bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical Approach to Identify Threshold and Point of Departure in Dose–Response Data
Authors: Spassova Maria A.
Published: September 2018

The study presents an integrated, rigorous statistical approach to define the likelihood of a threshold and point of departure (POD) based on dose–response data using nested family of bent‐hyperbola models. The family includes four models: the full bent‐hyperbola model, which allows for transition between two linear regiments with various levels of smoothness; a bent‐hyperbola model reduced to a spline model, where the transition is fixed to a knot; a bent‐hyperbola model with a restricted negative asymptote slope of zero, named hockey‐stick with arc (HS‐Arc); and spline model reduced further to a hockey‐stick type model (HS), where the first linear segment has a slope of zero. A likelihood‐ratio test is used to discriminate between the models and determine if the more flexible versions of the model provide better or significantly better fit than a hockey‐stick type model. The full bent‐hyperbola model can accommodate both threshold and nonthreshold behavior, can take on concave up and concave down shapes with various levels of curvature, can approximate the biochemically relevant Michaelis–Menten model, and even be reduced to a straight line. Therefore, with the use of this model, the presence or absence of a threshold may even become irrelevant and the best fit of the full bent‐hyperbola model be used to characterize the dose–response behavior and risk levels, with no need for mode of action (MOA) information. Point of departure (POD), characterized by exposure level at which some predetermined response is reached, can be defined using the full model or one of the better fitting reduced models.
Human herpesvirus 6 associated post‐transplant acute limbic encephalitis: Clinical observations of biomarkers for risk of seizure in a pediatric population
Authors: Santoro Jonathan D. , Hemond Christopher C.
Published: September 2018

Background

Human herpesvirus 6 (HHV6) is a cause of post‐transplant acute limbic encephalitis (PALE). Seizures are associated with this disorder yet no predictive biomarkers have been identified. The objective of this study was to evaluate lab and neurodiagnostic biomarkers in patients with HHV6 associated PALE.

Methods

A retrospective chart review was performed at our institutions

between 2000 and 2017. Patients were identified through a clinical database. Inclusion criteria included: age less than 18 years, HHV6 (quantitative real‐time PCR or meningoencephalitis panel) tested in CSF and serum. Biomarkers of serum and CSF viral load, EEG, and MRI were reviewed along with clinical data.

Results

In total, 11 patients met inclusion criteria. All patients had undergone hematopoietic stem cell transplantation. Five of 11 patients had seizures as part of their clinical course, all being controlled with antiepileptic monotherapy. Seizure semiology was focal‐onset in three cases and generalized in two. Neuroimaging was normal in all patients within seven days but six patients developed T2 signal intensities in the temporal lobes on repeat imaging between 14‐28 days. The median CSF HHV6 viral load for all patients was 47 300 copies/mL although the median viral load was 2586 copies/mL in patients who had seizure compared to 473 969 copies/mL in those who had not (P = 0.02). Those with seizures tended to be younger (median 6.5 years compared to 11 years, P = 0.27). All patients with seizures had an EEG with 80% demonstrating abnormalities.

Conclusion

In patients with post‐hematopoietic stem cell transplant HHV6 associated PALE, lower CSF viral load may be associated with a higher likelihood to have seizures. This may indicate a primary infection as opposed to secondary reactivation phenomenon.
ELONGATED HYPOCOTYL 5 mediates blue light signalling to the Arabidopsis circadian clock
Authors: Hajdu Anita , Dobos Orsolya , Domijan Mirela , Bálint Balázs , Nagy István , Nagy Ferenc , Kozma‐Bognár László
Published: September 2018

Circadian clocks are gene networks producing 24‐h oscillations at the level of clock gene expression that are synchronized to environmental cycles via light signals. The ELONGATED HYPOCOTYL 5 (HY5) transcription factor is a signalling hub acting downstream of several photoreceptors and is a key mediator of photomorphogenesis. Here we describe a mechanism by which light quality could modulate the pace of the circadian clock through governing abundance of HY5. We show that hy5 mutants display remarkably shorter period rhythms in blue but not in red light or darkness, and blue light is more efficient than red to induce accumulation of HY5 at transcriptional and post‐transcriptional levels. We demonstrate that the pattern and level of HY5 accumulation modulates its binding to specific promoter elements of the majority of clock genes, but only a few of these show altered transcription in the hy5 mutant. Mathematical modelling suggests that the direct effect of HY5 on the apparently non‐responsive clock genes could be masked by feedback from the clock gene network. We conclude that the information on the ratio of blue and red components of the white light spectrum is decoded and relayed to the circadian oscillator, at least partially, by HY5.
Completion of the canonical pathway for assembly of anticancer drugs vincristine/vinblastine in Catharanthus roseus
Authors: Qu Yang , Safonova Olga , De Luca Vincenzo
Published: September 2018

