Quoc Viet Nguyen

Characteristics of a Beetle's Free Flight and a Flapping-Wing System that Mimics Beetle Flight

In this work, we first present a method to experimentally capture the free flight of a beetle (Allomyrina dichotoma), which is not an active flyer. The beetle is suspended in the air by a hanger to induce the free flight. This flight is filmed using two high-speed cameras. The high speed images are then examined to obtain flapping angle, flapping frequency, and wing rotation of the hind wing. The acquired data of beetle free flight are used to design a motor-driven flapper that can approximately mimic the beetle in terms of size, flapping frequency and wing kinematics. The flapper can create a large flapping angle over 140° with a large passive wing rotation angle. Even though the flapping frequency of the flapper is not high enough compared to that of a real beetle due to the limited motor torque, the flapper could produce positive average vertical force. This work will provide important experience for future development of a beetle-mimicking Flapping-Wing Micro Air Vehicle (FWMAV).

Stable Vertical Takeoff of an Insect-Mimicking Flapping-Wing System Without Guide Implementing Inherent Pitching Stability

We briefly summarized how to design and fabricate an insect-mimicking flapping-wing system and demonstrate how to implement inherent pitching stability for stable vertical takeoff. The effect of relative locations of the Center of Gravity (CG) and the mean Aerodynamic Center (AC) on vertical flight was theoretically examined through static force balance consideration. We conducted a series of vertical takeoff tests in which the location of the mean AC was determined using an unsteady Blade Element Theory (BET) previously developed by the authors. Sequential images were captured during the takeoff tests using a high-speed camera. The results demonstrated that inherent pitching stability for vertical takeoff can be achieved by controlling the relative position between the CG and the mean AC of the flapping system.

Measurement of Force Produced by an Insect-Mimicking Flapping-Wing System

We present a new version of a compact insect-mimicking flapping-wing system driven by a small motor, and suggest two testing approaches to measure the thrust or lift generated by a flapping-wing system. Flapping performance tests show the proposed flapping-wing system, which is powered by an onboard battery (lithium, 3.7 V, 180 mAh), could flap at flapping frequency of 25 Hz, and produce an average thrust or lift of about 3 g. In a wired-flight test under constrained conditions, the flapping-wing system could fly at an average forward velocity of 700 mm·s−1. For measuring the average thrust or lift produced by the flapping-wing system, we propose two testing approaches of wired-flight test and swing test with the aid of a high-speed camera and they are compared with a load cell measurement. The average thrust or lift values from the two proposed approaches agree well with the average thrust or lift values measured by a load cell.

Improvement of Artificial Foldable Wing Models by Mimicking the Unfolding/Folding Mechanism of a Beetle Hind Wing

In an attempt to realize a flapping wing micro-air vehicle with morphing wings, we report on improvements to our previous foldable artificial hind wing. Multiple hinges, which were implemented to mimic the bending zone of a beetle hind wing, were made of small composite hinge plates and tiny aluminum rivets. The buck-tails of rivets were flared after the hinge plates were assembled with the rivets so that the folding/unfolding motions could be completed in less time, and the straight shape of the artificial hind wing could be maintained after fabrication. Folding and unfolding actions were triggered by electrically-activated Shape Memory Alloy (SMA) wires. For wing folding, the actuation characteristics of the SMA wire actuator were modified through heat treatment. Through a series of flapping tests, we confirmed that the artificial wings did not fold back and arbitrarily fluctuate during the flapping motion.

Verification of Beam Models for Ionic Polymer-Metal Composite Actuator

Ionic Polymer-Metal Composite (IPMC) can work as an actuator by applying a few voltages. A thick IPMC actuator, where Nafion-117 membrane was synthesized with polypyrrole/alumina composite filler, was analyzed to verify the equivalent beam and equivalent bimorph beam models. The blocking force and tip displacement of the IPMC actuator were measured with a DC power supply and Young’s modulus of the IPMC strip was measured by bending and tensile tests respectively. The calculated maximum tip displacement and the Young’s modulus by the equivalent beam model were almost identical to the corresponding measured data. Finite element analysis with thermal analogy technique was utilized in the equivalent bimorph beam model to numerically reproduce the force-displacement relationship of the IPMC actuator. The results by the equivalent bimorph beam model agreed well with the force-displacement relationship acquired by the measured data. It is confirmed that the equivalent beam and equivalent bimorph beam models are practically and effectively suitable for predicting the tip displacement, blocking force and Young’s modulus of IPMC actuators with different thickness and different composite of ionic polymer membrane.

A motor-driven flapping-wing system mimicking beetle flight

In this work, we present an insect-inspired design of a motor-driven flapping wing system that mimics beetle in terms of beetles dimension, flapping frequency and wing kinematics. In the design, we used a combination of a Scotch yoke mechanism and a linkage system to transform the rotary motion of a motor into a large flapping motion. A passive wing rotation mechanism was implemented into the flapper by means of flexible members. The flapper was powered by an onboard lithium battery (3.7 V, 180 mAh) for flapping test; it can produce a flapping angle of 148o, a wing rotation angle of 105o at a flapping frequency of 17 Hz, and a maximum average forward velocity of 360 mm/s in a constrained condition. The flapping test and force measurement confirm that the wing rotation significantly contributes to the force generation, consequently, to the forward velocity, and the flapper can generate a positive average vertical force of about 2 grams during flapping motion.

