Department of Civil & Infrastructure Engineering

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IIT Jodhpur

First, a semi-analytical model for determining inter-yarn static and kinetic coefficients of friction for plain woven fabric is derived. The model requires few parameters from the load-displacement curve obtained in a pull-out experiment. The derived model is then applied to determine friction coefficients of Kevlar and the obtained values are found to be very consistent with the range reported in the literature. Next the ballistic response of plain woven Kevlar fabric structure is numerically studied through a simple FE model, wherein yarns are modeled by 1D truss element. The simplified model is validated against some equivalent experimental and numerical results reported in the literature. Effect of inter-yarn friction coefficient on failure mechanism and energy distribution characteristic of fabric structure are investigated. Based on the several numerical simulations, it is observed that higher inter-yarn friction may not always give better ballistic performance. Inter-yarn friction improves the ballistic performance up to a limiting value. Beyond this threshold value, increasing friction may adversely affect the energy dissipation and failure mechanism. © 2014 Elsevier Ltd.

World University root node

Composite Structures

Determination of inter-yarn friction and its effect on ballistic response of para-aramid woven fabric under low velocity impact

An undular hydraulic jump corresponds to the weak transition from super- to subcritical-flow in the form of steady free surface undulations. Previous models on undular hydraulic jumps employed the potential flow theory, i.e., the solitary and cnoidal wave theories. Experimental observations indicate the inadequacy of this theory, which motivated the development of more advanced approximations. Basic flow features including friction effects on the velocity profile, modelling of the bed-shear stress, and Reynolds stresses are considered. However, none of the models currently available include all these aspects. In this study, a general depth-averaged model is developed based on the κ- ε turbulence closure. The general depth-averaged equations are applied to the undular jump problem, introducing a suitable time-averaged velocity distribution based on a composite power-law model, in which both streamline curvature and vorticity are accounted for. The bed-shear stress closure is included by a boundary layer method. Predictions of the depth-averaged Reynolds averaged Navier-Stokes (RANS) model are shown to be close to the 2D RANS solution and to experimental observations. © 2014 International Association for Hydro-Environment Engineering and Research.

Journal of Hydraulic Research

Depth-averaged model for undular hydraulic jump

This study presents a detailed cloud condensation nuclei (CCN) closure study that investigates the effects of chemical composition (bulk and size resolved) and mixing state (internal and external) on CCN activity of aerosols. Measurements of the chemical composition, aerosol size distribution, total number concentration, and CCN concentration at supersaturation (SS = 0.2-1.0%) were performed during the winter season in Kanpur, India. Among the two cases considered here, better closure results are obtained for case 1 (low total aerosol loading, 49.54 ± 26.42 µg m-3, and high O:C ratio, 0.61 ± 0.07) compared to case 2 (high total aerosol loading, 101.05 ± 18.73 µg m-3, and low O:C ratio, 0.42 ± 0.06), with a maximum reduction of 3-81% in CCN overprediction for all depleted SS values (0.18-0.60%). Including the assumption that less volatile oxidized organic aerosols represent the soluble organic fraction reduced the overprediction to at most 40% and 129% in the internal and external mixing scenarios, respectively. At higher depleted SS values (0.34-0.60%), size-resolved chemical composition with an internal mixing state performed well in CCN closure among all organic solubility scenarios. However, at a lower depleted SS value (0.18%), closure is found to be more sensitive to both the chemical composition and mixing state of aerosols. At higher SS values, information on the solubility of organics and size-resolved chemical composition is required for accurate CCN predictions, whereas at lower SS values, information on the mixing state in addition to the solubility of organics and size-resolved chemical composition is required. Overall, κtotal values are observed to be independent of the O:C ratio [κtotal = (0.36 ± 0.01) × O:C - (0.03 ± 0.01)] in the range of 0.2&lt;O:C&lt;0.81, which indicates that the variation in the chemical composition of aerosols is not well represented by the changes in the O:C ratio alone. © 2014. American Geophysical Union. All Rights Reserved.

Fulltext

Journal of Geophysical Research

CCN closure study: Effects of aerosol chemical composition andmixing state

Natural streambed does not exhibit a plane bed surface, but takes various geometrical forms known as bedforms. In this book chapter, the studies dealing with the formation mechanism of bedforms and their stability are discussed. The important feature of this chapter is the presentation of mathematical models proposed by various researchers. © Springer International Publishing Switzerland 2015.

GeoPlanet: Earth and Planetary Sciences

Principles of mechanics of bedforms

Journal of Hydraulic Engineering

Closure to "sediment entrainment probability and threshold of sediment suspension: Exponential-based approach" by Sujit K. Bose and Subhasish Dey

