Use of a Stem Device for VIV Mitigation on a Dry Tree Semi-Submersible

2009 ◽  
Author(s):  
Apurva Gupta ◽  
John Murray ◽  
Bin Li ◽  
Harish Mukundan ◽  
Anis Hussain
Keyword(s):  
Gulf Of Mexico ◽  
Fatigue Damage ◽  
Production Systems ◽  
High Surface ◽  
Surface Current ◽  
Water Current ◽  
Surface Currents ◽  
Offshore Industry ◽  
Viv Suppression ◽  
Tree Production

The offshore industry is devoting considerable effort to develop a dry tree production Semi-submersible with motion characteristics similar to a Spar but with the functionality of a Tension Leg Platform (TLP) or a Semi-submersible in terms of fabrication, installation and commissioning. Installation of these Semi-submersibles in the Gulf of Mexico environment exposes the risers to high surface current which result in high fatigue damage due to Vortex Induced Vibration (VIV). In the existing dry tree production systems, the Spar shields the riser from the high velocity surface currents in depths to approximately 600 ft. In the dry tree Semi-submersible the upper sections of the risers are exposed to surface currents. In addition, most dry tree Semi-submersibles designs have to support Keel Joints similar to a Spar. Thus, installing and replacing conventional VIV mitigation devices like the fairings and strakes could become difficult. In comparison, the TLP has no keel guides making it easier to install risers with strakes or fairings to improve the riser’s response to currents in terms of VIV. There are two basic proven techniques to reduce VIV damage on a riser. These involve application of standard fairings or strakes and direct protection of an exposed riser to currents. This paper discusses a methodology for VIV suppression using a riser stem. This mechanism does not reduce the VIV directly on the riser, but it in fact shields the riser from the surface currents, and thus reduces the fatigue damage on risers. This riser is shielded inside a conduit section called a stem which extends from the deck of the Semi-submersible to the keel. The paper quantifies and discusses the reduction in fatigue damage when the stem is used. The analysis is based on typical deep water current conditions for the Gulf of Mexico.

scholarly journals A New Small Drifter for Shallow Water Basins: Application to the Study of Surface Currents in the Muggia Bay (Italy)

2016 ◽  
Vol 2016 ◽  
pp. 1-5 ◽  
Author(s):  
Carmelo Nasello ◽  
Vincenzo Armenio
Keyword(s):  
Free Surface ◽  
Shallow Water ◽  
Coriolis Force ◽  
Surface Current ◽  
Meteorological Conditions ◽  
Water Current ◽  
Surface Currents ◽  
Water Basin ◽  
Surface Circulation ◽  
The City

A new small drifter prototype for measuring current immediately below the free surface in a water basin is proposed in this paper. The drifter dimensions make it useful for shallow water applications. The drifter transmits its GPS location via GSM phone network. The drifter was used to study the trajectory of the surface current in the Muggia bay, the latter containing the industrial harbor of the city of Trieste (Italy). The analysis has been carried out under a wide variety of wind conditions. As regards the behavior of the drifter, the analysis has shown that it is well suited to detect the water current since its motion is marginally affected by the wind. The study has allowed detecting the main features of the surface circulation within the Muggia bay under different meteorological conditions. Also, the study has shown that the trajectory of the surface current within the bay is weakly affected by the Coriolis force.

scholarly journals A gridded surface current product for the Gulf of Mexico from consolidated drifter measurements

2021 ◽  
Vol 13 (2) ◽  
pp. 645-669
Author(s):  
Jonathan M. Lilly ◽  
Paula Pérez-Brunius
Keyword(s):  
Gulf Of Mexico ◽  
Temporal Distribution ◽  
Surface Current ◽  
Large Set ◽  
Surface Currents ◽  
Important Region ◽  
Surface Drifter ◽  
Current Product ◽  
The Mean ◽  
Separate Product

