Solve Block Issue - Improvement Required

[MikeArmstrong]

I have a spreadsheet which calculates the reaction, deflection and slope of a HDPE pipeline as it is being flooded to the seabed for a given water depth. There is 7 no. simultaneous equations which have to be solved in order to obtain the results.

My issue is that the solve block is very sensitive to the guess values, and I often find myself tweaking them until the solve block returns a solution which can be extremely tedious. - Changing Ra to 50 in this instance.

So my question is, can this method be improved and could the equations be solved symbolically?

Cheers,

Mike

[AlanStevens]

Mike Armstrong wrote:

However, when I solve symbolically I am not getting the same reaction forces as the numerical solution, which doesn't seem correct.

Here's a different formulation using a solve block only for L1 and L2.  The same results are obtained as solving for all 7 parameters at once.

Alan

[MikeArmstrong]

AlanStevens wrote:

Mike Armstrong wrote:

However, when I solve symbolically I am not getting the same reaction forces as the numerical solution, which doesn't seem correct.

Here's a different formulation using a solve block only for L1 and L2.  The same results are obtained as solving for all 7 parameters at once.

Alan

Superb work Alan. Thank you for all your effort.

Mike

[MikeArmstrong]

Hi Luc,

I managed to copy your method and got similar results. So as you previously mentioned I will have to go back to basics and look were the formulae came from.

Attached in M11 format also.

Mike

[MikeArmstrong]

Following on from this I started to compare the answers from the numerical solve block to the answers yielded by the symbolic approach.

I compared the above three formulas and got the following:

That seems to indicate that the issue is with either Rb or L2, as Omega(b) and Delta(b) are the same.

Mike

[RichardJ]

Maybe it is time to start again with it.

I think you are probably right. Given this mistake, I wouldn't assume that there are no other mistakes higher up the worksheet.

[RichardJ]

the assignment of symbolic results to variables is not supported anymore).

Sure it is.

[AlanStevens]

Mike Armstrong wrote:

. I believe the signs are correct as the deflection and slope graphs in the attached sheet visually look correct.

Mike

You can change the initial guesses to get different outputs with the deflection and slope graphs being essentially unchanged!  I'm afraid it's as Andy, Richard and Luc are saying: you are missing a seventh independent equation.

Alan

[MikeArmstrong]

AlanStevens wrote:

You can change the initial guesses to get different outputs with the deflection and slope graphs being essentially unchanged!  I'm afraid it's as Andy, Richard and Luc are saying: you are missing a seventh independent equation.

Alan

Hi Alan,

Well spotted.

Mike

[MikeArmstrong]

MikeArmstrong wrote:

A Westerman wrote:

Hi Mike,

   I'm not sure, but do you have 7 independent equations?

I've read through the attached & I can't see an obvious error.

looks like equations 5 & 7 can be manipulated to give equation 6.

Hope this helps

Andy

Hi Alan,

I believe I do have 7 independent equations, but unsure why it cannot be solved symbolically. Still digesting Richards sheet

Mike

Sorry, I meant Andy