The Experts below are selected from a list of 144 Experts worldwide ranked by ideXlab platform
Anthony E. Walsby - One of the best experts on this subject based on the ideXlab platform.
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Analysis of tryptic digests indicates regions of GvpC that bind to gas vesicles of Anabaena flos-aquae.
Microbiology, 2006Co-Authors: Peter G. Dunton, W. J. Mawby, Virginia A. Shaw, Anthony E. WalsbyAbstract:The gas vesicles of the cyanobacterium Anabaena flos-aquae contain two main proteins: GvpA, which forms the ribs of the hollow cylindrical shell, and GvpC, which occurs on the outer surface. Analysis by MALDI-TOF MS shows that after incubating Anabaena gas vesicles in trypsin, GvpA was cleaved only at sites near the N-terminus, whereas GvpC was cleaved at most of its potential tryptic sites. Many of the resulting tryptic peptides from GvpC remained attached to the underlying GvpA shell: the pattern of attachment indicated that there are binding sites to GvpA at both ends of the 33-residue repeats (33RRs) in GvpC, although one of the tryptic peptides within the 33RR did not remain attached. Tryptic peptides near the two ends of the GvpC molecule were also lost. The mean Critical Collapse Pressure of Anabaena gas vesicles decreased from 0.63 MPa to 0.20 MPa when GvpC was removed with urea or fully digested with trypsin; partial digestion resulted in partial decrease in Critical Pressure.
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The diameter and Critical Collapse Pressure of gas vesicles in Microcystis are correlated with GvpCs of different length.
FEMS microbiology letters, 2005Co-Authors: Peter G. Dunton, Anthony E. WalsbyAbstract:In cyanobacteria the protein on the outside of the gas vesicle, GvpC, is characterised by the presence of a 33 amino acid residue repeat (33RR), which in some genera is highly conserved. The number of 33RRs correlates with the diameter of the gas vesicle and inversely with its strength. Gas vesicles isolated from Microcystis aeruginosa strain PCC 7806 were found to be wider and have a lower Critical Collapse Pressure than those from Microcystis sp. strain BC 8401. The entire gas-vesicle gene cluster of the latter strain was sequenced and compared with the published sequence of the former: the sequences of nine of the ten gvp genes differed by only 1-5% between the two strains; the only substantial difference was in gvpC which in strain BC 8401 lacked a 99-nucleotide section encoding a 33RR. This observation further narrows the correlation of gas vesicle width to the number of 33RRs and suggests how Microcystis strains might be used in experimental manipulation of gas vesicle width and strength.
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the relationship between Critical Pressure and width of gas vesicles in isolates of planktothrix rubescens from lake zurich
Microbiology, 1999Co-Authors: Dylan I Bright, Anthony E. WalsbyAbstract:The mean Critical Collapse Pressure (p c) of gas vesicles in 81 strains of the cyanobacterium Planktothrix rubescens from Lake Zurich, Switzerland, was bimodally distributed between a minimum of 0·86 MPa and a maximum of 1·17 MPa. Measurements were made of the cylinder diameter (d) of gas vesicles isolated from seven of the strains. The mean diameter, which varied from 48 to 61 nm, was inversely related to p c, in keeping with the theory of strength of thin-walled rigid cylinders. These measurements extended the range of p c–width relationship of gas vesicles, which can be described by the expression p c=461(d/nm)−1·53 MPa. p c was correlated with gas vesicle genotype (see the accompanying paper by S. J. Beard, B. A. Handley, P. K. Hayes & A. E. Walsby, Microbiology 145, 2757–2768): of the 81 strains investigated, all those with the gas vesicle genotype GV2 produced gas vesicles with a mean p c of less than 1·0 MPa, whereas those of GV3 had a mean p c of greater than 1·0 MPa. It is suggested that gas vesicles of the GV3 strains, which are narrower and stronger than any previously recorded in freshwater cyanobacteria, have evolved to withstand the high hydrostatic Pressures during deep winter mixing in Lake Zurich.
