No description available.

No description available.

No description available.

No description available.

During the period 1970-76, Siletz Spit on the mid-Oregon coast has suffered foredune erosion. This erosion is associated with high wave conditions along the coast, produced by intense storms in the North Pacific. During the winter of 1972-73 and during January through March 1976 the erosion was particularly severe. The pre-1975 erosion of the spit has been documented in a previous study. One of the main purposes of the present study is to document the 1976 erosion and to contrast it with the earlier episodes. It differed principally in that a small wash-over of the spit occurred in one area and beach drift logs were thrown up onto the dunes. Neither occurred during previous erosion episodes, even during the 25 December 1972 storm when wave breakers exceeded a significant wave height of 7 meters. This is because the 1972 storm occurred at a time of low water level, neap tide conditions. In contrast, the 18 February 1976 major storm occurred during spring tide conditions, causing the wash-over and log throwing, even though the waves were smaller than in December 1972. The amount of dune retreat was somewhat less in 1976 than in 1972-73, partly because of the shorter time period over which the 1976 erosion occurred and partly because of the use of protective riprap. The large waves causing the erosion at Siletz Spit are generated by storms in the North Pacific. The storm systems for December 1972, January 1973, and February 1976 were analyzed as to fetch distances, wind speeds and directions, movements of the fetches, and other factors important in the generation of waves. Waves hindcasted from these data were compared with measurements of the waves obtained from a seismometer system at the Marine Science Center in Newport, Oregon. This comparison demonstrated that these distant fetches were responsible for the waves causing erosion on Siletz Spit. Waves generated locally by coastal winds appear to be of negligible importance in the erosion. This is also shown by a comparison between the wave measurements and data on the coastal winds at Newport during the times of maximum erosion. Tides were investigated for their role in contributing to coastal erosion. High spring tides allow the storm waves to better reach the dunes or sea cliffs and so permit greater erosion. Neap tides, with their lower water levels, diminish the amount of erosion. Many of the differences in the December 1972 and February 1976 erosion episodes were due to the difference in tide levels. Storm surges were determined for Yaquina Bay, Oregon, by subtracting the predicted high-tide levels from the observed levels. It was concluded that significant storm surges did not occur at the times of maximum spit erosion and therefore did not contribute to the erosion processes. / Graduation date: 1977

The erosion behaviour of clay soils has been investigated through a comprehensive program of laboratory testing. Three different erosion test methods have been employed including the rotating cylinder test (RCT), the hole erosion test (HET), and the slaking test (SLT). A new rotating cylinder test device is designed and manufactured capable of testing disturbed and undisturbed soil samples in saturated and unsaturated states. Details of the equipment along with its calibration, testing and sampling procedures are provided. The HET has been reviewed and modified to provide consistent test results. In addition, the slaking test has been customised to accept samples identical to those used in the RCT. A total 111 RCT, 139 HET, and 108 slaking tests have been conducted and analysed. Typical shapes of the erosion curves are identified, based on a wide range of shear stresses and erosion rates analysed. Correlations are presented between the RCT and HET, and between the RCT and SLT to allow characterisation of clay soil erosion in a consistent and unified manner. The erosion modes of clay soils are investigated and categorised into three main groups: ???dispersive erosion???, ???saturated non-dispersive erosion???, and ???unsaturated non-dispersive erosion???. It is shown that soils falling in the same category exhibit near identical erosion characteristics. Factors affecting clay soil erodibility are investigated and displayed for each erosion mode. All findings are presented in a unified framework. A suggested procedure is provided for the evaluation erosion potential in clay soils for practical applications.

