This paper addresses the design of a biomimetic fish robot actuated by piezoeeramic actuators and the effect of artificial caudal fins on the fish robot＇s performance. The limited bending displacement produced by a l...This paper addresses the design of a biomimetic fish robot actuated by piezoeeramic actuators and the effect of artificial caudal fins on the fish robot＇s performance. The limited bending displacement produced by a lightweight piezocomposite actuator was amplified and transformed into a large tail beat motion by means of a linkage system. Caudal fins that mimic the shape of a mackerel fin were fabricated for the purpose of examining the effect of caudal fm characteristics on thrust production at an operating frequency range. The thickness distribution of a real mackerel＇s fin was measured and used to design artificial caudal fins. The thrust performance of the biomimetic fish robot propelled by fins of various thicknesses was examined in terms of the Strouhal number, the Froude number, the Reynolds number, and the power consumption. For the same fm area and aspect ratio, an artificial caudal fin with a distributed thickness shows the best forward speed and the least power consumption.展开更多
In an attempt to realize a flapping wing micro-air vehicle with morphing wings, we report on improvements to our previousfoldable artificial hind wing.Multiple hinges, which were implemented to mimic the bending zone ...In an attempt to realize a flapping wing micro-air vehicle with morphing wings, we report on improvements to our previousfoldable artificial hind wing.Multiple hinges, which were implemented to mimic the bending zone of a beetle hind wing, weremade of small composite hinge plates and tiny aluminum rivets.The buck-tails of rivets were flared after the hinge plates wereassembled with the rivets so that the folding/unfolding motions could be completed in less time, and the straight shape of theartificial hind wing could be maintained after fabrication.Folding and unfolding actions were triggered by electrically-activatedShape Memory Alloy (SMA) wires.For wing folding, the actuation characteristics of the SMA wire actuator were modifiedthrough heat treatment.Through a series of flapping tests, we confirmed that the artificial wings did not fold back and arbitrarilyfluctuate during the flapping motion.展开更多
Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves,which have an effect on the coloration of Morpho butterflies and enhance the hydrophobicity of natural surfaces.We investiga...Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves,which have an effect on the coloration of Morpho butterflies and enhance the hydrophobicity of natural surfaces.We investigated the micro-scale and nano-scale structures on the wing surfaces of insects and found that the hierarchical multiple roughness structures help in enhancing the hydrophobicity.After examining 10 orders and 24 species of flying Pterygotan insects,we found that micro-scale and nano-scale structures typically exist on both the upper and lower wing surfaces of flying insects.The tiny structures such as denticle or setae on the insect wings enhance the hydrophobicity,thereby enabling the wings to be cleaned more easily.And the hydrophobic insect wings undergo a transition from Cassie to Wenzel states at pitch/size ratio of about 20.In order to examine the wetting characteristics on a rough surface,a biomimetic surface with micro-scale pillars is fabricated on a silicon wafer, which exhibits the same behavior as the insect wing,with the Cassie-Wenzel transition occurring consistently around a pitch/width value of 20.展开更多
In this work, a three-dimensional （3D） Computational Fluid Dynamics （CFD） model was built to simulate the tail fin motion of a fish robot actuated by a piezoceramic composite actuator, and to determine the maximum...In this work, a three-dimensional （3D） Computational Fluid Dynamics （CFD） model was built to simulate the tail fin motion of a fish robot actuated by a piezoceramic composite actuator, and to determine the maximum thrust tail-beat frequency. A simulation of the tail fin at a tail-beat frequency was performed to confirm measured thrust data from a previous study. The computed and measured thrusts were in good agreement. A series of thrust simulations were conducted for various tail-beat frequencies to confirm the maximum thrust frequency that was obtained from thrust measurements in the previous study. The largest thrust was calculated at a tail-beat frequency of 3.7 Hz and vortices around the tail were fully separated. The calculated maximum thrust tail-beat frequency was in good agreement with the measured frequency. Flow characteristics during tail fin motion were examined to explain why the largest thrust occurred at this particular tail-beat frequency.展开更多
We have studied a biomimetic swimmer based on the motion of bacteria such as Escherichia coli (E. coli) theoretically andexperimentally. The swimmer has an ellipsoidal cell body propelled by a helical filament. The pe...We have studied a biomimetic swimmer based on the motion of bacteria such as Escherichia coli (E. coli) theoretically andexperimentally. The swimmer has an ellipsoidal cell body propelled by a helical filament. The performance of this swimmer wasestimated by modeling the dynamics of a swimmer in viscous fluid. We applied the Resistive Force Theory (RFT) on this modelto calculate the linear swimming speed and the efficiency of the model. A parametric study on linear velocity and efficiency tooptimize the design of this swimmer was demonstrated. In order to validate the theoretical results, a biomimetic swimmer wasfabricated and an experiment setup was prepared to measure the swimming speed and thrust force in silicone oil. The experimentalresults agree well with the theoretical values predicted by RFT. In addition, we studied the flow patterns surrounding thefilament with a finite element simulation with different Reynolds number (Re) to understand the mechanism of propulsion. Thesimulation results provide information on the nature of flow patterns generated by swimming filament. Furthermore, the thrustforces from the simulation were compared with the thrust forces from theory. The simulation results are in good agreement withthe theoretical results.展开更多
