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Chloride ion erosion of concrete in dry wet cycle

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In the simulation process of chloride ion in concrete drying and wetting cycle, I use the convection diffusion model and coefficient type partial differential equation, but these two physical fields include drying process and wetting process respectively. The parameters of different processes are different. How should I express the two processes in one physical field and how to make the two processes cycle alternately.


2 Replies Last Post 27/08/2020, 07:57 GMT-4
Jeff Hiller COMSOL Employee

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Posted: 10 months ago 20/08/2020, 14:27 GMT-4
Updated: 10 months ago 20/08/2020, 16:12 GMT-4

Hello,

If the times at which the switches between the two processes occur are known a priori, you could use explicit expressions depending on t (time) for the coefficients in the equations and boundary conditions.

On the other hand, if those times are not known ahead of time, you'd want to use the Events interface. That approach is illustrated in this blog post.

Best regards,

Jeff

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Jeff Hiller
Hello, If the times at which the switches between the two processes occur are known a priori, you could use explicit expressions depending on t (time) for the coefficients in the equations and boundary conditions. On the other hand, if those times are not known ahead of time, you'd want to use the Events interface. That approach is illustrated in [this blog post](https://www.comsol.com/blogs/implementing-a-thermostat-with-the-events-interface/). Best regards, Jeff

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Posted: 10 months ago 27/08/2020, 07:57 GMT-4

Hello,如果两个进程之间的切换发生时间是先验的,您可以根据方程和边界条件中的系数使用显式表达式(时间)。另一方面,如果这些时间不是提前知道的,则要使用 Events 接口。这种方法在[这篇博文](https://www.comsol.com/blogs/实现一个温度与事件接口/)中进行了说明。最好的问候, 杰夫

Thank you for your answer! In my model, the switching time between wetting and drying is fixed. For example, the drying and wetting cycle of my concrete specimen is wetting for 1D and drying for 1D. However, I don't know how to take the result of wetting process as the initial condition of drying process and continue to cycle. Second, after looking up some data, I found that in their model, the pore saturation of concrete is used as the dependent variable to connect the whole migration of pore liquid and the convection diffusion migration of chloride ions. I don't know how to define this saturation to achieve the effect of connecting the two physical fields. Hope to get your answer or recommended case guidance.

>Hello,如果两个进程之间的切换发生时间是先验的,您可以根据方程和边界条件中的系数使用显式表达式(时间)。另一方面,如果这些时间不是提前知道的,则要使用 Events 接口。这种方法在[这篇博文](https://www.comsol.com/blogs/实现一个温度与事件接口/)中进行了说明。最好的问候, 杰夫 Thank you for your answer! In my model, the switching time between wetting and drying is fixed. For example, the drying and wetting cycle of my concrete specimen is wetting for 1D and drying for 1D. However, I don't know how to take the result of wetting process as the initial condition of drying process and continue to cycle. Second, after looking up some data, I found that in their model, the pore saturation of concrete is used as the dependent variable to connect the whole migration of pore liquid and the convection diffusion migration of chloride ions. I don't know how to define this saturation to achieve the effect of connecting the two physical fields. Hope to get your answer or recommended case guidance.

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