Measurement of Global Loads on a Full-Scale SES Vessel Using Networks of Fiber Optic Sensors

2001 ◽  
Vol 45 (03) ◽  
pp. 205-215
Author(s):  
A. E. Jensen ◽  
J. Taby ◽  
K. Pran ◽  
G. Sagvolden ◽  
G. Wang
Keyword(s):  
Surface Effect ◽  
Bending Moment ◽  
Computational Effort ◽  
Full Scale ◽  
Strain Sensors ◽  
Algebraic Equations ◽  
The North ◽  
Linear Algebraic Equations ◽  
Surface Effect Ship ◽  
The North Sea

A method for measurement of global loads on a vessel, using strain measurements from a network of strain sensors and extensive Žnite-element analyses (FEA) with idealistic load cases, is presented. The sensors are attached at carefully selected locations at a cross section amidships, where the most signiŽcant loads have their maximum values. The Žnite-element (FE) strain values are used in precalculations to reduce the computational effort to solve a set of linear algebraic equations in real time. The method has been successfully tried out on the full-scale surface effect ship (SES) KNM Skjold (47 m, 270 tons, and 50 knots) instrumented with a network of Žber optic Bragg strain sensors. The seakeeping tests were performed in the North Sea (1999) in sea states 3, 5, and upper 6. Other parameters that were varied during the test program were the heading, forward speed, and on/off-cushion. The loads measured during the tests were the sagging/hogging moment, the horizontal bending moment, and the longitudinal twisting moment. The measured loads were compared with respective dimensioning loads based on DNV rules (HSLC) (1996). The results showed that when the vessel is subjected to bow flare slamming impacts, the sagging moment exceeded the DNV dimensioning value by a factor of 1.6, indicating that the HSLC rules do not provide conservative global loads when these extreme events occur. However, the peak loads were well within the design limits.

A Full Scale Instrumented Pile Test In The North Sea

1979 ◽  
Author(s):  
V.J. Sutton ◽  
W.J. Rigden ◽  
E.L. James ◽  
H.D. St. John ◽  
R.J. Poskitt
Keyword(s):  
North Sea ◽  
Full Scale ◽  
Pile Test ◽  
The North ◽  
The North Sea

Time-Variant Ultimate Strength Reliability of FPSOs Including Corrosion and Slamming Effects

2005 ◽  
Author(s):  
Ioannis Moatsos ◽  
Purnendu K. Das
Keyword(s):  
Reliability Analysis ◽  
Ultimate Strength ◽  
North Sea ◽  
Structural Reliability ◽  
Bending Moment ◽  
Green Water ◽  
Component Level ◽  
Reliability Indices ◽  
The North ◽  
The North Sea

This paper discusses the effects of corrosion and slamming on Floating Production Storage and Offloading (FPSO) structures in the North Sea by using a time variant structural reliability based approach. An FPSO structure currently in operation in the North Sea is analysed, an analytical approach is suggested and used to determine the Ultimate Strength of the FPSO structure and compared with other published methods. A non-linear corrosion method is then used to determine the effect of corrosion on the ultimate strength and subsequently in the reliability of the structure. Slamming loads on the midship section of the FPSO are calculated using closed form expressions. The effect of slamming and green water load on the overall vertical bending moment applied on the structure is combined with the vertical wave bending and still water loads using the Ferry Borges- Castanheta method and the SRSS rule, to provide the distribution and variation of a loading component for structural reliability analysis to be performed. Time variant reliability analysis using Monte Carlo Simulation is then used to determine reliability indices and probabilities of failure for the structural system analysed on a component level.

DEH Cable System Preventive Protection With Distributed Temperature and Strain Sensors

2012 ◽  
Author(s):  
Fabien Ravet ◽  
Atle Børnes ◽  
Carlos Borda ◽  
Even Tjåland ◽  
Halfdan Hilde ◽  
...  
Keyword(s):  
Fault Detection ◽  
Brillouin Scattering ◽  
Single Mode ◽  
Strain Sensors ◽  
Electrical Heating ◽  
Detection Methods ◽  
Strain Sensing ◽  
The North ◽  
The North Sea ◽  
Stimulated Brillouin

