Experiences With VIV Analyses of SCR’s Using Complex Modes

2002 ◽  
Author(s):  
Geir Moe ◽  
O̸vind A. Amitsen
Keyword(s):  
Modal Analysis ◽  
Added Mass ◽  
Computer Programme ◽  
Complex Modes ◽  
Vortex Induced Vibrations ◽  
Motion Amplitude

The theory behind a computer programme for prediction of Vortex Induced Vibrations (VIV) of risers is summarised, and some experiences with its use are given. The programme in question is named VICoMo (VIV by Complex Modes) and is based on modal analysis by means of complex modes. The approach is iterative in nature because the added mass and damping forces depend nonlinearly on motion amplitude and frequency. Experiences with some runs to model a prototype Steel Caternary Riser (SCR) are summarised. A key element herein is the strategy for the choice of the parameters governing the iterations.

Hydrodynamic Coefficients for In-Line Vortex Induced Vibrations

2007 ◽  
Author(s):  
Kristoffer H. Aronsen ◽  
Carl Martin Larsen
Keyword(s):  
Driving Force ◽  
Added Mass ◽  
Large Set ◽  
Hydrodynamic Coefficients ◽  
Marine Structures ◽  
Force Coefficient ◽  
Vortex Induced Vibrations ◽  
Line Force ◽  
Set Up ◽  
Motion Amplitude

The paper presents results from an experimental investigation of hydrodynamic forces on a cylinder under forced in-line motions. Measured forces are decomposed into added mass, driving force and average drag components. From a large set of experiments it has been possible to draw a complete map for in-line force coefficients as function of arbitrary combinations of motion amplitude and frequency. The paper presents test set-up, data processing and how the coefficients can be used in an empirical force coefficient model for calculation of in-line vibrations of slender marine structures with arbitrary damping. Such analyses are in particular important for free spanning pipelines, where damping from pipe/seafloor interaction will reduce the response amplitudes and hence also stresses and fatigue damage.

Riser Fatigue Due to Currents and Waves

2002 ◽  
Author(s):  
C. Le Cunff ◽  
E. Fontaine ◽  
F. Biolley
Keyword(s):  
Modal Analysis ◽  
Environmental Conditions ◽  
Navier Stokes ◽  
Vortex Induced Vibrations ◽  
Two Factors ◽  
Shedding Frequency ◽  
The Waves ◽  
Structural Mode ◽  
A Current

Fatigue due to environmental conditions is studied on a top-tensioned riser. The fatigue is due to two factors. First, the waves produce a displacement of the top of the riser, which excites the structure. Secondly, currents create vortices behind the structures. The phenomenon is then referred to as vortex-induced vibrations (VIV), whereby the vortices can lock onto a structural mode through the shedding frequency. In the present paper, we have two objectives. The first is to compare the fatigue estimates given either by a modal analysis or by Navier-Stokes calculations for a riser in a current. The second is to determine if studying the wave and current effects separately produces conservative results or if they must be studied together.

Forced Vibration Tests for In-Line Vortex-Induced Vibration to Assess Partially Strake-Covered Pipeline Spans

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Jie Wu ◽  
Decao Yin ◽  
Elizabeth Passano ◽  
Halvor Lie ◽  
Ralf Peek ◽  
...  
Keyword(s):  
Forced Vibration ◽  
Hydrodynamic Force ◽  
Cross Flow ◽  
Added Mass ◽  
Vortex Induced Vibrations ◽  
Helical Strakes ◽  
Vibration Tests ◽  
Flow Vortex ◽  
Hydrodynamic Data ◽  
Mass Functions

Abstract Helical strakes can suppress vortex-induced vibrations (VIVs) in pipelines spans and risers. Pure in-line (IL) VIV is more of a concern for pipelines than for risers. To make it possible to assess the effectiveness of partial strake coverage for this case, an important gap in the hydrodynamic data for strakes is filled by the reported IL forced-vibration tests. Therein, a strake-covered rigid cylinder undergoes harmonic purely IL motion while subject to a uniform “flow” created by towing the test rig along SINTEF Ocean's towing tank. These tests cover 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 deg 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 “An Experimental Investigation of In-Line and Combined In-Line and Cross-Flow Vortex Induced Vibrations,” Ph.D. thesis, Norwegian University of Science and Technology, Trondheim, Norway.), the IL 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 IL VIV.

