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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

A mathematical and experimental study on the surface water quality in Tehran

Asadollah-Fardi, Gholamreza January 2000 (has links)
No description available.

Multivariable control systems design using multiobjective evolutionary computing

Rocha e Silva, Valceres Vieira January 1999 (has links)
No description available.

Data assimilation in ocean circulation models with systematic errors

Martin, Matthew J. January 2001 (has links)
No description available.

Applications of statistical physics to finance

D'Hulst, Rene January 2001 (has links)
No description available.

Air pollution in northern Czech Republic

Surapipith, Vanisa January 2002 (has links)
No description available.

A macroscopic traffic flow model for adverse weather conditions.

Shah, Syed Abid Ali 06 April 2017 (has links)
Adverse weather has a direct effect on traffic congestion and the time delay on roads. Weather conditions today are changing rapidly and are more likely to have a severe effect on traffic in the future. Although different measures have been taken to mitigate these conditions, it is important to study the impact of these events on road conditions and traffic flow. For example, the surface of a road is affected by snow, compacted snow and ice. The objective of this thesis is to characterize the effect of road surface conditions on traffic flow. To date, traffic flow under adverse weather conditions has not been characterized. A macroscopic traffic flow model based on the transition velocity distribution is proposed which characterizes traffic behavior during traffic alignment under adverse weather conditions. The model proposed realistically characterizes the traffic flow based on snow, compacted snow, and ice. Results are presented which show that this model provides a more accurate characterization of traffic flow behavior than the well known Payne-Whitham model. / Graduate

Multi-scale tilt depth estimation

Van Buren, Reece 04 March 2014 (has links)
Many an approach to the estimation of magnetic source depths from magnetic data has been investigated over the past half a century. These approaches have been shown to have particular strengths and weaknesses with few implemented on a wide scale, commercial basis. A review of many of the more popular, as well as a few of the more obscure methods, is presented within this work. The history of multi-scale computation, with emphasis on its application to potential fields is summarized. A newly developed depth estimation technique dubbed Multi-Scale Tilt Depth Estimation is offered. The method has been shown to derive suitable depth estimates when applied to modelled data computed from a range of simple synthetic models. Sensitivity of the method to model type, dip, interference and noise has been tested. A number of mitigating strategies to improve and stabilize the method’s performance have been proposed. Results of the successful application of the method to field datasets from the Bushveld Complex and surrounding areas in South Africa are shown. Code to execute the method, written in Matlab is offered in Appendix A. Figures of the application of the method to all synthetic models have been included in Appendix B and C. A portion of this work has been presented at the South African Geophysical Association’s 11th Biennial Technical Meeting and Exhibition in the form of verbal and poster presentations accompanied by a short paper which is included here in Appendix D.

On Material Modelling of High Strength Steel Sheets

Larsson, Rikard January 2012 (has links)
The work done in this thesis aims at developing and improving material models for use in industrial applications. The mechanical behaviour of three advanced high strength steel grades, Docol 600DP, Docol 1200M and HyTens 1000, has been experimentally investigated under various types of deformation, and material models of their behaviour have been developed. The origins of all these material models are experimental findings from physical tests on the materials. Sheet metal forming is an important industrial process and is used to produce a wide range of products. The continuously increasing demand on the weight to performance ratio of many products promotes the use of advanced high strength steel. In order to take full advantage of such steel, most product development is done by means of computer aided engineering, CAE. In advanced product development, the use of simulation based design, SBD, is continuously increasing. With SBD, the functionality of a product, as well as its manufacturing process, can be analysed and optimised with a minimum of physical prototype testing. Accurate numerical tools are absolutely necessary with this methodology, and the model of the material behaviour is one important aspect of such tools. This thesis consists of an introduction followed by five appended papers. In the first paper, the dual phase Docol 600DP steel and the martensitic Docol 1200M steel were subjected to deformations, both under linear and non-linear strain paths. Plastic anisotropy and hardening were evaluated and modelled using both virgin materials, i.e. as received, and materials which were pre-strained in various material directions. In the second paper, the austenitic stainless steel HyTens 1000 was subjected to deformations under various proportional strain paths and strain rates. It was experimentally shown that this material is sensitive both to dynamic and static strain ageing. A constitutive model accounting for these effects was developed, calibrated, implemented in a Finite Element software and, finally, validated on physical test data. The third paper concerns the material dispersions in batches of Docol 600DP. A material model was calibrated to a number of material batches of the same steel grade. The paper provides a statistical analysis of the resulting material parameters. The fourth paper deals with a simple modelling of distortional hardening. This type of hardening is able to represent the variation of plastic anisotropy during deformation. This is not the case with a regular isotropic hardening, where the anisotropy is fixed during deformation. The strain rate effect is an important phenomenon, which often needs to be considered in a material model. In the fifth paper, the strain rate effects in Docol 600DP are investigated and modelled. Furthermore, the strain rate effect on strain localisation is discussed. / SFS ProViking Super Light Steel Structures

