Water Drop Impact Research Articles

Transition metal oxide anti-reflection coatings for airborne diamond optics

Recent progress in CVD diamond technology has resulted in the commercial availability of large area (≈200 cm 2) components with the required optical and mechanical properties to be used for airborne imaging applications in the 8–12 μm band. Some of these applications require an anti-reflection (AR) coating on the outside surface of the diamond. These AR coatings have to be extremely durable and adherent to the diamond if they are to survive the rigors of high-speed flight. The mechanical durability has been assessed using water drop impact erosions tests. AR coatings which, reduce reflection to less than 5% and survive impact at 400 ms −1, have been developed, based on transition metal oxides and nitrides deposited by reactive sputtering. This paper discusses the properties of these coatings and the mechanisms of adhesion in the diamond to coating interface.

Splash formation by spherical drops

The impact of a spherical water drop onto a water surface has been studied experimentally with the aid of a 35 mm drum camera giving high-resolution images that provided qualitative and quantitative data on the phenomena. Scaling laws for the time to reach maximum cavity sizes have been derived and provide a good fit to the experimental results. Transitions between the regimes for coalescence-only, the formation of a high-speed jet and bubble entrapment have been delineated. The high-speed jet was found to occur without bubble entrapment. This was caused by the rapid retraction of the trough formed by a capillary wave converging to the centre of the cavity base. The converging capillary wave has a profile similar to a Crapper wave. A plot showing the different regimes of cavity and impact drop behaviour in the Weber–Froude number-plane has been constructed for Fr and We less than 1000.

Stress Wave Propagation in a Coated Elastic Half-Space due to Water Drop Impact

Stress wave propagation in a coated elastic half-space due to water drop impact is studied by using the Cagniard-de Hoop method. The stresses have singularity at the Rayleigh wavefront whose location and singular behavior are determined from the pressure model and independent of the coating thickness, while reflected waves cause minor changes in amplitudes.

Water Drop Impact Angle and Soybean Protein Amendment Effects on Soil Detachment

To improve soil erosion prediction technology, the mechanics of each erosion process must be understood sufficiently to predict soil loss on an event basis. The mechanics of the initial erosion process, soil detachment caused by falling raindrops, requires greater understanding to improve mechanics‐based prediction. This laboratory study addressed the effect of soil shear strength and raindrop impact angle on soil detachment. Loess (fine‐silty, mixed, superactive, mesic Typic Hapludoll) and glacial till (fine‐loamy, mixed, superactive, mesic Aquic Hapludoll) A and C horizon soil materials were used. To vary soil shear strength, soybean protein material was added to each soil material at concentrations of 0.0, 0.5, and 1.0% by weight. Soil shear strength and soil detachment were measured on preformed soil cores. Soil detachment tests were performed at water drop impact angles of 90, 80, 70, and 60°. Soil strength increased and detachment decreased with increasing soybean protein concentrations. Shear strength of the loess C horizon increased 0.61 to 1.85 Mg m−2, while that of the till C horizon material increased 0.57 to 0.98 Mg m−2 with addition of 1% soybean protein. A 1%–soybean protein addition reduced soil detachment 26% compared with unamended soil. Significant soil detachment interactions existed between waterdrop impact angle and the other variables. These interactions were due to different mechanical behavior of the soils and changing strength caused by soybean protein additions. Interactions observed are explained based on differences in the lateral jet for varying impact angles and for elastic vs. inelastic impacts.

Water repellency and feather structure of the Blue Swallow Hirundo atrocaerulea

Rijke, A.M., Jesser, W.A., Evans, S.W & Bouwman, H. 2000. Water repellency and feather structure of the Blue Swallow Hirundo atrocaerulea. Ostrich 71 (1 & 2): 143–145. The Blue Swallow is an endangered species in southern Africa and is probably the most endangered passerine. It is restricted to escarpments with grasslands above 1 000 m where mists are frequent. It appears to forage on the wing even in thick mist raising the question of feather wettability in relation to its adaptation. Extensive physical and behaviourial adaptations are known to occur in a wide variety of birds to deal with the problem of shedding water continuously. To study the water repellency and resistance to water penetration of Blue Swallow feathers, we have examined the microscopic structure of head, back, throat, breast and abdominal feathers as well as remiges and tail feathers by transmission light microscopy. The width (2R) and separation (2D) of rami and barbules have been measured and were used to calculate the parameter (R + D)/R that serves as an indicator ofwater shedding potential. For the remiges and tail feathers the values of the (R+D)/R range from 5 to 10 which is comparable to values for other terrestrial birds. However, for body feathers the range is from 10 (head) and 35 (abdomen)-higher than previously observed for any other bird including Swifts, Apodidae. Blue Swallow feathers are thus the most effective feather yet discovered at repelling water drops. The water repellency is highest in those feathers that are relatively shielded From the direct impact of small water drops (throat, breast, abdomen, back). By contrast, the flight feathers must possess a relatively large resistance to water penetration to avoid becoming waterlogged and this is coupled to low (R+D)/R values. Values for the barbules lay between 2 and 6—the same as found for other bird families—supporting an earlier conclusion that they have little direct effect in repelling water.

