Daniel Prata Vieira

Friedel oscillations in one-dimensional metals: From Luttinger's theorem to the Luttinger liquid

Abstract Charge density and magnetization density profiles of one-dimensional metals are investigated by two complementary many-body methods: numerically exact (Lanczos) diagonalization, and the Bethe–Ansatz local-density approximation with and without a simple self-interaction correction. Depending on the magnetization of the system, local approximations reproduce different Fourier components of the exact Friedel oscillations.

Simple implementation of complex functionals: Scaled self-consistency

We explore and compare three approximate schemes allowing simple implementation of complex density functionals by making use of self-consistent implementation of simpler functionals: (i) post-local-density approximation (LDA) evaluation of complex functionals at the LDA densities (or those of other simple functionals) (ii) application of a global scaling factor to the potential of the simple functional, and (iii) application of a local scaling factor to that potential. Option (i) is a common choice in density-functional calculations. Option (ii) was recently proposed by Cafiero and Gonzalez [Phys. Rev. A 71, 042505 (2005)]. We here put their proposal on a more rigorous basis, by deriving it, and explaining why it works, directly from the theorems of density-functional theory. Option (iii) is proposed here for the first time. We provide detailed comparisons of the three approaches among each other and with fully self-consistent implementations for Hartree, local-density, generalized-gradient, self-interaction corrected, and meta-generalized-gradient approximations, for atoms, ions, quantum wells, and model Hamiltonians. Scaled approaches turn out to be, on average, better than post approaches, and unlike these also provide corrections to eigenvalues and orbitals. Scaled self-consistency thus opens the possibility of efficient and reliable implementation of density functionals of hitherto unprecedented complexity.

Effects of Coupled Hydrodynamic in the Performance of a DP Barge Operating Close to a FPSO

In ocean systems composed by two or more closing floating bodies, coupled hydrodynamics effects must be considered. Dynamic positioned systems (DP), for example, need an accurate determination of environmental forces to guarantee a safe operation. This work presents a numerical methodology, using the WAMIT code, to evaluate both first order motions and mean drift forces of a system composed by a DP Crane Barge operating close to a turret-moored FPSO. The first order wave forces were evaluated using the code standard method. The second order forces (or mean drift forces) were obtained using the alternative control surface method. The work discussions are centered on the effects of FPSO presence on DP Barge hydrodynamics. Two relative positions between vessels were evaluated as well as three FPSO drafts (full, intermediate and ballasted). The effects of wave incidence angle were also discussed.Copyright

EXPERIMENTAL STUDY OF THE COUPLED HYDRODYNAMICS OF A DP BARGE OPERATING CLOSE TO A FPSO

The coupled hydrodynamic of a DP Barge operating close to a FPSO is evaluated. Experimental tests in a wave basin were performed to obtain the system dynamic behavior for several relative positions and environmental incidences. Two small scale models with factor 1:48 were tested in three different relative positions, five incidence angles and two irregular seas. The industry experience in operating barges was used to provide the insight to select these configurations. The DP Barge model was equipped with a dynamic positioning (DP) system, in order to keep its position relative to the FPSO. The FPSO model uses a scaled spread mooring system. Motions for DP Barge only were also obtained. Discussions are centered in reduction or amplification of DP Barge motions due the FPSO presence. Results are presented in terms of motions significant amplitude and RAO curves. A numerical model was evaluated and its results compared with the experiments. Some considerations, problems and conclusions about the operation were also obtained. These discussions complement the study presented by Vieira et al. (2011), which explored this operation numerically. A companion paper (Tannuri et al., 2012) will discuss the effects of the hydrodynamic coupling on the DP performance of the barge.

