Defence Science Journal
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Delamination Buckling of Composite Conical Shells Under External Pressure
Get PDFAirframe construction in conical form is the most desired shape of flight hardware due to their low drag profileand are located at the fore-end region of flight vehicles encountering high drag loads. Owing to their tailoringcapability, materials with orthotropic mechanical properties are preferred choice. Delamination defects formed inthem while manufacturing or when subjected to loads would unfavorably influence the mechanical performanceof the orthotropic airframe. In the current work, FE simulation of delamination which is embedded in orthotropiccone shaped shells under external pressure load is performed as per the method cited in published literature. A layer wise element based on shell theory has been used and the effect of delamination size and its through the thickness position on the mechanical performance of the cone shaped shell is investigated. Circumferential and rectangular shapes of defects have been simulated. The investigation is performed for metal and composite materials with 3 types of stacking sequences generally used in practical designs. Verification of the procedure is carried out by equating with the procedure cited in published studies on shells of thin orthotropic cylinders. The eigen value of the first mode is taken as the critical buckling factor under external pressure. The buckling factor of the delaminated cone is normalized with the buckling factor of the ideal cone. The normalized buckling factor is showed graphically with the normalised defect size. Global, as well as local buckling and also symmetric as well as asymmetric buckling shapes, are observed in the results of the simulation. Shift from global mode to local mode of buckling is also observed in certain cases. Drastic reduction in buckling capability with the local mode is observed when the defect location is close to the surface and more prominent for an outer surface case
Life Saving Aspects of Pilot for Escape Aid Explosive (EAX) System Applications Some Considerations
Get PDFThis manuscript deals with life saving aspects of the pilot for escape aid explosive (EAX) system applicationsunder emergency situation. During the ejection from the aircraft, the pilot is subjected to the various forces suchas linear, angular and transverse accelerations, decelerations, wind drag accelerations, wind blast, dynamic forces,aerodynamic forces, spinning and tumbling. Linear accelerations (decelerations) of major interest in aviation arethose of a high magnitude and a short duration that occur in emergency ejection from the aircraft or occasionallyin a high altitude at high-speed parachute opening, as they tend to exceed the strength limitations of the skeletalstructure of the pilot body. The human body is a heterogeneous mass that is made up of solid, liquid and viscoelastic components. The effects of these forces on the pilot’s body are crucial in nature and significant pertains toan injury. This article is described with some considerations of ballistics, kinematics with different forces and theireffects on the pilot body for aircraft applications during an entire flight trajectory. In conclusion, this kind of studyis very essential considering the pilots safety and its performance at low and high altitudes during an emergency
Detection of Abnormal Vessel Behaviours Based on AIS Data Features Using HDBSCAN+
Get PDF Achieving maritime security is challenging due to the vastness and complexity of the domain. Monitoring all Achieving maritime security is challenging due to the vastness and complexity of the domain. Monitoringall vessels that use this medium is humanly impossible but is needed for law enforcement. This paper proposes amachine learning solution based on HDBSCAN+ to classify the movements of vessels into ‘normal’ or ‘abnormal’.This classification reduces the number of vessels that have to be monitored by law enforcement agencies to amanageable size. To date, AIS is the primary source of information that can represent vessel movements andenable the detection of maritime anomalies. The proposed model uses latitude, longitude, type of vessel, courseand speed as features of the AIS data for analysis. The performance of the proposed model is validated against the marine incidents reported by Information Fusion Centre-Indian Ocean Region (IFC-IOR). The proposed model has successfully detected the incidents reported by IFC-IOR
Technological Perspectives of Countering UAV Swarms
Get PDFConventional AD systems have been found less effective for countering UAVs and loitering munitions. Thishas necessitated the development of counter-UAV systems with different functionalities. A cluster of armed UAVsas swarm formations has further rendered the conventional AD systems far from effective, emphasizing the need to consider countering swarms as the most crucial element in new-generation aerial threat mitigation strategies. In this paper, the capabilities of UAV swarms and vital military assets exposed to such attacks are identified. To protect the vital assets from aerial swarm threats, ideal system characteristics of a counter-UAV (C-UAV) swarm system to overcome the challenges are discussed. Currently available acquisition & engagement technology is analyzed and the application of these systems to counter swarm applications is brought out. New requirements are discussed and a conceptual design of a layered system is derived which can handle a large spectrum of aerial threats including a swarm of UAVs. This system is expected to have a higher rate of engagement and can be designed with low-cost network-integrated systems
Estimation of Trajectory of High speed Artillery Shell
Get PDFThis paper presents a novel technique that uses the stereoscopic arrangement of multiple cameras to determine the trajectory of a high-speed projectile. It can be used to detect and track artillery shells moving at high speed in the air toward friendly territory. A system with the proposed concept can enhance retaliation success in battlefield countermeasures. There are many state-of-the-art Radar-based systems to detect moving artillery shells and mortars, but the cost and size of those products make them not so easily deployable in all kinds of terrains. A system with multiple cameras is discussed in this paper as an alternative solution. The experimental results, after algorithms were applied to simulated videos of expected scenes showed that the proposed technique is feasible. The proposed technique is fast and accurate and can be converted into deployable hardware. It can lead to realizing a system that has utility in saving precious lives in critical circumstances
