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NSTL as a premier systems laboratory is working to ensure excellence in design, development and testing of surface & sub-surface vehicles, weapon control systems, surface and submerged platforms conforming to state-of-art technology apart from rendering expert services in all grey areas of associated science and technology.

The main task of NSTL is to attain self-reliance in underwater technology. The domain of work includes design & development of underwater weapons, Counter measures, Target, Decoys and Fire Control Systems, ship and submarine design validation. In order to carry out the complex task of designing underwater systems certain main unique Infrastructure Facilities are essential. Therefore some unique facilities of International Standards like Acoustic Test Facility, High Pressure Test Chambers, Torpedo Engineering Center, Hydrodynamic Test Facility and associated facilities are created at NSTL to carry out the surface & sub-surface vehicles development. A few of them are given below:

 
(I) HYDRODYNAMIC TEST FACILITIES
 
1.) High Speed Towing Tank (HSTT)
 

It is a hydrodynamic test facility recognized by International Towing Tank Conference (ITTC). The tank is fitted with a high speed towing carriage which runs at a maximum speed of 20m/sec and runs on parallel rails which are fitted to have a tolerance of 0.2mm over 100m length to follow the earth's curvature. It is fitted with a wave generator at one end to simulate random and irregular sea conditions while testing the models. It is also equipped with a model making workshop to make the scale down models of ships and submarines to carry out the model tests for determining the performance characteristics and evaluation of the power plant requirements, etc. The other features of High Speed Towing Tank (HSTT) are given below:

 
Tank dimension 500m x 8m x8m
Carriage speed Ahead 20m/ sec (max) Astern 4m/sec ( max)
With accuracy of 0.1% of set speed
Wave Generator Dual flap type capable of generating regular and irregular waves (unidirectional) up to wave height of 0.5m.
Speed Control By Ward Leonard System feeding power through current conductors to 8 in no 129 kW DC drive motors.
 
Tests Performed in HSTT
 
Resistance and self propulsion tests to assess speed power characteristics.
Flow visualization to identify flow separation, if any.
Open water test to obtain propeller characteristics.
Wake survey to determine flow velocities.
Sea-keeping tests for head sea only.
Dynamic tests for high speed vessels, such as, planning, multi-hulls, hydrofoil, SES, etc.
 

The facility is equipped with a Large Amplitude Horizontal Planar Motion Mechanism(LAHPMM) for carrying out planar motion studies of maneuvering characteristics of surface ships and submerged vehicles in surface condition.

 
Model of Extended Performance Hydofoil (EPH) - Resistance Tests
 
VIEW OF TOWING CARRIAGE
 
Wave Generator of HSTT
 
2.) Large Amplitude Horizontal Planar Motion Mechanism
 

Naval Science and Technological Laboratory(NSTL), Visakhapatnam has acquired a state-of-the-art Large Amplitude Horizontal Planar Motion Mechanism(LAHPMM) to augment the High Speed Towing Tank (HSTT) for carrying out planar motion studies of maneuvering characteristics and control effectiveness of surface ship and submerged body models in surface condition. In the absence of a full fledged and expensive Sea keeping and Maneuvering Basin(SMB), the LAHPMM and the already existing Vertical Planar Motion Mechanism(VPMM) procured for conducting tests on submerged bodies in the vertical plane, could be used to carry out some of the maneuverability tests for the surface ships and submerged bodies in surface condition at HSTT.

 

LAHPMM measures the various forces and moments acting on the model during tests to determine the complete set of hydrodynamic coefficients for formulating mathematical models which in turn can be used for computer simulation of trajectories under various maneuverabilities, including extreme turning maneuverabilities.

 
Features of LAHPMM:
 
An Integrated Towing Mechanism to tow models weighing up to 3 tones, length 4 to 7m and speeds up to 7.5m/s (max)
Capable of imparting sway, yaw, surge, roll and heel motions to the model
Frequency of oscillation: 0.01 to 0.3 Hz
 
Frequency of oscillation: 0.01 to 0.3 Hz
Amplitude of oscillation (max): 1000 mm (Sway);
500 mm Surge);
300 Roll, Yaw and Drift
Instrumentation 3-Component balance; Rudder and Propulsion Dynamometer; PC based data acquisition and control system
 
Ship Model connected to LAHPMM
 
3.) Cavitation Tunnel
 

The Cavitation Tunnel at NSTL is one of the most modern and the state of the art facilities in the world. This is used for study of cavitation inception of body profile and propellers. It is also used for study of Acoustic measurements due to cavitation of propellers.

