Estimating Long-Term Distributions of Extreme Response of a Catenary Riser

Volume 4: Pipeline and Riser Technology ◽

10.1115/omae2011-50151 ◽

2011 ◽

Cited By ~ 2

Author(s):

Elizabeth Passano ◽

Philippe Mainc¸on

Keyword(s):

Nonlinear Response ◽

Unbiased Estimation ◽

Reliable Estimate ◽

Response Distribution ◽

Short Term ◽

Response Predictors ◽

Extreme Response ◽

Nonlinear Simulations ◽

Term Response

The purpose of this paper is to present a method for efficient and unbiased estimation of the long-term extreme response distribution of a catenary riser. In this approach a computationally inexpensive, nonlinear response predictor is used to estimate the response in all sea states, thus allowing selection of relevant sea states and intervals within sea states for detailed, nonlinear finite element simulations. This method requires significantly less simulation time than the conventional approach with extensive nonlinear simulations of many sea states. The method is applied to a catenary riser case. In an earlier study (Passano and Larsen, OMAE 2006), a strong relation was found between the prescribed vertical motions at the top and the axial force and bending moment near the touch down area. This relation was then used to limit simulations to intervals where the largest maxima values were expected. This gave an estimate of the upper part or tail of the extreme response in the selected sea states. In a later study (Passano and Larsen, OMAE 2007), nonlinear response predictors based on the prescribed vertical motions were established. These were used to estimate the short-term extreme response distribution directly. In the case study of this paper three long-term response distributions are compared: 1) A distribution established directly from the predicted short-term response distributions. 2) A distribution based on response simulated in the relevant time intervals of the relevant sea states. 3) A distribution obtained from extensive nonlinear simulations of the sea states in the scatter diagram. It is found that distribution 2) provides a fast and reliable estimate of 3). This allows a significant reduction in analysis work.

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Long-Term Extreme Response Analysis of Marine Structures Using Inverse SORM

Volume 3A: Structures, Safety and Reliability ◽

10.1115/omae2017-61409 ◽

2017 ◽

Cited By ~ 2

Author(s):

Finn-Idar G. Giske ◽

Bernt Johan Leira ◽

Ole Øiseth

Keyword(s):

Structural Reliability ◽

New Method ◽

Response Analysis ◽

Marine Structures ◽

Short Term ◽

Reliability Method ◽

Extreme Response ◽

Improved Accuracy ◽

Term Response

In this paper the first order reliability method (FORM) found in connection with structural reliability analysis is first used in an inverse manner to efficiently obtain an approximate solution of the full long-term extreme response of marine structures. A new method is then proposed where the second order reliability method (SORM) is used to improve the accuracy of the approximation. This method is compared with exact results obtained using full numerical integration. The new method is seen to achieve improved accuracy for large return periods, yet keep the number of required short-term response analyses within acceptable levels.

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Long-term extreme response analysis for semi-submersible platform mooring systems

Proceedings of the Institution of Mechanical Engineers Part M Journal of Engineering for the Maritime Environment ◽

10.1177/1475090220976515 ◽

2020 ◽

pp. 147509022097651

Author(s):

Yuliang Zhao ◽

Sheng Dong

Keyword(s):

Environmental Data ◽

Distribution Model ◽

Response Analysis ◽

Accurate Assessment ◽

Response Distribution ◽

Short Term ◽

Floating Structure ◽

Extreme Response ◽

Term Analysis

The accurate assessment of long-term extreme responses of floating-structure mooring system designs is important because of small failure probabilities caused by long-term and complex ocean conditions. The most accurate assessment would involve considering all conceivable sea states in which each sea state is regarded as a stochastic process and performing nonlinear time-domain numerical simulations of mooring systems to estimate the extreme response from a long-term analysis. This procedure would be computationally intensive because of the numerous short-term sea states involved. Here, a more feasible approach to evaluate the long-term extreme response is presented through immediate integration combined with Monte Carlo simulations. A parameter fitting procedure of the short-term extreme response distribution under irregular wave conditions is employed to solve the long-term response integration. Case studies were conducted on a semi-submersible platform using environmental data measurements of the Gulf of Mexico and a joint distribution model of the environmental parameters was considered. This approach was observed to be effective and the results were compared with those of traditional methodologies (univariate extreme value design and environmental contour methods). The differences were reflected using a reliability analysis of mooring lines, which indicated that the design standards must be stricter when using long-term analysis.

