Hydrodynamics of Flexible Pipe With Staggered Buoyancy Elements Undergoing Vortex-Induced Vibrations

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Mengmeng Zhang ◽  
Shixiao Fu ◽  
Leijian Song ◽  
Jie Wu ◽  
Halvor Lie ◽  
...  
Keyword(s):  
Unit Length ◽  
Added Mass ◽  
Hydrodynamic Characteristics ◽  
Ocean Engineering ◽  
Flexible Pipe ◽  
Excitation Coefficient ◽  
Vortex Induced Vibrations ◽  
Sea Current ◽  
Coefficients Identification ◽  
Structural Mass

Flexible pipe with staggered buoyancy elements such as lazy wave riser and drilling riser has been widely used in ocean engineering. Under the influence of sea current, both of the buoyancy elements and the riser may experience vortex induced vibrations (VIV). However, when VIV occurs, hydrodynamic characteristics of the buoyancy elements and its influence on hydrodynamic force of the bare pipe still need investigation. The purpose of this paper is to reveal the hydrodynamic characteristics of flexible pipe with staggered buoyancy elements undergoing VIV. The crossflow (CF) hydrodynamic coefficients of the flexible pipe with 25%, 50%, and 100% coverage of staggered buoyancy are obtained from model tests, using hydrodynamic forces and coefficients identification method. Then, the characteristics of added mass coefficients and excitation coefficients in CF direction are analyzed. The results show that the added-mass coefficients of bare pipe are relatively larger than those of buoyancy module, while the total mass per unit length (sum of structural mass and added mass) is consistent along the pipe. Similarly, the range of excitation coefficient on the buoyancy elements is smaller than that on the bare pipe, and their ratio is equal to the reciprocal of diameter ratio 2.5.

Hydrodynamics of Flexible Pipe With Staggered Buoyancy Elements Undergoing Vortex-Induced Vibrations

2017 ◽  
Author(s):  
Mengmeng Zhang ◽  
Shixiao Fu ◽  
Leijian Song ◽  
Jie Wu ◽  
Halvor Lie ◽  
...  
Keyword(s):  
Cross Flow ◽  
Added Mass ◽  
Forced Oscillations ◽  
Hydrodynamic Characteristics ◽  
Ocean Engineering ◽  
Flexible Riser ◽  
Flexible Pipe ◽  
Vortex Induced Vibrations ◽  
Coefficients Identification ◽  
The Relationship

Flexible riser with staggered buoyancy elements has been widely used in ocean engineering, such as steel lazy wave riser, drilling riser, etc. Both the buoyancy elements and the riser may experience vortex induced vibrations (VIV), subject to sea current. However, hydrodynamic characteristics of the buoyancy elements undergoing VIV and influence of buoyancy elements on hydrodynamic force of the bare section are still under discussion. The purpose of this paper is to reveal the hydrodynamic characteristics of flexible riser with staggered buoyancy elements, both for buoyancy element and bare pipe section. The cross flow hydrodynamic coefficients of the flexible riser with 25%, 50% and 100% staggered buoyancy covered are obtained from VIV model tests, using hydrodynamic forces and coefficients identification method. Distribution of the added mass coefficients and excitation coefficients along the flexible riser were investigated, and compared with those on the bare flexible pipe and rigid cylinders under forced oscillations. In addition, the relationship between added-mass coefficients of buoyancy element and that of bare section were obtained.

