Long-Term Extreme Response of Marine Structures Considering the Combination of First and Second Order Wave Effects

2013 ◽  
Author(s):  
Luis Volnei Sudati Sagrilo ◽  
Fernando Jorge Mendes de Sousa ◽  
José Antonio Vargas Bazán ◽  
Zhen Gao ◽  
Arvid Naess
Keyword(s):  
Hermite Polynomials ◽  
Second Order ◽  
Short Term ◽  
Marine Structure ◽  
Slow Drift ◽  
Extreme Response ◽  
Wave Effects ◽  
Speed Up ◽  
Non Gaussian

In this paper, the long-term extreme response of a floating marine structure subjected to first and second order (slow-drift) wave effects is addressed. The proposed formulation is based on the long-term up-crossing rate, which is obtained by integrating the contribution of all short-term sea states. In order to speed up the evaluation of the long-term integral, an analytical expression for the short-term responses up-crossing rates was adopted. This expression is based on Hermite polynomials, and considers the response as a second order Volterra stochastic process. This formulation was applied to evaluate the 1-yr, 10-yr and 100-yr lateral motions of a circular-shaped monocolumn platform, and the non-Gaussian (nonlinear) results are compared with those obtained by assuming the response as a Gaussian process.

Long-Term Area Statistics for Maximum Crest Height Under a Fixed Platform Deck

2018 ◽  
Author(s):  
Øistein Hagen ◽  
Jørn Birknes-Berg ◽  
Ida Håøy Grue ◽  
Gunnar Lian ◽  
Kjersti Bruserud ◽  
...  
Keyword(s):  
Time Series ◽  
North Sea ◽  
Extreme Values ◽  
Second Order ◽  
Irregular Waves ◽  
Scatter Diagram ◽  
Short Term ◽  
Wave Impact ◽  
Crest Height

As offshore reservoirs are depleted, the seabed may subside. Furthermore, the extreme crests estimates are now commonly higher than obtained previously due to improved understanding of statistics of non-linear irregular waves. Consequently, bottom fixed installations which have previously had sufficient clearance between the deck and the sea surface may be in a situation where wave impact with the deck must be considered at relevant probability levels. In the present paper, we investigate the long-term area statistics for maximum crest height under a fixed platform deck for 2nd order short crested and long crested sea based on numerical simulations as a function of platform deck dimension for jackets. The results are for one location in the northern North Sea, but some key results are also reported and verified for a more benign southern North Sea location. Time domain simulations for long crested and short crested waves over a spatial domain with dimension of a platform deck are performed, and relevant statistics for airgap assessment determined. Second order waves are simulated for the different cells in the (Hs, Tp) scatter diagram for Torsethaugen two-peak wave spectrum for long-crested and short-crested sea. A total of 1000 3-hour sea states are generated per cell, and time series generated for 160 spatial points under a platform deck. Short-term and long-term statistics are established for the maximum crest height as function of platform dimension; inline and transverse to the wave direction, and over the area. Results are given for the linear sea and for the second order time series. The annual q-probability estimates for the maximum crest height over area as a function of platform dimension is determined for a location at the Norwegian Continental Shelf by weighting the short-term statistics for the individual cells in the scatter diagram with the long-term probability of occurrence of the sea state. To reduce the number of numerical second order simulations, the effect of excluding cells that have a negligible effect on the long term extreme crest estimate is discussed. The percentiles in the distribution of maximum crest (over area) in design sea states that corresponds to the extreme values obtained from the long-term analysis are determined for long crested and short crested sea. The increase in the extreme crest over an area compared to the point in space estimate is estimated for both linear and second order surface elevation.

A Feasibility Investigation for Developing Artificial Beachrocks: A Potential Measure for Coastal Protection in Southeast Yogyakarta Coast, Indonesia

2020 ◽  
Author(s):  
Lutfian Rusdi Daryono ◽  
Kazunori Nakashima ◽  
Satoru Kawasaki ◽  
Koichi Suzuki ◽  
Anastasia Dewi Titisari ◽  
...  
Keyword(s):  
Physical And Mechanical Properties ◽  
Sandy Beaches ◽  
Coastal Sediments ◽  
Coastal Protection ◽  
Optimum Conditions ◽  
Short Term ◽  
Resistivity Survey ◽  
Wave Effects ◽  
Potential Measure

