The amount of green water and the associated loads that an ocean-going vessel may encounter during its service life are important aspects to consider in the vessel’s design and classification. As green water is typically a highly non-linear phenomenon, commonly the maritime industry relies on model tests to predict green water loads and their occurrence. In recent years, however, a lot of progress with Computation Fluid Dynamics (CFD) has been made in predicting non-linear flows and associated loads at a high level of accuracy. Especially in the field of wave impacts on (moored) offshore structures at zero speed, significant progress has been made and documented using CFD. A natural extension of this progress is to expand the obtained confidence in the applicability of CFD for simulating extreme wave events to applications involving vessels at forward speed. To that end, this paper presents a validation study towards the prediction of green water loading on a (typical) container vessel at forward speed by CFD. For validation, two extreme green water events were selected from a model test campaign carried out at MARIN within the context of the CRS (Cooperative Research Ships) working group ‘green water dynamics’. In these tests a KRISO Container Ship (KCS) is sailing in head seas when encountering severe green water. As CFD tool, the Cartesian-grid based Volume-of-Fluid CFD solver ComFLOW was selected. Furthermore, a deterministic approach is taken for the validation, by reconstructing the non-linear incoming wave in a high amount of detail and imposing the 6 degrees of motion of the vessel using the wave basin measurements. Time traces of the green water flow on deck and local- and global impact loads on the breakwater are presented and compared against the experimental data. Detailed visualizations of the CFD results are presented to further illustrate the obtained match with the model test results and emphasize the additional value of complementing model tests with deterministic CFD analysis.
{"title":"On the Validity of CFD for Simulating Extreme Green Water Loads on Ocean-Going Vessels","authors":"Henry Bandringa, J. Helder, Sanne van Essen","doi":"10.1115/omae2020-18290","DOIUrl":"https://doi.org/10.1115/omae2020-18290","url":null,"abstract":"\u0000 The amount of green water and the associated loads that an ocean-going vessel may encounter during its service life are important aspects to consider in the vessel’s design and classification. As green water is typically a highly non-linear phenomenon, commonly the maritime industry relies on model tests to predict green water loads and their occurrence. In recent years, however, a lot of progress with Computation Fluid Dynamics (CFD) has been made in predicting non-linear flows and associated loads at a high level of accuracy. Especially in the field of wave impacts on (moored) offshore structures at zero speed, significant progress has been made and documented using CFD. A natural extension of this progress is to expand the obtained confidence in the applicability of CFD for simulating extreme wave events to applications involving vessels at forward speed. To that end, this paper presents a validation study towards the prediction of green water loading on a (typical) container vessel at forward speed by CFD.\u0000 For validation, two extreme green water events were selected from a model test campaign carried out at MARIN within the context of the CRS (Cooperative Research Ships) working group ‘green water dynamics’. In these tests a KRISO Container Ship (KCS) is sailing in head seas when encountering severe green water. As CFD tool, the Cartesian-grid based Volume-of-Fluid CFD solver ComFLOW was selected. Furthermore, a deterministic approach is taken for the validation, by reconstructing the non-linear incoming wave in a high amount of detail and imposing the 6 degrees of motion of the vessel using the wave basin measurements. Time traces of the green water flow on deck and local- and global impact loads on the breakwater are presented and compared against the experimental data. Detailed visualizations of the CFD results are presented to further illustrate the obtained match with the model test results and emphasize the additional value of complementing model tests with deterministic CFD analysis.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"61 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80287856","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The traditional industry approach to drilling riser joint inspection and maintenance has centered on recertification of riser joints at fixed five-yearly intervals. There are significant potential efficiencies to be gained from moving to a condition-based maintenance regime where inspection intervals are determined based on the actual usage of the riser joint. One of the critical factors driving the requirement for inspection is the fatigue damage sustained by the riser joint during use. This paper describes a unique drilling riser joint fatigue tracking system that uses the latest digital technologies, advanced automation processes and a state-of-the-art finite element model of the drilling riser to provide an accurate and efficient solution to the challenge of long-term riser joint fatigue tracking. The architecture and operation of the system is described in detail and the application of a fracture mechanics-based approach to fatigue calculation versus the traditional S-N curve-based approach is discussed.