Research Doctorate - Doctor of Philosophy (PhD) / The impact of a small particle with a wear surface can lead to very high strain-rates in the material being encountered. Often predictive erosion models are based on material property parameters taken from quasistatic test conditions. However, the material properties of the impacted wear surface can change dramatically with strain and strain-rate, leaving some doubt as to the validity of an erosion model based on quasistatic parameter values. In this study, a new stress-wave monitoring process is developed for the study of material characteristics and erosion phenomena, at strain-rates approaching 10e6s-1. For this study a newly designed piezo-electric transducer was used to monitor the stress-waves produced by small erosive particle impact events. A computational study was also conducted to aid in the transducer design and location distance from the impact source by considering the effects caused by spatial averaging. Spatial averaging affects the recorded stress-wave signal and is caused by the curvature of the stress-wave as the wave passes through the flat piezo-electric sensing element. This study was conducted using a computational and experimental approach. The joint study allowed significant knowledge to be gained for the study of elasto-plastic impact and stress-wave motion. Finite element analysis (FEA) was used to model the experimental system in detail. The stress-waves produced by the experimental process were directly compared to the FEA model. Once the FEA model was validated, detailed information from the impact event at the surface could be obtained from the model, which would otherwise be difficult if not impossible to obtain experimentally. The issues of wave dispersion have been an underlying problem in the correct interpretation of stress-wave phenomena for many years. The impact of the wear surface causes stress-waves with many frequency components, each component propagating through the wear material at distinct wave velocities. Wave dispersion causes the initial stress-wave pulse to be dispersed into many waveforms. In this study the longitudinal stress-wave was the main waveform studied. FEA simulations were conducted for a purely elastic impact and an impact causing significant plastic deformation of the surface. A comparison between these waveforms showed that in the case of impacts causing plastic deformation, the initial part of the stress-wave, measured from the time of arrival to the first peak, corresponded to the elastic stress component of the impact event at the surface. The characterisation of the waveform in regards to elastic and plastic stress components at the surface was significant for validating model parameters of the Johnson-Cook material model. The stress-wave monitoring process was applied in the first instance to erosive particle impacts to AISI 1020 steel at impact velocities up to 104m/s. A specially designed erosion apparatus, fitted with a modified double disc system was used to impact the 10mm thick steel plate. The piezo-electric transducer was firmly clamped to the rear surface, directly behind the point of impact to obtain the stress-wave signals produced by impacts of 0.4mm zirconia spheres. The study showed that the contact interface of the wear material and the piezo-electric transducer could cause a phase change and amplitude reduction of the stress-wave transmitted to the transducer at wave frequencies above 0.9MHz. The results showed that the most likely cause for the phase shift to occur was the restriction of tensile stresses across the contact interface. For wave frequencies below 0.9MHz, no phase shift or amplitude reduction was apparent in the experimental stress-wave recordings. The combined experimental / FEA study was shown to be able to validate the strain-rate parameter of the Johnson-Cook model. The parameters, which could not be validated by the stress-wave monitoring process, were the parameters relating to plastic deformation of the surface, which were the strain-hardening terms of the Johnson-Cook model. These terms were later validated by studying the extent of plastic deformation at the surface, which occurred in the form of impact craters. By comparing the predicted impact crater depths from the FEA model with the experimental results, the strain-hardening parameters of the Johnson-Cook model could be validated. The robustness of the stress-wave monitoring process was proven for the impact study of ultra high molecular weight polyethylene (UHMWPE) and vinyl ester resin (VER). Unlike AISI 1020 steel, little is know about the high strain-rate response of these polymers. Initial estimates of material property parameters were made by applying computational curve fitting techniques to the stress-strain curves of similar polymers, which were from published results obtained from split Hopkinson’s pressure bar method. The impact and stress-wave study showed UHMWPE and VER to be highly sensitive to strain-rate effects. The main effect was a substantial increase in hardness with increasing strain-rate and it was considered that the hydrostatic stress component contributed to the strain hardening of the polymers. The stress-wave monitoring and FEA computational techniques developed in this study were implemented in the development of an improved erosion model. The model form is similar to that of the well-known Ratner-Lancaster model. The Ratner-Lancaster model assumes wear rate to be proportional to the inverse of deformation energy, where deformation energy is approximated as the product of the ultimate stress and ultimate strain. The improved Ratner-Lancaster model uses the Johnson-Cook model to obtain the von-Mises stress as a function of strain. The area integral of the stress-strain curve is used to derive the deformation energy capacity of the material in the deformed zone close to the surface. The model accounts for strain, strain-rate and thermal effects and is therefore more soundly based on material deformation characteristics valid for erosion events than the Ratner-Lancaster model assumptions. The model developed in this work was applied to the erosion study of 1020 steel, UHMWPE and VER, with good correlation being obtained between experimental erosion rates and model predictions.

Thesis (M.S. - Renewable Natural Resources)--University of Arizona. / Includes bibliographical references.

Thesis (M.S. - Civil Engineering and Engineering Mechanics)--University of Arizona. / Includes bibliographical references.

Thesis (Ph. D. - Renewable Natural Resources)--University of Arizona, 1992. / Includes bibliographical references (leaves 194-202).