bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Novel Approach to Improving the Structural Reliability of a Fixed Offshore Platform Subject to Wave-in-Deck Loading Using a Holistic Structural Integrity Management (SIM) TRIAD Approach
Authors: Kimiaei Mehrdad , Mirzadeh Jalal , Dev Partha , Efthymiou Mike , Khan Riaz 
Published: December 2020

Abstract
Fixed offshore platforms subject to wave-in-deck loading have historically encountered challenges in meeting target reliability levels. This has often resulted in costly subsea remediation, impacted platform occupancy levels or premature decommissioning of critical structural assets due to safety concerns. This paper addresses the long-standing industry challenge by presenting a novel structural reliability approach that involves converging the analytical behavior of a structure to its measured dynamic response for assessment. In this approach, called the Structural Integrity Management (SIM) TRIAD method, the platform model is calibrated based on the measured in-field platform natural frequencies using a structural health monitoring (SHM) system, so that the reliability assessment can be performed on a structural model whose stiffness is simulated as close to reality as possible. The methodology demonstrates the potential of unlocking structural capacity of offshore structures by removing conservatism normally associated with traditional reliability assessment methods, thus significantly improving the ability to achieve target structural reliability levels in a cost effective manner. The SIM TRIAD method has been implemented while assessing an existing fixed offshore platform subject to wave-in-deck loads, which is located in East Malaysian waters. It has enabled the facility operator to achieve acceptable target structural reliability and has assisted in developing an optimized risk-based inspection (RBI) plan for ensuring safe operations to end of asset field life. The methodology and findings of the assessment are presented in this paper to illustrate the benefits of the SIM TRIAD method.
Time Domain Structural Fatigue Analysis of Floating Offshore Platforms: A Response Based Technique
Authors: Kyoung Johyun , Samaria Sagar , Kim Jang Whan 
Published: December 2020

Abstract
This paper presents a response-based, time-domain structural fatigue analysis of a floating offshore platform. The conventional technique for structural fatigue assessments of offshore platforms uses a linear, frequency-domain analysis based on the spectral method. Although this conventional method is computationally efficient, there is a room for improving accuracy and reducing uncertainties because it cannot accurately address non-linear loadings on the offshore platform. Such non-linear loads arise from the wave, wind, and current as well as from the riser and mooring systems; these non-linearities necessitate large factors of safety that lead to conservative design and frequent inspection.
As an extension of previous work (Kyoung et al.[12]), this study presents the development of a time-domain, structural fatigue analysis that explicitly addresses non-linear loading on the platform. The external load time-histories are directly mapped onto the structure at every time interval to create a stress-based response with the varying environment. In each time step, the load mapping accurately captures the phase relationship between the external loading and hull inertial response. Therefore, present method reduces uncertainties in the fatigue damage computation and overcomes the assumptions of spectral method. Present load component-based approach is applied onto a finite element structural model, which provides unit structural response at locations of interest. Time history of structural response is obtained by synthesizing the obtained unit stress-based structural response with environmental loading and platform motion response. Fatigue damage can be computed from the obtained time series of structural response using rain-flow counting.
As an application, a conventional semisubmersible platform is used to evaluate structural fatigue damage for a given wave scatter diagram. A comparison between results from this response-based time-domain approach and the conventional spectral method is presented.
Case Based Scaling: Recent Developments in Ice Model Testing Technology
Authors: von Bock und Polach R. U. Franz , Ziemer Gesa , Klein Marco , Hartmann Moritz C. N. , Toffoli Alessandro , Monty Jason 
Published: December 2020

