Ming Chen, S. Yim, D. Cox, Zhaoqing Yang, M. Huesemann, T. Mumford, Taiping Wang
The investigation of innovative macroalgal cultivation is important and needed to optimize farming operations, increase biomass production, reduce the impact on the ecosystem, and lower system and operational costs. However, most macroalgal farming systems (MFSs) are stationary, which need to occupy a substantial coastal area, require extensive investment in farm infrastructure, and cost high fertilizer and anchoring expenses. This study aims to model, analyze, and support a novel binary species free-floating longline macroalgal cultivation concept. The expected outcomes could provide a basis for the design and application of the novel MFS to improve biomass production, decrease costs, and reduce the impact on the local ecosystem. In this paper, the Saccharina latissima and Nereocystis luetkeana were modeled and validated and coupled with longline to simulate the binary species MFS free float in various growth periods and associated locations along the U.S. west coast. The numerical predictions indicated the possibility of failure on the longline and breakage at the kelp holdfasts is low. However, the large forces due to instantaneous change in dynamic loads caused by loss of hydrostatic buoyancy when the longline stretches out of the water would damage the kelps. Buoy-longline contact interactions could damage the buoy, resulting in the loss of the system by sinking. Furthermore, the kelp-longline and kelp-kelp entanglements could potentially cause kelp damage.
{"title":"Modeling and Analysis of a Novel Offshore Binary Species Free-Floating Longline Macroalgal Farming System","authors":"Ming Chen, S. Yim, D. Cox, Zhaoqing Yang, M. Huesemann, T. Mumford, Taiping Wang","doi":"10.1115/1.4055803","DOIUrl":"https://doi.org/10.1115/1.4055803","url":null,"abstract":"\u0000 The investigation of innovative macroalgal cultivation is important and needed to optimize farming operations, increase biomass production, reduce the impact on the ecosystem, and lower system and operational costs. However, most macroalgal farming systems (MFSs) are stationary, which need to occupy a substantial coastal area, require extensive investment in farm infrastructure, and cost high fertilizer and anchoring expenses. This study aims to model, analyze, and support a novel binary species free-floating longline macroalgal cultivation concept. The expected outcomes could provide a basis for the design and application of the novel MFS to improve biomass production, decrease costs, and reduce the impact on the local ecosystem. In this paper, the Saccharina latissima and Nereocystis luetkeana were modeled and validated and coupled with longline to simulate the binary species MFS free float in various growth periods and associated locations along the U.S. west coast. The numerical predictions indicated the possibility of failure on the longline and breakage at the kelp holdfasts is low. However, the large forces due to instantaneous change in dynamic loads caused by loss of hydrostatic buoyancy when the longline stretches out of the water would damage the kelps. Buoy-longline contact interactions could damage the buoy, resulting in the loss of the system by sinking. Furthermore, the kelp-longline and kelp-kelp entanglements could potentially cause kelp damage.","PeriodicalId":50106,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48337246","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Csaba Pákozdi, A. Kamath, Weizhi Wang, T. Martin, H. Bihs
Estimation of the hydrodynamic loads based on strip theory using the Morrison equation provides an inexpen- sive method for load estimation for the offshore industry. The advantage of this approach is that it requires only the undisturbed wave kinematics along with inertia and viscous force coefficients. Over the recent years, the de- velopment in numerical wave tank simulations makes it possible to simulate nonlinear three-hour sea states, with computational times in the order of real time. This presents the possibility to calculate loads using wave spectrum input in numerical simulations with reasonable computational time and effort. In the current paper, the open-source fully nonlinear potential flow model REEF3D::FNPF is employed for calculating the nonlinear wave kinematics. Here, the Laplace equation for the velocity potential is solved on a s-coordinate mesh with the nonlinear free sur- face boundary conditions to close the system. A technique to calculate the total acceleration on the σ-coordinate grid is introduced which makes it possible to apply strip theory in a moving grid framework. With the combination of strip theory and three-hour wave simulations, a unique possibility to estimate the hydrodynamic loads in real time for all discrete positions in space within the domain of the numerical wave tank is presented in this paper. The numerical results for inline forces on an offshore wind mono-pile substructure are compared with measurements, and the new approach shows good agreement.
