Problem Force Compression at Boom with Luffing Slink & Hoisting Slink

[Herbrata]

Dear All


Sorry for my English, I an from Indonesia.


I have problem to calculate the force compression from the real world that combined tension from luffing slink and hoisting slink (with pulley).

I search a ton of source, only can find both of the calculation separately.

It is only a luffing slink

It is only with Pulley and Hoisting Slink.
http://cbafaculty.org/Dynamics/Chapter 13.pdf
13-15 (page 15/132)


9 out 10 of my friends that I asked my pictures attach,
have the same answer that both compression force in Hinge A are the same.

And the same case about weight of the pulley system in my 3rd / katrol picture attach.
They sure that the weight of the pulley system is 10 kg (weight of pulley and slink rope is neglected).

For the boom, I believe the force compression in one with hoisting slink and pulley (even all slinks and pulley weight are neglected) is bigger than the one without.

For 3 rd / katrol picture, I believe the weight is not less than 20 kg.


What is your explanation sir?


Thanks for your attention.

Warm Regards,
Herbrata Moeljo

 

[Urwumpe]

Weeeeeeeelll....

Interesting question after thinking abit about it. I first wanted to declare: No difference, since the pulley on the top of the luffing boom is not forming a tackle.

But then I noticed: There should be a pulling force on the hoisting line of 10 N at its other end too. Without, the line would simply slip and the weight fall down.

And if that is the case, the pulley on top of the luffing boom should excert a force on the luffing boom AND the luffing line and it must not be the same force as excerted if the hoisting line would be directly tied to the luffing boom, because the weight force on the hoisting line is acting on both pulley and the opposite end of the hoisting line.

So, its a two stage problem: Solving the forces on the hoisting line and the pulley. And then attaching this substitute force on the top of the luffing boom to calculate the forces on luffing boom and luffing line.

Since the first problem is simply a fixed pulley with an angle of 135° between the ropes, the force on the pulley should be

[math]2 \cdot \sin {\frac{135°}{2}} * 10N = 18.48 N[/math]

pointing at a 22.5° angle to the vertical.

Now, the rest should exceed my legally allowed mechanical skills as software developer, but if you simply create a new force network with a force that replaces the pulley and the hoist line....... Don't report me to the union. :tiphat: