In this paper, the effect of a significant phenomenon in fluid-structure interaction (FSI), known as vortex-induced vibrations (VIV), is numerically investigated for two fully submerged cylinders located near the free surface. The Volume of Fluid (VOF) method is used to track the free surface. The study is conducted for a range of reduced velocities from 2 to 14, Froude numbers of 0.3 and 1, and different distances between cylinders. The impact of the free surface, cylinder vibrations on vortex patterns, hydrodynamic characteristics, and the vibrational response of cylinders are studied. Findings indicate that the rear cylinder generally exhibits greater inline and transverse displacement amplitudes, along with more significant variations in lift and drag coefficients compared to the front cylinder. An increase in the Froude number contributes to free surface instability and suppresses vortex shedding. Furthermore, increasing the distance between the cylinders amplifies free surface instability and vortex interactions, underscoring the relevance of these factors for engineering applications in marine environments.
{"title":"Numerical study of vortex-induced vibrations in two cylinders near a free surface","authors":"Pedram Latifkar , Ehsan Izadpanah , Seyed Hamed Meraji , Mohammad Vaghefi","doi":"10.1016/j.oceaneng.2024.119762","DOIUrl":"10.1016/j.oceaneng.2024.119762","url":null,"abstract":"<div><div>In this paper, the effect of a significant phenomenon in fluid-structure interaction (FSI), known as vortex-induced vibrations (VIV), is numerically investigated for two fully submerged cylinders located near the free surface. The Volume of Fluid (VOF) method is used to track the free surface. The study is conducted for a range of reduced velocities from 2 to 14, Froude numbers of 0.3 and 1, and different distances between cylinders. The impact of the free surface, cylinder vibrations on vortex patterns, hydrodynamic characteristics, and the vibrational response of cylinders are studied. Findings indicate that the rear cylinder generally exhibits greater inline and transverse displacement amplitudes, along with more significant variations in lift and drag coefficients compared to the front cylinder. An increase in the Froude number contributes to free surface instability and suppresses vortex shedding. Furthermore, increasing the distance between the cylinders amplifies free surface instability and vortex interactions, underscoring the relevance of these factors for engineering applications in marine environments.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"314 ","pages":"Article 119762"},"PeriodicalIF":4.6,"publicationDate":"2024-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142658678","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-16DOI: 10.1016/j.oceaneng.2024.119685
Andre Cahyadi Salim , Yining Zhang , Lili Hu , Chengjian Shao
Carbon fiber reinforced polymer (CFRP) has proven to be effective for repairing and strengthening existing structures. Spiral welded steel tubes (SWTs), extensively utilized for steel tube piles in bridges and offshore wind turbines, frequently experience fatigue loadings. This paper explores the spiral welded steel tube's static bending and fatigue behavior with initial damage before and after CFRP strengthening. An initial crack was introduced at the weld toe in the tensile area. Under static loading, CFRP strengthening increased the tube's stiffness and bending capacity by 175.4% and 27.45%, respectively. Under fatigue loading, crack growth was observed in two directions with different rates: circumferentially along the loading direction and along the weld seam, penetrating through the weld and continuing along the loading direction. This highlights how weld geometry and residual stress significantly influence the fatigue crack growth. CFRP strengthening reduced the crack's stress intensity, considerably decreasing the crack growth rate and extending fatigue life by two to three times. Moreover, the CFRP wrapping orientation had significantly impacted fatigue strengthening, with inverse-diagonal wrapping proving to be most effective. The debonding area of the strengthened specimens is also estimated. These findings provide valuable insights for practical engineering applications.
