Unsteady separated flow behind a bluff body causes fluctuating drag and transverse forces on the body, which is of great significance in many offshore and marine engineering applications. While physical experimental and computational techniques provide valuable physics insight, they are generally time-consuming and expensive for design space exploration and flow control of such practical scenarios. We present an efficient Convolutional Neural Network (CNN) based deep-learning technique to predict the unsteady fluid forces for different bluff body shapes. The discrete convolution process with a non-linear rectification is employed to approximate the mapping between the bluff-body shape and the fluid forces. The deep neural network is fed by the Euclidean distance function as the input and the target data generated by the full-order Navier-Stokes computations for primitive bluff body shapes. The convolutional networks are iteratively trained using a stochastic gradient descent method to predict the fluid force coefficients of different geometries and the results are compared with the full-order computations. We have extended this CNN-based technique to predict the variation of force coefficients with the Reynolds number as well. Within the error threshold, the predictions based on our deep convolutional network have a speed-up nearly three orders of magnitude compared to the full-order results and consumes an insignificant fraction of computational resources. The deep CNN-based model can predict the hydrodynamic coefficients required for the well-known Lighthill’s force decomposition in almost real time which is extremely advantageous for offshore applications. Overall, the proposed CNN-based approximation procedure has a profound impact on the parametric design of bluff bodies and the feedback control of separated flows.
{"title":"A Novel Deep Learning Method for the Predictions of Current Forces on Bluff Bodies","authors":"T. P. Miyanawala, R. Jaiman","doi":"10.1115/OMAE2018-78338","DOIUrl":"https://doi.org/10.1115/OMAE2018-78338","url":null,"abstract":"Unsteady separated flow behind a bluff body causes fluctuating drag and transverse forces on the body, which is of great significance in many offshore and marine engineering applications. While physical experimental and computational techniques provide valuable physics insight, they are generally time-consuming and expensive for design space exploration and flow control of such practical scenarios. We present an efficient Convolutional Neural Network (CNN) based deep-learning technique to predict the unsteady fluid forces for different bluff body shapes. The discrete convolution process with a non-linear rectification is employed to approximate the mapping between the bluff-body shape and the fluid forces. The deep neural network is fed by the Euclidean distance function as the input and the target data generated by the full-order Navier-Stokes computations for primitive bluff body shapes. The convolutional networks are iteratively trained using a stochastic gradient descent method to predict the fluid force coefficients of different geometries and the results are compared with the full-order computations. We have extended this CNN-based technique to predict the variation of force coefficients with the Reynolds number as well. Within the error threshold, the predictions based on our deep convolutional network have a speed-up nearly three orders of magnitude compared to the full-order results and consumes an insignificant fraction of computational resources. The deep CNN-based model can predict the hydrodynamic coefficients required for the well-known Lighthill’s force decomposition in almost real time which is extremely advantageous for offshore applications. Overall, the proposed CNN-based approximation procedure has a profound impact on the parametric design of bluff bodies and the feedback control of separated flows.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"60 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116251803","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}
Here, we experimentally studied the vortex-induced motion (VIM) of a free-standing riser (FSR; 1:65 scale model) with and without a porous metal screen (‘sheath’) placed co-centrically around the buoyancy can (BC). Specifically, we investigated the effects of mesh orientation (square and square rotated 45° in its own plane) and screen-BC diameter ratio (1.1 and 1.2) over a range of flow velocities. BC motions were recorded with a submersible camera; and inline (IL) and cross-flow (CF) amplitudes were then estimated with a motion tracking software. As expected, the installation of the screen changed the natural frequency of the models. Furthermore, the screen increased the reduced velocity at which the lock-in occurred, delaying it by a factor of ∼1.2 and ∼1.4 for the CF and IL respectively. All sheathed models had a prominent reduction in IL amplitudes compared to the bare/unsheathed BC; and at smaller flow velocities, the sheathed models also exhibited significantly lower CF motions, particularly those with a greater screen-BC diameter ratio.
