Showing 8 results for edalat
Ali Beigi, Pedram Edalat, Mohammad Reza Khedmati, Manouchehr Fadavi,
Volume 2, Issue 0 (Summer and Autumn 2014 2014)
Abstract
In the current study, the effect of such parameters as the length, position and angle of crack on free vibrations of a cracked plate was examined by finite element method. The assumed crack was internal and through and its growth was ignored. In the proposed finite element model, crack was considered as a discontinuity on the plate surface and the results were compared with the results of other studies for validation which proved its acceptable precision. The studies show that the thickness and mechanical properties of the plate do not influence the ratio of natural frequency of a cracked plate to natural frequency of an intact plate and that the other parameters change the stiffness and natural frequencies of a plate through affecting the modal shapes and stress intensity factors.
Sina Taghizadeh Edmollaii, Pedram Edalat,
Volume 8, Issue 0 (Summer and Autumn 2017 2017)
Abstract
Submarine pipelines failures lead to oil spills in water and may even lead to explosions
with heavy financial and environmental damages. Trawl gear is one of the main factors in the failure of the submarine pipelines. In this paper, sensitivity analysis is performed on influence of height and span length alternations on the response of pipeline against the traction caused by trawling pull-over load. The FE model is presented using OrcaFlex software including modeling of seabed, pipeline and trawl gear parameters. To model soil and reinforced concrete, nonlinear parameters are considered. To verify the models, DNV-RP-F111 and results of modeling by SAGE Profile software is used. The results indicated that increase in span gap resulted in the increase in pipeline responses, but with the increase in span length, only the lateral displacement exhibited a considerable increment. Finally, Maximum time for pipeline to fail and system response to become greater than the standard level has been calculated.
Navid Baghernezhad, Pedram Edalat, Mahmoud Etemaddar,
Volume 8, Issue 0 (Summer and Autumn 2017 2017)
Abstract
Floating, Production, Storage and Offloading “FPSO” have become a popular choice since 1980s for marginal and fast-track developments where subsea pipeline is not an economic or feasible solution for export. Field development usually starts with a concept selection procedure which is constituted from a sequence of multi-disciplinary decision making tasks. As limited data is available in the early phase of the development, operators require a robust and rational decision making process to reduce the drawback of immature information. The Multi-Criteria Decision Making (MCDM) process which is used in this paper is an industrial approved and accepted decision making process that can resolve this requirement. This method is commonly used as a decision making method for multiple attributes problems.
The main objective of this study is to illustrate the application of this method for concept selection for shallow water fields. Here the problem is reduced to a selection among two common FPSO concepts: ship-shaped and cylindrical by assessing their performances for the same location. The primary attributes which have been used for performance assessment includes: stability, motions and accelerations, riser stresses and mooring line tensions under both intact and damaged conditions. To simplify the problem, the same topside weight and tank capacity are considered and response comparison is limited to the linear responses induced by wave under full loaded conditions. For both FPSOs spread mooring system with steep-s flexible riser system are considered.
For the given environmental conditions, cylindrical FPSO shows better motion characteristics which leads to smaller mooring and riser loads. This method should be generalized for other shallow water production system by including all the attributes used in the shallow water field development concept selection
Shahab Shahriari, Pedram Edalat, Gholamreza Salehi,
Volume 9, Issue 0 (Winter and Spring 2018 2018)
Abstract
Iranian offshore oil and gas platforms are mostly located in the Persian Gulf. Technical and environmental challenges resulted from an off-design running condition of processes on a platform are important issues. The weakness of strategies to stop or decrease the amount of greenhouse gas emission production rate in the Persian Gulf; which is intensively increasing, is another matter of concern. modern methods of energy generation from available renewable potentials near offshore platforms are suggested. Integration of renewable energy converters with offshore oil and gas platforms can solve both problems with machinery and environment to an acceptable extent. In this study, the economics of the Soroush offshore complex is subjected to two scenarios. The first scenario defines the present condition in which the total power demand of the complex is supplied by burning the associated extracted natural gas on board the platform in its thermal power plant and the second scenario considers a wind farm located near Bardekhun in Bushehr province to be connected to the complex power network and shares its renewable source generated power with the platform. The economics of both scenarios are compared in terms of total annual power cost. The second scenario shows more beneficial, although there are some conservative assumptions included due to a shortage of data and limitations.
