Numerical Simulation of Two-Dimensional Shear Flow

Numerical experiments on finite difference solutions of time dependent two-dimensional Navier-Stokes equations are used to study the transition triggering off in a mixing layer of initial tanh(y) profile. The inflow is excited by sinusoidal waves resulting from the linear theory of hydrodynamic instability. Numerical realizations are compared, through stream wise growth of momentum thickness and vorticity plots, with Winant and Browand experiments. The transition control and triggering off are studied through the finite difference solution of the two-dimensional time dependant Navier-Stokes equations.  In a shear flow, the transition results from hydrodynamic amplification of unstable disturbances stimulated by perturbations of diverse origin.  In a unidirectional flow, the most unstable disturbances are two-dimensional transverse waves {2, 3} and experiments have shown the area where small disturbances grow exponentially {5,8,9,10}.  Thus, a two dimensional numerical simulation is well suited to the study of transition triggering off

Bumper landing of common dolphin fish Coryphaena hippurus at Sassoon Dock, Mumbai

On 29.10.05, an unprecedented twelve tons of common dolphinfish, Coryphaena hippurus was landed at Sassoon Dock by gill netters. The catch was made by 22 gill netters on a four day voyage, operating surface drift nets of mesh 80-120 rnrn upto 40 m depth of Murud, about 100 km south of Mumabi. The fish is sexually dimorphic with mature males having a pronounced bony crest in the frontal portion of the head

Account of wetland flora of Devgad Island, off Karwar, Karnataka

The maritime state of Karnataka is situated between 11° 31' and 18° 45' N and 74° 12‘ and 78° 40' E along the south-western peninsular India. The state consists of three coastal districts, namely Uttara Kannda, Udupi and Dakshina Kannada. There are eight islands off Karwar, the district head quarter of Uttara Kannada District. These tropical islands are confined between 140 45’ N to 140 55’ N and 740 00’ to 740 07’ 30” E. The vicinities of these islands are key areas where commercial fishing is concentrated and these islands also act as refuges for many commercial and ecologically important flora and fauna. Devagad Island, regionally known as Devagadagudda Island, is one of the important Oyster rock Islands, with light house in it. This island is a reserve forest which covers 2.5 sq. km. with 41m elevation above MSL. The climate is wet monsoon type, with average total rainfall of around 3000mm/yr and temperature range between 20 0C to 38 0C. Though this island is important from the ecological and economic point of view, no detailed study is conducted to know the floral and faunal diversity of this island. Hence a study was conducted to assess the floral diversity of the island with special emphasis on the wetland floral diversity

Unprecedented landing of sharks by hook and lines at New Ferry Wharf, Mumbai

About twelve hand-operated hook and linersfrom southern Tamil Nadu regularly fish off Okha, Gujarat for pelagic sharks and these vessels land their catch at New Ferry Wharf.On 31.08.06, an unprecedented catch of about 3.2 t (300 Nos.) of sharks was landed by two hook and liners. The catch comprised of 270 numbers (90%) of Carcharhinus limbatus measuring 110-125cm in total length, 21 numbers (7%) of Galeocerdo cuvieri measuring 173-210 cm and 3 numbers (3%) of Carcharhinus sorrah measuring 115-128 cm. The weight range was 8-11 kg. The catch was sold for Rs. 2 lakhs at the rate of Rs. 60/kg

‘Pakshi Pitti’: a robust haven for pelagic birds in the Indian Ocean

India, a land of distinct climatic and geographic zones, supports a remarkable diversity of avian fauna within both its mainland and its seas. There are over 1200 species of birds recorded in India, with the majority occurring in the mainland (Praveen et al., 2016). Surrounded by extensive marine zones on its three sides, territorial waters and marginal seas around India form seamless habitats for a significant number of marine avian species. Seventy species of marine birds are observed in the region (BirdLife International 2015). These include predominantly open oceanic species like frigate birds, tropicbirds, shearwaters and petrels which are winter visitors or vagrants, but birds like gulls and terns are more commonly found along the coastal waters of India

Observations on the flesh-footed shearwater

A dead specimen of the flesh- footed shearwater Ardenna carneipes (Gould, 1844) was collected on 21.07.2017 from Paravoor beach, Alappuzha district, Kerala. The bird had a total length of 40 cm (bill tip to tail tip) and a wingspan of 86 cm. The specimen was deposited in the National Designated Repository, ICAR- CMFRI, Kochi under the Accession No. Misc.36. The bird is distinguished from other shearwaters in this area, namely, the Persian shearwater, Audubon’s shearwater, Sooty shearwater, Wedge-tailed shearwater, Short-tailed shearwater and Streaked shearwater by its pale bill with distinct black tips. It also has darker underwings and a shorter rounded tail as compared to other shearwaters of the region. Its flight is described as “a stiff-winged glide interspersed with slow lazy flaps” (Kazmierczak, 2015, A field guide to the birds of the Indian Subcontinent, p.34)