Hydrate and wax formation in subsea flowlines is a major cause of production impairment. Among various approaches used to minimize the risk, Direct Electrical Heating (DEH) is being applied. DEH is based on passing a current through the pipe wall to mitigate heat losses from the fluid to the surroundings during events which require flow assurance measures. The Piggyback Cable, a high voltage cable attached to the DEH pipeline, is during operation exposed to thermal and mechanical loads which may be critical for the integrity of the DEH system. The overall safety requirement is that any potential Piggyback Cable fault is detected and disconnected from the power source before damage is caused to the pipeline. Conventional cable fault detection methods based on current measurements give adequate protection for the main part of the pipeline. However, for the far end of the Piggyback Cable complementary fault detection is required. A method based on fiber break monitoring has been qualified for this purpose. The new method is implemented in the North Sea on two DEH pipelines operated by Statoil, 43 and 21 km long respectively. The protection is facilitated by standard single-mode fibers integrated into the DEH cables. Although not basis for the design the integrated fibers open up possibilities for temperature and strain sensing using stimulated Brillouin scattering. Sensing has been performed on a 43 km DEH pipeline using the DITEST AIM (Distributed Temperature and Strain Asset Integrity Monitoring). Analysis of the sensing results reveal that distributed fiber optic sensing is capable of pin-pointing thermal events and strain induced loads for an object of this length.

A Reactive Flex Joint System for Reducing Wellhead Fatigue: Analysis and Measurement

2021 ◽  
Author(s):  
Halvor S. Gustad ◽  
Per Thomas Moe ◽  
Dag André Fjeldstad ◽  
Knut Olav Sønåsen ◽  
Arve Bjørset
Keyword(s):  
Measurement System ◽  
Barents Sea ◽  
Bending Moment ◽  
Dynamic Loads ◽  
Test Rig ◽  
Nitrogen Gas ◽  
Joint System ◽  
The North ◽  
Drilling Operations ◽  
The North Sea

Abstract The Reactive Flex-Joint (RFJ) is a nitrogen gas torsion springfully integrated in the LMRP-BOP stack. Its purpose is to reduce the dynamic loads and the fatigue damage applied to wellheads during drilling operations. The system achieves the reduction by applying a bending moment opposing and inverting the bending moment at the Lower Flex-Joint (LFJ). The RFJ is continuously monitored by the WAMS measurement system. The second generation RFJ has been extensively tested in a full scale workshop test rig before being shipped offshore for a year of operations on two semi-submersible rigs operating in the North Sea/Barents Sea. This paper demonstrates by calculation and measurement that the RFJ is capable of reducing wellhead loads by more than 50% and the wellhead fatigue by more than 95%. The accuracy of the measurement system is discussed.

Propellers for High-Performance Craft

1978 ◽  
Vol 15 (04) ◽  
pp. 335-380 ◽  
Author(s):  
John L. Allison
Keyword(s):  
High Speed ◽  
High Performance ◽  
Surface Effect ◽  
Historical Review ◽  
Full Scale ◽  
Design Procedures ◽  
Surface Effect Ship ◽  
Design Selection ◽  
Improved Performance ◽  
Model Versus

This paper presents a brief historical review of marine propeller development leading to modern design, selection, and matching methods for high-performance craft such as planing hulls, hydrofoils and surface effect ships. Subcavitating propeller theory is summarized, and some limitations are discussed with regard to high-speed applications. An outline of supercavitating propeller theory is provided together with brief details of design procedures and the limitations of available data. The special problems of application of supercavitating propellers to surface effect ships are discussed briefly. Topics include sidehull installations, matching for hump and cruise, need for partial submergence and controllable pitch, strength considerations, and model versus full-scale performance. A review of recent progress in the application of supercavitating propellers to surface effect ships is presented, including comparisons of predicted full-scale blade pressures and stresses with actual full-scale measurements of speeds up to 80 knots. Future trends and goals are discussed, including development of improved performance prediction methods, rational structural design procedures, and new types of installation configuration. Much of the new information contained in this paper arises out of work performed under contract for the U. S. Navy Surface Effect Ship Program Office (PMS304) by Bell Aerospace Textron.

