Takaaki Takeuchi, T. Utsunomiya, K. Gotoh, I. Sato
For the development of floating offshore wind turbines (FOWTs) in Japan, reliability assessment and cost reduction by efficient maintenance on mooring chains are part of the key issues because sites deeper than 60 m require mooring systems for station keeping. In this paper, attempts have been made to simplify the wear estimation method which was previously proposed by using a 3-D rigid-body link model for improvement of accuracy. These investigations are performed about a spar-type floating structure moored with three catenary lines at Goto, Nagasaki prefecture, Japan. In the previous study, it was confirmed that the estimation method using the 3-D link model can calculate the interlink wear amount closer to the chain diameter measurements and more reasonable than the method using the conventional mass-spring model by removing the rolling distance from the displacement of contact points. However, the estimation method has technical difficulty in terms of calculation of contact properties and analysis costs for the mooring chain design. For this reason, the wear estimation method is simplified and verified by considering the rolling motion between mooring chain links modeled by the widely employed mass-spring model based on the method proposed by Mooring Integrity JIP. Firstly, the wear due to the rolling is reproduced by a three-dimensional FE analysis to investigate the actual wear phenomenon including the effect of the proof load test as well as the idealized configuration. Secondly, the application method is proposed against the response of the mooring chain subjected to irregular waves Finally, a comparison with the measurement is conducted to verify the proposed wear estimation method.
{"title":"Development of Simplified Wear Estimation Method Considering Rolling Motion Between Mooring Chain Links for Floating Structures","authors":"Takaaki Takeuchi, T. Utsunomiya, K. Gotoh, I. Sato","doi":"10.1115/omae2021-62574","DOIUrl":"https://doi.org/10.1115/omae2021-62574","url":null,"abstract":"\u0000 For the development of floating offshore wind turbines (FOWTs) in Japan, reliability assessment and cost reduction by efficient maintenance on mooring chains are part of the key issues because sites deeper than 60 m require mooring systems for station keeping. In this paper, attempts have been made to simplify the wear estimation method which was previously proposed by using a 3-D rigid-body link model for improvement of accuracy. These investigations are performed about a spar-type floating structure moored with three catenary lines at Goto, Nagasaki prefecture, Japan.\u0000 In the previous study, it was confirmed that the estimation method using the 3-D link model can calculate the interlink wear amount closer to the chain diameter measurements and more reasonable than the method using the conventional mass-spring model by removing the rolling distance from the displacement of contact points. However, the estimation method has technical difficulty in terms of calculation of contact properties and analysis costs for the mooring chain design. For this reason, the wear estimation method is simplified and verified by considering the rolling motion between mooring chain links modeled by the widely employed mass-spring model based on the method proposed by Mooring Integrity JIP. Firstly, the wear due to the rolling is reproduced by a three-dimensional FE analysis to investigate the actual wear phenomenon including the effect of the proof load test as well as the idealized configuration. Secondly, the application method is proposed against the response of the mooring chain subjected to irregular waves Finally, a comparison with the measurement is conducted to verify the proposed wear estimation method.","PeriodicalId":269406,"journal":{"name":"Volume 5: Ocean Space Utilization","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131469271","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Vegard J. Berge, Christoffer R. Helgesen, Dimitar Z. Ivanov, Marianne H. Jahren, Pauline S. Opstad, Petter S. Sletten, A. Nejad
The main aim of this article is to study and evaluate existing and potential lifting technologies used in deep sea mining. The lifting is an energy intensive operation and can be decisive if a mining operation is feasible or not. An additional goal for this study was to see if it can be rewarding to utilise the potential energy in the returned masses, because the excess material has to be returned to the ocean bottom so that no microorganisms would be released on the ocean surface. After a general study of possible solutions, regulations and existing projects, the technologies further explored in this study include an in-line pump system, a tubular-disc conveyor and a bucket conveyor, all with modifications to suit deep sea mining. To compare different lifting technologies an estimate for power consumption to lift the mined material from 1000 m depth at three different rates, namely 75, 150, 300 tons/hour, is considered. To calculate the power requirements realistic system parameters are considered and internal system resistance are also taken into account. The results show that the power consumption for the tubular and bucket conveyor are almost in the same range, while the pump system requires about two to three times more power than them. This indicates that there are feasible alternatives to hydraulic lifting by adapting existing onshore based technologies for deep sea mining.
