The focal point of the current study lies in investigating oblique wave scattering within the framework of linearized theory, with particular attention to scenarios involving asymmetric trenches of both finite and infinite depths. By employing the eigenfunction expansion method, the physical problem undergoes a transformation into an equivalent boundary value problem. This newly formulated problem is characterized by a system of four weakly singular integral equations, which pertain to the horizontal component of velocity across the gaps situated above the edges of the trenches. The solution to these integral equations is achieved through the utilization of a multi-term Galerkin approximation method. This approach involves expansions using ultraspherical Gegenbauer polynomials as basis functions, coupled with the appropriate weight functions tailored to address the one-third singularity. Graphical representations are employed to depict the numerical evaluations of reflection and transmission coefficients across various non-dimensional parameters. These visualizations offer insight into the behavior and dependencies of these coefficients under different conditions. To validate the accuracy of the current model, it is compared against previously published results available in the literature.
{"title":"Oblique wave scattering by a combination of two asymmetric trenches of finite and infinite depth","authors":"Swagata Ray, Soumen De","doi":"10.1115/1.4064392","DOIUrl":"https://doi.org/10.1115/1.4064392","url":null,"abstract":"\u0000 The focal point of the current study lies in investigating oblique wave scattering within the framework of linearized theory, with particular attention to scenarios involving asymmetric trenches of both finite and infinite depths. By employing the eigenfunction expansion method, the physical problem undergoes a transformation into an equivalent boundary value problem. This newly formulated problem is characterized by a system of four weakly singular integral equations, which pertain to the horizontal component of velocity across the gaps situated above the edges of the trenches. The solution to these integral equations is achieved through the utilization of a multi-term Galerkin approximation method. This approach involves expansions using ultraspherical Gegenbauer polynomials as basis functions, coupled with the appropriate weight functions tailored to address the one-third singularity. Graphical representations are employed to depict the numerical evaluations of reflection and transmission coefficients across various non-dimensional parameters. These visualizations offer insight into the behavior and dependencies of these coefficients under different conditions. To validate the accuracy of the current model, it is compared against previously published results available in the literature.","PeriodicalId":509714,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139389842","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Owing to the simplification of the wind turbine, it is difficult to accurately simulate the interaction between the rotor system and the supporting structure using decoupling finite element method. Therefore, when using this method for safety assessment and dynamic response research of the offshore wind turbine (OWT), there is a deviation between the simulation result and the real response of the OWT. In this study, an improved decoupled finite element analysis method is proposed based on a theoretical derivation. A simplified finite element model of a 10 MW jacket OWT with an equivalent substructure was established, and the dynamic response of the OWT under wind and waves was studied. By comparing the results of the fully coupled analysis method and the traditional finite element method, the applicability of the traditional finite element analysis method to the dynamic analysis of an OWT under typical winds and waves is discussed. The limitations of using the traditional finite element method to study or evaluate an OWT complex dynamic system were revealed, and the effectiveness and applicability of the improved method proposed in this study were qualitatively and quantitatively verified. Subsequently, based on the proposed improved decoupled finite element analysis method, a numerical calculation corresponding to a fully coupled test was performed. Compared with the numerical results obtained by the traditional finite element method, the improved decoupled finite element method proposed in this study obtained more consistent results with the fully coupled test.
{"title":"An Improved Decoupled Finite Element Analysis Method of Ultra-Large Offshore Wind Turbine Subjected to Combined Wind-wave Actions","authors":"D. Lu, Wenhua Wang, Xin Li","doi":"10.1115/1.4064298","DOIUrl":"https://doi.org/10.1115/1.4064298","url":null,"abstract":"Owing to the simplification of the wind turbine, it is difficult to accurately simulate the interaction between the rotor system and the supporting structure using decoupling finite element method. Therefore, when using this method for safety assessment and dynamic response research of the offshore wind turbine (OWT), there is a deviation between the simulation result and the real response of the OWT. In this study, an improved decoupled finite element analysis method is proposed based on a theoretical derivation. A simplified finite element model of a 10 MW jacket OWT with an equivalent substructure was established, and the dynamic response of the OWT under wind and waves was studied. By comparing the results of the fully coupled analysis method and the traditional finite element method, the applicability of the traditional finite element analysis method to the dynamic analysis of an OWT under typical winds and waves is discussed. The limitations of using the traditional finite element method to study or evaluate an OWT complex dynamic system were revealed, and the effectiveness and applicability of the improved method proposed in this study were qualitatively and quantitatively verified. Subsequently, based on the proposed improved decoupled finite element analysis method, a numerical calculation corresponding to a fully coupled test was performed. Compared with the numerical results obtained by the traditional finite element method, the improved decoupled finite element method proposed in this study obtained more consistent results with the fully coupled test.","PeriodicalId":509714,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139179135","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The purpose of the current study is to recommend an offshore tension leg platform (TLP) semi-active control system to lessen vibrations caused by various risks, such as the wind load and regular and irregular waves. State-of-the-art indicates that there has not been much study on semi-active management of offshore TLPs exposed to numerous hazards while taking into account system nonlinearities and employing a control method that is resilient to uncertainty. An Augmented Velocity-Displacement Based Groundhook (AVDB-GH) semi-active control scheme using MR dampers, which is an improvement over the displacement based Groundhook (DB-GH) control algorithm is proposed. The proposed controller uses a semi-active TMD (SATMD) consisting of a passive tuned mass damper (TMD) and two semi-active magneto-rheological (MR) dampers as the control devices. Constrained non-linear optimization is used to determine the SATMD's optimized parameters in order to produce the best control performance. A significant reduction in surge response of TLP is observed both in the time domain and the frequency domain. Compared to the SATMD using the usual DB-GH algorithm, the suggested control strategy more successfully decreases the key response variables—deck displacement, power spectral density, and acceleration. The effectiveness of the controller is better for regular waves than for irregular waves and wind forces. Because the performance of the controller is unaffected by changes in the mass and stiffness of the TLP, the controller can be regarded as robust.
