at 6 bar. With decreasing pressure, the predictions yielded gradually increasing but still modest underpredictions (up to 11.2% at 3 bar) of the homogeneous ignition

关键词： Ignition

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Numerical investigation of light scattering by coupled plasmonic nanospheres using a high-accuracy multidomain Legendre pseudospectral time-domain method

Numerical investigation of light scattering by coupled plasm...

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2011 30th URSI General Assembly and scientific Symposium, URSIGASS 2011

作者： Chung, Shih-Yung Wang, Chih-Yu Teng, Chun-Hao Chen, Chung-Ping Chang, Hung-Chun Graduate Institute of Electronics Engineering National Taiwan University Taipei 10617 Taiwan Department of Applied Mathematics Center of Mathematical Modeling and Scientific Computing National Chiao Tung University Hsinchu 30010 Taiwan Graduate Institute of Electronics Engineering Department of Electrical Engineering National Taiwan University Taipei 10617 Taiwan Department of Electrical Engineering Graduate Institute of Photonics and Optoelectronics National Taiwan University Taipei 10617 Taiwan

ISBN: (纸本)9781424451173

A high-numerical-accuracy multidomain Legendre pseudospectral time-domain (PSTD) method is utilized to study the three-dimensional problem of light scattering by coupled metallic nanospheres and associated plasmonic resonances. With the multidomain technique, the simulation environment is partitioned into curvilinear hexahedral subdomains that well match the geometrical profile and material interfaces, which is an essential treatment to assure numerical accuracy, in particular, in near-field calculations. Cross sections are accurately calculated for studying the effects of different sphere radii and spacings. Interactions between two silver spheres are investigated for different incident wave propagation directions and polarizations. Electric near fields at plasmon resonances are examined. © 2011 IEEE.

关键词： Nanospheres

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Local Precipitation Forecast with LSTM for Greenhouse Environmental Control 1

Local Precipitation Forecast with LSTM for Greenhouse Enviro...

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1st International Conference on Pervasive Artificial Intelligence, ICPAI 2020

作者： Hsieh, Hsing-Chuan Chiu, Yi-Wei Lin, Yong-Xiang Yao, Ming-Hwi Lee, Yuh-Jye National Chiao Tung University Institute of Statistics Hsinchu Taiwan National Chiao Tung University Institute of Mathematical Modeling and Scientific Computing Hsinchu Taiwan Taiwan Agricultural Research Institute Council of Agriculture Executive Yuan Agricultural Engineering Division Taichung Taiwan Academia Sinica Research Center for Information Technology Innovation Taipei Taiwan

ISBN: (纸本)9781665404839

With the rise of AI technology, it can be applied to smart greenhouse. In our research, we design a prevention mechanism against instant heavy rainfall using Long Short-Term Memory (LSTM) networks to forecast the local precipitation at the next hour near the greenhouse. Besides, missing data and imbalanced data issues are also tackled. Our experiments show that linear interpolation is enough to deal with sporadic missing data. Moreover, two approaches of imbalanced data handling can also enhance the performance of our proposed seasonal LSTM models, including oversampling methods which manipulate the imbalanced training data, as well as cost-sensitive learning methods which modify the loss function in some way. Finally, we also provide the reference result for the greenhouse farmers, so as to decide how much trade-off between Recall and Accuracy they can bear. This is done by tuning parameters related to imbalanced data handling techniques. © 2020 IEEE.

关键词： Weather forecasting

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Three-stage GA-LM algorithm for surface roughness parameters formula construction

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Jisuanji Fuzhu Sheji Yu Tuxingxue Xuebao/Journal of Computer-Aided Design and Computer Graphics 2015年第11期27卷 2192-2200页

作者： Liu, Xinru Liu, Shengjun Tang, Jinyuan Zhou, Wei Institute of Engineering Modeling and Scientific Computing School of Mathematics and Statistics Central South University Changsha410083 China State Key Laboratory of High Performance Complex Manufacturing Central South University Changsha410083 China

Based on the function approximation theory, the formulas for calculating surface roughness parameters are obtained by optimizing the coefficients of the function template. At first, a global approximate solution set is obtained by optimizing the initial function template using genetic algorithm. Then, the set is taken as the initial value of Levenberg-Marquardt (LM) algorithm to obtain the better local optimal solution set, and the two algorithms are used in turn until the solutions are convergent or the largest switching times are reached. At last, according to the convergence precision of the solutions and the value of each monomial, the growth or trim operation is conducted on the function template, and the two optimization algorithms are executed again;until the termination conditions are satisfied. The numerical simulation examples show the algorithm has the better ability to find the optimal solution and the good robustness. Moreover, the method is easy to carry out, and can be used in engineering practice. ©, 2015, institute of computing Technology. All right reserved.

关键词： Genetic algorithms

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