12 replies to this topic

[Dudesons123]

Dear Engineers/ Scientists,

 

How to solve the simultaneous equations using Mathcad 15.0? Help me, please.  It takes a long time to do it on a piece of paper so I have tried doing it on Mathcad 15.0.

 

 

Attached Files

•  simultaneous equations 123.docx   17.07KB   27 downloads
•  Mathcad 15.0.docx   33.77KB   11 downloads
•  mathcad 15.0 simultaneous eqns.docx   26.8KB   15 downloads
•  mathcad 15.0 simultaneous eqns (on paintbrush).docx   202.48KB   5 downloads

Edited by Dudesons123, 08 June 2017 - 10:14 AM.

[Pilesar]

Mathcad is not hard to learn. Read the manual. Try a few sample problems. You should be able to get the hang of it pretty quickly.

[Dudesons123]

The problem is that there are several equations I have to deal with. The figures keep turning red after I have made several tries on fixing equations.

[Pilesar]

My approach would be:

 

Variables:

Q1

Q2

S

T1

T2

G1

 

Equations:

Q1=f(S)

Q1=f(T1)

Q2=f(T1,T2)

Q2=f(G1,T1)

Q1=f(G1,T1)

Q2=f(G1,T1,T2)

 

For any T1, you can solve for Q1 (eq 2), then for S (eq 1), then for G1 (eq 5), then for Q2 (eq 4), then for T2 (eq 3).

The last equation may not be compatible with the first five equations over the entire range of possible T1.

Adjust T1 so that Q2 found in equation 6 is the same as in equation 4. If there is no value of T1 that satisfies, then the solution sets do not intersect.

Plotting T1 vs Q2 using equations 4 and 6 would be a useful visual aid to show whether there is intersection.

[PaoloPemi]

There are several examples with mathcad provided by Harvey Hensley

http://www.harveyhen...ool-and-new-sch

(And several threads related to mathcad at cheresources.com)

[breizh]

Hi ,

Did you try google ?

I'm pretty sure if you key in : mathcad 15 system of equation you will find pointers .

 

I found some examples on youtube too.https://www.youtube....h?v=i3Z53i0szs8

 

Good luck.

Breizh

Edited by breizh, 01 June 2017 - 04:28 AM.

[Dudesons123]

Dear Engineers/Scientists,

 

My working is given in the file below. After working on this for several days I am still having problems with Mathcad 15.0. I have tried using solve block but with no success. Please tell me whereabouts I'm going wrong here.

 

Thanks.

Attached Files

•  mathcad 15.0 thursday.docx   213.15KB   12 downloads

Edited by Dudesons123, 08 June 2017 - 11:09 AM.

[Francisco Angel]

Is there a particular reason why you are sticking to mathcad?

Edited by Francisco Angel, 08 June 2017 - 12:14 PM.

[Dudesons123]

Dear Francisco Angel,

 

Mathcad is one of the softwares I need to be familiar with to help me with my 4th year in chemical engineering. I have stuck on this problem for a long time and I have tried to fix it several times but with no success.

 

Thanks.

Edited by Dudesons123, 08 June 2017 - 12:21 PM.

[Dudesons123]

Dear Scientist/Engineers,

 

I am only familiar with Mathcad 15 and not any other softwares.

[Pilesar]

Did you try solving without using the last equation? See my detailed response from a week ago indicating that the problem may be over specified. Did you plot the solution sets for Q2 for equations 4 and 6 over values of T1 to find out if they intersect? What did you find?

[Dudesons123]

I have tried to solve without using the last equation. But since there are 6 unknowns I would need 6 equations. I tried plotting Q2 for equations 4 and 6 over values of T1 but the T1 variable on the graph keeps going red. I feel hopeless with Mathcad 15, is there a way you can show me how to do it? Do you have Mathcad 15.0?

Edited by Dudesons123, 08 June 2017 - 01:55 PM.

[Pilesar]

To begin, use four equations only.

Equations 2, 3, 4, 5 contain unknowns T1, T2, G1, Q1, Q2.

You must supply the value for T1. This adds an additional equation like: 'T1 = 10'.

This set of 5 equations should be solvable by Mathcad. Is it?

Now for any T1 you supply, Mathcad should give the answer to T2, G1, Q1, Q2.

You have additional inequalities for the five variables at the top of your recent docx file.

These inequalities are constraints on the solution set.

Try to solve the problem without constraints initially.

Then add the constraints one at a time to restrict the available space containing the solution.

It is possible that these constraints can be too restrictive and leave you with no solution.

The unconstrained solution may be easier to locate, so experiment to find out how the constraints are affecting the answer.

Equation 6 was not yet needed, but also gives Q2 as a function of G1, T1, T2.

Change Equation 6 so that variable Q2 is replaced with the new variable Q2Prime.

Plot T1 vs Q2 and T1 vs Q2Prime on the same graph over a range of values for T1.

The intersection of the curves will give you the solution for T1.

If they intersect, this would be equivalent to adding the equation 'Q2 = Q2Prime'.

If the plotted curves never intersect, then there does not exist a value for T1 which will satisfy all the equations.

The plots would be your proof that there is no real solution.

(I used Mathcad briefly about 30 years ago, but have not used it since. It can make you feel really smart when it solves complicated problems. But it can be frustrating to troubleshoot. Solve it a step at a time and do not add all the equations at once. See my first reply for the suggested order. Supply a value for T1, then solve for Equation 2, then 1, then 5, then 4, then 3. You will also need to add your constraints. If the solution fails, stop and fix it before proceeding. Plots can help you visualize what is happening.)