The important anticancer drugs, vinblastine, vincristine and analogs, are composed of the monoterpenoid indole alkaloids (MIAs), catharanthine and vindoline, found uniquely in the medicinal plant, Catharanthus roseus. While 26 genes involved in the assembly of these two MIAs are known, two key reactions have eluded characterization to complete the documentation of the vinblastine pathway in this plant species. The assembly of these dimeric MIAs requires O‐acetylstemmadenine oxidase (ASO) and a dual function geissoschizine synthase (GS) that reduces cathenamine to form geissoschizine, and that also reduces the ASO product to form a common intermediate for subsequent conversion by four separate hydrolases to catharanthine, tabersonine or vincadifformine, respectively. The in planta role of ASO is supported by identifying a single amino acid‐substituted ASO mutant with very low enzyme activity and by virus‐induced gene silencing of ASO to produce plants that accumulate O‐acetylstemmadenine rather than catharanthine and vindoline found in wild‐type (WT) plants. The in planta role of GS is supported by showing that a low GS‐expressing mutant accumulating lower levels of catharanthine and vindoline also displays significantly lower tabersonine‐forming activity in coupled enzyme assays than in the WT background. Gene expression analyses demonstrate that both ASO and GS are highly enriched in the leaf epidermis where the pathways for catharanthine and tabersonine biosynthesis are expressed. The full elucidation of this canonical pathway enables synthetic biology approaches for manufacturing a broad range of MIAs, including these dimers used in cancer treatment.
India’s Finance-Growth Nexus: Cointegration and Causality Analysis with Income Inequality and Globalization
Authors: Fukuda Takashi
Published: September 2018

This paper investigates India’s finance-growth nexus―the relationship between financial development and economic growth―taking the weakly exogenous variables of income inequality, trade openness and financial openness together with the structural break dummy into the cointegration analysis of the vector error correction model. Implementing the Granger causality tests we have detected that both financial size and financial efficiency exhibit a negative impact on economic growth with no feedback from the latter to each of the former. It is important for policy makers to recognize that finance does not always promote economic growth, considering how to convert the effect of financial development from “growth-retarding” to “growth-enhancing”.
Boosting Speed and Accuracy in Precision Motion Control
Authors: Ramani Keval S. , Duan Molong , Yoon Deokkyun , Okwudire Chinedum E. , Ulsoy A. Galip
Published: September 2018

Feedforward (FF) control uses a priori knowledge about a given system and its disturbances to influence the system’s behavior in a pre-defined way. However, unlike feedback (FB) control, it does not adjust the control signal (or manipulated variable) in response to how the system actually reacts. In other words, FF control is proactive while FB control is reactive. Model-inversion-based FF (MIBFF) control is a specific type of FF control where the control variable is determined by inverting a model of the system to be controlled. It is very popular for its use in output tracking control problems, where the goal is to force the system’s output to follow a desired trajectory. Output tracking is critical in several different applications, e.g., in manufacturing, robotics, automotive, aerospace, and is typically achieved using a combination of FF and FB control. As motivating examples, consider MIBFF in ultra-precise wafer scanners used in photolithography (see Sidebar S1) and in desktop 3D printing (see Sidebar S2). As these motivating examples illustrate, non-minimum phase (NMP) zeros often arise in practical engineering applications due to non-collocated sensors and actuators, fast sampling, etc. MIBFF for systems with NMP zeros is arguably the most important (and certainly the most researched) issue related to MIBFF.
Hydroelastic Analysis of a 3D Floating Body Considering Uncoupled Flexural and Torsional Vibrations
Authors: Sengupta Debasmit , Datta Ranadev , Sen Debabrata
Published: September 2018

A semi analytic three-dimensional time domain method is developed to predict the hydroelastic effect due to wave induced loads on a floating body. The methodology being a semi analytic approach is able to capture real life scenario of bending of a ship like structure on sea taking both flexural and torsional vibrations. A prismatic beam equation with analytically defined modeshapes is taken into consideration to represent the structural response. The elastic deformation is solved using modal superposition technique. The radiation forces for elastic modes are obtained through impulse response function in time domain where frequency domain added mass, damping coefficients and wave exciting forces for the flexible modes are derived from a frequency domain panel method code. The Duhamel integral is employed in order to get the flexural and torsional deflection, velocity. A rectangular barge with zero forward speed is chosen for the analysis. Structural responses, torque, bending moments are calculated to assess the wave induced loads on the floating elastic body. The proposed technique, developed in Fortran, appears to be robust, efficient and computationally less expensive and can be used to predict the wave induced loads on a flexible structure as a first approximation in the initial design stage.
Development of Water Tank Test Device for Deep-Water Mooring
Authors: Oishi Go , Yamaguchi Hiroshi , Shimada Kiyoshi , Kayajima Kouichi
Published: September 2018

When conducting model tests in a water tank, available model sizes and wave conditions are determined for each tank, depending on measurement accuracy and tank specifications. For deep-water mooring of a floater, a mooring extent in model scale is presumably over 10 meters in depth, making it difficult to be conducted in small-sized tanks without mooring line truncation. The purpose of the research is to develop a device, which could be used as deep-water mooring system in small-sized tanks. Although the law of geometrical similarity is compelled to quit because of the line truncation, the law of mechanical similarity can be maintained by keeping the same restoring, damping and inertia characteristics as those of the full-scale mooring system obtained by numerical simulations.

