bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reliability and Robustness Based Design Attributes for Multi-Criteria Decision Making
Authors: Žanić Vedran , Pirić Karlo , Kitarović Stanislav 
Published: November 2013

Novel design methodology with inclusion of reliability and robustness-based design criteria is presented. Robustness is defined as the insensitivity of a design attribute to uncontrollable design parameters. The developed design procedure for the concept design phase is divided into two basic, coordinated tasks: (1) multi-criteria topology/geometry optimization of the ship structural model; (2) scantlings / material multi-criteria optimization of structural panels.
Reliability criteria and robustness of design attributes are applied as relative measures of quality, besides standard design attributes such as costs and weight. They are used in generation of Pareto-optimal design variants. Reliability attributes used for the panel design are compared with respect to fidelity and computational efficiency. A novel method for fast reliability calculations is presented using dimension reduction method (DRM) as implemented into FASTREL software. The method is verified with respect to accuracy and speed on the box girder design and panel design with CalREL methods (MC, FORM).
The design procedure steps are executed in the predefined sequence of design sub-problems, using the fast and balanced collection of analysis and synthesis modules/methods of the MAESTRO/OCTOPUS design system. They are as follows: • Probabilistic determination of design loads; • Calculation of the structural serviceability and ultimate strength criteria on the panel (macro-element) level; • Calculation of the cross section ultimate longitudinal strength criterion; • Calculation of reliability and robustness measures on the panel level (safety) and on the global level. Other design attributes (initial cost, structural weight, etc.) are also determined; • Generation of the Pareto frontier for the selected test structure based upon the cost–safety design paradigm; • Generation of insight into the multilevel optimization process with graphic presentation of designs in design and attribute spaces.
Practical application of the developed concept design methodology and of the design environment to the structural design of modern multi-deck ship elements (panels) is presented for verification/validation of accuracy and speed of FASTREL module.
Investigation to Air Compressibility of Oscillating Water Column Wave Energy Converters
Authors: Sheng Wanan , Thiebaut Florent , Babuchon Marie , Brooks Joseph , Lewis Anthony , Alcorn Raymond 
Published: November 2013

It has been suggested that for full scale oscillating water column (OWC) devices, the pressure in and the volume of the air chambers can be large to create air compressibility in the air chamber. Due to compressibility, its density and temperature are different from those in atmosphere. When in exhalation, the pressurized air is driven out of the air chamber and mixes into the atmosphere outside the air chamber; whilst in inhalation, the atmosphere is sucked through the power take-off (PTO) system into the air chamber, and mixes with the de-pressurized air in the chamber.
This paper presents a study on air compressibility in OWC air chambers by theoretical analyses and the relevant experimental studies. The theoretical analysis is based on the first-order differential equation for the flowrate and the chamber pressure, which has been derived for the air flow under the assumptions of the isentropic process and the known power take-off characteristics. In the study, an orifice type of PTO and a porous membrane type PTO, which are supposed to represent a typical nonlinear and linear PTO for small models, respectively, are both investigated. The investigation has shown the feasibility of the theoretical method on the air compressibility and the possible power loss due to the air compressibility.
Global Buckling of a Pre-Pressurized Flexible Flowline
Authors: Yang Zhengmao , Karunakaran Daniel 
Published: November 2013

For the protection from object drop/fishing trawl impact, flexible flowline is normally trenched or rock-dumped. And hence, upheaval buckling is promoted by the elevated temperatures and high pressures. In order to reduce the rock cover requirement for mitigation of upheaval buckling, rock-dumping or trenching while the flexible pipe are pressurized has been performed successfully in several north sea projects.
The temperature and pressure induced elongation of flexible pipe are design dependent. For high pressure flexible flowline, the pressure expansion is significantly higher than conventional rigid pipelines. Due to the low bending stiffness and high pressure expansion, a flexible flowline will buckle laterally when it is pre-pressurized in hydro-test before trenching or rock-dumping. As a consequence, lateral imperfections are induced and will be kept after trenching or rock-dumping due to lateral resistance and bending stress relaxation of the flowline. In these locations, the flowline tends to deform laterally in operating. On the other hand, when the flowline is de-pressurized after trenching or rock-dumping the contraction of the flowline is restrained by the surrounding soils or rocks, and hence axial tension force can be obtained. When the flowline starts to operate, this tensile force will neutralize part of the compressive axial force, and therefore the required upheaval resistance is reduced.
In this paper, global buckling of a pre-pressurized flexible flowline has been studied, and the influence on the requirement of rock covers is presented.
Measurement and Modelling of Residual Stresses in Offshore Circumferential Welds
Authors: Zhang Yan-Hui , Smith Simon , Wei Liwu , Johnston Carol , Stacey Alexander 
Published: November 2013

