Instability-induced wrinkle patterns of thin sheets are ubiquitous in nature,which often result in origami-like patterns that provide inspiration for the engineering of origami designs.Inspired by instability-induced ...Instability-induced wrinkle patterns of thin sheets are ubiquitous in nature,which often result in origami-like patterns that provide inspiration for the engineering of origami designs.Inspired by instability-induced origami patterns,we propose a computational origami design method based on the nonlinear analysis of loaded thin sheets and topology optimization.The bar-and-hinge model is employed for the nonlinear structural analysis,added with a displacement perturbation strategy to initiate out-of-plane buckling.Borrowing ideas from topology optimization,a continuous crease indicator is introduced as the design variable to indicate the state of a crease,which is penalized by power functions to establish the mapping relationships between the crease indicator and hinge properties.Minimizing the structural strain energy with a crease length constraint,we are able to evolve a thin sheet into an origami structure with an optimized crease pattern.Two examples with different initial setups are illustrated,demonstrating the effectiveness and feasibility of the method.展开更多
In this study the effects of the actuation waveforms on the droplet generation in a drop-on-demand inkjet printing are studied systematically by numerical simulations.Two different types of waveforms,namely the unipol...In this study the effects of the actuation waveforms on the droplet generation in a drop-on-demand inkjet printing are studied systematically by numerical simulations.Two different types of waveforms,namely the unipolar and bipolar actuations,are investigated for three fluids with different physical properties.We focus on two key parameters,which are the dwell time and the velocity amplitude.For the unipolar driving,the ejection velocity and the ejected liquid volume are both increased as the velocity amplitude becomes larger.The dwell time only has minor effects on both the ejection velocity and the ejected liquid volume.The ejection velocity decreases significantly for large liquid viscosity,while the influences of viscosity on the ejected liquid volume are much weaker.Four different droplet morphologies and the corresponding parameter ranges are identified.The droplet radius can be successfully reduced to about 40%e of the nozzle exit radius.For the bipolar waveforms,same droplet morphologies are observed but with shifted boundaries in the phase space.The minimal radius of stable droplet produced by the bipolar waveforms is even smaller compared to the unipolar ones.展开更多
The droplet formation dynamics of a Newtonian liquid in a drop-on-demand (DOD) inkjet process is numerically investigated by using a volume-of-fluid (VOF) method. We focus on the nozzle geometry, wettability of the in...The droplet formation dynamics of a Newtonian liquid in a drop-on-demand (DOD) inkjet process is numerically investigated by using a volume-of-fluid (VOF) method. We focus on the nozzle geometry, wettability of the interior surface, and the fluid properties to achieve the stable droplet formation with higher velocity. It is found that a nozzle with contracting angle of 45° generates the most stable and fastest single droplet, which is beneficial for the enhanced printing quality and high-throughput printing rate. For this nozzle with the optimal geometry, we systematically change the wettability of the interior surface, i.e., different contact angles. As the contact angle increases, pinch-off time increases and the droplet speed reduces. Finally, fluids with different properties are investigated to identify the printability range.展开更多
In this work,we numerically study the impact of a water droplet onto a deep oil pool.Two fluids are immiscible and the viscosity of the pool liquid is changed systematically.We focus on the cavity dynamics during the ...In this work,we numerically study the impact of a water droplet onto a deep oil pool.Two fluids are immiscible and the viscosity of the pool liquid is changed systematically.We focus on the cavity dynamics during the impact and especially the effects of the pool liquid viscosity and the impacting velocity.For the parameter range explored,we identify the regime where splashing occurs with corolla breaking into droplets,and the regime where no splashing is observed.Similarity is found for the time evolution of cavity depth for fixed impact velocity and different viscosity,if the cavity depth and time are nondimensionalized by the maximal depth and the time when the maximal depth is reached.Effective power-law scalings are also proposed to describe the dependence of the maximal cavity depth and the corresponding time on the impact velocity and pool liquid viscosity,in the term of Froude and Reynolds numbers.展开更多