The mooring device consists of a cylinder, a piston, an orifice, springs, pulleys and weights. A spring attached to the mooring line is to generate required restoring force. The orifice, together with the piston, is to generate required damping forces. Inertia forces are generated by the motions of hanged weights, also by the motion of the fluid inside the cylinder. Even negative inertia forces can be given by adjusting natural frequencies of the weight-spring system. With all these examined elements, the mooring device works like the full-depth mooring system. Particulars of the elements of the device have been determined by numerical simulations of the floater moored in the full-depth condition. It has been confirmed that the mooring device behaves as expected in comparison with forced oscillation tests, where prescribed motions were given to the floater-side end point of the mooring line.

A tank test has been conducted of a floater with a turret multipoint-moored with the devices and has been satisfactorily compared with numerical simulations of the full-depth system. With the present research it is verified that the mooring device can well simulate actual deep-water mooring system, which makes it possible for small water tanks to deal with deep water mooring experiments.
Wave Buoy Performance in Short and Long Waves, Evaluated Using Tests on a Hexapod
Authors: van Essen Sanne , Ewans Kevin , McConochie Jason
Published: September 2018

Offshore wave conditions can be measured using wave buoys, which are generally designed for wind waves. Longer waves (swell or bound second-order waves) are very relevant for certain maritime structures. The accuracy of the instrumentation in a typical wave buoy in long and short waves was therefore studied, and it was investigated if the buoy can be applied in longer waves.

A Waverider buoy was placed on a hexapod, which applied regular and irregular prescribed motions in multiple degrees of freedom. The hydrodynamic response of the buoy in waves and the effect of its mooring system were not evaluated; the buoy was assumed to follow the orbital motions of a wave and to rotate with its slope.

The tests showed that the buoy sensors measure accelerations and rotations with periods between 1.5 and 35 s very well. Vertical displacements derived from the accelerations by the buoy are accurate for the period range of 2 to 20 s. In longer waves, the motions are significantly underestimated, even though the accelerations are accurately measured. This will not lead to large errors in normal operation, as the energy of such long waves is generally low. This explains why the buoy also performs well when it is subjected to irregular motions (less than 2% error in the significant wave height of a half-hour measurement in realistic irregular sea states with peak periods between 5 and 20 s can be expected).

It can be concluded that the buoy accurately measures accelerations. The accuracy of the derived displacements decreases when very long swell wave energy (> 20 s) is present. Review of the internal integration procedure may be considered when there is a specific interest in measuring longer waves.
Study of Frictional Forces Between Rotating Pipe and Wellbore in Horizontal Wells: Experimental and Modeling
Authors: Wiktorski Ekaterina , Khatibi Milad , Sui Dan , Time Rune Wiggo
Published: September 2018

Downhole torque measurements have become an inherent part of MWD (measurement while drilling) systems. It allows drilling engineers to estimate the downhole friction and detect the presence of obstructions, for instance, cuttings bed caused by insufficient cuttings transport. The latter is a big concern when drilling horizontal and extended-reach wells.

This paper describes a method of well friction analysis as a function of adjustable drilling parameters and parameters that describe moving cuttings dune. Experiments are performed in a pipe with an internal diameter of 0.04 m and 5° inclination from the horizon, which represents a wellbore. An inside rotating pipe with an outer diameter of 0.025 m simulates a drillpipe, with a possibility of rotating speed from 0 to 1000 RPM (revolutions per minute). Glass pellets are used to simulate and display cuttings behavior in the wellbore. An electric motor is used to provide rotation of the drillpipe, supplied with an encoder to measure the electric current associated with the torque. The measurements are used to calculate the torque loss over the studied pipe length. A high-speed camera installed outside the outer pipe allows capturing images of the height of the particle bed as well as the pipe eccentricity, which increases with distance from the origin (rotating mechanism) due to the pipe’s weight and inclination.

The combined effect of these factors on the kinetic friction between the outer and inner pipes is investigated in this paper. Ultimately, the friction factor is calculated by equating measured motor torque to the theoretical torque.

