Determining Appropriate Stiffness Levels for Spudcan Foundations Using Jack-Up Case Records

2002 ◽  
Author(s):  
M. J. Cassidy ◽  
G. T. Houlsby ◽  
M. Hoyle ◽  
M. R. Marcom
Keyword(s):  
Numerical Simulation ◽  
Back Analysis ◽  
Soil Conditions ◽  
Sea State ◽  
Soil Stiffness ◽  
The North ◽  
Assessment Guidelines ◽  
The North Sea ◽  
Specific Assessment ◽  
Jack Up

The level of soil stiffness under spudcan footings is an area of intense interest and debate, with many practitioners believing that current jack-up assessment guidelines are overly conservative. In order to evaluate appropriate stiffness parameters, back-analysis of case records of jack-up platforms in the North Sea has been performed. The records relate to three different rigs at a total of eight locations, which include a variety of soil conditions, water depths and sea-state severity. For each site the horizontal deck displacements and the sea-state conditions under storm loading are available. Numerical simulation of the platforms under storm loading was undertaken with varying levels of foundation stiffness. For each set of stiffness one-hour of numerical simulation was performed, with the most severe recorded environmental loading conditions for that site used. The horizontal deck displacements of the measured data and the numerical simulation results have been compared in both the frequency domain and by the magnitude of response. On the basis of the analyses, recommendations can be made for higher stiffness factors then are currently suggested in the SNAME, 1997 Technical & Research Bulletin 5-5A, Site Specific Assessment of Mobile Jack-up Units (SNAME, 1997).

scholarly journals Influence of Sea State on Sea Surface Height Oscillation from Doppler Altimeter Measurements in the North Sea

2018 ◽  
Vol 10 (7) ◽  
pp. 1100 ◽  
Author(s):  
Ferdinando Reale ◽  
Fabio Dentale ◽  
Eugenio Carratelli ◽  
Luciana Fenoglio-Marc
Keyword(s):  
North Sea ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Sea State ◽  
The North ◽  
The North Sea

Case Study: Non-Conventional Remaining Life Assessment of a Significant Dent in a Subsea Pipeline Scheduled for Decommissioning

2019 ◽  
Author(s):  
A. Brett ◽  
A. Russell
Keyword(s):  
Life Assessment ◽  
Remaining Life ◽  
Element Analysis ◽  
Oil Pipeline ◽  
The North ◽  
Pressure Spike ◽  
The North Sea ◽  
Specific Assessment ◽  
Remaining Life Assessment

Abstract An inline inspection of a subsea oil pipeline located in the North Sea identified a large top of line dent. The pipeline was scheduled for decommissioning within 3 years, however conventional fatigue assessment of the dent indicated that the pipeline could become unsafe before the scheduled decommissioning date. As the required remaining life could not be justified by conventional assessment, a review was completed to determine whether a case-specific assessment methodology could be developed to reduce the conservatism, while reliably demonstrating that the pipeline could be safely operated up until the planned decommissioning date. This review identified that the pipeline had a unique pressure history, which included a large one-off pressure spike that had occurred following detection of the dent. This raised the possibility of a pseudo-hydrotest type assessment to justify the required remaining life. This paper describes the non-conventional pseudo-hydrotest assessment that was undertaken for the dent to demonstrate acceptability, which used a combination of state of the art finite element analysis and fatigue crack growth assessment.

scholarly journals Wave current interaction: Effect on force prediction for fixed offshore structures

2018 ◽  
Vol 203 ◽  
pp. 01011
Author(s):  
Mohamed Latheef ◽  
Nasir Abdulla ◽  
Mohd Faieez Mohd Jupri
Keyword(s):  
Vertical Structure ◽  
Offshore Structures ◽  
Base Shear ◽  
Sea State ◽  
Clear Trend ◽  
The North ◽  
Relative Water ◽  
The North Sea ◽  
Current Interaction ◽  
Typical Design

MetOcean conditions in the South China Sea (SCS) indicates that unlike other locations such as the North Sea, the magnitude of the currents can be relatively large. In addition, these currents are strongly sheared. The present study focused on the typical design problem of calculating the ultimate base shear and overturning moments for slender fixed structureswiththe inclusion of the interaction between the currents and the wave field. It has been found that the loads on average can be around 15% larger when this interaction is accounted for in the calculation of the loads, highlighting the importance. In addition, the level of these amplifications were found to be dependent on the sea state steepness and the relative water depth. While no clear trend was found (changed case by case) in the present work, incorporating the vertical structure of the current was found to change the pattern of the amplification of the loads.

Statistics of Greater Sea States

2011 ◽  
Author(s):  
Anne M. Fullerton ◽  
Thomas C. Fu
Keyword(s):  
Numerical Models ◽  
Ship Motions ◽  
Frequency Range ◽  
Sea State ◽  
The North ◽  
Spectral Models ◽  
Wave Heights ◽  
The North Sea ◽  
Computational Predictions ◽  
The Ideal

Accurate representations of seaway statistics are important for physical and computational predictions of ship motions. The spectra that are most typically used in these applications are the Pierson-Moskowitz or Bretschneider. While these spectra are useful for fully developed seas, the larger sea states (Sea State (SS) 7 and higher) are typically not fully developed. In these cases, other spectral models may be more appropriate. It is critical to ship motion prediction, for both physical and numerical models, to accurately capture the frequency range for the sea state of interest. Sea state statistics, including wave heights, periods, and spectral bandwidths from various buoys and a platform in the North Sea are collected and compared with statistics from lower sea states. The spectral data are then averaged to generate a typical spectrum under the measured conditions. These developed spectra are compared with the ideal spectra mentioned previously.

