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ianjlockwood December 6, 2005 13:10

Wave modelling
Hi, I was hoping that somebody maybe able to offer me some advice (or a lot if they can). I am a mechanical engineer doing my dissertation/thesis. I am designing wave focusing walls for use with a wave energy converter. I am looking for someone to give advice on whether CFX could model the wave amplification of the designs and if so how? Thank you to anybody who can help. Ianjlockwood Modelling

Mike December 6, 2005 17:21

Re: Wave modelling
You should be able to model this in CFX without any problems. If you are not familiar with modeling free surface flows, then you should start with the free surface tutorial (flow over a bump). Once you are familiar with free surface flows, the following will be helpful: I assume you'll have a transient simulation and will need to generate waves at an inlet boundary condition - you can do this by setting the inlet volume fraction to an appropriate sin/cos function. It is a little harder to set the correct inlet velocity, this will vary in time as the waves pass. With a little waves theory it is possible to come up with expressions to describe the varying inlet velocity. Mike

bioman December 6, 2005 20:41

Re: Wave modelling
I think the setting of pressure is a key because I meet the same problem. From that tutorial, we have to make an assumption about water level height and use step function to describe the static pressure at inlet and outlet. As to the flow in a duck, the level may be identified easily, but in some case, we never know the water level at outlet because it is dynamic like wave.

Ian Lockwood December 7, 2005 07:15

Re: Wave modelling
Hi Mike, Thank you for your help, I was wondering how i find tutorial 7, flow over a bump. I have found tutorials on CFX-mesh tutorial 1-7 static mixer etc....However i can not find your paticular tutorial section. Can you help or anybody else? Thank you again ianjlockwood

Ian Lockwood December 7, 2005 07:23

Re: Wave modelling
Hi, Sorry found the tutorial now thank you. Anymore advice on the intial subject would be useful though. Thanks ianjlockwood

Mike December 7, 2005 12:29

Re: Wave modelling
Yes, for sub-critical flow the outlet pressure boundary condition is a problem. You can often get away with just setting a constant hydrostatic pressure. The solution at the outlet will not be correct (the free surface height will rise/fall to meet the pressure condition), but as long as that doesn't affect the solution away from the outlet then it can be OK. What you really want is a zero gradient boundary condition, but that's not available just yet. For super critical flow you can set the Supercritical condition and the free surface height will be part of the solution. Mike

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