The main objective of the study is a development of a methodology to express the friction factor in terms of adjustable drilling parameters in an environment, complicated with the presence of moving cuttings bed and varying pipe eccentricity. This study can supplement other research that is aimed to improve understanding of the intricate phenomenon of the wellbore friction.
Experimental and Numerical Analysis on the K-Joint Laterally Impacted by a Knife Edge Indenter
Authors: Liu Kun , Wang Zili , Tang Wenyong
Published: September 2018

Experimental and numerical studies are carried out to investigate the performance of K joints of a jack-up structure under lateral impact loading. The dynamic response is studied in a drop weight impact testing machine using three different falling heights and the failure mode and local damages of the specimens were investigated. The experimental results show that the force-time curves corresponding to the three falling heights have similar tendency during the plastic deformation process and three stages are observed in each force-time curve. The failure mode of K joints is commonly concave at the impacted area of the chord member and is buckled at the section near the mid-span of the branch members. When both ends are fixed, the chord member shows the conventional plastic failure mechanism due to bending. Numerical simulations that consider the material nonlinearity are conducted to investigate the performance of K the joints. Coupon tests of the steel are conducted to obtain the mechanical properties under both quasi-static and dynamic conditions; and these test results were then inputted as material properties for the above numerical simulating. Good agreement was achieved between the responses obtained by the FEM and the experimental results.
New Moonpool Design of Drillship for Operability Improvement
Authors: Yoo Seon oh , Kim Hyun Joe , Lee Dong Yeon , Kim Booki , Yang Seung Ho
Published: September 2018

This study suggests the three different designs of the moonpool to reduce the internal flow of the moonpool. The experimental and numerical studies were performed to improve the dillship’s operability by internal flow reduction of the moonpool. Based on the previous result of the moonpool only model tests in 2D wave flume, three different moonpool designs; Design-1) combination of forward recess deck, vertical bulkhead and beach-type wave absorber, Design-2) a step-type forward recess deck, and Design-3) a forward recess deck with beach-type wave absorber were selected. Experimental study was carried out in the Offshore Engineering Basin for 87K compact drillship with a moonpool. To verify the experimental results and clearly understand the internal flow of the drillship’s moonpool, numerical study was carried out using RANS based CFD. From these studies, it was found that all the proposed designs showed significantly reduced internal flow at resonance frequency compared to the 87K drillship’s moonpool, although the characteristic of internal flow reduction were different for each moonpool design. Additional studies were carried out to obtain the improved moonpool design that is expected to further reduce the internal flow of moonpool through CFD. Based on the result of three moonpool designs, a design combined with the step-type recess deck and the wave absorber was selected. As a result, the internal flow was effectively reduced in the overall wave period.
Modelling of Drilling Fluid Thixotropy
Authors: Cayeux Eric , Leulseged Amare
Published: September 2018

Drilling fluids are visco-elastic materials, i.e. they behave as a viscous fluid when subject to a sufficient shear stress and like an elastic solid otherwise. Both their elastic and viscous properties are time-dependent, i.e. drilling fluids are thixotropic. Because of thixotropy, it takes a finite time before the effective viscosity of a drilling fluid attains an equilibrium when the fluid is subject to a change of shear rate. This effect is visible when one changes the applied shear rate in a rheometer, as the fluid will gradually adapt to the new shearing conditions.

When the velocity of a drilling fluid changes, for instance due to a change in pump flow rate, movement of the drill string, or change of flow geometry, the fluid will exhibit a time-dependent response to the new shearing conditions, requiring a certain time to reach the new equilibrium condition.

Unfortunately, the time-dependence of the rheological properties of drilling fluids are usually not measured during drilling operations and therefore it is difficult to estimate how thixotropy impacts pressure losses in drilling operations. For that reason, we have systematically measured the time-dependence of the rheological properties of several samples of water-based, oil-based and micronized drilling fluids with a scientific rheometer in order to capture how drilling fluids systems respond to variations of shear rates.

Based on these measurements, we propose to investigate how one existing thixotropic model manages to predict the shear stress as a function of the shear rate while accounting for the shear history and gelling conditions. Then we propose a modified model that fits better, overall, with the measurements even though there are still noticeable discrepancies, especially when switching back to low shear rates.
A Comparison of Fracture Toughness and Fatigue Crack Propagation Characteristics of High Manganese and Nickel Steels
Authors: Park Jeong-Yeol , Kim Myung-Hyun
Published: September 2018

Recently, demands for liquefied natural gas (LNG) are increased by developing countries such as China, India and Middle East area. In addition, the International Maritime Organization (IMO) reinforced regulations to avoid the serious environmental pollution. This trend has led to manufacturing and operating various LNG vessels such as liquefied natural gas carrier (LNGC), floating liquefied natural gas (FLNG) and very large gas carrier (VLGC). In the design of LNG vessels, the structural integrity of LNG storage tank is of significant importance to satisfy the service conditions. In order to secure structural integrity, LNG storage tank is fabricated with low temperature materials. In general, low temperature materials such as SUS304L, Invar alloy, Al 5083-O, nickel alloy steel and high manganese steel exhibit excellent fatigue and fracture performances at cryogenic temperature. In particular, high manganese steel has attracted interest because they are potentially less expensive than the competing other low temperature materials.

