Sharif Digital Repository

In stressful situations such as severe accidents in nuclear power plants, operators need support tools to ease decision making in the selection of accident management measures. Following the Three Mile Island (TMI) accident in 1979, the first severe accident in a nuclear power plant, Accident Management Support Tools (AMSTs) were extensively developed and installed in a number of nuclear power plants. Lessons learned from the Fukushima accident highlighted the importance of accident management in mitigation severe accidents and suggested the reconsideration of accident management programs, which in turn created the need for AMSTs adaption and modernization. This paper provides the first... 

This paper deals with break size estimation of loss of coolant accidents (LOCA) using a nonlinear autoregressive with exogenous inputs (NARX) neural network. Previous studies used static approaches, requiring time-integrated parameters and independent firing algorithms. NARX neural network is able to directly deal with time-dependent signals for dynamic estimation of break sizes in real-time. The case studied is a LOCA in the primary system of Bushehr nuclear power plant (NPP). In this study, number of hidden layers, neurons, feedbacks, inputs, and training duration of transients are selected by performing parametric studies to determine the network architecture with minimum error. The... 

Artificial Neural networks offer viable solution to identification and modeling of aerospace dynamic systems. This paper proposes a new approach to the nonlinear modeling of agile aircraft which is applicable to develop flight simulators. In contrary to classical methods, neural-network-based modeling of aircraft dynamics does not require any aerodynamic or propulsion model and a few flight test measured data suffice. The obtained model is shown valid for arbitrary pilot inputs within a region of mach-altitude around the pre-specified flight condition  

In this paper, the ability of the neural network based system identification for aircraft modeling and simulation is investigated. The focus of this paper is to obtain methods for improving generalization of the neural network based aircraft models which are going to be used in aircraft simulators. The genetic algorithm is used to simultaneously train and optimize a modified Elman network architecture. It is shown that this method improves generalization in system identification of aircraft dynamics  

Bibliometric, and scientometric approaches are used to provide appropriate tools for evaluating scientific products at local, national, and international levels. Iran, the same as other countries, has many universities and research centers in the field of engineering that Iran's most of the scientific products account for the field of engineering. This study is a descriptive approach using scientometric methods. is The present paper mainly focuses on visualizing the structure of the Iranian scientific publications in the field of engineering indexed in Thomson Reuters (ISI) accessible via WoS during 1939-2011. To draw the historiographical map of Iranian scientific outputs in the field of... 

This paper deals with the simulation-based design optimization and experimental validation of the characteristics of an in-core silver Self-Powered Neutron Detector (SPND). Optimized dimensions of the SPND are determined by combining Monte Carlo simulations and analytical methods. As a first step, the Monte Carlo transport code MCNPX is used to follow the trajectory and fate of the neutrons emitted from an external source. This simulation is able to seamlessly integrate various phenomena, including neutron slowing-down and shielding effects. Then, the expected number of beta particles and their energy spectrum following a neutron capture reaction in the silver emitter are fetched from the... 

This paper deals with the application of Fast Fourier Transform Base Method (FFTBM) with signal mirroring (FFTBM-SM) to assess accuracy of MELCOR code. This provides deeper insights into how the accuracy of MELCOR code in predictions of thermal-hydraulic parameters varies during transients. The case studied was modeling of Station Black-Out (SBO) accident in PSB-VVER integral test facility by MELCOR code. The accuracy of this thermal-hydraulic modeling was previously quantified using original FFTBM in a few number of time-intervals, based on phenomenological windows of SBO accident. Accuracy indices calculated by original FFTBM in a series of time-intervals unreasonably fluctuate when the... 

This paper deals with the development of a qualified thermal-hydraulic nodalization for modeling Station Black-Out (SBO) accident in PSB-VVER Integral Test Facility (ITF). This study has been performed in the framework of a research project, aiming to develop an appropriate accident management support tool for Bushehr nuclear power plant. In this regard, a nodalization has been developed for thermal-hydraulic modeling of the PSB-VVER ITF by MELCOR integrated code. The nodalization is qualitatively and quantitatively qualified at both steady-state and transient levels. The accuracy of the MELCOR predictions is quantified in the transient level using the Fast Fourier Transform Base Method... 