Hydrodynamic Properties of a Suction Can Oscillating Near the Free Surface

2009 ◽  
Author(s):  
C. Plummer ◽  
G. Macfarlane ◽  
Y. Drobyshevski
Keyword(s):  
Free Surface ◽  
Added Mass ◽  
Hydrodynamic Properties ◽  
Noticeable Effect ◽  
Sea Floor ◽  
Notable Effect ◽  
Free Decay ◽  
Decay Tests ◽  
Quadratic Damping ◽  
Motion Amplitude

Offshore operations often require heavy subsea equipment, such as suction piles or cans, to be lowered by a support vessel into the sea. A lifting device must have adequate capacity to withstand the dynamic loads generated by the motions of the vessel and the heave response of the structure. The objective of this study is to determine the added mass and damping of a suction can oscillating in heave near the free surface; knowledge of these hydrodynamic properties is required for the accurate prediction of the dynamic lift forces during the deployment. This project is a logical progression following two similar studies, which investigated these hydrodynamic properties for the suction can in the mid-water position and when approaching the seabed. All three studies involved the conduct of model tests to determine the hydrodynamic properties. Free decay tests were conducted at several heave frequencies, and the added mass, linear and quadratic damping components were determined. In addition, the effect of varying the percentage of open hatch area has been investigated. Test data demonstrates that the heave added mass is strongly dependent on the frequency of motion, and its values are significantly smaller than those measured in the unrestricted flow. From observations, there was no dependency on the motion amplitude, nor did the size of open hatches have notable effect on the added mass. It was observed that when the top plate of the structure was in contact with the free surface a mean “pull down” force appeared. This force is caused by the suction underneath the top plate when the can moves upwards. As opposed to the mid-water position and near the sea floor, the study indicates that the area of open hatches has no noticeable effect on the heave damping when the suction can is oscillating near the free surface.

Reynolds Number Effects on Hydrodynamic Coefficients for Pure In-Line and Pure Cross-Flow Forced Vortex Induced Vibrations

2009 ◽  
Author(s):  
Jamison L. Szwalek ◽  
Carl M. Larsen
Keyword(s):  
Reynolds Number ◽  
Prediction Models ◽  
Current Knowledge ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Added Mass ◽  
Hydrodynamic Coefficients ◽  
Vortex Induced Vibrations ◽  
Reynolds Number Effects ◽  
Sinusoidal Oscillations

In-line vibrations have been noted to have an important contribution to the fatigue of free spanning pipelines. Still, in-line contributions are not usually accounted for in current VIV prediction models. The present study seeks to broaden the current knowledge regarding in-line vibrations by expanding the work of Aronsen (2007) to include possible Reynolds number effects on pure in-line forced, sinusoidal oscillations for four Reynolds numbers ranging from 9,000 to 36,200. Similar tests were performed for pure cross-flow forced motion as well, mostly to confirm findings from previous research. When experimental uncertainties are accounted for, there appears to be little dependence on Reynolds number for all three hydrodynamic coefficients considered: the force in phase with velocity, the force in phase with acceleration, and the mean drag coefficient. However, trends can still be observed for the in-line added mass in the first instability region and for the transition between the two instability regions for in-line oscillations, and also between the low and high cross-flow added mass regimes. For Re = 9,000, the hydrodynamic coefficients do not appear to be stable and can be regarded as highly Reynolds number dependent.

Added Mass of Elastically Mounted Rigid Cylinder in Water Subjected to Vortex-Induced Vibrations

2002 ◽  
Author(s):  
Andre´ L. C. Fujarra ◽  
Celso P. Pesce
Keyword(s):  
Added Mass ◽  
Leaf Spring ◽  
Technical Literature ◽  
Experimental Calibration ◽  
Rigid Cylinder ◽  
Vortex Induced Vibrations ◽  
Mass Coefficient ◽  
Added Mass Coefficient ◽  
The Cross ◽  
Technological Research Institute

