Numerical investigation on crack identification using natural frequencies and mode shapes of a drilling riser during deployment and retrieval

Zhou, Xingkun; Sun, Yuqing; Duan, Menglan; Li, Wenhua

doi:10.1016/j.petrol.2020.107721

Cited by 18 publications

(6 citation statements)

References 22 publications

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“…(2) Under the soft hang-off condition, the displacement Y 0 and bending moment M 0 are zeros, i.e., the state vector of the riser at the top boundary is, Regardless of the top constraints, the bottom end of the riser is usually seen as a free end, where the rotational stiffness of the lower flex/ball joint is neglected and the LMRP and/or BOP is simplified as a lumped mass (Liu et al 2018;Zhou et al 2020). Therefore, the bottom boundary condition expressed by state vectors is, where…”

Section: Boundary Conditions and Different Casesmentioning

confidence: 99%

“…Lu et al (2018) predicted a riser's modal shapes and exciting and damping regions of excited modes by a proposed modal-space-based direct method for the prediction of vortex-induced vibration. Zhou et al (2020) studied the variation of natural frequencies and modal displacements versus cracks in hang-off risers. Yu et al (2018) analyzed the intrinsic relationships between natural frequency and oscillating frequency to explain the occurrence of the dominant mode.…”

Section: Introductionmentioning

confidence: 99%

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Modal state vectors of a free-hanging drilling riser during deployment and retrieval

Zhou

Chen

et al. 2022

J Petrol Explor Prod Technol

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To prevent marine risers' resonance and eliminate potential threats, sufficient inherent dynamic characteristics such as natural frequency, modal displacement, slope, bending moment, and shear are necessary to be calculated and analyzed. However, most studies calculate the natural frequencies and modal displacements directly rather than the modal slopes and forces. The additional calculations of modal slopes and forces likely result in issue complications, time-consuming, or even errors especially when the boundaries at both ends are solved by a finite difference method. To solve the above problems, a state-vector approach is developed herein based on the precise integration method. Two traditional methods, i.e., differential transformation method and finite element method, are utilized to verify the validation of the approach. The modal state vectors of a marine drilling riser, i.e., not only modal displacements but also modal slopes, bending moments, and shears, are studied in detail under four classic cases according to the hard and soft hang-off modes and the deployment and retrieval processes. Besides, the natural frequencies versus the riser suspension lengths are investigated during the deployment and retrieval. The critical resonance suspension lengths of the riser are discussed via a double-peaked sea irregular wave spectrum. Based on the analyses presented in this study and their generic findings, powerful tools can be designed to prevent riser resonance and associated threats in operation.

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Section: Boundary Conditions and Different Casesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Modal state vectors of a free-hanging drilling riser during deployment and retrieval

Zhou

Chen

et al. 2022

J Petrol Explor Prod Technol

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“…The promising results confirm that, on the one hand, the effects of nonstationary excitations are significantly suppressed by the cointegration analysis with exogenous variables, allowing an output-only damage identification; on the other hand, the intrinsic long-run equilibrium relationship between the endogenous variables is sensitive to structural damage. Unlike the modal parameter-based damage detection methods, 11,12 the DSF of the CAX method is directly extracted from the strain signals, avoiding the cumbersome modal identification analysis.…”

Section: Damage Localization By Only Using Two Measurementsmentioning

confidence: 99%

“…These methods can identify the damage to a structure by examining the changes in the dynamic responses 5–7 or the modal parameters extracted from them, for example, natural frequencies and mode shapes. 8–10 Several numerical and experimental studies 11,12 have illustrated the effectiveness of using modal parameters for the damage identification of risers. However, these structures are extraordinarily slender and tend to vibrate at ultralow frequencies, posing a practical challenge to monitoring their vibration and extracting the modal parameters precisely.…”

Section: Introductionmentioning

confidence: 99%

Output-only structural damage localization for deepsea mining risers using cointegration analysis

Wang

et al. 2022

Structural Health Monitoring

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Deepsea mining risers, which transport mineral resources from the seafloor to surface facilities, are critical components of deepsea mining systems. This article presents a novel cointegration-based method for localizing structural damage in risers subjected to random excitations from waves, currents, and moving floating facilities. Although the dynamic responses of a riser (usually consisting of multiple segments) are often nonstationary, those within an individual pipe segment often have synchronous fluctuations with a common trend, allowing the application of a multivariate time series analysis. Cointegration can thus be performed for a pipe segment by treating the internal responses as the endogenous variables and those of the other pipe segments as the exogenous variables. Consequently, a stationary cointegrating residual for the dynamic responses purged of the influence of nonstationary excitations can be obtained. The cointegrating residual in conjunction with a statistical hypothesis test scheme is used to create an output-only damage indicator. The effectiveness of the proposed damage localization method is demonstrated with a numerical and experimental multi-segment riser. The results indicate that the strain responses of both risers exhibit nonstationary fluctuations due to the changeable environmental excitations. As the proposed method is robust to the external loading, it can accurately identify the damage location.

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“…The wellhead is easily and inevitably 2 damaged due to a variety of factors, including the low-cycle and huge loads transmitted through the global riser system and the soil-casing weak interaction (especially in soft or very soft seabed soils) [4,5,6]. Currently, many studies are focusing on the hydrodynamic characteristics of floating units, as well as the static and dynamic behaviors, strength, and stability of riser joints [7,8,9,10,11]. However, those studies are focused on the global riser system rather than the detailed subsea wellhead.…”

Section: Introductionmentioning

confidence: 99%

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2022

Brodogradnja

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Deepwater subsea wellheads may be significantly threatened under extreme sea conditions and operations, especially when the seabed is composed of very soft clay properties. A numerical model of a deepwater wellhead system is established using the classic ocean pipe element and nonlinear spring element of ANSYS to examine the behaviors of subsea wellheads in diverse seabed soil. Nonlinear spring elements coded in the APDL language are used to model three types of seabed soils: very soft soil, soft soil, and firm soil. The dynamic and quasi-static behaviors of the wellhead system in the typical coupled and decoupled models of the drilling riser system are particularly investigated in depth. The effects of the nonlinear seabed soil properties on the detailed wellhead are realistically simulated using time domain and extremum analysis. The results show that the softer the seabed soil, the greater the displacement, rotation angle, curvature, and bending moment of deepwater subsea wellheads. When the seabed soil reaches a particular depth, the mechanical characteristics of the wellheads under the three types of seabed soil conditions are almost simultaneously close to zero. Overall, several conclusions reached in this study may provide some useful references for design and stability analysis.

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Numerical investigation on crack identification using natural frequencies and mode shapes of a drilling riser during deployment and retrieval

Cited by 18 publications

References 22 publications

Modal state vectors of a free-hanging drilling riser during deployment and retrieval

Modal state vectors of a free-hanging drilling riser during deployment and retrieval

Output-only structural damage localization for deepsea mining risers using cointegration analysis

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