This study reports the progress made towards understanding of the low energy propulsion mechanism of medusae (jellyfish) for developing energy efficient unmanned underwater vehicles (UUV). The focus of this investigation is on identifying the techniques required for prolonged sustainability of UUVs. Inspiration is taken from the constant feeding and energy generation achieved by Rhizostomeae. Rhizostomeae, in particular, utilize oral structures comprised of internal channels that capture zooplankton entrained in flow surrounding and in the wake of jellyfish on distal capture surfaces. A passive model was generated for the capture surfaces utilizing the physical dimensions based upon the morphology of <i>Mastigias papua</i> with a bell diameter of 17.2 cm. Geometry and structure of the oral components were derived from literature, live samples, and digitization of video. Based upon this data, a mold was created using silicone and assembled to achieve jellyfish inspired architecture. Geometries used to create the passive model were input into a Finite Element Analysis (FEA) simulation along with the experimental material properties of jellyfish mesoglea to ascertain the affect that the oral structure has on the kinematics and bell stresses. A forcing function was derived to achieve a close approximation of the jellyfish kinematics for the case of a jellyfish bell with oral structure attached. The same forcing function was applied to the singular bell and an increase in the bending was observed. With the escalation in bending came an increased level of principle stress within the bell closer to the margin. From this the stiffness elements that must be compensated with increased actuation force applied to the bell achieving proper swimming kinematics can be identified.
Shape memory alloy (SMA) wires are capable of providing contractile strain mimicking the functionality of muscle
fibers. They are promising for the development of biomimetic robots due to their high power density and desired
form factor. However, they suffer from significantly high power consumption. The focus of this paper was to
address this drawback associated with SMAs. Two different parameters were investigated in this study: i) lowering
of the martensite to austentite phase transition temperatures and ii) the reduction of the thermal hysteresis. For an
equiatomic Ni-Ti alloy, replacing nickel with 10 at% copper reduces the thermal hysteresis by 50% or more. For Ni-
Ti alloys with nickel content greater than 50 at%, transition temperature decreases linearly at a rate of 100 °C/Ni
at%. Given these two power reducing factors, an alloy with composition of Ni<sub>40+x</sub>Ti<sub>50-x</sub>Cu<sub>10</sub> was synthesized with x
= 0, ±1, ±2, ±3, ±4, ±5. Metal powders were melted in an argon atmosphere using an RF induction furnace to
produce ingots. All the synthesized samples were characterized by differential scanning calorimetric (DSC) analysis
to reveal martensite to austenite and austenite to martensite transition temperatures during heating and cooling
cycles respectively. Scanning electron microscopy (SEM) was conducted to identify the density and microstructure
of the fractured samples. The alloy composition and synthesis method presented in this preliminary work shows the
possibility of achieving low power consuming, high performance SMAs.
Recently, bio-inspired shape memory alloy composite (BISMAC) actuators have been shown to be promising for the
design of medusae rowing propulsion. BISMAC actuators were able to recreate bell deformation of Aurelia aurita by
controlling shape memory alloy (SMA) deformation that allowed matching the contraction-relaxation deformation
profile. In this study, we improve upon the control system and demonstrate feedback control using SMA wire resistance
to decrease contraction time and power consumption. The controller requires the knowledge of threshold resistance and
safe current inputs which were determined experimentally. The overheating effect of SMA wires was analyzed for
BioMetal Fiber (BMF) and Flexinol 100 μm diameter wires revealing an increase in resistance as the wires overheated.
The controller was first characterized on a SMA wire with bias spring system for a BMF 100 using I<sub>hi</sub> = 0.5 A and
I<sub>low</sub> = 0.2 A, where hi corresponds to peak current for fast actuation and low corresponds to the safe current which
prevents overheating and maintains desired deformation. A contraction of 4.59% was achieved in 0.06 s using the
controller and the deformation was maintained for 2 s at low current. The BISMAC actuator was operated using the
controller with I<sub>hi</sub> = 1.1 A and I<sub>low</sub> = 0.65 A achieving a 67% decrease in contraction time compared to using a constant driving current of I<sub>low</sub> = 0.2 A and a 60% decrease in energy consumption compared to using constant I<sub>hi</sub> = 0.5 A while
still exceeding the contraction requirements of the Aurelia aurita.
In this paper, we investigated two geometries of conductive polymer-metal composite actuators: stripe and
axial. The stripe actuator design consisted of gold coated poly(vinylidene difluoride) (PVDF) membrane with
polypyrrole film grown potentiodynamically on top and bottom in sandwich structure. For axial type actuator, a gold
coated core substrate was used which can be easily dissolved after polymerization of pyrrole. Synthesis of all samples
was conducted using cyclic voltammometry technique. Results indicate that axial type actuator consisting of 0.25 M
Pyrrole, 0.10 M TBAP and 0.5 M KCl in aqueous solution exhibits strain up to 6% and 18 kPa blocking stress for
applied potential of 6V DC after 80 sec stimulation time. The axial type of actuator also exhibits rotary motion under DC
voltage in electrolytic media. Experimental data was used to establish stress-strain and energy density-time response
relationships. The stripe actuator with dimensions of 20mm length, 5mm width and 63μm thickness exhibited 2.8 mm
transversal deflection at 7V and 0.2 Hz. Potential applications of conducting polymer based actuators include biometric
jellyfish and expressive robotic head.
Previously, we reported an undersea unmanned vehicle (UUV) termed as JetSum, inspired by the
locomotion of medusa jellyfish, . The propulsion of JetSum was based on shape memory alloy (SMA) wires
replicating the contraction-relaxation cycle of natural jellyfish locomotion. In this paper, we report modified design
of JetSum that addresses problems related to electrical isolation and power consumption. The modifications lead to
significant improvement in functionality, providing implementation of a full continuous bell, bolstering critical
sealing junctions, and reducing the overall power requirement. A LabVIEW controller program was developed to
automate and optimize the driving of JetSum enabling reduction in power consumption for full contraction of SMA.
JetSum locomotion in underwater conditions was recorded by using a high-speed camera and analyzed with image
processing techniques developed in MatLab. The results show that JetSum was able to achieve velocity of 7 cm/s
with power consumption of 8.94 W per cycle.
An unmanned underwater vehicle (UUV) was designed inspired by the form and
functionality of a Jellyfish. These natural organisms were chosen as bio-inspiration for a
multitude of reasons including: efficiency of locomotion, lack of natural predators, proper form
and shape to incorporate payload, and varying range of sizes. The structure consists of a hub
body surrounded by bell segments and microcontroller based drive system. The locomotion of
UUV was achieved by shape memory alloy "Biometal Fiber" actuation which possesses large
strain and blocking force with adequate response time. The main criterion in design of UUV was
the use of low-profile shape memory alloy actuators which act as artificial muscles. In this
manuscript, we discuss the design of two Jellyfish prototypes and present experimental results
illustrating the performance and power consumption.