Beetle wings are very specialized flight organs consisting of the veins and membranes.Therefore it is necessary from a bionic view to investigate the material properties of a beetle wing experimentally.In the present ...Beetle wings are very specialized flight organs consisting of the veins and membranes.Therefore it is necessary from a bionic view to investigate the material properties of a beetle wing experimentally.In the present study,we have used a Digital Image Correlation (DIC) technique to measure the elastic modulus of a beetle wing membrane.Specimens were prepared by carefully cutting a beetle hind wing into 3.0 mm by 7.0 mm segments (the gage length was 5 mm).We used a scanning electron microscope for a precise measurement of the thickness of the beetle wing membrane.The specimen was attached to a designed fixture to induce a uniform displacement by means of a micromanipulator.We used an ARAMISTM system based on the digital image correlation technique to measure the corresponding displacement of a specimen.The thickness of the beetle wing varied at different points of the membrane.The elastic modulus differed in relation to the membrane arrangement showing a structural anisotropy;the elastic modulus in the chordwise direction is approximately 2.65 GPa,which is three times larger than the elastic modulus in the spanwise direction of 0.84 GPa.As a result,the digital image correlation-based ARAMIS system was suc- cessfully used to measure the elastic modulus of a beetle wing.In addition to membrane's elastic modulus,we considered the Poisson's ratio of the membrane and measured the elastic modulus of a vein using an Instron universal tensile machine.The result reveals the Poisson's ratio is nearly zero and the elastic modulus of a vein is about 11 GPa.展开更多
We conducted a comprehensive study to investigate the aerodynamic characteristics and force generation of the elytra of abeetle,Allomyrina dichotoma.Our analysis included wind tunnel experiments and three-dimensional ...We conducted a comprehensive study to investigate the aerodynamic characteristics and force generation of the elytra of abeetle,Allomyrina dichotoma.Our analysis included wind tunnel experiments and three-dimensional computational fluiddynamics simulations using ANSYS-CFX software.Our first approach was a quasi-static study that considered the effect ofinduced flapping flow due to the flapping motion of the fore-wings (elytra) at a frequency of around 30 Hz to 40 Hz.The dihedralangle was varied to represent flapping motion during the upstroke and downstroke.We found that an elytron producespositive lift at 0° geometric angle of attack,negative lift during the upstroke,and always produces drag during both the upstrokeand downstroke.We also found that the lift coefficient of an elytron does not drop even at a very high geometric angle of attack.For a beetle with a body weight of 5 g,based on the quasi-static method,the fore-wings (elytra) can produce lift of less than 1%of its body weight.展开更多
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 ...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.展开更多
For the global commercialization of highly efficient and stable perovskite solar cells(PSCs),it is necessary to effectively suppress the formation of various defects acting as nonradiative recombination sources in per...For the global commercialization of highly efficient and stable perovskite solar cells(PSCs),it is necessary to effectively suppress the formation of various defects acting as nonradiative recombination sources in perovskite light-harvesting materials.Interfacial defects between the charge-selective layer and the perovskite are easily formed in the solution process used to fabricate perovskite films.In addition,owing to the difference in thermal expansion coefficients between the substrate and the perovskite film,internal residual tensile stress inevitably occurs,resulting in increased nonradiative recombination.Herein,a simple compositional engineering scheme for realizing efficient and stable PSCs,which incorporates acetamidinium bromide(AABr)as an additive into the MAPbI_(3) lattice,is proposed.As an additive,AABr has been found to provide synergistic multiple passivation for both internal and interfacial defects.AABr was found to effectively release the tensile strain of the MAPbI_(3) film by forming a structure stabilized by NH-I hydrogen bonds,as evidenced by calculations based on density functional theory(DFT).Furthermore,the incorporated AABr additives created a charge carrier recombination barrier to enhance charge collection capability by reducing interfacial defects.Accordingly,a power conversion efficiency(PCE)of 20.18%was achieved using a planar device employing AABr-incorporated MAPbI_(3).This was substantially higher than the 18.32% PCE of a pristine MAPbI_(3)-based device.Notably,unencapsulated PSCs using AABr-incorporated MAPbI_(3) absorbers exhibited excellent long-term stability,maintaining>95% of initial PCE up to 1200 hours in ambient air.展开更多
文摘This paper addresses the design of a biomimetic fish robot actuated by piezoeeramic actuators and the effect of artificial caudal fins on the fish robot＇s performance. The limited bending displacement produced by a lightweight piezocomposite actuator was amplified and transformed into a large tail beat motion by means of a linkage system. Caudal fins that mimic the shape of a mackerel fin were fabricated for the purpose of examining the effect of caudal fm characteristics on thrust production at an operating frequency range. The thickness distribution of a real mackerel＇s fin was measured and used to design artificial caudal fins. The thrust performance of the biomimetic fish robot propelled by fins of various thicknesses was examined in terms of the Strouhal number, the Froude number, the Reynolds number, and the power consumption. For the same fm area and aspect ratio, an artificial caudal fin with a distributed thickness shows the best forward speed and the least power consumption.
