Pub Date : 2024-11-28DOI: 10.1016/j.apor.2024.104341
K. Takamure , T. Uchiyama , T. Degawa
A vented sphere with a density of 2.6 × 103 kg/m3 and a diameter of 25.4 mm containing a circular uniaxial through-hole (diameter: 6 mm) was launched vertically upward from stationary water toward the air–water interface. The launch speed was adjusted such that the Reynolds number of the sphere was approximately 3000 immediately after it passed through the air–water interface. The effects of varying the submergence depth on the motion of the vented motion and behavior of the air–water interface were investigated. The entrained water mass increased with the submergence depth, resulting in an increase in the kinetic energy loss of the vented sphere. As the submergence depth increased, the vented sphere rotated as it passed through the air–water interface, and a sheet-like water mass was formed parallel to the direction of the through-hole. The vented sphere moved in the direction opposite to the scattering of the water mass. The vented sphere lost more kinetic energy compared to a normal sphere (without through-holes) while passing through the air–water interface at the same Reynolds number. These results indicated that the presence of the through-hole affected the motion characteristics of the sphere and behavior of the entrained water mass. These findings provide useful information for effectively controlling the attitude of artificial swimming devices that pass-through air–water interfaces.
{"title":"Motion characteristics of sphere with uniaxial through-hole after passing through air–water interface: Case study with different submergence depths","authors":"K. Takamure , T. Uchiyama , T. Degawa","doi":"10.1016/j.apor.2024.104341","DOIUrl":"10.1016/j.apor.2024.104341","url":null,"abstract":"<div><div>A vented sphere with a density of 2.6 × 10<sup>3</sup> kg/m<sup>3</sup> and a diameter of 25.4 mm containing a circular uniaxial through-hole (diameter: 6 mm) was launched vertically upward from stationary water toward the air–water interface. The launch speed was adjusted such that the Reynolds number of the sphere was approximately 3000 immediately after it passed through the air–water interface. The effects of varying the submergence depth on the motion of the vented motion and behavior of the air–water interface were investigated. The entrained water mass increased with the submergence depth, resulting in an increase in the kinetic energy loss of the vented sphere. As the submergence depth increased, the vented sphere rotated as it passed through the air–water interface, and a sheet-like water mass was formed parallel to the direction of the through-hole. The vented sphere moved in the direction opposite to the scattering of the water mass. The vented sphere lost more kinetic energy compared to a normal sphere (without through-holes) while passing through the air–water interface at the same Reynolds number. These results indicated that the presence of the through-hole affected the motion characteristics of the sphere and behavior of the entrained water mass. These findings provide useful information for effectively controlling the attitude of artificial swimming devices that pass-through air–water interfaces.</div></div>","PeriodicalId":8261,"journal":{"name":"Applied Ocean Research","volume":"154 ","pages":"Article 104341"},"PeriodicalIF":4.3,"publicationDate":"2024-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142743395","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The impact of an elliptic disc submerged in water of infinite depth on radiation and scattering phenomena is analyzed employing linear water wave theory. The problem is tackled by reducing it into two-dimensional hypersingular integral equations over the surface of the disc. Utilizing a spectral method, where the hypersingularity is evaluated analytically, we obtain numerical solutions for the integral equations. This study presents numerical findings concerning various hydrodynamic parameters relevant to disc scattering and radiation. Initially it compares numerical outcomes with those of a circular disc, before conducting a comprehensive parametric investigation for the elliptic disc. The primary focus is on investigating how the submerged depth and the geometry of the disc impact physical quantities such as added mass, damping coefficient, surface elevation, differential cross-section, and exciting forces. The results reveal a noticeable change in the pressure field around the disc as it approaches the free surface, leading to resonance. Due to the geometry of the submerged rigid elliptic disc, notable alterations in wave profile are noted in the results for both radiation and scattering problems. Furthermore, the radiation problem results reveal significant variations in the added mass and the damping coefficient for non-circular bodies, particularly with a high ratio of the semi-major axis to the semi-minor axis. Overall, this investigation provides a significant benchmark and valuable insights into potential applications in ocean energy and indicates a new design idea of an elliptic base oscillator alongside the commonly used circular designs.
