An investigation of the applicability of SPIV for the analysis of the dynamics of floating offshore wind platforms
Abstract. There is a need for new numerical tools to capture the physics of floating wind platforms more accurately to refine engineering designs and reduce costs. The conventional measurements apparatus in tank tests, including wave probs, velocity and current profiler, as well as doppler sensors, are unable to give a full 3D picture of velocity, pressure, and turbulence. In tank testing, the use of the underwater stereoscopic PIV method to fully characterise the 3D flow field around floating platforms can provide a rich source of validation data and overcome some of the limitations associated with more classical measurement techniques. This optical technique can be used to accurately measure the random and chaotic structure of turbulent flows around the floater. Moreover, the main characteristics of turbulence of the flow around the floater, such as rotationality, diffusivity, irregularity, as well as dissipation, can be extracted and studied. The underwater S-PIV method has been widely used for marine and offshore applications, including studies on ship and propeller wakes and tidal stream turbines; however, to date, this technology has not seen widespread use for the hydrodynamic study of floating offshore wind turbines. Therefore, in the current study, the key considerations for using S-PIV for this purpose are discussed; meanwhile, the related studies in the field of quantitative flow measurements are reviewed.
Navid Belvasi et al.
Navid Belvasi et al.
Navid Belvasi et al.
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The reviewer wants to thank the authors for submitting their manuscript “An investigation of the applicability of SPIV for the analysis of the dynamics of floating offshore wind platforms.” The development of more and more advanced numerical tools asks for novel and advanced experimental methods, that can validate these. Furthermore, these experimental methods can contribute to the understanding of the underlying physical phenomena, where numerical models still have their limitations or are computationally too expensive. In this context particle image velocimetry (PIV) has become a valid tool for both, validation, as also for understanding certain flow phenomena.
The current paper reviews the application of the PIV technique in maritime testing facilities such as towing tanks and evaluates its value for the assessment of the performance of floating offshore wind platforms (FOWT). While an application of the technique might be relatively new within the field of FOWTs, the PIV technique has become a reliable and commonly used tool in maritime testing facilities with published applications ranging from ship hydrodynamic problems, but also offshore applications, such as wave dynamics and recently also FOWTs (Anglada-Revenga, Elena, et al. "Scale Effects in Heave Plates: PIV Investigation." International Conference on Offshore Mechanics and Arctic Engineering. Vol. 84416. American Society of Mechanical Engineers, 2020.). Next to presenting commonly known principles of PIV and already published applications and limitations in towing tank environments, the article discusses possible applications for FOWTs. However, to the opinion of the reviewer, the pure discussion of possible fields of applications does not justify a publication of this article due to the lack of novelty.
P1 L20: “Therefore, in the current study, the key considerations for using S-PIV for this purpose are discussed; meanwhile the related studies in the field of quantitative flow measurements are reviewed.” Comment: What makes this application so different to other applications in maritime testing facilities such as towing tanks, that a separate review is necessary?
The introduction is missing a general description of the flow problem. What kind of flow characteristics are necessary to be studied for FOWTs? Maybe also a general description of the geometry of FOWTs and their submerged parts helps to define the problem.
The comparison with numerical methods is important to mention, but too detailed for introducing the main problem.
It is also not clearly defined what the limitations of the numerical models are and how PIV can contribute to improving the numerical codes.
P3 L70: The authors start immediately with stereo PIV. This is very specific, as most of the described features are also valid for PIV in general, which includes next to single-camera PIV also stereo and volumetric PIV.
The subsection 2.1 Theory of particle image velocimetry extensively (p5 -9) describes the well-known and published principle of PIV. For the understanding of the technique, a short introduction with references to the most important literature would be sufficient as it does not add any novelty to the article. Also, it is not referred to later in the paper. While the title also lets the reader assume, that the focus is on stereo PIV, this is not even mentioned in this section, but included in Section 2.2 PIV in tank tests, this should be shifted to this section.
Section 2.2 reviews the main applications of PIV in towing tanks. While the focus of the paper should be on offshore structures and FOWTS, here only applications of towed ship models are mentioned, which in terms of measurement setup would differ significantly from testing FOWTs. More important applications would be PIV applications for the measurement of (breaking)waves, the flow around cylinders, etc...
P 15 L255: “The high-resolution data of vorticity, full velocity distribution, and turbulent kinetic energy then can be used as a source of validation data for numerical codes for FOWTs.” Comment: At this point, it is still not clear to the reader what type of flow problem needs to be validated.
Section 3 describes the critical parameters when applying PIV in general and a few aspects which are important for testing in towing tanks. This is all well known and published. Specific aspects which should be considered when testing FOWTS are not mentioned.
Section 4 reviews the hydrodynamical phenomena related to floater design identified in (Robertson et al. 2017). While extensively reviewing the published literature with respect to all phenomena, the possible contribution of PIV measurements is formulated very vague and not detailed enough, to add any novelty to the paper.