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2022年 第43卷 第2期    刊出日期：2022-02-01

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论文

A station-data-based model residual machine learning method for fine-grained meteorological grid prediction

Chuansai ZHOU, Haochen LI, Chen YU, Jiangjiang XIA, Pingwen ZHANG

2022, 43(2):  155-166.  doi:10.1007/s10483-022-2822-9

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Fine-grained weather forecasting data, i.e., the grid data with high-resolution, have attracted increasing attention in recent years, especially for some specific applications such as the Winter Olympic Games. Although European Centre for Medium-Range Weather Forecasts (ECMWF) provides grid prediction up to 240 hours, the coarse data are unable to meet high requirements of these major events. In this paper, we propose a method, called model residual machine learning (MRML), to generate grid prediction with high-resolution based on high-precision stations forecasting. MRML applies model output machine learning (MOML) for stations forecasting. Subsequently, MRML utilizes these forecasts to improve the quality of the grid data by fitting a machine learning (ML) model to the residuals. We demonstrate that MRML achieves high capability at diverse meteorological elements, specifically, temperature, relative humidity, and wind speed. In addition, MRML could be easily extended to other post-processing methods by invoking different techniques. In our experiments, MRML outperforms the traditional downscaling methods such as piecewise linear interpolation (PLI) on the testing data.



Tunable three-dimensional nonreciprocal transmission in a layered nonlinear elastic wave metamaterial by initial stresses

Zhenni LI, Yize WANG, Yuesheng WANG

2022, 43(2):  167-184.  doi:10.1007/s10483-021-2808-9

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In this work, the three-dimensional (3D) propagation behaviors in the nonlinear phononic crystal and elastic wave metamaterial with initial stresses are investigated. The analytical solutions of the fundamental wave and second harmonic with the quasi-longitudinal (qP) and quasi-shear (qS₁ and qS₂) modes are derived. Based on the transfer and stiffness matrices, band gaps with initial stresses are obtained by the Bloch theorem. The transmission coefficients are calculated to support the band gap property, and the tunability of the nonreciprocal transmission by the initial stress is discussed. This work is expected to provide a way to tune the nonreciprocal transmission with vector characteristics.

Nonlinear dynamics and performance analysis of modified snap-through vibration energy harvester with time-varying potential function

K. DEVARAJAN, B. SANTHOSH

2022, 43(2):  185-202.  doi:10.1007/s10483-022-2812-8

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Vibration energy harvesting has emerged as a promising method to harvest energy for small-scale applications. Enhancing the performance of a vibration energy harvester (VEH) incorporating nonlinear techniques, for example, the snap-through VEH with geometric non-linearity, has gained attention in recent years. A conventional snap-through VEH is a bi-stable system with a time-invariant potential function, which was investigated extensively in the past. In this work, a modified snap-through VEH with a time-varying potential function subject to harmonic and random base excitations is investigated. Modified snap-through VEHs, such as the one considered in this study, are used in wave energy harvesters. However, the studies on their dynamics and energy harvesting under harmonic and random excitations are limited. The dynamics of the modified snap-through VEH is represented by a system of differential algebraic equations (DAEs), and the numerical schemes are proposed for its solutions. Under a harmonic excitation, the system exhibits periodic and chaotic motions, and the energy harvesting is superior compared with the conventional counterpart. The dynamics under a random excitation is investigated by the moment differential method and the numerical scheme based on the modified Euler-Maruyama method. The Fokker-Planck equation representing the dynamics is derived, and the marginal and joint probability density functions (PDFs) are obtained by the Monte Carlo simulation. The study shows that the modified snap-through oscillator based VEH performs better under both harmonic and random excitations. The dynamics of the system under stochastic resonance (SR) is investigated, and performance enhancement is observed. The results from this study will help in the development of adaptive VEH techniques in the future.

