1. Numerical Modeling of Flow Pattern at a Right-angled River Bend Using CCHE2D Model

Animesh Das (PhD scholar)
Dr. Sushant Kumar Biswal (Supervisor)

In this study, the CCHE2D model is used to analyse the flow pattern in a meander reach of the Gomati River. The finite volume method is used by the numerical model to solve the depth-averaged two-dimensional equations with k - e turbulence closure. The numerical findings were compared with field data for two different flow rates in order to calibrate the CCHE2D model using various Manning's roughness coefficients. The results show that for the minimum and maximum discharges, a smaller Manning's roughness factor (0.015 ≥ Ā ≥ 0.025) is more favorable to a higher Manning's roughness factor (0.030 ≤ Ā ≤ 0.040). The results of the numerical model demonstrated that fluctuations in hydraulic parameters including shear stress, velocity, flow depth, and Froude number in the river bend are greatly influenced by the existence of centrifugal force and helical cells. The linear relationship between velocity and shear stress is presented across the whole study reach, as indicated by the R-square and linear correlation coefficient (r) components. The results of the model show that the flow field within the river bend can be accurately simulated by the computational model.

The key findings of the research such as:

• The Manning’s roughness coefficient ranges of 0.030–0.040 will have better results, and for medium and high discharges, the roughness coefficient ranges of 0.015–0.025 provide the more accurate result.
• The analysis suggests that the water surface and the maximum velocities in the river arch develop toward the outer bank. The simulation results also indicate that, on average, the average velocity for the discharges of 68 m^3/s and 102 m^3/s in the study reach is 0.56 and 0.77 m/s, respectively.
• Moreover, the average shear stress for the two discharges mentioned above is 27.99 and 35.62 N/m², respectively.
• The results of the study show that the CCHE2D model has the ability to simulate the complex rivers with varying river morphology. Therefore, in the engineering and operational projects of the Gomati River, the results of this numerical model can be trusted and used.

2. Fabrication of PANI@Fe-Mn-Zr hybrid material and assessments in sono-assisted adsorption of methyl red dye: Uptake performance and response surface optimization

Bibek Saha (PhD scholar)
Dr. Animesh Debnath (Supervisor)

In recent decades, industrial wastewater discharge containing toxic or hazardous manufactured dyes has risen tremendously, creating a serious environmental threat. A new hybrid adsorbent, PANI@Fe–Mn–Zr synthesized by mixing Fe–Mn–Zr metal oxide composite with polyaniline (PANI), was used to study methyl red (MR) dye removal from aqueous solution. The crystalline nature, surface characteristics, and shape of produced nanoparticles were investigated using different characterization techniques such as energy dispersive X-ray (EDX) analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD) pattern, Brunauer-Emmett-Teller (BET) analysis and Fourier transform infrared (FTIR) analysis. The conceptual framework of anionic dye ion sorption onto manufactured nanomaterials was investigated using kinetic and isotherm analyses. Using experimental data on adsorption, mathematical models based on response surface methodology (RSM) were designed to analyse adsorption behavior for correct assessment of MR dye removal efficiencies. Natural water and real wastewater samples were employed to observe the extant of interferences in MR dye uptake capacity with respect to blank or controlled samples. Finally, the performance of the PANI@Fe–Mn– Zr was evaluated by comparing with other studies where several kinds of adsorbents have been used to remove different dye pollutants. The adsorption process was observed to be influenced by the sonication time, dose of PANI@Fe–Mn–Zr, and initial concentration of MR dye.

The following results were obtained by conducting the adsorption experiments:

• At an initial MR dye concentration of 25 mg/L, 0.25 g/L of PANI@Fe–Mn–Zr dose, 15 min of sonication, and pH 7.0, the maximum MR dye adsorption efficiency of 90.34% was achieved.
• Kinetic analysis was performed using five different kinetic models, which shows that the pseudo-second-order kinetic model had the best fit among the five models. The Langmuir isotherm best fits the adsorption experiments at pH 7.0, yielding a significant MR dye uptake capacity of 434.78 mgg-1.
• The most significant adsorption mechanisms that have been observed in uptake of MR dye onto PANI@Fe–Mn–Zr were electrostatic attraction, π-π bond interactions and hydrogen bonding.
• Response surface optimization study was performed for optimizing the experimental conditions from which maximum dye removal of 98.19% was obtained at contact time of 12 min, initial MR dye concentration of 15 mg/L and PANI@Fe–Mn–Zr dose of 0.4 g/L.
• Use of real wastewater and water samples suggest that there is only 6– 19%reduction in the dye removal efficiency as compared to the blank orcontrolled experiments conducted with deionized water.

3. Study on Cyclic Response of Dry Uniform Soil Deposit using Shake Table Tests and DEEPSOIL Program

Debnath Mondal (M.Tech Scholar)
Dr. Sanjay Paul (Supervisor)

Ground response analysis describes the free-field response of soil deposit to an input ground motion which is used to analyze the instability of soil deposit and surface mounted structures. This paper presents a study of such response of dry uniform soil deposit on bed rock subjected to sinusoidal motion of significant frequency range comparable with typical seismic recordings at geotechnical engineering laboratory, NIT Agartala. For this a series of single-axis shake table tests were carried out on uniform dry silty clay, sand and gravel model subjecting sinusoidal motion of suitable frequency ranges. The length to height ratio of the laboratory soil model was kept about 1.71 for shake table tests. The models were prepared by dry pluviation technique. The height and rate of pluviation were adjusted accordingly to achieve the target relative density of the soil model. An assessment of the one dimensional ground response analysis has been carried out for similar characteristics soil column model subjected to identical ground motion using DEEPSOIL v7.0.

The result obtained from the shake table tests shows the influence of frequency on response of soil model and the variation of strength and displacement parameters at different depth. These results have been compared with the DEEPSOIL assessment to show the relative difference of the parameters to express the cyclic response of dry uniform soil deposit.