August 2014 Mission Statement Background
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6. ConclusionsOf the three requirements of the sand anchor mentioned, two of them directly relate to the objectives set to see if friction created was enough to hold the waves’ force and if fluidisation enabled the anchor leg to embed itself and be removed. The anchor leg was embedded easily into the sand and water mixture, indicating sufficient fluidisation. With maximum force measured at 391 N and minimum at 124 N, it was clear that the friction created is strong enough for a wave, since maximum Atlantic wave force is 40 MN, a full-scale model will satisfy this requirement. The anchor leg alone measured 164 in the fourth test with plastic sheet working as a thin layer of clay, which according to scaling rule would enable a full scale model to hold roughly 164 MN. It was evident from test 6 that pulling a vacuum increased the anchor’s grip significantly. For this project’s experiments, all fluidisation was carried out with water, resulting in full potential of the anchor not being investigated since the removing of anchor leg should be done with air. However, the seabed re-fluidised with water enabled the model to be removed and calculations in 4.2.2 indicate that concrete anchor legs will be able to float when filled with air if wall thickness is at least 0.12 of the outer diameter. The majority of the aims identified in mission statement were achieved apart from scale underneath water butt to find exact volume of water in voids when filled with sand and measuring the vacuum pressure. This was due to being unexpectedly unable to source the required equipment, but should be considered for next stage, especially measuring pressure using pressure transducers. Suction flow rates were found to be high reaching up to 188 mL/s, but were slightly decreased and less varied with a plastic sheet acting as a thin layer of clay on top of the sand. This concept should be taken to next phase, with the recommendations of further work being considered. It proves that the design can provide a temporary, but powerful, sand anchor for the wave powered desalination device and for other WECs. AcknowledgementsI would like to thank my supervisor Stephen Salter for his support and infinite ideas. I would also like to acknowledge the support from my family, motivating me throughout the project. BibliographyAll14: , , Uit07: , , Uni12: , , Bro14: , , Sal11: , , Tay75: , , Pom14: , , How11: , , Tan77: , , Rho73: , , Win14: , , Suk14: , , Per97: , , McC93: , , MPA14: , , New14: , , Oba14: , , Wav78: , , Sub14: , , Bri09: , , Wen22: , , Dav08: , , Par11: , , BQ14: , , Eng142: , , Eng14: , , Kol09: , , Eng141: , , Azo14: , , Edi78: , , Tem53: , , Sch79: , , Eng143: , , Eng144: , , AppendicesSymbols A = Area (m2) a=Acceleration (m/s2) Cp=Discharge coefficient d= Diameter (m) g= Acceleration due to gravity (m/s2)  = Newton’s law proportionality factor (=1 for SI units [All14]1)
F = Force (N)  = Height (m)
L = Length of bed (m) m=Mass (kg)  = Pressure drop N/m2
P = Pressure (Pa) Q=Volumetric flow rate (m3/s) q=Angle (degrees) sp = Surface area of single particle (m2) t= Wall thickness (m) U=Velocity (m/s)  = Superficial velocity (m/s)
 = Minimum fluidising velocity (m/s)
V=Volume (m3) v=Velocity (m/s) xi= Weight fraction of particle size = Specific gravity = Porosity/void fraction 
= Absolute viscosity (Pa*s) ρ= density (kg/m3)
T=Total
V=Void space vac=Vacuum w=Water wv=Water in voids Appendix ADerivation of Ergun equation (equation 1.5) to find minimum velocity from [McC93]14 Details of notations on page 51 Ergun equation (as explained in section 2.2): 
At minimum fluidising velocity, the pressure drop across the bed equals the bed per unit area of cross section. This is what allows buoyant force:  (A-1)
When fluidisation is first introduced to the seabed, the porosity, , will be minimum porosity, M.  (A-2)
Rearranging Ergun equation:  (A-3)
If A-3 is applied to A-2, where fluidisation occurs, then a quadratic equation may be obtained. 
 (A-4)
When the particles are very small, then it is only the laminar-flow part that has a big impact. This would be when Reynolds number,  , <1; Dp is particle diameter (m), v is velocity (m/s), is density (kg/m3) and is viscosity (Pa*s). This leads to a simplified definition for minimum fluidising velocity:
 (A-5)
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