Stability and performance analysis of hybrid braceless semisubmersible platform installed in real seas
Wind Engineering
The possibility of combining Floating Offshore Wind Turbines (FOWT) and Wave Energy Converters (W... more The possibility of combining Floating Offshore Wind Turbines (FOWT) and Wave Energy Converters (WEC) on one single platform is proposed here. To understand how the presence of two flap type WEC influences the platforms’ stabilities and subsequently turbine’s performances, an extensive study is carried out in real seas under two imperative states of turbine viz. operational & survival state. Accordingly, an integrated aero-hydro-elastic numerical model is developed with the help of multiple software, and finally coupled dynamic analysis is carried out in Orcaflex. After performing the analysis, it shows that wave and wind have synchronizing effects on the system’s stability and subsequently decide the turbine’s power. It is observed that the presence of WEC exhibits lesser platform responses with more turbine power from the base platform. Finally, the size and layout of the flap type WEC along with the flexibility of the supporting arm are compared and recommended the suitable.
Effect of wave spreading including multi-directional wave interaction on the responses of a spar platform
Marine Systems & Ocean Technology, 2019
This paper deals with the effect of directionality of waves on the responses of a spar-type float... more This paper deals with the effect of directionality of waves on the responses of a spar-type floating offshore platform. Here, a spar-type offshore platform restrained by four catenary mooring cables is modelled as per the work done by Chen et al. (Ocean Eng 28:863–887, 2001). The numerical model and numerical simulation have been validated by comparing the results (natural periods, RAOs and statistics of response) available in the literature (Steen et al. in Offshore Technology Conference 2004; Wangz et al. in J Mar Sci Appl 8:168–174, 2010). The multi-directional sea spectrum is represented by the product of a cosine power spreading function and a uni-directional JONSWAP wave spectrum. The Quadratic Transfer Functions have been generated for the calculation of drift loads, taking into account the multi-directional wave interaction. The responses of the platform have been obtained under long-crested (uni-directional) and short-crested (multi-directional) sea states and the results thus obtained are compared. Further, the variations in responses due to change in power of spreading function and total spreading angle are also investigated. It is found that due to the multi-directional wave interaction, the second order drift loads assume higher values in all degrees of freedom. Subsequently, in short-crested seas, the structure exhibits higher responses in all degrees of freedom when multi-directional wave interaction is considered. This highlights the need for incorporation of the multi-directional wave interaction while modelling short-crested seas for a realistic assessment of response behaviour of the system.
A coupled numerical analysis has been carried out for the structural responses and motion behavio... more A coupled numerical analysis has been carried out for the structural responses and motion behaviour of a classical spar structure subjected to irregular waves represented by JONSWAP (Joint North Sea Wave Project) spectrum. The motion of the floating body is restrained by the four catenary mooring lines with the generation of tension due to change in their nonlinear profile. The surface of the spar is represented by hydrodynamic pressure panels while cables are discretised using a series of Morison elements. A comprehensive sensitivity analysis under two sea depths is carried out by changing (1) the length of mooring lines, (2) the vertical position of fairlead point, (3) incident angle of long crested unidirectional single spectrum, and (4) the number of short crested sub segmented spreading spectra. The effect of second-order hydrodynamic loading on the structure is also taken into account in the analysis procedure by using quadratic transfer function.
A coupled dynamic analysis of a semisubmersible-type FOWT has been carried out in time domain und... more A coupled dynamic analysis of a semisubmersible-type FOWT has been carried out in time domain under the combined action of irregular wave and turbulent wind represented respectively by JONSWAP spectrum and Kaimal spectrum. To account for the turbine-floater motion coupling in a more realistic way, the wind turbulence has been incorporated into the calculation of aerodynamic loads. The platform model was referred from the DeepCwind project and the turbine considered here was the NREL 5MW Baseline. To account for the operationality of the turbine, two different environmental conditions (operational and survival) have been considered and the aerodynamic effect of turbine-rotation on actual responses of the FOWT has been studied. Higher mean offsets in surge and pitch responses were obtained under the operational condition as compared to the survival condition. The mooring line tensions were also observed to be sensitive to the rotation of turbine due to the turbulence of wind and overestimated responses were found when the constant wind was considered in the analysis. Additionally, a special analysis case of sudden shutdown of the turbine has also been considered to study the swift modification of responses and tension in the mooring cables.
