Damping-Controlled Response of a Truss-Pontoon Semi-Submersible With Heave-Plates

2005 ◽  
Author(s):  
Nagan Srinivasan ◽  
Subrata Chakrabarti ◽  
R. Radha
Keyword(s):  
Separated Flow ◽  
Cost Effective ◽  
Added Mass ◽  
Offshore Structures ◽  
Field Application ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Scaled Model ◽  
Large Wave ◽  
Truss Spar

Hydrodynamic added mass and damping are old and popular research topics in the field of offshore structures engineering. The concept of added mass has been used very intelligently in the design of modern deepwater floating vessels. The turning point of the conventional Spar to a Truss-Spar is a typical example in which the added mass created by the heave plates in a Truss Spar efficiently reduced the steel weight and the subsequent cost of the Spar hull. However, the damping is not utilized as efficiently as the added mass in the design of the floating offshore platforms. It should be noted that at resonance damping plays an important role in controlling the response amplitude. This resonance is called damping controlled response. An offshore platform efficiently designed to reduce the wave excitation forces and increase the separated-flow damping could qualify as a platform to operate even near resonance. Such design could make this concept cost effective, as well as operationally more productive with minimum downtime. The principal purpose of this paper is to describe an offshore platform design that could face the resonance efficiently. The paper applies the concept of both hydrodynamic added mass and separated-flow damping intelligently in the design of a large floating vessel on column-stabilized principle. The platform is designed to face resonance due to extreme waves and utilizes the damping to control its motion, thereby qualifying its field application. The design is verified and justified with the help of a scaled-model study in a large wave tank. The results are presented herein.

Response Analysis of a Truss-Pontoon Semisubmersible With Heave-Plates

2005 ◽  
Vol 128 (2) ◽  
pp. 100-107 ◽  
Author(s):  
Nagan Srinivasan ◽  
Subrata Chakrabarti ◽  
R. Radha
Keyword(s):  
Separated Flow ◽  
Cost Effective ◽  
Field Application ◽  
Offshore Platform ◽  
Response Analysis ◽  
Test Results ◽  
Extreme Waves ◽  
Scaled Model ◽  
Large Wave ◽  
Model Study

An offshore platform that is efficiently designed to reduce the wave excitation forces and increase the separated-flow damping could qualify as a platform operating even near its resonance. Such design could make this concept cost-effective, as well as operationally more productive with minimum downtime. The principal purpose of this paper is to describe an offshore platform design that could face the resonance efficiently. The paper applies the concept of both hydrodynamic added mass and separated-flow damping intelligently in the design of a large deepwater floating vessel on column-stabilized principle. The platform is designed to face resonance due to extreme waves and utilizes the damping to control its motion, thereby qualifying its field application. The design is justified and verified with the results of a scaled-model study in a large wave tank. The results of the correlation of theoretical study with the model test results are presented herein. A few variations of the deepwater platform concept are discussed.

Rapid Preliminary Design of Floating Offshore Structures Using a Modified Genetic Algorithm

2007 ◽  
Author(s):  
Michael J. Perry ◽  
John E. Halkyard ◽  
C. G. Koh
Keyword(s):  
Genetic Algorithm ◽  
Cost Effective ◽  
Offshore Structures ◽  
Preliminary Design ◽  
Optimization Strategy ◽  
Empirical Estimates ◽  
Wind Speed Maximum ◽  
Design Wind Speed ◽  
Truss Spar ◽  
Weight Design

Preliminary design of floating offshore structures involves determining structural dimensions able to provide sufficient buoyancy to carry the required topside, at the lowest possible cost, while satisfying various stability, strength, installation, and response requirements. A novel optimization strategy, capable of carrying out the preliminary design of floating offshore structures, is presented in this paper. The genetic algorithm based strategy searches within prescribed parameter limits for the most cost effective design, while ensuring the design conforms to the constraints given. The design of a truss spar is used to illustrate how the strategy can be applied. The topside weight, design wind speed, maximum wave height, etc are input along with constraints such as, maximum draft at floatoff, maximum heel angle, allowable stress in the truss and limits on pitch and heave period and response. Using empirical estimates for hull weights and simplified response calculations, the strategy is then able to rapidly determine parameters such as hull diameter, hard tank depth, length of keel tank, total length and truss leg diameter such that the total cost of the structure is minimized. The strategy allows for the preliminary design phase to be completed in only a few seconds, while providing initial weight and cost estimates.

