scholarly journals Modelling Risers With Partial Strake Coverage

2011 ◽  
Author(s):  
Themistocles L. Resvanis ◽  
J. Kim Vandiver
Keyword(s):  
Experimental Data ◽  
Test Data ◽  
Model Test ◽  
Vortex Induced Vibration ◽  
Partial Coverage ◽  
Prediction Program ◽  
New Methods ◽  
Helical Strakes

This paper compares model test data for risers with partial strake coverage to predictions made with the Vortex-Induced Vibration (VIV) prediction program SHEAR7 Versions 4.5 and 4.6. It is shown that new features in Version 4.6 substantially enhance the capability for predicting the VIV response of risers with partial coverage. Experimental data is taken from two large L/D tests: the NDP 38 m long riser tests and the Deepstar-Miami, 500 foot long riser. New methods are described for modeling risers partially covered with helical strakes. Key SHEAR7 parameters are recommended, based on parametric investigations to calibrate the model against the available experimental data. Recommended modeling procedures are described so as to facilitate implementation by SHEAR7 users in their VIV modeling tasks.

Integral Force/Moment Waterjet Model for CFD Simulations

2010 ◽  
Vol 132 (10) ◽  
Author(s):  
Manivannan Kandasamy ◽  
Seng Keat Ooi ◽  
Pablo Carrica ◽  
Frederick Stern
Keyword(s):  
Experimental Data ◽  
Test Data ◽  
Model Test ◽  
Additional Data ◽  
Inlet Pressure ◽  
Working Fluid ◽  
Local Flow ◽  
Force Moment ◽  
Sinkage And Trim ◽  
Input Variables

An integral force/moment waterjet model for computational fluid dynamics (CFD) is derived for ship local flow/powering predictions, including sinkage and trim. The waterjet induced reaction forces and moment and waterjet/hull interaction stern force replicate the effects of the waterjet without requiring detailed simulations of the waterjet system. The model extends the International Towing Tank Conference (ITTC) waterjet model for sinkage and trim by using an alternative control volume also appropriate for CFD and by including vertical forces and pitching moment in the waterjet/hull force/moment balance. The same grid is used for both without and with waterjet simulations. The CFD waterjet model requires limited waterjet geometry (inlet and outlet areas and locations, and weight of working fluid) and several waterjet flow (mass flow rate, inlet pressure force, inlet and outlet momentum correction factors and flow angles, and stern force and location) input variables. The CFD waterjet model can be used for local flow predictions by using waterjet flow input variables provided by ITTC waterjet model test data, including additional data for waterjet induced inlet pressure and stern forces. It can also be used for powering predictions once waterjet flow input variable correlations are available based on CFD for the waterjet system and/or experimental data. The CFD waterjet model is demonstrated for local flow predictions for the DTMB 5594 high-speed sealift ship model for which ITTC waterjet model test data, including additional data for waterjet induced stern forces, are available. Correlations for the waterjet flow input variables are shown to be feasible using a combination of CFD and experimental data for the waterjet system for three different hulls.

scholarly journals An Experimental Evaluation of Vortex-Induced Vibration of a Riser Bundle With Gaps

2009 ◽  
Author(s):  
J. Kim Vandiver ◽  
Yongming Cheng ◽  
Vivek Jaiswal ◽  
Aditi Sheshadri ◽  
Alan Yu
Keyword(s):  
Free Vibration ◽  
Model Test ◽  
Flow Direction ◽  
Angle Of Attack ◽  
Cross Flow ◽  
Test Results ◽  
Vortex Induced Vibration ◽  
Towing Tank ◽  
Helical Strakes ◽  
Rigid Model

VIV model test results are presented for a bundle of three parallel pipes all lying in the same plane, similar to a riser with large kill and choke lines. The rigid model was attached to a spring-mounted frame in the MIT towing tank. The horizontal model was towed in the tank and allowed to respond in free vibration to vortex-induced vibration in the cross-flow direction. The angle of attack of the model was varied from 0 to 90 degrees. The model was tested with and without helical strakes. Without strakes the model exhibited significant vibration at 0 and 90 degrees angle of attack. Strakes suppressed VIV at all angles of attack.

