Spectral Formulations for Vortex Induced Vibration Modal Decomposition and Reconstruction

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
S. I. McNeill
Keyword(s):  
Fatigue Damage ◽  
Angular Rate ◽  
Computational Cost ◽  
Time History ◽  
Computational Effort ◽  
Measured Data ◽  
Scale Model ◽  
Mode Shapes ◽  
Modal Decomposition ◽  
Vortex Induced Vibration

Modal decomposition and reconstruction (MDR) of marine riser vortex induced vibration (VIV) is a technique where vibration is measured using accelerometers and/or angular rate sensors, the modal displacements are solved for and the stress and fatigue damage is reconstructed along the riser. Recent developments have greatly increased the accuracy and reliability of the method. However the computational burden is onerous due to stress time history reconstruction and rainflow cycle counting at every desired location along the riser. In addition, fully synchronous data are required to reconstruct the stress histories. Dirlik’s method for obtaining rainflow damage for Gaussian random stress using only spectral information (four spectral automoments) has proven to be quite accurate with a significant reduction in computational effort. In this paper two spectral formulations of MDR are introduced. The first method is applicable when all the measured data are synchronous. In this method, spectral cross moments of the modal displacements are solved from the spectral cross moments of the measured data using basis vectors consisting of normal mode shapes. The spectral automoments of stress are obtained from the modal displacement cross moments and analytical stress mode shapes. Dirlik’s method is then applied to obtain rainflow damage. The second method is a generalization of the first, where the measured data cross moments are only partially known. This method is applicable when measured data are partially synchronous or asynchronous. A numerical root-finding technique is employed to solve for the modal response cross moments. The method then proceeds in the same manner as the first. The spectral methods are applied to simulated VIV data of a full-scale deepwater riser and to Norwegian Deepwater Program (NDP) scale-model test data on a 38 m long slender riser. Comparisons of reconstructed fatigue damage versus simulated or measured damage indicate that the method is capable of estimating fatigue damage accurately for Gaussian VIV even when data are not fully synchronous. It is also shown that computational cost is greatly reduced.

Efficient Modal Decomposition and Reconstruction of Riser Response due to VIV

2011 ◽  
Author(s):  
S. I. McNeill ◽  
P. Agarwal
Keyword(s):  
Fatigue Damage ◽  
Traveling Wave ◽  
Angular Rate ◽  
Normal Modes ◽  
Structural Response ◽  
Measured Data ◽  
Vibration Monitoring ◽  
Wave Number ◽  
Modal Decomposition ◽  
Basis Vectors

Vortex-Induced-Vibrations (VIV) due to ocean currents can consume a sizable portion of the allotted fatigue life of marine risers. Vibration monitoring and concurrent estimation of fatigue damage due to VIV can significantly enhance the safe and reliable operation of risers. To this end, riser response can be characterized by using sensors (e.g. accelerometers and/or angular rate sensors) to measure the motion of the riser at a few locations. Fatigue damage can be predicted along the entire length of riser from measured data using the method of modal decomposition and reconstruction. In this method the structural response of interest, such as stress and fatigue damage, is expressed by modal superposition, where the modal weights are estimated using measured data and analytical modeshapes. However the accuracy of this method declines as the sensor density (number of sensors per unit riser length) decreases, especially when the riser vibrates in high-order modes and exhibits traveling wave behavior. In this paper, an efficient frequency-domain methodology allowing for accurate reconstruction of the riser response along the entire riser using a limited number of sensors is proposed. We first identify the excited VIV modes (natural frequency and modeshape) using principal vectors of the cross spectral density. Modal decomposition and reconstruction is performed separately for each VIV band surrounding each excited mode. This allows us to use several (as many as the number of sensors) participating modes in each band, and thus improve the accuracy. Since the stress distribution is sensitive to the chosen set of participating modes, we optimize over several candidate sets, selecting the set of modes that result in the lowest prediction error. In order to improve the reconstruction of complex modes, particularly traveling waves, the modeshapes can be augmented with additional basis vectors. The additional basis vectors are obtained by shifting the phase of the normal modes by 90 degrees at every wave number using the Hilbert transform. Though developed in the context of VIV, the method can be used to estimate fatigue damage due to vibrations regardless of the excitation mechanism. The methodology is demonstrated using the NDP (Norwegian Deepwater Program) test data on a 38 meter long slender riser, using data from eight accelerometers. Results show that the proposed algorithm can reconstruct stresses and fatigue damage accurately along the length of the riser in the presence of traveling wave behavior using relatively few sensors.