Polyacrylamide adsorption and aggregate stability

The adsorption characteristics of synthetic organic polymers play a major role in their effects on the stabilization of aggregates. We hypothesized that high molecular weight polymers adsorb on both outer and inner surfaces of large aggregates (>1.0 mm), and thus enhance the resistance of aggregates to external forces (e.g., water drop impact). Adsorption of an anionic polyacrylamide (PAM) on aggregates of different sizes from a Worsham (Typic Ochraquults), and a Cecil (Typic Hapludults), Georgia, USA, and the resultant stability of the PAM-treated aggregates to wet sieving, were studied. Aggregates were packed in a small chamber, saturated with a polymer solution, and after 24 h leached with distilled water. PAM adsorption was calculated from carbon content in the leachate. Amount of adsorbed PAM from a 200 g/m 3 polymer solution ranged between 72 and 81 mg/kg in the Cecil; lower amounts (37–56 mg/kg) were obtained in the Worsham. Adsorption efficiency (ratio of the amount of PAM adsorbed to that added) remained unchanged in the Worsham, and decreased moderately in a linear fashion in the Cecil, with increases in aggregate size. Conversely, computed external surface area (ESA) of aggregates of the different size classes decreased hyperbolically with an increase in aggregate size. The significant difference in the pattern of the adsorption and ESA curves may serve as an indication that PAM adsorption could have taken place on both outer and inner aggregate surfaces. Aggregate stability results showed that mean weight diameter (MWD) of PAM-treated intact as well as broken aggregates was higher than that of untreated aggregates. This observation supported the conclusion drawn from the adsorption study, namely that PAM adsorption may not be restricted to outer aggregate surfaces only. It further indicated that the favorable effect of PAM on stabilizing aggregates lasts also after the initial aggregates were broken at plains of weakness.

Waterdrop impact modeling

The complete spatial and temporal interaction of a waterdrop impacting a deformable target can now be described using a three-dimensional finite element model. The advantage of the finite element formulation is that the stresses generated in structurally complex targets can be determined. The geometry of the target is also accurately represented in the model. A brief account of previous waterdrop impact modeling approaches is provided to illustrate the significance of what can be accomplished with the current model. A broad range of constitutive behavior and failure criteria are available within the finite element analysis, however implementation of the finite element analysis depends in many cases on how well the high rate of loading behavior of the components in the target is known. Experimentation to define the relevant material response models is being developed. Currently predictions for the onset of failure are based on the magnitude and duration of the stresses generated within the target. The finite element analysis is being extended to include the propagation of damage and the associated redistribution of stress around the failed elements. It will then be possible to predict the full extent of the damage produced by an arbitrary waterdrop impact.

Optical, mechanical and water drop impact characteristics of polycrystalline GaP

A polycrystalline form of GaP has been synthesized and its optical and mechanical properties determined. The optical transmission is found to be intrinsic at long wavelengths in the infrared, being limited only by Fresnel reflection and multiphonon absorptions, beginning at approximately 1100 cm−1. The optical cut-off at short wavelengths is in agreement with earlier measurements on single crystal material. The fracture toughness of the polycrystailine material is found to be greater than that previously reported for single-crystal material. The single impact water drop damage velocity threshold (2 mm drop diameter) was estimated to be 250–280 ms−1, which is consistent with the measured polycrystalline fracture toughness.

On a Model of Soil Detachment by Waterdrop Impact on the Water's Surface Based on the Idea of Pressure Impulse

On a Model of Soil Detachment by Waterdrop Impact on the Water's Surface Based on the Idea of Pressure Impulse

