ABSTRACT A certain barge widely used for offshore operations in Brazil has a ramp to allow riser ... more ABSTRACT A certain barge widely used for offshore operations in Brazil has a ramp to allow riser and pipeline installations. This ramp crosses the free surface, leading to a non-linear restoring force. The restoring force is also asymmetric, since the ramp is placed in starboard side. Because of the irregular geometry, the predicted hydrodynamic behavior obtained considering potential theory is affected. It is usual consider using duffing equation (inclusion of a cubic term in restoring force) to reproduce GZ curve for analysis at large angles. Although non-linear, the behavior of Duffing model (limits of stability) has been stressed by scientific community and can be considered well-known. Unfortunately, for this analysis, duffing model is not the most appropriated to be used, because of the asymmetry. A quadratic model of restoring force may present better results describing roll evolution and should be investigated. Several studies have been done to improve the dynamic behavior of the barge. As a part of this effort, model tests have been conducted to allow the installation of bilge keels to control the rolling behavior. This was a good opportunity to access the non-linear behavior what will permit comparison with theoretical analysis.
ABSTRACT The MPSO is characterized by the use of hydrodynamics appendages, such as moonpool, beac... more ABSTRACT 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.
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 2011
ABSTRACT A great deal of work has been developed on the spar and monocolumn vortex-induced motion... more ABSTRACT A great deal of work has been developed on the spar and monocolumn vortex-induced motion (VIM) issue. However, there are very few published works concerning VIM of semi-submersible platforms, partly due to the fact that VIM studies for this type of platform recently became interesting particularly due to the increasing semi-submersible dimensions (columns diameter and height. In this context, a meticulous experimental study on VIM for this type of platform concept is presented here. Model test experiments were performed to check the influence of many factors on VIM, such as different headings and hull appendages. The results comply with in-line, cross-flow and yaw motion amplitudes, as well as with combined motions in the XY plane.
ABSTRACT Aiming to complete the results presented before by Gonçalves et al. (2012d. Ocean Eng. 5... more ABSTRACT Aiming to complete the results presented before by Gonçalves et al. (2012d. Ocean Eng. 54, 150–169) the present work brings new experimental results on VIM of a semi-submersible platform with four square columns, particularly concerning changes in three different aspects: simultaneous presence of current and surface waves in the same direction, external damping level, and draft conditions. The VIM tests were performed in the presence of regular and irregular waves, both conditions with simultaneous current presence, to understand the wave effects. Considerable differences between the presences of regular and irregular waves were observed. The motion amplitudes in the transverse direction, in the tests with regular waves, were markedly lower than those with irregular waves, and the VIM behavior was not observed. In the sea state tests, the amplitudes are lower than current-only ones, yet a periodic motion characterized by VIM was observed. Furthermore, the effects of the lower draft condition and damping level were addressed, showing they are important for model tests because they contribute to decreasing VIM amplitudes.
FPSO and TLWP Interacting at a Reduced Distance for Dry Tree Completion System. [ASME Conference ... more FPSO and TLWP Interacting at a Reduced Distance for Dry Tree Completion System. [ASME Conference Proceedings 2009, 81 (2009)]. Edgard B. Malta, Fabiano P. Rampazzo, Roberto E. Cruz, Allan C. de Oliveira, Kazuo Nishimoto. Abstract. ...
FPSO and TLWP Interacting at a Reduced Distance for Dry Tree Completion System. [ASME Conference ... more FPSO and TLWP Interacting at a Reduced Distance for Dry Tree Completion System. [ASME Conference Proceedings 2009, 81 (2009)]. Edgard B. Malta, Fabiano P. Rampazzo, Roberto E. Cruz, Allan C. de Oliveira, Kazuo Nishimoto. Abstract. ...
ABSTRACT A certain barge widely used for offshore operations in Brazil has a ramp to allow riser ... more ABSTRACT A certain barge widely used for offshore operations in Brazil has a ramp to allow riser and pipeline installations. This ramp crosses the free surface, leading to a non-linear restoring force. The restoring force is also asymmetric, since the ramp is placed in starboard side. Because of the irregular geometry, the predicted hydrodynamic behavior obtained considering potential theory is affected. It is usual consider using duffing equation (inclusion of a cubic term in restoring force) to reproduce GZ curve for analysis at large angles. Although non-linear, the behavior of Duffing model (limits of stability) has been stressed by scientific community and can be considered well-known. Unfortunately, for this analysis, duffing model is not the most appropriated to be used, because of the asymmetry. A quadratic model of restoring force may present better results describing roll evolution and should be investigated. Several studies have been done to improve the dynamic behavior of the barge. As a part of this effort, model tests have been conducted to allow the installation of bilge keels to control the rolling behavior. This was a good opportunity to access the non-linear behavior what will permit comparison with theoretical analysis.
