Defence Science Journal
Not a member yet
3794 research outputs found
Sort by
Simulation Model for Studying the Effect of Function Distribution on the Evaluation of Building Damage Caused by Missile Attack
Get PDFWhen a building is hit by a missile, the most important parts are usually destroyed first to achieve maximum damage to the functions of the building. To accurately quantify the damage to a building, a function distribution density is constructed to describe the importance of different parts, and is applied to the probability damage calculation of a building under a missile strike. Based on the objective characteristics, the building is divided into several modules. The importance of the different modules is calculated using the damage tree. The distribution densities of the physical and system functions are constructed separately and combined into the function distribution density of the building. Meanwhile, the landing points of the missile are simulated using the Monte Carlo method, and depending on whether the function distribution density is considered, a probability damage calculation is performed. In comparison, the calculation results considering the function distribution density have a larger irregular shape, which can describe the damage to the building more accurately. This study can provide support for improving the physical protection of buildings and ensuring the operational reliability of their functions
Novel Dual Band Frequency Selective Surface and its Applications on the Gain Improvements of Compact UWB Monopole Antenna
Get PDFIn this work, a highly directional ultra-wideband (UWB) microstrip patch antenna as a single-element is suggested. The proposed antenna’s gain is enhanced with a novel dual-band frequency selective surface (FSS) placed beneath it. The FSS design has a hexagonal structure with meander line inductances and a capacitance-like structure connecting all of the corners to the middle. There is no metallic layer on the other side of the substrate, which shows transmission zeros at 4.95 GHz and 12.7 GHz, and a modified U-shaped monopole antenna is developed. First, the performance characteristics of the antenna and FSS are analyzed from the simulation results, and they are validated experimentally after fabrication, followed by measurement. The compact configuration comprises an antenna loaded with the proposed FSS results S11 less than -10 dB from 3.15 GHz to 22.65 GHz, covering the UWB band together with the X, Ku-band with a bandwidth of 19.5 GHz (151.16% FBW). The antenna’s overall physical dimensions would be 38.8 mm×38.8 mm×25.2 mm (0.407λo×0.407λo×0.265λo), with λo denoting the lowest frequency’s free-space wavelength. The FSS loading results in a 9.9 dBi maximum gain at 10 GHz. The antenna’s small size increases bandwidth, and its high peak gain makes it ideal for use in real-time applications
Aero structural and Electromagnetic Design Optimisation of Maritime Patrol Aircraft Radome Using Direct Search Algorithms
Get PDFAirborne surveillance systems such as Maritime Patrol Aircraft are deployed by armed forces to collect surveillance information on airborne and sea surface enemy targets. Airborne Electronically Scanned Array Radar is an electromagnetic sensor integrated on this aircraft. The antenna of this radar is installed generally in belly of a turboprop aircraft. An electro-magnetically transparent cover, called radome, protects this antenna to protect itfrom various environmental effects, like rain, dust, etc. Installation of the radome results in additional drag, weightand electromagnetic signal loss. The Pareto optimality involving three design disciplines of structure, erodynamicsand electromagnetics is attempted with direct search optimisation algorithm NSGA II
A Frequency Tunable Dielectric Resonator Antenna with Reduction of Cross Polarisation for Wi MAX and Sub 6 GHz 5G Applications
Get PDFA frequency Tunable (mechanical tuning) Linearly Polarized (TLP) rectangular Dielectric Resonator Antenna(DRA) coupled with a horizontal/vertical-slot and excited with circular-ring type feed is investigated in this article.The frequency tunability (mechanical tuning) is achieved by the rotation of slot at different angles of the proposedstructure. Hence, two linearly polarized antennas have been proposed for different frequency bands such as Wi-MAX and Sub-6 GHz/5G, respectively, using slot variations (named as DRA-1 and DRA-2). TE 11δ mode has been excited in both the DRAs and confirmed by orientation of electric field inside the rectangular DRA. The measured -10 dB input impedance bandwidths of DRA-1 offer 21.60 % being centered at 2.87 GHz and the separation of co-polarized and cross-polarized field levels is above -24 dB in the broadside direction (xz-plane). Whereas DRA-2 offers measured -10 dB input impedance bandwidths of 23.03% being centered at 3.56 GHz having a separation of co-polarized and cross-polarized field levels are above -23 dB in the broadside direction (xz-plane). In addition, the proposed DRA-1 and DRA-2 show a maximum gain of 5.23 dBi and 4.75 dBi in broadside direction, respectively
Rapid and Accurate INS Transfer Alignment for Air Launched Tactical Missile Using Kalman Filter
Get PDFAn Inertial Navigation System (INS) independently measures the Position, Velocity, and Attitude (PVA) of thevehicle to navigate it towards the target. Since INS is a dead-reckoning system, it requires accurate initialization toprovide the navigation (PVA) solution. In the case of an air-launched tactical missile, the aircraft navigation system(Master INS) information is used to initialize accurately the missile INS (Slave INS). Rapid transfer alignment isneeded in today’s combat operation to converge slave INS initialization in the shortest possible time using aircraftnavigation information. The transfer alignment consists of first initializing the missile INS and establishing anavigation solution (PVA) using the missile IMU rates and accelerations, then a Kalman filter is used to, estimatethe errors between the Slave INS and Master INS. The proposed method’s simulation results show that a tacticalmissile INS can be aligned to an acceptable accuracy in a very short time based on the aircraft’s attitude information and with natural maneuvers experienced during aircraft take-off
Monopole Cavity Resonator Antenna with AMC and Superstrate for 5G WiMAX Applications