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On the Long-Term Reliability Analysis of a Point Absorber Wave Energy Converter

Volume 10: Ocean Renewable Energy ◽

10.1115/omae2017-62141 ◽

2017 ◽

Cited By ~ 1

Author(s):

Jarred Canning ◽

Phong Nguyen ◽

Lance Manuel ◽

Ryan G. Coe

Keyword(s):

Wave Energy ◽

Reference Model ◽

Wave Energy Converter ◽

Environmental Data ◽

Energy Converter ◽

Short Term ◽

Point Absorber ◽

Extreme Response ◽

Term Response

Of interest in this study is the long-term response and performance of a two-body wave point absorber (“Reference Model 3”), which serves as a wave energy converter (WEC). In a previous study, the short-term uncertainty in this device’s response was studied for an extreme sea state. We now focus on the assessment of the long-term response of the device where we consider all possible sea states at a site of interest. We demonstrate how simulation tools may be used to evaluate the long-term response and consider key performance parameters of the WEC device, which are the heave and surge forces on the power take-off system and the power take-off extension. We employ environmental data at a designated deployment site in Northern California. Metocean information is generated using approximately 15 years of data from this site (National Data Buoy Center site no. 46022). For various sea states, a selected significant wave height and peak period are chosen to describe representative conditions. Then, using a public-domain simulation tool (Wave Energy Converter Simulator or WEC-Sim), we generate various short-term time-domain response measure for these sea states. Distribution fits to extreme response statistics are generated, for each bin that represents a cluster of sea states, using the open-source toolbox, WDRT (WEC Design Response Toolbox). Long-term distributions for each response variable of interest are estimated by weighting short-term distributions by the likelihood of the sea states; from these distributions, the 50-year response can be derived. The 50-year response is also estimated using an approximate but more efficient inverse reliability approach. Comparisons are made between the two approaches.

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Long-Term Extreme Response Analysis of Marine Structures Using Inverse SORM

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4039718 ◽

2018 ◽

Vol 140 (5) ◽

Cited By ~ 3

Author(s):

Finn-Idar G. Giske ◽

Bernt Johan Leira ◽

Ole Øiseth

Keyword(s):

Structural Reliability ◽

New Method ◽

Response Analysis ◽

Marine Structures ◽

Short Term ◽

Reliability Method ◽

Extreme Response ◽

Improved Accuracy ◽

Term Response

In this paper, the first-order reliability method (FORM) found in connection with structural reliability analysis is first used in an inverse manner to efficiently obtain an approximate solution of the full long-term extreme response of marine structures. A new method is then proposed where the second-order reliability method (SORM) is used to improve the accuracy of the approximation, resulting in an inverse SORM (ISORM) approach. This method is compared with exact results obtained using full numerical integration. The new method is seen to achieve significantly improved accuracy, yet keep the number of required short-term response analyses within acceptable levels.

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Unfolding the case of returnees: How the European Union and its member States are addressing the return of foreign fighters and their families

International Review of the Red Cross ◽

10.1017/s1816383121000217 ◽

2021 ◽

pp. 1-23

Author(s):

Carlota Rigotti ◽

Júlia Zomignani Barboza

Keyword(s):

European Union ◽

Perceived Threat ◽

The European Union ◽

Security Threat ◽

Short Term ◽

Member States ◽

Foreign Fighters ◽

Term Response

Abstract The return of foreign fighters and their families to the European Union has mostly been considered a security threat by member States, which consequently adopt repressive measures aimed at providing an immediate, short-term response to this perceived threat. In addition to this strong-arm approach, reintegration strategies have also been used to prevent returnees from falling back into terrorism and to break down barriers of hostility between citizens in the long term. Amidst these different strategies, this paper seeks to identify which methods are most desirable for handling returnees.

