Influence Of Rolling Resistance Research Articles

Influence of Rolling Resistance and Particle Size Distribution in the Simulation of Sand Infiltration into the Static Gravel Bed

Fine sediment infiltration and subsequent clogging in a gravel bed affect several fluvial, ecological, and biological processes, resulting in the degradation of the river ecosystem. Despite many experimental and a few numerical studies, the process is yet to be entirely understood. We employed a pure Lagrangian framework, called the Discrete Element Method (DEM), to numerically investigate the infiltration process. Special attention is given to tackling the issue of non-spherical and irregular particle shapes and particle size distributions (PSDs) in numerical simulations. Due to computational limitations, these aspects were either not considered or simplified in previous numerical studies. We implicitly included non-spherical and irregular shape effects through rolling resistance models, which do not cause excessive computational overhead. Our study shows that rolling resistance models greatly influence packing and fine sediment infiltration. However, they may also lead to unphysical particle behavior; thus, they should be carefully used in numerical simulations. Oversimplified PSDs do not mirror natural systems, and full PSDs pose computational challenges. Sufficient grain classes are needed to mimic the non-homogeneity and poly-dispersity found in natural fluvial sediments. The infiltrating characteristics of sand concerning PSD and shape effects are linked to size ratio D15,Gravel/D85,Sand, assuring physical and realistic modeling of the infiltration process.

The influence of rolling resistance on the stress-dilatancy and fabric anisotropy of granular materials

The effects of rolling resistance on the stress-dilatancy behavior and fabric anisotropy of granular materials were investigated through a three-dimensional discrete element method (DEM). A rolling resistance model was incorporated into the DEM code PFC3D and triaxial DEM simulations under simulated drained and undrained conditions were carried out. The results show that there existed a threshold value of the rolling friction. When the rolling friction was smaller than this value, the mechanical behavior of granular materials under both drained and undrained conditions were substantially influenced by the rolling friction, but the influence diminished when it was larger than the threshold value. A linear relationship has been observed between the dilatancy coefficient and the natural logarithm of the rolling-friction coefficient when it was smaller than the threshold value. An increase in the rolling friction led to an increase in the fabric anisotropy of all strong contacts under both testing conditions until the threshold value was attained. The investigation on the effect of rolling friction on the microstructure of granular materials revealed that the rolling friction enhanced the stability of force chains, which resulted in the difference in the stress-dilatancy behavior. Finally, the relationship between the stress ratio q/p $$^{\prime }$$ and the fabric measure at strong contacts $$\hbox {H}_{\mathrm{d}}^{\mathrm{s}} /\hbox {H}_{\mathrm{m}}^{\mathrm{s}}$$ was found independent of the inter-particle friction, rolling friction and testing conditions.

Influence of rolling resistance on manual wheelchair dynamics and mechanical efficiency

The anatomical model propulsion system (AMPS) was designed to propel manual wheelchairs in a highly repeatable manner while emulating human weight distribution and force application. This paper details the development of two control systems for the AMPS and their application on several sets of experiments. The first system allows the AMPS to maneuver with precision along straight and curvilinear trajectories. The second system mimics human pulsatile propulsion of a manual wheelchair for tests on a dynamometer. In both cases, the controller used an estimation of input forces provided by a model along with real-time feedback to create an appropriate maneuver control of the wheelchair. Several studies have measured rolling resistance using diverse methodologies and equipment including dynamometers, treadmills, and instrumented wheelchairs. A new approach for testing rolling resistance by using the AMPS is presented in this work. This new approach was able to test the wheelchair behavior on actual floor while all wheels are making contact, with precise control on velocity and acceleration, a combination unattainable with previous methods. Results confirm other researchers’ conclusion that rolling resistance increases with velocity, but also add new evidence that rolling resistance increases significantly with acceleration on a manual wheelchair. The AMPS was also used to estimate turning resistance in manual wheelchairs. Results offer new evidence that turning resistance increases as the instantaneous radius of rotation of the trajectory shortens. Additionally, the AMPS was provided with the ability to propel a manual wheelchair emulating human pulsatile propulsion on a single-roller dynamometer. Various pushing frequencies and duration of pulses were tested to compare the efficiency of different propulsion techniques. Two indices, energy conversion efficiency (η) and cost of transport (COT), were used to quantify wheelchair mechanical efficiency due to their relevance for vehicles. Energy conversion efficiency was found to vary significantly for different values of acceleration. COT was found to increase as linear velocity increased and the radius of curvature was reduced. Initial findings on COT for these pulsatile propulsion experiments suggest propelling techniques might have an effect in overall mechanical efficiency. Wheelchair mechanical efficiency could be used to compare the performance of different wheelchair models over common maneuvers, helping clinicians do more informed decisions for their patients. Further development and exhaustive testing of the system presented in this work could potentially become a standard for the manual wheelchair industry.

Influence of rolling resistance on the shear curve of granular particles

Abstract The rotation of a single particle plays a very important role in the simulation of granular flow through the discrete element method (DEM). Many researchers have noted that the effect of rolling resistance at the contact points should be considered in DEM simulations. The rolling resistance between particles, which is mainly introduced from the force or rolling deformation (velocity) between particles, is indicated in different models. However, various models cause different results. Hence, the most feasible model should be determined. For this purpose, five models are adopted to simulate the simple shear flow by DEM in this work. Simulation indicates that the contraction/dilatancy and force–displacement curves at different volume fractions are in good agreement with the experimental findings. The curves of Models 1 to 3 computed by force and angular velocity separate at different shear speeds, but this result does not satisfy the rate independent theory. The curves of Models 4 and 5, which are calculated by the rolling deformation, are better in keeping with the rate independence than the three previous models. After increasing the particle-size distribution, Model 5 appears to be more reliable. The defects of the four other models are discussed from the physical mechanism perspective. The force–displacement curves of Model 5 at a difference of 20 times in shear speed coincide perfectly. Overall, the findings satisfy both the objectivity and the rate independent theory.

Distinct simulation of earth pressure against a rigid retaining wall considering inter-particle rolling resistance in sandy backfill

The focus of this paper is to analyze earth pres- sure against a rigid retaining wall under various wall move- ment modes with a contact model considering inter-particle rolling resistance implemented into the distinct element method (DEM). Firstly, a contact model considering rolling resistance in particles was generally explained and imple- mented into the DEM. The parameters of the contact model are determined from DEM simulation of biaxial tests on a sandy specimen. Then, the influence of inter-particle rolling resistance in the backfill is discussed by comparing the active and passive earth pressure against a rigid wall subjected to a translational displacement with and without inter-particle rolling resistance in the material. Third, the DEM model con- sidering the rolling resistance is used to investigate active and passive earth pressures while the rigid wall moves in a more general manner such as rotation or translation. The influence of rolling resistance on the earth pressures is examined from the microscopic particle scale (e.g., shear strain field) as well as the macroscopic scale (e.g., the magnitude and action point of resultant earth pressures). Finally, the effect of the initial density and the particle size of the backfill are discussed. The results show that when rolling resistance in the particles is taken into account in the DEM simulation, the simulation results are more appropriate and are in line with practical