Reliability Modelling and Analysis of the Power Take-Off System of an Oscillating Wave Surge Converter

Round 1

Reviewer 1 Report

The article describes a methodology for WEC development, based on the use of a reliability block diagram.

The topic is quite interesting, although some aspects should be improved.

Comments

Line 50 – Please, provide a representation of the device and its PTO system.

Equation 3 – Please, correct this relationship.

Line 330 – Please, provide more information on the software ReliaSoft BlockSim 2018.

Line 355 – Provide more information on the probability distributions (how were estimated the parameters? Which are the results of the distribution tests?)

Table 1 – Table 1 does not explain why the specific distribution was chosen.

Figures 4 and 5 - Authors should provide more information on the methodology adopted. For example: what is meant by Point Availability? Why was a period of 5 years chosen?

Line 388 – Explain the symbol FCI.

Line 390 – Please, show the reliability distribution assigned to the components.

Line 425 – There is no discussion of the results achieved. The analysis of the output data is therefore lacking.

Line 473 – Authors write “In this study, the reliability analysis approach based on RBD modelling was successfully applied to the MegaRoller PTO concept.”. Authors should consider that the data have not been validated by field measurements. The activity carried out represents the application of a stochastic methodology for estimating the availability of the device.

Author Response

We are grateful for the valuable and constructive comments and suggestions. Each comment has been considered and the article has been improved with the following modifications::

Line 50 – Please, provide a representation of the device and its PTO system.

• A description of the MegaRoller device and PTO system was added into Section 1.2.

Equation 3 – Please, correct this relationship.

• The equation was corrected.

Line 330 – Please, provide more information on the software ReliaSoft BlockSim 2018.

• Added a description and a reference on the key features of the ReliaSoft BlockSim 2018 software.

Line 355 – Provide more information on the probability distributions (how were estimated the parameters? Which are the results of the distribution tests?).

• Restructured the text so that it more clearly describes the parameter estimation (line 364 onwards). None of the parameters are based on testing.

Table 1 – Table 1 does not explain why the specific distribution was chosen.

• The explanation is provided in the text, which has been restructured so that the descriptions directly precede the table.

Figures 4 and 5 - Authors should provide more information on the methodology adopted. For example: what is meant by Point Availability? Why was a period of 5 years chosen?

• Added explanation of the terms. The period of 5 years was chosen to illustrate the results on a realistic timescale for an OWSC device maintenance interval.

Line 388 – Explain the symbol FCI.

• FCI is now explained on line 405.

Line 390 – Please, show the reliability distribution assigned to the components.

• The assigned distributions are described from line 394. As an illustrative example, the numeric values are not emphasized here.

Line 425 – There is no discussion of the results achieved. The analysis of the output data is therefore lacking.

• The aim of the paper is to describe the modelling approach and data sources and the discussion section is intended to focus on these aspects. Thus, the discussion does not cover specific quantitative data or calculation results.

Line 473 – Authors write “In this study, the reliability analysis approach based on RBD modelling was successfully applied to the MegaRoller PTO concept.”. Authors should consider that the data have not been validated by field measurements. The activity carried out represents the application of a stochastic methodology for estimating the availability of the device.

• Field measurements will be conducted at a later stage of the system development and they will be partly designed based on the findings of the reliability modelling activities. A description of this future work has been added to the article.

Reviewer 2 Report

The manuscript describes a methodology to perform reliability analysis of PTO system of MegaRoller WEC, which is an oscillating wave surge converter.
The Authors specify that the three main contributions are, to describe the reliability prediction approach based on reliability block diagram (RBD); to describe the data sources for gathering reliability data for components used in the system, to focus on example on MegaRoller WEC.
I am very sorry but the paper disappoints these expectations: the procedure is not described with scientific details, the data are those of wind turbine and the examples lack of scientific contents.

The Authors describe a procedure to be applied to a specific WEC, using general consideration of reliability block diagram method without providing specific results.
My opinion is that the procedure should be detailed with more specific considerations, based on the functioning of the mechanical/hydraulic parts of the PTO system of the WEC, and maybe considered for pubblication on a different journal.

My opinion is that the manuscript is not considerable accepted for pubblication due to lack of significant scientific content. 

Author Response

We are grateful for the reviewer’s honest feedback. The article describes the procedure for reliability estimation in case of a new technology and describes a methodology that can be applied to support system design. Thus, we cite various data sources (including wind power, as well as offshore industry) that can be applied in a field of technology with no domain-specific data available. The examples are illustrative to give the reader a better understanding of how the procedure can be applied. The authors view the article fitting for the scope of the special issue - but in case it would be found unsuitable for the scope, any recommendations for more suitable journals are appreciated.

Reviewer 3 Report

The paper presents reliability analysis approach based on RBD modelling was applied to the MegaRoller PTO concept which includes failure probability of PTO system during maintenance, critical components and visual representation of PTO system. The paper is well written, organized and discussed within the scope of the RBD modeling.

I recommend the paper can be considered in the present form.

Author Response

We are grateful for the positive feedback provided by the reviewer.

Round 2

Reviewer 1 Report

The authors have answered all of my questions.

Reviewer 2 Report

The revised manuscript is acceptable in the present form