Effect of wave spreading including multi-directional wave interaction on the responses of a spar platform
Marine Systems & Ocean Technology
This paper deals with the effect of directionality of waves on the responses of a spar-type float... more This paper deals with the effect of directionality of waves on the responses of a spar-type floating offshore platform. Here, a spar-type offshore platform restrained by four catenary mooring cables is modelled as per the work done by Chen et al. (Ocean Eng 28:863–887, 2001). The numerical model and numerical simulation have been validated by comparing the results (natural periods, RAOs and statistics of response) available in the literature (Steen et al. in Offshore Technology Conference 2004; Wangz et al. in J Mar Sci Appl 8:168–174, 2010). The multi-directional sea spectrum is represented by the product of a cosine power spreading function and a uni-directional JONSWAP wave spectrum. The Quadratic Transfer Functions have been generated for the calculation of drift loads, taking into account the multi-directional wave interaction. The responses of the platform have been obtained under long-crested (uni-directional) and short-crested (multi-directional) sea states and the results thus obtained are compared. Further, the variations in responses due to change in power of spreading function and total spreading angle are also investigated. It is found that due to the multi-directional wave interaction, the second order drift loads assume higher values in all degrees of freedom. Subsequently, in short-crested seas, the structure exhibits higher responses in all degrees of freedom when multi-directional wave interaction is considered. This highlights the need for incorporation of the multi-directional wave interaction while modelling short-crested seas for a realistic assessment of response behaviour of the system.
A coupled dynamic analysis of a semisubmersible-type FOWT has been carried out in time domain und... more A coupled dynamic analysis of a semisubmersible-type FOWT has been carried out in time domain under the combined action of irregular wave and turbulent wind represented respectively by JONSWAP spectrum and Kaimal spectrum. To account for the turbine-floater motion coupling in a more realistic way, the wind turbulence has been incorporated into the calculation of aerodynamic loads. The platform model was referred from the DeepCwind project and the turbine considered here was the NREL 5MW Baseline. To account for the operationality of the turbine, two different environmental conditions (operational and survival) have been considered and the aerodynamic effect of turbine-rotation on actual responses of the FOWT has been studied. Higher mean offsets in surge and pitch responses were obtained under the operational condition as compared to the survival condition. The mooring line tensions were also observed to be sensitive to the rotation of turbine due to the turbulence of wind and overe...
Stability and performance analysis of hybrid braceless semisubmersible platform installed in real seas
Wind Engineering
The possibility of combining Floating Offshore Wind Turbines (FOWT) and Wave Energy Converters (W... more The possibility of combining Floating Offshore Wind Turbines (FOWT) and Wave Energy Converters (WEC) on one single platform is proposed here. To understand how the presence of two flap type WEC influences the platforms’ stabilities and subsequently turbine’s performances, an extensive study is carried out in real seas under two imperative states of turbine viz. operational & survival state. Accordingly, an integrated aero-hydro-elastic numerical model is developed with the help of multiple software, and finally coupled dynamic analysis is carried out in Orcaflex. After performing the analysis, it shows that wave and wind have synchronizing effects on the system’s stability and subsequently decide the turbine’s power. It is observed that the presence of WEC exhibits lesser platform responses with more turbine power from the base platform. Finally, the size and layout of the flap type WEC along with the flexibility of the supporting arm are compared and recommended the suitable.
Effect of wave spreading including multi-directional wave interaction on the responses of a spar platform
Marine Systems & Ocean Technology, 2019
This paper deals with the effect of directionality of waves on the responses of a spar-type float... more This paper deals with the effect of directionality of waves on the responses of a spar-type floating offshore platform. Here, a spar-type offshore platform restrained by four catenary mooring cables is modelled as per the work done by Chen et al. (Ocean Eng 28:863–887, 2001). The numerical model and numerical simulation have been validated by comparing the results (natural periods, RAOs and statistics of response) available in the literature (Steen et al. in Offshore Technology Conference 2004; Wangz et al. in J Mar Sci Appl 8:168–174, 2010). The multi-directional sea spectrum is represented by the product of a cosine power spreading function and a uni-directional JONSWAP wave spectrum. The Quadratic Transfer Functions have been generated for the calculation of drift loads, taking into account the multi-directional wave interaction. The responses of the platform have been obtained under long-crested (uni-directional) and short-crested (multi-directional) sea states and the results thus obtained are compared. Further, the variations in responses due to change in power of spreading function and total spreading angle are also investigated. It is found that due to the multi-directional wave interaction, the second order drift loads assume higher values in all degrees of freedom. Subsequently, in short-crested seas, the structure exhibits higher responses in all degrees of freedom when multi-directional wave interaction is considered. This highlights the need for incorporation of the multi-directional wave interaction while modelling short-crested seas for a realistic assessment of response behaviour of the system.
