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Longbin Tao - One of the best experts on this subject based on the ideXlab platform.
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experimental and numerical studies of the pontoon effect on vortex induced motions of deep draft semi submersibles
Journal of Fluids and Structures, 2017Co-Authors: Mingyue Liu, Longfei Xiao, Yibo Liang, Longbin TaoAbstract:The vortex-induced motion (VIM) is a critical issue in mooring and riser system design for column-type deepwater platforms. As regards to deep-draft semi-submersibles (DDS), even though VIM is mainly excited by vortex shedding around columns, the large-volume Pontoons beneath the columns are also responsible for the wake interference, implying a non-negligible influence on VIM behavior. An experimental study and three-dimensional numerical simulations were performed to analyze the pontoon effect on the VIM of two semi-submersibles and a four-column structure without Pontoons. The numerical results using Detached Eddy Simulation (DES) are in good agreement with the experimental measurements obtained from the towing model tests. The present investigations indicate that the resonant phenomenon is observed for all configurations. However, the four-column structure without Pontoons shows the most significant transverse responses and yaw motions at both 0°- and 45°-incidences owing to the largest fluctuating lift forces induced by the well-established wake. Additionally, the negative values of work done by the Pontoons at all reduced velocities confirm their damping effect on the VIM response.
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numerical analysis of pontoon effect on flow induced forces of the deep draft semisubmersible in a cross flow
ASME 2015 34th International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 2015Co-Authors: Mingyue Liu, Longfei Xiao, Haining Lyu, Longbin TaoAbstract:Deep draft semisubmersible (DDS) concepts have been developed recently in order to improve the vertical motion characteristics of the platform, due to the smaller wave exciting forces on the Pontoons than a conventional semisubmersible. However, the DDS may experience critical vortex-induced motions (VIM) stemming from the fluctuating forces in a strong current environment. Aiming to investigate the excitation loads and the mechanism of VIM, Computational Fluid Dynamics (CFD) analyses are performed to study the flow around the DDS in a cross-flow. Special attentions are paid to the effect of the pontoon and the heading angle. Good agreement between CFD simulations and model test results for the current loads of a DDS is observed. Detailed computational results including hydrodynamic loads and flow patterns are presented.Copyright © 2015 by ASME
Mingyue Liu - One of the best experts on this subject based on the ideXlab platform.
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experimental and numerical studies of the pontoon effect on vortex induced motions of deep draft semi submersibles
Journal of Fluids and Structures, 2017Co-Authors: Mingyue Liu, Longfei Xiao, Yibo Liang, Longbin TaoAbstract:The vortex-induced motion (VIM) is a critical issue in mooring and riser system design for column-type deepwater platforms. As regards to deep-draft semi-submersibles (DDS), even though VIM is mainly excited by vortex shedding around columns, the large-volume Pontoons beneath the columns are also responsible for the wake interference, implying a non-negligible influence on VIM behavior. An experimental study and three-dimensional numerical simulations were performed to analyze the pontoon effect on the VIM of two semi-submersibles and a four-column structure without Pontoons. The numerical results using Detached Eddy Simulation (DES) are in good agreement with the experimental measurements obtained from the towing model tests. The present investigations indicate that the resonant phenomenon is observed for all configurations. However, the four-column structure without Pontoons shows the most significant transverse responses and yaw motions at both 0°- and 45°-incidences owing to the largest fluctuating lift forces induced by the well-established wake. Additionally, the negative values of work done by the Pontoons at all reduced velocities confirm their damping effect on the VIM response.
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experimental investigation into the influences of pontoon and column configuration on vortex induced motions of deep draft semi submersibles
Ocean Engineering, 2016Co-Authors: Mingyue Liu, Longfei Xiao, Junqi ShiAbstract:Abstract Deep-draft design of semi-submersibles improves vertical motions but leads to critical vortex-induced motions (VIM) attributable to fluctuating loads on columns. As characteristic components, both columns and Pontoons produce complex wake interference and thus have significant influences on the VIM of semi-submersibles. This paper presents an experimental study on VIM of deep-draft semi-submersibles (DDS) to examine the effects of Pontoons and column configuration. There were four test models including four-pontoon DDS, two-pontoon DDS, four-square-column structure and four-rhombic-column structure with no Pontoons. A number of current headings and reduced velocities were considered. The main results reveal that the two-pontoon DDS can generate larger lift forces in comparison with the four-pontoon DDS; consequently, the transverse motion amplitudes at high reduced velocities are larger. However, the four-square-column structure with no Pontoons shows the most significant transverse and yaw responses owing to the largest excitation forces induced by the well-established wake. On the other hand, similar trend and values in the transverse response are observed for the four-square-column structure at the 45° current heading and for the four-rhombic-column structure at the 0° current heading. The incidence angle related to columns has more significant effect on the VIM of DDS than that related to the platform.