{"title":"On State-of-the-Art and Alternative Energy-Efficient Lifting Technologies for Deep Sea Mining","authors":"Vegard J. Berge, Christoffer R. Helgesen, Dimitar Z. Ivanov, Marianne H. Jahren, Pauline S. Opstad, Petter S. Sletten, A. Nejad","doi":"10.1115/omae2021-63844","DOIUrl":"https://doi.org/10.1115/omae2021-63844","url":null,"abstract":"\u0000 The main aim of this article is to study and evaluate existing and potential lifting technologies used in deep sea mining. The lifting is an energy intensive operation and can be decisive if a mining operation is feasible or not. An additional goal for this study was to see if it can be rewarding to utilise the potential energy in the returned masses, because the excess material has to be returned to the ocean bottom so that no microorganisms would be released on the ocean surface. After a general study of possible solutions, regulations and existing projects, the technologies further explored in this study include an in-line pump system, a tubular-disc conveyor and a bucket conveyor, all with modifications to suit deep sea mining. To compare different lifting technologies an estimate for power consumption to lift the mined material from 1000 m depth at three different rates, namely 75, 150, 300 tons/hour, is considered. To calculate the power requirements realistic system parameters are considered and internal system resistance are also taken into account. The results show that the power consumption for the tubular and bucket conveyor are almost in the same range, while the pump system requires about two to three times more power than them. This indicates that there are feasible alternatives to hydraulic lifting by adapting existing onshore based technologies for deep sea mining.","PeriodicalId":269406,"journal":{"name":"Volume 5: Ocean Space Utilization","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116937996","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. Hamada, Shoichi Morita, Ayumu Iiboshi, T. Hiraishi
The Anti-Tsunami Laboratory (ATL) invented and developed the Anti-Tsunami Door (ATD) barrier as an automatic tsunami barrier. In September 2018, ATL and Kyoto University tested a mid-scale model of a three-stage ATD unit and confirmed its performance: (1) functioning automatically (refer to Figure 9); (2) achieving reasonable wave height reduction, which is approximately 40%–80% that of a solid barrier of the same height; and (3) demonstrating reasonable strength for a wooden structure under the mid-scale model test conditions. ATL had planned to test a large-scale model of an ATD unit in Oregon State University in May 2020, but that test has been delayed owing to the COVID-19 pandemic. Because the wave pressure on the ATD unit is expected to be high during the large-scale model test, ATL requested that the Explosion Research Institute (ERI) simulate the wave pressure on a large-scale model ATD unit, and based on the results, ATL will reinforce the ATD unit. After testing the large-scale model unit, ATL will install ATD barriers along the coast of Japan, customizing the barrier for specific tsunami hazards.
{"title":"Automatic Tsunami Barrier","authors":"E. Hamada, Shoichi Morita, Ayumu Iiboshi, T. Hiraishi","doi":"10.1115/omae2021-62575","DOIUrl":"https://doi.org/10.1115/omae2021-62575","url":null,"abstract":"\u0000 The Anti-Tsunami Laboratory (ATL) invented and developed the Anti-Tsunami Door (ATD) barrier as an automatic tsunami barrier. In September 2018, ATL and Kyoto University tested a mid-scale model of a three-stage ATD unit and confirmed its performance: (1) functioning automatically (refer to Figure 9); (2) achieving reasonable wave height reduction, which is approximately 40%–80% that of a solid barrier of the same height; and (3) demonstrating reasonable strength for a wooden structure under the mid-scale model test conditions. ATL had planned to test a large-scale model of an ATD unit in Oregon State University in May 2020, but that test has been delayed owing to the COVID-19 pandemic. Because the wave pressure on the ATD unit is expected to be high during the large-scale model test, ATL requested that the Explosion Research Institute (ERI) simulate the wave pressure on a large-scale model ATD unit, and based on the results, ATL will reinforce the ATD unit. After testing the large-scale model unit, ATL will install ATD barriers along the coast of Japan, customizing the barrier for specific tsunami hazards.","PeriodicalId":269406,"journal":{"name":"Volume 5: Ocean Space Utilization","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114099531","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kazuki Murata, S. Sassa, T. Takagawa, T. Ebisuzaki, S. Maruyama
We first propose and examine a method for digitizing analog data of submarine topography by focusing on the seafloor survey records available in the literature to facilitate a detailed analysis of submarine landslides and landslide-induced tsunamis. Second, we apply this digitization method to the seafloor topographic changes recorded before and after the 1923 Great Kanto earthquake tsunami event and evaluate its effectiveness. Third, we discuss the coseismic large-scale seafloor deformation at the Sagami Bay and the mouth of the Tokyo Bay, Japan. The results confirmed that the latitude / longitude and water depth values recorded by the lead sounding measurement method can be approximately extracted from the sea depth coordinates by triangulation survey through the overlaying of the currently available GIS map data without geometric correction such as affine transformation. Further, this proposed method allows us to obtain mesh data of depth changes in the sea area by using the interpolation method based on the IDW (Inverse Distance Weighted) average method through its application to the case of the 1923 Great Kanto Earthquake. Finally, we analyzed and compared the submarine topography before and after the 1923 tsunami event and the current seabed topography. Consequently, we found that these large-scale depth changes correspond to the valley lines that flow down as the topography of the Sagami Bay and the Tokyo Bay mouth.