Residual stresses (RS) are unavoidably generated in components after welding. Tensile residual stresses in engineering structures generally have an adverse effect on structural integrity, with detrimental effects on brittle fracture, corrosion properties and fatigue performance.
Residual stress measurements for offshore welded joints are generally very limited. In this study, experimental measurements and numerical modelling of residual stresses were carried out and the through-thickness residual stress distributions in circumferential butt welds are presented. Pipes of two different dimensions and steels were investigated: a seamless X70 steel pipe with an outside diameter of 406mm and a seam-welded X65 steel with an outside diameter of 508mm. The measurement methods used included the centrehole air abrasion drilling, the deep-hole drilling (DHD) and the block removal, splitting and layering (BRSL). The numerical modelling was undertaken to determine whether modelling could provide a satisfactory prediction of the final residual stresses. Finally, the new experimental data were combined with the BS 7910 database to derive revised upper bound through-thickness residual stress distributions for girth welds and to provide an assessment of the impact of residual stresses on the structural integrity of circumferential welds in offshore structures.
Improvement of Wave Power Take-Off Performance due to the Projecting Walls for OWC Type WEC
Authors: Ikoma Tomoki , Masuda Koichi , Omori Hikaru , Osawa Hiroyuki , Maeda Hisaaki 
Published: November 2013

This paper describes a method in order to improve the performance of the primary conversion of wave power take-off. A corresponding wave energy convertor (WEC) is an oscillating water column (OWC) type. The method of the improvement has been proposed and its usefulness has been confirmed in past researches. In the method, projecting walls were attached onto front of inlet-outlet of OWC.
The prediction method of hydrodynamic behaviors for the projecting walls installed OWC type WEC is explained in the paper. The boundary element method with the Green’s function is applied and influence of air pressure and free surface within every an air-chamber was directly taken into consideration in the prediction method based on a linear potential theory. Validity of the prediction method was proved comparing with results of model experiments.
Series calculations are performed with the prediction method. Behaviors of air pressure, water elevation and the efficiency of primary conversion of wave power are investigated. From the calculations, length of the projecting walls was shown to affect the efficiency of primary conversion. It was available to equip the projecting walls for the improvement in oblique waves to beam sea condition as well as head sea condition. As well as only the projecting walls, application and effects of the end walls with the slit were investigated in the paper. The end walls were very useful to improve the efficiency.
Evaluation of Safe and Failure Zones of Risers and Mooring Lines of Floating Production Systems
Authors: Cruces Girón Aldo Roberto , Corrêa Fabrício Nogueira , Jacob Breno Pinheiro 
Published: November 2013

In recent years, the design procedures of risers and mooring system for floating production systems (FPS) have had more feedback. In this way mooring and risers designers can identify, even in an early stage, the constraints imposed by one system over the other.
This work presents an evaluation of the crossing of the information obtained from the analyses of risers and mooring system. Different riser and mooring analysis procedures are applied to a typical FPS for deep water applications. First, failure zones of the riser system are identified, so a safe operating limit zone can be defined. Then, the excursions of the platform are calculated taking into account the global response of the coupled system (hull, mooring lines and risers). Finally, the results are crossed in order to verify if the excursions of the platform are within the safe operating area.
The evaluation presented here shows the important of correctly defining the safe operational zones and how the crossing of information can be conservative or not within the design process of mooring lines and risers.
Metallurgical Design and Performance of HFW Linepipe With a High-Quality Weld Seam Suitable for Sour Services
Authors: Toyoda Shunsuke , Goto Sota , Okabe Takatoshi , Kimura Hideto , Sato Shuichi , Kumazawa Shintaro , Yabumoto Satoru , Sato Akio , Inoue Tomohiro 
Published: November 2013