{"title":"Hydrodynamic response of a submerged elliptic disc to surface water waves","authors":"Ajijul Hoque , Leandro Farina , Ranadev Datta , R. Gayen","doi":"10.1016/j.apor.2024.104327","DOIUrl":"10.1016/j.apor.2024.104327","url":null,"abstract":"<div><div>The impact of an elliptic disc submerged in water of infinite depth on radiation and scattering phenomena is analyzed employing linear water wave theory. The problem is tackled by reducing it into two-dimensional hypersingular integral equations over the surface of the disc. Utilizing a spectral method, where the hypersingularity is evaluated analytically, we obtain numerical solutions for the integral equations. This study presents numerical findings concerning various hydrodynamic parameters relevant to disc scattering and radiation. Initially it compares numerical outcomes with those of a circular disc, before conducting a comprehensive parametric investigation for the elliptic disc. The primary focus is on investigating how the submerged depth and the geometry of the disc impact physical quantities such as added mass, damping coefficient, surface elevation, differential cross-section, and exciting forces. The results reveal a noticeable change in the pressure field around the disc as it approaches the free surface, leading to resonance. Due to the geometry of the submerged rigid elliptic disc, notable alterations in wave profile are noted in the results for both radiation and scattering problems. Furthermore, the radiation problem results reveal significant variations in the added mass and the damping coefficient for non-circular bodies, particularly with a high ratio of the semi-major axis to the semi-minor axis. Overall, this investigation provides a significant benchmark and valuable insights into potential applications in ocean energy and indicates a new design idea of an elliptic base oscillator alongside the commonly used circular designs.</div></div>","PeriodicalId":8261,"journal":{"name":"Applied Ocean Research","volume":"154 ","pages":"Article 104327"},"PeriodicalIF":4.3,"publicationDate":"2024-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142743397","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-28DOI: 10.1016/j.apor.2024.104339
Shi-Min Li , Nai-Zheng Tan , Hao Chen , Wen-Chao Zhang
Predicting the collapse direction of large-scale pulsating bubbles is crucial for evaluating the safety performance of marine vessels in ocean applications involving underwater explosions and high-pressure bubble detection. This study develops a rapid forecasting method for large-scale pulsating bubbles under the influence of hybrid boundaries (free surface, bottom, and sidewall) based on the Kelvin impulse theory. The boundary element method was used to simulate bubble jets and clarify the applicability of the analytical solution in predicting the direction of large-scale bubbles. The analytical solution of the Kelvin impulse underestimates the buoyancy effects of bubbles near the bottom. However, near the free surface, the strong interaction between the bubble and free surface strengthens the downward movement of the bubble, resulting in an analytical solution with improved accuracy. A buoyancy correction factor was introduced to rectify inaccuracies in the analytical solution near the bottom. The correction factor was obtained under the condition of a vertically neutral collapse for the bubbles. Comparison of the simulation results with theoretical values across various buoyancy parameters indicate that the modified analytical solution can effectively predict the direction of bubble collapse across most parameter domains. The modification method for analytical solution proposed in this study may serve as a reference for practical operations aimed at protecting marine vessels near underwater explosions or marine seismic sources.