{"title":"Efficient calculation of hydrodynamic loads on offshore wind substructures including slamming forces","authors":"Csaba Pákozdi, A. Kamath, Weizhi Wang, T. Martin, H. Bihs","doi":"10.1115/1.4055701","DOIUrl":"https://doi.org/10.1115/1.4055701","url":null,"abstract":"\u0000 Estimation of the hydrodynamic loads based on strip theory using the Morrison equation provides an inexpen- sive method for load estimation for the offshore industry. The advantage of this approach is that it requires only the undisturbed wave kinematics along with inertia and viscous force coefficients. Over the recent years, the de- velopment in numerical wave tank simulations makes it possible to simulate nonlinear three-hour sea states, with computational times in the order of real time. This presents the possibility to calculate loads using wave spectrum input in numerical simulations with reasonable computational time and effort. In the current paper, the open-source fully nonlinear potential flow model REEF3D::FNPF is employed for calculating the nonlinear wave kinematics. Here, the Laplace equation for the velocity potential is solved on a s-coordinate mesh with the nonlinear free sur- face boundary conditions to close the system. A technique to calculate the total acceleration on the σ-coordinate grid is introduced which makes it possible to apply strip theory in a moving grid framework. With the combination of strip theory and three-hour wave simulations, a unique possibility to estimate the hydrodynamic loads in real time for all discrete positions in space within the domain of the numerical wave tank is presented in this paper. The numerical results for inline forces on an offshore wind mono-pile substructure are compared with measurements, and the new approach shows good agreement.","PeriodicalId":50106,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48691729","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The present study focuses on the wave trapping due to the submerged horizontal porous plate combined with bottom-standing porous structure and surface-piercing porous structure. The submerged plate thickness is considered to be negligible as compared to the incident wavelength and water depth and the porous structure is considered to be of finite width. The orthogonal mode-coupling relation is used to analyse the wave interaction with the combined structure. The reflection, transmission and dissipation coefficients along with wave force on the porous structure and surface deflection in the incident and transmitted region is investigated for the study of hydrodynamic performance of the composite porous breakwater system. Further, the effect of porosity of submerged plate and structure, friction factor, submerged depth of plate and structure angle of incidence and gap between the submerged plate and porous structure are investigated to analyse the effective wave dissipation by the porous breakwater system. In addition, the comparative study of the present method is performed with the results available in the literatures. The study noted that wave damping due to the submerged porous plate backed by surface-piercing porous structure is more as compared to the submerged porous plate backed by bottom-standing porous structure. The study will be helpful to scientist and engineers in the design of suitable composite breakwater system for wave attenuation in the coastal region.
{"title":"Dissipation of gravity waves due to submerged porous plate coupled with porous structures","authors":"Athul Krishna, Khansa Abdulla, D. Karmakar","doi":"10.1115/1.4055702","DOIUrl":"https://doi.org/10.1115/1.4055702","url":null,"abstract":"\u0000 The present study focuses on the wave trapping due to the submerged horizontal porous plate combined with bottom-standing porous structure and surface-piercing porous structure. The submerged plate thickness is considered to be negligible as compared to the incident wavelength and water depth and the porous structure is considered to be of finite width. The orthogonal mode-coupling relation is used to analyse the wave interaction with the combined structure. The reflection, transmission and dissipation coefficients along with wave force on the porous structure and surface deflection in the incident and transmitted region is investigated for the study of hydrodynamic performance of the composite porous breakwater system. Further, the effect of porosity of submerged plate and structure, friction factor, submerged depth of plate and structure angle of incidence and gap between the submerged plate and porous structure are investigated to analyse the effective wave dissipation by the porous breakwater system. In addition, the comparative study of the present method is performed with the results available in the literatures. The study noted that wave damping due to the submerged porous plate backed by surface-piercing porous structure is more as compared to the submerged porous plate backed by bottom-standing porous structure. The study will be helpful to scientist and engineers in the design of suitable composite breakwater system for wave attenuation in the coastal region.","PeriodicalId":50106,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48018026","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this article a virtual sensor for online load monitoring and subsequent remaining useful life (RUL) assessment of wind turbine gearbox bearings is presented. Utilizing a Digital Twin framework the virtual sensor combines data from readily available sensors of the condition monitoring (CMS) and supervisory control and data acquisition (SCADA) system with a physics-based gearbox model. Different state estimation methods including Kalman Filter, Least Square estimator and a quasi-static approach are employed for load estimation. For RUL assessment the accumulated fatigue damage is calculated with the Palmgren-Miner model. A case study using simulation measurements from a high-fidelity gearbox model is conducted to evaluate the proposed method. Estimated loads at the considered IMS and HSS bearings show moderate to high correlation (R = 0.50-0.96) to measurements, as lower frequency internal dynamics are not fully captured. The estimated fatigue damage differs by 5-15 % from measurements.
