Showing papers by "K. Murali published in 2009"

Application of low-Re turbulence models for flow simulations past underwater vehicle hull forms

Abstract: Minimum power requirement is one of the important design criteria for successful operation of underwater vehicles. CFD based prediction and estimation of power requirement is increasingly carried out in practice. However, reliable prediction depends on suitable turbulence models. This paper presents a comparative assessment of four low Reynolds number (low-Re) k- Iµ models for computation of hydrodynamic forces on underwater vehicle hull forms. The low-Re models are being considered more suitable for underwater axisymmetric bodies due to the following merits (i) they have no wall function approximations, (ii) they could compute low turbulence levels such as in the viscous sub-layer and (iii) they could account for the effect of damped turbulence. The low-Re models used in the present study are namely the models of Abe-Kondoh-Nagano (k- Iµ AKN), Chang-Hsieh-Chen (k- Iµ CHC), Launder-Sharma (k- Iµ LS), and Yang-Shih (k- Iµ YS). It has been found that the k- Iµ AKN low-Re model consistently provided superior performance in predicting the flow characteristics around underwater vehicle hull forms. Keywords: Axisymmetric bodies, autonomous underwater vehicle, CFD, damping functions, low Reynolds k- Iµ models, QUICK scheme doi: 10.3329/jname.v2i1.2029 Journal of Naval Architecture and Marine Engineering 2(1)(2005) 41-54

Wave-Induced Pressures and Forces on Deck Slabs near the Free Surface

Abstract: The hydrodynamic interaction of regular and random waves with a model offshore deck has been investigated in a wave flume. The hydrodynamic pressures and forces on the model as well as its reflection and transmission characteristics are investigated in a dimensionless form. The experiments were carried out for three different clearances (e) between the still water level and the subface of the model. In order to investigate the effects of relative clearance of the deck ( e/H in case of regular waves and e/ Hs in case of random waves), different wave steepnesses ( H/L in case of regular waves and Hs / Lp in case of random waves) were employed by varying wave height (H) and wavelength (L) . The effects of the wave steepness, relative clearance of the deck, relative length of the model ( B/L in case of regular waves and B/ Lp in case of random waves) on the pressures and forces on the deck slab are investigated with a well controlled experimental program. The variation of the pressures along the length of the...

Laboratory Investigation of Clay Mineral Fines as Dispersant for Combating Oil Spill

Abstract: The oil-mineral aggregate formation tests are commonly conducted in batch-scale testing apparatus in order to find the effectiveness in reducing the oil concentration in water column. However, for the assessment of effectiveness of mineral as dispersant under real sea state conditions, test protocols are required to have hydrodynamic conditions closer to the natural sea state environment, including transport and dilution effects. To achieve this goal, experimental program designed and constructed in a wave flume system to study the oil-mineral aggregation and it’s effectiveness in reducing the oil toxicity, in a controlled mixing energy conditions (non-breaking and breaking waves). Quantification of oil mineral aggregation effectiveness was based on observed changes in dispersed oil concentrations and distribution of oil in the beach sediments. The study results quantitatively demonstrated that total dispersed oil concentration in the water column were strongly dependent on the presence of mineral aggregates and the influence of breaking waves. The effectiveness of application of minerals, as a function of sea state was studied and would be useful in drafting of future operational guidelines for mineral dispersant use at sea.Copyright © 2009 by ASME

Simulation and Prediction of Runup Heights Due to Great Indian Ocean Tsunami

Abstract: An Explicit Finite Element Method has been applied to simulate the 2004 Great Indian Ocean Tsunami (IOT). The Sperical Shallow Water Equations (SSWE) is used to model the oceanic flow. The domain comprising of Bay of Bengal, Arabian Sea and Indian Ocean has been considered for simulation with an initial disturbance resembling the type and location of the 2004 IOT. The Wave elevations and its deformations have been depicted in the results. The wave heights obtained from the numerical simulation have been compared with the signature data for the Tamil Nadu Coast. The Effect of coriolis force on tsunami has also been studied and reported in this paper.

Role of vegetation on the attenuation of forces on structures due to Cnoidal waves

Abstract: The evaluation of forces on structures in the marine environment due to ocean waves is absolutely essential in the planning and development of mitigation measures against natural coastal hazards and dictates their design. Further, studies on the forces on coastal structures due to regular and random waves are well entrenched in literature, whereas, that due to shallow water waves are rather scanty. The recent tsunami has added a new dimension on the role of vegetation on the forces on structures. Due the propagation of tsunami, a number of signature studies have revealed that structures fronted by vegetation have suffered minimum damage compared to that in its absence and as also reported by Yanagisawa (2008). In the present paper, the results from an experimental study to investigate the effect of vegetation on a typical structure located onshore over a slope of 1:30 are reported. The tests were carried out in a wave flume of length 72m, width 2m and 2.7m depth. The water depth at the toe of the slope was 1m. Slender flexible cylindrical members that represent plantation along the coast have been adopted for the tests. Experiments were carried out for different G/B ratios of 0, 0.5,1 and 1.5. (Where G is the distance between front face of vegetation/ green belt and the rear face of the building and B is width of the building). Experiments were repeated for three widths of Green belts (BG) and for each of the green belt, two different diameters of the cylinders of 10mm and 3.0mm were used. The forces on structure were measured with load cells in the presence and absence of the green belt. The Cnoidal waves covering a range of Ursell parameter between 18 and 700 were employed for the experiments. The different vegetal and flow parameters in a non-dimensional form have been identified. The variation of non-dimensionalised force over the slope in the presence and absence of vegetation as a function of the Ursell parameter, Relative rigidity and Reduced velocity for different dimensionless SP/D of the green belt (where SP is the spacing between plantation/diameter of plantation) clearly indicates that there is a significant reduction in the force due to the presence of vegetation. Prior to the experiments with the green belt, for the purpose of validation tests were carried out on the force measurements of waves over a plane slope, the results of which compared with existing results exhibited a good agreement. The details of the experimental set-up, procedure and analysis and discussion of the results are reported in this paper. It has been found that, • The non-dimensional Forces on the structure increases by about 80 %, when the distance between the structure and the Green Belt is in the range of 0.5B to 1.5B. • The most favorable location for the Structure is adjacent to the Green Belt or away from the Green Belt by more than twice the width of the structure. For this configuration, the forces were found to reduce to an extent ranging between 50% and 90%.