http://hdl.handle.net/11422/94 Tue, 07 Apr 2026 21:45:32 GMT 2026-04-07T21:45:32Z http://hdl.handle.net/11422/28341 Title: Evaluation of a linear expression for retrieval of directional wave spectra from complex sar look cross spectra Author(s)/Inventor(s): Corrêa, Yuri de Oliveira Brasil Advisor: Carvalho, Nelson Violante Abstract: The feasibility of a Linear Inversion Method applied to SAR cross spectra to retrieve wave directional spectra is investigated. The proposed method is compu tationally efficient and does not require any a priori information from wave or at mospheric models. Several test cases of complex SAR image spectra were simulated considering a broad range of values of steepness for different satellite configurations. The results of the simulated cases were employed to correct biases while retrieving directional wave spectra from Level 1 cross spectra. The nonlinearities, not accounted for when applying a linear inversion, are quantifiable as they depend on the satellite configuration and the relative position of the peak wave spectrum in relation to the azimuth cut-off. The wave spectra retrieved with the Linear Inversion Method from an Envisat ground track were evaluated against the ECMWF reanalysis ERA5 and compared to the results of ESA Level 2 WVW wave mode spectra. Both meth ods presented similar results in terms of RMSE and SI for significant wave height, peak wavelength and peak propagation direction. The shape of the directional wave spectra retrieved with the Linear Inversion Method presented better similarity with the ERA5 spectra, in comparison with the WVW spectra. Moreover, in around one third of the cases, the ESA method did not resolve the directional ambiguity. The preliminary results employing the Linear Inversion Method are encouraging, specially considering its simplicity and performance against the ESA distributed wave spectra Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação Tue, 01 Feb 2022 00:00:00 GMT http://hdl.handle.net/11422/28341 2022-02-01T00:00:00Z http://hdl.handle.net/11422/28215 Title: On the performance of multi-stable wave energy converter Author(s)/Inventor(s): Liu, Bingqi Advisor: Estefen, Segen Farid Abstract: The thesis investigated the performance of multi-stable wave energy converter (WEC). First, the static analysis of the two-/three-/four-spring coupled WEC found that these WECs have mono-/bi-/tri-/quad-stable modes under specific spring parameters. Then, the dynamic analysis of bi-/tri-/quad-stable WECs is conducted, and the performance of these WECs is evaluated mainly from three aspects: the efficiency, the frequency bandwidth and the device robustness. Compared with the bi-stable mode generated by two-spring coupled WEC (conventional bi-stable WEC or CB-WEC), it is found that part of the bi-stable mode generated by three-/four-spring coupled WEC (improved bi-stable WEC or IB-WEC) has higher efficiency, wider frequency bandwidth and larger robustness against the PTO damping disorder and sea state changes. Furthermore, a tri-stable WEC (Tri-WEC) and a quad-stable WEC (Quad-WEC) are selected and compared with IB-WEC. Results show that these two WECs can achieve higher efficiency than IB-WEC, especially under ultra-low-energy sea states. Moreover, their robustness against PTO damping detuning and sea state changes is also more substantial than IB-WEC. Finally, the four-spring coupled WEC (FS-WEC) performance is assessed at a specific sea site. The power output performance comparison with linear WEC (LN-WEC) shows that the well-tuned FS-WEC has higher energy production and smoother power output flow. The study also shows that the robustness of the FS-WEC against spring parameter changes increases as wave energy level increases. Publisher: Universidade Federal do Rio de Janeiro Type: Tese Fri, 01 Oct 2021 00:00:00 GMT http://hdl.handle.net/11422/28215 2021-10-01T00:00:00Z http://hdl.handle.net/11422/27598 Title: Ship emissions assessment by automatic identification system and big data in Latin America Author(s)/Inventor(s): Cepeda, Maricruz Aurelia Fun Sang Advisor: Caprace, Jean David Job Emmanuel Marie Abstract: Automatic Identification System (AIS) data records a high quantity of information regarding the safety and security of ships and port facilities in the international maritime transport sector. However, the big databases are not only useful for these safety functions. It can also be helpful for other areas in maritime traffic, such as reducing environmental impacts, improving logistics, and examining compliance with current International Maritime Organization (IMO) regulations. The purpose of this research is to provide a ship emission inventory and an assessment of the efficiency of several technical options to reduce the impact of ocean-going ships on the atmosphere and climate. In other words, this work aims to examine how technological improvements and policy strategies might help reducing emissions from international shipping in the future. Input data for these approaches were collected from different sources and maritime databases such as the worldwide ship fleet register and AIS database. The present proposal assess how possible improvements in technology or alternative energies and fuels could impact the future evolution of ship emissions. Three cases of studies are developed to estimate ship emissions based on AIS. The last case study added an application of scenarios, and it defined considering a combination of technologies and several future ship traffic demand scenarios mainly determined by the economic growth. The prediction is for 2050. The result shows how alternative energies and fuels could impact almost 50% of most minor ship emissions, concurrently implementing newly introduced international policy measures. In conclusion, a better quantitative understanding of the efficiency and impact of the technical alternative to reduce ship emissions may help the decision-makers to improve their strategies. Publisher: Universidade Federal do Rio de Janeiro Type: Tese Sun, 01 May 2022 00:00:00 GMT http://hdl.handle.net/11422/27598 2022-05-01T00:00:00Z http://hdl.handle.net/11422/27595 Title: Desenvolvimento e avaliação de aplicações em realidade aumentada para melhoria de segurança marítima e de navegação Author(s)/Inventor(s): Léo, Luiz Felipe de Sousa Advisor: Esperança, Paulo de Tarso Themistocles Abstract: This work develops and evaluates two applications based on augmented reality in order to validate their efficiency in aiding maritime and navigation safety. In this context, the applications aim to bring greater situational awareness to its operator and, through augmented reality, improve the efficiency of their work, displaying a compilation of data overlaying a real image of a certain vessel, thus facilitating the verification of its data and aiming faster and more efficient operator response. In addition, simulations were developed to compare the use of new programs in a controlled environment in relation to current equipment normally used, thus validating their advantages and disadvantages and using metrics to calculate their efficiency. The opinions of officers and users of maritime safety and navigation systems with more user experience than is currently available were also considered to evaluate new applications in real use situations and improve their performance by adding new features and validating their use Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação Tue, 01 Feb 2022 00:00:00 GMT http://hdl.handle.net/11422/27595 2022-02-01T00:00:00Z