Numerical and Experimental Comparisons of Vortex-Induced Vibrations of Marine Risers in Uniform/Sheared Currents

2010 ◽  
Author(s):  
Narakorn Srinil ◽  
Patrick O’Brien ◽  
Marian Wiercigroch
Keyword(s):  
Nonlinear Models ◽  
Cross Flow ◽  
Experimental Results ◽  
Beam Model ◽  
Geometric Nonlinearities ◽  
Marine Risers ◽  
Wake Oscillator ◽  
Damage Indices ◽  
Multi Mode ◽  
Experimental Comparisons

This paper presents a general theoretical reduced-order model capable of evaluating the multi-mode nonlinear dynamics of marine risers subject to uniform and sheared currents. The main objectives are to predict the vortex-induced vibration responses and parametrically compare between numerical and experimental results. The emphasis is placed on the analysis of cross-flow vibrations due to unsteady lift forces. The nonlinear equations governing riser axial/transversal motions are derived based on a top-tensioned beam model with typical pinned-pinned boundary conditions. The riser geometric nonlinearities owing to possible large dynamic displacements and multi-mode interactions are accounted for. To approximate the space-time varying lift force, the empirical hydrodynamic model, based on a nonlinear van der Pol wake oscillator with a distributed diffusive term, is used. A low-dimensional dynamic model and computationally-robust time-domain tool are then developed to evaluate the multi-mode fluid-riser interactions. These are very useful in dealing with large parametric studies involving varying system parameters. Comparisons of numerical and experimental results are performed by estimating riser response amplitudes and fatigue damage indices. Both linear and nonlinear risers are considered in the present numerical model whereas only linear riser has been considered by a referenced literature in the reconstruction of experimental displacements through measured strains. It is found that riser geometric nonlinearities play a significant role in both numerical simulations and comparisons with experiment post-processed results. In some cases, quantitative/qualitative discrepancies in riser response predictions are remarkable with linear vs. nonlinear models. These may be recognized as one of the factors why recent numerical and experimental comparisons in literature have been unsuccessful.

Coupled Axial/Lateral VIV of Marine Risers in Sheared Currents

2015 ◽  
Author(s):  
Hossein Zanganeh ◽  
Narakorn Srinil
Keyword(s):  
Degrees Of Freedom ◽  
Cross Flow ◽  
Travelling Wave ◽  
Longitudinal Motion ◽  
Nonlinear Coupling ◽  
Axial Motion ◽  
Flexible Cylinder ◽  
Fluid Structure ◽  
Marine Risers ◽  
Multi Mode

Modelling and prediction of vortex-induced vibrations (VIV) of marine risers is a challenging task due to the associated multi degrees of freedom in both cross-flow/in-line directions and the multi-mode fluid-structure interactions. In addition, the axial motion and its geometrically nonlinear coupling with lateral responses can be significant, especially at higher-order modes. Nevertheless, several papers in the literature dealing with VIV predictions have often overlooked such aspects. Therefore, this study aims to investigate and understand the effect of axial or longitudinal motion through a theoretical model and numerical approach in time domain. Attention is paid to VIV of vertical risers subjected to linearly sheared currents. To capture a three-dimensional aspect of the flexible cylinder experiencing VIV, a semi-empirical model is developed consisting of nonlinear equations of cross-flow, in-line and axial structural oscillations which are coupled with the distributed van der Pol-type wake-oscillators modelling the fluctuating fluid lift/drag forces. The mean drag force is also taken into account. These model equations are numerically solved via a space-time finite difference scheme, and the obtained numerical results highlight several aspects of VIV of elastic cylinders along with the axial motion effects. Apart from the validation of the numerical model with published experimental results, this study reveals how the effect of axial motion and its nonlinear coupling with the two lateral cross-flow/in-line motions can be very important. These depend on the flow velocity, the fluid-structure parameters, the single or multi-mode lock-in condition, and the standing-wave or travelling-wave feature. We recommend that the axial response should be accounted for in VIV analysis and prediction model.

