bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kriging-Based Surrogate Model Combined With Weighted Expected Improvement for Ship Hull Form Optimization
Authors: Liu Xinwang , Wan Decheng , Chen Gang 
Published: September 2018

The paper explores Kriging-based surrogate model combined with Weighted Expected Improvement approach and for the ship hull form optimization. The training dataset of the Kriging-based surrogate model is obtained by sampling the design space (Design of Experiments, DOE) and performing expensive high-fidelity computations on the selected points. Expected Improvement (EI) is used as a criterion to select one additional sample point in each iteration. The Weighted Expected Improvement (WEI) is derived from EI by adding a tunable parameter which can adjust the weights on exploration and exploitation in the Efficient Global Optimization (EGO).
The proposed method selects more than one new sample point by changing the weight parameter for each optimization iteration, thus it can be performed by parallel computation or multi-computer runs which improves the computational efficiency distinctly. This makes it possible not only to improve the accuracy of the surrogate model, but also to explore the global optimum much more quickly. The present method is applied to mathematical test function and a ship hull form optimization design in order to find the optimal hull form with best resistance performance in calm water in different speeds.
The result shows that the criterion of WEI can be applied in EGO for optimization design and can be easily extended to other hull form optimization design problems based on computational fluid dynamics.
Risk Analysis and Management of Moored Ships in Ports
Authors: Pinheiro Liliana V. , Fortes Conceição J. E. M. , Santos João A. 
Published: September 2018

The risks associated with mooring of ships are a major concern for port and maritime authorities.
Sea waves and extreme weather conditions can lead to excessive movements of vessels and mooring loads affecting the safety of ships, cargo, passengers, crew or port infrastructures.
Normally, port activities such as ships’ approach manoeuvres and loading/unloading operations, are conditioned or suspended based solely on weather or wave forecasts, causing large economic losses. Nevertheless, it has been shown that some of the most hazardous events with moored ships happen on days with mild sea and wind conditions, being the culprit long waves and resonance phenomena. Bad weather conditions can be managed with an appropriate or reinforced mooring arrangement.
A correct risk assessment must be based on the movements of the ship and on the mooring loads, taking into account all the moored ship’s system.
In this paper, the development of a forecast and warning system based on the assessment of risks associated with moored ships in port areas, SWAMS ALERT, is detailed.
This modular system can be scaled and adapted to any port, providing decision-makers with accurate and complete information on the behaviour of moored ships, movements and mooring loads, allowing a better planning and integrated management of port areas.
Efficient Computation of Irregular Wave Wire Stresses in Flexible Risers
Authors: Rombado Gabriel , Cooke Nathan , Pasala Dharma , Ni Xianglei , Low Andrew , Majed Arya 
Published: September 2018

Accurate computation of tensile armor wire stresses remains a major challenge in flexible riser fatigue life predictions and integrity management. Accuracy of the results relies heavily on capturing the kinematics of the flexible’s helically contra-wound tensile armor layers and their interaction with the other metallic and thermo-plastic layers in a dynamic simulation. The standard industry practice to assess the fatigue life of flexibles is to use high fidelity 3D Finite Element Models (FEMs) to capture the complex kinematics and produce accurate stresses. However, direct simulation of flexible riser detailed FEMs is limited to regular wave analyses and computation of wire stress time-histories subjected to irregular waves have been computationally infeasible. This is due to the complexity of the nonlinear FEM and the long simulation time of the irregular wave environment coupled with large number of fatigue sea states. As a result, simplified approaches which do not directly simulate the local model and instead assume that wire stresses can be interpolated based on static stress versus curvature material curves within a pre-defined tension /pressure envelope have been utilized.
This paper utilizes Nonlinear Dynamic Substructuring (NDS), a simulation-based approach that that extends the framework of dynamic substructuring to nonlinear problems. NDS enables the efficient nonlinear dynamic simulation of multiple pitch lengths of detailed flexible riser FEM subjected to irregular wave inputs and the computation of wire stress time-histories at any location on the local model.
In this paper, a 14-inch diameter flexible riser under consideration by ExxonMobil is subjected to vessel motion and wave load in irregular wave environments and is modeled using a detailed 3D FEM and simulated via NDS. The flexible riser design features four tensile armor layers to mitigate localized lateral buckling of the wires near the touch down point. Tension and curvature time-histories of the riser near the hang-off, calculated from a conventional beam model global analysis, is used to drive a 5.1m long local model. Irregular wave wire stress time-histories extracted at the corners of the tensile armor wires are used to compute the fatigue life of the flexible. To demonstrate the inaccuracies associated with the regular wave approach, fatigue life is computed via the regular wave approach and compared against the irregular wave approach. It is shown that the NDS capability to efficiently compute irregular waves mitigates over- and under-predictions due to environment idealizations leading to a more accurate and reliable flexible riser life prediction and structural integrity assessment.
Improving the Installation Criterion for Concrete Coated Pipelines
Authors: Nguyen Ngoc , Fyrileiv Olav , Chia Chor Yew 
Published: September 2018

