Usually, mooring system restoring forces acting on floating offshore structures are obtained from a quasi-static mooring model alone or from a coupled analysis based on potential flow solvers that do not always consider nonlinear mooring-induced phenomena or fluid-structure interactions and the associated viscous damping effects. By assuming that only the mooring system influences the restoring force characteristics, the contribution of mooring-induced damping to total system damping is neglected. This paper presents a technique to predict hydrodynamic damping of moored structures based on coupling the dynamic mooring model with a Reynolds-averaged Navier-Stokes (RANS) equations solver. We obtained hydrodynamic damping coefficients using a least-square algorithm to fit the time trace of decay tests. We analyzed a moored offshore buoy and validated our predictions against experimental measurements. The mooring system consisted of three catenary chains. The analyzed response comprised the decaying oscillating buoy motions, the natural periods, and the associated linear and quadratic damping characteristics. Predicted motions, natural periods, and hydrodynamic damping generally well agreed to comparable experimental data.
{"title":"Prediction of Hydrodynamic Damping of Moored Offshore Structures Using CFD","authors":"Changqing Jiang, O. E. Moctar, T. Schellin","doi":"10.1115/omae2019-95935","DOIUrl":"https://doi.org/10.1115/omae2019-95935","url":null,"abstract":"\u0000 Usually, mooring system restoring forces acting on floating offshore structures are obtained from a quasi-static mooring model alone or from a coupled analysis based on potential flow solvers that do not always consider nonlinear mooring-induced phenomena or fluid-structure interactions and the associated viscous damping effects. By assuming that only the mooring system influences the restoring force characteristics, the contribution of mooring-induced damping to total system damping is neglected. This paper presents a technique to predict hydrodynamic damping of moored structures based on coupling the dynamic mooring model with a Reynolds-averaged Navier-Stokes (RANS) equations solver. We obtained hydrodynamic damping coefficients using a least-square algorithm to fit the time trace of decay tests. We analyzed a moored offshore buoy and validated our predictions against experimental measurements. The mooring system consisted of three catenary chains. The analyzed response comprised the decaying oscillating buoy motions, the natural periods, and the associated linear and quadratic damping characteristics. Predicted motions, natural periods, and hydrodynamic damping generally well agreed to comparable experimental data.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"386 2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122358260","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}
Yakun Zhao, Xinliang Tian, Xia Wu, Xiantao Zhang, Xin Li
Direct numerical simulations are performed for the flow past an inclined square plate. The side length-thickness ratio of the plate is selected as 50, representing a reasonably thin plate. Various incidence angles of the plate with respect to the flow are considered from 0° to 75°, where 0° refers to the condition in which the flow is normal to the plate. The Reynolds number (Re) based on the flow velocity and the side length in the streamwise direction of the plate is up to 300. The hydrodynamic characteristics, including the force coefficients, the three-dimensional vortical structures and vortex shedding process, are presented. The effects of incidence angle on the wake transition are also discussed. It is observed that as the incidence angle increases, the flow firstly changes from a chaotic state to a periodic state and finally returns to chaos again at high incidence angles.
{"title":"Numerical Investigations on the Flow Past an Inclined Thin Square Plate at Re = 300","authors":"Yakun Zhao, Xinliang Tian, Xia Wu, Xiantao Zhang, Xin Li","doi":"10.1115/omae2019-95744","DOIUrl":"https://doi.org/10.1115/omae2019-95744","url":null,"abstract":"\u0000 Direct numerical simulations are performed for the flow past an inclined square plate. The side length-thickness ratio of the plate is selected as 50, representing a reasonably thin plate. Various incidence angles of the plate with respect to the flow are considered from 0° to 75°, where 0° refers to the condition in which the flow is normal to the plate. The Reynolds number (Re) based on the flow velocity and the side length in the streamwise direction of the plate is up to 300. The hydrodynamic characteristics, including the force coefficients, the three-dimensional vortical structures and vortex shedding process, are presented. The effects of incidence angle on the wake transition are also discussed. It is observed that as the incidence angle increases, the flow firstly changes from a chaotic state to a periodic state and finally returns to chaos again at high incidence angles.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"52 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131479570","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}
Zhiguo Zhang, Lixiang Guo, Shuang Wang, Yecheng Yuan, Can Chen
In this paper, an in-house CFD code HUST-Ship is used for the numerical simulation of parametric rolling phenomena of ONR Tumblehome in regular head wave. Preliminary resistance and roll decay simulations at Fr = 0.2 were carried out and compared with existed INSEAN experimental data. Following, three DOFs’ ship motions in regular head wave with an initial roll angle of 30 degrees was calculated to examine the possibility of occurrence of parametric rolling. Finally, a simulation without initial roll disturbance was performed to investigate its influence to the steady roll amplitude. By conducting fast Fourier transform of the time history of motions, forces and moments, the characteristics are analyzed and co-related with wave frequency. Results can be concluded that the in-house code has the ability to perform the parametric rolling simulation, and that the final steady roll amplitude is not affected by the initial disturbance. In addition, heave and pitch motions are dominantly affected by wave characteristic, roll frequency is about half that of wave, and that forces and moments in x direction exhibit high-order non-linearity.
