Research: Shock Wave Physics

Qualifications

I graduated with a PhD in Aeronautical Engineering in 2015, specialising in unsteady shock wave dynamics. Although I left academia shortly after, I do still miss the days of running around in a grease-stained lab coat. My thesis covered three main areas:

  • Design of novel shock tube apparatus — Starting from a conceptual design from my research advisor, I simulated and confirmed the feasibility of a novel shock tube apparatus that could produce imploding shock waves of an arbitrary shape. I completed the mechanical design and drew CAD drawings for the equipment, supervised manufacture of the parts, and assembled and commissioned of the equipment.
  • Propagation of arbitrarily shaped shock waves — To test the limits and capabilities of the equipment, I ran simulations and experiments to produce and measure shock waves with shapes that had never been produced before. Some shapes, such as a shock wave with sharp convex corner, do not exist in nature, but the equipment was able to produce a close approximation, whose downstream behaviour matched Computational Fluid Dynamics (CFD) simulations almost perfectly.
  • Reflection of imploding cylindrical shock waves — The primary focus of the research was to study the reflection of converging cylindrical shock waves. Although these shock waves have a range of applications, from lithotripsy to nuclear fusion, their reflection behaviour had not been studied in detail as these shock waves are incredibly sensitive to any disturbances and notoriously difficult to produce in a laboratory setting. I was able to produce these shock waves reliably and study how they reflected off flat obstacles. I developed a numerical method to predict the geometry of these reflections, detailed the conditions leading to transition between different reflection configurations, and documented a powerful shock wave focusing effect that could amplify pressures by a factor of 100 or more.

Publications

Reflection Transition of Converging Cylindrical Shock Wave Segments

B. J. Gray, B. W. Skews (2012).

28th International Symposium on Shock Waves. ISSW 2011.

Propagation of arbitrarily-shaped shock waves

B. J. Gray, B. W. Skews (2012).

8th South African Conference on Computational and Applied Mechanics, SACAM 2012

Experimental production of two-dimensional shock waves of arbitrary profile

B. W. Skews, B. J. Gray, R. T. Paton (2015).

Shock Waves 25

Experimental Investigation into Converging Cylindrical Shock Wave Reflection

B. J. Gray, B. W. Skews (2015).

29th International Symposium on Shock Waves vol. 2. ISSW 2013.

The Mach Reflection of a Converging Cylindrical Shock Wave Segment Encountering a Straight Wedge

B. J. Gray, B. W. Skews (2017).

30th International Symposium on Shock Waves vol. 1. ISSW 2015.

The Context

A doctoral degree involves discovering and contributing brand new knowledge to the world. Inevitably, this will be in a very specific niche field. The niche that I landed in for my PhD was unsteady shock wave dynamics. Here's where this fits in the grand scheme of things:

  • The science of physical matter is called physics.
  • The area of physics that deals with how matter moves in response to forces is called mechanics.
  • We split mechanics into three sub-disciplines based on the complications that are involved — the mechanics complicated by things that are really really small (quantum mechanics), the mechanics complicated by things moving really really fast (relativistic mechanics), and the mechanics of things that are neither too small nor too fast — classical mechanics.
  • Within the field of classical mechanics, there is an area called continuum mechanics that deals with the motion and deformation of materials that can be treated as continuous substances.
  • Solid mechanics is the physics of materials which have a definite rest shape and volume. The study of materials that can flow and change shape is called fluid mechanics.
  • Sometimes fluid mechanics is split into fluid statics which deals with fluids at rest, and fluid dynamics which deals with how fluids flow.
  • Fluid dynamics is split into incompressible flow where it's safe to assume that the density of the fluid doesn't change much as you apply forces to it (as is the case with water), and compressible flow (also called gas dynamics) where the density of the fluid changes significantly as you apply forces to it (such as fast moving air).
  • One particular area within compressible flow is shock wave dynamics, which deals with the physics of shock waves.
© 2025 Brendan James Gray. All rights reserved.