Real-Time Riser Fatigue Monitoring Routine: Architecture, Data and Results

2013 ◽  
Author(s):  
Scot McNeill ◽  
Puneet Agarwal ◽  
Dan Kluk ◽  
Kenneth Bhalla ◽  
Tomokazu Saruhashi ◽  
...  
Keyword(s):  
Real Time ◽  
Fatigue Damage ◽  
Water Depth ◽  
Angular Rate ◽  
Measured Data ◽  
Automated System ◽  
Time Data ◽  
Joint Rotation ◽  
Computational Environment ◽  
Fatigue Monitoring

Recently, the Modal Decomposition and Reconstruction (MDR) algorithm was developed to accurately estimate fatigue damage in marine risers based on measured acceleration and angular rates at several locations. The greatest benefit for drilling risers can be derived by incorporating the method in an online, fully automated system. In this way, fatigue damage estimates are available to the crew on the rig in real-time for risk quantification and mitigation. To this end, the MDR routine was implemented for online assessment of fatigue damage along the entire riser from acceleration and angular rate measurements at typically 5–10 elevations. This paper discusses the architecture, highlights some measured data and provides results for modes, stress and fatigue damage rate for the Chikyu drilling vessel during two scientific drilling campaigns. These campaigns occurred at the Shimokita site (1180-meter water depth) and the Nankai trough site (1939-meter water depth). To the authors’ knowledge, real-time fatigue monitoring of the entire riser has not been accomplished previously. Robust incorporation of the MDR algorithm into an online computational environment is detailed, including incorporation of top tension and mud weight data from the rig, detection and removal of data errors, and streamlined flow of the data through the computational modules. Subsequently, it is shown by example how the measured accelerations and angular rates are used to determine excited modes, participating modes, stress distribution and fatigue damage along the entire Chikyu drilling riser in an online setting. The technology highlighted advances riser integrity management two steps forward by first using measured data at 5–10 locations and the MDR algorithm to reconstruct stress and fatigue damage along the entire riser, and secondly integrating this approach into a fully automated, real-time computational environment. As a result, drilling engineers are empowered with a tool that provides real-time data on the integrity of the drilling riser, enabling informed decisions to be made in adverse current or wave conditions. Measured data also serves as a benchmark for analytical model calibration activities, reducing conservatism in stress and fatigue in future deployments. Furthermore, cumulative fatigue damage can be tracked in each riser joint, enabling more effective joint rotation and inspection programs.

Experimental Study of the Dynamic Response of Partially Filled Pipes Focused on Natural Frequencies and Mode Shapes

2017 ◽  
Author(s):  
Oscar de la Torre ◽  
Xavier Escaler ◽  
Jamie Goggins
Keyword(s):  
Natural Frequencies ◽  
Dynamic Properties ◽  
Computational Cost ◽  
Computational Effort ◽  
Mode Shapes ◽  
Significant Drop ◽  
Fluid Structure ◽  
Hydraulic Machinery ◽  
Piping Systems ◽  
Pipe Geometry

The presence of air in piping systems is a major concern in the industry. Problems like flow disruption, reduction of hydraulic machinery efficiencies or a significant drop in pipe capacity are many times related to this fact. The present paper aims to find a simple and non-intrusive experimental method to detect air in piping systems. The method, based on the dynamic properties of fluid-structure systems and underpinned by a novel low computational cost numerical simulation, accurately predicts the volume of water present in a pipe. Good agreement between numerical and experimental solutions has been obtained using much less computational effort than traditional fully coupled Fluid Structure Interaction with CFD analysis. From the numerical and experimental data, two different mathematical expressions relating the system natural frequencies, both vertically and horizontally, and the area occupied by the water have been obtained. These expressions account for the pipe geometry which theoretically would make them suitable for other diameter and wall thickness values. The paper is combined with a preliminary study of the system’s mode shapes for the different volumes of water.