{"title":"Static and fatigue behavior of CFRP strengthened spiral welded steel tubes subjected to four-point bending","authors":"Andre Cahyadi Salim , Yining Zhang , Lili Hu , Chengjian Shao","doi":"10.1016/j.oceaneng.2024.119685","DOIUrl":"10.1016/j.oceaneng.2024.119685","url":null,"abstract":"<div><div>Carbon fiber reinforced polymer (CFRP) has proven to be effective for repairing and strengthening existing structures. Spiral welded steel tubes (SWTs), extensively utilized for steel tube piles in bridges and offshore wind turbines, frequently experience fatigue loadings. This paper explores the spiral welded steel tube's static bending and fatigue behavior with initial damage before and after CFRP strengthening. An initial crack was introduced at the weld toe in the tensile area. Under static loading, CFRP strengthening increased the tube's stiffness and bending capacity by 175.4% and 27.45%, respectively. Under fatigue loading, crack growth was observed in two directions with different rates: circumferentially along the loading direction and along the weld seam, penetrating through the weld and continuing along the loading direction. This highlights how weld geometry and residual stress significantly influence the fatigue crack growth. CFRP strengthening reduced the crack's stress intensity, considerably decreasing the crack growth rate and extending fatigue life by two to three times. Moreover, the CFRP wrapping orientation had significantly impacted fatigue strengthening, with inverse-diagonal wrapping proving to be most effective. The debonding area of the strengthened specimens is also estimated. These findings provide valuable insights for practical engineering applications.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"314 ","pages":"Article 119685"},"PeriodicalIF":4.6,"publicationDate":"2024-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142658684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-15DOI: 10.1016/j.oceaneng.2024.119712
Yunbiao Jiang , Liyuan Wang , Jian Sun , Haomiao Yu
This paper investigates distributed formation control problem of multiple unmanned surface vessels (USVs) with directed communication networks. Several practical factors are taken into consideration, including the dynamic uncertainty of and prescribed output constraints imposed on each USV, as well as deception attacks against communication networks. Firstly, a new construction of formation error is proposed, which can be combined with any conventional controller to handle the output constraint problem of distributed systems without using leader observers and additional initial conditions. Importantly, this output constraint solution is also effective in situations where interactive information is tampered with due to deception attacks. Subsequently, based on the backstepping method and Lyapunov theory, a non-singular finite-time quantized controller is proposed by indirectly using fuzzy logic systems. The proposed controller achieves a proper balance between ensuring control performance and saving control resources. Finally, a comprehensive system stability analysis and numerical simulation are presented.
{"title":"Attack-resistant distributed formation control for multiple unmanned surface vessels subject to output constraints","authors":"Yunbiao Jiang , Liyuan Wang , Jian Sun , Haomiao Yu","doi":"10.1016/j.oceaneng.2024.119712","DOIUrl":"10.1016/j.oceaneng.2024.119712","url":null,"abstract":"<div><div>This paper investigates distributed formation control problem of multiple unmanned surface vessels (USVs) with directed communication networks. Several practical factors are taken into consideration, including the dynamic uncertainty of and prescribed output constraints imposed on each USV, as well as deception attacks against communication networks. Firstly, a new construction of formation error is proposed, which can be combined with any conventional controller to handle the output constraint problem of distributed systems without using leader observers and additional initial conditions. Importantly, this output constraint solution is also effective in situations where interactive information is tampered with due to deception attacks. Subsequently, based on the backstepping method and Lyapunov theory, a non-singular finite-time quantized controller is proposed by indirectly using fuzzy logic systems. The proposed controller achieves a proper balance between ensuring control performance and saving control resources. Finally, a comprehensive system stability analysis and numerical simulation are presented.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"314 ","pages":"Article 119712"},"PeriodicalIF":4.6,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142659206","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-15DOI: 10.1016/j.oceaneng.2024.119746
Yang Han , Jue-yu Dong , Ruo-xin Li , Yan-yuan Wu , Ming-lei Ji
Bubbles in underwater vehicle wakes vary in size. However, there are limited studies on the influence of bubbles of different sizes on the bubble wake. In this investigation, the bubble wake generated by SUBOFF navigation was numerically simulated for a mixed-size bubble group using a mixture model. The overall distribution of the bubble wake was determined, and the effect of speed and exhaust velocity on the bubble wake were explored. The results indicate that a gradually diffused bubble band appears at the tail of the underwater vehicle. An increase in the speed and exhaust velocity accelerated the speed of bubble diffusion and floatation in the bubble wake, and the influence of speed on the bubble wake of the vehicle was greater than that of the exhaust velocity. After a period of navigation, the proportion of small bubbles increased, the proportion of medium-sized and large-sized bubbles decreased, and the proportion of small bubbles on the surface of the vehicle was higher than that on the entire XZ plane.
