Coupled Analysis of Deepwater Floating System Including VIV in Time Domain

2007 ◽  
Author(s):  
Jun-Bumn Rho ◽  
Alexander A. Korobkin ◽  
Jong-Jun Jung ◽  
Hyun-Soo Shin ◽  
Woo-Seob Lee
Keyword(s):  
Finite Element ◽  
Time Domain ◽  
Torsional Stiffness ◽  
Time Step ◽  
Vortex Induced Vibration ◽  
Coupled Equations ◽  
Floating System ◽  
Vessel Motion ◽  
Floating Systems ◽  
The Way

Deepwater floating systems consist of a vessel, risers, and mooring lines. To accurately simulate the floating systems in current, wind, and waves considering (1) bending and torsional stiffness of riser, (2) elongation of the mooring/riser elements, (3) complex end conditions, (4) internal flow effects, and (5) vortex induced vibration, it is necessary to evaluate the vessel motions and mooring/riser behaviors simultaneously in time domain. However, because the size of the system matrix increases significantly as the number of mooring/riser increases, it is quite time-consuming to solve all equations including both mooring/riser and vessel dynamics simultaneously. The present study was performed in order to develop a program for this problem. The 6DOF vessel dynamics is described by the Cummins equation. And the mooring and riser are modeled with the help of finite-element beam. The Newmark method is used as the time marching scheme of the FEM equations for each mooring/riser and the vessel. The coupled equations of the mooring/riser segments and vessel are solved alternatively at each time step. Mooring/riser and the vessel motion affect to each other in the way that the components of the forces at the segment ends are determined as functions of displacements and slopes of them. This procedure makes it possible to consider the coupling effects between vessel and mooring/riser efficiently. Also no iterations are required to match the vessel motion with the riser dynamics. This new approach allows us to use parallel computations and to deal with as many mooring/riser at the same time as necessary. The hydrodynamic forces induced by current are calculated by using the Morison’s formula. The VIV (Vortex Induced Vibration) effects are included in the way that the frequency and the shape of the riser vibration due to VIV are pre-calculated by iterations in the frequency domain. Then the finite element mooring/riser model is modified to consider the hydrodynamic loads including VIV and integrated in the final equations of the floating system in time domain.

scholarly journals Fluid–Structure Interaction Simulation of Vortex-Induced Vibration of a Flexible Hydrofoil

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Abe H. Lee ◽  
Robert L. Campbell ◽  
Brent A. Craven ◽  
Stephen A. Hambric
Keyword(s):  
Finite Element ◽  
Fluid Structure Interaction ◽  
Computational Cost ◽  
Vortical Flow ◽  
Time Step ◽  
Fluid Structure ◽  
Vortex Induced Vibration ◽  
Structure Interaction ◽  
Eddy Simulation ◽  
Tightly Coupled

Fluid–structure interaction (FSI) is investigated in this study for vortex-induced vibration (VIV) of a flexible, backward skewed hydrofoil. An in-house finite element structural solver finite element analysis nonlinear (FEANL) is tightly coupled with the open-source computational fluid dynamics (CFD) library openfoam to simulate the interaction of a flexible hydrofoil with vortical flow structures shed from a large upstream rigid cylinder. To simulate the turbulent flow at a moderate computational cost, hybrid Reynolds-averaged Navier–Stokes–large eddy simulation (RANS–LES) is used. Simulations are first performed to investigate key modeling aspects that include the influence of CFD mesh resolution and topology (structured versus unstructured mesh), time-step size, and turbulence model (delayed-detached-eddy-simulation and k−ω shear stress transport-scale adaptive simulation). Final FSI simulations are then performed and compared against experimental data acquired from the Penn State-ARL 12 in water tunnel at two flow conditions, 2.5 m/s and 3.0 m/s, corresponding to Reynolds numbers of 153,000 and 184,000 (based on the cylinder diameter), respectively. Comparisons of the hydrofoil tip-deflections, reaction forces, and velocity fields (contours and profiles) show reasonable agreement between the tightly coupled FSI simulations and experiments. The primary motivation of this study is to assess the capability of a tightly coupled FSI approach to model such a problem and to provide modeling guidance for future FSI simulations of rotating propellers in crashback (reverse propeller operation).