scholarly journals Development of Risk-Reliability Based Underwater Inspection for Fixed Offshore Platforms in Indonesia

2018 ◽  
Vol 147 ◽  
pp. 05002
Author(s):  
Ricky L. Tawekal ◽  
Faisal D. Purnawarman ◽  
Yati Muliati
Keyword(s):  
Structural Reliability ◽  
Structural Integrity ◽  
Damage Mechanism ◽  
Offshore Structures ◽  
Probability Of Failure ◽  
American Petroleum Institute ◽  
Offshore Platform ◽  
Risk Level ◽  
Offshore Platforms ◽  
Fixed Offshore Platform

In RBUI method, platform with higher risk level will need inspection done more intensively than those with lower risk level. However, the probability of failure (PoF) evaluation in RBUI method is usually carried out in semi quantitative way by comparing failure parameters associated with the same damage mechanism between a group of platforms located in the same area. Therefore, RBUI will not be effective for platforms spread in distant areas where failure parameter associated with the same damage mechanism may not be the same. The existing standard, American Petroleum Institute, Recommended Practice for Structural Integrity Management of Fixed Offshore Structures (API RP-2SIM), is limited on the general instructions in determining the risk value of a platform, yet it does not provide a detail instruction on how determining the Probability of Failure (PoF) of platform. In this paper, the PoF is determined quantitatively by calculating structural reliability index based on structural collapse failure mode, thus the method in determining the inspection schedule is called Risk-Reliability Based Underwater Inspection (RReBUI). Models of 3-legs jacket fixed offshore platform in Java Sea and 4-legs jacket fixed offshore platform in Natuna Sea are used to study the implementation of RReBUI.

Coupled Eulerian Lagrangian Approach to Model Offshore Platform Movements in Strong Tidal Flows

2011 ◽  
Author(s):  
F. Van den Abeele ◽  
J. Vande Voorde
Keyword(s):  
Fluid Flow ◽  
Wind Waves ◽  
Offshore Structures ◽  
Offshore Platform ◽  
Added Value ◽  
Inertia Force ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Operational Conditions ◽  
Tidal Flows

Offshore platforms are subjected to wind, waves and tidal flows. Tidal flow will generate a steady current, which induces a lift force and a drag force on the platform legs. In addition, water particle velocities induced by waves give rise to an oscillatory flow. As a result, the structure will experience a lift, drag and inertia force when subjected to wave-induced flow patterns. On top of that, a turbulent Von Karman vortex street can appear in the wake of the platform legs for certain combinations of dimensions and flow velocities. Vortex shedding can lead to vortex induced vibrations, which may jeopardize the integrity of the entire offshore platform. Environmental loads can cause significant deformations of offshore structures, which can in turn influence the fluid flow. Multiphysics modelling is required to capture the mechanisms governing fluid-structure interaction. In this paper, a Coupled Eulerian Lagrangian (CEL) approach is pursued to simulate offshore platform movements in strong tidal flows. In a CEL analysis, the fluid flow is modelled in an Eulerian framework: the water is described by an equation of state, and can flow freely through a fixed mesh. The offshore platform is modelled as a compliant structure in a traditional Lagrangian formulation, where the nodes move with the underlying material. Interaction between the fluid domain and the offshore structure is enforced using general contact conditions. The strongly coupled problem is then tackled with an explicit solver. Here, the CEL approach is demonstrated to simulate the movement of an offshore jack-up barge. The response of the vessel is calculated for different flow conditions. The multiphysics model allows evaluating the added value of structural redundancy, e.g. in the number of platform legs required for a safe design. In addition, it provides a valuable tool to predict the tidal windows allowed for given operational conditions.

