Yanwei Zhai

The formation of a landslide dam is strongly influenced by the properties of the source debris, yet the formation interval has received less systematic attention from a material perspective than stability and breach behavior. This review synthesizes field cases, flume experiments, and numerical simulations to develop a material-centered framework that traces key source descriptors through sequential formation stages to both macroscopic geometry and inherited internal structure, two outcomes that jointly determine how a formed dam responds to overtopping, seepage, and breach. The synthesis shows that multiple material descriptors, spanning grain size distribution, grading continuity, fines fraction, density state, and water-bearing condition, jointly regulate momentum retention, energy dissipation, blockage state, and depositional structure across the formation sequence, with their combined expression recorded in the spatial organization of the dam body. To characterize this organization in a reproducible way, directional indices are proposed that capture internal structural contrasts and serve as a reference for experimental and field studies on dam stability and breach development.

The beneficial utilization of small and medium floods requires a clear flood-control safety boundary before floodwater can be moderately stored and regulated as a water resource. For the Three Gorges Reservoir, a large river-type reservoir with long-distance backwater effects and tributary blocking, this boundary cannot be determined solely from the dam-front water level. This study developed a one-dimensional unsteady hydrodynamic model with dynamic roughness calibration to investigate the risk-constrained flood-season operating water level of the Three Gorges Reservoir. Typical flood events and the 20-year return period design flood were used to examine the responses of the maximum dam-front flood-regulation water level, excess flood volume, longitudinal water levels, and exceedance risk at key reservoir-area sections under different initial regulation water levels and release-discharge conditions. The results show that the Changshou reach is the main control section for high-water-level inundation risk under the study scenarios. When the initial regulation water level is at or below 155 m, the dam-front flood-regulation water level, the peak water level at Changshou, and the exceedance duration generally vary only slightly. When the initial regulation water level exceeds 155 m, these risk indicators increase markedly, indicating a reduced flood-control safety margin. Perturbation analysis further shows that the dam-front flood-regulation indicators are relatively insensitive to small roughness and dam-front boundary perturbations, whereas the Changshou water level and exceedance duration are more sensitive to roughness and flood-volume perturbations. Therefore, 155 m should be interpreted as a conservative operational reference boundary under the current design-flood framework, existing operation rules, and the assumption of no forecast-based pre-release, rather than as an absolute safety threshold. Increasing release discharge can reduce high-water-level risk in the reservoir area under preset release limits, but its practical application must remain conditional on downstream flood-control constraints and real-time flood-conveyance capacity. The results provide a hydrodynamic basis for risk-constrained flood-season operation of large river-type reservoirs.

Understanding the mechanisms behind the cavitation erosion resistance of elastic materials is the basis for the development of new cavitation erosion resistance materials. This paper employs underwater low-voltage discharge to induce cavitation bubble, combined with high-speed photography, shadowgraph methods, and transient pressure measurement systems to experimentally investigate the evolution and intensity of shockwave from bubble collapse near elastic-rigid composite boundary. Under the condition of constant elastic material thickness, with the bubble–wall distance increasing, shockwave shape evolves from multi-layers to single-layer. The peak pressure of the shockwave shows a trend of decreasing, then increasing, and finally stabilizing with increase in the bubble–wall distance. Furthermore, it was found that the elastic-rigid composite boundary causes the shockwave to reflect twice. As the material thickness increases, the intensity of the first reflected shockwave from the elastic surface decreases initially, then increases, and eventually stabilizes. However, that of the second reflected shockwave decreases. The total energy of the two reflections at the elastic interface is less than 4% of the mechanical energy of the bubble at its maximum volume. Finally, after the energy dissipation by the two reflections and material deformation, the elastic layer substrate withstands over 70% of the total mechanical energy of the cavitation bubble. There is an optimal elastic material thickness to minimize the shockwave load on the elastic layer substrate under the condition that the elastic-rigid composite boundary does not affect the evolution of cavitation bubble shape. These findings are significant for understanding bubble dynamics near elastic-rigid composite boundaries and provide theoretical support for developing cavitation erosion-resistant materials in engineering.

