Streamlined Body Research Articles

An interspecific comparison between morphology and swimming performance in cyprinids

Flow regimes are believed to be of major evolutionary significance in fish. The flow regimes inhabited by cyprinids vary extensively from still flow regimes to riptide flow regimes. To test (i) whether flow-driven swimming performance and relevant morphological differentiation are present among fish species and (ii) whether evolutionary shifts between high-flow and low-flow habitats in cyprinids are associated with evolutionary trade-offs in locomotor performance, we obtained data on both steady and unsteady swimming performance and external body shape for 19 species of cyprinids that typically occur in different flow regimes (still, intermediate and riptide). We also measured the routine energy expenditure (RMR) and maximum metabolic rate (MMR) and calculated the optimal swimming speed. Our results showed that fish species from riptide groups tend to have a higher critical swimming speed (Ucrit ), maximum linear velocity (Vmax ) and fineness ratio (FR) than fish from the other two groups. However, there was no correlation between the reconstructed changes in the steady and unsteady swimming performance of the 19 species. According to the phylogenetically independent contrast (PIC) method, the Ucrit was actively correlated with the MMR. These results indicated that selection will favour both higher steady and unsteady swimming performance and a more streamlined body shape in environments with high water velocities. The results suggested that steady swimming performance was more sensitive to the flow regime and that for this reason, changes in body shape resulted more from selective pressure on steady swimming performance than on unsteady swimming performance. No evolutionary trade-off was observed between steady and unsteady swimming performance, although Ucrit and MMR were found to have coevolved. However, a further analysis within each typically occurring habitat group suggested that the trade-off that may exist between steady and unsteady swimming performance may be concealed by the effect of habitat.

Integrating environmental variation, predation pressure, phenotypic plasticity and locomotor performance

The Wujiang River, a tributary of the Three Gorges Reservoir, has many dams along its length. These dams alter the river's natural habitat and produce various flow regimes and degrees of predator stress. To test whether the swimming performance and external body shape of pale chub (Zacco platypus) have changed as a result of alterations in the flow regime and predator conditions, we measured the steady (U(crit)) and unsteady (fast-start) swimming performances and morphological characteristics of fish collected from different sites along the Wujiang River. We also calculated the maximum respiratory capacity and cost of transport (COT). We demonstrated significant differences in swimming performance and morphological traits among the sampling sites. Steady swimming performance was positively correlated with water velocity and negatively correlated with the abundance of predators, whereas unsteady swimming performance was negatively correlated with water velocity. The body shape was significantly correlated with both swimming performance and ecological parameters. These findings suggested that selection pressure on swimming performance results in a higher U(crit) and a more streamlined body shape in fast-flow and (or) in habitats with low predator stress and subsequently results in a lower COT. These characteristics were accompanied by a poorer fast-start performance than that of the fish from the slow-flow and (or) high-predator habitats. The divergence in U(crit) may also be due in part to variation in respiratory capacity.

Effects of predation pressure and resource use on morphological divergence in omnivorous prey fish

BackgroundBody shape is one of the most variable traits of organisms and responds to a broad array of local selective forces. In freshwater fish, divergent body shapes within single species have been repeatedly observed along the littoral-pelagic axes of lakes, where the structural complexity of near shore habitats provides a more diverse set of resources compared to the open-water zones. It remains poorly understood whether similar resource-driven polymorphism occurs among lakes that vary in structural complexity and predation pressure, and whether this variation is heritable. Here, we analyzed body shape in four populations of omnivorous roach (Rutilus rutilus) inhabiting shallow lakes. We tested the relationship between body shape, gradients of resources, predation pressure, and, in a subset of two lakes, diet composition. We used genome scans of 331 polymorphic AFLP markers to test whether there was a heritable component to the observed morphological diversification.ResultsBody shape differed among lakes and was significantly correlated to differences in predation pressure. Roach from the lake with highest predation pressure were most divergent from the average body shape of all populations, characterized by a more streamlined body and caudally inserted dorsal fins; features that facilitate predator escape. Surprisingly, diet composition was not associated with morphology. AFLP analysis revealed weak genetic differentiation among lakes and no isolation by distance (IBD). Outlier analysis detected three loci under positive selection with differing frequencies in the four populations. General linear models did not support an association of lake-specific genotypes with morphological variation.ConclusionBody shape was divergent among lakes, suggesting that processes previously reported from within single lakes may also be operating at the scale of whole lakes. We found no evidence for body shape being heritable, although sample size was small in these natural populations. Rather than habitat structure and diet, we conclude that predation had a stronger effect on the prevalence of local morphotypes. A variable morphotype facilitating the efficient uptake of a variety of spatially and temporarily scattered resources seems to be favored in these small aquatic systems.

