bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Distortion Nature of the Collapse Behaviors for Geometrically Distorted Thin-Walled Hull Girder Subjected to Combined Loads
Authors: Wang Qinghu , Wang Deyu
Published: October 2022

The objective of this research is to reveal the nonlinear distortion nature of the collapse behaviors of geometrically distorted scale models subjected to combined bottom local lateral pressure and hogging moment, aiming at improving the accuracy of the linear scaling law which is currently most used to convert the ultimate strength between geometrically distorted scale models and prototype (CL = 1; Ct = 1). To achieve this aim, firstly, a typical thin-walled hull girder was designed and manufactured, with which a physical collapse test was conducted to experimentally observe its collapse behaviors. Then the physical validation of the finite element model was demonstrated by experimental results. To apply a combined action of bottom local lateral pressure and hogging moment, a similarity criterion of the bottom local lateral pressure was analytically derived based on dimension analysis. After that, a series of geometrically distorted scale models were designed to study the distortion nature of hull girder’s ultimate strength under above combined loads. Finally, for engineering application, we proposed two new scaling criterions for converting the ultimate strength between geometrically distorted scale models and prototype.
Primary Cementing of Horizontal Wellbores With Solid Cutting Beds
Authors: Mitishita Rodrigo S. , Sarmadi Parisa , Waldal Nile , Vogl Anastasia , Frigaard Ian A.
Published: October 2022

We present an experimental and numerical investigation of displacements of viscoplastic fluids in an eccentric, horizontal annulus with a cutting bed left in the well. This problem is of interest to both industrial and academic viewpoints. Firstly, the experiment provides a simplified, analogous effect to a cuttings bed in industrial situations. Secondly, while successful and failed displacements of viscoplastic fluids with various eccentricities have been well documented in the literature, displacements with a blockage in the annular geometry have not been experimentally studied before. We carry out the experiments with a pump driven flow loop with a 7.5m annular test section, with a borosilicate glass outer pipe and stainless steel inner pipe. To model the cutting bed, a solid insert is attached to the narrow side of the annulus. Carbopol solutions, widely known as model yield-stress fluids, are displaced from the blocked annulus. Our protocol consists of direct visualization of the interface between the displaced and displacing fluids with a high-speed camera and UV-lighting setup, along with pressure and flow rate measurements. We compare our experimental data and images with 3D numerical simulations, using a Volume of Fluid method to capture the interface between the fluids. The 3D model provides us with a more detailed analysis of the concentration and velocity profiles, along with comparisons to snapshots of the experimental displacements.

The dynamics of the displacement of two fluids in a horizontal circular annulus is governed by buoyancy, eccentricity and the rheology of the fluids. A positive density difference promotes slumping of the displacing fluid towards the bottom of the annulus. Nevertheless, high eccentricity values (e = 1-standoff) are common due to the weight of the casing pulling downwards, opposing the buoyancy force. Finally, the rheology of the fluids is relevant to determine the presence of un-displaced layers of mud, e.g. at the walls. The same competition described above holds true in the annulus with cutting beds. The blockage incorporates an additional way of altering the velocity field around the annulus. Here we show that the blockage can affect the mud removal in the annular space of the well.
Application of Dipole Damper Panels in Modelling Gap Resonance
Authors: Ommani Babak , Ravinthrakumar Senthuran , Kristiansen Trygve , Olimb Idunn , Lyngvær Bernt Karsten
Published: October 2022

Modelling the fluid response in a gap using conventional frequency domain potential flow solvers is a challenge due to its resonance behavior and the importance of viscous effects. Damping panels, or lids, are usually used to represent the main viscous effects, when more direct method of calculation is not applicable due to limitations on time or computation resources. Although, it is known that the main contributor to the damping is the flow separation at the gap inlet, these methods usually relate the magnitude of the effective damping to the vertical fluid velocity at the surface. In the present study, the application of dipole damping surfaces, as introduced in potential flow code WAMIT, is studied for modelling the flow separation effects more consistently. The relative fluid velocity at the inlet is used to model the damping effect of flow separation. Simplified empirical models are proposed to estimate the magnitude of the damping. The experimental study of flow between two side by side barges by Molin et a. 2009 [1] has been selected to evaluate the present modelling approach. The numerical results show good agreement with the measurements while providing a more consistent basis to apply stochastic linearization of the quadratic damping due to flow separation at the gap inlet.
URANS Predictions of Drift Loads on a Semi Submersible in Steep Waves
Authors: Jaouën Frédérick , Koop Arjen , Bunnik Tim
Published: October 2022

