bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time Domain Fatigue Analysis of the Pin for Offshore Bridges Considering the Nonlinear Effect of Sliding Connections
Authors: Dong Wenbin , Scherf Ingar , Sigurdsson Gudfinnur 
Published: October 2017

A bridge between platforms needs to operate safely and continuously over its lifecycle. This paper focuses on the fatigue assessment of the bridge pin connection due to relative movements between platforms. A nonlinear time domain stochastic fatigue analysis of the pin connection in a bridge in the North Sea using a combined model of the jacket platforms and the interconnecting bridge is presented. The fatigue life is compared to the fatigue life from a linear frequency domain stochastic analysis.
The facility has been in operation for more than 40 years and the operator requested an update of the inspection plans for the bridge. An RBI analysis has been done according to [1] based on fatigue results from wind gusts and relative movements. Regarding the fatigue assessment due to relative movements there are uncertainties related to selection of the friction coefficient. It was assessed that a friction coefficient of 0.4 is slightly conservative in this case. The fatigue life of the pin was calculated based on a linear frequency domain stochastic analysis, assuming that the bridge was fixed at both ends and this was considered reasonable conservative for fatigue estimation. Efforts have been made in the study presented here to assess the conservatism through a nonlinear time domain stochastic fatigue analysis. The sliding connections of the bridge are simulated by nonlinear springs. The effects of assuming different friction coefficients and different nonlinear spring models for a certain friction coefficient on the fatigue damage of the pin are investigated by a sensitivity study. The fatigue lives of the pin thus computed for a series of short-term sea states for the different assumptions for the friction coefficient and the nonlinear spring model are then compared to the result from a corresponding frequency domain approach.
Scale Effects Influence on the Fatigue Crack Growth of an Offshore Steel
Authors: Micone Nahuel , De Waele Wim 
Published: October 2017

Offshore tubular members are manufactured in a very wide thicknesses and diameters. The design curves considered for the fatigue design of such structures are assessed based on testing small scale laboratory specimens. A correction factor is applied to account for differences in thickness and weld geometry. However crack growth behaviour in tubular elements is complex and it is not totally clear if this can accurately be represented by testing small-scale coupons. Large scale fatigue tests aim to characterize the fatigue behaviour in a more realistic manner. However conducting such tests is very expensive. Hence, a medium scale strip type specimen with dimensions between small scale standardized specimens and a full pipe is designed. It has the same curvature and thickness as the pipe from which it is extracted and a quasi semi-elliptical notch is introduced. It is hypothesized that can account for most of the scale effects. Furthermore it can be tested in conventional test rigs at rather high frequencies.
With the objective of quantifying the scale effects between standardized ESE(T) specimens and medium size coupons, a series of crack growth based tests on a high strength offshore steel are carried out. By comparing the corresponding da/dn-ΔK curves it will be possible to evaluate possible scale effects.
Development of the Next Generation Thermoplastic Hose Umbilical
Authors: Rutherford Alan , Dobson Alan 
Published: October 2017