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FRI0178 Positivity for Rheumatoid Factor is Associated with a Better Short-Term Response and Long-Term Drug Retention of Abatacept: Results from Consecutive 508 Patients with Rheumatoid Arthritis in a Japanese Multicenter Registry

Annals of the Rheumatic Diseases ◽

10.1136/annrheumdis-2015-eular.2120 ◽

2015 ◽

Vol 74 (Suppl 2) ◽

pp. 488.1-488

Author(s):

N. Takahashi ◽

T. Kojima ◽

K. Funahashi ◽

N. Ishiguro

Keyword(s):

Rheumatoid Arthritis ◽

Rheumatoid Factor ◽

Short Term ◽

Drug Retention ◽

Multicenter Registry ◽

Term Response

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Efficient Analysis of a Catenary Riser

Volume 1: Offshore Technology; Offshore Wind Energy; Ocean Research Technology; LNG Specialty Symposium ◽

10.1115/omae2006-92308 ◽

2006 ◽

Cited By ~ 6

Author(s):

Elizabeth Passano ◽

Carl M. Larsen

Keyword(s):

Operating Conditions ◽

Stochastic Simulations ◽

Worst Case ◽

Nonlinear Structure ◽

Tension Response ◽

Extreme Response ◽

Analysis Strategies ◽

Low Tension ◽

Term Response

The paper deals with the challenge of predicting the extreme response of catenary risers, a topic of both industry and academic interest. Large heave motions introduced at the upper end of a catenary riser can lead to compression and large bending moments in the region immediately above the touch down area. In the worst case, dynamic beam buckling may occur. The focus of the paper will be on understanding the riser behaviour in extreme, low-tension response and in establishing suitable analysis strategies to predict the extreme response. Results from long nonlinear stochastic simulations of many sea states with varying environmental and operating conditions may be combined to describe the long-term response of a nonlinear structure such as a catenary riser. However, this theoretically straight-forward approach is very demanding computationally and ways to limit the extent of nonlinear stochastic simulations are therefore sought. The usefulness of simpler methods such as regular wave analysis to improve understanding of the physical behaviour and to aid in concentrating the nonlinear simulations to where they are most useful, will be demonstrated.

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An oncology clinical trial design with randomization adaptive to both short- and long-term responses

Statistical Methods in Medical Research ◽

10.1177/0962280217744816 ◽

2017 ◽

Vol 28 (7) ◽

pp. 2015-2031 ◽

Cited By ~ 2

Author(s):

Hao Liu ◽

Xiao Lin ◽

Xuelin Huang

Keyword(s):

Trial Design ◽

Clinical Trial Design ◽

Therapeutic Benefit ◽

Survival Outcome ◽

Operating Characteristics ◽

Short Term ◽

Term Survival ◽

Long Term Survival ◽

Term Response

In oncology clinical trials, both short-term response and long-term survival are important. We propose an urn-based adaptive randomization design to incorporate both of these two outcomes. While short-term response can update the randomization probability quickly to benefit the trial participants, long-term survival outcome can also change the randomization to favor the treatment arm with definitive therapeutic benefit. Using generalized Friedman’s urn, we derive an explicit formula for the limiting distribution of the number of subjects assigned to each arm. With prior or hypothetical knowledge on treatment effects, this formula can be used to guide the selection of parameters for the proposed design to achieve desirable patient number ratios between different treatment arms, and thus optimize the operating characteristics of the trial design. Simulation studies show that the proposed design successfully assign more patients to the treatment arms with either better short-term tumor response or long-term survival outcome or both.

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