Sharif Digital Repository

In this paper, a "Game Theory" approach for finding an optimal path in a "Wireless Sensor Network" is discussed. WSN is one of the most interesting research fields in the communication networks, and is the center of attention in recent years. In our model, a pricing and payment technique is presented to obtain an optimal path in a WSN by considering reliability, energy and traffic load. The proposed algorithm is able to find a path which improves network lifetime, load distribution and path reliability  

This paper models and analyses the dynamic response of a synchronous generator driven off-grid micro hydro power system using Simulink tool of MATLAB software. The results are assessed from various perspectives including regulation through no load to full load and overload scenarios under normal and abnormal operating conditions. The investigation under the normal conditions of no load, linearly changing load and full load divulges that the system operates in a satisfactory manner as generator voltage and frequency remain approximately constant at 1 pu. However, at full load generator voltage and frequency drop 3% and 0.5% respectively from its nominal values but remain within prescribed... 

Flow-mediated dilation measurement in the brachial artery using ultrasound imaging (FMD-US) is a common noninvasive procedure for endothelial function evaluation in the peripheral arteries. As FMD-US is operator-dependent and involves onerous equipment, its use has been mostly confined to research settings. In this paper, we propose to use the more accessible finger photoplethysmogram signal in conjunction with the FMD test (FMD-PPG) as a surrogate method. To this end, a tube-load physiological model of the upper arterial path in the arm is developed. Signals acquired from young and elderly subjects (N=20) are then investigated using model parameter estimation by the genetic algorithm. Our... 

The standard power flow (PF) equations are nonlinear, and their integration in the optimal PF (OPF) problem leads to a nonconvex hard-to-solve model. To attack the issue, this paper presents a linear PF model wherein real and imaginary parts of nodal voltages are variables. In the model, loads are interpreted via ZIP model including constant impedance, constant current, and constant power components. To preserve linearity of the model, the complex power is represented via a quadratic function of the hosting node voltage. The function coefficients are derived via curve fitting approaches. Since the model is linear, its solution does not need repetition and can be effectively integrated in the... 

This paper proposes a new algorithm to determine the best connection of multiple distributed generations (DGs) on distribution networks according to type of customers. The considered DG technology is combined heat and power (CHP) in various sizes which can be extended to other technologies. Different types of demand, such as industrial, residential and commercial are defined by the load model that is voltage dependent and the load patterns from real life hourly demand data. This method which is based on multi-year multi-period power flow is useful for Distribution Network Operators (DNOs) when they are faced with voltage dependent load models in their networks. However it can be used in... 

This paper develops a general framework for reliability assessment of multi-microgrid (MMG) distribution systems. It also investigates reliability impacts of coordinated outage man-agement strategies in a MMG distribution network. According to the proposed reliability evaluation framework, which is based on sequential Monte Carlo simulation method, distribution system is divided into smaller sections/microgrids based on protection sys-tem configuration and operating measures are efficiently simulat-ed considering different operation modes. In order to demonstrate the role of outage management strategy in reliability performance of MMG distribution systems, at first, the required features of... 

A new shear strengthening method involving post-tensioning of the critical shear region of reinforced concrete beams is investigated. Thirty-one experiments were carried out using 24 specimens. Theoretical load-deflection relations are obtained from moment-curvature analysis using fiber cross sections and taking into consideration the effects of different concrete confinements along the beam length. A theoretical shear strength model that includes three shear resisting components in the critical shear region of the strengthened beams is provided. Experimental results from beams with and without shear strengthening are compared with calculated load-deflection relations and predicted shear... 

Frequency control during power system restoration has not been strongly addressed. Operators are often concerned with the offline sizing of load and generation steps, but, nowadays, the introduction of Wide Area Measurement System (WAMS) makes it possible to monitor the stability of power system online. The constraints of WAMS operation result in some changes in power system frequency control. This paper proposes a novel methodology for frequency control and monitoring during the early steps of power system restoration based on WAMS. Detailed load modeling is achieved based on the static load modeling approach. Power generators' modeling is also accomplished utilizing the single machine... 

A stress-based forming limit diagram for necking prediction which is based on the strain gradient theory of plasticity in conjunction with the M-K model has been represented and used in tube hydroforming. In this study, the finite element model for bulge forming of straight tube has been constructed and verified with published experimental data. The adaptive simulation technique is based on the ability to detect the onset and growth of defects (e.g., wrinkling, and bursting) and to promptly readjust the loading paths. Thus, a suitable load path has been obtained by applying Adaptive Simulation Method in ANSYS Parametric Design Language (APDL)  

Load pay back effect is the excess of load as a result of load curtailment, observed in direct load control programs related to thermostatically controlled appliances. In this paper, according to a stochastic difference equation, the load profile of an aggregation of customers without control will be attained. Then the assumption to consider load pay back as linear will be examined through simulations. Afterwards, based on a data structure gained from performing load curtailments at each interval, least-square method will be used to fit load pay back factors for each interval. It is notable that there are some significant differences between the results attained in this paper and what was... 

