DSTO Scientific Publications

Scaling of cavity-flow wind-tunnel data

Author: Jones, M.; Watmuff, J.
Issue Date: 10-Aug-2009
Citation: 13th Australian Aeronautical Conference, 9-12 March 2009, Melbourne, Australia

Abstract

This paper examines the issues relevant to the interpretation and scaling of data obtained from wind tunnel experiments on flows over cavities. Data from twelve previously published experiments has been extracted and compared. A characteristic of cavity flows is the aeroacoustic resonance that may occur under certain circumstances. Based on the comparison of the existing data sources, the important parameters affecting the observed resonant frequencies are identified and discussed. To provide a framework for the data analysis existing mathematical and physical models of cavity resonance are reviewed. Finally, some of the experimental issues surrounding measurements of aeroacoustic flows are discussed.

Fractal Effects in Lanchester Models of Combat.

Report Number: DSTO-TR-2331
Author: Perry, N.
Issue Date: 2009-08
AR Number: AR-014-597
Classification: Unclassified
Report Type: Technical Report
Division: Joint Operations Division (JOD)
Release Authority: Chief, Joint Operations Division

Abstract

Executive Summary

Lanchesters Equations are one of the most misunderstood and misused models of combat, yet they remain in widespread use as the combat mechanism behind many simulation systems. Previous work by the author examined the impact of a fractal distribution of forces on Lanchesters theory of combat. The present work extends that examination to conceptual issues regarding interpretation of Lanchester's Equations and to additional parameters beyond those examined previously. A fractal model for the distribution of each sides forces in space is shown to produce general force on force attrition expressions which describe the ability of each side to apply its strength effectively, due to battlefield congestion and finite engagement ranges. This is reflected in the logarithmic dependence of the Combat Intensity, Relative Effectiveness and Defenders Advantage parameter on the initial force ratio. It confirms the functional form for the equation of state which had previously been derived for a few special cases. This is consistent with previous derivations of that expression, which had also linked the functional form to limiting a forces ability to apply its strength, and agrees well with historical data analysis. It concludes that spatial effects in combat are necessary to obtain this equation of state instead of Lanchesters original equation of state, which would suggest that the major shortfall of Lanchesters combat model is the lack of a mechanism describing the effects of movement and spatial limitations on interaction between forces. An important consequence of the model proposed as a force on force attrition model incorporating battlefield congestion, is that all the previously derived quantities from the original Lanchester model still apply if the simple attrition coefficients are replaced by the force level attrition coefficients that are developed. This work appears to be the first report that the force level Combat Intensity and Relative Effectiveness, both of which are key parameters in the results of Lanchesters combat model, have a logarithmic dependence on force ratio. This has yet to be investigated using available historical data. The major shortcoming of the present work is the lack of processes to determine the attrition rate coefficients and fractal dimensions. However, it should be realised that these limitations apply not only to Lanchester models of combat but to all models of combat. In spite of all these issues, the model developed here is useful as a combat metamodel to illustrate relationships between select combat parameters and facilitate comparison between model and historical data, as indeed are all Lanchester like models.

Emergent Naval Technology

Author: Byrne, Duncan
Issue Date: 26-Jul-2009
Citation: Navy Futures Week 2009 at the Australian Command and Staff College Navy Single Service Future's Week, 9th June 2009.

Abstract

Advances in technology will facilitate the development of a number of emerging concepts in the maritime environment that will increasingly be joint in nature. This presentation focuses on technologies and concepts that should be feasible in the 2020-2030 timeframe.

Testing Flight Paths for Collecting 3D LADAR Imagery of Inconspicuous Targets

Author: Mewett, David; Graham, Mark; Davies, Adam
Issue Date: Jul-2009
Citation: Mewett, D.T., M.D. Graham and A.H. Davies (2009). Testing flight paths for collecting 3D LADAR imagery of inconspicuous targets. In Anderssen, R.S., R.D. Braddock and L.T.H. Newham (eds) 18th World IMACS Congress and MODSIM09 International Congress on Modelling and Simulation. Modelling and Simulation Society of Australia and New Zealand and International Association for Mathematics and Computers in Simulation, July 2009, pp. 1636-1642. ISBN: 978-0-9758400-7-8. http://www.mssanz.org.au/modsim09/E1/mewett.pdf