{"title":"URANS Simulation of ONR Tumblehome Parametric Rolling in Regular Head Waves","authors":"Zhiguo Zhang, Lixiang Guo, Shuang Wang, Yecheng Yuan, Can Chen","doi":"10.1115/omae2019-96425","DOIUrl":"https://doi.org/10.1115/omae2019-96425","url":null,"abstract":"\u0000 In this paper, an in-house CFD code HUST-Ship is used for the numerical simulation of parametric rolling phenomena of ONR Tumblehome in regular head wave. Preliminary resistance and roll decay simulations at Fr = 0.2 were carried out and compared with existed INSEAN experimental data. Following, three DOFs’ ship motions in regular head wave with an initial roll angle of 30 degrees was calculated to examine the possibility of occurrence of parametric rolling. Finally, a simulation without initial roll disturbance was performed to investigate its influence to the steady roll amplitude. By conducting fast Fourier transform of the time history of motions, forces and moments, the characteristics are analyzed and co-related with wave frequency. Results can be concluded that the in-house code has the ability to perform the parametric rolling simulation, and that the final steady roll amplitude is not affected by the initial disturbance. In addition, heave and pitch motions are dominantly affected by wave characteristic, roll frequency is about half that of wave, and that forces and moments in x direction exhibit high-order non-linearity.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129383898","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 assessment of design loads acting on Liquefied Natural Gas (LNG) pump tower are widely based on Morison equation. However, the Morison equation lacks consideration of transverse flow, impact loads and the interaction between fluid and structure. Studies dealing with a direct simulation of LNG pump tower loads by means of Computational Fluid Dynamics (CFD), which can cover the aforementioned effects, are currently not available. A comparative numerical study on LNG pump tower loads is presented in this paper focusing on the following two questions: Are impact loads relevant for the structural design of LNG pump towers? In which way does the fluid-structure interaction influence the loads? Numerical simulations of the multiphase problem were conducted using field methods. Firstly, Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations, extended by the Volume of Fluid (VoF) approach were used to simulate the flow inside a three-dimensional LNG tank in model scale without tower structure. The results were used to validate the numerical model against model tests. Motion periods and amplitudes were systematically varied. Velocities and accelerations along the positions of the main structural members of the pump tower were extracted and used as input data for load approximations with the Morison equation. Morison equation, URANS and Delayed Detached Eddy Simulation (DDES) computed tower loads were compared. Time histories as well as statistically processed data were used. Global loads acting on the full (with tower structure) and simplified structure (no tower structure, but using Morison equation) are in the same order of magnitude. However, their time evolution is different, especially at peaks, which is considered significant for the structural design.