{"title":"Utilising Advanced Digital Technologies to Provide Automated Drilling Riser Fatigue Tracking to Support Condition Based Maintenance","authors":"Paul Bohan, D. Lang, Dara Williams","doi":"10.1115/omae2020-19198","DOIUrl":"https://doi.org/10.1115/omae2020-19198","url":null,"abstract":"\u0000 The traditional industry approach to drilling riser joint inspection and maintenance has centered on recertification of riser joints at fixed five-yearly intervals. There are significant potential efficiencies to be gained from moving to a condition-based maintenance regime where inspection intervals are determined based on the actual usage of the riser joint. One of the critical factors driving the requirement for inspection is the fatigue damage sustained by the riser joint during use.\u0000 This paper describes a unique drilling riser joint fatigue tracking system that uses the latest digital technologies, advanced automation processes and a state-of-the-art finite element model of the drilling riser to provide an accurate and efficient solution to the challenge of long-term riser joint fatigue tracking. The architecture and operation of the system is described in detail and the application of a fracture mechanics-based approach to fatigue calculation versus the traditional S-N curve-based approach is discussed.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"25 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83838396","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}
Sanne van Essen, Henry Bandringa, J. Helder, B. Buchner
Experiments with a flat plate in oblique waves at different speeds, wave conditions, headings and drift speed were done to evaluate non-linear wave run-up along a sailing ship. Both the incoming and diffracted part of the run-up were highly nonlinear in all test conditions. The run-up was larger at 135 than at 150 deg heading, the influence of speed was small, wave steepness increased run-up up to the point of breaking and a drift speed decreased the run-up. Most of the observed differences were larger than the seed and basin variability. (Semi-) linear diffraction methods are not sufficient to predict the highest runup crests, but applying them to screen for critical events could be further studied. CFD is able to accurately predict the nonlinear run-up in such selected events. Combining different levels of tools seems the most efficient way to predict extreme wave events such as green water due to run-up.
{"title":"Non-Linear Wave Run-Up Along the Side of Sailing Ships Causing Green Water on Deck: Experiments and Deterministic Calculations","authors":"Sanne van Essen, Henry Bandringa, J. Helder, B. Buchner","doi":"10.1115/omae2020-18130","DOIUrl":"https://doi.org/10.1115/omae2020-18130","url":null,"abstract":"\u0000 Experiments with a flat plate in oblique waves at different speeds, wave conditions, headings and drift speed were done to evaluate non-linear wave run-up along a sailing ship. Both the incoming and diffracted part of the run-up were highly nonlinear in all test conditions. The run-up was larger at 135 than at 150 deg heading, the influence of speed was small, wave steepness increased run-up up to the point of breaking and a drift speed decreased the run-up. Most of the observed differences were larger than the seed and basin variability. (Semi-) linear diffraction methods are not sufficient to predict the highest runup crests, but applying them to screen for critical events could be further studied. CFD is able to accurately predict the nonlinear run-up in such selected events. Combining different levels of tools seems the most efficient way to predict extreme wave events such as green water due to run-up.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"11 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84773555","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}
Wei Yuefeng, Yi Yang, Fan Sheming, Liu Zhen, Pei-yuan Feng
Model test is carried out to study the anti-rolling method of ship at zero speed in the present paper. First of all, based on the longitudinal flap mode, a zero speed fin stabilizer is designed. Furthermore, a control strategy for anti-rolling of ship at zero speed is proposed. At last, both regular and irregular wave tests are performed in towing tank. It can be shown from the test results that anti-rolling effectiveness of the zero speed fin stabilizer is obvious. Under level four sea condition, the effectiveness of anti-rolling is more than 40%. And under level five sea condition, the effectiveness of anti-rolling is more than 35%.
