Algebraic_Solutions_for_2 Node_Cases - nasa/gunns GitHub Wiki

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Algebraic Solutions for 2-Node Cases

We can solve for 2-node cases by hand. Some cases and their solutions are given here. These can be useful for understanding how GUNNS effects behave, such as capacitance, conductance, etc. We won’t give all the algebra, but it can all be derived by building the [A]{p} = {w} system of equations and solving for {p} by hand.

1. Two Capacitive Nodes with a Conductance Between

Here we have two nodes given capacitance C 1 and C 2, respectively, connected by a conductor with admittance A:

2. Two Capacitive Nodes with a Conductance Between and an External Flow Source

This is same as Case 1 but we add a flow source F onto Node 2.

3. Two Capacitive Nodes with a Conductance Between and an External Potential Source

This is the same as Case 2 but we’ve replaced the flow source with a potential source with admittance A e and source potential P e.

4. Two Capacitive Nodes with a Potential Source Between

This is the same as Case 1 except we’ve replaced the conductor with a potential source with admittance A and source potential P.

5. A Capacitive and a Non-Capacitive Node with a Conductance Between

This is the same as Case 1 except Node 2 is non-capacitive. This is a trivial case: no matter what the starting potentials P 1,0 and P 2,0 are, since Node 2 has no capacitance, it cannot receive any flow from Node 1, there is no flow through A, Node 1 keeps the same quantity and therefore potential, and the Node 2 potential is always equal to Node 1.

6. A Capacitive and a Non-Capacitive Node with a Conductance Between and an External Flow Source on the Non-Capacitive Node

This is the same as Case 2 except Node 2 is non-capacitive. Note the solution for P 2: it clearly shows the behavior of a conductor, i.e. V = IR, where R = 1/A, I = F, V = dP = P 2 – P 1.

7. A Capacitive and a Non-Capacitive Node with a Conductance Between and an External Potential Source on the Non-Capacitive Node

This is the same as Case 3 except Node 2 is non-capacitive.

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