Signature Сontrol & Ocean Physical Field Division

EXTREMELY LOW-FREQUENCY ELECTROMAGNETIC SIGNATURE CONTROL

The Krylov Institute is involved in theoretical and experimental research and development in the field of extremely low-frequency electromagnetic (ELFE) fields to protect and ensure stealth of surface ships and submarines.

For extremely low-frequency electromagnetic signature control the Krylov Institute offers:

• Regulatory documents to ensure development of efficient tools and measures for reducing ELFE of surface ships and submarines;
• EMSS software for estimations of anticipated ELFE levels for ship under design;
• Guidelines and EMSS software on ELFE measurements:
  • Measurements of electric and magnetic fields in water;
  • On board monitoring of current fluctuations in propeller shaft, residual magnetization of propeller shaft, current ripple in degaussing coils, electric equipment currents;
  • Revealing the main ELFE sources on the base of measurement processing;
  • Definition of electric and magnetic dipole moments;
  • Extrapolation of measurement results for other conditions and visualization of ELFE parameters;
• Expert evaluation of ELFE signature control.

Guideline on ship ELFE measurements

As a result of full-scale test is issue technical conclusion. The goal of technical conclusion is:

• to define the ELFE level;
• to find the main ELFE sources;
• to evaluate the efficiency of the protection systems;
• to develop the proposals and recommendations.

EMSS Software

EMSS software is intended for computing ELFE of moving surface ships and submarines, processing results of the full-scale measurements and detecting field sources. This software calculates electric and magnetic components of ELFE related to following sources:

– static magnetization; – static galvanic couples; – electric equipment; – degaussing coils; – hull vibration; – galvanic current modulation; – rotation of magnetized shafts; – eddy currents in propellers; – ship rolling and pitching.

Spectrogram of simulated ELFE sources

Computer model considers three main factors influencing the ELFE levels – media interface, effect of ship structures on field generation process, ship (or sensor) movement. Calculation results are time-domain signals, which can be mixed with typical noise obtained from full-scale measurements.
During full-scale measurements EMSS software makes it possible to record signals of sensors placed in water, air or on board of the monitored ship. Measurement results are processed using advanced digital filtering techniques.

EMSS software reveals the field sources on board of the monitored ship by comparing the solutions of direct problems with specially-processed full-scale measurement data.

Narrowband spectral representation of ELFE signals

Application of EMSS software enables: – checking the efficiency of electric and magnetic signature control systems; – processing the full-scale measurements results; – revealing the main sources of field based on comparing measurement results    with numerical simulation; – predicting ELFE parameters for various ship operation scenarios; – 3D visualization of ELFE electric and magnetic components.

X-component of magnetic field. Time domain (0.02s)

The identification of ELFE sources with estimation of their contribution in total ELFE fields is realizing by method of comparison of results of spectral analysis obtained in compared modes of tests. Under the favorable conditions of measurements, when the level of noise is less by at least 10 dB in comparison with level of ELFE field of ship, we can usually content with use of results of 1/3-octave analysis.

In more difficult cases it is necessary to resort to special methods of signal processing, to use in addition the results of control of parameters of ELFE fields sources (the pulses of current in shaft line and in windings of degaussing coils, the residue magnetization of shaft line, the field and moments of separate most strong elements of electric equipment). Finally, it is necessary to use such means, as formation on the base of results of measurements, the passage characteristics at individual frequencies and comparison with results of numerical simulation of ship ELFE field.