{"title":"Model Test Study on Anti-Rolling of Ship at Zero Speed","authors":"Wei Yuefeng, Yi Yang, Fan Sheming, Liu Zhen, Pei-yuan Feng","doi":"10.1115/omae2020-19343","DOIUrl":"https://doi.org/10.1115/omae2020-19343","url":null,"abstract":"\u0000 Model test is carried out to study the anti-rolling method of ship at zero speed in the present paper. First of all, based on the longitudinal flap mode, a zero speed fin stabilizer is designed. Furthermore, a control strategy for anti-rolling of ship at zero speed is proposed. At last, both regular and irregular wave tests are performed in towing tank. It can be shown from the test results that anti-rolling effectiveness of the zero speed fin stabilizer is obvious. Under level four sea condition, the effectiveness of anti-rolling is more than 40%. And under level five sea condition, the effectiveness of anti-rolling is more than 35%.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"25 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84778070","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}
Duan Yuchun, Chen Zhimei, Yang Hankun, Zhou Bo, Ling Chunhui
Ship undocking is an essential process in the construction of large ship. Nowadays, the traditional empirical method is usually used to calculate the environmental load during large ship undocking of large ship and to determine the power and number of assistant tugboats in the world shipbuilding industry. Firstly, the OCIMF with traditional empirical formula mathematical model for solving the environmental load problem is established in this paper. According to the location of the dry dock and the meteorological and hydrological conditions while undocking, the environmental load of a large FPSO with different wind, wave, and current combination from 0°to 90°are is calculated by using the OCIMF with traditional empirical formula method, and then the influence of the wind, wave and current load on large FPSO are is analyzed. Secondly, the environmental load is calculated by using numerical simulation calculation method based on the same environment conditions. Through comparing the analysis results between the two calculation methods, the reliability of using the OCIMF method is testified reliable to large barge-type FPSO, and the maximum environmental load is determined. Lastly, as a result the undocking plan and the power and number of assistant tugboats are finally determined. The actual undocking project shows that the OCIMF with traditional empirical formula method is reliable for calculating the environmental load of a large barge-type FPSO.
{"title":"Calculation of Environmental Load for a Large FPSO Undocking","authors":"Duan Yuchun, Chen Zhimei, Yang Hankun, Zhou Bo, Ling Chunhui","doi":"10.1115/omae2020-18542","DOIUrl":"https://doi.org/10.1115/omae2020-18542","url":null,"abstract":"\u0000 Ship undocking is an essential process in the construction of large ship. Nowadays, the traditional empirical method is usually used to calculate the environmental load during large ship undocking of large ship and to determine the power and number of assistant tugboats in the world shipbuilding industry. Firstly, the OCIMF with traditional empirical formula mathematical model for solving the environmental load problem is established in this paper. According to the location of the dry dock and the meteorological and hydrological conditions while undocking, the environmental load of a large FPSO with different wind, wave, and current combination from 0°to 90°are is calculated by using the OCIMF with traditional empirical formula method, and then the influence of the wind, wave and current load on large FPSO are is analyzed. Secondly, the environmental load is calculated by using numerical simulation calculation method based on the same environment conditions. Through comparing the analysis results between the two calculation methods, the reliability of using the OCIMF method is testified reliable to large barge-type FPSO, and the maximum environmental load is determined. Lastly, as a result the undocking plan and the power and number of assistant tugboats are finally determined. The actual undocking project shows that the OCIMF with traditional empirical formula method is reliable for calculating the environmental load of a large barge-type FPSO.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79823035","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}
Yuan Hongtao, C. Gang, Zhang Wei, Yin Yan, Wang Yuhan, W. Chao
For the connector between the modules of a regular hexagonal multi-floating structure, it designed a flexible connector based on hinge joints and spin joints, which allowed part of rolling, pitching and torsion between adjacent modules to release bending moment and strain. A 221m multi-floating structure hydrodynamic calculation model was modeled in this paper. Firstly, the connector loads under the regular waves were calculated by ANSYS Aqwa. Secondly, structural model of a flexible connector was built by SolidWorks basing on the finite element theory. It analyzed structural strength of the flexible connectors under different load conditions of a series of wave direction angles by ANSYS Static Structral. Lastly, the results show that the design of the multi-floating structure connectors met the design requirements in different working conditions.