Abstract

A pilot study was performed to examine flight paths for an airborne foliage-penetrating Laser Detection and Ranging (LADAR) three-dimensional (3D) imaging system. Such systems form 3D images based on time-of-flight of laser photons, some of which pass through gaps in foliage or other partial obscurants such as camouflage nets. Hence the 3D image will contain partial information about any objects behind or underneath such obscurants. The obscurant can be removed from the image by only keeping points within some appropriate range, leaving a partial image of the hidden objects which may include targets of interest. An improved overall image can be formed by combining images taken from several different viewpoints, using knowledge of the LADAR sensors location at each viewpoint. In this study, we compared the overall 3D images obtained from an airborne LADAR system during different flight paths. The scene for each flight path consisted of a four-wheel-drive vehicle placed in a section of a eucalypt forest. Models for the vehicle and the individual trees were created in the 3D modelling software Maya, and exported as point clouds to be used in the general-purpose analysis software MATLAB. The overall forest scene was then assembled from the individual trees. The amount of light penetrating the foliage was determined at three different locations within the scene. On average, results were found to roughly agree with the prediction that light penetration scales with the sine of the angle from horizontal. Formation of LADAR images was modelled by determining the set of points in the scene that had a direct line-of-sight to the airborne sensor. This low-fidelity approach was taken because the aim of the study was to investigate ways of tasking the sensor system, rather than using the model as part of a hardware design process or a testbed for data processing algorithms. Since there is already a random effect due to line-of-sight through the forest canopy, it was decided that further random effects leading to false returns or missed returns would unnecessarily complicate the comparison between results from different flight paths. The flight paths in this study were intended to keep the sensor footprint directed at a known or assumed target area on the ground. One type of path was an arc centred at this location, with the sensor constantly directed sideways at an appropriate elevation. The other type of path went straight past the target area, with the sensor needing to be constantly redirected. Different scan spacings along the path were also investigated. It was assumed that the unobscured view from each flight path would be sufficient for the surveillance or reconnaissance task. So for each flight path, the Hausdorff distance was calculated as a measure of the difference between the 3D image of the target taken through the foliage and the corresponding unobscured image from the same flight path. No significant difference was found between results for the straight and arc paths, but the 3D images were closest to the unobscured views for the smallest scan spacing.

Benchmark Testing of Naval Threat Countermeasure Simulation (NTCS) Development from Version 2.4c to 3.2.

Report Number: DSTO-TR-2315
Author: Smith, S.E.
Issue Date: 2009-07
AR Number: AR-014-578
Classification: Unclassified
Report Type: Technical Report
Division: Maritime Platforms Division (MPD)
Release Authority: Chief, Maritime Platforms Division

Abstract

The Naval Threat Countermeasure Simulator (NTCS) is a commercial code accepted as the NATO standard for ship Infrared (IR) signature modelling. This code has undergone extensive development, in conjunction with measurement trials, since 1997. A set of benchmark test cases was developed to track the development of NTCS since 1997 paying particular attention to the effect on the computed IR signature of a test target. In this report, the results from these benchmark tests are presented for NTCS versions from 2.4c to 3.2. It will be shown that improvements to the NTCS code from version to version result in significant changes in computed IR signatures. In addition to code changes, other parameters such as choice of environmental data generation software (e.g. LOWTRAN/MODTRAN) and choice of solar scattering flag also influence the computed IR signature. Timing information was also assessed as part of this study and reveals increases in run-time requirements as NTCS has evolved. In light of these results, caution should be exercised when comparing results from different versions of NTCS. It is also recommended that details of the NTCS version and parameters used are specified when presenting NTCS results.

Executive Summary

The Naval Threat Countermeasure Simulator (NTCS) is a commercial code accepted as the NATO standard for ship infrared (IR) signature modelling. This code has undergone extensive development, in conjunction with measurement trials, since 1997. A set of benchmark test cases was developed to track the development of NTCS since 1997 paying particular attention to the effect on the computed IR signature of a test target. In this report, the results from these benchmark tests are presented for NTCS versions from 2.4c to 3.2. In addition to the changes resulting from different version, two other parameters within NTCS were also investigated. The first is the choice of environmental data generation software (e.g. LOWTRAN/MODTRAN) and the second is the choice of the solar scattering flag. These were included since they were changed or added to NTCS within the series of NTCS from 2.4c to 3.2. Improvements to the NTCS code from version to version result in significant changes in computed IR signatures. In addition to code changes, the parameters such as choice of environmental data generation software and choice of solar scattering flag also influence the computed IR signature. Timing information was also assessed during this study and reveals that the run-time requirements for NTCS have increased during the evolution of NTCS. It is recommended that caution is exercised when comparing results from different versions of NTCS. It is also recommended that details of the NTCS version and parameters used are specified when presenting NTCS results. Accurate comparisons of computed IR contrast signature data for different naval platforms can only be made reliably when the same NTCS version is used and the same background, environmental data generation software and solar scattering flag are selected.

Survey of Knowledge Representation and Reasoning Systems.

