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uncertainty-analysis
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System dynamics to assess the effectiveness of restoration scenarios for the Urmia Lake: A prey-predator approach for the human-environment uncertain interactions
, Article Journal of Hydrology ; Volume 593 , 2021 ; 00221694 (ISSN) ; Zarghami, M ; Alizade Govarchin Ghale, Y ; Shahbazbegian, M. R ; Sharif University of Technology
Elsevier B.V
2021
Abstract
In recent decades, population growth, agricultural development and climate change have caused environmental problems in the world, especially in the arid and semi-arid regions such as Iran. Urmia Lake, one of the unique biosphere reserves of the world, has suffered from these problems in the last 20 years. Although many studies conducted to the negative impacts of human-induced activities, especially agricultural expansion on the lake, few studies focused on providing restoration plans for that. This study uses a system dynamics method for modelling the restorations scenarios of Urmia Lake based on the prey-predator approach. This method is helpful to simplify the complicated feedbacks and...
A new Optimization Approach for Solving Well Placement Problem under Uncertainty Assessment
, M.Sc. Thesis Sharif University of Technology ; Massihi, Mohsen (Supervisor) ; Roosta Azad, Reza (Supervisor)
Abstract
Determining the best location for new wells is a complex problem that depends on reservoir and fluid properties, well and surface equipment specifications, and economic criteria. Various approaches have been proposed for this problem. Among those, direct optimization using the simulator as the evaluation function, although accurate, is in most cases infeasible due to the number of simulations required. This study proposes a hybrid optimization technique (HGA) based on the genetic algorithm (GA) with helper functions based on the polytope algorithm and the neural network. Hybridization of the GA with these helper methods introduces hill-climbing into the stochastic search and also makes use...
A Real Option Model to Evaluate Investments in Combined Heat and Power (CHP)Projects
, M.Sc. Thesis Sharif University of Technology ; Haj Kazem Kashani, Hamed (Supervisor)
Abstract
Cogeneration technologies such as Combined Heat and Power (CHP) have promising features for providing the electrical energy that various industries require while reducing the emissions and other environmental impacts of these industries. Investments in CHP systems require substantial implementation costs followed by a relatively long period of recovering the invested capital through savings in utilities bills. Appropriate timing of CHP system investments can reduce capital expenses and enhance returns on investments. An appropriate investment valuation method is needed to identify the appropriate time to implement a given CHP system and to find the values of properly scheduled investments....
Uncertainty Analysis and Inverse Modeling of Seawater Intrusion in Coastal Aquifers
, Ph.D. Dissertation Sharif University of Technology ; Ataei Ashtiani, Behzad (Supervisor)
Abstract
Groundwater is the primary source of freshwater in many coastal areas and small islands around the world. The most important hazard to groundwater quality in coastal aquifers is seawater intrusion (SWI) resulting from over pumping, prolonged drought conditions and sea level rise due to climate change impacts. Numerical models of SWI are an important tool in the management of coastal aquifers. However, numerical modeling of SWI is one of the most challenging problems in groundwater hydrology. One of the reasons for the challenging nature of SWI numerical modeling is the relatively large level of uncertainty associated with the estimation of the model input parameters. This study focused on...
Safety Assessment for H2S Releasing in Arak Heavy Water Factory (GS(03) Plant) Using Probabilistic Safety Assessment Method (PSA)
, M.Sc. Thesis Sharif University of Technology ; Ghofrani, Mohammad Bagher (Supervisor)
Abstract
In general, release of hazardous gas in chemical process plants could be due to two reasons. First is failures due to degradation of components that have inventory of hazardous gas in standard process conditions, and the second is deviation of system from standard process conditions because of different failure modes of related components, e.g. controller equipments. The purpose of this study is, calculating the probability of H2S releasing in GS(03) plant of Arak Heavy Water factory, using PSA methods and its risk assessment. At First, fifteen groups of initiating events were identified with Hazop study for desired system. Then, for calculating the frequency of each event, the combination...