Surface effect on band structure of magneto-elastic phononic crystal nanoplates subject to magnetic and stress loadings

Shunzu ZHANG, Qianqian HU, Wenjuan ZHAO

2022, 43(2):  203-218.  doi:10.1007/s10483-022-2806-7

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This paper presents a theoretical model for the size-dependent band structure of magneto-elastic phononic crystal (PC) nanoplates according to the Kirchhoff plate theory and Gurtin-Murdoch theory, in which the surface effect and magneto-elastic coupling are considered. By introducing the nonlinear coupling constitutive relation of magnetostrictive materials, Terfenol-D/epoxy PC nanoplates are carried out as an example to investigate the dependence of the band structure on the surface effect, magnetic field, pre-stress, and geometric parameters. The results show that the surface effect has promotive influence on dispersion curves of the band structure, and the band gaps can be improved gradually with the increase in the material intrinsic length. Meanwhile, the band gaps exhibit obvious nonlinear coupling characteristics owing to the competition between the magnetic field and the pre-stress. By considering the surface effect and magneto-elastic coupling, the open and closed points of band gaps are found when the lattice constant to thickness ratio increases. The study may provide a method for flexible tunability of elastic wave propagation in magneto-elastic PC nanoplates and functional design of high-performance nanoplate-based devices.

Surface deformation-dependent mechanical properties of bending nanowires: an ab initio core-shell model

Ye XIAO, J. SHANG, L. Z. KOU, Chun LI

2022, 43(2):  219-232.  doi:10.1007/s10483-022-2814-6

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An ab initio core-shell model is proposed to evaluate the surface effect in bending nanowires, in which the elastic modulus depends on the surface relaxation and deformation induced by external loading. By using first-principles calculations based on the density functional theory (DFT), the surface and bulk properties are calculated for Ag, Pb, and Si nanowires. The obtained theoretical predictions of the effective Young's modulus of nanowires agree well with the experimental data, which shows that the fixed-fixed nanowire is stiffened and the cantilevered nanowire is softened as the characteristic size of the cross section decreases. Furthermore, the contrastive analysis on the two kinds of nanowires demonstrates that increasing the nanowire aspect ratio would enhance the surface effect. The present results could be helpful for understanding the size effect in nanowires and designing nanobeam-based devices in nanoelectromechanical systems (NEMSs).

Effects of grain boundary on irradiation-induced zero-dimensional defects in an irradiated copper

Jing PENG, Shiyong CUI, Yuanyuan TIAN, Qihong FANG, Jia LI, P. K. LIAW

2022, 43(2):  233-246.  doi:10.1007/s10483-022-2803-5

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Grain boundaries (GBs) can serve as efiective sinks for radiation-induced defects, thus notably influencing the service performance of materials. However, the efiect of GB structures on the zero-dimensional defects induced by irradiation has not been fully elucidated. Here, the evolution of cascade collision in the single-crystal (SC), bicrystalline (BC), and twinned crystalline (TC) copper is studied by atomic simulations during irradiation. The spatial distributions of vacancies and interstitials are closely related to the GB at a certain primary knock-on atom (PKA) energy. Compared with the TC, the BC displays a more obvious segregation of the interstitial atoms near GB, due to the characteristic of the greater interstitial binding energy. The evolution of Frenkel pairs is more sensitive to the change of the GB position in the BC. A more prominent defect annihilation rate is caused by the efiect of the GB than that of the twin boundary (TB). The marked secondary emission phenomenon has been observed in the BC, which promotes the formation of an inverted pagoda-like defect distribution. There are similar sub-conical defect distributions and microstructures induced by cascade collision in the TC and the SC. It has been found that the influence range of the GB is wider in the BC. Meanwhile, the average flow stress of the irradiated copper is quantitatively calculated by establishing a physical strengthening model. The contribution of vacancy to the average flow stress in the irradiated BC and TC is obvious than that in the SC, due to the formation of many vacancies. This study provides a theoretical basis for further understanding and customization of the metal-based equipment with good radiation resistance.

