bluuebunny/crossref_metadata_2025 huggingface dataset:
A Semi-Analytical Method for Calculating the Hydrodynamic Force on Perforated Plates in Oscillating Flow
Authors: Mentzoni Fredrik , Kristiansen Trygve
Published: November 2019

A two-dimensional numerical analysis on the hydrodynamic force of perforated plates in oscillating flow is presented, and a new semi-analytical force model is proposed. Plates with ten different perforation ratios, τ, from 0.05 to 0.50 are simulated. The Keulegan–Carpenter numbers in the simulations cover a range from 0.002 to 2.2 when made nondimensional with the width of the plates. Resulting hydrodynamic added mass and damping coefficients are presented. All perforated plates with perforation ratios greater than or equal to 10% are found to be damping dominant. The numerical results are obtained using a two-dimensional Navier–Stokes solver (CFD), previously validated against dedicated 2D experiments on perforated plates. Furthermore, we present verification of the code against the analytical solid flat plate results by Graham. The presently obtained hydrodynamic coefficients are compared with the state-of-the-art semi-analytical method for force coefficient calculation of perforated plates by Molin, as well as the recommended practice for estimating hydrodynamic coefficients of perforated structures by DNV GL. Based on the CFD results, a new method for calculating the hydrodynamic force on perforated plates in oscillating flow is presented. The method is based on curve fitting the present CFD results for perforated plates, to the analytical expressions obtained for solid plates by Graham. In addition to its simplicity, a strength of the method is that coefficients for both the added mass and damping are obtained.
Airgap Assessment of Semi-Submersible Accounting for Simultaneous Occurrence of Wind Sea and Swell
Authors: Haver Sverre , Patiño Julio
Published: November 2019

Necessary still water airgap in order to avoid major wave – deck impacts are considered at two target annual exceedance probabilities; 10−2 and 10−4. Major purpose of study was to investigate if joint modelling of wind sea and swell was required for a reliable estimation of necessary still water airgap. The assessment shows that for the selected position in the North Sea, swell sea could be neglected. An additional investigation of severity regarding airgap between wind sea from different directions is done. The study indicates that wind sea from the southern sector seems to govern airgap requirements. The reason being that the expected number of severe storms is highest for the southern sector. Additionally, stormy seas from South are more often associated with an unfavourable spectral peak period regarding airgap than storms from North.
Evaluation of Contact Forces in the Vertical Connection of a Flexible Riser in the Subsea Equipment
Authors: Coelho Del’ Sarto Yuri , Franciss Ricardo , Morooka Celso Kazuyuki
Published: November 2019

Flexible risers are commonly used in ultra deepwater offshore fields to convey fluids from the subsea equipment to the floating production unit. During the development of the production systems, the flexible pipe installation is a critical operation. In this scenario, an operational procedure for the installation frequently used in offshore Brazil is known as Direct Vertical Connection. In this concept, the Vertical Connection Module (VCM) is connected to the flexible pipe through a flanged joint, and lowered in to the subsea equipment with assistance of an installing cable. During the installation procedure, excessive loads may occur in the VCM due to reaction loads induced by the flexible pipe.

The present paper aims to describe the Direct Vertical Connection installation and to propose a methodology to study the forces induced by the flexible pipe into the VCM during such operation. For this purpose, a numerical model is developed for the Direct Vertical Connection and it is represented to simulate the installation procedure through a commercial software OrcaFlex.

The dynamic behavior of the system is investigated by varying the payout velocity of the installing cable, and the results are shown in terms of bending moment, wall tension and shear forces acting in the flange of the VCM. Numerical simulation result in the present work allows to evaluate the range of loading which acts during the Direct Vertical Connection to help operational design of the installation process, and avoid failure of components during the procedure.
Numerical Investigation of the Roll Decay of a Container Ship Moving With Forward Speed in Calm Water
Authors: Lungu Adrian
Published: November 2019

In the present paper the roll damping decay is investigated for the KRISO Container Ship in various working conditions. For this purpose flow is simulated by solving numerically the unsteady three dimensional equations of fluid motion in which closure to the turbulence is achieved through the DES-SST model. The governing equations are solved by using the finite volume method and the free surface elevation is determined by using a VOF technique. Comparisons with the experimental data are provided to validate the numerical approach in terms of the time history of the roll angle variation for different roll motions and ship speeds.
Experimental Investigation of Stresses in Winch Drums Subjected to Multilayer Spooling Loads From Synthetic Fibre Ropes
Authors: Skarbøvik Reidar André , Piehl Henry , Torben Sverre , Nedreberg Mette Lokna , Æsøy Vilmar
Published: November 2019