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numerical analysis of pontoon effect on flow induced forces of the deep draft semisubmersible in a cross flow
ASME 2015 34th International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 2015Co-Authors: Mingyue Liu, Longfei Xiao, Haining Lyu, Longbin TaoAbstract:Deep draft semisubmersible (DDS) concepts have been developed recently in order to improve the vertical motion characteristics of the platform, due to the smaller wave exciting forces on the Pontoons than a conventional semisubmersible. However, the DDS may experience critical vortex-induced motions (VIM) stemming from the fluctuating forces in a strong current environment. Aiming to investigate the excitation loads and the mechanism of VIM, Computational Fluid Dynamics (CFD) analyses are performed to study the flow around the DDS in a cross-flow. Special attentions are paid to the effect of the pontoon and the heading angle. Good agreement between CFD simulations and model test results for the current loads of a DDS is observed. Detailed computational results including hydrodynamic loads and flow patterns are presented.Copyright © 2015 by ASME
Nathan J Bott - One of the best experts on this subject based on the ideXlab platform.
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the effect of different treatment strategies on cardicola spp trematoda aporocotylidae infection in ranched southern bluefin tuna thunnus maccoyii from port lincoln south australia
Aquaculture, 2019Co-Authors: Cecilia Power, Claire Webber, Kirsten Rough, Robin Staunton, B F Nowak, Nathan J BottAbstract:The aporocotylids Cardicola forsteri and C. orientalis are considered one of the most significant health concerns for Southern Bluefin Tuna (SBT) ranched off Port Lincoln, South Australia. In this study we compared the effects of different treatment strategies on blood fluke infections in ranched SBT by sampling from one untreated and two praziquantel treated Pontoons progressively throughout the 2018 season. Severity of infection was assessed relative to a number of criteria including adult fluke counts from hearts, egg counts from gill filaments and the use of specific quantitative polymerase chain reaction (qPCR) for detection of C. forsteri and C. orientalis ITS-2 DNA in SBT hearts and gills. Cardicola forsteri was the dominant species detected in this study, and intensity of C. forsteri infection in SBT was significantly higher in the untreated pontoon than the two treated Pontoons from week 8 of ranching. Cardicola orientalis in SBT was rarely detected, and no significant differences were seen in mortalities or condition of SBT between Pontoons. Comparing diagnostic methods for C. forsteri in SBT heart demonstrated qPCR as the gold standard. This study provides important insights into the continued efficacy of praziquantel on blood fluke infections in ranched SBT.
