Academic literature on the topic 'Raindrop energy'

In the process of UAV line inspection, there may be raindrops on the camera lens. Raindrops have a serious impact on the details of the image, reducing the identification of the target transmission equipment in the image, reducing the accuracy of the target detection algorithm, and hindering the practicability of UAV line inspection technology in cyber-physical energy systems. In this paper, the principle of raindrop image formation is studied, and a method of raindrop removal based on generation countermeasure network is proposed. In this method, the attention recurrent network is used to generate the raindrop attention map, and the context code decoder is used to generate the raindrop image. The experimental results show that the proposed method can remove the raindrops in the image and repair the background image of raindrop coverage area and can generate a higher quality raindrop removal image than the traditional method.

Abstract. The Loess Plateau of China is regarded as the most intensively eroded region in the world and soil erosion caused by raindrop impact is a common occurrence on agricultural land within this region. Therefore, understanding the influence of rainfall energy on the soil surface is needed to improve prescriptions for best management practices aimed at mitigating erosion. Disdrometers for measuring rainfall energy are presently available; however, these are relatively expensive and their use may not be justified for determining raindrop energy for predictive soil erosion models in regions where there are limited economic resources. To overcome this constraint, a device was tested for evaluating size and velocity of water drops during rainfall events. This device utilized two rotating disks combined with filter paper to obtain raindrop diameter and velocity which can then be used for determining the kinetic energy of falling raindrops. With this device, raindrop diameter was determined from the resultant raindrop stain left on the filter paper during rainfall events and velocity was calculated from the time it took a falling raindrop to travel between the pair of rotating disks. Measurements were taken for approximately 10 minutes during each of six rainfall events of different intensities over a three month period (from June to August of 2013). The smallest raindrop measured was 0.39 mm diameter and the largest was 5.92 mm diameter. The event average raindrop diameter increased with increasing event rainfall intensity. The minimum raindrop impact velocity was 1.47 m s-1, the maximum was 9.45 m s-1, and the event average terminal velocity increased as event rainfall intensity increased. Estimated raindrop kinetic energy ranged from 0.04 × 10-6 J to 4728.21 × 10-6 J, with event mean raindrop kinetic energy ranging from 40.33 x 10-6 J to 276.94 × 10-6 J. The relationship between estimated event rainfall kinetic energy and event rainfall intensity was represented by an exponential function. The disk device was also compared to an optical disdrometer. The data collected for rainfall intensity, raindrop diameter, and velocity were statistically similar between the two devices. Results from this study show that this low-cost method can be used to estimate rainfall kinetic energy in the Loess Plateau region of Northwest China. Keywords: Loess Plateau, Raindrop diameter, Raindrop velocity, Rainfall intensity.

Rainfall erosivity and rainfall kinetic energy are predominantly affected by the rainfall droplet size distribution characteristics. This study aims to determine the raindrop size distribution with different rainfall intensities in East Malaysia using photographic method and MATLAB image processing tools. A total of five natural rainfall intensities of different ranges were analyzed: 5.51 mm hr-1, 14.20 mm hr-1, 28.80 mm hr-1, 32.41 mm hr-1 and 58.11 mm hr-1. A digital camera with fast capturing mode was used to capture falling raindrops and the droplets were then processed in MATLAB to determine the raindrop size distribution. It was found that the captured raindrop diameters were within the range of 0.1 mm and 5.0 mm, and a higher portion of the raindrops fell between 0.1 mm and 1.0 mm. The results also showed that higher rainfall intensities would promote the formation of larger raindrop sizes, i.e., from 1.0 mm to 5.0 mm, and lower rainfall intensities tended result in higher drop counts in smaller raindrop sizes of <1.0 mm. The modified image processing tools of MATLAB had proved a shorter analysis duration and higher accuracy of the raindrop size determination than the human visual system. The novelty of this study contributes to the understanding of the equatorial rainfall properties. This enhances the study of the rainfall kinetic energy and soil erosion rate estimation. The findings demonstrate the capability of photogrammetric techniques for determination of raindrop size distribution.

