Sharif Digital Repository

Synthetic fiber rope mooring systems, are increasingly finding applications as offshore oil exploration goes to deeper sites. Synthetic fiber cables provide numerous advantages over steel mooring lines, particularly in deeper water that large self-weight of steel lines is prohibitive, synthetic fiber ropes could be a good selection for mooring system. In order to reduce the need for expensive tests under varying parameters and operating conditions it is essential to be able to model the mechanical behavior of very long synthetic mooring lines. The purpose of modeling mechanical behavior of cables is to determine global stiffness matrix Coefficients to correlate the forces and strains for... 

This project deals with the global buckling in high pressure/high temperature (HP/HT) subsea pipelines. Some subsea pipelines are laid directly on the seabed. Large axial forces will generally cause an exposed pipeline to buckle sideways, or laterally, on the seabed. Pipelines may significantly expand during start-up and shutdown cycles, resulting in global buckle formation with high out-of-straightness (OOS).This global buckling behavior may be unacceptable if it is not properly managed. Global buckling mitigation can be achieved by providing controlled lateral movements of pipeline. Buckle mitigation devices are installed along the pipeline to provide buckle initiation sites, there by... 

When a submarine pipeline is laid, pipeline spans may exist due to the unevenness of the seabed. Such pipeline spans when exposed to currents, may undergo vortex-induced vibration (VIV). As the flow velocity increases, the cross-flow oscillation begins to occur and vortex shedding frequency may approach the natural frequency of the pipe span. Amplified response due to resonance between the vortex shedding frequency of the free span may cause fatigue damage. Thus, the determination of the critical allowable span length under the various environments becomes the most challenging areas in the offshore industry. A substantial research effort related to various aspects of VIV and free span... 

This thesis addresses the main stages of ship vibration analysis and introduces applied strategies for vibration reduction of an existing ship. First, the basic theory of ship vibration is considered and the main sources of ship vibration are enumerated. Then, the manner and the steps of vibration measurement on ship structure are presented and a summary of vibration measurement guidelines is mentioned. Afterward, the procedure how to analyze the measured data of ship vibration is outlined and a comparison between the measured data and standard limits for vibration level considering structural vibration, machinery vibration and human comfort is done. Next, human response to vibration and the... 

In this research, multi-disciplinary design optimization (MDO) of a flying vehicle has been done based on the flight simulation. A meta-heuristic algorithm called Multi-objective Adaptive Real-coded Memetic Algorithm (MARCOMA) has been used for optimization. Since solving a MDO problem is a time consuming process, a RBF neural network has been used in the optimization algorithm as a surrogate model. The new algorithm, called MARCOMA+NN, has been tested with some standard benchmarks. MDO problem has six disciplines consists structure, aerodynamic, propulsion, guidance, control, and fire control. The MDO problem has 31 design variables and two objective functions. The objective functions are... 

Due to large range searches (there are various alignments between two points) as well as the complex and non-linear cost functions and a variety of geometric constraints, the problem of optimal railway alignment is known as a difficult problem. For this reason, choosing an alignment between two points is usually done based on a limited number of alignments put forward by experts. In recent years, the study of the railway alignment optimization raised again due to the importance of optimization and introduction of various algorithms and their progress in solving various problems. It is expected that applying metaheuristic optimization algorithms, such as methods based on Swarm intelligence... 

Peoples need financial resources to improve their quality of life, and companies need them to progress and increase their comparative advantage. Borrowing is one of the most popular methods of financing. Peer-to-peer lending, also known as "marketplace" or "social" lending, is a novel form of intermediation that expunges the role of financial institutions (like banks) as an intermediary and allows entities (individuals or businesses) to raise loans directly from other entities. This lending platform can provide better quality services to borrowers (by quickly providing a simple loan application process through a transparent and flexible portal) and lenders (by managing their funding and live... 

Because of lower energy consumption and lower capital cost, divided wall columns attracted wide attention. The main challenge of these units is their controllability. In this thesis dynamic simulation and control of a divided wall column is investigated and an adaptive model predictive controller has been used for control purpose. For dynamic simulation the Aspen Dynamics software and for applying control strategy the MATLAB software have been utilized. The model used for model predictive controller has been obtained by using open loop responses of the system. The main advantage of presented work over the existing ones is using the input-output transfer function of the system model instead... 

Vibration control is one of the most critical aspects of designing space structures, as it can significantly impact the performance and operational lifespan of satellites. The launch phase is the most sensitive and critical stage in the satellite mission lifecycle, as intense vibrations are generated and transmitted to the satellite during this phase. To mitigate the severity of these transmitted vibrations, vibration isolators are employed. The objective of this study is to design and model a vibration isolator to control the vibrations transmitted from the launcher to the satellite during launch. To achieve this, an extensive investigation into vibration isolators used in the space... 

The use of polymers is increasing day by day due to low density, reasonable price and ability to produce different products. On the other hand, the accumulation of polymer wastes in nature is one of the environmental concerns in today's world, which is mainly due to the widespread use of polymers in the packaging industry and disposable applications. In order to solve this problem, recycling is recommended as the most appropriate and economical solution. Because in addition to consuming polymer waste, it also saves energy and reduces carbon footprint.Polyethylene terephthalate (PET) is one of the polymeric materials which; It has a special place in the packaging industry and is widely used... 

The improved properties of nanocomposites are not achievable with conventional composites. Scale effect is one the most important parameters in the physical and mechanical properties of polymeric nanocomposites. One of the physical phenomena, which can be related to the scale effect, is the very large interface between the nanoparticles and the polymeric matrices. Motional behavior and conformation of polymeric chains change near the nanoparticles surfaces. Due to high interface of the nanoparticles with the polymeric matrices the amount of these types of changes in the polymeric chains are so large that can change the physical and mechanical properties of polymeric nanocomposites. In this... 

In the field of high-pressure material science, diverse carbon systems under pressure have been intensively studied with interest in synthesizing new phases. A variety of these synthetic phases which have met various applications in today technology are called the amorphous diamond. The pressure-induced structural transition of carbonaceous material to amorphous diamond is realized by shock compression and rapid quenching. The shock compression and rapid quenching generate the high pressure (several GPa) and the temperature (several hundred K) in a fraction of a microsecond.Since the mechanical and electrical properties of the synthetic diamond are severely sensitive to the atomic structure,...