In response to the UNCCC held in Paris in 2015 the need to reduce the global warming, due to CO2 release in atmosphere, led to a new business for the capture and storage of CO2 in dedicated deep water reservoir. In this sense the transport of the CO2 at low temperature, necessary to condensate the gas, through offshore pipeline is a commercial and technical valid strategy. One of the issues related to the transport of a condensate gas is the thermal exchange between the transport system, in this case offshore pipelines, and the environment. The gas is usually carried by ships in a liquid phase at very low temperatures, for example −30 °C in case of CO2. The fluid is introduced into the pipeline at the same temperature to not further consume energy for warming up. The design of the offshore pipeline subject to these operating conditions, very cold fluid internally and a water temperature slightly over 0°C at external side, can be affected by the ice formation around the pipe. The ice thickness formation is primarily governed by the external convection coefficient. For the offshore pipelines located in deep waters where the sea currents are negligible, only the natural convection phenomena can occur on the external surface of the pipeline. Considering steady state scenario the heat transfer from the internal fluid to the external environmental is governed by the thermal resistance of each component of the system like fluid, steel, anticorrosion coating, thermal insulation if any and external convection due to the seawater. The low temperatures of both seawater and ice formation, approximately at −2°C, allow to be close to the maximum value of the seawater density: usually this occurs at a slightly colder temperatures depending on salinity and water depth (for the fresh water the maximum is at 4°C). The natural convection is driven by the buoyancy effect due to fluid density variation with temperature: the scenario described above lead to minimizes these effects and consequently the heat transfer due to the natural convection (increasing the thermal resistance). Most of the correlations in literature are related to different temperature ranges, far away from this particular situation: a numerical investigation using computational fluid dynamics technique has been performed. The analysis is executed by means of commercial CFD software FLUENT: the model is based on a two dimensional grid of a pipe submerged in water. In this paper: • The state-of-the-art about the natural convection coefficient estimate for submerged cylinders proposed by different authors through Nusselt number assessment; • A description of the proposed numerical approach is given highlighting the different approaches based on the boundary layer behavior; • A typical application is shown.
{"title":"Fluid Dynamics Numerical Assessment to Evaluate the Ice Formation Around the Pipeline","authors":"Giuseppe Blasioli, F. Marchesani","doi":"10.1115/omae2019-95528","DOIUrl":"https://doi.org/10.1115/omae2019-95528","url":null,"abstract":"\u0000 In response to the UNCCC held in Paris in 2015 the need to reduce the global warming, due to CO2 release in atmosphere, led to a new business for the capture and storage of CO2 in dedicated deep water reservoir. In this sense the transport of the CO2 at low temperature, necessary to condensate the gas, through offshore pipeline is a commercial and technical valid strategy.\u0000 One of the issues related to the transport of a condensate gas is the thermal exchange between the transport system, in this case offshore pipelines, and the environment. The gas is usually carried by ships in a liquid phase at very low temperatures, for example −30 °C in case of CO2. The fluid is introduced into the pipeline at the same temperature to not further consume energy for warming up.\u0000 The design of the offshore pipeline subject to these operating conditions, very cold fluid internally and a water temperature slightly over 0°C at external side, can be affected by the ice formation around the pipe. The ice thickness formation is primarily governed by the external convection coefficient.\u0000 For the offshore pipelines located in deep waters where the sea currents are negligible, only the natural convection phenomena can occur on the external surface of the pipeline. Considering steady state scenario the heat transfer from the internal fluid to the external environmental is governed by the thermal resistance of each component of the system like fluid, steel, anticorrosion coating, thermal insulation if any and external convection due to the seawater. The low temperatures of both seawater and ice formation, approximately at −2°C, allow to be close to the maximum value of the seawater density: usually this occurs at a slightly colder temperatures depending on salinity and water depth (for the fresh water the maximum is at 4°C).\u0000 The natural convection is driven by the buoyancy effect due to fluid density variation with temperature: the scenario described above lead to minimizes these effects and consequently the heat transfer due to the natural convection (increasing the thermal resistance).\u0000 Most of the correlations in literature are related to different temperature ranges, far away from this particular situation: a numerical investigation using computational fluid dynamics technique has been performed.\u0000 The analysis is executed by means of commercial CFD software FLUENT: the model is based on a two dimensional grid of a pipe submerged in water.\u0000 In this paper:\u0000 • The state-of-the-art about the natural convection coefficient estimate for submerged cylinders proposed by different authors through Nusselt number assessment;\u0000 • A description of the proposed numerical approach is given highlighting the different approaches based on the boundary layer behavior;\u0000 • A typical application is shown.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"81 2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121284308","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}
In the present paper the roll damping decay is investigated for the KRISO Container Ship in various working conditions. For this purpose flow is simulated by solving numerically the unsteady three dimensional equations of fluid motion in which closure to the turbulence is achieved through the DES-SST model. The governing equations are solved by using the finite volume method and the free surface elevation is determined by using a VOF technique. Comparisons with the experimental data are provided to validate the numerical approach in terms of the time history of the roll angle variation for different roll motions and ship speeds.
