# Models Methods Software

## Fluid Systems Mechanically Coupled Through a Wall

Method of Exact Solutions Verification Problems for Transient Compressible Flows: Two Fluid Systems Mechanically Coupled Through a Wall

The analysis given in these previous notes:

Implicit Function Theory Introduction

Initial Method of Exact Solutions Calculations

Single Isolated Node Calculations

are expanded to include the case of coupled fluid systems. Numerical solution results are given for an illustrative application.

The mathematical model, an exact continuous analogue of the discrete approximations used in many numerical solution methods, provides analytical and numerical-benchmark problems for verification by the Method of Exact Solutions ( MES ).

March 15, 2011

## Implicit Function Theory: Single Fluid System Calculations

I have completed some additional verification of the single-node calculations, and other results, given in the previous notes here.

A short introduction to implicit function theory was given in the notes here.

In the present notes I’ve tuned up the original calculations and cleared out a few bugs as follows.

(1) I found some bugs in the summary tables of the EOS derivatives and give new Tables below in these notes. I have also posted the corrected Tables with the notes introducing implicit function theory.

(2) I have made the fluid thermodynamic state and thermophysical properties more consistent by using a single source for these numbers. The source is an old National Research Council ( Canada )/ National Bureau of Standards ( USA ) water property program. For the original calculations I had used whatever convenient values could find and these did not always correspond to the exact same fluid state. The program is based on the equations in this document.

(3) I coded the fluid properties and the primitive elements of the derivatives along with a routine to numerically evaluate the various determinants in order to compare these with my analytically derived derivatives. This process led to discovery of several coding errors that, when cleared, led to agreement with my analytical derivatives. And, yes, coding of the analytical derivatives was also verified by various means. I have abandoned the original spread sheet approach and now rely on the new coded routines.

(4) I have tuned up the wall-material properties and at the same time expanded the discussion of the interaction of the fluid and wall material relative to the base pressure-wave speed.

(5) I dug into the fluid-structure literature a little bit to see if my derivation of the effective sound speed was correct. I discovered that the formulation obtained by use of implicit function theory and the equation of state gives exactly the classical value. That equation was first obtained, as reported by Tijsseling ( 1996 ), by Korteweg in 1878. The center of the hydraulic-transient / fluid-structure-interaction universe seems to have moved from the University of Michigan and Wiggert, Wylie, and Streeter, to Tijsseling and Eindhoven University of Technology.

(6) I have investigated the numerical solution method in some more detail. The second-order explicit Euler method shows growth of the difference between the analytical and numerical solutions. The fourth-order explicit Runga-Kutta method shows much improved performance.

All these changes have been implemented and additional calculations carried out for the single-node case. The better focus on the calculations in contrast to the theory has also led to corrections in the consistency of the reported values for the calculations. The length of the node was incorrectly reported in parts of the previous notes.

The mathematical model seems to be a very good candidate for production of Method of Exact Solutions ( MES ) and Numerical Benchmark results for Verification of numerical solution methods for transient, compressible hydraulic-transient codes.

I see that the Table 3 did not come out too good in the file. A copy is also here. There was a bug in the first column of the third row.

February 26, 2011

## Implicit Function Theory Applications; Part 1: Method of Exact Solutions

In a previous post I gave some background info about implicit function theory and how it might be useful. In these notes I have used results from applications to the equation of state to develop a few exact solutions for extremely simple transient, compressible flows that include fluid-structure interaction. These notes address the case of mechanical coupling of the fluid to a deformable / flexible wall. I have also included an introduction to the case of coupling of fluid systems through a common deformable / flexible wall. Additional notes will address the case of thermal interactions for both a single fluid system and coupled systems.

I kind of ran out of steam when I got to coupled-systems part of the present notes. There’s a lot of ground to cover for this case and I’m thinking a separate report might be the way to go. With coupled systems you get more that just twice as many things to look at compared to the single-system case.

I think these solutions might be candidates for analytical, and numerical-benchmark-grade, Method of Exact Solutions ( MES ) for verification of limited aspects of coding of transient compressible fluid flow model equation systems and solution methods.

Consider these notes as a rough draft of a report and let me know what you think about all aspects.