In many marine applications, modern high-performance synthetic fibre ropes have replaced, and are continuing to replace, well-known steel wire rope solutions due to the low weight of the synthetic ropes removing limitations for operations at large water depths. In some cases, replacement of steel wires with synthetic ropes has caused permanent deformations and damage to multilayer winch drums, indicating that synthetic fibre ropes can cause larger pressure on winch drums than steel wire. This paper presents the first results from a novel experimental investigation of a multilayer winch subjected to a selection of braided high-performance synthetic fibre ropes and a reference steel wire rope. The tested ropes, with nominal diameters between 12 and 20mm, are spooled at different tensile loads and with maximum number of layers in the range of 10 to 19. The experiments utilize a test rig with two winch drums, controllable spooling gear and sheaves with load cells to apply and control required load and speed during spooling. Measurements from twelve biaxial strain gauges on the inside of a thick high-strength drum are used to measure stresses in the structure. The results show that the selected fibre ropes induce considerably larger stress in the winch drum than the steel wire rope. This confirms that design of multilayer winch drums with high-performance synthetic fibre ropes requires special considerations and that the guidance for multilayer stress calculations, related to steel wire ropes, in DNV-GL-0378 “Standard for offshore and platform lifting appliances” is not applicable for synthetic fibre rope applications.
Effect of Local Model Dynamics on Flexible Riser Tensile Armor Wire Stress Predictions
Authors: Rombado Gabriel , Doynov Krassimir , Cooke Nathan , Majed Arya
Published: November 2019

Accurate time-consistent computation of tensile armor wire stresses remains a major challenge in flexible riser fatigue life predictions and integrity management. Accuracy requires capturing the kinematics of the flexible’s helically contra-wound tensile armor layers and their interaction with the other metallic and thermo-plastic layers in a dynamic simulation. It is generally accepted that high fidelity 3D Finite Element Models (FEMs) can best capture the complex kinematics and produce accurate stresses. The local model is typically constructed of few “pitch lengths” of the 3D FEM. Local analysis involves enforcing tension and nodal rotation time-histories on the local model and extracting wire stresses at critical fatigue locations along risers. While local analysis involving a few bending cycles can be executed on modern multi-core computers, static simulations typically require computation times of 24–48 hours for a single cycle and do not capture the effect of dynamics of the local model. With this computational constraint, 1-hr long irregular wave fatigue simulations with 3D FEM local model become computationally infeasible. The nonlinear dynamic substructuring (NDS) approach has been utilized in the past to overcome this computation challenge.

Reduced order models are numerical methods for efficiently solving high fidelity FEM. NDS utilizes reduced-order models and numerical algorithms to significantly decrease the computation time associated with the irregular wave fatigue simulations of the high fidelity flexible FEM. Because NDS is a simulation-based approach, effects such as local model tension stiffening and inertial resistance to the global rotation inputs are fully captured and the impact on wire stresses can be discerned.

A 14” inner diameter (ID) flexible riser with a four-tensile armor layer configuration is modeled and simulated using the NDS approach. The 5m long local model is first driven at different “speeds” of harmonic (regular wave) rotation inputs to illustrate inertial effects. For the faster input, the impact of local model inertia on wire stresses is immediately apparent by the increase in wire stresses and change in the shape of the wire stress hysteresis curve. Next, the local model is simulated to irregular wave inputs. It is again shown that the inclusion of local model inertia increases wire stresses and modifies the shape of the wire stress hysteresis.
Predicting Roll Damping for Barge-Type FPSO Using CFD
Authors: Koop Arjen , Jaouën Frédérick , Wadbled Xavier , Corbineau Erwan
Published: November 2019

An accurate prediction of the non-linear roll damping is required in order to calculate the resonant roll motion of moored FPSO’s. Traditionally, the roll damping is obtained with model tests using decays or forced roll oscillation tests. Calculation methods based on potential flow are not capable of predicting this hydrodynamic damping accurately as it originates from the viscous nature of the fluid and the complex vortical flow structures around a rolling vessel. In recent years Computational Fluid Dynamics (CFD) has advanced such that accurate predictions for the roll damping can be obtained.

In this paper CFD is employed to predict the roll damping for a barge-type FPSO. The objectives of the paper are to investigate the capability and accuracy of CFD to determine roll damping of an FPSO and to investigate whether two-dimensional calculations can be used to estimate the roll damping of a three-dimensional FPSO geometry.

To meet these objectives, extensive numerical sensitivity studies are carried out for a 2D hull section mimicking the midsection of the FPSO. The numerical uncertainty for the added mass and damping coefficients were found to be 0.5% and 2%, respectively. The influence of the turbulence model was found to be significant for the damping coefficient with differences up to 14%. The 2D CFD results are compared to results from two-dimensional model tests. The calculated roll damping using the k-ω SST 2003 turbulence model matches the value from the experiments within 2%.

The influence of various physical parameters on the damping was investigated through additional 2D calculations by changing the scale ratio, the roll amplitude, the roll period, the water depth, the origin of rotation and the bilge keel height.