Thermoplastic Control Umbilicals, as shown in Figure 1, have been deployed subsea for decades globally. Typically, these have been installed in harsh dynamic environments such as the North Sea, very cold environments such as the North Atlantic and very warm environments such as the coastal waters of Middle East and Asia Pacific. The inherent fatigue and corrosion resistance of the functional components can offer significant operational advantages while umbilical make-up and manufacturing process can offer significant cost and schedule advantages.
As the industry has moved into deeper warmer water regions since the late 1990’s, such as the Gulf of Mexico and West Africa, some of the limitations of conventional thermoplastic umbilicals, such as inherent collapse resistance or design working pressures became barriers for the adoption of the technology.
In recent years there have been many new polymer materials developed that provide increased tenacity and temperature stability which subsequently have enabled an evolution in thermoplastic hose technology. This has facilitated the development of the next generation of high temperature, high pressure, collapse resistant hoses that can be deployed in deep water.
This paper defines the testing carried out on the constituent parts of the composite hose primarily focusing on the liner and details typical modes of degradation associated with high temperature, pressure or tension. The new material technologies will be benchmarked against conventional materials traditionally used in less aggressive environments.
This paper will detail the results of the development program aimed at optimising the hose design process and implementing the cutting edge materials in order to qualify a robust series of hose designs qualified to the stringent requirements of ISO 13628-5 [1].
The paper will also detail the development of the new termination coupling which has been developed in parallel with the next generation hose and which provides a reliable and robust method of coupling the hose to the subsea control system or joining two lengths of hose together.
The paper will conclude with a case study comparing a typical deep water installation of a steel tube umbilical with an equivalent thermoplastic umbilical, highlighting the benefits of the new thermoplastic umbilical designs.
Effect of Coal Loading Conditions on Elastic Behavior of Large-Scale Floating Transshipment Station (LFTS)
Authors: Eto Hiroaki , Sato Chiaki , Masuda Koichi , Ikoma Tomoki , Kubota Mitsuru , Kishida Tomoyuki 
Published: October 2017

Japan imports coal from Indonesia, the main coal supplier in the Asia-Pacific region. Effective and efficient movement of coal down the Markham River in East Kalimantan, Indonesia, and onto bulk carriers is challenging because the river is shallow and generally cannot accommodate bulk carriers. The primary transportation system comprises small barges that are shuttled back and forth between the inland barge ports along the river and bulk carriers offshore. This system is very time-consuming.
This paper proposes a large-scale floating coal transshipment station (LFTS) for loading, storing, and offloading coal. It will act as a relay base for barges and bulk carriers. Installing an LFTS offshore from East Kalimantan is expected to improve coal transport productivity. The proposed LFTS can store 5 times the capacity of one bulk carrier and can accommodate 2 bulk carriers at the same time during offloading. The LFTS is compartmentalized by bulkheads to segregate coal according to quality. This paper discusses LFTS static stability and its elastic deformation characteristics during coal loading operations.
In this study, linear potential theory and the finite element method (FEM) were used to analyze the LFTS static hydroelastic motion. Due to the compartments, coal loading conditions can vary significantly and affect the local static deflection, so we modeled the overall deformation and rigidity under various operational scenarios. The results were compared to the allowable material stress to identify conditions that will produce material failure. Moreover, we evaluated operation in the shallow Kalimantan River, since the weight of loaded coal deepens the LFTS draft, reducing the clearance between the LFTS and sea bed. We found that this reduced clearance and large added mass impact the natural frequency of the LFTS.
Ice Load Calculation on Semi-Submersible Platform
Authors: Cahay Marc , Roberts Brian A. , Sadouni Sami , Béal Pierre-Antoine , Septseault Cyril , Mravak Zoran , Benoit Claudie 
Published: October 2017

In 2012 TechnipFMC, Cervval and Bureau Veritas initiated a common development program to offer a new tool for the design of offshore structures interacting with ice combining a variety of models and approaches.
This numerical tool called Ice-MAS (www.ice-mas.com) is using a multi-agent technology and has the possibility to combine in a common framework multiple phenomena from various natures and heterogeneous scales (i.e. drag, friction, ice-sheet bending failure, local crushing and rubble stack up). It can simulate the ice loadings of a drifting ice-sheet (including ridge or not) on predefined structures such as conical, cylindrical, sloping & vertical wall, artificial islands or more complex geometry by user input file like semi-submersible floaters with pontoon and columns allowing to obtain the detailed results on the different parts of the structure.
This paper presents the overall functionalities of Ice-MAS and the different possibilities to model a semi-submersible floater. It will focus on the results obtained for different geometries subject to ice sheet loading through different incidence angles. The issues related to the anchoring of the platform are addressed in a simplified way.
Study on Ship Manoeuvering in Adverse Sea State
Authors: Guo Bingjie , Ruth Eivind , Austefjord Håvard , Bitner-Gregersen Elzbieta M. , Gramstad Odin 
Published: October 2017