ABSTRACT A certain barge widely used for offshore operations in Brazil has a ramp to allow riser ... more ABSTRACT A certain barge widely used for offshore operations in Brazil has a ramp to allow riser and pipeline installations. This ramp crosses the free surface, leading to a non-linear restoring force. The restoring force is also asymmetric, since the ramp is placed in starboard side. Because of the irregular geometry, the predicted hydrodynamic behavior obtained considering potential theory is affected. It is usual consider using duffing equation (inclusion of a cubic term in restoring force) to reproduce GZ curve for analysis at large angles. Although non-linear, the behavior of Duffing model (limits of stability) has been stressed by scientific community and can be considered well-known. Unfortunately, for this analysis, duffing model is not the most appropriated to be used, because of the asymmetry. A quadratic model of restoring force may present better results describing roll evolution and should be investigated. Several studies have been done to improve the dynamic behavior of the barge. As a part of this effort, model tests have been conducted to allow the installation of bilge keels to control the rolling behavior. This was a good opportunity to access the non-linear behavior what will permit comparison with theoretical analysis.
ABSTRACT The MPSO is characterized by the use of hydrodynamics appendages, such as moonpool, beac... more ABSTRACT 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.
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 2011
ABSTRACT A great deal of work has been developed on the spar and monocolumn vortex-induced motion... more ABSTRACT A great deal of work has been developed on the spar and monocolumn vortex-induced motion (VIM) issue. However, there are very few published works concerning VIM of semi-submersible platforms, partly due to the fact that VIM studies for this type of platform recently became interesting particularly due to the increasing semi-submersible dimensions (columns diameter and height. In this context, a meticulous experimental study on VIM for this type of platform concept is presented here. Model test experiments were performed to check the influence of many factors on VIM, such as different headings and hull appendages. The results comply with in-line, cross-flow and yaw motion amplitudes, as well as with combined motions in the XY plane.
ABSTRACT Aiming to complete the results presented before by Gonçalves et al. (2012d. Ocean Eng. 5... more ABSTRACT Aiming to complete the results presented before by Gonçalves et al. (2012d. Ocean Eng. 54, 150–169) the present work brings new experimental results on VIM of a semi-submersible platform with four square columns, particularly concerning changes in three different aspects: simultaneous presence of current and surface waves in the same direction, external damping level, and draft conditions. The VIM tests were performed in the presence of regular and irregular waves, both conditions with simultaneous current presence, to understand the wave effects. Considerable differences between the presences of regular and irregular waves were observed. The motion amplitudes in the transverse direction, in the tests with regular waves, were markedly lower than those with irregular waves, and the VIM behavior was not observed. In the sea state tests, the amplitudes are lower than current-only ones, yet a periodic motion characterized by VIM was observed. Furthermore, the effects of the lower draft condition and damping level were addressed, showing they are important for model tests because they contribute to decreasing VIM amplitudes.
FPSO and TLWP Interacting at a Reduced Distance for Dry Tree Completion System. [ASME Conference ... more FPSO and TLWP Interacting at a Reduced Distance for Dry Tree Completion System. [ASME Conference Proceedings 2009, 81 (2009)]. Edgard B. Malta, Fabiano P. Rampazzo, Roberto E. Cruz, Allan C. de Oliveira, Kazuo Nishimoto. Abstract. ...
FPSO and TLWP Interacting at a Reduced Distance for Dry Tree Completion System. [ASME Conference ... more FPSO and TLWP Interacting at a Reduced Distance for Dry Tree Completion System. [ASME Conference Proceedings 2009, 81 (2009)]. Edgard B. Malta, Fabiano P. Rampazzo, Roberto E. Cruz, Allan C. de Oliveira, Kazuo Nishimoto. Abstract. ...
ABSTRACT A certain barge widely used for offshore operations in Brazil has a ramp to allow riser ... more ABSTRACT A certain barge widely used for offshore operations in Brazil has a ramp to allow riser and pipeline installations. This ramp crosses the free surface, leading to a non-linear restoring force. The restoring force is also asymmetric, since the ramp is placed in starboard side. Because of the irregular geometry, the predicted hydrodynamic behavior obtained considering potential theory is affected. It is usual consider using duffing equation (inclusion of a cubic term in restoring force) to reproduce GZ curve for analysis at large angles. Although non-linear, the behavior of Duffing model (limits of stability) has been stressed by scientific community and can be considered well-known. Unfortunately, for this analysis, duffing model is not the most appropriated to be used, because of the asymmetry. A quadratic model of restoring force may present better results describing roll evolution and should be investigated. Several studies have been done to improve the dynamic behavior of the barge. As a part of this effort, model tests have been conducted to allow the installation of bilge keels to control the rolling behavior. This was a good opportunity to access the non-linear behavior what will permit comparison with theoretical analysis.
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