bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Numerical Prediction of Transitional Flows With Reynolds-Averaged Navier-Stokes and Scale-Resolving Simulation Models
Authors: Pereira Filipe S. , Vaz Guilherme , Eça Luís , Lemaire Sébastien
Published: October 2016

The present work investigates the transitional flow around a smooth circular cylinder at Reynolds number Re = 140,000. The flow is resolved using the viscous-flow solver ReFRESCO, and distinct mathematical models are applied to assess their ability to handle transitional flows. The selected mathematical models are the Reynolds-Averaged Navier-Stokes equations (RANS), Scale-Adaptive Simulation (SAS), Delayed Detached-Eddy Simulation (DDES), eXtra Large-Eddy Simulation (XLES) and Partially-Averaged Navier-Stokes (PANS) equations. The RANS equations are supplemented with the k–ω Shear-Stress Transport (SST) with and without the Local Correlation Transition Model (LCTM). The numerical simulations are carried out using structured grids ranging from 9.32 × 104 to 2.24 × 107 cells, and a dimensionless time-step of 1.50 × 10−3. As expected, the outcome demonstrates that transition from laminar to turbulent regime is incorrectly predicted by the k–ω SST model. Transition occurs upstream of the flow separation, which is typical of the supercritical regime and so the flow physics is incorrectly modelled. Naturally, all Scale-Resolving Simulation (SRS) models that rely on RANS to solve the boundary-layer, called hybrid models, will exhibit a similar trend. On the other hand, mathematical models capable to resolve part of the turbulence field in the boundary layer (PANS) lead to a better agreement with the experimental data. Furthermore, the k–ω SST LCTM is also able to improve the modelling accuracy when compared to the k–ω SST. Therefore, it might be a valuable engineering tool if its computational demands are considered (in the RANS context). Therefore, the results confirm that the choice of the most appropriate mathematical model for the simulation of turbulent flows is not straightforward and it may depend on the details of the flow physics.
Yield Surface of Deeply Buried Square Anchors Under Out-of-Plane Loading
Authors: Zheng Tianyuan , Cassidy Mark J. , Tian Yinghui , Gaudin Christophe
Published: October 2016

Anchors are widely used offshore as foundation systems to moor floating platforms and renewable energy devices to provide uplift resistance in vertical or resistance in inclined direction. Most of the available research work has concentrated on in-plane loading. However, any failure of a single mooring line in a storm can cause out-of-plane loading on the remaining anchoring system. This research targets how this out-of-plane loading can affect the trajectory and ultimate holding capacity of the anchors. This paper presents results of a numerical investigation of the undrained bearing capacity of deeply buried square plate anchor in clay under six degrees-of-freedom loading. Finite element analyses are conducted to define the combined loading yield surface (or yield surface for the anchor in its current position) and an analytical expression of the yield surface is proposed and written directly in the six degrees-of-freedom loads. This analytical expression allows implementation of the yield surface in a plasticity approach, where the load-displacement relationship of the anchor can be described. The method to achieve this and also an illustration of how this framework on a simple plate anchor can be extended to predict the performance of more complex anchor geometries is described at the end of the paper in a description of future research.
Vortex Induced Vibrations of Pipelines With Non-Linear Seabed Contact Properties
Authors: Ulveseter Jan V. , Sævik Svein , Larsen Carl M.
Published: October 2016

A promising time domain model for calculation of cross-flow vortex induced vibrations (VIV) is under development at the Norwegian University of Science and Technology. Time domain, as oppose to frequency domain, makes it possible to include non-linearities in the structural model. Pipelines that rest on an irregular seabed will experience free spans. In these areas VIV is a concern with respect to the fatigue life. In this paper, a time domain model for calculation of VIV on free spanning pipelines is proposed. The model has non-linear interaction properties consisting of discrete soil dampers and soil springs turning on or off depending on the pipeline response. The non-linear model is compared to two linear models with linear stiffness and damping properties. One linear model is based on the promising time domain VIV model, while the other one is based on RIFLEX and VIVANA, which calculates VIV in frequency domain. Through four case studies the effect of seabed geometry, current velocity and varying soil damping and soil stiffness is investigated for a specific pipeline. The results show that there is good agreement between the results produced by VIVANA and the linear model. The non-linear model predicts smaller stresses at the pipe shoulders, which is positive for the life time estimations. Soil damping does not influence the response significantly.
Computation of Added Mass and Damping Coefficients of a Horizontal Circular Cylinder in OpenFOAM
Authors: Chen Hao , Christensen Erik Damgaard
Published: October 2016

