bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characteristic Levels of Strongly Nonlinear Extreme Wave Load Effects
Authors: Johannessen Thomas B. , Hagen Øistein 
Published: October 2016

Offshore structures are typically required to withstand extreme and abnormal load effects with annual probabilities of occurrence of 10−2 and 10−4 respectively. For linear or weakly nonlinear problems, the load effects with the prescribed annual probabilities of occurrence are typically estimated as a relatively rare occurrence in the short term distribution of 100 year and 10 000 year seastates. For strongly nonlinear load effects, it is not given that an extreme seastate can be used reliably to estimate the characteristic load effect. The governing load may occur as an extremely rare event in a much lower seastate.
In attempting to model the load effect in an extreme seastate, the short term probability level is not known nor is it known whether the physics of the wave loading is captured correctly in an extreme seastate. Examples of such strongly nonlinear load effects are slamming loads on large volume offshore structures or wave in deck loads on jacket structures subject to seabed subsidence. Similarly, for structures which are unmanned in extreme weather, the governing load effects for the manned structure will occur as extremely rare events in a relatively frequent seastate.
The present paper is concerned with the long term distribution of strongly nonlinear load effects. Using a simple point estimate of the wave elevation correct to second order and a crest kinematics model which takes into account the possibility of wave breaking, the long term distribution of drag load on a column above the still water level is studied and compared with a similar loading model based on second order kinematics which does not include the effect of wave breaking.
The findings illustrate the challenges listed above. Model tests are useful in quantifying strongly nonlinear load effects which cannot be calculated accurately. But only a relatively small number of seastates can be run in a model test campaign and it is not feasible to estimate short term responses far beyond the three hour 90% fractile level. Similarly, Computational Fluid Dynamics (CFD) is increasingly useful in investigating complex wave induced load effects. But only a relatively small number of wave events can be run using CFD, a long term analysis of load effects cannot in general be carried out.
It appears that there is a class of nonlinear problems which require a long term analysis of the load effect in order for the annual probability of occurrence to be estimated accurately. For problems which cannot be estimated by simple analytical means, the governing wave events can be identified by long term analysis of a simple model which capture the essential physics of the problem and then analysed in detail by use of CFD or model tests.
Impact of Bathymetry on the Mooring Design of an Offshore Floating Unit
Authors: Jaiswal Vivek , Vishnubhotla Srinivas , Cole Sean , Gordon Robert B. , Sharma Partha 
Published: October 2016

Moored offshore floating units may operate in regions where the bathymetry changes significantly over the mooring spread. Traditional mooring analysis methods make the assumption that the seabed slope is constant along the azimuth direction of each mooring line. This assumption, while reasonable for a seabed with nearly constant slope, can lead to significant errors with respect to the line tensions and vessel offsets in the mooring design assessment when the seabed slope is variable.
This paper demonstrates the impact of bathymetry changes on the mooring design with the help of numerical analysis examples. The floating vessel considered is a semi-submersible moored by an eight point all chain catenary mooring system.
Two methods of analysis are compared. In the first method, a true representation of the seabed surface that accounts for all variations in the bathymetry is used. In the second method, the anchor depths and the seabed slopes at the anchor locations estimated in the previous method are used, however, with the assumption of constant seabed slopes along the line azimuth directions. The dynamic analysis program Orcaflex is used for performing the numerical analyses in the time domain for both the methods. Differences in the performance of the mooring system are demonstrated by comparing the static and the dynamic line tensions as well as the vessel offsets in different environmental conditions. The paper also discusses how maximum offsets and line tensions are estimated.
Crack Propagation and Local Failure Simulation of Reinforced Concrete Subjected to Projectile Impact Using RBSM
Authors: Yamamoto Yoshihito , Okazaki Soichiro , Nakamura Hikaru , Beppu Masuhiro , Shibata Taiki 
Published: October 2016