{"title":"VIM Suppression for a FSR With a Co-Centric Porous Sheath Around the Buoyancy Can: Effects of Mesh Orientation and Diameter Ratio","authors":"J. Crosswell, Cheslav Balash","doi":"10.1115/OMAE2018-77251","DOIUrl":"https://doi.org/10.1115/OMAE2018-77251","url":null,"abstract":"Here, we experimentally studied the vortex-induced motion (VIM) of a free-standing riser (FSR; 1:65 scale model) with and without a porous metal screen (‘sheath’) placed co-centrically around the buoyancy can (BC). Specifically, we investigated the effects of mesh orientation (square and square rotated 45° in its own plane) and screen-BC diameter ratio (1.1 and 1.2) over a range of flow velocities. BC motions were recorded with a submersible camera; and inline (IL) and cross-flow (CF) amplitudes were then estimated with a motion tracking software. As expected, the installation of the screen changed the natural frequency of the models. Furthermore, the screen increased the reduced velocity at which the lock-in occurred, delaying it by a factor of ∼1.2 and ∼1.4 for the CF and IL respectively. All sheathed models had a prominent reduction in IL amplitudes compared to the bare/unsheathed BC; and at smaller flow velocities, the sheathed models also exhibited significantly lower CF motions, particularly those with a greater screen-BC diameter ratio.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130527397","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 an investigation of the suppression of vortex shedding of a larger circular cylinder by the interference of smaller rotating wake-control cylinders positioned around its center. Three-dimensional numerical simulations have been conducted at a moderate Reynolds number of 10,000, thus complementing the previous experimental results by offering a better understanding of the physical mechanisms behind the suppression. Visualization of the vortex wakes revealed a complex disruption of the vortex tubes for the higher rotation speeds, with consequent reduction in the mean drag of almost 52% when compared with that of a bare cylinder. Fluctuating lift has also been drastically reduced in 90%. Configurations of control cylinder that can suppress vortex shedding may produce more efficient suppressors for flow-induced vibrations.
{"title":"Suppression of Vortex Shedding With Rotating Wake-Control Cylinders: Numerical Investigation at a Moderate Reynolds Number","authors":"G. Assi, R. Orselli, M. Silva-Ortega","doi":"10.1115/OMAE2018-78316","DOIUrl":"https://doi.org/10.1115/OMAE2018-78316","url":null,"abstract":"This paper presents an investigation of the suppression of vortex shedding of a larger circular cylinder by the interference of smaller rotating wake-control cylinders positioned around its center. Three-dimensional numerical simulations have been conducted at a moderate Reynolds number of 10,000, thus complementing the previous experimental results by offering a better understanding of the physical mechanisms behind the suppression. Visualization of the vortex wakes revealed a complex disruption of the vortex tubes for the higher rotation speeds, with consequent reduction in the mean drag of almost 52% when compared with that of a bare cylinder. Fluctuating lift has also been drastically reduced in 90%. Configurations of control cylinder that can suppress vortex shedding may produce more efficient suppressors for flow-induced vibrations.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128773663","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}
Yuxin Xu, Guowei Sun, Songhua Liu, F. Xue, Yong Bai
Burner booms, one of the most important pieces of equipment for well testing procedures, are used to burn associated gas or oil-and-gas mixture. This paper first conducts a mesh sensitivity analysis to find a proper grid size. Grid independence is evaluated by the correlation value in different monitoring points. Then, the heat radiation of the burner boom on the semi-submersible drilling platform is analyzed using FDS. Without water curtain, it researches and compares the impact of low, medium and high speed wind condition on heat radiation. Without the wind influence, the simulation on heat radiation is done on the optimized water curtain design. The results show that the water curtain design can efficiently reduce the heat radiation on the platform, which has guiding significance for engineering design.