This study compares the fracture toughness and fatigue crack growth characteristics of high manganese steel with those of nickel steels. In addition, fracture toughness and fatigue crack growth rate tests for various nickel steels are conducted according to BS 7448 and ASTM E647, respectively. In order to obtain less conservative design values, the results of high manganese steel and various nickel steels were compared to those of BS7910. As a result, the CTOD value of high manganese steel is higher than that of 9% nickel steel at cryogenic temperature. In case of FCGR, the high manganese steel and 9% nickel steel are found to be similar to each other.
Study on Force and Movement of Unconstrained Ice Fronting a Propeller
Authors: Li Xing , Wang Chao
Published: September 2018

In order to simulate the movement of ice more accurately, this paper use overlapping grid methods combined with DFBI model to calculate the mutual interaction between an unconstrained ice cube and propeller, then the movement and force of the ice under the influence of propeller suction effect are analyzed. In the computational process, different working conditions are carried out by altering propeller rotation speed and ice-propeller radical distance. According to the computational results, when ice move near to the propeller disk, the force peak value in 3 directions will appear; and when the flow speed remain constant, the bigger of advance velocity coefficient, the higher probability of ice-propeller crashing.
Optimization of Heave Motions for a Four Column Semi-Submersible Based on Genetic Algorithm
Authors: Zhu Suji
Published: September 2018

Semi-submersible is designed with low heave motions compared with conventional ships by utilizing the cancelation effects between pontoons and columns. During the past years, continuous efforts have been devoted to reducing the heave amplitudes considering utilizing dry-tree system. Different concepts of semi-submersible have been proposed with favorable heave response. Deep draft semi-submersibles have been proved to be efficient in reducing the heave motions, and the damper structures under the pontoon may also reduce the heave responses significantly. Those concepts are beyond the conventional semi-submersible design, which may bring high costs for fabrication and installations. During computer-aided design and analysis, optimization algorithms are used to search for the optimal hull configuration. However, due to the restrictions of computer capacities, the global optimization algorithm, in some cases, have difficulties in finding out the optimal solutions without the aid from engineering experience. In this paper, the geometry of a ring-pontoon four-column semi-submersible is generated by parametric modelling. The heave transfer functions at center of gravity are calculated using WADAM. Genetic algorithm is used to find the most favorable heave responses. In the end, the parameters that influence the heave motions are summarized and discussed.
Validation of Numerical Models for the Drift-Off Study in Drilling Vessels Using Full Scale Measurements
Authors: Dotta Raul , Tannuri Eduardo A. , de Mello Pedro C. , Diederichs Gustavo R. , Cruz Daniel F. , Oshiro Anderson T.
Published: September 2018

In drilling vessels, the dynamic positioning (DP) system has great importance for the operation, since it ensures the station keeping ability for carrying out the drilling operation. However, an emergency situation involves ungoverned drift due to problems associated with the DP system failures, such as thrusters, generators, powerbus or control system. During this emergency situation, the vessel drift is subjected to the influence of environmental conditions and the drift can lead to collisions with floating obstacles or submerged systems, wellhead emergency disconnection, damage to equipments and potentially causing major environmental disasters. Due to the possible occurrence of this emergency condition, it is necessary to define a safety region for the drilling ship operation and to determine the limiting operation offset that the drilling vessel can disconnect from the wellhead without damage to any equipment. This limit offset is obtained through a riser analysis and drift-off study, being an important input for WSOG (Well Specific Operating Guidelines). The study will provide vessel drift trajectory after the DP failure under several environmental conditions. A validated time domain simulator must be used for obtaining such data. In the present work, the Dynasim software, developed from the partnership between Petrobras and Brazilian universities, is applied. Thus, the aim of this work is to validate the Dynasim numerical model using drift data from full scale tests performed on vessels operated by Petrobras and under several environmental conditions. For the validation and calibration of the numerical model, three main parameters were compared: distance time-series, heading variation and trajectory during the drift of the vessel. The comparisons between full scale data and numerical simulation results demonstrated the accuracy of the numerical model. Therefore, the application of this tool provides a valuable contribution to the reliability of WSOG analysis, planning of the operations, allowing the determination of the drift path in relation to the wind, current and waves, and the definition of drift maps and establishing safety zones for the drilling vessel operation, minimizing the risk of collisions.
Investigation on Temperature Compensation of Fiber Bragg Grating Sensors for Hull Monitoring
Authors: Ma Ruiqi , Feng Guoqing , Ren Huilong , Fu Peng , Wu Shuang , Wang Youzhen
Published: September 2018

