10,861 research outputs found
Prediction of stress concentrations and degrees of bending in axially loaded tubular K-joints
No full textAn extensive database of stress concentrations and degree of bending in tubular K-joints under balanced axial loading, generated recently in a finite element parametric study, has been used to develop parametric equations. The study covers a comprehensive range of geometric joint parameters which are commonly found in offshore structures. This database of thin shell finite element results was used to develop parametric equations for estimating stress concentration factors and the degree of bending at key locations on both the chord and brace. Formulae for the stress distributions around the intersection of K-joints were also derived using the parametric equations at key locations as input parameters, thus allowing the stress distributions to be predicted from the geometric joint parameters. Fracture mechanics fatigue calculations were performed to demonstrate that the information provided from the proposed equations could be used to obtain safe estimates of fatigue lives of tubular K-joints
Parametric equations for distributions of stress concentration factors in tubular K-joints under out-of-plane moment loading
No full textAn extensive parametric study, using finite elements, of the stress concentration factors in tubular K-joints commonly found in offshore platforms is presented. This study covers a comprehensive range of geometric joint parameters for unbalanced out-of-plane moment loading. The results of the study were first used to assess the widely used parametric equations of Efthymiou (Proceedings of the Conference on Recent Developments in Tubular Joints Technology, Surrey, 1988, p. 2–1) and Lloyds Register (Proceedings of the 1st International Society of Offshore Polar Engineers Conference, 1991, Edinburgh), which provide predictions of stress concentration factors at the saddle on the outer surfaces of the chord and the brace as a function of the joint geometric ratios. The database of thin shell finite element results generated was then used to develop parametric equations for predicting stress concentration factors at key locations around the joint intersection on the outer, as well as the inner, surfaces of the chord. The reliability of the proposed and existing parametric equations was then assessed using the acrylic joint database published by the UK Department of Energy (Draft Background to New Fatigue Design Guidance for Steel Joints and Connections in Offshore Structures, 1995). The paper concludes with fracture mechanics fatigue calculations to demonstrate that the information provided from the proposed equations could be utilised to obtain accurate, and safe, fatigue life estimates
Sequential injection analysis Ferrozine spectrophotometry versus Luminol chemiluminescence for continuous online monitoring of the concentration and speciation of iron
No full textWe designed two sequential injection analysis systems (Luminol chemiluminescent and Ferrozine spectrophotometric) that are capable of monitoring the concentration of soluble iron(II) and reducible iron(III) in natural waters over extended periods (>120 h). The method based on Luminol chemiluminescence estimated the iron(II) concentration as the difference in signal with or without the addition of the strong iron(II) ligand, Ferrozine (TM) (iron complexing reagent). Iron(II) in the sample without the iron complexing reagent induced a chemiluminescence signal whereas iron(II) in the presence of the iron complexing reagent did not induce a signal. The second method, based on Ferrozine (TM) spectrophotometry, measured iron(II) and reducible iron(III) in a 100 cm path length liquid wave capillary cell. Both methods provided stability for >120 h and yielded similar analytical detection limits equal to ten standard deviations of the blank; 2.2 nM for Luminol chemiluminescence with a calibration concentration range of 0 - 12 nM, and 3.9 nM for Ferrozine (TM) spectrophotometry with a calibration concentration range of 0 - 120 nM. The two chemical techniques do not appear to be directly comparable for practical monitoring purposes, and we suggest that Luminol-chemiluminescence is unable to measure strong ligand complexes of iron(II). Both methods used iron(II) as the analytical standard rather than a reduced iron(III) standard. The analysis based on the iron(II) standard was able to be performed without additional buffers and reducing reagents, which significantly minimized contamination.11Nsciescopu
Stress concentration factors in tubular K-joints under in-plane moment loading
No full textAn extensive parametric study is presented of the distributions of stress concentration factors in tubular K-joints commonly found in offshore platforms. The study covers a comprehensive range of geometric joint parameters for balanced in-plane moment loading. The results of the study were first used to assess two sets of widely used parametric equations, which predict the maximum stress concentration factors on the outer surfaces of the chord and the brace. The new database of finite-element results was then used to develop parametric equations for predicting stress concentration factors at key locations around the intersection on the outer as well as the inner surfaces of the chord. The reliability of the proposed and existing parametric equations was then assessed using an acrylic test joint database and some published test data measured from a steel model. Fracture mechanics fatigue calculations were also performed to demonstrate that the information provided from the proposed equations could be utilized to obtain accurate, and safe, fatigue life estimates
Determination of environmental H2O2 for extended periods by chemiluminescence with real-time inhibition of iron interferences
No full textSoluble iron hinders the accurate analysis of hydrogen peroxide (H2O2) in environmental systems. We present a chemiluminescence sequential injection (SIA) system capable of the continuous analysis of H2O2 over extended periods (48 h) by the real-time addition of an iron complexing reagent (ICR; masking compounds) which inhibits > 98% of the interference caused by iron species. The measurement error based on repeat analysis of a sample within 10 min was +/- 2.2%, and over 48 h was +/- 6%. The preparation and analysis of standards, the ability for discrete and continuous sampling, and the real-time addition of the ICR to minimize chemical interference were integrated within the SIA system. Evaluation of the analytical probe showed that the optimum concentration and pH of the luminol reagent for the analysis of H2O2 were 100 mu M luminol and pH = 10.7, respectively; this enabled the analysis over a concentration range of 0.25-900 nM H(2)O(2)at a detection limit of 0.14 nM. The proposed SIA system requires only small amounts of reagents (33 mu L luminol and 24 mu L ICR) and sample (240 mu L). We used the system to measure the H2O2 concentration in a coastal seawater sample that was subject to natural photochemical reactions and the direct input of rainwater, both of which introduce soluble iron. Rainwater H2O2 increased the H2O2 concentration in the coastal seawater sample by a factor of up to 40 relative to the amounts produced by natural photochemical reactions. The H2O2 concentration in the coastal seawater sample showed high short-term variability.11Nsciescopu
New parametric equations for stress concentrations in tubular K-joints under balanced axial loading
No full textAn extensive parametric study is presented on stress concentrations in tubular K-joints calculated using thin shell finite elements. This study covers a comprehensive range of geometric joint parameters under balanced axial loading. The results of this investigation were used to assess the existing parametric equations of Efthymiou (Proc. Conf. Recent Dev. Tubular Joints Technol., Surrey, 1988, p. 2-1) and Lloyds Register (Proc. 1st Int. Soc. Offshore Polar Eng. Conf., 1991, Edinburgh). These equations predict stress concentration factors on the chord and the brace at selected locations as a function of the joint geometry, and are based upon databases which cover relatively narrow ranges of geometric parameters. The new database of thin shell finite element results was used to develop new parametric equations for estimating stress concentration factors on the chord and on the brace. The reliability of the proposed parametric equations was then assessed using the database of steel and acrylic joints published recently by the Department of Energy (Draft Background to New Fatigue Design Guidance for Steel Joints and Connections in Offshore Structures, 1995).<br/
Nanoparticles in wastewater from a science-based industrial park—Coagulation using polyaluminum chloride
No full textMurskii's algebra does not satisfy min
No full textThis note shows that the variety generated by Murskii's 3-element algebra contains an infinite descending chain of subvarieties, thus falsifying a conjecture made previously by the author and M.R. Vaughan-Lee
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