Erosion modeling

The mining industry is crucial for global economic growth but faces environmental challenges, especially in designing stable rehabilitated landforms. To tackle these issues, rainfall simulators have been recognized for their value in providing data for erosion modeling and analysis, aiding the development of effective land cover systems for long-term stability. This chapter provides an overview of the theory, specifications, and design principles of rainfall simulators. It explores the detailed design and construction of a well-known model, along with its calibration process ensuring accurate rainfall production and distribution. The chapter also discusses raindrop size distribution and associated kinetic energy calculations. Calibration results demonstrate satisfactory outcomes with Christiansen’s uniformity coefficient exceeding 85% and a median raindrop size of 2.15 mm. The device successfully generates desired kinetic energy for simulated rainstorms, crucial for studying soil er...

The mining industry is crucial for global economic growth but faces environmental challenges, especially in designing stable rehabilitated landforms. To tackle these issues, rainfall simulators have been recognized for their value in providing data for erosion modeling and analysis, aiding the development of effective land cover systems for long-term stability. This chapter provides an overview of the theory, specifications, and design principles of rainfall simulators. It explores the detailed design and construction of a well-known model, along with its calibration process ensuring accurate rainfall production and distribution. The chapter also discusses raindrop size distribution and associated kinetic energy calculations. Calibration results demonstrate satisfactory outcomes with Christiansen’s uniformity coefficient exceeding 85% and a median raindrop size of 2.15 mm. The device successfully generates desired kinetic energy for simulated rainstorms, crucial for studying soil er...

Soil loss expectation and possible relationships among soil erosion, riparian vegetation and water quality were studied in the São José dos Dourados River basin, State of São Paulo, Brazil. Through Geographic Information System (GIS) resources and technology, Soil Loss Expectation (SLE) data obtained using the Universal Soil Loss Equation (USLE) model were analyzed. For the whole catchment area and for the 30 m buffer strips of the streams of 22 randomly selected catchments, the predominant land use and habitat quality were studied. Owing mainly to the high soil erodibility, the river basin is highly susceptible to erosive processes. Habitat quality analyses revealed that the superficial water from the catchments is not chemically impacted but suffers physical damage. A high chemical purity is observed since there are no urban areas along the catchments. The water is physically poor because of high rates of sediment delivery and the almost nonexistence of riparian vegetation.

Coastal hazard at the residential scale, resulting from the combined effects of storm surge and waves including dynamic setup and wave runup, is assessed for the local 100-year Synthetic Design Storm (SDS) in Narragansett, RI, USA, based on high resolution (2 m) simulations with the nonlinear phase-resolving Boussinesq wave model FUNWAVE. The accuracy of wave-flow-structure interaction modeling is improved using a built-up DEM, defined by adding coastal structures to the bare-earth DEM. In addition, bathymetry and topography are modified to reflect post-storm conditions based on simulating the same storm with the morphodynamic model XBeach. Comparisons of FUNWAVE results with those of the phase-averaged model STWAVE, for the same storm conditions, show that including individual wave effects increases the inundated area by 13% and maximum water levels (TWL) across the shoreline by 11%, in average; however, in high runup areas (such as along exposed structures), the predicted maximum water levels can increase by up to 100%. FUNWAVE predicts maximum runups on the order of ∼1.5 (with the offshore significant wave height), which is consistent with empirical formulae for steep seawalls (Van der Meer, 2002), and these occur at the most exposed structures, which historical records show have been periodically damaged by large storms. The maximum momentum forces predicted by FUNWAVE are much larger than those derived from STWAVE simulations (based on linear wave theory and assuming Rayleigh distributed waves), and also occur on the most exposed structures. The study provides a quantitative assessment of the local coastal hazard associated with the selected SDS at the scale of individual structures, and stresses the importance of accurately modeling individual wave effects, runups and associated forces in coastal hazard assessment modeling studies.