Polymer Effects on Erosion under Laboratory Rainfall Simulator Conditions

AbstractSoil erosion by water is a serious problem in several parts of the world. Incorporation of polymers into water applied to soil by a rainfall simulator can improve infiltration rates. This study was conducted to determine the effects of nonionic, anionic, and two charge densities of cationic derivatized guar products on erosion and infiltration rates. The polymers were mixed with distilled water at concentrations from 0 to 20 g m−3 and applied through a rainfall simulator in the laboratory. Untreated distilled water was applied to an Arlington sandy loam soil (Haplic Durixeralf) with the soil surface both unprotected and protected by a fiberglass sheet placed 0.5 cm above the soil surface. All polymer treatments were applied to the unprotected soil surface. Distilled water drop impact greatly reduced infiltration rate and increased erosion, compared with no impact. The anionic and nonionic polymers did not significantly affect erosion or infiltration rate, compared with distilled water. The cationic polymers significantly increased infiltration rate and erosion, compared with distilled water. The higher charge cationic polymer produced significantly higher values than the lower charge polymer at the same concentration. The distilled‐water treatment with impact caused severe aggregate disruption and dispersion, producting a layer of fine material at the surface that decreased infiltration rate. Apparently, the very‐fine particulates became imbedded in the soil matrix, which made them less susceptible to lateral transfer with flowing water. The flocculating action of the cationic polymer created larger particulates, which had very little effect in reducing infiltration rate but were more susceptible to erosion. Under the conditions of the experiment, particulates between 0.05 and 0.25 mm were most susceptible to transport by a thin sheet of flowing water.

Rainfall and soil detachment

Literature reviews on (1) process of water drop impact on dry or wet surfaces and (2) splash soil loss due to water drop impact are presented. It appears that water drop impact generates large instantaneous pressure of a magnitude comparable to that of water hammer pressure. However, this pressure only lasted for a very short time and decays within milliseconds. Published studies on soil loss due to water splashing on soil surface shows that splash soil loss is largest when the soil is covered by a thin film of water. This feature is made use of to develop a soil detachment model based on eroding pressure. The various parameters needed in the model are derived from published data. The developed model appears to produce encouraging results.

Water Drop Kinetic Energy and Momentum Measurement Considerations

The impulse applied to a surface from water drop impact can be measured experimentally by recording and integrating impact force over time. A momentum number, defined as measured impulse divided by the drop's momentum, is a dimensionless physically-based parameter which can be used for modeling soil movement due to water drop impact. Impact forces were measured and integrated over time and the momentum number equals one for a smooth-dry surface and is greater than one for a smooth-wet or a rough surface. Accurate impulse measurements do not require sensors with fast dynamic response or calibration, but reasonant frequencies must be sufficient to minimize signal amplification. The factors to be considered when measuring impulse or work from water drop impact are identified.

Measurement of Waterdrop Impact Pressures on Soil Surfaces

AbstractLimited data on pressures induced by waterdrop impact on soil surfaces restricts our understanding the mechanism of soil detachment due to raindrop impact. Impact pressures on rigid surfaces are known but their application to soil surfaces is questionable. This study was undertaken to measure vertical pressures of waterdrop impact on soil surfaces. A 1‐mm diam piezoelectric transducer was developed and measurements of impact pressures as a function of radial distance from drop center were made. Dickinson loam (coarse‐loamy, mixed, mesic Typic Hapludoll) and Ida silt loam (fine‐silty, mixed [calcareous] mesic Typic Udorthent) with bulk densities of 1.0 and 1.2 Mg/m3 and with matric potentials of −0.5 and −2.5 kPa were used. The waterdrop had a diameter of 5.6 mm and a fall height of 14 m. Average peak impact pressures were greatest at a distance of 1.8 to 2.3 mm from center of impact and of the order of 190 to 290 kPa. These stress levels are almost two orders of magnitude less than those for impact on a rigid surface. Much of the difference between soil and rigid cases was due to nonrigid, nonhomogeneous nature of the soil material. The remainder of the difference in stress levels was thought to be due to the effect of soil granularity or to the presence of surface and shear waves generated by impact.

Development Of Design Data For Rain Impact Damage In Infrared-Transmitting Windows And Radomes

Laboratory erosion data, estimates of the rain environment, and the desired capabilities of the aircraft or missile can be utilized with a rain erosion damage model to provide a fairly reliable estimate of environmental degradation of infrared-transmitting windows and radomes throughout a flight trajectory. If water drop interactions with the flow field around the vehicle are ignored, the suggested approach will provide an upper bound on the extent of the water drop impact damage associated with a particular mission. The design philosophy is that if this level of damage can be tolerated, the actual impact conditions will not be detrimental. A wide range of flight scenarios can be examined on this basis. If the upper bound computation indicates that the resulting level of damage will be well beyond the tolerable limit, then aerodynamic analyses of water drop interactions with the flow field around the vehicle and a more complete statistical analysis of the impact damage will have to be undertaken.