Lastly, three-dimensional calculations are carried out with the complete FPSO geometry. The 3D results agree with the 2D results except for the largest roll amplitude calculated, i.e. for 15 degrees, where the damping coefficient was found to be 7% smaller. For this amplitude end-effects from the ends of the bilge keels seem to have a small influence on the flow field around the bilge keels. This indicates that the 2D approach is a cost-effective method to determine the roll damping of a barge-type FPSO, but for large roll amplitudes or for different vessel geometries the 2D approach may not be valid due to 3D effects.
A Critical Review of Rules and Regulations for Permanently Plugged and Abandoned Wells
Authors: Khalifeh Mahmoud , Akbari Babak , Khan Ahsan , Braga Daniel C.
Published: November 2019

Permanent Plug and Abandonment (P&A) of wells has been an inevitable part of hydrocarbon exploration and production; however, the methodology has not evolved with the same pace as the rest of the industry. Nonetheless, after the environmental impact of some recent events including the Deepwater Horizon oil spill, permanent P&A of hydrocarbon wells has been receiving more attention. Accordingly, regulatory authorities who oversee the P&A activities and operators have tried to improve the pre-existing P&A methodology by defining a modern P&A philosophy, zero leakage criterion. Although the legislated criterion, adapted by most authorities, has challenged the industry and it had a constructive impact on P&A operations, due to technology deficiencies, the associated cost of operation has significantly increased. In this work, most of the publicly available regulations and their recommended practices addressing P&A have been reviewed and discussed. The focus has been given to zero leakage acceptance policy, conventional versus risk-based approach, barrier verification, human factor in P&A, and technology deficiencies. Although Norway is not a major hydrocarbon producer based on the daily production rate, but because of its stricter requirement on P&A, its recommended practice (NORSOK D-010) for P&A has been used in different oil producing countries. As P&A and its impact on environment is a transnational subject, it is suggested to formulate an international guideline or standard on P&A, given the fact that every well is unique when considering P&A operation.
Experimental and Numerical Study of Oil Whip in Propeller Shaft
Authors: Divakaran Adarsh , Vijayan K. , Kartheek A.
Published: November 2019

An experimental study and theoretical study is carried out to understand the vibration signature of a propeller shaft. A test rig consists of a rotor shaft and three-disc supported on hydrodynamic bearing was analyzed.

Presence of hydrodynamic bearing makes the systems natural frequency speed dependent. A theoretical model of the rotor disc system was developed using FEM. The rotor was formulated on Euler–Bernoulli beam theory. Proportional damping was assumed for the shaft. The stiffness and damping coefficients of the bearing are calculated by short bearing assumption. A Campbell diagram was plotted to observe the variation in natural frequencies with rotational speed. There was an indication of mode approaching each other with a speed which could result in the self-excited phenomena such as “Oil whip”. The hydrodynamic forces in the fluid film produce Oil whip. The presence of Oil whip was ascertained by carrying out the experimental study. The time-frequency plot during the run-up indicated the presence of a whip. The study indicated the influence of modes on the whip phenomena. This can be used in forming guidelines for the safe operating regime for the propeller shaft.
Local Blockage Effects for Idealised Turbines in Tidal Channels
Authors: Chen Lei , Bonar Paul A. J. , Vogel Christopher R. , Adcock Thomas A. A.
Published: November 2019

In this paper, idealised analytical and numerical models are used to explore the potential for local blockage effects to enhance the performance of turbines in tidal channels. Arrays of turbines modelled using the volume-flux-constrained actuator disc and blade element momentum theories are embedded within one-dimensional analytical and two-dimensional numerical channel domains. The effects of local blockage on the performance of arrays comprising one and five rows of actuator discs and tidal rotors operating in steady and oscillatory channel flow are then examined. In the case of steady flow, numerical results are found to agree very well with the two-scale actuator disc theory of Nishino & Willden [1]. In the case of oscillatory flow, however, numerical results show that the shorter and more highly blocked arrays produce considerably more power than predicted by the one-dimensional two-scale theory. These results support the findings of Bonar et al. [2], who showed that under certain oscillatory flow conditions, the power produced by a partial-width tidal turbine array can be much greater than predicted by two-scale theory. The departure from theory is most noticeable in the case of five turbine rows, where the two-scale theory predicts that the maximum available power should decrease with increasing local blockage but the numerical model shows the maximum available power to increase. The effects of local blockage are found to be less pronounced for the more realistic tidal rotor than for the highly idealised actuator disc but for both models, the results show that in oscillatory flow, considerably more power is available to the shorter and more highly blocked turbine arrays.
Nano-Modified Rock-Based Geopolymers As Supplement to Portland Cement for Oil Well Cementing
Authors: Khalifeh Mahmoud , Salehi Saeed , Jamrozik Aleksandra , Kimanzi Raymos , Abdollahpour Saeid
Published: November 2019

Geopolymers being inorganic polymers, pumpable, gaining compressive strength, bonding to steel and formation, and showing durability at downhole conditions make them a possible barrier material. However, having low tensile strength, and being contaminated severely with water-based fluids are the challenges to be mitigated. These challenges have also been observed in recently developed rock-based geopolymers. Different researchers have suggested the application of nanoparticles as additive to geopolymers for increasing the mechanical properties. Of these one could list nanosilica, nano titanium di-oxide, nanocarbon graphene, carbon nanotubes, and nano aluminium. However, their reasoning for utilization of these nano particles originated from their effect on properties of Portland cement.