<p>Erosion prone sandy beaches are frequently covered by cement and mortar to preserve the coastal zone, but the conventional approach has an adverse impact on the environment, altering the coastal landscape and processes unfavorably. The term “beachrock” refers to cemented coastal sediments through a long-term formation of CaCO<sub>3</sub> cement, and which is an important feature in many tropical coastlines as it appears to have a substantial anchoring effect against wave effects and erodibility. Therefore, the objective of this study is to evaluate the feasibility in progressing the formation of artificial beachrocks using natural materials (e.g., microbes, sand, shell, pieces of coral, and seaweed etc.) within a short-term, and to introduce the method as a novel candidate for coastal protection. In this study, both resistivity survey and multi analysis seismic wave (MASW) survey along the same lines were performed at first to elucidate the subsurface structure of existing beachrocks in the Southeast Yogyakarta coastal area (Indonesia), followed by the laboratory analysis, which is aimed understand the basics in the formation mechanism. Peloidal micrite cement, the cement comprised of aragonite needles, micritized granules and the cover of micritic were observed in natural beachrocks. Mimicking the mechanism, an attempt has been undertaken to develop artificial beachrocks in the laboratory via microbial induced carbonate precipitation (MICP). Finally, the physical and mechanical properties were well compared between the artificially formed beachrocks and natural beachrocks collected from the survey lines. The results suggest that the artificial deposits treated for 14 days under optimum conditions, achieved a peak unconfined compressive strength of around 6 MPa similar to that of weak-consolidated natural beachrock. The comparison further reveals that the variables such as porosity, Vp, Vs, and strength are primarily rely on the precipitated morphology of the crystals.</p>

scholarly journals Glacier dynamics at Helheim and Kangerdlugssuaq glaciers, southeast Greenland, since the Little Ice Age

2014 ◽  
Vol 8 (1) ◽  
pp. 1257-1278
Author(s):  
S. A. Khan ◽  
K. K. Kjeldsen ◽  
K. H. Kjær ◽  
S. Bevan ◽  
A. Luckman ◽  
...  
Keyword(s):  
Mass Balance ◽  
Little Ice Age ◽  
Initial Conditions ◽  
Ice Age ◽  
Short Term ◽  
Episodic Events ◽  
Highly Sensitive ◽  
Decadal Scale ◽  
Speed Up

Abstract. Observations over the past decade show significant ice loss associated with the speed-up of glaciers in southeast Greenland from 2003, followed by a deceleration from 2006. These short-term, episodic, dynamic perturbations have a major impact on the mass balance at the decadal scale. To improve the projection of future sea level rise, a long-term data record that reveals the mass balance beyond such episodic events is required. Here, we extend the observational record of marginal thinning of Helheim glacier (HG) and Kangerdlugssuaq glacier (KG) from 10 to more than 150 yr. We show that although the frontal portion of HG thinned by more than 100 m between 2003 and 2006, it thickened by more than 50 m during the previous two decades. In contrast, KG was stable from 1981 to 1998 and experienced major thinning only after 2003. Extending the record back to the end of the Little Ice Age (ca. 1850) shows no significant thinning of HG from 1850 to 1981, while KG underwent substantial thinning of ~265 m. Analyses of their sensitivity to sub-surface water temperature anomalies and variations in air temperature suggest that both HG and KG are highly sensitive to short-term atmospheric and ocean forcing, and respond very quickly to small fluctuations. At century time-scales, however, multiple external parameters (e.g. outlet shape) dominate the mass change. These findings undermine attempts to use measurements over the last decade as initial conditions to project future dynamic ice loss.

Efficient Calculation of Low Frequency Motions for Air-Gap Prediction

2018 ◽  
Author(s):  
Zhiyuan Pan ◽  
Torgeir Kirkhorn Vada ◽  
Arne Nestegård
Keyword(s):  
Potential Flow ◽  
Low Frequency ◽  
Air Gap ◽  
Second Order ◽  
Short Term ◽  
Sea State ◽  
Order Analysis ◽  
Analysis Process ◽  
Efficient Calculation ◽  
Speed Up

The importance of the low frequency motions to air-gap estimation is evaluated on a column-based unit by using a computer program based on the linear and second-order potential theory. First and second order upwells are combined statistically and examined for different short term sea state conditions. To be able to speed up the analysis process, the potential flow code used in this study had been optimized in efficiency by introducing the multithreaded computation for the iterations of second order analysis.