A coupled numerical analysis has been carried out for the structural responses and motion behavio... more A coupled numerical analysis has been carried out for the structural responses and motion behaviour of a classical spar structure subjected to irregular waves represented by JONSWAP (Joint North Sea Wave Project) spectrum. The motion of the floating body is restrained by the four catenary mooring lines with the generation of tension due to change in their nonlinear profile. The surface of the spar is represented by hydrodynamic pressure panels while cables are discretised using a series of Morison elements. A comprehensive sensitivity analysis under two sea depths is carried out by changing (1) the length of mooring lines, (2) the vertical position of fairlead point, (3) incident angle of long crested unidirectional single spectrum, and (4) the number of short crested sub segmented spreading spectra. The effect of second-order hydrodynamic loading on the structure is also taken into account in the analysis procedure by using quadratic transfer function.
A coupled dynamic analysis of a semisubmersible-type FOWT has been carried out in time domain und... more A coupled dynamic analysis of a semisubmersible-type FOWT has been carried out in time domain under the combined action of irregular wave and turbulent wind represented respectively by JONSWAP spectrum and Kaimal spectrum. To account for the turbine-floater motion coupling in a more realistic way, the wind turbulence has been incorporated into the calculation of aerodynamic loads. The platform model was referred from the DeepCwind project and the turbine considered here was the NREL 5MW Baseline. To account for the operationality of the turbine, two different environmental conditions (operational and survival) have been considered and the aerodynamic effect of turbine-rotation on actual responses of the FOWT has been studied. Higher mean offsets in surge and pitch responses were obtained under the operational condition as compared to the survival condition. The mooring line tensions were also observed to be sensitive to the rotation of turbine due to the turbulence of wind and overestimated responses were found when the constant wind was considered in the analysis. Additionally, a special analysis case of sudden shutdown of the turbine has also been considered to study the swift modification of responses and tension in the mooring cables.
Effect of wave spreading including multi-directional wave interaction on the responses of a spar platform
Marine Systems & Ocean Technology
This paper deals with the effect of directionality of waves on the responses of a spar-type float... more This paper deals with the effect of directionality of waves on the responses of a spar-type floating offshore platform. Here, a spar-type offshore platform restrained by four catenary mooring cables is modelled as per the work done by Chen et al. (Ocean Eng 28:863–887, 2001). The numerical model and numerical simulation have been validated by comparing the results (natural periods, RAOs and statistics of response) available in the literature (Steen et al. in Offshore Technology Conference 2004; Wangz et al. in J Mar Sci Appl 8:168–174, 2010). The multi-directional sea spectrum is represented by the product of a cosine power spreading function and a uni-directional JONSWAP wave spectrum. The Quadratic Transfer Functions have been generated for the calculation of drift loads, taking into account the multi-directional wave interaction. The responses of the platform have been obtained under long-crested (uni-directional) and short-crested (multi-directional) sea states and the results thus obtained are compared. Further, the variations in responses due to change in power of spreading function and total spreading angle are also investigated. It is found that due to the multi-directional wave interaction, the second order drift loads assume higher values in all degrees of freedom. Subsequently, in short-crested seas, the structure exhibits higher responses in all degrees of freedom when multi-directional wave interaction is considered. This highlights the need for incorporation of the multi-directional wave interaction while modelling short-crested seas for a realistic assessment of response behaviour of the system.
A coupled dynamic analysis of a semisubmersible-type FOWT has been carried out in time domain und... more A coupled dynamic analysis of a semisubmersible-type FOWT has been carried out in time domain under the combined action of irregular wave and turbulent wind represented respectively by JONSWAP spectrum and Kaimal spectrum. To account for the turbine-floater motion coupling in a more realistic way, the wind turbulence has been incorporated into the calculation of aerodynamic loads. The platform model was referred from the DeepCwind project and the turbine considered here was the NREL 5MW Baseline. To account for the operationality of the turbine, two different environmental conditions (operational and survival) have been considered and the aerodynamic effect of turbine-rotation on actual responses of the FOWT has been studied. Higher mean offsets in surge and pitch responses were obtained under the operational condition as compared to the survival condition. The mooring line tensions were also observed to be sensitive to the rotation of turbine due to the turbulence of wind and overe...
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