Joint High Speed Sealift (JHSS) Segmented Model Test Data Analysis and Validation of Numerical Simulations

2012 ◽  
Author(s):  
Dominic Piro ◽  
Kyle A. Brucker ◽  
Thomas T. O'Shea ◽  
Donald Wyatt ◽  
Douglas Dommermuth ◽  
...  
Keyword(s):  
Data Analysis ◽  
Numerical Simulations ◽  
Test Data ◽  
Model Test ◽  
High Speed ◽  
Segmented Model

Performance prediction of transonic axial multistage compressor based on one-dimensional meanline method

2021 ◽  
pp. 095765092199881
Author(s):  
Yingying Zhang ◽  
Shijie Zhang
Keyword(s):  
Experimental Data ◽  
Mass Flow ◽  
Flow Separation ◽  
Performance Prediction ◽  
Factor Model ◽  
Separation Method ◽  
Prediction Program ◽  
Blockage Factor ◽  
Reliability And Robustness ◽  
Work Done

This study proposes a 1D meanline program for the modeling of modern transonic axial multistage compressors. In this method, an improved blockage factor model is proposed. Work-done factor that varies with the compressor performance conditions is added in this program, and at the same time a notional blockage factor is kept. The coefficient of deviation angle model is tuned according to experimental data. In addition, two surge methods that originated from different sources are chosen to add in and compare with the new method called mass flow separation method. The salient issues presented here deal first with the construction of the compressor program. Three well-documented National Aerodynamics and Space Administration (NASA) axial transonic compressors are calculated, and the speedlines and aerodynamic parameters are compared with the experimental data to verify the reliability and robustness of the proposed method. Results show that consistent agreement can be obtained with such a performance prediction program. It was also apparent that the two common methods of surge prediction, which rely upon either stage or overall characteristic gradients, gave less agreement than the method called mass flow separation method.

scholarly journals VIV Excitation Competition Between Bare and Buoyant Segments of Flexible Cylinders

2013 ◽  
Author(s):  
Zhibiao Rao ◽  
J. Kim Vandiver ◽  
Vikas Jhingran
Keyword(s):  
Model Test ◽  
Practical Problem ◽  
Excitation Frequency ◽  
Ocean Basin ◽  
Recent Model ◽  
Total Amplitude ◽  
Vortex Induced Vibration ◽  
Pipe Model ◽  
Exploration And Production ◽  
Different Diameters

This paper addresses a practical problem: “Under which coverage of buoyancy modules, would the Vortex Induced Vibration (VIV) excitation on buoyant segments dominate the response?” This paper explores the excitation competition between bare and buoyant segments of a 38 meter long model riser. The source of data is a recent model test, conducted by SHELL Exploration and Production at the MARINTEK Ocean Basin in Trondheim Norway. A pipe model with five buoyancy configurations was tested. The results of these tests show that (1) the excitation on the bare and buoyant regions could be identified by frequency, because the bare and buoyant regions are associated with two different frequencies due to the different diameters; (2) a new phenomenon was observed; A third frequency in the spectrum is found not to be a multiple of the frequency associated with either bare or buoyancy regions, but the sum of the frequency associated with bare region and twice of the frequency associated with buoyancy region; (3) the contribution of the response at this third frequency to the total amplitude is small; (4) the power dissipated by damping at each excitation frequency is the metric used to determine the winner of excitation competition. For most buoyancy configurations, the excitation on buoyancy regions dominates the VIV response; (5) a formula is proposed to predict the winner of the excitation competition between bare and buoyant segments for a given buoyancy coverage.

Guidelines for CFD Simulations of Spar VIM

2013 ◽  
Author(s):  
Charles Lefevre ◽  
Yiannis Constantinides ◽  
Jang Whan Kim ◽  
Mike Henneke ◽  
Robert Gordon ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Test Data ◽  
Model Test ◽  
Model Tests ◽  
Full Scale ◽  
Mooring System ◽  
Time Step ◽  
Cfd Simulations ◽  
Scaled Model ◽  
Sway Motion

Vortex-Induced Motion (VIM), which occurs as a consequence of exposure to strong current such as Loop Current eddies in the Gulf of Mexico, is one of the critical factors in the design of the mooring and riser systems for deepwater offshore structures such as Spars and multi-column Deep Draft Floaters (DDFs). The VIM response can have a significant impact on the fatigue life of mooring and riser components. In particular, Steel Catenary Risers (SCRs) suspended from the floater can be sensitive to VIM-induced fatigue at their mudline touchdown points. Industry currently relies on scaled model testing to determine VIM for design. However, scaled model tests are limited in their ability to represent VIM for the full scale structure since they are generally not able to represent the full scale Reynolds number and also cannot fully represent waves effects, nonlinear mooring system behavior or sheared and unsteady currents. The use of Computational Fluid Dynamics (CFD) to simulate VIM can more realistically represent the full scale Reynolds number, waves effects, mooring system, and ocean currents than scaled physical model tests. This paper describes a set of VIM CFD simulations for a Spar hard tank with appurtenances and their comparison against a high quality scaled model test. The test data showed considerable sensitivity to heading angle relative to the incident flow as well as to reduced velocity. The simulated VIM-induced sway motion was compared against the model test data for different reduced velocities (Vm) and Spar headings. Agreement between CFD and model test VIM-induced sway motion was within 9% over the full range of Vm and headings. Use of the Improved Delayed Detached Eddy Simulation (IDDES, Shur et al 2008) turbulence model gives the best agreement with the model test measurements. Guidelines are provided for meshing and time step/solver setting selection.

