Sea Technology

JUL 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Schematic of the turbine mechanism. Ingvar Tjostheim / Shuterstock.com MoogFocaloferscombinatonunits thatincludeelectricalandfberpasses forthemarineindustry.Thissoluton isidealforremotelyoperated vehicles,winchesandsubsea equipment. TheModel176 electricalslipringis comprisedofpowerandsignal electricalpassesandprovides superiorperformanceandreliability indemandingenvironments. Designedforthemarineenvironment, theModel176ishighlyconfgurable andcanbecustomizedforspecifc applicatons. Integratedwithourfberoptcrotary jointsandfuidrotaryunions,the 176slipringcanprovideacomplete rotatnginterfacesoluton. Model 176 Electrical Slip Ring Features: • • • • • • • • Passesratedto5kV Stainlesssteelenclosure Sealedhousingdesign testedtoIP66standards Accommodatesvarious wireandcabletypes Maintenancefree operaton Optonalfameproof/ explosion-proofcapability HeathandUsage MonitoringSystemopton Pressurecompensated subseaopton Looking for more? Scan to view marine slip ring specifcatons. +1-902-468-2263 | mcg@moog.com www.moog.com/marine 26 st / July 2013 keeps the two shafts rotating at the same speed. The blades project to the outside of the drum through several rectangular openings. Blades are connected to the eccentric disc, which is fxed on the eccentric shaft, through rigid links with hinge joints at both ends. The SNAIL turbine works on the principle that blades are frst pushed to the outside of the drum by the links as the turbine rotates, generating positive torque to drive the rotor. After fully opened, the blades retract to the inside of the drum, allowing water past the turbine with minimal resistance. The resultant torque drives the turbine and produces power. The main geometrical parameters of the turbine include: R, the radius of the drum; r, the radius of the eccentric disc; c, the eccentricity between the power shaft and the eccentric shaft; l, the length of the link; L, the length of blade; and N, the number of blades. In the prototype design, these parameters are determined as R = 0.5 meters, r = 0.05 meters, c = l = 0.225 meters, L = 0.45 meters and N = 4. In the following equation where θ is the rotational angle of the blade relative to the incident fow, the distance between the outer edge of the blade and the drum axis, Ll , can be calculated as: This equation states that the blade frst stretches and then retracts in the advancing half cycle (0 ≤ θ < π) following a sine law. The maximum of Ll is obtained when θ = π / 2. At this point, water impacts perpendicularly on the blade, allowing it to achieve a higher driving torque. In the returning half cycle (0 ≤ θ < 2π), Ll remains constant, equal to r + L. This is an interesting fnding because it means that the blades are entirely hidden in the drum and only rotate around the power shaft. Negative torques can be considerably deduced as the drum shields the blades. CFD Method Hydrodynamic performance is an important design consideration for water turbines and is investigated with a CFD method, which has been proven to give relatively accurate results for a 2D rotating rotor. Numerical simulations were carried out using the commercial code FLUENT 13.0, which is a widely used commercial CFD code based on the fnite volume method. www.sea-technology.com

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