{"title":"Predicting the collapse direction of large-scale pulsating bubbles based on Kelvin impulse theory","authors":"Shi-Min Li , Nai-Zheng Tan , Hao Chen , Wen-Chao Zhang","doi":"10.1016/j.apor.2024.104339","DOIUrl":"10.1016/j.apor.2024.104339","url":null,"abstract":"<div><div>Predicting the collapse direction of large-scale pulsating bubbles is crucial for evaluating the safety performance of marine vessels in ocean applications involving underwater explosions and high-pressure bubble detection. This study develops a rapid forecasting method for large-scale pulsating bubbles under the influence of hybrid boundaries (free surface, bottom, and sidewall) based on the Kelvin impulse theory. The boundary element method was used to simulate bubble jets and clarify the applicability of the analytical solution in predicting the direction of large-scale bubbles. The analytical solution of the Kelvin impulse underestimates the buoyancy effects of bubbles near the bottom. However, near the free surface, the strong interaction between the bubble and free surface strengthens the downward movement of the bubble, resulting in an analytical solution with improved accuracy. A buoyancy correction factor was introduced to rectify inaccuracies in the analytical solution near the bottom. The correction factor was obtained under the condition of a vertically neutral collapse for the bubbles. Comparison of the simulation results with theoretical values across various buoyancy parameters indicate that the modified analytical solution can effectively predict the direction of bubble collapse across most parameter domains. The modification method for analytical solution proposed in this study may serve as a reference for practical operations aimed at protecting marine vessels near underwater explosions or marine seismic sources.</div></div>","PeriodicalId":8261,"journal":{"name":"Applied Ocean Research","volume":"154 ","pages":"Article 104339"},"PeriodicalIF":4.3,"publicationDate":"2024-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142743400","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-27DOI: 10.1016/j.apor.2024.104343
Deyu Li , Longfei Xiao , Handi Wei , Lijun Yang , Meng Shan
Accurate estimation of wave run-up is crucial for the design and safety of marine structures. To facilitate more precise and convenient predictions of wave run-up on vertical columns, including circular and square columns, many empirical formulas have been proposed. However, those derived from wave probe measurements typically underestimate the maximum wave run-up height due to the inability of wire-type wave gauges to closely adhere to the column surface. This study employed the non-contact wave measurement technology based on thermal stereography to measure the wave run-up distributions on vertical columns under regular waves, providing a more accurate measurements of wave run-up closer to the column surface. Utilizing the measurements, a modified formula was proposed to predict the wave run-up on circular columns. Additionally, considering the effects of scattering parameter (kD) and wave steepness (), a new empirical formula for predicting the wave run-up on square columns was developed based on the velocity stagnation head theory. These formulas were validated using the experimental data from the present study and the literature, demonstrating their ability to provide satisfactory wave run-up predictions. Furthermore, the spatiotemporal wave evolution for circular and square columns were compared. The wave profile in front of the circular cylinder at a half diameter tends to flatten, with water flowing along the cylinder surface to the sides, leading to a significantly lower wave run-up height ratio compared to the square column. This study provides the valuable insights for predicting the wave run-up on vertical columns, contributing to the design and safety assurance of marine structures.
{"title":"Predicting wave run-up on vertical columns based on thermal stereography measurements","authors":"Deyu Li , Longfei Xiao , Handi Wei , Lijun Yang , Meng Shan","doi":"10.1016/j.apor.2024.104343","DOIUrl":"10.1016/j.apor.2024.104343","url":null,"abstract":"<div><div>Accurate estimation of wave run-up is crucial for the design and safety of marine structures. To facilitate more precise and convenient predictions of wave run-up on vertical columns, including circular and square columns, many empirical formulas have been proposed. However, those derived from wave probe measurements typically underestimate the maximum wave run-up height due to the inability of wire-type wave gauges to closely adhere to the column surface. This study employed the non-contact wave measurement technology based on thermal stereography to measure the wave run-up distributions on vertical columns under regular waves, providing a more accurate measurements of wave run-up closer to the column surface. Utilizing the measurements, a modified formula was proposed to predict the wave run-up on circular columns. Additionally, considering the effects of scattering parameter (<em>kD</em>) and wave steepness (<span><math><mrow><mi>k</mi><msub><mi>η</mi><mrow><mi>m</mi><mi>a</mi><mi>x</mi></mrow></msub></mrow></math></span>), a new empirical formula for predicting the wave run-up on square columns was developed based on the velocity stagnation head theory. These formulas were validated using the experimental data from the present study and the literature, demonstrating their ability to provide satisfactory wave run-up predictions. Furthermore, the spatiotemporal wave evolution for circular and square columns were compared. The wave profile in front of the circular cylinder at a half diameter tends to flatten, with water flowing along the cylinder surface to the sides, leading to a significantly lower wave run-up height ratio compared to the square column. This study provides the valuable insights for predicting the wave run-up on vertical columns, contributing to the design and safety assurance of marine structures.</div></div>","PeriodicalId":8261,"journal":{"name":"Applied Ocean Research","volume":"154 ","pages":"Article 104343"},"PeriodicalIF":4.3,"publicationDate":"2024-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142722101","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-26DOI: 10.1016/j.apor.2024.104333