液化天然气(LNG)泵塔的设计荷载评估普遍采用莫里森方程。但是，morrison方程没有考虑横向流动、冲击载荷以及流体与结构的相互作用。利用计算流体动力学(CFD)直接模拟LNG泵塔载荷的研究，目前还没有涵盖上述影响的研究。本文针对以下两个问题，对LNG泵塔的载荷进行了数值比较研究:冲击载荷是否与LNG泵塔的结构设计相关?流固耦合以何种方式影响载荷?采用场法对多相问题进行了数值模拟。首先，采用非定常reynolds - average Navier-Stokes (URANS)方程，通过流体体积(VoF)方法进行扩展，在模型尺度下模拟了不含塔结构的三维LNG储罐内部流动。通过模型试验验证了数值模型的正确性。运动周期和振幅有系统地变化。提取了泵塔主要结构构件位置上的速度和加速度，并将其作为输入数据，用morrison方程进行荷载近似。比较了Morison方程、URANS和延迟分离涡模拟(DDES)计算的塔荷载。使用了时间历史和经过统计处理的数据。作用于全结构(有塔式结构)和简化结构(无塔式结构，但采用morrison方程)的整体荷载在同一数量级。然而，它们的时间演化是不同的，特别是在峰值处，这对结构设计具有重要意义。
{"title":"Assessment of LNG Pump Tower Loads","authors":"Michael Thome, J. Neugebauer, O. E. Moctar","doi":"10.1115/omae2019-96138","DOIUrl":"https://doi.org/10.1115/omae2019-96138","url":null,"abstract":"\u0000 The assessment of design loads acting on Liquefied Natural Gas (LNG) pump tower are widely based on Morison equation. However, the Morison equation lacks consideration of transverse flow, impact loads and the interaction between fluid and structure. Studies dealing with a direct simulation of LNG pump tower loads by means of Computational Fluid Dynamics (CFD), which can cover the aforementioned effects, are currently not available.\u0000 A comparative numerical study on LNG pump tower loads is presented in this paper focusing on the following two questions: Are impact loads relevant for the structural design of LNG pump towers? In which way does the fluid-structure interaction influence the loads?\u0000 Numerical simulations of the multiphase problem were conducted using field methods. Firstly, Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations, extended by the Volume of Fluid (VoF) approach were used to simulate the flow inside a three-dimensional LNG tank in model scale without tower structure. The results were used to validate the numerical model against model tests. Motion periods and amplitudes were systematically varied. Velocities and accelerations along the positions of the main structural members of the pump tower were extracted and used as input data for load approximations with the Morison equation.\u0000 Morison equation, URANS and Delayed Detached Eddy Simulation (DDES) computed tower loads were compared. Time histories as well as statistically processed data were used. Global loads acting on the full (with tower structure) and simplified structure (no tower structure, but using Morison equation) are in the same order of magnitude. However, their time evolution is different, especially at peaks, which is considered significant for the structural design.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129463159","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}
Fully turbulent channel flow is a very common and effective way to investigate the boundary layer flow over the flat plates. Mean flow characteristics of the channel flow can be predicted using steady Reynolds Averaged Navier-Stokes (RANS) simulations although the turbulent flow has an unsteady nature. The objective of the present study is to evaluate the predictive capability of the turbulence models, which are based on RANS decomposition, in channel flow involving smooth surfaces. The study covers the application of the Reynolds-stress based second-moment turbulence closure model and the most preferred linear eddy viscosity models to determine the mean flow characteristics. The turbulence properties were compared with the DNS data obtained from the open literature. Also, an iterative study was performed for the fine-tuning of the coefficients appearing in the Reynolds-stress turbulence model. A tuned version of the Reynolds-stress model for two different frictional Reynolds numbers (Reτ) of 180 and 590 is presented. These studies will form a basis for further computations on the channel flow with a higher Reynolds number range and different channel sections. They will also serve as the initial steps for the future experimental and computational studies that will focus on the understanding of the flow mechanism over the dimpled surfaces at Reynolds numbers (based on half channel height and mean bulk velocity) up to 2.105.