{"title":"Numerical Investigation of the Roll Decay of a Container Ship Moving With Forward Speed in Calm Water","authors":"A. Lungu","doi":"10.1115/omae2019-95240","DOIUrl":"https://doi.org/10.1115/omae2019-95240","url":null,"abstract":"\u0000 In the present paper the roll damping decay is investigated for the KRISO Container Ship in various working conditions. For this purpose flow is simulated by solving numerically the unsteady three dimensional equations of fluid motion in which closure to the turbulence is achieved through the DES-SST model. The governing equations are solved by using the finite volume method and the free surface elevation is determined by using a VOF technique. Comparisons with the experimental data are provided to validate the numerical approach in terms of the time history of the roll angle variation for different roll motions and ship speeds.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116432113","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 paper follows a previous work of the author that dealt with ship resistance and self-propulsion numerical investigations, proposing a series of numerical simulations performed to assess the seakeeping performances of the KCS model which moves in regular head waves. Various simulations of the free-surface flow around the hull equipped with rudder moving either in calm water or in heading waves are proposed. For the calm water case, in which a series of six Fr numbers is considered, verification and validation based on the grid convergence tests are performed. Then, a series of five different simulations for various incoming wave characteristics are presented and discussed in every detail. Comparisons with the experimental data [1], [2] are provided aimed at validating the numerical approaches in terms of the total resistance coefficients as well as the heave and pitch motions characteristics. Several remarks will conclude the findings of the present work.
{"title":"Unsteady Numerical Simulation of the Behavior of a Ship Moving in Head Sea","authors":"A. Lungu","doi":"10.1115/omae2019-95239","DOIUrl":"https://doi.org/10.1115/omae2019-95239","url":null,"abstract":"\u0000 The paper follows a previous work of the author that dealt with ship resistance and self-propulsion numerical investigations, proposing a series of numerical simulations performed to assess the seakeeping performances of the KCS model which moves in regular head waves. Various simulations of the free-surface flow around the hull equipped with rudder moving either in calm water or in heading waves are proposed. For the calm water case, in which a series of six Fr numbers is considered, verification and validation based on the grid convergence tests are performed. Then, a series of five different simulations for various incoming wave characteristics are presented and discussed in every detail. Comparisons with the experimental data [1], [2] are provided aimed at validating the numerical approaches in terms of the total resistance coefficients as well as the heave and pitch motions characteristics. Several remarks will conclude the findings of the present work.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"17 5","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114128548","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}
B. Decrop, R. Kulkarni, A. Breugem, Damian Villaverde Vega
Two caissons with complex geometry need to be towed to an installation site in a straight with potentially strong currents, fairly strong wind and moderate wave conditions. In order to design the mooring system, current, wind and wave forces need to be assessed. Both time-averaged and oscillating components are important. A methodology in which the degree of complexity is gradually increased has been conceived. In this methodology, first an assessment of the order of magnitude of each force is determined, after which it is decided whether in-depth computation of higher accuracy is required. This led to a methodology in which wind forces have been determined analytically, current forces and Vortex Induced Motions (VIM) have been determined using CFD and wave forces by means of a panel method. The resulting forces have been combined in a numerical mooring analysis. The focus of the presented paper is on the CFD model applied to determine VIM and a comparison with resonance frequencies determined analytically.
