bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hyperbaric Testing of an Alternative Approach to Remove Carbon Dioxide From Underwater Life Support Equipment
Authors: Nuckols M. , Kolaczkowski S. , Awdry S. , Smith T. , Thomas D. 
Published: September 2014

Traditional CO2 absorption methods for underwater life support equipment use alkali metal hydroxide chemical beds — mostly calcium hydroxide — that have been shown to have poor absorption efficiencies at cold temperatures, and must be replaced at considerable trouble and expense on a frequent basis. With chemical utilizations as low as 20% in water temperatures of 2°C, these hydroxides do not lend themselves to applications requiring extended durations in cold water due to the inability to carry sufficient quantities of expendables. A joint research effort between Duke University and the University of Bath has verified the feasibility in laboratory trials of an alternative carbon dioxide removal method that intimately mixes seawater with breathing circuit gases within a packed bed of Dixon rings. Based on the results of these laboratory trials, two multi-path scrubber prototypes were designed and fabricated for unmanned testing. In March 2013, the hyperbaric performance of these prototype scrubbers was characterized over a wide range of gas and water flow rates when operating the scrubbers in counter-current (water flowing in the opposite direction as gas flow) and co-current (water flowing in the same direction as gas flow) fashion. Significant findings from these tests included the following:
• Both scrubber prototypes were found to be capable of delivering exit CO2 levels below 0.5 vol% (surface equivalent) at respiratory rates up to 22.5 liters per minute and at depths ranging from 0 to 40 meters of seawater (MSW).
• Negligible collateral O2 absorption was observed at surface pressure (exit O2 levels were typically above 20.2 vol%), and exit O2 levels were typically above 18.4% during testing at 10 MSW.
• At surface pressure, both prototypes had significantly lower breathing resistances than design goals established by the U. S. Navy.
Advantages of Using a Time-Domain Approach for Dynamic Positioning (DP) Pipelay Studies
Authors: Armaoğlu Evren , Monti Paolo 
Published: September 2014

Normally, the DP capability of a vessel is calculated through the use of static force equilibrium programs in which the dynamic effects are either not taken into account or taken into account by empirical load amplification factors. However, competitive and safe S-laying of large diameter pipelines in deep waters lead to large and long pipe lay vessels for which DP requirements are demanding. The power/propulsion requirement of the vessel needs to be considered from an early stage especially when accounting for the pipe laying equipment demands. This imposes a need for detailed dynamic analysis of the lay vessel. This analysis needs to include the slow drift oscillations counteracted by DP and the analysis in entirety needs to ensure the pipe string integrity is maintained.
To this purpose Saipem developed in-house a time-domain simulator (FIPLA – Fully Integrated Pipe LAying) that employs all environmental forces (i.e. wind, wave, current) as well as the pipe tension on the vessel. It is used to assess the DP performances and laying capabilities of pipe lay vessels in harsh dynamic environments as well as critical areas for operations. The software can also be used to assess the performance of the vessel in case of failure of thrusters, power generators or bus bars, study DP Control System improvements, and assess the interaction between vessel, tensioner and pipe in deep and shallow waters.
This paper focuses on the advantages of using dynamic simulations as an enhancement to the static DP capability charts, to produce detailed information for the DP Operator (DPO) in terms of setting of the DP parameters and to analyze critical laying events. This information can be used together with the weather forecast and can help getting the best performance out of the DP system in harsh environments, reducing downtime, improving operability and ensuring a safe operation.
Monohull Dynamics During Heavy Lift
Authors: Vu Khac Kien , Zhang Yang , Deng Xiaofang , Yang Zhibin 
Published: September 2014

The dynamics of offshore heavy lift remains complex due to the interaction between the monohull construction vessel and the lifting object under the challenging environmental loads. This system becomes even more difficult to judge by common sense as the lifting weight offshore is usually above the motion reference point (the center of flotation of vessel), which makes the coupled system more unstable than the vessel without the lifting weight. This study proposes an analytical formula using the double pendulum, based on the Euler-Lagrangian equations, to explore the insight of the heavy lift dynamics. The effect of initial lifting condition is investigated to explain different possible outcomes for lifting similar weights. A range of vessel stiffness (GM), lifting heights and weights are considered in the parametric study for a better understanding of the coupled dynamic behaviour. While such analytical model is convenient for the understanding of the system mechanism, it is difficult to capture the effect from the wave loading. Therefore numerical models are used for this purpose. A comparison between the analytical model and the numerical model, performed in the frequency domain, evaluates the quality of ship motion response analysis performed by the numerical model. Results of these works will be useful in development of offshore crane curves for heavy lift offshore.
Apart from the theoretical formulation, several real time ship instrumentation records including the ship motion and the crane hook load have been collected and investigated in this paper. The offshore instrumentation records provide a valuable benchmark to calibrate the numerical model or to accumulate “experience” for future projects. Challenges in such process are depicted and possible solutions are discussed. To make the comparison a fair “apple to apple”, the major difficulty arises from the “unknown” environment itself, where wave is not always measured and operation relies heavily on weather forecast and “experience”. There are also limitations in offshore measurement itself. Possibility of using the ship motion as the indicator is explored for decision making (to lift or not to lift). The paper develops a practical approach for obtaining reasonable numerical results in the engineering office and investigates scientifically sound interpretation of the ship motion time history onboard towards a safe offshore heavy lift.
Prediction of Irregular Motions of Free-Fall Lifeboats During Drops From Damaged FPSO
Authors: Tregde Vidar , Nestegård Arne 
Published: September 2014