In this study, the effect of nano titanium di-oxide and nanocarbon graphene is considered on the rock-based geopolymers. The two main criteria for selection of these materials are in-house availability, and the published prior art. The effect of the nano materials on rheological behavior, mechanical strength and microstructure of the geopolymers are the main investigated parameters. The obtained result shows that the nano materials improve the pumpability of the geopolymers but not improving the tensile strength effectively.
Experimental Assessment of Form Based Approach for Predicting Extreme Value Distribution of Hull Girder Bending Moment in a Ship
Authors: Takami Tomoki , Komoriyama Yusuke , Ando Takahiro , Iijima Kazuhiro
Published: November 2019

This paper describes a series of towing tank tests using a scaled model of a recent container ship for validating the First Order Reliability Method (FORM) based approach to predict the maximum response. The FORM based approach is adopted in conjunction with the nonlinear strip method as an estimation method for the most probable wave episodes (MPWEs) leading to the given extreme wave-induced vertical bending moments (VBMs). Tank tests under the pre-determined MPWEs are conducted to evaluate the extreme wave-induced VBMs. Numerical simulations based on the coupled Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) are also conducted and are compared with the test results under the MPWEs. Furthermore, to estimate the extreme VBM statistics, tank tests under random irregular waves are conducted. A series of validations of the probability of exceedances (PoEs) of the VBM evaluated from the FORM based approach is carried out. The effect of hydroelastic (whipping) vibrations on the extreme VBM statistics are finally discussed.
Edge Effect on Numerical Calculation of Nonlinear Radiation Forces for a Submerged Body
Authors: Yang Jianye , Teng Bin , Gou Ying
Published: November 2019

To investigate the edge effect on numerical calculation of nonlinear forces for a moving body in the time domain, a large body motion model with linear free surface condition is developed with higher-order boundary element method. Five numerical formulations are used to compute the nonlinear radiation forces on submerged surging bodies with sharp edge and a small chamfer radius at the edge. It is found that for those bodies with smooth surface, the nonlinear radiation forces obtained by all of the numerical formulations are close to each other, but large disperses exist for the body with sharp edge. Examination on the vertical nonlinear radiation forces shows that the method on momentum change rate is insensitive to the small edge radius even the chamfer radius is zero, but the other formulations diverse when the edge radius approaches zero. It is suggested that for a body with sharp edge, the method on momentum change rate should be used, or to replace the body surface by the body with a small radius at its sharp edge.
Numerical Simulation of the Fluid-Solid Two-Phase in the Horizontal Pipe Based on DEM-CFD Coupling Method
Authors: Pu Jin-Shan , Chen Yong-Ping , Yao Peng
Published: November 2019

Compared to the conventional CFD method, the CFD–DEM coupling is proposed to simulate the solid–liquid two–phase flow in the horizontal pipe in this paper. The standard k–ε model was utilized for fluid turbulent flow, the standard wall functions for near-wall zone treatment, and the Hertz–Mindlin (no slip) model for particle–particle and particle–wall contact. The movements and distribution of particles in different inlet velocities and pressure drop in pipeline are investigated in this paper. The results show that the coarse particles appear starting, discontinuous movement as bedload, continuous movement as bedload, and suspension in order with mean velocity of fluid media increase; with the increasing inlet velocity, the distribution of partilces in the pipe becomes more even, however, the concentration of the particles on the botton is larger than that on the top. Moreover, the pressure drop predicted by this method is compared with the Churchill pressure drop model and results are not identical. Therefore, the regular of pressure drop is demonstrated in this paper.
Theoretical Modeling of Steel Strip Reinforced Flexible Pipe With Swaging End Fitting by Taking Into Account Stress Concentration Effect
Authors: Gao Yifan , Chen Wei , Bai Yong
Published: November 2019