Abstract
Model ice testing is the state of the art validation and testing method for ships and structures interacting with ice. Its initial design objective was the prediction of resistance forces of ice breaking ships by using Froude and Cauchy similitude to account to the most significant force ratios. In the ice breaking process the forces due to downward bending are considered most significant and therewith much emphasis was spent on the correct scaling of the bending strength or flexural strength of the model ice. Recent research on the mechanical behavior of model ice shows a significantly higher compliance in downward bending than targeted when following the applied scaling laws. This can lead to scale effects in the resistance force also when testing ice breaking ships. The too compliant ice facilitates an additional ride-up of the ship onto the ice and the vertical motions manifest as additional resistance contribution. The low compliance of model ice also imposes uncertainties on wave-ice interaction tests, which gain increasing significance due to the climatic changes in Polar regions. The modeling of ice break-up due to waves, with the current standard model ice, requires much steeper waves than in full scale as the ice surface needs to experience a much higher deflection to reach the critical failure stress. A similar issue arises for vertical structures exposed to drifting ice. In full-scale a pile-up of ice around the structure is observed and in the contact area so called high-pressure zones may form. Such effects cannot be modeled with classic model ice as it easily bends downwards and produces a failure pattern and failure process very different from full-scale as well as high-pressure zones do not form which is due to the string property gradient in model ice. The mentioned three scenarios are considered being highly relevant in marine research and for the marine industry and therefore this paper introduces two new model ice types with which those scenarios can be modeled. The ‘model ice of virtual equivalent thickness’ uses a different modeling approach to reach a scaled stiffness for improved modeling of waves in ice and ships’ resistance in thicker ice. The ‘wave model ice’ is modeled by using waves in the formation process and can resemble high-pressure-zones acting on a vertical structure. Both methods are considered as an extension to the existing standard model ice for dedicated scenarios by scaling or putting emphasis on different ice properties by altering the production process. The presented approach also emphasizes case-based-scaling, which means that the scaling or the model ice type needs is defined by the modeled scenario as the standard model ice is obviously not fully capable to reflect all properties of sea ice in scale.
Study on Influx Risk Evaluation of Horizontal Gas Wells With High-Pressure High-Temperature in the South China Sea
Authors: Luo Ming , Gao Deli , Zhao Xin , Chen Yuan , Yang Yupeng , Li Zhong , Zhang Wandong , Zhou Xu 
Published: December 2020

Abstract
The South China Sea has rich natural gas source with typical high-pressure high-temperature (HPHT) and the extremely narrow drilling window, which leads to frequent influx, even borehole abandonment. However, horizontal gas wells have been placed in the area to develop the gas reservoir, which presents greater well control challenges. Therefore, the influx risk evaluation is quite necessary to guide the well control design.
Firstly, the influx mechanism is analyzed based on gas intrusion to provide a theoretical basis for well control design. It is found that influx usually occurs when drilling the high-temperature stratums and target layers. Secondly, the relationship between horizontal open-hole length and influx volume is calculated under different reservoir permeability, reservoir thickness, negative bottom hole pressure and horizontal open-hole section length. Thirdly, the characteristics of gas-liquid two-phase flow are described. Fourthly, the inflow risk evaluation and well control strategies of the target horizontal gas wells are proposed, and the influx risk evaluation envelope was established.
The influx risk evaluation and well control strategies have been successfully applied to the DF gas field featuring offshore HPHT. Horizontal gas wells were drilled in the micro pressure window without accidents and the well cost was significantly reduced.
Comparative Study on RAOs of a Ship Under Transient Gaussian Wave Packets by Marginal Hilbert Spectrum and Fourier Spectrum
Authors: Liu Zhen , Fan Sheming , Tao Longbin 
Published: December 2020

