Comparative study of TLP and ETLP performance in Caspian Sea environment using numerical method. (November 2022)

• Record Type: Journal Article
• Authors: Akbarizadeh, Naghmeh; Ketabdari, Mohammad Javad
• Is Part Of: Marine structures. Volume 86(2022)
• Publication Date: 2022-11
• Subjects: Conventional and extended TLPs -- Numerical modeling -- Fatigue damage -- Irregular waves -- Wind and currents -- Caspian sea conditions; Naval architecture -- Periodicals; Offshore structures -- Periodicals; Architecture navale -- Périodiques; Structures offshore -- Périodiques; Naval architecture; Offshore structures; Periodicals; 620.4162
• DOI: 10.1016/j.marstruc.2022.103279
• Languages: English
• ISSNs: 0951-8339

Abstract

Abstract: This paper presents a numerical analysis to compare a Conventional TLP (CTLP) and an Extended TLP (ETLP) performance in marine environmental conditions. Both platforms have 12 tethers installed in a water depth of 700 m located in the Caspian Sea under irregular JONSWAP waves, wind and current loads. A coupled BEM-FEM numerical time and frequency domain analysis was performed to estimate motions and mooring line cumulative fatigue damage of two kinds of tension leg platforms. Besides, power spectra density (PSD) of heave motion, which is the most important displacement in the vertical plane for TLPs, under different wave periods at a wave angle of 30 deg was investigated. Finally, to have an in-detailed overlook, surge, heave and pitch RAO of platforms in critical wave periods under wave angles from 0 to 45 deg were studied. Model results showed that the CTLP demonstrate larger mooring fatigue damage and therefore less safety against wave, wind and current loads. However, perturbed waves induce more perturbance around the ETLP than the CTLP which in turn needs a proper control system to damp it. In addition, the obtained results show that in the Caspian Sea condition, mainly the ETLP demonstrates a smaller heave, surge and pitch motions than those of the CTLP under various wave periods. Altogether these results show that using a control system ETLP with respect to the CTLP demonstrates more efficient performance. Highlights: A numerical study was performed aiming to compare CTLP and ETLP performance in the Caspian Sea. The TLPs were exposed to irregular JONSWAP waves, wind and current loads in the Caspian Sea. Cumulative fatigue damage of ETLP's mooring lines is smaller than those of CTLP leading to greater fatigue life for ETLP. ETLP's heave motion, which is very important for TLPs performance, is smaller compared to that of CTLP. Wave frequency responses increase by increasing the incident wave periods from 5 to 17secs.