A new theoretical model was proposed to calculate the burst pressure of steel strip reinforced flexible composite pipes (steel strip PSP) based on the thin wall cylindrical shell theory and the squeeze pressure expression between layers was derived. The radial displacement discontinuity of pipe wall in pipe-end fitting joint area takes in account in this model which could result in Stress Concentration Effect (SCE) in reinforcement layers. The SCE is caused by swaging end fitting clamped tightly at the end of the pipe. The result of the hoop strain in the joint area calculated by this model is greater than the one calculated by the classic elastic model, which leads to relative conservative burst strength of the pipe. The hoop stress variation via internal pressure on innermost reinforcement layer is introduced to predict the burst strength of the pipe. As the stress in the joint area reaches its ultimate strength, the strain on the same layer in the point far away from this area (x→∞) is extracted and the corresponding internal pressure is obtained as the burst strength of the pipe. The calculated data from two models were compared with the experiment results and the proposed new model showed better accuracy than the classic elastic model. Final additional parametric studies were conducted, while the effect of the pipe diameter, the winding angle, the number and thickness of the reinforcement layer on the burst strength of the pipe were studied. Useful conclusions were drawn for the design and application of the steel strip PSP in offshore engineering.
An Ontology-Based Approach for Developing Offshore and Onshore Process Equipment Inspection Knowledge Base
Authors: Rachman Andika , Ratnayake R. M. Chandima
Published: November 2019

A collection of inspection results is an essential input in assessing and managing the technical integrity of offshore and onshore process equipment. The inspection results enable the current condition of the equipment, the type of damage mechanism, and the severity and location of the degradation to be investigated. Typically, the inspection results are documented in a text-format report and stored in a conventional data repository. Conventional inspection data storage has drawbacks in terms of the sharing, exchange, and retrieval of information within an inspection knowledge domain, due to the lack of knowledge representation. This study proposes an ontology-based approach for developing an inspection knowledge base, in order to improve the degree of retrieval, distribution, and administration of inspection results. Ontology provides a semantic structure and relations for concepts in the inspection knowledge domain, which facilitate semantic search capability and enable increased utilization, enhanced communication and improved exchange of inspection information. A case study of a static equipment inspection is shown, to demonstrate the application of an ontology-based approach in facilitating data and information retrieval from an inspection knowledge base.
Fluid Dynamics Numerical Assessment to Evaluate the Ice Formation Around the Pipeline
Authors: Blasioli Giuseppe , Marchesani Furio
Published: November 2019

In response to the UNCCC held in Paris in 2015 the need to reduce the global warming, due to CO2 release in atmosphere, led to a new business for the capture and storage of CO2 in dedicated deep water reservoir. In this sense the transport of the CO2 at low temperature, necessary to condensate the gas, through offshore pipeline is a commercial and technical valid strategy.

One of the issues related to the transport of a condensate gas is the thermal exchange between the transport system, in this case offshore pipelines, and the environment. The gas is usually carried by ships in a liquid phase at very low temperatures, for example −30 °C in case of CO2. The fluid is introduced into the pipeline at the same temperature to not further consume energy for warming up.

The design of the offshore pipeline subject to these operating conditions, very cold fluid internally and a water temperature slightly over 0°C at external side, can be affected by the ice formation around the pipe. The ice thickness formation is primarily governed by the external convection coefficient.

For the offshore pipelines located in deep waters where the sea currents are negligible, only the natural convection phenomena can occur on the external surface of the pipeline. Considering steady state scenario the heat transfer from the internal fluid to the external environmental is governed by the thermal resistance of each component of the system like fluid, steel, anticorrosion coating, thermal insulation if any and external convection due to the seawater. The low temperatures of both seawater and ice formation, approximately at −2°C, allow to be close to the maximum value of the seawater density: usually this occurs at a slightly colder temperatures depending on salinity and water depth (for the fresh water the maximum is at 4°C).

The natural convection is driven by the buoyancy effect due to fluid density variation with temperature: the scenario described above lead to minimizes these effects and consequently the heat transfer due to the natural convection (increasing the thermal resistance).

Most of the correlations in literature are related to different temperature ranges, far away from this particular situation: a numerical investigation using computational fluid dynamics technique has been performed.

The analysis is executed by means of commercial CFD software FLUENT: the model is based on a two dimensional grid of a pipe submerged in water.

In this paper:

• The state-of-the-art about the natural convection coefficient estimate for submerged cylinders proposed by different authors through Nusselt number assessment;

• A description of the proposed numerical approach is given highlighting the different approaches based on the boundary layer behavior;

• A typical application is shown.
Mode Selection for Offshore Platform Damage Identification Using CMSE Sensitivity
Authors: Xu Mingqiang , Liu Yuchi , Jiang Yufeng , Wang Shuqing
Published: November 2019

A sensitivity-based mode selection strategy for cross modal strain energy (CMSE) method is proposed to identify damage more effectively. The cross modal strain energy sensitivity is defined as the sensitivity index. For this purpose, the cross modal strain energy sensitivity to structural damage is deduced, and is used to select the preferable mode combinations that are sensitive to damage. By using the preferable mode combinations, the CMSE system is refined and the degree of ill-posedness of the CMSE system is reduced. A numerical study is conducted on an offshore platform structure to demonstrate the effectiveness of the proposed scheme. The performances of the CMSE method with and without using the mode selection strategy are compared in the presence of noise. Results show that: (1) the accuracy of damage localization is improved when only a few mode combinations are utilized; (2) On account of excluding substantial low-sensitivity mode combinations, the amount of computation is significantly reduced.
Experimental Study on a Relation Between Nonlinear Hydrodynamic Forces and Wave-Induced Ship Motions
Authors: Taguchi Masakazu , Kashiwagi Masashi
Published: November 2019