We present long-term measurements of sub-micron particle number size distributions (PNSDs) conducted at an urban location, Kanpur, in India, from September 2007 to July 2011. The mean Aitken mode (NAIT), accumulation mode (NACCU), the total particle (NTOT), and black carbon (BC) mass concentrations were 12.4×103cm-3, 18.9×103cm-3, 31.9×103cm-3, and 7.96μgm-3, respectively, within the observed range at other urban locations worldwide, but much higher than those reported at urban sites in the developed nations. The total particle volume concentration appears to be dominated mainly by the accumulation mode particles, except during the monsoon months, perhaps due to efficient wet deposition of accumulation mode particles by precipitation. At Kanpur, the diurnal variation of particle number concentrations was very distinct, with highest during morning and late evening hours, and lowest during the afternoon hours. This behavior could be attributed to the large primary emissions of aerosol particles and temporal evolution of the planetary boundary layer. A distinct seasonal variation in the total particle number and BC mass concentrations was observed, with the maximum in winter and minimum during the rainy season, however, the Aitken mode particles did not show a clear seasonal fluctuation. The ratio of Aitken to accumulation mode particles, NAIT/NACCU, was varied from 0.1 to 14.2, with maximum during April to September months, probably suggesting the importance of new particle formation processes and subsequent particle growth. This finding suggests that dedicated long-term measurements of PNSDs (from a few nanometer to one micron) are required to systematically characterize new particle formation over the Indian subcontinent that has been largely unstudied so far. Contrarily, the low NAIT/NACCU during post-monsoon and winter indicated the dominance of biomass/biofuel burning aerosol emissions at this site. © 2014 Elsevier B.V.

Atmospheric Research

Sub-micron particle number size distributions characteristics at an urban location, Kanpur, in the Indo-Gangetic Plain

We present properties of size-resolved cloud condensation nuclei (CCN) over the central Indo-Gangetic Basin (IGB) station, Kanpur, India. The measurements were done during three different seasons: spring, summer and monsoon in 2012. Size-resolved CCN efficiency spectra (20-280nm), measured at 0.2-1% supersaturation (SS), resulted in an average activation diameter (Da) of 148-45nm. The activation diameter was found to be maximum in spring followed by monsoon and summer at all SS except at SS=1%. The size-averaged hygroscopicity (κ) of CCN-active particles for all SS was found to be 0.11±0.03, 0.24±0.13 and 0.14±0.06 in spring, summer, and monsoon, respectively. κ increased with increasing particle diameter, suggesting change in chemical composition with size which further leads to change in CCN activity. In comparison to summer and monsoon, despite the presence of lower κ in spring, the higher activation fraction in Aitken mode is observed due to the shift of CN size distribution towards larger diameter. κ is observed to be lower in first half of the day (0900-1400h) for SS=0.2-0.5% due to relatively less photochemical activity compared to second half of the day. Size-and-time averaged κ value over all three seasons (0.16±0.08) suggests dominance of organic species, as reported in previous studies. © 2013 Elsevier Ltd.

Atmospheric Environment

Inter-seasonal variability in size-resolved CCN properties at Kanpur, India

Blade failure is a common problem of a steam turbine and it's failure in-service results in safety risks, repair cost and non operational revenue losses. Thus, the reliability of these blades is very important for the successful operation of a steam turbine. Dynamic analysis of a steam turbine blade in computational environment is carried out in the present work. In order to gain physical insight into the flexural dynamics of such turbine blades with the inclusion of the rotor dynamic effect, the turbine blade was approximated as a twisted cantilever beam with an asymmetric aerofoil cross-section fixed on a rigid rotor disk. Methods to validate the computational procedures for cantilever beam were established. Similar computational procedures were leveraged for the turbine blade. Critical speeds were obtained for different excitations.

INTERNOISE 2014 - 43rd International Congress on Noise Control Engineering: Improving the World Through Noise Control

Vibration analysis of a steam turbine blade

An accurate Dynamic Traffic Assignment (DTA) model should capture real world traffic flow dynamics and predict ‘dynamic’ travel times. Traditional DTA models used simple traffic flow functions such as exit flow functions, delay functions, point queues, and deterministic physical queue models. Recently, simulation based models apply well accepted traffic flow theoretic models to simulate traffic flow. However, a significant number of papers over the last decade have adopted an approximation of LWR traffic flow model, the cell transmission model, for simulating traffic flow in a DTA model. This paper compares three models, namely, LWR, Payne and Aw-Rascle, models, for their suitability to be embedded in a DTA model. Model calibration and flow simulation is performed separately using two different speed–density relationships. Results showed the importance of choice of speed-density relationship in traffic flow simulation. Models were used to simulate traffic state at different discretization levels and it was observed that as discretization becomes finer, the models' accuracy increases. Finally, the models were applied to a two node, two link network to analyze their performance in a DTA framework. The higher-order models captured congestion dissipation better than LWR model which consistently underestimates congestion and travel time. © 2014, Springer Science+Business Media New York.

Networks and Spatial Economics

Submission to the DTA2012 Special Issue: A Case for Higher-Order Traffic Flow Models in DTA

The total amount of sediment transported through a given section of a river for the given flow and sediment bed conditions is called total-load transport. Based on the mode of sediment transport, the total load is the sum of the bed, suspended, and wash load. The total load is also informally called the bed-material load as it contains only those sediment particles that come from the sediment bed excluding the wash load. There are two general approaches to determine the total load. They are indirect approach and direct approach. In indirect approach, bed and suspended loads are estimated separately and then added together to quantify the total load. In direct approach, the total-load function is directly determined without dividing it into bed and suspended loads. The method of computation of total-load transport is illustrated through worked out examples. © 2014, Springer-Verlag Berlin Heidelberg.