In this paper, numerical simulations of reinforced mortar beams subjected to projectile impact are conducted by using the proposed 3-D Rigid-Body-Spring Model (RBSM) in order to investigate mechanisms of crack propagation and scabbing mode of concrete members under high-velocity impact.
The RBSM is one of the discrete-type numerical methods, which represents a continuum material as an assemblage of rigid particle interconnected by springs. The RBSM have advantages in modeling localized and oriented phenomena, such as cracking, its propagation, frictional slip and so on, in concrete structures. The authors have already developed constitutive models for the 3D RBSM with random geometry generated Voronoi diagram in order to quantitatively evaluate the mechanical responses of concrete including softening and localization fractures, and have shown that the model can simulate cracking and various failure modes of reinforced concrete structures.
In the target tests, projectile velocity is set 200m/s. The reinforced mortar beams with or without the shear reinforcing steel plates were used to investigate the effects of shear reinforcement on the crack propagation and the local failure modes. By comparing the numerical results with the test results, it is confirmed that the proposed model can reproduce well the crack propagation and the local failure behaviors. In addition, effects of the reinforcing plates on the stress wave and the crack propagation behaviors are discussed from the observation of the numerical simulation results. As a result, it was found that scabbing of reinforced mortar beams subjected to high velocity impact which is in the range of the tests is caused by mainly shear deformation of a beam.
Study on Weld Fatigue Evaluation Incorporating Welding Induced Residual Stress Effect
Authors: Hong Jeong K. 
Published: October 2016

For fatigue assessment of a welded structure, an important characteristic is the failure location. The fatigue crack begins from the pre-existing crack-like flaw which is an inherent feature of a weld toe or root. Residual stress in the welded joints is another important characteristic. It is also well known that tensile residual stress in welded structures can be as high as the material yield strength level and so the fatigue strength of the welded joint is governed by the applied stress range regardless of the applied load ratio. However, when the presumed conditions with high tensile residual stress in the weld regime are not satisfied, the fatigue behavior in welded structure deviates from the general weld fatigue behavior.
In this paper, firstly the applied load ratio effect on fatigue behavior is investigated for two different residual stress levels of welds, i.e., as-welded and stress relieved. It has been observed that stress-relieving effect of welds is apparent when the applied loading introduces stress fluctuations in compressive loading. When the load ratio effect is considered in Battelle structural stress based fatigue parameter, the stress relieved weld fatigue data was consolidated within the master S-N curve.
Based on this investigation, the Battelle structural stress based effective load ratio considering both applied loading and detailed residual stress is introduced for the weld fatigue behavior. The two-stage crack growth model is reformulated with the structural stress based effective load ratio, which is a function of crack length.
Lastly, a fatigue life prediction procedure incorporating residual stress effect is proposed and validated using the existing fatigue test results. The proposed procedure clearly shows that the compressive residual stress distributions at the weld prone to crack provide great benefits for fatigue life improvement.
A Study on Motion Characteristics of Wind Turbine on a Floating Platform in Blade Pitch Control Malfunction
Authors: Mizukami Yuki , Nihei Yasunori , Iijima Kazuhiro , Hara Naoyuki 
Published: October 2016

Wind power generation has been paid much attention all over the world with the increasing crisis awareness of climate change mainly caused by excessive fuel consumption. For real wind turbine, each blade pitch angle is controlled not only to keep output power constant depending on fluctuation of wind speed but also to avoid the failure of generating system due to over speed of the rotor rotation.
Nowadays, a few demonstration projects for Floating Offshore Wind Turbine (FOWT) are under way. It is essential to improve the safety of FOWT. For that, it will be more required to conduct tank test with scale model including control system so as to provide the behavior similar to the actual FOWT. However, almost every institute has never incorporated control system in scale model. This is because every institute faces to the difficulty of incorporating control system in scale model in terms of weight. The larger FOWT would be from now on, the more necessary it is to lighten scale model in consideration of the capacity of existing facilities.
Therefore, we conducted 1/100th-scale model tests with control system using a geometrically scaled model of the National Renewable Energy Laboratory (NREL) 5MW reference wind turbine. As for this model, a new control system consisting of bevel gears was developed. Owing to this system, the mass of the scaled turbine is 41% lighter than the conventional one. In addition, this control system realized the shortening of control period in reference to scaling down of the actual control period. This tank test showed this control system is enough effective to keep rotor rotation frequency.
Moreover, this paper clarifies the motion of FOWT in control malfunction. If blade pitch angle abruptly changes due to the failure of control system, the number of the rotor rotation increases and floating platform inclines greatly. This great inclination causes the sudden rise of mooring tension and bending moment on the base of tower. This phenomenon jeopardizes the base of tower or the mooring line. We call this phenomenon “Pitch Error”. This is because of the rapid increase of thrust. In addition to this, the influence of nacelle’s inertia induces the inclination of FOWT. In case of offshore, we have to pay attention to nacelle’s inertia caused by inclination because the base of tower is not fixed. FOWT would be more severe than onshore in control malfunction. Finally, how dangerous Pitch Error would be for real FOWT is discussed.
Structural Engineering of Aluminum Helideck Structure Based on the NORSOK Requirement
Authors: Park Joo Shin , Kishore R. Krishna , Ha Yeong Su , Jang Ki Bok 
Published: October 2016