Design and Verification of Carefree Maneuvering Protection for a High Performance Fighter Aircraft
Get PDFFlight envelope protection for a high-performance aircraft poses a challenge to the designers and involves a time-consuming procedure to verify the provided protection. This paper presents a design approach to protect the aircraft from departure by a command path limiter for a rate command attitude hold controller in both the pitch and roll axes. In this approach, the maximum and minimum rates are scheduled as a function of the dynamic pressure on the basis of the open loop aircraft capabilities. This is then augmented with a novel angle of attack protection that comes into play only when the pilot inputs cause the aircraft to exceed the incidence on the positive or negative side (one sided protection), while maintaining the rate command attitude hold behavior within the normal operational bounds of angle of attack. Traditional methods of piloted simulation with a representative cohort of pilots can be time consuming to set up and may not give sufficient confidence whether a departure protection scheme is effective. To address this, a unique multi-modal search using genetic algorithm is developed to verify that this command path protection is able to achieve carefree maneuvering of a fighter aircraft in its entire flight envelope. The sequence of rapid pilot control inputs is coded into a chromosome. The multi-modal genetic algorithm then uses operators like cross-over and mutation on a starting population of chromosomes to evolve new inputs sequences which are then run to obtain the aircraft response. The cost function of the genetic algorithm which is constructed from the aircraft time response is designed to favor the search for multiple maxima which drive the aircraft to departure. The open domain ADMIRE model has been used to demonstrate the approach. Results indicate that the command path design proposed in this paper can be used to protect against departure and the novel multi-modal genetic algorithm helps to verify the departure protection
A Low Noise Variable Gain Amplifier with 97.2 dB Linear Gain Range for CW Radar
Get PDFThis manuscript reports the design of a low noise variable gain amplifier (VGA) having wide dB linear gain characteristics for a continuous wave (CW) radar. A pseudo-exponential gain control function has been adopted in this VGA for the wide dB-linear behavior. Also, a BJT-based gain stage has been proposed to improve the gain dynamic range and low noise performance due to its higher transconductance/gain and lower flicker noise contribution. This proposed 2-gain stage VGA has been implemented in 130 nm SiGe bipolar complementary metal–oxide–semiconductor (BiCMOS) technology. This design performance has been benchmarked by post-layout simulation results. It has demonstrated a voltage-controlled gain from -33.6 dB to 74.4 dB (total 108 dB), with a 97.2 dB linear gain range, input referred noise of 2.4 nV /√Hz, and power consumption of 4.25 mW. This VGA has a 3-dB bandwidth of 10 MHz at a maximum gain of 74.4 dB and 251 MHz at a minimum gain of -33.6 dB with a chip layout area of 0.0682 mm2 . Compared to the latest available CMOS/BiCMOS VGAs in the literature, this proposed VGA has the highest gain dynamic range and dB-linear gain range with minimum input referred noise simultaneously across the operation bandwidth
Hybrid Composites for the Design and Development of Pressure Vessel for Underwater Applications
Get PDFThe study’s main objective is to design and develop pressure vessels in underwater applications using Hybrid composites-Fibre Metal Laminates (FML) so that the weight will be reduced. The proposed pressure vesselaccommodates electronics in the underwater ambient noise measurement system under an external hydrostatic pressure of 1 MPa (10 bar). The research study aims initially to design and develop a pressure vessel with stainless steel 316 L and subsequently design a pressure vessel with hybrid composites with a combination of composite materials of E-glass and carbon/epoxy materials with a metal alloy stainless steel 316 L. The pressure vessel has been optimised with varying metal and composite percentage combinations. The cylinder’s wall thickness has been pivotal in optimizing pressure vessel design. Classical Laminate Theory (CLT) transforms the FML pressure vessel or cylinder into a rectangular plate. As preliminary measures, FML specimen with a size of 0.45 m square laminate and 0°orientation has been developed with 50 % metal layer and 50 % fibre composites, and corresponding mechanical tests have been carried out as per the standards. The tensile strength of the developed FML is 420 MPa compared to base metal (SS316 L) strength of 556 MPa, and similarly, Flexural and Impact properties have shown a higher level when compared to other types of FMLs
Gait Parameter Tuning Using Bayesian Optimization for an Alligator Inspired Amphibious Robot
Get PDFThis paper reports a sample-efficient Bayesian optimization approach for tuning the locomotion parameters of an in-house developed twelve degrees of freedom alligator-inspired amphibious robot. An optimization framework is used wherein the objective is to maximize the mean robot speed obtained via physical experiments performed on terrains with varying friction and inclinations and in the aquatic environment for swimming locomotion. We obtained an improvement in the mean robot speed by a factor of up to 6.38 using the developed approach over randomly generated locomotion parameters in 15 iterations.
 
Design and Performance Analysis of a Switched Reluctance Motor Using Finite Element Analysis and Magnetic Equivalent Circuit Model
Get PDFBy being magnet-free, and mechanically robust with a longer constant power range, switched reluctance motor (SRM) is gathering much attention as a potential choice to propel electric vehicles (EVs) and hybrid electric vehicles (HEVs). This paper comprehensively investigates the performance sensitivity to geometric design variables such as rotor diameter, pole arc angles, and yoke thicknesses for an SRM using static two-dimensional (2D) electromagnetic Finite-Element Analysis (FEA). The reason for the change in static characteristics due to variation in reluctance between SRM designs has not been detailed previously. This is addressed by the magnetic equivalent circuit (MEC) model that simplifies the design analysis. Results indicate that stator pole reluctance needs to be given due importance while studying the influence of rotor diameter. Also, it is imperative to set an adequate thickness of the stator and rotor yokes to minimize the effect of saturation on the performance. Rotor diameter and stator pole arc angle have a pronounced influence on the performance while the influence of rotor pole arc angle and yoke thicknesses was relatively less