{"title":"CFD for Vortex-Induced Motions and Line Forces of a Floating Caisson With Complex Geometry","authors":"B. Decrop, R. Kulkarni, A. Breugem, Damian Villaverde Vega","doi":"10.1115/omae2019-95789","DOIUrl":"https://doi.org/10.1115/omae2019-95789","url":null,"abstract":"\u0000 Two caissons with complex geometry need to be towed to an installation site in a straight with potentially strong currents, fairly strong wind and moderate wave conditions. In order to design the mooring system, current, wind and wave forces need to be assessed. Both time-averaged and oscillating components are important. A methodology in which the degree of complexity is gradually increased has been conceived. In this methodology, first an assessment of the order of magnitude of each force is determined, after which it is decided whether in-depth computation of higher accuracy is required. This led to a methodology in which wind forces have been determined analytically, current forces and Vortex Induced Motions (VIM) have been determined using CFD and wave forces by means of a panel method. The resulting forces have been combined in a numerical mooring analysis. The focus of the presented paper is on the CFD model applied to determine VIM and a comparison with resonance frequencies determined analytically.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"84 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121957255","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 key objective of this paper is to perform a fully nonlinear unsteady RANS simulation to predict the self-propulsion performance of KCS at two different scales. This simulations are performed at design speeds in calm water, using inhouse computational fluid dynamics (CFD) to solve RANS equation coupled with two degrees of freedom (2DOF) solid body motion equations including heave and pitch. The SST k-ω turbulence equation is discretized by finite difference method. The velocity pressure coupling is solved by PISO algorithm. Computations have used structured grid with overset technology. The single-phase level-set method is used to capture the free surface. The simulations of self-propulsion are based on the body-force method. The PID control method is applied to match the speed of KCS by changing the propeller rotation speed automatically. In this paper, the self-propulsion factors of KCS at two scales are predicted and the results from inhouse CFD code are compared with the EFD date, and then the reasons for the scale effect have been discussed.
{"title":"Numerical Study on Scale Effect of KCS","authors":"Yujie Zhou, Liwei Liu, X. Cai, D. Feng, Bin Guo","doi":"10.1115/omae2019-96831","DOIUrl":"https://doi.org/10.1115/omae2019-96831","url":null,"abstract":"\u0000 The key objective of this paper is to perform a fully nonlinear unsteady RANS simulation to predict the self-propulsion performance of KCS at two different scales. This simulations are performed at design speeds in calm water, using inhouse computational fluid dynamics (CFD) to solve RANS equation coupled with two degrees of freedom (2DOF) solid body motion equations including heave and pitch. The SST k-ω turbulence equation is discretized by finite difference method. The velocity pressure coupling is solved by PISO algorithm. Computations have used structured grid with overset technology. The single-phase level-set method is used to capture the free surface. The simulations of self-propulsion are based on the body-force method. The PID control method is applied to match the speed of KCS by changing the propeller rotation speed automatically. In this paper, the self-propulsion factors of KCS at two scales are predicted and the results from inhouse CFD code are compared with the EFD date, and then the reasons for the scale effect have been discussed.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130846817","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}
D. Feng, X. Cai, Yue Sun, Zhiguo Zhang, Xiaowei Huang
The maneuvering motion simulation of ship in waves needs large space, the simulation based static domain requires a large amount of mesh. On the contrary, the moving domain can reduce the grid amount and improve the simulation speed. This paper studies the establishment of numerical wave tank based moving domain. The wave-generation method of defining inlet boundary conditions is proposed. The level set method is used to solve the free surface. The URANS equation is solved by finite difference method and the projection algorithm. For the wave-generation method of defining inlet boundary conditions, the velocity inlet direction is always fixed because the direction of incident wave is always fixed. Specifically, the yaw should be turned off avoid the disturbance of wave in the y direction. Comparing the simulated wave with the target wave, the numerical results show that the simulated value is coincident with the theoretical value in the moving domain, and there are no obvious signs of dissipation over time. The established moving domain can produce a continuous and qualified wave, which provides a theoretical basis for the study of maneuvering simulation of ship in waves.
