Study on the Vibration Characteristics of Marine Riser Based on Flume Experiment and Numerical Simulation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

(Editorial part)

-      Negative frequency range(below 0) is meaningless in this paper. So, all graphs should be drawn again only for positive frequency range.

-      Please add the unit of Sacc, same as Acceleration.

-      All y-axis in Fig. 4 need to be same to compare the data each other quantitatively.

 

(Comments)

-      Table 1. Vibration frequency of V=0.111m/s is quite high compared to the Strouhal number(0.2*0.111/0.016 = 1.3875Hz). Maybe it is quite small quantity compared to other cases, even so this kind of comments needs of be added.

-      Fig.4 and Table1. Also, after 0.494 m/s, the vibration frequency is getting lower even the velocity is increasing. The physical meaning on this phenomenon shall be discussed because it is unusual. As you have shown us the data in Fig. 11, this vibration frequency is getting higher when the current velocity is increasing.

-      Please explain the resonance at around 5.0-5.5Hz in all graphs of Fig. 1. I cannot understand that this irregular secondary peak is exist in all velocity condition.

-       

There is indeed a wealth of research on comparative analysis and numerical simulations of laser models. Recently, it is difficult to find additional studies specifically focusing on cylindrical cylinders in the current industrial sector.

Compared to recent research focusing on complex laser surface shapes or intricate flow profiles, this study falls short in terms of introducing novel methods, results, and content.

Please understand that the current contents and findings may not be suitable for publication as a research paper. I recommend revising the submission by incorporating a comprehensive analysis of the extensive data, conducting a more in-depth analysis of the second peak, and including a comparison with computational fluid dynamics (CFD) studies. These additions would enhance the overall quality of the research.

Comments on the Quality of English Language

Extensive editing of English language required

Author Response

Dear Reviewer,

Thank you for reviewing our paper and providing feedback. Please find our responses to your questions below:

• The acceleration power spectral density plot has been redrawn, and the frequency axis now only includes positive frequencies. We have made the necessary adjustments to ensure that the frequency axis corresponds only to positive frequencies.
• We have added the units for the power spectral density. In the figures, we have explicitly labeled the units of the power spectral density to ensure proper understanding and analysis of the results.
• By conducting a recalculation and considering the exclusion of noisy signals, a conspicuous peak has been observed in the riser that is fixed at the bottom. Additionally, the power spectrum of acceleration has been adjusted to a uniform semi-logarithmic scale along the y-axis, which facilitates the quantitative comparison of data.
• After the flow velocity exceeds 0.494 m/s, there might be a slight decrease in frequency. This could be due to the continued presence of vortex-induced vibration lock-in, where the frequency approaches the structural natural frequency.
• We acknowledge your comment regarding Figure 1 not being the acceleration power spectral density plot. The peak value around 5.0-5.5 Hz in the overall acceleration power spectral density of the floating platform and riser is observed in Figure 7. This peak may be attributed to the relatively weak stiffness of the floating platform. The frequency near 5Hz is mainly the vibration frequency of the floating body platform.
• The primary objective of this study is to validate the feasibility of numerical simulations using Orcaflex through experimental tests in flume experiment. The results demonstrate a certain level of agreement between our experimental method and the numerical simulations. Considering the longer computation time required for CFD simulations, we plan to further explore fluid-structure coupling using CFD in future research.

Thank you once again for your valuable review and comments. We have incorporated the necessary revisions into the paper, and we hope these improvements enhance the quality and comprehensibility of the article. If you have any further questions or concerns, please feel free to contact us.

Best regards,

Qiurui Cai

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper presents an investigation of vortex-induced vibrations of marine risers in Ocean Thermal Energy Conversion systems. Flume experiments were conducted under two conditions: Condition 1 with a fixed riser bottom; Condition 2 with a fixed bottom on a mooring platform. Cross-flow acceleration of the riser was measured at different current velocities, and corresponding vibration responses were analysed. Numerical simulations based on the flume experiments were employed to validate the reliability of the simulation method.

 

In the article, my remarks are:

·       Flume experiment of riser:

o   line 141:  write also the definition of St number in the same line

o   Figure 4: every figure needs a separate index like a), b), c), … 

o   Figure 7: every figure needs a separate index like a), b), c), …

·       Numerical simulation:

o   Figure 11: every figure needs a separate index like a), b), c), …

o   Figure 15: every figure needs a separate index like a), b), c), …

 

General remark: 

 

In my humble opinion, the article is solid and provides new and important results. A comparison of experiments with Orcalex software shows very good agreement and proves its reliability for platform-riser system design.

Author Response

Dear Reviewer,

Thank you very much for your valuable feedback on our paper. We have made the necessary revisions and additions based on your suggestions.

Firstly, As the definition of the Strouhal number and Equation 1 are identical, we have already modified the equation to correspond to the definition of the Strouhal number at line 141. We believe that this addition will enhance the understanding of the background and methodology of our research for the readers.

Secondly, we have followed your instructions and added separate index to Figures 4, 7, 11, and 15 as requested. This will improve the readability of the figures and better align them with the relevant content referenced in the paper.

Once again, we appreciate your insightful comments and thorough review. We have made the necessary modifications to the paper according to your suggestions, and we believe that these improvements will further enhance the quality and comprehensibility of our research. If you have any other questions or areas that need further improvement, please feel free to let us know, and we will make every effort to accommodate your requests.

Best regards,

Qiurui Cai

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for your efforts. I believe that the revised paper is now suitable for publication. Please just modify and arrange the sub-numbering of following figures consistently: Figures 4, 7, 11, and 15. 

Comments on the Quality of English Language

Minor editing of English language required