scholarly journals Innovation Concept Model and Prototype Validation of Robotic Fish with a Spatial Oscillating Rigid Caudal Fin

2021 ◽  
Vol 9 (4) ◽  
pp. 435
Author(s):  
Shuyan Wang ◽  
Yu Han ◽  
Shiteng Mao
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Robotic Fish ◽  
Caudal Fin ◽  
Concept Model ◽  
Lateral Forces ◽  
Comparison Results ◽  
Experimental Apparatus ◽  
Lift Forces

Inspired by carangiform fish with a high-aspect ratio of the caudal fin’s up-down swing, but also by dolphins with a similar caudal fin’s left-right swing, a robotic fish with a spatial oscillating rigid caudal fin is implemented to optimize propulsion and maneuverability, whose orientation could be transformed to any position of a taper domain. First, three steering-engines were adopted to make the conceptual prototype, and an experimental apparatus for measuring thrust, lift forces, lateral forces and torque was developed. Then, three comparison experiments, respectively corresponding to the three modes of cruise, diving and maneuvering in random space, were conducted to imitate bionic fish’s hydrodynamics. The comparison results of the experiments proved that propelling and maneuvering in any direction could be realized through changing the orientation of the spatial oscillating rigid caudal fin.

Effects of Tail Geometries on the Performance and Wake Pattern in Flapping Propulsion

2016 ◽  
Author(s):  
Geng Liu ◽  
Haibo Dong
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Computational Study ◽  
Hydrodynamic Performance ◽  
Immersed Boundary ◽  
Caudal Fin ◽  
Flow Solver ◽  
Wide Range ◽  
Wake Patterns ◽  
Caudal Fin Shape

Swimming fishes exhibit remarkable diversities of the caudal fin geometries. In this work, a computational study is conducted to investigate the effects of the caudal fin shape on the hydrodynamic performance and wake patterns in flapping propulsion. We construct the propulsor models in different shapes by digitizing the real caudal fins of fish across a wide range of species spanning homocercal tails with low aspect ratio (square shape used by bluegill sunfish, rainbow trout, etc.) or high aspect ratio (lunate shape adopted by tuna, swordfish, etc.), and even heterocercal caudal fin adopted by sharks. Those fin models perform the same flapping motion in a uniform flow to mimic fish’s forward swimming. We then simulate the flow around the flapping fins by an in-house immersed-boundary-method based flow solver. According to the analysis of the hydrodynamic performance, we have found that the lunate shape model (high aspect-ratio) always generates a larger thrust compared to other models. The comparison of the propulsive efficiency shows that the large aspect ratio fins (tuna and shark) have a higher efficiency when the Strouhal number (St) is in the range of steady swimming (0.2<St<0.4), while the lower aspect ratio caudal fins (catfish, trout, etc.) are more efficient when St>0.4, in which the fish is accelerating or maneuvering. Finally, the 3D wake patterns of those propulsors are analyzed in detail.

The Effect of a Translating High Aspect Ratio Particle in a Plane Slider Bearing

1983 ◽  
Vol 105 (3) ◽  
pp. 396-404 ◽  
Author(s):  
M. T. Languirand ◽  
J. A. Tichy
Keyword(s):  
Aspect Ratio ◽  
Theoretical Analysis ◽  
High Aspect Ratio ◽  
Pressure Field ◽  
Stokes Equations ◽  
Velocity Fields ◽  
Two Dimensional ◽  
Slider Bearing ◽  
Experimental Apparatus ◽  
Initial Starting

An approximate solution of Stokes equations is presented to determine the pressure and velocity fields in an infinite slider bearing containing a two-dimensional high aspect ratio particle of arbitrary cross-section. The particle may translate in two directions as well as rotate about its centroid. The fluid field is divided into four regions: upstream, above, below, and downstream of the particle. The governing Stokes equations are applied to each region and solved through specific continuity requirements and pressure matching conditions. For illustrative purposes, this method of analysis is applied to a plane slider bearing containing a rectangular particle which can translate in one direction. Approximate solutions are given for the pressure and velocity fields. The solution reveals a pressure drop which develops in the pressure field at the particle location. The magnitude of this drop is shown to be dependent on a particle size, velocity, and location. It is shown that the particle has a major effect on the bearing pressure field when it is able to significantly obstruct the flow of the lubricant. To support the theoretical analysis, experimental research is performed. An experimental apparatus is used to measure the transient pressure in a slider bearing as a high aspect ratio two-dimensional rectangular particle is passed through the fluid film. The apparatus measures pressure at a particular location in the bearing and simultaneously measures the particle’s displacement with respect to its initial starting location. Results are given to demonstrate the effect of particle velocity on the pressure field in the bearing. The experimental results presented are in good agreement with analytical results obtained from the theoretical analysis.

Boehmite Nanofibers as a Dispersant for Nanotubes in an Aqueous Sol

2018 ◽  
Author(s):  
Gen Hayase
Keyword(s):  
Carbon Nanotubes ◽  
Aspect Ratio ◽  
Aqueous Solutions ◽  
High Aspect Ratio ◽  
Multiwall Carbon Nanotubes ◽  
Multiwall Carbon ◽  
Nanotube Films

By exploiting the dispersibility and rigidity of boehmite nanofibers (BNFs) with a high aspect ratio of 4 nm in diameter and several micrometers in length, multiwall-carbon nanotubes (MWCNTs) were successfully dispersed in aqueous solutions. In these sols, the MWCNTs were dispersed at a ratio of about 5–8% relative to BNFs. Self-standing BNF–nanotube films were also obtained by filtering these dispersions and showing their functionality. These films can be expected to be applied to sensing materials.

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