bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of Thermally Induced Stresses for Effective Remediation of Lost Circulation Through Drilling Induced Fractures
Authors: Wang Ze , Nielsen James , Chen Yuanhang 
Published: October 2017

Lost circulation events during drilling are associated with the initiation of new fractures or the reopening of pre-existing fractures from the wellbore. Practices frequently implemented to combat lost circulation, including wellbore strengthening (WBS), are employed by plugging and propping the newly induced and pre-existing fractures to limit further propagation from the wellbore. One observation that was noted is that there is a discrepancy in the performance of lost circulation prevention methods for different temperatures between the fluids used and the surrounding formation. However, it is not yet fully understood how temperature affects pre-existing fractures and newly initiated fractures during these practices.
This study discusses how the stress state around fractures is influenced by a change in temperature considering fluid flow into a formation through drilling induced fractures. A finite element analysis with a coupled thermal-hydrologic-mechanical processes simulation was established to demonstrate how the stress redistributes around the fractures while considering fluid invasion and heat transmission. The results of the changing thermal stress around the fractures under various scenarios have been investigated. Included in our analysis is the potential risk of reinitiating fractures. The conclusions from this study indicate that a large temperature difference between the formation rock and fluid flow into the fractures could be a major concern when trying to prevent fracture propagation and control lost circulation events. It could potentially diminish the effect of enhanced hoop stress provided by WBS and fracture plugging by lost circulation materials. Such information is important to facilitate a successful management of lost circulation by taking into accounts the thermal impact of different lost circulation prevention approaches. The results from this paper are particularly important when a large temperature difference exists between circulating fluids and surrounding rock as commonly seen in HPHT and deep water wells.
Numerical Investigation of Wave Kinematics Inside Berm Breakwaters With Varying Berm Geometry Using REEF3D
Authors: Sasikumar Athul , Bihs Hans , Kamath Arun , Musch Onno , Arntsen Øivind A. 
Published: October 2017

Harbours are important infrastructures for an offshore production chain. These harbours are protected from the actions of sea by breakwaters to ensure safe loading, unloading of vessels and also to protect the infrastructure. One of the important hydrodynamic processes in these regions is the interaction of water waves with permeable breakwaters such as rubble mound breakwaters or berm breakwaters. It is important to study the wave-breakwater interactions in order to have an optimal design of these structures. In current literature, research regarding the design of these structures is majorly based on physical model tests. Empirical formulations are derived based on these test, which can have a relatively narrow range of applicability. In this study a new tool, a three-dimensional numerical model is introduced. Physical and numerical models have limitations that can restrict their independent use. A combined use of both can lead to different forms of improvements: being able to model problems that cannot be modelled by either physical or numerical modelling alone; increasing quality at the same cost or obtaining the same quality at reduced cost.
In this study, the open-source CFD model REEF3D is used to study the design of berm breakwaters. The model uses the Volume averaged Reynolds Averaged Navier-Stokes (VRANS) equations to solve the porous flows. At first the VRANS approach in REEF3D is validated for flow through porous media. A dam break case is simulated for two different porous materials. Comparisons are made for the free surface both inside and outside the porous medium. The numerical model REEF3D is applied to show how to extend the database obtained with purely numerical results, simulating different structural alternatives for the berm in a berm breakwater. Different simulations are conducted with varying berm geometry. The influence of the berm geometry on the pore pressure and velocities are studied. The resulting optimal berm geometry is compared to the geometry according to empirical formulations.
Residual Stresses in Strength Mismatched Welded Pipes
Authors: Mirzaee-Sisan Ali , Wang Junkan 
Published: October 2017