Report Number: DSTO-TR-2324
Author: Trentelman, K.
Issue Date: 2009-07
AR Number: AR-014-588
Classification: Unclassified
Report Type: Technical Report
Division: Command, Control, Communication and Intelligence Division (C3ID)
Release Authority: Chief, Command, Control, Communication and Intelligence Division

Abstract

Executive Summary

As part of the information fusion task we wish to automatically fuse information derived from the text extraction process with data from a structured knowledge base. This process will involve resolving, aggregating, integrating and abstracting information - via the methodologies of Knowledge Representation and Reasoning - into a single comprehensive description of an individual or event. This report surveys the key principles underlying research in the field of Knowledge Representation and Reasoning. It represents an initial step in deciding upon a Knowledge Representation and Reasoning system for our information fusion task. We find that although first-order logic is a highly expressive knowledge representation language, a major drawback of the logic as a Knowledge Representation and Reasoning system for our information fusion task is its undecidability. Moreover, most first-order automated theorem provers are not designed for large knowledge-based applications. Modal logics are gradually receiving more attention by the Artificial Intelligence community, but research in modal logics for knowledge representation still has a long way to go. A production rule (expert) system is viable as a Knowledge Representation and Reasoning system, but these systems are optimally suited for small, specific domains. To build an intelligence expert system we would require expert knowledge in pretty much everything. Frame systems are limited in their expressiveness, and moreover - in regards to knowledge representation - have been superceded by description logics. Semantic networks are excellent for taxonomies, but are not particularly suitable for our information fusion task. On a more positive note, description logics are currently very popular and are actively being researched. They are (in the most part) decidable and their open-world semantics would allow us to represent incomplete information. A further advantage is the availability of Semantic Web technologies. Description logics are still limited however; for our task, wed need to look at very expressive logics which might lose us decidability.

Giselle: A Mutually Orthogonal Triple Twin-loop Ground-symmetrical Broadband Receiving Antenna for the HF Band.

Report Number: DSTO-TR-2321
Author: Martinsen, W.
Issue Date: 2009-07
AR Number: AR-014-584
Classification: Unclassified
Report Type: Technical Report
Division: Command, Control, Communication and Intelligence Division (C3ID)
Release Authority: Chief, Command, Control, Communication and Intelligence Division

Abstract

This report describes development of a tri-axial mutually orthogonal broadband twin-loop receiving antenna for the HF band. The three twin-loops have been arranged so that they exhibit the same distributed parameters between themselves and ground. The upper frequency limit of the antenna is discussed and a method for extending the low frequency cut-off is presented. The antenna noise factor is calculated from measured data.

Executive Summary

Traditional mutually orthogonal tri-axial loop antennas have distributed parameters to the ground that are not consistent between the three loops. This non-symmetrical characteristic adds complexity to the analysis of signals received from each of the loops. Also, the distributed inductance (L) and capacitance (C) of each loop form a resonant circuit limiting the loops usefulness for broadband work. The tri-axial twin-loop antenna design presented in this report has the same distributed parameters to ground on all three loops (ground-symmetrical) easing the analysis burden on the received data. The final version of the antenna presented can cover the complete HF band and is ideal for studying the polarisation of received signals with the view of mitigating HF polarisation fading. The inherent noise produced by the Giselle antenna is less than the expected man-made noise for a quiet rural site; therefore the Giselle antenna can also be used as a compact triaxial polarisation diversity surveillance antenna for the whole of the HF band. It is capable of discriminating between locally transmitted ground wave signals and those transmitted at some distance and received via sky-wave by monitoring for any signs of rotation in the received signals polarisation.

Synthetic Electronic Imaging System.

Report Number: DSTO-TN-0903
Author: Ide, K.M.; Jarvis, B.J.; Lucas, M.A.
Issue Date: 2009-07
AR Number: AR-014-574
Classification: Unclassified
Report Type: Technical Note
Division: Weapon Systems Division (WSD)
Release Authority: Chief, Weapons Systems Division

Abstract

The Synthetic Electronic Imaging System employs electronic components to combine multiple images from a plurality of cameras which are processed with inertial data from the vehicle on which the system is mounted to yield stabilised video images without resorting to complicated optics or a stabilised platform. It was devised as an alternative to stabilised ball turrets fitted with electro-optic and infrared cameras. Intended as an imaging system for Unmanned Aerial Vehicles (UAV), it may be employed in any manned or Unmanned System (UMS) where situation awareness is aided by the use of an imaging system. This report describes the development of the Synthetic Electronic Imaging System and assembly of a simple concept demonstrator in 2005.

