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
Evaluation of Overtopping Riprap Design Relationships
Rock riprap is one of the most widely used erosion control methods for protecting embankments, levees, spillways, and instream structures subjected to overtopping flow conditions. At least 21 stone‐sizing relationships exist to determine the median stone size of a protective riprap layer based on the results of 96 overtopping, laboratory experiments. Test parameters include median stone size, slope, unit discharge, coefficient of uniformity, and riprap layer thickness. A regression analysis was performed relating the observed median stone size to the predicted median stone size to each of the 21 relationships, yielding a coefficient of determination (R2) and percent error for the full spectrum of data. Zonal (partial spectrum of rock sizes) and complexity analyses were also conducted for each relationship. It was resolved that the Khan and Ahmad, and Chang relationships best aligned with the composite dataset. The predictive expressions by Olivier, Hartung and Scheuerlein, Knauss, Maynord, Abt and Johnson, and Siebel yield a noteworthy second tier of stone‐sizing relationships for overtopping conditions.
Quantitative and qualitative relationship between swirl burner operatingconditions and pulverized coal flame length
Abstract Currently, there are used in power plants two types of burners to combustion the pulverized coal: jet burners and swirl burners. Most of the published works in the field of analysis of burners operating conditions are related to jet burners and are limited to initial region of the flame at the outlet of the burner. For jet burners an offset between the burner outlet and the flame beginning point could be analyzed. In the case of swirl burners with the pre-mixing diffuser chamber an offset between flame ignition point and burner outlet is usually not visible. Because already in the pre-mixing diffuser chamber of swirl burner occurs the ignition of coal-dust together with oxidant-gas cloud and thereby the formation of the flame. Therefore, the analysis of operating conditions for this types of burners requires a different approach. There is a lack of researches, in which will be analyzed changes of the flame length, that are caused by changes of design and operating parameters of swirl burner with the pre-mixing diffuser chamber. Therefore the aim of this study was to implement and verify the methodology for estimating the flame length, which will allow monitoring changes of operating conditions, that are caused by changes of design and operating parameters of swirl burner with the pre-mixing diffuser chamber. To carry out the analysis of the image of the coal flame, the two algorithms have been presented. This two algorithms, being based on the video images of the coal flame allows to specify and detect the end point of the flame and on that basis the length of the flame, as well as the fluctuation changes of flame length can be later determined. Both, the change thermal loads of coal burner, streams of secondary air, as well as the constructional change of the angle of swirler assemblies, resulted in distinct changes in the length of the pulverized coal flame.