Pub Date : 2024-12-12DOI: 10.1016/j.marstruc.2024.103760
Yushun Lian , Zhenghu Pan , Jinhai Zheng , WenXing Chen , Solomon C. Yim
This paper investigates the residual strength and stiffness evolution characteristics of high-modulus polyethylene (HMPE) ropes used in seaweed farms service. In some cases, polypropylene (PE) ropes commonly used in seaweed farms are more prone to failure in severe marine conditions, and HMPE ropes may be a more suitable alternative. Normally, damages occur during the service life of ropes in marine environments, such as marine biofouling, corrosion and internal abrasion from fine sand infiltration into the strands. Early studies on the mechanical properties of aged ropes (due to field service) suggest that both the strength and stiffness may be affected. In addition, the damage patterns of artificially induced cutting may not faithfully replicate the damaged state of the ropes in field service marine environments. Hence, the residual strength and stiffness evolution of the aged ropes with damage induced under service loads is investigated by using experimental testing techniques of fiber ropes. Additionally, by analyzing the residual strength, as well as the static and dynamic stiffness of the new (i.e., intact) and aged HMPE ropes, the damage that occurred by artificial cutting is compared with the damage that occurred under service loads.
{"title":"Experimental investigation on mechanical behavior of damaged HMPE mooring ropes under service loads","authors":"Yushun Lian , Zhenghu Pan , Jinhai Zheng , WenXing Chen , Solomon C. Yim","doi":"10.1016/j.marstruc.2024.103760","DOIUrl":"10.1016/j.marstruc.2024.103760","url":null,"abstract":"<div><div>This paper investigates the residual strength and stiffness evolution characteristics of high-modulus polyethylene (HMPE) ropes used in seaweed farms service. In some cases, polypropylene (PE) ropes commonly used in seaweed farms are more prone to failure in severe marine conditions, and HMPE ropes may be a more suitable alternative. Normally, damages occur during the service life of ropes in marine environments, such as marine biofouling, corrosion and internal abrasion from fine sand infiltration into the strands. Early studies on the mechanical properties of aged ropes (due to field service) suggest that both the strength and stiffness may be affected. In addition, the damage patterns of artificially induced cutting may not faithfully replicate the damaged state of the ropes in field service marine environments. Hence, the residual strength and stiffness evolution of the aged ropes with damage induced under service loads is investigated by using experimental testing techniques of fiber ropes. Additionally, by analyzing the residual strength, as well as the static and dynamic stiffness of the new (i.e., intact) and aged HMPE ropes, the damage that occurred by artificial cutting is compared with the damage that occurred under service loads.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"101 ","pages":"Article 103760"},"PeriodicalIF":4.0,"publicationDate":"2024-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143147547","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 : 2024-12-12DOI: 10.1016/j.marstruc.2024.103756
Wenchi Ni , Wenzha Yang , Xu Zhang , Yuan Du , Cheng Zhang , Yong Ma , Liangbin Xu , Gengqing Tian , Lina Yi , Zhuang Kang
Although particle damping has proven to be an effective passive vibration control technique widely applied across a variety of industries, research on its effectiveness and mechanism for suppressing vortex-induced vibrations (VIV) in marine structures remains unclear. This paper investigates the effects of particle dampers on VIV in different branches of a cylinder, determining rules and mechanisms of vibration suppression through a combination of experimental and theoretical analysis methods. Key conclusions drawn from our study include: 1. Optimal filling ratios vary for different VIV branches, with the highest overall VIV suppression effect at a filling rate of approximately 85 %, resulting in amplitude suppression ratios of 30 %-40 %. 2. Particle dampers exhibit an amplitude modulation effect on VIV, with the ability to excite a vibration mode that has the same frequency as the vortex shedding frequency of stationary cylinders. Furthermore, a parameterized study of particle damping systems is conducted in this paper, based on experimental results and theoretical models. Our findings demonstrate the feasibility of applying particle damping to suppress VIV in marine engineering structures, providing valuable reference for selecting optimal parameters of particle dampers.