Vortex Induced Vibrations (VIV) of elastically mounted rigid cylinders, with low mass-damping parameter values, are strongly dependent on the added mass coefficient. This paper aims to contribute to the technical literature by presenting some results from experiments carried out at University of Sa˜o Paulo – USP and at the Sa˜o Paulo State Technological Research Institute – IPT. A cantilevered rigid cylinder was mounted on an elastic (leaf spring) two-degree-of-freedom device. The device is not only an elastic support, but acts also as a special mechanical transducer to measure accelerations/forces/displacements in the stream-wise (x) and the cross-wise (y) directions. A comprehensive experimental calibration of such a device was carried out, both “in air” and “in water”. The added mass coefficient in the cross-wise direction was indirectly determined from forces and acceleration measurements as a function of the reduced velocity. Results from time-domain and frequency-domain analyses are compared with those obtained by Vikestad et al. (2000) [1].

scholarly journals Numerical study on Modal Analysis of a typical bridge section with the influence of Aeroelastic effect

2019 ◽  
Vol 11 (4) ◽  
pp. 133-138 ◽  
Author(s):  
G. PRASAD
Keyword(s):  
Numerical Simulation ◽  
Modal Analysis ◽  
Mode Shape ◽  
Structural Design ◽  
Numerical Study ◽  
Analysis Software ◽  
Transportation Management ◽  
Structure Interaction ◽  
Vortex Induced Vibrations ◽  
Design Software

Due to the increase in the number of vehicles, transportation management is achieved through the construction of bridges. This article discusses the vibrational effect in the design of bridges. In the structural design of the bridges proper planning is necessary, as gusts may occur, leading to aeroelastic instabilities. In this article a typical bridge is designed using the design software CATIA and a numerical simulation using analysis software ANSYS. Further, the aeroelastic phenomenon involved in coupling of Fluid Structure Interaction is discussed. The results of Mode shape show vortex-induced vibrations which can lead to Flutter.

Calculation of In-Line Vortex Induced Vibrations of Free Spanning Pipelines

2007 ◽  
Author(s):  
Carl M. Larsen ◽  
Rune Yttervik ◽  
Kristoffer Aronsen
Keyword(s):  
Cross Flow ◽  
Added Mass ◽  
Response Analysis ◽  
Hydrodynamic Coefficients ◽  
Response Model ◽  
Analysis Method ◽  
Vortex Induced Vibrations ◽  
Long Time ◽  
General Response

Pure in-line (IL) vibrations will in many cases contribute significantly to fatigue damage for free spanning pipelines. This might be the case even if IL amplitudes are smaller than cross-flow (CF). While CF response has been subjected to research for a long time, little attention has so far been given to the pure IL VIV case. The hydrodynamic coefficients needed for response calculation have in fact not been available until recently, but results from forced IL oscillations have improved this situation. Data for added mass and force in IL direction has been used to establish a general response model along the same lines as for traditional CF response analysis. This has made it possible to calculate stresses from IL VIV in free spanning pipelines, and include the influence from interaction with the seafloor at the span shoulders. A brief presentation of the analysis method is given, but the main part of the paper gives results from a case study that illustrates important effects and the significance of IL response as compared to CF.

Fluid-Structure Interaction Effects Modeling for the Modal Analysis of a Nuclear Pressure Vessel

2006 ◽  
Vol 129 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Jean-François Sigrist ◽  
Daniel Broc ◽  
Christian Lainé
Keyword(s):  
Finite Element ◽  
Modal Analysis ◽  
Pressure Vessel ◽  
Nuclear Reactor ◽  
Fluid Structure Interaction ◽  
Added Mass ◽  
Interaction Effects ◽  
Element Discretization ◽  
Fluid Structure ◽  
Structure Interaction

The present paper deals with the modal analysis of a nuclear reactor with fluid-structure interaction effects. The proposed study aims at describing various fluid-structure interaction effects using several numerical approaches. The modeling lies on a classical finite element discretization of the coupled fluid-structure equation, enabling the description of added mass and added stiffness effects. A specific procedure is developed in order to model the presence of internal structures within the nuclear reactor, based on periodical homogenization techniques. The numerical model of the nuclear pressure vessel is developed in a finite element code in which the homogenization method is implemented. The proposed methodology enables a convenient analysis from the engineering point of view and gives an example of the fluid-structure interaction effects, which are expected on an industrial structure. The modal analysis of the nuclear pressure vessel is then performed and highlights of the relative importance of FSI effects for the industrial case are evaluated: the analysis shows that added mass effects and confinement effects are of paramount importance in comparison to added stiffness effects.

Sign in / Sign up

Export Citation Format

Share Document