The last decade, many semi-submersible designs have been tested in MARIN’s wave basins as a result of recently modified classification society guidelines requiring to investigate the air-gap of semi-submersibles in waves and the occurrence of wave impacts on deck. The main objective of these tests is to investigate the motions, air-gap and mooring line loads in extreme irregular seas. In several of these model test projects, it was found that accurately predicting the motions of the platform using numerical simulations is not an easy task. Especially, the measured horizontal and vertical low-frequency resonant motions were regularly found to be much larger than predicted by numerical results based on linear potential flow theory. These low-frequency motions are mainly caused by the wave drift loads, i.e. the mean and low-frequency wave loads resulting from the non-linear behavior of the structure in the waves. As these drift loads can be affected by higher than second order effects, model testing is still the preferred method to quantify the loads and resulting motions in survival sea states. However, model test results are most often not available in the early design stage and modifying the design may not be easy when model test results become available, further on in the project. Therefore, the development of a reliable and fast prediction technique would be valuable to improve the design of moored semi-submersibles. Such a method may be CFD, which has the potential to predict the motions and drift loads applied on semi-submersibles in steep waves, without and with the presence of current. To obtain confidence in the accuracy of the CFD results, a validation of these results is essential in the first place.

In this paper, the motions and loads applied on the Stena Don semi-submersible in head-on waves are calculated using MARIN’s CFD code ReFRESCO. The objective is to assess whether the motions and the mean drift loads can be correctly predicted using CFD for regular waves of different steepness. The horizontal drift loads are focused on in this paper. In order to assess the accuracy of the results and the capability of CFD, a stepwise approach has been followed. First, the wave generation and propagation is investigated without any floater present. Then, the soft-moored semi-submersible is simulated in regular waves, with and without current, and the vessel motions and mean drift loads are analyzed. Finally, the CFD results are compared to results from potential flow based linear diffraction calculations, and to results from the wave basin. This study confirms that CFD is able to calculate the drift loads accurately in various regular waves. Furthermore, it can be observed that linear potential flow theory severely underpredicts the mean drift loads for steep waves with or without current.
Experimental Studies of Additive Manufacturing for Subsea Enclosures
Authors: Krohmann Sascha , Rautmann Louis Leon , Glatzer Lars , Kosleck Sascha
Published: October 2022

Additive manufacturing has become an essential part of rapid prototyping. In ocean engineering and especially ocean research technology, additive manufacturing can be an effective and cost-efficient way of creating highly customized products such as pressure-resistant enclosures with complex requirements. Furthermore, using lightweight 3D-printing materials significantly reduces the component’s weight. Conversely, payloads can be increased — another advantage compared to pressure enclosures built from conventional materials.

In this context, an experimental study of the behaviour of additive manufactured enclosures for subsea applications is performed. For this purpose, a suitable design is selected and adapted to meet manufacturing process requirements. Polyethylene terephthalate (PETG) and polycarbonate (PC) are selected as filament materials. In addition, post-printing treatments are studied. The various specimens are immersed in water to ensure a sufficient saturation level. After a period of three days, each sample is then exposed to increased hydrostatic pressure until collapse.

Finally, all experimental results are used to establish initial design and safety factors, reflecting the mechanical properties of the materials as well as the specific characteristics of the selected additive manufacturing process.
Vortex-Induced Vibrations of a Top-Tensioned Riser in Combined Currents and Waves
Authors: Yin Decao , Wu Jie , Lie Halvor , Passano Elizabeth , Sævik Svein , Grytoyr Guttorm , Tognarelli Michael A. , Andersen Torgrim , Igland Ragnar , Karunakaran Daniel , Gaskill Collin
Published: October 2022

Offshore drilling risers, top-tensioned risers and many production risers are top tensioned, connecting the vessel and seabed via joints. External loads such as currents, waves and vessel motions introduce cyclic loads and motions on riser sections, which may shorten the service life due to accumulated fatigue damage. Dynamic responses under combined currents and waves are more complicated than vortex-induced vibrations (VIV) due to pure currents, and it is not fully understood.

Several model test campaigns on top-tensioned riser (TTR) have been carried out at SINTEF Ocean (former MARINTEK) during the past decades. Currents, waves and vessel motions were modelled, and the riser model responses were measured. In this study, selected cases from such model tests are analysed, and used to validate a semi-empirical time domain VIV prediction tool — VIVANA-TD.

A better understanding of the dynamic responses of TTR under combined currents and waves has been achieved. By comparing the results from numerical simulation using VIVANA-TD and model test measurements, validity and limitation of the time domain tool have been investigated. Important features that need to be considered are discussed. The experience gained from the present study establishes a good basis for VIV and wave load prediction of full-scale TTRs under combined currents and waves where the uncertainty of VIV prediction is further reduced.
Ice-Induced Loads on Offshore Wind Turbines in the Baltic Sea
Authors: Tabri Kristjan , Tõns Tõnis , Suominen Mikko , Kõrgesaar Mihkel
Published: October 2022

The interaction of sea ice with offshore structures is an important engineering concern in ice-infested areas. This paper presents a procedure to evaluate ice loads acting at the sloping offshore wind turbines in the Estonian territorial waters at the Baltic Sea, where the waters are seasonally covered by ice. Region-specific characterization of ice thickness and ice days is done with the help of assessing ice maps from a period of 15 years. For each year, the number of days with ice coverage and thickness are determined. The extreme value probability distribution for annual maximum ice thickness is determined by fitting an asymptotic extreme value distribution to the maximum annual ice thickness.