Hongwei Wang , Jin Wen , Gang Ma , Lin Yuan , Qingao Ran , Jianhua Zhang , Sulian Zhou
Extreme operational gust (EOG), defined by sudden increases in wind speed, is one of the most hazardous situations for wind turbines and the mooring system. A coupled aero-hydro-servo-elastic simulation model is developed using a dynamic link library and a reserved interface between the upper wind turbine and the platform with the mooring system. The blade element momentum (BEM) theory, potential flow theory and lumped-mass model is used to simulate the aerodynamic loads, hydrodynamic forces and mooring tension. The motion response and mooring tension of the OC4-DeepCwind FOWT under EOG are calculated, and the effects of different gust durations and gust amplitudes on the response of the FOWT system are analyzed. It has also been discovered that when gusts and waves cooperate on the FOWT, impact tension occurs in the mooring line, which can cause line breakage. The 107 s interval preceding the peak mooring tension post-EOG emergence presents an opportune moment for an emergency shutdown, with the potential to mitigate maximum tension by 20–42 %. A mooring line break induced by EOG will result in long-distance drift, and a significant reduction in the safety factors of the remaining mooring lines could lead to subsequent breaks. An emergency shutdown following a mooring line break can prevent successive mooring line breaks and limit long-distance drifting. The above study is intended to serve as a reference for future research into the motion performance of the FOWT mooring systems under extreme sea states.
{"title":"Coupled dynamics analysis of floating wind turbine mooring system under extreme operating gust","authors":"Hongwei Wang , Jin Wen , Gang Ma , Lin Yuan , Qingao Ran , Jianhua Zhang , Sulian Zhou","doi":"10.1016/j.apor.2024.104333","DOIUrl":"10.1016/j.apor.2024.104333","url":null,"abstract":"<div><div>Extreme operational gust (EOG), defined by sudden increases in wind speed, is one of the most hazardous situations for wind turbines and the mooring system. A coupled aero-hydro-servo-elastic simulation model is developed using a dynamic link library and a reserved interface between the upper wind turbine and the platform with the mooring system. The blade element momentum (BEM) theory, potential flow theory and lumped-mass model is used to simulate the aerodynamic loads, hydrodynamic forces and mooring tension. The motion response and mooring tension of the OC4-DeepCwind FOWT under EOG are calculated, and the effects of different gust durations and gust amplitudes on the response of the FOWT system are analyzed. It has also been discovered that when gusts and waves cooperate on the FOWT, impact tension occurs in the mooring line, which can cause line breakage. The 107 s interval preceding the peak mooring tension post-EOG emergence presents an opportune moment for an emergency shutdown, with the potential to mitigate maximum tension by 20–42 %. A mooring line break induced by EOG will result in long-distance drift, and a significant reduction in the safety factors of the remaining mooring lines could lead to subsequent breaks. An emergency shutdown following a mooring line break can prevent successive mooring line breaks and limit long-distance drifting. The above study is intended to serve as a reference for future research into the motion performance of the FOWT mooring systems under extreme sea states.</div></div>","PeriodicalId":8261,"journal":{"name":"Applied Ocean Research","volume":"154 ","pages":"Article 104333"},"PeriodicalIF":4.3,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142698578","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-26DOI: 10.1016/j.apor.2024.104336
Xiaoyu Bai , Yingjie Zhang , Nan Yan , Junwei Liu , Yamei Zhang
In this study, six rock-socketed bored piles were tested in the field to investigate the bearing characteristics of rock-socketed bored piles in silty clay formations in coastal areas, and the model piles were simulated and optimized using the finite element (FE) method. The results showed that the lateral resistance of the piles in the clay layer is less than 50 kPa, and the lateral resistance of the rock-embedded portion is within 136.2−166.4 kPa. Compared with increasing the rock-embedded depth, increasing the diameter of the test piles can improve their vertical bearing capacity more effectively. The average horizontal critical load (Hcr) increased by 84.54 %, and the average horizontal ultimate load (Hu) increased by 50.3 % for the 800 mm diameter piles compared to the 600 mm diameter piles. Also, at the end of the test, the 600 mm diameter test piles showed severe damage at 6−9.5 D below the mud surface and were more susceptible to instability damage than the 800 mm diameter test piles. In soft clay strata, the 'm' values converged rapidly with increasing horizontal displacement and stabilized when the displacement exceeded 10 mm. The FE simulations confirmed that the horizontal displacement of the pile mainly occurs at 4 m depth below the mud surface, and the displacement of the test pile can be effectively reduced by reinforcing the soil around the pile. The silt at the bottom of the pile is one of the critical factors causing the uneven settlement of the test pile, severely affecting the vertical bearing capacity of the pile foundation.