This paper presents numerical computation of added mass and damping coefficients of a slender horizontal cylinder in the free surface zone, which typically serves as a fish cage floater. A fully viscous two phase flow solver in OpenFOAM was employed in the numerical computation. The purpose was to validate the capability of this solver and dynamic mesh functionality. A two dimensional numerical wave tank was set up, and two wave relaxation zones were used to reduce the size of the computational domain. Harmonic forced oscillations of the cylinder were performed at different frequencies and amplitudes. The mesh at free surface zone was refined based on the radiated wave heights at different oscillation frequencies in order to properly resolve the radiated waves. The result shows that in most frequency ranges, the numerical computation agreed well with the experimental data and analytical solution. However at low frequency range for added mass coefficient in heave motion, deviations were observed, and it was due to the effect of finite water depth. In addition for sway motion at high frequency range, the damping coefficient was underestimated comparing with analytical solution. This was believed to be as a result of high steepness of the radiated waves.
Reliability Assessment of Marine Drilling Risers With Correlated Random Variables
Authors: Sengupta Piyali , Low Ying Min , Zhang Xiaodong , Adaikalaraj Peter Francis Bernad , Koh Chan Ghee
Published: October 2016

Marine drilling risers are integral parts of the deep water offshore oil and gas industry. They are required to be designed for safe operations during their service lives with appropriate degree of reliability. With limited experience present in ultra-deep water, drilling risers are subjected to a range of uncertainties arising from untested environmental conditions. However, the current industry practice is limited to deterministic design of drilling risers which cannot account for uncertainties present in real life scenario. Under uncertain environmental conditions, deterministic methods may lead to undesired consequences, i.e. over conservative or unsafe design and misguided estimates of operability and down time of ultra-deep water drilling risers affecting the total life cycle cost. Thus, structural reliability analysis is particularly useful for prediction of the probabilities of downtime and disconnection of drilling risers incorporating the environmental uncertainties. In addition, structural reliability analysis can be used to reduce the total life cycle cost of ultra-deep water drilling risers.

In reliability analysis, many studies use uncorrelated random variables to represent uncertainties for simplification. Nevertheless, uncertainties in environmental conditions may be strongly correlated (for example wind and wave loads). If the correlation is not accounted for, it may lead to erroneous probability estimates. Thus, a joint environmental model is proposed in this paper using the conditional modeling approach where a joint density function is defined in terms of a marginal distribution and a series of conditional density functions. The joint density functions of environmental conditions are constructed in the current study using the recorded metocean data for Gulf of Mexico available from National Oceanic and Atmospheric Administration (NOAA) website. Then a computational model of connected ultra-deep water drilling riser system is constructed in ORCAFLEX to conduct time domain dynamic analysis. Thereafter, the correlated random variables in combination with the drilling riser computational model are utilized for conducting Monte Carlo Simulation (MCS) to evaluate the probabilities of downtime and disconnection. MCS is a widely accepted and robust approach and generally used as a benchmark to verify the accuracy of other reliability methods. But, in presence of large number of random variables representing environmental uncertainties, MCS is computationally demanding especially for the large number of simulations required to estimate small failure probabilities associated with extreme values. To this end, probability density functions of drilling riser responses are evaluated using Shifted Generalized Lognormal Distribution (SGLD) and Generalized Extreme-Value (GEV) Distribution both of which show similar accuracy (compared to MCS results) at a fraction of computing time (around 1/500 times).
Spectral Fatigue Analysis Considering Probabilistic Corrosion Effects: A Case Study of a Container Ship’s Hatch Coaming Detail
Authors: Cui Jinju , Wang Deyu , Ma Ning
Published: October 2016

Firstly, the fatigue strength of container ship hatch coaming structural detail is studied by Spectral Fatigue Analysis in this paper, and influencing factors are investigated. Secondly, corrosion effects with uncertainty are introduced, and thus the probabilistic characteristics under simultaneous uniform corrosions (however, with different scales) throughout the cargo tank structure are obtained, and surrogate models are built to replace the Finite Element Analyses that are time consuming. Additionally, corrosion models are modified so as to deal with the gradual corrosion problem while maintain probabilistic features. Finally, the fatigue strength’s probabilistic characteristics as a function of time is investigated numerically, and regression form models are derived.
Effect of Nano-Silicon Dioxide (SiO2) on Polymer/Salt Treated Bentonite Drilling Fluid Systems
Authors: Belayneh Mesfin , Aadnøy Bernt S.
Published: October 2016

Recently the application of nanomaterial is attracting the oil and gas industry. The preliminary nanomaterials research results show an improving performance of cement, drilling fluid and Enhanced Oil Recovery.

In this paper, the effect of nano Silicon dioxide (SiO2) on polymer (HV-CMC, Xanthan gum, LV-CMC) and salt (KCl, NaCl) treated bentonite drilling fluid systems has been studied at room temperature.