For ice-structure interaction, a numerical ice model suitable for the Baltic Sea ice is implemented. The ice is treated as an isotropic, brittle material described by stress-strain curves for compression and tension. Numerical assessment is conducted to evaluate the ice load history, load maxima, and variations for a selected wind turbine foundation design.
High Frequency Tail in Measured Wave Spectra of Steep to Breaking Sea States
Authors: Scharnke Jule , Ewans Kevin , Kirezci Cagil , Babanin Alexander
Published: October 2022

A recent study investigated whether it is physically feasible to generate the tail of a JONSWAP wave spectrum in a basin, and what the influence of wave breaking is on the energy content of this high frequency tail. It has been observed in basin measurements at MARIN that in steep sea states a dip starts to develop in the high frequency tail of the spectrum. This dip occurs due to non-linear wave interactions and/or wave breaking and a resulting energy shift and dissipation. This effect cannot be compensated by adding more energy at the wave maker at these frequencies, as the energy will continue to shift/dissipate as more non-linear interaction and wave breaking occurs. The objective of this research was to investigate whether a similar energy dip would occur in real environments or whether the effect is related to the fact that in lab environments the waves are generated at one location of the basin and not through wind blowing over the sea surface continuously.

In cooperation with the University of Melbourne and MetOcean Research, several examples have been found in full scale measurements as well as non-linear wave simulations where a similar energy dip appears to occur. In this paper the physics involved in the reduced energy of the high frequency tail of very steep wave spectra are discussed and basin wave measurements are compared to nonlinear simulations and full scale measurements.
Performance of PA6C Plastic Sheaves Used for Mooring Line Installation
Authors: Hellum Vidar , Vaalandsmyr Anders , Schonlau Thomas , Heimdal Anette , Meijer Jawk
Published: October 2022

Mooring lines are important components in floating offshore energy installations such as wind turbines and oil and gas vessels. Efficient installation of the mooring lines is important to reduce costly and energy consuming offshore operations. In the present paper investigations have been performed on the performance of sheaves made from Lamigamid® 319, which is a specific type of PA6C plastic. The sheaves are intended for subsea pull-in operations of mooring lines during mooring line installation. The sheaves are a vital component of a proposed installation system which could limit the time spent on subsea operations. Additionally, the low density of the material, the possibility of using it without bearings and using highly stressed sheaves makes it possible to reduce the necessary material for temporary equipment to a minimum. Initial Finite Element Analyses based on material models from tension tests showed that the designed sheaves would suffer large deformations when subject to the design loads. A full-scale test was performed to corroborate these results but during this test almost no permanent deformation was recorded on the sheave. Further, a test series with compression tests of different shaped samples were initiated. The first results from this test series showed a remarkable strength of the material in compression and raised several questions regarding models for predicting the behavior of Lamigamid® 319 during loading. Hence, further tests were done and modelling techniques for finding structural capacity are discussed.
Experimental Investigation of Slamming Loads on Vertical Column Exposed to Short and Long Crested Waves
Authors: Økland Ole David , Lian Gunnar , Vestbøstad Tone
Published: October 2022

Model test campaigns conducted recent years indicate large wave impact loads on vertical surfaces above the waterline for various types of moored floating structures. These impacts are caused by breaking or near breaking waves in extreme sea states. Due to the large variability of the load, it is challenging to estimate the characteristic slamming loads, defined as the q-annual extreme 3-hour slamming load level of 10-2 for the Ultimate Limit State (ULS) and 10-4 for the Accidental Limit State (ALS). Hence, many tests realizations are necessary to assess extreme loads.

It is common practice to assume long crested waves in design against slamming loads. This assumption is regarded as conservative, and there have been indications that the effect of short crested waves on impact loads could be significant. In the present work an experimental investigation was set up to study effect of short crested waves for slamming against a rigid vertical column. Influence of current and other modeling parameters like type of wavemaker (single vs double flap), were also studied. A test model in scale 1:55 of a 31m diameter column at water depth 121m was used. The area of the column facing the incoming wave was instrumented by slamming panels. The setup covers 80 degrees of the cylinder circumference over a height of 24 meters from the still water surface and upwards. In addition to the slamming loads measured on the column, shear force and bending moment at the base of the column and global accelerations for the column were measured. High-speed video recordings were made for slamming events above a given threshold.
Modification of Double Bottom Height and Its Effect to the Ultimate Strength
Authors: Muis Alie Muhammad Zubair , Suci Indah Melati , Arafat Andi Muhammad Alfian , Juswan  , Mustafa Wahyuddin
Published: October 2022

Double bottom is one part of the ship’s construction which is located at the bottom and it functioned to overcome when the ship collides with the other object at the outer of ship’s bottom. One of the parameters of the double bottom that must be considered is double bottom height. These would affects to the section inertia, section modulus and neutral axis position leading to the ultimate strength of ship.