MPSO Design: Part 1 — Wave Excitation Forces and Moments

The MPSO is characterized by the use of hydrodynamics appendages, such as moonpool, beach and skirts, which improve the hydrodynamic behavior of the unit in waves. This type of platform may be designed for different offshore scenarios as, for example: the possibility of oil and gas storage, dry tree completion system and the use of steel catenary risers (SCR). An optimization procedure to choose the geometric dimensions of the MPSO becomes important in order to achieve the optimum hydrodynamic behavior to operate in harsh environmental conditions for each scenario. The optimization procedure might be useful in the preliminary design phases to reduce the verification time of the solution evaluated with model tests; for that reason it is necessary to create a database with experimental results to make the optimization procedure possible. The main idea of the study is to carry out an extensive experimental model test aimed at obtaining the parameters not well predicted using numerical codes. With this intent, the work is subdivided into three parts: Part 1 – Wave Excitation Forces and Moments; Part 2 – Damping and Added Mass Forces and Part 3 – Optimization Process. Results will be presented in different papers. The first one presents the experimental results for captive tests, the second one the experimental results for forced oscillation tests and the last one the methodology to use the experimental results as input in an optimization tool. The first paper presents the methodology in which nondimensional variables based on MPSO geometric characteristics were defined. These variables were related to a fixed moonpool diameter and they were determined in terms of four geometric dimensions: external diameter; height and diameter of the beach and platform draft. As a consequence, 21 different MPSO model geometries could be defined and experimentally tested in order to obtain the wave excitation forces and moments in 6 DOF. The experiments included transient waves so as to better understand the hydrodynamic behavior of the hull, such as, the response amplitude operator (RAO), cancelation points, the beach/bottom/moonpool effects for the different dimensions. The wave forces and moments obtained experimentally were compared to the results of a numerical code based on potential wave theory.Copyright

Methodology for evaluating DP crane-barge operation in close proximity of a FPSO

Abstract This paper presents an analysis methodology for evaluating the operation of a DP crane-barge in close proximity to a FPSO. Offshore crane operations are critical, since the barge is kept in close proximity with other vessel or platform, and large loads are transported in a pendulum configuration. A precise positioning of the crane-barge is required, in order to avoid unsafe relative motions, as well as keep the load being transported on a stable position. The operation analyzed in the present paper, as an example, is the replacement of a process equipment from the plant of a turret moored FPSO. Several aspects are previously assessed by means of numerical simulation in order to guarantee a safe operation, such as: relative motions between both vessels, relative motion of the FPSO and the equipment in pendulum configuration, tension in the lifting cables, barge DP performance and station keeping capacity. A full nonlinear time domain simulator (Numerical Offshore Tank – TPN) is used to perform the coupled analysis of the system subjected to several environmental conditions, considering also the dynamics of the suspended load. The hydrodynamic interference between the FPSO and the barge are considered by means of potential calculation of wave effects. CFD model is used to a preliminary assessment of the current shadow zone induced by the FPSO and the effects on the barge DP power requirement. The simulator also considers the DP follow-target mode that is used during the operation, in which the barge follows the FPSO guaranteeing a safe distance between them.

Investigation on the Effects of Risers in the Dynamics of Floating Systems

This paper presents the experimental results obtained by means of model tests, focused on the analysis of the influence of current effects in the dynamic behavior of a semi-submersible. The tests were accomplished with and without current, in order to establish the comparison basis. As an additional investigation procedure, the experimental results were compared to a numerical code based on the potential theory. As will be seen, considerable changes in the natural periods and in the damping levels was observed.Copyright

PARAMETRIC COMFORT ANALYSIS OF A STANDARD SWATH VESSEL

A parametric analysis which investigates the effects of the hull main dimensions on the seakeeping comfort was proposed to improve a standard SWATH vessel. This study was numerically carried out involving some comfort parameters and worldwide sea conditions. Some types of SWATH and their non-dimensional ratios were considered. The main dimensions of a standard SWATH vessel are: length (L), beam (B), pontoons radius (R), draft (T) and strut thickness (t). Some secondary dimensions were assumed so that a parametric model of wet surface could be designed using MULTISURF, which later was used on WAMIT to evaluate the hydrodynamics coefficients. The TPN receives these coefficients as a basic tool to provide the dynamic response of each SWATH case. The parametric comfort analysis was performed using three usual methodologies applied to evaluate the ship behavior: The ISO2631/3 Severe Discomfort, the MSI (Motion Sickness Incidence) and the VI (Vomiting Incidence).Copyright