Recently, the numbers of large offshore structures and fixed jacket type platforms are rapidly increasing for oil and gas companies. Generally, a shuttle vessel or helicopter is used to access offshore structures such as a fixed platform, floating platform, jack-up rig and so on. The helideck structure should be installed in these offshore structures for landing and taking-off of the helicopter. The helideck structure comprises of pancakes, girders using aluminum materials and supporting steel structures. The helideck structure should be designed to accommodate a safe landing area suitable for the largest and heaviest helicopter that is anticipated to land on the helideck. The helideck and its supporting structure are safety critical elements as a result of their role in emergency evacuation, as well as during normal operations.
The codes and standards applicable for the structural design of the helideck will be determined by where the helideck is to be operated and the national jurisdiction governing the installation or vessel of which the helideck will become part. International standards such as ISO(International Organization for Standardization) codes, Eurocodes, or national standards, e.g. BS(British Standards)5950, NORSOK N-004 or AISC(American Institute of Steel Construction) may be specified for detailed design.
The objective of this study is to present the results of structural analysis and design that has been performed for a 28.54 meter diameter octagonal standard aluminum helideck with support truss & lower steel support structure of jackup drilling rig based on the NORSOK requirements. The supporting structure is designed to provide the adequate resistance to the external force produced by the design helicopter and environmental conditions.
Numerical Investigation on Gas Hydrate Production by Depressurization in Hydrate-Bearing Reservoir
Authors: Long Xiaoyan , Tjok Komin , Adhikari Sudarshan 
Published: October 2016

Gas hydrates are anticipated to be a promising energy source with global distribution underneath the oceans and in permafrost regions. Hydrate dissociation referring to the phase transition of the solid gas hydrate into gas and liquid water, can occur due to altered environmental conditions like increase in temperature, decrease in pressure, or the injection of hydrate inhibitors. Numerical modeling work suggested that energy efficiency of the thermal simulation and inhibitor injection to dissociate gas hydrate in geological formations are quite low, and possibly negative. Depressurization is expected to be effective in many situations; however, the hydrate bearing sediments should be well enough confined by low permeability strata for the depressurization to be effective.
In current study, numerical analyses were performed using the open-source reservoir simulator HYDRATERESSIM (HRS) to investigate methane gas hydrate dissociation behavior and production by depressurization, where the system pressure is lowered below the hydrate three-phase (gas-MH-water) stability pressure. Two-dimensional (2D) axisymmetric radial coordinates are used for the numerical simulations with local grid refinement.
This paper presents the approach and results of numerical investigation conducted for a hypothetical hydrate-bearing reservoir in an offshore deep water site. A comprehensive parametric sensitivity study was undertaken to assess the effects of (1) various reservoir properties including sediment permeability (absolute permeability and relative permeability function), hydrate distribution, pore compressibility, porosity formation heterogeneity and thermal conductivity; and (2) operational condition on hydrate dissociation and production. Gas productivity and advance of hydrate dissociation front with time after the commencement of depressurization are discussed. This numerical study highlights the need and importance to obtain an accurate evaluation of reservoir properties from different data source, including seismic data, logging while drilling (LWD) data, core samples, field and laboratory testing data and drilling information, on gas hydrate production prediction. It can provide useful insights on the planning and design of a field production well test.
The Influence of Familiarization on Physical Fitness Test Results in Primary School-Aged Children
Authors: Vrbik Ivan , Sporiš Goran , Štefan Lovro , Madić Dejan , Trajković Nebojša , Valantine Irena , Milanović Zoran 
Published: October 2016

