Sādhanā

Computational investigation was conducted to understand the effects of various parameters on nozzle flow and cavitation in a diesel fuel injector for a diesel engine. The effects of injector parameters were simulated for different conditions including the injection pressure, the outlet pressure, the position of the needle lift, and the length of the nozzle. Results show that some parameters have obvious influence on cavitation associated with nozzle flow. When the outlet pressure was constant, the velocity through the nozzle increased with the injection pressure, resulting in the cavitation at the injection pressure over 120 MPa. When the injection pressure was constant, the velocity inside nozzle decreased with the outlet pressure. As the needle tip moved closer to the bottom of minisac, the velocity inside nozzle decreased and the cavitation did not take place. The length of the nozzle hole had little effect on the velocity at inlet, but it affected the velocity distribution at outlet.

Porous cellulose nanocrystals (CNCs) have been fabricated by acid hydrolysis of pre-treated Crotalaria juncea bast fibers, a major agricultural waste. The objective of this study is to explore the efficacy of cellulose nanocrystals obtained from C. juncea (CJ) as adsorbent for the removal of dyes. Response surface methodology has been employed to model statistically and optimize the process variables for the removal of methylene blue (MB) using Design Expert Software. The CNC obtained has also been characterized using BET, FTIR, and SEM. The BET surface area is found to be 7.5 m2, with pore sizes ranging from 2 to 8 nm. The adsorption of methylene blue by CNC has been observed to be most improved at neutral pH, lower MB concentration and higher loading (4 g/l). The equilibrium is achieved within 1 h of contact and maximum MB removal of 69% was achieved. In order to improve the adsorption efficiency, surface modification with 2,2,6,6-Tetramethylpiperidinyloxy (TEMPO) was carried out to both pre-treated CJ and CNC. The surface modification had a negative impact on adsorption efficiency of MB while better adsorption efficiency was imparted towards malachite green (MG). An increase in adsorption efficiency from 62% to 92% was observed for TEMPO modified CNC. The variations in the adsorption performance of CNC and TEMPO CNC towards the two cationic dyes are due to varying charge density, surface area and shape of both the adsorbate and the adsorbent, with stearic hindrance being the major factor in regulating adsorption in case of unmodified CNC, and electronic nature dominating in case of TEMPO CNC.

This study considers numerical simulation of the combustion of methane with air, including oxygen and nitrogen, in a burner and the numerical solution of local entropy generation rate due to high temperature and velocity gradients in the combustion chamber. The effects of equivalence ratio (Φ) and oxygen percentage (γ ) on combustion and entropy generation rates are investigated for different Φ (from 0.5 to 1.0) andγ values (from 10 to 30%). Combustion is simulated for the fuel mass flow rate resulting in the same heat transfer rate (Q)y to the combustion chamber in each case. Numerical calculation of combustion is performed individually for all cases with the use of the Fluent CFD code. Furthermore, a computer program has been developed to calculate the volumetric entropy generation rate and the other thermodynamic parameters numerically by using the results of the calculations performed with the FLUENT code. The predictions show that the increase of Φ (or the decrease of λ) significantly reduces the reaction rate levels. Average temperature in the combustion chamber increases by about 70 and 35% with increase ofγ (from 10 to 30%) and Φ (from 0.5 to 1.0) respectively. With increase ofγ from 10 to 30%, volumetric local entropy generation rate decreases by about 9 and 4% for Φ = 0.5 and 1.0 respectively, while total entropy generation rate decreases exponentially and the merit numbers increase. The ratio of the rates useful energy transfer to irreversibility therefore improves as the oxygen percentage increases

Laser forming of non-developable surfaces necessitates simultaneous bending and shrinkage of the sheet blank. This can be obtained by coupling mechanism based laser forming. However, soft computing based modeling of this process as well as different laser parameter sets under coupling mechanism giving different optimum combinations of simultaneous bending and shrinkage is rarely reported. In this work, experiments have been carried out following a design of experiments with considered suitable ranges of the input factors, i.e., laser power, travel speed and laser beam diameter activating coupling mechanism. Response surface models for the outputs namely bending and thickening (resulted due to shrinkage) were developed in terms of the considered inputs and parametric effects were analyzed. Finite element modeling was also carried out to analyze the deformation behavior. Multi-objective optimization of laser parameters for different combinations of maximum/minimum of bending and thickening of the sheet material undergoing coupling mechanism has been shown. Forward and inverse models of the process have been built with the help of a backpropagation neural network (BPNN) and genetic algorithm-based neural network (GANN) based on experimental data. Because of the ability of genetic algorithm (GA) to obtain global search, GANN models provide better estimation of the input parameters for inverse modeling or process synthesis compared to that by the BPNN model. Finally, several dome-shaped surfaces were built with constant line energy but different Fourier numbers and hence, different proportions of bending and shrinkage. This was to demonstrate the importance of simultaneous bending and thickening of the sheet (achievable only by coupling mechanism) to generate such non-developable surface with minimal distortion.