Surface treatment methods like shot peening are used to introduce compressive residual stresses in metals and alloys. The presence of compressive stresses prevent the initiation and growth of cracks and hence improve the fatigue life of mechanical parts. Cavitation peening is a similar surface treatment process

Submitted for the MAR13 Meeting of The American Physical Society Dynamics of a Cylindrical Bubble between Two Parallel Plates for Biomedical Applications SOWMITRA SINGH, JIN-KEUN CHOI, GEORGES CHAHINE, Dynaflow, Inc.-Microbubbles have been shown to produce directional and targeted membrane poration of individual cells in microfluidic systems, which could be of use in ultrasound-mediated drug and gene delivery. To study and understand the mechanisms at play in such interactions, a full three-dimensional Boundary Element Method (BEM) has been developed to describe complex bubble deformations, jet formation, and bubble splitting. The present work aims at providing analytical validation for the three-dimensional BEM code, 3Dy-naFS c ⃝ , when the dynamics of a bubble between two parallel plates is studied. The analytical equations of a cylindrical (2-D) bubble between two flat plates were derived without accounting for any shape deformation. Comparisons between the analytical model and the numerical model were carried out in scenarios where the shape of an expanding/collapsing bubble between two parallel plates is nearly cylindrical (large maximum equivalent bubble radius to plate gap ratio). Interestingly, both the analytical and the numerical methods predict a strong dependence of the bubble period on the plate size.

Material pitting from cavitation has been used on and off as an indicator of the vague concept of 'cavitation intensity'. Periodically, some researchers suggest the use of pitting tests as a means to provide quantitative measurements of the amplitude of the impulsive pressures in the cavitation field, especially when combined with Tabor's formula or with finite element computations with idealized synthetic loads. This paper examines the viability of such a suggested method using fully coupled bubble dynamics and material response, and strongly concludes that the method provides at best a qualitative assessment of the cavitation erosion potential. Peak pressures deduced from pit geometry are significantly lower than the ones actually applied. In addition the correspondence is highly dependent on the way the load is applied and different loading scenarios with the same amplitude of the cavitation impulsive pressure result in different pit aspect ratios.

View the article online for updates and enhancements. You may also like Investigation of the cavitation fluctuation characteristics in a Venturi injector Yuncheng Xu, Yan Chen, Zijun Wang et al.-Power cavitation-guided blood-brain barrier opening with focused ultrasound and microbubbles M T Burgess, I Apostolakis and E E Konofagou-Non-invasive and real-time passive acoustic mapping of ultrasound-mediated drug delivery James J Choi, Robert C Carlisle, Christian Coviello et al.

Surface cleaning using cavitation bubble dynamics is investigated numerically through modeling of bubble dynamics, dirt particle motion, and fluid material interaction. Three fluid dynamics models; a potential flow model, a viscous model, and a compressible model, are used to describe the flow field generated by the bubble all showing the strong effects bubble explosive growth and collapse have on a dirt particle and on a layer of material to remove. Bubble deformation and reentrant jet formation are seen to be responsible for generating concentrated pressures, shear, and lift forces on the dirt particle and high impulsive loads on a layer of material to remove. Bubble explosive growth is also an important mechanism for removal of dirt particles, since strong suction forces in addition to shear are generated around the explosively growing bubble and can exert strong forces lifting the particles from the surface to clean and sucking them toward the bubble. To model material failure and removal, a finite element structure code is used and enables simulation of full fluid-structure interaction and investigation of the effects of various parameters. High impulsive pressures are generated during bubble collapse due to the impact of the bubble reentrant jet on the material surface and the subsequent collapse of the resulting toroidal bubble. Pits and material removal develop on the material surface when the impulsive pressure is large enough to result in high equivalent stresses exceeding the material yield stress or its ultimate strain. Cleaning depends on parameters such as the relative size between the bubble at its maximum volume and the particle size, the bubble standoff distance from the particle and from the material wall, and the excitation pressure field driving the bubble dynamics. These effects are discussed in this contribution.

Cavitation pressure fields under a cavitating jet and an ultrasonic horn were recorded for different conditions using high frequency response pressure transducers. This aimed at characterizing the impulsive pressures generated by cavitation at different intensities. The pressure signals were analyzed and statistics of the amplitudes and widths of the impulsive pressure peaks were extracted. Plots of number densities and cumulative numbers of peaks as functions of peak amplitude, peak width, and the power of the ultrasonic horn or the jet were generated. The analysis revealed the dominance of pulses with smaller amplitudes and larger durations at lower cavitation intensities and the increase of the amplitudes and reduction of the pulse widths at higher intensities. The ratio of the most probable peak amplitude to peak width was computed. A representative Gaussian curve was then generated for each signal using a characteristic peak amplitude and the corresponding most probable peak duration/width. This resulted in a proposed statistical representation of a cavitation field, useful to characterize cavitation fields of various intensities.