Prediction of Combined Inline and Crossflow Vortex-Induced Vibrations Response of Deepwater Risers

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Jie Wu ◽  
Malakonda Reddy Lekkala ◽  
Muk Chen Ong ◽  
Elizabeth Passano ◽  
Per Erlend Voie
Keyword(s):  
Fatigue Damage ◽  
Massachusetts Institute Of Technology ◽  
Ocean Engineering ◽  
Flexible Cylinder ◽  
Load Model ◽  
Cylinder Test ◽  
Excitation Coefficient ◽  
Vortex Induced Vibrations ◽  
Institute Of Technology ◽  
Deepwater Risers

Deepwater risers are susceptible to vortex-induced vibrations (VIV) when subjected to currents. When responding at high modes, fatigue damage in the inline (IL) direction may become equally important as the crossflow (CF) components. Accurate calculation of both IL and CF responses is therefore needed. Empirical VIV prediction programs, such as VIVANA “Passano et al. (2016, “VIVANA—Theory Manual Version 4.8,” Trondheim, Norway),” SHEAR7 “(Vandiver, J. K., and Li, L., 2007, “Shear7 v4.5 Program Theoretical Manual,” Department of Ocean Engineering, Massachusetts Institute of Technology, Cambridge, MA),” and VIVA “Triantafyllou et al. (1999, “Pragmatic Riser VIV Analysis,” Offshore Technology Conference, Houston, TX, May 3–6, Paper No. OTC-10931-MS.)” are the most common tools used by the offshore industry. Progress has been seen in the prediction of CF responses. Efforts have also been made to include an IL load model in VIVANA. A set of excitation coefficient parameters were obtained from rigid cylinder test and adjusted using measured responses of one of the flexible cylinder VIV tests. This set of excitation coefficient parameters is still considered preliminary and further validation is required. Without an accurate IL response prediction, a conservative approach in VIV analysis has to be followed, i.e., all current profiles have to be assumed to be unidirectional or acting in the same direction. The purpose of this paper is to provide a reliable combined IL and CF load model for the empirical VIV prediction programs. VIV prediction using the existing combined IL and CF load model in VIVANA is validated against selected flexible cylinder test data. A case study of a deepwater top tension riser (TTR) has been carried out. The results indicate that VIV fatigue damage using two-dimensional directional current profiles is less conservative compared to the traditional way of using unidirectional current profiles.

Optimal design of 6-DOF eclipse mechanism based on task-oriented workspace

Robotica ◽  
2011 ◽  
Vol 30 (7) ◽  
pp. 1041-1048 ◽  
Author(s):  
Donghun Lee ◽  
Jongwon Kim ◽  
TaeWon Seo
Keyword(s):  
Optimal Design ◽  
Unit Length ◽  
Numerical Procedure ◽  
Design Procedure ◽  
Mass Reduction ◽  
Objective Functions ◽  
Design Efficiency ◽  
Task Oriented ◽  
Structural Mass ◽  
Optimal Set

SUMMARYWe present a new numerical optimal design for a redundant parallel manipulator, the eclipse, which has a geometrically symmetric workspace shape. We simultaneously consider the structural mass and design efficiency as objective functions to maximize the mass reduction and minimize the loss of design efficiency. The task-oriented workspace (TOW) and its partial workspace (PW) are considered in efficiently obtaining an optimal design by excluding useless orientations of the end-effector and by including just one cross-sectional area of the TOW. The proposed numerical procedure is composed of coarse and fine search steps. In the coarse search step, we find the feasible parameter regions (FPR) in which the set of parameters only satisfy the marginal constraints. In the fine search step, we consider the multiobjective function in the FPR to find the optimal set of parameters. In this step, fine search will be kept until it reaches the optimal set of parameters that minimize the proposed objective functions by continuously updating the PW in every iteration. By applying the proposed approach to an eclipse-rapid prototyping machine, the structural mass of the machine can be reduced by 8.79% while the design efficiency is increased by 6.2%. This can be physically interpreted as a mass reduction of 49 kg (the initial structural mass was 554.7 kg) and a loss of 496 mm3/mm in the workspace volume per unit length. The proposed optimal design procedure could be applied to other serial or parallel mechanism platforms that have geometrically symmetric workspace shapes.

