Comparison of linear spring and nonlinear FEM methods in dynamic coupled analysis of floating structure and mooring system

Kim, Byoung Wan; Sung, Hong Gun; Kim, Jin Ha; Hong, Sa Young

doi:10.1016/j.jfluidstructs.2013.07.002

Cited by 73 publications

(29 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Such considerations are particularly important if one needs to undertake an analysis where the power take-off is nonlinear. In such a case, it would be straightforward to extend the whole methodology presented here into the time domain, using the Cummins equation as described by Kim et al (2013) and implemented using state space modelling by, for example, Taghipour et al (2008) and Chen et al (2014).…”

Section: Discussionmentioning

confidence: 99%

A coupled hydrodynamic–structural model of the M4 wave energy converter

Taylor

Stansby

2016

Journal of Fluids and Structures

View full text Add to dashboard Cite

a b s t r a c tA method is developed for modelling wave energy converters consisting of floats connected by slender structural elements. The hydrodynamic and structural dynamic analyses are separated in a two-stage process, though the model is fully coupled. The method of dynamic substructuring is used to achieve this separation. The linear diffraction/ radiation problem is solved with a finite element idealisation for axisymmetric floats, and drag forces are incorporated by equivalent linearization. Results for a planar representation of the M4 device, and comparisons of theory and experiments undertaken for two scale models tested in regular and random waves, confirm the validity of the theoretical approach. A series of parametric studies is performed to clarify the important physical variables, including natural periods, the ratio of a characteristic length of the device to the wave length, and power take-off.

show abstract

Section: Discussionmentioning

confidence: 99%

A coupled hydrodynamic–structural model of the M4 wave energy converter

Taylor

Stansby

2016

Journal of Fluids and Structures

View full text Add to dashboard Cite

show abstract

“…Coupled analysis of moored SPAR platforms have been reported in Chen et al (2001), Kim and Sclavounos (2001), Tahar et al (2006), Zhang et al (2008), Chen and Zhu (2011), and Yang et al (2012). For a turret moored FPSO, a coupled dynamics analysis have been reported by Ormberg and Larsen (1998), Heurtier et al (2001) and Kim et al (2013) have discussed the importance of mooring line dynamics in deeper water. Column stabilised spread moored semisubmersible coupled analysis have been presented in Garrett (2005) and Kim et al (2013).…”

Section: Introductionmentioning

confidence: 97%

“…For a turret moored FPSO, a coupled dynamics analysis have been reported by Ormberg and Larsen (1998), Heurtier et al (2001) and Kim et al (2013) have discussed the importance of mooring line dynamics in deeper water. Column stabilised spread moored semisubmersible coupled analysis have been presented in Garrett (2005) and Kim et al (2013). Almost in all of the above time domain studies except Chen and Zhu (2011) and Yang et al (2012) have followed a similar approach in which the frequency-dependent hydrodynamic coefficients (added mass, and damping) are usually computed by Morison equations, strip theory, or by linear radiation-diffraction theory, and frequency domain equations of motion are then transformed into time domain through impulse response function as suggested by Cummins (1962).…”

Section: Introductionmentioning

confidence: 99%

A 3D Numerical Wave Tank Study for Offshore Structures with Linear and Nonlinear Mooring