Enhancement of a unimorph actuator performance implementing the nonlinear characteristics of piezoceramic wafer (3203HD, CTS)

In this study, the actuation displacement and blocking force of the LIPCA (Lightweight Piezo-Composite Actuator) under various combination of the external compressive load and prescribed voltage have been numerically and experimentally examined. For numerical analysis, the full three-dimensional model of the LIPCA including two end-tabs in the simply supported configuration was used and the measured nonlinear behavior of the bare piezoceramic wafer (3203HD, CTS) was implemented in the geometrically nonlinear finite element analysis. The central out-of-plane displacement of the LIPCA was measured while applying various electric fields and compressive loads at the same time. Dummy weights were added at the center of the LIPCA until the LIPCA cannot produce additional central actuation displacement for a given excitation voltage and the sum of the dummy weight was regarded as the blocking force. The numerical results acquired by geometrical/material nonlinear finite element analysis and the measured data showed a good agreement even for high electric field and compressive load. The investigation showed that the actuation displacement and blocking force of the LIPCA were significantly increased by pre-applied compressive load. At the same electric field, the actuation displacements of the LIPCA under nearly buckling load could be about two times larger than those without compressive load. The results also indicate that the positive voltage should be better applied to the actuator than the negative voltage. Therefore, the high negative electric field, which causes the polarization switching in the piezoceramic wafer, can be avoided in applications. At +150V, the blocking force of the compressed actuator under near buckling load was also increased around 26% higher than that of the actuator without compressive load.

Dynamic Characteristic of an Artificial Wing Mimicking a Beetle Hind Wing

Biomimetics is one of the most important paradigms as researchers seek to invent better engineering designs over human history. However, the observation of insect flight is a relatively recent work. Several researchers have tried to address the aerodynamic performance of flapping creatures and other natural properties of insects, although there are still many unsolved questions. In this study, we have attempted to investigate the structural dynamic characteristic of an artificial wing that mimicked the wing shape and main venation structure of a beetle hind wing using a non contact measurement method. The structural dynamic characteristic of the artificial wing was measured and compared to the real beetle hind wing by determining the natural frequencies and damping factor. The artificial wing was glued with the cyanoacrylate adhesive at the wing base onto the acrylic stand which was attached to the base of a shaker. The shaker produces the translation motion in the lateral direction of the wing plane. A non-contact laser sensor was used to measure the displacement history of the painted spots on the hind wing. A Bruel & Kjaer FFT analyzer was adopted to calculate the frequency response functions where the natural frequencies of the wing structure can be extracted. The fundamental natural frequency of artificial wing is 51.3 Hz while the natural frequency of the beetle hind wing is 48.8 Hz. In addition, the wing structures were lightly damped with damping factor around 3.1% that is close to the one of beetle hind wing. We found that, in terms of the wing elasticity, the plastic wing frame of artificial wing was suitable for beetle-like flight.Copyright

Improvement of actuation displacement of LIPCA implementing bifurcation phenomena

In this work, behavior of a unimorph piezoceramic actuator, LIPCA (Lightweight Piezo-Composite Actuator) under compression has been experimentally and numerically investigated. The LIPCA composed of composite laminated tabs, piezoceramic material layer, glass/epoxy composite and carbon fiber composite layers was modeled and analyzed by using a full three-dimensional finite element modeling technique. The geometrically nonlinear analysis was used in the analysis because the LIPCA has the initial curvature due to the curing process, which acts like an initial geometric imperfection. The LIPCA was installed in the simply supported configuration and compressive load was applied in the test jig. By measuring the lateral displacement created by the compressive load, the buckling load of the LIPCA was determined. The measured buckling load agreed well with the computed linear buckling load from the finite element analysis based on the thermal analogy. As various electric fields were applied to the LIPCA under the compressive load, the lateral displacement was measured to examine behavior of the LIPCA under the compressive load and electric field at the same time. From this test, proper combinations of the compressive load and prescribed voltage could be figured out, which can create controlled buckling of the LIPCA under compression by applying the electric field. The measured data showed that the lateral displacement of the LIPCA is significantly increased when a proper electric field is prescribed to the LIPCA in addition to the pre-determined compressive load. The measured data was compared with the computed result from the geometrically nonlinear finite element analysis based on the thermal analogy. The numerical simulation agreed well with the measurement for low compressive load (< 3N) and low electric field (< 150V). The strength of the LIPCA is also calculated to make sure that the actuator can be operated without fracture.

Improvement of stability for vertical take-off of an insect-mimicking flapping-wing system

In recent years, there has been a lot of progress in developing Flapping-Wing Micro Air Vehicles (FW-MAVs) [1–2]. Most of them were designed for low Reynolds numbers environment (in the range of 5,000 to 10,000 [3]). Therefore, many researchers have been paying attention to principle of insect flight for potential application to improve FW-MAVs or to develop even smaller system, called Nano Air Vehicles (NAVs) [4].