Defence Science And Technology Organisation Research Articles

High frequency over-the-horizon radar [Book review

HF radar is sometimes regarded as an unusual and mysterious subject - after all, the signals don't even propagate in straight lines, and the signal design, interference environment and radar hardware are all rather different to those of microwave radars. The chapters by James Headrick and Stuart Anderson in Skol-nik's Radar Handbook (2nd edition and 3rd edition respectively) are well known and excellent, but are necessarily quite short. A book that provides a comprehensive and detailed treatment of HF radar is therefore very welcome, and Dr Joe Fabrizio - winner of the 2011 IEEE AES Nathanson Award - is very well qualifed to write it. Joe has spent the bulk of his career at the Defence Science and Technology Organisation (DSTO) in Australia, where pioneering work on HF radar has been carried out for several decades. In 2007 he received the coveted DSTO Science Excellence award in recognition of his contributions to adaptive signal processing for Australia's Jindalee Operational Radar Network (JORN). He currently serves as Vice-President for Education on the AES Board of Governors.

High Temporal Accuracy for Extensive Sensor Networks

The Defence Science and Technology Organisation (DSTO) has developed a versatile, low power, and networked sensor interface design suitable for use with a wide range of sensors. The sensor interfaces consist of: 1) core hardware and software that is the same for any sensor and 2) sensor specific hardware and software. The core software provides basic communications routines and manages a simple file operating system. These files constitute the software for interfacing and control of the hardware for specific sensors. The whole system is implemented on the low power Texas Instruments MSP430 series of microcontrollers and results in a consistent interface to a data logging or network control system, no matter what sensor is in use. A network approach has been adopted to reduce the wiring requirements for large numbers of sensors. However, networking introduces complexity, especially in regards to time synchronization of medium-to-high speed sensors, considered here as sensors requiring measurements rates in the range 100-5000-Hz range, such as strain gauges and accelerometers. In these applications, it can also be useful to only acquire data when there is interesting activity to avoid collecting large amounts of essentially zero valued data points and thus reduce the data storage requirements. This paper covers the software and hardware design considerations to achieve temporally correlated measurements from a widely distributed sensor network based on the DSTO sensor interface. The ultimate performance of the DSTO implementation is investigated and experimental results are compared with the predicted response.

Finite element simulation of blank torpedo impact on submarine hulls

The paper presents the development, evaluation and validation of a finite element model for the simulation of the impact of a blank torpedo against a submarine pressure hull. A parametric, shell finite element model was generated and analysed using ANSYS Finite Element Package to explore the effects of different loading conditions and analysis types in the accuracy of the results. Results were compared to a series of drop tests conducted by the Australian Defence, Science and Technology Organisation (DSTO). Geometric and material non-linear models were compared against varying methods of load applications. A numerical model subjected to a concentrated load was found to provide a poor representation of the drop tests. A clear improvement in the accuracy of the results was achieved by implementing a distributed impact load case; however, a full nonlinear analysis involving large deflection, plasticity and contact was found to offer the best agreement with the experimental test results.

Analysis of Black Hawk Main Transmission Support Beam In-Service Fatigue Crack

The Australian Defence Science and Technology Organisation (DSTO) was recently tasked with evaluating an in-service fatigue crack discovered in the primary structure of an Australian Army Black Hawk helicopter. This crack, discovered early in the affected components service life, was quite large and subsequent fractographic analysis generated substantial information with respect to its growth characteristics. Consequently, it was decided to use this in-service fatigue crack to test the ability of those methods and technologies being developed at DSTO to model and assess a ‘real’ example of helicopter airframe fatigue cracking. This paper details the process of analysing an in-service fatigue crack using methods and technologies developed and/or improved at DSTO in the areas of visualisation, fatigue spectra generation, load and stress analysis, and crack growth prediction. Results will highlight the effectiveness of the methods and techniques in modelling the observed fatigue damage and areas where further improvements are required.