{"title":"Numerical simulation of bubble wakes with mixed scales of underwater vehicles","authors":"Yang Han , Jue-yu Dong , Ruo-xin Li , Yan-yuan Wu , Ming-lei Ji","doi":"10.1016/j.oceaneng.2024.119746","DOIUrl":"10.1016/j.oceaneng.2024.119746","url":null,"abstract":"<div><div>Bubbles in underwater vehicle wakes vary in size. However, there are limited studies on the influence of bubbles of different sizes on the bubble wake. In this investigation, the bubble wake generated by SUBOFF navigation was numerically simulated for a mixed-size bubble group using a mixture model. The overall distribution of the bubble wake was determined, and the effect of speed and exhaust velocity on the bubble wake were explored. The results indicate that a gradually diffused bubble band appears at the tail of the underwater vehicle. An increase in the speed and exhaust velocity accelerated the speed of bubble diffusion and floatation in the bubble wake, and the influence of speed on the bubble wake of the vehicle was greater than that of the exhaust velocity. After a period of navigation, the proportion of small bubbles increased, the proportion of medium-sized and large-sized bubbles decreased, and the proportion of small bubbles on the surface of the vehicle was higher than that on the entire XZ plane.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"314 ","pages":"Article 119746"},"PeriodicalIF":4.6,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142659209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-15DOI: 10.1016/j.oceaneng.2024.119774
Boyu Huang , Guan Guan , Weidi Sun , Qu Yang
Extreme weather conditions in marine environments significantly increase the risk of sliding for submersible platforms, making skirted edges design crucial for the platform's anti-sliding performance. However, the impact of skirted edges size parameters and arrangements on anti-sliding performance requires further investigation. This study employs the Coupled Eulerian-Lagrangian (CEL) method to establish a comprehensive simulation process for platform sliding. It analyses the effects of skirted edges length, thickness, and arrangements on anti-sliding performance. The findings indicate that increasing skirted edges length within a certain range improves anti-sliding performance, but when the length L equals 0.007D, 0.043D, or 0.06D (where D is the side length of the mat), anti-sliding performance sharply declines. Furthermore, an increase in skirted edges thickness T reduces the contact area with the soil, leading to a decrease in anti-sliding performance. By defining seven anti-sliding performance indicators, the study identifies the optimal skirted edges length L as 0.057D, thickness T as 0.0013D, and the best arrangement as orthogonal. This research reveals the influence of skirted edges shape on the anti-sliding performance of submersible platforms and establishes the optimal shape, providing important theoretical and design guidance for enhancing platform stability and ensuring safe operation.
