Friction dependence of shallow granular flows from discrete particle simulations

A shallow-layer model for granular flows is completed with a closure relation for the macroscopic bed friction or basal roughness obtained from micro-scale discrete particle simulations of steady flows. We systematically vary the bed friction by changing the contact friction coefficient between basal and flowing particles, while the base remains geometrically rough. By simulating steady uniform flow over a wide parameter range, we obtain a friction law that is a function of both flow and bed variables. Surprisingly, we find that the macroscopic bed friction is only weakly dependent on the contact friction of bed particles and predominantly determined by the properties of the flowing particles

Surface flow profiles for dry and wet granular materials by Particle Tracking Velocimetry; the effect of wall roughness

Two-dimensional Particle Tracking Velocimetry (PTV) is a promising technique to study the behaviour of granular flows. The aim is to experimentally determine the free surface width and position of the shear band from the velocity profile to validate simulations in a split-bottom shear cell geometry. The position and velocities of scattered tracer particles are tracked as they move with the bulk flow by analyzing images. We then use a new technique to extract the continuum velocity field, applying coarse-graining with the postprocessing toolbox MercuryCG on the discrete experimental PTV data. For intermediate filling heights, the dependence of the shear (or angular) velocity on the radial coordinate at the free surface is well fitted by an error function. From the error function, we get the width and the centre position of the shear band. We investigate the dependence of these shear band properties on filling height and rotation frequencies of the shear cell for dry glass beads for rough and smooth wall surfaces. For rough surfaces, the data agrees with the existing experimental results and theoretical scaling predictions. For smooth surfaces, particle-wall slippage is significant and the data deviates from the predictions. We further study the effect of cohesion on the shear band properties by using small amount of silicon oil and glycerol as interstitial liquids with the glass beads. While silicon oil does not lead to big changes, glycerol changes the shear band properties considerably. The shear band gets wider and is situated further inward with increasing liquid saturation, due to the correspondingly increasing trend of particles to stick together

Segregation of large particles in dense granular flows: A granular Saffman effect?

We report on the scaling between the lift force and the velocity lag experienced by a single particle of different size in a monodisperse dense granular chute flow. The similarity of this scaling to the Saffman lift force in (micro) fluids, suggests an inertial origin for the lift force responsible for segregation of (isolated, large) intruders in dense granular flows. We also observe an anisotropic pressure/stress field surrounding the particle, which potentially lies at the origin of the velocity lag. These findings are relevant for modelling and theoretical predictions of particle-size segregation. At the same time, the suggested interplay between polydispersity and inertial effects in dense granular flows with stress- and strain-gradients, implies striking new parallels between fluids, suspensions and granular flows with wide application perspectives

Closure Relations for Shallow Granular Flows from Particle Simulations

The Discrete Particle Method (DPM) is used to model granular flows down an inclined chute. We observe three major regimes: static piles, steady uniform flows and accelerating flows. For flows over a smooth base, other (quasi-steady) regimes are observed where the flow is either highly energetic and strongly layered in depth for small inclinations, or non-uniform and oscillating for larger inclinations. For steady uniform flows, depth profiles of density, velocity and stress have been obtained using an improved coarse-graining method, which allows accurate statistics even at the base of the flow. A shallow-layer model for granular flows is completed with macro-scale closure relations obtained from micro-scale DPM simulations of steady flows. We thus obtain relations for the effective basal friction, shape factor, mean density, and the normal stress anisotropy as functions of layer thickness, flow velocity and basal roughness. For collisional flows, the functional dependencies are well determined and have been obtained.Comment: Will be presented at PARTICLES 2011 - CIMN

Development of the Oklahoma rapid assessment method for floodplain wetlands

Wetlands provide many important services to society, but degradation of wetlands reduces their ability to provide those services. Loss and degradation of wetlands have been ongoing in Oklahoma since settlement though recent efforts may have begun to reverse some of the damage. To ensure these efforts are working, we need to monitor the ecological condition of wetlands in the state. The Oklahoma Rapid Assessment Method (OKRAM) has been developed as a way to accomplish this goal and has been proven to be an effective tool for measuring the condition of depressional wetlands. OKRAMs intended use is to assess any wetland in the state so it will need to be calibrated for and validated in each wetland type in the state. The goal of this study was to calibrate OKRAM to Riverine Floodplain Wetlands to account for the unique biotic and abiotic conditions within them by altering or changing metrics and/or their scoring. Calibration of OKRAM will serve to prepare it for a statewide validation for Floodplain Wetlands. We performed Level 1, 2, and 3 assessments at 30 wetlands within the North Canadian and Deep Fork River Watersheds and used Level 1 and 3 data to assess Level 2 metrics. Our evaluation showed consistent relationships of OKRAM to Level 1 (e.g., Landscape Development Intensity index) and Level 3 (e.g., Floristic Quality Index) data at 30 floodplain wetland sites within the Deep Fork River and North Canadian River Watersheds of Oklahoma. This study shows that OKRAM can be used as an effective tool to assess floodplain wetlands rapidly and affordably. OKRAM still needs further calibration before I would recommend its use in wetland monitoring programs. I present recommendations for improving poor performing metrics and directions for future research in floodplain wetlands in Oklahoma

Work quality in the avocation of sports officiating as determined by selected members of the Texas Association of Sports Officials

The major purpose of this study was to examine work quality in the avocation of sports officiating, as determined by selected Texas High School Sports Officials. Specifically, the study investigated work quality indicators and the relationship between those indicators and the officials overall perception of the avocation of Texas High School sports officiating. To accomplish this purpose, two different survey methods were used. A convenience sample of 125 sports officials participated in a qualitative questionnaire. Usable data was obtained from 114 officials. Utilizing both the qualitative research and information gathered from relevant literature, a web-based survey was constructed and used to contact selected members of the Texas Association of Sports Officials. A total of 1075 responses were received. The web-based instrument integrated items related to basic demographic information, as outlined by Quinn and Staines, (1979). These items included, but were not limited to the following: gender, age, economic information, marital status, educational background, ethnic background and primary occupation. The instrument also investigated the following indicators of work quality: Vocational and avocational information, work environment, personal health and wellbeing, organizational and administrative support, and organizational commitment and officiating career outcomes. These indicators were further explored through the development of work quality constructs, which related to each indicator. The constructs were further studied as to their relationship with certain demographic information. The results of this study indicate that although there are significant work quality issues as they relate to sports officiating, the majority of the constructs studied showed little negative impact on the sports officialsâ perception of the work quality of the officiating avocation

Development of a Large Scale, High Speed Wheel Test Facility

Draper Laboratory, with its internal research and development budget, has for the past two years been funding a joint effort with the Massachusetts Institute of Technology (MIT) for the development of a large scale, high speed wheel test facility. This facility was developed to perform experiments and carry out evaluations on levitation and propulsion designs for MagLev systems currently under consideration. The facility was developed to rotate a large (2 meter) wheel which could operate with peripheral speeds of greater than 100 meters/second. The rim of the wheel was constructed of a non-magnetic, non-conductive composite material to avoid the generation of errors from spurious forces. A sensor package containing a multi-axis force and torque sensor mounted to the base of the station, provides a signal of the lift and drag forces on the package being tested. Position tables mounted on the station allow for the introduction of errors in real time. A computer controlled data acquisition system was developed around a Macintosh IIfx to record the test data and control the speed of the wheel. This paper describes the development of this test facility. A detailed description of the major components is presented. Recently completed tests carried out on a novel Electrodynamic (EDS) suspension system, developed by MIT as part of this joint effort are described and presented. Adaptation of this facility for linear motor and other propulsion and levitation testing is described