Three Dimensional Measurement of Shark Body Based on Monocular and Binocular Vision

To provide precise configuration reference for the engineering bionics, high accuracy detection in large field of view on the natural biological body is a prerequisite. Targeting the streamline body of carcharhinus brachyurous, 3D (three dimensional) measurement was carried out with monocular and binocular vision inspecting system based on sinusoidal structure light. By means of moving the vision sensor driven by a stepper motor, fringe patterns with variable fringe spacing were projected to every parts of the shark body, then the point clouds of different parts of the whole shark body were obtained. Using the quaternion method to joint the edges of these point clouds together, surface reconstruction was conducted. Finally the digital model of the low resistance body of shark was achieved. It would be useful reference for the configuration design of underwater vehicles, especially microminiature biomimetic underwater vehicles.

Simulation of the heat exchange between the supersonic flow and the stationary body in a gas centrifuge

We have made comparative calculations of the heat exchange in the subpersonic flow of gaseous UF6 around the stationary cylindrical body inside the rotating rotor of the gas centrifuge. It has been revealed that the integral heat flux from the gas to the body calculated with the use of the ANSYS-CFX program complex from the viewpoint of the continuum model is much smaller than the heat flow calculated by the Monte Carlo method of direct statistical simulation. Estimates show that under the conditions being considered the boundary layer on the surface of the body has no time to be formed and has a thickness of the order of the mean free path of the gas molecules and, therefore, the use of the methods of continuum mechanics in this region is incorrect. On the contrary, the method of direct statistical simulation permits taking into account the interaction of gas molecules directly with the surface of the streamline body and obtaining more correct results.

On the optimal model configuration for aerodynamic modeling of open cargo railway train

This study is concerned with the optimal model configuration for aerodynamic modeling of long open cargo railway trains. Frontal air drag of several train configurations was studied using numerical modeling and physical i.e. wind tunnel testing of 1:40 scale railcar models in a range of cross-wind angles. In a long train, the locomotive and the last railcar influence the aerodynamic characteristics of the first three and the last three railcars only. Aerodynamic performance of all other railcars in the long train is similar and can be represented by two inner-train railcars only. A model train configuration combining the shortest computation time with the lowest experimental error was determined from numerical modeling and this was then used for wind tunnel testing. It has been shown that, for long open cargo railway trains the model consisting of six railcars with two streamlined bodies is the optimal configuration, with both the numerical modeling and wind tunnel testing results in good agreement.

수중운동체의 실린더 관 내부 이동시 작용력 예측에 대한 실험적 접근

The main object of this experiment is to estimate the hydrodynamic forces acting on a submerged streamlined body placed in a one-end-opened cylindrical tube moving with certain translational velocity. The best experimental design for this object is mimicking real situation, however sizes of model body and cylinder tube are just the same as those of real, for avoiding scale effects, mimicking real situation is not realizable. Hence, in this experiment, target body and cylindrical tube were designed to be towed with varying body position relative to cylindrical tube. For measuring hydrodynamic forces and flow velocity in the cylindrical tube, six one-component load cells and several one-hole Pitot tubes were used. Several conditions were checked with various end-plates those had different opening areas. Experiment results show that forces and flow velocity had different tendency with those expected, and the presence of a end-plate slows down the flow velocity in the cylindrical tube and affects pressure field in the tube to push the model submerged body forward of the tube. This tendency grows with decreasing opened area.

Condensation of steam-air mixture in a film-type apparatus

The results from a study of heat transfer during condensation of steam and air-steam mixture in a film-type tubular apparatus with heat transfer enhancement by streamlined bodies are presented. Dependencies for calculating the heat transfer coefficient are proposed.