Endurance Testing of a Vibration Energy Harvester for Structural Health Monitoring

The Australian Defence Science and Technology Organisation (DSTO) is developing a variety of in-situ structural health monitoring (SHM) approaches for potential use in high value platforms across the Australian Defence Force (ADF). The implementation of SHM systems would allow the ADF to move from expensive interval based inspection and maintenance regimes for ageing platforms to more cost-effective condition-based approaches, and therefore reduce aircraft through - life support costs. One critical issue is determining the optimal means of supplying power to these in-situ SHM systems. To address this issue DSTO has developed a bi-axial vibration energy harvesting approach based on a vibrating spherical-mass, magnet and wire-coil transducer arrangement. It is important that the vibration energy harvesting devices themselves are resistant to fatigue and wear related damage as they may need to operate in service for many years. This paper examines work done on mitigating wear effects in vibration energy harvesting devices, with the goal of ensuring device longevity.

Helicopter Airframe Fatigue Spectra Truncation and Verification

Helicopter airframe fatigue cracking is a cause of significant and growing cost of ownership and operational readiness concerns for the operators of (primarily) metallic airframe helicopters. Airframe fatigue has often had relatively low priority for helicopters, with research and design concentrated on the fatigue of flight critical rotating structural components such as rotor blades and pitch links. The Australian Defence Science and Technology Organisation (DSTO) and Naval Air Systems Command (NAVAIR) of the US Navy are collaborating to develop improved methods and technologies that can be used to assess the fatigue damage accrued by ageing helicopter airframes. The flight load sequences, or fatigue spectra, experienced by a helicopter airframe in its lifetime contain many billions of load cycles due to rotor revolutions. The application of spectra containing such vast numbers of load cycles is often impractical for reasons of test duration and cost, therefore spectra simplification techniques must be employed. To this end, truncation is a technique that is used to eliminate non-or lesser-damaging load cycles, producing spectra equivalent in terms of theoretical fatigue damage but with substantially fewer load cycles. This paper describes several truncation techniques that have recently been developed at DSTO specifically to deal with the very large numbers of load cycles that are characteristic of helicopter airframe fatigue spectra. These techniques, which include both sequence and frequency based approaches, feature tunable levels of truncation and allow for large reductions in numbers of turning points while maintaining high-fidelity and realistic fatigue spectra. Also detailed are preliminary results from a comprehensive coupon test program, which DSTO is using to experimentally verify that truncated and un-truncated spectra are approximately equivalent in terms of the fatigue damage that they produce.

A Brief History of Structural Fatigue Testing at Fishermans Bend Australia

This paper presents a brief history of fatigue research at the Fishermans Bend Australia Defence Science and Technology Organisation (DSTO) facility from the early days in the 1940s when Mr. H.A. Wills, Head of the then Structures Division, foresaw with remarkable insight the emerging danger of fatigue in aircraft structures. He presented a historic paper at the Second International Aeronautical Conference in 1949 and instituted a comprehensive programme of research on the fatigue of materials and structures which proved to be invaluable within the next decade as fatigue failures began to plague first civil and then military aircraft fleets worldwide. DSTO is still amongst the world leaders on the fatigue of aircraft structures, as many of these research programmes have won international recognition and as fatigue investigations expeditiously undertaken for the RAAF (and at times civil regulators) have supplied valuable information to the aircraft manufacturers, operators and researchers.

Helicopter Airframe Fatigue Spectra Generation

Helicopter airframe fatigue cracking is a cause of significant and growing cost of ownership and operational readiness concerns for the operators of (primarily) metallic airframe helicopters. Airframe fatigue has often had relatively low priority for helicopters, with research and design concentrated on the fatigue of flight critical rotating structural components such as rotor blades and pitch links. The Australian Defence Science and Technology Organisation (DSTO) and the US Naval Air Systems Command are collaborating to develop improved methods and technologies that can be used to assess the fatigue damage endured by ageing helicopter airframes. The flight load sequencesor fatigue spectraexperienced by a helicopter airframe in its lifetime contain many billions of load cycles due to rotor revolutions. Fatigue spectra developed for helicopter airframe certification tests are heavily simplified for reasons such as computational efficiency, test practicality and cost. Real airframe fatigue spectra are likely to be influenced by the modes of vibration that might be present on the airframe, the attenuation of the vibratory loading that is introduced at the main and tail rotors and the relative magnitudes and influences of both quasi-static (manoeuvre induced) and vibratory loading. To better capture such complexity, more realistic, higher fidelity fatigue spectra are required. Fatigue spectra generation involves creating realistic flight-by-flight sequences of flight conditions and assigning high-fidelity flight loads data to those sequences. This paper details DSTOs development of a novel computer-automated process which pseudo-randomly generates realistic sequences of flight conditions to match a known or assumed usage spectrum.

