Keyur Joshi

A bio-inspired shape memory alloy composite (BISMAC) actuator

A beam-shape composite actuator using shape memory alloy (SMA) wires as the active component, termed a Bio-Inspired Shape Memory Alloy Composite (BISMAC), was designed to provide a large deformation profile. The BISMAC design was inspired by contraction of a jellyfish bell, utilizing the rowing mechanism for locomotion. Characterization of maximum deformation in underwater conditions was performed for different actuator configurations to analyze the effect of different design parameters, including silicone thickness, flexible steel thickness and distance between the SMA and flexible steel. A constant cross-section (CC)-BISMAC of length 16 cm was found to achieve deformation with a radius of curvature of 3.5 cm. Under equilibrium conditions, the CC-BISMAC was found to achieve 80% of maximum deformation, consuming 7.9 J/cycle driven at 16.2 V/0.98 A and a frequency of 0.25 Hz. A detailed analytical model was developed using the transfer matrix method and a 1D finite beam element (FE) model to simulate the behavior of the BISMAC incorporating gravity, buoyancy and SMA parameters. The FE and transfer matrix models had a maximum deformation error norm of 1.505 and 1.917 cm in comparison with experimentally observed beam deformation in the CC-BISMAC. The mean curvatures predicted by the FE and transfer matrix methods were 0.292 cm−1 and 0.295 cm−1 compared to a mean experimental curvature of 0.294 cm−1, a percentage error of −5.4% and 2.77%, respectively. Using the developed analytical model, an actuator design was fabricated mimicking the maximum deformation profile of jellyfish of the species Aurelia aurita (AA). The designed AA-BISMAC achieved a maximum curvature of 0.428 cm−1 as compared to 0.438 cm−1 for A. aurita with an average square root error of 0.043 cm−1, 10.2% of maximum A. aurita curvature.

Working principle of bio-inspired shape memory alloy composite actuators

Recently, bio-inspired shape memory alloy composite (BISMAC) actuators have been shown to mimic the deformation characteristics of natural jellyfish medusa. In this study, a constant cross-section BISMAC actuator was characterized in terms of bending deflection and force in conjunction with microscopy to understand its deformation mechanism. The actuator showed bending deflection of 111% with respect to the active length along with a blocking force of 0.061?N. The resulting energy density of the composite actuator was 4929?J?m ? 3 at an input voltage and current level of 12?V and 0.7?A, respectively. For a dry-state actuator, this performance is extremely high and represents an optimum combination of force and deflection. Experiments reveal that BISMACs performance is related to the moment induced from tip attachment of the shape memory alloy (SMA) rather than to friction within the composite structure. A physics-based model of BISMAC structure is presented which shows that the actuator is highly sensitive to the distance between the SMA wire and the incompressible component. While SMA has both stress and strain limitations, the limiting factor in BISMAC actuators is dependent on separation distance. The limiting factor in BISMACs suitability for mimicking the performance of medusa was experimentally found to be related to the maximum 4% strain of the SMA and not its force generation.

Multi-physics model of a thermo-magnetic energy harvester

Harvesting small thermal gradients effectively to generate electricity still remains a challenge. Ujihara et al (2007 Appl. Phys. Lett. 91 093508) have recently proposed a thermo-magnetic energy harvester that incorporates a combination of hard and soft magnets on a vibrating beam structure and two opposing heat transfer surfaces. This design has many advantages and could present an optimum solution to harvest energy in low temperature gradient conditions. In this paper, we describe a multi-physics numerical model for this harvester configuration that incorporates all the relevant parameters, including heat transfer, magnetic force, beam vibration, contact surface and piezoelectricity. The model was used to simulate the complete transient behavior of the system. Results are presented for the evolution of the magnetic force, changes in the internal temperature of the soft magnet (gadolinium (Gd)), thermal contact conductance, contact pressure and heat transfer over a complete cycle. Variation of the vibration frequency with contact stiffness and gap distance was also modeled. Limit cycle behavior and its bifurcations are illustrated as a function of device parameters. The model was extended to include a piezoelectric energy harvesting mechanism and, using a piezoelectric bimorph as spring material, a maximum power of 318 μW was predicted across a 100 kΩ external load.

Estimation of Solar Energy Harvested for Autonomous Jellyfish Vehicles (AJVs)

There is significant interest in harvesting ocean energy for powering the autonomous vehicles that can conduct surveillance for long durations. In this paper, we analyze the applicability of solar cells as a power source for medusa-inspired biomimetic vehicles. Since these vehicles will be operating under ocean waters and may need to dive at various depths, a systematic investigation was conducted to determine the variation of output power as a function of depth and salinity levels. We modeled solar energy harvested by flexible amorphous solar cell coated jellyfish vehicles by considering the variables bell diameter, turbidity, depth, and fineness ratio. Low fineness ratio shapes were found to be better for solar energy powered vehicles. Study of three representative species, Aurelia aurita (AA), Mastigias sp., and Cyanea capillata indicates that harvested power was proportional to bell diameter. Optimum power can be harvested by tilting the vehicle axis to face refracted sunrays. Depending on a swimming pattern, power harvested in charging mode and in propulsion mode could vary significantly. The model indicates that, under some circumstances, amorphous silicon solar cell may be a cost-effective way to power autonomous underwater vehicles (AUVs) operating in shallow-water conditions with large lateral travel distances.

