Comparative Study of Extreme Value Estimation Approaches for Mooring Lines Top Tension Responses

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Marina Leivas Simão ◽  
Luis Volnei Sudati Sagrilo ◽  
Paulo Maurício Videiro ◽  
Mauro Costa de Oliveira ◽  
Arvid Naess
Keyword(s):  
Probability Distributions ◽  
Wave Spectrum ◽  
Line Tension ◽  
Chain Condition ◽  
System Response ◽  
Short Term ◽  
Mooring Lines ◽  
Time Histories ◽  
The One ◽  
Nataf Transformation

Abstract It is known that the mooring system response of floating production units subjected to environmental loads is nonlinear. Even though wave elevations can be assumed as Gaussian processes for short-term periods, corresponding line tension responses generally are not, due to second-order slow-drift floater motions and intrinsic nonlinearities of the system. In this work, short-term extreme responses are estimated based on two different approaches. In the first one, a number of probability distributions are fitted to the tension time histories’ peaks samples and classic order statistics is applied to determine the most probable extreme line tension corresponding to a short-time period (3-h) in order to identify the one with best performance. The effect of correlation between consecutive peaks in the extremes estimation is investigated through the one-step Markov chain condition by using a Nataf transformation-based model. In the second approach, a more robust and recently developed method named average conditional exceedance rate (ACER) is investigated, where dependencies between maxima can be easily taken into account. Additionally, effects of major parameters in dynamic analyses, such as simulation length and discretization level of the wave spectrum, are evaluated. All time-series-based extreme estimates are compared with the estimates directly obtained from a sample of epochal maxima (Gumbel method). Numerical examples cover two study cases for mooring lines belonging to Floating Production Storage and Offloading (FPSO) units installed offshore Brazil. It is shown that the consideration of dependence between peaks leads to lower extreme estimates and that both approaches return accurate results.

Extreme Value Estimation of Mooring Lines Top Tension

2019 ◽  
Author(s):  
Marina Leivas Simão ◽  
Paulo Mauricio Videiro ◽  
Mauro Costa Oliveira ◽  
Luís Volnei Sudati Sagrilo
Keyword(s):  
Probability Distribution ◽  
Weibull Distribution ◽  
Time Domain ◽  
Extreme Values ◽  
Wave Spectrum ◽  
Line Tension ◽  
Short Term ◽  
Mooring Lines ◽  
Tension Time ◽  
The One

Abstract It is known that the mooring system of floating platforms responds non-linearly to environmental loads. Even though the wave-frequency excitation can be assumed as a Gaussian process, the line tension generally is not a Gaussian process due to the second-order slow-drift floater motions and the nonlinearities of the system itself. Distinct short-term time-domain analyses with the same wave spectrum excitation, i.e., distinct realizations of the response process, lead to a set of distinct values for the simulated individual maximum observed line tensions. Therefore, the ideal practice for estimating extreme tension values should be to perform a sufficiently large number of independent simulations along with an extreme statistical analysis considering the sample of the maximum line tension identified in each simulation. However, this process can be very time-consuming and cumbersome for everyday design applications. In this paper, the short-term line tension is assumed to be a non-Gaussian ergodic process. The extreme tension is then estimated based on the peaks sample of just a single simulated tension time-history. A number of known probability distributions are fitted to the peaks of the time series and classic order statistics theory is applied to determine the most probable extreme line tension corresponding to a specified short-time period (3-h) in order to identify the one with best performance. The proposed probability distribution models for the tension peaks are the 3-parameter Weibull distribution, the Weibull distribution fitted to the tail of the data (Weibull-tail) and the Shifted Generalized Lognormal Distribution (SGLD). The estimated extreme values are also prone to uncertainties due to time-domain simulation details. The effects of the major parameters in the dynamic analysis, such as simulation length and discretization level of the wave spectrum, are therefore investigated using several simulated mooring line tension time-histories. Furthermore, the effect of correlation between consecutive line tension peaks in the extreme values estimation is investigated through a Nataf transformation-based model for joint probability distribution for the peaks and the one step Markov chain condition. It is shown that this latter consideration leads to extreme value estimates that are invariably smaller than those obtained by standard order statistics. These estimates are also shown to be closer to the extreme estimates directly obtained from a sample of largest values taken from several distinct numerical simulations. Numerical examples cover two study cases for mooring lines belonging to FPSO (Floating, Production, Storage and Offloading) units to be installed in Brazilian waters.

