Recent advances in the computation of nonlinear wave effects on offshore structures

1985 ◽  
Vol 12 (3) ◽  
pp. 439-453 ◽  
Author(s):  
Michael de St. Q. Isaacson
Keyword(s):  
Nonlinear Wave ◽  
Diffraction Problem ◽  
Flexible Structures ◽  
Nonlinear Problems ◽  
Offshore Structures ◽  
Nonlinear Flow ◽  
Ocean Engineering ◽  
Wave Interactions ◽  
Large Structures ◽  
Wave Effects

The present paper provides a review of recent research on various nonlinearities that arise in ocean wave interactions with offshore structures. These include nonlinearities associated with the incident waves alone, the response of slender structural members to waves, and the nonlinear diffraction problem involving wave interactions with large structures. Emphasis is given to areas of current research into two particular nonlinear problems. One concerns an investigation into alternative approximations to the Morison equation for flexible structures and the other concerns the numerical simulation of nonlinear wave diffraction around large structures. Key words: diffraction, hydrodynamics, nonlinear flow, ocean engineering, offshore structures, waves.

Nonlinear wave forces on a circular cylinder

1989 ◽  
Vol 16 (2) ◽  
pp. 182-187 ◽  
Author(s):  
Michael Isaacson ◽  
Qi-Hua Zuo
Keyword(s):  
Circular Cylinder ◽  
Nonlinear Wave ◽  
Perturbation Methods ◽  
Wave Force ◽  
Offshore Structures ◽  
Wave Forces ◽  
Ocean Engineering ◽  
Time Stepping ◽  
Wave Effects ◽  
Accuracy And Stability

Nonlinear wave forces on a surface-piercing vertical circular cylinder are considered using a time-stepping method previously developed which is based on Green's theorem. Possible improvements in the efficiency, accuracy, and stability of the method are considered. Results based on this method are compared with those obtained previously using perturbation methods as well as with experimental results. It is found that the time-stepping method adopted here is quite reasonable. Wave force coefficients are given as functions of the governing parameters of the problem and the importance of nonlinear wave effects on the forces is assessed. Key words: hydrodynamics, ocean engineering, offshore structures, waves, wave forces.

Experimental Investigation of Vortex-Induced Vibrations on Yawed and Inclined Flexible Cylinders

2021 ◽  
pp. 1-16
Author(s):  
Daniel P. Vieira ◽  
Guilherme R. Franzini ◽  
Fredi Cenci ◽  
Andre Fujarra
Keyword(s):  
A Priori ◽  
Flexible Structures ◽  
Resonance Region ◽  
Offshore Structures ◽  
Natural Mode ◽  
Flexible Cylinder ◽  
Decomposition Scheme ◽  
Independence Principle ◽  
Modal Amplitude ◽  
Time Histories

Abstract An experimental setup was built to investigate the Vortex-Induced Vibration (VIV) phenomenon on yawed and inclined flexible cylinders, in which five yaw angles θ = 0°, 10°, 20°, 30° and 45° and five azimuth angles ß = 0°, 45°, 90°, 135°, and 180° were combined. The experiments were carried out in a towing tank facility at Reynolds numbers from 1800 to 18000, comprising vibrations up to the eighth natural mode. Time histories of displacements were recorded using a submerged optical system that tracks 17 reflective targets. A modal decomposition scheme based on Galerkin's method was applied, aiming multimodal behavior investigations. Such an approach allowed the analysis of the modal amplitude throughout time, revealing interesting results for such a class of VIV tests. The flexible cylinder total response is generally a combination of two or more modes. Only for azimuths 0°, 90°, and 180°, a unimodal response was observed for the two first lock-in regimes. The frequency response showed that, when the response was multimodal, non-dominant modes can follow the vibration frequency of the dominant one. Assuming a priori the Independence Principle (IP) valid to define the reduced velocities (Vr), it was observed that the resonance region was restricted to 3 <= Vr <= 8 for the tested cases, indicating that the IP can be at least partially applied for flexible structures. As the literature scarcely explores the simultaneous yawed and inclined configurations, the present work may contribute to further code validation and improvements regarding the design of slender offshore structures.