{"title":"Heat Radiation Research and Optimized Analysis of Burner Boom on Semi-Submersible Drilling Platform","authors":"Yuxin Xu, Guowei Sun, Songhua Liu, F. Xue, Yong Bai","doi":"10.1115/OMAE2018-77368","DOIUrl":"https://doi.org/10.1115/OMAE2018-77368","url":null,"abstract":"Burner booms, one of the most important pieces of equipment for well testing procedures, are used to burn associated gas or oil-and-gas mixture. This paper first conducts a mesh sensitivity analysis to find a proper grid size. Grid independence is evaluated by the correlation value in different monitoring points. Then, the heat radiation of the burner boom on the semi-submersible drilling platform is analyzed using FDS. Without water curtain, it researches and compares the impact of low, medium and high speed wind condition on heat radiation. Without the wind influence, the simulation on heat radiation is done on the optimized water curtain design. The results show that the water curtain design can efficiently reduce the heat radiation on the platform, which has guiding significance for engineering design.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121471218","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}
Induced vibrations are three-dimensional oscillations in a structure, whereby maximum amplitude is mostly perpendicular to sustained action. In this paper, we discuss the specific physics for how induced-vibrations evolve with space and time in a few example structures. We demonstrate how a sustained action (particularly fluid drag and gravity loading) rotates and reshapes these slender structures. We demonstrate how this then shifts and expands the dynamic nature of the structure, making the structure more receptive to vibrational inducements of any kind. Contrary to historical focus, the structure (not the fluid) primarily determines the physical nature of any induced vibrations, including fluid-induced vibrations.
{"title":"Insights of the Vortex-Induced Vibration Phenomenon: Ideal Models Versus Reality","authors":"R. Zueck","doi":"10.1115/OMAE2018-77708","DOIUrl":"https://doi.org/10.1115/OMAE2018-77708","url":null,"abstract":"Induced vibrations are three-dimensional oscillations in a structure, whereby maximum amplitude is mostly perpendicular to sustained action. In this paper, we discuss the specific physics for how induced-vibrations evolve with space and time in a few example structures. We demonstrate how a sustained action (particularly fluid drag and gravity loading) rotates and reshapes these slender structures. We demonstrate how this then shifts and expands the dynamic nature of the structure, making the structure more receptive to vibrational inducements of any kind. Contrary to historical focus, the structure (not the fluid) primarily determines the physical nature of any induced vibrations, including fluid-induced vibrations.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126503042","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 proposes a series of numerical investigations performed to test and demonstrate the capabilities of a RANS solver in the area of complex ship flow simulations. Focus is on a complete numerical model for hull, propeller and rudder that can account for the mutual interaction between these components. The paper presents the results of a complex investigation of the flow computations around the hull model of the 3600 TEU MOERI containership (KCS hereafter). The resistance for the hull equipped with rudder, the POW computations as well as the self-propulsion simulation are presented. Comparisons with the experimental data provided at the Tokyo 2015 Workshop on CFD in Ship Hydrodynamics are given to validate the numerical approach in terms of the total and wave resistance coefficients, sinkage and trim, thrust and torque coefficients, propeller efficiency and local flow features. Verification and validation based on the grid convergence tests are performed for each computational case. Discussions on the efficiency of the turbulence models used in the computations as well as on the main flow features are provided aimed at clarifying the complex structure of the flow around the stern.
本文提出了一系列的数值研究，以测试和证明RANS求解器在复杂船舶流动模拟领域的能力。重点是建立一个完整的船体、螺旋桨和舵的数值模型，该模型可以解释这些部件之间的相互作用。本文介绍了3600 TEU MOERI集装箱船(以下简称KCS)船体模型周围流动计算的复杂研究结果。给出了装舵船体的阻力计算和自推进仿真。通过与东京2015船舶流体力学CFD研讨会的实验数据对比，验证了总阻力系数和波浪阻力系数、下沉和纵倾系数、推力和扭矩系数、螺旋桨效率和局部流动特性的数值方法。基于网格收敛测试对每个计算案例进行了验证和验证。讨论了计算中使用的湍流模型的效率以及主要的流动特征，目的是澄清船尾周围流动的复杂结构。
{"title":"Numerical Simulation of the Resistance and Self-Propulsion Model Tests","authors":"A. Lungu","doi":"10.1115/OMAE2018-77767","DOIUrl":"https://doi.org/10.1115/OMAE2018-77767","url":null,"abstract":"The paper proposes a series of numerical investigations performed to test and demonstrate the capabilities of a RANS solver in the area of complex ship flow simulations. Focus is on a complete numerical model for hull, propeller and rudder that can account for the mutual interaction between these components. The paper presents the results of a complex investigation of the flow computations around the hull model of the 3600 TEU MOERI containership (KCS hereafter). The resistance for the hull equipped with rudder, the POW computations as well as the self-propulsion simulation are presented. Comparisons with the experimental data provided at the Tokyo 2015 Workshop on CFD in Ship Hydrodynamics are given to validate the numerical approach in terms of the total and wave resistance coefficients, sinkage and trim, thrust and torque coefficients, propeller efficiency and local flow features. Verification and validation based on the grid convergence tests are performed for each computational case. Discussions on the efficiency of the turbulence models used in the computations as well as on the main flow features are provided aimed at clarifying the complex structure of the flow around the stern.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115256749","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}