Abstract. A large set of historical surface drifter data from the Gulf of Mexico – 3770 trajectories spanning 28 years and more than a dozen data sources – are collected, uniformly processed and quality controlled, and assimilated into a spatially and temporally gridded dataset called GulfFlow. This dataset is available in two versions, with 1/4∘ or 1/12∘ spatial resolution respectively, both of which have overlapping monthly temporal bins with semimonthly spacing and which extend from the years 1992 through 2020. Together these form a significant resource for studying the circulation and variability in this important region. The uniformly processed historical drifter data from all publicly available sources, interpolated to hourly resolution, are also distributed in a separate product called GulfDriftersOpen. Forming a mean surface current map by directly bin-averaging the hourly drifter data is found to lead to severe artifacts, a consequence of the extremely inhomogeneous temporal distribution of the drifters. Averaging instead the already monthly-averaged data in GulfFlow avoids these problems, resulting in the highest-resolution map of the mean Gulf of Mexico surface currents yet produced. The consolidated drifter dataset is freely available at https://doi.org/10.5281/zenodo.3985916 (Lilly and Pérez-Brunius, 2021a), while the gridded products are available for noncommercial use only (for reasons discussed herein) at https://doi.org/10.5281/zenodo.3978793 (Lilly and Pérez-Brunius, 2021b).

The action of a surface current used as a breakwater

1955 ◽  
Vol 231 (1187) ◽  
pp. 466-478 ◽  
Keyword(s):  
Surface Current ◽  
Water Current ◽  
Air Bubbles ◽  
Surface Currents ◽  
Mean Velocity ◽  
Uniform Velocity ◽  
Sea Bottom ◽  
The Mean ◽  
Perforated Tube ◽  
A Current

The conditions under which an outward-flowing surface current can prevent the passage of waves coming in from the sea are investigated mathematically. Two types of current are considered: ( a ) a current with uniform velocity extending to a depth h ; ( b ) a current with velocity decreasing uniformly and vanishing at depth h . They have very similar effects. The mean velocity required to stop waves of given frequency is rather greater in case ( a ) than in case ( b ). The water current produced by a curtain of air bubbles from a perforated tube on the sea bottom is investigated theoretically on the assumption that the bubbles are very small. Evans (1955) has measured the surface currents produced in a tank by a bubble curtain and finds them smaller than predicted. The discrepancy is partly due to the fact that the bubbles were not very small.

scholarly journals A gridded surface current product for the Gulf of Mexico from consolidated drifter measurements

2020 ◽  
Author(s):  
Jonathan M. Lilly ◽  
Paula Pérez-Brunius
Keyword(s):  
Gulf Of Mexico ◽  
Temporal Distribution ◽  
Surface Current ◽  
Large Set ◽  
Surface Currents ◽  
Important Region ◽  
Surface Drifter ◽  
Current Product ◽  
The Mean ◽  
Separate Product

Abstract. A large set of historical surface drifter data from the Gulf of Mexico – 3761 trajectories spanning 27 years and more than a dozen data sources – are collected, uniformly processed and quality controlled, and assimilated into a spatially and temporally gridded dataset called GulfFlow. This dataset is available in two versions, with one-quarter degree or one-twelfth degree spatial resolution respectively, both of which have overlapping monthly temporal bins with semimonthly spacing, and extend from the years 1992 through 2019. Together these form a significant resource for studying the circulation and variability in this important region. The uniformly processed historical drifter data interpolated to hourly resolution from all publicly available sources are also distributed in a separate product called GulfDriftersOpen. Forming a mean surface current map by directly bin-averaging the hourly drifter data is found to lead to severe artifacts, a consequence of the extremely inhomogeneous temporal distribution of the drifters. Averaging instead the already monthly-averaged data in GulfFlow avoids these problems, resulting in the highest-resolution map of the mean Gulf of Mexico surface currents yet produced. The consolidated drifter dataset is freely available from https://doi.org/10.5281/zenodo.3985916 (Lilly and Pérez-Brunius, 2020a), while the gridded products are available for noncommercial use at https://doi.org/https://doi.org/10.5281/zenodo.3978793 (Lilly and Pérez-Brunius, 2020b), the latter being freely available for noncommercial use only for reasons discussed herein.

