Determining Internal Node Values

Determining Internal Node Values:

As perceives in the previous section a finite element solution of a boundary value problem boils down to finding the best values of the constants {Cj}nj=1 which are the values of the solution at the nodes.

The interior nodes values are resolute by variational principles. Variational principles typically amount to minimizing internal energy. It is a physical principle that systems look for to be in a state of minimal energy and this principle is used to find the internal node values.

Variational Principles:

For the differential equations that describe several physical systems the internal energy of the system is an integral. For example for the steady state heat equation

uxx+ uyy= g(x, y)

the internal energy is the integral:

441_internal energy of integral.jpg

where R is the region on which we are working it is able to be shown that u(x, u) is a solution of  it and only if it is minimizer of I[u] in.

The finite element solution:

Evoke that a finite element solution is a linear combination of finite element functions

58_finite element solution.jpg

Where n is the number of nodes. To acquire the values at the internal nodes we will plug U(x, y) into the energy integral and minimize. That is we get the minimum of:

I[U]

For every choices of {Cj}mj=1 where m is the number of internal nodes. In this as with any other minimization problem the manner to find a possible minimum is to differentiate the quantity with respect to the variables and set the results to zero. In this circumstances the free variables are {Cj}mj=1. Therefore to find the minimizer we should try to solve:

∂I[U]/ ∂Cj= 0 for 1 ≤ j ≤ m.

We describe this set of equations the internal node equations. At this point we must ask whether the internal node equations can be solved as well as if so is the solution actually a minimizer (and not a maximizer). The subsequent two facts answer these questions. These facts create the finite element method practical

• For largely applications the internal node equations are linear.
• For generally applications the internal node equations give a minimizer.

We are able to demonstrate the first fact using an example.

Application to the steady state heat equation:

If we plug the entrant finite element solution U(x, y) into the energy integral for the heat equation, we obtain

505_finite element solution.jpg

Differentiating with respect to Cjwe acquire the internal node equations

1291_finite element solution_2.jpg

 
Now we have numerous simplifications first note that since:

2069_finite element solution_3.jpg

Likewise ∂Uy/∂Cj= (Φj)y. The integral subsequently becomes:

39_finite element solution_4.jpg

Next we utilize the fact that the region R is subdivided into triangles {Ti}pi=1 and the functions in question have different definitions on each triangle. The integral afterwards is a sum of the integrals:

1922_finite element solution_5.jpg

At this time note that the function Φj(x, y) is linear on triangle Tiand so Φij(x, y) = Φj|Ti (x, y) = aij+ bijx + cijy.

Latest technology based Matlab Programming Online Tutoring Assistance

Tutors, at the www.tutorsglobe.com, take pledge to provide full satisfaction and assurance in Matlab Programming help via online tutoring. Students are getting 100% satisfaction by online tutors across the globe. Here you can get homework help for Matlab Programming, project ideas and tutorials. We provide email based Matlab Programming help. You can join us to ask queries 24x7 with live, experienced and qualified online tutors specialized in Matlab Programming. Through Online Tutoring, you would be able to complete your homework or assignments at your home. Tutors at the TutorsGlobe are committed to provide the best quality online tutoring assistance for Matlab Programming Homework help and assignment help services. They use their experience, as they have solved thousands of the Matlab Programming assignments, which may help you to solve your complex issues of Matlab Programming. TutorsGlobe assure for the best quality compliance to your homework. Compromise with quality is not in our dictionary. If we feel that we are not able to provide the homework help as per the deadline or given instruction by the student, we refund the money of the student without any delay.

2015 ©TutorsGlobe All rights reserved. TutorsGlobe Rated 4.8/5 based on 34139 reviews.