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The Critical Pressures of gas vesicles in Planktorhrix rubescens in relation tothe depth of winter mixing in Lake Zürich, Switzerland
Journal of Plankton Research, 1998Co-Authors: Anthony E. Walsby, Avril Avery, Ferdinand SchanzAbstract:The vertical distribution of the cyanobacterium Planktothrix (Oscillatoria) rubescens in Lake Zurich was investigated from March 1993 to June 1995 by collecting filaments on filters and measuring them by epifluorescence microscopy and computer image analysis. The initial population, which began to stratify in April, decreased by up to 99% by June. During the summer, the population peaked at depths of 8—15 m; it reached a maximum areal filament-volume concentration of -60 cm3 m~2 of lake surface in early September and was then entrained in the deepening surface layer. It became mixed progressively deeper, to the lake bottom in the cold winter of 1993-94, but less completely in the milder winter of 1994-95. Most of the filaments remained viable during the winter. At the end of the mild winter of 1994-5, 70% of filaments in the water column retained buoyancy, but after the cold winter of 1996-7 only 22% were buoyant. Few remained buoyant below 80 m, where the hydrostatic Pressure caused gas vesicle Collapse. The proportion that remain buoyant decreases with the depth and duration of winter mixing, and increases with the Critical Collapse Pressure (pc) of the gas vesicles, which provide buoyancy. Strains of P.rubescens isolated from Lake Zurich differed in mean pc of their gas vesicles, from 0.9 to 1.1 MPa, the highest values in freshwater cyanobacteria. Allowing for a turgor Pressure of 0.2 MPa, these strains would remain buoyant at depths down to 70 and 90 m, respectively. Natural selection for gas vesicles of high pc will operate by increasing the proportion of filaments that remain buoyant in the upper parts of the water column after circulation to various depths during the winter because only buoyant filaments will form the inoculum for the following season.
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GvpCs with reduced numbers of repeating sequence elements bind to and strengthen cyanobacterial gas vesicles
Molecular microbiology, 1995Co-Authors: R. Kinsman, Anthony E. Walsby, Paul K. HayesAbstract:We have previously shown that the gas-vesicle protein GvpC is present on the outer surface of the gas vesicle, can be reversibly removed and rebound to the surface, and increases the Critical Collapse Pressure of the gas vesicle. The GvpC molecule, which contains five partially conserved repeats of 33 amino acids (33-RR) sandwiched between 18 N-terminal and 10 C-terminal amino acids, is present in a ratio of 1:25 with the GvpA molecule, which forms the ribs of the gas vesicle. By using recombinant techniques we have now made modified versions of GvpC that contain only the first two, three or four of the 33-amino-acid repeats. All of these proteins bind to and strengthen gas vesicles that have been stripped of their native GvpC. Recombinant proteins containing three or four repeats bind in amounts that give the same ratio of 33-RR:GvpA (i.e. 1:5) as the native protein, and they restore much of the strength of the gas vesicle; the protein containing only two repeats binds at a lower ratio (1:7.7), however, and restores less of the strength. Ancestral proteins with only two, three or four of the 33-amino-acid repeats would have been functional in strengthening the gas vesicle but the progressive increase in number of repeats would have provided strength with increased efficiency.
Hans Hopman - One of the best experts on this subject based on the ideXlab platform.
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An Analytical Approach for Predicting the Collapse Pressure of the Flexible Risers With Initial Ovalization and Gap
Volume 5A: Pipelines Risers and Subsea Systems, 2019Co-Authors: Xiao Li, Xiaoli Jiang, Hans HopmanAbstract:Abstract A flexible riser is a flexible pipe that transports materials between seafloor and topside structures. As oil and gas production heads to water depths greater than 3000 meters, huge hydrostatic Pressure may cause the Collapse failure of flexible risers. Generally, the Collapse strength of a flexible riser is designed by considering the effects of initial imperfections, e.g., ovality of the carcass, and radial gap between the carcass/liner and Pressure armor. These two imperfections may cause a significant reduction in the Collapse strength of flexible risers under the flooded annulus condition. However, there are few analytical models available in the public literature that could take those factors into account. In this paper, an analytical approach is presented to predict the Critical Collapse Pressure of the flexible risers with initial imperfections. The analytical results were compared with the numerical simulation, which showed reasonably good agreement.
