Siheyuan: I eat melons while doing scientific research

Chapter 1218: The Complete Foundation of Silent Technology (5k)

Regarding Gao Zhendong's "domineering" behavior of "giving fish and teaching how to fish", comrades called Chief Engineer Gao a righteous man.

The only regret is that it seems like the sense of accomplishment has been weakened. What’s going on?
Thinking of this, Engineer Hong almost wanted to slap himself in the face. What the hell was he thinking? If he wanted a sense of accomplishment, he could make good use of the knowledge and experience shared by Chief Engineer Gao in the future and make something better.

From Gao Zhendong's own perspective, he doesn't mind this somewhat forced approach. He believes that his comrades can come up with a better answer given that there is already an answer. This ready-made answer can at least be a guarantee, but it can probably only be a guarantee. After all, the data in publicly published materials are reliable, but they are definitely not the most reliable.

The reason why we have to give a guarantee first is because sound-absorbing tiles are so important.

There is a very counterintuitive conclusion that laying anechoic tiles can not only reduce the distance at which the enemy's sonar can detect our submarines, but also increase the distance at which our submarines can detect enemy submarines. The most counterintuitive thing is that even if our sonar is covered by anechoic tiles, this effect still exists.

And this effect works on both active sonar and passive sonar.

This is completely different from the use of wave-transparent materials in radar.

The reason is that whether it is active or passive sonar, there is a very important parameter in the sonar equation: the platform self-noise level.

The laying of anechoic tiles can greatly reduce the platform's self-noise level, delaying the occurrence of enemy signals being submerged in the noise, and naturally increasing the detection distance.

This is valid until the submarine's self-noise level drops to a certain level. The self-noise level here refers to the self-noise level before the anechoic tiles are laid.

It was impossible for submarines in the 60s to reduce their own noise levels to such a low level, so the importance of anechoic tiles was further highlighted.

The fundamental reason why Gao Zhendong is trying to force things to happen is that he wants to ensure that our self-developed submarines, no matter whether they are black or not, must at least have anechoic tiles that meet the basic performance requirements!

After teaching him how to fish, Gao Zhendong added: "By the way, I will omit the calculation process here. It is difficult to calculate this by hand. I calculated and simulated it on a computer."

If there were no computers, it would almost require a large abacus team to do the calculations.

But now it is not necessary, even Miss Qiu doesn’t want so many abacus as dowry.

Hearing him say this, Hong Gong remembered something.

"Chief Engineer Gao, do you have this finite element analysis simulation calculation program? Can you..."

Who is Chief Engineer Gao? If he has a ready-made program here, how much time can be saved? If Chief Engineer Gao makes the finite element analysis software more universal, it will not only save time for us.

This statement silenced Gao Zhendong. There was no such procedure for the moment... The picture was copied from a book. Its purpose was to boost the confidence of his comrades. Anyway, this thing was real, and that was enough.

As for the calculation process and calculation software, there really is none.

Seeing Gao Zhendong fall into "contemplation", Engineer Hong thought that what he said violated the discipline and quickly said: "Look at my brain, I forgot the discipline again."

Gao Zhendong came back to his senses from silence: "That's not the case. It's just that this software is not mature enough now. It's OK for me to use it myself, but it's hard for other comrades to use it. Any small change requires changing the original code, which is not very user-friendly. Moreover, this program is very targeted, and the learning experience of learning the original code is unlikely to be reused, so it's not worth it. At the same time, this program takes up a lot of memory, and it's hard to say whether the computer you have can run it. So, I'll find time to modify it later, and give it to you when it's done."

This thing is really important. Finite element method can be used not only in structural design but even in unconventional areas like heat dissipation design.

Moreover, the mathematical software that can support finite element analysis is itself a set of extremely important mathematical tools, which is of great significance to our scientific research work.

We still have to think of a way, this thing is important. As for how to do it, we will talk about it later. Gao Zhendong has some ideas in his mind, so he will find an excuse to fool around.

And what he said was not completely nonsense, the storage capacity of this thing is really large, even if sparse matrices are used to reduce the storage requirements, it is still a very large number for the computers at that time and they cannot support it at all.

Hong Gong and his colleagues did not feel anything strange about Gao Zhendong's words. Instead, they were overjoyed.

The first half of what Gao Zhendong said is too familiar to people with some programming experience. There is such a problem: when a professional program that solves professional problems does not consider universality at the beginning but only wants to temporarily solve the problem at hand, this result will occur.

As for the second half, we can see from the fact that this finite element analysis requires a lot of matrix calculations, so the storage capacity is not small.

Chief Engineer Gao was willing to take time out of his busy schedule to standardize the software specifically for the use of his comrades, which deeply touched his comrades. Some of them even felt guilty for holding Chief Engineer Gao back and taking up his time.

"This... Chief Engineer Gao, will it affect your work too much?" Engineer Hong was a little nervous.

Gao Zhendong smiled and waved his hands: "Not really, it's all work anyway, it's all the same."

Our job is also formal work for Chief Engineer Gao, which even makes our comrades feel proud.