The results show that the performance of nano SiO2 in bentonite mud system depends on its concentration and the types of salt and polymer systems used. In the considered fluid systems, it is also observed that the addition of about 0.06% SiO2 influences rheology, and filtrate loss of the drilling fluid systems. The viscoelasticity of the selected best system further studied and their hole -cleaning and hydraulics performances are simulated. The overall result shows that the formulated optimum concentration of nano-system shows good performances and rheological behavior.
Parametric Analysis on the Crushing Resistance of Flexible Pipes Under Installation Loads
Authors: Guedes Mendonça Heloisa , de Arruda Martins Clóvis
Published: October 2016

Flexible pipes are essential elements for offshore production systems. Such structures can be severely damaged during the operational phase due to adverse environmental conditions and dynamic loads in deep water applications. The laying operation is considered one of the most critical stages in the flexible pipe life-time since the structures are subject to severe crushing-traction loads. These loads are the result of dynamic effects from sea and static loading applied by shoes of the caterpillars on the launching vessel. To study the influence of static loading parameters in the flexible pipe crushing load resistance, this paper will present a numerical analysis through the Finite Element Method. In order to carry on the qualitative analysis, tridimensional models were built considering the parametrization of geometry, materials, boundary conditions and contact pairs. The layers represented in these models are resistant to radial loads (interlocked carcass and pressure armor), internal and external polymeric sheath and the caterpillar shoes. Important parameters from this aforementioned model were taken into account as: number of caterpillar shoes, opening angle of those shoes and contact between layers. Three different case studies are presented considering these parameters. The failure results are addressed and discussed based on specific regulations for installation loads of flexible pipes.
Non-Linear Static Analysis of 2D Steep Wave Riser Under Current Load
Authors: Qiao Hongdong , Ruan Weidong , Shang Zhaohui , Bai Yong
Published: October 2016

A new solution combining finite difference method and shooting method is developed to analyze the behavior of steep wave riser subjected to current loading. Based on the large deformation beam theory and mechanics equilibrium principle, a set of non-linear ordinary differential equations describing the motion of the steep wave riser are obtained. Then, finite difference method and shooting method are adopted and combined to solve the ordinary differential equations with zero moment boundary conditions at both the seabed end and surface end of the steep wave riser. The resulting non-linear finite difference formulations can be solved effectively by Newton-Raphson method. To improve iterative efficiency, shooting method is also employed to obtain the initial value for Newton-Raphson method. Results are compared with that of FEM by OrcaFlex, to verify the accuracy and reliability of the numerical method. Finally, a series of sensitivity analyses are also performed to highlight the influencing parameters in the steep wave riser.
Estimating Extreme Waves in Brazil Using Regional Frequency Analysis
Authors: Campos Ricardo M. , Guedes Soares C.
Published: October 2016

Regional Frequency Analysis (RFA) based on L-moments is used to calculate spatial extreme return values of significant wave height. The RFA consists of using data from different sites with similar statistical characterisation to better estimate quantile functions, which can be used for regional or site-specific analyses. This technique is applied to a selected area in the South Atlantic Ocean (Brazil) using a group of wave hindcasts produced by a simulation with WAVEWATCH III model. The statistical approach of RFA is divided into four steps: (1) First inspection of the data; (2) Regionalization and definitions of statistically homogeneous sub-regions; (3) choice of Probabilistic Distribution and test of hypothesis; (4) Calculation of L-moments and final regional quantile function. The results of RFA are reliable extreme return values at each grid point with very low variance of the distribution parameters estimators and narrow confidence intervals. Considering the return period of 100 years, the significant wave heights vary from 5.5 to 11.2 meters within the considered domain in southern and southeastern Brazil.
Preliminary Results of Numerical Simulations of a Bio-Mimetic Wells Turbine
Authors: Hu Qiuhao , Li Ye , Wei Fangyi
Published: October 2016

Wells turbine is a kind of self-rectified air turbines used in an oscillatory water column (OWC) device for wave energy conversion. In this study, a steady three-dimensional simulation of a fan-shaped Wells turbine is performed on Star CCM+ commercial software by solving the Reynolds-averaged Navier-Stokes (RANS) equations. The turbulence effects are taken into account by using the Spalart-Allmaras turbulence model. Good agreement between the numerical results and the experimental results within the operation region (5< α <11 degrees) is observed. The geometry of the turbine rotor has a significant effect on the performance of energy conversion. Inspired by the aerodynamics of low Reynolds flyer, the normal fan-shaped Wells turbine is optimized by a bio-mimetic method in which the profile of a hawk moth wing of Manduca Sexta is applied on the blades. The modified turbine has a lower torque and pressure drop coefficient with higher efficiency. The maximum efficiency for the modified turbine is 0.61, compared to 0.48 for the normal fan-shaped one. By analysis of the detailed flow-field, it has also been found that only the middle parts of the blade can effectively generate the momentum. In order to acquire a higher efficiency, further optimization is carried out by refining some blade parts in the tip and the hub which cannot effectively produce power.
Effects on Drillship Resistance of a Large Moonpool Using CFD Simulations With Experimental Validation
Authors: do Vale Machado Lucas , Fernandes Antonio Carlos , Hussain Anis Altaf
Published: October 2016