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A review on predicting Critical Collapse Pressure of flexible risers for ultra-deep oil and gas production
Applied Ocean Research, 2018Co-Authors: Xiao Li, Xiaoli Jiang, Hans HopmanAbstract:Abstract Flexible riser is a key enabler for the oil and gas production in ultra-deep water which transports production fluids between floating production systems and subsea wells. As oil and production heads to water depths in excess of 3000 m, high hydrostatic Pressure has been one primary challenge facing the riser operators. Excessive hydrostatic Pressure may cause Collapse failure of flexible risers and thus predicting the Critical Collapse Pressure is of significant importance to their anti-Collapse design. Collapse is a complex phenomenon related to the material properties, the geometry of the pipe and its overall surface topography and, therefore, makes the prediction of Critical Pressure challenging. Related prediction approaches of flexible risers have been developed for decades, yet a comprehensive review of their predictive capabilities, efficiency and drawbacks is lacking. This paper reviews the recent advances on Collapse studies of flexible risers and highlights the gaps in existing prediction methods, aiming to facilitate the current anti-Collapse design and be a baseline for future utilization of flexible risers in deeper water expansion.
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a strain energy based equivalent layer method for the prediction of Critical Collapse Pressure of flexible risers
Ocean Engineering, 2018Co-Authors: Xiao Li, Xiaoli Jiang, Hans HopmanAbstract:Abstract Flexible risers are being required to be installed in a water depth of over 3000 m for fewer remaining easy-to-access oil fields nowadays. Their innermost carcass layers are designed for external Pressure resistance since the hydrostatic Pressure at such a water depth may cause the Collapse failure of flexible risers. Determining a Critical Collapse Pressure for the carcass is of great importance to the whole structural safety of flexible risers. However, the complexity of the carcass profile always makes FE analysis computational intensive. To overcome that problem, the treatment of the interlocked carcass as an equivalent layer is adopted by researchers to accelerate the anti-Collapse analyses. This paper presents an equivalent layer method to enable that treatment, which obtains the equivalent properties for the layer through strain energy and membrane stiffness equivalences. The strain energy of the carcass was obtained through FE models and then used in a derived equation set to calculate the geometric and material properties for the equivalent layer. After all the equivalent properties have been determined, the FE model of the equivalent layer was developed to predict the Critical Pressure of the carcass. The result of prediction was compared with that of the full 3D carcass model as well as the equivalent models that built based on other existing equivalent methods, which showed that the proposed equivalent layer method performs better on predicting the Critical Pressure of the carcass.
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A Strain Energy-Based Equivalent Layer Method for the Prediction of Critical Collapse Pressure of Flexible Risers
Volume 5: Pipelines Risers and Subsea Systems, 2018Co-Authors: Xiaoli Jiang, Hans HopmanAbstract:Flexible risers are one kind of flexible pipes that transport fluid between subsea facilities and topside structures. This pipe-like structure consists of multiple layers and its innermost carcass layer is designed for external hydrostatic Pressure resistance. For the flexible risers used in ultra-deep water fields, the Critical Collapse Pressure of the carcass layers is one of the dominant factors in their safety design. However, the complexity of the interlocked carcass design introduces significant difficulties and constraints into the engineering analysis. To facilitate the anti-Collapse analysis, equivalent layer methods are demanded to help construct an equivalent pipe that performs a similar Collapse behavior of the carcass. This paper proposes a strain energy based equivalent layer method which trying to bridge the equivalence between those two structures by considering equivalent geometric and material properties for the equivalent layer. Those properties are determined through strain energy equivalence and membrane stiffness equivalence. The strain energy of the carcass is obtained through numerical models and is then used in a derived equation set to calculate the equivalent properties for the equivalent layer. After all the equivalent properties have been determined, an equivalent layer FE model is built and used to predict the Critical Pressure of the carcass. The prediction result is compared to that of the full 3D carcass model as well as the equivalent models that built based on other existing equivalent methods, which shows that the proposed equivalent layer method gives a better performance on predicting the Critical Pressure of the carcass.
