Adaptation of Directional Wave Measurement in 3D Physical Model to Eliminate the Reflection Component in Uni-Directional Waves

Ranasinghe, D. P. L. (Lanka Hydraulic Institute Ltd.) | Kumara, I. G. I. K. (Lanka Hydraulic Institute Ltd.) | Caldera, H. P. G. M. (Lanka Hydraulic Institute Ltd.) | Engiliyage, N. L. (Lanka Hydraulic Institute Ltd.)

OnePetro 

ABSTRACT

Directional wave gauges are used to estimate the directional spreading of the generated wave energy spectrum in 3D basin despite the high cost involved in. In this study, five non-directional wave gauges array has been used to capture the directional distribution at desired locations to omit the reflection component in uni-directional waves (175°N and 195°N). The directional wave measurements have been carried out at the nearshore during the calibration to assess wave reflection from the boundaries if any. During the testing, directional gauge system was placed at the offshore to assess the incident wave climate. The spectral analysis has been performed to identify the incident wave component by selecting a narrow direction band of 120°N −240°N out of the entire direction band of 0°N-360°N. The results depicted that 3% of the observed wave heights at −20 m depth contains the reflected waves from the breakwater structure at −14 m depth. Further, this method has been successfully used to generate the required wave condition at the offshore depth (-20 m depth) with the minor deviation of ±3%. Additionally, the results confirmed the appropriateness of the model setup for the basin extent as the generated reflection from the boundary walls was negligible.

INTRODUCTION

Background

Unlike in inland developments, design and construction of coastal structures is still a challenging task due to the complexity and variability of coastal environment. As the behaviour of a coastal zone is completely different from one to another, site specific parameters need to be found prior to the design of coastal structures. Therefore, numerical models play a vital role in obtaining the design parameters. Furthermore, empirical formulae to estimate hydraulic stability and overtopping are useful for the preliminary design of coastal structures. However, physical models are necessary to assess the hydraulic performance of a coastal structure as it reproduces the actual phenomenon in a small scale without any schematization. Apart from that, physical models are the key tools in optimizing the breakwater structures and the layouts which could be utilized for reducing the construction cost by considerable amount. However, there are some disadvantages associated with physical model testing that are related to experimenting in facilities of limited spatial extent which require that phenomena are scaled down from the natural system and which can, by their design, produce laboratory effects not present in nature (IAHR, 2011).