Reliability estimation of jacket type offshore platforms against seismic and wave loadings applied in time domain

2020 ◽  
pp. 1-10
Author(s):  
Sayyed Mohsen Vazirizade ◽  
Hamoon Azizsoltani ◽  
Achintya Haldar
Keyword(s):  
Time Domain ◽  
Reliability Estimation ◽  
Offshore Platforms

Experimental and Numerical Study of Coupled Dynamic Response of a Mini Tension Leg Platform

2004 ◽  
Vol 126 (4) ◽  
pp. 318-330 ◽  
Author(s):  
Anitha Joseph ◽  
V. G. Idichandy ◽  
S. K. Bhattacharyya
Keyword(s):  
Finite Element Method ◽  
Time Domain ◽  
Natural Frequencies ◽  
Numerical Study ◽  
Offshore Platforms ◽  
Wave Loading ◽  
Scaled Model ◽  
Wave Flume ◽  
Exploration And Production

Role of mini tension leg platforms (TLP) in oil exploration and production in marginal deepwater fields is becoming increasingly important. Mini TLP combines the simplicity of a spar and favorable response features of a TLP. In this paper, the results of a detailed experimental and numerical investigation of the coupled dynamic behavior of a mini TLP are reported with special attention to hull-tether coupling. The experimental study has been carried out using a scaled model in wave flume with specially designed tethers whose first two “string” natural frequencies are excited by waves, thus achieving strong hull-tether coupling. The numerical study has been carried out using a nonlinear time domain finite element method specifically addressed to compliant offshore platforms using a combination of potential theory based wave loading and Morison-type wave loading. Extensive comparisons between numerical and experimental results have been made both for platform motions and deflected shapes of the tethers and conclusions drawn.

Engineering Criticality Assessments of Floating Offshore Platforms Based on Time Domain Structural Response Analysis

2021 ◽  
Author(s):  
Jeffrey O’Donnell ◽  
Johyun Kyoung ◽  
Sagar Samaria ◽  
Anil Sablok
Keyword(s):  
Fracture Mechanics ◽  
Time Domain ◽  
Structural Integrity ◽  
Structural Response ◽  
Life Extension ◽  
Response Analysis ◽  
Offshore Platforms ◽  
Industry Standards ◽  
Offshore Industry ◽  
Integrity Assessments

Abstract This paper presents a time-domain S-N fatigue analysis and an approach to reliable and robust engineering criticality assessments to supplement or provide an alternative to S-N fatigue assessments of offshore platform structures based on time domain structural response analysis. It also provides recommendations for industry standards to improve guidance for structural integrity assessments of offshore platforms using fracture mechanics. Demand continues to grow in the offshore industry to attain value from captured operational data for a number of purposes, including the reduction of uncertainties in structural integrity assessments during design and over the operational lifetime of floating offshore platforms. Recent advances in time domain structural analysis technology demonstrate substantially more accurate assessments of non-linear platform loadings and responses with enhanced computational efficiency. The current S-N approach for fatigue design and integrity assessments calculates a fatigue damage factor that does not address how loading occurs over time (ABS, DNVGL-RP-C203). For the present study, engineering criticality assessments (ECAs) based on fracture mechanics theory (BS 7910) are applied utilizing time-domain loading information theory. The ECA returns the smallest initial flaws that can grow to a critical size during a design lifetime, which can serve as an indicator of acceptability during design, a technical basis for in-service inspection intervals and facilitates asset integrity and life extension assessments. Critical initial flaws are calculated using the Paris Law (BS 7910) and cumulative fatigue crack growth in two ways: with and without an integrated and consistent check for fracture instability. The results are compared with those from S-N fatigue analyses and recommendations are provided.

Integrating Constrained Random Waves in Endurance Time Analysis of Offshore Structures Subjected to Sea Waves

2012 ◽  
Author(s):  
H. Matin Nikoo ◽  
M. Zeinoddini ◽  
H. Estekanchi ◽  
M. Golestani
Keyword(s):  
Time Domain ◽  
Offshore Structures ◽  
Design Stage ◽  
Offshore Platforms ◽  
Sea Waves ◽  
Base Shear ◽  
Time Analysis ◽  
Offshore Structure ◽  
Endurance Time ◽  
Damage Indices

This paper introduces a novel methodology for design and assessment of offshore structures exposed to irregular sea waves. For this, Constrained NewWave (CNW) is integrated with the Endurance Time Analysis (ETA) methodology, which is basically developed for the performance based analysis of onshore structures to earthquake loads. In this approach, the offshore structure is simulated in time-domain under a set of calibrated intensifying wave functions. They are devised to represent a gradually increasing roughness of the sea state by time. A performance index such as base shear, drift or stress in a critical structural members are monitored until they reach to a predefined maximum value. A higher endurance time (corresponding to a higher wave height) is to be interpreted as a better performance of structure. Ability to consider spectral features of waves, waves’ irregularity, the wave-in-deck impacts, utilizing a relatively simple approach, requiring relatively low computational times and capability to consider any desirable damage indices are the advantages of this novel method. The method can be used in the design stage, collapse analysis and for the assessment of existing offshore platforms. In this paper the effectiveness of this method has been examined on offshore jacket platforms. The results obviously have highlighted the potentials of this approach for the dynamic, time-domain, non-linear analysis and assessment of offshore platforms.

scholarly journals Study on Mooring Design and Calculation Method of Ocean Farm Based on Time-Domain Potential Flow Theory

2020 ◽  
Vol 2 (3) ◽  
Author(s):  
Baoji Zhang ◽  
Yuhang Sun
Keyword(s):  
Time Domain ◽  
Potential Flow ◽  
Wave Spectrum ◽  
Flow Theory ◽  
Offshore Platforms ◽  
Potential Flow Theory ◽  
Mooring Cable ◽  
The Time Domain ◽  
Control Equation ◽  
Force Calculation