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Prediction of the Critical Collapse Pressure of ultra-deep water flexible risers : A literature review
FME Transaction, 2018Co-Authors: Li Xiao, Xiaoli Jiang, Hans HopmanAbstract:Flexible riser is a device which transports production fluids between floating vessels and subsea wells. With fewer remaining easy-to-access oil fields nowadays, flexible risers are being required to be installed in a water depth of over 3000m. However, the hydrostatic Pressure at such a water depth may cause the Collapse of flexible risers, and therefore predicting the Critical Collapse Pressure is of great importance to their design. Riser Collapse is a complex phenomenon related to material properties, geometry of the pipe and its overall surface topography and, therefore, makes the prediction of Critical Pressure challenging. Collapse prediction approaches of flexible risers have been developed for decades, yet a comprehensive review on their predictive capabilities, efficiency and drawbacks is lacking. In this paper, the recent advances on Collapse studies of flexible risers are reviewed, which summarizes the methods developed for Critical Pressure prediction and highlights the related gaps in current research. This review aims to facilitate the current anti-Collapse design and be a baseline for future utilization of flexible risers in deeper water expansion.
Ronald N Zuckermann - One of the best experts on this subject based on the ideXlab platform.
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shaken not stirred collapsing a peptoid monolayer to produce free floating stable nanosheets
Biophysical Journal, 2012Co-Authors: Babak Sanii, Romas Kudirka, Andrew Cho, Neeraja Venkateswaran, Alexander M Olson, Helen Tran, Marika R Harada, Gloria K. Olivier, Li Tan, Ronald N ZuckermannAbstract:Two-dimensional nanomaterials play a Critical role in biology (e.g., lipid bilayers) and electronics (e.g., graphene), but are difficult to directly synthesize with a high level of precision. Biomimetic peptoid nanosheet bilayers are a versatile synthetic platform for constructing multifunctional, precisely ordered two-dimensional nanostructures. Here we show that nanosheet formation occurs through an unusual monolayer intermediate at the air-water interface. Lateral compression of a self-assembled peptoid monolayer beyond a Critical Collapse Pressure results in the irreversible production of nanosheets. An unusual thermodynamic cycle is employed on a preparative scale, where mechanical energy is used to buckle an intermediate monolayer into a more stable nanosheet. Detailed physical studies of the monolayer-compression mechanism revealed a simple preparative technique to produce nanosheets in 95% overall yield, by cyclical monolayer compressions in a rotating closed vial. Compression of monolayers into stable, free-floating products may be a general and preparative approach to access two-dimensional nanomaterials.View Large Image | View Hi-Res Image | Download PowerPoint Slide
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Shaken, not stirred: collapsing a peptoid monolayer to produce free-floating, stable nanosheets.
Journal of the American Chemical Society, 2011Co-Authors: Babak Sanii, Romas Kudirka, Andrew Cho, Neeraja Venkateswaran, Alexander M Olson, Helen Tran, Gloria K. Olivier, Li Tan, R. Marika Harada, Ronald N ZuckermannAbstract:Two-dimensional nanomaterials play a Critical role in biology (e.g., lipid bilayers) and electronics (e.g., graphene) but are difficult to directly synthesize with a high level of precision. Peptoid nanosheet bilayers are a versatile synthetic platform for constructing multifunctional, precisely ordered two-dimensional nanostructures. Here we show that nanosheet formation occurs through an unusual monolayer intermediate at the air–water interface. Lateral compression of a self-assembled peptoid monolayer beyond a Critical Collapse Pressure results in the irreversible production of nanosheets. An unusual thermodynamic cycle is employed on a preparative scale, where mechanical energy is used to buckle an intermediate monolayer into a more stable nanosheet. Detailed physical studies of the monolayer-compression mechanism revealed a simple preparative technique to produce nanosheets in 95% overall yield by cyclical monolayer compressions in a rotating closed vial. Compression of monolayers into stable, free-f...
Babak Sanii - One of the best experts on this subject based on the ideXlab platform.