A simple mathematical expression is presented to describe cavitation mean depth of erosion versus time for cavitating jets and ultrasonic cavitation. Following normalization with a characteristic time, t*, which occurs at 75% of the time of maximum rate of erosion, and a corresponding material characteristic mean erosion depth, h*, the normalized erosion depth is related to the normalized time by

The effects of cavitation bubble dynamics on material peening and pitting is investigated numerically using a coupled fluid and material dynamics approach. The model is applied here to the study of peening and pitting of metallic materials resulting from non-spherical cavitation bubble collapse near the material. Bubble reentrant jet impact and shock wave emission from the jet impact and from the collapse of the remaining bubble ring can induce permanent micro-deformation, pitting, and residual stresses, which modify the roughness of the material and harden it through pre-stressing. These effects are investigated through a parametric study for different bubble material standoff distances. Quantities such as bubble collapse peak pressure, pit depth, and residual stresses depend strongly on bubble standoff distance, which is an important factor in whether hardening or erosion of the material occurs.

The mining industry is crucial for global economic growth but faces environmental challenges, especially in designing stable rehabilitated landforms. To tackle these issues, rainfall simulators have been recognized for their value in providing data for erosion modeling and analysis, aiding the development of effective land cover systems for long-term stability. This chapter provides an overview of the theory, specifications, and design principles of rainfall simulators. It explores the detailed design and construction of a well-known model, along with its calibration process ensuring accurate rainfall production and distribution. The chapter also discusses raindrop size distribution and associated kinetic energy calculations. Calibration results demonstrate satisfactory outcomes with Christiansen’s uniformity coefficient exceeding 85% and a median raindrop size of 2.15 mm. The device successfully generates desired kinetic energy for simulated rainstorms, crucial for studying soil er...

In many practical applications involving underwater explosions near a solid structure, competition between the forces due to gravity and those due to the presence of a nearby structure leads to highly distorted bubble shapes. In order to accurately simulate such problems, a 3-dimensional model is required. In this paper, we present results of a validation study of DyNeruoWs 3-D Boundary Element Code, 3DvNaFS, that has been successful in predicting and reproducing a host of Narry underwater explosion problerns. We present ...

Simulations involving a large number of interacting bubbles in a bubble cloud are conducted to assess the effect of frequency and amplitude of a sinusoidal driving pressure on the bubble cloud behavior. As the pressure amplitude increases strong nonlinear bubble dynamics become more pronounced and higher pressures are generated at the wall. A resonance frequency, corresponding to the highest collective bubble behavior, results in a pressure peak orders of magnitudes higher than the excitation pressure. This frequency is significantly different from the natural frequency of a spherical cloud executing small amplitude oscillations.

An unclassified compilation of underwater explosion (UNDEX) bench- marks is presented in the interest of initiating a dialog within the UNDEX community on validation techniques. The compilation is preliminary; some information is incomplete, only minimal detail is provided, and the focus is limited to the response of submerged structures to underwater explosions. Both analytical and empirical benchmarks are presented. Each type has ad- vantages and disadvantages for the purposes of model validation, though no methodology for employing these benchmarks in a model validation ef- fort is proposed. A list of benchmark simulations known to the author is also compiled. Finally, extension of this compilation to the UNDEX re- sponse of internal equipment and floating structures, and to hydrody- namic/hydraulic ram problems, is proposed.

Spark-generated bubbles are strong candidates for laboratory-scale models of underwater explosion (UNDEX) bubble dynamics and are, therefore, excellent sources of data for validation of simulation tools. Their relative safety, cleanliness and compactness enable high quality observations of bubble dynamics at relatively low cost compared to experiments involving explosives. This document addresses the relevant advantages of spark-generated bubbles, focusing on re-entrant jet visualization. It also addresses scaling issues and concerns about the deposition of energy into the bubble as a result of the electric discharge process. In conclusion, a procedure is specified for using spark-generated bubbles as laboratory-scale models of UNDEX bubble dynamics and as data for validation of simulation tools.