IMO introduced Energy Efficiency Design Index (EEDI) to regulate the greenhouse gas (GHG) emissions from ships. The cheapest and easiest way to fulfil the EEDI requirement is to reduce installed power for most ships. Therefore, it has raised serious concerns that some ship designers might choose to lower the installed power to achieve EEDI requirements and not consider ship safety in a satisfactory way. This could induce ship manoeuvrability and safety problems in adverse seas, which needs urgent investigations on minimum power to maintain ship manoeuvrability in adverse sea.
A time domain code ‘Waqum’ has been developed based on the force superposition of unified theory to study the minimum required power for maintaining ship manoeuvring ability in adverse sea states. The code combines sea-keeping and maneuvering equations, together with an engine model to predict ship responses in waves. The code can help us to study ship responses in transit situation and give us better insight into ship maneuvering ability in adverse sea states. In order to improve the simulation speed, the time domain code does not calculate all the hydrodynamic forces directly. Thus, some precalculations should be done for some force components before launching the simulation for a new ship. Therefore, the methodology and accuracy of each force component will influence the accuracy of the manoeuvring code. The methodology for determining each force component will be discussed, especially the identification of maneuvering derivatives based on CFD simulations. The code has been improved recently, and another rudder model has been implemented. Further, the the code with new rudder model is verified in calm water. The code’s ability to capture ship maneuvering in waves is also demonstrated.
Numerical Investigation on Wave Induced Vortex Dynamics Around Cylindrical Pile With Considering Varying Keulegan-Carpenter Number
Authors: Mohammad Beigi Kasvaei M. , Kazeminezhad M. H. , Yeganeh-Bakhtiary A. 
Published: October 2017

Three-dimensional numerical simulation of regular waves passing over cylindrical monopile has been conducted to investigate the vortex dynamics. To do so the rectangular wave flume and monopile is modeled on a solver, available in the open-source CFD toolkit OpenFOAM®. The solver applied RANS equations with VOF method for tracking free surface. Model validation has been done by comparison numerical results with the experimental ones and admissible agreement has been seen. Computations have been done for three cases with different pile diameters consequently for different Keulegan-Carpenter numbers (KC).
The vorticity field around the pile was investigated as well as vortices by means of Q criterion. It was seen that by increasing KC number, horseshoe vortices will be formed and vortex shedding will be happened. Moreover, Bed shear stress around the pile has been extracted and it has been seen that, the bed shear stress is influenced by KC value which result of existence of horseshoe vortices and vortex shedding.
Observation of Subsea BOP Response From Field Measurements and Reflections on Conductor Design Challenges
Authors: Holden Harald , Holm Heidi Gryteland , Zhang Youhu , Smith Victor , Næss Randi 
Published: October 2017

Subsea exploration well systems are subjected to complex loading due to vessel motion and hydrodynamic forces on the riser. In design of the wells, both the ULS/ALS design under extreme loading and fatigue design under operational loading are heavily dependent on the soil support along the uppermost 20 m of the conductor casing. In today’s practice, design of the conductor against extreme loading is typically performed using the soil reaction curves (p-y springs) recommended in API RP 2GEO [1].
In recent years, 4Subsea have been monitoring the BOP and riser responses during exploration drilling campaigns for Lundin Norway. The purpose of these monitoring campaigns is to track the performance of the wells with time, based on integrity parameters such as well stiffness, BOP resonance frequency and BOP motion rotational depth. This paper summarizes the monitoring results from seven well locations in the North Sea and the Barents Sea. The observed well response is compared with up-front design analyses. The discrepancy between up-front design analyses and the observed performances is discussed in light of the uncertainties associated with the geotechnical input parameters and soil reaction models. The purpose of the paper is to reflect on the challenges faced with exploration well design and highlight areas that improvements can be made.
An Experimental Assessment of the Hysteresis Behavior of Umbilical Cables Under Cyclic Traction
Authors: Santos Caio C. P. , Pesce Celso P. , Salles Rafael , Franzini Guilherme R. , Gonçalves Rodolfo T. , Morini Rafael 
Published: October 2017