To clarify the effects of inclusions on the sour resistance properties of X60- to X70-grade steel, their resistance to hydrogen-induced cracking (HIC) was numerically simulated. The steel was assumed to have a yield strength of 562 MPa and a tensile strength of 644 MPa for the simulation. To estimate the effect of nonmetallic inclusions, a virtual inclusion was situated at the center of a 10-mm-thick HIC test specimen. Tests were performed using NACE test solution A. The crack initiation criterion was determined as a function of the diffusible hydrogen concentration, the diameter of the inclusion, the edge radius of the inclusion, and the fracture toughness of the matrix after hydrogen absorption. The crack propagation was calculated as a function of the diffusion coefficient of hydrogen in the steel matrix and the gasification reaction ratio of hydrogen at the interface of the steel matrix and the inclusion.
Based on the results of the numerical estimation, high-frequency electric resistance welded (HFW) Linepipe with a high-quality weld seam was developed. Controlling the morphology and distribution of oxides generated during the welding process by means of temperature and deformation distribution control is the key factor for improving resistance to HIC.
Experimental Analysis of Higher-Order Sliding Mode Control Applied to Dynamic Positioning Systems
Authors: de Sousa Tadeu F. , Tannuri Eduardo A. 
Published: November 2013

The control algorithm normally used in Dynamic Positioning (DP) Systems is based on linear control theory (proportional-derivative or linear quadratic MIMO controller), coupled to an Extended Kalman Filter (EKF) to estimate the environmental forces and wave filtering. Such controllers and estimators have problems of performance and stability related to large variations of loading (for tankers for example) or environmental conditions. The adjustment of controller gains and parameters of EKF is a complex process. Therefore, other techniques are being applied.
An investigation into the area of control of mechanical systems was made, carrying out theoretical and experimental studies involving nonlinear robust control techniques applied to dynamic positioning of floating vessels. Two robust control techniques were applied and compared: first order sliding mode control (SMC) and higher order sliding mode control (HOSM). It is known that the main drawback of SMC is the presence of high-frequency oscillations called chattering. This undesirable effect can be eliminated by using HOSM. In order to ascertain the performance of the controller under the DP system, time-domain simulations were done. Furthermore, the technique of sliding mode requires higher order derivatives of the vessel’s position signal. Therefore was developed an exact real-time differentiator, a mathematical technique used to obtain the signal derived from the position signal in real time. To validate the simulated controller, experimental tests were performed considering a small-scale model of a DP tanker.
The results confirmed the robustness of the HOSM controller, the good performance of the differentiator and the elimination of the chattering problem.
Fatigue Crack Growth Rate and Fracture Toughness of Non-Sour Service Grade X65 and X80 in Sour Environments
Authors: Nakamura Jun , Hisamune Nobuyuki , Fukuba Tetsuya , Thodla Ramgopal , Scott Colin Stuart , Gui Feng 
Published: November 2013

Offshore flowlines are subject to large thermal transients particularly during shut down. These thermal transients tend to vary from about 200°F to ambient temperature and place a large fatigue demand on the pipelines. The transients typically are very low frequency events with high amplitudes, which can lead to lateral buckling. The loading rates associated with the transients are very slow, hence the toughness properties of the material in environments at low loading rates is important. The pipelines are also subject to high stress and thus need to have good toughness properties. Riser materials are also subject to significant fatigue loading, though under conditions different from flow lines. They are typically pre-loaded and operate under smaller amplitudes of loading and at higher frequencies associated with wave motion.
There has been some work performed to understand the performance of carbon steels in dynamic applications like risers and flow lines in sour service. This work is focused on exploring a range of environmental and loading conditions that are relevant to offshore production to evaluate the non-sour service grades X65 and X80 to gain greater insight into the role of chemistry and thermo mechanical processing on the sour service fatigue and fracture behavior of line pipe steels. Two different grades of non-sour service grade seamless pipe X65 and X80 were investigated in a range of sour environments. The concentration of diffusible hydrogen in the range of environments to relate the environment assisted cracking properties to the concentration of hydrogen. Fracture toughness measurements indicated that crack initiation and tearing modulus were dependent on the concentration of diffusible hydrogen. The lowest toughness properties was obtained in pH = 5, 4.6psia H2S. FCGR exhibited a1/√f dependence in all conditions suggesting that hydrogen diffusion was likely the rate limiting step before reaching a plateau. X65 and X80 exhibited the highest FCGR in pH = 5, 4.6psia H2S. The FCGR of X80 was lower than X65 under the same environmental conditions in all cases while the plateau frequency was very similar for both X65 and X80. Paris law measurements performed at constant Kmax and decreasing ΔK at plateau frequencies exhibited elevated FCGR levels above the in-air values consistent with the frequency scan data.
Noise Prediction and Control of Floating, Production, Storage and Offloading (FPSO)
Authors: Song Keun Bok , Kim Hyung Taek , Kim Sung Hoon , Joo Won Ho 
Published: November 2013

