Pore Stabilization in Cohesive Granular Systems

Cohesive powders tend to form porous aggregates which can be compacted by applying an external pressure. This process is modelled using the Contact Dynamics method supplemented with a cohesion law and rolling friction. Starting with ballistic deposits of varying density, we investigate how the porosity of the compacted sample depends on the cohesion strength and the friction coefficients. This allows to explain different pore stabilization mechanisms. The final porosity depends on the cohesion force scaled by the external pressure and on the lateral distance between branches of the ballistic deposit r_capt. Even if cohesion is switched off, pores can be stabilized by Coulomb friction alone. This effect is weak for round particles, as long as the friction coefficient is smaller than 1. However, for nonspherical particles the effect is much stronger.Comment: 10 pages, 15 figure

Cob Property Analysis

The goal of this project was to research the material properties of the green building material COB in order to better understand how to apply COB in real world applications. The research portion included soil analysis, compression, modulus of rupture and elasticity tests, hydrometer analysis, and atterberg limits tests. Additionally, through a partnership with the professionals of the COB Research Institute team and another COB-centric senior design group, this team was able to produce the first full-scale wall tests for COB. Four 7-foot walls were constructed and in-plane lateral cyclic loading was applied to create the effects of a COB structure under lateral loading. The results of the full-scale tests are in the process of being incorporated in the entry for COB into the California Residential Code, with a recommendation given for the reinforcing design that performed the best, through allowable load and deflection calculations. Finally, the team used a sample footprint for a simple house to develop structural house components for a COB structure that could benefit COB application in the real world. The simulated application of COB is helping the COB Research Institute formulate their submittal and ultimately provide a jumping off point for further research of this nature. The ultimate goal was to spread awareness of sustainable building practices and make them more accessible to the general public

The design and implementation of a radar simulator

Includes bibliographical references.This dissertation describes the design and implementation of a radar simulator called Sarsim2. The radar simulator was originally developed to produce synthetic range profiles (SRPs) of complex aircraft models. It was then expanded and upgraded to generate simulated synthetic aperture radar (SAR) data. Over the last few years a substantial amount of work has been carried out by the Radar Remote Sensing Group (RRSG) at the University of Cape Town (UCT) to produce SRPs of aircraft targets using an 1-Band search radar of Reutech Systems. The high range resolution that can be obtained from SRP processing makes it feasible to extract characteristic features from a profile obtained from an aircraft. The ultimate aim of producing SRPs is to use these extracted features for non-cooperative target recognition (NCTR) , i.e. to be able to identify an aircraft type from the echo signal received by the radar. The radar simulator was written to produce SRPs of aircraft models, which could then be used to investigate the feasibility of various aircraft-identification algorithms. The stepped-frequency processing required to obtain SRPs of aircraft targets has initiated further research in the RRSG into more efficient stepped-frequency processing techniques, and the radar simulator has been used extensively to generate simulated data . The RRSG group is also actively involved with SAR processing techniques, and the radar simulator has been invaluable in providing necessary simulation data to test various processing algorithms . One of the main objectives of this simulator was to have an easy-to-use graph ical interface, which can show results in real-time . This requirement makes it necessary to find some way of reducing the required computation. The solution implemented may be called VYSIWIC (what you see is what is calculated). This means that the data is only calculated to a resolution depending on the screen resolution. Only when the data is saved to disk will it be calculated and written with the required sampling rate

Automatic polishing process of plastic injection molds on a 5-axis milling center

The plastic injection mold manufacturing process includes polishing operations when surface roughness is critical or mirror effect is required to produce transparent parts. This polishing operation is mainly carried out manually by skilled workers of subcontractor companies. In this paper, we propose an automatic polishing technique on a 5-axis milling center in order to use the same means of production from machining to polishing and reduce the costs. We develop special algorithms to compute 5-axis cutter locations on free-form cavities in order to imitate the skills of the workers. These are based on both filling curves and trochoidal curves. The polishing force is ensured by the compliance of the passive tool itself and set-up by calibration between displacement and force based on a force sensor. The compliance of the tool helps to avoid kinematical error effects on the part during 5-axis tool movements. The effectiveness of the method in terms of the surface roughness quality and the simplicity of implementation is shown through experiments on a 5-axis machining center with a rotary and tilt table

Scaling of the buckling transition of ridges in thin sheets

When a thin elastic sheet crumples, the elastic energy condenses into a network of folding lines and point vertices. These folds and vertices have elastic energy densities much greater than the surrounding areas, and most of the work required to crumple the sheet is consumed in breaking the folding lines or ``ridges''. To understand crumpling it is then necessary to understand the strength of ridges. In this work, we consider the buckling of a single ridge under the action of inward forcing applied at its ends. We demonstrate a simple scaling relation for the response of the ridge to the force prior to buckling. We also show that the buckling instability depends only on the ratio of strain along the ridge to curvature across it. Numerically, we find for a wide range of boundary conditions that ridges buckle when our forcing has increased their elastic energy by 20% over their resting state value. We also observe a correlation between neighbor interactions and the location of initial buckling. Analytic arguments and numerical simulations are employed to prove these results. Implications for the strength of ridges as structural elements are discussed.Comment: 42 pages, latex, doctoral dissertation, to be submitted to Phys Rev

An Evaluation of a Networked Radiation Detection System

First responders assess a Nuclear/Radiological (NUCRAD) event in a timely and accurate manner by creating a site characterization that reflects the location of various levels of contamination based on their instruments’ readings. The survey team experiences difficulty in accurately recording this critical data due to the challenge of operating multiple devices and communicating the devices’ readings to other survey members. First responders produce a representation of the contamination or activity on a map that contain rings outlining the levels of activity and/or single locations of a single activity. Recently, several agencies began creating software programs that record a first responder’s instrument readings, time, and the global positioning system (GPS) location plotting the information in real-time. The Environmental Protection Agency (EPA) Region 5 developed the Rapid Assessment Tool (RAT). This research evaluates the effectiveness of RAT by comparing the timeliness and accuracy of the site characterization created by multiple survey teams (one team not using RAT and another team using RAT). All of the Bioenvironmental Engineer (BEE) Survey Teams using RAT decreased their survey times for all scenarios. The Weapons of Mass Destruction – Civil Support Team (WMD-CST) survey teams using RAT decreased their survey times during the lane, bounce and bypass, star, and cloverleaf scenarios. However, survey times increased for the zigzag and radial scenarios