Title Page
Contents
Abstract 10
1. Introduction 12
1.1. Tuna production and purse seine fishery in Vietnam 12
1.1.1. Tuna speices in Vietnam seawater and target species of tuna purrse seine fishiery 12
1.1.2. Tuna purse seine fishery in Vietnam 13
1.1.3. Problem of tuna purse seine fishery in Vietnam 16
1.2. Numerical method in mechanical properties research of purse seine 18
1.3. Previous study results 21
1.4. Objectives 23
2. Material and method 24
2.1. Study material 24
2.1.1. The prototype tuna purse seines 24
2.1.2. The tuna purse seiners 32
2.1.3. Fishing ground 33
2.2. Mathematical model 34
2.2.1. Mathematical equation 34
2.2.2. Computation method 40
2.2.3. Dynamic simulation 42
2.3. Improving the tuna purse seine gear 45
2.4. Data collection and analysis method 48
3. Results 50
3.1. Simulation results of Vietnamese tuna purse seines 50
3.1.1. Sinking performance 50
3.1.2. Tension on ring line 55
3.1.3. Surround area and shape of nets 56
3.2. Simulation of improved tuna purse seines 59
3.2.1. Comparison of sinking performance 59
3.2.2. Comparison of tension on ring line 61
3.3. Comparison of the improved and the present gears 62
3.3.1. Sinking performance 62
3.3.2. Tension on ring line 65
3.3.3. Surround area and shape of net 66
4. Discussion 68
4.1. The Vietnamese tuna purse seine 68
4.2. The comparison improved tuna purse seines 70
4.3. Comparison between the improved gear and present gears 71
5. Conclusion 75
Reference 77
Table 1. Production rate of some tuna species in Vietnam seawater (gillnet... 13
Table 2. Specification of The gear 2003 26
Table 3. Specification of The gear 2014 29
Figure 1. Net hauler and pursing winch of tuna purse seine in Vietnam 14
Figure 2. The Schematic diagram of the drawing plan of the Vietnamese tuna... 32
Figure 3. The Schematic diagram of the drawing plan of the Vietnamese tuna... 32
Figure 4. Operation seawater region of the gears. 33
Figure 5. Mesh into mass point and spring. 35
Figure 6. Illustration of mesh approximation method 35
Figure 7. Designed tool of purse seine (SIMUPURSE software). 43
Figure 8. Simulation tool of purse seine (SPURSE software). 44
Figure 9. The schematic diagram of the drawing plan and mesh size distribution... 46
Figure 10. The improved gear I. 47
Figure 11. The improved gear II. 47
Figure 12. The improved gear III. 48
Figure 13. The improved gear IV. 48
Figure 14. The depths of the lead-lines under no current. 51
Figure 15. The depths of the lead-lines under the currents. 52
Figure 16. The sinking speed of the lead-lines under no current. 53
Figure 17. The sinking speed of the lead-lines under the currents. 54
Figure 18. The tensional force on ring line under: (a) no current and (b) the... 55
Figure 19. Surround area of the float lines of the gears under the currents. 56
Figure 20. The shape of the Vietnamese gear 2003 under the currents. 57
Figure 21. The shape of the Vietnamese gear 2014 under the currents. 58
Figure 22. The depth by time at intermediate part of the improved gears under... 59
Figure 23. The speed by time at intermediate part of the improved gears under... 60
Figure 24. The speed by depth at intermediate part of the improved gears under... 61
Figure 25. Tension on ring line of the improved gears under the currents. 62
Figure 26. The speed by depth of the improved and present gears. 63
Figure 27. The speed by time of the improved and present gears. 63
Figure 28. The depth by time of the improved and the present gears 64
Figure 29. Tension on ring line under the currents. 65
Figure 30. Surround area after finish shooting time. 66
Figure 31. The net wall shape. 66
Figure 32. Comparison between the Vietnamese gear 2014 and the improved... 67