Nonlinear stiffness models of a net twine to describe mesh resistance to opening of flexible net structures

Abstract

Numerical simulation of marine flexible net structures allows predicting the behavior of fishing gears and aquaculture cages. In recent years, the tendency toward the use of thicker and stronger twines in netting materials has made its resistance to opening a key factor in the performance of such structures. To accurately describe the mesh resistance to opening, a net twine was modeled as a double-clamped beam and its force–displacement response was calculated by finite element analysis. Fitting techniques were used to develop three different dimensionless stiffness models that express elastic forces in the twine as an explicit nonlinear function of its deformation: (1) a polynomial fitting of the force, (2) a spline fitting of the potential energy, and (3) a spring-based model able to deal with large axial deformations. Each model has different characteristics and advantages. Numerical and experimental tests were used to assess and compare them with previous models described in the literature. The results show that the presented models have very good accuracy and high computational efficiency. They will allow introducing accurate simulation of mesh resistance to opening in numerical simulations of marine netting structures without a high impact in the computational performance.