Back Eddy Research Articles

A Numerical Simulation Study and Effectiveness Evaluation on the Flow Field Effect of Trapezoidal Artificial Reefs in Different Layouts

The combined release of artificial reefs in different quantities and arrangements leads to different flow field effects. This study designs a small trapezoidal artificial reef. To optimize the quantity and layout of these reefs, trapezoidal reefs in three different layouts were selected for analysis at five different velocity gradients (0.1, 0.5, 1.0, 1.5, and 2.0 m/s). The effects of disposal spacing and layout on the flow field effect of trapezoidal artificial reefs at different flow velocities were simulated using Ansys Fluent. According to the findings: after simulation, flow velocity could indirectly reflect the distribution of upwelling and back eddy, the scale and strength of upwelling increased as flow velocity increased, and the back eddy showed no obvious variation with flow velocity. In transverse combination mode, both the scale and strength of the upwelling and back eddy were maximized when the reef spacing was 1.0 L; in longitudinal combination mode, upwelling and back eddy reached maximum scale and strength when the disposal spacing of the reefs was 1.5 L of a single reef. In 2020, flow mapping and fishery surveys were carried out in the engineering pilot area. The results showed that the number and species of fish populations with 1.5 L spacing in the vertical combination method were significantly higher than those in other forms, and the structure of the fish reef was stable without any flipping or sliding phenomenon. This study can provide a theoretical reference for the design and the actual deployment of artificial reefs to improve the ecological restoration of the water.

A CFD Analysis of Decommissioned Oil Platforms Jackets on the Brazilian Coast

Every facility reaches the last phase in its life cycle, which is decommissioning. Since the last decade, this subject has been gaining importance in Brazil’s offshore oil and gas companies. For jacket type rigs, one of the methods widely applied after idling the production is the conversion of these structures into artificial reefs (ARs). There are several critical aspects for choosing the best strategy for cutting and sinking a platform jacket, ensuring the success of an AR from a biological point of view. One of them is the influence of marine currents and their fluid-structure interaction which, by maximizing local upwelling and back vortex effects, favours the growth of aggregated flora and fauna. This study consists in the application of computational fluid dynamics (CFD) techniques for studying the marine flow around a disassembled and sunk jacket in the seabed for the purpose of converting it into an artificial reef. An FVM (Finite Volume Method) from a commercial software (most recent version of ANSYS FLUENT®) is applied with the upwind scheme. A k-ε turbulence model on steady state is chosen. Field data about Brazilian coastal currents are collected and analysed from the amount of information available on a Brazilian Navy's meteoceanographic program. Next, different combinations of cutting and sinking a jacket are studied, always keeping a minimum 55m free water column. The objective is to verify where the formation of local upwelling regions - that is, where the vertical velocity component reaches values equal or greater than 10% of the magnitude of the free flow velocity - is more significant, without decreasing back eddy formation. It is observed that the dismemberment of the jacket with the positioning of its parts in an increasing height sequence in the direction of the prevailing current is favourable to generate local upwelling while tipping the structure at 90° to the prevailing current results in the most voluminous back eddy region.

Computational Fluid Dynamics Analysis of Rigs-to-Reefs (R2R) Jacket Structures

Platform decommissioning activities have been increasing due to unproductive fields and unstable oil prices. One of the decommissioning methods used by the oil and gas companies is by converting the platform into an artificial reef through the rigs-to-reef (R2R) programme. The programme benefits the marine life and increases the marine productions. In this study, the dynamic responses and flow characteristics of jacket platforms were investigated using computational fluid dynamics (CFD) analysis. Three jacket structures with different sizes were used to investigate the suitability of the structure as a potential artificial reef. The pressure exerted on the structure as well as the back eddies and upwelling phenomenon were also investigated. This is to ensure the settlement of the coral larvae and attract marine life to inhabit around the artificial reef. The results show that the platform size and configurations are the significant criteria to design any artificial reef. The pressure on the jacket member is in the acceptable range. Higher efficiency index of back eddy and upwelling could also be obtained by smaller jacket structures.

