Fatigue analysis of mooring system for net cage under random loads

Mooring system for net cage plays a pivotal role in the aquaculture industry. Much room exists for further development in relation to the mooring line analysis. A statistical analysis of stress range of mooring line is presented. The fatigue design analysis is based on the time domain analysis of net cage and mooring system in irregular waves. The statistical properties of stress range are analyzed using the Weibull plots, histogram, damage plot and evaluation of its applicability in relation to simplified methods. In addition, the fatigue damage of mooring line is also analyzed using spectrum analysis method and compared with the result from rainflow counting method. A visual inspection of Weibull plots indicates a good fit, and the shape parameter is typically between 0.8 and 1.2. The fatigue damage is underestimated based on the Weibull parameters, while it is predicted accurately based on the Rayleigh distribution. The results also show that the fatigue damage of mooring line can be underestimated 10–30% using the spectrum analysis method.

[1]  M M Winkler,et al.  THE POLYESTER ROPE TAUT LEG MOORING CONCEPT: A FEASIBLE MEANS FOR REDUCING DEEPWATER MOORING COST AND IMPROVING STATION KEEPING PERFORMANCE , 1995 .

[3]  Chai-Cheng Huang,et al.  Numerical Modeling for an In Situ Single-Point-Mooring Cage System , 2010, IEEE Journal of Oceanic Engineering.

[4]  Emmanuel Chailleux,et al.  A Non-Linear Viscoelastic Viscoplastic Model for the Behaviour of Polyester Fibres , 2005 .

[5]  J. Flory.  Assessing Strength Loss of Abraded and Damaged Fiber Rope , 2008, OCEANS 2008 - MTS/IEEE Kobe Techno-Ocean.

[6]  J. F. Mandell,et al.  Modeling of Marine Rope Fatigue Behavior , 1987 .

[7]  K. Larsen,et al.  Reliability-based fatigue analysis of mooring lines , 1996 .

[8]  J. Flory,et al.  Durability of Polyester Ropes Used as Deepwater Mooring Lines , 2006, OCEANS 2006.

[9]  H. Choi,et al.  A comparative study on the fatigue life of mooring systems with different composition , 2010 .

[10]  Yun-Peng Zhao,et al.  Analysis of hydrodynamic behaviors of multiple net cages in combined wave–current flow , 2013 .

[11]  Yun-Peng Zhao,et al.  Analysis of hydrodynamic behaviors of gravity net cage in irregular waves , 2011 .

[12]  P. Lader,et al.  Experimental investigation of forces and geometry of a net cage in uniform flow , 2005, IEEE Journal of Oceanic Engineering.

[13]  N. Barltrop,et al.  Dynamics of Fixed Marine Structures , 1991 .

[14]  Odd Sture Hopperstad,et al.  Temporary-creep and post-creep properties of aquaculture netting materials , 2009 .

[15]  David W. Fredriksson,et al.  Finite element modeling of net panels using a consistent net element , 2003 .

[16]  Zhen Gao.  Stochastic Response Analysis of Mooring Systems with Emphasis on Frequency-domain Analysis of Fatigue due to Wide-band Response Processes , 2008 .

[17]  Yun-Peng Zhao,et al.  Numerical investigation of the hydrodynamic behaviors of multiple net cages in waves , 2012 .

[18]  Eric B. Williamson,et al.  Computational Model For the Analysis of Damaged Ropes , 2003 .

[19]  Jerry G. Williams,et al.  Small-Scale Testing of Damaged Synthetic Fiber Mooring Ropes , 2002 .

[20]  D. B. Colbourne,et al.  Observations on motions and loads in aquaculture cages from full scale and model scale measurements , 2001 .

[21]  Chai-Cheng Huang,et al.  Mooring line fatigue: a risk analysis for an SPM cage system. , 2010 .

[22]  David W. Fredriksson,et al.  The design and analysis of a four-cage grid mooring for open ocean aquaculture , 2004 .

[23]  Barbaros Celikkol,et al.  Modeling of dynamic behavior of a single-point moored submersible fish cage under currents , 2010 .

[24]  Ying Min Low.  Extending a time/frequency domain hybrid method for riser fatigue analysis , 2011 .

[25]  James D. Irish,et al.  Development of large fish farm numerical modeling techniques with in situ mooring tension comparisons , 2007 .