Seismic response evaluation of fixed jacket-type offshore structures by random vibration analysis

Shehata E. Abdel Raheem,Elsayed M. Abdel Aal,Aly G.A. AbdelShafy,Mohamed F.M. Fahmy 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.2

Offshore platforms in seismically active areas must be designed to survive in the face of intense earthquakes without a global structural collapse. This paper scrutinizes the seismic performance of a newly designed and established jacket type offshore platform situated in the entrance of the Gulf of Suez region based on the API-RP2A normalized response spectra during seismic events. A nonlinear finite element model of a typical jacket type offshore platform is constructed taking into consideration the effect of structure-soil-interaction. Soil properties at the site were manipulated to generate the pile lateral soil properties in the form of load deflection curves, based on API-RP2A recommendations. Dynamic characteristics of the offshore platform, the response function, output power spectral density and transfer functions for different elements of the platform are discussed. The joints deflection and acceleration responses demands are presented. It is generally concluded that consideration of the interaction between structure, piles and soil leads to higher deflections and less stresses in platform elements due to soil elasticity, nonlinearity, and damping and leads to a more realistic platform design. The earthquake-based analysis for offshore platform structure is essential for the safe design and operation of offshore platforms.

Development of offshore drilling platform simulation for virtual onboard experience

박광필,함승호 대한조선학회 2022 International Journal of Naval Architecture and Oc Vol.14 No.1

As marine resources have been actively explored, a large number of offshore drilling platforms such as drillships and semi-submersible rigs have been built in many shipyards. The drilling system is the key feature that defines the characteristics of the platform. The operation of the drilling system is usually focused on the tubular handling, hoisting, and rotating systems which are directly handling drilling pipes and risers on the drill floor. Therefore, most of the training simulators have been developed only for controlling the drilling equipment. However, not only the drilling equipment handling on the drill floor, but also compensations systems such as heave compensation system and DPS (Dynamic Positioning System) to reduce the effect of the motion, ROV (Remotely Operated Vehicle) operation, well control including BOP (Blow-Out Preventer) should be integrated systematically because these systems on the offshore drilling platform are operated at the same time. Therefore, we propose the integrated offshore drilling platform simulation for virtual onboard experience which is composed of a virtual driller's cabin for handling drilling equipment, well control simulator to remove a kick, DPS simulator to control the motion of the platform, walk-through simulator to monitor the operation from the worker's viewpoint on the platform, and dynamic analyses of heave compensation system. All data such as the movement of the drilling equipment, platform position, driller's command, etc. are shared among systems in real-time. The proposed virtual offshore drilling platform can effectively show the various situations that occur during drilling operations.

Numerical analysis for structure-pile-fluid-soil interaction model of fixed offshore platform

Raheem, Shehata E. Abdel,Aal, Elsayed M. Abdel,AbdelShafy, Aly G.A.,Mansour, Mahmoud H.,Omar, Mohamed Techno-Press 2020 Ocean systems engineering Vol.10 No.3

In-place analysis for offshore platforms is required to make proper design for new structures and true assessment for existing structures. In addition, ensure the structural integrity of platforms components under the maximum and minimum operating loads and environmental conditions. In-place analysis was carried out to verify the robustness and capability of structural members with all appurtenances to support the applied loads in either operating condition or storm conditions. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The SACS software is utilized to calculate the natural frequencies of the model and to obtain the response of platform joints according to in-place analysis then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have an important effect on the results of the in-place analysis behavior. The influence of the soil-structure interaction on the response of the jacket foundation predicts is necessary to estimate the loads of the offshore platform well and real simulation of offshore foundation for the in-place analysis. The result of the study shows that the in-place response investigation is quite crucial for safe design and operation of offshore platform against the variation of environmental loads.

