Development of 2-Phase CFD Models for Marine Environmental Issues

在海洋环境问题中，我们经常面临两个或多个阶段的问题，例如海洋封存CO2被认为是减少大气中CO2排放的可行和经济的选择之一。这里的问题是富含二氧化碳的海水对生物的影响。因此，对深海二氧化碳稀释过程进行数值模拟具有重要意义。从流体动力学的角度考虑海洋环境问题，会发现这些问题有几个特殊的尺度。在这个研究项目中，我们选取了两个相当小的尺度。对于液滴尺度（0.001-0.1m）和局部海洋尺度（100- 1000 m），有两种求解有界面流动的数值方法：前沿捕捉法和前沿跟踪法。我们已经开发了两个新的数值模拟程序在这个规模，其中每一个对应的每一种方法，分别。的 关于我们 前捕获型采用标记密度概念表达界面的位置和形状，解决了上升液滴的振荡变形与顶点脱落之间的关系;前跟踪型采用移动非结构网格系统和新发展的超薄层方法求解液滴的高施密特数问题。通过这种方法，可以生成从上升和变形的液滴的溶解的数值经验方程。该方程可作为一个子类模型用于以下大尺度模拟中。在非常局部的海洋尺度中，液滴不是单独处理的，而是作为体积分数和数密度处理的。因此，这种类型的模拟设法阐明在深海中的注入点附近的液滴羽流的行为。此外，同时解决了二氧化碳溶解到海水中的化学过程及其对个体生物的生物影响。结果表明，对于我们在模拟中合理设置的CO2量和注入时间，每个生物体所经历的pH几乎不会导致死亡。我们还做了室内尺寸的羽流行为实验，并与数值模拟的结果进行了比较。少

We often face two/multi-phase problems in marine environmental issues, such as the ocean sequestration of carbon dioxide, which is regarded as one of feasible and economical choices to reduce carbon dioxide in the atmosphere. Here the problem is the biological impact of CO2-rich seawater. Therefore, it is very important to simulate the dilution process of carbon dioxide in the deep ocean numerically. When one considers marine environmental issues from a viewpoint of fluid dynamics, he/she finds that there are several special scales in these problems. We picked up two rather small scales in this research project. One is the droplet scale (0.001-0.1m), and the other is the very local ocean scale (100-1000m).For the droplet scale, there are two kinds of numerical methods to solve flows with interfaces : i.e. the front-capturing and front-tracking methods. We have developed two new numerical simulation codes in this scale, each of which corresponds to each of the methods, respectively. The … More front-capturing type utilizes the marker density concept to express the position and shape of the interface and solved the relationship between oscillatory deformation of a rising droplet and vertex shedding from it. In the front-tracking type, we adopt moving unstructured mesh systems and newly developed very thin layer method to solve high Schmidt number problems about a droplet. By this method, numerically empirical equations can be generated for the dissolution from a rising and deforming droplet. This equation can be used in the following larger-scale simulations as a sub-class model.In the very local ocean scale, droplets are not treated individually but as volume fraction and number density. Therefore, this type of simulations manages to elucidate the behavior of droplet plume near the injection point in the deep ocean. Moreover, the chemical process of dissolution of carbon dioxide into seawater and its biological impact to individual organism are simultaneously solved. The results said that the pH experience each organism suffers hardly causes mortality for the amount of CO2 and injection period we set reasonably in the simulations. We also did plume-behavior experiments in room size and compared well the results with those of numerical simulations. Less