Hello everyone, I am simulating Riemann problem in 2D, I met two questons: I’m using Gmsh to generate the grid in this format, this is different from grid in examples, and it doesn’t work. I set the initial value in the.ini file, such as below, it also comes error. I don’t know if I can do that. …

I don’t think you can use if statements in the ini file, but I might be wrong. There is support for max and min functions, but I think that you should try using tanh functions. i.e. u = 0.5 + 0.5tanh(100*x), approximately gives a step function.

But my function values are discontinuous, maybe not in terms of trigonometry. I think only be represented by an if statement. And do you know if there is a problem with my grid ? Best regards

If you use tanh(c*x) and increase c, after the function is sampled to grid it will look identical to the discontinuous function. This the same method Tarik has used in our recent shock capturing work, including when Tarik has run the 2D Riemann problem. In terms of your grid, it is hard to say from…

I don’t understand this sentence, tanh function is continuous,the value of tanh function is also continuous with increasing c. [image] WillT: after the function is sampled to grid it will look identical to the discontinuous function The grid is ok.

A discontinuous function makes no sense within the context of a high order method wherein the solution inside of each element is represented by a smooth polynomial. Hence, Will’s suggestion to use tanh with a suitable constant (which will be more robust against round off errors and minor perturbati…

@WillT @fdw I use max, min and tanh function to initialize the solution points. and periodic boundary conditions are set in x and y directions respectively. Then it comes error TypeError: 'NoneType' object is not subscriptable. Did I do something wrong? [backend] precision = double rank-alloc…

The syntax you are using to substitute expressions in the initial condition is not correct. I think you need something like: c = max(0, y) u = -0.75 + 1.5*tanh(1000*%(c)s)

Boundary conditions for Riemann problems in 2D. I set the left and right boundary to be periodic boundary, the up and down boundary to be periodic boundary, and can’t get right contour. Are the boundary conditions right? Thanks a lot. Best regaeds

I think they need to inviscid walls throughout, no periodics.

If you want to use periodics, however, I think this paper has some details on the case setup: Redirecting

Riemann problem in 2D

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Riemann problem in 2D

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