Effect of Fluidized Bed on Permeate Flux in Ceramic Membrane Cross-Flow Microfiltration

1995 ◽  
Vol 60 (12) ◽  
pp. 2074-2084
Author(s):  
Petr Mikulášek
Keyword(s):  
Fluidized Bed ◽  
Ceramic Membrane ◽  
Cross Flow ◽  
Experimental System ◽  
Experimental Results ◽  
Spherical Particles ◽  
Permeate Flux ◽  
Model Fluid ◽  
Optimum Porosity ◽  
Tubular Membranes

The microfiltration of a model fluid on an α-alumina microfiltration tubular membrane in the presence of a fluidized bed has been examined. Following the description of the basic characteristic of alumina tubular membranes, model dispersion and spherical particles used, some comments on the experimental system and experimental results for different microfiltration systems are presented. From the analysis of experimental results it may be concluded that the use of turbulence-promoting agents resulted in a significant increase of permeate flux through the membrane. It was found out that the optimum porosity of fluidized bed for which the maximum values of permeate flux were reached is approximately 0.8.

The Study on the Influence of Pipe-Soil Interaction on VIV for Different Free Span Types

2017 ◽  
Author(s):  
Chongyao Zhou ◽  
Gang Xu ◽  
Zhiming Huang ◽  
Dagang Zhang ◽  
Naiquan Ye ◽  
...  
Keyword(s):  
Time Domain ◽  
Cross Flow ◽  
Sensitivity Study ◽  
Structural Damping ◽  
Flexible Pipe ◽  
Wake Oscillator Model ◽  
Wake Oscillator ◽  
Different Types ◽  
Main Factors ◽  
Parameter Influence

Subsea pipeline laid on the seabed will experience free span when the lay path is long and seabed is rugged. Hydrodynamic loads caused by the currents around the pipeline can induce oscillations in both cross-flow and in-line directions. This phenomenon is called vortex-induced vibration (VIV) which is the most common case that could induce serious fatigue problems. The pipe-soil interaction is one of the main factors that influence the vibration. In this paper, a study focusing on the effect of pipe-soil interaction on VIV for different types of free span is presented. The Milan wake oscillator is applied to calculate the dynamic response induced by VIV in Orcaflex, and the results are compared with experimental data to identify its validity. A sensitivity study is also performed to study the parameter influence of the Milan wake oscillator model. Four types of free span (including the multiple free spans) are modeled in Orcaflex and time domain VIV analysis is carried out to study the influence of pipe-soil interaction. Comparison among different types of free span is discussed. The influence of structural damping is studied for flexible pipe only because its influence on steel pipe is negligible. The influence of structural damping on flexible pipe is studied by means of a predefined moment-curvature curve. In addition, several cases are studied to investigate the influence of tension on VIV by Milan wake oscillator.

Prediction of the FOM FEM experimental results using multi-mode time-dependent simulations

1998 ◽  
pp. 45-49
Author(s):  
M. Caplan ◽  
W.A. Bongers ◽  
M. Valentini ◽  
W.H. Urbanus ◽  
A.G.A. Verhoeven ◽  
...  
Keyword(s):  
Experimental Results ◽  
Time Dependent ◽  
Multi Mode

Gap Effect on the Random and Fluid-Elastic Forces Acting in the Vibration of a Loosely Supported Tube Under Cross-Flow

2017 ◽  
Author(s):  
Laurent Borsoi ◽  
Philippe Piteau ◽  
Xavier Delaune ◽  
Jose Antunes
Keyword(s):  
Numerical Simulations ◽  
Limit Cycles ◽  
Relative Weight ◽  
Cross Flow ◽  
Gap Effect ◽  
Beam Model ◽  
Fluid Forces ◽  
Straight Beam ◽  
Starting Point ◽  
Elastic Forces

