Level III Reliability Design of an Armor Block of Rubble Mound Breakwater Using Probabilistic Model of Wave Height Optimized for the Korean Sea Wave Conditions and Non-Gaussian Wave Slope Distribution

Round 1

Reviewer 1 Report

Review of the paper ‘Level III Reliability Design of an Armor block of Rubble Mound Breakwater Using the Probabilistic Model of Wave Height Optimized for the Korean Sea Wave Conditions and the Non-Gaussian Wave Slope Distribution’ by Young Jun Cho, submitted to Journal of Marine Science and Engineering.

The paper presents development of level 3 reliability design model for armor units of offshore breakwaters in Korea. The Author demonstrates limitations of previous concepts and introduces his model, based on solid scientific background with the overall aim of establishing a universal tool for the entire Korean coast. The amount of work involved is very impressive and the aim of the study is well defined. In all, the paper requires publication in JMSE. However, there is a number of issues that need to be corrected before the manuscript achieves sufficient quality to be published in a scientific journal. These issues are described below. The reviewer thus recommends a moderate but in-depth revision of the manuscript.

1. Although linguistic improvements are usually listed as the least item to be amended, this particular paper suffers significantly from language flaws, which hampers a clear perception of Author’s line of thinking. Therefore, the paper must be reviewed by a native speaker to enable much clearer presentation of assumptions, analysis, modeling results and conclusions throughout the whole paper.
2. In Sect. 2 a review of reliability methods is given. The Author explains that it was done to enhance integrity of the paper. However, this review is incomplete, including levels 1, 2 and 3 of reliability design, implicitly providing information on level 0 and entirely omitting level 4. Therefore, an amended description is required starting with level 0 (deterministic calculations – here goes van der Meer equation in Sect. 2.1), level 1 (semi-probabilistic design based on partial coefficients [γ’s concept]), level 2 (approximation - parameters are modeled by the mean values, standard deviations and by the correlation coefficients between the stochastic variables, implicitly assumed to be normally distributed), level 3 (uncertain quantities are modeled by their joint distribution functions - failure probability is calculated directly, usually by numerical integration) and level 4 (consequences [cost] of failure are taken into account and the risk [product of consequence the probability of failure] is used as a reliability measure - thus different designs are compared on an economic basis taking into consideration uncertainty, costs and benefits). Such structuring will help to better understand why the level 3 method was adopted and why a more advanced level 4 approach is impractical for breakwater engineering.
3. The Author refers to Ulsan as a representative location for the entire Korean coast, for which the wave data was reconstructed, based on the Japanese and NOAA meteorological information. Information on where Ulsan is located is nowhere to be found. Since it is claimed representative, then it should be plotted in Fig. 1 for readers to evaluate whether and to what extent this assumption is correct. Also, a paragraph why it is representative should be added.
4. The Author did not admit that the only novel element in terms of wave height distribution in Sect. 3 is fitting the parameters of modified Glukhovskiy distribution to Ulsan location. Hence, this conclusion demonstrates versatility of that distribution, as it appears from the analysis it can be recommended for other sites as well, provided sufficient wave data for the calibration of the parameters exist or can be hindast. If indeed so, it could be one of the most important products of the paper.
5. The next issue is related to elaboration of wave slope probabilistic model in Sect. 3. The Author says it was derived based on measurements between 20^th and 26^th 2018 near Mang Bang harbor. First, this location seems representative for the East Sea part of the Korean coast with less relevance for the Yellow Sea part. Second, this is a very short period, which may severely impact the modeling results. For example, it can be expected that the divergence between the new model and PIANC Weibull distributions in Fig. 16 might be less significant. Therefore, a suitable comment should be given, or a restriction provided that ultimate testing of the model should require longer data sets to achieve undisputable values of the wave slope distribution parameters and the presented results are preliminary. Moreover, Fig. 10 seems inconsistent with its caption – the reviewer has a feeling that Fig. 10 demonstrates the time between 26^th Apr. and a date somewhat beyond 11^th Nov. 2018. Please, correct/verify where necessary, also in the following Sect. 4 and particularly 5, which is directly associated with Sect. 3.
6. Instead of indicating the progress reached through the study, the conclusions largely re-summarize the paper. The main missing element is a decisive statement whether the presented methodology can be recommended for other marine basins/coastlines. Furthermore, the guidelines regarding the modeling accuracy, e.g. the amount of data needed for precise estimation of the parameters of probability distribution functions, the number of sampling points of wave climate in case of complicated coastlines, etc. should be specified. It appears that this absence is linked with insufficient description of the data used in the study.
7. Even though Fig. 19 is referred to in the text and its caption is present, it is entirely missing!
8. Both panels of Figs. 15 and 17 should be plotted opposite each other at the same vertical location of the page for easier comparison.
9. Almost all equations are double-numbered – please correct!
10. The term armor strength suggests unit’s internal structural strength against tension, compression and shear. However, most failures consist in translation /rotation of units leading to changes in breakwater geometry and disintegration of individual units is much more seldom. For this reason preferred term could be e.g. ‘unit stability strength’.
11. The overall edition of the manuscript is somewhat reckless – cf. points 7 and 9. A thorough re-editing is therefore needed.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Outline