Surface treatment methods like shot peening are used to introduce compressive residual stresses in metals and alloys. The presence of compressive stresses prevent the initiation and growth of cracks and hence improve the fatigue life of mechanical parts. Cavitation peening is a similar surface treatment process

Spark-generated bubbles are strong candidates for laboratory-scale models of underwater explosion (UNDEX) bubble dynamics and are, therefore, excellent sources of data for validation of simulation tools. Their relative safety, cleanliness and compactness enable high quality observations of bubble dynamics at relatively low cost compared to experiments involving explosives. This document addresses the relevant advantages of spark-generated bubbles, focusing on re-entrant jet visualization. It also addresses scaling issues and concerns about the deposition of energy into the bubble as a result of the electric discharge process. In conclusion, a procedure is specified for using spark-generated bubbles as laboratory-scale models of UNDEX bubble dynamics and as data for validation of simulation tools.

Material pitting from cavitation has been used on and off as an indicator of the vague concept of 'cavitation intensity'. Periodically, some researchers suggest the use of pitting tests as a means to provide quantitative measurements of the amplitude of the impulsive pressures in the cavitation field, especially when combined with Tabor's formula or with finite element computations with idealized synthetic loads. This paper examines the viability of such a suggested method using fully coupled bubble dynamics and material response, and strongly concludes that the method provides at best a qualitative assessment of the cavitation erosion potential. Peak pressures deduced from pit geometry are significantly lower than the ones actually applied. In addition the correspondence is highly dependent on the way the load is applied and different loading scenarios with the same amplitude of the cavitation impulsive pressure result in different pit aspect ratios.

The motivation behind this research lies in understanding the physical mechanism of cavitation erosion in compressible liquid flows, with applications in the field of aerospace, hydrodynamics, diesel injectors etc. As a consequence of collapsing vapor cavities in cavitating flow near solid boundaries, high pressure impact loads are generated. These pressure loads are believed to be responsible for the erosive damages on solid surface observed in most applications. For our investigation, the initial geometry is a single vapor bubble near a solid boundary collapsing due to the pressure difference between the bubble and surrounding liquid. The numerical approach employs a simplified homogenous mixture or 'single fluid' model with barotropic assumption in a fully compressible finite-volume fluid solver. The numerical method is validated against the well-known Rayleigh collapse of a pure 3D vapour bubble. It is then used for the simulation of a 2D vapour bubble collapsing in the proximity of a solid boundary placed at a specified distance from the centre of the bubble. The pressure loads are computed from the evolving dynamics of collapsing bubble near a solid boundary which can be used to determine the resulting surface deformation. The developed compressible cavitation solver in the CFD code 2 can efficiently model small and large scale cavitating structures in a fully resolved three dimensional flow.

The motivation behind this research lies in understanding the physical mechanism of cavitation erosion in compressible liquid flows, with applications in the field of aerospace, hydrodynamics, diesel injectors etc. As a consequence of collapsing vapor cavities in cavitating flow near solid boundaries, high pressure impact loads are generated. These pressure loads are believed to be responsible for the erosive damages on solid surface observed in most applications. For our investigation, the initial geometry is a single vapor bubble near a solid boundary collapsing due to the pressure difference between the bubble and surrounding liquid. The numerical approach employs a simplified homogenous mixture or 'single fluid' model with barotropic assumption in a fully compressible finite-volume fluid solver. The numerical method is validated against the well-known Rayleigh collapse of a pure 3D vapour bubble. It is then used for the simulation of a 2D vapour bubble collapsing in the ...

A new boundary element model for simulating the interaction of one or more bubbles and a free surface is described. An important feature of this model is the utilization of a nine-noded Lagrangian interpolation for the computation of surface characteristics and material velocity. Solid angles on the free surface are computed via a direct approach, as opposed to the indirect approach usually employed for closed surfaces. The evolution of the bubble is followed until the point before the reentrant jet impacts on the opposite wall of the bubble. The results of the 3D code are compared against those of a one-dimensional Rayleigh-Plesset model and an axisymmetric code. New results are presented for the interaction of two bubbles and a free surface, where fully three-dimensional features are expected.