In degraded situations of heat-exchangers, tubes may become loosely supported while subjected to intense crossflow which generates both turbulent and fluid-elastic forces. The vibro-impacting regimes that result have been studied by the authors during these last few years, based on analytical experiments and numerical simulations. Taking advantage of this material, the paper aims at showing some dynamic effects that have been observed and drawing lessons concerning the vibration of tubes under cross-flow when they are linearly unstable. If the fluid-elastic damping drops until the total damping becomes negative when the flow reduced velocity increases, a non-linear gap-system escapes from instability by reinforcing the sequence of impacts and its apparent frequency. On the other hand, the turbulent excitation is characterized by broadband PSDs that decrease with frequency. Thus the vibro-impacting response of the tubes results from a competition between the turbulent and fluid-elastic forces, according to a process that depends on the gap size. The fluid-elastic coupling forces may be either stabilizing (positive damping) or destabilizing (negative one), and, in a more amazing way, the random forces may be dissipative. The paper illustrates the previous points from the tested experimental configuration which was mainly 1-DOF. Dimensionless results are given for this configuration. Extensions to more realistic tubes are discussed from numerical simulations of a straight beam with three loosely supports. The starting point of simulations is though experiments where the fluid-elastic forces would act, but not the turbulent ones, which would produce limit cycles in the phase space. Turbulence is then considered as perturbation of limit cycles, and as shown below by notably introducing a dimensionless “gap-turbulence” parameter, smaller the gap sizes are, larger the relative weight of turbulence is. The Rice frequency and the mean impact force are indicators of this relative weight and the competition between the fluid-forces. From this general understanding, and using preliminary results with the beam model, a few guidelines are finally evoked for determining allowable gaps sizes in degraded situations. But a lot of work has to be done with more sophisticated models to concretize these ideas.

Dynamic Analysis of Marine Risers With Vortex Excitation

1982 ◽  
Vol 104 (1) ◽  
pp. 14-19 ◽  
Author(s):  
R. P. Nordgren
Keyword(s):  
Finite Element Method ◽  
Time Integration ◽  
Elastic Rods ◽  
Hybrid Finite Element Method ◽  
Marine Risers ◽  
Hybrid Finite Element ◽  
Wake Oscillator ◽  
Transverse Vibrations ◽  
Basic Equations ◽  
Oscillator Equations

The basic equations for nonplanar transverse vibrations of marine risers are derived from the theory of elastic rods. A numerical method is developed for solution of the equations by time integration. Spatial discretization is accomplished by a hybrid finite element method. Vortex excitation is modeled by the coupled wake oscillator proposed by Iwan and Blevins. The vortex oscillator equations are integrated numerically in time along with the riser equations. By way of example, several typical riser problems are analyzed including forced vibration and vortex-induced vibration.

scholarly journals Simple and Accurate Analytical Solutions of the Electrostatically Actuated Curled Beam Problem

2014 ◽  
Author(s):  
Mohammad I. Younis
Keyword(s):  
Analytical Solutions ◽  
Galerkin Approximation ◽  
Single Mode ◽  
Beam Model ◽  
Reduced Order ◽  
Electrostatically Actuated ◽  
Analytical Formulas ◽  
Euler Bernoulli Beam ◽  
Analytical Expressions ◽  
Multi Mode

We present analytical solutions of the electrostatically actuated initially deformed cantilever beam problem. We use a continuous Euler-Bernoulli beam model combined with a single-mode Galerkin approximation. We derive simple analytical expressions for two commonly observed deformed beams configurations: the curled and tilted configurations. The derived analytical formulas are validated by comparing their results to experimental data in the literature and numerical results of a multi-mode reduced order model. The derived expressions do not involve any complicated integrals or complex terms and can be conveniently used by designers for quick, yet accurate, estimations. The formulas are found to yield accurate results for most commonly encountered microbeams of initial tip deflections of few microns. For largely deformed beams, we found that these formulas yield less accurate results due to the limitations of the single-mode approximations they are based on. In such cases, multi-mode reduced order models need to be utilized.

scholarly journals Enhancement of Impingement Heat Transfer With the Crossflow Normal to Ribs and Pins Between Each Row of Holes

