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robust-optimization
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Operating Room Scheduling with Data driven Robust Optimization Approach
, M.Sc. Thesis Sharif University of Technology ; Rafiee, Majid (Supervisor)
Abstract
In this thesis we will focus on operating room scheduling considering open strategy and uncertainty in the duration of operations for elective patients. A mixed integer programming model will be proposed having the expected list of patients that are going to be scheduled in the specific time horizon and working hours of doctors with the purpose of maximizing the number of scheduled elective patients in the determined time horizon. We aim to assign each patient to an operating room and a start time regarding operating rooms and surgeons working hours, care units capacity constraints and sequencing constraints. We will define three possible ways for each patient after their operations, naming...
Designing a Blood Distribution System Using Heterogeneous Vehicles- a Heuristic and Robust Optimization Approach
,
M.Sc. Thesis
Sharif University of Technology
;
Modarres Yazdi, Mohammad
(Supervisor)
Abstract
Human blood is a valuable and scarce product which is only produced by human body. There is no replaceable material for our blood and there has always been a constant need to donors and blood products in societies. Like every other product, blood has to be transfused to patients after it is donated and this process requires a complete and effective blood supply chain. Considering all properties, complexities and uncertainties of a blood supply chain, we need to develop stable methodologies in order to simplify decision making in blood supply chain. In this research, we develop a novel blood distribution system from a regional blood center (RBC) to its nearby hospitals. It helps RBCs plan the...
Optimization in Vehicle Routing Problem for Delivering Goods Considering Uncertainty in Delivery Locations
, M.Sc. Thesis Sharif University of Technology ; Akbari Jokar, Mohammad Reza (Supervisor)
Abstract
Transportation is an essential part of the economic growth in every country in the nowadays industrial era by making the possibility of good’s consuming, far from its origin. Delivery of a final product to the customer’s needs transportation of raw materials from suppliers to producers, transportation of semi-final products between companies, and, finally, delivery of the final product to customers and destination markets. Transportation costs include the majority of logistic expenses because of their abundance (between 30-60 percent). Traveling salesman problem and after that vehicle routing problem have been proposed about 70 years ago. In the last few decades, mathematical models, precise...
A Robust Conditional Value-at-Risk (C-VaR) Optimization Approach for Direct Optimization of Beam Directions and Apertures in Intensity Modulated Radiation Therapy Method
, M.Sc. Thesis Sharif University of Technology ; Eshghi, Kourosh (Supervisor)
Abstract
Breast cancer has been one of the main causes of women's deaths in recent years. Today, various methods are used to treat this disease, among which intensity-modulated radiation therapy is one of the most common methods. The goal of radiation therapy is to destroy cancer cells while protecting the surrounding healthy tissues. In left breast cancer, due to the proximity of the heart and breast tissue, we are at risk of delivering an excessive dose to the heart and increasing cardiac complications after the treatment. In addition, due to the irregular and unpredictable breathing movements of the patient during the treatment and the resulting uncertainty, we face more challenges. In order to...
Improving the Decision-Making Process under the Presence of Uncertainty in Airplane Conceptual Design, Creating an Intuitive Platform
, M.Sc. Thesis Sharif University of Technology ; Banazadeh, Afshin (Supervisor)
Abstract
Improving performance and reducing costs is a constant competition between aircraft designers, which has made multi-disciplinary optimization always part of the design process. In the design process of a conventional aircraft, there are various uncertainties in technology levels, mission parameters, costs and operating environment. It is clear that these uncertainties will make the decision-making difficult and lead to uncertainties in the output of the design; on the other hand, considering them will increase the computational cost. Understanding how much the uncertainty of each parameter will affect the overall output of the design and its performance, makes it possible to ignore the...