A new boundary element model for simulating the interaction of one or more bubbles and a free surface is described. An important feature of this model is the utilization of a nine-noded Lagrangian interpolation for the computation of surface characteristics and material velocity. Solid angles on the free surface are computed via a direct approach, as opposed to the indirect approach usually employed for closed surfaces. The evolution of the bubble is followed until the point before the reentrant jet impacts on the opposite wall of the bubble. The results of the 3D code are compared against those of a one-dimensional Rayleigh-Plesset model and an axisymmetric code. New results are presented for the interaction of two bubbles and a free surface, where fully three-dimensional features are expected.

An unclassified compilation of underwater explosion (UNDEX) bench- marks is presented in the interest of initiating a dialog within the UNDEX community on validation techniques. The compilation is preliminary; some information is incomplete, only minimal detail is provided, and the focus is limited to the response of submerged structures to underwater explosions. Both analytical and empirical benchmarks are presented. Each type has ad- vantages and disadvantages for the purposes of model validation, though no methodology for employing these benchmarks in a model validation ef- fort is proposed. A list of benchmark simulations known to the author is also compiled. Finally, extension of this compilation to the UNDEX re- sponse of internal equipment and floating structures, and to hydrody- namic/hydraulic ram problems, is proposed.

The effects of cavitation bubble dynamics on material peening and pitting is investigated numerically using a coupled fluid and material dynamics approach. The model is applied here to the study of peening and pitting of metallic materials resulting from non-spherical cavitation bubble collapse near the material. Bubble reentrant jet impact and shock wave emission from the jet impact and from the collapse of the remaining bubble ring can induce permanent micro-deformation, pitting, and residual stresses, which modify the roughness of the material and harden it through pre-stressing. These effects are investigated through a parametric study for different bubble material standoff distances. Quantities such as bubble collapse peak pressure, pit depth, and residual stresses depend strongly on bubble standoff distance, which is an important factor in whether hardening or erosion of the material occurs.

Numerical prediction of mass loss due to cavitation erosion requires the knowledge of the hydrodynamic impact loads generated by cavitation bubble collapses. Experimental measurements of such impact loads using conventional pressure sensors are not reliable (if not impossible) due to the micron size and the very small duration of the loading. In this paper, a new method to estimate these loading conditions is proposed based on cavitation pitting tests and an iterative inverse finite element modeling. The principle of the method is as follows. First, numerous pits corresponding to localized plastically deformed regions are identified from a cavitation test performed in a dedicated tunnel. Then each pit is numerically reproduced by finite element simulations of the material response to a representative Gaussian pressure field supposed to mimic a single bubble collapse. This gives the size and pressure distribution of the bubble impacts. The prime objective of this study is to find out if the target material itself could be used as a pressure sensor or not, i.e., if the cavitation pits left on the surface of the tested specimen could provide the characteristics of the cavitating flow in terms of pressure fields independently of the target material. Pitting tests were done on three materials, namely, 7075 Aluminum alloy (Al-7075), 2205 duplex stainless steel (A-2205), and Nickel-Aluminum Bronze (NAB) at three different flow conditions and the impact loads have been estimated for each identified pit. Very interestingly, a statistical analysis shows that the estimated impact loads are material independent at all flow conditions, provided the material properties are characterized properly. It is also shown that for some materials, the constitutive parameters obtained from compression tests are not satisfactory. V C 2015 AIP Publishing LLC. [http://dx.

Simulations involving a large number of interacting bubbles in a bubble cloud are conducted to assess the effect of frequency and amplitude of a sinusoidal driving pressure on the bubble cloud behavior. As the pressure amplitude increases strong nonlinear bubble dynamics become more pronounced and higher pressures are generated at the wall. A resonance frequency, corresponding to the highest collective bubble behavior, results in a pressure peak orders of magnitudes higher than the excitation pressure. This frequency is significantly different from the natural frequency of a spherical cloud executing small amplitude oscillations.