{"title":"Semi-active Groundhook Control of Offshore Tension Leg Platforms using TMD with Optimized Parameters and MR Damper under Multiple Hazards","authors":"Suryasish Patra, Diptesh Das","doi":"10.1115/1.4064299","DOIUrl":"https://doi.org/10.1115/1.4064299","url":null,"abstract":"The purpose of the current study is to recommend an offshore tension leg platform (TLP) semi-active control system to lessen vibrations caused by various risks, such as the wind load and regular and irregular waves. State-of-the-art indicates that there has not been much study on semi-active management of offshore TLPs exposed to numerous hazards while taking into account system nonlinearities and employing a control method that is resilient to uncertainty. An Augmented Velocity-Displacement Based Groundhook (AVDB-GH) semi-active control scheme using MR dampers, which is an improvement over the displacement based Groundhook (DB-GH) control algorithm is proposed. The proposed controller uses a semi-active TMD (SATMD) consisting of a passive tuned mass damper (TMD) and two semi-active magneto-rheological (MR) dampers as the control devices. Constrained non-linear optimization is used to determine the SATMD's optimized parameters in order to produce the best control performance. A significant reduction in surge response of TLP is observed both in the time domain and the frequency domain. Compared to the SATMD using the usual DB-GH algorithm, the suggested control strategy more successfully decreases the key response variables—deck displacement, power spectral density, and acceleration. The effectiveness of the controller is better for regular waves than for irregular waves and wind forces. Because the performance of the controller is unaffected by changes in the mass and stiffness of the TLP, the controller can be regarded as robust.","PeriodicalId":509714,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139180091","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Marine icing due to freezing sea spray has been attributed to many safety incidences. Prediction of sea spray icing is necessary for operational safety, design optimization, and structural health. In general, lack of detailed full-scale measurements due to the complexity and costs make validation difficult. The next best option is that of controlled laboratory experiments. The current study is the first study in this field of research that investigates the use of new data science technologies like machine learning and feature engineering for the prediction of sea spray icing based on data collected from controlled laboratory experiments. A new prediction model dubbed ‘Spice’ is proposed. Spice has its basis on experimentally collected data and thus could be said to be highly accurate. Results from the current study show promising trends, however, more experiments are suggested for increasing the range of confident predictions and reducing the skewness of the training data. Results from spice are compared with five existing models and give icing rates in various conditions in the middle of the spectrum of the other models. It is discussed on how validation from two existing full-scale icing measurements from literature prove to be challenging and more detailed measurements are suggested for the purpose of validation.
{"title":"A Machine Learning Model for Prediction of Marine Icing","authors":"S. Deshpande","doi":"10.1115/1.4064108","DOIUrl":"https://doi.org/10.1115/1.4064108","url":null,"abstract":"Marine icing due to freezing sea spray has been attributed to many safety incidences. Prediction of sea spray icing is necessary for operational safety, design optimization, and structural health. In general, lack of detailed full-scale measurements due to the complexity and costs make validation difficult. The next best option is that of controlled laboratory experiments. The current study is the first study in this field of research that investigates the use of new data science technologies like machine learning and feature engineering for the prediction of sea spray icing based on data collected from controlled laboratory experiments. A new prediction model dubbed ‘Spice’ is proposed. Spice has its basis on experimentally collected data and thus could be said to be highly accurate. Results from the current study show promising trends, however, more experiments are suggested for increasing the range of confident predictions and reducing the skewness of the training data. Results from spice are compared with five existing models and give icing rates in various conditions in the middle of the spectrum of the other models. It is discussed on how validation from two existing full-scale icing measurements from literature prove to be challenging and more detailed measurements are suggested for the purpose of validation.","PeriodicalId":509714,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139258658","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Reviewer's Recognition","authors":"","doi":"10.1115/1.4046391","DOIUrl":"https://doi.org/10.1115/1.4046391","url":null,"abstract":"","PeriodicalId":509714,"journal":{"name":"Journal of Offshore Mechanics and Arctic Engineering","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141224120","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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