Modeling ionospheric disturbance features in quasi‐vertically incident ionograms using 3‐D magnetoionic ray tracing and atmospheric gravity waves

The Defence Science and Technology Organisation (DSTO) has initiated an experimental program, Spatial Ionospheric Correlation Experiment, utilizing state‐of‐the‐art DSTO‐designed high frequency digital receivers. This program seeks to understand ionospheric disturbances at scales < 150 km and temporal resolutions under 1 min through the simultaneous observation and recording of multiple quasi‐vertical ionograms (QVI) with closely spaced ionospheric control points. A detailed description of and results from the first campaign conducted in February 2008 were presented by Harris et al. (2012). In this paper we employ a 3‐D magnetoionic Hamiltonian ray tracing engine, developed by DSTO, to (1) model the various disturbance features observed on both the O and X polarization modes in our QVI data and (2) understand how they are produced. The ionospheric disturbances which produce the observed features were modeled by perturbing the ionosphere with atmospheric gravity waves.

Development of assurance techniques for information quality on technical advice

The Maritime Division (MD) of the Defence Science and Technology Organisation (DSTO), undertakes the development of platform models to support the provision of technical advice to Royal Australian Navy (RAN) acquisition projects. This requires the synthesis of different types and sources of information into the advice given. The information can include pure scientific data through to technical data from industry and may even include rules of thumb. This variation in the data source and types has led DSTO to seek methods to assess the quality of the information used in the advice they provide. In this paper, a method is presented for the selection of dimensions, their categorisation and development of a rating scale for information quality. The research does not consider database data quality issues, as these are outside the scope of the problem. A scale is developed from weighted values of 15 quality dimensions considered important for this work. The quality dimension weightings were developed using a pair-wise comparison.

An Enhanced Experimental Facility for Durability and Performance Characterisation of Piezoelectric Transducers for Structural Health Monitoring

With any structural health monitoring (SHM) system, verification of the health of the sensing elements is essential in ensuring confidence in the measurements furnished by the system. In particular, SHM systems utilised for structural hot spot monitoring applications will conceivably require transducers to operate reliably after sustained exposure to severe mechanical loading. Consequently, a good understanding of the long term mechanical durability performance of structurally integrated piezoelectric transducers is vital when designing and implementing robust SHM systems. An experimental facility has been developed at the Australian Defence Science and Technology Organisation (DSTO) capable of performing an autonomous long-term mechanical durability test on piezoceramic transducers. The Autonomous Mechanical Durability Experimentation and Analysis System (AMeDEAS) incorporates a general purpose data acquisition program controlling up to three 8-channel relay multiplexers and two instruments. AMeDEAS is highly flexible, allowing user-specified channel configurations and automatic interrogation of selected instruments. The system also interfaces with the uni-axial mechanical testing machine to provide control of the load sequence allowing transducer elements to be interrogated under stable load-free conditions after being subject to a predefined loading regime. AMeDEAS was used to investigate the fatigue characteristics of a low-profile layered piezoceramic transducer package developed by DSTO. A total of 16 transducers were tested under tension-dominated cyclic loading with peak-to-peak strain amplitude increasing from 400 με to a maximum of 3000 με, with periodic acoustic transduction efficiency and electromechanical impedance measurements taken throughout the test. This paper details the AMeDEAS and includes preliminary results which confirm the efficacy of the new facility.

Development and Validation Roadmap for <i>In Situ</i> Structural Health Monitoring of ADF Aircraft

In recent times there has been concerted pressure on military organisations worldwide to push for significant reductions in through-life support costs while maintaining and improving aircraft availability and safety. These goals, which on the surface may appear contradictory, can be achieved through the introduction of Structural Health Monitoring (SHM) systems. The paper describes the Australian Defence Science and Technology Organisation (DSTO) roadmap for SHM system development, validation, certification and implementation, in the context of technologies and systems that meet Australian Defence Force (ADF) future requirements. The current approach focuses on wide-area damage detection SHM systems using acousto-ultrasonic techniques.

