This is the second article on the application of resonances to the destruction of physical objects.
The first article "Russian trail of the virus Stuxnet" was of an introductory nature, and was designed for a wide non-professional audience.
It is time to get acquainted with this method in detail, but first, watch the video with a clear example of resonance, then I think the topic of the article will become clearer, because it’s better to see once than read a hundred times ...
Here's the video:
So please treat resonance with respect.
Such a famous, unknown Stuxnet
The world-famous virus Stuxnet has now turned into a kind of horror story, everyone knows about it, but nobody fully understands how he managed to secretly destroy centrifuges to enrich uranium over the course of two years. This is not even sabotage, but a more sophisticated method of sabotage - sabotage.
Just think over the course of two years, hundreds of centrifuges are constantly breaking down, all production schedules are broken, experts call it “on ears” and cannot do anything until a message is received from Belarus about the detection of a virus whose combat load was the internal software update modules for industrial automation company Siemens.
Later, this virus was called Stuxnet. Understood using the method of infection, with the methods of its penetration to the kernel level, and the method of breaking the password protection of Simatic S7 controllers in the local network. Something was understood from what the firmware of the group centrifuge group controller software updated by the virus does.
But no one has yet explained the physical method of disabling equipment in this act of sabotage. Therefore, we will try to deal with this most important riddle.
What we know
This controller Simatic S7 complete with peripheral modules:
The microprocessor unit itself is a box with a blue key, the rest is the periphery. The microcontroller software (using a special STEP 7 interpreter language) is placed in the internal flash memory. The software and firmware firmware of the controller itself is updated via the network, or physically, through a removable flash drive. Such controllers were grouped control devices immediately for the 31 gas centrifuge.
But the centrifuges were directly broken through other devices, - a frequency converter for the operation of an electric motor, approximately as follows:
This is how frequency converters (converters) for asynchronous electric motors of various powers look like. The name implies the functional purpose of this device, it converts the voltage of a standard network (three phases 360V) into a three-phase voltage of a different frequency and a different rating. The voltage conversion is controlled by signals from the network, or is set manually from the control panel.
One Simatic S7 controller controlled the group (31 device) of the frequency converters at once, respectively, was a group of CUs for the 31 centrifuge.
According to experts, the semantics of the software of the group control controller was strongly modified by the Stuxnet virus, and they considered the immediate cause of the centrifuge breaks to be the output of modified controller software. Simatic S7 commands of group SU on frequency converters.
Modified by the virus, the control unit's software once during the five-hour interval on 15 minutes changed the frequency of operation of each frequency converter and, accordingly, the frequency of rotation of the centrifuge electric motor connected to it.
Here is how it is described in the research firm Semantics:
Thus, it changes from 1410Hz to 2Hz to 1064Hz and then over again. 807 Hz and 1210 Hz.
So the motor speed changes from 1410Hz in 2Hz steps to 1064Hz and then reverses back. As a reminder, the normal operating frequency at this time was maintained between 807 Hz and 1210 Hz.
And Semantics makes a conclusion based on this:
Thus, Stuxnet sabotage
(Thus, Stuxnet sabotages the system by slowing or speeding up the engine to different speeds at different times).
For modern programmers who know physics and electrical engineering only in the volume of secondary school, this is probably enough, but for more competent specialists such an explanation is not consistent. Changing the rotational speed of the centrifuge rotor within the permitted range and a short-term excess of the operating frequency by 200 Hz (about 15%) from the nominal value in itself cannot lead to massive equipment breakdowns.
Few technical details
This is a cascade of gas centrifuges for the production of enriched uranium:
There are dozens of such cascades in uranium enrichment factories, the total number of centrifuges passes for 20-30 thousand ...
The centrifuge itself is a fairly simple device, its schematic drawing:
But this constructive simplicity is deceptive, the fact is that the rotor of such a centrifuge, about two meters long, rotates at a speed of about 50 000 revolutions per minute. Balancing a rotor with a complex spatial configuration, almost two meters in length, is a very difficult task.
In addition, special methods of rotor suspension in bearings are required; for this purpose, special flexible needle bearings are used complete with a complex self-centering magnetic suspension.