Computational Fluid Dynamics (CFD) is widely used in industry and academic research to investigate complex fluid flow. The bottleneck of a realistic CFD simulation is its long simulation time. The simulation time is generally reduced by massively parallel Central Processing Unit (CPU) clusters, which are very expensive. In this paper, it is shown that the CFD simulation can be accelerated significantly by a novel hardware called General Purpose Computing on Graphical Processing Units (GPGPU). GPGPU is a cost-effective computing cluster, which uses the Compute Unified Device Architecture (CUDA) of NVIDIA devices to transform the GPU into a massively parallel processor. The paper demonstrates the faster computing ability of GPU compared to a traditional multi-core CPU. Two scenarios are simulated; one is a 2-dimensional simulation of regular wave and another one is a 3-dimensional motion of a floating ship on a regular wave. A smoothed particle hydrodynamics (SPH) based CFD solver is used for simulating the complex free-surface flow. The performance of a single GPU is compared against a commonly used 16 core CPU. For a large simulation of 6 degrees of freedom (DOF) ship motion simulation, the comparative study exhibits a speedup of more than an order of magnitude, reducing simulation time from 30 hours to about 2 hours. This indicates a CUDA enabled GPU card can be used as a cost-effective computing tool for a reliable and accurate SPH-based CFD simulation. The cost-benefit analysis of GPU over a CPU cluster is also discussed.
{"title":"Application of GPGPU to Accelerate CFD Simulation","authors":"S. Mintu, D. Molyneux","doi":"10.1115/OMAE2018-77649","DOIUrl":"https://doi.org/10.1115/OMAE2018-77649","url":null,"abstract":"Computational Fluid Dynamics (CFD) is widely used in industry and academic research to investigate complex fluid flow. The bottleneck of a realistic CFD simulation is its long simulation time. The simulation time is generally reduced by massively parallel Central Processing Unit (CPU) clusters, which are very expensive. In this paper, it is shown that the CFD simulation can be accelerated significantly by a novel hardware called General Purpose Computing on Graphical Processing Units (GPGPU). GPGPU is a cost-effective computing cluster, which uses the Compute Unified Device Architecture (CUDA) of NVIDIA devices to transform the GPU into a massively parallel processor. The paper demonstrates the faster computing ability of GPU compared to a traditional multi-core CPU. Two scenarios are simulated; one is a 2-dimensional simulation of regular wave and another one is a 3-dimensional motion of a floating ship on a regular wave. A smoothed particle hydrodynamics (SPH) based CFD solver is used for simulating the complex free-surface flow. The performance of a single GPU is compared against a commonly used 16 core CPU. For a large simulation of 6 degrees of freedom (DOF) ship motion simulation, the comparative study exhibits a speedup of more than an order of magnitude, reducing simulation time from 30 hours to about 2 hours. This indicates a CUDA enabled GPU card can be used as a cost-effective computing tool for a reliable and accurate SPH-based CFD simulation. The cost-benefit analysis of GPU over a CPU cluster is also discussed.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122823109","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}
Using the computational fluid domain for propagation of ocean waves have become an important tool for the calculation of highly nonlinear wave loading on offshore structures such as run-up, wave slamming and non-linear breaking wave kinematics. At present, there are many computational fluid dynamics (CFD) codes available which can be employed to calculate water wave propagation and wave induced loading on structures. For practical reasons, however, the use of these codes is often limited to the propagation of regular uni-directional waves initiated very close to the structure, or to investigating the properties and loading due to measured waves by fitting a numerical wave to a measured wave profile. The present paper focuses on the propagation of steep irregular and short crested wave groups up to the point of breaking. Indeed, this is challenging because of the highly nonlinear behavior of irregular wave groups as steepness increases and they approach the point of breaking. The complexity further increases with the introduction of short-crestedness requiring computation in a large 3-dimentional domain. Two CFD codes are used in this comparison study which are believed to be well conditioned for wave propagation, the commercial code ComFLOW (available through the ComFLOW JIP project) and the open-source code BASILISK. The primary objective of this paper to show the two CFD codes capability of recreating measured irregular wave groups, using the known linear wave components from the model test as input to fluid domain. Wave elevation is measured at several locations in the close vicinity of the focus point. The comparison is carried out for a selection of events with variation in steepness, wave spreading and wave spectrum.