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shaken not stirred collapsing a peptoid monolayer to produce free floating stable nanosheets
Biophysical Journal, 2012Co-Authors: Babak Sanii, Romas Kudirka, Andrew Cho, Neeraja Venkateswaran, Alexander M Olson, Helen Tran, Marika R Harada, Gloria K. Olivier, Li Tan, Ronald N ZuckermannAbstract:Two-dimensional nanomaterials play a Critical role in biology (e.g., lipid bilayers) and electronics (e.g., graphene), but are difficult to directly synthesize with a high level of precision. Biomimetic peptoid nanosheet bilayers are a versatile synthetic platform for constructing multifunctional, precisely ordered two-dimensional nanostructures. Here we show that nanosheet formation occurs through an unusual monolayer intermediate at the air-water interface. Lateral compression of a self-assembled peptoid monolayer beyond a Critical Collapse Pressure results in the irreversible production of nanosheets. An unusual thermodynamic cycle is employed on a preparative scale, where mechanical energy is used to buckle an intermediate monolayer into a more stable nanosheet. Detailed physical studies of the monolayer-compression mechanism revealed a simple preparative technique to produce nanosheets in 95% overall yield, by cyclical monolayer compressions in a rotating closed vial. Compression of monolayers into stable, free-floating products may be a general and preparative approach to access two-dimensional nanomaterials.View Large Image | View Hi-Res Image | Download PowerPoint Slide
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Shaken, not stirred: collapsing a peptoid monolayer to produce free-floating, stable nanosheets.
Journal of the American Chemical Society, 2011Co-Authors: Babak Sanii, Romas Kudirka, Andrew Cho, Neeraja Venkateswaran, Alexander M Olson, Helen Tran, Gloria K. Olivier, Li Tan, R. Marika Harada, Ronald N ZuckermannAbstract:Two-dimensional nanomaterials play a Critical role in biology (e.g., lipid bilayers) and electronics (e.g., graphene) but are difficult to directly synthesize with a high level of precision. Peptoid nanosheet bilayers are a versatile synthetic platform for constructing multifunctional, precisely ordered two-dimensional nanostructures. Here we show that nanosheet formation occurs through an unusual monolayer intermediate at the air–water interface. Lateral compression of a self-assembled peptoid monolayer beyond a Critical Collapse Pressure results in the irreversible production of nanosheets. An unusual thermodynamic cycle is employed on a preparative scale, where mechanical energy is used to buckle an intermediate monolayer into a more stable nanosheet. Detailed physical studies of the monolayer-compression mechanism revealed a simple preparative technique to produce nanosheets in 95% overall yield by cyclical monolayer compressions in a rotating closed vial. Compression of monolayers into stable, free-f...
Xiaoli Jiang - One of the best experts on this subject based on the ideXlab platform.
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An Analytical Approach for Predicting the Collapse Pressure of the Flexible Risers With Initial Ovalization and Gap
Volume 5A: Pipelines Risers and Subsea Systems, 2019Co-Authors: Xiao Li, Xiaoli Jiang, Hans HopmanAbstract:Abstract A flexible riser is a flexible pipe that transports materials between seafloor and topside structures. As oil and gas production heads to water depths greater than 3000 meters, huge hydrostatic Pressure may cause the Collapse failure of flexible risers. Generally, the Collapse strength of a flexible riser is designed by considering the effects of initial imperfections, e.g., ovality of the carcass, and radial gap between the carcass/liner and Pressure armor. These two imperfections may cause a significant reduction in the Collapse strength of flexible risers under the flooded annulus condition. However, there are few analytical models available in the public literature that could take those factors into account. In this paper, an analytical approach is presented to predict the Critical Collapse Pressure of the flexible risers with initial imperfections. The analytical results were compared with the numerical simulation, which showed reasonably good agreement.
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A review on predicting Critical Collapse Pressure of flexible risers for ultra-deep oil and gas production
Applied Ocean Research, 2018Co-Authors: Xiao Li, Xiaoli Jiang, Hans HopmanAbstract:Abstract Flexible riser is a key enabler for the oil and gas production in ultra-deep water which transports production fluids between floating production systems and subsea wells. As oil and production heads to water depths in excess of 3000 m, high hydrostatic Pressure has been one primary challenge facing the riser operators. Excessive hydrostatic Pressure may cause Collapse failure of flexible risers and thus predicting the Critical Collapse Pressure is of significant importance to their anti-Collapse design. Collapse is a complex phenomenon related to the material properties, the geometry of the pipe and its overall surface topography and, therefore, makes the prediction of Critical Pressure challenging. Related prediction approaches of flexible risers have been developed for decades, yet a comprehensive review of their predictive capabilities, efficiency and drawbacks is lacking. This paper reviews the recent advances on Collapse studies of flexible risers and highlights the gaps in existing prediction methods, aiming to facilitate the current anti-Collapse design and be a baseline for future utilization of flexible risers in deeper water expansion.
