In this paper, we applied an incompressible Smoothed Particle Hydrodynamics (SPH) method to investigate the impact of solitary waves on seawalls, especially movable seawalls. The SPH method is a mesh-free numerical approach particularly suitable for dealing with large free surface deformations and complex fluid-structure interactions. The incompressible SPH (ISPH) method solves the pressure field using the pressure Poisson equation (PPE), rather than relying on the equation of state. It has the advantage of producing more stable and accurate pressure fields and impact forces on structures. We first applied the model to simulate the solitary wave propagation and runup against a fixed vertical wall. The computations compared well with previous experimental and numerical results. Then, the solitary wave impact on a movable structure was investigated by replacing the fixed wall with a spring-controlled seawall subject to different spring stiffness and mass settings. Particular attention was paid to the prediction of the seawall movement, wave runup height and hydrodynamic loading. The incident wave height was found to be the dominant factor for the movable seawall movement during and immediately after the wave crest arrival at the seawall. Other factors, such as the seawall mass and spring stiffness, become important to the seawall's responses only after the maximum impact.
In this paper, 3D weakly compressible and incompressible Smoothed Particle Hydrodynamics (WCSPH & ISPH) models are used to study dam-break flows impacting on either a fixed or a movable structure. First, the two models' performances are compared in terms of CPU time efficiency and numerical accuracy, as well as the water surface shapes and pressure fields. Then, they are applied to investigate dambreak flow interactions with structures placed in the path of the flood. The study found that the ISPH modelling approach is slightly superior to the WCSPH approach, since more stable particle motion and pressure distribution can be achieved with reasonable CPU load.
The Pearl River Delta metropolitan region is one of the most densely urbanized megapolises worldwide with high exposure to weather-related disasters such as storms, storm surges and river floods. Shenzhen megacity has been the fastest growing city in the Pearl River Delta region with a significant increase of resident population from 0.32 million in 1980 to 13.03 million in 2018. Being a flood-prone city, Shenzhen’s rapid urbanization has further exacerbated potential flood losses and forthcoming risk. Thus, evaluating the changes in its exposure from present to future is essential for flood risk assessment, mitigation and management purposes. The main objective of this study is to present a methodology to assess the spatio-temporal dynamics of flood exposure from present to future using high-resolution and open-source data with a particular focus on the built-up area. To achieve this, the SLEUTH model, a cellular automata-based urban growth model, was employed for predicting the built-up area in Shenzhen in 2030. An almost threefold increase was observed in total built-up area from 421 km2 in 1995 to 1166 km2 in 2030, with the 2016 built-up area being 858 km2. Built-up areas, both present (2016) and projected (2030), were then used as the land cover input for flood hazard assessment based on a fuzzy comprehensive evaluation model, which classified the flood hazard into five levels. The analysis indicates that the built-up area subjected to the two highest flood hazard levels will increase by almost 88% (212 km2) from present to future. The approach presented here can be leveraged by policymakers to identify critical areas that should be prioritized for flood mitigation and protection actions to minimize potential losses.
Rapid urbanisation and economic growth in developing Asian countries have exacerbated their exposure to flood hazards, particularly evident in low-lying urban cities that are currently facing increasing risks from extreme precipitations, likely made worse by the impending climate change. We present a set of simplified indices representative of the characteristics of rainfall-runoff process for evaluating pluvial flood hazard using the fuzzy comprehensive evaluation method. The highly urbanised Pearl River Delta (PRD) region in southern China is studied as an example of mapping the regional pluvial flood hazard and assessing the socio-economic exposure at risk. The developed hazard map captures the broad patterns of high flood hazard zones when compared with reported surface water flooding hotspots and the PRD riverine flood map from the 2015 Global Assessment Report. Further analysis on the regional socio-economic profiles suggests that most PRD cities are faced with large flood loss potential, with estimates of approximate 23 million people and 2.4 trillion RMB Gross Domestic Product (GDP) exposed to high flood hazard. Mega cities Guangzhou and Shenzhen top the ranking with over 20% to 40% of their dense urban settlements in the high flood hazard zone. This highlights the impact of human activities on the natural surface runoff process, and the need for robust flood hazard assessment for better understanding and design of holistic solutions towards more adequate flood mitigation systems for continuous urbanisation and future climate conditions.
The mixing process of upstream and downstream waters in the dam break flow could generate significant ecological impact on the downstream reaches and influence the environmental damages caused by the dam break flood. This is not easily investigated with the analytical and numerical models based on the grid method due to the large deformation of free surface and the water-water interface. In this paper, a weakly
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