Simulation of the Dynamic Behaviour of a Thin-Walled Meshing Gear Using Duhamel’s Integral

2010 ◽  
Author(s):  
Costantino Carmignani ◽  
Paola Forte ◽  
Gabriele Melani ◽  
Ugo Buffa
Keyword(s):  
Dynamic Behaviour ◽  
Computational Cost ◽  
Time History ◽  
Realistic Model ◽  
Computational Effort ◽  
Design Development ◽  
Virtual Displacement ◽  
Displacement Sensors ◽  
Duhamel’S Integral

Aircraft transmissions have the peculiar characteristics of light structures and high operating speeds, therefore relatively low flexural natural frequencies and high excitation frequencies due to rotation and meshing. Resonance vibrations can create serious problems of malfunctions and even catastrophic failures. A reliable numerical model is surely a convenient means to perform preliminary simulations to identify the most critical resonance conditions and evaluate the effect of structural modifications on the dynamic behaviour of the component in the design development phase. Most numerical investigations found in the literature are carried out on simplified models of the rotating bodies likened to discs to reduce the computational effort. In this work a novel approach based on the application of Duhamel’s integral for the determination of the dynamic behaviour of a rotating gear subject to meshing forces has been developed to obtain more reliable results with a realistic model at an affordable computational cost. The gear response to dynamic excitation is obtained by the determination of its response to impulse using a single 3D finite element transient analysis taking afterwards into account the effect of the gear rotation. Subsequently, the Duhamel’s integral is applied using the tooth load time history in order to simulate as realistically as possible the gear load conditions. This paper presents the case of a real bi-helicoidal gear. A test bench was simulated measuring the displacement observed by some non-rotating virtual displacement sensors, located near the gear rim and disc. The signal was processed identifying the most critical rotating speeds on the basis of its RMS value. The numerical Campbell speed/frequency diagrams are in good agreement with experimental results.

On the Vortex-Induced Vibration Response of a Model Riser and Location of Sensors for Fatigue Damage Prediction

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
C. Shi ◽  
L. Manuel ◽  
M. A. Tognarelli ◽  
T. Botros
Keyword(s):  
Fatigue Damage ◽  
Measured Data ◽  
Vibration Response ◽  
Data Sets ◽  
Flexible Riser ◽  
Vortex Induced Vibration ◽  
Damage Prediction ◽  
Marine Risers ◽  
Deepwater Risers ◽  
Critical Interest

This study is concerned with vortex-induced vibration (VIV) of deepwater marine risers. Riser response measurements from model tests on a densely instrumented long, flexible riser in uniform and sheared currents offer an almost ideal setup for our work. Our objectives are two-fold: (i) we use the measured data to describe complexities inherent in riser motions accompanying VIV; and (ii) we discuss how such data sets (and even less spatially dense monitoring) can be used effectively in predicting fatigue damage rates, which are of critical interest for deepwater risers.

Stationary and Transient Response of Cylindrical Shells Under Random Excitation

1988 ◽  
Vol 110 (2) ◽  
pp. 205-209
Author(s):  
A. V. Singh
Keyword(s):  
Transient Response ◽  
Random Vibration ◽  
Time History ◽  
Wide Band ◽  
Random Excitation ◽  
Mode Shapes ◽  
The Finite Element Method ◽  
History Of ◽  
The Mean ◽  
Random Vibration Analysis

This paper presents the random vibration analysis of a simply supported cylindrical shell under a ring load which is uniform around the circumference. The time history of the excitation is assumed to be a stationary wide-band random process. The finite element method and the condition of symmetry along the length of the cylinder are used to calculate the natural frequencies and associated mode shapes. Maximum values of the mean square displacements and velocities occur at the point of application of the load. It is seen that the transient response of the shell under wide band stationary excitation is nonstationary in the initial stages and approaches the stationary solution for large value of time.

