Wave‐Current Coupling Effects on the Variation Modes of Pore Pressure Response in a Sandy Seabed: Physical Modeling and Explicit Approximations

Abstract

AbstractPrevious flume observations on the response of pore pressure in the seabed induced by the combined wave‐current were mainly limited to relatively deep‐water waves with wavenumber times water depth approximately above 1.0. Meanwhile, existing theoretical solutions neglected the variation of wave height induced by wave‐current coupling effects, limiting the accuracy of the predictions. In this study, the combined wave‐current induced pore pressure response within a sandy seabed is physically modeled in a water flume. A wide range of wave‐current parameters is examined. The effects of wave period, water depth, and wave height with the superimposed following and opposing currents on the change of pore pressure are investigated. The present experiments identify two new particular modes of pore pressure changing under superimposed current on waves, that is, the transition mode and the opposing‐current enhancing mode, besides the well‐recognized following‐current enhancing mode. The specific modes are determined by a dimensionless parameter characterizing the value of wavenumber times water depth for waves in the absence of a current. Based on the conservation of mass, momentum, and energy flux, an explicit solution for the wave height under the wave‐current coupling effect is derived. With this updated wave height, an analytical solution for combined wave‐current induced pore pressure response is further proposed, which agrees with the measured data. Based on this solution, a general diagram for the current effect on the mudline pore pressure amplitude is proposed, which is applicable for both laboratory and field conditions. Finally, the physical mechanism in three variation modes is discussed.