A finite element modelling to investigate the mitigation of blast effects on reinforced concrete panel using foam cladding

Protection of critical infrastructure against bomb attacks due to the rising threat of terrorism requires more attention. An effective solution to mitigate blast effects on infrastructure is to protect them with cellular foam material cladding. This paper investigates the capabilities of metallic foam cladding, which can absorb a significantly high blast energy being a cellular solid, in protecting critical reinforced concrete slabs against blast loadings. A coupled cladding structure interaction model based on the finite element technique has been developed to quantify the interaction between the cladding and the reinforced concrete (RC) slab subjected to blast loads. As the RC slab is supported at its two opposite edges and other edges are free in the present investigation, the slab is idealised as a beam in the proposed model where the small localised regions subjected to high moments are referred to as hinged regions which are connected with the large remaining parts of the structure referred to as non-hinge regions. The foam cladding layer over the RC slab is modelled as a lumped mass spring system which considers deformation of the foam layer in the loading direction. The hinge regions of the beam are simulated with interface elements having rotational stiffness which is obtained from a moment rotation model. The foam is modelled by an array of lumped masses over each beam element node connected by a number of inelastic extensional springs in the loading direction which help to model the progressive densification of the foam layer. Meanwhile a series of blast tests have been carried out by the DSTO (Defence Science and Technology Organisation, Australia) at their blast testing site at Port Wakefield, South Australia to investigate the effectiveness of the foam protected RC slabs against blast loads. The data recorded from the blast tests have also been used for the validation of the coupled cladding structure interaction model.

Australian Defence Applications of Advanced Smart Materials Research

This paper overviews some recent S&T innovations in smart materials and structures at the Australian Defence Science and Technology Organisation (DSTO) under a Corporate Enabling Research Program (CERP) on Signatures, Materials and Energy. The CERP program includes development and transitioning of technology across the maritime, air and land domains, with the major focus of the smart materials program component being to increase the safety, availability and maintainability of Defence assets. Three specific examples are provided of the smart materials and structures program, ranging across the spectrum of technology readiness from new concept phase to technology transitioning, viz.: (i) Advances in smart sensing for prognostics-based platform management; (ii) Fabrication of nanostructured and ultrafine grained materials through top-down severe plastic deformation processing of bulk materials; (iii) Innovative application of carbon nanotubes/conducting polymers as artificial muscles for low-power propulsion and control of small autonomous underwater systems. In each case, the DSTO effort is underpinned by strong university or industry linkages to deliver challenging interdisciplinary S&T.

Analysis of L-band multi-channel sea clutter

The authors conducted a sea clutter trial using a DSTO (Defence Science and Technology Organisation, Australia) built, vertically polarised, L-band, 16-channel receive array during May 2008, at Kangaroo Island, South Australia. This study reports various properties of sea clutter which the authors measured including the backscatter coefficient, spatial and temporal correlations, distributions and Doppler spectra. Observed phenomena are explained. Techniques for calibrating the collected data are also presented.

Adaptive beamforming for high-frequency over-the-horizon passive radar

Target detection and tracking systems using emitters of opportunity have received significant interest recently, especially those which exploit VHF and UHF broadcasts as signal sources in so-called passive radar systems. Here, the authors discuss an experimental system in the high-frequency (HF) band, where due to long-distance ionospheric propagation of radio waves in the 3–30 MHz spectrum, the illuminator may be located well beyond the line-of-sight. In this study, live data was recorded by a high dynamic range multi-channel digital receiver connected to a two-dimensional (L-shaped) antenna array, and signals from an uncooperative HF over-the-horizon (OTH) radar transmitter have been captured and analysed. As a preliminary step towards the development of a general HF-OTH passive radar system, the scope of this work is to compare the performance of conventional and adaptive spatial processing techniques in terms of their ability to cancel direct-wave interference and protect useful signal echoes to detect a small cooperative aircraft target. In particular, an alternative adaptive beamforming method specifically tailored to this application is proposed, and its practical performance is compared with classical and standard adaptive beamforming approaches. GPS data measured on-board the cooperative aircraft provided accurate ground truth of the flight path, enabling target profiles in bi-static range, Doppler frequency and direction-of-arrival (azimuth/elevation) to be calculated as a function of time. This information permitted the different processing schemes to be evaluated with a high degree of confidence. The experimental system and live data analysed are exclusively from the HF Radar program of the Defence Science and Technology Organisation (DSTO), Australia.