{"title":"Digital twin based virtual sensor for online fatigue damage monitoring in offshore wind turbine drivetrains","authors":"F. C. Mehlan, A. Nejad, Zhenghua Gao","doi":"10.1115/1.4055551","DOIUrl":"https://doi.org/10.1115/1.4055551","url":null,"abstract":"\u0000 In this article a virtual sensor for online load monitoring and subsequent remaining useful life (RUL) assessment of wind turbine gearbox bearings is presented. Utilizing a Digital Twin framework the virtual sensor combines data from readily available sensors of the condition monitoring (CMS) and supervisory control and data acquisition (SCADA) system with a physics-based gearbox model. Different state estimation methods including Kalman Filter, Least Square estimator and a quasi-static approach are employed for load estimation. For RUL assessment the accumulated fatigue damage is calculated with the Palmgren-Miner model. A case study using simulation measurements from a high-fidelity gearbox model is conducted to evaluate the proposed method. Estimated loads at the considered IMS and HSS bearings show moderate to high correlation (R = 0.50-0.96) to measurements, as lower frequency internal dynamics are not fully captured. The estimated fatigue damage differs by 5-15 % from measurements.","PeriodicalId":50106,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42189352","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rodrigo M Kochem, Fabrício Nogueira Correa, B. P. Jacob
This work proposes a taut-leg deep-water mooring configuration with buoys, designed specifically to allow a quick and easy visual identification of the rupture of any mooring line of the system. This addresses one of the main concerns of the offshore oil & gas industry: the significant number of events of mooring line failure that has been recently observed in actual operations in deep and ultra-deep water scenarios; field experience indicates that, in current spread-mooring systems, several weeks may pass until a failure is detected. The proposed configuration also presents the additional advantages of reducing the mooring radius and the tensions on the top of the lines. The configuration is evaluated and compared with a standard taut-leg system, considering the same base case study of a typical deep-water FPSO, and using up-to-date numerical methods implemented into an in-house fully coupled nonlinear time-domain dynamic analysis tool. The results indicated that the proposed configuration provided significant improvements in the cost and performance of the mooring system, in terms of line lengths, mooring radii, tensions and offsets; and confirmed that the buoy emerges and reaches the surface in the event of a line rupture, irrespective of the point where the line has broken. This indicates that the resulting configuration is a promising technical alternative to traditional standard taut-leg systems in deep and ultra-deep water scenarios.
