# Pressure oscillation problem

hello everyone

The wave length is 121m, the wave height is 2m, the water depth is 20m, and the wave cycle is 10s. Piston +AWAS was used to generate the wave. The result shows that the wave shape is correct, but the pressure oscillation at the bottom is abnormal.

Particle dp = 0.2

The pressure monitoring point is

100.0 0.0 0.1

1, 0.0 0

50 1.0 1

• Where is the pressure point in your drawing? I cannot see it.

Secondly, what is the value you expect?

Thirdly, what happens as resolution changes.

Kind regards

• thank you for your replay

1、My monitoring points are set between Y =0 and x=100m-150m, and one detection point is taken every 1m, as shown in the figure below.

2、I hope that the pressure that can be achieved can show regular fluctuations just like the effect after 600 time steps in the figure below.

I have two questions

（1） The result of this graph is the same as the result model of the above two graphs. The difference is that dp of this case is 0.5, while DP of the above case is 0.2.

（2） Why is the oscillation so big before 400 time steps, and tends to be regular after it? Is there any way to improve it?

• edited June 12

I do not understand point (1)

Considering there is waves in the domain, results after 400 time steps seem reasonable.

The reason there is big oscillations is particle noise, initialization and transient nature of the simulations.

You can improve some of them but it requires a lot of hard work.

You results after 400 time steps seem reasonable though.

Kind regards

• Do you mean that it is normal to simulate pressure shock in the early stage? I can understand that it takes a while for the simulation to stabilize at the beginning, but the amplitude of the initial oscillation is too large, and the period to reach relative stability is too long (the wave period is 10 seconds, and it takes 40 seconds to stabilize).

• Yes.

If you improve your setup, you can minimize the time to stable.

Perhaps look into restart option.

Kind regards

• Thank you. I seem to have found the problem. When I set COEFh =1.5, the pressure obtained was relatively small, but I also encountered other problems, my wave height looked unstable, I set a second-order regular wave.How to set the wave height to be stable?

• Here I would use AWAS to get stable wave heights. It alters the motion of the piston to consistently produce similar heights - as long as reflection in domain is not too high.

Kind regards