The objective of the present study is to analyze the ultimate strength caused by the double bottom height before and after modification. The double bottom height is analyzed according to the existing condition, national and international classification. Those formulas are different so that it is very important to know those effects. The numerical method is adopted to analyze the tankers ship caused by changing the double bottom height before and after modification. The force rotation is given at the master node since it is placed after determined the position of neutral axis as reference point.

It is observed that the double bottom height gives significant influence to the ultimate strength according to existing condition, national and international classification before and after modification under hogging and sagging conditions. The ultimate strength in terms of the moment-curvature relationship including their behavior is presented in this study.
Structural Response of Subsea Pipe Elbows Under Monotonic and Cyclic Loading
Authors: Varelis George E. , Dib Elie , Karamanos Spyros A.
Published: October 2022

Pipe bends (elbows) are commonly used components in subsea piping systems. They are quite flexible compared to the corresponding straight pipes and are used to reduce the reaction forces and moments at the supports and the bending moments within the piping system, as well as to accommodate pipeline thermal expansion requirements. Because of their flexibility though, they develop significant deformations, mainly in the form of cross-sectional deformation (ovalization), which are associated with the development of local stresses and strains, significantly larger than those in the corresponding straight pipe, and may cause either buckling or rupture of the elbow pipe wall.

Several works have been reported on the structural performance and integrity of elbows in piping systems, in power plants or process industries. Under extreme loading conditions, e.g. seismic, or under shutdown/startup conditions, those elbows are subjected to bending under internal pressure, which may cause either plastic collapse or fracture due to low-cycle fatigue. On the other hand, the response of externally pressurised thick-walled elbows used in subsea systems, has received much less attention. The main feature in those elbows is the presence of external pressure, which has a destabilizing effect, especially in deep water applications. Under monotonic load, in the presence of external pressure, elbow ovalization is accentuated leading to pipe collapse at relatively low levels of structural loading. Under cyclic loading, progressive ovalization of the elbow occurs due to accumulation of plastic deformation, which may also result in rapid collapse due to the presence of external pressure.

The present paper, motivated by the use of steel elbows in subsea systems, describes a finite element simulation of elbow response under static and cyclic loading, in the presence of external pressure. Particular emphasis is given on the constitutive model, which should be capable of simulating the response of steel material under cyclic loading, and primarily, the accumulation of plastic strain over the loading cycles. The numerical results are compared with the design provisions in DNVGL-ST-F101.
FRyFAST : A Coupling Between FRyDoM and OpenFAST for the Simulation of Floating Offshore Wind Turbines With High Complexity Platforms
Authors: Chauvigné Camille , Letournel Lucas , Rongère François , Wuillaume Pierre-Yves , Castro Casas Natalia , Maréchal Benjamin , Kerkeni Sofien
Published: October 2022

The present paper describes the coupling between two open source software packages, OpenFAST and FRyDoM (named FRyFAST), dedicated to the floating offshore wind turbine (FOWT) dynamics simulation. FRyDoM (Flexible and Rigid body Dynamic modelling for Marine operations) is a multi-body and multi-physics framework, mainly dedicated to complex offshore systems, developed by D-ICE Engineering and Ecole Centrale Nantes. This framework is coupled with OpenFAST in order to simulate FOWT with advanced platform system, corresponding to multi-body system, platform with high interaction with other bodies in close environment or in contact with those bodies. This coupling enables also the used of an advanced Finite Element Model (FEM) based on an iso-geometric representation of the mooring lines. A lot of dedicated models for the platform can also be added through this coupling thanks to the FRyDoM API. In the first part, the coupling between OpenFAST and FRyDoM is presented. Particular attention has been paid to the integration of the added mass term to enable stability of this coupling, and to the synchronization between the two time integration schemes. Verification and validation results of this coupling will be presented. Tension in the mooring lines, dynamic behaviour of the FOWT in different wind and sea conditions have been analysed and show the capacity of this model to perform FOWT design.
The Impact of Climate Change on Offshore Operations and Design Considerations for Offshore Vessels and Installations
Authors: Rosen Jordan , Kilner Andrew , Gumley Jonathan , Jayasinghe Kanishka , Thurumella Hemant
Published: October 2022

This paper investigates the impact on the availability, uptime, and design conditions of offshore facilities and operations due to climate change. As the physical processes that generate ocean waves are intrinsically linked to atmospheric conditions, the ocean wave climate will change as global temperatures increase and global winds change. The impacts on offshore facilities have been investigated by studying and comparing wave climate predictions for a range of climate change scenarios, considering both the magnitude of temperature increase and the time horizon of the scenario. This paper relies on the scenarios generated in multiple revisions of the Coupled Model Intercomparison Project (CMIP).

