Project Background and Scope The purpose of the project is to generate a design that can easily and effectively convert a Laser sailboat to a human powered Flettner ship. A Flettner ship is a ship that generates its thrust via the Magnus effect on a rotating cylinder. As wind flows over the cylinder, the spinning of the rotor accelerates the air flow on the side of the cylinder spinning in the same direction. This acceleration reduces the pressure on that side of the cylinder, resulting in a thrust force on the rotor. This is easily shown in the diagram: Figure 1: Flettner Rotor Diagram [1] The use of a Flettner rotor for propulsion has several advantages, including: In a cross-wind, the Magnus effect can produce a thrust several times larger than a sail of an equivalent area, leading it to be used in energy-optimized applications [2]. The Flettner rotor can compensate more easily for changes in wind direction. The Flettner rotor can compensate more easily for changes in wind speed by increasing the rotational speed in low-speed winds and reducing the rotational speed in the event of gusts. The use of a Flettner rotor makes the ship easier to sail because there is no changes in weight distribution and the lack of a sail trim and course trim. The replacement of a sail with a Flettner rotor reduces the risk of injury from an uncontrolled boom. The goal of this design project is important as it makes these advantages accessible to the owner of a small-scale sailboat. The use of human power to rotate the Flettner rotor means that the conversion to a Flettner ship does not require the introduction of fuels or stored energy. The scope of the project includes the design and development of the following: A method of securing the rotor and power train to the Laser. The Flettner rotor that will generate the thrust required to drive the boat. The power train to convert the human input to the rotational motion of the rotor. The design of these components will include a full analysis of different concepts, detailed drawings of all components, and detailed records of all project management materials including scheduling and budgeting. The final design will be manufactured and assembled and tested against the requirements agreed to through the development of the project.
Project Requirements umber Criterion Owner Critical Change Record The frame of the Flettner mechanism shall 1 attach to the ship with no permanent TO Y modifications. 2 The Flettner rotor shall be able to rotate in both clockwise and counterclockwise directions. 3 The Flettner ship shall operate with either one or two sailors. 4 The frame of the Flettner mechanism shall fit within the space of the cockpit. 5 The Flettner assembly shall not detach in the TO Y event of capsizing. The ship shall be capable of obtaining a speed 6 of 5 knots. TG 7 The rotor of the Flettner ship shall not deflect more than 1 in. under thrust. The Flettner mechanism shall take no more 8 time to install than a standard mast, boom and sail. The Flettner assembly shall take no more 9 time to disassemble than a standard mast, boom and sail. 10 Flettner assembly, hull and mast shall be All transportable by a mid-size SUV. The Flettner assembly shall weigh no more 11 than 50 lbs. All 12 The Flettner rotor shall be no more than 20% of the total weight of the ship. The production cost of the Flettner apparatus 13 shall be no more than 20% of the total Laser cost. 14 The design shall use corrosion-resistant materials. DG DG TO TG All All All All All Y Y Y 10/17/2013
Requirements Testing umber Testing Method Test Date Status 1 Prototyping and Design /A Incomplete 2 Attempt to rotate the rotor both ways when assembled. 15/03/2014 Incomplete 3 Sail the ship with both one and two users. 15/03/2014 Incomplete 4 Install the frame in the Laser cockpit. 15/03/2014 Incomplete 5 6 7 8 9 10 11 12 13 Purposely capsize the boat in a pool to determine if assembly detaches. Measure the boat speed in the water using a GPS signal. Measure wind speed using available instrumentation. Measure the deflection of the rotor under loading from the wind. Time the installation of the Flettner frame, power train and rotor. Time the removal of the Flettner frame, power train and rotor. Measure the disassembled components. Try to fit in a mid-size SUV. Weigh a team member alone and again while holding the Flettner mechanism and take the difference. Weight the Flettner rotor individually and calculate its percentage of the total mass. Divide the budget used to produce the Flettner design by the cost of a Laser ship. 15/03/2014 Incomplete 15/03/2014 Incomplete 15/03/2014 Incomplete 15/03/2014 Incomplete 15/03/2014 Incomplete 31/01/2014 Incomplete 31/01/2014 Incomplete 01/03/2014 Incomplete 01/03/2014 Incomplete 14 Prototyping and Design /A Incomplete
High Risk Elements Risk Probability Consequence Priority Mitigation The project falls behind schedule 5 8 40 Delegate team member to monitor project schedule Unable to balance the ship with the Lower Center of Gravity 3 10 30 Flettner Rotor Design Calculations The project costs go over budget 5 5 25 Delegate team member to monitor project budget Required materials cannot be obtained in time for building 3 7 21 Plan for lead-time in ordering of materials in the schedule The testing of the finished prototype is deemed unsafe 7 3 21 Develop secondary testing method for approval Testing conditions are not optimal (e.g. not enough wind) 5 3 21 Reschedule testing or develop secondary testing method The design is found to not be structurally sound 2 8 16 Perform design analysis before building Finite Element Analysis ote: Probability and Consequence is estimated out of 10. The priority is the product of probability and consequence.
Preliminary Design Sketches
Rotor Calculations Preliminary calculations for the rotor sizing and rotational speed were performed using Excel. Given values include: Boat Waterline = 3.81 m Assumed Equivalent Width = 1.5 m ν water = 1.01E-06 m 2 /s Water Density = 1000 kg/m 3 Air Density = 1.225 kg/m 3 Then, a boat speed and wind speed are assumed given the project requirements and typical sailing conditions. In this case, the boat speed is 5 knots and the wind speed is 15 knots. The drag of the boat in the water is calculated by modeling the bottom of the ship as a flat plate and using turbulent drag theory: With the friction drag known, it is assumed that the total drag on the boat is 1.25D, and this is set to the thrust required by the rotor to reach the given speed. Assuming a rotational speed and rotor radius, the ratio of the circumferential speed over the wind speed can be calculated. This value is used to acquire lift and drag coefficients from reference [2]. Finally, the required height of the rotor is calculated and evaluated for practicality. Possible design solutions include: Parameter Option 1 Option 2 Option 3 Boat Speed 5 knots 6 knots 7 knots Wind Speed 15 knots 15 knots 15 knots Rotor Radius 1 ft. 1 ft. 1.25 ft. RPM 240 360 240 Rotor Height 8.89 ft. 8.26 ft. 9.80 ft. More options can be calculated based on the combination of rotor radius, RPM and rotor height.
Wind and Boat Speeds Boat Speed = 5 knots 2.57 m/s 9.26 km/h Wind Speed = 15 knots 7.72 m/s Boat Dimensions Length = 3.81 m Width = 1.5 m Rotor Radius = 1 ft 0.3048 m Properties v Water = 1.01E-06 m2/s Water Density = 1000 kg/m3 Air Density = 1.225 kg/m3 Calculation of Thrust Required ReL = 9.75E+06 Cd, boat = 0.003111 Drag = 59 Thrust Req = 74 Lift and Drag Coefficients RPM = 240 Alpha = 0.992717 From Figures: CL = 1 CD = 0.7 Calculation of Rotor Lift and Drag L = 22.23 b2 D = 15.56 b2 Calculation of Required Rotor Height b = 2.71 m 8.89 ft ote: Yellow Cells are Inputs
References [1] Magnus Effect at Flettner Rotor Boat. Wikipedia. Oct. 17, 2013. Available: http://commons.wikimedia.org/wiki/file:magnus_effect_at_flettner_rotor_boat.svg [2] Seifer J. A review of the Magnus effect in aeronautics. Progress in Aerospace Sciences, 55 (2012) 17-45.