{"title":"Design for Flexible Connector of Multi-Floating Structure","authors":"Yuan Hongtao, C. Gang, Zhang Wei, Yin Yan, Wang Yuhan, W. Chao","doi":"10.1115/omae2020-18533","DOIUrl":"https://doi.org/10.1115/omae2020-18533","url":null,"abstract":"\u0000 For the connector between the modules of a regular hexagonal multi-floating structure, it designed a flexible connector based on hinge joints and spin joints, which allowed part of rolling, pitching and torsion between adjacent modules to release bending moment and strain. A 221m multi-floating structure hydrodynamic calculation model was modeled in this paper. Firstly, the connector loads under the regular waves were calculated by ANSYS Aqwa. Secondly, structural model of a flexible connector was built by SolidWorks basing on the finite element theory. It analyzed structural strength of the flexible connectors under different load conditions of a series of wave direction angles by ANSYS Static Structral. Lastly, the results show that the design of the multi-floating structure connectors met the design requirements in different working conditions.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"42 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89603297","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 presents a response-based, time-domain structural fatigue analysis of a floating offshore platform. The conventional technique for structural fatigue assessments of offshore platforms uses a linear, frequency-domain analysis based on the spectral method. Although this conventional method is computationally efficient, there is a room for improving accuracy and reducing uncertainties because it cannot accurately address non-linear loadings on the offshore platform. Such non-linear loads arise from the wave, wind, and current as well as from the riser and mooring systems; these non-linearities necessitate large factors of safety that lead to conservative design and frequent inspection. As an extension of previous work (Kyoung et al.[12]), this study presents the development of a time-domain, structural fatigue analysis that explicitly addresses non-linear loading on the platform. The external load time-histories are directly mapped onto the structure at every time interval to create a stress-based response with the varying environment. In each time step, the load mapping accurately captures the phase relationship between the external loading and hull inertial response. Therefore, present method reduces uncertainties in the fatigue damage computation and overcomes the assumptions of spectral method. Present load component-based approach is applied onto a finite element structural model, which provides unit structural response at locations of interest. Time history of structural response is obtained by synthesizing the obtained unit stress-based structural response with environmental loading and platform motion response. Fatigue damage can be computed from the obtained time series of structural response using rain-flow counting. As an application, a conventional semisubmersible platform is used to evaluate structural fatigue damage for a given wave scatter diagram. A comparison between results from this response-based time-domain approach and the conventional spectral method is presented.
