Manasa Ranjan Behera

Temporal variability and climatology of hydrodynamic, water property and water quality parameters in the West Johor Strait of Singapore.

The study presents a baseline variability and climatology study of measured hydrodynamic, water properties and some water quality parameters of West Johor Strait, Singapore at hourly-to-seasonal scales to uncover their dependency and correlation to one or more drivers. The considered parameters include, but not limited by sea surface elevation, current magnitude and direction, solar radiation and air temperature, water temperature, salinity, chlorophyll-a and turbidity. FFT (Fast Fourier Transform) analysis is carried out for the parameters to delineate relative effect of tidal and weather drivers. The group and individual correlations between the parameters are obtained by principal component analysis (PCA) and cross-correlation (CC) technique, respectively. The CC technique also identifies the dependency and time lag between driving natural forces and dependent water property and water quality parameters. The temporal variability and climatology of the driving forces and the dependent parameters are established at the hourly, daily, fortnightly and seasonal scales.

Effect of the Tidal Currents at the Amphidromes on the Characteristics of an N-Wave-Type Tsunami

The disturbance due to a tsunami is always coupled with permanent harmonic ocean tides. The tsunami based on its time of occurrence will combine with a particular tidal phase. Thus, a coast will experience a modified water level due to a high- or low-tide situation. On the other hand, the tidal current at the amphidromes may act as an attenuator or amplifier of the tsunami prior to its arrival at the shore. A one-dimensional numerical study has been carried out to demonstrate the effect of the amphidromic current on tsunami characteristics. A realistic N-wave profile of the initial perturbation has been considered for the initiation of a tsunami. The interaction of the amphidromic current with the phase velocity of an N-wave-type tsunami and the subsequent run-up along the shore has been investigated in this paper.

Assessment of kinetic tidal energy resources using SELFE

An investigation is carried out to study the theoretical tidal stream energy resource in the Singapore Strait to support the search for renewable energy in the effort to reduce the carbon footprints in the Southeast Asia. The tidal hydrodynamics in the Singapore Strait has been simulated using a Semi-implicit Eulerian-Lagrangian Finite-Element (SELFE) model solving the 3D shallow water equations with Boussinesq approximations. Potential sites, with high tidal current (2.5 m/s) and suitable for Tidal Energy Converter (TEC) array installation to generate sustainable energy, have been identified. Further, various operational factors for installation of Tidal Energy Converters are considered before computing the theoretical power output for a typical TEC array. An approximate estimation of the possible theoretical power extraction from a TEC array shows an energy potential of up to 4.36% of the total energy demand of Singapore in 2011. Thus, the study suggests a detailed investigation of potential sites to quantify the total tidal stream energy potential in the Singapore Strait.

Nearshore Sediment Transport in a Changing Climate

The impact of changing wave climate on the most important nearshore process, longshore sediment transport (LST), along the central west coast of India is investigated. The main purpose of this study is to provide a better understanding of the meteo-marine climate of the central west coast of India, which is highly influenced by the Arabian Sea and the Indian Ocean. To understand the contemporary evolution of the coastline, hindcast wave climate from ERA-Interim wave data (1979–2016) is used. The annual average significant wave height (Hs), wave period (Tp) and wave direction (α0) are obtained and used to estimate annual LST. This region receives oblique waves from the W-SW direction which induces a huge gross northerly transport. It experiences two types of waves, swell waves (remotely generated waves that travel thousands of kilometres before hitting the coastline) and wind waves (also known as seas, which are locally generated), both of which are responsible for coastal sediment transport. The swell waves are the major component of a total wave system. It has more strength than the locally generated wind waves and dictates the wave direction and significant wave height at any given point of time. Therefore, the swell wave-induced LST is an order of magnitude higher than the wind wave-induced LST. It was observed that the sediment transport has a seasonal nature due to the influence of monsoonal winds in this region. The total LST in the central west coast of India shows a decreasing trend due to the reduced swell generation in the lower latitudes of the Arabian Sea and the Indian Ocean.