{"title":"Experimental and theoretical studies of particle damping for the suppression of vortex-induced vibrations in different branches","authors":"Wenchi Ni , Wenzha Yang , Xu Zhang , Yuan Du , Cheng Zhang , Yong Ma , Liangbin Xu , Gengqing Tian , Lina Yi , Zhuang Kang","doi":"10.1016/j.marstruc.2024.103756","DOIUrl":"10.1016/j.marstruc.2024.103756","url":null,"abstract":"<div><div>Although particle damping has proven to be an effective passive vibration control technique widely applied across a variety of industries, research on its effectiveness and mechanism for suppressing vortex-induced vibrations (VIV) in marine structures remains unclear. This paper investigates the effects of particle dampers on VIV in different branches of a cylinder, determining rules and mechanisms of vibration suppression through a combination of experimental and theoretical analysis methods. Key conclusions drawn from our study include: 1. Optimal filling ratios vary for different VIV branches, with the highest overall VIV suppression effect at a filling rate of approximately 85 %, resulting in amplitude suppression ratios of 30 %-40 %. 2. Particle dampers exhibit an amplitude modulation effect on VIV, with the ability to excite a vibration mode that has the same frequency as the vortex shedding frequency of stationary cylinders. Furthermore, a parameterized study of particle damping systems is conducted in this paper, based on experimental results and theoretical models. Our findings demonstrate the feasibility of applying particle damping to suppress VIV in marine engineering structures, providing valuable reference for selecting optimal parameters of particle dampers.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"101 ","pages":"Article 103756"},"PeriodicalIF":4.0,"publicationDate":"2024-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143147681","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 : 2024-12-09DOI: 10.1016/j.marstruc.2024.103747
S. Hemanth, D. Karmakar
The present study analyses the feasibility of integrating a Very Large Floating Structure (VLFS) with a porous floating box-type breakwater kept fixed in its position to analyze the hydroelastic responses within the integrated system based on linearized wave theory. The integrated VLFS-breakwater system, comprising the VLFS and the porous box-type breakwater assures in mitigating the structural effects induced by waves. The coupled Multi-Domain Boundary Element Method (MDBEM) and Finite Difference Method (FDM) are employed to investigate the performance of integrated VLFS-breakwater system. The computational framework employs the MDBEM to model the fluid domain and the floating breakwaters, while the VLFS is modeled using the FDM approach. The study considers three distinct relative positions of the VLFS integrated with a floating breakwater on (i) the leeside, (ii) the seaside, and (iii) on both leeside and seaside of the VLFS. The numerical study is performed based on thin-plate theory and small amplitude wave theory. The study corroborates its numerical findings with existing literature, supporting the validity of its methodology. The integrated system effectively reduces forces acting on the VLFS by absorbing the primary impact of waves. Consequently, the hydroelastic response of the VLFS is reduced, preserving its structural integrity and enhancing overall safety. The study signifies the importance of integrating the porous box-type breakwater with the VLFS. The importance of the orientation of the structure towards the sea waves, the porosity of the breakwater, the effect of relative spacing between the breakwater and VLFS and variations in hydrodynamic responses with respect to the placement of the floating breakwater are thoroughly discussed. The study performed will be helpful in the design and implementation of integrated VLFS-breakwater system, enhancing their robustness and safety in maritime environments.
{"title":"Hydroelastic analysis of VLFS integrated with porous floating box breakwater using multi-domain boundary element method","authors":"S. Hemanth, D. Karmakar","doi":"10.1016/j.marstruc.2024.103747","DOIUrl":"10.1016/j.marstruc.2024.103747","url":null,"abstract":"<div><div>The present study analyses the feasibility of integrating a Very Large Floating Structure (VLFS) with a porous floating box-type breakwater kept fixed in its position to analyze the hydroelastic responses within the integrated system based on linearized wave theory. The integrated VLFS-breakwater system, comprising the VLFS and the porous box-type breakwater assures in mitigating the structural effects induced by waves. The coupled Multi-Domain Boundary Element Method (MDBEM) and Finite Difference Method (FDM) are employed to investigate the performance of integrated VLFS-breakwater system. The computational framework employs the MDBEM to model the fluid domain and the floating breakwaters, while the VLFS is modeled using the FDM approach. The study considers three distinct relative positions of the VLFS integrated with a floating breakwater on (i) the leeside, (ii) the seaside, and (iii) on both leeside and seaside of the VLFS. The numerical study is performed based on thin-plate theory and small amplitude wave theory. The study corroborates its numerical findings with existing literature, supporting the validity of its methodology. The integrated system effectively reduces forces acting on the VLFS by absorbing the primary impact of waves. Consequently, the hydroelastic response of the VLFS is reduced, preserving its structural integrity and enhancing overall safety. The study signifies the importance of integrating the porous box-type breakwater with the VLFS. The importance of the orientation of the structure towards the sea waves, the porosity of the breakwater, the effect of relative spacing between the breakwater and VLFS and variations in hydrodynamic responses with respect to the placement of the floating breakwater are thoroughly discussed. The study performed will be helpful in the design and implementation of integrated VLFS-breakwater system, enhancing their robustness and safety in maritime environments.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"101 ","pages":"Article 103747"},"PeriodicalIF":4.0,"publicationDate":"2024-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143147680","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 : 2024-12-07DOI: 10.1016/j.marstruc.2024.103733
