AiMT Volume 13 (2018), Issue 1

Deciding DUT Proper Functionality in Non Metrological Measurements

Z. Růžička

Establishing the criterion for whether a device under test (DUT) operates correctly or not is a complex issue. For devices used in a military setting, it is essential to know if the equipment will perform accurately under adverse conditions. In this paper, the example of testing resistive temperature sensors demonstrates how to manage the evaluation of errors expressed as uncertainties and tolerances. These sensors’ errors are used to address the total standard uncertainty, to determine the effective degree of freedom and to determine the coverage probability for deriving the coverage factor to establish the Student’s quantile as the specific criteria relating to the DUT results.

Keywords: RTD’s class of accuracy, expanded uncertainty, tolerance, standard uncertainty, dynamic error, coverage probability, coverage factor.

Pages: 5–12  [References]   [Download Citation]

TECHNICAL INFORMATION
Measurement of Pressure Field on Stationary Rotary Wing Model for Further Computation of Chaff Cloud Bloom

J. Žák, D. Rozehnal, J. Hnidka, M. Mach and F. Dvořáček

This article describes the current situation in the area of electronic warfare. Aircraft protection can be greatly utilised not only in military but also in civilian applications. Active radar signal jamming methods are costly and therefore, aircraft protection using Chaff jamming increases efficiency, application variability and makes aircraft protection affordable. The article describes Chaff and the initial set of measurements designed for measuring aerodynamic pressure around a stationary helicopter model. This data lays foundations for the direction of further development, which is introduced at the end of the article.

Keywords: chaff, jamming, self-defence, aerodynamic pressure

Pages: 13–21  [References]   [Download Citation]

Possibilities of Assessing Objectively a Flight Illusion Effect on a Pilot’s Spatial Orientation

J. Boril, V. Smrz and R. Jalovecky

The pilot’s spatial orientation, the same as the one of any other human, relies on a combination of stimuli coming from their audio-visual, vestibular and proprioceptive perception systems. However, these instinctive perceptual methods can easily fail while pilot is perceiving real changes of attitude, position or movement and they can also generate false illusions to each of the aforementioned parameters. This failure in a real flight is called “flight illusion” which can negatively affect the pilot’s spatial orientation. The influence of a flight illusion on the pilot’s spatial orientation can be assessed either subjectively or objectively. The aim of this paper is to demonstrate one of the possible objective assessments of the flight illusions influence on the pilot’s spatial orientation using the flight data generated by an appropriate flight simulator which were analysed in MATLAB® software. The chosen method is based on a comparison of the digitalized standard instrument flight trajectories with the real flown trajectories in the time interval with potential flight illusion influence.

Keywords: flight illusion, spatial orientation, flight data analysis, flight simulator, simulator-based training, flight safety

Pages: 23–32  [References]   [Download Citation]

Identification of Concrete Material Model Parameters Using Optimisation Algorithms

P. Král, M. Hušek, P. Hradil, J. Kala and P. Maňas

The application of nonlinear material models of concrete within numerical simulations focused on the design of safer and more economical protective concrete structures is currently the subject of investigation of many scientific researchers. However, one basic problem related to the nonlinear modelling of concrete is that very often there is a lack of knowledge about the material model parameters whose values must be defined. The solution to this problem can be in what is termed as inverse parameter identification, an approach which is presented in this paper. Specifically, the material parameters of the Continuous Surface Cap Model for concrete are identified within this paper using optimisation algorithms. The subsequent comparison of parameter identification results with experimental data shows the efficiency of the presented approach.

Keywords: LS-Dyna, material model of concrete, numerical simulation, optiSLang, parameter identification

Pages: 33–45  [References]   [Download Citation]

Experimental Investigation of CFRP Impact Toughness and Failure Modes

O. Flášar

The experimental investigation assesses the capability of Carbon Fibre Reinforced Plastics (CFRP) to absorb impact energy. The method is based on measuring impact toughness of unnotched beam specimens made of laminates with woven and unidirectional reinforcement in either cross-ply [0/90]n or angle-ply [±45]n orientation using impact pendulum testing machine. Low-velocity impact produces interlaminar and intralaminar failures of beams which affect their energy absorptions. The resulting energy absorptions are evaluated from force-displacement curves and subsequently discussed using assessment of loading processes and final failure modes.

Keywords: composite, impact, pendulum, impact toughness, bending, failure mode

Pages: 47–58  [References]   [Download Citation]

Influence of Impact Velocity and Steel Armour Hardness on Breakage of Projectile 14.5×114 API/B32

R. Mikulikova, R. Ridky, S. Rolc and J. Krestan

The goal of this article was focused on the study of projectile breakage after impact on steel armour depending on projectile impact velocity and steel armour hardness. Steel armour samples of hardness HBW500 and HBW600 were impacted by steel core projectile 14.5×114 API/B32 using three different impact velocities. The depth of the projectile penetration into steel armour of hardness HBW400, which was placed 65 mm behind the steel armour samples, was measured. The projectile remains after each impact were searched for their evaluation. For better visualization of the projectile breaking process after the impact on steel armour, the numerical simulations were performed. Experimental and numerical results were compared and combined in a graph showing the dependence of the depth of penetration on the projectile impact velocity for two different steel armour hardnesses and with indication of projectile coherence after impact.