Natural Frequencies of a Railroad Track

1987 ◽  
Vol 54 (2) ◽  
pp. 299-304 ◽  
Author(s):  
S. P. Patil
Keyword(s):  
Natural Frequency ◽  
Elastic Layer ◽  
Natural Frequencies ◽  
Unit Length ◽  
Added Mass ◽  
Winkler Foundation ◽  
Railroad Track

The natural frequency of an infinite railroad track was first determined by Timoshenko as ωR = √k/m, where k is the constant for the massless Winkler foundation and m is the mass per unit length of the rail. The natural frequencies of the track are determined here by modeling the track as a beam resting on a 3-D inertial elastic layer. It is shown that the mass of the supporting foundation has a significant effect on the natural frequencies of a railroad track. Finally, the concept of “added mass” is introduced in order to determine the natural frequency in a desired mode of vibration, by modeling the track as a beam on the massless Winkler foundation and adding the mass of the foundation to the beam.

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.

Physical Model Testing of the TetraSpar Demo Floating Wind Turbine Prototype

2019 ◽  
Author(s):  
Michael Borg ◽  
Anthony Viselli ◽  
Christopher K. Allen ◽  
Matthew Fowler ◽  
Christoffer Sigshøj ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Numerical Models ◽  
Model Testing ◽  
Offshore Wind ◽  
Scale Model ◽  
Test Facility ◽  
Hydrodynamic Characteristics ◽  
Ocean Engineering ◽  
Floating Wind Turbine ◽  
Floating Offshore Wind Turbines

Abstract As part of the process of deploying new floating offshore wind turbines, scale model testing is carried out to de-risk and verify the design of novel foundation concepts. This paper describes the testing of a 1:43 Froude-scaled model of the TetraSpar Demo floating wind turbine prototype that shall be installed at the Metcentre test facility, Norway. The TetraSpar floating foundation concept consists of a floater tetrahedral structure comprising of braces connected together through pinned connections, and a triangular keel structure suspended below the floater by six suspension lines. A description of the experimental setup and program at the Alfond W2 Ocean Engineering Lab at University of Maine is given. The objective of the test campaign was to validate the initial design, and contribute to the development of the final demonstrator design and numerical models. The nonlinear hydrodynamic characteristics of the design are illustrated experimentally and the keel suspension system is shown to satisfy design criteria.

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].

Improved In-Line Vortex-Induced Vibrations Prediction for Combined In-Line and Cross-Flow Vortex-Induced Vibrations Responses

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Decao Yin ◽  
Elizabeth Passano ◽  
Carl M. Larsen
Keyword(s):  
Cross Flow ◽  
Hydrodynamic Coefficients ◽  
Marine Structures ◽  
Flexible Pipe ◽  
Flexible Beams ◽  
Forced Motion ◽  
Pipe Model ◽  
Vortex Induced Vibrations ◽  
Flow Vortex ◽  
Semi Empirical

Slender marine structures are subjected to ocean currents, which can cause vortex-induced vibrations (VIV). Accumulated damage due to VIV can shorten the fatigue life of marine structures, so it needs to be considered in the design and operation phase. Semi-empirical VIV prediction tools are based on hydrodynamic coefficients. The hydrodynamic coefficients can either be calculated from experiments on flexible beams by using inverse analysis or theoretical methods, or obtained from forced motion experiments on a circular cylinder. Most of the forced motion experiments apply harmonic motions in either in-line (IL) or crossflow (CF) direction. Combined IL and CF forced motion experiments are also reported. However, measured motions from flexible pipe VIV tests contain higher order harmonic components, which have not yet been extensively studied. This paper presents results from conventional forced motion VIV experiments, but using measured motions taken from a flexible pipe undergoing VIV. The IL excitation coefficients were used by semi-empirical VIV prediction software vivana to perform combined IL and CF VIV calculation. The key IL results are compared with Norwegian Deepwater Programme (NDP) flexible pipe model test results. By using present IL excitation coefficients, the prediction of IL responses for combined IL and CF VIV responses is improved.

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