Continuum theory for rapid cohesive-particle flows: general balance equations and discrete-element-method-based closure of cohesion-specific quantities

2017 ◽  
Vol 832 ◽  
pp. 345-382 ◽  
Author(s):  
Kevin M. Kellogg ◽  
Peiyuan Liu ◽  
Casey Q. LaMarche ◽  
Christine M. Hrenya
Keyword(s):  
Kinetic Theory ◽  
Discrete Element Method ◽  
Impact Velocity ◽  
Normal Component ◽  
Discrete Element ◽  
Granular Temperature ◽  
Success Factor ◽  
Particle Flows ◽  
The Impact ◽  
Element Method

The continuum description of rapid cohesive-particle flows comprises the population balance, which tracks various agglomerate sizes in space and time, and kinetic-theory-based balances for momentum and granular energy. Here, fundamental closures are provided in their most general form. In previous population balances, the probability (‘success factor’) that a given collision results in agglomeration or breakage has been set to a constant even though it is well established that the outcome of a collision depends on the impact (relative) velocity. Here, physically based closures that relate the success factors to the granular temperature, a (continuum) measure of the impact velocity, are derived. A key aspect of this derivation is the recognition that the normal component of the impact velocity dictates whether agglomeration occurs. With regard to the kinetic-theory balances, cohesion between particles makes the collisions more dissipative, thereby decreasing the granular temperature. The extra dissipation due to cohesion is accounted for using an effective coefficient of restitution, again determined using the derived distribution of normal impact velocities. This collective treatment of the population and kinetic-theory balances results in a general set of equations that contain several parameters (e.g. critical velocities of agglomeration) that are cohesion-specific (van der Waals, liquid bridging, etc.). The determination of these cohesion-specific quantities using simple discrete element method simulations, as well as validation of the resulting theory, is also presented.

Simulation of Failure of a Fixed Beam Subjected to Impact Load Using Quadrilateral Discrete Element Method

2012 ◽  
Author(s):  
Rajesh P. Nair ◽  
C. Lakshmana Rao
Keyword(s):  
Discrete Element Method ◽  
Impact Analysis ◽  
Mechanical Response ◽  
Impact Load ◽  
Discrete Element ◽  
Failure Criteria ◽  
Discrete Elements ◽  
The Impact ◽  
Fixed Beam ◽  
Element Method

Discrete Element Method (DEM) is an explicit numerical scheme to model the mechanical response of solid and particulate media. In our paper, we are introducing Quadrilateral Discrete Element Method (QDEM) for the simulation of the separation of elements in fixed beam subjected to impact load. QDEM results are compared with other DEM results available in literature. Impact loads include two cases: (a) a half sine wave and (b) a penetrator hitting the fixed beam. Separation criteria used for the discrete elements is maximum principal stress failure criteria. In QDEM, convergence study for the response of fixed beam is obtained using MATLAB platform. Validation of quadrilateral elements in fixed beam is being carried out by comparing the results with empirical formula available in literature for the impact analysis.

scholarly journals Music of grain crushing with the Discrete Element Method

2021 ◽  
Vol 249 ◽  
pp. 07009
Author(s):  
Li Zeng ◽  
Andres Alfonso Peña Olarte ◽  
Roberto Cudmani
Keyword(s):  
Discrete Element Method ◽  
3D Visualization ◽  
Acoustic Emissions ◽  
Discrete Element ◽  
Compression Tests ◽  
Compression Process ◽  
Practical Applications ◽  
Grain Crushing ◽  
The Impact ◽  
Element Method

A series of compression tests on agglomerates of microspheres representing a single grain are conducted to investigate the impact of heterogeneity on the acoustic emissions (AE) generation. The grain heterogeneity is realized by using a Weibull shape parameter-augmented traditional discrete element method (DEM). During the compression process the development of the micro-cracks, and the magnitude and location of the AE events are tracked and recorded. Through a 3D visualization of the AE events, their location and the clustered broken bonds are identified. The current study demonstrates the potential of AE measurements to track changes in the fabric and structure of granular materials. The results of this DEM study will contribute to clarify the mechanism of particle breakage and its consideration in practical applications.

scholarly journals Assessment of the Mixing of Polydisperse Solid Particles in the Rotary Drum and Slant Cone Mixers Using Discrete Element Method

2021 ◽  
Author(s):  
Basel Alchikh-Sulaiman
Keyword(s):  
Discrete Element Method ◽  
Discrete Element ◽  
Direct Result ◽  
Disperse Particles ◽  
Loading Method ◽  
Mixing Quality ◽  
Rotary Drum ◽  
Loading Methods ◽  
The Impact ◽  
Element Method