A Comparison of Analytical Predictions With Experimental Measurements of Transmission Error of Misaligned Loaded Gears

1992 ◽  
Author(s):  
Harsh Vinayak ◽  
Donald R. Houser
Keyword(s):  
Experimental Data ◽  
Load Distribution ◽  
Theoretical Calculations ◽  
Data Acquisition System ◽  
Transmission Error ◽  
Test Facility ◽  
Experimental Measurements ◽  
Gear Pair ◽  
Prediction Program ◽  
Dynamic Transmission Error

Abstract This paper deals with the experimental study of dynamic transmission error of a gear pair. Two aspects of the experiment are discussed : 1) design of the test facility and data acquisition system and 2) comparison of transmission error and load distribution with experimental data. Several gears were tested under varying misalignments. A prediction program LDP (Load distribution Program) was used for theoretical calculations of dynamic transmission error.

A Joint-Industry Effort to Develop and Verify CFD Modeling Practice for Vortex-Induced Motion of a Deep-Draft Semi-Submersible

2021 ◽  
Author(s):  
Hyunchul Jang ◽  
Dae-Hyun Kim ◽  
Madhusuden Agrawal ◽  
Sebastien Loubeyre ◽  
Dongwhan Lee ◽  
...  
Keyword(s):  
Test Data ◽  
Model Test ◽  
Working Group ◽  
Cfd Modeling ◽  
Physical Model Test ◽  
Mooring Lines ◽  
Cfd Models ◽  
Induced Motion ◽  
Modeling Practice ◽  
Decay Tests

Abstract Platform Vortex Induced Motion (VIM) is an important cause of fatigue damage on risers and mooring lines connected to deep-draft semi-submersible floating platforms. The VIM design criteria have been typically obtained from towing tank model testing. Recently, computational fluid dynamics (CFD) analysis has been used to assess the VIM response and to augment the understanding of physical model test results. A joint industry effort has been conducted for developing and verifying a CFD modeling practice for the semi-submersible VIM through a working group of the Reproducible Offshore CFD JIP. The objectives of the working group are to write a CFD modeling practice document based on existing practices validated for model test data, and to verify the written practice by blind calculations with five CFD practitioners acting as verifiers. This paper presents the working group’s verification process, consisting of two stages. In the initial verification stage, the verifiers independently performed free-decay tests for 3-DOF motions (surge, sway, yaw) to check if the mechanical system in the CFD model is the same as in the benchmark test. Additionally, VIM simulations were conducted at two current headings with a reduced velocity within the lock-in range, where large sway motion responses are expected,. In the final verification stage, the verifiers performed a complete set of test cases with small revisions of their CFD models based on the results from the initial verification. The VIM responses from these blind calculations are presented, showing close agreement with the model test data.

Influence From Helical Strakes on Vortex Induced Vibrations and Static Deflection of Drilling Risers

2005 ◽  
Author(s):  
Carl M. Larsen ◽  
Gro Sagli Baarholm ◽  
Halvor Lie
Keyword(s):  
Dynamic Response ◽  
Test Data ◽  
Oscillation Amplitude ◽  
Cross Flow ◽  
Current Profile ◽  
Dynamic Stresses ◽  
Drag Forces ◽  
Vortex Induced Vibrations ◽  
Bending Stresses ◽  
Helical Strakes

Helical strakes are known to reduce and even eliminate the oscillation amplitude of vortex induced vibrations (VIV). This reduction will increase fatigue life, and also reduce drag magnification from cross-flow vibrations. But sections with strakes will also have a larger drag coefficient than the bare riser. Hence, the extension of a section with strakes along a riser should be large enough to reduce oscillations, but not too long in order to limit drag forces from current and waves. The optimum length and position for a given riser will therefore vary with current profile. Dynamic response from waves should also be taken into account. The purpose of the present paper is to illustrate the influence from strakes on VIV, as well as on static and dynamic response for a drilling riser. Hydrodynamic coefficients for a cylinder with helical strakes are found from experiments and applied in an empirical model for the analysis of VIV. The result from the VIV analysis is used for a second calculation of drag forces that are applied in an updated static analysis. Dynamic stresses from regular waves are also presented, but VIV are not considered for these cases. A simple study of length and position of the section with strakes is carried out for some standard current profiles. Results are presented in terms of oscillation amplitudes, fatigue damage, bending stresses and riser angles at ends. The study is based on test data for one particular strake geometry, but the analysis method as such is general, and the computer programs used in the study can easily apply other test data.

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