Traffic information, now available through a number of different sources, is re-shaping the way planners, operators and users think about the transportation network. It provides a powerful tool to mitigate the negative impacts of uncertainty, and an invaluable resource to manage and operate the network in real-time. More information also invites to think about traditional transportation problems from a different perspective, searching for a better utilization of the improved knowledge of the network state. This dissertation is concerned with modeling and evaluating the system-level impacts of providing information to network users, assuming that the data is utilized to guide an Adaptive System-Optimum (ASO) routing behavior. Within this context, it studies the optimal deployment of sensors for the support of ASO strategies, and it introduces a novel SO assignment approach, the Information-Based System Optimum (IBSO) assignment paradigm. The proposed sensor deployment model explicitly captures the impact of sensors' location on the expected cost of ASO assignment strategies. Under such strategies, a-priori routing decisions may be adjusted based on real-time information. The IBSO assignment paradigm leads to optimal flow patterns which take into account the ability of vehicles to collect information as they travel. The approach regards a subset of the system's assets as probes, which may face higher expected costs than regular vehicles in the search for information. The collected data is utilized to adjust routing decisions in real time, improving the expected system performance. The proposed problem captures the system-level impact of adaptive route choices on stochastic networks. The models developed in this work are rigorously formulated, and their properties analyzed to support the generation of specialized solution methodologies based on state-space partitioning and Tabu Search principles. Solution techniques are tested under a variety of scenarios, and implemented to the solution of several case studies. The magnitude and nature of the information impacts observed in this study illustrate problem characteristics with important theoretical, methodological and practical implications. The findings presented in this dissertation allow envisioning a number of practical applications which may promote a more efficient utilization of novel sensing and communication technologies, allowing the full realization of their potential. / text

Manufacturers are increasingly being held responsible for the fate of their products once they reach their end-of-life phase. This research uses a combination of total disassembly time and recyclability to gauge the environmental impact of a product at this stage of its use. Recyclability, or wasted weight, is a function of the material contained by a product’s subassemblies as it is taken apart. This project suggests a graph-based method of representing product assemblies. Unlike many existing representation methods which are used in the field of automated disassembly, the method proposed here takes component connection methods into account. This, combined with a library of disassembly defining graph grammars, ensures that the disassembly simulation performed on this assembly approximates real-life disassembly procedures as closely as possible. The results of this simulation are Pareto sets whose contents represent various points in the disassembly process. Each member of the set is evaluated using the two primary parameters of disassembly time and wasted weight. This Pareto set can be used to judge a particular product’s performance during end-of-life, from the perspective of recyclability, against that of another product. / text

The primary purpose of this study is to model the water vapor flow produced by a comet impact on the Moon using the Direct Simulation Monte Carlo (DSMC) method. Toward that end, our DSMC solver was modified in order to model the cometary water from the time of impact until it is either destroyed due to escape or photodestruction processes or captured inside one of the lunar polar cold traps. In order to model the complex flow induced by a comet impact, a 3D spherical parallel version of the DSMC method was implemented. The DSMC solver was also modified to take as input the solution from the SOVA hydrocode for the impact event at a fixed interface. An unsteady multi-domain approach and a collision limiting scheme were also added to the previous implementation in order to follow the water from the continuum regions near the point of impact to the much later rarefied atmospheric flow around the Moon. The present implementation was tested on a simple unsteady hemispherical expansion flow into a vacuum. For these simulations, the data at the interface were provided by a 1D analytical model instead of the SOVA solution. Good results were obtained downstream of the interface for density, temperature and radial velocity. Freezing of the vibrational modes was also observed in the transitional regime as the flow became collisionless. The 45° oblique impact of a 1 km radius ice sphere at 30 km/s was simulated up to several months after impact. Most of the water crosses the interface under 5 s moving mostly directly downstream of the interface. Most of the water escapes the gravity well of the Moon within the first few hours after impact. For such a comet impact, only ~3% of the comet mass remains on the Moon after impact. As the Moon rotates, the molecules begin to migrate until they are destroyed or captured in a cold trap. Of the 3% of the water remaining on the Moon after impact, only a small fraction, ~0.14% of the comet mass, actually reaches the cold traps; nearly all of the rest is photo-destroyed. Based on the surface area of the cold traps used in the present simulations, ~1 mm of ice would have accumulated in the polar cold traps after such an impact. Estimates for the total mass of water accumulated in the polar cold traps over one billion years are consistent with recent observations. / text