{"title":"Pre- and Post-Tsunami Depth Changes of Submarine Topography for the Analysis of Submarine Landslide-Induced Tsunami: Proposal of Digitization Method and Application to the Case of the 1923 Great Kanto Earthquake Tsunamis","authors":"Kazuki Murata, S. Sassa, T. Takagawa, T. Ebisuzaki, S. Maruyama","doi":"10.1115/omae2021-63096","DOIUrl":"https://doi.org/10.1115/omae2021-63096","url":null,"abstract":"\u0000 We first propose and examine a method for digitizing analog data of submarine topography by focusing on the seafloor survey records available in the literature to facilitate a detailed analysis of submarine landslides and landslide-induced tsunamis. Second, we apply this digitization method to the seafloor topographic changes recorded before and after the 1923 Great Kanto earthquake tsunami event and evaluate its effectiveness. Third, we discuss the coseismic large-scale seafloor deformation at the Sagami Bay and the mouth of the Tokyo Bay, Japan.\u0000 The results confirmed that the latitude / longitude and water depth values recorded by the lead sounding measurement method can be approximately extracted from the sea depth coordinates by triangulation survey through the overlaying of the currently available GIS map data without geometric correction such as affine transformation. Further, this proposed method allows us to obtain mesh data of depth changes in the sea area by using the interpolation method based on the IDW (Inverse Distance Weighted) average method through its application to the case of the 1923 Great Kanto Earthquake. Finally, we analyzed and compared the submarine topography before and after the 1923 tsunami event and the current seabed topography. Consequently, we found that these large-scale depth changes correspond to the valley lines that flow down as the topography of the Sagami Bay and the Tokyo Bay mouth.","PeriodicalId":269406,"journal":{"name":"Volume 5: Ocean Space Utilization","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125835795","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Gyroscopic motion is considered as an appropriate approach to suppress the shaking motion of rigid bodies. Its spatial orientation is also used to make gyro compasses in the marine industry. In this paper, the floating offshore wind turbine (FOWT) was designed based on potential theory and gyroscopic effect and rotational axis retention effect were also considered, so that FOWT could obtain better hydrodynamic response. However, gyroscopic motion was generated through an annular flow in the internal torus instead of rigid body rotation. The scale of torus and the angular velocity of the annular flow were the design parameters that this article was eager to understand obviously. By vast quantity of calculations, the suitable range of design parameters was obtained.