Current design practice limits the concrete strain to approximately 0.2% in a simplified design criterion. In most standard cases, this has proved to be safe and adequate. However, in recent years, the pipeline industry is extending into more remote, harsher environments and larger diameter pipelines. The use of the simplified design criterion has, in some circumstances, resulted in too strict installation requirements which limit the number of relevant installation vessels.
This paper presents some findings on the concrete strain for submarine pipelines with concrete weight coating (CWC) derived from the numerical program performed within the scope of Phase 1 of the joint industry project “Design of concrete coating for submarine pipelines”.
Non-linearities in the concrete weight coating, anti-corrosion coating (ACC) and steel material properties, as well as large deformation and the sequence of load application were included in the numerical model. The results from the numerical analyses have been well validated against existing experimental data, and the numerical model was subsequently used in an extensive parametric study, where the behaviour of concrete coated pipelines was investigated for monotonic and reversed bending with nominal strain up to 0.4%.
These numerical results can be used to widen the applicable range of the simplified concrete crushing criterion in DNVGL-ST-F101 (2017), and to formulate a rational approach for the design of pipeline concrete weight coating under typical installation and operation conditions. The rational design approach will allow for a wider range of installation vessels to select from for installation of the pipeline, and relaxation of the installation weather window criterion.
Enhance Reliability of Structural Bonding: An Advance Solution of Repair for Corrosion Onboard Offshore Units
Authors: Mouton Luc , Errotabehere Xabier , Paboeuf Stéphane , Ahmad Firas Sayed 
Published: September 2018

An increasing number of Floating offshore units reach maturity (> 10 years). This induces costly maintenance operations related to hull structure corrosion damage. While crop and renew operations are generally performed in dry docks for supertankers, the FPSO are maintained afloat offshore on the oil field. For obvious security reasons hot work such as welding and gauging are prohibited without a heavy set of recommendations. Naturally, FPSO’s operators have sought “cold” solutions for decades.
This paper describes the specificities of a particular structural bonded reinforcement (ColdShield developed by COLDPAD). A general description of its particularity in the fields of installation and durability is given, but this article is mainly focused on reinforcement strength criterion. Bonded reinforcement strength is known as difficult to predict, making design methodologies not compatible with industrial applications. The innovation in the design of the presented solution leads to a special behavior in terms of strength. It is revealed by the comparison of results of the qualification test campaign with results of tests realized on a standard bonded patch application. Finite element modelling computed parallelly to the tests are used to analyze the test results. The robustness of the reached strength criteria is discussed.
Drag Coefficients of Vertically-Mounted Full-Scale Blue Mussel Dropper Lines
Authors: Hildebrandt Arndt , Landmann Jannis , Ongsiek Thorsten , Goseberg Nils 
Published: September 2018

Developments in marine aquaculture in the last 30 years indicate that the bivalve-related industry is feasible offshore and that opportunities for large-scale, industrious production of shellfish stock exists. The objective of the project “CAWX1607” is to develop, model and test such systems. However, the forces acting on suspension cultures, the most likely form of marine farm systems are unknown. Here, drag coefficients provide an efficient approach for the calculation of arbitrary complex structures by using the Morison equation. The CD-coefficients take into account vortex shedding effects as well as the surface roughness of the structure.
This paper reports on developed and conducted tests at the medium wave and towing tank “Schneiderberg” (WKS) at the Ludwig-Franzius-Institute for Hydraulic, Estuarine and Coastal Engineering of the Leibniz University Hanover, Germany. The tests were conducted for current velocities between 0.25–1.0 m/s for three samples of blue-lipped mussel specimens. During physical testing the forces and moments in x-, y- and z-direction, the elevation of the water surface, a velocity profile in the vicinity of the live-blue mussels, as well as the velocities of the towing carriage were recorded. The developed methodology, data treatment as well as the resulting CD-coefficients are presented. Further, the CD-coefficients obtained are presented in the context of natural variation of living structures and discussed in comparison to CD—curve characteristics of offshore structures, e.g. rough cylinders.
Useful Indicators for Screening of Sea States for Wave Impacts on Fixed and Floating Platforms
Authors: Bunnik Tim , Stansberg Carl Trygve , Pakozdi Csaba , Fouques Sebastien , Somers Luke 
Published: September 2018

