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Theunissen E.,Netherlands Defence Academy
AIAA/IEEE Digital Avionics Systems Conference - Proceedings | Year: 2012

Since the beginning of Aviation, instruments have been designed to provide the pilot with the information needed to control the aircraft. During the past 30 years, pilot involvement in aircraft navigation, guidance and control has shifted from manual control to supervision of the navigation system. The domain of digital avionics provided the enablers for this shift, and several important developments started already over half a century ago. One aspect of these developments concerns the instruments designed to provide the pilot with the required information. When considering today's systems, it is not immediately obvious that for several of the currently implemented concepts there have been other, competing ones that for some reason did not make it. It may come as a surprise that some of these alternatives are conceptually superior but required technology that at the time was not sufficiently mature for implementation in an aircraft. In this paper, the history of some promising alternatives is provided, and it is speculated why these ended up as missed opportunities. To illustrate how certain instrument /data presentation concepts are better suited to provide the required guidance, navigation and control information for both skill and knowledge-based involvement of the pilot, a classification based on the inner-, directional-, and outer-loop closure of the navigation function is used. It is argued that due to the increased complexity of the pilot's supervisory control task in a future air-traffic environment, some of these alternatives need to be reconsidered as a basis for decision support, and it is illustrated what opportunities exist. © 2012 IEEE.

Theunissen E.,Netherlands Defence Academy
AIAA/IEEE Digital Avionics Systems Conference - Proceedings | Year: 2012

An autonomous, adaptive navigation system, tightly coupled with the overall mission management system, can provide unmanned systems with the capability to autonomously change and execute mission plans. Legislative issues, the difficulty to meet the extremely high reliability requirements of an autonomous collision avoidance function and the associated development and certification challenges can all be reasons to limit the authority of such an adaptive system by involving/requiring a human operator at the decision making level. The role of the human operator is to make decisions during situations in which significant changes in the navigation plan are needed to accomplish the mission. Such a concept of operation imposes specific challenges that must be addressed during the design of the systems that support the operator with this supervisory task. The paper starts with addressing the commonality in the associated challenges between nautical and aeronautical platforms and between manned and unmanned systems. It will be illustrated how during the past 60 years, research in both the nautical and the aeronautical domain has addressed aspects of these challenges and how developments in the area of sensors, processors and display capabilities increased the possibilities to both increase system autonomy and keep the human operator involved with the required authority. Following this background, it will be discussed how components of a system designed to support a UAS pilot with the separation assurance task have been re-used in the realization of a prototype operator support system for an unmanned vessel, the CSHIELD platform. Results of an initial simulation-based evaluation are also presented. © 2012 IEEE.

Tinga T.,Netherlands Defence Academy
Reliability Engineering and System Safety | Year: 2010

The efficiency of a preventive maintenance process largely depends on the ability to predict the replacement intervals of components. Considering the actual usage of the system increases the accuracy of this prediction. The present paper proposes two new maintenance concepts, that combine the benefits of traditional static concepts and condition based maintenance. These new concepts, usage based maintenance and load based maintenance, apply usage or load parameters that are monitored during service to perform a physical model-based assessment of the system condition. The new concepts are positioned within the range of existing maintenance concepts. Also, the role of physical models in maintenance modelling in general is explained and the origin of uncertainty in the predicted service life is discussed. Moreover, it is demonstrated how the monitoring of usage, loads or condition can reduce this uncertainty and increase the service life, by extending existing work in this field. Finally, the different concepts are applied to a gas turbine blade case study to illustrate the benefits of the proposed concepts. © 2010 Elsevier Ltd. All rights reserved.

Jansen J.M.,Netherlands Defence Academy
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2013

Although the λ-calculus is well known as a universal programming language, it is seldom used for actual programming or expressing algorithms. Here we demonstrate that it is possible to use the λ-calculus as a comprehensive formalism for programming by showing how to convert programs written in functional programming languages like Clean and Haskell to closed λ-expressions. The transformation is based on using the Scott-encoding for Algebraic Data Types instead of the more common Church encoding. In this way we not only obtain an encoding that is better comprehensible but that is also more efficient. As a proof of the pudding we provide an implementation of Eratosthenes' prime sieve algorithm as a self-contained, 143 character length, λ-expression. © 2013 Springer-Verlag Berlin Heidelberg.

Lubbers B.,Netherlands Defence Academy
2016 European Navigation Conference, ENC 2016 | Year: 2016

For safety-of-life applications, such as landing an aircraft, the detection of ionospheric gradients is important both for the integrity of single frequency GBAS users as the availability for dual frequency users. In this paper an ionospheric gradient monitor is proposed, based on carrier phase observations. Carrier phase observations are very precise, but ambiguous. Although in aviation carrier phase ambiguity resolution is not yet commonly accepted, this research investigates whether it is possible to solve the ambiguities with acceptable success-rates in order to estimate and detect ionospheric gradients. © 2016 IEEE.

