The Hindu Business Line : NSTL: Making waves in ship design

NESTLING amid rich greenery, the Naval Science and Technology Laboratory (NSTL) at Visakhapatnam lies totally hidden from public gaze. But inside this sprawling institute, a team of highly qualified scientists are skillfully working on critical and strategic research projects, including in the areas of missile, torpedo and ship design.

Indeed, few will be aware of the fact that the institute houses a premier research facility for ship designs, one of its kind in the country. With the recent expansion of this facility, NSTL is now set to make waves in the realm of ship design, drawing up plans for shipyards and shipping companies on a commercial basis.

The hydrodynamics testing facility has a high speed towing tank (HSTT) for studying the hydrodynamics of ships and propellers through model experiments and a cavitation tunnel, which was commissioned a few weeks ago. A third facility, a sea -keeping and manoeuvring basin, is likely to be added in the coming years, which will enable NSTL undertake a full package of studies related to ship and propeller design.

The HSTT is equipped with a tank, 500 m long and 8 m wide and a overhead carriage that can tow a model ship across the surface of the water at a speed of 20 m per second. It also has a wave generator capable of generating regular and irregular (multi-directional) waves and a planar motion mechanism.

According to a NSTL scientist: ``The HSTT is mainly used to design hull and propellers for ships. Hull shape is vital for a ship as it gives the vessel the required speed, capacity to carry weight and decides the power requirement.

Even a one per cent decrease in power consumption can mean a significant saving. Also, the efficiency of the propeller will depend on the hull shape — different hulls come with different propulsion packages.

With this facility, we can now design the most suitable hull shape and propeller for different types of sea-going vessels.''

This facility assumes significance in the light of the fact that shipyards and shipping companies have had to depend on foreign institutes to get the hull and propeller design. In fact, the HSTT has already undertaken some major orders.

For example, it recently modified the original hull design of a tanker being constructed at Cochin Shipyard and designed a propeller for a 400-capacity passenger vessel for Alcock Ashdown (Gujarat) Ltd, a shipyard owned by the Gujarat State Government.

``We have also given a hull for a model container vessel being constructed jointly by the Ministry of Shipping, Indian Register of Shipping, Alcock Ashdown and IIT Kharagpur. In fact, they had got the designs from overseas, but when we tested them here, we discovered that they offered higher resistance. We modified the designs and they (the consortium) are very happy,'' the scientist said.

The HSTT is capable of carrying out a string of hydrodynamics tests, including the self-propulsion test, to estimate the delivered power at various speeds, open water test to determine the "open water characteristics'' of the propeller and wake measurement test to determine the wake velocities in the plane of the propeller disc so as to study the influence of ship's wake on the propeller performance.

The HSTT facility was recently expanded with the addition of the cavitation tunnel (CT). Explained the scientist heading the CT operations: "What is cavitation? When a propeller rotates, the water pressure in the surrounding area goes down and correspondingly water evaporates faster, leading to formation of bubbles. When these bubbles burst, a relatively huge water force smashes on to the propeller, causing damage to the blades and vibration, apart from reducing speed of the vessel. The formation of bubbles is cavitation and its study is vital for ship design.''

The CT is a closed tunnel, 31 m long, with a 5.2-m long acoustic trough, an automatic control system (ACS) and a data acquisition and analysis system (DAAS).

The facility contains a contraction nozzle to create a favourable influence on the flow quality in the test section of the tunnel, turning elbows to induce smooth change in direction of flow of water inside the tunnel and a pressure control system to change the pressure inside the test section of the tunnel through an air compressor capable of generating high tunnel pressure of 3 kg/sq cm and a vacuum pump for generating a vacuum of 0.1 kg/sq cm.

The facility is backed by a software that can produce off-line and online analysis of the data acquired and give outputs accordingly.

The facility can be used to perform a wide range of tests, including propeller tests in uniform flow to measure open water characteristics such as thrust, torque and efficiency in cavitating, tests with hull-propeller model to measure self- propulsion characteristics behind the wake of the ship and analysis of acoustic radiation caused by propellers.

NSTL is now drawing up plans to make commercial use of this premier research facility, which will help save significant foreign exchange as India has had to depend largely on foreign institutes and shipyards for ship, hull and propeller design.

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