Study On The Expansion-performance Of Mesh Of Cod-end Of Filterable Fishing Gear

This study is on the basis of the criterion in Fishing gear hydrodynamic modeling and the theory of the fishing gear hydrodynamic and by using the modern facilities and technique to proceed the experiment in laboratory flumes. This experiment designed two different test-models and performed five kinds of comparison experiments on premise of analyzing different influenced factors for mesh expansion-performance. The comparison experiments included:"different mesh-size series","different Mesh-structure series","different hanging ratio series","different frame series"and"different manropes series"and two kinds of working condition, no load test and load test. The experiment was conducted at Tokyo University of Marine Science and Technology and Zhejiang Ocean University. We researched the hydraulic resistance and mesh expansion-performance of different working conditions by using image processing and data analysis. The changing of screen angle with different corrective measures and the diversity of different position of the cod-end, combining with the changing of the hydraulic resistance were analyzed.From the experimental results, we concluded that longitudinal diamond mesh and horizontal diamond mesh were all closed gradually, with the increasing of velocity of flow, but the variation tendency of horizontal diamond mesh is less, the square mesh keep intact. The cod-end comprises two different types of meshes, had the largest angle and the least hydraulic resistance at the 0.5 (m/s). The back-end mesh had larger angle than others, at the same velocity of flow, the cod-ends with the larger shrink-coefficient had lesser angle and larger angle. The angle of the cod-end with the hanging ratio equal to 0.707 could be the maximum at the 0.5 (m/s), and the mesh near the manrope was square. The change of hydraulic resistance of cod-end hadn't obvious relativity with the hanging ratio.The rigid frame could help the mesh expanding efficiently; especially the back-frame had more significant effects. At the same velocity of flow, the cod-end with one manrope had the least diameter and the cod-end with three manropes had the largest diameter, the cod-ends with two or four manropes had nearly the same shape, the diameter was between them. The hydraulic resistance of cod-end with big meshes was smaller than the cod-end with small meshes highly in no-load test. But in load test the two cod-ends had the almost same hydraulic resistance and variation tendency of it. The variation tendency of the cod-end of horizontal diamond mesh was the other way round to the cod-end of the longitudinal diamond mesh.