Modelling the water mass exchange through navigational channels connecting adjacent coastal basins - application to the Channel of Potidea (North Aegean Sea)

The research objective is the detection of the mechanism of the water mass exchange through a navigational channel connecting two adjacent coastal basins. The research involves the application of a mathematical model in parallel to in-situ measurements. The hydrodynamic circulation in the greater area of the NW Aegean Sea is modeled by means of a barotropic circulation model. Wind, Coriolis and Tide are the main forcings taken into account. The flow through the channel is resolved at a subgrid scale by means of a local open channel flow model. The comparison between field measurements, recorded during a limited period, and the model results supports the model verification. The study is integrated by an operational application of the model under various realistic forcings. The results help to gain a better understanding of the mechanisms regulating the water mass exchange and the consequent interaction between two adjacent connected coastal basins. From the case study of the Potidea channel it is revealed that the water mass exchange under mean wind forcing is of the same order as the one induced by the tidal forcing

Energy-Aware Base Stations: The Effect of Planning, Management, and Femto Layers

We compare the performance of three base station management schemes on three different network topologies. In addition, we explore the effect of offloading traffic to heterogeneous femtocell layer upon energy savings taking into account the increase of base station switch-off time intervals. Fairness between mobile operator and femtocell owners is maintained since current femtocell technologies present flat power consumption curves with respect to served traffic. We model two different user-to-femtocell association rules in order to capture realistic and maximum gains from the heterogeneous network. To provide accurate findings and a holistic overview of the techniques, we explore a real urban district where channel estimations and power control are modeled using deterministic algorithms. Finally, we explore energy efficiency metrics that capture savings in the mobile network operator, the required watts per user and watts per bitrate. It is found that the newly established pseudo distributed management scheme is the most preferable solution for practical implementations and together with the femotcell layer the network can handle dynamic load control that is regarded as the basic element of future demand response programs

Control of Flexible Smart Devices in the Smart Grid

This paper investigates load control and demand response in a smart grid environment where a bidirectional communication link between the operator and the smart flexible devices supports command and data flow. Two control schemes are investigated that can provide energy management, taking into account user's comfort, via binary on-off policies of the smart flexible devices. A dynamic control algorithm is introduced that considers real time network characteristics and initiates command flow when critical parameters exceed predefined thresholds. To sustain fairness in the system, priority based and round robin scheduling algorithms are proposed. A continuous control algorithm is also explored to define the higher bounds of energy savings. To quantify the discomfort of users that participate in this type of services, a heuristic consumer utility metric is proposed and measurements with a flexible device (air conditioning unit) are performed to model empirically possible time intervals of the control scheme. Reciprocal fair energy management schemes are investigated being both operator and user centric. It is shown that great energy and cost savings can be achieved providing the required degrees of freedom to the smart grid to self-adapt during peak hours

Advanced physical techniques for radio channel modeling

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Advanced physical techniques for radio channel modeling.

Wireless technology constitutes the basis of the majority of modem communication systems. The deployment of wireless systems mainly concerns data services such as mobile and broadcasting applications, or target identification and military services. The key element for the successful planning of any kind of wireless network is the detailed and in depth knowledge of the propagation channel. The mobility of the user and the physical obstructions that may intervene in the propagation path between the communication points cause distortion to the transmitted information. The understanding of the propagation conditions and the channel characterisation is achieved either by extensive measurement campaigns or by employing sophisticated propagation algorithms. Since the measurement campaign is an expensive and time consuming task, contemporary research is focused on the development of deterministic models that can accurately predict the channel behaviour in real environments. The demand for high data delivery services in modem communication systems requires the utilisation of large bandwidth at high frequency regions of the available spectrum. Therefore, asymptotic high frequency modelling techniques and relevant algorithms have emerged as the major propagation modelling tools for modern radio systems analysis and design. In this thesis, we address the problem of high frequency diffraction over complex structures and scenarios that incorporate a cascade of physical canonical obstructions in the propagation path between the two ends. New formulations are derived for field predictions over rounded surfaces and a cascade of multi-shape structures. The Uniform Theory of Diffraction (UTD) is applied in all the work and it is further extended to account for transition zone diffraction over scenarios that incorporate arbitrary multiple canonical objects being multi-shaped in nature. The concept of continuity equations and slope diffraction are also emphasized. The simulation results show uniform and accurate field predictions and extensive comparison tests are performed with other diffraction theories and measurements. The developed formulations are incorporated in a propagation tool for irregular terrain channel modelling. An unambiguous terrain modelling algorithm is synthesized and used to assign optimum fitted canonical shapes to the terrain irregularities. The results of the simulations are compared with real measurements over irregular scenarios and a very good fit is observed. The importance of the choice of the used canonical shape to the terrain modelling is also highlighted