This paper presents the impacts of climate change in a series of case studies:

• Changing design wave conditions for several potential offshore wind farm developments around Australia.

• The predicted change in the availability and uptime of five Single Point Mooring (SPM) terminals around South America.

• The predicted change in durations of offshore platform decommissioning activities and the duration of operations to install new floating facilities.
Wave Attenuation Performance of Arranging a Rectangular Buoy in a Perforated Caisson Using Quadratic Pressure Drop Condition
Authors: Wang Yuhan , Dong Sheng
Published: October 2022

Integrating a rectangular buoy type wave energy converter (WEC) inside the perforated caisson can be advantageous to the wave attenuation performance as well as the stability of the WEC. As a preliminary study on such integration system, a theoretical model was established to investigate the wave attenuation performance of the integration system with a fixed buoy inside a perforated caisson. The methods of separation of variables and eigenfunction function expansion were used to determine the velocity potentials in different fluid domains. Instead of the traditional linear pressure drop condition for perforated walls, a quadratic condition, which is more consistent with the practical truth, was used in this study. The proposed model was validated by results in a former research. The wave attenuation performance was then investigated and discussed through a parametric study.
Load Capacity of Sandwich Panel With Core Foam Evaluated by 3-Point Bending Test
Authors: Josefson B. L. , Paboeuf S. , Anyfantis K. , Zamarin A. , Oddy C. , Collier B. , Ntouni K. , Bolf D.
Published: October 2022

The classification society Bureau Veritas requires a structural assessment of composite materials structures to confirm the compliance with applicable rules, like 3-point bending tests. However, for sandwich panels with a low-density foam core, local phenomena like indentation and wrinkling may occur in the upper face sheet at the loading punch, thus the intended load capacity of the sandwich panel will not be reached. It is then proposed to perform complementary shear tests to capture the behaviour of the core of the sandwich panel.

In the present paper, the load capacity in a 3-point bending test is simulated with emphasis on the influence of the constitutive modelling of the core foam, as calibrated against experimental results for shear tests. It is carried out as a benchmark exercise, with participation from three universities.

The FE-simulations show that the shear test can be used to accurately model the load capacity of the core foam. However, for the 3-point bending test using specimen with a very high panel length / thickness ratio a large part of the load transfer is done in the upper face sheet with less involvement of shear in the core. Although core fracture is observed in the experiments, both the FE-simulated and experimentally found maximum load agree well with the load capacity as determined from analytical formula for local failure in the upper face sheet. The FE-simulated vertical displacement at maximum load differs though.
Topology Optimization of Joints Between Prismatic Sandwich Panels and Girders Under In-Plane and Bending Loads
Authors: Yan Shengyu , Jelovica Jasmin
Published: October 2022

Prismatic sandwich structures offer improved mechanical properties over traditional structures used in ships and other vehicles. While research on their response and strength under local and hull girder loads has been advancing, insufficient attention has been placed on their joints, i.e. connections to surrounding structure, such as girders and bulkheads. It is important to seek appropriate topology of the joints to minimize stress they experience. We conduct this investigation via topology optimization, minimizing stress for a given volume fraction of a material. Aggregation approach is used where a p-norm function approximates the maximum stress in the finite element analysis to reduce the number of iterations to reach converged solution. Optimization is performed using sequential convex approximations via Method of Moving Asymptotes (MMA). The optimization is performed in Matlab. Maximum stress of optimized designs is validated using Abaqus. Joints are optimized for three load cases, combining moment on the joint (coming from lateral pressure on the panel) with in-plane tension and compression. Several topologies of the joint were found which feature 2–3 times smaller maximum stress than the conventional joint, even for lower structural weight (material volume fraction). However, the complexity of the joint is increased, which can be controlled effectively by the filter radius and passive elements.
Validation of a Simplified Numerical FLNG-Carrier Side-by-Side Offloading Model With Experiment
Authors: Wang Yutao , Wolgamot Hugh , Zhao Wenhua , Draper Scott , Milne Ian
Published: October 2022

One of the key challenges associated with an FLNG facility is to optimise its offloading operability. LNG offloading operations typically use a side-by-side (SBS) configuration, where a carrier is moored parallel to the FLNG, leaving only a relatively small gap between the two vessels. In this paper, a numerical model for predicting the relative motion between an FLNG vessel and LNG carrier during offloading is developed using potential flow theory, and compared to wave basin experiments on simplified box geometries.