This facility can provide a water flow speed of 15m/sec and create cavitation numbers 0.03 to 10. In order to design highly efficient propellers for applications to naval ships and platforms it is essential to carry out tests on these propeller models in the cavitation tunnel. The features of cavitation tunnel are given below:

 
Test Section Size 1.0m x 1.0 m x 6.0 long with an acoustic trough positioned below the test section housing 8 in no. B&K hydro-phone array (PULSE) for recording noise signals generated by the radiating hull and propeller in the test section
Drive System Thyristor controlled 700 kW DC electric motor driving 2.1 m dia fixed pitch 7 bladed axial flow impeller with 9 stator blades
Maximum Velocity in Test Section 15 m/sec
Pressure Range 10-300 kPa (absolute)
Minimum Cavitation 0.03 + 10/v2, where v is the flow velocity in test section.
Back ground noise <90 dB ref 1mPa in 1-100 kHz band, 1/3 Octave scale.
 

The tunnel is equipped with an Automatic Control System (ACS) for its operation and control; Data Acquisition & Analysis System (DAAS) for conduct of tests, acquisition of test data, analysis and prediction of results. It is also provided with a stand alone Acoustic Measurement System (AMS) for acoustic measurements, analysis and extrapolation to full-scale results. Various types of towing and propulsion dynamometers, 1/3/6 component balances, wake rake, hydro-phones pressure transducers, photographic and video recording systems and stroboscopes are also available to conduct model tests.

 
Tests Performed in CT:
 
Propeller tests in open water to measure performance characteristics in cavitating and non-cavitating conditions.
Tests with hull propeller model to measure self propulsion characteristics, propeller working in the wake of the model in cavitating and non- cavitating conditions. Hull propeller interaction.
Measurement of forces and moments on surface ships and submerged bodies including their control surfaces.
Determination of towing resistance of surface ships and submerged bodies.
Cavitation tests. Inception and decay.
Flow visualization.
Wake survey.
Measurement of hull pressure fluctuations induced by propeller and cavitation.
Measurement of acoustic radiation caused by cavitating and non-cavitating propeller and hull.
 
Cavitation Tunnel Test Section
 
4.) Wind Tunnel:
 

A wind tunnel to study the aerodynamic characteristics of surface and submerged platforms and underwater weapons has been set up at NSTL with a test section of 1.5m 1.5m x 4m x. A maximum speed of 60m/sec can be produced with a125 KW fan in this wind tunnel. The detailed features are given below:

 
Test Section Size 1.5 m x 1.5 m x 4.0 m long
Plenum Chamber 4.3 m x 4.3 m x 4.0 m long
Contraction Nozzle Varying from 4.3m x 4.3 m square to 1.5 m x1.5 m square; 4.0 m long
Diffuser Varying from1.5m x 1.5 m square to 3.5 m dia; 7.8 m long
Fan Size 3.04 m dia made of CFRP
Drive Motor 125 KW dc motor at 750 rpm
Maximum Speed at Test Section 60 m/sec
 

The Wind Tunnel is equipped with projection manometers, differential pressure transducers, velocity measuring probes, vertical catheto-meters, hot film anemometers, 48 port Scanivalve traversing gear as well as PC based data acquisition system and analysis software packages.

 
Tests Performed in WT:
 
Flow visualization and boundary layer studies for underwater vehicles.
Wake survey and velocity distribution behind a body for propulsor development.
Pressure and velocity distribution over axi-symetric bodie.
Estimation of forces and moments on control surfaces of a submerged body, etc.
 
WIND TUNNEL FACILITY
 
(II) SHOCK AND VIBRATION TEST FACILITIES
 
Shock Test Facility:
 

Measurement, study, analysis and mitigation of underwater noise generated by ship and submarines are essential requirements to have a healthy and stealthy Naval Fleet. Achieving the objective of having a silent ship is possible only if the machinery and the equipment fitted on these ships are also silent and their vibrations isolated. This is achieved through proper condition- monitoring of machines and design and development of shock & vibration mounts of appropriate type. The Ships and machinery may also be subjected to explosive shock loading due to enemy weapons in the event of conflict. The design of these ships and equipment should be such that they will withstand such shock and still be operational. Therefore to understand and design such systems NSTL has set up several facilities in the field of underwater shock, noise and vibration

 

A field Shock Testing Platform, a Shock Testing Tank, a Shock Platform and a Vibration Shaker are established at NSTL. NSTL is the qualifying agency for equipment to be fitted on board Naval Ships.

