Artificial reefs
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This document discusses the hydrodynamic design of a new type of artificial reef based on a streamlined bicycle helmet compared to a hollow cube design. Results from computational fluid dynamics simulations indicate that the helmet artificial reef experiences lower drag and inertia forces, leading to improved flow patterns, which can provide better shelter and nutrient distribution for marine life. Further research is necessary to enhance understanding of flow characteristics in various conditions.
Artificial reefs
- 1. Hydrodynamic Design of New Type of Artificial Reefs O. B. Yaakob1,2,* , Yasser M. Ahmed1,2 , M. Rajali Jalal1 , Faizul A. A.1,2 , K. K. Koh1,2 , Tarmizi J. Zaid2 1 Marine Technology Center, Universiti Teknologi Malaysia, 2 Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, omar@fkm.utm.my, yasser@mail.fkm.utm.my
- 2. Introduction Determination of Water Particle Velocity Computational Domains and Grids Results and Comparisons Conclusion OutlinePresentation Outline
- 3. Introduction • Fisheries industry is one of the important industries in Malaysia. Majority of the citizen who live near the sea are involved in this industry and make profit from it. • Artificial reefs are man-made structures, placed on the seabed deliberately for reducing beach erosion, maintaining coasts, protecting habitats, boosting recreational fishing and increasing biotic diversity. • There are different types of ARs such as cube, pipes, cross-shaped and…et, which provide good mediums for fish perching, foraging, breeding and defense from enemies
- 4. Some types of ARs in Malaysia Due to the importance of studying the flow pattern around ARs, many studies have been conducted experimentally in wind tunnel and using CFD simulations to study the effect of geometry of these ARs on the flow pattern around them.
- 5. • In this research work, the flow field patterns around and inside a new type of artificial reef, based on the design of streamlined bicycle helmet and hollow cube artificial reef of the same volume were studied by employing FVM code Ansys CFX and Potential Flow Code Aqwa. New type of artificial reef (helmet artificial reef) Hollow cube artificial reef
- 6. Determination of Water Particle Velocity• The horizontal forces which acted on both ARs had been calculated using Ansys CFX for the viscous drag force (FD), while the inertia force (FI) due to wave effect on the bodies of the ARs had been calculated using the potential flow code, Ansys Aqwa. • Based on the linear wave theory, the horizontal water particle velocity (u) which moves towards the reef body in x direction can be calculated using • The range of ω was taken from 0.5 to 1.5 rad/sec and a was equal to 1 m based on the environmental data for Malaysia seas. • Three values for h were considered in this study, which were 20, 30 and 40 m. Determination of Water Particle Velocity
- 7. Computational Domains and Grids
- 8. Numbers of unstructured, panel mesh and total mesh elements used in each case in this study
- 9. Results and Comparisons The numerical results for the hydrodynamic drag force FD , inertia force FI and wave force FW FW = FD + FI
- 10. 0 100 200 300 400 500 600 0 0.25 0.5 0.75 1 1.25 1.5 1.75 FD(N) Wave frequency ω (rad/sec) FD H C h = 20 m FD Hel h = 20 m FD H C h = 30 m FD Hel h = 30 m FD H C h = 40 m FD Hel h = 40 m FD for helmet (Hel) and hollow cube (H C) ARs at different water depths (Ansys CFX) 0 20 40 60 80 100 120 140 160 180 200 0 0.25 0.5 0.75 1 1.25 1.5 1.75 FI(N) Wave frequency ω (rad/sec) FI H C h = 20 m FI Hel h = 20 m FI H C h = 30 m FI Hel h = 30 m FI H C h = 40 m FI Hel h = 40 m FI for helmet (Hel) and hollow cube (H C) ARs at different water depths (Ansys Aqwa) 0 100 200 300 400 500 600 700 0 0.25 0.5 0.75 1 1.25 1.5 1.75 FW(N) Wave frequency ω (rad/sec) FW H C h = 20 m FW Hel h = 20 m FW H C h = 30 m FW Hel h = 30 m FW H C h = 40 m FW Hel h = 40 m FW on helmet (Hel) and hollow cube (H C) ARs at different water depths
- 11. 0 100 200 300 400 500 600 700 800 900 0 0.25 0.5 0.75 1 1.25 1.5 1.75 FD(N) Wave frequency ω (rad/sec) FD H C 0 deg FD Hel 0 deg FD H C 45 deg FD Hel 45 deg FD H C 90 deg FD Hel 90 deg Drag force FD for helmet (Hel) and hollow cube (H C) ARs at different flow directions at h = 20 m (Ansys CFX) 0 50 100 150 200 250 0 0.25 0.5 0.75 1 1.25 1.5 1.75 FI(N) Wave frequency ω (rad/sec) FI H C 0 deg FI Hel 0 deg FI H C 45 deg FI Hel 45 deg FI H C 90 deg FI Hel 90 deg Inertia force FI for helmet (Hel) and hollow cube (H C) ARs at different flow directions at h = 20 m (Ansys CFX) 0 100 200 300 400 500 600 700 800 900 0 0.25 0.5 0.75 1 1.25 1.5 1.75 FW(N) Wave frequency ω (rad/sec) FW H C 0 deg FW Hel 0 deg FW H C 45 deg FW Hel 45 deg FW H C 90 deg FW Hel 90 deg Wave force FW for helmet (Hel) and hollow cube (H C) ARs at different flow directions at h = 20 m
- 12. Velocity vectors for flow direction 0o
- 14. Velocity vectors for flow direction 45o
- 15. Velocity vectors for flow direction 90o
- 17. • The numerical results showed that the hollow cube artificial reef was always subjected to higher FD and FI than the helmet artificial reef at all water depths and flow directions, except for h = 20 m and flow direction 45o , where there were little increases in the values of FI of the helmet unit than that of hollow cube artificial reef in this case. • The streamlined design of the new artificial reef always had less FW than that of the hollow cube artificial reef at all water depths and flow directions. • The flow pattern in front of the helmet reef was always subjected to less resistance than that of the hollow cube artificial reef, which led to the reduced area of the stagnation pressure on the unit body in front of the water flow. Conclusion
- 18. • The streamlined body of the helmet artificial reef improved the flow pattern at its rear region and provided zones with moderate flow, which can help fishes and marine organisms from finding good shelter. • The different openings in the body of the helmet artificial reef improved the condition of the flow velocity distribution inside the unit than that of the hollow cube unit, which can increase the amount of the nutrient to the living fishes and organisms inside the reef. • However, more studies are still required, such as using PIV measurements, for discovering more details about the flow pattern of the helmet artificial reef in different conditions. Conclusion (cont.)
- 19. Thank You