Study on the influence of cut-opening ratio, cut-opening shape, and cut-opening number on the flow field of a cubic artificial reef

Upwelling and back eddy are usually selected as obvious indices to study the characteristics of the flow field of artificial reefs. The influences of cut-opening ratio (OR), cut-opening shape (OS), and cut-opening number (ON) on the flow field of a cubic artificial reef were investigated. A Reynolds-averaged Navier–Stokes equation was established to solve the flow field of an artificial reef. Based on the finite volume method, the standard k-ε model was used to discretize the Reynolds-averaged Navier–Stokes equation. Flume model experiments were carried out to validate the accuracy of the numerical simulation. A multivariate analysis of variance was used to analyze the diversities of the OR, OS, and ON. The results showed that the upwelling velocities, including the maximum upwelling velocity and the volume-weighted average velocity, changed less with the above three factors. The ON and OR had prominent effects on the volume of upwelling and back eddy, while the OS had the least effect. A reasonable arrangement of ON and OR can enhance the field of upwelling and back eddy while an excessive OR or ON can weaken them. This study provided a scientific reference for the optimal design of cubic artificial reefs.

Analysis and Study of Back Eddy Flow Field Effecting Compact by Angle of Meeting Flow of Reef

By changing artificial-reefs meeting flow angle, Use the CFD imitate three-dimensional flow field under the compaction of constant flow, and analyze the effect of back eddy flow field quantitatively. The results show that, with the reduction of the angle of the meeting flow, the length; height; width of back eddy has the tendency of becoming small; when the angle become Ninety the effecting of the back eddys flow field is the best.

Airflow reversal and alternating corkscrew vortices in foredune wake zones during perpendicular and oblique offshore winds

On all sandy coastlines fringed by dunes, understanding localised air flow allows us to examine the potential sand transfer between the beach and dunes by wind-blown (Aeolian) action. Traditional thinking into this phenomenon had previously included only onshore winds as effective drivers of this transfer. Recent research by the authors, however, has shown that offshore air-flow too can contribute significantly, through lee-side back eddies, to the overall windblown sediment budget to coastal dunes. Under rising sea levels and increased erosion scenarios, this is an important process in any post-storm recovery of sandy beaches. Until now though, full visualisation in 3D of this newly recognised mechanism in offshore flows has not been achieved. Here, we show for the first time, this return flow eddy system using 3D computational fluid dynamics modelling, and reveal the presence of complex corkscrew vortices and other phenomena. The work highlights the importance of relatively small surface undulations in the dune crest which act to induce the spatial patterns of airflow (and transport) found on the adjacent beach.

Summer habitat use and feeding of juvenile Arctic charr, Salvelinus alpinus, in the Canadian High Arctic

Abstract – Owing to limited knowledge of the habitat use and diet of juvenile Arctic charr from the High Arctic, particularly young‐of‐the‐year (YOY), we assembled data obtained from samples taken in and around Lake Hazen, Nunavut, Canada, to assess juvenile habitat use and feeding. Juvenile charr demonstrated a preference for stream environments, particularly those fed by warm upstream ponds. Charr occupying both stream and nearshore lake habitats were found to feed similarly, with chironomids occurring most frequently in diets. Some older stream‐dwelling charr preyed on smaller, younger Arctic charr. Preferred stream occupancy is likely mediated by physical barriers created mainly by water velocity, and by distance from the lake, lake‐ice dynamics, low water depth, and turbidity. Water velocities resulted in stream habitat segregation by size, with YOY mainly found in low‐velocity pools and back eddies adjacent to stream banks, but not in water velocities >0.1 m·s−1. Greatest charr densities in streams were found in small, shallow, slow‐flowing side channels, which are highly susceptible to drought. Under predicted climate change scenarios, streams fed by small ponds will be susceptible to intermittent flow conditions, which could result in increased competition among juvenile charr for the remaining stream habitats. In addition, glacier‐fed streams are likely to experience increased flow conditions that will exacerbate physical barriers created by water velocity and further reduce the availability of preferred stream habitat.