{"title":"Propagation of Steep and Breaking Short-Crested Waves: A Comparison of CFD Codes","authors":"Øystein Lande, T. B. Johannessen","doi":"10.1115/OMAE2018-78288","DOIUrl":"https://doi.org/10.1115/OMAE2018-78288","url":null,"abstract":"Using the computational fluid domain for propagation of ocean waves have become an important tool for the calculation of highly nonlinear wave loading on offshore structures such as run-up, wave slamming and non-linear breaking wave kinematics.\u0000 At present, there are many computational fluid dynamics (CFD) codes available which can be employed to calculate water wave propagation and wave induced loading on structures. For practical reasons, however, the use of these codes is often limited to the propagation of regular uni-directional waves initiated very close to the structure, or to investigating the properties and loading due to measured waves by fitting a numerical wave to a measured wave profile.\u0000 The present paper focuses on the propagation of steep irregular and short crested wave groups up to the point of breaking. Indeed, this is challenging because of the highly nonlinear behavior of irregular wave groups as steepness increases and they approach the point of breaking. The complexity further increases with the introduction of short-crestedness requiring computation in a large 3-dimentional domain.\u0000 Two CFD codes are used in this comparison study which are believed to be well conditioned for wave propagation, the commercial code ComFLOW (available through the ComFLOW JIP project) and the open-source code BASILISK. The primary objective of this paper to show the two CFD codes capability of recreating measured irregular wave groups, using the known linear wave components from the model test as input to fluid domain. Wave elevation is measured at several locations in the close vicinity of the focus point. The comparison is carried out for a selection of events with variation in steepness, wave spreading and wave spectrum.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129117789","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}
Fairings have historically been known to achieve in-line drag coefficients (Cdx) of approximately 0.60 across the Reynolds number (Re) range of 100,000 to 1,000,000, typical for the offshore environment [1]. The recent development of helically grooved drill riser buoyancy was shown to achieve Cdx values of 0.65 for this Re range [2], presenting a strong alternative to fairing products especially considering the additional installation, storage and maintenance requirements of fairings. Therefore it is the purpose of this paper to investigate possible fairing designs capable of achieving even lower Cdx values where fairings can still be beneficial in further reducing drag loading. This paper proposes a non-parallel reduced chord horseshoe (RCH) fairing design and is analysed using computational fluid dynamics (CFD) in 3-d using the transient k-epsilon (Reynolds-averaged Navier-Stokes) turbulence model. The modelling approach is validated against tow tank test data of a previous teardrop-shaped (TD) fairing design which showed good agreement with published, peer-reviewed literature. It was found CFD simulations with axially continuous fairings provide artificially low Cdx values due to the absence of fairing end-effects and gaps between fairing sections. In essence, an infinitely long and uninterrupted fairing in the riser axial dimension is not realistic. Incorporation of this discontinuity sees a significant increase in Cdx compared to the axially continuous fairing configuration. Although this is the case, it was found Cdx of approximately 0.48 or lower is achievable for the entire offshore Re range for the discontinuous fairing configuration (assuming a chord/diameter ratio of 2.0). Larger chord/diameter ratios would provide lower Cdx at the cost of a longer chord length which may impact fairing installation efficiency. Longer axial lengths would also achieve lower Cdx but with the risk of flutter instability. This development in RCH fairing design sees a possible option for further fairing applicability to offshore drilling operations where lower drag is desirable beyond that offered by the helically grooved buoyancy.