Shiyuan Zhang , Shixiao Fu , Zhiyuan Pan , Kaijia Han , Yusong Ye
A hydroelastic analysis method for flexible ships with forward speed is developed based on the beam-connected-discrete-modules (BCDM) approach. In this method, the flexible ship is first discretized into multiple rigid modules connected by a hull girder, thereby establishing the hydroelastic analysis model. The time-domain Rankine source method, which incorporates steady flow through the double body flow model, is employed to calculate the hydrodynamic forces acting on the multi-module system. The subsequent application of Fourier transformation facilitates the conversion of these forces into the frequency domain, where they are coupled with the structural stiffness of the hull girder to formulate the hydroelastic equations for advancing ships. Additionally, the time-domain hydroelastic equation is derived based on Cummins’ equation. The validity of the proposed method is conducted by comparing the zero-speed hydroelastic responses and the motions of advancing ships with the published data and numerical results from commercial software. Furthermore, the global responses of both flexible and rigid ships under varying forward speed conditions are thoroughly investigated. The results demonstrate that the flexible deformation plays a crucial role in the global responses of advancing ships, and hydrodynamic forces associated with forward speed have significant contribution to the hydroelastic responses.
{"title":"Springing responses of ships with forward speed based on a multi-module hydroelastic method","authors":"Shiyuan Zhang , Shixiao Fu , Zhiyuan Pan , Kaijia Han , Yusong Ye","doi":"10.1016/j.marstruc.2024.103733","DOIUrl":"10.1016/j.marstruc.2024.103733","url":null,"abstract":"<div><div>A hydroelastic analysis method for flexible ships with forward speed is developed based on the beam-connected-discrete-modules (BCDM) approach. In this method, the flexible ship is first discretized into multiple rigid modules connected by a hull girder, thereby establishing the hydroelastic analysis model. The time-domain Rankine source method, which incorporates steady flow through the double body flow model, is employed to calculate the hydrodynamic forces acting on the multi-module system. The subsequent application of Fourier transformation facilitates the conversion of these forces into the frequency domain, where they are coupled with the structural stiffness of the hull girder to formulate the hydroelastic equations for advancing ships. Additionally, the time-domain hydroelastic equation is derived based on Cummins’ equation. The validity of the proposed method is conducted by comparing the zero-speed hydroelastic responses and the motions of advancing ships with the published data and numerical results from commercial software. Furthermore, the global responses of both flexible and rigid ships under varying forward speed conditions are thoroughly investigated. The results demonstrate that the flexible deformation plays a crucial role in the global responses of advancing ships, and hydrodynamic forces associated with forward speed have significant contribution to the hydroelastic responses.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"101 ","pages":"Article 103733"},"PeriodicalIF":4.0,"publicationDate":"2024-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143147662","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 : 2024-12-04DOI: 10.1016/j.marstruc.2024.103726
Yerong Zhang, Yongchang Pu, Zhiqiang Hu
For some types of special-purpose marine vessels, such as dredgers, the variation of mass onboard derived from their working conditions may induce unforeseen loads within a short time, which will lead to unexpected structural responses and fatigue damage. For dredgers, additional loads induced by the mass-variation in their specific working conditions are of significant concern and have not been effectively considered during the design stage. This paper proposes a mathematical and numerical model for structural dynamic analysis of variable cross-section hull girder with time-varying mass characteristics. It leverages the modified Euler-Bernoulli beam theory to accommodate variable mass functions and employs a semi-analytical approach for the analysis of vibration characteristics in the variable cross-section beam. The excitation loads acting on the hull girder are composed of engine loads, propeller loads, and hydrodynamic loads respectively defined in the dynamic model. Furthermore, an improved Kane's dynamic equation is integrated into the mathematical and numerical model, tailored for time-varying mass systems, serving as the primary dynamic solver module. A customized program, written in FORTRAN language, is developed based on the proposed model. In addition, a user-defined case study is given in this paper. The varying wet surface and trim characteristics of the ship hull within a short period are also taken into consideration via dividing wet surface into ten shifting waterlines and loading conditions in variable mass properties. Hydrodynamic analysis results pre-calculated by SESAM are transferred into the program. Finally, dynamic response results including displacement and angular responses of each pre-defined rigid cross-section in the hull girder are generated by the self-developed program, which can be used for further FEA analysis to achieve detailed stress and deformation results. The proposed mathematical and numerical model can be used in the design stage for ships and offshore vessels that have time-varying mass features to evaluate their special structural responses during variable mass operations.