Drillship is a marine vessel designed for drilling purposes of oil and gas wells. This kind of vessel has what is called a moonpool that is an opening on the base of the hull used for drilling operation. Nowadays, in search of better process efficiency, some of these drillships are being constructed with dual-derrick and are in need of a larger moonpool, which results in some effects on the floating structure, such as resistance increase. The main objective of this paper is to investigate the influence of shape and size of the moonpool on the resistance of a drillship dual derrick, while in transit. It presents the application of a commercial CFD (Computational Fluid Dynamics) software as a numerical approach to calculate the flow around a drillship without neglecting free surface effects. Throughout this work, the made assumptions, applied boundary conditions and appropriate mesh density studies are thoroughly discussed. Verification assessment is part of the work. In addition to the numerical study, some experimental tests were done at LOC/UFRJ (Laboratório de Ondas e Correntes – Laboratory of Waves and Currents) to validate the numerical approach. The comparison between simulation results and experiments allows the analysis of the present CFD models benefits and limitations, providing guidelines for similar future studies. The overall match between laboratory and virtual tests results supports the expansion of this procedure to other vessels and offshore floating units. The results of this work clarify the motion inside the moonpool and its effects. Furthermore, it gives the results of several different moonpool profiles that were optimized for this specific hull.
Self-Adaptive Wave Absorbing Technique for Nonlinear Shallow Water Waves
Authors: Yan S. , Ma Q. W. , Wang Jinghua , Zhou Juntao
Published: October 2016

A key challenge in long-duration modelling of ocean waves or wave-structure interactions in numerical wave tanks (NWT) is how to effectively absorb undesirable waves on the boundaries of the wave tanks. The self-adaptive wavemaker theory is one technique developed for this purpose. However, it was derived based on the linear wavemaker theory, in which the free surface elevation and the motion of the wavemaker are assumed to be approximately zero. Numerical investigations using the fully nonlinear potential theory based Quasi Arbitrary Lagrangian Eulerian Finite Element Method (QALE-FEM) suggested that its efficiency is relatively lower when dealing with nonlinear waves, especially for shallow water waves due to three typical issues associated with the wave nonlinearity including (1) significant wavemaker motion for extreme waves; (2) the mean wave elevation (i.e. the component corresponding to zero frequency), leading to a constant velocity component, thus a significant slow shift of the wavemaker; (3) the nonlinear components, especially high-order harmonics, may significantly influence the wavemaker transfer functions. The paper presents a new approach to numerically implement the existing self-adaptive wavemaker theory and focuses on its application on the open boundary, where all incident waves are expected to be fully absorbed. The approach is implemented by the NWT based on the QALE-FEM method. A systematic numerical investigation on uni-directional waves is carried out, following the corresponding validation through comparing the numerical prediction with experimental data for highly nonlinear shallow water waves.
The Effect of Stick Slip Vibration on the Backward Whirl of Bottom Hole Assembly in Drillstring
Authors: Zhao Dapeng , Hovda Sigve , Sangesland Sigbjørn
Published: October 2016

The whirl phenomena in the bottom hole assembly (BHA) is believed to be formed by the imbalance of the rotational drill collar. Backward whirl is caused by the nonlinear contact between the BHA and the borehole, and can be extremely damaging to the down hole tools and borehole. In the previous studies, a two-degrees-of-freedom lumped parameter model is developed for representing the drill collar in lateral motions (whirl). Due to the bit-rock interaction, the stick slip torsional vibration is very common. In the current work, therefore, the torsional vibration causing fluctuation of rotary speed is taken into account. The simulation results indicate that the drill collar whirls forward at lower constant rotary speed. With increasing rotary speed, the backward whirl is activated by the contact between the drill collar and the borehole wall. The nonlinear contact forces obey the Hertzian contact law, which led to lateral bounce of the drill collar and impact borehole wall chaotically. The modified Karnopp friction model is adopted to simulate the stick slip rotary vibration of the BHA. The different characters of lateral vibrations are identified by a power spectrum density diagram with and without consideration of the stick slip vibration.
ISUM: Its Birth, Growth and Future
Authors: Rashed Sherif
Published: October 2016

ISUM (The Idealized Structural Unit Method) was born in 1972 to efficiently and accurately analyze the behavior of large size structures up to and beyond their ultimate strength. In this method a structure is divided into large elements, basically its structural units (members). Geometric and material non-linear behavior inside the element is formulated and expressed at a limited number of nodal points at the element boundaries. In this way a large structure can be modeled using a coarse mesh while still being able to consider the nonlinear behavior until the collapse of the structure.

Several ISUM elements have been formulated and used to analyze the non-linear behavior of large ship structures. In further developments, more elements with more accurate formulations have been developed and more types of structures have been analyzed using this method. The same ISUM concept has been applied to the analysis of welding deformation of large welded structures and to failure analysis of structural and mechanical components subjected to impact loads.