Design approaches for wave impact on marine structures in storm sea-states are being reconsidered due to events related to the safety of North Sea offshore structures, both fixed and floating (Valhall QP extended lifetime; COSL Innovator accident). There has been a strong research and tool development within the field during the last decade, both within model testing and numerical analysis, including CFD. However, there is still a lack of efficient methods and tools to properly analyze these phenomena and their probably of occurrence.
One major aspect in this is to reduce the statistical uncertainties that are naturally arising in estimates of design loads related to extreme waves. In order to estimate the design loads it is common practice not to investigate all possible sea states (i.e. long-term analysis) but to investigate a few sea states and assume that the design value occurs at a prescribed probability level in the sea states with the same probability level (i.e. contour line approach). The estimate of the design value at that probability level is then based on results from a limited number of random realizations of these sea states. For linear or weakly nonlinear response types it is possible to estimate design loads accurately with a quite limited number of realizations. For strongly nonlinear/badly behaved problems however this is not possible due to the large variations in the tail of the distribution of the impact load, and many more realizations are required. This means that much more of these extreme, rare impact-related events should be collected to reduce the statistical uncertainty in the design load. This approach is restricted by time and costs and eventually one may have to accept an estimated design load with a large statistical uncertainty and account for the uncertainty with a higher safety margin.
In this paper an improved methodology for estimating design loads related to extreme wave impacts will be presented. The methodology is based on screening many 3-hour realizations of the design sea states with simplified, fast but sufficiently accurate methods and to focus only on the potentially critical events with a model containing a more complete description of the physics. This can be either a model test or a non-linear impact simulation (i.e. CFD analysis). By doing this many more rare/critical events can be assessed, reducing the statistical uncertainty in the estimate of the design load. The main challenge is to find suitable screening methods, which may be different for different structures (fixed, floating, etc.). Several screening methods/wave impact indicators will be discussed, and their capability will be illustrated by analyzing existing model test data for fixed and floating structures, showing the correlation between indicator and actual impact events.
Analytical Models to Estimate Temperature Profiles During Drilling and Shut-In in Deepwater Environment
Authors: Hasan A. Rashid , Xu Boyue , Fyfe Dave 
Published: September 2018

Drilling operations involve significant heat transfer between the drilling mud, downhole tubulars, and surrounding formation. Such heat transfer causes changes in drilling fluid temperature that alters drilling fluid density and viscosity, as well as changes near-wellbore formation temperature. Temperature changes in the near-wellbore formation need to be understood so that useful interpretation of often available temperature data from multiple discrete temperature sensors (MDTS) may be made.
In deepwater assets, fluid circulation through cold water makes the problem more complex. Deepwater drilling operation could be viewed as consisting of four processes: (1) mud circulation in the riser affected by surrounding cold sea water; (2) mud circulation in the cased and cemented zone; (3) mud circulation through the target zone (open hole); (4) shut-in after drilling through the target zone. Forced convective heat transfer dominates in the first three processes while conductive heat transfer is dominant during the shut-in period. Estimating temperature in the wellbore during and after circulation is critical for mud rheology, tubular thermal stress, and cement design. Application of “rule-of-thumb” and/or complicated numerical simulation is often unreliable and/or impractical.
This paper presents analytic models to estimate temperature profile during and after drilling fluid circulation in deepwater environment. Steady heat transfer is assumed in during fluid circulation, and transient modeling is performed for shut-in periods. Energy balance is set up over the differential control volume to develop the models. The end of circulation would provide the initial condition for the shut-in period. The models are used to estimate bottomhole temperature distribution during and after circulation. The analytical model is verified using data from a real deepwater well that had permanent downhole gauges (PDGs) installed at the bottomhole.
Increasing Performance of Smart Well Systems by Downhole Chemical Injection
Authors: Aadnøy Bernt S. 
Published: September 2018

There are many different types of smart well systems such as Inflow Control Valves, Inflow Control Devices and autonomous devices of various designs. The most common inflow system is blank pipe, producing through a screen and into the control valve at the connection sub.
To control the functionalities one may use surface control lines, dropping balls or darts or simply let the valves react autonomously to changes downhole. These tools can be deteriorated by erosion, plugging of fines, plugging of of heavy oil residue or by scaling.
Scaling is a complicated issue as it often builds up near critical parts of the tool, changing the flow pattern and affecting or offsetting the flow assurance. This paper will present a new concept in chemical well injection. It is proposed to connect a capillary tube through the entire completion string to inject chemicals to prevent scaling of critical tools before the oil enters the tool, thereby increasing the time the tool will function.
A new downhole chemical injection valve is developed. It is located near the injection point to prevent U-tube pressure effects often associated with surface injection systems. This injection valve can also easily be adjusted downhole or shut off if required. The advent of water production often changes chemical injection requirements. The new system can accommodate any changes in chemical or flow rates. The system is fully mechanical and does not rely on electrical control cables. Flow regulation is performed through the capillary tube.
The paper will describe the new downhole chemical injection system and its application to smart well technology.
Model Tests and Numerical Analysis for a Floating Mega Island
Authors: Waals O. J. , Bunnik T. H. J. , Otto W. J. 
Published: September 2018

