scholarly journals Optimization-based calibration of hydrodynamic drag coefficients for a semisubmersible platform using experimental data of an irregular sea state

2020 ◽  
Vol 1669 ◽  
pp. 012023 ◽  
Author(s):  
M Böhm ◽  
A Robertson ◽  
C Hübler ◽  
R Rolfes ◽  
P Schaumann
Author(s):  
Sheng Xu ◽  
C. Guedes Soares ◽  
Ângelo P. Teixeira

A detail procedure to study mooring line strength reliability is presented. A fully coupled analysis is carried out to get the mooring tensions of a deep water semi-submersible floating systems operated in 100 year wave condition in South China Sea. The ACER method is applied to predict the 3h extreme mooring tension, and the results are validated by global maximum method. The hydrodynamic sampling points are generated by Latin Hypercube Sampling technique. The 3h extreme mooring tension is calculated by the ACER method with 10 minutes fully coupled dynamic simulation for each sampling point. The Kriging meta model method is trained to predict 3h mooring extreme tension under the effects of random hydrodynamic drag coefficients. A reliability analysis is carried out by implementing Monte Carlo simulation with the random hydrodynamic drag coefficients and mooring breaking strength considered.


Author(s):  
Petter Andreas Berthelsen ◽  
Erin E. Bachynski ◽  
Madjid Karimirad ◽  
Maxime Thys

In this paper, a numerical model of a braceless semi-submersible floating wind turbine (FWT) is calibrated against model test data. Experimental data from a 1:30 scaled model tested at MARINTEK’s Ocean Basin in 2015 using real-time hybrid model testing (ReaTHM) is used for the calibration of the time-domain simulation model. In these tests, aerodynamic loads were simulated in real-time and applied to the physical model. The simulation model is based on the as-built model at full scale. The hull and turbine are considered as rigid, while bar elements are used to model the mooring system in a coupled finite element approach. Frequency-dependent added mass, radiation damping, and excitation forces/moments are evaluated using a panel method based on potential theory. Distributed viscous forces on the hull and mooring lines are added to the numerical model applying Morison’s equation. The viscous drag coefficients in Morison’s equation are calibrated against selected test data, including decay tests in calm water and test with irregular waves. Simulations show that the drag coefficients change when waves are present. Aerodynamic loads are included as time varying loads applied directly at the hub based on the actual physical loads from the experiment. This way, uncertainties related to the aerodynamic loads in the calibrations are removed. The calibrated numerical model shows good agreement with experimental data.


2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Sheng Xu ◽  
A. P. Teixeira ◽  
C. Guedes Soares

Abstract In this paper, a detailed procedure to study the mooring line conditional strength reliability of a semi-submersible platform in a 100-year sea state is presented. A fully coupled analysis is conducted to calculate the mooring line tension of a deepwater semi-submersible floating system operated in the 100-year wave condition in South China Sea. 3-h extreme mooring line tensions are estimated by the average conditional exceedance rate (ACER) method from the data obtained by 10 and 20 min fully coupled dynamic simulations, and the results are validated by the global maximum method. A kriging metamodel is trained to predict the 3-h mooring line extreme tension taking into account the effect of random hydrodynamic drag coefficients. The hydrodynamic sampling points are generated by Latin hypercube sampling technique. A reliability analysis is carried out by Monte Carlo simulation considering the random hydrodynamic drag coefficients and mooring line breaking strength.


1991 ◽  
Vol 113 (3) ◽  
pp. 199-204 ◽  
Author(s):  
M. A. Grosenbaugh ◽  
D. R. Yoerger ◽  
F. S. Hover ◽  
M. S. Triantafyllou

Full-scale experimental data on the dynamics and flow-induced vibrations of a long vertical tow cable are analyzed. The data were measured while the surface ship was going through a series of starting, stopping, and backing maneuvers. The results of the study show that the amplitude of the flow-induced vibrations of the cable is strongly modulated during maneuvering operations. Maneuvering creates situations where different sections of the cable are translating at different speeds. This causes an “artificial” shear current which at times is severe, depending on the difference in speed between the top and bottom of the cable. The artificial shear is responsible for the intensification of the amplitude modulation above the level that is observed during steady-state towing conditions. The overall effect of the amplitude modulation is a reduction in the hydrodynamic drag forces. It is shown that the drag coefficient measured during maneuvering operations is lower than the steady-state value.


2000 ◽  
Vol 15 (4) ◽  
pp. 256-260 ◽  
Author(s):  
Tapani Pöyhönen ◽  
Kari L. Keskinen ◽  
Arto Hautala ◽  
Esko Mälkiä

Author(s):  
A. Gómez ◽  
P. Schabes-Retchkiman ◽  
M. José-Yacamán ◽  
T. Ocaña

The splitting effect that is observed in microdiffraction pat-terns of small metallic particles in the size range 50-500 Å can be understood using the dynamical theory of electron diffraction for the case of a crystal containing a finite wedge. For the experimental data we refer to part I of this work in these proceedings.


Author(s):  
K.B. Reuter ◽  
D.B. Williams ◽  
J.I. Goldstein

In the Fe-Ni system, although ordered FeNi and ordered Ni3Fe are experimentally well established, direct evidence for ordered Fe3Ni is unconvincing. Little experimental data for Fe3Ni exists because diffusion is sluggish at temperatures below 400°C and because alloys containing less than 29 wt% Ni undergo a martensitic transformation at room temperature. Fe-Ni phases in iron meteorites were examined in this study because iron meteorites have cooled at slow rates of about 10°C/106 years, allowing phase transformations below 400°C to occur. One low temperature transformation product, called clear taenite 2 (CT2), was of particular interest because it contains less than 30 wtZ Ni and is not martensitic. Because CT2 is only a few microns in size, the structure and Ni content were determined through electron diffraction and x-ray microanalysis. A Philips EM400T operated at 120 kV, equipped with a Tracor Northern 2000 multichannel analyzer, was used.


Author(s):  
C. C. Ahn ◽  
D. H. Pearson ◽  
P. Rez ◽  
B. Fultz

Previous experimental measurements of the total white line intensities from L2,3 energy loss spectra of 3d transition metals reported a linear dependence of the white line intensity on 3d occupancy. These results are inconsistent, however, with behavior inferred from relativistic one electron Dirac-Fock calculations, which show an initial increase followed by a decrease of total white line intensity across the 3d series. This inconsistency with experimental data is especially puzzling in light of work by Thole, et al., which successfully calculates x-ray absorption spectra of the lanthanide M4,5 white lines by employing a less rigorous Hartree-Fock calculation with relativistic corrections based on the work of Cowan. When restricted to transitions allowed by dipole selection rules, the calculated spectra of the lanthanide M4,5 white lines show a decreasing intensity as a function of Z that was consistent with the available experimental data.Here we report the results of Dirac-Fock calculations of the L2,3 white lines of the 3d and 4d elements, and compare the results to the experimental work of Pearson et al. In a previous study, similar calculations helped to account for the non-statistical behavior of L3/L2 ratios of the 3d metals. We assumed that all metals had a single 4s electron. Because these calculations provide absolute transition probabilities, to compare the calculated white line intensities to the experimental data, we normalized the calculated intensities to the intensity of the continuum above the L3 edges. The continuum intensity was obtained by Hartree-Slater calculations, and the normalization factor for the white line intensities was the integrated intensity in an energy window of fixed width and position above the L3 edge of each element.


Sign in / Sign up

Export Citation Format

Share Document