Umbilical cables are composed by several internal components helically disposed and externally protected by an outer polymeric sheath. With these elements wound in different directions, internal friction is a well-known structural feature, originating hysteretic loops when umbilicals are subject to cyclic loads. On the other hand, polymeric materials represent a substantial part of an umbilical composition. These materials present a viscoelastic character, introducing a second energy dissipation mechanism to these flexible structures. Therefore, this paper aims to assess the hysteresis phenomenon observed under different periodic axial loading conditions.
The study is based on experimental campaigns carried out with two umbilical cables, proposing and testing a new experimental methodology based on standard instrumentation combined with optical tracking measurement. The hysteresis loops are evaluated considering ‘slow’ and ‘very-slow’ axial cyclic loads. The results indicates that an equivalent viscoelastic damping behavior could be adopted to model the umbilical cable response under ‘slow’ axial cyclic loads. In contrast, the ‘very-slow’ tests indicate that the energy dissipation process is dominated by a dry friction mechanism.
Wear of Outer Sheath Materials in Flexible Pipes: Testing Methodology
Authors: Øren Einar , Larsen Marit , Kvilhaug Frode Andres , Melve Bjørn 
Published: October 2017

Outer sheath wear of polymers in flexible risers has been experienced with risers anchored with guide tubes and bellmouths. In addition, wear damages have been observed at touch down points and on subsea arch support structures.
A wear test methodology was developed with the purpose to mimic the observations from pipes in operation. The test apparatus used was similar to a pin-on-disc measurement method, but with emphasis on reproducing the exact environment and temperature.
Comparative tests have been done between different materials, and for some conditions the differences are significant.
Effect of Wind Loads and Damping on Heading Stability of FPSOs
Authors: Zangeneh Razieh , Thiagarajan Krish P. , Cameron Matthew 
Published: October 2017

Tanker vessels used for offshore oil production and storage are kept at station by turret mooring systems, enabling the vessel to weathervane in the direction of dominant environmental loads. The disruption of heading equilibrium for a turret-moored tanker was predicted by experiments and numerical studies. A vessel was observed to lose control in head sea condition, wherein for wavelength from 0.73 < λ/L < 2 (L-ship length) the model drifted to a large angle of 45–60 degrees (Thiagarajan et al. 2013). Previous numerical analyses conducted by the authors identified that this heading drift reduced remarkably in the presence of wind. This finding is confirmed by an experimental study and reported in this paper.
A geometrically scaled down version of a turret-moored FPSO at 1:120 scale of a prototype VLCC was tested at the Alfond W2 Wind & Wave Ocean Engineering facility of the University of Maine. This lab is a unique facility equipped with a high-performance wind machine over a multidirectional wave generator, and can create regular or random sea-states with wind speeds up to 7 m/s. The tests reported here were conducted with regular waves under two wind speeds (12 and 25 m/s full scale). It was observed that the presence of an initially bow wind can minimize the heading instability. The reason for this observation is described by analyzing the effect of the wind induced moments on the equilibrium condition.
Free-decay tests were also conducted to investigate the contribution of the wind damping to the total damping. Measured results show that in the presence of wind, the damping values are higher than those estimated due to hydrodynamics only. It also has been discussed that this wind induced damping on FPSOs, can result in smaller heading angles. From this study, it is concluded that the wind can play a large role in the station-keeping dynamics of the moored-tankers.
Considerations on Numerical Procedure for Stick-Slip Analysis of Drill String
Authors: Katsui Tokihiro , Inoue Tomoya , Izutani Kenta , Nagaishi Yuhi , Rheem Chang-Kyu , Matsuo Miki Y. 
Published: October 2017

