Study on fatigue experiment for transverse butt weldsunder 2G and 3G weld positions

ABSTRACTAlthough the transverse butt weld method with ceramic backing strip has been widely used in various industrial fields for its fabricational convenience, it is rarely used in offshore industries since the fatigue strength of the weld joint has not been proved sufficiently. This study conducted fatigue tests for series of butt weld specimens with horizontal (2G) and vertical (3G) welding positions in order to verify the fatigue strength compared to S-N curve by DNV (Det Norske Veritas), IIW (International Institute of Welding) and Eurocode 3. The difference of the 2G specimens and the 3G specimens are investigated in terms of angular distortion and the effect on the fatigue strength are analyzed

Atrasentan and renal events in patients with type 2 diabetes and chronic kidney disease (SONAR): a double-blind, randomised, placebo-controlled trial

Background: Short-term treatment for people with type 2 diabetes using a low dose of the selective endothelin A receptor antagonist atrasentan reduces albuminuria without causing significant sodium retention. We report the long-term effects of treatment with atrasentan on major renal outcomes. Methods: We did this double-blind, randomised, placebo-controlled trial at 689 sites in 41 countries. We enrolled adults aged 18–85 years with type 2 diabetes, estimated glomerular filtration rate (eGFR)25–75 mL/min per 1·73 m 2 of body surface area, and a urine albumin-to-creatinine ratio (UACR)of 300–5000 mg/g who had received maximum labelled or tolerated renin–angiotensin system inhibition for at least 4 weeks. Participants were given atrasentan 0·75 mg orally daily during an enrichment period before random group assignment. Those with a UACR decrease of at least 30% with no substantial fluid retention during the enrichment period (responders)were included in the double-blind treatment period. Responders were randomly assigned to receive either atrasentan 0·75 mg orally daily or placebo. All patients and investigators were masked to treatment assignment. The primary endpoint was a composite of doubling of serum creatinine (sustained for ≥30 days)or end-stage kidney disease (eGFR <15 mL/min per 1·73 m 2 sustained for ≥90 days, chronic dialysis for ≥90 days, kidney transplantation, or death from kidney failure)in the intention-to-treat population of all responders. Safety was assessed in all patients who received at least one dose of their assigned study treatment. The study is registered with ClinicalTrials.gov, number NCT01858532. Findings: Between May 17, 2013, and July 13, 2017, 11 087 patients were screened; 5117 entered the enrichment period, and 4711 completed the enrichment period. Of these, 2648 patients were responders and were randomly assigned to the atrasentan group (n=1325)or placebo group (n=1323). Median follow-up was 2·2 years (IQR 1·4–2·9). 79 (6·0%)of 1325 patients in the atrasentan group and 105 (7·9%)of 1323 in the placebo group had a primary composite renal endpoint event (hazard ratio [HR]0·65 [95% CI 0·49–0·88]; p=0·0047). Fluid retention and anaemia adverse events, which have been previously attributed to endothelin receptor antagonists, were more frequent in the atrasentan group than in the placebo group. Hospital admission for heart failure occurred in 47 (3·5%)of 1325 patients in the atrasentan group and 34 (2·6%)of 1323 patients in the placebo group (HR 1·33 [95% CI 0·85–2·07]; p=0·208). 58 (4·4%)patients in the atrasentan group and 52 (3·9%)in the placebo group died (HR 1·09 [95% CI 0·75–1·59]; p=0·65). Interpretation: Atrasentan reduced the risk of renal events in patients with diabetes and chronic kidney disease who were selected to optimise efficacy and safety. These data support a potential role for selective endothelin receptor antagonists in protecting renal function in patients with type 2 diabetes at high risk of developing end-stage kidney disease. Funding: AbbVie

Estimation of ice loads on offshore structures using simulations of level ice-structure collisions with an influence coefficient method

During their service, ice-class vessels are exposed to ice collision loads. Precise estimation of such ice loads is essential to the design of ice-class vessels. Due to difficulties encountered in real measurement of ice loads, a simple yet logically straightforward method, namely the influence coefficient method (ICM), has been widely employed to convert strain data to ice pressures. However, the method&apos;s accuracy and reliability depend on how strain gauges are arranged and load cells are divided accordingly. This study investigated those aspects in order to enhance the accuracy and reliability of the ICM in estimating ice loads incurred in collisions of ice with offshore structures. It began by developing a numerical model of level ice-structure interactions. For this, an icematerial model applying the Drucker-Prager (DP) plasticity model combined with an element erosion technique&apos;s simplified damage mechanics was developed. The developed numerical model was verified by comparing its results with the relevant model test data and corresponding numerical results available in the open literature, and good agreement was achieved. Next, the present study performed, based on the numerical simulation strategy thus validated, simulations of level ice collisions with actual offshore structures showing inflexible and deformable behaviors. Subsequently, a finite element (FE) model of the structures&apos; instrumented area, which is the same as the scantling used in the ice collision simulation, was developed to construct an influence coefficient matrix for the ICM. The structural responses, including stress/strain data and ice-contact pressure observed numerically, were then applied to an investigation of the ICM capability. The effects of the strain gage arrangements and corresponding load cells on the estimation of the local ice pressures acting on actual offshore structures were demonstrated. The proposed procedure is expected to provide insights into how the ICM can be improved in reliably and cost-effectively estimating ice loads on ice-class offshore structures.N