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concurrent epizootic hyperinfections of sea lice predominantly caligus chiastos and blood flukes cardicola forsteri in ranched southern bluefin tuna
Veterinary Parasitology, 2010Co-Authors: C Hayward, Nathan J Bott, David Ellis, Danielle Foote, Ryan J Wilkinson, Phillip B B Crosbie, B F NowakAbstract:Peaks in epizootics of sea lice (mostly Caligus chiastos) and blood flukes (Cardicola forsteri) among Southern Bluefin tuna (Thunnus maccoyii) appear to coincide with the onset of an increased mortality. The mortality event occurs 6–12 weeks after T. maccoyii have been transferred into static ranching Pontoons from the wild. However, to date available data on parasite occurrence before commercial harvesting begins, are scant. This research gathered epizootiological data from weeks 4 to 13 post-transfer, for 153 T. maccoyii sampled from two research and four commercial Pontoons. Counts of both parasites in the research Pontoons reached levels far heavier than previously documented in ranched T. maccoyii. For sea lice, the prevalence in most Pontoons was 100%; the highest intensity reached 495 individuals, and mean counts at the peak of the infection exceeded 265 lice per fish. Almost all of the 5407 individual lice counted were identified as adult C. chiastos (89.44% female, 10.14% male); adult females of two other species were also present, C. amblygenitalis (0.13%), in addition to an undescribed species, C. sp. (0.04%). Lice counts were correlated positively with gross eye pathology scores (rs,151df = 0.3394, p = 0.0000), negatively correlated with condition index (rs,151df = −0.5396, p = 0.0000), and positively correlated with plasma cortisol (rs,131df = 0.3906, p = 0.0000) and glucose (rs,131df = 0.2240, p = 0.0096). For the blood fluke, prevalences were less uniform than those of sea lice, with lower rates of infection at the beginning (ranging from 10% to 40%), reaching 100% mid-study, and declining again (40% in one pontoon). The highest intensity reached 441 individual flukes. Fluke counts were negatively correlated with plasma haemoglobin (rs,151df = −0.2436, p = 0.0051) and positively with lysozyme (rs,151df = 0.3013, p = 0.0019). Fluke counts were also correlated with sea lice counts (rs,150df = 0.3143, p = 0.0000). Peaks in these epizootics occurred near the onset of elevated mortalities, which started after 7 weeks of ranching.
B F Nowak - One of the best experts on this subject based on the ideXlab platform.
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the effect of different treatment strategies on cardicola spp trematoda aporocotylidae infection in ranched southern bluefin tuna thunnus maccoyii from port lincoln south australia
Aquaculture, 2019Co-Authors: Cecilia Power, Claire Webber, Kirsten Rough, Robin Staunton, B F Nowak, Nathan J BottAbstract:The aporocotylids Cardicola forsteri and C. orientalis are considered one of the most significant health concerns for Southern Bluefin Tuna (SBT) ranched off Port Lincoln, South Australia. In this study we compared the effects of different treatment strategies on blood fluke infections in ranched SBT by sampling from one untreated and two praziquantel treated Pontoons progressively throughout the 2018 season. Severity of infection was assessed relative to a number of criteria including adult fluke counts from hearts, egg counts from gill filaments and the use of specific quantitative polymerase chain reaction (qPCR) for detection of C. forsteri and C. orientalis ITS-2 DNA in SBT hearts and gills. Cardicola forsteri was the dominant species detected in this study, and intensity of C. forsteri infection in SBT was significantly higher in the untreated pontoon than the two treated Pontoons from week 8 of ranching. Cardicola orientalis in SBT was rarely detected, and no significant differences were seen in mortalities or condition of SBT between Pontoons. Comparing diagnostic methods for C. forsteri in SBT heart demonstrated qPCR as the gold standard. This study provides important insights into the continued efficacy of praziquantel on blood fluke infections in ranched SBT.
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concurrent epizootic hyperinfections of sea lice predominantly caligus chiastos and blood flukes cardicola forsteri in ranched southern bluefin tuna
Veterinary Parasitology, 2010Co-Authors: C Hayward, Nathan J Bott, David Ellis, Danielle Foote, Ryan J Wilkinson, Phillip B B Crosbie, B F NowakAbstract:Peaks in epizootics of sea lice (mostly Caligus chiastos) and blood flukes (Cardicola forsteri) among Southern Bluefin tuna (Thunnus maccoyii) appear to coincide with the onset of an increased mortality. The mortality event occurs 6–12 weeks after T. maccoyii have been transferred into static ranching Pontoons from the wild. However, to date available data on parasite occurrence before commercial harvesting begins, are scant. This research gathered epizootiological data from weeks 4 to 13 post-transfer, for 153 T. maccoyii sampled from two research and four commercial Pontoons. Counts of both parasites in the research Pontoons reached levels far heavier than previously documented in ranched T. maccoyii. For sea lice, the prevalence in most Pontoons was 100%; the highest intensity reached 495 individuals, and mean counts at the peak of the infection exceeded 265 lice per fish. Almost all of the 5407 individual lice counted were identified as adult C. chiastos (89.44% female, 10.14% male); adult females of two other species were also present, C. amblygenitalis (0.13%), in addition to an undescribed species, C. sp. (0.04%). Lice counts were correlated positively with gross eye pathology scores (rs,151df = 0.3394, p = 0.0000), negatively correlated with condition index (rs,151df = −0.5396, p = 0.0000), and positively correlated with plasma cortisol (rs,131df = 0.3906, p = 0.0000) and glucose (rs,131df = 0.2240, p = 0.0096). For the blood fluke, prevalences were less uniform than those of sea lice, with lower rates of infection at the beginning (ranging from 10% to 40%), reaching 100% mid-study, and declining again (40% in one pontoon). The highest intensity reached 441 individual flukes. Fluke counts were negatively correlated with plasma haemoglobin (rs,151df = −0.2436, p = 0.0051) and positively with lysozyme (rs,151df = 0.3013, p = 0.0019). Fluke counts were also correlated with sea lice counts (rs,150df = 0.3143, p = 0.0000). Peaks in these epizootics occurred near the onset of elevated mortalities, which started after 7 weeks of ranching.
