WAVE INTERACTION WITH FLUID MUD IN RECTANGULAR TRENCH

Wave interaction with fluid mud in a rectangular trench is studied the oretically based on small-amplitude wave theory. The motion of fluid m ud is modeled using the Voigt model for a viscoelastic medium. It is f ound that the elastic and viscous properties of a Voigt body result in a wide range of frictional characteristics and dynamic responses in t he trench, depending on the magnitude of the elasticity parameter m(G/ rho2sigma2)1/2 and the viscosity parameter m(nu2/sigma)1/2. The relati ve importance of viscous effects and elastic effects is given by the r atio mu2sigma/G, which is a wave frequency normalized by the retardati on time of the Voigt material. For an almost rigid bed, where either t he values of the elasticity parameter are high or the values of the vi scosity parameter are high, amplitudes of mud waves are small and moti ons of surface waves are similar to those for homogeneous fluids. For a soft bed, when the frequency of incident waves corresponds to the na tural frequency of mud waves, surface waves with relatively small ampl itudes can result in large amplitude oscillations in the trench thus l eading to more serious bed erosion. The response curve for the interfa cial waves is very sensitive to viscous effects. As the depth of fluid mud decreases, viscous dissipation in the mud bed increases so wave a mplitudes and shear stresses at the water-mud interface decrease. This study indicates that th response of fluid mud to wave action may have significant effects on sedimentation characteristics in dredged navig ation channels.