For the reliability of gas centrifuges, the main problem is the resonance of the mechanical structure, which is associated with certain speeds of rotation of the rotor. Gas centrifuges are even categorized on this basis. A centrifuge operating at a rotor speed above the resonant one is called supercritical, below - subcritical.
No need to think that the frequency of rotation of the rotor is the frequency of mechanical resonance. Nothing of the kind, mechanical resonance is associated with the speed of rotation of the centrifuge rotor through a very complex relationship. The resonance frequency and rotor speed can vary by an order of magnitude.
For example, a typical resonant region of a centrifuge is a frequency within 10Hz-100Hz, while the rotor speed is 40-50 thousands of revolutions per minute. In addition, the resonance frequency is not a fixed parameter, but a floating one; it depends on the current mode of operation of the centrifuge (composition, density of the gas temperature in the first place) and backlash in the design of the rotor suspension.
The main task of the equipment developer is to prevent the centrifuge from operating in modes of increased vibration (resonances), for this, automatic emergency blocking systems for vibration level (strain gauges), operation at rotor speeds causing resonance of the mechanical structure (tachometers), increased current loads of the motor ( current protection).
Emergency systems are never combined with the equipment responsible for the normal operation of the installation, they are separate, usually very simple electromechanical systems for stopping work (just emergency switches). So do not programmatically disable and reconfigure them.
The colleagues from the USA and Israel had to solve a completely non-trivial task, - destroy the centrifuge without at the same time triggering protective automation.
And now about the unknown, how it was done
With the light hand of the translators of the scientific center "NAUTSILUS", who translated the research of the Symantik specialists into Russian, many specialists who did not read the Symantik report in the original had the opinion that the accident was caused by the operating voltage frequency reduced to 2Hz to the centrifuge electric motor.
This is not the case; the correct translation is given at the beginning of the text of the article.
And in principle, it is impossible to reduce the frequency of the supply voltage of a high-speed asynchronous electric motor to 2Hz. Even a short-term supply of such a low-frequency voltage to the windings will cause a short-circuit of the windings and an overcurrent protection.
Everything was made much smarter.
The method of excitation of resonance in electromechanical systems described below could claim to be new, and I am considered to be its author, but the authors of the Stuxnet virus most likely have already applied it, so, alas, all that remains is to plagiarize ...
And nevertheless, I explain on fingers, spending at the same time an educational program on the basics of physics. Mentally imagine a massive load, say a ton, hanging on a cable, suppose a long 10 meter. We have the simplest pendulum with its own resonant frequency.
Suppose further that you want to shake his little finger, applying force in 1kg. A single attempt will not lead to any visible result.
So you need to push it repeatedly, putting efforts into it in 1k, say 1000 times, then you can assume that such a multiple force will be equivalent in sum to a single force application per ton, which is quite enough to build such a pendulum.
And so, we change tactics, and start repeatedly pushing the suspended load with the little finger, each time putting effort into 1kg. We will fail again, because physicists do not know ...
And if they knew, they would first consider the period of oscillation of the pendulum (the weight is absolutely unimportant, the suspension of 10 meters, the force of gravity 1g) and began to push the load with this little finger with the little finger. The formula is well known:
Minutes through 10-20 this pendulum weighing in ton swings so that “Mama Do not Cry.”
And it is not necessary to press the little finger on every swing of the pendulum; this can be done both once and after two, and even after a hundred oscillations of the pendulum. It is just that the time for the buildup will increase proportionally in this case, but the effect of the buildup will be completely preserved.
And I will surprise people who know physics and mathematics in the secondary school (the level of knowledge of a typical modern programmer), the period of oscillations of such a pendulum does not depend on the amplitude of oscillations, swing it a millimeter or meter from the point of rest, the oscillation period and, accordingly, the oscillation frequency of the pendulum is constant.
Any spatial structure has not even one, but several resonant frequencies, in fact there are several such pendulums in it. Due to their technical features, gas centrifuges have the so-called fundamental resonance frequency of high quality (they effectively accumulate oscillation energy).
