The agreement between various methods is less satisfactory for predicting the nonlinear low- and high-frequency loads and responses partly because the underlying modeling assumptions differ and partly because the accurate computation of the sum- and difference-frequency QTFs is a complex and time-consuming task. Because it is a time-domain method that may treat slender and large-volume structures, the fluid-impulse method developed by [8,9] addresses the gap between the long-wavelength approximations in the time-domain Morison-based method for slender members and frequency-domain approaches.