It is commonly understood that residual stresses can have significant effects on structural integrity. The extent of such influence varies and is affected by material properties, manufacturing methods and thermal history. Welded components such as pipelines are subject to complex transient temperature fields and associated thermal stresses near the welded regions. These thermal stresses are often high in magnitude and could cause localized yielding around the deposited weld metal. Because of differential thermal expansion/contraction episodes, misfits are introduced into the welded regions which in turn generate residual stresses when the structure has cooled to ambient temperature.
This paper is based on a recently completed Joint Industry Project (JIP) led by DNV GL. It briefly reviews published experimental and numerical studies on residual stresses and strength-mismatched girth welds in pipelines. Several Finite Element Analysis (FEA) models of a reeling simulation have been developed including mapping an initial axial residual stress (transverse to the weld) profile onto a seamless girth-welded pipe. The initial welding residual stress distribution used for mapping was measured along the circumference of the girth welds. The predicted residual stresses after reeling simulation was subsequently compared with experimental measurements.
An Efficient Convex Formulation for Model-Predictive Control on Wave-Energy Converters
Authors: Zhong Qian , Yeung Ronald W. 
Published: October 2017

Model-Predictive Control (MPC) has shown its strong potential in maximizing energy extraction for Wave-Energy Converters (WECs) while handling hard constraints. As MPC can solve the optimization problem on-line, it can better account for state changes and reject disturbances from the harsh sea environment. Interests have arisen in applying MPC to an array of WECs, since researchers found that multiple small-size WECs are more economically viable than a single large-size WEC. However, the computational demand is known to be a primary concern for applying MPC in real-time, which can determine the feasibility of such a controller, particularly when it comes to controlling an array of absorbers.
In this paper, we construct a cost function and cast the problem into a Quadratic Programming (QP) with the machinery force being the “optimizer,” for which the convexity can be guaranteed by introducing a penalty term on the slew rate of the machinery force. The optimization problem can then be solved efficiently, and a feasible solution will be assured as the global optima. Constraints on the motion of the WEC and the machinery force will be taken into account. The current MPC will be compared to others existing in literature, including a nonlinear MPC [1] which has been applied in wave-tank tests. The effects of constraints on the control law and the absorbed power are investigated. Performances of the WEC are shown for both regular and irregular wave conditions. The current MPC is found to have good energy-capture capability and is able to broaden the band-width for capturing wave energy. The reactive power required by the PTO system is presented. The additional penalty term provides a tuning parameter, of which the effects on the MPC performance and the reactive power requirement are discussed.
Offloading Operability of Small Scale AG FLNG With Side-by-Side Moored Small Scale LNG Carrier in Offshore West Africa
Authors: Kim Mun-sung , Morilhat Eric , Nguyen X. C. , Kim Bo-hee , Jang Jung-moon , Jeong Hyun-su 
Published: October 2017

This study describes one of the technical solutions for Small Scale FLNG (SSFLNG)[1] development specifically designed to monetize Associated Gas (AG) of producing oil fields located within convenient distance of an existing LNG Plant or Port with LNG storage facility. Limited production capacity combined with short range small scale LNG carriers (SSLNGC), provide a cost effective means for LNG production. Ship to ship off-loading operation by loading arm has been considered in AG SSFLNG. Produced LNG is to be off-loaded from the SSFLNG to side-by-side moored SSLNGC. Relative motion and dynamic load acting on loading arm system in side-by-side mooring arrangement is one of key factors to estimate the offloading operability of the AG SSFLNG. In this paper, a numerical two-body motion analysis for the side-by-side moored SSFLNG in frequency- and time-domain is carried out.
Also, the basic engineering work is carried out for the marine loading arms (MLA). Since the MLA reacts approximately as a linear system, it is calculated by a full spectral RAO analysis for each of the worst load cases issued from the spectral ranking. All loads and stresses inside the MLA are verified in accordance with EN1474-1[2] for the situations identified in the previous step. A high level fatigue analysis focused on the cryogenic swivel joints is carried out.
Based on the numerical calculation for relative motion in side-by-side moored FLNG, we have been performed structural assessment for MLA in several environment conditions. The structural integrity of both MLA and the LNGC manifold are validated during offloading for Offshore West Africa.
The Consequence Method: An Approach for Estimating Roll Damping in Transportation Fatigue Analyses
Authors: Bøe Tormod , Yang Limin , Falkenberg Erik 
Published: October 2017