Shivaji

Sen

2015

Aquatic Procedia

View full text Add to dashboard Cite

As offshore industry progressively moves towards deeper water, coupled dynamic analysis of such structures with mooring lines and risers becomes increasingly important because of the growing influence of mooring lines on the response of these structures. Experimental studies for such deepwater structures with mooring lines face serious problems due to the involved scaling and modeling issues. For such studies therefore a numerical tool capable of simulating the coupled dynamics of offshore structures is almost indispensable where the effect of mooring lines, loads arising from structural elements such as heave damping plates which are primarily due to fluid viscosity, external effects such as wind loads in case of floating wind turbines etc. are all coupled with the wave loads acting on the structure. It is widely acknowledged that for such a general and versatile numerical tool a time domain solution scheme is preferred over frequency domain solutions, particularly if nonlinearities in wave loads, mooring lines etc. are to be considered albeit in some simplified way. Based on such a premise, a solution scheme following a 3D numerical wave tank approach but with significant difference and novelty in its implementation have been under development. The developed method is capable of simulating long duration wave-structure interactions including important nonlinearities in wave loads, and in principle can also consider effects from many external sources such as linear and nonlinear mooring stiffness. While many aspects of the scheme including a validation and verification process is reported elsewhere, the purpose of the present paper is to study in detail the effect of linear and nonlinear mooring line stiffness on practical offshore configurations. As regards wave induced hydrodynamic loads, both linear loads as well as nonlinear loads arising from steep nonlinear incident wavers are considered. Results demonstrate that nonlinear mooring stiffness can have significant influence on the response of the structure. The influence of nonlinearities in mooring stiffness is relatively more pronounced when water depth is less while in deeper water a linear stiffness appears to be adequate in capturing the structure's response. The influence of hydrodynamic nonlinearity is however significant in all cases. These and other important results for practical offshore structures with different mooring configurations are presented and discussed in the paper.

show abstract

“…The frequency-dependent added mass and damping needed for evaluating the memory-integral term in these formulations are usually found from a linear frequency-domain hydrodynamic solution. For simulations involving speeddependent ship motions, these are usually determined from strip-theory formulations with suitable modifications to take into account the forward speed-dependent corrections (De Kat and Paulling 1989;Fonseca and Guedes-Soares 1998;Ayaz et al 2006), while 3D linear hydrodynamic solvers are used for simulations involving stationary floating offshore configurations (Chitrapu et al 1993;Kim et al 2013). Similarly the diffraction forces are also usually determined from linear frequency-domain solutions and transformed into time domain.…”

Section: Introductionmentioning

confidence: 99%

Time-domain simulation of large-amplitude wave–structure interactions by a 3D numerical tank approach

Ganesan

Sen

2015

J. Ocean Eng. Mar. Energy

View full text Add to dashboard Cite

A time-domain 3D Rankine panel method based on a simplified variant of the mixed Eulerian-Lagrangian scheme under certain approximations is developed for studying steep nonlinear waves interacting with practical ship and offshore configurations at zero speed. Appropriate techniques have been developed that enable the method to produce very long-duration simulation results. Two levels of time-domain computations are performed: (1) a fully linear formulation where all external forces are computed on the mean wetted surface, and (2) an approximate nonlinear computation where the hydrodynamics interaction forces (diffraction and radiation forces) are determined on the mean surface and the forces arising from the incident steep waves and hydrostatic restoring forces are determined based upon the exact wetted surface under the nonlinear incident wave. Numerical computations for three practical marine structures, the barge, the S175 hull, and the semisubmersible are presented. The linear computations for which very longduration simulations are achievable from the present method are validated against results from other available methods. As the method is developed for stationary floating bodies undergoing oscillation about their mean location, it cannot be applied for a fully unrestrained body which can freely drift. In absence of physical restraints, the approximate nonlinear calculation requires imposition of artificial constraints partially or fully restraining the horizontal motions. Very long-duration simulations under the influence of steep nonlinear large-amplitude waves for all the three structures considered could be achieved. Comparative studies between different force and motion components in large-amplitude waves from linear and the approximate nonlinear computations are made to bring out the influence of the incident wave nonlinearities on these structures. It is found that the nonlinearities of the forces and motions are strongly dependent on the above water hull geometry. Compared to a small water-plane area hull (the semisubmersible), or a wall-sided hull (the barge), a flared hull (S175) results in pronounced nonlinear features in the forces and motion time-histories.

show abstract

Comparison of linear spring and nonlinear FEM methods in dynamic coupled analysis of floating structure and mooring system

Cited by 73 publications

References 6 publications

A coupled hydrodynamic–structural model of the M4 wave energy converter

A coupled hydrodynamic–structural model of the M4 wave energy converter

A 3D Numerical Wave Tank Study for Offshore Structures with Linear and Nonlinear Mooring

Time-domain simulation of large-amplitude wave–structure interactions by a 3D numerical tank approach

Contact Info

Product

Resources

About