Sharif Digital Repository

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.... 

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... 

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... 

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 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... 

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... 

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... 

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... 

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... 

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... 

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 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... 

The pervious Iranian seismic code has not considered the ductility parameter in the seismic design of (steel) structures. , therefore; seismic vulnerability and retrofit of existing steel structures is becoming a vital engineering problem. Common ways of seismic retrofit such as adding a shear wall or bracing the structure cause huge forces in elements and foundations. Rehabilitation on the foundation has many constructional problems and leads to long down time. As far as known, the Infill Walls increase the lateral stiffness of frames and lead to reducing the period of the structure. Therefore, to have a reliable design, it is important to consider the effects of Infill Walls. It can be... 

Nowadays, according to existence of oil resources in offshore areas and the necessity of extracting, constructing of offshore platforms is developed. The design of these structures has high effect on the cost of construction and maintenance and the performance under the loads such as wave, earthquake, impact, etc. Therefore, if the analysis of platform structure is more accurate the evaluation of the behavior and consequently the better design in different conditions is better. In this thesis, a modification of Endurance Wave Analysis (EWA) in evaluation of offshore structures is introduced in this study. EWA is a new method to predict the response of offshore structures in different sea... 

In mostbuildings,wallpanels andarchitecturalreasonsaremanufactured. Butbecause of thecomplexity ofthe issueandthe lack oflogicaland yetsimpleanalytical modelof thecombinedfillerpanels and its effectonthe structural behaviorlargelyaffectedcarefulconsiderationin analysisofbuildingstructuresbeneglected. This assumptionmay reducethe accuracy oftheestimation oflateral stiffness, strengthand ductilityofthestructureloading. Althoughthe2800 Iranian Standard stipulated that thewallsshouldbe consideredin loading and design but anywhere the code don’t talk about method, and details needs toshouldbe taken intoconsideration. Among theimportantissuestobe mentioned, effect of infills in creation of soft... 

In past few decades researchers and engineers have researched extensively on the effects of masonry infill walls in structural frames and the effects of masonry infill walls on the structural response was a concern for them. Since used materials and therefore the strength and stiffness of these walls are extremely depends on construction site and available mate-rials, according to geographical conditions most of countries inserted their own rules for considering effects of masonry infill walls in their codes and standards. Our country, Iran was not excepted from this regularity and in past few years the effect of existence of ma-sonry infill walls in structural response has been considered... 

Tension leg platforms (TLPs) are well-known structures for oil exploitation in deep water. Tethers are one of the most important component of these structures. Nonlinear response of TLP tethers under the combined action of wave and current was investigated in the present issue. Both the quadratic damping due to fluid resistance and parametric excitation due to top tension variations are included in the mathematical model. Only the vortex-induced transverse oscillations under lock on conditions were examined. A fourth order runge-kutta method was used to solve the equations of motion of tendons. The effects of surge motion coupling on the heave motion, the effects of tendon's oscillation on... 

Tension leg platforms (TLP) are vertically moored with reserved buoyancy used for drilling and production in deep waters. Pre-tensioned tendons controls the heave, pitch and roll motions due to marine currents and waves efficiently. Seastar platforms are new generation of tension leg platforms that are similar to spar platforms that has the advantages of TLP besides spar simultaneously. This platform is usually considered as an alternative for large and cost consuming platforms. Seastar has a cylindrical surface piercing hull that creates the required buoyancy along with three submerged additional bodies. Pre-tensioned cables are attached to platform through these three submerged bodies. The... 

A Tension Leg Platform (TLP) can be difined as a vertically moored, buoyant and compliant platform, where the excess buoyancy of the platform maintains tension in the mooring system (tethers). This platform type is usually used for drilling in deep water and includes the following sections, foundation, tendons, risers, hull and deck which is the most important section in terms of hydrodynamic forces and weight. Enough initial tension can be used to inhibit vertical movement of the structure. one of The main properties of this oil platform is extraction at large oil fields. Body of TLP is consist of vertical column, horizontal circular or rectangular cross section Pantoons and circular... 

Oil is being discussed as the main source of producing energy in the world. Thus its exploration and exploitation from the sea or land is very important. Most of these resources exist in the depths of the sea. Exploitation of these resources demands to reach knowledge of design and technology of manufacturing platforms and devices for exploitation in the deep waters. There are massive oil reserves in the context of deep waters. Using fixed platforms in depth is very uneconomic; also we know the natural period of these structures is close to the wave period in deep waters. As a result researches and mining industry in the deep waters have gone to use comparative platforms such as: TBT, TLP,...