Filter paper splash procedure is a kind of measuring means to raindrop size. It is used widely and operated briefly and its cost is low. The article mainly introduces the influence of different heights to the stain diameter and the relationship between stain diameter and the raindrops. According to the experiment, the relation between the stain diameter and the raindrops is d=0.478D0.610.it is the research foundation of filter paper stain method. According to the data from Fangxian area using the method of filter paper splash procedure, we can conclude that the raindrop kinetic energy has a positive relationship with rainfall intensity. The research is useful for measuring the water and soil loss.Water and soil loss is one of the global environment problems. The most important factor which can cause water and soil loss is rainfall. The research on raindrop kinetic energy is important for the further analysis of water and soil loss. A classical approach for the research on raindrop kinetic energy is paper splash procedure. The relationship between stain diameter and raindrop diameter shall be calibrated in this approach. In general, influences from titrated water drop height and stain diameter are not considered in the calibration process. In this experiment, influences of rain drop height on stain diameter are researched in the stain calibration, settling basis for the research on local volume of water and soil loss.

The impact of raindrops on a dry surface leads to a splashing phenomenon that dissipates a lot of energy. To improve energy collection, a novel piezoelectric raindrop energy harvester equipped with a spoonful of water was developed. The advantages and the drawbacks of this solution were analyzed with the aid of numerical simulations. A series of experimental tests were carried out in a laboratory with simulated raindrops. Experimental results showed that the negative effect of the added water mass was exceeded by the positive effects related to the impact of the raindrop on a liquid surface. Tests carried out connecting the harvester to a resistive load showed that the prototype was able to collect more energy than a simple cantilever harvester.

Indonesia is a country that has a fairly high rainfall, because it is located in the tropical area. This condition could be a potential for generating electrical energy from raindrops. If the heavy raindrop collide the piezoelectric materials, it can generate electrical energy. The piezoelectric effect was discovered by Jacques and Pierre Curie in 1880. They found that certain materials, when subjected to mechanical strain, suffered an electrical polarization that was proportional to the applied strain. This piezoelectric effect converts mechanical strain into electrical voltage. The molecular structure of piezoelectric materials produces a coupling between electrical and mechanical domains. In this research, raindrops will be exploited to produce electric voltage by piezoelectric transducer. Piezoelectric transducer used in this research is Lead Zirconate Titanate type. Energy conversion processing occurred when raindrop collide the polymer layer of piezoelectric and make an unelastic thrust on its surface. The designed system consists of raindrops collector board and serial connected piezoelectric transducer. From system above, highest voltage, reach is 3.13 VAC for 30 piezoelectric and the average voltage is 2.617 V. This results show us the potential usage of raindrops energy generator using piezoelectric transducer for tropical countries.

Population balance equation is converted to three moment equations to describe the dynamical behavior of particle size distribution in air in the rainfall. The scavenging coefficient is expressed as a polynomial function of the particle diameter, the raindrop diameter and the raindrop velocity. The evolutions of particle size distribution are simulated numerically and the effects of the raindrop size distribution on particle size distribution are studied. The results show that the raindrops with smaller geometric mean diameter and geometric standard deviation of size remove particles much more efficiently. The particles which fall in the ?greenfield gap? are the most difficult to be scavenged from the air.

Underwater noise produced by rainfall is an important part of underwater ambient noise. The bubbles produced by raindrops are the main noise source of underwater noise. Generally, the sound pressure signal of individual bubbles is easily contaminated by tank reverberation, hydrodynamic flow, and laboratory electrical noise. In order to solve this problem, this study proposes a method for calculating the acoustic energy of the bubble produced by a raindrop when the latter falls onto a plane water surface. For this purpose, a series of experiments was conducted in a 15 m × 9 m × 6 m reverberation tank filled with tap water. The bubble produced by a raindrop behaves as a simple exponentially damped sinusoidal oscillator. Based on the dipole radiation pattern, a formula was derived to predict the sound energy of these bubbles. The damping coefficient of the bubble formed by raindrops is found to differ appreciably from the empirical value of the bubble formed by other mechanisms. The resonance frequency of the bubbles is found to decrease with time. It is due to the rapid increase in the distance between the bubble and the interface. Then, the formula is optimized by using these two improved variables. The experimental results agree well with the theoretical derivation.

