A Theoretical Study on the Second-Order Wave Forces for Two-Dimensional Bodies

1989 ◽  
Vol 111 (1) ◽  
pp. 37-42 ◽  
Author(s):  
G. P. Miao ◽  
Y. Z. Liu
Keyword(s):  
Nonlinear Wave ◽  
Incident Wave ◽  
Theoretical Study ◽  
Nonlinear Effects ◽  
Offshore Structures ◽  
Second Order ◽  
Wave Forces ◽  
Two Dimensional ◽  
Regular Waves ◽  
Steady Wave

Nonlinear wave forces on fixed or floating offshore structures have attracted much attention recently. This paper deals with the nonlinear effects of regular waves on fixed two-dimensional bodies up to second-order terms. The second-order diffraction potential is solved consistently and the second-order steady wave forces and the biharmonic wave forces with frequency corresponding to the double of the incident wave frequency are obtained.

Nonlinear Wave Forces Acting on Submerged Horizontal Cylinders

1988 ◽  
Vol 110 (1) ◽  
pp. 62-70 ◽  
Author(s):  
R. Inoue ◽  
Y. Kyozuka
Keyword(s):  
Perturbation Theory ◽  
Free Surface ◽  
Nonlinear Wave ◽  
Wave Breaking ◽  
Nonlinear Effects ◽  
Second Order ◽  
Experimental Results ◽  
Wave Forces ◽  
Regular Perturbation ◽  
Horizontal Cylinders

This paper is to present experimental results of the first and second-order wave forces acting on three kinds of horizontally submerged cylinders. Wave height, wave frequency and the models’ submergence were varied in the experiments. These results are compared with the numerical calculations based on the regular perturbation theory. Through this study, it was found that the calculations of both the first and second-order wave forces coincide with the experiments when the cylinders are submerged at a sufficient depth. However, in the case that the cylinders are close to the free surface and/or wave amplitudes are relatively large, the experimental results become small compared with the calculations because of nonlinear effects, such as wave breaking observed in the experiments.

scholarly journals A theory of nonlinear wave loading on offshore structures

1981 ◽  
Vol 4 (3) ◽  
pp. 589-613 ◽  
Author(s):  
Lokenath Debnath ◽  
Matiur Rahman
Keyword(s):  
Nonlinear Wave ◽  
Vertical Cylinder ◽  
Nonlinear Effects ◽  
Diffraction Theory ◽  
Offshore Structures ◽  
The Body ◽  
Wave Number ◽  
Wave Forces ◽  
Wave Loading ◽  
Nonlinear Contribution

A theoretical study is made of the nonlinear wave loading on offshore structures using the diffraction theory of hydrodynamics. A nonlinear modification of the classical Morison equation,D≡Fℓ+FDfor estimating wave forces on offshore structures is suggested in this paper. The modified equation is found in the formD≡Fℓ+Fnℓ+FDwhereFnℓ≡Fd+Fw+Fqis the nonlinear contribution made up of the dynamic, waterline, and the quadratic forces associated with the irrotational-flow part of the wave loading on structures. The study has then been applied to calculate the linear and the nonlinear wave loadings on a large vertical cylinder partially immersed in an ocean of arbitrary uniform depth. All the linear and nonlinear forces exerting on the cylinder are determined explicitly. A comparison is made between these two kinds of forces. Special attention is given to the nonlinear wave loadings on the cylinder. It is shown that all nonlinear effects come from the interaction between the body's responses to the oncoming wave's fluctuating velocity and its fluctuating extension. It is found that the nonlinear effects are dominated by the sum of the dynamic and waterline forces. The nonlinear correction to Morison's equation increases with increasingkbwherebis the characteristic dimension of the body andkis the wave number. This prediction is shown to be contrary to that of the linear diffraction theory which predicted that the Morison coefficient decreases with increasingkb. Several interesting results and limiting cases are discussed in some detail.