Smart Grid Technologies for Future Radio and Data Center Networks

This article explores smart grid technologies that can be applied to a telecommunication network to achieve energy-efficient networking, autonomous operation, and adaptation to real-time electricity pricing schemes. With the fast penetration of renewable energy sources within base stations and data centers, the telecommunication operator can establish an active role in the energy market by adjusting power consumption in real time. In the telecommunications sector, energy management technologies have recently emerged with BS management schemes and virtual machine migration/allocation strategies. In the energy sector, smart grid technologies and new standards enable real-time management and pricing. The only brick missing is the orchestration of the technologies in the two sectors to enable smart telecommunications network operation in terms of energy consumption. In this article, concepts such as demand response, supply load control, and the model of the "prosumer" in the smart grid are correlated to the operation of modern radio and data center networks. The main outcome of the research is to provide new ideas for net zero service delivery and explore the role of the telecommunication provider in the energy market where dynamic electricity pricing is expected to hold a critical role in decision making processes

Comparison of three longshore sediment transport rate formulae in shoreline evolution modeling near stream mouths

Longshore sediment transport (LST) rate is the most essential quantity to be defined in shoreline evolution models. Intercomparisons of different formulae on the basis of laboratory or field measurements of LST rate values are commonly found in literature; however, examples of comparison based on long-term shoreline evolution observations are scarce. Moreover, applications of shoreline evolution models near stream mouths (where the sediment input affects coastal morphology) are also scarce. In the present paper, three well-known LST rate formulae are compared, as part of a model used to simulate shoreline evolution in the vicinity of a stream mouth. The model was properly adapted by the authors to provide with new capabilities regarding: (a1) the use of wind data to simulate wave climate, (b1) the description of coastal morphology and sediment transport and (c1) the introduction of sediment sources. Results show the relative efficiency of the three formulae in terms of: (a2) the stream sediment discharge needed to simulate measured shorelines, and (b2) the divergence observed between simulations and measurements; analysis is deemed to provide a useful perspective on the importance of LST rate formula selection in similar engineering applications

Periodic Flexible Demand: Optimization and Phase Management in the Smart Grid

Based on measurements obtained by commodity wireless sensors, we observe that the majority of thermostatic loads in a user premise are described by periodic pulse waves. We propose a novel first stage of optimization in the smart grid which reduces external on/off command flow for demand response between the controller and the smart appliances. A phase management scheme is developed that defines optimal time shifts on the periodic loads in order to provide peak power and energy cost reduction over a limited time horizon. A gradient descent optimization technique, based on Taylor series, is applied to determine the phases of the pulses in discrete time steps. Three optimization strategies and two control schemes are explored. Minimization of peak power loads, minimization of energy costs and flattening of the power curve are modeled. A centralized and a distributed control scheme are explored. It is found that respectable peak power and cost reduction can be achieved in the centralized control scheme but redundant data transfer in the network and increased complexity is necessary. On the other hand, the distributed control scheme reduces the overall complexity but does not present significant savings