CFD Simulation of Truss Spar Vortex-Induced Motion

2006 ◽  
Author(s):  
Sampath Atluri ◽  
John Halkyard ◽  
Senu Sirnivas
Keyword(s):  
Cfd Simulation ◽  
Turbulence Modeling ◽  
General Purpose ◽  
Scale Model ◽  
Cfd Simulations ◽  
Model Experiments ◽  
Helical Strakes ◽  
Induced Motion ◽  
Truss Spar ◽  
Hydrodynamic Effects

Helical strakes are used to suppress the Vortex-Induced Motion of Truss Spars. Model experiments have demonstrated the efficiency of strakes in the Truss Spar design but also indicate that the VIM response is sensitive to the details of strake design and placement of appurtenances around the Spar hull. It is desirable to study these hydrodynamic effects using CFD. The following paper is a continuation of some of the earlier CFD simulations on this subject (see, J. Halkyard, et al., “Benchmarking of Truss Spar Vortex-Induced Motions Derived from CFD with Experiments”, Proceedings of OMAE’05). This paper in particular deals with the effect of holes in the strakes and appurtenances and their placement. All the simulations were done at model scale (1:40 scale model of an actual Truss Spar design) to compare the motions with experimental results. Mesh sensitivity and turbulence modeling issues are also discussed. Calculations were done using general purpose CFD code Acusolve™.

Benchmarking of Truss Spar Vortex Induced Motions Derived From CFD With Experiments

2005 ◽  
Author(s):  
John Halkyard ◽  
Senu Sirnivas ◽  
Samuel Holmes ◽  
Yiannis Constantinides ◽  
Owen H. Oakley ◽  
...  
Keyword(s):  
Scale Up ◽  
Vertical Cylinder ◽  
Reynolds Numbers ◽  
Full Scale ◽  
Scale Model ◽  
Current Direction ◽  
Test Results ◽  
Helical Strakes ◽  
Truss Spar ◽  
Scale Data

Floating spar platforms are widely used in the Gulf of Mexico for oil production. The spar is a bluff, vertical cylinder which is subject to Vortex Induced Motions (VIM) when current velocities exceed a few knots. All spars to date have been constructed with helical strakes to mitigate VIM in order to reduce the loads on the risers and moorings. Model tests have indicated that the effectiveness of these strakes is influenced greatly by details of their design, by appurtenances placed on the outside of the hull and by current direction. At this time there is limited full scale data to validate the model test results and little understanding of the mechanisms at work in strake performance. The authors have been investigating the use of CFD as a means for predicting full scale VIM performance and for facilitating the design of spars for reduced VIM. This paper reports on the results of a study to benchmark the CFD results for a truss spar with a set of model experiments carried out in a towing tank. The focus is on the effect of current direction, reduced velocity and strake pitch on the VIM response. The tests were carried out on a 1:40 scale model of an actual truss spar design, and all computations were carried out at model scale. Future study will consider the effect of external appurtenances on the hull and scale-up to full scale Reynolds’ numbers on the results.

Vortex Induced Motion of TLP With Consideration of Appurtenances

2014 ◽  
Author(s):  
Jaime Hui Choo Tan ◽  
Yih Jeng Teng ◽  
Allan Magee ◽  
Benedict Toong Heng Ly ◽  
Shankar Bhat Aramanadka
Keyword(s):  
Cfd Simulation ◽  
Scale Effects ◽  
Floating Platform ◽  
Steel Catenary Riser ◽  
Aspect Ratios ◽  
Significant Difference ◽  
Helical Strakes ◽  
Induced Motion ◽  
Set Up ◽  
Comparison Of The Results