Nowadays, in maritime industries, container ships increase in size and they have large flares, which may induce nonlinear wave loads in large-amplitude waves. It is also well known that hydrodynamic forces acting on a ship and resulting ship motions show nonlinearities at some range of wave frequencies. Therefore, we should investigate not only correct estimation of wave loads and ship motions, but also nonlinear ship-motion characteristics in large-amplitude waves. However, it is not that clear which nonlinear hydrodynamic force terms are dominating for the nonlinearity in the ship motions. Although the linear equations of motion have been used, they should be modified to incorporate at least the most important nonlinear hydrodynamic forces and to establish a practical calculation method taking account of only the indispensable nonlinear terms. In this research, we did extensive experimental measurement of hydrodynamic forces and wave-induced ship motions, with which we aim to understand what are practically important nonlinear terms, and to derive practical nonlinear ship motion equations through numerical computation and comparison with experimental data.
Ship Manoeuvring Model Parameter Identification Using Intelligent Machine Learning Method and the Beetle Antennae Search Algorithm
Authors: Chen Changyuan , Tello Ruiz Manases , Lataire Evert , Delefortrie Guillaume , Mansuy Marc , Mei Tianlong , Vantorre Marc
Published: November 2019

In order to identify more accurately and efficiently the unknown parameters of a ship motions model, a novel Nonlinear Least Squares Support Vector Machine (NLSSVM) algorithm, whose penalty factor and Radial Basis Function (RBF) kernel parameters are optimised by the Beetle Antennae Search algorithm (BAS), is proposed and investigated. Aiming at validating the accuracy and applicability of the proposed method, the method is employed to identify the linear and nonlinear parameters of the first-order nonlinear Nomoto model with training samples from numerical simulation and experimental data. Subsequently, the identified parameters are applied in predicting the ship motion. The predicted results illustrate that the new NLSSVM-BAS algorithm can be applied in identifying ship motion’s model, and the effectiveness is verified. Compared among traditional identification approaches with the proposed method, the results display that the accuracy is improved. Moreover, the robust and stability of the NLSSVM-BAS are verified by adding noise in the training sample data.
Numerical Modelling of the Mooring Line Failure Induced Performance Changes of a Marine Fish Cage in Irregular Waves and Currents
Authors: Tang Hung-Jie , Yang Ray-Yeng , Huang Chai-Cheng
Published: November 2019

This study aims to investigate the performance changes resulted from a mooring line failure of a marine fish cage exposed to irregular waves and current. A numerical model based on the lumped mass method and Morison equation was extended to simulate the mooring line failure scenario. In this study, the failed resulting changes were compared with its normal counterpart in both the time domain and the frequency domain. After one upstream anchor loss, the maximum tension on the remaining anchor has increased significantly, as well as the drift distance of the rearing part (net chamber, floating collar, and tube-sinker) of the fish cage. The resulting changes can also be seen in both the wave-frequency and the low-frequency region in the spectra, including mooring tensions and body motions.
Analysis of Fatigue Life of Ship Structure Under the Non-Linear Slamming Load
Authors: Ren Huilong , Ma He
Published: November 2019

As one of the hot topics in ship structures, hull structural fatigue has been widely studied by overseas and domestic scholars in recent years. And fatigue assessment methods can be divided into simplified calculation method and direct calculation method. However most of the calculation methods are based on liner wave load. Some high-speed ships, large external floats and larger ships may have frequent outflows and inflows during the voyage. These ships can be influenced by more serious wave attack. In this situation, the influence of nonlinear slamming load on ship structures cannot be ignored. In this paper, the author selected the deck longitudinal and the bottom longitudinal of the example ship midship section, then calculated the fatigue damage under the action of liner load and total fatigue damage under non-linear slamming load respectively.

And the effect of non-linear slamming load on the fatigue life of hull structure can be obtained: it is 49% larger than that without attack fatigue damage in the deck longitudinal, and 35% larger in the bottom longitudinal. Based on the results, the author got the influence coefficient of non-linear slamming load on the fatigue life of the ship. Finally, a nonlinear correction method of fatigue damage is proposed.
Statistical Analysis for the Duration and Time Intervals of Tropical Cyclones, Hong Kong
Authors: Tao Shanshan , Song Jialing , Wang Zhifeng , Liu Yong , Dong Sheng
Published: November 2019

