# Relaxation Zone geometry

Hi DSPH team,

I am exploring the Relaxation Zone example on V5.0 (/path/examples/wavecoupling/02_RZ_RegularWaves) and have a couple of questions

- any reason why the coef sound is reduced from typical value of 20 to 18? I can't see any difference in the simulation outputs.
- The paper from Corrado et al (2018) "Improved relaxation zone method in SPH-based model for coastal engineering applications" sets out a 5 step methodology (attached) in section 4.2.2 to define the RZ, however I am struggling to understand the following:
- i) With Weff 0.08*L and keff=0.8, it results WRZ > 0.08*L/0.8 >0.1*L. However, the WRZ=L is adopted which is a large difference.
- ii) It is recommended that keff € [0.8,0.9], yet the paper suggests ψ=0.35 and β=5, which leads to keff=0.55.
- iii) The choice of ψ and β appear to affect the profile of the wave and the energy flux without changing the wave height and wave period (based on a screenshot from Corrado's presentation attached). Is this correct? I am confused how ψ and β pair can be arbitrary.

## Comments

Let us ask @iarba27 here, he will help better