Power system dynamic state estimation with synchronized phasor measurements
, Article IEEE Transactions on Instrumentation and Measurement ; Vol. 63, issue. 2 , 2014 , p. 352-363 ; ISSN: 189456 ; Shahidehpour, M ; Fotuhi-Firuzabad, M ; Kamalinia, S ; Sharif University of Technology
Abstract
The dynamic state estimation (DSE) applied to power systems with synchrophasor measurements would estimate the system's true state based on measurements and predictions. In this application, as phasor measurement units (PMUs) are not deployed at all power system buses, state predictions would enhance the redundancy of DSE input data. The significance of predicted and measured data in DSE is affected by their confidence levels, which are inversely proportional to the corresponding variances. In practice, power system states may undergo drastic changes during hourly load fluctuations, component outages, or network switchings. In such conditions, the inclusion of predicted values could degrade...
Probabilistic power flow of correlated hybrid wind-photovoltaic power systems
, Article IET Renewable Power Generation ; Vol. 8, issue. 6 , 2014 , p. 649-658 ; ISSN: 17521416 ; Khajeh, M. G ; Rashidinejad, M ; Fotuhi-Firuzabad, M ; Sharif University of Technology
Abstract
As a matter of course, the unprecedented ascending penetration of distributed energy resources, mainly harvesting renewable energies such as wind and solar, is concomitant with environmentally friendly concerns. This type of energy resources are innately uncertain and bring about more uncertainties in the power system context, consequently, necessitates probabilistic analysis of the system performance. Moreover, the uncertain parameters may have a considerable level of correlation to each other, in addition to their uncertainties. The two point estimation method (2PEM) is recognised as an appropriate probabilistic method. This study proposes a new methodology for probabilistic power flow...
On possibilistic and probabilistic uncertainty assessment of power flow problem: A review and a new approach
, Article Renewable and Sustainable Energy Reviews ; Vol. 37 , 2014 , p. 883-895 ; ISSN: 13640321 ; Rashidinejad, M ; Fotuhi-Firuzabad, M ; Sharif University of Technology
Abstract
As energy resource planning associated with environmental consideration are getting more and more challenging all around the world, the penetration of distributed energy resources (DERs) mainly those harvesting renewable energies (REs) ascend with an unprecedented rate. This fact causes new uncertainties to the power system context; ergo, the uncertainty analysis of the system performance seems necessary. In general, uncertainties in any engineering system study can be represented probabilistically or possibilistically. When sufficient historical data of the system variables is not available, a probability density function (PDF) might not be defined, while they must be represented in another...
A comparison between the minimum-order & full-order observers in robust control of the air handling units in the presence of uncertainty
, Article Energy and Buildings ; Volume 91 , 15 March , 2015 , Pages 115-130 ; ISSN: 3787788 ; Moradi, H ; Alasty, A ; Sharif University of Technology
Abstract
Control of the air-handling units (AHU) is required to maintain satisfactory comfort conditions with low energy consumption. In the case of failure in sensor fusion systems of AHUs, full-order observers can be used as the supportive tool to provide an acceptable estimation of state variables. In this paper, a multivariable nonlinear model of the AHU is considered in the presence of uncertainties. The indoor temperature and relative humidity are controlled via manipulation of valve positions of air and cold water flow rates. In proposed hybrid control system, full and minimum-order observers are designed for the estimation of indoor temperature and relative humidity. Also, a regulator for...
History matching of naturally fractured reservoirs based on the recovery curve method
, Article Journal of Petroleum Science and Engineering ; Vol. 126, issue , February , 2015 , p. 211-221 ; ISSN: 09204105 ; Masihi, M ; Heinemann, Z. E ; Ghazanfari, M. H ; Sharif University of Technology
Abstract
The discrete fracture network (DFN) and Multiple-Continua concept are among the most widely used methods to model naturally fractured reservoirs. Each faces specific limitations. The recently introduced recovery curve method (RCM) is believed to be a compromise between these two current methods. In this method the recovery curves are used to determine the amount of mass exchanges between the matrix and fracture mediums. Two recovery curves are assigned for each simulation cell, one curve for gas displacement in the presence of the gravity drainage mechanism, and another for water displacement in the case of the occurrence of the imbibition mechanism. These curves describe matrix-fracture...
