The role of mini tension leg platforms (TLP) in oil exploration and production in marginal deepwater fields is becoming increasingly important. SeaStar is a mini TLP that combines the simplicity of a spar and favourable response features of a TLP. In this paper, the results of a detailed numerical investigation of the coupled dynamic behaviour of SeaStar are reported with special attention to platform-tether coupling. The numerical study has been carried out using a finite element computer code developed for the nonlinear dynamic analysis of compliant offshore platforms in the time domain using Morison type wave loading. A typical SeaStar platform has been considered at two water depths, 215 m and 1000 m. Experimental investigation was conducted for a scaled model corresponding to 215 m water depth for validation of the numerical model. The model-prototype correlation studies have been conducted using the numerical model. Response amplitude operators of motion and tether tension are presented for the two typical water depths and conclusions drawn. © 2002 Elsevier Science Ltd. All rights reserved.

S. K. Bhattacharyya

Department of Ocean Engineering

S. Sreekumar

V. G. Idichandy

Correlation methods

Crude petroleum

finite element method

Numerical methods

Time domain analysis

WAVE EFFECTS

TENSION LEG PLATFORMS (TLP)

Ocean Engineering

DEEP WATER

Dynamic analysis

TENSION LEG OFFSHORE PLATFORM

WAVE LOAD

Wave-structure interaction

TENSION LEG PLATFORM

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Coupled dynamics of SeaStar mini tension leg platform

Offshore systems consisting of floaters linked to line structures such as risers and mooring lines are favoured for deepwater applications. The dynamic coupling analysis of a floater together with the line structures has been the subject of several studies in recent years. Powerful numerical tools have been developed implementing full-fledged time-domain approaches as well as more efficient frequency-domain approaches for the analysis of deepwater systems. The present article provides a brief overview of coupled analysis techniques employing both time-domain and frequency-domain approaches, focusing on the basic modelling issues and challenges. It is worth formulating compact but sufficiently accurate dynamic models of line structures. The consequence of truncation errors of numerical integration schemes in long-term time-domain simulations needs to be studied. There is a need to standardise the statistical linearisation approach applied to dynamic response which spreads over a very wide frequency range. Verification of the nonlinear drag force model in the Morison equation through basic computational fluid dynamics studies may be undertaken. © 2014, © 2014 Informa UK Limited, trading as Taylor & Francis Group.

Ships and Offshore Structures

Coupled dynamics of deepwater structures–issues and challenges

The common types of deep-water offshore structures have rigid connections, resulting in more stresses on members subjected to environmental loads. On the contrary, the relatively new offshore triceratops alleviates the encountered environmental loads by virtue of its innovative structural form and design. The top deck and the buoyant leg structure (BLS) are connected to each other by universal joints that permit transfer of translations from the BLS to the top deck but restrain transfer of rotations. The present study develops a mathematical formulation for the aerodynamic analysis of offshore triceratops and examines its response under regular waves in the presence of wind. Based on the numerical studies conducted here, it is observed that triceratops shows significant reduction in deck response, with no transfer of rotation from the BLS; the deck remains horizontal under the encountered wave loads. Lateral displacement of the deck is restrained due to the compliancy offered by the ball joints. The heave response is less in comparison with the surge response; this implies that the platform is stiff in heave degree-of-freedom, which is required for deep-water compliant platforms. A lesser response in the deck confirms that the deck remains horizontal even when the pitch response is significant in the BLS units. Offshore triceratops derives an advantage through the chosen geometric form for ultra-deep-water applications. © 2013 Copyright Taylor and Francis Group, LLC.

Aerodynamic response of offshore triceratops

A brief overview of analysis of deepwater offshore structures with reference to modeling issues is presented. Floaters with moorings and risers exhibit nonlinear response under environmental loads. The modeling of such structures poses many challenges because of the flexibility of the riser/mooring system, fluid-structure interaction and random nature of wave loads. Tensioned beam finite elements can be used for structural modeling of line elements. Computational fluid dynamic modeling may be used to firm up hydrodynamic coefficients required in the Morison equation for the estimation of fluid loads on structural elements, as well as to evolve simplified models to represent vortex-induced motions. While wave-body interaction of large-volume structures may be modeled using computational fluid dynamic tools, the use of numerical models employing the fully nonlinear potential flow theory is worth exploring. Simpler analytical models for use in design analysis may be developed by employing coupled models based on nonlinear structural finite element methods and computational fluid dynamic tools. Simpler methods of evaluating stress-range statistics required for fatigue damage estimation need to be developed for the case of nonlinear stochastic response of deepwater systems. © IMechE 2013.

Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment

Analysis of deepwater offshore structures: Issues and challenges

Tension Leg Platforms (TLPs) are one of the best options for offshore industry in deep waters due to proven motion response characteristics. These are water depth sensitive structures and the motion responses in vertical plane motions (heave, roll and pitch) are critical for a TLP. Tension Based TLP (TBTLP) is a new concept and finds application in much deeper waters. A provision of a tension base at mid-depth results in an economical design of TLP. In fact, the TLP installed at a certain depth without any modifications can be made to be deployed in much deeper water depths by means of a tension base. In this paper, the concept of TBTLP is highlighted and hydrodynamic analysis of the chosen platform has been carried out using ANSYS AQWA package. The motion responses in terms of Response Amplitude Operators (RAOs) of TBTLP with one Tension Base in surge, heave and pitch have been obtained and compared with a TLP without a tension base. Copyright © 2012 by ASME.

Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE

Hydrodynamic analysis of Tension Based Tension Leg Platform

The effect of tether-riser dynamics on the response characteristics of deep water tension leg platforms in water depths 900 m and 1800 m under random waves is investigated using a developed nonlinear finite element analysis program in the time-domain. Updated Lagrangian coordinates and incremental iterative solution based on Newmark's integration scheme are adopted. Linear wave theory is used. Relative velocity form of Morison's equation is used for estimating the wave forces. Current forces are also included in the analysis. Results are reported in the form of statistical values of responses. The statistical values of responses are found to increase with water depth and significant increase is observed when risers are included. © 2010 American Society of Mechanical Engineers.

Journal of Offshore Mechanics and Arctic Engineering

Dynamic analysis of deep water tension leg platforms under random waves

Subsea and Deepwater Oil and Gas Science and Technology

World Offshore Oil and Gas Projects

Handbook of Offshore Engineering

Physical Modelling of Offshore Structures

Hydrodynamic Coefficient Estimation for TLP and Spar Structures

Coupled Dynamic Analysis of a Moored Spar in Random Waves and Currents (Time-Domain Versus Frequency-Domain Analysis)

Offshore Technology Conference

Morpeth SeaStar Mini-TLP

Journal	Data powered by TypesetOcean Engineering
Publisher	Data powered by TypesetElsevier BV
Open Access	No