ORCID Profile
0000-0002-5470-915X
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Publisher: American Society of Mechanical Engineers
Date: 11-06-2023
Publisher: MDPI AG
Date: 06-09-2022
DOI: 10.3390/JMSE10091260
Abstract: Ocean wave design criteria are required for the design of offshore platforms and floating systems, which are derived using in situ measurements. However, there is uncertainty regarding the performance of the instruments used for the in situ measurements. The main instruments used by the offshore industry are the Datawell Directional Waverider buoy and Rosemount WaveRadar, with Laser instruments also having been used for specific studies. Recent reports indicate measurements from these three instruments differ in the order of 10% but given the quite disparate nature of the measurements made by these instruments, it is far from clear what the source of this difference is. This paper investigates the wave measurement principles of Radar and Laser instruments using linear wave field simulations to better understand how the instruments perform. The Radar and Laser simulations include modeling electromagnetic signal beam reflections from water surfaces of an area equal to their footprint sizes, considering their beam characteristics and antenna pattern. The study confirms that the Radar underestimates spectral levels at frequencies above 0.5 Hz due to its significantly larger footprint at the water sea surface compared to the Laser (5.25 m vs. 0.15 m). The Laser performs well for almost the entire frequency range for all the cases considered.
Publisher: American Meteorological Society
Date: 08-2023
DOI: 10.1175/JTECH-D-22-0123.1
Abstract: Accurate measurements of ocean waves underpin efficient offshore operations and optimal offshore structure design, helping to ensure the offshore industry can operate both safely and economically. Popular instruments used by the offshore industry are the Rosemount WaveRadar (Radar) and the Waverider Buoy. The Optech Laser has been used at some locations for specific studies. Recent reports indicate systematic differences of order 10% among the wave measurements made by these instruments. This paper examines the relative performance of these instruments based upon various time-domain comparisons, including results from a quality control (QC) procedure, capabilities of measuring the wave surface profile (skewness), and crest heights for varying wind sea and swell conditions. The QC check provides good-quality data that can be further investigated with an assurance of error-free data, suggesting that the Waverider produces the best-quality data with the lowest failure rate compared to the Laser and Radar. A significant number of the Waverider surface elevation records have negative skewness, particularly at higher sea states, affecting its crest height measurements, which are lower than those from the Laser and Radar. Additionally, the significant wave height ( H 1/3 ) estimates of the Radar are lower than the Laser and Waverider, but its zero-crossing wave periods ( T Z ), on average, are longer than the Laser and the Waverider. The significant heights ( H 1/3 ) of Laser and Waverider are in good agreement for all three datasets, but the Waverider’s zero-crossing wave period ( T Z ) estimates are significantly longer than the Laser.
Publisher: American Meteorological Society
Date: 05-2023
DOI: 10.1175/JTECH-D-22-0108.1
Abstract: Accurate ocean wave measurements are needed for the safe design and operation of offshore facilities, but despite many ocean wave measurements, the accuracy of wave measurement systems remains an ongoing issue. Of paramount importance are measurements during extreme sea states. This paper examines wave measurements made with an Optech Laser (Laser), a Rosemount WaveRadar (Radar), and a Datawell Waverider buoy at North Rankin A (NRA) platform, Australia Ekofisk, North Sea and several South China Sea locations. We evaluate the relative performance of these instruments based upon various frequency domain comparisons, including comparisons of their 1D frequency spectra using spectrograms, spectral moments, high-frequency tail slopes, and significant wave heights derived from their wave spectra. A spectral relationship (transfer function) in terms of mean spectral ratio of the instruments is developed, which can be used for spectral calibration. On average, Laser and Waverider spectral estimates agree well at all sea states. However, at low wind speeds, the higher-frequency spectral levels of the Laser are relatively high and noisy compared with the other two instruments. Radar higher-frequency spectral estimates are relatively low compared to the other two instruments, particularly at lower sea states. In addition, the higher-frequency tail slopes of all three instruments vary between f −4 and f −5 . However, at higher sea states, the Waverider tail slopes become steeper than f −5 . The Radar produces the lowest significant wave heights ( H m 0 ) compared to the Laser and Waverider, but its second-moment period ( T m 02 ) estimates are longer than the Laser and Waverider.
No related grants have been discovered for Pramod Kumar Jangir.