Burial of Short Cylinders Induced by Scour under Combined Waves and Currents

Results of an experimental study of the scour and burial of cylinders placed on a sandy bed under the combined flow of regular waves and currents are presented. Experiments were conducted for cylinder Reynolds wave number and Keulegan-Carpenter number within the ranges $1.5\times {10}^4⩽{\mathsf{R}}_{\mathrm{e}}⩽1.2\times {10}^5$ and $2⩽\mathsf{KC}⩽48$ , respectively. Analysis of the observations indicates that existing semiempirical formulas for prediction of equilibrium-burial-depth and time scales for pipelines are not suitable for the case of a cylinder having a finite length. Thus the need for developing new expressions for both final-burial-depth and time scales based on new observations. In these experiments burial depth shows stronger dependency on the Shields parameter $\theta$ than on the $\mathsf{KC}$ , whereas burial-time scales seem to be influenced by both $\mathsf{KC}$ and $\theta$ . A new empirical predictor for estimating the equilibrium burial of short cylinders under combined flows is presented. The equation is based on the combination of $\theta$ , $\mathsf{KC}$ and the ratio of current velocity to the effective wave plus current velocity.