Gesture recognition is a popular technology in the field of computer vision and an important technical mean of achieving human-computer interaction. To address problems such as the limited long-range ...feature extraction capability of existing dynamic gesture recognition networks based on convolutional operators, we propose a dynamic gesture recognition algorithm based on spatial pyramid pooling Transformer and optical flow information fusion. We take advantage of Transformer’s large receptive field to reduce model computation while improving the model’s ability to extract features at different scales by embedding spatial pyramid pooling. We use the optical flow algorithm with the global motion aggregation module to obtain an optical flow map of hand motion, and to extract the key frames based on the similarity minimization principle. We also design an adaptive feature fusion method to fuse the spatial and temporal features of the dual channels. Finally, we demonstrate the effectiveness of model components on model recognition enhancement through ablation experiments. We conduct training and validation on the SCUT-DHGA dynamic gesture dataset and on a dataset we collected, and we perform real-time dynamic gesture recognition tests using the trained model. The results show that our algorithm achieves high accuracy even while keeping the parameters balanced. It also achieves fast and accurate recognition of dynamic gestures in real-time tests.
Accurate tritium transport properties of prospective tritium permeation barriers (TPBs) are essential to tritium systems in fusion reactors. By passing a temperature and rate-controlled sweeping gas ...over specimen surfaces to carry the permeated tritium to an ion chamber, the gas-driven permeation of tritium has been performed on 321 type stainless steel containers with Al2O3/FeAl barriers, to determine the T-permeation resistant performance and mechanism of the barrier. The tritium permeability of the Al2O3/FeAl coated container was reduced by 3 orders of magnitude at 500–700 °C by contrast with that of the bare one, which meets the requirement of the tritium permeation reduction factor (PRF) of TPBs for tritium operating components in the CN-HCCB TBM. The Al2O3/FeAl barrier resists the tritium permeation by the diffusion in the bulk substrate at a limited number of defect sites with an effective area and thickness, suggesting that the TPB quality is a very important factor for efficient T-permeation resistance.
•T-permeation has been measured on bare and coated type 321 SS containers.•Al2O3/FeAl coating give a reduction of T-permeability of 3 orders of magnitude.•Mechanism of Al2O3/FeAl barrier resisting T-permeation has obtained.•Quality of TPB is a very important factor for efficient T-permeating reduction.
Gait recognition is one of the important research directions of biometric authentication technology. However, in practical applications, the original gait data is often short, and a long and complete ...gait video is required for successful recognition. Also, the gait images from different views have a great influence on the recognition effect. To address the above problems, we designed a gait data generation network for expanding the cross-view image data required for gait recognition, which provides sufficient data input for feature extraction branching with gait silhouette as the criterion. In addition, we propose a gait motion feature extraction network based on regional time-series coding. By independently time-series coding the joint motion data within different regions of the body, and then combining the time-series data features of each region with secondary coding, we obtain the unique motion relationships between regions of the body. Finally, bilinear matrix decomposition pooling is used to fuse spatial silhouette features and motion time-series features to obtain complete gait recognition under shorter time-length video input. We use the OUMVLP-Pose and CASIA-B datasets to validate the silhouette image branching and motion time-series branching, respectively, and employ evaluation metrics such as IS entropy value and Rank-1 accuracy to demonstrate the effectiveness of our design network. Finally, we also collect gait-motion data in the real world and test them in a complete two-branch fusion network. The experimental results show that the network we designed can effectively extract the time-series features of human motion and achieve the expansion of multi-view gait data. The real-world tests also prove that our designed method has good results and feasibility in the problem of gait recognition with short-time video as input data.
Crack initiation and propagation simulation is crucial for the safety and integrity assessment of structures. Though to this problem great efforts have been devoted and great advances have been made ...in both theory and numerical implementation, challenges still exist. To this end, inspired by the peridynamics and the unified phase-field method, in the present paper a novel nonlocal macro-meso-scale consistent damage model is proposed to simulate fracture process without prescribed initial crack and potential crack path. In this method, a meso-scale damage is firstly defined in terms of the stretch rate of bonds of material points. Then the macro-scale topologic damage is evaluated as the weighted averaging of meso-scale damage over bonds in the influence domain. Through the energetic degradation function, which connects the energy-based damage and the macro-scale topologic damage, the above damage model is inserted into the framework of irreversible thermodynamics consistent continuum damage mechanics. Numerical algorithms by the finite element discretization are elaborated. Three examples, including the Mode I and Mixed-Mode cracking simulation, are studied. It is shown that the proposed method can capture not only the crack pattern but also the load-deformation curves quantitatively. Moreover, there is no mesh sensitivity. Computationally, the proposed method belongs to the smeared crack modeling. The proposed method is presently limited to quasi-static crack modeling of isotropic quasi-brittle materials. The extension to anisotropic materials and dynamic crack modeling is possible and shall be studied in the future.
•A new nonlocal damage model by synthesizing the meso-scale and macro-scale damage.•An energetic degradation function with physical interpretation.•Detailed numerical algorithms in the framework of finite element discretization.•Without prescribed initial crack and potential crack path, no mesh sensitivity.
