Research ArticleANIMAL ROBOTS

Tuna robotics: A high-frequency experimental platform exploring the performance space of swimming fishes

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Science Robotics  18 Sep 2019:
Vol. 4, Issue 34, eaax4615
DOI: 10.1126/scirobotics.aax4615
  • Fig. 1 Locomotor performance space of swimming fishes and robots.

    Fishes are capable of locomotion at much higher speeds and frequencies than most current robotic systems. Current fish-like robotic platforms (pink dots) occupy only a small region of the fish swimming performance space (blue dots) considering both speed and tail beat frequency (A), and absolute and length-specific speeds (B). Points represent literature data from different robotic platforms, literature data for multiple individuals of one fish species [e.g., (17)], or new measurements of fish swimming speeds and tail beat frequencies conducted by the authors.

  • Fig. 2 Design of the Tunabot platform.

    (A) Overall Tunabot body plan showing the major components of the tuna-like mechanical system. The Tunabot is 255 mm in total length. Body shape (B) was based on a simplified yellowfin tuna (T. albacares) body plan (C) and features a streamlined shape with a narrow caudal peduncular region anterior to the tail. During testing, the Tunabot was suspended by two thin vertical threads, and one lateral thread at the nose prevented extreme motion in the event of failure but did not restrict lateral Tunabot oscillation during swimming. The power cable (red) is visible and also did not restrict robot motion in any way. Tunabot tail morphology (D) was manufactured on the basis of the yellowfin tuna tail (E). The tail is supported by a metal peduncle with lateral keels (F) designed from the lateral keels of yellowfin tuna (G). Images of tuna in (E) and (G) are from a fish about 1 m in length.

  • Fig. 3 Swimming kinematics.

    (A) Tunabot, (B) Yellowfin tuna, and (C) mackerel. Kinematic snapshots showing the displacement of the body midline at 10 equally spaced time intervals during a single tail beat cycle (D to F) during swimming at 2.2, 1.0, and 2.0 BL/s, respectively. We calculated midline curvature along the body for 270, 168, and 85 midlines, corresponding to 27, 15, and 7 tail beats (G to I), respectively. Black lines (G to I) show the mean body curvature. Tuna in (B) is about 1 m in length. The negatively buoyant Tunabot in (A) was supported by two vertical threads (not visible in this image), and a thin black lateral thread was loosely attached to the nose (visibly attached to near the first black dot) to prevent potentially damaging movements. This thread did not restrict lateral movement of the robot in any way.

  • Fig. 4 Tail kinematics and thrust in the Tunabot and swimming mackerel.

    (A) Effective angle of attack profile for the Tunabot caudal fin over one tail beat period during locomotion at 0.78 ± 0.2 BL/s and a tail beat frequency of 3.7 ± 0.2 Hz (n = 3). The rigid caudal fin is treated as a single segment. Error bars indicate SD. (B) Effective angle of attack profiles for the mackerel caudal fin, with each profile representing a quarter segment of the caudal fin, as seen in ventral view. These data are from mackerel swimming at 1.2 ± 0.1 BL/s with a tail beat frequency of 3.7 ± 0.9 Hz (n = 20). (C) Static thrust of the Tunabot measured at a tail beat frequency of 3.9 ± 0.1 Hz (n = 9), represented with 95% confidence level. Two thrust peaks are evident for each complete tail beat cycle.

  • Fig. 5 Comparison of Tunabot swimming performance with fishes and other fish robotic platforms.

    (A) Swimming speeds (in body lengths per second) compared for swimming fish, fish-like robotic systems, and the Tunabot. (B) Tail beat frequencies (in hertz) compared for swimming fish, fish-like robotic systems, the Tunabot, and yellowfin tuna. Black horizontal lines indicate the group medians, colored boxes indicate the lower and upper data quartiles (25 and 75% levels), and dashed lines indicate the minimum and maximum data values for each group. The Tunabot has significantly higher tail beat frequencies than other fish-like robotic platforms (P < 0.001) and a higher length-specific swimming speed. Lowercase letters indicate significant differences among group means.

  • Fig. 6 Tunabot swimming performance.

    (A) Swimming speed versus tail beat frequency. (B) COT in joules per meter versus swimming speed given in body lengths per second. (C) St versus swimming speed. (D) Measured static thrust (in newtons) versus tail beat frequency (in hertz). Points are the means of n = 3 trials; error bars are SDs from the means. Error bars are obscured by the symbols for some points.