{"title":"Numerical Manoeuvrable Tank on Wave Based Moving Domain","authors":"D. Feng, X. Cai, Yue Sun, Zhiguo Zhang, Xiaowei Huang","doi":"10.1115/omae2019-95714","DOIUrl":"https://doi.org/10.1115/omae2019-95714","url":null,"abstract":"\u0000 The maneuvering motion simulation of ship in waves needs large space, the simulation based static domain requires a large amount of mesh. On the contrary, the moving domain can reduce the grid amount and improve the simulation speed. This paper studies the establishment of numerical wave tank based moving domain. The wave-generation method of defining inlet boundary conditions is proposed. The level set method is used to solve the free surface. The URANS equation is solved by finite difference method and the projection algorithm. For the wave-generation method of defining inlet boundary conditions, the velocity inlet direction is always fixed because the direction of incident wave is always fixed. Specifically, the yaw should be turned off avoid the disturbance of wave in the y direction. Comparing the simulated wave with the target wave, the numerical results show that the simulated value is coincident with the theoretical value in the moving domain, and there are no obvious signs of dissipation over time. The established moving domain can produce a continuous and qualified wave, which provides a theoretical basis for the study of maneuvering simulation of ship in waves.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121415706","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 CFD analysis of added resistance of a KVLCC2 ship model is presented in this paper. The Naval Hydro Pack, an open source software library for computational naval hydrodynamics based on OpenFOAM is used to perform the simulations. Ten head wave cases are considered in this study ranging from short waves to long waves (wave length to length between perpendiculars ranging from 0.3 to 2). During the initial stages of our research, we had noticed significant over-prediction of added resistance compared to experimental results. After thorough analysis, the issue was found to be related to inadequate turbulence modeling using the standard k-ω SST model. Using the free surface sensitised model, the prediction of the added resistance improves significantly Compared to the experimental results, majority of the cases with different wave lengths have errors smaller than several percent. In addition to added resistance, heave and pitch motion amplitudes are compared to recent experimental results by Park et al. [1], showing good agreement. CPU time required to perform the computations is also discussed.
{"title":"Added Resistance CFD Analysis of the KVLCC2 With the Naval Hydro Pack","authors":"V. Vukcevic, I. Gatin, Ghuiyeon Kim, H. Jasak","doi":"10.1115/omae2019-95293","DOIUrl":"https://doi.org/10.1115/omae2019-95293","url":null,"abstract":"\u0000 A CFD analysis of added resistance of a KVLCC2 ship model is presented in this paper. The Naval Hydro Pack, an open source software library for computational naval hydrodynamics based on OpenFOAM is used to perform the simulations.\u0000 Ten head wave cases are considered in this study ranging from short waves to long waves (wave length to length between perpendiculars ranging from 0.3 to 2). During the initial stages of our research, we had noticed significant over-prediction of added resistance compared to experimental results. After thorough analysis, the issue was found to be related to inadequate turbulence modeling using the standard k-ω SST model. Using the free surface sensitised model, the prediction of the added resistance improves significantly Compared to the experimental results, majority of the cases with different wave lengths have errors smaller than several percent. In addition to added resistance, heave and pitch motion amplitudes are compared to recent experimental results by Park et al. [1], showing good agreement. CPU time required to perform the computations is also discussed.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124842876","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. Veldman, H. Seubers, Matin Hosseini, X. Chang, P. Wellens, P. V. D. Plas, J. Helder
Wave forces can form a serious threat to offshore platforms and ships. The damage produced by these forces of nature jeopardizes their operability as well as the well-being of their crews. Similar remarks apply to coastal defense systems. To develop the knowledge needed to safely design these constructions, in close cooperation with MARIN and the offshore industry the numerical simulation method ComFLOW is being developed. So far, its development was focussed on predicting wave loads (green water, slamming) on fixed structures, and for those applications the method is already being used successfully by the offshore industry. Often, the investigated object (ship, floating platform) is dynamically moving under the influence of these wave forces, and its hydrodynamic loading depends upon the position of the object with respect to the oncoming waves. Predicting the position (and deformation) of the body is an integral part of the (scientific and engineering) problem. The paper will give an overview of the algorithmic developments necessary to describe the above-mentioned physical phenomena. In particular attention will be paid to fluid-solid body and fluid-structure interaction and non-reflecting outflow boundary conditions. Several illustrations including validation, will demonstrate the prediction capabilities of the simulation method.