State-of-the-art least square support vector machine application for accurate determination of natural gas viscosity
, Article Industrial and Engineering Chemistry Research ; Vol. 53, issue. 2 , 2014 , pp. 945-958 ; ISSN: 08885885 ; Arabloo, M ; Shokrollahi, A ; Zargari, M. H ; Ghazanfari, M. H ; Sharif University of Technology
Abstract
Estimation of the viscosity of naturally occurring petroleum gases is essential to provide more accurate analysis of gas reservoir engineering problems. In this study, a new soft computing approach, namely, least square support vector machine (LSSVM) modeling, optimized with a coupled simulated annealing technique was applied for estimation of the natural gas viscosities at different temperature and pressure conditions. This model was developed based on 2485 viscosity data sets of 22 gas mixtures. The model predictions showed an average absolute relative error of 0.26% and a correlation coefficient of 0.99. The results of the proposed model were also compared with the well-known predictive...
A robust R&D project portfolio optimization model for pharmaceutical contract research organizations
, Article International Journal of Production Economics ; Vol. 158, issue , 2014 , p. 18-27 ; Modarres, M ; Nemati, H. R ; Amoako-Gyampah, K ; Sharif University of Technology
Abstract
Pharmaceutical drug Research and Development (R&D) outsourcing to contract research organizations (CROs) has experienced a significant growth in recent decades and the trend is expected to continue. A key question for CROs and firms in similar environments is which projects should be included in the firm's portfolio of projects. As a distinctive contribution to the literature this paper develops and evaluates a business support tool to help a CRO decide on clinical R&D project opportunities and revise its portfolio of R&D projects given the existing constraints, and financial and resource capabilities. A new mathematical programming model in the form of a capital budgeting problem is...
Continuous ant colony filter applied to online estimation and compensation of ground effect in automatic landing of quadrotor
, Article Engineering Applications of Artificial Intelligence ; Vol. 32, issue , June , 2014 , p. 100-111 ; Sharifi, A. R ; Sharif University of Technology
Abstract
The automatic landing of a quadrotor is often associated with model uncertainties, measurement noises, and ground effect phenomenon. To mitigate these challenges, the accurate estimation of states especially the height above the ground, and its rate of change is vital. Moreover, the error of ground effect model can also be estimated and compensated during landing. In this paper, the recently developed continuous ant colony filter is implemented for integrated estimation of states and parameters. The estimated states are used in height control loop. To investigate the closed loop performance of the filter, two control strategies, a classical proportional-integral-derivative controller and a...
Robust optimization approach for an aggregate production–distribution planning in a three-level supply chain
, Article International Journal of Advanced Manufacturing Technology ; Vol. 76, issue. 1-4 , 2014 , p. 623-634 ; Niaki, S. T. A ; Pasandideh, S. H. R ; Sharif University of Technology
Abstract
An aggregate production–distribution (P-D) planning generates an aggregate plan for regular time, overtime, outsourcing, hiring, and firing that takes into account distributing, inventory holding, backordering, and machine capacity for a definite planning horizon. A large number of P-D problems require decisions to be made in the presence of uncertainty. Previous research on this topic mainly utilized either stochastic programming or fuzzy programming to cope with the uncertainty. This may lead into huge challenges for supply chain managers that use non-robust P-D planning in uncertain environments. Moreover, there has been little discussion about robust optimization approach in aggregate...
Geometrical analysis of localization error in stereo vision systems
, Article IEEE Sensors Journal ; Volume 13, Issue 11 , 2013 , Pages 4236-4246 ; 1530437X (ISSN) ; Samavi, S ; Soroushmehr, S. M. R ; Shirani, S ; Sharif University of Technology
2013
Abstract
Determining an object location in a specific region is an important task in many machine vision applications. Different parameters affect the accuracy of the localization process. The quantization process in charge-coupled device of a camera is one of the sources of error that causes estimation rather than identifying the exact position of the observed object. A cluster of points, in the field of view of a camera are mapped into a pixel. These points form an uncertainty region. In this paper, we present a geometrical model to analyze the volume of this uncertainty region as a criterion for object localization error. The proposed approach models the field of view of each pixel as an oblique...
