Incorporating magneto-Rheological damper into riser tensioner system to restrict riser stroke in moderate-size semisubmersibles

Zainuddin, Zaid,Kim, Moo-Hyun,Kang, Heon-Yong,Bhat, Shankar Techno-Press 2018 Ocean systems engineering Vol.8 No.2

In case of conventional shallow-draft semisubmersibles, unacceptably large riser stroke was the restricting factor for dry-tree-riser-semisubmersible development. Many attempts to address this issue have focused on using larger draft and size with extra heave-damping plates, which results in a huge cost increase. The objective of this paper is to investigate an alternative solution by improving riser systems through the implementation of a magneto-rheological damper (MR Damper) so that it can be used with moderate-size/draft semisubmersibles. In this regard, MR-damper riser systems and connections are numerically modeled so that they can couple with hull-mooring time-domain simulations. The simulation results show that the moderate-size semisubmersible with MR damper system can be used with conventional dry-tree pneumatic tensioners by effectively reducing stroke-distance even in the most severe (1000-yr) storm environments. Furthermore, the damping level of the MR damper can be controlled to best fit target cases by changing input electric currents. The reduction in stroke allows smaller topside deck spacing, which in turn leads to smaller deck and hull. As the penalty of reducing riser stroke by MR damper, the force on the MR-damper can significantly be increased, which requires applying optimal electric currents.

Coupled dynamic responses of a semisubmersible under the irregular wave and turbulent wind

Dey, Swarnadip,Saha, Kaushik,Acharya, Pooja,Roy, Shovan,Banik, Atul K. Techno-Press 2018 Ocean systems engineering Vol.8 No.4

A coupled dynamic analysis of a semisubmersible-type FOWT has been carried out in time domain under the combined action of irregular wave and turbulent wind represented respectively by JONSWAP spectrum and Kaimal spectrum. To account for the turbine-floater motion coupling in a more realistic way, the wind turbulence has been incorporated into the calculation of aerodynamic loads. The platform model was referred from the DeepCwind project and the turbine considered here was the NREL 5MW Baseline. To account for the operationality of the turbine, two different environmental conditions (operational and survival) have been considered and the aerodynamic effect of turbine-rotation on actual responses of the FOWT has been studied. Higher mean offsets in surge and pitch responses were obtained under the operational condition as compared to the survival condition. The mooring line tensions were also observed to be sensitive to the rotation of turbine due to the turbulence of wind and overestimated responses were found when the constant wind was considered in the analysis. Additionally, a special analysis case of sudden shutdown of the turbine has also been considered to study the swift modification of responses and tension in the mooring cables.

Tension variations of hydro-pneumatic riser tensioner and implications for dry-tree interface in semisubmersible

Kang, Hooi-Siang,Kim, Moo-Hyun,Aramanadka, Shankar S. Bhat Techno-Press 2017 Ocean systems engineering Vol.7 No.1

In real sea environments, excessive dynamic axial tension variations can be exerted on the top-tensioned risers (TTRs) and lead to structural integrity issues. The traditional riser-tension-variation analysis, however, by using parametric formulation is only conditionally valid under certain strict limits and potentially underestimates the total magnitudes of tension variations. This phenomenon is especially important for the long stroke tensioner in dry-tree semisubmersible with larger global heave motion and longer stroke. In this paper, the hydro-pneumatic tensioner (HPT) is modeled in detailed component-level which includes a set of hydraulic and pneumatic components. The viscous fluid frictional effect in the HPT is considered. The main objectives are (i) to develop a detailed tension variation model of the HPT; (ii) to identify the deviations between the conventional parametric formulation and component-level formulation; (iii) to numerically analyze the tension variation of long stroke tensioner in a dry-tree semisubmersible (DTS). The results demonstrate the necessity of component-level formulation for long stroke tensioner in the development of DTS.

심흘수 반잠수식 해양구조물(DDS) 형상 개발 연구

이진호(JIN-HO LEE),이준영(JUNE-YOUNG LEE),김병우(BYUNG-WOO KIM) 한국해양공학회 2008 韓國海洋工學會誌 Vol.22 No.5

This paper treats the development of a new type of deep draught semisubmersible offshore structural shape that has excellent heave motion response and less dawn-time. This new type of semisubmersible shape is characterized by heave dampers at each pontoon comer and appropriate column size adjustment to achieve the desired cancellation and resonance motion period. It was found that the final model had efficient workability, based on the wavescatter diagrams for the GoM and North Atlantic ocean, due to less heave motion, although the specific heave response at the 100 year return period wave condition in the North Atlantic was more or less increased.

Investigation of jack-up leg extension for deep water operations

Yousri M. A. Welaya,Ahmed Elhewy,Mohamed Hegazy 대한조선학회 2015 International Journal of Naval Architecture and Oc Vol.7 No.2

Since the first jack-up was built, jackups have become the most popular type of mobile offshore drilling unit (MODU) for offshore exploration and development purposes in shallow water. The most pivotal component of the jack-up unit is the leg, which can directly affect the global performance of the unit. In this paper, an investigation into extending the length of the jack up leg is carried out in order to study the enhancement of the rig capability to drill in deeper water approaching the range of the Semisubmersible Drilling Unit (SSDU) (300-1000ft). A study of the performance of a deep-water jack-up unit is performed with different leg lengths. Typical leg scantling dimensions and identical external loads are assigned, and then a detailed Finite Element Analysis (FEA) model is created in order to simulate the jack-up leg unit’s structural behavior. A Multi-point Constraint (MPC) element together with the spring element is used to deal with the boundary conditions. Finally, a comparative analysis for five leg lengths is carried out to illustrate their performance, including the ultimate static strength, and weight.