About 70% of the earth’s surface area is covered with water. Due to the sea level rise and increasing population in coastal areas we need to use our oceans more for energy production, food production, working and living.
In the present paper we discuss the results of a model test for a floating mega island in large waves up to 15.5 m significant wave height. The objective of this study is to investigate the motion response and loads on the island. These results may then be used to support further innovation of these islands.
The proposed island comprises 87 large floating triangles that are connected to one another. Together they form a flexible floating island of 1.5 by 2 km in cross-section at scale 1:250. The results are presented for the motion response of the island as well as the forces between the islands triangular modules and the mooring loads. These were measured using forces transducers and motion sensors.
The present work is part of a conceptual test carried out at MARIN. The island modules are interconnected with springs and fenders. This method is much similar to what is used in side by side offshore operations in the oil and gas industry.
Due to the flexibility in the connections the island will follow the waves in high seas. The forward two rows of the island will move in phase with the sea and therefore the amount of green water is much smaller than for a rigid island.
A Novel Semi-Empirical Non-Linear Time-Domain Formulation of Wave Elevation Diffracted by a Vertical Column
Authors: Pakozdi Csaba , Reinholdtsen Svein-Arne , Stansberg Carl T. 
Published: September 2018

A novel semi-empirical non-linear formulation for fast and efficient computation of the disturbed elevation time series under large-volume platform in steep irregular waves is described and validated against model test data with a single fixed circular column. The method makes use of a linear diffraction model as a basis, which is then subject to non-linear amplification derived from a previous established crest amplification formula.
The validation test data includes a large test matrix of regular waves with systematic variations in the wave period and steepness, some tests were also run in a steep irregular wave as well as various bi-chromatic waves. The simulations show a good agreement with model test time series.
Initial simulations in the irregular waves disclosed some steep wave events for which the model predicted too strong non-linear amplification due to high local steepness close to or beyond breaking. A threshold criterion were introduced. Leeward (shadow) effects are also addressed, and a practical model for this is proposed.
Numerical Study of Density Ratio Influence on Global Wave Shapes Before Impact
Authors: Etienne Stéphane , Scolan Yves-Marie , Brosset Laurent 
Published: September 2018

The influence of the gas-to-liquid density ratio (DR) on the global wave shape before impact is studied through numerical simulations of the propagation of two different waves in a rectangular wave canal. Two different codes are used: the first one, named FSID, is a highly non-linear 2D bi-fluid potential code initially developed in the frame of SLOSHEL JIP (Kaminski et al. (2011)) to simulate incompressible inviscid free-surface flows without surface tension thanks to a desingularized technique and series of conformal mappings; the second one, named CADYF, is a bi-fluid high-fidelity front-tracking software developed by Ecole Polytechnique Montreal to simulate separated two-phase incompressible viscous flows with surface tension.
The first studied wave leads to a flip-through impact while the second one leads to a large gas-pocket impact. Each condition is studied with water and three different gases with increasing densities corresponding to DR = 0.001, 0.003 and 0.005. The global wave shapes are compared a few tenths of second before the impact, before free surface instabilities triggered by the shearing gas flow have developed and also before any gas compressibility matters. Both codes give precisely the same global wave shapes.
Whatever the condition studied, it is shown that DR has an influence on these global wave shapes. The trends observed from the simulations are the same as those described in Karimi et al. (2016) obtained from sloshing model tests with Single Impact Waves (SIW) in a 2D tank with a low filling level. A small part of the mechanical energy of the liquid is progressively given to the gas. The larger the DR, the larger this transfer of energy from the liquid to the gas. This explains an increasing delay of the wave front for increasing DRs.
High Geostress Advantageous for Arctic Field Developments
Authors: Aadnøy Bernt S. , Belayneh Mesfin A. 
Published: September 2018

The Arctic areas of Norway has brought many new challenges. In addition to harsh weather, drilling conditions are different.
The Barents Sea is different geologically compared to the North Sea area. A considerable amount of erosion bring older rocks higher up. It is observed that leak-off tests measured in Barents Sea wells shows abnormally high values. This is interpreted as a high stress state.
The paper analyze the stresses around a number of wells and conclude that it is very likely that a reverse fault stress state exists in these areas of the Barents Sea. This can bring positive effects because such a stress state may constrain induced fractures to propagate in a horizontal plane rather than towards surface, reducing the risk for reservoir leaks to surface. Also, a high compressive state may lead to more sealed faults, indicating a higher possibility for oil in place.
The paper will present the stress model and compare Barent Sea area to the North Sea. It will also show implications for wellbore stability, leaks from reservoirs and effects on sealing of major faults. Of particular interest is that leak potential from the reservoir is reduced in the Barent Sea as compared to other Norwegian oil fields. This may encourage more development in the Arctic areas.