1 2345-6000 Iranian Association of Naval Architecture & Marine Engineering 612 Offshore Structure Hull Performance Assessment and Comparison of Ship-Shaped and Cylindrical FPSOs With Regards To: Stability, Sea-Keeping, Mooring and Riser Loads In Shallow Water Baghernezhad Navid b Edalat Pedram c Etemaddar Mahmoud d b Faculty of marine engineering, Petroleum University of Technology c Faculty of marine engineering, Petroleum University of Technology d Center of ships and offshore structures, Trondheim, NORWAY 1 9 2017 8 Summer and Autumn 2017 1 13 06 05 2017 25 11 2017 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
600 Ship Hydrodynamic Numerical Evaluation of Cushioning Pressure in Water Entry of Rigid Bodies Barjasteh Mojtaba e Zeraatgar Hamid f e Faculty of maritime engineering f Faculty of maritime engineering 1 9 2017 8 Summer and Autumn 2017 15 24 11 03 2017 25 11 2017 Effect of air cushion layer right before impact of a rigid body onto water surface has been investigated in this paper. The study is mainly focused on evaluation of cushioning pressure and the resulting free surface elevation. The air flow is assumed to be an irrotational flow which is governed by Laplace equation. The air problem and the resulting response of the water free surface are supposed to be weakly coupled because of very low air pressure. Integral equation for each medium has been numerically solved separately using boundary element method. The problem is assumed to be unsteady with a constant body speed. The numerical results have been also compared with analytical method which shows a fair agreement. Results show that the geometry of impacting body and particularly its bluntness are the primary affecting parameter which can dramatically influence the free surface profile and air pressure. Such a behavior has been observed for two different geometries, ellipse and wedge section, having identical breadth. 622 Offshore Structure Investigation of Drag Coefficient at Subcritical and Critical Reynolds Number Region for Circular Cylinder with Helical Grooves Ahmed Dewan Hasan g Haque Md. Ashraful h Rauf Md, Abdur i g Mechanical and Production Engineering Department, Ahsanullah University of Science and Technology, Bangladesh h Mechanical and Production Engineering Department, Ahsanullah University of Science and Technology, Bangladesh i Mechanical and Production Engineering Department, Ahsanullah University of Science and Technology, Bangladesh 1 9 2017 8 Summer and Autumn 2017 25 33 01 07 2017 25 11 2017 Drag reduction of an object is the major concern in many engineering applications. Experimental studies have been carried out on circular cylinder with helical grooves in a subsonic wind tunnel. Different cases of helical grooves with different pitches, helical groove angles and number of starts of helical groove on circular cylinder are tested. Experimental results show the drag coefficient is sensitive with Reynolds number and decreases at critical Reynolds number and at subcritical and supercritical or transcritical Reynolds number the drag coefficient increases as compared with smooth cylinder. The longitudinal grooves over the cylinder surface are tested and showed that drag coefficient much decreases at the subcritical and critical Reynolds number region. The experimental results are validated with available literature and obtained good agreement. 575 Submarine Hydrodynamic & Design A New Propulsion System for Microswimmer Robot and Optimizing Geometrical Parameters Using PSO Algorithm Sayyaadi Hassan j Motekallem Abolfazl k j Sharif University of Technology k Sharif University of Technology 1 9 2017 8 Summer and Autumn 2017 35 45 26 12 2016 25 11 2017 Mini and micro robots, which can swim in an underwater environment, have drawn widespread research interests because of their potential applications to the clinical drug delivery, biotechnology, manufacturing, mobile sensor networks, etc. In this paper, a prototype of microrobot based on the motion principle of living microorganisms such as E. Coli Bacteria is presented. The properties of this propulsive mechanism are estimated by modeling the dynamics of the swimming methods. For dynamic modeling and analysis of a tiny microrobot, which composed of a spherical head and four helix tail, the resistance force theory (RFT) is used to calculate thrust force, required torque, linear and angular velocities and then these physical and geometrical parameters are used to optimize the microrobot. In addition, a novel design method for determining the optimal geometrical parameters of dynamic system using the particle swarm optimization (PSO) reinforcement evolutionary algorithm is presented. Finally, the dynamical behavior of the optimized microrobot are simulated and the results are presented. 610 Offshore Structure Accidental Limit State of Submarine Pipeline: Trawl Gears Pull-Over Loads and Effect of Free Span Taghizadeh Edmollaii Sina l Edalat Pedram m l Faculty of Marine Engineering, Petroleum University of Technology m Faculty of Marine Engineering, Petroleum University of Technology 1 9 2017 8 Summer and Autumn 2017 47 58 24 04 2017 25 11 2017 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. 617 Offshore Structure Investigation of the Pile Aging Effect of a Fixed Offshore Platform Located in Persian Gulf using Nonlinear Soil-Pile Interactions Emamverdizadeh beyg Ghafour n Taheri Abdolrahim o n Petroleum University of Technology o Petroleum University of Technology 1 9 2017 8 Summer and Autumn 2017 59 64 27 05 2017 25 11 2017 The study about the jacket platforms in the past has revealed that the most of the collapse failures occur due to the lack of strength of the pile foundation. However, when the jacket platforms which have been collapsed due to extreme condition were looked into, it was found that most of them had their foundations intact. These contrasting facts can be explained with the help of the phenomenon called “aging of piles”. Aging effect of piles has been proven by experiments indicating gradual increase in pile capacity which is due to the thixotropic characteristics of clayey soils, leading to gradual improvement of soil clamping property. But due to lack of proper understanding and suitable techniques to incorporate them, these aging effects have been ignored during the pushover analysis. In this study, a simple technique of stepping up of the soil curves in order to accommodate the increase in capacity of pile foundation due to aging is utilized, and then the pushover analysis is performed using commercial software SACS. SPD19C (South Pars gas field Development, phase 19) is a new constructed jacket platform in Persian Gulf which is used as the case study in this paper. The platform is considered to be under the storm condition in 180º direction which is the worst condition. This study shows that the incorporation of pile aging effect results in the improvement the piles performance and Reserve Strength Ratio (RSR) about 10 percent. This research also has provided a deeper knowledge into the behavior of aged offshore jacket platforms.