ABSTRQCT Structural perturbation theory has been developed over the past 16 years to relate two structural states modeled by the same Finite Element (FE) model but described by di$erent values of the design variables. Relating an intact/ damaged (initial) structure to a limit state structure produces the reserve/ residual redundancy. Invariant and consistent redundancy, redundancy functions, and injective mappings are defined and related to the design variables. General perturbation equations are derived to relate the two states andproducefailuresuflaceequations. Individual andjointfailurepoints are identtfied and redundancy is computed without linearization of failure surfaces, enumeration of failure paths, trial and error, or repeated FE Analyses (FEAs). This is achieved by large admissible perturbations using a prediction-correction algorithm and postprocessing FEA results of the initial structure only. The latter may dtferfiom the limit state structure in sti&ess, mass, geometry, or response by as much as 1 &I-300% depending on the size of the FE model. Structural perturbation theory treats discrete and continuous structures as the FE method does: modeling of the structure as a simpltjkd system of components is not needed. To introduce this new approach to redundancy, modal dynamic and stank deflection failure criteria are used in the elastic range. Numerical applications on a beam, a small, and a large o$shore tower are used to test the method. Future developments and impact to design are discussed as the new methodology introduces an alternative to systems reliabiliry and stochastic FE.

The perturbation approach to reliability (PAR) is a powerful methodology for reliability analysis and design of large structures. Its main features are: F1) PAR provides the exact global failure equation for any failure criterion for which the corresponding structural analysis can be performed by finite elements. F2) Geometry, material, and loads appear explicitly in the global failure equations and are treated as random variables. No need arises for load path selection or load pattern specification. F3) PAR introduces an invariant and consistent redundancy definition as an injective mapping restricted on the failure surface. Thus, the redundancy/reliability of the structure is expressed in terms of the redundancy/reliability of its structural components. F4) The norm of the Rosenblatt transformed reliability injection is the reliability index. F5) For each global failure equation or combination of failure equations, PAR computes the individual or joint design points without enumerating paths to failure, trial and error, or repeated finite element analyses. F6) Serviceability or ultimate global structural failure is defined by specifying a threshold value of any quantity that can be computed by finite elements: natural frequencies, dynamic normal modes, static deflections, static stresses, buckling loads, and buckling modes are implemented in PAR. Stress failure equations are used along with linearized plasticity surfaces to identify element failure. Several applications are presented to assess PAR.

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There are several substantial advantages to installing an integrated deck on a Spar using floatover installation, particularly for large topsides which exceed the single lift capacity of the available heavy lift derrick barge fleet. These advantages include schedule and cost savings for the integration and commissioning of modules on land rather than at sea. Uncoupling the deck fabrication schedules from the availability of heavy lift vessels is another advantage. The purpose of the model tests described in this paper was to generate data on motions and loads for the operational sea states in the Gulf of Mexico, and to define and validate different approaches of transferring the topsides to the Spar, using a catamaran configuration. The data are intended to (1) demonstrate the feasibility of the installation method for the GOM, and (2) validate Technip’s analysis tools. The model tests were performed at OTRC (Texas A&M) with a model set-up corresponding to a 1:60 model scale. The simulated topsides was about 18,000Te, and Jones Act compliant barges were modeled for the catamaran configuration. The paper will describe the catamaran and spar models, and the instrumentation to measure motions and loads for transportation and installation. It will also describe the shock cell configuration used for the mating operation, and several alternative methods for performing the mating. The environmental conditions tested included several random sea states, harmonic waves, and three headings (beam, head, and quartering seas). Selected data will be shown to demonstrate the range of motions and loads associated with the floatover installation in the GOM. Estimates of limiting sea states for the GOM will be discussed. The validation of the analysis tools is the subject of another paper in Ref [1].

A normally un-manned minimal floating platform can be used for several applications to support subsea development. The applications include enabling Long Subsea Tiebacks by supporting power generation and distribution equipment, when the host facility doesn't have excess power capacity (Power Buoy) or the required footprint and space to support the required power distribution hardware or locate the distribution equipment to distribute the power imported from shore. It can also serve as a partial processing host with functionality ranging from Chemicals and Artificial Lift all the way to Multi-Phase Pumping or Gas Compression, as required. An un-manned floating platform can be a cost-efficient solution, where the economics of a very Long Subsea Tieback or a Host Facility with full processing capacity become prohibitive for developing small to medium size fields. The substructures for these platforms have reduced and simplified systems resulting in lower Capex, Opex and minimal maintenance requirements. This platform is safer to operate than conventional host platforms because it is un-manned, and it also deploys robotics and remotely controlled equipment, using the latest advances in digital, robotics, and autonomous control technologies. The paper reviews the different floating unmanned minimal platform configurations that are designed for this purpose. The following aspects of the normally un-manned floating platform are discussed: Functionality Cost-Efficient Design alternatives Construction/Installation efficiency Operations/ Maintenance principles Possible applications of the normally un-manned floating platform include small to medium size fields, remote gas fields requiring compression to export gas to shore that would otherwise prove to be un-economical to develop. The normally un-manned floating platform helps improve the development economics and the operational safety of these fields. The industry's response to the oil price slump in the past few years combined with the latest advances in technology led to the evolution of these minimal unmanned floating platforms.