{"title":"Time Domain Structural Fatigue Analysis of Floating Offshore Platforms: A Response Based Technique","authors":"J. Kyoung, Sagar Samaria, Jang-Whan Kim","doi":"10.1115/omae2020-18314","DOIUrl":"https://doi.org/10.1115/omae2020-18314","url":null,"abstract":"\u0000 This paper presents a response-based, time-domain structural fatigue analysis of a floating offshore platform. The conventional technique for structural fatigue assessments of offshore platforms uses a linear, frequency-domain analysis based on the spectral method. Although this conventional method is computationally efficient, there is a room for improving accuracy and reducing uncertainties because it cannot accurately address non-linear loadings on the offshore platform. Such non-linear loads arise from the wave, wind, and current as well as from the riser and mooring systems; these non-linearities necessitate large factors of safety that lead to conservative design and frequent inspection.\u0000 As an extension of previous work (Kyoung et al.[12]), this study presents the development of a time-domain, structural fatigue analysis that explicitly addresses non-linear loading on the platform. The external load time-histories are directly mapped onto the structure at every time interval to create a stress-based response with the varying environment. In each time step, the load mapping accurately captures the phase relationship between the external loading and hull inertial response. Therefore, present method reduces uncertainties in the fatigue damage computation and overcomes the assumptions of spectral method. Present load component-based approach is applied onto a finite element structural model, which provides unit structural response at locations of interest. Time history of structural response is obtained by synthesizing the obtained unit stress-based structural response with environmental loading and platform motion response. Fatigue damage can be computed from the obtained time series of structural response using rain-flow counting.\u0000 As an application, a conventional semisubmersible platform is used to evaluate structural fatigue damage for a given wave scatter diagram. A comparison between results from this response-based time-domain approach and the conventional spectral method is presented.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"11 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89009847","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The motion analysis of floating offshore structures is a major design aspect which has to be considered in the early design stage. The existing design environment E4 is an open software framework, which is being developed by the Institute of Ship Design and Ship Safety, comprising various methods for design and analysis of mainly ship-type structures. In context of the development to enhance the design environment E4 for offshore applications this paper presents a method to calculate the response motions of semi-submersibles in regular waves. The linearised equations of motion are set up in frequency domain in six degrees of freedom and the seakeeping behaviour is calculated in terms of the amplitudes of the harmonic responses. The hydrodynamic forces onto the slender elements of the semi-submersible are accounted for by a Morison approach. As the drag and damping forces depend quadratically on the amplitudes, these forces are linearised by an energy-equivalence principle. The resulting response amplitude operators of the semi-submersible are validated by comparison with model tests. The method represents a fast computational tool for the analysis of the seakeeping behaviour of floating offshore structures consisting of slender elements with circular cross sections in the early design stage.
{"title":"A Method for the Frequency Domain Seakeeping Analysis of Offshore Structures in the Early Design Stage","authors":"M. Liebert","doi":"10.1115/omae2020-18126","DOIUrl":"https://doi.org/10.1115/omae2020-18126","url":null,"abstract":"\u0000 The motion analysis of floating offshore structures is a major design aspect which has to be considered in the early design stage. The existing design environment E4 is an open software framework, which is being developed by the Institute of Ship Design and Ship Safety, comprising various methods for design and analysis of mainly ship-type structures. In context of the development to enhance the design environment E4 for offshore applications this paper presents a method to calculate the response motions of semi-submersibles in regular waves. The linearised equations of motion are set up in frequency domain in six degrees of freedom and the seakeeping behaviour is calculated in terms of the amplitudes of the harmonic responses. The hydrodynamic forces onto the slender elements of the semi-submersible are accounted for by a Morison approach. As the drag and damping forces depend quadratically on the amplitudes, these forces are linearised by an energy-equivalence principle. The resulting response amplitude operators of the semi-submersible are validated by comparison with model tests. The method represents a fast computational tool for the analysis of the seakeeping behaviour of floating offshore structures consisting of slender elements with circular cross sections in the early design stage.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"8 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76426258","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}
Sagar Samaria, Bob Zhang, S. Tallavajhula, J. Kyoung
