Accelerated Motions of a Fish-Like Foil from Impulsive Starts to Terminal States

Ogata, Youichi; Ogasawara, Tsuyoshi

doi:10.1299/jfst.7.358

Cited by 3 publications

(5 citation statements)

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“…(4) are concave and convex functions, respectively. Thus, fish swimming characteristics under any kinds of function   x H between (A) and (B) (Ogata and Ogasawara, 2012) can be also presumed by results shown later. …”

Section: Basic Equations and Numerical Methodsmentioning

confidence: 88%

“…Equation (2) is solved using a first-order explicit scheme, and Eqs. (6) and (7) are solved using the CIP-CUP (combined unified procedure) method (Yabe et al, 2001) with a fractional step and a bi-conjugate gradient stabilization (Bi-CGSTAB) method to solve the Poisson-type equation for calculating pressure such as that used in the previous two-dimensional study (Ogata and Ogasawara, 2012).…”

Section: Basic Equations and Numerical Methodsmentioning

confidence: 99%

“…(11) consists of a constant first term and a second term that is proportional to est U . In the previous two-dimensional simulations (Ogata and Ogasawara, 2012), it was found that the speed of a two-dimensional deforming airfoil could also be estimated using Eq. (10).…”

Section: Flow Patterns Of a Small Fish During Accelerationmentioning

confidence: 99%

“…(16) can be applied up to Ogata, Azama and Moriyama, Journal of Fluid Science and Technology, Vol.12, No.1 (2017) Various important points are yet to be discussed, not least the efficiency determined by the swimming power, the thrust, and the drag. There have been previous studies of fish in uniform flow (Borazjani and Sotiropoulos, 2009;Liu and Kawachi, 1999) and two-dimensional fish undergoing acceleration (Ogata and Ogasawara, 2012). A challenge remains to optimize the design of a three-dimensional fish shape that includes fins, because a number of parameters would have to be considered for optimization.…”

Section: Flow Patterns Of a Small Fish During Accelerationmentioning

confidence: 99%

“…Moreover, numerical studies have helped us to understand the mechanisms of fish swimming by showing that the 1 Yoichi OGATA*, Takayuki AZAMA* and Yuji MORIYAMA* *Department of Mechanical System Engineering, Hiroshima University 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8527, Japan model for predicting the speed of its center of mass (Ogata and Ogasawara, 2012). The present paper extends that work to a small three-dimensional fish that is accelerated by fluid forces that it generates by swimming.…”

Section: Introductionmentioning

confidence: 99%

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Numerical investigation of small fish accelerating impulsively to terminal speed

Ogata

Azama

Moriyama

2017

JFST

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The present paper discusses acceleration in the swimming of a small three-dimensional fish with two motions, carangiform and anguilliform. Flow fields generated by fish deformations are investigated numerically by the constrained interpolation profile method in combination with an immersed boundary method. The three-dimensional vortical structure visualized using a second invariant and the pressure field around the fish body show that a fish with anguilliform motion accelerates more rapidly than one with carangiform motion because of a larger thrust due to the strong transverse vortex in the wake of the fish and a large pressure variation around the fish body. It is also found that the time variations of inline swimming speed of a small fish and the fluid force acting on it can be estimated using a free-fall model, and the fluid force can be expressed by a linear function of the fish speed. This function consists of a thrust part that is independent of fish speed and a viscous drag part that is proportional to fish speed. Thus, time histories of swimming speed, swimming distance, and fluid force can be predicted by simple functions from rest to terminal speed. IntroductionFish morphology and motion are being applied increasingly to robotics as a new form of underwater propulsion that does not use screws. For example, biomimetic two-joint robots have been developed that capitalize on the high maneuverability and speed of swimming dolphins (Nakashima et al., 2006). Differences in thrust and lift between robots modeled on dolphins and sea turtles have been discussed to establish an efficient propulsion system; these robots have great potential for applications such as water quality surveys in particularly shallow areas (Hosotani et al., 2010). In addition, small aquatic robots (e.g., those the size of a killifish; about 5 cm long) powered by compact fuel cells are expected to become available as lightweight and long-running propulsors (Takada et al., 2010).A great deal of knowledge gleaned from fish swimming has been used to design propulsion systems and develop their swimming capabilities. Lighthill (1960Lighthill ( , 1969 established the fundamental theoretical aspects of fish swimming, and Newman (Newman, 1973;Newman and Wu, 1973) proposed generalized slender-body and fluid-force models for a fish-like body. Since then, a general equation has been suggested to represent the Froude efficiency of a slender body placed in a uniform potential flow in relation to the motion of the body (Cheng and Blickhan, 1994). From an experimental point of view, cumulative observations and measurements have led to bending rules for natural propulsors (including fish) during steady motion-a mean flexion ratio of 0.65 and a mean flexion angle of 26.5° (Kelsey et al., 2014)-and the fact that the Strouhal number St of most swimming animals is in the range of 0.25-0.35 (Eloy, 2012). The flow velocity fields generated by swimming fish have been gradually revealed by measurements such as those made using particle image velocimetr...

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Section: Basic Equations and Numerical Methodsmentioning

confidence: 88%

Section: Basic Equations and Numerical Methodsmentioning

confidence: 99%

Section: Flow Patterns Of a Small Fish During Accelerationmentioning

confidence: 99%