BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Computational AeroAcoustics: how they got it wrong (repeatedly) - 
 Dr Ed Brambley\, University of Warwick\, UK
DTSTART:20181023T093000Z
DTEND:20181023T103000Z
UID:TALK113140@talks.cam.ac.uk
CONTACT:Matthew Priddin
DESCRIPTION:Despite the best efforts of mathematicians\, aircraft still do
  not use infinite straight engine-ducts with thin zero-angle-of-attack bla
 des\, and so unfortunately good Computational AeroAcoustics (CAA) simulati
 ons remain necessary in order to calculate the sound produced in the actua
 l geometry and CFD-computed flows within aircraft engines.  CAA simulation
 s push the limits of current computing power\, and so try to be as efficie
 nt as possible\, while also being precariously balanced on the knife edge 
 between being overly dissipative and being unstable.\n\nMost CAA simulatio
 ns today use optimized Dispersion Relation Preserving (DRP) spatial deriva
 tives\, which claim to be accurate down to 5 points per wavelength.  They 
 aren't.\n\nMost CAA researchers are aware there are problems with numerica
 l instability near boundaries due to the use of asymmetric stencils. There
  are a number of papers proposing optimized spatial derivatives near bound
 aries that are supposedly stable.  They aren't.\n\nMost CAA simulations us
 e optimized Runge-Kutta time stepping to evolve the solution forwards in t
 ime\, (most commonly LDDRK56\, Low Dispersion and Dissipation Runge-Kutta 
 5stage/6stage)\, which are claimed to be optimized for wave propagation.  
 They aren't.\n\nThere is some theory of finite difference schemes that are
  provably stable\, and which do work near boundaries.  These are called Su
 mmation By Parts (SBP) schemes\, with the important property that they hav
 e a discretized version of Integration By Parts (IBP)\, which could be use
 d for CAA simulations.  They aren't.\n\nThis talk will explain some of the
  maths behind the claims above\, and some recent work to bring adapt recen
 t best practice (SBP) finite differences to CAA simulations.
LOCATION:CMS\, MR15
END:VEVENT
END:VCALENDAR