Offshore floating platform configurations often consist of geometrically simple and symmetrical shapes which are made complicated by the presence of appurtenances such as helical strakes, tendon porches, steel catenary riser (SCR) porches, pipes, chains, fairleads and anodes on the surface of the hull. Previous studies mainly on spars show that these hull external features affect the Vortex Induced Motion (VIM) performance of the platform significantly. This is to be expected since VIM is controlled by the flow separation on the hull surface and the resulting vortex shedding patterns. Scale effects may also play a role in model tests for bare cylinders or hulls with bare cylindrical columns, whereas previous studies have shown less Reynolds dependence when appurtenances are modelled. This study investigates the effect of hull appurtenances on VIM of a multi-column floating platform, i.e. a Tension Leg Platform (TLP) designed for Southeast Asian environment. Significant difference in VIM behaviors is expected between spars and TLPs since the column aspect ratios are very different and TLPs do not have helical strakes that are commonly fitted on spars. Model testing and Computational Fluid Dynamics (CFD) simulation are used in this VIM study, with the former being the emphasis of this paper. Descriptions of the respective experimental and numerical methodologies are presented and the comparison of the results is made. Further work required to improve the model test set-up and the CFD simulation are suggested. From this study, it is shown that the effect of appurtenances on TLP VIM simulation is important and must be taken into account to obtain realistic results.

Truss Spar Vortex Induced Motions: Benchmarking of CFD and Model Tests

2006 ◽  
Author(s):  
John Halkyard ◽  
Sampath Atluri ◽  
Senu Sirnivas
Keyword(s):  
Fluid Dynamics ◽  
Best Practices ◽  
Turbulence Modeling ◽  
Production Systems ◽  
Model Tests ◽  
The Past ◽  
Helical Strakes ◽  
Truss Spar ◽  
Computational Fluid Dynamics Cfd ◽  
Riser Design

Spar production systems are subject to Vortex Induced Motions (VIM) which may impact mooring and riser design. Helical strakes are employed to mitigate VIM. Model tests are typically required to validate the performance of the strakes. This paper will report on the results of benchmarking studies that have been conducted over the past few years to compare model tests with computational fluid dynamics (CFD). The paper discusses comparisons of CFD with model tests, “best practices” for the use of CFD for these classes of problems and issues related to turbulence modeling and meshing of problems at large Reynold’s numbers. This work is ongoing.

Model Test Study on Vortex-Induced Motions of a Floating Cylinder

2009 ◽  
Author(s):  
Ying Wang ◽  
Jianmin Yang ◽  
Tao Peng ◽  
Xin Li
Keyword(s):  
Circular Cylinder ◽  
Scale Model ◽  
Visualization System ◽  
Forced Motion ◽  
Drag Forces ◽  
Fluid Field ◽  
Helical Strakes ◽  
Induced Motion ◽  
Motion Characteristics ◽  
Lift And Drag

Vortex-Induced Motions (VIM) under current flow is an important issue for surface piercing cylinders, such as Spar platforms and floating buoys, since it affects the motion performance of these structures greatly. In recent years this phenomenon attracts much attention and many researchers have been making efforts to deal with this problem. VIM is such a complicated phenomenon that more fundamental studies are needed to understand the essence behind VIM. This paper mainly concentrates on a circular cylinder, aiming to eliminate outside influences and reveal the inherent characteristic of vortex-induced motion mechanism. A circular cylinder with an aspect ratio of 1:2.4, which could be considered as a scale model for the hard tank of a typical Truss Spar, is studied by experimental method to investigate the surrounding fluid field, the excitation forces and Vortex-Induced Motion characteristics under various governing parameters, such as the current velocity and direction, the mooring stiffness and distribution, the use and efficiency of helical strakes, and so on. By using a simple flow visualization system, the unsteady flow passing the circular cylinder and the vortices in the wake are captured and recorded. The cylinder is tested respectively under fixed, forced-motion and elastically moored conditions. The fluid field, the vortex structures, and the lift and drag forces under fixed and forced-motion conditions are measured, the VIM performance of the cylinder with two different mooring distributions are studied, and strake efficiency is studied considering current directionality and strake height influence.

CFD Analysis of Vortex-Induced Motions of Bare and Straked Cylinders in Currents

2005 ◽  
Author(s):  
K. P. Thiagarajan ◽  
Y. Constantinides ◽  
L. Finn
Keyword(s):  
Turbulence Modeling ◽  
Equations Of Motion ◽  
Transverse Displacement ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Hexahedral Elements ◽  
Helical Strakes ◽  
Truss Spar ◽  
Uniform Currents ◽  
Tank Geometry