{"title":"Numerical evaluation of an efficient deep-water mooring configuration designed to allow a fast identification of failure events","authors":"Rodrigo M Kochem, Fabrício Nogueira Correa, B. P. Jacob","doi":"10.1115/1.4055550","DOIUrl":"https://doi.org/10.1115/1.4055550","url":null,"abstract":"\u0000 This work proposes a taut-leg deep-water mooring configuration with buoys, designed specifically to allow a quick and easy visual identification of the rupture of any mooring line of the system. This addresses one of the main concerns of the offshore oil & gas industry: the significant number of events of mooring line failure that has been recently observed in actual operations in deep and ultra-deep water scenarios; field experience indicates that, in current spread-mooring systems, several weeks may pass until a failure is detected. The proposed configuration also presents the additional advantages of reducing the mooring radius and the tensions on the top of the lines. The configuration is evaluated and compared with a standard taut-leg system, considering the same base case study of a typical deep-water FPSO, and using up-to-date numerical methods implemented into an in-house fully coupled nonlinear time-domain dynamic analysis tool. The results indicated that the proposed configuration provided significant improvements in the cost and performance of the mooring system, in terms of line lengths, mooring radii, tensions and offsets; and confirmed that the buoy emerges and reaches the surface in the event of a line rupture, irrespective of the point where the line has broken. This indicates that the resulting configuration is a promising technical alternative to traditional standard taut-leg systems in deep and ultra-deep water scenarios.","PeriodicalId":50106,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47918359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mohammad Arif, Faisal Khan, Salim Ahmed, S. Imtiaz
The primary aim of this research is to consider the correlation among environmental factors in calculating 100 and 1000 years of extreme load design criteria. This is done by considering load as energy transferred from external environment to the offshore system. Also, incorporating spatial and temporal dependence of environmental variables in the context of offshore design. A bivariate extreme value distribution and a conditional joint return level function are developed using the Gumbel- Hougaard copula. The offshore design risk criteria are developed for the finer grid locations (0.10 × 0.10 latitude/longitude grid) considering joint extreme wind and wave energy. The developed approach is tested using data for the Flemish Pass basin off the east coast of Canada. Along with the primary aim, the impact of climate change is investigated (time and space variability) by implementing the proposed methodology in two cases: the periods from 1959 to 1988 and 1989 to 2018. This study observed that climate change has caused 30% less correlation between wind speed and wave height in recent years [1989-2018] compared to the period of 1959 to 1988. The proposed extreme design wind speed is 39.7 m/s, significant wave height is 16.4 m; their joint exceeding probability is 5.80E-05 over an annual basis for a scenario of 100-year.
{"title":"A generalized framework for risk-based extreme load analysis in offshore system design","authors":"Mohammad Arif, Faisal Khan, Salim Ahmed, S. Imtiaz","doi":"10.1115/1.4055553","DOIUrl":"https://doi.org/10.1115/1.4055553","url":null,"abstract":"\u0000 The primary aim of this research is to consider the correlation among environmental factors in calculating 100 and 1000 years of extreme load design criteria. This is done by considering load as energy transferred from external environment to the offshore system. Also, incorporating spatial and temporal dependence of environmental variables in the context of offshore design. A bivariate extreme value distribution and a conditional joint return level function are developed using the Gumbel- Hougaard copula. The offshore design risk criteria are developed for the finer grid locations (0.10 × 0.10 latitude/longitude grid) considering joint extreme wind and wave energy. The developed approach is tested using data for the Flemish Pass basin off the east coast of Canada. Along with the primary aim, the impact of climate change is investigated (time and space variability) by implementing the proposed methodology in two cases: the periods from 1959 to 1988 and 1989 to 2018. This study observed that climate change has caused 30% less correlation between wind speed and wave height in recent years [1989-2018] compared to the period of 1959 to 1988. The proposed extreme design wind speed is 39.7 m/s, significant wave height is 16.4 m; their joint exceeding probability is 5.80E-05 over an annual basis for a scenario of 100-year.","PeriodicalId":50106,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45501082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abdullahi Abba Dalhatu, A. M. Sa'ad, R. Cabral, G. de Tomi
Remotely Operated Vehicle (ROV) based Inspection, Maintenance and Repairs (IMR) services are costly be- cause operations are traditionally executed by a hired subsea contractor, who then hires a specialized vessel with an entire crew from the vessel owner or the shipping company. Even though this is an established method considered relatively reliable in comparison to human divers, there is a growing need for more versatile, efficient and economical IMR methods. Innovations that require no or less use of support vessels are mitigating this challenge. The current ROV classifications do not adapt to these innovations. Hence, the lack of a widely accepted ROV classification. Thus, this paper reviews ROV classifications and proposes a classification that poses no hindrance to innovation and conforms to modern developments. The paper then illustrates and reviews the emerging methods of conducting IMR operations by putting together in a concise, yet resourceful manner the ROV technologies and their various configurations to provide a basic meaningful understanding to the audience. This paper also provides a summary of the comparison of the methods and some of their challenges.