Single-Pile Offshore Structures as a Cost-Effective Alternative to Small Fixed Platforms in Shallow Water

2021 ◽  
Author(s):  
Prabir Kumar Chatterjee
Keyword(s):  
Shallow Water ◽  
Design Method ◽  
Cost Effective ◽  
Offshore Structures ◽  
Single Pile ◽  
Offshore Platforms ◽  
Environmental Loads ◽  
Working Stress ◽  
Cost Effective Alternative ◽  
Water Depths

Abstract The present paper proposes an alternative to small offshore platforms with tripods and four-legged jackets by a single-pile structure for shallow water depths. The pile will be driven into seabed without a jacket and stability of the structure against environmental loads will be ensured by a few tie members connected to seabed with the help of specially-designed small concrete foundations. Tie members will be bolted to both the pile and the foundation. Four different cases of single-pile structures in three different water depths (20.0m, 31.5m and 15.0m) are presented. Omnidirectional waves of 10.0m height along with wind and current are considered in the study. Analytical method is suggested to simulate interaction of concrete foundations with soil that can be easily implemented in structural analysis. Structural design is performed as per API RP 2A working stress design method. The results indicate that the proposed single-pile structures have considerable reserve strength against failure due to extreme environmental loads and impact from medium sized boats.

Response Control of TLP Using Tuned Mass Dampers

2014 ◽  
Author(s):  
Srinivasan Chandrasekaran ◽  
Deepak Kumar ◽  
Ranjani Ramanathan
Keyword(s):  
Large Amplitude ◽  
Experimental Studies ◽  
Tuned Mass Damper ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Scaled Model ◽  
Response Control ◽  
Extreme Loads ◽  
Mass Damper

Offshore tension leg platform (TLP) is a compliant type offshore structure where the tendons are deployed under initial pretension to counteract the excessive buoyancy. TLPs show large amplitude response under environmental loads due to their compliancy, which poses threat under extreme loads. Use of passive dampers like Tuned Mass Damper (TMD) is common to control such large amplitude motion, however their deployment in offshore structures is relatively new. Response control of a scaled model of TLP is attempted using tuned mass damper of pendulum type under regular waves. Based on the experimental studies carried out, it is seen that there is a significant reduction in the surge response under the folded pendulum type damper. Results also show that there is a reduction in the heave response due to the control envisaged in the surge motion. The discussed method of response control is one of the effective methods of retrofitting offshore platforms whose operability at rough sea states is a serious concern.

A Novel Approach to Improving the Structural Reliability of a Fixed Offshore Platform Subject to Wave-in-Deck Loading Using a Holistic Structural Integrity Management (SIM) TRIAD Approach

2020 ◽  
Author(s):  
Mehrdad Kimiaei ◽  
Jalal Mirzadeh ◽  
Partha Dev ◽  
Mike Efthymiou ◽  
Riaz Khan
Keyword(s):  
Structural Reliability ◽  
Structural Model ◽  
Structural Integrity ◽  
Reliability Assessment ◽  
Offshore Structures ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Effective Manner ◽  
Integrity Management ◽  
Fixed Offshore Platform

Abstract Fixed offshore platforms subject to wave-in-deck loading have historically encountered challenges in meeting target reliability levels. This has often resulted in costly subsea remediation, impacted platform occupancy levels or premature decommissioning of critical structural assets due to safety concerns. This paper addresses the long-standing industry challenge by presenting a novel structural reliability approach that involves converging the analytical behavior of a structure to its measured dynamic response for assessment. In this approach, called the Structural Integrity Management (SIM) TRIAD method, the platform model is calibrated based on the measured in-field platform natural frequencies using a structural health monitoring (SHM) system, so that the reliability assessment can be performed on a structural model whose stiffness is simulated as close to reality as possible. The methodology demonstrates the potential of unlocking structural capacity of offshore structures by removing conservatism normally associated with traditional reliability assessment methods, thus significantly improving the ability to achieve target structural reliability levels in a cost effective manner. The SIM TRIAD method has been implemented while assessing an existing fixed offshore platform subject to wave-in-deck loads, which is located in East Malaysian waters. It has enabled the facility operator to achieve acceptable target structural reliability and has assisted in developing an optimized risk-based inspection (RBI) plan for ensuring safe operations to end of asset field life. The methodology and findings of the assessment are presented in this paper to illustrate the benefits of the SIM TRIAD method.

scholarly journals The Limpet: A ROS-Enabled Multi-Sensing Platform for the ORCA Hub

2018 ◽  
Author(s):  
Mohammed E. Sayed ◽  
Markus P. Nemitz ◽  
Simona Aracri ◽  
Alistair C. McConnell ◽  
Ross M. McKenzie ◽  
...  
Keyword(s):  
Condition Monitoring ◽  
Communication Systems ◽  
Oil And Gas ◽  
Low Cost ◽  
Cost Effective ◽  
Oil And Gas Industry ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Sensor Data ◽  
Offshore Platforms

