Keeping quiet about DCNS

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DCNS, one of Europe’s leading naval defence groups and contractor for integrated warships and systems, is a dedicated user of Brüel & Kjær sound and vibration solutions. This article, written with the support of DCNS, illustrate show PULSE™ is playing a central role at key DCNS operation centres in Northern France; helping with design, maintenance, acceptance testing and troubleshooting – in other words, helping to keep ships running and to keep them quiet.

PULSE at DCNS

In an organisation like DCNS with its diverse needs and expectations, the PULSE platform is expected to play many different roles. Different operations utilise PULSE for widely different applications such as acceptance testing, design, R&D, maintenance and troubleshooting. Measurements for sound intensity, underwater acoustics, radiated noise, vibration analysis and modal analysis are collected, processed, analysed, stored and managed by the PULSE platform.

Seven PULSE systems are in use at the DCNS Brest site for maintenance of SNLE (Sousmarin Nucléaire Lanceur d’Engins) strategic submarines and surface ships, whilst a further six systems are operated by the French Navy on board SNLE submarines. At the Lorient site, a 17-channel PULSE system is in action for design of naval systems and construction of surface ships. At Nantes-Indret, a 261-channelPULSE system played an integral role in the testing of the propulsion system of the latest SNLE strategic submarine. Eight PULSE frontends(C-, D- and E-frames) are now used as five independent systems for machine diagnostics, modal analysis and intensity measurements. At the Cherbourg site, where all the submarines for the French navy are constructed, DCNS has an extensive programme for acceptance testing and troubleshooting of all auxiliary equipment. For nuclear-powered strategic and attack, and conventional submarines, four PULSE systems measure from microphones, accelerometers, hydrophones, intensity probes and force transducers.

This article focuses on the Cherbourg operation, where sound and vibration test programmes are in place at the workshop, and on board submarines during both harbour and sea trials. The measurement programme is diverse, and huge amounts of data can be generated and must be readily accessible. Here, engineers have automated many of the PULSE measurement tasks and put PULSE Data Manager (PDM) to good use to organise some 15 years’ worth of data from thousands of measurements.

Silent Running at the DCNS Cherbourg Operation

DCNS Cherbourg is the principal site for manufacture of SNA attack and SNLE strategic submarines. It is here that the new Barracuda class programme is at work.

Arnaud Mesnil, Measurement Technician Sound & Vibration Dept., is well underway with integrating a PULSE programme for acceptance testing of auxiliary equipment – fans, pumps, superchargers and motors. New equipment must be vetted by a team of eight technicians and three engineers, and the vibration and acoustic signatures measured, analysed and matched up to stringent acceptance limits.

The team needs tools that handle, process and store a huge amount of measurement data. Sound intensity, vibration, underwater acoustics, modal analysis, sound power and mobility all contribute to the extensive measurement programme. Measurements are made on board during harbour tests and sea trials, and in the workshop at the central office at CETEC(Centre d’Etudes Techniques et d’Evaluationde Cherbourg). The same equipment also needs to be tested on several different submarines. Coupling this with tests made for different operational conditions, different speeds, different pressures all leads to an extremely comprehensive test programme that needs significant data management!

The Data Challenge

Before embarking on the measurement programme with PULSE and PDM, the acoustic team had a number of other measurement and data-storage systems to contend with. Both Windows®-based and UNIX-based systems were in use, and measurement data saved on several hard drives, and in different formats not directly compatible with PULSE. All this provided a challenge to both systems and personnel. Finding and accessing specific data was very difficult – and integrating data into meaningful reports almost impossible! Moreover, two different technicians could not access data simultaneously, making for a very inefficient system.

Today, with everything centred around PULSE and PDM, life is so much easier. Huge amounts of PULSE measurement data is stored and is readily accessible via PDM. Some 15– 16 years’ worth of measurement data is now available with a few mouse clicks. And when considering that in one year they can collect data from up to 700 test trials with 50 to 100autospectra per trial, this adds up to a considerable amount of data!