This paper mainly focuses on operational reliability studies of modern power systems taking into consideration the effects of energy storage systems (ESSs). The aim is to develop a new evaluation tool to assess the effects of different factors such as penetration rate, operational strategies and capacities of the ESSs in determining the role of these systems as an operating reserve resource. In this regard, at first, some modifications are made to the PJM method aimed to precisely model the short-term variability in output generation of wind farms in reliability studies. Then, this algorithm is employed to examine the effects of ESSs operating strategies in operational reliability level of... 

Computation of Loss of Load Probability (LOLP) is a challenge in Generation Expansion Planning (GEP) problem. This paper presents a dynamic GEP model considering LOLP as a reliability criterion. The objective function of the proposed dynamic GEP model includes the discounted total costs of investment cost, operation cost, and maintenance cost. The proposed LOLP constrained GEP problem is formulated as a mixed integer nonlinear programming (MINLP) problem. The MINLP formulation of GEP problem is then converted to a mixed integer linear programming (MIP) problem by applying several approximations to LOLP constraint. The utilized approximations are divided into two clusters for low and high... 

This paper mainly focuses on operational reliability studies of modern power systems taking into consideration the effects of energy storage systems (ESSs). The aim is to develop a new evaluation tool to assess the effects of different factors such as penetration rate, operational strategies, and capacities of the ESSs in determining the role of these systems as a source of operating reserve. In this regard, at first, some modifications are made to the Pennsylvania-New Jersey-Maryland (PJM) method aimed to precisely model the short-term variability in output generation of wind farms in reliability studies. Then, this algorithm is employed to examine the effects of ESSs operating strategies... 

We consider load balancing in a network of caching servers delivering contents to end users. Randomized load balancing via the so-called power of two choices is a well-known approach in parallel and distributed systems. In this framework, we investigate the tension between storage resources, communication cost, and load balancing performance. To this end, we propose a randomized load balancing scheme which simultaneously considers cache size limitation and proximity in the server redirection process. In contrast to the classical power of two choices setup, since the memory limitation and the proximity constraint cause correlation in the server selection process, we may not benefit from the... 

Stalling of residential air conditioners (RACs) following a transient fault can delay the voltage recovery ranging from 3 to 20 seconds. This phenomenon is referred to as fault-induced delayed voltage recovery (FIDVR). Several aggregated RAC models have been presented to replicate the actual FIDVR events. However, they usually have two main drawbacks as: i) considering independent stalling voltage and stalling time for all RACs, ii) resulting in only two ultimate modes; either 100% stalled or 100% normal running. This paper amends the abovementioned shortcomings by proposing a simple and effective performance-based RAC model. The proposed model utilizes a simple explicit relation between the... 

We present a nonlinear geometric approach to fault detection and isolation (FDI) in a grid-connected inverter system. Open-switch faults in inverter power transistors together with faults in grid voltages and source current sensors are detected and isolated in the presence of disturbance. The detection process is based on dynamic model of an inverter, including a dc-bus capacitor and an output RL filter. The proposed FDI system does not rely on balanced or zero-sum conditions in the grid point and is functional under nonsinusoidal voltages and currents. IEEE  

Non-invasive measurement of flow-mediated dilation (FMD) in the brachial artery for assessing endothelial function is costly and operator-dependent, limiting its application to research cases. In this paper, an approach based on a physiological model between normalized central blood pressure and finger photoplethysmogram is presented. Baseline model parameters are estimated using a genetic algorithm in 30 subjects consisting of ten normal blood pressure (BP), ten high-BP and ten elderly volunteers. Beat-to-beat fitness values after reactive hyperaemia are calculated using baseline (before cuff occlusion) data. Results show that stimulus-induced changes are fairly described with a first order... 

The paper illustrates an extended effective load model including the capacities and uncertainties of generators and transmission lines. The conventional effective load model only considers the uncertainties of generators. An extended ELDC (effective load duration curve) based on the effective load model is proposed in the paper. The proposed nodal ELDC is able to supply information on nodal indices for probabilistic production cost simulation and reliability evaluation at the load points in a power system. It is expected that the effective load model presented in the paper will prove useful in many problems dealing with nodal and decentralised operation and control of electric power systems...