Design procedures for moment end-plate connections, which include prying action effects, have been verified for five end-plate configurations. The design procedures include the use of yield-line theory for determining the end-plate thickness and the so-called modified Kennedy method for determining bolt forces. This investigation extends these design procedures to include the four-bolt extended unstiffened moment end-plate connection. The results of four experimental tests are evaluated and compared to the predicted results obtained from yield-line theory and the modified Kennedy method. Using the finite element method, analyses to determine the stress in the beam at a cross-section near to the connection are also performed. The results from the finite element analyses are compared to experimental results. In addition, the type of construction suitable for this connection is assessed. Modifications to the analytical predictions are made based on the above comparisons. Results indicate that the flange force is distributed equally to the inner and outer end-plate. Also, prying action is included for the inner bolts at all times, and for the outer bolts when failure is controlled by the end-plates. Design recommendations and an example using the modified design procedure are presented in this thesis. / Master of Science

Modem systems are characterized by a multifunctional capability. They are designed to accomplish not one but a series of missions, each one requiring the performance of certain functions. Each of those functions requires the support of some system elements. The fact that an element is not available at certain point in time by no means implies that the entire system is "down" at that moment as the traditional availability definition and formulation requires. Depending on what the mission-function and function-element support requirements are, the "down" condition of a certain element may prevent the accomplishment of some system missions, but some others will still be available. Moreover, the traditional approach assumes that the time to failure and the time to repair associated to each element follow both a negative exponential distribution. Therefore, a more comprehensive treatment of the concept of system availability is required. All the necessary assumptions to enable the definition and quantification of availability figures of merit are listed. Then, definitions are established for availability and degraded availability at different levels in the system structure, from element to system. In addition, some related concepts such as mission reliability and dependability are defined. The developed model enables the prediction of the defined availability figures of merit. The foundation of the model is the renewal process associated with each system element and the links that specify the mission-function and function-element support requirements. The formulation for some related concepts is also presented. Some well-known pairs of distributions are considered and the general expressions are particularized for them. Finally, an example is conducted in order to show the applicability of the derived expressions and to compare the obtained results with those obtained using the traditional approach. / Master of Science

A simple, design-oriented model of joints in vehicle structures is developed. This model accounts for the flexibility, the offsets of rotation centers of joint branches, and the coupling between rotations of a joint branch in different planes. The model parameters consist of torsional spring rates, the coordinates of the flexible hinges, and the orientations of planes in which the torsional springs are located. The model parameters are selected to be physically meaningful. In some cases, the behavior of joints can be accurately represented by using simpler models. The conditions under which the joint model can be simplified are discussed. A family of joint models with different levels of complexity are also defined. A probabilistic system identification is used to estimate the joint parameters by using the measured displacements. The parameters are estimated by minimizing the discrepancies between the measured and predicted displacements. Statistical tests which identify important parameters are also presented. These tests can be used to simplify the joint models without significantly reducing the accuracy in predicting structural responses. The identification methodology is applied to automotive structures with joints and also to isolated subassemblies consisting of joints and attached branches. / Ph. D.

No description available.

No description available.

With the remarkable increase in the population and number of vehicles, traffic has become a severe problem in most metropolitan areas. Traffic congestion has imposed tight constraints on economic growth, national security, and mobility of riders and goods. The open-mode integrated transportation system (OMITS) has been designed to improve the traffic condition of roadways by increasing the ridership of vehicles and optimizing transportation modes through smart services integrating emerging information communication technologies, big data management, social networking, and transportation management. Even a modest reduction in the number of vehicles on roadways will lead to a considerable cost savings in terms of time and money. Additionally the reduction in traffic jams will lead to a significant decrease in both gasoline consumption and greenhouse gas emissions. As a result, novel transportation management is critical to reduce vehicle mileage in the peak time of the road network. The OMITS was proposed to enhance transportation services in respect to the following three aspects: optimization of the transportation modes by multimodal traveling assignment, dynamic routing and ridesharing service with advanced traveler information systems, and interactive user interface for social networking and traveling information. Therefore, the OMITS encompasses a broad range of advanced transportation research topics, say dynamic trip- match, transportation-mode optimization, traffic prediction, dynamic routing, and social network- based carpooling. This dissertation will focus on a kernel part of the OMITS, namely traffic simulation and prediction based on data containing the distribution of vehicles and the road network configuration. A microscopic traffic simulation framework has been developed to take into account various traffic phenomena, such as traffic jams resulting from bottlenecking, incidents, and traffic flow shock waves. Four fundamental contributions of the present study are summarized as follows: Firstly, an accurate and robust vehicle trajectory data collection method based on image data of unmanned aerial vehicle (UAV) has been presented, which can be used to rapidly and accurately acquire the real-time traffic conditions of the region of interest. Historically, a lack in the availability of trajectory data has posed a significant obstacle to the enhancement of microscopic simulation models. To overcome this obstacle, a UAV based vehicle trajectory data collection algorithm has been developed. This method extracts vehicle trajectory data from the UAV’s video at different altitudes with different view scopes. Compared with traditional methods, the present data collection algorithm incorporates many unique features to customize the vehicle and traffic flow, through which vehicle detection and tracking system accuracy can be considerably increased. Secondly, an open mechanics-based acceleration model has been presented to simulate the longitudinal motion of vehicles, in which five general factors—namely the subject vehicle’s speed and acceleration sensitivity, safety consideration, relative speed sensitivity and gap reducing desire—have been identified to describe drivers’ preferences and the interactions between vehicles. Inspired by the similarity between vehicle interactions and particle interactions, a mechanical system with force elements has been introduced to quantify the vehicle’s acceleration. Accordingly, each of the aforementioned five factors are assumed to function as an individual trigger to alter each vehicle’s speed. Based on Newton’s second law of motion, the subject vehicle’s longitudinal behavior can be simulated by the present open mechanics-based acceleration model. By introducing feeling gap, multilane acceleration behavior is included in the presented model. The simulation results fit realistic conditions for the traffic flow and the road capacity very well, where traffic shockwaves can be observed for a certain range of the traffic density. This model can be extended to more general scenarios if other factors can be recognized and introduced into the modeling framework. Thirdly, a driver decision-based lane change execution model has been developed to describe a vehicle’s lane change execution process, which includes two steps, i.e. driver’s lane selection and lane change execution. Currently, most lane change models focus on the driver’s lane selection, and overlook the driver’s behavior during a process of lane change execution which plays a significant role in the simulation of traffic flow characteristics. In this model, a lane change execution is analyzed as a driver’s decision-making process, which consists of desire point setting, priority decision-making, corresponding actions and achievement of consensus analysis. Compared with the traditional lane change execution models, the present model describes a realistic lane change process, and it provides more accurate and detailed simulation results in the microscopic traffic simulation. Based on the presented open mechanics-based acceleration model and the driver decision- based lane change execution model, a reverse lane change model has further been developed to simulate some complex traffic situations such as reverse lane change process at a two-way-two- lane road section where one lane is blocked by a traffic incident. Based on this reverse lane change model, information on the average waiting time and road capability can be obtained. The simulation results show that the present model is able to reflect real driver behavior and the corresponding traffic phenomenon during a reverse lane change process Through a homogenization process of the microscopic vehicle motion, we can obtain the macroscopic traffic flow of the roadway network within certain time and spatial ranges, which will be integrated into the OMITS system for traffic prediction. The validation of the models through future OMITS operations will also enable them to be high fidelity models in future driverless technologies and autonomous vehicles.

