Efficient and accurate methods for computational simulation of netting structures with mesh resistance to opening

[Resumen]La investigación actual en simulación computacional de artes de pesca se centra en modelos numéricos eficientes capaces de predecir con precisión el comportamiento del material de la red. Esta tesis es un compendio de artículos relativos al desarrollo de un nuevo modelo que incluye la resistencia a la apertura. En primer lugar, se desarrollan varios modelos de rigidez no lineal para un hilo de red. El hilo es modelado como una viga biempotrada y su respuesta fuerzadesplazamiento es calculada mediante análisis por elementos finitos y aproximada por tres modelos diferentes. Se obtienen diferentes variantes en función de la expresión utilizada para aproximar dicha respuesta. El modelo propuesto supera las desventajas de los modelos previos. El modelo está basado en la rigidez a flexión, por tanto, se presenta también un procedimiento para cuantificarla. Aunque la metodología es similar a la de estudios previos, en esta tesis se aportan nuevas contribuciones, como un montaje experimental más simple.En cuanto a la simulación, el funcionamiento de un arte de pesca viene determinado principalmente por su posición de equilibrio. En esta tesis se comparan la robustez y eficiencia de los métodos de minimización de energía basados en el gradiente y del método de Newton-Raphson, aplicándolos a un conjunto de problemas representativos. Finalmente, se desarrolla una formulación basada en masas suspendidas para modelar la red. La formulación de masas suspendidas es ampliamente utilizada para modelar la red, pero en esta tesis los muelles que radicionalmente conectan los nodos son remplazados por el modelo de hilo propuesto. Además, los nudos de la red son modelados como esferas en lugar de masas puntuales. Aunque las expresiones del modelo propuesto son más complejas que las de los muelles, se demuestra que ambos modelos tienen un coste computacional similar. Para validar el modelo, un paño de red es simulado y comparado con resultados experimentales En cuanto a la simulación, el funcionamiento de un arte de pesca viene determinado principalmente por su posición de equilibrio. En esta tesis se comparanla robustez y eficiencia de los métodos de minimización de energía basados en el gradiente y del método de Newton-Raphson, aplicándolos a un conjunto de problemas representativos. Finalmente, se desarrolla una formulación basada en masas suspendidas para modelar la red. La formulación de masas suspendidas es ampliamente utilizada para modelar la red, pero en esta tesis los muelles que tradicionalmente conectan los nodos son remplazados por el modelo de hilo propuesto. Además, los nudos de la red son modelados como esferas en lugar de masas puntuales. Aunque las expresiones del modelo propuesto son más complejas que las de los muelles, se demuestra que ambos modelos tienen un coste computacional similar. Para validar el modelo, un paño de red es simulado y comparado con resultados experimentales.[Abstract] 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.[Resumo] 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

Real-time Simulation of Cable Pay-Out and Reel-In with Towed Fishing Gears

[Abstract] Achieving real-time simulation of fast cable pay-out and reel-in manoeuvres with towed fishing gears is a challenging task. This work presents two new simulation methods based on simplified cable models for this kind of application. First, three numerical techniques are proposed to enhance a classical spring-based cable model, increasing its computational efficiency in manoeuvres that involve reeling the cable around a winch drum. Second, the development of an efficient multibody modelling approach based on natural coordinates is reported. The performance of these methods was assessed with two realistic examples. The numerical experiments involved different values of cable axial stiffness and spatial discretization levels, since these parameters were found to have a major impact on computational efficiency. The proposed methods achieved real-time performance in the simulation of systems modelled with up to a few thousand variables. Each modelling approach has advantages and limitations that must be considered when addressing a given application.MINECO; JCI-2012-1237

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

The effect of the bottom boundary layer on trawl behaviour

Thirty-seven hauls of a bottom trawl were carried out, as part of a national French project. These sea trials were undertaken in an area with strong currents: up to 1 knot. The measurements at sea of the bottom bridle’s tension show a clear effect of the current. Although the water speed relative to the trawl is constant, when the boat tows with current, the bottom bridle’s tension increases, and when the boat tows against the current, the bottom bridle’s tension decreases. The mean bottom bridle tension is 7840 N and increases with a slope of 1197 N for each m/s of current. The current has almost no effect on the top bridle’s tension: for a mean value of approximately 9810 N, the increment is 106 N for each m/s of current. The modelling of the trawl gear and the boundary layer explains this behaviour. Boundary layers of different thicknesses have been simulated. A boundary layer of 0.9 m height shows the best fit between simulation and measurements. The simulated bottom bridle’s tension increases to 1343 N each m/s of current while the top bridle’s tension decreases to 320 N each m/s. These values are inside the standard deviation of the measurements

An experimental/numerical study of the catch weight influence on trawl behavior

Measurements at sea during fishing trials on bottom trawl have revealed that the geometry of the trawl is affected by the catch. A series of 37 hauls of around 3 h were carried out during the French EFFICHALUT project. The aim of this project was to carry out improvements on the fishing gear in order to reduce energy consumption. For this project, numerous sensors were used: for bridle tension, door spread, vertical opening, and door attitude. The measurements show quite clearly that the door spread decreases and the bridle tension increases during most of the hauls. The door spread decreased by 1.35 m/h, with a standard deviation of 1.98 m/h while the top bridle tension increased by 47 kg/h, with a standard deviation of 59 kg/h. The mean catch per haul was around 1.48 t. The modeling of the trawl gear and the catch with a FEM model helps to explain the variation in the door spread and the bridle tension: the numerical model shows a mean decrease of 1.06 m/h for the door spread and a mean increase of 76.0 kg/h for the top bridle tension. The modeling were developed by the first author in previous studies