Battle damage repair of a helicopter composite frame-skin junction. Part 1: Depot repair

The Defence Science and Technology Organisation (DSTO), Australia, Delegation Generale Pour L’Armement (DGA), France and Eurocopter have carried out collaborative research in the area of battle damage repair techniques for military helicopter structures. Australian and French participants have focused on depot and field repairs, respectively. This paper summarises the research conducted at DSTO to develop battle damage repair methods for a helicopter composite frame-skin junction (FSJ) subjected to damage caused by a typical threat weapon. A generic BDR design approach was successfully applied, which involved use of a reverse engineering approach to determine the load requirements, application of a rapid repair design approach, and validation of the design using finite element analyses and experimental testing.

Investigation using quantitative fractography of an unexpected failure in an F/A-18 centre fuselage bulkhead in the FINAL teardown program

As part of the structural life assessment of the F/A-18 aircraft in service in the Royal Australian Air Force (RAAF), the Defence Science and Technology Organisation (DSTO) have completed the teardown of several ex-service F/A-18 wing attachment centre barrels in the Flaw IdentificatioN through the Application of Loads (FINAL) program. Prior to teardown, each centre barrel was fatigue cycled under a wing root spectrum in a test rig until each of the three fracture-critical bulkheads (denoted Y453, Y470.5 and Y488) had failed. The Y488 bulkhead of the third centre barrel cycled in the FINAL program failed after approximately 24 blocks of applied loading from fatigue cracking in one of the left-hand side main landing gear uplock attachment holes. Even with the addition of the bulkhead’s service life, the time to failure was well short of the demonstrated fatigue test life on which the RAAF fleet is managed. Thus, the cause of this failure needed to be investigated. A failure investigation using quantitative fractography and finite element analyses of these fatigue cracks, as well as an examination of fatigue cracks at similar locations on other FINAL centre barrels was conducted. Crack depth versus time during FINAL cycling data were generated and these data were used to show that the rate of crack growth for the cracks that grew from the failed hole was much greater than the rate of crack growth at the other identically loaded main landing gear uplock holes. Examination of the crack growth led to the conclusion that this hole had not been cold expanded correctly in production, whereas the other holes examined had. In addition, the examination of the other cracks at this location showed that cracking is likely to be found in service at these holes regardless of the cold expansion process, and that these cracks are very unlikely to cause a failure within the planned life of the centre barrel when the cold expansion process has been implemented correctly.

Helicopter gearbox bearing blind fault identification using a range of analysis techniques

Vibration acceleration signals were obtained from an overload test of a Bell 206 helicopter main rotor gearbox in order to complete a blind bearing fault analysis where no knowledge of the fault was made available prior to the analysis. A range of diagnostic techniques was applied. These included power spectral density comparisons, constant percentage bandwidth (CPB) spectrum analysis, SK analysis to determine the frequency bands with maximum impulsiveness and to filter the signal to maximise that impulsiveness, and envelope analysis to determine the fault frequencies. Order tracking was used to compensate for speed fluctuations, while linear prediction using autoregressive models (AR) was used to remove the regular gear meshing contribution in the signals. As a result of applying these techniques, a fault in one of the planetary bearings was identified. A match with the cage frequency and the inner race ball pass frequency indicated deterioration associated with these components. Roller fault frequencies were not directly detected, but the fact that roller faults give a modulation at cage frequency shows that their effect was still detected. SK gave a good measure of the severity of the fault when compared to the amount of metal wear debris in the oil. Details of the test, as well as application of a statistical fault detection technique can be found in a companion paper submitted by the Defence Science and Technology Organisation (DSTO) Australia.

PC4 laboratory construction: a users’ point of view

The Sydney 2000 Olympic Games was a tremendous event for Australia, bringing the world?s best athletes and thousands of visitors to Sydney. As it was a global event with comprehensive media coverage, it also bought to our shores the possibility of terrorist activity. During the period the games were held, the Centre for Infectious Diseases and Microbiology (CIDM) performed laboratory investigations of suspicious substances found at Olympic Games venues and Sydney airport and worked with the Defence Science and Technology Organisation (DSTO) testing air samples, taken at venues, for the presence of bioterrorism agents.