{"title":"Possibility of Reducing Spar-Type FOWT Hydrodynamic Response Using a Torus Structure With Annular Flow","authors":"M. Murai, Xiaolei Liu","doi":"10.1115/omae2021-62385","DOIUrl":"https://doi.org/10.1115/omae2021-62385","url":null,"abstract":"\u0000 Gyroscopic motion is considered as an appropriate approach to suppress the shaking motion of rigid bodies. Its spatial orientation is also used to make gyro compasses in the marine industry. In this paper, the floating offshore wind turbine (FOWT) was designed based on potential theory and gyroscopic effect and rotational axis retention effect were also considered, so that FOWT could obtain better hydrodynamic response. However, gyroscopic motion was generated through an annular flow in the internal torus instead of rigid body rotation. The scale of torus and the angular velocity of the annular flow were the design parameters that this article was eager to understand obviously. By vast quantity of calculations, the suitable range of design parameters was obtained.","PeriodicalId":269406,"journal":{"name":"Volume 5: Ocean Space Utilization","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127532709","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper aims to study the successive mooring line failure (also known as the domino effect) and the collision between floating collars for aquaculture net cages subjected to currents. The numerical model of this study is developed based on the Morison equation and the lumped-mass scheme in the time domain. This model is then applied to see if the domino effect of moorings will happen after releasing the anchor point #1 on the upstream side. In this study, we adopt four different current speeds (0.5, 1.0, 1.5, 2.0 m/s) and three different safety factors (SF, 1.0, 1.5, 2.0) settings to calculate the number of mooring failures, and to see whether it will cause floating collars collision. The results show that in the case of the SF is 2.0, the domino effect will not be triggered, and the floating collar collision will not occur. When the SF is 1.5, and the current speed is up to 1.0 m/s or higher, only the two anchor points on the upstream side will fail and no collision will occur. However, if the SF is not considered (that is, 1.0), the domino effect will occur under all the four current speeds, and the floating collar collision will all occur. Therefore, we suggest that in order to avoid the domino effect of the mooring system of aquaculture net cages from currents, the SF of the mooring system design must be at least 2 times.
{"title":"Hydrodynamic Behaviors of Aquaculture Net Cages After the Successive Mooring Lines Failure","authors":"H. Tang, Ray-Yeng Yang","doi":"10.1115/omae2021-62253","DOIUrl":"https://doi.org/10.1115/omae2021-62253","url":null,"abstract":"\u0000 This paper aims to study the successive mooring line failure (also known as the domino effect) and the collision between floating collars for aquaculture net cages subjected to currents. The numerical model of this study is developed based on the Morison equation and the lumped-mass scheme in the time domain. This model is then applied to see if the domino effect of moorings will happen after releasing the anchor point #1 on the upstream side. In this study, we adopt four different current speeds (0.5, 1.0, 1.5, 2.0 m/s) and three different safety factors (SF, 1.0, 1.5, 2.0) settings to calculate the number of mooring failures, and to see whether it will cause floating collars collision. The results show that in the case of the SF is 2.0, the domino effect will not be triggered, and the floating collar collision will not occur. When the SF is 1.5, and the current speed is up to 1.0 m/s or higher, only the two anchor points on the upstream side will fail and no collision will occur. However, if the SF is not considered (that is, 1.0), the domino effect will occur under all the four current speeds, and the floating collar collision will all occur. Therefore, we suggest that in order to avoid the domino effect of the mooring system of aquaculture net cages from currents, the SF of the mooring system design must be at least 2 times.","PeriodicalId":269406,"journal":{"name":"Volume 5: Ocean Space Utilization","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122246893","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An innovation in aquaculture fisheries around the world is in progress. More and more fish cages have been put into use to meet the needs of human for protein. However, the fish cage shows violent dynamic response and structural destruction while suffering to unpredictable marine environment. As the main component of the cage, floating collar plays an important role in providing buoyancy and ensuring the shape of cage. Thus, the dynamic response of the floating collar and the variation of flow field around the floating collar under extreme wave condition were studied in this paper. Referring to the previous literature, considering the motion form of the floating collar under waves, only the heave and pitch motions of the floating collar were obtained. Results obtained by Computational Fluid Dynamics method were compared with that obtained by potential flow theory. We found that the viscosity of the water has greater influence on heave motion of the floating collar rather than the pitch motion. At the same time, the flow field surrounding the floating collar was analyzed, and an overtopping phenomenon on both sides of the floating collar along the wave propagation direction was observed when the wave was passing through the floating collar.