In order to compute fatigue damage during offshore transports it is necessary to assume a description of the sea states encountered during the voyage. In recent years, it has become a common approach to apply directional long-term scatter diagrams for the transportation route, taking into account vessel speed, course and time of year for the departure.
An important contribution to the transportation fatigue damage is usually the wave induced inertia load. For ship shaped vessels additional viscous damping needs to be included in order to estimate correct roll response. However, since viscous roll damping is non-linear, correct estimation of fatigue damage can only be obtained by computing partial damage for all individual sea states in the scatter diagram. This becomes very time-consuming and is usually not done.
Instead, the roll damping level is tuned to match typical mean sea states in the scatter diagram. The roll damping will then be too low for higher sea states and too large for smaller sea states. When choosing the roll damping level, the aim should be to obtain an overall error in transportation fatigue damage which is minimized.
This paper describes a method to estimate a representative viscous roll damping level for transportation fatigue analyses.
Visual Image Correlation Compared to Discrete Instrumentation for Measurement of Compressive Strains for Strain Based Design
Authors: Bergman Jason , Liu Ming , Timms Chris 
Published: October 2017

Strain-based design philosophies have been developed to ensure safe pipeline operation through regions of slope instability, seismic activity or discontinuous permafrost while extending the life expectancy of the pipeline in those zones. Strain-based design methodology typically involves a comparison of the strain demand (estimated conservatively using numerical pipe-soil interaction analysis techniques) to the strain capacity (predicted using experimentally benchmarked models).
This paper presents a comparison of measurement techniques for laboratory testing of critical compressive strain capacity (CCS). The CCS is defined as the strain coinciding with the peak bending moment, averaged over a gauge length often selected as one pipe diameter across the buckle location. As explored in previous work [1], the three most common methods to measure strain on the specimen intrados, with respect to bending, include 1) direct measurement using strain gauges on the intrados with respect to bending, 2) calculation of CCS from the output of discrete instrumentation (DI) including strain gauges and inclinometers; and 3) direct measurement of surface strains using Visual Image Correlation (VIC) techniques.
In 2015 and 2016, the Centre for Reliable Energy Systems (CRES) and C-FER Technologies 1999 Inc. (C-FER) collaborated on a series of full-scale experiments (performed by C-FER) and detailed finite element analysis (FEA) (performed by CRES) intended to assess and understand the effect of various anomalies on the strain capacity of line pipe. To facilitate comparison of the DI strain measurement method and the newer VIC method, these tests were conducted using both methods. The results demonstrate that the VIC technique can provide a more complete measure of the strain field and greater accuracy in cases where uneven strain distributions challenge the assumptions associated with DI methods. High level test data is presented and one test displaying the discrepancy between VIC and DI results is described. Finite element modelling, employed to explore the digression observed between the two strain measurement methods, is also presented and the comparative results of the two strain measurement techniques are discussed.
Development of the Hywind Concept
Authors: Skaare Bjørn 
Published: October 2017

An overview of the development of the Hywind concept is presented with focus on numerical analysis tools, model and full scale experiments, and control systems.
Several analysis tools have been developed and matured over several years, and verified against model and full scale experiments.
Special purpose control systems have been developed for the Hywind concept for the purpose of stabilization of floater motions as well as motion control.
Simulating Large-Scale Fatigue Test Specimens for Offshore Wind Monopiles
Authors: Brennan Feargal , Kolios Athanasios , Tavares Isaac 
Published: October 2017

Size effects are extremely important to understand and accounting for their inclusion in fatigue tests is imperative in order to produce meaningful results. This can however be problematic as in dealing with very large offshore structural details and sections, testing to destruction can involve extremely large loads and gripping arrangements that can be cost prohibitive. It is therefore important to be able to simplify test specimens so that the local detail is retained without losing important size influences.
This paper describes an investigation into whether or not extracted specimens from actual Offshore Wind Monopile Sections are in fact the best choice for fatigue testing. The results are analysed and a recommendation is made for future test programmes involving offshore wind monopile and tower applications.
On the Application of Structural Reliability Analysis
Authors: Hørte Torfinn , Sigurdsson Gudfinnur 
Published: October 2017