A Free Fall Lifeboat (FFLB) which is evacuating from a damaged host in storm conditions must to be able to safely run away from the host. For a safe evacuation, the FFLB must first of all avoid irregular motion (“log dive”), and secondly resurface at a sufficient distance away from host (headway) to be able to run away. The design standard [1] requires a controlled motion trajectory for the FFLB in waves.
A drop simulator for random drops of FFLBs from a floating host in storm conditions, intact or damaged has been developed. Time histories of the host motions are generated and random drops of the FFLBs are done during three hour duration of each sea state. The FFLB point of impact in the wave is identified and the local wave height, wave length and hit point in the wave cycle is found for each of the impact points.
A structured database with results from a large number of Computational Fluid Dynamics (CFD) simulations has been made for a specific FFLB. In this CFD screening process the lifeboat has been dropped with variations in wind and waves, as well as varying conditions of host during launch. This database forms the basis for a regression analysis used to estimate responses for each drop of free fall lifeboat found from the drop simulator.
The present study proposes a definition and a method to identify irregular motions for FFLBs, and this definition is used as a motion indicator in the regression analysis. By using the proposed motion indicator, the regression analysis provides percentage of acceptable vs. non-acceptable motion trajectories for a given intact or damaged host during a storm condition. The worst conditions are found, and can be used for further analysis of headway, i.e. the ability of the FFLB to escape from the host after resurfacing.
The Effect of Coverage Length and Density on the Performance of Fairings
Authors: Allen Don W. , Liapis Stergios 
Published: September 2014

While the application of fairings can both increase a tubular’s fatigue life and decrease a tubular’s drag, it is not always possible or economical to fully cover a tubular with fairings. Aside from the desire to minimize the cost of VIV suppression by only covering the necessary portion of a tubular’s span, the presence of connectors, anodes, and other appurtenances can restrict the ability to install fairings over the entire tubular’s length. The result is that it is critical to understand how much of a tubular’s span should be covered with fairings and the effect of partial coverage on the overall suppression performance, and drag reduction, of the fairings system.
This paper utilizes data from a two similar test programs to examine the effects of coverage length and density on the performance of fairings. The results show that the location of the fairings has a substantial effect on both the local and global response of the tubular. In practical terms, having fairings present in the high current region can suppress VIV in both the high current and low current regions of the tubular.
Determination of the Effect of Second Order Motions of Moored MODU on Wellhead Fatigue
Authors: Williams Dara , Ashton Patrick 
Published: September 2014

As has been noted in industry publications and conferences in the recent past the use of more modern deepwater capable 5th and 6th generation semisubmersible drilling rigs in relatively shallow water applications (when compared to design water depth) is likely to become more commonplace. Water depths of 500m or less will necessitate the use of mooring systems in order to maintain position close to the well centre whilst drilling. For fatigue assessments of moored MODUs, the current industry practice to estimate fatigue damage in the drilling riser and the wellhead, using global riser analysis techniques, is to consider both wave and VIV fatigue effects. Standard wave fatigue analysis considers two key response parameters, firstly the impact of the hydrodynamic loading on the riser joints due to drag forces, inertia and added mass effects, and secondly the effects of vessel motions on the riser system and wellhead loading. Standard practice for wave fatigue analysis is to consider only first order motion effects as described by the vessel RAO (response amplitude operator). However, for a moored MODU low frequency (100s-200s period) vessel response can have a significant impact on the overall vessel motions.
The actual response and magnitude of MODU motion will be influenced by the size and displacement of the vessel in addition to the configuration of the mooring system. First order lateral motions for a semisubmersible tend to increase as wave period is increased and therefore at lower periods first order motions can be quite low. However, the opposite can be said of wave drift forces that contribute to second order response. Although the wave drift forces are largest for lower wave periods, these low period drift forces have a significant influence on the resulting long period second order response of a moored MODU. This has important implications for drilling riser and wellhead fatigue analysis as in many cases the critical seastates for fatigue damage are low period seastates with a large number of occurrences. Thus the current global analysis techniques for fatigue calculations may lead to an underestimation of fatigue damage contribution from low period seastates.
The purpose of this paper is to present the key conclusions and findings of a study carried out in order to determine the effects of low frequency moored MODU motions on wellhead fatigue. These results are derived from a case study of a moored 6th generation semi-submersible drilling vessel in 500m water depth.
Force in the Connection Line for a Wave Energy Converter: Simulation and Measurement Experimental Setup
Authors: Hai Ling , Svensson Olle , Castellucci Valeria , Lejerskog Erik , Waters Rafael , Leijon Mats 
Published: September 2014