{"title":"REMOTELY OPERATED VEHICLE TAXONOMY AND EMERGING METHODS OF INSPECTION, MAINTENANCE AND REPAIR OPERATIONS: AN OVERVIEW AND OUTLOOK","authors":"Abdullahi Abba Dalhatu, A. M. Sa'ad, R. Cabral, G. de Tomi","doi":"10.1115/1.4055476","DOIUrl":"https://doi.org/10.1115/1.4055476","url":null,"abstract":"\u0000 Remotely Operated Vehicle (ROV) based Inspection, Maintenance and Repairs (IMR) services are costly be- cause operations are traditionally executed by a hired subsea contractor, who then hires a specialized vessel with an entire crew from the vessel owner or the shipping company. Even though this is an established method considered relatively reliable in comparison to human divers, there is a growing need for more versatile, efficient and economical IMR methods. Innovations that require no or less use of support vessels are mitigating this challenge. The current ROV classifications do not adapt to these innovations. Hence, the lack of a widely accepted ROV classification. Thus, this paper reviews ROV classifications and proposes a classification that poses no hindrance to innovation and conforms to modern developments. The paper then illustrates and reviews the emerging methods of conducting IMR operations by putting together in a concise, yet resourceful manner the ROV technologies and their various configurations to provide a basic meaningful understanding to the audience. This paper also provides a summary of the comparison of the methods and some of their challenges.","PeriodicalId":50106,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46987766","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Barratt, T. S. van den Bremer, Thomas A. A. Adcock
We perform simulations of random seas based on narrow-banded spectra with directional spreading. Our wavefields are spatially homogeneous and non-stationary in time. We truncate the spectral tail for the initial conditions at different cut-off wavenumbers to assess the impact of the spectral tail on the kurtosis and spectral evolution. We consider two cases based on truncation of the wavenumber tail at k/kp = 2.4 and k/kp = 6. Our simulations indicate that the peak kurtosis value increases if the tail is truncated at |k|/kp = 2.4 rather than k/kp = 6. For the case with a wavenumber cut-off at k/kp = 2.4, augmented kurtosis is accompanied by comparatively more aggressive spectral changes including redevelopment of the spectral tail. Similar trends are observed for the case with a wavenumber cut-off at |k|/kp = 6, but the spectral changes are less substantial. Thus, the spectral tail appears to play an important role in a form of spectral equilibrium that reduces spectral changes and decreases the peak kurtosis value. Our findings suggest that care should be taken when truncating the spectral tail for the purpose of simulations/experiments. We also find that the equation of Fedele (2015, textit{J. Fluid Mech.}, vol. 782, pp. 25--36) provides an excellent estimate of the peak kurtosis value. However, the bandwidth parameter must account for the spectral tail to provide accurate estimates of the peak kurtosis.
{"title":"The impact of the spectral tail on the evolution of the kurtosis of random seas","authors":"D. Barratt, T. S. van den Bremer, Thomas A. A. Adcock","doi":"10.1115/1.4055480","DOIUrl":"https://doi.org/10.1115/1.4055480","url":null,"abstract":"\u0000 We perform simulations of random seas based on narrow-banded spectra with directional spreading. Our wavefields are spatially homogeneous and non-stationary in time. We truncate the spectral tail for the initial conditions at different cut-off wavenumbers to assess the impact of the spectral tail on the kurtosis and spectral evolution. We consider two cases based on truncation of the wavenumber tail at k/kp = 2.4 and k/kp = 6. Our simulations indicate that the peak kurtosis value increases if the tail is truncated at |k|/kp = 2.4 rather than k/kp = 6. For the case with a wavenumber cut-off at k/kp = 2.4, augmented kurtosis is accompanied by comparatively more aggressive spectral changes including redevelopment of the spectral tail. Similar trends are observed for the case with a wavenumber cut-off at |k|/kp = 6, but the spectral changes are less substantial. Thus, the spectral tail appears to play an important role in a form of spectral equilibrium that reduces spectral changes and decreases the peak kurtosis value. Our findings suggest that care should be taken when truncating the spectral tail for the purpose of simulations/experiments. We also find that the equation of Fedele (2015, textit{J. Fluid Mech.}, vol. 782, pp. 25--36) provides an excellent estimate of the peak kurtosis value. However, the bandwidth parameter must account for the spectral tail to provide accurate estimates of the peak kurtosis.","PeriodicalId":50106,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46532826","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Diffraction and refraction of nonlinear shallow water waves due to uneven bathymetry are studied by use of the Green-Naghdi (GN) equations in two and three dimensions. A numerical wave tank consisting of deep, transitional and shallow regions is created. Various forms of three-dimensional bathymetry, consisting of ramps with nonuniform profiles and large slopes are used to connect the deep-water side of the tank to the shallow-water shelf. A wavemaker is placed at the upwave side of the domain, capable of generating solitary and cnoidal waves of the GN equations. A numerical wave absorber is located downwave of the domain to minimize the wave reflection back into the domain. The system of equations are solved numerically in time domain by use of a second-order finite difference approach for spatial discretization, and in a boundary-fitted coordinate system, and by use of the Modified Euler method for time marching. Results include solitary and cnoidal wave surface elevation and particle velocities and are compared with the existing solutions where possible. Overall very good agreement is observed. Discussion is provided on the nonlinearity and dispersion effects on the wave diffraction and refraction by the various forms of the ramps, as well as on the performance of the GN equations in solving these problems.