Taking the time to assess the effects of remote sensing and tracking devices on animals

AbstractThe remote monitoring of animal behaviour using telemetry and bio-logging has become popular due to technological advances, falling costs of devices and the need to understand behaviour without causing disturbance to subjects. Over the past three decades thousands of animals have had their movements tracked by these devices; however, attaching devices to streamlined bodies raises concerns about energetic costs and effects on vital rates and the reliability of the data collected (eg survival probability). We encourage researchers to discuss concerns, quantify the possible effects that devices and attachment methods have on subjects and present this work for peer review.

Study on the maximum operation speeds of metro trains for energy saving as well as transport efficiency improvement

By following a computer-aided simulation procedure, this research analyzes the traction energy cost and transport operation time per 10,000 passenger-kilometers of two representative types of metro trains in China under various top speeds between different stations along a hypothetically straight and smooth metro line, from the perspective of both energy saving and transport efficiency improvement in consideration of multi-factors. It is empirically confirmed that if the transport distance between stops is shorter than 1,800 m, the metro trains should set their maximum speeds lower than 70 km/h but higher than 30 km/h. And a shorter stop-spacing requires a lower maximum speed in this speed range to get the least costs of energy and time. The exact value of the maximum speed in this speed range ought to be further determined based on the integrated performances of the train’s passenger capacity, engines, streamline body design, etc. If the transport distance is longer than 1,800 m, the generalized expense of energy and time per 10,000 passenger-kilometers decreases with the increase of the maximum speed of a train. Nevertheless, such decreases become very slow when the maximum speeds of the trains exceed 70 km/h.

Simulation of porous transpiration cooling of the leading semicylindrical edge of a streamlined body

Experiments are carried out for simulating the efficiency of cooling the leading edge of a blunt streamlined body made of porous reticular material with an impermeable insert placed along the stagnation zone. Satisfactory results are obtained that make it possible to recommend the proposed method of organizing transpiration porous cooling of the leading edge of the blades used in high-temperature gas turbines for implementation.

Aerodynamics and interaction noise of streamlined bodies in nonuniform flows

The unsteady aerodynamics and interaction noise of streamlined bodies are modeled in terms of the Euler equations linearized about a nonuniform flow. The validity of the inviscid approach is supported by recent LES simulations of an airfoil in a gust indicating that for not-too-small impinging excitations, the interaction process is dominated by inertia forces. Results in the present paper are focused on the aerodynamics and interaction noise of a turbofan modeled as an annular cascade. The model accounts for the inflow-fan-duct coupling and the high frequency of the interaction process. Two high-order numerical algorithms are developed with body-fitted coordinate system. One algorithm uses a primitive variable formulation, the other uses an efficient velocity splitting algorithm and is suitable for broadband computations. Analytical and numerical analysis of disturbances in rotational flows is developed and exact inflow/outflow boundary conditions are derived, yielding directly the radiated acoustics. The upstream disturbances evolve in rotational flows and as a result the aerodynamic–aeroacoustic response of the annular cascade depends on the initial conditions location. Computational results show that the three-dimensional geometry of the annular cascade, the mean flow swirl, and the blade geometry have strong influence on the blade sectional lift and the radiated sound. These results also show the inadequacy of using the popular linear cascade model particularly for realistic fan geometry and inflow conditions.

Experimental study on the instability of wake of axisymmetric streamlined body

The instability of wake of an axisymmetric body with the NACA aerofoil section was experimentally studied under low background turbulence. The body was suspended using a magnetic suspension and balance system to avoid undesirable influences of mechanical supports on the disturbance development. The Reynolds number based on the chord length of the aerofoil section ranged from 5.3 × 104 to 2.1 × 105. For the body with a NACA0015 aerofoil section where there is no boundary-layer separation on the body surface, the wake was convectively unstable, even at the highest Reynolds number examined. Although the wake maintained axisymmetry of mean flow, the instability waves often took a planar-symmetric form, indicating that the occurrence of disturbance can be influenced by minute variations in the position and orientation of the suspended body. For bodies with thicker NACA0018 and NACA0024 aerofoil sections where the flow involved a region of absolute instability immediately downstream of the trailing edge, the global mode could grow rapidly and attain saturation amplitude within a very short distance from the trailing edge despite that the region of absolute instability was limited only to small streamwise distance, about one tenth of the instability wavelength. The predominant frequency of vortex shedding was found to be very close to the absolute frequency near the trailing edge, especially at the upstream boundary of the region of absolute instability. This is consistent with the theoretical model for the development of a nonlinear global mode. It was also found that the mean flow axisymmetry was broken around the critical Reynolds number for global instability, which led to the appearance and growth of a planar-symmetric global mode.

