Hydrodynamic Interaction of Floating Structure in Regular Waves (original) (raw)
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Experimental Study of Motions of Two Floating Offshore Structures in Waves
Brodogradnja, 2016
Drilling is carried out in deeper to deeper waters around the globe to meet growing demands for oil and natural gas, and a number of multi body structures are deployed in various oil fields in the world. Investigation of hydrodynamic interaction of offshore structures is therefore worthwhile. Hydrodynamic interaction between floating offshore structures affects motion and relative motion especially during loading and offloading operations. Hydrodynamic interactions may lead to large motions of floating bodies that would cause damage to moorings and offloading systems and may collide with each other. This research work discusses experimental results of hydrodynamic interaction in surge, heave and pitch motion, relative motion and relative distance between a Tension Leg Platform (TLP) and semi-submersible (Tender Assisted Drilling) in regular waves. The experiment is conducted without tendon because of the depth limitation of the Towing Tank. However, in order to consider the contribution of mooring in linear direction, appropriate stiffness of horizontal springs have been used. The experiment was conducted for a full scale wave height of 3.77 m to 12.49 m for a separation distance of 21.7 m. From the analyses of the experimental and numerical results, it can be concluded that nonlinearity of the wave has an important effect on increasing the motion especially in the natural frequency region. Finally, a number of recommendations have been made for further study.
Wave Induced Coupled Motions and Structural Loads Between Two Offshore Floating Structures in Waves
Brodogradnja, 2018
As oil or gas field moves deeper offshore area, offshore offloading operations such as Tandem or Side-by-Side arrangement between two floating structures take place in many locations throughout the world and also have many hydrodynamic problems. Therefore, the researches on the motion response and hydrodynamic force including first and second order between two floating structures are needed to have the more safe offloading operability in waves. In this paper, prediction of wave induced motion responses and structural loads at mid-ship section with hydrodynamic interaction effect between two offshore floating structures in various heading waves are studied by using a linearized three-dimensional potential theory. Numerical calculations using three-dimensional pulsating source distribution techniques have been carried out for hydrodynamic pressure distribution, wave exciting force, twelve coupled linear motion responses, relative motions and wave loads of the barge and the ship in obl...
2004
Triangular configuration tension leg platforms (TLPs) are used for deep-water oil/gas exploration. The mechanics of TLP is highly nonlinear due to larger structural displacements and fluid motion-structure interaction. Triangular TLP has major consideration for deepwater application also due to its relative insensitivity with increasing water depth, excellent station keeping characteristics, etc. which makes this as a most cost effective and practical production system for deep waters. This study focuses on the influence of hydrodynamic drag coefficient (Cd) and hydrodynamic inertia coefficient (C m ) on the nonlinear response behavior of triangular TLP models under regular waves. Two typical triangular TLP models vis-a-vis TLP1 and TLP 2 are taken for the study at 600 and 1200 m water depths, respectively. Hydrodynamic forces on these TLPs are evaluated using modified Morison equation under regular waves. Diffraction effects are neglected. Various nonlinearities arising due to relative velocity term in drag force, change in tether tension due to TLP movement, and set down effect are being considered in the analysis. The dynamic equation of motion has been solved in time-domain by employing Newmark's b numerical integration technique. Based on the numerical study conducted, it is seen that the response evaluated using varying hydrodynamic coefficients through the water depth is significantly lesser in comparison to the response with constant coefficients in all activated degrees-of-freedom. However, sway, roll, and yaw degrees-of-freedom are not present due to the unidirectional wave loading considered for the study. The influence of hydrodynamic coefficients in wave period of 15 s is more in comparison with that of 10 s, and is nonlinear. The hydrodynamic coefficients also influence the plan dimension of TLP and its site location (geometry). Therefore, it may
Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment, 2004
A combined experimental/numerical investigation of a moored floating structure response to incoming waves to incoming waves is proposed. The floating structure consists of three bodies, equipped with fenders, joined by elastic cables. The system is also moored to the seabed with eight mooring lines. This corresponds to an actual configuration of a floating structure used for ships and submarines in special docking operations. The dynamic wave response is investigated by performing experiments in a towing tank equipped with a wave maker. Experimental results are compared with numerical simulations in regular and irregular waves, showing a good agreement. In regular waves the predicted time histories of pitch, heave and surge motions of the three-body structure and of the mooring line forces, bear very satisfactorily the experimental results. The case of irregular waves is also encouraging, since the statistics of the response is correctly kept up to the fourth order statistical moments. This confirms that the theoretical model proposed in this paper is a suitable tool to predict the actual behaviour of a complex moored structure at sea.