Airborne GNSS reflectometry for coastal monitoring of sea state

2020 ◽  
Author(s):  
Mario Moreno ◽  
Maximilian Semmling ◽  
Georges Stienne ◽  
Serge Reboul ◽  
Jens Wickert
Keyword(s):  
Carrier Phase ◽  
Signal Amplitude ◽  
Navigation Systems ◽  
Sea State ◽  
Wind Retrieval ◽  
The North ◽  
Front End ◽  
The North Sea ◽  
Gnss Reflectometry ◽  
Satellite Navigation Systems

<p>Global Satellite Navigation Systems (GNSS) applications like navigation and positioning generally focus on the use of the direct radio signal broadcasted by the navigation satellites. From these signals, very highly precise coordinates can be obtained. However, there is a proportion of signals, that do not reach the receivers directly, that is, the signals that are reflected off Earth’s surface before reaching the receivers. That phenomenon gave way to one of the techniques that is taking an important role in the scope of GNSS remote sensing called GNSS-Reflectometry (GNSS-R). Due to the high reflection coefficient of the water and its importance within the climate system, the ocean is one of the surfaces with greatest interest in GNSS-R research projects. The objective of this study is to retrieve information about ocean height measured through the delay of the signal, and sea state and wind retrieval (ocean surface roughness) from the analysis of the signal amplitude.</p><p>During this study, GNSS-R measurements were executed along the North Sea coast between the cities of Calais and Boulogne, France, onboard of a gyrocopter. The setup consisted of a front-end data recorder with a right-handed circular polarization (RHCP) antenna. The campaign was conducted in July 2019 within a total of 9h 40m flight time. Each flight was performed at an altitude of about 800 m above sea level going on two legs forth and back along the coast. The legs differed in the distance from the coastline, of 700 m and 2 km, respectively.</p><p>Reflectometry signal processing involves three data levels. Level (0): The raw data samples of Syntony front-end receiver. Level (1): The Delay-Doppler Map (DDM) of the correlated reflected signal and the carrier phase, from which geophysical information can be derived. And Level (2): height estimation (from signal correlation in delay and frequency domain) and roughness estimation (from signal amplitude).</p><p>By using the DDM and the carrier phase delay the sea state shall be assessed including the achievable precision and reliability of estimates. An additional aim is also to validate the configuration in terms of the used platform, antenna setup, and flight design.</p>

scholarly journals NEW DESIGN OF THE BALTRUM DUNE REVETMENT BASED ON HYDRAULIC MODEL TESTS

2012 ◽  
Vol 1 (33) ◽  
pp. 75
Author(s):  
Frank Thorenz ◽  
Holger Blum ◽  
Andreas Kortenhaus
Keyword(s):  
Storm Surges ◽  
Model Tests ◽  
Federal State ◽  
Lower Saxony ◽  
Sea State ◽  
Design Storm ◽  
The North ◽  
The North Sea ◽  
Run Up ◽  
North Western

The sandy barrier island of Baltrum is located in the north-western part of the German Federal State Lower Saxony in the North Sea. The north-western part of the island is protected by a dune revetment against storm surges and erosion. In order to determine the functionality and loading of the construction under design storm surge conditions and investigate planning alternatives, numerical modeling of sea state conditions in combination with hydraulical model tests for the construction were executed. Measured overtopping rates of up to 125 l/(s.m) and loads up to 150 kPa showed the necessity to strengthen and heighten the initial construction. A combination of wall elements for wave run-up and overtopping reduction in combination with a crest wall were designed in order to meet the technical demands of coastal defence as well as the touristical needs of an important recreation locality.

scholarly journals ESTIMATES OF LONG WAVES IN THE WESER ESTUARY

1984 ◽  
Vol 1 (19) ◽  
pp. 53
Author(s):  
V. Barthel ◽  
E.R. Funke
Keyword(s):  
Wave Climate ◽  
Long Waves ◽  
Sea State ◽  
Floating Structures ◽  
Weser Estuary ◽  
Model Studies ◽  
The North ◽  
Frequency Components ◽  
The North Sea ◽  
Harbour Oscillations

Long waves of small amplitudes can excite harbour oscillations as well as the motion of floating structures or vessels. Field data from the Weser Estuary, German Bight of the North Sea were analysed with respect to waves with periods greater than 8 s. After preprocessing of the mostly noisy data records, special analysis incorporated the reconstruction of incorrectly recorded frequency components below .03 Hz and bivariate distributions of heights and periods. Results suggest that long wave activity increases towards the inner estuary. Grouping properties are dependent on wind direction and on directionality of the sea state. Further investigations and model studies for the response of travelling vessels to this wave climate are recommended.

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