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A
awibroe1-Visitor
1-Visitor
March 31, 2017
Solved

2nd moment of area again

  • March 31, 2017
  • 1 reply
  • 6373 views

Hi Guys,

I have another 2nd moment issue I am struggling with.

This is the overall task:

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So far I have calculated the area, centroid and second moments for the waterplane as follows:

Capture.PNG

and

Capture.PNG

What I then struggle with is combining the second moments of the two shapes. I am of the belief that I can get the overall second moment of the entire waterplane by adding the two individual second moments about centroids i.e. JoL = JL (for the ship) + JL (for the appendage)

I have JL for the ship and I believe to get JL for the appendage I need to convert the second moment about the aft perpendicular to the centroid which I thought could be done as follows:

Capture.PNG

But I am obviously not getting the answer right for JL. I have also not even got to thinking how the overall JT value is obtainable?

Any help warmly welcomed as always.

Andy

Best answer by Fred_Kohlhepp

An example

1 reply

F
Fred_Kohlhepp23-Emerald I
23-Emerald I
March 31, 2017

Your calculation of areas and moments is some form of finite difference scheme.

If I fit a polynomial to your data points I can apply the integration scheme.  (attached.)

Note that I believe there's a typo in the answer given for total longitudinal moment.

A
awibroe1-VisitorAuthor
1-Visitor
March 31, 2017

Hi Fred,

I was hoping you would pick this up.

The problem is to be done using simpson's first rule which I have done and that is the method it needs to be competed in I believe.

Did you say you attached a file?

Andy

F
Fred_Kohlhepp23-Emerald I
23-Emerald I
March 31, 2017

Let's try this again

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