1,721,101 research outputs found
Real time control of public transit
No full textThe objective of this Thesis is the improvement in speed and regularity of transit systems, using real-time control strategies, in particular, vehicle holding and conditional transit priority. This objective is attained by taking into account the inherent uncertainty
of transit operation, due to the random travel times and passenger arrivals at stops. A simulation model of a single transit route is presented, with explicit representation of traffic lights. Priority at intersections is assumed to be given only by green extension
actuated by local sensors, with upstream stop location, while the vehicle holding strategies are based also on the availability of real time information at stops, by means of a prevision for the future arrivals. The results are evaluated and compared using suitably defined performance indicators. In a parallel study, some relations between transit assignment and operation models and between transit operation and dwell time models are highlighted by identifying some features of the transit headway distributions
and comparing the results obtained, in carrying out a sensitivity analysis of the operation model, if different dwell time models are utilized
A Risk Analysis Framework for Offshore Wind Turbines
No full textThis paper defines a risk analysis framework for offshore wind turbines (OWTs) and OWT farms. OWTs, due to their exposure to a demanding climatic environment, the use of particularly innovative construction methods and materials, and the relatively limited knowhow in the design and construction, are prone to elevated risk. The risk analysis problem is defined within a more global risk management framework, where several steps are foreseen in order to accomplish predetermined objectives. Starting from the establishment of the specific risk management context, the various steps for risk assessment are presented, together with the methods for risk identification, analysis, evaluation and mitigation, strictly related with the complexity of the system. As a final step, the options for risk treatment are considered. In addition, for the purpose of risk identification, a system decomposition of the relevant elements is performed, both physical related (e.g. the constituting parts) and for the external conditions and interactions. © 2010 ASCE
Energy Harvesting for Structural Health Monitoring Systems: State of art and recent developments
No full textA structural system can be defined as complex if its behavior is influenced from nonlinearities, uncertainties or interactions. For such systems, it is consistent to comply with precise levels of safety and serviceability. The correct functioning of complex systems has been in the recent years a concern and a subject of studying in engineering. In particular, in the field of electronic systems engineering, the concepts of dependability and dependable system have been defined since the early days. This dependability framework is extended to complex structural systems, as integration to the broadly accepted structural requirements for the design, construction and maintenance of structures, when considering the optimization of the design process of the system within a performance based approach.
Considering the above, the knowledge of the loads and the consequent response of the structural system become important. In the past 30 years, a great research effort has been devoted to establishing effective local and global SHM methods. Structural health monitoring (SHM) technology provides a way to evaluate the safety and durability of a structure during its service life, to ensure its serviceability and sustainability. Analyzing the problem in terms of the expected payoff, the outcome is that, in cases of complex structure and infrastructure systems (long span bridges, high rise buildings etc.) the monitoring process should be planned during
the design phase and should be carried out during the entire life cycle to assess the structural health and performance under in-service and accidental conditions. The latter concept has been
introduced during the last years in large scale structures and infrastructures in China.
Long-term monitoring (of bridges or high rise buildings for example, where long-term designates a period of time from 1 year to decades and desirably the entire life cycle, was pioneered in China and in Japan, and is a quite recent concept, made possible by recent advances in sensing, data acquisition, computing, communication, data, and information management.
Modern advances in wireless technology and low-power electronics implemented in SHM, led to a huge research in the area of energy harvesting. The term energy harvesting indicates the process of extracting energy from the environment or from a surrounding system and converting it to useable electrical energy. Due to the remote placement of SHM devices, it is desirable to capture and utilize ambient energy (e.g. sunlight, thermal gradient, wind, vibration, ambient RF energy), where available, in order to provide unlimited energy for the lifespan of the electronic devices (sensors, electronics, etc). As a consequence, devices powered by energy harvesters, can be placed in any inaccessible location, and also can be embedded into the structures, since battery replacement is not a challenge anymore. The feasibility of fabrication of such devices at
an industrial level is nowadays realistic
Implementation of the LinTim package for evaluating delay management strategies in public transportation
No full textThe proposed research builds on current applications and findings of LinTim, a collection of different algorithms for planning steps in public transportation (currently railway lines). The objective of the research was twofold. In a first place, to implement a bus typical dataset to LinTim and compare delays in bus and in railway settings. In a second place, to evaluate delay management policies where bus lines are included.
At the end of the research, a comparative service reliability analysis of high frequency (e.g. metro) and low frequency (e.g. railway) public transport systems takes place. Known reliability indices with respect to this question are critically reviewed, and a novel index accounting for the average delay experienced by the passengers in the network is introduced. Numerical tests on the performance of this index, using close to real world data from the German railway system and from the Athens metro, are also presented. Finally, the effects of delay management strategies in high and low frequency systems are discussed
Requirements and main aspects of an intelligent Monitoring System for Long Span Bridges
No full textThis paper shows how a well designed monitoring system can help to acquire information about the state of a complex structural system, such as a long span bridge, in real time, with the purpose of limiting the occurrence of structural strength or serviceability failure
Energy harvesting in bridges and transportation infrastructure networks: state of art, recent trends and future developments
No full textIn the upward trend of renewable energy growth, several proposals have been made concerning energy harvesting devices in transportation infrastructure networks. The objective, concerning higher power extraction, is to supply power to auxiliary systems (e.g. road lights or information panels), thus, satisfying the requirement for sustainable transportation infrastructures. This paper deals with the state of art, the recent trends and the future developments in energy harvesting for bridges and transportation infrastructure networks. Particular focus is given to the definition of a broader framework of energy extraction for such systems. Finally, a survey takes place for the possible research issues and synergies among different research sectors
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