There is an ever-increasing demand for life extension of existing floating platforms worldwide. To adequately support these life extension projects there is a need to predict fatigue life of floating structures more accurately using a time domain approach. However, structural fatigue damage calculations using time domain response analysis can be very time consuming and challenging. An efficient and effective structural analysis methodology is developed to calculate accumulated fatigue damage for structural connections in a floating offshore platform using a response-based time domain routine. The methodology discussed in this paper can be applied to estimate fatigue life for hull critical connections in floaters such as Spars, TLPs or Semis as well as local structural supports such as mooring foundations and riser foundations. It also provides the option to generate stress histograms that can be utilized for Fracture Mechanics Evaluation (FME) of welds in structural connections. To calculate the accumulated fatigue damage at desired locations on a floating platform, the time domain analysis employs a Stress Intensification Factor (SIF) which correlates global loads with local stresses. In cases where a crack initiation is observed on a structural connection, fracture mechanics is used to evaluate the structural integrity of the weld. The FME requires fatigue stress range histograms as one of the input parameters. The stress ranges and cycles that are calculated and used to compute the fatigue damage using this methodology can be converted to stress range histograms which can then be used in the FME. The standard method to compute fatigue damage for a structural connection is by using an S-N fatigue approach under the assumption of linear cumulative damage (Palmgren-Miner rule). The methodology discussed in this paper uses a rainflow counting algorithm to effectively calculate the stress range and cycles which are then utilized for computing the fatigue damage. This methodology can be applied to green field projects involving a new design or for life of field studies of an existing platform requiring life extensions. It is particularly beneficial for brownfield projects where more accurate re-evaluation of fatigue life is needed. It can also provide Clients with reliable Engineering Criticality Assessments (ECA) and enable them to plan in-service inspections and repair work. As an application, a typical truss connection for a Spar platform is used to evaluate structural fatigue damage and generate the stress range histogram for FME. Also, a comparative study is performed for a typical truss connection fatigue damage result between the traditional approach used and the method discussed in this paper.
{"title":"Structural Connection Fatigue Evaluation Methodology Using Time Domain Approach","authors":"Sagar Samaria, Bob Zhang, S. Tallavajhula, J. Kyoung","doi":"10.1115/omae2020-18229","DOIUrl":"https://doi.org/10.1115/omae2020-18229","url":null,"abstract":"\u0000 There is an ever-increasing demand for life extension of existing floating platforms worldwide. To adequately support these life extension projects there is a need to predict fatigue life of floating structures more accurately using a time domain approach. However, structural fatigue damage calculations using time domain response analysis can be very time consuming and challenging. An efficient and effective structural analysis methodology is developed to calculate accumulated fatigue damage for structural connections in a floating offshore platform using a response-based time domain routine. The methodology discussed in this paper can be applied to estimate fatigue life for hull critical connections in floaters such as Spars, TLPs or Semis as well as local structural supports such as mooring foundations and riser foundations. It also provides the option to generate stress histograms that can be utilized for Fracture Mechanics Evaluation (FME) of welds in structural connections.\u0000 To calculate the accumulated fatigue damage at desired locations on a floating platform, the time domain analysis employs a Stress Intensification Factor (SIF) which correlates global loads with local stresses. In cases where a crack initiation is observed on a structural connection, fracture mechanics is used to evaluate the structural integrity of the weld. The FME requires fatigue stress range histograms as one of the input parameters. The stress ranges and cycles that are calculated and used to compute the fatigue damage using this methodology can be converted to stress range histograms which can then be used in the FME. The standard method to compute fatigue damage for a structural connection is by using an S-N fatigue approach under the assumption of linear cumulative damage (Palmgren-Miner rule). The methodology discussed in this paper uses a rainflow counting algorithm to effectively calculate the stress range and cycles which are then utilized for computing the fatigue damage.\u0000 This methodology can be applied to green field projects involving a new design or for life of field studies of an existing platform requiring life extensions. It is particularly beneficial for brownfield projects where more accurate re-evaluation of fatigue life is needed. It can also provide Clients with reliable Engineering Criticality Assessments (ECA) and enable them to plan in-service inspections and repair work. As an application, a typical truss connection for a Spar platform is used to evaluate structural fatigue damage and generate the stress range histogram for FME. Also, a comparative study is performed for a typical truss connection fatigue damage result between the traditional approach used and the method discussed in this paper.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"6 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79990454","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}
