摘要 :
It is well-known that the standard finite element method (FEM) has the disadvantage of 'overly-stiff and could not offer reliable enough solutions. We proposed a novel stabilized node-based smoothed radial point interpolation meth...
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It is well-known that the standard finite element method (FEM) has the disadvantage of 'overly-stiff and could not offer reliable enough solutions. We proposed a novel stabilized node-based smoothed radial point interpolation method (SNS-RPIM) to analyze the free vibration and the behavior of functionally graded magnetoelectro-elastic (FGMEE) devices under mechanical and thermal load, which cured the 'overly-soft' and temporally instability of traditional NS-RPIM. The gradient variance items associated with the field nodes are applied to construct the system stiffness matrix. The detailed numerical study has shown the superiority of the proposed method. SNS-RPIM performs well in solving static magneto-electro-thermo-elastic (METE) multi-physics coupling field problems, which validates the accuracy, convergence of the proposed method. Moreover, SNS-RPIM is less insensitive to mesh distortion than FEM and NS-RPIM. The advantages mentioned above make SNS-RPIM very helpful for the design of the actual intelligent devices.
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To improve the precision in resolving interfacial crack intensity factor of piezoelectric bimaterials in practical engineering, we proposed a cell-based smoothed finite element method (CS-FEM) that simulated the displacement field...
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To improve the precision in resolving interfacial crack intensity factor of piezoelectric bimaterials in practical engineering, we proposed a cell-based smoothed finite element method (CS-FEM) that simulated the displacement field and electric field near the crack tips of piezoelectric bimaterials. The displacement field and electric field at the nodes behind crack tips were extracted and substituted into the extrapolation method of interfacial cracks of out-of-phase anisotropic piezoelectric bimaterials, aiming to solve the interfacial crack intensity factor of transversally isotropic piezoelectric bimaterials. With double-piezoelectric flat-plates containing center cracks as example, we investigated the intensity factors of different materials, loads, cell number and encryption modes. The results were compared with FEM and analytic solutions. Results of numerical cases showed that CS-FEM was computationally simple, precise and reliable and thus was attractive to engineers.
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Recent studies using observations, reanalysis data and climate model simulations documented that 2 m surface air temperature (T2m) has been amplified over the world's hottest and driest Sahara Desert and the Arabian Peninsula, ref...
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Recent studies using observations, reanalysis data and climate model simulations documented that 2 m surface air temperature (T2m) has been amplified over the world's hottest and driest Sahara Desert and the Arabian Peninsula, referred to as desert amplification (DA). This study presents a comprehensive analysis of hourly surface observations, radiosonde measurements, and two latest state-of-the-art reanalysis products for the period 1979-2018 to examine the diurnal and vertical variations of DA and their connections with planetary boundary layer height (PBLH). It focuses on the Arabian Peninsula (AP), where observations are relatively abundant compared to the data scarce Sahara regions. Both observational and reanalysis data show that the diurnal cycle of surface warming rate depends, to some extent, inversely on the magnitude of climatological PBLH, and so DA has a distinct diurnal asymmetry with a stronger warming for a shallower PBLH. Results of upper air profiles reveal that DA is a bottom-heavy warming profile, which maximizes near the surface, decreases quickly with height, and is limited to the lower troposphere (> 700 hPa) and surface. The major PBLH biases could explain, at least partially, some of the diurnal and vertical warming/cooling biases in the reanalyses. These results suggest that besides the surface radiative forcing, the PBLH may play an important role in modulating the diurnal and vertical structure of DA over the AP through heat redistributing via turbulent mixing.
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In this article, a stabilized node-based smoothed radial point interpolation method (SNS-RPIM) was proposed to simulate the magneto-electro-elastic (MEE) structures in hygrothermal environment. The node-based smoothing domains wer...