In this paper, the basic ISUM concept is outlined, and several elements are presented. Examples of applications to ships and marine structures are presented demonstrating the effectiveness of the method. Recent developments are also reviewed and future potential is explored.
Efficient Collapse Analysis of Ductile Components Subjected to Impact Loads
Authors: Yasuda Akihiro , Rashed Sherif
Published: October 2016

In collapse analysis of mechanical or structural components made of ductile materials and subjected to impact loads, it is necessary to consider material tearing (cracking and crack propagation). Traditional methods that focus on material behavior at crack tip require very fine FE meshes and are not suitable for impact analysis where explicit integration codes, for very good reasons, are used. On the other hand, in methods which utilize surface separation such as the interface element approach or node break approach, crack propagation route needs to be known beforehand.

In this paper, the development of an efficient 3-D Finite element for such collapse analysis is reported. This element utilizes the ISUM concept and may be used in relatively coarse meshes at crack tips. Stress-strain relationship takes account of element size and strain rate effects. Crack propagation through the element (tearing of the element) is based on the sum of the strain energy and surface creation energy, and takes account of the effects of element size and strain rate on the tearing energy. Comparison of test and analysis results of a conical impactor dropped on a circular steel plate is utilized to confirm the validity of the element.
An Environmentally Friendly Alternative for the Conventional Acids Used in Acid Fracturing of Carbonate Reservoirs
Authors: Nawik Adisak , Taylor Kyle , Barati Ghahfarokhi Reza
Published: October 2016

The acid fracturing techniques developed for well stimulation purposes have been applied to maximize oil production while bypassing the near wellbore damage. Commonly used acids such as hydrochloric acid (HCl) and hydrofluoric acid (HF) damage equipment, are not environmentally friendly and, most importantly, they are harmful to oil field workers. Moreover, transportation of such fluids to the well-head and neutralization of the flow-back products is costly.

The Ultra Series FF-01 is an environmentally- and equipment-friendly alternative to the commercially available products. The Ultra Series FF-01 is very acidic, its pH is less than 1, and has a slower reaction rate compared to the HCl. It can work up to 72 times longer than hydrochloric acid. Most importantly, it is biodegradable and is non-corrosive to the field equipment.

Acid conductivity measurement tests were designed to simulate acid fracturing for comparing the performance of acid fracturing fluids. The main objectives of this study is to compare the ability of Ultra Series FF-01 samples in etching the surface of carbonate rocks by measuring the conductivity of the simulated etched fracture. The two acid fracturing fluids that are used in these experiments are the Ultra series FF-01 and a conventional 15% hydrochloric acid with the iron control agent, non-emulsifier, and corrosion inhibitors. The injection rate is at 100 mL/min and the total time of injection is 1 hr. Experiments were performed on carbonate rocks at 40° C and 70° C and the leak-off pressure was set to be 100 psi lower than the overall pressure. Then the conductivity was measured at different closure stress after the injection time is complete.

Conductivity after etching by the Ultra series FF-01 was significantly improved compared to that obtained with 15% hydrochloric acid with additives when the leak off was set at 100 psi lower than the system pressure for all values of closure stress. It was very evident from the difference in the etching patterns between the two fluids. The etching pattern that was created by the Ultra series FF-01 was in the shape of human veins, visible and connected. In contrast, the surface of the core samples that were etched by 15% hydrochloric acid with additive were bouncy but shallow, producing inferior conductivity. In addition, the performance of the Ultra series FF-01 was slightly better than 15% hydrochloric acid with additives when the leak off pressure was set at 50 psi lower than the system pressure for all closure stress pressure except for 1000 psi.
Seaquake Loads Acting on Offshore Wind Turbine
Authors: Fujioka Katsunari , Nihei Yasunori , Iijima Kazuhiro
Published: October 2016

In this paper, we will discuss the effects of seaquake loads acting on offshore wind turbine in case of earthquake. It may be assumed that offshore structures are generally free from the effects of earthquakes. However, even floating structures can be subjected to serious shock by earthquake induced waves which propagate through sea water. This phenomenon is called seaquake, and caused by compressibility of the sea water. The effects of seaquakes acting on the float of offshore wind turbine have to be considered to ensure the safety in earthquakes which occur at the bottom of the sea. In this study, seaquake load acting on the float of wind turbine is simulated by using Boundary Element Method. Helmholtz equation which dominates compressible fluid is solved in the frequency domain. The calculation results in both 2-dimensional and 3-dimensional domains are compared to understand qualitative behavior of seaquake. After understanding the basic characteristics of seaquake loads, the load effects on TLP (Tension Leg Platform) type of offshore wind turbine are discussed. A design flow of TLP type offshore wind turbine is reviewed, considering the effects of seaquake.
Collapse Analysis of Ship Hull Girder in Waves Using Idealized Structural Unit Method
Authors: Fujikubo Masahiko , Iijima Kazuhiro , Pei Zhiyong , Ko Han Htoo Htoo
Published: October 2016

