scholarly journals Lifting a sessile oil drop from a superamphiphobic surface with an impacting one

2020 ◽  
Vol 6 (34) ◽  
pp. eaba4330
Author(s):  
Olinka Ramírez-Soto ◽  
Vatsal Sanjay ◽  
Detlef Lohse ◽  
Jonathan T. Pham ◽  
Doris Vollmer
Keyword(s):  
Surface Tension ◽  
Energy Transfer ◽  
Impact Velocity ◽  
Sessile Drop ◽  
Cloud Formation ◽  
Impact Dynamics ◽  
Combustion Engines ◽  
Intrinsic Properties ◽  
Natural Processes ◽  
The Impact

Colliding drops are encountered in everyday technologies and natural processes, from combustion engines and commodity sprays to raindrops and cloud formation. The outcome of a collision depends on many factors, including the impact velocity and the degree of alignment, and intrinsic properties like surface tension. Yet, little is known on binary impact dynamics of low-surface-tension drops on a low-wetting surface. We investigate the dynamics of an oil drop impacting an identical sessile drop sitting on a superamphiphobic surface. We observe five rebound scenarios, four of which do not involve coalescence. We describe two previously unexplored cases for sessile drop liftoff, resulting from drop-on-drop impact. Numerical simulations quantitatively reproduce the rebound scenarios and enable quantification of velocity profiles, energy transfer, and viscous dissipation. Our results illustrate how varying the offset from head-on alignment and the impact velocity results in controllable rebound dynamics for oil drop collisions on superamphiphobic surfaces.

Impact compression behaviors of high-capacity long piles

2010 ◽  
Vol 47 (12) ◽  
pp. 1335-1350 ◽  
Author(s):  
Arthur K.O. So ◽  
Charles W.W. Ng
Keyword(s):  
Energy Transfer ◽  
Impact Velocity ◽  
Stress Wave ◽  
Impact Energy ◽  
High Capacity ◽  
Measured Data ◽  
Impact Compression ◽  
Impact Forces ◽  
The Impact ◽  
Pile Length

The Hiley formula underestimates driving resistance of long piles. Methods using affected pile length have been suggested, but have been found to be inapplicable for high-capacity piles. The impact compression behaviors of about 4700 high-capacity H-piles that were 14–80 m long at final set were studied. Measured data revealed that maximum impact forces are very scattered, but their means are independent of the hammer type, ram weight, ram drop, impact velocity, and pile length. Maximum impact compression of pile and affected pile length exist in both long and short piles. The affected pile length in turn is significant to the blow efficiency, hammer constant, and energy transfer ratio. This length is governed by the impact momentum and impact energy, and can be estimated by an energy-based equation. If the affected pile length determined by this equation is substituted into the Hiley formula to back-analyze the driving resistance, predictability of the driving formula can be improved by about 8%. This improvement is significant enough to reduce the number of hammer blows required at very hard driving conditions and reduce pile damage. Furthermore, this proposed equation is simple to use in the field and is more economical compared with stress-wave monitoring techniques.

scholarly journals Exploring droplet impact near a millimetre-sized hole: comparing a closed pit with an open-ended pore

2015 ◽  
Vol 772 ◽  
pp. 427-444 ◽  
Author(s):  
Rianne de Jong ◽  
Oscar R. Enríquez ◽  
Devaraj van der Meer
Keyword(s):  
Impact Velocity ◽  
Crucial Role ◽  
Drop Impact ◽  
Impact Dynamics ◽  
Air Bubbles ◽  
Air Bubble ◽  
Impact Location ◽  
Impact Phenomena ◽  
The Impact

We investigate drop impact dynamics near closed pits and open-ended pores experimentally. The resulting impact phenomena differ greatly in each case. For a pit, we observe three distinct phenomena, which we denote as a splash, a jet and an air bubble, whose appearance depends on the distance between impact location and pit. Furthermore, we found that splash velocities can reach up to seven times the impact velocity. Drop impact near a pore, however, results solely in splashing. Interestingly, two distinct and disconnected splashing regimes occur, with a region of planar spreading in between. For pores, splashes are less pronounced than in the pit case. We state that, for the pit case, the presence of air inside it plays the crucial role of promoting splashing and allowing for air bubbles to appear.