Structural Reliability Analysis (SRA) is a useful tool in structural engineering. Uncertainty in input parameters and model uncertainties in the analysis predictions are explicitly modelled by random variables. With this methodology, the uncertainties involved are handled in a consistent and transparent way. Compared to a deterministic analysis, SRA provides improved insight in how the various uncertainties involved influence the results. The main results from SRA is the calculated probability of structural failure, but other useful results such as uncertainty importance factors and design points being the most likely combination of all variables at failure represent helpful information.
The present paper illustrates some the features using SRA for two different types of application. The first application is the use of SRA as a tool for code calibration and the second shows the application of SRA to a problem where common practice is likely to be rather conservative and therefore leading to unacceptable results, but where the degree of conservatism is not known.
Two examples are chosen to illustrate code calibration; i.e. hull girder ultimate limit state (ULS) for tankers and ULS for mooring design in the ULS for floating offshore vessels. Code calibration involves both SRA and design analysis following the code. It is shown how the design analysis can be modified in order to better reflect a chosen target reliability level across a selected set of test cases representative for what the code should cover.
Fatigue of subsea wellhead systems is selected as an example of a special case when application of existing rules may lead to unsatisfactory results which are likely to be rather conservative. It is shown how results can be presented in terms of the accumulated probability of fatigue failure as a function of time. This may be a more suitable basis for decision making than a calculated fatigue life from a standard analysis. It is also illustrated how importance factors from the SRA can be used as guidance on how to prioritize effort in order to improve prediction of the fatigue damage.
The present paper is not intended to be detailed in all input and analysis methodology, but draw the attention towards the possibilities and benefits of applying SRA in structural engineering, where the examples are used to illustrate this potential.
Susceptibility of Pseudomonas aeruginosa Dispersed Cells to Antimicrobial Agents Is Dependent on the Dispersion Cue and Class of the Antimicrobial Agent Used
Authors: Chambers Jacob R. , Cherny Kathryn E. , Sauer Karin 
Published: October 2017

ABSTRACT
The biofilm life cycle is characterized by the transition of planktonic cells exhibiting high susceptibly to antimicrobial agents to a biofilm mode of growth characterized by high tolerance to antimicrobials, followed by dispersion of cells from the biofilm back into the environment. Dispersed cells, however, are not identical to planktonic cells but have been characterized as having a unique transitionary phenotype relative to biofilm and planktonic cells, with dispersed cells attaching in a manner similar to exponential-phase cells, but demonstrating gene expression patterns that are distinct from both exponential and stationary-phase planktonic cells. This raised the question whether dispersed cells are as susceptible as planktonic cells and whether the dispersion inducer or the antibiotic class affects the drug susceptibility of dispersed cells. Dispersed cells obtained in response to dispersion cues glutamate and nitric oxide (NO) were thus exposed to tobramycin and colistin. Although NO-induced dispersed cells were as susceptible to colistin and tobramycin as exponential-phase planktonic cells, glutamate-induced dispersed cells were susceptible to tobramycin but resistant to colistin. The difference in colistin susceptibility was independent of cellular c-di-GMP levels, with modulation of c-di-GMP failing to induce dispersion. Instead, drug susceptibility was inversely correlated with LPS modification system and the biofilm-specific transcriptional regulator BrlR. The susceptibility phenotype of glutamate-induced dispersed cells to colistin was found to be reversible, with dispersed cells being rendered as susceptible to colistin within 2 h postdispersion, though additional time was required for dispersed cells to display expression of genes indicative of exponential growth.
In Vitro
Activity of the Novel Lactone Ketolide Nafithromycin (WCK 4873) against Contemporary Clinical Bacteria from a Global Surveillance Program
Authors: Flamm R. K. , Rhomberg P. R. , Sader H. S. 
Published: October 2017