2018 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pressure Loss ◽  
Cross Flow ◽  
Experimental Results ◽  
Hole Density ◽  
Impingement Heat Transfer ◽  
The Cross ◽  
Flow Maldistribution

Impingement heat transfer investigations with obstacle (fins) on the target surface were carried out with the obstacles aligned normal to the cross-flow. Conjugate heat transfer (CHT) computational fluid dynamics (CFD) analysis were used for the geometries previously been investigated experimentally. A 10 × 10 row of impingement jet holes or hole density, n, of 4306 m−2 with ten rows of holes in the cross-flow direction was used. The impingement hole pitch X to diameter D, X/D, and gap Z to diameter, Z/D, ratios were kept constant at 4.66 and 3.06 for X, D and Z of 15.24, 3.27 and 10.00 mm, respectively. Nimonic 75 test walls were used with a thickness of 6.35 mm. Two different shaped obstacles of the same flow blockage were investigated: a continuous rectangular ribbed wall of 4.5 mm height, H, and 3.0 mm thick and 8 mm high rectangular pin-fins that were 8.6 mm wide and 3.0 mm thick. The obstacles were equally spaced on the centre-line between each row of impingement jets and aligned normal to the cross-flow. The two obstacles had height to diameter ratios, H/D, of 1.38 and 2.45, respectively. Comparison of the predictions and experimental results were made for the flow pressure loss, ΔP/P, and the surface average heat transfer coefficient (HTC), h. The computations were carried out for air coolant mass flux, G, of 1.08, 1.48 and 1.94 kg/sm2bar. The pressure loss and surface average HTC for all the predicted G showed reasonable agreement with the experimental results, but the predictions for surface averaged h were below the measured values by 5–10%. The predictions showed that the main effect of the ribs and pins was to increase the pressure loss, which led to an increased flow maldistribution between the ten rows of holes. This led to lower heat transfer over the first 5 holes and higher heat transfer over the last 3 holes and the net result was little benefit of either obstacle relative to a smooth wall. The results were significantly worse than the same obstacles aligned for co-flow, where the flow maldistribution changes were lower and there was a net benefit of the obstacles on the surface averaged heat transfer coefficient.

Study of the Vortex-Induced Vibration of the Marine Risers With the Buoyancy

2019 ◽  
Author(s):  
Lin Zhao ◽  
Hang Su ◽  
Yanju Yin
Keyword(s):  
Vibration Frequency ◽  
Cross Flow ◽  
Experimental Results ◽  
Resonance Phenomenon ◽  
Feature Points ◽  
System A ◽  
Acceleration Amplitude ◽  
Floating System ◽  
Modal Vibration ◽  
Flow Velocities

Abstract Regarding the very large top tension of ocean deep water riser which is caused by the heavy self-weight, a innovated buoyancy system is designed. This system can effectively decrease the top tension and improve the performance of the riser movement. In order to study the upper and lower part of the floating system, a specialized model test is carried out, where the acceleration, amplitude, frequency and trajectory of the interested points along the risers are investigated. It has been observed that with the increase of the current speed, both the vibration acceleration and the vibration frequency are increasing but the bare riser amplitude is decreasing. At the speed of 0.2m/s, the resonance phenomenon is observed, but the same phenomenon is not observed for the middle floating riser subjecting to different flow velocities. At the speed of 0.4 m/s, the largest amplitude is captured. Due to the response differences of the floating riser at the up and down parts of the middle floating riser, when the amplitude is increasing, the vibration frequency is decreasing, both at cross flow (CF) direction and inline flow (IL) direction. Especially the vibration behavior of the interested points is most influenced by the buoyancy. Under different models, vibration at different flow velocities is presented along bare riser, the modal vibration effects of the floating riser will decrease In addition, according to the experiment condition, Orcaflex is applied to conduct the numerical simulation to get the vibration law of the corresponding feature points and compare it with the experimental results. The results indicate that the numerical analysis reasonably match with experimental results.

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