In order to capture ocean wave energy and transform it into electric energy, Uppsala University has developed a point absorber wave energy converter (WEC) for electricity production. For a better understanding of a torus shaped buoy’s performance, this paper conducts a force analysis under linear conditions, to investigate the hydrodynamic characteristic and line force differences between the torus buoy that is going to be deployed, and two similar cylindrical buoys. The result reveals the line force from this torus buoy is roughly 5% larger than from cylindrical buoys for the most energy dense wave climate in Lysekil test site, and negative added mass phenomena won’t have a significant impact for the line force.
To measure the line force, a force measurement system has been designed. A detailed description is given on the design of the 500 kN force measurement system, and the major differences compared with former force measurement systems. Onshore test result has also been presented. With the force measurement experiment, hydrodynamic analysis for torus buoy can be validated when the system performs linearly, and extreme force for storm weather can be monitored to provide information for future WEC structure’s mechanical design.
Estimation of Storm Peak and Intra-Storm Directional-Seasonal Design Conditions in the North Sea
Authors: Feld Graham , Randell David , Wu Yanyun , Ewans Kevin , Jonathan Philip 
Published: September 2014

Specification of realistic environmental design conditions for marine structures is of fundamental importance to their reliability over time. Design conditions for extreme waves and storm severities are typically estimated by extreme value analysis of time series of measured or hindcast significant wave height, HS. This analysis is complicated by two effects. Firstly, HS exhibits temporal dependence. Secondly, the characteristics of HSsp are non-stationary with respect to multiple covariates, particularly wave direction and season.
We develop directional-seasonal design values for storm peak significant wave height (HSsp) by estimation of, and simulation under a non-stationary extreme value model for HSsp. Design values for significant wave height (HS) are estimated by simulating storm trajectories of HS consistent with the simulated storm peak events. Design distributions for individual maximum wave height (Hmax) are estimated by marginalisation using the known conditional distribution for Hmax given HS. Particular attention is paid to the assessment of model bias and quantification of model parameter and design value uncertainty using bootstrap resampling. We also outline existing work on extension to estimation of maximum crest elevation and total extreme water level.
Fatigue Failure Analysis of Fillet Welded Joints Used in Offshore Structures
Authors: Ringsberg Jonas W. , Anvari Majid , Djavit Djan Eirik , Strande Erik 
Published: September 2014

This paper presents a comparison made of different fatigue calculation methods used in the maritime industry today, with the aim of having a higher control of a fatigue failure site. To provide an overview of the different fatigue calculation methods, a comparison study was performed, as well as a local weld parameter study for two typical fillet welded joints. The two methods used for this study were the structural hot spot and effective notch stress method. Two fillet welded joints were provided by Aker Solutions MMO AS, Bergen, Norway. The first joint is a rectangular hollow section from a davit, built as a truss. The second model is a part of a K-joint from a semi-submersible (Aker H3 design). Both joints were analysed using fine 3D finite element models.
The two different fatigue life calculation methods yielded different fatigue lives for the weld toe, with inconclusive results regarding their conservatism which is discussed in the paper. An increased weld toe radius gave a higher fatigue life for the weld toe, while the larger weld size increased the fatigue life in the weld root. Any weld size effect regarding fatigue life in the weld toe could not be established. Based on the effective notch stress method calculations, there was an indication of weld root failure for the K-joint of the drilling unit. Fatigue life improvement methods only increasing weld toe fatigue life are not recommended based on these results.
Numerical Modeling of Released Subsea Buoyancy Module for Reliable Prediction of its Trajectory and Velocity Using Transient CFD Analysis for Risk Assessment
Authors: Jia David , Agrawal Madhusuden , Malachowski Jim 
Published: September 2014