Nonlinear wave effects in a closed tube

1978 ◽  
Vol 13 (3) ◽  
pp. 483-486
Author(s):  
G. E. Dumnov ◽  
G. F. Telenin
Keyword(s):  
Nonlinear Wave ◽  
Closed Tube ◽  
Wave Effects

Structural Dynamics

1985 ◽  
Vol 38 (10) ◽  
pp. 1287-1289
Author(s):  
F. C. Moon ◽  
E. H. Dowell
Keyword(s):  
Structural Dynamics ◽  
Optimization Problems ◽  
Acoustic Noise ◽  
Flexible Structures ◽  
Computer Software ◽  
Nonlinear Problems ◽  
Great Promise ◽  
Bluff Bodies ◽  
Building Structures ◽  
Dynamics And Control

While much of the linear theory of structural dynamics has been codified in numerous computer software, important problems remain such as inverse methods (modal synthesis or system identification) and optimization problems. Nonlinear problems, however, are a fertile ground for new research, especially those involving large deformations (e.g., crash simulation) and material nonlinearities. Structure interaction problems will continue to be a fruitful area of research including fluid-structure dynamics and interaction with acoustic noise, thermal fields, soils, and electromagnetic forces. For example, new knowledge about unsteady flows around bluff bodies is needed to make significant progress with dynamic interaction problems with bridge and building structures in unsteady winds. A new field which shows great promise for application is the theory of feedback control of flexible structures. Advances in this area could pay off in near-space engineering and robotics. The training of new researchers with backgrounds in both structural dynamics and control theory and experience is a high priority for the control-structure field, however.

Experimental Investigation on the Dynamic Response of a Three Legged Articulated Type Offshore Wind Tower

2016 ◽  
Author(s):  
Chinsu Mereena Joy ◽  
Anitha Joseph ◽  
Lalu Mangal
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Renewable Energy Sources ◽  
Offshore Structures ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Experimental Investigations ◽  
Offshore Wind Turbine ◽  
Ocean Engineering ◽  
Study Results

Demand for renewable energy sources is rapidly increasing since they are able to replace depleting fossil fuels and their capacity to act as a carbon neutral energy source. A substantial amount of such clean, renewable and reliable energy potential exists in offshore winds. The major engineering challenge in establishing an offshore wind energy facility is the design of a reliable and financially viable offshore support for the wind turbine tower. An economically feasible support for an offshore wind turbine is a compliant platform since it moves with wave forces and offer less resistance to them. Amongst the several compliant type offshore structures, articulated type is an innovative one. It is flexibly linked to the seafloor and can move along with the waves and restoring is achieved by large buoyancy force. This study focuses on the experimental investigations on the dynamic response of a three-legged articulated structure supporting a 5MW wind turbine. The experimental investigations are done on a 1: 60 scaled model in a 4m wide wave flume at the Department of Ocean Engineering, Indian Institute of Technology, Madras. The tests were conducted for regular waves of various wave periods and wave heights and for various orientations of the platform. The dynamic responses are presented in the form of Response Amplitude Operators (RAO). The study results revealed that the proposed articulated structure is technically feasible in supporting an offshore wind turbine because the natural frequencies are away from ocean wave frequencies and the RAOs obtained are relatively small.

Nonlinear wave interactions and evolution of a ring-beam distribution of energetic electrons

1988 ◽  
Vol 31 (8) ◽  
pp. 2238 ◽  
Author(s):  
S. Kainer ◽  
J. D. Gaffey ◽  
C. P. Price ◽  
X. W. Hu ◽  
G. C. Zhou
Keyword(s):  
Nonlinear Wave ◽  
Wave Interactions ◽  
Energetic Electrons ◽  
Nonlinear Wave Interactions

Numerical Investigation of Dynamics of the Flexible Riser by Applying Absolute Nodal Coordinate Formulation

2021 ◽  
Vol 55 (5) ◽  
pp. 179-195
Author(s):  
Luu Quang Hung ◽  
Zhuang Kang ◽  
Li Shaojie
Keyword(s):  
Absolute Nodal Coordinate Formulation ◽  
Flexible Structures ◽  
Beam Model ◽  
Environmental Load ◽  
The Finite Element Method ◽  
Ocean Engineering ◽  
Flexible Riser ◽  
Absolute Nodal Coordinate ◽  
Static And Dynamic Characteristics ◽  
Load Conditions

Abstract In this paper, the dynamics of the flexible riser are investigated based on the absolute nodal coordinate formulation (ANCF). The stiffness, generalized elastic force, external load, and mass matrixes of the element are deduced based on the principle of energy conversion and assembled with the finite element method. The motion equation of the flexible riser is established. The influence of the environmental load conditions on the flexible riser model is studied in the MATLAB environment. Moreover, the accuracy and reliability of the programs are verified for a beam model with theoretical solutions. Finally, the static and dynamic characteristics of the flexible riser are analyzed, systematically adopting the ANCF method, which in turn proves the effectiveness and feasibility of the ANCF. Therefore, the proposed method is a powerful scheme for investigating the dynamics of flexible structures with large deformation in ocean engineering.

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