The dynamic model of a bistable laminated composite shell simply supported by four corners is further developed to investigate the resonance responses and chaotic behaviors.The existence of the 1:1 resonance relations...The dynamic model of a bistable laminated composite shell simply supported by four corners is further developed to investigate the resonance responses and chaotic behaviors.The existence of the 1:1 resonance relationship between two order vibration modes of the system is verified.The resonance response of this class of bistable structures in the dynamic snap-through mode is investigated,and the four-dimensional(4D)nonlinear modulation equations are derived based on the 1:1 internal resonance relationship by means of the multiple scales method.The Hopf bifurcation and instability interval of the amplitude frequency and force amplitude curves are analyzed.The discussion focuses on investigating the effects of key parameters,e.g.,excitation amplitude,damping coefficient,and detuning parameters,on the resonance responses.The numerical simulations show that the foundation excitation and the degree of coupling between the vibration modes exert a substantial effect on the chaotic dynamics of the system.Furthermore,the significant motions under particular excitation conditions are visualized by bifurcation diagrams,time histories,phase portraits,three-dimensional(3D)phase portraits,and Poincare maps.Finally,the vibration experiment is carried out to study the amplitude frequency responses and bifurcation characteristics for the bistable laminated composite shell,yielding results that are qualitatively consistent with the theoretical results.展开更多
Solid–liquid composites(SLCs)with novel thermal/electronic/mechanical properties imparted by programmable and functional liquid inclusions have attracted considerable research interest in recent years,and are widely ...Solid–liquid composites(SLCs)with novel thermal/electronic/mechanical properties imparted by programmable and functional liquid inclusions have attracted considerable research interest in recent years,and are widely used in smart electronics and soft robotics.The feasible application of SLCs requires that they exhibit excellent static physical properties as well as dynamic impact resistance to satisfy complex service conditions,such as drops and impacts.This paper examined the impact resistance of SLCs fabricated by using microfluidic 3D printing.The results of dynamic split-Hopkinson pressure bar(SHPB)tests showed that the performance of the fabricated SLCs improved in terms of energy dissipation and impact resistance compared with pristine materials.In case of dynamic impact in the strain rates ranging from 100 to 400s−1,the SLC specimen deformed without fracture,and its energy dissipation was dominated by the viscosity of the liquid inclusions.For dynamic impact in the strain rates ranging from 500 to 800s−1,the SLC specimen fractured and its energy dissipation was determined by the volume fraction of the liquid inclusions.Thus,the energy dissipation of the SLCs could be tuned by regulating the viscosity and volume fraction of the liquid inclusions to satisfy the requirements of protection against different strain rates.Furthermore,the process of fracture of the SLCs under the dynamic SHPB tests was recorded and analyzed by using a high-speed camera.The results showed that distributed liquid inclusions changed the paths of crack propagation to enhance energy dissipation in the SLCs.This study experimentally verified the enhancement in the energy dissipation of SLCs,and provided design strategies for developing multifunctional SLCs with high impact resistance.展开更多
Intelligent machines are capable of switching shape configurations to adapt to changes in dynamic environments and thus have offered the potentials in many applications such as precision medicine,lab on a chip,and bio...Intelligent machines are capable of switching shape configurations to adapt to changes in dynamic environments and thus have offered the potentials in many applications such as precision medicine,lab on a chip,and bioengineering.Even though the developments of smart materials and advanced micro/nanomanufacturing are flouring,how to achieve intelligent shapemorphing machines at micro/nanoscales is still significantly challenging due to the lack of design methods and strategies especially for small-scale shape transformations.This review is aimed at summarizing the principles and methods for the construction of intelligent shape-morphing micromachines by introducing the dimensions,modes,realization methods,and applications of shape-morphing micromachines.Meanwhile,this review highlights the advantages and challenges in shape transformations by comparing micromachines with the macroscale counterparts and presents the future outlines for the next generation of intelligent shape-morphing micromachines.展开更多
基金National Key Research and Development Program of China(2020YFE0204200,2022YFB4701900)National Natural Science Foundation of China(11988102,12202008)Experiments for Space Exploration Program and the Qian Xuesen Laboratory,China Academy of Space Technology(TKTSPY-2020-03-05).