In this paper a fuzzy controller is developed for automatic landing of fixed wing Unmanned Aerial Vehicles (UAVs). It is assumed that the vehicle has a built in vision system which provides the runway relative position and orientation to be used in the designed tracking system. The stability of the controller was analyzed through vector field diagrams, and the system performance is tested through a complete 6DOF computer simulation. The results show a satisfactory performance of the controller all through the automatic landing phase. ©2009 IEEE  

This research is dedicated to investigating the dynamics identification and periodic control of a mono-wing aerial vehicle. The study employs well-established system identification strategies in both time and frequency domains to extract equivalent linear models. By exciting the system dynamics with a frequency sweep signal, non-parametric and parametric models are derived for each control channel, namely the flap and thrust. Furthermore, a comprehensive nonlinear simulation model is developed to facilitate trade study and design optimization. The identified models undergo careful validation using a two-square wave input signal, demonstrating their accuracy through a comparison with flight... 

The performance of Co-flow fluidic thrust vectoring is a function of secondary flow characteristics and the fluidic nozzle geometry. In terms of nozzle geometry, wall shape and the secondary slot aspect ratio are the main parameters that control the vector angle. The present study aims to find a high quality wall shape to achieve the best thrust vectoring performance, which is characterized by the maximum thrust deflection angle with respect to the injected secondary air. A 3D computational fluid dynamics (CFD) model is employed to investigate the flow characteristics in thrust vectoring system. This model is validated using experimental data collected from the deflection of exhaust gases of... 

Surface mounted piezoelectric sensors and actuators on elastic structures are often connected to electrical networks. The coupled equations of motion of the elastic structure with piezoelectric elements are already well known. However, due to complex behavior of some electrical elements in the electrical network, it is not an easy task to obtain the integrated equations of the whole system. A good remedy for this problem is to take advantage of an equivalent electrical circuit (EEC) representation of the mechanical part, leading the entire system to be represented as an electrical circuit. In this study, the authors propose a new method for constructing the EEC. This method is based upon the... 

This paper describes a feasibility study of using numerical analysis technique, coupled with a non-linear simulation model of a conceptual fluidic-thrust-vectored unmanned aerial tailsitter to obtain required thrust deflection angles for a transition manoeuvre in take-off. It also studies the aircraft behaviour in transition subjected to the changes in specified parameters like the thrust value and the engine distance from the centre of gravity. The focus of the research presented was to get the vehicle from zero speed on the ground, in vertical position, to a specified velocity at a specified attitude, in cruise position. It was also specified that, when the vehicle was considered to be... 

The feasibility of using fluidic thrust-vectoring system, as a control technique for the longitudinal and lateral trim purpose was investigated in this study. For this purpose, integration of a Co-flow method into the propulsion unit of a conceptual aerial vehicle was assumed. The focus of the research presented was to estimate the required thrust vector angle in order to trim the aerial vehicle in different flight phases. Since the fluidic thrust vectoring requires secondary air flow to deflect the engine exhaust gas, this research also provides an analytical toolset for preliminary sizing of a suitable secondary air supply. It was found that thrust vectoring could be an effective mean of... 

In this paper, the dynamic stability of a small thrust-vectored flapless aerial vehicle is investigated. The study was based on linearization of nonlinear equations of motion, using the aircraft longitudinal and lateral-directional stability derivatives. Since the aircraft was supposed to be merely controlled by fluidic thrust vectoring, the concept was novel and some innovative derivatives had to be introduced. The aircraft characteristic equations were then derived in terms of the obtained derivatives and used for dynamic stability analysis and flying quality assessment in horizontal flight. As well, nonlinear simulation modeling was used for dynamical mode excitation and observation. All...