A wind tunnel simulation of the effects of stoss slope on the lee airflow pattern over a two-dimensional transverse dune

[1] Secondary airflow plays an important role in dune formation and development. The lee airflow pattern over transverse dunes is important in determining the shape, alignment, and spacing of dunes and is influenced significantly by the lee slope angle. In this paper we present the results of scaled wind tunnel simulations of the effects of stoss slope on the mean lee airflow patterns of transverse dunes. The leeward velocity field was measured nonintrusively using particle image velocimetry to assess the airflow pattern. We found that the flow separated over the dunes with a leeward angle close to the slip face angle of natural transverse dunes and was insensitive to stoss angle. Separation cells were characterized by a back eddy. Reattachment distance, height, area, and aspect ratio were used to characterize the separation cell. The first three parameters increased with increasing stoss angle for angles less than 15° but remained constant or decreased slightly with angles greater than 15°. On the basis of the leeward velocity profiles, six flow regions corresponding to those in previous models were recognized. These regions are initially bounded by kinks but gradually transition downwind and merge to recover a uniform velocity profile after a significant distance. We suggest that the separation cell is most developed when the angle of stoss slope reaches 15°, but the significance of this angle in the evolution of transverse dunes needs further exploration.

Back Eddies of Learning In the Recognition of Prior Learning: A Case Study

The limited research that exists in the area of prior learning assessment (PLA) has tended to be descriptive and conceptual in nature. Where empirical studies have been done, they have focussed mainly on PLA as a means of credentialing rather than as a learning experience. Furthermore, there has been very little empirical research into the educational effectiveness of PLA from the student’s point of view. This empirical study used a qualitative approach to investigate the perceptions of a focus group of 32 adult learners who were engaged in portfolio-based PLA in an open and distance education university. The study explored students’ initial expectations of PLA, what they think they got out of the process, and the extent to which these perceived benefits of PLA would extend to other adult students. The study examined the question of whether PLA operates as a motivator or as a selection mechanism and concluded that there was evidence for both factors. Further results indicated that, in general, PLA learners were surprised to find they had been engaged in a learning process. The study concludes that PLA can be an effective educational opportunity for certain kinds of adult learners, but it should not be taken as a panacea.

Bubbles in a back eddy: A commentary on “The origin, diagnostic attributes and practical application of coevolutionary theory”

Winder, McIntosh, and Jeffrey (2005) thread acritique of bDevelopment BetrayedQ through an unu-sual reading of the history of evolutionary thought.Some of their commentary is interesting; frequently itis colorfully portrayed. For example, Winder et al.write that bIn emphasising the pervasiveness of co-evolution in socio-natural dynamics, Norgaard isdecanting the old wine of complex system theoryinto co-evolutionary skins. But there is even olderwine in those skins; the Darwin–Huxley synthesis,and we are reluctant to see it poured into the sandto accommodate the later vintage.Q These are grandwords a little harshly delivered from the perspectiveof a historian of science.Let me ascend to their rhetorical heights and reflecton the history of evolutionary thought from on high aswell. Winder et al. focus on a supposed bDarwin–HuxleyQsynthesis,aparticularjoiningofthought.Loo-kingatthehistoryofbiology,Iseealargebraidedriver,like the big rivers I have known carving broad valleysas they come out of the mountains of Alaska. Streamsofthoughtintheriverjoin,theirwatersforevermixing,yet the river keeps dividing while new rivers join in aswell. I see the currents of evolutionary thinking todayswelling with turbulence as they mix with new knowl-edgeindevelopmentalbiology.Andfromthisperspec-tive, the critique of Winder et al. on bDevelopmentBetrayedQ looks like bubbles in a back eddy.Winder et al. note bNorgaard has found in biologya set of ideas that are dgood to think withT and usedthem to communicate important ideas about connect-edness and complexity.Q I like this constructive char-acterization of my work. It conveys the pragmatism ofmy effort quite well. And how can I argue againstpraise like bthe pioneering work of Richard Norgaard(1984, 1994)...undoubtedly represents an importantformative contribution to both the current state and thefuture trajectory of co-evolutionary theory as appliedto socio-natural scienceQ?The problem is that Winder et al. rally little evi-dence to support the argument that bDevelopmentBetrayedQ represents a significant joining of currentsitself. Does it really demarcate an important conflu-ence in the river of thought, a joining of significantstreams that now have a momentum of their own.Might the work of C.J. Lumsden and E.O. Wilson(1981), Peter Corning (1983),orWilliam Durham(1991), for example, better demarcate the joining ofcurrents? Indeed, looking more closely, I see that theproblem is that we are multiple communities of scho-