Buoyancy modules are widely used in offshore and subsea fields, such as on pipelines, risers, umbilicals, and ROVs, etc. in operation and installation. Accidental release of subsea buoyancy modules due to broken or damaged parts may pose a potential risk and hazard to offshore vessels, floating platforms and risers & surrounding umbilicals. A released buoyancy module rises and may collide with any floating structures or pipes above it. For offshore and subsea field development, it is important to assess such potential risk to offshore vessels, floating platforms, and risers & umbilicals around them. Accurate prediction of the trajectory and the impact speed of the released buoyancy module is the key component for risk assessment in offshore and subsea field development. This paper presents a Computational Fluid Dynamics (CFD) solution for prediction of the trajectory and velocity of the released buoyancy modules from subsea. Six Degree of Freedom (DOF) rigid body motion of buoyancy module is modeled using an efficient moving mesh approach in transient CFD simulation. The effect of ocean currents at different water depths is considered in the motion of buoyancy modules.
This methodology has potential applications in many areas, such as, offshore vessel and floating platform protection, riser and umbilical protection, offshore and subsea field planning and layout, etc.
This transient CFD approach has been successfully implemented on typical buoyancy modules and demonstrated effect of ocean currents on the trajectory of the buoyancy modules. Hydrostatic forces, 6DOF motion and the velocities of the buoyancy module were predicted with different ocean current velocities.
The approach proposed in this paper captures the physics of released buoyance module in transient CFD and provides a practical tool for determining the trajectory and velocity of the released buoyancy modules from subsea and quantifying the risk for such an event. It can potentially be used for assessing the risk to offshore vessels and floating platforms, risers and umbilicals, as well as for offshore and subsea field planning and layout.
Influence of the Produced Fluids Properties and Flow Behavior on the Separation Efficiency of a Subsea Gas-Liquid Separator: A Sensitivity Analysis
Authors: Ramos Roberto Marcello Augustus , Estevam Valdir 
Published: September 2014

The development of deep and ultra deep water fields, especially in marginal areas, always presents challenges related to profitability or associated flow assurance issues for subsea equipment.
Currently, Petrobras has a great number of production wells operating in deepwater, mainly in its mature fields (brown fields), therefore we are constantly motivated to improve production capacity and reduce operational costs (OPEX) in these scenarios.
In order to overcome this challenge (reduce OPEX and CAPEX) and keep focus in scenarios with high GOR, Petrobras has applied efforts in developing a high efficiency subsea gas-liquid separation system, particularly through PROCAP Technology Program - Future Vision [1]. The development of this technology is important to confirm whether is sound and reliable for use in large scale applications to increase oil production and, as well, improve both the flow assurance performance and recovery factor.
In the subsea gas-liquid separation technology one of the main challenges is related to variation in the design parameters and in the flowrate range expected during the life cycle of the project. The subsea separator has to be able to handle large flowrate variations since it can work with more than one production well connected.
The objective of this paper is to present the main results of the analysis carried out regarding the influence of the produced fluids properties and the flow behavior on the separation efficiency of a vertical annular subsea separator system (VASPS) [2]. The paper will present the subsea separator design and its performance when subjected to variations of fluid viscosity, fluid density, liquid and gas flowrates, bubble cut off diameter and water cut.
Fatigue of Risers: Calibrating Reliability Estimates From Full-Scale Data
Authors: Tognarelli Michael A. , Winterstein Steven R. 
Published: September 2014

A number of measurement campaigns have sought to quantify fatigue damage on drilling and production risers in the field. The data from these campaigns have recently been used to test the accuracy of software predictions of riser motions and hence fatigue. It is often found that state-of-the-art software shows a conservative bias in predicting fatigue damage — conservative factors of 10 or more. At the same time, short-term damage estimates (e.g., over 10-minute intervals) show significant scatter: COV (coefficient of variation) values of 1.0–2.0 are typical.
We suggest methods here to better incorporate the information from these measurements into fatigue reliability predictions. We note that (1) software error statistics show markedly different behavior in different regimes; e.g., for different levels of predicted damage; and (2) our fatigue reliability concern lies with the variability not in individual 10-minute damage rates, but rather in the long-run damage rate over the entire structural life. These features suggest a non-parametric approach, in which software error statistics are binned and separately analyzed for different predicted damage levels. The sample means in each bin, together with their variabilities, then form the basis for our reliability assessment.
Because our interest lies with the average behavior in each bin, variability reduces notably: COVs of 1.0–2.0 (on individual 10-minute rates) are reduced by an order of magnitude or more. This variability is commonly dominated by the uncertainty in fatigue capacity (S–N curve, Miner’s rule, etc.) Thus, our measurement campaigns are of most interest in predicting only the mean bias in damage predictions; conventional methods are then available to propagate these into a standard fatigue reliability analysis. Results are shown for a number of applications, and implications considered for design (i.e., load factors).