Sharif Digital Repository

This study was conducted to investigate a theoretical and experimental two-dimensional model of a floating fish cage in regular waves and uniform current. Due to the inefficiency of computational fluid dynamics (CFD) in solving such problems, developing a simple model to predict the results is highly advantageous. In this study, a simple mass-spring model was developed to simulate the problem. After validating the results of this simple model through a series of model tests in a wave tank, it was further utilized to extract additional results. Experiments were conducted at six different wave heights and four current velocities. In all experiments, wave steepness was maintained at a ratio of... 

Offshore platforms are one of the most important structures in oil-rich countries, so that their economic benefit makes it very expensive to stop their usage. Therefore, it is essential that their performance is not disrupted by earthquake or the tidal waves made by severe storms. In the conventional bracing systems, it is assumed that the braces buckle under compressive forces; but Buckling Restrained Brace (BRB) does not buckle under pressure. In this study performance of BRB in jacket platform, with a case study of Resalat platform, has been investigated under earthquake load and powerful wave. The modeling of jacket equipped with this brace has been done in Abaqus software, and results... 

Offshore platforms are one of the most important structures in oil-rich countries, so that their economic benefit makes it very expensive to stop their usage. Therefore, it is essential that their performance is not disrupted by earthquake or the tidal waves made by severe storms. The new high performance semi-active bracing system, developed by Golafshani et al, is capable of removing the permanent drift of stories at the end of excitation and concentrating structural damage in braces. In the conventional bracing systems it is assumed that the braces buckle under little compressive forces; but in this new presented completely tensile-ribbed bracing system (RBS), buckling of compressive... 

Selective laser sintering is a technique which uses a laser as the power source to sintering some selected points at a bed of powder in order to create a solid structure. In this research the SLS mechanisms of powder deposition is simulated and surface smoothness and layer density created by each mechanism is computed. For this purpose roller, blade and hopper mechanisms are simulated. For this simulation, polyamide 12 (PA2200) which is a common material is used. In this simulation at first powder specifications are extracted according to the references and for particle shape instead of using the spherical particle shape we use a certain shape that is more close to reality which created by... 

In recent decades due to declining reserves of fossil fuels on land and in shallow water areas, exploration and exploitation of oil and gas from deeper seas and oceans are rapidly making progress and since there are huge volumes of oil and gas reserves in deep waters of the Caspian Sea bed, in order to fulfill the purpose of oil exploration and exploitation in all sectors of the Caspian Sea, it seems mandatory to study in the field of platforms required for use in this area. One of these platforms is Tension Leg Platform with mooring lines called tendons that directly connected to the seabed. High axial stiffness makes this type of mooring lines constrained the vertical degrees of freedom... 

TLP is membership of compliant structures. In these platforms buoyancy is more than the weight and pretension compensates extra buoyancy. TLP is consisting of pontoons, columns and a deck. TLP is vertically moored with tendons and tendons extend from under the columns to sea bed. Marine structures vibrate due to applying environmental loads such as wind, waves, currents, earthquakes. Therefore vibration control of TLP is very important problem not only from motion aspect but also from design and fatigue point of view. In this thesis, passive vibration control of TLP with different TMDs are investigated. In first part, introduction of tension leg platforms, types of control mechanisms and... 

The primary objective of this research is probabilistic quantification of the fatigue life of tension-leg platforms (TLP) using reliability methods. The need for such methods stems from the significant uncertainty in the loads exerted on offshore structures. The scope of this paper is limited to the study of fatigue in TLP tendons. For this purpose, nonlinear force time history response of the TLP tendon under random wave loads is computed and the damage due to fatigue is estimated in accordance with the Palmgren-Miners rule. Assuming a Rayleigh distribution for stress variation and eight different sea states, the ultimate fatigue damage is computed by accumulating the damage over all... 

Offshore wind energy is widely recognized as a renewable energy source that has the potential as a global energy source. Although the use of coastal wind turbines has been successful, it has been challenged in terms of visual, acoustic and environmental impacts. In addition, in terms of technology, it is difficult to achieve high levels of energy from coastal wind resources due to low annual average speed; Therefore, the wind energy industry is trying to make more use of the deep-water wind resources. However, before developing these types of deep-water turbines, economic challenges and technical problems must be resolved. Mooring failure is one of the major issues in the design of offshore... 

Nowadays, energy harvesting from the sea is developing for a variety of applications, including small-scale technologies for the production of small amounts of energy, including the use of low-speed currents to power ocean floor sensors. Ocean floor sensors are currently working with batteries. The cost of replacing or recharging these batteries is high, and the technology of these conventional batteries does not keep up with the rapid development of these sensors. Using new energy harvesting technologies has made the ocean current harvesting system as an adequate replacement for the batteries. According to operating principles, energy harvester can be broadly classified into three general... 

The ultimate goal of this study is to provide a general framework for assessing the reliability of different layouts of marine structures. This reliability is a yardstick for determining the safety level of marine structures at any given time. Using this criterion, it is possible to prioritize structures for maintenance operations and, by performing appropriate operations, create a uniform level of safety for all marine structures in a region, or the best type of fixed platform arrangement for structural strength He chose economics and so on. This framework is flexible and expandable, which means that its generalization to various hazards and the various effects of these hazards is possible... 