Jiaming Wu, Dongjun Chen, Jinhua Lin, Yan Chen, Yizhe Dou
The trajectory of tethered underwater robot is usually controlled by actuating the rotating speeds of control propellers attached to the robot and/or adjusting the length of umbilical cable. When the trajectory control problem of a tethered underwater robot is studied, it is necessary to couple the main body of underwater robot, umbilical cable and control propellers together forming an integrated hydrodynamic model so that the robot is in a comprehensive dynamic equilibrium condition, suitable control algorithms are then jointed into the hydrodynamic model constructing a hydrodynamic and control model for the tethered underwater robot system. Only in this way the hydrodynamic and control nature of a tethered underwater robot during different kinds of control manipulations can be numerically revealed objectively. In this paper, a hydrodynamic and control model to simulate the trajectory following control of a tethered underwater robot system is proposed, and the hydrodynamic performances of the robot and the umbilical cable are observed. To achieve this goal, three-dimensional hydrodynamic model of tethered underwater robot system is first introduced, feed-forward control technique for adjusting the length of umbilical cable and incremental PID algorithm for regulating the rotating speeds of propellers are then incorporated into the hydrodynamic model forming the hydrodynamic and control model. Based on the established hydrodynamic and control mode, relationships between the thrusts from the propellers and the rotating speeds of the propellers, and those among the trajectory following of the underwater robot and the control actions of adjusting the length of umbilical cable and governing the rotating speeds of the propellers are analyzed, and also the hydrodynamic performances of the tethered underwater robot system under the control manipulation are observed. In the research, the amplitude limit filtering method is applied in solving the governing equations of the umbilical cable, this technique is applied to avoid the chattering effect in the cable tension computation, so that a successive and stable computation process is maintained. The main factors affecting the singular nature of coefficient matrices during the numerical solutions of the proposed model are also investigated in the paper.
{"title":"Hydrodynamic Response of Tethered Underwater Robot by Feed-Forward and Incremental PID Control Techniques","authors":"Jiaming Wu, Dongjun Chen, Jinhua Lin, Yan Chen, Yizhe Dou","doi":"10.1115/omae2020-18362","DOIUrl":"https://doi.org/10.1115/omae2020-18362","url":null,"abstract":"\u0000 The trajectory of tethered underwater robot is usually controlled by actuating the rotating speeds of control propellers attached to the robot and/or adjusting the length of umbilical cable. When the trajectory control problem of a tethered underwater robot is studied, it is necessary to couple the main body of underwater robot, umbilical cable and control propellers together forming an integrated hydrodynamic model so that the robot is in a comprehensive dynamic equilibrium condition, suitable control algorithms are then jointed into the hydrodynamic model constructing a hydrodynamic and control model for the tethered underwater robot system. Only in this way the hydrodynamic and control nature of a tethered underwater robot during different kinds of control manipulations can be numerically revealed objectively.\u0000 In this paper, a hydrodynamic and control model to simulate the trajectory following control of a tethered underwater robot system is proposed, and the hydrodynamic performances of the robot and the umbilical cable are observed. To achieve this goal, three-dimensional hydrodynamic model of tethered underwater robot system is first introduced, feed-forward control technique for adjusting the length of umbilical cable and incremental PID algorithm for regulating the rotating speeds of propellers are then incorporated into the hydrodynamic model forming the hydrodynamic and control model. Based on the established hydrodynamic and control mode, relationships between the thrusts from the propellers and the rotating speeds of the propellers, and those among the trajectory following of the underwater robot and the control actions of adjusting the length of umbilical cable and governing the rotating speeds of the propellers are analyzed, and also the hydrodynamic performances of the tethered underwater robot system under the control manipulation are observed. In the research, the amplitude limit filtering method is applied in solving the governing equations of the umbilical cable, this technique is applied to avoid the chattering effect in the cable tension computation, so that a successive and stable computation process is maintained. The main factors affecting the singular nature of coefficient matrices during the numerical solutions of the proposed model are also investigated in the paper.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"36 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90596809","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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