scholarly journals Drop Impact onto a Metallic Porous Layer: Effect of Liquid Viscosity and Air Entrapment

2017 ◽  
Author(s):  
Cristina Boscariol ◽  
Dipak Sarker ◽  
Boseon Kang ◽  
Cyril Crua ◽  
Marco Marengo
Keyword(s):  
Surface Tension ◽  
Pore Size ◽  
Impact Velocity ◽  
Lower Surface ◽  
Deposition Process ◽  
Drop Impact ◽  
Theoretical Modelling ◽  
Glycerol Solution ◽  
Porous Surfaces ◽  
The Impact

The drop impact onto porous surfaces has important applications in many fields, such as painting, paper coating,drug delivery and cosmetic sprays. In most of these applications, the optimisation of the deposition process is carried out empirically, without a proper understanding of the physics and a theoretical modelling of the spreading and the imbibition phenomena. The purpose of this study is to analyse droplet impacts on metallic meshes to define a general modelling strategy of the impact regimen on particular 2D regular porous surfaces. The application of this structure is relevant in process like filtration but also in the medical field, considering for example reconstructive surgery. By analysing the impact of droplets of water, acetone and a mixture of glycerol and water, having a diameter and an impact velocity in a range of 1.5-3mm and 2-4m/s, respectively, on meshes with a pore size ranging between 25 and 400 µm, a regime map was built considering 6 different impact outcomes. The outcomes were characterised by a deposition of the droplet on the substrate, or a partial imbibition, or a total imbibition. By increasing the impact velocity, a splash region was defined, which is still characterised by a final deposition, a partial imbibition and a total imbibition. It is found that the most influencing parameters are closely linked to the liquid properties and the impact velocity, more specifically liquid surface tension plays a major role in defining the impact outcome. In the case of Acetone, the lower surface tension brings to an almost instantaneous total imbibition whereas the experiments conducted using water and glycerol solution, showed a major distribution of the deposition regimes with respect to the other outcomes, due to the effect of a higher viscosity. It was found that the geometrical characteristics of the mesh such as pore size and wire diameter, play an important role as well in defining the total imbibition outcome. Finally, the defined transition maps, shows that for a certain combination of physical properties and initial condition,the outcome of the droplet impact is predictable.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4973

Stability and Hopf Bifurcation of Impact Dynamics Considering Delay in a Semi-Active Energy Absorbing Suspension System

2011 ◽  
Author(s):  
Xiaomin Dong ◽  
Wei Hu ◽  
Miao Yu ◽  
Norman M. Wereley
Keyword(s):  
Hopf Bifurcation ◽  
Time Delay ◽  
Impact Velocity ◽  
Suspension System ◽  
Impact Dynamics ◽  
Ground Vehicles ◽  
Payload Mass ◽  
Energy Absorbers ◽  
Energy Absorbing ◽  
The Impact

In a crash event, such as the crash of an aircraft or the collision of two ground vehicles, the impact dynamics are a function of the impact velocity and payload mass. A typical bumper system on a ground vehicle has passive viscous energy absorbers (PVEAs) that are optimally designed for a specific impact velocity and payload, so that off-design performance may be suboptimal, and may even be unacceptable for large perturbations in sink rate and payload mass from the designed values. This is because the load-stroke profile of the energy absorbing suspension system (EASS) is passive in that spring stiffness and damping of the energy absorbers is fixed. Therefore, in this study, the PVEA in an EASS is replaced by an active or semi-active energy absorber (SAEA), and the effects of time delay in achieving controllable semi-active damping is analyzed in the context of impact dynamics. To accomplish this, a three degree-of-freedom dynamic model of an EASS is presented, and the effect of the time delay in commanding the controllable force of the EA is analyzed. The asymptotic stability and Hopf bifurcation of the trivial steady state response are analyzed for a range of time delay. A technique to stabilize the impact dynamic is developed, and it is shown that the impact dynamics can be stabilized using appropriate feedback control.