{"title":"A mathematical and numerical model for variable cross-section hull girder with time-varying mass systems applied in marine vessels","authors":"Yerong Zhang, Yongchang Pu, Zhiqiang Hu","doi":"10.1016/j.marstruc.2024.103726","DOIUrl":"10.1016/j.marstruc.2024.103726","url":null,"abstract":"<div><div>For some types of special-purpose marine vessels, such as dredgers, the variation of mass onboard derived from their working conditions may induce unforeseen loads within a short time, which will lead to unexpected structural responses and fatigue damage. For dredgers, additional loads induced by the mass-variation in their specific working conditions are of significant concern and have not been effectively considered during the design stage. This paper proposes a mathematical and numerical model for structural dynamic analysis of variable cross-section hull girder with time-varying mass characteristics. It leverages the modified Euler-Bernoulli beam theory to accommodate variable mass functions and employs a semi-analytical approach for the analysis of vibration characteristics in the variable cross-section beam. The excitation loads acting on the hull girder are composed of engine loads, propeller loads, and hydrodynamic loads respectively defined in the dynamic model. Furthermore, an improved Kane's dynamic equation is integrated into the mathematical and numerical model, tailored for time-varying mass systems, serving as the primary dynamic solver module. A customized program, written in FORTRAN language, is developed based on the proposed model. In addition, a user-defined case study is given in this paper. The varying wet surface and trim characteristics of the ship hull within a short period are also taken into consideration via dividing wet surface into ten shifting waterlines and loading conditions in variable mass properties. Hydrodynamic analysis results pre-calculated by SESAM are transferred into the program. Finally, dynamic response results including displacement and angular responses of each pre-defined rigid cross-section in the hull girder are generated by the self-developed program, which can be used for further FEA analysis to achieve detailed stress and deformation results. The proposed mathematical and numerical model can be used in the design stage for ships and offshore vessels that have time-varying mass features to evaluate their special structural responses during variable mass operations.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"101 ","pages":"Article 103726"},"PeriodicalIF":4.0,"publicationDate":"2024-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143146728","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 : 2024-11-29DOI: 10.1016/j.marstruc.2024.103732
Shi Song , Sören Ehlers , Franz von Bock und Polach , Moritz Braun
Ultra-low cycle fatigue (ULCF) refers to material failure at small number of loading cycles. For large complex structures like ships, the damage from ULCF can bring hazardous consequences. In this study, an alternately-cyclically loaded four-point bending test of a large box girder is introduced as the specimen to represent the ULCF of ship hull structure. In every load during the test, large deformation is applied to the specimen even after reaching its ultimate hull girder strength (UHGS), thus extensive plastic deformation and obvious fracture can occur in the specimen. The severely damaged specimen is further tested until 1.5 cycles of bending are finished, thus the test of post-damage box girder is realized. Moreover, the box girder is divided into 3 sub-sections, which show different but still interacting structural behavior. The result of the test shows the structural behavior of a large complex structure suffering severe damage during alternate hogging and sagging after reaching its UHGS, which corresponds to the consequence of ULCF. The presented ULCF test also provides experiences for investigations of large complex structures with existing damages or after accidental loads. Considering the number of cycles in the test, this study can bridge the gap between monotonic overload and ultra-low cycle fatigue.