In particular, this study addresses the prediction of roll motion, which is critical to SBS operation but difficult to model within the potential theory framework due to its dependence on viscous damping. The Ikeda method, which is an industry standard method for calculating ship roll damping, is applied in the model. However, since the Ikeda method was developed for a single hull, a modification is proposed to deliver improved performance in the context of the SBS offloading operation. More specifically, the small clearance between the vessels will influence the flow field and subsequently modify the fluid velocity around the bilge. This study suggests that the relative velocity between the fluid and hull roll motion is a better input for the original Ikeda method.
Flow Around Curved Tandem Cylinders
Authors: Aasland Tale E. , Pettersen Bjørnar , Andersson Helge I. , Jiang Fengjian
Published: October 2022

The flow around curved tandem cylinders of equal diameter has been investigated for the first time, by means of direct numerical simulations. A convex configuration was used. The nominal gap ratio was L/D = 3.0 and a Reynolds number of 500 was chosen. Due to the change in effective gap ratio along the cylinder axis, there is a variation of tandem flow regimes, from alternating overshoot/reattachment, via stable reattachment, to co-shedding, in this case called gap shedding. The combination of reattachment and gap shedding gives near-zero drag and vertical forces for the downstream cylinder, whereas the corresponding forces on the upstream cylinder are comparable to single curved cylinders. Meanwhile, the opposite is true for the lift forces. A low-frequency variation of horizontal and vertical forces is seen, and this is attributed to a slow variation of the position where gap shedding commences. Finally, the concept of a critical angle is proposed to describe the transition to gap shedding, for a given combination of nominal gap ratio and Reynolds number.
An Evaluation of Consequence Severity of Ship Evacuations in the Canadian Arctic
Authors: Browne Thomas , Kennedy Allison , Piercey Caitlin , Power Jonathan , Veitch Brian
Published: October 2022

Ship evacuations in Arctic waters expose crew and passengers to the potential for severe life-safety consequences. Effective planning and allocation of Arctic SAR services should be supported by evidence-based assessments of the consequence severity of ship evacuations. This paper provides an evaluation of life-safety consequence severity for ship evacuation scenarios in the Canadian Arctic. Exposure time is a predominant factor influencing consequence severity of Arctic ship evacuations. The study integrates existing models for exposure time estimation [1,2] and life-safety consequence [3]. Exposure time is estimated for air- and marine-based SAR assets, considering associated capacities, speeds, and operating ranges. Evacuation scenario factors include ship type, number of POB, and geographic location. The methodology provides Arctic SAR service providers with a tool for planning effective resource allocation and response efforts. As a base case, exposure times and consequence severities are estimated for SAR response with a single asset. The effect of deploying multiple SAR assets is demonstrated. Results indicate that the deployment of air-based SAR assets contributes to reduced exposure times and mitigation of life-safety consequence severity. Evacuation of a passenger vessel is a worst-case scenario. Evacuations of high POB vessels require the deployment of multiple SAR assets to prevent potential disastrous life-safety consequences.
Optimizing Models for Predicting Torque on Bit Using Data From the Volve Field in Norway
Authors: Höhn Patrick , Bashara Ahmed Rahim Kreem , Paz Carlos , Oppelt Joachim
Published: October 2022

Torsional oscillations can cause severe damage to downhole tools and may result in expensive fishing and sidetracking operations. The drilling industry is aware of this problem and still looking for suitable solutions to determine the drivers of the oscillations, and to quantify their effects. The mitigation of this problem requires a detailed knowledge of the parameters controlling the drilling process. Nowadays, modeling is a useful tool for describing the downhole processes using the stream of data acquired from the sensors installed in the drilling equipment.

This paper focuses on torque on bit which is directly connected with torsional oscillations. The model generation is performed, either by fitting empirical models with measured data or by creating new machine learning models. Five empirical literature models are parametrized using the optimization module of the Python library SciPy. Machine learning models are generated using Scikit-learn with measurement data from the Volve field in Norway. For the current testing dataset Random Forest showed the highest accuracy with a R2-score of 0.767. Other machine learning algorithms showed a comparable accuracy. However, empirical models failed to achieve reliable results. In future, the generated models can be used to optimize drilling parameters to prevent technical drilling problems.
Simulation of a Moored Multibody Offshore Structure Articulated by Different Joints in Waves
Authors: Jiang Changqing , el Moctar Ould , Zhang Guiyong , Schellin Thomas E.
Published: October 2022

Within the framework of the Space@Sea project, a modular floating structure (MFS) was developed to serve as building blocks for artificial islands. The modularity was one of the key elements, intended to provide the desired flexibility of additional deck space at sea. Depending on the purpose of a modular floating concept, various articulation techniques, such as hinge, prismatic, cylindrical and screw joints can be applied to connect MFSs. This paper presents numerical simulations of moored and articulated multibody offshore structures in waves, via a coupled mooring-joint-viscous flow solver accounting for mooring dynamics, joint restrictions, nonlinear rigid body motions, and viscous flow effects. The considered concepts consisted of two MFSs connected by two kinds of connections, namely a rigid joint and a flexible joint, and positioned by four symmetrical catenary mooring lines. The analyzed responses comprised multibody motions as well as associated forces acting in the hinged joints and the mooring lines. Results indicated that surge motions of the articulated bodies were almost identical to each other, whereas the effects of the joint on heave motions were not pronounced. However, highly dynamic pitch motions between two hinged MFSs were observed. Apart from motion responses, forces acting on the hinge joint and the mooring lines were considered. The coupled mooring-joint-viscous flow solver demonstrated its ability to predict responses of moored and articulated offshore structures in waves.
The Comparison of Two Kinematic Motion Models for Autonomous Shipping Maneuvers
Authors: Wang Yufei , Perera Lokukaluge P. , Batalden Bjørn-Morten
Published: October 2022