scholarly journals On the development of a nonlinear time-domain numerical method for describing vortex-induced vibration and wake interference of two cylinders using experimental results

2021 ◽  
Author(s):  
Milad Armin ◽  
Sandy Day ◽  
Madjid Karimirad ◽  
Mahdi Khorasanchi
Keyword(s):  
Time Domain ◽  
Hydrodynamic Force ◽  
Maximum Amplitude ◽  
Added Mass ◽  
Duffing Equation ◽  
Experimental Results ◽  
Interference Phenomenon ◽  
Vortex Induced Vibration ◽  
Coupled Equations ◽  
Wake Interference

AbstractA nonlinear mathematical model is developed in the time domain to simulate the behaviour of two identical flexibly mounted cylinders in tandem while undergoing vortex-induced vibration (VIV). Subsequently, the model is validated and modified against experimental results. Placing an array of bluff bodies in proximity frequently happens in different engineering fields. Chimney stacks, power transmission lines and oil production risers are few engineering structures that may be impacted by VIV. The coinciding of the vibration frequency with the structure natural frequency could have destructive consequences. The main objective of this study is to provide a symplectic and reliable model capable of capturing the wake interference phenomenon. This study shows the influence of the leading cylinder on the trailing body and attempts to capture the change in added mass and damping coefficients due to the upstream wake. The model is using two coupled equations to simulate the structural response and hydrodynamic force in each of cross-flow and stream-wise directions. Thus, four equations describe the fluid–structure interaction of each cylinder. A Duffing equation describes the structural motion, and the van der Pol wake oscillator defines the hydrodynamic force. The system of equations is solved analytically. Two modification terms are added to the excitation side of the Duffing equation to adjust the hydrodynamic force and incorporate the effect of upstream wake on the trailing cylinder. Both terms are functions of upstream shedding frequency (Strouhal number). Additionally, the added mass modification coefficient is a function of structural acceleration and the damping modification coefficient is a function of velocity. The modification coefficients values are determined by curve fitting to the difference between upstream and downstream wake forces, obtained from experiments. The damping modification coefficient is determined by optimizing the model against the same set of experiments. Values of the coefficients at seven different spacings are used to define a universal function of spacing for each modification coefficient so that they can be obtained for any given distance between two cylinders. The model is capable of capturing lock-in range and maximum amplitude.

3D time-domain simulation of electromagnetic diffusion phenomena: A finite-element electric-field approach

Geophysics ◽  
2010 ◽  
Vol 75 (4) ◽  
pp. F115-F126 ◽  
Author(s):  
Evan Schankee Um ◽  
Jerry M. Harris ◽  
David L. Alumbaugh
Keyword(s):  
Finite Element ◽  
Differential Equations ◽  
Electric Field ◽  
Time Domain ◽  
Dirichlet Boundary Conditions ◽  
Earth Model ◽  
Time Step ◽  
Transient Electromagnetic ◽  
Backward Euler ◽  
Diffusion Phenomena