Recent progress in the development and application of the ISUM plate element is highlighted with a particular focus on its application to the progressive collapse analysis of a ship hull structure. The plate element is characterized by idealized shape functions for defection based on buckling collapse mode and a simple procedure for element formulation similar to that for standard displacement-based finite elements. The formulation of the plate element under in-plane loads is presented, and then the plate element and the plate-stiffener combination model are applied to the progressive collapse analysis of a hull-girder cross section and double bottom structure. The development of a total system for motion/collapse analysis of a whole ship in waves is also presented. The effectiveness of these ISUM models is demonstrated.
Numerical Estimation on Stress Intensity Factors for Surface Cracks in a Welding Residual Stress Field
Authors: Gadallah Ramy , Osawa Naoki , Tanaka Satoyuki
Published: October 2016

Cracks are frequently found in complicated residual stress fields. It is therefore necessary to take the influence of stress field into account when calculating stress intensity factors (SIFs). In this study, SIFs for 3-D surface cracks in a flat plate model and a T-butt welded model with different dimensions are evaluated using the superposition method. To implement the superposition method, two codes are utilized, a commercial nonlinear finite element (FE) code that will progress the domain integral method using MSC Marc. The other is an open source research code that will progress the interaction integral method using WARP3D, both solutions will be applied to evaluate the SIFs. The crack face traction term (CFT-term) is neglected for the MSC Marc solution. However, the CFT-term is included in the WARP3D solution to examine the significance of this term on the accuracy of the solutions obtained by crack face traction. The SIFs calculated by direct solution, for a flat plate model and a T-butt welded model, are validated through well-established results. The accuracy of the superposition method is verified by comparing the SIFs obtained by crack face traction with those given by direct solution.

It was found that the difference between the solutions at the deepest point of the crack was less than 5%, even when the CFT-term in the domain integral method was neglected. This shows that commercial nonlinear FE codes that neglect the CFT-term can be applied for engineering problems under the conditions examined in this study. As well, the CFT-term in the interaction integral method showed a significant improvement in the accuracy of the solutions given by crack face traction for a flat plate model. It was found that the difference between the solutions was less than 0.5% at the crack deepest point.
Towards Nonlinear Wave Reconstruction and Prediction From Synthetic Radar Images
Authors: Wijaya A. P.
Published: October 2016

The use of remotely wave sensing by a marine radar is increasingly needed to provide wave information for the sake of safety and operational effectiveness in many offshore activities. Reconstruction of radar images needs to be carried out since radar images are a poor representation of the sea surface elevation: effects like shadowing and tilt determine the backscattered intensity of the images. In [1], the sea state reconstruction and wave propagation to the radar has been tackled successfully for synthetic radar images of linear seas, except for a scaling in the vertical direction. The determination of the significant wave height from the shadowed images only has been described in [2]. This paper will summarize these methods, and provides the first results for the extension to nonlinear seas.
NDP Riser VIV Model Test With Staggered Buoyancy Elements
Authors: Wu Jie , Lie Halvor , Constantinides Yiannis , Baarholm Rolf J.
Published: October 2016

The Norwegian Deepwater Program (NDP) has over several years working on conceptual development and design of new steel riser solutions for deep water and harsh environment. For the steel lazy wave riser (SLWR) design, the buoyancy section is a critical segment. When subjected to current, both the buoyancy elements and the riser may experience vortex induced vibrations (VIV), which can lead to fast accumulation of fatigue damage and amplified drag loads. As part of developing robust SLWR, it is crucial to understand the current induced loads and responses on various staggered buoyancy configurations.

In order to investigate the interaction of bare pipe section and buoyancy elements and its effect on VIV, hydrodynamic model tests were carried out in MARINTEK’s ocean basin in 2014. The test pipe is 38 m in length and 3 cm in diameter. The length of each buoyancy element 0.15 m and its diameter is 0.15 m. The ratio between buoyancy element diameter and riser diameter is 5. VIV response may depend on the spacing ratio of the length of the buoyancy segments and the gaps between two adjacent buoyancy elements, aspect ratio of the buoyancy element, and coverage percentage of buoyancy elements. Hence these parameters were varied and 6 different staggered buoyancy configurations were tested in uniform flows. The use of strakes to suppress VIV was also evaluated. The primary objective is to determine a range for these parameters that leads to the smallest VIV curvature (and hence an optimal riser fatigue design).

