Showing papers by "Defence Research and Development Laboratory published in 2011"
TL;DR: In this paper, the buckling analysis of isotropic nanoplates using the two variable refined plate theory and nonlocal small scale effects is presented, which does not require shear correction factors.
112 citations
TL;DR: In this article, the wave dispersion behavior of a rotating nanotube using the nonlocal elasticity theory has been analyzed using an Euler-Bernoulli theory and it has been shown that the dispersive flexural wave tends to behave non-dispersively at high rotation speeds.
Abstract: The present work deals with the wave dispersion behavior of a rotating nanotube using the nonlocal elasticity theory. The rotating nanobeam is modeled as an Euler–Bernoulli theory. The governing partial differential equation for a uniform rotating beam is derived incorporating the nonlocal scale effects. The spatial variation in centrifugal force is modeled in an average sense. Even though this averaging seems to be a crude approximation, one can use this as a powerful model in analyzing the wave dispersion characteristics of the rotating nanobeam. Spectrum and dispersion curves are obtained as a function of rotating speed and nonlocal scaling parameter. It has been shown that the dispersive flexural wave tends to behave non-dispersively at very high rotation speeds. Understanding the dynamic behavior of rotating nanostructures is important for practical development of nanomachines. At the nanoscale, the nonlocal effects often become more prominent. The numerical results are simulated for a rotating nanobeam as a waveguide. The results can provide useful guidance for the study and design of the next generation of nanodevices such as blades of a nanoturbine, nanogears, nanoscale molecular bearings etc, that make use of the wave propagation properties of rotating single-walled carbon nanotubes.
84 citations
TL;DR: In this article, C-SiC composite Jet-Vanes were fabricated using liquid silicon infiltration and tested in a plume of aluminum-based solid propellant to study erosion resistance.
Abstract: C–SiC composite Jet-Vanes were fabricated using liquid silicon infiltration and tested in a plume of aluminum based solid propellant to study erosion resistance. The Jet-Vanes showed excellent resistance to thermo-oxidative erosion; average linear and mass erosion rates were 1 mm/s and 5 g/s, respectively. Morphology of the eroded surfaces suggests that alumina particles in the plume hit the leading edge of the Jet-Vane, damage it and some material is eroded away. Residual silicon melts and reacts with oxygen to form silica which in turn reacts with SiC matrix. The matrix of SiC, silicon and un-reacted carbon is loosened and erode by high shear forces. Once carbon fibers get exposed directly to the plume, these may be both eroded and oxidized.
52 citations
TL;DR: In this paper, the axial wave propagation properties of a coupled nanorod system with consideration of small scale effects were analyzed and explicit expressions were derived for the wavenumber, cut-off frequency, and escape frequency of nanorods.
Abstract: This article deals with the axial wave propagation properties of a coupled nanorod system with consideration of small scale effects. The nonlocal elasticity theory has been incorporated into classical rod/bar model to capture unique features of the coupled nanorods under the umbrella of continuum mechanics theory. Nonlocal rod model is developed for coupled nanorods. The strong effect of the nonlocal scale has been obtained which leads to substantially different wave behavior of nanorods from those of macroscopic rods. Explicit expressions are derived for wavenumber, cut-off frequency and escape frequency of nanorods. The analysis shows that the wave characteristics of nanorods are highly over estimated by the classical rod model, which ignores the effect of small-length scale. The studies also shows that the nonlocal scale parameter introduces certain band gap region in axial or longitudinal wave mode, where no wave propagation occurs. This is manifested in the spectrum cures as the region, where the wavenumber tends to infinite or wave speed tends to zero. The effect of the coupled spring stiffness is also capture in the present analysis. It has been also shown that the cut-off frequency increases as the stiffness of the coupled spring increases and also the coupled spring stiffness has no effect on escape frequency of the axial wave mode in the nanorod. This cut-off frequency is also independent of the nonlocal small scale parameter. The present study may bring in helpful insights while investigating multiple-nanorod-system-models for future nano-optomechanical systems applications. The results can also provide useful guidance for the study and design of the next generation of nanodevices that make use of the wave propagation properties of coupled single-walled carbon nanotubes or coupled nanorods. (C) 2011 Elsevier Ltd. All rights reserved.
51 citations
TL;DR: In this article, the spectral finite element (SFE) formulation of nanorods is performed and the exact shape functions (frequency dependent) and dynamic stiffness matrix are obtained as function of nonlocal scale parameter.
