A Design Method to Assess the Primary Strength of the Delta-Type VLFS

Abstract

Very large floating structure (VLFS) is a sustainable concept centered around creating solid platforms at sea. The Delta is a new type of VLFS, designed to withstand open-sea conditions and to form, in addition to a broad deck areas, a sheltered basin of year-round operability. The design of this unique hull relies on direct calculations in order to identify critical load cases and assess their load effects. This study formulates a theoretical procedure for the initial assessment of the primary strength. The procedure analytically integrates the floatation loads while the hull rests at hydrostatic equilibrium on a wave surface and obtains the vertical and horizontal bending moment. This preliminary assessment tool enables a fast review of many load cases and provides the basic insights necessary for a reasonable initial design. Using the procedure, we conducted a primary load assessment for the design of Delta. By calculating the load response to 588 load cases, we identified the critical load scenario and the maximal axial stress. As the stress was too high, we improved the geometry in order to reduce loads and assessed proper scantlings for the critical section. We present the formulation of the procedure, the validation of the results, and the implementation for the structural design of the Delta VLFS.

Nonlinear Hydrodynamic Analysis of Ships Moored in a VLFS Service Basin in the East Mediterranean Sea

“…Figure 3 and Table 1 present the geometry and main dimensions of the Delta VLFS as modeled for the mooring analysis. This geometry results from a previous design and analysis of the hydrodynamic and structural aspects [10,11]. Figure 3 and Table 1 present the geometry and main dimensions of the as modeled for the mooring analysis.…”

“…This geometry results from a previous Figure 3 and Table 1 present the geometry and main dimensions of the Delta as modeled for the mooring analysis. This geometry results from a previous desig analysis of the hydrodynamic and structural aspects [10,11]. The Delta, anchored at 50 m water depth, was moored to the seabed by a SPM consisting of 24 catenary lines of 3 segments each, as shown in Figure 4.…”

“…VLFS types are traditionally categorized by their hull configurations into the pontoon or the semisubmersible types [8,9]. The Delta-type VLFS [10,11] is a newly developed concept. It is designed to operate at intermediate open sea condition and to withstand severe weather conditions with minimal downtime.…”

“…Drimer and Gafter [10] introduced the Delta VLFS, elaborated on the design considerations, studied the hydrodynamic attributes, and showed the favorable performance of the structure. Focusing on the structural design aspects of the Delta, [11] presented a primary strength assessment tool, developed for the Delta. This study focuses on the sheltered basin and examines its operability as a service port and, as an expansion to the mentioned hydrodynamic study, we constructed an analysis procedure so it may be utilized as a design evaluation tool.…”

“…For the mooring design [10], as well as for the structural design of the VLFS [11], we applied extreme storms. However, for the operability aspects, as the downtime is in the order of few percent, we indicated the limit storms that will disturb the operability, which are storms that statistically appear every year.…”