{"title":"Ultra-low cycle fatigue of ship hull structure – an alternately-cyclically loaded four-point bending test of a large box girder","authors":"Shi Song , Sören Ehlers , Franz von Bock und Polach , Moritz Braun","doi":"10.1016/j.marstruc.2024.103732","DOIUrl":"10.1016/j.marstruc.2024.103732","url":null,"abstract":"<div><div>Ultra-low cycle fatigue (ULCF) refers to material failure at small number of loading cycles. For large complex structures like ships, the damage from ULCF can bring hazardous consequences. In this study, an alternately-cyclically loaded four-point bending test of a large box girder is introduced as the specimen to represent the ULCF of ship hull structure. In every load during the test, large deformation is applied to the specimen even after reaching its ultimate hull girder strength (UHGS), thus extensive plastic deformation and obvious fracture can occur in the specimen. The severely damaged specimen is further tested until 1.5 cycles of bending are finished, thus the test of post-damage box girder is realized. Moreover, the box girder is divided into 3 sub-sections, which show different but still interacting structural behavior. The result of the test shows the structural behavior of a large complex structure suffering severe damage during alternate hogging and sagging after reaching its UHGS, which corresponds to the consequence of ULCF. The presented ULCF test also provides experiences for investigations of large complex structures with existing damages or after accidental loads. Considering the number of cycles in the test, this study can bridge the gap between monotonic overload and ultra-low cycle fatigue.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"100 ","pages":"Article 103732"},"PeriodicalIF":4.0,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142745634","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.marstruc.2024.103728
Guangsi Chen, Hao Gu, Run Liu, Tianliang Li, Chao Liang
Pile-bucket composite foundations are regarded as a promising solution for offshore wind power infrastructure. However, accurately assessing their vertical ultimate bearing capacity remains a technical challenge. Therefore, establishing an upper bound solution of the ultimate bearing capacity of the composite foundations is of significant importance for their promotion and application. This study begins with small-scale model tests, using Abaqus for modeling based on the relevant test conditions. Next, following model validation, the vertical bearing capacity of the composite foundations under different H/D ratios and the corresponding soil failure modes are investigated. According to the upper limit method and the ultimate equilibrium theory, the kinematic velocity field is subsequently constructed to derive the upper bound solution of the vertical bearing capacity. Finally, the effectiveness and accuracy of the proposed theoretical upper bound solution are verified against the results of model tests, and this study hopes to provide a reference for the future design of vertical bearing capacity of pile-bucket composite foundations.
{"title":"Upper bound solution of the vertical bearing capacity of the pile-bucket composite foundation of offshore wind turbines","authors":"Guangsi Chen, Hao Gu, Run Liu, Tianliang Li, Chao Liang","doi":"10.1016/j.marstruc.2024.103728","DOIUrl":"10.1016/j.marstruc.2024.103728","url":null,"abstract":"<div><div>Pile-bucket composite foundations are regarded as a promising solution for offshore wind power infrastructure. However, accurately assessing their vertical ultimate bearing capacity remains a technical challenge. Therefore, establishing an upper bound solution of the ultimate bearing capacity of the composite foundations is of significant importance for their promotion and application. This study begins with small-scale model tests, using Abaqus for modeling based on the relevant test conditions. Next, following model validation, the vertical bearing capacity of the composite foundations under different <em>H/D</em> ratios and the corresponding soil failure modes are investigated. According to the upper limit method and the ultimate equilibrium theory, the kinematic velocity field is subsequently constructed to derive the upper bound solution of the vertical bearing capacity. Finally, the effectiveness and accuracy of the proposed theoretical upper bound solution are verified against the results of model tests, and this study hopes to provide a reference for the future design of vertical bearing capacity of pile-bucket composite foundations.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"100 ","pages":"Article 103728"},"PeriodicalIF":4.0,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142699126","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 : 2024-11-25DOI: 10.1016/j.marstruc.2024.103724
Ikjae Lee , Moohyun Kim , Chungkuk Jin
In this study, we investigated the impact of the hull flexibility of 15MW spar-type FOWT (floating offshore wind turbine) on the global dynamics/performance analysis. Until recently, the rigid hull (floating foundation) model with flexible tower and RNA (rotor-nacelle assembly) has been used as industry standard procedure in the global performance analysis of FOWTs. Since the FOWT size continues to increase beyond 20MW, there has been increasing concern of the effect of hull flexibility on its global performance. The present study is intended to provide representative insights on this subject. Global performance analysis of the 15MW WindCrete spar is examined based on the conventional hull-rigid and the DMB (discrete-module-beam) models including hull flexibility. Coupled aero-hydro-servo-elastic-mooring dynamic simulations were carried out with the rigid-hull and DMB (discrete-module-beam) models under various combinations of irregular waves, sheared currents, and full-field turbulent winds. The lowest fore-aft bending-mode natural frequency is shifted toward lower frequency from 0.52 to 0.41 Hz after including hull flexibility. Platform rigid 6-DOF (degree-of-freedom) motions and mooring tensions by the DMB model are little changed but nacelle horizontal accelerations and tower-base bending moments may be appreciably increased compared to the rigid-hull model.