Developing a Market-based Framework for Exploiting Flexibility Capabilities of Distribution Network’s Resources Using the Concept of Virtual Power Plant
, Ph.D. Dissertation Sharif University of Technology ; Fotuhi Firuzabad, Mahmud (Supervisor) ; Moeini Aghtaie, Moein (Co-Supervisor)
Abstract
Increasing variability and uncertainty in modern power systems may affect the systems’ reliable operation. This means higher needs for flexibility provision in power systems to meet the net load variability and uncertainty. Distributed energy resources (DERs) dispersed in distribution networks have noticeable flexibility capabilities which can provide required flexibility of distribution network while they can help the transmission network to acquire the flexibility requirements if appropriately aggregated and coordinated. This thesis presents a market-based hierarchical framework for exploiting DERs’ flexibility provision to meet intra-hourly variability and uncertainty of net loads in...
Robust optimal control for large-scale systems with state delay
, Article Transactions of the Institute of Measurement and Control ; Vol. 36, Issue. 4 , June , 2014 , pp. 551-558 ; ISSN: 01423312 ; Sadati, N ; Sharif University of Technology
Abstract
Optimal control of large-scale uncertain dynamic systems with time delays in states is considered in this paper. For this purpose, a two-level strategy is proposed to decompose the large-scale system into several interconnected subsystems at the first level. Then optimal control inputs are obtained by minimization of convex performance indices in presence of uncertainties, in the form of states and interactions feedback. The solution is achieved by bounded data uncertainty problems, where the uncertainties are only needed to be bounded and it is not required to satisfy the so-called 'matching conditions'. At the second level, a simple substitution-type interaction prediction method is used...
Two-level robust optimal control of large-scale nonlinear systems
, Article IEEE Systems Journal ; Volume 9, Issue 1 , 2015 , Pages 242-251 ; 19328184 (ISSN) ; Rahmani, M ; Saif, M ; Sharif University of Technology
Abstract
Finding an optimal control strategy for a nonlinear uncertain system is a challenging problem in the area of nonlinear controller design. In this paper, a two-level control algorithm is developed for robust optimal control of large-scale nonlinear systems. For this purpose, using a decomposition/coordination framework, the large-scale nonlinear system is first decomposed into several smaller subsystems, at the first level, where a closed-form solution as a feedback of states and interactions is obtained to optimize each subsystem. At the second level, a substitution-type prediction method, as a coordination strategy, is used to compensate the nonlinear terms of the system and to predict the...
Application of the adjoint multi-point and the robust optimization of shock control bump for transonic aerofoils and wings
, Article Engineering Optimization ; Volume 48, Issue 11 , 2016 , Pages 1887-1909 ; 0305215X (ISSN) ; Nejati, A ; Chaharlang Kiani, K ; Sharif University of Technology
Taylor and Francis Ltd
Abstract
A shock control bump (SCB) is a flow control method which uses a local small deformation in a flexible wing surface to considerably reduce the strength of shock waves and the resulting wave drag in transonic flows. Most of the reported research is devoted to optimization in a single flow condition. Here, both equally and variably weighted multi-point optimization and a robust adjoint optimization scheme are used to optimize the SCB. The numerical simulation of the turbulent viscous flow and a gradient-based adjoint algorithm are used to find the optimum location and shape of the SCB for two benchmark aerofoils. A multi-point optimization method under a constant-lift-coefficient constraint is...
Optimum damping resistance of potential transformers for mitigating ferro-resonance in gas insulated substations
, Article International Journal of Electrical Power and Energy Systems ; Volume 103 , 2018 , Pages 553-561 ; 01420615 (ISSN) ; Ranjbar, A. M ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
Different methods are developed for mitigation of ferro-resonance in high-voltage gas insulated substations (GISs). The main components, which have impacts on probability of occurrence of ferro-resonance, are grading capacitance of circuit breakers (CBs) and internal loss of potential transformers (PTs). However, by using active or passive damping resistance in the secondary of PTs, the probability of occurrence of ferro-resonance can be decreased substantially. It is worth mentioning that the thermal limitations of PTs restrict us to dissipate a lot of energy in the damping resistance. Therefore, in this paper, both thermal and electrical aspects of ferro-resonance are considered and...