{"title":"Experimental investigation on bearing capacity of rock-socketed bored piles in silty clay stratum in beach areas","authors":"Xiaoyu Bai , Yingjie Zhang , Nan Yan , Junwei Liu , Yamei Zhang","doi":"10.1016/j.apor.2024.104336","DOIUrl":"10.1016/j.apor.2024.104336","url":null,"abstract":"<div><div>In this study, six rock-socketed bored piles were tested in the field to investigate the bearing characteristics of rock-socketed bored piles in silty clay formations in coastal areas, and the model piles were simulated and optimized using the finite element (FE) method. The results showed that the lateral resistance of the piles in the clay layer is less than 50 kPa, and the lateral resistance of the rock-embedded portion is within 136.2−166.4 kPa. Compared with increasing the rock-embedded depth, increasing the diameter of the test piles can improve their vertical bearing capacity more effectively. The average horizontal critical load (<em>H</em><sub>cr</sub>) increased by 84.54 %, and the average horizontal ultimate load (<em>H</em><sub>u</sub>) increased by 50.3 % for the 800 mm diameter piles compared to the 600 mm diameter piles. Also, at the end of the test, the 600 mm diameter test piles showed severe damage at 6−9.5 <em>D</em> below the mud surface and were more susceptible to instability damage than the 800 mm diameter test piles. In soft clay strata, the 'm' values converged rapidly with increasing horizontal displacement and stabilized when the displacement exceeded 10 mm. The FE simulations confirmed that the horizontal displacement of the pile mainly occurs at 4 m depth below the mud surface, and the displacement of the test pile can be effectively reduced by reinforcing the soil around the pile. The silt at the bottom of the pile is one of the critical factors causing the uneven settlement of the test pile, severely affecting the vertical bearing capacity of the pile foundation.</div></div>","PeriodicalId":8261,"journal":{"name":"Applied Ocean Research","volume":"154 ","pages":"Article 104336"},"PeriodicalIF":4.3,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142722099","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-26DOI: 10.1016/j.apor.2024.104340
Dimitrios N. Konispoliatis
Enhancements to the hydrodynamic effectiveness of oscillating water columns (OWC) have the potential to impact their absorption of wave power and enhance their efficiency. The primary objective of this study is to ascertain whether dual-chamber OWCs can enhance the hydrodynamic efficiency of the OWC through a three-dimensional theoretical formulation. To fulfil this objective, a parametric geometric analysis is undertaken for various types of OWCs with diverse geometric attributes of their oscillating chambers to identify the optimal configuration. Various parameters, such as the device's draft, the chamber's thickness, and the quantity and type of oscillating chambers, are taken into account. This research aims to outline the design parameters of the OWC device and the influential factors influencing its hydrodynamics. The analysis revealed that a dual-chamber OWC demonstrates improved hydrodynamic properties at specific wave frequencies when compared to a single-chamber converter, suggesting it as a viable solution for enhancing wave power absorption efficiency.
