Defence Science Journal
Not a member yet
3794 research outputs found
Sort by
Development of Subcarangiform Bionic Robotic Fish Propelled by Shape Memory Alloy Actuators
Get PDFIn this paper, a shape memory alloy (SMA) actuated subcarangiform robotic fish has been demonstrated using a spring based propulsion mechanism. The bionic robotic fish developed using SMA spring actuators and light weight 3D printed components can be employed for under water applications. The proposed SMA spring-based design without conventional motor and other rotary actuators was able to achieve two-way shape memory effect and has reproduced the subcarangiform locomotion pattern. The positional kinematic model has been developed and the dynamics of the proposed mechanism were analysed and simulated using Automated Dynamic Analysis of Mechanical Systems (ADAMS). An open loop Arduino-relay based switching control has been adopted to control the periodic actuation of the SMA spring mechanism. The undulation of caudal fin in air and water medium has been analysed. The caudal fin and posterior body of the developed fish prototype have taken part in undulation resembling subcarangiform locomotion pattern and steady swimming was achieved in water with a forward velocity of 24.5 mm/s. The proposed design is scalable, light weight and cost effective which may be suitable for underwater surveillance application
Impact and Ricochet of a High Speed Projectile from a Plate
Get PDFA computational study of a projectile (either 2024 aluminum or TiAl6V4 titanium alloy) impacting a plate (either titanium alloy or aluminum) is presented in this paper. Projectile velocity (ranging from 250 m/s to 1500 m/s) with varying impact angles are considered. The presence of ricochet (if any) is identified over the ranges of the projectile velocity and impact angle considered. For the cases where ricochet is identified, the ricochet angle and velocity are predicted as functions of the incident angle and the incident velocity. The numerical results are compared with an analytical solution of the ricochet problem. The analytical solutions are from a model developed to predict the ballistic ricochet of a projectile (projectile) penetrator. The dynamics and the deformation of an aluminum (or a titanium alloy) projectile impacting on a finite thickness titanium alloy (or aluminum) plate are simulated. The current work is interesting in that it looks in the field of ballistics of different material combinations than are traditionally studied. The present simulations based on detailed material models for the aluminum and the titanium alloy and the impact physics modelling features in the LS-DYNA code provide interesting details regarding the projectile/plate deformations and post-impact projectile shape and geometry. The present results indicate that for no cases (for specified incoming velocities and impact angles considered) can an aluminum projectile penetrate a titanium alloy plate. The ricochet ‘mode predictions ‘obtained from the present simulations agree well with the ricochet ‘mode predictions’ given in an analytical model
Application of Sigma Point Particle Filter Method for Passive State Estimation in Underwater
Get PDFBearings-only tracking (BOT) plays a vital role in underwater surveillance. In BOT, measurement is tangentially related to state of the system. This measurement is also corrupted with noise due to turbulent underwater environment. Hence state estimation process using BOT becomes nonlinear. This necessitates the use of nonlinear filtering algorithms in place of traditional linear filters like Kalman filter. In general, these nonlinear filters utilize the assumption of measurements being corrupted with Gaussian noise for state estimation. The measurements cannot be always corrupted with Gaussian noise because of the highly unstable sea environment. These problems indicate the necessity for development of nonlinear non-Gaussian filters like particle filter (PF) for underwater tracking. However, PF suffers from severe problems like sample degeneracy and impoverishment and also it is tedious to select an appropriate technique for resampling. To overcome these difficulties in PF implementation, the strategy of combining PF with another filter like unscented Kalman filter is proposed for target’s state estimation. The detailed analysis of the same is presented in comparison with other particle filter combinations using the simulation results obtained in Matlab
Effect of Hull Obliquity on Crew Protection, Mass and Space Occupancy of Light Armoured Vehicle
Get PDFApart from strengthening crew protective capability from gunfire, the hull obliquity in a light armoured vehicle (LAV) affects its weight and comfortable occupancy. Thus, it requires a critical design analysis for the obliqued hull. The study aims to present the optimal design analysis of an obliqued hull structure to ensure comfortable occupancy of the crew along with its minimum attainable weight and higher protection capability from the gunfire. Three geometric models (G1, G2, and G3) were investigated for the LAV hull’s optimal design. The analytical approach was used to investigate the hull obliquity’s effect, and the results were validated using experimental data reported by other researchers. Digital human modelling was adopted for validating the space adequacy of the hull. It was observed that the hull’s crew protection capabilities from the horizontal strike of armour piercing rounds/bullets were improved almost by half and double for G2 and G3, respectively, when compared with G1. The analytical results are also in good agreement with globally accepted experimental data at reasonable variations. The highest protection capability and comfortable occupancy for the targeted users can be achieved by G3 without affecting the mobility of LAV
CMAC Trained Optimum Mid course Guidance for Tactical Flight Vehicle
