Analyzing the Stabilizing Tank for the Control of Rolling Motion by Model Testing and the Dynamic Absorber Theory

2007 ◽  
Author(s):  
Arthur Curty Saad ◽  
Antonio Carlos Fernandes ◽  
Paulo de Tarso T. Esperanc¸a ◽  
Joel Sena Sales Junior
Keyword(s):  
Degrees Of Freedom ◽  
Ocean Basin ◽  
Offshore Platforms ◽  
Concentrated Mass ◽  
Classical Dynamic ◽  
Six Degrees Of Freedom ◽  
Resonant Wave ◽  
Parametric Studies ◽  
Dynamic Absorber ◽  
Bilge Keel

The FPSOs are a type of offshore platforms that are directional in nature. Since a large ship (presently the use of a VLCC - Very Large Crude Carrier - is very common) is used, there is a great importance the direction the waves hit the hull. Differently from a real ship, the FPSO cannot resort to maneuvering to avoid waves. It has been found that there is a possibility, in certain cases, that a rolling resonant wave may reach some stationary FPSOs and consequently, a very high response may be obtained. Sometimes, it is not possible to use large bilge keel and the alternative is to consider the use of other devices such as stabilizing tanks and U-tubes. Faced with this problem, the present work performed model tests in a deepwater ocean basin showing the effectiveness of the stabilizing tank. On the other hand, it is clear that due to the presence of mass, restoring motion and damping that the design problem may be tackled by the use of classical dynamic absorber theory. For this reason, a simplified problem was formulated by replacing the stabilizing tank by a passive concentrated mass on board. The fully nine dimensional and non-linear model are then recovered. Six degrees of freedom are to describe the ship motion and the renaming three are for the mass on board. Based on these preliminary studies, the work describes the use of tests with reduced models showing the usefulness of the theory in practice. The test results together with 2 and 4 degrees of freedom system addresses the importance of the roll-sway coupling. Subsequently, a careful linearization is made for the purpose of identifying the commanding variables such as the mass, the position above the keel, the damping, the dynamic absorber natural frequencies, etc. After that, several parametric studies have been performed, identifying the range of applicability of the variables. Finally, this theoretical-experimental exercise addresses back the use of the applicability of the stabilizing tank.

An Experimental Investigation of Roll Motions of an FPSO

2008 ◽  
Author(s):  
Paulo T. T. Esperanc¸a ◽  
Joel S. Sales ◽  
Stergios Liapis ◽  
Joa˜o Paulo J. Matsuura ◽  
Wes Schott
Keyword(s):  
Degrees Of Freedom ◽  
Wind Waves ◽  
Scale Model ◽  
Ship Motions ◽  
Random Waves ◽  
Six Degrees Of Freedom ◽  
Campos Basin ◽  
Waves And Currents ◽  
Offshore Development ◽  
Bilge Keel

FPSO roll motions can be major contributor to riser fatigue. This is especially true in regions where wind, waves and currents are non-collinear. Roll motions as high as 23 degrees have been reported in the Campos Basin. The most common roll mitigation strategy consists of adding bilge keels to the FPSO. Motivation for this work came from a need to develop a better understanding of roll motions as a function of bilge keel width. In addition to roll motions, the hydrodynamic forces on the bilge keels were measured. A series of tests were conducted at the LabOceano offshore basin. This new facility has a length of 4 0 m, a width of 30 m, a depth of 15 m and is equipped with a multi-flap wave generator on one side. A ship-shaped FPSO design with sponsons for a deepwater offshore development in Brazil was tested. It has a length of 316 m, a breadth of 57.2 m and a draft of 28.3 m. A 1:70 scale model was constructed. A horizontal soft mooring system consisting of four lines with springs was used. Regular waves of different amplitudes as well as random waves were generated in the basin. Two different loading conditions, ballast (draft = 6.7 m) and loaded (draft = 21.7 m), as well as three wave headings, beam seas (90°), and quartering seas (22.5°, 45°) were considered. Tests were undertaken for four bilge keel configurations, corresponding to a case without bilge keels, as well as bilge keels of 3 different widths (1 m, 2 m and 3 m). In all cases, the bilge keels had a length of 200 m. An optical system was used to measure ship motions in all six degrees of freedom. The hydrodynamic loads on the bilge keels were measured using strain gages.