{"title":"Dynamic Response and Flow Field Variation of a Floating Collar Under Extreme Wave Condition Using Computational Fluid Dynamics","authors":"Songchen Yu, Peng Li, Hongde Qin, Lingyun Xu","doi":"10.1115/omae2021-64384","DOIUrl":"https://doi.org/10.1115/omae2021-64384","url":null,"abstract":"\u0000 An innovation in aquaculture fisheries around the world is in progress. More and more fish cages have been put into use to meet the needs of human for protein. However, the fish cage shows violent dynamic response and structural destruction while suffering to unpredictable marine environment. As the main component of the cage, floating collar plays an important role in providing buoyancy and ensuring the shape of cage. Thus, the dynamic response of the floating collar and the variation of flow field around the floating collar under extreme wave condition were studied in this paper. Referring to the previous literature, considering the motion form of the floating collar under waves, only the heave and pitch motions of the floating collar were obtained. Results obtained by Computational Fluid Dynamics method were compared with that obtained by potential flow theory. We found that the viscosity of the water has greater influence on heave motion of the floating collar rather than the pitch motion. At the same time, the flow field surrounding the floating collar was analyzed, and an overtopping phenomenon on both sides of the floating collar along the wave propagation direction was observed when the wave was passing through the floating collar.","PeriodicalId":269406,"journal":{"name":"Volume 5: Ocean Space Utilization","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129236472","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A novel subsea shuttle tanker (SST) concept was recently proposed as a cost-effective alternative to subsea pipelines and tanker ships for liquid CO2 transportation between a source facility and a subsea well. It is envisioned that the SST will be deployed to transport CO2 to marginal subsea fields with an annual CO2 storage capacity less than 1 million metric tons; volumes that do not justify a full subsea field development. The SST is designed to be a fully autonomous underwater vessel with a cargo capacity of over 17,000 metric tons. It is 155 m long and it has a 17 m diameter hull. The vessel may operate at a water depth of between 50 to 200 m in a weather-independent environment. Furthermore, it travels at a slow speed for minimal energy consumption and maximal range. During the offloading process, the SST will approach the subsea well and land on the seabed just outside the safety radius of the well. After that, a remotely operated vehicle (ROV) will mate the offloading flowline to the SST, and the offloading process will start. The landing sequence is technically challenging for various reasons and warrants detailed analysis. First, the SST would have limited manoeuvrability due to the large inertia of the vessel and low effectiveness of the hydroplanes to provide steering at low speeds. Second, during the final phase before the SST lands, seabed boundary effects will intensify and lead to increased non-uniform, time-varying and drag-dominated load-effects. Third, the impact forces during landing should be minimised to allow for the lowest design load. Solving these technical challenges is crucial to meet SST’s design goals of having the least possible control appendices for maximum efficiency/range, and minimal structural weight for the largest cargo capacity. This paper will describe the development of a fully coupled 2D planar model that considers the most relevant load-effects. This model is developed with the feasibility to implement any control schemes and has the potential to plug observers or control modules in future study. This paper performs open loop test and applies simple control cases to explore the depth control in landing sequence. A feed-forward heading control method that achieves the fastest control response and best path following ability is then proposed based on the results obtained.
{"title":"Depth Control Modelling and Analysis of a Subsea Shuttle Tanker","authors":"Yucong Ma, D. Sui, Y. Xing, M. Ong, T. Hemmingsen","doi":"10.1115/omae2021-61827","DOIUrl":"https://doi.org/10.1115/omae2021-61827","url":null,"abstract":"\u0000 A novel subsea shuttle tanker (SST) concept was recently proposed as a cost-effective alternative to subsea pipelines and tanker ships for liquid CO2 transportation between a source facility and a subsea well. It is envisioned that the SST will be deployed to transport CO2 to marginal subsea fields with an annual CO2 storage capacity less than 1 million metric tons; volumes that do not justify a full subsea field development. The SST is designed to be a fully autonomous underwater vessel with a cargo capacity of over 17,000 metric tons. It is 155 m long and it has a 17 m diameter hull. The vessel may operate at a water depth of between 50 to 200 m in a weather-independent environment. Furthermore, it travels at a slow speed for minimal energy consumption and maximal range. During the offloading process, the SST will