  • Fig. 7 Visualizing water flow in the wake and around the tail of the Tunabot.

    The Tunabot body and tail in the laser light sheet (A) and a close view of the Tunabot caudal fin with the laser light sheet positioned at the midspan location (B). Flow visualization using particle image velocimetry was conducted both in the midbody wake and on the tail surface at the midbody and midspan locations, over the complete range of swimming speeds corresponding to the points shown in Fig. 6. (C) A classic reverse Kármán wake is generated by the Tunabot swimming at 0.87 m/s with counter-rotating vortices and high-velocity thrust jets between shed vortex centers. The caudal fin has been highlighted in white. After the start of the tail beat (D), a trailing vortex has just been shed from the tail (blue vorticity), and the initial stages of LEV formation can be seen (red, near the tail). Thirteen milliseconds later, during the last half of the tail beat (E), a strong LEV is present on the tail (red vorticity). Flows shown in (D) and (E) are at the midspan location. Mean free-stream flow has been subtracted; vorticity scale applies to (C) to (E).

  • Fig. 8 Measuring swimming performance.

    (A) High-speed video recording of swimming kinematics in yellowfin tuna. A high-speed camera is suspended above swimming tuna in an enclosed waterproof container (visible in the top right) and provides dorsal views of tuna body deformation during swimming. (B) Measuring thrust in the Tunabot. Spectra line (highlighted in yellow) connects the tip of the Tunabot to the load cell through three hinged pulleys. Swimming thrust is directly transferred to the load cell. (C) Tunabot suspended in a testing tank. Further information on testing protocols is provided in Materials and Methods and the Supplementary Materials.

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/4/34/eaax4615/DC1

    Text

    Fig. S1. Internal structure of fusion deposition modeling (FDM) 3D-printed materials with different part fill densities.

    Fig. S2. Elastomer infiltration for a 3D-printed material.

    Fig. S3. Airtight testing of an elastomer-infiltrated 3D-printed closed chamber.

    Fig. S4. Kinematic and lift-based swimming principles.

    Fig. S5. Drag force on a wire in a steady fluid flow.

    Fig. S6. Drag versus flow speed for the Tunabot body.

    Fig. S7. Tunabot body drag coefficients.

    Fig. S8. Tunabot head and tail oscillation amplitude.

    Fig. S9. Scombrid fish 3D anatomy.

    Fig. S10. Scombrid fish 3D anatomy.

    Table S1. Data used for Fig. 1: Fish and robot locomotor performance space.

    Movie S1. Yellowfin tuna steady swimming.

    Movie S2. Atlantic mackerel steady swimming.

    Movie S3. Tunabot swimming in a flow tank.

    Movie S4. Tunabot swimming in laser light sheet.

    Movie S5. Wide view of Tunabot wake flow patterns.

    Movie S6. Close view of Tunabot wake flow visualization around the caudal fin.

    Movie S7. Animation of the Tunabot propulsive mechanism.

    References (9193)

  • Supplementary Materials

    The PDF file includes:

    • Text
    • Fig. S1. Internal structure of fusion deposition modeling (FDM) 3D-printed materials with different part fill densities.
    • Fig. S2. Elastomer infiltration for a 3D-printed material.
    • Fig. S3. Airtight testing of an elastomer-infiltrated 3D-printed closed chamber.
    • Fig. S4. Kinematic and lift-based swimming principles.
    • Fig. S5. Drag force on a wire in a steady fluid flow.
    • Fig. S6. Drag versus flow speed for the Tunabot body.
    • Fig. S7. Tunabot body drag coefficients.
    • Fig. S8. Tunabot head and tail oscillation amplitude.
    • Fig. S9. Scombrid fish 3D anatomy.
    • Fig. S10. Scombrid fish 3D anatomy.
    • References (9193)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Table S1 (Microsoft Excel format). Data used for Fig. 1: Fish and robot locomotor performance space.
    • Movie S1 (.mp4 format). Yellowfin tuna steady swimming.
    • Movie S2 (.mp4 format). Atlantic mackerel steady swimming.
    • Movie S3 (.mp4 format). Tunabot swimming in a flow tank.
    • Movie S4 (.mp4 format). Tunabot swimming in laser light sheet.
    • Movie S5 (.mp4 format). Wide view of Tunabot wake flow patterns.
    • Movie S6 (.mp4 format). Close view of Tunabot wake flow visualization around the caudal fin.
    • Movie S7 (.mp4 format). Animation of the Tunabot propulsive mechanism.

    Files in this Data Supplement:

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