海洋环境中的极端天气条件大大增加了潜水平台滑动的风险，因此裙边设计对平台的防滑动性能至关重要。然而，需要进一步研究裙边尺寸参数和排列方式对防滑动性能的影响。本研究采用欧拉-拉格朗日（CEL）耦合方法建立了平台滑动的综合模拟过程。它分析了裙边长度、厚度和排列方式对防滑动性能的影响。研究结果表明，在一定范围内增加裙边长度可提高抗滑动性能，但当长度 L 等于 0.007D、0.043D 或 0.06D（其中 D 为垫子的边长）时，抗滑动性能急剧下降。此外，增加裙边厚度 T 会减少与土壤的接触面积，从而导致抗滑动性能下降。通过定义七个抗滑动性能指标，该研究确定了最佳裙边长度 L 为 0.057D，厚度 T 为 0.0013D，最佳排列方式为正交。该研究揭示了裙边形状对潜水平台防滑性能的影响，并确定了最佳裙边形状，为增强平台稳定性、确保安全运行提供了重要的理论和设计指导。
{"title":"Analysis of the anti-sliding performance of skirted edges on the submersible platforms using the CEL method","authors":"Boyu Huang , Guan Guan , Weidi Sun , Qu Yang","doi":"10.1016/j.oceaneng.2024.119774","DOIUrl":"10.1016/j.oceaneng.2024.119774","url":null,"abstract":"<div><div>Extreme weather conditions in marine environments significantly increase the risk of sliding for submersible platforms, making skirted edges design crucial for the platform's anti-sliding performance. However, the impact of skirted edges size parameters and arrangements on anti-sliding performance requires further investigation. This study employs the Coupled Eulerian-Lagrangian (CEL) method to establish a comprehensive simulation process for platform sliding. It analyses the effects of skirted edges length, thickness, and arrangements on anti-sliding performance. The findings indicate that increasing skirted edges length within a certain range improves anti-sliding performance, but when the length <em>L</em> equals 0.007<em>D</em>, 0.043<em>D</em>, or 0.06<em>D</em> (where <em>D</em> is the side length of the mat), anti-sliding performance sharply declines. Furthermore, an increase in skirted edges thickness <em>T</em> reduces the contact area with the soil, leading to a decrease in anti-sliding performance. By defining seven anti-sliding performance indicators, the study identifies the optimal skirted edges length <em>L</em> as 0.057<em>D</em>, thickness <em>T</em> as 0.0013<em>D</em>, and the best arrangement as orthogonal. This research reveals the influence of skirted edges shape on the anti-sliding performance of submersible platforms and establishes the optimal shape, providing important theoretical and design guidance for enhancing platform stability and ensuring safe operation.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"314 ","pages":"Article 119774"},"PeriodicalIF":4.6,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142659214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-15DOI: 10.1016/j.oceaneng.2024.119676
Gaosheng Luo , Chuankun Luo , Shimin Gao , Jingxiang Xu , Xuteng Bao , Zhiqiang Ma , Zhe Jiang
The marine growth cleaning and structural defect detection of steel structures of offshore underwater facilities are essential parts of the inspection and maintenance of offshore platforms. However, a majority part of underwater structures of offshore facilities, such as offshore wind turbines, Jacket platforms, Jack-up platforms, etc., are cylindrical structures. Compared with the planar structures, cylindrical structures have large curvature, and less supporting area, and therefore put forward higher requirements for the performance of the attached surface working robot. This paper proposes a wall-climbing cleaning robot that can move freely on the wall of cylindrical steel structures and passively adapt to cylindrical structures with various curvatures and diameters. According to the structural characteristics of the robot, a static failure model is established to analyze the different instability forms of the robot and the minimum critical magnetic adsorption force is determined. To ensure the minimum mass and the maximum magnetic adsorption force of the conical magnetic adsorption wheelsets, the effects of air gap and cone angle on the performance of the conical magnetic adsorption wheelsets were analyzed parametrically, and the optimal structural size was obtained. Finally, the mobility and capability of the robot on the surface of the different diameter cylindrical structures has been validated through prototype experiments.