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a strain energy based equivalent layer method for the prediction of Critical Collapse Pressure of flexible risers
Ocean Engineering, 2018Co-Authors: Xiao Li, Xiaoli Jiang, Hans HopmanAbstract:Abstract Flexible risers are being required to be installed in a water depth of over 3000 m for fewer remaining easy-to-access oil fields nowadays. Their innermost carcass layers are designed for external Pressure resistance since the hydrostatic Pressure at such a water depth may cause the Collapse failure of flexible risers. Determining a Critical Collapse Pressure for the carcass is of great importance to the whole structural safety of flexible risers. However, the complexity of the carcass profile always makes FE analysis computational intensive. To overcome that problem, the treatment of the interlocked carcass as an equivalent layer is adopted by researchers to accelerate the anti-Collapse analyses. This paper presents an equivalent layer method to enable that treatment, which obtains the equivalent properties for the layer through strain energy and membrane stiffness equivalences. The strain energy of the carcass was obtained through FE models and then used in a derived equation set to calculate the geometric and material properties for the equivalent layer. After all the equivalent properties have been determined, the FE model of the equivalent layer was developed to predict the Critical Pressure of the carcass. The result of prediction was compared with that of the full 3D carcass model as well as the equivalent models that built based on other existing equivalent methods, which showed that the proposed equivalent layer method performs better on predicting the Critical Pressure of the carcass.
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A Strain Energy-Based Equivalent Layer Method for the Prediction of Critical Collapse Pressure of Flexible Risers
Volume 5: Pipelines Risers and Subsea Systems, 2018Co-Authors: Xiaoli Jiang, Hans HopmanAbstract:Flexible risers are one kind of flexible pipes that transport fluid between subsea facilities and topside structures. This pipe-like structure consists of multiple layers and its innermost carcass layer is designed for external hydrostatic Pressure resistance. For the flexible risers used in ultra-deep water fields, the Critical Collapse Pressure of the carcass layers is one of the dominant factors in their safety design. However, the complexity of the interlocked carcass design introduces significant difficulties and constraints into the engineering analysis. To facilitate the anti-Collapse analysis, equivalent layer methods are demanded to help construct an equivalent pipe that performs a similar Collapse behavior of the carcass. This paper proposes a strain energy based equivalent layer method which trying to bridge the equivalence between those two structures by considering equivalent geometric and material properties for the equivalent layer. Those properties are determined through strain energy equivalence and membrane stiffness equivalence. The strain energy of the carcass is obtained through numerical models and is then used in a derived equation set to calculate the equivalent properties for the equivalent layer. After all the equivalent properties have been determined, an equivalent layer FE model is built and used to predict the Critical Pressure of the carcass. The prediction result is compared to that of the full 3D carcass model as well as the equivalent models that built based on other existing equivalent methods, which shows that the proposed equivalent layer method gives a better performance on predicting the Critical Pressure of the carcass.
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Prediction of the Critical Collapse Pressure of ultra-deep water flexible risers : A literature review
FME Transaction, 2018Co-Authors: Li Xiao, Xiaoli Jiang, Hans HopmanAbstract:Flexible riser is a device which transports production fluids between floating vessels and subsea wells. With fewer remaining easy-to-access oil fields nowadays, flexible risers are being required to be installed in a water depth of over 3000m. However, the hydrostatic Pressure at such a water depth may cause the Collapse of flexible risers, and therefore predicting the Critical Collapse Pressure is of great importance to their design. Riser Collapse is a complex phenomenon related to material properties, geometry of the pipe and its overall surface topography and, therefore, makes the prediction of Critical Pressure challenging. Collapse prediction approaches of flexible risers have been developed for decades, yet a comprehensive review on their predictive capabilities, efficiency and drawbacks is lacking. In this paper, the recent advances on Collapse studies of flexible risers are reviewed, which summarizes the methods developed for Critical Pressure prediction and highlights the related gaps in current research. This review aims to facilitate the current anti-Collapse design and be a baseline for future utilization of flexible risers in deeper water expansion.