[en] Current research in computational simulation of fishing gears focuses on efficient numerical models that accurately predict the behaviour of the netting structure. This thesis is collection of four papers related to the development of a new model that includes the mesh resistance to opening. Firstly, several nonlinear stiffness models of a net twine are developed. The net twine is modelled as a double-clamped beam and its force-displacement response is calculated by finite element analysis and approximated with three different models. The proposed models overcome the drawbacks of previous models. The twine model is based on the bending stiffness and other geometrical properties of the netting material, so, a procedure to quantify them is presented. Although the methodology is similar to the previous studies, several original contributions are introduced, like a simpler experimental set-up. This procedure is also used to validate the presented twine models with experimental data. Regarding the simulation, the performance of a fishing gear is mainly determined by its equilibrium shape. In this thesis, the robustness and efficiency of gradient-based energy minimization methods and Newton iteration are compared by applying them to a set of benchmark problems. Finally, a lumped mass formulation for netting structures is developed. The lumped mass formulation is widely used to model netting structures, but in this thesis the linear springs that traditionally connect the nodes are replaced by the developed twine model. Besides, the knots are modeled as spheres instead of point masses. Although the expressions of the presented model are more complex than those of the spring model, it has been demonstrated that both models have a similar computational overhead. To validate the model, a netting panel is simulated and compared with experimental results.

[gl] A investigación actual en simulación computacional de redes de pesca céntrase en modelos numéricos eficientes, capaces de prever con precisión o comportamento da estructura da rede. Esta tese é un compendio de artigos sobre o desenvolvemento dun novo modelo que inclúe a resistencia á abertura. En primeiro lugar, desenvólvense varios modelos de rixidez non lineal para fíos de redes. O fío é modelado como unha viga biempotrada e a súa resposta de forza-desprazamento foi calculada mediante análise de elementos finitos e aproximada mediante diferentes modelos. O modelo proposto supera as desvantaxes dos modelos anteriores. O modelo baséase na rixidez a flexión, e polo tanto, tamén se presenta un novo método para cuantificala. Aínda que a metodoloxía é semellante á de estudos anteriores, o novo método ten importantes vantaxas, como por exemplo unha configuración experimental máis simple. Con respecto á simulación, compárase a robustez e eficiencia de dúas familias de métodos para calcular a posición de equilibrio: métodos de minimización baseados no gradiente e método de Newton-Raphson, aplicándose a un conxunto de problemas representativos. Por último, desenvólvese unha nova formulación de masas suspendidas para estruturas de rede. A formulación de masa suspendida é amplamente utilizada para modelar a rede, pero nesta tese os resortes que tradicionalmente conectando os nodos son reemplazados polo modelo desenvolvido nesta tese. Ademais, os nós da rede son modelados como esferas, en vez de masas puntuais. Aínda que as ecuacións do modelo proposto son máis complexas do que as resortes, móstrase que ambos modelos posúen un custo computacional similar. Para validar o modelo, un pano de rede é simulado e comparado cos resultados experimentais.