Wednesday, September 23, 2015

A One-Equation Local Correlation-Based Transition Model

This article is available for free download until 15 Oct 2015, h/t ANSYS blog.

Here's the Abstract:
A model for the prediction of laminar-turbulent transition processes was formulated. It is based on the LCTM (‘Local Correlation-based Transition Modelling’) concept, where experimental correlations are being integrated into standard convection-diffusion transport equations using local variables. The starting point for the model was the γ-Re θ model already widely used in aerodynamics and turbomachinery CFD applications. Some of the deficiencies of the γ-Re θ model, like the lack of Galilean invariance were removed. Furthermore, the Re θ equation was avoided and the correlations for transition onset prediction have been significantly simplified. The model has been calibrated against a wide range of Falkner-Skan flows and has been applied to a variety of test cases.
Keywords: Laminar-turbulent transition, Correlation, Local variables
Authors: Florian R. Menter, Pavel E. Smirnov , Tao Liu, Ravikanth Avancha

Transition location, and subsequent turbulence modeling remain the largest source of uncertainty for most engineering flows. Even for chemically reacting flows the source of uncertainty is often less the parameters and reactions for the chemistry, and more the uncertainty in the fluid state driven by shortcomings in turbulence and transition modeling.

Sunday, March 22, 2015

Reliability Growth: Enhancing Defense System Reliability

This report (pdf) from the National academies on reliability growth is interesting. There's a lot of good stuff on design for reliability, physics of failure, highly accelerated life testing, accelerated life testing and reliability growth modeling. Especially useful is the discussion about the suitability of assumptions underlying some of the different reliability growth models.

The authors provide a thorough critique of MIL-HDBK-217, Reliability Prediction of Electronic Equipment, in Appendix D, which is probably worth the price of admission by itself. If you're concerned with product reliability you should read this report (lots of good pointers to the lit).

Tuesday, January 13, 2015

Guidelines for Planning and Evidence for Assessing a Well-Designed Experiment

This paper is full of great guidance for planning a campaign of experimentation, or assessing the sufficiency of a plan that already exists. The authors break up the effort into four phases:
  1. Plan a Series of Experiments to Accelerate Discovery
    1. Design Alternatives to Span the Factor Space
    2. Decide on a Design Strategy to Control the Risk of Wrong Conclusions
  2. Execute the Test
  3. Analyze the Experimental Design
They give a handy checklist for each phase (reproduced below). The checklists are comprehensive (significantly more than my little list of questions) and I think they stand-alone, but the whole paper is well worth a read. Design of experiments is more than just math, as this paper stresses it is a strategy for discovery.

Tuesday, December 30, 2014

Starscraper Sounding Rocket Kickstarter

The Boston University Rocket Propulsion Group (BURPG) is developing a sounding rocket designed to top 150km and funding it partially through a kickstarter campaign. They plan on launching from Blackrock next year like Qu8k, but this is a more ambitious and complex effort.

The rocket will be controlled using fluid injection thrust vectoring. The thrust levels of their hybrid motor are comparable to Qu8k, but it is a significantly larger (30 vs 14ft long, 12 vs 8in diameter) and heavier (1100 vs 320 lbs) and aims higher (150km vs 120kft). It's hard to tell, but it also seems to be an order of magnitude or so more expensive.

The advantage the BURPG folks claim for their concept over traditional solid fuel sounding rockets is a gentler ride for payloads on the longer, smoother burning hybrid.

Saturday, December 6, 2014

Fully Scripted Open Source Topology Optimization

Helical Extruder Gear for Printrbot with Optimized Topology

I've used a couple different methods for stringing together open source tools to do topology optimization, but they have all required some interactive user input. Here are some previous posts demonstrating those manual methods:
Those approaches are fine if you've got time to fiddle with interactive software, but I wanted to do some parametric studies, so I need an automated approach that would be scalable to lots and lots of optimizations.

Thursday, November 20, 2014

119 Open Source Aeronautical Engineering Tools

I posted a list of 33 open source aeronautical engineering tools on LinkedIn a couple days ago. One of the comments was a question about how open they all really were so I added a column to the list for the license and any non-free dependencies (i.e. Matlab). I went ahead and made an entry for each of the pieces of software from Ralph Carmichael's PDAS collection, which added 84 public domain pieces of software. In addition, there are 23 with various flavors of GNU, 4 BSD-style, and 3 NASA open source agreement (NOSA) codes. See the whole list below the fold. Please suggest adds/changes/deletes in the comments.

Monday, August 18, 2014

Validation & Verification in Physics of Plasmas

Physics of Plasmas is making a collection of 20 papers on verification and validation available for free download for a limited time.
Theoretical models, both analytical and numerical, are playing an increasingly important role in predicting complex plasma behavior, and providing a scientific understanding of the underlying physical processes.

Since the ability of a theoretical model to predict plasma behavior is a key measure of the model’s accuracy and its ability to advance scientific understanding, it is Physics of Plasmas’ Editorial Policy to encourage the submission of manuscripts whose primary focus is the verification and/or validation of codes and analytical models aimed at predicting plasma behavior.

Saturday, July 19, 2014

FreeFem++ Topology Optimization Scripts

There are lots of open source topology optimization options out there (e.g. 99 line code, ToPy) that I've written about before. One that I haven't posted about yet is a collection of FreeFem++ scripts by Allaire, et al. that illustrate a variety of topology optimization approaches and problems. FreeFem++ is a partial differential equation solver based on the finite element method. FreeFem++problems are defined in scripts that use a high level language. FreeFem++ itself is written in C++.