Multibody Dynamics Versus Fluid Dynamics: Two Perspectives on the Dynamics of Granular Flows

2020 ◽  
Vol 15 (9) ◽  
Author(s):  
Milad Rakhsha ◽  
Conlain Kelly ◽  
Nic Olsen ◽  
Radu Serban ◽  
Dan Negrut
Keyword(s):  
Fluid Dynamics ◽  
Granular Material ◽  
Equations Of Motion ◽  
Dam Break ◽  
Granular System ◽  
Processing Unit ◽  
Static Case ◽  
Granular Dynamics ◽  
Numerical Solution Methods ◽  
Solution Methods

Abstract Considering that granular material is second only to water in how often it is handled in practical applications, characterizing its dynamics represents a ubiquitous problem. However, studying the motion of granular material poses stiff computational challenges. The underlying question in this contribution is whether a continuum representation of the granular material, established in the framework of the smoothed particle hydrodynamics (SPH) method, can provide a good proxy for the fully resolved granular dynamics solution. To this end, two approaches described herein were implemented to run on graphics processing unit (GPU) cards to solve the three-dimensional (3D) dynamics of the granular material via two solution methods: a discrete one, and a continuum one. The study concentrates on the case when the granular material is packed but shows fluid-like behavior under large strains. On the one hand, we solve the Newton–Euler equations of motion to fully resolve the motion of the granular system. On the other hand, we solve the Navier–Stokes equations to describe the evolution of the granular material when treated as a homogenized continuum. To demonstrate the similarities and differences between the multibody and fluid dynamics, we consider three representative problems: (i) a compressibility test (highlighting a static case); (ii) the classical dam break problem (highlighting high transients); and (iii) the dam break simulation with an obstacle (highlighting impact). These experiments provide insights into conditions under which one can expect similar macroscale behavior from multibody and fluid dynamics systems governed by manifestly different equations of motion and solved by vastly different numerical solution methods. The models and simulation platform used are publicly available and part of an open source code called Chrono. Timing results are reported to gauge the efficiency gains associated with treating the granular material as a continuum.

Multibody Dynamics vs. Fluid Dynamics: Similarities and Differences

2019 ◽  
Author(s):  
Milad Rakhsha ◽  
Conlain Kelly ◽  
Nic Olsen ◽  
Radu Serban ◽  
Dan Negrut
Keyword(s):  
Fluid Dynamics ◽  
Multibody Dynamics ◽  
Stokes Equations ◽  
Gpu Computing ◽  
Equations Of Motion ◽  
Dam Break ◽  
System Level ◽  
Large Strains ◽  
Numerical Solution Methods ◽  
Similarities And Differences

Abstract In large, rigid multibody dynamics problems with friction and contact, encountered for instance in granular flows, one can witness distinctly different system-level dynamics. This contribution concentrates on the case of fluid-like behavior of large multibody dynamics systems such as granular materials, when the system experiences large strains. The results reported herein draw on computer simulation; on the one hand, we solve the Newton-Euler equations of motion, which govern the evolution of multibody dynamics system featuring frictional contact. On the other hand, we solve the Navier-Stokes equations which describe the time evolution of fluids. To demonstrate the similarities and differences between the multibody and fluid dynamics we consider three problems modeled and solved using different methods; (i) a compressibility test; (ii) the classical dam break problem, and (iii) the dam break simulation with an obstacle. These experiments provide insights into conditions under which on can expect similar characteristics from multibody and fluid dynamics systems governed by manifestly different equations of motion and solved by vastly different numerical solution methods. The models and simulation platform used are publicly available and part of an open source code called Chrono. Both the multibody and fluid dynamics simulations are carried out using GPU computing.

scholarly journals The iFlow Modelling Framework v2.4. A modular idealised process-based model for flow and transport in estuaries

2017 ◽  
Author(s):  
Yoeri M. Dijkstra ◽  
Ronald L. Brouwer ◽  
Henk M. Schuttelaars ◽  
George P. Schramkowski
Keyword(s):  
Equations Of Motion ◽  
Transport Processes ◽  
Computational Grids ◽  
Model Parameters ◽  
Systematic Analysis ◽  
Modelling Framework ◽  
Numerical Solution Methods ◽  
Tidal Rivers ◽  
Solution Methods ◽  
Model Components