{"title":"Understanding the Capability of RANS Based Turbulence Models on Fully Turbulent Channel Flow","authors":"Y. K. İlter, U. Ünal","doi":"10.1115/omae2019-96290","DOIUrl":"https://doi.org/10.1115/omae2019-96290","url":null,"abstract":"\u0000 Fully turbulent channel flow is a very common and effective way to investigate the boundary layer flow over the flat plates. Mean flow characteristics of the channel flow can be predicted using steady Reynolds Averaged Navier-Stokes (RANS) simulations although the turbulent flow has an unsteady nature. The objective of the present study is to evaluate the predictive capability of the turbulence models, which are based on RANS decomposition, in channel flow involving smooth surfaces. The study covers the application of the Reynolds-stress based second-moment turbulence closure model and the most preferred linear eddy viscosity models to determine the mean flow characteristics. The turbulence properties were compared with the DNS data obtained from the open literature. Also, an iterative study was performed for the fine-tuning of the coefficients appearing in the Reynolds-stress turbulence model. A tuned version of the Reynolds-stress model for two different frictional Reynolds numbers (Reτ) of 180 and 590 is presented. These studies will form a basis for further computations on the channel flow with a higher Reynolds number range and different channel sections. They will also serve as the initial steps for the future experimental and computational studies that will focus on the understanding of the flow mechanism over the dimpled surfaces at Reynolds numbers (based on half channel height and mean bulk velocity) up to 2.105.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"09 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116852369","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}
Zurwa Khan, R. Tafreshi, M. Franchek, K. Grigoriadis
Pressure drop estimation across orifices for two-phase liquid-gas flow is essential to size valves and pipelines and decrease the probability of unsafe consequences or high costs in petroleum, chemical, and nuclear industries. While numerically modeling flow across orifices is a complex task, it can assess the effect of numerous orifice designs and operation parameters. In this paper, two-phase flow across orifices has been numerically modeled to investigate the effect of different fluid combinations and orifice geometries on pressure drop. The orifice is assumed to be located in a pipe with fully-developed upstream and downstream flow. Two liquid-gas fluid combinations, namely water-air, and gasoil liquid-gas mixture were investigated for different orifice to pipe area ratios ranging from 0.01 to 1 for the superficial velocity of 10 m/s. Volume of Fluid multiphase flow model along with k-epsilon turbulence model were used to estimate the pressure distribution of liquid-gas mixture along the pipe. The numerical model was validated for water-air with mean relative error less than 10.5%. As expected, a decrease in orifice to pipe area ratio resulted in larger pressure drops due to an increase in the contraction coefficients of the orifice assembly. It was also found that water-air had larger pressure drops relative to gasoil mixture due to larger vortex formation downstream of orifices. In parallel, a mechanistic model to directly estimate the local two-phase pressure drop across orifices was developed. The gas void fraction was predicted using a correlation by Woldesemayat and Ghajar, and applied to separated two-phase flow undergoing contraction and expansion due to an orifice. The model results were validated for different orifices and velocities, with the overall relative error of less than 40%, which is acceptable due to the uncertainties associated with measuring experimental pressure drop. Comparison of the developed numerical and mechanistic model showed that the numerical model is able to achieve a higher accuracy, while the mechanistic model requires minimal computation.
{"title":"Numerical and Mechanistic Modelling of Two-Phase Liquid-Gas Flow’s Pressure Drop Across Sharp-Edged Orifices","authors":"Zurwa Khan, R. Tafreshi, M. Franchek, K. Grigoriadis","doi":"10.1115/omae2019-96305","DOIUrl":"https://doi.org/10.1115/omae2019-96305","url":null,"abstract":"\u0000 Pressure drop estimation across orifices for two-phase liquid-gas flow is essential to size valves and pipelines and decrease the probability of unsafe consequences or high costs in petroleum, chemical, and nuclear industries. While numerically modeling flow across orifices is a complex task, it can assess the effect of numerous orifice designs and operation parameters. In this paper, two-phase flow across orifices has been numerically modeled to investigate the effect of different fluid combinations and orifice geometries on pressure drop. The orifice is assumed to be located in a pipe with fully-developed upstream and downstream flow. Two liquid-gas fluid combinations, namely water-air, and gasoil liquid-gas mixture were investigated for different orifice to pipe area ratios ranging from 0.01 to 1 for the superficial velocity of 10 m/s. Volume of Fluid multiphase flow model along with k-epsilon turbulence model were used to estimate the pressure distribution of liquid-gas mixture along the pipe. The numerical model was validated for water-air with mean relative error less than 10.5%. As expected, a decrease in orifice to pipe area ratio resulted in larger pressure drops due to an increase in the contraction coefficients of the orifice assembly. It was also found that water-air had larger pressure drops relative to gasoil mixture due to larger vortex formation downstream of orifices. In parallel, a mechanistic model to directly estimate the local two-phase pressure drop across orifices was developed. The gas void fraction was predicted using a correlation by Woldesemayat and Ghajar, and applied to separated two-phase flow undergoing contraction and expansion due to an orifice. The model results were validated for different orifices and velocities, with the overall relative error of less than 40%, which is acceptable due to the uncertainties associated with measuring experimental pressure drop. Comparison of the developed numerical and mechanistic model showed that the numerical model is able to achieve a higher accuracy, while the mechanistic model requires minimal computation.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121690498","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}