Purpose:The number of familiarization sessions in fitness assessments seems to be critical and inconsistent. Therefore, the primary aim of this research was to determine the number of familiarization attempts that stabilize the results in particular physical fitness tests. The secondary aim was to establish the test reliability through familiarization sessions.Methods:Thirty-nine primary school children participated in this research (age: 10.8 years, body mass: 40.6 ± 8.9 kg, and body height: 145.3 ± 7.2 cm). During six sessions, with one session every third day, participants performed the following tests to assess explosive strength (vertical jump and standing long jump), coordination (polygon backward and polygon with turn) and flexibility (toe touch).Results:The results of repeated analysis of variance (ANOVA) showed that there were significant increases (p < .05) in the polygon backward and polygon with turn performances from the first to third familiarization session. The standard error of measurement decreased as sessions progressed, indicating little within subject variation between the coordination test results following a familiarization period. Statistically significant differences were identified in the vertical jump test from the fourth test session compared with the first session. On the other hand, statistically significant differences for the standing long jump test were only found in the final session compared with the initial session. In the toe touch test, there were no significant increases from the first to the final familiarization session. All tests showed high a reliability coefficients, ranging from 0.979 to 0.991.Conclusion:Polygon backward and polygon with turn performance may be a practical, reliable method to assess coordination in primary school-aged children. However, completion of at least 3 practice sessions is suggested for participants to obtain a stable score. In addition, both jump tests are feasible for assessing skill-related fitness in young children, although the scientific reliability of the two tests should be questioned and the tests should be tailored to fit the age group of the children.
Escherichia coli Probiotic Strain ED1a in Pigs Has a Limited Impact on the Gut Carriage of Extended-Spectrum-β-Lactamase-Producing E. coli
Authors: Mourand G. , Paboeuf F. , Fleury M. A. , Jouy E. , Bougeard S. , Denamur E. , Kempf I. 
Published: October 2016

ABSTRACT

Four trials were conducted to evaluate the impact of
Escherichia coli
probiotic strain ED1a administration to pigs on the gut carriage or survival in manure of extended-spectrum-β-lactamase-producing
E. coli
. Groups of pigs were orally inoculated with strain
E. coli
M63 carrying the
bla
CTX-M-1
gene (
n
= 84) or used as a control (
n
= 26). In the first two trials, 24 of 40
E. coli
M63-inoculated pigs were given
E. coli
ED1a orally for 6 days starting 8 days after oral inoculation. In the third trial, 10
E. coli
M63-inoculated pigs were given either
E. coli
ED1a or probiotic
E. coli
Nissle 1917 for 5 days. In the fourth trial,
E. coli
ED1a was given to a sow and its 12 piglets, and these 12 piglets plus 12 piglets that had not received
E. coli
ED1a were then inoculated with
E. coli
M63. Fecal shedding of cefotaxime-resistant
Enterobacteriaceae
(CTX-RE) was studied by culture, and
bla
CTX-M-1
genes were quantified by PCR. The persistence of CTX-RE in manure samples from inoculated pigs or manure samples inoculated
in vitro
with
E. coli
M63 with or without probiotics was studied. The results showed that
E. coli
M63 and ED1a were good gut colonizers. The reduction in the level of fecal excretion of CTX-RE in
E. coli
ED1a-treated pigs compared to that in nontreated pigs was usually less than 1 log
10
CFU and was mainly observed during the probiotic administration period. The results obtained with
E. coli
Nissle 1917 did not differ significantly from those obtained with
E. coli
ED1a. CTX-RE survival did not differ significantly in manure samples with or without probiotic treatment. In conclusion, under our experimental conditions,
E. coli
ED1a and
E. coli
Nissle 1917 could not durably prevent CTX-RE colonization of the pig gut.
Pharmacokinetic/Pharmacodynamic Modeling and Simulation of Cefiderocol, a Parenteral Siderophore Cephalosporin, for Dose Adjustment Based on Renal Function
Authors: Katsube Takayuki , Wajima Toshihiro , Ishibashi Toru , Arjona Ferreira Juan Camilo , Echols Roger 
Published: October 2016

