Statics and Dynamics Problem

O
O
2013 12 4
0 个回答
更新时间：2013 12 7
3 次查看（30 天）

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I'm having issues with even starting this problem. There's a billboard on a ball and socket joint at the base and cables to keep it in place. The banner hanging from the billboard weighs 300 kg. I am trying to create a program that will allow the user to input vectors of both the force of the wind and the angle of the wind.
In the attached image, you will see a diagram of this situation. The distances L1, L2, L3, L4, D are 10 , 5 , 3 , 2 , 4 m, respectively.
The goal of this program is to find the tension in the cables and find the reactions at the base of the pole and then plot a graph of force of the wind vs the tension in the cables.
Any suggestions/tips?

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dpb
dpb 2013-12-4
Just start writing the moment and force balances for the free body diagram and then implement.
O
O 2013-12-6
编辑：O 2013-12-6
So I'm having an issue with this code at the moment.
alpha=55;
g=9.81;
loadW=input('Enter the wind load in a vector form in N: ');
forceW=[loadW.*cosd(alpha) loadW.*sind(alpha) 0];
forceB=[0 0 ((-1)*W*g)];
b=[forceW+forceB]';
When I enter the wind load as a vector, I get error "Error using + Matrix dimensions must agree." Any suggestions on how I could switch this? I see why the dimensions don't agree, but I don't know how to do it otherwise.
dpb
dpb 2013-12-6
Well, not knowing what you used for inputs it's hard to say, precisely.
Given an example and can undoubtedly resolve the problem...
O
O 2013-12-6
An example would be when I enter 1500. The calculations go through and there is no problem. When I enter any type of vector (no matter the length), the dimensions problem comes up. That is because forceW and forceB are not the same length anymore. Would it be possible to change forceB so it is something like this (although this probably isn't correct at all).
forceB=[0:length(forceW) 0:length(forceW) ((-1)*W*g):length(forceW)];
Walter Roberson
Walter Roberson 2013-12-7
something like
bsxfun(@plus, forceB(:), ForceW)
?
O
O 2013-12-7
Is there a specific place that I would enter that? I just put it before the force statements, but it doesn't work either.
Walter Roberson
Walter Roberson 2013-12-7
It would replace the addition.
b = bsxfun(@plus, forceB(:), ForceW);
but double-check whether it gives you the orientation of matrix that you want.

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O
O
2013-12-4

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Walter Roberson
Walter Roberson
2013-12-7

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