Estimation of Extreme Ship Response

2012 ◽  
Vol 56 (01) ◽  
pp. 23-34
Author(s):  
Wengang Mao ◽  
Igor Rychlik
Keyword(s):  
Gaussian Model ◽  
Container Ship ◽  
Short Term ◽  
Sea State ◽  
High Quantiles ◽  
Alternative Approach ◽  
Extreme Response ◽  
Heading Angle ◽  
Ship Speed

In practice the severity of ship response is measured by high quantiles of long-term distribution of the response. The distribution is estimated by combining the short-term distribution of the response with a long-term probability distribution of encountered sea states. The paper describes an alternative approach, the so-called Rice's method, based on estimation of expected number of upcrossings of high levels by stress during 1 year. The method requires description of long-term variability of the standard deviation, skewness, kurtosis, and zero upcrossing frequency of ship response. It is assumed that the parameters are functions of encountered significant wave height, heading angle, and ship speed. The relation can be estimated from the measured stresses or computed by dedicated software assuming rigid ship hull model. Then Winterstein's transformed Gaussian model is used to estimate the upcrossing rates of response during a sea state. The proposed method is validated using the full-scale measurements of a 2,800 TEU container ship during the first 6 months of 2008. Numerical estimation of 4,400 TEU container ship extreme of the extreme response for a 4400 TEU container ship illustrates the approach when no measurements are available.

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

2017 ◽  
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.

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

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.

scholarly journals Management of Geriatric Anesthesia on Emergency Surgery

2021 ◽  
Vol 2 (2) ◽  
pp. 70-75
Author(s):  
Achmad Hariyanto ◽  
◽  
Isngadi Isngadi ◽  
Keyword(s):  
Postoperative Complications ◽  
Emergency Surgery ◽  
Geriatric Patients ◽  
Elective Surgery ◽  
Medical Complications ◽  
Short Term ◽  
Term Survival ◽  
Speed Up ◽  
Geriatric Anesthesia

In geriatric patients, emergency surgery is more common than elective surgery. The incidence of medical complications increases along with aging while the rate of surgical complications remains constant. Postoperative complications escalates short-term morbidity and mortality and also associated with decreasing long-term survival. The main purposes of geriatric patients' care were to maintain hemodynamics, speed up recovery, and perform an assessment to avoid any further decline in functional capacity. The choice of anesthesia and how to administer anesthesia agents should be adjusted for the geriatric patient.

Long-Term Analysis Applied to Mooring Systems Design

2020 ◽  
Author(s):  
Pedro Seabra ◽  
Luis Volnei Sudati Sagrilo ◽  
Paulo Esperança
Keyword(s):  
Time Domain ◽  
Environmental Conditions ◽  
Systems Design ◽  
Environmental Data ◽  
Coupled Analysis ◽  
Offshore Structure ◽  
Short Term ◽  
Extreme Response ◽  
Term Analysis

Abstract Nowadays, the most used methodology to predict line tensions is the short-term coupled analysis, where the mooring system responses are obtained by a time-domain analysis for only some specific design combinations of extreme environmental conditions. This mooring analysis demands certain considerations and it is not the best way to obtain the offshore structure responses. The advances in both quantity and quality of collected environmental data and the increase of the computers processing power has enabled to consider the approach of more accurate long-term methodologies for mooring systems design. This paper proposes a numerical/computational procedure to obtain the extreme loads (ULS) acting on offshore platforms’ mooring lines. The work is based on the methodology of long-term analysis, employing a 10-yr long short-term environmental dataset of 3-h sea-states, where each short-term environmental condition is composed of the simultaneously observed environmental parameters of wave (sea and swell), wind and current. The methodology is applied to the analysis of three different mooring systems: a) spread-moored FPSO, b) Semi-Submersible platform and c) turret-moored FPSO. The Bootstrap approach is employed in order to take into account the statistical uncertainty associated to the estimated long-term most probable extreme response due to the limited number of short-term environmental conditions. The work was carried out using Dynasim software [1] to generate the time domain tension time series, which were later post-processed by using computational codes developed with Python software. Longer short-term numerical simulations lengths than the short-term period (3-h) have been investigated in order to understand the influence of this parameter on the final extreme long-term top tensions.

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