文摘Instability-induced wrinkle patterns of thin sheets are ubiquitous in nature,which often result in origami-like patterns that provide inspiration for the engineering of origami designs.Inspired by instability-induced origami patterns,we propose a computational origami design method based on the nonlinear analysis of loaded thin sheets and topology optimization.The bar-and-hinge model is employed for the nonlinear structural analysis,added with a displacement perturbation strategy to initiate out-of-plane buckling.Borrowing ideas from topology optimization,a continuous crease indicator is introduced as the design variable to indicate the state of a crease,which is penalized by power functions to establish the mapping relationships between the crease indicator and hinge properties.Minimizing the structural strain energy with a crease length constraint,we are able to evolve a thin sheet into an origami structure with an optimized crease pattern.Two examples with different initial setups are illustrated,demonstrating the effectiveness and feasibility of the method.
基金National Natural Science Foundation of China(Grants 91848201,11988102,11521202,11872004.11802004)The authors also acknowledge the partial support from the Beijing Natural Science Foundation(Grants L172002)+1 种基金A.B.Aqecl would like to thank the Chinese Scholarship Council(CSC)for providing Chinese Government Scholarship(CGs)The numericalsimulations were performed on the National Super Computing Centerin Tianjin.China.
文摘In this study the effects of the actuation waveforms on the droplet generation in a drop-on-demand inkjet printing are studied systematically by numerical simulations.Two different types of waveforms,namely the unipolar and bipolar actuations,are investigated for three fluids with different physical properties.We focus on two key parameters,which are the dwell time and the velocity amplitude.For the unipolar driving,the ejection velocity and the ejected liquid volume are both increased as the velocity amplitude becomes larger.The dwell time only has minor effects on both the ejection velocity and the ejected liquid volume.The ejection velocity decreases significantly for large liquid viscosity,while the influences of viscosity on the ejected liquid volume are much weaker.Four different droplet morphologies and the corresponding parameter ranges are identified.The droplet radius can be successfully reduced to about 40%e of the nozzle exit radius.For the bipolar waveforms,same droplet morphologies are observed but with shifted boundaries in the phase space.The minimal radius of stable droplet produced by the bipolar waveforms is even smaller compared to the unipolar ones.
基金Project supported by the National Natural Science Foundation of China(No.11802004)
文摘The droplet formation dynamics of a Newtonian liquid in a drop-on-demand (DOD) inkjet process is numerically investigated by using a volume-of-fluid (VOF) method. We focus on the nozzle geometry, wettability of the interior surface, and the fluid properties to achieve the stable droplet formation with higher velocity. It is found that a nozzle with contracting angle of 45° generates the most stable and fastest single droplet, which is beneficial for the enhanced printing quality and high-throughput printing rate. For this nozzle with the optimal geometry, we systematically change the wettability of the interior surface, i.e., different contact angles. As the contact angle increases, pinch-off time increases and the droplet speed reduces. Finally, fluids with different properties are investigated to identify the printability range.
基金This work was supported by the National Natural Science Foundation of China(Grants 91848201,11988102,11521202,11872004,and 11802004)The authors also acknowledge the partial support from the Beijing Natural Science Foundation(Grants L172002)The numerical simulations were performed on Tianhe-1 A,the National Super Computing Center in Tianjin,China.Muhammad Mohasan would like to thank Chinese Scholarship Council for providing Chinese Government Scholarship.
文摘In this work,we numerically study the impact of a water droplet onto a deep oil pool.Two fluids are immiscible and the viscosity of the pool liquid is changed systematically.We focus on the cavity dynamics during the impact and especially the effects of the pool liquid viscosity and the impacting velocity.For the parameter range explored,we identify the regime where splashing occurs with corolla breaking into droplets,and the regime where no splashing is observed.Similarity is found for the time evolution of cavity depth for fixed impact velocity and different viscosity,if the cavity depth and time are nondimensionalized by the maximal depth and the time when the maximal depth is reached.Effective power-law scalings are also proposed to describe the dependence of the maximal cavity depth and the corresponding time on the impact velocity and pool liquid viscosity,in the term of Froude and Reynolds numbers.