{"title":"Diffraction and refraction of nonlinear waves by the Green-Naghdi equations","authors":"M. Hayatdavoodi, Cengiz Ertekin, R. Cengiz","doi":"10.1115/1.4055484","DOIUrl":"https://doi.org/10.1115/1.4055484","url":null,"abstract":"\u0000 Diffraction and refraction of nonlinear shallow water waves due to uneven bathymetry are studied by use of the Green-Naghdi (GN) equations in two and three dimensions. A numerical wave tank consisting of deep, transitional and shallow regions is created. Various forms of three-dimensional bathymetry, consisting of ramps with nonuniform profiles and large slopes are used to connect the deep-water side of the tank to the shallow-water shelf. A wavemaker is placed at the upwave side of the domain, capable of generating solitary and cnoidal waves of the GN equations. A numerical wave absorber is located downwave of the domain to minimize the wave reflection back into the domain. The system of equations are solved numerically in time domain by use of a second-order finite difference approach for spatial discretization, and in a boundary-fitted coordinate system, and by use of the Modified Euler method for time marching. Results include solitary and cnoidal wave surface elevation and particle velocities and are compared with the existing solutions where possible. Overall very good agreement is observed. Discussion is provided on the nonlinearity and dispersion effects on the wave diffraction and refraction by the various forms of the ramps, as well as on the performance of the GN equations in solving these problems.","PeriodicalId":50106,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42867073","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jun-yi Liu, Xunjun Chen, Heng Huang, Song Ji, Qunzhang Tu
A two-dimensional (2D) simplified model of the very large floating structure (VLFS) is formulated based on Huston's interpretation of the Kane methodology. In this proposed model, the VLFS is considered as a serial of discrete floating bodies connected by elastic hinges. The rotation stiffness of elastic hinges has a great influence on the dynamic responses of VLFS and its value is determined based on the vertical displacements equivalent between the simply supported beam model and the elastically hinged multiple bodies model with the same boundary conditions on a concentrated load. Reduced Kane equations are used in the actual dynamic analysis, once initial conditions and mechanical analysis of system have been formulated. Validation of the Kane-based method and the reliability of corresponding program developed are established by several comparative study on a continuous structure and a hinged structure with three parts. The predictions based on the proposed method are essentially identical to the model test data and calculation results provided by related literatures.
{"title":"A Simplified Method to Analyse Dynamic Response of VLFS Based on the Kane Method","authors":"Jun-yi Liu, Xunjun Chen, Heng Huang, Song Ji, Qunzhang Tu","doi":"10.1115/1.4055487","DOIUrl":"https://doi.org/10.1115/1.4055487","url":null,"abstract":"\u0000 A two-dimensional (2D) simplified model of the very large floating structure (VLFS) is formulated based on Huston's interpretation of the Kane methodology. In this proposed model, the VLFS is considered as a serial of discrete floating bodies connected by elastic hinges. The rotation stiffness of elastic hinges has a great influence on the dynamic responses of VLFS and its value is determined based on the vertical displacements equivalent between the simply supported beam model and the elastically hinged multiple bodies model with the same boundary conditions on a concentrated load. Reduced Kane equations are used in the actual dynamic analysis, once initial conditions and mechanical analysis of system have been formulated. Validation of the Kane-based method and the reliability of corresponding program developed are established by several comparative study on a continuous structure and a hinged structure with three parts. The predictions based on the proposed method are essentially identical to the model test data and calculation results provided by related literatures.","PeriodicalId":50106,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48946882","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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