Asdrubal N. Queiroz Filho

Experimental Results of Cooperative Control Applied to Multi-Vessel DP Operations

Offshore operations involving several floating units are becoming more frequent nowadays. Such operations are used for sub-sea equipment installation and undersea structures launching, for example. This kind of operations requires a high level of coordination between the vessels, which today is made without the ship’s information exchange, being each ship individually commanded. Therefore, in those cases a cooperative control could be applied, ensuring that the relative distance between the ships are maintained in limited range, controlling operational parameters such as the lifting line traction. The benefits of this control are shown when compared to the non cooperative control by means of a experimental setup with two DP vessels.Copyright

Development of an On-Board Wave Estimation System Based on the Motions of a Moored FPSO: Preliminary Assessments From a Field Campaign

This paper addresses a wave inference system developed for on-site estimation of directional wave spectra from the measurements of the wave-frequency motions of moored vessels. As a preliminary evaluation of the system’s performance, the results obtained in a 9-month field campaign based on an FPSO operating in Brazil’s Campos Basin are compared to hindcast predictions for the same region displayed by NOAA. The estimation method is based on Bayesian inference algorithms, previously validated by means of numerical and small-scale experimental analysis. A 6-dof inertial measurement unit (IMU) is used for monitoring the motions of the platform. The algorithm also requires the Response Amplitude Operators (RAOs), which in turn depend on the loading conditions of the FPSO. Those are defined before each estimation is performed by means of readings of the tanks’ levels. The accuracy of the predictions also depends on the calibration of two parameters (the so-called hyperparameters of the Bayesian method) and those are specified with respect to the mean period of heave motion. The system is able to identify unimodal or bimodal (cross) spectra using a bimodality criterion combined to an iterative algorithm for separating each component of the global spectrum. As a result, besides the global energy matrix, the statistical parameters required for reproducing the measured directional spectra by means of Jonswap and cosine2s models are provided. The system was commissioned and a 9-month validation campaign was executed. It is shown that the estimated parameters show quite reasonable correlation with satellite-based hindcasts from NOAA for sea states with peak periods larger than 8sec.© 2013 ASME

A Shuttle Tanker Position Cooperative Control Applied to Oil Transfer Operations Based on the LQG/LTR Method

Abstract The present paper addresses the development of a cooperative control applied to Ships with Dynamic Position Systems (DP) under oil transfer operation. The objective of the cooperative control is to maintain constant the relative distance between the two shuttle tankers. The benefits of this control will be evaluated by numerical simulation. The obtained results will be compared to the non cooperative control.

Development of an On-Board Wave Estimation System Based on the Motions of a Moored FPSO: Commissioning and Preliminary Validation

This paper addresses the development, installation and initial tests of a system for wave spectra estimation from the measurements of the first order motions of a moored FPSO located in Campos Basin, Brazil. The estimation is based on Bayesian inference algorithms, previously validated by means of numerical and small-scale experimental analysis. A 6-dof inertial measurement unit (IMU) is used for monitoring the motions of the platform, and this information is sent to a remote data-base, also accessed by the wave-estimation system. The algorithm also requires the Response Amplitude Operators (RAOs), and they depend on the loading conditions of the FPSO.A previous analysis considering typical loading configurations of the tanks showed that the wave estimation is mainly dependent on the total displacement of the vessel, and not on the load distribution among the tanks. Hence, the RAOs for the full-range of drafts (or total displacements) were numerically generated, considering a uniform distribution of the load among the tanks. Since the draft of the platform was not directly measured, the loading levels of the tanks are obtained from the automation system of the platform, and the draft is then estimated. Finally, the heading is measured by a gyrocompass, and it is necessary for the definition of the global wave direction. The Bayesian estimation is executed at time-spans of 30min. A parametric optimization algorithm is then applied for the calculation of the wave spectrum parameters from the raw-spectrum obtained by the Bayesian estimation.A user-friendly interface was also developed, with on-line information about platform motions, estimated wave spectrum, peak statistics and data history. Since all information is accessed by network, the wave system can be installed either on-board or in the on-shore monitoring center.The system was commissioned and a partial 3-month validation campaign was executed. The spectrum results were compared to NOAA estimates. As expected, low-period wave components (smaller than 8s) could not be estimated with accuracy, since the FPSO presents small motion response for these components. Swell and high-period wave components estimates presented good qualitative and quantitative agreement with satellite prediction.Copyright

DP Offloading Operation: a Numerical Evaluation of Wave Shielding Effect

Abstract The propose of this paper is to discuss the advantages obtained by the simulations of offloading operations in the presence of waves, detailing the effects that arise when bodys interactions are taken into account. Effects are sensed in the equilibrium position, on the drifts forces and the necessary power to dynamic position system. On this paper a simulation of a real offloading operation is presented. Results are shown with and without the shielding effect.

Development and Validation of a Customizable DP System for a Full Bridge Real Time Simulator

This paper presents the development and validation of a customizable Dynamic Positioning (DP) System for a real time full bridge simulator. The Maritime Waterway Simulator (SMH) was developed based on the code of the Numerical Offshore Tank (TPN) simulator. It is able to perform study of maneuvers feasibility and crew training. Many simulated operations such as oil offloading, pipe-laying, support to platforms or station keeping, require a DP system. In order to meet the demand for such a system, a complete system was developed with an important requirement in mind: The DP system of a full bridge simulator must be easily customizable for different types of vessels. In order to validate the developed DP system, a commercial DP system is used for comparison. DP operations with the vessel is conducted with both systems: the in house developed DP and the commercial one. The results obtained with the developed DP system are compared with the one obtained with the commercial system. This comparison demonstrates that the in-house DP system can indeed be used for simulating different types of DP vessels.© 2014 ASME

Cooperative Control applied to DP Systems – Numerical Analysis

Abstract The present paper addresses the development of a cooperative control based on the consensus control concepts applied to Ships with Dynamic Positioning Systems (DP). The objective of the cooperative control is to maintain constant the relative distance between the two tugboats. The benefits of this control will be evaluated by numerical simulation.