Hull monitoring system with Fiber Bragg Grating (FBG) sensors increasingly receives people’s attentions. However, for the ship hull monitoring, the deformation of hull girder changes a lot as is subjected to a huge temperature variation. Therefore, the compensation method with only FBG temperature self-correction is not suitable for the hull monitoring sensors because no material thermal expansion effects are reasonably included. In this paper, the new compensation method of hull monitoring FBG sensor based on the sensor theory with both FBG temperature self-correction and steel thermal expansion effects correction is studied. The coupled compensation method suitable for hull monitoring sensor is obtained by theoretical derivation. As the comparison, the coupled compensation experiment was carried out. The results show that the relative error under the temperature compensation method is large in the case of drastic strain and temperature changes, and the correction results of the tested method will be closer to the true level.
Numerical Study of the Wake Behind an Inclined Prolate Spheroid at Re=10000 Using LES
Authors: Zhou Hongyu , Liu Hao , Zhang Zhiguo , Wang Xianzhou , Feng Dakui
Published: September 2018

The viscous flow past a prolate spheroid is always complicated and often three-dimensional, thereby fascinating scientists in fluid dynamics and aerodynamics. The objective of this paper is to investigate the asymmetric wake behind a 6:1 prolate spheroid at 45-deg angle of attack by means of Large-Eddy simulations(LESs). The LES was performed at a Reynolds number of 10000, based on the free stream velocity U0 and minor axis diameter D. Results in the paper were compared with the previous LES results for different Re. The simulation revealed that there was a pair of counter-rotating vortex in the near wake field, which developed from a pair of vortex sheet separating from the sides of prolate spheroid. The vortex broke and the coherence of vortex tube lost because of the influence of vortex shedding from the tip of the prolate spheroid and energy dissipation. The asymmetry could be observed evidently from several physical quantities, such as velocity, vorticity, pressure and side force. The results showed an obvious skew of vortex structure, the direction of which was random and could be explained by pitchfork theory. The comparison between near field and far field was present to show the development and features of the flow characteristics. The asymmetric wake should be given more attention as it may be detrimental to underwater vehicle performance and submarine maneuverability.
Heat Radiation Research and Optimized Analysis of Burner Boom on Semi-Submersible Drilling Platform
Authors: Xu Yuxin , Sun Guowei , Liu Songhua , Xue Fengguang , Bai Yong
Published: September 2018

Burner booms, one of the most important pieces of equipment for well testing procedures, are used to burn associated gas or oil-and-gas mixture. This paper first conducts a mesh sensitivity analysis to find a proper grid size. Grid independence is evaluated by the correlation value in different monitoring points. Then, the heat radiation of the burner boom on the semi-submersible drilling platform is analyzed using FDS. Without water curtain, it researches and compares the impact of low, medium and high speed wind condition on heat radiation. Without the wind influence, the simulation on heat radiation is done on the optimized water curtain design. The results show that the water curtain design can efficiently reduce the heat radiation on the platform, which has guiding significance for engineering design.
Preliminary Design and Hydrodynamic Analysis on the Offshore Integrated Anemometer Mast During Wet-Towing
Authors: Puyang Zhang , Ruiqi Hu , Hongyan Ding , Conghuan Le
Published: September 2018

An offshore integrated anemometer mast (OIAM) is proposed to integrate the offshore installation of the foundation and steel mast into one operation. It can be prefabricated onshore and transported to the installation site which is simple in construction, rapid in speed and saving in cost. The most critical technique of the OIAM is the self-floating towing technique with a reasonable subdivision inside the floating tank. These subdivisions of OIAM facilitate the floating stability in case the occurrence of a damaged compartment. The tank will be ballasted to lower OIAM down and to penetrate these shallow skirt plates underneath into the sea bed after a free-floating towing process. To study and predict the dynamic behaviors of the OIAM in different sea conditions considering different towing critical factors, the hydrodynamic software MOSES is used to simulate the three-dimensional motion of the OIAM in the towing operation. Before that the integrated installation technique is introduced in terms of structure design, towing operation, and sinking on-site. The numerical results show that multiple subdivisions guarantee an adequate floating stability, and the hydrodynamic features indicate that a relative small dynamic response in some extreme sea state can be obtained by this OIAM structure. The self-floating technique of OIAM in sea is highly competitive for saving cost by using less expensive equipment in towing transportation.
A Benchmark Study on Applying Extended Finite Element Method to the Structural Integrity Assessment of Subsea Pipelines at HPHT Service Conditions
Authors: Cheng Ankang , Chen Nian-Zhong
Published: September 2018

Structural integrity assessment for subsea pipelines at high pressure high temperature (HPHT) service conditions is one of the most challenging research topics in offshore engineering sector. This paper is to introduce an extended finite element method (XFEM) based numerical approach for structural integrity assessment for subsea pipelines serving HPHT reservoir. A 3D model of a quarter of subsea pipe section with an external semi-elliptical surface crack located at the weld toe is built and the crack propagation under fatigue load is simulated using the XFEM. Results are presented and investigated from both geometric and mechanical aspects. Theoretical basis and limitation for this technique are discussed. Suggestions are given for future application of the XFEM technique based on fracture mechanics when assessing the structural integrity of subsea pipelines at HPHT service conditions.
Collapse of Tubes Under Combined Bending and Axial Compression Loads
Authors: Jin Shan , Yuan Shuai , Bai Yong
Published: September 2018

