scholarly journals Numerical Investigation of Top Coal Drawing Evolution in Longwall Top Coal Caving by the Coupled Finite Difference Method-Discrete Element Method

Energies ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 219
Author(s):  
Yuming Huo ◽  
Defu Zhu ◽  
Zhonglun Wang ◽  
Xuanmin Song
Keyword(s):  
Finite Difference ◽  
Finite Difference Method ◽  
Discrete Element Method ◽  
Difference Method ◽  
Discrete Element ◽  
Recovery Ratio ◽  
Coal Recovery ◽  
Working Face ◽  
The Common ◽  
Longwall Top Coal Caving

In longwall top coal caving (LTCC), the resource recovery ratio of the working face is directly determined by the top coal recovery ratio. An investigation of the evolution of top coal drawing characteristics and revealing the evolution of top coal drawing parameters is necessary when providing guidance for caving parameter selection and improving the top coal recovery ratio. Based on in-situ measurements of the size distribution of caved top coal blocks in Wangjialing coal mine, a finite difference method (FDM)–discrete element method (DEM) coupled method was applied to establish a “continuous–discontinuous” numerical model and the process from the first coal drawing to the common coal drawing was simulated with 17 separate working face advances. The evolution of the drawing body (DB), loose body (LB), and top coal boundary (TCB) was obtained. The results show that, the evolution of parameters of DB such as shape and size, drawing amount, length and deflection angle of the long axis of the profile ellipsoid tended to decrease first, then increase, decrease again, and finally stabilise; the increment of the LB advance coal wall distance and the coal pillar distance was close to 0 m in the common coal drawing stage, while width increment of the LB was close to the drawing interval (0.865 m). The TCB formed after each coal drawing round was fitted based on the improved “Hook” function. The evolution of height and radius of curvature of TCB’s stagnation point was analysed. This was divided into three stages: the first (first to third drawing rounds) was the initial mining influence stage, the second (fourth to ninth drawing rounds) was the transitional caving stage, and the third (after tenth drawing round) was the common coal drawing stage.

Coupled Discrete Element-Finite Difference Method Simulations of OMNI-Max Anchor Installation in Granular Seabed

2020 ◽  
Author(s):  
Yancheng Yang ◽  
Haixiao Liu
Keyword(s):  
Finite Difference ◽  
Finite Difference Method ◽  
Penetration Depth ◽  
Impact Velocity ◽  
Deep Water ◽  
Difference Method ◽  
Surface Friction ◽  
Discrete Element ◽  
Granular Soil ◽  
System Response

Abstract The ocean resources development is becoming increasingly urgent as the depletion of land reserves combine to enhance demand. In some of the deep-water areas, terrigenous deposits are found near landmasses, which are formed from material eroded from the land surface. They are constituted of clay, silt, sand, and granular soil. More and more gravity installed anchors (GIA) are employed as a part of the offshore foundation systems in these deep-water areas. A kind of newly developed GIA, called OMNI-Max anchor, with a mooring arm located near the anchor tip that is free to rotate about the anchor length, are an effective approach for mooring marine devices to the ocean floor. While providing the reaction force, these anchors can maintain the stability of offshore facilities. The ability of the anchor to achieve these duties relies on its keying and diving behaviors after penetration. Both shallow and deep penetrations, including offshore foundations and anchors penetrations, in granular media are what long interests geotechnical and geophysical fields. The final penetration depth of GIA in the granular seabed is also influenced by quite a few factors, such as impact velocity, particle size distribution (PSD) and anchor surface friction. However, this kind of large-strain problem is not agreeable to typical continuum numerical methods. In the current work, we propose that the coupled discrete element method (DEM) and finite difference method (FDM) is a more proper and efficient tool to investigate the penetration of OMNI-Max anchors in granular soil. The effects of the factors mentioned above are considered in the coupled DEM-FDM simulations. The relative ultimate penetration depths for different penetration conditions are presented and quantified. The response of granular material during penetration is applied to provide insight into system response at the microscale. Energy dissipation in the assembly by both friction and collision at the particle scale is considered. Results show that anchor penetration depth grows with rising impact velocity, while it decreases with an increase of anchor surface friction. When the ratio of fluke width and median diameter of granular size is smaller than 5.6, even under a relatively loose state, the application of OMNI-Max anchor is not recommended because of difficulty in assuring the required penetration depth (about 1.3 anchor lengths, 11.90 m). Although, at the similar impact velocity, the GIA tip embedment in sand is quite shallower than that in clay, alternative GIA designs may realize higher penetrations in the sand, and prove to be viable anchoring solution for granular seabed sediments. Finally, the fabric characters after penetrations are presented to analyze and reveal the state of soil experienced drastic disturbance. The characteristics of these distributions tend to particular states depending on the relative position to the anchor, which have a significant influence on subsequent behaviors of OMNI-Max anchor during the keying process.

HEAT TRANSFER IN LARGE RUBBER ELEMENTS THROUGH OF MODELING BY FINITE DIFFERENCE METHOD

2019 ◽  
Author(s):  
Lucas Peixoto ◽  
Ane Lis Marocki ◽  
Celso Vieira Junior ◽  
Viviana Mariani
Keyword(s):  
Heat Transfer ◽  
Finite Difference ◽  
Finite Difference Method ◽  
Difference Method
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