Alireza Soleymani, Seyed Mohammad Hossein Sharifi, Pedram Edalat, Seyed Mohammad Mahdi Sharifi, Samad Karim Zadeh,
Volume 10, Issue 0 (Summer and Autumn 2018 2018)
Abstract
An approach to deal with the phenomenon of maritime fuel smuggling is to control the quantity of fuel that is supplied to vessels. For the same reason, fuel is delivered to marine vessels in Iran in accordance with the ration defined by the National Iranian Oil Products Distribution Company (NIOPDC). The ration is determined by a fuel consumption formula defined by the Food and Agriculture Organization of the United Nations (FAO) which is used to estimate the fuel cost of agricultural and road construction equipment and machinery. The use of this formula for maritime usage renders fuel allocation to vessels inappropriate. This paper makes a database containing the specifications of 452 vessels, including length, width, summer draft, economical speed, engine power and hourly fuel consumption values. Then, a linear model is estimated over the available database. Ordinary least square method is used for regression analysis. Then, the estimated linear model is compared with FAO formula and linear model is selected as the optimum model to estimate vessel fuel consumption as close to the actual value of fuel consumption as possible. This linear model contains three parameters: engines power, economical speed, and immersed volume as defined by multiplying three parameters of length, width, and summer draft. In general, the amount of fuel consumption estimated by FAO formula is about 50% greater than that estimated by the linear model.
Seyed Mohammad Hossein Sharifi, Pedram Edalat, Babak Najafi, Masoud Bolfakeh,
Volume 14, Issue 0 (Summer and Fall 2020 2020)
Abstract
The present research addresses the crack arrest in the submarine pipeline under internal pressure, axial force, and bending moment. The main purpose of the research is to consider tight-fit sleeves as a solution to crack arrest. The stress intensity factor criteria are used to describe the crack behavior. It should be noted that the cracks examined here are inclined through-thickness cracks, which the ABAQUS commercial software used to simulate them. It's noteworthy that Mode I fracture is dealt with, and the other fracture modes are omitted. The results show that the tight-fit sleeves, preferentially arrest the inclined cracks; so that the amounts of the stress intensity factors decrease for all the cracks except for the circumferential cracks to the extent that they become closed. As a result, their growth stops in practice; however, it best reduces the stress intensity factors by up to 65.36% at the circumferential cracks, and their amounts remain non-negative. Tight-fit sleeves create a pressurized region around the inclined cracks. This causes that inclined cracks remain closed.
Pedram Eedalat, Esmaeil Hasanvand,
Volume 15, Issue 0 (Winter and Spring 2021 2021)
Abstract
Offshore oil terminals are a cheaper and safer solution than conventional shore terminals for unloading and loading tankers. There are several types of offshore terminals, including Catenary Anchor Leg Mooring (CALM) and Single Anchor Leg Mooring (SALM). Safety is crucially important for offshore terminals. However, over the past few decades, mooring accidents of permanent floating structures have occurred quite frequently in the last few decades. Most of these failures have been caused by fatigue load. T-N curves-based mooring system fatigue analyses for a CALM and SALM oil terminal are presented. Stress amplitudes are calculated based on the tension amplitudes of the mooring lines under the combined loading process due to wave frequency (WF) and low frequency (LF) motion. A comparison is made between CALM and SALM mooring fatigue designs based on the conditions of the Persian Gulf region. For simulation, the hydrodynamic response characteristics of terminals and tankers are first calculated using ANSYS AQWA software, and then the outputs are imported into ORCAFLEX software for fatigue analysis. The results show that under the same environmental conditions with the same tanker tonnage, the SALM terminal mooring system shows a greater fatigue life. The minimum fatigue life of the mooring system for CALM and SALM terminals occurs at near the touch-down position (TDP) and the near of connection to the seabed, respectively. It is revealed that by changing the value of minimum breaking strength (MBS) the fatigue life of the CALM and SALM terminals changes by 119% and 100%, respectively. It is also observed that by changing the amount of K value (the value for platted T-N curve), the fatigue life of the CALM and SALM terminals changes by the same amount. In all cases, the value of R (the ratio of tension range to reference breaking strength), in the mooring line of SALM terminal, although more tension is generated, the ratio of R is less and will improve the life of fatigue.
Pedram Edalat, Saeed Imani Bidgoli,
Volume 17, Issue 0 (2-2023)
Abstract
The effects of mooring system selection (turret and spread) are investigated on dynamic performance and fatigue life of steel catenary riser (SCR) and lazy-wave steel catenary riser (LWSCR) as two of the most conventionally used flexible risers. The fully coupled hull, mooring, and riser models are simulated by finite element method under the same environmental conditions and floater specification. It was demonstrated that the changes in the mooring system from turret to spread have more influence on SCR than LWSCR in terms of the displacement range of the TDP, dynamic response, and maximum von-misses stress. The fatigue results of the two types of risers are considerably affected by mooring systems selection. According to the results, it can be inferred that the use of the turret mooring system increases the fatigue life of SCR while in LWSCR, the spread mooring system improves fatigue life.