{"title":"Research on passive adaptive wall-climbing cleaning and inspection robot of marine cylindrical steel structure based on conical magnetic adsorption wheel","authors":"Gaosheng Luo , Chuankun Luo , Shimin Gao , Jingxiang Xu , Xuteng Bao , Zhiqiang Ma , Zhe Jiang","doi":"10.1016/j.oceaneng.2024.119676","DOIUrl":"10.1016/j.oceaneng.2024.119676","url":null,"abstract":"<div><div>The marine growth cleaning and structural defect detection of steel structures of offshore underwater facilities are essential parts of the inspection and maintenance of offshore platforms. However, a majority part of underwater structures of offshore facilities, such as offshore wind turbines, Jacket platforms, Jack-up platforms, etc., are cylindrical structures. Compared with the planar structures, cylindrical structures have large curvature, and less supporting area, and therefore put forward higher requirements for the performance of the attached surface working robot. This paper proposes a wall-climbing cleaning robot that can move freely on the wall of cylindrical steel structures and passively adapt to cylindrical structures with various curvatures and diameters. According to the structural characteristics of the robot, a static failure model is established to analyze the different instability forms of the robot and the minimum critical magnetic adsorption force is determined. To ensure the minimum mass and the maximum magnetic adsorption force of the conical magnetic adsorption wheelsets, the effects of air gap and cone angle on the performance of the conical magnetic adsorption wheelsets were analyzed parametrically, and the optimal structural size was obtained. Finally, the mobility and capability of the robot on the surface of the different diameter cylindrical structures has been validated through prototype experiments.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"314 ","pages":"Article 119676"},"PeriodicalIF":4.6,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142659215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-15DOI: 10.1016/j.oceaneng.2024.119739
Linfeng Li , Jianjun Qin , Yue Pan , Junxiang Xu , Michael Havbro Faber
A critical task for the reliability analysis and risk management of offshore wind turbines (OWT) is to accurately and efficiently predict the fatigue crack propagation over the service life. To realize the goal, a novel long and short-term network (LSTM)-based deep learning model integrated with full probabilistic perspectives is proposed to effectively handle time-varying and multi-source uncertainties associated with long-term fatigue crack propagation in OWTs. Based on the identification of the imbalance in the instance set and the inconsistency of the prediction model within the feasible regions of multiple uncertain parameters, a multi-bin progressive self-supervised learning (MPSL) framework is formulated afterwards. The trustworthiness of this framework is validated by the investigations on the fatigue crack propagation prediction of the National Renewable Energy Laboratory (NREL) 5 MW OWT. Our findings demonstrate significant gains in prediction accuracy and efficiency, juxtaposed with the traditional Paris model-based numerical simulation framework. Ultimately, the proposed trustworthy MPSL framework offers the stakeholders a robust tool for identifying the OWT fatigue crack propagation, advancing early risk perception and management in practice engineering.
{"title":"A trustworthy intelligent offshore wind turbine fatigue crack propagation prediction framework from the probabilistic perspective","authors":"Linfeng Li , Jianjun Qin , Yue Pan , Junxiang Xu , Michael Havbro Faber","doi":"10.1016/j.oceaneng.2024.119739","DOIUrl":"10.1016/j.oceaneng.2024.119739","url":null,"abstract":"<div><div>A critical task for the reliability analysis and risk management of offshore wind turbines (OWT) is to accurately and efficiently predict the fatigue crack propagation over the service life. To realize the goal, a novel long and short-term network (LSTM)-based deep learning model integrated with full probabilistic perspectives is proposed to effectively handle time-varying and multi-source uncertainties associated with long-term fatigue crack propagation in OWTs. Based on the identification of the imbalance in the instance set and the inconsistency of the prediction model within the feasible regions of multiple uncertain parameters, a multi-bin progressive self-supervised learning (MPSL) framework is formulated afterwards. The trustworthiness of this framework is validated by the investigations on the fatigue crack propagation prediction of the National Renewable Energy Laboratory (NREL) 5 MW OWT. Our findings demonstrate significant gains in prediction accuracy and efficiency, juxtaposed with the traditional Paris model-based numerical simulation framework. Ultimately, the proposed trustworthy MPSL framework offers the stakeholders a robust tool for identifying the OWT fatigue crack propagation, advancing early risk perception and management in practice engineering.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"314 ","pages":"Article 119739"},"PeriodicalIF":4.6,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142659205","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-15DOI: 10.1016/j.oceaneng.2024.119766
Lalit Kumar , Mohammad Saud Afzal , Said Alhaddad
This study explores the scour phenomenon around a submerged square pile under the combined influence of waves and currents. To this end, a three-dimensional Computational Fluid Dynamics model was developed. The numerical model solves the Reynolds-averaged Navier-Stokes (RANS) equations with k-ω turbulence closure model. The Level-Set method is utilized to monitor free surface interface realistically within the computational model. The Exner formulation is used to compute the bed elevation variations. An extensive validation is conducted for square pile scour in steady current, wave only, and wave–current conditions. Subsequently, the validated numerical model is utilized to analyze the impact of the submergence ratio, wave-current parameter (Ucw), and Keulegan–Carpenter (KC) number on the normalized scour depth around the submerged square pile in combined wave-current flows. The numerical results show that an increase in submergence ratio leads to an increased normalized scour depth around submerged piles in wave-current flows. Furthermore, it was found that a larger Ucw results in a larger normalized scour depth around the submerged square pile. However, for larger KC values of 12 and 18, the effect of Ucw becomes negligible due to the suppression of lee-wake vortices by developed trailing vortices.