{"title":"Impact of hull flexibility on the global performance of a 15 MW concrete-spar floating offshore wind turbine","authors":"Ikjae Lee , Moohyun Kim , Chungkuk Jin","doi":"10.1016/j.marstruc.2024.103724","DOIUrl":"10.1016/j.marstruc.2024.103724","url":null,"abstract":"<div><div>In this study, we investigated the impact of the hull flexibility of 15MW spar-type FOWT (floating offshore wind turbine) on the global dynamics/performance analysis. Until recently, the rigid hull (floating foundation) model with flexible tower and RNA (rotor-nacelle assembly) has been used as industry standard procedure in the global performance analysis of FOWTs. Since the FOWT size continues to increase beyond 20MW, there has been increasing concern of the effect of hull flexibility on its global performance. The present study is intended to provide representative insights on this subject. Global performance analysis of the 15MW WindCrete spar is examined based on the conventional hull-rigid and the DMB (discrete-module-beam) models including hull flexibility. Coupled aero-hydro-servo-elastic-mooring dynamic simulations were carried out with the rigid-hull and DMB (discrete-module-beam) models under various combinations of irregular waves, sheared currents, and full-field turbulent winds. The lowest fore-aft bending-mode natural frequency is shifted toward lower frequency from 0.52 to 0.41 Hz after including hull flexibility. Platform rigid 6-DOF (degree-of-freedom) motions and mooring tensions by the DMB model are little changed but nacelle horizontal accelerations and tower-base bending moments may be appreciably increased compared to the rigid-hull model.</div></div>","PeriodicalId":49879,"journal":{"name":"Marine Structures","volume":"100 ","pages":"Article 103724"},"PeriodicalIF":4.0,"publicationDate":"2024-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142699164","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 : 2024-11-23DOI: 10.1016/j.marstruc.2024.103727
Bruno Thierry Nyatchouba Nsangue , Hao Tang , Ruben Mouangue , Wei Liu , Achille Njomoue Pandong , Liuxiong Xu , Fuxiang Hu , Leopold Tcham
Although adopting the T90 mesh orientation on the trawl net can improve the selectivity of the trawl codend, it is unknown whether the T90 mesh orientation influences the dynamic behavior of the trawl system. Therefore, this study uses non-linear dynamic analysis to examine the effect of mesh orientations, mesh size, and twine diameter on the mesopelagic trawls' fluttering motions and hydrodynamic force responses. Three trawls are designed with different mesh orientations (T0 and T90), mesh sizes (40 mm and 60 mm), and twine diameters (0.96 mm and 1.11 mm) on the codend and codend extension sections of the trawl model based on Tauti's law. These trawls are tested in a flume tank under various flow velocities and catch sizes. A time-frequency analysis method based on the Hilbert–Huang transform is utilized to analyze each trawl's dynamic responses, including motions and drag force responses. The results are compared with those obtained through Fourier analysis using power spectral density. The results highlight that the oscillation amplitude of the surge motion of the T90 trawl is higher than that of the T0 trawl. In contrast, the T90 trawl's heave motion oscillation amplitude is smaller. The dominant frequency of the periodic high-energy coherent structures of the surge and heave motions are detected at a low frequency. The surge and heave motions of the T0 trawl have a greater response to the current components with lower frequencies than that of the T90 trawl. An increase in mesh size, a decrease in twine diameter, and a change in mesh orientation decrease the drag force. The inherent characteristic oscillations of the drag force response for the three trawl models are synchronized with the low-frequency characteristic of surge and heave motions. The gravity periods of the low-frequency mode components of drag force, surge motion, and heave motion for the T90 trawl are higher than those for the T0 trawls. In other words, the T90 trawl is more stable and selective than the T0 trawl. The findings of this study offer important information for comprehending and enhancing the selectivity of trawls in marine mesopelagic fisheries, particularly for exposing the effects of mesh orientation and design parameters on trawl performances.
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