A F-shapedprinted dipole antenna, designed to operate simultaneously at 1.8 GHz, 2.45 GHz and 5.8 GHz is proposed in this work. The main challenge of the project is to find the antenna optimal geometry so that its gain has a higher value in the three operating frequencies in order to be efficiently applied it in the energy harvesting and wireless communication systems.To achieve the proposed operating condition, reduce the antenna return loss and enhance its bandwidth and gain a metamaterial surface was incorporated into its structure.All simulations and optimizations were performed using the Computer Simulation Technology software by employing the Finite Difference Time Domain technique for the electromagnetic equations evaluation. The antenna and metamaterial geometrical dimensions were optimized by using the Genetic Algorithm technique. Numerical and experimental evaluations were performed for the antenna with and without the metamaterial structure incorporated. The results obtained demonstrate the appropriately designed metamaterial ability to improve the antennas performance, increasing their bandwidth and gain and decreasing the return loss value.
Oil offloading from Spread Mooring System (SMS) FPSO is usually done by means of a dynamically positioned shuttle tanker (DPST) in tandem configuration. The ST receives the oil pumped by the FPSO from a bow or stern offloading station, and the operation may take up to 3 days. In order to minimize the risks associated with the operation, the shuttle tanker (ST) should be kept within a safety zone with respect to the FPSO, which is usually given as a minimum distance between the two ships and an aperture angle from the FPSO centerline. In order to guarantee the tanker position during the whole operation, the operation must be performed with tankers provided with DP (dynamic positioning) systems. Since SMS FPSOs may be not aligned to the environmental forces, keeping the shuttle tanker in position may be a hard task for the DP system, depending on the environmental conditions. There are non-rare situations in which the ST must be disconnected and the operation interrupted. The present paper applies a methodology based on static calculation of DP capacity for evaluating the downtime of such offloading operation. The three generations of DP tankers applied in Brazilian waters are considered. Santos and Campos Basin long-term (8-year) environmental conditions (current, wind, local-sea and swell) are used in the downtime calculation. The main objective is to provide a quantitative tool to analyze important parameters of the operation, in order to support some redefinitions in the operational procedure adopted by Petrobras. The main parameters are: the angle of the safe green-zone defined from the FPSO centerline, the installed DP power, the necessity of bow and stern offloading stations in the FPSO, among others. The results indicated that due to the large variation of wave-wind conditions along the year, both offloading stations are indeed necessary, since the ST can avoid the conditions in which it is pushed towards the FPSO. The results also indicated that incrementing the angle that defines the green-zone substantially decreases the offloading downtime. However, such decision also depends on a comprehensive risk analysis, since in that case the ST may be kept in a perpendicular position related to the FPSO. The risk analysis is beyond the scope of the present work. The DP power specified for the ST generations 2 and 3 are shown to be quite adequate, since it is demonstrated that increasing this power will not lead to a substantial reduction in the downtime.
Many situations in the Offshore Industry require equipment to be launched to the sea floor, becoming important to measure or to estimate their final position and/or to determine the complete trajectory. Some examples are the installation of anchorage devices, manifolds or production line supports. The main problem associated with the estimation of the position and the trajectory of the equipment is related to the fact that, systems such as GPSs and magnetometers cannot be used in subsea conditions. Gyrocompass and precise inertial sensors can be used, but they are expensive equipments and there is the risk of damaging during the launch process. The solution is to develop cost-effective inertial positioning systems that reach the operational requirements related to measuring accuracy. These equipments are based on MEMS (Micro-Electrical Mechanical Systems) inertial sensors that are relatively cheap. However, without the proper care, the signals obtained by these equipments present large levels of noise, bias and poor repeatability. The aim is to show a sequence of test procedures, treatment and processing of signals that leads one to know the position, attitude and trajectory of a submarine device. Furthermore, it allows the quantification of errors and, eventually, their sources. A commercial IMU (Inertial Measurement Unit) was chosen as a case study. It is equipped with MEMS sensors, usually adopted by the automobile industry. Tests with IMU were carried out intending to find the sensors scale factors, their bias and temperature sensitivity. Thereafter, the data were processed by two distinct algorithms. The first one is a simple algorithm that computes the attitude, azimuth at the final position and calculates the terminal velocity during the launch. The second one integrates the signal along all the movement by using quaternions algebra, resulting in the complete trajectory of the body. Discussions about the accuracy, applicability and limitations of each method are presented.
Torpedo pile has become one of the most popular foundation systems in Brazil’s offshore oil exploitation, mostly, due to its low installation cost. Additionally, torpedo piles have shown good fixation capability even when applied in mooring configuration such as taut leg with relatively close angles to the vertical. This fixation capability is closely dependent to the depth of penetration and the final attitude of the pile. In order to determine these parameters, MEMS-based Inertial Measurement Units have been used. Units of this kind are known for high noise density and, alone, are not adequate to any kind of navigation. Concerning these limitations, other sources of data are added to the inertial measurements, in order to improve the system state estimation. This data fusion is carried out by the Kalman Filtering and is also called Aided Inertial Measurement Units. This paper presents the Kalman Filter implementation and the results obtained from the fusion of the pressure gage signal, alternative pitch and roll measurements and the inertial measurements applied to the torpedo pile deployment.
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