If Gao Zhendong knew what they were thinking, he would definitely tell them that they should be the ones to be proud of.

After saying this, Gao Zhendong said to his comrades: "Okay, let's not talk about this anymore. I have already exhausted all the theoretical matters. Comrades, do you have any ideas about the experiment?"

No matter how beautiful a theory is, it is just a theory. Ultimately, it still needs to be verified and implemented through experiments. Nowadays, a large amount of research work is actually empirical. Theory is reliable, but not completely reliable.

NS Equation: That’s right! My Bro!

The Citigroup guys who believed that everything could be simulated by computers suffered a lot in this regard.

Wind tunnel group in a certain province: Are you thinking about us?
I have gone off topic. At this moment, Hong Gong and his companions were in a state of surprise and disbelief.

If Chief Engineer Gao is far ahead in theory due to his talent, then he has ideas in experiments that they have never thought of. After all, this thing really requires experience. Otherwise, even the most talented person can hardly have many reliable ideas.

With such doubts, Engineer Hong and his team asked Gao Zhendong sincerely: "Chief Engineer Gao, do you have any suggestions for the experiment?"

Gao Zhendong nodded and said, I don’t have any suggestions, but they are in the book, and there are quite a lot of them.

"Yes, are you using acoustic tubes to measure the underwater acoustic measurement test now?" Gao Zhendong asked.

Although there are no tests on sound-absorbing materials, there are still some tests on water sound. Sound tubes are still used as a standard measurement method and comrades have also come into contact with them.

To put it bluntly, an acoustic tube is a tube with a thick enough wall that is close to an ideal rigid body for underwater acoustic testing. It is filled with the medium to be tested, and acoustic transducers are installed at the bottom and some of the tested parts to measure the underwater acoustic data. For Hong and his team, the medium to be tested here is naturally water.

Gao Zhendong's question made Engineer Hong once again marvel at his erudition and talent. Anyone who could say the word "sound tube" must know nothing about hydroacoustic testing.

"Yes, acoustic tubes. I have just thought about the testing of this material. The acoustic tube pulse method can measure both reflected waves and transmitted waves. Moreover, different tube diameters can be used to basically cover the measurement needs from low frequency to high frequency."

Gao Zhendong nodded: "Well, your consideration is correct. The pulse method is simple in principle and the device is reliable. In theory, it can indeed cover all frequency bands..." Engineer Hong already had enough experience with Gao Zhendong, and he knew it was not a good thing when he heard this: "Chief Engineer Gao, in theory? Then there are some problems in practice?"

Gao Zhendong laughed. It turned out that this comrade was quite quick-witted.

"Yes, think about it, when measuring low frequencies, especially when the frequency is lower, how long should your tube be?"

Gao Zhendong's question immediately confused Engineer Hong. Damn it! I forgot about it! The main reason was that I had considered the reality more in the past, and did not consider the future development of sonar too much, and did not measure low frequencies much.

However, here, low-frequency measurement really becomes a major problem.

Anyone who has studied physics knows that the speed of sound is the product of frequency and wavelength. If you want to test relevant acoustic data, you must allow the sound to transmit a certain number of complete cycles in the sound tube. One cycle is one wavelength.

The speed of sound in water is 1485m/s, which means that when the frequency is as low as 100Hz, a wavelength is as long as 14 meters!
Not to mention lower frequencies, this makes it extremely difficult to test low frequencies using the pulse method, because such a long sound tube is very difficult from an engineering perspective, and it will also bring other problems.

After much thought, Engineer Hong could think of only one solution: to use great force to create a miracle and forcibly increase the height. However, since Chief Engineer Gao raised this question, according to his habit, it meant that he must have a solution.

"Chief Engineer Gao, what is your opinion on low-frequency measurement?"

"Use the continuous wave method! Using continuous waves, a traveling wave field is formed in the transmission area, and a standing wave field is formed in the reflection area. The incident wave and the reflected wave are separated using the transfer function. In this way, a sufficient number of sound wave cycles can be transmitted in the sound tube using continuous waves to measure data."

After saying that, Gao Zhendong stood up and drew a picture on the blackboard.

Engineer Hong looked at it for a while and suddenly realized: "Yes, yes, this method can indeed use the characteristics of continuous waves to obtain data and use transfer functions to separate incident waves and reflected waves. Why didn't I think of this method?"

Gao Zhendong didn't know how to respond to this, so he could only smile.

The comrades were still not satisfied: "The only problem is that the end of the tube must be a non-reflective surface, so that no reflection can be generated, so that the reflected wave will not interfere with the data... Got it, if we install a sound-absorbing spike at the end of the tube, it can absorb the sound waves and prevent them from causing reflections!"

Sound-absorbing wedges are a very common structure in super-quiet rooms. They are pyramids with very small top angles and made of sound-absorbing materials. The electromagnetic shielding room used for electromagnetic testing also uses this structure, but the materials are different.

After all, Engineer Hong and his colleagues are experts in water sound research. Once that little bit of window paper is broken, his ideas will flow like a surging river.

"Transfer function... Well, we can install dual hydrophones in the standing wave zone and process the data from the hydrophones to separate the incident wave from the reflected wave..."