Abstract: In this article, the Eringen's nonlocal elasticity theory has been incorporated into classical/local Bernoulli-Euler rod model to capture unique properties of the nanorods under the umbrella of continuum mechanics theory. The spectral finite element (SFE) formulation of nanorods is performed. SFE formulation is carried out and the exact shape functions (frequency dependent) and dynamic stiffness matrix are obtained as function of nonlocal scale parameter. It has been found that the small scale affects the exact shape functions and the elements of the dynamic stiffness matrix. The results presented in this paper can provide useful guidance for the study and design of the next generation of nanodevices that make use of the wave dispersion properties of carbon nanotubes.
26 citations
TL;DR: In this article, a rotating single-walled carbon nanotube (SWCNT) is modelled as an Euler-Bernoulli beam using the non-local/non-classical continuum mechanics.
Abstract: In this study, a rotating single-walled carbon nanotube (SWCNT) is modelled as an Euler-Bernoulli beam using the non-local/non-classical continuum mechanics. These rotating SWCNTs are used in nanoscale rotational actuators. The mathematical model has been used to study the wave behaviour in rotating SWCNTs. The governingpartial differential equation for a uniform rotating beam is derived incorporating the non-local scale effects. The spatial variation in centrifugal force has been modelled in an average sense. Even though this averaging seems to be a crude approximation, one can use this as a powerful model in analysing the wave dispersion characteristics ofthe rotating CNTs. Spectrum and dispersion curves as a function of rotating speed and non-local scaling parameter were obtained. It has been shown that the dispersive flexural wave tends to behave non-dispersively at very high rotation speeds. The numerical results have been simulated for a rotating SWCNT as a waveguide. Defence Science Journal, 2011, 61(4), pp.317-324 , DOI:http://dx.doi.org/10.14429/dsj.61.1091
21 citations
TL;DR: In this article, an atomistic model of a hybrid lattice involving a hexagonal lattice of graphene and surface atoms of diamond lattice is developed to identify the carbon-silicon bond stiffness.
19 citations
TL;DR: In this paper, an ecofriendly cadmium- and chromate-free coating scheme comprised of zinc nickel alloy plating, trivalent chromium-based passivation, followed by a primer based on polyaniline phosphate, is studied for its anticorrosive properties.
12 citations
TL;DR: In this article, the authors used an indigenously developed three-dimensional Reynolds Averaged Navier Stokes solver with Roe's scheme and k-w turbulence model to simulate transverse sonic injection into supersonic flow in a confined environment.
Abstract: Staged transverse sonic injection into supersonic flow in a confined environment usually employed in scramjet combustor has been explored numerically using an indigenously developed three-dimensional Reynolds Averaged Navier Stokes solver with Roe's scheme and k-w turbulence model. Simulations were carried out for both without injection and with injection in Mach 2 flow behind a backward-facing step in a rectangular duct. Simulation captured all finer details of flow structures including recirculation bubble behind a backward-facing step, barrel shocks and Mach discs caused due to transverse injection and reattachment of shear layer in the downstream wake region. K-w turbulence model with compressibility correction performed extremely well in predicting the overall behaviour of the flow field. The jet from the second injector was found to penetrate more in the free-stream due to the loss of free-stream total pressure across the barrel shock of the first injection point. Excellent agreement of computed profiles of various flow parameters at different axial locations in the duct with experimental results and other numerical results available in the literature demonstrate the robustness and accuracy of the indigenously developed code. Defence Science Journal, 2011, 61(1), pp.3-11 , DOI:http://dx.doi.org/10.14429/dsj.61.20
10 citations
TL;DR: A series of combustion experiments have been conducted for investigating the regression rates of mixed hybrid propellants using Red Fuming Nitrous Acid (RFNA) as liquid oxidizer and Hydroxyl-Terminated Polybutadiene (HTPB) with the addition of Ammonium Perchlorate (AP) upto 20 percent as the solid fuel as mentioned in this paper.
Abstract: A series of combustion experiments have been conducted for investigating the regression rates of mixed hybrid propellants using Red Fuming Nitrous Acid (RFNA) as liquid oxidizer and Hydroxyl-Terminated Polybutadiene (HTPB) with the addition of Ammonium Perchlorate (AP) upto 20 percent as the solid fuel. HTPB is the state-of-theart binder used in solid propellant rocket motors and is considered to be a potential candidate fuel for hybrid rocket applications due to its higher regression rate characteristics, greater fuel value, higher carbon/hydrogen ratio and solid loading capability. One of the effective ways of increasing the regression rates in hybrids is the addition of solid oxidizer such as AP in the fuel in small percentages. This type of configuration is called "mixed hybrid" and regression rate enhancement upto 100% is obtained. A series of static tests are conducted to establish the ignition and combustion in the hybrid mode. It is seen that the hybrid propellant has burnt smoothly. The ignition pressure could also be controlled and kept to a reasonable value. Stable combustion within a variation of chamber pressure ±2% and combustion efficiency above 0.95 was achieved. The characteristics of the combustion products are calculated using the NASA CEA code. Regression rate correlations for the different combinations are obtained using the experimental data and ballistic code developed for predicting the performance of hybrid system.