Holding the Indigenous Voice Hostage

It is a point well documented in American history, and well remembered, that the firearm has been a favorite tool wielded by Euroamericans to subdue, colonize, and silence Native Americans since the two groups first met. Anyone exercising a modicum of intellect can easily compile their own mental count of past atrocities by racist-minded, gun-toting Euroamericans against America's Indigenous peoples. Some incidents that come to mind are obvious ones: the removal of southeastern tribes westward or the Dine's Long Walk eastward, both the nineteenthand the twentieth-century Wounded Knee episodes, Bacon's Rebellion, Prophetstown, Horseshoe Bend, the killing fields of California, Sand Creek, the Washita, the murders of Crazy Horse and Sitting Bull, and so on. But be cautious of cataloguing such injustices or you are bound to send your blood pressure shooting skyward. Beyond divesting Native Americans of their lands, such nefarious behavior was also intended to silence their voices. And as reprehensible as these past atrocities were (and still are), what is as morally objectionable today (and what many may not realize) is that even in the outer rings of academia the firearm remains an instrument of colonization by white power elites that keeps the Native American voice silent; and that alone is disturbing. Where in academia is the still put to such troubling use? At institutions masquerading as centers of academic worth and legitimacy known as museums. Even in the twenty-first century, following decades of social, subaltern, and revisionist study, museums remain intellectual back eddies where certain segments of society intentionally and emphatically silence Indigenous voices. How? Why? Typically, an establishment of administrators and powerful gun nuts (most often wealthy white

Theoretical Bases for Karyotype Evolution. 1. The Minimum-Interaction Hypothesis

Data from the literature (tables 1, 2; fig. 1) show that the relative probabilities of occurrence for the various categories of spontaneous chromosomal mutations do not match those predicted by both the random-contact-and-exchange model (basically equivalent to the exchange theory of Revell) and the random-breakage-and-reunion model (i.e., the breakage-and-reunion theory of Sax or of Muller). These models do not take into account recent findings that, during the meiotic prophase and especially at pachytene, eukaryote chromosomes are attached by each end to the nuclear membrane, leading to a configuration we term the "suspension-arch structure" (fig. 3). We recalculated the relative probabilities of the occurrence of spontaneous chromosomal mutations given the suspension-arch structure and assuming that these rearrangements arise from errors in the resolution of interlockings between bivalents and a special type of crossover that we call the "hetero-site" crossover (figs. 2, 3, 6, 7). From these calculations we found that the relative probability of the occurrence of reciprocal translocations (the most fitness-damaging rearrangement) declines with increases in chromosome number and in nuclear volume (fig. 5). We also found that paracentric inversions occur increasingly more often than pericentric ones as the centromere position becomes more terminal and the distance between attachments to the nuclear membrane becomes greater (this distance increases as nuclear volume increases; fig. 8). These results are in accord with the cytogenetic data from Drosophila, humans, and ants. A puzzling phenomenon is that the relative rates of radiation-induced chromosomal mutations differ greatly from those calculated under the suspension-archstructure model and from rates of spontaneous chromosomal mutations. We propose the testable hypotheses that (1) most spontaneous chromosomal mutations occur in synaptonemal complexes and involve crossovers and errors in the resolution of interlockings, and (2) radiation and chemical mutagens allow rearrangements when chromosomes intersect at any stage (fig. 10). These considerations lead to the "minimum-interaction hypothesis," which states that karyotype evolution has been in large part shaped by selection to reduce the occurrence of such fitness-reducing spontaneous chromosomal mutations as reciprocal translocations. Some of the response to this selection is the result of the improvement of DNA-repair mechanisms, increased contraction of the chromosomes caused by higher-order helix formation, and the development of sex-chromosome heteropycnosis. We concentrate on examining two further, interacting responses in the light of the hypothesis. One of these is increase in nuclear volume (fig. 9), but if the ratio of genome size to nuclear volume is high, then an increase in chromosome number, caused by such factors as centric fission, is adaptive because it reduces the occurrence of reciprocal translocation. Although chromosome number can be reduced by centric fusion, such instances seem to be "back eddies" in the mainstream of karyotype evolution.

Quantitative Analysis of Directionality in Mammalian Karyotype Evolution.

