Image based simulation of one-dimensional compression tests on carbonate sand

High factors of safety and conservative methods are commonly used on foundation design on shelly carbonate soils. A better understanding of the behavior of this material is, thus, critical for more sustainable approaches for the design of a number of offshore structures and submarine pipelines. In particular, understanding the physical phenomena taking place at the microscale has the potential to spur the development of robust computational methods. In this study, a one-dimensional compression test was performed inside an X-ray scanner to obtain 3D images of the evolving internal structure of a shelly carbonate sand. A preliminary inspection of the images through five loading increments has shown that the grains rearrange under loading and in some cases cracks develop at the contacts. In order to replicate of the experiments in the numerical domain, the 3D image of the soil prior to loading was imported into a micro Finite Element (µFE) framework. This image-based modelling tool enables measurements of the contact force and stress map inside the grains while making use of the real microstructure of the soil. The potential of the µFE model to contribute insights into yield initiation within the grain is demonstrated here. This is of particular interest to better understand the breakage of shelly grains underpinning their highly compressive behavior

07.15: Experimental and numerical investigation of cold‐formed steel built‐up stub columns

This paper describes a numerical and experimental programme carried out at the University of Sheffield on built‐up stub columns fabricated from cold‐formed steel. A total of 20 built‐up columns with four different cross‐sectional geometries were tested between fixed end conditions. Two of the cross‐sectional geometries were assembled using M6 bolts and the other two using M5.5 self‐drilling sheet metal screws. The connector spacing was varied among specimens of the same cross‐sectional geometry. The cross‐sections were assembled from flat plate, plain channels and lipped channels with nominal thicknesses ranging from 1.2 mm to 2.4 mm. The initial geometric imperfections of each specimen were recorded prior to testing and their material properties were determined by means of tensile coupon tests. Single lap shear tests were also carried out in order to study the connector behaviour of the bolts and the screws used to assemble the specimens. As part of the numerical part of the study, the test specimens were modelled using the commercially available ABAQUS software package. The recorded geometric imperfections, the measured material properties and the connector behaviour data obtained from the lap shear tests were incorporated into the FE models. Special attention was paid to the connector modelling in order to find an effective and simple way to represent their actual behaviour. The FE models were further used to quantify the effect of the connector behaviour on the buckling response of cold‐formed steel built‐up stub columns

Risk and sensitivity quantification of fracture failure employing cohesive zone elements

Many structures are subjected to the risk of fatigue failure. For their reliability-based design, it is thus important to calculate the probability of fatigue failure and assess the relative importance of the involved parameters. Although various studies have analyzed the fatigue failure, the stage of fracture failure has been less focused. In particular, the risk analysis of fracture failure needs to be conducted considering its importance in actual structures. This article proposes a new probabilistic framework for the risk and sensitivity analysis of structural fatigue failure employing cohesive zone elements. The proposed framework comprises three steps, namely finite element analysis using cohesive zone elements, response surface construction, and risk and sensitivity analysis of fatigue failure, which require several mathematical techniques and algorithms. The proposed framework is tested by applying it to an illustrative example, and the corresponding analysis results of fracture failure probability with different threshold values of a limit-state function are presented. In addition, the sensitivities of failure risk with respect to the statistical parameters of random variables are presented and their relative importance is discussed

Computational study of reservoir sand production mechanisms

A numerical model is developed to simulate fluid flow conditions around a wellbore and to evaluate mechanisms governing fluid flow, pressure gradients, rock failure and the ensuing sand production. The rock material behaviour matches sandstone described by the Drucker–Prager material failure model. Conditions for erosion are governed through two criteria: a material failure criterion described by the Drucker–Prager model and a sanding criterion expressed by an eroded solid mass generation model. The interplay between controlling operating and reservoir conditions is assessed. In addition, contributions of the following key factors to interstitial fluid velocity, plastic strain, pore pressure variation and sand production are appraised: drawdown, wellbore perforation depth, mud pressure and erosion criteria. Despite a decrease in pore fluid velocity at the vicinity of the wellbore at increasing depth, sand production increases with wellbore/perforation depth. Likewise, at constant drawdown, sand production is aggravated as wellbore/perforation depth increases. The rate of increase in the plastic zone following the onset of sand production is inconstant. Furthermore, mud pressure is demonstrated as an effective tool for attenuating sand production. An understanding of interactions between key parameters governing reservoir responses and the effect on sanding during oil/gas production is imperative if extraction operations are to be optimised.Published onlin

Alu insertion/deletion of ACE gene polymorphism might not affect significantly the serum bradykinin level in hypertensive patients taking ACE inhibitors

Background Angiotensin I-converting enzyme (ACE) has two homologous catalytic domains, the N- and C-domains. Our previous study suggested that Alu insertion (I allele) in the intron 16 of ACE resulted in premature codon termination. The I allele has only one active site in the N-domain while the Alu deletion (D allele) still has two active sites of ACE. Therefore the effect of I/D polymorphism of ACE on the enzyme's ability to catalyse bradykinin is still not widely known. Aims This study aimed to examine the serum bradykinin level in hypertensive patients with I/D polymorphism of ACE, who were treated with ACE inhibitor. Subjects and methods The serum bradykinin and I/D polymorphism have been detected in 64 hypertensive patients taking ACE inhibitor (lisinopril or captopril) for at least eight weeks with good medication adherence. The binding affinity of ACE with its receptor was calculated by molecular docking. Results The findings show that genotype II is more frequent in the population the researchers observed (53.12%) compared to ID (23.44%) and DD (23.44%) variances. On the other hand, the bradykinin level is not affected by genotype of the ACE genes on the population. Bradykinin increases in patients with genotype II who are given captopril, but decreases in patients treated with lisinopril. Nevertheless, there is no statistically significant difference. Conclusion This study suggests that the polymorphism might not significantly affect the serum bradykinin level in hypertensive patients taking ACE inhibitors