In practical application, pipelines will inevitably experience bending and compression during manufacture, transportation and offshore installation. The mechanical behavior of tubes under combined axial compression and bending loads is investigated using experiments and finite element method in this paper. Tubes with D/t ratios in the range of 40 and 97 are adopted in the experiments. Then, the ultimate loads and the local buckling modes of tubes are studied. The commercial software ABAQUS is used to build FE models to simulate the load-shortening responses of tubes under combined loads. The results acquired from the ABAQUS simulation are compared with the ones from verification bending experiment, which are in good agreement with each other. The models in this paper are feasible to analyze the mechanical properties of tubes under combined axial compression and bending loads. The related results may be of interest to the manufacture engineers.
Corrosion Assessment of Aluminium Conductor for Medium Voltage Cables for Subsea Umbilical System
Authors: Socariceanu M. , An X. , Deighton A. , Friday A.
Published: September 2018

High tensile strength aluminum offers great potential as a conductor material for Medium Voltage power cables within subsea umbilicals. Its excellent fatigue performance makes it suitable for dynamic umbilicals and its high tensile strength and light weight make it an ideal candidate for deepwater dynamic umbilicals either as an independent load bearing member or as an electrical conductor taking load share in an armoured or steel tube umbilical.

Umbilicals, are the bundles of electrical and hydraulic components that connect and control elements of a subsea Oil and Gas production system.

6000 series aluminum conductors, commonly known as AAAC (All Aluminum Alloy) conductors are widely used on high voltage overhead transmission lines, primarily on long spans due to their increased tensile strength. They have been widely used in various environments and possess an excellent track record. However, the use of AAAC 6000 series in a subsea umbilical system is novel. The cable located inside an umbilical bundle is normally of a wet insulation design, and an area of concern is that the seawater may permeate through the cable insulation allowing the conductor material to be in contact with water throughout its design life. Hence the corrosion resistance of the AAAC 6000 series in a seawater environment is of paramount importance and therefore must be assessed.

This paper details the corrosion assessment of the 6000 series aluminum power cable conductor at RINA Consulting Ltd’s laboratories together with complimentary field testing. The presented test results are based on long term (6–12 months) laboratory testing. The test programme investigated permeation, impact of temperature, effect of hydrostatic pressure and galvanic corrosion, with the tests being performed on material coupons and cable samples in a simulated seawater environment. Also detailed is the outcome of a full-scale cable field immersion test, 6 months under 1000m depth at seabed temperature of 10°C.

The results demonstrated that there was no Cl− and Na+ ion permeation through the insulation layer. Also, there is no sign of aluminium conductor corrosion and no drop-in insulation resistance witnessed for all tested samples at temperatures up to 90°C and under a high pressure of 300bar after a one year test period, which is sufficient to qualify use in a subsea application.

Based on the results of the presented laboratory testing and field immersion testing, it can be concluded that 6000 series aluminium conductors within ‘wet design’ Medium Voltage power cables will not be susceptible to corrosion in a subsea environment and could be used in other applications such as renewables.
The Application of Caisson-Type Solutions to the Current Offshore Wind Energy Market
Authors: Abanades Javier , Ivars Javier , Molina Rafael , García Carlos
Published: September 2018

The current offshore wind energy market is not only focused on the design of WTG foundations, but also on the design of offshore infrastructures that lead to an improvement in the current grid connection system, such as artificial islands. For all these type of projects, caisson-type solutions can be applied with numerous advantages. The present article present three different projects in which caisson-type solutions were used: the foundation of a WTG (Gravi3® patent) in the Portuguese Coast, the foundation of a meteorological mast installed in Scotland and the design of an artificial island in the North Sea.

The main advantage of this solution is the well-developed construction principle to build the caissons, which is based in the employ of a floating dock in a shelter area. As the caissons are cellular elements, the interior is empty; they float, so they are transported to the place in question to be deployed by means of filling with water the cells that comprised the caisson. This technology is rather used in Spain, being most of the kilometres of breakwater built using caissons thank to their high production rates. The three examples that will be presented in the article are proof of the versatility of this solution. Whereas the case of Gravi3® consists in a gravity based solution for WTG, which is comprised of 3 circular caissons connected by means of a steel tripod; the meteorological mast is formed by a rectangular caisson and a steel shaft. Finally, the artificial island is a mixed solution that uses caissons in the perimeter and hydraulic filling in the inner part. Furthermore, these solutions could be also applied in ports, integrating the WTG on the current or future dikes.
CFD Simulations of Multi-Directional Irregular Wave Interaction With a Large Cylinder
Authors: Wang Weizhi , Kamath Arun , Bihs Hans
Published: September 2018