approach the subsea well and land on the seabed just outside the safety radius of the well. After that, a remotely operated vehicle (ROV) will mate the offloading flowline to the SST, and the offloading process will start. The landing sequence is technically challenging for various reasons and warrants detailed analysis. First, the SST would have limited manoeuvrability due to the large inertia of the vessel and low effectiveness of the hydroplanes to provide steering at low speeds. Second, during the final phase before the SST lands, seabed boundary effects will intensify and lead to increased non-uniform, time-varying and drag-dominated load-effects. Third, the impact forces during landing should be minimised to allow for the lowest design load. Solving these technical challenges is crucial to meet SST’s design goals of having the least possible control appendices for maximum efficiency/range, and minimal structural weight for the largest cargo capacity. This paper will describe the development of a fully coupled 2D planar model that considers the most relevant load-effects. This model is developed with the feasibility to implement any control schemes and has the potential to plug observers or control modules in future study. This paper performs open loop test and applies simple control cases to explore the depth control in landing sequence. A feed-forward heading control method that achieves the fastest control response and best path following ability is then proposed based on the results obtained.","PeriodicalId":269406,"journal":{"name":"Volume 5: Ocean Space Utilization","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134007438","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shuchuang Dong, Jinxin Zhou, Qiao Li, Takero Yoshida, D. Kitazawa
In the present study, three flexible net cage groups (a single net cage, two net cages arrayed in one column, and three net cages arrayed in one column) were investigated in a flume tank, in order to analyze the hydrodynamic characteristics of the flow and linked flexible net cage, such as the drag force, cage deformation, and flow field inside and around. Based on these results, the fluid-structure interactions of the flexible net cage were discussed. The drag forces and cage deformation of a single flexible net cage were first studied, and their relationships to the current speed were found consistent with existing literature. The averaged current speed inside the single net cage was 0.72 for all incoming current speeds. Furthermore, significant current speed reductions occurred behind the single net cage, at the downstream, for all incoming current speeds. Within the measurement range, the current speed reduction area downstream from the single net cage was almost as wide as the cage diameter, and the length was up to 1.4 times cage diameters along the incoming current direction. The location of this area gradually approached the water surface as the current speed increased. In the case of two flexible net cages arrayed in one column, the differences in drag force occurred when the distance between the two cages was changed. In addition, the current speed incident on the downstream cage tended to decrease, as the distance between the cages increased. The averaged current speeds incident on the downstream cage were 0.54, 0.44, 0.77, and 0.40 when the distances between two cages were 30.0 cm, 60.0 cm, and 90.0 cm, respectively. In the case of three flexible net cages arrayed in one column, the total drag force of three flexible net cages was 2.2 times that of a single net cage. On the other hand, at the maximum current speed of 50 cm/s, the cross-sectional areas of the first net cage, the second net cage, and the third net cage were 177.10 cm2, 274.19 cm2, and 277.37 cm2, respectively. Overall, the findings of this study could not only help to understand and optimize flexible net cage structures but also provide useful information for the configuration of the net cages at the farm sites.
{"title":"Experimental Investigation of Fluid-Structure Interaction in Linked Flexible Net Cages","authors":"Shuchuang Dong, Jinxin Zhou, Qiao Li, Takero Yoshida, D. Kitazawa","doi":"10.1115/omae2021-62266","DOIUrl":"https://doi.org/10.1115/omae2021-62266","url":null,"abstract":"\u0000 In the present study, three flexible net cage groups (a single net cage, two net cages arrayed in one column, and three net cages arrayed in one column) were investigated in a flume tank, in order to analyze the hydrodynamic characteristics of the flow and linked flexible net cage, such as the drag force, cage deformation, and flow field inside and around. Based on these results, the fluid-structure interactions of the flexible net cage were discussed. The drag forces and cage deformation of a single flexible net cage were first studied, and their relationships to the current speed were found consistent with existing literature. The averaged current speed inside the single net cage was 0.72 for all incoming current speeds. Furthermore, significant current speed reductions occurred behind the single net cage, at the downstream, for all incoming current speeds. Within the measurement