Floatover Deck Installation Research Articles

Numerical modelling of a catamaran float-over deck installation for a spar platform with complex hydrodynamic interactions and mechanical couplings

Multi-body system is becoming common in engineering practice, such as the catamaran float-over installation for a Spar platform, one of the most complex marine systems. Gap resonance phenomenon occurs in the catamaran float-over system due to strong hydrodynamic interactions, inducing inaccuracy in evaluations of the hydrodynamic coefficients. To obtain reasonable hydrodynamic coefficients, the damping lid method in AQWA, which provide viscous correction for the potential flow theory, is first validated and then applied to the model in this study. It is found that the damping lid is capable of dealing with the gap resonance phenomenon. With the introduction of the damp lid method in the catamaran float-over system with α = 0.20, the relative error between frequency-domain and time-domain declined from 690% to 1.7%. Based on the corrected frequency-domain results, a time-domain model, considering various types of mechanical coupling components in the float-over system, including LMUs, DSUs, steel-to-steel impacts on LMUs, lateral constrains of LMUs and DSUs, sway fenders, hawsers and the mooring system. Simulations for first contact stage and last contact stage under different incident wave angle are performed. It is observed that the relative motions under quartering sea in first contact stage are the largest. Furthermore, in order to reveal the coupling mechanism, different configurations of the barges and Spar are investigated for the first contact stage under irregular waves. It is found that the relative heave motions on the LMUs are larger when the deck and barges are rigidly connected to form a catamaran-barge.

Numerical modeling of nonstationary hydrodynamic forces and induced motions of a coupled offshore floating installation system

Offshore installations always involve multi-body systems in which the hydrodynamic and mechanical interactions are complicated for the properties keep changing under certain operation procedures. Float-over deck (FOD) installation is a typical example, where the draft of barge continuously varies during the load transfer operation. Numerical analysis of such continuous operation is crucial to identify the extreme responses, but it's difficult to model the nonstationary properties involved in the hydrodynamic loads and motions and contact loads of the system. In the study, a numerical modeling methodology is developed to calculate these nonstationary hydrodynamic forces and induced responses, considering an active update of the hydrodynamic properties with the time varying body boundary conditions. The effects of time varying body boundary conditions on hydrodynamic forces and induced nonstationary motions and contact loads of a FOD installation system is studied. The results indicate that the dynamic analysis of the continuous load transfer operation could be effectively carried out with one update of hydrodynamic forces at the end of the operation. The barge roll motions and its natural period are the most affected. The proposed method could be used in intensive simulation of offshore multi-body systems with obvious draft variation during operations.

Nonlinear dynamic analysis of float-over deck installation for a GBS platform based on a constant parameter time domain model

Float-over deck installation has become a reliable and cost-effective method of installing heavy integrated decks for various types of offshore platforms, such as the jacket and GBS platforms. This operation involves a number of inherent complexities such as the strong nonlinear interactions between the multi-body system and environment. Therefore, dynamic modelling of the float-over system during the deck load transfer stage is a challenging task. Particularly, the wave-induced impacts among the deck, barge and platform substructure may generate strong nonlinear dynamics that cannot be accurately investigated by the current standard simulation packages. This study develops a constant parameter time domain model (CPTDM) based on Cummins equation and state-space model for analysing the nonlinear dynamics arising from the float-over deck installation of a GBS platform. Frequency domain hydrodynamic analyses of the installation barge carrying the deck with and without the presence of the GBS are both carried to identify hydrodynamic interactions. A code-to-code verification is performed to verify the accuracy and efficiency of the developed CPTDM by comparing the present results with ANSYS-AQWA. Based on the verified model, the nonlinear dynamics of the GBS platform at different load transfer stages are investigated by using Poincare maps, bifurcation diagrams and phase trajectories.

Continuous multi-body dynamic analysis of float-over deck installation with rapid load transfer technique in open waters

Targeting at the innovative float-over deck (FOD) installation with rapid load transfer technique, the continuous numerical simulations of the specific mating process are conducted based on the coupled multi-body model developed in the paper, where the detailed interaction effects of the Leg mating unit (LMU) and the Deck support unit (DSU), especially the time-varying hydrodynamic forces are considered simultaneously. The established model coincides with the experimental and SIMO results in terms of barge motion responses both at regular and random wave excitations. The motions of barge and topside as well as the corresponding loads of the LMU and DSU are analyzed. It shows that the quick load transferring operation leads to significant changes on barge motion responses and the trim angles of barge and topside have significantly influence on the loads of DSU and LMU. Moreover, the feasibility of the rapid FOD installation system at harsh open sea condition is carried out and arriving that it is functional well when suffering from long period swell. The results prove that the continuous simulation method representing the real-situation of the rapid load transfer technique can constantly investigate the consecutive responses and detect the potential risk of the FOD installation in advance.

