Department of Civil & Infrastructure Engineering

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IIT Jodhpur

We evaluate numerical simulations of surface ozone mixing ratios over the south Asian region during the pre-monsoon season, employing three different emission inventories in the Weather Research and Forecasting model with Chemistry (WRF-Chem) with the second-generation Regional Acid Deposition Model (RADM2) chemical mechanism: the Emissions Database for Global Atmospheric Research - Hemispheric Transport of Air Pollution (EDGAR-HTAP), the Intercontinental Chemical Transport Experiment phase B (INTEX-B) and the Southeast Asia Composition, Cloud, Climate Coupling Regional Study (SEAC4RS). Evaluation of diurnal variability in modelled ozone compared to observational data from 15 monitoring stations across south Asia shows the model ability to reproduce the clean, rural and polluted urban conditions over this region. In contrast to the diurnal average, the modelled ozone mixing ratios during noontime, i.e. hours of intense photochemistry (11:30-16:30gIST - Indian Standard Time - UTC +5:30), are found to differ among the three inventories. This suggests that evaluations of the modelled ozone limited to 24gh average are insufficient to assess uncertainties associated with ozone buildup. HTAP generally shows 10-30gppbv higher noontime ozone mixing ratios than SEAC4RS and INTEX-B, especially over the north-west Indo-Gangetic Plain (IGP), central India and southern India. The HTAP simulation repeated with the alternative Model for Ozone and Related Chemical Tracers (MOZART) chemical mechanism showed even more strongly enhanced surface ozone mixing ratios due to vertical mixing of enhanced ozone that has been produced aloft. Our study indicates the need to also evaluate the O3 precursors across a network of stations and the development of high-resolution regional inventories for the anthropogenic emissions over south Asia accounting for year-to-year changes to further reduce uncertainties in modelled ozone over this region. © Author(s) 2017.

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Atmospheric Chemistry and Physics

WRF-Chem simulated surface ozone over south Asia during the pre-monsoon: Effects of emission inventories and chemical mechanisms

In this paper, we explore the hydrodynamic instability of meandering channels driven by the turbulent flow. The governing equations of channel dynamics with suitable boundary conditions are closed with the fluid and granular constitutive relationships. A regular expansion of the fundamental variables is employed to linearize the parent equations by superimposing the perturbations on the basic unperturbed flow. The channel dynamics reveal a resonance phenomenon which occurs when the key variables fall in the vicinity of the distinct critical values. The resonance phenomenon preserves its distinctive signature in different flow regimes which are guided by the characteristic values of the shear Reynolds number. The hydrodynamic analysis indicates that the fluid friction and the volumetric sediment flux play a decisive role to characterize the channel instability in different flow regimes. The growths of azimuthal velocity perturbation in phase with curvature, bed topography perturbation, bend amplification rate, and meander propagation speed in different flow regimes are investigated by varying the meander wavenumber, Shields number, channel aspect ratio, and relative roughness number. The analysis is capable to capture the effects of grain size on azimuthal velocity perturbation, bed topography perturbation, bend amplification rate, and meandering propagation speed over a wide range of shear Reynolds numbers. The variations of resonant wavenumbers in different flow regimes with the Shields number, channel aspect ratio, and relative roughness number are addressed. For a specific flow regime, the upstream and downstream migrations of meandering channels are typically governed by the Shields number, channel aspect ratio, and relative roughness number. © 2017 Author(s).

Physics of Fluids

Hydrodynamic instability of meandering channels

In this paper, to explore the origin of the onset of meandering of a straight river, we, first, analyse the linear stability of a straight river. We discover that the natural perturbation modes of a straight river maintain an equilibrium state by confining themselves to an onset wavenumber band that is dependent on the flow regimes, aspect ratio, relative roughness number and Shields number. Then, we put forward a phenomenological description of the onset of meandering of a straight river. Its mechanism is governed by turbulent flow, with counter-rotation of neighbouring large-scale ormacroturbulent eddies in succession to generate the processes of alternating erosion and deposition of sediment grains of the riverbed. This concept is explained by a theorem (universal scaling law) stemming from the phenomenology of a turbulent energy cascade to provide a quantitative insight into the criterion for the onset of meandering of a straight river. It is revealed from this universal scaling law that, at the onset of meandering of a river, the longitudinal riverbed slope is a unique function of the river width, flow discharge and sediment grain size. This unique functional relationship is corroborated by the data obtained from the measurements in natural and model rivers. © 2017 The Author(s) Published by the Royal Society. All rights reserved.

