Wenang XIE

This study aims to provide a preliminary semi-analytical description of the momentum reduction in a bouncing cylindrical container filled with swirling fluid upon normal impact with a flat rigid surface, from a hydrodynamic perspective. The focus is on the pressure impulse generated beneath the central jet flow immediately after impact. The fluid motion is modeled using simplified Euler equations with idealized initial conditions and moving boundary conditions. By applying a self-similarity transform, we analytically solve an initial–boundary value problem of the velocity field in a confined target region. This solution allows for a quantitative evaluation of the pressure field. The analysis demonstrates that the rotational motion of the descending flow significantly increases the hydrodynamic pressure near the central axis, thereby exerting a substantial downward stomping pressure impulse on the bottom of the container. This pressure impulse is assumed to be responsible for reducing the momentum of the container, thus also suppressing its bouncing velocity. Based on the analytical results, a semi-analytical method calculating the pressure impulse is proposed, which describes the trend of existing laboratory data.

This research is dedicated to examining downslope sediment transport on steep shorefaces. We present a model that incorporates nonlinear surface wave profiles, sediment movement thresholds, and slope effects, utilizing a set of semi-empirical formulas. The model quantitatively assesses the disparity between wave-augmented upslope transport and gravity-augmented downslope transport, and computes sediment transport rates using a single calibration coefficient. Validation of the model is carried out in the Fuji coast of Japan, where offshore wave conditions and seabed topography with a uniform grain size distribution serve as inputs. The computational outcomes reveal that sediment transport primarily occurs under high wave conditions, and downslope transport dominates on steep slopes. The calibration coefficient is determined through a comparison with observed data, demonstrating a strong agreement in the average annual sediment loss in the target area. Moreover, the model offers insights into the possible mechanism behind the existence of a transition area between the upper and lower shoreface, marked by an abrupt change in seabed slope.

The impingement process of water surge onto a vertical wall and the impact pressure are studied analytically in this work. We propose a new initial-boundary value problem particularly for the fluid motion near the corner of the horizontal bed and the vertical wall. The explicit solutions of the velocity and the pressure fields are analytically obtained using the self-similarity method under some verifiable physical assumptions. The impact pressure is found to be proportional to the product of the squared incident surge front velocity and the density of water, with a constant coefficient of around 0.867. We compare the analytical solution of the impact pressure with some existing laboratory data. The analytical solution agrees with the median value of the stochastic data of impact pressure from laboratory experiments. Subsequently, the velocity and the pressure fields from the analytical model are compared to the numerical simulation results based on OpenFOAM. The comparisons validate the physical assumptions made in the analytical derivation, demonstrating fair consistency. The analytical model successfully describes the early stage of the contact process between the surge front and the wall and provides a theoretical basis for the physics of water surge impingement.

This study aimed to propose a stochastic model for the impact pressure generated by water surge impingement onto a vertical wall. Carefully controlled laboratory experiments were conducted in a small-scale flume under four different surge conditions. Using pressure sensors and a high-speed video camera, we repeatedly measured the surge-induced pressures on the wall together with the surge parameters right before impingement, e.g. the surge front velocity and slope, under each condition. The impact pressure tended to increase linearly with the squared surge front velocity but with high data scattering, reflecting its stochastic nature. Meanwhile, it exhibited limited dependency on the surge front slope, especially at the bottom of the wall, contrary to Cumberbatch's theory of surge impact pressure. We investigated the stochastic properties of the impingement process from the experimental data and proposed a stochastic model of the impact pressure based on an extreme value probability distribution (the Fréchet distribution). The proposed model, which involved only the surge front velocity, fit well with the present dataset and experimental data randomly collected from various literature works. We confirmed that the predictive model is potentially applicable to a wide range of surge impingement problems.

A new semi-empirical formula for calculating the breaking depth of plunging breakers is proposed in this study. The shallow water equation is used as the governing equation, and the wave front slope, which is one of the key parameters that governs the breaking criterion, is obtained from it analytically. The analytical formula was then modified based on both physical considerations and historical laboratory data. The accuracy of the resulting semi-empirical formula was examined using two sets of new laboratory data - including laboratory experiments performed by the authors - in order to verify its applicability. The results indicate that the proposed new formula is more accurate than existing formulas.