A Benders decomposition for the location-allocation and scheduling model in a healthcare system regarding robust optimization
, Article Neural Computing and Applications ; Volume 29, Issue 10 , 2018 , Pages 873-886 ; 09410643 (ISSN) ; Sadeghi, J ; Modarres Yazdi, M ; Sharif University of Technology
Springer London
2018
Abstract
The hospital location and service allocation is one of the most important aspects of healthcare systems. Due to lack of studies on covering location-allocation and scheduling problems with respect to the uncertain budget, this paper develops a bi-objective hybrid model to locate hospitals and allocate machines and services scheduled. The costs of establishing facilities are assumed to be uncertain, while a robust counterpart model is employed to overcome the uncertainty. Covering the demand of each service is limited as well. Moreover, hospitals have a limited space to the specialized equipment like CT scan and MRI machines, while there is a cost constraint on hospitals and the specialized...
Robust model and solution algorithm for the railroad blocking problem under uncertainty
, Article Scientia Iranica ; Volume 25, Issue 4 , 2018 , Pages 1916-1930 ; 10263098 (ISSN) ; Shafahi, Y ; Sharif University of Technology
Sharif University of Technology
2018
Abstract
The railroad blocking problem emerges as an important issue at the tactical level of planning in freight rail transportation. This problem consists of determining the optimal paths for freight cars in a rail network. Often, demand and supply resource indicators are assumed certain; hence, the solution obtained from a certain model might not be optimal or even feasible in practice due to the stochastic nature of these parameters. To address this issue, this paper develops a robust model for this problem with uncertain demand and travel time as supply resource indicators. Since the model combines integer variables and nonlinear functions, a branch-And-cut algorithm is used to solve the...
Real-Time cooperative adaptive robust relay beamforming based on kalman filtering channel estimation
, Article IEEE Transactions on Wireless Communications ; Volume 18, Issue 12 , 2019 , Pages 5600-5612 ; 15361276 (ISSN) ; Ahmadian Attari, M ; Amiri, R ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
In this paper, an adaptive channel estimation algorithm is proposed for the multi-user robust relay beamforming problem. We propose a norm-bounded channel uncertainty model for all of the channels. We employ the Extended Kalman Filter (EKF) and the Unscented Kalman Filter (UKF) for joint estimation of channel coefficients and beamforming weights, and propose a Markov model for source-relay and relay-destination channels as well as the beamforming weights in the relays. The channel coefficients and bemforming weights are shown to be well-estimated in order to minimize the total relays power transmission subject to worst-case signal to interference and noise ratio (SINR) criterion at each...
Multi-objective robust design optimization (MORDO) of an aeroelastic high-aspect-ratio wing
, Article Journal of the Brazilian Society of Mechanical Sciences and Engineering ; Volume 42, Issue 11 , 2020 ; Roudbari, A ; Hajipourzadeh, P ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2020
Abstract
In this paper, a new approach for multi-objective robust optimization of flutter velocity and maximum displacement of the wing tip are investigated. The wing is under the influence of bending–torsion coupling and its design variables have different levels of uncertainty. In designing and optimizing wings with a high aspect ratio, the optimization process can be done in such a way to increase the flutter velocity, but this can increase the amplitude of the wing tip displacement to a point that leads to the wings damage and structural failure. Therefore, single-objective design optimization may lead to infeasible designs. Thus, for multi-objective optimization, modeling is based on the...
Estimating abilities of distributed energy resources in providing flexible ramp products for active distribution networks
, Article Sustainable Cities and Society ; 2020 ; Salehi, J ; Moeini Aghtaie, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Growing demand for flexible ramp products (FRPs) to maintain the power balance in active distribution networks (ADNs) has expanded the use of costly fast-start generators in the upstream real-time market. In order to limit the power system's reliance on these units, it is necessary to establish new sources for providing ADNs with FRPs. In this context, the present paper examines the abilities of distributed energy resources (DERs) and active loads for supplying the ramp capacity demands of ADNs. Accordingly, a local real-time market was established in the ADN, empowering several DERs and active loads to provide the network's FRPs demands. The proposed market was formed in the context of a...