{"title":"Hydrodynamic analysis of a dual chamber floating oscillating water column device","authors":"Dimitrios N. Konispoliatis","doi":"10.1016/j.apor.2024.104340","DOIUrl":"10.1016/j.apor.2024.104340","url":null,"abstract":"<div><div>Enhancements to the hydrodynamic effectiveness of oscillating water columns (OWC) have the potential to impact their absorption of wave power and enhance their efficiency. The primary objective of this study is to ascertain whether dual-chamber OWCs can enhance the hydrodynamic efficiency of the OWC through a three-dimensional theoretical formulation. To fulfil this objective, a parametric geometric analysis is undertaken for various types of OWCs with diverse geometric attributes of their oscillating chambers to identify the optimal configuration. Various parameters, such as the device's draft, the chamber's thickness, and the quantity and type of oscillating chambers, are taken into account. This research aims to outline the design parameters of the OWC device and the influential factors influencing its hydrodynamics. The analysis revealed that a dual-chamber OWC demonstrates improved hydrodynamic properties at specific wave frequencies when compared to a single-chamber converter, suggesting it as a viable solution for enhancing wave power absorption efficiency.</div></div>","PeriodicalId":8261,"journal":{"name":"Applied Ocean Research","volume":"154 ","pages":"Article 104340"},"PeriodicalIF":4.3,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142698577","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-25DOI: 10.1016/j.apor.2024.104291
Jeffrey C. Harris
A machine learning time-series prediction approach is proposed for wave propagation and wave load prediction. Under unidirectional wave conditions and variable bathymetry, given a wave gauge upstream, a model is shown to reproduce wave elevation or wave forces downstream under irregular steep and either non-breaking or breaking conditions. Attempts to perform the opposite calculation, predicting upstream conditions from downstream measurements, results in higher error, likely due to information loss under breaking conditions. For choice of machine learning approach, comparisons show that the Time-series Dense Encoder (TiDE) approach results in a good balance between model complexity, stability, computational time, and error. Over a flat bottom, time-series of wave elevation can be predicted up to 10 wavelengths away, though with a degraded accuracy compared to shorter distances. Similar results are shown for time-series of forces on a vertical cylinder, showing better results than a simple Morison approach, as used in engineering tools such as OpenFAST, but with a similarly fast computational time. Generalizations show that training on irregular wave data permit extrapolations to periodic wave cases. Finally, the same method also is also demonstrated at field-scale, comparing results between two offshore buoys.
{"title":"Faster than real-time, phase-resolving, data-driven model of wave propagation and wave–structure interaction","authors":"Jeffrey C. Harris","doi":"10.1016/j.apor.2024.104291","DOIUrl":"10.1016/j.apor.2024.104291","url":null,"abstract":"<div><div>A machine learning time-series prediction approach is proposed for wave propagation and wave load prediction. Under unidirectional wave conditions and variable bathymetry, given a wave gauge upstream, a model is shown to reproduce wave elevation or wave forces downstream under irregular steep and either non-breaking or breaking conditions. Attempts to perform the opposite calculation, predicting upstream conditions from downstream measurements, results in higher error, likely due to information loss under breaking conditions. For choice of machine learning approach, comparisons show that the Time-series Dense Encoder (TiDE) approach results in a good balance between model complexity, stability, computational time, and error. Over a flat bottom, time-series of wave elevation can be predicted up to 10 wavelengths away, though with a degraded accuracy compared to shorter distances. Similar results are shown for time-series of forces on a vertical cylinder, showing better results than a simple Morison approach, as used in engineering tools such as OpenFAST, but with a similarly fast computational time. Generalizations show that training on irregular wave data permit extrapolations to periodic wave cases. Finally, the same method also is also demonstrated at field-scale, comparing results between two offshore buoys.</div></div>","PeriodicalId":8261,"journal":{"name":"Applied Ocean Research","volume":"154 ","pages":"Article 104291"},"PeriodicalIF":4.3,"publicationDate":"2024-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142698613","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-24DOI: 10.1016/j.apor.2024.104331
Maria Acanfora, Fabio De Luca, Riccardo Pigazzini, Marco Altosole
This paper deals with the assessment of the propeller performances in waves, by means of experimental open water tests. The focus of this study is on the propeller behaviour, neglecting, at this stage, the interaction with the hull dynamics. The towing tank experiments are carried out in calm water deeply immersed (nominal condition), and then repeated by reducing the head at the propeller tip, up to the point where ventilation and cavitation phenomena occur. The regular waves tests are conducted for several wave frequencies and amplitudes up to the complete emersion of the blade in correspondence of the wave trough. The averaged values of the propeller characteristics are compared to the ones obtained at nominal condition, and their time history is analysed with respect to the wave profile (i.e. local head of water at the propeller). Attention is given to frequency domain analyses and to the presence of hysteretic phenomena. The entire range of advance coefficients is investigated, i.e. from bollard pull up to windmilling condition.