Limited CFETR-scale experience of engineering preparation techniques of tritium permeation barrier (TPB) exists up to date. Aimed at processing some real components that are usually tubular ...components sealed in one end, in the tritium cycling systems of China Fusion Engineering Test Reactor (CFETR), an Al
2
O
3
/FeAl coatings as TPB was prepared on tubular components of 321 type stainless steel components with a length of 400 mm and an external diameter of 150 mm, by Al-electroplating followed by heat treating and selective oxidation. The ability to construct TPB coated components on quasi-CFETR scale was demonstrated, with fabricating a TPB of Al
2
O
3
/FeAl coating with a double-layered structure, consisted of an outer γ-Al
2
O
3
layer with a thickness of 0.3 µm and an inner (Fe,Cr,Ni)Al/(Fe,Cr,Ni)
3
Al layer of 40 µm in thickness. The tritium permeation reduction factors of the Al
2
O
3
/FeAl TPB on component were 229 and 96 at 500 and 600 °C respectively. Finally, signatures and gaps of TPB mass process on CFETR-scale were discussed.
The newly proposed nonlocal macro‐meso‐scale damage (NMMD) model is extended to dynamic cracking simulation. For this purpose, the framework of continuum damage mechanics and damage constitutive ...model are firstly described. The NMMD, where the meso‐scale damage is determined according to the deformation of material bond and then the macroscopic topologic damage is endowed with the weighted averaging over the meso‐scale damage in the influence domain of the material point, is then elaborated and incorporated into the framework. Specifically, the criterion of meso‐scale damage is renormalized. The numerical algorithms including the spatial discretization by the finite element methods and the time integration methods by an explicit scheme are outlined. Several examples are studied in detail, showing the effectiveness of the proposed method. In particular, due to the nonlocal property, there is no spatial mesh size sensitivity. Owing to the scale renormalization of the meso‐scale damage, the results are insensitive to the influence radius in some examples. The dynamic cracking, including the crack propagation velocity, the damage dissipation rate, and the connection to the dynamic crack branching, is discussed in detail based on the computed results.
An extended bond-based peridynamic (PD) approach is presented for quasi-static mechanical behavior and brittle failure analysis of materials and structures. A local artificial damping is introduced ...into the peridynamic equations of motion, and a step-by-step loading method and a non-equilibrium criterion are employed to calculate the elastic response quantitatively, simulate the crack initiation and propagation and predict the extreme failure load of structures. The effect of the magnitude of the local damping on the accuracy and efficiency of elastic calculation is investigated. In the proposed model, another important feature lies in the micromodulus of the pair-wise bond, which is described as a continuous function of the distance between two particles within the material horizon and is demonstrated to be more accurate when compared to the earlier PD models using a fixed stiffness constant to describe the interaction of particles. The qualitative and quantitative validity of the approach is established through simulating the mechanical response and fracture of a cantilever concrete beam, including the whole process from the earlier elastic deformation stage to crack initiation and propagation, and making comparisons to the analytical and other numerical data. To further demonstrate the capabilities of the proposed model, the crack propagation and fracture mechanism of a cantilever concrete beam with pre-existing notch is studied, and the effect of the notch location on the extreme failure load and fracture mode of the structure is examined.
●Extended bond-based peridynamics for quasi-static behavior and brittle fracture.●The micromodulus of the pair-wise bond described as a continuous function.●A local damping introduced in the peridynamic equations of motion.●A step-by-step loading method and a non-equilibrium criterion in computation.●Capable of quantitative simulation of the crack initiation and propagation.
The newly proposed nonlocal macro-meso-scale consistent damage model (NMMD) is extended to compression/shear-dominate failure problems. For this purpose, the nonlocal strain of a material point pair ...in the NMMD is split into elastic strain and structured strain according to the theory of structured deformation. Then the structured part of the deformation of a material point pair, i.e., the structured positive elongation quantity, can be evaluated based on the structured strain. When the structured positive elongation quantity, rather than the original full positive elongation, of a material point pair exceeds a critical value, the material point pair become damaged, leading to mesoscopic damage. The macroscopic topologic damage at one point is then given by the weighted summation of mesoscopic damage of the point pairs connected to this point within its influence domain. Through the energetic degradation function, which bridges the damage in the geometric sense and the damage in the energetic sense, the topologic damage is incorporated into the framework of continuum damage mechanics. This model can be solved numerically. In contrast to the original NMMD for tensile-failure dominate problems, the driving force of topologic damage, i.e., the positive elongation quantity of material point pairs, is modified according to different types of structured strain, and thus the extended model is appropriate for various fracture mechanisms if a proper structured strain is adopted. The proposed model facilitates implementation, and can not only trace the crack path automatically without initial cracks, but also accurately predict the load–deformation curves without mesh sensitivity. The computational efficiency of the proposed model is illustrated via a benchmark problem. Examples verifies that when the masonry-like structured strain is adopted the structured deformation driven NMMD can well capture the vertical crack in quasi-brittle materials under uniaxial compression. In addition, an intuitive interpretation in the principal strain space is given to reveal the underlying physical mechanism for this problem. Alternatively, if the deviatoric structured strain is adopted to modify the driving force of topologic damage, the horizontal crack (true mode II crack) under pure shear can be obtained via NMMD. It is numerically verified that the mode II crack evolves according to the von Mises criterion, i.e., the crack propagates along the direction of the largest distortion energy density. Numerical results also indicate that the key features of the crack patterns from the NMMD and the phase field model are similar when the same structured strain is adopted to decompose the driving force of damage in these two models. This consistency between NMMD and the phase field model is preliminarily interpreted by Green’s function theory. Problems to be further investigated are also discussed, especially for the extension to anisotropic materials.