Get PDFFor 5G and WiMAX applications, a coplanar waveguide (CPW)-fed monopole antenna sandwiched between an artificial magnetic conductor (AMC) and a superstrate is investigated. Because traditional planar antennas have low gains, they are unsuitable for a wide range of applications. This paper explores scientific strategies for increasing radiation gain in low-gain antennas such as planar monopoles. We use AMC in conjunction with superstrate to achieve a high gain antenna, with the monopole antenna serving as the primary radiator. However, a superstate like this demands the use of materials with high permittivity, and most of such materials are not readily available on the market. Even if such materials are available, they are mostly expensive and unsuitable for commercial systems. We investigate various superstrates and elaborate on which way these superstrates can be used interchangeably without compromising antenna performance. In the end, we fabricate one of these three superstrates. The antenna, which also employs AMC in tandem with the superstrate, has an impedance bandwidth ranging from 3.2 GHz to 3.75 GHz with 7 dBi gain, so it can be a viable candidate for 5G and WiMAX application
Machining and Tribological Characterisation of Uncoated and Coated Carbide Inserts while Turning Tungsten Heavy Alloy
Get PDFTungsten heavy alloys are high density alloys containing 80 to 98 wt.% tungsten and the balance is a matrix made of relatively low melting elements such as copper, nickel and iron. These alloys are used as radiation shields, CG adjusters and also in armour piercing ammunition. Machining these alloys to close tolerances and finish leads to excessive tool wear, surface damage and hence proves to be a challenging task. This study focuses on turning operation carried out under dry and wet cutting conditions using three different commercially available cemented carbide inserts. Three different feed rates have been used at a constant depth of cut and cutting speed. The best possible cemented carbide tooling solution for machining tungsten heavy alloys has been determined based on the surface finish obtained, chip geometry, cutting forces, and machining temperature. The observations made during machining are correlated to the tribological behavior of the inserts and the alloy with the help of pin-on disc tests. Coated cemented carbide inserts provide surface roughness values lower than 1 µm under finish turning conditions. On the other hand, PVD coated inserts give consistently better results over different feed rates and are found to experience lower tool wear for the specific cutting conditions. Analytical tool wear model suggests better tool life for the PVD coated insert
Experimental and Computing Methods to Determine the External Surface Temperature of the Small Arms Weapon Systems Barrel
Get PDFThe need to determine the small arms weapon system barrel temperature under a variety of conditions makes modelling and simulation a good alternative to the expensive real tests. Therefore, in a unique way, this paper includes three alternatives to assess the external surface temperature in order to better understand the balance between the chosen calculation method accuracy and the computed time. For numerical simulations, the initial conditions were established based on STANREC 4367 thermodynamic interior ballistic model. The heat transfer was solved for One-Dimensional and Two-Dimensional model using the finite difference discretisation method, with code written in Matlab. The Three-Dimensional model was resolved by finite element analysis method in Ansys. The simulations results are validated by means of the results obtained in case of two real firing scenarios. During the field testing, a new detection method based on shockwaves microphones was used in order to exactly establish the moment of each shoot and to precisely observe the temperature evolution on barrel surface
Computational Studies of the Aerophysical Characteristics on the Head Part of the Supersonic Body of Rotation During Flight Along Trajectories
Get PDFThe use of modern computer systems for calculating the aerophysical characteristics of supersonic bodies of revolution together with the calculation of the flight trajectory under conditions of continuously changing Mach and Reynolds numbers of the oncoming flow, the presence of transient regimes and non-isothermality in near-wall flows is often not possible due to the complexity of the organisation of the computational process. By using a number of integral methods for calculating inviscid flows and viscous compressible near-wall flows, taking into account the non isothermality and intermittency of the boundary layer, a method has been developed for calculating the friction and heating of supersonic bodies of revolution on the flight trajectory. On the basis of well-known flight experiments, the correlation dependences of the Reynolds numbers of the beginning of the transition on sharp cones were obtained and the method of corrections for spherical blunting of the head part was implemented. By calculating the intermittency function, the changeability of flow regimes in the boundary layer is established for a number of trajectories of the supersonic uncontrolled rocket projectile. Calculated dependences for aerodynamic friction, heat fluxes and projectile wall temperature on the flight time are obtained. The concept of combined calculation of aerophysical characteristics on the flight trajectory using numerical and integral methods is proposed
A Planar Dual Notched Band Vivaldi Antenna for Wireless Communication Applications
Get PDFWith the aim of realizing a Vivaldi Antenna (VA) with stop bands for wireless communication applications, this paper introduces a novel, uncomplicated, easily fabricated, and compact planar VA featuring two distinctive rejected frequency bands. The designed VA is engraved onto an FR4-epoxy substrate, measuring 0.4243λ0×0.4296λ0 ×0.01315λ0 at 2.63 GHz. The integration of dual notched band functionality is ingeniously achieved through the implementation of a simple additional strip and a U-formed slit. A physical prototype of the VA was successfully constructed and meticulously measured with the R&S®ZNB Vector Network Analyser. The measured impedance bandwidth demonstrates that the realised VA operates from 2.63 GHz to beyond 12 GHz while effectively excluding two bands: 3.46-4.16 GHz (18.37 %) and 5.32-6.5 GHz (19.97 %). Simulated results indicate that the designed VA can provide stable unidirectional radiation patterns, reasonable realized gain, and acceptable radiation efficiency across its operating ranges, with notable drops observed at the two notched bands. As a result, these findings highlight the practical value of the designed VA for wireless communication applications, particularly in scenarios where the integration of filtering structures in antennas becomes essential to prevent interference with co-existing systems. The presented VA opens new avenues for enhancing wireless communication performance, catering to the increasing demand for reliable and interference-resistant solutions