Differences in the Upscaling Procedure for Compositional Reservoir Simulations of Immiscible and Miscible Gas Flooding

2021 ◽  
Author(s):  
Victor de Souza Rios ◽  
Arne Skauge ◽  
Ken Sorbie ◽  
Gang Wang ◽  
Denis José Schiozer ◽  
...  
Keyword(s):  
Computational Cost ◽  
Specific Treatment ◽  
Dynamic Responses ◽  
Scale Model ◽  
Small Scale ◽  
Coarse Scale ◽  
Reservoir Models ◽  
Permeability Upscaling ◽  
Gas Flooding ◽  
Grid Block

Abstract Compositional reservoir simulation is essential to represent the complex interactions associated with gas flooding processes. Generally, an improved description of such small-scale phenomena requires the use of very detailed reservoir models, which impact the computational cost. We provide a practical and general upscaling procedure to guide a robust selection of the upscaling approaches considering the nature and limitations of each reservoir model, exploring the differences between the upscaling of immiscible and miscible gas injection problems. We highlight the different challenges to achieve improved upscaled models for immiscible and miscible gas displacement conditions with a stepwise workflow. We first identify the need for a special permeability upscaling technique to improve the representation of the main reservoir heterogeneities and sub-grid features, smoothed during the upscaling process. Then, we verify if the use of pseudo-functions is necessary to correct the multiphase flow dynamic behavior. At this stage, different pseudoization approaches are recommended according to the miscibility conditions of the problem. This study evaluates highly heterogeneous reservoir models submitted to immiscible and miscible gas flooding. The fine models represent a small part of a reservoir with a highly refined set of grid-block cells, with 5 × 5 cm2 area. The upscaled coarse models present grid-block cells of 8 × 10 m2 area, which is compatible with a refined geological model in reservoir engineering studies. This process results in a challenging upscaling ratio of 32 000. We show a consistent procedure to achieve reliable results with the coarse-scale model under the different miscibility conditions. For immiscible displacement situations, accurate results can be obtained with the coarse models after a proper permeability upscaling procedure and the use of pseudo-relative permeability curves to improve the dynamic responses. Miscible displacements, however, requires a specific treatment of the fluid modeling process to overcome the limitations arising from the thermodynamic equilibrium assumption. For all the situations, the workflow can lead to a robust choice of techniques to satisfactorily improve the coarse-scale simulation results. Our approach works on two fronts. (1) We apply a dual-porosity/dual-permeability upscaling process, developed by Rios et al. (2020a), to enable the representation of sub-grid heterogeneities in the coarse-scale model, providing consistent improvements on the upscaling results. (2) We generate specific pseudo-functions according to the miscibility conditions of the gas flooding process. We developed a stepwise procedure to deal with the upscaling problems consistently and to enable a better understanding of the coarsening process.

Comparative Analysis of Methodologies for Uncertainty Propagation and Quantification

2017 ◽  
Author(s):  
Alessandra Cuneo ◽  
Alberto Traverso ◽  
Shahrokh Shahpar
Keyword(s):  
Engineering Design ◽  
Polynomial Chaos ◽  
Epistemic Uncertainty ◽  
Uncertainty Propagation ◽  
Computational Cost ◽  
Computational Effort ◽  
Optimization Under Uncertainty ◽  
Design Parameters ◽  
Test Case ◽  
Aleatory And Epistemic Uncertainty