Autonomous shipping with adequate decision support systems is widely considered as a high-potential development direction in the maritime industry in the upcoming years. Prediction technologies are one of the key components in these decision support systems and they usually require a large number of data sets to estimate vessel states. Certain vessel motion models are generally implemented with the above-mentioned prediction technologies to improve the accuracy and robustness of the estimated states. In contrast to wider research studies of different motion models for the applications of ground vehicles, the studies of appropriate motion models for maritime transport applications are still insufficient. Therefore, it is necessary to develop reliable motion models for vessels, and that can improve the decision supporting capabilities in future vessels, especially in autonomous shipping.

In this paper, two kinematic motion models which can be used to estimate various vessel maneuvering states are examined and compared. In the current stage, the proposed models are used to investigate ship maneuvers produced by a ship bridge simulator. Two nonlinear filter algorithms combined with Monte Carlo-based simulation tests are applied to estimate the respective vessel states. In the conclusion, a comprehensive comparison of the estimation algorithms is presented with the estimated vessel states. Hence, this study provides robust and convenient estimation algorithms that can support autonomous shipping navigation in the future.
Development of Guar Gum Fracturing Fluid With Temperature Resistance of 150°C and Specific Gravity of 1.0~1.2g/m3
Authors: Xue Meng , Liyan Zhu , Yongchang Zhao , Zhishuo Chen , Abulimiti Waili , Erdong Yao
Published: October 2022

For major high temperature and deep reservoir in West China, hydraulic stimulation confronts challenges of true vertical depth more than 6000 m and bottom hole temperature beyond 150°C. The long injection path from surface to stimulated formation induces significant friction. It commonly leads to very high ground pressure, which will exceed the limit of ground pumping equipment. In addition, conventional fracture fluid systems lost their fracturing ability and sand carrying capacity under high temperature. Therefore, it is urgent to develop a novel fracture fluid system with adjustable specific gravity and high temperature resistance for high temperature deep reservoir fracturing.

In this article, the basic properties of guar gum were determined at first, and a high temperature and salt resistant organic boron crosslinking agent was synthesized. The optimal dosage and the optimal crosslinking pH, and the delayed time for crosslinking was studied. Then, the relationship between fluid density and weighting agent dosage is measured, which will facilitate the fracturing fluid density adjustment in the field. Three specific gravity formulas of fracturing fluid, that is 1.10, 1.15 and 1.20g/cm3, is optimized. Finally, the performance of fracturing fluid was evaluated comprehensively, and its gel-breaking and formation damage performance were tested.

The apparent viscosity of 0.5wt% guar gum solution was 57.2mPa · s at room temperature (25 °C), and 29.1mPa · s at 150 °C. The synthesized high-temperature boron crosslinking agent YP-4 is colorless, transparent, and miscible with water. The optimal crosslinking concentration is 0.65wt%. The crosslinking occurred in the range of pH = 9∼12. The crosslinking time can be controlled within 3∼10min by adjusting the dosage and pH value. NaCl weighting fluid formulas with a density of 1.0∼1.2g/cm3 was optimized. The optimal fracturing fluid formulation was 0%∼26.4wt% NaCl brine +0.5wt% hydroxypropyl guar gum +0.3wt% alkaline pH regulator +0.65wt% crosslinking agent YP-4. This fracturing fluid can stable for more than 60min at 150 °C and 170s−1, and the final viscosity was high than 100 mPa·s. If the guar gum concentration was increased to 0.55wt%, the viscosity would exceed 260 mPa·s. 0.2wt% amine persulfate can be used to break the fracturing fluid, and the viscosity after breaking is less than 4mPa·s. What’s more, the fracturing fluid has good compatibility with various additives, and no flocculation or precipitation occurs within 24h. The average damage of gel breaking liquid to the core is 24.81%, which is relatively small. High temperature resistance and adjustable weight density have great advantages in field applications. Equipment constraints can be met while fracturing can be performed at minimal cost. This fluid system will provide beneficial support for high temperature and deep well fracturing.
A Deep Learning Model for Rate of Penetration Prediction and Drilling Performance Optimization Using Genetic Algorithm
Authors: Erge Oney , Ozbayoglu Murat , Ozbayoglu Evren
Published: October 2022

In this study, a deep learning model is proposed that can accurately predict the rate of penetration during geothermal or oil and gas well construction operations. Also, a genetic algorithm is applied and used together with the deep learning model to determine the optimum values for the drilling parameters: weight on bit (WOB) and drillstring rotation rate (RPM).