Experimental study on the instability of wake of axisymmetric streamlined body

The instability of wake of an axisymmetric body with the NACA aerofoil section was experimentally studied under low background turbulence. The body was suspended using a magnetic suspension and balance system to avoid undesirable influences of mechanical supports on the disturbance development. The Reynolds number based on the chord length of the aerofoil section ranged from 5.3 × 104 to 2.1 × 105. For the body with a NACA0015 aerofoil section where there is no boundary-layer separation on the body surface, the wake was convectively unstable, even at the highest Reynolds number examined. Although the wake maintained axisymmetry of mean flow, the instability waves often took a planar-symmetric form, indicating that the occurrence of disturbance can be influenced by minute variations in the position and orientation of the suspended body. For bodies with thicker NACA0018 and NACA0024 aerofoil sections where the flow involved a region of absolute instability immediately downstream of the trailing edge, the global mode could grow rapidly and attain saturation amplitude within a very short distance from the trailing edge despite that the region of absolute instability was limited only to small streamwise distance, about one tenth of the instability wavelength. The predominant frequency of vortex shedding was found to be very close to the absolute frequency near the trailing edge, especially at the upstream boundary of the region of absolute instability. This is consistent with the theoretical model for the development of a nonlinear global mode. It was also found that the mean flow axisymmetry was broken around the critical Reynolds number for global instability, which led to the appearance and growth of a planar-symmetric global mode.

Morphological adaptations to marine life in snakes

We investigated morphological adaptations to aquatic life within animals that exhibit a structurally simple, elongate body form, i.e., snakes. This linear body plan should impose different biomechanical constraints than the classical streamlined body shape associated with propulsion by fins, feet, or wings. Our measurements of general body shape of terrestrial, amphibious, and marine snakes (all from the same phylogenetic lineage, the Elapidae) show that seasnakes display specialized morphological attributes for life in water. Most notably, the cross-sectional body shape is circular in terrestrial snakes but dorso-ventrally elongated in seasnakes (due to a prominent ventral keel); amphibious species (sea kraits) exhibit an intermediate shape. The tail of amphibious and marine species (a major propulsive structure during swimming) is higher and thinner than in terrestrial snakes (i.e., paddle-shaped) but shorter relative to body length. The evolution of a laterally compressed shape has been achieved by an increase in body height rather than a decrease in body width, possibly reflecting selection for more effective propulsive thrust, and for an ability to maintain hydrodynamic efficiency despite the minor bodily distension inevitably caused by prey items and developing offspring.

Ecological transcriptomics of lake-type and riverine sockeye salmon (Oncorhynchus nerka)

BackgroundThere are a growing number of genomes sequenced with tentative functions assigned to a large proportion of the individual genes. Model organisms in laboratory settings form the basis for the assignment of gene function, and the ecological context of gene function is lacking. This work addresses this shortcoming by investigating expressed genes of sockeye salmon (Oncorhynchus nerka) muscle tissue. We compared morphology and gene expression in natural juvenile sockeye populations related to river and lake habitats. Based on previously documented divergent morphology, feeding strategy, and predation in association with these distinct environments, we expect that burst swimming is favored in riverine population and continuous swimming is favored in lake-type population. In turn we predict that morphology and expressed genes promote burst swimming in riverine sockeye and continuous swimming in lake-type sockeye.ResultsWe found the riverine sockeye population had deep, robust bodies and lake-type had shallow, streamlined bodies. Gene expression patterns were measured using a 16K microarray, discovering 141 genes with significant differential expression. Overall, the identity and function of these genes was consistent with our hypothesis. In addition, Gene Ontology (GO) enrichment analyses with a larger set of differentially expressed genes found the "biosynthesis" category enriched for the riverine population and the "metabolism" category enriched for the lake-type population.ConclusionsThis study provides a framework for understanding sockeye life history from a transcriptomic perspective and a starting point for more extensive, targeted studies determining the ecological context of genes.