The shedding frequency of the bare riser section is significantly higher than the buoyancy element due to its smaller diameter. Therefore, the bare riser section will excite much higher modes. As observed from the present tests, the fatigue damage is dominated by the bare riser component for all of the test configurations. The CF displacement of cases with the highest buoyancy coverage (50%) is often dominated by the vortex shedding of the buoyancy element. The use of stakes can effectively suppress the vortex shedding and leads to lowest fatigue damage in the test. In addition, the non-dimensional frequency of the buoyancy element is low (about 0.087–0.122) due to its small aspect ratios (1/1 and 2/1) in present tests. The vortex shedding of the buoyancy element seems to be weakened when the spacing ratio is larger than 1/1, which is different than earlier tests using buoyancy element with larger aspect ratio (≥5/1). The impact on the SLWR design is evaluated based on both present and other relevant model tests results.
Critical Shock Response Spectrum of a Beam Under Shock Loading
Authors: Li Bingwei , Li Qingming , Liu Bo , Niu Zhiling , Nangong Zijun , Zhao Changjian
Published: October 2016

The offshore structures experience severe shock environment caused by storms, episodic waves, icebergs or supply ships. The aerospace equipment may also encounter severe shock loadings due to pyrotechnic shock. The intensive shock causes structural failures, or even results in fatal consequences on the related facilities and persons. Therefore it is important to study the response and the damage behavior of structures under shock loading. The damage boundary of a beam under shock is studied, based on the structural dynamics and the shock response spectrum analysis. The relationship between the critical real velocity and the critical pseudo velocity is investigated, and the concept of loading factor is proposed. A simple and practical rule of estimating structure fragility is developed based on the pseudo velocity shock response spectrum and the loading factor. The explicit numerical simulation of a beam under shock loading is carried out using LS-DYNA. The critical shock response spectrums as well as the loading factor of the beam is obtained. This paper has an important significance of helping structural engineers to design the offshore and aerospace equipment under shock environment.
Development of Under-Film Corrosion Simulation Method Based on Cellular Automaton
Authors: Osawa Naoki , Kanou Yasuhide , Kawamura Yasumi , Takada Atsushi , Shiotani Kazuhiko , Takeno Seiru , Katayama Shino , William Kristov Ivan
Published: October 2016

A simulation method for under-film corrosion has been developed for epoxy coated steel panels within a ship’s Water Ballast Tank (WBT) environment. The incubation and extension of coating failure is simulated by using two-dimensional cellular automaton, and the steel diminution is simulated by modifying IACS CSR-H’s 3-phases probabilistic model. Analysis parameters are determined by using the results of onboard exposure and cyclic corrosion tests performed by Shiotani et al. (2012, 2015). The change in corroded surface shape of epoxy coated scribed steel panels made of conventional steel and corrosion resistant steel (CRS) exposed in an ore carrier’s WBT for 4.8 years is simulated. The simulated coating deterioration (blister) area and the corroded surface profile agree well with those measured. This demonstrates the effectiveness of the developed simulation method and the determined parameters. The differences in analysis parameters between conventional steel and CRS suggest that CRS can reduce the harmful effect of the active corrosion region on the remaining coating life at the blister’s frontline and the corrosion under the blister.
A Wake Oscillator Model With Nonlinear Coupling for the VIV of Rigid Cylinder Constrained to Vibrate in the Cross-Flow Direction
Authors: Qu Y. , Metrikine A. V.
Published: October 2016

In this paper a new wake oscillator model with nonlinear coupling term is proposed to model the vortex-induced vibration of an elastically supported rigid cylinder constrained to vibrate in the cross-flow direction. The superiority of this new model lies in its ability to satisfy at the same time both free and forced vibration experiments. The new wake oscillator model is based on an existing van der Pol wake oscillator model and nonlinear coupling terms are added to improve its performance in the modelling of forced vibration. The tuning of this new model to the forced vibration shows good agreement with experiments in terms of the added damping but failed to capture the negative added mass at high reduced velocities. To eliminate this discrepancy the model is further enhanced by relaxing the assumption of constant potential added mass. Using the parameters obtained from the forced vibration experiments, the free vibration simulation is conducted and results are compared with the experiments. Comparison indicates good agreement between simulation and experiments, and the main features of VIV are captured.
Numerical Simulation of the Influence of Rounded Corners on Flow Around a Square Column
Authors: Dai S. S. , Younis B. A. , Zhang H. Y. , Zhang R. Y.
Published: October 2016

The flow around a two-dimensional smooth square column with rounded corners at subcritical Reynolds number is simulated using the finite-volume open-source software OpenFOAM. The effects of turbulence are accounted for by using a two-equation turbulence closure specifically adapted to account for the interactions between periodic vortex shedding and random turbulence. The computational approach is first validated against data for the flow past a sharp square column. The purpose of this paper is to assess the model’s applicability to the more challenging case where the column corners are rounded. Of special interest is the prediction of the pressure distribution and the unsteady force coefficients induced by periodic vortex shedding from this geometry. The computed results show that the effects of rounded corners are to progressively reduce the drag and lift coefficients, while increasing the base pressure levels relative to the case of sharp corners.
Numerical Prediction of Ship Hydrodynamic Derivatives in Close Proximity to a Vertical Bank and Maneuvering Stability Analysis
Authors: Liu Han , Ma Ning , Gu Xiechong
Published: October 2016