On the Probability Distribution of Mooring Line Tensions in a Directional Environment

2011 ◽  
Author(s):  
Jan Mathisen ◽  
Siril Okkenhaug ◽  
Kjell Larsen
Keyword(s):  
Time Series ◽  
Probability Distributions ◽  
Extreme Value Distribution ◽  
Line Tension ◽  
Extreme Value ◽  
Mooring Line ◽  
Large Set ◽  
Short Term ◽  
Reliability Method ◽  
Line Design

A joint probabilistic model of the metocean environment is assembled, taking account of wind, wave and current and their respective heading angles. Mooring line tensions are computed in the time domain, for a large set of short-term stationary conditions, intended to span the domain of metocean conditions that contribute significantly to the probabilities of high tensions. Weibull probability distributions are fitted to local tension maxima extracted from each time series. Long time series of 30 hours duration are used to reduce statistical uncertainty. Short-term, Gumbel extreme value distributions of line tension are derived from the maxima distributions. A response surface is fitted to the distribution parameters for line tension, to allow interpolation between the metocean conditions that have been explicitly analysed. A second order reliability method is applied to integrate the short-term tension distributions over the probability of the metocean conditions and obtain the annual extreme value distribution of line tension. Results are given for the most heavily loaded mooring line in two mooring systems: a mobile drilling unit and a production platform. The effects of different assumptions concerning the distribution of wave heading angles in simplified analysis for mooring line design are quantified by comparison with the detailed calculations.

Catheter-directed foam sclerotherapy treatment of saphenous vein incompetence

VASA ◽  
2012 ◽  
Vol 41 (2) ◽  
pp. 120-124 ◽  
Author(s):  
Asciutto ◽  
Lindblad
Keyword(s):  
Saphenous Vein ◽  
Short Term ◽  
Foam Sclerotherapy ◽  
Results Of Treatment ◽  
Ulcer Healing Rate ◽  
Complete Obliteration ◽  
Ceap Classification ◽  
One Year ◽  
The One

Background: The aim of this study is to report the short-term results of catheter-directed foam sclerotherapy (CDFS) in the treatment of axial saphenous vein incompetence. Patients and methods: Data of all patients undergoing CDFS for symptomatic primary incompetence of the great or small saphenous vein were prospectively collected. Treatment results in terms of occlusion rate and patients’ grade of satisfaction were analysed. All successfully treated patients underwent clinical and duplex follow-up examinations one year postoperatively. Results: Between September 2006 and September 2010, 357 limbs (337 patients) were treated with CDFS at our institution. Based on the CEAP classification, 64 were allocated to clinical class C3 , 128 to class C4, 102 to class C5 and 63 to class C6. Of the 188 patients who completed the one year follow up examination, 67 % had a complete and 14 % a near complete obliteration of the treated vessel. An ulcer-healing rate of 54 % was detected. 92 % of the patients were satisfied with the results of treatment. We registered six cases of thrombophlebitis and two cases of venous thromboembolism, all requiring treatment. Conclusions: The short-term results of CDFS in patients with axial vein incompetence are acceptable in terms of occlusion and complications rates.

Hidden “holes” in the capital of banks and the supply of credit to the real sector of economy

2018 ◽  
pp. 49-68 ◽  
Author(s):  
M. E. Mamonov
Keyword(s):  
Credit Risk ◽  
The Other ◽  
Real Sector ◽  
Capital Management ◽  
Loan Loss ◽  
Short Term ◽  
The Real ◽  
Ex Post ◽  
The One

Our analysis documents that the existence of hidden “holes” in the capital of not yet failed banks - while creating intertemporal pressure on the actual level of capital - leads to changing of maturity of loans supplied rather than to contracting of their volume. Long-term loans decrease, whereas short-term loans rise - and, what is most remarkably, by approximately the same amounts. Standardly, the higher the maturity of loans the higher the credit risk and, thus, the more loan loss reserves (LLP) banks are forced to create, increasing the pressure on capital. Banks that already hide “holes” in the capital, but have not yet faced with license withdrawal, must possess strong incentives to shorten the maturity of supplied loans. On the one hand, it raises the turnovers of LLP and facilitates the flexibility of capital management; on the other hand, it allows increasing the speed of shifting of attracted deposits to loans to related parties in domestic or foreign jurisdictions. This enlarges the potential size of ex post revealed “hole” in the capital and, therefore, allows us to assume that not every loan might be viewed as a good for the economy: excessive short-term and insufficient long-term loans can produce the source for future losses.

Experimental Investigation vs Numerical Simulation of the Dynamic Response of a Moored Floating Structure to Waves

2014 ◽  
Author(s):  
Daniele Dessi ◽  
Sara Siniscalchi Minna
Keyword(s):  
Dynamical Behavior ◽  
Irregular Waves ◽  
Mooring Line ◽  
Floating Structure ◽  
Mooring Lines ◽  
Wave Energy Converters ◽  
Time Histories ◽  
Actual Configuration ◽  
Proper Orthogonal ◽  
Dynamic Wave

A combined numerical/theoretical investigation of a moored floating structure response to incoming waves is presented. The floating structure consists of three bodies, equipped with fenders, joined by elastic cables. The system is also moored to the seabed with eight mooring lines. This corresponds to an actual configuration of a floating structure used as a multipurpose platform for hosting wind-turbines, aquaculture farms or wave-energy converters. The dynamic wave response is investigated with numerical simulations in regular and irregular waves, showing a good agreement with experiments in terms of time histories of pitch, heave and surge motions as well as of the mooring line forces. To highlight the dynamical behavior of this complex configuration, the proper orthogonal decomposition is used for extracting the principal modes by which the moored structure oscillates in waves giving further insights about the way waves excites the structure.

scholarly journals Analytical Determination of the Brake Temperature Mode During Repetitive Short-Term Braking