 

Floating Shock Platform: A field of shock testing facility using floating shock platform and mobile-instrumented van for data acquisition are created by NSTL. Using the twin facilities ships main machinery such as the gas turbines, diesel alternators, etc., weighing up to 15 tons can be subjected to the desired shock levels to pass qualifying criterion before installation

 

Shock Testing Tank: A double walled steel shock testing tank created at NSTL with a cross section of 15m x 12m x 10m is capable of handling equipment weighing up to 2.5 tons and can subject them to desired shock loads. The equipment is placed inside an open floating shock barge and an underwater explosion is set off by firing a charge. The behavior of the specimen is recorded through accelerometers placed on its body. The desired shock level can be achieved by varying the quantity of charge, stand off distance and depth.

 
SHOCK TESTING TANK
 

Shock Testing Machine: A shock-testing machine is also installed at shock and vibration center of NSTL. This micro-processor controlled machine is capable of generating variety of shock pulses such as - half sine square waves ranging from 2 - 40 m/sec pulse duration. It can generate acceleration of 90g on payloads up to 500kgs.

 

Vibration Shaker: In order to study the response of equipment and machinery subjected to severe vibration levels Vibration Excitation Platform is set up at NSTL. This platform with a load capacity of 220 Kg can generate vibration in the frequency range of 1 to 5000Hzs varying 'g' values up to 10. This machine is extensively used to test the shock and vibration isolation rubber mounts and various subsystems of torpedoes and mines.

 
Torpedo Tail-undergoing Vibration Test
 

Shock and Vibration Mounts: The shock and Vibration Mounts are used to reduce radiated noise due to vibration of various machinery and safeguard the machinery and equipment against underwater explosion. NSTL has developed several types of mounts such as plate, angular and cylindrical types for use with gas turbine engines, reduction gears, and diesel engines on board ships. The imported mounts are no longer available for replacement. The performance of NSTL mounts are superior to those of foreign origin. They can withstand shock loads up to six G at the maximum weight of 1.5tons. Vibration isolation of 20 dB and shock isolation of 15 dB were achieved with these mounts.

 

Condition Monitoring System: Vibration signature analysis is an important tool in diagnosing faults on rotating machinery. NSTL has developed Microprocessor based on line Condition Monitoring System exclusively for monitoring vibration levels of main propulsion gas turbines and gearing of different classes of ships meeting the NI Naval Standards. These systems are operational onboard front line ships of Navy.

 
(III) ACOUSTIC TEST FACILITIES
 
ACOUSTIC TEST CENTER
 

An Acoustic Test Center is established at NSTL for noise evaluation and qualification of various types of equipment, machinery, torpedoes etc. the test center consists of an Anechoic Room and a Reverberation Room.

 

Anechoic Room: It is used to evaluate noise radiation characteristics of equipment. machinery over a wide frequency range of naval interest. It is basically a room inside room type construction having 1m air gap between inner and outer walls, floor and ceiling. These inner rooms are floating on a heavy duty rubber pads. The dimensions of the inner room are 10 x 10 m and height 6.8 m. The inner walls of the inner room are lined with wedge shaped noise absorbers.

 
Anechoic Room
 

Reverberation Room: It is used for measuring acoustic properties of material. It is also a room inside room type construction having 1 m air gap all around between inner room walls and outer room. The roof height is 5.14 m. The inner room of this reverberation room also is floating or rubber pads. The walls are non parallel, the opposite walls making 5o angle with each other. The roof also makes 5o angle with the floor.

 
Reverberation Room
 

ACOUSTIC TANK FACILITY: The Acoustic Tank Facility is also established for calibration of underwater transducers in which near field and far field conditions can be simulated. The tank is of 8m x 8m x 8m size. The transducers operating at frequency of 3KHzs and above can be calibrated.

 
 
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