{"title":"Drill Riser Fairing Hydrodynamic Assessment With 3-Dimensional Computational Fluid Dynamics Simulations","authors":"L. Lai","doi":"10.1115/OMAE2018-77063","DOIUrl":"https://doi.org/10.1115/OMAE2018-77063","url":null,"abstract":"Fairings have historically been known to achieve in-line drag coefficients (Cdx) of approximately 0.60 across the Reynolds number (Re) range of 100,000 to 1,000,000, typical for the offshore environment [1]. The recent development of helically grooved drill riser buoyancy was shown to achieve Cdx values of 0.65 for this Re range [2], presenting a strong alternative to fairing products especially considering the additional installation, storage and maintenance requirements of fairings.\u0000 Therefore it is the purpose of this paper to investigate possible fairing designs capable of achieving even lower Cdx values where fairings can still be beneficial in further reducing drag loading. This paper proposes a non-parallel reduced chord horseshoe (RCH) fairing design and is analysed using computational fluid dynamics (CFD) in 3-d using the transient k-epsilon (Reynolds-averaged Navier-Stokes) turbulence model. The modelling approach is validated against tow tank test data of a previous teardrop-shaped (TD) fairing design which showed good agreement with published, peer-reviewed literature.\u0000 It was found CFD simulations with axially continuous fairings provide artificially low Cdx values due to the absence of fairing end-effects and gaps between fairing sections. In essence, an infinitely long and uninterrupted fairing in the riser axial dimension is not realistic. Incorporation of this discontinuity sees a significant increase in Cdx compared to the axially continuous fairing configuration. Although this is the case, it was found Cdx of approximately 0.48 or lower is achievable for the entire offshore Re range for the discontinuous fairing configuration (assuming a chord/diameter ratio of 2.0). Larger chord/diameter ratios would provide lower Cdx at the cost of a longer chord length which may impact fairing installation efficiency. Longer axial lengths would also achieve lower Cdx but with the risk of flutter instability.\u0000 This development in RCH fairing design sees a possible option for further fairing applicability to offshore drilling operations where lower drag is desirable beyond that offered by the helically grooved buoyancy.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125394472","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}
Felipe Santos de Castro, Eduardo Tadashi Katsuno, G. Assi, J. Dantas
The large-scale presence of debris is a recurrent issue in the Madeira River, located on Amazon rainforest, North of Brazil, and it is a major concern for the Santo Antonio hydropower plant, located at this region. In order to avoid the abundant amount of debris, floating structures called log booms are installed across the river to retain and deflect them. This paper aims to present the methods used to investigate the structural characteristics of a truncated scale model of a log boom line, through water proof strain-gauges and load cells in hydrodynamic experiments. For that, the model was towed along the model basin of the Institute for Technological Research and wooden scale logs were included to simulate the log jam phenomenon. The paper covers experiment methods, from model design to setting of data acquisition devices and system, characteristics of the experimental runs, and further data analysis. The influence of the scale debris on the structural elements are presented, which can leads to develop a correlation model to scale the fluid-structure interactions in the real prototype.
{"title":"Structural Investigation of the Log Accumulation Effect in a Debris Containment Grid Through Towing Tank Experiments","authors":"Felipe Santos de Castro, Eduardo Tadashi Katsuno, G. Assi, J. Dantas","doi":"10.1115/OMAE2018-78097","DOIUrl":"https://doi.org/10.1115/OMAE2018-78097","url":null,"abstract":"The large-scale presence of debris is a recurrent issue in the Madeira River, located on Amazon rainforest, North of Brazil, and it is a major concern for the Santo Antonio hydropower plant, located at this region. In order to avoid the abundant amount of debris, floating structures called log booms are installed across the river to retain and deflect them. This paper aims to present the methods used to investigate the structural characteristics of a truncated scale model of a log boom line, through water proof strain-gauges and load cells in hydrodynamic experiments. For that, the model was towed along the model basin of the Institute for Technological Research and wooden scale logs were included to simulate the log jam phenomenon. The paper covers experiment methods, from model design to setting of data acquisition devices and system, characteristics of the experimental runs, and further data analysis. The influence of the scale debris on the structural elements are presented, which can leads to develop a correlation model to scale the fluid-structure interactions in the real prototype.","PeriodicalId":345141,"journal":{"name":"Volume 2: CFD and FSI","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128760447","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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