{"title":"Computational investigation of scour around submerged square piles in wave-current flows","authors":"Lalit Kumar , Mohammad Saud Afzal , Said Alhaddad","doi":"10.1016/j.oceaneng.2024.119766","DOIUrl":"10.1016/j.oceaneng.2024.119766","url":null,"abstract":"<div><div>This study explores the scour phenomenon around a submerged square pile under the combined influence of waves and currents. To this end, a three-dimensional Computational Fluid Dynamics model was developed. The numerical model solves the Reynolds-averaged Navier-Stokes (RANS) equations with <em>k-ω</em> turbulence closure model. The Level-Set method is utilized to monitor free surface interface realistically within the computational model. The Exner formulation is used to compute the bed elevation variations. An extensive validation is conducted for square pile scour in steady current, wave only, and wave–current conditions. Subsequently, the validated numerical model is utilized to analyze the impact of the submergence ratio, wave-current parameter (<em>U</em><sub><em>cw</em></sub>), and Keulegan–Carpenter (<em>KC</em>) number on the normalized scour depth around the submerged square pile in combined wave-current flows. The numerical results show that an increase in submergence ratio leads to an increased normalized scour depth around submerged piles in wave-current flows. Furthermore, it was found that a larger <em>U</em><sub><em>cw</em></sub> results in a larger normalized scour depth around the submerged square pile. However, for larger <em>KC</em> values of 12 and 18, the effect of <em>U</em><sub><em>cw</em></sub> becomes negligible due to the suppression of lee-wake vortices by developed trailing vortices.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"314 ","pages":"Article 119766"},"PeriodicalIF":4.6,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142659213","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 objective of this study is to propose an improved direct predictive speed control (IDPSC) scheme for three-level neutral point clamped (NPC) converter-fed permanent magnet synchronous generator (PMSG)-based offshore wind turbine systems (OWTSs) with minimal computation. Conventional direct predictive speed control systems applied to OWTS machine-side converters face challenges due to the larger inertia. In these systems, the deviation between the predicted electromagnetic torque and load torque in different switching states has a reduced influence on the cost function because of the larger OWTS inertia. To address this, the IDPSC introduces additional weighting for torque deviations in the cost function, enhancing control performance and eliminating the need for integral action. Additionally, to reduce computation, the IDPSC incorporates revised switching state formulations based on the optimal switching states from the previous instant, which optimizes switching frequency without requiring a switching frequency constraint in the cost function. The proposed scheme is validated through simulations of a 1.5MW PMSG-based OWTS with a 3L-NPC converter, demonstrating effective speed control under step-varying and randomly varying wind profiles. Furthermore, the performance of the proposed IDPSC is compared with other relevant predictive control schemes, showcasing its improvements.
