A Wiener-Laguerre model of VIV forces given recent cylinder velocities

Slender structures immersed in a cross flow can experience vibrations induced by vortex shedding (VIV), which cause fatigue damage and other problems. VIV models in engineering use today tend to operate in the frequency domain. A time domain model would allow to capture the chaotic nature of VIV and to model interactions with other loads and non-linearities. Such a model was developed in the present work: for each cross section, recent velocity history is compressed using Laguerre polynomials. The compressed information is used to enter an interpolation function to predict the instantaneous force, allowing to step the dynamic analysis. An offshore riser was modeled in this way: Some analyses provided an unusually fine level of realism, while in other analyses, the riser fell into an unphysical pattern of vibration. It is concluded that the concept is promissing, yet that more work is needed to understand orbit stability and related issues, in order to further progress towards an engineering tool

The Torsion Handbook, Understanding and addressing torsion in the handling of cables, umbilicals and flexible pipes

This document was a deliverable in the Torsion JIP (Joint Industry Project) carried out by SINTEF from 2018 to 2022 on behalf of Aker Solutions, Equinor, Hellenic Cables, NKT, Petrobras and Ørsted. It will be freely available for download here, from 18th April 2023. The document gives a comprehensive description of why torsion appears when handling (producing, transferring, loading out, installing, and in some cases operating) power cables, umbilicals and flexible pipes. The document also provides a first generation of approaches to design products and handling operations to prevent torsion related issues

EspyInsideFunction.jl-extracting intermediate results from numerical functions

EspyInsideFunction allows to write software in the Julia programming language Julia (2017) [1] to make the value of variables within a function’s local scope — variables that are neither arguments nor return values, available to the caller. This is relevant for functions within a solution process (e.g. a function which return value is to be minimized by some iterative scheme). In such a setting it is natural to tailor the function’s interface to the solution process. However, internal results within the function, while not relevant to the solution process, may be wanted output from the analysis. The package allows to write such a function with an interface tailored for the solution process, and then uses meta-programming to create a second version of the function, with a modified interface, which can be called to extract relevant intermediate results.publishedVersio

Novel computational tool for efficient structural analyses of geothermal wells

In geothermal energy, a huge energy potential lies in hydrothermal reservoirs close to magma where ultra-high temperature fluids (>450 C) can be harnessed. Well casing system needs to be properly designed to ensure its integrity during its service lifetime. There currently exist neither any commonly accepted design tools nor standards regulating geothermal well design under such conditions. In this study a novel tool, Casinteg, was developed for structural analyses of geothermal wells. The tool is intended to bridge the gap between simplified analytic solutions and complex FE-based commercial software. The reliability and efficiency of the constitutive models implemented in Casinteg were verified in comparison with Abaqus. Casinteg's capability for structural analyses of full geothermal wells was preliminarily investigated, using IDDP-1 well as a case study. The calculated stress in the production casing was in a good agreement between Casinteg and Ansys models, while the computational time of Casinteg simulations was within minutes. Further developments are still needed. However, preliminary results were encouraging and have demonstrated the benefit of Casinteg for efficient structural analyses of full geothermal wells.publishedVersio

Estimation of top tensions in mooring lines by sensor fusion

The paper describes a sensor fusion method that provides reliable, uninterrupted and bias-free estimates of the top tension in a mooring line. The method exploits the geometric nonlinearity of mooring systems installed in shallow to moderate water depths: a change of line length (due to winching) affects the local dynamic stiffness of the mooring line. Based on measurements of fairlead displacements and of the dynamic part of the top tension, the line length and true (unbiased) mean tension can be inferred. The method combines the use of (1) a classical kinematic observer to derive fairlead motions, (2) the compression of the recent history of fairlead motions to a few parameters, (3) a bank of neural networks, each network modelling the response corresponding to a given line length/static tension, and (4) a heuristic approach to selecting the most promising model among the candidates. One major advantage of the method is its sparsity, making it computationally efficient so it can be applied both offline, on large sets of recorded historical data, and online running on lightweight embedded hardware. The paper presents in detail each component listed above, and the method as a whole is verified on a realistic case. Given that enough excitation is present, the estimator was found to converge towards the true value of the tension, and to cope well with transient conditions such as winching operations, and with the presence of oceanic current.publishedVersio

Analysis of S–N data for new and corroded mooring chains at varying mean load levels using a hierarchical linear model

Results from full scale fatigue tests of offshore mooring chains are analyzed. The data set includes new and used chains, tested at a variety of mean load levels. The used chains have been retrieved after operation offshore and include samples with varying surface conditions, ranging from as-new to heavily corroded. Based on a parameterized S–N curve intercept parameter, the effects of mean load and chain condition are estimated empirically by regression analysis. A hierarchical linear model is used, to account for and quantify correlations within subsets of the data. The choice of grouping criterion for the hierarchical model is discussed, and assessed based on the current data. Results show that the mean load and corrosion effects are both significant. Differences in the fatigue performance of new versus used chains are quantified and discussed.publishedVersio

Torsion in Flexible Pipes, Umbilicals and Cables Under Loadout to Installation Vessels

Operations where a flexible pipe, umbilical or cable is loaded out from an on-shore spool to the hold of an installation vessel can cause a build-up of torsion. In unfavourable cases, the torsion has been known to cause spiralling or various forms of damage to the tensile armour. This paper presents a vocabulary for the description of torsion. It then gives a short review of design codes, enumerates known failure modes (some of which have not always been identified as torsion related), and discusses the mechanisms of torsion generation, with an emphasis on the effect of internal friction. It concludes with some ideas on torsion prevention.acceptedVersio

Modeling hydrogen transport and hydrogen-induced embrittlement

This document provides the theory manual and user manual for two finite elements for the modeling of hydrogen-induced embrittlement of metallic materials. The cohesive zone element (CZE) allows to simulate the creation of new surfaces and the corresponding absorption of energy. The absorption of energy is made a function of the hydrogen concentration. The volume element (DIFEL) accounts for mechanical deformation, the transport of hydrogen, and the kinetics of trapping and detrapping.publishedVersio

Modeling hydrogen transport and hydrogen-induced embrittlement

This document provides the theory manual and user manual for two finite elements for the modeling of hydrogen-induced embrittlement of metallic materials. The cohesive zone element (CZE) allows to simulate the creation of new surfaces and the corresponding absorption of energy. The absorption of energy is made a function of the hydrogen concentration. The volume element (DIFEL) accounts for mechanical deformation, the transport of hydrogen, and the kinetics of trapping and detrapping

EspyInsideFunction.jl-extracting intermediate results from numerical functions

EspyInsideFunction allows to write software in the Julia programming language Julia (2017) [1] to make the value of variables within a function’s local scope — variables that are neither arguments nor return values, available to the caller. This is relevant for functions within a solution process (e.g. a function which return value is to be minimized by some iterative scheme). In such a setting it is natural to tailor the function’s interface to the solution process. However, internal results within the function, while not relevant to the solution process, may be wanted output from the analysis. The package allows to write such a function with an interface tailored for the solution process, and then uses meta-programming to create a second version of the function, with a modified interface, which can be called to extract relevant intermediate results