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Abstract
Offshore structures (Fig. 9.1) with their facilities are used to drill wells, to extract and process oil and natural gas, or to temporarily store product until it can be brought to shore for refining and marketing.
Fig. 9.1
Various types of offshore structures. 1 and 2 Conventional fixed jacket platforms; 3 Compliant piled tower; 4 and 5 Vertically moored tension leg and mini-tension leg platform (TLP); 6 Single point anchor reservoir platform (SPAR); 7 and 8 Semi-submersibles; 9 Floating production, storage, and offloading facility (FPSO); 10 Subsea completion and tie-back to host facility
(courtesy of US National Oceanic and Atmospheric Administration)
Fig. 9.2
An artificial island (Northstar Island) for oil drilling in the Beaufort Sea
Fig. 9.3
A floating drilling platform Aker H6e
(courtesy of Aker Solutions)
Fig. 9.4
Subsea wells
(courtesy of Aker Solutions)
Fig. 9.5
Piles subjected to tensile and compressive axial loading due to the lateral wind and wave loading transferred from the upper part of the structure
Fig. 9.6
Troll A platform
Fig. 9.7
Illustration of a guyed tower
Fig. 9.8
Fixed jacket structures (left), pile foundations of a fixed monopile (middle) and of a jacket structure (right)
Fig. 9.9
Fixed GBS offshore structures with gravity-based foundation design
(courtesy of Aker Solutions)
Fig. 9.10
A tension leg drilling platform (left) and a semi-submersible platform (right)
(courtesy of Aker Solutions)
Fig. 9.11
Accounting of dynamics in the design of offshore structures (from a short course presentation “Dynamic Analysis and Design of Offshore Structures” by Junbo Jia and Lance Manuel at OMAE 2016, Pusan)
Fig. 9.12
Wind turbines with their substructures and electrical substation located in the North Sea
(license under CC BY-SA 3.0, by StekrueBe)
Fig. 9.13
Types of existing substructures and foundations for fixed offshore wind turbines [503]
Fig. 9.14
Schematic illustration of a TLP used for an OWT substructure
Fig. 9.15
Schematic illustration of a single floating cylindrical spar buoy moored by catenary cables
Fig. 9.16
WindFloat, which is a semi-submersible structure for an OWT operating at a rated capacity of 2 MW approximately 5 km offshore of Aguçadoura, Portugal
(under license CC BY-SA 3.0 by untrakdrover)
Fig. 9.17
A close look at a tripod used as a substructure for OWT
(courtesy of Aker Solutions)
Fig. 9.18
Period interval for stiff-stiff, soft-stiff and soft-soft design of OWT substructures
Fig. 9.19
Wave-induced static versus instantaneous dynamic forces and moments in a bottom-fixed cantilevered tower [504]
Fig. 9.20
A GBS with a heavy topside supported by four concrete shafts (legs)
Fig. 9.21
Ground motions EW component (upper) recorded during El Centro earthquake and its Fourier amplitude (lower)
Fig. 9.22
Acceleration at the shaft-topside connection with various leg/shaft stiffness (peak acceleration: 4.7 m/s2 for double leg thickness, 5.8 m/s2 for reference leg thickness, 4.2 m/s2 for double leg thickness)
Fig. 9.23
An offshore jacket structure subjected to a wave with a wave height of 31.5 m and a wave peak period 15.6 s
(courtesy of Aker Solutions)
Fig. 9.24
Axial force time history on the lower part of leg C1 of the offshore jacket with and without dynamic inertia effects. (The exact magnitude of axial forces are omitted to protect the interests of the relevant parties)
Fig. 9.25
An SDOF spring-mass-damper system under an external force F(t)
Fig. 9.26
Transient and steady-state responses due to external harmonic force excitations applied on a system with ωn = 1.0, Ω = 0.8, ζ = 0.05, and \( \varphi \) = 0.1
Fig. 9.27
Damped responses due to harmonic excitations with the characteristics of a quasi-static (Ω/ωn ≪ 1); b resonance (Ω/ωn close to 1); and c inertia dominant responses (Ω/ωn ≫ 1), for a system with ωn = 1.0 and viscous damping ratio ζ = 0.03 [123]
Fig. 9.28
Response of various types of offshore and land-based structures in three frequency ranges subjected to external environmental loading with a frequency of Ω, the natural frequency of the structure is denoted as ωn (from an oral presentation by the author at the 11th International Conference on Recent Advances in Structural Dynamics, Pisa, 2013)
Fig. 9.29
Frequency responses of the axial force (Dof 1) [N], in-plane bending moments (Dof 5) [Nm] and out-of-plane bending moments (Dof 6) [Nm] for a weld joint 10,803 (Fig. 9.30) at the top of a jacket, and the jacket is subject to wave loading corresponding to a sea state with a significant wave height Hs = 8.8 m, and a modal wave period Tp = 13.2 s (0.08 Hz) [505]
Fig. 9.30
Location of the welded joint 10,803 on the jacket
Fig. 9.31
Typical short-term environmental loading frequency/period (from an oral presentation by the author at the 11th International Conference on Recent Advances in Structural Dynamics, Pisa, 2013)
Fig. 9.32
A tuned mass damper (upper) suspended from the 92nd to the 87th floor at Taipei 101 (lower) (under licenses of CC BY-SA 3.0 by Guillom and Peellden)