基金supported by the Korea Science and Engineering Foundation Grant(National Research Laboratory Program,R0A-2007-000-200012-0)the Korea Research Foundation(KRF-006-005-J03301)partially supported by the 2009 KU Brain Pool of Konkuk University
文摘In an attempt to realize a flapping wing micro-air vehicle with morphing wings, we report on improvements to our previousfoldable artificial hind wing.Multiple hinges, which were implemented to mimic the bending zone of a beetle hind wing, weremade of small composite hinge plates and tiny aluminum rivets.The buck-tails of rivets were flared after the hinge plates wereassembled with the rivets so that the folding/unfolding motions could be completed in less time, and the straight shape of theartificial hind wing could be maintained after fabrication.Folding and unfolding actions were triggered by electrically-activatedShape Memory Alloy (SMA) wires.For wing folding, the actuation characteristics of the SMA wire actuator were modifiedthrough heat treatment.Through a series of flapping tests, we confirmed that the artificial wings did not fold back and arbitrarilyfluctuate during the flapping motion.
基金supported by the National Research Laboratory Program, Korea Science and Engineering Foundation Grant (Grant No. R0A-2007-000-20012-0)the Korea Research Foundation Grant (Grant No. KRF-2006-005-J03301)+1 种基金J. Hong was partially supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (Grant No. KRP-2006-214-D00056)J. R. Lukes acknowledges partial support from the National Science Foundation (Grant No.CBET-0424101)
文摘Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves,which have an effect on the coloration of Morpho butterflies and enhance the hydrophobicity of natural surfaces.We investigated the micro-scale and nano-scale structures on the wing surfaces of insects and found that the hierarchical multiple roughness structures help in enhancing the hydrophobicity.After examining 10 orders and 24 species of flying Pterygotan insects,we found that micro-scale and nano-scale structures typically exist on both the upper and lower wing surfaces of flying insects.The tiny structures such as denticle or setae on the insect wings enhance the hydrophobicity,thereby enabling the wings to be cleaned more easily.And the hydrophobic insect wings undergo a transition from Cassie to Wenzel states at pitch/size ratio of about 20.In order to examine the wetting characteristics on a rough surface,a biomimetic surface with micro-scale pillars is fabricated on a silicon wafer, which exhibits the same behavior as the insect wing,with the Cassie-Wenzel transition occurring consistently around a pitch/width value of 20.
文摘In this work, a three-dimensional （3D） Computational Fluid Dynamics （CFD） model was built to simulate the tail fin motion of a fish robot actuated by a piezoceramic composite actuator, and to determine the maximum thrust tail-beat frequency. A simulation of the tail fin at a tail-beat frequency was performed to confirm measured thrust data from a previous study. The computed and measured thrusts were in good agreement. A series of thrust simulations were conducted for various tail-beat frequencies to confirm the maximum thrust frequency that was obtained from thrust measurements in the previous study. The largest thrust was calculated at a tail-beat frequency of 3.7 Hz and vortices around the tail were fully separated. The calculated maximum thrust tail-beat frequency was in good agreement with the measured frequency. Flow characteristics during tail fin motion were examined to explain why the largest thrust occurred at this particular tail-beat frequency.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education Science and Technology(Grant number:2010-0018884)
文摘We have studied a biomimetic swimmer based on the motion of bacteria such as Escherichia coli (E. coli) theoretically andexperimentally. The swimmer has an ellipsoidal cell body propelled by a helical filament. The performance of this swimmer wasestimated by modeling the dynamics of a swimmer in viscous fluid. We applied the Resistive Force Theory (RFT) on this modelto calculate the linear swimming speed and the efficiency of the model. A parametric study on linear velocity and efficiency tooptimize the design of this swimmer was demonstrated. In order to validate the theoretical results, a biomimetic swimmer wasfabricated and an experiment setup was prepared to measure the swimming speed and thrust force in silicone oil. The experimentalresults agree well with the theoretical values predicted by RFT. In addition, we studied the flow patterns surrounding thefilament with a finite element simulation with different Reynolds number (Re) to understand the mechanism of propulsion. Thesimulation results provide information on the nature of flow patterns generated by swimming filament. Furthermore, the thrustforces from the simulation were compared with the thrust forces from theory. The simulation results are in good agreement withthe theoretical results.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF)the Ministry of Education, Science and Technology (Grant number: 2009-0083068)