Ocean waves are random by nature and can be regarded as a superposition of a finite number of regular waves travelling in different directions with different frequencies and phases. Cylinder-shaped objects are commonly present in most coastal structures. An irregular bottom topography has a significant influence on the wave behaviours and therefore the wave forces on the coastal structures. A numerical approach that is able to calculate the wave forces on a cylinder in a multi-directional irregular wave field over an irregular bottom is desired. As Computational Fluid Dynamics (CFD) is able to represent most of the wave behaviour with few assumptions, it is considered to be an attractive option to address these issues. The open-source CFD wave model REEF3D has shown good performances in simulating wave propagation over irregular bottoms and a good prediction of wave forces on a cylinder in a uni-directional wave field, yet the ability to calculate the wave force in a multi-directional irregular sea needs to be validated. Therefore, this paper attempts to simulate the multi-directional random sea interaction with a large cylinder using REEF3D and validate the results. A novel approach of multi-directional irregular wave generation method in a CFD-based numerical wave tank is introduced. Only even-bottom tanks are considered in this study, leaving the irregular bottom simulation for future studies. Furthermore, among many factors that influence the wave forces, this paper focuses particularly on the effect of the wave steepness. The effects of wave steepness in regular waves, uni-directional irregular waves and multi-directional irregular waves are investigated. Goda’s JONSWAP frequency spectrum and the frequency-independent Mitsuyasu directional spreading function are used to generate the multi-directional irregular waves. The wave forces due to the multi-directional irregular waves in the numerical tank are compared with experimental data. The performance of the CFD simulation is analysed and discussed.
Safe Operation of Jacket Platforms in a Major Oil Field in the North Sea
Authors: Scherf Ingar , Hansen Trine , Sigurdsson Gudfinnur
Published: September 2018

Offshore Structures operate for decades in extremely hostile environments. It is important during this period that the structural integrity is efficiently managed to ensure continuous and safe operation.

Increased use of enhanced oil and gas recovery means it is likely that many existing installations will remain operational for a significant period beyond the original design life.

The operator needs to capture, evaluate and, if necessary, mitigate design premise changes which inevitably occur during the life of a structure. Further, advances in knowledge and technology may imply changes in codes and standards as well as in analysis methodologies.

Changes in corporate structures, transfer of operator responsibility and retirement of experienced engineers call for reliable means to transfer historical data and experience to new stakeholders.

Effective emergency preparedness capabilities, structural integrity assessments and inspection planning presuppose that as-is analysis models and corresponding information are easily accessible.

This paper presents an implementation of the in-service integrity management process described in the new revision of NORSOK standard N-005 [1] for a large fleet of jackets at the Norwegian Continental Shelf.

The process, comprising management of design premise changes as well as state-of-the-art technical solutions over a range of disciplines, has enabled the operator to prolong the service life with decades at minimum investments.

A structure integrity management system (SIMS) has been developed and digitized over years and streamlined to meet the needs and challenges in the operation and management of the jacket platforms. SIMS enables a rather lean organization to control the structural integrity status of all load-bearing structures at any time.

Platform reinforcements and modifications along with other operational risk reducing measures like unman the platforms in severe storms enable continued use with the same level of safety as for new manned platforms. Advanced analyses are used to document regulatory compliance.

Modern fatigue and reliability based inspection planning analyses have reduced the costs needed for inspection of fatigue cracks significantly.

The benefits from the SIMS system are substantial and the resulting safety and productivity gains are apparent. The continuity of knowledge and experience is maintained, reducing risk to safety and regularity.

The digital transformation related to management of structural integrity status as described in NORSOK standard N-005 is realized through SIMS.
An Experimental Investigation of Inflatable Fabric Beams of Floating Composite Causeway
Authors: Ye Yunling , Gan Jin , Wu Weiguo , Li Jiawei , Guo Guohu
Published: September 2018

Inflated membrane structures make of high-strength fabric material that can be used as beams when inflated at high internal pressure. Due to their physical characteristics which are deployed and lightweight, they can be used as off-shore floating structures such as floating breakwaters and floating causeways. The paper is devoted to present experimental studies on the behavior of fabric inflated beams. The experimental result was compared with wrinkling theory. This experiment consisted of three parts. First, the beams were tested under bending load with different internal pressures and then the different diameters specimens were tested with identical pressure. The results showed that the deformation depended on the applied load, the internal pressure and the diameter. The amount of deformation increased sharply when the local wrinkles occurred and the load-displacement curve manifested strong nonlinearity. Then, an experiment of the parallel-connected beams was performed to obtain the parallel-connected effect of the load-deflection response of inflated beams. The results showed the deflection of the single beam was not twice of the deflection of double parallel beams. A floating causeway model experiment was also finished, the results confirmed the previous conclusions and the floating composite causeway was enough stable. These experimental results can be applied to provide theoretical guidance and scientific basis for design method of the floating composite structure.