We present a finite-element time-domain (FETD) approach for the simulation of 3D electromagnetic (EM) diffusion phenomena. The finite-element algorithm efficiently simulates transient electric fields and the time derivatives of magnetic fields in general anisotropic earth media excited by multiple arbitrarily configured electric dipoles with various signal waveforms. To compute transient electromagnetic fields, the electric field diffusion equation is transformed into a system of differential equations via Galerkin’s method with homogeneous Dirichlet boundary conditions. To ensure numerical stability and an efficient time step, the system of the differential equations is discretized in time using an implicit backward Euler scheme. The resultant FETD matrix-vector equation is solved using a sparse direct solver along with a fill-in reduced ordering technique. When advancing the solution in time, the FETD algorithm adjusts the time step by examining whether or not the current step size can be doubled without unacceptably affecting the accuracy of the solution. To simulate a step-off source waveform, the 3D FETD algorithm also incorporates a 3D finite-element direct current (FEDC) algorithm that solves Poisson’s equation using a secondary potential method for a general anisotropic earth model. Examples of controlled-source FETD simulations are compared with analytic and/or 3D finite-difference time-domain solutions and are used to confirm the accuracy and efficiency of the 3D FETD algorithm.

Dynamic Analysis of Mooring Lines for Deep Water Floating Systems

2011 ◽  
Author(s):  
K. Gurumurthy ◽  
Suhail Ahmad ◽  
A. S. Chitrapu
Keyword(s):  
Finite Element ◽  
Dynamic Analysis ◽  
Deep Water ◽  
Time Domain ◽  
Accurate Prediction ◽  
Coupled Analysis ◽  
Analysis Method ◽  
Mooring Lines ◽  
Coupled Dynamic Analysis ◽  
Floating Systems

Efficient dynamic analysis of mooring lines and risers is necessary for deepwater floating systems that typically consist of a number of mooring lines and risers. In deepwater, the interactions between the floater motions and the large number of risers and mooring lines become significant and must be considered for accurate prediction of floater motions as well as line dynamics. Time-domain coupled dynamic analysis procedures have been proposed which can account for the coupling effects and consider most of the nonlinearities present in the problem. These methods have been shown to give more accurate results compared to traditional de-coupled analysis methods although they tend to be computationally more expensive. If the system has a large number of mooring lines and risers, it becomes very difficult and impractical to perform time domain coupled analysis. A number of efficient methodologies have therefore been proposed in the past to balance the accuracy of results with computational efficiency. Such methods include the frequency domain approach, combination of frequency and time domain methods, and combination of coupled and uncoupled analysis methodologies. Enhanced de-coupled dynamic analysis is an efficient method and is similar to the traditional de-coupled dynamic analysis method except that the floater motions are computed by coupled analysis considering a coarse finite element model of the mooring lines. In this paper, dynamic analysis of mooring lines for a deep water classical spar floater under random waves is performed by using the enhanced de-coupled dynamic analysis method and the response statistics are compared with results obtained from coupled dynamic analysis. The spar is modeled as a rigid body with six degrees-of-freedom and the mooring lines are modeled as finite element assemblage of elastic rods. All major non-linearities and the dynamic interaction between spar and its mooring lines are considered while determining the tension time histories. Hinge connection is assumed at the fairleads. At every time step of the integration of equations of motion of the spar, a series of nonlinear dynamic analyses of the mooring lines is performed using a subcycling technique. From the analyses, it is found that the enhanced de-coupled dynamic analysis provides results comparable in accuracy with the results obtained from coupled dynamic analysis in terms of predicting the response statistics, but requires only one third of the computational time. Therefore, enhanced de-coupled dynamic analysis can be used for accurate prediction of mooring line dynamics for deep water floating systems.

Numerical Vortex-Induced Vibration Prediction of Marine Risers in Time-Domain Based on a Forcing Algorithm

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Peter Ma ◽  
Wei Qiu ◽  
Don Spencer
Keyword(s):  
Experimental Data ◽  
Time Domain ◽  
Oil And Gas ◽  
Oil And Gas Industry ◽  
Analysis Tool ◽  
Time Step ◽  
Vortex Induced Vibration ◽  
Marine Risers ◽  
Hydrodynamic Damping ◽  
Vibration Prediction