Given the increasing development of exploitation of deepwater oil and gas resources, access to realistic solutions for analyzing and designing offshore platforms is a major factor in facilitating the exploitation of oil and gas resources in these areas. There is a huge amount of oil reservoirs in deep water beds, and Tension leg platform (TLP), as a compliant structure, are suitable for oil extraction in deep water.The advantage of using these platforms is the ability to rotate and move at a rate of rotational and transient freedom. Surge motion The TLP is a 120-second long period; In high-amplitude and low period waves, the platform faces a tendon rupture due to high waves forces and bad... 

The use of wind energy due to the clean and unlimited nature of this energy has received more attention and for this purpose, the types of wind turbines that mainly include; monopile turbines and jacket-based turbines; is used In this research project, it has been tried using criteria such as equal weight of structures with different bracing shapes and taking into account the normalized energy and redundancy factors of the platforms; An optimal structure that can achieve a better capacity curve with the same material cost, which includes ultimate stress and greater ductility, and along with all the above factors; The redundancy of the structure has also been considered to minimize the risk... 

Designing of giant oil platforms in deep seas is one of the most important challenges of the country’s oil industry. The valuable reservoirs of oil and gas in caspian sea, increases the need of designing platforms for drilling these regions. One of the platforms which is drilling in this region, is Amirkabir platform. In this research, at first this platform is modelled in AQWA software and analyzed. This analysis includes finding loads acting on the platform and consequently RAOs of different degrees of freedom in different directions and also the time history of motions of the platform and tensions in its mooring cables. Motions of moored floating platform consists of two types of motions.... 

Global energy consumption is on a trajectory to surge by 50% by 2050, primarily driven by prevailing energy consumption patterns. Consequently, the imperative to innovate and develop novel energy sources, such as the utilization of recycled waste heat, has become paramount for the foreseeable future. In light of this, this paper delves into the transformative potential of employing Phase Change Materials (PCMs) for cooling Thermoelectric Generators (TEGs) and harnessing waste heat for productive purposes. The research investigates three distinct configurations to evaluate the efficacy of PCMs in enhancing thermal management. Configuration 1 exclusively relies on an active cooling fan, while... 

Every day requirements for oil, gas and exploration in deep water have pushed offshore industries into deeper water. Oil production is expensive, so a designed platform should be cost saving. The clear and logical part is that, testing a model will be an important part of these kind of researches. In this thesis we are trying to obtain numerical results from ANSYS AQWA and experimental results for surge, heave and pitch motions, then compare experimental results with numerical one. Second order effects are ignored in designs and experiments because of laboratory conditions and limits that we are faced with in there. 1/250 scale ratio has been chosen because of limits. First we get into... 

The tension leg platform is one of the compliant structures which are generally utilized for deep water oil explorations. With respect to the horizontal degrees of freedom, it behaves like a floating structure moored by vertical tethers which are pretension due to the excess buoyancy of the platform, whereas with respect to vertical degrees of freedom it is stiff and resembles a fixed structure and is not allowed to float freely. A sudden disconnection of a tendon causes a change of stiffness and unbalance of forces and moments of the total system. The objective of this study is experimental and numerical investigation on behavior of ISSC TLP. Experiments were performed in the National... 

Mechanical behavior of tissue engineering scaffolds plays a key role in their biological performance; however the effect of microstructural features on mechanical behavior of such scaffolds is still under investigation. The objective of this study was to investigate the influence of pore architecture and relative density on mechanical behavior of rapid prototyped scaffolds. In this regard, scaffolds with different cubic, hexagonal and trigonal unit cells were designed. These unit cells were repeated in different arrangements in 3D space to produce different nodal connectivities. The internal dimension of pores varied from 500 to 600 μm. Plastic models of scaffolds then fabricated by 3D... 

The discovery of oil and gas resources in deep waters led to the invention of various platforms adapted to these waters. As the search for oil and gas resources is advanced to deep water, it is impossible to use fixed platforms in these depths. Hence, the idea of using floating platforms that can be used in deep waters has been increasingly considered. An option for the exploration and extraction of offshore oil resources is semi-submersible platforms. Under wave, wind, and current forces, a floating structure moves from its initial location. Types of mooring systems are used to maintain the position of the platform. During the life of a platform, mooring lines may be damaged under... 

Considering the widespread applications of amides, synthesis of these compounds is of great importance. The one pot oxidative addition of amines to aldehydes is one of the most simple and appealing approaches to synthesis amides. With the aim of developing a mild and convenient approach towards preparation of amides, numerous methods have been reported for this important process over the past few decades. These improvements have been mostly related to the optimization of reaction conditions and the use of more challenging substrates including diverse derivatives of aldehydes, and also design a novel and effective catalytic systems. Due to the various advantages of supported heterogeneous... 

In the current research, colloidal stability of two different types of coating on the surface of Superparamagnetic Iron Oxide nanoparticles (SPIONs) was studied. In the first triumph, a dual-layer coating was achieved by utilizing optimum amount of Dextran and different PEG (Poly(ethylene glycol)) concentrations which the weight ratios of iron oxide/PEG were 1/1, 2/1, 4/1, 8/1, and 16/1. Then, the presence of the coating was characterized by XRD, FT-IR, DLS and FE-SEM methods. These results together with the TGA ones revealed that as the concentration of PEG surfactant increases, the thickness of coating increases. Moreover, VSM test was performed to specify the effect of coating on the...