This paper serves as a “kicking-the-tires” analysis of low impact developments as a method of stormwater management. Specifically, this paper examines the feasibility, benefit, and current practice of low impact developments in Austin, Texas. Merits, strengths, and weakness are comparatively determined primarily on the basis of the impact and efficiency of design, particularly relating to ability to handle water volume and potential to improve water quality. By examining case studies and “applied” examples the potential of low impact development application is considered for the expected, potential, and/or alleged benefits of low impact implementation. / text

Building pounding is a recognised phenomenon where adjacent buildings collide under lateral loading due to insufficient provision of building separation. The consequences of this interaction are known to be complex, and both buildings’ responses can be significantly affected. In the absence of extensive experimental data, numerical modelling has been frequently adopted as a means of evaluating building pounding risk during earthquakes. In performing numerical analysis, it becomes necessary to create specialised ‘contact’ elements to simulate building contact. While many contact elements have been previously proposed, detailed consideration of their inherent assumptions has frequently been overlooked. This thesis considers the significance and consequences of using the Kelvin contact element for a variety of pounding situations and with varying levels of model detail. Pounding between two adjacent floors (floor/floor collision) is considered as a one dimensional wave propagation problem. By modelling each floor as a flexible rod (termed distributed mass modelling), theoretical relationships for collision force, collision duration and post-collision velocity are derived. This theory is then compared to the predictions made when using the traditionally adopted assumptions of fully rigid colliding floors (termed lumped mass modelling). The post-collision velocities obtained from each method are found to agree only when the axial period of both floors is identical. Relationships between lumped mass and distributed mass models are formed, and an ‘equivalent lumped mass’ method is developed where distributed mass effects can be emulated without explicit modelling of floor flexibility. The theoretical solution method is then adapted for use in Non-Linear Time History Analysis (NLTHA) software to model specific pounding situations. Numerical modelling of a single collision is performed to compare these results to the theoretical predictions. Good agreement is found, and the model’s complexity is simplified until a sufficiently accurate simulation is performed without overly onerous computational requirements. Five methods are detailed that incorporate energy loss during collision into the distributed mass models and a calibration method is developed that enables researchers to define the level of energy loss that occurs during a single collision. Using the developed modelling methods, the pounding response of two existing Wellington buildings is predicted. This is first performed using 2D analysis of the stiffest frame from each building. The predicted building pounding damage is categorised into local damage (damageresulting from the magnitude of the force applied during contact) and global damage (damage due to the change in dynamic building properties resulting from momentum transfer during collision). Local and global damage effects are found to be fundamentally different consequences of collision, with the two categories responding differently to changes in the modelled system. The effects of building separation, scaling of input motion, modelling of soil-structure-interaction, collision damping, and floor rigidity are investigated for the considered system. 3D analysis of the building configuration is then investigated. Additional complications arising from the transverse movement of buildings prior to and during collision are identified and refined modelling methods are developed. The 3D configuration of these buildings causes torsional interaction, despite both buildings being perfectly symmetrical. This torsion is due to the eccentric positioning of the buildings relative to each other, which causes an eccentric contact load when pounding occurs. The 3D models are used to test the effects of building separation, 2D vs. 3D modelling, collision damping, floor rigidity, and the significance of the torsional interactions. Attention is then focused on collisions between a building’s floors and an adjacent building’s columns (floor/column collision). Due to the high frequency content of pounding impacts, the significance of using Timoshenko beam theory instead of Euler-Bernoulli theory is assessed. The shear stiffness in the Timoshenko formulation is found to significantly affect the columns’ predicted performance, and is used in subsequent modelling. An appropriately accurate method of modelling that minimises computational effort is then developed. The simplified model is used to predict the performance of two three-storey buildings that experience floor/column collision. The effects of floor/column impact are predicted for collisions at mid-height, and near the support of the impacted column. Each of these scenarios investigates the effect of building separation on local damage and global damage. Finally, a method to model collision between two adjacent walls that collide out-of-plane is developed (wall/wall contact). The adopted contact element properties are selected using analogous situations that have been previously investigated. The method is used to investigate a single collision between two different wall configurations. In the conclusions, the developed modelling methods from all the considered collision configurations are collected and presented in a summary table. It is intended that these recommendations will assist other researchers in selecting appropriate building pounding modelling properties.