Abstract Kinetic energy and corresponding erosive force of rainfall are strongly influenced by raindrop. The present paper aims to explore the raindrop size variation during rainfall events with different intensities in northern Iran by applying the processes of camera-taken photographs. Five rainfall intensities of 1 to 10 mm h–1 that occur frequently in the study area were analyzed. A camera with a very short exposure time was used to record the distribution of raindrops size. The raindrops diameters of the rain events ranged from <0.2 to 5.1 mm while the majority of them were between 1 and 2 mm. The results also showed that the variation of rainfall intensity significantly influenced (P< 0.05) raindrops size. Image processing was proven as an accurate technique of translation between the human visual system and digital imaging devices. The findings of the study can be practically utilized by researchers who work in the field of soil erosion and meteorology.

Over the last decade, advancement of microelectronics has triggered a growing interest in ambient energy harvesting. Ambient energy can be found in various forms such as: thermoelectric, acoustic, solar, and mechanical vibrations. Most of the stated ambient energy sources have been thoroughly investigated. One of the relatively unexplored ambient energy sources is raindrop impact energy. Raindrop impact energy harvesting is achieved by converting the strain induced by an impinging raindrop on a piezoelectric beam into usable electrical energy. Most of the conducted research from the literature only considered single droplet impact on a piezoelectric beam. More interestingly, actual field test has yet to be conducted. These are the areas that the research will cover. A commercial piezoelectric beam (Mide-v25w) is utilised for this research. In this work, the piezoelectric beam is modelled as a distributed parameter system. To describe the post impact behaviours and water layer formed on the piezoelectric beam, impact coefficient and added mass coefficient are introduced for respective cases. Excitation models for single droplet, multiple droplet, artificial rain, and actual rain are developed. The models presented here were validated via experimental results. A hybrid bridge rectifier is designed and tested under actual rain. Experiment results showed that the half bridge rectifier is able to produce 95.12 % more energy than the full bridge rectifier during low voltage operation. From the actual rain experiment, the raindrop impact energy harvester was able to produce 1564 µJ energy over a rain period of 3539 s. The maximum instantaneous power generated by the piezoelectric was found to be 3.75 mW. This is higher compared the highest instantaneous power recorded in the literatures, which was 23 µW.

The relationships between contaminant removal from impervious pavements and raindrop impact energy, cumulative kinetic energy of rainfall events, and rainwater fit were evaluated. A commercial urban area was chosen to perform simulated rainfall experiments. The runoff from these experiments was collected and analyzed for total suspended solids, volatile suspended solids, total Kjeldahl nitrogen, soluble Kjeldahl nitrogen, oxidized nitrogen, ammonia, ortho-phosphate, total phosphorus, soluble phosphorus, total lead and total zinc. Raindrop impact energy, rainfall intensity, rainfall duration, and rainwater pH were factors which were varied to examine their effect on contaminant wash-off phenomena. The present exponential decay theory of contaminant removal was verified and modified to incorporate the cumulative kinetic energy of rainfall events. An empirical model for contaminant removal was also developed. Data showed that both raindrop impact energy and cumulative storm energy had significant effects on contaminant removal. Contaminant wash-off was found to be independent of rainwater pH except for solids removal at low rain intensities. Additional results indicated that there is a "threshold impact energy" necessary before significant removal of contaminants associated with insoluble material can occur. The kinetic energy attributed to surface runoff overflow was found to be very important in the mechanisms responsible for contaminant removal at high rainfall intensities.
M.S.