基金Project supported by the National Natural Science Foundation of China(Nos.12293000,12293001,11988102,12172006,and 12202011)。
文摘The dynamic model of a bistable laminated composite shell simply supported by four corners is further developed to investigate the resonance responses and chaotic behaviors.The existence of the 1:1 resonance relationship between two order vibration modes of the system is verified.The resonance response of this class of bistable structures in the dynamic snap-through mode is investigated,and the four-dimensional(4D)nonlinear modulation equations are derived based on the 1:1 internal resonance relationship by means of the multiple scales method.The Hopf bifurcation and instability interval of the amplitude frequency and force amplitude curves are analyzed.The discussion focuses on investigating the effects of key parameters,e.g.,excitation amplitude,damping coefficient,and detuning parameters,on the resonance responses.The numerical simulations show that the foundation excitation and the degree of coupling between the vibration modes exert a substantial effect on the chaotic dynamics of the system.Furthermore,the significant motions under particular excitation conditions are visualized by bifurcation diagrams,time histories,phase portraits,three-dimensional(3D)phase portraits,and Poincare maps.Finally,the vibration experiment is carried out to study the amplitude frequency responses and bifurcation characteristics for the bistable laminated composite shell,yielding results that are qualitatively consistent with the theoretical results.
基金the National Natural Science Foundation of China(NSFC)under Grant nos.11988102,91848201,11521202,11872004,and 11802004China Postdoctoral Science Foundation under Grant no.2020M680222.
文摘Solid–liquid composites(SLCs)with novel thermal/electronic/mechanical properties imparted by programmable and functional liquid inclusions have attracted considerable research interest in recent years,and are widely used in smart electronics and soft robotics.The feasible application of SLCs requires that they exhibit excellent static physical properties as well as dynamic impact resistance to satisfy complex service conditions,such as drops and impacts.This paper examined the impact resistance of SLCs fabricated by using microfluidic 3D printing.The results of dynamic split-Hopkinson pressure bar(SHPB)tests showed that the performance of the fabricated SLCs improved in terms of energy dissipation and impact resistance compared with pristine materials.In case of dynamic impact in the strain rates ranging from 100 to 400s−1,the SLC specimen deformed without fracture,and its energy dissipation was dominated by the viscosity of the liquid inclusions.For dynamic impact in the strain rates ranging from 500 to 800s−1,the SLC specimen fractured and its energy dissipation was determined by the volume fraction of the liquid inclusions.Thus,the energy dissipation of the SLCs could be tuned by regulating the viscosity and volume fraction of the liquid inclusions to satisfy the requirements of protection against different strain rates.Furthermore,the process of fracture of the SLCs under the dynamic SHPB tests was recorded and analyzed by using a high-speed camera.The results showed that distributed liquid inclusions changed the paths of crack propagation to enhance energy dissipation in the SLCs.This study experimentally verified the enhancement in the energy dissipation of SLCs,and provided design strategies for developing multifunctional SLCs with high impact resistance.
基金supported by the National Natural Science Foundation of China(grant nos.91848201,11521202,11988102,11872004,11802004,and 11702003)the Beijing Natural Science Foundation under grant no.L172002.
文摘Intelligent machines are capable of switching shape configurations to adapt to changes in dynamic environments and thus have offered the potentials in many applications such as precision medicine,lab on a chip,and bioengineering.Even though the developments of smart materials and advanced micro/nanomanufacturing are flouring,how to achieve intelligent shapemorphing machines at micro/nanoscales is still significantly challenging due to the lack of design methods and strategies especially for small-scale shape transformations.This review is aimed at summarizing the principles and methods for the construction of intelligent shape-morphing micromachines by introducing the dimensions,modes,realization methods,and applications of shape-morphing micromachines.Meanwhile,this review highlights the advantages and challenges in shape transformations by comparing micromachines with the macroscale counterparts and presents the future outlines for the next generation of intelligent shape-morphing micromachines.