Sean D. Connell - One of the best experts on this subject based on the ideXlab platform.
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urban structures as marine habitats an experimental comparison of the composition and abundance of subtidal epibiota among pilings Pontoons and rocky reefs
Marine Environmental Research, 2001Co-Authors: Sean D. ConnellAbstract:There remains little understanding of the relationship between the ecologies of urban habitats (pilings and Pontoons) and natural habitats (rocky reef) for sessile plants and animals (epibiota) living on urbanised coasts. This study describes the structure of subtidal assemblages of epibiota among pilings, Pontoons and adjacent rocky reef in Sydney Harbour, Australia. I tested the prediction that the experimental provision of substrata of the same age and composition in all three habitats would produce assemblages that: (1) differed among all three habitats; and (2) differed most on floating Pontoons relative to the two fixed habitats (pilings and reef). As predicted, the results suggested that both pilings and Pontoons, particularly the latter, create novel habitats for epibiotic assemblages independent of age and composition of substratum. It is not fully understood why these urban structures act as such different habitats from natural rocky reefs. The important point is that they are different and we are yet to understand the implications of this for the ecology of coastal areas subject to urbanisation.
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Predatory fish do not always affect the early development of epibiotic assemblages.
Journal of experimental marine biology and ecology, 2001Co-Authors: Sean D. ConnellAbstract:Foraging by predatory fish is thought to be one of the primary ecological processes affecting the abundances of plants and animals in subtidal habitats. The importance of this process was assessed on the subtidal surfaces of urban structures (Pontoons and pilings) that represent major coastal habitats for marine organisms. Fish feed with greater intensity on epibiota attached to pilings than Pontoons and it was hypothesised that greater predation on pilings explained why the structure of epibiotic assemblages differs between these habitats. I predicted that the structure of epibiotic assemblages would develop differently between pilings and Pontoons in the presence of fish (plates open to predation) but not in the absence of fish (plates inside exclusion cages). Results revealed large differences in abundance between pilings and Pontoons that were largely independent of the caged and uncaged plates. Predation may be intense (as it appeared on pilings) but unimportant because it does not explain observed abundances of prey (epibiota between pilings and Pontoons).
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Floating Pontoons create novel habitats for subtidal epibiota
Journal of Experimental Marine Biology and Ecology, 2000Co-Authors: Sean D. ConnellAbstract:Urban structures in the form of Pontoons and pilings represent major coastal habitats for marine organisms and understanding the factors causing abundances of organisms to differ between these and natural habitat has been neglected in the study of coastal ecology. It has been proposed that composition of substrata explain differences previously described between subtidal assemblages of epibiota on rocky reef (sandstone) and Pontoons (concrete) in Sydney Harbour, Australia. This study tested the hypothesis that differences in the composition of substratum (sandstone vs. concrete) independent of type of habitat (rocky reef vs. pontoon) affects the development of epibiotic assemblages. This was tested by experimentally providing substratum of the two types in both habitats. Epibiotic assemblages were unaffected by the composition of substratum but strongly affected by the type of habitat; demonstrating that Pontoons constitute novel habitats for epibiota. This result highlights a need for determining how current ecological understanding of subtidal epibiota, which is heavily based on studies of urban structures (pilings and Pontoons), relates to natural reef. Future tests of hypotheses about the nature of these differences will not only contribute to better ecological understanding of epibiota and their use of urban structures as habitats, but also to better predictions of future changes to the ecology of coastal habitats.
