Department of Civil & Infrastructure Engineering

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Environmental Fluid Mechanics

Preface: special issue on the hydrodynamic and fluvial instabilities

Global warming is one of the biggest challenges that we are facing today. Construction industry is also contributing to the problem by emitting greenhouse gases. In order to deal with this issue sustainable products are being adopted by all the industries. Similarly, highway industry is also adopting several measures to reduce its carbon footprint. One of such measures is cold mix asphalt technology (CMA). CMA does not require any heating of material. This is achieved by using asphalt emulsion and cutback as binding material. Since these materials are liquid at room temperature, they do not require any heating for mixing and compaction. This gives many environmental and economic benefits to CMA over hot mix asphalt (HMA). Despite having these advantages, inferior performance makes CMA undesirable to be used in the construction of roads having high density traffic. Although some studies have been taken to improve the performance of CMA but those are limited in their scope. Present paper gives an overview of the different aspects of CMA technology. It discusses materials, design procedure, field utilisation, performance, effect of different performance enhancing measures of CMA. In the end benefits, drawbacks and future scope of CMA are also presented. © 2020 Elsevier Ltd

World University root node

Journal of Cleaner Production

Cold mix asphalt: An overview

This paper presents the state-of-the-art on different moving least square (MLS)-based dimension decomposition schemes for reliability analysis and demonstrates a modified version for high fidelity applications. The aim is to improve the performance of MLS-based dimension decomposition in terms of accuracy, number of function evaluations and computational time for large-dimensional problems. With this in view, multiple finite difference high dimension model representation (HDMR) scheme is developed. This anchored decomposition is implemented starting from an initial reference point and progressively evolving in successive iterations. Most probable point (MPP) of failure is identified in every iteration and is used as the reference point for the next decomposition until it converges. Hermite polynomials in MLS framework are used between the support points for efficient interpolation. The support points are generated sequentially using multiple sparse grids based on the Clenshaw-Curtis scheme. Once the global response surface is constructed using the support points generated in each iteration, importance sampling is employed for reliability analysis. Six different benchmark problems are solved to show its performance vis-à-vis other methods. Finally, reliability-based design of a composite plate is demonstrated, clearly showing the advantage and superiority of the proposed improvements in MLS-based multiple dimension decomposition (MDD). © 2021 World Scientific Publishing Company.

International Journal of Computational Methods

Improved Moving Least Square-Based Multiple Dimension Decomposition (MDD) Technique for Structural Reliability Analysis

Atmospheric secondary organic aerosol (SOA) undergoes chemical and physical changes when exposed to UV radiation, affecting the atmospheric lifetime of the involved molecules. However, these photolytic processes remain poorly constrained. Here, we present a study aimed at characterizing, at a molecular level and in real time, the chemical composition of α-pinene SOA exposed to UV-A light at 50% relative humidity in an atmospheric simulation chamber. Significant SOA mass loss is observed at high loadings (∼100 μg m-3), whereas the effect is less prevalent at lower loadings (∼20 μg m-3). For the vast majority of molecules measured by the extractive electrospray time-of-flight mass spectrometer, there is a fraction that is photoactive and decays when exposed to UV-A radiation and a fraction that appears photorecalcitrant. The molecules that are most photoactive contain between 4 and 6 oxygen atoms, while the more highly oxygenated compounds and dimers do not exhibit significant decay. Overall, photolysis results in a reduction of the volatility of SOA, which cannot be explained by simple evaporative losses but requires either a change in volatility related to changes in functional groups or a change in physical parameters (i.e., viscosity). ©

Environmental Science and Technology

Photodegradation of α-Pinene Secondary Organic Aerosol Dominated by Moderately Oxidized Molecules

A year-long offline based study was performed at five sites of Indo-Gangetic plain to get the spatio-temporal variation in elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC) and secondary organic aerosol (SOA) in PM2.5 fraction. OC constitutes ~70–90% of the total carbon with high water-soluble fraction (60–70%) during winter, except at Hisar. The change in concentration of OC was insignificant during summer, whereas the water-soluble fraction increased by 75–85%. The relatively high OC/EC ratio (7–11) and OC/K+ ratio (10–52) during winter and post-monsoon suggest the dominance of biomass burning from wood fuel and agricultural waste. EC is nearly constant over the seasons at all sites suggesting the dominant presence of traffic-originated EC throughout the year. Interestingly, a low correlation (~0.3) between OC and EC at IITD and IITMD indicates their source from different origins. Exceptionally, the daytime OC/EC ratio was slightly higher than night time during winter at Hisar. However, other sites showed the opposite trend. A significant linear relationship between WSOC and secondary organic carbon suggests dominant contribution from SOA. A paired t-test results indicate much of WSOC is of secondary origin and regional in nature. The secondary fraction contributed 30–60% of OC during winter across all the sites in IGP, whereas during summer it varied between 20 and 40%. SOA estimated by the EC- tracer method has the highest contribution at IITMD (~138 μg/m3) among all the sites and peaked during post-monsoon. © 2020 Turkish National Committee for Air Pollution Research and Control

Atmospheric Pollution Research

Temporal and spatial variability of carbonaceous species (EC; OC; WSOC and SOA) in PM2.5 aerosol over five sites of Indo-Gangetic Plain