Call number: LD2668 .T4 1978 B42 / Master of Science

In this dissertation the estimation of reliability for a developmental process generating attribute type data is examined. It is assumed that the process consists of m stages, and the probability of failure is constant or decreasing from stage to stage. Several models for estimating the reliability at each stage of the developmental process are examined. In the classical area, Barlow and Scheuer's model, Lloyd and Lipow's model and a cumulative maximum likelihood estimation model are investigated. In the Bayesian area A.F.M. Smith's model, an empirical Bayes model and a cumulative beta Bayes model are investigated. These models are analyzed both theoretically and by computer simulation. The strengths and weaknesses of each are pointed out, and modifications are made in an attempt to improve their accuracy. The constrained maximum likelihood estimation model of Barlow and Scheuer is shown to be inaccurate when no failures occur at the final stage. Smith's model is shown to be incorrect and a corrected algorithm is presented. The simulation results of these models with the same data indicate that with the exception of the Barlow and Scheuer's model they are all conservative estimators. When reliability estimation with growth is considered, it is reasonable to emphasize data obtained at recent stages and de-emphasize data from the earlier stages. A methodology is developed using geometric weights to improve the estimates. This modification is applied to the cumulative MLE model, Lloyd and Lipow's model, Barlow and Scheuer's model and cumulative beta Bayes model. The simulation results of these modified models show considerable improvement is obtained in the cumulative MLE model and the cumulative beta Bayes model. For Bayesian models, in the absence of prior knowledge, the uniform prior is usually used. A prior with maximum variance is examined theoretically and through simulation experiments for use with the cumulative beta Bayes model. These results show that the maximum variance prior results in faster convergence of the posterior distribution than the uniform prior. The revised Smith's model is shown to provide good estimates of the unknown parameter during the developmental process, particularly for the later stages. The beta Bayes model with maximum variance prior and geometric weights also provides good estimates.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, May 2016. / This thesis presents work on four problems identi ed in the Zomba Water Distribution Network. The research was carried out on the existing network infrastructure with the aim of improving e ciency by reducing Unaccounted-For Water (UFW). The rst challenge was to develop a demand model for the city based on its in uencing factors: daily and seasonal uctuations as well as population dynamics. The model was to capture demand patterns for short-term, medium-term to long-term time periods, thereby becoming an important input factor into decision making. The developed model may be employed to generate demand which can be input into the city's 10 year infrastructure expansion plan. The second problem was to explain why houses built too close to tanks are at risk of inconsistent water supply. It was found that the requirement of observing the tank elevations, helv, had been violated. As a result, the discontinued supplies occurred. Once the required tank elevation helv had been established, an extra increase in the elevation so as to accommodate a larger population was determined to be on the order of one centimeter. Third problem was to explain the continued mains pipe failures observed in the network. It was established that the main cause was the hammering e ects started through the process of manually closing ow control valves (FCVs) tted next to tanks. A possible remedy was to rather t the FCVs at joint nodes and not at the tanks. This was estimated to greatly reduce the hammering e ects, eventually turning them into minor head losses due to elbow bends. Finally, a structural approach to designing tanks that optimize the use of gravity is presented. This is an input into the infrastructure expansion planning of the city. Regardless of any design shapes they may take, tanks with height-radius, h=r, ratio of less than 1 exhibit diminished, as opposed to increased, height changes with demand changes. Such a property would ensure consistency in the pressure at the tank, allowing for delivery of the demanded load. / GR2016