Papers by Keyword: DEM

Abstract: In mechanical equipment interacting with impingement particles, worn surface morphology of parts and components is formed by an accumulative action of a large number of single-particle erosions. To exhibit the mechanism of multi-particle erosion of target, three physical experiments and Discrete Element Method (DEM) simulations of erosion of iron target by the two vertical impingements of Al₂O₃ particle are carried out under three different landing errors x of the two impingements. The experimental results showed that each of two overlapping worn morphologies by the two impingements has an spherical cap shape. When x is larger than radius R₁ of worn morphology of target by the first erosion, two morphologies with an spherical cap shape are very close in size; while the size of worn morphology by the second erosion increases with the decrease of x, when x is smaller than R₁. The predicting worn morphologies by DEM are almost consistent with the experimental results, where the maximum relative deviation in size of worn morphology is 2.98% in the direction along x, and is 3.93% in the direction perpendicular to x. All these proved the effectiveness of the DEM model in predicting erosion of target by two impingements of particle.

Abstract: A biaxial test model was established based on the discrete element method to simulate the microscopic evolution of non-viscous soil upon loading. The shear strain, deviator stress and volumetric strain of the samples at different time steps were recorded, the evolution process of the force chain in the samples was observed, and the average degree (coordination number), 3-cycle and average clustering coefficient over force-chain particles were also analyzed respectively from the perspective of complex network. The following analysis results are obtained. The larger the value of inter-particle friction coefficient, the higher the peak value of shear stress, and the more obvious the strain softening phenomenon. The force chains in the samples with higher inter-particle friction coefficient tend to be more vulnerable to damage during loading. In the loading process, the average degree first increases, then decreases and finally tends to be stable. The value of average degree increases with the increase of confining pressure, and decreases with the increase of friction coefficient. The clustering coefficient of the particles within the force-chain particles is linearly related to the average length of the force chains at critical state.

Abstract: In fertilizers industries the granulation is an essential operation to form pellets with good quality. The granular product has improved handling, hardness, solubility, resistance to segregation and meets requirements such as the size, shape and particle size distribution through appropriate manipulation of the process variables. There are several types of granulators, however, this work is intended to study a granulator known as rotating disk, which promotes agitation of the particles by rotating around its axis. Although these devices are used industrially, cannot be found in the literature many details about the fluid dynamics in these operations. To study the fluid dynamics behavior of these particles on a rotation disk was analyzed the variables: rotation axis and filling degree. It was verified the existence of flow regimes which depends on these variables: rolling, cascading and centrifugation. Also, it was evaluated the dynamic angle of repose, that characterizes the rolling regime. This work aimed to obtain results of fluid dynamics that describe the behavior of solids flowing in a rotating disk. Thus, to meet the objectives of this work, simulations was carried out through the techniques of Computational Fluid Dynamics (CFD) and Discrete Element (DEM) to evaluate different parameter values: restitution coefficient (η), friction coefficient (μ) and the coefficient of elasticity (k) of the linear model "spring-dashpot" to find a good set of parameters that characterizes this system.

Abstract: Dynamic elastic Finite Element Method (FEM) and Discrete element method (DEM) simulations are carried out to investigate dynamic penetration of a projectile into a target of granular medium. It was found that the highly densified region of granular medium was generated just ahead of the projectile and began to propagate spherically with much higher velocity than that of projectile which leaves relatively rarefied medium region. This propagation phenomenon was probably the result of a collision and momentum transfer between particles in target granular medium. The propagation velocity of the densified region decreased during penetration as depending not only on the packing ratio of target medium but also on the projectile velocity. The resistance force of projectile was also investigated in the case of penetration of projectiles with various body lengths. The resistance force increased rapidly and reached to the peak. The peak value was expressed in terms of momentum change of target particles. The resistance force decreased periodically after the peak value. The period clearly depended on the length of projectile. It is obvious that this was caused by the stress wave reverberations in the projectiles with various body lengths.

Abstract: Digital Elevation Model (DEM) is an important data source for topographic analysis, 3D visualization and satellite image ortho-rectification. This paper focused on the DEM extraction and accuracy assessment from ZY-3 satellite with 3 stereo images. DEM was extracted using three different stereo pair image groups composed of forward and nadir view images, nadir and backward view images as well as forward and backward view images. The accuracy of the DEM was indicated by root-mean-square error (RMSE) values. The results showed that the stereo pair of nadir and forward view images achieved the best accuracy, while the pair of forward and backward view images obtained the worst. This might be useful for the selection of the stereo pair images for extracting DEM using ZY-3 satellite images.

Abstract: Geographic Information Service is open service based on the network environment. DEM should be protected because of its significance. This paper gives three methods for DEM information protecting, they are DEM encrypting, DEM information hiding and DEM Information disguising, and researches their theories and techniques. Then, this paper analyses their differences and relation. This paper could provide theory support for DEM information security research in Geographic Information Service.

Abstract: UAV simulative training system can insure the time and effect of training through reducing training cost. Scene simulation system in this paper is the vital component of the system. The comparability to real equipment is the ultimate request to the simulative training system, as to the scene simulation system, the reality and the veracity of changing rule of scene is most important. Simulation systems existing have deficiencies in these parts. Through studying on these aspects, the system in this paper uses DEM data and airscape to display lifelike vision of real terrain, scene drive model is designed to simulate the influence to the scene from the state changing of the flight and vidicon, real-time interconnection is realized.

Abstract: Coal seam floor contours are one of the most important 8 mine maps, and was usually used for coal mine decision-making. However, the graph, which was expressed as lines, has many disadvantages, including inadequate intuitive, poor visibility, and weak in expression of three-dimensional morphology formation. Thus, the readers have to spend more time to reveal the spatial distribution of coal deposits. According to the coal seam floors contours, and considering the constraints of faults in coal seams, the following steps were implemented to acquire coal seam floor DEM, which are: 1) contours discrete; and 2) interpolation using Inverse Distance Weighted method (IDW). The process was easy-manipulated, and the results could reflect the spatial distribution of coal seams in an objective, intuitively, and strong visibility manner. The method could facilitate and guide the analysis of mine design and coal production.

Abstract: Used the numerical method, considered the rising speed of head of seepage deformation, with the aid of the method of particle flow in micro layer to study the occurrence and development of the law of seepage failure. Numerical simulation was designed based on the study of the theory. Conducting piping tests of the soil samples by controlling water head. The results show that, the effects of loaded once on the orifice area was large, and also the most insecure. And the test result verifies the correctness of theoretical analysis. The results are valuable to further probing into the piping mechanism in sandy soils.

Abstract: Neighbor statistic algorithm is a kind of commonly used algorithm, statistical analysis was carried out on certain analysis value through the grid in the window, to reflect the local and zone terrain feature. This paper discussed the method of parallel algorithm based on neighborhood statistics serial algorithm parses and terrain algorithm. Focus on the data partition strategy and aperture effects processing strategy. Experiments show that, the two optimization method proposed can make the parallel program neighborhood grid processing algorithms make full use of parallel computing resources, and then further enhance its parallel performance on the general parallelization.