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In this article, a stabilized node-based smoothed radial point interpolation method (SNS-RPIM) was proposed to simulate the magneto-electro-elastic (MEE) structures in hygrothermal environment. The node-based smoothing domains were constructed based on triangular background elements, and the approximate strain, electric field intensity and magnetic flux density were derived using node-based strain smoothing operation. In the present formulation, the stabilization term related to the gradient variance of the field variables was used to obtain the system stiffness matrices. Then, by using the smoothed Galerkin weak form, discrete equations of the system were established to solve the generalized displacement of the structure. The numerical experiments validated the feasibility of SNS-RPIM for solving hygrothermo-magneto-electro-elastic (HMEE) coupling problems with different hygrothermal loadings and boundary conditions. Results proved that the introduction of the stabilization term made the SNS-RPIM had a 'close-to-exact' stiffness, thereby solving the 'overly-soft' in the traditional node-based smoothed radial point interpolation method (NS-RPIM). SNS-RPIM was in good agreement with the reference solution when using the same fewer nodes as finite element method (FEM), and the errors were much smaller than those of FEM. Moreover, SNS-RPIM performed better than NS-RPIM and FEM when processing distorted meshes. Therefore, the developed method showed great potential in simulating MEE structure in hygrothermal environment. (C) 2020 Elsevier B.V. All rights reserved.
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In recent years, significant progress has been obtained in object detection using Convolutional Neural Networks (CNNs). However, owing to the particularity of Remote Sensing Images (RSIs), common object detection methods are not w...
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In recent years, significant progress has been obtained in object detection using Convolutional Neural Networks (CNNs). However, owing to the particularity of Remote Sensing Images (RSIs), common object detection methods are not well suited for RSIs. Aiming at the difficulties in RSIs, this paper proposes an object detection method based on the Dense Feature Fusion Path Aggregation Network (DFF-PANet). Firstly, for better improving the detection performance of small and medium-sized instances, we propose Feature Reuse Module (FRM), which can integrate semantic and location information contained in feature maps; this module can reuse feature maps in the backbone to enhance the detection capability of small and medium-sized instances. After that, we design the DFF-PANet, which can help feature information extracted from the backbone to be fused more efficiently, and thus cope with the problem of external interference factors. We performed experiments on the Dataset of Object deTection in Aerial images (DOTA) dataset and the HRSC2016 dataset; the accuracy reached 71.5% mAP, which exceeds most object detectors of one-stage and two-stages at present. Meanwhile, the size of our model is only 9.2 M, which satisfies the requirement of being lightweight. The experimental results demonstrate that our method not only has better detection accuracy but also maintains high efficiency in RSIs.
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In this paper, the dynamic response of piezoelectric structures under hygrothermal environment is studied by using cell-based smoothed finite element method (CS-FEM). Ignoring the influence of temperature and moisture on the respo...
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In this paper, the dynamic response of piezoelectric structures under hygrothermal environment is studied by using cell-based smoothed finite element method (CS-FEM). Ignoring the influence of temperature and moisture on the response of elastic matrix, we derive the basic equations of the piezoelectric materials under hygrothermal environment. Then the CS-FEM equations of piezoelectric problem are deduced based on the constitutive equation of the material. The improved Newmark scheme is used to solve the transient response of this problem. Several numerical examples are given to illustrate the advantage of CS-FEM in dealing with piezoelectric materials in hygrothermal environment. Results of this study provides some ideas for the design and manufacture of piezoelectric smart structures in hygrothermal environment.
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To accurately simulate the steady-state responses of a functionally graded piezoelectric structure (FGPS) and cure the "overly-stiff" of finite element method (FEM), the coupled thermal-electrical-mechanical inhomogeneous cell-bas...
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To accurately simulate the steady-state responses of a functionally graded piezoelectric structure (FGPS) and cure the "overly-stiff" of finite element method (FEM), the coupled thermal-electrical-mechanical inhomogeneous cell-based smoothed finite element method (CICS-FEM) is proposed. The gradient smoothing technique is introduced into FEM and a "close-to-exact" stiffness is obtained. Based on the basic theory of FGPS, the thermal field is introduced into the electrical-mechanical coupling field and the multi-physics coupling equations are given in conjunction with the cell-based smoothed finite element method. CICS-FEM is verified with several examples, and there is a satisfactory agreement between the current solution and the reference solution. Therefore, the developed method to solve the steady-state response of FGPS can provide a reference for the design and manufacture of smart devices.