Fine grain solid bulk cargo with “sufficient” moisture content may undergo liquefaction during a voyage, posing a danger to the bulk carrier and the crew on-board due to its potential to shift and adversely affect the vessel’s stability. Between the years 2005 to 2017, it is believed that at least 21 bulk carriers have been lost due to cargo liquefaction. Most of these vessels are of 60,000 deadweight tonnes (DWT) and below, i.e. belonging to the “handysize” class. At the present moment, liquefaction is thought to occur through either conventional liquefaction or dynamic separation. In the former, wet granular cargo particles are rearranged through cyclic loads induced by the ship’s motions, resulting in overall compaction of the cargo and a corresponding increase in pore pressure between the particle grains. Shear resistance of the cargo pile decreases and movement of significant portions of the liquefied cargo material may occur, which in turn poses significant risks for the vessel. In dynamic separation, a pile of wet granular cargo particles undergo progressive transformation through intermediate stages, where the moisture separates from the cargo pile, forming fluid slurry comprising water and entrained particles that would be denser than water perched on top of a drier, compacted particle pile. The slurry will slosh with the vessel motion adversely influencing the stability of the vessel. Compared to conventional liquefaction, the compacted particle pile is drier and less susceptible to shift under vessel movement. In this study, a numerical modelling to assess the impact of the two cargo liquefaction mechanisms on a vessel’s stability is undertaken. The numerical models will be described and the results will be discussed.
{"title":"Cargo Liquefaction and Influence on Ship Stability","authors":"Kie Hian Chua, Yali Zhang, D. Konovessis","doi":"10.1115/omae2019-96448","DOIUrl":"https://doi.org/10.1115/omae2019-96448","url":null,"abstract":"\u0000 Fine grain solid bulk cargo with “sufficient” moisture content may undergo liquefaction during a voyage, posing a danger to the bulk carrier and the crew on-board due to its potential to shift and adversely affect the vessel’s stability. Between the years 2005 to 2017, it is believed that at least 21 bulk carriers have been lost due to cargo liquefaction. Most of these vessels are of 60,000 deadweight tonnes (DWT) and below, i.e. belonging to the “handysize” class. At the present moment, liquefaction is thought to occur through either conventional liquefaction or dynamic separation. In the former, wet granular cargo particles are rearranged through cyclic loads induced by the ship’s motions, resulting in overall compaction of the cargo and a corresponding increase in pore pressure between the particle grains. Shear resistance of the cargo pile decreases and movement of significant portions of the liquefied cargo material may occur, which in turn poses significant risks for the vessel. In dynamic separation, a pile of wet granular cargo particles undergo progressive transformation through intermediate stages, where the moisture separates from the cargo pile, forming fluid slurry comprising water and entrained particles that would be denser than water perched on top of a drier, compacted particle pile. The slurry will slosh with the vessel motion adversely influencing the stability of the vessel. Compared to conventional liquefaction, the compacted particle pile is drier and less susceptible to shift under vessel movement. In this study, a numerical modelling to assess the impact of the two cargo liquefaction mechanisms on a vessel’s stability is undertaken. The numerical models will be described and the results will be discussed.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131489571","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}
Yunxing Zhang, W. Duan, K. Liao, Shan Ma, Guihua Xia
The numerical simulation of wave breaking problem is still a tough challenge, partly due to the large grid number and CPU time requirement for capturing the multi-scale structures embedded in it. In this paper, a two-dimensional two-phase flow model with Adaptive Mesh Refinement (AMR) is proposed for simulating solitary wave breaking problems. Fractional step method is employed for the velocity-pressure decoupling. The free surface flow is captured with the Volume-of-Fluid (VOF) method combined with Piecewise Linear Interface Calculation (PLIC) for the reconstruction of the interface. Immersed boundary (IB) method is utilized to account for the existence of solid bodies. A geometric multigrid method is adopted for the solution of Pressure Poisson Equation (PPE). Benchmark case of advection test is considered first to test the VOF method. Then the solitary wave propagation problem is utilized to validate the model on AMR grid as well as analyze the efficiency of AMR. Furthermore, the solitary wave past a submerged stationary stage problem is simulated to validate the combined IB-VOF-AMR model. All the numerical results are compared with analytic solutions, experimental data or other published numerical results, and good agreements are obtained. Finally, the influence of stage height on the occurrence of wave breaking is analyzed. The locations of wave breaking are summarized for different stage heights.