Reply to “Comments on ‘Energy Dissipation During Water Drop Impact In Shallow Pools’”

Soil Science Society of America JournalVolume 50, Issue 6 p. 1644-1645 Comment and Letter to the Editor Reply to “Comments on ‘Energy Dissipation During Water Drop Impact In Shallow Pools’” Alfredo G. Ferreira, Alfredo G. Ferreira Univ. de Évora, Div. de Engenharia, Rua Dos Duques de Cadaval 2, 7000 Évora, PortugalSearch for more papers by this authorBruce E. Larock, Bruce E. Larock Dep. of Civil Engineering, Univ. of California, Davis, CA, 95616Search for more papers by this authorMichael J. Singer, Michael J. Singer Dep. Land, Air and Water Resources, Univ. of California, Davis, CA, 95616Search for more papers by this author Alfredo G. Ferreira, Alfredo G. Ferreira Univ. de Évora, Div. de Engenharia, Rua Dos Duques de Cadaval 2, 7000 Évora, PortugalSearch for more papers by this authorBruce E. Larock, Bruce E. Larock Dep. of Civil Engineering, Univ. of California, Davis, CA, 95616Search for more papers by this authorMichael J. Singer, Michael J. Singer Dep. Land, Air and Water Resources, Univ. of California, Davis, CA, 95616Search for more papers by this author First published: 01 November 1986 https://doi.org/10.2136/sssaj1986.03615995005000060052xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume50, Issue6November-December 1986Pages 1644-1645 RelatedInformation

Measurement of Force vs. Time Relations for Waterdrop Impact

AbstractForce vs. time relationships of waterdrop impact are important for understanding the process of erosion caused by soil splash. Waterdrop impact forces were measured for 3.31‐, 3.83‐, 4.51‐, and 5.25‐mm diam drops falling from a height of 14.0 m onto piezoelectric transducers with rise times of 2 and 5 µs. Peak forces occurred within 13 to 21 µs of initial contact, ranged from 1.0 to 3.8 N, and decreased to 0.5 N after approximately 100 µs. Average pressures under impact were calculated from the force measurements and an approximateion of waterdrop contact area as a function of time and decreased to 100 kPa after 50 µs. The results indicated that the times and magnitudes of the force of impact were poorly predicted from currently used models and that the compressional wave generated in the water upon impact is probably an important parameter in determining the level and time distribution of forces during impact.

Comments on “Energy Dissipation During Water Drop Impact in Shallow Pools”

Comments on “Energy Dissipation During Water Drop Impact in Shallow Pools”

Effect of Soil Surface Sealing on Splash from a Single Waterdrop

AbstractMost soil erosion prediction models do not account for surface sealing and soil crusting effects on soil detachment. The objective of this research was to evaluate surface seal formation and subsequent drying effects on amount of soil detached by single waterdrop impact. Twenty soils ranging in texture from sand to clay were tested. Single drop splash and fall‐cone strength determinations were made on each soil in an uncrusted condition, in a crusted condition immediately following 1 h of simulated rainfall (63 mm/h), and after 2 to 4 weeks of drying. Splash for the uncrusted condition ranged from 8.9 to 61.0 mg/drop and from 0.8 to 13.7 mg/drop for the crusted condition. Subjecting crusted soils to one drying cycle did not significantly alter splash amount. Splash was correlated with soil strength for both uncrusted and crusted conditions for finertextured soils; however, for sands and sandy loams additional research is required for soil strength‐based splash model for crusted conditions.

A physically‐based model of the dispersion of splash droplets ejected from a water drop impact

AbstractA model has been developed which predicts the dispersion of splash droplets produced by the impact of a water drop on a sloping soil surface.Experimental results of the ejection velocities and ejection angles of the splash droplets are generalized to a planar slope and the resulting splash distances are calculated taking into account the effects of air resistance. The predictions are presented in terms of the numbers of splash droplets from the impact point to surrounding squares arranged in a grid on the slope.The model explains many experimentally observed features of raindrop splash in terms of the mechanics of the processes involved and can make predictions of the effects of slope, wind, raindrop size, and soil properties on droplet dispersion. The component of the raindrop velocity parallel to the surface of the slope is identified as the main factor determining the degree and the direction of the asymmetry in the splash droplet dispersion.By combining the model with a theory of the entrapment of soil in the splash droplets it is possible to extend it to predict the dispersion of soil particles by raindrop impact, which is the basis of a model of soil erosion by rainsplash.

Computer Simulation of Water Drop Impact in a 9.6‐mm Deep Pool

AbstractThe interaction between impact of a 3.2‐mm drop and a water layer over the soil surface was studied by simulating drop impact through the solution of the Navier‐Stokes and continuity equations for a viscous and incompressible fluid on an Eulerian grid, using a finite difference method. The simulation was validated by experiments. The velocity field produced by the simulation showed a reversal of the velocity vectors at the time of maximum crater development, followed by crater collapse and formation of the Rayleigh jet. A comparison of measured and simulated crater and crown development showed good agreement. The energy balance from the computer simulation showed that the shear energy development along the bottom of the pool reached a maximum value during the crater collapse when the velocity vectors in the corresponding velocity field were pointing inwards and upwards.