Gao Zhendong didn't say anything else, but watched his comrades perform quietly. Facts have proved that once the window paper is broken, his comrades are much more awesome than he is.

He held the names of several recommended national standards in his hands, including GB/T 5266 "Pulse tube method for measurement of longitudinal wave velocity and attenuation coefficient of acoustic and hydroacoustic materials" and GB/T 14369 "Measurement method for insertion loss, echo reduction and sound absorption coefficient of acoustic and hydroacoustic material samples", and did not move.

The names of these national standards all come from the material testing and measurement chapter of the anechoic tile monograph. They are national standards for the measurement of hydroacoustic materials. The measurement contents, from principles to equipment to error processing, are very detailed. Gao Zhendong originally considered publishing them, but now it seems that there is no need.

Firstly, these things are very expensive. Since he had never saved them or seen them in his previous life, it would be very costly to get them.

Secondly, although the monograph is not as comprehensive as the standard, it still contains the most core and important principles and formula derivations, important intermediate results, and equipment principle structures. It is sufficient to copy these things out when necessary, but it is too detailed and not suitable for the time being.

Most importantly, looking at the performance of his comrades, Gao Zhendong felt that it would be a good thing to let them do their research freely.

After getting the last harvest from Gao Zhendong, Engineer Hong and his colleagues firmly refused Gao Zhendong's "invitation to dinner" and took their harvest and quickly returned to the northeast coast in the car sent by the Defense Work Committee. This time it was a great harvest, so they had to go back to work quickly. As for eating, they had eaten a lot of good food in the Third Factory during this period.

Watching their car drive out of the gate of the third factory, Gao Zhendong completely put his worries to rest.

Cavitation prevention, float valve isolation, anechoic tiles...

The technical seeds of submarine silencing have been planted thoroughly. It doesn't matter whether we are there or not in the future. I believe that comrades can work hard to grow a towering tree based on these little seeds, even if it starts from a seedling. It doesn't matter. Our starting point is already higher than that of the Russians and the American people. Everyone started from a seedling. It is estimated that our tree will grow stronger. Even if it experiences wind and rain in the middle, its final growth will not be too ugly.

This matter can basically be put aside and just wait for good news. Maybe even if these good news are heard, it will take decades for Gao Zhendong to hear them, but it doesn't matter. What's important is that they really sound, and it doesn't matter when he hears them.

Gao Zhendong turned around and sat down, starting to think about the debt he had just owed.

When it comes to finite element calculation, one of the most famous ones is undoubtedly Ansys, but Gao Zhendong is not going to choose it, mainly because it is not open source software. Even if he uses the only two remaining full-network searches, he cannot find the source code.

And from the perspective of mathematics and engineering, this thing is a bit lackluster.

Now that we have come to this, we have to mention another famous engineering mathematics software, which is indispensable for many science and engineering majors - MATLAB (matrix & laboratory). As the name suggests, this thing is best at matrices. Just take a look at the introduction of this thing to know how powerful it is.

——“Used in data analysis, wireless communications, deep learning, image processing and computer vision, signal processing, quantitative finance and risk management, robotics, control systems and other fields.”

Compared to Mathematica, which is better at numerical calculations, MATLAB is undoubtedly more suitable for the current national conditions. It is good at engineering applications!

Unfortunately, this thing cannot be used because it is not open source software. And for software like this, Gao Zhendong must get the source code.

But for Gao Zhendong, this was not a problem at all, because he knew that there was a suitable open source software that could replace MATLAB, and even in the current environment, this replacement was perfect.

When there was no search function that could create something out of nothing on the entire Internet, he had no way to deal with this thing. After all, he would not save the source code of so many open source software, and he mainly used MATLAB in his previous life, so he would not save that thing. Those who understand will understand the reason why he mainly uses MATLAB.

But now he still has two opportunities to search the entire Internet, and he feels that what he is about to create is simply great value.

He quickly opened the system and issued a search command.

Then he got a bunch of floppy disks, a huge bunch.

The software he was looking for was Octave, an open source alternative that is basically compatible with MATLAB. Its source code is public. It is basically the same as MATLAB and the two are highly compatible.

The source code of this thing can be directly compiled and used under Linux, which coincides with the multi-user network operating system that Gao Zhendong is organizing people to compile based on POSIX... no, POSIL.

In terms of compatibility, it can be said that anyone who knows MATLAB will have no difficulty learning this thing, and its basic ability in matrix calculations is almost the same as MATLAB. It just may be lacking in the richness of plug-ins and advanced functions. Although it is claimed to be almost completely compatible, people who work in computers know that this is impossible.

At this stage, the advanced functions and rich plug-ins of the later versions of MATLAB are almost useless. What Gao Zhendong wants is to have as many functions as possible while being able to run on the current computer.

Gao Zhendong believes that a perfect alternative mathematical software to MATLAB with source code available can play a huge role in the hands of our scientific researchers.

The version he chose was Octave 2.0.16, which was released after 2000, but not too late. It is just right for our current computer environment and also solves the YK problem.

(End of this chapter)