波浪与抛石潜堤相互作用的MPS法数值模型研究

为了研究波浪与抛石潜堤相互作用过程中大自由表面变形和堤内渗流等强非线性紊流运动问题，利用改进的MPS法，建立了模拟波浪与抛石潜堤相互作用的MPS法数值计算模型。模型将抛石潜堤假定为均质多孔介质，采用Drew的二相流运动方程描述多孔介质内外的流体运动；通过在动量方程中增加非线性阻力项，并引入亚粒子尺度紊流模型，模拟波浪与可渗结构物相互作用过程中的紊流运动。选取“U”型管中多孔介质内渗流过程和孤立波与可渗潜堤相互作用两个典型的渗流问题，通过将数值计算结果与理论解和实测值的对比分析，对所提出的MPS法紊流渗流模型的模拟精度进行验证。结果表明：基于改进的MPS法构建的垂向二维紊流渗流模型可以很好地再现 “U”型管中多孔介质内渗流以及波浪作用下可渗潜堤内外的复杂流场，显著缓解流-固界面处的压力震荡与粒子分布不均匀问题，实现了较高的模拟精度。     

The livestock revolution, food safety, and small-scale farmers: why they matter to us all

Global consumption, production, and trade of livestock products have increased rapidly in the last two decades and are expected to continue. At the same time, safety concerns regarding human and animal disease associated with livestock products are increasing. Efforts to increase public health safety standards aimed at legitimately reducing the risks of human and animal disease have focused internationally on standards to regulate the movement of livestock products. There is concern, though, that measures to regulate these standards internationally, such as the WTO SPS measures that in part aim to open international markets, may marginalize small-scale poor producers. The cycle of poverty they are trying to escape through livestock production may, in fact, widen, leading to increased global poverty, malnutrition, and disease. Developing and developed nations alike should be concerned with public and private efforts to address appropriate food safety policies to reduce the likelihood of this effect. Analysis of the impact on small-scale livestock farmers is needed, as well as solutions that consider joint public and private sector initiatives. Costly farm to table tracking systems are not an option, but locally orchestrated vertically integrated systems may have merit in reducing food safety risks and in providing small-scale farmers with increased access to markets, locally and internationally. Increased scientific and technical capacity, and training of WTO officials from developing nations is also needed.