In order to calculate the mooring force of a new semi-submerged Ocean Farm quickly and accurately, based on the unsteady time-domain potential flow theory and combined the catenary model, the control equation of mooring cable is established, and the mooring force of the platform under the wave spectrum is calculated. First of all, based on the actual situation of the ocean environment and platform, the mooring design of the platform is carried out, and the failure analysis and sensitivity analysis of the single anchor chain by the time domain coupling method are adopted: including different water depth, cycle, pretension size, anchor chain layout direction and wind speed, etc. The analysis results confirm the reliability of anchoring method. Based on this, the mooring point location of the platform is determined, the force of each anchor chain in the anchoring process is calculated, and the mooring force and the number of mooring cables are obtained for each cable that satisfies the specification, the results of this paper can provide theoretical calculation methods for mooring setting and mooring force calculation of similar offshore platforms.

Effect of Dynamic Behaviour of Piles on Offshore Towers Response

2002 ◽  
Author(s):  
Yasser E. Mostafa ◽  
M. Hesham El Naggar
Keyword(s):  
Time Domain ◽  
Dynamic Behaviour ◽  
Wave Forces ◽  
Nonlinear Behaviour ◽  
Offshore Platforms ◽  
Soil Resistance ◽  
Marine Structures ◽  
Finite Element Package ◽  
The Time Domain ◽  
Soil Interface

Pile foundations supporting offshore platforms and marine structures are required to resist dynamic lateral loading due to wind and wave forces. The response of a jacket offshore tower is affected by the foundation flexibility and the nonlinear behaviour of the supporting piles. In the present study, the soil resistance to the pile movement is modeled using dynamic p-y curves and t-z curves to account for soil nonlinearity and energy dissipation through radiation damping. The model also allows separation at the pile soil interface. The wave forces on the tower members and the tower response are calculated in the time domain using a finite element package (ASAS). The tower response is calculated with emphasis placed on the effects of dynamic pile-soil interaction on the tower performance and the forces acting on the piles for a range of wave conditions.

Time Domain Structural Fatigue Analysis of Floating Offshore Platforms: A Response Based Technique

2020 ◽  
Author(s):  
Johyun Kyoung ◽  
Sagar Samaria ◽  
Jang Whan Kim
Keyword(s):  
Spectral Method ◽  
Fatigue Damage ◽  
Time Domain ◽  
Structural Response ◽  
Fatigue Analysis ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Time Step ◽  
Structural Fatigue ◽  
Non Linear

Abstract This paper presents a response-based, time-domain structural fatigue analysis of a floating offshore platform. The conventional technique for structural fatigue assessments of offshore platforms uses a linear, frequency-domain analysis based on the spectral method. Although this conventional method is computationally efficient, there is a room for improving accuracy and reducing uncertainties because it cannot accurately address non-linear loadings on the offshore platform. Such non-linear loads arise from the wave, wind, and current as well as from the riser and mooring systems; these non-linearities necessitate large factors of safety that lead to conservative design and frequent inspection. As an extension of previous work (Kyoung et al.[12]), this study presents the development of a time-domain, structural fatigue analysis that explicitly addresses non-linear loading on the platform. The external load time-histories are directly mapped onto the structure at every time interval to create a stress-based response with the varying environment. In each time step, the load mapping accurately captures the phase relationship between the external loading and hull inertial response. Therefore, present method reduces uncertainties in the fatigue damage computation and overcomes the assumptions of spectral method. Present load component-based approach is applied onto a finite element structural model, which provides unit structural response at locations of interest. Time history of structural response is obtained by synthesizing the obtained unit stress-based structural response with environmental loading and platform motion response. Fatigue damage can be computed from the obtained time series of structural response using rain-flow counting. As an application, a conventional semisubmersible platform is used to evaluate structural fatigue damage for a given wave scatter diagram. A comparison between results from this response-based time-domain approach and the conventional spectral method is presented.

Nonlinear Dynamic Analysis of Jack-Up Platforms Exposed to Extreme Random Waves

2012 ◽  
Author(s):  
Jalal Mirzadehniasar ◽  
Mehrdad Kimiaei ◽  
Mark J. Cassidy
Keyword(s):  
Dynamic Response ◽  
Dynamic Analysis ◽  
Time Domain ◽  
Nonlinear Dynamic ◽  
Spectral Composition ◽  
Random Time ◽  
Offshore Platforms ◽  
Wave Loading ◽  
Nonlinear Dynamic Response ◽  
Jack Up

Deterministic waves with uniquely specified parameters remains widely used in the analysis of offshore platforms, even though the random nature of the sea-state is one of the main uncertainties in loading. The response of dynamically sensitive and highly redundant structures is significantly changed when random wave loading is considered. Therefore, to more confidently simulate wave loads, all of the randomness of water surface should be taken into account. Load history also plays an important role in the nonlinear dynamic response of structures. Accordingly, an appropriate way to consider these effects is dynamic analysis of offshore platforms using random time-domain generation of the sea surface over a long period of time. However, in general, this method is very complex and time consuming. Constrained NewWave theory is an alternative method that can effectively simulate many hours of random time domain simulation for wave loading but in a more computationally efficient manner. It takes a NewWave — a deterministic wave of predetermined height that accounts for the spectral composition of the sea — and constrains it within a random background. In this paper, both the singular NewWave and multiple constrained NewWaves are employed to simulate random sea-states in order to investigate the nonlinear dynamic response and collapse mechanisms of a jack-up platform subjected to extreme waves. Different assumptions of the behavior of the jack-up spudcan-soil interaction are considered.

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