Recently, the noise regulations are being reinforced to restrict the noise levels in the workplace and to protect the operator on the offshore structures. So, the noise levels of indoor and outdoor are one of the crucial barometers for determining the quality of offshore structures.
In this paper, an efficient and accurate noise analysis method, which is used to calculate the indoor and outdoor noise levels for Floating, Production, Storage and Offloading (FPSO) vessel, is introduced. The indoor noise level is calculated through summing up structure-borne noise, airborne noise from machinery, HVAC noise and transmitted noise from topside. Each noise level is predicted using appropriate methods by HHI’s procedures, which consider room acoustic theories, numerical methods like SEA and measured database at various ships and offshore structures. The outdoor noise level is predicted by using ray tracing method. Noise control procedures to improve acoustic properties of cabin/machinery room and to reduce the indoor/outdoor noise levels of offshore structures are also introduced: these procedures are produced by numerous experiments at the large scale acoustic test facilities like reverberant rooms and cabin mock-up.
The established method has been applied to various types of real projects for FPSOs. The predicted results are confirmed to agree well with measurements results. It is expected to be very helpful to design the low noise FPSO.
Roll Damping Coefficients Assessment and Comparison for Round Bilge and Hard Chine Hullforms
Authors: Begovic Ermina , Bertorello Carlo , Prpic Orsic Jasna 
Published: November 2013

The sustainable design of small passenger vessels and large size pleasure craft indicates new trends: lower speed, reduced fuel consumption and better seakeeping in all range of velocities. Small amplitudes of roll motion are considered one of the most important comfort parameter. These trends call for reviewing some commonly used concepts and designer practice. Fundamental parameters as metacentric height and midsection form affect comfort as well as ship safety in counteracting way.
Round bilge, due to good seakeeping characteristics and to large amount of available data from systematic series is the most common hull form choice when cruising speed implies displacement or semi displacement mode. Hard chine hull forms are generally chosen when relative speed leads to some hydrodynamic lift, although recently they have been considered for low relative speed. They allow simplified and cheaper construction and among their interesting features is higher roll damping. This appears very attractive for craft that are generally fitted with stabilizing systems and ask for the most reduced roll motions at any and zero speed.
This paper presents the results of experimental tests relative to roll decay of two ship models of the same dimensions, displacement and GM values: they have the same warped bottom hull form developed at University of Naples, the first is hard chine and the second has round bilge from transom to midship. Both of them are suitable for displacement and semi-displacement craft operating at medium-low relative speed. The tests have been carried out at University of Naples towing tank, in calm water, at Fn ranging from 0.0 to 0.45. Natural roll frequencies and linear and non linear damping coefficients are reported for all tested speeds allowing a fair comparison of the roll characteristics due to the variation in hull form.
2D and 3D CFD Investigations of Seabed Shear Stresses Around Subsea Pipelines
Authors: Shen Wenwen , Griffiths Terry , Xu Mengmeng , Leggoe Jeremy 
Published: November 2013

For well over a decade it has been widely recognised that existing models and tools for subsea pipeline stability design fail to account for the fact that seabed soils tend to become mobile well before the onset of pipeline instability. Despite ample evidence obtained from both laboratory and field observations that sediment mobility has a key role to play in understanding pipeline/soil interaction, no models have been presented previously which account for the tripartite interaction between the fluid and the pipe, the fluid and the soil, and the pipe and the soil.
There are numerous well developed and widely used theories available to model pipe-fluid and pipe-soil interactions. A challenge lies in the way to develop a satisfactory fluid-soil interaction algorithm that has the potential for broad implementation under both ambient and extreme sea conditions due to the complexity of flow in the vicinity of a seabed pipeline or cable. A widely used relationship by Shields [1] links the bedload and suspended sediment transport to the seabed shear stresses. This paper presents details of computational fluid dynamics (CFD) research which has been undertaken to investigate the variation of seabed shear stresses around subsea pipelines as a parametric function of pipeline spanning/embedment, trench configuration and wave/current properties using the commercial RANS-based software ANSYS Fluent. The modelling work has been undertaken for a wide range of seabed geometries, including cases in 3D to evaluate the effects of finite span length, span depth and flow attack angle on shear stresses.
These seabed shear stresses have been analysed and used as the basis for predicting sediment transport within the Pipe-Soil-Fluid (PSF) Interaction Model [2] in determining the suspended sediment concentration and the advection velocity in the vicinity of pipelines. The model has significant potential to be of use to operators who struggle with conventional stabilisation techniques for the pipelines, such as those which cross Australia’s North West Shelf, where shallow water depths, highly variable calcareous soils and extreme metocean conditions driven by frequent tropical cyclones result in the requirement for expensive and logistically challenging secondary stabilisation measures.