Arnaud proposed a PDM client/server architecture. He developed PULSE automation software that enables users to store data on laptops with specific information attached (PDM metadata), and to copy this data to the server when finished. The original Unix-based vibration measurement system was replaced by this PULSE automation software, and conversion software written to convert the old measurement data to PDM format. Finally, a database called “SALEM” was created to handle all the metadata, and bind the system together.

Automating Application-specific Setups

Setting up complex measurements and tight measurement time-frames often don’t go hand in-hand! Application-specific GUIs come to the rescue here by confining the measurement process to just that which is necessary. Here, DCNS exploit the versatile PULSE VBA/OLE2 programming tools to develop intuitive application-specific user-interfaces to automate PULSE operation for specific tasks. Without necessitating an expert in application programming, the VBA interface is an excellent tool for automating PULSE measurements. The time saving benefits to DCNS are obvious. Application-specific GUIs make the whole measurement process so much easier – just enter metadata, choose a few configuration parameters and press ‘Start’. This saves valuable measurement time – especially for personnel not familiar with the standard PULSE user-interface, and removes the risk of wrong measurement set up – it’s all done for you. The following three application examples show how DCNS has designed time-saving solutions for its measurement programme. Each example shows how, with just a little thought and some versatile tools, potentially complex time consuming tasks can be turned into efficient streamlined measurement procedures.

Example 1: Automating Sound Power Measurements
 
In the first example, Arnaud had the task of making a simple Sound Intensity measurement procedure that set up PULSE, informed the operator which faces on the object to measure, and converted and saved the intensity data in a format compatible with sound power calculation software.

To speed up measurement times, a specially built double sound intensity probe was used. The double intensity probe consisted of two pairs of microphones. One pair of ½-inch microphones spaced by 50 mm gave a frequency range of 63 to 1250 Hz, and one pair of 1/4-inchmicrophones spaced by 6 mm for a frequency range of 500 to 10000 Hz. So, in one sweep, they covered the whole frequency range of 63to 10000 Hz, and the software then combined the two frequency ranges into one.

Example 2: Hull Measurements in a Hurry

“Hurry up the tide’s going out!” Making over400 accelerometer and hydrophone measurements on a ship’s hull can be quite a business when you’ve only got a couple of hours (and you haven’t got 400 accelerometers).

Measurements had to be made during high tide to ensure uniform measurement. The test necessitated recording the signals from 16hydrophones and 400 accelerometers. It was decided to do this with 40 accelerometers at a time, using four sources of excitation – two acoustic sources and two shakers – over several frequency spans. Quite a process, but with an intelligent GUI the whole procedure was reduced to just selecting the measurement configuration and pressing Start!

By automating the data collection by PULSE, what previously took five days could be donein just two sessions!

Mobility Measurements

Here’s yet another measurement process where time was of essence.

The task was to carry out a large number of mobility measurements on a submarine diesel platform. The measurements had to be made under silent conditions as some measurement points were located on the submarine hull, necessitating cooperation throughout the ship and consequently a tight time frame.

PULSE programming tools were again put to good use to design a user-friendly measurement GUI that could set up and make the modal measurements, and save the data using a compatible format with modal analysis calculation software. From this user-interface the user could quickly set up and configure the following:

  • Measurements in 3 axes or 1 axis The type of hammer – one for the low frequencies and another for higher frequencies
  • The number of frequency spans to be measured, and the frequency span values
  • The number of measurement points – up to3 points in 3 axes simultaneously
  • The location of hammer strike and position of the accelerometers
  • Change in number and position of the accelerometers after saving a measurement
  • Autoscale of the measurement display for different frequency spans

So, these are three good examples of how PULSE and the PDM are playing a central and very important role in ‘silent’ operations at DCNS. Stealth and acoustic discretion don’t just come by themselves. It takes a lot of good engineering backed up by the right tools. By effectively automating the use of PULSE and by using PDM to manage the large amounts of data generated, Arnaud Mesnil and the team at DCNS have built a comprehensive and effective measurement programme.

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