Aggregate breakdown is an important process controlling the availability of fine soil material necessary for structural sealing of soil surfaces under rainfall. It may be caused by slaking resulting from rapid soil wetting and by physical dispersion resulting from direct and indirect energetic raindrop impacts. Relationships have been proposed by others predicting steady infiltration rate and saturated hydraulic conductivity from final aggregate size following high energy rainfall on initially dry, uncovered soil surfaces. Under these extreme conditions, both rapid wetting and energetic raindrop impact result in maximum aggregate breakdown and surface sealing. Knowledge of the relative importance of these two agents under less severe conditions and knowledge of how increased aggregate stability due to conservative soil management may ameliorate them should improve prediction and management of aggregate breakdown and surface sealing. ¶ This study has isolated and quantified effects of rapid soil wetting and energetic raindrop impact on aggregate breakdown and surface sealing. Simulated rainfall was applied to re-packed soils from differing tillage treatments on light textured soils from near Cowra and Condobolin in New South Wales, Australia. Aggregate breakdown was assessed using aggregate size distribution, determined by wet sieving and summarised by a range of statistics. The degree of breakdown was assessed after 66 mm of simulated rainfall whilst the rate of change in aggregate size distribution was assessed by sampling after 5, 10, 15, 30 and 60 mm. The degree of surface sealing was assessed using final surface hydraulic conductivity after 66 mm rainfall calculated from inferred infiltration and measured sub-seal soil water potential. The rate of surface sealing was assessed prior to ponding using cumulative rainfall volume at ponding and throughout the post-ponding phase by decline in surface hydraulic conductivity as a function of cumulative rainfall kinetic energy. Two levels of raindrop kinetic energy flux and three wetting treatments were used to isolate effects of these agents of aggregate breakdown and surface sealing. ¶ Significant surface aggregate breakdown was observed when either rapid soil wetting or highly energetic raindrop impact were allowed to occur. The majority of the data suggest a negative interaction between the two agents. When soil was initially dry rapid soil wetting was the dominant agent causing rapid aggregate breakdown, generally within the first 5 mm of rainfall. When rapid soil wetting was prevented by tension pre-wetting, energetic raindrop impact was the dominant agent and was able to cause aggregate breakdown of an almost equivalent degree. This breakdown occurred over a period lasting for up to 30 mm of rainfall. In contrast, the rate and degree of surface sealing were influenced primarily by raindrop kinetic energy with highly energetic impact leading to significant surface sealing, irrespective of soil wetting. For the soils studied, it was concluded that structural sealing of surface soil, could be significantly reduced by protecting the soil surface from energetic raindrop impact but that prevention of surface aggregate breakdown required amelioration of both processes. ¶ In addition to the negative interaction referred to above, a positive interaction was observed whereby energetic raindrop impact occurring concurrently with rapid soil wetting caused a greater degree of aggregate breakdown and a greater degree of surface sealing than energetic raindrop impact occurring subsequent to rapid soil wetting. The effect on surface sealing may be explained by the effect of lower sub-seal water potential that necessarily results from initially dry soil condition required for concurrent rapid wetting. However, the effect on aggregate breakdown remains unexplained. ¶ Notwithstanding the above, permeability was reduced under high kinetic energy rainfall even when soil wetting was reduced to very slow rates by tension pre-wetting. Likewise, surface sealing did occur under low kinetic energy rainfall for the least stable soil following rapid soil wetting. It was concluded that threshold soil wetting rates and threshold rainfall energy levels, proposed by others, are either not applicable to these soils or are negligible. ¶ The rate and degree of aggregate breakdown was also dependent on the soil with the Cowra soil being more stable than the Condobolin soil. Greater aggregate stability brought about by conservative tillage treatments at both soil locations retarded and reduced surface sealing. Unvalidated simulation modelling was used to illustrate possible effects for the soil water balance. In contrast to the conclusions of Loch (1994b), that were based on soils throughout eastern Queensland, the soil water balance simulations predicted that the residual benefits in ameliorating surface sealing resulting from improved aggregate stability could significantly reduce point runoff under the lower intensity winter rainfalls experienced in southern New South Wales. ¶ Limited testing with Condobolin soil following tension pre-wetting showed that rainfall intensity, varying over the range from 16.5 to 66 mm h-1, had little effect on the decline in surface hydraulic conductivity as a function of cumulative rainfall kinetic energy. This contrasts with greater seal permeability under higher rainfall intensities observed by Romkens et al. (1985) and others. It is proposed that an alternative explanation exists for the observations of Romkens et al. based on reduction in seal permeability due to lower sub-seal water potential under lower intensity rainfall. ¶ Post-ponding reduction in K[subscript sat] under high kinetic energy rainfall exhibited exponential decline as a function of cumulative raindrop kinetic energy as proposed by Moore (1981b). However, inferred rates of decline prior to ponding were more rapid than measured post-ponding rates suggesting that infiltration models using only a single exponential rate of surface K[subscript sat] decline based on post-ponding measurements may be in error. Potential for error is greatest at early times for loose soil that is highly susceptible to sealing. ¶ Pre-ponding decline in surface aggregation was also relatively more rapid than post-ponding decline. This discrepancy was evident irrespective of soil pre-wetting. From this it was concluded that the more rapid initial aggregate breakdown and surface sealing was due, at least in part, to processes other than aggregate slaking due to rapid soil wetting. An explanation has been proposed as follows. Raindrops initially fall on aggregates that have not been subjected to rainfall and therefore each drop has the capacity to cause greater aggregate breakdown than subsequent raindrops that fall on aggregates or soil fragments that have been strong enough to survive preceding rainfall impacts. Such a mechanism could provide an alternative explanation of the findings of Baumhardt et al. (1991) who found that less cumulative raindrop kinetic energy was necessary to achieve a given reduction in surface conductance when the cumulative energy was supplied through lower energy drops. ¶ Relationships predicting rates of surface sealing using aggregate breakdown under rainfall and aggregate stability were evaluated. Post-ponding infiltration rate and surface K[subscript sat] were related to aggregate size by exponential functions. The proportion of surface aggregates less than 0.125 mm in diameter provided slightly more consistent relationships. Parameters of fitted relationships differed among wetting pre-treatments suggesting that the influence of sub-seal water potential on surface K[subscript sat] must be considered whenever such relationships are developed or applied. Aggregate stability determined by wet sieving was related to rainfall volume required for ponding, final K[subscript sat] and final aggregate size but only for initially dry soil suggesting that such relationships may be unique to the rainfall, soils and flow conditions used to develop them. ¶ This study has established the relative importance of rapid soil wetting and energetic raindrop impact in both aggregate breakdown and surface sealing over a range of antecedent soil water and rainfall conditions. It has quantified the effectiveness of culturally induced aggregate stability in ameliorating effects of these two important agents and illustrated the potentially significant consequences for the soil water balance. It has quantified temporal patterns of surface sealing and aggregate breakdown and proposed an alternative mechanism explaining more rapid aggregate breakdown during the initial stages of rainfall. It has identified possible explanations for effects of rainfall intensity on surface sealing observed in other studies. It has also partially evaluated a mechanism proposed to explain important effects of subseal water potential on seal permeability found in this and other studies. These significant findings have been used with the findings of other studies to amend the conceptual model proposed by Le Bissonnias (1990). The amended model gives a more complete description of the relationships between parameters and processes determining aggregate breakdown and structural surface sealing under rainfall.