Koene L.,Netherlands Defence Academy | Papy A.,Royal Military Academy
25th International Symposium on Ballistics, ISB 2010 | Year: 2010

Ballistic gelatine is commonly used as a representative simulant for soft tissues of the human body. However, its exact mechanical properties are not well known. At three different 'low' velocities three different spherical projectiles of 20, 40 and 50 mm diameter were fired at ballistic gelatine from a distance of 3 m. The selected velocities are representative for so- called 'non-lethal' or 'less-lethal' projectiles. The projectiles were made from ABS plastic. The velocity of the projectile was measured at a distance of 1 m from the muzzle of the canon using a photoelectric counter chronometer. Positions and velocities of the projectile in the gelatine were measured as a function of time using a high-speed camera. The experimental data were fitted using AUTODYN® software to obtain physical properties of ballistic gelatine.

Van Der Wal A.J.,Netherlands Defence Academy
International Journal of General Systems | Year: 2013

One of the most challenging phenomena that can be observed in an ensemble of interacting agents is that of self-organization, viz. emergent, collective behaviour, also known as synergy. The concept of synergy is also the key idea behind sensor fusion. The idea often loosely phrased as 1+1>2, strongly suggests that it is possible to make up an ensemble of similar agents, assume some kind of interaction and that in such a system synergy will automatically evolve. In a more rigorous approach, the paradigm may be expressed by identifying an ensemble performance measure that yields more than a superposition of the individual performance measures of the constituents. In this study, we demonstrate that distributed decision making in a sensor network can be described by a simple system consisting of phase oscillators. In the thermodynamic limit, this system shows spontaneous organization. Simulations indicate that also for finite populations, phase synchronization spontaneously emerges if the coupling strength is strong enough. © 2013 Copyright Taylor and Francis Group, LLC.

Savelsberg R.,Netherlands Defence Academy
AIAA Modeling and Simulation Technologies (MST) Conference | Year: 2013

The People's Republic of China is reportedly developing an antiship version of its DF-21 ballistic missile, intended against aircraft carriers in particular. This missile, known as the DF-21D, follows a ballistic trajectory towards the approximate target coordinates. During re-entry, its maneuverable re-entry vehicle (MaRV) can be steered towards the target using control fins, guided by an on-board radar. If effective, this weapon may cause a shift in the naval power balance in the Pacific. The performance of the DF-21D is analyzed based on technical information from open sources and assuming that the MaRV is similar to the U.S. Pershing II MaRV. It is sufficiently maneuverable to ensure that, during the flight of the missile, the aircraft carrier cannot travel far enough to escape. If the ballistic trajectory is aimed to overshoot the aircraft carrier, the MaRV pitches down during the guided phase. In theory, the lateral acceleration can peak at almost 50 g and the MaRV approaches the target at a high speed (Ma ≈ 6) from almost directly overhead, which will make intercepting it extremely diffcult.

Tinga T.,Netherlands Defence Academy | Janssen R.,Netherlands Defence Academy
Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability | Year: 2013

Instead of performing maintenance at fixed intervals, the operational efficiency of assets can be improved significantly by taking into account the variations in usage and operating environment of the asset. In that way, the traditional static maintenance policy is replaced by a dynamic maintenance policy. In the present work, this concept is demonstrated by modeling the failure behavior of a rather complex multi-component system, i.e. a navy frigate. For this system, several non-identical subsystems are included. Some of the systems are unique on board, while others have been made redundant, which means that the criticality of the subsystems to the mission capability of the frigate varies. Moreover, the variation in deployment of the frigate in terms of mission types and operating environments is translated into various usage profiles for the subsystems. Simulations are then performed to obtain the optimal maintenance policy in terms of interval length and preventive maintenance threshold, given certain requirements for the deployability of the frigate in a certain period. Moreover, the sensitivity of the results for different subsystem initial service life times and variations in usage profile are investigated. The results show a clear dependence of the optimal interval on the mission program of the frigate and the subsystem failure behavior. © IMechE 2013.

Koene L.,Netherlands Defence Academy
Proceedings - 29th International Symposium on Ballistics, BALLISTICS 2016 | Year: 2016

Recently, in the Netherlands impact experiments were performed using flat wooden targets with different physical properties. Materials studied include Obeche, Meranti, Beech, Spruce, Pine, and Ipé. In these ricochet experiments 7.65 mm Browning (.32 Auto) and 9 mm Luger projectiles were used. In this paper the critical impact angle ac for bullet ricochet is studied using analytical models. For the modelling work physical properties of wood and the projectile relevant to ricochet will be discussed. In a first approximation, deformations and grain structure of the wood will be neglected. The bullet ricochets will be evaluated using the analytical ricochet models of Tate and Rosenberg et al. developed for impacting rods. However, the ricochet model of Wijk predicts the critical impact angle ac best. Possible reasons for differences between the model and experimental results are given.

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