Stick-slip is one of the typical phenomenon which is observed in offshore drilling and considered as a critical problem for the drilling operation. The stick-slip makes a large fluctuation of drill bit rotation, even though the top of the drill pipe is rotating at a steady velocity and sometimes causes the damage of the drill bit. Additionally, it leads a crushing of the sediment layer which is a big problem especially for the scientific drilling [1][2][3]. The main purpose of the scientific drilling is to correct high quality core samples of sediment layers under the seabed. However, once the stick-slip occurs, it makes difficult to recover a high-quality sediment layer core sample. Therefore, it is necessary to detect the occurrence of stick-slip and its fundamental characteristics such as oscillation periods and amplitudes by simulation with the aid of surface drilling data, which can be monitored during the drilling operation to mitigate or prevent stick-slip. It would be advantageous to identify the characteristics of the stick-slip from the surface drilling data.
The past study [4][5][6] investigated a numerical method to analyze the stick-slip by solving the NDDE (Neutral Delay Differential Equation) which is derived from torsional vibration equation. A small-scale model experiment was conducted in a water tank to observe the stick-slip phenomenon, and the result from the analytical model is evaluated with that obtained from the experiments.
In this study, the numerical model is applied for the stick-slip analysis not only of the drill pipe model but also the actual drill pipe in operation. The solutions of the NDDE is depend on not the initial value but the initial history of the solution, because NDDE contains a delayed function term. Especially, the initial history settings have much effect on the numerical solution of NDDE in case of the actual drill pipe. Additionally, to solve the NDDE for stick-slip analysis, we must set some model parameters concerned with the frictional torque on drill bit. The present study investigated the effects of the initial history and the model parameters settings on numerical solutions in detail and presented an procedure to determine the appropriate settings of the initial history and the model parameters by reference to the measured top drive torque.
Explosion Risk Analysis on the Liquefaction Process of LNG-FPSO at the PFD Level
Authors: You Wonwo , Park Jaeuk , Lim Youngsub 
Published: October 2017

The potential risk of an offshore processing facility is the major important part in the oil and gas industry due to its limited space causing difficulties in evacuation. An offshore processing facility is normally exposed to flammable oil and gas in the operating phase. Especially, uncontrolled hydrocarbon leaks or ruptures of the equipment present main threats. These failures can lead to fire and explosion disaster. Some studies have proposed fire and explosion assessment methodologies and made fire and explosion assessment tools. These tools can provide risk assessments result using physical effect modelling software and following the related standards or engineering practices according to accident scenarios. Nevertheless, existing fire and explosion assessment procedures are still not comprehensive enough to applicate a specific process due to its complexity and are not clear which stage in a project is appropriate for applying it.
This paper focuses only on explosion accidents and discusses the development of an explosion risk analysis procedure possible to apply at process flow diagram (PFD) level. The explosion risk analysis procedure using PFD has 6 steps; modelling of a process, scenario selection, inventory calculation, frequency calculation, consequence modelling and risk estimation. It starts at modelling of a specific process using process simulation software, HYSYS. The process modelling can be optimized by the existing methods and finally provide the PFD for the specific process. In the scenario selection step, the information required to perform a risk analysis is identified. The inventory calculation conducts to calculate the inventory of a defined segment after sizing of the equipment in the PFD. The frequency calculation consists of leak frequency and ignition probability. The leak frequency can be calculated with historical database and the ignition probability can be calculated with a specific ignition probability model. The consequence modelling is conducted by using physical effect modelling software, PHAST. It can provide the distance to specified overpressure. Finally, at the risk estimation step, the risk results are evaluated. This procedure can help to applicate a specific process easily and provide explosion risk assessment tool at PFD level.
This paper conducts the case study for a liquefied natural gas floating production storage offloading (LNG-FPSO) which is one of the representative offshore processing facilities. Especially, a natural liquefaction process in a LNG-FPSO, which liquefies the processed natural gas to store in a storage tank of a LNG-FPSO, is the most important process in terms of cost and risk. In the situation the most of ongoing or prospective projects for LNG-FPSO adopt dual mixed refrigerants (DMR) liquefaction process, the representative configurations of the DMR liquefaction processes are evaluated and compared. It can help decision making through providing which configuration has an advantage in terms of explosion accidents.