Get PDFThis paper discusses design and validation of neural network based mid-course guidance law of a surface to air flight vehicle. In present study, initially different optimal trajectories have been generated off-line of different pursuer-evader engagements by ensuring minimum flight time, maximum terminal velocity and favorable handing over conditions for seeker based terminal guidance. These optimal trajectories have been evolved by nonlinear programming based direct method of optimisation. The kinematic information of both pursuer and evader, generated based on these trajectories have been used to train cerebellar model articulate controller (CMAC) neural network. Later for a given engagement scenario an on-line near optimal mid-course guidance law has been evolved based on output of trained network. Training has been carried out by CMAC type supervisory neural network. The tested engagement condition is within input/output training space of neural network. Seeker based homing guidance has been used for terminal phase. Complete methodology has been validated along pitch plane of pursuer-evader engagement. During mid-course phase, the guidance demand has been tracked by attitude hold autopilot and during terminal phase, the guidance demanded lateral acceleration has been tracked by acceleration autopilot. System robustness has been studied in presence of plant parameter variations and sensor noise under Monte Carlo Platform
Choice of Interceptor Aerodynamic Lifting Surface Location based on Autopilot Design Considerations
Get PDFInterceptors operate at wide range of operating conditions in terms of Mach number, altitude and angle of attack. The aerodynamic design caters for such wide operating envelope by appropriate sizing of lifting and control surfaces for meeting the normal acceleration capability requirements. The wide range of operating conditions leads to an inevitable spread in center of pressure location and hence spread in static stability. The performance of control design is a strong function of the aerodynamic static stability. The total operating envelope can be bifurcated into statically stable and unstable zones and the aerodynamic lifting surface location can be used as a control parameter to identify the neutral stability point. During the homing phase lesser static stability is desirable for good speed of response, hence the lifting surface location needs to be chosen based on the capability of control to handle instability. This paper analyses the limitations of autopilot design for the control of an unstable interceptor and brings out a method to identify the optimum aerodynamic lifting surface location for efficiently managing static margin while satisfying the control limitations and homing phase performance. This provides an input on the most appropriate lifting surface location to the aerodynamic designer during the initial CFD based aerodynamic characterisation stage itself, before commencing the rigorous wind tunnel based characterisation
Hematite Suspension based Absorbent Pad Inclined Slider Influenced by Slip and Squeeze Velocity with Altering Film Ratio
Get PDFThe effects of various entities like slip and squeeze velocities, inlet-outlet film ratio, and the material parameter have been fairly explored in a hematite suspension based absorbent (porous) pad inclined slider. Mathematical expressions for pressure, load capacity (lifting force), friction, friction coefficient, and position of centre of pressure (COP) in terms of the above physical parameters have been acquired. Jenkins model has been employed as a mathematical set of governing equations. It has been found that an increase in the squeeze velocity has enhanced the load capacity and diminished the friction coefficient whereas the escalating values of slip velocity and material properties have reversed the trends. Besides, the optimum value of the inlet-outlet film ratio for maximum load capacity has reduced with a rise in the squeeze velocity. Improvement in material parameters shifted the position of COP slightly towards the inlet while an enhancement in the squeeze velocity and film ratio shifted the same slightly towards the outlet. The results acquired in the present paper will be helpful in designing and modifying the various types of fluid dynamic slider bearings
The Effect of Co doping on Structural, Optical and Dielectric Behaviour of TiO2 Nanoparticles
Get PDFChemical precipitation method was used to synthesise pure and Co-doped TiO2 nanoparticles. The synthesised nanoparticles were studied for its structural optical and dielectric properties. X-Ray diffraction (XRD) confirmed the anatase phase with the tetragonal structure obtained for both samples. No extra peak was obtained in the pattern indicates that cobalt ions were successfully incorporated. The crystallite size of both samples were determined by using Debye-Scherrer’s method, and it was found that it decreases with the dopant addition. UV vis spectroscopy was performed to study the optical properties of both samples. The dielectric constant (εʹ), dielectric loss and ac conductivity (σac) of both samples were studied against the frequency. The dielectric constant, dielectric loss and ac conductivity results showed that Co-doping has a significant effect
Multipaction Susceptibility Margins in Space Travelling wave Tubes
Get PDFStudy of multipaction breakdown margins in the output connector of a travelling-wave tube (TWT) is essential for application in satellite-borne systems. A TWT uses a coaxial ceramic window, a coaxial output coupler and / or a waveguide output coupler that are prone to multipaction breakdown boosted by high RF power due to the ion accumulation in critical regions during the transition of the satellite through plasma pockets in space. A detailed procedure for estimating the multipaction susceptibility margins in a TWT using CST studio and analytical equations is presented in this paper, and output couplers of two typical TWTs are analysed and the results are presented