The objectives of this study were two fold. The first was to quantify the nature and extent of current levels of human impact in alpine areas at four sites within Fiordland and Mount Aspiring National Parks along walking tracks at Key Summit, Gertrude Saddle, Borland Saddle and Sugarloaf Pass. In order to do so, a survey was carried out with transects placed perpendicular to the track, and distributed among different vegetation types. In each transect, plant structural and compositional aspects, and soil and environmental parameters were measured. Transects were divided into track, transition, undisturbed and control zones, and changes to dependent variables were compared with distance from the track centre. Damage from visitor impact was largely restricted to within 1m from the track centre. The most significant impacts were to structural aspects of plant and soil properties with significant reductions in plant height, total vegetation cover and bryophyte cover, and increases in bareground and erosion on tracks. Erosion was more prevalent on slopes greater than 25°, while tracks on peat soils contained greater bareground exposure, particularly of organic soil. The second study objective was to investigate the relationship between specific levels of impact and the resulting damage to two key alpine vegetation types, tussock herb field and cushion bog. This was undertaken by carrying out controlled trampling experiments, measuring changes to plant structural and compositional aspects four weeks and one year after treatment. Both vegetation types saw dramatic reductions in total vegetation cover and height immediately after trampling, however overall composition and species richness varied little. These two alpine vegetation types showed moderate-low resistance to initial impact and low resilience, with very little recovery evident one year later. Research intothese two areas is important for managing visitor use within alpine areas in order to meet conservation and recreation goals. The survey indicates that alpine community types are very sensitive to visitor use, showing significant structural damage, however the spatial extent of impact is limited within the broader landscape. Instead, visitor impacts associated with tracks are likely to be more visually and aesthetically significant, influencing the visitor experience. The trampling experiments indicate that use levels over 25-75 passes per year within tussock herbfield and cushion bog vegetation on peat soils will result in ongoing damage to previously undisturbed sites. Methods for minimising impacts include limiting visitor numbers, public education in low impact practices, redirection of tracks and use to areas that are less sensitive, the dispersal of visitor activity at very low use intensities (less than 75 direct passes per year) and the concentration of activity on tracks above this level.

Atmospheric interactions affected both the mechanics of impact ejecta deposition and the environmental effects from the catastrophic Chicxulub impact at the Cretaceous-Paleogene (K-Pg) boundary. Hypervelocity reentry and subsequent sedimentation of Chicxulub impact spherules through the Earth's atmosphere was modeled using the KFIX-LPL two-phase flow code, which includes thermal radiation and operates at the necessary range of flow regimes and velocities. Spherules were injected into a model mesh approximating a two-dimensional slice of atmosphere at rates based on ballistic models of impact plume expansion. The spherules decelerate due to drag, compressing the upper atmosphere and reaching terminal velocity at ~70 km in altitude. A band of spherules accumulates at this altitude, below which is compressed cool air and above which is hot (>3000 K) relatively-empty atmosphere.Eventually the spherule-laden air becomes unstable and density currents form, transporting the spherules through the lower atmosphere collectively as plumes rather than individually at terminal velocity. This has implications for the depositional style and sedimentation rate of the global K-Pg boundary layer. Vertical density current formation in both incompressible (water) and compressible (air) fluids is evaluated numerically via KFIX-LPL simulations and analytically using new instability criteria. Models of density current formation due to particulate loading of water are compared to tephra fall experiments in order to validate the model instabilities.The impact spherules themselves obtain peak temperatures of 1300-1600 K and efficiently radiate that heat as thermal radiation. However, the downward thermal radiation emitted from decelerating spherules is increasingly blocked by previously-entered spherules settling lower in the atmosphere. This self-shielding effect strengthens with time as the settling spherule cloud thickens and becomes increasingly opaque, limiting both the magnitude and duration of the thermal pulse at the ground. For a nominal Chicxulub reentry model, the surface irradiance peaks at 6 kW/m <super>2 </super> and is above normal solar fluxes for ~25 minutes. Although biologic effects are still likely, self-shielding by spherules may have prevented the global wildfires previously postulated. However, submicron dust may act as a hot opaque cap in the upper atmosphere, potentially increasing the thermal pulse beyond the threshold for forest ignition.

Prepared by the Arid Lands Information Center, Office of Arid Lands Studies, University of Arizona ; Robert G. Varady, compiler.

Prepared by the Arid Lands Information Center, Office of Arid Lands Studies, University of Arizona ; Susan Parker, compiler. / February 1980 (revised January 1981)

Prepared by the Arid Lands Information Center, Office of Arid Lands Studies, University of Arizona ; A. Paige Grant, compiler.