15 MW급 부유식 해상풍력발전시스템 반잠수식 플랫폼의 운용 조건 중 응답 특성 비교 연구

안현정,하윤진,박세완,김경환 한국풍력에너지학회 2022 풍력에너지저널 Vol.13 No.4

In this study, the response characteristics of two semi-submersible platforms with an IEA 15 MW reference wind turbine are compared. The nacelle acceleration, platform motion and generator power of FOWT applying a VolturnUS-S platform developed by the University of Maine and PentaSemi platform developed by the Korea Research Institute of Ships and Ocean Engineering are compared in operational conditions. Numerical simulations are performed based on the marine environmental conditions of the U.S east coast. In the FOWT to which the PentaSemi platform is applied, the nacelle acceleration and platform pitch angle are rather high, but the results of both platforms satisfied the design criteria at all operating wind speeds. The platform yaw angle of PentaSemi platform to which a yaw control catenary mooring system is applied is significantly smaller than the platform yaw angle of VolturnUS-S. Also, despite the relatively large nacelle acceleration and platform pitch angle, the generator power is higher on the PentaSemi platform. This means that the generator power dominates the control system rather than the nacelle and platform motion.

Structural performance assessment of fixed offshore platform based on in-place analysis

Raheem, Shehata E. Abdel,Aal, Elsayed M. Abdel,AbdelShafy, Aly G.A.,Mansour, Mahmoud H.,Omar, Mohamed Techno-Press 2020 Coupled systems mechanics Vol.9 No.5

In-place analysis for offshore platforms is essentially required to make proper design for new structures and true assessment for existing structures. The structural integrity of platform components under the maximum and minimum operating loads of environmental conditions is required for risk assessment and inspection plan development. In-place analyses have been executed to check that the structural member with all appurtenances robustness and capability to support the applied loads in either storm condition or operating condition. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The analysis includes interpretation of dynamic design parameters based on the available site-specific data, together with foundation design recommendations for in-place loading conditions. The SACS software is utilized to calculate the natural frequencies of the model and to obtain the response of platform joints according to in-place analysis then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have important effects on the results of the in-place analysis behavior. The result shows that the in-place analysis is quite crucial for safe design and operation of offshore platform and assessment for existing offshore structures.

Nonlinear response of fixed jacket offshore platform under structural and wave loads

Abdel Raheem, Shehata E. Techno-Press 2013 Coupled systems mechanics Vol.2 No.1

The structural design requirements of an offshore platform subjected to wave induced forces and moments in the jacket can play a major role in the design of the offshore structures. For an economic and reliable design; good estimation of wave loadings are essential. A nonlinear response analysis of a fixed offshore platform under structural and wave loading is presented, the structure is discretized using the finite element method, wave plus current kinematics (velocity and acceleration fields) are generated using 5th order Stokes wave theory, the wave force acting on the member is calculated using Morison's equation. Hydrodynamic loading on horizontal and vertical tubular members and the dynamic response of fixed offshore structure together with the distribution of displacement, axial force and bending moment along the leg are investigated for regular and extreme conditions, where the structure should keep production capability in conditions of the 1-yr return period wave and must be able to survive the 100-yr return period storm conditions. The result of the study shows that the nonlinear response investigation is quite crucial for safe design and operation of offshore platform.

Damage analysis of three-leg jacket platform due to ship collision

Jeremy Gunawan,Jessica Rikanti Tawekal,Ricky Lukman Tawekal,Eko Charnius Ilman Techno-Press 2023 Ocean systems engineering Vol.13 No.4

A collision between a ship and an offshore platform may result in structural damage and closure; therefore, damage analysis is required to ensure the platform's integrity. This paper presents a damage assessment of a three-legged jacket platform subjected to ship collisions using the industrial finite element program Bentley SACS. This study considers two ships with displacements of 2,000 and 5,000 tons and forward speeds of 2 and 6.17 meters per second. Ship collision loads are applied as a simplified point load on the center of the platform's legs at inclinations of 1/7 and 1/8; diagonal bracing is also included. The jacket platform is modelled as beam elements, with the exception of the impacted jacket members, which are modelled as nonlinear shell elements with elasto-plastic material and constant isotropic hardening to provide realistic dented behavior due to ship collision load. The structural response is investigated, including kinetic energy transfer, stress distribution, and denting damage. The simulation results revealed that the difference in leg inclination has no effect on the level of localized denting damage. However, it was discovered that a leg with a greater inclination (1/8) resists structural displacement more effectively and absorbs less kinetic energy. In this instance, the three-legged platform collapses due to the absorption of 27.30 MJ of energy. These results provide crucial insights for enhancing offshore platform resilience and safety in high-traffic maritime regions, with implications for design and collision mitigation strategies.