A Dynamic Simulation of Wave Impact Loads on Offshore Floating Platforms

1976 ◽  
Vol 98 (2) ◽  
pp. 550-557
Author(s):  
J. G. Giannotti
Keyword(s):  
Structural Analysis ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Impulsive Loading ◽  
Impact Loads ◽  
Offshore Platforms ◽  
Wave Impact ◽  
Six Degrees Of Freedom ◽  
Marine Vehicles ◽  
Floating Platforms

Some of the most critical loads to consider in developing design criteria for offshore platforms are those caused by wave hydrodynamic impact. The effect of these loads can be of a local nature in the form of plating damage as a result of impulsive loading, or it can be felt on the overall structure in the form of induced vibration, and increased bending moments and shears. Traditionally, the prediction of these loads has been highly empirical and designers have had to rely heavily on conservative factors of safety in order to account for the lack of confidence in these predictions. The current degree of sophistication of advanced techniques of structural analysis such as the finite element method has not been matched by equally sophisticated loads prediction methods. Consequently, the advantages offered by the computerized structural analysis schemes are considerably reduced due to the unacceptable load inputs. This paper fills part of this void by presenting an analytical model for predicting wave impact loads for the design of offshore platforms. The method is based on the Payne Impact Program which has been used before for predicting impact pressures and loads acting on high speed marine vehicles. The model simulates six-degrees-of-freedom and allows impacts at any wave heading. As inputs it requires geometric information, sea state definition, and a description of the relative motion of platform and wave. It is particularly suited to allow analysis of the results in probabilistic form, so that the severity and frequency of occurrence of impacts can be predicted.

Control of processing at multi-tool two-support setup

2020 ◽  
pp. 67-73
Author(s):  
N.D. YUsubov ◽  
G.M. Abbasova
Keyword(s):  
Degrees Of Freedom ◽  
Factor Model ◽  
Angular Displacement ◽  
Factor Models ◽  
Technological System ◽  
Displacement Control ◽  
Model Accuracy ◽  
Six Degrees Of Freedom ◽  
Angular Displacements ◽  
And Control

The accuracy of two-tool machining on automatic lathes is analyzed. Full-factor models of distortions and scattering fields of the performed dimensions, taking into account the flexibility of the technological system on six degrees of freedom, i. e. angular displacements in the technological system, were used in the research. Possibilities of design and control of two-tool adjustment are considered. Keywords turning processing, cutting mode, two-tool setup, full-factor model, accuracy, angular displacement, control, calculation [email protected]

scholarly journals Design and Calibration of a Hall Effect System for Measurement of Six-Degree-of-Freedom Motion within a Stacked Column

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3740
Author(s):  
Olafur Oddbjornsson ◽  
Panos Kloukinas ◽  
Tansu Gokce ◽  
Kate Bourne ◽  
Tony Horseman ◽  
...  
Keyword(s):  
Hall Effect ◽  
Degrees Of Freedom ◽  
Reactor Core ◽  
Degree Of Freedom ◽  
Life Extension ◽  
Scale Model ◽  
Design Development ◽  
Seismic Safety ◽  
Six Degrees Of Freedom ◽  
Six Degree Of Freedom

This paper presents the design, development and evaluation of a unique non-contact instrumentation system that can accurately measure the interface displacement between two rigid components in six degrees of freedom. The system was developed to allow measurement of the relative displacements between interfaces within a stacked column of brick-like components, with an accuracy of 0.05 mm and 0.1 degrees. The columns comprised up to 14 components, with each component being a scale model of a graphite brick within an Advanced Gas-cooled Reactor core. A set of 585 of these columns makes up the Multi Layer Array, which was designed to investigate the response of the reactor core to seismic inputs, with excitation levels up to 1 g from 0 to 100 Hz. The nature of the application required a compact and robust design capable of accurately recording fully coupled motion in all six degrees of freedom during dynamic testing. The novel design implemented 12 Hall effect sensors with a calibration procedure based on system identification techniques. The measurement uncertainty was ±0.050 mm for displacement and ±0.052 degrees for rotation, and the system can tolerate loss of data from two sensors with the uncertainly increasing to only 0.061 mm in translation and 0.088 degrees in rotation. The system has been deployed in a research programme that has enabled EDF to present seismic safety cases to the Office for Nuclear Regulation, resulting in life extension approvals for several reactors. The measurement system developed could be readily applied to other situations where the imposed level of stress at the interface causes negligible material strain, and accurate non-contact six-degree-of-freedom interface measurement is required.

scholarly journals Designing of Drive Systems in the Aspect of the Desired Spectrum of Operation

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2562
Author(s):  
Tomasz Dzitkowski ◽  
Andrzej Dymarek ◽  
Jerzy Margielewicz ◽  
Damian Gąska ◽  
Lukasz Orzech ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Dynamic Properties ◽  
Dynamic Parameters ◽  
Synthesis Algorithm ◽  
Moments Of Inertia ◽  
Driving System ◽  
Six Degrees Of Freedom ◽  
Resonance Frequencies ◽  
Drive Systems ◽  
Power Component

A method for selecting dynamic parameters and structures of drive systems using the synthesis algorithm is presented. The dynamic parameters of the system with six degrees of freedom, consisting of a power component (motor) and a two-speed gearbox, were determined, based on a formalized methodology. The required gearbox is to work in specific resonance zones, i.e., meet the required dynamic properties such as the required resonance frequencies. In the result of the tests, a series of parameters of the drive system, defining the required dynamic properties such as the resonance and anti-resonance frequencies were recorded. Mass moments of inertia of the wheels and elastic components, contained in the required structure of the driving system, were determined for the selected parameters obtained during the synthesis.

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