Development of 2-Phase CFD Models for Marine Environmental Issues

在海洋环境问题中，我们经常面临两阶段/多阶段的问题，例如二氧化碳的海洋固存被认为是减少大气中二氧化碳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，对二氧化碳在深海中的稀释过程进行数值模拟是非常重要的。当人们从流体力学的角度考虑海洋环境问题时，他/她会发现这些问题中有几个特殊的尺度。我们在这个研究项目中选取了两个相当小的尺度。一个是液滴尺度（0.001-0.1m），另一个是非常局部的海洋尺度（100-1000m）。对于液滴尺度，求解具有界面的流动有两种数值方法：前捕获法和前跟踪法。我们在这个尺度上开发了两个新的数值模拟代码，每个代码分别对应于每种方法。More前捕获型利用标记密度的概念来表示界面的位置和形状，解决了上升液滴的振荡变形与顶点脱落之间的关系。在前跟踪类型中，我们采用移动非结构化网格系统和新开发的极薄层方法来解决液滴的高施密特数问题。利用该方法，可以建立上升变形液滴溶解的数值经验方程。该方程可作为子类模型用于以下更大规模的模拟。在非常局部的海洋尺度上，液滴不是单独处理，而是按体积分数和数目密度处理。因此，这种模拟能够很好地解释深海中喷射点附近液滴羽流的行为。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影响。结果表明，在模拟中合理设置CO2的量和注射周期，每个生物所遭受的pH体验几乎不会导致死亡。我们还在不同的房间尺度下进行了羽流行为实验，并与数值模拟结果进行了比较。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