Sādhanā

A parametric time-frequency representation is presented based on time-varying autoregressive model (TVAR), followed by applications to non-stationary vibration signal processing. The identification of time-varying model coefficients and the determination of model order, are addressed by means of neural networks and genetic algorithms, respectively. Firstly, a simulated signal which mimic the rotor vibration during run-up stages was processed for a comparative study on TVAR and other non-parametric time-frequency representations such as Short Time Fourier Transform, Continuous Wavelet Transform, Empirical Mode Decomposition, Wigner-Ville Distribution and Choi-Williams Distribution, in terms of their resolutions, accuracy, cross term suppression as well as noise resistance. Secondly, TVAR was applied to analyse non-stationary vibration signals collected from a rotor test rig during run-up stages, with an aim to extract fault symptoms under non-stationary operating conditions. Simulation and experimental results demonstrate that TVAR is an effective solution to non-stationary signal analysis and has strong capability in signal time-frequency feature extraction.

Xu hướng vĩ mô của số người tử vong do tai nạn giao thông ở bất kỳ quốc gia nào có động cơ được mô tả và dự đoán bởi sản phẩm của các hàm phù hợp khá tốt theo thời gian cho sự suy giảm hàm số nguy cơ tử vong theo đơn vị lưu lượng giao thông và hàm Gompertz hình chữ S cho sự tăng trưởng lưu lượng giao thông. Sản phẩm này định nghĩa sự phát triển có đỉnh đơn trong số người chết do tai nạn giao thông, trong đó đỉnh này đạt được sớm hơn khi một quốc gia hoặc vùng miền công nghiệp hóa mạnh mẽ hơn. Vì ở các nước đang phát triển thiếu dữ liệu dài hạn về lưu lượng giao thông, một mô hình khác cho việc phù hợp và dự đoán số người chết do tai nạn giao thông cho các nước đang phát triển được sử dụng, dựa trên mối quan hệ giữa mức thu nhập bình quân đầu người với tỷ lệ tử vong giao thông đường bộ. Mô hình này cũng suy luận rằng vào một thời điểm nào đó, số người chết do tai nạn giao thông sẽ bắt đầu giảm mãi mãi, cũng trên toàn cầu. Sau khi thực hiện các điều chỉnh thực nghiệm cho dữ liệu thiếu hoặc không đầy đủ và báo cáo thiếu sót của cảnh sát, ước tính rằng có 1,2 triệu ca tử vong và gần 8 triệu ca thương tích nghiêm trọng do tai nạn giao thông trên toàn thế giới vào năm 2000. Sử dụng những dự đoán về mức thu nhập thực tế, mô hình phụ thuộc vào thu nhập mới dự đoán những đỉnh cao về tử vong rõ rệt sau và cao hơn so với mô hình phụ thuộc vào thời gian đã được xác thực. Có thể giả định rằng các quốc gia đang phát triển có thể học hỏi nhanh hơn để nâng cao an toàn giao thông của họ thông qua việc chuyển giao kiến thức từ các nước phát triển. Bốn kịch bản dự đoán được xác định cho các mô hình phụ thuộc vào thu nhập đã được điều chỉnh về sự phát triển số người chết và thương tích nghiêm trọng do tai nạn giao thông đến năm 2050. Tùy thuộc vào kịch bản, tổng số người chết do tai nạn giao thông trên toàn thế giới bắt đầu giảm sớm hoặc chỉ sau năm 2035 với một đỉnh toàn cầu khoảng 1,8 triệu ca tử vong do tai nạn giao thông, trong đó sự giảm tử vong quốc gia bắt đầu muộn hơn khi thu nhập bình quân đầu người quốc gia thấp hơn. Nếu không có kịch bản học tập có thể đạt được, sự giảm tử vong do tai nạn giao thông ở các nước phát triển có thể không đủ để bù đắp cho sự gia tăng tử vong do tai nạn giao thông ở các nước đang phát triển, trong khi sự gia tăng tử vong do tai nạn có thể xảy ra thậm chí sau năm 2060 ở các quốc gia có mức thu nhập bình quân thấp nhất.

Ni-Mo low alloy steel exhibits an admirable amalgamation of high strength and toughness at subzero temperature and show resistance to brittle fracture with good weldability. This steel has been established to fulfill the needs of specific applications, such as the construction of ships and submarines. To develop a companionable wire for welding of Ni-Mo low alloy steel, the amount of the alloying elements in a wire is increased to toughen of weld metal, the wire itself has high strength so that the wire is hardened at the wire drawing, making the wire production difficult. In order to avoid the problems related to the solid wires, various flux cored wires have been developed. In this work, the effect of flux basicity index and heat input on chemical composition, oxygen-nitrogen analysis, mechanical properties and microstructure of Ni-Mo low alloy steel welded by SAW welding using flux cored wires are presented along with the effect of flux cored wire and basicity index on deposition rate.

In this paper, a design methodology of Voltage-Controlled Oscillator (VCO) for long-range automotive RAdio Detection And Ranging (RADAR) is proposed and simulation analysis is carried out over Virtuoso SpectreRF software on Cadence tool. The frequency ranges of the mm-wave CMOS current-starved ring and LC VCOs for 45-nm CMOS technology are 24 and 76 GHz, respectively. The ring VCO at 25 GHz oscillation frequency demonstrates 2.06% tuning range, phase noise −71.61 dBc/Hz at 1-MHz offset, 3.43 mW power dissipation and layout area of $$20\times 20 \,\upmu {\mathrm{m}}^2$$ whereas cross-coupled LC VCO achieves an oscillation frequency of 76.25 GHz for frequency tuning range of 0.65%, a phase noise of −92.44 dBc/Hz at 1-MHz offset, 8.59 mW power dissipation and $$320\times 320 \,\upmu {\mathrm{m}}^2$$ layout area. The proposed design of efficient VCOs shows an excellent performance for long-range automotive RADAR.

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.