•A nonlocal macro-meso-scale damage model for compression/shear failure issues.•Vertical crack under uniaxial compression is captured with a straightforward reason.•True mode II crack is captured and the fracture criterion is discussed.•Connection between this model and phase field model is bridged by Green’s function.
Despite great efforts in capturing the damage evolution law in multiscale approaches in damage mechanics, much less attention has been paid to the conversion from geometric damage to energy ...dissipation. In the present paper, the newly proposed nonlocal macro–meso-scale damage (NMMD) model is physically consolidated and a multiscale point of view is consistently adopted in both the damage evolution and energy dissipation. In this model, for each macroscopic material point a mesoscopic structure is attached such that all the point pairs composed of this point and the points in its influence domain are connected to it when the material is intact. The deformation field under loading will result in deformation of point pairs, and thus mesoscopic damage related to a point pair will occur if the deformation index of this point pair exceeds the prescribed threshold. Such mesoscopic change among point pairs connected to a material point within its influence domain has two-fold consequences: geometrically the accumulation of mesoscopic damage will result in macroscopic discontinuity, and simultaneously the free energy will be dissipated, leading to degradation of mechanical behavior of quasi-brittle materials. In other words, the damage as a metric of the geometric discontinuity will lead to the damage in the sense of energy dissipation and degradation of mechanical behavior for quasi-brittle materials, which can be physically captured by the ratio of summation of all the dissipated mesoscopic free energy in point pairs to the free energy of intact material within the influence domain. This energy-based macroscopic damage could then be inserted into the framework of continuum damage mechanics. Therefore, the conversion from geometric damage to energetic damage is implemented on the mesoscale instead of the macroscale, and thus a macroscopic energetic degradation function is not needed. In addition, the structured strain which is suitable for quasi-brittle materials can be adopted to determine the deformation index of point pairs. Correspondingly, the macroscopic free energy can be split into dissipative and non-dissipative parts. In this way, several inconsistencies in the previous NMMD models are remedied. The influence of mesoscopic model parameters is investigated in depth, and several numerical examples including mode-I, mixed-mode and compressive splitting fracture problems of quasi-brittle materials are carried out. Numerical results indicate that the proposed model can not only well capture the cracking process with or without initial cracks but also quantitatively predict the load–deformation curves without mesh size sensitivity. Moreover, due to the inherent physical consistency, in mixed-mode cracking problems the proposed model performs better than the previous NMMD model. Problems to be further studied are also discussed.
•A unified multiscale perspective in damage evolution and energy dissipation.•A two-scale physical model for topologic damage evolution.•Mesoscopic conversion from geometric damage to energetic damage.•Several inconsistencies in the previous models are well resolved.•Numerical examples demonstrate the effectiveness of the model.
To capture the uniaxial compression fracture of concrete composite is still a great challenging problem. To this end, the newly proposed nonlocal macro–meso-scale consistent damage (NMMD) model is ...extended to simulate uniaxial compression fracture of concrete composites. In the NMMD model, a mesoscopic structure composed of material point pairs is attached to each material point. A decomposition scheme suitable for masonry-like materials is adopted to decompose the elongation quantity of point pairs. The topologic damage is defined as the weighted summation of mesoscopic damage in neighboring material point pairs driven by the decomposed elongation quantity. The physically-based energetic degradation function is employed to bridge the geometric discontinuity in solids and the energy dissipation, and thus the topologic damage is integrated into the framework of continuum damage mechanics. The Monte-Carlo method and two-phase random field model are employed to generate stochastic circular and irregular aggregates representing the meso structure of concrete, respectively. The interface transition zone is prescribed by reducing the critical value of interface point pairs. Numerical results indicate that both the crack patterns and stress–strain curves of the uniaxial compression experiments on concrete panels can be well captured by the proposed NMMD model without mesh size sensitivity. The influence of horizontal constraints on the top and bottom surfaces is investigated and shown to have an effect on the crack patterns, strength and deformation capability of the specimen. The necessity of decomposition is also illustrated.
•The NMMD model is extended to compressive failure simulation of concrete composite.•Both the crack patterns and stress–strain curves can be captured by the NMMD model objectively.•The influence of horizontal constraints is investigated.•The necessity of damage driving force decomposition is illustrated.