Control of Dynamic Responses of Towerlike Offshore Structures in Waves

1990 ◽  
Vol 112 (1) ◽  
pp. 14-20 ◽  
Author(s):  
K. Yoshida ◽  
H. Suzuki ◽  
N. Oka
Keyword(s):  
Feedforward Control ◽  
Offshore Structures ◽  
The Other ◽  
Dynamic Responses ◽  
Wave Forces ◽  
Regular Waves ◽  
Offshore Structure ◽  
Flexible Pipe ◽  
Controlled Structure ◽  
Uncontrolled System

This paper presents a preliminary attempt to control the dynamic response of a towerlike offshore structure subjected to regular waves. The structures are modeled in two ways. One is a vertical rigid pipe supported at the lower end by a pin joint. The other is a vertical flexible pipe fixed at the lower end. The formulation of the optimal control shows that the control consists of a feedback control and a feedforward control based on the disturbance. In this research, two types of feedforward control are employed apart from the optimality. One is to compensate the entire wave forces acting on the structure. The other is on-off control to compensate the principal Fourier component of the wave forces by using the three states of the thruster, forward, stop and backward. The displacement and deformation of the structures were measured by an ultrasonic measurement system. The surface elevation was measured by a capacitance-type wave height meter. These data were sampled and processed by a 16-bit microprocessor, and the thrust was applied by a propeller-type thruster. The performance of the control was satisfactory, and the responses of the controlled structure were reduced to about 30 percent of those of the uncontrolled system.

Asymptotic Solutions and Radiation Conditions for Second-Order Diffracted Waves

1989 ◽  
Vol 111 (3) ◽  
pp. 203-207
Author(s):  
H. Huang ◽  
J. Li ◽  
X. Wang
Keyword(s):  
Finite Element ◽  
Circular Cylinder ◽  
Second Order ◽  
Asymptotic Solutions ◽  
Wave Forces ◽  
Far Field ◽  
Two Dimensional ◽  
Diffracted Waves ◽  
Artificial Boundaries ◽  
Radiation Conditions

The far-field asymptotic solutions for the second-order diffracted waves have been developed, both in three and two-dimensional problems. The radiation conditions for the second-order diffracted waves are derived by using the asymptotic solutions. The nonlinear wave forces on a half-circular cylinder on seabed are presented by using finite element methods with the radiation conditions imposed on the artificial boundaries.

A Multipole Accelerated Desingularized Method for Computing Nonlinear Wave Forces on Bodies

1998 ◽  
Vol 120 (2) ◽  
pp. 71-76 ◽  
Author(s):  
S. M. Scorpio ◽  
R. F. Beck
Keyword(s):  
Boundary Conditions ◽  
Nonlinear Wave ◽  
Mixed Boundary ◽  
Offshore Structures ◽  
Computational Effort ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Wave Forces ◽  
Surface Boundary ◽  
Time Step

Nonlinear wave forces on offshore structures are investigated. The fluid motion is computed using a Euler-Lagrange time-domain approach. Nonlinear free surface boundary conditions are stepped forward in time using an accurate and stable integration technique. The field equation with mixed boundary conditions that result at each time step are solved at N nodes using a desingularized boundary integral method with multipole acceleration. Multipole accelerated solutions require O(N) computational effort and computer storage, while conventional solvers require O(N2) effort and storage for an iterative solution and O(N3) effort for direct inversion of the influence matrix. These methods are applied to the three-dimensional problem of wave diffraction by a vertical cylinder.

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.

Time-Domain Analysis of Floating Bodies with Forward Speed

2002 ◽  
Vol 124 (2) ◽  
pp. 66-73 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Katja Stutz
Keyword(s):  
Nonlinear Wave ◽  
Time Domain ◽  
Degrees Of Freedom ◽  
Wave Structure ◽  
Nonlinear Effects ◽  
Time Domain Analysis ◽  
Offshore Structures ◽  
Driving Mechanism ◽  
Forward Speed ◽  
Transient Wave

Broaching, surf-riding, and capsizing of ships and offshore structures are transient wave-structure interactions which imply high risks for crew, vessel and cargo. As nonlinear effects are of great importance, time-domain investigations are indispensable. For unveiling the associated driving mechanism of these critical motions, it is desirable to analyze the cause-reaction chains in detail: Depending on the transient wave elevation, we obtain an instationary pressure distribution on the wetted surface of the cruising vessel. Resulting forces and moments excite vessel motions in six degrees of freedom. Based on the linear panel-method program for transient wave-body interactions, TiMIT [Korsmeyer et al. (1999)], this paper investigates seakeeping characteristics of offshore structures with forward speed. Results are presented in frequency and time domain. The procedure allows to identify critical seaways, and to analyze cause-reaction chains in deterministic wave sequences where critical and steep wave packets are embedded in random seas. The detailed evaluation reveals that large roll and pitch motions are easily reduced by variation of course and speed. For investigating the mechanism of wave/structure interactions, this paper introduces the relevant time-domain methodology, and indicates how nonlinear wave characteristics can be introduced in the time-stepping analysis. In subsequent steps nonlinear wave/structure interactions will also be considered.

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