Cette étude propose une unification des formulations mono- et multi-moments de la distribution granulométrique des pluies (DSD pour " drop size distribution ") proposées dans la littérature dans le cadre des techniques de mise à l'échelle (scaling). On considère dans un premier temps que la DSD normalisée par la concentration en gouttes (Nt, moment d'ordre 0 de la DSD) peut s'écrire comme une fonction de densité de probabilité (ddp) du diamètre normalisé par un diamètre caractéristique (Dc). Cette ddp, notée g(x) avec x=D/Dc, aussi appelé distribution générale, semble être bien représentée par une loi gamma à deux paramètres. Le choix d'un diamètre caractéristique particulier, le rapport des moments d'ordre 4 et 3, conduit à une relation d'auto-consistance entre les paramètres de la fonction g(x). Deux méthodes différentes, fondées sur 3 moments particuliers de la DSD (M0, M3 et M4) ou bien sur des moments multiples (de M0 à M6) sont proposées pour l'estimation des paramètres et ensuite évaluées sur 3 ans d'observations de DSD recueillies à Alès dans le cadre de l'Observatoire Hydrométéorologique Méditerranéen Cévennes-Vivarais (OHMCV). Les résultats révèlent que: 1) les deux méthodes d'estimation des paramètres ont des performances équivalentes; 2) malgré la normalisation, une grande variabilité de la DSD est toujours observée dans le jeu de données mis à l'échelle. Ce dernier point semble résulter de la diversité des processus micro-physiques qui conditionnent la forme de la DSD.Cette formulation est ensuite adaptée pour une mise à l'échelle avec un ou deux moments de la DSD en introduisant des modèles en loi puissance entre des moments dits de référence (par exemple l'intensité de la pluie R et / ou le facteur de réflectivité radar Z) et les moments expliqués (concentration en gouttes Nt, diamètre caractéristique Dc). De manière analogue à la première partie du travail, deux méthodes sont proposées pour estimer des paramètres climatologiques des DSD mises à l'échelle par un ou deux DSD moment(s). Les résultats montrent que: 1) la méthode d'estimation a un impact significatif pour la formulation de mise à l'échelle par un seul moment; 2) le choix du moment de référence dépend des objectifs d'étude: par exemple, le modèle mis à l'échelle par des moments d'ordre élevé produit une bonne performance pour les grosses gouttes mais pas pour les petites; 3) l'utilisation de deux moments au lieu d'un seul améliore significativement la performance du modèle pour représenter les DSD.Notre modèle est ensuite appliqué pour analyser la variabilité inter- événementielle selon trois paramètres (Nt, Dc et μ, ce dernier paramètre µ décrivant la forme de la fonction gamma). Différentes séquences de pluie ont été identifiées de façon subjective pour l'événement pluvieux intense des 21-22 octobre 2008 par des changements brusques des moments et/ou paramètres dans les séries temporelles correspondantes. Ces phases de pluie sont liées à des processus météorologiques différents. Une relation préliminaire est établie entre les observations radar et la variation des paramètres des DSD au sol telle que mesurée par le disdromètre. Les formulations de mise à l'échelle sont également appliquées pour des estimations des densités de flux d'énergie cinétique des précipitations à partir de l'intensité de la pluie et / ou de la réflectivité radar. Les résultats confirment que l'utilisation de deux moments (R et Z) améliore significativement les performances de ces modèles, malgré les caractéristiques d'échantillonnage très différentes des radars et des pluviomètres. Cette application ouvre des perspectives intéressantes pour la spatialisation de l'énergie cinétique des pluies dans le cadre des études sur le pouvoir érosif des pluies.