文摘Beetle wings are very specialized flight organs consisting of the veins and membranes.Therefore it is necessary from a bionic view to investigate the material properties of a beetle wing experimentally.In the present study,we have used a Digital Image Correlation (DIC) technique to measure the elastic modulus of a beetle wing membrane.Specimens were prepared by carefully cutting a beetle hind wing into 3.0 mm by 7.0 mm segments (the gage length was 5 mm).We used a scanning electron microscope for a precise measurement of the thickness of the beetle wing membrane.The specimen was attached to a designed fixture to induce a uniform displacement by means of a micromanipulator.We used an ARAMISTM system based on the digital image correlation technique to measure the corresponding displacement of a specimen.The thickness of the beetle wing varied at different points of the membrane.The elastic modulus differed in relation to the membrane arrangement showing a structural anisotropy;the elastic modulus in the chordwise direction is approximately 2.65 GPa,which is three times larger than the elastic modulus in the spanwise direction of 0.84 GPa.As a result,the digital image correlation-based ARAMIS system was suc- cessfully used to measure the elastic modulus of a beetle wing.In addition to membrane's elastic modulus,we considered the Poisson's ratio of the membrane and measured the elastic modulus of a vein using an Instron universal tensile machine.The result reveals the Poisson's ratio is nearly zero and the elastic modulus of a vein is about 11 GPa.
基金supported by the Basic Science Research Program of the National Research Foundation of Korea (NRF)funded by the Ministry of Education,Science and Technology of the Korean government (Grant No.2010-0018884)
文摘We conducted a comprehensive study to investigate the aerodynamic characteristics and force generation of the elytra of abeetle,Allomyrina dichotoma.Our analysis included wind tunnel experiments and three-dimensional computational fluiddynamics simulations using ANSYS-CFX software.Our first approach was a quasi-static study that considered the effect ofinduced flapping flow due to the flapping motion of the fore-wings (elytra) at a frequency of around 30 Hz to 40 Hz.The dihedralangle was varied to represent flapping motion during the upstroke and downstroke.We found that an elytron producespositive lift at 0° geometric angle of attack,negative lift during the upstroke,and always produces drag during both the upstrokeand downstroke.We also found that the lift coefficient of an elytron does not drop even at a very high geometric angle of attack.For a beetle with a body weight of 5 g,based on the quasi-static method,the fore-wings (elytra) can produce lift of less than 1%of its body weight.
基金supported by the Defense Acquisition Program Administration (DAPA)the Agency for Defense Development (ADD) in Korea+1 种基金the Korea Research Foundation (KRF-2006-005-J03301)the National Research Foundation (Grant number: 2009-0083068).
文摘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.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Science and ICT(2020R1F1A1068664)。
文摘For the global commercialization of highly efficient and stable perovskite solar cells(PSCs),it is necessary to effectively suppress the formation of various defects acting as nonradiative recombination sources in perovskite light-harvesting materials.Interfacial defects between the charge-selective layer and the perovskite are easily formed in the solution process used to fabricate perovskite films.In addition,owing to the difference in thermal expansion coefficients between the substrate and the perovskite film,internal residual tensile stress inevitably occurs,resulting in increased nonradiative recombination.Herein,a simple compositional engineering scheme for realizing efficient and stable PSCs,which incorporates acetamidinium bromide(AABr)as an additive into the MAPbI_(3) lattice,is proposed.As an additive,AABr has been found to provide synergistic multiple passivation for both internal and interfacial defects.AABr was found to effectively release the tensile strain of the MAPbI_(3) film by forming a structure stabilized by NH-I hydrogen bonds,as evidenced by calculations based on density functional theory(DFT).Furthermore,the incorporated AABr additives created a charge carrier recombination barrier to enhance charge collection capability by reducing interfacial defects.Accordingly,a power conversion efficiency(PCE)of 20.18%was achieved using a planar device employing AABr-incorporated MAPbI_(3).This was substantially higher than the 18.32% PCE of a pristine MAPbI_(3)-based device.Notably,unencapsulated PSCs using AABr-incorporated MAPbI_(3) absorbers exhibited excellent long-term stability,maintaining>95% of initial PCE up to 1200 hours in ambient air.