Twin Barge-Spar Hydrodynamic Interaction on Floatover Deck Installation

Jurnal ini berisi tentang instalasi floatover sebuah heavy weight topside deck pada fasilitas terapung minyak dan gas. Dalam penelitian ini bangunan apung yang ditinjau adalah SPAR dengan diameter 25m x tinggi 100 m dan 5m sarat air yang akan ditempatkan pada lokasi tertentu dengan tinggi gelombang signifikan (Hs) mencapai 3 meter, periode gelombang (Tp) bervariasi antara 6s sampai 10s, kecepatan arus 0.4 m/s, dan kecepatan angin 26 knots. Dengan pendekatan teknis secara benar maka konsep instalasi floatover dapat dilakukan daripada menggunakan metode instalasi heavy lift. Analisa floatover telah dilakukan menggunakan perangkat lunak MOSES dan hasilnya menunjukkan jenis instalasi ini dapat dikerjakan sebagai alternatif yang bagus untuk instalasi topside pada fasilitas terapung lepas pantai. Hasil untuk kondisi ekstrem saat instalasi menunjukkan nilai maksimum RMS roll, pitch, dan heave adalah 1.11 degree, 1.13 degree, dan 0.057g secara berurutan. Nilai maksimum tersubut terjadi saat tahap instalasi docking stage.

Investigation of the complex dynamics of float-over deck installation based on a coupled heave-roll-pitch impact model

This paper describes an efficient methodology for analysing the dynamics of float-over deck installation, particularly arising from the wave-induced impacts between multiple structures. A coupled heave-roll-pitch impact model is developed in the time-domain to analyse the complex impact behaviour associated with float-over deck installations. The resulting time-domain model is very efficient since the time-consuming convolution terms are replaced by state-space models. The shock absorbers known as Leg Mating Units (LMUs) at the deck-to-substructure (DTS) connections, and Deck Support Units (DSUs) at the deck-to-barge (DTB) connections, are modelled as spring-damper systems with limited load capacities. By considering the coupled heave-roll-pitch motions of the float-over system, the resulting impact model is applied to analyse the complex vertical interactions between the deck and barge and between the deck and substructure at both the 0% and 100% load transfer stages. LMU/DSU impacts and DTS/DTB impacts are analysed here. In addition, the effects of varying wave excitations are investigated based on the coupled impact model.

Float Over Installation Method—Comprehensive Comparison Between Numerical and Model Test Results

Installing a large deck onto a platform, such as a spar, using the floatover method is gaining popularity. This is because the operational cost is much lower than other methods of installation, such as modular lifts or a single piece installation by a heavy lift barge. Deck integration can be performed on land, at quay side and will not depend on a heavy lift barge. A new concept for a floatover vessel has been developed for operations in the Gulf of Mexico and West Africa. In this application sea state conditions are essential factors that must be considered in the Gulf of Mexico, especially for transportation. In West Africa, swell conditions will govern floatover deck (FOD) installation. Based on these two different environmental conditions, Technip Offshore, Inc. developed the FOD installation concept using semi-submersible barge type vessels. A significant amount of development work and model testing has been done on this method in recent years on spar floatover. These tests have validated our numerical methods. Another test was conducted to investigate the feasibility of a deck float-over operation onto a compliant tower for a West Africa project. The project consists of a compliant tower supporting a 25,401metricton(28,000s.ton) integrated deck. This paper will describe comparisons between model test data and numerical predictions of the compliant tower floatover operation.

A Methodology to Simulate Floating Offshore Operations Using a Design Wave Theory

Numerical techniques are extensively used to predict vessel motions and associated contact forces for offshore operations such as lift and floatover deck installations. The accuracy of such predictions however is highly dependent on the comprehensive modeling of sea state conditions, which is often limited by computational power and time constraints. A time-efficient methodology, suitable for modeling large numbers of installation sea states, is developed to alleviate this problem. The methodology is based on the Constrained New Wave model which has been previously used to overcome similar problems. However this has only been for individual, extreme storm conditions. The accuracy, time-efficiency, and practicality of the revised methodology is demonstrated by means of direct comparison of simulation results obtained for a floatover deck installation on the North West Shelf of Australia. The ability to perform a large number of simulations in a time and cost efficient manner is of paramount importance in assessing the system limitations to varying installation conditions, a case that has always been challenging to designers during the development of oil and gas projects. Such flexibility improves confidence in the overall system, necessary for the accurate assessment of the commercial viability of marginal developments.