On the dynamics of flexible risers and suspended pipes

This thesis describes a theoretical and numerical study of the static and dynamic behaviour of flexible pipes and risers. Although the effects of conventional loadings due to self-weight, current, waves and surface vessel excitation are included, this work is specifically aimed at identifying the effects of internal and external fluid pressures as well as both constant density and alternating gas-fluid internal flows on the static and dynamic behaviour of risers. Particular emphasis is placed on research and development of advanced numerical analysis methods for solving the non-linear riser equations in the frequency and time domains. Theoretically calculated responses have been compared with results of model tests carried out at Heriot-Watt University and University College London and with theoretical predictions from alternative formulations. Modified forms of the governing equations for flexible risers have been derived from first principles to include the effects of internal and external hydrostatic pressures and a steady internal flow. It is rigorously shown that the conventional derivation of effective tension using a buoyancy analogy is equivalent to that obtained through exact integration of fluid pressures over the curved surface of the riser pipe. It is also demonstrated that the effect of a steady internal flow is analogous to that of hydrostatic pressure and may be included in the governing equations through the effective tension term. The riser governing equations have been solved using a finite element analysis program written specifically for flexible risers and similar pipe geometries. The static analysis of the riser is carried out using an iterative approach that can accommodate general loading conditions using an incremental shifting procedure. Modifications to the standard non-linear static analysis techniques have been proposed and are shown to provide a more accurate representation of the deformation dependence of loading whilst retaining the non-linear influence of tensile forces on pipe geometry. Dynamic analyses have been carried out using both frequency and time domain techniques. The frequency domain approach is a regular wave analysis based on a combined wave and current linearisation whilst the time domain analysis uses the Newmark method and can accommodate regular and irregular sea states as well as geometric non-linearities. Results of this numerical work have been verified by comparison with model tests and analysis results from several sources. Model tests carried out at Heriot-Watt University at 1:50th. scale have been used to verify global predictions for riser responses and tensile forces. Specially designed model tests at University College London have been used to confirm the validity of predicted riser responses to internal flow. Comparisons have also been made with the analysis results of parallel research works. Case studies of typical North Sea flexible risers are presented. The analytical and numerical work demonstrates that it is essential to include the effects of internal and external hydrostatic pressures and internal flow for accurate prediction of the overall response of a flexible riser. In particular, internal flow composed of alternating gas-liquid phases (slug flow) is shown to induce large oscillations in riser tensions at frequencies defined by the flow parameters. These oscillations are comparable to those induced by wave action and have a significant impact on the fatigue life of flexible risers

Evaluating the relationship between serum immunoglobulin G (IgG) and A (IgA) anti-cagA antibody and the cagA gene in patients with dyspepsia

Peer reviewedPublisher PD

Sevelamer, a phosphate-binding resin with beneficial effect in diabetic kidney disease; a modern paradigm shift

The proportion of individuals diagnosed with diabetes mellitus is increasing throughout the world, which sequentially drives upward the global frequency of diabetic kidney disease (1, 2). Diabetes is a costly and deadly disease. Patients with diabetic kidney disease are at an increased risk for cardiovascular disease, premature death, and other severe diseases that ensue in increased health-care utilization and frequent hospitalizations (1, 2). In fact, type II diabetes mellitus is an ongoing medical dilemma that clinicians deal with on a daily basis

Erythropoietin ameliorates genetamicin-induced renal toxicity: A biochemical and histopathological study.

BACKGROUND Investigations have attempted to modify the outcome of tubular injury by either ameliorating renal tubular damage or promoting tubular regeneration in the case of acute tubular necrosis. OBJECTIVES We investigated the protective effect of Eprex an erythropoietin analogue on tubular injury induced by gentamicin (GM). MATERIALS AND METHODS Forty male Wistar rats were randomly divided into four groups. In group 1,rats were served as a sham group. In group 2, rats were injected intraperitoneally with 100 mg/kg of GM for 10 consecutive days (positive control group) and then were sacrificed. In group 3, rats received GM for 10 days then Eprex 100U/kg was injected intraperitoneally for the next 10 days and then they were sacrificed at the day 20th. In group 4 rats were injected a combination of GM (80 mg/kg) and Eprex 100U/kg intraperitoneally for 10 days and then were sacrificed. RESULTS The results indicated that, Eprex prevented the increase in serum creatinine (Cr) and blood urea nitrogen (BUN). The effect of Eprex on damage score, showed that co-administration of GM and Eprex (group 3 and 4) reduced the kidney tissue damage compared to positive control group (P<0.05). This result indicat that Eprex potentially can reduce or prevent the kidney tissue damage. CONCLUSIONS Ameliorative effect of Eprex when the drug was given in combination with GM and also when the drug was applied after GM-induced tubular damage, revealed the renoprotective potency of Eprex. Eprex is a promising drug to prevent or attenuate tubular damage induced by GM or other nephrotoxic agents which act through the same mechanisms as gentamicin

How to develop clinical reasoning in medical students and interns based on illness script theory : An experimental study

Acknowledgments Authors would like to acknowledge Iran University of Medical Sciences for providing financial support. Extend thanks to medical students and interns for their participation in the study. Funding The present study was financially supported by Iran University of Medical Sciences, for partial fulfillment of Ph.D. dissertation, (Grant No: 6784). The funding organization did not play any roles in the study design, collection, analysis, and interpretation of data, or in writing the manuscript.Peer reviewedPublisher PD

Rapid screening of diabetic polyneuropathy : Selection of accurate symptoms and signs in an outpatient clinical setting

Authors would like to thank Ms. Ameneh Ebrahim Valojerdi for her great help in preparation of this manuscript.Peer reviewedPublisher PD

Oxford-MEST classification in IgA nephropathy patients: A report from Iran.

BACKGROUND There is a limited knowledge about the morphological features of IgA nephropathy (IgAN)in the middle east region. OBJECTIVES The objective of this study was to evaluate the spectrum of histopathological findings in IgAN patients at our laboratory. PATIENTS AND METHODS At this work, an observational study reported which was conducted on IgAN patients using the Oxford-MEST classification system. RESULTS In this survey, of 102 patients 71.6 % were male. The mean age of the patients was 37.7 ± 13.6 years. Morphologic variables of MEST classification was as follows; M1: 90.2 %, E: 32 %, S: 67 % also,T in grads I and II were in 30% and 19% respectively, while 51% were in grade zero. A significant difference was observed in segmental glomerulosclerosis (P=0.003) and interstitial fibrosis/tubular atrophy frequency distribution (P= 0.045), between males and females . Furthermore, it was found that mesangial hypercellularity was more prevalent in yonger patients. Moreover, there was a significant correlation between serum creatinine and crescents (P<0.001). There was also significant correlation of serum creatinine with segmental glomerulosclerosis (P<0.001). CONCLUSIONS Higher prevalence of segmental glomerulosclerosis and interstitial fibrosis/ tubular atrophy, as the two of, four variables of Oxford-MEST classification of IgAN in male patients further attests that male gender is a risk factor in this disease.In this study the significant correlation between serum creatinine and crescent was in an agreement with previous studies and suggests for the probable accomodation of extracapillary proliferation as a new variable in MEST system

Challenging script concordance test reference standard by evidence : Do judgments by emergency medicine consultants agree with likelihood ratios?

Acknowledgements We would like to acknowledge Dr. Amir Nejati for his contributions in collecting data for this study. Sources of funding This study was the M.D. thesis of SK and was funded by Iran University of Medical Sciences. The authors have not received fund from any other source.Peer reviewedPublisher PD