Abstract. The iFlow modelling framework allows for a systematic analysis of the water motion and sediment transport processes in estuaries and tidal rivers and the sensitivity of these processes to model parameters. iFlow has a modular structure, making the model easily extendible. This allows one to use iFlow to construct anything from very simple to rather complex models. The iFlow core is designed to make it easy to include, exclude or change model components, called modules. The core automatically ensures modules are called in the correct order, inserting iteration loops over groups of modules that are mutually dependent. The iFlow core also ensures a smooth coupling of modules using analytical and numerical solution methods or modules that use different computational grids. iFlow includes a range of modules for computing the hydrodynamics and suspended sediment dynamics in estuaries and tidal rivers. These modules employ perturbation methods, which allow for distinguishing the effect of individual forcing terms in the equations of motion and transport. Also included are several modules for computing turbulence and salinity. These modules are supported by auxiliary modules, including a module that facilitates sensitivity studies. Additional to an explanation of the model functionality, we present two case studies, demonstrating how iFlow facilitates the analysis of model results, the understanding of the underlying physics and the testing of parameter sensitivity. A comparison of the model results to measurements show a good qualitative agreement.

An Investigation Into the Compliance of SCARA Robots. Part II: Experimental and Numerical Validation

1988 ◽  
Vol 110 (1) ◽  
pp. 23-30 ◽  
Author(s):  
H. A. ElMaraghy ◽  
B. Johns
Keyword(s):  
Elastic Compliance ◽  
Servo Control ◽  
Compliance Matrix ◽  
End Effector ◽  
Prismatic Parts ◽  
Numerical Solution Methods ◽  
Solution Methods ◽  
Using Data ◽  
Assembly Performance ◽  
Robot Configurations

A model of inherent elastic compliance was developed for general position-controlled SCARA, with conventional joint feedback control, for both rotational and prismatic part insertion (Part I). The developed model was applied to the SKILAM and ADEPT I robots for validation. Experimental procedures and numerical solution methods are described. It was found that the ADEPT I robot employs a coupled control strategy between joints one and two which produces a constant, decoupled end effector compliance. The applicable compliance matrix, in this case, is presented and the experimental results are discussed. The model may be used to develop compliance maps that define the amount of end effector compliance, as a function of the joints compliance, as well as its variation for different robot configurations. This is illustrated using data for the SKILAM SCARA robot. Results are plotted and discussed. The most appropriate robot postures for assembly were found for both rotational and prismatic parts. The conditions necessary to achieve compliance or semicompliance centers with the SKILAM robot were examined. The results and methods demonstrated in these examples may be used to select appropriate robots for given applications. They can also guide robot designers in selecting joint servo-control gains to obtain the desired joints compliance ratio and improve assembly performance.

Nonequilibrium Continuum Traffic Flow Model with Frozen Sound Wave Speed

2003 ◽  
Vol 1852 (1) ◽  
pp. 183-192
Author(s):  
W. L. Jin ◽  
H. M. Zhang
Keyword(s):  
Traffic Flow ◽  
Sound Speed ◽  
Flow Model ◽  
Wave Model ◽  
Homogeneous System ◽  
Traffic Flow Model ◽  
Traffic Conditions ◽  
Numerical Solution Methods ◽  
Stable Conditions ◽  
Solution Methods

Results are presented from a recent study on a variation of a new non-equilibrium continuum traffic flow model in which traffic sound speed is constant. Hence this model is called the frozen-wave model. This model resembles the Payne–Whitham model but avoids the “back-traveling” of the latter. For this frozen-wave model, the Riemann problem is analyzed for its homogeneous system, two numerical solution methods are developed to solve it, and numerical simulations are carried out under both stable and unstable traffic conditions. These results show that under stable conditions, the model behaves similarly to the Payne–Whitham model. However, under unstable traffic conditions, it has nonphysical solutions or no solutions when a vacuum problem occurs. This study, on the one hand, provides a more complete picture of the properties of this frozen-wave model and reduces the risk of improper applications of it. On the other hand, it also highlights the need to adopt a density-dependent sound speed.

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