An adaptive artificial viscosity for the displacement shallow water wave equation

Keqi YE, Yuelin ZHAO, Feng WU, Wanxie ZHONG

2022, 43(2):  247-262.  doi:10.1007/s10483-022-2815-7

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The numerical oscillation problem is a difficulty for the simulation of rapidly varying shallow water surfaces which are often caused by the unsmooth uneven bottom, the moving wet-dry interface, and so on. In this paper, an adaptive artificial viscosity (AAV) is proposed and combined with the displacement shallow water wave equation (DSWWE) to establish an effective model which can accurately predict the evolution of multiple shocks effected by the uneven bottom and the wet-dry interface. The effectiveness of the proposed AAV is first illustrated by using the steady-state solution and the small perturbation analysis. Then, the action mechanism of the AAV on the shallow water waves with the uneven bottom is explained by using the Fourier theory. It is shown that the AVV can suppress the wave with the large wave number, and can also suppress the numerical oscillations for the rapidly varying bottom. Finally, four numerical examples are given, and the numerical results show that the DSWWE combined with the AAV can effectively simulate the shock waves, accurately capture the movements of wet-dry interfaces, and precisely preserve the mass.

On the energy conversion in electrokinetic transports

Zhaodong DING, Long CHANG, Kai TIAN, Yongjun JIAN

2022, 43(2):  263-274.  doi:10.1007/s10483-022-2810-7

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Energy conversion in micro/nano-systems is a subject of current research, among which the electrokinetic energy conversion has attracted extensive attention. However, there exist two difierent deflnitions on the electrokinetic energy conversion e–ciency in literature. A few researchers deflned the e–ciency using the pure pressure-driven flow rate, while other groups deflned the e–ciency based on the flow rate with the inclusion of the efiect of the streaming potential fleld. In this work, both deflnitions are investigated for difierent fluid types under the periodic electrokinetic flow condition. For Newtonian fluids, the two deflnitions give similar results. However, for viscoelastic fluids, these two deflnitions lead to signiflcant difierence. The e–ciency deflned by the pure pressure-driven flow rate even exceeds 100% in a certain range of the parameters. The result shows that in the case of viscoelastic flow, it is incorrect to deflne the energy conversion e–ciency by pure pressure-driven flow rate. At the same time, the reason for this problem is clarifled through comprehensive analysis.

Dynamic analysis of geared transmission system for wind turbines with mixed aleatory and epistemic uncertainties

Chao FU, Kuan LU, Y. D. XU, Yongfeng YANG, F. S. GU, Yushu CHEN

2022, 43(2):  275-294.  doi:10.1007/s10483-022-2816-8

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This paper deals with the co-existence of mixed aleatory and epistemic uncertainties in a wind turbine geared system for more reliable and robust vibration analyses. To this end, the regression-based polynomial chaos expansion (PCE) is used to track aleatory uncertainties, and the polynomial surrogate approach (PSA) is developed to treat the epistemic uncertainties. This non-intrusive dual-layer framework shares the same collocation pool, which is extracted from the Legendre series. Moreover, the regression technique has been implemented in both layers to enhance calculation efficiency. Numerical validation is carried out to show the effectiveness of the proposed method. New vibration behaviors of the geared transmission system are observed, and the mechanism behind is discussed in detail. The findings of this paper will contribute to the insightful understanding of such wind turbine geared systems under hybrid uncertainties and are beneficial for the condition monitoring.

Stability of plane-parallel flow of magnetic fluids under external magnetic flelds

P. Z. S. PAZ, F. R. CUNHA, Y. D. SOBRAL

2022, 43(2):  295-310.  doi:10.1007/s10483-022-2813-9

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In this work, we present a theoretical study on the stability of a twodimensional plane Poiseuille flow of magnetic fluids in the presence of externally applied magnetic flelds. The fluids are assumed to be incompressible, and their magnetization is coupled to the flow through a simple phenomenological equation. Dimensionless parameters are deflned, and the equations are perturbed around the base state. The eigenvalues of the linearized system are computed using a flnite difierence scheme and studied with respect to the dimensionless parameters of the problem. We examine the cases of both the horizontal and vertical magnetic flelds. The obtained results indicate that the flow is destabilized in the horizontally applied magnetic fleld, but stabilized in the vertically applied fleld. We characterize the stability of the flow by computing the stability diagrams in terms of the dimensionless parameters and determine the variation in the critical Reynolds number in terms of the magnetic parameters. Furthermore, we show that the superparamagnetic limit, in which the magnetization of the fluids decouples from hydrodynamics, recovers the same purely hydrodynamic critical Reynolds number, regardless of the applied fleld direction and of the values of the other dimensionless magnetic parameters.