{"title":"Computational Methods for Moving and Deforming Objects in Extreme Waves","authors":"A. Veldman, H. Seubers, Matin Hosseini, X. Chang, P. Wellens, P. V. D. Plas, J. Helder","doi":"10.1115/omae2019-96321","DOIUrl":"https://doi.org/10.1115/omae2019-96321","url":null,"abstract":"\u0000 Wave forces can form a serious threat to offshore platforms and ships. The damage produced by these forces of nature jeopardizes their operability as well as the well-being of their crews. Similar remarks apply to coastal defense systems. To develop the knowledge needed to safely design these constructions, in close cooperation with MARIN and the offshore industry the numerical simulation method ComFLOW is being developed. So far, its development was focussed on predicting wave loads (green water, slamming) on fixed structures, and for those applications the method is already being used successfully by the offshore industry. Often, the investigated object (ship, floating platform) is dynamically moving under the influence of these wave forces, and its hydrodynamic loading depends upon the position of the object with respect to the oncoming waves. Predicting the position (and deformation) of the body is an integral part of the (scientific and engineering) problem. The paper will give an overview of the algorithmic developments necessary to describe the above-mentioned physical phenomena. In particular attention will be paid to fluid-solid body and fluid-structure interaction and non-reflecting outflow boundary conditions. Several illustrations including validation, will demonstrate the prediction capabilities of the simulation method.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131300772","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. Koop, Frederick Jaouen, Xavier Wadbled, Erwan Corbineau
An accurate prediction of the non-linear roll damping is required in order to calculate the resonant roll motion of moored FPSO’s. Traditionally, the roll damping is obtained with model tests using decays or forced roll oscillation tests. Calculation methods based on potential flow are not capable of predicting this hydrodynamic damping accurately as it originates from the viscous nature of the fluid and the complex vortical flow structures around a rolling vessel. In recent years Computational Fluid Dynamics (CFD) has advanced such that accurate predictions for the roll damping can be obtained. In this paper CFD is employed to predict the roll damping for a barge-type FPSO. The objectives of the paper are to investigate the capability and accuracy of CFD to determine roll damping of an FPSO and to investigate whether two-dimensional calculations can be used to estimate the roll damping of a three-dimensional FPSO geometry. To meet these objectives, extensive numerical sensitivity studies are carried out for a 2D hull section mimicking the midsection of the FPSO. The numerical uncertainty for the added mass and damping coefficients were found to be 0.5% and 2%, respectively. The influence of the turbulence model was found to be significant for the damping coefficient with differences up to 14%. The 2D CFD results are compared to results from two-dimensional model tests. The calculated roll damping using the k-ω SST 2003 turbulence model matches the value from the experiments within 2%. The influence of various physical parameters on the damping was investigated through additional 2D calculations by changing the scale ratio, the roll amplitude, the roll period, the water depth, the origin of rotation and the bilge keel height. Lastly, three-dimensional calculations are carried out with the complete FPSO geometry. The 3D results agree with the 2D results except for the largest roll amplitude calculated, i.e. for 15 degrees, where the damping coefficient was found to be 7% smaller. For this amplitude end-effects from the ends of the bilge keels seem to have a small influence on the flow field around the bilge keels. This indicates that the 2D approach is a cost-effective method to determine the roll damping of a barge-type FPSO, but for large roll amplitudes or for different vessel geometries the 2D approach may not be valid due to 3D effects.
