Resumo

MATOS, Maria de Fátima Alves de; FORTES, Conceição Juana E.M.; AMARO, Venerando Eustáquio  e  SCUDELARI, Ada Cristina. Comparative Analysis of Agitation Obtained the Numeric Model (SWAN) in Modeling Rio Grande do Norte (Brazil) Northern Coastal Waves and Field Data. RGCI [online]. 2013, vol.13, n.3, pp.283-299. ISSN 1646-8872.  https://doi.org/10.5894/rgci378.

This article presents the comparative analysis of wave propagation between measurements obtained from the results of numerical modeling, with the application of the model SWAN (Booij et al., 1999), and the results of in situ measurements during two campaigns carried out from December 20th through December 27th 2010, and from February 15th through February 22nd 2011, on the northern coast of Rio Grande do Norte, Northeastern Brazil. The SWAN model permits the calculation of the evolution of spectrum from the directional generation zone to the coastline. But like any numerical model is based on approximations and hypotheses, presenting therefore limitations in accurate description of the waves in the area under study. The study’s main objective is to evaluate the performance of the SWAN model regarding prediction of sea disturbance, assessing their strengths and limitations for the region of interest. The in situ measurements were made at two locations near the shore at depths of 5m to 9m, respectively, measured with instruments AWAC and Aquadopp PROFILE, where the data were processed to obtain spectral analysis (significant wave height, HS, period , Tmed, and average direction, DIRmed) and employed the statistical analyzes of all data valid. In the boundary conditions, was considered the estimated sea states (H_m0 - significant wave height, T_p -peak period and Dir - direction average peak frequency) by the model of an oceanic scale, provided WWIII (Tolman 1999, 2002). The information of the boundary conditions have been subjected to a refinement to enhance the applicability of the model, where the tide variable considered for two different periods in spring tide conditions, since the amplitude of the local tide comes to exceed 2 m for phases of spring tide. The data were interpolated hourly to be introduced in the dataset agitation forcing the model. The numerical values ​​were obtained for the entire domain of the calculation, which considered as mesh exterior dimensions of 720 Nautical Chart, provided by the Directorate of Hydrography and Navigation of the Marine of Brazil, however, the model calculations performed in two meshes smaller than outer: one intermediate and one interior, the latter in the insertion of reference points (PT1 and PT2), thereby providing the parameters of wave propagation along the coast. The formulations were considered to SWAN in stationary patterns, formulation KOMEN (1984), with a coefficient of friction c=0.015 m²s^-3. We also analyzed the statistics assigning the concordance index (ic) of the measured values ​​and numeric values as a form of evaluation, as well, are presented and discussed comparative analysis of in situ measurements with the estimates obtained with the numerical modeling, which serve to validation of simulations, and to quantify the differences observed for both periods studied. It is concluded that in general the model represented reasonably well the evolution off from the wave to the beach area. Statistical analyzes to significant heights, although there is similarity in behavior, the level of agreement between the numerical and measured was below 0.5. In both cases, compared with the observations of behavior were similar to significant heights and medium periods, although the measured values ​​show is always higher than the numeric values. However, it is the station PT1 to the model leads to the closest numerical results measured in this shallower depth. The execution of this study allowed for the tests and the ability of the SWAN model to characterize the state of sea waves in shallow coastal zone, with regional coverage of 300 km2 and satisfactory results.

Palavras-chave : Numeric modeling; wave; Northeastern Brazil.

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