In engineering design, uncertainty is inevitable and can cause a significant deviation in the performance of a system. Uncertainty in input parameters can be categorized into two groups: aleatory and epistemic uncertainty. The work presented here is focused on aleatory uncertainty, which can cause natural, unpredictable and uncontrollable variations in performance of the system under study. Such uncertainty can be quantified using statistical methods, but the main obstacle is often the computational cost, because the representative model is typically highly non-linear and complex. Therefore, it is necessary to have a robust tool that can perform the uncertainty propagation with as few evaluations as possible. In the last few years, different methodologies for uncertainty propagation and quantification have been proposed. The focus of this study is to evaluate four different methods to demonstrate strengths and weaknesses of each approach. The first method considered is Monte Carlo simulation, a sampling method that can give high accuracy but needs a relatively large computational effort. The second method is Polynomial Chaos, an approximated method where the probabilistic parameters of the response function are modelled with orthogonal polynomials. The third method considered is Mid-range Approximation Method. This approach is based on the assembly of multiple meta-models into one model to perform optimization under uncertainty. The fourth method is the application of the first two methods not directly to the model but to a response surface representing the model of the simulation, to decrease computational cost. All these methods have been applied to a set of analytical test functions and engineering test cases. Relevant aspects of the engineering design and analysis such as high number of stochastic variables and optimised design problem with and without stochastic design parameters were assessed. Polynomial Chaos emerges as the most promising methodology, and was then applied to a turbomachinery test case based on a thermal analysis of a high-pressure turbine disk.

Fatigue Damage From High Mode Number Vortex-Induced Vibration

2006 ◽  
Author(s):  
J. Kim Vandiver ◽  
Susan B. Swithenbank ◽  
Vivek Jaiswal ◽  
Vikas Jhingran
Keyword(s):  
Fatigue Damage ◽  
Field Experiments ◽  
Higher Harmonics ◽  
Vortex Induced Vibration ◽  
Third Harmonic ◽  
The Third ◽  
Damage Rate ◽  
Surface Vessels ◽  
Vortex Shedding Frequency ◽  
First Time

This paper presents results from two field experiments using long flexible cylinders, suspended vertically from surface vessels. The experiments were designed to investigate vortex-induced vibration (VIV) at higher than tenth mode in uniform and sheared flows. The results of both experiments revealed significant vibration energy at the expected Strouhal frequency (referred to in this paper as the fundamental frequency) and also at two and three times the Strouhal frequency. Although higher harmonics have been reported before, this was the first time that the contribution to fatigue damage, resulting from the third harmonic, could be estimated with some certainty. This was enabled by the direct measurement of closely spaced strain gauges in one of the experiments. In some circumstances the largest RMS stress and fatigue damage due to VIV are caused by these higher harmonics. The total fatigue damage rate including the third harmonic is shown to be up to forty times greater than the damage rate due to the vibration at the fundamental vortex-shedding frequency alone. This dramatic increase in damage rate due to the third harmonic appears to be associated with a narrow range of reduced velocities in regions of the pipe associated with significant flow-induced excitation.

High-resolution imaging: An approach by incorporating stationary-phase implementation into deabsorption prestack time migration

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. S317-S331 ◽  
Author(s):  
Jianfeng Zhang ◽  
Zhengwei Li ◽  
Linong Liu ◽  
Jin Wang ◽  
Jincheng Xu
Keyword(s):  
Stationary Phase ◽  
Fresnel Zone ◽  
Computational Cost ◽  
Computational Effort ◽  
Propagation Path ◽  
Time Migration ◽  
Resolution Imaging ◽  
Prestack Time Migration ◽  
Dip Angle ◽  
Absorption And Dispersion

We have improved the so-called deabsorption prestack time migration (PSTM) by introducing a dip-angle domain stationary-phase implementation. Deabsorption PSTM compensates absorption and dispersion via an actual wave propagation path using effective [Formula: see text] parameters that are obtained during migration. However, noises induced by the compensation degrade the resolution gained and deabsorption PSTM requires more computational effort than conventional PSTM. Our stationary-phase implementation improves deabsorption PSTM through the determination of an optimal migration aperture based on an estimate of the Fresnel zone. This significantly attenuates the noises and reduces the computational cost of 3D deabsorption PSTM. We have estimated the 2D Fresnel zone in terms of two dip angles through building a pair of 1D migrated dip-angle gathers using PSTM. Our stationary-phase QPSTM (deabsorption PSTM) was implemented as a two-stage process. First, we used conventional PSTM to obtain the Fresnel zones. Then, we performed deabsorption PSTM with the Fresnel-zone-based optimized migration aperture. We applied stationary-phase QPSTM to a 3D field data. Comparison with synthetic seismogram generated from well log data validates the resolution enhancements.

Sign in / Sign up

Export Citation Format

Share Document