{"title":"Numerical Simulation of Solitary Wave Breaking With Adaptive Mesh Refinement","authors":"Yunxing Zhang, W. Duan, K. Liao, Shan Ma, Guihua Xia","doi":"10.1115/omae2019-95224","DOIUrl":"https://doi.org/10.1115/omae2019-95224","url":null,"abstract":"\u0000 The numerical simulation of wave breaking problem is still a tough challenge, partly due to the large grid number and CPU time requirement for capturing the multi-scale structures embedded in it. In this paper, a two-dimensional two-phase flow model with Adaptive Mesh Refinement (AMR) is proposed for simulating solitary wave breaking problems. Fractional step method is employed for the velocity-pressure decoupling. The free surface flow is captured with the Volume-of-Fluid (VOF) method combined with Piecewise Linear Interface Calculation (PLIC) for the reconstruction of the interface. Immersed boundary (IB) method is utilized to account for the existence of solid bodies. A geometric multigrid method is adopted for the solution of Pressure Poisson Equation (PPE).\u0000 Benchmark case of advection test is considered first to test the VOF method. Then the solitary wave propagation problem is utilized to validate the model on AMR grid as well as analyze the efficiency of AMR. Furthermore, the solitary wave past a submerged stationary stage problem is simulated to validate the combined IB-VOF-AMR model. All the numerical results are compared with analytic solutions, experimental data or other published numerical results, and good agreements are obtained. Finally, the influence of stage height on the occurrence of wave breaking is analyzed. The locations of wave breaking are summarized for different stage heights.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129956760","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}
Jie Wu, Decao Yin, E. Passano, H. Lie, R. Peek, Octavio E. Sequeiros, S. Ang, Chiara A. Bernardo, Meliza Atienza
A series of experiments is performed in which a strake-covered rigid cylinder undergoes harmonic purely in-line motion while subject to a uniform “flow” created by towing the test rig along SINTEF Ocean’s towing tank. These tests are performed for a range of frequencies and amplitudes of the harmonic motion, to generate added-mass and excitation functions are derived from the in-phase and 90° out-of-phase components of the hydrodynamic force on the pipe, respectively. Using these excitation- and added-mass functions in VIVANA together with those from experiments on bare pipe by Aronsen (2007), the in-line VIV response of partially strake-covered pipeline spans is calculated. It is found that as little as 10% strake coverage at the optimal location effectively suppresses pure in-line VIV. Further advantages of strakes rather than intermediate supports to suppress in-line VIV include: strakes are not affected by the scour which can lower an intermediate support (in addition to creating the span in the first place). Further they do not prevent self-lowering of the pipeline or act as a point of concentration of VIV damage as the spans to each side of the intermediate support grow again.
{"title":"Forced Vibration Tests for In-Line VIV to Assess Partially Strake-Covered Pipeline Spans","authors":"Jie Wu, Decao Yin, E. Passano, H. Lie, R. Peek, Octavio E. Sequeiros, S. Ang, Chiara A. Bernardo, Meliza Atienza","doi":"10.1115/omae2019-95970","DOIUrl":"https://doi.org/10.1115/omae2019-95970","url":null,"abstract":"\u0000 A series of experiments is performed in which a strake-covered rigid cylinder undergoes harmonic purely in-line motion while subject to a uniform “flow” created by towing the test rig along SINTEF Ocean’s towing tank. These tests are performed for a range of frequencies and amplitudes of the harmonic motion, to generate added-mass and excitation functions are derived from the in-phase and 90° out-of-phase components of the hydrodynamic force on the pipe, respectively.\u0000 Using these excitation- and added-mass functions in VIVANA together with those from experiments on bare pipe by Aronsen (2007), the in-line VIV response of partially strake-covered pipeline spans is calculated. It is found that as little as 10% strake coverage at the optimal location effectively suppresses pure in-line VIV.\u0000 Further advantages of strakes rather than intermediate supports to suppress in-line VIV include: strakes are not affected by the scour which can lower an intermediate support (in addition to creating the span in the first place). Further they do not prevent self-lowering of the pipeline or act as a point of concentration of VIV damage as the spans to each side of the intermediate support grow again.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"58 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121007993","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}
M. Bernitsas, James Ofuegbe, Jau-Uei Chen, Hai Sun
