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.

scholarly journals A Finite Element Study of Multi-Mode VIV of Slender Riser Experiencing Non-Uniform Flow

2011 ◽  
Author(s):  
Min Li ◽  
Weimin Chen ◽  
Liwu Zhang
Keyword(s):  
Finite Element ◽  
Time Domain ◽  
Coupling Model ◽  
Uniform Flow ◽  
Structural Flexibility ◽  
Element Simulation ◽  
Mode Vibration ◽  
Deepwater Riser ◽  
Multi Mode ◽  
Element Study

The dynamic characteristics of deepwater riser usually present serried modes with lower frequencies, because structural flexibility is very large due to high aspect ratio (ratio of length to diameter of riser). Moreover, in practice flow velocity usually distributes non-uniformly along the riser length. A coupling model, for multi-mode VIV (vortex-induced vibration) of slender riser experiencing non-uniform flow, by means of finite element simulation combined with the hydrodynamic model taking account of the interaction between fluid and structure in time-domain, is proposed. VIV responses of slender risers respectively in uniform, stepped and shear flow are explored. Satisfied agreements with experiment results are observed. Additionally, based on the numerical simulations effects of reduced velocity and modal energy on modal weight are explored. We note that for case of multi-mode vibration the participating modes tend to distribute by groups.

Modeling Method of Constitutive Law of Rubber Hyperelasticity Based on Finite Element Simulations

2003 ◽  
Vol 76 (1) ◽  
pp. 271-285 ◽  
Author(s):  
Li-Rong Wang ◽  
Zhen-Hua Lu
Keyword(s):  
Finite Element ◽  
Finite Element Simulations ◽  
Constitutive Law ◽  
Modeling Technique ◽  
Characteristic Analysis ◽  
Rubber Material ◽  
Element Simulation ◽  
Tension And Compression ◽  
Nonlinear Elastic ◽  
Elastic Characteristics

Abstract This paper is to present a method and procedure for modeling the constitutive law of anti-vibration rubber hyperelasticity based on finite element simulations. The hyperelasticity of rubber-like material is briefly summarized first. Then a method and procedure for determining an accurate constitutive law of rubber hyperelasticity from uniaxial tension and compression experiment data is presented and implemented. Due to nonlinear elastic properties of rubber and application limitations of various forms of constitutive law, results of finite element simulation to rubber material experiments show that different forms of constitutive law have to be adopted in different ranges of strain. The proposed procedure to obtain an appropriate constitutive law of rubber hyperelasticity of vibration isolator provides engineers with an effective modeling technique for design and analysis of anti-vibration rubber components. Finally, models of three kinds of rubber materials of a hydraulically damped rubber mount (HDM) are determined by tests and finite element simulations and applied to static and dynamic characteristic analysis of the HDM. The predicted elastic characteristics of the HDM and its major rubber components agree well with experimental data, which demonstrates the practicability and effectiveness of the presented modeling technique to modeling engineering rubber materials in dynamic systems.

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.

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