The purpose of this research work is to study the hydrodynamic characteristics of a new type of artificial reef structure, in order to provide a structure with low flow resistance, which will be a more suitable shelter for fishes and marine organisms. The idea of the new artificial reef is based on the streamlined bicycle helmet design concept. The hydrodynamic characteristics of the helmet and hollow cube artificial reefs (ARs) of the same volume have been studied at different water depths and wave frequencies of Malaysia seas using Computational Fluid Dynamics (CFD) method. The finite volume RANSE code Ansys CFX was used for calculating the reefs drag force (FD) and flow characteristics, while the potential flow code Ansys Aqwa was used for calculating the reefs inertia force (FI). The Shear Stress Transport (SST) turbulence model was used in the RANSE code. The results of the two ARs were then compared for studying the hydrodynamic improvement due to the use of streamlined helmet artificial reef on the flow pattern around it. The streamlined body of the helmet artificial reef enhances the flow pattern at the aft region of the reef and provides flow zones with moderate flow speed at this area, which can help fishes and marine organisms from finding good shelter. The special shape of the different openings in the body of the helmet artificial reef improves 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.

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