Hydrodynamic Investigation on a Land-Fixed OWC Wave Energy Device under Irregular Waves

Round 1

Reviewer 1 Report

This paper show a numerical analysis on the land-based oscillating water column under various conditions. It has been shown that the hydrodynamic efficiency of the OWC device in irregular wave conditions is found to be lower than that in regular waves. The paper is well written and well presented. There are one only two minor concerns to be addressed: a) fluid-solid interaction analysis could be potentially used to reveal important insights on the oscilating phenomenum; 2) the discussion section should reports the advance in knowledge with respect to current research to highlight the novelty of the present study.

Author Response

The authors are grateful for the positve comments.

1. The discussion on fluid-solid interaction is added to the revised manuscript (see lines 407-412): " The viscous effects which could induce vortex shedding at the front wall and boundary layer shear stresses at the OWC device chamber walls are neglected in the present study. Future studies should consider these effects in order to obtain more realistic prediction of the fluid structure-interactions, the forces applied to the OWC chamber walls and the free surface displacement. It is suggested that a systematic, fully nonlinear CFD study be undertaken in the future to investigate and quantify these aspects thoroughly."
2.  Relative reference (Ref. [17]) was added in the revised manuscript. The novelty of the present study is dicrible as follows (lines 81-89):" In the present study, the hydrodynamic performance of a land-fixed OWC device in the irregular wave conditions are numerically investigated using the fully nonlinear potential flow theory and higher-order boundary element method (HOBEM). Due to the fact that the numerical tests conducted using irregular waves require longer simulation times to ensure sufficient statistical data, this model adopts an inner-source wave generation technique to generate waves, which can eliminate re-reflection and maintain model stability in the long duration simulations [6]. The characteristics of the wave height and air pressure inside the chamber, comparison of hydrodynamic performance between the irregular and regular waves and, specifically, the water motion inside the chamber is analyzed. "

Reviewer 2 Report

The manuscript is The hydrodynamic efficiency response of a land-based oscillating water column wave energy converter. The hydrodynamic performance of a land-fixed OWC wave energy converter under the action of irregular wave conditions was numerically evaluated.

The Authors did valuable work. The manuscript is well-composed, written, and nicely discussed. In my opinion, the manuscript is suitable for publication in Applied Sciences in its present form.

Author Response

The authors thanks for the positve comments.

 

Reviewer 3 Report

The paper is well written and the analysis is competently done, so the paper can be accepted as is.
It can be improved by expanding the comparisons and discussion of other recent related work.
The authors are right to indicate that few studies exist using irregular waves in the study of fixed OWC devices.  In this context it might be useful referring also to the irregular wave experiments in:
http://dx.doi.org/10.1016/j.renene.2017.01.003
Concerning the nonlinear nature of the free surface elevation inside the chamber and the effect of air compressibility, it may be relevant to discuss:
https://doi.org/10.1016/j.enganabound.2021.08.018

Author Response

The authors are grateful for the positve comments.

Thanks for giving the meaningful and useful references.

The relative references are added to the revised manuscript:

1. (lines66-69)  "The effect of turbine damping and wave conditions on the hydrodynamic performance of an OWC device was evaluated in both regular and random waves by Rezanejad et al. [17]. They found that the influence of the wave height has less importance than the wave period and turbine damping. "
2. (line145) "....under the assumption that the air volume is incompressible" [24]

[17] Rezanejad, K., Guedes Soares, C., López, I., Carballo, R., Experimental and numerical investigation of the hydrodynamic performance of an oscillating water column wave energy converter, Renew. Energy 2017, 106, 1-16.

[24] Abbasnia, A., Rezanejad, K., Guedes Soares, C., Adaptive fully nonlinear potential model for the free surface under compressible air pressure of oscillating water column devices, Eng. Anal. Boundary Elem. 2021, 133, 153-164.