A robust loss function approach for a multi-objective redundancy allocation problem
, Article Applied Mathematical Modelling ; 2015 ; 0307904X (ISSN) ; Ameri, E ; Niaki, S. T .A ; Sharif University of Technology
Elsevier Inc
2015
Abstract
A redundancy allocation problem consists of the selection of a number of redundancies to be allocated in each subsystem of a series-parallel configuration to maximize system reliability, while minimizing overall system cost. Most existing studies either ignore system cost or assume deterministic component reliabilities. However, the selection of a network system design requires the estimation of its reliability and cost. Therefore, the uncertainty associated with such estimates must be considered in the decision process. In this study, an efficient method based on the loss function approach is proposed to solve the redundancy allocation problem. This approach not only optimizes the overall...
Sensitivity measures for optimal mitigation of risk and reduction of model uncertainty
, Article Reliability Engineering and System Safety ; Volume 117 , 2013 , Pages 9-20 ; 09518320 (ISSN) ; Haukaas, T ; Sharif University of Technology
2013
Abstract
This paper presents a new set of reliability sensitivity measures. The purpose is to identify the optimal manner in which to mitigate risk to civil infrastructure, and reduce model uncertainty in order to improve risk estimates. Three measures are presented. One identifies the infrastructure components that should be prioritized for retrofit. Another measure identifies the infrastructure that should be prioritized for more refined modeling. The third measure identifies the models that should be prioritized in research to improve models, for example by gathering new data. The developments are presented in the context of a region with 622 buildings that are subjected to seismicity from several...
Effects of inaccuracy of material permittivities on ray tracing results for site- Specific indoor propagation modeling
, Article Proceedings of the 2013 IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications, IEEE APWC 2013 ; Sept , 2013 , Pages 1172-1175 ; 9781467356893 (ISBN) ; Shishegar, A. A ; Sharif University of Technology
IEEE Computer Society
2013
Abstract
The complex dielectric constants of building materials are present in the reflection, transmission and diffraction coefficients of the ray tracing formulation. Any deviation of the dielectric constants included in ray tracing simulation from the actual material properties may be a source of inaccuracy of the simulation results. This paper explores the sensitivity of ray tracing results to the inaccuracy of the dielectric constants of building materials. To do this, the real and imaginary parts of the dielectric constants are considered as random variables to account for the present uncertainty. The propagation of uncertainty in the ray tracing simulation is then obtained by means of the...
IGDT based robust decision making tool for DNOs in load procurement under severe uncertainty
, Article IEEE Transactions on Smart Grid ; Volume 4, Issue 2 , 2013 , Pages 886-895 ; 19493053 (ISSN) ; Ehsan, M ; Sharif University of Technology
2013
Abstract
This paper presents the application of information gap decision theory (IGDT) to help the distribution network operators (DNOs) in choosing the supplying resources for meeting the demand of their customers. The three main energy resources are pool market, distributed generations (DGs), and the bilateral contracts. In deregulated environment, the DNO is faced with many uncertainties associated to the mentioned resources which may not have enough information about their nature and behaviors. In such cases, the classical methods like probabilistic methods or fuzzy methods are not applicable for uncertainty modeling because they need some information about the uncertainty behaviors like...
A new hybrid model for performance evaluation of IEEE 802.11p broadcast mode in vehicular ad hoc networks: A numerical analysis
, Article 2013 International Conference on Connected Vehicles and Expo, ICCVE 2013 - Proceedings ; 2013 , Pages 719-725 ; Hemmatyar, A. M. A ; Sharif University of Technology
2013
Abstract
In this paper, we will propose a new methodology for performance modeling of IEEE 802.11p medium access control (MAC) sub-layer in broadcast mode. In most of the current works, it is assumed that the number of contending nodes is deterministic and constant. However, in vehicular ad hoc networks, we can observe a kind of uncertainty in number of contending vehicles, which try to get access to the shared wireless channel. This uncertainty can affect the performance analysis of MAC protocols in vehicular environments. In this paper, we will try to model the dynamicity of number of contending vehicles based on the distribution of vehicles' velocity. This model will be combined with the current...