Development of an Acoustic-Based Riser Monitoring System

2009 ◽  
Author(s):  
Dai Wei ◽  
Yong Bai
Keyword(s):  
Gulf Of Mexico ◽  
Monitoring System ◽  
Fatigue Damage ◽  
Monitoring Systems ◽  
Design Tools ◽  
Complex Behavior ◽  
Maintenance And Repair ◽  
Future Design ◽  
Integrity Assurance ◽  
Deepwater Risers

Recent incidents with drilling risers in the Gulf of Mexico have led the industry’s application of more stringent integrity assurance requirements to its deepwater risers. Riser monitoring provides information that enables the operator to measure riser configurations and fatigue damage, confirm the integrity of the riser, assist with operational decisions, optimize inspection, maintenance and repair schedules /procedures and calibrate design tools. Monitoring can also improve the understanding of complex behavior of risers for the improvement to future design and analysis tools. This paper presents the characters of three different monitoring systems that suit specific objectives and requirements. An example project of acoustic approach is introduced with its working mode and design scheme.

scholarly journals Characteristic Mode Analysis of surface current distributions on metallic structures exposed to HIRF- and DCI-excitations

2020 ◽  
Vol 18 ◽  
pp. 33-41
Author(s):  
Jan Ückerseifer ◽  
Frank Gronwald
Keyword(s):  
Three Dimensional ◽  
Surface Current ◽  
Resonance Region ◽  
Mode Analysis ◽  
Surface Currents ◽  
Characteristic Mode ◽  
Metallic Structures ◽  
Current Distributions ◽  
Characteristic Modes ◽  
Physical Quantities

Abstract. This paper treats Characteristic Mode Analyses of three-dimensional test objects in the context of EMC. Based on computed Characteristic Modes and mode-specific physical quantities, series expansions for HIRF- and DCI-induced surface currents are deduced. The contribution of single Characteristic Modes to surface currents at different test frequencies is analyzed. HIRF- and DCI-excitations are compared with regard to their surface current distributions in their resonance region determined by Characteristic Mode Analysis.

An Approach to Include Observed VIV Likelihood in Drilling Riser Fatigue Analyses

2009 ◽  
Author(s):  
Michael A. Tognarelli ◽  
Rene D. Gabbai ◽  
Mike Campbell
Keyword(s):  
Fatigue Damage ◽  
Field Measurements ◽  
Scaling Analysis ◽  
Current Profile ◽  
Vortex Induced Vibration ◽  
Probability Of Occurrence ◽  
Industry Standard ◽  
Annual Probability ◽  
Analysis Computer ◽  
Viv Suppression

Field measurements of the response of a number of drilling risers indicate that vortex-induced vibration (VIV) occurs significantly less often than predicted by the industry-standard fatigue analysis computer program SHEAR7 V4.4. Several comparisons to model tests and field data, including one published by BP and 2H in 2007 [1], demonstrate that this analysis program is generally quite conservative, given that VIV occurs. Furthermore, this conservatism does not take into account those situations in which VIV fatigue is predicted but none is observed in the field, which adds yet another layer of “hidden” conservatism to design analyses. In an effort to address this and reduce conservatism to a more appropriate level, the probability of occurrence of vortex-induced vibration (VIV) is examined using full-scale measured data. The data has been collected over the past several years from five drilling risers without VIV suppression devices. These risers are on rigs under contract to BP at high-current-susceptible sites worldwide. Collectively, the data correspond to 9,600 10-minute field measurements, equivalent to 0.18 years of continuous monitoring. The riser response is obtained from motion loggers placed at selected positions along the riser as described in [1]. Each logger measures 3D accelerations and 2D angular rates. Through-depth currents are measured via Acoustic Doppler Current Profilers (ADCP). By comparison of measurements to computer predictions based on the observed current profile, a relationship is developed between the intensity of the fatigue damage predicted and the probability that VIV is observed in the field. Subsequently, an approach is proposed for scaling analysis predictions to reflect the relative likelihood of VIV. The database of measured and SHEAR7 maximum predicted fatigue damage rates is statistically characterized to determine how it may be used to determine factors of safety (FOS) for VIV design. A worked example for a deepwater drilling riser in the GoM is used to show how the FOS methodology can be applied in the case of multiple design currents each with a different annual probability of occurrence.