Investigation of jack-up leg extension for deep water operations

Welaya, Yousri M.A.,Elhewy, Ahmed,Hegazy, Mohamed The Society of Naval Architects of Korea 2015 International Journal of Naval Architecture and Oc Vol.7 No.2

Since the first jack-up was built, jackups have become the most popular type of mobile offshore drilling unit (MODU) for offshore exploration and development purposes in shallow water. The most pivotal component of the jack-up unit is the leg, which can directly affect the global performance of the unit. In this paper, an investigation into extending the length of the jack up leg is carried out in order to study the enhancement of the rig capability to drill in deeper water approaching the range of the Semisubmersible Drilling Unit (SSDU) (300-1000ft). A study of the performance of a deep-water jack-up unit is performed with different leg lengths. Typical leg scantling dimensions and identical external loads are assigned, and then a detailed Finite Element Analysis (FEA) model is created in order to simulate the jack-up leg unit's structural behavior. A Multi-point Constraint (MPC) element together with the spring element is used to deal with the boundary conditions. Finally, a comparative analysis for five leg lengths is carried out to illustrate their performance, including the ultimate static strength, and weight.

Systematic comparisons among OpenFAST, Charm3D-FAST simulations and DeepCWind model test for 5 MW OC4 semisubmersible offshore wind turbine

Jieyan Chen,Chungkuk Jin,Moo-Hyun Kim Techno-Press 2023 Ocean systems engineering Vol.13 No.2

Reliable prediction of the motion of FOWT (floating offshore wind turbine) and associated mooring line tension is important in both design and operation/monitoring processes. In the present study, a 5MW OC4 semisubmersible wind turbine is numerically modeled, simulated, and analyzed by the open-source numerical tool, OpenFAST and in-house numerical tool, Charm3D-FAST. Another commercial-level program FASTv8-OrcaFlex is also introduced for comparison for selected cases. The three simulation programs solve the same turbine-floater-mooring coupled dynamics in time domain while there exist minor differences in the details of the program. Both the motions and mooring-line tensions are calculated and compared with the DeepCWind 1/50 scale model-testing results. The system identification between the numerical and physical models is checked through the static-offset test and free-decay test. Then the system motions and mooring tensions are systematically compared among the simulated results and measured values. Reasonably good agreements between the simulation and measurement are demonstrated for (i) white-noise random waves, (ii) typical random waves, and (iii) typical random waves with steady wind. Based on the comparison between numerical results and experimental data, the relative importance and role of the differences in the numerical methodologies of those three programs can be observed and interpreted. These comparative-study results may provide a certain confidence level and some insight of potential variability in motion and tension predictions for future FOWT designs and applications.

Comparative study for motion performance of the various FOWT platforms in waves

Zhenhao Song,Jeong-Seok Kim,Bo Woo Nam 한국해양환경·에너지학회 2021 한국해양환경공학회 학술대회논문집 Vol.2021 No.5

Recently, many countries have concentrated on the development of offshore wind power generation because of the limited space on land and considering the problems of noise and pollution. Compared with the nearshore wind resources, many countries, including China, America and Norway have found that more wind resources are existing in the deep water. For this reason, proper floating body for the FOWT which gives better motion performance in the deep sea is needed to be developed. In the deep sea, semi-submersible offshore platforms are currently most used as the support structure for FOWT since it is easier to install in actual engineering with lower cost compared with TLP and Spar. In this paper, a motion response analysis of different semisubmersible platforms for FOWT is carried out. In the present article, several semi-submersible supporting structure of floating offshore wind turbines concepts which have been already applied in the actual engineering installation are contained like Wind Float (Roddier et al., 2010), OC4-DeepCwind (Robertson et al., 2014). Additionally, some new designed platforms for the FOWT were also discussed. The main object of the present study is to investigate and compare the motion response of the platform due to the effect given by horizontal pontoon and damping plate respectively. Since the heave motion and pitch motion amplitude determine whether the wind turbine part will sink or not, and the pitch motion will affect the windward area which determine the efficiency of the electric generation, heave motion and pitch motion performance were discussed only in this article. The simulation tool used in this research is WADAM which is a commercial software developed by DNV GL based on the potential theory. For obtaining exact motion response results, except for the wave damping force, viscous damping force were also added manually by using a certain ratio of critical damping force. The viscous damping ratio value was calculated by comparing with a OC4 FOWT model test result (Koo et al., 2014). Besides, the FOWT platform models presented in previous studies were modified with equivalent displacement constraint and similar viscous damping ratio to evaluate the motion performance in fair comparing approach.

반잠수식 초대형 해양구조물의 파랑중 탄성응답특성

구자삼(Ja-Sam Goo),김경태(Kyung-Tae Kim),홍봉기(Bong-Ki Hong) 한국해양공학회 1999 韓國海洋工學會誌 Vol.13 No.4

To design a very large floating structure, such as a floating airport, we have to estimate the hydroelastic responses of a very large floating structure (VLFS) exactly. We developed the numerical method for estimating the hydroelastic responses of the VLFS. The developed numerical approach is based on a combination of the three-dimensional source distribution method, the wave interaction theory and the finite element method for structurally treating the space frame elements. The Numerical results of the hydroelastic responses and steady drift forces of a semisubmersible type offshore structure, which is supported by the 33(3 by 11) floating bodies, with various bending rigidities are illustrated.

반잠수식 부유식 풍력터빈 제어기 기초 설계

송원(Yuan Song),전태수(Taesu Jeon),백인수(Insu Paek) 한국태양에너지학회 2020 한국태양에너지학회 학술대회논문집 Vol.2020 No.6