range, the current speed reduction area downstream from the single net cage was almost as wide as the cage diameter, and the length was up to 1.4 times cage diameters along the incoming current direction. The location of this area gradually approached the water surface as the current speed increased. In the case of two flexible net cages arrayed in one column, the differences in drag force occurred when the distance between the two cages was changed. In addition, the current speed incident on the downstream cage tended to decrease, as the distance between the cages increased. The averaged current speeds incident on the downstream cage were 0.54, 0.44, 0.77, and 0.40 when the distances between two cages were 30.0 cm, 60.0 cm, and 90.0 cm, respectively. In the case of three flexible net cages arrayed in one column, the total drag force of three flexible net cages was 2.2 times that of a single net cage. On the other hand, at the maximum current speed of 50 cm/s, the cross-sectional areas of the first net cage, the second net cage, and the third net cage were 177.10 cm2, 274.19 cm2, and 277.37 cm2, respectively. Overall, the findings of this study could not only help to understand and optimize flexible net cage structures but also provide useful information for the configuration of the net cages at the farm sites.","PeriodicalId":269406,"journal":{"name":"Volume 5: Ocean Space Utilization","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123359153","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yusuke Yamamoto, Taishi Morimoto, T. Katayama, M. Goto, Ryo Kodama
The purpose of this study is to propose an optimal design method of the spar-buoy with ring-fin motion stabilizer for shallow sea and its mooring system, in order to avoid the occurrence of snap load. The mechanism of occurrence of snap load is investigated by model tests, and design parameters for avoiding the occurrence of snap load are investigated. From the observation of model’s motion, it has been realized that the snap load is caused by the tension of mooring line to stop the buoy’s horizontal motion, which relaxes the mooring line. Moreover, it has been confirmed that the horizontal motion is caused by the horizontal forces acting on the center pipe and float of the buoy, which relates to the acceleration component of wave excitation forces. In this paper, the effects of changing of design of the buoy (: diameter of center pipe and float, size of stabilizer, density of the buoy, length of mooring line) on avoiding or reducing snap load are investigated by using a numerical simulation (OrcaFlexver.11.0b), and the wear amounts are also estimated by using an empirical method (Takeuchi et al., 2019). From the results, it is confirmed that changing the buoy’s motion mode by shortening mooring line is effective to avoiding the occurrence of snap load, and to reduce the wear amount of the mooring line.
本研究的目的是提出一种浅海用带环鳍运动稳定器的桅杆浮标及其系泊系统的优化设计方法，以避免突然载荷的发生。通过模型试验研究了弹击荷载的产生机理，探讨了避免弹击荷载产生的设计参数。通过对模型运动的观察，认识到系泊线的张力引起的弹跳载荷使浮标的水平运动停止，从而使系泊线松弛。此外，还证实了水平运动是由作用在浮标中心管和浮子上的水平力引起的，这与波浪激振力的加速度分量有关。本文通过数值模拟(orca - lexver.11.0b)研究了改变浮筒设计(中心管和浮筒直径、稳定器尺寸、浮筒密度、系泊绳长度)对避免或减少卡箍载荷的影响，并采用经验方法估算了磨损量(Takeuchi et al.， 2019)。结果表明，通过缩短系泊线来改变浮筒的运动方式，可以有效地避免弹跳载荷的发生，减少系泊线的磨损量。
{"title":"Effects of Design Parameter on Occurrence of Snap Load and Wear of Mooring Line for Spar-Buoy With Ring-Fin Motion Stabilizer for Shallow Sea","authors":"Yusuke Yamamoto, Taishi Morimoto, T. Katayama, M. Goto, Ryo Kodama","doi":"10.1115/omae2021-62337","DOIUrl":"https://doi.org/10.1115/omae2021-62337","url":null,"abstract":"\u0000 The purpose of this study is to propose an optimal design method of the spar-buoy with ring-fin motion stabilizer for shallow sea and its mooring system, in order to avoid the occurrence of snap load. The mechanism of occurrence of snap load is investigated by model tests, and design parameters for avoiding the occurrence of snap load are investigated. From the observation of model’s motion, it has been realized that the snap load is caused by the tension of mooring line to stop the buoy’s horizontal motion, which relaxes the mooring line. Moreover, it has been confirmed that the horizontal motion is caused by the horizontal forces acting on the center pipe and float of the buoy, which relates to the acceleration component of wave excitation forces.\u0000 In this paper, the effects of changing of design of the buoy (: diameter of center pipe and float, size of stabilizer, density of the buoy, length of mooring line) on avoiding or reducing snap load are investigated by using a numerical simulation (OrcaFlexver.11.0b), and the wear amounts are also estimated by using an empirical method (Takeuchi et al., 2019). From the results, it is confirmed that changing the buoy’s motion mode by shortening mooring line is effective to avoiding the occurrence of snap load, and to reduce the wear amount of the mooring line.","PeriodicalId":269406,"journal":{"name":"Volume 5: Ocean Space Utilization","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131614978","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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