The interaction between an explosion bubble and a floating body involves several physical phenomena that an accurate numerical simulation needs to capture. These include proper description of the initial shock wave and its propagation and interaction with the floating body and free surface and the subsequent growth, dynamics, collapse, and interaction of the resulting bubble with the structure. A numerical procedure which links a compressible finite difference flow solver with an incompressible boundary element method was applied to capture both shock and bubble phases efficiently and accurately. Both codes solved the fluid dynamics problem and coupled with a finite element structure code to simulate fluid-structure interaction. This numerical approach was validated by comparing the numerical results with available experimental measurements. The effects of including or neglecting some modeling aspects on the solution were considered.

The interaction between an explosion bubble and a floating body involves several physical phenomena that an accurate numerical simulation needs to capture. These include proper description of the initial shock wave and its propagation and interaction with the floating body and free surface and the subsequent growth, dynamics, collapse, and interaction of the resulting bubble with the structure. A numerical procedure which links a compressible finite difference flow solver with an incompressible boundary element method was applied to capture both shock and bubble phases efficiently and accurately. Both codes solved the fluid dynamics problem and coupled with a finite element structure code to simulate fluid-structure interaction. This numerical approach was validated by comparing the numerical results with available experimental measurements. The effects of including or neglecting some modeling aspects on the solution were considered.

An understanding of the fundamental mechanisms involved in the interaction between bubbles and structures is of importance for many applications involving cavitation erosion. Generally, the final stage of bubble collapse is associated with the formation of a highspeed reentrant liquid jet directed toward the solid surface. Local forces associated with the collapse of such bubbles can be very high and can exert significant loads on the materials. This formation and impact of liquid jet is an area of intense research. Under some conditions, the presence of gravity and other nearby boundaries and free surfaces alters the jet direction and need to be understood, especially that in the laboratory, small scale tests in finite containers have these effects inherently present. In this work, experiments and numerical simulations of the interaction between a vertical wall and a bubble are carried out using Dynaflow's three-dimensional code, 3DYNAFS-BEM, which models the unsteady dynamics of a liquid flow including the presence of highly nonlinear time evolving gas-liquid interfaces. The numerical predictions were validated using scaled experiments carried out using spark generated bubbles. These spark bubble tests produced high fidelity test data that properly scale the fluid dynamics as long as the geometric nondimensional parameters, gravity and time are properly scaled. The use of a high speed camera allowing framing rates as high as 50,000 frames per second to photograph the bubbles produced high quality observations of bubble dynamics including clear visualizations of the reentrant jet formation inside the bubble. Such observations were very useful in developing and validating the numerical models. The cases studied showed very good correlation between the numerical simulations and the experimental observations and allowed development of predictive rules for the re-entrant jet characteristics, including jet angle, jet speed, and various geometric characteristics of the jet.

We have developed a three-dimensional BEM based code (3DYNAFS  ) to study nonlinear free surface flows. The code is being used here to study bubble dynamics, such as that due to an underwater explosion, beneath surface piercing bodies. Six degree-of-freedom rigid body motion of the surface piercing bodies are modeled producing a fully coupled fluid-structure interaction effect simulation. Validation of the code is presented by comparison of simulations with laboratory experimental data obtained from high speed video recordings of surface piercing bodies interacting with bubbles generated by electric spark discharge. Two cylindrical body configurations are considered under both free floating and rigidly constrained conditions. The results of the numerical simulation show very good comparison to the experimental data in terms of bubble shapes and periods, the time evolution of the bubble and the induced motion of the bodies.

Underwater explosions present a significant risk to structures because they were not designed for these types of loads and because water transmits explosive energy much more efficiently than air. The US Navy demonstrated that the effect of bubble jetting from an underwater explosion can result in significant late-time loading compared to the initial shock loading. However, neither the effects of bubble jetting on structures, where the explosion is likely to be lateral to the target rather than beneath it, nor the loading conditions required to produce bubble jetting effects on such structures (charge weight, submerged depth, and standoff distance to structure) are well understood. This investigation improves characterizations of bubble formation, collapse, and jetting near lateral targets. The research includes very small-scale tests to observe bubble jetting, slightly larger underwater blast experiments to determine bubble jetting loads on vertical structures, and larger-scale experiments to measure bubble jetting effects on the structural deformation to structures.

