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CONTENTS
Volume 10, Number 3, September 2020
 

Abstract
In-place analysis for offshore platforms is required to make proper design for new structures and true assessment for existing structures. In addition, ensure the structural integrity of platforms components under the maximum and minimum operating loads and environmental conditions. In-place analysis was carried out to verify the robustness and capability of structural members with all appurtenances to support the applied loads in either operating condition or storm conditions. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the pile–soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The SACS software is utilized to calculate the natural frequencies of the model and to obtain the response of platform joints according to in-place analysis then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have an important effect on the results of the in-place analysis behavior. The influence of the soil-structure interaction on the response of the jacket foundation predicts is necessary to estimate the loads of the offshore platform well and real simulation of offshore foundation for the in-place analysis. The result of the study shows that the in-place response investigation is quite crucial for safe design and operation of offshore platform against the variation of environmental loads.

Key Words
FEM; offshore platform; storm conditions; pile soil interaction; in-place analysis

Address
Shehata E. Abdel Raheem, Aly G.A. AbdelShafy and Mahmoud H. Mansour: Department of Civil Engineering, Faculty of Engineering, Assuit University, Assiut 71516, Egypt
Elsayed M. Abdel Aal: Egypt Gas Company, Alexandria, Egypt
Mohamed Omar: Department of Civil Engineering, Faculty of Engineering, Aswan University, Aswan, Egypt

Abstract
The dropped objects are identified as one of the top ten causes of fatalities and serious injuries in the oil and gas industry. It is of importance to understand dynamics of dropped objects under water to accurately predict the motion of dropped objects and protect the underwater structures and facilities from being damaged. In this paper, we study non-dimensionalization of two-dimensional (2D) theory for dropped cylindrical objects. Non-dimensionalization helps to reduce the number of free parameters, identify the relative size of effects of force and moments, and gain a deeper insight of the essential nature of dynamics of dropped cylindrical objects under water. The resulting simulations of dimensionless trajectory confirms that drop angle, trailing edge and drag coefficient have the significant effects on dynamics of trajectories and landing location of dropped cylindrical objects under water.

Key Words
non-dimensionalization; dropped cylindrical objects; slender body; trailing edge; offshore engineering

Address
Yi Zhen: Natural Sciences Department, Southern University at New Orleans, New Orleans, LA, USA;
Mathematics Department, University of New Orleans, New Orleans, LA, USA
Xiaochuan Yu: School of Naval Architecture and Marine Engineering, University of New Orleans, New Orleans, LA, USA
Haozhan Meng: Department of Electrical and Computer Engineering, University of New Orleans, New Orleans, LA, USA
Linxiong Li: Mathematics Department, University of New Orleans, New Orleans, LA, USA

Abstract
In the present paper, the effect of the location of stern planes on the flow entering the submarine propeller is studied numerically. These planes are mounted on three longitudinal positions on the submarine stern. The results are presented considering the flow field characteristics such as non-dimensional pressure coefficient, effective drag and lift forces on the stern plane, and the wake flow formed at the rear of the submarine where the propeller is located. In the present study, the submarine is studied at fully immersed condition without considering the free surface effects. The numerical results are verified with the experimental data. It is concluded that as the number of planes installed at the end of the stern section along the submarine model increases, the average velocity, width of the wake flow and its turbulence intensity formed at the end of the submarine enhance. This leads to a reduction in the non-uniformity of the inlet flow to the propulsion system.

Key Words
numerical simulation; submarine model; stern planes; displacement; wake flow

Address
Shokrallah M. Beigi and Alireza Shateri: 1Department of Mechanical Engineering, Engineering Faculty of Shahrekord University, Shahrekord, Iran
Mojtaba D. Manshadi: Department of Mechanical Engineering, Malek Ashtar University, Esfahan, Iran


Abstract
This study examines the behaviors and properties of discharged liquid CO2 from a long elastic pipe moving with a vessel for the oceanic CO2 sequestration by considering pipe dynamics and vessel motions. The coupled vessel-pipe dynamic analysis for a typical configuration is done in the frequency and time domain using the ORCAFLEX program. The system\' s characteristics, such as vessel RAOs and pipe-axial-velocity transfer function, are identified by applying a broadband white noise wave spectrum to the vessel-pipe dynamic system. The frequency shift of the vessel\' s RAO due to the encounter-frequency effect is also investigated through the system identification method. Additionally, the time histories of the tip-of-pipe velocities, along with the corresponding discharged droplet size and Weber numbers, are generated for two different sea states. The comparison between the stiff non-oscillating pipe with the flexible oscillating pipe shows the effect of the vessel and pipe dynamics to the discharged CO2 droplet size and Weber number. The pipe\'s axial-mode resonance is the leading cause of the fluctuation of the discharged CO2 properties. The significant variation of the discharged CO2 properties observed in this study shows the importance of considering the vessel-pipe motions when designing oceanic CO2 sequestration strategy, including suitable sequestration locations, discharge rate, towing speed, and sea states.

Key Words
CO2 sequestration; fluid-structure interaction; system identification; vessel-pipe coupled dynamic analysis, pipe axial vibration, resonance, discharged fluid properties, operable sea state

Address
Farid P. Bakti and Moo-Hyun Kim: Department of Ocean Engineering, Texas A&M University, College Station, Texas, USA

Abstract
International Maritime Organisation (IMO) regulations insist on reduced emission of CO2, noxious and other environmentally dangerous gases from ship, which are usually let out while burning fossil fuel for running its propulsive machinery. Contrallability of ship during sailing has a direct implication on its course keeping and changing ability, and tries to have an optimised routing. Bad coursekeeping ability of a ship may lead to frequent use of rudder and resulting changes in the ship\'s drift angle. Consequently, it increases vessels resistance and also may lead to longer path for its journey due to zigzag movements. These adverse effects on the ship journey obviously lead to the increase in fuel consumption and higher emission. Hence, IMO has made it mandatory to evaluate the manoeuvring qualities of a ship at the designed stage itself. In this paper a numerical horizontal planar motion mechanism is simulated in CFD environment and from the force history, the hydrodynamic derivatives appearing in the manoeuvring equation of motion of a ship are estimated. These derivatives along with propeller thrust and rudder effects are used to simulate different standard manoeuvres of the vessel and check its parameters against the IMO requirements. The present study also simulates these manoeuvres by using numerical free running model for the same ship. The results obtained from both these studies are presented and discussed here.

Key Words
planar motion mechanism; oceanographic research vessel; turning circle manoeuvre; hydrodynamic derivatives

Address
Kunal Tiwari and T.V. Rameesha: Department of Ocean Engineering, Indian Institute of Technology Madras, Chennai, India
K. Hariharan and P. Krishnankutty: Department of Mechanical Engineering, Pusan National University, South Korea-46241


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