Climate change has resulted in an increase in extreme weather events, with a sharp rise in droughts and floods. To establish a long-term mechanism for ensuring the safe operation of the Three Gorges Project, it is imperative to utilize hydrodynamic methods to analyze the water level operation mode during the flood season. This is crucial to enhancing the flood control safety and maximizing the overall benefits of this project. Therefore, this study obtained four different frequency design flood processes for each year by utilizing data from typical years. And the influence of different starting water level and discharge flows on the high water level and excess flood volume of flood regulation were revealed under the existing scheduling protocols and a one-dimensional hydrodynamic model. The results indicated that the water level operation modes of floods from different typical years were significantly different under the same scheduling rules, and when faced with the extreme flood conditions, discharge flow is a primary determinant of reservoir safety. Furthermore, the current scheduling scheme for the Three Gorges Reservoir has an extra safety margin. As a result, even without forecasting inflows, elevating the operating water level to 155 m during the flood season effectively mitigates risks from floods with a return period of 100 years or less, while maintaining risk control over floods with 1,000-year or 10,000-year return periods.

Cavitation erosion is a fundamental concern in many fields of engineering, e.g. the flow separation zone in high speed flow and the blade area of hydraulic machinery. However, the influence of the physical characteristics of the environmental medium in these engineering facilities on cavitation erosion is still unclear. In this paper, we adopted underwater low-voltage discharge technology to generate cavitation bubbles, and studied the mesoscale causes of material erosion in solutions with different surface tensions. It is found that with the decrease of liquid surface tension, the radial velocity of cavitation bubbles decreases significantly during the shrinkage of the cavitation bubble and the minimum radius to which the cavitation bubble shrinks increases, the micro-jet generated by the cavitation bubble develops more slowly, and the impact strength of cavitation bubble collapses on the wall decreases. The findings reveal new physical mechanisms of the cavitation-induced material erosion in liquids with different surface tensions at the macroscopic level. These will provide significant guidance for cavitation prevention in various applications such as aeration cavitation-alleviation, hydraulic machinery, ultrasonic cleaning and the medical industry.

Cavitation phenomena widely exist in many fields such as medical treatment, chemical engineering, and hydraulic engineering. The boundary properties have a great influence on the collapse characteristics of a cavitation bubble. The interaction between a cavitation bubble and a boundary of different properties is an important part in the cavitation erosion mechanism. In this paper, cavitation bubbles under in-water pulse discharge and cavitation erosion under ultrasonic vibration were used to study the effect of a deformable boundary on the collapse characteristics of a cavitation bubble, which reveals the cavitation-resistance performance of different materials on the macroscopic scale. The main experimental results showed that on a deformable boundary, the cavitation bubble does not collapse toward the boundary in the later collapse stage compared with on the rigid boundary. The collapse process of the cavitation bubble is aggravated on the deformable boundary. In the condition of same cavitation strength, the cavitation's erosion loss amount on the rigid boundary material is much higher than that on the deformable boundary material. The experimental conclusions have an important reference value for the development of cavitation erosion prevention and the exploration of cavitation-resistance materials.

An underwater spark is able to induce a cavitation bubble, and this principle has been utilized to make cavitation bubble generators for several decades. In this paper, an improved instrument for generating spark-induced cavitation bubbles is described in detail. The voltage time history inside the instrument is measured to show the working process and principle. Cavitation bubbles are generated by the instrument and recorded by a high-speed camera. The radius time history of the bubble is obtained using an image processing algorithm. The ratio of its minimum radius to its maximum radius reaches ~0.2, which indicates that there is little undissolved gas in the bubble. With the radius time history, the velocity fields around the bubbles were calculated by the 1D continuity flow equation, and the pressure fields were calculated by the 1D Euler equation. One cavitation bubble is chosen and discussed in detail. The velocity and pressure on the bubble interface achieve their maximums (~25 m/s and ~1.2 MPa, respectively) at the same time, when the radius is at its minimum (~1 mm). Some statistical results are also presented to show the effect of the instrument.