Vortex-induced vibration (VIV) of marine risers poses a significant challenge as the offshore oil and gas industry moves into deep water. A time-domain analysis tool has been developed to predict the VIV of marine risers based on a forcing algorithm and by making full use of the available high Reynolds number experimental data. In the formulation, the hydrodynamic damping is not treated as a special case but simply an extension of the experimentally derived lift curves. The forcing algorithm was integrated into a mooring analysis program based on the global coordinate-based finite element method. At each time step, the added mass, lifting force, and drag force coefficients and their corresponding loads are computed for each element. Validation studies have been carried out for a full-scale rigid riser segment and a model-scale flexible riser. The numerical results were compared with experimental data and solutions by other programs.

scholarly journals Study on Multimode Vortex-Induced Vibration of Deepwater Riser in Different Flow Fields by Finite Element Simulations

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Weimin Chen ◽  
Min Li ◽  
Liwu Zhang ◽  
Tiancai Tan
Keyword(s):  
Finite Element ◽  
Shear Flow ◽  
Time Domain ◽  
Flow Fields ◽  
Finite Element Simulations ◽  
Vortex Induced Vibration ◽  
Excitation Region ◽  
Element Simulation ◽  
Deepwater Riser ◽  
Semi Empirical

Multimode vortex-induced vibration (VIV) of slender risers, respectively, in stepped and shear flows is explored by finite element simulations. Taking account of the interaction between fluid and structure, a hydrodynamic model is proposed and embedded into the finite element simulation so as to carry out dynamic response of multimode VIV in time-domain. Multimode VIV in both stepped and shear flow fields is examined. In the case of stepped flow, a semi-empirical formula of modal weight is given. In the case of shear flow, modal excitation region can be determined based on modal energy, and participating modes approximately distribute in scattering groups.

Prediction of Vortex-Induced Vibration Response of a Pipeline Span by Coupling a Viscous Flow Solver and a Beam Finite Element Solver

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Juan P. Pontaza ◽  
Raghu G. Menon
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Vibration Response ◽  
Navier Stokes ◽  
Time Step ◽  
Vortex Induced Vibration ◽  
Flow Solver ◽  
Instantaneous Flow ◽  
Numerical Predictions ◽  
Instantaneous Flow Field

This paper describes a fluid-structure interaction (FSI) modeling approach to predict the vortex-induced vibration response of a pipeline span by coupling a three-dimensional viscous incompressible Navier–Stokes solver with a beam finite element solver in time domain. The pipeline span is modeled as an Euler–Bernoulli beam subject to instantaneous flow-induced forces and solved using finite element basis functions in space and an unconditionally stable Newmark-type discretization scheme in time. At each time step, the instantaneous incremental displacement is fed back to the fluid flow solver, where the position of the pipeline is updated to compute the resulting instantaneous flow field and associated flow-induced forces. Numerical predictions from the FSI model are compared to current tank experimental measurements of a pipeline span subject to uniform free-stream currents.

Torsional Analysis of a Steel Cord-Rubber Tire Belt Structure

1996 ◽  
Vol 24 (4) ◽  
pp. 339-348 ◽  
Author(s):  
R. M. V. Pidaparti
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Composite Structures ◽  
Three Dimensional ◽  
Element Model ◽  
Torsional Stiffness ◽  
Element Analysis ◽  
Rubber Belt ◽  
Steel Cord ◽  
Torsional Analysis

Abstract A three-dimensional (3D) beam finite element model was developed to investigate the torsional stiffness of a twisted steel-reinforced cord-rubber belt structure. The present 3D beam element takes into account the coupled extension, bending, and twisting deformations characteristic of the complex behavior of cord-rubber composite structures. The extension-twisting coupling due to the twisted nature of the cords was also considered in the finite element model. The results of torsional stiffness obtained from the finite element analysis for twisted cords and the two-ply steel cord-rubber belt structure are compared to the experimental data and other alternate solutions available in the literature. The effects of cord orientation, anisotropy, and rubber core surrounding the twisted cords on the torsional stiffness properties are presented and discussed.

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