Abstract
Sea-keeping model tests of ships based on transient waves have been widely applied over the past several decades. In order to obtain response amplitude operators (RAOs) of a ship, most of the post-processing of the experimental data uses the fast Fourier transform (FFT) to obtain the wave spectrum and the corresponding response spectrum. However, for transient waves related model tests, FFT may produce larger errors due to its characteristics. Hilbert-Huang transform (HHT) is a newly developed signal analysis tool which is suitable for nonlinear and non-stationary data. The application of HHT to the post-processing of the experimental data of sea-keeping model tests of ships has not yet been investigated. In this study, the transient wave packets satisfying a Gaussian wave spectrum were generated in a large towing tank to conduct the sea-keeping model tests of a drilling ship under the condition of head waves, oblique waves and beam waves, respectively. Then the marginal Hilbert spectrum (MHS) in the framework of HHT is introduced to obtain the motion and the acceleration RAOs the drilling ship. In order to demonstrate the effectiveness of the approach, the results based on FFT and regular waves are also presented. It is found that in most cases, in comparison to that by means of FFT, the RAOs of the ship based on the transient Gaussian wave packets by means of MHS agree better with the results based on regular waves, especially for roll motion with significant nonlinear characteristics. Due to the advantages of HHT, the MHS approach employed in this study is expected to play a vital role in more sea-keeping related model tests of ships.
Configuration and Performance Analysis of Deep Ocean Mining Flexible Riser
Authors: Gai Yuxin , Guo Shuangxi , Li Yilun , Li Min , Chen Weimin 
Published: December 2020

Abstract
Deep-sea minerals such as polymetallic nodule, hydrothermal sulphides and ferro-manganese crusts have for long attracted attention as an alternative source of metals to terrestrial deposits. To bring these minerals up to the land, flexible risers are needed. As the mining industry developing towards deep sea area, the conveying system is usually designed as a combination of steel riser and flexible riser. According to different transport requirements, various flexible riser configurations, such as steel catenary riser, lazy-wave riser and saddle-shaped riser, have been proposed. During mining operation, the riser bears gravity, buoyancy, wave and current force, therefore the assessment of structural safety and reliability is quite challenging. In addition, the riser response caused by the mining vehicle motion during working process in a large area should also be considered. To guarantee a safe operation and service life of the riser, it is necessary to carefully design its configuration and to analyze its performance.
In this study, taking the saddle-shaped riser as our model, the influences of main design parameters on the riser configuration, tension and stress are examined. These parameters include the installation position of buoyancy modules, the buoyancy ratio and motion of mining vehicle. Firstly, the analysis model of the riser response is established based on FEM in which the nonlinear large displacement and deformation of the structure are considered. Secondly, through our FEM simulation, the distribution and variation of tension and stress along the axial length of risers with different configurations are presented. Finally, the impacts of the mining vehicle motion on riser response are discussed. Our numerical results show that a small change of the buoyancy position and buoyancy ratio may lead to a significant change of the riser configuration, but a little change of riser tension/stress. And the saddle-shaped riser has a good tolerance performance to the bottom-end excitation.
A Study on Hydrate Inhibition of Marginal Gas Field Development
Authors: Yi Hualei 
Published: December 2020

Abstract
In the marginal gas field development engineering, considering the low gas production with complex reservoir condition, it is difficult to develop independently because of the low economic efficiency. It is usually developed by relying on an existing offshore platform or facility nearby, in which hydrate inhibition is an important issue, and in order to inhibit hydrate formation in the subsea pipeline, hydrate inhibition method should be studied. Based on certain marginal gas field development project in South China Sea, which relies on nearby DPP platform, the paper studies methanol and MEG as inhibitor and application of double-layer insulated subsea pipeline. Finally by technical and economic comparisons, for the first time double-layer insulated pipeline is selected as the hydrate inhibition method to meet requirements of both relying on DPP and achieving better economic benefits, which is expected to provide reference for similar marginal gas field development.
Dynamic Responses of a Spar Type Floating Offshore Wind Turbine With Failed Moorings
Authors: Ren Yajun , Venugopal Vengatesan 
Published: December 2020

