Sharif Digital Repository

Planning safe rendezvous and docking trajectories between two spacecrafts has a high importance in the space applications. In order to make two spacecrafts moving in different orbits closer, two stages must be completed simultaneously: First the implementation of rendezvous maneuver which deals with the generation of control/guidance commands leading to trajectories that lead the chaser towards the target. Second the docking maneuver incorporation which makes the two spacecrafts closer with the relative zero attitude. Various approaches have been dealt with till now using the analytical and numerical approaches generally considering rendezvous, not the docking maneuver. These approaches... 

Systems thinking is considered to be an indispensible competency in dealing with complex issues. Although several studies tried to substantiate this claim in the past from different perspectives, none rigorously focused on how the practitioners' characteristics affect systems thinking practice. In this paper we propose that a person's narcissism hinders his/her ability to practice systems thinking effectively in ego-relevant issues, although he/she might be relatively capable to think systemically in general. Ego-relevant issues are defined as those matters that may cause eventual threat to the person's self-esteem or provide opportunities to self-promote. A systems thinking questionnaire... 

Identifying fractional systems and designing controllers for these systems is one of the leading challenges due to their limitations. Systems can have constraints on output, input, and states. These constraints make it difficult to design a controller. In this project, controller design methods for fractional-order systems with output constraints are investigated. A controller is designed for a strict feedback nonlinear system with unknown dynamics subject to asymmetric and variable output constraints, unknown direction of the controller, and unmeasurable states. To design the controller, the direct and backstepping technique is used and the Lyapunov barrier function is applied for the first... 

Controlling the nonlinear processes is very important in industry. In this thesis, model predictive control is considered as a nonlinear control strategy and two nonlinear models, namely wiener and Hammerstein models are used and their identification methods are described. State-space model is also considered and closed-loop stability has been studied. Another strategy for controlling the nonlinear process is global linearization control. Some concepts and related theorems for this strategy are stated. PID controller is used as a linear controller for this strategy. In this model for estimating the state and load, two nonlinear observers are used. Stability analysis of output feedback... 

Measuring the speed and position of the rotating part and using the speed and position information in the closed loop control of electric machines is very important. Various sensors are available for this purpose, including resistive sensors, capacitive sensors, encoders, synchros, resolvers, Halleffect sensors, and etc. Common encoders include optical and magnetic types. There are two main problems in using an encoder as a sensor: determining/maintaining accuracy during change of rotational direction and determining the absolute position. Both of the mentioned challenges have been investigated in the case of optical encoders and some solutions have been provided to overcome them. Although... 

Permanent Magnet Synchronous Motors (PMSMs) are more conventional and widely employed in Electric Vehicles (EVs) applications. The rotor position performed an essential role through PMSMs drive; therefore, any deviation in the detected position will be evaded in coordinate transformations, originating from external or inherence sources. Subsequently, the discussed faults will be conducted to three-phase currents and output torque through erroneous transformations. Resolver’s estimated rotor position due to fault occurrence will be defined as aggregating ideal and non-ideal components. Moreover, based on inherence periodic in resolvers’ principle, non-ideal components could be written by the... 

In this project a complete simulator for a two-winding, 25cm air gap Maglev system by considering the pratical constaritns, position and velocity observer and the current sensor dynamics was derived. In order to control the ball in any desired position a twisting sliding mode controller was designed as the basic controller in the rest of project. The designed controller can not transfer the ball in far trajectory. In first step we modify that to reach a better performance by changing the value of current, passing through the coils in steady state. In the second step, the far trajectories are divided to a finite number of sub-trajectory such that the ball can pass these sub-trajectory by... 

Quantum interference and coherence are responsible for a novel set of physical phenomena, where Electromagnetically Induced Transparency is one of the most important of them. Each of these phenomena can make a new possibility for modifying the optical properties of a coherently prepared medium. Fast controllability of optical properties in one hand and flexibility of this control process in the other hand, are important factors that attract interests into coherent control of light .Coherent control of optical properties of the medium can be used in designing some advanced and challenging devices including All-Optical Switches. In this work , in a consistent picture, using a step by step... 

Designing a supply chain of a network is the most important strategic decisions that contribute to the overall stability of it. One of the most sustainable competitive advantage for countries is to make the supply chain activities more efficient and effective. One of the major activities that could be saving a lot on costs, is the logistics activities. Forward and reverse logistics to design independently and asynchronously could provide sub-optimality. Therefore, many companies have been increasingly integrated into the supply chain and logistics networks. Furthermore, concerns for the environmental issues were lead the companies to the closed-loop supply chain that is provided by... 

These days, most companies are creating Closed-loop Supply Chains or they are adding Reverse Supply Chain to their existing Forward Supply Chain. Reducing raw material consumption, profit, customer satisfaction and environmental laws are most important reasons of this phenomenon. In the Closed-loop Supply Chains, companies collect the end of life and the end of use products and then if the quality of the returned product is good enough, that product with be refurbished and will be sold again and if the quality of returned products is not good enough to be refurbished, companies will use its good parts in manufacturing new products and the rest of the parts would be sent to disposal centers.... 

Fulfilling the demands of customers, used to be the main purpose of Supply Chain Network Designers. Soon after that, the environmental concerns created the concept of Reverse Logistic in order to prevent goods from being scattered in the environment after their disposal. Governmental regulations and people's concerns, forced the factories to gather the created pollutions of the environment. They gradualy confessed the positive impacts of these ruturns on their financials. The flow of forward and reverse logistics establishes a Closed-Loop in which the returning economical circumstances were transferd into original factories. Later, Open-Loops were created. In open-loops the returns have to... 

Network design is one of the major strategic decisions of a supply chain which leads to the whole sustainability of the chain. Besides, due to an increase in carbon dioxide emissions and its harmful effects, recently there has been an growing interest in green supply chain network design. In this thesis, a mixed integer linear programming is developed to formulate a closed-loop supply chain with forward and reverse logistics. Moreover, social cost rate of carbon dioxide is used to consider environmental impact. Considering uncertainty in closed-loop supply chains is crucial. To do so, three robust optimization methods including Soyster, Ben-tal and Nemirovski and Bertsimas and Sim approaches...