A robust optimization approach for the production-inventory-routing problem with simultaneous pickup and delivery
, Article Computers and Industrial Engineering ; Volume 143 , May , 2020 ; Akbari Jokar, M. R ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
The production routing problem (PRP) merges the lot-sizing problem and the vehicle routing problem, two classical problems that have been the focus of comprehensive studies for over half a century. Solving the PRP is an effort to optimize decisions about the production, inventory, distribution, and routing in an integrated manner. In the literature of the recent decade, due to economic changes and regulatory issues, reverse logistics has become a focal point. Subsequently, the vehicle routing problem with simultaneous pickup and delivery (VRPSPD) has drawn more and more attention for its considerable effect on the reverse logistics problem. In addition, one of the major arguments in supply...
Designing a sustainable reverse supply chain network for COVID-19 vaccine waste under uncertainty
, Article Computers and Industrial Engineering ; Volume 174 , 2022 ; 03608352 (ISSN) ; Fallahi, A ; Varmazyar, M ; Fathi, M ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
The vast nationwide COVID-19 vaccination programs are implemented in many countries worldwide. Mass vaccination is causing a rapid increase in infectious and non-infectious vaccine wastes, potentially posing a severe threat if there is no well-organized management plan. This paper develops a mixed-integer mathematical programming model to design a COVID-19 vaccine waste reverse supply chain (CVWRSC) for the first time. The presented problem is based on minimizing the system's total cost and carbon emission. The uncertainty in the tendency rate of vaccination is considered, and a robust optimization approach is used to deal with it, where an interactive fuzzy approach converts the model into...
Cooperative fixed-time/finite-time distributed robust optimization of multi-agent systems
, Article Automatica ; Volume 142 , 2022 ; 00051098 (ISSN) ; Nobakhti, A ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
A new robust continuous-time optimization algorithm for distributed problems is presented which guarantees fixed-time convergence. The algorithm is based on a Lyapunov function technique and applied to a class of problems with coupled local cost functions. The algorithm applies a methodology with no expansion of the local variables. This reduces the computation complexities of the solution and improves scalability. Using an integral sliding mode strategy we incorporate effective disturbances rejection on the decision variables as experienced in a wide range of industrial applications. It is shown that the algorithm can easily be modified to a finite-time solution when evaluations of the...
Multi-objective optimization of acetone droplet impingement on phase change material in direct-contact discharge method
, Article Journal of Energy Storage ; Volume 46 , 2022 ; 2352152X (ISSN) ; Aria, H. P ; Shafii, M. B ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
Improving the discharge process of phase change materials (PCMs) is of great importance and can be effective for thermal energy storage (TES) systems. In this research, the direct-contact method for acetone droplet on molten paraffin is optimized to enhance the efficiency of the discharge process of PCMs and TES systems working with intermediate boiling fluid (IBF). In order to improve the storage rate and increase the freezing rate in the system, the NSGA-II algorithm is used. When the acetone droplet hits, owing to its low boiling point relative to the temperature of molten paraffin, the acetone evaporates, causing the creation of solidified paraffin area. The main goal of the current...
Application of an improved harmony search algorithm in well placement optimization using streamline simulation
, Article Journal of Petroleum Science and Engineering ; Volume 78, Issue 3-4 , 2011 , Pages 664-678 ; 09204105 (ISSN) ; Aminshahidy, B ; Pishvaie, M. R ; Sharif University of Technology
2011
Abstract
Optimal well placement is a crucial step in efficient reservoir development process which significantly affects the productivity and economical benefits of an oil reservoir. However, it is a complex and challenging problem due to the different engineering, geological and economical variables involved. This leads to a very large number of potential scenarios that must be evaluated using numerical reservoir simulations. The key points in such an optimization process are using a fast function evaluation tool and development of an efficient and robust optimization algorithm that can find good solutions with a minimum required number of function evaluations. This study presents an approach that...