3D Simulation of Drop Impact on Dry Surface Using SPH Method

2018 ◽  
Vol 15 (03) ◽  
pp. 1850011 ◽  
Author(s):  
Xiufeng Yang ◽  
Song-Charng Kong
Keyword(s):  
Surface Tension ◽  
Impact Velocity ◽  
Free Particle ◽  
Particle Method ◽  
Drop Impact ◽  
Sph Method ◽  
Spherical Drop ◽  
Mesh Free ◽  
Particle Hydrodynamics ◽  
The Impact

The purpose of this paper is to present and illustrate a smoothed particle hydrodynamics (SPH) method to study the process of a drop impacting on a dry solid surface. SPH is a Lagrangian mesh-free particle method that offers advantages in modeling the evolution of the liquid surface during drop impact. A new surface tension model is used. The artificial viscosity is also used, which is demonstrated to be, approximately, a linear function of the dynamic viscosity of the liquid. The SPH method is used to simulate different liquid drops impacting on dry surfaces. The numerical results agree with experimental data obtained from the literature. The influence of various parameters on the drop impact, including impact velocity, diameter, viscosity, surface tension, and density of the drop, is also studied. The results show that the dimensionless spreading diameter of the drop increases if the impact velocity, diameter, or density increases, while the increase in viscosity and surface tension decreases the spreading diameter. The results indicate that the drop impact depends more strongly on the viscosity and impact velocity than on the diameter, surface tension, and density of the drop. In addition to the impact of a spherical drop, the impact of an ellipsoidal drop on a dry surface is also studied. The results show that the aspect ratio of the drop has a significant influence on the outcome of drop impact.

Experimental research on dynamic characteristics of viscous droplets impacting rough solid surfaces at different temperatures

2019 ◽  
Vol 97 (12) ◽  
pp. 1288-1300
Author(s):  
Yuan Zhong ◽  
Haicun Du ◽  
Ying Zhang ◽  
Yue Chen ◽  
Qiang Liu ◽  
...  
Keyword(s):  
Surface Tension ◽  
Impact Velocity ◽  
Wall Temperature ◽  
Experimental Results ◽  
Viscous Force ◽  
Equilibrium Contact Angle ◽  
High Speed Photography ◽  
Spreading Factor ◽  
The Impact ◽  
Maximum Spreading

In view of different factors that influence dynamic behavior of a droplet impacting a solid surface, high-speed photography technology was used to capture oscillation processes and splash forms after changing seven kinds of physical properties, droplets impacting different roughness and temperature walls, and with different velocities and sizes. A physical model was established, and the theoretical value correlation of maximum spreading factor was derived to compare the theoretical analysis with experimental results. The effects of viscosity, surface tension, impact velocity, diameter of droplet, roughness, and temperature of the substrates on movement characteristics during the droplet’s impact on the wall surface were investigated. As the research indicates, the rebound and oscillatory phenomena of the fluid become more obvious with an increase in surface tension, and viscous force restricts the spreading of droplets. The higher the impact velocity, the greater the spreading factor at the same time, and the more pronounced the splashing phenomenon will be. The growth rate of maximum spreading factor (βmax) increases at first and then decreases with increasing initial diameter (d0) of the droplets. The smaller the d0, the more consistent the experimental results with the analytical solutions. The equilibrium contact angle (θe) of the droplet increases with surface roughness (Ra), whereas the surface wettability degrades. θe decreases with rising wall temperature. The increase of Ra promotes the “finger-like edge” and the splash motion of droplets; moreover, the critical velocity of splash declines with Ra. The optimum temperature (Tc) of a droplet impacting the high-temperature wall reduces with a decrease of Re. Furthermore, the greater the difference between wall temperature and Tc, the more significantly βmax changes. Droplet spreading is hindered on the low-temperature wall, and the lower Re is, the smaller the decrease in amplitude of βmax with dropping wall temperature.

