A Method for Energy and Resource Assessment of Waves in Finite Water Depths

Abstract

This paper presents a new method for improving the assessment of energy and resources of waves in the cases of finite water depths in which the historical and some ongoing sea wave measurements are simply given in forms of scatter diagrams or the forms of (significant) wave heights and the relevant statistical wave periods, whilst the detailed spectrum information has been discarded, thus no longer available for the purpose of analysis. As a result of such simplified wave data, the assessment for embracing the effects of water depths on wave energy and resources becomes either difficult or inaccurate. In many practical cases, the effects of water depths are simply ignored because the formulas for deep-water waves are frequently employed. This simplification may cause large energy under-estimations for the sea waves in finite water depths. To improve the wave energy assessment for such much-simplified wave data, an approximate method is proposed for approximating the effect of water depth in this research, for which the wave energy period or the calculated peak period can be taken as the reference period for implementing the approximation. The examples for both theoretical and measured spectra show that the proposed method can significantly reduce the errors on wave energy assessment due to the approximations and inclusions of the effects of finite water depths.

Identifying the Optimal Offshore Areas for Wave Energy Converter Deployments in Taiwanese Waters Based on 12-Year Model Hindcasts

“…This simplification may underestimate the wave energy in finite water depths. Sheng and Li [63] conducted wave power assessment at a water depth of 50 m using the deep-water formula and the proposed method in their study and compared the results to the actual values. They found that the deep-water formula underestimated the annual mean wave power by up to 10.18% at the studied finite water depth (50 m).…”

An Improved Method for Energy and Resource Assessment of Waves in Finite Water Depths

“…Thus, in finite water depths, the effect of water depths on resource assessment becomes an important factor for accurate assessment of wave energy resources. It has been shown by Sheng and Li [16] that without water depth correction wave energy assessments could lead to errors of more than 10%. Conventionally, the effect of water depths on wave power could be easily considered if the detailed spectral distributions are available for analysis as seen when wave resource assessments [1,3,[12][13][14][17][18][19] or the numerical models (such as the open source SWAN model [20,21]) are used [5][6][7][8]14].…”

“…For instance, for some confidential reasons, only some statistic parameters may be given instead of wave spectra, or for some economic reasons, there may be no numerical wave models available. In this regard, the wave energy assessments have been traditionally done either using the formula for deep water, by ignoring the effect of water depths [12,22] or using the simplified approximations to the water depth effect on wave energy calculations [1,14,16]. This paper aims to develop new approximation methods to improve the wave energy assessment in absence of detailed wave spectra or commercial wave models.…”

“…In this research field, Cornett [1] suggests a constant wave group velocity calculated based on the wave energy period to approximate the effect of water depth. Recently, Sheng and Li [16] studied the approximation method and found that if the wave group velocity is calculated using the spectral peak period, the approximation may be more accurate and reliable, and as a result of the simple approximation, the error of the wave energy assessment can be reduced from more than 10% to less than 5% (Atan et al [14] also suggest a formula using a single wave group velocity in the approximation, but no details are given on how the wave group velocity is calculated).…”

“…Compared to the zero-order approximation proposed by the authors in previous work [16], more available wave statistical periods, including the popular spectral peak period, energy period, mean spectral period and zero up-crossing period are used for the assessment. Because these statistic periods are calculated from the spectral moments of different orders, they contain different information from the spectrum distribution on frequencies to allow a more accurate approximation to the wave energy assessment.…”