Stabilization of Angular-Shaped Riprap under Overtopping Flows
Riprap is mostly used to prevent erosion by flows down the steep slopes in river engineering. A total of 53 stability tests performed on angular riprap with a median stone size ranging from 15 to 278 mm and slope ranging from 1 to 40% are used in this study. The existing equations for the prediction of medium size of angular stones are checked for their accuracy using the available data. Predictions of median size using these equations are not satisfactory and results show deviation by more than ±20% from the observed values. A multivariable power regression analysis is performed to propose a new equation relating the median size with unit discharge, bed slope, riprap thickness and coefficient of uniformity. The proposed relationship satisfactorily predicts the median angular stone size with ±20% error. Further, the required size of the rounded stone is more than the angular stone for the same unit discharge and the ratio increases with unit discharge and also with embankment slope of the riprap. Keywords—Angularity, Gradation, Riprap, Stabilization
Stability of Rounded Riprap in Overtopping Flow
Riprap design procedures often stipulate the use of angular shaped stone materials. However, angular shaped riprap materials are not always available nor economically feasible at all construction locales. Alluvial materials are often available at remote locations that yield relatively high quality materials, but the rock is usually rounded in shape. Currently, the stability of rounded riprap compared to angular riprap is unknown. A physical testing program was performed subjecting rounded rock to overtopping flow. Soil embankments 76 cm in height with slopes of 20%, 25%, and 30% were constructed in a recirculating flume. A geotextile was placed atop of the embankment, followed by a shallow (6 cm) filter/bedding material layer. Rounded riprap with median stone sizes of 2.4 to 9.9 cm (0.94 to 3.9 inches) was placed in layer thicknesses of 1.5 to 3 times the median stone size on the bedding. Flow was conveyed over 12 test configurations and slowly increased until the rock layer integrity was disrupted. The data analysis yielded a procedure through which the stable median rock size may be determined as a function of the degree of roundness, rock uniformity, slope, and unit discharge.
Surface roughness monitoring by singular spectrum analysis of vibration signals
Abstract This study assessed two methods for enhanced surface roughness (Ra) monitoring based on the application of singular spectrum analysis (SSA) to vibrations signals generated in workpiece-cutting tool interaction in CNC finish turning operations i.e., the individual analysis of principal components (I-SSA), and the grouping analysis of correlated principal components (G-SSA). Singular spectrum analysis is a non-parametric technique of time series analysis that decomposes a signal into a set of independent additive time series referred to as principal components. A number of experiments with different cutting conditions were performed to assess surface roughness monitoring using both of these methods. The results show that singular spectrum analysis of vibration signal processing discriminated the frequency ranges effective for predicting surface roughness. Grouping analysis of correlated principal components (G-SSA) proved to be the most efficient method for monitoring surface roughness, with optimum prediction and reliability results at a lower analytical-computational cost. Finally, the results show that singular spectrum analysis is an ideal method for analyzing vibration signals applied to the on-line monitoring of surface roughness.