The oil and gas industry faces increasing pressure to remove people from dangerous offshore environments. Robots present a cost-effective and safe method for inspection, repair and maintenance of topside and marine offshore infrastructure. In this work, we introduce a new immobile multi-sensing robot, the Limpet, which is designed to be low-cost and highly manufacturable, and thus can be deployed in huge collectives for monitoring offshore platforms. The Limpet can be considered an instrument, where in abstract terms, an instrument is a device that transforms a physical variable of interest (measurand) into a form that is suitable for recording (measurement). The Limpet is designed to be part of the ORCA (Offshore Robotics for Certification of Assets) Hub System, which consists of the offshore assets and all the robots (UAVs, drones, mobile legged robots etc.) interacting with them. The Limpet comprises the sensing aspect of the ORCA Hub System. We integrated the Limpet with Robot Operating System (ROS), which allows it to interact with other robots in the ORCA Hub System. In this work, we demonstrate how the Limpet can be used to achieve real-time condition monitoring for offshore structures, by combining remote sensing with signal processing techniques. We show an example of this approach for monitoring offshore wind turbines. We demonstrate the use of four different communication systems (WiFi, serial, LoRa and optical communication) for the condition monitoring process. By processing the sensor data on-board, we reduce the information density of our transmissions, which allows us to substitute short-range high-bandwidth communication systems with low-bandwidth long-range communication systems. We train our classifier offline and transfer its parameters to the Limpet for online classification, where it makes an autonomous decision based on the condition of the monitored structure.

Finite Element Analysis for Structural Performance of Offshore Platforms under Environmental Loads

2013 ◽  
Vol 569-570 ◽  
pp. 159-166 ◽  
Author(s):  
Shehata E. Abdel Raheem ◽  
Elsayed M.A. Abdel Aal
Keyword(s):  
Finite Element ◽  
Return Period ◽  
Wave Force ◽  
Offshore Structures ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Current Increase ◽  
Environmental Loads ◽  
Highly Nonlinear

Offshore structures for oil and gas exploitation are subjected to various ocean environmental phenomena which can cause highly nonlinear action effects. Offshore structures should be designed for severe environmental loads and strict requirements should set for the optimum performance. 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. The structure is discretized using the finite element method, wave force is determined according to linearized Morison 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 one year return period wave and must be able to survive the 100 year return period storm conditions. The results show that the nonlinear response analysis is quite crucial for safe design and operation of offshore platform. Fixed Jacket type offshore platforms under extreme wave loading conditions may exhibit significant nonlinear behavior. The effect of current with different angles when hitting the offshore structure with the wave and wind forces, is very important for calculate the stress, the response displacement and deformation shapes. As the current increase or decrease the effect of wave force according to the hitting angle of current.

Niobium-Bearing Offshore Plate Steel Process Metallurgy, Design and Quality

2016 ◽  
Author(s):  
Steven G. Jansto
Keyword(s):  
Corrosion Resistance ◽  
High Performance ◽  
Cost Savings ◽  
Value Added ◽  
Cost Effective ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Low Carbon ◽  
Steel Mill ◽  
Excellent Corrosion Resistance

Offshore structural steel design and material requirements continue to present increasing challenges for the steelmaker and fabricators. Niobium-bearing steels currently play a key role in meeting these objectives through the Nb-grain refinement mechanism of the microstructure and cost effective steelmaking. These steels possess a combination of exceptional properties with high strength, excellent weldability, high toughness at low temperature, good ductility, excellent corrosion resistance, and high formability. Reduced variation of Charpy toughness through the thickness of heavy plates is imperative in these offshore platforms to enhance reliability and performance. Toughness variation can be reduced through the proper continuous casting and hot rolling mechanical metallurgy process. These high-performance steels (HPS) possess an optimized balance of these properties to provide maximum cost effective performance in offshore structures at strength levels from 355 to 700MPa with excellent corrosion resistance. This combination of good strength-toughness balance, excellent weathering properties and reduced preheat temperatures for welding in these low carbon Nb-structural steels result in significant cost savings. These enhancements provide structural engineers the opportunity to further improve the structural design and offshore platform performance. Lower carbon Nb-alloy designs have exhibited reduced operational production cost at the steel mill as well, thereby embracing the value-added attribute Nb provides to benefit both the producer and the end user throughout the supply chain.

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