Superimposition of Kansan Drift on Subaftonian Drift in Eastern Iowa

Many new exposures have been made by the Chicago, Milwaukee and St. Paul Railway in the reconstruction of their line across Iowa, Various ones of these have proved to be of especial interest to Pleistocene geologists, and among them are several cuts in the northern part of Clinton County, showing superimposition of the two oldest drifts, the Kansan drift on the Sub- Aftonian drift. This paper is devoted to a description of these and their interpretation

Additional Evidence of Post-Kansan Glaciation in Johnson County, Iowa

Johnson County offers a field of phenomena that are strikingly applicable to the theme of our late Pleistocene controversy, namely. “Has the northeast quarter of Iowa, except the Driftless Area, been invaded by an ice-sheet later than the Kansan?

Leaching of the Pleistocene Drifts of Eastern Iowa

The term leaching is applied by glaciologists to that process of dissolving and carrying out in solution by ground water the soluble constituents of the drift, of which lime carbonate is the most notable in the Mississippi Valley. This discussion of that phenomenon is based on observations made by the writer on Pleistocene deposits of the larger part of the east half of Iowa, and in the vicinity of Chicago, Illinois

Loess formations of the Mississippi Valley

Cover title."Reprinted from the Journal of geology, vol. 58, no. 6, November, 1950."Bibliography: p. 622-623

Asperity Contact Modelling for Measured Surfaces

The analysis of surface roughness in contacts forms a major part of tribology in almost all application. In any contact in which asperity interactions occur their load carrying capacity must be considered however the separation at which asperity interaction first occurs and the load carrying capacity at that separation are due to the stochastic nature of the surface roughness of the two surfaces. A model that can accurately and quickly provide an estimation of the load carrying capacity as a function of surface separation is required for the specific surfaces used in such conjunctions from implementing surface data. The paper presented provides details of a procedure for modeling asperity interactions of rough surfaces from measured data. The model is validated against a deterministic approach before being applied to measured surfaces

Hydrodynamic flow analysis for determination of the location of surface texture features

Hydrodynamic flow analysis for determination of the location of surface texture feature

An Averaged Approach to Asperity Contact Interactions for Non-Gaussian Lubricated Surfaces

1 Proceedings of the 42th Leeds-Lyon Symposium on TribologySeptember 7-9, 2015, Lyon, France AN AVERAGED APPROACH TO ASPERITY CONTACT INTERACTIONS FOR NON-GAUSSIAN LUBRICATED SURFACESM. Leighton*, N. Morris, R. Rahmani, H. Rahnejat*[email protected] School of Mechanical and Manufacturing Engineering, Loughborough University, Leicestershire, UKABSTRACTThe contiguous surfaces of tribological contacts are often subjected to a period of embedding during the initial stages of operation commonly referred to as the running-in period. Asperity interactions and increased frictional losses are often prevalent during this period. After the transience of the surface roughness during the initial running-in phase, the resultant surface contributes to the tribological behaviour of the contactthroughout the majority of its remaining usable life. The analysis of the surface roughness as a number of spherical Hertzian contacts was provided by the work of Greenwood and Williamsons [1]. Later Greenwood and Tripp[2, 3] adapted the model provided for the probability of asperity interaction between two surfaces. The aforementioned asperity contact models are adapted in the current study to model the asperity interactions throughout a contact’s running-in phase. The adapted model considers non-Gaussian surface roughness distributions and account for the significant change of geometry of the highest summits by considering the mean asperity radius of curvature as a function of the peak height. A mixed regime of lubrication model is developed in which the Patir and Cheng [4, 5] Average Reynolds modelaccounts for the surface roughness effect on the generated hydrodynamic pressure. The model relies on the use of statistical sampling assuming that the surface topographical regions are repeatable in nature in a similar way to Greenwood and Williamson [1]. The asperity interactions are considered using the modified Greenwood and Tripp model described previously.The frictional losses predicted by the numerical model are compared with the experimental results. The tests areconducted under such conditions that the contact resides in the mixed regime of lubrication and experiences wear during the early stages of running. The surface is periodically measured using an Infinite Focus Microscope until such point as the surface roughness sufficiently stabilises (signifying the end of the running-in process). The measured roughness data is used as the input data for the numerical model.The paper presents an adapted asperity contact model capable of considering the effect of roughness interactions on frictional losses during the formative embedding process. The numerical results are compared with experimental test results. The combined numerical and experimental approach allows for an improved understanding of the frictional losses during the running-in

The influence of large scale surface roughness on flow factors

The influence of large scale surface roughness on flow factor

Fully coupled simulations of non-colloidal monodisperse sheared suspensions

In this work we investigate numerically the dynamics of sheared suspensions in the limit of vanishingly small fluid and particle inertia. The numerical model we used is able to handle the multi-body hydrodynamic interactions between thousands of particles embedded in a linear shear flow. The presence of the particles is modeled by momentum source terms spread out on a spherical envelop forcing the Stokes equations of the creeping flow. Therefore all the velocity perturbations induced by the moving particles are simultaneously accounted for. The statistical properties of the sheared suspensions are related to the velocity fluctuation of the particles. We formed averages for the resulting velocity fluctuation and rotation rate tensors. We found that the latter are highly anisotropic and that all the velocity fluctuation terms grow linearly with particle volume fraction. Only one off-diagonal term is found to be non zero (clearly related to trajectory symmetry breaking induced by the non-hydrodynamic repulsion force). We also found a strong correlation of positive/negative velocities in the shear plane, on a time scale controlled by the shear rate (direct interaction of two particles). The time scale required to restore uncorrelated velocity fluctuations decreases continuously as the concentration increases. We calculated the shear induced self-diffusion coefficients using two different methods and the resulting diffusion tensor appears to be anisotropic too. The microstructure of the suspension is found to be drastically modified by particle interactions. First the probability density function of velocity fluctuations showed a transition from exponential to Gaussian behavior as particle concentration varies. Second the probability of finding close pairs while the particles move under shear flow is strongly enhanced by hydrodynamic interactions when the concentration increases