It is vital to estimate the optimal set of values for drilling parameters to construct wellbores quickly and efficiently. Traditionally, drill-off tests are conducted by halting the normal drilling operation and manually changing the WOB and RPM values to search for the highest ROP output. This operation can be repetitive and can lead to an inaccurate estimation of parameters because only a few different parameters are tried. The proposed learning algorithm estimates the optimum WOB and RPM, based on the historical values and can keep learning as the drilling proceeds, which is essential for fully automated well construction.

The proposed deep learning model is trained with actual drilling datasets that showed an accurate prediction of the rate of penetration and mechanical specific energy (MSE). This model is used together with the genetic algorithm and the optimum drilling parameters are determined that yield minimum MSE. The results showed a significant performance improvement compared to the historical values.

The proposed model can be used as an advisory system to the driller or the output can be used within the control system to automate the drilling process. The proposed learning model showed the capability to further optimize the drilling-rate and mitigate any invisible lost time (ILT) and potential nonproductive time (NPT) by completing the well as soon as possible.
On the Structural Analysis of Icebreakers Due to Ramming of First-Year Ice Ridges
Authors: Zhao Weidong , Johan Leira Bernt , Vilhelm Høyland Knut , Kim Ekaterina , Feng Guoqing , Chen Zhanyang , Gui Hongbin
Published: October 2022

Sea ice ridges, formed by compression or shear in the ice cover, bring additional challenges to the structural safety of icebreakers navigating in polar regions. The purpose of this work is to carry out the structural analysis of an icebreaker during ramming of first-year ice ridges. A heavy icebreaker is chosen for the analysis, and the geometrical and physical properties of the ice ridge are determined based on empirical data. The ice ridge is modeled by solid elements deploying the continuous surface cap model (CSCM) with different materials’ parameters for the consolidated part and the unconsolidated part. Based on the numerical simulations of the ship-ridge interactions, the local ice-induced pressure on the hull shell is obtained. Subsequently, the local ice pressure is applied to local deformable sub-structural models of the heavy icebreaker. Subsequently, the ice-induced structural responses of the local sub-structural models are evaluated. Furthermore, the effect of model parameter settings related to the ice ridge on local ice pressures and structural responses are analyzed. Finally, the structural responses of the icebreaker navigating at the ship speed limit is also discussed.
A Semi-Analytical Methodology to Assess the Dynamic Elastic Response of a Monopile Offshore Wind Turbine Subjected to Low-Energy Ship Impacts
Authors: Ladeira Icaro , Le Sourne Hervé , Moran Jonathan , Salazar Priscilla
Published: October 2022

Low-energy impacts between ships and offshore wind turbines (OWT) can occur during maintenance operations, when service vessels need to approach the turbine at low speeds. While this type of accident might not result in significant permanent damage of the tower or the foundation, the whipping elastic response of the overall structure can induce high accelerations at the rotor-nacelle assembly (RNA), where sensitive subcomponents such as the generator, bearings and gearbox are contained.

This study presents a two-step methodology to quickly assess the whipping elastic response of a monopile OWT subjected to a low-energy ship impact. The first step consists of modelling the monopile as a reduced set of Euler-Bernoulli beams with different cross-sections and a tip lumped mass representing the RNA. A semi-analytical framework is used to derive closed-form expressions to calculate natural frequencies and mode shapes of the beam assembly. Once these properties are obtained, the modal superposition method is applied to calculate the monopile’s response to a pre-defined collision force. Validation of this semi-analytical methodology is performed using the nonlinear FEM code LS-DYNA.

The proposed method is intended for pre-design stages, when risk assessments are performed and a large number of collision simulations is required. In this case, fast calculation tools are generally more suitable than FEM, allowing for a good compromise between computational cost and accuracy.
Wave Loads and Ship Motions Evaluated by Linear Strip and Panel Methods
Authors: Karola Aaro , Hirdaris Spyros , Matusiak Jerzy , Mikkola Tommi
Published: October 2022

Despite the rapid development of Computational Fluid Dynamics (CFD) the demand for potential flow hydrodynamics in ship design remains relevant. This is because 2D and 3D Boundary Element Methods (BEM) can be applied for rapid prediction of motions and wave loads. This paper compares results from linear 2D strip-theory and 3D Green function methods with empirical forward speed correction factors in terms of ship motions, radiation forces and wave loads. The former approach applies a “Frank Close-fit” method to solve the radiation problem in 2D. The latter utilizes a pulsating “Green function” source distribution method to solve the radiation problem in 3D. Results are validated against experimental data available for a container ship. It is shown that the motion RAOs obtained by both methods are similar and agree with the experimental values. However, responses in terms of longitudinal distribution of wave loads show discrepancies which increase with wave length shortening and closer to the bow region. An increasing role of diffraction and disregarding forward speed wave making affect the results in short waves. Moreover, it is concluded that solving the linear seakeeping problem is not very sensitive to hull form details and to the modelling of forward speed effects on radiation.