Determine Force require to lift turbine monopole. 1

[Pechan]

A question from a computer dweeb to you Mechanical Engineers.
We need to size a hydraulic cylinder for a wind turbine tower. The tower is hinged 2 feet up the base and the cylinder attaches 4.5 feet from the hinge. The bottom of the cylinder attaches 1 ft from the tower base. Total height of the tower is 70 ft.
This would be classified as a class 3 lever.
The formula I found is Fe = Fl dl / de
Fe being the required effort.

Fl being the load.(tower weighs 8000 lbs)

dl being the distance from the load to the point of effort (cylinder attachment point on tower)

de being the distance from the fulcrum (tower hinge) to the point of effort ( cylinder attachment point on tower) ( this is 4.5 feet)

Since this is a distributed load can I just find the center of gravity of the tower and
make that my load?

So if the center of gravity ends up being at 35 ft could I solve this with the following equation?
Fe = 8000 * 35 / 4.5
Fe = 280k /4.5
Fe=62,222 lbs

Thanks,

 

[desertfox]

A sketch speaks a 1000 words can you please provide one?
The method you've posted seems reasonable however I would like to see a sketch has I feel we might be missing something.

 

[Pechan]

Here is a crude drawing, not to scale.

 

[Pechan]

Based on this I came up with this data:

Fe = 8000 * 29 / 4.5
Fe = 232k /4.5
Fe=51,556 lbs

 

[desertfox]

Hi Pechan

I think you will need a larger cylinder than that, if the force supplied by the cylinder was at right angles to the mast you would be correct in summing moments about the hinge, however the cylinder appears to be at some angle angle to the mast which I work out to be approximately 66 degrees from the vertical and taking that into account you need a force more like 8757ilbs in your cylinder.
That's only half the story though because as the mast rotates to vertical the mechanical advantage decreases.
What you need to do is plot the centre of gravity of the mast at say every 10 degree rotation and also draw the cylinder in its respective position for those angles, then workout the moments round the hinge similar to what you did in the first post but remember to take the angle of the cylinder into account.

 

[desertfox]

I should of added whatever maximum force you calculate you need to add say 25% to ensure the cylinder raises the mast.

 

[Pechan]

Wouldn't the force required to raise the mast decrease as it becomes more vertical?
I would expect the hinge to take more force off the cylinder as it lifts.

 

[Pechan]

With this type of lever I lose mechanical advantage, so wouldn't the "Mechanical Disadvantage" decrease? Making it easier to lift?

 

[desertfox]

Hi

Yes the mast does become easier to lift as it raises but without plotting out a loci of the cylinder and mast I cannot tell you whether the cylinder force can lift it all the way, hats why I suggested laying it out.

 

[Pechan]

Thank you makes sense now.
What is the proper way to factor in the angle of the cylinder?

 

[desertfox]

Hi Pechan

See attached sketch, draw the mast in several positions and then draw in the cylinder for each position, put a line parallel through the top and bottom of cylinder for each position and then measure from that line perpendicular to the mast hinge point.

 

[tbuelna]

You also need to take the frictions at each hinge/pivot joint into account when calculating the force required from the hydraulic cylinder to raise the tower to a vertical position.

One other potential issue I see with your sketch is that the cylinder may not have sufficient linear travel to fully raise the tower.

 

[Occupant]

I've done somewhat more, but, as already mentioned, the cylinder will not be long enough and I have not included frictional torques which will change the picture considerably.

 

[Pechan]

Thanks for the replys, I will get back on this project after the holidays and will do some more calculating.

 

[kiwitom235]

i think this should be in fluid power section? however... i get a force of approx 72kN required to balance the moments of tower at the bottom, not taking into account additional force to accelerate against friction etc.

also, you will need to slow the cylinder down (flow control) as it nears full stroke as the angular speed of the tower will increase as it raises due to the geometry of the situation, and you don't want it to be going fast when it reaches a vertical position!

eye to eye cylinder length will need to be min 1.509m fully retracted and 4.01m length at full stroke.

just from my calcs, could have an error in there though

 

[tbuelna]

I would agree that this is not a problem suitable for the gear & pulley forum. Probably more appropriate for the mechanical engineering forum since it involves a mechanical system analysis that must include stresses/forces/frictions/hydraulic pressures/etc. Definitely not a simple problem to solve. Once you include factors like the joint end moment frictions, bending stresses in the tower and base, design factors of safety of around 3.0 or 4.0, and pressure limits of the commercial hydraulic system, the problem gets quite complicated.