The manuscript deals with the Level III Reliability Design of rubble mound breakwaters armored with tetrapods. The proposed method is intended to be used for Korean Sea Wave Conditions. A non-gaussian distribution of wave slope is proposed and tested for Korean Sea Wave Conditions by means of comparison of other methods.

I found the manuscript interesting and the topic worth to be investigated. I can recommend the manuscript for publication once the author has addressed the following concerns.

Concerns

1 – In general, it seems that the proposed method works only for rubble mound breakwaters armored with tetrapods. Indeed, all the method relies on the design criterion proposed by Van der Meer (by the way, the reference Van der Meer, 1988 " Stability of cubes, tetrapods and accropode " is not cited in the manuscript, the citation follows). Of course, the method can be extended also for other blocks (either natural or other artificial blocks), but the manuscript is limited to analyze tetrapods. I can agree with this choice based on the armouring of Korean structures. Nevertheless, this should be stressed in the abstract, in the introduction and in the title as well.

Citation: Van der Meer, J. W. (1988). Stability of cubes, tetrapods and accropode. In Conference Breakwaters 88 (pp. 71-80).

2 – If I catch correctly the essence of the manuscript aims, it seems that the study is aimed to demonstrate that the harbor structures in Korea are oversized and to propose a method to correctly design them. This is clear in the "Conclusion" section where the author states " These design practices have raised a critique in the coastal engineering community that the port's outskirts facilities in Korea are too conservatively designed." In my opinion, this is the most important "technical message" the author wants to spread to the scientific and technical community. In the introduction, this aspect is briefly highlighted ("Moreover, by allowing a reasonable failure probability of the armor block, design factors that can be conservatively evaluated in a deterministic design can be easily specified, leading to significant cost savings."). In section 5.1 this is briefly described ("which means that the armor block has been designed too conservatively"). I suggest highlighting this aspect in the abstract and the introduction with more emphasis.

3 – Torough the manuscript, it seems that the "hydraulic stability" of blocks is referred to as "block's strength". In my opinion, this could lead to a misunderstanding as the readers can refer the term "strength" to the materials and not to the (hydraulic) stability of the blocks. I suggest using "block's hydraulic stability" instead of "block's strength".

4 – Torough the manuscript, the symbol "Dn50" is used for the nominal diameter of tetrapods. I suggest dropping "50" and to use "Dn".

5 – Just before equation (10) "relative depth d" should be defined (I guess the ratio of wave height and water depth).

6 – The bandwidth parameter is part of the proposed model. It is then related to the "wave age" within the frame of theories of wind-wave generation (P. 14). Its influence on the PDF of wave slope seems to be very large (see Figures 6, 18, 20; Table 3). The reader may be interested in a suggestion to select the more correct (conservative) value of bandwidth parameter to use at the design stage.

7 – I suggest the author to add a further section aimed to demonstrate the applicability of the proposed method. I am thinking about a further section (something like "Example application") in which the author could show the results of a typical design carried out with the deterministic method (I guess used to design Korean Harbor Structures so far), with the reliability design with Gaussian wave slope distribution and by means of the proposed method. I would like to read about the mass difference of stable tetrapods with different methods. This aspect could enrich the manuscript other than the parametric analysis (Section 5).  

8 – Some minor concerns:

• It seems that equation numbering is doubled.
• Just before equation (14), "transient wave height" should be "transition wave height"
• Page 14, "wave filed" should be "wave field"
• Torough the manuscript "outskirts facilities" should be "outer facilities" or "outer breakwater".

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I thank the author for having addressed my concerns. I am satisfied with his replies and I can now recommend the manuscript for publication in the journal.