The ancestral mammalian karyotype had been hypothesized to have had 2n ≈ 80 (the "fusion hypothesis"), 2n = 6-14 (the "fission hypothesis") or a diploid number close to the present mode (the "modal hypothesis"). The fusion hypothesis has long been the dominant paradigm in the study of karyotype evolution, but recent evidence favors the fission hypothesis, and our analysis also strongly supports fission as the predominant rearrangement compared to fusion. To formalize our analysis, we first define $$\overline A$$ chromosomes as a group containing both acrocentrics and telocentrics, and $$\overline M$$ chromosomes as all the rest. Given this dichotomy, we then divide pericentric inversions into three types according to whether they convert $$\overline A$$ chromosomes to $$\overline M$$ , $$\overline M$$ to $$\overline A$$ or make no interchange. Only the first two types, denoted p.i. $$(\overline {AM})$$ and p.i. $$(\overline {MA})$$ , are important for the analysis. If fusion predominates, the direction of karyotype evolution is determined by the overall joint action of centric fusions and p.i. $$(\overline {MA})$$ (the "fusion cycle"), whereas, if fission predominates, the chief rearrangements are fission and p.i. $$(\overline {AM})$$ (the "fission cycle"). The necessary predominance of p.i. $$(\overline {MA})$$ over p.i. $$(\overline {AM})$$ in the fusion cycle makes it extremely unlikely on a priori grounds that this cycle has been very important in mammalian karyotype evolution, because a probabilistic analysis shows that p.i. $$(\overline {AM})$$ should occur many times more often than the reverse rearrangement, especially when the chromosome number is low. Chromosomes will therefore seldom be available for fusion. On the other hand, given duplication of both heterochromatic and centromeric material, there are no obstacles to the operation of the fission cycle. The modal hypothesis is also implausible on a priori grounds because of the many fusions required for most groups. We next define the karyograph as a graph on which karyotypes are plotted in terms of chromosome number (2n) versus arm number (2AN). We determine 2AN by counting one for each $$\overline A$$ and two for each $$\overline M$$ chromosome. Robertsonian changes each alter 2n by one while leaving 2AN constant while p.i. $$(\overline AM)$$ and p.i. $$(\overline MA)$$ do the reverse. An extensive karyograph analysis of the known mammalian karyotypes shows that there is little correlation between karyotypic and morphological level under any of the three hypotheses, and that there is a strong tendency for linear patterns to emerge when families are plotted separately. This linearity consists of either vertical or horizontal lines on the karyograph, or some combination of the two. Such linearity would be unexpected if the fusion cycle dominated mammalian karyotype evolution, but is readily understandable under the fission cycle as resulting from the development of synchrony between large sections of the genome. This synchrony can develop readily under the fission cycle in that fission produces two $$\overline A$$ chromosomes constrained to evolve by inversion for some time. The resulting $$\overline M$$ chromosomes would later become available for fission following duplication of centromeric material and give rise to four $$\overline A$$ chromosomes, again constrained to evolve by inversion for a while also. The frequently observed linearity of family karyograph distributions, and the above argument concerning the development of synchrony, suggests that mammalian karyotypes tend to follow an upwardly zig-zag course (with occasional "back eddies" by centric fusion) during evolution when plotted on the karyograph.

Fahrenwald浮選機のインペラーにおける気泡の流れ模様 (第3報)

The defect of this type of flotator is that of correlationship of aeration with the pump action of impellers and that of poor efficiency accordingly derived.With the object of comparative study, the author selected the “JETAIR” type of impeller which is made ot jet from the outer circular edge, and examining the moving status of bubbles and measuring the pump efficiency and checking up the frother effects he came to the following conclusion:-1) Part of jet-bubbles is observed rolled into the impeller according to back eddy. Consequently for the increase of the pump efficiency and for independence of the aeration action, preventive measures of this back eddy is necessary.2) The uprising bubbles are readily broken up into minuter particles at rather slow rotating speeds, and that with less pattering.3) The frother effects are to be rapidly increased with the increase of the rotating speed, but above the limit speed the increase of effects is seen decreasing.4) By means of a bubble vane, the dispersion of bubbles can be uniformalized deriving the increase of the frother effects.