Consistent rather than heuristic nondimensionalization of the fluid and oscillator dynamics in fluid-structure interaction, leads to decoupling of amplitude from frequency response. Further, recognizing that the number of governing dimensionless parameters should decrease, rather than increase, due to the fluid-structure synergy at the interface, an eigen-relation is revealed for a cylinder in Flow Induced Oscillations (FIO), including VIV and galloping: mA/mbod = CA/m* = 1/f*2-1. It shows that, for a given dimensionless oscillation frequency f*, the ratio of real added-mass to oscillating-mass is fully defined. Amplitude decoupling and the eigen-relation, lead to explicit expressions for coefficients, phases, and magnitudes of total, added-mass, and in-phase-with-velocity forces; revealing their dependence on the generic Strouhal number (Stn = fn*), damping, and Reynolds. Heuristic dimensionless parameters, (mass-damping, reduced velocity, mass-ratio, force coefficients) used in VIV data presentation are not needed. Theoretical derivations and force reconstruction match nearly perfectly with extensive experimental data collected over a decade in the Marine Renewable Energy Laboratory (MRELab) at the University of Michigan using four different oscillator test-models. Beyond the single frequency response model, the residuary force is derived by comparison to experiments. Established facts regarding VIV and galloping and new important observations are readily explained: (1) The effects of Strouhal, damping-ratio, mass-ratio, Reynolds, reduced velocity, and stagnation pressure. (2) The cause of expansion/contraction of the VIV range of synchronization. (3) The corresponding slope-change in oscillation frequency with respect to the Strouhal frequency of a stationary-cylinder. (4) The critical mass-ratio m* implying perpetual VIV. (5) The significance of the natural frequency of the oscillator in vacuo. (6) The effect of vortices on VIV and galloping. (7) The magnitude of vortex forces. (8) The indirect and direct vortex effects. (9) The unification of VIV and galloping onset. (10) Defining the next step in higher order theories for VIV and galloping beyond the eigen-relation.
{"title":"Eigen-Solution for Flow Induced Oscillations (VIV and Galloping) Revealed at the Fluid-Structure Interface","authors":"M. Bernitsas, James Ofuegbe, Jau-Uei Chen, Hai Sun","doi":"10.1115/omae2019-96823","DOIUrl":"https://doi.org/10.1115/omae2019-96823","url":null,"abstract":"\u0000 Consistent rather than heuristic nondimensionalization of the fluid and oscillator dynamics in fluid-structure interaction, leads to decoupling of amplitude from frequency response. Further, recognizing that the number of governing dimensionless parameters should decrease, rather than increase, due to the fluid-structure synergy at the interface, an eigen-relation is revealed for a cylinder in Flow Induced Oscillations (FIO), including VIV and galloping: mA/mbod = CA/m* = 1/f*2-1. It shows that, for a given dimensionless oscillation frequency f*, the ratio of real added-mass to oscillating-mass is fully defined. Amplitude decoupling and the eigen-relation, lead to explicit expressions for coefficients, phases, and magnitudes of total, added-mass, and in-phase-with-velocity forces; revealing their dependence on the generic Strouhal number (Stn = fn*), damping, and Reynolds. Heuristic dimensionless parameters, (mass-damping, reduced velocity, mass-ratio, force coefficients) used in VIV data presentation are not needed. Theoretical derivations and force reconstruction match nearly perfectly with extensive experimental data collected over a decade in the Marine Renewable Energy Laboratory (MRELab) at the University of Michigan using four different oscillator test-models. Beyond the single frequency response model, the residuary force is derived by comparison to experiments. Established facts regarding VIV and galloping and new important observations are readily explained: (1) The effects of Strouhal, damping-ratio, mass-ratio, Reynolds, reduced velocity, and stagnation pressure. (2) The cause of expansion/contraction of the VIV range of synchronization. (3) The corresponding slope-change in oscillation frequency with respect to the Strouhal frequency of a stationary-cylinder. (4) The critical mass-ratio m* implying perpetual VIV. (5) The significance of the natural frequency of the oscillator in vacuo. (6) The effect of vortices on VIV and galloping. (7) The magnitude of vortex forces. (8) The indirect and direct vortex effects. (9) The unification of VIV and galloping onset. (10) Defining the next step in higher order theories for VIV and galloping beyond the eigen-relation.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127406651","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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