As bank effect has a remarkable influence on the maneuverability of a ship proceeding close to a vertical bank, the assessment of ship maneuvering stability is of great importance. The hydrodynamic derivatives of a ship can reflect the change of the ship’s maneuverability and they are determined with the method of planar motion mechanism (PMM) tests. This paper presents a numerical way to simulate the PMM captive model tests for the ship KVLCC2. A general purpose viscous flow solver was adopted to solve unsteady Reynolds averaged Navier Stokes (RANS) equations in conjunction with a RNG k-ε turbulence model. A hybrid dynamic mesh technique is developed to update the mesh volume around the ship hull when the ship is undertaking pure yaw motions and it turns out efficient and effective to solve the limitation of small ship-bank distance to the mesh configuration and remeshing.. The numerical simulations and the accuracy of the numerical method was validated in comparison with the results of PMM tests in a circulating water channel. Then a series of distances between ship and bank together with different water depths were set for simulating the PMM tests of the KVLCC2 model in proximity to a vertical bank. The first order hydrodynamic derivatives of the ship were analyzed from the time history of lateral force and yaw moment according to the multiple-run simulating procedure. The values of derivatives in different lateral proximities to the bank and variant water depths were compared and it showed some favorable trends for predicting the ship’s maneuverability in the restricted waterways. For example, the influence of velocity derivatives on lateral force reduces while that of velocity derivatives on yaw moment strengthens and this is partly due to the suction force and bow-out moment caused by bank wall effect. The straight line stability and directional stability in terms of the calculated hydrodynamic derivatives were also discussed based on the MMG model for ship maneuvering. Results indicate that the ship is inherently unstable without control and the enhancement of bank effect makes the condition even worse. Moreover, a stable or unstable zone of PD controller parameters focusing on the directional stability was illustrated and setting the values of controller parameters in the range of “Control with high sensitivity” is recommended for cases of the ship navigating in very close proximity to a bank.
Field Observation Site for Air-Sea Interactions in Tropical Cyclones
Authors: Babanin Alexander V. , Wake Geoff G. , McConochie Jason
Published: October 2016

Accurate predictions of winds, waves and currents within extreme tropical cyclones are critical for shipping, offshore oil and gas, ports and harbours, coastal erosion, tourism and fishing. The paper will describe a unique field observation programme intended to gather in situ data about air-sea interactions in tropical cyclones. The site has been established on the Woodside-operated North Rankin Complex, an offshore gas production facility located off the north-west coast of Western Australia. The facility is multi-purpose. It will assist Woodside to manage platform operations during the cyclone season and to make advances in the estimate of extreme wave crest heights for platform loading while enabling academic researchers to measure air-sea interactions. Concurrent measurements are conducted in the atmospheric boundary layer, on the ocean surface and below the surface all the way to the bottom at 120 m depth. The measurements include fluxes of momentum and energy across the air-sea interface, spray production, directional wave spectra up to high wavenumbers, and will allow us to close the balance of the air-sea exchanges for the first time in extreme field conditions.
Dynamic Analysis of a Tension Leg Platform Under Combined Wind and Wave Loads Within the Typhoon Area
Authors: Wang Bin , Tang Yougang , Li Wei , Zhai Jiawei
Published: October 2016

The dynamic analysis of a Tension Leg Platform (TLP) is investigated by combining wind and wave loads within the typhoon area. By considering different typhoon parameters, such as the tangential velocity, the radius of maximum velocity, the translational direction and velocity, the model of typhoon is established. The wave height and period are obtained by the empirical formula related to the parameters of typhoon. The nonlinear restoring stiffness of TLP is derived with the set-down motion of platform and the coupled motion of the tension leg and platform. The results in this paper indicates that typhoon has a major impact on the safety of the platform in production operation, and it is also a threat to the strength of tension legs and risers.
Towing Analysis of Multi-Cylinder Platform for Offshore Marginal Oil Field Development
Authors: Zhao Zhijuan , Tang Yougang , Wu Zhirong , Li Yan , Wang Zhenkui
Published: October 2016

As the development of offshore marginal field becomes a heated topic, various design selections of offshore platform have already been put forward in the community such as Sevan SSP, IQFP-FPSO, octagonal FPSO or sandglass-type FDPSO. In this paper, a new Muliti-Cylinder FPSO (MCPSO) with section pile foundation is proposed for developing offshore marginal field in South China Sea. And the structure design in detail has been described.

The MCPSO consists of six cylindrical concrete tanks and six suction piles. The suction piles can be raised up during platform towing process. Considering the effects of tanks and piles on the towing stability, both intact and damage stability analysis of MCPSO were performed under different towing conditions. The influence of ballast ratio, towing direction and different damaged modes on the towing stability is analyzed.

The results indicate that the MCPSO has the characteristics of self-installation, movable, reusable and so on, which is suitable for the development of marginal oil field. The MCPSO filled with 40% seawater in ballast tank and towed in 90 direction has the best intact and damage stability characteristic.