Abstract
The complex dynamic characteristics of Floating Offshore Wind Turbines (FOWTs) have raised wider consideration, as they are likely to experience harsher environments and higher instabilities than the bottom fixed offshore wind turbines. Safer design of a mooring system is critical for floating offshore wind turbine structures for station keeping. Failure of mooring lines may lead to further destruction, such as significant changes to the platform’s location and possible collisions with a neighbouring platform and eventually complete loss of the turbine structure may occur.
The present study focuses on the dynamic responses of the National Renewable Energy Laboratory (NREL)’s OC3-Hywind spar type floating platform with a NREL offshore 5-MW baseline wind turbine under failed mooring conditions using the fully coupled numerical simulation tool FAST. The platform motions in surge, heave and pitch under multiple scenarios are calculated in time-domain. The results describing the FOWT motions in the form of response amplitude operators (RAOs) and spectral densities are presented and discussed in detail. The results indicate that the loss of the mooring system firstly leads to longdistance drift and changes in platform motions. The natural frequencies and the energy contents of the platform motion, the RAOs of the floating structures are affected by the mooring failure to different degrees.
Effect of Spudcan Sliding on Structure and RPD of Jack-Up Platform
Authors: Gao Jie , Duan Menglan 
Published: December 2020

Abstract
In the same sea area, with the increase of the number of operations, the situation of jack up offshore drilling platform carrying out secondary or multiple Jack-up leg embedment operations in the vicinity, or even in the same location will increase year by year. Therefore, the operation of jack up offshore drilling platform makes the sea area “step on the footprints” The problems become more and more frequent, and have a significant impact on the operation safety of offshore platforms. During the “footprint” process of jack-up drilling platform, the spudcan will slide transversely along the direction of Jack-up leg pits to varying degrees. If the sliding distance is too large, the leg or platform structure will be damaged. Based on the symmetrical structure of the three-leg jack-up offshore platform, the bow and the starboard spudcan are slided along x-axis at different angles, respectively. According to the critical bearing capacity of the platform legs, the critical distance of spudcans sliding is calculated. Finally, the relationship between the sliding distance of spudcan in different directions and RPD (Rack phase difference) is obtained by monitoring the RPD value of legs. It provides meaningful guidance for platform designers and operators.
Design Challenges of SCRs in Deepwater and Ultra Deepwater
Authors: Cheng Yongming , Yu Chenteh Alan , Song Hao 
Published: December 2020

Abstract
A riser is a fluid conduit connecting from a subsea well to a surface floating production vessel such as a spar, TLP, or a semi-submersible. It is a key component for transporting produced oil and gas from the subsea wells to the surface production vessel. Through nearly 30 years of design and implementation, Steel Catenary Risers (SCRs) have been found to have the advantages of relatively low manufacturing cost and good adaptability to floating platform’s motion. Thus, SCRs are widely used in GoM and Brazilian water. This paper investigates design challenges of SCRs used for a semi-submersible in deepwater and ultra deepwater.
As the application moves to deepwater and ultra deepwater, challenges of a conventional SCRs increase significantly in terms of global performance, fabrication, and installation. This paper first introduces an SCR system used for a semi-submersible platform. One of the challenges is the harsh environmental condition such as hurricanes or tropical cyclones. Severe motions of a semi-submersible platform may cause significant compression loads on SCRs at the Touch Down Zone (TDZ). It is challenging to design the SCRs to meet API RP 2RD requirement for the riser dynamic strength. Multiple seeds of random motion simulations for irregular wave are necessary for the evaluation. The new riser design code of API STD 2RD can also be used to assess riser strength, especially under 1000-yr survival environmental conditions.
It is challenging to design SCRs to meet a design life of 30 years and beyond. The fatigue assessment of the SCRs considers the damage contributions from the semi wave motions, riser Vortex-Induced Vibration (VIV) due to ambient current, and Vortex-Induced Motion (VIM) of a semi-submersible platform. Fatigue contribution from installation is also considered and included in the combined fatigue damage calculation. The long term combined factored fatigue life is computed to ensure that the SCRs meet the requirement of design life.
This paper further investigates intermittent Vortex-Induced Vibration (VIV) caused by heave motions of a semi-submersible platform. This VIV phenomenon has an impact on SCR strength due to the drag amplification as well as fatigue damage. The installation concerns come from riser pipe size, installation method and capacity of an installation vessel. Examples are provided for illustrations of the design challenges. In addition, this paper explores likely solutions to meet SCR design challenges for the applications in deepwater and ultra deepwater.
Structural Control of the Ultra-Large Semi-Submersible Floating Offshore Wind Turbine
Authors: Li Xin , Zhao Zhixin , Han Dongdong , Zhao Haisheng 
Published: December 2020