Effect of tilt actuator manipulation on suspended boom sprayer roll

Hicks, Brad Geoffrey 19 August 2005
Agricultural sprayers are used to apply chemical treatments (pesticides and fertilizer) to crops. A sprayer distributes the chemical by employing many nozzles spaced evenly along a boom structure oriented perpendicular to the direction of travel to cover large areas with each machine pass. To maximize spray efficacy, the nozzles must be held a specific distance from the target to be sprayed. With diversification of crop types grown in Western Canada, foliar application of chemical treatments at multiple points during the plants life cycles are now required. This multi-growth-stage application process requires a machine with a large range of vertical adjustment; thus permitting the nozzles to be maintained the correct distance from the target (crop) as it grows. Suspended boom sprayers provide the range of adjustment required.<p> The suspended boom structure consists of three controlled sections which are positioned via use of hydraulic actuators. To reduce the effect of terrain inputs through the carrying frame on the booms orientation, most suspended boom sprayers incorporate a passive suspension system to limit coupling between the carrying frame and boom. By doing this however, a negative effect is created. During typical operation, the operator will use the actuator to reorient one section thereby maintaining the desired distance from the boom to the target; the opposing section will deviate from its desired position due to coupling of the boom sections through the passive suspension system. The quantification of this problem was the basis for this research. <p> A computer simulation model of the boom structure, passive suspension system, hydraulic actuator, and on/off type directional valve was created. Comparisons to experimental data showed the model was applicable for predicting trends in boom performance related to manipulation of actuator velocity profiles. Standardized changes in the actuated sections orientation were used to establish the existing performance baseline and quantify the problem. Alternative commercially available directional valves (proportional and pulse width modulated) were then simulated and used in conjunction with the boom model to determine if boom performance improvements may be realized by defining the actuators acceleration rate during orientation changes. <p> The proportional valve was able to limit the acceleration and deceleration of the actuated section to reduce the coupling effect and improve the non-actuated sections performance. However, the performance of the actuated section degraded more significantly in all trials regardless of input profile. The performance degradation resulted as slower acceleration and deceleration of the actuator required an increased amount of time for the desired orientation of the actuated section to be reached. It was also concluded that performance of the dynamic orientation of the boom structure was equivalent for orientation changes driven wither by pulse width modulation of an on/off valve or a true proportional valve. The boom structures large inertia and low natural frequency acted as a suitable filter for the flow and pressure pulsations introduced by pulse width modulation.

RTDS modelling of battery energy storage system

Rydberg, Lova January 2011 (has links)
This thesis describes the development of a simplified model of a battery energy storage. The battery energy storage is part of the ABB energy storage system DynaPeaQ®. The model has been built to be run in RTDS, a real time digital simulator. Batteries can be represented by equivalent electric circuits, built up of e.g voltage sources and resistances. The magnitude of the components in an equivalent circuit varies with a number of parameters, e.g. state of charge of the battery and current flow through the battery. In order to get a model of how the resistive behaviour of the batteries is influenced by various parameters, a number of simulations have been run on a Matlab/Simulink model provided by the battery manufacturer. This model is implemented as a black box with certain inputs and outputs, and simulates the battery behaviour. From the simulation results a set of equations have been derived, which approximately give the battery resistance under different operational conditions. The equations have been integrated in the RTDS model, together with a number of controls to calculate e.g. state of charge of the batteries and battery temperature. Results from the RTDS model have been compared with results from the Simulink model. The results coincide reasonably well for the conditions tested. However, further testing is needed to ensure that the RTDS model produces results similar enough to the ones from the Simulink model, over the entire operational range.

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