Experimental Investigation on the Suppression Device of VIV of a Flexible Riser

2014 ◽  
Author(s):  
Yun Gao ◽  
Shixiao Fu ◽  
Leijian Song ◽  
Tao Peng ◽  
Runpei Lei
Keyword(s):  
Fatigue Damage ◽  
Experimental Results ◽  
Experimental Investigations ◽  
Flexible Riser ◽  
Excited Mode ◽  
Response Characteristics ◽  
Helical Strakes ◽  
Uniform Current ◽  
Viv Suppression ◽  
Synchronization Regime

Experimental investigations were conducted on a flexible riser with and without helical strakes. A uniform current was obtained by towing a riser model in a tank, and the vortex-induced vibration (VIV) suppression of strakes with different heights and pitches was studied. The results of the bare riser show that the characteristics of the synchronization of the VIV for a flexible riser have many orders, and the excited mode jumps from one to another abruptly. During the high order synchronization regime, the VIV response decreases with the increased order of the synchronization. The experimental results also indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical strakes, and the suppression performance depends on the geometry of the helical strakes. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser fitted with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that strake height has a greater influence on the VIV response than the strake pitch, and the drag exerted on the riser increases with strake pitch and height.

Status of Deepwater Production Systems

1991 ◽  
Vol 28 (01) ◽  
pp. 39-45
Author(s):  
Edward E. Horton
Keyword(s):  
Gulf Of Mexico ◽  
Oil And Gas ◽  
Production Systems ◽  
Energy Resources ◽  
Innovative Technology ◽  
Oil Exploration ◽  
Exploration And Production ◽  
Near Future

As oil exploration and production moves farther offshore, innovative technology is required to exploit energy resources in ever deeper waters. This paper covers two areas of deepwater production: offshore Brazil and the Gulf of Mexico. The types of wells and their capacity are described as well as the alternative platform designs, both fixed and semisubmersible, being used to recover both oil and gas from depths greater than 1500 ft. The paper outlines why these deepwater regions are of interest now and describes developments that are expected in the near future.

MACRO-GOM: Long Term Multi-Resolution Ocean Current Reanalysis Dataset for the Gulf of Mexico

2021 ◽  
Author(s):  
Neha Groves ◽  
Ashwanth Srinivasan ◽  
Leonid Ivanov ◽  
Jill Storie ◽  
Drew Gustafson ◽  
...  
Keyword(s):  
High Resolution ◽  
Gulf Of Mexico ◽  
Observational Data ◽  
Hydrodynamic Model ◽  
Life Extension ◽  
Ocean Current ◽  
Reanalysis Dataset ◽  
Time Period ◽  
Offshore Industry

Abstract The Gulf of Mexico's unique circulation characteristics pose a particular threat to marine operations and play a significant role in driving the criteria used for design and life extension analyses of offshore infrastructure. Estimates from existing reanalysis datasets used by operators in GOM show less than ideal correlation with in situ measurements and have a limited resolution that disallows for the capture of ocean features of interest. In this paper, we introduce a new high-resolution long-term reanalysis dataset, Multi-resolution Advanced Current Reanalysis for the Ocean – Gulf of Mexico (MACRO-GOM), based on a state-of the-science hydrodynamic model configured specifically for ocean current forecasting and hindcasting services for the offshore industry that assimilates extensive non-conventional observational data. The underlying hydrodynamic model used is the Woods Hole Group – Tendral Ocean Prediction System (WHG-TOPS). MACRO-GOM is being developed at the native resolution of the TOPS-GOM domain, i.e. 1/32° (~3 km) hourly grid for the 1994-2019 time period (25 years). A 3-level downscaling methodology is used wherein observation based estimates are first dynamically interpolated using a 1/4° model before being downscaled to the 1/16° Inter-American Seas (IAS) domain, which in turn is used to generate time-consistent boundary conditions for the 1/32° reanalysis. A multiscale data assimilation technique is used to constrain the model at synoptic and longer time scales. For this paper, a shorter, 5-year reanalysis run was conducted for the 2015-2019 time period for verification against assimilated and unassimilated observations, WHG's proprietary frontal analyses, and other reanalyses. Both the frontal analyses and Notice to Lesses (NTL) rig mounted ADCP data was withheld from assimilation for comparison. Offshore operations in the GOM can benefit from an improved reanalysis dataset capable of assimilating existing non-conventional observational datasets. Existing hindcast and reanalysis model datasets are limited in their ability to comprehensively and reliably quantify the 3D circulation and kinematic properties of the main features partly because of limited assimilation of observational data. MACRO-GOM incorporates all the advantages of available HYCOM-based reanalyses and further enhances the resolution, accuracy, and reliability by the assimilation of over three decades of WHG's proprietary datasets and frontal analyses for continuous model correction and ground-truthing. The final 25-year high resolution dataset will provide highly reliable design and operational criteria for new and existing infrastructure in GOM.

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