# Damping of Liquid Sloshing Using Hydrophobic Walls in the Off-Impulse Regime
## 6 Conclusions  
In this work, we have experimentally studied how applying a hydrophobic coating to the walls of a container can drastically dampen sloshing waves compared to an identical uncoated container. Previous work on sloshing damping has been performed both numerically [6, 8, 9, 15] and experimentally [5, 7, 8, 10, 13]. Usually, sloshing damping is obtained through the installation of baffles inside the moving container; alternatively, different types of foam can be placed on the fluid surface for the same purpose [4, 11, 12]. In the present study, following the results of [13], we coated the walls of a container with a hydrophobic substance (Vaseline). We observed that when periodic external forcing was applied, the amplitude of the free surface in the container without the hydrophobic coating is always up to 30% higher. In addition, we characterized the regime after forcing was suddenly stopped. In this case, we used an exponential function to fit the oscillation amplitude decrement through the damping time \(\tau\). This quantity was always lower for the container with the hydrophobic coating than for the uncoated container. This behavior is consistent with the observations of [13], who measured lower pressure loads when using a hydrophobic oil coating on the walls. We think that this result leads to interesting options for sloshing reduction through the application of hydrophobic adhesives to the internal walls of containers. Moreover, we found the value of \(\tau\) to be strongly influenced by the container's aspect ratio \(\lambda\). For values of \(0.69<\lambda<1.00\), the damping coefficient was reduced up to \(\sim 80\%\) compared to the corresponding value for the uncoated container. Therefore, the energy loss due to interaction of the fluid with the hydrophobic walls together with the influence of the aspect ratio can provide a guideline for experiments performed through both numerical models and laboratory studies. Convenient container dimensions and hydrophobic wall coatings could also be combined with other techniques to reduce damping, such as baffles or foams.  
Conceptualization, R.C.C.-G. and A.C.; methodology, L.E.C.-P.; software, R.C.C.-G. and L.E.C.-P.; validation, C.O.M., R.C.C.-G. and A.C.; formal analysis, C.O.M.; investigation, R.C.C.-G.; resources, L.E.C.-P.; data curation, R.C.C.-G.; writing--original draft preparation, R.C.C.-G.; writing--review and editing, A.C and C.O.M.; visualization, R.C.C.-G.; supervision, C.O.M. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
The first author is grateful to the Geophysical Fluid Dynamics Laboratory and to the Fluid Mechanics Laboratory of CUCEI, Guadalajara University, for allowing us to perform the experiments. The authors gratefully acknowledge the comments of three anonymous reviewers for their careful reading and for providing very constructive comments that improved the paper.  
The authors declare no conflicts of interest.