BuildSysPro.IBPSA.Fluid.Examples.ResistanceVolumeFlowReversal

# .BuildSysPro.IBPSA.Fluid.Examples.ResistanceVolumeFlowReversal

System demonstrating impact of allowFlowReversal on number/size of non-linear systems

## Information

This model demonstrates the impact of the `allowFlowReversal` parameter on the size of nonlinear systems of equations. The user can change the parameter value in the `allowFlowReversal` block and rerun the simulation. The results are also demonstrated below for `nRes.k = 10`, which is the number of parallel branches containing one pressure drop element and one mixing volume each.

This model was created to demonstrate the influence of a new implementation of IBPSA.Fluid.Interfaces.ConservationEquation. The old implementation used the `actualStream()` function whereas the new implementation uses the `semiLinear()` function. This change allows Dymola to exploit knowledge about the `min` and `max` attributes of `m_flow`. When Dymola knows in which way the medium will flow, nonlinear systems can be simplified or completely removed. This is illustrated by the results below. See issue 216 for a discussion.

Note that Dymola 2015FD01 can only reliably solve the last case. For the other two cases the Newton solver of the nonlinear system does not converge.

These results were generated using Dymola 2015FD01 64 bit on Ubuntu 14.04 and with `Evaluate=false`.

#### ResistanceVolumeFlowReversal = true

Sizes of nonlinear systems of equations: {6, 11, 56}
Sizes after manipulation of the nonlinear systems: {1, 9, 12}

#### ResistanceVolumeFlowReversal = false

Old implementation

Sizes of nonlinear systems of equations: {6, 11, 44}
Sizes after manipulation of the nonlinear systems: {1, 9, 11}

New implementation

Sizes of nonlinear systems of equations: {6, 11, 4}
Sizes after manipulation of the nonlinear systems: {1, 9, 1}

## Contents

Name | Description
--- | ---
Medium |

## Revisions

- September 21, 2017, by Michael Wetter:
  Corrected parameterization to be independent of `k`.
  This is for IBPSA, #825.
- May 8, 2017, by Michael Wetter:
  Updated heater model.
  This is for IBPSA, #763.
- April 11, 2016 by Michael Wetter:
  Corrected wrong hyperlink in documentation for issue 450.
- February 22, 2016, by Michael Wetter:
  Removed parameter `dynamicBalance` for issue 411.
- April 17, 2015, by Filip Jorissen:
  First implementation.

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