碩士
國立臺灣大學
生物環境系統工程學研究所
104
The equation for evaluating rainfall kinetic energy currently used in Taiwan is not derived from the local rainfall data. Because rainfall kinetic energy is quite related to the region, it is necessary to develop an equation of rainfall kinetic energy for each area. The main purposes of this study are to measure the rain drop size distribution in northern Taiwan using disdrometer and to establish the equation for evaluating rainfall kinetic energy using the measured data. In this study, the data of rainfall and rain drop size distribution collected at three observation stations, namely, National Central University station, Xiayun station and Feitsui station, using disdrometer from 2012 to the Jun. of 2016 were used to evaluate the rainfall kinetic energy. To accomplish this, three methods for evaluating rainfall kinetic energy were applied. The first is the method of energy per unit volume (KEmm ), a conventional method, and its coefficient of determination( R2) between rainfall kinetic energy and rainfall intensity is approximately 0.6. The second is the method of energy per unit time (KEtime ), a relatively newly developed method, and the coefficient of determination( R2) between rainfall kinetic energy and rainfall intensity is greater than 0.97. The third is the method using attribute characteristics such as drop size distribution, precipitation types and the rainfall intensity to categorize the rainfall events and develop the KE-I relationship. While the rainfall is categorized with the drop size distribution (DSD), the KEmm remains constant over various rainfall intensities, and the results are very good. However, while the precipitation types and the rainfall intensity are used for categorizing, the results are not satisfactory. In this study, several methods are used to develop the equations for evaluating rainfall kinetic energy using the local rainfall data. Among these, the results of the KEtime method and the third method using the drop size distribution (DSD) to categorize the rainfall are much better. Accordingly, the findings in this study are expected to be useful for evaluating rainfall kinetic energy and rainfall erosion index in the future.

Aggregate breakdown is an important process controlling the availability of fine soil material necessary for structural sealing of soil surfaces under rainfall. It may be caused by slaking resulting from rapid soil wetting and by physical dispersion resulting from direct and indirect energetic raindrop impacts. Relationships have been proposed by others predicting steady infiltration rate and saturated hydraulic conductivity from final aggregate size following high energy rainfall on initially dry, uncovered soil surfaces. Under these extreme conditions, both rapid wetting and energetic raindrop impact result in maximum aggregate breakdown and surface sealing. ¶ This study has isolated and quantified effects of rapid soil wetting and energetic raindrop impact on aggregate breakdown and surface sealing. Simulated rainfall was applied to re-packed soils from differing tillage treatments on light textured soils from near Cowra and Condobolin in New South Wales, Australia. ...