{"title":"An improved direct predictive speed control for three-level NPC converter fed PMSG-based offshore wind turbine system with minimum computation","authors":"Mayilsamy Ganesh, Seong Ryong Lee, Jae Hoon Jeong, Young Hoon Joo","doi":"10.1016/j.oceaneng.2024.119705","DOIUrl":"10.1016/j.oceaneng.2024.119705","url":null,"abstract":"<div><div>The objective of this study is to propose an improved direct predictive speed control (IDPSC) scheme for three-level neutral point clamped (NPC) converter-fed permanent magnet synchronous generator (PMSG)-based offshore wind turbine systems (OWTSs) with minimal computation. Conventional direct predictive speed control systems applied to OWTS machine-side converters face challenges due to the larger inertia. In these systems, the deviation between the predicted electromagnetic torque and load torque in different switching states has a reduced influence on the cost function because of the larger OWTS inertia. To address this, the IDPSC introduces additional weighting for torque deviations in the cost function, enhancing control performance and eliminating the need for integral action. Additionally, to reduce computation, the IDPSC incorporates revised switching state formulations based on the optimal switching states from the previous instant, which optimizes switching frequency without requiring a switching frequency constraint in the cost function. The proposed scheme is validated through simulations of a 1.5MW PMSG-based OWTS with a 3L-NPC converter, demonstrating effective speed control under step-varying and randomly varying wind profiles. Furthermore, the performance of the proposed IDPSC is compared with other relevant predictive control schemes, showcasing its improvements.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"314 ","pages":"Article 119705"},"PeriodicalIF":4.6,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142659208","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-15DOI: 10.1016/j.oceaneng.2024.119708
Huajun Li , Qiujue Jiang , Deqing Zhang , Junfeng Du , Zhi-Ming Yuan , Anteng Chang
Marine floating photovoltaics (MFPV) systems emerge as a promising frontier in the development of offshore clean energy, with their primary applications being in nearshore shallow waters. In these areas, the shallow depths, intricate seabed topographies and rugged shorelines profoundly affect wave propagation and transformation processes, leading to highly inhomogeneous wave conditions and thereby rendering traditional hydrodynamic theories based on assumptions of open seas inadequate. This study employs a hybrid Boussinesq-Panel Method (HBPM) to incorporate the effects of topography on wave dynamics into hydrodynamic calculations, striking a balance between computational accuracy and efficiency. A series of validation cases demonstrate the accuracy and necessity of the HBPM in shallow water environments. Computational results from typical bay scenarios reveal that variations in water depth and coastline reflections create multidirectional, non-uniform wave fields, which lead to complex force and motion characteristics of the structure. To ensure structural integrity, it is recommended to select installation sites located away from the breakwater entrance and close to the breakwater itself.
{"title":"Hydrodynamic analysis of marine floating photovoltaics under the influence of seabed topography and coastlines","authors":"Huajun Li , Qiujue Jiang , Deqing Zhang , Junfeng Du , Zhi-Ming Yuan , Anteng Chang","doi":"10.1016/j.oceaneng.2024.119708","DOIUrl":"10.1016/j.oceaneng.2024.119708","url":null,"abstract":"<div><div>Marine floating photovoltaics (MFPV) systems emerge as a promising frontier in the development of offshore clean energy, with their primary applications being in nearshore shallow waters. In these areas, the shallow depths, intricate seabed topographies and rugged shorelines profoundly affect wave propagation and transformation processes, leading to highly inhomogeneous wave conditions and thereby rendering traditional hydrodynamic theories based on assumptions of open seas inadequate. This study employs a hybrid Boussinesq-Panel Method (HBPM) to incorporate the effects of topography on wave dynamics into hydrodynamic calculations, striking a balance between computational accuracy and efficiency. A series of validation cases demonstrate the accuracy and necessity of the HBPM in shallow water environments. Computational results from typical bay scenarios reveal that variations in water depth and coastline reflections create multidirectional, non-uniform wave fields, which lead to complex force and motion characteristics of the structure. To ensure structural integrity, it is recommended to select installation sites located away from the breakwater entrance and close to the breakwater itself.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"314 ","pages":"Article 119708"},"PeriodicalIF":4.6,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142658674","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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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