Cavitation erosion prediction and characterization of cavitation field strength are of interest to industries suffering from cavitation erosion detrimental effects. One means to evaluate cavitation fields and materials is to examine pitting rates during the incubation period, where the test sample undergoes localized permanent deformations shaped as individual pits. In this study, samples from three metallic materials, an Aluminum alloy (Al7075), a Nickel Aluminum Bronze (NAB) and a Duplex Stainless Steel (SS A2205) were subjected to a vast range of cavitation intensities generated by cavitating jets at different driving pressures and by an ultrasonic horn. The resulting pitted sample surfaces were examined and characterized with a noncontact 3D optical scanner and the resulting damage computer-analyzed. A statistical analysis of the pit population and its characteristics was then carried out. It was found that the various cavitation field strengths can be correlated to the measured pit distributions and that two characteristic quantities: a characteristic number of pits per unit surface area and unit time, and a characteristic pit diameter or a characteristic pit depth can be attributed to a given "cavitation intensity level". This characterization concept can be used in the future to study the cavitation intensity of the full scale and to develop methods of full scale predictions based on model scale erosion data.

A simple mathematical expression is presented to describe cavitation mean depth of erosion versus time for cavitating jets and ultrasonic cavitation. Following normalization with a characteristic time, t*, which occurs at 75% of the time of maximum rate of erosion, and a corresponding material characteristic mean erosion depth, h*, the normalized erosion depth is related to the normalized time byh = 1 − e −t 2 + e −1t1.2 . This was obtained by conducting systematic erosion progression tests on several materials and varying erosion field intensities. Both a modified ASTM-G32 method and Dynaflow's cavitating jets techniques were used and the jet pressures were varied between 1000 and 7000 psi. The characteristic parameters were obtained for the different configurations and the correlation was found to be very good, exceeding an R 2 of 0.988 for all cases. Relationships between these parameters and the jet pressure were obtained and resemble familiar trends presented in the literature for mass loss. The study allowed a comparative evaluation and ranking of the various materials with the two accelerated erosion testing methods used. While several materials ranked the same way with the different erosion intensities and testing method, the relative ranking of erosion resistance of some materials was seen to be dependent on the cavitation intensity.

Material pitting from cavitation has been used on and off as an indicator of the vague concept of 'cavitation intensity'. Periodically, some researchers suggest the use of pitting tests as a means to provide quantitative measurements of the amplitude of the impulsive pressures in the cavitation field, especially when combined with Tabor's formula or with finite element computations with idealized synthetic loads. This paper examines the viability of such a suggested method using fully coupled bubble dynamics and material response, and strongly concludes that the method provides at best a qualitative assessment of the cavitation erosion potential. Peak pressures deduced from pit geometry are significantly lower than the ones actually applied. In addition the correspondence is highly dependent on the way the load is applied and different loading scenarios with the same amplitude of the cavitation impulsive pressure result in different pit aspect ratios.

Cavitation erosion prediction and characterization of cavitation field strength are of interest to industries suffering from cavitation erosion detrimental effects. One means to evaluate cavitation fields and materials is to examine pitting rates during the incubation period, where the test sample undergoes localized permanent deformations shaped as individual pits. In this study, samples from three metallic materials, an Aluminum alloy (Al7075), a Nickel Aluminum Bronze (NAB) and a Duplex Stainless Steel (SS A2205) were subjected to a vast range of cavitation intensities generated by cavitating jets at different driving pressures and by an ultrasonic horn. The resulting pitted sample surfaces were examined and characterized with a noncontact 3D optical scanner and the resulting damage computer-analyzed. A statistical analysis of the pit population and its characteristics was then carried out. It was found that the various cavitation field strengths can be correlated to the measured pit distributions and that two characteristic quantities: a characteristic number of pits per unit surface area and unit time, and a characteristic pit diameter or a characteristic pit depth can be attributed to a given "cavitation intensity level". This characterization concept can be used in the future to study the cavitation intensity of the full scale and to develop methods of full scale predictions based on model scale erosion data.

In many practical applications involving underwater explosions near a solid structure, competition between the forces due to gravity and those due to the presence of a nearby structure leads to highly distorted bubble shapes. In order to accurately simulate such problems, a 3-dimensional model is required. In this paper, we present results of a validation study of DyNeruoWs 3-D Boundary Element Code, 3DvNaFS, that has been successful in predicting and reproducing a host of Narry underwater explosion problerns.