In spite of wide applications of powders in industry, there is a lack of sufficient knowledge regarding the mixing of poly-disperse particles in rotary drum and slant cone mixers. The main objective of this study was to explore the mixing quality of mono-disperse, bi-disperse, tri-disperse, and poly-disperse particles inside rotary drum and slant cone mixers as a function of the drum speed, particle size, agitator speed, and the initial loading method through the discrete element method (DEM). To achieve this objective, experimental work and simulations were carried out. DEM results were validated using experimental data obtained from both sampling and image analysis techniques. DEM simulation results were in good agreement with the experimentally determined data, both qualitatively and quantitatively. Three major loading methods were defined: side-side, top-bottom, and back-front. Also, the mixing metric was utilized to measure the mixing quality. For bi-disperse particles inside the slant cone mixer, the mixing index increased to a maximum and decreased slightly before reaching a plateau at the drum speed of 15 rpm with different loading methods as a direct result of the segregation of particles of different sizes. The same behavior was observed in the rotary drum for bi-disperse, tri-disperse, and poly-disperse particles. The effect of agitator speed on the mixing performance for bi-disperse particles inside the slant cone mixer was also investigated. The addition of the agitator increased the mixing quality and reduced the segregation of particles with different sizes. The best mixing qualities for the tri-disperse and poly-disperse particles inside the rotary drum were recorded for the top-bottom smaller-to-larger loading method. For the slant cone mixer, highest mixing indices for tri-disperse and poly-disperse particles with the top-bottom smaller-to-larger loading method were obtained at drum speeds of 15 and 55 rpm, respectively. The impact of segregation for both mixers was reduced by introducing additional intermediate size particles.

scholarly journals Determining the loose medium movement parameters in a centrifugal continuous mixer using a discrete element method

2021 ◽  
Vol 3 (7 (111)) ◽  
pp. 59-67
Author(s):  
Volodymyr Statsenko ◽  
Oleksandr Burmistenkov ◽  
Tetiana Bila ◽  
Svitlana Demishonkova
Keyword(s):  
Mathematical Model ◽  
Differential Equations ◽  
Discrete Element Method ◽  
Pearson Correlation ◽  
Discrete Element ◽  
System Of Differential Equations ◽  
Continuous Action ◽  
Centrifugal Mixer ◽  
The Impact ◽  
Element Method

The processes to form the compositions of loose materials in centrifugal mixers of continuous action have been considered. Based on the method of discrete elements, a mathematical model of the movement of particles in the rotor of the centrifugal mixer was built, taking into consideration their geometric and physical-mechanical parameters. To assess the extent of influence of these parameters on the nature of particle movement, a well-known mathematical model in the form of a system of differential equations was used, which was built on the basis of classical laws of mechanics. The process of mixing particles of two loose materials under different initial conditions of movement was modeled. The trajectories of individual particles along the bottom and side wall of the rotor were calculated. The results of the research reported here have established that the model built on the basis of the discrete element method makes it possible to improve the accuracy of determining the parameters of the movement of loose materials in the mixing zone. Calculations that involved this method show that the length of the particle trajectory is 2.9, and the movement time is 9 times greater than those calculated by the system of differential equations. The built and known mathematical models demonstrated the same nature of the distribution of components in the mixer. The value of the Pearson correlation coefficient between the calculated values of the coefficients of variation is 0.758. The best homogeneity is achieved by separating the flows of the mixture components and reducing the distance between their centers. The experimental study was carried out using a centrifugal mixer of continuous action with a conical rotor. Particle trajectories were constructed; it was established that the shape of the trajectory built by a discrete element method is closer to the experimental one. The results reported in this paper make it possible to predict the impact of the structural and technological parameters of the mixers of continuous action on the uniformity of the mixture

scholarly journals Research on the Obstruction Process of Rigid Netting Barriers toward Granular Flow

2019 ◽  
Vol 2019 ◽  
pp. 1-18 ◽  
Author(s):  
Yunyun Fan ◽  
Fengyuan Wu
Keyword(s):  
Discrete Element Method ◽  
Granular Flow ◽  
Engineering Application ◽  
Time History ◽  
Discrete Element ◽  
Primary Concern ◽  
Size Segregation ◽  
Protective Structures ◽  
The Impact ◽  
Element Method

With the advantages of a simple structure and rapid construction, the rigid netting barrier (RNB) exerts a good obstruction effect on granular flow and is a common engineering measure used to prevent geological disasters in the form of granular flows. However, due to the limitations of current measuring and testing techniques, it is difficult to obtain an accurate measurement of the granular flow velocity and the impact force of granular flow on the mesh structures that are of primary concern in the design of protective structures. To study the characteristics of the obstruction process of RNBs toward granular flow, a typical impact experiment involving granular flow was numerically simulated by the discrete element method, and the correctness and effectiveness of the calculation method were also verified. On this basis, the discrete element method was applied to simulate the obstruction process affecting granular flow under different RNB setting conditions, and the calculation results clearly present the phenomena that occur during the obstruction process of RNBs toward granular flow, such as “run-up,” “overflow,” “passing-through,” and “grain-size segregation.” By analyzing the effects of these phenomena on the obstruction efficiency and the time history of the forces acting on the RNB, the rational setting of an RNB was further discussed. This study can provide a reference for the engineering application of RNB.

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