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences

Origin of the onset of meandering of a straight river

Fracture toughness (FT) and tensile strength (TS) indicate a rock's susceptibility to fracturing. Past studies showed that mechanical properties and FT of homogeneous rocks can be correlated well. In the present study, this capability has been extended to the jointed sedimentary rocks. Sandstone with a wide combination of analogue joints were tested in the laboratory, and the control of joint geometrical properties on the FT, TS, and development of fracture process zone (FPZ) were investigated. A FT prediction model was developed based on the TS of the jointed specimens. Multifractal scaling law (MFSL) was utilized to extend the laboratory results to the field scale. Further, the interaction of propagating crack with the already existing joints were investigated and post-peak behavior were studied. Results show that FT and TS decrease with decreasing joint spacing, but they are more sensitive at higher joint spacing. It is also possible to construct a linear prediction model between the FT and TS of rock. FPZ of jointed rock is less sensitive to joint orientation and more related to joint spacing. A negative correlation between the FPZ size and joint spacing is established in this study. Post-peak behavior of the jointed specimens indicate that crack-joint interaction increases the frictional resistance and dissipated fracture energy of the specimens. Further, comparison of mixed-mode fracture criteria with the experimental results show that Maximum Tangential Stress (MTS) criterion can successfully predict the mixed-mode fracture behavior of jointed sandstone. © 2017 Elsevier B.V.

Engineering Geology

Influence of joint anisotropy on the fracturing behavior of a sedimentary rock

Rock Mechanics and Rock Engineering

Correlating the Mechanical and Physical Properties with Mode-I Fracture Toughness of Rocks

Stiffness and damping properties of soil are essential parameters for any dynamic soil structure interaction analysis. Often the required stiffness and damping properties are obtained from the empirical curves. This paper presents the stiffness and damping properties of two naturally occurring sandy soils collected from a river bed in a highly active seismic zone in the Himalayan belt. A series of resonant column tests are performed on the soil specimens with relative densities representative of the field and with varying confining pressures. The test results are compared with the available empirical curves. Furthermore, a ground response analysis study is also carried out for a bridge site in the region using both the empirical curves and experimentally obtained curves. It has been observed that the application of empirical modulus and damping curves in ground response prediction often leads to underestimation of the seismic demands on the structures. The established soil curves can thus be utilized in performing seismic ground response studies for the design of new structures or requalification/reassessment of existing structures in the northeastern part of India. © 2017 Elsevier Ltd

Soil Dynamics and Earthquake Engineering

Dynamic soil properties for seismic ground response studies in Northeastern India

High fidelity models for uncertainty quantification of large structures in finite element framework are computationally exhaustive. Thus, there is a constant demand for efficient algorithm that uses optimal computational cost without compromising with the quality of the end results. With this in view, present study aims to develop a sequentially evolving stochastic response surface using Hermite family of orthogonal polynomials whose support points are generated in sparse grid framework. Using the values of the original model at these support points, unknown coefficients of the stochastic response surface are optimized by moving least square technique. It helps to reduce the number of original function evaluations to determine the coefficients as compared to other deterministic or random sampling techniques. Besides sparse grid scheme for support point generation, they are also populated sequentially as the optimization progresses in every iteration. The uniqueness of the proposed scheme is its adaptability by changing the order of the polynomials and the level of the sparse grid to minimize the overall computational cost. Multiple optima present in the original response can be identified by introducing additional penalty functions whenever they are required. Once the global response surface is ready, Monte-Carlo simulation or its advance version (e.g. Latin Hypercube Sampling) is adopted to generate the probability density functions for the output variables. Numerical studies are presented to prove the efficiency and accuracy of the proposed scheme as compared to other techniques available in the literature. © 2017 The Authors.

UNCECOMP 2017 - Proceedings of the 2nd International Conference on Uncertainty Quantification in Computational Sciences and Engineering

Mls based sequential srsm in sparse grid framework for efficient uncertainty quantification

Primary constituents of bituminous concrete are coarse aggregate, fine aggregate, binder and additive (optional). The basic properties of these constituents govern the characteristics of the bituminous mix (viz. stability, durability, temperature, stress and rutting resistance). When the basic properties of the core material are below-graded, the bituminous concrete mix fail to meet the required standard. One of the feasible solution to overcome this problem is the use of additives in order to improve the properties of bituminous mix. In this study, locally available poor quality stone aggregate and asphalt were treated with liquid Nano-material, zycosoil. The bituminous concrete prepared using Zycosoil treated stone aggregate and bitumen, yield better results compared to mix prepared with locally available conventional materials. Moreover, when zycosoil was added with bitumen as 0.5% of the weight of bitumen, the bituminous mixture gave superior results in terms of stability, rutting and temperature resistance. Apart from the improved performance, bituminous macadam prepared using zycosoil modified stone and asphalt was found to be economical.

European Transport - Trasporti Europei

Effect of nano-materials on asphalt concrete mixes; a case study

The present study aims at studying ageing characteristics of conventional bitumen, polymer modified bitumen (PMB) and warm mix asphalt (WMA) by using FTIR. Results of obtained FTIR spectrum were quantified by calculating different indices and finally based on these indices ageing index of the binders for short- and long-term ageing were calculated. Results showed ageing increased amount of complex and high molecular weight components of the binders. PMB was found to have greater ageing resistance than conventional asphalt binders. In case of WMA, results found to be inconclusive, requiring further investigation. © 2017 Taylor & Francis Group, LLC.