Interacting Species in Identical Reservoirs

1991 ◽  
Author(s):  
James C. G. Walker
Keyword(s):  
Organic Carbon ◽  
Computational Effort ◽  
Chemical Activity ◽  
Carbonate Sediments ◽  
Algebraic Equations ◽  
Linear Diffusion ◽  
Interacting Species ◽  
Linear Algebraic Equations ◽  
Method Of Solution ◽  
A Chain

In Chapter 7 I showed how much computational effort could be avoided in a system consisting of a chain of identical equations each coupled just to its neighboring equations. Such systems arise in linear diffusion and heat conduction problems. It is possible to save computational effort because the sleq array that describes the system of simultaneous linear algebraic equations that must be solved has elements different from zero on and immediately adjacent to the diagonal only. This general approach works also for one-dimensional diffusion problems involving several interacting species. In such a system the concentration of a particular species in a particular reservoir is coupled to the concentrations of other species in the same reservoir by reactions between species and is coupled also to adjacent reservoirs by transport between reservoirs. If the differential equations that describe such a system are arranged in appropriate order, with the equations for each species in a given reservoir followed by the equations for each species in the next reservoir and so on, the sleq array still will have elements different from zero close to the diagonal only. All the nonzero elements lie no farther from the diagonal than the number of species. More distant elements are zero. Again, much computation can be eliminated by taking advantage of this pattern. I will show how to solve such a system in this chapter, introducing two new solution subroutines, GAUSSND and SLOPERND, to replace GAUSSD and SLOPERD. I shall apply the new method of solution to a problem of early diagenesis in carbonate sediments. I calculate the properties of the pore fluid in the sediment as a function of depth and time. The different reservoirs are successive layers of sediment at increasing depth. The fluid's composition is affected by diffusion between sedimentary layers and between the top layer and the overlying seawater, the oxidation of organic carbon, and the dissolution or precipitation of calcium carbonate. Because I assume that the rate of oxidation of organic carbon decreases exponentially with increasing depth, there must be more chemical activity at shallow depths in the sediment than at great depths.

The Nonoriented, Multiple Passageway Flowline Connection System

2000 ◽  
Vol 122 (1) ◽  
pp. 42-47
Author(s):  
Gary Galle ◽  
Rudolf Bond
Keyword(s):  
System Reliability ◽  
Full Scale ◽  
Operational Cost ◽  
Flow Paths ◽  
The North ◽  
Major Development ◽  
Connection System ◽  
Rotational Orientation ◽  
The North Sea ◽  
Operational Activities

The remote, diverless, simultaneous connection of multiple subsea flowlines has historically been a difficult and costly operation. Difficulties and intensified operational activities stem from the need to orient the multiple flow paths prior to the final connection of the tubulars. This rotational orientation has proven to be very difficult for randomly prelaid flowlines or flowlines which must be rotated a relatively large amount prior to makeup. A new, innovative method has been developed whereby multiple flowlines can be connected without¯ the need to rotationally orient the multiple tubulars. This new connection system technology has undergone full-scale subsea testing and will be implemented in a major development in the North Sea. The significance of this achievement is assessed in this paper with a focus on the design philosophies used, the principles of operation, the overall system reliability, the projected amount of operational cost reduction, and the full-scale testing results. Additional comments are made concerning the applicability of this technology in various other subsea applications. [S0195-0738(00)00501-X]

Analysis of Riser Measurements in the North Sea

1984 ◽  
Vol 28 (04) ◽  
pp. 272-281
Author(s):  
P. H. J. Verbeek
Keyword(s):  
North Sea ◽  
Active Zone ◽  
Probability Distributions ◽  
Bending Moment ◽  
The North ◽  
Simulation Techniques ◽  
Theoretical Predictions ◽  
Solution Methods ◽  
The North Sea ◽  
Non Gaussian

Riser measurements in the field have provided a variety of data collected from several locations in the North Sea. Data were obtained by means of instrumented riser joints installed in both a 24-in. and a 16-in. drilling riser. Bending moments in the riser, riser tensions, motions of the semisubmersible, and wave heights were recorded simultaneously. The measurement program was aimed at verifying predictions from theoretical riser models in the typical regions of riser response; namely, the wave-active zone at the top, the "boundary layer" at the bottom, and the riser main section in between. In this paper attention is focused on the data obtained for riser response in the wave-active zone. Measured results are compared with theoretical predictions based on both analytical solution methods and numerical time-domain simulation techniques. In particular, the relationship between the standard deviation of riser bending response and significant wave height is discussed, as is the probabilistic nature of riser response. It is concluded that standard deviations of measured bending moment response agree well with theoretical results. The probability distributions of measured response were found to be non-Gaussian and consistent with theoretical predictions based on Morison-type wave loading.

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