Development of 2DOF Actuation Slosh Rig: A Novel Mechatronic System

Sloshing of liquid in a tank is important in several areas including launch vehicles carrying liquid fuel in space application, ships, and liquid cargo carriages. Hence modeling and characterization of nonlinear slosh dynamics is critical for study of dynamics of these systems. Additionally control of sloshing liquid offers a challenging problem of control of underactuated systems. To study slosh dynamics, develop useful identification schemes, and design and verify slosh control algorithms, a new 2DOF actuation slosh rig is reported in this paper considering the fact that most of the times the liquid tanks are subjected to linear as well as pitching excitation. The paper discusses mechatronic design and several advantages offered by the new design. Furthermore, a mathematical model of the rig is developed using Lagrange formulation assuming two-pendulum model for slosh. Slosh parameter identification with the rig is demonstrated in pitching and linear excitation cases. Nonlinear parameter identification schemes developed using simplified version of rig model are used for the purpose. Further results on compensation of slosh and rotary slosh phenomena are presented. Thus the proposed rig is ideal tool for study, identification, and control of slosh phenomena.

Novel Methods for Slosh Parameter Estimation Using Pendulum Analogy

Liquid slosh is modeled as simple pendulum. Parameter estimation strategies for this model are developed using translational and pitching excitations. Translational excitation and quick stop gives the parameters like natural frequency, slosh mass and hinge point location. Moment of inertia of rigid mass of liquid is estimated by giving pitching excitation to the tank. It is observed that moment of inertia of rigid liquid mass has a strong dependency on frequency of excitation.

Study of Fluid Structure Interaction Using Sharp Interface Immersed Boundary Method

In this work, we present an approach for solving fluid structure interaction problems by combining a non-linear structure solver with an incompressible fluid solver using immersed boundary method. The implementation of the sharp-interface immersed boundary method with the fluid solver is described. A structure solver with the ability to handle geometric nonlinearly is developed and tested with benchmark cases. The partitioned fluid-structure coupling algorithm with the strategy of enforcing boundary conditions at the fluid/structure interaction is given in detail. The fully coupled FSI approach is tested with the Turek and Hron fluid-structure interaction benchmark case. Both strong coupling and weak coupling algorithms are examined. Predictions from the current approach show good agreement with the results reported by other researchers.Copyright

Aurelia aurita Inspired Artificial Mesoglea

In this preliminary study, we report the mechanical and dielectric properties of polyvinyl alcohol (PVA)-ferritin hydrogel. This material was found to exhibit close resemblance to Aurelia aurita (jellyfish) mesoglea in terms of stiffness modulus and water content. Systematic experiments were conducted on natural jellyfish to identify its compression modulus a function of deformation. In compressive testing Aurelia aurita mesoglea was found to exhibit nonlinear modulus in the range of −10 kPa to 70 kPa depending upon the compressive strain (0–50% strain). The negative stiffness is an artifact of tensile force experienced by the specimen at the beginning of the test due to surface tension. PVA hydrogels with 60% water to dimethyl sulfoxide (DMSO) ratio without ferritin particle (H60) and PVA hydrogels with 80% water to DMSO ratio with ferritin particle (F80) provided a good alternative to natural jellyfish mesoglea exhibiting shear modulus of 33.06 Pa and 39.99 Pa respectively as compared to 4.75 Pa for Aurelia aurita mesoglea. This is a significantly better match compared to the 1041.67 Pa shear modulus of Ecoflex, a soft polymer material commonly used in biomimetic robotics. A Mooney Rivlin model suggests that H60 and F80 compositions are about 6.9 times and 8.4 times stiffer than natural Aurelia aurtia mesoglea whereas Ecoflex is 219 times as stiff. Nanocomposite hydrogel consisting of PVA matrix and ferritin nanoparticles were found to exhibit higher durability over regular PVA hydrogels and had more consistent properties due to increased cross-linking at ferritin nanoparticle sites. The ferritin nanoparticles were found to act as springs, increasing the modulus by increasing the surface area of the cross-linked polymer chains and disrupting long linear chain patterns of the polymer. Natural Aurelia aurita was found to have water content of 96.3% with a standard deviation of 0.57% as compared to 85% water content of PVA-ferritin hydrogels. Use of this material in the design of biomimetic unmanned underwater vehicles is expected to reduce the power consumption, increase swimming efficiency, and better replicate the rowing kinematics of naturally occurring Aurelia aurita.

Physical modeling of Mastigias papua feeding structures and simulation of their effect on bell stress and kinematics

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 Mastigias papua 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.

Modeling and optimization of IPMC actuator for autonomous jellyfish vehicle (AJV)

Ionomeric Polymer Metal Composite (IPMC) actuators generate high flexural strains at small voltage amplitudes of 2-5V. IPMCs bend toward the anode when a potential drop is applied across its thickness. The actuation mechanism is due to the motion of ions inside it; which requires a form of hydration to dissociate and mobilize the charges. In our group IPMCs are developed either water based or Ionic Liquid based which is also known as the dry IPMCs. This combination of small voltage requirement with operation in both dry and underwater conditions makes the IPMCs a viable alternative for an Autonomous Jellyfish Vehicle (AJV). In this study, we estimate the mechanical properties of IPMC actuator having curved geometry using FEM model to match the experimental deformation. We combine the results from an electric model to estimate charge accumulated on electrode surface with piezoelectric model to estimate stress due to this charge accumulation. In the last step, the results are integrated with a structural model to simulate the actuator deformation. We have designed an AJV with embedded IPMC actuators using these properties to achieve the curvature of relaxed and contracted Jellyfish (Aurelia Aurita). Bio-mimetic deformation profile was achieved by using structural mechanics of beams with large deformation with only application of +/- 0.8V to optimized beam within 8.1% error norm in relaxed state and 21.3% in contracted state, with only -0.24% to 0.26% maximum flexural strain at maximum curvature point in contracted state.