We review the biomechanics, functional morphology, and physiology of motile traps. The movements of snap traps in Aldrovanda and Dionaea, motile adhesive traps in Drosera and Pinguicula, and suction traps in Utricularia are driven by active water displacement processes leading to reversible turgor changes of motor cells, irreversible growth, or mechanical pre-stressing of tissues. In some cases, the motion is amplified by the release of elastic energy stored in these tissues. The only known case of a passive motile trapping movement is the ‘springboard’ trapping mechanism of Nepenthes gracilis, in which a rapid vibration of the pitcher lid is actuated by the impact force of raindrops. Open research questions are summarized and future studies are suggested.

Erosion is the physical wearing away of the land surface by running water, wind, or ice. Soil or rock is initially detached by falling water, running water, wind, ice or freezing conditions, or gravity. Movement of the rock or soil may follow. Erosion is the combination of detachment and movement of soil or rock. Water erosion can be subdivided into either natural or man-made. Natural or geologic erosion does not require the presence of man. This process has been going on from the moment that land masses were uplifted. An example of geologic erosion is the Grand Canyon in Arizona. Man-made erosion is also called “accelerated erosion” as it is more rapid than natural erosion. Changes that man or animals have made to the soil by cultivation, construction, or any movement of earth often result in loss of soil by erosion. Accelerated erosion involves raindrop erosion, sheet erosion, surface flow, and landscapes. For raindrop erosion to occur, there must be detachment of soil particles followed by either transportation or compaction. Sheet erosion is the slow wearing away of the surface of soil. Surface flow occurs when sufficient water collects to run downhill, resulting in small soil cuts (rills) that often develop into large ruts (gullies). Landslides or slips occur when large chunks of soil move as a unit downhill, often resulting in drops of several feet or more. As rain falls, the drops strike the soil surface moving the soil particles with energy being expended in three kinds of ways: (a) detachment— soil particles are broken into smaller pieces, (b) transportation— small soil grains are moved to a new location as they splash into the air; movement can be downward, to sides, or up eventually acting as a smoothing agent, or (c) compaction—raindrops compact soil surface on bare soil forming a crust, resulting in running the soil particles together (puddling) so that air and water can no longer enter the soil. This causes loss of infiltration and results in runoff.

This chapter provides a detailed study on the harvest of the energy contained in raindrops by means of piezoelectric transducers. The energy harvester has the role of an electric source, able to recharge storage devices of small electronic components, such wireless sensors, by using the vibrational energy released by the drops hitting the transducer, reducing in such a way the chemical waste of conventional batteries. In technical literature, diverse studies agree on the level of suitable generated voltage on the electrodes of a piezoelectric transducer subjected to rainfall, but a complete characterization on the supplied power is still missing. This work, also to limit optimistic forecasts, takes into account the behavior of the transducers in different scenarios: subjected to real and artificial rainfall, standalone or in parallel configuration, in conventional geometries, due to the commercial format or in customized shape, free to move or with an imposed optimal deflection.

Abstract With the increase of wind energy production demand, the need to manufacture larger wind turbine blades is on the rise. Because of the high tip speed of the large blade, the blade could be impacted by high-speed objects such as raindrops. This research focuses on developing a computational model for analyzing wind turbine blade coating fatigue induced by raindrop impact. A stochastic rain texture model is used to simulate a realistic rain event determined by a rain intensity and a rain duration. A smoothed particle hydrodynamic approach is implemented to calculate the impact stress considering a single raindrop. A stress interpolation method is proposed to accurately and efficiently estimate the impact of stress under a random rain event. Besides, a crack growth law is used to explain the process of coating shedding. Through a method for calculating crack growth length based on stress, this paper analyzes crack growth life as a function of the rain intensity and the rain duration. This function, together with the statistics of rainfall history, provides a new approach for estimating the expected fatigue life of the blade coating.