Abstract
Taking the DTU 10 MW braceless semi-submersible floating offshore wind turbine (FOWT) as the research object, an ideal tuned mass damper (TMD) installed in platform of the 10 MW semi-submersible FOWT is investigated to dynamically compensate the vibrations and reduce the structural loads. Considering the hydrodynamic and mooring effects, a simplified model of FOWT with four degrees of freedom (DOFs) including platform surge, pitch, tower fore-aft bending and TMD translation is established according to the D’Alembert’s principle. Then, based on the Levenberg-Marquardt (LM) algorithm, the unknown parameters related to the simplified model are estimated. Compared with results from FAST-SC, the simplified dynamic model is validated. Furthermore, the response surface method and genetic algorithm (GA) are used to determine the optimized TMD parameter. Finally, the fully coupled time-domain simulation of the FOWT with active TMD subjected to environmental loadings is conducted by using FAST-SC, and the effect of the TMD on the load reduction of the 10 MW braceless semi-submersible FOWT is analyzed. The study provides a feasible method for the structural control of the ultra-large semi-submersible FOWTs.
Model Experimental Research of Ship Section on Structural Ultimate Strength
Authors: Xianyin Chen , Wenyuan Zeng , Cong Li , Wei Wang 
Published: December 2020

Abstract
Focusing on the model design and experimental method research of ultimate strength of ship hull typical section, a large ship with complex section structure was taken in this paper as the research object. The nonlinear analysis on the failure mode and ultimate strength of the hull structure were carried out. The similarity model for ultimate strength experiment was designed, and the validity of the similarity model in reflecting the ultimate bearing capacity of the real ship was verified. According to the experimental results, the ultimate strength experimental value was obtained by numerical conversion. The ultimate bearing capacity of the example ship was then checked with reference to several classification society rules to verify the structural safety of the ship hull.
Lifting Technique of Composite Bucket Foundation for Offshore Wind Turbines
Authors: Ding Hongyan , Feng Zuntao , Zhang Puyang , Le Conghuan 
Published: December 2020

Abstract
The onshore pre-fabrication technology for composite bucket foundations takes “prefabrication-assembly-lifting” as the core concept. The practice of pre-fabrication of upper and lower structures is prefabricated respectively. In the research of hoisting engineering technology, combined with the structural form and construction requirements of composite bucket foundation, the assembly scheme of the upper prestressed concrete transition section and the lower steel bucket and the hoisting scheme of integral foundation with compartments were designed. The finite element model in the lifting process of composite bucket foundation was established by the large-scale general finite element analysis software ABAQUS. For the optimization analysis of the lifting point arrangement during hoisting process, the number, position and arrangement form of lifting points are simulated and analyzed. The results show that the maximum value of the principal stress of the concrete transition section structure appears in the assembly stage with the lower steel bucket, and the structure checking calculation should be carried out as the most unfavorable lifting condition in construction; the peak point of structural stress is at the junction of girder and secondary beams and inner ring beams of concrete roof, which belongs to the weak position of force transmission. In construction, it should be paid attention to as the key part of monitoring to ensure composite bucket foundation is under reasonable stress and the stability in the lifting process. The research results can provide guidance and reference for the future batch production and standardization production construction for composite bucket foundations.