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- 2.3.2 The Tripod
- 2.3.3 Forces on Tripod and Forces According to Scaling
2.3 Sand Anchor Concept2.3.1 Reasons for Developed DesignA rocky seabed is preferred for anchoring WECs, since it is then easy to create a secure attachment. The project’s sand anchor was developed by S. Salter as a solution to mooring for the wave power desalination project at locations consisting of a sandy seabed. Such seabeds require a secure mooring created, adding further issues when the device, and possibly the mooring system, might be removed for maintenance reasons or end of life. Due to the natural motion of the waves, the anchoring must enable the device maximum movement, 180° about the vertical axis. Finally, a permanent foundation into the seabed may not be allowed in a worst-case scenario, and so a heavy and hard-to-handle anchor was not desired, since these are often left in seabed as seen in 2.1.1 [Sal11]5. 2.3.2 The TripodThe self-embedding and self-removing sand anchor design, discussed in [Sal11]5, consists of three straight anchor legs forming a tripod as shown in Figure 5. The hollow legs have a wall thickness thin enough to enable the anchor to float when filled with air. By adding water into the hollow legs, the anchor will sink until it reaches the seabed. At the ends of each anchor leg there will be water jets to create a localised fluidisation, resulting in a quicksand-behaviour of the seabed so that the anchor embeds itself easily by its own weight. The water flow direction will be reversed once embedment is completed to remove water from the voids between the sand grains located close to the anchor leg. A vacuum is needed for the desalination process, which will be achieved using a vacuum pump for the full-scale anchor. Creating a partial vacuum will produce high radial forces towards the surface of each leg, resulting in a strong grip, securing the tripod in a set location. At the point of removing the sand anchor, the vacuum will be released and air will fill the hollow legs. By re-fluidising the seabed, the anchor may float up. A cast steel shell joins the tripod’s legs and has a hollow design big enough to enable workers to carry out tension and post-tension checking [Sal11]5. 
Figure 5 The Tripod Design by S. Salter [Sal11]5 The legs should be post-tension concrete tubes that may be created by slip forming. This is a process where the set framework is raised vertically in a continuous manner. The framework consists of three platforms: storage and distribution area, main working platform and finally concrete finishing platform. It can be used for any regular shape, and is ideal for various high cylindrical towers since it creates robust and economical solutions [MPA14]15. An example of slip forming is seen in Figure 6. Concrete is not good with tension, but has excellent compressive properties. By using post-tensioned concrete, where strong bars between the two ends cause constant compression, tensile forces on the anchor legs in various directions will be contoured by the pre loading of the wires. It will only vary in amount of compression as explained in [New14]16. 
Figure 6 Slip forming a concrete tower found in [Oba14]17 2.3.3 Forces on Tripod and Forces According to ScalingThe tripod is designed to be able to hold against a 100-year Atlantic wave, which is roughly 40 MN [Sal11]5. It was found during slamming tests in 1978 for the desalination model, that the maximum forces produced were at a 45° angle below the forward horizontal [Wav78]18. Each anchor leg should therefore be designed to individually be able to resist 40 MN at 45°. This can be applied to smaller models by including influence of scaling. For a model that is the inverse of a scale, the force it can resist should be multiplied by cube of scale to achieve the equivalent force by the full-scale model [Wav78]18. Directory: shs shs -> Stonelaw Mathematics Department Green Course Revision Sheets Block E shs -> Core Classes Offered by Department Indicates ncaa clearinghouse Approved Core Class english shs -> Identify the prepositional phrases in the following sentences. Write them on a separate piece of paper shs -> Smart Phone Class Security and Safety shs -> Bordon Luciano shs -> 1 Week before Scheduled Contact shs -> Informative Research Essay Assignment shs -> 10th Daily “Fix It” Sentences shs -> The story of Perseus as told by Diodorus Download 11.38 Mb. Share with your friends:
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