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 1912
Author(s):  
Aleksander Yevtushenko ◽  
Katarzyna Topczewska ◽  
Michal Kuciej
Keyword(s):  
Friction Pair ◽  
Thermal Sensitivity ◽  
Finite Difference Methods ◽  
Temporal Variations ◽  
Frictional Heat ◽  
Maximum Temperature ◽  
Analytical Determination ◽  
Flash Temperature ◽  
Short Term ◽  
The One

An algorithm to determine the maximum temperature of brake systems during repetitive short-term (RST) braking mode has been proposed. For this purpose, the intermittent mode of braking was given in the form of a few cyclic stages consisting of subsequent braking and acceleration processes. Based on the Chichinadze’s hypothesis of temperature summation, the evolutions of the maximum temperature during each cycle were calculated as the sum of the mean temperature on the nominal contact surface of the friction pair elements and temperature attained on the real contact areas (flash temperature). In order to find the first component, the analytical solution to the one-dimensional thermal problem of friction for two semi-spaces taking into account frictional heat generation was adapted. To find the flash temperature, the solution to the problem for the semi-infinite rod sliding with variable velocity against a smooth surface was used. In both solutions, the temperature-dependent coefficient of friction and thermal sensitivity of materials were taken into account. Numerical calculations were carried out for disc and drum brake systems. The obtained temporal variations of sliding velocity, friction power and temperature were investigated on each stage of braking. It was found that the obtained results agree well with the corresponding data established by finite element and finite-difference methods.

Measuring Absolute Membrane Potential Across Space and Time

2021 ◽  
Vol 50 (1) ◽  
Author(s):  
Julia R. Lazzari-Dean ◽  
Anneliese M.M. Gest ◽  
Evan W. Miller
Keyword(s):  
Membrane Potential ◽  
Neurotransmitter Release ◽  
Cell Cycle Control ◽  
The Other ◽  
Annual Review ◽  
Publication Date ◽  
Short Term ◽  
Cellular Processes ◽  
Sensing Platform ◽  
The One

Membrane potential (Vmem) is a fundamental biophysical signal present in all cells. Vmem signals range in time from milliseconds to days, and they span lengths from microns to centimeters. Vmem affects many cellular processes, ranging from neurotransmitter release to cell cycle control to tissue patterning. However, existing tools are not suitable for Vmem quantification in many of these areas. In this review, we outline the diverse biology of Vmem, drafting a wish list of features for a Vmem sensing platform. We then use these guidelines to discuss electrode-based and optical platforms for interrogating Vmem. On the one hand, electrode-based strategies exhibit excellent quantification but are most effective in short-term, cellular recordings. On the other hand, optical strategies provide easier access to diverse samples but generally only detect relative changes in Vmem. By combining the respective strengths of these technologies, recent advances in optical quantification of absolute Vmem enable new inquiries into Vmem biology. Expected final online publication date for the Annual Review of Biophysics, Volume 50 is May 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Spin-Wave Spectrum in the Sinusoidal Superlattice with Amplitude and Phase Inhomogeneities

2014 ◽  
Vol 215 ◽  
pp. 385-388
Author(s):  
Valter A. Ignatchenko ◽  
Denis S. Tsikalov
Keyword(s):  
Spin Wave ◽  
Density Of States ◽  
Wave Spectrum ◽  
The Self ◽  
One Dimensional ◽  
Consistent Approximation ◽  
Self Consistent ◽  
Greens Function ◽  
The One ◽  
Spin Wave Spectrum

Effects of both the phase and the amplitude inhomogeneities of different dimensionalities on the Greens function and on the one-dimensional density of states of spin waves in the sinusoidal superlattice have been studied. Processes of multiple scattering of waves from inhomogeneities have been taken into account in the self-consistent approximation.

Comparison of Spar and Semisubmersible Floater Concepts of Offshore Wind Turbines Using Long-Term Analysis

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Hasan Bagbanci ◽  
D. Karmakar ◽  
C. Guedes Soares
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Transfer Functions ◽  
Probability Distributions ◽  
Offshore Wind ◽  
Short Term ◽  
Offshore Wind Turbines ◽  
Floating Wind Turbine ◽  
Offshore Floating Wind Turbine

The long-term probability distributions of a spar-type and a semisubmersible-type offshore floating wind turbine response are calculated for surge, heave, and pitch motions along with the side-to-side, fore–aft, and yaw tower base bending moments. The transfer functions for surge, heave, and pitch motions for both spar-type and semisubmersible-type floaters are obtained using the fast code and the results are also compared with the results obtained in an experimental study. The long-term predictions of the most probable maximum values of motion amplitudes are used for design purposes, so as to guarantee the safety of the floating wind turbines against overturning in high waves and wind speed. The long-term distribution is carried out using North Atlantic wave data and the short-term floating wind turbine responses are represented using Rayleigh distributions. The transfer functions are used in the procedure to calculate the variances of the short-term responses. The results obtained for both spar-type and semisubmersible-type offshore floating wind turbine are compared, and the study will be helpful in the assessments of the long-term availability and economic performance of the spar-type and semisubmersible-type offshore floating wind turbine.

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