It remains only to swing the gas centrifuge at the resonant frequency with your finger. A joke, of course, if there is an electric motor with an automatic control system, then the same thing can be done much more inconspicuously.
To do this, you need to increase / decrease the speed of the electric motor in spurts (as the virus did, according to 2Hz) and produce these jerks with the resonance frequency of the mechanical design of the centrifuge.
In other words, it is necessary to output the frequency of the mechanical resonance to the motor using a variable frequency frequency converter. The moment of force arising in the motor when the frequency of the supply voltage changes will be transmitted to the case with the frequency of mechanical resonance and gradually resonant oscillations will reach the level at which the installation will begin to collapse.
Frequency fluctuations around a certain average value are called “beats”, this is the standard effect of any frequency converter, the frequency is said to “walk” within certain limits, usually no more than tenths of a percent of the nominal value. The saboteurs disguised under these natural frequency beats, their own, artificially introduced, modulation of the frequency of the electric motor and synchronized it with the frequency of the mechanical resonance of the spatial design of the centrifuge.
I will not go into the subject any more, otherwise they will accuse me of writing step-by-step instructions for saboteurs. Therefore, outside the discussion I will leave the question of finding the resonant frequency for a specific centrifuge (it is individual for each centrifuge). For the same reason, I will not describe the “fine” adjustment method when you need to balance on the verge of triggering an emergency protection against vibrations.
These tasks are solved through programmatically available current output voltage sensors installed in frequency converters. Believe the word - it is quite realizable, it is only in the algorithms.
Again about the accident at the Sayano-Shushenskaya HPP
In a previous article, it was hypothesized that a hydroelectric station accident was caused by the same method (resonance method) as in a uranium concentration plant in Iran, using special software.
This of course does not mean that the same Stuxnet virus worked here and there, of course not. The same physical principle of the destruction of an object, the artificially induced resonance of a mechanical structure, worked.
The presence of resonance is indicated by the presence of the unscrewed nuts securing the turbine cover and the indication of the only operating sensor at the time of the accident of the axial vibration sensor.
Taking into account the coincidence of the time and causes of the HPP accident with the fact of sabotage at the Iranian uranium enrichment plant, the continuous vibration control system turned off at the time of the accident, the operation of the unit under the control of the automatic control system of the turbine unit, it can be assumed that the resonance was not an accidental phenomenon, but a man-made one.
If this assumption is true, then, in contrast to the situation with gas centrifuges, the task of destroying a turbine unit required manual intervention. The equipment available at the hydroelectric station did not allow the tamper software to automatically detect the individual resonance frequency and then keep the vibrations in the emergency mode without triggering the alarm sensors.
At the hydroelectric power station, the work of the sabotage software required the use of the “human factor”. Someone somehow had to turn off the vibration control server, and before that, transfer to the developers of the sabotage software the resonance parameters of a specific turbine unit, which were removed from it six months before the accident during scheduled maintenance.
The rest was a trick.
No need to think that the resonance occurred in the very body of the turbine rotor, of course not. Was caused by the resonance of the water layer, saturated with elastic cavitation cavities located between the turbine rotor and the blades of the guide vane.
It is easy to imagine such an analogy, below is a spring from cavitation cavities between the turbine rotor and the blades of the guide vane, and this spring is supported by a column of water one hundred meters high. It turns out the perfect oscillating circuit. To shake such a pendulum system is a very real task.
It is because of this resonance. ALL the blades of the guide vane were broken, and not mechanically, from impacts, but broken by dynamic load. Here are photos of these broken blades; there are no traces of mechanical shocks on their surfaces:
The broken blades of the guide vane blocked the drain hole of the turbine, and it was from this unforeseen circumstance that the accident began to develop into a catastrophe.
The turbine rotor became similar to the screw of a supertanker, and began to rotate in a “closed can of water” having a mass of one and a half thousand tons and a rotation speed of 150 revolutions per minute. In the working area of the turbine, such an excessive pressure of water was created that the lid was blown off, and the turbine itself, according to eyewitnesses, together with the generator rotor (a machine in one and a half thousand tons) flew up to the ceiling of the machine hall.
What was further known to all.