6 citations
TL;DR: In this article, an aerodynamic characterization of the flight vehicle mounted on a fighter aircraft has been carried out using an in-house developed 3D grid-free Euler solver.
Abstract: NTEGRATION of a new weapon to a highly agile aircraft is an exigent task, as the weapon and its supporting systems should structurally endure during stern maneuvers of the aircraft. Fighter aircraft has maneuvering capability of about 9 g and, therefore, the support systems of flight vehicles (launcher, launcher rail, launch shoe, and adapter) on the fighter aircraft should be designed to withstand the loads experienced by the vehicle at critical maneuvering conditions. Guidelines for weapon-aircraft integration are provided through military specification MIL-STD-8591 [1]. The specification provides weapon design load requirements for unusual flightconditionsthatsometimeariseonspecificaircraft.Itisbasedon using actual or predicted aircraft flight performance data to examine the full flight envelope and generate consistent set of inertial and aerodynamic loads [2]. In the present work, aerodynamic characterization of the flight vehicle mounted on a fighter aircraft has been carried out using an in-house developed 3-D grid-free Euler solver [3]. Further, the numerical simulations are carried out to estimate the captive loads acting on the flight vehicle integrated with fighteraircraftatspecified flowconditionsandthemaximumloading conditions are identified. The load distribution is extracted at that condition to verify the structural integrity of the flight vehicle and supporting systems. Grid generation around a complex fighter aircraft is the most time consuming task in the numerical simulation and presence of flight vehicle poses a formidable challenge. A grid-free q-LSKUM [3] (entropyvariables-basedleast-squareskineticupwindmethod)Euler solver has been used for the computational fluid dynamics (CFD) analysis. The grid-free solver requires a cloud of points around the configuration and a set of neighbors around each point. The cloud of points was obtained by overlapping grids around fighter aircraft and flightvehicles.CADmodelsof flightvehicleand fighteraircraftwere imported, repaired, and cleaned up to obtain watertight solid models suitableforgridgeneration.Simpleunstructuredgridsaround fighter aircraft and flight vehicles are generated independently and then the grids are overlapped to get the distribution of points around the full configuration. An efficient preprocessor [4] has been developed and applied to generate the connectivity. A parallel version of the 3-D grid-free Euler solver q-LSKUM has been used to obtain the aerodynamic characteristics of the aerospace vehicle configuration. Inviscidsteady flowsimulationfor fighteraircrafthasbeencarried out using q-LSKUM code. The simulations at various Mach numbers, angles of attack, and sideslip angles have been carried out to obtain aerodynamic forces and moments acting on the integrated fighter aircraft with flight vehicles. The captive loads on all the four flight vehicles are computed at specified critical flow conditions.
TL;DR: In this paper, the authors present the design of a hybrid rocket motor and the experiments carried out for investigation of hybrid combustion and regression rates for a combination of liquid oxidiser red fuming nitric acid with solid fuel hydroxyl-terminated polybutadiene.
Abstract: This paper presents the design of a hybrid rocket motor and the experiments carried out for investigation of hybrid combustion and regression rates for a combination of liquid oxidiser red fuming nitric acid with solid fuel hydroxyl-terminated Polybutadiene. The regression rate is enhanced with the addition of small quantity of solid oxidiser ammonium perchlorate in the fuel. The characteristics of the combustion products were calculated using the NASA CEA Code and were used in a ballistic code developed for predicting the performance of the hybrid rocket motor. A lab-scale motor was designed and the oxidiser mass flow requirements of the hybrid motor for the above combination of fuel and oxidiser have been calculated using the developed ballistic code. A static rocket motor testing facility has been realised for conducting the hybrid experiments. A series of tests were conducted and proper ignition with stable combustion in the hybrid mode has been established. The regression rate correlations were obtained as a function of the oxidiser mass flux and chamber pressure from the experiments for the various combinations. Defence Science Journal, 2011, 61(6), pp.515-522 , DOI:http://dx.doi.org/10.14429/dsj.61.873