A parametric study on the use of passive fire protection in FPSO topside module

Fire is a continuous threat to FPSO topside modules as large amounts of oil and gas are passing through the modules. As a conventional measure to mitigate structural failure under fire, passive fire protection (PFP) coatings are widely used on main structural members. However, an excessive use of PFP coatings can cause considerable cost for material purchase, installation, inspection and maintenance. Long installation time can be a risk since the work should be done nearly at the last fabrication stage. Thus, the minimal use of PFP can be beneficial to the reduction of construction cost and the avoidance of schedule delay. This paper presents a few case studies on how different applications of PFP have influence on collapse time of a FPSO module structure. A series of heat analysis and thermal elasto-plastic FE analysis are performed for different PFP coatings and the resultant collapse time and the amount of PFP coatings are compared with each other

Hull structural response prediction using distortion base modes

The hull structure health monitoring system is attracting attention by many ongoing vessels to prevent possible failure of the hull structure. As one of these efficient monitoring methods, the conversion method based on the mode superposition assumption had been introduced (Baudin et al., 2013, Bigot et al., 2015). It has the advantage that once the modal amplitudes are determined, it enables to estimate lots of structural behavior such as hull girder loads or stresses of structural members in a simply way. In this research, a case study of applying the conversion method on floating production storage and offloading unit (FPSO) hull model is introduced. Furthermore, the empirical processes in the mode selection stage have been optimized with respect to the target performance accuracy. The validity of this modification is verified by several case studies

A study on an efficient prediction of welding deformation for T-joint laser welding of sandwich panel Part II : Proposal of a method to use shell element model

I-core sandwich panel that has been used more widely is assembled using high power CO₂laser welding. Kim et al. (2013) proposed a circular cone type heat source model for the T-joint laser welding between face plate and core. It can cover the negative defocus which is commonly adopted in T-joint laser welding to provide deeper penetration. In part I, a volumetric heat source model is proposed and it is verified thorough a comparison of melting zone on the cross section with experiment results. The proposed model can be used for heat transfer analysis and thermal elasto-plastic analysis to predict welding deformation that occurs during laser welding. In terms of computational time, since the thermal elasto-plastic analysis using 3D solid elements is quite time consuming, shell element model with multi-layers have been employed instead. However, the conventional layered approach is not appropriate for the application of heat load at T-Joint. This paper, Part II, suggests a new method to arrange different number of layers for face plate and core in order to impose heat load only to the face plate

Quasi-static assessment of response to slamming impact on free fall lifeboats

Design against impact loads (slamming) can be challenging and time consuming and can involve complex calculations. Application of simplified, quasi-static calculation approaches will make the design process much easier. In this paper, such simplified methods are discussed using free fall lifeboats as a case. Results from non-linear FE-analysis show that the response is non-linear due to large deformations. The impact pressure is then mainly carried by membrane stress and the dynamic response is small. A non-linear beam theory approach for hand calculation is established. As the non-linear calculation model is the most realistic, it is recommended that this is used in an initial design assessment. Although the results are on the conservative side, simple hand calculations including non-linear geometry can be used to predict the maximum strain. Linear methods are also investigated. However, these methods should be used with more rigid structures such as stiffened steel and aluminium panels

Quasi-static assessment of response to slamming impact on free fall lifeboats

Design against impact loads (slamming) can be challenging and time consuming and can involve complex calculations. Application of simplified, quasi-static calculation approaches will make the design process much easier. In this paper, such simplified methods are discussed using free fall lifeboats as a case. Results from non-linear FE-analysis show that the response is non-linear due to large deformations. The impact pressure is then mainly carried by membrane stress and the dynamic response is small. A non-linear beam theory approach for hand calculation is established. As the non-linear calculation model is the most realistic, it is recommended that this is used in an initial design assessment. Although the results are on the conservative side, simple hand calculations including non-linear geometry can be used to predict the maximum strain. Linear methods are also investigated. However, these methods should be used with more rigid structures such as stiffened steel and aluminium panels

Structural response analysis of slamming impact on free fall lifeboats

The evaluation of impact induced slamming loads experienced by ships and offshore structures using advanced fluid structure interaction methods may be a challenging task involving complex and time consuming engineering solutions. This is the reason why to date the application of well understood and validated quasi-response approaches remains the most rational alternative used by experts for preliminary design assessment. Based on a benchmark study carried out by the International Ship and Offshore Structures Congress Technical Committee II.1 on Quasi-Static Response this paper demonstrates the practical use of quasi response prediction methods for the assessment of impact loads on modern free fall lifeboats. The case study presented is considered relevant in terms of technical background and ship design for safety. Following a brief review rationalising the practical relevance of the engineering solutions examined, the influence of high speed impact is evaluated using linear-elastic and nonlinear beam models, as well as a nonlinear transient dynamic finite element analysis idealisation. Comparisons of the methods presented against experimental results led to the conclusion that the nonlinear quasi-dynamic beam approach accounts for the influence of the dynamic effects of strain by suitably idealising the effects of nonlinear geometric stiffness. It may therefore be more appropriate to employ this approach at preliminary stage, especially when conducting comparisons against simplistic linear methods used for rigid structures (e.g. stiffened steel and aluminium panels), or advanced nonlinear finite element analysis, and other multi-physics methods that may be computationally complex and time consuming