The rich interaction of multiple bubbles with multiple vortical structures makes the study of bubbly turbulent flows quite challenging. An idealisation of this problem would be the interaction between a single bubble and an elliptic vortex ring, the latter of which can be considered a representative vortical structure. The elliptic vortex ring is characterised by its initial aspect ratio $$AR_0$$ , defined as the ratio of the semi-minor to semi-major axes of the ellipse, with $$AR_0=1$$ corresponding to a circular vortex ring. In the first part, we focus on the interaction between the elliptic vortex ring ( $$AR_0 = 0.6$$ ) and a bubble, where we explore the effects of the capture angle ( $$\theta _C$$ ) on the different quantities relevant to the ring as well as the bubble, using simultaneous side and top-view high-speed visualisations; $$\theta _C$$ is defined as the angle subtended by the bubble with the instantaneous major axis of the elliptic vortex ring at bubble capture. We study the effect of $$\theta _C$$ on the reduction in the ring’s convection speed $$\Delta U^*$$ and the number of daughter bubbles $$N_b$$ , computed at a later stage of the interaction. For this part of the study, the Weber number $$We=\rho U_0^2 D_b/\sigma $$ , defined as the ratio of the ring’s inertial effects to surface tension effects, is fixed at $$We=11$$ . We find that bubble capture at lower capture angles ( $$\theta _C \approx 0^\circ $$ ) corresponding to the high-curvature part of the elliptic vortex ring is found to be more probable compared to that at higher capture angles ( $$\theta _C \approx 90^\circ $$ ). Further, a lower capture angle ( $$\theta _C \approx 0^\circ $$ ) leads to a larger number of daughter bubbles $$N_b$$ and a slightly higher reduction in ring speed $$\Delta U^*$$ . In the second part, we study the effect of $$AR_0$$ by contrasting the elliptic ring ( $$AR_0 = 0.6$$ ) with a circular ring ( $$AR_0 = 1$$ ) over a range of Weber numbers, in which the parameters of interest are the ring’s speed and the number of daughter bubbles. We observe that the elliptic vortex ring produces fewer daughter bubbles than the circular ring, with the difference increasing at larger ring strengths corresponding to higher Weber numbers. At higher We, the elliptic ring deviates from the $$N_b \propto We^{0.42}$$ scaling, which holds for the circular ring. The current study thus helps to gain a better insight into the complex problem of bubbly turbulent flows.

In this paper, the effect of surface radiation in a square cavity containing an absorbing, emitting and scattering medium with four heated boundaries is investigated, numerically. Lattice Boltzmann method (LBM) is used to solve the energy equation of a transient conduction–radiation heat transfer problem and the radiative heat transfer equation is solved using finite-volume method (FVM). In this work, two different heat flux boundary conditions are considered for the east wall: a uniform and a sinusoidally varying heat flux profile. The results show that as the value of conduction–radiation decreases, the dimensionless temperature in the medium increases. Also, it is clarified that, for an arbitrary value of the conduction–radiation parameter, the temperature decreases with decreasing scattering albedo. It is observed that when the boundaries reflect more, a higher temperature is achieved in the medium and on boundaries.

Pricing financial options is amongst the most important and challenging problems in the modern financial industry. Except in the simplest cases, the prices of options do not have a simple closed form solution and efficient computational methods are needed to determine them. Monte Carlo methods have increasingly become a popular computational tool to price complex financial options, especially when the underlying space of assets has a large dimensionality, as the performance of other numerical methods typically suffer from the ‘curse of dimensionality’. However, even Monte-Carlo techniques can be quite slow as the problem-size increases, motivating research in variance reduction techniques to increase the efficiency of the simulations. In this paper, we review some of the popular variance reduction techniques and their application to pricing options. We particularly focus on the recent Monte-Carlo techniques proposed to tackle the difficult problem of pricing American options. These include: regression-based methods, random tree methods and stochastic mesh methods. Further, we show how importance sampling, a popular variance reduction technique, may be combined with these methods to enhance their effectiveness. We also briefly review the evolving options market in India.

Most wind tunnel models are fabricated of all metal components using computerized numerical control (CNC) milling machines. Fabrication of metal wind tunnel models is very expensive and time consuming. The models can require months to manufacture and are often made by small high technology companies that specialize in wind tunnel model manufacture. Using rapid prototype manufacturing techniques and materials in this way significantly reduces time and cost of production of wind tunnel models. This study was done by fused deposition modelling and their ability to make components for wind tunnel models in a timely and cost effective manner. This paper discusses the application of wind tunnel model configuration constructed using FDM and FDM with chromium coating for subsonic wind tunnel testing. A study was undertaken comparing a rapid prototyping model constructed of FDM technologies using polycarbonate to that of a standard machined steel model. Results from this study show relatively good agreement among the three models and rapid prototyping method with chromium coating does have an effect on the aerodynamic characteristics which produced satisfactory results.

Magnesium and its alloys like AZ91 are used for various automotive, military and aviation applications. Nanocomposite coatings on AZ91 show significant improvement in the surface properties like wear resistance, hardness and corrosion properties. Electroless coatings have unique physicochemical and mechanical properties, for which they are being used increasingly. Most applications of the electroless coatings are based on their wear and corrosion resistance. However, the characteristic like luminescence has a great potential in defence and aerospace applications. In this research, surface roughness of AZ91 magnesium alloy due to nanocomposite coating processes of ENi–B–TiO2 is experimentally investigated. It has been observed that as concentration of second-phase (TiO2) particles increases, the surface roughness of coatings also increases.