International Journal of Advanced and Applied Sciences

Int. j. adv. appl. sci.

EISSN: 2313-3724

Print ISSN: 2313-626X

Volume 4, Issue 9  (September 2017), Pages:  70-79

Title: Instability estimation of irregularly shaped bodies moving through a resistive medium with high velocity

Author(s):  Elvedin Kljuno *, Alan Catovic


Mechanical Engineering Faculty, University of Sarajevo, Sarajevo, Bosnia and Herzegovina

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The purpose of the paper was to show an idea how numerical simulations of flow around a stationary irregularly shaped body can be used to estimate instability of the body during a real-world motion of such a body (e.g. a metal fragment). To the best of our knowledge, there is no evidence that such an analysis is available in literature for irregularly shaped bodies. The novelty is in the introduced method for the stability analysis and the fact that a real-world fragment shape was digitized and used for the analysis. However, the disadvantage is in necessity that real fragments need to be scanned and digitized for the analysis, but the future work should give improvements in this direction. The focus was on the rotational part of the motion, particularly on obtaining the period of the motion when the body rotates, but the solving for angles of rotation was not the objective. We showed an idea on how to estimate the period of instability when continuous rotation occurs after the initial projection of the fragment. We assumed that relatively high angular velocity occurs at the initial condition (initial projection of the fragment), which provided an opportunity to assume further that the axis of rotation remains unchanged during the motion. By analyzing the kinetic energy of rotation, we estimated the period of body rotation until it reached a stable orientation during the high velocity motion.  To employ this approach that uses the mechanical energy, it was necessary to obtain the work done by the (aerodynamic) moments of resistance forces about the center of mass. These resistance (aerodynamic) moments were obtained for various orientations of the body using simulations of fluid flow around the real geometry of the body, which was obtained by scanning a real-world fragment, digitizing it, and importing it in a CAD software, which provided the inertial properties through moments of inertia. At each rotation, the kinetic energy of rotation is dissipated through work of the aerodynamic moment which was the basis for calculation when the body takes a steady orientation for the rest of the motion. 

© 2017 The Authors. Published by IASE.

This is an open access article under the CC BY-NC-ND license (

Keywords: Fragment, Aerodynamic force, Orientation instability

Article History: Received 8 June 2017, Received in revised form 27 July 2017, Accepted 29 July 2017

Digital Object Identifier:


Kljuno E and Catovic A (2017). Instability estimation of irregularly shaped bodies moving through a resistive medium with high velocity. International Journal of Advanced and Applied Sciences, 4(9): 70-79


  1. Anderson Jr JD(1991). Fundamentals of aerodynamics. MacGraw-Hill, New York,USA. 
  2. Buresti G (2000). Bluff-body aerodynamics. International Advanced School on Wind-Excited and Aeroelastic Vibrations, Genoa, Italy.     
  3. Fluent ANSYS (2011). Ansys fluent theory guide. ANSYS Inc., 15317: 724-746.     
  4. Moxnes JF, Frøyland Ø, Øye IJ, Brate TI, Friis E, Ødegårdstuen G, and Risdal TH (2017). Projected area and drag coefficient of high velocity irregular fragments that rotate or tumble. Defence Technology. 
  5. Pope SB (2000). Turbulent flows. Cambridge University Press, Cambridge, UK. 
  6. Rumsey C (2012). Turbulence modeling resource. Langley Research Center. Available online at: 
  7. Schamberger RL (1971). An Investigation of the use of spin-stabilized cubes as fragment simulators in armor evaluation (No. GAM/MC/71-8). M.Sc. Thesis, Air Force Institute of Technology, Wright-Patterson Afb Oh School Of Engineering. Ohio, USA.     
  8. Tu J, Yeah HG, and Liu C (2008). Computational fluid dynamics: A practical approach. Butterworth-Heinemann, Oxford, UK.