Contrasting Ecology Shapes Juvenile Lake‐Type and Riverine Sockeye Salmon

AbstractHere we compare the body shape of juvenile (age‐0) sockeye salmon Oncorhynchus nerka that rear in lakes (lake type) with that of those that rear in rivers (riverine) and relate rearing habitat to morphology and ecology. The two habitats present different swimming challenges with respect to water flow, foraging strategy, habitat complexity, and predation level. We present morphological data from three riverine and three lake‐type populations in southwest Alaska. Using multivariate analyses conducted via geometric morphometrics, we determine population‐ and habitat‐specific body shape. As predicted, riverine sockeye salmon have a more robust body shape, whereas lake‐type sockeye salmon have a more streamlined body shape. In particular, we found differences in caudal peduncle depth (riverine deeper), eye size (riverine larger), and overall body depth (riverine deeper). One lake‐type population did not follow the predicted pattern, exhibiting an overall exaggerated riverine body shape. Differences between the habitats in terms of predation, complexity, and foraging ecology are probably drivers of these differences. Allometry differed between life history types, suggesting that there are habitat‐specific developmental differences.

Comparative jet wake structure and swimming performance of salps

Salps are barrel-shaped marine invertebrates that swim by jet propulsion. Morphological variations among species and life-cycle stages are accompanied by differences in swimming mode. The goal of this investigation was to compare propulsive jet wakes and swimming performance variables among morphologically distinct salp species (Pegea confoederata, Weelia (Salpa) cylindrica, Cyclosalpa sp.) and relate swimming patterns to ecological function. Using a combination of in situ dye visualization and particle image velocimetry (PIV) measurements, we describe properties of the jet wake and swimming performance variables including thrust, drag and propulsive efficiency. Locomotion by all species investigated was achieved via vortex ring propulsion. The slow-swimming P. confoederata produced the highest weight-specific thrust (T=53 N kg(-1)) and swam with the highest whole-cycle propulsive efficiency (eta(wc)=55%). The fast-swimming W. cylindrica had the most streamlined body shape but produced an intermediate weight-specific thrust (T=30 N kg(-1)) and swam with an intermediate whole-cycle propulsive efficiency (eta(wc)=52%). Weak swimming performance variables in the slow-swimming C. affinis, including the lowest weight-specific thrust (T=25 N kg(-1)) and lowest whole-cycle propulsive efficiency (eta(wc)=47%), may be compensated by low energetic requirements. Swimming performance variables are considered in the context of ecological roles and evolutionary relationships.

A Force Estimation Method for Viscous Separated Flow Over Slender Axisymmetric Bodies With Tapered Tails

A new impulse method for modeling the normal force distributions along slender axisymmetric bodies with tapered tails is presented. This method is based on a decomposition of the hydrodynamic impulse along the body into an inviscid, profile-dependent component and a viscous, profile-independent component. It is applicable to separated flows up to 30 deg of incidence. Model results for the normal force distributions, total normal force, and total moment on axisymmetric streamlined bodies with tapered tails are compared with computational fluid dynamics (CFD) simulations and experimental data up to a Reynolds number of 23 × 106 with good agreement. The model was also tested on a missile-shaped body and was found to be in excellent agreement with experimental results.

Span Efficiencies of Wings at Low Reynolds Numbers

Elegant and inviscid analytical theory can predict the induced drag on lifting wings of finite span. The theoretical prediction is then often modified by multiplication with a dimensionless coefficient for which the departure from a value of 1 is used as a way to incorporate realistic and necessary departures from the idealized model. Unfortunately, there are conflicting definitions of these dimensionless coefficients, often known as span efficiencies, so that even if numerical values are assigned in a clear and transparent fashion, their application and validity remain unclear. Here, the differences between two commonly used definitions of span efficiency are identified and it is shown that for the case of airfoil sections and finite wings at chordwise Reynolds numbers less than 10 5 , neither one has values close to those commonly assumed in the aeronautics literature. The cause of these significant viscous modifications to inviscid theory is traced to the movement of separation points from the trailing edge of real airfoils. A modified nomenclature is suggested to reduce the likelihood of confusion, and appropriate formulations for the drag of streamlined bodies in viscous flows at moderate Reynolds number are considered, with application to small-scale flying devices, both natural and engineered.