The International Conference on Civil and Architecture Engineering
compliant structures like triangular tension leg platforms (TLPs) are proven to be highly cost effective in deep waters. The estimation of hydraulic forces due to waves on structural member of TLP is vital for its economic and safe design. In the current study, a numerical study for a triangular TLP using modified Morison equation was carried out in the time domain with water particle kinematics using Airy's linear wave theory to investigate the effect of changing the tether tension force on the stiffness matrix of TLP's, the dynamic behavior of TLP's; and on the fatigue stresses in the cables. The effect was investigated for different parameters of the hydrodynamic forces such as wave periods, and wave heights. The numerical study takes into consideration the effect of coupling between various degrees of freedom. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables. Nonlinear equation was solved using Newmark's beta integration method. Only uni-directional waves in the surge direction was considered in the analysis. Keywords-Tethers tension, triangular tension leg platforms, hydrodynamic wave forces, wave characteristic. rilling of oil wells in deeper sea is continuing with striking advances, reaching a water depth of more than 1000 m. These water depths are associated with larger hydrodynamic effects and total base moment, finally resulting in more material. Offshore platforms are usually divided into two general categories, fixed and compliant. Fixed types extend to the seabed and remain in place by their weight or by piles driven into the soil. Compliant-type platforms are more responsive to external effects and their movements are controlled by mooring systems. The increase in cost of fixed offshore structures with depth of water encouraged the development of compliant-type structures. The key idea behind their installation is the minimization of the resistance of the structure to environmental loads by making the structure flexible. The
Hydrodynamic Interaction of Three Floating Structures
2014
This study will highlight the motion characteristic s of single body and multiple bodies of offshore structures due to t he effect of hydrodynamic interaction by considering the gap dis tance, the presence of number of neighboring structures and th e wave direction headings. In order to analyze the added m ass, radiation damping and motion responses that are developed dur ing the interaction between structures, commercial software ANSYS AQWA is used. The analysis are executed by using 10 0 m diameter of round-shaped FPSO as the reference poin t for a single body where it is compared with two bodies and three bodies by using 70 m diameter round-shaped FPSO and LNG vesse l for gap distance of 25 m and 50 m and wave directions at 00 , 45 , 900, 1350 and 1800 headings. The results show same trend with previous studies and researches in which the motion responses due to the effect from other structures occur signi ficantly on surge and pitch motions compare to heave motion though th ere ...
A comparative evaluation of the behaviour of some typical floating offshore structures
Analele Universităţii "Dunărea de Jos" din Galaţi. Fascicula XI, Construcţii navale/ Annals of "Dunărea de Jos" of Galati, Fascicle XI, Shipbuilding, 2019
It is commonly accepted that, during the design process, the characteristics of the location play a major influence leading to the design wave principle. In fact, as compared to ship design process, in case of offshore structures including the ship shaped ones, conceptual design plays a decisive role regarding the capability to safely operate at zero speed on locations in order to reach a high operational index in rough seas. This is directly linked to the limits of the accelerations due to body behaviour in waves which are clearly stated related to the comfort on board corresponding to different types of activities (intellectual work, manual work etc.). On the other hand, the above mentioned restrictions and the operational limits related to the body motions amplitudes, need to be considered. Consequently, the body geometry as well as the masses distribution solutions is mandatory to be carefully evaluated taking also into account the direct influences on the induced structural loads. To this purpose, a comparative evaluation of the Response Amplitude Operators (RAO's) has been performed for six different bodies consisting in an AHTS ship, a floating crane, a semisubmersible and a group of three pipe laying vessels. The results presented in the paper could be useful when future development of activities on a certain location is envisaged providing quantitative data as well as qualitative ones, giving reliable information depending on the geometry and mass distribution.