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Investigating the mechanical behavior of composites materials under harsh environments is of great importance. A standard finite element method (FEM) is still one of the main methods to investigate properties and mechanical respon...
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Investigating the mechanical behavior of composites materials under harsh environments is of great importance. A standard finite element method (FEM) is still one of the main methods to investigate properties and mechanical responses of magnetoelectro-elastic (MEE) materials and structures. However, the computational features of FEM lead to some limitations. In this paper, we proposed the cell-based smoothed finite element method (CS-FEM) for superior calculations, in which the strain smoothing technique is introduced into FEM. We showed, that CS-FEM possesses high accuracy, low mesh restriction, much less computational-cost than FEM, and stronger handling ability when encountering strong mesh distortions and large deformations. CS-FEM with modified Newmark scheme was defined to show an effect of the high-temperature environment and mechanical load on the time-dependent responses of MEE structures. The convergence, effectiveness, and efficiency of CS-FEM were validated via the numerical examples for simplified bi-layer transducer and an energy harvester as MEE intelligent structures. Additionally, the transient performance of intelligent structures around Curie temperature was comprehensively discussed. The presented CS-FEM and obtained results can be used for future studies of the coupled multi-physical problems as well as investigations of the accuracy of intelligent structure models subjected to extreme conditions. (C) 2020 Elsevier B.V. All reserved.
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The light fastness of fabrics dyed with natural dyes is not satisfactory, which limits their applications in the textile industry. So far, the detailed photofading mechanism of natural dyes remains unclear. To improve the light fa...
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The light fastness of fabrics dyed with natural dyes is not satisfactory, which limits their applications in the textile industry. So far, the detailed photofading mechanism of natural dyes remains unclear. To improve the light fastness of cotton fabrics dyed with two natural dyes (sodium copper chlorophyllin and gardenia yellow), two additives ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) and sodium citrate were used to treat the dyed cotton fabrics via the dipping-padding method. The performance results showed that both the two additives had good effects on inhibiting the photofading of the dyed fabrics. The photofading mechanism of the two natural dyes was also investigated. The results from 1,1-Diphenyl-2-picrylhydrazyl free radical (DPPH) scavenging assay and cyclic voltammetry tests demonstrated very limited antioxidant properties of the two dyes. Singlet oxygen and hydroxyl radical were detected in the photosensitizing process of the two dyes by electron paramagnetic resonance method. The photo-induced chemiluminescence (PICL) tests confirmed that the color changes of the dyed cotton fabrics were reduced because the reactivities of the two dyes to react with reactive oxygen species were dramatically reduced in the presence of EDTA-2Na and sodium citrate. End products generated in the photofading of the two dyes were detected by high-performance liquid chromatography-mass spectrometry (HPLC-MS). Based on the comprehensive analysis of above results, possible degradation pathways of the two dyes were proposed. The mechanism study in this research may help shed light on proposing universal solutions to the poor light fastness of most natural dyes on cotton.
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A coupled multi-physical cell-based smoothed finite element method (CPCS-FEM) which took account into the coupling effects among elastic, electric, magnetic and thermal fields was proposed to investigate the static behavior of fun...
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A coupled multi-physical cell-based smoothed finite element method (CPCS-FEM) which took account into the coupling effects among elastic, electric, magnetic and thermal fields was proposed to investigate the static behavior of functionally grade magneto-electro-elastic (FG-MEEs) structures under thermal conditions. The proposed CPCS-FEM integrating the standard FEM with gradient smoothing possessed many important features and properties, including the simplified computation (the process of calculating shape functions derivatives was replaced by computing outward normal); arbitrary element shape usage; strong mesh distortion and large deformation issues handling ability. The accuracy, convergence and effectiveness of CPCS-FEM were verified through several numerical examples. With CPCS-FEM the temperature influence on generalized displacements (w- and v- direction displacement components U-w and U-v, electric potential Phi and magnetic potential phi) of FGMEEs structures were explored. The effect of the index factor was simulated through a comparative study. This study offers an efficient technique to model the complex multi-physical problem, and the simulation results can significantly contribute to enhancing the performance and applicability of MEE-based intelligence structures under thermal conditions.
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