Executive Summary

Conventional ball turret imaging systems are mechanically complex requiring continued calibration and maintenance. Hence, their purchase and support involves significant costs. The dimensions and weight of a ball turret demand an airframe with significant payload capacity. These restrictions led the authors to develop the Synthetic Electronic Imaging System. It is a highly capable alternative but without the complexity, cost and support necessary for a comparable ball turret imaging system. The Synthetic Electronic Imaging System employs electronic components to combine multiple images from a plurality of cameras which are processed with inertial data from the vehicle on which the system is mounted to yield stabilised video images without resorting to complicated optics or a stabilised platform. A full field of view wide angle composite image is displayed on one monitor with a box overlay representing the region of interest. A second monitor shows a telephoto image within the designated region of interest. As the operator moves the region of interest, images in the second display are updated in real-time. The two complementary video streams provide an excellent aid to situation awareness and analysis. The two video channels are transmitted to the Ground Control Station as television images requiring very low bandwidth. Operators can time-slip the video images by using Digital Video Recorder software controls for review and analysis. Frames that merit further analysis or examination can be downloaded from the remote vehicle as a series of still images with the maximum resolution of the sensor. Intended as an imaging system for Unmanned Aerial Vehicles, it may be employed in any manned or Unmanned System where situation awareness is aided by the use of an imaging system. This report describes the development of the Synthetic Electronic Imaging System and assembly of a simple concept demonstrator in 2005.

Application of Black Scholes Complexity Concepts to Combat Modelling.

Report Number: DSTO-TR-2318
Author: Perry, N.
Issue Date: 2009-07
AR Number: AR-014-581
Classification: Unclassified
Report Type: Technical Report
Division: Joint Operations Division (JOD)
Release Authority: Chief, Joint Operations Division

Abstract

Lanchesters equations are commonly used as the basis for force-on-force combat models, even if only as a metamodel for a more complex combat simulation. This report examines whether attrition is adequately modelled by such Markov processes. It shows that the distribution of historical battle casualties is consistent with that obtained when attrition is modelled as an Ito process. The additional Wiener term can be regarded as representing the impact of the wider environment on attrition rates.

Executive Summary

Lanchesters equations are commonly used as the basis for force-on-force combat models, even if only as a metamodel for a more complex combat model. These equations define a system with the strengths of the forces involved comprising its internal parameters. Many systems are adequately described using just their internal parameters, without consideration of any interactions between that system and its wider environment. However, it is apparent from the work on extending combat models based on Lanchesters equations to include additional parameters such as morale, spatial force dispersion and movement, that such quantities do affect attrition rates. The inclusion of additional parameters also results in additional complexity and the loss of insight that a simple model provides. ideally what is desired is a means to include the effect of the wider environment on attrition rates without also increasing the models complexity. The standard model for the behaviour of stock prices in time assumes they are a continuous Markov process with a constant fractional drift rate. The Black and Scholes model of stock prices treats price volatility as resulting from the action of the rest of the market on the system comprised of the one stock price being modelled. Furthermore, it does not attempt to model the processes by which the market might affect the stock price, arguing that the mechanisms are too complex to model or are not known. Lanchesters Equations are similar to the starting point for the derivation of the Black Scholes Equation. This suggests an obvious approach for including the effect of the wider environment in the evaluation of combat attrition rates, through the addition of a Wiener process, turning Lanchesters Markov process into an Ito process. The present work has used an existing database of historical battle results to show that the frequency distribution of battle casualties is consistent with that expected when Lanchesters equations are augmented to form an Ito Process rather than the conventional Markov Process. The additional Wiener term can be regarded as representing the impact of the wider environment on attrition rates. The shape of the casualty frequency distribution was not observed in the initial force strength distribution. This supports the contention that such distributions result from the attrition process itself and are not artefacts of the sampling or analysis procedure. The database used, and indeed all such databases, was shown to include an inherent bias which under-represents the number of small battles. While the effect of such bias was observed, by incorporating strata sampling concepts it was possible to confine the effects of such bias into a single stratum and a small number of data points, which can then be allowed for.

User Guide to the Aircraft Cumulative Probability Chart Template.

Report Number: DSTO-TR-2332
Author: Murtagh, B.; Maxfield, K.
Issue Date: 2009-07
AR Number: AR-014-601
Classification: Unclassified
Report Type: Technical Report
Division: Air Vehicles Division (AVD)
Release Authority: Chief, Air Vehicles Division

Abstract

To ensure aircraft structural integrity is maintained to an acceptable level, probabilistic approaches may be used to calculate the risk of cracking (or failure) over the life of the aircraft or fleet. One such risk analysis technique employs a lognormal probability distribution to model the likelihood of cracking (or failure) in the fleet with respect to hours. This technique was programmed into Microsoft Excel to create a simple and easy to use template. An outline of the theory behind the probabilistic approach is provided as well as a comprehensive user guide to the template. This template allows the quick and simple determination of probability distributions of cracking (or failure) which may be used to assess the life of aircraft structures.