Problem with Volume Fraction
 

I try to simulate a spashdown of a body that landing on the sea surface in wave condition. I build a mesh (see attached) of fluid region with body, I perform a volume fraction with iso value of 0.5 (like explain on the tutorial of boat on head wave), but the iso surface position is not in the right position, on the middle of the fluid domain in z direction. How do I do to have the free surface positioned on the middle of fluid domain respect to Z direction?
The iso surface is blue color in the picture attached.

To me it looks like you set up the problem with a wave inlet as per tutorial. You should change the wave to flat and then set the positon of the free surface to the correct Z coordinate you want. This normally is in the global coordinate system

Problem with volume fraction
 

Thank for your suggestion.
If I correct understand, I have to use a flat wave, but I need to simulate body spalsh down in wave condition, whith flat is this possible?
I have positioned the free surface trough volume fraction using the value of 0.5, I have see that changing this value the position of the free surface don't change a lot. The global coordinate system have origin on the bottom surface of the body, pheraps I have to change the origin of global coordinate system positioning it on the middle of the fluid domain?

Any suggestion will be appreciate.

thanks

You do not have to use the flat wave if you want to simulate the splashdown in waves.
The volume fraction is an indication of the amount of water in a cell. It does not control the water level. You need to set it in the panel you specify your wave. When you change that and re initialize the water should be changing.

Use VOF of 0.5 for visualizing the water surface.

Problem with volume fraction
 

Thanks, I will try and I will keep you informed.