Minimum life-cycle cost design of ice-resistant offshore platforms

Li, Gang,Zhang, Da-Yong,Yue, Qian-Jin Techno-Press 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.31 No.1

In China, the oil and natural gas resources of Bohai Bay are mainly marginal oil fields. It is necessary to build both ice-resistant and economical offshore platforms. However, risk is involved in the design, construction, utilization, maintenance of offshore platforms as uncertain events may occur within the life-cycle of a platform under the extreme ice load. In this study, the optimum design model of the expected life-cycle cost for ice-resistant platforms based on cost-effectiveness criterion is proposed. Multiple performance demands of the structure, facilities and crew members, associated with the failure assessment criteria and evaluation functions of costs of construction, consequences of structural failure modes including damage, revenue loss, death and injury as well as discounting cost over time are considered. An efficient approximate method of the global reliability analysis for the offshore platforms is provided, which converts the implicit nonlinear performance function in the conventional reliability analysis to linear explicit one. The proposed life-cycle optimum design formula are applied to a typical ice-resistant platform in Bohai Bay, and the results demonstrate that the life-cycle cost-effective optimum design model is more rational compared to the conventional design.

Minimum life-cycle cost design of ice-resistant offshore platforms

Da-yong Zhang,Gang Li,Qian-jin Yue 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.31 No.1

In China, the oil and natural gas resources of Bohai Bay are mainly marginal oil fields. It is necessary to build both ice-resistant and economical offshore platforms. However, risk is involved in the design, construction, utilization, maintenance of offshore platforms as uncertain events may occur within the life-cycle of a platform under the extreme ice load. In this study, the optimum design model of the expected life-cycle cost for ice-resistant platforms based on cost-effectiveness criterion is proposed. Multiple performance demands of the structure, facilities and crew members, associated with the failure assessment criteria and evaluation functions of costs of construction, consequences of structural failure modes including damage, revenue loss, death and injury as well as discounting cost over time are considered. An efficient approximate method of the global reliability analysis for the offshore platforms is provided, which converts the implicit nonlinear performance function in the conventional reliability analysis to linear explicit one. The proposed life-cycle optimum design formula are applied to a typical ice-resistant platform in Bohai Bay, and the results demonstrate that the life-cycle cost-effective optimum design model is more rational compared to the conventional design.

인장각형 부유식 해상풍력발전시스템의 하부 플랫폼 설계 및 운송⸳설치 관련 특성 고찰

안현정,하윤진,박지용,김경환 한국풍력에너지학회 2023 풍력에너지저널 Vol.14 No.4

In this study, research and empirical cases of floating offshore wind turbine systems with a tension-leg platform are investigated, and hydrodynamic and structural characteristics according to platform shapes and characteristics during transportation and installation are confirmed. Most platforms are composed of pontoons or corner columns, and these are mainly located below the waterline to minimize the impact of breaking waves and supplement the lack of buoyancy of the center column. These pontoons and corner columns are designed with a simple shape to reduce manufacturing and assembly costs, and some platforms additionally have reinforcements such as braces to improve structural strength. Most of the systems are assembled in the yard and then moved by tugboat and installed, and some platforms have been developed with a dedicated barge for simultaneous assembly, transportation and installation. In this study, we intend to secure the basic data necessary for the design, transportation, and installation procedures of floating offshore wind turbine systems with a tension-leg platform.