Sharif Digital Repository

In this thesis, the multidisciplinary design of liquid propellant satellite launch vehicle has been done by taking into consideration the effects of fuel sloshing. At first, the theory of multidisciplinary design and one-level architecture with the label of multidisciplinary feasibility have been used. In the following, Gravitational Search Algorithm (GSA) and Particle swarm optimization (PSO) have been developed. Then, the multidisciplinary design cycle began with the design of the liquid propellant system. In the propulsion section, the selection of the optimal fuel, the design of the nozzle, motor and the selection of the optimal engine cycle considering the geometric and mass... 

Quality and intelligibility are two aspects of speech that are affected by various factors, such as background noise and echo. The performance of many commercial and military speech-based systems depends on at least one of these aspects of speech. Therefore, this research aims to design an improvement model to remove background noise and reverberation from the speech signal. The model training framework is based on deep learning methods and has a supervised approach in the time domain. The input of this system is the raw waveform of the speech signal mixed with noise and reverberation, and the output is the enhanced waveform of this signal. An architecture is proposed in this thesis based on... 

New product development (NPD) is a crucial process in maintaining a company’s competitive position and succeeding in dynamic markets. One of contemporary trends in the global economy is mass customisation that bases on modifications of existing products instead of designing everything as a new project. Product development can be achieved in design, planning or production phases. Specifications of previous products deliver information of design, cost and time of past NPD projects that can be the basis for developing new products. Given the low chance of technical success, market change and high cost research, market demand, product development management is important to increase the quality... 

This study presents a Machine Learning framework for post-earthquake structural damage state and economic loss estimation. The framework is proposed to rapidly determine whether a structure is safe or unsafe to be occupied following a seismic event, to predict the detailed structural response, and finally to evaluate the economic loss of the buildings. An extensive database is developed by analyzing twelve low-rise, mid-rise, and high-rise eccentrically braced frames (EBFs) under 44 scaled ground motion records through incremental dynamic analysis (IDA) to train the Machine Learning algorithms. Machine Learning algorithms are employed to classify the structural damage state of the buildings... 

The Reconfigurable manufacturing system (RMS) was first introduced in 1996 with the ability to respond quickly to market changes and in response to global competition between companies. The effort of this research is to expand the problem presented in the Moghaddam et al. (2019) by introducing the concept of raw materials for the production of parts and related issues such as purchasing and warehousing raw materials, and providing a suitable solution to the problem. In the basic article, the RMS should utilize the best combination of machines and their configurations in proportion to the demand of the products in order to minimize the cost and produce all the demand. In this study, a large... 

In general, the output power of the gas turbines decreases as the ambient temperature increases. One of the ways to deal with such a performance loss is to use a wet compression system, which reduces the air temperature rise throughout the compressor. In this system, the water droplets are injected into the compressor inlet and evaporated throughout the stages. As a result, the work of the compressor decreases, and the power and efficiency of the whole engine increase. Most of the researchers in this field have tried to develop mathematical models to investigate the effects of this system on compressor and gas turbine performance in steady-state conditions. However, it is necessary to... 

Channel equalization is a crucial part of the OFDM communications protocols, which in turn requires channel estimation. Pilot-based methods are one the most popular channel estimation approaches in OFDM systems. The pilot signals are generally classified as orthogonal and nonorthogonal pilots. Orthogonal pilots can better estimate the channels and are widely used in communications systems. The number of orthogonal pilots is proportional to the number of transmitters. Therefore, utilizing orthogonal pilots are not amenable for the increasing number of users in communications systems and the emerging of new technologies such as Massive-MIMO employing a large number of antennas. Consequently,... 

Shape memory polymers have the potential to use in the field of biomedical applications. In this research, polyurethane structures have been synthesized based on the Diol mixtures, consisting of polycaprolactane diol (PCL-diol) and poly (lactic acid) diol (PLA-diol). Aim of reasearch is about evaluating poly (lactic acid) effect in structure of the polyurethane. At the same time, cellulose nanocrystals (CNC) have been added to polymer matrix to improve properties. The synthesis of acrylated polyurethane, included the synthesis of polyurethane acrylate prepolymer. Next, this prepolymer has been cured by adding the reactive diluent and some polyol. The cured systems were investigated, finally,...