ABSTRACT

Nafithromycin (WCK 4873), a novel antimicrobial agent of the lactone ketolide class, is currently in phase 2 development for treatment of community-acquired bacterial pneumonia (CABP). A total of 4,739 nonduplicate isolates were selected from a 2014 global surveillance program at medical institutions located in 43 countries within the United States, Europe, Latin America, and the Asia-Pacific region. Nafithromycin and comparator agents were used for susceptibility testing by reference broth microdilution methods. Nafithromycin was active against
Staphylococcus aureus
(MIC
50/90
, 0.06/>2 μg/ml), including erythromycin-resistant strains exhibiting an inducible clindamycin resistance phenotype (MIC
50/90
, 0.06/0.06 μg/ml) and telithromycin-susceptible strains (MIC
50/90
, 0.06/0.06 μg/ml), but it exhibited limited activity against most telithromycin-resistant and clindamycin-resistant isolates that were constitutively resistant to macrolides (MIC
50/90
, >2/>2 μg/ml). Nafithromycin was very active (MIC
50/90
, 0.015/0.06 μg/ml) against 1,911
Streptococcus pneumoniae
strains, inhibiting all strains, with MIC values of ≤0.25 μg/ml. Telithromycin susceptibility was 99.9% for
Streptococcus pneumoniae
strains, and nafithromycin was up to 8-fold more potent than telithromycin. Overall, 37.9% of
S. pneumoniae
strains were resistant to erythromycin, and 19.7% were resistant to clindamycin. Nafithromycin was highly active against 606
Streptococcus pyogenes
strains (MIC
50/90
, 0.015/0.015 μg/ml), inhibiting 100.0% of isolates at ≤0.5 μg/ml, and MIC
50/90
values (0.015/0.015 to 0.03 μg/ml) were similar for the 4 geographic regions. Nafithromycin and telithromycin demonstrated comparable
in vitro
activities against 1,002
Haemophilus influenzae
isolates and 504
Moraxella catarrhalis
isolates. Overall, nafithromycin showed potent
in vitro
activity against a broad range of contemporary (2014) global pathogens. These results support the continued clinical development of nafithromycin for treatment of CABP.
Modified Penicillin Molecule with Carbapenem-Like Stereochemistry Specifically Inhibits Class C β-Lactamases
Authors: Pan Xuehua , He Yunjiao , Chen Tianfeng , Chan Kin-Fai , Zhao Yanxiang 
Published: October 2017

ABSTRACT

Bacterial β-lactamases readily inactivate most penicillins and cephalosporins by hydrolyzing and “opening” their signature β-lactam ring. In contrast, carbapenems resist hydrolysis by many serine-based class A, C, and D β-lactamases due to their unique stereochemical features. To improve the resistance profile of penicillins, we synthesized a modified penicillin molecule, MPC-1, by “grafting” carbapenem-like stereochemistry onto the penicillin core. Chemical modifications include the
trans
conformation of hydrogen atoms at C-5 and C-6 instead of
cis
, and a 6-α hydroxyethyl moiety to replace the original 6-β aminoacyl group. MPC-1 selectively inhibits class C β-lactamases, such as P99, by forming a nonhydrolyzable acyl adduct, and its inhibitory potency is ∼2 to 5 times higher than that for clinically used β-lactamase inhibitors clavulanate and sulbactam. The crystal structure of MPC-1 forming the acyl adduct with P99 reveals a novel binding mode for MPC-1 that resembles carbapenem bound in the active site of class A β-lactamases. Furthermore, in this novel binding mode, the carboxyl group of MPC-1 blocks the deacylation reaction by occluding the critical catalytic water molecule and renders the acyl adduct nonhydrolyzable. Our results suggest that by incorporating carbapenem-like stereochemistry, the current collection of over 100 penicillins and cephalosporins can be modified into candidate compounds for development of novel β-lactamase inhibitors.