Keywords: projectile breakage, impact velocity, hardness, depth of penetration

Pages: 59–69  [References]   [Download Citation]

TECHNICAL INFORMATION
Determinants of Military Robotics Proliferation

A. Olejníček, J. Odehnal, V. Holcner and M. Krč

The aim of the article is to define and quantify the determinants influencing the proliferation of robotic technology into the armament of the national armies and their use in combat operations. At the same time, the article focuses on identifying those countries which will deploy and use these advanced military technologies. Based on the literary research and its analysis, four categories of factors have been identified as the ones having influence on the military robotics proliferation. From the results of the classification model, it is clear that 78 analysed countries were classified on the basis of defined determinants into three groups with different assumptions of proliferation of military robotics. Based on the result of the cluster analysis, it is evident that military robotics proliferation was mainly affected by economic determinants in cluster 1, by security and political determinants in cluster 2 and by political and economic determinants in cluster 3.

Keywords: military robotics, proliferation, security, political, military and economic determinants, cluster analysis, dendrogram

Pages: 71–86  [References]   [Download Citation]

Detection of Attacks Causing Network Service Denial

V. Ďurčeková, L. Schwartz, V. Hottmar and B. Adamec

This article deals with ICT security and particularly the Denial of Service (DoS) executed on the application layer. The main objective of the article is to describe the original algorithm designed for timely detection of DoS application attacks and, subsequently, on the results of experimental verification of the designed process. This algorithm is focused on the detection of HTTP GET Flood attack, which will cause a crash of the attacked server. Appropriate detection of attack from the analysis of incoming traffic is able to prevent a crash of server from happening. To detect such an attack, an original algorithm designed by our team was used.

Keywords: Denial of Service – DoS, Distributed Denial of Service – DDoS, HTTP GET Flood attack, algorithm, simulation, theory of queuing systems

Pages: 87–94  [References]   [Download Citation]

TECHNICAL INFORMATION
Evolution of Flight Data Recorders

M. Dub and J. Parizek

A flight recorder, commonly known as a black box, is considered the most important witness in the investigation of air accidents. Flight recorders have been considered important parts of onboard equipment for both military and civilian aircraft all over the world already from 1950s. They are used not only for flight evaluation after an unexpected event, but also for a pilot training, pilot skills assessment, diagnostics of on-board systems, and evaluation of aircraft systems as a whole. Thus, these flight recorders contribute to high aircraft reliability and aviation operation safety. This article focuses on Automatic Deployable Flight Recorders (ADFR), currently not often used in the military or civilian aircraft. ADFRs are mainly used for aircraft that fly over vast water areas as classic concept recorders were hard to find when the aircraft crashed into water. This deployable recorder is a reliable flight safety system used e.g. in US Navy F/A-18 multirole combat jets. In addition, creation of this article was inspired by the change in ICAO Standards and Recommended Practices for Operation of Aircraft, implemented in July 2016 in the tenth edition of ICAO Annex 6.

Keywords: aviation safety, flight data recorders, ICAO

Pages: 95–106  [References]   [Download Citation]

Concrete Targets with Heterogeneities under Impact Loading

M. Hušek, P. Král, J. Kala, P. Hradil and P. Maňas

The main aim of the paper is to present an elegant procedure for introducing heterogeneity to simplified computational models. A computational model is considered here to be theoretically any numerical model that includes material with structural strength. Heterogeneity then means the randomness in material parameters, which allows a simplified model to behave like the comprehensively described structure of a material. The whole procedure is explained using the example of a material model of concrete in the form of a concrete block (target) which is exposed to high-speed impact loading. Even though the described procedure for the introduction of heterogeneity to computational models can be applied during the use of practically all numerical methods, the Smoothed Particle Hydrodynamics (SPH) method will be used due to the type of loading involved. The creation of the presented procedure was prompted by the constantly increasing number of input parameters used with material models. Elementary material models with a minimum of inputs can be used when applying the procedure. The end of the paper deals with the improvement in use that enables heterogeneity (i.e. randomness of material structure) to be created in such a way that a simplified model reflects as much as possible the real material structure, not only the variations of mathematical functions.

Keywords: concrete, heterogeneity, impact, noise, Smoothed Particle Hydrodynamics

Pages: 107–118  [References]   [Download Citation]

Critical Crack Size Investigation Method for a Land Launcher

A. Yetgin, B. Acar and S. Kadioglu

Structural integrity evaluation of military systems is vital in such applications as rocket launchers. In safe life design, for a certain operational life the system is ensured to function well and no failure would occur even in the presence of some imperfections or flaws. This paper considers the fracture analysis as part of the safe life design approach that is used in the design of a rocket launcher. A methodology based on sub modelling technique is introduced. It was made sure that unstable crack growth would not occur upto certain crack sizes. Subsequently, after actual manufacturing of the launcher, critical locations of welds in the system were checked for presence of any cracks after repeated firing loads. After these controls no cracks were detected due to operational conditions until the time when this document was prepared.

Keywords: fracture mechanics, weld, finite element, launcher, structural integrity

Pages: 119–131  [References]   [Download Citation]