Hong Kong is impacted by tropical cyclones from April to December each year. The duration of tropical cyclones is one key factor to impact the normal operation of port or coastal engineering, and longer time interval between two tropical cyclones can provide longer operation or construction time. Therefore, it is quite important to study on the long-term laws of the duration and time intervals of tropical cyclones which attacked Hong Kong. The Hong Kong Observatory issues the warning signals to warn the public of the threat of winds associated with a tropical cyclone. Choose the tropical cyclones with warning signal No. 3 or above as the research object. A statistical study was conducted on the duration of each tropical cyclone, the time interval between every two continuous tropical cyclones during the year, and the time interval between the last cyclone of each year and the first cyclone of the following year. Poisson compound extreme value distributions are constructed to calculate the return values, which can make people know how long a tropical cyclone with a fixed duration or time interval occurs once in statistical average sense. Based on bivariate copulas, the joint probability distribution of duration and time intervals of tropical cyclones are presented. Then when the duration of a tropical cyclone is known, the conditional probability that the time interval before the next tropical cyclone occurs is greater than a certain value can be calculated. The results provide corresponding conditional probability distributions. Similarly, for the sum of the duration of tropical cyclones each year, and the time interval between the last cyclone of each year and the first cyclone of the following year, their joint probability distribution and conditional probability distributions are also presented. The conditional probability can provide the probabilistic prediction of the length of the stationary period (with no impact of tropical cyclones).
Flexible Riser Top Connection Analysis With I-Tube Interface and Bending Hysteresis Effect
Authors: He Yangye , Lu Hailong , Vaz Murilo Augusto , Caire Marcelo
Published: November 2019

The flexible riser top connection to the floating production platform is a critical region for fatigue lifetime (re)assessment. The interface with the I-tube and its curved sleeve combined with the gap between the riser and bend stiffener may lead to different curvature distribution when compared to the traditional modeling approach that considers the bend stiffener attached to the pipe. For a more accurate top connection assessment, the flexible riser bending hysteresis can also be directly incorporated in the global dynamic analysis helping to reduce curvature amplitude and lifetime prediction conservatism. This work investigates a 7” flexible riser-bend stiffener top connection with I-tube interface by performing irregular wave global dynamic analyses with the OrcaFlex package and considering a nonlinear bending moment vs curvature riser behavior obtained from a detailed cross sectional model developed in Abaqus. OrcaFlex curvature distribution results are also compared with a quasi-static finite element model that uses an elasto-plastic formulation with kinematic hardening to represent riser hysteresis through an equivalent beam model. A good curvature distribution correlation is observed for both top connection models (OrcaFlex x Abaqus) in the bend stiffener area with reduced amplitudes when riser bending hysteresis is considered.
The Tentative Case Study of Annulus Build Up Pressure in the Deepwater Gas Production Well in South China Sea
Authors: Feng Ming
Published: November 2019

As China’s offshore drilling and production projects gradually march into the deep water, the requirements for scientific and technological progress are imminent. The occurrence of the 2010 Macondo disaster has presented a serious challenge to the safety of deepwater in technology. The deepwater wellbore consists of several layers/channel barriers, which constitute the wellbore barrier system and have a complicated structure. With the increase of water depth and well depth, the temperature of oil and gas produced at the wellhead is getting higher and higher, and the fluid in the annulus of the casing is heated by the conduction and convection of fluids such as oil and gas produced in the high temperature formation. Up to 60 degrees Celsius, the thermal expansion of the annulus fluid can cause the casing to burst, which can cause significant loss of personnel and property. Therefore, accurate temperature calculation of deep water wellbore is the key to the calculation of trap pressure prediction. The calculation of the wellbore temperature is affected by the oil casing and the thermophysical parameters such as the size of the wellbore, fluid composition, flow regime, casing and cementing sheave. By appropriately simplifying the model and sensitivity analysis, it is found out the dominant factors which affect the temperature profile.
System Based Prediction of Ship’s Manoeuverability in Varying Water Depth Area
Authors: He Shi , Incecik Atilla , Yuan Zhiming , Kellett Paula
Published: November 2019

In this study, numerical prediction of a ship maneuvering in calm water area with varying water depth are carried out to investigate the shallow water effect on ship’s maneuverability. The system based prediction approach is adopted by establishing a 3 degrees of freedom (DOF) mathematical model based on the modular concept. The lateral added mass and added moment of inertia are obtained by a strip theory method. Other coefficients including the longitudinal added mass, the maneuvering derivatives and the coefficients for estimating the resistance on the hull in straight moving, the propulsive force by the propeller, steering force by the rudder, and the interaction between hull-propeller-rudder are obtained by commonly used empirical and semi-empirical formulae, or directly from published data. The MOERI KVLCC2 tanker vessel is selected as the sample ship. The free running manoeuvers in deep and shallow water at different water depths are simulated and compared with available experimental results for validation. A special simulation case of stepped bottom varying from deep water to shallow water which resembles the real situation in harbor area is also carried out. The shallow water effects on ship’s maneuverability are discussed and recommendations on steering operations in shallow water are given.
Modal Interactions in Drillstring Borehole Interactions
Authors: Kartheek A. , Vijayan K. , Friswell M. I.
Published: November 2019

