critical load shaft

[Etruria89]

Hello everyone,

are struggling with the calculation of critical load on a marine engine propeller tree; the system I schematized for the careful calculation of the critical load on this tree appears as:

beams having as a section that of less resistance of the entire tree (i.e. a tubular section), bound to an estermum with a hinge (conical roller shutter on which the propeller is discharged), in the central section with a support (ball clamp) and with the other free exterminity (where the propeller is present and therefore the resulting load from it).
to study the system I have exploited both the equations of the elastic line and the energy method in such case exploiting as functions of form a double sinusoid deformed in the tract between the two bearings and a linear deformed in the tract between the central support and the free estermo, however the problem is that for the so set problem I always obtain as a result as root of the problem to the autovalues a accept nothing and other two high minds.
you would know how to justify the presence of this root nothing if the problem was correctly set.

Thank you.

 

[Fulvio Romano]

Huh? ! ?
What are you talking about? A box? What are you doing with the stretch line? torsion or bending? and with the energy method?

What is a "double sinusoid"? what?

Generally, self-responsible values are simply discarded because they come from the mathematical model to the greater dimension of physical reality. For example, if you throw a stone in the air, the hourly equation will tell you that it will touch the ground before it has launched. This solution should simply be rejected.

However, if you write as if you're talking to your countermate who has been following the same lessons you've been following for two months, it will be quite difficult for someone to give you an adequate answer. . .

 

[Etruria89]

actually rereading I realized that I was not clear..... .

Let's say the main problem is that by going to calculate the value of the critical load of the system I am encapsulated in a null value of the critical load and my doubt was if this solution was simply to be rejected as not physically acceptable or if there were errors in my model....... .

because the only possible error at model level is the choice of the shape functions of the deformed of the axis line of the tree I was wondering if to put:


a) Synusoidal deformity of the type


v= a+sin(pi*x/l)+b*sin(2*pi*x/l)

for the shaft tract between 2 supports (i.e. 2 bearings)

b) Linear typedeformity of the type


♪


for the section of tree bound to one end from one opposite and free to the other extreme ( bearing + extreme free)

it was a right choice or not... .

where : v= vertical positioning of the beam axis line
x= curved shaft line ascissa
a,b,c=uncognite costs of the shaft axis line

I hope I've been a little clearer, I thank you, since I think you have solved my problem

Sorry again for the little initial clarity I will try in a future to be much more clear both in exposing my doubts and in any answers. . .