January 19, 2011

## Looks like we’re getting some Traction

This is interesting; Computational science: …Error. From Nature News, even. Comments allowed over there.

October 17, 2010

## More on ODEs, MMS and Ill-Posed IVPs

First for the nomenclature: ODEs means Ordinary Differential Equations, MMS means the Method of Manufactured Solutions, and IVPs means Initial Value Problems.

This previous post provided some information on these subjects. So far as I know, that post presented the first results for application of MMS to ill-posed IVPs. That post suggested that for the numerical solution methods used therein, the original Lorenz system of 1963 has yet to be correctly solved.

I have some additional results, a summary of which is:
I think the Lorenz system has not yet been accurately integrated by any numerical solution methods. Higher-order methods plus, at the same time, higher precision representation of numbers will give results that might appear to be solutions. But, calculations for sufficiently long time spans will show that errors always increase.

October 8, 2010

## Internal Variability=Weather and Numerical Artifacts

This post is based on some notes related to verification and numerical artifacts that I made back in early July.

August 18, 2010

## V&V and SQA: Part 3, Verification

Verification Activities
The focus of verification is the actual coding of the software with objectives to determine: (1) that the coding corresponds to the equations given in the specification document, (2) the order of accuracy of the numerical methods, and (3) the order of convergence of the numerical methods. In general, the latter two objectives are purely mathematical and go to the heart of the coding of the solution methods. Several of the procedures that are used to pursue these objectives are given in the following discussions.

August 16, 2010

## New V&V Book by Pat Roache

I received the following e-mail from Pat Roache regarding his new book about Verification and Validation. He has also made arrangements for reduced prices on two others of his books.

I am pleased to announce the publication of
“Fundamentals of Verification and Validation” by Patrick J. Roache.
Copyright 2009, ISBN 978-0-93478-12-7. 476 pages, subject index.

The book is the successor to my 1998 book “Verification and Validation in Computational Science and Engineering.” About 1/3 of the material is new, including a new Chapter 11 describing the Total Validation Uncertainty approach of ASME ANSI Standard V&V 20 (2009).

The attached file outlines the new features of the book. A complete Table of Contents, including designators for new and modified Sections, will be found on the website.

The price is the same as the 1998 book, U.S. \$85.00 (but shipping charges have increased). The book is available directly from our fulfillment house, BookMasters, by email order to

orders@BookMasters.com

The orders to BookMasters tend to ship faster since they do not run out of stock. Also, wholesale orders can be placed by contacting BookMasters at orders@BookMasters.com.

I would appreciate it if you would forward this email to any of your colleagues who might be interested.

Respectfully,
Patrick Roache

p.s.
If anyone is interested, the 1998 V&V book is on clearance sale for 1/2 price at US \$42.50. Available from orders@BookMasters.com or from Amazon at
http://www.amazon.com/Verification-Validation-Computational-Science-Engineering/dp/0913478083/ref=sr_1_4?ie=UTF8&s=books&qid=1253718713&sr=8-4.

Likewise, the book “Fundamentals of Computational Fluid Dynamics” is on clearance sale for 1/2 price at US \$37.50. Available from orders@BookMasters.com or from Amazon at
http://www.amazon.com/Fundamentals-Computational-Dynamics-Patrick-Roache/dp/0913478091/ref=sr_1_5?ie=UTF8&s=books&qid=1253718713&sr=8-5

September 24, 2009

## V&V and NNSA Advanced Strategic Computing at LANL

[Updated September 26]
I think the name of the program originally known as the Advanced Strategic Computing Initiative ( ASCI ) is now known as Advanced Simulation & Computing ( ASC ).

[Updated August 26]

I have uploaded an excellent summary, developed by Los Alamos, of the ASC V&V Program at LANL. It is here.

A couple of quotes.

Confidence in simulation extrapolation comes via confidence in physics & numerics models, not calibration to experimental data.

Having “good agreement” between calculations and observations is not sufficient to establish scientifically credible predictive capability.

More and more it seems that the Climate Change Community remains the only holdout among all compute-intensive enterprises relative to application of rigorous, independent V&V to computer software.

Update