Pseudo-static approaches often become handy due to their simplicity compared to the complex coupled continuum dynamic analysis and yield satisfactory results. A pseudo-static approach is employed herein to evaluate the response of a pile-supported structure located in a highly active seismic zone in northeast India. Pseudo-static approach essentially involves two main steps: estimation of maximum ground deformations and surface accelerations from a free field ground response study, combined with static analysis considering the surface acceleration and superstructure mass. In the present study, dynamic behavior of underlying soil strata was investigated using two high-quality element testing techniques—resonant column and dynamic simple shear tests. The dynamic soil properties were established and site-specific ground response study was conducted for the chosen site, using the artificially generated ground motions for the region. Equivalent static load was estimated from the surface acceleration obtained from free field ground response study. A three-dimensional finite element model has been developed and validated against the field lateral load test results. An increased magnitude of displacement and bending moment was observed with increased ground motion intensity. The peak bending moments induced for the scenario ground motions is higher than the plastic moment capacity of the pile section, displaying the probable failure of considered pile-supported structure. © Springer Nature Singapore Pte Ltd. 2021.

Lecture Notes in Civil Engineering

Seismic requalification of pile-supported structure: Pseudo-static approach

Journal of Hydrologic Engineering

Discussion of "multivariate Modeling of Projected Drought Frequency and Hazard over India" by Vivek Gupta, Manoj Kumar Jain, and Vijay P. Singh

We present highly time-resolved (30 to 120 min) measurements of size-fractionated (PM10 and PM2.5) elements in two cities in Asia (Delhi and Beijing) and Europe (Krakow and London). For most elements, the mean concentrations in PM10 and PM2.5 are higher in the Asian cities (up to 24 and 28 times, respectively) than in Krakow and often higher in Delhi than in Beijing. Among European cities, Krakow shows higher elemental concentrations (up to 20 and 27 times, respectively) than London. Hourly maximum concentrations of Pb and Zn reach up to 1 μg m-3 in Delhi, substantially higher than at the other sites. The enrichment factor of an element together with the size distribution allows for a rough classification of elements by major source. We define five groups: (1) dust emissions, (2) non-exhaust traffic emissions, (3) solid fuel combustion, (4) mixed traffic/industrial emissions, and (5) industrial/coal/waste burning emissions, with the last group exhibiting the most site-To-site variability. We demonstrate that the high time resolution and size-segregated elemental dataset can be a powerful tool to assess aerosol composition and sources in urban environments. Our results highlight the need to consider the size distributions of toxic elements, diurnal patterns of targeted emissions, and local vs. regional effects in formulating effective environmental policies to protect public health.. © 2021 Mary Ann Liebert Inc.. All rights reserved.

Department of Electrical Engineering

Atmospheric Chemistry and Physics

Highly time-resolved measurements of element concentrations in PM10 and PM2.5: Comparison of Delhi, Beijing, London, and Krakow

Erosional failure of granular dams by an overtopping body of water is investigated using a depth-averaged morphodynamic model. The transport of sediment by the flow assumes the sediment flux to remain in equilibrium with the local bed shear stress. Accordingly, the shallow-water hydrodynamic equations are coupled with the Exner equation for mass conservation of the sediment. The system of equations is solved using a fully coupled well-balanced finite volume method, second-order accurate in time and space. The effect of the steep bed slope of a dam face is incorporated into both the hydrodynamics and sediment transport equations, leading to improved predictions. Comparison with results obtained from nonequilibrium sediment transport models indicates that such models perform poorly while predicting the bed evolution near the toe of an eroding dam. Observations from experimental studies demonstrate that the amount of sediment entrained by the flow is not significant, except during the initial moments of failure. This suggests that the vertical exchange of mass between the bed and the flow layer, as assumed by the nonequilibrium models, may not be completely valid during the failure. The equilibrium model results, reproducing the key flow features of the overtopping failure process, are validated by experimental measurements. The study provides fresh insights into the sediment transport processes associated with the erosion of a granular dam by overtopping, establishes the appropriateness of the equilibrium approach for its numerical modeling, and proposes a well-balanced second-order accurate solution technique for solving the resulting coupled equations of flow and sediment transport. © 2021 Author(s).

Physics of Fluids

Equilibrium approach for modeling erosional failure of granular dams

Hydrogels exhibit a wide range of responses to various stimuli, which makes them useful in myriad applications including the biomedical industry. To capture certain features of this varied response, several constitutive models have been proposed. However, few attempts have been made at the predictive modelling of temperature and moisture driven transition between fast and slowly relaxing states in physical hydrogels. We in this article focus on the changes that occur in the mechanical response due to such phase transitions. We propose a unified and thermodynamically consistent poro-visco-elastic framework for modelling the transition and the associated mechanical behaviour. Towards that, the effective temperature framework that has been previously exploited for such transitions by the authors and other researchers is used. The constitutive model is numerically solved for the uniaxial tensile response of equilibrated hydrogels and also validated against experimental data from the literature. It is also used for certain transient problems involving solvent diffusion with or without mechanical constrains. The aim of this exercise is to assess the predictive fidelity of the model against some standard poro-elastic problems and examine the influence of inter-molecular interactions on the saturation. The numerical studies are concluded with a set of simulations to showcase certain other capabilities of our approach such as modelling of visco-hyperelastic phase transitions. We also investigate through these simulations a few other coupling effects caused by changes in moisture, temperature, loading rates and prior ageing. © 2021 Elsevier Ltd