The outcomes of the current study are meant to support the development of a numerical method for the evaluation of the effective propeller characteristics in waves, in view of further analyses taking into account the effects of hull dynamics.
{"title":"An experimental study on the open water characteristics of a ship propeller in waves","authors":"Maria Acanfora, Fabio De Luca, Riccardo Pigazzini, Marco Altosole","doi":"10.1016/j.apor.2024.104331","DOIUrl":"10.1016/j.apor.2024.104331","url":null,"abstract":"<div><div>This paper deals with the assessment of the propeller performances in waves, by means of experimental open water tests. The focus of this study is on the propeller behaviour, neglecting, at this stage, the interaction with the hull dynamics. The towing tank experiments are carried out in calm water deeply immersed (nominal condition), and then repeated by reducing the head at the propeller tip, up to the point where ventilation and cavitation phenomena occur. The regular waves tests are conducted for several wave frequencies and amplitudes up to the complete emersion of the blade in correspondence of the wave trough. The averaged values of the propeller characteristics are compared to the ones obtained at nominal condition, and their time history is analysed with respect to the wave profile (i.e. local head of water at the propeller). Attention is given to frequency domain analyses and to the presence of hysteretic phenomena. The entire range of advance coefficients is investigated, i.e. from bollard pull up to windmilling condition.</div><div>The outcomes of the current study are meant to support the development of a numerical method for the evaluation of the effective propeller characteristics in waves, in view of further analyses taking into account the effects of hull dynamics.</div></div>","PeriodicalId":8261,"journal":{"name":"Applied Ocean Research","volume":"154 ","pages":"Article 104331"},"PeriodicalIF":4.3,"publicationDate":"2024-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142698569","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-22DOI: 10.1016/j.apor.2024.104318
Lei Yang , Binbin Li , Kai Zhang , Menglan Duan , Xiaobo Chen
The impact of wave loads on the structural integrity of floating foundation for wind turbine is crucial. However, the structural design standards of hull for floating offshore wind turbine (FOWT) are typically derived from the design specifications of oil and gas platforms, which leads to uneconomical designs and high steel consumption. The economic design of the floater will provide a new approach to the cost reduction of FOWT. Therefore, it is of great importance to better understand the structural response characteristics such as the relationship between internal loads and wave parameters under different wave loading conditions. To achieve this goal, one of the most difficult problem is the interaction between hydrodynamic and structural analysis because the philosophies of these methodologies are completely different. In this study, a typical 5 MW Semi-submersible FOWT is selected, the finite element model is established for the floater. Given the primary emphasis on wave-induced structural response in the frequency domain, the impact of wind and current loads is not considered. Therefore, the tower and rotor nacelle assembly of the wind turbine are simplified as an equivalent concentrated mass point. An implicitly balanced model is proposed, the hydrodynamic pressure based on the 3D diffraction and radiation theory is recalculated at structural points, and different pressure components are separately transferred from the hydrodynamic to the structural model. Global motion response are validated by comparing the results of numerical simulation and a 1:50 Froude scaling model test. Wave-induced global structural response amplitude operator (RAO) and local stress RAO are calculated, the long-term extreme stress analysis based on 2,592 sea-states from a scatter diagram is performed. The mechanism and characteristics of structural response and waves are investigated. Results indicate that the internal loads are significant when the corresponding wavelength satisfies some relations with the geometry dimensions of the Semi-submersible floater, which is credited to the phase difference of hydrodynamic pressure. Stress hot spots appear at the intersection between the floater and tower, column and bracing, and hull around the still water level due to various causes e.g. hydrodynamic pressure, and internal loads. These findings can guide the engineering design and optimization of the Semi-submersible floater.
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