The hydrodynamics of dolphin drafting

BACKGROUND: Drafting in cetaceans is defined as the transfer of forces between individuals without actual physical contact between them. This behavior has long been surmised to explain how young dolphin calves keep up with their rapidly moving mothers. It has recently been observed that a significant number of calves become permanently separated from their mothers during chases by tuna vessels. A study of the hydrodynamics of drafting, initiated in the hope of understanding the mechanisms causing the separation of mothers and calves during fishing-related activities, is reported here. RESULTS: Quantitative results are shown for the forces and moments around a pair of unequally sized dolphin-like slender bodies. These include two major effects. First, the so-called Bernoulli suction, which stems from the fact that the local pressure drops in areas of high speed, results in an attractive force between mother and calf. Second is the displacement effect, in which the motion of the mother causes the water in front to move forwards and radially outwards, and water behind the body to move forwards to replace the animal's mass. Thus, the calf can gain a 'free ride' in the forward-moving areas. Utilizing these effects, the neonate can gain up to 90% of the thrust needed to move alongside the mother at speeds of up to 2.4 m/sec. A comparison with observations of eastern spinner dolphins (Stenella longirostris) is presented, showing savings of up to 60% in the thrust that calves require if they are to keep up with their mothers. CONCLUSIONS: A theoretical analysis, backed by observations of free-swimming dolphin schools, indicates that hydrodynamic interactions with mothers play an important role in enabling dolphin calves to keep up with rapidly moving adult school members

Mechanically efficient swimming techniques for fish with negative bouyancy

An efficient technique for long-distance swimming by fish with negative buoyancy is suggested and described. This includes a phase of powerless gliding with a gradual increase of depth followed by active upward swimming at an angle to the original height...

Classification-relevant Importance Measures for the West German Business Cycle

When analyzing business cycle data, one observes that the relevant predictor variables are often highly correlated. This paper presents a method to obtain measures of importance for the classification of data in which such multicollinearity is present. In systems with highly correlated variables it is interesting to know what changes are inflicted when a certain predictor is changed by one unit and all other predictors according to their correlation to the first instead of a ceteris paribus analysis. The approach described in this paper uses directional derivatives to obtain such importance measures. It is shown how the interesting directions can be estimated and different evaluation strategies for characteristics of classification models are presented. The method is then applied to linear discriminant analysis and multinomial logit for the classification of west German business cycle phases. --

Importance Assessment of Correlated Predictors in Business Cycles Classification

When trying to interpret estimated parameters the researcher is interested in the (relative) importance of the individual predictors. However, if the predictors are highly correlated, the interpretation of coefficients, e.g. as economic "multipliers", is not applicable in standard regression or classification models. The goal of this paper is to develop a procedure to obtain such measures of importance for classification methods and to apply them to models for the classification of german business cycle phases

Energy-Saving Periodic Flight at Transonic Speeds Abstract:

We examine possible energy saving by periodicchanges in speed and altitude relative to steady state cruise, inthe transonic regime. We develop a theoretical model of twophase periodic flight with altitude variation in the transonicregime and compare it with a steady horizontal flight at thesame average speed. The model predictions are verified by windtunnel experiments. For example, by periodically acceleratingfrom M=0.7 to M=1.1 while losing altitude, and then climbingback to the original height while decelerating, one can achievesavings of about 20% relative to steady flight at the sameaverage speed and constant altitude.

Higher order hydrodynamic interaction between two slender bodies in potential flow

In this paper, we apply the slender body theory to study the effect of higher order hydrodynamic interactions between two slender bodies of revolution moving in close proximity, in an unbounded, inviscid, and incompressible fluid. We compare between leading and second-order approximations, as well as approximate and exact separation distances. The total solution is found to be valid for both small and large lateral separation distances. The contribution of the higher order forces is found to be relatively small for large separation distances, though significant for small separation distances. Comparisons with measurements and simulations are satisfactory

Functional Locomotor Morphology of Early Life History Stages of Fishes

Routine activities of early life history stages of fishes occur in an intermediate hydrodynamic environment (as identified by Reynolds numbers), between a zone where drag is linearly dependent on velocity and resistive forces make large contributions to thrust, and a zone where inertial forces dominate except in the boundary layer immediately adjacent to the body surface. Sprint performance carries larvae into this latter zone; thus, locomotor activities important for survival of both larvae and adults occur in the same hydrodynamic environment and similar selective pressures would be expected to influence locomotor morphology of larvae and adults. The simplest framework for evaluating and interpreting development of larvae recognizes the parental form as the developmental terminus and uses adult forms as references to identify similarities and discrepancies in larva structure. Three measures of locomotor structure are used to examine changes during development: (a) the ratio of caudal peduncle depth to maximum body depth, which is small in thunniform fish; (b) a body shape factor, which is small in chaetodontiform fishes; and (c) a transient swimming thrust factor, which is large in esociform fish. Similarities in form are found in yolk‐bearing larvae and are attributed to oxygen demand. Similarities in the pattern of development of larvae directly towards the parental form are found for fusiform species, except for delayed development of the caudal fin in tunas that probably is due to the hydrodynamic regime of the tail. Convergence with parents does not occur during the larva stage of deep‐bodied, compressed species. This is attributed to high drag of compressed forms at low Reynolds numbers and diet differences between larvae and parents. Although this framework is successful in identifying and interpreting problems, comparative studies of form, kinematics, and performance during biologically important activities are essential.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141928/1/tafs0115.pd

Classification-relevant Importance Measures for the West German Business Cycle

When analyzing business cycle data, one observes that the relevant predictor variables are often highly correlated. This paper presents a method to obtain measures of importance for the classification of data in which such multicollinearity is present. In systems with highly correlated variables it is interesting to know what changes are inflicted when a certain predictor is changed by one unit and all other predictors according to their correlation to the first instead of a ceteris paribus analysis. The approach described in this paper uses directional derivatives to obtain such importance measures. It is shown how the interesting directions can be estimated and different evaluation strategies for characteristics of classification models are presented. The method is then applied to linear discriminant analysis and multinomial logit for the classification of west German business cycle phases