It is widely acknowledged that the use of helical strakes for mitigation of vortex-induced motions (VIM) of surface piercing cylinders, such as spar platforms, is only partially effective. Using computational fluid dynamics tools, we compare the oscillation characteristics of a bare cylinder and a straked cylinder in uniform currents. Our model comprised of a straked cylinder with diameter of 0.741 m, aspect ratio of 1:1.9 and three helical strakes of height 13% of cylinder diameter. This geometry corresponds to the hard tank geometry of a scaled truss spar model known to exhibit VIM in tow tank testing. In the CFD simulations the cylinder is moored with linear springs to provide a range of reduced velocities. The fluid domain is made of an unstructured grid comprising of hexahedral elements. Fluid structure interaction utilizes grid stretching and a user defined function for solving the equations of motion. Turbulence modeling uses Detached Eddy Simulation (DES) and the boundary layer is modeled using a wall function with a surface roughness of 0.0003 m. Reynolds numbers are in the range of 50,000 to 100,000. Results for straked cylinder compares reasonably with published results, but under-predicts the peak response. In comparing with corresponding results for a bare cylinder without strakes, the spectral features of the transverse displacement show variations, which are found to be due to the spoiling effect of the strakes.

CFD Simulations of Boron Mixing in ESBWR Core Bypass Regions During an Anticipated Transient Without Scram (ATWS) Event

2008 ◽  
Author(s):  
James A. Tallman ◽  
Wayne Marquino ◽  
M. D. Alamgir
Keyword(s):  
Control System ◽  
Design Process ◽  
Cfd Simulation ◽  
Turbulence Modeling ◽  
Navier Stokes ◽  
Cfd Simulations ◽  
The Core ◽  
Time Prediction ◽  
Transport And Mixing ◽  
Borate Solution

CFD was used to simulate boron mixing in the ESBWR core during a limiting ATWS event. During the ESBWR design process, questions were raised regarding the Standby Liquid Control System (SLCS), which adds a sodium penta-borate solution to the core during ATWS events for the purpose of halting reactivity and core shutdown. The questions involved the design prediction of boron transport and mixing in the core bypass spaces, and how that influenced the core shutdown time prediction associated with the SLCS. In response, a CFD simulation was performed to study the mixing of the sodium penta-borate solution in bypass spaces of the ESBWR core. The CFD solution was a transient, Reynolds-Averaged Navier-Stokes (RANS) solution using two-equation turbulence modeling and 25 million computational nodes. Compared with the design predictions, the CFD results showed a much faster transport of boron toward the center of the core and a much greater quantity of boron is ingested into the fuel bundles. These findings demonstrate an adequate level of conservativism in the core shutdown time predictions, and confirm the effectiveness of the ESBWR SLCS system.

CFD Simulations of Helical Strakes Reducing Vortex Induced Motion of a Semi-Submersible

2018 ◽  
Author(s):  
Jiawei He ◽  
Decheng Wan ◽  
Zhiqiang Hu
Keyword(s):  
Vortex Shedding ◽  
Flow Characteristics ◽  
Boundary Region ◽  
Detached Eddy Simulation ◽  
Cfd Simulations ◽  
Mooring Lines ◽  
Boundary Area ◽  
Eddy Simulation ◽  
Helical Strakes ◽  
Induced Motion

This paper describes a set of VIM CFD simulations for a semi-submersible with and without helical strakes. The numerical investigations are conducted under low Reynolds number (Re) using naoe-FOAM-SJTU, a solver developed based on the open source framework OpenFOAM. The self-developed six degree-of-freedom (6DoF) motion module and mooring system module are applied to model motions of semi-submersible and the constraint of mooring lines, respectively. To carry out the calculations, turbulence closure has been chosen the Shear Stress Transport (SST) based Delay Detached eddy simulation (DDES), which uses the RANS model inside the boundary region and LES model outside the boundary area. This allows a realistic simulation within the boundary region where the vortex shedding is taking place, while not using unnecessary amounts of computational power. The Vortex Induced Motion (VIM) of semi-submersible with and without helical strakes was compared against each other for different reduced velocities (Ur). The flow characteristics of the semi-submersible platform is studied based on the characteristics of vortex shedding. For different current incident angles, time histories, trajectories and vorticity of the semi-submersible at different reduced velocities are reported. The result shows our CFD solver naoe-FOAM-SJTU is applicable and reliable to study VIM of semi-submersibles.

