Development of physical and mathematical models for the Porous Ceramic Tube Plant Nutrification System (PCTPNS)

A physical model of the Porous Ceramic Tube Plant Nutrification System (PCTPNS) was developed through microscopic observations of the tube surface under various operational conditions. In addition, a mathematical model of this system was developed which incorporated the effects of the applied suction pressure, surface tension, and gravitational forces as well as the porosity and physical dimensions of the tubes. The flow of liquid through the PCTPNS was thus characterized for non-biological situations. One of the key factors in the verification of these models is the accurate and rapid measurement of the 'wetness' or holding capacity of the ceramic tubes. This study evaluated a thermistor based moisture sensor device and recommendations for future research on alternative sensing devices are proposed. In addition, extensions of the physical and mathematical models to include the effects of plant physiology and growth are also discussed for future research

A kinematic wave theory of capacity drop

Capacity drop at active bottlenecks is one of the most puzzling traffic phenomena, but a thorough understanding is practically important for designing variable speed limit and ramp metering strategies. In this study, we attempt to develop a simple model of capacity drop within the framework of kinematic wave theory based on the observation that capacity drop occurs when an upstream queue forms at an active bottleneck. In addition, we assume that the fundamental diagrams are continuous in steady states. This assumption is consistent with observations and can avoid unrealistic infinite characteristic wave speeds in discontinuous fundamental diagrams. A core component of the new model is an entropy condition defined by a discontinuous boundary flux function. For a lane-drop area, we demonstrate that the model is well-defined, and its Riemann problem can be uniquely solved. We theoretically discuss traffic stability with this model subject to perturbations in density, upstream demand, and downstream supply. We clarify that discontinuous flow-density relations, or so-called "discontinuous" fundamental diagrams, are caused by incomplete observations of traffic states. Theoretical results are consistent with observations in the literature and are verified by numerical simulations and empirical observations. We finally discuss potential applications and future studies.Comment: 29 pages, 10 figure

MEASUREMENT AND MODELLING OF STRUCTURE AND PORE LEVEL PROCESSES IN FILTERS AND WICKS

Characterisation of new filtration and wicking materials through a 'wet-bench" testing process is a requirement for many filtration companies before new products can be released to market. A reduction in this testing commitment through the application of successful computational based models, requiring minimal empirical input, would undoubtedly result in huge financial savings and reductions in testing lead times. Such models could offer total media characterisation and could also aid further insights into many filtration and wicking processes which before would have required an expensive combination of different testing procedures. In this research, a depth filtration model has been developed, based on the three-dimensional void network model Pore-Cor, The geometry of the void network is fitted, by means of an 8-dimensional Boltzmann annealed amoeboid simplex, to the porosity and percolation characteristics of stainless steel sintered filters measured by mercury intrusion porosimetry (MIP). Preferential and critical flow paths through the network are calculated via a newly developed algorithm which allows a representation of net flow within individual pore/throat clusters. Particles from an experimental size distribution are fed along these flow-biased paths, using a newly developed random-particle-selection algorithm and, when straining occurs, the flow paths are re-calculated. The model is shown usefully to reproduce experimental filtration efficiencies as a function of pressure drop, measured by single pass tests. A critique of filtration efficiency measurements is given, suggesting use of a new 'alpha efficiency' rather than standard beta efficiency. The model is currently being adapted to accept porometry as well as porosimetry data, hence avoiding the use of mercury in future testing. Further to development of the filtration model the research associated with this thesis has also investigated two related areas. One is an investigation of a hydrophilic treatment of a series of polymeric sinters using oxidizing plasma. The investigation shows an improved method of data analysis of capillary rise measurements. An optimization process for determining the correct hydrophilic treatment parameters is proposed based on the variance across sample sets, and results are interpreted with respect to the Vyon® samples analysed. Secondly an investigation of anomalous compression characteristics found in the MIP of stainless steel Sinterflo® media is presented. Hypotheses were proposed for the observed increase in media compressibility and these were investigated using the Pore-Cor void network model for comparison with other investigations of porosity and compression analysis. Preliminary results suggest increased compressibility arises from microscopic material deformities and micro-fractures found in the media.Porvair Filtration Group Lt

A dynamic traffic assignment model for highly congested urban networks

The management of severe congestion in complex urban networks calls for dynamic traffic assignment (DTA) models that can replicate real traffic situations with long queues and spillbacks. DynaMIT-P, a mesoscopic traffic simulation system, was enhanced and calibrated to capture the traffic characteristics in a sub-area of Beijing, China. The network had 1698 nodes and 3180 directed links in an area of around 18 square miles. There were 2927 non-zero origin–destination (OD) pairs and around 630,000 vehicles were simulated over 4 h of the morning peak. All demand and supply parameters were calibrated simultaneously using sensor counts and floating car travel time data. Successful calibration was achieved with the Path-size Logit route choice model, which accounted for overlapping routes. Furthermore, explicit representations of lane groups were required to properly model traffic delays and queues. A modified treatment of acceptance capacity was required to model the large number of short links in the transportation network (close to the length of one vehicle). In addition, even though bicycles and pedestrians were not explicitly modeled, their impacts on auto traffic were captured by dynamic road segment capacities.Beijing Transportation Research Cente

Dissipation of stop-and-go waves via control of autonomous vehicles: Field experiments

Traffic waves are phenomena that emerge when the vehicular density exceeds a critical threshold. Considering the presence of increasingly automated vehicles in the traffic stream, a number of research activities have focused on the influence of automated vehicles on the bulk traffic flow. In the present article, we demonstrate experimentally that intelligent control of an autonomous vehicle is able to dampen stop-and-go waves that can arise even in the absence of geometric or lane changing triggers. Precisely, our experiments on a circular track with more than 20 vehicles show that traffic waves emerge consistently, and that they can be dampened by controlling the velocity of a single vehicle in the flow. We compare metrics for velocity, braking events, and fuel economy across experiments. These experimental findings suggest a paradigm shift in traffic management: flow control will be possible via a few mobile actuators (less than 5%) long before a majority of vehicles have autonomous capabilities

Simulating and Validating the Traffic of Blackwall Tunnel Using TfL Jam Cam Data and Simulation of Urban Mobility (SUMO) (Short Paper)

Blackwall Tunnel is one of the most congested roadways in London. By simulating the tunnel and the connecting roads, information can be obtained about the traffic conditions and bottlenecks. In this paper, a model will be created using the Simulation of Urban Mobility (SUMO) tool and traffic flow data gathered from Transport for London (TfL) traffic cameras. The result from the simulation will be compared to the journey time data of Blackwall Tunnel in order to determine the accuracy of simulation