ABSTRACT

Cefiderocol, a novel parenteral siderophore cephalosporin, exhibits potent efficacy against most Gram-negative bacteria, including carbapenem-resistant strains. Since cefiderocol is excreted primarily via the kidneys, this study was conducted to develop a population pharmacokinetics (PK) model to determine dose adjustment based on renal function. Population PK models were developed based on data for cefiderocol concentrations in plasma, urine, and dialysate with a nonlinear mixed-effects model approach. Monte-Carlo simulations were conducted to calculate the probability of target attainment (PTA) of fraction of time during the dosing interval where the free drug concentration in plasma exceeds the MIC (

T
f

>MIC
) for an MIC range of 0.25 to 16 μg/ml. For the simulations, dose regimens were selected to compare cefiderocol exposure among groups with different levels of renal function. The developed models well described the PK of cefiderocol for each renal function group. A dose of 2 g every 8 h with 3-h infusions provided >90% PTA for 75%

T
f

>MIC
for an MIC of ≤4 μg/ml for patients with normal renal function, while a more frequent dose (every 6 h) could be used for patients with augmented renal function. A reduced dose and/or extended dosing interval was selected for patients with impaired renal function. A supplemental dose immediately after intermittent hemodialysis was proposed for patients requiring intermittent hemodialysis. The PK of cefiderocol could be adequately modeled, and the modeling-and-simulation approach suggested dose regimens based on renal function, ensuring drug exposure with adequate bactericidal effect.
Evaluating Polymyxin B-Based Combinations against Carbapenem-Resistant Escherichia coli in Time-Kill Studies and in a Hollow-Fiber Infection Model
Authors: Cai Yiying , Lim Tze-Peng , Teo Jocelyn Qi-Min , Sasikala Suranthran , Chan Eric Chun Yong , Hong Yan Jun , Lee Winnie , Tan Thean Yen , Tan Thuan Tong , Koh Tse Hsien , Hsu Li Yang , Kwa Andrea L. 
Published: October 2016

ABSTRACT

Polymyxin B-based combinations have emerged as a mainstay treatment against carbapenem-resistant
Escherichia coli
(CREC). We investigated the activity of polymyxin B-based two-antibiotic combinations against CREC using time-kill studies (TKS) and validated the findings in a hollow-fiber infection model (HFIM). TKS were conducted using 5 clinical CREC strains at 5 log
10
CFU/ml against 10 polymyxin B-based two-antibiotic combinations at maximum clinically achievable concentrations. HFIMs simulating dosing regimens with polymyxin B (30,000U/kg/day) and tigecycline (100 mg every 12 h) alone and in combination were conducted against two CREC strains at 5 log
10
CFU/ml over 120 h. Emergence of resistance was quantified using antibiotic-containing media. Phenotypic characterization (growth rate and stability of resistant phenotypes) of the resistant isolates was performed. All five CREC strains harbored carbapenemases. Polymyxin B and tigecycline MICs ranged from 0.5 mg/liter to 2 mg/liter and from 0.25 mg/liter to 8 mg/liter, respectively. All antibiotics alone did not have bactericidal activity at 24 h in the TKS, except for polymyxin B against two strains. In combination TKS, only polymyxin B plus tigecycline demonstrated both bactericidal activity and synergy in two out of five strains. In the HFIM, polymyxin B alone was bactericidal against both CREC strains before regrowth was observed at 8 h. Phenotypically stable polymyxin B-resistant mutants were observed for both strains, with a reduced growth rate observed in one strain. Tigecycline alone resulted in a slow reduction in bacterial counts. Polymyxin B plus tigecycline resulted in rapid and sustained bactericidal killing up to 120 h. Polymyxin B plus tigecycline is a promising combination against CREC. The clinical relevance of our results warrants further investigations.