Monitoring the Structural Dynamics of U2 snRNA Via Single-Molecule Förster Resonance Energy Transfer

2018 ◽  
Author(s):  
Alexander Carl DeHaven
Keyword(s):  
Energy Transfer ◽  
Structural Dynamics ◽  
Single Molecule ◽  
Conformational Dynamics ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Förster Resonance Energy Transfer ◽  
U2 Snrna ◽  
Folding Dynamics ◽  
The Impact

This thesis contains four topic areas: a review of single-molecule microscropy methods and splicing, conformational dynamics of stem II of the U2 snRNA, the impact of post-transcriptional modifications on U2 snRNA folding dynamics, and preliminary findings on Mango aptamer folding dynamics.

scholarly journals A Rational Numerical Method for Simulation of Drop-Impact Dynamics of Oleo-Pneumatic Landing Gear

2021 ◽  
Vol 11 (9) ◽  
pp. 4136
Author(s):  
Rosario Pecora
Keyword(s):  
Numerical Method ◽  
Initial Conditions ◽  
Impact Load ◽  
Numerical Models ◽  
Landing Gear ◽  
Design Stage ◽  
Impact Dynamics ◽  
State Variables ◽  
Adopted Model ◽  
The Impact

Oleo-pneumatic landing gear is a complex mechanical system conceived to efficiently absorb and dissipate an aircraft’s kinetic energy at touchdown, thus reducing the impact load and acceleration transmitted to the airframe. Due to its significant influence on ground loads, this system is generally designed in parallel with the main structural components of the aircraft, such as the fuselage and wings. Robust numerical models for simulating landing gear impact dynamics are essential from the preliminary design stage in order to properly assess aircraft configuration and structural arrangements. Finite element (FE) analysis is a viable solution for supporting the design. However, regarding the oleo-pneumatic struts, FE-based simulation may become unpractical, since detailed models are required to obtain reliable results. Moreover, FE models could not be very versatile for accommodating the many design updates that usually occur at the beginning of the landing gear project or during the layout optimization process. In this work, a numerical method for simulating oleo-pneumatic landing gear drop dynamics is presented. To effectively support both the preliminary and advanced design of landing gear units, the proposed simulation approach rationally balances the level of sophistication of the adopted model with the need for accurate results. Although based on a formulation assuming only four state variables for the description of landing gear dynamics, the approach successfully accounts for all the relevant forces that arise during the drop and their influence on landing gear motion. A set of intercommunicating routines was implemented in MATLAB® environment to integrate the dynamic impact equations, starting from user-defined initial conditions and general parameters related to the geometric and structural configuration of the landing gear. The tool was then used to simulate a drop test of a reference landing gear, and the obtained results were successfully validated against available experimental data.

scholarly journals Buoyancy control in ammonoid cephalopods refined by complex internal shell architecture

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
David J. Peterman ◽  
Kathleen A. Ritterbush ◽  
Charles N. Ciampaglio ◽  
Erynn H. Johnson ◽  
Shinya Inoue ◽  
...  
Keyword(s):  
Surface Tension ◽  
Water Retention Capacity ◽  
Functional Explanation ◽  
Retention Capacity ◽  
Biomechanical Stress ◽  
Liquid Retention ◽  
3D Printed ◽  
Functional Explanations ◽  
Hydrophilic Coatings ◽  
The Impact

AbstractThe internal architecture of chambered ammonoid conchs profoundly increased in complexity through geologic time, but the adaptive value of these structures is disputed. Specifically, these cephalopods developed fractal-like folds along the edges of their internal divider walls (septa). Traditionally, functional explanations for septal complexity have largely focused on biomechanical stress resistance. However, the impact of these structures on buoyancy manipulation deserves fresh scrutiny. We propose increased septal complexity conveyed comparable shifts in fluid retention capacity within each chamber. We test this interpretation by measuring the liquid retained by septa, and within entire chambers, in several 3D-printed cephalopod shell archetypes, treated with (and without) biomimetic hydrophilic coatings. Results show that surface tension regulates water retention capacity in the chambers, which positively scales with septal complexity and membrane capillarity, and negatively scales with size. A greater capacity for liquid retention in ammonoids may have improved buoyancy regulation, or compensated for mass changes during life. Increased liquid retention in our experiments demonstrate an increase in areas of greater surface tension potential, supporting improved chamber refilling. These findings support interpretations that ammonoids with complex sutures may have had more active buoyancy regulation compared to other groups of ectocochleate cephalopods. Overall, the relationship between septal complexity and liquid retention capacity through surface tension presents a robust yet simple functional explanation for the mechanisms driving this global biotic pattern.

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