Effect of continental slope on N-wave type tsunami run-up

Frequent tsunamis across the globe have devastated the coasts and led to significant loss of life and property. This calls for a better understanding and estimation of the tsunami characteristics. Considering the scale of the problem, numerical modelling is the most suitable method for tsunami simulation and understanding. Most tsunamis are long-period wave and governed by shallow water equations. Although tsunami is expected to initiate in the deeper waters with very less height, it may have significant amplification while traversing over the slopes. In this study, an attempt is made to understand the effect of continental slope on the transmission, propagation and run-up of tsunami. This study provides better understanding of the physical process through computation of tsunami run-up height and arrival time. To carry out this investigation and to get a preliminary understanding, a one-dimensional numerical model study is carried out using shallow water equations. These equations are solved using Crank–Nicolson finite difference approximation method on a staggered grid. This study is carried out by considering N-wave-type tsunami profile with leading depression (trough). In this study, various continental slope profiles available along the Indian coast were considered. The amplification or attenuation of the tsunami characteristics over these cross-sections was studied. Significant change in the tsunami run-up is observed for different continental slope and water depth on continental shelf.

Experimental study of scour around a complex pier with elliptical pile-cap

A complex bridge pier is an assembly of a column and foundation such as pile foundation with a pile-cap, partially or completely exposed to the flow. Considering the interaction of various factors around the pier, the pile-cap elevation in relation to the sand bed is expected to differ with time. Therefore, it is necessary to assess scouring over various potential pile-cap elevations. In this paper, laboratory experiments were carried out to analyze scour and mean velocity profiles around complex pier under the effect of low Reynolds numbers. Three pile-cap elevation cases were studied here, viz, the sand bed depth taken above the pile-cap level; the sand bed depth taken below the pile-cap top; and the sand bed depth taken at the level of pile-cap bottom. The results showed different scour patterns in the three cases considered. It was also noted that the least scour-depth occurred in the second case and maximum in the first one.

Identification of Suitable Grid Size for Accurate Computation of Run-up Height

A numerical investigation has been carried out to obtain a non-dimensional grid size (grid size/ tsunami base width) for the near shore discretisation of computational domains for long wave modelling. A 1D domain has been considered in which, the flow has been solved by 1D shallow water equations with vertically integrated flow variables. The sensitivity study of the grid size was carried out in the 1D channel with an open boundary at one end and shelf boundary at the other end. The grid size was varied from 10 m to 1000 m and its effect on the computation of the tsunami run-up along the shoreline has been investigated. The non-dimensional grid size for the computation of run-up was optimised by comparing the non-dimensional run-up (tsunami run-up/initial tsunami height) and a threshold value of 5.0e-4 was obtained. Further, the study was extended to real scenario by adopting various grids for the shelf region of northern Tamil Nadu coast, south east coast of India in 2D and a suitable grid size was obtained.

Modeling of the Indian Ocean Tsunami

Shallow Water Equations are solved using an Unstructured Explicit Finite Element Method (UEFEM) to simulate long waves in the ocean. The formulation of the UEFEM has been described and found to be computationally efficient for large problems such as basin level modeling of tsunamis. Different domains have been considered to simulate the propagation of the waves due to an artificially imposed initial disturbance. The domain of Bay of Bengal has been considered for simulation with an initial disturbance which resembles the type and location of the 2004 Indian Ocean Tsunami. The Wave elevation and deformations as well as time of travel of tsunami are reproduced. The method hence has high potential of being attractive for application of simulation of global tsunamis.Copyright

Front Tracking Approach and Application to Multi-Fluid Flow

Multiphase flows simulations using a robust interface-tracking method, are presented. The method is based on writing one set of governing equations for the whole computational domain and treating the different phases as single fluid domain with variable material properties. Interfacial terms are accounted for by adding the appropriate sources as δ functions at the boundary separating the phases. The unsteady Navier-Stokes equations are solved by finite volume method on a fixed, structured grid and the interface, or front, is tracked explicitly by a lower dimensional grid. Interfacial source terms are computed on the front and transferred to the fixed grid. Advection of fluid properties such as density and viscosity is done by following the motion of the front. The method has been implemented for interfacial flow problems, depicting the interface and topology change capturing capability. The representation of the moving interface and its dynamic restructuring, as well as the transfer of information between the moving front and the fixed grid, is discussed. Extensions of the method to density stratified flows, and interfacial movements are then presented.Copyright