Understanding the vibration of drillstrings is important for the economical and efficient extraction of oil. Vibrations involve bending, axial, and torsional vibration. Drillstring interaction with the borehole during whirling involves nonlinearities. For the present work the whirling interaction of the drillstring and borehole is studied using an equivalent conceptual experimental test rig and a theoretical model of the drillstring. The drillstring is modeled as an Euler Bernoulli beam with multiple discs considering damping and gyroscopic effects. The finite element method is used as a numerical technique and the eigenvalue problem is solved using a state space formulation. The forward whirling frequency obtained from the experiments was used to update the bearing stiffness of the theoretical model. The contact is modeled experimentally using a tube for the stator with added roughness to aggravate the friction effect. A run up analysis was carried out within the safe operating regime of the test rig and the frequencies were analyzed using a time frequency plot. The effect of typical system parameters was considered such as the location of the contact, the mode excited and the clearance. The results from the study indicated the possibility of interaction between the forward and backward whirling modes which increased the bandwidth of acceleration response.
Comparison of Dynamic Response in a 2MW Floating Offshore Wind Turbine During Typhoon Approaches
Authors: Tanaka Koji , Sato Iku , Utsunomiya Tomoaki , Kakuya Hiromu
Published: November 2019

In this paper, we describe the analysis of the dynamic response of a 2 MW floating offshore wind turbine (FOWT) at the time of typhoon attack in the actual sea area. In order to introduce floating offshore wind turbine in Asia, it is essential to evaluate the influence of typhoon attack accurately. This FOWT, named HAENKAZE is the only FOWT to operate commercially in areas where typhoons occur. On July 3rd, 2018, the strongest typhoon (Prapiroon) at the installed area of the FOWT since its installation approached the HAENKAZE. The central atmospheric pressure of the typhoon at the closest time was 965 hPa, the maximum instantaneous wind speed at the hub height was 52.2 m/s, and the maximum wave height was 7.1 m. In this paper, the dynamic response of the floating body at the time of typhoon attack is compared for the measured and the simulated values. As a result of the comparison, basically a good agreement has been obtained between the measured and the simulated values except for yaw response, for which the simulated values considerably overestimate the measured values.
Next Generation Well Design and Integrity Digital Tools: Boosting Drilling Systems Automation (DSA)
Authors: Brechan B. , Dale S. , Sangesland S.
Published: November 2019

The first of the next generation applications for well planning and operational support is under development. All aspects of construction, integrity, intervention and final plugging of wells are supported and fully automated into digital programs and procedures. Expanding the scope of software support entails a change from current practice of simulating all activity upfront to keep the model active and updated to supply all integrity data through production and final plugging of the well.

The software is built to carry executable experience. These “digital experiences” range from the single event type often noted during operations, to complex sets of instructions in governing documentation. Experiences act as rules for how the software select methods outlined in activity plans and how these plans are executed by the equipment on drill floor. Any activity plan, e.g. drilling, completion, intervention or plug and abandonment (P&A), will be established using the entire company portfolio of experience regardless of the capacity and experience of the planning team.

Engineers working with the next generation software will focus on ensuring the quality of the produced digital procedures. The software will handle administrative routines, such as invoicing and logistics, which will free up capacity for engineers. The user threshold of the next generation software will be low for any person familiar with the daily operational reporting system.
Feasibility Study of Mooring Lines Design for a Floating Tidal Turbine Platform Using Double Hull Structure
Authors: Arini Nu Rhahida , Thies Philipp R. , Johanning Lars , Ransley Edward , Brown Scott , Xie Nan , Greaves Deborah
Published: November 2019

The aim of this paper is to study the mooring tension characteristics on a tidal energy converter (TIC) platform considering i) a horizontal and ii) a vertical tidal turbine. The study examines numerically the feasibility of a catenary mooring line for a modular tidal energy platform. A modular platform is designed and modelled with two floating hulls and anchored by studlink catenary mooring chains on the seabed. Vertical and horizontal axis turbines which have similar Cp are selected and modelled separately. The effect of those turbines on the mooring system are compared and the results informs lifetime of the mooring component for each turbine connection. The hydrodynamic model with no turbine is firstly developed and validated against an experiment with 1:12 scale ratio. The starboard fore mooring line tension, platform surge and pitch displacements are validated against the experiment. The model results show identical signal frequency with slightly different magnitude from the experiment. The mooring tension under vertical and horizontal tidal turbine operations in the particular environment is further examined. The result shows that the mooring line using selected vertical axis turbine experiences higher tension. For platform motions, the horizontal turbine generates slightly larger displacement in surge. However the pitch motion record shows equal displacement under both turbine operations. The selected vertical axis tidal turbine also produces longer lifetime mooring components.