Overview
During Summer 2017, I worked in the MIT Tow Tank Lab, in the Mechanical Engineering - Ocean Engineering department, using SolidWorks to design a wave absorber.
The MIT Tow Tank Lab contains a 30 meter tow tank with a wave maker on one end of the tank. The waves are used to test ships, offshore wind turbines, unsteady flow sensors, and other individual projects done by the MIT Graduate Students. The objective of the project was to replace, design, and build a wave absorber at the end of the tank to absorb the waves made from the single paddle wave maker.
By utilizing the measurements of the tank and the specifications of the wave maker, I worked with a given design of the wave absorber provided by the Wolfson Unit in the UK to create, adapt, and modify an optimal end beach redesigned for the MIT Tow Tank.
The MIT Tow Tank Lab contains a 30 meter tow tank with a wave maker on one end of the tank. The waves are used to test ships, offshore wind turbines, unsteady flow sensors, and other individual projects done by the MIT Graduate Students. The objective of the project was to replace, design, and build a wave absorber at the end of the tank to absorb the waves made from the single paddle wave maker.
By utilizing the measurements of the tank and the specifications of the wave maker, I worked with a given design of the wave absorber provided by the Wolfson Unit in the UK to create, adapt, and modify an optimal end beach redesigned for the MIT Tow Tank.
Design Points
Our approach is a parabolic slope which absorbs the waves, created by a wave maker, to minimize wave reflection and prevent standing waves for testing in the tank. The beach is about 9'4" long x 8'3" wide x 4'7" tall with the top of the parabolic beach itself about 3'9" tall from the tank floor. The critical features of the design are:
Materials were also precisely chosen to suit the purpose of the wave absorber, most often immersed underwater. All steel will be AISI 304 stainless steel, and most fastenings will be AISI 316 steel as both are highly corrosion resistant especially for chemicals and wet environments.
- Parabolic beach shape to absorb wave energy
- Vertical plate below design water line (DWL) to stop long wave lengths being reflected
- Gradually increasing porosity in beach surface above DWL
- Gap between beach and end wall to allow wave "run up"
- Easy access underneath beach for maintenance
Materials were also precisely chosen to suit the purpose of the wave absorber, most often immersed underwater. All steel will be AISI 304 stainless steel, and most fastenings will be AISI 316 steel as both are highly corrosion resistant especially for chemicals and wet environments.
Outcome
With pipes in the back corner of the tank and the pipe leading to the filter along the edge of the tank, the beach itself could not be bolted to the back of the tank as they obstruct the pipes. I designed a back support for the beach structure so the beach could still be attached to the end of the tank without the force of the waves ramming the beach into the pipes and the wall of the tank. The back support was analyzed using finite element analysis (FEA) with an equally distributed 750 Newton force against the front of the structure. The safety factor generated was 11, above the minimum safety factor of 2.5 suggested in the Wolfson Unit report.
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The sheet metal beach has four pieces, three for the parabolic beach – two without holes below DWL, one with holes above DWL – and one front plate. The top piece has holes that gradually increase the porosity to 60%. The design and curvature of the sheet metal is specifically designed to maximally absorb waves made by the wave maker For access to repair or clean underneath the beach and the pipes, I cut the bottom sheet metal into two parts and added hinges so you can open it like the hood of a car and climb in. The bottom parabolic piece is shorter in length because that is where the filter sits in the tank, and the filter itself will break the waves in that section where the parabolic beach would be.
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Other parts to the beach assembly include longitudinal frames that make up the main support of the entire beach, formers which sit on the longitudinal frames, and bracing struts and transverse supports which hold the frames together and provide extra support. A few designs are shown below.
Additionally, I designed the end of the tow tank with pipes to simulate how the wave absorber would fit. Below are the designs of the tank and an exploded view of the wave absorber.
Further Steps
By the end of the summer, I finished the design of wave absorber. Given the large pieces, I acted as a liaison between manufacturing companies to weld and laser cut materials for us.