Hyun Joe Kim

Hydrostatic Stability and Global Performance Analysis for Set TLP

SET (Samsung Enhanced hull for Tendon) TLP (Tension Leg Platform) has been designed as an innovative TLP hull form with optimized number of tendons compared to conventional TLP design. SHI (Samsung Heavy Industries) designed the SET TLP to have the minimized hull weight with narrow and thin pontoon which results in the less number of tendons without any outboard extension of column or pontoon.The SET TLP has 8 tendons which are evenly attached along with the octagonal shaped-ring pontoon. The unique shape of octagonal ring pontoon distributes the wave load and concentrated tendon loads in larger areas, which can minimize the structural reinforcement.To verify the feasibility of the proposed hull concept with regard to the hydrostatic/hydrodynamic characteristics and tendon design, the numerical analyses for the hydrostatic stability and global performance are carried out. Hydrostatic stability is investigated for all the possible loading cases such as float-off, wet transit, tendon installation and operational conditions, and the proper tank compartments are achieved for all the scenarios without using any temporary stability module.The global performance is validated for all the possible combinations of wave, swell, wind, current and/or squall for a site in Western Africa. Through the frequency-domain analysis and nonlinear time-domain analysis as well, the essential items such as the maximum offset/set-down/top tendon tension, minimum bottom tendon tension are examined and confirms that the certain design criteria of TLP operation are satisfied.Copyright

Practical Review on Fatigue Damage Estimation Under Combinations of Global and Local Loadings

In this paper, reviews on the fatigue damage estimation are presented in case that both the global and the local loadings are applied and two practical approaches are proposed if the statistical data of the local loading are not available. So far the fatigue damage has been estimated through Rules from Classification of Societies if the statistical data such as the standard deviation and the up-crossing rate of the stress processes are available. However, in many cases, it’s hard to prepare enough data for the fatigue damage estimation, which results in very severe design.Hence two practical approaches are presented which can be applied if the statistical data of the local loading are not available. In practice, only the maximum stress range and the total cycles of the local loading are available very often. In the practical approach 1, it is assumed that the maximum stress range always occurs during the total cycles. Then, the local fatigue damage is very conservatively estimated and the total fatigue damage is obtained by the way of summation of the global fatigue damage and the local fatigue damage. In the practical approach 2, the local fatigue damage is estimated based on the assumption of the Weibull fitted local loading. And the use of the cube root summation is proposed between the global fatigue damage and the local fatigue damage. The presented two practical approaches are applied to the side appurtenances of a FPSO and the resultant fatigue damages are compared and discussed. The results of this study can be expected as practical and useful data for the fatigue analysis of the marine and offshore structures.Copyright

Offloading Operability With Heading Control of Side-by-Side Moored FLNG and LNGC

In this study, a series of model tests was performed and the effect of the heading control on the offloading operability of side-by-side moored vessels in multidirectional environments was investigated. During the tests, hawser tensions, fender loads, and relative motions between two vessels were focused, which are the key factors defining the offloading operability. Basically, the heading control is designed to maintain the FLNG (LNG FPSO)’s heading at between wind wave and swell. In the model tests, several heading angles were selected to investigate the impact of the heading control on the offloading operability, which includes the heading angles aligned with swell and between swell and wind wave. The loading conditions of the FLNG and LNGC were chosen to have a similar roll natural period, and the period of swell was also selected close to the roll natural period, which realizes an worst situation.The model tests proved that heading control improves the offloading operability in the multi-directional environments. However, in the test, as vessel’s heading angle approaches to the direction of swell, the LNGC is exposed to wind wave as much as to increase the relative motion between the two vessels and deteriorate the offloading operability. In the model test campaign, the motion RAOs and horizontal drift forces/moment due to waves for the side-by-side moored vessels were measured and compared with the analytical calculations, which show the strong shielding effect on the wind wave by the FLNG.Copyright