scholarly journals Prediction of Wind Erosion over a Heritage Site: A Case Study of Yongling Mausoleum, China

2019 ◽  
Vol 3 (4) ◽  
pp. 41-57
Author(s):  
Xiaoyu Wang ◽  
Jinzhu Meng ◽  
Tianwei Zhu ◽  
Jingyu Zhang
Keyword(s):  
Wind Erosion ◽  
Cfd Simulation ◽  
Scale Model ◽  
Weather Data ◽  
Cfd Simulations ◽  
Wind Speeds ◽  
Heritage Site ◽  
Heritage Buildings ◽  
Computational Fluid Dynamics Cfd

AbstractTo protect heritage buildings better, a method exploiting computational fluid dynamics (CFD) was developed for the analysis of wind erosion at a heritage site. Over a two-year period, we collected measurements of hourly weather data at Xinbin County to obtain statistics of wind speeds and directions for the Yongling Mausoleum. Subsequent results from CFD simulations show that before greening, with wind speeds reaching 10 m/s, certain structures (southwest-facing corners, doors and windows on open sides, places where swirling winds develop, and eaves of sloping roofs) of four heritage buildings were eroded more severely. With appropriate greening, plants may exert their unique ecological presence to better protect heritage buildings and their historical environments. After greening, the severity of damage to these vulnerable structures by wind was reduced. With wind speeds reaching 10 m/s, the average pressure on the structures of each building was 0.41–27.85 Pa, representing a reduction of 2.4%–75.6% from pressures before greening. We also constructed a 1:500-scale model to verify in experiments the correctness of CFD simulation qualitatively. The CFD simulations were found to provide an effective method to investigate and predict wind erosion of the heritage site.

CFD Simulation of Flow-Induced Motions of a Multi-Column Floating Platform

2011 ◽  
Author(s):  
Jang-Whan Kim ◽  
Allan Magee ◽  
Kenneth Yeoh Hock Guan
Keyword(s):  
Fluid Transport ◽  
Cross Validation ◽  
Cfd Simulation ◽  
Model Tests ◽  
Scale Model ◽  
Test Results ◽  
Floating Platform ◽  
Induced Motion ◽  
Rigid Body Motions ◽  
Floating Platforms

Recent improvements in capabilities of both hardware and software allow solving the coupled rigid body motions for the floating platform together with the fluid transport equations. This makes CFD a possible alternative or complement to model tests for predicting VIM performance. In addition, CFD allows simulating certain factors which cannot be addressed in scale model tests, and the two methods can ideally serve as cross-validation tools to bound the remaining uncertainties. Previous applications of CFD to Spar VIM predictions have shown promising results. Building on this, flow-induced motion simulations of multi-column floating platforms are being carried out using CFD as part of the R&D effort within Technip. The purpose of this paper is to present the results of two separate preliminary simulations applied to the prediction of vortex-induced motions of a TLP design and compare to the model test results.

Numerical Hull Resistance and Hydrodynamic Characteristics of an Independently Rotating Multi-Hull Vessel

2019 ◽  
Author(s):  
Sharath Srinivasamurthy ◽  
Hiroshi Sakamoto ◽  
Tatsuo Nishikawa ◽  
Yasunori Nihei
Keyword(s):  
Numerical Simulation ◽  
Pressure Distribution ◽  
Cfd Simulation ◽  
Hydrodynamic Characteristics ◽  
Cfd Simulations ◽  
Basic Framework ◽  
Wave Patterns ◽  
Experimental Findings ◽  
Hydrodynamic Effects ◽  
Simulation Scheme

Abstract In this study, an attempt is made to understand the hydrodynamic characteristics of an automated multi-hull vessel named as Quadmaran. Firstly, a single hull of the Quadmaran vessel is considered and numerical CFD simulation is performed using OpenFOAM. Hull resistance predictions are compared with the experimental findings and numerical simulation is validated. After validating the simulation scheme, further CFD simulations are performed on two hulls with varying distance between them to understand the hydrodynamic characteristics of different configurations. Pressure distribution and wave patterns around the hulls are also summarized and discussed in the paper. Further, efforts are made to optimize the distance between the hulls for reducing hull resistance. A basic framework is suggested to carefully consider the hydrodynamic effects for multi-hull vessels.

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