{"title":"Predicting Roll Damping for Barge-Type FPSO Using CFD","authors":"A. Koop, Frederick Jaouen, Xavier Wadbled, Erwan Corbineau","doi":"10.1115/omae2019-95306","DOIUrl":"https://doi.org/10.1115/omae2019-95306","url":null,"abstract":"\u0000 An accurate prediction of the non-linear roll damping is required in order to calculate the resonant roll motion of moored FPSO’s. Traditionally, the roll damping is obtained with model tests using decays or forced roll oscillation tests. Calculation methods based on potential flow are not capable of predicting this hydrodynamic damping accurately as it originates from the viscous nature of the fluid and the complex vortical flow structures around a rolling vessel. In recent years Computational Fluid Dynamics (CFD) has advanced such that accurate predictions for the roll damping can be obtained.\u0000 In this paper CFD is employed to predict the roll damping for a barge-type FPSO. The objectives of the paper are to investigate the capability and accuracy of CFD to determine roll damping of an FPSO and to investigate whether two-dimensional calculations can be used to estimate the roll damping of a three-dimensional FPSO geometry.\u0000 To meet these objectives, extensive numerical sensitivity studies are carried out for a 2D hull section mimicking the midsection of the FPSO. The numerical uncertainty for the added mass and damping coefficients were found to be 0.5% and 2%, respectively. The influence of the turbulence model was found to be significant for the damping coefficient with differences up to 14%. The 2D CFD results are compared to results from two-dimensional model tests. The calculated roll damping using the k-ω SST 2003 turbulence model matches the value from the experiments within 2%.\u0000 The influence of various physical parameters on the damping was investigated through additional 2D calculations by changing the scale ratio, the roll amplitude, the roll period, the water depth, the origin of rotation and the bilge keel height.\u0000 Lastly, three-dimensional calculations are carried out with the complete FPSO geometry. The 3D results agree with the 2D results except for the largest roll amplitude calculated, i.e. for 15 degrees, where the damping coefficient was found to be 7% smaller. For this amplitude end-effects from the ends of the bilge keels seem to have a small influence on the flow field around the bilge keels. This indicates that the 2D approach is a cost-effective method to determine the roll damping of a barge-type FPSO, but for large roll amplitudes or for different vessel geometries the 2D approach may not be valid due to 3D effects.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131606070","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}
In the process of bubbling from two submerged adjacent orifices, bubbles coalescence becomes inevitable. But the study of the evolution and interaction of bubbles from submerged orifices is little, especially numerical simulation. In this paper, combined with mesh smoothing technique, mesh subdivision technique and the technique of axisymmetric coalescence and 3D coalescence, a three-dimensional model of bubbles coalescence at two submerged adjacent orifices on the wall is established by the boundary element method. Then, numerical simulations were carried out for horizontal and vertical coalescence before detachment. Finally, by changing the ventilation rate and the Froude number, the effects of different ventilation rates and buoyancy on the process of bubbles coalescence at two adjacent orifices were investigated. The results show that for horizontal coalescence, the effect of ventilation rate is more pronounced than buoyancy. As the ventilation rate increases or the influence of buoyancy is decreased, the amplitude of internal pressure fluctuation of the bubble decreases and the coalescence time decreases. For vertical coalescence, the effect of buoyancy is more pronounced than ventilation rate. With the influence of buoyancy is decreased, the vertical coalescence time is increased, the internal pressure of the bubble is decreased. The influence of ventilation rate is similar to that of horizontal coalescence.
{"title":"Three-Dimensional Numerical Analysis of Horizontal and Vertical Coalescence of Bubbles at Two Submerged Horizontal Orifices on the Wall","authors":"Z. P. Li, L. Sun, X. Yao, Y. Piao","doi":"10.1115/omae2019-95850","DOIUrl":"https://doi.org/10.1115/omae2019-95850","url":null,"abstract":"\u0000 In the process of bubbling from two submerged adjacent orifices, bubbles coalescence becomes inevitable. But the study of the evolution and interaction of bubbles from submerged orifices is little, especially numerical simulation. In this paper, combined with mesh smoothing technique, mesh subdivision technique and the technique of axisymmetric coalescence and 3D coalescence, a three-dimensional model of bubbles coalescence at two submerged adjacent orifices on the wall is established by the boundary element method. Then, numerical simulations were carried out for horizontal and vertical coalescence before detachment. Finally, by changing the ventilation rate and the Froude number, the effects of different ventilation rates and buoyancy on the process of bubbles coalescence at two adjacent orifices were investigated. The results show that for horizontal coalescence, the effect of ventilation rate is more pronounced than buoyancy. As the ventilation rate increases or the influence of buoyancy is decreased, the amplitude of internal pressure fluctuation of the bubble decreases and the coalescence time decreases. For vertical coalescence, the effect of buoyancy is more pronounced than ventilation rate. With the influence of buoyancy is decreased, the vertical coalescence time is increased, the internal pressure of the bubble is decreased. The influence of ventilation rate is similar to that of horizontal coalescence.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"35 7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121161460","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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